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The prize is being awarded with one half jointly to Zhores I. Alferov, A.F. Ioffe Physico-Technical Institute, St. Petersburg, Russia, and Herbert Kroemer, University of California at Santa Barbara, California, USA, "for developing semiconductor heterostructures used in high-speed- and opto-electronics" and one half to Jack S. Kilby, Texas Instruments, Dallas, Texas, USA "for
his part in the invention of the integrated circuit" Physics
and Information Technology The rapid development of electronic computer technology really started with the invention of the integrated circuit around 1960 and the microprocessor in the 1970s, when the number of com-ponents on a chip became sufficiently large to allow the creation of a complete micro computer. The rapid increase in the number of components was formulated as a prediction in "Moore's law": the number of components on a chip will double every eighteen months. This has happened since the 1960s and today there are chips with millions of separate components, at prices that are largely unchanged. Chip development has been matched by equally dynamic and powerful developments in telecommunications technology. Just as the integrated circuit has been and is a prime mover for electronic computer technology, ultra-rapid transistors and semiconductor lasers based on heterostructures of semiconductors are playing a decisive part in modern telecommunications. Heterostructures
in mobile telephones, CD-players, bar-code readers, brake-lights
etc. Most semiconductor components are made of silicon, but composite semiconductors of type gallium arsenide are growing in importance. A semiconductor, consisting of several thin layers with differing band gaps is termed a heterostructured semiconductor. The layers can have a thickness varying from a few atom layers to micrometres and may consist of gallium arsenide (GaAs) and aluminium gallium arsenide (AlGaAs). The layers are generally selected so that their crystal structures fit one another and the charge-bearers can move almost freely at the interface. It is this property of heterostructures that can be exploited in a number of different ways. Heterostructures are very important in technology. Low-noise high-frequency amplifiers using heterotransistors are used in satellite communications and for improving the signal-to-noise ratio in mobile telephony. Semiconductor lasers based on heterostructures are used in fibre-optical communication, in optical data storage, as reading heads in CD players, as bar-code readers and laser markers, etc. Heterostructure-based light-emitting diodes are used in car brake-lights and other warning signals and may one day replace electric bulbs. Heterostructures have also been of great importance for scientific research. Properties of what is called a two-dimensional electron gas formed in the interface layer between semiconductors was the starting point for the study of the quantised Hall effects (Nobel Prize in Physics 1985 to Klaus von Klitzing and 1998 to Robert B. Laughlin, Horst L. Störmer and Daniel C.Tsui). Quantised conductance has also been studied in one-dimensional channels and point contacts, artificial atoms and molecules based on "quantum dots" with a limited number of free conduction electrons enclosed in very small spaces, one-electron components, etc. The
Heterotransistor
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