Epitaxial growth of thin films

The term ‘epitaxial’ is applied to a film grown on top of the crystalline substrate in ordered fashion that atomic arrangement of the film accepts crystallographic structure of the substrate. Epitaxial growth is one of the most important techniques to fabricate various ‘state of the art’ electronic and optical devices. Modern devices require very sophisticated structure, which are composed of thin layers with various compositions. Quality, performance and lifetime of these devices are determined by the purity, structural perfection and homogeneity of the epitaxial layers. Epitaxial crystal growth resulting in epitaxial layer perfection, surface flatness and interface abruptness depend on number of factors like: the epitaxial layer growth method, the interfacial energy between substrate and epitaxial film, as well as the growth parameters – thermodynamic driving force, substrate and layer misfit, substrate misorientation, growth temperature, etc... Recently epitaxial growth is also used for fabrication of semiconductor quantum structures like quantum dots giving highly perfect structures with high density. In this report the aspect determining the epitaxial growth mode, epitaxial layer growth techniques and additional focusing on SiC epitaxial growth is discussed. 1. Epitaxial growth modes The occurrence of the epitaxial growth modes depends on various parameters of which the most important are the thermodynamic driving force and the misfit between substrate and layer. The growth mode characterizes the nucleation and growth process. There is a direct correspondence between the growth mode and the film morphology, which gives the structural properties such as perfection, flatness and interface abruptness of the layers. It is determined by the kinetics of the transport and diffusion processes on the surface. Different atomistic processes may occur on the surface during film growth: deposition, diffusion on terraces, nucleation on islands, nucleation on second-layer island, diffusion to a lower terrace, attachment to an island, diffusion along a step edge, detachment from an island, diffusion of dimmer (see Figure 1). Experimentally, the distinction between three classical growth modes is well known: Frank-van der Merwe (FV), Volmer-Weber (VW) and Stranski-Krastonov (SK). In addition to the three well-known epitaxial growth modes mentioned above there are four distinct growth modes: step flow mode, columnar growth, step bunching, screw-island growth (see Figure 2) [1, 2].