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Fabrication and characterization of native non-polar GaN substrates

Thick c-plane (0 0 0 1)-oriented native GaN boules that have been produced by hydride vapor phase epitaxy and non-polar native m-plane (1 1 0 0) and a-plane (1 1 2 0) GaN substrates have been sliced from these crystals using a multiwire saw. An optimized polishing procedure was used to achieve a smooth epi-ready surface morphology on the finished substrates, with an RMS roughness of 0.43 nm. The non-polar substrates had two types of structural characteristics in appearance : one group was uniform, transparent and nearly colorless; while the second group had regions of varying coloration resulting from transecting V-shape pitting defects in the bulk GaN crystal. These regions had different cathodoluminescence properties but similar dislocation densities of <106 cm−2. The native non-polar GaN substrates had orders of magnitude lower defect densities, including stacking faults, in comparison to heteroepitaxially grown quasi-substrates in non-polar direction on foreign substrates and subsequently delaminated. The structural characteristics demonstrated the current state-of-the-art in non-polar GaN substrate quality and additionally point at remaining improvement opportunities in substrate size and uniformity.
Source: Journal of Crystal Growth
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