Control of wet-etching thickness in the vertical cavity surface emitting laser structure by in situ laser reflectometry

We have investigated the use of in situ laser reflectometry for etch depth control in vertical cavity surface emitting laser (VCSEL) structures. We can obtain the precise etch depth by simply counting the number of oscillations during the wet-etching process. After calibration on an AlGaAs/GaAs 20-period distributed Bragg reflector (DBR) structure, this technique was applied to the monolithic 1.55 μm VCSEL device process that is required to etch epilayers of several μm thickness. In the 1.55 μm VCSEL structure, the mesa was generated by monitoring the number of peaks in the bottom DBR that corresponded to an etch depth of about 11 μm. The overall spatial uniformity of the etched sample was within a layer (1000 A) by the distinction between layers. This process offers the possibility of precise control of etch depth for any multilayer structure.