Energy bandgap of ZnSe bulk crystal between 300K and 1000K

The direct energy bandgap between conduction and valance bands at  point for ZnSe with zinc-blende structure has been determined by optical transmission measurements. The starting material of ZnSe powder was loaded inside an optical cell with windows. After the heat treatments to de-oxidized impurities and adjust the stoichiometry, a bulk crystal of ZnSe was grown in the window area by physical vapor transport. The optical transmission through the ZnSe crystal was measured from 297K to 992K and the energy bandgaps were derived from the corresponding optical absorption spectra. The measured values of the bandgaps were fit as a function of temperature using the Varshni expression with two of the three parameters, i.e., the Debye temperature and energy bandgap at temperature of 4K, fixed from the literature data.