Kelvin Probes: Measuring Built-in Voltage in Semiconductors

This lecture discusses the built-in voltage in semiconductor junctions, particularly focusing on P-N junctions. The instructor begins by correcting a problem related to a capacitor formed by P-silicon and N-silicon plates. The lecture covers the equilibrium state of the energy bands when the plates touch and the implications of introducing a gap between them. The instructor explains how the built-in voltage is affected by the distance between the plates and how variations in this distance can generate a current. The concept of the Kelvin probe is introduced, detailing its historical context and its application in measuring surface potential. The lecture also describes the setup of Kelvin probe force microscopy, emphasizing how it can be used to measure the built-in voltage by observing the vibrations of a cantilever in response to charge variations. The practical applications of this technique in measuring solar cells and semiconductor structures are also highlighted, providing a comprehensive understanding of the topic.