Non-steady state effects in MBE: Oscillations of the step density at the crystal surface

Abstract

An analysis of the microscopic processes (surface diffusion, nucleation) at the crystal surface during MBE provides a comparatively simple expression for the temperature dependence of the amplitude of the step density oscillations at a two-level and a three-level growth front. The time evolution of the terrace areas (in the case of complete condensation) is found to be temperature independent which leads to a temperature independent amplitude of the RHEED intensity oscillations when they originate from the interference of beams scattered by different terraces. The evolution of the growth front (the increase of its thickness) is found to depend only on the number of atoms in the critical nucleus. This provides the underlying physics for an understanding of the damping of the oscillations. When the RHEED intensity changes originate from diffuse scattering from the step edges, the oscillation amplitudes observed at different temperatures are expected to be essentially different, but the damped oscillations should coincide after appropriate scaling.