Numerical and Multiphysics simulation(Electronic and Electromagnetic)and optimization of waveguide photodetectors for Silicon Photonics integrated circuits

photodetectors are the essential device in the front end of an optical receiver that converts the incoming optical signal into an electrical signal in communication systems, known as O/E convertor. Semiconductor photodetectors, commonly referred to as photodiodes, are the prevalent types of photodetectors used in optical communication systems because of their small size, fast detection speed, and high detection efficiency. Similar to the structures of laser diodes, photodiodes are also based on the PN junctions. However, unlike a laser diode in which the PN junction is forward biased, the PN junction of a photodetector is reversely biased so that only a very small reverse saturation current flows through the diode without an input optical signal. Although the basic structure of a photodiode can be a simple PN junction, practical photodiodes can have various device structures to enhance quantum efficiency. For example, the popular PIN structure has an intrinsic layer sandwiched between the p- and n-type layers, and that is why a semiconductor photodetector is also known as a PIN diode. An avalanche photodiode (APD) is another type of often used detector that can introduce significant photon amplification through avalanche gain when the bias voltage is high enough. The need of detectors with higher speed is more obvious these days since a great advancement has been made in SiPh technologies and communication systems, To this end, many structures have been proposed for this goal, one of the many quantities that makes those devices different from each other is the position of the Si waveguide since we have some major drawbacks in different coupling methods such as having a large impedance mismatch between the silicon bus waveguide and Ge-on-Si structure and having a significant absorption of the incident light in the first few micrometers of the detector. The mentioned issues can lead to some major problems such as saturation in DC and compression in RF current generation under high power illumination, in another word, the cut-off frequency and bandwidth of the device deteriorate as the power of the incident light increases and this makes the PD to have a slow response. This thesis is dedicated to tackle the above hassles and address the challenges we face during designing the PDs, many solutions have been proposed by different research groups, one of them is to re-engineer the device with respect to the structure and position of the wave-guide (coupler) so we can reach more effective illumination of the germanium region of a single waveguide-coupled photodetector approach. This can be done by using Si side coupled waveguide and this results in transferring the light from the silicon waveguide into the detector gradually and effectively and will eliminate the modal interference that causes the absorption peak and lead to having a uniform absorption throughout the device. Another advantage of the approach which can be addressed is that this method makes the device more broadband and it has a better response in high power il-luminations in comparison to its counterparts. This method initially introduced by it research group of electronic 2017. This thesis is comprised of four chapters each address a challenge in designing the Ge-on-Si PiN waveguide photodetectors and their optimizations.