Transport Imaging of Spatial Distribution of Mobility- Lifetime () Product in Bulk Semiconductors for Nuclear Radiation Detection

Abstract

The objective of this research is to advance the development of a micro-analysis technique for characterizing the charge transport properties in bulk semiconductor materials for room temperature nuclear radiation detection. The technique is applied to bulk semi-insulating thallium bromide (TlBr) and cadmium zinc telluride (CZT) and uses a two-dimensional diffusion model and transport imaging to make rapid contact-free measurements of the magnitude and spatial variation in the mobility-lifetime () product at 2 m resolution. The product is a key measure of charge transport, and a uniform product is critical for optimum energy resolution in gamma ray detectors. Spatial variations in the ambipolar diffusion length are observed in TlBr on a scale of ~10 m, and the cathodoluminescence (CL) spectrum in TlBr at 5 K is reported. Using CL and photo-induced conductivity transient spectroscopy (PICTS), an empirical energy level diagram for Se and Pb defect levels in TlBr is reported. The product in TlBr is generally found to decrease with increasing impurities/defects. The product in TlBr and CZT is found to decrease with increasing temperature over the ranges of 8 K 102 K and 5 K 60 K, respectively. Transport imaging is applied for the first time to investigate the effects of Te inclusions in CZT and the role of photon recycling in TlBr and CZT.