KR101060231B1 - Semiconductor nanocrystal with charge introduced on its surface and optical device comprising the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor nanocrystal having a multi-layer structure having one or more semiconductor interfaces having cross band intervals and to which charges are introduced on a surface thereof, and to an optical device including the same. When applied, a reversible change in the emission wavelength occurs and shows a high photon emission efficiency, so it can be applied to various optical devices.

Semiconductor nanocrystals, band gap crossing, multilayer structure, surface charge, optical device

Description

Semiconductor Nanocrystals with Surface Charge and Optoelectric Devices Comprising the Same

Embodiments of the present invention relate to semiconductor nanocrystals having surface charges and optical devices including the same, and more particularly, to a multi-layer structure having one or more semiconductor interfaces having cross band gaps, and to which charges are introduced into the photons. The present invention relates to a semiconductor nanocrystal with improved luminous efficiency and an optical device including the same.

Nanocrystals are materials with crystal structures of several nanoscales and are made up of hundreds to thousands of atoms. Nanocrystals have a large surface area per unit volume, causing most atoms to be present on the surface, exhibiting quantum confinement effects, etc., which are distinctive from electrical, magnetic, optical, chemical, Mechanical properties.

Semiconductor nanocrystals can be used in various light emitting devices (LEDs, ELs, lasers, holography, sensors, etc.) and electrical devices (solar cells, photodetectors) because they can adjust the size and composition, etc. Can be. Therefore, development of semiconductor nanocrystals having better characteristics is required to improve performance of various electronic devices that are miniaturized, high performance, and highly integrated.

Embodiments of the present invention are to meet the above technical requirements, and one object of the present invention is to provide a semiconductor nanocrystal excellent in photon emission efficiency.

Another object of the present invention is to provide an optical device including a semiconductor nanocrystal with improved photon emission efficiency.

One embodiment of the present invention for solving the above technical problem is a semiconductor nanocrystal of a multi-layer structure including two or more semiconductor layers composed of one or more semiconductor materials, at least one of the semiconductor nanocrystals cross band interval The present invention relates to a semiconductor nanocrystal having an interface, wherein charge is introduced to a surface of the semiconductor nanocrystal.

The semiconductor nanocrystal has a positive charge or a negative charge introduced to its surface, and may have a core-shell, core-multishell, multicore-shell, multicore-multishell, or core-interlayer-shell structure.

In the semiconductor nanocrystal, the conduction band of the semiconductor material of the first semiconductor layer is higher than the conduction band of the semiconductor material of the second semiconductor layer, and the valence band of the semiconductor material of the first semiconductor layer is a household appliance of the semiconductor material of the second semiconductor layer. Higher than Jati In the semiconductor nanocrystal, the conduction band of the semiconductor material of the first semiconductor layer is lower than the conduction band of the semiconductor material of the second semiconductor layer, and the valence band of the semiconductor material of the first semiconductor layer of the semiconductor material of the second semiconductor layer. It may be lower than the valence band.

Another aspect of the present invention for solving the above problems relates to an optical device such as an optical modulator including a semiconductor nanocrystal having a multi-layer structure, having at least one semiconductor interface with cross band intervals, and having a charge introduced therein. .

The semiconductor nanocrystals according to various embodiments of the present invention are type II semiconductor nanocrystals having one or more semiconductor interfaces having cross band intervals and having charges introduced thereon, and exhibit a reversible change in emission wavelength and high photon emission efficiency when an electric field is applied. Since it can be applied to various optical devices such as an electro-optic modulator.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As used herein, the terms "semiconductor nanocrystal" and "quantum dot" are used interchangeably with each other to refer to a semiconductor nanocrystal composed of a crystalline inorganic material having luminescent properties. The expression “CdSe / CdTe” herein refers to a quantum dot of a core-shell structure in which the core is composed of CdSe and the shell is composed of CdTe.

A semiconductor nanocrystal of an embodiment of the present invention is a semiconductor nanocrystal having a multilayer structure including two or more semiconductor layers composed of one or more semiconductor materials, wherein the semiconductor nanocrystal has one or more interfaces where band intervals intersect, and the semiconductor An electric charge is introduced to the surface of the nanocrystal. The term "crossing the band gap" means that in a semiconductor nanocrystal composed of two or more layers of different semiconductor materials, both the conduction band and the valence band of the semiconductor material of one layer are more than the conduction band and valence band of the semiconductor material of another layer. High or low.

1 is a schematic diagram of a semiconductor nanocrystal of one embodiment of the present invention. Referring to FIG. 1, a semiconductor nanocrystal of an embodiment of the present invention includes a first semiconductor layer 10 and a second semiconductor layer 20. Although FIG. 1 illustrates a semiconductor nanocrystal composed of two layers, another semiconductor layer may be included as necessary.

1, the valence band and conduction band of the material of the second semiconductor layer 20 are lower than those of the material of the first semiconductor layer 10, as shown in FIG. 1. As shown in FIG. 2, the valence band and conduction band of the material of the second semiconductor layer 20 are higher than the valence band and conduction band of the material of the first semiconductor layer 10.

In general multilayer semiconductor nanocrystals, the conduction band and valence band of the material constituting the shell are located at a higher energy and lower energy than the conduction band and valence band of the core material, respectively. There is a high probability of being bound to the core material.

In contrast, semiconductor nanocrystals of embodiments of the present invention tend to be spatially separated from each other by electrons and holes not bound to one layer due to the intersecting band gaps. First, the electrostatic attraction of electrons and holes is reduced compared to general semiconductor nanocrystals. Second, the interference effect of electrons and holes by external electric fields may be different from that of general semiconductor nanocrystals.

In the semiconductor nanocrystal of the embodiment of the present invention, electrons and holes are spatially distributed in different semiconductor layers. In other words, one carrier (electron or hole) has a high probability of being present in the first semiconductor layer 10 and another carrier having an opposite polarity has a high probability of being present in the second semiconductor layer 20. Specifically, as shown in FIG. 1, semiconductor nanocrystals (eg, CdTe /) having a valence band and a conduction band of the material of the second semiconductor layer 20 are lower than those of the material of the first semiconductor layer 10. In CdSe), the electron (e ⁻ ) excited at the time of excitation is relatively high in the second semiconductor layer 20, and the hole (h ⁺ ) is more likely in the first semiconductor layer 10. Meanwhile, as shown in FIG. 2, the semiconductor nanocrystal (eg, CdSe / CdTe) having a valence band and a conduction band of the material of the second semiconductor layer 20 having a higher valence band and conduction band of the material of the first semiconductor layer 10. ), Electron (e ⁻ ) has a high probability of being present in the first semiconductor layer 10, and hole (h ⁺ ) has a high probability of being present in the second semiconductor layer 20.

The semiconductor nanocrystals of various embodiments of the present invention are greatly influenced by the spatial separation of electrons and holes and the different quantum limiting effects of electrons and holes present in different spaces (first semiconductor layer and second semiconductor layer). Will receive. Because of these physical properties, the semiconductor nanocrystal of the present invention can exhibit a large change in luminescence properties in accordance with a change in the distribution of electrons and holes due to changes in charging or electric fields. Due to the light emission characteristics of the semiconductor nanocrystals that are sensitive to such charging or changes in the surrounding electric field, the semiconductor nanocrystals of the present invention can be applied to a wide range of optoelectronic devices. For example, it is possible to apply to an optical modulation device that changes the optical signal emitted in different wavelength bands according to the sign and intensity of an external electric field.

When an externally charged electric field or an electric field capable of such an influence is applied, electrons (e ⁻ ) existing outside the semiconductor nanocrystals are more affected than holes (h ⁺ ), and the generated electric field Due to the strong electrostatic repulsion, the probability distribution of electrons is expected to shrink to the center of the semiconductor nanocrystals rather than without an electric field. However, the hole is located in the center of the semiconductor nanocrystals rather than electrons, and due to weak interaction with the external electric field, the change in the probability distribution of the holes is not expected to be large.

When a negative charge is introduced to a surface or an electric field of a negative voltage is applied, in a semiconductor nanocrystal (eg, CdTe / CdSe) as shown in FIG. 1, the probability distribution of electrons is contracted toward the center of the semiconductor nanocrystal, and the electrons and holes are mutually different. The probability of coexisting in the same space increases and the emission wavelength shifts toward shorter wavelengths as the CdTe single structure becomes closer to the general semiconductor nanocrystal properties.

The change in the luminescence properties of the semiconductor nanocrystal of the present invention according to the change of the charging or the external electric field is reversibly returned when the charging or the external electric field is in place. The change in the emission wavelength due to the charging of the semiconductor nanocrystal or the external electric field may be reversibly repeated several times or more.

In the case of semiconductor nanocrystals (eg, CdSe / CdTe) as shown in FIG. 2, electrons (e ⁻ ) are mainly distributed in the first semiconductor layer (CdSe core), and holes (h ⁺ ) are in the second semiconductor layer (CdTe). Shell). Therefore, when an external negative voltage electric field is applied, the electrostatic attraction with the hole is stronger than the electrostatic repulsion with the electron. The probability distribution of holes is ubiquitous toward the surface, and the probability of electrons and holes coexisting in the same space is substantially the same as that of the shell of a type-II semiconductor nanocrystal. Therefore, the emission wavelength is shifted toward the longer wavelength (red wavelength).

On the other hand, when a positive voltage is applied to the same semiconductor nanocrystal instead of a negative voltage, it is displaced to a long wavelength in the case of CdTe / CdSe, and is shifted toward a shorter wavelength (blue wavelength) in the case of CdSe / CdTe.

The semiconductor nanocrystal may be a core-shell, core-multishell, multicore-multishell, or core-intermediate-shell structure. When the core and the shell are multi-layered, the band gaps intersect according to the energy levels of the valence and conduction bands of each layer and the thickness of each layer, and thus the electrons and holes can be separated into space. I can regulate it. In addition, the semiconductor nanocrystal of the present invention may further include a protective layer that does not significantly affect light emission in the intermediate layer or the outermost layer of the semiconductor nanocrystal.

The core of the semiconductor nanocrystal may include a semiconductor material selected from the group consisting of Group II-VI compounds, Group III-V compounds, Group IV-VI compounds, and mixtures thereof.

Group II-VI compounds include CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe isotopic compounds; CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe; And HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, and HgZnSTe.

Examples of the group III-V compound semiconductor include GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb; Three-element compounds of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP; And a material selected from the group consisting of GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, but not necessarily limited thereto. .

The group IV-VI compound is a binary element compound of SnS, SnSe, SnTe, PbS, PbSe, PbTe; Three-element compounds of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe; And SnPbSSe, SnPbSeTe, or SnPbSTe is an element selected from the group consisting of an isotropic compound.

The shell of the semiconductor nanocrystals may be a material selected from Group II-VI compounds, Group III-V compounds, Group IV-VI compounds, Group IV compounds, or mixtures thereof.

Group II-VI compounds include CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, HgO, HgS, HgSe, HgTe and other binary compounds, or CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeS, HgSeS , Ternary compounds such as CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, or CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgZTS, H It may be a substance.

Non-limiting examples of the group III-V compound semiconductors are binary elements such as GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, or GaNP, GaNAs, GaNSb, GaPAs , Three-element compounds such as GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, or GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb , InAlNAs, InAlNSb, InAlPAs, InAlPSb and the like may include a material selected from the group consisting of elemental compounds.

Examples of the IV-VI compound include binary elements such as SnS, SnSe, SnTe, PbS, PbSe, PbTe, or tri-element compounds such as SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, or SnPbSSe. , SnPbSeTe, SnPbSTe and the like, but includes a material selected from the group consisting of quaternary compounds, but is not necessarily limited thereto.

Examples of semiconductor nanocrystals of preferred embodiments of the present invention are CdSe / CdTe, CdTe / CdSe, CdTe / CdS, CdS / CdTe, ZnTe / ZnO, ZnO / ZnTe, ZnSe / ZnO, ZnO / ZnTe, ZnS / ZnO, ZnO / ZnO / ZnS, ZnTe / ZnSe, ZnSe / ZnTe ZnTe / ZnS, ZnS / ZnTe, ZnSe / CdS, CdS / ZnSe, CdSe / ZnTe, ZnTe / CdSe, ZnO / CdSe, CdSe / ZnO, ZnO / SnZn / PbSe, PbSe / ZnTe, InAs / InSb, InSb / InAs, InP / ZnTe, ZnTe / InP, but are not necessarily limited to these.

The method of manufacturing the semiconductor nanocrystal of the present invention is not particularly limited, and examples thereof include an organic metal chemical vapor deposition (OMCVD) system or a molecular beam epitaxy (MBE) system and a chemical wet method. Can be prepared by

The semiconductor nanocrystal of one embodiment of the present invention is synthesized mainly by a chemical wet method of generating a uniform nucleus and then growing around the nucleus with temperature and time. In the chemical wet synthesis method, a precursor material capable of growing crystals in a coordinable organic solvent is coated to grow the crystals, and the organic solvent naturally coordinates on the quantum dot crystal surface to act as a dispersant, thereby controlling the size of the quantum dots. Chemical wet manufacturing methods of quantum dots are well known in the art, and, for example, disclosed are methods of preparing quantum dots in US Pat. Nos. 6,322,901 and 6,207,229, US Pat. No. 7374824, and US Pat. It is. In the present invention, it is prepared by a method similar to that disclosed in this document, but is produced by selecting the semiconductor material of each layer such that the semiconductor nanocrystals at one or more interfaces cross the band gap.

An example of the manufacturing method of this invention is as follows. After mixing a surfactant and a solvent in a reaction vessel and heating to 100 ° C. to 400 ° C. under an inert gas environment, a precursor material constituting the first semiconductor layer (core) is inserted into the reaction vessel to synthesize a first semiconductor layer quantum dot. do. Subsequently, a surfactant, a solvent, and a first semiconductor layer quantum dot were mixed in a reaction vessel and heated to 100 ° C to 300 ° C under an inert gas environment, and then a precursor material constituting the second semiconductor layer (shell) was added dropwise to the reaction vessel. Core / shell Type II quantum dots can be prepared.

After the synthesis of the semiconductor nanocrystals, positive or negative charges are introduced to the surface, and charges may be introduced to the surface of the semiconductor nanocrystals by chemical or electrical methods. When charge is injected by an electrical method, electron injection or hole injection is performed on the surface of the semiconductor nanocrystal. For example, in order to inject electrons, negative and positive charges may be introduced into the semiconductor nanocrystals by placing a semiconductor nanocrystal in a cell including a working electrode, a reference electrode, a counter electrode, and an electrolyte, and then applying a voltage.

As an example of a chemical method, semiconductor nanocrystals are dispersed in a suitable solvent and then stored for several days with the addition of sodium. At this time, as sodium is oxidized, negative charges are introduced to the surface of the quantum dot, and as a long time passes, a large amount of negative charge is charged to the quantum dot and the displacement of the light emission wavelength increases.

In the synthesis and charge introduction of semiconductor nanocrystals, both the organic and organometallic compounds used in the synthesis process are sensitive to air and water, so that a vacuum apparatus having a nitrogen line and a vacuum line can be connected to the reaction vessel. It is necessary to remove oxygen and water in the reaction vessel.

The semiconductor nanocrystals in which charge is introduced to the surface of the present invention are exposed to the external air for about 1 second to 60 minutes in a solution of the semiconductor nanocrystals in which the negative charges are charged, thereby removing the negative charges charged to the quantum dots. It can be recovered to the emission wavelength.

Another aspect of the invention relates to an optical device comprising semiconductor nanocrystals of various embodiments of the invention. Since the semiconductor nanocrystal according to the present invention exhibits high photoconductivity efficiency when irradiated with light in the ultraviolet / visible ray region, the semiconductor nanocrystal may be used in photodiodes, photocells, or photoelectric devices such as optical sensors. In addition, the semiconductor nanocrystals of various embodiments of the present invention may be applied to all kinds of electronic devices in which semiconductor nanocrystals, such as photoelectric conversion devices, may be used.

FIG. 7 is a schematic view for explaining a principle of implementing an optoelectronic modulation device using the semiconductor nanocrystal of the embodiment of the present invention. When the semiconductor nanocrystal of the present invention is used in a device or an optical fiber, the band of the emission wavelength which appears when irradiated by light or excited by an electrical method is changed by electric charging or electric field. Therefore, it is possible to have an analog modulation device whose wavelength band varies in proportion to the applied electric field.If a constant voltage is applied in the on / off format, the light emission wavelength is reversibly changed in the two wavelength bands, thereby electro-optic modulation of the digital signal ( electro-optic modulation) becomes possible.

7A-B are diagrams illustrating digital modulation, and PL (Photoluminance) arrows of different colors mean different emission wavelength signals. In other words. When no electric field is applied, as shown in FIG. 7A, the irradiated light emits light of energy corresponding to a band gap of the original semiconductor nanocrystal, and the state at this time is “0”. Can be defined. On the other hand, when a negative electric field is applied to the outside, as shown in Fig. 7b, in the case of CdTe / CdSe semiconductor nanocrystals, the emission wavelength is shifted to a short wavelength, and the state of this state is defined as "1" state or not According to the present invention, a binary signal of 0 or 1 may be represented.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments, but these are merely for illustrative purposes and should not be construed as limiting the protection scope of the present invention.

Example

Manufacturing example  One: CdTe Of CdSe  Semiconductor Nanocrystal Synthesis

266 mg of cadmium acetate and 1 ml of oleic acid as cadmium precursor materials of CdTe semiconductor nanocrystals are stirred and heated in a 100 degree vacuum environment for 1 hour. As telenium precursor material, 510 mg of telenium was added to 8 ml of trioctylphosphine and heated by stirring in a nitrogen environment. CdTe semiconductor nanocrystals were synthesized by dispersing the cadmium and telenium precursor materials in trioctylphosphine (4 ml), and then injecting 15 g of trioctylphosphine oxide and 3 g of hexadecylamine solution in a nitrogen environment at 300 degrees. .

The synthesized CdTe semiconductor nanocrystals and 20 g of trioctylphosphine oxide were heated to 150 to 180 degrees in a nitrogen environment. Subsequently, 266 mg of cadmium acetate and 1 ml of oleic acid as a cadmium precursor material of CdSe shell semiconductor nanocrystals and 1 ml of oleic acid were stirred and heated for 1 hour in a vacuum environment at 100 ° C. To 1 ml of trioctylphosphine as selenium precursor material 78 mg of selenium was added and stirred and heated in a nitrogen environment The cadmium and telenium precursor materials were dispersed in 6 ml of trioctylphosphine, followed by dropwise addition of the solution dispersed in trioctylphosphine. By stirring and heating at 250 ° C., a CdTe / CdSe semiconductor nanocrystal having a CdSe crystal structure grown on the CdTe semiconductor nanocrystal surface was synthesized.

The obtained semiconductor nanocrystals were dispersed in anhydrous hexane solvent (5 ml), diluted to a concentration of about 10 uM, and then mixed with about 30 mg of sodium mass (particle size: about 0.1 mm) in a nitrogen environment in which oxygen and moisture were not present. After storage for about 3 days to obtain a negative charge introduced CdTe / CdSe nanocrystals. At this time, as sodium was oxidized, a negative charge was introduced to the surface of the CdTe / CdSe quantum dot.

Example  2

As a cadmium precursor material of CdSe semiconductor nanocrystals, 266 mg of cadmium acetate and 1 ml of oleic acid were stirred and heated in a 100 degree vacuum environment for 1 hour. As selenium precursor material, 312 mg of selenium is added to 4 ml of trioctylphosphine and heated by stirring in a nitrogen environment. The cadmium and selenium precursor materials were dispersed in 2 ml of trioctylphosphine, and then injected into 15 g of trioctylphosphine oxide and 5 g of hexadecylamine solution in a nitrogen environment at 300 degrees to synthesize CdSe semiconductor nanocrystals.

The synthesized CdSe semiconductor nanocrystals and 20 g of trioctylphosphine oxide were heated to 150 to 180 degrees in a nitrogen environment. Subsequently, 266 mg of cadmium acetate and 1 ml of oleic acid were stirred and heated for 1 hour in a 100 degree vacuum environment as a cadmium precursor material of CdTe shell semiconductor nanocrystals. As a telenium precursor, 127 mg of telenium is added to 2 ml of trioctylphosphine and heated by stirring in a nitrogen environment. The cadmium and telenium precursor materials were dispersed in 6 ml trioctylphosphine, and then the solution dispersed in trioctylphosphine was added dropwise. The reaction mixture was stirred and heated at 180 to 250 degrees to synthesize CdSe / CdTe semiconductor nanocrystals in which CdTe crystal structures were grown on CdSe semiconductor nanocrystal surfaces.

The obtained semiconductor nanocrystals were dispersed in anhydrous hexane solvent (5 ml), diluted to a concentration of about 10 uM, and then mixed with about 30 mg of sodium mass (particle size: about 0.1 mm) in a nitrogen environment in which oxygen and moisture were not present. After storage for about 3 days to obtain a negative charge introduced CdSe / CdTe nanocrystals. At this time, as sodium was oxidized, a negative charge was introduced to the surface of the CdSe / CdTe quantum dot.

Experimental Example  One

The emission spectrum of the negatively charged CdTe / CdSe semiconductor nanocrystals obtained in Example 1 is shown in FIG. 3. All luminescence measurements were excited under the same conditions by the same wavelength and intensity (light source of 1 μW of 400 nm wavelength) and the intensity of luminescence was normalized and displayed. In FIG. 3, the emission wavelengths of the CdTe / CdSe semiconductor nanocrystals that are not negatively charged are shown in black, and are sequentially displayed in red, blue, green, and pink as the amount of charged charge increases.

Referring to FIG. 3, as the amount of charge introduced to the surface of the semiconductor nanocrystal increases, the emission wavelength of the semiconductor nanocrystal gradually shifts toward the short wavelength.

The result of introducing charge to the surface of the nanocrystals for 2, 5, 8, and 10 days using sodium in the same manner as in Example 1, which is because the amount of charge introduced to the surface increases with time. As the amount of charge introduced to the surface of the crystal increases, the emission wavelength of the semiconductor nanocrystal gradually shifts toward the short wavelength. As the amount of charge introduced to the surface of the semiconductor nanocrystals increases, the emission wavelength of the semiconductor nanocrystals gradually shifts toward the shorter wavelength.

Experimental Example 2 :

In Example 1, the electrons were removed by exposing the quantum dots with negative charges to the surface for 3 minutes by a chemical method. 4 shows fluorescence spectra of the CdTe / CdSe semiconductor nanocrystals synthesized in Example 1, the CdTe / CdSe semiconductor nanocrystals with charges introduced on the surface, and the CdTe / CdSe semiconductor nanocrystals with the charges removed therefrom.

In FIG. 4, the luminescence properties of the CdTe / CdSe semiconductor nanocrystals before being charged are shown in black. The luminescence properties of the semiconductor nanocrystals, in which the surface of the semiconductor nanocrystals were charged with negative charge, are shown in blue. After removing the charged negative charges, the light emitting characteristics of the semiconductor nanocrystals in the neutral state are shown in red.

Experimental Example  3

In Example 2, emission spectra of the negatively charged CdSe / CdTe semiconductor nanocrystals are shown in FIG. 5. In FIG. 5, the light emission characteristics of the CdSe / CdTe semiconductor nanocrystals before charging were indicated in black, and the light emission characteristics of the semiconductor nanocrystals in which the surface of the semiconductor nanocrystals were charged with negative charges were indicated in blue. The luminescence properties of the semiconductor nanocrystals restored to the neutral state after removing the charged negative charges are shown in red.

Referring to FIG. 5, the negatively charged CdSe / CdTe semiconductor nanocrystals have a maximum emission wavelength of about 775 before the maximum emission wavelength of the emission wavelength is charged, as opposed to the negatively charged CdTe / CdSe semiconductor nanocrystals. After charging at nm, it can be seen that the maximum emission wavelength is shifted toward the long wavelength of about 25 nm to about 800 nm. In addition, it can be seen that the emission characteristics are reversibly recovered when the quasi-negative charge introduced is removed.

Experimental Example  4

PL decay of the CdTe / CdSe semiconductor nanocrystals with time obtained in Example 1 was measured and shown in FIG. 6. A total of four times the same CdTe / CdSe semiconductor nanocrystal sample was repeated to remove the negative charge to the surface through a chemical method and the results are shown in FIG. In Fig. 6, it can be seen that the uncharged (indicated by the emission wavelength is indicated by ○) and the case where a negative charge is introduced to the surface (indicated by the emission wavelength by ■) are binaryly emitted at different wavelengths, such as on-off. have. However, due to the characteristics of the chemical test method that cannot accurately control the amount of negative charge introduced and the change of the surface of the semiconductor nanocrystal resulting from the introduction and removal of chemical charges, the emission wavelength changes in the same state depending on the number of trials. have.

Although the preferred embodiments of the present invention have been described in detail above by way of example, the present invention is not limited to the embodiments disclosed or referred to in the claims, and many other variations and modifications of the invention are defined in the appended claims. It will be apparent to those skilled in the art that this is possible within the scope of the inventive idea.

1 is a schematic diagram showing a semiconductor nanocrystal and one embodiment thereof in one embodiment of the present invention.

2 is a schematic diagram showing a semiconductor nanocrystal and another band gap thereof according to another embodiment of the present invention.

FIG. 3 is a light emission spectrum showing a change in light emission wavelength when the surface of the CdTe / CdSe semiconductor nanocrystals obtained in Example 1 is charged with a negative charge.

FIG. 4 is a fluorescence spectrum of CdTe / CdSe semiconductor nanocrystals synthesized in Example 1, CdTe / CdSe semiconductor nanocrystals with charges introduced on the surface, and CdTe / CdSe semiconductor nanocrystals with removed charges.

FIG. 5 is a fluorescence spectrum of CdSe / CdTe semiconductor nanocrystals synthesized in Example 2, CdSe / CdTe semiconductor nanocrystals with charges introduced on the surface, and CdSe / CdTe semiconductor nanocrystals with the charges removed therefrom.

FIG. 6 is a graph showing changes in the emission wavelength of semiconductor nanocrystals when the introduction and removal of charges on the surface of the CdTe / CdSe semiconductor nanocrystals obtained in Example 1 are repeated several times.

7A-B are schematic diagrams for describing an implementation principle of an optical device including a semiconductor nanocrystal according to an embodiment of the present invention.

Claims (13)

A semiconductor nanocrystal having a multilayer structure including two or more semiconductor layers composed of one or more semiconductor materials, wherein the semiconductor nanocrystals have one or more interfaces where a band gap intersects, and the semiconductor nanocrystals comprise a first semiconductor. The conduction band of the semiconductor material of the layer is higher than the conduction band of the semiconductor material of the second semiconductor layer, and the valence band of the semiconductor material of the first semiconductor layer is higher than that of the semiconductor material of the second semiconductor layer, The conduction band of the semiconductor material of the first semiconductor layer of the crystal is lower than the conduction band of the semiconductor material of the second semiconductor layer, and the valence band of the semiconductor material of the first semiconductor layer is lower than that of the semiconductor material of the second semiconductor layer. In addition, the semiconductor nanocrystals are prepared by dispersing the nanocrystals in a solvent, followed by addition of a reducing agent, or by applying an external electric field. Charges are introduced directly into the surface or inside of the nanocrystal, and when excited, the electrons or holes are spatially separated and the electrons and holes are localized in different semiconductor layers. A semiconductor nanocrystal in which charge is introduced to a surface thereof. delete delete delete The semiconductor nanocrystal according to claim 1, wherein the semiconductor nanocrystal is a core-shell, core-multishell, multicore-multishell, or core-intermediate-shell structure. The semiconductor nanocrystal according to claim 1, wherein the semiconductor nanocrystal has positive or negative charge introduced therein. 6. The core of the semiconductor nanocrystals according to claim 5, characterized in that it comprises a material selected from the group consisting of Group II-VI compounds, Group III-V compounds, Group IV-VI compounds, and mixtures thereof. Semiconductor nanocrystal with charge introduced on its surface. The method of claim 7, wherein the group II-VI compound is CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, HgO, HgS, HgSe, HgTe isotopic compounds; CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe; And HggZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, and a substance selected from the group consisting of The group III-V compound semiconductors include GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb; Three-element compounds of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP; And GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and a material selected from the group consisting of The group IV-VI compound is a binary element compound of SnS, SnSe, SnTe, PbS, PbSe, PbTe; Three-element compounds of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe; And SnPbSSe, SnPbSeTe, or SnPbSTe is an element selected from the group consisting of quaternary compounds. The surface of claim 5, wherein the shell of the semiconductor nanocrystals comprises a material selected from Group II-VI compounds, Group III-V compounds, Group IV-VI compounds, Group IV compounds, or mixtures thereof. Semiconductor nanocrystals with charge introduced into them. The compound of claim 9, wherein the II-VI compound is CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe isotopic compound, or CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe Tri-element compounds of HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, or CdZnSeS, CdZnSeTe, CdZnSTe, CdHgZgSe, CdHgZgSe Material, the group III-V compound semiconductor is GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, or a binary compound of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, Ternary compounds of AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, or GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNPAlNAl , InAlPAs, InAlPSb is a material selected from the group consisting of an element compound, the IV-VI compound is a binary element of SnS, SnSe, SnTe, PbS, PbSe, PbTe The charge is introduced to the surface characterized in that the material is selected from the group consisting of water or a three-element compound of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, or an elemental compound of SnPbSSe, SnPbSeTe, SnPbSTe Semiconductor nanocrystals. The method of claim 1, wherein the semiconductor nanocrystals are CdSe / CdTe, CdTe / CdSe, CdTe / CdS, CdS / CdTe, ZnTe / ZnO, ZnO / ZnTe, ZnSe / ZnO, ZnO / ZnO, ZnS / ZnO, ZnO / ZnS , ZnTe / ZnSe, ZnSe / ZnTe ZnTe / ZnS, ZnS / ZnTe, ZnSe / CdS, CdS / ZnSe, CdSe / ZnTe, ZnTe / CdSe, ZnO / CdSe, CdSe / ZnO, ZnO / CdS, ZdSn A semiconductor nanocrystal having an electric charge introduced on a surface thereof, which is selected from the group consisting of PbSe, PbSe / ZnTe, InAs / InSb, InSb / InAs, InP / ZnTe, and ZnTe / InP. The optical element containing the semiconductor nanocrystal which the electric charge was introduce | transduced into the surface in any one of Claims 1-5. 13. The photon device according to claim 12, wherein the optical device is an optical modulation device.

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