BALLISTIC-ELECTRON-EMISSION MICROSCOPY AT EPITAXIAL METAL SEMICONDUCTOR INTERFACES/

The invention of ballistic-electron-emission microscopy (BEEM) has mad e it possible to study hot electron transport across interfaces with a spatial resolution unparalleled before. In order to exploit the limit s of the method, we have applied BEEM experiments carried out in UHV a nd at 77 K to epitaxial CoSi2 films on silicon. CoSi2/Si may be consid ered as a model system for the metal/semiconductor interface, because its atomic structure can be rather well controlled experimentally and has been well characterized by transmission electron microscopy. This overview contains a discussion of the various processes leading to con trast in BEEM images for CoSi2/Si interfaces. The BEEM current may be affected by (a) the atomic surface structure or surface defects, both of which can change the tunneling distribution, (b) inelastic and elas tic scattering processes within the metal films and (c) interface scat tering or variations of the Schottky barrier height, resulting from in terfacial defects. Scattering processes will be shown to be dominant i n the case of CoSi2/Si(111) interfaces, since the Schottky barrier hei ght is not measurably affected by interfacial dislocations and other d efects. Here, the ultimate resolution limits of the BEEM technique hav e been reached, in the sense that individual point defects can be reso lved. The CoSi2/Si(100) interface represents a more complicated case, where extended defects lead to significant barrier lowering, whereas i nterface scattering is obscured by the strong modification of the tunn eling distribution by surface reconstructions.