ELECTRICAL AND OPTICAL STUDIES ON AMORPHOUS SE-TE ALLOYS

Se1-xTex semiconducting glasses have been prepared and characterized by optical, electrical and x-ray measurements. It is found that homogeneous Se1-xTex glasses can only be prepared, without any trace of detectable crystallinity, up to x congruent-to 0.30 by the usual conventional quenching technique. Due to the high absorbance of Se1-xTex glasses in the visible region, photoacoustic absorption spectroscopy has been used for the first time to study their optical energy gap variation as a function of x. The optical energy gap E(g) of amorphous Se is found to be about 0.12 eV higher than that of c-Se. It is observed that initial small substitution of Te into a-Se rapidly decreases E(g). For x > 0.10, the variation in E(g) becomes smaller and linear with x. Temperature dependence of the conductivity suggests that the electronic conduction in these glasses takes place via extended states. The activation energy and conductivity prefactor both decrease with x and show sudden changes at x congruent-to 0.1. An attempt is made to explain these results based on the charge defect model and the tailing of energy bands in the gap region.