Abstract
It is shown that narrow band gap semiconductors Tl1-xIn1-xGexSe2 are able effectively to vary the values of the energy gap. DFT simulations of the principal bands during the cationic substitutions is done. Changes of carrier transport features is explored. Relation with the changes of the near the surface states is explored. Comparison on a common energy scale of the x-ray emission Se K beta(2) bands, representing energy distribution of the Se 4p states, indicates that these states contribute preliminary to the top of the valence band. The temperature dependence of electrical conductivity and spectral dependence photoconductivity for the Tl1-xIn1-xGexSe2 and Tl1-xIn1-xSixSe2 single crystals were explored and compared with previously reported Tl1-xIn1-xSnxSe2. Based on our investigations, a model of centre re-charging is proposed. Contrary to other investigated crystals in Tl1-xIn1-xGexSe2 single crystals for x = 0.1 we observe extraordinarily enormous photoresponse, which exceed more than nine times the dark current. X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces of Tl1-xIn1-xGexSe2 (x = 0.1 and 0.2) single crystals have been studied. These results indicate that the relatively low hygroscopicity of the studied single crystals is typical for the Tl1-xIn1-xGexSe2 crystals, a property that is very important for handling these quaternary selenides as infrared materials operating at ambient conditions.