Growth of GaN(0001)1×1 on Al2O3(0001) by gas-source molecular beam epitaxy

Abstract

Gas‐source molecular beam epitaxy (GSMBE), utilizing Ga and NH₃, has been used to grow single‐crystal GaN(0001)1×1 on Al₂O₃(0001) substrates at temperatures T_s between 700 and 850 °C. In situ reflection high‐energy electron diffraction studies show a transition from three‐dimensional to two‐dimensional growth at T_s≳770 °C. For ≂1‐μm‐thick GaN layers, the best room‐temperature carrier mobilities, 100–110 cm² V⁻¹ s⁻¹, with carrier concentrations of 1–4×10¹⁸ cm⁻³, were obtained at T_s≥780 °C. These are the highest reported mobilities for MBE GaN. Band‐to‐band photoluminescence was observed in these films at room temperature. Cross‐sectional transmission electron microscopy showed that the primary defects in the films were threading dislocations, with Burgers vectors a₀/3〈21̄1̄0〉, and stacking faults.