Unstable Growth and Coarsening in Molecular-Beam Epitaxy

TL;DR

This paper investigates the coarsening behavior of 3D islands during molecular-beam epitaxy, focusing on instability origins and mechanisms, providing estimates for coarsening times and identifying a dynamical exponent.

Contribution

It introduces a detailed analysis of coarsening mechanisms in epitaxial growth, emphasizing the role of Ehrlich-Schwoebel barriers and deriving asymptotic dynamical exponents.

Findings

Two coarsening mechanisms identified: surface diffusion and mound coalescence.

Coarsening time estimates provided for each mechanism.

Asymptotic dynamical exponent z=4 when surface slope saturates.

Abstract

The coarsening dynamics of three-dimensional islands on a growing film is discussed. It is assumed that the origin of the initial instability of a planar surface is the Ehrlich-Schwoebel step-edge barrier for adatom diffusion. Two mechanisms of coarsening are identified: (i) surface diffusion driven by an uneven distribution of bonding energies, and (ii) mound coalescence driven by random deposition. Semiquantitative estimates of the coarsening time are given in each case. When the surface slope saturates, an asymptotic dynamical exponent $z=4$ is obtained.