Photoconductivity of vanadium-doped lead telluride in the terahertz spectral region

It is shown that PbTe:V single crystals are photosensitive in the terahertz spectral region up to the wavelength 280 $\mu$m. The measurements are conducted in the temperature range from 8 to 300 K. In this temperature range, the dark conductivity of the crystals exhibits the activation character of the temperature dependence and varies by four orders of magnitude, which is due to Fermi-level pinning 20 meV below the bottom of the conduction band. As the temperature is elevated and, correspondingly, the conductivity increases, the amplitude of the photoresponse substantially increases. This result is interpreted in the context of the model that takes into account significant broadening of the vanadium impurity level and its shift to the bottom of the conduction band with increasing temperature.