Characterization of polycrystalline TlBr films for radiographic detectors

Vapor deposited films of thallium bromide are evaluated as potential photoc onductive layers in new large-area radiographic detectors. The attractivene ss of the material lies in iis inherent high effective atomic number and hi gh density. Polycrystalline films up to 200 mu m have been grown and show a columnar structure with grains reaching 100 mu m in diameter. Current-volt age (IV) tests indicate a bulk resistivity of 10(9)-10(10) Omega . cm, limi ted by,ionic conduction. Instability of current with time is also observed, but it can be minimized with cooling. The films demonstrate high gain at r elatively low field strengths as compared to other photoconductive layers. Benefits and drawbacks of TlBr are compared to other materials, and possibl e solutions are discussed.