High-performance visible/UV photocathodes formed on large-area microchannel plates

Reliable, high-sensitivity and high-resolution photon detectors, which can alleviate major limitations imposed by photomultiplier tubes (PMTs), for future high energy physics (HEP) and nuclear physics (NP) experiments, are of great interest to DOE. Other fields that could greatly benefit from these detectors include Cherenkov telescopes in astrophysics, positron emission tomography (PET) in medical imaging, space and planetary explorations, solar-blind UV missile tracking, and other scientific, industrial and military applications. For many of these applications, a photocathodes (PC) in conjunctions with a micro- channel plate (MCP) have been considered as a lower cost, less bulky and more robust alternative to PMTs. However, for detection of low level or fast transient signals, the standard geometry phototube, with a separate semi-transparent PC positioned above a MCP stack, does not have the required detection efficiency and/or spatial and temporal resolutions. This proposal is directed toward the development of an innovative metallic buffer for deposition of high- quality III-nitride based photocathode structures directly on operational MCPs. If successfully developed, the close proximity of the PC and MCP in addition to the operation in opaque (reflection) mode, will result in significant improvements in both detection efficiency and spatial and temporal resolution of these devices. The proposed metallic buffer for high quality deposition of III-N PCs on MCPs will also act as a mirror to reflect some the unabsorbed light back into the PC layer to further increase efficiency, as well as providing an effective backside metal contact to avoid charging effects, especially in large diameter detectors. Detection of light in the ultraviolet (UV) and blue range (< 450 nm) has a wide range of commercial, scientific and military applications, particularly in those areas where the shorter wavelength component of light needs to be analyzed in the presence of large visible and/or infrared (IR) backgrounds. Gallium nitride (GaN) and its alloys with indium and aluminum are the most promising semiconductors for development of photodetectors for applications in space-based spectroscopy and imaging. GaN-based devices are also extremely robust, and are suitable for operation in high temperature and high radiation environments, which is required for some of the future DOE HEP and NP projects.