Sensitvity leap for far ultraviolet single photon avalanche diodes

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The 2015 Nobel prize in physics was awarded for the discovery that neutrinos have mass. But their absolute mass is still unknown. Are neutrinos Majorana fermions, a theoretical particle type which is simultaneously matter and anti-matter? The field of astroparticle physics aims to answer these key questions in the coming years. The required experiments involve huge volumes of liquid Xe or Ar at cryogenic temperatures and 4 to 100 m2 of ultraviolet sensitive photodetectors.For an instrumentation engineer, this translates into creating a camera that has many m2 of sensitive area to count each of the few ultraviolet photons emitted in all direction by the liquid Xe or Ar scintillation. The technology identified to make this camera is based on Single Photon Avalanche Diodes (SPAD) made of silicon. I led the fabrication of a unique concept of fully digital photon counting called 3DdSiPM that will make scaling up to many m2 possible. A limiting issue for all silicon based SPAD detectors is the sensitivity of the photodiodes themselves in the VUV range (100-200 nm).The objective of my research program is to boost the sensitivity of SPAD detectors by at least a factor of three. To do so, special epitaxial techniques suited for mass production will be used to engineer the conduction band profile of the SPAD. This approach has allowed CCDs to perform very well in the VUV range. Antireflection coating of the surface of the SPAD will also be fabricated using the Atomic Layer Deposition technique. This technique can build the extremely thin layers needed to construct the antireflection multilayer structure for very short VUV wavelengths.Tripling the sensitivity of SPAD based detectors would be a game changer in many astroparticle physics experiments. It will also stimulate the field of medical imaging by enabling new techniques called Time-of-Flight Position-Emission-Tomography (ToF-PET) to make exams faster and the radiation dose lower.