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An Electronic Phonon Gate

IP.com Disclosure Number: IPCOM000096542D
Original Publication Date: 1963-Jul-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 25K

Publishing Venue

IBM

Related People

Keyes, RW: AUTHOR [+2]

Abstract

These devices are based on a combination of two effects: (1) the attenuation of ultrasonic waves by free electrons in a solid and (2), the increase in the concentration of free electrons in a semiconductor due to the phenomenon of impact ionization. These two effects are first reviewed. How they may be combined to control the transmission of ultrasonic waves is then described.

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An Electronic Phonon Gate

These devices are based on a combination of two effects: (1) the attenuation of ultrasonic waves by free electrons in a solid and (2), the increase in the concentration of free electrons in a semiconductor due to the phenomenon of impact ionization. These two effects are first reviewed. How they may be combined to control the transmission of ultrasonic waves is then described.

The attenuation of ultrasonic waves by electrons in solids was apparently first observed and understood around 1954. Since then, many authors have studied the phenomenon. In particular, it has been observed in semiconducting cadmium sulfide by Nine and Hutson, et al. The work of Nine and Hutson, et al, is especially relevant since they were able to control the ultrasonic attenuation by changing the concentration of free carriers. The free carriers involved were photo-excited. Their concentration was controlled by varying the intensity of illumination. The effect of electrons on the absorption of ultrasonic waves was also recognized by Weinreich, et al, who derived the theory of the absorption which is here used for the case of germanium.

The phenomenon of impact ionization of impurities in semiconductors in high electric fields at low temperatures has also been known for many years. The effect is basically similar to breakdown in gases. In a high electric field, a free electron can gain enough energy to excite an electron trapped on a donor into the conduction band by colliding with the trapped state. The concentration or electrons in the conduction band is thus increased.

The same phenomenon can also be produced by high microwave fields.

These two effects are combined to construct a phonon switch or gate. Two forms which such a gate takes are illustrated in the drawings. The rods X are constructed of a semiconductor containing donor impurities. They are maintained at a temperature sufficiently low that most of the electrons contributed by the donors are trapped on the donor atoms. The example could equally well be phrased in terms of acceptors and holes. In the trapped state the electrons do not produce the large free electron absorption referred to above. Now consider a beam of phonons being generated by the transducer A, in the drawing on the...