CURRENT SPREADING AND CARRIER DIFFUSION IN LONG-WAVELENGTH VERTICAL-CAVITY SURFACE-EMITTING LASERS

Current spreading and carrier diffusion in vertical-cavity surface-emi tting lasers (VCSEL's) critically affect the threshold current density , transverse gain profile, and optical modal characteristics of the de vices. We have numerically analyzed these effects for four popular lon g-wavelength VCSEL structures with wafer-bonded GaAs-AlGaAs Bragg bott om mirrors. The results show that current confinement for p-mirror VCS EL's is approximately twice as effective as the corresponding n-mirror VCSEL's, although the confinement factor for all practical VCSEL stru ctures studied here is considerably lower than the ''ideal'' structure . Calculations also show a strong dependence of current confinement on device aperture size and a tradeoff between the optical modal propert y and the current confinement efficiency for different apertured devic es.