Tapered air apertures for thermally robust VCL structures

We report on a vertical-cavity laser (VCL) process that allows high-temperature annealing up to 950/spl deg/C for 3 min while minimizing degradation of light-current-voltage characteristics. We used a wet chemical approach to form tapered undercut profiles in buried AlGaAs layers. This two-step process involves AlGaAs multilayers which have been graded to give a tapered oxidation front upon steam oxidation. The second step involves removal of the oxide by a KOH-based solution, keeping the original shape of the oxidized region intact. The air-apertured devices maintained their characteristics after high-temperature annealing while structures with oxide apertures showed a 50% reduction in external efficiency.