This Small Business Innovation Research (SBIR) Phase I project is directed toward the development of innovative high-efficiency UV photocathodes based on the wide bandgap III-nitride semiconductors. Photocathodes based on AlxGa1-xN alloy with a bandgap of 3.4 to 6.2 eV (for Al composition x from 0 to 1) can fill the gap in the 150-400 nm range between alkali halide photocathodes (lambda < 200nm) and various optical photocathodes including multialkali and GaAs (lambda > 400nm). In addition to high-performance UV image sensors, these structures are considered for high-brightness electron emitters in maskless electron lithography and solid-sate lighting. This project will integrate these high-efficiency UV photodetectors with intensifiers to fabricate high resolution and high sensitivity solar-blind UV sensors for photon-counting and imaging applications. Note that the chemical and thermal stability and radiation hardness of III-nitride materials make these detectors suitable for applications in harsh environments. The requirements of future instruments pose new challenges for cathode development, particularly in the production of highly efficient and stable photocathodes. The key improvements include higher detection efficiency, better stability under radiation and surface exposure, and stronger out-of-bandpass light rejection.
Detection of light in the ultraviolet (UV) range (lambda < 400 nm) has a wide range of applications, both commercial and military, particularly in those areas where the UV component of light needs to be analyzed in the presence of large visible and/or infrared (IR) backgrounds. High-quality photocathodes were grown by MBE technique, which means that they can be developed on large diameter substrates with uniform performance. Large-format UV image sensors are in great demand for space science and military application. The development of high-efficiency 'cesium-free" photocathodes in this program will result in versatile, more reliable and lower cost UV sensors for the applications mentioned above. Finally, the technology to be developed in this program can results in high-brightness electron emitters for applications in metrology and maskless electron lithography.
