Astrid Bingel,Kevin Füchsel Friedrich-Schiller-Univ. Jena (Germany) Norbert Kaiser Fraunhofer Institute for Applied Optics and Precision Engineering (Germany) Andreas Tünnermann Friedrich-Schiller-Univ. Jena (Germany)
The metal-like electrical conductivity in combination with a high visual transmittance is the characteristic property that
opens up a broad spectrum of applications to transparent conductive oxides (TCOs). To fulfill the manifold requirements
in each individual case, especially the optical properties of TCOs have to be adapted.
The transmittance in the near infrared spectral range can be tailored by a modification of the carrier concentration Ν and
mobility μ. The theoretical description for this behavior is based on the well-known Drude theory. Highly conductive
indium tin oxide films (ITO) have been prepared by pulsed DC magnetron sputtering. However, due to its excellent
electrical properties, the plasma resonance of free carriers occurs near the visual spectral range which results in a very
low transmittance in the NIR. In contrast, ITO films with a NIR transmittance of ca. 80% have been prepared by plasma
ion assisted evaporation. The combination of high transmittance and low resistivity of ρ=7.4x10-6Ω was achieved
by a decrease of the carrier concentration and a simultaneous enhancement of the electron mobility μ.
Secondary, the transmittance of aluminum doped zinc oxide films (AZO) in the UV spectral range could be adapted by
changing the doping concentration Ν. This is a direct consequence of the Burstein-Moss shift that leads to a band gap
widening dependent on Ν. However, the comparison of the experimental data with theory has shown that the contrary
effect of band gap narrowing is not negligible, too.