Hot-carrier scattering in a metal: A ballistic-electron-emission microscopy investigation on PtSi

Ballistic-electron-emission microscopy (BEEM) has been used to study the PtSi/n-type Si(100) interface. Hot-electron transport has been investigated by measuring the ballistic-electron transmission as a function of position (BEEM imaging), energy (BEEM spectroscopy), and PtSi thickness (BEEM attenuation length). Hot-hole transport and electron-electron scattering have also been investigated as a function of these parameters. This study has been conducted on in situ fabricated PtSi/n-type Si(100) Schottky diodes in UHV with the silicide thickness ranging from 20 to 500 \AA{}. The PtSi films were granular and the BEEM transmissivity was found to be homogeneous on individual grains but strongly varying from one grain to another. We attempt to compare the absolute BEEM current level with existing models and find its limiting value for small silicide thicknesses to be close to 1 depending on the model considered, indicating efficient transmission due to strong forward focusing of the electrons in the base or enhancement due to multiple scattering within the grains. BEEM current as a function of silicide thickness shows a change from a rapid to a slower decrease at about 150 \AA{}. Reverse BEEM (RBEEM) attenuation lengths also show this qualitative behavior, but the attenuation with increasing PtSi thickness is distinctly weaker, indicating that BEEM and RBEEM intensities are differently influenced by the elastic and inelastic hot-carrier mean free paths. RBEEM spectra are found to be anomalous, indicating an anomalous distribution of the tunnel-injected hot holes in the base.