STEP KINETICS IN THE PRESENCE OF MOBILE ADSORBED IMPURITY

Mobile adsorbed impurity is piled up in front of the moving step, whil e the impurity concentration behind the step is depleted. The concentr ation difference between the two adjacent terraces may lead to a stron g reduction in the step velocity, upsilon. A still more important effe ct of mobile adsorbed impurity is a complicated nonlinear dependence o f upsilon on the solution supersaturation, sigma. The kinetic curve, u psilon(sigma), is determined by the mechanism which controls the lifet ime of piled up impurity: either desorption, or incorporation into the growing layer, or migration to the back terrace over the step riser. At low sigma, the mobile impurity particles should be considered as a 2D gas; at higher sigma, one should treat each particle as an individu al obstacle for a moving step. These two approaches, although qualitat ively different, lead to identical expressions for upsilon(sigma).