Charge and Current in Solids: The Classical Drift–Diffusion Model
The first chapter reviews the steady-state “drift–diffusion model” of charge transport in solids that electrical engineers typically learn in their first undergraduate solid state device course. Physics undergraduates are less exposed to this topic, but should be able to grasp the concept easily. This chapter introduces the basic drift–diffusion model, starting with two important assumptions about the nature of charge conduction in solids, and emphasizes the notion that this model is valid only as long as nonlocal transport effects are absent. It ends with an introduction to the so-called “equations of state” (also known as drift–diffusion equations) that are used to compute the carrier concentration and current density in a solid state device self-consistently. Only steady-state transport is considered.