KR100638862B1 - flip-chip light emitting diodes and method of manufacturing thereof - Google Patents

Abstract

The present invention relates to a flip chip nitride light emitting device and a method for manufacturing the same, wherein the nitride light emitting device is an n-type cladding layer, an active layer and a p-type cladding layer are sequentially stacked, and formed of an aluminum material on the p-type cladding layer A reflective conductive layer and a transparent conductive thin film layer formed of a transparent conductive material capable of suppressing diffusion of aluminum between the p-type cladding layer and the reflective layer are provided. According to the flip chip type nitride-based light emitting device and a method of manufacturing the same, the ohmic contact property with the p-type cladding layer is improved to increase the wire bonding efficiency and the yield when packaging the light emitting device, and the low specific contact resistance and excellent current-voltage The characteristic provides the advantage of improving the luminous efficiency and device life of the device.

Description

Flip chip type nitride light emitting device and its manufacturing method

1 is a cross-sectional view showing a light emitting device according to a first embodiment of the present invention,

2 is a cross-sectional view showing a light emitting device according to a second embodiment of the present invention;

3 is a graph illustrating a result of measuring current-voltage characteristics of a light emitting device having a structure in which a reflective layer is omitted.

Figure 4 is a graph showing the results of measuring the current-voltage characteristics of the light emitting device according to the present invention.

<Description of Symbols for Main Parts of Drawings>

110: substrate 130: n-type cladding layer

140: active layer 150: p-type cladding layer

160: modified metal layer 170: transparent conductive thin film layer

180: reflective layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flip chip nitride light emitting device and a manufacturing method thereof, and more particularly, to a flip chip nitride light emitting device having an electrode structure capable of improving light emission efficiency and a method of manufacturing the same.

In order to implement a light emitting device such as a light emitting diode or a laser diode using a nitride compound semiconductor, for example, a gallium nitride (GaN) semiconductor emitting blue, green, and ultraviolet rays, an ohmic contact structure between the semiconductor and the electrode is very important. Currently commercially available gallium nitride-based light emitting device is formed on an insulating sapphire (Al ₂ O ₃ ) substrate.

Such gallium nitride-based light emitting devices are classified into top-emitting light emitting diodes (TLEDS) and flip-chip light emitting diodes (FCLEDS).

The top emit light emitting diode is formed such that light is emitted through the ohmic electrode layer in contact with the p-type cladding layer.

In addition, the top-emitting light emitting device is transparent and has low sheet resistance due to poor electrical characteristics such as low current injection and current spreading, which are derived from the thin film characteristics of the p-type cladding layer having low hole concentration. It is possible to overcome the problems of the light emitting device by developing an ohmic contact electrode having a) value.

This top-emitting light emitting device is generally a metal thin film structure based on transition metals such as nickel (Ni) metal, and a metal thin film of oxidized translucent nickel (Ni) / gold (Au) is widely used. It is becoming.

A metal thin film based on nickel (Ni) metal is heat-treated in an oxygen (O ₂ ) atmosphere to form a semi-transparent ohmic contact layer having a specific contact resistance of about 10 ^-3 to 10 ^-4 Ωcm ² . It is reported to be.

This low specific contact resistance is due to the p-type semiconductor oxide nickel oxide (NiO) at the interface between p-type gallium nitride and nickel (Ni) when heat-treated in an oxygen (O ₂ ) temperature range. It is formed between Au formed in the upper layer and the upper layer to reduce Schottky barrier height (HBT). Increase the effective carrier concentration near the gallium surface. On the other hand, nickel (Ni) / gold (Au) is contacted with p-type gallium nitride and then heat treated to remove Mg-H intermetallic complexes, thereby increasing the magnesium (Mg) dopant concentration on the gallium nitride surface. Increasing reactivation results in an effective carrier concentration of at least 10 ^{19 on} the surface of the p-type gallium nitride, thereby providing tunneling conduction between the p-type gallium nitride and the electrode layer (a nickel oxide layer containing gold). It is understood that it exhibits ohmic conductivity characteristics.

However, the top-emitting light emitting diode using a translucent electrode thin film formed of nickel / gold has low light utilization efficiency, making it difficult to realize a large capacity and high brightness light emitting device.

Recently, there is a need to develop a flip chip light emitting device using silver (Ag), silver oxide (Ag ₂ O), and aluminum (Al), which have been spotlighted as high reflective layer materials to realize high-capacity high-brightness light emitting devices.

However, these reflective metals can provide high luminous efficiency temporarily because they have high reflection efficiency, but due to the characteristics of small work function, it is difficult to form ohmic contact with low resistance, resulting in short device life. There is a problem in that the adhesion with gallium nitride is poor, and thus the device does not provide stable reliability.

In more detail, first, aluminum (Al) metals easily form nitrides (AlN) at low work function values and relatively low temperatures during heat treatment, making it difficult to form ohmic contacts with p-type gallium nitride.

Next, silver (Ag) forms a good ohmic contact and has a high reflectance, but due to thermal instability, it is difficult to form a high quality thin film through a thin film forming process. That is, the Ag thin film is caused by agglomeration at the initial stage of heat treatment due to thermal instability, and is changed into voids, hillocks and islands at the end of the heat treatment. Deteriorates properties.

Recently, in order to expand the field of use of light emitting devices to large area and high brightness light emitting devices such as automobile back light and home lighting, we have developed an ohmic contact layer that provides high reflectivity while having low specific resistance. The research to do is being actively conducted.

Mensz et al. The group proposed, in electronics letters 33 (24) pp. 2066, nickel (Ni) / aluminum (Al) and nickel (Ni) / silver (Ag) structures as two-layer structures, but these structures form ohmic contacts. This difficulty has a problem of causing a lot of heat generation due to high operating voltage during the operation of the light emitting diode.

Also recently, Michael R. Krames et al. The group reported that the study of nickel (Ni) / silver (Ag) and gold (Au) / nickel oxide (NiO _x ) / aluminum (Al) electrode structures was carried out through a US published patent (US 2002/0171087 A1). However, this structure also has a disadvantage in that the adhesion is lowered, and the luminous efficiency is lowered due to diffuse reflection.

The present invention has been made to improve the above problems, and provides a flip chip nitride light emitting device having excellent electrical characteristics by applying a high quality ohmic contact electrode having thermal stability and high reliability, and a method of manufacturing the same. There is a purpose.

In order to achieve the above object, a flip chip nitride light emitting device according to the present invention is a flip chip nitride light emitting device having an active layer between an n-type cladding layer and a p-type cladding layer, wherein the p-type cladding layer is made of aluminum. A reflection layer formed; And a transparent conductive thin film layer formed of a transparent conductive material capable of suppressing diffusion of the aluminum between the p-type cladding layer and the reflective layer.

The transparent conductive thin film layer is preferably formed of any one of a transparent conductive oxide and a transparent conductive nitride.

The transparent conductive oxide may be indium (In), tin (Sn), zinc (Zn), gallium (Ga), magnesium (Mg), beryllium (Be), silver (Ag), iridium (Ir), rhodium (Rh), It is formed by including oxygen and at least one component selected from ruthenium (Ru) and molybdenum (Mo).

In addition, as the transparent conductive nitride, any one of titanium nitride (TiN) and titanium nitride oxide (Ti-N-O) is applied.

Preferably, further comprising a modified metal layer formed between the reflective layer and the transparent conductive thin film layer, wherein the modified metal layer is indium (In), tin (Sn), zinc (Zn), magnesium (Mg), silver (Ag), An alloy containing any one element selected from iridium (Ir), ruthenium (Ru), rhodium (Rh), platinum (Pt), nickel (Ni) and palladium (Pd), and at least one element selected from the above elements , Solid solution.

The transparent conductive thin film layer is formed to a thickness of 1 nanometer to 100 nanometers, the modified metal layer is formed to a thickness of 0.1 nanometer to 50 nanometers, the reflective layer is formed to a thickness of 100 nanometers to 1000 nanometers desirable.

In addition, in order to achieve the above object, a method of manufacturing a flip chip nitride light emitting device according to the present invention is a method of manufacturing a flip chip nitride light emitting device having an active layer between an n-type cladding layer and a p-type cladding layer. . Forming a transparent conductive thin film layer on the p-type cladding layer of the light emitting structure in which the n-type cladding layer, the active layer and the p-type cladding layer are sequentially stacked on a substrate; I. Heat-treating the structure including the transparent conductive thin film layer at a set temperature in a gas atmosphere containing oxygen; All. Forming a reflective layer of aluminum on the transparent conductive thin film layer; la. And heat-treating the structure including the reflective layer in any one of nitrogen, argon, and vacuum.

Hereinafter, a flip chip type nitride light emitting device according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view illustrating a flip chip type nitride light emitting device according to a first embodiment of the present invention.

Referring to the drawings, the flip chip nitride-based light emitting device is a substrate 110, buffer layer 120, n-type cladding layer 130, active layer 140, p-type cladding layer 150, transparent conductive thin film layer 170 and The reflective layers 180 are sequentially stacked. Reference numeral 190 is a p-type electrode pad, and 200 is an n-type electrode pad.

The substrate 110 to the p-type cladding layer 150 correspond to the light emitting structure, and the transparent conductive thin film layer 170 stacked on the p-type cladding layer 150 corresponds to the ohmic contact structure.

The substrate 110 may be formed of any one of sapphire (Al ₂ O ₃ ), silicon carbide (SiC), silicon (Si), and gallium arsenide (GaAs).

The buffer layer 120 may be omitted.

Each layer from the buffer layer 120 to the p-type cladding layer 150 is Al _x In _y Ga _z N (0≤x≤1, 0≤y≤1, 0≤z≤1, which is a general formula of a group III nitride compound). , Based on any compound selected from the compounds represented by 0 ≦ x + y + z ≦ 1), and the dopant is added to the n-type cladding layer 130 and the p-type cladding layer 150.

In addition, the active layer 140 may be configured in various known manners, such as a monolayer or an MQW layer.

As an example, when a gallium nitride (GaN) -based compound semiconductor is applied, the buffer layer 120 is formed of GaN, and the n-type cladding layer 130 is added with Ga, Si, Ge, Se, Te, or the like as an n-type dopant. The active layer is formed of InGaN / GaN MQW or AlGaN / GaN MQW, and the p-type cladding layer 150 is formed by adding Mg, Zn, Ca, Sr, Ba, etc. to GaN as a P-type dopant.

An n-type ohmic contact layer (not shown) may be interposed between the n-type cladding layer 130 and the n-type electrode pad 200, and in the n-type ohmic contact layer, titanium (Ti) and aluminum (Al) may be sequentially formed. Various known structures, such as laminated layer structure, can be applied.

The p-type electrode pad 190 may have a layer structure in which nickel (Ni) / gold (Au) or silver (Ag) / gold (Au) is sequentially stacked.

Each layer may be formed by an electron beam evaporator, physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma laser deposition (PLD), dual-type thermal evaporator sputtering, or the like. .

The transparent conductive thin film layer 170 applied as the ohmic contact structure prevents aluminum, which is a material of the reflective layer 180 to be formed through the post-process, from being diffused into the p-type cladding layer 150 to function as a diffusion barrier for aluminum. It is formed of a material capable of providing high light transmittance and conductivity.

In addition, the transparent conductive thin film layer 170 may increase the effective carrier concentration of the p-type cladding layer 150, and a material that is preferentially reactive with components other than nitrogen among the compounds forming the p-type cladding layer 150 may be applied. do. For example, in the case of a light emitting device having a GaN-based compound as a main component, a transparent conductive thin film layer 170 is applied with a material that preferentially reacts with gallium (Ga) rather than nitrogen.

In this case, as an example, in the case of the p-type cladding layer 150 mainly composed of gallium nitride (GaN), the p-type cladding layer 150 and the transparent conductive thin film layer (by the transparent conductive thin film layer 170 having the characteristics described above) The reaction of 170 forms gallium vacancy on the surface of the p-type cladding layer 150. At this time, since the gallium vacancy formed in the p-type cladding layer 150 acts as a p-type dopant, the effective development of the surface of the p-type cladding layer 150 by the reaction between the p-type cladding layer 150 and the transparent conductive thin film layer 170 is performed. This will increase the rear concentration.

In addition, the transparent conductive thin film layer 170 remains on the surface of the p-type cladding layer 150 and reduces gallium oxide (Ga ₂ O ₃ ), which is a natural oxide layer that serves as an obstacle to carrier flow at the interface, thereby reducing the height of the Schottky barrier. Materials that can reduce the width are applied.

 As a material of the transparent conductive thin film layer 170 capable of satisfying such a condition, transparent conducting oxide or transparent conductive nitride may be applied.

Transparent conductive oxides include indium (In), tin (Sn), zinc (Zn), gallium (Ga), magnesium (Mg), beryllium (Be), silver (Ag), iridium (Ir), rhodium (Rh), and ruse A material in which oxygen is combined with at least one selected from nium (Ru) and molybdenum (Mo) may be applied.

In addition, the transparent conductive nitride is titanium nitride (TiN) or titanium nitride oxide (Ti-N-O) is applied.

At least one or more elements of the periodic metal of the element may be added as a dopant to improve the electrical properties to the transparent conductive oxide or the transparent conductive nitride.

Preferably, the addition ratio of the dopant added to the transparent conductive oxide or the transparent conductive nitride is applied within the range of 0.001 to 20 weight percent by weight (wt%). The weight percentage here refers to the weight ratio between the materials to be added.

The material of the transparent conductive thin film layer 170 may be selected in consideration of a work function value and sheet resistance value according to the use of the light emitting device to be applied.

The thickness of the transparent conductive thin film layer 170 is preferably formed to a thickness of 1 nanometer to 100 nanometers to have a suitable light transmittance and electrical conductivity.

The reflective layer 180 is formed of aluminum (Al) having high light reflectance for short wavelengths of 450 nanometers or less and excellent thermal stability.

The reflective layer 180 is formed of a thick film having a thickness of 100 nanometers to 1000 nanometers so as to provide an appropriate reflectance.

In the light emitting device having such a structure, the transparent conductive thin film layer 170 is formed of the material described above and heat treated at an appropriate temperature in an oxygen or air atmosphere to have a high light transmittance, that is, a transmittance of 90% or more in a wavelength range of 400 nanometers. A gallium oxide (Ga ₂ O ₃ ), a natural oxide layer that remains on the surface of the p-type cladding layer 150 and serves as an obstacle to carrier flow at the interface, becomes a transparent conductive material having a low sheet resistance (10 Ω / □ or less). Reduces the height and width of the Schottky barrier, induces a tunneling effect that is beneficial for forming ohmic contacts, improves electrical properties, and has light transmittance close to 100% .

In addition, the transparent conductive thin film layer 170 suppresses diffusion / contact of aluminum to the p-type cladding layer 150 when the reflective layer 180 is formed of aluminum.

2 is a cross-sectional view illustrating a flip chip nitride light emitting device according to another embodiment of the present invention. Elements having the same function as in the above-described drawings are denoted by the same reference numerals.

Referring to the drawings, the light emitting device includes a substrate 110, a buffer layer 120, an n-type cladding layer 130, an active layer 140, a p-type cladding layer 150, a modified metal layer 160, and a transparent conductive thin film layer 170. ) And the reflective layer 180 are sequentially stacked.

The modified metal layer 160 is applied to improve ohmic contact between the p-type cladding layer 150 and the transparent conductive thin film layer 170.

The modified metal layer 160 is formed of a material having high electrical conductivity and easily decomposed and formed into conductive nano phase oxide particles during heat treatment in a gas atmosphere including a temperature of 800 ° C. or lower and oxygen.

As a material for the modified metal layer 160 having such conditions, indium (In), tin (Sn), zinc (Zn), magnesium (Mg), silver (Ag), iridium (Ir), ruthenium (Ru), and rhodium ( It is preferable to apply any one element selected from Rh), platinum (Pt), nickel (Ni) and palladium (Pd), an alloy containing at least one element selected from the above elements, and a solid solution.

The thickness of the modified metal layer 160 is formed to be 0.1 nanometer to 50 nanometers, which is a thickness that can be easily decomposed and formed into conductive nanophase particles during heat treatment.

The transparent conductive oxide 170 may be formed of the material described above.

Hereinafter, a process of manufacturing a light emitting device having such a structure will be described.

First, the buffer layer 120, the n-type cladding layer 130, the active layer 140, and the p-type cladding layer 150 are sequentially formed on the substrate 110.

Thereafter, in order to secure a space for forming the n-type electrode pad 200, a mesa structure is formed by etching the p-type cladding layer 150 to a part of the n-type cladding layer 130.

Next, when the structure of FIG. 1 is applied, the transparent conductive thin film layer 170 is formed solely on the p-type cladding layer 150. When the structure of FIG. 2 is applied, the modified metal layer 160 and the transparent conductive thin film layer 170 are formed. Form sequentially.

The transparent conductive thin film layer 170 or the modified metal layer 160 and the transparent conductive thin film layer 170 may be an electron beam evaporator, physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma laser deposition (PLD), or dual thermal evaporator (dual). What is necessary is just to form by well-known evaporation methods, such as -type thermal evaporator sputtering.

In addition, the deposition temperature is in the range of 20 ℃ to 1500 ℃, the pressure in the evaporator is applied to atmospheric pressure or 10 ^-12 Torr.

After forming the transparent conductive thin film layer 170 or the modified metal layer 160 and the transparent conductive thin film layer 170 on the p-type cladding layer 150, the structure is subjected to heat treatment in a gas atmosphere containing oxygen, that is, an oxygen atmosphere or an air atmosphere. do.

The temperature in the reactor during the heat treatment is carried out at 100 ℃ to 800 ℃ 10 seconds to 3 hours.

Thereafter, the reflective layer 180 is formed of aluminum on the transparent conductive thin film layer 170.

The reflective layer 180 may be deposited by the deposition method described above.

After the reflective layer 180 is formed, the structure is subjected to 10 seconds to 3 hours at a temperature of 100 ° C. to 800 ° C. in one of vacuum, nitrogen, and argon in order to improve adhesion and thermal stability of the reflective layer 180. do.

According to the experiment, when the heat treatment of the reflective layer 180, it was confirmed that the characteristics deteriorated when treated in an atmosphere other than the vacuum, nitrogen and argon listed above.

Experimental results of measuring the characteristics of the light emitting device manufactured by such a process are shown in FIGS. 3 and 4.

FIG. 3 is a graph in which current / voltage characteristics are measured for light emitting devices fabricated after sequentially stacking Ag / ITO on the p-type cladding layer and performing heat treatment in an air atmosphere at 330 to 530 ° C. FIG.

4 is sequentially stacked on the p-type cladding layer Ag / ITO, and then heat treatment in an air atmosphere at 330 ~ 530 ℃, depositing an aluminum reflective layer, and measuring the current-voltage characteristics obtained by heat treatment at 330 ℃ vacuum One graph.

As can be seen from the comparison of FIG. 3 and FIG. 4, the structure in which the reflective layer 180 is further formed and heat-treated with aluminum can be seen to improve current-voltage driving characteristics.

As described above, according to the flip chip type nitride light emitting device and a method of manufacturing the same, the ohmic contact property with the p-type cladding layer is improved, so that the wire bonding efficiency and the yield can be increased when packaging the light emitting device. The low contact resistance and excellent current-voltage characteristics provide the advantage of improving the luminous efficiency and device life of the device.

Claims (10)

delete In a flip chip nitride light emitting device having an active layer between an n-type cladding layer and a p-type cladding layer, A reflective layer formed of aluminum on the p-type cladding layer; And a transparent conductive thin film layer formed of a transparent conductive material capable of suppressing diffusion of the aluminum between the p-type cladding layer and the reflective layer. The transparent conductive thin film layer is a flip chip type nitride-based light emitting device, characterized in that formed of any one of a transparent conductive oxide and a transparent conductive nitride. The method of claim 2, The transparent conductive oxide may be indium (In), tin (Sn), zinc (Zn), gallium (Ga), magnesium (Mg), beryllium (Be), silver (Ag), iridium (Ir), rhodium (Rh), Flip chip type nitride-based light emitting device, characterized in that formed containing at least one selected from ruthenium (Ru) and molybdenum (Mo) and oxygen. The flip chip type nitride-based light emitting device of claim 2, wherein the transparent conductive nitride is any one of titanium nitride (TiN) and titanium nitride oxide (Ti-N-O). In a flip chip nitride light emitting device having an active layer between an n-type cladding layer and a p-type cladding layer, A reflective layer formed of aluminum on the p-type cladding layer; A transparent conductive thin film layer formed of a transparent conductive material capable of suppressing diffusion of the aluminum between the p-type cladding layer and the reflective layer; And And a modified metal layer formed between the p-type cladding layer and the transparent conductive thin film layer. The modified metal layer includes indium (In), tin (Sn), zinc (Zn), magnesium (Mg), silver (Ag), iridium (Ir), ruthenium (Ru), rhodium (Rh), platinum (Pt), A flip chip nitride light emitting device comprising: any one element selected from nickel (Ni) and palladium (Pd), an alloy containing at least one element selected from the above elements, and a solid solution. The method of claim 5, wherein the transparent conductive thin film layer is formed to a thickness of 1 nanometer to 100 nanometers, the modified metal layer is formed to a thickness of 0.1 nanometer to 50 nanometers, the reflective layer is 100 nanometers to 1000 nanometers Flip chip type nitride-based light emitting device, characterized in that formed in the thickness of the meter. delete In the method of manufacturing a flip chip nitride light emitting device having an active layer between an n-type cladding layer and a p-type cladding layer, end. Forming a transparent conductive thin film layer on the p-type cladding layer of the light emitting structure in which the n-type cladding layer, the active layer and the p-type cladding layer are sequentially stacked on a substrate; I. Heat-treating the structure including the transparent conductive thin film layer at a set temperature in a gas atmosphere containing oxygen; All. Forming a reflective layer of aluminum on the transparent conductive thin film layer; la. And heat-treating the structure including the reflective layer in any one of nitrogen, argon, and vacuum. The transparent conductive thin film layer Indium (In), Tin (Sn), Zinc (Zn), Gallium (Ga), Magnesium (Mg), Beryllium (Be), Silver (Ag), Iridium (Ir), Rhodium (Rh), Ruthenium (Ru) And a transparent conductive oxide formed of molybdenum (Mo) and at least one selected from the group consisting of oxygen, titanium nitride (TiN), and titanium nitride oxide (Ti-NO). Manufacturing method. The method of claim 8, Forming a modified metal layer on the p-type cladding layer before the transparent conductive thin film layer forming step; The modified metal layer includes indium (In), tin (Sn), zinc (Zn), magnesium (Mg), silver (Ag), iridium (Ir), ruthenium (Ru), rhodium (Rh), platinum (Pt), A method for manufacturing a flip chip nitride light emitting device, characterized in that formed of any one element selected from nickel (Ni) and palladium (Pd), an alloy containing at least one element selected from the above elements, and a solid solution. The method of claim 9, wherein the transparent conductive thin film layer is formed to a thickness of 1 nanometer to 100 nanometers, the modified metal layer is formed to a thickness of 0.1 nanometer to 50 nanometers, and the reflective layer is 100 nanometers to 1000 nanometers. A method of manufacturing a flip chip nitride light emitting device, characterized in that formed in the thickness of the meter.

Images