Characterization of Conductivity in Single Crystal TlBr

Abstract

TlBr is an ionic material with good potential for use in high energy radiation detectors because of its relatively large band gap and heavy elements. In these sensors, incident radiation excites electron hole pairs that are collected as the response, and the mobility-lifetime product for electrons and holes, as well as low dark current are common figures of merit. TlBr reportedly displays ionic conductivity that leads to undesirable leakage, or dark current thereby reducing sensor response. This work focuses on the development of a defect and transport model appropriate to TlBr. The derived enthalpies of migration and Schottky defect formation are compared with literature values.

The defect and transport properties of acceptor doped TlBr: role of dopant exsolution and association

“…The comprehensive description of the defect structuredopant -transport correlations established in this and the related work of the authors [11][12][13] has allowed for the first predictive model of the electrical conductivity in TlBr and its optimization for detector operation. Acceptor doping should be avoided given the time dependent dark resistance and generation of precipitates with potential for decreased electronhole collection, resulting in degradation of radiation detector performance.…”

“…[8][9][10] To clarify the source and nature of ionic conduction in TlBr, a systematic examination of the roles of dopants and temperature in controlling defect generation and transport was undertaken by our group, with the present paper reporting a more detailed analysis of acceptor doped TlBr. [11][12][13] In these studies, the electrical properties of undoped and donor doped (Pb) TlBr single crystals were analyzed in terms of a Schottky defect chemical model (see Theory section), and found to be consistent with a purely ionic conduction mechanism dominated, in the intrinsic case, by Br vacancy transport due to the 3-5 orders of magnitude higher mobility versus that of Tl vacancies. With sufficient divalent donor dopant (44 ppm), Tl vacancy migration becomes the dominant conduction mechanism at reduced temperatures.…”

The Defect and Transport Properties of Donor Doped Single Crystal TlBr

“…3 To clarify the source and nature of the ionic conduction in TlBr, a systematic examination of the roles of dopants and temperature in controlling defect generation and transport was undertaken. 4,5 Toward this end, previous researchers used direct current or single frequency conductivity measurements to determine the ionic conductivity of TlBr. [6][7][8] These techniques suffer from the inability to isolate often significant contributions from electrode and grain boundary resistances ͑in polycrystalline samples͒.…”

Characterization of Plasma-etched Surfaces of TlBr Crystals for Radiation Detectors

“…We speculate that the differences in dark current among detectors and the poor fabrication yield are probably due to the same causes, such as the structure and condition of the electrode-crystal interface. Furthermore, TlBr is an ionic conductor, (7) and the large differences in dark current among detectors can be caused by the complex behavior of ionic conduction and electrode reactions in the detector. Because these electrode reactions are considered to be strongly affected by surface conditions, chemical etching (8) and plasma etching have been proposed as surface treatment methods.…”