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Conducting Oxides

David S. Ginley and Clark Bright, Guest Editors In the interim between the conception of this issue of MRS Bulletin on transparent conducting oxides (TCOs) and its publication, the remarkable applications dependent on these materials have continued to make sweeping strides. These include the advent of larger flat-screen high-definition televisions (HDTVs), larger and higher-resolution screens on portable computers, the increasing importance of low emissivity (“low-e”) and electrochromic windows, a significant increase in the manufacturing of thin-film photovoltaics (PV), and a plethora of new hand-held and smart devices, all with smart displays.1–7 Coupled with the increased importance of TCO materials to these application technologies has been a renaissance over the last two years in the science of these materials. This has included new n-type materials, the synthesis of true p-type materials, and the theoretical prediction and subsequent confirmation of the applicability of codoping to produce p-type ZnO. Considering that over the last 20 years much of the work on TCOs was empirical and focused on ZnO and variants of Inx Sn1–xO2, it is quite remarkable how this field has exploded. This may be a function of not only the need to achieve higher performance levels for these devices, but also of the increasing importance of transition-metalbased oxides in electro-optical devices. This issue of MRS Bulletin is thus well timed to provide an overview of this rapidly expanding area. Included are articles that cover the industrial perspective, new n-type materials, new p-type materials, novel deposition methods, and approaches to developing both an improved basic understanding of the materials themselves as well as models capable of predicting performance limits. The current TCO industry is dominated by just a few materials. We will present an overview of the current state of the field, in order to help the reader develop an appreciation for the size and demands of the industry as well as the need for new materials.

MRS BULLETIN/AUGUST 2000

The two dominant markets for TCOs are in architectural applications and flatpanel displays (FPDs). The architectural use of TCOs is for energy-efficient windows. Fluorine-doped tin oxide, deposited by a pyrolytic process, is the TCO most often used in this application. Windows with tin oxide coatings are efficient in preventing radiative heat loss, due to tin oxide’s low emissivity of about 0.16. Such “low-e” windows are ideal for cold or moderate climates. In addition, pyrolytic tin oxide is used for coating heated glass freezer doors in commercial use. The annual consumption (in 1996) of TCO-coated glass (primarily for low-e coatings) in the United States was 7.3  107 m2, or 27 mi2.8 Added to this output are the increasing amounts used in displays and PVs. Pyrolytic tin oxide is also used in PV modules, touch screens, and plasma displays. However, indium tin oxide (ITO) is the TCO used most often in the majority of FPD applications. In FPDs, the basic function o