Reflection high-energy electron diffraction intensity oscillations during growth of GaN(0001)A by plasma-assisted molecular beam epitaxy

Abstract

Reflection high-energy electron diffraction (RHEED) intensity oscillations have been observed during radio-frequency plasma-assisted molecular beam epitaxy of GaN on its (0001)A face. The starting A (Ga) face was prepared by growing a micrometer-thick GaN layer directly on a low-index 6H–SiC(0001) substrate at 650°C. RHEED intensity oscillations are measured with substrate temperatures less than 550°C in both Ga-limited and N-limited growth conditions. In the N-limited condition, an initial transient high-frequency oscillation is observed before it reaches a steady-state frequency. If the Ga flux is subsequently stopped while keeping the N flux unchanged, a few extra oscillations are recorded. Scanning tunneling microscopy images of surfaces quenched during growth show triangular-shaped islands, verifying a two-dimensional growth mode. At substrate temperatures greater than 550°C, neither island nucleation nor intensity oscillation is observed, suggesting a step-flow growth mode.