US3058002A - Light beam transducer - Google Patents

Description

United States Patent 6% lice 3,058,002 LIGHT BEAM TRANSDUCER Yro T. Sihvonen, Birmingham, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Nov. 29, 1957, Ser. No. 699,785 1 Claim. (Cl. 250-211) This invention relates to light transducing means and more particularly to means for elficiently converting light rays into electrical control currents.

Light sensitive materials used in control circuits for monitoring the current flow therethrough dependent upon the amount of incident light are of course in general use.

The present invention relates directly to the provision of a novel and highly eflicient light transducing means.

It is an object in making this invention to provide a light transducer fabricated of semiconductive materials.

It is a further object in making this invention to provide a laminar photosensitive light transducer formed of semiconductor elements.

It is a still further object in making this invention to provide a laminar assembly of semiconductor units for changing light rays into electrical control currents in which the rays are reflexed for amplification.

It is a yet further object in making this invention to provide a laminar light sensitive body in which an electroluminescent section is sandwiched between photoconductive sections to cause reflex action and amplify the response.

With these and other objects in view which will become apparent as the specification proceeds, the invention will be best understood by reference to the following specification and claim and the illustrations in the accompanying drawing in which:

FIGURE 1 is a diagrammatic showing of a light sensitive assembly embodying my invention, and

FIGURE 2 is a similar figure showing a multiple unit transducer.

As indicated in the above general discussion the light transducer which is the subject of the present invention is formed of a plurality of sections which are fixedly secured together to provide a light sensitive unit. Referring particularly to FIGURE 1, there is shown therein a compound light sensitive unit which consists of a first photoconducting semiconductor unit 2 or layer which may be formed of any one of several different activated elements such as CdS, ZnS, PbS or CdTe. On one surface of the layer 2 there is evaporated an electrode 4 for connection into an electrical circuit. To the opposite face of the layer 2 there is secured a layer of electroluminescent semiconductor 6. To the lower face of electroluminescent layer 6 there is applied a second conductive layer 8 which again may be a metallic film evaporated on the surface to provide an electrical contact. Completing the laminar body is a second layer of photoconducting semiconductor 10 which may be formed of one of the other compounds mentioned above with regard to layer 2. Lastly, the lower face of layer 10 has a final conductive film 12 evaporated thereon to provide for electrical connection.

A battery 14 is connected across conductive layers 4 and 8 to apply a desired potential across that part of the laminar body formed of photoconducting layer 2 and 3,058,002 Patented Oct. 9, 1962 electroluminescent layer 6. A second source of electrical power indicated by battery 16 is connected in series with any suitable load 18 and across the conductive films 8 and 12.

In the operation of this photosensitive assembly, light strikes the unit from the top as indicated by the arrow 20 passing down through the photoconducting semiconductor layer 2 as indicated by the path 22. It then proceeds through the interface between layers 2 and 6 and on into the electroluminescent semiconductor 6 which causes this to electroluminesce and transmit waves of a certain color or wave length which waves are inclined to spread from the beam through the first layer as indicated by the arrows and the angled rays are reflected from the interface 8 between layers 6 and 10 causing the rays to bounce back, induce new conductive areas 24 along the lower surface of the photoconductive layer 2 and be reflected therefrom. These areas 24 in turn induce further electr0 luminescence of the electroluminescent layer 6 thereby further increasing the total conductivity in the semiconductor 10. This dispersion continues until most of the area of the lower part of the layer 2 is conducting and electroluminescent layer 6 glows in proportion to the intensity of the incident light beam 20. Each of these additional areas now induce additional conductivity columns such as 26, 28 and 30 in the lower photoconducting layer 10 to amplify the response of the total unit to the incident light. Naturally each of these conductivity columns afiects the total flow of current I flowing through the load and thus a relatively weak beam of light can cause a considerable change in conductivity in the load circuit to control any desired device.

FIGURE 2 illustrates the use of several of these laminar units in series to produce an even greater response. In that case the upper unit indicated as transducer 1 could be the same as that shown in detail in FIGURE 1 and comprising a photoconducting layer 2, an electroluminescent layer 6 and a second photoconducting layer 10 all of which are bracketed and labeled transducer No. 1. However, in this case, photoconducting layer 10 may also act as the upper photoconductive layer of a similar laminar body labeled transducer No. 2. In that case it is also associated with a second electroluminescent layer 32 and a third photoconducting layer 34. Thus photoconducting layer 10 is common to both transducers but the result is that a double effect is obtained by such construction. Proper bias voltages are applied through voltage sources 14, 16 and 36 and in this case, of course, the output signal or control is taken off the conductive films 38 and 40 on opposite sides of the photoconductive layer 34.

It will thus be seen that this invention provides an efficient light sensitive transducer for converting ambient light into control currents or voltages.

I claim:

In photoelectric means for controlling a load, a source of light rays which vary in intensity, a laminated body one surface of which is exposed to the varying amounts of radiation from said source of light rays, said laminar body including a first and a second outside layer of photoconducting material on opposite sides of a central layer of electroluminescent semiconductor material, said central layer of electroluminescent material when excited emitting light rays having a wave length in the band con- 3 ducted by one of the photoconducting semiconductor layers, means to apply an electric voltage across the first photoconducting and electroluminescent layer, a second voltage supplying means, and circuit means connecting the second voltage supply means in series with the second photoconducting layer and the load which is affected by the variations in the intensity in incident light.

De Forest et al Apr. 29, 1952 Briggs Oct. 26, 1954 41 Sheldon Mar. 20, 1956 Ullery Dec. 11, 1956 Rosen Dec. 10, 1957 Halsted May 27, 1958 Rothschild Dec. 1, 1959 Hanlet Mar. 22, 1960 Kazan June 21, 1960 OTHER REFERENCES Bube: Photoconductivity of Solids, 1960, John Wiley 10 & Sons, New York, pp. 229-235.

Hausmann & Slack: Physics, 2nd edition, August 1939, D. Van Nostrand, New York, pp. 609-617.

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