Cathodoluminescence and Spatial Variation in Mobility-Lifetime $(\mu \tau)$ Product in Bulk Doped Thallium Bromide

Nonuniformity in charge transport properties is a limiting factor in energy resolution of radiation detectors. In this paper, we investigate variations in the low temperature ambipolar diffusion length and the mobility-lifetime (μτ) product in bulk doped TlBr using cathodoluminescence (CL) and transport imaging. One TlBr crystal was doped with sodium (Na), aluminum (Al), and silver (Ag). A second TlBr crystal was doped with copper (Cu), iron (Fe), and zinc (Zn). We report the first low temperature high resolution CL spectroscopy and mapping in bulk doped TlBr, showing spatial variation in recombination luminescence on a scale of ~10 μm. Transport imaging is applied to quantify these variations in TlBr at 5 K. Ambipolar diffusion lengths and μτ products, dominated by the transport of holes, are mapped across a 40 μm segment of TlBr at a resolution of 2 μm. Ambipolar diffusion lengths are found to vary between 4.6 μm and 11.2 μm, on a spatial scale comparable to the variation observed in the CL map.