JP4923003B2 - Nanowire fabrication method, nanowire element, and nanowire structure - Google Patents

Description

  The present invention relates to a nanowire manufacturing method, a nanowire element, and a nanowire structure in which nanometer-sized metal fine particles are used as a catalyst and crystal growth is performed using a gas phase-liquid phase-solid phase method. It can be applied to devices and optical devices.

Vapor-Liquid-Solid (VLS) method for growing nanowires using a metal catalyst is based on Au fine particles and Si semiconductors in the 1960s, as shown in Non-Patent Document 1 below. It is a semiconductor growth method confirmed as follows. As a result of the alloying of Au and Si, the temperature of the liquid state is significantly reduced as compared with the case of a single substance, and the eutectic point is lowered to nearly 400 ° C. In parts other than Au, the temperature is too low for crystal growth of the raw material, but in the Au alloy part, the raw material is liquefied and the raw material decomposes, and the raw material Si becomes supersaturated in the Au alloy, so that liquid phase epitaxy (LPE: Epitaxial growth similar to Liquid-Phase Epitaxy occurs. For example, Au fine particles are used as a catalyst, GaAs (111) B is used as a substrate, and trimethylgallium (TMGa) and arsine (AsH ₃ ) are used as raw materials. First, a metal catalyst is disposed on a substrate. Next, growth is performed in a crystal growth apparatus such as a metal organic vapor phase epitaxy (MOVPE) method. When the raw material is supplied at around 400 ° C., stable micro facets such as {111} face, {110}, {100}, {112} face are formed around, and side facets are formed so as to be stable as a whole. In particular, GaAs nanowires grow in a state of standing in space in the [111] B direction (free standing). Non-Patent Document 2 below refers to growth conditions such as the growth temperature of nanowires.
RSWagner and WCEllis, APL4 (1964) 89. M. Mattila, Nanotechnology 17 (2006) 1580.

However, since a stacking fault is easily formed in a {111} -direction nanowire such as a free-standing nanowire, many twins are formed in the axial direction. Further, as described in Non-Patent Document 2, depending on the material, a zinc-blende (Zincblende) structure may become a wurtzite structure. Therefore, there is a problem that the band structure changes in the nanowire, and the electronic conduction characteristics and optical characteristics are inferior to those of the single crystal.
The present invention has been developed by paying attention to these problems, and by controlling the growth direction of the nanowire, it is possible to maintain the crystal state of the crystal substrate and grow single-crystal nanowires without defects. An object of the present invention is to provide a nanowire manufacturing method, a nanowire element, and a nanowire structure.

In order to solve the above problems, the present inventor has a combination of trimethylindium (TMIn) and phosphine (PH ₃ ), which are lower than the free-standing nanowire growth temperature, and a GaAs (311) B substrate and InP raw materials. Thus, it has been found that growth occurs in a direction parallel to the surface of the crystal substrate (hereinafter also simply referred to as a lateral direction). FIG. 1a shows the substrate surface after growth by a scanning electron microscope. Also, as shown in FIG. 1b, nanowires can be grown on the surface of the substrate in the [110] direction with a combination of a GaAs (311) B substrate and trimethylaluminum (TMAl), TMGa, AsH ₃ which are AlGaAs raw materials. I confirmed that I can do it. Such laterally grown nanowires grow as a single crystal while maintaining the crystalline state of the substrate, so they have good electronic conductivity and optical properties, and are also flexible networks and cloths that are difficult to achieve with free standing. The structure can be easily obtained with good control, and a higher-density electronic circuit can be formed in a flexible panel sheet, which can be applied to displays, solar cells, and the like. In addition, a lateral nanowire growth technique on a substrate surface using such a VLS growth method has not been reported.

And Thus, nanowire manufacturing method of the present invention, vapor phase - liquid phase - a solid phase method, Ri nanowire manufacturing method der performing crystal growth of nanometric size of the fine metal particles as a catalyst, and the crystal substrate A method of growing nanowires in contact with the crystal substrate in a direction parallel to the surface of the substrate, wherein a groove or a step is formed on the surface of the crystal substrate, and the crystal state of the crystal substrate is maintained and defect-free A single-crystal nanowire is grown along the groove or step .

In addition, the nanowire manufacturing method of the present invention is characterized in that a nanowire having a heterostructure is grown by performing at least one of switching of raw material species and introduction of an additive during the growth of the nanowire. It is.

Further, in the nanowire manufacturing method of the present invention, after the plurality of first nanowires having the same growth direction aligned in the same direction, the growth direction is different from that of the first nanowires and the growth directions of the first nanowires are above the first nanowires. By forming a plurality of second nanowires having the same alignment in the same direction, a net-like semiconductor film made of nanowires is formed.

The nanowire element of the present invention is characterized in that an electrode is attached to a nanowire having a heterostructure produced by the nanowire production method.
Further, the nanowire structure of the present invention is characterized in that after forming a net-like semiconductor film by the nanowire manufacturing method, the crystal substrate is removed to make the semiconductor film float in the space. .

  According to the method for producing a nanowire of the present invention, in performing crystal growth using a metal fine particle of a nanometer class using a gas phase-liquid phase-solid phase method as a catalyst, in a direction parallel to the surface of the crystal substrate, By growing nanowires in contact with the crystal substrate, it is possible to grow single-crystal nanowires that maintain the crystal state of the crystal substrate and have no defects. Further, the growth of the nanowire in the direction parallel to the surface of the crystal substrate can be controlled by the groove, step, electric field or magnetic field. In addition, semiconductors having different characteristics can be continuously produced by switching the raw material species and introducing additives. In addition, by using this technology, not only nanometer-class semiconductors, electronic devices, and optical devices, but also flexible network semiconductor structures can be manufactured easily, inexpensively, and with high accuracy. It becomes possible to apply to the field.

Next, embodiments of the nanowire fabrication method, nanowire element, and nanowire structure of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 2a shows a state in which Au fine particles 2 as a catalyst are arranged on the surface of the crystal substrate 1 in order to grow the nanowire 3 from the crystal substrate 1 by the VLS method as a first embodiment of the nanowire production method of the present invention. 2b shows a state in which nanowires 3 that are in contact with the crystal substrate 1 are grown in a direction parallel to the surface of the crystal substrate 1 (lateral direction) from the Au fine particles 2, and FIG. 2c shows a conventional free-standing state. A nanowire 3 is shown.

  Growth conditions such as growth temperature, pressure, raw material supply amount, compound composition ratio, etc. that enable free standing nanowires standing in space are shown in the prior art. Since this growth condition is generally in a narrow range, by growing nanowires under growth conditions deviated from the growth condition range, the above-described side facet formation becomes unstable and lateral growth is possible. .

  In order to make the formation of the side facets unstable, the growth temperature is set to a temperature higher than 10 degrees or a temperature lower than 10 degrees from the growth conditions of the free-standing nanowires, / 2 or lower pressure, change the raw material supply amount to more than twice or less than 1/2, or add 10% or more of other elements different from the source gas to increase the compound composition ratio This is done by changing the material or selecting the material so that the difference in the lattice constant between the nanowire and the substrate material is 1% or more, but any one of these growth conditions, or a combination of a plurality of them. . Below, an example of the lateral growth of nanowires is shown.

Au fine particles having a diameter of 10 nm were dispersed on the surface of the GaAs (311) B substrate by a method such as self-formation by vapor deposition and annealing of Au, or application of a solution containing Au fine particles. Thereafter, the substrate was placed in a MOVPE apparatus, and TMIn 1 × 10 ⁻⁵ mol / min and PH ₃ 6 × 10 ⁻⁴ mol / min were introduced at 380 ° C. to grow InP nanowires for 5 minutes. The nanowire shown in FIG. 1a is an InP nanowire that has been VLS grown laterally under this growth condition. In this case, the lattice constant difference between InP and GaAs is 4%, and the temperature is about 20 ° C. lower than the growth temperature of the free-standing nanowire on the InP substrate. This is more stable and enables the nanowire to grow in the lateral direction.

[Second Embodiment]
Next, 2nd Embodiment of the nanowire preparation method of this invention is described. In the present embodiment, as shown in FIG. 3, a groove 4 having a width of 20 nm, a depth of 20 nm, and a length of 5 μm is formed in the [110] direction on the surface of the GaAs (100) substrate 1 by electron beam lithography. Thereafter, Au fine particles 2 having a diameter of 100 nm as a catalyst were arranged inside the grooves 3 by a method such as self-formation by Au deposition and annealing, patterning by electron beam lithography, or application of a solution containing Au fine particles 1.

After the formation of the Au fine particles 2, the substrate 1 is placed in the MOVPE apparatus, and the growth temperature, pressure, raw material supply amount, and compound composition ratio are set so that the side facet formation becomes unstable as in the first embodiment. As set, lateral growth of the nanowire 3 along the groove 4 was performed. As this lateral growth condition, for example, TMIn 1 × 10 ⁻⁵ mol / min and PH ₃ 6 × 10 ⁻⁴ mol / min were introduced at 380 ° C., and InP nanowires were grown along the grooves 4 for 5 minutes. When the emission characteristics of this sample were measured by photoluminescence measurement, the emission of InP having a peak near 910 nm was confirmed as shown in FIG. In this embodiment, a GaAs substrate is used as the crystal substrate. However, a Si, GaP, InP, sapphire substrate, or the like may be used, and a nanowire semiconductor material may be selected under the condition that the lattice constant difference does not exceed the critical film thickness. it can. Further, a ternary mixed crystal such as AlGaAs or GaInAs can be used for the crystal substrate.

[Third Embodiment]
Next, a third embodiment of the nanowire manufacturing method and the nanowire element of the present invention will be described. In this embodiment, first, as shown in FIG. 5a, Au fine particles 2 having a diameter of 40 nm as a catalyst are formed on the surface of a semi-insulating GaAs (311) B substrate 1 by self-forming by Au vapor deposition and annealing, or electron beam lithography. It arrange | positioned by methods, such as the patterning by A, or application | coating of the solution containing Au microparticles | fine-particles 2. After the formation of the Au fine particles 2, as shown in FIG. 5b, it is placed in a MOVPE apparatus, TMIn 1 × 10 ⁻⁵ mol / min and PH ₃ 6 × 10 ⁻⁴ mol / min at 380 ° C., and disilane (Si ₂ H ₆ ) was introduced at 2 × 10 ⁻⁷ mol / min to grow n-type InP nanowires 3n for 2 minutes. Subsequently, as shown in FIG. 5c, TMIn 1 × 10 ⁻⁵ mol / min and PH ₃ 6 × 10 ⁻⁴ mol / min and 2 × 10 ⁻⁷ mol / min of diethyl zinc (DEZn) as a dopant were introduced. Then, the p-type InP nanowire 3p was grown for 2 minutes. All the nanowires 3n and 3p were grown along the substrate surface in the [110] direction, which is the direction along the atomic step 8 in the figure. Finally, as shown in FIG. 6, an n-type electrode 5n was formed of AuGeNi on the n-type InP nanowire 3n portion, and a p-type electrode 5p of AuZnNi was formed on the p-type InP nanowire 3p portion. An i-GaInAs heterointerface 7 exists between the n-type InP nanowire 3n and the p-type InP nanowire 3p, and forms a heterostructure as a whole. When a current was applied by applying a voltage to the nanowires 3n and 3p, the nanowires 3n and 3p showed diode characteristics, and FIG. 7 shows the emission intensity with respect to the injected current. Good light-emitting diode characteristics were shown.

[Fourth Embodiment]
Next, a nanowire manufacturing method and a nanowire structure according to a fourth embodiment of the present invention will be described. In the present embodiment, first, as shown in FIG. 8a, seven Au fine particles 2 having a diameter of 100 nm as a catalyst are arranged on the surface of a GaAs (100) substrate 1 at regular intervals on a straight line by patterning by electron beam lithography. After the formation of the Au fine particles 2, the substrate 1 is placed in the MOVPE apparatus, and as shown in FIG. 8b, an electric field of 1.5 × 10 ⁵ V / m indicated by an arrow in the direction perpendicular to the arrangement direction of the Au fine particles 2 is applied. While adding TMIn 1 × 10 ⁻⁵ mol / min and PH ₃ 6 × 10 ⁻⁴ mol / min and disilane (Si ₂ H ₆ ) as a dopant 2 × 10 ⁻⁷ mol / min, 7 n-types were introduced. InP nanowires 3n were grown in parallel in the lateral direction, that is, in the electric field direction for 5 minutes. Next, as shown in FIG. 8 c, SiO is deposited on the Au fine particle 2 portion corresponding to the tip of the growth direction of the n-type InP nanowire 3 n to form a mask 6, and then on the surface of the GaAs (100) substrate 1. On the side of the growth direction of the n-type InP nanowires 3n, seven Au fine particles 2 having a diameter of 100 nm were also arranged on the straight line at equal intervals by electron beam lithography. Then, while applying an electric field indicated by an arrow in the direction orthogonal to the direction of arrangement of the newly formed Au fine particles 2, that is, the direction orthogonal to the growth direction of the n-type InP nanowire 3n, as shown in FIG. Seven n-type InP nanowires 3n orthogonal to the n-type InP nanowires 3n were grown in the electric field direction for 5 minutes to obtain a structure made of network-like nanowires 3n.

From this state, the substrate 1 is etched using a solution of H ₂ SO ₄ / H ₂ O ₂ / H ₂ O = 1/10/50, thereby forming a network-like nanowire film structure as shown in FIG. be able to. By applying a resin to this structure, a sheet-like semiconductor film that can be flexibly bent can be manufactured. It is also possible to transfer the network structure of InP nanowires to another substrate by transfer technology, so-called imprint technology. Further, by selectively etching the substrate 1, a structure in which the nanowire network structure floats in the space from the substrate 1 can also be obtained. Further, a large number of nanowire network structures can be made closely to form a cloth. The force for controlling the nanowire growth direction may be a magnetic field instead of an electric field.
In addition, the nanowire production method, nanowire element, and nanowire structure of the present invention are not limited to the above-described embodiments, and can be widely applied without departing from the gist of the present invention.

(A) is explanatory drawing of InP nanowire grown laterally on the surface of GaAs (311) B substrate, (b) is explanatory drawing of AlGaAs nanowire grown laterally on the surface of GaAs (311) B substrate. (A) is a cross-sectional view of a state in which a metal catalyst is disposed on the surface of the crystal substrate, (b) is a cross-sectional view of a nanowire grown laterally on the surface of the crystal substrate as a first embodiment of the present invention, and (c) is a cross-sectional view of the nanowire. It is sectional drawing of the conventional free standing nanowire. It is explanatory drawing of the nanowire grown along the groove | channel of the crystal substrate surface as 2nd Embodiment of this invention. It is explanatory drawing of the emitted light intensity of the nanowire of FIG. It is explanatory drawing of the nanowire which changed the dopant during the growth of the nanowire along the atomic step as 3rd Embodiment of this invention, and was set as the heterostructure. It is explanatory drawing of the state which attached the electrode to the nanowire of FIG. 5, and was set as the nanowire element. It is explanatory drawing of the light emission characteristic with respect to the injection current of the nanowire of FIG. It is explanatory drawing of the nanowire structure formed in the net-like semiconductor film on the surface of the crystal substrate as 4th Embodiment of this invention. It is explanatory drawing of the state which removed the board | substrate from the nanowire structure of FIG.

Explanation of symbols

  1 is substrate, 2 is Au fine particle (catalyst), 3n, 3p is nanowire, 4 is groove, 5n, 5p is electrode, 6 is mask, 7 is hetero interface, 8 is atomic step

Claims (6)

Vapor - liquid phase - a solid phase method, the nanometric size of the metal particles Ri nanowire manufacturing method der performing crystal growth as a catalyst, and in a direction parallel to the surface of the crystal substrate, on the crystal substrate A method of growing nanowires in contact with each other, wherein after forming grooves or steps on the surface of the crystal substrate, single crystal nanowires that maintain the crystal state of the crystal substrate and have no defects are formed along the grooves or steps. A method for producing nanowires, characterized in that the nanowires are grown. 2. The nanowire manufacturing method according to claim 1, wherein a nanowire having a heterostructure is grown by performing at least one of switching of raw material species and introduction of an additive during the growth of the nanowire. After producing a plurality of first nanowires having the same growth direction aligned in the same direction, a plurality of second nanowires having a growth direction different from that of the first nanowires and having the growth directions aligned in the same direction above the first nanowires. A nanowire production method according to claim 1 or 2 , wherein a network semiconductor film made of nanowires is formed by producing the nanowire. A nanowire element comprising an electrode attached to a nanowire having a heterostructure produced by the nanowire production method according to claim 2 . A nanowire structure characterized in that after forming a network semiconductor film by the nanowire manufacturing method according to claim 3 , the crystal substrate is removed to make the semiconductor film float in the space. As a nanowire manufacturing method for growing crystals using metal fine particles of nanometer size using a gas phase-liquid phase-solid phase method as a catalyst, nanowires in contact with the crystal substrate in a direction parallel to the surface of the crystal substrate By growing the single-crystal nanowires that maintain the crystal state of the crystal substrate and have no defects, and produce a plurality of first nanowires in which the growth directions are aligned in the same direction, A nanowire manufacturing method for forming a network semiconductor film made of nanowires by forming a plurality of second nanowires having a growth direction different from that of the first nanowires and in which the growth directions are aligned in the same direction. A nanowire structure characterized in that after a semiconductor film is formed, the crystal substrate is removed so that the semiconductor film floats in space.