The v-shaped pits (so-called V-pits) observed in hydride-vapor-phase-epitaxy-grown GaN and associated with the columnar inversion domains originating from foreign particles were investigated. The inversion domains on the front and back surfaces of the test sample were recognized after chemical mechanical polishing. It was found that the V-pits originate from the columnar inversion domains. The inversion domains, in turn, arise from the particles that exist on a low-temperature GaN buffer layer on sapphire substrate. Using transmission electron microscopy, these particles were found to be of α-Si3N4 and graphitic carbon. Such particles are attributable to the components of the reactor and adhere to the low-temperature GaN buffer layer, which has a surface roughness of the order of several nanometers. Thus, an effective way of obtaining HVPE-grown thick GaN layers without the V-pits associated with columnar IDs is to maintain the parts of the HVPE chamber properly to prevent foreign particles from being generated.
Matsubara, T., Denpo, Y., Okada, N., & Tadatomo, K. (2017). V-shaped pits in HVPE-grown GaN associated with columnar inversion domains originating from foreign particles of α-Si3N4 and graphitic carbon. Micron, 94, 9–14. https://doi.org/10.1016/j.micron.2016.11.008