Question

Photodiodes are mostly operated in reverse biased conditions because: 

• A. Fractional change in minority carriers produces higher forward current
• B. Fractional change in minority produce higher reverse current
• C. Fractional change in minority carriers produce higher reverse current
• D. Fractional change in majority carriers produce higher forward current

Answer 1

The Correct Option is C

The correct option is: (C): Fractional change in minority carriers produce higher reverse current.

When a photodiode is reverse biased, its depletion region widens, creating a larger space within which minority carriers (electrons in P-type material and holes in N-type material) can be generated by the absorption of photons. Here's how this principle justifies the operational mode:

Amplification of Minority Carrier Current: In reverse bias, the electric field across the depletion region pulls the generated minority carriers away from the region, contributing to an amplified current. Even a small change in the number of minority carriers can lead to a significant change in reverse current, making the photodiode highly sensitive to light variations.

Enhanced Sensitivity: The sensitivity of a photodiode depends on its ability to detect small changes in light intensity. Operating in reverse bias ensures that even a fractional change in the number of generated minority carriers results in a detectable change in reverse current, translating into a sensitive response to light.

Reduced Noise: The amplified current due to a fractional change in minority carriers can be more easily distinguished from background noise. This improves the signal-to-noise ratio and the accuracy of light detection.

Linearity: Operating in reverse bias provides a linear relationship between the incident light intensity and the generated photocurrent, allowing for accurate and predictable light measurements.

Reduced Dark Current Influence: Reverse bias minimizes the impact of dark current, the reverse current that flows in the absence of light. This is crucial for accurately measuring the light-generated current without interference from other sources of current.

In summary, reverse biasing a photodiode creates an environment where even small changes in minority carriers, caused by incident light, result in significant changes in reverse current. This sensitivity and linearity make reverse-biased photodiodes well-suited for light detection applications, ranging from simple light sensors to sophisticated optical communication systems.