Table of Contents
What Is PDE?
Photon Detection Efficiency (PDE) is the probability that a single photon hitting a Silicon Photomultiplier (SiPM) will produce a detectable electrical signal. SiPMs are arrays of single-photon avalanche diodes (SPADs) operated in Geiger mode, capable of detecting individual photons with high gain. PDE is the key performance metric for SiPM-based detectors.
SiPMs are used in medical imaging (PET scanners), high-energy physics (calorimeters), LIDAR, and fluorescence detection. Typical PDE values range from 20% to 60% depending on wavelength, overvoltage, and device design. PDE is the product of three independent factors: quantum efficiency, fill factor, and avalanche triggering probability.
Formula
Component Factors
| Factor | Description | Typical Range |
|---|---|---|
| QE | Probability of photon absorption and e-h pair creation | 60-90% |
| FF | Active area / Total area ratio | 50-80% |
| Pa | Probability of triggering avalanche | 70-95% |
Frequently Asked Questions
How does overvoltage affect PDE?
Increasing the overvoltage (V - Vbreakdown) increases the avalanche probability, raising PDE. However, it also increases dark count rate, optical crosstalk, and afterpulsing. There is an optimal overvoltage that maximizes signal-to-noise ratio, typically 2-5V above breakdown.
What wavelength has the highest PDE?
Standard silicon SiPMs peak around 420-450 nm (blue-green). This aligns well with common scintillators like LYSO and BGO used in PET imaging. Special designs with anti-reflective coatings or different silicon structures can shift the peak to red or near-infrared wavelengths.