TEMPERAMENTAL BEHAVIOUR OF THE OPTICAL ABSORPTION EDGE Of Ag8GeS6 SINGLE CRYSTAL

Abstract

The optical transmission spectra of single-crystal ternary sulfide Ag8GeS6 were measured in the temperature range 77-300 K on pre-prepared samples (plane-parallel with a polished surface to optical quality). The spectral dependences of lnα at all studied temperatures have an exponential shape near the absorption edge, which indicates that they obey the Urbach's rule. By extrapolating the spectral dependences of lnα, the presence of one point of convergence was established and its coordinates were determined: a0 = 5.25 × 107 cm-1 and E0 = 1.88 eV. The presence of a single point of convergence indicates the absence of phase transitions in the studied temperature range. The steepness parameter σ of the optical absorption edge in the studied temperature range was determined from the exponential sections of the spectral dependences of lnα. As a result, the effect of temperature on the electron-phonon interaction (EPI) is analyzed. The determined values of the optical pseudo-gap of the single crystal of ternary sulfide Ag8GeS6 Eg* = 1.466 eV and the Urbach energy EU = 21.90 meV suggest that the single crystal sample of silver thiogermanate Ag8GeS6 can be used as a promising material for collecting sunlight.