Improving polycrystalline GaN by controlling annealing temperature of ScN interlayer

This work describes crystal and surface properties of a ScN interlayer, which was deposited on GaAs substrate with successive ammonia annealing at different temperature; 700 °C, 800 °C, 850 °C and 900 °C. The crystal and surface of the ScN interlayer changed with the annealing temperature and this has influenced the crystal, surface and optical properties of an over-deposited polycrystalline GaN layer. The ScN interlayer formed well at the annealing temperature above 850 °C with the presence of GaN and ScAs inclusions, arising from the out-diffusion of Ga and As atoms from the GaAs substrate due to high temperature. Furthermore, the presence of voids on the surface was observed due to the decomposition of Sc and N atoms from the surface of the ScN interlayer at high temperature. However, the voids were insignificant at 900 °C. This is because the ScN interlayer was initially formed with bigger grains at 900 °C as compared other temperature. These bigger grains attracted the decomposed Sc and N atoms to re-deposit on them, thereby suppressing the voids. All samples of the over-deposited polycrystalline GaN layer were found to be preferably crystallized in (0002) orientation. In the case for the polycrystalline GaN layer deposited on the 900 °C annealed ScN interlayer, the layer was evidently formed towards (100), (101) and (110) orientations, in addition to the (0002) orientation. This can be associated to that presence of the aforementioned GaN inclusions, which served as the nucleation sites for the GaN to crystallize in such orientations. Moreover, the surface of the polycrystalline GaN layer exhibited more distinguishable and bigger GaN grains with improved coalescence compared to other samples. Therefore, it showed strong signals in Raman scattering.