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 oflateral 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.

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 oflateral 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.

These proceedings contain the majority of papers presented at
Symposium D, "Group IV heterostructures, physics and devices
(Si, Ge, C,&agr;-Sn)," of the Spring Meeting of the European
Materials Research Society, held at the Congress Centre,
Strasbourg, France, 4-7 June 1996. This Symposium was attended
by about 150 scientists from throughout the world, among whom 18
were invited speakers.

The aim of the Symposium was to discuss
the most recent results in all fields of Group IV
heterostructures and devices from fundamental physics to
industrial applications. Regular and invited contributions were
then welcomed which addressed the different aspects of growth,
the effects of strain relaxation, particularly in SiGeC alloys,
the basic optical and electrical properties of heterostructures
and low-dimensional structures, the microelectronic and
optoelectronics, such as rare-earth doping techniques, was also
selected. Except for minor changes, the order of papers presented
in this special issue of Thin Solid Films closely follows the
order of topics listed above as well as the order of sessions at
the Symposium.