HOT-ELECTRON TRANSPORT ACROSS METAL-SEMICONDUCTOR INTERFACES PROBED BY BALLISTIC-ELECTRON-EMISSION SPECTROSCOPY

Ballistic Electron Emission Microscopy (BEEM) can be a versatile spectroscopic technique to investigate electron scattering phenomena during transport across metal-semiconductor (M-S) interfaces. Two examples for obtaining numerical values of scattering parameters are discussed. In the first example the elastic and inelastic mean free paths of electrons in Pd are deduced over a 1-6 eV energy range from model fits of the attenuation of the collector current with film thickness for thin Pd films deposited on Si(lll) and Si(100) substrates. The results are used to demonstrate that electron scattering in the Ed film is insufficient to account for the spectral similarities for the two Si substrate orientations, which implies that the scattering occurs at the M-S interface and that transverse momentum is not conserved for electrons crossing the M-S interface. In the other example, the impact ionization quantum yield for electron-hole pair generation in Si is directly measured over an energy range from 1-7 eV by injection of electrons through pin holes in thin NiSi2 layers grown epitaxially on Si(111). The quantum yield is in excellent agreement with existing model calculations, which can be used to determine the primary component of the collector current for any energetic BEEM spectrum. The primary component is shown to exhibit structure that is interpreted as arising from density-of-states effects in the semiconductor.