Growth diagram of N-face GaN (0001¯) grown at high rate by plasma-assisted molecular beam epitaxy

Abstract

N-face GaN was grown on free-standing GaN (0001¯) substrates at a growth rate of 1.5 μm/h using plasma-assisted molecular beam epitaxy. Difference in growth rate between (0001¯) and (0001) oriented GaN depends on nitrogen plasma power, and the (0001¯) oriented GaN had only 70% of the growth rate of the (0001) oriented GaN at 300 W. Unintentional impurity concentrations of silicon, carbon, and oxygen were 2 × 1015, 2 × 1016, and 7 × 1016 cm−3, respectively. A growth diagram was constructed that shows the dependence of the growth modes on the difference in the Ga and active nitrogen flux, ΦGa − ΦN*, and the growth temperature. At high ΦGa − ΦN* (ΦGa ≫ ΦN*), two-dimensional (step-flow and layer-by-layer) growth modes were realized. High growth temperature (780 °C) expanded the growth window of the two-dimensional growth modes, achieving a surface with rms roughness of 0.48 nm without Ga droplets.