A new photodiode design for terahertz applications

As technology begins to play an important role in people's lives, developments in the field of telecommunication technologies are increasing rapidly. As a result of these developments, the increasing data usage rate brings the need for high-speed data usage. In order to achieve high data rates telecommunication systems containing high-speed electrical and optical components are required. This makes the importance of the generation of millimeter and terahertz waves more remarkable. Not only the generation of millimeter and terahertz waves, but also application areas such as wireless communication, imaging and spectroscopic sensing have gained importance thanks to these developments. With the importance of these potential applications in the THz range, the demand for devices with integrated antennas has increased day by day.UTC-PDs with integrated antennas and alternatives have been developed to compensate this demand. Promising UTC-PDs have been actively used recently in terms of being an alternative to expensive and bulk THz resources used in many areas such as millimeter and Terahertz (THz) signal (wave) production, communication, imaging and spectroscopy. In this thesis, a new design has been developed by modifying the geometric structure of UTC-PD, which has features such as room temperature usage, high operating speed and high operating frequency. In order to achieve higher bandwidth and higher output power, a geometric structure has been added between the absorber layers made of InGaAs material and the collector layers made of InP material. By making changes in the shape, material type and size of the added geometric structure, how much these changes affect the BW value is discussed. The most important feature of the design is that it performs successfully in 0 (zero) Volt, in other words zero-bias, applications and has approximately seven times more bandwidth than its equivalent. Also, in this thesis, optical and electrical simulations were performed using Lumerical software and the performances of UTC-PDs designed with this software are discussed. Optical simulations were performed in Lumerical FDTD and then the obtained optical generation rate was transferred to Lumerical Device software for electrical characterization. With these simulations, the optimization of the device structure of UTC-PD was investigated and the results were compared with the classical UTC-PD design, which is available and referenced in the literature. Also, the working principle of FDTD and Device submodule solvers are emphasized.