Heterostructures provide a wealth of physical phenomena and design options which may be exploited in advanced semiconductor devices, as the rest of the present volume attests. These advantages are traceable to the control which heterostructures provide over the motion of charge carriers. (In optoelectronic devices, the ability to confine the optical radiation is also extremely important.) This control can be exerted in the form of selective energy barriers (barriers for one carrier type different from that for the other) or quantum-scale potential variations.
An understanding of the physical properties of heterostructures is essential to their successful use in devices. The energy-band alignment is the most fundamental property of a heterojunction, and it determines the usefulness of various material combinations for different device applications. The band profile of a heterostructure is determined by the combined effects of heterojunction discontinuities and carrier screening, and it determines many of the electrical properties of the structure. Transport through a heterostructure can be described at a number of different levels, depending upon the size and abruptness of the structure.