Lecture
This lecture discusses the design and limitations of high-speed photodiodes, focusing on bandwidth constraints. It begins with an overview of the RC time constant, which is influenced by the diode's capacitance and resistance. The instructor explains the drift time through the depletion layer, emphasizing its dependence on the width of the depletion region. The diffusion of carriers in the PN junction is also addressed, highlighting the importance of using hetero PIN junctions to minimize absorption in diffusion regions. The lecture further explores the optimization of the intrinsic layer width to balance drift time and capacitance. The concept of waveguide photodiodes is introduced, showcasing how they can enhance absorption while maintaining a small width. The discussion extends to traveling wave photodiodes, which align the electrical and optical signals to overcome bandwidth limitations. The lecture concludes with practical considerations regarding impedance matching and its impact on signal integrity and bandwidth performance.