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

Reflection high-energy electron diffraction (RHEED) intensity oscillations have been observed during radiofrequency plasma-assisted molecular beam epi taxy of GaN on its (0001)A face. The starting A (Ga) face was prepared by g rowing a micrometer-thick GaN layer directly on a low-index 6H-SiC(0001) su bstrate at 650 degrees C. RHEED intensity oscillations are measured with su bstrate temperatures less than 550 degrees C in both Ga-limited and N-limit ed growth conditions. In the N-limited condition, an initial transient high -frequency oscillation is observed before it reaches a steady-state frequen cy. If the Ga flux is subsequently stopped while keeping the N flux unchang ed, a few extra oscillations are recorded. Scanning tunneling microscopy im ages of surfaces quenched during growth show triangular-shaped islands, ver ifying a two-dimensional growth mode. At substrate temperatures greater tha n 550 degrees C, neither island nucleation nor intensity oscillation is obs erved, suggesting a step-flow growth mode. (C) 2000 Elsevier Science B.V. A ll rights reserved.