Urbach-Martienssen tails in the absorption spectra of layered ternary semiconductor TlGaS2

The dependence of the absorption coefficient on the photon energy and sampl e temperature near the fundamental absorption edge (AE) was investigated fo r TlGaS2 layered semiconductor crystals. The exponential absorption tails o bserved in the 10-340 K temperature range were interpreted as Urbach-Martie nssen (U-M) tails. From the analysis of these tails, characteristic Urbach parameters were determined. The results lead to the conclusion that the tem perature dependence of the absorption tails near the fundamental AE of TlGa S2 is the result of thermal disorder.