DC current effects on step array on vicinal Si surfaces and structure of high index Si surfaces

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Studies of structures of high index Si surfaces (a Si (5 5 12) surface and a Si (hhm) m/h=1.4-1.5 surface) were performed by using STM.Atomic models of the surface structure of these two surfaces were proposed taking into account of the STM images. The STM observations showed us that the (5 5 12) surfaces has 2*1 structure and the proposed structure model includes adatoms at the bright point in the STM images. Our previous REM studies showed us that the (hhm) structure is modulated structure and unit length along [mm2h] direction varies on the sufaces. The (hhm) structure is constructed by three small (111) terraces. The STM images of the small (111) terraces on the (hhm) surface are similar to those of the part of the Si (111) DAS structure and sizes of these three terraces are smaller than that of submit of the 7*7 structure of the (111) surfaces. The modulated structures are formed by changing width of each terraces. Thus, the modulated structure of the (hhm) structure is considered to be related to step bunching on the (111) surfaces. It was well known that the step structure reversibly transforms between step bunching and regular array of the steps. For better understanding of DC heating effects step bunching speeds were measured at various temperature and at various heating current by using an indirect heating specimen holder. It was found that dispersions of the terrace widths that show the degree of the step bunching increase linearly with time. We measured the bunching speed from the time dependence of the dispersions of the terrace widths. Growth of the dispersions at high current is faster than those at low current. It was also found that the step bunching speed increases with temperature between 840ﾟC and 910ﾟC and it decreases with average terrace width.