CdTe X/γ-ray Detectors with Different Contact Materials

Different contact materials and optimization of techniques of their depositions expand the possibilities to obtain high performance room temperature CdTe-based X/γ-ray detectors. The heterostructures with ohmic (MoO_x) and Schottky (MoO_x, TiO_x, TiN, and In) contacts, created by DC reactive magnetron sputtering and vacuum thermal evaporation, as well as In/CdTe/Au diodes with a p-n junction, formed by laser-induced doping, have been developed and investigated. Depending on the surface pre-treatment of semi-insulating p-CdTe crystals, the deposition of a MoO_x film formed either ohmic or Schottky contacts. Based on the calculations and I-V characteristics of the Mo-MoO_x/p-CdTe/MoO_x-Mo, In/p-CdTe/MoO_x-Mo, Ti-TiO_x/p-CdTe/MoO_x-Mo, and Ti-TiN/p-CdTe/MoO_x-Mo Schottky-diode detectors, the current transport processes were described in the models of the carrier generation-recombination within the space-charge region (SCR) at low bias, and space-charge limited current incorporating the Poole-Frenkel effect at higher voltages, respectively. The energies of generation-recombination centers, density of trapping centers, and effective carrier lifetimes were determined. Nanosecond laser irradiation of the In electrode, pre-deposited on the p-CdTe crystals, resulted in extending the voltage range, corresponding to the carrier generation-recombination in the SCR in the I-V characteristics of the In/CdTe/Au diodes. Such In/CdTe/Au p-n junction diode detectors demonstrated high energy resolutions (7%@59.5 keV, 4%@122 keV, and 1.6%@662 keV).