KR101283368B1 - Fluorescence Resonance Energy Transfer-based Light Emitting Diode Device Using Quantum Dots - Google Patents

Abstract

The present invention relates to a light emitting diode device capable of achieving more improved quantum efficiency by using a FRET phenomenon caused between an active layer and a quantum dot of an LED structure. One material system may emit light over a full visible light spectrum region.

Description

Fluorescence Resonance Energy Transfer-based Light Emitting Diode Device Using Quantum Dots}

The present invention relates to a fluorescence resonance energy transfer (FRET) based light emitting diode (LED) device using quantum dots. More specifically, the present invention relates to a light emitting diode device capable of achieving improved quantum efficiency by using a FRET phenomenon caused between an active layer and a quantum dot of an LED structure.

BACKGROUND ART As a semiconductor light emitting device, LEDs applied to backlight light sources, display light sources, general light sources and full color displays, etc. are widely used by using the characteristics of compound semiconductors. Typical materials of such LEDs are group III-V nitride semiconductors such as GaN (Gallium Nitride), AlN (Aluminum Nitride), InN (Indium Nitride), and the like, and the materials are directly transition-type large energy band gaps. gap), it is possible to obtain almost full-wavelength light depending on the composition of the nitride.

1 is a cross-sectional view schematically showing the layer structure of a general planar LED 10.

According to the figure, the LED is configured in the order of the substrate 1, the n-type semiconductor layer 2, the active layer 3 and the p-type semiconductor layer 4 from below. The p-electrode 5 is formed on the p-type semiconductor layer 4, and the n-electrode 6 is formed on the exposed surface of the n-type semiconductor layer 2.

At this time, sapphire, Si, SiC or MgAl 2 O 4 materials are usually used as the substrate 1. The active layer 3 has, for example, a quantum well structure of InGaN / GaN, more typically a multiple quantum well structure. In the active layer, light is generated by recombination of holes flowing through the p-type semiconductor layer 4 and electrons flowing through the n-type semiconductor layer 2.

The principle of commercially available white LEDs, developed by Nichia, Japan, uses the principle of emitting white light by exciting YAG-based yellow phosphors by blue LEDs. In an effort to replace this, theoretically, only InGaN compound can realize optoelectronic devices in the wavelength region of about 365 to 1770 nm. However, due to the difference in the ion bonding radius and electronegativity of In and Ga, near 30% of In composition, InGaN causes spinodal decomposition to cause phase separation, thereby making it impossible to obtain a high quality thin film. For this reason, the internal quantum efficiency is drastically reduced above the wavelength of 520 nm, so there is a limit to fabricating LEDs using InGaN / GaN as the active layer above 550 nm.

On the other hand, nitride semiconductors based on GaN are spontaneous polarization is formed in the growth direction when the device structure is fabricated on the (0001) plane. In particular, an LED having a typical InGaN / GaN quantum well structure generates internal strain due to lattice mismatch in the quantum well structure when the structure is grown on the (0001) plane, and thus, due to piezoelectric fields. There is a limit to increasing the internal quantum efficiency since a quantum-confined Stark effect (QCSE) is caused. In addition, due to the difference in refractive index between the device material and air, the light extraction loss is caused when the light generated in the active layer is emitted to the outside by total internal reflection. Currently, as a method for increasing the internal quantum efficiency by applying the nano-concept, surface plasmon application technology, photonic crystal application technology to increase the light extraction efficiency, surface roughening and the like (roughening) have been studied.

Quantum dots are nano-sized crystals, such as spectral changes in size (i.e., properties that emit light of different wavelengths as the size changes), improved brightness, excellent stability against photo bleaching, simultaneous multiple fluorescence excitation, etc. The same characteristic optical characteristic is shown.

In this regard, in the related art, by including a quantum dot in an active layer having a quantum well (QW) structure among LED structures, it is possible to emit light of different wavelength ranges depending on the size of the quantum dots when the power is applied (Korean Patent Publication No. 2008 -74548), a technique for forming a quantum dot or quantum dot-like structure in a quantum well (Korean Patent Publication No. 2009-86942) is known. In addition, by forming a quantum well layer between the two barriers in the active layer, and by forming a two-layer quantum dot layer in the quantum well layer by participating in the recombination process more carriers by the three-dimensional carrier constraint effect by the quantum dots Techniques for improving the light emission intensity are also known (Domestic Patent Publication No. 2009-47034).

However, the above-described prior art still has a conceptual and technical limitation in producing a full visible light area LED with high light extraction efficiency. In addition, in the example in which nanotechnology is applied in order to increase light extraction efficiency in the related art, research has been mainly focused on photonic crystal or surface plasmon resonance phenomenon.

Accordingly, there is a demand for a new technical breakthrough that is based on a concept that is fundamentally different from the prior art, and that can be specifically realized.

In order to overcome the above-mentioned limitations of the prior art, the present inventors have developed a novel LED device based on the FRET phenomenon using quantum dots, and in particular, one material system can emit light over the full visible light spectrum region. Specific feasibility was secured.

Accordingly, the present invention seeks to provide a FRET-based LED device using quantum dots.

In particular, the present invention seeks to provide a FRET-based LED device capable of emitting light over the full visible light spectral region using one material system.

According to the first aspect of the invention,

A first conductivity type semiconductor region;

A second conductivity type semiconductor region;

An active layer region formed between the first conductive semiconductor region and the second conductive semiconductor region; And

Quantum dot containing regions;

As an LED device comprising a,

FRET phenomenon is caused by using the active layer region as a donor and the quantum dot as an acceptor,

The quantum dot-containing region is provided between the first conductive semiconductor region and the second conductive semiconductor region in the LED device is provided with a FRET-based LED device using a quantum dot.

According to a second aspect of the present invention,

A first conductivity type semiconductor region;

A second conductivity type semiconductor region;

An active layer region formed between the first conductive semiconductor region and the second conductive semiconductor region; And

A quantum dot-containing region positioned between the second conductive semiconductor region and the active layer region;

As an LED device comprising a,

Provided is a FRET-based LED device using a quantum dot, which causes a FRET phenomenon in which the active layer region is a donor and the quantum dot is an acceptor.

In the above embodiment, when the first conductivity type semiconductor region is located below and the second conductivity type semiconductor region is located above, the second conductivity type semiconductor region affects the band gap characteristics of the quantum dots during its formation. It is preferable to be made of a material that does not give or damage. To this end, a hybrid LED device in which the first conductive semiconductor region and the second conductive semiconductor region are formed of different materials may be preferable. More specifically, the second conductivity-type semiconductor region may be a material capable of forming a layer by a method that does not affect or damage the band gap characteristics of the quantum dots, such as, for example, sputtering, for example, an n-type ZnO material. have.

According to a third aspect of the invention,

A plurality of three-dimensional structure regions arranged to be spaced apart from each other and sequentially comprising a first conductive semiconductor region, an active layer region, and a second conductive semiconductor region;

A quantum dot-containing region formed between the three-dimensional structures; And

A transparent conductive region formed over the three-dimensional structure region;

As an LED device comprising a,

Provided is a FRET-based LED device using a quantum dot, characterized in that the FRET phenomenon is caused by using the active layer region as a donor and the quantum dot as an acceptor.

The three-dimensional structure region may preferably have various three-dimensional shapes, such as micro-sized or nano-sized rods, hollow cylinders, and the like.

In the FRET-based nanorod LED device using the quantum dots according to the present invention, the active layer region formed therein, in particular, the active layer region of the quantum well structure and the quantum dots are introduced to cause the FRET phenomenon by using a single material system to display the full-spectrum spectral region (eg For example, it is technically significant in that it can emit light over a wavelength range of about 200 to 1770 nm) and provides an improved structure for this. Therefore, it is expected to be used continuously in the future.

1 is a cross-sectional view schematically showing the layer structure of a typical planar LED;
2 is a diagram showing the difference between the FRET based color conversion principle and the phosphor-using color conversion principle according to the prior art;
3 is a diagram sequentially illustrating a process of manufacturing a FRET-based LED device using a quantum dot according to an embodiment of the present invention;
4 is a diagram sequentially illustrating a process of manufacturing a FRET-based LED device using a quantum dot according to another embodiment of the present invention;
FIG. 5 is a diagram sequentially illustrating a process of forming a nanorod structure in the embodiment shown in FIG. 4; FIG. And
FIG. 6 illustrates a FRET-based LED device using quantum dots in which a hollow cylinder or ring-shaped structure is formed instead of a rod shape as a variation of the embodiment shown in FIG. 4.
7 illustrates an LED device in which quantum dots and nanoparticles are contained between a first conductive semiconductor region and a second conductive semiconductor region.

The present invention can be all accomplished by the following description. The following description is to be understood as describing preferred embodiments of the invention, but the invention is not necessarily limited thereto.

In addition, the accompanying drawings may be somewhat exaggerated relative to the thickness (or height) of the actual layer or the ratio with other layers to facilitate understanding, the meaning of which will be appropriately understood by the specific purpose of the related description to be described later Can be.

In this specification, the expressions "on" and "on" are used to refer to the concept of relative location, where other components or layers are directly present in the layers mentioned, as well as other layers in between. (Intermediate layer) or components may be interposed or present, and may also be present in relation to the mentioned layer but not completely cover the surface of the mentioned layer (e.g., an embedded structure). can do. Similarly, the expressions "below", "below" and "below" may also be understood as a relative concept of position. In addition, the expression "between" may also be relatively understood as described above, and may be understood as a concept of longitudinal or lateral position.

* In this specification, each of the "first conductivity type semiconductor" and "second conductivity type semiconductor" may mean "n-type" or "p-type", and typically has opposite conductivity characteristics. . At this time, a semiconductor such as unintentionally doped GaN may be used as the first conductivity type semiconductor. More preferably, when the first conductivity type semiconductor is located relatively lower, it may be a p-type semiconductor, while the second conductivity type semiconductor may be an n-type semiconductor.

In addition, the term "region" can be understood in a broad sense, for example, not only the "continuous layer" structure, but also the overall meaning of various three-dimensional structures (rods, hollow cylinders or rings, etc.) or components thereof. It may be understood that the present invention may further include a case in which a specific component or particle (for example, a quantum dot) is contained or a specific component or particle is regularly or irregularly and continuously or discontinuously distributed or formed.

In the FRET-based LED device using the quantum dot according to the present invention, the light emitted from the active layer region using an active layer region, more specifically, a quantum well layer as a donor and a quantum dot as an acceptor, is used. It is based on the FRET phenomenon that the non-luminescent light is delivered and emitted.

 Quantum dots are nano-sized crystals, which have optically broad absorption spectra, narrow emission bands, good excitation coefficients, good stability against photobleaching, and spectral changes with size (i.e., emit light of different wavelengths as the size changes). Characteristic), and the like. As such, due to the broad absorption spectrum and narrow emission spectrum of the quantum dots, it is used as a donor or acceptor in the technical field based on the FRET phenomenon (for example, in a biosensor or a diagnostic system).

The FRET phenomenon is based on the interaction of two fluorescent materials, first introduced by Forster in 1964. The FRET phenomenon is a physical phenomenon in which energy is transferred from a single excited fluorescent molecule (chromophore) to another fluorescent molecule (chromophore) through a non-luminescent or non-luminescent process due to long-distance dipole-dipole interactions. At this time, the energy-imparting molecule is referred to as a "donor or donor" and the energy-receiving molecule is referred to as an "acceptor or acceptor". The light irradiated to excite the donor from the outside when the donor and the acceptor, which is a fluorescent material that can absorb energy by resonating with the energy emitted from the donor, are within a predetermined distance The energy is non-radiatively transitioned from the donor to the acceptor to reduce the emission of the donor's inherent wavelength band, and the light of the acceptor's inherent wavelength band that receives energy from the donor is emitted. Thus, when the acceptor is within the Forster radius, the emission intensity of the donor is reduced. The FRET phenomenon is known to occur when the distance between the donor and acceptor is typically within about 10 nm. In addition, the FRET phenomenon is characterized by the fact that the fluorescence spectrum of the donor overlaps with the absorption spectrum of the acceptor.

When the LED device is configured based on the FRET phenomenon as in the present invention, the light extraction efficiency can be improved as well as the light emission characteristics can be tuned through color conversion control as compared with the conventional fluorescent material. There is an advantage.

2 is a diagram showing the difference between the FRET-based color conversion principle and the phosphor-using color conversion principle according to the prior art.

The light emitting process (OUT _LED ) of the LED (especially the blue LED) is subjected to a current injection-carrier recombination-light extraction process. Non-luminescence recombination and light extraction efficiency of the carrier injected in the above process is a major cause of reducing the external quantum efficiency.

In the case of coating a phosphor on a blue LED as in color conversion using phosphors, the emission process (OUT _{LED + Ph} ) is in addition to the blue LED emission process and the energy of the phosphor host to the EL light absorber-activator Light-emitting process of the activator. In this case, each process inevitably causes a loss, and thus, as the complicated process is inherent, the quantum efficiency decreases.

On the other hand, when coating a quantum dot (especially colloidal quantum dot; CQD) on a blue LED as in the color conversion using the FRET phenomenon, the light emission process (OUT _FRET ) is only through the light emission process of energy transfer ?? CQD. In the FRET process, before the electron-hole pair (dipole) injected into the active layer region recombines, the binding energy of the electron-hole pair is resonated to the quantum dots without emitting light, and the quantum dots receive the transferred energy and emit electrons as they are excited. Done.

Therefore, in the FRET process, 100% color conversion is possible in principle, and since light is not emitted from the inside of the LED structure, there is no problem of light extraction efficiency. In addition, in the case of manufacturing the LED emitting light by the 100% FRET process, it is theoretically possible to produce a wavelength of longer than the Foster donor (active layer). For example, by applying quantum dots that emit light with a wavelength longer than blue on a blue LED, various colors of LEDs such as cyan / green / yellow / orange / red can be applied. It can be produced.

On the other hand, according to a preferred embodiment of the present invention, the quantum dot containing region is formed or located so that the quantum dots can cause the active layer region and the FRET phenomenon in the LED device. In this case, the lower conductive semiconductor region may be configured as a p-type, and the upper conductive semiconductor region may be configured as an n-type. In particular, an LED layer may include an active layer region having an InGaN / GaN single or multiple quantum well structure. It may be desirable in one case. Since the active layer region of the quantum well structure may exist in an inadvertently doped n-type, the thickness of the p-type GaN should be 100 nm or more when the p-type GaN having a low hole concentration is positioned on the top. This is because it is typically difficult to meet the distance requirement (within about 10 nm) between the donor and acceptor, which is typically required to cause the FRET phenomenon.

In view of the above, it is also possible to adjust the thickness of the n-type semiconductor within about 10 nm on the active layer region and to form a quantum dot containing region thereon. However, in consideration of the need to secure sufficient electrical characteristics, it may be desirable to form a quantum dot-containing region in a space between the first conductive semiconductor region and the second conductive semiconductor region.

At this time, even when the quantum dot containing region is present in the (horizontal) space between the plurality of three-dimensional structures (rods or hollow cylinders), the quantum dot containing region is the first in the relative position reference according to the height. It can be understood that there exists between the conductive semiconductor region and the second conductive semiconductor region.

On the other hand, according to one embodiment of the present invention, the LED element can be formed on the substrate, the lattice constant mismatch between the substrate and the first conductivity-type semiconductor region when the lower region is referred to as the first conductivity-type semiconductor region is alleviated And a buffer layer may optionally be formed there between to induce two-dimensional growth. As such, when the semiconductor layer is grown on the buffer layer, interfacial energy is reduced compared to when directly grown on the heterogeneous substrate, and thus high density nucleation is possible, and further, the lateral growth is promoted so that the plane is flat. The advantage of promoting growth can mitigate lattice mismatch to some extent.

In addition, unless otherwise stated in the present specification, the formation of the conductive semiconductor region (and the buffer layer) and the active layer region may be applied without any particular limitation to the layer formation or growth method involved in a conventional LED manufacturing process. Chemical Vapor Deposition (MOCVD), Molecular Beam Growth (MBE), Hydride Vapor Growth (HVPE) and the like can be exemplified, and in particular, organometallic chemical vapor deposition can be applied. The layer formation method can be easily accomplished by those skilled in the art.

The substrate is a substrate known in the art for manufacturing LEDs, typically a substrate for semiconductor single crystal growth, such as sapphire, silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), silicon (Si), Choose from substrates that can be grown epitaxially, such as GaN, GaN, InP, Zinc Oxide, ZnO, MgAl ₂ O ₄ MgO, LiAlO ₂ , LiGaO _2, etc. More typically, a sapphire substrate can be used. Further, the thickness of the substrate may typically range from about 100 to 500 μm, more typically from about 250 to 450 μm, unless stated otherwise in the description below, which is to be understood in an illustrative sense.

The first conductivity type semiconductor, and the active layer and the second conductivity type semiconductor are various semiconductor materials (III-V, II-VI, etc.) known in the art without particular limitation, for example, GaN, InN, AlN, InP , InS, GaAs, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, Al _x Ga _1-x N, In _x Ga _1-x N, In _x Ga _1-x As, Zn _x Cd _1-x S , InZnO (IZO), InSnO ₂ , zinc tin oxide (ZTO), Al-doped zinc oxide (AZO), In ₂ O ₃ , Ga ₂ O ₃ , InGaZnO (IGZO) and the like can be used, and these alone or in combination Can be used (in the above, 0 <x <1). The selection of such a conductive semiconductor will be described separately if necessary.

In an embodiment of the invention, the quantum dots may consist of a core and shell (or cap) of a single type of material or of another type of material.

The quantum dot has a very large surface area-to-volume ratio, so that most of the constituent atoms are exposed to the surface, leaving the form in which atoms or molecular orbits are not completely bound, which may act as a defect site that quenches the light emitted by the quantum dot. For this reason, an electronic insulation effect can be obtained by growing a shell of another semiconductor having a wider band gap on the core surface. Moreover, the shell serves to stabilize and enhance the light emitted by the excited core, preferably having a higher band gap than the core to passivate the core so that excitation of the quantum dots is confined to the core and oxidized In addition to protecting against, it is possible to prevent Cd / Se from leaching into the surrounding solution (type 1 structure).

According to an embodiment of the invention, the size of the quantum dots is typically in the range of about 0.5 to 50 nm, more typically about 1 to 40 nm, particularly typically about 1 to 20 nm, furthermore about 1 to 10 nm You can also specify a range. For example, in the case of CdSe quantum dots, when the size is about 1 nm, the entire color of the visible region may be continuously adjusted from blue to red when the size is about 8 nm. Specifically, quantum dots with 3 nm CdSe cores emit about 520 nm light, while quantum dots with 5.5 nm CdSe cores emit 630 nm light. In addition, the emission width is affected by the size distribution. In addition, the shape of the quantum dot is not particularly limited, and may have various shapes such as a sphere, a rod, a wire, a pyramid, and a cube. It is preferable to have a spherical shape.

In a preferred embodiment of the invention, the quantum dots are a group II-VI semiconductor compound (eg, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, or combinations thereof), III-V Group semiconductor compounds (eg, GaAs, InGaAs, InP, InAs, or combinations thereof) or group IV semiconductor compounds (eg, Ge or Si). More preferably, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe or CdSeTe may be used as the II-VI semiconductor compound, and InP, GaP or InAs may be used as the III-V semiconductor compound. Quantum dots having a core / shell structure of CdSe (core) / ZnS (shell) and CdSe (core) / CdZnS (shell) are preferable.

Quantum dots can be prepared by known methods, such as those disclosed in US Pat. No. 6,207,392 and the like. An exemplary synthesis process of a representative CdSe quantum dot is briefly described as Se precursors (complexes, oxides, metals, and the like; usually trioctylphosphine selenide or tributylphosphine selenide). Alkylphosphines having 5 to 20 carbon atoms, such as precursors (complexes of Cd, oxides, metals, etc.), usually dimethyl cadmium or cadmium oleate, and coordination ligands (trioctylphosphine oxide) Or injecting slowly into a hot solution containing 5 to 20 carbon atoms such as hexadecylamine (eg, about 300 ° C.) to form a CdSe nanocrystalline core. It binds to metal ions on the surface and stabilizes crystals in solution and controls growth rate. When the temperature is reached, the temperature is lowered to room temperature to stop growth.

In addition, in the case of a shell, such as a ZnS shell, which can be grown on the surface of the core according to a method known in the art, a method of forming a shell of a quantum dot is disclosed, for example, in US Patent Application No. 08 / 969,302. And the like. It is desirable to form a shell with high emission quantum efficiency and narrow size distribution by adjusting the temperature of the reaction mixture while monitoring the absorption spectrum of the core during the shell formation process.

Alternatively, the quantum dots are used in a colloidal state (eg, about 40-50 mg / 40 ml), which is present in a dispersed state without aggregation or precipitation in a fluid (eg, an organic solvent such as toluene or hexane) As described above, this is called a colloidal quantum dot (CQD), and may be diluted if necessary. The colloidal quantum dots described above may be manufactured directly, but a commercially available product may be used (for example, CS501 of QDsolution).

On the other hand, in forming the quantum dot-containing region in the LED element, for example, when quantum dots are located between the active layer region and the second conductive semiconductor region (upper semiconductor region), a high temperature growth method such as MOCVD (typically, When the second conductive semiconductor region is grown and formed at about 800 to 1200 ° C., the band gap of the quantum dots may be affected or damaged. The following describes a FRET-based LED device that can solve these problems, as well as improve the quantum efficiency and light extraction efficiency.

3 is a diagram sequentially illustrating a process of manufacturing a FRET-based LED device using a quantum dot according to an embodiment of the present invention.

A first conductivity type semiconductor layer 102 is formed on the substrate 101, where the first conductivity type semiconductor layer 102 may be a p-type semiconductor layer, typically a p-GaN layer. The thickness of the first conductivity type semiconductor layer may typically range from about 10 to 1000 nm, more typically about 100 to 500 nm, and the present invention is not necessarily limited thereto.

Next, an active layer 103 is formed on the first conductive semiconductor layer 102. According to a preferred embodiment of the present invention, the active layer is at least selected from GaN, AlN, InN, InGaN, AlGaN, InAlGaN, or the like. It can be made of two materials. Among them, a material having a small energy band gap may be used as a quantum well, and a material having a large energy band gap may be configured as a quantum barrier, and both single and multi quantum well structures may be used. In addition, for example, the thickness of the quantum well is about 1 to 4 nm, and the thickness of the quantum barrier may be adjusted to about 2 to 20 nm, but the present invention is not necessarily limited thereto. However, in the case of the final quantum barrier thickness (ie, the thickness of the quantum barrier closest to the quantum dot containing region), it is within about 10 nm, preferably within about 7 nm, more preferably about 5 to be suitable for inducing the FRET phenomenon. It is desirable to adjust within nm.

Thereafter, the quantum dot layer 104 is formed on the active layer 103. In this case, the quantum dot layer 104 may be referred to as a quantum dot containing region. As mentioned above, it is preferable to apply or coat using colloidal quantum dots.

For the application or coating of quantum dots, the following manner can be exemplified:

(i) The quantum dot colloid is dropped onto the specimen in a droplet manner and then dried (typically at a drying temperature of about 50 to 300 ° C.).

(ii) Spin coating using quantum dot colloid.

(iii) a method of forming a layer by a layer-by-layer (LBL) method using a so-called polyelecrolyte.

In particular, in the case of the method (iii), a commercially available quantum dot colloid has a slight charge by a polymer or the like contained therein, to form a polymer electrolyte layer having the opposite charge and by electrostatic attraction The quantum dots can be fixed to form a kind of layer (a state in which a plurality of quantum dots are distributed on the active layer). The thickness of the quantum dot layer 104 thus formed may be, for example, in the range of about 1 to 10 nm. If necessary, a rinse by dipping may be performed, and then the above steps may be repeated several times. Such an LBL method is, for example, Vol. 41, No. 12, December 2008, 1831-1841, ACCOUNTS OF CHEMICAL RESEARCH, which is incorporated herein by reference.

After the quantum dot layer 104 is formed, the second conductivity type semiconductor layer 105 is formed. In a preferred embodiment of the present invention, as described above, the second conductive semiconductor layer 105 is a step of changing the band gap characteristics of the quantum dots during its formation (eg, sputtering, IBD, MBE, etc.). It is possible to use a material, typically ZnO can be used. ZnO is a material having a wide band gap and has a similar structure and properties to GaN, and is capable of low temperature growth.

In particular, when the first conductivity-type semiconductor layer is p-type, the second conductivity-type semiconductor layer may be preferably composed of n-type ZnO. The thickness of the second conductivity-type semiconductor layer 105 may typically range from about 10 to 1000 nm, more typically about 50 to 500 nm.

In the case of n-type ZnO, it is particularly suitable for layering by sputtering (dc sputtering, rf sputtering, reactive sputtering, etc.). In the case of rf sputtering, the growth atmosphere can range from about 0 to 1 in O ₂ / Ar + O ₂ ratio (pressure: for example, about 10 ⁻³ to 10 ⁻² Torr). At this time, oxygen acts as a reaction gas, while argon acts as a sputtering enhancing gas. In the case of dc sputtering, ZnO can be grown from a Zn target in an Ar + O ₂ gas mixture. Since sputtering can be performed at a relatively low temperature (room temperature to about 150 ° C), not only the influence on the quantum dots is small, but also the damage of the quantum dots can be suppressed during the growth process.

After the above process, the electrodes 106 and 107 may be formed for electrical application. For example, platinum (Pt), palladium (Pd), gold (Au), nickel / gold (Ni / Au), or the like may be used alone. Or in combination. For this electrode pattern formation, conventional methods such as photoresist patterning-etching, which are known in the art, may be performed. In addition, the current diffusion layer may be selectively introduced before forming the electrodes 106 and 107 in the second conductivity-type semiconductor layer 105.

4 is a diagram sequentially illustrating a process of manufacturing a FRET-based LED device using a quantum dot according to another embodiment of the present invention.

The above embodiment is to form a rod (nanorod) structure in the LED device, can significantly mitigate the effect of the quantum efficiency degradation factors caused in the conventional planar structure, and improve the light extraction efficiency by the FRET phenomenon Effect can be achieved. According to the present embodiment, a method of manufacturing a FRET-based LED device having a rod structure, particularly a nanorod structure, is as follows.

First, as shown in FIG. 4A, a stacked structure in which a first conductive semiconductor layer 202, an active layer 203, and a second conductive semiconductor layer 205 are sequentially formed on a substrate 201 from below. An LED structure is provided that includes. Examples of the dimensions of each layer constituting the LED structure are shown in Table 1 below.

First conductive semiconductor layer Active layer (well: barrier) Second conductivity type semiconductor layer thickness About 50 nm to 10 μm, preferably about 100 to 500 nm -Well
About 1 to 4 nm, preferably about 2.5 to 3 nm

-Barrier
About 4-20 nm, preferably about 7-15 nm About 5-500 nm,
Preferably about 100 to 300 nm

Then, as shown in FIG. 4B, a process of forming a plurality of rods, preferably nanorods, is preferably performed by selectively removing the LED structure to a partial thickness of the first conductivity type semiconductor layer. As used herein, "nanorod" may mean a rod shape having a diameter of 1,000 nm or less, typically in the range of several nanometers to several hundred nanometers.

For selective removal of the LED structure, a selective etching process using nano patterning technology may be applied. For such selective etching processes, electron-beam lithography, focused ion beam (FIB) lithography, nano-imprint, mask formation using SiO ₂ nanoparticles, self-cohesive metals A mask patterning method such as a self-assembled metal mask is applicable. In addition, the etching method after the mask formation is a dry etching method, for example, reactive ion etching (RIE), inductively coupled plasma reactive ion etching (ICP-RIE), chemical ion beam Etching (chemically assisted ion beam etching (CAIBE)) and the like can be used.

FIG. 5 is a diagram sequentially illustrating a process of forming a nanorod structure in the embodiment shown in FIG. 4.

As illustrated in 5a, an interlayer 215 and a metal layer 216 are sequentially formed on the second conductivity-type semiconductor layer 205. The intermediate layer 215 preferably does not affect the underlying layer, and easily forms a metal nanodot pattern thereon in a subsequent heat treatment process, and may be easily removed later (SiO ₂ ) and silicon nitride ( Si ₃ N ₄ ) and the like, more preferably a silica layer. The layer can be formed by known methods, such as plasma enhanced chemical vapor deposition (PECVD). In this case, the intermediate layer 215 may be preferably formed to a thickness in the range of about 10 to 1,000 nm, more preferably about 50 to 100 nm.

The metal layer 216 is preferably gold (Au), silver (Ag), nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), platinum (Pt), palladium (Pd), aluminum (Al) or a combination thereof, more preferably nickel (Ni), can be formed into a thin film, preferably about 5 to 100 nm, more preferably about 5 to 15 nm thick. have. In this case, an electron-beam evaporation system, for example, an e-beam coater may be used to form the metal layer.

As shown in FIG. 5B, after the intermediate layer 215 and the metal layer 216 are formed, a pattern in which a plurality of metal nano dots 216 ′ are distributed is formed on the intermediate layer 215. That is, when the heat treatment is performed, the metal layer existing in the form of a thin film is melted to form a nano-sized self-cohesive mass, ie, metal nano dots 216 ′, on the intermediate layer 215. This heat treatment process is annealing, more typically a rapid thermal annealing (RTA) process, taking into account the melting point of the metal constituting the metal layer 216, and preferably about 500 to 1000 ° C, more preferably. May be carried out by selecting under a temperature of about 700 to 900 ℃, a nitrogen atmosphere and a time condition of about 1 to 6 minutes.

The plurality of metal nano dots 216 'formed as described above preferably have a width (diameter) of about 10 to 900 nm, more preferably about 50 to 300 nm, even more preferably about 100 to 200 nm. Distribution is formed on the intermediate layer. In addition, the spacing between each metal nano dot 216 'is typically in the range of about 50-500 nm, more typically about 100-250 nm.

As shown in Fig. 5C, etching is performed vertically through the above-mentioned manner using metal nano dots as a kind of mask. For example, in the case of using ICP-RIE, the component layers of the LED structure are etched while suppressing the etching of the metal nano dots 216 'by appropriately adjusting process parameters such as selectivity and etch rate. It is preferable. For example, the etching of the intermediate layer 215 may be performed for about 70 to 120 seconds using ICP-F, and the lower second conductive semiconductor layer 205, the active layer 203, and the first conductive type may be used. The semiconductor layer 202 may be performed for about 200 to 400 seconds using the ICP-CL. These process conditions are by way of example only, and it is obvious that the present invention is not limited thereto.

Meanwhile, the length of the nanorods is determined according to the depth to be etched. In this case, it is preferable to etch only a part of the depth of the first conductivity-type semiconductor layer 202 on the substrate 201. As such, the thickness of the remaining unetched residual layer of the first conductivity-type semiconductor layer 202 on the substrate 201 may be adjusted in consideration of the required characteristics of the device, for example, about 40 to 9,500 nm, preferably May range from about 100 to 2,000 nm.

Through the above process, nanorods having a size corresponding to a mask of the individual metal nanodots 216 'are formed, and the lower surfaces of the plurality of nanorods arranged while being spaced apart from each other are not selectively removed (etched). It has a nanorod structure that is integrated with the remaining layer of the first conductivity type semiconductor layer. In this case, the nanorod includes a first conductive semiconductor region 202 ', an active layer region 203' and a second conductive semiconductor region 205 'from below, and in theory, the width (diameter) of the metal nano dot. It will have a width equivalent to. Also, the distance between the individual metal nano dots 216 'will correspond to the spacing between nanorods. In addition, the region where the above-mentioned self-cohesive metal mask pattern is not formed will be etched by the above-described etching to form a region for forming an electrode for ohmic bonding later.

As shown in FIG. 5D, after the selective removal (or etching) process is performed, a process of removing the layers involved in mask formation, that is, the intermediate layer 215 ′ and the metal nano dots 216 ′, is performed. To this end, a lift-off method known in the art may be used, for example, using HF, Buffered Oxide Etchant (HF + NH ₄ F mixture; BOE), and the like. The mask region may be removed by removing the intermediate layer 215 '.

The dimensions of the nanorods formed as described above may vary depending on the thickness, etching process, lift-off conditions, etc. of the individual layers constituting the LED structure used, for example, preferably about 10 to 900 nm, More preferably, nanorods having a diameter (width) of about 50 to 300 nm and a length in the range of about 20 nm to 5 μm can be produced. In this case, the surface ratio (ratio of the length to the width of the nanorods) may range from about 1 to about 100. The dimension range of such nanorods is an exemplary meaning, and it is clear that the present invention is not limited thereto.

However, as will be described later, the quantum dots in the quantum dot-containing regions positioned between the nanorods may act as the active layer 203 'located in the lateral direction to cause a FRET phenomenon, and the quantum dot-containing regions may be effectively formed between the nanorods. It is desirable to determine the dimensions so that it can.

As a next step, the quantum dot layer 204 is formed, which has been described above and will be omitted. However, the thickness of the quantum dot layer 204 is preferably determined in consideration of the nanorod height and the ease of FRET. The thickness of the quantum dot layer 204 can be determined, for example, within the range of about 10 to 500 nm, more typically about 30 to 300 nm.

Thereafter, in order to fix the quantum dots between the nanorods and to fill or planarize the empty space, a spin-on-coating (SOG) technique is preferably used. SOG refers to a glass type that can be applied in a liquid phase (preferably transparent liquid) to be cured to form a glass layer having properties similar to silica (SiO ₂ ), and is commonly used as a dielectric material in the semiconductor field.

According to this embodiment, the SOG solution can be applied between nanorods through conventional SOG techniques. For example, SOG is applied (typically spin coating at about 2,500 to 3,500 rpm) and baked in the same manner as photoresist. At this time, the baking step may be performed step by step, depending on the number of heat plates, for example, in the case of one heating plate, typically at about 130 to 160 ° C. for about 0.5 to 1.5 minutes, more typically The baking can be carried out at about 150 ° C. for about 1 minute. Of course, when the heating plate is 2 or more, it is possible to gradually raise the temperature of the heating plate and bake. At the end of the baking step, for example, it can be cured under a nitrogen atmosphere.

In this case, the quantum dot-containing region is made of the quantum dot layer 204 and the SOG material 210, and is preferably formed at a height lower than the upper surface of the nanorods.

4E is a diagram showing an embodiment in which the transparent electrode layer 211 is formed on the nanorod structure.

Although the present invention does not exclude the formation of an independent electrode for each individual nanorod, as shown, the transparent electrode layer 211 is formed on the upper side of the nanorod structure, that is, the second conductive semiconductor region 205 'of the nanorod. It is preferable to configure so as to extend laterally on). As a result, each of the second conductivity type semiconductor regions 205 ′ of the plurality of nanorods will be electrically connected to the transparent electrode layer 211. The thickness of the transparent electrode layer (ie, the distance between the upper surface of the nanorods and the upper surface of the electrode) may be determined in consideration of an electrode material that is typically used within a range of about 100 to 300 nm. The electrode thickness range should be understood in an exemplary manner, and may be changed in consideration of characteristics of a specific technical field to which a kind of nanorod LED is applied.

According to one embodiment of the invention, examples of the transparent electrode material is a transparent conductive oxide (TCO), preferably indium tin oxide, indium zinc oxide, oxide Gallium zinc oxide, aluminum zinc oxide or combinations thereof. The method for forming the transparent electrode is not particularly limited, and conventionally known chemical vapor deposition (CVD), sputtering, reactive evaporation, and the like may be used.

In addition, as shown in FIG. 4F, patterned metal electrodes 206 and 207 may be further formed for ohmic bonding. At this time, platinum (Pt), gold (Au), palladium (Pd), nickel / gold (Ni / Au), or the like may be used alone as a metal electrode.

FIG. 6 illustrates a FRET-based LED device using quantum dots in which a hollow cylinder or ring-shaped structure is formed instead of a rod shape as a modification of the embodiment shown in FIG. 4.

In the embodiment shown above, the basic LED fabrication method is similar to the fabrication of the FRET-based nanorod LED device described above. However, in order to form a plurality of hollow cylinders or ring structures, a typical photoresist mask patterning-etching method may be used.

The outer diameter, the distance between the patterns, and the inner diameter of the mask pattern may have a micro size, and the “micro size” may mean a range of about 1 μm to several μm. For example, the outer diameter and the spacing between the patterns of the mask pattern may range from about 2 to 10 μm, and the inner diameter may range from about 1 to 8 μm. In this case, the outer and inner diameters of the hollow cylinders theoretically range from about 2 to 10 μm and about 1 to 8 μm, respectively, and the spacing between the hollow cylinders will correspond to about 2 to 10 μm. This numerical range is to be understood in an illustrative manner, it is possible to form a hollow cylinder of various dimensions, it is obvious that the nano-size hollow cylinder can also be applied to the present invention.

Other layer configurations, such as substrate 301, first conductive semiconductor layer 302, active layer 303, second conductive semiconductor layer 305, quantum dot layer 304, SOG material 310, transparent Details regarding the conductive layer 311, the electrodes 306 and 307, and the like are also described above.

In another aspect, the present invention includes metal nanoparticles capable of inducing surface plasmon shapes. The nanoparticles may be located in the quantum dot containing region described above. That is, the nanoparticles may be located between the first conductive semiconductor region and the second conductor semiconductor region in the LED device.

The LED device of the present invention comprises: a first conductive semiconductor region; A second conductivity type semiconductor region; An active layer region formed between the first conductive semiconductor region and the second conductive semiconductor region; And quantum dot and metal nanoparticle containing regions; An LED device comprising a FRET phenomenon in which the active layer region is a donor and the quantum dot is an acceptor, and surface plasmon resonance is induced around the metal nanoparticles by light emission of the active layer. The quantum dot-containing region is positioned between the first conductive semiconductor region and the second conductive semiconductor region in the LED device.

7 illustrates an LED device in which quantum dots and nanoparticles are contained between a first conductive semiconductor region and a second conductive semiconductor region. Referring to FIG. 7, the LED device includes a substrate 101, a first conductivity type semiconductor 102, an active layer 103, a quantum dot 104, a metal nanoparticle 108, and a second conductivity type semiconductor. Quantum dots 104 and metal nanoparticles 108 are formed on the active layer.

Surface plasmons are collective vibrations of electrons on the surface of metal particles, which are confined to the boundaries of metals and dielectrics (such as air or semiconductors), that is, very small regions, which are the boundaries of two materials. Known as surface electromagnetic waves.

The metal nanoparticles may be used alone or in combination with palladium (Pd), aluminum (Al), silver (Ag), platinum (Pt), copper (Cu), gold (Au), chromium (Cr) and the like. Preferably, silver (Ag) or gold (Au), most preferably silver (Ag) can be used. It is apparent that the metals listed above are for illustrative purposes and the invention is not necessarily limited thereto.

The metal nanoparticles may be core-shell type metal nanoparticles. As the core of the metal nanoparticles, the aforementioned metals may be used, and as the shell, silica (SiO ₂ ), tin oxide (SnO ₂ ), titania (TiO ₂ ), zirconia (ZrO ₂ ), and alumina (Al ₂ O _{3) may be used.} ), Etc.

The size of the metal nanoparticles is not particularly limited and may be changed according to the emission wavelength of the active layer. In one example, the size of the metal nanoparticle particles is 10 ~ 300nm or less, preferably 50 to 200nm, more preferably 50 to 100nm range.

In order to obtain the surface plasmon resonance effect in the metal nanoparticles, the wavelength of incident light and the refractive index of a material in contact with the metal may be considered.

7 shows embodiments of the quantum dot and the metal nanoparticle-containing LED device of the present invention. For the manufacturing method of FIG. 7, reference may be made to the illustrated method of FIG. 3. 7 (a) shows that quantum dots and metal nanoparticles can be formed together on the active layer. For example, by uniformly dispersing the quantum dot and the metal nanoparticles together, any one method selected from spray, drop casting, self-assembly, spin coating, dip coating, doctor blade, printing, chemical bath deposition and sputtering After coating using may be made by drying at 25 to 170 ° C.

FIG. 7B shows that the quantum dots 104 may be formed on the metal nanoparticles 108. The dispersion (colloid) of the metal nanoparticles is dropped onto the active layer 103 in a droplet manner, and then dried at about 50 to 300 ° C, more preferably about 70 to 150 ° C. Alternatively, it can be formed by spin coating using a metal nanoparticle dispersion. The quantum dot 104 may be formed by coating on the metal nanoparticles 108.

7C shows that the quantum dot 104 may be formed on a metal film. The metal 018 film may be a known method, that is, any one selected from spray, drop casting, self-assembly, spin coating, dip coating, doctor blade, printing, chemical bath deposition, and sputtering. Can be formed on the active layer. The quantum dots are then coated onto a metal film.

FIG. 7D illustrates a structure in which the quantum dots are formed after the metal film is coated and annealed to form the metal nanoparticle layer 108.

      Embodiments of the LED device containing the quantum dot and the metal nanoparticles according to the present invention are not limited to FIG. 7. For example, the metal nanoparticles may be located in the quantum dot-containing region of FIGS. 4 to 6.

In an embodiment of the present invention, surface plasmon resonance occurs around the metal nanoparticles 108 by the light emitted from the active layer. Accordingly, a localized strong electromagnetic field is induced in the nanoparticle proximity region, and the induced electromagnetic field may affect the quantum dots existing in the proximity region, thereby increasing the FRET efficiency. In addition, the intensity of light emitted from the active layer is amplified by the surface plasmon resonance phenomenon to increase the luminous efficiency of the quantum dot.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

1: substrate 2: n-type semiconductor layer
3: active layer 4: p-type semiconductor layer
5: p-electrode 6: n-electrode
101, 201, 301: substrate
102. 202, 202 ', and 302: first conductive semiconductor layer
103, 203, 203 ', 303: active layer
104, 204, 304: quantum dot layer
105, 205, 205 ', 305: second conductive semiconductor layer
106, 107, 206, 207, 306, 307: electrode
108: metal nanoparticles
210, 310: spin-on-glass
211 and 311: transparent electrode layer
215: middle layer
216: metal layer
216 ': metal nano dot

Claims (16)

A first conductivity type semiconductor region;
A second conductivity type semiconductor region;
An active layer region formed between the first conductive semiconductor region and the second conductive semiconductor region; And
Quantum dot containing regions;
As an LED device comprising a,
FRET phenomenon is caused by using the active layer region as a donor and the quantum dot as an acceptor,
The quantum dot-containing region is a region where the quantum dots are located, the quantum dot-containing region is located between the first conductivity type semiconductor and the active layer or between the second conductivity type semiconductor and the active layer, and the quantum dot contacts an outer surface of the active layer region. Or FRET-based LED device using a quantum dot, characterized in that located within a distance of less than 10nm to the active layer region. The method of claim 1,
And the first conductive semiconductor region is a p-type semiconductor material as the lower semiconductor region, and the second conductive semiconductor region is an n-type semiconductor material as the upper semiconductor region. delete The method of claim 1,
The LED device is a FRET-based LED device using a quantum dot characterized in that it further comprises a metal nanoparticle in the quantum dot containing region. The method of claim 1,
FRET-based LED device using a quantum dot characterized in that the size of the quantum dot ranges from 0.5 to 50 nm. The method of claim 1,
The LED device is a FRET-based LED device using a quantum dot characterized in that it has an emission band in the wavelength range of 200 to 1770 nm depending on the size of the quantum dot. The method of claim 1,
The first conductivity type semiconductor and the second conductivity type semiconductor are GaN, InN, AlN, InP, InS, GaAs, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, Al _x Ga _1-x N, In _x Ga _1-x N, In _x Ga _1-x As, Zn _x Cd _1-x S, InZnO (IZO), InSnO ₂ , zinc tin oxide (ZTO), Al-doped zinc oxide (AZO), In ₂ O ₃ , FRET-based LED device using quantum dots, characterized in that Ga ₂ O _3, InGaZnO (IGZO) or a combination thereof:
In the above, 0 <x <1. A first conductivity type semiconductor region;
A second conductivity type semiconductor region;
An active layer region formed between the first conductive semiconductor region and the second conductive semiconductor region; And
A quantum dot-containing region formed between the second conductive semiconductor region and the active layer region;
As an LED device comprising a,
FRET phenomenon is caused by using the active layer region as a donor and the quantum dot as an acceptor,
The quantum dot-containing region is a region in which the quantum dot is located, the quantum dot is located inside the second conductivity type semiconductor region, and the quantum dot is in contact with an outer surface of the active layer region or is located within a distance of 10 nm from the active layer region. FRET-based LED device using a quantum dot characterized in that. 9. The method of claim 8,
The first conductive semiconductor region and the second conductive semiconductor region are lower conductive semiconductor regions and upper conductive semiconductor regions, respectively, wherein the first conductive semiconductor region and the second conductive semiconductor region are different from each other.
The first conductive semiconductor region is a p- type GaN material, the second conductive semiconductor region is n-type ZnO, InZnO (IZO), InSnO ₂ (ITO), InGaZnO (IGZO) characterized in that the material FRET-based LED device using. 9. The method of claim 8,
The LED device is a FRET-based LED device using a quantum dot characterized in that it further comprises a metal nanoparticle in the quantum dot containing region. 9. The method of claim 8,
The active layer region has a single or multiple quantum well structure consisting of a quantum well and a quantum barrier, FRET-based LED device using a quantum dot characterized in that the thickness of the quantum barrier closest to the quantum dot containing region is 1 ~ 10 nm. A plurality of three-dimensional structure regions arranged to be spaced apart from each other and sequentially comprising a first conductive semiconductor region, an active layer region, and a second conductive semiconductor region;
A quantum dot-containing region formed between the three-dimensional structures; And
A transparent conductive region formed over the three-dimensional structure region;
As an LED device comprising a,
A FRET-based LED device using a quantum dot, characterized in that a FRET phenomenon is caused by using the active layer region as a donor and the quantum dot as an acceptor. delete The method of claim 12,
The plurality of three-dimensional structure region is rod-shaped, FRET-based LED device using a quantum dot characterized in that the diameter ranges from 10 to 900 nm, 20 nm to 5 ㎛ in length, and 50 to 500 nm intervals between the rods. The method of claim 12,
The plurality of three-dimensional structure region is a hollow cylinder shape, the outer diameter and the inner diameter of the hollow cylinder is in the range of 2 to 10㎛ and 1 to 8㎛, respectively, quantum dot characterized in that the interval between the hollow cylinder is in the range of 2 to 10㎛ FRET-based LED device using.
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