Lattice relaxation of AlN buffer on surface-treated SiC in molecular-beam epitaxy for growth of high-quality GaN

摘要

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.Highe-temperature HCl-gas etching resulted in an atomically flat SiC surface with (3X3)R30deg surface reconstruction,while HCl-gas etching followed by HF chemical treatment resulted in an atomically flat surface with (1X1) structure.The AlN layer grown on the (1X1) surface showed slower lattice relaxation.GaN grown on the AlN buffer layer exhibited a (0002) X-ray rocking curve of 70 arcsec and 10~7 cm~(-2) of screw-type dislocation density,which was superiof than that of GaN grown on (3X3)R30deg surface.