A germanium avalanche photodetector for 1.06 microns

A photodetector consisting of a germanium avalanche photodiode, thermo-electric cooler, amplifier, and biasing circuit is described. The photodiode is of the graded guardring structure and has an active avalanche region 10 mils in diameter and a depletion width at breakdown at 5.0 µm. The photodiode is mounted on a single-stage thermoelectric cooler for the purpose of reducing the bulk leakage current. Also mounted on the cold surface is a temperature sensing reference diode used to control the biasing circuit and provide constant avalanche gain in the photodiode. The amplifier was designed to be driven with the photodiode current source and provide a voltage output. The amplifier has a 2.6 K ohm transimpedance over the range from 30 kHz to 30 MHz.