Thallium Lead Iodide Radiation Detectors

Thallium lead iodide (TlPbI₃) is a compound semiconductor characterized with wide band gap (2.3 eV) and high photon stopping power. Thus, TlPbI₃ is an attractive material for fabrication of room temperature radiation detectors. In this study, TlPbI₃ crystals were grown by the vertical Bridgman technique using zone-purified materials. The starting materials for the crystal growth were synthesized from commercially available TlI and PbI₂ powders with nominal purity of 99.99%. Powder X-ray diffraction analysis was performed to evaluate chemical composition of the synthesized TlPbI₃. In order to fabricate radiation detectors, the grown crystals were cut into several wafers using a wire saw. The wafers were then polished using Al₂O₃ abrasives. Electrodes were formed on the wafers by vacuum evaporation of gold. The resultant TlPbI ₃ radiation detectors were evaluated by measuring their current-voltage characteristics and spectral responses. Most of TlPbI ₃ detectors exhibited resistivities more than 10¹¹ Ωcm. The TlPbI₃ detectors were irradiated with α-particles (5.48 MeV) from a ²⁴¹Am source or γ-rays (662 keV) from a ¹³⁷Cs source. The TlPbI₃ detectors exhibited a clear peak of 5.48 MeV α-particles. Although the 662 keV peak was not resolved in the energy spectra, increased counts above the noise spectrum were observed for the detectors. To our knowledge, it is the first time that TlPbI₃ detectors exhibit α-particle spectra with a clear peak and γ-ray spectra.