Cathode degradation in TlBr devices

Thallium bromide (TlBr) is a wide bandgap, compound semiconductor with high gamma-ray stopping power and promising physical properties. However, performance degradation and the eventual irreversible failure of TlBr devices can occur rapidly at room temperature, due to “polarization”, caused by the electromigration of Tl⁺ and Br^- ions to the electrical contacts across the device. Using the Accelerated Device Degradation (ADD) experiment, the degradation phenomena in TlBr devices has been visualized and recorded. This paper focuses on “ageing” of the device cathode at various temperatures. ADD is a fast and reliable direct characterization technique that can be used to identify the effects of various growth and post-growth process modifications on the device degradation. Using this technique we have identified cathode degradation with migration of Br^- ions and an associated generation and growth of Thallium-rich fractal “ferns” from the cathode. The effective migration energy of the Br^- ions was calculated to be 0.33 +/- 0.03 eV, which is consistent with other theoretical and experimental results.