High-performance avalanche photodiode with separate absorption `grading? and multiplication regions

High-speed operation of avalanche photodiodes with separated absorption and multiplication regions has been achieved by incorporating an intermediate bandgap InGaAsP `grading? layer between the InP multiplication layer and the InGaAs absorption layer. These APDs also exhibit low dark currents, high quantum efficiencies and good avalanche gains. Sensitivity measurements have been made at 1.3 ?m and 1.55 ?m with one of these APDs in a high-speed optical receiver: at bit rates of 420 Mbit/s and 1 Gbit/s the minimum average powers required for 10?9 BER are ?43 dBm and ?38 dBm at 1.55 ?m, and ?41.5 dBm and ?37.5 dBm at 1.3 ?m, respectively.