Question

Define the dark current of the photodiode. What are the advantages and disadvantages of a photodiode?  

Answer 1

When a photodiode is reverse biased, a reverse saturation current flows through the junction which depends only on the concentration of the minority carriers and not on the applied voltage. This reverse current that flows even when the photodiode is not illuminated is called a dark current.

Advantages of photodiode:

1. Quick response when exposed to light.
2. The reverse current is linearly proportional to the intensity of incident light. (Linear response)
3. High speed of operations.
4. Lightweight and compact size.
5. Wide spectral response. E.g., photodiodes made from silicon respond to radiation of wavelengths from 190 nm (UV) to 1100 nm (IR).
6. Relatively low cost. 

Disadvantages of photodiode:

1. Its properties are temperature-dependent, similar to many other semiconductor devices.
2. Low reverse current for low illumination levels.