Investigation of polarization mechanism in MSM TlBr crystal room-temperature nuclear radiation detector

Abstract

Thallium Bromide (TlBr) single crystal detector is widely recognized as an excellent semiconductor nuclear radiation detector. And its detection performance has already reached commercial level of the majority semiconductor detector. However, the long-term stability of TlBr detector always exhibited a serious polarization effect and the commercial application of TlBr detector is heavily limited. In this paper, the polarization phenomenon, polarization mechanism and the influence of polarization effect on detection performance are systematic investigated. As the metal-semiconductor interface plays an important role in detector performance, two typical metal-semiconductor-metal structure, Au/TlBr/Au and Ti/TlBr/Ti detectors are designed and fabricated in this paper. The XPS in-situ analysis results reveal that different oxidation/reduction reactions would happen at the metal-semiconductor interface of Au/TlBr/Au and Ti/TlBr/Ti detectors. The serious polarization effect in Au/TlBr/Au detectors resulted from the aggregated [AuBr4]- ion at the Au/TlBr interface. Meanwhile, the relative weaken polarization effect in Ti/TlBr/Ti detectors is ascribed to the combined effects of oxidic titanium ions (Ti3+, Ti4+) and metallic Ti–Tl layer at the Ti/TlBr interface. Thus, the detector Ti/TlBr/Ti has a relative better energy resolution and long-term stability compared to detector Au/TlBr/Au. This paper systematic investigate the polarization mechanism and the influence of polarization effects on TlBr detector performance, and this will provide a potential solution to suppress the polarization problem by electrode architecture designing in the near future.