Epitaxially-Grown Germanium/Silicon Avalanche Photodiodes for Near Infrared Light Detection

Avalanche Photodiodes (APDs) are widely used in fiber-optic communications as well as imaging and sensing applications where high sensitivities are needed. Traditional InP-based APD receivers typically offer a 10 dB improvement in sensitivity up to 10 Gb/s when compared to standard p-i-n based detector counterparts. As the data rates increase, however, a limited gain-bandwidth product (~100GHz) results in degraded receiver sensitivity. An increasing amount of research is now focusing on alternative multiplication materials for APDs to overcome this limitation, and one of the most promising is silicon. The difficulty in realizing a silicon-based APD device at near infrared wavelengths is that a compatible absorbing material is difficult to find. Research on germanium-on-silicon p-i-n detectors has shown acceptable responsivity at wavelengths as long as 1550 nm, and this work extends the approach to the more complicated APD structure. We are reporting here a germanium-on-silicon Separate Absorption Charge and Multiplication (SACM) APD which operates at 1310 nm, with a responsivity of 0.55A/W at unity gain with long dark current densities. The measured gain bandwidth product of this device is much higher than that of a typical III-V APD. Other device performances, like reliability, sensitivity and thermal stability, will also be discussed in this talk. This basic demonstration of a new silicon photonic device is an important step towards practical APD devices operating at 40 Gb/s, as well as for new applications which require low cost, high volume receivers with high sensitivity such as imaging and sensing.