Electronic structure, optical and photoelectrical properties of crystalline Si2Te3

In the framework of the density functional theory (DFT) in the approximation of local density adjusted for the strong correlation (LDA+U method), calculated were the band structure, total and partial densities of electronic states, as well as the spatial distribution of the electron density. According to the results of the calculation, Si2Te3 is an indirect-gap semiconductor with the calculated band gap E-gi(calc) = 2.05 cV, close to the experimentally measured E-g(opt) = 2.13 eV. The absorption edge and photoconductivity spectra of Si2Te3 crystal within the temperature range 80...293 K have been measured. It has been shown that the dependence of the absorption coefficient on the photon energy is described by the Urbach rule. The parameter sigma(0), associated with the constant of electron-phonon interaction, and the energy of effective phonons h omega(ph), involved in formation of the absorption edge of crystalline Si(2)Te3, were determined using the temperature dependence of the absorption edge slope. Deviation from the stoichiometric composition in the direction of excess tellurium significantly affects the spectral distribution of the photoconductivity of Si2Te3 crystals.