Overvoltage (Vov) is the bias voltage above breakdown. Higher Vov increases gain, PDE, and detection probability but also increases dark counts, crosstalk, and afterpulsing.

How does temperature affect SiPMs?

Dark count rate approximately doubles every 8°C. Breakdown voltage increases ~20-50 mV/°C. Cooling a SiPM dramatically reduces noise — medical PET scanners often operate at −20°C.

What limits SiPM dynamic range?

The finite number of microcells. Once all microcells have fired, additional photons produce no additional signal. For linear response, keep Npe < 0.1 × Nmicrocells.

What is crosstalk in SiPMs?

When one microcell fires, avalanche photons can trigger neighboring microcells. This "optical crosstalk" adds extra counts that inflate the apparent signal. It increases with overvoltage.

What is afterpulsing?

Charge carriers trapped during the avalanche are released after the microcell recharges, triggering a second avalanche. It produces delayed spurious counts on timescales of 10-100 ns.

How does PDE vary with wavelength?

SiPM PDE peaks at 400-450 nm (blue-green) for standard devices. UV-enhanced SiPMs peak at 350 nm. Near-infrared SiPMs use deeper junctions for sensitivity at 800-1000 nm.

SiPM / PDE Calculator

Calculate SiPM photon detection efficiency, fired microcells, saturation, signal-to-noise ratio, and dark count correction for silicon photomultiplier sensors.

Breakdown Voltage Vbr (V)

Bias Voltage (V)

Dark Count Rate (kHz)

Gain

PDE at peak λ (%)

Number of Microcells

Incident Photons

Temperature (°C)

Overvoltage

3.00 V

Vov = Vbias − Vbr

Photoelectrons (Npe)

40.0

Nph × PDE

Fired Microcells

39.8

Saturation-corrected

Saturation

1.1%

Nfired / Ntotal

Total Charge

10,833.3 fC

Nfired × G × q

Dynamic Range

35.6 dB

3600 microcells

DCR at T

500 kHz

At 25°C

SNR

6.3

100 ns gate window

Microcell Saturation

1.1% fired

SiPM Key Parameters

Parameter	Typical Range	Notes
Breakdown Voltage (Vbr)	20−70 V	Temperature dependent (~20 mV/°C)
Overvoltage (Vov)	1−5 V	Vbias − Vbr; controls gain & PDE
Gain	10⁵ − 10⁷	Gain = Cd × Vov / q
PDE	15−50%	Photon detection efficiency at peak λ
Dark Count Rate	10−10⁶ Hz	Thermal carriers; halves per ~8°C cooling
Cross Talk	1−30%	Correlated noise; increases with Vov
Afterpulse Prob	1−10%	Trapped carriers; worse at high gain
Recovery Time	10−100 ns	τ = Rq × Cd per microcell

Planning notes, formulas, and examples

About the SiPM / PDE Calculator

Silicon Photomultipliers (SiPMs) are arrays of single-photon avalanche diodes (SPADs) operating in Geiger mode. Each microcell fires independently when it detects a photon, producing a standardized charge pulse. The total signal is the sum of all fired microcells.

Photon Detection Efficiency (PDE) is the probability that an incident photon triggers a microcell — it depends on overvoltage, wavelength, and fill factor. This calculator computes the expected number of photoelectrons, the saturation-corrected number of fired microcells, total output charge, dynamic range, and signal-to-noise ratio.

SiPMs have a finite number of microcells, so they saturate when many photons arrive simultaneously. The saturation model accounts for this: N_fired = N_total × (1 − exp(−Npe/N_total)). The calculator also adjusts dark count rate for temperature (DCR doubles every ~8°C).

Presets for popular SiPMs from Hamamatsu, SensL, and OnSemi let you quickly explore real device performance. This calculator is essential for designing PET scanners, LiDAR detectors, fluorescence readers, and any photon counting system using SiPMs.

When This Page Helps

SiPMs are replacing traditional PMTs in many applications, but their nonlinear saturation, temperature-dependent noise, and correlated noise require careful analysis.

It gives the essential SiPM performance metrics including saturation correction and temperature-adjusted dark count rates.

How to Use the Inputs

Select a SiPM preset or enter device parameters manually.
Enter the breakdown and bias voltages to compute overvoltage.
Enter the PDE at peak wavelength and number of microcells.
Enter the number of incident photons for the signal.
Adjust the operating temperature to see DCR correction.
Read the fired microcells, saturation, charge output, and SNR.

Formula used

Overvoltage: Vov = Vbias − Vbr.
Photoelectrons: Npe = Nph × PDE.
Fired microcells: Nfired = Ntot × (1 − exp(−Npe/Ntot)).
Charge: Q = Nfired × Gain × q (q = 1.602×10⁻¹⁹ C).
DCR(T) = DCR(25°C) × 2^((T−25°C)/8°C).
SNR = Npe / √(Npe + DCR × t_gate).

Example Calculation

Result: Npe = 40, Nfired = 39.6, saturation = 1.1%, Q = 10.8 fC

Overvoltage = 3 V. Npe = 100 × 0.40 = 40 photoelectrons. Nfired = 3600 × (1 − exp(−40/3600)) = 39.6 (negligible saturation). Charge = 39.6 × 1.7×10⁶ × 1.6×10⁻¹⁹ = 10.8 fC.

Tips & Best Practices

Keep Npe below 10% of Nmicrocells for less than 5% nonlinearity.
Cooling from 25°C to 0°C reduces DCR by roughly 8×.
For timing applications, smaller microcells (10-15 µm) give faster recovery but lower PDE.
Use the SiPM at the manufacturer-recommended overvoltage — exceeding it gains little PDE but much more noise.
In high-rate environments, check that the photon rate × recovery time << Nmicrocells.

When To Use This Calculator

Calculate SiPM photon detection efficiency, fired microcells, saturation, signal-to-noise ratio, and dark count correction for silicon photomultiplier sensors. Use it when you need a repeatable calculation in the physics / general category and want the setup, result, and supporting values kept together. This is especially helpful when small input changes, unit choices, or rounding decisions can change the final number.

How To Check The Result

Start by confirming that the inputs match the formula shown on the page. Then compare the main output with the worked example and any secondary values shown by the calculator. If the result will be used in another calculation, keep extra precision until the final step and record the assumptions beside the number.

Practical Notes

Treat the result as a calculation aid rather than a substitute for context. For schoolwork, include the formula and substitution steps. For planning, technical, financial, or health-related decisions, verify important numbers against primary records, current rules, or a qualified professional before acting on them.

Sources & Methodology

Last updated: January 15, 2025

Frequently Asked Questions

Overvoltage (Vov) is the bias voltage above breakdown. Higher Vov increases gain, PDE, and detection probability but also increases dark counts, crosstalk, and afterpulsing.