Photodiodes: Design and Optimization of Heterojunctions

This lecture discusses the design and optimization of photodiodes, focusing on the working principles and the importance of the depletion region. The instructor explains the three regions where electron-hole pairs can be collected: the diffusion regions on the P and N sides, and the depletion region in the center. Emphasis is placed on the need to enhance light absorption in the depletion region to improve photodiode performance. The lecture introduces the concept of a P-I-N junction, highlighting how increasing the size of the intrinsic region can lead to a stronger electric field, facilitating quicker collection of charge carriers. The instructor also discusses the use of different materials for the P, N, and intrinsic regions to minimize absorption losses and maximize efficiency. The lecture concludes with an analysis of quantum efficiency in relation to the materials used, particularly indium-gallium arsenide and gallium arsenide, and their impact on photodiode performance at various wavelengths.