PREFACE
Technological advances in semiconductor growth has opened a broad horizon for semiconductor physics and applications during the past 20 years. High quality two-, dimensional systems are achieved with nearly atomic precision by direct epitaxial growth. Such structures led to novel applications like low noise high frequency modulation doped field effect transistors and quantum well lasers. Semiconductor heterostructures of lower dimensionality like quantum wires and quantum dots are not yet as mature, partly due to the lack in precision of lateral structuring technology. In recent years, however, there was an enormous progress in novel epitaxial growth methods. This opens a wide new area of basic and applied semiconductor physics with the hope of novel applications in near future making use of the advantageous properties of one- and zero-dimensional systems. Ideas for future device applications mainly stem from the altered density of states being discrete or atomic-like for quantum dots. Optical spectroscopy has played and is playing a crucial role in the advancement of this fascinating field of semiconductor physics.
The NATO school organized at Bilkent University in Ankara and in Antalya brought together experts in this field and newcomers, especially young Ph.D. students and postdocs, to learn about recent developments and to discuss open questions in the area of optical spectroscopy of low dimensional semiconductors. The school turned out to be extremely fruitful and there was a great enthusiasm among the lecturers and students during the whole two weeks.
The NATO Advanced Study Institute considered various aspects of optical spectroscopy of low dimensional semiconductor structures. This included basic physics aspects, novel technology and material fabrication tools, characterization methods and new devices with special emphasis on quantum wire and quantum dot lasers. The advance in special epitaxial growth techniques, especially on patterned substrates is remarkable and allows nowadays for fabrication of well defined 1- and 0-dimensional semiconductor systems. Based on the well controlled technology the realization of quantum wire and quantum dot lasers was demonstrated as one of the highlights of the school. Especially the self-ordering of semiconductor quantum dots in various materials was discussed during the whole school. Other major topics included so-called V-groove quantum wires, cleaved edge overgrowth, micro-cavities, electronic excitations in low dimensional systems, phonons and also dissipative transport in nanostructures. While most of the lectures on experimental results were devoted to III-V based semiconductor structures like GaAs, AIAs, InP and InAs, some talks also considered the improvement which was achieved in recent years with the group IV semiconductor microstructures based on Si, Ge and C and II-VI semiconductors based on ZnSe and CdSe. The theoretical lectures covered growth kinetics and electronic properties of low dimensional semiconductor structures including many-particle effects. Most of the aspects covered by the lectures are included in this book.
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We are grateful to the NATO Scientific Affairs Division, to TUBITAK, the Scientific and Teclmical Research Council of Turkey and to .Bilkent University for making this meeting possible through their financial support and to B. Tanatar and A. Serpenguzel for their assistance in the preparation for the school. We are also grateful to the lecturers for their excellent presentations and to all participants for their contributions in oral talks, posters and discussions. They made the meeting to a lively and memorable event. We also thank the local organizers of the side programs which provided a lot of insight into the rich ancient and present culture, the beautiful scenery and the warm hospitality of the people in Turkey.
Gerhard Abstreiter Atilla Aydinli Jean-Pierre Leburton
