Analysis, circuit modeling, and optimization of mushroom waveguide photodetector (mushroom-WGPD)

The waveguide photodetector (WGPD) is considered a leading candidate to overcome the bandwidth/quantum-efficiency tradeoff in conventional photodetectors (PDs). To overcome the tradeoff between the capacitance and contact resistance, the mushroom-WGPD was proposed. A calibrated circuit model for mushroom-WGPD, including all parasitics, is presented so that a complete circuit simulation of the entire photoreceiver circuit with WGPD now becomes feasible. Both the behavior of the PD and its transfer function for the optical-to-electrical response that can be implemented in a circuit simulator are studied to explore the relationships between performance and design/ material parameters. The effects of the parasitics are also studied for different PD areas. The results from this circuit model of the PD have been compared with a published experimental work and a good agreement is obtained. In addition, the characteristics of mushroom-WGPD are studied for the case of an inductor added in series to the load resistor, and better performance is achieved in comparison to the case with no inductor. Based on the studies of different parameters for design and materials, optimization has been performed for the mushroom-WGPD. With this optimization, the optimal values of the thickness of the absorption layer and the added inductor to produce the highest bandwidth of the PD are obtained. These optimizations are performed for different areas of the PD and also for different load resistors, and they result in a significant improvement in the performance of the mushroom-WGPDs.