• GaN grown on two-step cleaned C-terminated 6H–SiC by molecular-beam epitaxy

A contaminant-free C-terminated 6H–SiC (0001) surface has been successfully prepared by a two-step method, which combines ${\mathrm{H}}_{\mathrm{2}}\mathrm{:He}$ (1:1) plasma and heating at 940 °C for 100 min. On this surface, a high-quality GaN (0001) thin film is obtained by radio-frequency nitrogen-plasma- assisted molecular-beam epitaxy. Near-band-edge emissions have been observed from some of these epilayers, depending primarily on the substrate surface conditions. Auger electron spectroscopy measurements show that temperatures of 940–1245 °C are necessary to thermally desorb the oxide and carbide from 6H–SiC substrates. At 1040 °C for the C-face SiC and 1150 °C for the Si-face SiC, crystalline damage was reported in the form of graphite formation on the surface. This graphite was observed through x-ray photoelectron spectroscopy. Structural analysis by x-ray diffraction and photoluminescence indicates very good in-plane alignment of the GaN epilayers as the substrates are cleaned using ${\mathrm{H}}_{\mathrm{2}}\mathrm{:He}$ (1:1) plasma at 940 °C for 100 min.