Dependence of the lateral oxidation rate of an AlAs layer used as a current aperture in vertical-cavity surface-emitting lasers on different physical parameters

The wet oxidation kinetics of an AlAs layer used as a current aperture in selectively oxidized vertical-cavity- surface-emitting-lasers (VCSELs) is investigated in details. The process is modeled as a diffusion-reaction process. A strong dependence of the oxidation rate on the temperature, at which the wet oxidation is being carried out, is observed. The temperature dependence of the oxidation process is explained theoretically by considering equivalent reaction activation energies for the oxidation reaction. Also for oxidation over a long time interval, variation of the oxidation rate with the variation of the radius of the etched mesa of the VCSEL is observed. A theory has been developed considering the 3D diffusion of the oxidant modules is an already oxidized cylindrical AlAs region and the reaction of the diffusion of the oxidant molecules in an already oxidized cylindrical AlAs region and the reaction of the oxidant molecule at the oxidized-unoxidized AlAs interface. Relevant material parameters, that are independent of the size and geometry of the etched VCSELs, are extracted from the experimental results. Using them in the theoretical model, the rate equation of the lateral oxidation process is obtained. The theory predicts the dependence of the oxidation process on the size of the VCSEL, the AlAs layer thickness, as well as on the physical properties of the AlAs layer. The theoretical predictions have been verified by a number of experiments with reproducible results.