KR101805301B1 - Ultraviolet Light-Emitting Diode with p-type ohmic contact electrode pattern to enhance the light extraction - Google Patents

Abstract

The present invention provides an ultraviolet light-emitting diode element and a method of manufacturing the same. This ultraviolet light-emitting diode element comprises a conductive substrate; A metal reflective layer disposed on the conductive substrate; A p-electrode pattern disposed on the metal reflection layer; An insulating layer filling between the p-electrode patterns; A p-type GaN layer disposed on the p-electrode pattern and the insulating layer; An active layer disposed on the p-type GaN layer; An n-type AlGaN layer disposed on the active layer; And an n-electrode pattern disposed on the n-type AlGaN layer. The metal reflective layer may be aluminum or an aluminum alloy, and the p-electrode pattern may include ITO or silver.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an ultraviolet light-emitting diode (OLED) device having a p-type ohmic contact electrode pattern for improving light extraction efficiency,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode, and more particularly, to an ultraviolet light emitting diode having a p-type epitaxial contact layer structure for improving light extraction efficiency.

Ultraviolet Light-Emitting Diode (UV LED) uses AlGaN as an epitaxy layer. The more Al light emitted in a short wavelength region such as ultraviolet light, the higher the Al content in AlGaN. The higher the Al content in AlGaN, the lower the electrical conductivity of AlGaN and the doping efficiency sharply decreases. In particular, the p-type AlGaN and the metal electrode do not form Ohmic contact with each other, so that the contact resistance is high. This causes heat generation of the device and lowers the current injection efficiency.

In order to solve this problem, a contact layer or a metal having a large work function (Ni, Pd, Au, Pt, Ag) or the like is used for forming p- . Or a technique of forming an ohmic contact between a p-type semiconductor and a metal electrode by introducing a heat treatment, a plasma treatment, and various surface treatment processes has been developed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an aluminum (Al) based p-type ohmic contact of a UV LED.

According to an embodiment of the present invention, a p-type Ohmic contact electrode (or a p-InGaN) having a mesh structure that forms an ohmic contact with a p-type semiconductor such as ITO or silver (Ag) Type ohmic contact pattern is introduced and the space between the p-type ohmic contact electrode patterns is filled with an insulating layer. Accordingly, the semiconductor layer of the p- (In) GaN layer is electrically connected to the aluminum reflective layer through the p-type ohmic contact electrode pattern. The semiconductor layer, the insulating layer, and the metal reflective layer function as an omni-directional reflector (ODR) that reduces loss due to ultraviolet absorption. Therefore, the light extraction efficiency of the UV LED can be increased.

An ultraviolet light emitting diode device according to an embodiment of the present invention includes a conductive substrate; A metal reflective layer disposed on the conductive substrate; A p-electrode pattern disposed on the metal reflection layer; An insulating layer filling between the p-electrode patterns; A p-type GaN layer disposed on the p-electrode pattern and the insulating layer; An active layer disposed on the p-type GaN layer; An n-type AlGaN layer disposed on the active layer; And an n-electrode pattern disposed on the n-type AlGaN layer. The metal reflective layer may be aluminum or an aluminum alloy, and the p-electrode pattern may include ITO or silver.

In one embodiment of the present invention, the insulating layer may be a silicon oxide layer or magnesium fluoride (MgF2).

In one embodiment of the present invention, the p-electrode pattern may be a mesh structure having a polygonal unit pattern.

In one embodiment of the present invention, a wafer bonding layer disposed between the conductive substrate and the metal reflective layer; And an electron blocking layer disposed between the p-type GaN layer and the active layer; As shown in FIG.

In one embodiment of the present invention, the active layer may be a multiple quantum well structure of GaN / AlGaN.

A method of fabricating an ultraviolet light emitting diode device according to an embodiment of the present invention includes sequentially stacking an undoped AlGaN buffer layer, an n-type AlGaN layer, an active layer, a p-type GaN, and an insulating layer on a sapphire substrate; Forming an insulating layer pattern by patterning the insulating layer; Forming a p-electrode pattern by filling an ohmic contact material between the insulating layer patterns; Forming a metal reflective layer on the insulating layer pattern and the p-electrode pattern; Forming a wafer bonding layer on the sapphire substrate on which the metal reflection film is formed, and bonding the wafer bonding layer and the conductive substrate; Removing the sapphire substrate using a laser lift-off technique to expose the AlGaN buffer layer; Removing the exposed AlGaN buffer layer and forming an n-electrode pattern on the n-type AlGaN layer; And providing a surface roughness to the n-type AlGaN layer. The p-electrode pattern may be silver (Ag) or ITO, and the metal reflective layer may be aluminum or an aluminum alloy.

According to an embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: forming an electron blocking layer of a p-type AlGaN structure between the active layer and the p-type GaN layer; And patterning the n-type AlGaN layer, the active layer, the electron blocking layer, and the p-type GaN layer to form a trench and forming a protective layer on the sidewall of the trench.

According to an embodiment of the present invention, in order to improve the UV LED light extraction efficiency, a p-type ohmic contact electrode pattern composed of materials such as ITO and Ag having various net structures and an insulating layer Is used. Aluminum or an aluminum alloy is used as the metal reflection layer. As a result, it is possible to reduce the contact resistance by minimizing the light absorption at the UV wavelength. In addition, the p-type ohmic contact electrode pattern of the net structure can achieve both an optimal current spreading effect and a high light extraction effect by introducing ITO or silver (Ag) into the bonding layer.

In addition, an insulating layer such as a silicon oxide film is filled in the vacant region of the p-type ohmic contact electrode pattern. Accordingly, the aluminum reflective metal layer, the insulating layer, and the p- (In) GaN layer function as the ODR reflective electrode. The ODR reflective electrode provides a higher reflectivity in the UV region than the front metal reflective electrode and further enhances the overall light extraction efficiency of the UV LED.

1A is a plan view illustrating a vertical UV LED according to an embodiment of the present invention.
1B is a cross-sectional view taken along the line A-A 'in FIG. 1A.
1C is a cross-sectional view taken along the line B-B 'in FIG. 1A.
2A to 2H are cross-sectional views illustrating a method of manufacturing a vertical UV LED device according to an embodiment of the present invention.
3A is a diagram showing light output for a current of a light emitting diode having a p-type GaN layer / insulating layer / metal reflection layer of an ODR structure according to an embodiment of the present invention.
FIG. 3B is a graph illustrating light output of a light emitting diode having a p-type GaN layer / insulating layer / metal reflective layer of ODR structure according to an embodiment of the present invention.
4 is a plan view showing a p-electrode pattern according to another embodiment of the present invention.

Typical vertical type UV LEDs include a conductive substrate, a wafer bonding layer, a metal reflective layer, a p-electrode, p-GaN, an active layer, and n GaN, n contact electrodes. It is preferable that the metal reflection layer and the p electrode can increase both current injection efficiency and light extraction efficiency. However, for typical vertical UV LEDs, the p-electrode uses silver or ITO to form ohmic junctions with the p-type semiconductor. Materials such as silver (Ag) or ITO have a high absorption rate in the ultraviolet region, thereby reducing the light extraction efficiency. Therefore, a p electrode structure and a material having a new structure in which the ultraviolet absorption ratio is reduced are required.

The light extraction efficiency due to the light absorption of the p-ohmic contact layer with respect to the light with a wavelength band of 400 nm or less may be reduced. To solve this problem, the p-ohmic contact layer may have a p ohmic contact pattern of a mesh structure. The void space of the mesh structure can be filled with an insulating layer. The p ohmic contact pattern is designed to occupy a minimum area of the entire area, and the remaining area has an ODR structure including a semiconductor layer / insulating layer / aluminum metal reflective layer. The ODR structure provides high reflectivity in the ultraviolet region to provide high light extraction efficiency. In addition, the p ohmic contact pattern may provide a sufficiently low resistance to increase current injection efficiency. The p-ohmic contact pattern may be a material capable of making ohmic contact with p-type GaN (or p-type InGaN) such as ITO or silver (Ag). The ohmic contact electrode pattern having a mesh structure may be an electrode material (ITO, Ag, Ni, Au, Pd, Pt or the like) for forming an ohmic contact. The portion other than the ohmic contact pattern of the mesh structure may be filled with an insulating layer having a small refractive index such as SiO 2 or MgF 2. A metal reflection layer is formed on the p ohmic contact pattern and the insulating layer. The metal reflective layer may be Al, Ag, or Rh.

According to an embodiment of the present invention, a p-electrode pattern is formed by patterning a p-electrode, and conventional silver or ITO is used for the p-electrode pattern. The area of the p-electrode pattern can be sufficiently reduced so as to provide sufficient current injection efficiency. In addition, the metal reflective layer can maximize the reflectance in the ultraviolet region by using aluminum or an aluminum alloy. In addition, the p-GaN layer (or p-type InGaN) on the aluminum-based metal reflective layer, the insulating layer filling the space between the p-electrode patterns, and the insulating layer can provide an ODR structure with higher reflectivity in the UV region have. Specifically, the ODR structure can provide a reflectivity of about 90 percent in the region of 350 nm.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It should be understood that the various embodiments of the present invention are different, but need not be mutually exclusive. For example, certain features, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the invention in connection with an embodiment. It is also to be understood that the position or arrangement of the individual components within each disclosed embodiment may be varied without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is to be limited only by the appended claims, along with the full scope of equivalents to which the claims are entitled, if properly explained. In the drawings, like reference numerals refer to the same or similar functions throughout the several views.

1A is a plan view illustrating a vertical UV LED according to an embodiment of the present invention.

1B is a cross-sectional view taken along the line A-A 'in FIG. 1A.

1C is a cross-sectional view taken along the line B-B 'in FIG. 1A.

1A to 1C, an ultraviolet light-emitting diode device 100 includes a conductive substrate 110; A metal reflective layer 114 disposed on the conductive substrate 110; A p-electrode pattern 116 disposed on the metal reflection layer 114; An insulating layer 118 filling between the p-electrode patterns 116; A p-type GaN layer 122 disposed on the p-electrode pattern 116 and the insulating layer 118; An active layer 126 disposed on the p-type GaN layer 122; An n-type AlGaN layer 128 disposed on the active layer 126; And an n-electrode pattern 132 disposed on the n-type AlGaN layer 128. The metal reflection layer 114 is made of aluminum or an aluminum alloy, and the p-electrode pattern 116 includes ITO or silver.

The conductive substrate 110 may be a molybdenum substrate, a silicon substrate, a copper substrate, or an alloy substrate of molybdenum and copper.

The wafer bonding layer 112 may be disposed between the conductive substrate 110 and the metal reflective layer 114. The wafer bonding layer 112 may be an Au / Sn alloy or a Ni / Sn alloy, various alloys including Sn, and the like. The wafer bonding layer 112 may be bonded to the conductive substrate 110 by a low-temperature heat treatment at a temperature of 200 degrees Celsius.

The metal reflective layer 114 may be disposed on the wafer bonding layer 112. The metal reflective layer 114 may be aluminum or an aluminum alloy. Aluminum or an aluminum alloy (for example, an aluminum-copper alloy) can provide a higher reflectance than silver (Ag) or ITO (Indium Tin Oxide) in the ultraviolet region, especially around 350 nm.

A p electrode pattern 116 may be disposed on the metal reflective layer 114. The electrode pattern 116 may be a material capable of ohmic contact with p-type GaN (or p-type InGaN). Specifically, the p-electrode pattern 116 may include silver (Ag), silver alloy, Pd, Pt, Ni, Au, ITO and the like. Preferably, the p-electrode pattern may be a laminated structure of ITO / Ag. The p-electrode pattern 116 may be a mesh structure having a polygonal unit pattern. The unit mesh structure may be triangular, square, or hexagonal.

The insulating layer 118 may fill the space between the p-electrode patterns 116 and be disposed on the metal reflective layer 114. The insulating layer 118 may be a silicon oxide layer or magnesium fluoride (MgF2). The insulating layer 118 may include an insulating layer pattern, and the unit structure of the insulating layer pattern may be polygonal.

The p-type GaN layer 122 may be disposed on the insulating layer 118 and the p-electrode pattern 116. The p-type GaN layer 122 may be a GaN structure doped with a p-type impurity (Mg) or an InGaN structure doped with a p-type impurity. The thickness of the p-type GaN layer 122 may be several nanometers.

The p-type GaN layer 122, the insulating layer 118, and the metal reflective layer 114 may provide an ODR structure of semiconductor / insulator / metal. The ODR structure may provide a higher reflectance than the metal reflective layer alone. The p-electrode pattern 116 may have a sufficient line width to provide a sufficient current spreading function.

The electron blocking layer 124 may be disposed between the p-type GaN layer 122 and the active layer 126. The electron blocking layer 124 may be an AlGaN structure doped with a p-type impurity. The electron blocking layer 124 may block electrons transmitted through the active layer 126. The thickness of the electron blocking layer 124 may be on the order of tens of nanometers.

The active layer 126 may be a multiple quantum well structure of GaN / AlGaN. The active layer 126 may recombine electrons and holes to generate ultraviolet rays. The active layer 126 may have a thickness of several tens nm to several hundreds nm.

The n-type AlGaN layer 128 may be disposed on the active layer 126. The n-type AlGaN layer 128 may be an AlGaN structure doped with an n-type impurity (Si). The thickness of the n-type AlGaN layer 128 may be several micrometers. The upper surface of the n-type AlGaN layer 128 may have a surface roughness through a roughing process.

The n-electrode pattern 132 may be disposed on the n-type AlGaN layer 128. The n-electrode pattern 132 may be a multilayer structure based on Ti or Cr, such as Ti / Al structure, Ti / Al / Ni / Au, Cr / Al, Cr / Al / Ni / Au. The n-electrode pattern 132 may have a mesh structure. The n-electrode pattern 132 may be vertically aligned with the p-electrode pattern 116.

The protective layer 134 is formed on the side surfaces of the trench 125 penetrating the n-type AlGaN layer 128, the active layer 126, the electron blocking layer 124 and the p-type GaN layer 122, Type AlGaN layer 128, as shown in FIG. The protective layer 134 may be a silicon oxide layer or a silicon nitride layer. A portion of the protective layer 134 may be disposed on the insulating layer 118.

2A to 2H are cross-sectional views illustrating a method of manufacturing a vertical UV LED device according to an embodiment of the present invention.

Referring to FIG. 2A, a sapphire substrate 142 having irregularities on its surface is prepared. The sapphire substrate may have a (0001) structure. An undoped AlGaN buffer layer 144, an n-type AlGaN layer 128, an active layer 126, an electron blocking layer 124, a p-type GaN layer 122, and an insulating layer 118 (not shown) are formed on the sapphire substrate 142, ) Are stacked in this order. The sapphire substrate 142 may be a (0001) substrate. The AlGaN buffer layer 144, the n-type AlGaN layer 128, the active layer 126 and the electron blocking layer 124 and the p-type GaN layer 122 are formed by metal-organic chemical vapor deposition (MOCVD). The electron blocking layer 124 may be a p-type AlGaN structure. The p-type GaN layer 122 may be a GaN structure or an InGaN structure doped with a p-type impurity. The insulating layer 118 may be a silicon oxide film or a MgF2 film.

Referring to FIG. 2B, a photoresist mask pattern is formed on the insulating layer 118 through a photolithography process, and anisotropic etching (or isotropic etching) is performed using the photoresist mask pattern as an etching mask, Can be formed. The insulating layer pattern 118 may have a polygonal structure.

Referring to FIG. 2C, a p-electrode pattern 116 may be formed in an etched groove of the insulating layer pattern. The upper surface of the p-electrode pattern 116 may be the same as the upper surface of the insulating layer 118. The p-electrode pattern 116 may form an ohmic contact with the p-type GaN layer 122. The p contact electrode 116 may include Ag, Ag alloy, Pd, Pt, Ni, Au, ITO, and the like. Preferably, the p-electrode pattern 116 may be a laminated structure of ITO / Ag. The p-electrode pattern 116 may have a polygonal mesh structure.

Referring to FIG. 2D, a metal reflection layer 114 may be disposed on the insulating layer pattern 118 and the p-electrode pattern 116. The metal reflective layer 114 may be aluminum or an aluminum alloy. The p-type GaN layer 122, the insulating layer 118, and the metal reflection layer 114 may have an ODR structure. Thus, in the ultraviolet region near 350 nm, the reflectance can be at the level of 90 percent.

Referring to FIG. 2E, a wafer bonding layer 112 may be disposed on the metal reflective layer 114. The wafer bonding layer 112 may be an Au / Sn alloy or a Ni / Sn alloy, various alloys including Sn, and the like. Then, the wafer bonding layer 112 of the LED substrate can be bonded to the conductive substrate 110 through a low-temperature heat treatment at a level of 200 degrees Celsius. The conductive substrate 110 may be an alloy substrate of molybdenum, copper, silicon, or molybdenum and copper.

Referring to FIG. 2F, the sapphire substrate 142 may be removed using a laser lift-off technique. Specifically, a KrF laser beam can be incident on the sapphire substrate 142. When a laser beam is provided to the sapphire substrate, the laser beam is transmitted through the sapphire substrate 142 and absorbed between the AlGaN buffer layer 144 and the sapphire substrate 142 to form a split zone. Accordingly, the sapphire substrate 142 can be removed.

Referring to FIG. 2G, the AlGaN buffer layer 144 may be disposed on the upper surface.

Referring to FIG. 2H, the exposed AlGaN buffer layer 144 may be removed to expose the n-type AlGaN layer 128. The AlGaN buffer layer 144 may be formed by dry etching using a plasma.

A trench 135 may be formed to penetrate the n-type AlGaN layer 128, the active layer 126, the electron blocking layer 124, and the p-type GaN layer 122. The lower surface of the trench 135 may be disposed on the insulating layer 118. The protective layer 134 may be disposed to cover a side of the trench of the trench 135 and a portion of the n-type AlGaN layer 128. The protective layer 134 may be a silicon oxide film or a silicon nitride film. The protective layer 134 may expose the n-type AlGaN layer 128 through patterning.

 An n-electrode pattern 132 may be formed on the n-type AlGaN layer 128. The n-electrode pattern 132 may be formed using a lift-off process. The n-electrode pattern 132 may be a Cr / Al structure, a Cr / Au structure, a Cr / Al / Pt / Au structure, a Ti / Au structure, a Ti / Al structure, or a Ti / Al / Ni / Au structure.

Referring again to FIG. 1B, the exposed n-type AlGaN layer 128 may be surface treated to provide surface roughness. The surface roughness can increase the light extraction efficiency. The surface roughness can be formed by wet etching using a KOH solution.

3A is a diagram showing light output for a current of a light emitting diode having a p-type GaN layer / insulating layer / metal reflection layer of an ODR structure according to an embodiment of the present invention.

FIG. 3B is a graph illustrating light output of a light emitting diode having a p-type GaN layer / insulating layer / metal reflective layer of ODR structure according to an embodiment of the present invention.

Referring to FIG. 3A, the circular ITO / Al / Ni structure was used as a p-ohmic contact electrode. A triangular mesh electrode having a line width of 15 micrometers was used as a p-ohmic contact electrode pattern, and a stacked structure of Al / Ni was used. The triangle adopts the ODR structure. In the case of the light output according to the injection current, when the injection current is the same, the light output of the device is higher because the specimen incorporating the mesh ODR structure has higher reflectance characteristics.

  Referring to FIG. 3B, the circular ITO / Al / Ni structure was used as a p-ohmic contact electrode. A triangular mesh electrode having a line width of 15 micrometers was used as a p-ohmic contact electrode pattern, and a stacked structure of Al / Ni was used. The triangle adopts the ODR structure. In the case of the optical output according to the injection power, when the injection power is the same, the contact area is reduced because the contact is introduced into the mesh structure, and the electrical characteristics of the mesh ODR structure are slightly lower than that of the ITO / Al structure. However, the optical characteristics of the mesh ODR structure are better.

4 is a plan view showing a p-electrode pattern according to another embodiment of the present invention.

Referring to FIG. 4, the p-electrode pattern 116 may be a rhombic structure (matrix), a square structure, a triangular structure, or a hexagonal structure (honeycomb structure). The space between the p-electrode patterns 116 may be filled with an insulating layer. Accordingly, the ODR structure can be formed to increase the reflectivity of the ultraviolet region. In addition, the p-electrode pattern can provide a sufficient current spreading effect with a low contact resistance.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

100: ultraviolet light-emitting diode element
110: conductive substrate
114: metal reflective layer
116: p electrode pattern
118: Insulation layer
122: a p-type GaN layer
126:
128: n-type AlGaN layer

Claims (7)

A conductive substrate;
A metal reflective layer disposed on the conductive substrate;
A p-electrode pattern disposed on the metal reflection layer;
An insulating layer filling between the p-electrode patterns;
A p-type GaN layer disposed on the p-electrode pattern and the insulating layer;
An active layer disposed on the p-type GaN layer;
An n-type AlGaN layer disposed on the active layer and including irregularities on at least a part of the surface;
An n-electrode pattern disposed on the n-type AlGaN layer; And
And a protective film disposed on a side surface of the p-type GaN layer, the active layer, the n-type AlGaN layer, and a part of an upper surface of the n-type AlGaN layer,
The n-electrode pattern is disposed on a flat surface of an edge region of the top surface of the n-type AlGaN layer,
Wherein the n-electrode pattern and the protective film include a contact portion which is in contact with an edge region of an upper surface of the n-type AlGaN layer,
And the contact portion is vertically overlapped with the p-electrode pattern. The method according to claim 1,
Wherein the p electrode pattern is a mesh structure having a polygonal unit pattern. 3. The method according to claim 1 or 2,
Wherein the insulating layer is a silicon oxide film or magnesium fluoride (MgF ₂ ). 3. The method according to claim 1 or 2,
A wafer bonding layer disposed between the conductive substrate and the metal reflection layer; And
An electron blocking layer disposed between the p-type GaN layer and the active layer; Wherein the ultraviolet light emitting diode element further comprises at least one of the following elements. delete delete delete

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