An Avalanche Photodiode (APD) is a type of photodiode in a photodetector. By applying a high reverse bias voltage, an APD achieves significantly higher photosensitivity than a standard photodiode. This high voltage induces an internal gain mechanism known as avalanche multiplication, which amplifies the signal. This makes it possible to obtain signals with high sensitivity even in weak light.
The greatest feature of Matsusada Precision's APDs is that they use a P-incidence structure. Most conventional APDs utilize an N-incidence structure. In this configuration, especially with short-wavelength light, charge carriers are generated near the surface, outside the multiplication region. As a result, the full avalanche gain is not achieved, leading to reduced sensitivity.
On the other hand, with the P-incidence structure used by Matsusada Precision, carriers generated by light incident near the surface are efficiently guided into the avalanche layer. Our advanced crystal growth technology minimizes lattice defects, resulting in a low-noise device. Furthermore, since a stable P layer can be formed, the variation in the avalanche voltage of each device can be suppressed.
APD product page is here. (Japanese)
Example of Avalanche Photodiode (APD) Circuit
This circuit diagram is an example of a photon counting circuit using an APD. A high reverse bias voltage of up to about 300V is applied to the APD. The maximum voltage that can be applied varies depending on the APD, so check the specifications of the APD to be connected and make sure not to exceed the maximum value. Also, connect a current-limiting resistor for protection.
When a photon enters the APD, a current flows. This current is converted into a voltage signal by a current-to-voltage conversion circuit using a high-speed operational amplifier.
- Related words:
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- Photodiode
- PIN Photodiode
- Photomultiplier Tubes (PMT)
- Photodetector
- Hybrid Photodetector
- Flat Panel Detector (FPD)
