MOLECULAR-BEAM EPITAXY OF NONSTOICHIOMETRIC SEMICONDUCTORS AND MULTIPHASE MATERIAL SYSTEMS

When arsenides are grown by molecular beam epitaxy at low substrate te mperatures, as much as 2% excess arsenic can be incorporated into the epilayer. This excess arsenic is in the form of antisites, but there i s also a substantial concentration of gallium vacancies. With anneal, there is a significant decrease in the arsenic antisite and gallium va ncancy concentrations as the excess arsenic precipitates. With further anneal, the arsenic precipitates coarsen. This combination of low sub strate temperature molecular beam epitaxy and a subsequent anneal resu lts in a broad spectrum of materials, from highly defected epilayers t o a two-phase system of semimetallic arsenic precipitates in an arseni de semiconductor matrix. These materials exhibit some very interesting and useful electrical and optical properties.