Single-crystal growth of LiGaO 2 for a substrate of GaN thin films

Abstract

This paper describes the Czochralski growth of LiGaO 2 single crystal for use as a substrate for the epitaxial growth of hexagonal GaN. In c-axis pulling, unique crystalline defects were observed in a mechanochemically polished {0 0 1} substrate. Chemical etching revealed that the defect results from the boundary between two domains with different chemical etching rates, and that the crystal has a multi-domain structure. Since LiGaO 2 single crystal is polar along the c-axis, the formation of a multi-domain structure is due to the polarity inversion along the c-axis, i.e. polar-twin defects. We found that a- or b-axis-pulled crystals have a single domain structure. When we used a {0 0 1}LiGaO 2 substrate with a single-domain as a substrate in GaN thin film growth by MBE, hexagonal GaN thin films with good crystallinity grew epitaxially only on the hardly etched surface; the thin films on the easily etched surface peeled off.