Determination of the optical absorption coefficients of a weakly absorbing film on a transparent substrate by spectrophotometry

Thin films of aluminum doped zinc oxide were sputtered for various process conditions onto transparent 1 mm thick borosilicate glass slides and measured by spectrophotometry. A fit to the reflectance and transmittance spectra over the range of 350 nm to 1200 nm is described which determines the film thickness, the coefficients for a wavelength dependent model of the index of refraction, and the absorption coefficients. This fit accounts for reflection from the back of the glass slide.