Growth and characterization of millimeter-sized GaN crystals by carbothermal reduction and nitridation of Ga 2O 3

Abstract

Micrometer- to millimeter-sized wurtzite-type GaN crystals were grown on graphite substrates and at the edge of a silica glass tube at 840–1200 °C for 5–120 min by the reaction of NH 3 with Ga 2O vapor, produced by carbothermal reduction of Ga 2O 3 powder at 970 °C. The GaN crystals were characterized by scanning electron microscopy, optical microscopy, X-ray diffraction, Raman spectroscopy and cathodoluminescence. As the growth temperature and time were increased, the size of crystals grown on the graphite substrate drastically increased from several hundreds nanometer to a few hundred microns with the crystal habits changing from plate to bowtie or hexagonal prism. At the edge of a silica glass tube, the bar-shaped crystals of 1–3 mm in length were obtained at the 1200 °C for 120 min. It was found that carbothermal reduction and high-temperature nitridation of Ga 2O 3 produced relatively large crystals (∼3 mm) with better quality.