What can molecular beam epitaxy do for silicon devices?

Abstract

Molecular beam epitaxy offers three important advantages to the silicon device industry. The first is the capability of growing new structures which cannot otherwise be fabricated. Examples of these are planar barrier diodes with barrier widths of tens of ångströms, solar cells with built-in front and back surface fields, cascade solar cells and n-i-p-i layered structures with layer widths down to tens of ångströms. The second advantage is improved dopant control and profile resolution in a single growth process to replace the multiple processes needed for complex devices. Examples are millimeter wave diodes, four-layer semiconductor-controlled rectifiers, buried layer metal/oxide/semiconductor field effect transistors and charge-coupled devices, and precise profile varactors. The third advantage is new materials combinations possible with a low growth temperature and a high purity ultrahigh vacuum environment. Examples are metal silicides, silicon on insulators, Si-Ge alloy superlattices and silicon heterojunctions with III-V alloys such as AlP and GaP. Molecular beam epitaxial systems in use, the new technique of evaporative doping with solid phase epitaxial re-growth and the resulting crystal quality will be discussed.