Advanced Detectors, Systems, & Nanoscience
Solar-Blind Silicon and Applications
Ultrafast scintillation detectors are needed for fundamental scientific discoveries in particle physics and astronomy. Barium fluoride (BaF2) has the potential for detecting gamma rays with sub nanosecond timing resolution; however, the fast scintillation of BaF2 at 220 nm is accompanied by a larger, slower component at 300 nm. MDL developed integrated interference filters on superlattice-doped avalanche photodiodes (APDs) to detect the 220-nm light while rejecting the 300-nm light when combined with a BaF2 scintillator. This project is a collaboration with Radiation Monitoring Devices (RMD) and physics Professor David Hitlin (Caltech), who brings extensive experience with scintillation detectors for high-energy physics experiments. APDs offer high gain and the potential for single-photon counting as an alternate to image-tube devices. MDL demonstrated that superlattice-doped APDs have an order of magnitude faster response than standard APDs and are robust against irradiation with high-energy particles and photons. Our metal-dielectric coating enables the detector to achieve high QE at 220 nm, while rejecting out-of-band light. We have shown the rejection of out-of-band (300 nm) light with an unprecedented (for silicon) four orders of magnitude. For comparison, the response of superlattice-doped APDs with dielectric-only coatings does not exhibit this selective response (see plot below).