Effect of Schwoebel Barriers on Growth Mechanisms and Morphology of Thin Film

摘要

The molecular beam epitaxial (MBE) growth presents scientific challenges in thin -film and surface physics. In the past decade, the topic has attracted appreciable attention for a number of reasons, in particular due to the development of the innovative thin-film materials and sophisticated advanced nanoelectronics devices such as quantum dots and wires, tilted superlattices and quantum wells where the creation of layered structures with high crystalline quality and atomically sharp interfaces and of - well - defined island morphology is necessary. The detailed understanding of the basic mechanisms of thin-film growth at successive deposition stages and the relationship to film structure and morphology as a function of the controlling deposition parameters is therefore of both fundamental and technological importance. Nowadays it is well accepted that one of the most important growth parameters is the so called Schwoebel (S) barrier, i.e., the additional barrier for adatom diffusion over the step edge from an upper level to a lower one [1], The growth behaviour in the presence of S barriers is a subject of great current activity and it is shown that these barriers can regularize terrace widths on vicinal surfaces and lead to growth instabilities producing "wedding cake" structures on the growing surface [2-8] However, an exact quantitative kinetics and eventual fate of growth on a flat surface under the influence of a S barrier is still being discussed [2-8]. Recently we have developed a simple kinetic model for MBE growth on a singular surface which combines a traditional master equation approach with a concept of a feeding zone allowing to take into account the interiayer diffusion and we have shown that in the absence of S barrier with decreasing of the ratio of the diffusion and deposition rates the growth mechanism crosses over from smooth layer-by-layer growth to rough multilayer one and eventually to very rough Poisson random deposition growth process[9]. In this paper, we extend the model by including S barriers and investigate the growth kinetics as a-function of the S barrier height.