110 IEEE TRANSACTIONS ON ELECTRON E structure with a spaced contact covering a minor portion of the N-type face of the wafer through which the radiation is emitted. The infrared radiation is character- ized by a sharply defined peak at slightly less than band gap (E gap = 1.43ev a t 300" K) and a broad peak at about 1.0 ev.

The measured radiation pattern closely follows that expected of a flat plate, i.e., the intensity decreases as the cosine of the angle from the normal. The diode V-I curve is characterized by exp (qV/2kT) at low current (up to 1 ma), exp (qV/kT) a t moder- ate current (5-50 ma) and series IR drop at high current (above 200 ma).

Data will be presented for the electron to photon conversion efficiency, the photon emission efficiency and the over-all energy efficiency of the GaAs infrared source as a function of current level and temperature.

A four terminal device which exhibits significant power gain has been constructed by optically coupling a GaAs infrared source and a silicon photo transistor. A discussion of this device and the speed of response of the GaAs infrared source will also be presented.

3) Electroluminescent Gallium Arsenide D i o d e s 4 . Burns, A. E . Michel and M. I . Na than . IBM Thomas J. Watson ResearGh Center, Y o r k t m n Hts., N . Y .

Evidence will be presented in this paper which indicates that the emission from high efficiency electroluminescent gallium arsenide diodes is due to recombination involving an acceptor center. A correlation has been made between the energy of the fluorescence of crystals of known doping and the emission from junctions prepared by diffusion of zinc into tellurium doped gallium arsenide. The emission from the diodes is at the same photon energy as the fluorescence of zinc-doped samples and is several hundredths of an eV below the energy of the tellurium doped samples. Other properties of the diodes will be discussed and i t will be shown that the radiation comes from the p side of the junction.

to superheterodyne optical communica- tions, this technique can be used to shift, by a specified amount, the inherently fixed frequency of a laser beam without in- troducing additional frequency components.

One method uses two electrooptic crystals in a tandem arrangement and is capable of shifting about 45 per cent of the input light energy onto a sideband when a sinusoidal voltage is applied. The remaining energy is absorbed in the device. Principles of operation will be analyzed and the evolution of a simpler embodiment, which uses only one crystal, will be discussed. This latter device can completely convert an incident beam to a sideband and is easily adaptable to broadband operation far into the micro- wave region.

These modulators were demonstrated with coherent light obtained from a helium- neon gas laser using audio-frequency modulating signals. Two tone tests showing the expected intensity envelopes and confirming singlesideband suppressed- carrier modulation will be described.

5 ) Superconducting Magnet for a Travel- ing Wave Maser-M. D. Bonfeld, Bell Telephone Laboratories, Allen-

A superconducting magnet has been developed to supply the magnetic field necessary to operate a 4 Gc traveling wave ruby maser. The field required by the maser is about 3000 oersteds uniform throughout the volume of the ruby to one part in a thousand. The field is directed across a gap of about 0.8 inches whose cross section is 5 inches by 0.5 inches.

A close approach to the ideal magnetic circuit has been achieved by placing superconducting shields adjacent to the pole pieces. Circulating currents are set up in the shields which prevent the existence of leakage and fringing flux. Since there is no loss mechanism in the shields, the currents persist and the air-gap field remains every- where uniform. With the absence of leakage and fringing flux, the size and weight of the magnetic circuit is considerably reduced.

Superconducting coils allow the use of a

town, Pa.

persistent current to generate the field. A 4) Single Sideband Suppressed Carrier heater element encased in a glass sleeve is

Optical Modulation-C. F. Buhrer, V. used to initiate the persistent current. The J . Fowler, L. R. Bloom, Ha switching procedure is simple and involves

& Eleetronics Laboratories, Inc., Bay- side, N . Y .

and E. M - conwell, General Telephone no moving parts in the cryostat.

A brief review of the electrooptic effect 6 ) Semiconductor Pressure Transduc- in crystals as applied to light modulation ers-M. E. Sikorski, R. Edwards and will be given, then followed by a description P. Andreatch, Bell Telephone Lab- of the technique developed a t our labura- oratories, Inc., Murray Hill, N. J . tories for single-sideband modulation of When silicon diffused transistors are light by this effect. Aside from applications stressed by applying localized pressure to

)E VICES March the emitter surface, increases in base and collector current are observed. From the relationship between these currents and the emitter junction voltage, the changes are identified as increases in minority carrier currents. The results can be explained mainly by the decrease in energy gap in strained silicon. Detailed data on stressed diodes and transistors will be shown in support of this hypothesis.

This phenomenon can be used to ad- vantage in many kinds of pressure trans- ducers. Microphones have been constructed in which acoustic power is transmitted to a transistor emitter region by means of a diaphragm and point assembly. Typical values obtained are: a sensitivity of 1 d b above 1 volt for a pressure of 1 dyne/cmz (vs -34 db for a carbon microphone); a gain of 26 db (vs 14 db); a ratio of ac power out to de bias power of 11 per cent (vs .02 per cent); signal to noise ratio of 55 db; the frequency response was limited by the diaphragm. Other devices such as hydrophones, phonograph pickups, and microminiature microphones also suggest themselves.

7) A New Class of Devices Based on

tions-W. Rindner and R. Nelson, Stressed Single and Multiple Junc-

Raytheon Research Division, Waltham, Mass.

Recent investigations have shown that stress suitably applied over small areas of p-n junctions causes very large and reversi- ble changes in junction resistance.' The active semiconductor volume involved is of the order of a few cubic microns. The stress sensitivity cannot be expressed in conventional terms since the resistance change is a function of both mechanical and electrical bias and also because anisotropic stress is used. Under reverse bias resistance, ratios of 103-104 have been obtained reproducibly under forces of a few thousand dynes. Stress signals have also been applied to junctions in transistor structures where the stress sensitivity of the transfer charac- teristics causes a conversion of mechanical to electrical signals. For example, with forces of a few thousand dynes acting on the emitter junction, h f c has been changed by factors of 10-100. Experimental two- and three-terminal devices which incorporate stressed junctions will be described. These include microphones, hydrophones and phonograph pick-ups. Other device possibili- ties on the same principles will be discussed.

junctions." Bull.' Am. Phys. Soc., voi. 7, p. 65; 1962. 1 W. Rindner "Anisotropic strain effects in p-n