| With the ever-increasing bandwidth demands of the telecommunications industry, optical communications based on the "Fiber-to-the-home" architecture will soon become less of a novelty, and more of a necessity. A cost-effective way to enable such an architecture is to develop optoelectronics---photodetectors in particular---that can be monolithically integrated with silicon-based IC technologies. Ideally, these monolithically integrated photodetectors would also be Si devices. However, the energy bandgap cutoff wavelength of Si (lambda c ∼ 1100 nm) would prevent conventional Si photodetectors from being utilized for long-haul optical communications, at operating wavelengths around 1300 nm and 1550 nm. Alternatively, the photodetector can be fabricated of a semiconductor with strong absorptive characteristics at these wavelengths.; In this work we have designed and fabricated resonant cavity enhanced (RCE) germanium-on-silicon (Ge-on-Si) photodetectors, operating around the 1550 nm wavelength for applications in long-haul communications. Without sacrificing bandwidth, the spectral response of the Ge photodetector is enhanced by fabricating the Ge detector within a Fabry-Perot cavity, where the Ge active region is grown atop one or two-period silicon-on-insulator (SOI) substrates designed for maximum reflectivity (>80%) in the 1300 nm--1600 nm wavelength range. The responsivity of these Ge/SOI RCE photodetectors around 1550 nm is further enhanced by the increased absorption coefficient due to the tensile strain-induced bandgap narrowing effect within the Ge film. Detector bandwidths approaching 13 GHz and quantum efficiencies of nearly 60% have been measured around 1550 nm, which demonstrates the compatibility of these Ge/SOI photodetectors with 10 Gb/s data communication systems. In addition, the measured full-width at half-maximum (FWHM) of the spectral resonant peak is approximately 50 nm, encompassing the entire C-band wavelength range (1528 nm--1565 nm) used in long-haul optical communications, making these high-speed Ge detectors ideal for integration with WDM-based telecommunication systems. To the author's knowledge, these detectors are the fastest, most efficient Ge photodetectors fabricated directly on Si and optimized for 1550 nm operation. |
