The annealing of an AlN buffer layer in a carbon-saturated N2-CO gas on a sapphire substrate was investigated. The crystal quality of the buffer layer was significantly improved by annealing at 1650-1700 °C. An AlN buffer layer with a thickness of 300nm was grown by metalorganic vapor phase epitaxy (MOVPE), and was annealed at 1700 °C for 1 h. We fabricated a 2-μm-thick AlN layer on the annealed AlN buffer layer by MOVPE. The full widths at half maximum of the (0002)-and (10-12)-plane X-ray rocking curves were 16 and 154 arcsec, respectively, and the threading dislocation density was 4.7 × 108cm-2.
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