Optical Characterization of As_xTe_100-x Films Grown by Plasma Deposition Based on the Advanced Optimizing Envelope...

Three As_xTe_100-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 As_xTe_100-x films is computed more accurately from the quantity T_i(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).