KR100730537B1 - Light emitting diode with vertical structure and method manufacturing for the same - Google Patents

Abstract

The present invention relates to a gallium nitride-based vertical structure light emitting diode and a method for manufacturing the same, and more particularly, to form a vertical electrode structure in which p-type GaN is formed below the active layer and n-type GaN is formed above the active layer to minimize optical loss. To form a roughness to maximize the effect of the light emitted to the upper layer, and to form a conductive transparent conductive film (TCO) to reduce the operating voltage of the light emitting diode on the roughness. A gallium nitride-based vertical structure light emitting diode and a method of manufacturing the same.

GaN-based, TCO, vertical structure, n-type GaN, p-type GaN

Description

LIGHT EMITTING DIODE WITH VERTICAL STRUCTURE AND METHOD MANUFACTURING FOR THE SAME

1 is a cross-sectional view illustrating a conventional nitride semiconductor light emitting device;

2 is a cross-sectional view illustrating a gallium nitride-based vertical structure light emitting diode according to a preferred embodiment of the present invention;

3 is a view showing the result of observing the surface state through SEM after planarization and roughness formation on the buffer GaN or n-type GaN surface using a dry etching process;

4 is a view showing SEM observation results of the formation of buffer GaN or n-type GaN surface roughness using a wet etching process;

FIG. 5 is a diagram illustrating the results of SEM observation after forming a GaN lens on a buffer GaN or n-type GaN surface by using a dry etching process. FIG.

6 is a view showing a specific resistance measured using a 4-point probe after the heat treatment of the ITO thin film by the electron beam deposition method,

FIG. 7 is a view showing optical transmittance measurement results of a thin film measured using UV spectrometry during the heat treatment process by electron beam deposition;

8 is a view showing a measurement result of contact resistance of n-type GaN of ITO according to the change in heat treatment temperature by electron beam deposition;

9 is a view showing the results of measuring the specific resistance of the ITO thin film according to the change in the heat treatment time by the sputtering method,

10 is a view showing a value measured at a wavelength of 460 nm as a result of measuring optical transmittance of a thin film measured using the UV spectrophotometry by sputtering method;

11 is a view showing a change in the specific resistance value of the In ₂ O ₃ thin film according to the change in the voltage applied to the grid of the ion gun,

12 is a graph showing I-V characteristics of an LED device using ITO as a transparent contact and conventional Ti / Al as a contact;

FIG. 13A is a schematic diagram for understanding current flow and voltage drop when an n-type GaN surface is planarized in a gallium nitride based light emitting diode of the present invention; FIG.

FIG. 13B is a schematic diagram for understanding current flow and voltage drop when roughness is formed in the gallium nitride based light emitting diode of the present invention; FIG.

14 is a characteristic diagram of a voltage drop according to a thickness of an ITO thin film;

15 is a graph comparing the emission intensity of the vertical element,

16 is a graph comparing the external emission effect of light by applying an ITO contact layer,

FIG. 17 is a graph illustrating a result of comparing characteristics of a vertical device in which surface texturing or microlenses are formed using wet etching and dry etching;

18 is a view showing the operation taken through the SEM shape and optical microscope of the high brightness vertical structure light emitting diode of the present invention.

   Explanation of symbols on the main parts of the drawings

120: lower layer 130: active layer

140: upper layer 150: conductive oxide thin film layer

160: bonding pad

The present invention relates to a gallium nitride based vertical light emitting diode and a method of manufacturing the same.

The nitride semiconductor light emitting device disclosed in the prior patent application (application number: 2002-0053653) is a buffer layer (11), the lower layer 12 consisting of an n-type nitride semiconductor on the substrate 10, as shown in FIG. ), An active layer 13 made of nitride semiconductor, and an upper layer 14 made of p-type nitride semiconductor are sequentially crystal-grown, mesa-etched to expose the lower layer 12, and then resistive contact with the upper layer 14 is made. After the p-type resistive contact transparent metal layer 15 is formed, the n-type contact metal layer 16 and a bonding pad 17 for electrical connection to the outside are manufactured.

Such a light emitting diode device is basically a device in which light emits light at a junction of a pn junction, but in an actual transverse device, light is emitted through a portion of the p-type GaN layer 14, and as shown, a p-type The GaN layer 14 occupies a relatively large portion of the device configuration, and the p-type GaN layer 14 has a poor p-type GaN layer 14 due to poor electron spreading. The bonding layer 15 is formed to increase the spreading effect of electrons. However, in the case of the above-mentioned lateral light emitting diodes, a device having a good resistance in terms of low resistance or electron spreading effect is used, but the p-type bonding layer 15 uses a metal material and the light emitting area due to the lateral electrode arrangement is used. The loss causes problems with low utilization of materials or high optical losses.

Accordingly, the present invention has been made to solve the above conventional problems, an object of the present invention is to form a p-type GaN under the active layer and the n-type GaN formed on the active layer to make the light generated in the active layer opaque Conductive transparent to improve the problem lost by the metal electrode, to form a roughness (roughness) to maximize the effect of the light emitted to the upper layer to the outside, and to reduce the operating voltage of the light emitting diode on the roughness The present invention provides a gallium nitride-based vertical structure light emitting diode in which a conductive film (TCO) is formed.

A gallium nitride-based vertical structure light emitting diode according to the present invention for achieving the above object, and a lower layer formed on the substrate and made of p-type GaN; An active layer formed on top of the lower layer and made of GaN; An upper layer comprising at least an n-type GaN layer on top of the active layer; A conductive oxide thin film layer formed on the upper layer; Characterized in that configured to include.

Here, the n-type GaN layer constituting the upper layer, the upper surface is preferably formed by the planarization or roughness (roughness) through the etching process.

In addition, the upper layer is formed on the n-type GaN layer further comprises a buffer layer made of GaN, the buffer layer is preferably formed by the top surface is formed by planarization or roughness through an etching process.

In addition, the roughness is preferably characterized in that any one of the spherical, hemispherical, hexagonal pyramid, micro lens array form.

The conductive oxide thin film may be formed of any one of indium tin oxide (ITO), indium oxide (IO), tin oxide (SnO ₂ ), zinc oxide (ZnO), or indium zinc oxide (IZO). desirable.

In addition, the conductive oxide thin film is preferably made of a thickness of (wavelength generated in the gallium nitride-based device) × (2n-1) / 4n _tco .

In addition, the conductive oxide thin film is preferably formed by forming a multilayer structure in which different oxides among the oxides are stacked.

In addition, the conductive oxide thin film is preferably formed by laminating a metal oxide or a metal layer on the top or bottom.

A method of manufacturing a gallium nitride-based vertical structure light emitting diode according to the present invention for achieving the above object, the active layer, an upper layer of n-type GaN formed on top of the active layer, and a p-type GaN formed on the bottom of the active layer A first step of obtaining a self-supporting wafer comprising a lower layer comprising: a metal contact layer and an electrode layer sequentially stacked on the lower layer; And a second step of forming a conductive thin film layer on the upper layer of n-type GaN.

The first step may include forming a buffer layer made of GaN on a sapphire substrate; Forming an upper layer of n-type GaN on the GaN buffer layer;

Sequentially forming the active layer, the lower layer, the metal contact layer, and the electrode layer on the upper layer; And separating and removing the sapphire substrate and obtaining a self-supporting wafer for supporting the electrode layer.

In addition, the buffer layer is removed during separation and removal of the savia substrate.

It is preferable that the upper surface of the upper layer is partially configured to be flattened by an etching process or to form a roughness.

Further, the buffer layer is left during separation and removal of the savia substrate,

It is preferable that the upper surface of the upper layer is partially configured to be flattened by an etching process or to form a roughness.

In addition, the roughness is preferably formed by forming a hexagonal pyramid using a wet etching process using a KOH solution while irradiating UV light using a UV lamp.

In addition, the roughness is preferably formed by forming a microlens array using a dry etching process using a photoresist.

In addition, it is preferable to use any one of an electron beam deposition method, a sputtering method, or an oxygen ion beam assisted electron beam deposition method for forming the conductive oxide thin film layer on the upper layer.

In addition, the electron beam deposition method preferably comprises a heat treatment at a temperature of 250 ℃ to 700 ℃ after the conductive oxide thin film deposition.

In addition, the sputtering method preferably includes a step of heat treatment at a temperature of 450 ° C. or lower after the conductive oxide thin film is deposited.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

In the following description of the present invention, if it is determined that the detailed description of the related well-known technology or manufacturing process may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

2 is a cross-sectional view for a gallium nitride-based vertical structure light emitting diode according to a preferred embodiment of the present invention.

First, GaN is, for example, epitaxially grown on a sapphire substrate (not shown) to form a GaN buffer layer (not shown), and the n-type GaN layer 140 is epitaxially grown on the GaN buffer layer. To form. Thereafter, the active layer 130 and the p-type GaN layer 120 are sequentially stacked on the n-type GaN layer 140 by conventional techniques. Subsequently, Ni / Au, Pt, or Pd is coated on the p-type GaN layer 120 to a predetermined thickness to form a metal film, and a p-type metal contact layer 110 is formed through a heat treatment process. Thereafter, an Au layer 100 is formed on the p-type metal contact layer 110, and a thick metal layer to be used as a p-type electrode and a support of a GaN light emitting diode structure to be separated from a sapphire substrate in a subsequent process (not shown) Is formed using a plating technique or the like. Subsequently, the sapphire substrate is separated using a laser lift off method to obtain a self-standing wafer having a GaN light emitting diode structure. In the subsequent process, the thick metal layer, not shown, is used as the base layer support.

Thereafter, the remaining buffer GaN layer, which is not shown, is removed using a dry etching process, and then, the upper surface of the n-type GaN layer 140 is textured to partially cover the n-type GaN layer 140. After planarizing, roughness is formed. Thereafter, the conductive oxide thin film layer 150 is uniformly formed to a predetermined thickness on the n-type GaN layer 140 on which the roughness is formed, and then a bonding pad 160 is formed on a predetermined region of the conductive oxide thin film layer 150. Form. Here, in the above description, the roughness is formed on the n-type GaN layer 140 after the sapphire substrate is removed to remove the remaining GaN buffer layer from the self-standing wafer having the GaN light emitting diode structure, but the remaining GaN buffer layer is removed. Without forming a roughness on top of the GaN buffer layer by texturing an upper surface of the GaN buffer layer (not shown), and then forming a conductive oxide thin film layer 150 on the roughened GaN buffer layer, and forming the conductive oxide thin film layer. A bonding pad 160 is formed on the 150. In addition, after the GaN buffer layer or the n-type GaN layer 140 is partially planarized through an etching process, the conductive oxide thin film layer 150 may be formed without forming roughness.

In this embodiment, in order to reduce the loss of light generated in the existing multiple quantum well structure type active layer 130 by the opaque metal electrode, the existing p-type GaN layer is formed on the top of the device. The device structure of the device is changed from the device structure in which the n-type GaN layer exists in the lower part of the device, to the structure in which the n-type GaN layer 140 exists in the upper part of the device.

One of the most important problems for optimizing the device structure for manufacturing high-brightness light emitting diodes is that since the refractive index of the semiconductor material is much higher than that of air, the internal reflection of light generated in the semiconductor does not escape to the outside of the semiconductor. Since the internally reflected light is mostly absorbed by the material and the substrate material and is extinguished without disappearing to the outside of the device, the actual external emission efficiency of the device is about 10% or less. Therefore, in order to solve this problem, the inventors of the present invention perform a study to maximize the effect of releasing light generated inside the device to the outside by increasing the critical angle by forming a roughness on the surface by texturing the surface of the light emitting surface. It was. The surface roughness refers to a surface structure of a spherical shape, a hemispherical shape, a hexagonal pyramid shape, or a micro lens array type, and a detailed roughness forming method is as follows.

3 is a result of observing the surface state according to the gas combination by using a dry etching process through the SEM. In this embodiment, the surface planarization and roughening process were performed using a gas combination of Cl ₂ / BCl ₃ to control the roughness of the surface including the planarization of the surface. The gas combination of Cl ₂ / BCl _{3 means all} gas combinations in which BCl ₃ gas is added as a main gas and 0 to 100% of Cl ₂ gas is added thereto, and spherical through dry etching roughening process using such gas combination. Surface roughness structures in the form of, hemispherical, or micro lens arrays can be implemented.

4 is an SEM observation result of surface roughness formation using a wet etching process. In this embodiment, the surface of the buffer GaN and n-type GaN was etched using a KOH solution to form the surface roughness. As can be seen in Figure 4 it can be seen that the wet etching results in the form of GaN hexagonal pyramid KOH. The surface roughness formation through this wet etching process is based on using a KOH aqueous solution. In this embodiment, the KOH aqueous solution is heated to 80 ° C. or higher during the etching process, and the etching reaction is promoted by irradiating UV with a UV lamp. It was confirmed that the horn-shaped structure is implemented.

FIG. 5 is a SEM observation of a GaN lens fabricated on a surface of a device and a photoresist mask in the form of a lens for forming a microlens on an n-type GaN surface by using a dry etching process. When such a pattern was fabricated on the surface of the device using a dry etching process, a microlens array capable of controlling the radius of curvature could be formed.

In addition, the present embodiment is to form an ITO or IO (In ₂ O ₃ ) to the transparent contact on the GaN surface formed by the laser lift off technique to reduce the operating voltage and increase the external emission efficiency of light The experiment was conducted. As the method of depositing ITO or IO (In ₂ O ₃ ), an electron beam deposition method, a sputtering method, an ion beam assisted electron beam deposition method, or the like was used, and a detailed method thereof will be described below.

First, in the case of depositing an ITO thin film by using an electron beam deposition method it is was used as the typical 10 wt% SnO electron beam evaporation source of the _{2/90 wt% In 2 O} 3 composition which is used for the deposition of the ITO thin film of ITO thin films at room temperature Deposited. In this embodiment, in order to increase the electrical conductivity of the ITO, increase the optical transmittance, and also decrease the contact resistance to the upper layer, the heat treatment was carried out in a heat treatment furnace in a nitrogen (N ₂ ) atmosphere after the deposition of the ITO thin film. To 700 ° C. In addition, in the heat treatment process, the atmosphere may use an inert gas such as argon (Ar), and as an atmosphere gas, oxygen (O ₂ ) or nitrogen containing oxygen (N ₂ ) + oxygen (O ₂ ), argon (Ar) + oxygen ( In the case of using a gas combination such as O ₂ ), the heat treatment temperature was improved even at a low temperature of less than 500 ℃ to 250 ℃. Therefore, by controlling the heat treatment atmosphere in the heat treatment process, the heat treatment temperature in the process may be changed from 250 ℃ to about 700 ℃.

The ITO thin film before the heat treatment was dark brown and exhibited sheet resistance of several kΩ / □. The deposited ITO thin film did not increase the transmittance at the heat treatment temperature of less than 500 ℃ and showed a high resistance value. Therefore, in the case of the ITO thin film deposited by the electron beam deposition method, the transmittance may be increased through the heat treatment process at a heat treatment temperature of 500 ° C. or higher, and the resistance value may also be reduced. 6 shows that the resistivity of the ITO thin film was decreased up to 500 ° C. after the heat treatment at each temperature, but the value of the resistivity gradually increased when the heat treatment temperature was increased from 500 ° C., and after 700 ° C. This showed a sharp increase. In general, the resistivity of an ITO thin film is affected by the amount of free electrons obtained by oxygen depletion and the doping effect by tin atoms.In the case of amorphous ITO deposited at room temperature, it is difficult to activate tin atoms or oxygen depletion in the thin film. it's difficult. As the formation of oxygen depletion or tin atoms are replaced by indium, the amount of free electrons increases to act as a dopant, which lowers the specific resistance. However, as the heat treatment temperature increases, oxygen atoms enter oxygen depletion in the ITO thin film. As this decreases and thus the amount of free electrons decreases, the specific resistance also increases. In this embodiment, heat treatment was performed at 500 ° C. for 5 minutes to obtain a minimum resistivity value of 8 × 10 ⁻⁴ Ωcm. In addition, as a result of measuring the optical transmittance of the thin film measured by UV annealing process UV spectrometry at each temperature, it can be seen that the transmittance of the ITO thin film increases with increasing the heat treatment temperature. Since the oxygen depletion density in the thin film is increased, the permeability increase of the ITO thin film means a decrease in the oxygen depletion density. In other words, as described above, it means the reduction of free electrons. In this embodiment, the transmittance in the 460nm wavelength region of the ITO thin film was obtained at a value of 85% or more except for the thin film heat-treated at 500 ℃.

When depositing the ITO thin film by using a sputtering method, used was a typical ITO target composition of _{10wt% SnO 2 / 90wt% In} 2 O 3 sputtering target. Ar / O ₂ mixed gas was used as the sputter gas.

9 is a result of measuring the resistivity of the ITO thin film according to the change in heat treatment time after depositing the thin film with O ₂ inflow rate of 1.25sccm and 1.5sccm while the inflow of Ar is fixed. The difference in resistivity value of ITO thin film under the two conditions is due to the amount of O ₂ that can be included in the stoichiometric ITO thin film. The ITO thin film is characterized by both permeability and electrical conductivity when the amount of oxygen depletion in the thin film is insufficient. Is lowered. The heat treatment was carried out in a furnace (furnace) in a nitrogen atmosphere and the heat treatment temperature was 450 ℃ or less. As shown in FIG. 9, the ITO thin film deposited at 1.25 sccm of O ₂ flow rate showed a specific resistance value of 1.45 × 10 ⁻³ Ωcm before heat treatment, but the specific resistance of the thin film decreased as the heat treatment time was increased, and the heat treatment was performed for 7 minutes and 30 seconds. After that, a specific resistance value of 3.78 × 10 ⁻³ Ωcm was shown. The specific resistance decreased as the heat treatment time was increased up to 5 minutes after the heat treatment time at 1.5 sccm under the condition of O ₂ inflow. The change in resistivity due to the heat treatment or O ₂ inflow is due to the decrease of the defect density due to oxygen depletion in the thin film and the proper oxygen depletion due to the diffusion and activation of O _{2 as} the heat treatment time increases. The specific resistance was lowered because tin atoms were substituted in the indium site, but as the dopant, but as the heat treatment temperature increased, oxygen atoms filled oxygen depletion in the ITO thin film, reducing oxygen depletion and thus the amount of free electrons. As this decreases, the resistivity also increases. In addition, the contact resistance of n-type GaN of ITO was 1 × 10 ^-5 Ωcm ² .

In addition, as a result of measuring optical transmittance of thin film measured by UV spectrophotometry, the optical transmittance of ITO thin film measured at wavelength 460 nm can be seen to increase with increasing annealing time as in the previous experiment. The transmittance in the 460nm wavelength region of the ITO thin film obtained in this experiment increased by about 97% after heat treatment for thin films deposited with an O ₂ inflow rate of 1.25 sccm, and about 98.5 after heat treatment for thin films deposited with an O ₂ flow rate of 1.5 sccm. Increased by%. The electrical and optical characteristics of the ITO thin film deposited using such a sputter may change the thin film characteristics by changing the process variables such as the distance between the target and the substrate, the heating of the substrate, and the O ₂ inflow amount when the thin film is deposited. Can be. Therefore, the ITO thin film deposited using the sputter has the advantage that the heat treatment process after the thin film deposition can be omitted when applied to the device.

In the case of depositing the IO (In ₂ O ₃ ) thin film by using the ion beam assisted electron beam deposition, the reason for depositing the transparent conductive oxide thin film by using the ion beam assisted electron beam deposition is the case of depositing the ITO thin film using the electron beam deposition in the previous experiment. Due to the lack of oxygen depletion in the thin film, the heat treatment temperature must be increased to 600 ℃ or higher to obtain permeability. The heat treatment at such a high temperature requires consideration of defects due to the stress of the thin film in the fabrication of the device. This is because the device fabrication process dealing with GaN formed by the laser lift off technique is difficult to use. Therefore, by irradiating the substrate with oxygen radicals to produce the oxygen radicals in the deposition of the thin film inside the evaporator, it is possible to form an appropriate oxygen bond during the thin film deposition and to control the oxygen depletion in the thin film. In ₂ O ₃ thin films were deposited using oxygen ion beam assisted electron beam deposition, which enables the deposition of thin films with high resistance and high transmittance, and the electrical and optical properties of the thin films were investigated.

Figure 11 shows the change in the specific resistance value of the In ₂ O ₃ thin film with a change in the voltage applied to the grid of the ion gun. At this time, RF power was used to generate the oxygen plasma in the ion gun. As shown in FIG. 11, the lowest resistivity value was obtained with an acceleration voltage of 300 V according to the increase in the acceleration voltage applied to the grid. The resistivity value was 5 × 10 ⁻⁴ Ωcm and the transmittance of the thin film was increased. The measurement resulted in a transmittance of about 92% in the region of 460 nm wavelength. In addition, when the acceleration voltage was applied above 300V, the transmittance of the thin film was increased, but the resistivity value tended to increase again. This is due to the increase of the acceleration voltage and the increase of the energy of the thin film surface by the oxygen ion beam. By filling the oxygen depletion within the thin film, the permeability of the thin film increased, but the specific resistance of the thin film increased.

 As described above, in the present invention, a transparent conductive oxide thin film (TCO) junction is applied to the GaN surface formed by the laser lift off technique to reduce the operating voltage of the light emitting diode. The operating voltage of the device could be reduced.

FIG. 12 is a graph showing I-V characteristics of an LED device when ITO is used as a transparent contact on a GaN surface formed by a laser lift off technique and when Ti / Al is developed as a contact. As shown in FIG. 12, when Ti / Al was used as a contact, the operating voltage at 20 mA was about 10.24 V, and there was little change in the operating voltage even after the heat treatment. However, in the case of ITO junction, the operating voltage was lowered to 4.28V before heat treatment and 3.8V after heat treatment. The increase in contact resistance during Ti / Al contact is considered to be due to the poor current spreading in the plane direction due to the relatively high resistance of the n-GaN layer. The phenomenon is thought to be due to the improvement of current spreading in the plane direction of the device due to the overall deposition of the relatively low resistance ITO contact.

13 is a schematic diagram for understanding the current flow and the voltage drop of the vertical light emitting diode of the present invention. Arrows "A" and "B" in FIG. 13 mean arbitrary current paths, and we will consider voltage drop elements that can occur in devices with ITO junctions and devices without ITO junctions during these paths. It was. For convenience, only an n-type GaN upper layer is illustrated in FIG. 13A, and the surface is formed by forming a planarization layer and FIG. 13B is illustrated by dividing it into a case where a roughness layer is formed. do. First, in FIG. 13, the total voltage drop that may occur in the entire device may be expressed as follows during the paths "A" and "B", respectively.

(1)

(One)

(2)

(2)

Where J and Va represent the current density and voltage drop through the active layer, respectively, ρ _p and ρ _n are the specific resistances of p-GaN and n-GaN, and t _p and t _n are the p-type GaN and n-type GaN layers, respectively. Indicates thickness. And the distance of the electric current which flows from the edge of an electrode pad to the surface direction of an element is shown by distance l . From the relationship between equations (1) and (2), conditions for allowing a uniform current to pass through the entire active layer of the device can be obtained as shown in equation (3).

(3)

(3)

Under this relationship, the thickness t _{n of the} n-type GaN layer 140 should be as thick as the current path l in the plane direction. If the thickness of the n-type GaN layer 140 is increased by l , As the voltage drop passes through the n-type GaN layer, the resistivity of the device is further increased due to the specific resistance ρ _n of the n-type GaN layer 140. Therefore, it is not preferable that the thickness of the layer of the n-type GaN layer 140 is thick, and thus, it is concluded that the distance from the edge of the bonding pad to the end of the device should be as short as the thickness of the n-type GaN layer 140. That is, it means that the size of the n-type GaN layer 140 should be large enough to cover the entire device. Therefore, in this embodiment, in order to satisfy this condition, as shown in FIG. 13 (b), ITO, which is a transparent conductive material, is used as the n-type GaN junction layer. Equation (4) was obtained. In the device to which the ITO junction is applied, the voltage drop paths are sufficiently low in comparison with the n-type GaN layer because the specific resistance of the ITO can be compared by considering only the voltage drop through the plane path B of the device.

(4)

(4)

In the above equation, ρ _ITO represents the resistivity of the ITO thin film. Comparing this relation with Eq. (2), the difference in voltage drop of the device with or without ITO junction can be calculated from Equation (5).

(5)

(5)

In the above relation, in the term related to the specific resistance ( ρ _n ) of the n-type GaN layer 140, the thickness ( t _n ) is much smaller than the path ( l ) of the current flowing in the plane direction and can be ignored ( t _n << l ). Therefore, the difference in the voltage drop of the device depending on the presence or absence of ITO junction obtained from the relationship can be obtained as a function of the specific resistance ρ _ITO of _ITO and the specific resistance ρ _n of n-type GaN.

(6)

(6)

Accordingly, it can be seen that the decrease in operating voltage in the device using ITO as a junction in the current-voltage curve obtained from the device fabricated in FIG. 12 is caused by the difference between the resistivity of ITO and the resistivity of n-type GaN.

Figure 14 shows the operating voltage according to the thickness of the ITO in order to determine the characteristics of the voltage drop according to the thickness of the ITO thin film, and fabricated the same type of horizontal device, the vertical device having the operating voltage value and the ITO junction of the device The operating voltage values of can be compared. As shown in FIG. 14, the operating voltage of the device was decreased according to the thickness of the ITO junction thin film, and the thickness of the ITO junction of 100 nm or more was confirmed to have a value almost similar to that of the horizontal device. In the case of ITO thin film of about 50 nm thickness, the transmittance is good, but it is considered that the operating voltage is increased due to the high resistivity due to crystal defects in the thin film. In the thin film of 150 nm or more, the electrical conductivity improves as the thickness of the thin film increases. Could lower the voltage.

Therefore, the ITO thin film will be appropriately deposited with a thickness of wavelength x (2n-1) / 4n _tco (n = natural number, n _tco = refraction coefficient of the TCO thin film) generated at 100 nm or more gallium nitride considering the wavelength of 460 nm.

On the other hand, the external emission efficiency of the light for the light emitting diode formed with transparent contact of ITO and IO (In ₂ O ₃ ) of the present invention was measured using OES.

FIG. 15 compares the emission intensity of the device manufactured in the vertical direction, the device manufactured in the vertical direction, and the vertical device textured on the surface by dry etching. As can be seen in FIG. 15, when the conventional horizontal device and the vertical device were compared, the external emission effect of about 20% was increased, and the light emission characteristics of the device and the horizontal device manufactured by performing the surface texturing process were observed. Comparing the results, the light emission efficiency was increased by about 100%. The increase in the light emission efficiency may be due to the surface roughening using a dry etching process to reduce the loss due to the internal reflection of the device.

FIG. 16 compares the external emission efficiency of light of a device having a high operating voltage due to surface texturing and the effect of external emission of light of a device having a low operating voltage by applying an ITO contact layer. The experiment is based on the surface texturing device with Ti / Al junction, and the device with the ITO contact layer after the surface texturing, the device after the ITO contact layer formation and the heat treatment process, and the anti-reflection film after the ITO contact layer formation and the heat treatment process. It was intended to measure the external emission efficiency of the light of the device by measuring the luminous efficiency at 20 mA of the device laminated SiO ₂ on which the applicability was examined. As shown in FIG. 16, in the device using ITO as a contact layer, the emission intensity was slightly lowered before the heat treatment process, and the emission intensity increased after the heat treatment process. It is believed that this is due to the increase. In addition, the device after ITO contact layer formation and annealing after surface texturing exhibits almost similar emission intensity as the surface texturing device with Ti / Al junction. In addition, in the case of devices deposited with SiO ₂ anti-reflection film after the formation of the ITO contact layer and the heat treatment process, the efficiency was increased by about 11% based on the surface texturing device having the Ti / Al junction and the ITO contact after the surface texturing. After forming the layer, the efficiency increase of about 5% was expected based on the device subjected to the heat treatment process, but the emission intensity increased by about 5% and 4%, respectively. Although the loss of permeability was somewhat reduced, it was possible to fabricate a device having an emission increase efficiency of almost similar value based on the device subjected to heat treatment after forming the ITO contact layer after surface texturing.

FIG. 17 shows the result of comparing the characteristics of a vertical device formed with surface texturing or microlens using wet etching method and dry etching method, and surface-heat-deposited IO (In ₂ O ₃ ) contact device by dry etching method. Was applied to the textured device to observe its luminescence properties. The ITO contact film was applied to the surface of the device with the micro lens through the dry etching method and the vertical device with the hexagonal pyramid structure through the wet etching method, and the actual operating voltage of these devices was 3.6 ~ 3.8 V @ 20 mA. As shown in FIG. 17, the emission characteristics of the device surface-textured by the dry etching method were the highest, and compared to the device having the IO contact layer formed after the surface texturing, the emission property was reduced by about 5%. In the case of the device where the was formed, the decrease was about 18.7%. In addition, the vertical type device with hexagonal pyramid structure formed on the surface through wet etching resulted in about 30% emission reduction. These results indicate that the IO contact film is formed by the reduction of transmittance because the transmittance of the IO thin film is about 92% in the 460nm region, and the device with the microlens formed on the surface has a relatively low density of microlenses. It seems that the emission efficiency is reduced. In the case of the vertical device having the hexagonal pyramid structure formed by wet etching, the emission efficiency is greatly reduced because the light emission efficiency is lower than that of the lens.

18 is a view showing the operation of a completed high-brightness vertical light emitting diode photographed through an SEM and a SEM image of a vertical light emitting diode device having an ITO contact formed on a textured surface of the present invention.

As described above, in the present invention, the TCO contact is applied to the GaN surface formed by the laser lift off technique in order to reduce the operating voltage of the light emitting surface texturing high luminance light emitting diode. The voltage can be reduced, and the improved high brightness, high efficiency GaN-based vertical structure light emitting diode can be fabricated, and the electrical and light emission characteristics of the device can be observed. The efficiency of the conventional horizontal light emitting diodes can be more than doubled.

The TCO includes indium tin oxide (ITO) and indium oxide (IO) as examples, but transparent conduction such as tin oxide (SnO ₂ ), zinc oxide (ZnO), indium zinc oxide (IZO), and the like. Oxides can be used and it is also possible to form and use multi-layered contacts such as metal-TCO, TCO-TCO, TCO-metal and the like.

What has been described above is only one embodiment for carrying out the vertical photoelectric device having a transparent junction according to the present invention and a method for manufacturing the same, and the present invention is not limited to the above-described embodiment, it is within the technical spirit of the present invention. Of course, various modifications are possible by those skilled in the art.

As described above, the present invention forms a p-type GaN under the active layer and the n-type GaN formed on the active layer to improve the problem that the light generated in the active layer is lost by the opaque metal electrode, the n-type Roughness is formed in the upper layer of GaN to maximize the effect of emitting light to the outside, and a conductive transparent conductive film (TCO) is formed on the roughness to reduce the operating voltage of the light emitting diode. have.

Claims (17)

A lower layer formed on the substrate and made of p-type GaN, An active layer formed on top of the lower layer and made of GaN, An upper layer comprising at least an n-type GaN layer on top of the active layer; It comprises a conductive oxide thin film layer formed on the upper layer, The conductive oxide thin film is formed of a thickness of (gallium nitride-based device) × (2n-1) / 4n _tco , _Wherein n is a natural number and n _tco is a refractive _index of the conductive oxide thin film. The method of claim 1, The n-type GaN layer constituting the upper layer is a gallium nitride-based vertical structure light emitting diode, characterized in that the upper surface is formed by the planarization or roughness (roughness) through an etching process. The method of claim 1, The upper layer is formed on the n-type GaN layer further comprises a buffer layer made of GaN, The buffer layer is a gallium nitride-based vertical structure light emitting diode, characterized in that the upper surface is formed by the planarization or roughness through an etching process. The method of claim 2 or 3, The roughness is a gallium nitride-based vertical structure light emitting diode, characterized in that any one of spherical, hemispherical, hexagonal pyramid, micro lens array form. The method according to any one of claims 1 to 3, The conductive oxide thin film is formed of any one of indium tin oxide (ITO), indium oxide (IO), tin oxide (SnO ₂ ), zinc oxide (ZnO), or indium zinc oxide (IZO). Gallium nitride-based vertical structure light emitting diode. delete The method of claim 1, The conductive oxide thin film is a gallium nitride-based vertical structure light emitting diode, characterized in that formed by forming a multi-layer structure in which different oxides of the oxide are laminated. The method of claim 7, wherein The conductive oxide thin film is a gallium nitride-based vertical structure light emitting diode, characterized in that the metal oxide or metal layer is laminated on the top or bottom. A self-standing wafer comprising an active layer, an upper layer made of n-type GaN formed on top of the active layer, a lower layer made of p-type GaN formed on the bottom of the active layer, and a metal contact layer and an electrode layer sequentially stacked on the lower layer. The first step And a second step of forming a conductive oxide thin film layer on the upper layer of n-type GaN, The conductive oxide thin film is formed of a thickness of (gallium nitride-based device) × (2n-1) / 4n _tco , N is a natural number, and n _tco is a refractive _index of the conductive oxide thin film manufacturing method of a gallium nitride-based vertical structure light emitting diode. The method of claim 9, The first step includes forming a buffer layer made of GaN on a sapphire substrate; Forming an upper layer of n-type GaN on the GaN buffer layer; Sequentially forming the active layer, the lower layer, the metal contact layer, and the electrode layer on the upper layer; And separating and removing the sapphire substrate and obtaining a self-supporting wafer having the electrode layer as a support. The method of claim 10, The buffer layer is removed during separation and removal of the savia substrate, And partially planarizing the upper surface of the upper layer by an etching process or forming roughness. The method of claim 11, The buffer layer is left during separation and removal of the savia substrate, And partially planarizing the upper surface of the buffer layer by an etching process or forming roughness. The method of claim 11 or 12, The roughness formation is a method of manufacturing a gallium nitride-based vertical structure light emitting diode, characterized in that to form a hexagonal pyramid using a wet etching process using a KOH solution while irradiating UV light using a UV lamp. The method of claim 11 or 12, The roughness forming method of manufacturing a gallium nitride-based vertical structure light emitting diode, characterized in that to form a microlens array using a dry etching process using a photoresist. The method according to any one of claims 9 to 12, The method of forming the conductive oxide thin film layer on the upper layer is a method of manufacturing a gallium nitride-based vertical structure light emitting diode, characterized in that any one of the electron beam deposition method, sputtering method or oxygen ion beam assisted electron beam deposition method. The method of claim 15, The electron beam evaporation method is a method of manufacturing a gallium nitride-based vertical structure light emitting diode comprising the step of heat treatment at a temperature of 250 ℃ to 700 ℃ after the conductive oxide thin film deposition. The method of claim 15, The sputtering method is a method of manufacturing a gallium nitride-based vertical structure light emitting diode comprising the step of heat-treating at a temperature of more than 450 ℃ at room temperature after the deposition of the conductive oxide thin film.

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