1. Photodiode operation

A photodiode is generally operated in reverse bias. When light falls on the junction, electron-hole pairs are generated, producing a photocurrent.

2. Effect of increasing bias voltage

As the reverse bias voltage is increased:

• The depletion region width increases.
• The electric field across the junction becomes stronger.
• More of the generated charge carriers are swept across the junction before recombination.

So, the photocurrent increases initially with reverse bias.

3. Why saturation occurs

After a certain reverse bias, almost all the photogenerated carriers are already being collected efficiently. Increasing the voltage further cannot create extra carriers, because the number of carriers depends on the incident light intensity, not on the bias voltage.

Therefore, the photocurrent reaches a saturation value.

4. Checking the options

• A: Increases initially and then decreases
  $\rightarrow$ Incorrect. Photocurrent does not decrease like this under normal operation.

• B: Increases linearly
  $\rightarrow$ Incorrect. It does not keep increasing linearly forever; it saturates.

• C: Increases initially and saturates finally
  $\rightarrow$ Correct.

• D: Remains constant
  $\rightarrow$ Incorrect. It is not constant at low bias; it first increases.

5. Final answer

Hence, the correct option is:

$\boxed{\text{C: Increases initially and saturates finally}}$

6. Comparison with stored answer

Stored correct answer: C
Derived answer: C
So, they agree.