Analysis of dislocations and their correlation with dark currents in CdTe/Si heterojunction diode-type x-ray detectors

Abstract

Distribution and density of dislocations as a function of CdTe epilayer thickness as well as their effect on device dark current were studied using a p-CdTe/n-CdTe/n+-Si heterojunction diode type x-ray detector. A high dislocation density was found in thin devices, which decreased by more than an order of magnitude when the device thickness was increased to 35 μm. First, the dislocation density decreased rapidly with the CdTe thickness but the decrement was slowed down for the CdTe thicknesses above 20 μm. The device dark current showed a strong dependence on dislocation density, which increased with an increase in the dislocation density. A nearly temperature independent dark current was observed in thin devices suggesting that trap-assisted tunneling (TAT) through the dislocation-related current paths was dominant. Dark currents of thicker devices, on the other hand, could be explained due to contributions from both TAT and generation-recombination currents. Furthermore, one possible detector design that helps us to reduce the dark current is also proposed.