KR100862447B1 - High-transmissive optical thin film and semicondutor light emitting device having the same - Google Patents

Abstract

High-permeability optical thin film with improved structure to reduce light output loss and maximize light transmission efficiency by suppressing light reflection caused by difference in refractive index between semiconductor material and air or encapsulant during light extraction from semiconductor light emitting device One semiconductor light emitting device is disclosed. The optical thin film according to the present invention includes a first material layer having a first refractive index, and a second material layer having a second refractive index smaller than the first refractive index and formed on the first material layer. A grade-refractive index layer formed between the second material layers and having a multilayer structure in which the refractive index distribution is gradually reduced in the range between the first refractive index and the second refractive index as it progresses from the first material layer to the second material layer. (graded-refractive index layer).

Description

High-transmissive optical thin film and semicondutor light emitting device having the same

1 (a), (b) and (c) each shows a cross-sectional structure of the optical thin film according to the present invention, the refractive index distribution of the optical thin film and the composition distribution of the optical thin film.

2 is a refractive index distribution diagram of materials for forming an optical thin film according to the present invention.

3A is a SEM photograph showing a cross-sectional structure of an optical thin film implemented according to a first embodiment of the present invention.

3B is a graph showing the refractive index distribution of the optical thin film implemented according to the first embodiment.

3C is an apparatus diagram for forming an optical thin film according to the first embodiment.

4A is a graph illustrating a result of measuring transmittance of an optical thin film implemented according to the first embodiment.

4B is a graph illustrating a result of measuring reflectivity of the optical thin film implemented according to the first embodiment.

FIG. 5A is a cross-sectional SEM photograph showing a porosity density distribution according to a change in deposition angle or oblique angle in an optical thin film implemented according to a second exemplary embodiment of the present invention.

5B is a graph showing a refractive index distribution of the optical thin film implemented according to the second embodiment.

5C is an apparatus diagram for forming an optical thin film according to the second embodiment.

5D is a graph showing a change in refractive index distribution according to a deposition angle change in an optical thin film implemented according to a second exemplary embodiment of the present invention.

6 is a schematic cross-sectional view of a semiconductor light emitting device having a high transmissive optical thin film according to the present invention.

<Description of Symbols for Major Parts of Drawings>

10: substrate 11: first material layer

12: Grade-Refractive Index Layer

12a, 12b, 12c, 12d, 12e: constituent layers of the graded-index layer

14: second material layer 20: optical thin film

40: n-type semiconductor layer 50: active layer

60: p-type semiconductor layer 110: n-electrode

112: reflecting electrode 120: p-electrode

The present invention relates to a semiconductor light emitting device, which reduces light output loss and maximizes light transmission efficiency by suppressing light reflection caused by a difference in refractive index between a semiconductor material and air or encapsulating materials during light extraction from the semiconductor light emitting device. The present invention relates to a highly transmissive optical thin film and a semiconductor light emitting device having the same, the structure of which is improved.

A light emitting device, for example a light emitting diode (LED), is basically a semiconductor PN junction diode. Whereas silicon PN junctions were the key to the electronic information revolution, PN junctions of group III-V compound semiconductors are the key to the light revolution. Group III-V compound semiconductors are made by combining elements of group III and group V on the periodic table of elements, and have an advantage that the luminous efficiency is almost 100%. This is about 10,000 times higher than that of silicon. Therefore, LED has been widely applied to light emitting devices such as diode lasers since the early stage of material development. In addition, LEDs are widely used in high-speed and high-power electronic devices because of their high movement speed and high temperature operation. In particular, by mixing various elements of Group III and Group V has the advantage that it can produce a semiconductor of a wide variety of material compositions and properties.

As a basic characteristic of the light emitting diode, a light intensity (Candela, cd) is used in a light emitting diode in the visible light region, and a radiant flux [in Watts] in the invisible light region. Luminance is expressed as luminous flux per unit solid angle, and luminance is expressed as luminous intensity per unit area. A photometer is used to measure such luminous intensity. Radiation flux represents the total power emitted for all wavelengths in an LED and is expressed as the energy emitted per unit of time.

The main evaluation factor for determining visible LED performance is Luminous Efficiency, expressed in lumens per watt (lm / W). This corresponds to the wall plug efficiency (light output / input electric power) considering the visibility of the human eye. In addition, the luminous efficiency of the LED can be mainly determined by three factors such as internal quantum efficiency, extraction efficiency, operating voltage, and research for improving the luminous efficiency. Development is still ongoing.

Conventional LEDs are generally formed of a sapphire / n-GaN / MQW / p-GaN structure. In the conventional LEDs having such a structure, first, the internal quantum efficiency of the MQW layer is improved, and second, high power LED manufacturing technology There were structural limitations in solving the challenges. Therefore, it was necessary to improve the structure of the LED to overcome this limitation so that the light extraction efficiency can be increased.

The technical problem to be achieved by the present invention is to improve the above problems of the prior art, by suppressing the occurrence of light reflection due to the difference in refractive index between the semiconductor material and air or encapsulating materials during light extraction in the semiconductor light emitting device The present invention provides a high-permeability optical thin film and a semiconductor light emitting device having the same, the structure of which is improved to reduce light output loss and maximize light transmission efficiency.

The optical thin film according to the present invention,

A first material layer having a first refractive index;

A second material layer formed on the first material layer and having a second refractive index smaller than the first refractive index; And

It is interposed between the first material layer and the second material layer, a multi-layer structure in which the refractive index distribution is gradually reduced in the range between the first refractive index and the second refractive index as it proceeds from the first material layer toward the second material layer And a graded-refractive index layer formed.

In addition, the semiconductor light emitting device according to the present invention,

an n-electrode, an n-type semiconductor layer, an active layer, a p-type semiconductor layer and a p-electrode; And

The light generated from the active layer is formed on the light exit surface is emitted, and comprises an optical thin film for providing a light transmission path, the optical thin film,

A first material layer formed on the light exit surface and having a first refractive index;

A second material layer formed on the first material layer and having a second refractive index smaller than the first refractive index; And

It is interposed between the first material layer and the second material layer, a multi-layer structure in which the refractive index distribution is gradually reduced in the range between the first refractive index and the second refractive index as it proceeds from the first material layer toward the second material layer And a graded-refractive index layer formed.

In the optical thin film and the semiconductor light emitting device according to the present invention, the first refractive index and the second refractive index may be selected in the range of 1 to 5. Preferably, each of the first material layer, the second material layer, and the grade-refractive index layer may include TiO ₂ , SiC, GaN, GaP, SiN _y , ZrO ₂ , ITO, AlN, Al ₂ O ₃ , MgO, SiO ₂ , At least one selected from the group consisting of CaF ₂ and MgF ₂ . Here, the grade-refractive index layer is formed of (the first material) _x (the second material) _1-x (0 <x <1) composition, and the closer to the second material layer, the higher the grade- The composition ratio of the second material contained in each component layer constituting the refractive index layer is gradually increased. In addition, the second material layer and the grade-refractive index layer may be formed of a porous structure including micropores, and the porosity of each component layer constituting the grade-refractive index layer is closer to the second material layer. Gradually increasing.

Hereinafter, a preferred embodiment of a high transmissive optical thin film and a semiconductor light emitting device having the same according to the present invention will be described in detail with reference to the accompanying drawings. In the process, the thicknesses of layers or regions illustrated in the drawings are exaggerated for clarity.

1 (a), (b) and (c) each shows a cross-sectional structure of the optical thin film according to the present invention, the refractive index distribution of the optical thin film and the composition distribution of the optical thin film. And, Figure 2 is a refractive index distribution of the material forming the optical thin film according to the present invention.

Referring to FIG. 1, the high transmission optical thin film 20 according to the present invention may include a first material layer 11, a graded-refractive index layer 12, which are sequentially stacked on the substrate 10, and The second material layer 14 is included. Here each layer of material can be formed by sputtering or evaporation.

The first material layer (11) has a first refractive index (n _H) for having the second material layer 14 is the first small second index of refraction than the first refractive index (n _H) (n _L, n _L <n _H ) The first refractive index n _H and the second refractive index n _L may be selected from a range of 1 to 5, inclusive. Preferably, each of the first material layer 11 and the second material layer 14 may be formed of TiO ₂ , SiC, GaN, GaP, SiN _y , ZrO ₂ , ITO, AlN, Al ₂ O ₃ , MgO, SiO ₂ , At least one selected from the group consisting of CaF ₂ and MgF ₂ . These listed materials have a refractive index of 1 or more and 5 or less. Here, the refractive index is a refractive index for light having a wavelength of 350 nm to 700 nm.

The grade-refractive index layer 12 is interposed between the first material layer 11 and the second material layer 14 and progresses toward the second material layer 14 from the first material layer 11. The refractive index distribution is gradually reduced in the range between the first refractive index n _H and the second refractive index n _L. For example, the grade-refractive index layer 12 is n ₁ , n ₂ , n ₃ , ......, n _m , (n _L <n ₁ <n ₂ <n ₃ <... _m <n _H, m is a positive integer), and may comprise a plurality of constituent layers 12a, 12b, 12c, 12d, 12e. Each of these constituent layers 12a, 12b, 12c, 12d, 12e is composed of TiO ₂ , SiC, GaN, GaP, SiN _y , ZrO ₂ , ITO, AlN, Al ₂ O ₃ , MgO, SiO ₂ , CaF ₂ and MgF It may be formed of at least one selected from the group consisting of _two .

In the present invention, in order to implement a structure in which the refractive index gradually changes in the grade-refractive index layer 12, the following two embodiments may be possible, and these two embodiments may be carried out individually or in combination.

First, in the first embodiment, each of the constituent layers 12a, 12b, 12c, 12d, and 12e of the graded-refractive index layer 12 is co-sputtered (the first material) _x (The second material) _1-x (0 <x <1), and each component layer constituting the grade-refractive index layer 12 is closer to the second material layer 14 The composition ratio of the second material contained in 12a, 12b, 12c, 12d, 12e) was gradually increased. The grade-refractive index layer 12 is formed of a mixed composition of the first material and the second material having different refractive indices, wherein the refractive index n _L of the second material is the refractive index of the first material ( Since it is smaller than n _H ), the refractive indices of the constituent layers 12a, 12b, 12c, 12d, and 12e of the graded-index layer 12 may gradually decrease as the composition ratio of the second material increases.

In a second embodiment, the second material layer 14 and the grade-refractive index layer 12 were formed of a porous structure including micropores. At this time, the porosity density of the second material layer 14 is greater than the porosity of each of the constituent layers 12a, 12b, 12c, 12d, and 12e constituting the graded-refractive index layer 12, In addition, the porosity of each of the constituent layers 12a, 12b, 12c, 12d, and 12e constituting the grade-refractive index layer 12 increases gradually as the second material layer 14 is adjacent to the second material layer 14. Preferably, the porosity of the second material layer 14 may be formed up to about 90%, and the porosity of the grade-refractive index layer 12 may be controlled to be 90% or less. Herein, the micropores are a concept including a micropore air pore, that is, a nano-air pore. Since the microvoids contain air and the refractive index of the air is very small as about 1, as the porosity density of the microvoids increases, a component layer constituting the grade-refractive index layer 12 The refractive indices of the fields 12a, 12b, 12c, 12d, and 12e may gradually decrease. The micro-pores may be formed by changing the deposition angle (θ, deposition angle or oblique angle) of the substrate with respect to the flux of the vapor source during the deposition process of the thin film, the change in the deposition angle Accordingly, control of porosity density may be possible. Here, the deposition angle is defined as an angle formed by the deposition surface on the substrate with respect to the flux of the vapor source. In the second embodiment, preferably, the first material layer 11, the second material layer 14, and the grade-refractive index layer 12 may be formed of a material having the same chemical composition.

According to the present invention, an optical thin film having a structure in which the refractive index distribution is continuously reduced in the refractive index range between 1 and 5 can be obtained. As such, when light having a wavelength of 350 nm to 700 nm is transmitted through the optical thin film in which the refractive index distribution is continuously changed, light reflection may be suppressed due to a difference in refractive index with air, and thus light transmittance may be excellent. In particular, when the optical thin film is formed on the light emitting surface of the semiconductor light emitting device, the light reflection caused by the difference in refractive index between the semiconductor material and the air or encapsulating materials during light extraction from the semiconductor light emitting device is minimized. It can reduce the light output loss and maximize the light transmission efficiency. Here, the encapsulation material is a material for forming an encapsulating layer covering the semiconductor light emitting device, and may include silicon or epoxy resin.

3A is a SEM photograph showing a cross-sectional structure of an optical thin film implemented according to a first embodiment of the present invention, and FIG. 3B is a graph showing a refractive index distribution of the optical thin film implemented according to the first embodiment. 3C is an apparatus diagram for forming an optical thin film according to the first embodiment.

3A and 3B, the optical thin film according to the first embodiment of the present invention is a TiO ₂ layer having a high refractive index (a wavelength of 550 nm) of about 2.3, (TiO ₂ ) sequentially stacked on a substrate. _and a grade-refractive index layer having a composition of _x (SiO ₂ ) _1-x (0 <x <1) and a SiO ₂ layer having a low refractive index of about 1.44. Herein, the grade-refractive index layer has a refractive index distribution gradually decreasing in the range of 2.3 and 1.44 depending on the composition of (TiO ₂ ) _x (SiO ₂ ) _1-x (0 <x <1) (adjacent to the SiO ₂ layer As the composition ratio of SiO ₂ increases, the refractive index distribution gradually decreases), and a multi-target co-sputtering apparatus as shown in FIG. 3C was used. In the device diagram, each of the target 1 and the target 2 is a TiO ₂ source and a SiO ₂ source.

 4A and 4B are graphs showing the results of measuring the transmittance and reflectance of the optical thin film implemented according to the first embodiment. It was found that the transmittance characteristics of the optical thin film including the grade-refractive index layer according to the present invention were excellent.

5A is a porosity in the SiO ₂ layer according to the deposition angle (θ, deposition angle or oblique angle) change of the substrate with respect to the flux of the vapor source in the optical thin film implemented in accordance with the second embodiment of the present invention SEM image showing the distribution of porosity density. 5B is a graph showing refractive index distribution according to the light wavelength of the optical thin film implemented according to the second embodiment. 5C is an apparatus diagram for forming an optical thin film according to the second embodiment. 5D is a graph showing a change in refractive index distribution according to a deposition angle change in the optical thin film implemented according to the second embodiment of the present invention.

5A to 5D, in the optical thin film according to the second embodiment, the first material layer, the second material layer, and the grade-refractive index layer are all formed of SiO ₂ material, and micropores in the SiO ₂ layer By controlling the porosity of the structure, the refractive index distribution is gradually reduced. Specifically, in the range of 0 ° to 90 °, as the deposition angle θ increases, the porosity of the micropores in the SiO ₂ layer is gradually increased, and as the porosity increases, the refractive index of the SiO ₂ layer is 1.46. Could be gradually reduced to 1.1. Here, the deposition angle θ is defined as the angle formed by the deposition surface on the substrate with respect to the flux of the vapor source.

6 is a schematic cross-sectional view of a semiconductor light emitting device having a high transmissive optical thin film according to the present invention. Since the structures, forming materials, and effects of the highly transparent optical thin film 20 have been described in detail with reference to FIGS. 1 to 5D, redundant descriptions of the same components will be omitted.

Referring to FIG. 6, the semiconductor light emitting device according to the present invention includes an n-type semiconductor layer 40, an active layer 50, and a p-type semiconductor sequentially stacked between the n-electrode 110 and the p-electrode 120. It includes a layer 60, and also includes an optical thin film 20 formed on the light exit surface from which the light generated from the active layer 50 is emitted to provide a light transmission path. A reflective electrode 112 formed of a light reflective material such as Ag is formed between the p-type semiconductor layer 60 and the p-electrode 120.

The n-type semiconductor layer 40 is formed of an AlInGaN-based III-V nitride semiconductor material, but preferably an n-GaN layer. In addition, the p-type semiconductor layer 60 is formed of a p-GaN-based III-V nitride semiconductor layer, preferably, a p-GaN layer or a p-GaN / AlGaN layer.

The active layer 50 is formed of a GaN-based group III-V nitride semiconductor layer having In _x Al _y Ga _1-xy N (0 ≦ x <1, 0 ≦ y <1 and 0 ≦ x + y <1). In particular, it is preferable to form an InGaN layer or an AlGaN layer. Here, the active layer 50 may have a structure of any one of a multi-quantum well (hereinafter referred to as 'MQW') or a single quantum well, the structure of the active layer is within the technical scope of the present invention Do not limit. For example, the active layer 50 may be most preferably formed of a GaN / InGaN / GaN MQW or GaN / AlGaN / GaN MQW structure. The n-electrode 110 and the p-electrode 120 may be formed of a metal material such as Au, Al, Ag, or a transparent conductive material.

In the semiconductor light emitting device having such a structure, when a predetermined voltage is applied between the n-electrode 110 and the p-electrode 120, the n-type semiconductor layer 40 and the p-type semiconductor layer 60 are respectively provided. Electrons and holes may be injected into the active layer 50 so that light may be generated from the active layer 50 by combining in the active layer 50.

The optical thin film 20 may include a first material layer 11, a graded-refractive index layer 12, and a first material layer 11 sequentially stacked on a light exit surface, that is, an upper surface of the n-type semiconductor layer 40. Two material layers 14. Here each layer of material can be formed by sputtering or evaporation.

The first material layer (11) has a first refractive index (n _H) for having the second material layer 14 is the first small second index of refraction than the first refractive index (n _H) (n _L, n _L <n _H ) The first refractive index n _H and the second refractive index n _L may be selected from a range of 1 to 5, inclusive. Specifically, each of the first material layer 11 and the second material layer 14 may be formed of TiO ₂ , SiC, GaN, GaP, SiN _y , ZrO ₂ , ITO, AlN, Al ₂ O ₃ , MgO, SiO ₂ , At least one selected from the group consisting of CaF ₂ and MgF ₂ . In particular, the first material layer 11 may be formed of a material having the light exit surface, that is, a material having the same refractive index as that of n-GaN, which is a material of the n-type semiconductor layer. Here, the refractive index will be defined as a concept that refers to the refractive index for light having a wavelength of 350 nm to 700 nm. The grade-refractive index layer 12 is interposed between the first material layer 11 and the second material layer 14 and progresses toward the second material layer 14 from the first material layer 11. The refractive index distribution is gradually reduced in the range between the first refractive index n _H and the second refractive index n _L.

Since the light emitting surface may vary according to a structure of a semiconductor light emitting device, for example, a top emitter type and a flip chip type, the light emitting surface may include light generated from the active layer 50. It is defined as referring to the outermost surface or boundary surface emitted to the outside air (air or suture layer). Accordingly, the light exit surface is any one selected from the group consisting of a substrate (not shown), an n-electrode 110, an n-type semiconductor layer 40, a p-type semiconductor layer 60, and a p-electrode 120. Can be provided by In the semiconductor light emitting device structure illustrated in FIG. 6, an upper surface of the n-type semiconductor layer 40 may be a light exit surface, and an optical thin film 20 is formed on the upper surface of the n-type semiconductor layer 40.

However, in the case of a semiconductor light emitting device having a different structure (not shown), for example, when the light exit surface is provided by the n-electrode 110, the n-electrode 110 may be a light transmitting material, for example. For example, it should be formed of a transparent nitride or a transparent conductive oxide. Likewise, when the light exit surface is provided by the p-electrode 120, the p-electrode 110 should be formed of a light transmitting material, for example, a transparent conductive nitride or a transparent conductive oxide. Examples of such transparent electrode forming materials include indium tin oxide (ITO), zinc-doped indium tin oxide (ZITO), zinc indium oxide (ZIO), gallium indium oxide (GIO), zinc tin oxide (ZTO), Fluorine-doped Tin Oxide (FTO), Aluminum-doped Zinc Oxide (AZO), Gallium-doped Zinc Oxide (GZO), In ₄ Sn ₃ O ₁₂ or Zn _(1-x) Mg _x O (Zinc Magnesium Oxide, 0≤ x≤1), and may be any one selected from the group consisting of Zn ₂ In ₂ O ₅ , GaInO ₃ , ZnSnO ₃ , F-doped SnO ₂ , Al-doped ZnO, Ga-doped ZnO, MgO, ZnO and the like.

According to the present invention, the structure is improved high transmission so as to reduce the light output loss and maximize the light transmission efficiency by suppressing the light reflection caused by the difference in refractive index between the semiconductor material and air or the sealing material during light extraction in the semiconductor light emitting device An optical thin film can be obtained. When the high-transmissive optical thin film according to the present invention is formed on the light exit surface of the semiconductor light emitting device, the light output loss of the semiconductor light emitting device is minimized, thereby improving the light output efficiency of the semiconductor light emitting device.

In the above, some exemplary embodiments have been described and illustrated in the accompanying drawings in order to facilitate understanding of the present invention, but these embodiments are merely exemplary and various modifications from the embodiments can be made by those skilled in the art. And it should be understood that other equivalent embodiments are possible. Therefore, the present invention is not limited to the illustrated and described structures and process sequences, but should be protected based on the technical spirit of the invention described in the claims.

Claims (24)

A first material layer having a first refractive index; A second material layer formed on the first material layer and having a second refractive index smaller than the first refractive index; And It is interposed between the first material layer and the second material layer, a multi-layer structure in which the refractive index distribution is gradually reduced in the range between the first refractive index and the second refractive index as it proceeds from the first material layer toward the second material layer A graded-refractive index layer formed; And the second material layer and the grade-refractive index layer are formed of a porous structure including micropores. The method of claim 1, The first and second refractive indices are selected from the range of 1 to 5, the optical thin film. The method of claim 2, The first material layer, the second material layer, and the grade-refractive index layer each include TiO ₂ , SiC, GaN, GaP, SiN _y , ZrO ₂ , ITO, AlN, Al ₂ O ₃ , MgO, SiO ₂ , CaF ₂ and An optical thin film formed from at least one selected from the group consisting of MgF ₂ . delete delete delete The method of claim 1, And a porosity density of the second material layer is greater than a porosity of the grade-refractive index layer. The method of claim 7, wherein Adjacent to the second material layer is an optical thin film, characterized in that the porosity of each component layer constituting the grade-index layer gradually increases. The method of claim 8, And the second material layer and the grade-refractive index layer are formed of a material of the same component. The method of claim 1, The micropores are optical thin film, characterized in that it comprises a nano-air pore (nano-air pore). an n-electrode, an n-type semiconductor layer, an active layer, a p-type semiconductor layer and a p-electrode; And The light generated from the active layer is formed on the light exit surface is emitted, and comprises an optical thin film for providing a light transmission path, the optical thin film, A first material layer formed on the light exit surface and having a first refractive index; A second material layer formed on the first material layer and having a second refractive index smaller than the first refractive index; And It is interposed between the first material layer and the second material layer, a multi-layer structure in which the refractive index distribution is gradually reduced in the range between the first refractive index and the second refractive index as it proceeds from the first material layer toward the second material layer A graded-refractive index layer formed; The second material layer and the grade-refractive index layer is a semiconductor light emitting device, characterized in that formed of a porous structure containing micropores. The method of claim 11, And the light emitting surface is provided by any one selected from the group consisting of the n-electrode, the n-type semiconductor layer, the p-type semiconductor layer and the p-electrode. The method of claim 11, The first and second refractive index is a semiconductor light emitting device, characterized in that selected in the range of 1 to 5. The method of claim 13, The first material layer, the second material layer, and the grade-refractive index layer each include TiO ₂ , SiC, GaN, GaP, SiN _y , ZrO ₂ , ITO, AlN, Al ₂ O ₃ , MgO, SiO ₂ , CaF ₂ and And at least one selected from the group consisting of MgF ₂ . The method of claim 14, And the first material layer has the same refractive index as that of the material constituting the light exit surface. delete delete delete The method of claim 11, And a porosity density of the second material layer is greater than that of the grade-refractive index layer. The method of claim 19, And the porosity of each component layer constituting the grade-refractive index layer gradually increases closer to the second material layer. The method of claim 20, And the second material layer and the grade-refractive index layer are formed of the same material. The method of claim 11, The micro-pore is a semiconductor light emitting device, characterized in that it comprises a nano-air pore (nano-air pore). The method of claim 14, And the optical thin film is formed on the n-electrode, and the n-electrode is formed of a transparent conductive nitride or a transparent conductive oxide. The method of claim 14, And the optical thin film is formed on the p-electrode, and the p-electrode is formed of a transparent conductive nitride or a transparent conductive oxide.

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