Cross-Sectional Scanning Tunneling Microscopy.

Since its invention in the early 1980, scanning tunneling microscopy1-4 (STM) and techniques such as atomic force microscopy5 (AFM) that have evolved from it have become tools of paramount importance in fundamental studies of surfaces. In addition, increasing effort has been directed towards the use of STM and related techniques to address problems of technological interest, particularly in the area of semiconductor materials and devices. The extremely high spatial resolution afforded by these techniques has led naturally to their application to a wide range of scientific and technological problems in semiconductor device physics. Indeed, their growing importance in semiconductor science and technology is a natural consequence of the desire to design and fabricate ever smaller structures to improve device performance or achieve new device functionality, and of the limitations of more traditional experimental techniques in performing detailed and comprehensive characterization at the nanometer to atomic scale. The unique and powerful advantage offered by STM and other scanning probe techniques is the ability to perform direct studies of structural, electronic, and other properties of materials with extremely high spatial resolution. Many other techniques, such as X-ray diffraction, electron diffraction, and transmission electron microscopy, typically provide only indirect information about sample structure and, while offering the ability to probe certain structural or compositional features at the atomic scale, inevitably average these properties over substantially larger areas or volumes. In scanning tunneling microscopy, however, direct imaging of features corresponding to individual atoms on a surface has been demonstrated for a wide range of materials. Other scanning probe techniques, while usually providing somewhat lower spatial resolution than STM, allow greater flexibility in samples that can be studied, imaging conditions that can be tolerated, and properties that can be characterized. Rapid progress in the development of new scanning probe techniques and in the commercial availability Edward Yu is Associate Professor in the Department of Electrical and Computer Engineering at the University of California, San Diego. He received his A.B. (summa cum laude) and A.M. degrees in Physics from Harvard University in 1986, and his Ph.D. degree in Applied Physics from the California Institute of Technology in 1991. While at Caltech he was the recipient of a National Science Foundation Graduate Fellowship and an AT&T Bell Laboratories Ph.D. Scholarship. He joined the faculty of UCSD in September 1992 following a one-year postdoctoral appointment at the IBM Thomas J. Watson Research Center in Yorktown Heights, NY. Professor Yu’s research interests are in the area of semiconductor materials and devices, including atomic-scale characterization of semiconductor heterostructures and devices; fundamental properties and applications of novel heterojunction material systems; and techniques for the fabrication and characterization of nanometer-scale semiconductor device structures. Recent activities in his research group at UCSD have included extensive studies using cross-sectional scanning tunneling microscopy of atomic-scale properties, and their relation to epitaxial growth conditions and device performance, of a wide range of III−V compound semiconductor heterostructures. Professor Yu has been the recipient of an Office of Naval Research Young Investigator Award, and Alfred P. Sloan Research Fellowship, and a National Science Foundation CAREER Award. 1017 Chem. Rev. 1997, 97, 1017−1044