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

• Published in: Physica Status Solidi B. Basic Solid State Physics 2015-02, Vol.252 (6)
• Main Authors: Varley, J. B., Conway, A. M., Voss, L. F., Swanberg, E., Graff, R. T., Nikolic, R. J., Payne, S. A., Lordi, V., Nelson, A. J.
• Format: Article
• Language: English
• Subjects: density functional theory; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; MATERIALS SCIENCE; radiation detector; surface treatment; thallium halide; X-ray photoemission spectroscopy
• ISSN: 0370-1972; 1521-3951

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 in this paper, 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 TIBr1-xC1X. 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.