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It is shown that PbTe:V single crystals are photosensitive in the terahertz spectral region up to the wavelength 280 μm. 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.

Temperature dependences of resistivity, magnetic susceptibility, and charge-carrier concentration and mobility in single-crystalline PbTe:V samples with a varied impurity content are investigated. It is shown that vanadium forms a donor level located ∼20 meV below the conduction-band bottom. The electron mobility is as high as 105 cm2 V−1 s−1 in the samples with N V ≤ 0.21 at % and proves to be more than an order of magnitude higher in the samples with the highest vanadium content N V = 0.26 at %. In the same samples, the real part of the conductivity is characterized by a pronounced frequency dependence. An increase in vanadium concentration is accompanied by a decrease in the effective magnetic moment of impurity atoms. The features of electron transport in PbTe:V may be caused by a variable vanadium valence and by the effect of interimpurity correlations.

The T-x phase diagram along the PbTe-VTe2 join of the Pb-V-Te system has been studied. Vanadium-doped lead telluride crystals have been grown, and the longitudinal vanadium and carrier profiles in the crystals have been investigated. The temperature dependences of resistivity for the crystals lend support to the conclusion drawn earlier that PbTe〈V〉 is in a semi-insulating state at low temperatures. The crystals offer a high 20-K electron mobility, on the order of 105 cm2/(V s), which attests to high electrical homogeneity of the material and stabilization of the Fermi level.

We have studied a portion of the ternary system Pb-V-Te. Pseudobinary joins have been identified, the vanadium solubility along the V3Te4-PbTe join has been determined, and the lattice parameter of the solid solution has been measured as a function of vanadium content at 800 and 870°C. Six PbTe〈V〉 crystals have been grown by the Bridgman method, and their microstructure and transport properties have been investigated. The results indicate that vanadium in PbTe is not a simple donor: its effect depends on those growth conditions that determine the degree of compensation of the donor effect of vanadium and native defects. PbTe〈V〉 samples have been found to pass into a high-resistivity state on cooling and to be photosensitive. The depth of the vanadium donor level in the band gap of lead telluride has been evaluated.

Doping of the lead telluride and related alloys with the group III impurities results in appearance of unique physical features of a material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. As a result, single photodetectors based on Pb 1-x Sn x Te(In) demonstrate extremely high performance in the Terahertz wavelength range. Furthermore, it is shown that local long-lived non-equilibrium states are generated in Pb 1-x Sn x Te(In) alloys at low temperatures under the action of local Terahertz excitation. This result opens a possibility for construction of a “continuous” focal-plane array for detection of Terahertz radiation. Ideas for readout of information from this array are discussed. Keywords: Terahertz, Radiation, Dept ector, Focal-Plane Array. 1. INTRODUCTION Investigation of impurity states in the group III - doped narrow-gap IV-VI semiconductors based on the lead telluride started in early 70's