MEASUREMENT OF SURFACE-STATE CONDUCTANCE USING STM POINT CONTACTS

It is shown that the STM can be used to measure the electrical conduct ance of surface states via tip-sample point contacts. In particular, t he electrical conductance of the Si(111)7 x 7 surface is discussed. Th e experimental results indicate that the conductance consists of two c omponents. One involves transport through the Schottky barrier formed at the interface while the ether is sensitive to surface properties. T he surface sensitive conductance depends on the amount of adsorbed oxy gen and the step structure surrounding the contact area, but does not depend on bulk properties such as the type of dopant of the semiconduc tor substrate. These findings cannot be explained by models of convent ional surface conductance due to a space charge layer formation. The c onductance thus should he closely related with surface slate conductan ce of the Si(111)7 x 7 structure.