PN Junctions: Equilibrium and Built-in Potential

This lecture describes the behavior of p-n junctions, starting with a historical overview of their discovery and development. The instructor explains the fundamental concepts of p-n junctions, including the built-in potential and the formation of depletion zones. The lecture covers the differences between p-n junctions and Schottky junctions, emphasizing the current flow characteristics and the implications of minority carrier injection. The formation of a p-n junction at equilibrium is detailed, illustrating how electrons and holes diffuse across the junction, leading to the establishment of a depletion region. The instructor discusses the electric field created by fixed charges in the depletion zone and how it balances the diffusion current. The built-in potential is derived from the energy levels of the materials involved, and the relationship between doping concentrations and built-in potential is explored. The lecture concludes with mathematical expressions for the depletion width and electric field, providing a comprehensive understanding of the equilibrium state of p-n junctions.