Effect of chlorination on the TlBr band edges for improved room temperature radiation detectors

Abstract

Thallium bromide (TlBr) crystals subjected to hydrochloric acid (HCl) chemical treatments have been shown to advantageously affect device performance and longevity in TlBr‐based room temperature radiation detectors, yet the exact mechanisms of the improvements remain poorly understood. Here, we investigate the influence of several HCl chemical treatments on device‐grade TlBr and describe the changes in the composition and electronic structure of the surface. Composition analysis and depth profiles obtained from secondary ion mass spectrometry (SIMS) identify the extent to which each HCl etch condition affects the detector surface region and forms of a graded TlBr/TlBr1−xClx surface heterojunction. Using a combination of X‐ray photoemission spectroscopy (XPS) and hybrid density functional calculations, we are able to determine the valence band offsets, band gaps, and conduction band offsets as a function of Cl content over the entire composition range of TlBr1−xClx. This study establishes a strong correlation between device process conditions, surface chemistry, and electronic structure with the goal of further optimizing the long‐term stability and radiation response of TlBr‐based detectors.

Thallium Bromide Gamma-Ray Spectrometers and Pixel Arrays

“…Research on the properties of TlBr has shown that ionic conduction contributes to deterioration of TlBr device performance at room temperature [30]. Methods have been developed involving crystal growth, surface processing, and electrode deposition that have enabled TlBr detectors to operate [31][32][33] for many months under continuous bias. Figure 12 shows photo peak channel and 241 Am pulse height spectra vs. time under 100 V bias for a 1 mm thick planar detector.…”

Band offsets of metal oxide contacts on TlBr radiation detectors

“…4,5 Reducing the reaction of the Br À ions with the electrode material has been the focus of a large body of TlBr research. Approaches include chemically treating the TlBr crystal to reduce defects at the surface, 6,7 altering the electronic structure at the interface, 8,9 and determining the optimal metallic electrode material. 10 The use of thallium contacts has shown promising results, with extended lifetimes of over 10 000 h being reported.…”