Band offsets of metal oxide contacts on TlBr radiation detectors

Olivia K Voyce,Amlan Datta,Laura J Harkness-Brennan,Dan S Judson,Tim D Veal,Shariar Motakef,Mark A Isaacs

doi:10.1063/5.0063365

Abstract

Metal oxides are investigated as an alternative to metal contacts on thallium bromide (TlBr) radiation detectors. X-ray photoelectron spectroscopy studies of SnO2/TlBr and ITO/TlBr devices indicate that a type-II staggered heterojunction forms between TlBr and metal oxides upon contacting. By using the Kraut method of valence band offset (VBO) determination, the VBOs of SnO2/TlBr and ITO/TlBr heterojunctions are determined to be 1.05±0.17 and 0.70±0.17 eV, respectively. The corresponding conduction band offsets are then found to be 0.13±0.17 and 0.45±0.17 eV, respectively. The I–V response of symmetric In/SnO2/TlBr and In/ITO/TlBr planar devices is almost Ohmic with a leakage current of less than 2.5 nA at 100 V.

Highlights

Thallium bromide (TlBr) is a promising material for the handheld detection of gamma rays, owing to its large bandgap (2.68 eV), high resistivity, and stopping power.[1]
This paper explores the use of metal oxide electrodes further by using x-ray photoelectron spectroscopy (XPS) and the Kraut method to determine the valence band offset and the resulting heterojunction at the contact/thallium bromide (TlBr) interface.[14]
XPS measurements of the Br 3p doublet, Tl 4f doublet, and the valence band maximum (VBM) region for the uncontacted TlBr sample are shown in Figs. 1(a), 1(b), and 1(c), respectively

Summary

Introduction

Thallium bromide (TlBr) is a promising material for the handheld detection of gamma rays, owing to its large bandgap (2.68 eV), high resistivity, and stopping power.[1]. Reducing the reaction of the BrÀ 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.[11,12]. This often has to be used in tandem with bias switching techniques, which are not readily deployed for an in situ radioactive assay The use of thallium contacts has shown promising results, with extended lifetimes of over 10 000 h being reported.[11,12] this often has to be used in tandem with bias switching techniques, which are not readily deployed for an in situ radioactive assay

Methods

Results

Discussion

Conclusion