This chapter discusses models of nucleation and growth on surfaces, in the context of producing epitaxial thin films. Section 5.1 gives some of the reasons for studying this topic and introduces some ideas needed as background. In section 5.2, we discuss differential equation formulations used to describe nucleation experiments quantitatively, and show how experiment-model comparisons can yield energies for characteristic surface processes. Sections 5.3 and 5.4 describe such comparisons in the case of metals growing on insulators and on metals. Section 5.5 explores steps, ripening and interdiffusion on insulator and metal surfaces. Although many of the same experiments and models are used in studying the growth of semiconductors, the role of surface reconstruction is much more important, so this topic is deferred to chapter 7.

Introduction: growth modes and nucleation barriers

Why are we studying epitaxial growth?

Epitaxial growth is a subject with considerable practical application, most obviously in relation to the production of semiconductor devices, but also to a whole range of other items. For example, magnetic devices such as recording heads have been produced by using metallic multilayers, in which alternating layers of magnetic and nonmagnetic materials produces high sensitivity to magnetic fields; other magnetic examples are bistable switches, where the alignment of the magnetic moments can be parallel or antiparallel in the neighboring layers. Many such films are required to be single crystals with low defect density, and are produced via epitaxial growth processes. The term epitaxy has come to mean the growth of one layer in a particular crystallographic orientation relationship to the underlying, or substrate layer (Schneider & Ruth 1971, Bauer & Poppa 1972, Matthews 1975, Kern et al. 1979).