Effect of Rapid Thermal Annealing on Thermal Evaporated CdSe Thin Film for Solar Cell Application

Abstract

Cadmium Selenide (CdSe) thin films have been deposited on a cleaned glass substrate by thermal vacuum evaporation method under the pressure of 10-5 torr. These CdSe thin films were also kept into a quart glass tube for rapid thermal annealing at 60 and 120 second using a 500 W halogen lamp for crystalline the structure. These thin films were characterized for structural, optical and thermo-electrical properties. The optical studies have been done using UV-VIS-NIR, shows that the transition of the deposited film is found to be a direct band gap of 1.74, 1.70 and 1.67 eV for asdeposited, 60 sec and 120 sec annealed thin films respectively. It was also found that absorbance has increased and transmission decreased with increasing annealing time, the change in the extinction coefficient with energy (hν) has been also measured. The Thermoelectric power (TEP) studies confirm the n-type nature of CdSe thin films but as well as annealing time increased the hole concentration increased resultant n-nature of CdSe thin film changing toward p-type nature, the Seebeck coefficient for different annealing time at as-deposited (RT), 60 seconds and 120 seconds have observed 549, 949 and 1031 μV/K respectively. The SEM result shows that with increasing annealing time the grain size and roughness of surface are increased. X-ray diffraction (XRD) studies indicate that the film is like a cubic crystal structure with average crystalline size (D) was measured using Scherrer formula and it is 16.44 nm.