Self-Diffusion in Intrinsic and Extrinsic Silicon

TLDR

Silicon diffusion is assumed to occur via vacancies acting as acceptors, with n‑type doping increasing vacancy concentration through a mass‑action principle. Silicon self‑diffusion coefficients were determined by studying the diffusion of ³¹Si into silicon crystals of various degrees of perfection and doping. In intrinsic silicon, the self‑diffusion coefficient follows D = 9 000 exp(−5.13 eV/kT) cm²/s, and doping above intrinsic levels increases the coefficient; the data support a vacancy‑acceptor mechanism with a vacancy‑acceptor level about 0.34 eV below the conduction band.

Abstract

Silicon self-diffusion coefficients were determined by studying the diffusion of 31Si into silicon crystals of various degrees of perfection and doping. For intrinsic silicon, the self-diffusion coefficient can be represented by D=9,000 exp− (5.13 eV/kT) cm2/sec. Doping above intrinsic levels increases the diffusion coefficient. It it is assumed that silicon diffuses by means of vacancies, which act as acceptors, the influence of n-type doping can be attributed to the increase in total vacancy concentration caused by the excess electrons through a mass-action principle. It is concluded that the vacancy mechanism is the most probable for silicon diffusion. The data of this investigation would indicate that the vacancy-acceptor level is about 0.34 eV below the conduction band in silicon.