Dielectric mirror and manufacturing the same

Abstract

One embodiment of the present invention provides a dielectric mirror comprising at least one first thin film including quantum dots and a first ligand bonded to the surface of each of the quantum dots, and at least one second thin film including the quantum dots and a second ligand bonded to the surface of each of the quantum dots, wherein the at least one first thin film and the at least one second thin film are alternately stacked, and the length of the first ligand and the length of the second ligand are different.

Description

Technology Field

[0001] The present invention relates to a dielectric mirror, and more specifically, to a dielectric mirror comprising thin films with different refractive indices. Background Technology

[0002] A dielectric mirror is a reflector that possesses high reflectivity in a specific wavelength band by stacking thin films with different refractive indices. Generally, a dielectric mirror is formed by stacking one or more pairs of thin films, each containing a film with a high refractive index and a film with a low refractive index. Light incident on the dielectric mirror is reflected at the interfaces of each film, and the reflected light can undergo constructive interference. In this case, the reflection band with high reflectivity is called the stop band, and the width of the stop band can be controlled by adjusting the difference in refractive index between the two films forming the pair.

[0003] Dielectric mirrors can be applied to optoelectronic devices such as optical sensors, solar cells, light-emitting diodes, and laser diodes, as well as optical devices including optical filters. The problem to be solved

[0004] When forming thin films using conventional thermal deposition or chemical vapor deposition methods, there is a problem in that not only can devices coupled to dielectric mirrors (e.g., diodes) be damaged due to the high temperature and high vacuum process environment, but manufacturing costs also increase.

[0005] The present invention aims to solve various problems, including those mentioned above, by providing a dielectric mirror having high reflectivity while lowering manufacturing costs and a method for manufacturing the same. However, these problems are exemplary and do not limit the scope of the present invention. means of solving the problem

[0006] According to one aspect of the present invention, a dielectric mirror is provided comprising: at least one first thin film including quantum dots and a first ligand bonded to the surface of each of the quantum dots; and at least one second thin film including quantum dots and a second ligand bonded to the surface of each of the quantum dots, wherein the at least one first thin film and the at least one second thin film are alternately stacked, and the length of the first ligand and the length of the second ligand are different.

[0007] In one embodiment, the quantum dot has a first refractive index, the first ligand has a second refractive index, the second ligand has a third refractive index, each of the at least one first thin film has a first effective refractive index between the first refractive index and the second refractive index, each of the at least one second thin film has a second effective refractive index between the first refractive index and the third refractive index, and the first effective refractive index and the second effective refractive index may be different.

[0008] In one embodiment, the first effective refractive index is determined by the volume ratio of the quantum dots in the first thin film to the volume of the first ligand, and the second effective refractive index can be determined by the volume ratio of the quantum dots in the second thin film to the volume of the second ligand.

[0009] In one embodiment, the thickness of each of the at least one first thin film may be proportional to the wavelength of the target light and inversely proportional to the first effective refractive index, and the thickness of each of the at least one second thin film may be proportional to the wavelength of the target light and inversely proportional to the second effective refractive index.

[0010] In one embodiment, the wavelength of the target light may be included in the transmission band of the quantum dots.

[0011] In one embodiment, the first ligand is any one of alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion, and the second ligand may be any one other than the first ligand among alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion.

[0012] In one embodiment, the first ligand may be oleic acid, and the second ligand may be an iodine ion.

[0013] In one embodiment, the quantum dots may be chalcogenide-based quantum dots.

[0014] According to another aspect of the present invention, a method for manufacturing a dielectric mirror is provided, comprising the steps of: forming a first colloidal solution comprising quantum dots and a first ligand bound to the surface of the quantum dots; forming a second colloidal solution comprising quantum dots and a second ligand bound to the surface of the quantum dots; forming a first thin film by coating the first colloidal solution; and forming a second thin film by coating the second colloidal solution on the first thin film, wherein the length of the first ligand and the length of the second ligand are different.

[0015] In one embodiment, the step of forming a first thin film by coating the first colloidal solution and the step of forming a second thin film by coating the second colloidal solution on the first thin film may be repeated alternately.

[0016] In one embodiment, the quantum dot has a first refractive index, the first ligand has a second refractive index, the second ligand has a third refractive index, the first thin film has a first effective refractive index between the first refractive index and the second refractive index, the second thin film has a second effective refractive index between the first refractive index and the third refractive index, and the first effective refractive index and the second effective refractive index may be different.

[0017] In one embodiment, in the step of forming the first thin film, the thickness of the first thin film may be formed to be proportional to the wavelength of the target light and inversely proportional to the first effective refractive index, and in the step of forming the second thin film, the thickness of the second thin film may be formed to be proportional to the wavelength of the target light and inversely proportional to the second effective refractive index.

[0018] In one embodiment, the quantum dots may be selected such that the wavelength of the target light is included in the transmission band of the quantum dots.

[0019] In one embodiment, the first ligand is any one of alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion, and the second ligand may be any one other than the first ligand among alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion.

[0020] In one embodiment, the first ligand may be oleic acid, and the second ligand may be an iodine ion.

[0021] In one embodiment, the quantum dots may be chalcogenide-based quantum dots.

[0022] According to another aspect of the present invention, a method for manufacturing a dielectric mirror is provided, comprising the steps of forming a first thin film on a substrate, forming a quantum dot colloidal solution comprising quantum dots and a ligand bonded to the surface of the quantum dots, and forming a second thin film by coating the quantum dot colloidal solution on the first thin film, wherein the ligand is selected such that the effective refractive index of the second thin film is different from the refractive index of the first thin film.

[0023] In one embodiment, the step of forming the first thin film and the step of forming the second thin film may be repeated alternately.

[0024] In one embodiment, the quantum dot has a first refractive index, the ligand has a second refractive index, and the second thin film may have an effective refractive index between the first refractive index and the second refractive index.

[0025] In one embodiment, in the step of forming the second thin film, the thickness of the second thin film may be formed to be proportional to the wavelength of the target light and inversely proportional to the effective refractive index.

[0026] Other aspects, features, and advantages other than those described above will become clear from the following drawings, claims, and detailed description of the invention. Effects of the invention

[0027] According to one embodiment of the present invention as described above, a dielectric mirror having high reflectivity can be realized even at a low manufacturing cost. Of course, the scope of the present invention is not limited by this effect. Brief explanation of the drawing

[0028] FIG. 1 is a cross-sectional view schematically illustrating a dielectric mirror according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a quantum dot colloid according to one embodiment of the present invention. FIG. 3 is a diagram schematically illustrating a part of a dielectric mirror according to one embodiment of the present invention. FIG. 4 is a diagram schematically illustrating the path of light at each interface of a dielectric mirror according to one embodiment of the present invention. FIG. 5 is a cross-sectional view schematically illustrating a dielectric mirror according to one embodiment of the present invention. FIG. 6 is a cross-sectional view schematically illustrating a dielectric mirror according to one embodiment of the present invention. FIG. 7 is a graph showing the refractive indices of thin films according to one embodiment of the present invention by wavelength band. FIG. 8 is a graph showing the reflectance of dielectric mirrors according to embodiments of the present invention. Specific details for implementing the invention

[0029] The present invention is capable of various modifications and may have various embodiments; specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, and the methods for achieving them, will become clear by referring to the embodiments described below in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various forms.

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. When describing with reference to the drawings, identical or corresponding components are given the same reference numerals, and redundant descriptions thereof will be omitted.

[0031] In this specification, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another.

[0032] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0033] In this specification, terms such as "include" or "have" mean that the features or components described in the specification exist, and do not preclude the possibility that one or more other features or components may be added.

[0034] In this specification, when a part such as a film, region, or component is described as being on or above another part, it includes not only cases where it is immediately above the other part, but also cases where another film, region, or component is interposed therein.

[0035] In this specification, when it is stated that a membrane, region, component, etc. is connected, it includes cases where the membrane, region, or component is directly connected, or / or cases where other membranes, regions, or components are interposed between them to form an indirect connection. For example, when it is stated that a membrane, region, or component, etc. is electrically connected in this specification, it indicates cases where the membrane, region, or component, etc. are directly electrically connected, and / or cases where other membranes, regions, or components are interposed between them to form an indirect electrical connection.

[0036] In this specification, "A and / or B" indicates the case where it is A, B, or both A and B. And, "at least one of A and B" indicates the case where it is A, B, or both A and B.

[0037] In this specification, the x direction, y direction, and z direction are not limited to directions along the three axes of an orthogonal coordinate system, but can be interpreted in a broad sense that includes them. For example, the x direction, y direction, and z direction may be orthogonal to each other, but may also refer to different directions that are not orthogonal to each other.

[0038] In this specification, "the first component overlaps" the second component, meaning that the first component is positioned above or below the second component so that at least a portion overlaps on a plane.

[0039] Where any embodiment in this specification can be implemented differently, a specific process sequence may be performed differently from the order described. For example, two processes described consecutively may be performed substantially simultaneously or proceed in the reverse order of the order described.

[0040] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, so the present invention is not necessarily limited to what is illustrated.

[0041] FIG. 1 is a cross-sectional view schematically illustrating a dielectric mirror according to one embodiment of the present invention, and FIG. 2 is a diagram schematically illustrating a quantum dot colloid according to one embodiment of the present invention. FIG. 3 is a diagram schematically illustrating a part of a dielectric mirror according to one embodiment of the present invention.

[0042] Referring to FIG. 1, the dielectric mirror (DM) may include a substrate (100) and a thin film pair (200) disposed on the substrate (100). The substrate (100) may include glass, metal, or polymer resin. In one embodiment, the substrate (100) may be a quartz or silicon substrate.

[0043] A thin film pair (200) comprising a first thin film (210) and a second thin film (220) may be disposed on a substrate (100). The first thin film (210) may be disposed on the substrate (100), and the second thin film (220) may be disposed on the first thin film (210). The first thin film (210) and the second thin film (220) may be stacked alternately in the thickness direction (a direction perpendicular to the substrate (100), e.g., the z-direction).

[0044] A dielectric mirror (DM) may have high reflectivity for light of a specific wavelength band. The wavelength band in which the dielectric mirror (DM) has high reflectivity may be represented as a reflection band. The width (or stop band) of the reflection band is determined by the effective refractive index of the first thin film (210) (hereinafter referred to as the first effective refractive index) and the effective refractive index of the second thin film (220) (hereinafter referred to as the second effective refractive index).

[0045] [Equation 1]

[0046]

[0047] Here, Δλ is the width of the reflection band, and n eff1 is the first effective refractive index, and n eff2 is the second effective refractive index. λ is the center wavelength of the reflection band, which can be expressed as the wavelength of the target light below.

[0048] Referring to Equation 1, the first effective refractive index (n eff1 ) and the second effective refractive index (n eff2 The greater the difference ), the wider the width (Δλ) of the reflection band of the dielectric mirror (DM) can become. Therefore, the first effective refractive index (n eff1 ) and the second effective refractive index (n eff2 By adjusting ), the width (Δλ) of the reflection band can be adjusted. Each of the first thin film (210) and the second thin film (220) may contain a quantum dot colloid.

[0049] Referring to FIG. 2, the quantum dot colloid may include a quantum dot (QP) and a ligand (30) that binds to the surface of the quantum dot (QP). In one embodiment, the quantum dot (QP) may have a core-shell structure comprising a core (10) and a shell (20) surrounding the core (10). The material contained in the core (10) and the material contained in the shell (20) may be different from each other. The shell (20) may cover at least a portion of the core (10). The shell (20) can improve the quantum efficiency of the core (10) and improve the stability of the quantum dot (QP) by preventing oxidation of the core (10).

[0050] The core (10) of the quantum dot (QP) may include a semiconductor compound. The quantum dot (QP) may include a group II-VI semiconductor compound, a group III-V semiconductor compound, a group III-VI semiconductor compound, a group I-III-VI semiconductor compound, a group IV-VI semiconductor compound, a group IV element or compound, or a combination thereof. In one embodiment, the quantum dot (QP) may be a chalcogenide quantum dot comprising a chalcogenide semiconductor compound as the material forming the core (10). For example, the core (10) of the quantum dot (QP) may include CdS, CdSe, ZnSe, InP, PbS, CuInS2, CuInSe2, InAs, or a combination thereof.

[0051] The shell (20) of the quantum dot (QP) may include a metal or non-metal oxide, a semiconductor compound, or a combination thereof. Here, the metal or non-metal oxide may include SiO2, Al2O3, TiO2, ZnO, MnO, Mn2O3, Mn3O4, CuO, FeO, Fe2O3, Fe3O4, CoO, Co3O4, NiO, MgAl2O4, CoFe2O4, NiFe2O4, CoMn2O4, or a combination thereof. The semiconductor compound may include a Group III-VI semiconductor compound, a Group II-VI semiconductor compound, a Group III-V semiconductor compound, a Group III-VI semiconductor compound, a Group I-III-VI semiconductor compound, a Group IV-VI semiconductor compound, or a combination thereof. For example, the semiconductor compound may include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnSeS, ZnTeS, GaAs, GaP, GaS, GaSe, AgGaS, AgGaS2, GaSb, HgS, HgSe, HgTe, InAs, InP, InGaP, InSb, AlAs, AlP, AlSb, or a combination thereof. The shell (20) may be a single layer or a multilayer.

[0052] FIGS. 2 and 3 illustrate that the quantum dot (QP) has a core / shell structure having a core (10) and a shell (20), but the present invention is not limited thereto. In other embodiments, the quantum dot (QP) may be a single quantum dot without a shell. The quantum dot (QP) may have the shape of a spherical, pyramidal, multi-arm, or cubic nanoparticle, nanotube, nanowire, nanofiber, nanoplate-like particle, etc.

[0053] The material forming the quantum dot (QP) can be selected as a material that does not absorb the target light of the dielectric mirror (DM). Depending on the material forming the quantum dot (QP), the absorption band of the quantum dot (QP) may differ. For example, if the quantum dot (QP) contains CdS, CdSe, ZnSe, InP, etc., the quantum dot (QP) may absorb light in the visible light band (wavelength range of about 380 nm to about 780 nm). If the quantum dot (QP) contains PbS, CuInS2, CuInSe2, InAs, etc., the quantum dot (QP) may absorb light in the infrared band (wavelength range of about 780 nm to several micrometers). The material forming the quantum dot (QP) is selected such that the wavelength of the target light falls within the transmission band (or non-absorption band) of the quantum dot (QP), thereby reducing the absorption of the target light by the dielectric mirror (DM) and increasing the reflectance.

[0054] The ligand (30) may be an organic or inorganic ion that forms a bond with the quantum dot (QP). In one embodiment, the ligand (30) may be an X-type ligand or an L-type ligand. In one embodiment, the ligand (30) may be any one of an alkyl ammonium halide, an alkyl thiol, an alkyl sulfate, an alkyl phosphate, a sulfonic acid, an alkyl phosphine, an alkyl carboxylic acid, and an inorganic ion.

[0055] Referring to FIG. 3, the quantum dots (QP) of the quantum dot colloid included in the first thin film (210) and the quantum dots (QP) of the quantum dot colloid included in the second thin film (220) may have the same structure and / or composition. Here, the fact that the quantum dots (QP) have the same structure and / or composition may mean that the material, diameter, and shape forming each of the two quantum dots (QP) are the same, and thus the optical and electrical properties are the same. However, the present invention is not limited thereto, and the quantum dots (QP) of the quantum dot colloid included in the first thin film (210) and the quantum dots (QP) of the quantum dot colloid included in the second thin film (220) may have different structures and / or compositions.

[0056] The ligand of the quantum dot colloid included in the first thin film (210) (hereinafter, the first ligand, 31) may be different from the ligand of the quantum dot colloid included in the second thin film (220) (hereinafter, the second ligand, 32). For example, the length of the first ligand (31) may be different from the length of the second ligand (32). In one embodiment, the length of the first ligand (31) may be longer than the length of the second ligand (32).

[0057] The diameter of the quantum dots (QP) is 10 nm or less, and has a size much smaller than the wavelength of light in the visible light band and the wavelength of light in the infrared band. Therefore, Mie scattering by the quantum dots (QP) can be ignored in the quantum dot colloidal thin film. The quantum dot colloidal thin film can be treated as a single optical medium, and the effective refractive index of the quantum dot colloidal thin film can be determined by the ratio of the volume occupied by the quantum dots (QP) to the volume occupied by the ligand (30).

[0058] For example, when the refractive index of a quantum dot (QP) is called the first refractive index (n1) and the refractive index of a first ligand (31) is called the second refractive index (n2), the first refractive index (n1) may be greater than the second refractive index (n2). The first effective refractive index (n) of the first thin film (210). eff1) may be equal to or smaller than the first refractive index (n1) and equal to or larger than the second refractive index (n2) (n2≤n eff1 ≤n1). First effective refractive index (n eff1 ) can have a value between the first refractive index (n1) and the second refractive index (n2), depending on the ratio of the volume occupied by the quantum dot (QP) to the volume occupied by the first ligand (31). That is, depending on the length of the first ligand (31), the first effective refractive index (n) of the first thin film (210) eff1 ) can be determined.

[0059] Likewise, when the refractive index of the second ligand (32) is called the third refractive index (n3), the first refractive index (n1) may be greater than the third refractive index (n3). The second effective refractive index (n) of the second thin film (220) eff2 ) is equal to or smaller than the first refractive index (n1) and may be equal to or larger than the third refractive index (n3) (n3≤n eff2 ≤n1). Second effective refractive index (n eff2 ) can have a value between the first refractive index (n1) and the third refractive index (n3), depending on the ratio of the volume occupied by the quantum dot (QP) to the volume occupied by the second ligand (32). That is, depending on the length of the second ligand (32), the second effective refractive index (n) of the second thin film (220) eff2 ) can be determined.

[0060] Since the length of the first ligand (31) is different from the length of the second ligand (32), the first effective refractive index (n eff1 ) and the second effective refractive index (n eff2 ) may differ. For example, if the length of the first ligand (31) is longer than the length of the second ligand (32), the volume ratio occupied by the first ligand (31) in the first thin film (210) may be relatively larger than the volume ratio occupied by the second ligand (32) in the second thin film (220). Therefore, the first effective refractive index (n eff1 ) is the second effective refractive index (n eff2 It can be smaller than ).

[0061] To control the width (△λ) of the reflection band of the dielectric mirror (DM), the first effective refractive index (neff1 ) and the second effective refractive index (n eff2 The first ligand (31) and the second ligand (32) may be selected so that ) has an appropriate value. For example, in order to increase the width (△λ) of the reflection band, the first effective refractive index (n eff1 ) and the second effective refractive index (n eff2 A core-ligand combination with a large difference in ) can be selected. The first effective refractive index (n eff1 ) and the second effective refractive index (n eff2 Each of these can be measured using ellipsometry.

[0062] Each of the first thin film (210) and the second thin film (220) can be formed through a solution process. For example, a first colloidal solution comprising quantum dots (QPs) and a first ligand (31) bound to the surface of the quantum dots (QPs) can be formed, and a second colloidal solution comprising a second ligand (32) comprising quantum dots (QPs) and a second ligand (32) bound to the surface of the quantum dots (QPs) can be formed. The first colloidal solution and the second colloidal solution may be solutions in which the quantum dot colloid is uniformly dispersed in a dispersion medium. As described above, the quantum dots (QPs), the first ligand (31), and the second ligand (32) can be selected by considering the wavelength of the target light and the width (△λ) of the reflection band.

[0063] For example, a material forming the quantum dot (QP) can be selected such that the wavelength of the target light is included in the transmission band of the quantum dot (QP). The first ligand (31) may be selected from any one of alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion, and the second ligand (32) may be selected from any one other than the first ligand (31) among alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion. At this time, the length of the selected first ligand (31) and the length of the second ligand (32) may be different.

[0064] A first thin film (210) can be formed by coating a first colloidal solution on a substrate (100), and a second thin film (220) can be formed by coating a second colloidal solution on the first thin film (210). In one embodiment, the first thin film (210) and the second thin film (220) can each be formed through a spin coating process or a dip coating process. The first colloidal solution and the second colloidal solution can each be dried, heated, or exposed to light after spin coating.

[0065] The dielectric mirror (DM) according to the embodiments of the present invention can be mass-produced at a low manufacturing cost through a solution process. The dielectric mirror (DM) can be easily applied to various devices formed through a solution process. Furthermore, since quantum dots with easily adjustable band gaps are used, it functions as a dielectric mirror (DM) in the transmission band of the quantum dots, while also being utilized as an optical filter that absorbs light of a specific wavelength band.

[0066] FIG. 4 is a diagram schematically illustrating the path of light at each interface of a dielectric mirror according to one embodiment of the present invention.

[0067] Referring to FIG. 4, incident light (Lin) incident on the dielectric mirror (DM) can be reflected at the interface of each of the thin films (210, 220) forming the thin film pair (200). For example, the incident light (Lin) can be reflected at the interface between the substrate (100) and the first thin film (210), the interface between the first thin film (210) and the second thin film (220), and the interface between the second thin film (220) and air, and proceed as reflected light (Lr).

[0068] Each of the thin films (210, 220) can be formed with a thickness that satisfies the Bragg reflection condition so that reflected light (Lr) reflected from the interface of each of the thin films (210, 220) forming the thin film pair (200) overlaps to cause constructive interference. For example, the first thin film (210) can be formed with a first thickness (t1) according to Equation 2 below, and the second thin film (220) can be formed with a second thickness (t2) according to Equation 3 below.

[0069] [Equation 2]

[0070]

[0071] [Equation 3]

[0072]

[0073] Here, λ is the wavelength of the target light, and n eff1 is the first effective refractive index of the first thin film (210), and n eff2 is the second effective refractive index of the second thin film (220).

[0074] That is, the first thickness (t1) of the first thin film (210) is proportional to the wavelength of the target light, and the first effective refractive index (n) of the first thin film (210) eff1 It can be formed to be inversely proportional to ). The second thickness (t2) of the second thin film (220) is proportional to the wavelength of the target light, and the second effective refractive index (n) of the second thin film (220) eff2 It can be formed to be inversely proportional to ).

[0075] The thickness of the first thin film (210) can be controlled by the quantum dot concentration of the first colloidal solution forming the first thin film (210). The thickness of the second thin film (220) can be controlled by the quantum dot concentration of the second colloidal solution forming the second thin film (220). By controlling the quantum dot concentration of the first colloidal solution during the solution process, a first thin film (210) having a first thickness (t1) can be formed. Similarly, by controlling the quantum dot concentration of the second colloidal solution, a second thin film (220) having a second thickness (t2) can be formed.

[0076] FIG. 5 is a cross-sectional view schematically illustrating a dielectric mirror according to one embodiment of the present invention.

[0077] Referring to FIG. 5, the dielectric mirror (DM) may include a substrate (100) and a plurality of thin film pairs (200). Each of the thin film pairs (200) may include a first thin film (210) and a second thin film (220).

[0078] Each of the first thin films (210) may include quantum dots and a first ligand bonded to the surface of each of the quantum dots, and each of the second thin films (220) may include quantum dots and a second ligand bonded to the surface of each of the quantum dots. The length of the first ligand and the length of the second ligand may be different. For example, the length of the first ligand may be longer than the length of the second ligand.

[0079] When the quantum dots have a first refractive index, the first ligand has a second refractive index, and the second ligand has a third refractive index, each of the first thin films (210) may have a first effective refractive index between the first and second refractive indices, and each of the second thin films (220) may have a second effective refractive index between the first and third refractive indices. In this case, the first effective refractive index may be determined by the volume ratio of the quantum dots to the volume of the first ligand in the first thin film (210), and the second effective refractive index may be determined by the volume ratio of the quantum dots to the volume of the second ligand in the second thin film (220). The first effective refractive index and the second effective refractive index may be different. For example, the first effective refractive index may be smaller than the second effective refractive index.

[0080] The thickness of each of the first thin films (210) along the thickness direction (e.g., z-direction) may be proportional to the wavelength of the target light, which is the center wavelength of the reflection band that the dielectric mirror (DM) intends to reflect, and may be inversely proportional to the first effective refractive index. The thickness of each of the second thin films (220) along the thickness direction (e.g., z-direction) may be proportional to the wavelength of the target light and may be inversely proportional to the second effective refractive index.

[0081] The first thin film (210) and the second thin film (220) may be alternately stacked on the substrate (100). In one embodiment, a first colloidal solution may be formed by dispersing quantum dots and a first ligand bound to the surface of the quantum dots in a dispersion medium, and a second colloidal solution may be formed by dispersing quantum dots and a second ligand bound to the surface of the quantum dots in a dispersion medium. A first thin film (210) may be formed by coating the first colloidal solution on the substrate (100), and a first thin film (220) may be formed by coating the second colloidal solution on the first thin film (210) to form the first thin film pair (200). A second first thin film (210) can be formed by coating a first colloidal solution onto a first thin film pair (200), and a second second thin film (220) can be formed by coating a second colloidal solution onto the second first thin film (210). In this way, by alternately repeating the step of forming a first thin film (210) by coating a first colloidal solution and the step of forming a second thin film (220) by coating a second colloidal solution, a dielectric mirror (DM) comprising a plurality of thin film pairs (200) can be formed.

[0082] As the number of stacked thin film pairs (200) increases, the reflectance of the dielectric mirror (DM) can increase. Therefore, the number of stacked thin film pairs (200) can be determined based on the target reflectance.

[0083] FIG. 6 is a cross-sectional view schematically illustrating a dielectric mirror according to one embodiment of the present invention.

[0084] Referring to FIG. 6, the dielectric mirror (DM) may include a substrate (100) and multilayer structures (ML) disposed on the substrate (100). The substrate (100) may include glass, metal, or polymer resin. In one embodiment, the substrate (100) may be a quartz or silicon substrate.

[0085] At least one multilayer structure (ML) including a third thin film (310) and a fourth thin film (230) may be disposed on a substrate (100). For example, the first third thin film (310) may be disposed on the substrate (100), the first fourth thin film (230) may be disposed on the third thin film (310), the second third thin film (310) may be disposed on the first fourth thin film (230), and the second fourth thin film (230) may be disposed on the second third thin film (310). That is, the third thin film (310) and the fourth thin film (230) may be stacked alternately in the thickness direction (e.g., z-direction).

[0086] The third thin film (310) may include a transparent organic or inorganic material. In one embodiment, the third thin film (310) may be a material capable of forming a thin film through a solution process. The transparent organic material may include acrylic resin, epoxy resin, polyimide, and polyethylene. The transparent inorganic material may include silicon oxide (SiO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), zinc oxide (ZnO), hafnium oxide (HfO2), zirconium oxide (ZrO2), and cerium oxide (CeO2). The third thin film (310) may be a single material layer that does not include quantum dots.

[0087] The fourth thin film (230) may be a quantum dot colloidal thin film comprising quantum dots and ligands bonded to the surface of the quantum dots. The quantum dots may include a group II-VI semiconductor compound, a group III-V semiconductor compound, a group III-VI semiconductor compound, a group I-III-VI semiconductor compound, a group IV-VI semiconductor compound, a group IV element or compound, or a combination thereof. In one embodiment, the quantum dots may be chalcogenide semiconductor compounds. The material forming the quantum dots is selected such that the wavelength of the target light falls within the transmission band (or non-absorption band) of the quantum dots, thereby reducing the absorption of the target light by the dielectric mirror (DM) and increasing the reflectance.

[0088] The ligand may be an organic or inorganic ion that forms a bond with the quantum dot. The ligand may be an X-type ligand or an L-type ligand. In one embodiment, the ligand may be any one of an alkyl ammonium halide, an alkyl thiol, an alkyl sulfate, an alkyl phosphate, a sulfonic acid, an alkyl phosphine, an alkyl carboxylic acid, and an inorganic ion.

[0089] A ligand can be selected by considering the effective refractive index of the fourth thin film (230). For example, when the quantum dots have a first refractive index and the ligand has a second refractive index, the effective refractive index of the fourth thin film (230) can have a value between the first and second refractive indices, and can be determined by the volume ratio of the quantum dots and the ligand in the fourth thin film (230). Accordingly, the shorter the length of the ligand, the higher the effective refractive index of the fourth thin film (230) is close to the first refractive index, and the longer the length of the ligand, the lower the effective refractive index of the fourth thin film (230) is close to the second refractive index. In one embodiment, in order to increase the width (△λ) of the reflection band of the dielectric mirror (DM), a short inorganic ion can be selected as the ligand.

[0090] The thickness of the third thin film (310) can be formed to be proportional to the wavelength of the target light and inversely proportional to the refractive index of the material forming the third thin film (310). The thickness of the fourth thin film (230) can be formed to be proportional to the wavelength of the target light and inversely proportional to the effective refractive index of the fourth thin film (230). The thickness of the fourth thin film (230) can be controlled by the quantum dot concentration of the colloidal solution forming the fourth thin film (230). For example, the quantum dot concentration of the colloidal solution can be controlled during the solution process to form a fourth thin film (230) having an optimal thickness.

[0091] As the number of stacked multilayer structures (ML) increases, the reflectance of the dielectric mirror (DM) can increase. Therefore, the number of stacked dielectric mirrors (DM) can be determined based on the target reflectance. The fourth thin film (230) according to the present embodiment can control the effective refractive index by controlling the length of the ligand. Thus, it is easy to control the width of the reflection band by making the difference in refractive index between the thin films larger or smaller, and a dielectric mirror (DM) with a high reflectance of 90% or more can be realized with a small number of stacked layers.

[0092] FIG. 7 is a graph showing the refractive indices of thin films according to one embodiment of the present invention by wavelength band.

[0093] The first quantum dot colloidal film (QCF1) contains lead sulfide (PbS) particles as quantum dots and oleic acid (OA) as a ligand. The second quantum dot colloidal film (QCF2) contains lead sulfide (PbS) particles as quantum dots and ethanedithiol (EDT) as a ligand. The third quantum dot colloidal film (QCF3) contains lead sulfide (PbS) particles as quantum dots and iodide ions (I + ...includes ). That is, the first quantum dot colloidal film (QCF1), the second quantum dot colloidal film (QCF2), and the third quantum dot colloidal film (QCF3) contain the same lead sulfide (PbS) quantum dots, but have ligands of different lengths. Here, the lengths of the ligands are oleic acid (OA) > ethanedithiol (EDT) > iodide ion (I + The absorption band of lead sulfide quantum dots is approximately 800 nm. The refractive index of each thin film was measured using ellipsometry.

[0094] Referring to Fig. 7, the zinc oxide thin film (ZnO) has a refractive index of approximately 1.5 for light of a wavelength of 1,000 nm. It was confirmed that the first quantum dot colloid thin film (QCF1) has an effective refractive index of approximately 1.65 for light of a wavelength of 1,000 nm, the second quantum dot colloid thin film (QCF2) has an effective refractive index of approximately 2.3 for light of a wavelength of 1,000 nm, and the third quantum dot colloid thin film (QCF3) has an effective refractive index of approximately 2.6 for light of a wavelength of 1,000 nm. In other words, it was confirmed that even with the same quantum dots, the effective refractive index of the thin film can be easily controlled by varying the length of the ligand.

[0095] FIG. 8 is a graph showing the reflectance of dielectric mirrors according to embodiments of the present invention.

[0096] A dielectric mirror was fabricated to include at least one pair of thin films. One pair of thin films comprises a first quantum dot colloidal thin film containing lead sulfide (PbS) particles as quantum dots and oleic acid (OA) as a ligand, and a second thin film containing lead sulfide (PbS) particles as quantum dots and iodide ions (I) as a ligand. + It includes a third quantum dot colloidal thin film containing ). The wavelength of the target light of the dielectric mirror is 1,000 nm, and each thin film is formed with a thickness that satisfies the conditions for Bragg reflection to occur.

[0097] A dielectric mirror according to the first embodiment (DM1) comprises one pair of thin films, a dielectric mirror according to the second embodiment (DM2) comprises two pairs of thin films, a dielectric mirror according to the third embodiment (DM3) comprises three pairs of thin films, and a dielectric mirror according to the fourth embodiment (DM4) is formed to comprise four pairs of thin films.

[0098] Referring to FIG. 8, it was confirmed that for a target light with a wavelength of 1,000 nm, the first embodiment (DM1) has a reflectance of about 70%, the second embodiment (DM2) has a reflectance of about 90%, the third embodiment (DM3) has a reflectance of about 98%, and the fourth embodiment (DM4) has a reflectance of about 99%. It was confirmed that the reflectance of the dielectric mirror tends to increase depending on the number of stacked thin film pairs, and it was confirmed that a reflectance of 95% can be achieved when the number of stacked thin film pairs is 3 or more.

[0099] The present invention has been described with reference to the embodiments illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims. Explanation of the symbols

[0100] DM: Genome Mirror 100: Substrate 200: Thin film pair 210: First thin film 220: Second thin film ML: Multilayer structure 310: Third thin film 230: 4th thin film

Claims

Claim 1 A dielectric mirror comprising: at least one first thin film including quantum dots and a first ligand bonded to the surface of each of the quantum dots; and at least one second thin film including quantum dots and a second ligand bonded to the surface of each of the quantum dots, wherein the at least one first thin film and the at least one second thin film are alternately stacked, and the length of the first ligand and the length of the second ligand are different. Claim 2 In claim 1, the quantum dot has a first refractive index, the first ligand has a second refractive index, the second ligand has a third refractive index, each of the at least one first thin film has a first effective refractive index between the first refractive index and the second refractive index, each of the at least one second thin film has a second effective refractive index between the first refractive index and the third refractive index, and the first effective refractive index and the second effective refractive index are different, dielectric mirror. Claim 3 A dielectric mirror according to paragraph 2, wherein the first effective refractive index is determined by the volume ratio of the quantum dots to the volume of the first ligand in the first thin film, and the second effective refractive index is determined by the volume ratio of the quantum dots to the volume of the second ligand in the second thin film. Claim 4 A dielectric mirror according to paragraph 2, wherein the thickness of each of the at least one first thin film is proportional to the wavelength of the target light and inversely proportional to the first effective refractive index, and the thickness of each of the at least one second thin film is proportional to the wavelength of the target light and inversely proportional to the second effective refractive index. Claim 5 In claim 1, a dielectric mirror in which the wavelength of the target light is included in the transmission band of the quantum dots. Claim 6 A dielectric mirror according to claim 1, wherein the first ligand is any one of alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion, and the second ligand is any one other than the first ligand among alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion. Claim 7 In claim 6, the dielectric mirror, wherein the first ligand is oleic acid and the second ligand is an iodine ion. Claim 8 In paragraph 6, the above quantum dots are dielectric mirrors that are chalcogenide-based quantum dots. Claim 9 A method for manufacturing a dielectric mirror comprising: a step of forming a first colloidal solution comprising quantum dots and a first ligand bound to the surface of the quantum dots; a step of forming a second colloidal solution comprising quantum dots and a second ligand bound to the surface of the quantum dots; a step of forming a first thin film by coating the first colloidal solution; and a step of forming a second thin film by coating the second colloidal solution on the first thin film, wherein the length of the first ligand and the length of the second ligand are different. Claim 10 A method for manufacturing a dielectric mirror according to claim 9, wherein the step of forming the first thin film and the step of forming the second thin film are alternately repeated. Claim 11 A method for manufacturing a dielectric mirror according to claim 9, wherein the quantum dot has a first refractive index, the first ligand has a second refractive index, the second ligand has a third refractive index, the first thin film has a first effective refractive index between the first refractive index and the second refractive index, the second thin film has a second effective refractive index between the first refractive index and the third refractive index, and the first effective refractive index and the second effective refractive index are different. Claim 12 A method for manufacturing a dielectric mirror according to claim 11, wherein, in the step of forming the first thin film, the thickness of the first thin film is formed to be proportional to the wavelength of the target light and inversely proportional to the first effective refractive index, and in the step of forming the second thin film, the thickness of the second thin film is formed to be proportional to the wavelength of the target light and inversely proportional to the second effective refractive index. Claim 13 A method for manufacturing a dielectric mirror according to claim 9, wherein the quantum dots are selected such that the wavelength of the target light is included in the transmission band of the quantum dots. Claim 14 A method for manufacturing a dielectric mirror according to claim 9, wherein the first ligand is any one of alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion, and the second ligand is any one other than the first ligand among alkyl ammonium halide, alkyl thiol, alkyl sulfate, alkyl phosphate, sulfonic acid, alkyl phosphine, alkyl carboxylic acid, and inorganic ion. Claim 15 A method for manufacturing a dielectric mirror according to claim 14, wherein the first ligand is oleic acid and the second ligand is an iodine ion. Claim 16 In claim 14, a method for manufacturing a dielectric mirror, wherein the above quantum dots are chalcogenide-based quantum dots. Claim 17 A method for manufacturing a dielectric mirror comprising: a step of forming a first thin film comprising a transparent organic or transparent inorganic material; a step of forming a quantum dot colloidal solution comprising quantum dots and a ligand bonded to the surface of said quantum dots; and a step of forming a second thin film by coating said quantum dot colloidal solution onto said first thin film, wherein said ligand is selected such that the effective refractive index of said second thin film is different from the refractive index of said first thin film. Claim 18 A method for manufacturing a dielectric mirror according to claim 17, wherein the step of forming the first thin film and the step of forming the second thin film are alternately repeated. Claim 19 A method for manufacturing a dielectric mirror according to claim 17, wherein the quantum dot has a first refractive index, the ligand has a second refractive index, and the second thin film has an effective refractive index between the first refractive index and the second refractive index. Claim 20 A method for manufacturing a dielectric mirror according to claim 19, wherein, in the step of forming the second thin film, the thickness of the second thin film is formed to be proportional to the wavelength of the target light and inversely proportional to the effective refractive index.

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