JP5347340B2 - Resonant tunnel diode manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resonance tunnel diode which can be manufactured inexpensively as compared with a conventional method and is suited also to area increase. <P>SOLUTION: The resonance tunnel diode has a structure sandwiching a quantum well layer between a pair of energy barrier layers, and the quantum well layer is composed of a semiconductor nano-structure (e.g. a single-layer carbon nanotube (CNT)) having an anisotropic atomic arrangement. Since the semiconductor nano-structure itself used for the quantum well layer exists in nano-size, the semiconductor nano-structure can be uniformly dispersed by a simple coating method such as spin coating and dip coating. Thereby, use of epitaxial growth, ion implantation or the like in ultra-high vacuum is unnecessary. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a resonant tunneling diode and a manufacturing method thereof.

A resonant tunneling diode has a structure in which a quantum well layer is sandwiched between a pair of energy barrier layers. In such a resonant tunneling diode, when electrons pass through two energy barrier layers, the energy of the incident electrons coincides with the energy level localized in the quantum well layer sandwiched between the energy barrier layers. The probability increases resonancely and a large differential negative resistance is observed in the current-voltage characteristics. A resonant tunneling diode can perform microwave oscillation and high-speed switching by utilizing these properties. As such a resonant tunneling diode, for example, Non-Patent Document 1 reports that SiO ₂ is used as an energy barrier layer and a single crystal silicon thin film is used as a quantum well layer.
Applied Physics Letters, 86, 013508, 2005

  However, conventional methods for fabricating resonant tunneling diodes use epitaxial growth in ultra-high vacuum, ion implantation, etc. when forming a quantum well layer, which increases costs and is not suitable for increasing the area. was there.

  The present invention has been made to solve such problems, and it is a main object of the present invention to provide a resonant tunneling diode that is low in cost and suitable for a large area and a manufacturing method thereof.

  In order to achieve the above-described object, the present inventors fabricated an element having a structure in which a carbon nanotube is sandwiched between a pair of silicon oxide thin films. This element sandwiched a single crystal silicon thin film between a pair of silicon oxide thin films. The inventors have found that the current-voltage characteristics equivalent to those of the resonant tunneling diode having the structure are found, and have completed the present invention.

That is, the resonant tunnel diode of the present invention is
The resonant tunneling diode has a structure in which a quantum well layer is sandwiched between a pair of energy barrier layers, and the quantum well layer is made of a semiconductor nanostructure having an anisotropic atomic arrangement.

  The method of manufacturing the resonant tunneling diode of the present invention is a method of manufacturing the above-described resonant tunneling diode of the present invention, wherein after forming a dielectric film that becomes one of the pair of energy barrier layers on a substrate, The quantum well layer is formed by coating the semiconductor nanostructure dispersed in a solvent on the dielectric film, and the dielectric film serving as the other of the pair of energy barrier layers is formed on the quantum well layer. Is.

  According to the resonant tunneling diode and the manufacturing method thereof of the present invention, the following effects can be obtained. That is, since the semiconductor nanostructure used for the quantum well layer itself has a nano size, it is uniformly dispersed by a simple coating method such as spin coating or dip coating. Therefore, since it is not necessary to use epitaxial growth or ion implantation in an ultra-high vacuum, it can be produced at a lower cost than the conventional one, and is suitable for a large area.

  The resonant tunnel diode of the present invention is a resonant tunnel diode having a structure in which a quantum well layer is sandwiched between a pair of energy barrier layers, and the quantum well layer is composed of a semiconductor nanostructure having an anisotropic atomic arrangement. is there.

  Here, the anisotropic atomic arrangement means that the atomic arrangement along one of the XYZ axes defining the three-dimensional space is greatly different from the atomic arrangement along the other axial direction. As the semiconductor nanostructure having such an anisotropic atomic arrangement, for example, a semiconductor having a sheet structure in which one or more kinds of atoms are arranged two-dimensionally, or a sheet in which one or more kinds of atoms are arranged two-dimensionally is used. For example, a semiconductor having a structure rounded into a shape. Here, examples of the material for the semiconductor nanostructure include carbon, boron nitride, carbon boron nitride, tungsten sulfide, and molybdenum sulfide. Examples of the material for the energy barrier layer include insulators such as silicon oxide, aluminum oxide, and magnesium oxide, wide gap semiconductors such as silicon carbide and gallium nitride, 4,4 ′, 4 ″ -tris- [N- (3- And a flexible polymer such as methylphenyl) -N-phenylamino] triphenylamine (m-MTDATA) and 4,7-diphenyl-1,10-phenanthroline (Bphen).

  In the resonant tunneling diode of the present invention, the semiconductor nanostructure is preferably a carbon nanotube, and more preferably a single-walled carbon nanotube. Since the carbon nanotube has resistance to high temperature, resistance to mechanical strain, and resistance to a chemically active atmosphere, it can provide a resonant tunnel diode excellent in environmental resistance. At this time, if a flexible polymer (described above) is employed as the energy barrier layer, a resonant tunneling diode having flexibility can be provided. Carbon nanotubes have metal and semiconductor properties that are contradictory, but it is preferable to use semiconductor-type carbon nanotubes. The semiconducting carbon nanotube may be one obtained by performing electrophoresis on a gel sample in which a mixture of a metallic type and a semiconducting type is included in a dispersed state in advance. You may use what was selectively synthesize | combined by using a molybdenum catalyst. Further, a mixture of a metal mold and a semiconductor mold may be used.

  In the resonant tunnel diode of the present invention, a dielectric film serving as one of the pair of energy barrier layers is formed on a substrate, and then the semiconductor nanostructure dispersed in a solvent is coated on the dielectric film. It can be produced by forming a quantum well layer and forming a dielectric film on the other side of the pair of energy barrier layers on the quantum well layer.

  Here, examples of the substrate include conductive substrates such as a silicon substrate, a GaAs substrate, a metal substrate, and a glass with a transparent conductive film. Examples of the dielectric film include insulator films such as silicon oxide, aluminum oxide, and magnesium oxide, wide gap semiconductor films such as silicon carbide and gallium nitride, and 4,4 ′, 4 ″ -tris- [ Examples thereof include flexible polymer membranes such as N- (3-methylphenyl) -N-phenylamino] triphenylamine (m-MTDATA) and 4,7-diphenyl-1,10-phenanthroline (Bphen). Examples of the coating include spin coating, dip coating, etc. Among them, it is preferable to carry out by spin coating, whereby an ultrathin film of a semiconductor nanostructure can be easily generated.

  Alternatively, in the resonant tunnel diode of the present invention, after forming a dielectric film to be one of the pair of energy barrier layers on a substrate, the raw material of the semiconductor nanostructure is supplied onto the dielectric film, and the semiconductor The quantum well layer can be formed by growing a nanostructure, and a dielectric film serving as the other of the pair of energy barrier layers can be formed on the quantum well layer.

  Here, as the substrate and the dielectric film, those described above can be used. When the semiconductor nanostructure is a carbon nanotube, a catalyst metal pattern serving as a base point for growing the carbon nanotube is formed on the dielectric film, and the carbon source gas is supplied in a state where the substrate is heated. Carbon nanotubes may be grown on the metal. As the catalyst metal, cobalt, iron, nickel, gold, or an alloy thereof is preferable, and at least one of molybdenum, platinum, copper, chromium, palladium, rhodium, alumina, and zeolite may be added thereto. As the carbon source gas, methane gas, acetylene gas, ethylene gas, alcohol gas, and carbon monoxide gas are preferable. The temperature of the substrate may be experimentally determined according to the catalyst metal and carbon source gas used.

An element having a SiO ₂ / CNT / SiO ₂ structure was formed on a silicon substrate by the following procedure. CNT is an abbreviation for carbon nanotube.
(1) A Si (100) wafer (manufactured by Niraco) having a 10 mm square, a thickness of 525 μm, and a resistivity <0.02 Ωcm was prepared as a silicon substrate, and the surface was cleaned by treating the silicon substrate with hydrofluoric acid. That is, since the surface of the silicon substrate was covered with silicon oxide by air oxidation, this silicon oxide was removed.
(2) A silicon oxide thin film having a thickness of 3 nm was deposited on the surface of the cleaned silicon substrate by high-frequency magnetron sputtering at room temperature. Table 1 shows the conditions for forming the silicon oxide thin film.
(3) A single-walled carbon nanotube having a diameter of 1 to 2.5 nm (FH purified type, manufactured by Meijo Nanocarbon) is dispersed in ethanol, which is an organic solvent for dispersion, so as to be about 5 μg / mL. Was prepared. The nanotube dispersion liquid may be prepared by dispersing single-walled carbon nanotubes in water containing a surfactant such as SDS (sodium dodecyl sulfate) or SDBS (sodium dodecylbenzenesulfonate).
(4) The nanotube dispersion liquid of (3) above was dropped onto the silicon oxide thin film of the silicon substrate of (2) above using a spin coater (manufactured by Mikasa) at a rotational speed of 2000 rpm for 30 seconds. As a result, single-walled carbon nanotubes were dispersed on the silicon oxide thin film of the silicon substrate.
(5) A silicon oxide thin film having a thickness of 3 nm was deposited on the surface on which the single-walled carbon nanotubes were dispersed in this manner by high-frequency magnetron sputtering. The conditions for forming the silicon oxide thin film are the same as in (2) above. Subsequently, this silicon substrate was heat-treated at a base pressure of 5 × 10 ⁻⁶ Torr, a temperature of 900 ° C., a heating time of 1 minute, and a heating time of 30 minutes (no gas introduction). As a result, a silicon substrate having a SiO ₂ / CNT / SiO ₂ structure laminated on the surface was obtained.
(6) A Si-doped Al electrode was produced on the SiO ₂ / CNT / SiO ₂ structure of the obtained silicon substrate by photolithography. The size of the electrode was 0.5 mm or 1.0 mm in diameter and 300 nm in thickness. A schematic view of the silicon substrate thus obtained is shown in FIG.

About the obtained element of SiO ₂ / CNT / SiO ₂ structure, current-voltage characteristics were measured at a temperature of 5K. The result is shown in FIG. As is apparent from FIG. 2, a characteristic peak was observed at about 0.24 V, and it was found that this element exhibited resonant tunnel diode characteristics. Here, the resonant tunnel diode having the SiO ₂ / Si / SiO ₂ structure of Non-Patent Document 1 is used as a comparative example, and a graph of the current-voltage characteristics is shown in FIG. As is apparent from FIGS. 2 and 3, the peak position and current value of the device having the SiO ₂ / CNT / SiO ₂ structure of the example are almost the same as those of the device having the SiO ₂ / Si / SiO ₂ structure of the comparative example. I understood that I have it.

It is a schematic view of a silicon substrate that element of SiO ₂ / CNT / SiO ₂ structure is formed. It is a graph of the current-voltage characteristic of the element of an Example. It is a graph of the current-voltage characteristic of the element of a comparative example.

Claims (2)

Having a structure in which a quantum well layer is sandwiched between a pair of energy barrier layers, the quantum well layer is made of a semiconductor nanostructure having an anisotropic atomic arrangement, and the semiconductor nanostructure is a carbon nanotube. A method of manufacturing a tunnel diode, comprising:
After forming a dielectric film to be one of the pair of energy barrier layers on the substrate, the quantum well layer is formed by coating the dielectric film with carbon nanotubes dispersed in a solvent, and the quantum well layer Forming a dielectric film on the other of the pair of energy barrier layers;
A manufacturing method for resonant tunneling diodes. The coating is performed by spin coating.
The method for producing a resonant tunneling diode according to claim 1 .

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