Nucleation mechanism for epitaxial growth of GaN on patterned sapphire substrates

The nucleation behaviors of GaN epitaxially grown on the patterned sapphire substrate (PSS) at different growth stages are investigated in detail. It is demonstrated that, unlike the non-PSS case, the proposed patterns can induce the selective deposition of GaN grains at the stage of buffer layer growth. Afterwards, the uniformity in lateral growth is promoted at the subsequent stage of GaN islands growth, accompanied by the rearrangement of GaN grains at high temperature. Finally, the crystal quality of the films is improved evidently at the stage of GaN recovery-mode growth. As confirmed by Raman spectroscopy and microscopy measurements, stress relaxation and lateral overgrowth acceleration are revealed to show good prospects in the application of PSS. The underlying mechanisms for both GaN nucleation and lateral overgrowth acceleration on PSS are elucidated carefully.