  Electron beam induced current (EBIC) is a powerful characterization technique
which offers the high spatial resolution needed to study polycrystalline solar
cells. Ideally, an EBIC measurement reflects the spatially resolved quantum
efficiency of the device. In this work, a model for EBIC measurements is
presented which applies when recombination within the depletion region is
substantial. This model is motivated by cross-sectional EBIC experiments on
CdS-CdTe photovoltaic cells which show that the maximum efficiency of carrier
collection is less than 100 \% and varies throughout the depletion region. The
model can reproduce experimental results only if the mobility-lifetime product
$\mu\tau$ is spatially varying within the depletion region. The reduced
collection efficiency is speculated to be related to high-injection effects,
and the resulting increased radiative recombination.
