Thallium Bromide Semiconductor Radiation Detectors With Thallium Contacts

Thallium bromide (TlBr) 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 TlBr devices. We report on the performance of TlBr devices with Tl contacts which minimizes the effects of polarization. Results indicate that vapor-deposited Tl contacts are highly ohmic and adhere strongly to TlBr. Long-term lifetime tests were performed under alternating bias with a 17.4-μHz duty cycle. Unlike devices with Pt and Au contacts, devices with Tl 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) TlBr devices with Tl 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 Tl contacts.