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Nobel Laureate Delivers Munushian Lecture

If researchers follow the physics, the applications will show up, says 2000 prizewinner
Eric Mankin
February 21, 2008 —
Dr. Herbert Kroemer, 2000 Nobel laureate in physics.
To hear the speech, click on the image.
Introduced by Hsieh Department Electrophysics  Chair P. Daniel Dapkus, UCSB's Herbert Kroemer spoke on "Heterostructures: From Physics to Devices and Back (A Personal Perspective),"  on February 20.

The speech was presented by the Hsieh Department of Electrical Engineering as the Jack Manushian Lecture, part of the Viterbi School's Engineering Keynote lecture series.

Kroemer began his remarks by underlining his personal ties to members of the Viterbi School faculty, including Dapkus, noting that he agreed to accept the invitation to deliver the endowed lecture named after Jack Manushian specifically because of these ties.

His remarks discussed the technicaliies of using exotic materials to create environments in which the reciprocal activities electrons and holes could produce interesting effects — underlining that his highly influential research had always been based on following the physics.

"You can't predict applications," he said, "but you can identify promising directions."

Dr. Kroemer's speech abstract and biography appear below.

Heterostructures: From Physics to Devices and Back (A Personal Perspective)
From left:  Senior Associate Dean for Strategic Initiatives Cauligi Raghavendra,  Kroemer, P. Daniel Dapkus, electrophysics chair of the Ming Hsieh Department of Electrical Engineering.
In semiconductor heterostructures the basic semiconductor itself– not just the doping– changes with position, and the transition region between the different semiconductors plays an essential role in the operation of the device. The underlying physics is that in the transition region the forces acting on electrons and holes are no longer of purely electrostatic origin, but contain an essentially quantum-mechanical component that is decoupled from the electrostatic forces. In fact, the resulting net forces can act in the same direction for electrons and holes, something fundamentally impossible with purely electrostatic forces.

The added forces give the device designer a powerful new degree of freedom that ranges from performance improvements in already-existing devices, to the creation of devices that are fundamentally unachievable in homostructures, like the double-heterostructure laser.

Today, all compound semiconductor devices of importance are heterostructure devices, and Si-Ge heterostructures have invaded mainstream silicon technology. In addition to their importance in practical devices, heterostructures are playing a similarly dominant role in basic semiconductor physics. The best-known example–recognized by the 1998 Nobel Prize in Physics–is the fractional quantum Hall effect in the 2D electron gas at certain hetero-interfaces. Numerous other research areas in semiconductor physics involve heterostructures in an essential way.
Senior Associate Dean for Academic Affairs John O'Brien and Kroemer.
Examples are nanostructures like quantum wires and quantum dots, superlattice Bloch Oscillators, and induced superconductivity in InAs quantum wells.

Herbert Kroemer was born in 1928 in Weimar, Germany. He received a doctorate in Theoretical Solid-State Physics in 1952 from the University of Göttingen, Germany. Since then, he has worked on the physics and technology of semiconductors and semiconductor devices in a number of research laboratories in Germany and the U.S. He has been on the faculty of the University of California - Santa Barbara since 1976.

Kroemer is the originator of several device concepts, including the heterostructure bipolar transistor, the double-heterostructure laser, and other heterostructure topics. During the '60s, he also worked on microwave device problems, and in 1964 he was the first to publish an explanation for the Gunn Effect. With the emergence of molecular beam epitaxy in the mid-'70s, he returned to heterostructure devices, and he was one of the first to apply the emerging new technology to new and unconventional materials combinations, such as GaP-on-Si, GaAs-on-Si, and InAs/(Al,Ga)Sb structures, making several contributions to the development of MBE itself.

Kroemer is a Fellow of the IEEE and of the APS, and a Member of both the National Academy of Engineering and the National Academy of Sciences. He holds honorary doctorates from the Technical University of Aachen, Germany, the University of Lund, Sweden, the University of Colorado, and the University of Duisburg-Essen, Germany. He has received numerous awards, most recently, in 2000, the Nobel Prize in Physics, "for developing semiconductor heterostructures used in high-speed and optoelectronics," and in 2002 the IEEE Medal of Honor. His research interests continue to be in the physics and technology of semiconductor heterostructures.