Semiconductor Optics and Transport Phenomena , Wilfried Schäfer and Martin Wegener Springer-Verlag, New York, 2002. $74.95 (495 pp.). ISBN 3-540-61614-4
In the past three or four decades, the development of semiconductors has led not only to well-known advances in devices, but also to new physics. The root of that development is the ability to make a semiconductor structure whose charge carriers are confined to a nanometer region in one, two, or three dimensions. Electrons interact more strongly with each other under such confinement. In a strong magnetic field normal to a layer of electrons, the electrons’ transport reveals the famous integer and fractional quantum Hall effects. These effects have inspired elegant theories that have wider applications in many-body physics. The confinement of electrons in quantum dots has led to mesoscopic physical effects and to a new understanding of electron transport.
Meanwhile, the development of laser optics, especially that of picosecond and, subsequently, femtosecond lasers, has made it possible to optically excite the electron—hole pairs and to measure the phase of the pairs. The resultant motion is known as coherent dynamics. Semiconductor physics has now advanced almost to the point at which specific designs of electrical and optical control of the dynamics of the electron position and spin are possible.
The rapid pace of discovery in semiconductor physics makes it difficult to initiate neophytes to the field. To be sure, excellent monographs exist, but teaching a monograph-based course to cover such a wide range of topics would place great demands on the instructor. With Semiconductor Optics and Transport Phenomena, Wilfried Schäfer and Martin Wegener have come to the rescue. Their book, aimed at graduate students who have had an introductory course in solid-state physics, covers most of the developments described above.
The authors are important figures in semiconductor optics. Schäfer has made definitive contributions to the theory of interacting electrons and collaborated with experimentalists to explain exciton dynamics under ultrafast optical excitation. Wegener is prominently known for his experimental exploration of the new world of exciton dynamics in the first few femtoseconds of their creation. The collaboration of a theorist and an experimentalist in this book fulfills the authors’ intent to synthesize theory and empiricism. It is delightful to find that, after reading about the Bloch theory, one can understand the four-wave mixing experiment and measurements of the dephasing time. If readers find some parts of the Green’s function theory heavy going, they can skip such parts (perhaps temporarily) in favor of the phenomenology.
The text covers basic electron properties, optics, and transport. The optics part provides important paradigms of decoherence and of nonequilibrium physics, both of which are essential to the modern physics of the small. The book also carefully describes such fundamentals as the gauge relation between the p · A and r · E expressions for light—matter interaction. Had those expositions been omitted, the thoughtful student might have been frustrated.
The authors missed some opportunities to present exact theory in place of approximations. One instance is their treatment of electron dynamics near the band edge. An electron near the band edge can be proved, to all orders of the electron-electron interaction in a static lattice, to be a well-defined quasiparticle with a renormalized mass and a dielectric-screened interaction with other band-edge electrons and holes. Then, in chapters 3 and 6, the Hartree–Fock approximation for the electron is unnecessary; in that approximation, one must, ad hoc, add the dielectric screening to the exciton equation. That difficulty is avoidable, because the standard effective-mass equation for the exciton has been shown to be exact in the Wannier limit.
It would be churlish to dwell on the few flaws (or perhaps merely disagreements between us) in such a large undertaking. I mention them here only for consideration in the next edition. It may lead to errors to assign damping rates (for example, on page 90) without basing them on a microscopic theory. The recombination rate of electrons and holes would give the same decay rate for each species, but some mechanisms that affect the lifetime of only one species contribute to pure dephasing. The statement on page 110 that the semiclassical treatment of the electric field is valid when the field is quantized neglects the correlation between the field and the exciton. The current count in the photodetector, equation 4.79, should be either the electron or the hole contribution.
I believe (with perhaps the excessive fervor of a convert) that interdisciplinary knowledge in coherent optics, in strong-interaction physics, and in mesoscopic physics will play an expanding role in semiconductor and metal physics and thus help physicists to understand nanosystems that are far from equilibrium. The traditional semiconductor physics curriculum—electrons, phonons, transport, and a bit on optical properties (but not coherent dynamics)—is insufficient to prepare a student for the increasingly quantum world. I recommend Schäfer and Wegener’s timely and pioneering text for a cohesive presentation of modern semiconductor physics.
