  We investigated the possibility of augmenting the fluence of electrons
traversing CdTe thin film and thus increasing the detected signal pursuing two
venues: adding a high-Z metal layer to the back of the detector surface, and
adding a top low-Z material to the detector layer to return its backscattered
electrons. Copper (Cu) and lead (Pb) layers of varying thickness were
investigated as potential metal back-reflectors, while PMMA was tried as the
top cover in multilayer detector structures. The Monte Carlo (MC) radiation
transport package MCNP5 was first used to model a basic multilayer structure
under a Varian 6MV. It was then modified by the addition of Cu and Pb to
analyze the extent of the signal enhancement and changes in secondary electron
fluence spectra. Backscattering coefficients were then calculated using EGSnrc
for electron sources. Analytical functions were established to represent the
best-fitting curves to the simulation data. Finally, electron backscattering
data were related to signal enhancement. It was found that adding a metal film
below the sensitive volume of a detector increases the fraction of reflected
electrons, especially in the low energy range, resulting in ~10% and 75%
increased energy deposition using Cu and Pb, respectively. We also established
a linear dependence between the energy deposition in the semiconductor layer
and the fluence of backscattered electrons in the corresponding multilayer
structure. The low-Z top layer in practically implemental thicknesses of tens
of microns has a positive effect due to partial electron reflection back to the
semiconductor layer. Signal enhancement in a thin-film CdTe radiation detector
could be achieved using electron backscattering from metal reflectors. The
methodology explored here warrants further studies to quantify achievable
signal enhancement for various thin-film and other small sensitive volume
detectors.
