Spatial mapping of the mobility-lifetime (MT) product in cadmium zinc telluride nuclear radiation detectors using transport imaging [video]

Abstract

Cadmium zinc telluride (Cd1-xZnxTe) is an important material for room temperature nuclear radiation detectors. However, CdZnTe crystals are susceptible to growth defects such as grain boundaries, twin boundaries, and tellurium (Te) inclusions which can compromise desirable energy resolution and electron/hole charge collection properties. The presence of these defects ultimately degrades the effectiveness of the nuclear radiation detector material. The ability to map transport properties at high spatial resolution can provide new insight into the roles of individual defects. This study employs high-resolution ( < 5μm) transport imaging to explore the effect of CdZnTe crystal defects on the spatial variation of carrier transport properties. The ambipolar diffusion length (Ld) and associated free carrier mobility-lifetime (μτ) product are determined by imaging the recombination luminescence from carriers generated by an electron beam. Crystal defects are marked by regions of low intensity luminescence. At the same time, we observe increasing ambipolar diffusion length in the region immediately surrounding the defect. One explanation is that the gettering of point defects, such as interstitials and vacancies, associated with the formation of point defects results in localized increases in the μτ product. Initial results indicate that these variations occur over a region extending ~ 10 μm from the edge of the defect.