JP2011076770A - Electroluminescent element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroluminescent element achieving light emission with high luminescence from each quantum dot and high color purity in a narrow-band spectrum. <P>SOLUTION: The electroluminescent element is constructed by layering a transparent electrode 12, a first insulating layer 13, an adhesion layer 14, a light emission active layer 20, a flattening layer 15, a second insulating layer 16, and an electrode 17 sequentially on a glass substrate 11. The adhesion layer 14 is formed of an inorganic layer having a Young's modulus not higher than that of a shell layer 23 and disposed on the surface of the light emission active layer 20, and the bonding surface with the light emission active layer 20 protrudes to get into the clearances between the quantum dots 21. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electroluminescent device, and more particularly to an electroluminescent device having a light emitting active layer containing so-called quantum dots and a method for manufacturing the same.

  In recent years, attention has been focused on the application of phosphors having a quantum dot structure to light-emitting elements as a technique for developing self-luminous flat displays. Usually, a quantum dot refers to a state that achieves carrier confinement in all three dimensions in real space, but a quantum dot here refers to the confinement of carriers in all three dimensions in real space. It is defined as the structure that creates the state to be realized. As an example of this quantum dot, the inorganic semiconductor particle (core part) having a spherical shape with a diameter of several nanometers and a relatively small band gap energy, and a relatively band gap covering the surface of the inorganic semiconductor particle -There is a composite material composed of a high energy coating (shell layer). Such a quantum dot has a feature that it can artificially define a gap energy and emit a desired color by precisely controlling its size (diameter).

  The present inventors have developed an all-inorganic electroluminescent device using the quantum dots produced by a wet chemical synthesis technique (see, for example, Patent Document 1 and Patent Document 2). This electroluminescent element has a double insulation structure in which a light emitting active layer containing quantum dots is sandwiched between carrier barrier layers, and excites and emits light by injecting carriers into the quantum dots by applying an alternating electric field. It is a quantum dot light emitting inorganic electroluminescence (EL) element.

  The electroluminescent element has a structure in which a first electrode, a first insulating layer, a light emitting active layer including quantum dots, a second insulating layer, and a second electrode are sequentially stacked on a substrate. Here, the light emitting active layer is formed by forming a large number of quantum dots on a substrate by using a so-called electrospray ion beam deposition method (hereinafter referred to as an ES-IBD method) disclosed in Patent Document 1. The first insulating layer is formed by sequentially irradiating and depositing the surface of the first insulating layer in the form of an ion beam. The raw material used in this ES-IBD method is a solution in which an organic ligand functioning as a surfactant is bonded and attached to the surface of the quantum dot shell layer in a colloidal form in a solvent. In this method, the bond of the organic ligand is dissociated while changing the quantum dot into an ion beam. Therefore, in this ES-IBD method, most of the quantum dots deposited on the deposition substrate side are deposited in a state where the organic ligands are excluded, so that there is an advantage that unnecessary impurities are reduced in the light emitting active layer. is there. Therefore, according to this method, a high-quality light-emitting active layer hardly affected by impurities can be formed.

  Moreover, as an electroluminescent element disclosed by the said patent document 1, the light emitting active layer consists of the buffer layer and quantum dot which consist of inorganic-semiconductor materials, and there exists a thing of the state by which the quantum dot was included in the buffer layer.

International Publication No. 2007/142203 International Publication No. 2008/013069

  When the above-mentioned electroluminescent device is applied to a self-luminous flat display, an emission peak other than the emission spectrum derived from the confinement level in the quantum dot is used in order to further increase the emission intensity and improve the color purity of the emission. Improvements such as suppression of the occurrence of this are desired. Such an improvement is intended to prevent a decrease in the quantum confinement effect in the quantum dots, a decrease in emission intensity due to an interaction with a close well or formation of a subband, and a broadening of the emission spectrum.

  When quantum dots are deposited by applying energy to the quantum dots using the ES-IBD method described in Patent Document 1, depending on the kinetic energy of the ion beam, the quantum dots may be separated from the insulating layer or buffer. There is a concern that the layer may collide with the surface of the layer and be deformed or damaged. As a result, there is a concern that the size of the quantum dot changes and the wavelength of light emitted from the quantum dot changes.

  In addition, as disclosed in Patent Document 1, when the light emitting active layer is configured such that quantum dots are included in a buffer layer made of an inorganic semiconductor material, the quantum dot and the material of the buffer layer (inorganic semiconductor material) However, there is a problem that the film forming apparatus becomes complicated and the energy imparted to the quantum dot ions changes due to collision with other deposited species.

When only the quantum dots are deposited on the first insulating layer by using the ES-IBD method, there is no buffer layer (matrix material) between the quantum dots, so that a gap is formed, and the light emitting active layer is formed. There is a problem that the transportability or conductivity of the carrier is lowered.

  Furthermore, the surface of the light emitting active layer in which quantum dots are deposited alone without a matrix material is an uneven surface on which spherical quantum dots are arranged. For this reason, the flatness of the constituent film (second insulating layer) grown thereon is lowered. Thus, when the flatness of an insulating layer falls, the problem that dielectric breakdown will occur easily or the uniformity of an electric field strength will arise. Such a problem causes a bright spot or a dark spot to partially occur in the display area in the self-luminous flat display, or to deteriorate the in-plane uniformity of display characteristics.

  In addition, in the electroluminescence device that applies an alternating electric field as described above, it is considered that the interface state between the light emitting active layer and the insulating layer contributes to supplying electrons to the light emitting active layer. It is desired to improve the interface state between the layer and the light emitting active layer (quantum dots contained in the light emitting active layer) and increase the number of electrons emitted to the light emitting active layer.

  The present invention was created by paying attention to such problems, and its main purpose is to provide an electroluminescent device that emits light from each quantum dot with a narrow band spectrum, high color purity, and high brightness. There is to do.

  Another object of the present invention is to provide an electroluminescent device capable of suppressing the occurrence of light emission defects and having in-plane uniformity of light emission characteristics.

  The first feature of the present invention is that an insulating layer is disposed on at least one surface side of a light emitting active layer including a quantum dot having a structure in which a surface of a core portion is covered with a shell layer, and the light emitting active layer and the insulating layer are thick. An electroluminescent element having a pair of electrodes sandwiched in the vertical direction and emitting a light-emitting active layer by applying an alternating voltage to the pair of electrodes, wherein a shell layer is formed on one surface side of the light-emitting active layer. The gist of the present invention is that an adhesion layer is formed which is an inorganic layer having a Young's modulus equal to or less than the ratio and protrudes and adheres so that the bonding surface with the light emitting active layer enters the gap between the quantum dots. Here, the adhesion layer whose band offset with the material of the shell layer is 0.1 eV or less is preferable.

  In the present invention, since the adhesion layer protrudes into the gap between the quantum dots and the band offset with the shell layer is small, the adhesion layer and the quantum dot can be kept in a tightly bonded state, and the light emitting active layer Easy to transport carriers. In addition, the structure in which the adhesion layer is interposed between the light emitting active layer and the insulating layer has an effect of promoting the generation of carriers at the interface between the adhesion layer and the insulating layer. Therefore, in the present invention, the light emission intensity in the light emitting active layer can be improved. In particular, since the adhesion layer is an inorganic layer having a Young's modulus equal to or lower than the Young's modulus of the shell layer in the quantum dots, the quantum dots can be prevented from being deformed or damaged by the adhesion layer. As a result, the size of the quantum dots does not change, and the color of light emitted from the quantum dots can be prevented from changing. Moreover, in the electroluminescent element of such a structure, since generation | occurrence | production of a surface state or an interface state is suppressed, light other than the wavelength from which the emission spectrum from a quantum dot originates in a quantum dot can be suppressed. For this reason, there exists an effect | action which prevents that an emission spectrum becomes a broadband.

  Here, the material of the quantum dot shell layer is zinc sulfide (ZnS), zinc selenide (ZnSe), cadmium sulfide (CdS), or a compound or mixed crystal selected from Zn, Cd, S, Se, or In, Ga , P, Si, Ge, Sn, As, or a mixed crystal. In this case, the Young's modulus of the adhesion layer is preferably 1 to 100 GPa.

  As described above, since the material of the adhesion layer is an inorganic layer having a Young's modulus equal to or less than the Young's modulus of the shell layer in the quantum dot, the ES− deposited by irradiating the ion beam of the quantum dot on the adhesion layer When the film is formed by the IBD method, the quantum dot size can be prevented from changing during the irradiation process.

  In addition, the material of the adhesion layer has a conduction band edge level larger than the conduction band edge level of the core part material in the quantum dot, and the valence band edge level is equal to the valence band edge level of the material of the core part. Is preferably smaller.

  Furthermore, the material of the adhesion layer preferably contains at least one kind of atom selected from Group II, Group III, Group V and Group VI, and particularly preferably contains Group II and Group VI atoms as the main material. Note that typical atoms selected as the material for the adhesion layer include zinc (Zn), sulfur (S), selenium (Se), arsenic (As), and phosphorus (P).

  Further, the material of the adhesion layer is preferably such that the difference in lattice constant from the material of the shell layer in the quantum dots is within 5%. Thus, by limiting the difference in lattice constant between the material of the adhesion layer and the material of the shell layer to 5% or less, the continuity of the interface between the crystal structure of the adhesion layer and the crystal structure of the shell layer is not disturbed. Since it is possible to form a junction with good matching, it is possible to improve the effect of suppressing the generation of emission peaks other than the emission spectrum derived from the confining levels in the quantum dots. In addition, since the material of the adhesion layer and the material of the shell layer are similar substances from the viewpoint of the lattice constant in this way, when depositing the quantum dots to form the light emitting active layer, defects in the shell layer are eliminated. Since the material of the adhesion layer is repaired and the voids can be embedded with the material of the adhesion layer, continuity between the quantum dots and the adhesion layer can be provided. In addition, by setting the band offset between the shell material and the adhesion layer to 0.1 eV or less, it is possible to promote the movement of carriers and suppress the formation of space charges.

  The adhesion layer may have a structure in which a plurality of layers are laminated. By laminating a plurality of adhesion layers, it can be expected to promote the generation of carriers from the interface state between the layers. Therefore, the number of injected carriers that contribute to light emission per unit time in the quantum dot can be increased, and it is possible to apply to applications that require higher luminance.

  On the other surface side of the light emitting active layer, it is preferable to form a flattened layer that is flattened so as to cover the light emitting active layer. And it is preferable that the material which comprises this planarization layer is the same inorganic material as the material of the said contact | adherence layer.

  In this way, by forming a planarization layer on the other surface side of the light emitting active layer, the unevenness of the surface of the light emitting active layer after film formation is corrected, and for example, the flatness of the insulating layer formed thereon is improved. Can be increased. Therefore, the electrode formed on the insulating layer can be formed flat. For this reason, since the distance between the electrode and the light emitting active layer becomes uniform in the light emitting region plane, dielectric breakdown hardly occurs and the in-plane uniformity of the electric field strength can be improved. Therefore, by applying the present invention to a self-luminous flat display, it is possible to eliminate the cause of the occurrence of a bright spot or dark spot in the display area, or the deterioration of the in-plane uniformity of display characteristics. It becomes.

  Although the present invention is characterized in that an adhesion layer is interposed between the quantum dots and the insulating layer, a buffer layer may be further provided between the adhesion layer and the insulating layer. In this case, the buffer layer needs to be designed so that the difference in lattice constant with the adhesion layer is within 5% and the band offset with the adhesion layer material is 0.1 eV. If the buffer layer is designed in this way, a high-luminance electroluminescent device can be realized without deteriorating carrier transport properties and conductivity to the quantum dots.

  In the case where the structure further includes a planarization layer, a buffer layer may be further provided between the planarization layer and the insulating layer. In this case, the buffer layer needs to be designed so that the difference in lattice constant with the planarization layer is within 5% and the band offset with the planarization layer material is 0.1 eV. If the buffer layer is designed in this way, a high-luminance electroluminescent device can be realized without deteriorating carrier transport properties and conductivity to the quantum dots.

  The second feature of the present invention is that an insulating layer is laminated on at least one surface side of a light emitting active layer including quantum dots having a structure in which the surface of the core portion is covered with a shell layer, and the light emitting active layer and the insulating layer are thick. A method of manufacturing an electroluminescent element having a pair of electrodes sandwiched in a direction and causing a light emitting active layer to emit light by applying an alternating voltage to the pair of electrodes, wherein the first electrode is formed on a substrate. An inorganic layer having a Young's modulus equal to or lower than the Young's modulus of the shell layer, which is applied after the first electrode forming step and before the light emitting active layer forming step for forming the light emitting active layer. An adhesion layer forming step of forming an adhesion layer; and a light emitting active layer forming step of forming a light emitting active layer by depositing the surface of the adhesion layer by irradiating quantum dots on the adhesion layer by an ES-IBD method; On top of this luminescent active layer, conduction A planarization layer made of an inorganic material having an edge level larger than the conduction band edge level of the material of the quantum dot core portion and having a valence band edge level smaller than the valence band edge level of the core portion material. A planarization layer forming step of forming a surface flatness using any one of chemical vapor deposition (CVD), liquid phase growth, molecular beam epitaxy, vacuum deposition, and sputtering, and The gist is to include a second electrode forming step of forming a second electrode after the flattening layer forming step.

  In the manufacturing method according to the present invention, the quantum dots are deposited by the ES-IBD method after forming an adhesion layer made of a layer having a Young's modulus equal to or lower than the Young's modulus of the shell layer. It can be prevented from being damaged. As a result, the size and shape of the quantum dots are not changed, and the color of light emitted from the quantum dots can be prevented from changing. In addition, since the material of the adhesion layer enters the gap between the quantum dots at the bonding surface between the adhesion layer and the light-emitting active layer, filling the gap between the quantum dots facilitates carrier transport and increases the emission intensity. It becomes possible to improve. In addition, since the continuity of the band structure of the quantum dots and the adhesion layer is improved, the emission spectrum becomes only a wavelength derived from the quantum dots, and it is possible to prevent the emission spectrum from becoming a broadband.

  In addition, a planarization layer formed on the light-emitting active layer is formed using any one of chemical vapor deposition (CVD), liquid phase growth, molecular beam epitaxy, vacuum deposition, and sputtering. As a result, the surface of the planarization layer becomes flat. When, for example, an insulating layer is formed on the planarizing layer and the second electrode is further formed thereon, the insulating layer can also be formed flat, and the distance between the second electrode and the light emitting active layer is the light emission. It becomes uniform in the area plane. Therefore, dielectric breakdown is less likely to occur in the electroluminescent element, and the in-plane uniformity of the electric field strength can be improved. In addition, by applying this manufacturing method to a self-luminous flat display, it is possible to eliminate the cause of the occurrence of a bright spot or dark spot partially in the display area, or impairing the in-plane uniformity of display characteristics. It becomes possible.

  According to the present invention, it is possible to realize an electroluminescent element in which light emission from each quantum dot has a narrow band spectrum, high color purity, and high luminance. Further, according to the present invention, it is possible to realize an electroluminescent element that can suppress the occurrence of display defects and has in-plane uniformity of display characteristics.

1 is a perspective view showing an electroluminescent element according to a first embodiment of the present invention. It is process sectional drawing which shows the 1st electrode formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the 1st insulating layer formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the contact | glue layer formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the light emission active layer formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the planarization layer formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the 2nd insulating layer formation process and 2nd electrode formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the state by which the quantum dot was driven into the contact | adherence layer in the light emission active layer formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the state in which the quantum dot is deposited on the contact | adherence layer in the light emission active layer formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is process sectional drawing which shows the state which covered the light emission active layer with the planarization layer in the light emission active layer formation process of the manufacturing method of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is a schematic explanatory drawing of the ES-IBD apparatus used with the manufacturing method of the electroluminescent element of this invention. It is sectional drawing of the electroluminescent element which concerns on the 3rd Embodiment of this invention. PL spectrum and EL of a sample having the configuration of the electroluminescent element according to the first embodiment of the present invention (Experimental example 2: having both an adhesion layer and a planarization layer made of ZnS and a film thickness of 2.5 nm) It is a figure which shows the measurement result of a spectrum. FIG. 6 is a diagram showing a PL spectrum of a sample (Experimental Example 4: having both an adhesion layer and a planarization layer made of ZnS and a film thickness of 20 nm) having the configuration of the electroluminescent element according to the first embodiment of the present invention. is there. FIG. 7 is a diagram showing an EL spectrum of a sample (Experimental Example 4: having both an adhesion layer and a planarization layer made of ZnS and having a thickness of 20 nm) having the configuration of the electroluminescent element according to the first embodiment of the present invention. is there. FIG. 6 is a diagram showing a PL spectrum of a sample having a configuration of the electroluminescent element according to the first embodiment of the present invention (Experimental Example 5: having both an adhesion layer and a planarization layer made of ZnS and a film thickness of 80 nm). is there. FIG. 5 is a diagram showing an EL spectrum of a sample (Experimental Example 5: having both an adhesion layer and a planarization layer made of ZnS and having a thickness of 80 nm) having the configuration of the electroluminescent element according to the first embodiment of the present invention. is there. It is a figure which shows PL spectrum of the sample (Experimental example 6: It has only the contact | adherence layer which consists of ZnS, and the film thickness is 5 nm) with the structure of the electroluminescent element which concerns on the 1st Embodiment of this invention. It is a figure which shows the EL spectrum of the sample (Experimental example 6: It has only the contact | adherence layer which consists of ZnS, and the film thickness is 5 nm) with the structure of the electroluminescent element which concerns on the 1st Embodiment of this invention. A sample having the configuration of the electroluminescence device according to the first embodiment of the present invention (Experimental example 6: having only an adhesion layer made of ZnS and having a film thickness of 5 nm) is AC-driven to time-resolve the emission intensity. It is a figure which shows the result observed by doing.

  Hereinafter, an electroluminescent element and a method for manufacturing the same according to an embodiment of the present invention will be described with reference to the drawings. However, it should be noted that the drawings are schematic, and the thicknesses and ratios of the layers are different from actual ones. Moreover, the part from which the relationship and ratio of a mutual dimension differ also in between drawings is contained. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description.

[First embodiment]
(Schematic configuration of electroluminescent element)
FIG. 1 is a sectional view showing an electroluminescent element according to the first embodiment of the present invention. As shown in the figure, an electroluminescent element 10A is formed on a transparent substrate 11 made of glass or plastic, in order, a transparent electrode 12 as a first electrode, a first insulating layer 13, an adhesion layer 14, and a light emitting active layer. 20, a planarization layer 15, a second insulating layer 16, and an electrode 17 as a second electrode are laminated. The electroluminescent element 10 </ b> A according to the present embodiment has a structure in which the light emitting active layer 20 is sandwiched between the adhesion layer 14 and the planarizing layer 15. As shown in FIG. 1, in this electroluminescent element 10A, an alternating current drive source 30 is connected to the transparent electrode 12 and the electrode 17 and an alternating electric field is applied, thereby emitting light from the light emitting active layer 20 from the transparent substrate 11 side. It is made to emit.

(About the light emitting active layer)
As shown in FIGS. 9 and 10, the light emitting active layer 20 is formed by depositing a large number of substantially spherical quantum dots 21. The light emitting active layer 20 is formed to have a thickness of 20 to 100 nm by using the ES-IBD method. Details of the ES-IBD method will be described later. Each quantum dot 21 has a nanocrystal structure in which the surface of the core portion 22 is covered with a shell layer 23. Such quantum dots 21 can artificially define the gap energy and emit light of a desired color by precisely controlling the material and crystal size of the core portion.

  In the present embodiment, the diameter of the core portion 22 is sequentially 1.9 nm, 2.4 nm, and 5.2 nm, and the film thickness of the shell layer 23 is sequentially 0.4 nm, 1.0 nm, and 1. The thickness was 4 nm. In the present embodiment, a quantum dot 21 in which the core portion 22 is formed of cadmium selenide (CdSe) and the shell layer 23 is formed of zinc sulfide (ZnS) or zinc selenide (ZnSe) is used. Further, the core portion 22 of the quantum dot 21 in the present embodiment is made of CdS, PbSe, HgTe, CdTe, InP, GaP, InGaP, GaAs, InGaN, GaN, or a mixed crystal thereof other than CdSe. Can be selected as appropriate.

(About electrodes)
The transparent electrode 12 is made of tin-doped indium oxide (ITO) with a thickness of about 100 nm. The electrode 17 is made of gold (Au) and has a thickness of about 50 nm. The transparent electrode 12 can be made of any transparent conductor such as zinc-doped indium oxide (IZO), indium gallium zinc oxide (IGZO), conductive zinc oxide (ZnO), amorphous oxide conductor, etc. in addition to ITO. It doesn't matter. The film thickness of the electrode 17 is appropriately increased or decreased depending on the material so that necessary electrical conductivity can be obtained. The electrode 17 may be the same material as the transparent electrode described above, or may be a metal electrode.

(Insulation layer)
The first insulating layer 13 and the second insulating layer 16 are made of tantalum oxide (TaOx) and have a thickness of about 50 to 500 nm. This film thickness is sufficiently thick so as to cover the unevenness of the surface of the transparent electrode 12 as a base and ensure a smooth morphology, and thin enough to obtain a strong electric field at a low voltage. The first insulating layer 13 and the second insulating layer 16 are not limited to this, and can be selected from silicon nitride, silicon oxide, yttrium oxide, alumina, hafnium oxide, barium tantalum oxide, and the like. is there.

(About adhesion layer)
The adhesion layer 14 is a layer having a Young's modulus equal to or less than that of ZnS or ZnSe which is the shell layer 23 in the quantum dot 21. In general, the Young's modulus may show different values depending on the crystal orientation and the like even if it is the same material, but the Young's modulus in the present invention means the Young's modulus in the direction perpendicular to the surface of the adhesion layer and the shell layer. Point to. The Young's modulus (E) of ZnS and ZnSe are 74.5 GPa and 67.2 GPa in sequence. In the present embodiment, the Young's modulus of the material of the adhesion layer 14 is preferably 1 to 100 GPa from the viewpoint of protecting the quantum dots 21 and filling the gaps between the quantum dots 21. Moreover, it is preferable that the film thickness of the contact | adherence layer 14 is a dimension of 0.1-20.0 nm. The material of the adhesion layer 14 is preferably a continuous film, but in the case of crystal grains, it is necessary to have a diameter (for example, 1 nm or less) that can enter the gap between the quantum dots 21.

  As a material for the adhesion layer 14, in addition to the above conditions, the conduction band edge level as a negative charge energy level is larger than the conduction band edge level of the material of the core portion 22 of the quantum dot 21 (for example, CdSe), It is preferable to select a valence band edge level smaller than that of the material of the core portion 22.

  The material of the adhesion layer 14 preferably contains at least one kind of atom selected from Group II, Group III, Group V, and Group VI. Further, the material of the adhesion layer 14 is preferably such that the difference in lattice constant with the material of the shell layer 23 in the quantum dots 21 is within 5%, and may be the same material as the material of the shell layer 23.

  Specifically, as the adhesion layer 14, a single atomic layer made of a single element of sulfur (S), selenium (Se), arsenic (As), or phosphorus (P), or a material having the above-mentioned conditions for these single elements. It is good also as a layer to contain. Further, a second adhesion layer made of the same material as that of the adhesion layer 14 may be further interposed between the adhesion layer 14 and the first insulating layer 13. The second adhesion layer may be a metal film having a thickness of about 0.1 to 5 nm. Furthermore, a third adhesion layer made of the same material as that of the adhesion layer 14 may be interposed between the second adhesion layer and the first insulating layer 13. The thickness of the third adhesion layer is suitably about 0.1 to 5 nm.

(About flattening layer)
In the present embodiment, the material of the planarization layer 15 is the same as the material of the adhesion layer 14. In addition to protecting the quantum dots 21 and filling the gaps between the quantum dots 21, the planarization layer 15 fills the unevenness on the surface of the light emitting active layer 20 formed by stacking the quantum dots 21 and flattens the surface.

  As a material for the planarization layer 15, in addition to the above conditions, the conduction band edge level is larger than the conduction band edge level of the material of the core portion 22 of the quantum dot 21 (for example, CdSe), and the valence band edge level is It is preferable to select a material smaller than the valence band edge level of the material of the core portion 22. The material of the planarizing layer 15 preferably contains at least one kind of atom selected from Group II, Group III, Group V, and Group VI. Furthermore, the material of the planarizing layer 15 is preferably such that the difference in lattice constant with the material of the shell layer 23 in the quantum dots 21 is within 5%, and may be the same material as the shell layer 23.

  Specifically, as the planarizing layer 15, a single atomic layer made of a single element of sulfur (S), selenium (Se), arsenic (As), or phosphorus (P), or a material having the above-mentioned conditions for these single elements It is good also as a layer containing. Further, a second planarizing layer made of the same material as that of the planarizing layer 15 may be interposed between the planarizing layer 15 and the second insulating layer 16. The second planarization layer may be a metal film having a thickness of about 0.1 to 5 nm. Further, a third planarizing layer made of the same material as the planarizing layer 15 may be interposed between the second planarizing layer 15 and the second insulating layer 16. The thickness of the third planarizing layer is suitably about 0.1 to 5 nm. In addition, by setting the band offset between the shell material and the planarization layer to 0.1 eV or less, it is possible to promote the movement of carriers and suppress the formation of space charges.

(Operation / Effect of Electroluminescent Device According to First Embodiment)
In the present embodiment, since the adhesion layer 14 protrudes so as to enter the gap between the quantum dots 21, the adhesion layer 14 and the light emitting active layer 20 (quantum dots 21) can be kept in a tightly bonded state. It is easy to transport carriers to the light emitting active layer 20 (quantum dots 21). In addition, since the adhesion layer 14 is interposed between the light emitting active layer 20 and the first insulating layer 13, there is an effect of promoting the generation of carriers at the interface between the adhesion layer 14 and the first insulating layer 13. is there. Therefore, in the present embodiment, the light emission intensity from the light emitting active layer 20 can be improved.

  In particular, since the adhesion layer 14 is made of an inorganic layer having a Young's modulus equal to or less than the Young's modulus of the material of the shell layer 23 in the quantum dots 21, the adhesion layer 14 adheres to the gap between the quantum dots 21 at the bonding surface with the light emitting active layer 20. It becomes easy to let the material of the layer 14 enter. Therefore, the quantum dots 21 can be prevented from being deformed or damaged by the adhesion layer 14. As a result, the size and shape of the quantum dots 21 do not change, and the color of light emitted from the quantum dots 21 can be prevented from changing. In such an electroluminescent element 10A, since the emission spectrum from the quantum dot 21 has a wavelength derived from the quantum dot 21, the effect of preventing the emission spectrum from becoming a broadband is achieved.

  When the adhesion layer 14 is made of a relatively soft inorganic layer having a Young's modulus equal to or lower than the Young's modulus of the material of the shell layer 23 in the quantum dot 21, the quantum dot 21 is formed using the ES-IBD method. Can prevent the quantum dots 21 from being changed by collision. In addition, even when the light emitting active layer 20 including the quantum dots 21 is formed on the adhesion layer 14 without using such an ES-IBD method, the adhesion layer 14 is formed by applying pressure in the thickness direction. It is possible to enter the gap between the 21 members. Also in this case, the adhesion layer 14 is projected so as to enter the gap between the quantum dots 21, the adhesion layer 14 and the quantum dot 21 are in a tightly bonded state, and a structure that facilitates transport of carriers to the light emitting active layer 20 can be achieved. . Therefore, the light emission intensity from the light emitting active layer 20 can be improved.

  Further, the difference in lattice constant between the material of the adhesion layer 14 and the material of the shell layer 23 may be limited to 5% or less. In this case, it is possible to make the bonding with good consistency without disturbing the continuity of the interface between the crystal structure of the adhesion layer 14 and the crystal structure of the shell layer 23 and without forming lattice defects or the interface and the accompanying levels. Therefore, the generation of emission peaks other than the emission spectrum derived from the confinement levels in the quantum dots 21 can be suppressed. In addition, the material of the adhesion layer 14 and the material of the shell layer 23 are similar substances from the viewpoint of the lattice constant. For this reason, when the quantum dots 21 are deposited, defects in the shell layer 23 can be repaired by the material of the adhesion layer 14, the surface can be terminated, and voids can be embedded with the material of the adhesion layer 14. Thus, by limiting the difference in lattice constant between the material of the adhesion layer 14 and the material of the shell layer 23 to 5% or less, the continuity between the quantum dots 21 and the adhesion layer 14 can be provided.

  Furthermore, as described above, by laminating a plurality of the adhesion layers 14, it can be expected that the generation of carriers is promoted from the interface state between these layers. Therefore, the number of injected carriers that contribute to light emission per unit time in the quantum dots 21 can be increased, and application to applications that require higher luminance is possible.

  As in the first embodiment, the planarization layer 15 is formed on the other surface side of the light emitting active layer 20 to correct the unevenness of the surface of the light emitting active layer 20 after film formation. The flatness of the second insulating layer 16 formed thereon can be improved. Therefore, the electrode 17 formed on the second insulating layer 16 can also be formed flat. For this reason, since the distance between the electrode 17 and the light emitting active layer 20 is uniform within the light emitting region (or pixel region), dielectric breakdown is less likely to occur and the in-plane uniformity of the electric field strength can be improved. Therefore, when the present invention is applied to a self-luminous flat display, a bright spot or dark spot is partially generated in the display area (or pixel area), or the in-plane uniformity of display characteristics is impaired. Can be removed.

(Method for manufacturing electroluminescent element)
Next, a method for manufacturing the electroluminescent element according to this embodiment will be described with reference to FIGS.

<First electrode forming step>
As shown in FIG. 2, a glass substrate 11 on which a transparent electrode 12 made of ITO is formed in advance is prepared, or a transparent electrode 12 made of ITO is formed on the glass substrate 11. In the present embodiment, the transparent electrode 12 has a film thickness of, for example, 100 nm and a surface roughness Ra of, for example, about 5 nm. The glass substrate 11 is subjected to ultrasonic cleaning with an organic solvent, and then blown and dried with an inert gas.

<First insulating layer forming step>
Thereafter, as shown in FIG. 3, the first insulating layer 13 is formed on the transparent electrode 12 with an insulator such as tantalum oxide (TaOx). For example, when using a TaOx film, the film was formed by reactive sputtering in an Ar + O ₂ mixed gas atmosphere of a metal Ta target using a normal high frequency (13.56 MHz) magnetron sputtering apparatus. The temperature of the substrate during deposition was from room temperature to 200 ° C. The film thickness is 50 to 500 nm as a thickness that is sufficiently thick so as to cover the surface irregularities of the transparent electrode 12 as a base and ensure a smooth morphology and sufficiently thin to obtain a strong electric field at a low voltage. did.

<Adhesion layer formation process>
Next, as shown in FIG. 4, the adhesion layer 14 is formed on the first insulating layer 13. The adhesion layer 14 was formed by depositing sulfur (S) by a molecular beam epitaxy (MBE) method or a normal vacuum deposition method. A sulfur (S) source is heated to 100 to 200 ° C. in a synthetic quartz cell with a flow control valve, and the resulting sulfur gas is heated to 400 to 1000 ° C., and then 2 × 10 ⁻⁷ to 1 × 10 ⁻⁵ Torr. The pressure flux was obtained. Each was irradiated on the board | substrate after 1st insulating layer 13 formation, and the contact | adherence layer 14 which consists of S was formed. The temperature of the substrate was appropriately determined between room temperature and 80 ° C., and the film thickness was set to 1 to 3 nm.

  Here, prior to the description of the light emitting active layer forming step, an ES-IBD device used in the light emitting active layer forming step will be described with reference to FIG.

About ES-IBD equipment
Here, in order to clarify the embodiment and the examples to be described later, the ES-IBD apparatus will be described with reference to FIG. This ES-IBD apparatus is a film forming apparatus to which an ES-IBD method is applied.

  In this ES-IBD apparatus, first, a solution containing quantum dots 21 is supplied to a microsyringe pump. The microsyringe pump 2 extrudes the fine particle dispersion solution 1 in the cylindrical main body 2b by a piston 2a, sends it to the capillary 3 through the tube 2c, and discharges it from the capillary tip 3a. A predetermined voltage can be applied to the capillary 3 by the voltage applying means 3b. The solution supply rate by the microsyringe pump 2 is 0.5 to 4 μl / min (preferably 1 to 2 μl / min).

  Further, although not shown, the capillary 3 is provided with a micrometer in the X, Y, and Z directions, and the position of the capillary tip 3a can be finely adjusted. Although the above-described configuration is used as the capillary, in this embodiment, the capillary is defined as a solution delivery device that exposes the surface of the solution by capillary action or wetting phenomenon.

  The fine particle dispersion discharged from the capillary tip 3 a is introduced into the decompression chamber 4 through the jet nozzle 4 a provided at the upstream tip of the decompression chamber 4, and further provided at the upstream tip of the film forming chamber 5. It is introduced into the film forming chamber 5 through the skimmer nozzle 5a. The distance between the capillary tip 3a and the jet nozzle 4a is set to 0 to 50 mm, preferably 4 to 10 mm. In this embodiment, the distance is set to 8 mm.

  Note that the pressure between the capillary tip and the jet nozzle is almost atmospheric pressure. A capillary tip 3a having an inner diameter of 20 μm was used. The center positions of the jet nozzle 4a and the skimmer nozzle 5a coincide with each other, and the distance between the jet nozzle 4a and the skimmer nozzle 5a is appropriately set between 1 and 10 mm (in this embodiment, 3 mm). A predetermined voltage can be applied to the jet nozzle 4a and the skimmer nozzle 5a by voltage applying means 4c and 5c, respectively.

  The film forming chamber 5 includes an ion optical system region 51 and a high vacuum region 52. The ion optical system region 51 and the high vacuum region 52 are partitioned by a partition wall 5e having an opening 5b, and their reference axes (center axes in the direction in which the fine particles travel) are orthogonal to each other. Particles can move through the opening 5b. The diameter of the opening 5b was 20 mm.

The decompression chamber 4, the ion optical system region 51, and the high vacuum region 52 are evacuated through the exhaust ports 4d, 51d, and 52d so as to maintain an appropriate degree of vacuum by a vacuum pump (not shown). For example, differential evacuation means is used for these evacuations, whereby the pressure has a relationship of “capillary tip (atmospheric pressure)> depressurization chamber> ion optical system region> high vacuum region”. Here, the pressure in the decompression chamber was set to 1 Torr, the pressure in the ion optical system region was set to 1 × 10 ⁻⁵ Torr, and the pressure in the high vacuum region was set to about 1 × 10 ⁻⁶ Torr.

Here, the differential exhaust is performed as follows. That is, an area from the jet nozzle 4a (φ0.5 mm) to the skimmer nozzle 5a (φ0.7 mm) is exhausted by a mechanical booster pump or a rotary pump having an exhaust speed of about 100 to 500 [m ³ / h], and about 1 [ The vacuum state of about 10 ⁻⁴ [Torr] is obtained by maintaining the vacuum state of about Torr] and exhausting the ion optical system region 51 corresponding to the subsequent stage by a turbo molecular pump of about 300 to 1000 [L / s]. Try to keep. Further, an orifice having a diameter of about 20 mm and a thickness of several mm is provided between the ion optical region 51 and the high vacuum region 52 (region for film formation), and the high vacuum region is about 1000 to 2000 [L / s]. By exhausting with a pump or the like, this region is maintained in a high vacuum state of about 10 ⁻⁶ [Torr].

  In the ion optical system region 51, an electric field type ion lens 6 as a lens device and an energy separation device 71 as a separation device are provided on the coaxial extension of the jet nozzle 4a and the skimmer nozzle 5a. The electrolytic ion lens 6 is an Einzel lens composed of three cylindrical electrodes 6a, 6b and 6c. A voltage can be applied to the cylindrical electrodes 6a and 6b by voltage applying means 6d and 6e. The cylindrical electrode 6c is set to ground potential. The electric field type ion lens 6 has a function of focusing the ion beam. Here, although the electric field type ion lens 6 functions as long as it is one or more, it is composed of three cylindrical electrodes 6a, 6b, 6c having the same diameter as in the present embodiment, each of which is coaxial. It is preferable that they are installed in an array structure. By controlling the voltage applied to the three electric field type ion lenses, it serves as a focusing electrode for the ion beam. The voltage to be applied is appropriately determined depending on the type (size, molecular weight, etc.) of the fine particles. Needless to focus the fine particles, it is also effective to focus light ions such as solvent molecular ions so that they can be efficiently removed in a subsequent process (for example, magnetic field generation means, energy separation means, etc.).

  In the present embodiment, an energy separation device 71 is used as the separation device. The energy separation device 71 includes a first electrode plate 71a set at a ground potential and a second electrode plate 71b disposed in parallel with a predetermined distance from the first electrode plate 71a.

  The first electrode plate 71a is provided with an entrance hole 71c and an exit hole 71d. The incident hole 71c is on the coaxial extension of the jet nozzle 4a and the skimmer nozzle 5a. The second electrode plate 71b is set to a predetermined potential by the voltage applying means 71e.

  The energy separator 71 bends the ion beam incident on the incident hole 71c to a predetermined angle, classifies fine particles having a desired energy, and emits the fine particles from the emission hole 71d. The bending angle is preferably 90 degrees because the highest resolution can be obtained. The energy separation device 71 allows components having a small mass number (for example, solvent molecular ions or side chain molecular ions) or flying before fine particles emitted from the capillary tip 3a reach the deposition target substrate (glass substrate) 11. It has the role (mass, energy separation function) of removing the agglomerates of organic molecules that also become fine particles, solvents, and side chain materials.

The energy separation device 71 is a separation mechanism using electrostatic deflection. When trying to obtain a certain amount of electrostatic deflection, the deflection voltage is proportional to the kinetic energy of the charged particles. Therefore, the kinetic energy of charged particles can be separated by the deflection voltage. In the apparatus shown in FIG. 11, a parallel plate electrode structure is used. One electrode 71a has two openings, one is an incident hole 71c and the other is an emission hole 71d. A voltage ± V _d for decelerating charged particles (+ V _d when the charged particles are positive ions, −V _d when the charged particles are negative ions) is applied to the electrode 71b that does not have an opening. First, a charged particle beam is incident obliquely from the entrance hole, and the charged particle entering the electrode is repelled and emitted when it has a specific value (energy value) determined by the kinetic energy of the particle. It exits from the hole. Here, since the energy value is determined by the distance between the electrodes, the distance between the holes, and the voltage, the energy value to be classified can be determined by changing these parameters.

Here, the operation of the energy separation device 71 will be briefly described. The capillary 3 and the counter electrode (jet nozzle capable of applying a voltage here) can form an electric field between the solution supply device and the decompression chamber, and can be said to be a so-called electrospray device. The fluid flow containing ions discharged from the electrospray can be said to form a free jet when introduced into the jet nozzle 4a. In other words, the ionic species generated by this electrospray ride on a free jet of gas and are introduced into the vacuum. At that time (the free jet has a viscosity of λ ₀ (mean free path) <D (orifice aperture)). The velocity of the flow is generally determined by changing all the enthalpy that the gas had before expansion into translational energy by an adiabatic process. The mean free path of air (also diatomic molecules such as nitrogen and oxygen) is about 10 ⁻⁷ [m], and a free jet can be formed by introducing it into a vacuum through an orifice of several hundred μm. At this time, the velocity v [m / s] of the free jet is a function of the distance x [m] from the orifice,
v = {3.65 (x / D) ^2/5 −0.82 (x / D) ^−2/5 } {γkT / m}, T = T ₀ (P ₀ / P) ^{(1−γ) / γ}
D: Orifice diameter [m] ≈5 × 10 ⁻⁴ [m]
γ: Specific heat ratio of gas ≒ 1.4
T: Jet temperature [K]
T ₀ : temperature of the introduced gas [K] ≈3 × 10 ² [K]
P: Pressure on the low pressure side of the orifice [Pa] ≈1 × 10 ² [Pa]
P ₀ : Pressure on the high pressure side of the orifice [Pa] ≈1 × 10 ⁵ [Pa]
And a value of about 10 ³ [m / s].

In the case of a mixture, the velocity of the main gas (this time air) in the free jet and the other mixture will fly at almost the same speed. Therefore, the heavy component has very high kinetic energy (in fact, the larger the differential pressure (pressing pressure) at the orifice, the smaller the difference in velocity due to mass, and the sharper the velocity distribution of the heavy molecule). Also, some speed differences, temperature differences, and heavy things on the central axis of the jet will become rich, but can be ignored here. On the other hand, the electric field mobility η = v / E (E is an electric field) of fine particles (diameter number [nm]) in this gas (viscosity coefficient is about 2 × 10 ⁻⁵ [Pa · s]) is P ≈1 When x10 ⁵ [Pa], approximately η≈10 ⁻⁵ [m ² / s · V], and when P≈1 × 10 ² [Pa], approximately η≈10 ⁻² [m ² / s · V] Is the value of

Therefore, due to the contribution of an applied electric field (about 10 ⁶ [V / m]) used for electrospray on the high pressure side of the orifice and an applied electric field (about 10 ⁴ [V / m]) used for glow discharge on the low pressure side of the orifice. The terminal speeds are about 10 ¹ [m / s] and about 10 ² [m / s], respectively. Further, in the ion optical system region before the energy separation mechanism, the electrostatic potential is the same in the initial state and the final state, and therefore, acceleration / deceleration due to the electric field does not occur during this period. Therefore, the ions that enter the energy separation mechanism have a device configuration that gives almost the same velocity regardless of the type. Needless to say, the present invention is not limited to this embodiment, and an energy separation mechanism can be configured in which an additional acceleration mechanism is inserted in the ion beam path and the energy added in the mechanism is taken into consideration.

In the energy separation mechanism, when particles enter the entrance hole and jump out of the exit hole,
L = 2V ₀ / V _d · sin 2α
It is. here,
L: Distance between the holes provided in the electrodes (this time 26.5 mm)
α: Incident angle (45 degrees this time)
V ₀ : acceleration voltage of charged particles (V ₀ = E _m / q, E _m : kinetic energy, q: charge)
V _d : Since the voltage L and α for decelerating charged particles are constant, V ₀ can be analyzed by V _d .
Also, V ₀ = E _m / q
E _m = (mv ² ) / 2
More ^{_{V 0 = (mv 2) /}} 2q = a ^{(m / q) · (v} 2/2), v are as described earlier, since considered the free jet in with all of the ion substantially the same speed, Separating energy with this device means separating the mass-to-charge ratio m / q (mass / charge).

  In the high vacuum region 52, a substrate holder 52g for holding the glass substrate 11, a converging electrode 52b as a converging device for converging the charged particle beam toward the glass substrate 11, and the converged charged particle beam are decelerated. And a deceleration electrode 52c as a deceleration device to be deposited on the glass substrate 11 is provided. The exit hole 71d of the energy separator 71—the opening 5b of the partition wall 5a, the converging electrodes 52a and 52b, and the deceleration electrode 52c are each provided on a coaxial extension.

<Light emitting active layer forming step>
Using the above-described ES-IBD apparatus, the light emitting active layer forming step described below is performed. In the light emitting active layer forming step, the light emitting active layer 20 is formed on the adhesion layer 14 as shown in FIG. 5 using the above-described ES-IBD apparatus. The diameter of the quantum dot 21 having a structure in which the core portion 22 is covered with the shell layer 23 used in the present embodiment is about 1.9 to 5.2 nm, and this forms a single monovalent ion. Even in that case, the energy is 1.4 × 10 ^{2 to} 9.8 × 10 ³ eV (typically 1.7 × 10 ^{2 to} 3.4 × 10 ³ eV). When ions having excessive energy directly collide with the substrate surface, the dissipated energy inevitably alters the substrate and the nanocrystal. Therefore, a mechanism may be adopted in which the surface of the substrate is insulated from the ground potential, the potential is increased spontaneously by the charge of the reached ions, and ions that arrive thereafter are decelerated.

  In the present embodiment, since the quantum dots 21 are irradiated and deposited on the adhesion layer 14 as an ion beam, deformation of the quantum dots 21 can be suppressed by the above-described physical characteristics of the adhesion layer 14. FIG. 8 shows a state where the surface of the adhesion layer 14 is recessed to a predetermined depth. Then, the light emitting active layer 20 as shown in FIG. 9 is formed by continuously irradiating the quantum dots 21 with the ES-IBD apparatus. On the lower surface side of the light emitting active layer 20, the upper surface of the adhesion layer 14 protrudes into the gap between the quantum dots 21 and is in close contact so as to fill the gap.

<Planarization layer formation process>
Next, as shown in FIGS. 6 and 10, the planarization layer 15 is formed on the light emitting active layer 20. In the present embodiment, sulfur (S) is used as the material of the planarizing layer 15 as in the case of the material of the adhesion layer 14. As a method for forming the planarizing layer 15, any one of an electron beam epitaxy method, a vacuum deposition method, and a sputtering method is used. In the step of forming the planarization layer 15, it is preferable to set the temperature to a high temperature within a range where the quantum dots 21 are not deteriorated so as to prevent impurities from being mixed into the planarization layer 15 and to facilitate planarization.

<Second insulating layer forming step and second electrode forming step>
FIG. 7 shows a first insulating layer forming step and a second electrode forming step. After the second insulating layer 16 is formed on the planarizing layer 15 by the same material and method as the first insulating layer 13, an electrode 17 made of Au as a second electrode is formed by a vapor deposition method.

  As mentioned above, although the manufacturing method of the electroluminescent element which concerns on 1st Embodiment was demonstrated, the contact | adherence layer 14 and the quantum dot 21 can maintain the state joined closely by performing the light emission active layer formation process. It becomes easier to transport carriers to the light emitting active layer 20. In addition, if the adhesive layer 14 is interposed between the light emitting active layer 20 and the first insulating layer 13 in this manner, the generation of carriers at the interface between the adhesive layer 14 and the first insulating layer 13 is promoted. There is an effect. Therefore, in the present embodiment, the light emission intensity from the light emitting active layer 20 can be improved. In particular, the adhesion layer 14 is composed of a layer having a Young's modulus equal to or lower than the Young's modulus of the shell layer 23 in the quantum dots 21, and therefore, as shown in FIG. It becomes easy to allow the material of the adhesion layer 14 to enter the gap. Therefore, the quantum dots 21 can be prevented from being deformed or damaged by the adhesion layer 14. As a result, the size of the quantum dot 21 does not change, and the color of the light emitted from the quantum dot 21 can be prevented from changing. In such an electroluminescent element 10A, since the emission spectrum from the quantum dot 21 has a wavelength derived from the quantum dot 21, the effect of preventing the emission spectrum from becoming a broadband is achieved.

  In the first embodiment, since the light emitting active layer 20 is covered with the planarizing layer 15, the unevenness of the surface of the light emitting active layer 20 after film formation is corrected, for example, a film is formed thereon. The flatness of the second insulating layer 16 and the electrode 17 can be improved. Therefore, since the distance between the electrode 17 and the light emitting active layer 20 is uniform in the light emitting region plane, dielectric breakdown is less likely to occur, and the in-plane uniformity of the electric field strength can be improved.

[Second Embodiment]
(Schematic configuration of electroluminescent element)
The electroluminescent element according to the second embodiment of the present invention includes, in addition to the first embodiment, between the first insulating layer 13 and the adhesion layer 14 and the planarizing layer 15 and the second insulating layer 16. Each of the electroluminescent elements has a buffer layer therebetween. The electroluminescent element of the second embodiment is an element that can obtain higher emission luminance.

(Method for manufacturing electroluminescent element)
Since the manufacturing method of the electroluminescent element of this embodiment can be manufactured in the same manner as the element of the first embodiment except for the buffer layer forming process, only the buffer layer forming process will be described here.
On the first insulating layer 13 (50 to 500 nm TaOx), 10 nm ZnS was formed as a first buffer layer. ZnS was formed by the MBE method. An adhesion layer 14 (1 to 3 nm S) was formed on the first buffer layer.
Also, 10 nm of ZnS was formed as the second buffer layer on the planarizing layer 15 (1 to 3 nm of S). ZnS was formed by the MBE method. A second insulating layer (TaOx of 50 to 500 nm) was formed on the second buffer layer.
The electroluminescent element of the present embodiment thus obtained has substantially the same emission spectrum and higher emission luminance than the electroluminescent element of the first embodiment.

<Experimental Examples 1-5>
In the configuration of the electroluminescent element 10A according to the first embodiment, when the adhesion layer 14 and the planarization layer 15 sandwiching the light emitting active layer 20 are not present (Comparative Example 1), the adhesion layer 14 and the planarization layer 15 Both materials were prepared from ZnS. The thicknesses of the adhesion layer 14 and the planarization layer 15 are 1.25 nm (Experimental Example 1), 2.5 nm (Experimental Example 2), 5.0 nm (Experimental Example 3), and 20.0 nm (Experimental Example). 4) Electroluminescent devices of Experimental Examples 1 to 5 different from 80 nm (Experimental Example 5) were produced, and the behavior was observed. In addition, an element (Comparative Example 2) in which both the adhesion layer 14 and the flattening layer 15 were Ta ₂ O ₅ (Young's modulus 133 GPa) of 5.0 nm was fabricated, and the behavior was observed.

  As a result, as shown in FIGS. 13 to 17, the behavior is changed (different) in Experimental Examples 1 to 5 as compared with Comparative Example 1 in which the adhesion layer 14 and the planarization layer 15 are not provided, and 1.25 nm to 5. It was confirmed that the electroluminescence device up to 0 nm has the effect of increasing the emission intensity and narrowing the emission spectrum. Although the results of Example 1 and Example 3 are not shown, a spectrum equivalent to that of Example 2 was observed. On the other hand, when the adhesion layer 14 and the flattening layer 15 having a thickness of 20.0 nm or more were interposed, a spectrum including an emission peak different from that of the quantum dots 21 was observed. Therefore, it was found that the thickness of the adhesion layer 14 and the planarization layer 15 is desirably less than 20.0 nm. Further, it was found that by depositing the planarization layer 15, the material of the planarization layer 15 fills the gaps between the quantum dots 21, so that the carrier transfer efficiency in the light emitting active layer 20 is improved. In Comparative Example 2, the emission spectrum was very wide, and the emission luminance was considerably reduced as compared with each Example.

  Similarly, elementary electroluminescent elements using Zn, Se, and S as the adhesion layer 14 and the planarizing layer 15 were produced. Here, an element in which the adhesion layer 14 and the planarization layer 15 have a film thickness of 1.25 nm and a film thickness of 10.0 nm, respectively, was manufactured. When the emission spectrum was measured for each of the created elements, the emission intensity increased compared to the comparative example and the effect of narrowing the emission spectrum was confirmed in each element as in Experimental Examples 1 to 3.

<Experimental example 6>
In the configuration of the electroluminescent element 10A according to the first embodiment, an electroluminescent element having a structure in which the planarizing layer 15 is not provided and only the adhesion layer 14 is interposed is manufactured, and the AC driving is performed to change the emission intensity over time. Decomposed and observed. The result is as shown in FIG. From this result, since strong light emission is observed only on one side of one reciprocating electric field of alternating current, a certain effect can be obtained to improve the light emission intensity even if only the adhesion layer 14 is interposed. I found it preferable.

[Third embodiment]
FIG. 12 is an explanatory cross-sectional view showing an electroluminescent element 10B according to a third embodiment of the present invention. In the present embodiment, the substrate is not glass but a silicon substrate 18 is used. The electroluminescent element 10B according to the present embodiment has an electrode 17, a first insulating layer 13, an adhesion layer 14, a light emitting active layer 20, a planarizing layer 15, a second insulating layer 16, and a silicon substrate 18 in order. A transparent electrode 12 is formed. In the electroluminescent element 10B of the present embodiment, light emission is emitted to the transparent electrode 12 side.

Since the operation, operation, and effect of the electroluminescent element 10B according to the present embodiment are substantially the same as those of the first embodiment, description thereof is omitted.
[Other embodiments]

  Although the first to third embodiments of the present invention have been described above, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the above embodiment, the adhesion layer 14 is formed of sulfur (S), but is not limited thereto, and may be a single atomic layer such as Se, As, P, or various kinds of materials such as ZnS and ZnSe. It may be a composite atomic layer. Using ZnS as the material of the adhesion layer 14 and the planarization layer 15 can improve carrier generation efficiency, carrier movement efficiency, the repair effect of the quantum dots 21 and the like, and realize a colorless and transparent display for visible light. Is also possible.

  Further, as the adhesion layer 14, the conduction band edge level is larger than the conduction band edge level of the material of the core portion 22 of the quantum dot 21, and the valence band edge level is the valence band edge level of the material of the core portion 22. It may be a layer containing at least one kind of atom selected from, for example, Group II, Group III, Group V, and Group VI, which is smaller than the position. Further, the material of the adhesion layer 14 may be selected from inorganic materials having a lattice constant difference of 5% or less from the material of the shell layer 23. Further, the material of the adhesion layer 14 may be selected from materials whose band offset with respect to the shell is 0.1 eV or less. The planarization layer 15 can also be made of the same material as that of the adhesion layer 14 as long as the planarization layer 15 can be planarized according to the film formation conditions. In the above embodiment, the adhesion layer 14 and the planarization layer 15 are formed of the same material, but may be formed using different materials.

  In the second embodiment, the silicon substrate 18 having an opaque substrate is used. However, other inorganic materials may be used as long as the electrode 17 can be formed using an opaque material. It is also possible to apply a flexible plastic substrate.

DESCRIPTION OF SYMBOLS 10A, 10B ... Electroluminescent element 11 ... Glass substrate 12 ... Transparent electrode 13 ... 1st insulating layer 14 ... Adhesion layer 15 ... Planarization layer 16 ... 2nd insulating layer 17 ... Electrode 18 ... Silicon substrate 20 ... Luminescence active layer 30 ... AC drive source

Claims (10)

An insulating layer is disposed on at least one surface side of a light emitting active layer including a quantum dot having a structure in which the surface of the core portion is covered with a shell layer, and a pair of electrodes sandwiching the light emitting active layer and the insulating layer in a thickness direction is provided. An electroluminescent element that emits light from the light emitting active layer by applying an alternating voltage to the pair of electrodes,
On the lower surface side of the light emitting active layer, an inorganic layer having a Young's modulus equal to or lower than the Young's modulus of the shell layer, and the bonding surface with the light emitting active layer protrudes so as to enter the gap between quantum dots. An electroluminescent element characterized in that an adhesion layer that adheres to each other is formed.   The shell layer is made of ZnS, ZnSe, CdS, or a compound or mixed crystal selected from Zn, Cd, S, Se, or a compound or mixed crystal selected from In, Ga, P, Si, Ge, Sn, As. The electroluminescent device according to claim 1, wherein the adhesion layer has a Young's modulus of 1 to 100 GPa.   The electroluminescent device according to claim 1, wherein the light emitting active layer is formed by depositing the quantum dots on the adhesion layer by an ES-IBD method.   The material of the adhesion layer has a conduction band edge level larger than a conduction band edge level of the material of the core part of the quantum dot, and a valence band edge level of the material of the core part than a valence band edge level of the material of the core part. The electroluminescent element according to claim 1, wherein the electroluminescent element is also small.   5. The electroluminescent element according to claim 1, wherein a material of the adhesion layer has a difference in lattice constant within 5% from a material of the shell layer. 6.   6. The electroluminescent element according to claim 1, wherein the material of the adhesion layer has a band offset of 0.1 eV or less with respect to the material of the shell layer.   The electroluminescent element according to any one of claims 1 to 6, wherein the adhesion layer has a structure in which a plurality of layers are laminated.   8. A planarizing layer made of an inorganic material, which is planarized so as to cover the light emitting active layer, is formed on the surface side above the light emitting active layer. The electroluminescent element according to claim 1.   The electroluminescent device according to claim 7, wherein a material of the planarizing layer is the same as a material of the adhesion layer. An insulating layer is laminated on at least one surface side of a light emitting active layer including a quantum dot having a structure in which a surface of a core portion is covered with a shell layer, and a pair of electrodes sandwiching the light emitting active layer and the insulating layer in a thickness direction is provided. A method of manufacturing an electroluminescent element that emits light from the light emitting active layer by applying an alternating voltage to the pair of electrodes,
A first electrode forming step of forming a first electrode on the substrate;
An adhesion layer made of an inorganic layer having a Young's modulus equal to or lower than the Young's modulus of the shell layer, which is applied after the first electrode forming step and before the light emitting active layer forming step of forming the light emitting active layer. An adhesion layer forming step to be formed;
A light emitting active layer forming step of forming a light emitting active layer by depositing the quantum dots continuously irradiated by an ES-IBD method on the surface of the adhesive layer;
A planarizing layer forming step of forming a planarizing layer made of an inorganic material having a band offset with respect to the shell layer of 0.1 eV on the light emitting active layer so as to have surface flatness;
A second electrode forming step of forming a second electrode applied after the planarizing layer forming step;
A method for manufacturing an electroluminescent element, comprising:

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