KR100599011B1 - Light emitting diode having a plurality of light emitting cells each employing a mesh electrode and method of fabricating the same - Google Patents

Abstract

A light emitting diode having a plurality of light emitting cells employing a mesh electrode and a method of manufacturing the same are disclosed. The light emitting diode is disposed on the substrate, and includes a plurality of N-type semiconductor layers, a P-type semiconductor layer located on a portion of the N-type semiconductor layer, and an active layer interposed between the N-type semiconductor layer and the P-type semiconductor layer, respectively. Light emitting cells. A mesh electrode is located on the P-type semiconductor layer of each light emitting cell, and each P-type semiconductor layer has recesses and convex portions corresponding to the mesh electrodes. On the other hand, a buffer layer is interposed between the substrate and each light emitting cell. By adopting the mesh electrode, the light loss caused by the electrode can be reduced, and the light extraction efficiency is improved by the unevenness formed by the mesh electrode and the P-type semiconductor layer.

Light Emitting Diodes, AC LEDs, Mesh Electrodes

Description

LIGHT EMITTING DIODE HAVING A PLURALITY OF LIGHT EMITTING CELLS EACH EMPLOYING A MESH ELECTRODE AND METHOD OF FABRICATING THE SAME}

1 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

2 to 4 are cross-sectional views illustrating a method of manufacturing a light emitting diode according to an embodiment of the present invention.

5 is a cross-sectional view for describing a light emitting diode according to another exemplary embodiment of the present invention.

 The present invention relates to a light emitting diode and a method of manufacturing the same, and more particularly, to a light emitting diode having a plurality of light emitting cells employing a mesh electrode to improve light extraction efficiency and a method of manufacturing the same.

A light emitting diode is a photoelectric conversion semiconductor device having a structure in which an N-type semiconductor and a P-type semiconductor are bonded to each other, and emit light by recombination of electrons and holes. Such light emitting diodes are widely used as display devices and backlights. In addition, the light emitting diode consumes less power and has a longer lifespan than existing light bulbs or fluorescent lamps, thereby replacing its incandescent lamps and fluorescent lamps, thereby expanding its use area for general lighting.

The light emitting diode is repeatedly turned on and off in accordance with the direction of the current under AC power. Therefore, when the light emitting diode is directly connected to an AC power source, the light emitting diode does not emit light continuously and is easily damaged by reverse current.

In order to solve the problem of the light emitting diode, a light emitting diode that can be directly connected to a high voltage AC power source is disclosed in International Publication No. WO 2004/023568 (Al). EMITTING ELEMENTS, which was disclosed by SAKAI et. Al.

According to WO 2004/023568 (Al), LEDs (light emitting cells) are two-dimensionally connected in series on an insulating substrate such as a sapphire substrate to form an LED array. These two LED arrays are connected in anti-parallel on the sapphire substrate. As a result, a single chip light emitting device that can be driven by an AC power supply is provided.

In such a light emitting device, since the LED arrays alternately operate under an AC power source, the light output is considerably limited as compared with the case where the light emitting cells operate simultaneously. Therefore, it is necessary to improve the light extraction efficiency of each light emitting cell in order to increase the maximum light output.

The present invention has been made in an effort to provide a light emitting diode having light emitting cells having improved light extraction efficiency.

Another object of the present invention is to provide a method of manufacturing the light emitting diode.

In order to achieve the above technical problem, the present invention discloses a light emitting diode having a plurality of light emitting cells employing a mesh electrode and a method of manufacturing the same. A light emitting diode according to an aspect of the present invention includes a plurality of light emitting cells. The light emitting cells are disposed on an upper substrate, and include an N-type semiconductor layer, a P-type semiconductor layer positioned on a portion of the N-type semiconductor layer, and an active layer interposed between the N-type semiconductor layer and the P-type semiconductor layer. do. A mesh electrode is positioned on the P-type semiconductor layer of each light emitting cell. Each of the P-type semiconductor layers has recesses and concave portions corresponding to the mesh electrodes. In addition, a buffer layer is interposed between the substrate and each light emitting cell.

According to embodiments of the present invention, by adopting a mesh electrode, it is possible to reduce the light loss by the electrode, and to reduce the light totally reflected by the irregularities formed by the mesh electrode and the P-type semiconductor layer to improve the light extraction efficiency can do.

Meanwhile, a light transmitting layer may cover the mesh electrode. The light transmitting layer covers the convex portions of the mesh electrode and the P-type semiconductor layer. The light transmitting layer may have a refractive index within a range of 1.3 ~ 1.8. Accordingly, by using the light transmitting layer having a small refractive index, the amount of light emitted to the outside may be increased, that is, the light extraction efficiency may be improved.

Alternatively, the reflective metal layer may cover the mesh electrode. A metal bumper for flip chip bonding is formed on the reflective metal layer. Accordingly, it is possible to provide a flip chip type light emitting diode having improved light extraction efficiency.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples to ensure that the spirit of the present invention can be fully conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. And, in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like numbers refer to like elements throughout.

1 is a cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

Referring to FIG. 1, a plurality of patterned light emitting cells 30 are positioned on a substrate 21. The substrate 21 may be, for example, a sapphire substrate or a SiC substrate having a higher thermal conductivity than that of sapphire.

Each of the light emitting cells 30 includes an N-type semiconductor layer 25, an active layer 27, and a P-type semiconductor layer 29a. The active layer 27 and the P-type semiconductor layer 29a are located on a portion of the N-type semiconductor layer 25 as shown. Accordingly, other partial regions of the upper surface of the N-type semiconductor layer 25 are exposed.

The N-type semiconductor layer 25 may be formed of N-type Al _x In _y Ga _1-xy N (0 ≦ x, y, x + y ≦ 1), and may include an N-type cladding layer. In addition, the P-type semiconductor layer 29a may be formed of P-type Al _x In _y Ga _1-x-y N (0 ≦ x, y, x + y ≦ 1), and may include a P-type cladding layer. have. The N-type semiconductor layer 25 may be formed by doping silicon (Si), and the P-type semiconductor layer 29a may be formed by doping zinc (Zn) or magnesium (Mg).

The active layer 27 is a region where electrons and holes are recombined, and includes InGaN. The emission wavelength emitted from the light emitting cell is determined according to the type of material constituting the active layer 27. The active layer 27 may be a multilayer film in which a quantum well layer and a barrier layer are repeatedly formed. The barrier layer and the well layer may be binary to quaternary compound semiconductor layers represented by general formula Al _x In _y Ga _1-xy N (0 ≦ x, y, x + y ≦ 1).

A buffer layer 23 may be interposed between the substrate 21 and the light emitting cells 30. The buffer layer 23 is used to mitigate the lattice mismatch between the semiconductor layers to be formed thereon and the substrate 21. In addition, when the substrate 21 is conductive, the buffer layer 23 is formed of an insulating material or a semi-insulating material to electrically insulate the substrate 21 from the light emitting cells 30. The buffer layer 23 may be formed of, for example, nitride such as AlN or GaN. Meanwhile, when the substrate 21 is insulative, such as sapphire, the buffer layer 23 may be formed of a conductive material. In this case, the buffer layers 23 are spaced apart from each other in correspondence with the light emitting cells 30 to electrically separate the light emitting cells 30.

The mesh electrode 31b is positioned on the P-type semiconductor layer 29a of the light emitting cell 30. The mesh electrode 31b has openings that expose the P-type semiconductor layer 29a. In general, the plate-shaped transparent electrode may transmit light, but may also absorb light. Therefore, light loss occurs due to light absorption of the electrode. However, according to embodiments of the present invention, the light emitted from the active layer 27 may be emitted to the outside through the openings, thereby reducing the light loss compared to the plate-shaped transparent electrode, and thus light extraction The efficiency is improved. The mesh electrode 31b may be formed of a transparent material such as Ni / Au or indium tin oxide (ITO). That is, the mesh electrode 31b may be a transparent electrode.

Meanwhile, the pad electrode 31a electrically connected to the mesh electrode 31b may be disposed on the same plane as the mesh electrode 31b. The electrode 31a is preferably formed of the same material as the mesh electrode 31b.

The P-type semiconductor layer 29a has recesses and concave portions corresponding to the mesh electrodes 31b. Accordingly, irregularities are formed by the P-type semiconductor layer 29a and the mesh electrode 31b on the light emitting cell 30, that is, on the light exit surface. As the unevenness is formed on the emission surface from which light is emitted, total reflection of light can be reduced, thereby improving light extraction efficiency.

Meanwhile, the light transmitting layer 33 may cover the mesh electrode 31b. The light transmitting layer 33 may be formed of a light transmitting material, for example, SiO ₂ . The light transmitting layer has a refractive index lower than that of the P-type semiconductor layer 29a and the mesh electrode 31b, for example, in the range of 1.3 to 1.8. Therefore, it is possible to prevent the total reflection from the upper surface of the light transmitting layer 33 can further improve the light extraction efficiency.

An electrode pad 35a is positioned on the N-type semiconductor layer 25, and an electrode pad 35b is positioned on the P-type semiconductor layer 29a. When the pad electrode 31a is formed on the P-type semiconductor layer, the electrode pad 35b is formed on the pad electrode 31a.

The light emitting cells 30 are electrically connected through metal wires 37. The metal wires 37 connect the electrode pad 35a and the electrode pad 35b to electrically connect the P-type semiconductor layer 29a and the N-type semiconductor layer 25 of the adjacent light emitting cells 30. Connect. The light emitting cells 30 form an array connected in series by the metal wires 37. Arrays of two or more series-connected light emitting cells may be formed on the substrate 21, and the arrays may be connected in anti-parallel to each other and driven by an AC power source.

Hereinafter, a method of manufacturing a light emitting diode according to an embodiment of the present invention will be described with reference to FIGS. 2 to 4.

Referring to FIG. 2, a buffer layer 23 is formed on a substrate 21, and an N-type semiconductor layer 25, an active layer 27, and a P-type semiconductor layer 29 are sequentially formed on the buffer layer 23. do. The P-type semiconductor layer 29 may be formed to a sufficient thickness of 0.5 ~ 5㎛.

The buffer layer 23 and the semiconductor layers 25, 27, and 29 may be formed using metal organic chemical vapor deposition (MOCVD), molecular beam growth (MBE), or hydride vapor deposition (HVPE). In addition, the semiconductor layers 25, 27, and 29 may be continuously formed in the same process chamber.

The buffer layer 23 may be formed of an insulating material film, such as an AlN or semi-insulating GaN layer, but may be formed of a conductive material film, for example, an N-type GaN layer. That is, when the substrate 21 is an insulating substrate such as sapphire, the buffer layer may be formed of a conductive material film.

An electrode layer 31 is formed on the P-type semiconductor layer 29. The electrode layer 31 may be formed of a transparent material such as Ni / Au or ITO.

Referring to FIG. 3, a photoresist pattern is formed on the electrode layer 31, and the electrode layer 31 and a portion of the P-type semiconductor layer are removed using the photoresist pattern as an etching mask. As a result, a patterned P-type semiconductor layer 29a having a mesh electrode 31b and recesses and concave portions corresponding to the mesh electrode is formed. In this case, the pad electrode 31a may also be formed.

The light transmitting layer 33 is formed on the substrate on which the mesh electrode 31b is formed. The light transmitting layer 33 may be formed of a light transmitting material, for example, SiO ₂ , and preferably formed of a material having a smaller refractive index than the P-type semiconductor layer 29 and the electrode layer 31. The light transmitting layer 33 may be formed using chemical vapor deposition (CVD). The light transmitting layer 33 is formed along the irregularities formed by the recesses and the concave portions of the mesh electrode 31b and the P-type semiconductor layer 29a, and has grooves as shown.

Referring to FIG. 4, after the light transmission layer 33 is formed, the light transmission layer 33, the mesh electrode 31b, and the patterned P-type semiconductor layer 29a and the active layer are formed using a photolithography and etching process. And patterning the N-type semiconductor layer in order to form the light emitting cells 30 spaced apart from each other. In this case, a portion of the upper portion of the N-type semiconductor layer 25 is exposed.

An electrode pad 35a is formed on the exposed N-type semiconductor layer 25. The electrode pad 35a may be formed using a lift-off method. In addition, an electrode pad 35b is formed on the pad electrode 31a. When the light transmitting layer 33 is formed of an insulating material, the light transmitting layer 33 on the pad electrode 31a is removed in advance by using a photo and etching process. The electrode pad 35b can also be formed using the lift-off method.

Thereafter, metal wirings 37 electrically connecting the N-type semiconductor layer 25 and the P-type semiconductor layer 29a of the adjacent light emitting cells 30 are formed to complete the light emitting diode of FIG. 1. The metal wires 37 connect electrode pads 35a and 35b of adjacent light emitting cells. The metal wires 37 may be formed using an air bridge process or a step-cover process.

5 is a cross-sectional view for describing a flip chip type light emitting diode according to another exemplary embodiment of the present invention. Since the flip chip type light emitting diode according to the present exemplary embodiment is substantially the same as the light emitting diode of FIG. 1, only the differences will be briefly described.

Referring to FIG. 5, the substrate 21 according to the present embodiment uses a light transmissive substrate such as sapphire. In addition, the reflective metal layer 53 is formed instead of the light transmitting layer 33 of FIG. 1, and the metal bumper 55 is positioned on the reflective metal layer 53. The reflective metal layer 53 is formed of a metal material having a high reflectance such as Cu, Al, Ag, W, Cr, Au, Ni, Ru, Pt, Pd, In, Sn, Pb, or an alloy layer thereof. The reflective metal layer 55 may be formed as a single layer, but is not limited thereto and may be formed as a multilayer.

The reflective metal layer 53 reflects the light generated from the active layer 27 toward the substrate 21 to improve the light extraction efficiency. Since the reflective metal layer 53 is conductive, the reflective metal layer on the pad electrode 31a does not have to be removed. In addition, the pad electrode 31a may not be formed.

The metal bumper 55 may be formed using a plating technique. The metal bumper is used to bond the light emitting diode to a submount (not shown), and serves to transfer heat generated from the light emitting diode to the submount. The submount has metal pads corresponding to the metal bumper. Therefore, the heat dissipation may be promoted to the submount through the metal bumper 55 using the reflective metal layer 53 having high thermal conductivity.

According to embodiments of the present invention, a light emitting diode having improved light extraction efficiency may be provided by a P-type semiconductor layer having a mesh electrode and corresponding recesses and convex portions. In addition, by forming a light transmitting layer or a reflective metal layer covering the mesh electrode can further improve the light extraction efficiency. In addition, the light extraction efficiency can provide a method for manufacturing a light emitting diode.

Claims (13)

A plurality of light emitting devices, each of which includes an N-type semiconductor layer, a P-type semiconductor layer positioned on a portion of the N-type semiconductor layer, and an active layer interposed between the N-type semiconductor layer and the P-type semiconductor layer; Cells; A mesh electrode positioned on the P-type semiconductor layer of each light emitting cell; And It includes a buffer layer interposed between the substrate and each light emitting cell, Wherein each of the P-type semiconductor layers has recesses and concave portions corresponding to the mesh electrodes. The method according to claim 1, The light emitting diode further comprises a light transmitting layer covering the mesh electrode. The method according to claim 2, The mesh electrode is a transparent electrode, The light transmitting layer has a refractive index within the range of 1.3 to 1.8. The method according to claim 3, And metal wirings electrically connecting an N-type semiconductor layer and a P-type semiconductor layer of adjacent light emitting cells. The method according to claim 1, A light emitting diode further comprising a reflective metal layer covering the mesh electrode. The method according to claim 5, The reflective metal layer is at least one metal layer selected from the group consisting of Cu, Al, Ag, W, Cr, Au, Ni, Ru, Pt, Pd, In, Sn, Pb and alloys thereof. The method according to claim 6, Metal wires electrically connecting an N-type semiconductor layer and a P-type semiconductor layer of adjacent light emitting cells; And And a metal bumper formed on the reflective metal layer to enable flip chip bonding. Forming a buffer layer on the substrate, An N-type semiconductor layer, an active layer, a P-type semiconductor layer, and an electrode are sequentially formed on the buffer layer, Patterning the electrode and the P-type semiconductor layer to form a patterned P-type semiconductor layer having a mesh electrode and recesses and recesses corresponding to the mesh electrode. The method according to claim 8, Covering the mesh electrode, and further comprising forming a light transmitting layer having a refractive index within the range of 1.3 ~ 1.8. The method according to claim 9, The light transmitting layer, the mesh electrode, and the patterned P-type semiconductor layer, the active layer, and the N-type semiconductor layer are sequentially patterned to form light emitting cells spaced apart from each other, and a partial region of an upper surface of each N-type semiconductor layer of the light emitting cells. To expose And forming metal wires electrically connecting the N-type semiconductor layer and the P-type semiconductor layer of adjacent light emitting cells. The method according to claim 10, Before forming the metal wires, further comprising forming an N-type electrode pad and a P-type electrode pad on the N-type semiconductor layer and the P-type semiconductor layer of each light emitting cell, respectively. The method according to claim 8, The method of manufacturing a light emitting diode further comprising forming a reflective metal layer covering the mesh electrode. The method according to claim 12, The reflective metal layer, the mesh electrode, and the patterned P-type semiconductor layer, the active layer, and the N-type semiconductor layer are sequentially patterned to form light emitting cells spaced apart from each other. Exposed, Forming metal wires electrically connecting the N-type semiconductor layer and the P-type semiconductor layer of the adjacent light emitting cells; The light emitting diode manufacturing method comprising forming a metal bumper for flip chip bonding on the reflective metal layer of each light emitting cell.

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