Inorganic solids with wide bandgaps are usually classified as electrical insulators and are used in industry as insulators, dielectrics, and optical materials. Many metallic oxides have wide bandgaps because of the significant contribution of ionic character to the chemical bonds between metallic cations and oxide ions. Their ionic nature simultaneously suppresses the formation of easily ionizable shallow donors or acceptors and enhances the localization of electrons and positive holes. Thus it is understandable that interest in these wide-gap oxides as conductive materials has not been strong.

Transparent p -Type Conducting Oxides: Design and Fabrication of p-n Heterojunctions

High mobility transparent conducting oxides for thin film solar cells

Transparent conducting oxides (TCOs) have been known and employed technologically for more than 50 years, primarily in the form of doped single-cation oxides such as In2O3 and SnO2. Beginning in the 1990s, however, multi-cation oxide TCOs began to be developed in Japan (see the article by Minami in this issue and the references therein) and at the former Bell Laboratories. Since then, new TCO phases are being reported with increasing frequency as technological interest in this area heightens. At the same time, our fundamental understanding of the chemical and structural origins of transparent conductivity continues to expand and promises a pathway to dramatically improved materials for a host of applications. This article describes a collaborative, multi-investigator bulk an d thin-film research effort at Northwestern University aimed at the synthesis, characterization, and enhanced understanding of multi-cation (compound and solidsolution) TCOs, and provides a brief account of what we are discovering about this important class of materials.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0883769400027160

Chemical and Thin-Film Strategies for New Transparent Conducting Oxides

Experimental and computational studies were performed to understand the electronic structure of ternary perovskites (ASnO3, A = Ca, Sr, Ba, Cd), pyrochlores (RE2Sn2O7, RE = Y, La, Lu; Cd2Sb2O7), and defect pyrochlore oxides (Ag2Sb2O6) containing the main group ions Sn4+ and Sb5+. In all compounds, the lowest energy states in the conduction band arise primarily from the antibonding Sn/Sb 5s−O 2p interaction. In the alkaline-earth stannate perovskites (BaSnO3, SrSnO3, and CaSnO3) the conduction bandwidth decreases strongly in response to the octahedral tilting distortion triggered by the decreasing size of the alkaline-earth cation. This in turn leads to a corresponding increase in the band gap from 3.1 eV in BaSnO3 to 4.4 eV in CaSnO3. The band gap of CdSnO3 is relatively small (3.0 eV) considering the large octahedral tilting distortion. The origin of this apparent anomaly is the mixing between the empty Cd 5s orbitals and the antibonding Sn 5s−O 2p states. This mixing leads to a widening of the conductio...

R.J. Bouchard

Papers

Single crystal synthesis and electrical properties of CdSnO3, Cd2SnO4, In2TeO6 and Cdln2O4