Voltage drop in n- and p-type Bragg reflectors for vertical-cavity surface-emitting lasers

An analysis of carrier transport in n- and p-type distributed Bragg reflectors (DBR) of vertical-cavity surface-emitting lasers that consist of stacks of quarter-wave GaAs-AlAs layers is presented. The analysis is based on the diffusion-drift approximation with the thermionic boundary conditions at heterojunction interfaces. The spatial distribution of carrier effective masses and mobilities has been taken into account. While the voltage drop in n-type DBR is determined mostly by thermionic emission at the interfaces, the drift-diffusion component of the voltage drop is comparable with the thermionic emission in p-type DBR. We present the calculated resistance as a function of graded-region thicknesses and doping levels, which can be useful for low-resistive DBR design.<>