Modeling RHEED intensity oscillations in multilayer epitaxy: Determination of the Ehrlich-Schwoebel barrier in Ge(001) homoepitaxy

Abstract

We report the study of submonolayer growth of Ge(001) homoepitaxy by molecular beam epitaxy at low temperatures, 100-150 degrees C, using reflection high energy electron diffraction (RHEED) intensity oscillations obtained for a range of low incidence angles, where the influence of the dynamical nature of electron scattering such as the Kikuchi features is minimized. We develop a model for the RHEED specular intensity in multilayer growth that includes the diffuse scattering off surface steps and the layer interference between terraces of different heights using the kinematic approximation. The model describes the measured RHEED intensity oscillations very well for the entire range of incidence angles studied. We show that the first intensity minimum occurs well above 0.5 ML (monolayer) of the total deposited coverage, which contradicts the common practice of assigning the intensity minimum to 0.5 ML. By using the model to interpret the measured RHEED intensity, we find the evolution of the coverage of the first 1-2 ML. We find that second-layer nucleation takes place at low coverage, 0.3 ML, implying a substantial Ehrlich-Schwoebel (ES) barrier. The value inferred for the ES barrier height, 0.084 +/- 0.019 eV, includes an analysis of the beam steering effect by step edges. Comparison is made with the value of the barrier height inferred from other measurements. The model for RHEED intensity and the method of inferring the ES barrier height can be applied to any system for which RHEED measurements can be obtained without interference from Kikuchi features.