Electron Scattering in Dilute SiC
The introduction of carbon into SiGe/Ge heterostructures is of technological interest due the dual effects of strain-compensation in the Si(1-y)Ge(y) layers  and suppression of the out-diffusion of p-type acceptors, in particular boron  and indium , during wafer fabrication. The transport properties of the material are then expected to be modified by two competing processes. On the one hand, in silicon, the induced strain will lift the degeneracy of the Δ valleys allowing the conduction electrons to see a smaller effective mass. On the other hand, the substitutional carbon is likely to introduce alloy scattering, acting to reduce the mobility.
A method is developed to obtain the alloy scattering matrix from density functional theory calculations based on a similar approach to previous first principles work [4, 5]. It is found that the scattering matrix can be decomposed into two additive components: a chemical part due to pseudopotential substitution and a part due to ionic relaxation that we attribute to the deformation potential. The method is then applied to find the intravalley and intervalley electron scattering matrix for substitutional carbon in silicon. It is found that intravalley scattering is the dominant process. However, we find that alloy scattering due to substitutional carbon is too weak to reduce the mobility to the degree observed in strained Si(1-x)C(x) layers  and therefore support the conclusion that this degradation is due to interstitial carbon complexes.
The figure shows the experimental mobilities for strained Si(1-x)C(x) and the calculated alloy scattering-limited mobilities. The mobility for unstrained Si is shown as clear circles and clear triangles. For 0.4% C, the work of Eberl et al  (filled diamonds) shows an increase in the mobility. The calculated alloy scattering-limited mobility for this concentration is shown in comparison (solid line). The work of Osten et al  shows a degradation of the mobility, even for lower C concentrations. Here we show their results for 0.31% (filled circles) and 0.57% (filled squares). For comparison, the calculated alloy scattering-limited mobility for 0.31% is also shown (dashed line).
First principles calculations of the scattering cross section of substitutional carbon in silicon
M P Vaughan and S Fahy, J. Phys.: Conf. Ser. 242, 012003, (2010)
TMCS, York 2010
14th Irish Nanoscale Simulators Meeting, Cork 2011
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