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

我们在一个用于测量电性能的UHV室中安装了一个新的样品保持器，连接到去年开发的小型MBE-RHEED系统。该系统能够对（1）表面结构和化学成分、（2）表面电导率、（3）霍尔效应、（4）场效应和（5）光电导性进行现场分析和测量。我们继续研究了表面微观原子排列/电子态与宏观电学性质之间的关系，首先，通过表面场效应测量，明确了Si（111）-7 × 7清洁表面是金属表面，Si（111）<square root>-3 × <square root>3-Ag表面是半导体表面。通过将氧气暴露在7 × 7清洁表面上，由表面氧化引起的从金属表面到半导体表面的逐渐变化被揭示为场效应的变化。单色光照明的光电导也被发现是至关重要的依赖于表面的超结构。通过在Si（111）-<square root>3 × <square root>3-Ag表面上沉积单层Ag，发现了<square root>21 × <square root>21和6 × 6等新的超结构，表面电导率随这些超结构的形成而发生明显的变化，从而证实了表面空间电荷层中载流子浓度随表面结构和电子态而变化的表面电导率依赖于结构的假设。像这样关于原子尺度结构和电学性质之间的相关性的研究有望导致器件应用。

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.