A New “Three-Step Method” for High Quality MOVPE Growth of III-Nitrides on Sapphire

A new three-step method was developed to grow high-quality III-nitrides by LP-MOVPE. The first step is composed of nitridation of sapphire substrate and growth of thin AlN layer by a migration enhanced method at high temperature of 1100°C. The second step included a TMAl preflow and subsequent deposition of low temperature GaN buffer layer. The TMAl preflow was introduced at the buffer layer growth temperature to make at least a 2ML coverage on AlN surface, which served to obtain GaN buffer layer with Ga polarity. The third step was to grow epilayer at 1080°C. The mechanisms for quality improvement were discussed. It was proved that the three-step method could be a new approach to grow high quality epilayers on large-lattice-mismatched substrates.