Diffusion and Defects in Elementary and Compound Semiconductors
Radiation enhanced diffusion in silicon
Utilising isotopically controlled 28Si/natSi multilayer structures we performed
experiments on silicon self-diffusion under proton irradiation. For these experiments we used the
5 MeV Van der Graaf accelerator of the Institute of Physics and Astronomy at the University of
Aarhus (Denmark). The concentrations of vacancies and self-interstitials obtained during proton irradiation
exceed the concentration of the native defects under thermal equilibrium conditions. Secondary ion mass
spectrometry (SIMS) was performed to determine the diffusion of 30Si across the
28Si/natSi interfaces which are located at various distances from the surface. The
SIMS analysis reveals enhanced Si diffusion with increasing depth. This enhancement is directly
correlated to the native point defect concentrations established by irradiation. The magnitude of the
enhancement reveals that the concentration of vacancies in thermal equilibrium is significantly higher than the
thermal equilibrium concentration of self-interstitials. Detailed modelling of the radiation enhanced diffusion,
which is based on numerical solutions of the underlying kinetic equations, enables us to solve the
long-standing mystery of the formation and migration properties of vacancies in silicon at high temperatures.
