High temperature optical absorption edge of CdTe single crystal

The optical absorption edge of bulk CdTe single crystal was measured by infrared transmission under saturated Cd pressure in the temperature interval 295-1223 K. The absorption coefficient was directly determined up to the value of 100 cm^-1. For higher values, it was estimated by extrapolating the spectra according to the Urbach exponential rule. It was observed that the common temperature-independent intersection of extrapolated Urbach absorption edge, the "Urbach focus," does not exist in CdTe. The temperature dependence of band-gap energy E_g defined by E_g(300 K) = 1.518 eV and dE_g/dT = - 4.4 × 10^-4 eV/K was established, postulating linear temperature dependence of E_g by fitting the temperature dependent absorption coefficient at the band edge α_g(T) = 6600 - 4T (K) (cm^-1).