System for Bulk Growth of Gallium Nitride. Vapor Phase Epitaxy of Gallium Nitride by Gallium Arc Evaporation

摘要

A vapor phase growth system intended for the growth of bulk gallium nitride crystals was investigated. Potential advantages of the growth technique are cheap source materials of high purity, no corrosive gasses, and low operating and equipment costs. Ga contained in a crucible was evaporated by an arc discharge between a W-electrode and the Ga surface, and was transported to the growth zone by a carrier gas flowing over the Ga source. After mixing with ammonia, the mixture was passed between a top and a bottom susceptor, on which samples were mounted. High growth rates as high as 30 micrometers/hr were obtained on the top sample. The surface of deposited material was rough near the front of the susceptor, but was specular elsewhere and showed step-flow growth morphology in atomic force microscopy. The bottom sample experienced lower growth rates and a high density of macroscopic defects, presumably caused by Ga droplets in the gas phase. Computer flow dynamic simulations predicted growth rates 4 times higher than experiments. The discrepancy was attributed to ammonia pre-reactions, based on the experimental growth rate dependence on ammonia partial pressure. An additional factor 4 reduction in efficiency was due to Ga wall condensation between the evaporation and growth zones. The overall growth efficiency was 2 %.