US3018426A - Electric contacts - Google Patents

Electric contacts Download PDF

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Publication number
US3018426A
US3018426A US847166A US84716659A US3018426A US 3018426 A US3018426 A US 3018426A US 847166 A US847166 A US 847166A US 84716659 A US84716659 A US 84716659A US 3018426 A US3018426 A US 3018426A
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Prior art keywords
electrode
contact
tellurium
crystal
current
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US847166A
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English (en)
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Ruppel Wolfgang
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RCA Corp
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RCA Corp
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Priority to NL256979D priority Critical patent/NL256979A/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US847166A priority patent/US3018426A/en
Priority to GB34852/60A priority patent/GB971942A/en
Priority to DER28900A priority patent/DE1149460B/de
Priority to FR841176A priority patent/FR1270367A/fr
Application granted granted Critical
Publication of US3018426A publication Critical patent/US3018426A/en
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
    • H05B33/26—Light sources with substantially two-dimensional radiating surfaces characterised by the composition or arrangement of the conductive material used as an electrode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D99/00—Subject matter not provided for in other groups of this subclass

Definitions

  • This invention relates to novel ohmic electric contacts to insulators and to novel space charge limited current devices.
  • Solid state devices of this type are referred to herein as solid state space charge limited current de vices, because they are analogous in many respects to thermionic vacuum space charge limited current devices. In the vacuum devices, space charge limited currents are carried only by electrons travelling through a vacuum.
  • the solid state space charge limited current devices are more versatile than the vacuum device because in the former (1) either or both of two types of free charge carriers, electrons and holes, may carry the current, (2) heat is not necessary to produce the injection of charge carriers, (3) a vacuum is not necessary, and (4) the electrical characteristics of the devices may be modified by modifying the physical characteristics of the insulator.
  • Suitable crystals of cadmium sulfide and similar materials are available which have less than one trapping imperfection for every lattice sites. Such crystals are insulating and have an apparent volume resistivity greater than 10 ohm cm.
  • the prior art provides electric contacts to crystals of the type described above which are ohmic to electron current flow but are rectifying to hole current flow. Such electric contacts are made by contacting, as by pressing, indium or gallium metal against the insulator. There are no heating or forming steps involved. Upon removal of the contact from the insulator, the insulator surface appears to be free of chemical and physical action from the contact. However, the prior art does not provide similar electric contacts which are ohmic to hole current flow.
  • An object of this invention is to provide ohmic electric contacts for the injection of positive charge carriers or holes into insulators.
  • a further object is to provide to insulators, electric contacts which are ohmic to the flow of the hole currents and are rectifying to the flow of electron currents.
  • Another object is to provide electric contacts which are ohmic to the flow of holes for insulating single crystals of cadmium sulfide and similar materials.
  • the electric contacts of the invention herein include a tellurium electrode in physical contact with the surface of a crystalline insulator body selected from the group consisting of cadmium sulfide, cadmium selenide, zinc sulfide, zinc selenide and zinc oxide. It has been lice 2 found unexpectedly that such a combination provides an ohmic contact for hole current flow between the electrode and the insulator, while being highly resistive to electron current flow therebetween.
  • a fiat surface of a tellurium body is placed against the face of a single crystal of insulating cadmium sulfide to provide the ohmic contact.
  • the invention herein includes devices comprising the foregoing combination and, in addition, a second electrode, such as indium, gallium, tin, lead, or combinations thereof, which produces a contact which is ohmic to electron current flow into said body.
  • a second electrode such as indium, gallium, tin, lead, or combinations thereof, which produces a contact which is ohmic to electron current flow into said body.
  • Such devices with the two electrodes biased in the forward direction so that both holes and electrons are injected into the insulator, provide the maximum in electric current flow by providing a cross neutralization of the space charge produced in the insulator body near both contacts due to the injected carriers. Where the insulator is properly selected for the purpose, the injected carriers recombine radiatively in the insulator body to produce band gap electroluminescence.
  • the foregoing devices may include also control electrodes contacting the insulator body. Such electrodes, when biased in the backward direction and with a suitable signal voltage applied thereto, may modulate either or both the electron and hole current flow by controlling the magnitude of the space charge opposing the flow current through the insulator.
  • a suitable control electrode for electron currents comprises a material suitable as the hole injector contact.
  • a suitable control electrode for hole current comprises a material suitable as the electron injector contact.
  • FIGURE 1 is a partially elevational, partially sche-s matic view of an embodiment of the invention including a device and circuit therefore,
  • FIGURE 2 is a graph illustrating a typical voltage characteristic of the device of FIGURE 1.
  • FIGURE 3 is a partially elevational, partially schematic view of another embodiment of the invention including a device and circuit therefor.
  • FIGURE 4(a) and FIGURE 4(b) are respectively elevational and plan views of a device including a control electrode for electron current.
  • FIGURE 5(a) and 5(1)) are respectively elevational and plan views of a device including a control electrode for hole current, and
  • FIGURE 6(a) and 6(b) are respectively elevational and plan views of a device including control electrodes.
  • FIGURE 1 I tacts of the invention is illustrated in FIGURE 1.
  • Example.A simple device including the ohmic con-v The device comprises a single crystal 21 of insulating cadmium sulfide about 0.01 mm. thick and having a volume resistivity of about 10 ohm cm.
  • the crystal 21 has two plane opposed surfaces and is prepared by any convenient process, for example the vapor phase technique described by R. H. Bube and S. M. Thomsen in the Journal of Chemical Physics, volume 23, page 15 (1955). .A wafer of tellurium having a plane surface is attached to a first brass support 29 with silver paste 27 or other electrically conducting adhesive.
  • mm. radius is pressed against a face of a second brass support 31.
  • the plane surface of the tellurium wafer 23 is pressed against one face of the crystal 21 as with a spring 33 and, at the same time, the indium body 25 is pressed against the opposed face of the crystal 21 as with a spring 34 with a force of the order of grams.
  • a battery 37, a reversing switch 36, and a variable resistor 35 are connected in series to the brass supports 29 and 31, so that the tellurium wafer 23 and the indium layer 25 are biased in opposite polarity.
  • the forward direction for biasing the contacts with respect to the crystal 21 for injecting holes from the tellurium contact 23 and for the injecting electrons from the indium contact 25 is with the tellurium contact 23 biased positively and the indium contact 25 biased negatively.
  • the curve 39 of FIGURE 2 illustrates a typical voltagecurrent characteristic of the device of FIGURE 1.
  • the switch 36 is adjusted to apply the voltage polarity to the crystal 21 in the backward direction and the resistor 35 is varied to provide a range of voltages.
  • the total current is very low over the entire range of voltages below breakdown in the backward direction.
  • both contacts are non-injecting. No carriers diffuse from the contacts into the insulator, and the current is that of an insulator to which blocking contacts are applied.
  • the switch 36 is readjusted to apply a voltage polarity to the crystal 21 in the forward direction, and the resistor 35 is varied to provide a range of voltages.
  • the current remains low over a range of low voltages in the forward direction.
  • This low current is an ohmic current which results from free carriers originating in the body due to thermal action in the body.
  • the ohmic current is a linear function of the applied voltage.
  • the rapidly increasingportion of the curve 39 is due to injected carriers and is referred to as the space charge limited current region. Injection of carriers starts as soon as a forward bias is applied to the contacts, and becomes substantial at about 200 volts. At about 50 volts, the space charge limited current is of the order of one milliampere, or 0.4 ampere/cmfi. The space charge limited current is limited only by the space charge of injected carriers in the crystal 21.
  • the space charge limited current flow may be accompanied by emission of band gap light (electroluminescence).
  • band gap light electroluminescence
  • the light is green, peaking at about 5200 A. at room temperature. It is believed that injected electrons and holes recombine across the band gap of the insulator yielding one photon for each recombination.
  • Thedevices may be optimized so that they produce more efiicient electroluminescence.
  • FIG- URE 3 Another structural arrangement is illustrated in FIG- URE 3.
  • a layer 23a of tellurium is evaporated upon one face of a crystal 21a of insulating cadmium sulfide about 10 microns thick.
  • the tellurium contact therein has an area of aboutLO square mm.
  • the tellurium layer 23a is produced by placing a quantity of tellurium in a container, supporting the crystal above and spaced from the container about 20 cm., evacuating the region to about 10 ofHg and then heating the tellurium above its melting point to evaporate it, for example, at about 500 C.
  • a layer 25a of indium is evaporated on the opposite face ofthe crystal 21a. Electrical connections are made by spring clips 33a and 34a bearing against the evaporated layers 23a and 25a respectively.
  • the device is operated as described with respect to the device of FIGURE 1.
  • the current drawn in the steady state at 5 volts is about 4.0 amperes (0.4 ampere/cm?) in the forward direction and about 4.0x 1'0- amperes (4.0 1() arnperes/cm?) in the backward direction.
  • the device is an'efficient rectifier with relatively low leakage in the back direction.
  • Ohmic contacts for the flow of hole current into insulators may be obtained by using the crystalline variety of tellurium.
  • the tellurium should be as pure as possible. Certain materials, however such as selenium and sulfur,
  • the tellurium electrode of the embodiment of FIG-- URE 1 may be produced in any desired shape by any of the commonly known methods, for example rolling, punching, and stamping.
  • the electrode in its simplest form is a single composition that has been shaped as desired.
  • the electrode material may be coated or plated on some other material that will serve as a support.
  • suitably shaped sheet nickel having a layer of tellurium on one side makes a good ohmic contact.
  • the surface of the electrode is applied to the surface of the insulator. All that is necessary is that the two surfaces are in indmate physical contact with one another. If the electrode material is soft enough with respect to the insulator body, merely placing the two surfaces against one another with the slightest pressure will produce a good ohmic contact as well as good physical contact. In other cases, pressure and heating are used to facilitate intimate physical contact between the surfaces. If heating is employed, a nonreactive atmosphere is preferred. After the contact is made, the heat and pressure are removed.
  • While heating may be used to facilitate producing good contact, it should be clear that it is used for the purpose of making intimate physical contact between the electrode and the body surface, and that it is not for the purpose of diffusing the electrode material into the insulator body.
  • the electrode is removed from the insulator body after a successful ohmic contact has been made, there is no sign of the previous contact on the surface of the insulator, nor does a subsequent contact prefer the previous contact area.
  • Successful ohmic contacts for hole current injection into insulators may also be obtained by producing the tellurium electrode directly on the insulator body by any of several well known methods.
  • the tellurium electrode may be formed by evaporating, sputtering, or spraying tellurium on the surface of the insulator body.
  • ohmic contacts for space charge limited hole currents may be made with the tellurium electrodes de scribed above to bodies of material which are substantially free of charge carriers in their volume, asopposed to those bodies which have substantial amounts of free charge carriers, either electrons or holes, already present therein.
  • Materials which are substantially free of free charge carriers are frequently referred to as insulators.
  • the range of resistivity which is included is not sharply defined.
  • cadmium sulfide is generally classed as an insulator when its resistivity is greater than 10 ohm-cm, and as a semiconductor when its resistivity between 10 and 10 ohm-cm.
  • Ohmic contacts for hole currents may be made with tellurium in this entire resistivity range; that is, in the range of resistivity greater than 10 ohm-cm. However, it is preferred to use insulators with higher resistivities, preferably greater than 10 ohm-cm. Further, it is preferred that the insulator body have a minimum of impurities and traping imperfections. 'It is noteworthy that the ohmic contacts described herein are intended for use in bodies which are not sources of free charge carriers, but which merely provide a medium whose characteristics are similar in some respects to a vacuum into which injected free charge carriers interact with one another. Some typical insulators are cadmium sulfide, cadmium selenide, zinc sulfide, zinc selenide, and zinc oxide.
  • the ohmic contacts to insulators, for the injection of electron currents may be prepared in a manner similar to that of preparing the tellurium contacts, except that another material is substituted for the tellurium.
  • the ohmic contacts for the injection of electron currents may consist essentially of a metal or combination of metals selected from the group consisting of indium, gallium, tin, and lead. Other types of contacts that are ohmic for electron current flow to insulators may be used.
  • FIG- URE 4(a) is an elevational view
  • FIGURE 4(b) is a plan view of a device including an electrode for controlling the space charge limited electron current in a device of the type described with respect to FIG- URE l.
  • the device of FIGURES 4(a) and 4(b) includes a single crystal 21b of insulating cadmium sulfide contacted at one end by an indium electron injector contact 25b which is ohmic to electron current flow, and a tellurium hole injector contact 2312 which is ohmic to hole current flow.
  • batteries 43 and 45 and a load resistor 47 are connected in series between the injector contacts 23b and 25b, biasing the contacts in the forward direction for simultaneous injection of both electrons and holes.
  • An electron current control electrode 41 of tellurium contacts the crystal 21b at a position spaced from, but adjacent the electron injector contact 25b.
  • the electron current control electrode 41 is biased in the backward direction with respect to the crystal 21b as with a battery 55 and is not injecting. It is noteworthy that the electrode 41 is back biased with respect to the crystal 21b with low positive voltages as well as with negative voltages.
  • a signal voltage from a source 51 is coupled to the electron current control electrode 41 through a coupling transformer. The signal voltage produces in the crystal 21b a variable electric field in the negative space charge region adjacent to the electron injector contact 25b. This is the region of the crystal 21b into which the electrons or negative charge carriers are injected.
  • the electric field from the electron current control electrode 41 builds up or reduces the negative space charge present in the region, which in turn varies correspondingly the electron current output which may be monitored at terminals 49 as a voltage across the load resistor 47.
  • the output of the device shows both a current gain and a power gain over the input to the device.
  • the input signal on the control electrode appears in the output of the device.
  • FIGURE 5(a) is an elevational view
  • FIGURE 5 (b) is a plan view, of a device including an electrode for controlling the space charge limited hole current in the device.
  • the device of FIGURE 5 (b) is similar in structure and operation to the device of FIGURE 4(b) and includes a single crystal 210 of insulating cadmium sulfide contacted at one end by an indium electron injector contact 250 which isohmic to electron current, and a tellurium hole injector contact 230 which is ohmic to hole current.
  • batteries 43a and 45a and a load resistor 47a are connected in series to the ohmic contacts 230 and 250, biasing the contacts in the forward direction for simultaneous injection of both electrons and holes.
  • a hole current control electrode 61 of indium or gallium contacts the crystal 210 at a position spaced from, but adjacent, the hole injector contact 23c.
  • the hole current control electrode 61 is biased in the backward direction with respect to the crystal 21c as with a battery 75 and is not injecting carriers.
  • a signal from a source 71 is coupled to the positive control electrode 61 through a coupling transformer 73.
  • the signal voltage produces in the crystal 210 a variable electric field in the positive space charge region; that is, the region of the crystal 21c into which holes or positive charge carriers are injected.
  • the electric field from the hole current control electrode 61 builds up or reduces the positive space charge present in the region, which varies correspondingly the hole current.
  • the output signal which follows the input signal, may be read at terminals 49a as a voltage across 6 the load resistor 47a, in a manner similar to that described with respect to the operation of the device of FIGURE 4(b).
  • the device of FIGURES 6(a) and 6(b) includes both control features of the devices of both FIGURES 4(b) and 5 (b).
  • the device of FIGURE 6(b) is similar in structure and operation to the devices of FIGURES 4(b) and 5(b) and comprises the single crystal 21d of insulating cadmium sulfide, a hole injector contact 23d, electron injector contact 25d, a negative control electrode 41b and a positive control electrode 61b.
  • the device is connected and operated as in FIGURES 4(b) and 5 (b).
  • the circuit includes means for biasing the injector contacts 23d and 25d for simultaneous electron and hole injection.
  • the electron current control electrode 41b and the hole current control electrode 61b are connected to means for applying a signal to one or both of the electrodes 41b and 61b including batteries 55b and 75b, a coupling transformer with variable center tap 87 on the secondary and an input signal source 81 What is claimed is:
  • An electrical device comprising a crystalline body of insulating material selected from the class consisting of cadmium sulfide, cadmium selenide, zinc sulfide, zinc selenide, and zinc oxide, and at least one electrode consisting essentially of tellurium in contact with said body, said electrode providing ohmic contact for hole current fiow between said one electrode and said body.
  • An electrical device comprising a crystalline body selected from the class consisting of cadmium sulfide, cadmium selenide, zinc sulfide, zinc selenide, and Zinc oxide and at least one electrode consisting essentially of crystalline tellurium in contact with said body, said electrode providing ohmic contact for hole current flow between said one electrode and said body.
  • An electrical device comprising a single crystal body of material selected from the class consisting of cadmium sulfide, cadmium selenide, zinc sulfide, zinc selenide, and zinc oxide and at least one electrode consisting essentially of crystalline tellurium in contact with said body, said electrode providing an ohmic contact for hole current flow between said one electrode and said body.
  • An electrical device comprising a single crystal of cadmium sulfide having a resistivity greater than 10 ohm-cm. and being relatively free of trapping imperfections, and an electrode consisting essentially of crystalline tellurium contacting said crystal, said electrode providing ohmic contact for hole current flow between said electrode and said crystal.
  • An electrical device comprising a crystalline, insulating body selected from the group consisting of cadmium sulfide, cadmium selenide, zinc sulfide, zinc selenide, and zinc oxide, a first electrode consisting essentially of crystalline tellurium contacting said body, said first electrode providing ohmic contact for hole current flow between said first electrode and said body, and a second electrode contacting said body and spaced from said first electrode, said second electrode providing ohmic contact for electron current flow between said second electrode and said body.
  • said second electrode consists essentially of a metal or combination of metals selected from the group consisting of indium, gallium, tin, and lead.
  • the device of-claim '10 including a third electrode contacting said body intermediate said first and second electrodes for controlling one of said currents.
  • said third electrode is for controlling said hole current and consists essentially of a metal or combination of metals selected from the group consisting of indium, gallium, tin, and lead.
  • the device of claim 10 including a third and a fourth electrode contacting said body intermediate said first and second electrodes, said third electrode for separately controlling said hole current and said fourth electrode for separately controlling said electron current.
  • An electrical device comprising a single crystal of insulating cadmium sulfide having a resistivity greater than 10 ohm-cm. and being relatively free of trapping imperfections, a first electrode consisting essentially of crystalline tellurium contacting said crystal, said first electrode providing ohmic contact for hole current flow between said first electrode and said crystal, and a second electrode consisting essentially of a member of the group consisting of indium, gallium, tin, lead and combinations thereof, contacting said crystal, said second electrode providing ohmic contact for electron current flow between said second electrode and said crystal.
  • a device comprising a single crystal of insulating cadmium sulfide and being relatively free of trapping imperfections, a first electrode of crystalline tellurium in contact with said body, and a second electrode of indium in contact with said body.

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  • Engineering & Computer Science (AREA)
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US847166A 1959-10-19 1959-10-19 Electric contacts Expired - Lifetime US3018426A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
NL256979D NL256979A (en)) 1959-10-19
US847166A US3018426A (en) 1959-10-19 1959-10-19 Electric contacts
GB34852/60A GB971942A (en) 1959-10-19 1960-10-11 Electric device
DER28900A DE1149460B (de) 1959-10-19 1960-10-14 Elektrische Halbleiteranordnung mit einem eigenleitenden Kristall aus Cadmiumsulfid,Cadmiumselenid, Zinksulfid, Zinkselenid oder Zinkoxyd
FR841176A FR1270367A (fr) 1959-10-19 1960-10-14 Contact électrique ohmique

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3265899A (en) * 1962-07-25 1966-08-09 Gen Motors Corp Semiconductor amplifying radiation detector
US3309553A (en) * 1963-08-16 1967-03-14 Varian Associates Solid state radiation emitters
US3330983A (en) * 1962-07-06 1967-07-11 Gen Electric Heterojunction electroluminescent devices
US3510715A (en) * 1967-08-24 1970-05-05 Westinghouse Electric Corp Injection-electroluminescent device with graded heterojunctions and method of manufacturing such devices
US4213798A (en) * 1979-04-27 1980-07-22 Rca Corporation Tellurium schottky barrier contact for amorphous silicon solar cells
US5371409A (en) * 1992-05-19 1994-12-06 California Institute Of Technology Wide bandgap semiconductor light emitters

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1079204A (en) * 1963-12-24 1967-08-16 Hughes Aircraft Co Improvements in and relating to thin film electrical devices
US3370208A (en) * 1964-03-25 1968-02-20 Nippon Telegraph & Telephone Thin film negative resistance semiconductor device

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1961825A (en) * 1932-05-10 1934-06-05 Gen Electric Tellurium alloy rectifier
US2854611A (en) * 1953-05-25 1958-09-30 Rca Corp Rectifier

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2836797A (en) * 1953-03-23 1958-05-27 Gen Electric Multi-electrode field controlled germanium devices
DE1036393B (de) * 1954-08-05 1958-08-14 Siemens Ag Verfahren zur Herstellung von zwei p-n-UEbergaengen in Halbleiterkoerpern, z. B. Flaechentransistoren
NL88273C (en)) * 1954-12-01

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1961825A (en) * 1932-05-10 1934-06-05 Gen Electric Tellurium alloy rectifier
US2854611A (en) * 1953-05-25 1958-09-30 Rca Corp Rectifier

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3330983A (en) * 1962-07-06 1967-07-11 Gen Electric Heterojunction electroluminescent devices
US3265899A (en) * 1962-07-25 1966-08-09 Gen Motors Corp Semiconductor amplifying radiation detector
US3309553A (en) * 1963-08-16 1967-03-14 Varian Associates Solid state radiation emitters
US3510715A (en) * 1967-08-24 1970-05-05 Westinghouse Electric Corp Injection-electroluminescent device with graded heterojunctions and method of manufacturing such devices
US4213798A (en) * 1979-04-27 1980-07-22 Rca Corporation Tellurium schottky barrier contact for amorphous silicon solar cells
US5371409A (en) * 1992-05-19 1994-12-06 California Institute Of Technology Wide bandgap semiconductor light emitters

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GB971942A (en) 1964-10-07
NL256979A (en))

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