Preparation of epitaxial films of the transparent conductive oxide Al:ZnO by reactive high‐pressure sputtering in Ar/O₂ mixtures

Abstract

Transparent conductive metal oxides are interesting materials for various optoelectronic applications including solar cells and flat panel displays. This study focuses on the in situ deposition of aluminum-doped zinc oxide (AZO) thin layers on c-axis oriented sapphire substrates by dc sputtering and on the structural and electrical characterization. The films have a typical thickness of 90 nm and a roughness of 10 nm root mean square. An Al/Zn ratio of 2.4 at% Al was determined by X-ray photoelectron spectroscopy. X-ray diffraction shows a preferential growth in the (0002) c-axis direction. Films have an average transparency of 90% in the visible-light spectrum, a room-temperature resistivity of 3.7 Â 10 À3 V cm and a carrier mobility of 6.7 cm 2 V À1 s À1 .

Morphological TEM studies and magnetoresistance analysis of sputtered Al‐substituted ZnO films: The role of oxygen

“…There is little variation in temperature and there is no obvious reason why the mobility should increase with increasing temperature. Nevertheless, this agrees with previous observations on ZnO films with 2.4 at.% Al substitution . Increasing mobility values with increasing temperatures are also known from oligomer films (sexithiophene and octithiophene) and were explained by a less efficient charge‐carrier trapping in grain boundaries as temperature increases .…”

“…C. Most of the ZnO grains are c ‐oriented, as indicated also by previous X‐ray diffraction studies . It is important to point out that no amorphous interlayer is present between the AZO film and the substrate, indicating the efficacy of the growth methodology.…”

“…Moreover, thin films with this Al percentage show high electrical conductivities in combination with low optical absorption . Concentrations exceeding the 1 at.% level are supposed to result in phase separation with occurrence of the insulating ZnAl 2 O 4 spinel phase and smaller grain sizes . On the opposite, a substitution below the 1 at.% ratio reduces the density of free charge carriers while the carrier mobility should in principle come close to the value of 200 cm 2 /Vs as reported for pure, non‐substituted ZnO .…”

“…The thin films were prepared by DC sputtering without magnetron assistance in a home‐made sputtering system described in earlier publications by the authors . The sputtering target with 1.0 at.% Al content was prepared by thoroughly mixing appropriate amounts of Al:ZnO powder (Zano–Al with 2.4 at.% Al, Umicore, Belgium) and ZnO powder (purity 99.99% on trace metals basis, Sigma–Aldrich, USA).…”

Light-addressable Electrodes for Dynamic and Flexible Addressing of Biological Systems and Electrochemical Reactions

“…A semiconductor can be directly electrically connected (Figure 3a) or deposited as a thin film on a substrate material ( Figure 3b). Often, transparent conductive oxide (TCO) glasses such as indium tin oxide (ITO) [49], fluorine-doped tin oxide (FTO) [50], or aluminium-doped zinc oxide (AZO) [51] are used as substrate materials as they allow rear-side illumination and easy electrical connection. Since LAEs are mainly used with liquid environments, the semiconductor material should be stable under the prevailing conditions.…”