Semiconductor heterostructures have revolutionized solid-state physics and its applications. Most of us use the fruits of this revolution every day in CD and DVD recorders and players, cellular telephones, laser-based telecommunications, satellite television, and much more. The technology, based on atomic layer-by-layer growth using molecular beam epitaxy (MBE), is sophisticated, remarkable, and marketable.
One class of semiconductor heterostructures, the two-dimensional electron gas (2DEG), has been a focal point for theorists and experimentalists and a wellspring of new physics. A 2DEG can be produced at low temperatures at an interface of two distinct layers (a so-called heterojunction) doped nearby with atoms that donate electrons. The electrons at such a junction are confined to the lowest quantum state in the direction normal to the interface; by charging gate electrodes on the top surface of the heterostructure some distance away to repel them, the electrons can be further confined in the other...
