With increasing biasing voltage of a photodiode, the photocurrent magnitude
(a) increases initially

Q: Why is a photodiode operated in reverse bias?

In reverse bias, the intrinsic dark current is very small. This makes it much easier to detect the small changes in current caused by incident light, improving the signal-to-noise ratio.

Q: What determines the saturation current?

The saturation current depends primarily on the intensity of the incident light. Brighter light generates more electron-hole pairs per second, leading to a higher saturation current.

Q: Why doesn't the current increase indefinitely with voltage?

Because the number of charge carriers generated per second is limited by the light intensity. Once the voltage is high enough to sweep all generated carriers across the junction, the current cannot increase further.

Q: What is dark current?

It is the small reverse saturation current that flows even when no light is incident on the photodiode. It is caused by thermally generated minority carriers.

Q: Does the forward bias characteristics of a photodiode differ from a normal diode?

No, in forward bias, a photodiode behaves just like a normal p-n junction diode. The light-induced current is negligible compared to the large forward current.

Question

With increasing biasing voltage of a photodiode, the photocurrent magnitude

Options:

(A) increases initially and after attaining certain value, it decreases

(B) increases initially and saturates finally

(C) remains constant

(D) increases linearly

Sigma Percentile · Accepted Answer

### The Magic of Photodiodes

Imagine a device that can literally 'see' light and convert it into an electrical signal. That's exactly what a photodiode does! But to understand how it behaves when we tweak its settings, we need to dive into the physics of its operation.

### The Reverse Bias Setup

A photodiode is essentially a p-n junction, but it is intentionally operated in **reverse bias**. Why? Because in reverse bias, the normal current (called dark current) is extremely small. This makes it much easier to detect the tiny additional current created when light shines on it. When we apply a reverse biasing voltage, the depletion region at the junction widens, creating a strong electric field.

### The Birth of Photocurrent

When photons of light with sufficient energy hit the depletion region, they knock electrons loose, creating **electron-hole pairs**. The strong electric field immediately grabs these newly born carriers—sweeping electrons towards the n-side and holes towards the p-side. This flow of charges is what we call the **photocurrent**.

### The Saturation Phase

Now, what happens if we keep increasing the reverse biasing voltage? Initially, a stronger voltage means a stronger electric field, which sweeps the carriers more efficiently before they have a chance to recombine. So, the photocurrent **increases initially**.

However, there is a limit. The number of electron-hole pairs generated per second depends entirely on the **intensity of the incident light**, not the voltage. Once the voltage is high enough to sweep *all* the generated carriers across the junction, the current cannot increase any further. It hits a ceiling. We say the photocurrent **saturates finally**.

Therefore, the correct behavior of the photocurrent magnitude with increasing biasing voltage is that it increases initially and then saturates.

Animated Solution for Physics - Semiconductors: With increasing biasing voltage of a photodiode, the photocurrent magnitude

Select Answer:

Visualized Solution

Photodiode Biasing

Photocurrent Generation

Saturation of Photocurrent

Conclusion

The Sigma Insight: Optoelectronic Devices

The Magic of Photodiodes

The Reverse Bias Setup

The Birth of Photocurrent

The Saturation Phase

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