Electric-current-induced step bunching on Si(111)

We experimentally investigated step bunching induced by direct current on vicinal Si(111)"1x1" 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)similar to N-alpha, was determined for four step-bunching temperature regimes above the 7x7-"1x1" transition temperature. The step-bunching rate and scaling exponent differ between neighboring step-bunching regimes. The exponent alpha is 0.7 for the two regimes where the step-down current induces step bunching (860-960 and 1210-1300 degrees C), and 0.6 for the two regimes where the step-up current induces step bunching (1060-1190 and >1320 degrees C). The number of single steps on terraces also differs in each of the four temperature regimes. For temperatures higher than 1280 degrees 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.