LEDs as Photodiodes

Group Members

Abas Syahbana, Lu Xinghao

Introduction

In the LED, there is a region called the depletion region. Photons outside the LED can fall to this region. Photons with greater energy than the energy gap of the semiconductor that composes the LED will be absorbed and produce electron-hole pairs. Then, a current is produced caused by the electric field across the region that pulls those pairs. This resulting current, called photocurrent, is proportional to the number of photons that fall to the depletion region.

Setup

Equipment

Power Source

Arduino Uno

Resistors

Breadboard

Jump wires

Variety of LEDs

Oscilloscope

Probe

Experimental Setup

In this project, .... According to the specific experiment, we have designed two circuits. One of them was emitting circuit and the other one was receiving circuit. For the emitting circuit, we also used LED as the light source. By changing the voltage applied to that LED, we can control the intensity of emission. As the same time, we also measured the current through LED. For the receiving part, we also used LED to receive the light. However, by reversing the direction of LED, which would response to different wavelengths of light and produced the current. Then, by measuring the voltage of the resister, which was series connected in the circuit through oscillograph, we could detect the signals.

Results and Discussion

In the experiment, we have used 4 different colors red, blue, green and orange served as emitter color and receiver color separately. Then recorded the intensity showed in the oscillograph. Controlled the other parameters and concentrated just on the color. Mostly the voltage of signal we found are only around 0.5mV. However, we also discovered that some special LED pairs can reach the voltage about 20mV, which is far large than the others. We thought that situation was very interesting and tried to identify the inner relation between them.

References

PhysicsOpenLab. (2020) “Using LED as a single photon detector”. PhysicsOpenLab. https://physicsopenlab.org/2020/02/27/using-led-as-a-single-photon-detector/

Logbook

5 March 2024: we took variety of LEDs in the workshop. We detected avalanche.

7 March 2024: We tried all of the LEDs. almost all of them can not detect avalanche.

12 March 2024: We tried other variety of LEDs from the workshop. we can not see any detection of avalanche. Then, we knew that we use LEDs in unconventional way.

14 March 2024: We didn't see any detection. We plan to use function generator to see any detection.

19 March 2024: We used function generator to see the signal. We didn't see anything.

21 March 2024: We saw something that can be a signal with frequency of the function generator f=1858 Hz. We planned to use battery to lessen the noise.

26 March 2024: We were somehow doing the experiment wrongly. It was using battery for the transmitter and trying detecting avalanche

28 March 2024: We changed the power source of the receiver to battery. We still didn't get rid of the noise.

2 April 2024: We can see the difference in signal. However we need bigger sensing resistor to measure it better.

4 April 2024: We can detect the signal. Then, we changed the function generator with a power source for the transmitter. We started measuring all of the combination of LEDs as the emitter and the receiver.

9 April 2024: We continued measuring all of the combination with 10x probe. We didn't use some LEDs that cannot detect light as receiver.

11 April 2024: We completed the measurement of the combination of 5 different LEDs as emitter and receiver.

16 April 2024: We measured the same type of LEDs as the emitter and receiver. We also measured the current at the emitter

18 April 2024: We finished measuring the same type of LEDs as the emitter and receiver and the current at the emitter.