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

γ-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, γ-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)×10⁴ 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 H₂ 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.

 

 

 

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