1.1 NANOTECHNOLOGY, QUANTUM TECHNOLOGY, AND BEYOND

Nanotechnology has become one of the defining technologies for the beginning of the twenty-first century. Nanotechnology is about: (1) making things small because their properties change radically as their size is reduced, offering the promise of new artificial materials (man)made from the nanostructures; (2) unheard-of integration of nanodevices onto a single chip; (3) nanodevices functioning down almost to the atomic level; and (4) self-assembly of nanostructures into complex devices and structures. However, this is nothing new for semiconductor systems. In the late 1970s and early 1980s, rapid development of planar growth techniques, such as molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD), made possible the routine, precise growth of high-quality, layered, semiconductor heterostructures. Abrupt interfaces could be made between semiconductors with different bandgaps just by opening and closing valves to the material cells in the growth system. Exquisite control was achieved with layers as thin as a few nanometers grown with monolayer precision. Arbitrary sequences of these layers were grown routinely to form quantum wells and superlattices, as well as heterojunctions, as shown in Figure 1.1. At a hetero-junction, electrons are confined to move in a thin two-dimensional (2D) depletion layer just inside the low bandgap region. In a quantum well (QW), electrons are confined to a thin, low bandgap 2D layer sandwiched between high bandgap layers. These structures provided a quasi-2D world for electrons with properties...