Large Area, Robust GaN-Based Photocathodes for High-Efficiency UV and Cherenkov Light Detection

Improved, high-sensitivity, large-area UV detectors are sought for many photon-counting and imaging applications. In particular, for nuclear and high energy physics research, there is a need to extend the sensitivity of photon detectors to the blue and UV wavebands. In addition, the photocathodes must have uniform larger-area detection with lower noise and higher efficiency, better tolerance to radiation and surface contamination, stronger out-of-band light rejection, and a lower cost of production. This project will develop robust, large-area photocathodes, based on the wide-bandgap III-nitride semiconductors (GaN), for high-efficiency Cherenkov and UV light detection. The photocathodes will be incorporated on micro-channel plates (MCPs) and electron-bombardment charged coupled devices (EB-CCDs) for high-sensitivity photon counting and imaging. Phase I will address issues related to the design and fabrication of high-performance, large-area, nitride-based photocathode structures and their integration with intensifiers for UV photon-counting and imaging. In particular, Phase I will design novel nitride-based UV photocathode structures; use molecular beam epitaxy to grow large-area nitride-based UV photocathodes; fabricate, characterize, and perform lifetime testing of UV photocathodes; and integrate the UV photocathodes with suitable MCP and CCD structures. Commercial Applications And Other Benefits as described by the Applicant: In addition to applications in nuclear and high-energy physics, high-efficiency photon counting detectors should be an enabling technology for future space-borne astronomy, and many civilian and military applications. The GaN-based photocathodes also should be expected to impact the development of high-quality electron sources. More efficient electron sources would enhance the performance of polarized RF electron guns for synchrotron and free-electron lasers and contribute to developments in maskless electron lithography and semiconductor wafer metrology.