Chapter 5 Epitaxial growth techniques: Molecular beam epitaxy

Abstract

Publisher Summary Vapor-phase epitaxy (VPE) is the key technology used to form epitaxial silicon (Si) layers nowadays. Si VPE is classified into two groups: chemical vapor deposition (CVD) and vacuum deposition or evaporation, which is called molecular beam epitaxy (MBE). Both techniques can provide not only simple epitaxial growth, but also precise control of thickness with an atomic scale of grown layers including heterostructures, and the growth mechanisms are very different between the techniques. Chemical reaction of source materials both in the gas phase and on substrate surfaces governs the growth in CVD, while reaction on the substrate surface is important only in the case of MBE. This chapter describes the details of MBE that are, machines, processes, and growth mechanisms. The chapter presents an outline of MBE machines. There are two methods in MBE, depending on which source materials are used, solid or gas. They are called solid-source (SS) and gas-source (GS) MBE, respectively. A simple apparatus used for studies on GS-MBE growth is basically a SS-MBE machine equipped with gas inlets. Chambers are evacuated by large pumps such as chemical-type turbomolecular pumps (TMPs), cryopumps, or ultrahigh vacuum (UHV) diffusion pumps (DPs), and special precaution should be taken for safety, because these gases are toxic and/or combustible. Atomically clean surfaces are essential for achievement of high-quality epitaxial growth. A particular advantage of MBE is that it permits crystal growth at temperatures lower than those used in conventional techniques. Gas-source MBE growth is governed by dissociative adsorption of the gas molecules and the following desorption of dissociated products which leave Si atoms on Si substrates.