We have fabricated and characterized the first resonant cavity enhanced (RCE) germanium photodetectors on double silicon-on-insulator substrates (Ge/DSOI) for operation around the 1550 nm communication wavelength. The Ge layer is grown through a novel two-step UHV/CVD process, while the underlying double-SOI substrate is formed through an ion-cut process. Absorption measurements of an undoped Ge-on-Si (Ge/Si) structure reveal a red-shift of the Ge absorption edge in the NIR, due primarily to a strain-induced bandgap narrowing within the Ge film. By using the strained-Ge absorption coefficients extracted from the absorption measurements, in conjunction with the known properties of the DSOI substrate, we were able to design strained-Ge/DSOI photodetectors optimized for 1550 nm operation. We predict a quantum efficiency of 76% at 1550 nm for a Ge layer thickness of only 860 nm as a result of both strain-induced and resonant cavity enhancement, compared to 2.3% for the same unstrained Ge thickness in a single-pass configuration. We also estimate a transit-time limited bandwidth of 28 GHz. Although the fabricated Ge/DSOI photodetectors were not optimized for 1550 nm operation, we were able to demonstrate an over four-fold improvement in the quantum efficiency, compared to its single-pass counterpart.
High bandwidth short distance communications standards are being developed based on parallel optical interconnect fiber arrays to meet the needs of increasing data rates of inter-chip communication in modern computer architecture. To ensure that this standard becomes an attractive option for computer systems, low cost components must be implemented on both the transmitting and receiving end of the fibers. To meet this low cost requirement silicon based receiver circuits are the most viable option, however, manufacturing high speed, high efficiency silicon photodetectors presents a technical challenge. Resonant cavity enhanced (RCE) Si photodetectors have been shown to provide the required bandwidth-efficiency product and we have recently developed a method to reproduce them through commercially available fabrication techniques. In this work, commercially reproducible silicon wafers with a 90% reflectance buried distributed Bragg reflector (DBR) are used to create Si-RCE photodetector arrays for optical interconnects. The Si-RCE photodetectors have 40% quantum efficiency at 860 nm, a FWHM of 25 ps, and a 3dB bandwidth in excess of 10 GHz. We also demonstrate Si-RCE 12×1 photodetector arrays that have been fabricated and packaged with silicon based amplifiers to demonstrate the feasibility of a low cost monolithic silicon photoreceiver array.