The 28Si314N4/natSi315N4/28Si314N4 isotope heterostructures produced by reactive magnetron sputtering and subsequent in situ crystallization, in combination with secondary ion mass spectrometry, were used to study self-diffusion. The Si and N diffusivities were measured in polycrystalline α-Si3N4 by isotope interdiffusion at 1200 to 1700C. The diffusivities of the 2 elements coincided within error limits over the whole temperature range investigated and obeyed an Arrhenius law:

D (m2/s) = 6 x 10-6 exp[-5.0(eV)/kT]

Isotopic heterostructures which were composed of a phase mixture of α-Si3N4 and β-Si3N4 exhibited diffusivities which were not significantly lower and which had nearly the same activation enthalpy (4.9eV); indicating similar diffusivities in both polymorphic phases of silicon nitride. The entropy of self-diffusion was calculated to be about 2k. This hinted that diffusion was mediated by localized point defects, in contrast to the extended point defects usually found in semiconductors such as Si, Ge and GaAs.

Simultaneous Diffusion of Si and N in Silicon Nitride. H.Schmidt: Physical Review B, 2006, 74[4], 045203 (7pp)