Electronic and Optical Properties of Copper Halide Mixed Crystals CuBr1?xIx

The effects of chemical disorder on electronic and optical properties of mixed CuBr1—xIx crystals are studied on the basis of a modified virtual-crystal-approximation, which incorporates compositional disorder as an effective potential. We use a simple tight-binding (TB) theory including d-electron orbitals on the cation site. We show that such an approach provides analytical results for calculating energy gaps and bowing parameters. The band structures of CuBr and CuI are discussed. The variation of the energy with alloy concentration in the pseudobinary system formed with these compounds is reported and interpreted. The essential features of disorder-induced changes in electronic and optical structure are exhibited from the TB results by two characterization parameters: the subband energy spacing and the density of states.