Modelling of optical properties of amorphous selenium thin films

The investigated amorphous selenium (a-Se) films of different thicknesses (100–385 nm) were deposited by vacuum evaporation technique in a base pressure of 7.5×10−6 torr at room temperature. The transmission spectra T(λ) of the a-Se films were measured over a wide range of wavelengths from 200 to 2500 nm. The measured spectra were analyzed by applying O’Leary, Johnson, Lim (OJL) model. The photon energy dependence of the dielectric function, ε=ε1+iε2, of the investigated a-Se films was obtained. The film thickness, absorption coefficient α, refractive index n, high frequency dielectric constant ε∞ and optical band gap Eg have been deduced. Increasing the film thickness was found to increase the refractive index and optical band gap energy.