Scanning Probe Microscopy Studies of Polycrystalline and Nanocrystalline Semiconductors

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This project addresses materials issues in polycrystalline, semiconductor materials, with emphasis on the dominating influence which interfaces and grain boundaries have on film properties. Project goals are: to develop a new, comprehensive approach to polycrystalline film characterization based on exploring chemical, electronic, and optical properties of individual crystallites within a film, and to apply this approach to understanding and improving polycrystalline CdTe and GaAs for electronics and photonics applications such as displays and high efficiency solar cells. The approach utilizes scanning probe techniques including low temperature NSOM PL and AFM measurements of surface potential on polycrystalline films. This information will be correlated with that from other techniques such as scanning Auger spectroscopy, XPS, STM and transport measurements. CdTe has been chosen because existing approaches allow films with good minority carrier properties to be prepared making it a potential model system to study in terms of finding general methods for improving polycrystalline materials. High quality polycrystalline films of GaAs have been more problematic. Studies of GaAs and related III-V materials will be directed at characterizing the effects on electronic and optical performance of novel approaches for improving minority carrier properties. Success with this system would have important technological implications given the broad technological base which exists for III-V materials. Numerical modeling of NSOM excitation in the presence of surfaces and grain boundaries is included. As the study proceeds, information from these investigations will be fed back into the film growth processes to test results and, ultimately, to improve film quality.%%% The project addresses basic research issues in a topical area of materials science with high technological relevance. These studies will improve fundamental understanding of factors limiting the efficiency of displays and solar cells. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. The project is designed to develop strong technical, communication, and organizational/management skills in students through unique educational experiences made possible by a forefront research environment. There will be active involvement of undergraduates in the program and formal emphasis on developing effective oral and written communication skills. A new microelectronic processing course will provide students with expertise in materials preparation and processing. Collaboration of CSM students with students at the University of Wisconsin will be an additional, valuable, learning opportunity.***