JP4997464B2 - Quantum point contact, quantum dot, quantum wire, memory device, and quantum computer - Google Patents

Description

  The present invention relates to a quantum point contact, a quantum dot, a quantum wire, a memory device, and a quantum computer using carbon nanotubes.

  Conventionally, Patent Document 1 discloses a field effect transistor in which a gate is made of metallic CNT as a semiconductor technology using a carbon nanotube (hereinafter referred to as “CNT”). According to this field-effect transistor, the gate can be miniaturized, and the gate does not fluctuate in size.

  Further, Patent Document 2 discloses a memory element including a memory cell including a plurality of nano-sized quantum dots filled with an electron storage material that stores electrons. This quantum dot has a step of forming an aluminum film on top of an oxide film formed on a substrate, a step of oxidizing a part of the aluminum film by electrolysis with an electrolytic device, and a size of 10 nm or less formed by oxidation. And a step of depositing an electron storage material in the holes.

JP 2003-109974 A JP 2003-243615 A

  By the way, it is known that CNT has strength and flexibility, and can change electric conductivity according to the diameter. For this reason, various applications are conceivable, and research and development are also being conducted in the field of quantum conduction devices that control conduction at the quantum level.

  In addition, for example, in a quantum computer, a hardware manufacturing method is difficult, and as described in the cited document 2, a quantum dot of about 10 nm is finally formed through various manufacturing processes.

  Therefore, an object of the present invention is to control carrier conduction at the quantum level.

  Specifically, it is an object of the present invention to provide inexpensive quantum point contacts, quantum dots, quantum wires, memory elements, and quantum computers that are similar to the manufacturing steps of a field effect transistor.

  In order to solve the above problems, a quantum point contact according to the present invention includes a semiconductor substrate, a pair of metal gates formed on the semiconductor substrate, and a gap between the end portions of the metal gate that is about the Fermi wavelength. And a pair of carbon nanotubes connected to each other.

  In addition, the quantum dot of the present invention includes a semiconductor substrate, a pair of metal gates formed on the semiconductor substrate, and a pair of carbons whose ends are connected to the metal gates with an interval of about the Fermi wavelength. One of the carbon nanotubes is Y-shaped or ω-shaped at the end, the other of the carbon nanotubes is T-shaped, and the branch sides of the carbon nanotubes are spaced apart from each other by a Fermi wavelength. It is characterized by facing each other.

  Each carbon nanotube may have a Y shape or an ω shape at the end.

  Furthermore, the single channel quantum wire of the present invention is formed in a semiconductor substrate, first and second semiconductor layers sequentially formed on the semiconductor substrate, and a trench provided in the second semiconductor layer. A pair of metal gates and carbon nanotubes connected to the metal gates are provided.

  Furthermore, the memory element of the present invention is characterized by comprising a plurality of the quantum dots.

  In addition, a quantum computer of the present invention includes the quantum dot or the single channel quantum wire.

  As described above, according to the present invention, it is possible to control the conduction of carriers at the quantum level, so that it is the same as the manufacturing process of a field effect transistor, and a small quantum point contact, quantum dot, quantum Thin wires, memory elements, and quantum computers can be provided at low cost.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below with reference to the drawings.
(Embodiment 1)
FIG. 1 is a schematic perspective view of a quantum point contact 100 according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the quantum point contact 100 of this embodiment includes a semiconductor substrate 10 such as an AlGaAs / GaAshe hetero substrate, a pair of metal gates 12 and 14 formed on the semiconductor substrate 10, a metal gate 12, 14 is provided with a pair of CNTs 16 and 18 that are connected to each other with an interval of about the Fermi wavelength. A two-dimensional electron layer 20 is present on the semiconductor substrate 10.

  FIG. 2A is a perspective view showing a part of FIG. 1 in a state in which a nearby voltage is not applied to the CNTs 16 and 18. FIG. 2B is a perspective view showing a part of FIG. 1 in a state in which a nearby voltage is applied to the CNTs 16 and 18. The principle of the quantum point contact 100 shown in FIG. 1 will be described with reference to FIGS. 2 (a) and 2 (b).

  In the state where no voltage is applied to the CNTs 16 and 18, unlike the case described below, the operation of the two-dimensional electrons in the two-dimensional electron layer 20 is hindered by the presence of the CNTs 16 and 18, as shown in FIG. It will never be done.

  On the other hand, in the state where the voltage is applied to the CNTs 16 and 18 through the metal gates 12 and 14, similar to these shapes just below the metal gates 12 and 14 and the CNTs 16 and 18, as shown in FIG. Shaped depletion layers 22, 24 are formed. Therefore, the two-dimensional electrons in the two-dimensional electron layer 20 can operate only in a region where the depletion layers 22 and 24 are not formed, and the quantum point contact 100 can be configured.

  Next, a method for manufacturing the quantum point contact 100 will be described. First, the semiconductor substrate 10 is prepared. Then, an ohmic contact layer and a hole bar (not shown) are formed on the semiconductor substrate 10.

  Then, the CNTs 16 and 18 are disposed on the semiconductor substrate 10, respectively. Subsequently, the CNTs 16 and 18 are respectively moved to required positions by manipulation techniques. Thereafter, the metal gates 12 and 14 are attached on the CNTs 16 and 18 by using photolithography or the like. The metal gates 12 and 14 may be formed on the semiconductor substrate 10 in advance, and the CNTs 16 and 18 may be formed on the metal gates 12 and 14.

  As described above, in this embodiment, the quantum point contact 100 is realized only by a simple operation of devising the arrangement of the CNTs 16 and 18 and applying a voltage to the CNTs 16 and 18. In other words, according to the quantum point contact 100, a state where a plurality of carriers can be transported and a state where only one carrier can be transported can be realized.

  In the present embodiment, the quantum point contact 100 including the CNTs 16 and 18 has been described as an example. However, by using the CNTs 16 and 18 as a mask material, a metal layer having a size corresponding to the CNTs 16 and 18 is formed. Thus, the quantum point contact 100 may be manufactured. The same applies to the quantum dots and the like described below.

(Embodiment 2)
FIG. 3A is a perspective view in a state in which a nearby voltage is not applied to the CNTs 16, 18, 26, and 28, and corresponds to FIG. FIG. 3B is a perspective view in a state where a nearby voltage is applied to the CNTs 16, 18, 26, and 28, and corresponds to FIG. In FIG. 3, the same parts as those shown in FIG.

  As shown in FIGS. 2A and 2B, a U-shaped CNT 26 is connected to the end of the CNT 16, and an I-shaped CNT 28 is connected to the end of the CNT 18. In these connections, for example, in a state where the CNTs to be connected are in contact with each other, a part of the probe is melted by flowing a large current through the STM probe while bringing the STM probe made of titanium or the like close to or in contact with the contact point. The procedure is similar to welding. Further, the interval between the end portions of the CNTs 26 and 28 is set to about the Fermi wavelength. In addition, since conduction | electrical_connection can be taken and operation | movement is possible only by CNT mutually contacting, it is not limited to the said connection method.

  In a state where no voltage is applied to the CNTs 16, 18, 26, and 28, as shown in FIG. 3A, the operation of the two-dimensional electrons in the two-dimensional electron layer 20 is caused by the presence of the CNTs 16, 18, 26, and 28. There is no hindrance.

  On the other hand, in the state where the voltage is applied to the CNTs 16, 18, 26, and 28 through the metal gates 12 and 14, as shown in FIG. 3B, the metal gates 12 and 14 and the CNTs 16, 18, 26, and 28 are provided. The depletion layers 22 and 24 in a region that is similar to these shapes and slightly smaller than these shapes are formed immediately below. For this reason, the two-dimensional electrons in the two-dimensional electron layer 20 can operate only in a region where the depletion layers 22 and 24 are not formed.

  At this time, the electron storage region 30, which is a region surrounded by the depletion layers 22 and 24, can store electrons passing between the depletion layers 22 and 24, and thus forms a single quantum dot 200. be able to.

  The manufacturing method of the quantum dot 200 is the same as the manufacturing method of the quantum point contact 100, but in this embodiment, the CNTs 16 and 18 to which the CNTs 26 and 28 are connected are arranged on the metal gates 12 and 14, respectively. I am doing so.

  As described above, in this embodiment, the arrangement of the CNTs 16 and 18 and the shape of the CNTs 26 and 28 are devised, and only a simple operation of applying a voltage to the CNTs 16, 18, 26, 28 is performed. Is realized.

  Here, an example using four CNTs CNT16, 18, 26, and 28 has been described, but a CNT with one end bifurcated may be used. That is, the CNTs 16 and 26 may be Y-shaped, and the CNTs 18 and 28 may be T-shaped. Of course, the CNTs 18 and 28 may also be Y-shaped.

(Embodiment 3)
FIG. 4A is a perspective view in a state in which no nearby voltage is applied to the CNTs 16, 18, 26, and 28, and corresponds to FIG. FIG. 4B is a perspective view in a state where a nearby voltage is applied to the CNTs 16, 18, 26, and 28, and corresponds to FIG. In FIG. 4, the same parts as those shown in FIG.

  As shown in FIGS. 3A and 3B, an ω-shaped CNT 26 is connected to the end of the CNT 16, and an I-shaped CNT 28 is connected to the end of the CNT 18. These connections are made by the method described in the second embodiment. Further, the interval between the end portions of the CNTs 16 and 18 is set to about the Fermi wavelength. The distance between the end portions of the CNTs 26 and 28 is also set to about the Fermi wavelength. Of course, the ends of the CNTs 18 and 28 may be ω-shaped.

  In a state where no voltage is applied to the CNTs 16, 18, 26, 28, as shown in FIG. 4A, the operation of the two-dimensional electrons in the two-dimensional electron layer 20 is caused by the presence of the CNTs 16, 18, 26, 28. There is no hindrance.

  On the other hand, in the state where the voltage is applied to the CNTs 16, 18, 26, and 28 through the metal gates 12 and 14, as shown in FIG. 4B, the metal gates 12 and 14 and the CNTs 16, 18, 26, and 28 are applied. The depletion layers 22 and 24 in a region that is similar to these shapes and slightly smaller than these shapes are formed immediately below. For this reason, the two-dimensional electrons in the two-dimensional electron layer 20 can operate only in a region where the depletion layers 22 and 24 are not formed.

  At this time, the electron storage regions 30 and 32, which are regions surrounded by the depletion layers 22 and 24, can store electrons passing between the depletion layers 22 and 24, respectively. Can be configured.

  In the present embodiment, the coupled quantum dots 300 are realized only by a simple operation of devising the arrangement of the CNTs 16 and 18 and the shape of the CNTs 26 and 28 and applying a voltage to the CNTs 16, 18, 26, and 28.

  In addition, although the example using four CNTs of CNT16, 18, 26, and 28 has been described here, one end may be a bifurcated CNT, and furthermore, a multi-coupled quantum dot is formed by using three or more CNTs. It may be formed. Two or more sets of the CNTs 16 and 26 may be prepared.

  If a plurality of quantum dots described in the second and third embodiments are provided, a memory element can be configured. Furthermore, the quantum dot described in the second and third embodiments, or a plurality of these, or a combination of them, can be used to form a quantum computer of a unitary conversion gate type or a control NOT gate type.

  In the quantum computer, the quantum dots can be used mainly as a quantum operation circuit, but can also be used for a spin filter or the like that reads out the operation result of the quantum operation circuit.

(Embodiment 4)
FIG. 5A to FIG. 5D are schematic configuration diagrams of a single channel quantum wire 400 according to the fourth embodiment of the present invention. FIG. 5A is a cross-sectional view of the single channel quantum wire 400 when no voltage is applied to the metal gates 12 and 14. FIG. 5B is a plan view of FIG. FIG. 5C is a cross-sectional view of the single channel quantum wire 400 when a voltage is applied to the metal gates 12 and 14. FIG. 5D is a plan view of 5C.

In FIG. 5, a semiconductor substrate 10 such as an i ⁻ GaAs semiconductor substrate, an i ⁻ AlGaAs layer 34 and an n ⁻ AlGaAs layer 36 which are first and second semiconductor layers sequentially formed on the semiconductor substrate 10, are adjacent to each other. An ohmic contact layer 38 for connecting elements to be connected to each other, a trench 35 provided by removing a part of the n ⁻ AlGaAs layer 36, a pair of metal gates 12 and 14 formed in the trench 35, and a metal gate The voltage is applied to the CNT 40 connected to 12 and 14, the depletion layer 42 formed between the two-dimensional electron layers 20 a and 20 b when no voltage is applied to the metal gates 12 and 14, and the metal gates 12 and 14. A single channel 44 formed so as to cross the depletion layer 42 is shown. The voltage applied to the metal gates 12 and 14 is a reverse voltage with respect to the voltage applied in the first to third embodiments.

  As shown in FIGS. 5A and 5B, when no voltage is applied to the metal gates 12 and 14, a depletion layer 42 is formed between the two-dimensional electron layers 20a and 20b due to the presence of the trench 35. . For this reason, the movement of the two-dimensional electrons between the two-dimensional electron layers 20a and 20b does not occur.

  On the other hand, as shown in FIG. 5 (c) and FIG. 5 (d), when a voltage is applied to the metal gates 12 and 14, the depletion layer 42 has a similar shape to those immediately below the metal gates 12 and 14 and the CNT 40. Single channel 44 is formed. For this reason, movement of the two-dimensional electrons between the two-dimensional electron layers 20 a and 20 b occurs through the single channel 44.

  At this time, the level of the applied voltage and the diameter of the CNT 40 are adjusted so that the width of the single channel 44 is the same as or slightly larger than the diameter of one dimensional electron.

Next, a method for manufacturing the single channel quantum wire 400 will be described. First, the semiconductor substrate 10 is prepared. Then, an i ⁻ AlGaAs layer 34 and an n ⁻ AlGaAs layer 36 are sequentially formed on the semiconductor substrate 10, and then part of the i ⁻ AlGaAs layer 34 and the n ⁻ AlGaAs layer 36 is removed by etching or the like to form an ohmic contact layer. 38 is formed. Thereafter, a trench 35 is formed in the n ⁻ AlGaAs layer 36 by etching or the like.

  Then, the CNT 40 is disposed in the trench 35. Subsequently, the CNT 40 is moved to a required position by a manipulation technique. Thereafter, the metal gates 12 and 14 are attached on the CNT 40 using photolithography or the like. The metal gates 12 and 14 may be formed on the semiconductor substrate 10 in advance, and the CNTs 40 may be formed on the metal gates 12 and 14.

  As described above, in the present embodiment, since the single channel 44 attached to the CNT 40 can be formed in the depletion layer 42, the single channel quantum wire 400 that can transport the channels one by one is realized. Can do. In other words, according to the single channel quantum wire 400, it is possible to realize a state in which carriers cannot be transported and a state in which only one channel can be transported. As a result, like the single channel quantum wire 400 described in Embodiment 6, A quantum computer can also be realized. Note that a plurality of channels can be formed by increasing the gate voltage.

  Note that a tunnel diode can be realized by connecting a plurality of CNTs 40 with a distance of about the Fermi wavelength between the end portions in the central portion.

(Embodiment 5)
6A to 6D are schematic configuration examples of the CNTs of the single channel quantum wire 400 according to the fifth embodiment of the present invention. In FIG. 6, the same parts as those shown in FIG.

  FIG. 6A shows a CNT 40 having two branch points at both ends of the central portion, and the central portion having a ring shape. The CNT 40 may be configured by connecting a plurality of CNTs.

  FIG. 6B shows a plurality of CNTs 40, 40 ′ arranged at a distance (for example, several tens of nanometers) at which the carriers transmitting between the metal gates 12, 14 can interfere with each other at the central portion.

  FIG. 6 (c) shows a plurality of CNTs 40, 40 'arranged at a distance that allows transmission carriers to come out of the metal gates 12, 14 and return to the metal gates 12, 14 at the central portion. ing.

  FIG. 6D shows a CNT 40 having one branch point at the central portion. This is a form in which the ones shown in FIGS. 6B and 6C are mixed.

  When the CNTs having the above-described configurations are used, a so-called superposition state can be obtained, so that carriers that have entered the CNTs can move to both the metal gate 12 and the metal gate 14. Note that a magnetic field may be applied in the vicinity of the CNT when controlling the carrier transfer destination.

It is a typical perspective view of the quantum point contact 100 of Embodiment 1 of this invention. FIG. 2 is a diagram illustrating the principle of the quantum point contact 100 shown in FIG. 1. It is principle explanatory drawing of the single quantum dot 200 of Embodiment 2 of this invention. It is a principle explanatory view of coupled quantum dot 300 of Embodiment 3 of the present invention. It is a typical block diagram of the single channel quantum wire 400 of Embodiment 4 of this invention. It is a typical structural example of CNT of the single channel quantum wire 400 of Embodiment 5 of this invention.

Explanation of symbols

10 Semiconductor substrate 12, 14 Metal gate 16, 18, 26, 28, 40, 40 'CNT
20, 20a, 20b Two-dimensional electron layer 22, 24, 42 Depletion layer 30, 32 Electron storage region 34 i ^- AlGaAs layer (first semiconductor layer)
35 trench 36 n ⁻ AlGaAs layer (second semiconductor layer)
38 Ohmic contact layer 44 Single channel 100 Quantum point contact 200 Single quantum dot 300 Coupled quantum dot 400 Single channel quantum wire

Claims (6)

A hetero substrate, a pair of metal gates formed on the semiconductor substrate, and a pair of carbon nanotubes connected to the metal gate so that the end portions face each other with an interval of about Fermi wavelength,
One of the carbon nanotubes has a shape in which a U-shaped carbon nanotube is connected to an I-shaped carbon nanotube, or a shape in which a ω-shaped carbon nanotube is connected to an I-shaped carbon nanotube. The other of the nanotubes is a T-shape in which an I-shaped carbon nanotube is connected to an I-shaped carbon nanotube , and the open end of the one carbon nanotube and the straight portion of the other carbon nanotube are about the Fermi wavelength. Quantum dots characterized by facing each other at intervals. A hetero substrate, a pair of metal gates formed on the semiconductor substrate, and a pair of carbon nanotubes connected to the metal gate so that the end portions face each other with an interval of about Fermi wavelength,
Each carbon nanotube has a shape in which a U-shaped carbon nanotube is connected to an I-shaped carbon nanotube or a shape in which a ω-shaped carbon nanotube is connected to an I-shaped carbon nanotube. A quantum dot characterized in that the open ends of nanotubes are opposed to each other with an interval of about the Fermi wavelength. A semiconductor substrate; first and second semiconductor layers sequentially formed on the semiconductor substrate; a pair of metal gates formed in a trench provided in the second semiconductor layer; and the pair of metal gates And a pair of ohmic contact layers connected to the semiconductor substrate across the trench, and
A two-dimensional electron layer is formed on the semiconductor substrate,
When no voltage is applied to the pair of metal gates, a depletion layer is formed in the two-dimensional electron layer below the trench,
Wherein when voltage is applied to the pair of metal gates, of the depletion layer, the pair of metal gate and a single channel of similar shape and the carbon nanotubes are formed immediately below the pair of metal gates and the carbon nanotube, the pair Single-channel quantum wires characterized by connecting the ohmic contact layers of each other . The carbon nanotube is one carbon nanotube having a branching point, a plurality of carbon nanotubes arranged at a distance that allows transmission carriers to interfere with each other, or the ends are connected with an interval of about the Fermi wavelength. 4. The single channel quantum wire according to claim 3 , wherein the single channel quantum wire is a plurality of carbon nanotubes. Memory device, characterized in that it comprises a plurality of quantum dots of claim 1 or 2, wherein. A quantum computer comprising the quantum dot according to claim 1 or 2 , or the single channel quantum wire according to claim 3 or 4 .