Herbert Kroemer

Herbert Kroemer, professor of Electrical and Computer Engineering and Materials at the University of California – Santa Barbara will speak at the UNM Center for High Technology Materials on Friday, Sept. 24 at 11:30 a.m.  Kromer's talk is titled, "Heterostructure Lasers: How it all got started – and beyond."

Kroemer won the Nobel Prize for Physics in 2000 for developing semiconductor hetero structures used in high speed and opto-electronics.  In his talk he will discuss how all of today's semiconductor lasers are based on heterostructures, employing two or more different semiconductors within the same device.

The central idea is that in the presence of energy gap variations, the forces acting on electrons and holes are no longer equal in magnitude and necessarily opposite in direction.  In the transition region between the semiconductors, additional quantum-mechanical forces are present, and the resulting "quasi-electric" net forces may have the same direction for both electrons and holes.  This permits the accumulation and confinement of very large electron-hole pair concentrations and to the population inversions that are necessary for lasing.

The idea of quasi-electric forces originally arose in the mid-50's in the context of improving transistor performance, but in 1963, it was realized that it was going to be the key ingredient in achieving cw-lasing at room temperatures.  This goal was achieved in 1970, initially by liquid-phase epitaxy.  With the development of more advanced epitaxial techniques in the 70's, it became possible to build advanced structures in which quantum effects are utilized, such as energy level quantization in narrow quantum wells, tunneling through thin barriers, and modified band structures in superlattices.

Kroemer has explored the physics and technology of semiconductors and semiconductor devices, especially heterostructures, since 1952 when he received a doctorate in physics from the University of Göttingen, Germany.  He originated several key device concepts, including the heterostructure bipolar transistor and the double-heterostructure laser.

Kromer's talk is sponsored by the UNM-SPIE student chapter and CHTM.  The center is located at 1313 Goddard S.E.  The talk is free and the public is welcome.
