Ammonolysis of gallium phosphide GaP to the nanocrystalline wide bandgap semiconductor gallium nitride GaN

Abstract

The pnictogen-metathesis reaction of microcrystalline gallium phosphide GaP with ammonia NH₃ at temperatures of 900–1150 °C for 6–60 hours afforded in one step nanocrystalline powders of the wide bandgap semiconductor gallium nitride GaN. A suitable choice of conditions including variations of reaction temperature/time and manual grinding or high energy ball milling of the substrate enabled control over distinct GaN particle morphologies, regularly shaped particles or nanowires, and average crystallite sizes up to a few tens of nanometers. Under the applied conditions, all by-products were conveniently removed as volatiles affording pure GaN nanopowders. In contrast to ammonolysis of the related cubic GaAs and cubic GaSb, which yielded mixtures of the hexagonal and cubic GaN polytypes, here, the nitride was made exclusively as the stable hexagonal variety. All this supported specific reaction pathways with thermodynamics solely controlling the ammonolytical conversion of the cubic GaP substrate to the hexagonal GaN product.