Avalanche Photodiodes: Principles and Applications

This lecture covers the principles and applications of Avalanche Photodiodes (APDs). It begins with an explanation of the Avalanche process in semiconductors, detailing how electrons are accelerated by a strong electric field to generate electron-hole pairs. The instructor discusses the ionization coefficients for electrons and holes, emphasizing the significance of these coefficients in the operation of APDs. The lecture then explores the IV characteristics of photodiodes, particularly near the breakdown voltage, and the necessity of quenching mechanisms to manage gain. The structure of APDs is examined, including the use of guard rings to prevent breakdown at the boundaries. The instructor highlights the importance of optimizing gain and minimizing dark current, as well as the impact of temperature on breakdown voltage. Noise characteristics, including the excess noise factor, are also discussed, along with strategies for achieving optimal amplification. The lecture concludes with a summary of the performance metrics of APDs, including quantum efficiency, gain, and noise levels, and their compatibility with microelectronics.