Planar p- n junction germanium photodiodes for use at microwave modulation frequencies

Abstract

A small-area (∼ 5 × 10 −7 cm 2), near-planar, diffused p- n junction germanium photodiode has been fabricated for use at an optical wavelength near 1 μm. The fabrication of the diode is described, and its performance as a demodulator at microwave frequencies is discussed. The diode was evaluated at an optical wavelength of 1.15 μm and a modulation frequency of 4.18 GHz, where the detected signal power and the shot-noise power were measured. For an optical power input of 0.8 mW, an intensity modulation index of 0.24 and an effective bandwidth of 3 MHz, the signal-to-shot-noise ratio at the optimum bias point was about 64 dB.