THEORY OF HOMOEPITAXY ON SI(001) .1. KINETICS DURING GROWTH

Growth kinetics during Si(001) homoepitaxy are studied with a Monte Carlo computer simulation of a solid-on-solid model. The effect of the surface reconstruction, driven by the formation of dimers, is taken into account through longer residence times of atoms attached to other atoms or clusters perpendicular to the dimer-bond axis on the same layer than for atoms attached in the parallel direction. Although local fluctuations can bypass these rules, this prescription is correct on the average and leads naturally to the stability of steps for which the dimer axis is normal to the step edge in comparison to steps where the dimer axis is perpendicular to the step edge. By calculating the angle-resolved density of surface steps on the growing substrate, qualitative comparisons can be made between the simulations and the specular intensity measured in situ by reflection high-energy electron-diffraction (RHEED). Furthermore, by calculating the fractional coverages of 1 X 2 and 2 X 1 domains during growth, comparisons can be made with the fractional-order RHEED beams. Specific aspects of Si(001) homoepitaxy that are addressed are: (i) the azimuthal dependence of RHEED intensity oscillations and the formation of elongated clusters, (ii) the dependence of the growth characteristics upon the domain structure of the initial substrate, i.e., sustained RHEED oscillations for surfaces with a single 2 X 1 domain but decaying oscillations for a substrate with coexistent 2 X 1 and 1 X 2 domains, (iii) the observation of RHEED oscillations at temperatures too low (almost-equal-to 300-degrees-C) to promote the mobility of surface adatoms, as evidenced by the absence of recovery upon the termination of the incident molecular beam, and (iv) a temperature-induced monolayer-to-bilayer transition in the RHEED oscillations.