The basic structure of an avalanche photodiode is

The basic structure of an avalanche photodiode (APD) is:

In this structure:

P⁺ represent heavily doped p-type semiconductor

i represent Intrinsic semiconductor without doping.

p represents a p-type semiconductor.

n⁺ represent heavily doped n-type semiconductor.

Important Points:

• APD is a semiconductor photodiode device that is designed to operate under reverse biased condition.
• In optical communication, APD is used as a detector because it is very sensitive to light waves.
• APD works on the principle of photoelectric effect that converts light energy into electric energy.
• APD has high gain, smaller response time, and large responsivity value.