Growth Processes at Surfaces

Abstract

Thin films are of interest in industrial applications, and particularly in semiconductor devices technology.⁽¹⁾ From the physical point of view, they allow the study of two-dimensional systems, and their differences with three-dimensional states of matter. The confinement of particles in ultrathin layers places strong requirements on the quality of these layers: structural and chemical perfection, uniform and well-controlled thickness, uniformity of physical properties in the plane normal to the growth direction. Two major fabrication techniques have allowed the preparation of such high-quality thin films, namely, metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Major advantages of growth from a vapor phase are lower growth temperatures avoiding contamination and impurity diffusion, the control of the thickness, and the easy doping over a wide range of concentrations. However, the MBE technique is best suited for the observation of nucleation processes, since the reactant species are directly deposited at known rates on the substrate surface from the very beginning of the experiment. This is not the case in a MOCVD experiment where the stabilization time of the flow might be relatively long, and the arrival of species to the substrate is by diffusion through the gas phase.⁽²⁾ Indeed, the MBE technique has been used to grow a variety of elemental or compound semiconductor structures.