Electrical Modelling of High-speed Photodiodes

Abstract

Photodiodes are pivotal components in optoelectronic systems, converting light into electrical signals with applications spanning from telecommunications to medical devices. This thesis presents a comprehensive study on the electrical modeling of photodiodes, aiming to enhance their performance when integrated with transimpedance amplifiers (TIAs) in receivers. The research commences with an in-depth analysis of the physical principles governing photodiode operation. Various modeling techniques are examined, with a particular emphasis on equivalent circuit models that accurately represent the photodiode’s behavior under different biasing conditions. The model is constructed based on experimentally measured frequency response and single-port reflection of the device. Devices with varying optical apertures and different biasing pads are analyzed. It is observed that the ground-signal pad geometry introduces additional inductance to the electrical model, enhancing the frequency response by up to 5 GHz compared to the ground-signal-ground pads. The study also compares the performance of several photodiode prototypes, varying parameters such as absorber thickness and extraction layer thickness. Furthermore, the combined response of the photodiode and TIA was simulated. The results indicate that the frequency response, when combined with the TIA for ground-signal pad geometry, remains flat up to 35 GHz, outperforming the ground-signal-ground design. This ensures that the receiver is free from frequency-dependent distortions. The responsivity and dark current characteristics of the devices are also measured. In conclusion, the electrical modeling techniques presented in this thesis offer a powerful framework for understanding the photodiode performance with TIA in optical recievers. The findings contribute to the advancement of optoelectronic technology, paving the way for more efficient and versatile applications in various fields such as data centers and other high-speed communication systems.