Ultrahigh Sensitivity Zinc Oxide Nanowire UV Detectors
C. Soci, A. Zhang, B. Xiang, J. Park, S. Dayeh, X. Bao, Y. Lo and D. Wang
University of california, San Diego, US
A rich genre of ZnO nanostructures has been intensively studied for nanoscale optoelectronics, electronics, and biotechnology. We report here single crystal unintentionally doped ZnO NWs as ultrahigh sensitivity UV photodetectors with very large optical gain (at the order of more than 107). To understand the mechanism of optical gain, we performed time-dependence measurement of the photoconductivity response in air and under vacuum, which revealed the minority carrier lifetime of a few seconds and minutes, respectively. We have developed a space-charge model that explains the long minority lifetime arises from the special separation of e/h to NW core and surface sheath, respectively, due to the unique nanowire geometry and intrinsic electric field, and the holes trapping in the surface states. This model also includes the surface desorption/adsorption of oxygen under illumination, which agrees well with measurement under vacuum. Furthermore, we have also studied the photo-excitation intensity dependence to explore the dynamic range. Moreover, photoconductance and time-dependent photoconductivity measurement of p-type nanowires will be also reported. These results suggesting ZnO NWs offer significant opportunities as functional devices such as high efficient photodetesctor and optical intra-chip interconnects, and integration with CMOS system, for novel electronics and optoelectronics.
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Nanotech 2007 Conference Program Abstract