Separate absorption, charge, and multiplication staircase avalanche photodiodes

The wavelength 1550 nm is widely used in fiber-optic communications and imaging systems. Avalanche photodiodes (APDs) offer high sensitivity for detecting this wavelength. However, the noise caused by the stochastic nature of the impact ionization gain mechanism can temper the benefit of amplifying the signal. Here, we report a separate absorption, charge, and multiplication APD that uses a two-step staircase multiplication region exhibiting a near-unity excess noise factor. At a gain of four, the excess noise factor is approximately three times lower than conventionally used InGaAs/InP separate absorption, charge, and multiplication APDs. This improved excess noise coupled with 1550-nm operation offers the potential for enhanced performance in several key application areas.