optical properties of co-evaporated thin films of binary bi 0-te 0 and bi 0 -v 0 systems

thin films of binary bi 0 -teo and bi 0 -v 0 systems were prepared by the thermal co-evaporation technique in a vacuum at room temperature. the optical absorption edge of these systems are studied in the wavelength of 200-800 nm using a perkin-elmer uv/vis spectrophotometer. it is found that the value of n=3/2 in the davis-mott equation is best fitted for the fundamental absorption edge for these materials. it is also found that the optical energy gap (e ) for the bi o - v o system lies between 0.65 and 3.5 ev. and for the bi 0 -teo system between 0.95 and 3.25 ev. depending on the film composition. the exponential behaviour of the absorption coefficient with photon energy for the systems under invesgiation are verified as suggested by urbach