  Photon detectors featuring single-photon sensitivity play a crucial role in
various scientific domains, including high-energy physics, astronomy, and
quantum optics. Fast response time, high quantum efficiency, and minimal dark
counts are the characteristics that render them ideal candidates for detecting
individual photons with exceptional signal-to-noise ratios, at frequencies in
the the range of hundreds of MHz. Here, we report on our first design and
operational results on a Hybrid Photon Detector (HPD) that combines the high
quantum efficiency of a Gallium Nitride (GaN) photocathode and the low noise
characteristics of a Si-based Low-Gain Avalanche Diode (LGAD). This hybrid
detection scheme has the potential to reach single-photon detection sensitivity
with high quantum efficiency, low noise levels and capable of operating at
hundreds of MHz repetition rates.
