Study of InN nanorods growth mechanism using ultrathin Au layer by plasma-assisted MBE on Si(111)
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InN nanorods (NRs) were grown on Si(111) substrate by plasma-assisted molecular beam epitaxy. The growth of InN NRs has been demonstrated using an electron-beam evaporated (~2 nm) Au layer prior to the initiation of growth. The structure and morphology of as deposited Au film, annealed at 600 °C, and InN NRs were investigated using X-ray photoelectron spectroscopy and scanning electron microscopy. Chemical characterization was performed with energy dispersive X-ray analysis. Single-crystalline wurtzite structure of InN NRs is verified by transmission electron microscopy. The formation process of NRs is investigated and a qualitative mechanism is proposed.
KeywordsInN Nanostructures MBE
Group III nitrides represent a material class with promising electronic and optical properties (Nakamura 1998). Among these, InN possesses the lowest effective mass, the highest mobility, narrow band gap Eg of 0.7–0.9 eV and the highest saturation velocity (Wu et al. 2002; Goiran et al. 2010; Kumar et al. 2011) which makes it an attractive material for several applications such as solar cells, terahertz emitters, detectors, ion sensing and field emission (Yang et al. 2000; Bellotti et al. 1999; Chang et al. 2005; Lu et al. 2008; Wang et al. 2008). In recent years, due to distinctive properties and potentials of one dimensional (1D) structure (Fang et al. 2008; 2010) various kinds of InN nanostructures have been grown such as nanowires (NWs), nanotubes (NTs) and nanorods (NRs) by chemical vapor deposition (CVD) (Chang and Hong 2009), metalorganic chemical vapor deposition (MOCVD) (Chen et al. 2009), hydride metalorganic vapor phase epitaxy (H-MOVPE) (Park et al. 2007) and plasma-assisted molecular beam epitaxy (PAMBE) (Stoica et al. 2006). The nitrogen source for the growth of InN 1D structures is usually generated from the decomposition of ammonia at a relatively high temperature (>500 °C) for enough reactivity. However, since InN has low decomposition temperature (500–600 °C) and high vapor pressure above 500 °C, the process window for the growth of InN 1D structures has been very narrow. On the other hand, PAMBE uses reactive nitrogen plasma to replace ammonia as the nitrogen source, and it does not require high growth temperature. To date, there are already several publications on the growth of InN 1D structures with or without catalyst on different substrates such as Si, sapphire, SiC and GaAs. Many researchers have used Au catalyst to grow the InN 1D structures (Chang and Hong 2009) by different growth techniques. Here, we report the growth mechanism of InN NRs by PAMBE and the impact of Au layer on InN NRs growth. A systemic study of each growth steps are investigated using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The formation process of InN NRs is investigated and a qualitative mechanism is proposed.
The growth system used in this study was a PAMBE system (OMICRON) equipped with a radio frequency (RF) plasma source. The base pressure in the system was below 1 × 10−10 mbar. The n-Si(111) substrates were chemically cleaned followed by dipping in 5 % HF to remove the surface oxide, and Au layer of ~2 nm was deposited using electron beam evaporation. The Au film was annealed at 600 °C for 10 min. Further, the substrate temperature was decreased to 500 °C to fabricate the NRs. The duration of NR growth was kept for 2 h. The general set of growth conditions include indium beam equivalent pressure, nitrogen flow rate and RF-plasma power, which were kept at 4.6 × 10−8 mbar, 1 SCCM and 400 W, respectively. Nitrogen pressure was maintained 5.8 × 10−5 mbar during the growth. The structure and morphology of as deposited Au film, annealed at 600 °C and InN NRs were investigated using XPS and SEM. The structural evaluation of the as-grown NRs was carried out by transmission electron microscopy (TEM).
Results and discussion
In conclusion, the InN NRs were grown on Si(111) substrate by PAMBE using ~2 nm Au film prior to the initiation of growth. The structure and morphology of as deposited Au film, annealed at 600 °C, and InN NRs were investigated using XPS and FESEM. Chemical characterization of InN NRs were performed EDX. It is verified by TEM that the grown NRs are single-crystalline. The formation process of NRs is investigated and a qualitative mechanism is proposed. In the PAMBE, gold is converted into gold nitride which is not acting as a catalyst in PAMBE system.
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