Summary form only given. Vertical-cavity laser thresholds have recently been greatly reduced by replacing proton implantation with selective "wet oxidation" of the AlAs layers. At present, little has been reported about the structure or electronic properties of the oxide and its interface with the remaining semiconductor. In this paper, by measuring time-resolved photoluminescence at the GaAs band edge, we study the interface recombination at the GaAs/oxide interface. We also investigate the structural properties of the oxide using TEM diffraction.