Superlattice Doped APDs for Improved UV Sensitivity in Scintillator Calorimetry

One of the proposed next generation Intensity Frontier experiments is Mu2e. Mu2e will directly probe the Intensity Frontier as well as aid research on the Energy and Cosmic frontiers with precision measurements required to characterize the properties and interactions of new particles discovered at the Intensity Frontier. In order to reach its science goals, detector upgrades are required. A key apparatus of Mu2e is its calorimeter, which will need faster and more UV sensitive photodetectors for reading out the ultraviolet (UV) emission from fast scintillators located in the calorimeter disk. RMDs silicon avalanche photodiodes (APDs) have been identified as a potential photodetector for the Mu2e calorimeter, however, this will require an epitaxial modification (superlattice doping) of the APD to increase detector UV sensitivity and speed of response. In the proposed effort our optimization will involve exploiting an epitaxial fabrication process, which has been used successfully with silicon CCDs that will improve APD UV sensitivity and temporal properties for the detection of UV scintillation emission. During Phase I we explored the feasibility of modifying RMDs APD technology with epitaxial processes developed at Jet Propulsion Laboratory (JPL). We epitaxially modified RMD APDs, characterized the modified APDs basic properties and demonstrated that we successfully developed detectors that offer greater UV sensitivity with a faster detector response time compared to RMD standard APDs. In Phase II we will continue to improve upon the processes for modifying APDs with particular attention invested towards improving the APD durability, reducing the APD electronic noise, while maximizing the UV sensitivity at 220 nm and attenuating the sensitivity at longer wavelengths through the use of applying passband filters onto the APDs. At the end of Phase II we will have developed and tested calorimeter modules for Mu2e based on RMDs modified APDs. 5. Commercial Applications and Other Benefits Medical imaging modalities such as SPECT and PET, which use blue-UV emitting scintillators, would directly benefit from advances in the proposed technology. Likewise, hand held instruments and vehicle portals used for monitoring nuclear material movement using UV emitting scintillation crystals would benefit as well. Ultraviolet and optical astronomy would be another potential