γ-LiAlO2 single crystal:: a novel substrate for GaN epitaxy

gamma-LiAlO2 single crystals were expected to act as a promising substrate material for the epitaxy of GaN, the lattice mismatch between LiAlO2 and GaN is only 1.4%. In the present work, gamma-LiAlO2 single crystal has been grown using temperature gradient technique (TGT), in which a crucible with a cover was used to prevent the component of charge from vaporizing. The crystal quality was characterized by chemical etching, optical microscope, and high-resolution X-ray diffraction. The LiAlO2 crystal grown by TGT was free from bubbles and inclusions, and the dislocation density measured on (1 0 0) crystal plane was about (3.8-6.0) x 10(4) cm(-2). The main defects were subgrains or mosaic structures, which may be caused by the fluctuation of temperature field in the furnace. Growth of GaN on LiAlO2(1 0 0) was tried through MOCVD using H-2 as a carrier, the results showed that LiAlO2 substrate was stable enough to stand the high-temperature reductive atmosphere. Since the lattice mismatching between film and substrate was greatly decreased, single-oriented GaN film can be grown on LiAlO2 substrates without using low-temperature buffer layers. (C) 1998 Elsevier Science B.V. All rights reserved.