STEP KINETICS IN THE PRESENCE OF MOBILE ADSORBED IMPURITY

Mobile adsorbed impurity is piled up in front of the moving step, while the impurity concentration behind the step is depleted. The concentration difference between the two adjacent terraces may lead to a strong reduction in the step velocity, upsilon. A still more important effect of mobile adsorbed impurity is a complicated nonlinear dependence of upsilon on the solution supersaturation, sigma. The kinetic curve, upsilon(sigma), is determined by the mechanism which controls the lifetime 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 individual obstacle for a moving step. These two approaches, although qualitatively different, lead to identical expressions for upsilon(sigma).