Temperature dependence of the optical energy gap and Urbach-Martienssen's tail in the absorption spectra of the layered semiconductor Tl2GaInSe4

The effect of temperature on the optical energy gap for Tl2GaInSe4 layered crystals were investigated in the temperature range of 10-330 K. The variation of the optical absorption coefficient with energy near the band edge was analysed by Elliot's model. From the analysis of the temperature dependent band gap with Manoogian and Woolley's semi-empirical model, the Debye temperature, the dielectric constant and the effective masses of free excitons, electrons and holes were estimated as (373 +/- 13) K, 9.2 +/- 0.3, (0.31 +/- 0.06)m(0), (0.42 +/- 0.08)m(0), and (1.16 +/- 0.22)m(0), respectively. Effective phonon energy was obtained as h nu (p) = 56 +/- 1 meV from the temperature dependence of the Urbach's energy. This relatively large hv, value was associated with the electronic distortion in addition to the influence of electron/exciton-phonon interaction. The electronic distortion results from the existence of multiple structural defects associated with two dimensional dislocations or stacking faults, presumably originated from voids and precipitates of the component elements, in the Tl2GaInSe4 lattice. (C) 2001 Elsevier Science Ltd. All rights reserved.