A novel structure of unitraveling carrier photodiodes (UTC-PDs) with high-speed, high-efficiency, and wavelength selective characteristics is presented. Including the essential features of resonant cavity enhanced photodiodes and waveguide photodiodes, we propose microring-based UTC-PDs (MR-UTC-PDs) which can achieve excellent high-speed and high-quantum efficiency characteristics simultaneously. The photoresponse of MR-UTC-PDs is based on a drift-diffusion model. Photoresponse characteristics of MR-UTC-PDs, which depend on device parameters and coupling conditions, are investigated and it is shown that the overcoupled structures are suitable for high-speed photodetection. The important features of the device, such as efficiency enhancement and wavelength selectivity are discussed and the trade-off between 3 dB bandwidth and efficiency is solved for nanoscaled absorption layer. Additionally, the bandwidth-efficiency product in the order of several hundreds gigahertz can be obtained even with low photoabsorption layers.
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