Self-Diffusion in Intrinsic and Extrinsic Silicon

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.