Controlled fabrication of quantum dots and nanostructures by controlling high-index surfaces of group IV semiconductors

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Controlling the size and shape of Ge quantum dots formed on the Si(001) substrate is great technological importance for their application. Surfactant effects on this system are regarded as one of promising methods to achieve the controlled growth of quantum dots. Among them, hydrogen-adsorption effect, which has been studied intensively these days, is known to suppress the formation of the "hut" structure formed upon four Ge{105} facets. We have investigated the structure of the Ge(105) surface formed on a Si(105) substrate using STM and AFM to establish the surface structure. The strained structure model for this surface, which we have proposed based on comparison between experimental and theoretical STM images, is confirmed by an atomically resolved AFM image. Hydrogen adsorption on this system has been studied using STM, to show the role of surface strain on the stability of the Ge(105) under hydrogen-adsorption condition. The STM images of the Ge(105) surfaces with adsorbed hydrogen atoms are understood based on the newly-established atomic structure of Ge(105). We observed the stability of hydrogen-covered Ge(105) surface with different amounts of Ge to find that the hydrogen adsorption on the Ge(105) surfaces with Ge coverages of less than 1.4 ML makes the surface remarkably unstable and results in the roughening of the surface. This fact indicates that the hydrogen adsorption on Ge(105) increases the surface strain by arresting the strain-relief mechanism via the formation of sp^2-hybridized dimers on the Ge(105) surface. Thus, the formation of Ge(105) will be unfavorable and suppressed under the existence of adsorbed hydrogen.