Annealing temperature dependence of properties of CdSe thin films by RF-sputtering

Abstract

Cadmium Selenide (CdSe) is a II-VI group compound semiconducting material with a direct band gap about 1.74 eV, which is widely applied in thin film transistors, light emitting diodes and photoelectrochemical (PEC) cells. In recent years, the application of CdSe thin films to CdTe thin film solar cells has attracted the attention of people. CdSe thin films were synthesized using radio frequency magnetron sputtering method on Corning glass substrates at room temperature. The as-deposited films were annealed at various temperatures (200°C, 300°C, 400°C and 500°C) in N2 atmosphere for 1h and the effect of annealing temperature on structural, morphological, compositional, optical and electrical properties was studied. X-ray diffraction (XRD) indicates that the structure of CdSe thin films transforms from cubic to hexagonal structure when annealing temperature changes from room temperature to 500°C. Scanning electron microscope (SEM) images show that the crystallite size of CdSe thin films has no obvious increase with annealing temperature increasing from 200°C to 400°C, which is all about 33 nm. However, grains with size of 200 nm were precipitated on the surface of CdSe thin film annealed at 500°, and the Se content of CdSe thin film decreased. The band gaps of CdSe thin films were found to firstly decrease, and then gradually increase with the increase of annealing temperature. The minimal band gap of CdSe thin film is 1.63eV when annealed at 300°C. The conductivity of CdSe thin film annealed at 500° increased by two orders of magnitude compared with as-deposited CdSe thin film.