Comprehensive Analysis of Electric Properties of Oxide-Confined Vertical-Cavity Surface-Emitting Lasers

We present a comprehensive description of electric properties of vertical-cavity surface-emitting lasers (VCSELs). A complete drift-diffusion model is developed and applied for carrier transport in a multilayer semiconductor laser heterostructure with a p-n junction. We address the impact of interface grading in distributed Bragg reflectors (DBRs), modulation doping of the DBRs and surrounding layers of the quantum well as well as drastically material-dependent carrier mobilities and recombination constants. Solution of the drift-diffusion model yields spatial profiles of the nonequilibrium carrier concentrations and current. The focus is made on oxide-confined GaAs/AlGaAs VCSELs. We evaluate both depletion and diffusion capacitance of the device and show that both contributions to the capacitance as well as the differential series resistance critically depend on the injection current and VCSEL chip design such that, in general, VCSEL cannot be properly modeled by an equivalent circuit approximation. Solution for the current profile demonstrates significant enhancement of the current density at the edges of the oxide-confined aperture (current crowding). We show that, as long as the mesa diameter is small, the effective RC-product can be kept low at small aperture diameters.