Tracer diffusion coefficients, and their dependence upon temperature, pressure and isotope mass, were determined for B and Ga as impurities in (111)-oriented silicon single crystals. The diffusivities were evaluated by using stable isotopes and secondary ion mass spectrometry. The values, measured between 850 and 1150C, were found to be described by:

DB–Si(cm2/s) = 3.37 x 101exp[-3.93(eV)/kT]

DGa–Si(cm2/s) = 6.5 x 100exp[-3.59(eV)/kT]

The mean values of the isotope effects, between 850 and 1150C, were EB–Si = 0.39 and EGa–Si = 0.51. The relative activation volumes were (V*/Ω)B–Si = 0.27 (mean for 1050 to 1230C) and (V*/Ω)Ga–Si = -0.7 (at 1053C). These results, and their comparison with earlier data on diffusion in elemental semiconductors, suggested a predominantly interstitial diffusion mode for group-III impurities in Si. The behaviour was not entirely compatible with a conventional interstitialcy mechanism, and instead suggested a kick-out mechanism.

Atomic Transport of Trivalent Impurities in Silicon: Diffusion, Isotope Effects, Activation Volumes. U.Södervall, M.Friesel, A.Lodding: Journal of the Chemical Society - Faraday Transactions, 1990, 86, 1293-8