We evaluated the electrical properties of InGaN‐based light‐emitting diodes (LEDs) with a surperlattice (SL) layer just below the MQWs for forming V‐shaped pits (V‐pits) on underlying GaN substrates with different dislocation densities (DDs). The SL was effective for improving the EL intensity for all the LEDs with different DDs. However, the improvement ratio decreased with decreasing DD. The SL is effective for performance improvement of the LEDs with high DDs. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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-SiN 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.