Resonant cavity-enhanced photodiodes for optical communications.

摘要

Resonant cavity enhanced (RCE) photodiodes (PD) are promising candidates to overcome the bandwidth-efficiency product (BWE) limitation, for applications in optical communications and interconnects where high-speed, high-efficiency photodetection is desirable. In such structures, electrical properties of the photodetector remain mostly unchanged, however, presence of the microcavity causes wavelength selectivity and a drastic increase of the optical field at resonance wavelengths. Faster transit-time limited PDs with thinner absorption regions can maintain high efficiency due to the enhanced optical field. Combination of RCE detection scheme with Schottky- and p-i-n-type PDs allows for the fabrication of high-performance photodetectors with relatively simple material structures and fabrication processes.; This dissertation focuses on the design, simulation, optimization, fabrication, and characterization of RCE photodiodes with demonstrated devices based on the AlGaAs/GaAs/InGaAs material system. First, transit-time limited ultrafast RCE Schottky photodiodes with a semi-transparent Schottky contact, that also serves as the top cavity mirror are demonstrated. Also, experimental results are presented on ultrafast transit-time limited p-i-n photodiodes with nearly unity quantum efficiency, and a resonance wavelength that can be adjusted after fabrication. Furthermore, large active area RCE p-i-n photodiodes are demonstrated in order to complement high speed vertical cavity surface emitting lasers for the commercialization of 10 Gb/s and faster short-distance links. These devices have a thick depletion region, and they achieve higher bandwidth than transit-time limited devices that have the same size. The large active area makes these devices particularly suitable for applications employing multimode fiber.; The wavelength selectivity of RCE devices causes the effective quantum efficiency to degrade when the source wavelength does not match the cavity resonance-wavelength, or when the excitation has a broad spectral content. We also report our work on a novel cavity structure designed to yield a “flat-topped” spectral responsivity peak, in contrast to the “Lorentzian-like” response of the regular Fabry-Perot cavities employed in standard RCE devices. We employ a tunable spacer layer stacked on top of a regular RCE cavity in order to attain a nearly constant quantum efficiency over a 10–15 nm spectral region, eliminating the need to strictly match the resonant wavelength of the photodiode to the laser wavelength.