Giant variation in Schottky barrier height observed in the Co/Si system

In the literature, the Schottky barrier height (SBH) of Co/Si-related interfaces consistently has been found to lie close to 0.65 eV on n-type Si. This apparent insensitivity of the SBH to the phase of the silicide and crystallographic orientation of the substrate had previously been thought to support Fermi-level pinning mechanisms. We have, however, through careful control of molecular-beam epitaxy processing, grown single crystal type B CoSi2/Si(111) layers which exhibit a giant variation in SBH. CoSi2/Si(111) interfaces prepared by room temperature and high temperature processing exhibit n-type SBHs close to 0.7 eV and p-type SBHs close to 0.45 eV, in good agreement with the SBHs of other Co/Si-related interfaces. However, CoSi2/Si(111) interfaces prepared by special layered growth techniques (here labeled as ‘‘X’’ interfaces) exhibit n-type SBHs less than 0.3 eV and p-type SBHs over 0.7 eV—a difference of over 400 meV from the room temperature and high temperature interfaces. Other CoSi2/Si(111) interfaces prepared by different processing conditions also often exhibit low n-type SBHs and elevated p-type SBHs, but over a somewhat smaller range. Plan-view and high-resolution transmission electron microscopy clearly indicated the existence of structural defects or inhomogeneity in the low n-type SBH samples.