KR101063597B1 - Structure and Manufacturing Method of LED Element - Google Patents

Abstract

The present invention relates to a structure and a manufacturing method of the LED device for increasing the light extraction efficiency, the structure of the LED device according to the invention on the sapphire substrate; A buffer layer having a predetermined thickness; An LED structure comprising two opposing doped layers over the buffer layer and an active layer interposed between the doped layers; Consists of opposite electrodes formed on both ends of the LED structure, the thickness of the buffer layer to be thicker than conventional to improve the side emission characteristics of the light generated in the active layer, the structure of the LED device for increasing the overall light extraction efficiency and It provides a manufacturing method.

LED, total reflection, light extraction efficiency

Description

A structure for LED device and a manufacturing method

1 is a cross-sectional view showing the structure of a conventional AlGaInN-based LED device.

2 is a cross-sectional view showing the light transmission characteristics inside the LED device according to the total reflection.

3 is a cross-sectional view showing a concave-convex shape structure for reducing total reflection in a conventional LED device.

4 is a cross-sectional view showing total reflection characteristics at an interface between a buffer layer and a substrate in a conventional LED device.

5 is a cross-sectional view showing the operation principle of the total reflection reduction effect according to the increase in the buffer layer thickness according to the present invention.

Figure 6 is a cross-sectional view showing the structure of the LED device completed by increasing the buffer layer thickness according to the present invention.

7 is a cross-sectional view showing a structure for increasing light extraction efficiency by making the upper surface of the buffer layer according to the present invention into an uneven shape.

<Description of the symbols for the main parts of the drawings>

100: sapphire substrate 200: buffer layer                 

300: n-type cladding layer (n-type GaN) 301: LED device structure

400: active layer 500: p-type cladding layer (p-type GaN)

600: n-side electrode 700: current diffusion layer (transparent electrode)

800: p-side electrode

The present invention relates to a structure and a manufacturing method of an LED (Light Emitting Diode) device for increasing the light extraction efficiency, and more specifically, in the structure of the conventional AlGaInN-based LED device generated in the active layer by varying the thickness of the buffer layer on the sapphire substrate The present invention relates to a structure of a LED device and a method of manufacturing the same for improving the light extraction efficiency as a whole by improving the side emission characteristics of light.

LEDs are an important solid element that converts electrical energy into light and generally include an active layer of semiconductor material sandwiched between two opposing doped layers. When a bias is applied across the two doped layers, holes and electrons are injected into the active layer and then recombined there to generate light. Light generated in the active region is emitted in all directions and escapes the semiconductor chip through all exposed surfaces. The packaging of LEDs is generally used to direct the escaping light to the desired output emission form. In particular, semiconductor LEDs using AlGaInN-based materials have an output wavelength ranging from green to an ultraviolet range. Recently, as research applications are expanded and demand for high-power LED products increases, a lot of research and development have been conducted to improve light output.

The structure of the AlGaInN-based LED device generally manufactured in the prior art is as shown in FIG. Sapphire (Al ₂ O ₃ ) is used as the substrate 10 of the conventional AlGaInN-based LED device, the buffer layer 20, n-type GaN layer 30, AlGaInN quantum well active layer 40, p-type through the single crystal growth After forming each GaN layer 50, the n-type GaN layer 30 is exposed through an etching process to deposit the n-side electrode 60, and a transparent electrode for current diffusion on the p-type GaN layer 50. 70 and the p-side electrode 80 are formed, respectively. In such a conventional LED structure, approaches to maximize the internal quantum efficiency of the active layer 40 and approaches to extract light generated in the active layer to the outside of the LED chip as much as possible are the main means for increasing the light extraction efficiency.

 Two factors can be used to determine the light extraction efficiency in the LED device. First is the light loss due to the degree of transmission to the current diffusion layer, and second is the light loss due to total reflection at the interface where light is emitted.

In relation to the first factor, a Ni / Au alloy layer having a thickness of several nm and several tens of nm is mainly used as a current diffusion layer of a conventional LED device, which is about 60 to 80% of the emission wavelength depending on the thickness and alloy conditions. It has a transmittance of In order to overcome this problem, an approach using an electrode material with high permeability such as ITO has been recently made, but due to the high contact resistance with the p-type GaN layer, it has a difficulty in commercialization, such as np tunnel junction or InGaN / GaN superlattice. The technique which employ | adopts a structure is applied.

On the other hand, the light loss due to total reflection related to the second factor is, as shown in Fig. 2, the interface at which light is emitted from the top of the LED element to the outside, that is, p-type GaN and resin or p-type GaN and air or The difference in refractive index between adjacent materials occurs at the interface between other materials in contact with the p-type GaN or at the interface between the buffer layer 20 and the sapphire substrate 10 existing in the lower region of the LED device.

In order to change the incident angle or the emission angle at the interface in the conventional approach to reduce the light loss due to the total reflection, as shown in Fig. 3, the GaN top layer region 52 using a process such as etching using a rule And a method of patterning irregular or irregular irregular shapes. However, the improvement of light extraction obtained through such a conventional approach is limited, and additional lithography and etching processes are required, and there are disadvantages in that the process is complicated, such as complicated electrode design is inevitable.

Accordingly, an object of the present invention is to not only form a thick buffer layer to sufficiently avoid total reflection occurring at the interface between the buffer layer and the sapphire substrate in order to solve the problems of the conventional AlGaInN-based LED device, but also the thickness of the doping layer on the upper side of the active layer. The present invention provides a structure and a method of manufacturing the LED device which can improve the light extraction efficiency by avoiding total reflection at the interface and allowing more light to be emitted to the side of the LED device.

In order to achieve the above object, the structure of the LED device proposed in the present invention, as shown in Figure 6, on the sapphire substrate 100; A buffer layer 200 having a predetermined thickness; An LED structure (301) comprising two opposing doped layers over the buffer layer and an active layer interposed between the doped layers; Consists of opposite electrodes (600; 700, 800) formed on both ends of the LED structure, by increasing the thickness of the buffer layer 200 than the conventional to improve the side emission characteristics of the light generated in the active layer 400, It is characterized by increasing the light extraction efficiency as a whole.

Since the sapphire (Al ₂ O ₃ ) substrate 100 has a refractive index of about 1.8, when GaN having a refractive index of about 2.5 is used as the buffer layer 200, most of the light generated in the active layer 400 does not pass through the substrate due to the difference in refractive index. Not reflected inside the buffer layer. That is, according to Snell's law, as shown in FIG. 2, light incident at an arbitrary angle (θ ₁ ) with respect to the normal direction of the interface in the region of high refractive index n ₁ according to the following formula is a region of low refractive index n ₂ ) is refracted at a larger angle θ ₂ .

Eventually, light moving from the region of higher refractive index to the region of lower refractive index at an angle greater than a certain critical angle (θ ₃ , θ ₄ ) with respect to the normal direction of the interface proceeds to the region of higher refractive index and is not emitted to the region of lower refractive index. Total internal reflection occurs. Therefore, when GaN is used as the buffer layer 200 in the sapphire substrate 100, the critical angle that can cause total reflection is 48 to 50 ^o , and only about 15 to 20% of light passes through the sapphire substrate without causing total reflection. As a result, a reflection film such as a silver paste positioned between the package and the chip is reached. On the other hand, since a portion of the light totally reflected at these interfaces is lost by absorption and scattering during the reflection path inside the LED, it is important to reduce the light loss due to total reflection.

In the present invention, as a method for reducing the light loss due to total reflection at the interface between the sapphire substrate 100 and the buffer layer 200, the thickness of the buffer layer is conventionally thin as 2 to 4 micrometers as shown in Figure 4 As the total reflection occurs, as shown in FIG. 5 showing the operating principle of the present invention, by increasing the thickness of the buffer layer 200, the light generated in the active layer 400 does not relatively pass through the substrate and the buffer layer interface. More light is emitted through the side of the buffer layer, thereby increasing the light extraction efficiency of the LED device as a whole.

In addition to GaN, InGaN, AlGaN, and the like may be used as the buffer layer 200. When the buffer layer is different from the material of the adjacent doping layer (clad layer 300), the total reflection occurring between these interfaces and the bending of the wafer may be avoided. 7, the surface of the buffer layer may have a concave-convex shape, and the thickness of the buffer layer may be 10 to 40 micrometers thicker than conventional 2 to 4 micrometers in the crystal growth step. It is suitable to achieve the object of the present invention.

In addition, the LED structure 301 is composed of two opposing doped layers 300 and 500 and an active layer 400 interposed between these doped layers, wherein the two opposing doped layers are preferably The p-type cladding layer and the lower layer 300 is an n-type cladding layer, but the upper layer and the lower layer may be doped oppositely. The doped layer and the active layer may use GaN and AlGaInN materials, respectively. When GaN is used in the doping layer, as shown in FIG. 2, the refractive index difference is also used at the p-type GaN 500 and the resin (resin; refractive index is about 1.5) or p-type air (refractive index is about 1.0). The total reflection phenomenon causes most of the light to be reflected inside the GaN layer, and only about 5 to 8% of the light is emitted to the outside without going through the total reflection. A large part of the totally reflected light has a light loss here due to absorption and scattering in the LED, which is one cause of a decrease in light extraction efficiency of the LED device.

Therefore, in order to reduce the light loss due to total reflection at the top of the active layer in the LED device structure as described above, the thickness of the material on the active layer can be increased to 10 to 50 micrometers compared with the conventional, so that the total reflection at the upper layer interface The number of times is also relatively reduced, allowing more light to be emitted to the side of the top layer. The thicker the upper layer is, the better the release characteristics to the side, but the optimum thickness is determined in consideration of the ease of processing and the electrical properties of the upper layer. In particular, considering the electrical characteristics of the upper layer, the optimum thickness should be determined according to the area of the LED element. Usually, the thickness of the upper layer is 10 to 40 microns because the area of the LED element is 300 micrometers × 300 micrometers to several millimeters × several millimeters. The meter is suitable. Of course, if the area of the LED device is larger than the above, the thickness of the upper layer can be made larger.

Then, opposite electrodes are formed on both ends of the LED structure 301 to complete the LED device. Here, the p-side electrodes 700 and 800 are thin translucent metals such as Pd, Pt, Pd / Au, Pt / Au, Ni / Au, NiO / Au, or alloys thereof, and are preferably deposited on top of the p-type GaN layer. The n-side electrode 600 may expose and expose an n-type GaN layer by reactive ion etching for contact, and then Ni, Al / Ni / Au, Al / Ti / Au, or Al / Pt / Au may be used.

Method for manufacturing the LED device is another embodiment of the present invention will be described as follows.

First, the method of manufacturing the LED device comprises the first step of forming a buffer layer on the sapphire substrate (100); A second step of forming an n-type cladding layer (300) on the buffer layer; Forming an active layer (400) on the n-type cladding layer (300) with multi-quantum wells (MQWs); Forming a p-type clad layer (500) on the active layer (400); A fifth step of sequentially etching the p-type cladding layer 500 and the active layer 400 according to a pattern through a photolithography process to expose the n-type cladding layer 300; Comprising a sixth step of forming an electrode on the exposed n-type cladding layer 300 and the p-type cladding layer 500, respectively, the total reflection at the interface with the sapphire substrate in forming the buffer layer of the first step To reduce the buffer layer to a thickness of 10 to 40 micrometers thicker than conventionally and / or to form a p-type cladding layer of the fourth step, the p-type cladding layer is thicker than conventionally to reduce total reflection at the interface with the p-type electrode layer. It is characterized by having a thickness of 10 to 40 micrometers.

Wherein the buffer layer of the first stage is GaN, InGaN, or AlGaN, the n-type cladding layer 300 of the second stage is n-type GaN, the active layer 400 of the third stage is AlGaInN, and the fourth The p-type cladding layer 500 of step is p-type GaN, and the p-side electrodes 700 and 800 of the sixth step are Pd, Pt, Pd / Au, Pt / Au, Ni / Au, NiO / Au or these Alloy or a thin translucent metal, and the n-side electrode 600 may be formed of Ni, Al / Ni / Au, Al / Ti / Au, Al / Pt / Au, or an alloy thereof.

Furthermore, in order to reduce the total reflection between the buffer layer and the n-type clad layer interface between the first step and the second step and to avoid bending of the wafer, as shown in FIG. 8, forming an uneven shape on the surface of the buffer layer. And planarizing the upper part of the n-type cladding layer between the second step and the third step by a chemical mechanical polishing (CMP) process or the like.

In addition, the buffer layer, the n-type cladding layer, the active layer, and the p-type cladding layer may be sputtered, PECVD, or other crystal growth methods. An additional uneven shape of the upper surface of the buffer layer may be a lithography or mechanical polishing process. Reactive ion etching or the like may be used to form an n-type electrode contact, and evaporation or sputtering may be used to form an electrode.

As described above, according to the present invention, the structure of the LED device and the method of manufacturing the same according to the present invention are used to improve the thickness of the doping layer on the upper side of the buffer layer and / or the active layer in order to solve the light loss problem due to the total reflection of the AlGaInN-based LED device. By increasing, the light generated in the active layer is avoided to be totally reflected at each interface and can be emitted more to the side of the LED device, thereby improving the light extraction efficiency of the LED device.

Claims (14)

A buffer layer formed on the sapphire substrate; An LED structure composed of two opposing doped layers—an upper and a lower doped layer—over an active layer interposed between the doped layers over the buffer layer; Comprising opposite electrodes formed on both ends of the LED structure, the structure of the LED device, characterized in that the thickness of the buffer layer is 10 to 40 micrometers. The structure of the LED device according to claim 1, wherein the upper doping layer has a thickness of 10 to 40 micrometers. delete delete According to claim 1 or 2, wherein the upper doping layer is a p-type cladding layer, the lower doping layer is an n-type cladding layer, the electrodes formed on both ends of the LED structure includes an n-side electrode and a p-side electrode. And the p-side electrode comprises a transparent electrode layer. The method of claim 5, wherein the buffer layer is GaN, InGaN, or AlGaN, the n-type cladding layer is n-type GaN, the active layer is AlGaInN, the p-type cladding layer is p-type GaN, the p-side electrode Pd, Pt, Pd / Au, Pt / Au, Ni / Au, or NiO / Au, wherein the n-side electrode is formed of Ni, Al / Ni / Au, Al / Ti / Au or Al / Pt / Au The structure of the LED element characterized by the above-mentioned. A buffer layer formed on the sapphire substrate; An LED structure composed of two opposing doped layers—an upper and a lower doped layer—over an active layer interposed between the doped layers over the buffer layer; Comprising opposite electrodes formed on both ends of the LED structure, the lower doping layer and the buffer layer, characterized in that the structure of the LED device characterized in that the contact with the concave-convex shape. (a) forming a buffer layer on the sapphire substrate; (b) forming an n-type clad layer on the buffer layer; (c) forming an active layer of multi-quantum wells (MQW) on the n-type cladding layer; (d) forming a p-type cladding layer on the active layer; (e) sequentially etching the p-type cladding layer and the active layer to expose the n-type cladding layer; And (f) forming an electrode-an n-side electrode and a p-side electrode-on the exposed n-type cladding layer and the p-type cladding layer, respectively, wherein in forming the buffer layer of step (a), the The method of manufacturing an LED device, characterized in that the thickness of the buffer layer is formed from 10 to 40 micrometers. The method of claim 8, wherein in forming the p-type cladding layer of step (d), the thickness of the p-type cladding layer is 10 to 40 micrometers. delete delete The method according to claim 8 or 9, wherein the buffer layer of step (a) is GaN, InGaN, or AlGaN, and the n-type cladding layer of step (b) is n-type GaN, The active layer is AlGaInN, the p-type cladding layer in step (d) is p-type GaN, and the p-side electrode in step (f) is Pd, Pt, Pd / Au, Pt / Au, Ni / Au or NiO / Au, wherein the n-side electrode is formed of Ni, Al / Ni / Au, Al / Ti / Au or Al / Pt / Au. (a) forming a buffer layer on the sapphire substrate; (b) forming the buffer layer into an uneven shape; (c) forming an n-type clad layer on the buffer layer; (d) forming an active layer with multi-quantum wells (MQW) on the n-type cladding layer; (e) forming a p-type cladding layer on the active layer; (f) sequentially etching the p-type cladding layer and the active layer to expose the n-type cladding layer; And (g) forming an electrode on the exposed n-type cladding layer and the p-type cladding layer, respectively. The method of claim 13, wherein between step (c) and step (d), (h) planarizing an upper portion of the n-type cladding layer.

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