In situ cleaning of GaN/6H-SiC substrates in NH3

Metalorganic chemical vapor deposition-grown GaN on 6H-SiC substrates were cleaned by annealing in an NH, flux. Oxygen contamination was removed by th ermal desorption, and carbon removal was facilitated by reaction with NH3. The GaN(0 0 0 1) surface after NH3 beam cleaning at 730 degreesC 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 oxyg en concentrations were reduced to background levels (similar to1 at%) by an nealing in an NH3 flux at 800 degreesC. The surface step structure was dest royed by annealing in an NH3 flux of 4 x 10(15) cm(-2) s(-1) from a seeded supersonic beam; however, annealing in an NH3 flux of 7 x 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 root3 x root3 R30 degrees reconstructi on. We infer from the effects of annealing temperature and NH3 flux that th e observed surface roughening is due to GaN decomposition. (C) 2001 Elsevie r Science B.V. All rights reserved.