of matter and its reorganization at the lowest practical level. .... Germany. Since 1981, he has held the Chair of Applied Solid State Physics and, since 1990, has.
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Introduction to the Issue on Nanostructures and Quantum Dots
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N THE last few years, considerable effort and resources have been committed to the search for methods for synthesis of matter and its reorganization at the lowest practical level. Current efforts are focused on synthesis and fabrication at the nanometer scale. The promise of nanometer-scale science and engineering hinges on the premise that when matter is rearranged at this length scale, which is the scale at which molecular interactions occur, new properties emerge. It is the potential exploitation and application of these properties in a range of fields, from medicine to engineering, that is stimulating the spate of activity in this interdisciplinary area. The fields of nanoscience and nanoengineering are expected to lead to a profound understanding as well as control of matter at the nanometer scale. This understanding and control, in turn, could lead to new ways of designing devices and processes with ever more useful functionalities. There has been a great deal of emphasis placed on the control of the structural properties (which include, among others, size, shape, and composition). Conventional methods of synthesis and fabrication have been found to be wanting in this kind of endeavor. The majority of the activity in this area has therefore been directed at exploring new techniques and approaches for synthesis and assembly of the nanostructures. This issue of the IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS is devoted to “Nanostructures and Quantum Dots.” Because the area is so broad, encompassing many traditional fields of study—from the life sciences through engineering—the scope of this issue has been deliberately limited to nanostructures that have potential applications in photonics. Nanostructures that exhibit quantum effects are especially important for fundamental studies in optics; they are also important for applications in novel or improved optoelectronic devices. Structures with inherent quantum-size effects typically have dimensions on the order of the carrier de Broglie wavelength (or the mean free path) in the material; for semiconductors currently used in photonics, this dimension is in the range of several nanometers to tens of nanometers. Although the majority of quantum-dot structures discussed in this issue are three-dimensional, nanometer-sized objects, some of the papers address nanostructures that are two-dimensional in form. The papers presented in this issue fall roughly into three classes: 1) synthesis, fabrication, and characterization; 2) studies of fundamental processes; and 3) application of the nanostructures in lasers and photodetectors. One of the challenges facing researchers engaged in the synthesis of quantum-dot nanostructures today is the difficulty of cre-
Digital Object Identifier 10.1109/JSTQE.2002.804255
ating three-dimensional, ordered arrays of uniform-size dots. The current preferred method of synthesis, based on the Stranski–Krastanow growth mode, does not automatically form uniform-size dots. Regimented order is even harder to achieve. These difficulties are largely due to the fact that synthesis proceeds by self-organization, a process which occurs during the growth of lattice-mismatched epitaxial layers. Because of the mismatch, the layers are strained and it is the strain field that drives the process. This self-organization process, unlike that in biological systems, is generally not far from equilibrium. Control of the parameters that lead to order and to perfection has been difficult to achieve. A potential approach to regimentation is the use of templates. However, at this scale, conventional lithographic tools are time-consuming, expensive, and in most cases unsuitable for manufacturing the templates. One paper in this issue, by Liang et al., offers a potential alternative approach for creating such templates. Another, by Lee et al., discusses growth of layers on nanoscale faceted substrates; these facets, which essentially form templates, are created by interferometric lithography. The emerging theme in the synthesis is that, as much as possible, the desired order of the structures should be formed without reliance on conventional lithography, but rather on natural processes inherent to the synthesis technique. Another paper, which extends this idea further, is by Schmidt et al., where formation of unique structures is discussed. This paper presents results on self-assembled nanoholes, quantum-dot molecules, and rolled-up nanotubes—structures that are new to this class of materials. Once formed, quantum-dot nanostructures represent a very interesting ensemble of thousands of atoms in clusters for the study of fundamental carrier confinement effects. Carriers in dots tend to be in the strong or tight confinement regime. Exciton emission, absorption, and dephasing are particularly interesting characteristics to study in these structures. Two papers in this issue explore properties of excitons in quantum dots: one paper, by Borri et al., discusses relaxation and dephasing characteristics; another, by Goupalov et al., expands on the subject of dephasing to include a connection to the absorption lineshape. When an exciton and a photon are coupled inside a highcavity, they form a polariton. This object has very interesting properties that cannot be observed in plain bulk or quantum-well structures. The paper by Skolnick et al. discusses the effect of confining exciton–polaritons in microcavities. The authors of this paper explore the prospects of developing “polariton” lasers and optical parametric oscillators from these structures. The third class of papers discusses application of the nanostructures in optoelectronic devices. The papers on lasers highlight some of the unique properties of quantum dots. The paper by Ledentsov, for example, discusses some of the key achievements in lasers that are fabricated from quantum-dot media; among these are the lowest lasing threshold current
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ever achieved for a semiconductor laser; another achievement is a high characteristic temperature (which is a measure of the insensitivity of the lasing threshold current to temperature variations). Other unique characteristics are discussed in the paper by Reithmaier and Forchel. In particular, this paper presents results for quantum-dot lasers grown on conventional GaAs substrates, but emitting at the telecommunications wavelength of 1.3 m. This paper also presents results for broadly tunable devices; the tunability is a result of the large gain bandwidth of quantum-dot media. The 11 papers contained in this issue are representative of the state-of-the-art research in semiconductor nanostructures. To date, quantum dots are perhaps the only three-dimensional, semiconducting objects that have been used to demonstrate the potential of nanostructured materials. The lasers reported here are, in fact, useful devices that are already being seriously considered for commercial applications. This portends well for photonic applications of nanostructures. Much, however, still remains to be done. We hope you find the papers contained in this issue useful and that they convey to you the excitement of the field and its relationship to photonics. ACKNOWLEDGMENT
their time to review the papers in this issue. And of course, they also thank all the authors of the papers, for without their contributions, this issue would not exist. Finally, they want to acknowledge the tireless efforts of the IEEE/LEOS Editorial Staff members, Linda Matarazzo and Janet Reed, for making sure that the issue was actually produced. ELIAS TOWE, Guest Editor Carnegie Mellon University Department of Electrical and Computer Engineering Pittsburgh, PA 15213 USA DIETER BIMBERG, Guest Editor Technische Universitat Berlin Institut fur Festkorperphysik Berlin D-10623, Germany YASUHIKO ARAKAWA, Guest Editor University of Tokyo Research Center for Advanced Science and Technology Tokyo 153-8505, Japan
The editors would like to take this opportunity to thank the many anonymous reviewers who gave so generously of Elias Towe received the S.B., S.M., and Ph.D. degrees from the Massachusetts Insititute of Technology, Cambridge, where he was also a Vinton Hayes Fellow. He is currently on the faculty of Carnegie Mellon University, Pittsburgh, PA, where he is a Professor of electrical and computer engineering, and materials science and engineering. From 1997 to 2001, he divided his time between the Defense Advanced Research Projects Agency (DARPA), Arlington, VA, and the University of Virginia, Charlottesville. At DARPA, he led the agency’s research efforts in photonics. Prof. Towe is the recipient of several awards, including the National Science Foundation Young Investigator Award, the Outstanding Technical Achievement Award from the Office of the U.S. Secretary of Defense, the Commonwealth of Virginia Scholar Award, and the Young Faculty Teaching Award from the University of Virginia.
Dieter Bimberg (M’92) was born in Schrozberg, Germany, on July 10, 1942. He received the diploma in physics and the Ph.D. degree from Goethe University, Frankfurt, Germany, in 1968 and 1971, respectively. From 1972 to 1979, he was a Senior Scientist with the Max Planck-Institute for Solid State Research, Grenoble, France, and Stuttgart, Germany. From 1979 to 1981, he was an Associate Professor with the Department of Electrical Engineering, Technical University of Aachen, Aachen, Germany. Since 1981, he has held the Chair of Applied Solid State Physics and, since 1990, has been Executive Director of the Solid State Physics Institute at the Technical University of Berlin, Berlin, Germany. Since 1994, he has been chairman of the National Research Council “Center of Excellence” on “Growth Related Properties of Nanostructures” and, since 1998, chairman of the National “Center of Competence” on “Nano-Optoelectronics” of the German Federal Ministry of Research. Among others, he hold guest professorships at the University of California, Santa Barbara, and at Hewlett-Packard, Palo Alto, CA. He has authored more than 800 papers, patents, and books. His research interests include the physics of nanostructures and nanostructured devices, wide-gap semiconductor heterostructures, and high-speed photonic devices. Dr. Bimberg holds an honorary membership at the A.F. Ioffe Institute, St. Petersburg, Russia, and received the Russian State Prize in Science and Technology in 2001.
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Yasuhiko Arakawa (S’77–M’80) received the B.S., M.S., and Ph.D. degrees in electrical engineering from the University of Tokyo, Japan, in 1975, 1977, and 1980, respectively. In 1980, he joined the University of Tokyo as an Assistant Professor and was promoted to a Full Professor in 1993. He is now a Professor with the Research Center for Advanced Science and Technology, University of Tokyo. He is also the Director of the Nanoelectronics Collaborative Research Center, Institute of Industrial Science, University of Tokyo. He is an NTT Research Professor. His current research interests include growth and physics of semiconductor nanotechnologies for optoelectronic device applications, such as quantum dot lasers and various nanostructure devices. He is currently the Editor-in-Chief of Solid State Electronics and a Regional Editor-in-Chief of IOP’s New Journal of Physics. Dr. Arakawa is an IPAP board member. He was an Associate Editor with the IEEE JOURNAL OF QUANTUM ELECTRONICS. He has received numerous awards, including the Niwa Memorial Award, the Excellent Paper Award from IEICE, the Young Scientist Award, International Symposium on GaAs and Related Compound Semiconductors, the IBM Award, the Distinguished Achievement Award from IEICE, the Hattori Hoko Award, the Sakura-Kenjiro Award from OITDA, the Electronics Award from IEICE, and the Nissan Science Award.
