2015 IPFW Student Research and Creative Endeavor Symposium



Download Full Text (883 KB)

Faculty Sponsor

Dr. Mark Masters


Department of Physics

University Affiliation

Indiana University – Purdue University Fort Wayne


This project is an introduction to single photon avalanche diodes (SPAD) as a preliminary step to starting work in Quantum Optics. A SPAD is also becoming used in space missions as photon detector, medical imaging, optical fiber communications etc., replacing the vacuum photomultiplier tube. SPAD is a p-n junction diode used in reverse biased condition. These diodes when operated at a voltage higher than their breakdown threshold voltage act as photo detectors. A single photon causes an avalanche of electrons producing a large current pulse for a single photon. In this investigation, an LED (light emitting diode) is used. An LED when used in forward biased condition produces light due to current passing through it. When reverse biased it will act as a photon detector. My goal is to clearly understand how a SPAD (single photon avalanche diode) works. For this, I’m using an LED as a SPAD, a counter (gives the number of photons detected over a time period or frequency), an oscilloscope (displays the varying signal), a resistor, and a high voltage power supply. When a voltage of 133 volts (higher than the break down voltage) is applied, the LED becomes sensitive to light and a single photon hitting the active area (depletion region of p-n junction) can cause formation of carriers (electrons) and these carriers in turn produce secondary carriers. This leads to an avalanche of electrons moving through the diode. Every time a photon hits the depletion region of the LED there will be an avalanche of electrons and this can be seen as a signal in the oscilloscope and as a number in the counter. To vary the amount of light exposure, the diode is placed in a box that completely conceals the diode from the room light, and another LED (light source) in forward biased condition is used as a light source inside the box. The current through the light source inside the box can be changed to control how much light is emitted. I will present my results in a series of investigations that demonstrate how a SPAD functions.


Physical Sciences and Mathematics | Physics

Single Photon Avalanche Diode

Included in

Physics Commons