The constant photocurrent method has been widely used in hydrogenated amorphous silicon as an efficient way of determining the optical absorption coefficient in the low-absorption region, and of estimating the defect density in the band gap. However, while the analysis is generally carried out on the assumption of uniform material parameters throughout the sample the experimental situation may fail to approximate that model. We therefore examine the influence on the resolved defect density of an inhomogeneous spatial distribution of defects, and of surface recombination, by means of a steady-state diffusion equation for photoexcited carriers. Differences by as much as a factor of 2 are observed within the range of possible experimental circumstances. ©1997 American Institute of Physics.