JP4339822B2 - Light emitting device - Google Patents

Description

  The present invention relates to a light emitting device, and more particularly to a highly efficient light emitting device.

  Semiconductor light emitting devices are widely applied in optical display devices, traffic lights, data storage devices, communication devices, lighting devices, and medical equipment.

  Conventional nitride LEDs include a thin metal layer on top of the LED, such as Ni / Au group materials that are considered transparent conductive layers. However, LED light cannot partially pass through the metal. The light generated by the LED is absorbed by the thin metal layer and the light transmission is reduced. In order to have good transmission, the thickness of the thin metal layer is limited to tens to hundreds of angstroms. Although the thickness of the thin metal layer is limited, the thin metal layer simply has a visible light transmittance in the range of 60-70%, and the luminous efficiency of the LED remains low.

An LED structure included here as a reference is disclosed (for example, see Patent Document 1). The surface of the LED includes a transparent conductive oxide layer formed on a p-type contact layer having a high carrier concentration. Generally, the transparent conductive oxide layer has a high transmittance higher than 90%. Therefore, the thickness of such a layer can be increased, current spreading is good, and the brightness and luminous efficiency of the LED are improved. Note that the transparent conductive oxide layer should be in contact with a p-type contact layer with a carrier concentration higher than 5 × 10 ¹⁸ cm ³ so as to form a good ohmic contact.

  A method of forming a reverse tunneling layer is incorporated herein by reference and disclosed (see, for example, Patent Document 2). An N + reverse tunneling contact layer is formed between the transparent oxide electrode layer and the semiconductor light emitting layer, which achieves the purpose of good ohmic contact so as to improve the luminous efficiency of the LED and reduce the operating voltage. The

  In addition, a related method is disclosed (for example, refer nonpatent literature 1). It was disclosed that a thin metal layer was formed on the p-type contact layer of the nitride LED, and then a transparent conductive oxide layer was formed on the thin metal layer. This method can efficiently reduce the contact resistance between the p-type contact layer and the transparent conductive oxide layer. However, the transmittance is further reduced by the thin metal layer, and the luminous efficiency of the LED is further influenced by the thin metal layer.

Therefore, the present invention improves the brightness of the LED so as to solve the contact resistance problem between the contact layer and the transparent conductive oxide layer as described above and simplify the processing complexity. It is aimed at.
US Pat. No. 6,078,064 Taiwan Patent No. 144,415 Specification Y. C. Lin, “InGaN / GaN Light Emitting Diodes with Ni / Au, Ni / ITO and ITO p-Type Contacts” (Solid-State Electronics Vol. 47 Page 849-853)

  Accordingly, an object of the present invention is to provide a light-emitting device with high transmittance in order to solve the above-described problems.

  The present invention discloses a light emitting device. The light emitting device includes a substrate, a first nitride semiconductor stack formed on the substrate, a nitride light emitting layer formed on the first nitride semiconductor stack, and a first light emitting layer formed on the nitride light emitting layer. A second nitride semiconductor stack, the second nitride semiconductor stack having a plurality of hexagonal pyramidal holes on the surface of the second nitride semiconductor layer opposite the nitride light emitting layer; A hexagonal pyramidal hole extends downward from the surface of the second nitride semiconductor layer, and a first transparent conductive oxide layer is formed on the second nitride semiconductor stack. . The plurality of hexagonal pyramid-shaped holes of the second nitride semiconductor stack are filled with the first transparent conductive oxide layer, and a low resistance ohmic contact is formed between the transparent conductive oxide layer and the plurality of hexagonal holes. Occurs between the inner surface of a square pyramidal hole.

  In general, when the second nitride semiconductor stack is a p-type material and its surface relative to the nitride light emitting layer is smooth and parallel to the substrate surface, the transparent conductive oxide layer is a p-type material. A good ohmic contact cannot be directly formed with a nitride semiconductor stack, thereby increasing the operating voltage.

  In contrast, the present invention provides a plurality of hexagonal pyramid holes on the surface of the p-type nitride semiconductor stack opposite the nitride light emitting layer, wherein the hexagonal pyramid holes are the second ones. Extending downward from the surface of the nitride semiconductor layer and then forming a transparent conductive oxide layer on the surface, wherein the transparent conductive oxide layer is a p-type without a pore region It contacts not only the flat area of the nitride semiconductor surface (hereinafter referred to as the “flat outer surface”) but also the inner surface of the hexagonal pyramid-shaped hole (hereinafter referred to as the “inner surface of the hole”). . The surface energy state of the flat outer surface is different from the surface energy state of the inner surface of the hole. The difference between the surface energy states is contributed by the difference in crystal orientation as well as the difference in surface energy potential between the flat outer surface and the inner surface of the hole. When the transparent conductive oxide layer is formed directly on the flat outer surface of the p-type nitride semiconductor stack, the interface between the transparent conductive oxide layer and the flat outer surface has a high contact resistance. Has a high potential barrier to guide. However, when the transparent conductive oxide layer is in contact with the inner surface of the hole, a good ohmic contact can be formed because the interface between the inner surface of the hole and the transparent conductive oxide layer is a low potential barrier. . Therefore, the p-type layer does not require a high carrier concentration as mentioned in the previous prior art. The operating voltage of the device can be reduced to the level as a conventional Ni / Au based LED.

  When an operating current is applied, the current is first spread by the transparent conductive oxide layer and then mainly by the low resistance contact area on the inner surface of the hole in contact with the transparent conductive oxide layer. It flows into the nitride semiconductor stack and finally flows into the light emitting layer so as to generate light.

  Furthermore, another advantage of the present invention of the hexagonal pyramid hole is that the hexagonal pyramid hole effectively reduces both the total reflection effect on the device surface and the light absorption effect of the p-type nitride semiconductor stack. Can be reduced to Furthermore, the luminous efficiency can be increased. In addition, the light transmittance of the transparent conductive oxide layer is better than the light transmittance of the conventional thin metal layer. Being constant, the present invention can greatly improve the luminous efficiency of the device and provide a device with a low operating voltage.

  The foregoing and other objects of the invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, which is illustrated in the various drawings.

  Reference is made to FIG. 1, which is a diagram of a light emitting device according to the present invention. The light emitting device includes a sapphire substrate 10, a nitride buffer layer 11 formed on the sapphire substrate, and an n-type nitride semiconductor stack 12 formed on the nitride buffer layer 11, where the light emitting device is separated from the substrate. The n-type nitride semiconductor stack 12 has a first surface and a second surface, a nitride multiple quantum well structure light emitting layer 13 formed on the first surface, and a nitride multiple quantum well structure light emitting layer. A p-type nitride semiconductor stack 14 formed on the surface of the p-type nitride semiconductor stack 14 away from the light emitting layer 13 having a nitride multiple quantum well structure. A transparent conductive oxide layer 15 including a pyramidal hole 141 is formed on the p-type nitride semiconductor stack 14 and the hexagonal pyramid hole 141, where the transparent conductive oxide layer is formed. 15 The material contacts the inner surface 1411 of the hole, the n-type electrode 16 is formed on the second surface of the n-type nitride semiconductor stack 12, and the p-type electrode 17 is formed on the transparent conductive oxide layer 15. . FIG. 2 is a diagram of a p-type nitride semiconductor stack 14 having a plurality of hexagonal pyramidal holes 141.

  The contact resistance formed between the inner surface 1411 of the hole and the transparent conductive oxide layer 15 is between the flat outer surface 140 of the p-type nitride semiconductor stack 14 and the transparent conductive oxide layer 15. Lower than the formed contact resistance.

  The shape and angle of the hexagonal pyramidal hole 141 depends on the characteristics of the nitride's physical crystal, such as the crystal characteristics of the nitride. For example, taking a C (0001) sapphire substrate as an example, each angle between adjacent pyramid surfaces is substantially about 120 degrees, and the pyramid surface is a (10-11) or (11-22) lattice surface. Including groups.

  The method of forming the hexagonal pyramid-shaped hole 141 includes at least one step or two or more steps as described below.

  1. When the initial layer of the hexagonal pyramid hole 141 starts to be formed, the hexagonal pyramid hole 141 is formed on the surface of the p-type nitride semiconductor stack 14 or inside the p-type nitride semiconductor stack 14. As such, a surfactant such as Si or Mg can be provided to deform the crystal nucleation of the hexagonal pyramidal holes 141.

  2. The initial layer of the hexagonal pyramid hole 141 is a crystal so as to form a hexagonal pyramid hole 141 on the surface of the p-type nitride semiconductor stack 14 or inside the p-type nitride semiconductor stack 14. It is formed between an epitaxial temperature of 700 ° C. and 950 ° C. for deforming nucleation.

  3. The initial layer of the hexagonal pyramid hole 141 is a crystal so as to form a hexagonal pyramid hole 141 on the surface of the p-type nitride semiconductor stack 14 or inside the p-type nitride semiconductor stack 14. It forms in an atmosphere rich in nitrogen to deform nucleation.

4). After the p-type nitride semiconductor stack 14 is formed, the surface of the p-type nitride semiconductor stack 14 is chemically wetted with a high temperature H ³ PO ⁴ or the like to form hexagonal pyramid holes 141. It can etch by performing an etching process.

  5). Initially, small hexagonal pyramidal holes are formed by epitaxial growth. Thereafter, a large hexagonal pyramid hole 141 can be formed by performing a chemical wet etching process on the small hexagonal pyramid hole to improve luminous efficiency. When the hexagonal pyramidal hole 141 is formed directly by epitaxial growth, the stress is reduced to a hexagonal pyramidal shape so as to reduce epitaxial quality and cause epitaxial defects that affect the electrical characteristics of the LED. At the end of the hole 141. However, if a small hexagonal pyramid hole is first formed by epitaxial growth and then etched by a chemical wet etching process to make the small hexagonal pyramid hole larger and deeper, This may avoid damaging the epitaxial layer of the hexagonal pyramidal hole 141.

The density of the hexagonal pyramidal holes 141 of the present invention can be in the range of 1 × 10 ⁷ cm ^{−2 to 1} × 10 ¹¹ cm ⁻² . Reference is made to FIG. 3 showing the best density range of the hexagonal pyramid-shaped holes 141 of the present invention. From FIG. 3, when the density of the hexagonal pyramid holes 141 increases from 1 × 10 ⁸ cm ⁻² to 2 × 10 ⁹ cm ⁻² , the luminance increases from 117 mcd to 150 mcd. This indicates that increasing the density of the hexagonal pyramidal holes 141 improves the brightness of the LED.

  The length of the diagonal line at the top of the hexagonal pyramidal hole 141 is in the range of 10 nm to 1 μm. Reference is made to FIG. 4 which shows the best range of diagonal lengths for the hexagonal pyramidal hole 141. From FIG. 4, when the diagonal length of the hexagonal pyramid hole 141 is increased from 122 nm to 168 nm, the luminance increases from 128 mcd to 173 mcd, and when the hexagonal pyramid hole increases, the luminance of the LED becomes brighter. It means to become.

  The depth of the hexagonal pyramidal hole 141 of the present invention is in the range of 10 nm to 1 μm. Reference is made to FIG. 5 which shows the best range of depth for the hexagonal pyramid hole 141. From FIG. 5, when the depth of the hexagonal pyramid hole 141 increases from 60 nm to 125 nm, the luminance increases from 130 mcd to 150 mcd. That is, when the hexagonal pyramid hole is deepened, the brightness of the LED becomes brighter.

  Note that the bottom of the hexagonal pyramidal hole 141 is above the light emitting layer 13. If the bottom of the hexagonal pyramidal hole 141 extends to the light emitting layer 13, the electrical characteristics of the LED may be inferior.

  Further, the transparent conductive oxide layer 15 is continuous so that the periphery of each hexagonal pyramid hole 141 in contact with the transparent conductive oxide layer 15 is continuous, not discontinuous or damaged. It should be thick enough to fill and cover the periphery of the hexagonal pyramid hole 141. Otherwise, current may not pass through the nitride semiconductor stack 14 due to the low resistance contact of the inner surface of the hexagonal pyramid hole 141 in contact with the transparent conductive oxide layer 15, and thus The operating voltage will increase.

  Reference is made to FIG. 6 which is a table of the average depth of the hexagonal pyramidal holes 141, the thickness of the transparent conductive oxide layer 15, and the operating voltage. This example is a nitride LED having a hexagonal pyramidal hole 141, and the average depth of the holes is 150 nm. Assume that different thicknesses of the transparent conductive oxide layer 15 of 70 nm and 220 nm are respectively formed on the nitride semiconductor stack 14. When the current is 20 mA, the operating voltage of the LED with the transparent conductive oxide layer 15 of 70 nm is about 3.6V. However, the operating voltage of the LED with the 220 nm transparent conductive oxide layer 15 is about 3.3 V under the same conditions. This means that the operating voltage can be reduced when the thickness of the transparent conductive oxide layer 15 is sufficient.

  When the wavelength of light is in the range of 300 nm to 700 nm, the transmittance of the transparent conductive oxide layer 15 is higher than 50%. The transparent conductive oxide layer 15 may be formed by an electron beam evaporator, a sputter, a thermal coater, or any combination listed. The best approach is to fill the hexagonal pyramidal hole 141 so that the area of low resistance contact is increased to form the transparent conductive oxide layer 15 while effectively reducing the operating voltage of the LED. That is.

  In addition, after the transparent conductive oxide layer 15 fills the hexagonal pyramid hole 141, the surface of the transparent conductive oxide layer 15 does not have the characteristics of the hexagonal pyramid hole 141. In other words, the difference in the refractive index of the material should be maximized under and above the hexagonal pyramidal hole 141, and the light extraction effect can be improved. Therefore, the refractive index of the transparent conductive oxide layer 15 should be between the refractive index of the nitride material and the refractive index of the package material. Preferably, the absolute value of the difference in refractive index between the transparent conductive oxide layer 15 and the nitride material is higher than the absolute value of the difference in refractive index between the transparent conductive oxide layer 15 and the package material.

  FIG. 7 shows a comparison of light intensity and operating current graphs for three types of LEDs, where LED-A has a hexagonal pyramidal hole 141 and a transparent conductive oxide layer 15 of the present invention. LED-B is an LED with a thin metal layer but no hexagonal pyramid hole 141, and LED-C has a conductive oxide layer but a hexagonal pyramid hole 141. It is LED which does not have. From FIG. 7, LED-B has incomplete emission characteristics and low luminance because the light transmittance of the thin metal layer is inferior to the light transmittance of the conductive oxide layer. LED-C, in which a conventional thin metal layer is replaced with a transparent conductive oxide layer, has good light transmittance, thereby improving the light emission effect and increasing the light emission efficiency. However, LED-A utilizes hexagonal pyramidal holes 141 that increase the sum of the light emitting areas and reduce the light loss caused by all reflection effects and light absorption of the semiconductor stack on the light emitting layer. Therefore, LED-A can greatly increase the luminance and the luminous efficiency.

  FIG. 8 shows a comparison graph of positive current versus voltage in three types of LEDs, where LED-A is an LED having a hexagonal pyramidal hole 141 and a transparent conductive oxide layer 15 of the present invention. LED-B is an LED having a thin metal layer but not having a hexagonal pyramid hole 141, and LED-C has a conductive oxide layer but not having a hexagonal pyramid hole 141. LED. From FIG. 8, the operating voltage of LED-B having a thin metal layer is the lowest among the three types of LEDs. Due to imperfect ohmic contact, the operating voltage of LED-C with a conductive oxide layer is very high. For example, when the current is 20 mA, the operation voltage of LED-C is larger than 5V. Nevertheless, the operating voltage of LED-A having a conductive oxide layer and hexagonal pyramidal holes 141 can be reduced to the same operating voltage as LED-B. Therefore, the present invention can provide good performance.

  Reference is made to FIG. 9, which is a second embodiment of a light emitting device according to the present invention. The second surface of the n-type nitride semiconductor stack 12 of the light emitting device further includes a contact region 121 of the n-type electrode and a non-contact region 122 with the electrode. The n-type electrode 16 is formed on the contact region 121 of the n-type electrode. The non-contact region 122 with the electrode further includes a highly efficient light emitting surface. The rough surface or the plurality of hexagonal pyramidal holes are formed by etching or epitaxially growing a highly efficient light emitting surface. In this embodiment, the light emitting device includes a rough surface 123. The rough surface 123 of the non-contact region 122 with the electrode can reduce the side light reflected between the substrate 10 and the n-type nitride semiconductor stack 12, and the side light to increase the luminous efficiency of the LED. Can radiate effectively.

  Reference is made to FIG. 10, which is a third embodiment of a light emitting device according to the present invention. The light emitting device also includes a second transparent conductive oxide layer 18 formed on the rough surface 123 and on the non-contact region 122 with the electrode, and further includes a second transparent conductive oxide layer 18. Is in contact with the n-type electrode 16 and the current spread in the second transparent conductive oxide layer 18 is improved. Furthermore, if the refractive index of the second transparent conductive oxide layer 18 is between the refractive index of the nitride material and the refractive index of the package material, the luminous efficiency is improved.

  In the above-described embodiment, the transparent conductive oxide layer can be formed between the n-type electrode 16 and the contact surface 121 of the second surface of the n-type nitride semiconductor stack 12 with the n-type electrode.

  In the above embodiment, the transparent conductive oxide layer can be regarded as an n-type electrode.

  In the above-described embodiment, the contact surface 121 with the n-type electrode includes a plurality of hexagonal pyramidal holes.

In the embodiment described above, the sapphire substrate 10 has an off angle between 0 and 10 degrees. The sapphire substrate 10 can be replaced by a substrate made of a material selected from the group consisting of GaN, AlN, SiC, GaAs, GaP, Si, ZnO, MgO, MgAl ₂ O ₄ , and glass.

  In the embodiment described above, the nitride buffer layer 11 is made of AlN, GaN, AlGaN, InGaN, and AlInGaN. The n-type nitride semiconductor stack 12 is made of AlN, GaN, AlGaN, InGaN, and AlInGaN. The light emitting layer 13 having a nitride multiple quantum well structure is made of AlN, GaN, AlGaN, InGaN, and AlInGaN. The p-type nitride semiconductor stack 14 is made of AlN, GaN, AlGaN, InGaN, and AlInGaN. The transparent conductive oxide layers 15 and 18 are made of indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide (indium tin oxide). Zinc oxide, zinc aluminum oxide, and zinc tin oxide.

  Those skilled in the art will readily appreciate that numerous modifications and variations of the apparatus and method may be made in accordance with the teachings of the present invention. Accordingly, the above disclosure should be construed as limited only by the scope of the claims appended hereto.

It is a figure of the 1st embodiment of the light-emitting device by this invention. FIG. 4 is a diagram of a plurality of hexagonal pyramid hole p-type nitride semiconductor stacks according to the present invention. It is a graph of the relationship between the brightness | luminance of the light-emitting device of this invention, and the density of a hexagonal pyramid type | mold hole. It is a graph of the relationship between the brightness | luminance of the light-emitting device of this invention, and the length of the diagonal of a hexagonal pyramid type | mold hole. It is a graph of the relationship between the brightness | luminance of the light-emitting device of this invention, and the depth of a hexagonal pyramid type | mold hole. It is a table | surface of the average depth of a hexagonal pyramid type | mold hole, the thickness of a transparent conductive oxide layer, and an operating voltage. It is a graph of the relationship between the intensity | strength in different LED, and operating current. It is a graph of the relationship between positive current and voltage at different LEDs. It is a figure of the 2nd embodiment of the light-emitting device by this invention. FIG. 4 is a diagram of a third embodiment of a light emitting device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sapphire substrate 11 Nitride buffer layer 12 N-type nitride semiconductor stack 13 Light emitting layer 14 P-type nitride semiconductor stack 15 Transparent conductive oxide layer 16 N-type electrode 17 P-type electrode 121 Contact with n-type electrode Region 122 Non-contact region with electrode 123 Rough surface 140 Flat outer surface 141 Hexagonal pyramidal hole 1411 Inner surface of hole

Claims (26)

substrate,
A first nitride semiconductor stack formed on the substrate;
A nitride light-emitting layer formed on the first nitride semiconductor stack;
Light emission including a second nitride semiconductor stack formed on the nitride light emitting layer, and a first transparent conductive oxide layer formed on the second nitride semiconductor stack and having an electrode formed thereon A device,
The second nitride semiconductor stack includes a plurality of hexagonal pyramid holes extending downward from a surface of the second nitride semiconductor stack opposite the nitride light emitting layer;
The plurality of hexagonal pyramidal holes of the second nitride semiconductor stack are configured to make ohmic contact between the first transparent conductive oxide layer and the inner surfaces of the plurality of hexagonal pyramid holes. Substantially filled with the first transparent conductive oxide layer ;
The surface of the first nitride semiconductor stack remote from the substrate includes a first surface and a second surface;
The nitride light emitting layer is formed on a first surface of the first nitride semiconductor stack;
The light emitting device further comprising a second transparent conductive oxide layer formed on the second surface of the first nitride semiconductor stack .   2. The light emitting device according to claim 1, wherein a diagonal length of one hole of the hexagonal pyramid on a surface of the second nitride semiconductor stack is in a range from 10 nm to 1 μm. 2. The light emitting device according to claim 1, wherein a density of the holes of the hexagonal pyramid is in a range of 1 × 10 ⁷ cm ⁻² to 1 × 10 ¹¹ cm ⁻² .   The light emitting device according to claim 1, wherein a depth of one hole of the hexagonal pyramid is in a range of 10 nm to 1 μm.   The light emitting device of claim 1, further comprising a buffer layer formed between the substrate and the first nitride semiconductor stack.   The first transparent conductive oxide layer was selected from the group consisting of indium tin oxide (ITO), tin cadmium oxide (CTO), tin antimony oxide, indium zinc oxide, aluminum zinc oxide and zinc zinc oxide. The light emitting device of claim 1, comprising at least one material.   The light emitting device according to claim 1, wherein the transmittance of the first transparent conductive oxide layer is higher than 50% when the wavelength of light is in the range of 300 nm to 700 nm.   The light emitting device according to claim 1, wherein the thickness of the first transparent conductive oxide layer is in a range of 50 nm to 1 μm. The substrate is a C (0001) sapphire substrate;
The angle between the surfaces of every two adjacent cones of each of the hexagonal pyramid holes is substantially 120 degrees; and
2. The light emitting device according to claim 1, wherein each of the surfaces of the cones includes (10-11) or (11-22) lattice surface groups.   The light emitting device according to claim 1, wherein the substrate is a (0001) or (11-20) sapphire substrate having an off-angle of 0 degrees to 10 degrees. The light emitting device according to claim 1, wherein the substrate includes at least one material selected from the group consisting of GaN, AlN, SiC, GaAs, GaP, Si, ZnO, MgO, MgAl ₂ O ₄ , and glass.   The light emitting device of claim 1, wherein the first nitride semiconductor stack comprises at least one material selected from the group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN. The first nitride semiconductor stack includes at least one n-type nitride semiconductor layer; and
The light emitting device of claim 1, wherein the second nitride semiconductor stack includes at least one p-type nitride semiconductor layer. The first nitride semiconductor stack includes at least one p-type nitride semiconductor layer; and
The light emitting device of claim 1, wherein the second nitride semiconductor stack includes at least one n-type nitride semiconductor layer.   The light emitting device according to claim 1, wherein the nitride light emitting layer includes at least one material selected from the group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.   The light emitting device of claim 1, wherein the nitride light emitting layer comprises a double heterostructure, a single quantum well structure, or a multiple quantum well structure.   The light emitting device of claim 1, wherein the second nitride semiconductor stack comprises at least one material selected from the group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.   The light emitting device according to claim 5, wherein the buffer layer includes at least one material selected from the group consisting of AlN, GaN, AlGaN, InGaN, and AlInGaN.   The light-emitting device according to claim 1, wherein the hexagonal pyramid hole of the second nitride semiconductor stack is formed by epitaxial growth.   The light emitting device according to claim 1, wherein the hexagonal pyramid hole of the second nitride semiconductor stack is formed by performing a wet etching process.   The light emitting device of claim 1, wherein the hexagonal pyramidal holes of the second nitride semiconductor stack are formed by performing epitaxial growth and wet etching processes.   The light emitting device according to claim 1, wherein a distance from a bottom of the hexagonal pyramid hole to the substrate is longer than a distance from an upper surface of the nitride light emitting layer to the substrate.   The contact resistance formed on the inner surface of the hexagonal pyramid hole in contact with the first transparent conductive oxide layer is the second nitridation in contact with the first transparent conductive oxide layer. The light emitting device according to claim 1, wherein the light emitting device is lower than a contact resistance formed on a surface of the physical semiconductor stack.   The light emitting device of claim 1, wherein the refractive index of the first transparent conductive oxide layer is between the refractive index of the nitride material and the refractive index of the package material. The second transparent conductive oxide layer includes at least one material selected from the group consisting of indium tin oxide, tin cadmium oxide, tin antimony oxide, indium zinc oxide, zinc aluminum oxide, and zinc zinc oxide. The light emitting device according to claim 1 . The light emitting device of claim 1 , wherein the refractive index of the second transparent conductive oxide layer is between the refractive index of the nitride material and the refractive index of the package material.

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