Abstract
Self-diffusion of carbon (12C and 13C) and silicon (28Si and 30Si) in 4H silicon carbide has been investigated by utilizing a structure containing an isotope purified 4H-28Si12C epitaxial layer grown on an n-type (0001) 4H-SiC substrate, and finally covered by a carbon capping layer (C-cap). The 13C and 30Si isotope profiles were monitored using secondary ion mass spectrometry (SIMS) following successive heat treatments performed at 2300–2450∘C in Ar atmosphere using an inductively heated furnace. The 30Si profiles show little redistribution within the studied temperature range, with the extracted diffusion lengths for Si being within the error bar for surface roughening during annealing, as determined by profilometer measurements. On the other hand, a significant diffusion of 13C was observed into the isotope purified layer from both the substrate and the C-cap. A diffusivity of D=8.3×106e−10.4/kBT cm2/s for 13C was extracted, in contrast to previous findings that yielded lower both pre-factors and activation energies for C self-diffusion in SiC. The discrepancy between the present measurements and previous theoretical and experimental works is ascribed to the presence of the C-cap, which is responsible for continuous injection of C interstitials during annealing, and thereby suppressing the vacancy mediated diffusion.
Highlights
Self-diffusion of atomic species is a fundamental process in semiconductors, and vital for understanding both the thermally induced melting process and diffusion of impurities which are introduced during growth and doping
By comparing the present and previous experiments, we find that the mechanism for self-diffusion is significantly affected by the presence of the carbon capping layer (C-cap)
Please note that the secondary ion mass spectrometry (SIMS) signal in the C-cap layer has not been normalized, and that no correction was performed for the lower carbon ionization yield in the pure carbon (C-cap) matrix relative to the 4H-SiC matrix
Summary
Self-diffusion of atomic species is a fundamental process in semiconductors, and vital for understanding both the thermally induced melting process and diffusion of impurities which are introduced during growth and doping. Carbon self-diffusion was predicted to have an energy barrier of EA = 7.4 eV in intrinsic. 6H-SiC [2] using 14 C radio-tracer techniques, with silicon diffusivities being more than 2 orders of magnitude lower than those for carbon [2,3]. Experiments on the 4H polytype yielded activation energies for 13 C self-diffusion of 8.5 eV [5]. [6] suggested that Si and C diffusivities are of comparable magnitudes, in contrast to that of Hong et al [2] and Hon et al [3]. The experiments provide hints as to the mediating species for C and Si self-diffusion in SiC, they are not conclusive, with Ref. [5] predicting vacancy-mediated C self-diffusion and Ref.
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