WO2008032618A1 - Semiconductor nanoparticle and process for producing the same - Google Patents

Abstract

A semiconductor nanoparticle that attains not only conversion of the optical properties of semiconductor nanoparticle as a light emitting device material from indirect transition type to direct transition type but also enhancement of quantum yield; and a process for producing the same. The semiconductor nanoparticle is one of 2 to 50 nm average particle diameter with its surface modified, characterized in that the gradient of tangent obtained by Tauc plot with respect to the semiconductor nanoparticle is in the range of 2 to 5 times the gradient of tangent with respect to bulk crystal of the same chemical composition as that of the core portion of the semiconductor nanoparticle.

Description

 Specification

 Semiconductor nanoparticles and manufacturing method thereof

 Technical field

 The present invention relates to semiconductor nanoparticles and a method for producing the same. More specifically, the present invention relates to a semiconductor nanoparticle having optical properties converted from an indirect transition type to a direct transition type and an increased quantum yield as a light emitting device, and a method for producing the same.

 Background art

 [0002] In recent years, nanostructure crystals have attracted attention in II-VI group semiconductors such as ultrafine particles such as Si and Ge, and porous silicon. Here, the nanostructure crystal refers to a crystal grain having a nano-order particle size of about! ~ LOOnm, and is generally abbreviated as "nanoparticle" or "nanocrystal".

 [0003] In the case of II group VI semiconductors having a nanostructure crystal as described above and a Balta-like crystal, when the nanostructure crystal is used, the light absorption characteristics and light emission are good. It will show the characteristics. This is thought to be due to the fact that the group VI semiconductor with nanostructure crystals has a larger band gap than the Balta-like crystal structure because the quantum size effect appears. In other words, it is thought that the band gap may be widened by the quantum size effect in the II-VI group semiconductors having nanostructured crystals!

 [0004] By the way, semiconductors can be classified into two types according to the bandgap format.

 In other words, the direct transition type (direct type: gallium arsenide, etc.) with simple light absorption and emission, and the indirect transition type (indirect type: silicon, etc.) that require a slightly complicated process for absorption and emission of light.

[0005] For example, crystalline silicon is an indirect transition type semiconductor with a band gap of 1. leV, and hydrogenated amorphous silicon varies depending on the hydrogen content, from 1.5 to 1.5; 1.7 eV! It is a direct transition type semiconductor with a band gap of /. Solar cells made of amorphous silicon show an output voltage about 0.2-0.3% higher than crystalline silicon because of the deep band gap, whereas crystalline silicon is an indirect transition type. The optical characteristics are poor and there are disadvantageous aspects in the manufacture of light emitting elements and the like.

 [0006] When nano-semiconductor particles are used as a light-emitting element, it is preferable to use Si, Ge, etc., which are low in raw material cost and have no concern about toxicity, as a semiconductor material component. However, due to these toxicities, etc., there are few problems, semiconductors consisting of components are often indirect transition type, and the quantum yield is extremely low as a light emitting device material! It becomes a problem in practical use.

 [0007] Techniques for converting an indirect transition type to a direct transition type have been studied from various viewpoints, and some techniques have been disclosed (see, for example, patent documents;! To 3). However, all of these known examples are methods of converting an indirect transition type to a direct transition type by laminating and bonding crystals having different chemical compositions, etc., and both are semiconductor elements formed on a substrate. Therefore, application to semiconductor nanoparticle systems is considered to be difficult.

 Therefore, research and development of conversion technology applicable to semiconductor nanoparticle systems is desired.

 Patent Document 1: JP-A-5-82837

 Patent Document 2: Japanese Patent Laid-Open No. 7-79050

 Patent Document 3: Japanese Patent Laid-Open No. 2003-303983

 Disclosure of the invention

 Problems to be solved by the invention

[0009] The present invention has been made in view of the above problems, and a solution to the problem is to convert the optical properties of semiconductor nanoparticles as a light emitting device material into an indirect transition type force direct transition type, and to obtain a quantum yield. It is providing the semiconductor nanoparticle which improved, and its manufacturing method.

 Means for solving the problem

[0010] The above-mentioned problem according to the present invention is solved by the following means.

 [0011] 1. Semiconductor nanoparticles having an average particle diameter of 2 to 50 nm, the semiconductor nanoparticles having a modified surface, and a tangential tilt force obtained by Tauc plot for the semiconductor nanoparticles A semiconductor nanoparticle characterized by being 2 to 5 times the slope of the tangent to a Balta crystal having the same chemical composition as the core of the semiconductor nanoparticle.

[0012] 2. Bandgap force obtained by Tauc plot for the semiconductor nanoparticles with respect to the bandgap obtained by Tauc plot for a Balta crystal having the same chemical composition as the core part of the semiconductor nanoparticles. ~; 1. The above 1 characterized by being high in the range of 5eV Semiconductor nanoparticles described in 1.

[0013] 3. The semiconductor nanoparticle according to item 1 or 2, wherein the semiconductor nanoparticle is a core / shell type semiconductor nanoparticle.

[0014] 4. The semiconductor nanoparticles according to any one of 1 to 3, wherein S or Ge is contained as a constituent component of the semiconductor nanoparticles.

[0015] 5. A method for producing a semiconductor nanoparticle according to any one of the above;! To 4, comprising a step of subjecting the semiconductor nanoparticle to a surface treatment under a gas atmosphere. A method for producing nanoparticles. The invention's effect

 [0016] By the above-mentioned means of the present invention, a semiconductor nanoparticle and a method for producing the same, in which the optical property of the semiconductor nanoparticle as a light emitting device material is converted from an indirect transition type to a direct transition type and the quantum yield is improved. Can be provided.

 Brief Description of Drawings

[0017] [Figure l] Example of Tauc plot

 Explanation of symbols

[0018] Tauc plot of 1 Si Balta crystal

 2 Tauc plot of sample heat-treated in Si nanoparticle c + nitrogen atmosphere

 BEST MODE FOR CARRYING OUT THE INVENTION

The semiconductor nanoparticles of the present invention are surface-modified semiconductor nanoparticles having an average particle diameter of 2 to 50 nm, and a tangential gradient force obtained by Tauc plot for the semiconductor nanoparticles. It is characterized in that it is 2 to 5 times the inclination of the tangent for Balta having the same chemical composition as the core of the particle.

[0020] The core part of the semiconductor nanoparticles of the present invention referred to herein means the center part of the nanoparticles whose surface has been modified, and is in agreement with the semiconductor nanoparticles before modification.

[0021] Hereinafter, the present invention and its components will be described in detail.

[0022] (Semiconductor nanoparticles)

One semiconductor nanoparticle of the present invention is made of a semiconductor material and has an average particle diameter of 2 to 50 nm. The tangential tilt force obtained by the Tauc plot for the semiconductor nanoparticles is a surface modified semiconductor nanoparticle of the same chemical composition as the core (semiconductor nanoparticle before modification) of the semiconductor nanoparticle. It is characterized by being 2 to 5 times the slope of the tangent to the crystal.

 [0023] (Core / shell type semiconductor nanoparticles)

 One of the preferred embodiments of the semiconductor nanoparticles of the present invention has a core / shell structure in which the semiconductor nanoparticles are composed of a core portion made of a semiconductor material and a shell portion (shell layer) covering the core portion. So-called core / shell type semiconductor nanoparticles having an average particle diameter of 2 to 50 nm and a tangential gradient force obtained by Tauc plot for core / shell type semiconductor nanoparticles having a modified surface The semiconductor nanoparticles It is characterized in that it is 2 to 5 times the inclination of the tangent line for a Balta crystal having the same chemical composition as the core part.

 [0024] The "Tauc plot" is a method for obtaining an optical band gap from an electron spectrum generally used for amorphous semiconductors. In light absorption due to optical transitions between bands of amorphous semiconductors, the relationship between absorbance and photon energy is expressed by the following equation.

[0025] a = k (E- E) 2 / E (k is a constant)

 0

 Where α is the absorbance, Ε is the photon energy, and Ε is the optical band gap. this

 0

 From the equation, the horizontal axis represents photon energy, the vertical axis represents the square root of the product of absorbance and photon energy, and a tangent line is drawn. The intersection of this tangent and the horizontal axis is the optical band gap (written by Tatsuo Shimizu “Amorphous Semiconductor”, Baifukan (1994) · ρ201).

[0026] Further, the "Balta crystal" here refers to a collection of particle crystals having a particle size of 1 Hm or more.

[0027] "Average particle size" refers to the cumulative 50% volume particle size measured by the laser scattering method.

[0028] In the semiconductor nanoparticles having a modified surface according to the present invention, the difference in slope between the tangent line obtained by Tauc plot and the linear approximation line is 5% for Balta crystals having the same composition as the core part of the semiconductor nanoparticles. Is preferably within. Here, the “linear approximation straight line” is the straight line obtained when linear approximation is performed for values in the range lower than the contact point between the Tauc plot and the obtained tangent line. The Tauc plot of the indirect transition Balta crystal is almost straight, so the difference in slope between the tangent and the linear approximation line is within 5%. [0029] Further, in the semiconductor nanoparticles of the present invention, the Balta crystal having the same composition as the core part of the semiconductor nanoparticles is used. In the core / shell type semiconductor nanoparticles, the core part of the core / shell type semiconductor nanoparticles is used. For the Balta crystals with the same chemical composition as the above, it is preferable that the band gap is 0.2 to 1.5 eV higher than the band gap obtained by Tauc plot.

 <Formation of core particle>

 The core part of the semiconductor nanoparticle of the present invention or the semiconductor nanoparticle having a core / shell structure can be formed using various known semiconductor materials.

[0031] Examples of semiconductor materials used for the core include MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe,

CdTe, GaAs, GaP, GaSb, InGaAs, InP, InN, InSb, InAs, AlAs, A1P, A1Sb, A1S, PbS, PbSe, Ge, Si, or a mixture thereof. In the present invention, a particularly preferable semiconductor material is Si or Ge.

[0032] The average particle size of the core part according to the present invention is preferably 1 to 40 nm in order to achieve the effect of the invention! More preferred! / ヽ is 2-30nm.

[0033] The "average particle size" of the core according to the present invention refers to an accumulated 50% volume particle size measured by a laser scattering method.

[0034] <Shell part>

 The shell portion according to the present invention is a core / shell type semiconductor nanoparticle according to the present invention!

, A layer covering the core part, and a component layer for forming a core / shell structure

Yes

 [0035] It should be noted that the shell portion according to the present invention may not completely cover the entire surface of the core particle as long as the core particle is not partially exposed to cause a harmful effect.

 As the semiconductor material used for the shell portion, various known semiconductor materials can be used. Specific examples of the column include ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS, MgSe, GaS, GaN, GaP, GaAs, GaSb, In As, InN, InP, InSb, AlAs, A1N, A1P, AlSb, or a mixture thereof can be used.

[0037] In the present invention, particularly preferred! /, The semiconductor material is SiO or ZnS. <Method for producing fluorescent semiconductor fine particles>

 Various conventionally known methods can be used for producing the semiconductor nanoparticles before modifying the surface of the semiconductor nanoparticles or core / shell type semiconductor nanoparticles of the present invention.

 [0039] The production method of the liquid phase method includes a precipitation method such as a coprecipitation method, a sol-gel method, a uniform precipitation method, and a reduction method. In addition, the reverse micelle method, the supercritical hydrothermal synthesis method, and the like are also excellent methods for producing nanoparticles (for example, JP 2002-322468, JP 2005-239775, JP 10-10). (See 310770, JP 2000-104058, etc.).

 [0040] The manufacturing method of the vapor phase method includes (1) a second high temperature generated by electrodeless discharge in a reduced-pressure atmosphere by evaporating the opposing raw material semiconductor by the first high-temperature plasma generated between the electrodes. (2) A method of separating and removing nanoparticles from an anode made of a raw material semiconductor by electrochemical etching (for example, JP 2003-515459). And a laser ablation method (for example, see Japanese Patent Application Laid-Open No. 2004-356163). In addition, a method of synthesizing powder containing particles by reacting a raw material gas in a gas phase in a low pressure state is also preferably used.

 [0041] The method for producing semiconductor nanoparticles or core / shell type semiconductor nanoparticles according to the present invention is preferably a production method in which core particles are produced by a liquid phase method, and then the particles are coated with a shell material.

 In the present invention, as a method for modifying the surface of the semiconductor nanoparticles, the surface treatment of the semiconductor nanoparticles is performed in a gas atmosphere such as an oxygen atmosphere, an argon atmosphere, a nitrogen atmosphere, or a nitrogen + hydrogen atmosphere. It is necessary to optimize the conditions in order to satisfy the conditions of the tangential slope obtained by the Tauc plot.

 Example

 [0043] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

 1. Preparation of core part Si particles

Add tetraoctyl ammonium bromide (TOAB) to 100 ml of toluene, stir well, then add 92 SiCl and add dropwise. After stirring for 1 hour, the reducing agent (aluminum hydride Add 2 ml of THF in 1M solution over 2 minutes. After leaving for 3 hours, 20 ml of methanol is added to deactivate excess reducing agent to obtain silicon nanoparticles in an organic solvent. By using a spray pyrolyzer (Okawara Processing Machine Co., Ltd., RH-2), it is retained at 200 ° C for 1 minute and dried to obtain silicon nanoparticle powder.

[0044] The particle size of the silicon nanoparticles can be adjusted by the ratio of SiCl and TOAB. SiCl: TOAB 1

 4 4

 : 0.;! To 1: 100, monodisperse particles having the following four particle sizes were obtained.

 [0045] SiCl: TOAB average particle size

 Four

 Si nanoparticles a 1: 0.1 30 nm

 Si nanoparticles b 1: 1 10nm

 Si nanoparticles c 1: 10 5nm

 Si nanoparticles d 1: 100 2nm

 2. Shell part SiO layer coating

 The Si nanoparticles a to d are dispersed in a colloidal silica containing silicon dioxide (PL-3 manufactured by Fuso Chemical Industry Co., Ltd.) and potassium hydroxide mixed with pure water to adjust the liquid volume to 1500 ml.

 [0046] The dispersion was allowed to stay at 200 ° C for 5 minutes using a spray pyrolysis apparatus to cover the SiO shell layer, and powders of Si / SiO core / shell nanoparticles A to D were obtained. .

 2. Surface treatment of nanoparticle powder

 The obtained Si nanoparticles a to d and Si / SiO core / shell nanoparticles A to D coated with a shell layer on each were subjected to the following conditions: oxygen atmosphere, argon atmosphere, nitrogen atmosphere, nitrogen + 1% hydrogen atmosphere. Instead, the surface of the nanoparticles was modified at 900 ° C. for 10 minutes in a spray pyrolysis apparatus.

 [0047] (Evaluation)

Tauc plot: For comparison, measure the UV absorption spectrum of Balta's Si substrate (thickness 50 Hm) using a spectrophotometer. For each sample obtained, the visible ultraviolet absorption spectrum is measured under exactly the same conditions. Take the photon energy on the horizontal axis, the square root of the product of absorbance and photon energy on the vertical axis, plot each data, and draw the tangent line. The intersection of this tangent and the horizontal axis is the optical band gap. [0048] Figure 1 shows an example of a Tauc plot. 1 is a Tauc plot of a Si Balta crystal, and 2 is a Tauc plot of a sample whose surface was modified by heat-treating Si nanoparticle c in a nitrogen atmosphere, each showing its tangent line.

 [0049] Fluorescence quantum yield: A fluorescence spectrum generated by irradiating the obtained sample with excitation light having a wavelength of 350 nm was measured. The quantum yield is obtained by comparing the molar absorption coefficient obtained from the absorption spectrum of the sample, the wavenumber integral value of the fluorescence spectrum, and the refractive index of the solvent with a standard substance (rhodamine B, anthracene, etc.) with a known quantum yield. It was.

 [0050] If the quantum yield of the sample is φ and the quantum yield of the standard material is φ, φ is the force S obtained by the following equation.

φ = F n ² / F ² -ε cd / ε cd · φ… (A)

Where is the integral of the wave number of the sample, η _χ is the refractive index of the solvent of the standard material, ε cd is the absorbance of the sample, F is the integral of the wave number of the standard material, n is the refractive index of the solvent of the standard material, and ε cd is This is the absorbance of the standard substance.

 [0051] The above evaluation results are shown in Table 1.

[0052] [Table 1]

a u c蛍 光 Fluorescence quantum Surface heat treatment

 Tangential slope De gear ratio Remarks Atmosphere

 vsSi bulk crystal [eV] Difference from bulk crystal (%)

 Si bulk crystal-1 1.1-Comparison

 1.1 1.1 0.0 0 comparison Oxygen 1.4 1.2 0.1 0 comparison

Si nanoparticles a Argon 1.8 1.3 0.2 0 Comparison Nitrogen 1.8 1.3 0.2 0 Comparison Nitrogen + 1% Hydrogen 1.7 1.4 0.3 0 Comparison

 1.2 1.2 0.1 0 comparison Oxygen 1.5 1.2 0.1 0 comparison

Si nanoparticle b Argon 1.9 1.3 0.2 0 Comparison Nitrogen 1.9 1.3 0.2 0 Comparison Nitrogen + 1% Hydrogen 1.8 1.4 0.3 0 Comparison 1.5 1.3 0.2 0 Comparison Oxygen 1.6 1.3 0.2 0 Comparison

Si nanoparticles c Argon 2.1 1.3 0.2 60 Invention Nitrogen 2.1 1.6 0.5 60 Invention Nitrogen + 1% Hydrogen 3.5 2.6 1.5 45 Invention

-1.8 2.1 1.0 8 Comparison Oxygen 1.9 2.4 1.3 8 Comparison

Si nanoparticle d Argon 2.5 2.6 1.5 55 Invention nitrogen 2.5 2.6 1.5 55 Invention nitrogen + 1% hydrogen 4.2 3.2 2.1 40 Invention one 1.3 1.1 0.0 0 comparison Oxygen 1.3 1.1 0.0 0 comparison Core shell

 Argon 1.6 1.3 0.2 0 Nanoparticle A Comparison Nitrogen 1.6 1.3 0.2 0 Comparison Nitrogen + 1% Hydrogen 1.6 1.3 0.2 0 Comparison

― 1.5 1.2 0.1 0 comparison Oxygen 1.5 1.2 0.1 0 comparison Core / shell

 Argon 1.9 1.3 0.2 0 Nanoparticles B Comparison Nitrogen 1.9 1.3 0.2 0 Comparison Nitrogen + 1% Hydrogen 1.9 1.3 0.2 0 Comparison

-1-7 1.7 0.6 5 Comparison Oxygen 1.7 1.7 0.6 6 Comparison Core / shell

 Argon 3.5 2.5 1.4 60 One nanoparticle C Present invention Nitrogen 3.4 2.5 1.4 60 Present invention Nitrogen + 1% Hydrogen 4.8 2.8 1.7 50 Present invention

 1.9 2.8 1.7 8 comparison oxygen 1.9 2.8 1.7 8 comparison core / shell

Argon 4 3.1 2.0 50 Nanoparticles D The present invention Nitrogen 3.9 3-1 2.0 50 The present invention Nitrogen + 1% Hydrogen 5.2 3.6 2.5 0 Comparison The results shown in Table 1 Tangential gradient force obtained by Tauc plot for particles or core / shell type semiconductor nanoparticles For Balta crystals with the same chemical composition as the core of the semiconductor nanoparticles, or core / shell It can be seen that for a Balta crystal having the same chemical composition as the core part of the type semiconductor nanoparticle, particles satisfying the condition of 2 to 5 times the inclination of the tangential line have a high fluorescence quantum yield.

Claims

The scope of the claims  [1] Surface-modified semiconductor nanoparticles having an average particle diameter of 2 to 50 nm, the tangential gradient force S obtained by Tauc plot for the semiconductor nanoparticles, and the semiconductor nanoparticles before modification A semiconductor nanoparticle characterized by having 2 to 5 times the inclination of the tangent of a Balta crystal having the same chemical composition as the core. [2] The band gap force S obtained from the Tauc plot for the semiconductor nanoparticles and 0.2 to the band gap obtained from the Tauc plot for a Balta crystal having the same chemical composition as the core of the semiconductor nanoparticles. 1. The semiconductor nanoparticle according to claim 1, which is high in a range of 5 eV. [3] The semiconductor nanoparticle according to [1] or [2], wherein the semiconductor nanoparticle is a core / shell type semiconductor nanoparticle. [4] The semiconductor nanoparticles according to any one of claims 1 to 3, wherein S or Ge is contained as a constituent component of the core part of the semiconductor nanoparticles! / Semiconductor nanoparticles. [5] The method for producing semiconductor nanoparticles according to any one of claims 1 to 4, comprising a step of subjecting the semiconductor nanoparticles to a surface treatment in a gas atmosphere. A method for producing semiconductor nanoparticles.