Interface recombination at the selectively wet-oxidized AlAs-GaAs interface

The threshold of vertical cavity lasers has recently been greatly reduced by replacing proton implantation with selective “wet oxidation” of the AlAs layers in Bragg reflectors to provide lateral confinement of both the electrical current and the optical mode. With the oxidation technique, record low threshold currents below 100 μA at room temperature have been reported, which are far lower than those reported for implanted lasers. Here we report on the effects of the oxidation on the surface recombination of GaAs at the interface with the oxide. We show that the GaAs surface is pinned very much like a free surface of GaAs exposed to air. On the other hand, if the GaAs is isolated from the AlAs by a thin layer of Al_0.35Ga_0.65 As then the GaAs/Al_0.35Ga_0.65As interface preserves the low surface recombination velocity typical of such interfaces. In order to explore the nature of this semiconductor-oxide interface, we have grown two heterostructures, oxidized them, and measured the room temperature photoluminescence lifetime at the bulk GaAs bandedge