Effect of Cu additive on the electrical properties of Ge–Se alloy

Electrical measurements have been carried out on a-(Ge20Se80)100−xCux (x = 0.0, 0.5, 1.0, 1.5 and 2.0 at.%) thin films. The dark conductivity (σd) and photoconductivity (σph) measurements are done in the temperature range 252–349 K. The values of σd, σph increase and dark activation energy (ΔEd), photo activation energy (ΔEph) decrease as the concentration of Cu additive increases (up to 1.0 at.%). Photosensitivity (σph/σd) increases and decay time constant (τd) decreases as the concentration of Cu increases (up to 1.0 at.%). The charge carrier concentration (nσ) increases with Cu incorporation (up to 1.0 at.%). A reverse in the trend takes place in all these parameters as the Cu concentration is further increased (>1.0 at.%). These results are explained on the basis of change in the density of defect states present in the mobility gap of Ge–Se–Cu alloy.