Solar Blind AlGaN Photocathode

This Small Business Innovative Research Phase I Project proposes to use the semiconducting compound AlxGa1-xN to develop a photocathode for use in highly sensitive, solar-blind photomultipliers. The band gap of AlxGa1-xN has a long wavelength cutoff that can be varied from 365 to 200 nm as the AlN molar fraction increases from zero to one. Further, this compound can show a negative electron affinity (NEA) and can be used in high temperature and high power applications. The phase I effort will employ molecular beam epitaxy (MBE) to grow ordered thin-film AlxGa1-xN photocathodes on (0001) sapphire substrates. Surface analysis will be performed at different steps of the growth process to determine what conditions promote the development of the NEA surface. In Phase II, the photocathode will be coupled to micromachined silicon microchannel plate (MCP) and miniature photomultiplier tube (MPMT) technologies to produce high gain (>1,000) detectors that operate at low power, high speed, and over a large dynamic range. Sensitive in the short-wavelength ultraviolet (UV), l < 290 nm, region of the spectrum, these detectors respond to relevant emission bands for UV astronomy, atmospheric ozone monitoring, and the remote sensing of earth resources.