ECE Department and Materials Department, University of California, Santa Barbara, CA 93111, USA
In a compositionally heterogeneous semiconductor structure with a position-dependent energy gap, the conduction and valence band edges no longer have the same slope. Hence the forces on conduction electrons and holes are no longer equal in magnitude and opposite in direction; they may in fact be in the same direction. The utilization of these quasi-electric forces is the unifying principle underlying all semiconductor heterostructure devices, both for physics research and for practical applications. Essentially all modern compound semiconductor structures draw on this principle, which is also invading silicon-based device technology, In the limit of near-atomically abrupt transitions, the quasi-electric fields turn into true potential steps, with pronounced quantum effects in the space between closely spaced interfaces, as in quantum wells, tunneling barriers, and superlattices. The presentation will give several examples of this principle and its central role in fundamental research and practical devices.