Transparent conducting oxide semiconductors for transparent electrodes

TLDR

TCO semiconductors such as doped ZnO, In₂O₃, SnO₂, and multicomponent oxides are critical for transparent electrodes, but the growing demand threatens the scarce and costly indium in ITO. This paper reviews the status and prospects of polycrystalline or amorphous TCO semiconductors for thin‑film transparent electrodes, focusing on Al‑ and Ga‑doped ZnO as promising ITO alternatives. The study discusses deposition techniques like magnetron sputtering and vacuum arc plasma evaporation, and target development needed to produce large‑area AZO and GZO films at high deposition rates. AZO thin films exhibit low resistivity (~10⁻⁵ Ω·cm) and use inexpensive, non‑toxic materials, making them the best candidates.

Abstract

The present status and prospects for further development of polycrystalline or amorphous transparent conducting oxide (TCO) semiconductors used for practical thin-film transparent electrode applications are presented in this paper. The important TCO semiconductors are impurity-doped ZnO, In2O3 and SnO2 as well as multicomponent oxides consisting of combinations of ZnO, In2O3 and SnO2, including some ternary compounds existing in their systems. Development of these and other TCO semiconductors is important because the expanding need for transparent electrodes for optoelectronic device applications is jeopardizing the availability of indium-tin-oxide (ITO), whose main constituent, indium, is a very expensive and scarce material. Al- and Ga-doped ZnO (AZO and GZO) semiconductors are promising as alternatives to ITO for thin-film transparent electrode applications. In particular, AZO thin films, with a low resistivity of the order of 10−5 Ω cm and source materials that are inexpensive and non-toxic, are the best candidates. However, further development of the deposition techniques, such as magnetron sputtering or vacuum arc plasma evaporation, as well as of the targets is required to enable the preparation of AZO and GZO films on large area substrates with a high deposition rate.