The cathodoluminescence contrast formation of localized non-radiative defects in semiconductors

The contrast formation of localized non-radiative semiconductor defects in cathodoluminescence (CL) micrographs is analyzed using a linear relationship between the CL intensity and the excess carrier density δp. The latter is evaluated on the basis of Donolato's Born approximation and for generation by a point source. Numerical calculations for a threading dislocation at right angle to a surface of infinite recombination velocity yield an exponential decay of the CL contrast at sufficient distance from the dislocation with a decay constant of 0.63 minority carrier diffusion lengths. The contrast mechanism is seen to be based primarily on the reduction of the total number of excess carriers due to enhanced recombination at the dislocation rather than on the associated reduction of the luminescence quantum efficiency.