To realize quantum dots and quantum wires, so-called bottom-up techniques are often used in the fabrication. In such fabrication, it is essential to utilize appropriate substrates for the nanostructures. Since a Si(113) surface structure has a one-dimensional character as like as Si(100), and low surface energy comparable to Si(111) or Si(001), it is expected to a suitable substrate for the low-dimensional structure. Zhang et al. reported that Ge nanowires were grown on the Si(113) surface at high temperature [1]. However, the Ge nanowires were not uniform but random due to self-assembled growth. The purpose in this research is to control Ge nanostructures on the H/Si(113) surface by utilizing a surfactant effect of hydrogen. Here we demonstrate the surfactant effect of hydrogen for Ge growth on Si(113)-3x2 surface by using scanning tunneling microscopy (STM).
In order to investigate an effect of hydrogen termination, the Ge/Si(113) and Ge/H/Si(113) surface are examined by STM. Upon Ge deposition at room temperature, many bright spots are observed on both surfaces, but the size differs from each other; those on Ge/H/Si(113) surface was bigger than those on Ge/Si(113). That is because hydrogen terminated surface prolongs the diffusion length of Ge atoms. Then both surfaces are annealed at 300 °C. Flat 2D Ge islands are observed on both surfaces, but two different features are found. One is the shape of the Ge islands. Ge islands with hydrogen termination have an anisotropy. It is considered that the the hydrogen terminated surface prolongs the diffusion length of Ge atoms, and the Ge atoms forms in more stable shape. Another is the surface structure inside the Ge island. The 3x2 structure is formed without hydrogen, while the 2x2 structure is formed with hydrogen. The 2x2 structure is formed by hydrogen adsorption on Ge(113) surface, suggesting the possibility of site exchange of Ge and H [2]. Since the H-Ge bond is weak, hydrogen on Ge surface is partially desorbed at 300 °C[3]. Thus we conclude that there is no hydrogen in the boundary between Ge island and Si(113) surface.
[1] Z. Zhang et al., Surf. Sci. 497 (2002) 93. [2] A. Sakai et al., Appl. Phys. Lett. 64 (1994) 52. [3] L. Surnev et al., Surf. Sci. 138 (1984) 40.
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