On the optical properties of evaporated CdTe thin films

Some optical properties of CdTe thin films evaporated in vacuum by quasi closed volume technique onto glass substrates are discussed. transmission and reflection spectra (in the wavelength range of 550-1350 nm) for films with different thicknesses (150-2400 nm) deposited under various experimental conditions (substrate temperature: 290-700 K, source temperature: 1100-1270 K) were recorded. Stoichiometric, non-stoichiometric and specially Te-doped films were investigated. Film structures were analyzed by X-ray diffraction measurement. Optical parameters (absorption coefficient and refraction index) Were determined from transmission spectra. It was found that nonstoichiometric films have higher absorption coefficient and lower refraction index compared with those with stoichiometric composition. The results are correlated with the Te excess in respective films. The optical energy band. gaps determined from absorption spectra indicate direct interband transitions. The dispersion of the refraction index is interpreted in terms of a single electronic oscillator.