We have used reflection electron microscopy to study (1) the drift velocity of positive monolayer islands on Si(111) under near equilibrium conditions and direct current (dc) heating and (2) the difference between the velocity of monoatomic steps heated by direct current in the step-up and step-down direction under free sublimation. Our results obtained at around $1200°\mathrm{C}$ show that the islands move in the opposite direction of the dc and the step velocity for ascending steps with respect to the dc direction is smaller than the velocity for opposite steps with the same interstep distance. These two experimental results are a clear qualitative prove of the existence of an Ehrlich-Schwoebel effect on Si(111). We analyze the experimental results for the step dynamics within a modified Burton, Cabrera, and Frank model. We find that a quantitative agreement between the model and the experimental results needs an enhanced effect of the electric field on the diffusion species.

• Received 24 July 2001

DOI:https://doi.org/10.1103/PhysRevB.65.075409