High-Speed Photodetectors and Receivers for Long-Haul Communication Systems

For long-haul fiber-optic communication systems, the development of efficient high-speed photodiodes and transistors compatible with each other is essential for monolithic integration. This dissertation details the design, fabrication, and characterization of InP-based photodiodes and HEMTs suitable for operating in the low-loss low-dispersion window of the optical fibers used in telecommunication systems. High-speed photodiodes with bandwidths as high 60 GHz and a responsivity of 0.3 A/W have been achieved using a dual-depletion design. To achieve better bandwidth-efficiency products, a novel drift-enhanced dual-absorption design was developed and demonstrated. Diodes fabricated with this design achieved bandwidths of 30 GHz with a responsivity of 0.82 A/W. Numerical and analytical analyses have been performed to understand the bandwidth limitations of these photodiodes to optimize their performance. Ultrafast HEMTs with cutoff frequencies over 200 GHz have been demonstrated using a 0.1 ?m T-gate process. Non-linear models suitable for use in circuit simulators were developed to accurately describe the performance of both the photodiodes and the HEMTs. Using these models, a single-ended four-stage transimpedance amplifier has been designed exhibiting a gain of 4.5 k? with a 50 GHz bandwidth. A novel differential transimpedance amplifier utilizing the unique design of dual-absorption photodiodes was proposed and demonstrated. This design is shown to achieve improved responsivity-bandwidth product compared to conventional designs.