Analyzing UV/Vis/NIR Spectra—Addition of Oxygen and Nitrogen to ZnO:Al Thin Films

Exact optical analysis of transparent-conductive-oxide (TCO) thin films are necessary to optimize adequate materials for optical sensor and solar cell applications. A non-numerical theoretical concept has been used to extract approximation-free optical, structural and electrical data from ultraviolet/visible/near-infrared (UV/Vis/NIR) spectra. Special focus has been set on double-layer systems, as thin films upon substrates. Complex parameter evaluation is possible. Sputtered aluminum-doped zinc-oxide (ZnO: Al) thin films have been analyzed with respect to oxygen and nitrogen additions to the inert argon process-gas. Based on UV/Vis/NIR spectra and a novel analysis model, complex optical, structural and electrical data have been evaluated for these transparent-conductive-oxide (TCO) layers. Correct extracted physical values as refractive indices, permittivities, absorption coefficients, deposition rates, conductivities and band gap energies allow a reliable dimensioning for optical sensor and solar cell designs. Results are compared with those of the well-known Keradec/Swanepoel model (KSM). The necessity of taking both spectra-transmission and reflection spectra-into account was shown. Results are discussed with structural properties of the thin films, by help of XRD-measurements. A noncontact, optical conductivity measurement possibility by use of UV/Vis/NIR spectroscopy has been shown. Optically measured conductivities have been compared with electrically measured ones.