Band offsets and chemical bonding: The basis for heterostructure applications

The unifying concept underlying all heterostructure physics is the idea that energy gap variations act as quasi-electric forces on the electrons and holes in the structure, even in the absence of a true electric field. They give the device designer a new degree of freedom in designing structures exhibiting phenomena fundamentally unobtainable in homostructures. A useful classification of heterostructures is by lineup type, distinguishing straddling, staggered and broken-gap lineups. Examples of each type are discussed. The possible combinations of two or more semiconductors into a heterostructure are constrained by bonding considerations, both with regard to bond length compatibility (lattice matching) and valence compatibility. In quantized structures, strain may be a deliberate design element. The industrial impact of heterostructure devices is likely to be dominated by the large economic system leverage they tend to provide, more than by manufacturing volumes approaching those of mainstream silicon technology - with the possible exception of LEDs.