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Present Status of the Development and Application of Transparent Conductors Oxide Thin Solid Films

Author(s): Luis Castañeda

Journal: Materials Sciences and Applications
ISSN 2153-117X

Volume: 02;
Issue: 09;
Start page: 1233;
Date: 2011;
Original page

Keywords: Transparent Conductors | Semiconductors | Thin Solid Films

The present review paper reports on the physical properties, status, prospects for further development and applications of polycrystalline (or amorphous), transparent and conducting oxides (TCO) semiconductors. The coexistence of elec trical conductivity and optical transparency in these materials depends on the nature, number and atomic arrangements of metal cations in crystalline or amorphous oxide structures, on the resident morphology and on the presence of intrinsic or intentionally introduced defects. The main important TCO semiconductors are impurity-doped ZnO, In2O3, SnO2 and CdO, the ternary compounds Zn2SnO4, ZnSnO3, Zn2In2O5, Zn3In2O6, In2SnO4, CdSnO3, and multi-component oxides consisting of combinations of ZnO, In2O3 and SnO2. Sn doped In2O3 (ITO) and F doped SnO2 TCO thin solid films are the most preferable materials for most present applications. The expanding use of TCO materials, especially for the production of transparent electrodes for optoelectronic device applications, is endangered by the scarcity and high price of In. This situation drives for the search alternative TCO materials to replace ITO. The electrical resistivity of the novel TCO materials should be ~1.0 × 10-5 Ωcm, typical absorption coefficient smaller than 10.04 cm-1 in the near UV and visible range, with optical band gap ~3.0 eV. At present, ZnO:Al and ZnO:Ga (AZO and GZO) semiconductors are becoming good alternatives to ITO for thin solid films transparent electrode applications. The best candidates are AZO thin films, which are of low resistivity in the order of 1.0 × 10-4 Ωcm, have inexpensive source materials and are non-toxic. However, development of large area deposition techniques are still needed to enable the production of AZO and GZO films on large area substrates with a high deposition rate. In addition, applied TCO materials should be stable in hostile environment containing acidic and alkali solutions, oxidizing and reducing atmospheres, at high temperature. Most of the TCO materials are “n-type” semiconductors, but “p-type” TCO materials are also explored. Such TCO include: ZnO:Mg, ZnO:N, IZO, NiO, NiO:Li, CuAlO2, Cu2SrO2, and CuGaO2 thin films. These materials have not yet found place in actual applications.

Tango Jona
Tangokurs Rapperswil-Jona

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