Color Sensors: Photodiode Position and Performance

This lecture discusses the influence of photodiode positioning on the spectral characteristics of color sensors. It begins by analyzing two wavelengths, blue and red, and their interaction with silicon. The instructor explains how the absorption coefficient of silicon affects light penetration, noting that blue light is absorbed near the surface while red light penetrates deeper. The lecture details the calculation of electron-hole pair generation based on light intensity and absorption, leading to discussions on photocurrent, responsivity, and quantum efficiency. The instructor illustrates how the position of the photodiode impacts its sensitivity to different wavelengths, with surface-mounted detectors being more responsive to blue light and deeper detectors being more effective for red light. The lecture concludes with an overview of a color sensor designed for cameras, highlighting the responsivity and quantum efficiency across the spectrum for both types of detectors. This comprehensive analysis provides insights into the design and functionality of optical detection systems.