Limit of validity of the drift-diffusion approximation for simulation of photodiode characteristics

We have investigated the photoresponse of a Si p–n photodiode under different illumination and bias conditions. Under high illumination and low applied reverse bias, a clear discrepancy between experimental results and conventional two-dimensional device simulation results is observed. The discrepancy is found to be caused by the fact that the space-charge limitation effect under the drift-diffusion approximation used in conventional simulations does not describe the real situation. Thus, in the framework of the drift-diffusion approximation, modification of the mobility model is needed for the early stage of carrier transport under such operating conditions.