In situ cleaning of GaN/6H-SiC substrates in NH 3

Abstract

Metalorganic chemical vapor deposition-grown GaN on 6H-SiC substrates were cleaned by annealing in an NH 3 flux. Oxygen contamination was removed by thermal desorption, and carbon removal was facilitated by reaction with NH 3. The GaN(0 0 0 1) surface after NH 3 beam cleaning at 730°C was smooth with distinct atomic steps. The roughness (0.20 nm RMS) was only slightly greater than that of the untreated substrate (0.17 nm RMS). Carbon and oxygen concentrations were reduced to background levels (∼1 at%) by annealing in an NH 3 flux at 800°C. The surface step structure was destroyed by annealing in an NH 3 flux of 4×10 15 cm −2 s −1 from a seeded supersonic beam; however, annealing in an NH 3 flux of 7×10 15 cm −2 s −1 from a leak valve inhibited surface roughening and produced a relatively smooth surface (0.28 nm RMS) with a 3 × 3 R30° reconstruction. We infer from the effects of annealing temperature and NH 3 flux that the observed surface roughening is due to GaN decomposition.