Effect of composition and forming parameter on evaporated CdSeTe films deposited at room temperature

Amorphous films of the ternary compound CdSeTe, of composition in the range 0-10 at.% Cd and with a thickness of about 200 nm, have been prepared by thermal evaporation. The optical band gap was determined and found to be in the range 0.5-1.0 eV and arose from indirect transitions. A sharp decrease in the value of optical band gap (E_opt) is observed. The electrical properties of Cd thin films have been studied extensively. In general dc measurements have indicated Ohmic conductivity at low electric fields resulting from the thermal excitation of carriers from centers in the band gap. When the temperature is low enough so that carriers cannot be excited into one of the allowed bands, the dominant conduction may take place via hopping, whereby carriers hop from occupied to unoccupied sites located within a band of localized states situated within the band gap. The electrical and optical data were consistent and realized from the binding energy represented by the cohesive energy values. The generalized (8−n) rule was used to estimate the average co-ordination number. The obtained results were treated in the frame of the chemical bond approach proposed by Bicerano and Ovshinsky. The phase separation phenomena and the morphology were also studied for the prepared films.