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

Ballistic Electron Emission Microscopy (BEEM) can be a versatile spect roscopic technique to investigate electron scattering phenomena during transport across metal-semiconductor (M-S) interfaces. Two examples f or obtaining numerical values of scattering parameters are discussed. In the first example the elastic and inelastic mean free paths of elec trons 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 insuffi cient to account for the spectral similarities for the two Si substrat e orientations, which implies that the scattering occurs at the M-S in terface and that transverse momentum is not conserved for electrons cr ossing the M-S interface. In the other example, the impact ionization quantum yield for electron-hole pair generation in Si is directly meas ured over an energy range from 1-7 eV by injection of electrons throug h pin holes in thin NiSi2 layers grown epitaxially on Si(111). The qua ntum 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 sho wn to exhibit structure that is interpreted as arising from density-of -states effects in the semiconductor.