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 variat ion of the optical absorption coefficient with energy near the band edge wa s analysed by Elliot's model. From the analysis of the temperature dependen t band gap with Manoogian and Woolley's semi-empirical model, the Debye tem perature, 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 te mperature dependence of the Urbach's energy. This relatively large hv, valu e was associated with the electronic distortion in addition to the influenc e of electron/exciton-phonon interaction. The electronic distortion results from the existence of multiple structural defects associated with two dime nsional dislocations or stacking faults, presumably originated from voids a nd precipitates of the component elements, in the Tl2GaInSe4 lattice. (C) 2 001 Elsevier Science Ltd. All rights reserved.