JP2009038355A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively take out light emitted from a light emitting layer to the outside, and also to simplify a process for producing a light emitting device. <P>SOLUTION: The light emitting device 1 includes a stacked structure including a light emitting layer emitting light by supplying power and a reflection layer 30 for reflecting the light emitted from the light emitting layer. The reflection layer 30 has: a first conductive layer 300 made of titanium oxide (TiO<SB>2</SB>) presenting electrical conductivity with inclusion of impurities and having transparency to the light emitted from the light emitting layer; and also has a second conductive layer 302, which is provided contacting the first conductive layer 300, made of electrically conductive material having a refractive index smaller than that of the first conductive layer 300 and having transparency to the light emitted from the light emitting layer. The power is supplied to the light emitting layer through the first conductive layer 300 and the second conductive layer 302. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light emitting device including a conductive reflective layer.

  In Patent Document 1, a transparent conductive film is provided on a p-type contact layer, a multiple reflection film made of a dielectric is formed on the transparent conductive film, and an electrode layer that exists independently from the multiple reflection film. A flip-chip type III-nitride compound semiconductor light emitting device formed and further provided with a metal layer on a multiple reflection film is described.

  Patent Document 2 discloses a flip chip type group III nitride compound semiconductor light emitting device in which a main dynamic layer is provided on the first type semiconductor layer, and a second type semiconductor layer is provided on the main dynamic layer. A light emitting device is described in which a transparent conductive layer formed of an AlGaInSnO-based oxide or the like is provided on a second-type semiconductor layer, and a metal reflective layer is further provided on the transparent conductive layer.

  According to the light emitting element described in Patent Literature 1, light emitted from the light emitting layer of the semiconductor light emitting device is reflected by the multiple reflection film and the metal layer. And since the light reflected in the multiple reflection film | membrane and the metal layer is radiated | emitted outside the semiconductor light-emitting device, external quantum efficiency can be made high compared with the case where there are no multiple reflection film | membrane and a metal layer.

In addition, according to the light emitting device described in Patent Document 2, the transparent conductive layer provided on the second form semiconductor layer has electrical conductivity, so that the second form semiconductor layer is independent of the transparent conductive layer. It is not necessary to provide an electrode layer. Moreover, since the transparent conductive layer can be formed from a plurality of layers, the reflectance of the transparent conductive layer can be increased.
JP 2006-120913 A JP 2006-121084 A

  However, in the light emitting device described in Patent Document 1, since no current flows through the multiple reflection film made of a dielectric, an electrode layer is formed on the transparent conductive film independently of the multiple reflection film layer. It is necessary to pass a current through the p-type contact layer. Therefore, the manufacturing process of the light emitting device becomes complicated. Further, in the light emitting device described in Patent Document 2, a multilayer reflective film is formed from an AlGaInSnO-based oxide, and each of the plurality of layers is formed of the same material. It is difficult to ensure a large refractive index difference between a plurality of layers.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to emit light emitted from a light emitting layer using a multilayer reflective film including a transparent conductive material capable of easily controlling the refractive index. The object is to efficiently extract the outside and simplify the manufacturing process of the light emitting device.

In order to achieve the above object, the present invention includes a laminated structure including a light emitting layer that emits light when power is supplied and a reflective layer that reflects light emitted from the light emitting layer, and the reflective layer includes impurities. A first conductive layer formed of titanium oxide (TiO ₂ ) exhibiting electrical conductivity and having transparency to light emitted from the light emitting layer, and a refractive index smaller than the refractive index of the first conductive layer; And a second conductive layer formed in contact with the first conductive layer, the first conductive layer being interposed between the first conductive layer and the second conductive layer. Provided is a light emitting device for supplying power to a light emitting layer.

The reflective layer may have a structure in which a plurality of conductive unit layers including a first conductive layer and a second conductive layer in contact with the first conductive layer are stacked. Furthermore, the first conductive layer has a film thickness of 1 / (4n ₁ ) (n ₁ is the refractive index of the first conductive layer) of the wavelength of light emitted from the light emitting layer, and the second conductive layer emits light from the light emitting layer. The film thickness may be 1 / (4n ₂ ) (n ₂ is the refractive index of the second conductive layer) of the wavelength of light.

The first conductive layer is thicker than 1 / (4n ₁ ) (n ₁ is the refractive index of the first conductive layer) of the wavelength of light emitted from the light emitting layer, and the second conductive layer is a light emitting layer. The film thickness may be thicker than 1 / (4n ₂ ) (where n ₂ is the refractive index of the second conductive layer) of the wavelength of the light emitted by.

  The reflective layer may further include a metal layer that reflects light emitted from the light emitting layer on the side opposite to the light emitting layer.

  The electrically conductive material forming the second conductive layer may have a refractive index of 2.2 or less. The electrically conductive material forming the second conductive layer may be made of indium tin oxide (ITO), or the electrically conductive material forming the second conductive layer is zinc oxide. It may be formed from (ZnO).

  According to the present invention, it is possible to efficiently inject current into the light emitting layer by using the reflective layer having conductivity, and to efficiently extract light emitted from the light emitting layer to the outside. Also, the manufacturing process of the light emitting device Can be simplified.

[First Embodiment]
FIG. 1 shows a longitudinal sectional view of a light emitting device according to a first embodiment of the present invention. FIG. 2 is an enlarged view of a longitudinal section of the reflective layer according to the first embodiment.

(Configuration of light-emitting device 1)
The light-emitting device 1 according to the first embodiment of the present invention includes a sapphire substrate 10, an n-type GaN layer 20 provided on the sapphire substrate 10, and a light-emitting layer provided on the n-type GaN layer 20. InGaN light-emitting layer 22, p-type GaN layer 24 provided on InGaN light-emitting layer 22, and p ⁺ -type GaN layer 26 provided on p-type GaN layer 24 and having a higher impurity concentration than p-type GaN layer 24. With.

In addition, the light emitting device 1 includes a reflective layer 30 provided on the p ⁺ -type GaN layer 26, a p-type electrode 40 as a metal layer provided on the reflective layer 30, and a p-type electrode 40. A bonding pad 50 provided; and an n-type electrode 45 provided on the n-type GaN layer 20 exposed by etching from the p ⁺ -type GaN layer 26 to a part of the n-type GaN layer 20. .

Here, the n-type GaN layer 20, the InGaN light emitting layer 22, the p-type GaN layer 24, and the p ⁺ -type GaN layer 26 are, for example, metal organic chemical vapor deposition (MOCVD). Is a layer composed of a group III nitride compound semiconductor formed by:

For example, the n-type GaN layer 20 is formed by doping a predetermined amount of Si as an n-type dopant. The InGaN light emitting layer 22 is formed to have a multiple quantum well structure composed of In _x Ga _1-x N / GaN. Further, each of the p-type GaN layer 24 and the p + -type GaN layer 26 is formed by doping a predetermined amount of Mg as a p-type dopant.

  The light emitting device 1 of the present embodiment having such a configuration is a light emitting diode (LED) that emits light having a wavelength in the blue region. For example, the light-emitting device 1 is a flip-chip blue LED that emits light having a peak wavelength of 460 nm when the forward voltage is 3.5 V and the forward current is 20 mA. The light emitting device 1 is formed in a substantially square shape when viewed from above. The planar dimension of the light emitting device 1 is approximately 350 μm in vertical and horizontal dimensions.

As shown in FIG. 2, the reflective layer 30 has a structure in which the second conductive layer 302 and the first conductive layer 300 are alternately and periodically formed on the p ⁺ -type GaN layer 26. That is, the first conductive layer 300 and the second conductive layer 302 are in contact with each other, and one conductive unit layer 310 is formed by using the second conductive layer 302 and the first conductive layer 300 as one pair. The reflective layer 30 has a structure in which a plurality of conductive unit layers 310 are stacked on the p ⁺ -type GaN layer 26. For example, the reflective layer 30 is a distributed Bragg reflector (DBR) formed from a plurality of layers of two materials having different refractive indexes.

Here, the first conductive layer 300 is made of titanium oxide (TiO ₂ ) that exhibits electrical conductivity by containing Ta as an impurity at a predetermined concentration and that is transparent to the light emitted from the InGaN light emitting layer 22. Is done. Specifically, the first conductive layer 300 is formed of electrically conductive Ti _1-x Ta _x O ₂ having a refractive index of about 2.5 when doped with 3 to 5% of Ta. Here, the resistivity of Ti _1-x Ta _x O ₂ is 1 × 10 ⁻¹ Ωcm or less. The first conductive layer 300 has a thickness of 1 / (4n ₁ ) of the wavelength of light emitted from the InGaN light emitting layer 22 (n ₁ : refractive index of the first conductive layer 300). For example, since the wavelength of light emitted from the InGaN light emitting layer 22 is about 460 nm, the film thickness of the first conductive layer 300 is about 46 nm.

The second conductive layer 302 is made of, for example, indium tin oxide (ITO) as an electrically conductive material. The ITO forming the second conductive layer 302 has a refractive index (about 2.0) smaller than that of TiO ₂ forming the first conductive layer 300, and is transmissive to the light emitted from the InGaN light emitting layer 22. The second conductive layer 302 has a thickness of 1 / (4n ₂ ) of the wavelength of light emitted from the InGaN light emitting layer 22 (n ₂ : refractive index of the second conductive layer 302). For example, since the wavelength of light emitted from the InGaN light emitting layer 22 is about 460 nm, the film thickness of the second conductive layer 302 is about 57.5 nm.

  Here, the number of the conductive unit layers 310 included in the reflective layer 30 is formed so that the reflectance of the reflective layer 30 with respect to the wavelength of light emitted from the InGaN light emitting layer 22 becomes a desired value. For example, for the purpose of setting the reflectance of the reflective layer 30 to about 100%, the number of the conductive unit layers 310 is set to 15 to 20, and the reflective layer 30 is formed.

  The n-type electrode 45 provided on the n-type GaN layer 20 is one or more selected from the group consisting of metals such as Ti, Al, Pd, Pt, V, Ir, and Rh. It is formed including a metal. Further, the bonding pad 50 is formed including a metal such as Ti, Ni, and Au, for example.

  Furthermore, the p-type electrode 40 as a metal layer according to the present embodiment is provided on the opposite side of the InGaN light emitting layer 22 via the conductive unit layer 310 including the first conductive layer 300 and the second conductive layer 302. The p-type electrode 40 is made of, for example, Ag having a reflectance of 93% with respect to light (wavelength: about 460 nm) emitted from the InGaN light emitting layer 22.

Each layer from the n-type GaN layer 20 to the p ⁺ -type GaN layer 26 provided on the sapphire substrate 10 is formed by molecular beam epitaxy (Molecular Beam Epitaxy: MBE) or halide vapor phase epitaxy (Halide Vapor Phase). (Epitaxial: HVPE) or the like. Further, a buffer layer made of, for example, AlN or GaN may be formed on the sapphire substrate 10, and the n-type GaN layer 20 may be formed on the formed buffer layer. Furthermore, the quantum well structure of the InGaN light emitting layer 22 may be a single quantum well structure, or may be a bulk light emitting layer having no quantum well structure.

Further, TiO ₂ forming the first conductive layer 300 may be either anatase type or rutile type. Here, from the viewpoint of controlling the conductivity, it is preferable to form the first conductive layer 300 using anatase TiO _2, and from the viewpoint of controlling the refractive index, using rutile TiO _2. It is preferable to form the first conductive layer 300. The first conductive layer 300 containing anatase TiO ₂ and rutile TiO ₂ can also be formed for the purpose of controlling both the conductivity and the refractive index. The refractive index of the first conductive layer 300 can be changed within a range of about 2.0 to about 2.8 depending on the amount of Ta doped into the first conductive layer 300. Therefore, the second conductive layer 302 is formed so that the difference between the refractive index of the first conductive layer 300 and the refractive index of the second conductive layer 302 is set to a predetermined value (for example, 0.5 to 1.0) or more. The first conductive layer 300 can also be formed by changing the Ta doping amount of TiO ₂ forming the first conductive layer 300 in accordance with the refractive index of the material.

The impurity doped into the first conductive layer 300 may be Nb. When the impurity doped in the first conductive layer 300 is Nb, the first conductive layer 300 is Ti _1-x Nb _x O ₂ .

  Further, the second conductive layer 302 is transparent to light emitted from the InGaN light emitting layer 22 and has a refractive index of 2.2 or less so as to increase the difference in refractive index from the first conductive layer 300. Preferably, it is formed from a conductive material. For example, the second conductive layer 302 can be formed not only from ITO but also from zinc oxide (ZnO). Further, the conductive unit layer 310 may include a conductive layer formed of another electrically conductive material having a refractive index different from that of the first conductive layer 300 and the second conductive layer 302. And the number of the conductive unit layers 310 which form the reflective film 30 can also be controlled to an appropriate number according to a desired reflectance. Furthermore, the p-type electrode 40 can also be formed of a metal such as Al or Rh that exhibits a predetermined reflectance with respect to the light emitted from the InGaN light emitting layer 22.

  In the present embodiment, the light emitting device 1 is an LED that emits light having a wavelength in the blue region, but in other examples, light having a wavelength in the ultraviolet region, light having a wavelength in the purple region, or light having a wavelength in the green region. It may be an LED that emits light. In still another example, the light-emitting device 1 is an LED composed of a III-V group compound semiconductor or a II-VI group compound semiconductor (for example, ZnO-based, ZnSe-based, GaAs-based, GaP-based, or InP-based). Also good. In such a case, the film thickness of the first conductive layer 300 and the film thickness of the second conductive layer 302 constituting the reflective layer 30 are respectively formed according to the wavelength of light emitted from the light emitting layer. In addition, as for the planar dimension of the light-emitting device 1, a vertical dimension and a horizontal dimension may each be substantially 1 mm.

(Manufacturing process of the light emitting device 1)
First, a group III nitride compound semiconductor is epitaxially grown on the surface of the sapphire substrate 10 using MOCVD to form an epitaxial substrate. That is, an n-type GaN layer 20, an InGaN light-emitting layer 22, a p-type GaN layer 24, and a p + -type GaN layer 26 are epitaxially grown in this order on the sapphire substrate 10 to form an epitaxial substrate.

Subsequently, a mask made of a photoresist is formed in a predetermined region of the p ⁺ -type GaN layer 26 using a photolithography technique. Next, the portion other than the portion where the mask is formed is etched from the p ⁺ -type GaN layer 26 to a part of the n-type GaN layer 20. Then, the mask is removed. Thereby, a shape in which a part of the surface of the n-type GaN layer 20 is exposed is formed.

Next, the reflective layer 30 is formed on the p ⁺ -type GaN layer 26 by repeatedly laminating the second conductive layer 302 and the first conductive layer 300 in this order using, for example, sputtering. The reflective layer 30 can also be formed by a vacuum evaporation method such as an electron beam evaporation method. In the present embodiment, 20 conductive unit layers 310 including a first conductive layer 300 formed of TiO ₂ and a second conductive layer 302 formed of ITO are stacked.

  Subsequently, the p-type electrode 40 is formed on the reflective layer 30 using a vacuum deposition method and a photolithography technique. Similarly, an n-type electrode 45 is formed on the n-type GaN layer 20 using a vacuum deposition method and a photolithography technique. Then, a bonding pad 50 is formed on the p-type electrode 40 using a vacuum deposition method and a photolithography technique.

  The light emitting device 1 formed through such a process is mounted by flip chip bonding on a predetermined position of a substrate made of ceramic or the like on which a wiring pattern made of a conductive material is previously formed. The packaged light-emitting device 1 can be formed by sealing the light-emitting device 1 mounted on the substrate as a single unit with a sealing material such as epoxy resin or glass. Note that, in one example, the sealing material can be formed including a phosphor that is excited by light in a predetermined wavelength region and emits light in a wavelength region different from the light.

(Operation of the light emitting device 1)
First, when a predetermined power is supplied to the bonding pad 50, the power is supplied from the bonding pad 50 to the reflective layer 30 through the p-type electrode 40. In the present embodiment, the first conductive layer 300 and the second conductive layer 302 that form the reflective layer 30 have electrical conductivity. Therefore, the power supplied to the reflective layer 30 passes through the first conductive layer 300 and the second conductive layer 302. And supplied to the p ⁺ -type GaN layer 26. That is, the reflective layer 30 serves as an electrode that supplies power supplied from the outside of the light emitting device 1 to the InGaN light emitting layer 22.

The power supplied to the p ⁺ -type GaN layer 26 is supplied to the InGaN light emitting layer 22 through the p-type GaN layer. The InGaN light emitting layer 22 emits light in a predetermined wavelength region by the supplied power. A part of the light emitted from the InGaN light emitting layer 22 passes through the n-type GaN layer 20 and the sapphire substrate 10 and is emitted to the outside of the light emitting device 1. On the other hand, a part of the light emitted from the InGaN light emitting layer 22 is emitted to the reflective layer 30 side. A part of the light emitted to the reflective layer 30 side is reflected by the reflective layer 30 to the sapphire substrate 10 side, and is emitted from the sapphire substrate 10 to the outside of the light emitting device 1.

  Here, depending on the reflectance exhibited by the reflective layer 30, part of the light emitted from the InGaN light emitting layer 22 to the reflective layer 30 side passes through the reflective layer 30 and is used for the p-type electrode 40. To reach. Even in such a case, the light that has passed through the reflective layer 30 is reflected by the p-type electrode 40 toward the sapphire substrate 10 and is emitted to the outside of the light emitting device 1.

  FIG. 3 shows a change in refractive index according to the impurity concentration of the first conductive layer according to the first embodiment.

When TiO ₂ is doped with Ta as an impurity, TiO ₂ becomes Ti _1-x Ta _x O ₂ according to the concentration of doped Ta. FIG. 3 shows the refractive index of Ti _1-x Ta _x O ₂ with respect to light having a wavelength of 400 nm to 800 nm when x is changed from 0.01 to 0.2. Ti _1-x Ta _x O ₂ shows a tendency that the refractive index decreases in the wavelength range from 400 nm to 800 nm when the concentration of Ta to be doped increases. The refractive index at a wavelength of 460 nm is about 2.5 when Ta is doped from 3 atom% to 5 atom%. Here, the resistivity of Ti _1-x Ta _x O ₂ when Ta is doped in TiO ₂ by 3 to 5 atom% is 2 × 10 ⁻³ Ωcm or less. Therefore, in the present embodiment, Ti ₁ doped with 3 atom% to 5 atom% of Ta for the purpose of ensuring a difference in refractive index from ITO as the second conductive layer 302 and ensuring desired electrical conductivity. it is preferable to use the _-x Ta _x O ₂ as a first conductive layer 300.

  FIG. 4A shows the calculation result of the reflectance of a reflective layer composed of a material having a refractive index of 2.0 and a material having a refractive index of 2.1.

  In FIG. 4A, the conductive unit is set such that the incident medium is GaN (refractive index 2.45) and the output medium is air (refractive index: 1.0), and the wavelength at which the reflectivity is maximum is 460 nm. The thickness of ITO forming the layer was 57.5 nm, and the thickness of ZnO having a refractive index of 2.1 was 54.8 nm. The reflectance was calculated by changing the number of pairs of ITO and ZnO from 10 to 60.

  Referring to FIG. 4A, when the number of pairs is 40, the reflectance at a wavelength of 460 nm does not exceed 99%. On the other hand, when the number of pairs was 60, the reflectance at a wavelength of 460 nm exceeded 99%, but the wavelength range where the reflectance was 99% or more was 10 nm or less. Therefore, in a conductive unit layer formed of ITO and ZnO, it is difficult to maintain a reflectance of 99% or more when a shift in wavelength of light emitted from the InGaN light emitting layer 22 occurs. Further, it is difficult to maintain a reflectance of 99% or more even when the angle of light incident on the conductive reflective layer is large.

  FIG. 4B shows a calculation result of the reflectance of a reflective layer composed of a material having a refractive index of 2.0 and a material having a refractive index of 2.5.

In FIG. 4B, the conductive unit is set such that the incident medium is set to GaN (refractive index: 2.45) and the output medium is set to air (refractive index: 1.0), and the wavelength at which the reflectance becomes maximum is 460 nm. The thickness of ITO (refractive index 2.0) as the second conductive layer 302 forming the layer 310 is 57.5 nm, and the thickness of TiO ₂ (refractive index 2.5) as the first conductive layer 300 is 46. It was set to 0 nm. Then, the reflectance was calculated by changing the number of pairs composed of ITO and TiO ₂ from 5 to 20.

Referring to FIG. 4B, the number of pairs composed of ITO and TiO ₂ was 15 pairs or more, and the reflectance at a wavelength of 460 nm exceeded 99% and was almost 100%. Thereby, if there are at least 15 pairs of TiO ₂ (refractive index of 2.5) and ITO forming the conductive unit layer 310, the light emitted from the InGaN light emitting layer 22 can be reflected almost 100%. Indicated.

  FIG. 4C shows the calculation result of the reflectance of the reflective layer composed of a material having a refractive index of 2.0 and a material having a refractive index of 2.8.

In FIG. 4C, the conductive unit is set such that the incident medium is set to GaN (refractive index 2.45) and the output medium is set to air (refractive index: 1.0), and the wavelength at which the reflectivity is maximized is 460 nm. The thickness of ITO (refractive index 2.0) as the second conductive layer 302 forming the layer 310 is 57.5 nm, and the thickness of TiO ₂ (refractive index 2.8) as the first conductive layer 300 is 41. The thickness was 1 nm. Then, the reflectance was calculated by changing the number of pairs composed of ITO and TiO ₂ from 5 to 20.

Referring to FIG. 4C, the number of pairs composed of ITO and TiO ₂ was 10 pairs or more, and the reflectance at a wavelength of 460 nm exceeded 99% and was almost 100%. Thus, if there are at least 10 pairs of TiO ₂ (refractive index 2.8) and ITO forming the conductive unit layer 310, the light emitted from the InGaN light emitting layer 22 can be reflected almost 100%. Indicated.

  FIG. 5 shows the dependence of the reflectance on the number of pairs of conductive unit layers when materials having different refractive indexes are used.

Specifically, FIG. 5 shows the first conductive layer constituting the conductive unit layer 310 by fixing the material forming the second conductive layer 302 constituting the conductive unit layer 310 to ITO (refractive index 2.0). When the material forming 300 is ZnO (refractive index 2.1), TiO ₂ doped with impurities at a predetermined concentration (refractive index 2.5), and TiO ₂ doped with impurities at a predetermined concentration (refractive index). The reflectance at a wavelength of 460 nm due to the difference in the number of pairs of the conductive unit layer 310 in each case of 2.8) is shown.

In order to obtain a reflectance of 99% or more at a wavelength of 460 nm, when the first conductive layer 300 is ZnO, 53 pairs or more are required. On the other hand, in order to obtain a reflectance of 99% or more at a wavelength of 460 nm, when TiO ₂ having a refractive index of 2.5 is used as the first conductive layer 300, it may be 12 pairs or more, and the refractive index is 2.8. It was shown that when TiO ₂ was used as the first conductive layer 300, 8 pairs or more was sufficient.

  FIG. 6 shows the number of pairs of conductive unit layers required when the reflectance of the reflective layer at a wavelength of 460 nm exceeds 99% when the second conductive layer is made of ITO.

  Referring to FIG. 6, when a material having a refractive index of 2.3 or less is used for the first conductive layer 300, the number of pairs of the conductive unit layers 310 required when the reflectance of the reflective layer 30 at a wavelength of 460 nm exceeds 99% is obtained. It can be seen that it increases rapidly. Therefore, it can be seen that it is preferable to use a material having a refractive index of 2.3 or more for the first conductive layer 300.

  FIG. 7 shows the layer thickness of the reflective layer formed of a plurality of conductive unit layers when the second conductive layer is made of ITO and the reflectance of the reflective layer at a wavelength of 460 nm exceeds 99%.

  Referring to FIG. 7, if a material having a refractive index of 2.3 or less is used for the first conductive layer 300, the number of pairs of the conductive unit layers 310 required when the reflectance of the reflective layer 30 at a wavelength of 460 nm exceeds 99% is obtained. It can be seen that the film thickness of the reflective layer 30 increases rapidly as it increases rapidly. As the film thickness of the reflective layer 30 increases, the resistance in the thickness direction increases as the film thickness increases, and the manufacturing cost also increases. Therefore, it can be seen that it is preferable to use a material having a refractive index of 2.3 or more for the first conductive layer 300.

  FIG. 8 shows a reflection spectrum in the case where the reflective layer is formed with the number of pairs of conductive unit layers required to make the reflectance of the reflective layer 99% or more.

  Referring to FIG. 8, the reflectivity of the reflective layer 30 with respect to light having a wavelength of 460 nm is 1 in the case where the refractive index of the first conductive layer 300 is 2.1, 2.5, and 2.8. About 99% or more. However, when the refractive index is 2.1, the width of the wavelength at which the reflectance of the reflective layer 30 indicates about 90% or more is about 14 nm. On the other hand, when the refractive index is 2.5 and the refractive index is 2.8, the width of the wavelength at which the reflectance of the reflective layer 30 indicates about 90% or more is about 68 nm and about 104 nm, respectively.

  Therefore, by using a material having a refractive index of 2.5 or 2.8 for the first conductive layer 300, when the wavelength of light incident on the reflective layer 30 is shifted, or light is incident on the reflective layer 30 obliquely. Even in this case, it is possible to maintain a reflectance of 90% or more with respect to the predetermined wavelength.

(Effects of the first embodiment)
According to the embodiment of the present invention, the following effects can be obtained.

In this embodiment, the reflective layer 30 is made of a layer made of TiO ₂ having electric conductivity whose refractive index can be controlled by the doping amount of Ta, and a material having electric conductivity showing a refractive index smaller than that of TiO _2. And a plurality of layers to be formed. Therefore, the light emitted from the light emitting layer in the formed reflective layer 30 can be reflected to the outside of the light emitting device 1. Thereby, the light emitted from the light emitting layer can be efficiently extracted outside.

  Further, in the light emitting device 1 according to this embodiment, since the reflective layer 30 having electrical conductivity can be used as an electrode, it is not necessary to form an electrode separately from the reflective layer 30. Therefore, the manufacturing process of the light emitting device 1 can be simplified.

Conventionally, a reflective layer may be formed by laminating a plurality of ITO and ZnO as materials having electrical conductivity. Both the refractive index of ITO and the refractive index of ZnO are around 2.0. The refractive index difference between the refractive index of ITO and the refractive index of ZnO is small. Accordingly, in order to obtain a desired reflectance, for example, a unit containing ITO and ZnO must be stacked 50 to 60 times, with the refractive index of ITO being 2.0 and the refractive index of ZnO being 2.1. Don't be. On the other hand, in this embodiment, the refractive index of the refractive index (about 2.5) of TiO ₂ forming the first conductive layer 300 and the refractive index (about 2.0) of ITO forming the second conductive layer 302. Since the difference is significantly larger than that in the conventional case, the number of times of stacking units including the first conductive layer 300 and the second conductive layer 302 can be greatly reduced. Thereby, the manufacturing process of the light-emitting device 1 can be simplified compared with the past.

  Furthermore, since the refractive index difference between the refractive index of the first conductive layer 300 and the refractive index of the second conductive layer 302 constituting the reflective layer 30 according to this embodiment is large, the reflective bandwidth of the reflective layer 30 is increased. Can do. As a result, the reflective layer 30 has a high reflectance even with respect to variations in the emission wavelength of the InGaN light emitting layer 22 and variations occurring in the manufacturing process of the film thickness of the first conductive layer 300 and the film thickness of the second conductive layer 302. Can be maintained. In addition, by increasing the reflection bandwidth of the reflective layer 30, it is possible to provide a range in the emission wavelength range by the design of the quantum well structure of the InGaN light emitting layer 22, and the degree of freedom in designing the quantum well structure is increased.

  In the present embodiment, the p-type electrode 40 as a metal layer that reflects the light emitted from the light emitting layer can be provided on the reflective layer 30. Thereby, even if the light transmitted through the reflective layer 30 is reflected by the metal layer, the efficiency of extracting the light emitted from the light emitting layer to the outside of the light emitting device 1 can be improved.

In addition, since the refractive index of the first conductive layer 300 formed of TiO ₂ can be changed by controlling the impurity doping concentration, the reflection exhibiting high reflectance in a wide wavelength range including a desired wavelength region. Layer 30 can be formed.

[Modification of First Embodiment]
FIG. 9A is a calculation result of the wavelength dependence of the reflectance of the reflective layer according to the modification.

In the reference reflective layer 30 of FIG. 9A, the incident medium is set to GaN (refractive index 2.45) and the output medium is set to air (refractive index: 1.0), and the reflective layer 30 has a maximum reflectance (one example). The wavelength at which 99.2%) is set to 460 nm. Specifically, the thickness of ITO (refractive index 2.0) as the second conductive layer 302 forming the conductive unit layer 310 is 57.5 nm, and the thickness of TiO ₂ as the first conductive layer 300 (refractive index 2.5). ) Was 46.0 nm, and the reflective layer 30 in which 12 pairs of units each composed of the first conductive layer 300 and the second conductive layer 302 were laminated was used as the reference reflective layer 30. That is, the film thickness constituting the reflective layer 30 was set to ¼ n of a wavelength of 460 nm (n is a refractive index).

9A, the incident medium is set to GaN (refractive index 2.45) and the output medium is set to air (refractive index: 1.0). Specifically, the number of pairs composed of ITO and TiO ₂ was fixed at 12, and the film thickness of the first conductive layer 300 and the film thickness of the second conductive layer 302 were set to 1.05 times, respectively. The reflective layer 30 is the reflective layer 30 according to the first modification. That is, the thickness of the first conductive layer 300 of the reflective layer 30 according to the first modification was set to 48.3 nm, and the thickness of the second conductive layer 302 was set to 60.4 nm. With this configuration, the reflection layer 30 according to the first modification has a reflectance of 97.8% at a wavelength of 460 nm.

Furthermore, in the reflective layer 30 according to the second modification of FIG. 9A, the incident medium is set to GaN (refractive index 2.45) and the output medium is set to air (refractive index: 1.0). Specifically, the number of pairs composed of ITO and TiO ₂ was fixed at 12, and the film thickness of the first conductive layer 300 and the film thickness of the second conductive layer 302 were each set to 1.1 times. The reflective layer 30 is the reflective layer 30 according to the second modification. That is, the thickness of the first conductive layer 300 of the reflective layer 30 according to the first modification is set to 50.6 nm, and the thickness of the second conductive layer 302 is set to 63.3 nm. With this configuration, the reflection layer 30 according to the second modification has a reflectance of 6.0% at a wavelength of 460 nm.

  Referring to FIG. 9A, the reference reflective layer 30, the reflective layer 30 according to the first modification, and the reflective layer 30 according to the second modification are sequentially increased in film thickness. With reference to FIG. 9A, As can be seen, as the film thickness increases, the wavelength at which the reflectance is maximized becomes longer. That is, the highly reflective region of the reflective layer 30 moves to the long wavelength region as the thickness of the reflective layer 30 increases.

  FIG. 9B shows the incident angle dependency (s-wave) of the reflectance of the reflective layer according to the modification with respect to light having a wavelength of 460 nm, and FIG. 9C shows the reflectance of the light with a wavelength of 460 nm of the reflective layer according to the modification. The incident angle dependency (p wave) is shown.

  As can be seen with reference to FIGS. 9B and 9C, in the reflective layer 30 according to the first modification in which the film thickness is 1.05 times that of the standard reflective layer 30, compared to the case of the standard reflective layer 30. High reflectivity was exhibited even for light incident at a larger incident angle. That is, as shown in FIG. 9B, the reflection layer 30 according to the first modification example has a higher reflectance than the reference reflection layer 30 in the range where the incident angle is about 12 ° to about 24 ° in the s wave. The reflectance was 95% or more. Further, as shown in FIG. 9C, the reflection layer 30 according to the first modification example has a higher reflectivity than the reference reflection layer 30 in the incident angle range of about 12 ° to about 24 ° in the p-wave. A reflectance of 80% or more was exhibited.

  From the above results, the film thicknesses of the first conductive layer 300 and the second conductive layer 302 constituting the reflective layer 30 are each thicker than ¼n of the wavelength of light reflected by the reflective layer 30 (n is the refractive index). It was shown that it can be set and formed. In particular, the thickness of each of the first conductive layer 300 and the second conductive layer 302 is set to be larger than ¼ n (n is a refractive index) of the wavelength of light reflected by the reflective layer 30 and reflected by the reflective layer 30. The incident angle to the reflective layer 30 is large while ensuring the reflectivity of the light incident on the reflective layer 30 at a small incident angle by setting it to 1.05 times or less of 1 / 4n (n is the refractive index) of the wavelength of the light to be transmitted. It was shown that the incident light can be reflected with high reflectivity.

  Thereby, even when predetermined light is incident on the reflective layer 30 from an oblique direction, the film thickness of the first conductive layer 300 and the film thickness of the second conductive layer 302 are set to a predetermined ratio from the wavelength of the light. By forming it thick, high reflectance can be maintained not only when light enters the reflective layer 30 perpendicularly but also when the incident angle increases.

  FIG. 10 shows the number of pairs of conductive unit layers required for the reflectance of the reflective layer to be 99% or more when the refractive index of the second conductive layer is changed.

The first conductive layer 300 constituting the reflective layer 30 was fixed to TiO ₂ (refractive index 2.5), and the refractive index of the second conductive layer 302 was changed from 2.0 to 2.4. The incident medium is GaN (refractive index 2.45), the output medium is air (refractive index 1.0), and the film thicknesses of the first conductive layer 300 and the second conductive layer 302 constituting the reflective layer 30 are as follows. Are each 460 nm / 4n (n is a refractive index).

  Referring to FIG. 10, when the refractive index of the second conductive layer 302 exceeds 2.2, the number of pairs of the conductive unit layers 310 increases rapidly. On the other hand, when the refractive index of the second conductive layer 302 was 2.2 or less, the number of pairs of the conductive unit layers 310 was 20 pairs or less, and the reflectance of the reflective layer 30 was 99% or more. Thereby, when the reflectance of the reflective layer 30 is taken into consideration, the refractive index of the second conductive layer is preferably 2.2 or less.

[Second Embodiment]
FIG. 11 shows a longitudinal sectional view of a light emitting device according to the second embodiment of the present invention.

(Configuration of light-emitting device 2)
The light emitting device 2 includes a conductive GaN substrate 15, an n-type GaN layer 20 provided on the conductive GaN substrate 15, an InGaN light emitting layer 22 provided on the n-type GaN layer 20, and an InGaN light emitting layer 22. And a p-type GaN layer 24 provided thereon.

  The light emitting device 2 includes an ITO electrode 42 provided on the p-type GaN layer 24, a bonding pad 52 provided in a predetermined region on the ITO electrode 42, and the n-type GaN layer 20 of the conductive GaN substrate 15. The reflective layer 30 provided on the opposite side to the side on which the conductive layer is provided, the n-type electrode 45 provided on the opposite side of the reflective layer 30 from the side in contact with the conductive GaN substrate 15, and the reflective layer of the n-type electrode 45 And a bonding pad 50 provided on the side opposite to the side in contact with 30. Here, like the bonding pad 50, the bonding pad 52 includes, for example, a metal such as Ti, Ni, and Au.

  The light-emitting device 2 is different from the light-emitting device 1 except that the plurality of compound semiconductor layers are formed on the conductive GaN substrate 15 instead of the sapphire substrate 10. Since this is the same as the case, a detailed description of the compound semiconductor layer is omitted. Further, the reflective layer 30, the n-type electrode 45, and the bonding pad 50 have substantially the same configuration as that of the light emitting device 1 in the above description, and exhibit substantially the same operation and function, and thus detailed description thereof is omitted. To do.

(Operation of the light emitting device 2)
When power is supplied to the InGaN light emitting layer 22 from the bonding pad 52, a current flows between the ITO electrode 42 and the bonding pad 50 via the reflective layer 30. The InGaN light-emitting layer 22 emits light in a predetermined wavelength region by the power supplied from the bonding pad 52.

  A part of the light emitted from the InGaN light emitting layer 22 is emitted to the outside of the light emitting device 2 through the ITO electrode 42. On the other hand, part of the light emitted from the InGaN light emitting layer 22 is radiated to the reflective layer 30 side through the conductive GaN substrate 15. The reflective layer 30 reflects a part of the light emitted from the InGaN light emitting layer 22 to the ITO electrode 42 side. Further, the n-type electrode 45 reflects a part of the light transmitted through the reflective layer 30 to the ITO electrode 42 side.

(Effect of the second embodiment)
According to the light emitting device 2 according to the present embodiment, a layer made of TiO ₂ having electrical conductivity capable of controlling the refractive index by the Ta doping amount, and electrical conductivity exhibiting a refractive index smaller than the refractive index of TiO _2. The reflective layer 30 can be formed by laminating a plurality of layers made of the materials having the same, and a face-up type LED can be formed using the conductive GaN substrate 15. As a result, the light emitted from the light emitting layer is reflected to the outside of the light emitting device 2 by the reflective layer 30, so that the light extraction efficiency can be improved, and the p type GaN layer 24 side of the light emitting device 2 can be improved. Since it is not necessary to form a mold electrode and an n-type electrode, the manufacture of the light emitting device 2 can be simplified, and the element shape can be reduced in size.

  Further, according to the light emitting device 2 according to the present embodiment, the conductive GaN substrate 15 is used, and the conductive GaN substrate 15 is provided with the reflective layer 30 having electrical conductivity, and the light emitting device is interposed via the reflective layer 30. Since there is a current path 2 to the outside, the electrostatic resistance of the light emitting device 2 can be improved.

[Third Embodiment]
FIG. 12 shows a longitudinal sectional view of a light emitting device according to the third embodiment of the present invention.

(Configuration of light emitting device 3)
The light emitting device 3 includes a conductive GaN substrate 15, an n-type GaN layer 20 provided on the conductive GaN substrate 15, a quantum well layer 21 provided on the n-type GaN layer 20, and a quantum well layer 21. And a p-type GaN layer 24 provided thereon. The n-type GaN layer 20, the quantum well layer 21, and the p-type GaN layer 24 provided on the conductive GaN substrate 15 are each formed by MOCVD in the same manner as the light emitting device 1 in the description of FIGS. Therefore, detailed description thereof is omitted. The quantum well layer 21 has a multiple quantum well structure composed of In _x Ga _1-x N / GaN.

  The light emitting device 3 is in contact with a reflective layer 30b provided on the p-type GaN layer 24, an insulating layer 70 provided in a predetermined region on the reflective layer 30, and a part on the reflective layer 30. The p-type electrode 40 provided on the insulating layer 70 except for the portion in contact with the reflective layer 30 and the conductive GaN substrate 15 on the opposite side of the n-type GaN layer 20 provided on the conductive GaN substrate 15. And a n-type electrode 45 provided on the opposite side of the reflective layer 30a from the side in contact with the conductive GaN substrate 15.

  Here, the reflective layer 30a and the reflective layer 30b have substantially the same configuration as the reflective layer 30 in the above description of FIGS. 1 to 10, but the reflectance of the reflective layer 30a is higher than the reflectance of the reflective layer 30b. The reflective layer 30a and the reflective layer 30b are formed as much as possible. That is, the number of conductive unit layers 310 included in the reflective layer 30a and the number of conductive unit layers 310 included in the reflective layer 30b are controlled to form the reflective layer 30a and the reflective layer 30b. Further, the p-type electrode 40 and the n-type electrode 45 have substantially the same configuration, operation, and function as the p-type electrode 40 and the n-type electrode 45 in the above description of FIGS. Detailed description will be omitted.

The insulating layer 70 is formed on the reflective layer 30b by, for example, a vacuum deposition method. Specifically, the insulating layer 70 is formed from silicon dioxide (SiO ₂ ). Then, an opening 60 that exposes a part of the reflective layer 30 b is provided in a part of the insulating layer 70. The opening 60 is substantially circular in top view. Here, a part of the p-type electrode 40 is electrically connected to a part of the reflective layer 30 b in the opening 60.

(Operation of the light emitting device 3)
When the quantum well layer 21 receives the power supplied from the p-type electrode 40 via the reflective layer 30b, the quantum well layer 21 emits light in a predetermined wavelength region. The light emitted from the quantum well layer 21 is reflected by the reflective layer 30 a via the conductive GaN substrate 15. The reflective layer 30b reflects the light emitted from the quantum well layer 21 and the light reflected from the reflective layer 30a. Thereby, the light emitted from the quantum well layer 21 resonates between the reflective layer 30a and the reflective layer 30b. That is, the light emitting device 3 according to the present embodiment is a resonator type LED (RC-LED: Resonant-Cavity LED). In such a case, by forming the reflective layer 30a and the reflective layer 30b so that the reflectance of the reflective layer 30b is smaller than the reflectance of the reflective layer 30a, the light resonated between the reflective layer 30a and the reflective layer 30b is The light is emitted from the opening 60 to the outside of the light emitting device 3.

(Effect of the third embodiment)
In the light-emitting device 3 according to the present embodiment, the reflective layer 30a and the reflective layer 30b constitute a resonator-type LED, so that the light extraction efficiency is improved by the action of the angular selectivity of the resonator and the photon recycling. Can do.

[Fourth Embodiment]
FIG. 13 shows a longitudinal sectional view of a light emitting device according to the fourth embodiment of the present invention.

  In the light emitting device 5 according to this embodiment, the conductive GaN substrate 15 of the light emitting device 3 in the above description of FIG. 12 becomes the sapphire substrate 10, opposite to the surface in contact with the n-type GaN layer 20 of the sapphire substrate 10. Except for the point that the reflective layer 31 is formed, the configuration is substantially the same as that of the light-emitting device 3, and since it exhibits substantially the same operation and function, detailed description thereof is omitted.

  In the present embodiment, when the quantum well layer 21 receives the power supplied from the p-type electrode 40 via the reflective layer 30b, the quantum well layer 21 emits light in a predetermined wavelength region. A part of the light emitted from the quantum well layer 21 passes through the sapphire substrate 10 and is reflected by the reflection layer 31. Further, the light emitted from the quantum well layer 21 in the reflective layer 30b and the light reflected from the reflective layer 31 are reflected. Thereby, the light emitted from the quantum well layer 21 resonates between the reflective layer 31 and the reflective layer 30b.

Here, the reflective layer 31 according to the present embodiment does not need to have conductivity. As an example, the reflective layer 31 is formed by laminating a plurality of pair layers composed of a first layer formed of TiO ₂ having no conductivity and a _second layer formed of SiO _2. Is done. In addition, you may form the reflection layer 31 from the material similar to the reflection layer 30a with which the light-emitting device 3 in the said description is equipped.

[Fifth Embodiment]
FIG. 14 is a longitudinal sectional view of a light emitting device according to the fifth embodiment of the invention.

  In the light emitting device 6 according to the present embodiment, the conductive GaN substrate 15 of the light emitting device 3 in the above description of FIG. 12 becomes the sapphire substrate 10, and the reflective layer 32 is provided on the n-type GaN layer 20 formation side of the sapphire substrate 10. The n-type electrode is exposed on the exposed surface of the n-type GaN layer 20 exposed by etching of the reflective layer 30b, the p-type GaN layer 24, the quantum well layer 21 and the upper layer of the n-type GaN layer 20 at the corner of the light emitting device 6. Except for the point that 45 is provided, the configuration is substantially the same as that of the light-emitting device 3, and since it exhibits substantially the same operation and function, detailed description thereof is omitted.

  The light emitting device 6 according to the present embodiment includes a sapphire substrate 10, a reflective layer 32 formed from a nitride material provided on the sapphire substrate 10, and an n-type GaN layer 20 formed on the reflective layer 32. An n-type electrode 45 provided in a partial region on the n-type GaN layer 20, a quantum well layer 21 provided in a region of the n-type GaN layer 20 where the n-type electrode 45 is not provided, A p-type GaN layer 24 provided on the quantum well layer 21 and a reflective layer 30b provided on the p-type GaN layer 24 are provided.

  As an example, the reflective layer 32 according to the present embodiment includes a plurality of nitride layer pairs formed of a first nitride layer formed of AlN and a second nitride layer formed of GaN. To be formed. For example, the reflective layer 32 can be formed by stacking 25 pairs of the nitride layers.

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all combinations of the features described in the embodiments are essential to the means for solving the problems of the invention.

It is a longitudinal cross-sectional view of the light-emitting device which concerns on 1st Embodiment. It is an enlarged view of the longitudinal section of the reflective layer concerning a 1st embodiment. It is a graph which shows the change of the refractive index according to the impurity concentration of the 1st conductive layer concerning a 1st embodiment. It is a graph which shows the calculation result of the reflectance of the reflection layer comprised with the material whose refractive index is 2.0, and the material whose refractive index is 2.1. It is a graph which shows the calculation result of the reflectance of the reflection layer comprised with the material whose refractive index is 2.0, and the material whose refractive index is 2.5. It is a graph which shows the calculation result of the reflectance of the reflection layer comprised with the material whose refractive index is 2.0, and the material whose refractive index is 2.8. It is a graph which shows the dependence of the reflectance by the pair number of an electroconductive unit layer at the time of using the material from which a refractive index differs. It is a graph which shows the number of pairs of the conductive unit layer required when the reflectance of the reflective layer at a wavelength of 460 nm exceeds 99% when the second conductive layer is made of ITO. It is a graph which shows the layer thickness of the reflection layer formed with a some conductive unit layer, when the reflectance of the reflection layer in wavelength 460nm exceeds 99% when a 2nd conductive layer is ITO. It is a reflection spectrum in the case where the reflective layer is formed with the number of pairs of conductive unit layers required to make the reflectance of the reflective layer 99% or more. It is a graph which shows the wavelength dependence of the reflectance of the reflective layer which concerns on a modification. It is a graph which shows the incident angle dependence (s wave) of the reflectance with respect to the light of wavelength 460nm of the reflective layer which concerns on a modification. It is a graph which shows the incident angle dependence (p wave) of the reflectance with respect to the light of wavelength 460nm of the reflective layer which concerns on a modification. It is a graph which shows the number of pairs of the conductive unit layer required for the reflectance of a reflective layer to become 99% or more when the refractive index of a 2nd conductive layer is changed. It is a longitudinal cross-sectional view of the light-emitting device which concerns on 2nd Embodiment. It is a longitudinal cross-sectional view of the light-emitting device which concerns on 3rd Embodiment. It is a longitudinal cross-sectional view of the light-emitting device which concerns on 4th Embodiment. It is a longitudinal cross-sectional view of the light-emitting device which concerns on 5th Embodiment.

Explanation of symbols

1, 2, 3, 5, 6 Light-emitting device 10 Sapphire substrate 15 Conductive GaN substrate 20 n-type GaN layer 21 quantum well layer 22 InGaN light-emitting layer 24 p-type GaN layer 26 p ⁺ -type GaN layer 30, 30a, 30b, 31 , 32 Reflective layer 40 P-type electrode 42 ITO electrode 45 N-type electrode 50, 52 Bonding pad 60 Opening 70 Insulating film 300 First conductive layer 302 Second conductive layer 310 Conductive unit layer

Claims (9)

A laminated structure including a light emitting layer that emits light by supplying power and a reflective layer that reflects light emitted from the light emitting layer,
The reflective layer is
A first conductive layer formed of titanium oxide (TiO ₂ ) that exhibits electrical conductivity by containing impurities, and has transparency to light emitted from the light emitting layer;
Second conductive material formed from an electrically conductive material having a refractive index smaller than that of the first conductive layer and having transparency to light emitted from the light emitting layer, and provided in contact with the first conductive layer. And having a layer
A light emitting device that supplies the power to the light emitting layer through the first conductive layer and the second conductive layer.   2. The light emitting device according to claim 1, wherein the reflective layer has a structure in which a plurality of conductive unit layers including the first conductive layer and the second conductive layer in contact with the first conductive layer are stacked. The first conductive layer has a film thickness of 1 / (4n ₁ ) (n ₁ is the refractive index of the first conductive layer) of the wavelength of light emitted from the light emitting layer.
The light emitting device according to claim 2, wherein the second conductive layer has a thickness of 1 / (4n ₂ ) (n ₂ is a refractive index of the second conductive layer) of a wavelength of light emitted from the light emitting layer. The first conductive layer is thicker than 1 / (4n ₁ ) (n ₁ is the refractive index of the first conductive layer) of the wavelength of light emitted from the light emitting layer,
3. The light emitting device according to claim 2, wherein the second conductive layer is thicker than 1 / (4n ₂ ) (n ₂ is a refractive index of the second conductive layer) of a wavelength of light emitted from the light emitting layer. . The first conductive layer has a thickness of 1.05 or less of 1 / (4n ₁ ) (n ₁ is the refractive index of the first conductive layer) of the wavelength of light emitted from the light emitting layer,
5. The film thickness of the second conductive layer is 1.05 or less of 1 / (4n ₂ ) (n ₂ is a refractive index of the second conductive layer) of a wavelength of light emitted from the light emitting layer. The light-emitting device of description.   The light emitting device according to claim 1, wherein the reflective layer includes a metal layer that reflects light emitted from the light emitting layer on a side opposite to the light emitting layer.   The light emitting device according to any one of claims 1 to 6, wherein the electrically conductive material forming the second conductive layer has a refractive index of 2.2 or less.   The light emitting device according to any one of claims 1 to 7, wherein the electrically conductive material forming the second conductive layer is formed of indium tin oxide (ITO). 7. The light emitting device according to claim 1, wherein the electrically conductive material forming the second conductive layer is formed of zinc oxide (ZnO).

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