US2984795A - Microwave applications of semiconductors - Google Patents

Description

May 16, 1961 J. J. A. ROBILLARD MICROWAVE APPLICATIONS OF SEMICONDUCTORS Filed May 16, 1957 3 Sh Illlll MODULATING SIGNAL SOURCE eats-Sheet 1 MODULATING- SIGNAL SOURCE INVENTOR JEAN.IA.ROHLLARD BY 3 m Wm H IS ATTORNEYS May 16, 1961 J. J. A. ROBILLARD 2,984,795

MICROWAVE APPLICATIONS OF SEMICONDUCTORS Filed May 16, 1957 3 Sheets-Sheet 2 FIG.6.

IIIIIIIII'II'IIII INVENTQR JEAN JULES ACHILLE ROBILLARD BY MW 'l/um. QM DW HIS ATTORNEYS May 16, 1961 J. J. A. ROBILLARD MICROWAVE APPLICATIONS OF SEMICONDUCTORS Filed May 16, 1957 3 Sheets-Sheet 3 lllllllllllllllll llll.

IIIII'IIIIIIIIIIIIIIIIIIIIIIIIII a INVENTOR JEAN JULES ACHILLE ROBILLARD H IS ATTORNEYS United States Patent MICROWAVE APPLICATIONS OF SEMICONDUCTORS Jean Jules Achille Robillard, Stockholm-Vallingby, Sweden, assignor to Motorola, Inc., Chicago, 111., a corporation of Illinois Filed May 16, 1957, Ser. No. 659,615

19 Claims. (Cl. 332-31) This invention relates generally to methods and apparatuses wherein electrical energy is manifested as electromagnetic waves, the phrase electromagnetic wave being used herein to denote waves, as, say, microwaves, which are in the radio frequency region of the electromagnetic spectrum. More particularly, this invention relates to methods and apparatuses of the described sort which employ semiconductor means to effect the performance of various electrical functions.

This application is a continuation-in-part of my copending application Serial No. 591,862 filed June 18, 1956, now abandoned, for Electromagnetic Wave Apparatuses and Methods.

For a better understanding of the invention, reference is made to the following description and to the accompanying drawings wherein:

Fig. 1 is a diagram illustrative of conditions under which there may be obtained a semiconductor fieldeffect;

Fig. 2 illustrates, partly by a circuit diagram and partly by a front elevation view in cross-section, a representative embodiment of the invention;

Figs. 3 and 4 are diagrams explanatory of the mode of operation of the Fig. 2 embodiment;

Fig. 5 illustrates, partly by a circuit diagram and partly by a front elevation view in cross-section, another representative embodiment of the invention;

Fig. 6 illustrates some of the details of a modification of the Fig. 2 embodiment;

Fig. 7 shows, partly by a circuit diagram and partly by a front elevation view in cross-section, the Fig. 6 embodiment in further detail;

Fig. 8 shows, partly by a circuit diagram, and partly by a front elevation view in cross-section, the Fig. 2 embodiment in further detail; and

Fig. 9 illustrates, partly by a circuit diagram and partly by a front elevation view in cross-section, a modification of the Fig. 5 embodiment.

Referring to Fig. 1, the number 10 designates a thin elemental volume of semiconductor material (as, say, semiconductive germanium or semiconductive silicon) having the major faces 11, 12 and the edge faces 13, 14. It is known that if, in some manner an electric field e represented by the arrow 15, is generated inside the e1emental volume 10 to have a gradient as indicated by arrow '15, and to have an areal distribution, transverse to the gradient, which is coextensive with the major surfaces 11, 12, then the conductivity of the elemental volume between the edge faces 13, 14 will vary in accordance with the strength of the interior electric field. Accordingly, if a difference of potential, V V is caused to exist between the edge faces 13, 14, the intensity of current, represented by the arrows i, which flows between these edge faces, as a result of the potential difference, will be varied in intensity in accordance with the intensity of the interior electric field e. The phenomenon just described is known as the semicon- Patented May 16, 1961 ductor field-effect and is discussed in the following references.

Shockley and Pearson, Modulation of Conductance of Thin Films of Semi-Conductor by Surface Changes, Phys. Rev. Vol. 74, pp. 232-3, July 15, 1948.

Shockley, Electrons and Holes in Semi-Conductors, D. Van Nostrand Co. Inc., New York, 1950.

Shockley, A Unipolar Field Effect Transistor, Proc. IRE Vol. 40, Nr. 11, p. 1365, November 1952.

Dacey and Ross, Unipolar Field Effect Transistor, Proc. IRE Vol. 41, nr. 8, p. 970, August 1953.

In the prior art, it has been the practice to develop the described electric field e within semiconductor bodies by utilizing a conventional voltage source, and by applying the voltage of this source through ordinary electrical conductors or the like to two terminal plates which contact the semiconductor body on opposite sides thereof. Such mode of developing the interior field, while satisfactory for some applications, is not satisfactory for other applications. Thus, for example, the described prior art technique of developing the field e is not suitable in the instance where it is desired to vary the strength of this field at a very high frequency rate as, say, 3000 megacycles.

It is, accordingly, an object of this invention to provide methods and apparatuses which permit the semiconductor field-effect to be utilized in high frequency applications.

Another object of the invention is to provide methods and apparatuses wherein the semiconductor field-effect may be utilized at high frequencies to perform electrical functions as, say, maintenance of oscillations, amplification, modulation, and detection.

These and other objects are realized, according to the invention, by providing at least one semiconductor body, and by providing electroconductive closure means adapted to sustain electromagnetic waves in a localized region of space outside the semiconductor body, and to cause the waves and the body to be so coupled that the electric force lines of the waves intercept a surface of the body. Such mode of coupling of the body and the waves will be termed herein a capacitive coupling, and is to be distinguished from a coupling which is accomplished by magnetic-field lines, and which is usually termed an inductive coupling.

When the electromagnetic waves and the semiconductor body are capacitively coupled as described, the electric force lines which intercept the surface of the body will, in effect, penetrate this surface to set up an oscillatory electric field e interiorly of the body. As already indicated, this interior electric field, where present, affects, according to its strength, the conductivity of the body transverse to the gradient of the field. To take advantage of this relation between interior field and conductivity, there is provided, according to the invention, electrode means connected to the body to define therein a path of flow for current generated exteriorly of the body. This path of flow is defined by the electrode means to extend through the mentioned interior electric field transversely of the gradient thereof. The conductivity of this path will be modulated in accordance with the intensity of the interior electric field, and this modulation of conductivity may be utilized to obtain various useful electrical effects of which some will be later described.

Enlarging on the description just given, the electroconductive closure means may be in the form of electroconductive casing which bounds at least one resonant cavity in the sense that it forms the closure wall or walls for at least part of the cavity. The cavity is adapted to sustain electromagnetic waves oscillating in a predetermined, standing wave mode to produce at least one peak of electric field component in a predetermined region of the cavity. Neither the shape of the cavity, nor the particular mode in which the electromagnetic waves oscillate therein, nor the number of peaks and modes of electric field characterizing such mode of oscillation are factors which are particularly critical to the instant invention. Accordingly, various cavity configurations and various modes of oscillation may be used in the practice of the invention. It has been found convenient, however, to use a cylindrical cavity wherein the electromagnetic waves oscillate in the TM mode. Moreover, in order to improve the operating characteristics thereof, the cylindrical cavity may be of the so-called rhumbatron type wherein one or both of the members which close off the ends of the cylinder are made r e-entrant to increase the capacitive coupling between these end members.

The resonant cavity just described has associated therewith at least one thin semiconductor body having areal extension transverse to its thin extent, and having a surface concomitant to the mentioned areal extension. The body is disposed in relation to the cavity to have the mentioned surface of the body in exposed relation to the peak field in the mentioned cavity region to thereby render the semiconductor body in capacitively coupled relation with the peak field. Thus, for example, the semiconductor body may be disposed in relation to the cavity so that the surface of the semiconductor body forms a bounding area of the cavity at a space termination of the region of peak electric field.

Electrical connections may be made to the semiconductor body through electrodes therefor. A first of these electrodes may connect the semiconductor body, through a first portion thereof, to the electroconductive casing of the cavity, and a second of these electrodes may provide an electrical connection to the semiconductor body at a second portion thereof which is separated from the first portion, transversely of the thin extent of the body, in such manner that any current passing between the two mentioned portions will also pass beneath surface area of the body which is exposed to the peak region of electric field. The first electrode may be provided by a portion of the resonant cavity casing which extends about the perimeter of the semiconductor body to make an electrical connection at this perimeter. The second electrode may be provided by a conductor connected to the body at a portion thereof which is within the mentioned perimeter, and which is centrally located in relation thereto.

The ability of the electromagnetic waves in the resonant cavity to produce a substantial degree of modulation in the conductivity of the semiconductor body depends significantly upon the relation between the dimensional value of the semiconductor body in its thin extent, and the skin depth characterizing the electroconductive casing at the frequency of oscillation of the electromagnetic waves. By way of explanation, in a resonant cavity as described, the currents produced in the electroconductive casing of the cavity by the electromagnetic waves will have an intensity which varies with the depth of the current from the surface of the casing which bounds the cavity. More specifically, if current intensity is considered as a function of depth from the surface of the casing exposed to the electromagnetic waves, the value of current intensity will drop off asymptotically with depth such that, for any given frequency, the current intensity value approaches a limiting value of zero as the depth approaches a certain value as a limit. This limiting depth for current in the electroconductive material of the casing at a given frequency is known as the skin depth of the material at such frequency. The skin depth value for a given electroconductive material at a given frequency can be calculated'in a manner well known to the art.

It is fundamental that, where electric currents exist, an electric field also exists. Thus, there corresponds with the depth distribution of currents in the semiconductor body, an electric field which may be considered as extending inward from the surface of the body. The electric field just referred to is the same as the interior electric field e previously referred to and previously explained in terms of penetration into the semiconductor body of the electric field lines characterizing the elecgromagnetic waves in the region of space outside the ody.

It has been found in accordance with the invention that there is a direct relationship between the skin depth value to which the electromagnetic waves can be considered to penetrate the electroconductive casing of the resonant cavity, the thickness value of the semi-conductor body in its thin extent and the efiiciency of performance of the microwave devices described herein. More specifically, it has been found that for most efiicient performance there should be substantial correspondence in value between the skin depth characterizing the material of the casing at the frequency of the waves in the resonant cavity and the thickness of the semiconductor body in its thin extent. The described condition of substantial correspondence between the skin depth value of the casing at a given frequency and the thickness value of the thin dimension of the semiconductor body, represents a more eificient condition than if the semiconductor body were thinner than the skin depth value of the casing. This is so, since if the semiconductor body is thinner than is necessary, the current carrying capacity of the semiconductor body is lessened. Also, the described correspondence condition represents a condition giving more efficient performance than if the thin dimension of the semiconductor body were greater than the skin depth value of the casing at the given frequency. It has been found, if the thin dimension of the semiconductor body substantially exceeds the skin depth of the casing, that there is an undesirable lessening in the amount of energy which is transferred from the semiconductor body to the cavity, and that, moreover, an undesirable amount of energy is dissipated in or through the semiconductor body without doing any useful work. Accordingly, optimal performance is obtained in the embodiments to be described when the thin dimension of the semiconductor body exactly or closely corresponds in value with the skin depth value characterizing the material of the electroconductive casing for the frequency of oscillation of the electromagnetic waves in the resonant cavity. However, a less satisfactory but still usable performance may be obtained even though the thin dimension of the semiconductor body is somewhat lesser or somewhat greater than the skin depth value characterizing the material of electroconductive casing under the given operating conditions. Thus, the desideratum that the thin dimension of the semiconductor body correspond with the skin depth value of the casing under the given operating conditions is not to be given too rigid an interpretation.

As later described in further detail, if an electrical energy source means is coupled through the electroconductive casing and through the mentioned conductor (which, as described, respectively act as first and second electrodes) to the semiconductor body, the source means will apply to the body a voltage directed transversely of the thin dimension of the body. Accordingly, there will be developed, in the body, a current which flows transversely of the electric field e generated therein by the electromagnetic waves. The intensity of this current will be modulated by the electric field as this field varies in intensity at the oscillation frequency of the electromagnetic waves. This current modulation effect may be utilized for the purposes, say, of starting and maintaining electromagnetic wave oscillations in the resonant cavity, or for amplification, or for detection. If the electrical energy source means provides a variable output, the described current modulation eifect in the semiconductor body may be utilized for the purpose of modulation of electromagnetic waves in accordance with this .variable output. A further explanation of how these electrical functions may be performed is given in the followmg description of representative embodiments of the invention.

Referring now to Fig. 2, a cylindrical resonant cavity is defined by an electroconductive casing 21 comprismg a cylindrical shell 22 and a pair of annular plates 23, 24 which close off the two ends of the cylindrical shell. A pair of re-entrant cylinders 25, 26 extend from the inside perimeters of the annular plates 23, 24 towards each other to give the cavity 20 the well-known rhumbatron configuration. A disc 27, formed of a thin film of semiconductor material, extends across the inwardly located end of re-entrant cylinder 25 to close off this end of cylinder 25. Another disc 28, formed of a thin film of semiconductor material, extends in like manner across the inwardly-located end of re-entrant cylinder 26 to close ofi the said end of cylinder 26.

As shown in Fig. 2, the discs 27 and 28 are supported in position by being secured at their perimeters 29, 30, to, respectively, the cylinders 25, 26 by, say, silver brazing the discs to the cylinders to provide a good electrical contact between each disc and its supporting cylinder. If desired, however, the discs 27, 28 may be mounted on electroconductive substrate mem bers which extend across the inner ends of the cylinders 25, 26. Even if mounted on such substrate members, the discs should be electrically connected at their perimeters to their respectively associated cylinders.

As stated, the discs 27, 28 are formed of thin films of semiconductor material which may conveniently be semiconductive germanium. These films are sufficiently thin to provide that, when a predetermined standing wave move of electromagnetic wave oscillations is initiated in the cavity 20, the thickness of each of the discs in their thin dimension will substantially correspond with the skin depth value characterizing the material of the casing 21 at the oscillation frequency of the electromagnetic waves. The films of which the discs 27, 28 are formed have been films which are monocrystalline in internal structure. These monocrystalline films may be prepared in the manner taught in my copending US. pggent application, Serial No. 569,421, filed March 5, 1 6.

Excitation of the resonant cavity 2% by external electrical energy is provided for by a pair of similar electrio energy sources, represented in Fig. 2 by the batteries 35, 36; The negative terminal of battery is connected to a movable contact 38 selectively closable with either of two fixed contacts 39, 40, while the positive terminal of battery 36 is connected to a movable contact 38' selectively closable with either of two fixed contacts 39', 40'. The movable contacts 33, 33' are ganged together. The fixed contacts 39, 39 are connected to the cylindrical shell 22 at a portion thereof which is centrally located in relation to the extent of the shell in the direction of the axis of the cylinder defined by the shell. The fixed contacts 40, 40 are connected to opposite terminals of a balanced modulating signal source 41 whose point of zero modulating signal is connected to shell 22.

The positive terminal of battery 35 may be electrically connected to the center 45 of semiconductor disc 27 by way of single-pole, single-throw switch 43, and by way of a conductor 44 which serves as one electrode for this semiconductor disc. Similarly, the negative terminal of battery 36 is connected to the center 47 of semiconductor disc 28 by a conductor 46 which serves as the one electrode for this latter disc. As already indicated, the other electrodes for these discs are provided by the portions of re-entrant cylinders 25, 26 to which the discs 27 and 23 are respectively secured.

As will soon be described, the system shown in Fig. 2 is adapted to generate and to sustain electromagnetic wave oscillations in the resonant cavity 211). A portion of the electromagnetic wave energy developed by these oscillations may be extracted from the cavity 20 by output means shown in Fig. 2. as a coaxial line 50 whose inner conductor 51 forms, in effect, a single turn loop inside the cavity 20 to inductively couple the cavity 20 to the coaxial line. If convenient, however, energy may be extracted from the cavity by electromagnetic wave transmission means which is capacitively coupled rather than inductively coupled to the cavity.

In operation, the electromagnetic waves within cavity 20 will oscillate in the TM mode. For this mode of operation, a standing wave peak of electric field, repre sented by the arrows B, will appear in the region of space between the semiconductor discs 27, 28. The direction of this peak field will correspond to that shown by the arrows E for one half-cycle of each oscillation, and will be reverse to that shown by the arrows for the other halfcycle.

To ready the cavity 20 for the generation of simple oscillations, the movable contacts 38, 38 are set in closed positions with fixed contacts 39, 39' to thereby directly connect the negative and positive terminals of, respectiveiy, the batteries 35 and 36 to the casing 21. Thereafter, the switch 43 is thrown to closed position to initiate sustained electromagnetic wave oscillations in the cavity 20 in the manner which will now be explained.

Suppose that during a short time I an oscillation is produced in the cavity. Such an oscillation of short duration may be caused to arise by throwing of the switch 43 to closed position to produce a transient current I in the cavity. While this current I in the cavity rapidly decreases in time t due to losses in the walls of the cavity, at the same time the transient oscillation developed in the cavity will cause a strong electric field E to appear between the discs 27, 28. This strong electric field decreases the resistivity of the discs between the respective centers 45, 47 thereof and the respective perimeters 29, 30 thereof. As a result of this decrease in resistivity an extra increment of Ai of the current i from battery 35 will, as shown in Fig. 3, flow from the center 45 to the perimeter 29 of disc 27. Similarly an extra increment of current A1" of the current i from battery 36 will, as shown in Fig. 4, flow from the perimeter 30 to the center 47 of disc 28. These extra increments of current are more than enough to compensate for the losses sustained in the walls of the cavity by the initially developed current I. Accordingly, the mentioned extra increments of current will cause a further increase in the electric field between discs 27, 28. This further increase in the field causes a further increment of current to flow in each of discs 27, 28, and so on, in a cumulative action. The cumulative action just described represents the characteristic action whereby oscillations are produced. Accordingly, once a transient oscillation has been induced in cavity 20 by closure of switch 43, the oscillations in the cavity will be built up and sustained by the external energy supplied from the power sources 35, 36. Pre sented in another way, the semiconductor discs 27, 28 act as variable negative resistances which are modulated by the electric field in the cavity in order to inject into this cavity a certain amount of power from the sources 35, 36. This injected power serves to make up for the losses sustained in the cavity, and, accordingly, causes the oscillations in the cavity to continue.

In order to maintain oscillations in the resonant cavity 2!), it is necessary that the externally-applied voltage (from the batteries 35, 36) between the discs 27, 28 be such that this externally-applied voltage is equal to or exceeds a lower limit voltage whose value is determined by the operating parameters of the cavity circuit. When the externally-applied voltage just equals this lower limit voltage, oscillations will barely be maintained in the cavity 20. As the externally-applied voltage increases in value from the lower limit voltage, the strength of the cavity oscillations will also increase, and through a certain range of increase to an upper limit voltage the relation between the externally-applied voltage and the intensity of oscillations will be a linear one. Beyond this upper limit voltage, the oscillations will cease.

The phenomenon just described can be taken advantage of in the following manner. The batteries 35, 36 (or equivalent electrical energy sources) which are used in the Fig. 2 system may be selected to provide voltage outputs such that the externally-applied DC. voitage which appears between discs 27 and 28 has a value which is intermediate the values of the lower limit voltage and the upper limit voltage. The movable contacts 38, 38' are then thrown to close with fixed contacts 40, 40 such that the modulating signal source 41 is connected in series with the batteries 36, 36. In the present instance, it is assumed that the signal source 41 provides an A.C. modulating voltage. This A.C. modulating voltage will be superposed with the DC. voltages provided by batteries 35, 36 such that the externally-applied voltage which appears between the discs 27, 28- will be comprised of a DC. component and an A.C. modulating component. Provided that the modulating component does not swing the value of the externally-applied voltage below the lower limit voltage or above the upper limit voltage, the modulating component of the externally-applied voltage will cause the electromagnetic wave oscillations in cavity 20 to be amplitude modulated in a linear manner. These amplitude modulations of electromagnetic wave energy will appear in the energy which is extracted from the cavity by the coaxial line 50. Of course, when the cavity oscillations are to be modulated, the highest frequency component of the modulating signal should be substantially less than the oscillation frequency of the electromagnetic waves in the cavity.

Referring now to the embodiment shown in Fig. 5, the elements of this embodiment which are designated by the numerals 21-26, inclusive, 50, and 51 are counterparts of the similarly numbered elements in the Fig. 2 embodiment, and, hence, will not be described in detail in connection with the Fig. embodiment. As shown in Fig. 5, an annular plate 60 extends transversely of the interior of cylindrical shell 22 to subdivide the space within this shell into an input resonant cavity 61 and an output resonant cavity 62. Both cavities are shaped to give oscillations in the TM mode at the same frequency.

A semiconductor disc 63 extends across the central aperture of the annular partition plate 60 such that the lower surface of the disc forms a bounding area for cavity 61, and such that the upper surface of this disc forms a bounding area for the cavity 62. The inwardly located ends of the re-entrant cylinders 25, 26 are respectively closed off by plates 64 and 65 of electroconductive material as, say, copper.

External electric energy for exciting the cavity 62 is provided by an electrical energy source 70 represented in Fig. 5 by a battery. The positive terminal of battery 7 0 may be connected through a switch 71 and a lead 72 to the center of the plate 64 which closes off re-entrant cylinder 25. The negative terminal of battery 70 is connected to the fixed contact-73 of a switch comprised of the mentioned fixed contact, another fixed contact 74, and a movable contact 75 which is selectively closable with either fixed contact 73 or fixed contact 74. The negative terminal of battery 70 is also connected to one terminal of a modulating signal source 76 whose other terminal is connected to fixed contact 74. The movable contact 75 is connected through a lead 77' to the center point 78 of the disc 63. The lead 77 may reach this center point 78 by passing through an insulating plug (not shown) which is set into a small aperture formed in the wall of cylindrical shell 22.

Ash; the case of the Fig. 2 embodiment, the semiconductor disc 63 is constituted of a film of semiconductor material which has a monocrystalline internal structure. As before, the perimeter 80 of semiconductor disc 63 is in electrical contact with the rim of the central aperture of annular plate 66. The extent of disc 63 from its lower surface to its upper surface substantially corresponds with the skin-depth value for the electroconductive material of the casing of the resonant cavities at the frequency characterizing the electromagnetic wave oscillations in the cavities 61, 62.

The Fig. 5 embodiment is adapted, inter alia, to act as an amplifier of electromagnetic waves injected into the cavity 71. Such injection may be accomplished by an input coaxial line whose inner conductor 86 forms, in effect, a single turn loop inside cavity 61 to inductively couple the waves transmited by the coaxial line to the cavity.

The Fig. 5 embodiment is adapted to act as an electromagnetic wave amplifier when operated in the following manner. Assume that amplitude modulated electromagnetic waves are being injected from coaxial line 85 into cavity 61 to set up therein electromagnetic wave oscillations in the TM mode. To produce simple amplification, the movable contact 75 is thrown to close with fixed contact 73, and, thereafter, the switch 71 is closed. An externally-applied DC. voltage will now be developed between the connection of lead 72 with closure piate 64 and the center point 78 of the disc 63. At the same time, the peak of the oscillating electric field appearing between disc 63 and closure plate 65 in cavity 61 will (in the manner described for the Fig. 2 embodiment) produce high frequency variations in the conductivity of disc 63 between its center point 78 and its perimeter 80. The disc 63 not only forms a bounding area for cavity 61, but also forms a bounding area for the cavity 62. Accordingly, the D.C. voltage applied from battery 70 and the variations in conductivity produced in disc 63 by the oscillations in cavity 61 will, as a result of their combined action, establish electromagnetic wave oscillations of the TM mode in the resonant cavity 62. The oscillations so set up in cavity 62 will have a greater energy content than the oscillations developed in cavity 61. Accordingly, the Fig. 5 system acts as an amplifier wherein the energy drawn off from the system by coaxial line 50 exceeds the energy supplied to the system by coaxial line 8 5.

While the operation of the Fig. 5 system has been described in terms of amplification, the system is capable of performing other electrical functions as well. To wit, for a given intensity level of oscillations in cavity 61, there exists, for the DC. voltage applied to cavity 62, a lower critical value, at which oscillations just start in cavity 62, and an upper critical value at which oscillations will cease in cavity 62. (These critical values for the Fig. 5 system are not the same as the upper and lower limit voltages mentioned in connection with the Fig. 2 system.) Conversely, for a given value of DC. voltage, there is an upper critical intensity value for the oscillations in cavity 61 such that oscillations therein of greater intensity value than the upper critical value will not produce oscillations in cavity 62, whereas oscillations in cavity 61 of less intensity value than the upper critical value will produce oscillations in cavity 62.

Assume now, that the oscillations in cavity 61 are amplitude modulated so that the oscillations swing in intensity between upper and lower limiting values. Assume, moreover, that the DC. voltage is of a value such that the upper critical value for oscillation intensity in cavity 61 falls between the upper and lower limits of the intensity swings in cavity 61. It follows that oscillations will be produced in cavity 62 whenever the oscillations in cavity 61 swing in intensity below their critical intensity value, and that oscillations will not be produced in cavity 62 whenever the oscillations in cavity 61 swing in intensity above their critical value. If the amplitude modulation of the oscillations in cavity 61 is sinusoidal in nature, and if the upper critical intensity value for these oscillations is established as halfway between the upper and lower limits of the amplitude modulation swings, then the oscillations in cavity 62 will reproduce the amplitude modulation of the oscillations in cavity 61 only for negative half cycles of the modulation. Thus, the Fig. system, when appropriately operated, is adapted to give an action similar to rectification, and this action may be used to provide detection of the amplitude modulation.

The Fig. 5 system is also adapted to impress amplitude modulation on electromagnetic wave oscillations. As a simple example of the way in which such modulation can be produced, assume that the input to cavity 61 is an unmodulated input which establishes oscillations of given constant intensity value in the cavity 61. Assume further, that the DC. voltage from battery 70 is intermediate the lower and upper critical values therefor which correspond to the assumed constant intensity value of the oscillations in cavity 61. The movable contact 75 is thrown to close with fixed contact 74 to thereby couple the modulating signal source 76 in series circuit with the battery 70. By virtue of this series circuit connection, the external voltage applied to cavity 62 will be the resultant of a DC. component and a modulating component, the latter component being derived from source 76. So long as the voltage swings in the modulating component do not cause the mentioned externally-applied voltage to be driven further in value than the mentioned critical values (at which oscillations in cavity 62 will cease), electromagnetic wave oscillations will be continuously generated in cavity 62, and these last-named electromagnetic oscillations will be modulated in intensity in accordance with the modulating component of the externally-applied voltage. By utilizing appropriate values of DC. component and appropriate peak-to-peak swing values for the modulating component, it is possible, in the described manner, to obtain linear modulation.

Fig. 6 illustrates a modification of the oscillator embodiment shown in Fig. 2. The embodiment of Fig. 6 differs from that of Fig. 2 in the following respects. First, in Fig. 6 the plate 24 is a circular plate of continuous radius rather than an annular plate, the re-entrant cylinder 26 and the semiconductor disc 28 (Fig. 2) having been eliminated. Second, in Fig. 6 a single battery 90 and a serially-connected single pole, single throw switch 91 are shown (for purposes of simplifying the disclosure) as replacing the circuit of Fig. 2 which is external to the resonant cavity structure. It will be appreciated, however, that the source of modulating signal shown in Fig. 2 may, if desired, be used with the Fig. 6 embodiment to modulate the oscillations produced in the cavity. Third, in Fig. 6 a body 92 of material having a high dielectric constant is interposed between the semiconductor disc 27 and the end plate 24. This body 92 may be comprised, for example, of polystyrene impregnated with barium titanate. The Fig. 6 embodiment operates in much the same manner as the Fig. 2 embodiment in that the switch 91 is closed to produce a transient electromagnetic wave oscillation in the cavity 20, and in that this oscillation, when once produced, will be sustained indefinitely by virtue of the periodic variations in transverse conductivity which are induced in semiconductor disc 27 by the capacitive coupling thereof to the waves in the cavity. The'dielectric body 92 serves to intensify the capacitive coupling of the waves in cavity 20 to disc 27 to thereby increase the efliciency of the disc as a supplier of oscillatory energy to the cavity.

Fig. 7 represents another illustration of the embodiment shown by Fig. 6. It is to be noted that in Fig. 7 the elements of the embodiment are shown in the positions which they would occupy if the Fig. 6 drawing were turned upside down. Thus, for example, in Fig. 6 the 10 circular plate 24 is shown at the bottom of the resonant cavity structure, whereas in Fig. 7 the element 24 is shown at the top of the cavity structure.

Fig. 7 is of interest in that it goes beyond Fig. 6 to show certain features which, in practice, may be very usefully incorporated into the embodiment under consideration. With regard to these useful features, it will be noted that the annular plate 23 is extended radially outward beyond the cylindrical shell '22 to form a circular flange 95. An annular plate 96 having the same inner and outer radii as the annular plate 23 is disposed in relation to plate 23 to be coaxial therewith and to be axially spaced therefrom in a direction away from cavity 20. Interposed between the annular plates 23 and 96 is a disc 97 of a solid dielectric material as, say, polystyrene. The outer radius of plate 23 as extended, plate 96 and disc 97 is given by the expression:

4 /e where n is any odd integer, is the wave length corresponding to the resonance frequency of the cavity 20 and e is the dielectric constant of the material in the disc 97. Preferably, n has a value of 1.

As explained later in further detail, the structure formed of plate 23 as extended by flange 95, plate 96 and dielectric disc 97 is adapted to act as a wave trap. The dielectric disc 97 permits a given electrical length for the wave trap to be obtained with a mechanical radius which is shorter than that which would be required for the same electrical length if air dielectric were used. Also, the use of solid dielectric simplifies the support problem.

The cylinder 25, extending into cavity 20 from plate 23, has a counterpart in a hollow cylinder 100 which encompasses the circular aperture of annular plate 96, and which extends from this aperture in a direction outward and away from the cavity 20 and the cylinder 25. Electrically speaking, the cylinders 25 and 100 act as the single continuous outer conductor of a coaxial line whose inner conductor is represented in Fig. 7 by the rod 101. This rod acts as the central electrode for semiconductor disc 27. As shown, the rod 101 extends upwardly through cylinder 100, passes through a small aperture in the disc 97, and then extends upwardly through cylinder 25 to connect with the center 45 of the semiconductor disc 27. The lower portion of rod 101 is received into the aperture of an annular tuning piston 162 which is slidable on the rod to permit axial adjustment of the tuning piston within the cylinder 100. A handle 163 on the tuning piston makes for easier adjustment.

The tuning piston 102 provides an R.F. termination or short circuit for the coaxial line whose outer conductor is provided by the cylinders 25 and 100, and whose inner conductor is provided by the rod 101. By adjusting the axial position of the tuning piston, it is possible to match the impedance of the coaxial line to the impedance of the resonant cavity 20. For R.F. termination purposes, the piston 102 need not be so close fitting with the inner wall of cylinder 190 as to make mechanical contact therewith. If it is desired to have the piston 102 act as a bridge for DC. current from the cylinder 100 to the rod 191, the piston 192 may be provided around its periphery with a set of resilient conducting fingers (not shown) which slide over the inner surface of cylinder 100 as the tuning piston is moved. Alternatively, a flexible lead 104 may, as shown, be connected from cylinder 100 to rod 101 to conduct DC. current from the former to the latter.

in Fig. 7, the battery 96 and the switch 91 are shown as connected to the resonant cavity structure through a pair of RF. isolating chokes and 111. The path for DC. current flow is as follows: from the negative terminal of battery 99, through choke 110, plate 96, cylinder 19%), lead 104 and rod 101 to the center of semiconductor disc '27 and, from thence, radially through disc 27, through cylinder 25, annular plate 23 (including fiange 55), lead 111, switch 91, and back to the positive terminal of battery 90. As mentioned, in this circuit the combination of the annular plate 23 and flange 95, the annular plate 96 and the dielectric disc 97 act together as a wave trap which has an electrical length equivalent to an odd number of quarter waves at the frequency of resonance of the cavity. The wave trap isolates the battery 90 from most of the R.F. modulation which is impressed on the DC. current in the semiconductor disc 27. Any R.F. modulation which is not filtered out by the described wave trap will be filtered out by the chokes 110 and 111.

Fig. 8 is an illustration of the Fig. 2 embodiment when provided with elements forming coaxial lines leading to the semiconductor discs 27, 28, and when .provided with elements forming wave traps who'se function is to isolate the batteries 35, 36 from the RF. modulation impressed on the DC. current. (In this figure the circuits external to the resonant cavity structure are shown in a simplified form which, however, is a usable one if no modulating signal is desired.) As shown in Fig. 8, each of the semiconductor discs 27, 28 has a separate coaxial line associated therewith and a separate wave trap associated therewith. These coaxial lines and wave traps of Fig. 8 need not be discussed in detail since they are counterparts of the coaxial line and wave trap which have already been discussed in connection with Fig. 7. As in the case of Fig. 7, if desired, a body of material of high dielectric constant may be interposed between the semiconductor discs 27 and 28 of Fig. 8. This body of dielectric material will serve to intensify the capacitive coupling of the waves in the resonant cavity to the semiconductor discs.

It will be appreciated that the Fig. 5 embodiment may be equipped with coaxial lines and wave traps in the manner shown by Fig. 8. Also, bodies of dielectric material may be employed to increase the capacitive coupling of waves in cavities 61, 62 to the semiconductor disc 63. One of these dielectric bodies would be interposed between semiconductor disc 63 and the end plate 64 for re-entrant cylinder 25, While the other of these dielectric bodies would be interposed between semiconductor disc 63 and the end plate 65 for re-entrant cylinder 26.

Fig. 9 is an illustration of the Fig. 5 embodiment as modified to eliminate the lead 77 which passes through the resonant cavity 61. By the elimination of this lead, the cavity 61 is rendered more symmetrical and will operate with better efiiciency. The modification is effected by substituting a thin electroconductive window 110 (Fig. 9) for the semiconductor disc 63 (Fig. 5) in the aperture of partition plate 60, and by substituting a semiconductor disc 111 (Fig. 9) for the electroconductive plate 64 (Fig. 5) which closes off the lower end of the re-entrant cylinder 25.

The window 110 may take the form of a very thin film of electroconductive material such as copper or aluminum. For improved ruggedness, the window 110 may be in the form of a metallic film deposit on a thin disc (not shown) which is constituted of a dielectric material as, say, mica, and which is anchored in the aperture of the annular partition plate 60. The window 110 should be sufiiciently thin to permit transmission through the window and into cavity 62 of some of the electromagnetic wave energy developed in cavity 61. This transmission of electromagnetic wave energy will take place when the window in its thin extent has a value less than the skin depth characterizing the window at the frequency of the waves in the resonant cavity 61. For best results the window should be made as thin as is practicable.

As is to be expected from the previous discussion, the dimensional value in its thin extent of the semiconductor film member 111 is optimal when equal to or close to the value of the skin depth characterizing the electroconductive casing of the resonant cavities for the frequency at which the electromagnetic waves will oscillate in the 12 resonant cavity 62. The film member 111 has a monocrystalline internal structure. The transverse conductivity of the semiconductor film member 111 will be modulated by the electromagnetic wave energy which is transmitted through window 110, and this conductivity modulation serves to impress on the DC. current flowing through the film member 111 an R.F. modulation which reinforces the transmitted wave energy. In this manner, the energy value of the electromagnetic wave oscillations in cavity 62 will be made greater than the energy value transmitted through window and, in fact, can be made substantially greater than the energy value of the electromagnetic wave oscillations in cavity 61. Thus, the Fig. 9 embodiment is adapted to operate like the Fig. 5 embodiment to perform the function of amplification, for example.

As in like manner to the embodiments shown in Figs. 7 and 8, the Fig. 9 embodiment may be provided with a coaxial line which leads to semiconductor film member 111, and may also be provided with a wave trap. Moreover, while the DC. circuit external to the resonant cavity structure is shown in simplified (but usable) form in Fig. 9, this external circuit may, if desired, include a signal source which is connected to add a modulating component to the DC component which is supplied to the resonant cavity structure.

Among the advantages of the described embodiments should be mentioned the fact that these devices will be characterized by a high signal/noise ratio since no hot 7 cathode is involved. These devices are, thus, highly suitable for use, for example, as sources of a local microwave signal which is suppled to the mixer stage of a microwave receiver to effect a frequency conversion downward of a microwave signal transmitted through free space and received by an antenna coupled to the receiver.

As practical examples of some of the dimensions which are involved in devices according to the present invention, at 3,000 megacycles the skin depth value characterizing an electroconductive casing of copper will be of a value which has an upper limit on the order of one micron. The skin depth value of an electroconductive casing of silver will be somewhat less than the skin depth value characterizing the casing of copper. For best eificiency of performance, the semiconductor film members employed in the described microwave devices should, as stated, have a thickness value which is equal to or close to the skin depth value characterizing the electroconductive casing. Thus, if the frequency of operation is 3,000 megacycles, and the electroconductive casing is of copper, the thickness of the semiconductor film members should have as an upper limit a thickness value on the order of one micron. In like manner, for a 3,000 megacycle operating frequency and an electro-conductive casing of copper, the window 110 of the Fig. 9' embodiment may have a thickness whose upper limit value is of the order of one micron.

As stated, the semiconductor film members which have been described may have a monocrystalline internal structure and may be prepared in the manner taught in my copending U.S. application, Serial No. 569,421, filed March 5, 1956. While the method of preparation of monocrystalline semiconductor film members is fully described in this last-named application, for convenience a brief description of the method is given herein.

In the method, there is employed as a substrate member a monocrystal of a substance whose lattice constant approximates that of the semiconductor material of which a film is to be formed. For example, a monocrystal of sodium chloride may be used if the semiconductor film is to be formed of germanium.

The substrate crystal is placed in a vacuum. A surface of the crystal, corresponding to a principal plane of crystallizationthereof, is freed of occluding gases and of its Beilby layer by ionic bombardment as taught on pages 74 et seq. of'the textbook. Vacuum. Deposition ofThiu Films by Holland (published by Chapman and Hall, Limited, London, 1956). Next, a high vacuum is produced for the atmospheric environment surrounding the substrate crystal, and a quantity of highly purified semiconductor material is vaporized into the high vacuum and permitted to condense on the mentioned surface. During the condensation of the semiconductor material the substrate crystal is accurately maintained, in a heated condition, within the critical temperature range at which the semiconductor material will condense in monocrystalline form on the substrate. For germanium, this critical temperature range is 428 C. i An C.

The degree to which the semiconductor material is condensing in monocrystalline form can be observed by directing a beam of elliptically polarized light onto the crystal surface, and by determining the degree of elliptical polarization of the reflected beam. Any tendency of the condensing semiconductor material to depart from monocrystalline growth (because of a drifting of the temperature of the substrate crystal away from the critical temperature range) will be indicated by a deterioration of the elliptical polarization pattern of the reflected beam. Appropriate measures can then be taken to bring the temperature of the substrate crystal back to within the critical temperature range.

After a monocrystalline layer of pure semiconductor material has formed on the substrate, an alloy of the semiconductor material and of a doping agent (e.g., indium when germanium is used for the semiconductor material) is vaporized into the vacuum. This alloy will condense as a thin amorphous overcoatin-g on the monocrystalline layer. The amorphous nature of the overcoating causes a temporary loss of the elliptical polarization of the reflected beam.

After the overcoating of alloy has been deposited, the substrate crystal is heated to cause uniform diffusion of the doping agent throughout the semiconductor material which has condensed. Suitable diffusion has been obtained when there is a reappearance in the reflected beam of the elliptical polarization pattern. The doping agent is diifused into the semiconductor material for the purpose of making this material an extrinsic semiconductor.

The monocrystalline film is separated from the substrate crystal by immersing the crystal and film in a solvent of the material of the substrate crystal. The solvent has beforehand been rendered near saturated with the constituent material of the substrate crystal in order to assure that the crystal will dissolve very slowly. In this manner it is possible to avoid strains in the crystal which might rupture the semiconductor film during the dissolving action. Once the semiconductor film has become separated from the crystal, the film may be transferred from the solvent to thereafter be incorporated in the microwave device.

In connection with the semiconductor bodies described herein, it is to be understood that the conductivity thereof, transverse to the interior electric field set up therein, depends not only on the strength of the field but on its direction as well. More specifically, if the field has one direction in the thin extent of the body, the transverse conductivity of the body will be increased relative to its transverse conductivity value in the absence of any interior field, but if the field has the opposite direction in the thin extent of the body then the transverse conductivity of the body will be decreased relative to the said transverse conductivity value in the absence of any field.

It will be realized, moreover, that the foregoing description has been simplified to the extent of attributing variations in the conductivity of the described semiconductor bodies entirely to the electric field component of the electromagnetic waves. In fact, the semiconductor bodies in the Fig. 2. and Fig. 5 systems are also coupled, to some extent, with the magnetic field component of the electromagnetic waves, and this magnetic field compo- 14 heat has some effect on the conductivity of the bodies. The effect of the electric field component is, however, the primary effect.

The above-described embodiments being exemplary only, it will be understood that the invention comprehends embodiments differing in form or detail from the abovedescribed embodiments. For example, in both the Fig. 2 system and the Fig. 5 system it is possible to produce intermittent modulation, as, say, pulse modulation, by utilizing a DC. component which is above the value therefor at which oscillations will cease in cavity 20 or cavity 62, as the case may be, and by having the modulation component of the externally-applied voltage cause this voltage to periodically swing below the mentioned value to thereby induce oscillations in the cavity for the period during which the externally-applied voltage is below the mentioned value. The modulating signals need not necessarily be A.C. signals, but may be signals which are positive-going from a reference level or signals which are negative-going from a reference level. In every embodiment the one or more semiconductor film members may, for greater ruggedness, be supported by substrate members which, however, in the case of the Fig. 5 and Fig. 9 embodiments, should be of dielectric material. Also, alternative structures may be employed in place of the described coaxial lines and wave traps to perform the functions thereof. Accordingly, the invention is not to be considered as limited save as is consonant with the scope of the following claims.

I claim:

1. Apparatus comprising, electroconductive closure means defining interiorly thereof at least one resonant cavity for electromagnetic waves oscillating in a predetermined mode to produce a peak of electric field in a predetermined region of said cavity, at least one thin semiconductor crystal whose thin extent substantially corresponds in dimensional value to the skin depth characterizing said electroconductive closure means at the oscillatory frequency of said waves, and which has areal extension transverse to its thin extent and a surface concomitant to said areal extension, said crystal being disposed with said surface in exposed relation to said peak field in said region to be capacitively coupled with said peak field, and said crystal being electrically connected through a first portion thereof with said closure means, and an electrode providing an electrical connection to said crystal at a second portion thereof separated from said first portion transversely of the thin extent of said crystal.

2. Apparatus comprising, electroconductive closure means defining interiorly thereof at least one resonant cavity for electromagnetic waves oscillating in a predetermined mode to produce a peak of electric field in a predetermined region of said cavity, at least one thin semiconductor crystal whose thin extent substantially corresponds in dimensional value to the skin depth characterizing said electroconductive closure means at the oscillatory frequency of said waves, and which has areal extension transverse to its thin extent and a surface concomitant to said areal extension, said crystal being disposed to have said surface form a bounding area of said cavity at a space termination of said region of peak electric field, and said crystal being secured at the perimeter of said surface to said closure means, and an electrode providing an electrical connection to said crystal at a portion thereof which is within said perimeter and centrally located in relation thereto.

3. Apparatus comprising, electroconductive closure means bounding at least one cylindrical resonant cavity for electromagnetic waves oscillating in the TM mode, at least one circular monocrystalline semiconductor film member whose thickness substantially corresponds in dimensional value to the skin depth characterizing said electroconductive closure means at the oscilulatory frequency ofsaidwaves, said member being perirmetrically connected to said closure means and being relatively disposed therewith such that said member is concentric with the axis of said cavity to bound said cavity at one end of an aidally-extending, radially-central region thereof, and an electrode providing an electrical connection to the radial center of said semiconductor film member.

4. Apparatus comprising, electroconductive closure means enclosing at least one cylindrical resonant cavity, at least one hollow cylinder extending re-entrantly into said cavity to render said cavity of rhumbatron configuration a thin semiconductor body extending across the inner end of said cylinder to thereby bound a portion of saidcavity, said semiconductor body being electrically coupled with said cylinder, a conductor contained by said cylinder and extending axially therein to an electrical junction with a central portion of said semiconductor body, said cylinder and conductor forming outer and inner conductors of a coaxial line leading to said semiconductor body, and a shorting member spaced away from said semiconductor body and electrically coupled between said cylinder and conductor to provide a radio frequency termination for said coaxial line at a distance from said semiconductor body.

5. Apparatus as in claim 4 wherein said shorting member is in the nature of a tuning piston which is adjustable in its position along said line to permit adjustment in the matching of the impedance of said coaxial line to the impedance of said resonant cavity.

6. Apparatus comprising, electroconductive closure means to sustain oscillating electromagnetic waves of predetermined frequency in a localized region of space, a semiconductor body electrically connected with said closure means and disposed in relation to said closure means to be field coupled with said electromagnetic waves, electrode means to supply current having a direct current component from a current source, said electrode means being coupled to said closure means and to said semiconductor body to produce a flow of said current through both of them in a path in which said current is impressed with radio frequency variations at said frequency through the occurrence of corresponding variations induced by said field coupled waves in the conductivty presented by said body in said path, and means forming a wave trap in the direct current circuit provided by said electrode means, closure means and semiconductor body, said wave trap having an electrical length equivalent to an odd number of quarter waves at said frequency whereby said wave trap is adapted to isolate said source from the radio frequency variations impressed on said current.

7. Apparatus comprising, an electroconductivecylindrical shell enclosing at least one resonant cavity having a predetermined frequency of resonance, at least one circular electroconductive plate disposed coaxially with said shell at one end thereof, said plate bounding a radiallyperipheral end portion of said cavity towards said end of said shell, and said plate projecting radially beyond said shell to define a circular flange, a thin circular semiconductor body disposed coaxially with said shell in mechanically and electrically coupled relation with said plate to bound a radially-central end portion of said cavity towards said end of said shell, an additional ciroular'electroconductive plate coaxial with said one plate and axially spaced therefrom away from said shell, said two plates in the radial direction being substantially coextensive and having an electrical length equivalent to an odd number of quarter waves at said frequency of resonance, and electroconductive means electrically coupling said additional plate to a central portion of said semiconductor body.

8. Apparatus as in claim 7 further comprising a disc of solid dielectric material interposed between said two electroconductive plates.

9. Apparatus comprising, electroconductive closure means defining, interiorly thereof first and second resonant cavities and a passageway extending through said closure means between respective local regions of said cavities each cavity being adapted to sustain electromagnetic waves oscillating in a predetermined mode to .produce a peak of electric field in the said local region of the cavity, a thin, electroconductive member extending across said passageway to be interposed between the said local regions of said two cavities, said member being adapted to transmit through its thin extent and into the second cavity some of the electromagnetic wave energy developed in said first cavity, and means to synchronously reinforce the wave energy transmitted into said second cavity through said member to thereby produce in said second cavity electromagnetic waves of greater energy value than that of the wave energy transmitted through said member.

10. Apparatus as in claim 9 wherein said electroconductive member in the thin extent has a dimensional value which is less than the skin depth characterizing said member at the frequency of the electromagnetic waves in said first cavity.

11. Apparatus comprising, an electroconductive casing defining a cylindrical space interiorly thereof, an annular electroconductive partition plate having a central circular aperture formed therein and extending within said casing transversely and concentrically of the axis of said space to subdivide said space into first and second cylindrical resonant cavities, each cavity being adapted to sustain electromagnetic waves which oscillate in the TM mode and which are of the same frequency for both cavities, a thin electroconductive member extending across said aperture to be perimetrically connected with the portion of said partition plate forming the marginal rim of said aperture, said electroconductive member being adapted to transmit into said second cavity through its thin extent some of the electromagnetic wave energy of said first cavity, a semiconductor film member disposed across said second cavity from said electroconductive member in axially spaced relation therefrom, said semiconductor film member being operatively coupled electrically with said local region of said second cavity and being perimetrically connected with said electroconductive casing, and an electrode providing an electrical connection to a central portion of said semiconductor film member.

12. Electronic apparatus including in combination, an electrically conductive waveguide structure constructed to accentuate an electric field component in a predetermined region within said structure in response to electromagnetic waves produced therein, a semiconductor body at least a part of which is a single crystal having a thin dimension, said semiconductor body being mounted within said waveguide structure with said crystal positioned in said region such that the aforesaid electric field component produces in said crystal a field gradient across said thin dimension thereof, and electrical connections to said crystal for establishing a current path from an external source of electrical energy through said crystal in a direction transverse to the direction of said field gradient, said electromagnetic waves in said Waveguide structure causing the current flowing along said path in said crystal to vary.

13. Electronic apparatus as defined by claim 12 in which said apparatus further includes a second semiconductor body at least a part of which is a single crystal having a thin dimension, said second semiconductor body being mounted within said waveguide structure with said crystal thereof positioned in said region and spaced from the first semiconductor body in the field gradient direction so that said semiconductor bodies provide boundaries at said region, and means establishing further electrical connections to said crystal of said second semiconductor body for establishing a current path therethrough from the external source of electrical energy in a direction transverse to the gradient direction.

14. Electronic apparatus including in combination, an electrically conductive waveguide structure responsive to electromagnetic waves, a semiconductor body at least a part of which is a single crystal having a planar surface and a thin dimension in a direction normal to said planar surface, said semiconductor body being mounted in said waveguide structure in a predetermined region, and said waveguide structure being constructed to produce a peak electric field component in said predetermined region providing a field gradient across the thin dimension of said single crystal, and electrical connections for establishing a current path from an external source of electric energy through said waveguide structure and through said crystal in a direction parallel to said planar surface thereof, said electromagnetic waves causing current flowing along said path in said crystal to vary and affect said electric field component to produce amplified electromagnetic waves.

15. Apparatus comprising an electrically conductive waveguide structure including first and second sections responsive to electromagnetic waves, said waveguide structure being constructed to accentuate an electric field component in a predetermined region within said structure coupled to said first and second sections thereof, a semiconductor body at least a part of which is a single crystal having a thin dimension, said semiconductor body being mounted in said waveguide structure with said crystal positioned in said region such that the aforesaid electric field component produces a field gradient across the thin dimension of said crystal, and electrical connections to said crystal and said waveguide structure for establishing a current path from an external source of electrical energy through said waveguide structure and through said crystal in a direction transverse to the direction of said field gradient, with electromagnetic waves produced in said first section of said structure causing the current flowing along said path in said crystal to vary and produce amplified electromagnetic waves in said second section of said structure.

16. Electronic apparatus as defined by claim 15 in which said waveguide structure includes partition means having a passageway extending between said first and second sections, with said semiconductor body being a single crystal in thin film form positioned in said passage way to couple waves produced in said first section to said second section.

17. Electronic apparatus including in combination an electrically conductive Waveguide structure having first and second sections shaped to provide a resonant response to electromagnetic waves, said waveguide structure being constructed to produce a peak electric field component in a predetermined region in said structure coupled to said first and second sections thereof, a semiconductor body at least a part of which is a single crystal having a thin dimension, said semiconductor body being mounted within said waveguide structure in said predetermined region so that said electric field component produces a field gradient across the thin dimension of said 18 crystal, and electrical connections for establishing a current path from an external source of electric energy through said waveguide structure and through said crystal in a direction transverse to the direction of said field gradient, with electromagnetic waves produced in said first section of said structure causing current flow along said path in said crystal to vary such that said semiconductor crystal couples such electromagnetic waves to said second section of said structure with a gain in power.

18. Electronic apparatus including in combination an electrically conductive waveguide structure including a rhumbatron section, and a coaxial section having one end forming a re-entrant part of said rhumbatron section, said structure being symmetrical with respect to an axis extending through said sections, a semiconductor body at least a part of which is a single crystal having a planar surface and a thin dimension in a direction normal to said planar surface, said semiconductor body being mounted in said waveguide structure with said crystal positioned at said one end of said coaxial section and with said planar surface of said crystal normal to said axis, and electrical connections for establishing a current path from an external source of electrical energy through said waveguide structure and through said crystal in a direction parallel to said planar surface of said crystal.

19. Apparatus including in combination an electrically conductive waveguide structure for confining electromagnectic waves oscillating in a predetermined mode, said waveguide structure including a rhumbatron section, and a coaxial section having one end forming a re-entrant part of said rhumbatron section, said structure having an axis extending centrally through said sections, a semiconductor body at least a part of which is a single crystal having a planar surface and a thickness with respect to said surface substantially equal to the skin depth characterizing the response of said waveguide structure to said electromagnetic waves, said semiconductor body being mounted in said waveguide structure with said crystal positioned at said one end of said coaxial section and with said planar surface of said crystal normal to said axis, and electrical connections for establishing a current path from an external source of direct current through said waveguide structure and through said crystal in a direction parallel to said planar surface of said crystal.

References Cited in the file of this patent UNITED STATES PATENTS 2,692,950 Wallace Oct. 26, 1954 2,743,322 Pierce et a1. Apr. 24, 1956 2,777,906 Shockley Jan. 15, 1957 2,801,389 Linder July 30, 1957 2,817,813 Rowen et al. Dec. 24, 1957 2,849,687 Miller Aug. 26, 1958 OTHER REFERENCES The Hall Effect etc., by Barlow, pages -11, and 112 of the Proceedings of the Institute of Electrical Engineers, vol. 103, No. 7, January 1956.

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