KR100753677B1 - Light emitting element - Google Patents

Abstract

Disclosed is a light emitting device having an electrode capable of uniformly supplying current over the entire surface of a light emitting diode to output high brightness. The first semiconductor layer is formed over the substrate. The active layer is formed over the first semiconductor layer. The second semiconductor layer is formed over the active layer. The first semiconductor layer is doped with n-type or p-type and the second semiconductor layer is doped with a polarity opposite to the first semiconductor layer to form a p-n junction surface between the two semiconductor layers. The first electrode is formed entirely on the first semiconductor layer. The second electrode is formed in a region where a portion of the second semiconductor layer is peeled off and the first semiconductor layer is exposed in the form of fish thorns. Accordingly, by changing the electrode structure, the current flowing through the p-n junction surface of the light emitting diode can be made uniform and at the same time, the light emitting area can be kept wide to increase the amount of light emitted.

Light Emitting Diode, Gallium Nitride, Current Distribution

Description

Light emitting element {LIGHT EMITTING ELEMENT}

1 is a perspective view schematically showing a structure of a general gallium nitride-based light emitting diode.

2A and 2B are cross-sectional views illustrating a bonding method of the light emitting diode shown in FIG. 1.

FIG. 3 is an equivalent circuit diagram of the gallium nitride based light emitting diode shown in FIG. 1.

FIG. 4 is a graph showing a change in intensity according to a position of current density in the gallium nitride based light emitting diode shown in FIG. 1.

5A to 5C are diagrams illustrating a light emitting diode having a two-dimensional electrode structure.

6 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a first embodiment of the present invention.

FIG. 7 is a distribution diagram of current flowing through the p-n junction surface in FIG. 6.

8 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a comparative example.

FIG. 9 is a distribution diagram of current flowing through a p-n junction surface in the gallium nitride based light emitting diode shown in FIG. 8.

10A and 10B are graphs showing current distribution characteristics of the cross-section shown in FIGS. 7 and 9.

11 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a second embodiment of the present invention.

12 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a third embodiment of the present invention.

FIG. 13 is a distribution diagram of current flowing through the p-n junction surface in FIG. 12.

14A and 14B are graphs showing current distribution characteristics of the cross-section shown in FIGS. 9 and 13.

15 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a fourth embodiment of the present invention.

FIG. 16 is a distribution diagram of current flowing through the p-n junction surface in FIG. 15.

17A and 17B are graphs showing current distribution characteristics of the cross-section shown in FIGS. 9 and 16.

FIG. 18A is a plan view of a light emitting diode for flip chip bonding manufactured using the electrode structure illustrated in FIG. 12. 18B is a cross-sectional view of the light emitting diode of FIG. 18A.

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

10 substrate 11 n-type gallium nitride layer

12 gallium nitride active layer 13 p-type gallium nitride layer

20: n-electrode 21, 121: p-electrode

22, 121: p-electrode 123: basic n-electrode

124: secondary n-electrode 30: metal wire

31: solder bump 32: solder pad

33: metal pad 40: submount

The present invention relates to a light emitting device, and more particularly to a light emitting device having an electrode structure for high efficiency light emission.

In general, a light emitting diode, which is a light emitting device, is spotlighted as a next-generation lighting that replaces an incandescent bulb or a fluorescent lamp. In particular, demand is expected to increase further as it is used for lighting of large area LCDs with long lifespan.

However, there is a problem in the nonuniformity of the current distribution in implementing a high brightness light emitting diode. In particular, gallium nitride-based light emitting diodes, which are widely used as blue light sources, have higher nonuniformity in current distribution due to the structure of electrodes, compared with other light emitting diodes. That is, the current is locally distributed rather than evenly distributed over the entire surface of the light emitting diode.

This means that the intensity of light emission and the uniformity of wavelength are inferior on the surface of the light emitting device. In the region where the concentration of electron-holes is relatively high, the intensity of light emission by electron-hole coupling is large, and the wavelength is shortened by band filling phenomenon, and in the region where electron-hole concentration is relatively low, electron-holes The intensity of light emission by the coupling is small and the wavelength is relatively long.

The light having a short wavelength generated in a portion where the electron-hole concentration is relatively high is partially absorbed into a low current density region where the light emission wavelength is relatively low, thereby lowering the light emission internal quantum efficiency of the device.

Accordingly, the technical problem of the present invention is to solve such a conventional problem, and an object of the present invention is to provide a gallium nitride-based light emitting device having an electrode structure which induces a uniform current distribution to realize a large area light emitting diode having high power and high brightness. To provide.

In order to realize the above object of the present invention, a light emitting device includes: a first gallium nitride layer formed on a substrate; An active layer formed on the first gallium nitride layer; A second gallium nitride layer formed on the active layer; A second electrode formed entirely on the second gallium nitride layer; And the edge of the second gallium nitride layer, at least one line extending from one side of the edge to the opposite side, and the plurality of branch regions extending from the edge and the line are peeled off to form the first gallium nitride layer in the form of fish thorns. It includes a first electrode formed in the exposed area.

In order to achieve the above object of the present invention, a light emitting device according to another embodiment includes a first semiconductor layer formed on a substrate; A second semiconductor layer formed on the first semiconductor layer; A second electrode formed entirely on the second semiconductor layer; And the edge of the second semiconductor layer, at least one line extending from one side of the edge to the opposite side, and the plurality of branch regions extending from the edge and the line are peeled off to expose the first semiconductor layer in the form of fish thorns. And a first electrode formed in the region.

According to such a light emitting diode, by changing the electrode structure, it is possible to make the current distribution flowing to the p-n junction surface of the light emitting diode uniform and at the same time to keep the light emitting area wide, thereby increasing the amount of light emitted.

In addition, by providing a thick electrode in the light emitting diode, the contact resistance of the electrode can be reduced to reduce heat generation, and the current distribution can be made uniform, thereby increasing the internal quantum efficiency.

Hereinafter, with reference to the accompanying drawings, it will be described in detail the present invention.

1 is a perspective view schematically showing a structure of a general gallium nitride-based light emitting diode.

Referring to FIG. 1, a general gallium nitride based light emitting diode includes a substrate 10, a gallium nitride buffer layer, an n-type gallium nitride layer 11, an active layer 12, and a p-type gallium nitride layer ( 13), the p-type transparent electrode 22, the p-electrode 21, and the n-electrode 20. In operation, when current flows through the p-electrode 21 and the n-electrode 20, light is emitted while electron-hole recombination occurs in the active layer 12.

In order to grow the gallium nitride layer 11 on the substrate 10, a metal organic chemical vapor deposition (MOCVD) device is usually used. The substrate 10 is a sapphire substrate or a silicon carbide substrate.

First, a buffer layer (not shown) is formed on the substrate 10 to assist the growth of the gallium nitride layer 11. The n-type gallium nitride layer 11, the active layer 12, and The p-type gallium nitride layer 13 is grown in sequence.

In general, a diode forms an electrode on top of a p-type gallium nitride layer and a bottom of a substrate connected to an n-type gallium nitride layer to flow current through a p-n junction. However, since the sapphire used as the substrate of the gallium nitride-based diode is an insulator, an electrode cannot be formed on the sapphire substrate 10. Therefore, an electrode must be directly formed on the n-type gallium nitride layer 11.

To this end, partial regions of the p-type gallium nitride layer 13, the active layer 12, and the n-type gallium nitride layer 11 of the portion where the electrode is to be formed are removed, and the n-type gallium nitride layer 11 is exposed on the n-type gallium nitride layer 11. An electrode 20 is formed. Since the light is emitted from the p-n junction surface, the p-electrode 21 is formed at the corner of the p-type transparent electrode 22 so that the light is not obscured by the electrode.

As such, when both the p-electrode 21 and the n-electrode 20 are positioned at the top, the current is higher than that of a general diode structure in which the p-electrode 21 and the n-electrode 20 are located in parallel with each other. The distribution is not uniform.

In addition, the p-type gallium nitride layer 13 has a larger resistance than the n-type gallium nitride layer 11, and thus, it is more difficult for a current to flow uniformly through the p-type gallium nitride layer 13. To prevent this, a thin transparent electrode is formed on the entire upper surface of the p-type gallium nitride layer 13 so that current can be transferred to the entire surface of the p-type gallium nitride layer 13.

However, the transparent electrode is formed of a very thin metal layer of about 10 nanometers thick in order to allow light to be transmitted, so the resistance is high. There is a limit to uniform current transfer to the entire surface of the p-type gallium nitride layer using the high resistance transparent electrode.

In addition, the contact resistance with the p-type gallium nitride layer 13 is also high, the diode characteristics are deteriorated and may cause heat generation. The thickness of the transparent electrode can be increased to lower the resistance, but in this case, the absorption and reflectance of the light by the electrode are increased, which makes it difficult to emit light to the outside.

In order to reduce such drawbacks, a method of increasing light emission efficiency of a light emitting diode using a flip chip bonding method has been proposed. That is, a thick electrode may be formed on the entire surface of the p-type gallium nitride layer, the LED chip may be inverted, and then mounted in a package by flip chip bonding.

2A and 2B are cross-sectional views illustrating a bonding method of the light emitting diode chip illustrated in FIG. 1. In particular, FIG. 2 is a cross-sectional view showing a gallium nitride-based LED chip assembled by a wire bonding method, and FIG. 2B is a cross-sectional view showing a gallium nitride-based LED chip assembled by a flip chip bonding method.

As shown in FIG. 2A, a package containing a light emitting diode chip is provided with a lead frame for supplying current. A light emitting diode chip is attached to the lead frame, and the lead frame and the n-electrode 20 and the p-electrode 21 of the light emitting diode chip are electrically connected with thin metal wires 30a and 30b. In this case, a thin transparent electrode is formed so that light can be emitted through the p-type gallium nitride layer.

On the other hand, as shown in Figure 2b, the flip-chip bonding method is provided with another substrate 40 connected to the lead frame, the solder bump (a) in a position corresponding to the electrode of the light emitting diode on the substrate 40 solder bumps 31b are formed. The light emitting diode is turned upside down to attach a light emitting diode chip such that the electrodes of the light emitting diode and the solder bumps 31b are connected to each other.

Since sapphire used as a substrate of a gallium nitride-based light emitting diode is transparent to the emission wavelength, light can be emitted through the substrate even if the light emitting diode is turned over. In the case of using a substrate that is opaque to the emission wavelength, the substrate may be removed so that light can be emitted toward the substrate. At this time, the emitted light is not emitted through the p-type gallium nitride layer, but is emitted through the LED substrate, so that the entire surface of the p-type gallium nitride layer does not need to be transparent.

Accordingly, since an electrode having a thickness of about 100 nm or more is formed on the entire surface of the p-type, the resistance of the electrode and the contact resistance between the p-type gallium nitride layer can be reduced than in the case of using the transparent electrode, thereby further improving diode characteristics.

In addition, since the p-electrode serves as a reflector to reflect the light emitted toward the p-type gallium nitride layer and exits toward the substrate, the luminous efficiency may be further increased.

However, the above method also has a limitation in making the current distribution uniform. In particular, a current crowding effect in which current flows around the n-electrode occurs, resulting in a decrease in luminance and a decrease in lifetime due to local heat increase.

Guo et al. Applied Physics Letters Vol. According to a paper published on page 3337 of 78, a gallium nitride-based light emitting diode is interpreted as an equivalent circuit composed of a resistor and a diode as shown in FIG.

FIG. 3 is an equivalent circuit diagram of the gallium nitride based light emitting diode shown in FIG. 1.

As shown in FIG. 3, two paths of current that can flow from the p-electrode 21 to the n-electrode 20 are classified into two.

That is, in the first path Path 1, current flows through the p-electrode 21 to the vicinity of the n-electrode 20, and current flows through the pn junction surface of the diode near the n-electrode 20. This is the path to the n-electrode 20.

In addition, the second path Path 2 has a current flowing along the n-type gallium nitride layer 11 after a current flows through the pn junction surface at a distance away from the n-electrode 20. Is the path to.

Typically, since the resistance of the n-type gallium nitride layer 11 is greater than that of the p-electrode 21, current does not easily flow through the n-type gallium nitride layer 11. That is, a current tends to flow in the first path Path 1 more than the second path Path 2. According to this analysis, the amount of current flowing to the p-n junction near the n-electrode 20 is greater than that far from the n-electrode 20.

According to Guo's paper, the current density flowing from the n-electrode 20 to the p-n junction surface according to the distance x is expressed by Equation 1 below.

Here, Ls is represented by the following equation (2) as the current spreading length.

Where t _n is the thickness of the n-type gallium nitride layer, t _p is the thickness of the p-type gallium nitride layer, ρ _n is the resistivity of the n-type gallium nitride layer, ρ _p is the resistivity of the p-type gallium nitride layer , ρ _c is the contact resistance between the p-electrode and the p-type gallium nitride layer. For the analysis of the equivalent circuit, the resistivity of the n-type gallium nitride layer is 0.02 [Ohm-cm], the resistivity of the p-type gallium nitride layer is 4 [Ohm-cm], and the contact resistance between the p-electrode and the p-type gallium nitride layer is 0.02. [Ohm-cm ² ], the thickness of the n-type gallium nitride layer is assumed to be 2 mu m, the thickness of the p layer is 0.3 mu m, and the size of the light emitting diode is 1 mm x 1 mm.

Current density distribution according to Equation 1 is as shown in FIG.

FIG. 4 is a graph showing a change in intensity according to a position of current density in the gallium nitride based light emitting diode shown in FIG. 1.

1 and 4, it can be seen that the current density decreases away from the n-electrode 20. That is, a phenomenon in which current is driven near the n-electrode 20 occurs. The longer the current spreads over the entire p-type gallium nitride layer 13, the longer the current spreads. However, according to Equation 2, when the contact resistance decreases, the length of current spreading is shortened.

In order to increase the luminous efficiency of the light emitting diode and improve the diode characteristics, the p-electrode should be as thick as possible to reduce the resistance of the p-electrode. However, when the resistance of the p-electrode decreases, the current rushing phenomenon becomes noticeable, in which the current distribution flowing through the p-n junction nears the n-electrode. In order to prevent this, several n-electrodes may be provided. However, as the n-electrodes increase, the emission area may be reduced, thereby reducing the total amount of light emitted. The n-electrode must have a special structure in order to allow the current to flow uniformly and at the same time not to significantly reduce the light emitting area.

In order to find the most efficient structure of the n-electrode, it is necessary to know what distribution of current flows to the p-n junction according to the shape of the n-electrode. Gallium nitride-based diodes can be represented by equivalent circuits. Although the equivalent circuit shows a one-dimensional electrode structure, it can be extended to the equivalent circuit which shows a two-dimensional electrode structure. In other words, it can be interpreted that a light emitting diode is composed of very small resistors and diode pieces.

5A to 5C are diagrams illustrating a light emitting diode having a two-dimensional electrode structure. In particular, FIG. 5A is a perspective view of a light emitting diode, FIG. 5B is an equivalent circuit diagram, and FIG. 5C is an enlarged equivalent circuit diagram of region A of FIG. 5B.

As shown in Figs. 5A to 5C, there is a resistance Rv sensed by the current flowing through the p-n junction surface and a resistance Rn sensed by the current flowing toward the n-electrode in the horizontal direction in the n-type gallium nitride layer.

Here, Rv is the sum of the resistance of the p-type gallium nitride layer and the contact resistance between the p-electrode and the p-type gallium nitride layer, the specific resistance of the p-type gallium nitride layer, the contact resistance between the p-electrode and the p-type gallium nitride layer, It is proportional to the thickness of the p-type gallium nitride layer. Rn is a resistance of the n-type gallium nitride layer, the specific resistance of the n-type gallium nitride layer is proportional and inversely proportional to the thickness of the n-type gallium nitride layer.

The equivalent circuit representing the two-dimensional electrode structure can be analyzed using Kirchhoff's current law and Kirchhoff's voltage law, and the current flowing through each diode and resistor in the equivalent circuit can be obtained. have. This shows how the current is distributed at each point of the diode depending on the structure of the n-electrode. Based on this, we can find the optimal electrode structure that makes the current distribution uniform.

For the analysis of the equivalent circuit, the resistivity of the n-type gallium nitride layer is 0.02 [Ohm-cm], the resistivity of the p-type gallium nitride layer is 4 [Ohm-cm], and the contact resistance between the p-electrode and the p-type gallium nitride layer. The thickness of 0.02 [Ohm-cm ² ], n-type gallium nitride layer was 2 micrometers, the p-layer thickness was 0.3 micrometer, and the size of the light emitting diode was 1 mm x 1 mm.

As described above, as the contact resistance with the p-type gallium nitride layer 13 included in the general light emitting diode decreases, more current flows in the first path (path 1), thereby increasing the current driving.

Therefore, if the contact resistance is reduced by forming a thick electrode on the entire surface of the p-type gallium nitride layer 13, the diode characteristics are improved, and thus the device luminous efficiency may be increased by improving the supply efficiency of electrons and holes, but the current driving is also increased to increase the luminous efficiency. May be limited.

Another n-electrode can be placed to reduce the current draw. Accordingly, if a new n-electrode is placed on the opposite side of the n-electrode with the p-electrode interposed therebetween, the current will be attracted to the new n-electrode so that the two n-electrodes cancel the current flow.

Thus, the current can spread more evenly when two n-electrodes face each other than when there is one n-electrode. The closer the distance between the two n-electrodes, the more evenly the current spreads. Therefore, the larger the number of electrodes, the shorter the distance between n-electrodes, the smaller the current drift.

On the other hand, since the light is emitted from the pn junction surface, the pn junction surface must be wide to emit a large amount of light. Since the n-electrode part has no pn junction surface, the pn junction surface decreases as the number of n-electrodes increases. . Therefore, the number of n-electrodes should not be increased too much.

As such, in order to efficiently emit a large amount of light in the gallium nitride-based light emitting diode, the number and distance of the n-electrodes must be appropriately adjusted.

Example-1

6 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a first embodiment of the present invention.

Referring to FIG. 6, the gallium nitride based light emitting diode 100 according to the first exemplary embodiment of the present invention includes a basic n-electrode 123 formed on a substrate and an auxiliary n-electrode extending from the basic n-electrode 123. 124, and has a structure formed in the form of fish thorns so that the distribution of the current is uniform across the entire surface. The substrate may be a sapphire substrate or a silicon carbide substrate, and in some cases the substrate may be removed. A portion of the p-type gallium nitride layer (not shown) is peeled off from the primary n-electrode 123 and the auxiliary n-electrode 124, so that the n-type gallium nitride layer is formed in a region where fish-thorn is exposed.

In particular, the basic n-electrode 123 is formed in a closed loop shape in the edge region, and is formed in a band shape connecting the side facing the one side of the edge. The basic n-electrode 123 is formed in the outer region to define a quadrangular shape, and is arranged in the x-axis direction and divides the quadrangular region into four regions.

The auxiliary n-electrode 124 has a band shape extending from the basic n-electrode 123 and is formed to cross the longitudinal direction of the basic n-electrode 123 at regular intervals. The auxiliary n-electrode 124 is formed to extend from the basic n-electrode 123 to protrude toward the adjacent basic n-electrode 123. The length of the auxiliary n-electrode 124 is 1/2 of the spacing of the primary n-electrode 123.

The width of the basic n-electrode 123 is 10 to 50 μm, so that the current can be made slightly wider. The width of the auxiliary n-electrode 124 is less than or equal to the width of the primary n-electrode 123.

An end portion of the auxiliary n-electrode 124 is thin and a portion connected to the primary n-electrode 123 has a thick tapered shape. It is desirable to reduce the width of the electrode to increase the area of the p-electrode.

It is preferable that the auxiliary n-electrodes 124 are not arranged side by side but alternately arranged one or more between the two primary n-electrodes 123. That is, when the auxiliary n-electrode 124 is formed on one basic n-electrode 123, the auxiliary n-electrode 124 is positioned slightly off the electrode opposite to the basic n-electrode 123. .

FIG. 7 is a distribution diagram of current flowing through the p-n junction surface in FIG. 6. In particular, an equivalent circuit is used to calculate the current distribution flowing through the p-n junction surface in the electrode structure of FIG.

6 and 7, since the auxiliary n-electrodes 124 partition the area partitioned by the primary n-electrodes 123 while invading the predetermined area, the current distribution is uniform. It can be seen that the current distribution by the region cut along the x-axis or the current distribution by the region cut along the y-axis is symmetrical.

Comparative Example

8 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a comparative example.

Referring to FIG. 8, a thick p-electrode 54 is formed on the entire surface of the gallium nitride-based light emitting diode 50, and an n-electrode 52 is formed on an edge portion of the gallium nitride-based light emitting diode 50. The easiest way to generate high power in the light emitting diode 50 is to increase the size of the light emitting diode. However, the method of increasing the size does not greatly reduce the current bleeding phenomenon due to the distance between the n-electrodes adjacent to each other.

In order to realize a high power light emitting diode, the size of the light emitting diode is increased to 1 mm x 1 mm. According to Guo's paper, the current spreading length is only 100 μm. Therefore, light is strongly emitted only near the n-electrode 52, and little light is emitted far from the n-electrode 52. Although the n-electrode 52 is formed on the edge of the light emitting diode so that the n-electrodes 52 face each other, the distance between the n-electrodes 52 is too far and the current spreads only about 200 μm. Do not.

In order to increase the length of current spreading, as shown in FIG. 6, a plurality of n-electrodes 52 should be provided to reduce the distance between adjacent n-electrodes 52. However, as the number of n-electrodes 52 increases, the p-n junction surface decreases, and thus the light emitting area decreases. Therefore, it is not preferable that the number of n-electrodes 52 be excessively large.

FIG. 9 is a distribution diagram of current flowing through a pn junction surface in the gallium nitride based light emitting diode shown in FIG. 8. In particular, the current distribution flowing to the pn junction surface in the electrode structure of FIG. 8 using the analysis of the equivalent circuit is calculated and shown in the form of contour lines. In order to analyze the equivalent circuit, the resistivity of the n-type gallium nitride layer is 0.02 Ohm-cm, the resistivity of the p-type gallium nitride layer is 4 Ohm-cm, and the contact resistance between the p-electrode and the p-type gallium nitride layer is 0.02 Ohm- The thickness of the cm ² , n-type gallium nitride layer was 2 μm, and the thickness of the p layer was 0.3 μm. The size of the light emitting diode is 1 mm x 1 mm.

8 and 9, it can be seen that the most current flows around the n-electrode 52. The distribution of current along the shape of the n-electrode 52 is very asymmetrical and not uniform.

That is, the intensity of the current in the y-axis direction is distributed relatively uniformly, but in the x-axis direction, the amount of current is large only near the n-electrodes 52 at both ends, and the amount of current is small in the middle portion. Can be.

FIG. 10A is a graph illustrating a current distribution of a cross section cut by A-A 'in FIG. 7 and a current distribution of a cross section cut by C-C' in FIG. 9, and FIG. 10B is a cut line B-B 'in FIG. 7. It is a graph which shows the current distribution of one cross section and the current distribution of the cross section cut by D-D 'in FIG. Here, the current was normalized by defining the maximum value as 1. That is, as the minimum value of the current approaches 1, the current is uniformly distributed.

As shown in FIG. 10A, it can be seen that the current distribution of C-C 'cross-section is greatly increased near the n-electrode, and the current decreases rapidly away from the n-electrode. That is, a large amount of current collapse occurs near the n-electrode. On the other hand, in the AA 'cross-section current distribution, as in the cross-sectional current distribution of FIG. 9, the current is larger near the n-electrode and the current decreases as it moves away from the n-electrode. It can be seen that the decrease is small and the current increases again by another immediately adjacent n-electrode.

Accordingly, it can be seen that the current distribution of the A-A 'cross-section of the light emitting diode according to the embodiment of the present invention is closer to and uniform than the current distribution of C-C' cross-section of the light emitting diode according to the comparative example.

Similarly, as shown in FIG. 10B, the current distribution of the cross-section of D-D 'has the largest current near the n-electrode, and the current rapidly decreases away from the n-electrode.

However, in the current distribution of the B-B 'cross-section, the current decreases more slowly even if it moves away from the n-electrode, and the magnitude of the current is closer to 1.

As described above, the light emitting diode according to the present invention has a more uniform current distribution in the x-axis direction and the current distribution in the y-axis direction, and the amount of flowing current also increases compared to the light emitting diode according to the comparative example. .

On the other hand, although the current distribution is uniform, it can be predicted that the total amount of light emission can be slightly reduced because the area of the n-electrode is increased and the light emission area is slightly reduced. Next, the relationship between the uniformity of the current distribution and the variation of the total light emission amount will be described below.

In order to calculate the actual light emission amount, the current value calculated using the equivalent circuit is normalized and added together. If the current is perfectly uniform, the normalized current value is equal to 1 throughout the light emitting diode, so the total amount of current is the total area A of the diode.

However, since the actual current differs depending on the position of the light emitting diode surface, the total amount of current is calculated by multiplying the current density and the area at each part of the diode. Therefore, when the current distribution is uneven, when the total current amount and the current distribution are perfectly uniform, the ratio S of the total current amount is expressed by Equation 3 below.

However, the portion where the n-electrode is present has zero current.

The ratio S of the total amount of current represents the uniformity of the current distribution and the light emitting area. That is, the closer the ratio S of the total amount of current is to 1, the more uniform the current distribution and the larger the light emitting area.

The ratio S of the total amount of current can be calculated using the current value calculated using the equivalent circuit shown in FIGS. 5B and 5C. In the case of the electrode according to the comparative example (shown in FIG. 8), the ratio of the total current amount is 68%, but in the case of the electrode (shown in FIG. 6) according to the embodiment of the present invention, the ratio of the total current amount is 69.8%. In other words, even though the emission area is reduced, the increase in the total amount of current means that the current is uniformly distributed. Since the current is uniformly distributed, the emission wavelength and intensity are uniformly spread over the entire surface of the diode, thereby improving internal quantum efficiency.

Through the analysis of the equivalent circuit described above, it was confirmed that the electrode structure was optimized to make the current distribution uniform without greatly reducing the emission area.

Example-2

11 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a second embodiment of the present invention.

Referring to FIG. 11, the gallium nitride based light emitting diode 200 according to the second embodiment of the present invention includes a basic n-electrode 223 and an auxiliary n-electrode 224 extending from the basic n-electrode 223. It has a structure formed in the form of fish thorns so that the distribution of current is uniform across the entire surface. Since only the position of the auxiliary electrode is changed compared with that of FIG. 6, a detailed description thereof will be omitted.

That is, the region of the p-electrode 121 defined by the electrodes 123 and 124 of the light emitting diode shown in FIG. 6 defines an M-shape connected to each other, while the area of the light emitting diode shown in FIG. The region of the p-electrode 221 defined by the electrodes 223, 224 defines a W-shape connected to each other. When the current distribution is calculated using the equivalent circuit, it is obvious that the electrode is the same as that of FIG. 6 and that the ratio of the total amount of current is also 69.8%.

As such, the distribution of the current becomes more uniform when the auxiliary electrodes in the form of fish thorns are used. Therefore, even if the number of primary electrodes is reduced, the uniformity of the current distribution can be maintained using the auxiliary electrodes. As the base electrode is reduced, the area of the n-electrode is reduced, which means that the light emitting area is relatively increased, and thus the light emission amount can be expected to increase.

Example-3

12 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a third embodiment of the present invention.

Referring to FIG. 12, the gallium nitride based light emitting diode 300 according to the third embodiment of the present invention includes a primary n-electrode 323 and an auxiliary n-electrode 324 extending from the primary n-electrode 323. It has a structure formed in the form of fish thorns so that the distribution of current is uniform across the entire surface.

The basic n-electrode 323 is formed in the outer region to define a quadrangular shape, and is arranged in the x-axis direction and divides the quadrangular shape into three regions. In FIG. 6, the basic n-electrode 123 divides the quadrangular shape into four regions. However, in FIG. 12, the basic n-electrode 323 divides the quadrangular shape into three regions. Description thereof will be omitted. Here, the length of the auxiliary n-electrode 324 is 1/2 of the interval between the primary n-electrodes 323.

FIG. 13 is a distribution diagram of current flowing to the p-n junction surface in FIG. 12. In particular, an equivalent circuit is used to calculate the current distribution flowing through the p-n junction surface in the electrode structure of FIG. 12 and is shown in contour form.

As shown in FIG. 13, since the auxiliary n-electrodes 324 partition the region partitioned by the primary n-electrodes 323 while invading the predetermined region, the current distribution is uniform as a whole. It can be seen that the current distribution by the region cut along the -axis or the current distribution by the region cut along the y-axis is symmetrical.

In particular, it can be seen that the current distribution of the electrode of the light emitting diode 300 according to the third embodiment is more uniform and more symmetrical than the current distribution of the electrode of the light emitting diode 50 according to the comparative example illustrated in FIG. 9. .

FIG. 14A is a graph showing a current distribution of a cross section cut by C-C 'in FIG. 9 and a current distribution of a cross section cut by E-E' in FIG. 13, and FIG. 14B is a cut line D-D 'in FIG. It is a graph which shows the current distribution of one cross section and the current distribution of the cross section cut | disconnected by F-F 'in FIG. Here, the current was normalized by defining the maximum value as 1. That is, as the minimum value of the current approaches 1, the current is uniformly distributed.

As shown in FIG. 14A, when the CC ′ cross-sectional current distribution according to the comparative example is compared with the EE ′ cross-sectional current distribution according to the third embodiment, the reduction ratio of the current near the n-electrode is third than that of the comparative example. Although the embodiment is somewhat higher, it can be seen that the current is increased again by the immediately neighboring n-electrodes.

Therefore, it can be seen that the total amount of current of the light emitting diode according to the third embodiment of the present invention is closer to 1, the uniformity of the current is increased, and the total amount of current is also increased.

Similarly, as shown in FIG. 14B, when comparing the current distribution of the DD 'cross-section according to the comparative example and the current distribution of the FF' cross-section according to the third embodiment, the reduction ratio of the current near the n-electrode is higher than that of the comparative example. The third embodiment is slowed down, and the amount of current as a whole is closer to one. That is, it can be seen that even in the F-F 'cross-section, the current distribution becomes uniform and the total current amount also increases. Calculating the ratio of the total amount of current with respect to the electrode of FIG. 12 increased to 68.8% compared to the electrode structure of the light emitting diode according to the comparative example (shown in FIG. 6).

Example-4

15 is a plan view illustrating an electrode structure of a gallium nitride based light emitting diode according to a fourth embodiment of the present invention.

Referring to FIG. 15, the gallium nitride based light emitting diode 400 according to the fourth embodiment of the present invention may include a primary n-electrode 423 and an auxiliary n-electrode 424 extending from the basic n-electrode 423. It has a structure formed in the form of fish thorns so that the distribution of current is uniform across the entire surface.

The basic n-electrode 423 is formed in an outer region to define a quadrangular shape, and is arranged in the x-axis direction and divides the three rectangular regions into three regions. In FIG. 6, the basic n-electrode 123 divides the quadrangular shape into four regions. However, in FIG. 12, the basic n-electrode 423 divides the quadrangular shape into two regions. Description thereof will be omitted. Here, the length of the auxiliary n-electrode 424 is 3/4 of the interval between the primary n-electrodes 423.

FIG. 16 is a distribution diagram of currents flowing to the p-n junction surface in FIG. 15. In particular, an equivalent circuit is used to calculate the current distribution flowing from the electrode of FIG. 15 to the p-n junction surface and is shown in contour form.

As shown in FIG. 16, since the auxiliary n-electrodes 424 partition the region partitioned by the primary n-electrodes 423 while invading the predetermined region, the current distribution is uniform throughout, and the x-axis It can be confirmed that the current distribution due to the region cut by and the current distribution due to the region cut by the y-axis are symmetrical.

FIG. 17A is a graph illustrating a current distribution of a cross section cut by C-C 'in FIG. 9 and a current distribution of a cross section cut by G-G' in FIG. 16, and FIG. 17B is a cut line D-D 'in FIG. 9. It is a graph which shows the current distribution of one cross section and the current distribution of the cross section which cut H-H 'in FIG.

As shown in FIG. 17A, it can be seen that the current distribution of the cross section of G-G ′ according to the fourth embodiment increases the current in the middle portion compared to the current distribution of the cross section of C-C ′ according to the comparative example.

As shown in FIG. 17B, the current distribution of the HH 'cross-section portion according to the fourth embodiment is slightly lower than the current distribution of the DD' cross-section portion according to the comparative example, but the total current amount increases in the y-axis direction. It doesn't have a big impact.

In fact, when calculating the ratio of the total amount of current 68.4% was slightly increased compared to the electrode according to the comparative example shown in FIG. Although the total amount of current did not increase significantly, the distribution of currents is symmetrical, and the spacing between n-electrodes is uniform and larger in the y-axis direction than the electrode according to the comparative example shown in FIG.

The electrode structure of the light emitting diode according to the fourth embodiment of the present invention is uniform between n-electrodes compared to the electrode structure of the light emitting diode according to the comparative example. In addition, the spacing between n-electrodes can be widened by reducing the base electrode by using the auxiliary electrode.

On the other hand, in the case of the electrode of the light emitting diode according to the comparative example, in order to further increase the current uniformity, there is no choice but to increase the number of basic electrodes. In this case, a problem may occur during the flip chip bonding process. The diameter of the solder bumps used in the flip chip bonding is typically 100 μm, with a gap of 200 μm.

As the number of n-electrodes increases, the area of the p-electrodes decreases, and the area where solder bumps are disposed also decreases. As a result, the spacing tolerance of the solder bumps is reduced and the assembly tolerance is reduced, which requires more precise alignment when assembling the light emitting diode. This increases the price of the assembly equipment because it requires high precision of the assembly equipment.

On the other hand, the electrode structure of the light emitting diode according to the present invention can provide sufficient spacing allowance of the solder bumps by uniformly distributing the p-electrodes while sufficiently maintaining the area of the p-electrodes.

In addition, heat generated in the light emitting diode is transferred to the submount through the solder bumps. The heat dissipation capacity is proportional to the area of the solder bumps and inversely proportional to the thickness of the solder bumps. Therefore, larger solder bump diameters and smaller thicknesses are advantageous for heat dissipation.

According to the present invention, the current distribution can be made uniform without greatly reducing the area of the p-electrode on which the solder bumps are placed. Accordingly, the heat characteristics are greatly improved through the heat dissipation due to the uniform current distribution and the heat dissipation through the large diameter solder bumps. Therefore, a light emitting diode having higher output and longer life can be manufactured.

18A is a plan view of a flip chip bonding light emitting diode manufactured using the electrode structure according to the present invention, and FIG. 18B is a cross-sectional view taken along the line II ′ of FIG. 18A.

A method of manufacturing the flip chip bonding light emitting diode 500 will be briefly described with reference to FIGS. 18A and 18B.

First, an n-type gallium nitride layer 511, an active layer 512, and a p-type gallium nitride layer 513 are sequentially stacked on the substrate 510.

Next, the p-type gallium nitride layer 513 and the active layer 512 are patterned by a photolithography process to expose the surface of the n-type gallium nitride layer 511. Thus, the patterned gallium nitride layer and active layer remain in a zigzag shape. The n-type electrode 514 is formed on the exposed n-type gallium layer 511, and the p-type electrode 515 is formed on the p-type gallium layer 512, respectively.

Accordingly, the n-type electrode surrounding the zigzag-type p-type gallium layer is formed to have a fish visible shape because the auxiliary electrode 514b protrudes from the base electrode 514a to the left and right between the p-type gallium layers.

Bonding pads 516 are formed on the n-type electrode 514, and bonding pads 518 are formed on the p-type electrode 515, respectively.

The exposed portion between the bonding pads 516, 518 is covered with an insulating protective layer 519. Each of the bonding pads 516, 518 is in contact with a corresponding solder bump.

As described above, the light emitting diode according to the present invention has a gallium nitride-based pn junction structure by laminating a first gallium nitride layer and a second gallium nitride layer on the substrate and the substrate, and to transfer current to the pn junction surface. An opaque thick second electrode is formed on the entire upper surface of the second gallium nitride layer, and the first electrode is formed on the first gallium nitride layer exposed between the second gallium nitride layers. The edge-shaped first electrode is formed on the entire edge of the light emitting diode so as to uniformly flow current to the pn junction surface while maintaining the area of the second gallium nitride layer where the actual light is emitted as large as possible. Opposite sides facing one side of are connected to one or more first basic electrodes in the form of thin wires, and the first basic electrodes in the form of thin wires are periodically provided with a first auxiliary electrode of visible shape.

Accordingly, it is possible to improve the light emitting characteristics of the light emitting diode by providing an electrode structure that minimizes the phenomenon that the current flowing to the p-n junction surface is concentrated on the first electrode. In addition, the n-electrode and the p-electrode of the light emitting diode may be distributed symmetrically and uniformly to prevent local heat generation. In addition, when the light emitting diode is assembled into the package by increasing the area of the p-electrode, the size of the solder bumps can be increased and the assembly tolerance is increased. Therefore, it is easy to assemble and heat can be well discharged through large solder bumps, so that the heat dissipation efficiency can be further improved, which is suitable for high power and long life light emitting diodes.

Although described above with reference to the embodiments, those skilled in the art can be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below. I can understand.

Claims (17)

A first gallium nitride layer formed on the substrate; An active layer formed on the first gallium nitride layer; A second gallium nitride layer formed on the active layer; A second electrode formed entirely on the second gallium nitride layer; And The edge of the second gallium nitride layer, at least one line extending from one side of the edge to the opposite side, and the plurality of branch regions extending from the edge are peeled off to expose the first gallium nitride layer in the form of fish thorns. A first electrode formed in the recessed region, The first electrode is formed in a closed loop shape in the edge region, and includes a first basic electrode having at least one band connecting one side of the edge and a side facing the edge, and a band shape extending from the first basic electrode. And a first auxiliary electrode formed to cross the longitudinal direction of the first basic electrode at regular intervals. The light emitting device of claim 1, wherein the substrate is a sapphire substrate or a silicon carbide substrate. The method of claim 1, wherein the first gallium nitride layer is doped n-type or p-type, And the second gallium nitride layer is doped with the opposite polarity to the first gallium nitride layer to form a p-n junction surface. The light emitting device of claim 1, wherein the active layer comprises gallium nitride. delete The light emitting device of claim 1, wherein the first auxiliary electrode is formed to be perpendicular to a length direction of the first basic electrode. The light emitting device of claim 1, wherein the first auxiliary electrode is alternately formed between a pair of the first basic electrodes. The light emitting device of claim 1, wherein a length of the first auxiliary electrode is 1/2 to 3/4 of an interval between the first basic electrodes. The light emitting device of claim 1, wherein a width of the first basic electrode is 10 to 50 µm. The light emitting device of claim 1, wherein a width of the first auxiliary electrode is less than or equal to a width of the first basic electrode. The light emitting device of claim 10, wherein an end portion of the first auxiliary electrode is thin and a portion connected to the first basic electrode has a thick tapered structure. The light emitting device of claim 1, wherein the second electrode has a thickness of about 100 nm or more. A first semiconductor layer formed on the substrate; A second semiconductor layer formed on the first semiconductor layer; A second electrode formed entirely on the second semiconductor layer; And An edge of the second semiconductor layer, at least one line extending from one side of the edge to the opposite side, and a plurality of branch regions extending from the edge and the line are peeled off to expose the first semiconductor layer in the form of fish thorns A first electrode formed at the The first electrode is formed in a closed loop shape in the edge region, and includes a first basic electrode having at least one band connecting one side of the edge and a side facing the edge, and a band shape extending from the first basic electrode. And a first auxiliary electrode formed to be perpendicular to the longitudinal direction of the first basic electrode at regular intervals. delete The light emitting device of claim 13, wherein the first auxiliary electrode is alternately formed between a pair of the first basic electrodes. The light emitting device of claim 13, wherein a width of the first auxiliary electrode is less than or equal to a width of the first basic electrode. The light emitting device of claim 16, wherein an end portion of the first auxiliary electrode is thin and a portion connected to the first basic electrode has a thick tapered structure.

Images