TlBr and TlBrxI1−x crystals for γ-ray detectors

TlBr and TlBrxI1−x are wide bandgap semiconductor materials being investigated for applications in γ-ray spectroscopy. They have a good combination of density and atomic numbers, promising to make them very efficient detectors. Their low melting points and simple cubic and orthorhombic crystal structures are favorable for bulk crystal growth. However, these semiconductors need to be extremely pure to become useful as radiation detectors. Impurities can lead to charge trapping and scattering, reducing the charge transit lengths and limiting the detector thickness to <1 mm. Additional purification steps were implemented to improve the purity and mobility–lifetime product (μτ) of electrons. Detector-grade TlBr with the electron μτ product of up to 6×10−3 cm2/V has been produced, which allowed operation of detectors up to 15 mm thickness. The ternary TlBrxI1−x was investigated at different compositions to vary the bandgap and explore the effect of added TlI on the long term stability of detectors. The material analysis and detector characterization results are included.