Epitaxial silicon n+-p- π -p+avalanche photodiodes for optical fiber communications at 800 to 900 nanometers

Silicon n⁺-p-π-p⁺avalanche photodiodes, having high speed (1 ns response time), low noise and high current gain, have been developed for optical fiber communications. These detectors provide a 16 dB improvement in sensitivity over nonavalanching photodiodes in optical receivers operating at 825 nm and 44.7 Mbit/sec. To facilitate fabrication on large diameter wafers, achieve uniform avalanche gain, and obtain quantum efficiencies greater than 90% at 800 to 850 nm, the avalanche photodiodes are constructed from 50 µm thick, high resistivity epitaxial silicon. At an average gain of 100, their resulting excess noise factor is only 4 to 6 times the shot noise limit. Low dark currents and good reliability are achieved through the use of guard rings, channel stops, bulk and surface gettering, dielectric passivation and surface field plates.