On the growth of gallium phosphide layers on gallium phosphide substrates by MOVPE

Abstract

We have investigated the growth and luminescence of gallium phosphide layers grown by MOVPE at atmospheric pressure using trimethylgallium and phosphine in a hydrogen ambient. Both the morphology and the type of luminescence were found to be strongly dependent on growth conditions. Hexagonal defects are observed on the epitaxial surfaces, changing to rhombic defects when the growth takes place with a low V/III ratio. The origin of these defects is stacking faults. The density of these defects is dependent on the growth temperature. Photoluminescence studies at 2 K were also carried out. In the bound exciton spectrum of the gallium phosphide layers, the silicon impurity appears on the gallium site with sufficient phosphine excess and at sufficiently high growth temperatures. A deep impurity level, related to silicon on a phosphorus site, is present when growth takes place with a low phosphine excess. We explain all observations by a model that implies that the growing surface can be either gallium-rich (resulting in phosphorus vacancies) or phosphorus-rich, resulting in gallium vacancies. The phosphorus-rich surface enables smooth epitaxial layers to be grown. With growth taking place at a phosphine to trimethylgallium ratio greater than 2.5, the surface is in a configuration stabilized by phosphorus reconstructions.