Semiconductor Theory: Low Injection Approximation

This lecture covers the fundamental equations that describe semiconductor components under low injection conditions. It begins with a review of the three basic equations: Poisson's equation, and the continuity equations for electrons and holes. The instructor explains how these equations can be solved to find unknowns such as electric potential and carrier concentrations. The focus then shifts to the low injection approximation, where the concentration of majority carriers remains at equilibrium while minority carriers are significantly perturbed. The lecture details the continuity equations for minority carriers, emphasizing the net thermal recombination rate and its dependence on the lifetime of minority carriers. The instructor illustrates the concept of diffusion length and discusses experiments to measure minority carrier lifetime, including photoconductivity experiments. The Haynes-Shockley experiment is also introduced, demonstrating the behavior of minority carriers in a semiconductor under an electric field. The lecture concludes with a summary of the theoretical foundations necessary for practical applications in diodes and transistors.