Ballistic-electron-emission microscopy (BEEM) of Au and Mg films on n-
type GaP(110), with thicknesses as low as 12 angstrom, reveals strong
variations of spectral shape and magnitude of the BEEM current with me
tal-film thickness and surface gradient. Using Monte Carlo simulations
, the hot-electron transport between tip and semiconductor can be quan
titatively described, providing detailed information on tunneling, tra
nsport in the metal, transmission across the interface, and impact ion
ization in the semi-conductor.