We experimentally investigated step bunching induced by direct current on vicinal Si(111)''1ϫ1'' surfaces using scanning electron microscopy and atomic force microscopy. The scaling relation between the average step spacing l b and the number of steps N in a bunch, l b ϳN Ϫ␣ , was determined for four step-bunching temperature regimes above the 7ϫ7-''1ϫ1'' transition temperature. The step-bunching rate and scaling exponent differ between neighboring step-bunching regimes. The exponent ␣ is 0.7 for the two regimes where the step-down current induces step bunching ͑860-960 and 1210-1300°C͒, and 0.6 for the two regimes where the step-up current induces step bunching ͑1060-1190 and Ͼ1320°C͒. The number of single steps on terraces also differs in each of the four temperature regimes. For temperatures higher than 1280°C, the prefactor of the scaling relation increases, indicating an increase in step-step repulsion. The scaling exponents obtained agree reasonably well with those predicted by theoretical models. However, they give unrealistic values for the effective charges of adatoms for step-up-current-induced step bunching when the ''transparent'' step model is used.

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It is clarified that suboxides and interface traps are closely linked to threshold-voltage variation (ÁV th ) due to random telegraph noise (RTN) from an investigation of dependence of ÁV th on silicon-surface orientation: Si(100), (110), and (111). The amount of RTN traps increases with increasing amount of suboxides in the interfacial transition layer. With regard to the total amount of suboxides, the Si(110) surface orientation gives a larger amount than Si(100) and Si(111). Furthermore, we found that Si(110) has the potential to give fast RTNs with a larger ÁV th than Si(111). Accordingly, ÁV th for Si(110) is larger than those of Si(100) and Si(111). Attention should be paid to the possibility of the impact of RTN on Si(110) as the vertical plane of a three-dimensional device. #

We investigated sublimation of a heavily boron-doped Si͑111͒ surface in comparison with that of a normal Si͑111͒ surface in ultrahigh vacuum.Step spacing during step-flow sublimation is analyzed as a measure of the adatom diffusion length using Ͼ50-m-wide ͑111͒ planes created at the bottom of craters. On the heavily doped 1ϫ1 surface, the step spacing is smaller and the step-spacing transition ͑or ''incomplete surface melting'' transition͒ temperature is 60°higher than those on the normal 1ϫ1 surface. These results are interpreted in terms of the effect of boron at S 5 substitutional sites. Below 1100°C, the sublimation of heavily doped surface on the wide terrace turns into a two-dimensional vacancy-island nucleation mode from step-flow sublimation observed above 1100°C.

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