Thallium Bromide Semiconductor Radiation Detectors With Thallium Contacts

Thallium bromide (TIBr) is a wide bandgap, compound semiconductor with high gamma-ray stopping power and promising physical properties. The electro-migration of Br- ions toward the anode and their reaction with the contact have been long known to adversely influence the lifetime of TIBr devices. We report on the performance of TIBr devices with TI contacts which minimizes the effects of polarization. Results indicate that vapor-deposited TI contacts are highly ohmic and adhere strongly to TIBr. Long-term lifetime tests were performed under alternating bias with a 17A-mu Hz duty cycle. Unlike devices with Pt and Au contacts, devices with TI do not exhibit the short-term (in the order of hundreds of hours) fluctuations in the spectroscopic response. Furthermore, these devices show a stable behavior and can work under much lower electric fields. Energy resolution in the range of 2%-2.5% at 662 keV was obtained using virtual Frisch grid (10 mm thick) and pixelated (5.5 mm thick) TIBr devices with TI contacts without any digital correction at room temperature. Large area 20 mm x 20 mm x 5.5 mm pixelated detectors with 11 x 11 and 15 x 15 pixel patterns were also fabricated using TI contacts.