What This Calculator Does
A silicon photomultiplier (SiPM) is an array of tiny avalanche photodiode cells used to detect very low levels of light, down to single photons. Photon Detection Efficiency (PDE) describes the overall probability that an incoming photon actually produces a detectable signal, combining three separate loss mechanisms into one figure.
The Formula
PDE is the product of three efficiency terms: PDE = QE × εGeiger × Fill Factor, where QE (quantum efficiency) is the probability a photon generates an electron-hole pair in the silicon, εGeiger is the probability that pair triggers a full avalanche breakdown once it reaches the depletion region, and the fill factor is the fraction of the sensor’s surface area actually covered by active microcell area (the rest is dead space between cells and readout circuitry).
- Quantum efficiency depends on wavelength and the silicon’s absorption properties.
- Trigger probability increases with overvoltage (bias above breakdown) up to a saturation point.
- Fill factor is a fixed geometric property of the sensor’s microcell layout and pitch.
This is the standard multiplicative PDE model used in SiPM datasheets and photon-counting research for general reference and educational purposes; manufacturer-published PDE curves account for additional wavelength and temperature dependence not captured here.