JP2014120548A - Method of producing nanowire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a semiconductor nanowire by a simpler step, more inexpensively.SOLUTION: In a step S101, a carbon compound gas is supplied onto a heated substrate 101 made of iron to form a carbon layer 102 on the substrate 101 (a carbon layer formation step). For example, the substrate 101 is heated to approximately 600°C, and in this state, the carbon compound gas such as methane, acethylene, or methanol is supplied onto a surface of the substrate 101 to form the carbon layer 102. Next, in a step S102, a semiconductor nanowire 103 is formed on the carbon layer 102 by an organic metal vapor growth method (a nanowire formation step). For example, the nanowire 103 is formed by the organic metal vapor growth method using a metal fine particle (not shown) of such as Au, Al, In, as a catalyst.

Description

  The present invention relates to a nanowire forming method for forming a nanowire made of a semiconductor such as a III-V group compound on a carbon layer such as graphene or graphite.

  Nanowires made of nanometer-scale semiconductors have been studied for application to optical devices. In addition, a technique for forming such nanowires on a carbon layer such as graphene has been studied. Graphene is a sheet-like substance with one to several atomic layers composed of carbon atoms two-dimensionally bonded to each other, and has attracted attention as a material for high-speed devices because carriers have high mobility. . Recently, large-area single-layer or several-layer graphene sheets have been produced by roll-to-roll technology.

  The graphene sheet can be transferred to a plastic substrate that bends easily, and can be applied to transparent electronic and optical products that can be stretched and folded. If the above-mentioned nanowires can be grown on such a graphene sheet, for example, it will be possible to easily mount a high-efficiency light-emitting / receiving element on a flexible plastic substrate at a low cost, for example, application to various technologies There is expected. Further, according to this technology, the light emitting / receiving element can be easily mounted at a low cost in a large area.

  For example, recently, nanowire growth made of ZnO (see Non-patent Document 1), nanowire growth made of GaP (see Non-Patent Document 2), nanowire growth made of GaAs (see Non-Patent Document 2 and Non-Patent Document 3), InP Nanowire growth made of (see Non-Patent Document 2) and nanowire growth made of InAs (see Non-Patent Document 4) have been reported.

  On the other hand, graphene is generally formed on a metal such as Ni, Cu, or Fe (see Non-Patent Document 5). For example, good graphene production on inexpensive iron sheets has been reported, and it is considered that film formation of graphene occurs from carbon contained in iron below the eutectic point of 727 ° C. (non-patent document) 5). On the other hand, although the solar cell itself by nanowire is produced, for example, InP nanowire is produced by growing on an expensive InP substrate (see Non-Patent Document 6).

Y.J.Kim et al., "Vertically aligned ZnO nanostructures grown on graphene layers", Appl. Phys. Lett., Vol.95, 213101, 2009. K. Tateno et al., "VLS Growth of III-V Semiconductor Nanowires on Graphene Layers", MRS Proceedings, MRS Spring Meeting, mrss12-1439-aa04-11, 2012. A. M. Munshi et al., "Vertically Aligned GaAs Nanowires on Graphite and Few-Layer Graphene: Generic Model and Epitaxial Growth", Nano Lett., Vol.12, 4570, 2012. Y. J. Hong et al., "Van der Waals Epitaxy of InAs Nanowires Vertically Aligned on Single-Layer Graphene", Nano Lett., Vol.12, pp.1431-1436, 2012. Y. Xue et al., "Synthesis of Large-Area, Few-Layer Graphene on Iron Foil by Chemical Vapor Deposition", Nano Res., Vol.4, no.12, pp.1208-1214. 2011. H. Goto et al., "Growth of Core.Shell InP Nanowires for Photovoltaic Application by Selective-Area Metal Organic Vapor Phase Epitaxy", Applied Physics Express, vol.2, 035004, 2009.

  However, a technique for forming nanowires on graphene formed on a metal substrate as described above has not been made so far. If nanowires can be grown directly on such a substrate, roll-to-roll technology has the advantage that it can be performed consistently from graphene to nanowire formation, but now it is cheaper to use a substrate as described above. There was a problem that the technology to form semiconductor nanowires has not been established by a simple process.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to allow semiconductor nanowires to be formed at a lower cost and in a simpler process.

  The method for producing a nanowire according to the present invention includes a carbon layer forming step of supplying a carbon compound gas onto a heated substrate made of iron to form a carbon layer on the surface of the substrate, and an organic metal gas on the surface of the carbon layer. A nanowire forming step of forming a semiconductor nanowire by a phase growth method.

  The nanowire manufacturing method may include a substrate removing step of selectively removing the substrate after the nanowire is formed.

  In the nanowire manufacturing method, a metal fine particle forming step of arranging metal fine particles on the surface of the carbon layer is provided before the nanowire forming step, and in the nanowire forming step, an organic metal vapor phase growth method using the metal fine particles as a catalyst. A nanowire may be formed.

  In the nanowire manufacturing method, in the nanowire forming step, a first nanowire core of the first conductivity type is formed, an undoped second nanowire shell layer is formed around the first nanowire core, and the periphery of the second nanowire shell layer is formed. Alternatively, a third nanowire shell layer of the second conductivity type may be formed.

  As described above, according to the present invention, since a base made of iron is used, an excellent effect can be obtained that semiconductor nanowires can be formed at a lower cost and in a simpler process.

FIG. 1 is an explanatory view for explaining a method for producing nanowires in an embodiment of the present invention. FIG. 2 is a scanning electron micrograph showing the result when a graphene is formed using Ni (a), Cu (b), and Fe (c) as a metal to form a nanowire. FIG. 3A is a cross-sectional view schematically showing a state in each step for explaining a manufacturing method of the nanowire of Example 1 in the embodiment of the present invention. FIG. 3B is a cross-sectional view schematically showing a state in each step for explaining the manufacturing method of the nanowire of Example 1 in the embodiment of the present invention. FIG. 3C is a cross-sectional view schematically showing a state in each step for explaining the manufacturing method of the nanowire of Example 1 in the embodiment of the present invention. FIG. 3D is a cross-sectional view schematically showing a state in each step for explaining the manufacturing method of the nanowire of Example 1 in the embodiment of the present invention. FIG. 3E is a cross-sectional view schematically showing a state in each step for explaining the manufacturing method of the nanowire of Example 1 in the embodiment of the present invention. FIG. 4 is a perspective view showing the configuration of the nanowire of Example 2 in the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view for explaining a method for producing nanowires in an embodiment of the present invention.

  First, in step S101, as shown in FIG. 1A, a carbon compound gas is supplied onto a heated base 101 made of iron to form a carbon layer 102 on the base 101 (carbon layer formation). Process). For example, the carbon layer 102 can be formed by heating the substrate 101 to about 600 ° C. and supplying a gas of a carbon compound such as methane, acetylene, and methanol to the surface of the substrate 101 in this state.

  Here, the substrate 101 may be a plate-like substrate, an Fe film formed on another substrate, or a rod-like substrate. The carbon layer 102 is, for example, a graphene or graphite layer. When carbonized compound gas is supplied to the surface of the heated substrate 101, a carbon layer 102 is formed on the surface of the substrate 101, and the iron on the surface of the substrate 101 contains carbon, which is highly rigid and chemically stable. It becomes a state.

Next, in step S102, as shown in FIG. 1B, a semiconductor nanowire 103 is formed on the carbon layer 102 by metal organic vapor phase epitaxy (nanowire forming step). For example, the nanowire 103 can be formed by metal organic vapor phase epitaxy using metal fine particles (not shown) such as Au, Al, In, etc. as a catalyst. This nanowire forming technique is called a VLS (vapor-liquid-solid) growth method. Further, a mask layer (not shown) made of SiO ₂ or the like having a hole with a diameter of several nm is formed on the carbon layer 102, and on the carbon layer 102 exposed in the hole by metal organic chemical vapor deposition. Nanowires 103 can be formed.

  Next, the background to the above-described present invention will be described. The inventors conducted an investigation of forming graphene on a metal substrate and forming a nanowire made of InP on the graphene by a VLS growth method. FIG. 2 is a scanning electron micrograph showing the results when Ni (a), Cu (b), and Fe (c) are used as metals.

In the investigation, a substrate in which a Ni film, a Cu film, and an Fe film each having a thickness of 100 to 200 nm were formed on a sapphire substrate was used. In addition, nanowires were formed using a well-known chemical vapor deposition apparatus.
First, in the case of Ni, argon gas is supplied at 120 sccm and hydrogen gas is supplied at 30 sccm, the pressure in the processing chamber is set at 4666.27 Pa (35 Torr), the substrate temperature is raised to 900 ° C., and the condition is 10 sccm. Methane gas is supplied to the surface of the substrate, this is continued for 5 minutes, and then the temperature is lowered to grow graphene on the Ni film.

  In the case of Cu, the hydrogen gas is supplied at 50 sccm, the pressure in the processing chamber is set to 133.322 to 266.644 Pa (1 to 2 Torr), and the substrate temperature is raised to 1000 ° C. The pressure of 533.288 to 666.61 Pa (4 to 5 Torr) is supplied to the surface of the substrate under conditions of 10 sccm. This is continued for 30 minutes, and then the temperature is lowered to grow graphene on the Cu film.

In the case of Fe, argon gas is supplied at 120 sccm and hydrogen gas is supplied at 30 sccm, the pressure in the processing chamber is set at 4666.27 Pa (35 Torr), and the substrate temperature is raised to 950 ° C. Then, methane gas is supplied to the surface of the substrate, and this is continued for 5 minutes, and then the temperature is lowered to form graphene on the Fe film. Note that sccm is a unit of flow rate, and indicates that a fluid at 0 ° C. and 1013 hPa flows 1 cm ³ per minute.

  Au fine particles having a diameter of 5 to 10 nm are dispersed on each of the above-described substrates (metal films) on which graphene is formed, and in a hydrogen atmosphere (10132.472 Pa = 76 Torr) in a metal organic vapor phase epitaxy (MOVPE) apparatus. The temperature conditions were 365 ° C., trimethylindium (TMIn) was supplied at 5 sccm, and tertiary butylphosphine (TBP) was supplied at 27 sccm for 15 minutes.

  As a result, as shown in FIGS. 2A and 2B, InP nanowires were not formed in the case of Ni and Cu. This is because Ni and Cu are highly reactive with source gas, particularly TBP, which is a Group V source, and TBP and Ni and Cu that have entered through gaps such as defects and domain boundaries in graphene react. This is probably because nanowires were not produced.

  On the other hand, as shown in FIG. 2C, it was confirmed that InP nanowires can be generated in the case of Fe. The nanowire is photographed in a needle shape in FIG. Fe is considered to have a structure (steel) with a high carbon concentration on the surface by including carbon when the graphene layer is formed. Since iron containing carbon has high rigidity and high chemical stability, reaction with TBP hardly occurs. As a result, it is considered that the P generated by the decomposition of TBP into the gold fine particle catalyst on graphene was sufficiently supplied, and the InP nanowire growth was advanced. This is considered to be the same for other nanowire source gases.

  As described above, if a carbon layer such as graphene is formed on the surface of a substrate made of Fe, semiconductor nanowires such as InP can be stably formed on the carbon layer.

  Next, it demonstrates in detail using an Example.

[Example 1]
First, Example 1 will be described with reference to FIGS. 3A to 3E. FIG. 3A to FIG. 3E are cross-sectional views schematically showing states in respective steps for explaining the manufacturing method of the nanowire of Example 1 in the embodiment of the present invention.

  First, as shown in FIG. 3A, a substrate 201 made of Fe is prepared, the substrate 201 is heated to 600 ° C., methanol is introduced into the surface of the substrate 201 in this state, and graphene 202 is formed under saturated vapor pressure. According to the above conditions, in general, graphene can be formed on the surface of Fe at a temperature of 600 ° C. or higher. The surface after the graphene 202 is formed is thinly whitened. Next, a colloidal solution containing Au fine particles having a diameter of 10 nm is dropped to disperse the Au fine particles 211 on the graphene 202.

Next, the substrate 201 is carried into a processing chamber of a metal organic chemical vapor deposition (MOVPE) apparatus, and the substrate temperature condition is set to 370 ° C., TMIn is set to P1 × 10 ⁻⁶ mol / min, and TBP is set to 1. 2 × 10 ⁻³ mol / min and di-tert-butyl sulfur (DTBS) were introduced at 5 × 10 ⁻⁸ mol / min for 15 minutes, and as shown in FIG. 3B, a first n-InP layer was formed on graphene 202. A nanowire core 203 is formed.

Subsequently, the substrate temperature condition was set to 420 ° C. in the same processing chamber, and this time, TMIn was introduced at 2 × 10 ⁻⁶ mol / min and TBP at 1.2 × 10 ⁻³ mol / min for 1 minute. As shown in FIG. 2, a second nanowire shell layer 204 made of undoped InP (i-InP) is formed. The second nanowire shell layer 204 is formed around the first nanowire core 203.

Subsequently, in the same processing chamber, the substrate temperature condition was set to 420 ° C. This time, TMIn was 2 × 10 ⁻⁶ mol / min, TBP was 1.2 × 10 ⁻³ mol / min, and diethyl zinc (DEZn) was 5 Introducing 10 × 10 ⁻⁷ mol / min for 10 minutes, a third nanowire shell layer 205 made of p-InP is formed as shown in FIG. 3C. By these things, a pin-type core-shell nanowire can be produced. The figure shows a part of the substrate 201 and illustrates a part of one nanowire. In practice, a plurality of nanowires are formed on the surface of the graphene 202.

  Next, as shown in FIG. 3D, the core / shell nanowire made of the first nanowire core 203, the second nanowire shell layer 204, and the third nanowire shell layer 205 is embedded with a resin layer 206 made of polyimide. Next, the resin layer 206 is etched back by reactive ion etching using oxygen, and the tip of the core-shell nanowire (third nanowire shell layer 205) is exposed as shown in FIG. 3E. Next, the transparent electrode 207 is formed by vapor-depositing a transparent electrode material such as ITO (Indium Tin Oxide) by a sputtering method or the like. As a result, a diode element having a pin structure can be obtained. By using this element, it is expected that the diode characteristic is a rectifying characteristic and that an increase in current due to the photovoltaic power is expected.

[Example 2]
Next, Example 2 will be described with reference to FIG. FIG. 4 is a perspective view showing the configuration of the nanowire of Example 2 in the embodiment of the present invention.

  As shown in FIG. 4, graphene 302 is formed on the surface of a rod-shaped substrate 301 made of SUS430 (stainless steel) having a diameter of 250 μm, and a plurality of nanowires 303 are formed on the surface of graphene 302. The nanowire 303 is formed by a metal organic chemical vapor deposition method using Au fine particles 311 as a catalyst.

For example, the base 301 is heated to 800 ° C. in a predetermined treatment chamber, and ethylene gas is introduced into the graphene 302 to form the graphene 302. Next, after the substrate 301 is carried out of the processing chamber, it is immersed in a colloidal solution containing Au fine particles having a diameter of 10 nm, and Au fine particles 311 are dispersed and attached to the surface of the graphene 302. Next, the substrate 301 is carried in a processing chamber of a well-known metal organic chemical vapor deposition (MOVPE) apparatus, the temperature condition is 370 ° C., and trimethyl gallium (TMGa) is 1 × 10 ⁻⁶ mol / mol. By introducing min tertiary butylarsine (TBAs) into the processing chamber at 1.2 × 10 ⁻³ mol / min and maintaining this state for 15 minutes, a plurality of nanowires 303 made of GaAs are formed on the surface of the graphene 302. Can be formed.

  Thus, the nanowire 303 can be formed even on the surface of the graphene 302 having a three-dimensional shape. Moreover, by setting it as this state, it becomes possible to form more nanowires per unit area | region, and it is anticipated that more electronic and optical devices formed with nanowires will be integrated. Further, for example, by using an acid such as sulfuric acid, Fe can be selectively removed by etching from a semiconductor such as graphene and GaAs. Therefore, the substrate 301 can be selectively removed by an acid treatment such as sulfuric acid (substrate removal step), and the graphene 302 can have a hollow tube structure. By making it hollow, for example, light from more directions can be taken in.

  As described above, according to the present invention, since a nanowire is formed by forming a carbon layer such as graphene on the surface of a substrate made of Fe, the semiconductor can be manufactured at a lower cost and in a simpler process. Nanowires can be formed. In addition, according to the present invention, a flexible device can be easily manufactured in a bottom-up manner, with a large area at a low cost, and with good crystallinity, and thus can be widely used in various fields.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, in the above description, a group III-V compound semiconductor has been described as an example of the semiconductor, but the semiconductor is not limited to this, and the same applies to other semiconductors such as silicon and nitride semiconductors. In the second embodiment, the central portion is n-type and the peripheral portion is p-type. However, the central portion may be n-type and the peripheral portion may be p-type. Further, graphene may be used instead of ITO. In this case, graphene manufactured using another metal substrate may be attached and the metal substrate may be selectively removed by etching.

101 ... Substrate, 102 ... Carbon layer, 103 ... Nanowire.

Claims (4)

A carbon layer forming step of supplying a carbon compound gas on a heated substrate made of iron to form a carbon layer on the surface of the substrate;
And a nanowire forming step of forming a semiconductor nanowire on the surface of the carbon layer by metal organic vapor phase epitaxy. In the manufacturing method of the nanowire of Claim 1,
A method of producing a nanowire, comprising a substrate removing step of selectively removing the substrate after forming the nanowire. The method for producing a nanowire according to claim 1 or 2,
Prior to the nanowire forming step, a metal fine particle forming step of arranging metal fine particles on the surface of the carbon layer,
In the nanowire forming step, the nanowire is formed by metal organic vapor phase epitaxy using the metal fine particles as a catalyst. In the manufacturing method of the nanowire of any one of Claims 1-3,
In the nanowire forming step, a first conductivity type first nanowire core is formed, an undoped second nanowire shell layer is formed around the first nanowire core, and a second conductivity is formed around the second nanowire shell layer. Forming a third nanowire shell layer of the mold.