KR100649768B1 - Nitride semiconductor light emitting device - Google Patents

Abstract

A nitride semiconductor LED is provided to stably guarantee reliability of a light emitting device even in a condition of high output by greatly reducing a decrease of output efficiency even in a condition of a high current density. A light emitting structure includes p-type and n-type nitride semiconductor layers and an active layer formed between the p-type and n-type nitride semiconductor layers. P-side and n-side electrodes have a plurality of extension parts which are alternately arranged at regular intervals, respectively connected to the upper surfaces of the p-type and n-type nitride semiconductor layers. The extension part of the p-side electrode has a width of 2~50 micrometers. An interval between the extension part of the p-side electrode and the extension part of an adjacent p-side electrode is at least twice the width of the extension part of the p-side electrode.

Description

Nitride Semiconductor Light Emitting Device {NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE}

1A and 1B are a top plan view and a side cross-sectional view, respectively, of a conventional high output nitride semiconductor light emitting device.

2 is a graph showing a change in output with increasing current density.

3 is a schematic diagram showing a current distribution of a nitride semiconductor light emitting device for explaining the principle employed in the present invention.

4A and 4B are graphs showing the output change according to the change of the p-type electrode width.

5A and 5B are graphs showing a change in output according to a change in a p-type electrode gap.

<Code Description of Main Parts of Drawing>

11, 21, 61: substrate 15a, 25a, 65a: n-type nitride semiconductor layer

15b, 25b, 65b: active layer 15c, 25c, 65c: p-type nitride semiconductor layer

17,27,67: n-side electrode 17,27,67: p-side electrode

 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device, and more particularly to a high output nitride semiconductor light emitting device capable of preventing a decrease in output efficiency under high current density application conditions.

In general, nitride semiconductors are group III-V semiconductor crystals such as GaN, InN, AlN, and the like, and are widely used in light emitting devices capable of emitting short wavelength light (ultraviolet to green light), especially blue light.

In such a nitride semiconductor light emitting device, uniform current distribution is recognized as an important problem in order to improve luminous efficiency. In particular, planar nitride light emitting devices in which two electrodes are arranged almost horizontally on an upper surface of the light emitting structure have a uniform current flow in the entire light emitting area than a vertical structure light emitting device, There is a problem that the effective area to participate in is not large.

On the other hand, for high output, such as a light emitting device for lighting, the light emitting device has a tendency to gradually increase the large area (for example, 1000㎛ 1000㎛). However, the larger the light emitting element is, the more difficult it is to realize a uniform current distribution over the entire area. As such, the current dispersion efficiency problem due to the large area has been recognized as an important technical problem in not only the planar structure but also the vertical nitride light emitting device.

Background Art Conventionally, in order to improve current density and area efficiency, studies have been mainly conducted in improving the shape and arrangement of various p-side electrodes and n-side electrodes.

For example, US Patent No. 6,486,499 (notice date: November 26, 2002) discloses a method of increasing the effective light emitting area using an electrode finger structure as shown in FIG. This will be described with reference to FIGS. 1A and 1B.

Referring to FIG. 1A together with FIG. 1B, a planar structure nitride semiconductor light emitting device 10 is shown in which both the p-side electrode 18 and the n-side electrode 17 face upwards.

The nitride semiconductor light emitting device 10 includes a sapphire substrate 11, an n-type nitride semiconductor layer 15a, an active layer 15b, and a p-type nitride semiconductor layer 15c sequentially formed on the substrate 11. The structure may further include a transparent electrode layer (not shown) such as Ni / Au or ITO on the entire surface of the p-type nitride semiconductor layer 15c for current dispersing effect.

As shown in FIG. 1A, the n-side electrode 17 and the p-side electrode include a plurality of interdigitated electrode fingers extending to have a constant distance (d1 = d2) from each other. In such an electrode structure, an additional current path may be provided to ensure a wide effective light emitting area, and may be formed at regular intervals to form a uniform current flow.

As described above, even in the conventional scheme of improving the shape and arrangement of the electrodes, there is a problem in that the high output can be stably ensured. As the current density increases in the p-type conductive nitride semiconductor layer near the p-side electrode, the output efficiency rapidly decreases. More specifically, as shown in Figure 2, the output efficiency is rapidly reduced from about 2 A / ㎠ around 10 A / ㎠ was found to have a low output efficiency at the level of 60% of the initial output.

Such a problem of lowering the output efficiency due to the increase of the current density is not a problem that can be solved by a simple electrode arrangement as in the prior art, and has become a major obstacle in securing stable reliability of a high-power light emitting device for lighting.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art, and an object thereof is to provide a nitride semiconductor light emitting device which reduces the reduction in output efficiency caused by an increase in current density by limiting the width and spacing of the p-side electrode to an appropriate range. It is.

In order to achieve the above technical problem, the present invention

a light emitting structure having p-type and n-type nitride semiconductor layers and an active layer formed therebetween; And p-side and n-side electrodes connected to the p-type and n-type nitride semiconductor layers, respectively, and having a plurality of extension portions alternately arranged to have a predetermined distance from each other, wherein the extension portion of the p-side electrode is 2 A nitride semiconductor light emitting device having a width of ˜50 μm is provided.

Preferably, the interval between the extension of the p-side electrode and the extension of another adjacent p-side electrode is at least two times the width of the extension of the p-side electrode, and more preferably, the extension of the p-side electrode is 20 to Arrange to have a spacing of 200 μm.

The present invention can be similarly applied to vertical nitride light emitting devices as well as planar structures arranged on the same upper surface of the electrode. That is, the light emitting structure further includes an insulating substrate formed on one side of the n-type nitride semiconductor layer, the light emitting structure has a structure mesa-etched to expose a plurality of regions of the n-type nitride semiconductor layer, the p side And an n-side electrode may have a structure formed on an upper surface of the p-type nitride semiconductor layer and an exposed upper surface of the n-type nitride semiconductor layer, on the other hand, the light emitting structure may be a conductive substrate formed on one side of the p-type nitride semiconductor layer. Further, wherein the p-side and n-side electrode may have a structure formed on the lower surface of the conductive substrate and the upper surface of the n-type nitride semiconductor layer, respectively.

Although the shape and arrangement of the conventional electrodes improve the macroscopic current distribution, it has not solved the problem of lowering the output efficiency due to the increase of the current density. The present inventors have devised a solution to this problem, and have come to a new recognition that the decrease in output efficiency due to the increase of the current density is caused by the current concentration problem generated in the p-type nitride semiconductor layer. I found out that it can be mitigated.

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

3 is a schematic diagram showing a current distribution of a nitride semiconductor light emitting device for explaining the principle employed in the present invention.

Referring to FIG. 3, there is shown a nitride semiconductor light emitting device in which an n-type nitride semiconductor layer, an active layer and a p-type nitride semiconductor layer are sequentially formed on a substrate. The structure illustrated in Fig. 3 is a vertical nitride semiconductor light emitting device, wherein the substrate is a conductive substrate such as SiC.

When a voltage is applied between the n-side electrode provided on the lower surface of the conductive substrate and the p-side electrode provided on the upper surface of the p-type nitride semiconductor layer, a current flow is formed as indicated by the arrow to emit light of a desired wavelength from the active layer.

In general, the resistance value tends to decrease as the temperature rises. In particular, since the p-type nitride semiconductor layer has a relatively high resistivity compared to the n-type nitride semiconductor layer, the effect of the change in resistance with temperature Big.

As shown in Fig. 3, even if the arrangement of the p-side electrode and the n-side electrode is arranged at regular intervals from each other, it is impossible to realize a completely uniform current distribution. Thus, there is a local difference in current distribution, resulting in a rise in temperature and a decrease in resistance.

This phenomenon poses a serious problem in the p-type nitride semiconductor layer having a relatively high resistance as described above. For example, in area A where current is concentrated and area B where relatively current is less concentrated, and in a high output condition in which a high current density is formed as a whole, the area A increases in temperature than the area B. It is lowered more. As a result, current non-uniformity becomes more severe, and overall, the output efficiency is markedly lowered as the current density increases.

As described above, the problem of current unevenness and output decrease due to the increase of the current density is largely influenced by the high resistivity of the p-type nitride semiconductor layer. It has been found that it can be relaxed by appropriately designing the width and spacing of the p-side electrode associated with the semiconductor layer.

Hereinafter, the design conditions of the p-side electrode which can alleviate the output drop even under high current density will be described in more detail with reference to the following examples.

First, a light emitting device having a structure similar to that of Fig. 2 was fabricated, and the p-side electrode width W was gradually decreased at 100 mu m, which is usually used, under the same conditions in which the distance D of each p-side electrode was 100 mu m. While changing to 50 μm, 20 μm, and 10 μm, the change in output efficiency with increasing current density was observed. The results are shown graphically in Figures 4A and 4B.

Referring to FIG. 4A, when the p-type electrode width W is 100 μm, the output efficiency decreases with the increase of the current density, and the output efficiency is extremely low at about 60% while exceeding 10 A / cm 2. You can check it. On the other hand, when the width W of the p-side electrode is 50 μm, the tendency of output efficiency is remarkably alleviated, and even at a high current density of 30 A / cm 2 or more, the output efficiency of 80% is maintained. appear.

In addition, when the width W of the p-side electrode is 20 µm or less (including 10 µm), the problem of reduction in output efficiency is further alleviated, and the output efficiency is maintained at about the same level up to 10 A / cm 2. In the case of exceeding A / ㎠ it was confirmed that the output efficiency close to 90% level.

4B shows the change in output efficiency according to the p-side electrode width W at a current density of 10 A / cm 2. As shown in the graph of Figure 4b, based on 50 ㎛, the output efficiency is greatly improved, it can be seen that the highest output efficiency is maintained when less than 20 ㎛.

As such, it can be seen that the problem of reducing the output efficiency caused by the high current condition can be remarkably improved by limiting the width W of the p-side electrode to an appropriate range. That is, by designing the width W of the p-side electrode to 50 μm or less, preferably 20 μm or less, it is possible to alleviate the problem of intensification of current due to the increase of the current density and stably maintain the output efficiency of the light emitting device. As a result of the evaluation, it was found that the smaller the width W of the p-side electrode was, the more favorable. It is desirable to design.

In addition, in order to confirm the effect of the gap between the p-side electrode on the output decrease according to the current density, the change in output efficiency was measured under the same conditions as in the previous experiment under the condition of changing the gap between the p-side electrode.

That is, a light emitting device having a structure similar to that of FIG. 2 is manufactured, and the p-side electrode spacing D is 10 µm, 20 µm, 50 µm, 100 under the same conditions in which the width W of each p-side electrode is 10 µm. The change of the output efficiency with increase of the current density was observed, changing to micrometer and 500 micrometer. The results are shown graphically in FIGS. 5A and 5B.

Referring to FIG. 5A, when the p-type electrode gap D is 10 μm, the output efficiency decreases with the increase of the current density, but it becomes very low with the output efficiency of about 55% while exceeding 10 A / cm 2. You can check it. On the contrary, when the p-side electrode spacing D was 20 μm, the decrease in output efficiency was slightly alleviated, and as the p-side electrode spacing D increased, the tendency of relaxation increased.

FIG. 5B shows the change in output efficiency according to the p-side electrode spacing D at a current density of 10 A / cm 2. As shown in the graph of Figure 5b, the p-side electrode spacing (D) is based on 20 ㎛, the output efficiency is greatly improved, there is a problem due to the decrease in the number of electrodes as the interval (D) increases, 200㎛ It is preferable to design as follows.

The design condition of the p-side electrode proposed in the present invention is a method that can be advantageously applied to both light emitting devices having a vertical structure and a horizontal structure. That is, if the p-side and n-side electrodes both have extended electrode fingers, and the extended electrode fingers of different polarities are alternately arranged so as to have a constant interval for uniform current distribution in the entire light emitting area, the conditions of the present invention May be usefully employed.

As such, the present invention is not limited by the above-described embodiments and the accompanying drawings, and is intended to be limited by the appended claims, and various forms of substitution may be made without departing from the technical spirit of the present invention described in the claims. It will be apparent to one of ordinary skill in the art that modifications, variations and variations are possible.

As described above, according to the present invention, by limiting the width and the interval of the p-side electrode to an appropriate range, there is provided a method for solving the problem of equalization of current distribution due to current concentration in the p-type nitride semiconductor layer and the resulting temperature changes. . In particular, the nitride semiconductor light emitting device according to the present invention can reliably reduce the output efficiency even under high current density conditions, thereby ensuring stable reliability of the light emitting device even under high output conditions.

Claims (5)

a light emitting structure having p-type and n-type nitride semiconductor layers and an active layer formed therebetween; And p-side and n-side electrodes connected to the p-type and n-type nitride semiconductor layers, respectively, and having a plurality of extension parts alternately arranged to have a constant distance from each other. The extension portion of the p-side electrode has a width of 2 ~ 50㎛. The method of claim 1, And the distance between the extension of the p-side electrode and the extension of the other adjacent p-side electrode is at least twice the width of the extension of the p-side electrode. The method according to claim 1 or 2, The extension portion of the p-side electrode is arranged to have a spacing of 20 ~ 200㎛. The method of claim 1, The light emitting structure further includes a conductive substrate formed on one side of the p-type nitride semiconductor layer, the p-side and n-side electrodes are formed on the lower surface of the conductive substrate and the upper surface of the n-type nitride semiconductor layer, respectively Semiconductor light emitting device. The method of claim 1, The light emitting structure further includes an insulating substrate formed on one side of the n-type nitride semiconductor layer, the light emitting structure has a structure mesa-etched to expose a plurality of regions of the n-type nitride semiconductor layer, the p-side and n The side electrode is formed on the upper surface of the p-type nitride semiconductor layer and the exposed upper surface of the n-type nitride semiconductor layer, respectively.

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