Temperature-Dependent Photoconductivity Responce and Band Gap Variation of Tl$_{\mathbf{2}}${In}$_{\mathbf{2}}${S}$_{\mathbf{3}}${Se Layered Single Crystals}

Temperature variation of indirect band gap of Tl$_{2}$In$_{2}$S$_{3}$Se layered single crystals were obtained by means of absorption and photoconductivity measurements. The temperature coefficient of $-$7.1~$\times$ ~10$^{-4}$~eV/K from absorption measurements in the temperature range of 10--300~K in the wavelength range of 520--1100~nm and $-$5.0~$\times$ ~10$^{-4}$~eV/K from PC measurements in the temperature range of 132--291~K in the wavelength range of 443--620~nm upon supplying voltage~$V$~$=$~80~V were obtained. From the analysis of dark conductivity measurements in the temperature range of 150--300~K, conductivity activation energy was obtained as 0.51~eV above 242~K. The degree of the disorder, the density of localized states near Fermi level, the average hopping distance and average hopping energy of Tl$_{2}$In$_{2}$S$_{3}$Se crystals were found as, 1.9~$\times$ ~10$^{5}$~K, $N_{f}$~$=$~4~$\times$ ~10$^{20}$~cm$^{-3}$eV$^{-1}$, 29.1~{\AA} and 24.2~meV in the temperature range of 171--237~K, respectively. Activation energy of hopping conductivity at~$T$~$=$~171~K was obtained as 41.3~meV and the concentration of trapping states was found as 1.6~$\times$ ~10$^{19}$~cm$^{-3}$.