Abstract
The continuing growth of the semiconductor industry has relied on the development of new fabrication technologies that provide greater control over all aspects of the device properties. Molecular beam epitaxy, for example, has now become a standard technique for depositing materials in layers as thin as a single atom, and it allows properties such as the band gap and doping level to be defined to near atomic precision in the growth direction. The flexibility of this technique, together with the quality of the resulting structures, has been crucial to the development of many devices, ranging from the solid-state lasers used in compact disc systems to the high-electron-mobility transistors used in satellite receivers and mobile telephones.