A GENERALIZED-APPROACH TO SURFACE PHOTOVOLTAGE

A detailed majority and minority carrier current balance model for sur face photovoltage (SPV) is presented. A rigorous treatment of carrier junction generation and surface recombination is shown to be essential . We show that under weak above band gap photoexcitation, standard con stant open-circuit voltage and constant photon flux SPV measurements c an both reveal the bulk minority carrier diffusion length, provided th e initial band bending V-bi is sufficiently high. However, when V-bi i s small, approximate SPV expressions are inapplicable and both standar d SPV manifestations will then yield incorrect diffusion length values . We also show that for cases of low surface recombination velocity, t he SPV technique can be used to measure the width of the space charge region and V-bi; however, when the surface recombination velocity is l arge, this approach cannot be used as majority carrier backdiffusion c an play a dominant role under high photon energy excitation conditions . (C) 1996 American Institute of Physics.