CAREER: Synthesis, Processing and Characterization of Novel Electronic Oxides

Colorado School Of Mines, Golden CO

Investigators

Abstract

CTS-0093611 Colin A. Wolden Abstract This career project features a combination of materials discovery, undergraduate research experience, and curriculum development organized around the common theme of electronic materials. Electronic oxides are distinguished from common ceramics by their unique ability to conduct charge. Transparent conducting oxides (TCOs) are key components in nearly all display and photovoltaic devices. A second class of oxides conduct and react with ions, a process called intercalation, which is central to electrochromic windows and rechargeable batteries. As technologies reliant on these materials continue to advance, it has become clear that oxide quality is beginning to limit final device performance. This career project will be directed at the synthesis, processing, and characterization of novel oxides using plasma-enhanced chemical vapor deposition (PECVD). Optical interrogation of the plasma and fundamental evaluation of the films' electrical, optical, and structural characteristics will guide the experimental effort. Concurrent measurements will be used to develop processing-structure-property relationships. Expanded research opportunities for undergraduates and continued enhancement of our electronic materials curriculum will advance educational goals. Electronic oxides have been synthesized to date primarily by physical vapor deposition (PVD) techniques. PECVD offers significant advantages over PVD with respect to the development of new compounds, effective doping, and the production of functionally graded materials. The most interesting TCOs are either alloys (indium tin oxide, ITO) or doped materials ZnO:AL, SnO2:F), and their conductivity is invariably n-type. Our efforts will be directed at the discovery and characterization new n-type alloys with improved properties, as well as the synthesis of p-type TCOs. The development of p-type oxides will enable the formation of transparent p-n diodes and the advent of oxide-based electronics. The large bandgap and chemical stability of oxides make them attractive candidates for high temperature/harsh environment applications. Low resistivity p-type TCOs will be pursued through the use of co-doping, a kinetic process in which a donor atom (e.g. Ga) and two acceptor atoms (e.g. N) are simultaneously incorporated into the film. A second aspect of this career project will involve the use of undergraduate researchers to study the synthesis of oxides that are ion conductors. Tungsten oxide (WO3) is leading electrochromic material whose transparency is reversibly altered by reactions with small ions (H+, Li+). Device performance is often limited by cation transport through the film, which in turn depends strongly on film stoichiometry and microstructure. The physical properties and the transient electrochromic response of PECVD tungsten oxide will be investigated as a function of plasma operating conditions. The final phase of this career project is directed at the continued development of the electronic materials curriculum at CSM. The PI has created, with NSF-ILI support, a new laboratory course in silicon processing. The interdisciplinary lab, which features cooperative learning and curiosity-driven experiments, was successfully offered last year to 20 seniors from four departments. The PI will continue the expansion of this laboratory, creating a more advanced course for graduate students. Finally, computational tools will be incorporated into the undergraduate curriculum in order to promote higher order thinking skills.