Influence of heat treatment on the optoelectronic performance of electrodeposited CdSe thin films

In this work, a thin film of Cadmium selenide is deposited on fluorine tin oxide-coated glass substrate through a simplified 2-electrode electrodeposition technique. The performance of the as-deposited films is compared with its annealed counterparts at two different temperatures of 250 °C and 350 °C in air. The impacts of annealing on different physical characteristics of the prepared films were investigated with the help of an X-ray diffractometer (XRD), scanning electron microscopy, and UV–Vis spectrometer. Studies on the photoresponse characteristics of the deposited films were also carried out. Structural analysis was done to determine the lattice parameters, size of the crystallite, dislocation density, and microstrain, utilizing the data from XRD analysis which exhibits a predominant orientation of CdSe films along (002) direction and showed the presence of hexagonal nanocrystalline phase. Morphological analysis shows larger grains for 350 °C-annealed sample than the as-grown and the 250 °C-annealed sample. The analysis of the optical property confirms a higher absorption in the visible region and shows a band gap of 1.65 eV at the annealing temperature of 350 °C. The photoresponse characteristic recorded a responsivity of 109 × 10^–2 A/W, detectivity of 192 × 10⁸ Jones, and an external quantum efficiency of 253% for the same sample which is annealed at higher temperature. The calculated rise time and decay time from the transient current characteristics at different incident power intensities were found to be 4.4 s and 5.1 s, respectively. The I–V characterization curve of the 350 °C-annealed CdSe sample affirms a good photocurrent response demonstrating that the heat treatment on the electrodeposited CdSe films improves its photodetecting capability that can be exploited for photodetector device applications.