JP2008131022A - Electrode structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure capable of injecting holes or electrons into a wide-gap semiconductor which cannot form a p-type nor an n-type semiconductor, where impurities do not exist (such as, acceptors or donors), whose ionization energy is sufficiently small. <P>SOLUTION: The electrode structure comprises a wide-gap semiconductor in which impurities whose ionization energy is 0.2 to 1 eV are doped, and a metal layer which has a work function smaller than binding energy of the impurity ion and is jointed to the wide-gap semiconductor. By having an external electric field applied on the structure, holes are injected from the metal layer into the wide-gap semiconductor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode structure for injecting holes or electrons from a metal layer into a wide gap semiconductor.

  Many wide gap semiconductors exhibit physical properties useful for applications in the industrial field, such as light emitting diodes, laser diodes, and solar cells.

  Here, in order to inject holes or electrons into a wide gap semiconductor by forming an electrode structure by joining a wide gap semiconductor and a metal layer and applying an external electric field to the electrode structure, The band alignment with the metal needs to satisfy certain conditions (see, for example, Patent Document 1 and Patent Document 2).

That is, in order to inject holes into a wide gap semiconductor by a so-called Schottky junction, the wide gap semiconductor is doped with an impurity (acceptor) having a small ionization energy to form a p-type semiconductor, and the valence electrons of the wide gap semiconductor. It was necessary to join a metal layer made of a metal having a Fermi level at a position shallower than the band edge.
In order to inject electrons into a wide gap semiconductor by so-called Schottky junction, the wide gap semiconductor is doped with an impurity (donor) having a small ionization energy to form an n-type semiconductor, and the valence band of the wide gap semiconductor. It was necessary to join a metal layer made of a metal having a Fermi level at a position deeper than the end.
In order to make a wide gap semiconductor a p-type or n-type semiconductor, the ionization energy of an impurity doped into the wide gap semiconductor needs to be 0.1 eV or less, for example. Here, the ionization energy of the impurity is determined by the energy difference between the binding energy of the impurity level and the valence band edge (or conduction band edge).

In order to inject holes into a wide gap semiconductor by so-called ohmic junction, a wide gap semiconductor and a metal layer made of a metal having a Fermi level at a position deeper than the valence band edge of the wide gap semiconductor are joined. It was necessary to let them.
In addition, in order to inject electrons into a wide gap semiconductor by so-called ohmic junction, it is necessary to join a wide gap semiconductor and a metal layer made of a metal having a Fermi level at a position shallower than the conduction band edge of the wide gap semiconductor. was there.
Japanese Patent Application No. 4-291038 Japanese Patent Application No. 2001-96123

  However, even if an attempt is made to inject holes or electrons into the wide gap semiconductor by Schottky junction, there is no impurity having sufficiently small ionization energy in the wide gap semiconductor, and a p-type or n-type semiconductor is produced. In some cases, it was impossible. For example, in the case of ZnS, there is no acceptor with sufficiently small ionization energy, and p-type ZnS cannot be made. In the case of ZnTe, there is no donor with sufficiently small ionization energy, and n-type ZnTe cannot be produced.

In addition, in this way, even when trying to inject holes by ohmic junction into a wide gap semiconductor that cannot make a p-type or n-type semiconductor, a Fermi quasi at a position deeper than the valence band edge of the wide gap semiconductor. It was impossible because there was no metal with a position. Similarly, even if electrons are injected into such a wide gap semiconductor through a so-called ohmic junction, there is no or even a metal having a Fermi level at a position shallower than the conduction band edge of the wide gap semiconductor. It was impossible because it was chemically unstable. For example, there is no metal with a Fermi level at a position deeper than the valence band edge of ZnO, and there is a chemically stable metal with a Fermi level at a position shallower than the conduction band edge of MgTe. do not do.

  That is, there is no means for injecting holes or electrons for a wide gap semiconductor that does not have a sufficiently small ionization energy (acceptor or donor) and cannot form a p-type or n-type semiconductor. For this reason, although it is useful as a physical property, it may be difficult to actually apply it to the industrial field.

  Therefore, the present invention can inject holes or electrons into a wide gap semiconductor in which an impurity (acceptor or donor) having sufficiently small ionization energy does not exist and a p-type or n-type semiconductor cannot be formed. The object is to provide a possible electrode structure.

According to a first aspect of the present invention, there is provided a wide gap semiconductor doped with an impurity having an ionization energy of 0.2 to 1 eV, a work function smaller than the binding energy of impurity ions, and a junction with the wide gap semiconductor An electrode structure in which holes are injected from the metal layer into the wide gap semiconductor by applying an external electric field.
Here, the ionization energy generally means energy required to cation by separating electrons from neutral atoms or molecules. In a semiconductor, it means energy required to excite carriers from an impurity level to a conduction band or a valence band. The ionization energy in the present invention means the ionization energy of a semiconductor.
The binding energy (binding energy) is expressed using the energy of the impurity level and is defined with the vacuum level as a reference, and the energy required to bring electrons at a specific level to a stationary state at infinity. Means.

  According to a second aspect of the present invention, there is provided a wide gap semiconductor doped with an impurity having an ionization energy of 0.2 to 1 eV, a work function larger than the binding energy of impurity ions, and a junction with the wide gap semiconductor. And an electrode structure in which electrons are injected from the metal layer into the wide gap semiconductor by applying an external electric field.

A third aspect of the present invention is the electrode structure according to the first aspect or the second aspect of the present invention, wherein the concentration of the impurity in the wide gap semiconductor is 1 × 10 ^{18 to} 5 × 10 ²¹ cm ^−3. It is.

  According to a fourth aspect of the present invention, there is provided an electrode structure according to any one of the first to third aspects of the present invention, wherein the electrode structure is doped in a range of 100 nm from the joint surface with the metal layer.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the present invention, the wide gap semiconductor is a II-VI group compound semiconductor, a III-V group compound semiconductor, or It is an electrode structure which is an oxide semiconductor.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects of the present invention, the impurity is Ni, Co, Fe, Pd, Rh, Ru, Pt, Ir, Os, N, P, A
The electrode structure is one or more of s and Sb.

A seventh aspect of the present invention is an electrode structure according to any one of the first to sixth aspects of the present invention, wherein the carrier current density is 1 mA / cm ² or more.

  According to the present invention, holes or electrons are injected into a wide gap semiconductor in which no impurity (acceptor or donor) having sufficiently low ionization energy exists and a p-type or n-type semiconductor cannot be formed. It is possible to provide an electrode structure capable of.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.
<First Embodiment>
The electrode structure according to the first embodiment includes a wide gap semiconductor as an electrode layer and a metal layer bonded to the wide gap semiconductor. In the wide gap semiconductor of the first embodiment, impurities are uniformly doped in the entire semiconductor.

The wide gap semiconductor is doped with an impurity material having an ionization energy of 0.2 to 1 eV. The impurity concentration is preferably 1 × 10 ^{18 to} 5 × 10 ²¹ cm ⁻³ . The dope method is a well-known method and will not be described in detail.
Here, the ionization energy generally refers to the energy required to cation by separating electrons from neutral atoms or molecules. In a semiconductor, it means energy required to excite carriers from an impurity level to a conduction band or a valence band. That is, the ionization energy according to the present embodiment means the ionization energy of a semiconductor.

A wide gap semiconductor refers to a semiconductor having a larger band gap than p-type silicon or n-type silicon (band gap 1.1 eV). For example, the following three types of semiconductors (1) to (3) can be given.
(1) Group II-VI compound semiconductors consisting of Group II elements and Group VI elements: ZnTe, ZnSe, ZnS, CdTe, CdSe, CdS
(2) Group III-V compound semiconductors consisting of Group III elements and Group V elements: GaN, GaP, GaAs, InP
(3) Examples of oxide semiconductors: ZnO, In ₂ O ₃ , SnO ₂ , a-InZnO _x , a-InGaZnO _x

  As an impurity doped into the wide gap semiconductor, the ionization energy is preferably in the range of 0.2 to 1 eV corresponding to the band gap of the wide gap semiconductor. When an impurity in this range is doped, a deep level can be created in the wide gap semiconductor. Examples of the impurities include Ni, Co, Fe, Pd, Rh, Ru, Pt, Ir, Os, N, P, As, and Sb, and one or more of these are selected and used.

Moreover, the following example can be mention | raise | lifted as a combination from which ionization energy will be 0.2-1 eV. Here, it is expressed in the form of “wide gap semiconductor-impurity material”.
Examples: ZnTe-Ni, ZnSe-Co, ZnS-Ni, CdTe-Ni, CdSe-Fe, CdSe-Co, CdSe-Ni, CdS-Ni, GaP-Ti, GaP-Fe, GaP-Co, GaP-Ni, GaAs-Ti, GaAs-Fe, GaAs-Ni, InP-Ti, InP-Fe, InP-Co, InP-Ni
Note that the present invention is not limited to these combination examples, and for example, these impurities and the above-described oxide semiconductor can be combined.

Examples of the material used for the metal layer include ITO (indium tin oxide) and Au.
When injecting holes from a metal layer into a wide gap semiconductor, the work function of the metal layer material is smaller than the binding energy between the impurity material and the wide gap semiconductor, so that the wide gap semiconductor, the impurity material, And a combination of materials for the metal layer.
In contrast, when electrons are injected from a metal layer into a wide gap semiconductor, the work function of the metal layer material is larger than the binding energy between the impurity material and the wide gap semiconductor so that the wide gap semiconductor has a larger work function. The combination of the impurity material and the material of the metal layer is selected.
Here, the binding energy (binding energy) is expressed using the energy of the impurity level, and is defined with reference to the vacuum level, which is necessary for bringing electrons at a specific level to a stationary state at infinity. It means energy.

  Here, with reference to FIG. 1, a description will be given of a band change caused by joining the wide gap semiconductor 10 and the metal layer 20. In the drawings to be referred to, FIG. 1 shows an example of a band change when the wide gap semiconductor 10 and the metal layer 20 are joined when the wide gap semiconductor 10 is doped with Ni as an example of an impurity. (A) is the conceptual diagram which shows the state before joining, (b) is the state after joining, (c) is the conceptual diagram which respectively shows the state which applied the external electric field.

  As shown in FIG. 1A, the Fermi level 20 f of the metal layer 20 before bonding is above the Ni level (impurity level) 10 f in the wide gap semiconductor 10. That is, the work function Wf of the material of the metal layer 20 (Fermi level of the metal layer 20) than the binding energy Eb of Ni (impurity) ions (energy difference between the Ni level 10f of the wide gap semiconductor 10 and the vacuum level VL). The energy difference between the position 20f and the vacuum level VL is smaller.

  As shown in FIG. 1B, when the wide gap semiconductor 10 and the metal layer 20 are joined, the wide gap is extended from the metal layer 20 until the Ni level 10f of the wide gap semiconductor 10 matches the Fermi level 20f of the metal layer. Electrons move to the Ni level of the semiconductor 10. As a result, the bands of the conduction band edge 10c and the valence band edge 10v of the wide gap semiconductor 10 are sharply bent. In this state, no steady current flows between the wide gap semiconductor 10 and the metal layer 20.

  Next, as shown in FIG. 1C, when an anode is connected to the wide gap semiconductor 10 and a cathode is connected to the metal layer 20 and an external electric field is applied between the wide gap semiconductor 10 and the metal layer 20, the metal layer 20 The Fermi level 20f of the wide gap semiconductor 10 decreases relative to the valence band edge 10v. As a result, the spatial distance of the barrier due to the Schottky junction is shortened, so that holes are injected as a tunnel current (steady current) from the metal layer 20 side to the wide gap semiconductor 10 side.

  As described above, when the electrode structure shown in the present embodiment is formed, an external electric field is applied to the wide gap semiconductor 10 in which an impurity (acceptor) having a sufficiently small ionization energy does not exist and a p-type cannot be formed. By doing so, it becomes possible to inject holes from the metal layer 20 into the wide gap semiconductor 10. For example, holes can be injected into ZnO, and for example, a light emitting diode using ZnO can be manufactured.

FIG. 1 illustrates a case where the metal layer 20 is formed of a material having a work function Wf smaller than the binding energy Eb of impurity ions in order to inject holes from the metal layer 20 into the wide gap semiconductor 10. However, embodiments of the present invention are not limited to such a configuration. That is, in order to inject electrons from the metal layer 20 to the wide gap semiconductor 10,
The metal layer 20 can also be formed of a material having a work function Wf larger than the binding energy Eb of impurity ions. In this case, although illustration is omitted, the band change when the wide gap semiconductor 10 and the metal layer 20 are joined can be represented by a band diagram that is vertically symmetrical with FIG. 1, and when a negative voltage is applied to the metal layer 20, The band warps upward. As a result, by applying an external electric field to the wide gap semiconductor 10 in which an n-type semiconductor cannot be formed without an impurity (donor) having a sufficiently small ionization energy, the wide gap semiconductor 10 is formed from the metal layer 20. It becomes possible to inject electrons.

<Second Embodiment>
The electrode structure according to the second embodiment is that the wide gap semiconductor 10 is doped with an impurity material at a high concentration limited to a predetermined depth from the joint surface with the metal layer 20 in the first embodiment. It differs from the electrode structure which concerns on. Since the wide gap semiconductor 10, the impurity material, and the material of the metal layer 20 to be used are the same as those in the first embodiment, detailed description thereof is omitted.

The depth at which the impurity material is doped can be determined in accordance with the doping concentration. For example, the wide gap semiconductor 10 is doped with an impurity material at a concentration of 1 × 10 ^{18 to} 5 × 10 ²¹ cm ⁻³ within a range of a depth of 100 nm from the joint surface with the metal layer 20.

  In the second embodiment, the change in the band caused by joining the wide gap semiconductor 10 and the metal layer 20 is the same as in the first embodiment, and is not shown. In the first embodiment, the impurity material is doped throughout the wide gap semiconductor 10, but the impurity material doped throughout the wide gap semiconductor 10 scatters carriers (holes or electrons) in the wide gap semiconductor 10. Therefore, it may cause a decrease in carrier mobility. On the other hand, as in the second embodiment, when the wide gap semiconductor 10 is doped with impurities limited to a predetermined depth from the joint surface with the metal layer 20, the doped impurity material is used. As a result, carriers are less likely to be scattered, and the carrier mobility can be kept high. For this reason, higher performance can be expressed as a semiconductor element.

Next, an embodiment of the present invention will be described with reference to FIG. In any of the examples, the configuration of the first embodiment or the second embodiment described above can be used. Since the laminating method and the doping method are known methods, description thereof is omitted. According to these configurations, when the external voltage applied to the metal layer 20 is 10 V, for example, and the cross-sectional area of the metal layer 20 is 0.5 mm × 0.5 mm, for example, a carrier current density of 1 mA / cm ² or more is realized. I can.
In the drawings to be referred to, FIG. 2 is a conceptual diagram showing an element structure on a glass substrate according to an embodiment of the present invention. The numerical value shown in FIG. 2 is the film thickness of each layer (example: 100 nmt means film thickness of 100 nm). In addition to the following embodiments, a novel semiconductor element can be realized by using a material that has been conventionally recognized only as a dielectric or a magnetic material.

<Example 1>
Examples of the element structure ((1) to (4)) of the stacked diode when ZnSe is used as the wide gap semiconductor 10 are shown below.
(1) Al layer (cathode 30) / n-ZnSe: Cl (wide gap semiconductor 10, impurity material doping concentration 1 × 10 ²⁰ cm ⁻³ ) / ZnSe (wide gap semiconductor 10) / ZnSe: Ni (wide gap semiconductor) 10. Impurity material dope concentration 1 × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / glass substrate 40 (FIG. 2A)
(2) Al layer (cathode 30) / n-ZnSe: Cl, Ni (wide gap semiconductor 10, doping concentration of impurity material 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / Glass substrate 40 (FIG. 2B)
Here, when Cu is used instead of Ni, visible light emission called so-called Cu-Green and Cu-Red can be expected. That is, a light emitting element can be realized.
(3) Al layer (cathode 30) / n-ZnSe: Cl (wide gap semiconductor 10, doping concentration of impurity material 1 × 10 ²⁰ cm ⁻³ ) / ZnSe (wide gap semiconductor 10, containing InP nanocrystals) / ZnSe: Ni (wide gap semiconductor 10, impurity material doping concentration 1 × 10 ²⁰ cm ⁻³ ) / ITO (metal layer (anode) 20) / glass substrate 40 (FIG. 2C)
(4) Al layer (cathode 30) / n-ZnSe: Cl, Ni (wide gap semiconductor 10, doping concentration of impurity material 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ , containing InP nanocrystals) / ITO anode ( Metal layer 20) / glass substrate 40 (FIG. 2 (d))

<Example 2>
Examples of element structures of stacked diodes using ZnS as the wide gap semiconductor 10 ((1) to (4)) are shown. Since the laminated structure is the same as that of Example 1, the illustration is omitted.
(1) Al layer (cathode 30) / n-ZnS: Al (wide gap semiconductor 10, doping concentration of impurity material 1 × 10 ²⁰ cm ⁻³ ) / ZnS (wide gap semiconductor 10) / ZnS: Ni (wide gap semiconductor) 10. Impurity material dope concentration 1 × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / glass substrate 40
(2) Al layer (cathode 30) / n-ZnS: Al, Ni (wide gap semiconductor 10, impurity material doping concentration 1 × 10 ¹⁹ , 1 × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / Glass substrate 40
Here, when Cu is used instead of Ni, visible light emission called so-called Cu-Blue, Cu-Green, or Cu-Red can be expected. That is, a light emitting element can be realized.
(3) Al layer (cathode 30) / n-ZnS: Al (wide gap semiconductor 10, doping concentration of impurity material 1 × 10 ²⁰ cm ⁻³ ) / ZnS (InP nanocrystal-containing) / ZnS: Ni (wide gap semiconductor) 10. Impurity material dope concentration 1 × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / glass substrate 40
(4) Al layer (cathode 30) / n-ZnS: Al, Ni (wide gap semiconductor 10, impurity material doping concentration 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ , containing InP nanocrystals) / ITO anode ( Metal layer 20) / glass substrate 40

<Example 3>
Examples of element structures of stacked diodes using ZnO as the wide gap semiconductor 10 ((1) to (5)) are shown. Also here, since the laminated structure is the same as that of the first embodiment, the illustration is omitted.
(1) Al layer (cathode 30) / n-ZnO (wide gap semiconductor 10) / ZnO: Ni (wide gap semiconductor 10, doping concentration of impurity material 1 × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / Glass substrate 40
(2) Al layer (cathode 30) / n-ZnO (wide gap semiconductor 10) / MgZnO: Ni (wide gap semiconductor 10, doping concentration of impurity material 1 × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / Glass substrate 40
(3) Al layer (cathode 30) / n-MgZnO (wide gap semiconductor 10) / MgZnO: Ni (wide gap semiconductor 10, doping concentration of impurity material 1 × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / Glass substrate 40
(4) Al layer (cathode 30) / n-MgZnO (wide gap semiconductor 10) / i-MgZnO (wide gap semiconductor 10, containing InP nanocrystals) / MgZnO: Ni (wide gap semiconductor 10, doping concentration of impurity material 1) × 10 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / glass substrate 40
(5) Al layer (cathode 30) / n-MgZnO (wide gap semiconductor 10) / InP nanocrystal layer / MgZnO: Ni (wide gap semiconductor 10, doping concentration of impurity material 1 × 1)
0 ²⁰ cm ⁻³ ) / ITO anode (metal layer 20) / glass substrate 40

<Example 4>
Examples of the configuration of the epitaxial film on the single crystal substrate include the following (1) to (3).
(1) Au (metal layer 20) / ZnSe: Ni (wide gap semiconductor 10, impurity material doping concentration 1 × 10 ²⁰ cm ⁻³ ) / ZnSe: Cl (wide gap semiconductor 10, impurity material doping concentration 1 × 10) ²⁰ cm ⁻³ ) / n-GaAs single crystal substrate (2) Au (metal layer 20) / ZnS: Ni (wide gap semiconductor 10, impurity material doping concentration 1 × 10 ²⁰ cm ⁻³ ) / ZnS: In (wide Gap semiconductor 10, impurity material doping concentration 1 × 10 ²⁰ cm ⁻³ ) / n-GaP single crystal substrate (3) Au (metal layer 20) / ZnO: Ni (wide gap semiconductor 10, impurity material doping concentration 1 × ^{10 20 cm -3) / ZnO:} Ga ( wide-gap semiconductor 10, the doping concentration of impurity material ^{1 × 10 20 cm -3) /} YSZ single crystal base

<Example 5>
An example of the element structure of a planar diode using ZnSe as the wide gap semiconductor 10 is shown in FIG.
In this example, Au is used as the material of the metal layer 20, and Ni is doped into ZnSe as the impurity material. The dope concentration is 1 × 10 ²⁰ cm ⁻³ .

<Example 6>
An example of an FET (field effect transistor) using ZnSe as the wide gap semiconductor 10 is shown in FIG.
In this example, Au is used as the material of the metal layer 20, and Ni is doped into ZnSe as the impurity material. The dope concentration is 1 × 10 ²⁰ cm ⁻³ . The wide gap semiconductor 10 is formed on a Si substrate via a SiO ₂ film. The Si substrate functions as a gate electrode.

  Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment, and can be improved or changed within the scope of the purpose of the improvement or the idea of the present invention.

In the electrode structure according to the first embodiment of the present invention, when the wide gap semiconductor is doped with Ni as an example of an impurity material, an example of a band change when the wide gap semiconductor and the metal layer are joined is shown. (A) is a conceptual diagram showing a state before joining, (b) is a state after joining, and (c) is a conceptual diagram showing a state where an external electric field is applied. It is a conceptual diagram which shows the element structure on the glass substrate concerning the Example of this invention. It is a conceptual diagram which shows the element structure concerning the Example of this invention, (a) shows the element structure of the planar diode which used ZnSe as a wide gap semiconductor, (b) is FET which used ZnSe as a wide gap semiconductor The element structure of (field effect transistor) is shown.

Explanation of symbols

10 wide gap semiconductor 10c conduction band edge 10f Ni level (impurity level)
10v valence band edge 20 metal layer 20f Fermi level Eb binding energy Wf work function VL vacuum level

Claims (7)

A wide gap semiconductor doped with impurities having an ionization energy of 0.2 to 1 eV;
A metal layer having a work function smaller than the binding energy of impurity ions and bonded to the wide gap semiconductor,
An electrode structure, wherein holes are injected from the metal layer into the wide gap semiconductor by applying an external electric field. A wide gap semiconductor doped with impurities having an ionization energy of 0.2 to 1 eV;
A metal layer having a work function larger than the binding energy of impurity ions and bonded to the wide gap semiconductor,
An electrode structure wherein electrons are injected from the metal layer into the wide gap semiconductor by applying an external electric field. 3. The electrode structure according to claim 1, wherein a concentration of the impurity in the wide gap semiconductor is 1 × 10 ^{18 to} 5 × 10 ²¹ cm ⁻³ .   The electrode structure according to any one of claims 1 to 3, wherein the impurity is doped in a range of 100 nm from a joint surface with the metal layer.   The electrode structure according to any one of claims 1 to 4, wherein the wide gap semiconductor is a II-VI group compound semiconductor, a III-V group compound semiconductor, or an oxide semiconductor.   The impurity is one or more of Ni, Co, Fe, Pd, Rh, Ru, Pt, Ir, Os, N, P, As, and Sb. 6. The electrode structure according to any one of 5 above. The electrode structure according to any one of claims 1 to 6, wherein the carrier current density is 1 mA / cm ² or more.

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