KR20100042122A - Semiconductor light emitting device and method for fabricating the same - Google Patents

Abstract

PURPOSE: A semiconductor light emitting device and a manufacturing method thereof are provided to improve luminous efficiency of the semiconductor light emitting device by forming an electrode using graphene. CONSTITUTION: A first electrode and a second electrode(107) are respectively formed on both sides of a p-n junction and a semiconductor material layer. At least one of first and second electrodes is made of grapheme. A semiconductor material layer is formed on a substrate(101) with a multilayer structure. The semiconductor material layer includes a lowermost n type semiconductor layer and an uppermost p type semiconductor layer.

Description

Semiconductor light emitting device and method for manufacturing the same {Semiconductor light emitting device and method for fabricating the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device such as a light emitting diode (LED) or a laser diode (LD), and more particularly to a semiconductor light emitting device having an improved electrode and a method of manufacturing the same.

Semiconductor light emitting devices such as LEDs and LDs are manufactured with various wavelengths, brightness, and light intensities according to semiconductor materials and device structures. As the conventional semiconductor light emitting device can realize various colors of high brightness in a visible light low brightness device which is mainly used for a simple display, a letter board, etc., it is possible to apply in various fields of total color, high reliability, low power, and miniaturization.

When electrodes are formed across the p-n junction of a semiconductor and current flows therethrough, light is generated as electrons and holes recombine at the p-n junction. At this time, when the current is weak and the density inversion does not occur, the induced emission is not generated and only the light generated by the spontaneous emission is generated. This device is an LED. On the other hand, LD is a device that has high current density and resonant cavity, which induces emitted light to resonate. The wavelength of light generated at this time corresponds to the band gap determined by constituting the semiconductor.

Metals such as Ti, Ni, Cr, and Au, which are commonly used as electrodes of such semiconductor light emitting devices, are opaque and have a problem of obtaining light only at the edges of the electrodes. To solve this problem, transparent conductors such as indium thin oxide (ITO) may be used as transparent electrodes, but the amount of indium that can be collected is very limited, and since ITO is not a stable material, very careful attention is required during the process, making it difficult and expensive. In addition, a process of fabricating a semiconductor light emitting device using these electrode materials requires various complicated processes and expensive equipment for depositing and etching metals during electrode patterning.

In addition, heat is generated in a portion of the semiconductor light emitting device in which electricity flows, and as the temperature of the semiconductor light emitting device increases, the light emitting efficiency of the device decreases. However, the electrode material used in the past does not have high thermal conductivity and thus cannot disperse heat from the device effectively, resulting in a shortening of the life of the device due to heat.

The present invention has been made to solve the conventional problems, the problem to be solved by the present invention is to provide a semiconductor light emitting device with high luminous efficiency by improving the electrode material of the semiconductor light emitting device, and in particular to manufacture such a semiconductor light emitting device The purpose is to provide a way to reduce process costs.

According to an aspect of the present invention, there is provided a semiconductor light emitting device including a semiconductor material layer including a pn junction and first and second electrodes formed at both ends of the pn junction, respectively, and at least one of the first and second electrodes. One is characterized by graphene.

Graphene is a two-dimensional carbon structure with a single atom thickness. This material is made from the graphite found in pencils. Graphene has some unusual physical properties. One of these properties is that the electrons in graphene behave like relativistic particles with no stationary mass and move about 1 million meters per second. Although this speed is 300 times slower than the speed of light in a vacuum, it is much faster than the speed of electrons in ordinary conductors or semiconductors. Graphene is therefore a very good conductor of heat and electricity.

In a specific example, the semiconductor light emitting device according to the present invention has a multi-layer structure on a substrate, and includes at least a lowermost n-type semiconductor layer and an uppermost p-type semiconductor layer in the multilayer structure, wherein the first electrode is the n-type It is formed in contact with the semiconductor layer and the second electrode is formed on the p-type semiconductor layer, the second electrode is formed in a form covering the entire upper surface of the p-type semiconductor layer and is made of graphene. The semiconductor material layer may be formed of an In _x Ga _y Al _(1-xy) N layer (0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

In order to manufacture such a semiconductor light emitting device, graphite powder is attached to the surface of the flexible film to which the adhesive is applied, and then the flexible film is folded and detached to apply graphite. The flexible film coated with graphite is attached to the electrode forming position of the device, and then the flexible film is removed while leaving graphene at the electrode forming position.

At this time, during the repeated folding and release of the flexible film, the steps of rubbing so that no bubbles are visible when the flexible films are bonded to each other, and after attaching the flexible film to the electrode formation position of the device so that the bubble is not visible Rubbing may further comprise.

Through the present invention it is possible to generate a transparent electrode on a substrate in a simple process. In the formation of electrodes using graphene, the flexible film coated with adhesive such as adhesive cellophane tape, which is typically represented by Scotch tape, can be used to form electrodes without expensive equipment or complicated processes, thereby reducing manufacturing costs and time. Can save a great deal. Conventional electrode processes were only possible where clean room facilities were equipped, but the method proposed in the present invention can be performed anywhere without the constraints of these places.

Graphene is easy to collect because graphite is a raw material that exists a lot on the earth. In addition, since it is transparent, light is generated not only on the electrode edge but also on the entire electrode surface, and thus, light emission efficiency can be obtained. Moreover, because it is more transparent than ITO, less light is lost.

And since graphene has a very high thermal conductivity, it is advantageous to dissipate heat generated in the device, thereby lowering the temperature of the device. This results in better light emission efficiency of the semiconductor light emitting device and enables long life of the device.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. Like reference numerals in the drawings indicate like elements. The embodiments described below may be modified in many different forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

1 is a schematic cross-sectional view of a semiconductor light emitting device according to a first embodiment of the present invention.

The semiconductor light emitting device shown in Fig. 1 is a short wavelength LED, and includes a first cladding layer 102 of an n-type gallium nitride-based (GaN-based) semiconductor, an active layer 103 of a GaN-based semiconductor, and a p-type GaN-based semiconductor. It has two cladding layers 104. The first cladding layer 102 is on the buffer layer 120 on the sapphire substrate 101. In the active layer 103, for example, a thin GaN layer and a thin InGaN layer are alternately formed. The active layer 103 may include one or more pairs of thin GaN layers and thin InGaN layers, and additional thin GaN layers. Therefore, both sides of the active layer 103 are thin GaN layers. The thin GaN layer has a thickness of about 1-10 nm and is typically 4 nm. The InGaN layer has a thickness of about 1-5 nm and is typically 2 nm. Thus, when the active layer 103 comprises five pairs of thin GaN layers with typical thicknesses, the thickness of the active layer 103 is 34 nm.

By partially etching the second cladding layer 104, the active layer 103, and a small portion of the first cladding layer 102, a step with substantially vertical sidewalls is formed. The first electrode 105 is formed on the first cladding layer 102 at the bottom of the step. In the present embodiment, a second electrode 107 which is made of graphene and is transparent is formed on the second cladding layer 107. Light is emitted through the second electrode 107.

As such, one example of the semiconductor device according to the present invention includes a semiconductor material layer S having a multi-layer structure on the substrate 101 and including a pn junction, and the lowermost n-type semiconductor layer in the multi-layer structure (this embodiment At least one of the first cladding layer 102 and the uppermost p-type semiconductor layer (second cladding layer 104 in the present embodiment), the first electrode 105 is formed in contact with the n-type semiconductor layer And the second electrode 107 is formed on the p-type semiconductor layer. At least one of the first electrode 105 and the second electrode 107 is preferably made of graphene. In the present embodiment, the second electrode 107 is formed to cover the entire upper surface of the p-type semiconductor layer. It consists of graphene.

2 is a schematic cross-sectional view of a semiconductor light emitting device according to a second exemplary embodiment of the present invention.

The semiconductor light emitting device shown in FIG. 2 is a short wavelength LD, and includes a first contact layer 122 of n-type GaN, and a sapphire substrate 101 having a (0001) surface of the first cladding layer 102 of n-type GaN. An active layer 103 of undoped In _x Ga _(1-x) N is formed on the first cladding layer 102. A second cladding layer 104 of p-type GaN is formed on the active layer 103, and a current block layer 125 of n-type GaN is formed on the second cladding layer 104. A third cladding layer 126 of p-type GaN is formed between the current block layers 125 on the second cladding layer 104. A second contact layer 124 of p + GaN is formed on the third cladding layer 126 and the current block layer 125.

Steps having substantially vertical sidewalls include a second contact layer 124, a current block layer 125, a second cladding layer 104, an active layer 103, a first cladding layer 102, and a first contact layer. It is formed by partially etching the shallow portion of 122. The first electrode 105 is formed on the first contact layer 122 at the bottom of the step so as to be electrically connected to the first contact layer 122. In the present embodiment, a second electrode 107, which is made of graphene and is transparent, is formed on the second contact layer 124. Light is emitted through the second electrode 107.

As such, another example of the semiconductor device according to the present invention includes a semiconductor material layer S ′ having a multi-layer structure on the substrate 101 and including a pn junction, and having a lowermost n-type semiconductor layer in the multi-layer structure. In an embodiment, the semiconductor device includes at least a first contact layer 122 and an uppermost p-type semiconductor layer (second contact layer 124 in the present embodiment), and the first electrode 105 is formed on the n-type semiconductor layer. It is formed in contact with the second electrode 107 is formed on the p-type semiconductor layer. At least one of the first electrode 105 and the second electrode 107 is preferably made of graphene. In the present embodiment, the second electrode 107 is formed to cover the entire upper surface of the p-type semiconductor layer. It is made of graphene.

As such, graphene newly proposed as an electrode material in the present invention is easy to collect and stable since graphite is a raw material present on the earth. In addition, since the light is generated not only at the edge of the electrode but also at the entire electrode side, the light is also advantageous in terms of luminous efficiency.

And since graphene has a very high thermal conductivity, it is advantageous to dissipate heat generated in the device, thereby lowering the temperature of the device. This results in a better light emission efficiency of the semiconductor light emitting device and prevents shortening of the lifetime of the device, thereby enabling long life.

3 to 6 are photographs for explaining the electrode forming process of the semiconductor device manufacturing method according to the present invention. For example, the semiconductor material layers S and S 'as shown in FIGS. 1 and 2 are formed on the substrate 101, followed by mesa etching to form the first electrode 105, and then the second electrode 107. The following process can be applied to form. Alternatively, the semiconductor material layers S and S 'as shown in FIGS. 1 and 2 are formed on the substrate 101, and then the following process is applied to form the second electrode 107, followed by mesa etching. You may proceed in order of forming the 1st electrode 105. FIG. Of course, the following procedure may also be used to form the first electrode 105.

First, as shown in FIG. 3, the thin film of graphite 210 is attached to the surface of the flexible film 200 to which the adhesive is applied, and then the flexible film 200 is folded and detached, and the graphite 210 is further thinned. The flexible film 200 coated with an adhesive may be a cellophane film coated with a pressure-sensitive adhesive, and easily uses an adhesive cellophane tape commonly used as a scotch tape or a 3M tape.

By repeating this process, when the graphite 210 is spread thinly on the surface of the flexible film 200 as shown in FIG. 4, the flexible film 200 prepared above is evenly attached onto the prepared substrate 101 as shown in FIG. 5. When bubbles are removed between the flexible film 200 and the substrate 101 and the flexible film 200 is removed after a while, the thin graphene 230 adheres to the substrate 101 as shown in FIG. 6.

Figure 6 is a photograph of the device with the graphene 230 is raised under a microscope, the translucent portion at the corner corresponds to a place where one or two layers of graphene are raised. 7 is a photograph of graphene using an Atomic Force Microscope (AFM). It can be seen that “vert distance 0.511 nm” is in the box at the bottom right of FIG. 7, which is a result corresponding to the height of one graphene layer.

FIG. 8 is a spectrum taken by Raman spectroscopy of a device on which graphene 230 is raised, and it can be seen that a Raman shift corresponding to a peak is 1569 cm ⁻¹ . This is the Raman shift corresponding to the material of one graphene layer.

As such, the actual graphene 230 was formed on the semiconductor material layers S and S 'only about one or two layers. The graphene 230 generated as described above is used as an electrode of the semiconductor light emitting device.

Never before has graphene been used as an electrode material for semiconductor light emitting devices, and in the manufacture of graphene, conventionally, graphene is oxidized, the graphene layer is separated, made into a solution state, sprinkled onto a substrate, and then reduced again. Or annealing of silicon carbide (SiC) at about 1700 ° C. and raising graphene on SiC as the silicon evaporated. This method is very complicated and expensive equipment is used. In the present invention, it is possible to separate graphene by a physical method using a flexible film coated with an adhesive, and the flexible film area and the amount of starting graphite do not matter much. The process of wide application of graphite on the flexible film does not require constant pressure at all times, and it is enough to rub with a tweezer so that no bubbles are visible when the flexible films are glued together.

Since the electrode made of graphene is transparent, it can be seen that light is generated not only at the edge of the electrode but also as shown in FIG. 8.

Figure 9 (a) is a photograph of the substrate turned on the microscope lamp before applying a voltage to the device made of a real LED, (b) is a photograph of the LED is lit. The number on the arrow indicates the degree of brightness of the part, and the part labeled "60" is where the LED is lit. Unlike other parts, you can see that the light is fine.

As mentioned above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications may be made by those skilled in the art within the technical spirit of the present invention. It is obvious. Embodiments of the invention have been considered in all respects as illustrative and not restrictive, which include the scope of the invention as indicated by the appended claims rather than the detailed description therein, the equivalents of the claims and all modifications within the means. I want to.

1 is a schematic cross-sectional view of a semiconductor light emitting device according to a first embodiment of the present invention.

2 is a schematic cross-sectional view of a semiconductor light emitting device according to a second exemplary embodiment of the present invention.

3 to 6 are photographs for explaining the electrode forming process of the semiconductor device manufacturing method according to the present invention.

FIG. 7 is a photograph of the graphene of FIG. 6 with an Atomic Force Microscope (AFM).

8 is a spectrum taken with Raman spectroscopy of a device having graphene.

9 is a photograph confirming the operation of the device made of a real LED according to the present invention.

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

101 substrate 102 first cladding layer 103 active layer

104 second cladding layer 105 first electrode 107 second electrode

120 buffer layer 122 first contact layer 124 second contact layer

125 ... current block layer 126 ... third cladding layer S, S '... semiconductor material layer

200 ... flexible film coated with adhesive 210 ... graphite

230 Graphene

Claims (5)

A semiconductor light emitting device having a semiconductor material layer including a p-n junction and first and second electrodes formed at both ends of the p-n junction, respectively. At least one of the first and second electrodes is a semiconductor light emitting device, characterized in that made of graphene (graphene). The semiconductor device of claim 1, wherein the semiconductor material layer has a multilayer structure on a substrate, and includes at least a lowermost n-type semiconductor layer and an uppermost p-type semiconductor layer in the multilayer structure, wherein the first electrode is the n-type semiconductor layer. And a second electrode formed on the p-type semiconductor layer, wherein the second electrode is formed to cover the entire upper surface of the p-type semiconductor layer and is made of graphene. The semiconductor light emitting device of claim 1, wherein the semiconductor material layer comprises an In _x Ga _y Al ( _1-xy ) N layer (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). A semiconductor light emitting device manufacturing method comprising: a semiconductor material layer comprising a p-n junction; and first and second electrodes respectively formed at both ends of the p-n junction; In order to form at least one of the first and second electrodes of graphene (graphene), Attaching graphite powder to the flexible film surface to which the adhesive is applied, and then folding and removing the flexible film to apply graphite and repeating the coating; Attaching the graphite-coated flexible film to an electrode formation position of the device; And And removing the flexible film by leaving graphene at the electrode formation position. The method of claim 4, wherein Rubbing the flexible film so that bubbles are not visible when the flexible films are glued together while repeating the folding and releasing of the flexible film; and rubbing the flexible film to the electrode forming position of the device and rubbing so that no bubbles are visible. A method of manufacturing a semiconductor light emitting device further comprising.

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