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

Electrical measurements have been carried out on a-(Ge ₂₀Se ₈₀) _100−xCu _x ( x = 0.0, 0.5, 1.0, 1.5 and 2.0 at.%) thin films. The dark conductivity ( σ _d ) and photoconductivity ( σ _ph) measurements are done in the temperature range 252–349 K. The values of σ _d, σ _ph increase and dark activation energy (Δ E _d ), photo activation energy (Δ E _ph) decrease as the concentration of Cu additive increases (up to 1.0 at.%). Photosensitivity ( σ _ph/ σ _d) increases and decay time constant ( τ _d) decreases as the concentration of Cu increases (up to 1.0 at.%). The charge carrier concentration ( n _σ) 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.