Evidence for a large correlation length in surface roughness of ${\mathrm{CoSi}}_2$/Si

We present data on parallel electric transport in thin ${\mathrm{CoSi}}_2$/Si and Si/${\mathrm{CoSi}}_2$/Si layers from 50 down to 12 Å. The data show that the surface roughness must be described by a large correlation length ξ, i.e., much larger than ${\mathit{k}}_{\mathit{F}}^{\mathrm{-}1}$, where ${\mathit{k}}_{\mathit{F}}$ is the Fermi wave vector equal to 1 Å ${}_{}{}^{\mathrm{-}1}{}_{}{}^{}$ in ${\mathrm{CoSi}}_2$. This is true whatever the model (Gaussian or exponential) used for the autocorrelation function. For ${\mathrm{CoSi}}_2$/Si and Si/${\mathrm{CoSi}}_2$/Si films we obtain, respectively, ξ=5 and 8 Å in the Gaussian model and 10 and 12 Å in the exponential one.