Three AsxTe100-x films with different x and dissimilar average thickness are characterized mainly from one interference transmittance spectrum T(λ = 300 to 3000 nm) of such film on a substrate based on the advanced optimizing envelope method (AOEM). A simple dual transformation of T(λ) is proposed and used for increasing the accuracy of computation of its envelopes T+(λ) and T-(λ) accounting for the significant glass substrate absorption especially for λ > 2500 nm. The refractive index n(λ) of As40Te60 and As98Te2 films is determined with a relative error <0.30%. As far as we know, the As80Te20 film is the only one with anomalous dispersion and the thickest, with estimated = 1.1446 nm, ever characterized by an envelope method. It is also shown and explained why the extinction coefficient k(λ) of any of the three AsxTe100-x films is computed more accurately from the quantity Ti(λ) = [T+(λ)T-(λ)]0.5 compared to its commonly employed computation from T+(λ). The obtained results strengthen our conviction that the AOEM has a capacity for providing most accurate optical characterization of almost every dielectric or semiconductor film with > 300 nm on a substrate, compared to all the other methods for characterization of such films only from T(λ).
Keywords: AsxTe100−x films; advanced optimizing envelope method; light scattering; optical characterization; partial coherence; superior accuracy; surface roughness.