Measurement of surface state conductance using STM point contacts

Abstract

It is shown that the STM can be used to measure the electrical conductance of surface states via tip-sample point contacts. In particular, the electrical conductance of the Si(111)7 × 7 surface is discussed. The experimental results indicate that the conductance consists of two components. One involves transport through the Schottky barrier formed at the interface while the other is sensitive to surface properties. The surface sensitive conductance depends on the amount of adsorbed oxygen and the step structure surrounding the contact area, but does not depend on bulk properties such as the type of dopant of the semiconductor substrate. These findings cannot be explained by models of conventional surface conductance due to a space charge layer formation. The conductance thus should be closely related with surface state conductance of the Si(111)7 × 7 structure.