Free-standing non-polar gallium nitride substrates

A review is given of efforts to prepare thick gallium nitride films on lattice-matched gamma-LiAlO2 substrates. Much progress in the design of new high performance nitride device structures is presently impeded by the lack of GaN substrates, leading to large defect concentrations in layers grown on foreign materials. These problems could be alleviated if a true GaN substrate were to become available, allowing homoepitaxial growth. The preparation of 50 mm diameter boules of gamma-LiAlO2 from the melt will be discussed, including wafer preparation. Growth of thick (300-400 mum) GaN layers on the gamma-LiAlO2 wafers will be presented. The GaN is deposited by the halide vapour phase epitaxy (HVPE) method. Characteristics of these 50 mm diameter wafers are explained in detail. Much progress has been made, but several problems remain to be overcome.