Temperature Dependence of the Optical Absorption of the Ternary Compound Ag2SnS3

We report in this work for the first time the temperature dependence of the optical absorption of the ternary compound Ag2SnS3. The optical absorption of this compound has been investigated in three samples from room temperature to 10K. We found that the fundamental absorption edge of Ag2SnS3 is consistent with a direct energy gap by allowed transitions of 1.43(2) eV at the lowest temperature measured and of 1.26(5) eV at room temperature. In two samples, the existence of a broad peak or band between 1.24 eV to 1.28 eV for temperatures below 190K is observed. The temperature dependencies of the energy gap show a behavior typical of that found for most semiconductors, that is, the energy gap decreases monotonically with temperature. The most important models are used to explain the energy gap shift and several parameters from these models are reported.