The Pedagogy of the p-n Junction: Diffusion or Drift?

Abstract

The majority of current textbooks on device physics at the undergraduate level derive the diode equation based on the diffusion of injected minority carriers. Generally the drift of the majority carriers, or the extent of drift, is not discussed and the importance of drift in the presence of a field in the neutral regions is almost totally ignored. The assumptions of zero field in the neutral regions and conduction by minority carrier diffusion lead to a number of pedagogical problems and paradoxes for the student. The purpose of this paper is to address the pedagogical problems and paradoxes apparent in the current treatment of conduction in the pn junction as it appears in the majority of texts.