Growth of GaN on on-axis 6H-SiC (0001) Si substrates with an AlN buffer layer was performed by molecular-beam epitaxy. The effects of SiC surface reconstruction on the lattice relaxation of AlN buffer layers and the crystalline quality of GaN layers were studied. High-temperature HCl-gas etching followed by HF chemical treatment resulted in an atomically flat SiC surface with a 1ϫ1 structure. The AlN layer grown on the surface showed slow lattice relaxation. GaN grown on the AlN buffer layer exhibited the narrowest ͑0002͒ x-ray rocking curve of 70 arcsec and 10 7 cm Ϫ2 screw-type dislocation density, which was two orders of magnitude smaller than that of GaN grown on as-received substrates.
The effects of SiC surface treatment on the lattice relaxation of AlN buffer layers and the crystalline quality of GaN layers grown on the buffer layers were studied. AlN buffer layers and GaN main layers were grown by plasma-assisted molecular-beam epitaxy on on-axis 6H-SiC (0001)Si substrates. High-temperature HCl-gas etching resulted in an atomically flat SiC surface with (√3×√3)R30° surface reconstruction, while HCl-gas etching followed by HF chemical treatment resulted in an atomically flat surface with (1×1) structure. The AlN layer grown on the (1×1) surface showed slower lattice relaxation. GaN grown on the AlN buffer layer exhibited a (0002) X-ray rocking curve of 70 arcsec and 107 cm−2 of screw-type dislocation density, which was superior than that of GaN grown on (√3×√3)R30° surface.
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