Carrier diffusion inside active regions of gain-guided vertical-cavity surface-emitting lasers

Abstract

The radial carrier diffusion process inside active regions of gain-guided vertical-cavity surface-emitting lasers (VCSELs) is studied rigorously. To this end, a comprehensive three-dimensional self-consistent VCSEL simulation is used. In the modelling, carrier degeneracy as well as temperature and carrier-concentration dependencies of the diffusion coefficient are taken into account. For the room-temperature operation of the GaAs/AlGaAs/AlAs proton-implanted top-surface-emitting VCSELs, ambipolar diffusion coefficient was found to be relatively low (≃ 7.5 cm²/sec) and nearly constant inside the active region but it increases rapidly beyond this region. It is, however, proved that although very accurate VCSEL modelling requires rigorous treatment of the carrier diffusion process, an average constant value of the diffusion coefficient may be undoubtedly used in quite reliable VCSEL simulations.