Effect of boron implantation on the electrical and photoelectrical properties of e-beam deposited Ag–In–Se thin films

Abstract

In this study, e-beam evaporated Ag–In–Se (AIS) thin films were doped by the implantation of boron (B) ions at 75 keV with a dose of 1 × 1015 ions cm−2 and a subsequent annealing process was applied to the doped AIS films at different temperatures under nitrogen atmosphere. The effects of implantation and annealing on the electrical and photoelectrical properties of AIS thin films were investigated through temperature dependent conductivity, spectral photoresponse and photoconductivity measurements under different illumination intensities. The electrical conductivity measurements showed that the room temperature conductivity values were determined as 2.4 × 10−7 (Ω cm)−1, 1.7 × 10−6 (Ω cm)−1 and 8.9 × 10−5 (Ω cm)−1 for B-doped films (B0), B-doped and annealed films at 200 °C (B2) and at 300 °C (B3), respectively. It was observed that the electrical conductivity improved as the annealing temperature increased up to 400 °C at which the AIS thin films showed degenerate semiconductor behaviour. The spectral distribution of the photoresponse curves indicated three local maxima located at 1.63, 1.79 and 2.01 eV for B0 type films, 1.65, 1.87 and 2.07 eV for B2 type films and 1.73, 2.02 and 2.32 eV for B3 type films at room temperature. These three different energy values were ascribed to the splitting of the valence band due to spin–orbit interaction and crystalline lattice field effects. The first energy values of each set were determined to be energy band gaps of the AIS thin films. The photoconductivity measurements as a function of temperature and illumination intensity were performed on the B-doped AIS thin films in order to determine the nature of recombination processes in the films. The photoconductivity values were found to be thermally quenched for all types of thin films and the variation of photocurrent as a function of illumination intensity showed that the dependence of photocurrent on the intensity was supralinear. The two-centre recombination model was applied successfully in order to explain the photoconductivity behaviours of the films.