Two-dimensional cadmium selenide electronic and optical properties: first principles studies

Structural, electronic and optical properties of two-dimensional (2D) cadmium selenide (CdSe) structures with (2times 2) periodicities are investigated. First principles total energy calculations are performed within the periodic density functional theory. Initially, the structural properties are determined using the local density approximation as implemented in the PWscf code of quantum ESPRESSO package. To investigate the electronic properties, the GW method is applied to determine the energy gap within the plasmon pole and the random phase approximations. Optical properties are investigated to determine the dielectric constant and the Bethe–Salpeter theory is used to calculate the exciton binding energies. Zinc blende and wurtzite phases are considered to calculate the bulk energy gaps, which are compared to the experimental values, finding good agreement. The 2D structure exhibits an energy gap larger than that of the bulk, indicating the effects of reduction in dimensionality; these changes can be attributed to the dangling bonds that are present in the 2D layer.