High Gain-Bandwidth-Product Avalanche Photodiodes for Multigigabit Data Rates.

For long-wavelength (1.3microns and 1.5microns) high-bit-rate (>400 Mbit/s) lightwave systems the highest receiver sensitivities have been achieved with III-V compound avalanche photodiodes with separate absorption and multiplication regions (SAM-APDs). Initial APDs of this type exhibited poor frequency response owing to charge accumulation at the heterojunction interfaces. A significant improvement in the bandwidth was achieved by introducing a transition region between the multiplication and absorption layers (SAGM-APD's).