JP2006344877A - Manufacturing method of material for embedding metal nanoparticles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for utilizing as metal nanoparticles fine particles of a metal having a low melting point which are formed according to a liquid drop epitaxy method. <P>SOLUTION: This manufacturing method of a material for embedding metal nanoparticles comprises: irradiating a molecular beam of a metal having a low melting point to a substrate to form fine particles of the metal having a low melting point as metal nanoparticles on the surface of the substrate; and irradiating molecular beams of elements constituting a compound to grow the compound and consequently to embed the metal nanoparticles into the compound, wherein as the metal having a low melting point, a metal having a low melting point, such as Al which forms a compound semiconductor can be used; as the substrate, a substrate of a compound semiconductor, such as a GaAs substrate can be used; and as the elements constituting a compound, Ga and As, and the like can be used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for forming a nanometer-sized metal fine particle and using the metal nanoparticle as it is to produce a material in which the metal nanoparticle is embedded.

Conventionally, in the field of semiconductor crystal growth technology, a technology for forming metal fine particles has been applied in the droplet epitaxy method to form semiconductor quantum well boxes and the like (see, for example, Patent Documents 1 and 2).
Japanese Patent Publication No. 8-21538 Japanese Patent No. 2958442

Patent Document 1 discloses that “the first element component X is irradiated by irradiating the compound semiconductor substrate AB with the first element component X in an ultra-high vacuum at a temperature at which the first element component X is melted. A liquid phase of the first element component X having fine spheres is generated on the compound semiconductor substrate AB, and then the second element component Y is irradiated to the liquid phase to thereby finely crystallize the compound semiconductor XY. Furthermore, the compound semiconductor CD is epitaxially grown on the compound semiconductor XY fine epitaxial crystal to embed the compound semiconductor XY fine epitaxial crystal, and the embedded fine epitaxial crystal is used as a quantum well box. In the first embodiment, Ga is used as the first element component X, and “Ga on the substrate has a beam intensity of 4 × 10 ^{1. “} Deposit for 30 seconds at ⁴ atom / sec and make it about 20 nm” (to form Ga nanoparticles). In Example 2, In was used as the first element component, and the “substrate temperature was 250 "In depositing In at a temperature of 1.1 x 10 ¹⁴ atom / sec for 1 minute to form liquid phase microspheres In with a particle size of about 10 nm" (forming In nanoparticles). However, in the first embodiment, As is used as the second element component Y, “As is irradiated to Ga with a beam intensity of 4 × 10 ¹⁵ atom / sec, GaAs is applied to the Ga / ZnSe interface. In Example 2, subsequently, Sb is used as the second element component Y, and “Sb is irradiated at a beam intensity of 1.4 × 10 ¹⁴ atom / sec to form an InSb fine crystal. Therefore, metal (Ga or In) nanoparticles are not used as they are and are not embedded in the compound.

Patent Document 2 states that “at least the next step; <1> a group VI element is adsorbed on the surface of a semiconductor having a single or multiple quantum well structure, <2> a metal or semiconductor microcrystal by droplet epitaxy. <3> Chemical etching is performed using the generated microcrystal as a mask to remove a single or multiple quantum well structure in which the group VI element is adsorbed on the surface. <4> The microcrystal is <5> A method of forming a semiconductor quantum box comprising embedding a semiconductor in a region of a single or multiple quantum well structure removed by etching. "The group VI element S was adsorbed on the surface of a single or multiple quantum well of semiconductor GaAs / GaAlAs, and a metal In microcrystal was deposited on the surface by the droplet epitaxy method." (Formation of In nanoparticles) is shown, but “chemical etching was performed using In microcrystals as a mask”, “chemical etching was further performed to remove In and S, and GaAlAs was embedded by regrowth. As it is described, the metal (In) nanoparticles are removed and not used as they are but embedded in the compound.

Further, a technique related to general droplet epitaxy that can be used for the formation of fine particles is also known (see Non-Patent Document 1), but it is not shown that the metal nanoparticles formed at that time are used as they are.
N. Koguchi, et al., J. Cryst. Growth, 111,688 (1991)

  As described above, it has been publicly known to form metal nanoparticles using a method for producing fine particles based on a droplet epitaxy method. However, the formed metal nanoparticles may be compounded or removed. The formed metal nanoparticles were not used as they were.

  In addition, there are various methods such as ion implantation, sputtering, and laser ablation for the formation of metal fine particles. These methods differ in controllability, uniformity, and applicable materials, but generally the thickness of the metal fine particles It is difficult to control the position and form a multi-cycle laminated structure. However, according to the method of performing the sputtering method alternately (alternate sputtering method), fine particles in the stacking direction can be arranged to some extent, but it is difficult to obtain the atomic scale position controllability that is a feature of the method of the present invention. is the current situation.

  An object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a technique of using low-melting-point metal fine particles formed based on a droplet epitaxy method as metal nanoparticles.

In the present invention, the following means are adopted in order to solve the above problems.
(1) The substrate is irradiated with a molecular beam of a low-melting-point metal, the low-melting-point metal fine particles are formed as metal nanoparticles on the surface of the substrate, and then irradiated with a molecular beam of a compound constituent element. In which the metal nanoparticles are embedded in the compound.
(2) The method for producing a metal nanoparticle embedding material according to (1), wherein the low melting point metal is a low melting point metal forming a compound semiconductor.
(3) The method for producing a metal nanoparticle embedding material according to (2), wherein the low melting point metal is Al.
(4) The method for producing a metal nanoparticle embedding material according to any one of (1) to (3), wherein the substrate is a compound semiconductor substrate.
(5) The method for producing a metal nanoparticle embedding material according to (4) above, wherein the compound semiconductor substrate is a GaAs substrate.
(6) The method for producing a metal nanoparticle embedding material according to any one of (1) to (5), wherein the compound constituent elements are Ga and As, and the compound is GaAs.

The method of the present invention can embed metal nanoparticles at any position in the mother crystal. In particular, position control and multi-period embedding in a multilayer film structure are possible. Furthermore, a material in which a semiconductor and metal nanoparticles are fused can be easily produced using only an existing III-V group compound semiconductor material. In addition, due to the characteristics of this method, the method of the present invention can be applied not only to III-V group materials but also to various compound material systems such as nitride semiconductors and oxide materials such as II-VI zinc oxide. It is believed that there is. The method of the present invention can be combined with various ultra-thin heterostructures such as quantum wells and superlattice structures by combining with ultrathin crystal methods such as molecular beam epitaxy.

  In the method of forming metal nanoparticles by ion implantation or the like, an expensive apparatus is required. However, in the method of the present invention, if there is an existing molecular beam epitaxy apparatus, it can be used, so it is necessary to make a new investment economically. Absent.

As shown in Patent Document 1, GaAs quantum dots are formed by irradiating arsenic to Ga droplets of several tens of nanometers formed based on droplet epitaxy. The droplet is expected to develop into a logical operation device material as a nanostructure having characteristics as a metal. In particular, in the development of a material in which metal nanoparticles and a semiconductor are fused, it is necessary to embed metal fine particles in the semiconductor.
Therefore, when a metal nanoparticle was formed based on the droplet epitaxy method using Al, which has a melting point higher than Ga, and a material in which this metal nanoparticle was embedded in GaAs was produced, this material embedded a conventional semiconductor. The present invention has been achieved by finding out that it has significantly different properties compared to the material.

FIG. 1 shows a method for producing a buried structure of Al nanoparticles. Each line represents a different material.
First, a substrate is prepared as shown in (a). The type of the substrate is not limited, but a compound semiconductor substrate is preferable, and a semiconductor substrate such as GaAs or AlAs can be used.

Although it is possible to directly irradiate the substrate with a molecular beam of a low melting point metal (Al), it is preferable to use a substrate on which a buffer layer is grown as shown in (b). The material of the buffer layer may be the same material as the substrate or a different material. For example, an n-type GaAs layer doped with Si can be grown as a buffer layer on an n-type GaAs substrate doped with Si.

Subsequently, as shown in (c), a low melting point metal (Al) molecular beam is irradiated onto the buffer layer to form low melting point metal fine particles as metal nanoparticles.
The size and density of the metal nanoparticles can be controlled by the substrate temperature, the irradiation amount of the metal (Al) molecular beam, the flux and the like. A typical size of the metal nanoparticles can be 20 to 40 nm.

  Other than Al, any low melting point metal that forms a constituent element of a compound semiconductor can use the low melting point metal droplets to form metal nanoparticles. As materials other than Al, zinc (melting point: 419 ° C.), magnesium (melting point: 650 ° C.), copper (melting point: 1084 ° C.), and the like can be considered.

Next, the metal nanoparticles are embedded in the compound by irradiating the molecular beam of the compound constituent element as shown in (d).
The formed metal nanoparticles can be embedded in various compounds and applied to III-V group materials such as GaAs and AlAs, nitride semiconductors, and oxide materials such as II-VI type ZnO. Is considered promising. To embed in GaAs, Ga and As are simultaneously irradiated to grow GaAs.

  By adopting the method of the present invention, metal nanoparticles can be embedded at an arbitrary position in the mother crystal. Furthermore, it is possible to embed in multiple cycles and easily stack.

(Reference example)
Using (100) GaAs as the substrate, Al nanoparticles were formed by irradiating 6.2 × 10 ¹⁵ cm ⁻² Al atoms on the (100) GaAs surface at a substrate temperature of 300 ° C.
The shape and density were observed at room temperature with an atomic force microscope (AFM).
The result is shown in FIG.

In addition, after forming Al nanoparticles as described above, the substrate temperature was lowered to 200 ° C, and the formation process of the nanoparticles was observed in an ultrahigh vacuum apparatus using reflection high-energy electron diffraction (RHEED). . The incident directions of the electron beams are (a) [01-1] and (b) [011].
The result is shown in FIG. The speckled diffraction image results from the formation of three-dimensional nanoparticles.

Using n-type (100) GaAs as the substrate, a buffer layer was grown on the n-type (100) GaAs by molecular beam epitaxy at a substrate temperature of 580 ° C. and a vacuum degree of 1 × 10 ⁻⁷ Torr. From the substrate side, there were 1 × 10 ¹² cm ⁻² Si, a 500 nm n-type GaAs layer, and a 20 nm GaAs layer.
Subsequently, the cell valve for the arsenic molecular beam was closed on the buffer layer at a substrate temperature of 300 ° C., and after the degree of vacuum became approximately 2 × 10 ⁻⁸ Torr or less, only the Al molecular beam was irradiated, Particles were formed. The amount of Al atoms irradiated was 6.2 × 10 ¹⁵ cm ⁻² and the flux was 2.5 × 10 ¹⁴ cm ⁻² s ⁻¹ . Al nanoparticles with a size of 20-40 nm were formed.

Next, Ga and As were simultaneously irradiated at a substrate temperature of 300 ° C. to grow 20 nm GaAs, and Al nanoparticles were embedded in GaAs.
Thereafter, 2 nm AlAs and 2 nm GaAs were repeated 15 times at a substrate temperature of 580 ° C., and 10 nm GaAs was grown thereon to form a surface barrier layer and a cap layer to obtain a sample.
This example is a sample structure for measuring capacitance-voltage characteristics.

Except for the same buffer layer as in Example 1, except that the substrate temperature is 250 ° C., the irradiation amount of Al atoms is 9.4 × 10 ¹⁵ cm ⁻² , and the flux is 2.4 × 10 ¹⁴ cm ⁻² s ^−1. Al nanoparticles were formed in the same manner as in Example 1, and after Al nanoparticles were embedded in GaAs, a surface barrier layer and a cap layer were formed to obtain a sample. Samples embedded with Al nanoparticles with a size of 20-40 nm were obtained.

(Comparative example)
On the same buffer layer as in Example 1, by opening a cell valve for arsenic molecular beam at a substrate temperature of 300 ° C. and simultaneously irradiating arsenic when irradiating Al molecular beam, AlAs, which is a semiconductor, is used instead of Al nanoparticles. Formed. The film thickness of AlAs is about 2.8 nm with 10 atomic layers.
Next, as in Example 1, AlAs was embedded in GaAs, and then a surface barrier layer and a cap layer were formed to obtain a sample.

The electrical characteristics were measured under the following conditions.
Measuring equipment: Impedance analyzer 4294A (manufactured by Agilent Technologies)
Measurement temperature: 4.2K
Superimposed AC frequency and amplitude: 1kHz, 5mV
Element shape: Mesa shape with a diameter of 400 microns

Capacitance-voltage (CV) measurement was performed on the samples obtained in Example 1 and Comparative Example.
FIGS. 4A and 4B show band diagrams of the samples used in the capacity-voltage measurement.
(a) is a sample in which AlAs is embedded, and (b) is a sample in which Al nanoparticles are embedded. (
In the case of b) Al nanoparticles, the band diagram is expected from the experimental results.

In the measurement, a voltage (gate voltage) is applied between the metal gate formed on the surface and the n-type GaAs layer, and the capacitance (capacitance) between them is measured. The sample embedded with the Al nanoparticles of Example 1 exhibits different characteristics from the reference sample embedded with AlAs of the comparative example.

  In the reference sample, when the gate voltage changes, the charge on the semiconductor side changes only at the end of the depletion region. As the gate voltage (Vg) increases, the electrode spacing decreases monotonously, so the capacitance increases monotonously with the gate voltage. On the other hand, hysteresis is observed in the sample embedded with Al nanoparticles. This is thought to be due to the fact that the charging state of the Al particles changes by applying a gate voltage, and therefore the potential changes.

  A material embedded with metal nanoparticles produced by the method of the present invention can be applied to quantum information devices (quantum computers, etc.), single-electron elements, memory elements, optical nonlinear elements, and the like, and is extremely useful.

It is the schematic which shows the preparation methods of the embedded structure of Al nanoparticle. It is a figure which shows the atomic force microscope image of Al nanoparticle. It is a figure which shows the reflection high-energy electron diffraction image after Al nanoparticle formation. It is a band figure of the sample (what embedded AlAs) used by capacity-voltage measurement. It is a band figure of the sample (what embedded Al nanoparticle) used by the capacity-voltage measurement. It is a figure which shows the result of a capacitance-voltage measurement. In the figure, Al and AlAs represent samples in which Al nanoparticles and AlAs are embedded, respectively. An arrow indicates the scanning direction of the applied voltage.

Claims (6)

  The substrate is irradiated with a molecular beam of a low-melting-point metal, and after the fine particles of the low-melting-point metal are formed as metal nanoparticles on the surface of the substrate, the compound is grown by irradiating the molecular beam of the compound constituent element. A method for producing a metal nanoparticle embedding material, wherein the metal nanoparticle is embedded in the compound.   The method for producing a metal nanoparticle embedding material according to claim 1, wherein the low melting point metal is a low melting point metal forming a compound semiconductor.   3. The method for producing a metal nanoparticle embedding material according to claim 2, wherein the low melting point metal is Al.   The method for producing a metal nanoparticle embedding material according to any one of claims 1 to 3, wherein the substrate is a compound semiconductor substrate.   The method for producing a metal nanoparticle embedding material according to claim 4, wherein the compound semiconductor substrate is a GaAs substrate. The method for producing a metal nanoparticle embedding material according to claim 1, wherein the compound constituent elements are Ga and As, and the compound is GaAs.

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