Low noise avalanche photodiodes

Avalanche photodiodes (APDs) are used in many applications when conventional unity gain photodiodes cannot provide enough sensitivity and the extra amplification provided by the impact ionization process gives it an advantage. Unfortunately this amplification or gain of the incoming optical signal is always accompanied by some excess noise. Using avalanche photodiodes can reduce this excess noise. In addition to reducing the excess noise, thin avalanching widths offer APDs with lower operating voltages and a better temperature stability. The speed of the APD is also expected to increase at least in proportion to the decrease in avalanche width.