Introduction to Transparent Conductive Oxides (TCO)
S.M. Rozati
Physics Department, University of Guilan, Rasht, Iran
Abstract- The lecture reports on the physical properties, status, prospects for further development, and applications of transparent and conductive oxides (TCO) semiconductors. The coexistence of electrical conductivity and optical transparency in these unusual materials depends on the nature of metal cations in crystalline or amorphous oxide structures. Materials such as oxides of tin, indium, zinc and cadmium and their various alloys, have been extensively studied and applied as electrodes in thin film technologies. These materials possess a wide energy band gap (Eg>3eV) and are therefore transparent in the visible region, where the long wavelength cutoff depends on the charge carrier concentration.
At present, the advantages of AZO (ZnO:Al) thin films, which have low resistivity of the order of 10−4Ω.cm, inexpensive source materials, and are non-toxic could become good alternatives to ITO (In2O3:Sn)for thin-film transparent electrode applications.
In addition to the required electrical and optical characteristics, applied TCO materials should be stable in hostile environment containing acidic and alkali solutions, oxidizing and reducing atmospheres, and elevated temperature. Most of the TCO materials are n-type semiconductors, but p-type TCO materials such as ZnO:N and ZnO:Mg are also developed. Structural factors are important during the design of TCO for gas sensor. In the case of thin films, it was shown that structural engineering of sensing materials could be used for the optimization of sensing parameters as gas sensitivity, selectivity, and time response.