Thick c-plane (0001)-oriented native GaN boules that have been produced by hydride vapor phase epitaxy and non-polar native m-plane (1 (1) under bar 0 0) and a-plane (1 1 (2) under bar 0) GaN substrates have been sliced from these crystals using a multivariate 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 <10(6) 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. (c) 2008 Elsevier B.V. All rights reserved.
Fabrication and characterization of native non-polar GaN substrates