Photon Detection Efficiency Calculator (SiPM)

Compute a silicon photomultiplier's Photon Detection Efficiency (PDE) from quantum efficiency, geometric fill factor, and avalanche triggering probability using PDE = QE × fill factor × trigger probability.

Quick Facts

PDE formula
PDE = QE × εgeom × Pt(ΔV)
Product of quantum efficiency, geometric fill factor, and avalanche triggering probability.
Fill factor range
~30% to ~80%
Small microcells (15-25 µm) have more dead space than large ones (50-75 µm).
Overvoltage tradeoff
Pt(ΔV) rises, then saturates
Higher overvoltage boosts trigger probability but also raises dark counts, crosstalk, and afterpulsing.

Your Results

Calculated
Photon Detection Efficiency
-
PDE = QE × fill factor × trigger probability
PDE (decimal)
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Fraction of incident photons detected, 0-1
Detected Photon Rate
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Incident rate × PDE
Undetected Photon Rate
-
Incident rate × (1 - PDE)

Ready

Enter QE, fill factor, and trigger probability, then press Calculate.

Formula and Method for Photon Detection Efficiency (SiPM)

A silicon photomultiplier (SiPM) is an array of tiny single-photon avalanche diodes (SPADs), called microcells, each biased above its breakdown voltage in Geiger mode. Photon Detection Efficiency (PDE) is the probability that a photon landing on the sensor's active area produces a detectable output pulse. It is the product of three independent probabilities: PDE(λ, ΔV) = QE(λ) × εgeom × Pt(ΔV), where QE is the quantum efficiency of the silicon at the photon's wavelength, εgeom is the geometric fill factor of the microcell array, and Pt is the probability that a photo-generated carrier triggers a self-sustaining avalanche at the applied overvoltage ΔV.

How the calculation works

Enter quantum efficiency, fill factor, and avalanche triggering probability as percentages — these numbers usually come from a manufacturer's datasheet curve or a characterization measurement taken at a specific wavelength and overvoltage. The calculator converts each to a decimal (0-1) and multiplies them together to get PDE, then multiplies PDE by an optional incident photon rate to show how many photons per second are actually detected versus lost.

Common mistakes

  • Treating PDE as equal to quantum efficiency: QE alone ignores the fill factor and the avalanche triggering probability, both of which are usually well below 100% and pull the true PDE down significantly.
  • Ignoring wavelength dependence: QE — and therefore PDE — varies strongly with photon wavelength, so use the QE value for the wavelength you actually care about rather than a single "peak" number for every calculation.
  • Ignoring overvoltage dependence: Pt(ΔV) is not fixed — it changes with bias voltage, so a PDE measured at one overvoltage does not apply at another without re-checking the datasheet curve.

Real-world applications

  • Detector design for PET and SPECT medical imaging scanners, where PDE at the scintillator's emission wavelength sets the achievable energy and timing resolution.
  • High-energy physics calorimetry and particle-tracking detectors that read out scintillating fibers or tiles with SiPMs.
  • LiDAR and low-light optical receivers, where PDE at the laser wavelength directly limits detection range and signal-to-noise ratio.
  • Comparing SiPM models or bias points during sensor selection, using the same three-factor breakdown the datasheets report.

Frequently Asked Questions

What is Photon Detection Efficiency (PDE) for a SiPM?
Photon Detection Efficiency is the probability that a photon striking a silicon photomultiplier produces a detectable output pulse. It is the product of three factors: PDE = QE × fill factor × trigger probability, where QE is the quantum efficiency of the microcell material, fill factor is the fraction of the surface that is photosensitive, and trigger probability is the chance that a photo-generated carrier sets off a self-sustaining avalanche at the applied overvoltage.
Why is a SiPM's fill factor less than 100%?
Each SiPM is an array of many microcells (SPADs), and the space between them is taken up by quenching resistors, isolation trenches, and metal traces that are not photosensitive. Smaller microcells (around 15 µm) pack in more dead space per unit area and have lower fill factors, often 30-50%, while larger microcells (50-75 µm) can reach 70-80% at the cost of dynamic range and timing resolution.
How does overvoltage affect PDE?
Raising the bias voltage above the breakdown voltage increases the avalanche triggering probability, which raises PDE, but the gain saturates at high overvoltage. Higher overvoltage also increases dark count rate, optical crosstalk, and afterpulsing, so real devices are operated at an overvoltage that balances PDE against these noise sources.
What is a typical PDE value for a modern SiPM?
Peak PDE for commercial SiPMs commonly falls in the 40-60% range at their optimum wavelength, typically 400-550 nm for standard silicon devices, though newer NUV-HD or red-enhanced designs can exceed 60%. PDE always depends on wavelength, overvoltage, and microcell size, so check the datasheet curve for your exact operating point.

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