High-gain photodetectors for UV to visible light detection has a myriad of applications, such as ultra-high energy cosmic ray detection from air fluorescence, Cherenkov detectors, or scintillator detectors. For nuclear instruments, the silicon photomultiplier used with scintillation crystals has shown significant advances, yet silicon is a limiting material. The bandgap of the material, which is around 1 electron volt, can lead to a high generation of dark noise, wherein any slight increase (tenths of an electron volt) in the bandgap can reduce the dark noise by an order of magnitude. Radiation damage on a silicon photomultiplier that damages the bulk material of the silicon will result in an increase in the dark noise. Unlike other types of silicon technologies that can be tolerant by design, the silicon photomultiplier requires a volume of silicon across a p-n junction with a controlled electric field, making it intrinsically susceptible to radiation damage.
Gallium arsenide (GaAs) is a preferred material for solar arrays in space as it provides the required sensitivity with a slower degradation from radiation compared to silicon. Aluminum Gallium Arsenide (AlGaAs) is a variant of GaAs and has preferable characteristics for UV to visible light detection. A major limiting factor to the use of AlGaAs for photodetectors has been poor material quality, yet the bandgap can be controlled to enhance optical and electrical performance. We plan to address the material quality issues in this project to develop a high-performance solid-state photomultiplier.
The development of a solid-state photomultiplier using AlGaAs will support the development of gamma-ray and neutron detectors, which are used for planetary science to understand the geochemistry. The detector is compact compared to the photomultiplier tube and operates at a lower bias. As the photomultiplier is developed from a segmentation of diodes operated in parallel, development of instruments for imaging is viable, where x-ray and gamma-ray imaging is a critical tool for astronomy.
Radiation dosimetry, Cherenkov detectors, gamma/neutron spectroscopy, medical imaging such as PET and SPECT, LIDAR, monitors for nuclear materials, and radiation detectors for oil logging are a few applications. The silicon photomultiplier is the state of the art, and the AlGaAs photodetector will supplant this technology, as the anticipated dark noise will be significantly smaller.