Measurement of Lifetime by the Photoconductive Decay Method†

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Abstract
General equations have been derived for the decay of photo-injected carriers in a semiconductor with time by taking as the solution of the continuity equation an eigen series whoso parameters arc determined by the usual boundary condition at the surface and also by the condition that the series correctly describes the carrier distribution an instant before decay begins. Both steady-state and pulsed initial distributions are considered, and it is shown that the decay is exponential only for zero surface recombination. With high surface recombination velocities the loss of exponential nature of the decay leads to an error in the measured value of filament lifetime. This error has been found numerically and graphically for various lifetimes and penetration depths. With white light the error is estimated to be not more than 5 % for the steady state method and not more than 10 % for the pulsed state method, these extreme values occurring at lifetimes of about 1 μsec.

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