Recent Advances in Bulk Crystal Growth
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Bulk Crystal Growth Roberto Fornari and Michael Roth, Guest Editors
Abstract The growth of high-quality single crystals remains a challenging endeavor of materials science. Crystals of suitable size (from fiber crystals with diameters of tens of micrometers up to crystalline ingots or blocks with volumes up to 1 m3) and perfection (free from precipitates, inclusions, and twins with good uniformity and low concentration of dislocations) are required for fundamental research and practical implementation in microelectronic circuits, electro-optic switches and modulators, solid-state lasers, lightemitting diodes, sensors, and many other devices. In this introductory article of this issue of MRS Bulletin, we describe the two main challenges of today’s crystal growth, namely (1) the production of well-established crystalline materials with improved structural perfection and larger size at a lower cost and (2) the bulk growth of new categories of materials with extreme thermodynamic characteristics, such as a very high melting point, high melting dissociation pressure, incongruent phase diagram, and anisotropic segregation. The subsequent six articles provide examples of how the crystal growers took up these challenges, which led to new experimental approaches and technological advances.
Introduction The second half of the 20th century and the beginning of the 21st century have been marked by an explosive development of human-made single crystalline materials for widespread applications in industry, science, information processing, communications, environmental studies, medicine, and military. Most of the extraordinary achievements in modern technology have been accomplished through the development of microelectronic, optoelectronic, and optical devices made of artificial crystals. The most exciting discoveries of the last 30 years in the field of solid-state physics have been based on the ability to grow thin layers and nanostructures with exceptional control of size and composition. This ability has led to the discovery of “artificial” materials properties, which, in turn, has paved the way to entirely new generations of devices and components and stimulated extensive research in epitaxial technologies. As a side effect, there has been a certain drop of interest in bulk crystal growth. A quick survey of the scientific literature shows that the number of papers on nanostructures and quantum heterostructures is booming in compari-
son to a more or less steady number of publications on large single crystals. Even in MRS Bulletin, one has to go back to 1988 to find a special issue on this topic.1 Yet, in a great number of applications, bulk crystals are not just supports for the epitaxially grown active region of the devices, but are themselves active constituents. This is true every time the physical phenomena on which a given device is based take place within the device bulk. This happens, for instance, in silicon solar cells, where the generation of photocarriers occurs up to tens of micrometers from the surface; in n
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