KR101280501B1 - Light emitting diodes using a transparent electrode - Google Patents

Abstract

The present invention relates to a light emitting diode capable of improving luminous efficiency compared to the prior art by applying a transparent electrode made of an oxide film / metal / oxide film to a gallium nitride-based light emitting diode.
The light emitting diode according to the present invention is a light emitting diode comprising a transparent electrode formed on an n-type semiconductor having a surface semiconductor layer on the semiconductor layer having a light emitting structure or an N-face or Ga-face, the transparent electrode is the n-type An oxide layer, a metal layer, and an oxide layer are sequentially formed on a semiconductor.

Description

Light Emitting Diode Using Transparent Electrode {LIGHT EMITTING DIODES USING A TRANSPARENT ELECTRODE}

The present invention relates to a method of manufacturing a light emitting diode, and more particularly, to a light emitting diode capable of improving luminous efficiency compared to the prior art by applying a transparent electrode made of an oxide film / metal / oxide film to a gallium nitride-based light emitting diode. will be.

White light source gallium nitride-based light emitting diodes have various forms of energy conversion efficiency, long life, high light directivity, low voltage driving, no preheating time and complicated driving circuit, and strong against shock and vibration. It is expected to be a solid-state lighting source that will replace the existing light sources such as incandescent lamps, fluorescent lamps and mercury lamps within the next five years due to the implementation of high quality lighting systems.

In order to use a gallium nitride-based light emitting diode as a white light source to replace a mercury lamp or a fluorescent lamp, it must not only have excellent thermal stability but also be able to emit high power at low power consumption.

Horizontal gallium nitride-based light emitting diodes, which are widely used as white light sources, have the advantages of relatively low manufacturing cost and simple manufacturing process, but they are inadequate to be used as high power sources with high applied current and large area. There is.

A vertical structure light emitting diode is a device that overcomes the disadvantages of the horizontal structure light emitting diode and is easy to apply a large area high power light emitting diode. Such vertical structured light emitting diodes have various advantages compared to conventional horizontal structured devices. In the vertical light emitting diode, the current spreading resistance is small, so a very uniform current spreading can be obtained, resulting in a lower operating voltage and a large light output, and a smooth heat dissipation through a metal or semiconductor substrate having good thermal conductivity. Long device life and significantly improved high power operation are possible. In this vertical structured light emitting diode, the maximum applied current increases more than 3-4 times compared to the horizontal structured light emitting diode, so it is certain that it will be widely used as a white light source for illumination. Leading overseas LED companies such as OSRAM and domestic companies such as Seoul Semiconductor, Samsung Electro-Mechanics and LG Innotek are actively conducting R & D to commercialize and improve the performance of gallium nitride vertical light emitting diodes. It is already selling related products.

In order to further improve the light output of the light emitting diode of the gallium nitride-based vertical structure, a current diffusion layer is required to smooth current diffusion to the n-type semiconductor layer. As a current diffusion layer, studies using materials such as ITO and ZnO continue to be performed. It is becoming.

The present invention is to solve the problem to provide a light emitting diode that can obtain a light output improved compared to the conventional by applying a transparent electrode that enables a smooth current diffusion of the semiconductor layer to the light emitting diode structure.

As a means for solving the above problems, the present invention is a transparent semiconductor layer formed on an n-type semiconductor having an N-face or a Ga-face on the surface semiconductor layer on the semiconductor layer having a light emitting structure A light emitting diode including an electrode, wherein the transparent electrode has a multi-layer structure in which an oxide layer, a metal layer, and an oxide layer are sequentially formed on the n-type semiconductor.

In addition, as another aspect of the present invention, the light emitting diode according to the present invention may include a metal layer for current injection between the n-type semiconductor and the transparent electrode.

In still another aspect of the present invention, a light emitting diode according to the present invention comprises a transparent electrode on which a surface semiconductor layer on a semiconductor layer having a light emitting structure is formed on an n-type semiconductor having an N-face or a Ga-face; The transparent electrode may have a multilayer structure in which a metal layer and an oxide layer are sequentially formed on the n-type semiconductor.

In addition, in the light emitting diode, the surface of the upper oxide layer of the transparent electrode may be patterned.

In the light emitting diode, an n-type electrode may be formed on the upper oxide layer or the metal layer of the transparent electrode.

In the light emitting diode, the oxide layer is at least one selected from WO _x , ZnO _x , CaO _x , TiO _x , NiO _x , CoO _x , CeO _x , SiO _x , CuO _x , ITO, AZO, MoO _x . Can be made.

In the light emitting diode, the oxide layer preferably has a thickness of 1 nm to 10 μm.

In addition, in the light emitting diode, the metal layer may include at least one selected from Ag, Au or Al, the thickness of the metal layer is preferably 1nm ~ 100nm.

In the light emitting diode, the current injection metal layer may include Ti, Ni, Cr, or Ag, and the thickness of the current injection metal layer is preferably 0.1 nm to 100 nm.

In the light emitting diode, the patterning may be formed by a photolithography method or a nanoimprint method.

In the light emitting diode, the n-type electrode may be formed of at least one metal selected from Cr, Au, Ti, Al, Ni, Pd, Pt, or Ag.

The oxide / metal / oxide transparent ohmic electrode of the present invention can be immediately applied to a manufacturing process of a gallium nitride-based light emitting diode which is widely used at present, and the light output is remarkably improved compared with the prior art.

1 is a schematic cross-sectional view of a gallium nitride-based vertical light emitting diode according to a first embodiment of the present invention.
2A and 2B are cross-sectional views showing states when the positions of forming n-type electrodes of the gallium nitride-based vertical light emitting diodes according to Example 1 of the present invention are changed.
3 is a schematic cross-sectional view of a gallium nitride-based vertical light emitting diode according to a second embodiment of the present invention.
4 is a schematic cross-sectional view of a gallium nitride-based vertical light emitting diode according to a third embodiment of the present invention.
5 is a schematic cross-sectional view of a gallium nitride-based vertical light emitting diode according to a fourth embodiment of the present invention.
6 shows current-voltage curves of gallium nitride based light emitting diodes prepared according to Examples 1 and 2 of the present invention.
7 is a spectrum showing the transmittance of a gallium nitride-based vertical light emitting diode prepared according to Examples 1 and 2 of the present invention.

Hereinafter, the present invention will be described in more detail based on the preferred embodiments of the present invention. However, the following examples are merely examples to help the understanding of the present invention, whereby the scope of the present invention is not reduced or limited.

Since the n-type electrode formed on the n-type semiconductor layer is not transparent, when the area of the n-type electrode is large, the light escaping above is not blocked by the n-type electrode, and thus the light extraction efficiency from which the light escapes from the device becomes low. On the contrary, when the area of the n-type electrode is small, a problem arises in that electrons injected from the n-type electrode in a large area device do not spread to a wide range of devices and a current crowding effect occurs.

However, if a transparent and conductive transparent electrode is formed under the n-type electrode, even if a small area n-type electrode is used, electrons are dispersed throughout the device so that a current crowding effect does not occur, so that a high-efficiency high output light emitting diode Can make

Example 1

1 is a schematic view showing a cross-sectional structure of a gallium nitride-based vertical light emitting diode according to Example 1 of the present invention. As shown in FIGS. 1 and 2, the gallium nitride-based vertical light emitting diode according to the first embodiment of the present invention includes a conductive substrate 10 and a reflective p-type electrode 20 formed on the conductive substrate 10. ), a p-type GaN layer 30, an active layer 40, an n-type GaN layer 50, a transparent electrode 60, and an n-type electrode 70.

The conductive substrate 10 may be preferably made of one or more selected from the group consisting of Si, Mo, Cu, stainless steel, Invar steel, and a metal alloy, one side of which A heat dissipation pattern may be formed to increase the efficiency of dissipation of heat generated from the light emitting diode, such as a concave-convex shape, a sawtooth shape, a hemisphere shape, and a combination thereof.

The reflective p-type electrode 20 is a layer for applying power, preferably Ag, Al, or the like.

The p-type GaN layer 30 is a layer providing holes and may be formed of AlN, InGaN, AlGaN, AlInGaN, or the like in addition to GaN.

The active layer 40 is a layer that outputs light having a predetermined wavelength while electrons provided from the n-type GaN layer 50 and holes provided from the p-type GaN layer 30 are recombined, and include a well layer and a barrier layer ( barrier layers) may be alternately stacked to form a multilayer semiconductor thin film having a single or multiple quantum well structure, and the active layer 40 may vary in wavelength of light output according to its material. The appropriate material can be selected according to the desired output wavelength.

The n-type GaN layer 50 may be formed of a gallium nitride compound semiconductor as a layer for providing electrons, and may be formed of AlN, InGaN, AlGaN, AlInGaN, or the like in addition to GaN.

The transparent electrode 60 has a multilayer structure of a lower oxide layer 61, a metal layer 62, and an upper oxide layer 63. That is, the transparent electrode according to the first embodiment of the present invention is characterized by forming a multilayer structure of an oxide / metal / oxide. Thus, when the metal layer is interposed between the oxide layers, the difference in refractive index between the metal layer and the air is alleviated. As a result, it is possible to obtain a zero-reflection coating effect, thereby increasing the current injection effect while minimizing the decrease in the transmittance of light generated in the active layer, resulting in a reduction of the area of the n-type electrode. This greatly improves the light output of the light emitting diodes.

The lower and upper oxide layers 61 and 63 may be selected from WO _x , ZnO _x , CaO _x , TiO _x , NiO _x , CoO _x , CeO _x , SiO _x , CuO _x , ITO, AZO, and MoO _x . It is preferably made of more than one species, the thickness is preferably 1nm ~ 10㎛, which is less than 1nm when the oxide is not thin film is formed uniformly, when the thickness exceeds 10㎛ transmittance of the transparent electrode due to the thick thin film Because it decreases.

In addition, the metal layer is preferably made of one or more selected from Ag, Au or Al, the thickness is preferably 1nm ~ 100nm, which is less than 1nm, the uniform metal layer is not formed, the light scattering increases If the thickness exceeds 100 nm, the reflectivity of the metal layer is increased, thereby decreasing the transmittance of the transparent electrode.

The n-type electrode 70 serves to inject a current into the n-type semiconductor, preferably made of Cr, Au, Ti, Al, Ni, Pd, Pt or Ag. In Embodiment 1 of the present invention, the n-type electrode 70 is formed on a transparent electrode that facilitates the current diffusion to the n-type semiconductor layer, as shown in Figure 2a, photolithography on the upper oxide layer 63 And a part of the upper oxide layer 63 may be formed on the metal layer 62 after dry etching or wet etching a portion of the upper oxide layer 63 to increase current injection efficiency, as shown in FIG. 2B.

The light emitting diode having the structure as described above may be manufactured through the following process.

First, an n-type GaN layer made of Si-doped GaN is formed on a sapphire substrate using MOCVD (Metal Organic Chemical Vapor Deposition), and an active layer made of InGaN / GaN and a p-type GaN layer doped with Mg are sequentially formed. After washing with acetone, IPA (Iso-propanol alcohol) and deionized water, it is dried with nitrogen. After that, a reflective p-type electrode made of silver (Ag) and a protective layer were formed by electron beam evaporation, and Ni, Au, Cu, and Ni can support GaN having a thickness of several micrometers and have no problem in current injection. A metal substrate such as -Fe alloy or a conductive substrate made of Si, GaAs, or the like, is attached. Subsequently, when irradiated with KrF laser having a wavelength of 248 nm to the sapphire surface, the sapphire having an energy bandgap larger than the laser energy passes through the laser, and the laser is absorbed by the GaN semiconductor layer having a small bandgap. The layer will melt. After separating the sapphire and GaN by using the laser lift-off method using this principle, the metallic Ga generated during the laser lift-off is removed by a solution of 1: 1 hydrochloric acid and deionized water. Subsequently, a transparent electrode having an oxide film / metal / oxide structure is deposited on the n-type GaN layer by an electron beam deposition method, a sputter deposition method, or a thermal vapor deposition method.

In Example 1 of the present invention, after forming a thin film made of WO _x as the lower oxide layer 61 to a thickness of 30nm, a thin film made of Ag was formed as the metal layer 62 to 15nm, the upper oxide layer 63 By the method of forming a thin film made of WO _x to a thickness of 30nm, a transparent electrode 60 was formed.

Table 1 shows the results of measuring the light transmittance and the contact resistance of the 450 nm wavelength of the transparent electrode 60 formed as described above. 6 and 7 are graphs showing the result (indicated as 'DMD' in the figure).

WO _x / Ag / WO _x transparent electrode Contact resistance (Ω㎠) 5.2 × 10 ^-2 450nm light transmittance (%) 87

And may be used as a current diffusion layer of the n-type semiconductor to the ^second-, transmittance of the transparent electrode according to a first embodiment of the present invention was significantly higher to 87%, the contact resistance is 5.2 × 10 as identified in Table 1 above. Shows.

[Example 2]

3 is a schematic view showing a cross-sectional structure of a gallium nitride-based vertical light emitting diode according to Example 2 of the present invention. As shown, the gallium nitride-based vertical light emitting diode according to the second embodiment of the present invention, the conductive substrate 10, the reflective p-type electrode 20 formed on the conductive substrate 10 as in the first embodiment ), the p-type GaN layer 30, the active layer 40, the n-type GaN layer 50, the transparent electrode 60 and the n-type electrode 70, but the n-type GaN layer 50 and There is a difference in that the current injection metal layer 80 is further included between the transparent electrodes 60 (the same configuration as that of the first embodiment is denoted by the same reference numeral).

In Example 2, when an ultra-thin metal layer is formed, an oxide layer is formed directly on the n-type GaN layer, current injection into the n-type GaN layer can be further improved by lowering contact resistance while minimizing a decrease in transmittance. Considered.

The current injection metal layer 80 may be formed by photolithography after deposition by thermal deposition, sputtering, or electron beam deposition. Table 2 shows the results of measuring the light transmittance and the contact resistance of 450 nm wavelength after forming a 1 nm thick Ti, Ni and Cr ultra-thin films with the current injection metal layer 80, respectively, and FIGS. 6 and 7 show the results. It is a graph.

Ti / WO _x / Ag / WO _x Ni / WO _x / Ag / WO _x Cr / WO _x / Ag / WO _x Contact resistance (Ω㎠) 2.4 × 10 ^-4 1.3 × 10 ^-4 3.1 × 10 ^-4 450nm light transmittance (%) 80.83 77.58 82.35

As shown in FIG. 6, when the current injection metal layer is formed, the ohmic electrode characteristics are stronger than when the current injection metal layer is not formed, and thus, the contact resistance may be low.

When Ni was used as the current injection metal layer 80, the contact resistance was very low as 1.3 × 10 ⁻⁴ Ωcm ² , and when Ni, the transmittance was slightly lower as 77.58%, and when Ti and Cr were used. The contact resistances were 2.4 × 10 ⁻⁴ μm ² and 3.1 × 10 ⁻⁴ μm ^{2, respectively, which} were considerably lower than those of Example 1, and the transmittance was 80%. Therefore, when applying the current injection metal layer 80, as in the second embodiment of the present invention, it is possible to minimize the current crowding (phenomena crowding) in the vertical structure light emitting diode, it is possible to increase the light output compared to the conventional .

[Example 3]

In addition, Figure 4 is a transparent electrode structure according to the third embodiment of the present invention, by forming a pattern on the upper oxide layer 63, by allowing the light generated in the active layer to efficiently escape to the outside, the additional light extraction efficiency The vertical light emitting diode structure can be expected to be improved.

Example 4

In addition, Figure 5 is a transparent electrode structure according to the fourth embodiment, to replace the n-type GaN layer without forming a separate lower oxide layer, in the case of this structure while obtaining a similar effect as in Example 1, the lower oxide layer It is possible to reduce the process of forming a, it is a structure more considered in terms of cost.

10: conductive substrate
20: p-type electrode
30: p-type GaN layer
40: active layer
50: n-type GaN layer
60: transparent electrode
70: n-type electrode
80: current injection metal layer

Claims (13)

A light emitting diode comprising a transparent electrode formed on an n-type semiconductor having an N-face or a Ga-face, wherein the surface semiconductor layer on the semiconductor layer having a light emitting structure is provided.
The transparent electrode has a multilayer structure in which an oxide layer, a metal layer, and an oxide layer are sequentially formed on the n-type semiconductor,
A light emitting diode, characterized in that a current injection metal layer made of Ti or Cr is formed between the n-type semiconductor and the transparent electrode. delete delete The method of claim 1,
And a surface of an oxide layer formed on the metal layer in the transparent electrode is patterned. The method of claim 1,
The n-type electrode is formed on the metal layer or the oxide layer formed on the metal layer of the transparent electrode. The method of claim 1,
The oxide layer is a light emitting diode, characterized in that made of at least one selected from WO _x , ZnO _x , CaO _x , TiO _x , NiO _x , CoO _x , CeO _x , SiO _x , CuO _x , ITO, AZO, MoO _x . The method of claim 1,
The thickness of the oxide layer is a light emitting diode, characterized in that 1nm ~ 10㎛. The method of claim 1,
The metal layer is a light emitting diode, characterized in that it comprises at least one selected from Ag, Au or Al. The method of claim 1,
The thickness of the metal layer is a light emitting diode, characterized in that 1nm ~ 100nm. delete The method of claim 1,
The thickness of the current injection metal layer is a light emitting diode, characterized in that 0.1nm ~ 100nm. The method of claim 4, wherein
The patterning is a light emitting diode, characterized in that formed by photolithography or nanoimprint method. The method of claim 5, wherein
The n-type electrode is a light emitting diode, characterized in that made of at least one metal selected from Cr, Au, Ti, Al, Ni, Pd, Pt or Ag.

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