Thermally annealed GaN nucleation layers and the device-quality metal organic chemical vapor deposition growth of Si-doped GaN films on (00.1) sapphire

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Abstract
The effect of epitaxial growth temperature (985–1050 °C) on the properties of Si-doped GaN layers on self-nucleated (00.1) sapphire has been investigated. Several device-related properties monotonically improve with increasing growth temperature, including (a) carrier density and (b) volume fraction of heteroepitaxial domains. However, a number of equally important device-related properties show a local maximum and include (a) optical second-harmonic generation intensity, (b) structural coherence, and particularly (c) surface morphology. The antecedents of the first class lie in increases in surface and bulk diffusion and reductions in film defect incorporation and stress at the GaN/GaN (nucleation layer)/α-Al2O3 heterointerface. The second class arises from the quite limited range over which the thermally annealed GaN nucleation layer stimulates pseudo-two-dimensional growth of the GaN overlayer.