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

The energy resolution of room temperature radiation detectors is limited by material properties such as the atomic number of the constituent atoms, band gap, electrical transport coefficients and crystalline purity, which critically affect both the stopping distance of ionizing radiation and the carrier collection from the material. Thallium bromide (TlBr) possesses properties that satisfy these criteria and has emerged as a leading candidate for next-generation detectors, but it currently suffers from degradation phenomena that limit long-term performance. Chemical surface treatments can drastically improve the lifetime of TlBr-based devices, with hydrochloric acid etching in particular shown to increase longevity, but the exact role of these treatments has remained poorly understood. In our recent publication, we used a combination of experimental and theoretical methods to address how these treatments influence the surface composition and the underlying electronic structure. Their results indicate the etch treatment forms a TlBrxCl1-x  alloy at the surface whose composition is sensitive to the chemical conditions. The surface alloy suppresses hole injection but may also provide several other beneficial functions that will require further study.