Drift of two-dimensional vacancy islands on the Si(100) surface under electromigration conditions

The paper presents an experimental study of morphological changes of the Si(100) surface under electromigration conditions that was carried out using the in situ method involving ultrahigh vacuum reflection electron microscopy. The study aimsto determine the temperature dependence of the effective electric charge of an adsorbed atom on the Si(100) surface. Asystem of concentric two-dimensional vacancy islandswas formed on the surface of Si(100) samplesby lowenergy argon ion sputtering and subsequent high-temperature annealing. Quasi-equilibrium conditions were created on the sample surface by compensating the sublimating flow from the surface from an external silicon source. The video images of the drift of vacancy islands were recorded under the conditions of electromigration with the compensation of sublimation. Based on the processing and analysis of video images, the authors described the dependence of the velocity of motion of vacancy islands on the Si(100) surface for various temperatures and the direction of the electric current along and across the dimer rows with the (2 × 1) superstructure inside the island. It is shown that the drift rate of vacancy islands does not depend on their size under quasi-equilibrium conditions. A simplified one-dimensional theoretical model has been constructed. It includes one atomic step moving by a detachment of atoms from the step and their drift under the force of electromigration in the absence of desorption and deposition of atoms on the surface. Based on the proposed model, the effective electric charge is estimated, and the temperature dependence of the effective charge in the temperature range of 1010 to 1120°C is obtained. The absolute value of the effective charge decreases linearly with increasing temperature. The sign of the effective charge is negative, and its average value is Z = –0.5 ± 0.3 elementary charges. The obtained results can be used for creating structures with a countable number of atomic steps and act as secondary measures of height with reference to the silicon crystal lattice.