Temperature dependence of optical energy gap of gallium selenide

Spectral and temperature characteristics of real part of refractive index and the absorption coefficient of radiation have been derived from optical transmittance and reflectivity of gallium selenide (GaSe) illuminated in parallel to the c-axis of a single crystal. In every temperature (from 78 to 333 K) the dependence of absorption coefficient on photon energy has been least square fitted assuming direct allowed absorption including bound and continuum excition states and taking into account the lifetime broadening through a convolution integral. The temperature dependence of energy gap was derived from these fittings.