We present a comprehensive investigation of dopant diffusion in silicon under equilibrium and nonequilibrium concentrations of intrinsic point defects. Using first-principles total-energy calculations combined with available experimental data, we seek to resolve a series of outstanding controversies regarding the diffusion mechanisms of B, P, As, and Sb in silicon. We find that, under equilibrium conditions, vacancies and interstitials mediate the diffusion of all dopants with comparable activation energies, except Sb, for which the interstitial component has a high activation energy. Under nonequilibrium conditions, e.g., under injection of excess point defects, we derive the relevant expressions for the activation energy for a variety of possible diffusion mechanisms and injection conditions. Under oxidation, the calculated values are in excellent agreement with the available experimental data. In addition, theory and experiment suggest that the concerted exchange mechanism, involving no point defects, plays only a minor role in dopant diffusion. © 1989 The American Physical Society.