Accurate ab initio determination of ballistic electron emission spectroscopy: Application to Au/Ge

Ab initio nonequilibrium Keldysh formalism based on an N-order renormalization technique is used to compute I(V) ballistic electron emission microscopy characteristics at the Au/Ge(001) interface. Such a formalism quantitatively reproduces precise experimental measurements under ultrahigh vacuum and low-temperature conditions. At T=0 K, the ballistic current follows the law (V-VSB)2.1, VSB being the Schottky barrier. At T>0 K, temperature effects become significant near the onset and must be taken into account to identify an accurate value for VSB from a best-fit procedure. We find two values for VSB, 0.67 and 0.75 eV, which we associate with two different atomic registries at the interface.