Recombination and trapping centers in pure and doped TlBr crystals

TlBr is a promising wide-gap semiconductor for developing γ-radiation detectors. One of the limiting factors in developing the technology of detectors is the lack of experimentally determined trapping and recombination centers. In this paper, a generalized model of the formation and behavior of intrinsic defects in pure and doped TlBr single crystals is presented. The relation of intrinsic defects to growth conditions and electrical properties is determined. The previously obtained temperature dependences of the photoconductivity, the data of current deep level transient spectroscopy and microcathodoluminescence, and the kinetic characteristics of the photoconductivity are used as objects of analysis. It is shown that the compensation of charged centers control the transport properties of charge carriers. In compensated doped TlBr crystals, the product of the mobility and lifetime can reach μτ = 5 × 10−4 cm2 V−1. The energy-level diagram of local levels in pure and doped TlBr crystals is proposed. The ionization energies of major structural and impurity defects in TlBr, i.e., the anion vacancy Va+, cation vacancy Vc−, and Pb2+, O2−, S2− ions, are determined. The energy position of a single anion vacancy Va+ is Ec − 0.22 eV. The energy level of the cation vacancy is Ev + 0.85 eV for a single cation vacancy and Ev + 0.58 eV for a vacancy incorporated into the {Pb2+Vc−}0 complex. The ionization energy of the Pb2+ Coulomb trap is Ec − 0.08 eV in doped TlBr crystals.