Special issue paper. Detectors for fibre-optic communication

The silicon avalanche photodetector is the preferred photosensitive device for may fibre-optic applications except for relatively short links where the improvement in sensitivity arising from the internal gain mechanism is not required. Several structures have been devised for preparing these detectors which achieve distinct compromises in performance between the quantum efficiency to near infrared radiation, breakdown voltage and response time. An account of the noise sources of the detector is given and it is shown that the major source of noise, in the absense of microplasma breakdown, originates from shot noise arising from the thermally generated bulk leakage current. The future development of avalanche photodetectors is outlined; this indicates that the N+P¿P+ reachthrough structure is preferable for many applications. Circumstances are described in which detectors prepared in compound semiconductors may offer an improved performance compared with devices prepared in silicon.