Avalanche Photodiode vs. PIN Diode: A Detailed Comparison

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The photodiode is a semiconductor device that operates based on the photovoltaic effect. Essentially, when light strikes the semiconductor material, it generates a small electrical current. When a photodiode is reverse-biased using a DC power source, it operates in photoconductive mode, which results in a higher current output.

PIN Photodiode

A PIN photodiode, much like a regular PIN diode, features an intrinsic (undoped) layer sandwiched between the p-type and n-type doped layers. This design provides more sensitive and faster responses compared to standard PN photodiodes.

P-I-N diode structure

Figure 1: P-I-N diode structure, illustrating the intrinsic layer between the P and N doped layers.

Avalanche Photodiode

When light falls on the undoped region of an avalanche photodiode, it initiates the creation of electron-hole pairs. As electrons move towards the avalanche region, the cumulative electric field intensifies, accelerating them to a point where collisions with the crystal lattice create even more electron-hole pairs. This “avalanche” effect makes it significantly more sensitive than a PIN photodiode.

Avalanche Photodiode structure

Figure 2: Avalanche Photodiode structure.

However, this enhanced sensitivity also makes avalanche photodiodes more susceptible to electrical noise, which is considerably affected by temperature.

Key Differences: Avalanche Photodiode vs. PIN Photodiode

The following table summarizes the key differences between avalanche and PIN photodiodes:

FeaturesAvalanche PhotodiodePIN Photodiode
StructureAs shown in figure-2 (P+, I, P, N+)As shown in figure-1 (P, I, N)
Response timeVery highVery low
Internal gain200 dB , Internally amplified gainInsignificant
SensitivityHighLow
Electric noiseHighLow
Reverse bias voltageVery highVery low
Temperature stabilityHighLow
Amplifier requirementNot necessaryMandatory
SpeedGenerally slowerGenerally faster
Dark currentHigherLower
Quantum efficiencyTypically higherTypically lower

Conclusion

The decision of whether to use an Avalanche Photodiode or a PIN photodiode hinges on the specific application’s requirements. The optimal choice involves balancing factors like sensitivity, speed, noise levels, and dark current to achieve the desired performance.

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Diode Interview Questions and Answers

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