For three decades individual transistors in integrated semiconductor circuits have been getting smaller and smaller. Soon they will be approaching the 100‐nanometer regime, where the classical description of diffusive electron motion breaks down and quantum concepts become important, bringing about fundamental changes in electronic and optical properties. Already in the widely used siliconMOSFETtransistors, the interface between the semiconductor and the oxide layer serves as a potential well less than 10 nm wide. While electrons remain free to wander in the plane of the interface, their motion in the perpendicular direction is quantized by this very narrow well. Such two‐dimensional electron systems, best realized in high‐mobility modulation‐doped semiconductorheterostructures, have been found over the years to exhibit new and quite unexpected quantum phenomena, like the integral and fractional quantum Hall effects.
Arrays of nanometer potential wells, fabricated at semiconductor interfaces, exhibit infrared absorption lines reminiscent of atoms, molecules and even crystal lattices.