Means for utilizing solid-state materials and devices for the electronic control of guided electromagnetic wave energy

March 8, 1960 m. a. lampert 2,928,056

MEANS FOR UTILIZING SOLID-STATE MATERIALS AND DEVICES FOR THE ELECTRONIC CONTROL OF GUIDED ELECTROMAGNETIC WAVE ENERGY

Filed May 25, 1954 2 Sheets-Sheet 1

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March 8, 1960

Filed May 25, 1954

M. A. LAMPERT 2,928,056

MEANS FOR UTILIZING SOLID-STATE MATERIALS AND DEVICES FOR THE ELECTRONIC CONTROL OF GUIDED ELECTROMAGNETIC WAVE ENERGY

Sheets-Sheet 2

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INVENTOR.

M/pppy/7, Lpmp&amp;st

United States Patent Office

2,928,856

Patented Mar. 8, 1960 for utilizing solid-state materials and devices for controlling the propagation of guided electromagnetic wave energy.

Another object of the invention is to control the prop5 agation of guided electromagnetic wave energy.by controlling the density of charge-carriers in solid-state materials and devices.

A further object of the invention is to provide improved means for controlling guided wave propagation 10 in other than gaseous atmospheres.

A still further object of the invention is to utilize solidstate materials and devices for electronically controlling guided wave propagation in apparatus in which gas tubes or the like are mechanically inconvenient or cannot be 15 used.

A still further object of the invention is to control guided wave propagation by controlling the chargecarrier density of a semiconducting body.

Electronic propagation control with solid-state semi20 conducting devices may be achieved in several different ways: (1) through variation of the charge-carrier density, (2) through variation of the collision frequency of charge-carriers which is a rather difficult method of control from a practical standpoint), and (3) through 25 changes in the charge-carrier orbits in the solid by virtue of magnetic or electric fields impressed thereon. The present invention primarily is concerned with the first mechanism, namely, variation of the charge-carrier density. The charge-carrier density may be varied as de30 sired by iradiating the solid with one or a combination of neutral particles (light quanta, neutrons, gamma rays, ' etc.), charged particles (alpha particles, beta rays, thermally produced electrons, protons, ions, etc.) and by voltage’or current control applied to the semi-conductor 35 material.

Applications for solid-state wave propagation control devices are numerous. Particularly important applications for such control are amplitude-modulation, phasemodulation, frequency-modulation, and electronic switch40 ing. .

; The invention will be described in greater detail with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a first embodiment of the inVention in which the propagation of microwave 45 energy is controlled by utilizing a modulated beam of light or a nuclear emission source to control the density of charge-carriers in a semiconducting body;

Figure 2 is a perspective view of a second embodiment of the invention in which the propagation of microwave energy is controlled by voltage control of the density of charge-carriers at a p-n junction in a semiconducting body;

Figure 3 is a perspective view of a third embodiment of the invention in vzhich the propagation of wave en55 ergy in a broad-band ridge waveguide is controlled in accordance with the invention;

Figure 4 is a schematic diagram of a fourth embodiment of the invention wherein microwave energy propagated along a surface waveguide is controlled according 60 to the invention.

Similar reference characters are applied to similar elements throughout the drawings.

Referring to Figure 1, microwave energy from a source, not shown, is propagated through a hollow wave65 guide 10. A pair of inductive conductive diaphragm or iris elements 16 and 17 extend inwardly from the Hplane or narrow walls of the waveguide 10 and a pair of hollow conductive capacitive posts 11 and 12 extend into the waveguide from its E-plane or broad walls. 70 The diaphragms 16 and 17 and the posts 11 and 12 preferably are located in a common plane transverse to the longitudinal axis of the guide and comprise a resonant

2,928,056

MEANS FOR UTILIZING SOLID-STATE MATERIALS AND DEVICES FOR THE ELECTRONIC CONTROL OF GUIDED ELECTROMAGNETIC WAVE ENERGY

Murray A. Lampert, Brooklyn, N.Y., assignor to Radio Corporation of America, a corporation of Delaware

Application May 25, 1954, Serial No. 432,165

Claims. (Cl. 332—54)

This invention relates generally to the control of “J guided electromagnetic wave energy and particularly relates to means for achieving such control by varying the density of charge-carriers in semiconducting matejp rials and devices interposed in the path of the wave energy and external to the source of the electromagnetic energy.

An electromagnetic wave travelling in a selected mode along a transmission line is characterized by its phase and amplitude. In some instances such as where there is more degeneracy (as in circular waveguides) polarization also is important. However, the problem of propagation control is mainly a problem of phase and amplitude control.

At present there are a number of wave propagation control devices, usually gas-tubes, in which the controlling element is an electron gas which is created and maintained in a gaseous discharge. The term “electron gas” is well known and is defined as a cloud of electrons wherein the electrons move with random velocities (in both direction and magnitude), except for the drift velocity which the cloud as a whole may possess. The electron cloud thus constitutes a medium for energy propagation and, as such, may be used to determine the phase and amplitude of an electromagnetic wave propagated therethrough.

The parameters of the electron gas which govern the kind (i.e., phase shift or attenuation) and degree (magnitude) of propagation control are the electron density, the electron-molecule, collision frequency, and the effects of external magnetic or electric fields to which the electron gas is subjected.

Since the density of the electron gas in the discharge can be varied rapidly over a considerable range of values, correspondingly rapid and extensive control of wave propagation therethrough is possible. The control 50 of electron density may be attained by utilizing external voltages or currents for controlling the discharge. In some cases, for example, transmit-receive (TR) and antitransmit-receive (ATR) tubes, the radio-frequency power incident on the gas either partially or completely controls the electron gas density.

In accordance with the present invention, it has been found that improved wave propagation control and other features of the invention, mentioned below, are attainable by means other than a gaseous discharge. A medium for the control of the phase and amplitude of guided waves has been found to exist in solid-state semiconducting materials. This medium includes chargecarriers in the semiconducting material. These chargecarriers are the aggregates of electrons in the conduction band of the semiconducting material and holes in the highest valence band. Either aggregate (i.e., electrons or holes) is useful for purposes of propagation control,

An object of the present invention is to provide improved means for electronically controlling the propagation of guided electromagnetic wave energy.

Another object of the invention is to provide means

2,928,066 waveguide section resonant at the frequency of energy to be propagated through the guide.

A semiconducting device 13 is supported preferably between the posts 11 and 12 and is insulated therefrom. The insulating material 14, 15 may comprise any suitable insulating material such as polystyrene or polytetrafluoroethylene (the latter being sold commercially under the trade-name “Teflon”). Preferably, the device 13 includes both n-type and ρ-type conductivity regions formed in a body of semiconducting material having a conductivity in or near the intrinsic region. The term “intrinsic” is employed herein as definitive of a substantially pure semiconducting material, i.e., a material wherein relatively few donor or acceptor atoms are present. Typical materials which may be utilized in the present apparatus include germanium, silicon, and other semiconducting materials such as cadmium sulfide, the latter being one of the intermetallic compounds. For purposes of the present example a germanium body is selected, the intrinsic region preferably having a resistivity of at least 30 ohm-centimeters. The resultant nintrinsic-ρ device 13 preferably may comprise either a grown junction device or an alloy junction device. In the latter case the n-type conductivity region may be formed, for example, by alloying a pellet 3 of a material such as arsenic, antimony, or alloys including these materials into one surface of the semiconducting body. The p-type region is formed, for example, by alloying a pellet 5 such as indium, gallium, boron, or alloys including these materials into an opposed surface of the body. For a detailed description of the alloying technique per se, reference may be made to a copending application Serial No. 294,741, filed June 20, 1952, by Charles W. Mueller, now Pat. No. 2,894,862, issued July 14, 1959. Although the semiconducting device 13 shown preferably is an nintrinsic-p device, it will be appreciated that a p-n junction device or other type of semiconducting device may be employed.

The H-plane or narrow walls of the waveguide 10 each preferably include apertures 18 and 19 through which radiation from one or more radiation sources 8 and 9 outside the waveguide 10 may be directed to impinge upon the intrinsic region 7 of device 13. The apertures 18 and 19 preferably are longitudinally offset with respect to each other and are located on opposite sides of the plane in which the diaphragms 16 and 17 are located. The use of at least two oppositely disposed radiation sources permits substantially the entire surface area of the intrinsic region 7 of the semiconductive device 13 to be irradiated.

When the radiation from the sources 8 and 9 is incident upon the semiconducting device 13, the chargecarrier density within the intrinsic material is increased or varied in accordance with the intensity of the incident radiation. Changing the density of charge-carriers (electrons and holes) within the intrinsic region changes the conductivity of the device 13. This change in conductivity results in a detuning of the resonant section including the inductive diaphragms 16 and 17 and the capacitive posts 11 and 12 and thereby results in a modulation of the amplitude and phase of the electromagnetic wave energy propagated within the waveguide 10. Thus, by controlling the intensity of the radiation, the electromagnetic wave energy may be amplitude- and phasemodulated to the extent desired. In the event that electron-hole recombination occurs at a slower rate than the rate of formation of holes and electrons, it may be desirable to apply a voltage to the n and p regions to sweep these charge-carriers out of the intrinsic region and effectively increase the speed of recombination. Such voltage may be applied when the rate of change of modulation exceeds the recombination capabilities of the semiconductor material.

In the event that the structure heretofore described is to be utilized for affording switching action rather than attenuation or phase-shift of the propagated microwave energy, the intensity of the incident radiation need only be increased to the point where the density of the chargecarriers is sufficiently great to completely detune the resonant section of waveguide 10.

The radiation sources 8 and 9 may comprise either light ray emission sources or sources providing nuclear or charged particle emission. In the event that it is desirable to use nuclear emissions for controlling the semiconductor charge-carrier density, one or a combination of radioactive emitters such as strontium 90 (a beta particle emitter), cobalt 60 (a gamma ray emitter), or polonium and uranium (alpha particle emitters) may be employed. Control or modulation of the charge-carrier density when utilizing radioactive emission sources may be provided by interposing a variable density absorbing plate (not shown) between the sources 8 and 9 and the waveguide structure. Also, a thermionic emission source, such as a cathode ray gun, not shown, may be utilized to produce a modulated electron beam for bombarding i the semiconducting body. In this case, however, the region between the emission source and the semiconducting device 13 must be evacuated, and suitable electron generating and accelerating voltages must be provided.

In the second embodiment of the invention shown in Figure 2, a modulation source 20 is connected to the n and p regions of the semiconducting device 13 via leads 21 and 22. The leads 21 and 22 are brought into the waveguide 10 through apertures 25 and 26 located in the E-plane walls, the apertures being substantially aligned with the axis of the cylindrical hollow capacitive posts 11 and 12.

Control of the charge-carrier density is achieved in accordance with this feature of the invention by controlling the voltage applied across the semiconducting device 13. For the condition of zero modulation of the amplitude and phase of energy travelling through the waveguide 10, the modulation source 20 is adjusted to apply a strong reverse bias to the n and p regions of the device 13. This results in a condition of low conductivity in the semiconducting device 13, or substantial depletion of charge-carriers in the intrinsic region. Modulation of microwave energy is accomplished by decreasing the reverse voltage toward zero. If a greater range or modulation is desired, the applied voltage may be increased in the forward direction (i.e., the polarity of the applied voltage is reversed). Changing the applied voltage in this manner increases the density of electrons and holes in the intrinsic region and increases the conductivity of the device 13. Since the device 13 is located in the waveguide 10 at a point of high electric field intensity, the amplitude and phase of microwave energy propagated therethrough are modulated in accordance with the instantaneous value of applied voltage. Thus the attenuation and phase shift of energy propagated in the waveguide 10 variees in accordance with variations in polarity and amplitude of the modulating voltage applied to the semiconducting device 13.

In the embodiment shown in Figure 3, a ridge waveguide 49 is employed for broad-band propagation of electromagnetic wave energy. The waveguide 49 includes ridges 31 and 32 projecting inwardly from the broad walls 35, 37, each of which includes an aperture or slot 25, 26. A semiconductive device 13 of any of the types heretofore described extends along at least a portion of the guide length and is positioned in the waveguide 49 and insulated from the edges of the apertured ridges 31 and 32 by insulating members 14 and 15. The device 13 [ preferably is positioned so that only the intrinsic region 7 of the device 13 extends between the ridges and is in the path of microwave energy travelling through the guide. A modulation source 20 is coupled to the n and p regions of the semiconducting device. The amplitude and polarity of the bias applied to the device may be con2.938.066 .

trolled as described previously to modulate the phase and amplitude of the microwave energy.

A further embodiment of the invention shown, in Figure 4 utilizes a dielectric rod or filament 41 as a surface waveguide along which electromagnetic energy is propagated. The rod 41 includes two members 45 and 47, each of which has a tapered end 42 and 43 making ohmic or non-rectifying contact with opposed surfaces of the intrinsic region 7 of a semiconducting device 13. The device 13 preferably is of the n-intrinsic-p type described previously. A source of modulating voltage is coupled to the n and p regions of the semiconducting device 13 by leads 21 and 22.

The filamentary type of surface waveguide and control mechanism described is particularly desirable for controlling electromagnetic energy in the portion of the frequency spectrum between the microwave and infra-red wavelength bands. The ends 42 and 43 of the dielectric rod 41 are tapered to provide the proper impedance match between the dielectric rod 41 and the semiconducting device 13. The theory of operation of the propagation control mechanism for the instant structure is substantially the same as described with reference to the structure shown in Figures 2 and 3.

In summarizing, the present invention provides an effective and relatively simple means for controlling guided electromagnetic energy by controlling the density of charge-carriers in a semiconducting device. The semiconducting device is suitably situated in or coupled to the path of the electromagnetic waves, and the charge-carrier density is varied in accordance with desired modulation by any one of several methods. These methods include irradiation of a semiconducting body with neutral or charged particles, or light rays, or by varying the space charge at a p-n junction by varying the voltage across the junction. Variation of the charge-carrier density varies the phase and amplitude of energy propagated in the waveguide. The invention thus may be utilized to advantage for amplitude-modulation, phase-modulation, frequency-modulation, or electronic switching of microwaves.