Optical Second-Harmonic Generation as a Semiconductor Surface and Interface Probe

Optical second-harmonic generation, although a sophisticated technique, is making a significant contribution to the characterization of surfaces and interfaces. Advantages include: all pressure ranges being accessible; insulators being studied without the problem of charging effects; solid–solid and solid–liquid interfaces being characterized by utilizing the large penetration depth of optical radiation. Single wavelength studies yield information on the crystallographic and magnetic structure of surfaces and interfaces, and are particularly sensitive to symmetry changes. Spectroscopic and time-resolved studies, which have recently become simpler due to the availability of high pulse power, tunable, broad band laser sources, additionally provide electronic structure and dynamics information, although interpretation may not be simple. Recent examples from well-characterized semiconductor interfaces are discussed, and it is shown that the technique is now well understood at the phenomenological level, although theoretical calculations are proving to be difficult.