the effect of doping ratio on the opical properties

The films of CdSe pure and doped with copper of ratio (0.5, 1.5, 2.5, & 4wt%Cu) have been prepared by evaporation technique of thickness 1um onto clean glass substrate. The effect of Cu concentration on optical properties of CdSe pure and doped with copper has been studied. It s found that they have direct energy gap. The absorption edge was shift slightly towards higher wavelength for Cu- doped films and energy gaps(E) decrease with increasing of Cu concentration from 1. 83eV to 1.79eV for CdSe pure and doped with 4wt% respectively, due to increasing of impurity levels in the band gap. It was found that the absorption coefficient is increased with increase of Cu concentration from 7X10 cm at 0.75µm for pure CdSe to the 1.15X10 cm²¹ for 4wt% Cu at the same wavelength. The amorphousity of the films decreases with increasing of Cu concentration due to improve the structure of the film by adding the Cu. And the density of state increases with increasing copper from (0.119-0.15)eV for CdSe pure and doped with 4wt% respectively. The refractive index, extinction coefficient and dielectric constant were also studied.