Temperature dependence of the optical energy gap and thermoelectric studies of TlInS2 crystals

A single crystal of TlInS2 was prepared by a new crystal growth technique. The interband absorption coefficients were measured, near the fundamental absorption edge, as a function of the wavelength of the incident photons at various temperatures. The energy gap E-g is temperature dependent and the absorption edge shifts to lower energy values with increasing temperature. The energy gap, at room temperature, was found to be 2.24 eV. The dependence of the energy gap on temperature is linear in the temperature range 77 to 300 K with a negative temperature coefficient dE(g)/dT equal to 1.87 x 10(-4) eV K-1. The thermoelectric phenomenon is also investigated. On the basis of a two-band model the results are discussed.