A NATO workshop on "The Properties of Impurity States in Semiconductor Superlattices" was held at the University of Essex, Colchester, United Kingdom, from September 7 to 11, 1987. Doped semiconductor superlattices not only provide a unique opportunity for studying low dimensional electronic behavior, they can also be custom-designed to exhibit many other fascinating el~ctronic properties. The possibility of using these materials for new and novel devices has further induced many astonishing advances, especially in recent years. The purpose of this workshop was to review both advances in the state of the art and recent results in various areas of semiconductor superlattice research, including: (i) growth and characterization techniques, (ii) deep and shallow im purity states, (iii) quantum well states, and (iv) two-dimensional conduction and other novel electronic properties. This volume consists of all the papers presented at the workshop. Chapters 1-6 are concerned with growth and characterization techniques for superlattice semiconductors. The question of a-layer is also discussed in this section. Chapters 7-15 contain a discussion of various aspects of the impurity states. Chapters 16- 22 are devoted to quantum well states. Finally, two-dimensional conduction and other electronic properties are described in chapters 23-26.

Superlattice to Nanoelectronics, Second Edition, traces the history of the development of superlattices and quantum wells from their origins in 1969. Topics discussed include the birth of the superlattice; resonant tunneling via man-made quantum well states; optical properties and Raman scattering in man-made quantum systems; dielectric function and doping of a superlattice; and quantum step and activation energy. The book also covers semiconductor atomic superlattice; Si quantum dots fabricated from annealing amorphous silicon; capacitance, dielectric constant, and doping quantum dots; porous silicon; and quantum impedance of electrons. - Written by one of the founders of this field - Delivers over 20% new material, including new research and new technological applications - Provides a basic understanding of the physics involved from first principles, while adding new depth, using basic mathematics and an explanation of the background essentials

This volume represents the written account of the NATO Advanced Study Institute "Lower-Dimensional Systems and Molecular Electronics" held at Hotel Spetses, Spetses Island, Greece from 12 June to 23 June 1989. The goal of the Institute was to demonstrate the breadth of chemical and physical knowledge that has been acquired in the last 20 years in inorganic and organic crystals, polymers, and thin films, which exhibit phenomena of reduced dimensionality. The interest in these systems started in the late 1960's with lower-dimensional inorganic conductors, in the early 1970's with quasi-one-dimensional crystalline organic conductors. which by 1979 led to the first organic superconductors, and, in 1977, to the fITSt conducting polymers. The study of monolayer films (Langmuir-Blodgett films) had progressed since the 1930's, but reached a great upsurge in . the early 1980's. The pursuit of non-linear optical phenomena became increasingly popular in the early 1980's, as the attention turned from inorganic crystals to organic films and polymers. And in the last few years the term "moleculw' electronics" has gained ever-increasing acceptance, although it is used in several contexts. We now have organic superconductors with critical temperatures in excess of 10 K, conducting polymers that are soluble and processable, and used commercially; we have films of a few monolayers that have high in-plane electrical conductivity, and polymers that show great promise in photonics; we even have a few devices that function almost at the molecular level.

The understanding of electronic behaviour in solids when (some of) the valence electrons have both localized and band-like characteristics is one of the central problems of physics and chemistry in the second half of this century. Many advances have indeed been made using highly sophisticated techniques and concepts. Our objectives in bringing together specialists from different areas was cross-fertilization of ideas and redefinition of bottlenecks and problems. The testimony of the participants and the book which follows indicate a fair degree of success. This book is a record of discussions aimed at digestion and reassessment of some of the recent major advances in our understanding of narrow bands. Note that we expressly asked participants to give a short readable account of the major problems in their field and not to emphasize their latest results to be as "technical" as they might be in a normal scientific article. We did not ask for complete reviews of what was going on in the field and this book should not be read as such. Neither should it be approached as the sort of educational text which the NATO ASI proceedings are supposed to be. We have tried to produce a useable account of a workshop in which an attempt was made to define real problems and to distinguish them from illusory problems.

The rediscovery of fast ion conduction in solids in the 1960's stimulated interest both in the scientific community in which the fundamentals of diffusion, order-disorder phenomena and crystal structure evaluation required re-examination, and in the technical community in which novel approaches to energy conversion and chemical sensing became possible with the introduction of the new field of "Solid State Ionics. " Because of both the novelty and the vitality of this field, it has grown rapidly in many directions. This growth has included the discovery of many new crystalline fast ion conductors, and the extension to the fields of organic and amorphous compounds. The growth has involved the extension of classical diffusion theory in an attempt to account for carrier interactions and the development of sophisticated computer models. Diffraction techniques have been refined to detect carrier distributions and anharmonic vibrations. Similar advances in the application of other techniques such as NMR, Raman, IR, and Impedance Spectroscopies to this field have also occurred. The applications of fast ion conducting solid electrolytes have also developed in many directions. High energy density Na/S batteries are now reaching the last stages of development, Li batteries are being implanted in humans for heart pacemakers, and solid state fuel cells are again being considered for future power plants. The proliferation of inexpensive microcomputers has stimulated the need for improved chemical sensors--a major application now being the zirconia auto exhaust sensor being sold by the millions each year.

This book contains all the papers presented at the NATO workshop on "Optical Switching in Low Dimensional Systems" held in Marbella, Spain from October 6th to 8th, 1988. Optical switching is a basic function for optical data processing, which is of technological interest because of its potential parallelism and its potential speed. Semiconductors which exhibit resonance enhanced optical nonlinearities in the frequency range close to the band edge are the most intensively studied materials for optical bistability and fast gate operation. Modern crystal growth techniques, particularly molecular beam epitaxy, allow the manufacture of semiconductor microstructures such as quantum wells, quantum wires and quantum dots in which the electrons are only free to move in two, one or zero dimensions, of the optically excited electron-hole pairs in these low respectively. The spatial confinement dimensional structures gives rise to an enhancement of the excitonic nonlinearities. Furthermore, the variations of the microstruture extensions, of the compositions, and of the doping offer great new flexibility in engineering the desired optical properties. Recently, organic chain molecules (such as polydiacetilene) which are different realizations of one dimensional electronic systems, have been shown also to have interesting optical nonlinearities. Both the development and study of optical and electro-optical devices, as well as experimental and theoretical investigations of the underlying optical nonlinearities, are contained in this book.

This volume contains the papers presented at the NATO Advanced Research Workshop in "Reflection High Energy Electron Diffraction and Reflection Electron Imaging of Surfaces" held at the Koningshof conference center, Veldhoven, the Netherlands, June 15-19, 1987. The main topics of the workshop, Reflection High Energy Electron Diffraction (RHEED) and Reflection Electron Microscopy (REM), have a common basis in the diffraction processes which high energy electrons undergo when they interact with solid surfaces at grazing angles. However, while REM is a new technique developed on the basis of recent advances in transmission electron microscopy, RHEED is an old method in surface crystallography going back to the discovery of electron diffraction in 1927 by Davisson and Germer. Until the development of ultra high vacuum techniques in the 1960's made instruments using slow electrons more accessable, RHEED was the dominating electron diffraction technique. Since then and until recently the method of Low Energy Electron Diffraction (LEED) largely surpassed RHEED in popularity in surface studies. The two methods are closely related of course, each with its own specific advantages. The grazing angle geometry of RHEED has now become a very useful feature because this makes it ideally suited for combination with the thin growth technique of Molecular Beam Epitaxy (MBE). This combination allows in-situ studies of freshly grown and even growing surfaces, opening up new areas of research of both fundamental and technological importance.