Abstract
Transparent conductive oxides (TCOs) constitute a class of materials that combine high electrical conductivity and optical transparency. These features led to the development of the transparent electronics applications, such as flat panel displays, “smart” windows or functional glasses. N-type TCOs dominate the applications market, and the lack of a suitable p-type counterpart limits the fabrication of a completely transparent active device, which might be considered as a technological breakthrough. Among the wide range of p-type candidates, delafossite CuCrO2 (and its out-of-stoichiometry derivatives) is a promising material to achieve the desired p-type TCO properties as, up to date, it is presenting the foremost trade-off between optical and electrical properties. The present paper covers the research work and the major achievements related to copper chromium delafossite. A comprehensive overview of fabrication methods and opto-electronic properties is presented. The source of doping and the charge carriers transport mechanism are also thoroughly discussed.
Graphical abstract
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Introduction
High electrical conductivity and wide band gaps—leading to high optical transparencies—are sought but seemingly mutually exclusive properties. In this context, the transparent conductive oxides (TCOs) are a special class of materials that combine both these properties. Depending on the donor (electrons) or acceptor (holes) level in the band gap of such materials, they are either n- or p-type, with carrier concentration (n, p) and optical band gap (\({E}_{g}\)) typically around 1016–1021 cm−3 and 3 eV, respectively. The most employed TCOs at industrial scale—Sn-doped In2O3 (ITO), Al-doped ZnO (AZO) and F-doped SnO2 (FTO)—have n-type conductivity; among them, ITO stands out with electrical conductivity around 103 S cm−1 and transparency above 80% in the visible range [1, 2]. N-type TCOs have been reported and explored for more than half a century, and they dominate the transparent electronics market upon their two main applications: firstly, as transparent electrodes for flat panel displays and photovoltaic cells and secondly, as active layer for transparent thin film transistors (TFT), UV light-emitting diodes (LED), gas sensors or other transparent electronic devices [3, 4]. However, challenges are still faced to find a matching p-type counterpart. (Extensive reviews can be found in [5,6,7,8,9,10].) The unveiling of a p-type material with similar properties would open a new era in transparent electronics, by promoting the fabrication of fully transparent active devices such as p–n junctions [6, 11], or complementary transistors [12,13,14]. This would open a new range of invisible electronics devices including smart windows [3, 15, 16], transparent UV LEDs [17, 18], solar-cell heterojunctions [19, 20], gas sensors [21,22,23,24], electromagnetic shielding [25], etc. Since the first report of a semitransparent p-type oxide, NiO [26], a large variety of materials has been investigated as a p-type TCOs suitable for applications:
-
(i)
Binary oxides: ZnO [9, 27,28,29], B6O[9] [30], In2O3 [31], NiO [24, 26, 32, 33], SnO/SnOx [34,35,36,37] and β-Ga2O3 [38,39,40].
- (ii)
- (iii)
-
(iv)
Ag-, Cu-, Pd- and Pt-based delafossites [46,47,48,49,50,51,52,53,54,55,56];
-
(v)
Layered oxychalcogenides: LaCuOS [57,58,59] and LaCuOSe [60];
-
(vi)
Spinel oxides: NiCo2O4 [61, 62], ZnCo2O4 [63, 64], ZnIr2O4 [63] and ZnRh2O4 [65, 66], etc.;
-
(vii)
Others: SnSeO [67], Ba2BiTaO6 [68], SrCu2O2 [69,70,71], [Cu2S2][Sr3Sc2O5] [72] or La2/3Sr1/3VO3 [73].
From a general point of view, these materials have failed to fully comply with the requirements of a p-type TCO for application purposes as they demonstrate either low conductivity or low transparency. The electrical conductivity (σ) of a material is directly proportional to the carrier concentration (ne,h) and carrier mobility (μe,h) with the last term depending on the carrier scattering relaxation time (τ) and the effective mass (me,h*) of the carriers [74]:
Higher conductivities can be obtained by simply increasing n and/or the electrical mobility μ. For example, in n-type TCOs, the oxygen vacancies constitute one of the main defects inducing high carrier concentrations. The hybridization of s-orbitals—that compose mainly the conduction band minimum (CBM)—with heavy-metal cations leads to a high level of delocalization and hence to low electron effective mass and high electrical mobility [75,76,77]. Recently, Fleischer et al.[7] presented a thorough report on the actual p-type TCOs performances. In a thought-provoking approach, they have analysed the changes on opto-electronic properties with the temperature of synthesis (Fig. 1), an important parameter when technological applications are envisaged.
An important conclusion might be drawn from their data: a TCO with high electrical conductivity and optical transparency is very difficult to be synthesized at low cost and always a trade-off between all these requirements must be foreseen. The challenge in improving optoelectronic properties of these p-type TCOs arises from their intrinsic electronic structure. The valence band edge of most oxide materials is composed by strongly localized oxygen 2p levels, owing to its large electronegativity [9]. These levels lie far lower than the valence orbital of the metallic atoms, leading to a non-dispersive valence band maximum (VBM). The high-electronegative oxygen atoms trap the holes, impeding therefore the introduction of shallow acceptors and inducing high effective hole mass, which leads to poor transport characteristics [9, 78]. Few aspects must be considered to favour a considerable hole concentration in a p-type semiconductor when doping is based on point or extended defects engineering [8, 79, 80]:
-
(i)
a low formation energy of point/extended defects that produce holes (e.g. native acceptors such as cation vacancies or oxygen interstitials);
-
(ii)
small ionization energy of these defects in order to release holes (i.e. a shallow acceptor level with respect to the host valence band);
-
(iii)
very important and valid also whatever the doping strategy, a high formation energy of native defects that annihilate holes (e.g. native donors such as anion vacancies).
Amidst p-type semiconducting materials, those having a delafossite structure were thoroughly investigated due to their interesting properties with applications in various fields. They are usually ternary metal oxides, with an AMO2-layered structure, where A+ and M3+ are monovalent and trivalent cations, respectively. The A+ cations have small size, favouring a linear coordination (two oxygen atoms); M3+ cations have coordination VI (six oxygen atoms), whilst the oxygen has coordination IV (one A+ and three M3+). Their structure comprises alternating close-packed layers of slightly distorted edge-shared M3+O6 octahedra, sandwiching planes of close-packed A+ cations. The A+–O twofold coordination induces a dumbbell-shaped structure O–A–O unit placed parallel to the c-axis that connects to the adjacent M3+O6 octahedra [81,82,83,84]. Each O from the dumbbell is also coordinated to three M3+ cations, oriented in such form that the M3+O6 octahedron forms MO2 layers parallel to the ab plane [5]. Delafossite materials can be thus considered natural nanolaminates with a panoply of design possibilities, according to the choice of A+ and M3+ cations [85]. They can be divided into two groups, depending on the electronic configuration of A+ cation (a noble metal from group X or XI), characterized by a closed-shell energy level close to (just above) the O2p level [86,87,88]:
-
(i)
i) d10 ions (Cu+ and Ag+) [85, 89, 90]: usually present semiconducting or insulating behaviour and they are convenient for enhanced optical transparency.
-
(ii)
ii) d9 ions (Pd+ and Pt+ [91,92,93,94]): In these materials, an unusual oxidation state is stabilized by a metal–metal bonding [89]. Although these materials are metallic and opaque, ultrathin films have reasonably low sheet resistance and high transmittance, particularly in the near IR region.
Materials with delafossite structure have been known for more than 140 years; the first one, CuFeO2, was reported by Friedel in 1873 and named in honour of the French mineralogist and crystallographer Gabriel Delafosse. Yet, they became a subject to extensive interest after the 1997 report of Kawazoe and co-workers that successfully fabricated a stable p-type undoped CuAlO2 with a considerable p-type conductivity (≈1 S cm−1) at that time [49]. They proposed a strategy—the so-called chemical modulation of the valence band (CMVB)—for broadening the valence band and consequently achieve lighter effective mass/higher carriers’ mobility [71, 95]. Within this approach, they outlined three criteria that must be met in order to manipulate the valence band edge of p-type TCOs without compromising their optical transparency. Firstly, the nd energy levels of the shell of metallic cations and of O2p should be similar to promote hybridization, hence forming strong covalent bonds. This leads to a more dispersive valence band edge pushed up above the bonding O2p or metallic cations nd states. That furthermore ameliorates holes delocalization and consequently increases the carrier’s. Mobility. Secondly, these levels should have closed electronic shells (nd10) to avoid any coloration due by d–d excitations. Additionally, the coordination around oxygen atoms should be tetrahedral, allowing to pair the electrons from 2 s and 2p orbitals of oxygen to bond with two other atoms. This configuration reduces the strong localization of the carriers at the VBM and removes the non-bonding nature of the O anions [8, 49]. From the theoretical point of view, the achievement of a p-TCO with improved characteristics relies on the delocalization of the VB by promoting the orbital hybridization between nd10 metal cations and O2p orbitals. Figure 2 depicts a survey over the reports of electrical conductivity for Ag/Cu/Pd/Pt-based delafossite materials. A more comprehensive datasheet is presented in Table S I (Supplementary Information section). The values span a wide range of approximately eight orders of magnitude. Even in the case of the same material, the reported values vary due to the different method of synthesis or to the various approaches of tailoring the material. The highest values (with records beyond of 100 000 S cm−1) are reported for the Pd/Pt delafossite [53, 56, 96, 97] but, as mentioned before, these ones show typically high reflectivity (optical metallic behaviour). Nonetheless, the ultrathin films demonstrate concomitant high values of electrical conductivity (even at critical thickness) and optical transmittance, making these materials very promising candidates for transparent electrodes [93]. Ag-based delafossites are expected to have wider band gap and lower visible-light absorption, due to the shift in the VBM to lower energies from Ag4d states. Unfortunately, these delafossites have never been successfully synthesized in open systems due to the low free energy formation of Ag2O (−2.6 kcal mol−1) [98], which decompose to metallic Ag and O at 300 °C before the reaction occurs [55, 88, 90]. Successful deposition methods usually require ion-exchange synthesis rather than a simple solid-state reaction [54] (hydrothermal synthesis in sealed autoclaves [98, 99], metathetical cation exchange [100] and oxidizing flux [101]), but low electrical conductivities have been achieved until now [51, 99, 102]. Nagarajan reported various Ag-based delafossites (doped and non-doped) in powder form, but only with very low conductivities around 10–4–10–6 S cm−1 [89]. Research is still under development for Ag-based delafossites to meet the requirements of optoelectronic applications; for instance, Wei [55] reported a facile chemical solution synthesis in an open condition (spin coating + annealing) of 12% Mg-doped AgCrO2, obtaining a conductivity of 6.77 × 10–3 S cm−1.
Cu-based delafossites have attracted attention due to their expected large hole mobility, a result of the mixing of Cu3d and O2p states forming the valence band. It has been reported that this delafossite structure allows the hosting of a multitude of M cations, namely p-block elements (Al [49, 103, 104], B [105,106,107], Ga [54, 108, 109] or In [110,111,112,113]), transition metals (Co [114, 115], Cr [82, 116, 117], Fe [118,119,120], Mn [121, 122], Rh [123], Sc [124,125,126] and Y [89, 126,127,128]), or lanthanides (La [129,130,131], Nd [132], Pr [133], Sm and Eu [134]). These materials were thoroughly investigated as they demonstrated interesting properties in the different fields: antibacterial [135, 136], batteries [137], (photo)catalyse [83, 131, 138,139,140], luminescence [130], magnetic [141,142,143,144,145], ferroelectric [146], optoelectronics (most of the references of this article), supercapacitors [114], superconductors [147, 148] and thermoelectric [142, 149, 150].
Among Cu delafossites, the copper chromium oxide (CuCrO2) is considered the most promising, as it presents a favourable covalent mixing between Cr3+ and O2−, a high density of Cr3d states near the VBM and a high band gap. Additionally, its optoelectrical properties are easy tuneable as the structure allows facile substitution with aliovalent and/or isovalent cations at the Cr site [81, 82, 151, 152]. Finally, it has a low synthesis temperature and a favourable thermal stability in air. To date, the highest conductivity reported values for this material are 278 S cm−1 for Mg and N co-doped CuCrO2 using solid-state reaction, with a transmittance of 69% over the visible range [47] and 220 S cm−1 for a Mg/CuCrO2 with a transmittance around 30%, deposited by sputtering [117]. In the following, the present work will focus on synthesis and characterization of Cu–Cr–O delafossites. This review aims to give an overview of the studies on this material delafossites and of the most important reported results.
Structure of CuCrO2 delafossite
The CuCrO2 delafossite structure is composed of two alternating layers: a close-packed layer of slightly distorted edge-shared CrO6 octahedra sandwiching planes of close-packed Cu cations, in dumbbell-shaped linear coordination to oxygen anions in the adjacent CrO6 layers [82, 83]. The Cr cation is located in the centre of the distorted edge-shared CrO6, and it has a + 3 oxidation state. The oxygen ion is in pseudo-tetrahedral coordination with one Cu and three Cr cations. In a simpler way, the delafossite structure can be visualized as consisting of two alternating layers: a planar layer of Cu cations in a triangular pattern and a layer of edge-sharing CrO6 octahedra flattened with respect to the c-axis. Depending on the orientation of each layer in the stacking, CuCrO2 has two polytypes (Fig. 3): ABABAB stacking leads to hexagonal α-2H polymorph (P63/mmc) [ICDD PDF 04–010-3329], whereas ABCABC leads to the rhombohedral α-3R polymorph (R-3 m) [ICDD PDF 04–010-3330]. In the primitive rhombohedral cell, there are four atoms: one Cu, one Cr and two O atoms [154, 155]. Among the Cu-based delafossites, the CuCrO2 has relatively small a- and c-axes. However, the multitude of deposition or calculation techniques leads to an important span of values for lattice parameters. Table 1 depicts the values for the lattice parameters and the volume of unit cell from various experimental or theoretical works.
The calculated Cu–O and Cr–O bond lengths are 0.1881 nm and 0.1972 nm, respectively, in a good agreement with the values resulting from the Shannon atomic radii (IIO2− = 0.138 nm IICu1+ = 0.046 nm VICr3+ = 0.062 nm [156]). Significant deviations are then reported in the case of doped films. The size of the dopant (intrinsic or extrinsic) alters the normal inter-atomic distances. For example, in the case of Sc/CuCrO2 [157] the diffraction peaks shift to lower values of two-theta diffraction angles, in good correlation with the radius of the substituting cation. For the doped sample, the “a” parameter is mainly affected, whilst the “c” one, related to the Cu–O distance, remains more or less unaltered. A different behaviour was reported in the case of delafossite films with an important deficit of Cu atoms. (33% of them are missing) A significant increase of c parameter was reported, more probably due to the increase of Cu–O averaged distance [161]. Within all crystallographic data reported for the Cu–Cr–O thin films, the very important aspect of thermal expansion is often neglected. The films are deposited on various substrates at temperatures up to 800 °C, and then, the XRD analysis is generally performed at room temperature. During the deposition process, the substrate is thermally expanded. The coefficient of thermal expansion for the most reported substrates is 0.54 µK−1 for Quartz and 7.54 µK−1 for sapphire, an order of magnitude difference. During the cooling process, the substrate is coming back to a non-deformed state, forcing the much thinner delafossite layer to contract also. Hence, for thin films below the critical thickness (above which typically the material is relaxed), the XRD analysis performed at room temperatures are mostly characterizing strained delafossite structures. A negative expansion coefficient [162,163,164] reported sometimes in the case of delafossites layers might complicate more the estimation of the actual strain induced. This is a very important aspect, as the induced strain changes the energetic band structure of the material and hence the optoelectronic behaviour might be severely affected [165,166,167].
The band structure of CuCrO2 was theoretically determined using various approaches. The typical ones are: density functional theory (DFT) with a screened exchange local density approximation (sX-LDA) [168], the screened hybrid functional approach of Heyd, Scuseria and Ernzerhof (HSE06) [82], the generalized gradient approach (GGA) of Perdew, Burke and Ernzerhof (PBE) corrected for on-site Coulomb interactions (PBE + U) [82], the LDA + U approach [152] or many-body perturbation theory with the Green functions correlated with Coulomb interactions (GW approximation) [169]. In general, all these methods estimate a direct band gap between 2 and 4 eV and an indirect one between 1 and 3 eV. A summary of results is presented in Table 2. This relatively large dispersion of values is a result of the multitude of different assumptions, specific for each theoretical method. All approaches have their own advantages or disadvantages, offering good estimation for some parameters but getting loose for the others. For example, it is known the PBE overestimates the lattice parameters and underestimates the self-interaction, whilst HSE06 consistently produces structural data and band gap descriptions that are more accurate than LDA/GGA [82]. When comparing these theoretical estimations with the reported experimental values (Fig. 5 within the paragraph dedicated to optical properties), the most precise approach seems to be the sX-
LDA or PBE + U approach. However, the theoretical models deal in general with bulk materials, with a well-defined crystalline structure, whilst the deposited films often present random defects, impossible to be accurately modelized. When the total electronic density of states is investigated, the delafossite CuCrO2 presents few distinct regions (Fig. 4; from [82]). The levels below −4 eV are mainly broad and intense O2p states, followed by narrow but also intense Cu3d non-bonding states around −2 eV. These states are energetically degenerated with the weakly dispersive states from the non-bonding states of O2p orbitals (at -2 eV). Finally, the bonding Cu3d and O2p states interact together and push up a mixed Cu–O state above the undispersed background at the VBM. This distribution was confirmed by X-ray resonant photoemission and X-ray absorption spectroscopy experiments of Yokobori [152] and Arnold [116]. Both oxidation states of copper (+ 1 and + 2) were simultaneously observed in these experiments focused on.
Mg-doped CuCrO2. Finally, the Cr3d states contribute mainly to the CBM. A minor contribution to VBM is also expected because of the bonds between three Cr ions and one O ion which produce hybridized Cr–O bonds [81].
Deposition methods
Various methods were reported to synthesize delafossite CuCrO2 thin films, each of them leading to different morphological and optoelectronic properties. The majority of the reported fabrication techniques involves wet chemistry routes. Within this category, the most used seems to be the solid-state synthesis [47, 116, 143, 157, 174,175,176,177]. This consists in the mixing of Cu2O/CuO and Cr2O3 powders followed by high-temperature sintering and post-treatments under different atmospheres. The CuCrO2 is forming at temperatures higher than 800 °C under air and nitrogen atmosphere [158]. A special attention must be given in this case to avoid the formation of parasitic spinel CuCr2O4 phase that occurs at 500–700 °C. Under pure nitrogen atmosphere, the CuCrO2 results from the direct reaction between Cu2O and Cr2O3 around 700 °C. Usually, the solid-state processes take long time in order to remove moisture or any other organic impurity and for achieving good crystalline quality. In order to accelerate the synthesis, Kumar et al. use the microwave heating, as it enhances solid-state reaction kinetics [178]. Another chemical method of fabrication for copper chromium delafossite is the sol–gel process [179,180,181,182,183,184,185,186]. Copper and chromium hydrate precursors are dissolved in alcoholic or water-based solutions. For example, Wang [187] and Li [188] use copper acetate monohydrate (Cu(CH3COO)2·H2O) and chromium nitrate nonahydrate (Cr(NO3)3·9H2O) for fabricating CuCrO2 thin films or targets for physical vapour depositions. Ngo [189] uses the same precursors but dissolved in distilled water with NaOH as the mineralizer and citric acid as a chelating agent. The last method using a chemical route is the hydrothermal synthesis, one of the most commonly used for preparation of nanomaterials [21, 190,191,192,193]. In this case, the chemical formation occurs in a wide temperature range from room temperature to very high temperatures, typically above 800 °C. Low- or high-pressure conditions can be used, depending on the vapour pressure of the main composition in the reaction. Gil [194] uses copper nitrate hemipentahydrate Cu(NO3)2·2.5H2O and chromium(III) nitrate nonahydrate Cr(NO3)3·9H2O dissolved in deionized water and NaOH solution. Ngo [189] used Cr(NO3)3·H2O dissolved in water and Cu2O dissolved in 3 M NaOH solution. However, the peculiar conditions (high temperatures or pressures) required by these methods exclude the direct use for the fabrication of transparent electronic devices and hence they are typically used for the synthesis of targets for the physical deposition processes (pulsed laser deposition or sputtering) methods. These methods also allow the fabrication of doped delafossite. The typical final product has a powder form, and the spin coating is furthermore used for thin films deposition. However, this is not adequate for large scale deposition, due to a poor long-range uniformity or control of the process [195].
A second category of deposition methods refers to physical vapour deposition (PVD) mainly the sputtering [47, 117, 196,197,198,199,200,201,202,203] and pulsed laser deposition [47, 145, 188, 204,205,206,207,208]. Vacuum-based techniques are preferred as this addresses the issue of the instability of Cu+ and its sensibility to the oxygen partial pressure [209]. The PLD and some sputtering processes are used just as a material transfer method. A composite CuCrO2 pellet fabricated using a method described above is used as target, and no other chemical compounds are involved. Laser or plasma is used to extract the material from this target and deposited in thin films forms. During the deposition, the substrate is usually heated at temperatures between 450 and 750 °C, with a crystalline delafossite phase observed usually this for temperatures higher than 500 °C [184, 199, 200, 202]. The films deposited using technique are smoother and more compact than those fabricated using the wet chemistry. This approach is often used when the synthesis of doped thin films is envisaged. A target already prepared with the intended stoichiometry is used in this case [117, 188, 206]. The involving of nitrogen gas during the deposition process leads to a N2-doped films with higher electric conductivity [47, 210]. Sun et al. [211] used also the DC co-sputtering (Cr and Cu targets) with oxygen as reactive gas. The films deposited in this case were amorphous and showed high resistivity. Very frequent, high-temperature annealing post-treatments under different atmospheres are engaged in order to fully convert the parasitic phases (CuO and CuCr2O4) to the CuCrO2 phase or to engineer the thin films’ morphology, strongly related to the optical properties. It is worth mentioning here the work of Shin [212] reporting the growth of CuCrO2 thin films using the molecular beam epitaxy. This peculiar technique, despite its high energetic costs, is known to yield epitaxial thin films with almost no defects. The films deposited at a pressure of 5 × 10–10 mbar on Al2O3 (001) substrates showed (001) or (005) crystallographic orientations for temperatures of 700 and 800 °C, respectively.
The last category of methods for depositing the CuCrO2 refers to chemical vapour deposition (CVD). Vapour of Cu and Cr (and dopant if required) precursors is sent in the reactor where they decompose and further react with Oxygen. Copper and chromium metallo-organic precursors such as acetylacetonates (Cu(acac)2-CuC10H14O4, (Cr(acac)3-CrC15H21O6) or tetramethyl-heptadionates (Cu(thd)2-C22H38CuO4, Cr(thd)3-C33H57CrO6) in solution are generally used [11, 48, 161, 213,214,215,216]. The use of these precursors prevents the alteration of electronic properties due to the absence of halide ions on the substrate [217]. The reaction takes place within the volume of the reactor CVD [215, 218]) or on the substrate surface (atomic layer deposition (ALD) [219]). The main advantage of these methods consists of the high conformality of the deposits, and hence, they are suited for substrates with complex 3D geometries. Additionally, the temperatures required are lower than those for PVD and hence smaller energetic costs are achieved. Tripathi [219,220,221] used Cu(thd)2 and Cr(acac)3 as metallic precursors and ozone as oxygen source in his ALD process. Films with optical transmission up to 80% were synthesized at temperatures as low as 250 °C with a growth rate of 0.2 nm s−1. The films doped with 2.5% magnesium (using Mg(thd)2) presented high electric conductivities greater than 200 S cm−1. Within the CVD process, the delafossite thin film grows from the surface reaction between precursors being decomposed (thermally or plasma assisted) within the volume of the reactor or at the surface when they undergo the surface reaction. Growth rates of 5 nm/min are obtained for medium-scale depositions (up to 20 cm) at temperature down to 400 °C [48]. The last method presented here is the spray pyrolysis (SP) [217, 222,223,224]. Similar to the CVD method, this is a simple technique that is suited to deposit films over large areas. The precursor solution is sprayed directed onto the heated substrate where after decomposition, the oxidation leads to a metal oxide deposition. Cu–Cr–O delafossite films were synthesized on various substrates at temperatures as low as 345 °C [223]. What must be emphasized here is that the last two methods (CVD and SP) lead towards Cu–Cr–O films presenting a delafossite crystalline structure but far from a 1:1:2 classical stoichiometry (i.e. important excess/deficit of Cu or/and Cr) [225, 226]. These films present very promising optoelectronic properties, and studies are focusing lately on understanding the physical processes within [213, 216].
To summarize, the Cu–Cr–O delafossite films are deposited using a large panel of methods. The standard CuCrO2 films and the extrinsic doped (see extrinsic doping section) ones follow similar deposition procedures. The chemical sources of the components (Cu, Cr and the dopant) are initially mixed in the right proportion, and then, the synthesis process is started. A good example is described in Okuda et al.[142] where CuCr1-xMgxO2 (0 < x < 0.04) of Cu2O, Cr2O3 and MgO powders are initially weighted in order to ensure the right proportions (CuCrMg0O2, CuCr0.95Mg0.005O2, CuCr0.9Mg0.1O2, etc.). The situation is different in the case of the fabrication of defective delafossite (intrinsic doped) films. Non-equilibrium thermodynamic conditions must be achieved in order to stabilize the metastable states (with important deviances from the 1:1:2 stoichiometry). The fabrication methods able to provide this kind of thermodynamic environment are generally involving dynamic precursor injection (SP or DLI-MOCVD) or plasma (RF sputtering or plasma-enhanced CVD).
Optical properties
Typical values in the range of 30–70% are commonly reported for the optical through the delafossite Cu–Cr–O thin films within the visible wavelength range. However, this is not a reliable parameter for comparing optical properties of different films due to its thickness dependence (Lambert law I(d) = I0exp(-αd)). Additionally, the morphology of the films depends on the deposition methods and on the performed post-treatments. This influences the absorption processes, altering optical transition between bands, sub-bands or defects. Hereby, the optical band gap is mostly used for characterizing and comparing the optical response of the thin films as this is an intrinsic property of material, not depending on the geometry of the film. The first report (based on the photoelectrochemical measurements) of the CuCrO2 band gap [176] indicates an indirect band gap of 1.28 eV with one indirect.
and one direct allowed transition at 3.08 eV and 3.35 eV, respectively. The optical absorption appearing near 3 eV is due to the band-to-band transition Cu3d + O2p → Cr3d + O2p (Fig. 4). The absorption around 2 eV is associated with Cr3d (t2g) → Cr3d (teg) transition due to the octahedral environment of chromium atoms (crystal field splitting) [212]. Figure 5 depicts the experimental band gaps reported over the literature (Supplementary information section Table S.II). The significant span for the band gap’s values is again a result of the diversity of deposition methods and post-treatments. These band gaps might be tailored by tuning the deposition parameters [214] or the level of doping [181, 220]. For example, both direct and indirect band gaps are influenced by the content of Mg within the Mg/CuCrO2. They decrease for concentrations of Mg up to 8% but an increasing is then observed for greater dopant content [181]. This was attributed to the band gap renormalization and Burstein–Moss effect induced by the dopant. Finally, a decrease in transparency might be possible due to the Cr d–d transitions between the split energy levels of partially filled Cr3d shell [116]. The excitation of electrons from the lower to the upper of these levels might occur by absorbing photons in the visible range.
Transport properties
The most common methods for studying the transport properties in the delafossite materials are the four-point resistivity and the Seebeck coefficient. These allow the direct determination of the conductivity (when thickness is known) and the carrier concentration (presuming the charge transport mechanism as known); these furthermore grant the calculation of the mobility (σ = neµ). The temperature dependency of these parameters gives important information related to the transport mechanism. The use of Hall effect for investigating this material is challenging and generally questionable due to the usually very low mobilities of charge carriers. It requires very high magnetic fields or complex mathematic models that are not always reliable [227].
Pure (undoped) CuCrO2 shows a high resistivity due to low acceptor defects concentration and high acceptor energy levels [48]. The reported values depend mainly on the synthesis method. Poienar et al. [228] reported a conductivity of 0.003 S cm−1 in a single crystal fabricated by the flux technique, Yu [229] reported a value of 0.2 S cm−1 for films prepared using RF sputtering, whilst Sadik [206] measured a conductivity of 0.0001 S cm−1 for film grown by pulsed laser deposition. There is a general agreement that CuCrO2 in pure phase presents low conductivities and only the non-stoichiometric or doped delafossite phases show decent electrical conductivity, higher than 1 S cm−1. The maximum reported values in this case are 278 S cm−1 for a Mg–N co-doped delafossite [47] and 100 S cm−1 for a non-stoichiometric one [161].
Source of doping
Extrinsic doping
Many groups reported a significant improvement of electrical conductivity with the introduction of divalent cations at the Cr site. This is a result of the increase in the holes concentration due to the charge difference in the substituting site. This boost in conductivity has been linked to CuI /CuII and to CrIII /CrIV hole mechanisms [82, 103, 142, 149, 230].
The main role of the dopants is to increase the carrier concentration, without altering the delafossite structure. [47] As a general rule of thumb for the doping process, the smaller size difference between the dopant and the substituted cation and M cations, the easier will be to dope. Typically reported CuCrO2 dopants are Ba, Ca, Cd, Co, Fe [193], Mg, Mn[231, 232], N,[47], Ni [233], Sc [157], Sn and Zn [182]. Among all these, the magnesium has been reported as the dopant leading to the best performance in electrical properties of delafossite. When doping with a trivalent cation X3+ (isovalent doping), the resulting compound shows a mix of properties related to CuCrO2 and CuXO2 [234]. Although the carrier concentration is not modified (3 + replaced by 3 +), changes of electrical properties are often reported [148, 157]. This might be a result of the difference between the radii of the dopant and of the substituted atom. The internal stress induced this way might alter the band structure and consequently the electronic charge mobility, as already demonstrated for polycrystalline films of Ge [235], Si [166] or graphene [167]. Table 3 summarizes the studies related to the extrinsic doping of Cu–Cr–O delafossite.
Intrinsic doping
Point native defects are widely considered as the source of holes in pure stoichiometric delafossites. However, the cations’ vacancies and the excess oxygen (interstitial) anions have high formation energies and therefore are counterbalanced by the native hole killers, such as anion vacancies [67].
a) Cu vacancies (VCu → Cu0 + h+) [82]; they act as hole donors and introduce shallow acceptor states [249].
b) Oxygen interstitials (Oi) [250]—Intercalation with oxygen to form CuCrO2+δ phases improves the conductivity. The excess of oxygen intercalates within the crystal structure, trapping electrons and thus leaving behind two states in the VB:
This defect is more noticeable for larger B cations, because a bigger lattice would accommodate more excess of oxygen. The intercalation of oxygen creates tail states in the band gap, reducing the transmittance. It is difficult to observe oxygen intercalation for small B cations, probably due to the small size that shrinks the lattice enough to impede O penetration [128]. This phenomenon is strongly dependent on the oxygen conditions and annealing throughout the film’s deposition.
The energy formation enthalpy of various defects in CuCrO2 was also evaluated with LDA, PBE, PBE + U or HSE06 theoretical approaches [82, 251] (see the explanations sabove, within the paragraph related to the structure of delafossite), and the results are summarized in Table 4. All methods indicate the chromium substitution by magnesium (MgCr) the most thermodynamically favourable, followed by copper vacancies (VCu) and oxygen interstitial (Oi).
A special attention is given lately to the off-stoichiometric delafossite materials that are characterized by significant excess/deficit of copper and/or chromium [161, 223, 225, 252]. Although they demonstrate important deviation from the standard 1:1:2 stoichiometry, the structural analysis (XRD, Raman, XPS) indicates still a delafossite structure. Ling et al. [226] reported the fabrication of Cr deficient (CuCr1-xO2; 0 < x < 0.1) films fabricated via the solid-state reaction method. They observed an electrical behaviour similar to the Mg-doped CuCrO2, reporting a minimal resistivity of 2 kΩ cm for CuCr0.92O2. It was concluded that the increase in carriers’ concentration is a result of the excess holes doped into the Cu sites by the Cr deficiency. (One missing Cr atom might create three holes.) Next in order, researchers using the chemical vapour deposition started to report the synthesis of Cu–Cr–O delafossite layers with a significant Cu deficiency. Farrell et al. [223] reported first such a material with 20% copper deficit when using spray pyrolysis and acetylacetonate precursors for copper and chromium in methanol. An electrical conductivity of 12 S cm−1 and an optical transmission of 55% were determined for 90-nm thin films. Furthermore, the same group reported the obtention of a Cu0.4CrO2 film with interesting opto-electronic properties [225]. Raman, XPS and XRD analyses confirm the delafossite structure. However, they observed an increased number of Cr–O octahedra in these Cu deficient films when compared to crystalline CuCrO2. Finally, off-stoichiometric copper chromium delafossite showing simultaneously a copper deficiency and a chromium excess (i.e. Cu1-xCr1+xO2) was also synthesized using dynamic liquid injection—MOCVD [48, 215]. These films present a very peculiar 2/3:4/3:2 stoichiometry with one-third of the copper atoms missing and a supplementary one-third of chromium atoms. Up to now, these films show the highest values of conductivity (102 S cm−1 [161]) for a non-intentionally doped copper chromium delafossite.
Nevertheless, it is clear that the source of doping in these last off-stoichiometric delafossite materials cannot be related to (only) point defects and actual research trying to understand the charge source and transport mechanism within such particular materials is still conducted. Only recently, chains of Cu vacancies were observed [161] for the first time and investigated as an eventual source of doping in such materials. By using positron annihilation spectroscopy on Cu0.66Cr1.33O2 samples, Lunca-Popa et al. [213] associated the decrease in conductivity with a decrease in size of the chained vacancies. They suggest therefore the presence of a ripening mechanism based on the dissolution of the chains of copper vacancies being healed upon annealing, leading to a drop of electrical conductivity. The presence of these metallic chained vacancies is supported by the theoretical work of Art and Zunger [253, 254] showing that in the case of transparent conductors, the law of definite proportion can be broken and the formation of these type of defects is favoured thermodynamically as “it costs no energy”.
Howbeit, despite the significant differences between extrinsic doped CuCrO2 and highly conductive Cu0.66Cr1.33O2, there are important similarities on their electric properties. For example, in the case of Mg/CuCrO2, Okuda [142] finds different Seebeck effect temperatures dependencies (S = f (T)) (Fig. 6a) for non-doped (x = 0) and doped delafossite. The S value for x = 0 is about 350 µV K−1 at 300 K, whilst the T dependence shows a broad peak structure. The Seebeck coefficient decreases drastically with the increase of Mg content. The broad peak structure in the T dependence gradually disappears with x. Starting with a Mg content of 2%, the Seebeck coefficient is nearly proportional (linear dependence) with the temperature up to 300 K that corresponds to a decrease in the resistivity. A similar behaviour was observed within Cu0.66Cr1.33O2 delafossite films (Fig. 6b). As-deposited samples present an almost a linear dependence on T. After annealing, the curve captures a bell shape, similar to the non-doped (x = 0) previous CuCrO2. This semblance reinforces the idea that chained copper vacancies act as a dopant in Cu0.66Cr1.33O2 in a similar way that Mg acts as a dopant in standard CuCrO2.
Conduction mechanism in CuCrO2
In the semiconductors the charge carriers transport is governed by several main scattering mechanisms: intrinsic (lattice) scattering due to the band structure of the semiconductor and extrinsic scattering caused by impurities, ionized or dopants. The intrinsic scattering dominates for low carrier concentrations, usually below n < 1016 cm−3, whilst the scattering on the ionized impurities becomes important for concentrations beyond 1018 cm−3 (at room temperature). Moreover, in the case of polycrystalline films the scattering on the grain boundaries must be considered. Each mechanism is characterized by different relaxation times, which leads to different carrier mobilities. These mechanisms can be grouped into two main categories:
First stands the classical conduction band mode. In this case, the thermal energy is considered as enough for activating the carriers to the free delocalized states. The conductivity is expressed as:
where σ0 is a pre-exponential factor, Ea is the activation energy, kB is Boltzmann constant and T is the temperature. The charge carriers motion is activated at a certain temperature, corresponding to the activation energy. This mechanism was observed at high temperatures (typically above 200 K) in doped or non-doped Cu–Cr–O films [84, 181, 196, 210]. The values reported for the activation energies for undoped CuCrO2 are in the range of 100–300 meV (Fig. 7, ND on x-axis), much smaller than the band gap value, that proves a transport involving an acceptor level. Lower values, below 100 meV, are reported for the doped delafossites as in this case the doping leads to the displacement of the Fermi level next to the valence band. This was observed in Mg/CuCrO2 (σRT ≈ 1.6 S cm−1 [196], σRT ≈ 16 S cm−1 [142], σRT ≈220 S cm−1 [117], Ni/CuCrO2 (σRT ≈ 0.05 S cm−1 [233]), N/CuCrO2 (σRT ≈ 17 S cm−1[210]), Fe/CuCrO2 (σRT ≈ 28 S cm−1 [145]), Co/CuCrO2 (σRT ≈ 0.0002 S cm−1 [255]) or in off-stoichiometric Cu–Cr–O (σRT ≈ 12 S cm−1[215], σRT ≈ 102 S cm−1 [216]).
The second mechanism discussed here is the variable range hopping conduction, where the charges are moving through localized states. It is characterized by a strong relation between the level of hopping conductance and the concentration of localized states around the Fermi level. In the three-dimensional case, the expression for the conductivity might be written as:
where σ0 is a pre-exponential factor and EH is the activation energy for hopping. This is inversely proportional to the density of states at the Fermi level and the cube of the localization length, closely related to the average energy needed to push the localized charge carrier to nearest impurity. For CuCrO2 delafossite, this mechanism is reported occurring at temperatures typically below 200 K [140, 235], where the electrical transport properties are determined by the hopping of holes between the nearest-neighbour Cu sites. The energy activation, typically below 100 meV in this case, is smaller than that in the case of the conduction band. Figure 7 depicts reported values for both conductivity (band conduction) and for mobility (small polaron) energies activation.
Nevertheless, the delafossite has been consistently proposed to exhibit electrical transport limited by small polaron hopping [83, 103, 126, 196, 215, 256, 257]. This can be justified by the high effective mass, due to the polaronic interaction between carriers and the lattice. In the case of small polaronic conduction, the distortion of the lattice extends over distances smaller than the lattice constant. The strong interaction between the lattice and the carrier leads to a charge self-trapping due to their own polarization. Polaron conduction is characterized by hopping properties. In contrast to other conduction mechanisms, lattice vibrations do not inhibit conduction but rather allow it, like as in ionic conductivity. There are two types of polarons; in the case of large polarons, the distortion of the lattice extends over few lattice constants. The carrier transport is still called “band conduction” like classical semiconductors, but the effective mass at the VBM or CBM is much higher due to the polaronic interaction between carriers and the lattice [258, 259]. For small polarons, the distortion of the lattice extends over distances smaller than the lattice constant. The coupling is strong enough, and the carriers become self-trapped by its own polarization generated in the ionic lattice [260]. It should be emphasized here that the ¼ temperature dependence is not automatically implying the solely presence of small polaron mechanism. According to calculations, other conduction mechanisms, using specific presumptions, can also show a temperature dependence similar to the T−1/4 dependence [261,262,263]
Anisotropy of electronic properties
It has been reported that the crystalline structure of delafossites has a large anisotropic electrical conductivity, with the in-plane (ab) conductivity (σab) being far larger than along the c-axis (σc) [249]. CuCrO2 was reported with a resistivity ratio of ρc axis/ρab plane≈35 at 300 K, implying that [CrO2] and/or [Cu+] planes are better conducting path than Cu–O–Cu along c-axis [228]. According to electronic structure calculations performed (Fig. 4) for CuCrO2, the d orbitals of Cr3+ are mainly contributed near the Fermi level as compared to those of Cu+, which could imply that the carriers would be mainly in the Cr planes rather than in the Cu ones. An increase in the (00l) orientation implies a greater presence of Cu + (ab planes) in the conduction path [210].
Thermoelectric measurements
The debate concerning the mechanism governing the conduction in heavily doped delafossites is still active. According to the of Bosman-Van Daal [264] limit, small polaron transport is considered to occur for low mobilities, below 0.1 cm2 V−1 s−1. Such low values are burdensome to be determined by the Hall effect as very high magnetic fields or complicated mathematical model are required. For example, O’Sullivan et al. [265] measured a mobility of 0.04 cm2 V−1 s−1 for 10% Mg/CuCrO2 at 300 K by using a magnetic field of 14 T. Moreover, Werner et al. [227] engaged a complex model for off-set Hall coefficient corrections and estimated a mobility of 0.15 cm2 V−1 s−1 for off-stoichiometric Cu0.66Cr1.33O2 [215].
In order to circumvent the use of the Hall effect, thermoelectric measurements can be used. This allows to extract the carrier concentration and, when combined with resistivity measurements, the estimation of mobility values (σ = neµ). However, this method raises some debate regarding the approximation done for the effective density of states. For instance, in the case of ZnRhO2, a polaron conduction is demonstrated if the effective density of states is assumed constant, whilst band conduction properties are observed if a temperature dependence is assumed [266]. The Seebeck coefficient is defined as ΔV/ ΔT, where ΔV is the induced thermoelectric voltage as in response to a temperature difference ΔT across the material. If the energetic structure of a material is known, the position of the Fermi level can be thus deduced from the Seebeck coefficient. Furthermore, the charge carrier concentration can be determined assuming a known charge transport model. For the p-type semiconductors, the most often reported conduction models are the non-degenerate [267] and degenerate [268, 269] semiconductor or small polaron [258, 270, 271]. The relationship between the Seebeck coefficient and the carrier concentration in each of these cases has the following expression:
where h is the Planck constant, kB is the Boltzmann constant, NV is the effective density of states, A is a constant depending on the nature of scattering process (1 < A < 4; A = 0 for small polaron model), e is the electron charge, p is the carrier concentration, m* is the effective mass, T is the absolute temperature and c is the fraction of occupied sites by polarons.
As emphasized before, the small polaron mechanism onto Cu planes is the most often used to explain the charge transport within the delafossite. Within the formula above, for the Cu–Cr–O delafossite the fraction of occupied sites can be written as c = [Cu2+]/ [Cu+], where [Cu2+] is the number of occupied sites by polarons and [Cu +] is the concentration of copper atoms in a delafossite crystal.
Figure 8 depicts a summary of Seebeck coefficient and electric conductivity reported values in the literature. It can be seen that the highest conductive samples demonstrate the lowest Seebeck coefficients (typically below 200 µV K−1). This is the case of doped or off-stoichiometric Cu–Cr–O delafossites. For pure delafossite or generally, for low conductive delafossite films, values of thermopower coefficient are beyond 500 µV K−1. These reports might induce the idea that the high conductivity is driven by the big number of charge carriers (inversely proportional to S), whilst a direct influence of mobility is difficult to be extracted. Seebeck coefficient depends also on the temperature range. The Seebeck temperature dependence shows specific trends for the undoped and doped Cu–Cr–O delafossite (Fig. 7). In the case of low conductive delafossite thin films, the Seebeck coefficient decreases with the temperature, whilst an opposite trend is observed for highly conductive doped samples. Some deviations are observed below the room temperature due to the transition between the conduction mechanisms.
Carrier concentration and mobility
A plot of mobility versus carrier concentrations of undoped and doped copper chromium delafossite thin films reported in the literature is illustrated in Fig. 9. The conductive films are usually characterized by high levels of carrier concentration (> 1020 cm−3), typically featuring a degenerate semiconductor. The maximal reported values of holes concentration are around 1021–1022 cm−3 [142, 161, 265] for doped films fabricated by various methods. On the opposite, low carrier concentrations are describing the samples with low conductivity. Values below 1017 cm−3 are reported for low conductive, non-doped delafossite with a minimal value of 1014 cm−3 for CuCrO2 [84]. Most of the mobilities values are calculated from thermoelectric measurements (as described above, a direct measure using Hall effect is difficult) by using the σ = neµ, with the concentration estimated from the Seebeck coefficient. Its expression depends on the transport model considered, and one might think that assuming a wrong model will lead to erroneous values for electronic parameters. This is not entirely true as shown in the next example. In [161], the authors investigate (at room temperature) two Cu–Cr–O samples with different conductivities (102 S cm−1 and 0.7 mS cm−1, respectively). After a direct measure of sheet resistance and Seebeck coefficient, different transport models are used to estimate the carrier concentration and finally the mobility. The results are presented in Table 5. In the case of conductive sample, the use of small polaron model or degenerated semiconductor leads to comparable (same order of magnitude) values for p and µ. The same similarity is observed when the small polaron or non-degenerate semiconductor model is applied for low conductive samples. This invariance with the choice of the model enhances the reliability of data obtained from thermoelectric measures.
Conclusion
The CuCrO2 shows the highest p-type electrical conductivity among delafossite oxides. This contravenes [219] the tendency observed for several other CuMO2 (M = B, Al, Sc, Y) delafossites where a decrease in electrical conductivity with increasing size of the M3+ cation is observed. This discrepancy might be a result of the favourable covalent mixing between Cr3+ and O2− and of the high density of Cr3d states near the VBM. The values of electronic properties depend on the morphology of the film, which is strongly correlated with the deposition method. The pure delafossite phase demonstrates very low electrical conductivity. On the contrary, the off-stoichiometric phases and those doped with magnesium show electrical conductivities of hundreds of S cm−1. These values are a result of the high level of concentration carriers induced by the defects. The most used model used for explaining the charge carrier transport mechanisms is the small polaron, which might explain the low values of the electronic mobility. However, the degenerate or non-degenerate semiconductor models convey for reliable results in the case of high or, respectively, low conductive delafossite phases. There are two main prospective strategies for ameliorating the actual electrical performances of delafossite material. A first one resides in improving the very small carriers mobilities by manipulating the energy band structure of the material. This can be done, for example, by engineering the strain of the films as was already proven in for other semiconductors. A second strategy might be based on the doping of the off-stoichiometric Cu–Cr–O delafossite materials. This approach was fruitful on the case of standard 1:1:2 stoichiometry whereby the doping with 5% Mg led to two orders of magnitude increase in the electrical conductivity. A similar result might be expected than for an adequate doping of a defective delafossite material. This review provides convincing arguments that Cu–Cr–O delafossite materials are among the most suitable chemistry for the development and integration of functional transparent p-type semiconductors. The unique capability in adjusting the stoichiometry, the defects features, the residual stress of thin films together with the capability to grow well-controlled layers is still opening many routes of research to harness the full potential of such a complex material in real device applications.
References
Betz U, Kharrazi Olsson M, Marthy J et al (2006) Thin films engineering of indium tin oxide: large area flat panel displays application. Surf Coatings Technol 200:5751–5759. https://doi.org/10.1016/j.surfcoat.2005.08.144
Chen Z, Li W, Li R et al (2013) Fabrication of highly transparent and conductive indium-tin oxide thin films with a high figure of merit via solution processing. Langmuir 29:13836–13842. https://doi.org/10.1021/la4033282
Granqvist CG (2014) Electrochromics for smart windows: oxide-based thin films and devices. Thin Solid Films 564:1–38. https://doi.org/10.1016/j.tsf.2014.02.002
Granqvist CG (2007) Transparent conductors as solar energy materials: a panoramic review. Sol Energy Mater Sol Cells 91:1529–1598. https://doi.org/10.1016/j.solmat.2007.04.031
Zhang KHL, Xi K, Blamire MG, Egdell RG (2016) P -type transparent conducting oxides. J Phys Condens Matter 28:383002. https://doi.org/10.1088/0953-8984/28/38/383002
Grundmann M, Klüpfel F, Karsthof R et al (2016) Oxide bipolar electronics: materials, devices and circuits. J Phys D Appl Phys 49:213001. https://doi.org/10.1088/0022-3727/49/21/213001
Fleischer K, Norton E, Mullarkey D et al (2017) Quantifying the performance of P-type transparent conducting oxides by experimental methods. Materials (Basel) 10:19–22. https://doi.org/10.3390/ma10091019
Wang Z, Nayak PK, Caraveo-Frescas JA, Alshareef HN (2016) Recent developments in p-Type oxide semiconductor materials and devices. Adv Mater 28:3831–3892. https://doi.org/10.1002/adma.201503080
Hautier G, Miglio A, Ceder G et al (2013) Identification and design principles of low hole effective mass p-type transparent conducting oxides. Nat Commun 4:2292. https://doi.org/10.1038/ncomms3292
Brunin G, Rignanese GM, Hautier G (2019) High-performance transparent conducting oxides through small-polaron transport. Phys Rev Mater 3:1–7. https://doi.org/10.1103/PhysRevMaterials.3.064602
Afonso J, Leturcq R, Lunca-Popa P et al (2018) Transparent p-Cu0.66Cr1.33O2/n-ZnO heterojunction prepared in a five-step scalable process. J Mater Sci Mater Electron 30:1760–1766. https://doi.org/10.1007/s10854-018-0448-4
Nomura K, Kamiya T, Hosono H (2011) Ambipolar oxide thin-film transistor. Adv Mater 23:3431–3434. https://doi.org/10.1002/adma.201101410
Nomura K, Ohta H, Takagi A et al (2004) Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors. Nature 432:488–492. https://doi.org/10.1038/nature03090
Nomura K, Ohta H, Ueda K et al (2003) Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor. Science 300:1269–1272. https://doi.org/10.1126/science.1083212
Sialvi MZ, Mortimer RJ, Wilcox GD et al (2013) Electrochromic and colorimetric properties of nickel(II) oxide thin films prepared by aerosol-assisted chemical vapor deposition. ACS Appl Mater Interfaces 5:5675–5682. https://doi.org/10.1021/am401025v
Liu Q, Chen Q, Zhang Q et al (2018) In situ electrochromic efficiency of a nickel oxide thin film: origin of electrochemical process and electrochromic degradation. J Mater Chem C 6:646–653. https://doi.org/10.1039/c7tc04696k
Ohta H, Orita M, Hirano M, Hosono H (2001) Fabrication and characterization of ultraviolet-emitting diodes composed of transparent p-n heterojunction, p-SrCu2O2 and n-ZnO. J Appl Phys 89:5720–5725. https://doi.org/10.1063/1.1367315
Kim S, Kim SJ, Kim KH et al (2014) Improved performance of Ga2O3/ITO-based transparent conductive oxide films using hydrogen annealing for near-ultraviolet light-emitting diodes. Phys Status Solidi Appl Mater Sci 211:2569–2573. https://doi.org/10.1002/pssa.201431278
Battaglia C, Cuevas A, De Wolf S (2016) High-efficiency crystalline silicon solar cells: status and perspectives. Energy Environ Sci 9:1552–1576. https://doi.org/10.1039/c5ee03380b
Menchini F, Grilli ML, Dikonimos T et al (2016) Application of NiOx thin films as p-type emitter layer in heterojunction solar cells. Phys Status Solidi Curr Top Solid State Phys 13:1006–1010. https://doi.org/10.1002/pssc.201600121
Tong B, Deng Z, Xu B et al (2018) Oxygen vacancy defects boosted high performance p-type delafossite CuCrO2 gas sensors. ACS Appl Mater Interfaces 10:34727–34734. https://doi.org/10.1021/acsami.8b10485
Baratto C, Kumar R, Faglia G et al (2015) P-Type copper aluminum oxide thin films for gas-sensing applications. Sensors Actuators, B Chem 209:287–296. https://doi.org/10.1016/j.snb.2014.11.116
Upadhyay D, Roondhe B, Pratap A, Jha PK (2019) Two-dimensional delafossite cobalt oxyhydroxide as a toxic gas sensor. Appl Surf Sci 476:198–204. https://doi.org/10.1016/j.apsusc.2019.01.057
Mokoena TP, Swart HC, Motaung DE (2019) A review on recent progress of p-type nickel oxide based gas sensors: future perspectives. J Alloys Compd 805:267–294. https://doi.org/10.1016/j.jallcom.2019.06.329
Bhattacharya D, Ghoshal D, Mondal D et al (2021) Delafossite type CuCo0.5Ti0.5O2 composite structure: a futuristic ceramics for supercapacitor and EMI shielding application. Ceram Int 47:9907–9922. https://doi.org/10.1016/j.ceramint.2020.12.135
Sato H, Minami T, Takata S, Yamada T (1993) Transparent conducting p-type NiO thin films prepared by magnetron sputtering. Thin Solid Films 236:27–31. https://doi.org/10.1016/0040-6090(93)90636-4
Tsukazaki A, Ohtomo A, Onuma T et al (2005) Repeated temperature modulation epitaxy for p-type doping and light-emitting diode based on ZnO. Nat Mater 4:42–45. https://doi.org/10.1038/nmat1284
Qiu M, Zhang Y, Ye Z et al (2007) Effect of oxygen pressure on structural and electrical properties of pulsed laser deposition-derived Zn0.95Mg0.05O: Li thin films. J Phys D Appl Phys 40:3229–3232. https://doi.org/10.1088/0022-3727/40/10/030
Lyons JL, Janotti A, Van De Walle CG (2009) Why nitrogen cannot lead to p -type conductivity in ZnO. Appl Phys Lett 95:252105. https://doi.org/10.1063/1.3274043
Varley JB, Lordi V, Miglio A, Hautier G (2014) Electronic structure and defect properties of B6O from hybrid functional and many-body perturbation theory calculations: a possible ambipolar transparent conductor. Phys Rev B - Condens Matter Mater Phys 90:1–9. https://doi.org/10.1103/PhysRevB.90.045205
Bierwagen O, Speck JS (2012) Mg acceptor doping of In2O3 and overcompensation by oxygen vacancies. Appl Phys Lett 101:102107. https://doi.org/10.1063/1.4751854
Alshahrie A, Joudakzis S, Al-Ghamdi AA et al (2019) Synthesis and characterization of p-type transparent conducting Ni1-xRuxO (0 ≤x ≤ 0.1) films prepared by pulsed laser deposition. Ceram Int 45:7984–7994. https://doi.org/10.1016/j.ceramint.2018.09.214
Chen X, Zhao L, Niu Q (2012) Electrical and optical properties of p-type Li, Cu-codoped NiO thin films. J Electron Mater 41:3382–3386. https://doi.org/10.1007/s11664-012-2213-4
Caraveo-Frescas JA, Nayak PK, Al-Jawhari HA et al (2013) Record mobility in transparent p-type tin monoxide films and devices by phase engineering. ACS Nano. https://doi.org/10.1021/nn400852r
Ogo Y, Hiramatsu H, Nomura K et al (2008) P -channel thin-film transistor using p -type oxide semiconductor. SnO Appl Phys Lett 93:032113. https://doi.org/10.1063/1.2964197
Fortunato E, Barros R, Barquinha P et al (2010) Transparent p-type SnOx thin film transistors produced by reactive rf magnetron sputtering followed by low temperature annealing. Appl Phys Lett 97:052105. https://doi.org/10.1063/1.3469939
Yu S, Zhang W, Li L et al (2013) Fabrication of p-type SnO2 films via pulsed laser deposition method by using Sb as dopant. Appl Surf Sci 286:417–420. https://doi.org/10.1016/j.apsusc.2013.09.107
Chikoidze E, Fellous A, Perez-Tomas A et al (2017) P-type β-gallium oxide: A new perspective for power and optoelectronic devices. Mater Today Phys 3:1–9. https://doi.org/10.1016/j.mtphys.2017.10.002
Ueda N, Hosono H, Waseda R, Kawazoe H (1997) Synthesis and control of conductivity of ultraviolet transmitting β-Ga2O3 single crystals. Appl Phys Lett 70:3561–3563. https://doi.org/10.1063/1.119233
Orita M, Hiramatsu H, Ohta H et al (2002) Preparation of highly conductive, deep ultraviolet transparent β-Ga2O3 thin film at low deposition temperatures. Thin Solid Films 411:134–139. https://doi.org/10.1016/S0040-6090(02)00202-X
Minami T, Shimokawa K, Miyata T (1998) P-type transparent conducting In2O3–Ag2O thin films prepared by rf magnetron sputtering. J Vac Sci Technol A 6:1218–1221. https://doi.org/10.1116/1.581262
Asbalter J, Subrahmanyam A (2000) p -type transparent conducting In2O3–Ag2O thin films prepared by reactive electron beam evaporation technique. J Vac Sci Technol A 18:1672–1676. https://doi.org/10.1116/1.582405
Zhang KHL, Du Y, Papadogianni A et al (2015) Perovskite Sr-doped LaCrO3 as a new p-type transparent conducting oxide. Adv Mater 27:5191–5195. https://doi.org/10.1002/adma.201501959
Arca E, Fleischer K, Shvets IV (2011) Magnesium, nitrogen codoped Cr2O3: a p-type transparent conducting oxide. Appl Phys Lett 99:2011–2014. https://doi.org/10.1063/1.3638461
Norton E, Farrell L, Callaghan SD et al (2016) X-ray spectroscopic studies of the electronic structure of chromium-based p-type transparent conducting oxides. Phys Rev B 93:115302. https://doi.org/10.1103/PhysRevB.93.115302
Mohamed HA (2011) P-Type transparent conducting copper-strontium oxide thin films for optoelectronic devices. Eur Phys J Appl Phys 56:1–7. https://doi.org/10.1143/JPSJ.65.3973
Ahmadi M, Asemi M, Ghanaatshoar M (2018) Mg and N co-doped CuCrO2: a record breaking p-type TCO. Appl Phys Lett 113:242101. https://doi.org/10.1063/1.5051730
Crepelliere J (2016) Metalorganic Chemical Vapour Deposition of P- Type Delafossite CuCrO2 Semiconductor Thin Films:Characterization and application to transparent p-n junction. PhD Dissertation. University of Luxembourg
Kawazoe H, Yasukawa M, Hyodo H et al (1997) P-type electrical conduction in transparent thin films of CuAlO2. Nature 389:939. https://doi.org/10.1038/40087
Ok JM, Yoon S, Lupini AR et al (2020) Interfacial stabilization for epitaxial CuCrO2 delafossites. Sci Rep 10:1–8. https://doi.org/10.1038/s41598-020-68275-w
Ajimsha RS, Vanaja KA, Jayaraj MK et al (2007) Transparent p-AgCoO2/n-ZnO diode heterojunction fabricated by pulsed laser deposition. Thin Solid Films 515:7352–7356. https://doi.org/10.1016/j.tsf.2007.03.002
Ishiguro T, Ishizawa N, Mizutani N et al (1983) Charge-density distribution in crystals of CuAlO2 with d-s hybridization. Acta Crystallogr 22:564–569. https://doi.org/10.1107/S0108768183002980
Hicks CW, Gibbs AS, Mackenzie AP et al (2012) Quantum oscillations and high carrier mobility in the delafossite PdCoO2. Phys Rev Lett 109:116401. https://doi.org/10.1103/PhysRevLett.109.116401
Tate J, Jayaraj MK, Draeseke AD et al (2002) p-Type oxides for use in transparent diodes. Thin Solid Films 411:119–124. https://doi.org/10.1016/S0040-6090(02)00199-2
Wei R, Tang X, Hu L et al (2017) Facile chemical solution synthesis of p-type delafossite Ag-based transparent conducting AgCrO2 films in an open condition. J Mater Chem C 5:1885–1892. https://doi.org/10.1039/c6tc04848j
Kushwaha P, Sunko V, Moll PJW et al (2015) Nearly free electrons in a 5d delafossite oxide metal. Sci Adv 1:1–7. https://doi.org/10.1126/sciadv.1500692
Ueda K, Inoue S, Hirose S et al (2000) Transparent p-type semiconductor: LaCuOS layered oxysulfide. Appl Phys Lett 77:2701–2703. https://doi.org/10.1063/1.1319507
Hiramatsu H, Ueda K, Ohta H et al (2003) Degenerate p-type conductivity in wide-gap LaCuOS1-xSex (x = 0–1) epitaxial films. Appl Phys Lett 82:1048–1050. https://doi.org/10.1063/1.1544643
Ueda K, Inoue S, Hosono H et al (2001) Room-temperature excitons in wide-gap layered-oxysulfide semiconductor: LaCuOs. Appl Phys Lett 78:2333–2335. https://doi.org/10.1063/1.1364656
Hiramatsu H, Ueda K, Ohta H et al (2007) Heavy hole doping of epitaxial thin films of a wide gap p -type semiconductor, LaCuOSe, and analysis of the effective mass. Appl Phys Lett 91:012104. https://doi.org/10.1063/1.2753546
Windisch J, Exarhos GJ, Ferris KF et al (2001) Infrared transparent spinel films with p-type conductivity. Thin Solid Films 398–399:45–52. https://doi.org/10.1016/S0040-6090(01)01302-5
Dileep K, Loukya B, Silwal P et al (2014) Probing optical band gaps at nanoscale from tetrahedral cation vacancy defects and variation of cation ordering in NiCo2O4epitaxial thin films. J Phys D Appl Phys. https://doi.org/10.1088/0022-3727/47/40/405001
Dekkers M, Rijnders G, Blank DHA (2007) ZnIr2O4, a p-type transparent oxide semiconductor in the class of spinel zinc-d6-transition metal oxide. Appl Phys Lett 90:021903. https://doi.org/10.1063/1.2431548
Kim HJ, Song IC, Sim JH et al (2004) Electrical and magnetic properties of spinel-type magnetic semiconductor ZnCo2O4 grown by reactive magnetron sputtering. J Appl Phys 95:7387–7389. https://doi.org/10.1063/1.1688571
Mizoguchi H, Hirano M, Fujitsu S et al (2002) ZnRh2O4: a p-type semiconducting oxide with a valence band composed of a low spin state of Rh3+ in a 4d6 configuration. Appl Phys Lett 80:1207–1209. https://doi.org/10.1063/1.1450252
Mansourian-Hadavi N, Wansom S, Perry NH et al (2010) Transport and band structure studies of crystalline ZnRh2O4. Phys Rev B - Condens Matter Mater Phys 81:1–6. https://doi.org/10.1103/PhysRevB.81.075112
Kim T, Yoo B, Youn Y et al (2019) Material design of new p-Type tin oxyselenide semiconductor through valence band engineering and its device application. ACS Appl Mater Interfaces 11:40214–40221. https://doi.org/10.1021/acsami.9b12186
Bhatia A, Hautier G, Nilgianskul T et al (2016) High-mobility bismuth-based transparent p-type oxide from high-throughput material screening. Chem Mater 28:30–34. https://doi.org/10.1021/acs.chemmater.5b03794
Bobeico E, Varsano F, Minarini C, Roca F (2003) P-type strontium-copper mixed oxide deposited by e-beam evaporation. Thin Solid Films 444:70–74. https://doi.org/10.1016/S0040-6090(03)01023-X
Kudo A, Yanagi H, Hosono H, Kawazoe H (1998) SrCu2O2: A p-type conductive oxide with wide band gap. Appl Phys Lett 73:220–222. https://doi.org/10.1063/1.121761
Kawazoe H, Yanagi H, Ueda K, Hosono H (2000) Transparent p-type conducting oxides: design and fabrication of p-n heterojunctions. MRS Bull 25:28–36. https://doi.org/10.1557/mrs2000.148
Liu M-L, Wu L-B, Huang F-Q et al (2007) A promising p-type transparent conducting material: Layered oxysulfide [Cu2S2][Sr3Sc2O5]. J Appl Phys 102:116108. https://doi.org/10.1063/1.2817643
Hu L, Wei R, Yan J et al (2018) La2/3Sr1/3VO3 thin films : a new p-type transparent conducting oxide with very high figure of merit. Adv Electron Mater 4:1700476. https://doi.org/10.1002/aelm.201700476
Woods-Robinson R, Han Y, Zhang H et al (2020) Wide band gap chalcogenide semiconductors. Chem Rev 120:4007–4055. https://doi.org/10.1021/acs.chemrev.9b00600
Hosono H, Yasakawa M, Kawazoe H (1996) Novel oxide amorphous semiconductors : transparent conducting amorphous oxides Possible Candidate for HMCs. J Non Cryst Solids 203:334–344. https://doi.org/10.1016/0022-3093(96)00367-5
Hosono H (2006) Ionic amorphous oxide semiconductors: saterial design, carrier transport, and device application. J Non Cryst Solids 352:851–858. https://doi.org/10.1016/j.jnoncrysol.2006.01.073
Hosono H, Kikuchi N, Ueda N, Kawazoe H (1996) Working hypothesis to explore novel wide band gap electrically conducting amorphous oxides and examples. J Non Cryst Solids 198–200:165–169. https://doi.org/10.1016/0022-3093(96)80019-6
Sansonetti JE, Martin WC (2005) Handbook of basic atomic spectroscopic data. J Phys Chem Ref Data 34:1559–2259. https://doi.org/10.1063/1.1800011
Raebiger H, Lany S, Zunger A (2007) Origins of the p-type nature and cation deficiency in Cu2O and related materials. Phys Rev B - Condens Matter Mater Phys 76:045209. https://doi.org/10.1103/PhysRevB.76.045209
Zunger A (2003) Practical doping principles. Appl Phys Lett 83:57–59. https://doi.org/10.1063/1.1584074
Scanlon DO, Godinho KG, Morgan BJ, Watson GW (2010) Understanding conductivity anomalies in CuI -based delafossite transparent conducting oxides: theoretical insights. J Chem Phys 132:024707. https://doi.org/10.1063/1.3290815
Scanlon DO, Watson GW (2011) Understanding the p-type defect chemistry of CuCrO2. J Mater Chem 21:3655. https://doi.org/10.1039/c0jm03852k
Ketir W, Saadi S, Trari M (2012) Physical and photoelectrochemical characterization of CuCrO2 single crystal. J Solid State Electrochem 16:213–218. https://doi.org/10.1007/s10008-011-1307-x
Han M, Jiang K, Zhang J et al (2012) Structural, electronic band transition and optoelectronic properties of delafossite CuGa1−xCrxO2 (0 ≤ x ≤ 1) solid solution films grown by the sol–gel method. J Mater Chem 22:18463. https://doi.org/10.1039/c2jm33027j
Mao F, Nyberg T, Thersleff T et al (2016) Combinatorial magnetron sputtering of AgFeO2 thin films with the delafossite structure. Mater Des 91:132–142. https://doi.org/10.1016/j.matdes.2015.11.092
Shannon RD, Prewitt CT, Rogers DB (1971) Chemistry of noble metal oxides. II. Crystal structures of platinum cobalt dioxide, palladium cobalt dioxide, coper iron dioxide, and silver iron dioxide. Inorg Chem 10:719–723. https://doi.org/10.1021/ic50098a012
Rogers DB, Shannon RD, Prewitt CT, Gillson JL (1971) Chemistry of noble metal oxides. III. electrical transport properties and crystal chemistry of ABO2 compounds with the delafossite structure. Inorg Chem 10:723. https://doi.org/10.1021/ic50098a013
Shannon RD, Rogers DB, Prewitt CT (2015) Chemistry of noble metal oxides. I. Synthesis and properties of ABO2 delafossite compounds. Inorg Chem 10:713–718. https://doi.org/10.2307/2757505
Nagarajan R, Duan N, Jayaraj MK et al (2001) p-Type conductivity in the delafossite structure. Int J Inorg Mater 3:265–270. https://doi.org/10.1016/S1466-6049(01)00006-X
Sheets WC, Mugnier E, Barnabe A et al (2006) Hydrothermal synthesis of delafossite-type oxides william. Chem Mater 18:7–20. https://doi.org/10.1021/cm051791c
Mackenzie AP (2017) The properties of ultrapure delafossite metals. Reports Prog Phys 80:032501. https://doi.org/10.1088/1361-6633/aa50e5
Harada T (2021) Thin-film growth and application prospects of metallic delafossites. Mater Today Adv 11:100146. https://doi.org/10.1016/j.mtadv.2021.100146
Harada T, Fujiwara K, Tsukazaki A (2018) Highly conductive PdCoO2 ultrathin films for transparent electrodes. APL Mater 6:4–10. https://doi.org/10.1063/1.5027579
Takatsu H, Yonezawa S, Mouri S et al (2007) Roles of high-frequency optical phonons in the physical properties of the conductive delafossite PdCoO2. J Phys Soc Japan 76:1–7. https://doi.org/10.1143/JPSJ.76.104701
Yanagi H, Kawazoe H, Kudo A et al (2000) Chemical design and thin film preparation of p-type conductive transparent oxides. J Electroceramics 4(2/3):407–414. https://doi.org/10.1023/A:1009959920435
Tanaka M, Hasegawa M, Higuchi T et al (1998) Origin of the metallic conductivity in PdCoO2 with delafossite structure. Phys B Condens Matter 245:157–163. https://doi.org/10.1016/S0921-4526(97)00496-1
Tanaka M, Hasegawa M, Takei H (1996) Growth and anisotropic physical properties of PdCoO2 single crystals. J Phys Soc Japan 65:3973–3977. https://doi.org/10.1143/jpsj.65.3973
Kumar S, Miclau M, Martin C (2013) Hydrothermal synthesis of AgCrO2 delafossite in supercritical water: a new single-step process. Chem Mater 25:2083–2088. https://doi.org/10.1021/cm400420e
Xiong D, Wang H, Zhang W et al (2015) Preparation of p-type AgCrO2 nanocrystals through low-temperature hydrothermal method and the potential application in p-type dye-sensitized solar cell. J Alloys Compd 642:104–110. https://doi.org/10.1016/j.jallcom.2015.04.072
Ouyang S, Li Z, Ouyang Z et al (2008) Correlation of crystal structures, electronic structures, and photocatalytic properties in a series of Ag-based oxides: AgAlO2, AgCrO2, and Ag2CrO4. J Phys Chem C 112:3134–3141. https://doi.org/10.1021/jp077127w
Lopes AML, Oliveira GNP, Mendonça TM et al (2011) Local distortions in multiferroic AgCrO2 triangular spin lattice. Phys Rev B - Condens Matter Mater Phys 84:1–7. https://doi.org/10.1103/PhysRevB.84.014434
Ginley DS (2011) Handbook of Transparent Conductors. Springer, Boston
Ingram BJ, Gonzalez GB, Mason TO et al (2004) Transport and defect mechanisms in cuprous delafossites. 1. comparison of hydrothermal and standard solid-state synthesis in CuAlO2. Chem Mater 16:5616–5622. https://doi.org/10.1021/cm048983c
Scanlon DO, Watson GW (2010) Conductivity limits in CuAlO2 from screened-hybrid density functional theory. J Phys Chem Lett 1:3195–3199. https://doi.org/10.1021/jz1011725
Ruttanapun C (2013) Optical and electronic properties of delafossite CuBO2 p-type transparent conducting oxide. J Appl Phys 114:113108. https://doi.org/10.1063/1.4821960
Scanlon DO, Watson GW, Walsh A, Watson GW (2009) Understanding the p-type conduction properties of the transparent conducting oxide CuBO2: a density functional theory analysis. Chem Mater 21:3655–3663. https://doi.org/10.1021/cm9015113
Snure M, Tiwari A (2007) CuBO2: A p -type transparent oxide. Appl Phys Lett 91:092123. https://doi.org/10.1063/1.2778755
Ueda K, Hase T, Yanagi H et al (2001) Epitaxial growth of transparent p-type conducting CuGaO2 thin films on sapphire (001) substrates by pulsed laser deposition. J Appl Phys 89:1790–1793. https://doi.org/10.1063/1.1337587
Srinivasan R, Chavillon B, Doussier-Brochard C et al (2008) Tuning the size and color of the p-type wide band gap delafossite semiconductor CuGaO2 with ethylene glycol assisted hydrothermal synthesis. J Mater Chem 18:5647–5653. https://doi.org/10.1039/b810064k
Liu L, Bai K, Gong H, Wu P (2005) First-principles study of Sn and Ca doping in CuInO2. Phys Rev B - Condens Matter Mater Phys 72:125204. https://doi.org/10.1103/PhysRevB.72.125204
Singh M, Singh VN, Mehta BR (2008) Synthesis and properties of nanocrystalline copper indium oxide thin films deposited by Rf magnetron sputtering. J Nanosci Nanotechnol 8:3889–3894. https://doi.org/10.1166/jnn.2008.178
Sasaki M, Shimode M (2003) Fabrication of bipolar CuInO2 with delafossite structure. J Phys Chem Solids 64:1675–1679. https://doi.org/10.1016/S0022-3697(03)00071-4
Yanagi H, Hase T, Ibuki S et al (2001) Bipolarity in electrical conduction of transparent oxide semiconductor CuInO2 with delafossite structure. Appl Phys Lett 78:1583–1585. https://doi.org/10.1063/1.1355673
Isacfranklin M, Yuvakkumar R, Ravi G et al (2021) CuCoO2 electrodes for supercapacitor applications. Mater Lett. https://doi.org/10.1016/j.matlet.2021.129930
Du Z, Xiong D, Verma SK et al (2018) A low temperature hydrothermal synthesis of delafossite CuCoO2 as an efficient electrocatalyst for the oxygen evolution reaction in alkaline solutions. Inorg Chem Front 5:183–188. https://doi.org/10.1039/c7qi00621g
Arnold T, Payne DJJ, Bourlange A et al (2009) X-ray spectroscopic study of the electronic structure of CuCrO2. Phys Rev B 79:075102. https://doi.org/10.1103/PhysRevB.79.075102
Nagarajan R, Draeseke AD, Sleight AW, Tate J (2001) p-type conductivity in CuCr1-xMgxO2 films and powders. J Appl Phys 89:8022–8025. https://doi.org/10.1063/1.1372636
Wuttig A, Krizan JW, Gu J et al (2017) The effect of Mg-doping and Cu nonstoichiometry on the photoelectrochemical response of CuFeO2. J Mater Chem A 5:165–171. https://doi.org/10.1039/c6ta06504j
Ruttanapun C, Prachamon W, Wichainchai A (2012) Optoelectronic properties of Cu1-xPtxFeO2 (0 ≤ x ≤ 0.05) delafossite for p-type transparent conducting oxide. Curr Appl Phys 12:166–170. https://doi.org/10.1016/j.cap.2011.05.028
Kang JS, Kim DH, Hwang J et al (2011) Phase separation in thermoelectric delafossite CuFe1-xNixO2 observed by soft x-ray magnetic circular dichroism. Appl Phys Lett 99:2009–2012. https://doi.org/10.1063/1.3609248
Zhang Q, Xiong D, Li H et al (2015) A facile hydrothermal route to synthesize delafossite CuMnO2 nanocrystals. J Mater Sci Mater Electron 26:10159–10163. https://doi.org/10.1007/s10854-015-3702-z
Fathi AM, Abdel-Hameed SAM, Margha FH, Ghany NAA (2016) Electrocatalytic oxygen evolution on nanoscale crednerite (CuMnO2) composite electrode. Zeitschrift fur Phys Chemie 230:1519–1530. https://doi.org/10.1515/zpch-2015-0627
Shibasaki S, Kobayashi W, Terasaki I (2006) Transport properties of the delafossite Rh oxide Cu1−xAgxRh1−yMgyO2: effect of Mg substitution on the resistivity and Hall coefficient. Phys Rev B 74:235110. https://doi.org/10.1103/PhysRevB.74.235110
Kakehi Y, Satoh K, Yotsuya T et al (2009) Optical and electrical properties of CuScO2 epitaxial films prepared by combining two-step deposition and post-annealing techniques. J Cryst Growth 311:1117–1122. https://doi.org/10.1016/j.jcrysgro.2008.11.060
Kakehi Y, Satoh K, Yotsuya T et al (2005) Epitaxial growth of CuScO2 thin films on sapphire a-plane substrates by pulsed laser deposition. J Appl Phys 97:083535. https://doi.org/10.1063/1.1868061
Ingram BJ, Harder BJ, Hrabe NW et al (2004) Transport and defect mechanisms in cuprous delafossites 2 CuScO2 and CuYO2. Chem Mater 16:5623. https://doi.org/10.1021/cm048982k
Jayaraj MK, Draeseke AD, Tate J, Sleight AW (2001) p-type transparent thin films of CuY1-xCaxO2. Thin Solid Films 397:244–248. https://doi.org/10.1016/S0040-6090(01)01362-1
Jayaraj MK, Manoj R, Nisha M, Vanaja KA (2008) Effect of oxygen intercalation on properties of sputtered CuYO2 for potential use as p-type transparent conducting films. Bull Mater Sci 31:49–53. https://doi.org/10.1007/s12034-008-0009-1
Huda MN, Yan Y, Walsh A et al (2009) Group-IIIA versus IIIB delafossites: electronic structure study. Phys Rev B - Condens Matter Mater Phys 80:035205. https://doi.org/10.1103/PhysRevB.80.035205
Doumerc JP, Parent C, Chao ZJ et al (1989) Luminescence of the Cu+ ion in CuLaO2. J Less-Common Met 148:333–337. https://doi.org/10.1016/0022-5088(89)90048-9
Saadi S, Bouguelia A, Derbal A, Trari M (2007) Hydrogen photoproduction over new catalyst CuLaO2. J Photochem Photobiol A Chem 187:97–104. https://doi.org/10.1016/j.jphotochem.2006.09.017
Dong G, Zhang M, Wang M et al (2012) Synthesis, electrical and optical properties of CuNdO2 compound. J Phys Chem Solids 73:1170–1172. https://doi.org/10.1016/j.jpcs.2012.05.004
Miyasaka N, Doi Y, Hinatsu Y (2009) Synthesis and magnetic properties of ALnO2 (A=Cu or Ag; Ln=rare earths) with the delafossite structure. J Solid State Chem 182:2104–2110. https://doi.org/10.1016/j.jssc.2009.05.035
Linde J, Isawa K, Miettinen J et al (1999) Eu mossbauer study of the CuEuO delafossite. Phys B Condens Matter 271:223–229
Chiu T-WW, Yang Y-CC, Yeh A-CC et al (2013) Antibacterial property of CuCrO2 thin films prepared by RF magnetron sputtering deposition. Vacuum 87:174–177. https://doi.org/10.1016/j.vacuum.2012.04.026
Nien YT, Hu MR, Chiu TW, Chu JS (2016) Antibacterial property of CuCrO2 nanopowders prepared by a self-combustion glycine nitrate process. Mater Chem Phys 179:182–188. https://doi.org/10.1016/j.matchemphys.2016.05.026
Youn DH, Choi YH, Kim JH et al (2018) Simple microwave-assisted synthesis of delafossite CuFeO2 as an anode material for sodium-ion batteries. ChemElectroChem 5:2419–2423. https://doi.org/10.1002/celc.201800548
Saadi S, Bouguelia A, Trari M (2006) Photocatalytic hydrogen evolution over CuCrO2. Sol Energy 80:272–280. https://doi.org/10.1016/j.solener.2005.02.018
Xu J, Liu J, Wang J et al (2018) Prediction of novel p -type transparent conductors in layered double perovskites : a first-principles study. Adv Electron Mater 28:1800332. https://doi.org/10.1002/adfm.201800332
Liu QL, Zhao ZY, Zhao RD, Yi JH (2020) Fundamental properties of delafossite CuFeO2 as photocatalyst for solar energy conversion. J Alloys Compd 819:153032. https://doi.org/10.1016/j.jallcom.2019.153032
Okuda T, Beppu Y, Fujii Y et al (2009) Hole-doping effect on the magnetic state of delafossite oxide CuCrO2. J Phys Conf Ser 150:042157. https://doi.org/10.1088/1742-6596/150/4/042157
Okuda T, Jufuku N, Hidaka S, Terada N (2005) Magnetic, transport, and thermoelectric properties of the delafossite oxides CuCr1-xMgxO2 (0 x 0.04). Phys Rev B - Condens Matter Mater Phys 72:144403. https://doi.org/10.1103/PhysRevB.72.144403
Amami M, Colin CV, Strobel P, Ben Salah A (2011) Al-doping effect on the structural and physical properties of delafossite-type oxide CuCrO2. Phys B Condens Matter 406:2182–2185. https://doi.org/10.1016/j.physb.2011.03.027
Maignan A, Martin C, Frésard R et al (2009) On the strong impact of doping in the triangular antiferromagnet CuCrO2. Solid State Commun 149:962–967. https://doi.org/10.1016/j.ssc.2009.02.0265
Lin F, Gao C, Zhou X et al (2013) Magnetic, electrical and optical properties of p-type Fe-doped CuCrO2 semiconductor thin films. J Alloys Compd 581:502–507. https://doi.org/10.1016/j.jallcom.2013.07.160
Pokhriyal P, Bhakar A, Rajput P, et al Strain Induced Relaxor-type Ferroelectricity Near Room Temperature in Delafossite CuCrO2. https://arxiv.org/abs/2001.05772
Monteiro JFHL, Jurelo AR, Siqueira EC (2017) Raman spectroscopy of the superconductor CuCrO2 delafossite oxide. Solid State Commun 252:64–67. https://doi.org/10.1016/j.ssc.2017.01.014
Taddee C, Kamwanna T, Amornkitbamrung V (2016) Characterization of transparent superconductivity Fe-doped CuCrO2 delafossite oxide. Appl Surf Sci 380:237–242. https://doi.org/10.1016/j.apsusc.2016.01.120
Ono Y, Satoh K, Nozaki T, Kajitani T (2007) Structural, magnetic and thermoelectric properties of delafossite-type oxide, CuCr1-xMgxO2 (0≤x≤0.05). Jpn J Appl Phys 46:1071–1075. https://doi.org/10.1143/JJAP.46.1071
Hayashi K, Sato K, Nozaki T, Kajitani T (2008) Effect of doping on thermoelectric properties of delafossite-type oxide CuCrO2. Jpn J Appl Phys 47:59–63. https://doi.org/10.1143/JJAP.47.59
Barot N, Mehta PK, Rao A et al (2019) Effects of iso- and polyvalent substitutions on the short/long-range crystalline order in CuCrO2 compounds. J Alloys Compd 791:134–143. https://doi.org/10.1016/j.jallcom.2019.03.291
Yokobori T, Okawa M, Konishi K et al (2013) Electronic structure of the hole-doped delafossite oxides CuCr1-xMgxO2. Phys Rev B - Condens Matter Mater Phys. https://doi.org/10.1103/PhysRevB.87.195124
Momma K, Izumi F (2011) VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data. J Appl Crystallogr 44:1272–1276. https://doi.org/10.1107/S0021889811038970
Crottaz O, Kubel F (1996) Crystal structure of copper (I) chromium (III) oxide, 2H-CuCrCO2. Z Krist 47:2646. https://doi.org/10.1524/zkri.1996.211.7.481
Crottaz O, Kubel F (1996) Crystal structure of copper (I) chromium (III) oxide, 3R-CuCrO2. Z Krist 211:482. https://doi.org/10.1524/zkri.1996.211.7.482
Shannon RD (1976) Revised effective ionic radii and systematic studies of interatomie distances in halides and chaleogenides. Acta Crystallogr A 32:751. https://doi.org/10.1107/S0567739476001551
Amami M, Smari S, Tayeb K et al (2011) Cationic doping effect on the structural, magnetic and spectroscopic properties of delafossite oxides CuCr1-x(Sc, Mg)xO2. Mater Chem Phys 128:298–302. https://doi.org/10.1016/j.matchemphys.2011.03.021
Amrute AP, Łodziana Z, Mondelli C et al (2013) Solid-state chemistry of cuprous delafossites: synthesis and stability aspects. Chem Mater 25:4423–4435. https://doi.org/10.1021/cm402902m
Lin F, Shi W, Liu A (2012) Optical bandgap modulation and magnetic characterization of Fe-doped CuCrO2 nanopowders. J Alloys Compd 529:21–24. https://doi.org/10.1016/j.jallcom.2012.03.059
Crottaz O, Kubel F, Schmid H (1996) Preparation of trigonal and hexagonal cuprous chromite and phase transition study based on single crystal structure data. J Solid State Chem 122:247–250. https://doi.org/10.1006/jssc.1996.0109
Lunca-Popa P, Crepelliere J, Nukala P et al (2017) Invisible electronics: metastable Cu-vacancies chain defects for highly conductive p-type transparent oxide. Appl Mater Today 9:184–191. https://doi.org/10.1016/j.apmt.2017.07.004
Li J, Yokochi A, Amos TG, Sleight AW (2002) Strong negative thermal expansion along the O-Cu-O linkage in CuScO2. Chem Mater 14:2602–2606. https://doi.org/10.1021/cm011633v
Ahmed SI, Dalba G, Fornasini P et al (2009) Negative thermal expansion in crystals with the delafossite structure: An extended x-ray absorption fine structure study of CuScO2 and CuLaO2. Phys Rev B 79:104302. https://doi.org/10.1103/PhysRevB.79.104302
Li J, Sleight AW, Jones CY, Toby BH (2005) Trends in negative thermal expansion behavior for AMO2 (A = Cu or Ag; M = Al, Sc, In, or La) compounds with the delafossite structure. J Solid State Chem 178:285–294. https://doi.org/10.1016/j.jssc.2004.11.017
Kuo PC, Jamshidi-Roudbari A, Hatalis M (2007) Effect of mechanical strain on mobility of polycrystalline silicon thin-film transistors fabricated on stainless steel foil. Appl Phys Lett 91:243507. https://doi.org/10.1063/1.2824812
Kovalenko KL, Kozlovskiy SI, Sharan NN (2019) Strain induced mobility enhancement in p-type silicon structures: Bulk and quantum well (quantum kinetic approach). J Appl Phys 125:082515. https://doi.org/10.1063/1.5045620
Wang B, Puzyrev Y, Pantelides ST (2011) Strain enhanced defect reactivity at grain boundaries in polycrystalline graphene. Carbon 49:3983–3988. https://doi.org/10.1016/j.carbon.2011.05.038
Gillen R, Robertson J (2011) Band structure calculations of CuAlO2, CuGaO2, CuInO2 and CuCrO2 by screened exchange. Phys Rev B - Condens Matter Mater Phys 84:035125. https://doi.org/10.1103/PhysRevB.84.035125
Wang X, Meng W, Yan Y (2017) Electronic band structures and excitonic properties of delafossites: a GW -BSE study. J Appl Phys. https://doi.org/10.1063/1.4991913
Xu Y, Nie G-Z, Zou D-F et al (2016) N-Mg dual-acceptor co-doping in CuCrO2 studied by first-principles calculations. Phys Lett A 1:1–5. https://doi.org/10.1016/j.physleta.2016.08.029
Shook J, Scolfaro LM, Borges PD, Geerts WJ (2019) Structural stability and electronic properties of XTO2 (X= Cu, Ag; T=Al, Cr): An ab initio study including X vacancies and Mg doping. Solid State Sci 88:48–56. https://doi.org/10.1016/j.solidstatesciences.2018.12.009
Schwarting M, Siol S, Talley K et al (2017) Automated algorithms for band gap analysis from optical absorption spectra. Mater Discov 10:43–52. https://doi.org/10.1016/j.md.2018.04.003
Shook J, Borges PD, Scolfaro LM, Geerts WJ (2019) Effects of vacancies and p -doping on the optoelectronic properties of Cu- and Ag-based transparent conducting oxides. J Appl Phys 126:075702. https://doi.org/10.1063/1.5088711
Van Hoang D, Le Kieu TA, Pham ATT et al (2021) The roles of interstitial oxygen and phase compositions on the thermoelectric properties CuCr0.85Mg0.15O2 delafossite material. J Alloys Compd 867:158995. https://doi.org/10.1016/j.jallcom.2021.158995
Elkhouni T, Amami M, Colin CV et al (2013) Synthesis, structural and magnetic studies of the CuCr1-xCoxO2 delafossite oxide. J Magn Magn Mater 330:101–105. https://doi.org/10.1016/j.jmmm.2012.10.037
Benko FA, Koffyberg FP (1986) Preparation and opto-electronic properties of semiconducting CuCrO2. MatResBull 21:753–757. https://doi.org/10.1016/0025-5408(86)90156-X
Cui J, Cao H, Zhou W et al (2016) Composition dependence of the structure and optical properties of CuCrO2 powders. Mater Lett 163:28–31. https://doi.org/10.1016/j.matlet.2015.10.043
Kumar S, Marinel L, Miclau M, Martin C (2012) Fast synthesis of CuCrO2 delafossite by monomode microwave heating. Mater Lett 70:40–43. https://doi.org/10.1016/j.matlet.2011.11.091
Nie S, Liu A, Meng Y et al (2018) Solution-processed ternary p-type CuCrO2 semiconductor thin films and their application in transistors. J Mater Chem C 6:1393–1398. https://doi.org/10.1039/c7tc04810f
Chen H-Y, Chang K-P, Yang C-C (2013) Characterization of transparent conductive delafossite-CuCr1-xO2 films. Appl Surf Sci 273:324–329. https://doi.org/10.1016/j.apsusc.2013.02.038
Han MJ, Duan ZH, Zhang JZ et al (2013) Electronic transition and electrical transport properties of delafossite CuCr1-xMgxO2 (0 ≤ x ≤ 12%) films prepared by the sol-gel method: a composition dependence study. J Appl Phys 114:163526. https://doi.org/10.1063/1.4827856
Chen H-Y, Yang C-C (2013) Transparent p-type Zn-doped CuCrO2 films by sol-gel processing. Surf Coatings Technol 231:277–280. https://doi.org/10.1016/j.surfcoat.2012.06.006
Götzendörfer S, Bywalez R, Löbmann P (2009) Preparation of p-type conducting transparent CuCrO2 and CuAl0.5Cr0.5O2 thin films by sol-gel processing. J Sol-Gel Sci Technol 52:113–119. https://doi.org/10.1007/s10971-009-1989-z
Götzendörfer S, Polenzky C, Ulrich S, Löbmann P (2009) Preparation of CuAlO2 and CuCrO2 thin films by sol-gel processing. Thin Solid Films 518:1153–1156. https://doi.org/10.1016/j.tsf.2009.02.153
Chen H-Y, Chang K-P (2013) Influence of post-annealing conditions on the formation of delafossite-CuCrO2 films. ECS J Solid State Sci Technol 2:76–80. https://doi.org/10.1149/2.014303jss
Wang J, Zheng P, Li D et al (2011) Preparation of delafossite-type CuCrO2 films by sol-gel method. J Alloys Compd 509:5715–5719. https://doi.org/10.1016/j.jallcom.2011.02.149
Wang Y, Gu Y, Wang T, Shi W (2011) Structural, optical and electrical properties of Mg-doped CuCrO2 thin films by sol-gel processing. J Alloys Compd 509:5897–5902. https://doi.org/10.1016/j.jallcom.2011.02.175
Li D, Fang X, Deng Z et al (2007) Electrical, optical and structural properties of CuCrO2 films prepared by pulsed laser deposition. J Phys D Appl Phys 40:4910–4915. https://doi.org/10.1088/0022-3727/40/16/023
Ngo TNM, Palstra TTM, Blake GR (2016) Crystallite size dependence of thermoelectric performance of CuCrO2. RSC Adv 6:91171–91178. https://doi.org/10.1039/C6RA08035A
Jeong S, Seo S, Shin H (2018) P-Type CuCrO2 particulate films as the hole transporting layer for CH3NH3PbI3 perovskite solar cells. RSC Adv 8:27956–27962. https://doi.org/10.1039/c8ra02556h
Zhou S, Fang X, Deng Z et al (2008) Hydrothermal synthesis and characterization of CuCrO2 laminar nanocrystals. J Cryst Growth 310:5375–5379. https://doi.org/10.1016/j.jcrysgro.2008.09.193
Xiong D, Xu Z, Zeng X et al (2012) Hydrothermal synthesis of ultrasmall CuCrO2 nanocrystal alternatives to NiO nanoparticles in efficient p-type dye-sensitized solar cells. J Mater Chem 22:24760–24768. https://doi.org/10.1039/c2jm35101c
Kaya İC, Sevindik MA, Akyıldız H (2016) Characteristics of Fe- and Mg-doped CuCrO2 nanocrystals prepared by hydrothermal synthesis. J Mater Sci Mater Electron 27:2404–2411. https://doi.org/10.1007/s10854-015-4038-4
Gil B, Kim J, Yun AJ et al (2020) CuCrO2 nanoparticles incorporated into PTAA as a hole transport layer for 85 °C and light stabilities in perovskite solar cells. Nanomaterials 10:1669. https://doi.org/10.3390/nano10091669
Park JW, Kang BH, Kim HJ (2020) A review of low-temperature solution-processed metal oxide thin-film transistors for flexible electronics. Adv Funct Mater 30:1–40. https://doi.org/10.1002/adfm.201904632
Barnabe A, Thimont Y, Lalanne M et al (2015) P-Type conducting transparent characteristics of delafossite Mg-doped CuCrO2 thin films prepared by RF-sputtering. J Mater Chem C 3:6012–6024. https://doi.org/10.1039/c5tc01070e
Sun H, Arab Pour Yazdi M, Sanchette F, Billard A (2016) Optoelectronic properties of delafossite structure CuCr0.93Mg0.07O2 sputter deposited coatings. J Phys D Appl Phys 49:185105. https://doi.org/10.1088/0022-3727/49/18/185105
Ahmadi M, Asemi M, Ghanaatshoar M (2018) Improving the electrical and optical properties of CuCrO2 thin film deposited by reactive RF magnetron sputtering in controlled N2/Ar atmosphere. Appl Phys A 124:529. https://doi.org/10.1007/s00339-018-1945-2
Sun CH, Tsai DC, Chang ZC et al (2016) Structural, optical, and electrical properties of conducting p-type transparent Cu–Cr–O thin films. Ceram Int 42:13697–13703. https://doi.org/10.1016/j.ceramint.2016.05.168
Chiba H, Kawashima T, Washio K (2016) Optical and structural properties of CuCrO2 thin films on c-face sapphire substrate deposited by reactive RF magnetron sputtering. Mater Sci Semicond Process 70:234–238. https://doi.org/10.1016/j.mssp.2016.10.013
Tsai D-C, Chang Z-C, Kuo B-H et al (2019) Influence of chemical composition on phase transformation and optoelectronic properties of Cu-Cr-O thin films by reactive magnetron sputtering. J Mater Res Technol 8:690–696. https://doi.org/10.1016/j.jmrt.2018.05.013
Chen L-F, Wang Y-P, Chiu T-W et al (2013) Fabrication of transparent CuCrO2 Mg/ZnO p–n junctions prepared by magnetron sputtering on an indium tin oxide glass substrate. Jpn J Appl Phys 52:05EC02. https://doi.org/10.7567/JJAP.52.05EC02
Yu R-S, Tasi C-P (2014) Structure, composition and properties of p-type CuCrO2 thin films. Ceram Int 40:8211–8217. https://doi.org/10.1016/j.ceramint.2014.01.018
Kim SY, Lee JH, Kim JJ, Heo YW (2018) Effect of Ni doping on the structural, electrical, and optical properties of transparent CuCrO2 films grown using pulsed laser deposition. Ceram Int 44:17743–17748. https://doi.org/10.1016/j.ceramint.2018.06.241
Li D, Fang X, Zhao A et al (2010) Physical properties of CuCrO2 films prepared by pulsed laser deposition. Vacuum 84:851–856. https://doi.org/10.1016/j.vacuum.2009.11.014
Sadik PW, Ivill M, Craciun V, Norton DP (2009) Electrical transport and structural study of CuCr1 - xMgxO2 delafossite thin films grown by pulsed laser deposition. Thin Solid Films 517:3211–3215. https://doi.org/10.1016/j.tsf.2008.10.097
Sidik U, Lee HY, Lee JY (2015) Characteristics of the Mg-doped Cr-deficient CuCr0.95Mg0.02O2 thin films prepared by using pulsed laser deposition. J Nanosci Nanotechnol 15:5163–5166. https://doi.org/10.1166/jnn.2015.10401
Tonooka K, Kikuchi N (2006) Preparation of transparent CuCrO2:Mg/ZnO p-n junctions by pulsed laser deposition. Thin Solid Films 515:2415–2418. https://doi.org/10.1016/j.tsf.2006.05.023
Han M, Wang J, Deng Q et al (2015) Effect of annealing temperature on structural, optoelectronic properties and interband transitions of CuCrO2 nanocrystalline films prepared by the sol-gel method. J Alloys Compd 647:1028–1034. https://doi.org/10.1016/j.jallcom.2015.06.173
Dong G, Zhang M, Zhao X et al (2010) Improving the electrical conductivity of CuCrO2 thin film by N doping. Appl Surf Sci 256:4121–4124. https://doi.org/10.1016/j.apsusc.2010.01.094
Sun C-H, Tsai D-C, Chang Z-C et al (2016) Effects of annealing time on the structural and optoelectronic properties of p-type conductive transparent Cu–Cr–O films. J Mater Sci Mater Electron 27:9740–9747. https://doi.org/10.1007/s10854-016-5037-9
Shin D, Foord JS, Egdell RG, Walsh A (2012) Electronic structure of CuCrO2 thin films grown on Al2O3(001) by oxygen plasma assisted molecular beam epitaxy. J Appl Phys 112:113718. https://doi.org/10.1063/1.4768726
Lunca-Popa P, Botsoa J, Bahri M et al (2020) Tuneable interplay between atomistic defects morphology and electrical properties of transparent p-type highly conductive off-stoichiometric Cu-Cr-O delafossite thin films. Sci Rep 10:1416. https://doi.org/10.1038/s41598-020-58312-z
Lunca-Popa P, Crepelliere J, Leturcq R et al (2016) Electrical and optical properties of Cu–Cr–O thin films fabricated by chemical vapour deposition. Thin Solid Films 612:194–201. https://doi.org/10.1016/j.tsf.2016.05.052
Crepelliere J, Lunca-Popa P, Bahlawane N et al (2016) Transparent conductive CuCrO2 thin films deposited by pulsed injection metal organic chemical vapor: deposition up-scalable process technology for an improved transparency/conductivity trade-off. J Mater Chem C 4:4728. https://doi.org/10.1039/C6TC00383D10.1039
Lunca-Popa P, Afonso J, Grysan P et al (2018) Tuning the electrical properties of the p-type transparent conducting oxide Cu1-xCr1+xO2 by controlled annealing. Sci Rep 8:7216. https://doi.org/10.1038/s41598-018-25659-3
Lim SH, Desu S, Rastogi AC (2008) Chemical spray pyrolysis deposition and characterization of p-type CuCr1-xMgxO2 transparent oxide semiconductor thin films. J Phys Chem Solids 69:2047–2056. https://doi.org/10.1016/j.jpcs.2008.03.007
Mahapatra S, Shivashankar SA (2003) Low-pressure metal-organic CVD of transparent and p-type conducting CuCrO2 thin films with high conductivity. Chem Vap Depos. https://doi.org/10.1002/cvde.200304147
Tripathi TS, Karppinen M (2017) Enhanced p-type transparent semiconducting characteristics for ALD-grown Mg-substituted CuCrO2 thin films. Adv Electron Mater 3:1–7. https://doi.org/10.1002/aelm.201600341
Tripathi TS, Niemelä JP, Karppinen M (2015) Atomic layer deposition of transparent semiconducting oxide CuCrO2 thin films. J Mater Chem C 3:8364–8371. https://doi.org/10.1039/c5tc01384d
Tripathi TS, Karppinen M (2015) Structural optical and electrical transport properties of ALD-fabricated CuCrO2 films. Phys Procedia 75:488–494. https://doi.org/10.1016/j.phpro.2015.12.061
Farrell L, Norton E, Smith CM et al (2015) Synthesis of nanocrystalline Cu deficient CuCrO2-a high figure of merit p-type transparent semiconductor. J Mater Chem C 4:126–134. https://doi.org/10.1039/c5tc03161c
Farrell L, Norton E, O’Dowd BJ et al (2015) Spray pyrolysis growth of a high figure of merit, nano-crystalline, p -type transparent conducting material at low temperature. Appl Phys Lett 107:1–7. https://doi.org/10.1063/1.4927241
Sánchez-Alarcón RI, Oropeza-Rosario G, Gutierrez-Villalobos A et al (2016) Ultrasonic spray-pyrolyzed CuCrO2 thin films. J Phys D Appl Phys. https://doi.org/10.1088/0022-3727/49/17/175102
Norton E, Farrell L, Zhussupbekova A et al (2018) Bending stability of Cu0.4CrO2 - A transparent p-type conducting oxide for large area flexible electronics. AIP Adv 8:4–11. https://doi.org/10.1063/1.5027038
Ling DC, Chiang CW, Wang YF et al (2011) Effect of Cr deficiency on physical properties of triangular-lattice antiferromagnets CuCr1-xO2 (0≦x≦0.10). J Appl Phys 109:54–57. https://doi.org/10.1063/1.3544498
Werner F (2017) Hall measurements on low-mobility thin films. J Appl Phys. https://doi.org/10.1063/1.4990470
Poienar M, Hardy V, Kundys B et al (2012) Revisiting the properties of delafossite CuCrO2: a single crystal study. J Solid State Chem 185:56–61. https://doi.org/10.1016/j.jssc.2011.10.047
Ruei-Sung Y, Wu CM (2013) Characteristics of p-type transparent conductive CuCrO2 thin films. Appl Surf Sci 282:92–97. https://doi.org/10.1016/j.apsusc.2013.05.061
Okuda T, Onoe T, Beppu Y et al (2007) Magnetic and transport properties of delafossite oxides. J Magn Magn Mater 310:890–892. https://doi.org/10.1016/j.jmmm.2006.10.1141
Li D, Fang X, Dong W et al (2009) Magnetic and electrical properties of p-type Mn-doped CuCrO2 semiconductors. J Phys D Appl Phys 42:055009. https://doi.org/10.1088/0022-3727/42/5/055009
Zhao Y, Wang J, Deng Z et al (2009) Magnetic and electrical properties of p-type Mn-doped CuCrO2 semiconductors. J Phys D Appl Phys 42:055009. https://doi.org/10.1088/0022-3727/42/5/055009
Zheng SY, Jiang GS, Su JR, Zhu CF (2006) The structural and electrical property of CuCr1 - xNixO2 delafossite compounds. Mater Lett 60:3871–3873. https://doi.org/10.1016/j.matlet.2006.03.132
Marquardt MA, Ashmore NA, Cann DP (2006) Crystal chemistry and electrical properties of the delafossite structure. Thin Solid Films. 496:146–156. https://doi.org/10.1016/j.tsf.2005.08.316
Moto K, Yoshimine R, Suemasu T, Toko K (2018) Improving carrier mobility of polycrystalline Ge by Sn doping. Sci Rep 8:4–10. https://doi.org/10.1038/s41598-018-33161-z
Gao C, Lin F, Zhou X et al (2013) Fe concentration dependences of microstructure and magnetic properties for Cu(Cr1−xFex)O2 ceramics. J Alloys Compd 565:154–158. https://doi.org/10.1016/j.jallcom.2013.02.161
Madre MA, Torres MA, Gomez JA et al (2019) Effect of alkaline earth dopant on density, mechanical, and electrical properties of Cu0.97AE0.03CrO2 (AE = Mg, Ca, Sr, and Ba) delafossite oxide. J Aust Ceram Soc 55:257–263. https://doi.org/10.1007/s41779-018-0230-3
Chiu TW, Tsai SW, Wang YP, Hsu KH (2012) Preparation of p-type conductive transparent CuCrO2: Mg thin films by chemical solution deposition with two-step annealing. Ceram Int 38:S673–S676. https://doi.org/10.1016/j.ceramint.2011.09.048
Li D, Fang X, Deng Z et al (2009) Characteristics of CuCr1-xMgxO2 films prepared by pulsed laser deposition. J Alloys Compd 486:462–467. https://doi.org/10.1016/j.jallcom.2009.06.174
Monteiro JFHL, Monteiro FC, Jurelo AR, Mosca DH (2018) Conductivity in (Ag, Mg)-doped delafossite oxide CuCrO2. Ceram Int 44:14101–14107. https://doi.org/10.1016/j.ceramint.2018.05.008
Deng L, Lin F, Yu Q et al (2016) Improved ferromagnetic behavior and novel near-infrared photoluminescence in Mg/Mn-codoped CuCrO2 ceramics. J Mater Sci 51:7491–7501. https://doi.org/10.1007/s10853-016-0028-z
Mandal P, Mazumder N, Saha S et al (2016) A scheme of simultaneous cationic–anionic substitution in CuCrO2 for transparent and superior p -type transport. J Phys D Appl Phys 49:275109. https://doi.org/10.1088/0022-3727/49/27/275109
Zhou X, Lin F, Shi W, Liu A (2014) Structural, electrical, optical and magnetic properties of p-type Cu(Cr1-xMnx)O2 thin films prepared by pulsed laser deposition. J Alloys Compd 614:221–225. https://doi.org/10.1016/j.jallcom.2014.06.127
Amami M, Jlaiel F, Strobel P, Ben Salah A (2011) Synthesis, structural and magnetic studies of the CuCr1-xRhxO2 delafossite solid solution with 0 ≤ x ≤ 0.2. Mater Res Bull 46:1729–1733. https://doi.org/10.1016/j.materresbull.2011.05.033
Elkhouni T, Amami M, Strobel P, Ben SA (2013) Structural and magnetic properties of substituted delafossite-type oxides CuCr1−xScxO2. World J Condens Matter Phys 3:1–8. https://doi.org/10.4236/wjcmp.2013.31001
Jantrasee S, Ruttanapun C (2020) Impact of Sn4+ substitution at Cr3+ sites on thermoelectric and electronic properties of p-Type delafossite CuCrO2. J Electron Mater 49:601–610. https://doi.org/10.1007/s11664-019-07780-9
Yu R-S, Chu C (2019) Synthesis and characteristics of Zn-doped CuCrO2 transparent conductive thin films. Coatings 9:321. https://doi.org/10.3390/coatings9050321
Elkhouni T, Amami M, Strobel P, Ben Salah A (2013) Structural, Raman spectroscopy, and magnetic ordering in new delafossite-type oxide CuCr1-xTixO 2 (0≤x≤0.1). J Supercond Nov Magn 26:2795–2802. https://doi.org/10.1007/s10948-013-2256-7
Tate J, Ju HL, Moon JC et al (2009) Origin of p -type conduction in single-crystal CuAlO2. Phys Rev B - Condens Matter Mater Phys 80:1–8. https://doi.org/10.1103/PhysRevB.80.165206
Banerjee AN, Ghosh CK, Chattopadhyay KK (2005) Effect of excess oxygen on the electrical properties of transparent p-type conducting CuAlO2+x thin films. Sol Energy Mater Sol Cells 89:75–83. https://doi.org/10.1016/j.solmat.2005.01.003
Fang ZJ, Zhu JZ, Zhou J, Mo M (2012) Defect properties of CuCrO2: A density functional theory calculation. Chinese Phys B 21:087105. https://doi.org/10.1088/1674-1056/21/8/087105
Bottiglieri L, Resende J, Weber M et al (2021) Out of stoichiometry CuCrO2 films as a promising p-type TCO for transparent electronics. Mater Adv 2:4721. https://doi.org/10.1039/d1ma00156f
Hart GLW, Zunger A (2001) Origins of nonstoichiometry and vacancy ordering in Sc1−x□xS. Phys Rev Lett 87:275508-1-275508–4. https://doi.org/10.1103/PhysRevLett.87.275508
Zunger A (2018) The fundamentals of Transparent Oxides revisited: Band gap formation in classic Mott insulators and spontaneous non-stoichiometry in degenerate oxides. In: 7th International Symposium on Transparent Conductive Materials. Plenary 19. Crete, Greece
Ursu D, Dabici A, Sebarchievicia I, Miclau M (2017) Photovoltaic Performance of Co-doped CuCrO2 for p-type Dye-sensitized Solar Cells Application. Energy Procedia 112:497–503. https://doi.org/10.1016/j.egypro.2017.03.1129
Bywalez R, Götzendörfer S, Löbmann P (2010) Structural and physical effects of Mg-doping on p-type CuCrO2 and CuAl0.5Cr0.5O2 thin films. J Mater Chem 20:6562–6570. https://doi.org/10.1039/b926424h
Sinnarasa I, Thimont Y, Presmanes L, Tailhades P (2017) Thermoelectric and transport properties of delafossite CuCrO2: Mg thin films prepared by RF magnetron sputtering. Nanomaterials 7:157. https://doi.org/10.3390/nano7070157
Austin IG, Mott NF (2001) Polarons in crystalline and non-crystalline materials. Adv Phys 50:757–812. https://doi.org/10.1080/00018730110103249
van Hapert JJ (2002) Hopping Conduction and Chemical Structure - a study on Silicon Suboxides. PhD Dissertation. University of Utrecht, Netherland
Fröhlich H (1954) Electrons in lattice fields. Adv Phys 3(11):325–361. https://doi.org/10.1080/00018735400101213
Adler D, Flora LP, Senturia SD (1973) Electrical conductivity in disordered systems. Phys Rev B 7:2252–2260. https://doi.org/10.1103/PhysRevB.7.2252
Kuriyama K (1993) Hopping conductivity with distributed energy-barrier heights. Phys Rev B 47:415–419. https://doi.org/10.1103/PhysRevB.47.12415
Emin D (1974) Phonon-assisted jump rate in noncrystalline solids. Phys Rev Lett 32:303–307. https://doi.org/10.1103/PhysRevLett.32.303
Bosman AJ, van Daal HJ (1970) Small-polaron versus band conduction in some transition-metal oxides. Adv Phys 19:1–117. https://doi.org/10.1080/00018737000101071
O’Sullivan M, Stamenov P, Alaria J et al (2010) Magnetoresistance of CuCrO2 -based delafossite films. J Phys Conf Ser 200:1–5. https://doi.org/10.1088/1742-6596/200/5/052021
Nagaraja AR, Perry NH, Mason TO et al (2012) Band or polaron: The hole conduction mechanism in the p-Type spinel Rh2ZnO4. J Am Ceram Soc 95:269–274. https://doi.org/10.1111/j.1551-2916.2011.04771.x
Hossain MS, Islam R, Shahjahan M, Khan KA (2008) Studies on the thermoelectric effect in semiconducting ZnTe thin films. J Mater Sci Mater Electron 19:1114–1121. https://doi.org/10.1007/s10854-007-9483-2
Cui J, Li Y, Du Z-LZ et al (2013) Promising defect thermoelectric semiconductors Cu1-xGaSbxTe2 (x=0-0.1) with chalcopyrite structure. J Mater Chem A 1:677–683. https://doi.org/10.1039/c2ta00157h
Cutler M, Leavy JFF, Fitzpatrick RLL et al (1964) Electronic transport in semimetallic cerium sulfide. Phys Rev 133:A1143–A1152. https://doi.org/10.1103/PhysRev.133.A1143
Ingram BJ, Mason TO, Asahi R et al (2001) Electronic structure and small polaron hole transport of copper aluminate. Phys Rev B 64:1–7. https://doi.org/10.1103/PhysRevB.64.155114
Tuller HL, Nowick AS (1977) Small polaron electron transport in reduced CeO2 single crystals. J Phys Chem Solids 38:859–867. https://doi.org/10.1016/0022-3697(77)90124-X
Acknowledgements
This work was supported by the Fond National de la Recherche (FNR) Luxembourg (project number C19/MS/13577628—STEERMOB: Strain-Engineering the hole mobility in off-stoichiometric copper chromium delafossite).
Author information
Authors and Affiliations
Contributions
PLP and MM conceptualized the article. PLP and DL participated to funding acquisition and project administration. PLP, MM and JA wrote the first draft. MM, JC and JA performed the data curation. All authors participated to the review and the editing of the final manuscript.
Corresponding author
Ethics declarations
Conflict of interest
The authors declare no conflict of interest.
Additional information
Handling Editor: David Cann.
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Marco Moreira and Joao Afonso equally contributted to this work.
Supplementary Information
Below is the link to the electronic supplementary material.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Moreira, M., Afonso, J., Crepelliere, J. et al. A review on the p-type transparent Cu–Cr–O delafossite materials. J Mater Sci 57, 3114–3142 (2022). https://doi.org/10.1007/s10853-021-06815-z
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10853-021-06815-z