Current spreading in proton-implanted vertical-cavity top-surface-emitting

In the paper, the current spreading phenomenon is analysed in proton-implanted vertical-cavity top-surface-emitting lasers (VCSELs). A simple approximation analytical relation was derived for a radial distribution of the current density entering the active regions of these lasers. This distribution is nearly uniform in the case VCSELs with a very small active region of radius R(A) less than or similar to 2 mu m but becomes more and more non-uniform with an increase in the active region's size. In VCSELs with very large active regions (r(A) greater than or similar to 10 mu m), most current flows within a narrow annular area close to the active-region perimeter. This non-uniformity should be taken into account in modelling all physical phenomena in VCSEL structures that are influenced by distributions of a current density or a carrier concentration within their active regions.