Growth Control of N-Polar GaN in Plasma-Assisted Molecular Beam Epitaxy

The paper reports on plasma-assisted MBE growth of good quality N-face GaN layers directly on c-Al₂O₃ substrates. Growth kinetics under different growth conditions (substrate temperature, Ga to activated nitrogen flux ratio, etc.) during deposition of GaN(0001) and GaN(0001̅) both by the ammonia-based MBE or plasma-assisted MBE was studied. It was found that atomically smooth surface of 1 μm thick GaN(0001̅) films can be achieved by plasma-assisted MBE at the relatively high substrate temperature $T_S$ ≈ 760°C and Ga to activated nitrogen flux ratio $F_Ga//F_N^\ast$ ≈ 1.8