Visualization of TlBr ionic transport mechanism by the Accelerated Device Degradation technique

• A new technique was developed to visualize the ionic transport phenomena in TlBr.
• Tl-rich defects nucleate under cathode and propagates through bulk to the anode.
• Migration energy of Br− ions in TlBr was calculated to be 0.33 eV.

Thallium Bromide (TlBr) is a promising gamma radiation semiconductor detector material. However, it is an ionic semiconductor and suffers from polarization. As a result, TlBr devices degrade rapidly at room temperature. Polarization is associated with the flow of ionic current in the crystal under electrical bias, leading to the accumulation of charged ions at the device׳s electrical contacts. We report a fast and reliable direct characterization technique to identify the effects of various growth and post-growth process modifications on the polarization process. The Accelerated Device Degradation (ADD) characterization technique allows direct observation of nucleation and propagation of ionic transport channels within the TlBr crystals under applied bias. These channels are observed to be initiated both directly under the electrode as well as away from it. The propagation direction is always towards the anode indicating that Br− is the mobile diffusing species within the defect channels. 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.