Morphological evolution during epitaxial thin film growth: Formation of 2D islands and 3D mounds

Homoepitaxy provides an ideal testing ground for fundamental concepts in film growth. The rich variety of complex far-from-equilibrium morphologies which can form during deposition contrasts with the simple equilibrium structure of homoepitaxial films. These complex morphologies result from the inhibition on the time-scale of deposition of various equilibrating surface diffusion processes. A sophisticated framework for analysis of such phenomena derives from the concepts and methodology of Statistical Physics. Kinetic Monte Carlo (KMC) simulation of suitable atomistic lattice–gas models has elucidated the growth behavior of numerous specific systems. In this review, we describe in detail submonolayer nucleation and growth of two-dimensional islands during deposition. The traditional mean-field treatment is quite successful in capturing the behavior of mean island densities, but it fails to predict island size distributions. The latter are provided by simulation of appropriate atomistic models, as well as by suitable hybrid models. Recent developments towards providing reliable analytic beyond-mean-field theories are also discussed. Kinetic roughening of multilayer films during deposition is also described with particular emphasis on the formation of mounds (multilayer stacks of 2D islands) induced by step-edge barriers to downward transport. We describe results for mound evolution from realistic atomistic simulations, predictions of phenomenological continuum theories, and efforts to derive more reliable coarse-grained formulations. For both regimes, we demonstrate how atomistic modeling can be used extract key activation barriers by comparison with experimental data from scanning tunneling microscopy and surface sensitive diffraction. Significantly, suitable tailored atomistic models are often shown to have predictive capability for growth over a broad range of temperatures. Finally, we comment briefly on other deposition processes such as heteroepitaxial growth and chemisorption.