Abstract
The morphology, atomic structure, and chemical composition of small (4 nm average height and 20 nm average diameter), dense capped MBE-grown Ge/Si quantum dots are studied using an energy-differential extension of the direct X-ray phasing method, COBRA. Our results lead to the following conclusions: (i) the quantum dot system has a partial wetting layer; (ii) in the lower parts of the dots, the Ge content is small and increases toward the top; and (iii) the contact angle between the dots and the substrate is acute, consistent with the presence of a wetting layer. A growth mechanism compatible with these findings is proposed.
Similar content being viewed by others
References
Abstreiter G, Schittenhelm P, Engel C, Silveira E, Zrenner A, Meertens D, Jager W (1996) Growth and characterization of self-assembled Ge-rich islands on Si. Semicond Sci Technol 11:1521–1528
Alguno A, Usami N, Ujihara T, Fujiwara K, Sazaki G, Nakajima K, Shiraki Y (2003) Enhanced quantum efficiency of solar cells with self-assembled Ge dots stacked in multilayer structure. Appl Phys Lett 83:1258
Aroutiounian V, Petrosyan S, Khachatryan A, Touryan K (2001) Quantum dot solar cells. J Appl Phys 89:2268
Baribeau JM, Wu X, Lockwood DJ (2006a) Probing the composition of Ge dots and Si/Si1−xGex island superlattices. J Vac Sci Technol A 24:663
Baribeau JM, Wu X, Rowell NL, Lockwood DJ (2006b) Ge dots and nanostructures grown epitaxially on Si. J Phys Condens Matter 18:R139
Baskaran A, Smereka P (2012) Mechanisms of Stranski–Krastanow growth. J Appl Phys 111:044321
Biasiol G, Heun S (2011) Compositional mapping of semiconductor quantum dots and rings. Phys Rep 500:117–173
Capellini G, Motta N, Sgarlata A, Calarco R (1999) Evolution of strained Ge islands grown on Si(111): a scanning probe microscopy study. Solid State Commun 112:145–149
Caroff P, Bertru N, Platz C, Dehaese O, Le Corre A, Loualiche S (2005) Emission wavelength control of InAs dots quantum dots in a GaInP matrix grown on InP (311)B substrates. J Cryst Growth 273:357–362
Chaparro SA, Zhang Y, Drucker J, Chandrasekhar D, Smith DJ (2000) Evolution of Ge/Si(100) islands: island size and temperature dependence. J Appl Phys 87:2245
Cohen E, Yochelis S, Westreich O, Shusterman S, Kumah DP, Clarke R, Yacoby Y, Paltiel Y (2011) Structure of droplet-epitaxy-grown InAs/GaAs quantum dots. Appl Phys Lett 98:243115
Denker U, Stoffel M, Schmidt OG (2003) Probing the lateral composition profile of self-assembled islands. Phys Rev Lett 90:196102
Drucker J (2002) Self-assembling Ge (Si)/Si (100) quantum dots. IEEE J Quantum Electron 38:975
Floyd M, Zhang Y, Driver KP, Drucker J, Crozier PA, Smith DJ (2003) Nanometer-scale composition measurements of Ge/Si (100) islands. Appl Phys Lett 82:1473
Fong DD, Cionca C, Yacoby Y, Stephenson GB, Eastman JA, Fouss PH, Streiffer SK, Thompson C, Clarke R, Pindak R, Stern EA (2005) Direct structural determination in ultrathin ferroelectric films by analysis of synchrotron X-ray scattering measurements. Phys Rev B 71:144112
Grätzel M (2001) Photoelectrochemical cells. Nature 414:338
Hesse A, Stangl J, Holy V, Roch T, Bauer G, Schmidt OG, Denker U, Struth B (2002) Effect of overgrowth on shape, composition, and strain of SiGe islands on Si(001). Phys Rev B 66:085321
Kumah DP, Shusterman S, Paltiel Y, Yacoby Y, Clarke R (2009) Atomic-scale mapping of quantum dots formed by droplet epitaxy. Nat Nanotechnol 4:835
Kumah DP, Wu JH, Husseini NS, Dasika VD, Goldman RS, Yacoby Y, Clarke R (2011) Correlating structure, strain, and morphology of self-assembled InAs quantum dots on GaAs. Appl Phys Lett 98:021903
Lang C (2003) Composition of self-assembled quantum dots. Mater Sci Technol 19:411
Ledentsov NN, Ustinov VM, Shchukin VA, Kop’ev PS, Alferov ZI, Bimberg D (1998) Quantum dot heterostructures: fabrication, properties, lasers. Semiconductors 32:343
Liao XZ, Zou J, Cockayne DJH, Wan J, Jiang ZM, Jin G, Wang KL (2002) Alloying, elemental enrichment, and interdiffusion during the growth of GeSi 001 quantum dots. Phys Rev B 65:153306
Magidson V, Regelman DV, Beserman R, Dettmer K (1998) Evidence of Si presence in self-assembled Ge islands deposited on a Si, 001 substrate. Appl Phys Lett 73:1044–1046
Rastelli A, Stoffel M, Malachias A, Merdzhanova T, Katsaros G, Kern K, Metzger TH, Schmidt OG (2008) Three-dimensional composition profiles of single quantum dots determined by scanning-probe-microscopy-based nanotomography. Nano Lett 8:1404–1409
Robel I, Subramanian V, Kuno M, Kamat PV (2006) Quantum dot solar cells: harvesting light energy with CdSe nanocrystals moleculary linked to mesoscopic TiO2 films. J Am Chem Soc 128:2385
Schülli TU, Stangl J, Zhong Z, Lechner RT, Sztucki M, Metzger TH, Bauer G (2003) Direct determination of strain and composition profiles in Si Ge islands by anomalous X-ray diffraction at high momentum transfer. Phys Rev Lett 90:066105
Singha RK, Das S, Majumdar S, Das K, Dhar A, Ray SK (2008) Evolution of strain and composition of Ge islands on Si (001) grown by molecular beam epitaxy during post-growth annealing. J Appl Phys 103:114301
Singha RK, Manna S, Das S, Dhar A, Ray SK (2010) Room temperature infrared photoresponse of self assembled Ge/Si (001) quantum dots grown by molecular beam epitaxy. Appl Phys Lett 96:233113
Sowwan M, Yacoby Y, Pitney J, MacHarrie R, Hong M, Cross J, Walko DA, Clarke R, Pindak R, Stern EA (2002) Direct atomic structure determination of epitaxially grown films: Gd2O3 on GaAs(100). Phys Rev B 66:205311
Stangl J, Holý V, Bauer G (2004) Structural properties of self-organized semiconductor nanostructures. Rev Mod Phys 76:725
Wang KL, Cha D, Liu J, Chen C (2007) Ge/Si self-assembled quantum dots and their optoelectronic device applications. Proc IEEE 95:1866
Yacoby Y, Pindak R, MacHarrie R, Pfeiffer L, Berman L, Clarke R (2000) Direct structure determination of systems with two-dimensional periodicity. J Phys Condens Matter 12:3929–3938
Yoffe D (2001) Semiconductor quantum dots and related systems: electronic, optical, luminescence and related properties of low dimensional systems. Adv Phys 50:1
Zhang Y, Drucker J (2003) Annealing-induced Ge/Si (100) island evolution. J Appl Phys 93:15
Acknowledgments
This article is based on research supported as part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, under Award # DE-SC0000957 (x-ray surface scattering), and Israel Science Foundation Grant # 1005/11 (analysis and modeling). The use of the Advanced Photon Source, an Office of Science User Facility operated for the DOE, Office of Science, by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. This study was also performed as a part of the program at HUJI Center for Nanoscience and Nanotechnology. The authors are grateful to P. Smereka and J. Mirecki Millunchick for useful discussions.
Author information
Authors and Affiliations
Corresponding author
Additional information
Special Issue Editors: Juan Manuel Rojo, Vasileios Koutsos
This article is part of the topical collection on Nanostructured Materials 2012
Rights and permissions
About this article
Cite this article
Yacoby, Y., Elfassy, N., Ray, S.K. et al. Morphology and growth of capped Ge/Si quantum dots. J Nanopart Res 15, 1608 (2013). https://doi.org/10.1007/s11051-013-1608-3
Received:
Accepted:
Published:
DOI: https://doi.org/10.1007/s11051-013-1608-3