Near infrared detectors for fiber-optics

There is considerable interest in developing high-speed, low-noise avalanche photodiodes for operation in the 1.2-1.6 µm wavelength range where silicon detectors are inadequate. The lattice matched quaternary material systems InGaAsP/InP and GaAlAsSb/GaSb are being actively studied by many different research groups. Devices fabricated from both of these compound semiconductor materials systems have demonstrated high quantum efficiency (50-70% without antireflection coatings) and short response times (60-250psec). Unfortunately, the reported avalanche gains obtained from these devices have been quite low (<10-50), and although the reported dark currents at low bias voltage (∼1/2 of the breakdown voltage) have been very low, the leakage currents at the bias voltages required to achieve the moderate values of avalanche gain have been very large (≥10 µA). In the few cases where the noise performance of these devices has been measured, the shot noise due to the large leakage currents has been the dominant noise source. Recent results of attempts to improve this situation are reviewed.