Waveguide-integrated germanium photodetector design and optimization for sensing and telecom applications

With the developing technology, electronics has become unable to reach the high speeds and high efficiency required by new applications. Silicon photonic integrated circuit technology has been proposed to solve this problem. As part of silicon photonics, photodetectors are one of the cornerstones of silicon photonics technology. In the early years of silicon photonics, photodetectors were mainly designed for fiber optical telecom applications. Silicon photonics and photodetectors can be used in many other applications such as sensors, cameras, LIDAR, and photovoltaics. In this thesis, geometric optimization of waveguide integrated Ge VPIN photodetectors has been studied. Two different photodetector designs were developed with simulations for two different application types. The first design is a photodetector having ultra-high responsivity (1.17\ AW^{-1}) and ultra-low noise (\ 48.38\ nW NEP) at 0V bias operation that can be used in optical time domain reflectometer sensor applications. This photodetector adopts a 500\ nm-thick, 2.5\ \mu m-wide and 100\ \mu m-long Ge layer. It has a wide dynamic range (55.76\ dB) and could allow for high contrast readout in long-haul OTDR applications. The second photodetector adopts a 300\ nm-thick, 2\ \mu m-wide, and 10\ \mu m-long Ge layer showing a 0.972 AW^{-1} responsivity with a bandwidth of 84.26 GHz at -2V bias. Due to having ultra-high bandwidth, high responsivity, and low dark current (8.67\ nA), it could be suitable for state-of-the-art telecom applications such as the 400G-BASE-DR4 ethernet standard. These designs and our design guidelines could pave the way for optimized silicon waveguide-integrated germanium photodetectors with superior and refined performance in sensing, telecom, and imaging applications.