Atomic-scale structure control of silicon-metal interface and its macroscopic functional properties

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We have installed a new sample holder in a UHV chamber for measurements of electrical properties, connected to a small MBE-RHEED system developed in the last year. This system enables in-situ analyzes and measurements of (1) surface structures and chemical compositions, (2) surface conductivity, (3) Hall effect, (4) field effect, and (5) photoconductivity. We continued the studies on the correlation between the microscopic atomic arrangements/electronic states of surfaces and their macroscopic electrical properties.First of all, from the surface field effect measurements, it is clarified that the Si (111) -7x7 clean surface is metallic and the Si (111) -<square root>3x<square root>3-Ag surface is semiconducting. By exposing oxygen gas onto the 7x7 clean surface, the gradual change form metallic surface to semiconducting one caused by surface oxidation is revealed as a change in field effect. Photoconduction with monochromatic light illuminations is also found to be crucially dependent on the surface superstructures. By depositing Ag of about one monolayr on the Si (111) -<square root>3x<square root>3-Ag surface maintained at 150K,new superstructures such as <square root>21x<square root>21 and 6x6 are found. And the surface conductivity remarkbly changed with the formations of these structures.From the experiments above mentioned, we could proved our assumption on the structure-dependent surface conductivity that the carrier concentrations in the surface space-charge layr changes depending upon the surface structures and electronic states. Studies like this on the correlation between the atomic-scale structures and electrical properties are expected to lead to device applications.