Transient Characteristics of PME Effect –Theory–

Abstract

Assuming a single life time τ for both of the minority and majority carriers, a surface recombination velocity s, and an absorption coefficient k, the spatial and time distribution of excess minority carriers injected in a semiconductor by a monochromatic light pulse is expressed in terms of error functions with space and time variables normalized to diffusion length L and τ. The result is characterized by two material parameters α=kL and γ=sτ/L. PME output proportional to the surface density of excess carriers p(0, t) is shown to decay much faster than the PC output because for large α inward diffusion of carriers accelerates the decay of p(0, t) but has no effect on the total number of carriers. Results of preliminary measurements on n-Ge samples using a Q-switched ruby laser is shown to be in reasonable agreement with these theoretical conclusions.