Building on the Gunn Effect

Abstract

The solid-state scientists from industry, university and Government laboratories who gathered behind closed doors at the University of Colorado late in June weren't concerned with the leakage of industrial secrets. The competitors were all there; nobody without something to contribute was invited. The secrecy, in fact, was less to hinder the interchange of information than to permit such an interchange in a manner that would not be construed later as public disclosure. The secrecy was designed to guard property rights, not information, relating to what is called the Gunn effect, the electronic phenomenon discovered five years ago and now laying a base for what one Cornell University scientist believes to be the hottest new piece of industrial technology since the transistor. The Gunn effect and a successor, the limited space charge accumulation effect, were laboratory curiosities only a few years ago. They are dependent on oscillatory properties of the often-contrary semiconductor, gallium arsenide. The Gunn effect was discovered by Dr. Ian Gunn of IBM in 1963; the limited space charge effect was found by Dr. John Copeland of Bell Telephone Laboratories in October 1966. Now both are under intensive development by many organizations in the United States, Japan and several European nations. If development succeeds, the solidstate oscillators-little chips of gallium arsenide only a few times the diameter of a human hair-may do for microwave transmitters what transistors did for radio receivers: reduce them to pocket size. Oscillators now used in such circuitry are bulky and expensive vacuum tubes. Conventional microwave transmitters-frequencies in this range are in billions of cycles per second-can comprise rooms full of equipment. Miniaturization could accomplish such things as: * personalized radar, to be used by the blind, or by hunters, or as navigation aids on small craft and pleasure boats; * combined radio and television tieing home or office to all the world for the cost of a local phone call; * commercial radio-telephone links in remote areas where present heavy equipment can't be transported; * lightweight microwave transmitters for communications with spacecraft: an application already being tested by the National Aeronautics and Space Administration. All of this depends on the behavior of electrons in solids. The free electrons that are responsible for electrical conduction in solids occupy what are called energy bands: There are certain ranges of energy that the laws of quantum mechanics permit electrons to have, and these are separated by gaps, the energy values of which electrons may not have. When a voltage is applied across a piece of conductor, the electrons feel a force which causes them to move.