Scandium Nitride As An Intermediate Layer For Gallium Nitride Deposition
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Date
2017-08
Authors
Yong, Alvin Shee Meng
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Publisher
Universiti Sains Malaysia
Abstract
This work discloses a new approach to the ScN formation through a combined technique of e-beam evaporation and thermal annealing. In the beginning of this work, the formation of ScN layer is started with depositing Sc layer on GaAs substrates using e-beam evaporator, followed by thermal annealing in ammonia ambient using a customised furnace. ~500 nm ScN layer was initially formed, and annealing the layer at 900 °C revealed reinforced rock salt grain-like structures, improved photoluminescence, and phonon behaviour. The XPS measurement confirmed the existence of Sc–N bonds in the layer. However, thin ScN layer is needed to make it as a potential intermediate layer for improving the quality of the GaN layer. Hence, ScN layers with thicknesses of ~50 nm and ~100 nm were formed using the technique as described above. The XRD peaks of ScN were observed for both samples annealed at the temperature above 850 °C. Moreover, XRD signals of ScAs and GaN appears at this temperature, which could affect the quality of the ScN layer. Conversely, ~100 nm ScN samples exhibited improved grain coalescence, when it was annealed at 850 °C. Next, ~1.5μm GaN layer was deposited on both ScN samples using e-beam evaporator. The GaN layers exhibited rod grain-like structures in all samples. The XRD result indicates the presence of polycrystalline GaN with favourable hexagonal orientations. Then, the GaN samples were subjected to post-annealing in ammonia ambient at a fixed temperature of 900 °C. The GaN grains experienced a severe change to spiky rod grain-like structures when deposited on ~50 nm ScN layer annealed at 700 °C, but then it transforms into hexagonal grain-like structures with the use of the ScN layer annealed up to 900 °C. In contrast, GaN deposited on ~100 nm ScN layers exhibited improved coalescence of rod grain-like GaN structures, and it showed the best on ScN layer annealed at 850 °C. Interestingly, a dominant orientation of GaN (0002) with the insignificant appearance of other hexagonal GaN orientations was observed for the GaN layer deposited on ~100 nm ScN layer annealed at 850 °C. Furthermore, Raman measurement revealed well-resolved E2 (high) and A1 (LO) GaN peaks for the GaN layer deposited on ~100 nm ScN layers. At the end of this work, ~100 nm ScN layer annealed at 850 °C is proposed for high quality deposition of GaN and other nitride-based layers.
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Keywords
Scandium nitride as an intermediate layer , for gallium nitride deposition