<title>Multispectral photoelectric characteristics induced by metastable electronic states in PbTe(Ga)</title>

Abstract

The analysis of photoconductivity (PC) spectra in PbTe(Ga) single crystals and films shows that a pronounced photoresponse is observed at an energy approximately 20 meV less the energy gap value. The relative amplitude of the sub-band photoresponse depends on the method of the crystal synthesis, but its energy position does not depend on temperature or growth technique. For PbTe(Ga) thin films the structure of the absorption edge is similar to undoped PbTe and amplitude of the sub-band photoresponse appears to be small. The phenomenological description of the PC kinetics of the investigated samples under the IR-radiation of pulse and heat sources is done. It is established that under the radiation with pulse duration 10 mcs the characteristic relaxation times are 10<SUP>-3</SUP> s at 4.2 K, and the persistent PC can be observed only under the continuous radiation at T &lt; 80 K. Moreover, at low intensities of the continuous radiation PC relaxation time is about 1 ms and only the increase of radiation intensity results in appearance of the persistent PC with the relaxation times of 10<SUP>5</SUP> s. We propose a phenomenological model of energy spectrum and impurity states in PbTe(Ga), which is able to describe the experimental data. According to this model the metastable impurity states 20 meV lower the bottom of the conduction band exist in addition to the ground states 70 meV lower the bottom of the conduction band. The increase of the radiation intensity provides the growth of the metastable states concentration and the impurity band formation. So it can be concluded that PbTe(Ga) may be considered as an advanced material for the multispectral photodetectors operating in near IR-region if the ground state electrons are excited and in far IR-region if the excited from preliminary induced metastable states.