Electron and Hole Focusing in ${\mathrm{CoSi}}_2/\mathrm{Si}\left(111\right)$ Observed by Ballistic Electron Emission Microscopy

In ballistic electron emission microscopy (BEEM) the propagation of hot carriers in thin metal films has long been treated using a free electron model. While the model explains many experimental findings, it cannot account for the lateral resolution observed for both electrons and holes on epitaxial ${\mathrm{CoSi}}_2/\mathrm{Si}\left(111\right)$, where interfacial point defects of atomic size appear as small as 1.3 nm, even below a 5.6 nm thick film. We present ab initio calculations explaining this high resolution in terms of conduction (valence) band structure focusing of electrons (holes), according to a recent Green's function approach to the BEEM process.