Hot-electron scattering at [formula omitted] Schottky interfaces measured by temperature dependent ballistic electron emission microscopy

Abstract

Ballistic electron emission microscopy (BEEM) measurements have been performed on n-type Au Si(100) interfaces as a function of STM tip bias, Au film thickness, and temperature. From these measurements, the attenuation length, λ a, of the BEEM electrons in the metal overlayer has been determined to be 133 ± 2 A ̊ at room temperature (RT) and 147 ± 6 A ̊ at 77 K for tip biases from −1.20 V to −0.92 V. The ratio of the zero thickness BEEM transmittances at 77 K to that at RT, I 0(77 K) I 0( RT) , was determined to be 1.79 ± 0.09. Within the experimental uncertainties of these measurements, no energy dependence of λ a or I 0(77 K) I 0( RT) was observed. The large increase in the BEEM transmittance and the relatively small increase in λ a at 77 K indicate that the primary temperature dependent scattering mode affecting BEEM electron transport is phonon absorption in the Si substrate. Images with large reductions in the BEEM current at topographic locations which have a large surface gradient have been obtained at RT. Our calculations, which assume that the probability of transmission across the interface is independent of the electron's transverse momentum, correlate well with the experimentally observed reductions. This result indicates that the BEEM electrons remain forward focused with very little broadening as they pass through the Au overlayer, and also implies that strong scattering must occur at the Au Si interface to explain the previously documented non-conservation of transverse momentum at Au Si interfaces.