KR101078064B1 - A light emitting diode having uniform current density - Google Patents

Abstract

A first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer formed on the substrate; A first electrode formed on the first region of the first conductivity type semiconductor layer; A first ohmic between the first conductivity type semiconductor and the first electrode, the electrode extension part being formed on a second area different from the first area of the first conductivity type semiconductor layer and connected to the first electrode; A light emitting diode is provided, wherein the resistance and the second ohmic resistance between the first conductivity type semiconductor and the electrode extension portion are different from each other.

Description

A light emitting diode having uniform current density

The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having an electrode structure capable of inducing a uniform current distribution to implement high power and high brightness.

Gallium nitride (GaN) series light emitting diodes have been applied and developed for about 10 years. GaN-based LEDs have changed the LED technology considerably and are currently used in a variety of applications, including color LED displays, LED traffic signals and white LEDs. Recently, high-efficiency white LEDs are expected to replace fluorescent lamps. In particular, the efficiency of white LEDs has reached a level similar to that of conventional fluorescent lamps.

A gallium nitride-based light emitting diode is generally formed by growing epi layers on a substrate such as sapphire, and includes an N-type semiconductor layer, a P-type semiconductor layer, and an active layer interposed therebetween. Meanwhile, an N-electrode is formed on the N-type semiconductor layer, and a P-electrode is formed on the P-type semiconductor layer. The light emitting diode is electrically connected to and driven by an external power source through the electrodes. At this time, current flows from the P-electrode through the semiconductor layers to the N-electrode.

In general, since the P-type semiconductor layer has a high specific resistance, current is not evenly distributed in the P-type semiconductor layer, current is concentrated in a portion where the P-electrode is formed, and current flows intensively through a corner. do. Current concentration leads to a reduction of the light emitting area, and consequently lowers the light emitting efficiency. In order to solve this problem, a technique of forming a transparent electrode layer having a low specific resistance on the P-type semiconductor layer to achieve current dispersion is used. Since the current flowing from the P-electrode is dispersed in the transparent electrode layer and flows into the P-type semiconductor layer, the light emitting area of the light emitting diode can be widened.

However, since the transparent electrode layer absorbs light, its thickness is limited, and thus there is a limit in current dispersion. In particular, in the large area light emitting diode of about 1 mm 2 or more used for high power, current dispersion using the transparent electrode layer is limited.

On the other hand, the current flows through the semiconductor layers and exits to the N-electrode. Accordingly, the current is concentrated in the portion where the N-electrode is formed in the N-type semiconductor layer, which means that the current flowing in the semiconductor layer is concentrated near the region where the N-electrode is formed. Therefore, there is also a need for a light emitting diode capable of improving current concentration in the N-type semiconductor layer.

In general, a diagonal electrode structure shown in FIG. 1 and a large-area structure + a symmetric extended structure shown in FIG. 2 are introduced for uniform current spreading in a light emitting diode.

1 is a view for explaining a light emitting diode having a conventional diagonal electrode structure, FIG. 2 is a view for explaining a light emitting diode having a conventional large-area structure + symmetric extended electrode structure, Figure 3 is a cut line of FIG. 4 is a cross-sectional view taken along AA, and FIG. 4 is a cross-sectional view taken along cut line BB of FIG. In FIG. 1, 1 is an N-type electrode, 2 is a P-type electrode, 3 is an exposed N-type semiconductor layer, and 4 is a transparent electrode layer. 2 and 3, 111 is a substrate, 113 is an N-type semiconductor layer, 115 is an active layer, 117 is a P-type semiconductor layer, 119 is a transparent electrode layer, and 122 and 123 are extensions.

Referring to FIG. 1, the diagonal electrode structure may exhibit a large effect in a small sized light emitting diode, but as the area of the light emitting diode increases, a current concentration phenomenon is enhanced in the center, thereby preventing light emission except the center. This happens. In addition, the electrode pattern of the simple face-to-face structure also has the same problems as the diagonal electrode structure.

Meanwhile, referring to FIGS. 2, 3, and 4, in the case of the conventional large-area structure plus the symmetric extension structure, the extension part of the P electrode 131 is mainly used for a large light emitting diode. The portions 132 and 133 and the extension portions 122 and 123 of the N electrode 121 have insufficient portion to effectively solve the current concentration phenomenon generated in the N electrode 121 because the current spraying action is deteriorated due to its resistance.

An object of the present invention is to provide a light emitting diode having an electrode structure that can evenly distribute the current flowing during operation.

According to one aspect of the invention, the lower semiconductor layer formed on the substrate; An upper semiconductor layer disposed on the lower semiconductor layer to expose at least a portion of edge regions of the lower semiconductor layer; A lower electrode formed on the exposed lower semiconductor layer; An upper electrode formed on the upper semiconductor layer; An electrode extension extending from the lower electrode on the exposed lower semiconductor layer; The exposed lower semiconductor layer is provided with a light emitting diode having a step between at least a portion of the first region where the electrode extension is formed and the region other than the first region.

Preferably, the exposed lower semiconductor layer includes a first region and a second region in which the lower electrode is formed, and may have a step so that the first region is at a lower position than the second region.

Preferably, the exposed lower semiconductor layer may include a second region in which the first region and the lower electrode are formed, and the first region may be doped with higher concentrations of impurities than the second region.

Preferably, the electrode extension may be made of a material having a higher electrical conductivity than the lower electrode.

Preferably, the electrode extension portion may be formed to be wider as it moves away from the lower electrode.

Preferably, the electrode extension may be a distance spaced apart from the upper semiconductor layer.

Preferably, the upper portion of the electrode extension may be narrower than the lower portion.

Preferably, the light emitting diode further includes an active layer formed between the lower semiconductor layer and the upper semiconductor layer, and the lower electrode or the electrode extension portion may be formed to be lower than the active layer.

Preferably, the lower semiconductor layer is exposed at least a portion of the edge region, the electrode extension may be formed in at least a portion of the edge region.

Preferably, the lower semiconductor layer may expose at least a portion of the central regions, and the electrode extension may be formed in at least a portion of the central regions.

Preferably, the lower electrode may be formed at an edge between the first and second sides adjacent to each other of the substrate.

Preferably, the lower electrode may be formed in the middle of the first side, and the upper electrode may be formed in the middle of the second side.

Preferably, the lower electrode and the upper electrode may be formed at positions deflected to one side and the other side from the middle portion of the first side and the second side, respectively.

Preferably, the electrode extension part includes a first lower electrode extension part formed on the exposed lower semiconductor layer in a first direction extending from the lower electrode and a second lower electrode extension formed on the exposed lower semiconductor layer in a second direction. It may include wealth.

Preferably, the lower electrode may further have a third lower electrode extension formed on the first lower electrode extension or the second lower electrode extension.

Preferably, the light emitting diode may further include a transparent electrode layer formed on the upper semiconductor layer.

According to the present invention, the exposed lower semiconductor layer has a step between the first region where the electrode extension is formed and the region where the electrode extension is not formed, for example, the second region where the lower electrode is formed. The current path formed with respect to the lower electrode may be relatively longer than the current path formed with respect to the electrode extension to evenly distribute the current flowing during the operation of the light emitting diode.

1 is a view for explaining a light emitting diode having a conventional diagonal electrode structure.
2 is a view for explaining a light emitting diode having a conventional large surface structure + symmetric extended electrode structure.
3 is a cross-sectional view taken along the line AA in FIG. 2.
4 is a cross-sectional view taken along the line BB of FIG. 2.
5 is a plan view illustrating a light emitting diode having an electrode extension structure for dispersing current according to an embodiment of the present invention.
6 is a cross-sectional view taken along the cut line CC of FIG. 5.
FIG. 7 is a cross-sectional view taken along the cut line DD of FIG. 5.
8 is a plan view illustrating a light emitting diode having an electrode extension structure for current distribution according to another embodiment of the present invention.
9 is a plan view illustrating a light emitting diode having an electrode extension structure for current distribution according to another embodiment of the present invention.
10 to 15 are cross-sectional views corresponding to FIG. 6 for describing a light emitting diode according to various embodiments of the present disclosure.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention; The following embodiments are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, it is to be understood that the present invention is not limited to the embodiments described below and may be embodied in other forms.

5 is a plan view illustrating a light emitting diode having an electrode structure for current dispersion according to an embodiment of the present invention, FIG. 6 is a cross-sectional view taken along the cut line CC of FIG. 5, and FIG. 7 is a cut line DD of FIG. 5. A cross section taken along.

5 to 7, the first conductivity type lower semiconductor layer 13 is positioned on the substrate 11. The substrate 11 is not particularly limited and may be a sapphire substrate.

The second conductive upper semiconductor layer 17 is positioned on the first conductive lower semiconductor layer 13. Meanwhile, the upper semiconductor layer 17 is located in an area surrounded by the edges of the lower semiconductor layer 13 so that at least some of the edge regions of the lower semiconductor layer 13 are exposed. Meanwhile, an active layer 15 is interposed between the lower semiconductor layer 13 and the upper semiconductor layer 17. The active layer 15 is located below the upper semiconductor layer 17 so that at least some of the edge regions of the lower semiconductor layer 13 are still exposed.

Meanwhile, in the lower semiconductor layer 13, some regions 13a are formed to have a first height, and other partial regions 13b are formed to have a second height and have steps. The partial region 13a of the first height is at a lower position than the other partial region 13b of the second height.

The step difference between the partial region 13a having the first height and the other partial region 13b having the second height in the lower semiconductor layer 13 affects the length of the current passage path. The length of the current pass path will affect the current spreading.

The lower semiconductor layer 13, the active layer 15, and the upper semiconductor layer 17 may be formed of a gallium nitride-based compound semiconductor material, that is, (B, Al, In, Ga) N, but are not limited thereto. . The active layer 15 has a composition element and composition ratio determined so as to emit light of a desired wavelength such as ultraviolet light or blue light, and the lower semiconductor layer 13 and the upper semiconductor layer 17 have a bandgap compared to the active layer 15. It is formed of large material.

The lower semiconductor layer 13 and / or the upper semiconductor layer 17 may be formed as a single layer, as shown, but may be formed in a multilayer structure. In addition, the active layer 15 may have a single quantum well or multiple quantum well structures. In addition, a buffer layer (not shown) may be interposed between the substrate 11 and the lower semiconductor layer 13. The buffer layer is employed to mitigate lattice mismatch between the substrate 11 and the underlying semiconductor layer 13 to be formed thereon.

The semiconductor layers 13, 15, and 17 may be formed using MOCVD or MBE technology, and may be patterned to expose regions of the lower semiconductor layer 13 using a photolithography and etching process. In this case, the lower semiconductor layer 13 is exposed by placing a step on a portion where the lower electrode 21 is to be formed and a portion where the lower electrode extensions 22 and 23 are to be formed.

The lower electrode 21 is positioned on the exposed lower semiconductor layer 13 at a portion adjacent to the first side of the substrate 11 (the lower middle in FIG. 5). In addition, a transparent electrode layer 19 is formed on the upper semiconductor layer 17, and an upper portion is formed on the transparent electrode layer 19 in a portion adjacent to the second side opposite to the first side (upper middle in FIG. 5). The electrode 31 is located. In this case, the lower electrode 21 is formed in the region 13b having the second height.

On the exposed edge regions of the lower semiconductor layer 13, a first lower electrode extension extending from the lower electrode 21 adjacent to a first side and a third side adjacent to the first side in a right direction. A second lower electrode extension 23 extending from the lower electrode 21 is formed adjacent to the first and second sides 22 and 1 and the fourth side adjacent to the left side of the first side. In this case, the lower electrode extensions 22 and 23 are formed in the region 13a having the first height. In the exposed lower semiconductor layer 13, the region 13c adjacent to the region 13b having the second height where the lower electrode 21 is formed is formed with the lower electrode extensions 22 and 23. It is exposed at the same height as the region 13a having the first height. However, the present invention is not limited to this and various modifications are possible.

The lower electrode 21, the first lower electrode extension 22, and the second lower electrode extension 23 may be formed together through the same material and the same process. For example, when the lower semiconductor layer is N-type, the lower electrode and the lower electrode extensions may be formed of Ti / Al using a lift off technique. However, the lower electrodes 21, the first lower electrode extensions 22, and the second lower electrode extensions 23 are two regions 13a and 13b of the lower semiconductor layer 13 exposed with steps. To be formed.

The transparent electrode layer 19 may have an opening that exposes a portion of the upper semiconductor layer 17 of the second region of the substrate. In this case, the upper electrode 31 covers the opening and contacts the upper semiconductor layer 17.

In general, the transparent electrode layer 19 is formed of ITO or Ni / Au to transmit light, and also has ohmic contact with the upper semiconductor layer to lower the contact resistance. However, the upper electrode 31 is not light-transmitting and cannot be ohmic contacted to the upper semiconductor layer. Therefore, by bringing the upper electrode 31 directly into the upper semiconductor layer 17, it is possible to prevent the current flowing below the upper electrode 31, the light generated by this is absorbed by the upper electrode 31 is lost Can be prevented.

Meanwhile, a first upper electrode extension part 32 extends from the upper electrode 31 to correspond to the first lower electrode extension part 22 and is formed on the transparent electrode layer 19, and a second upper electrode extension part is formed. Reference numeral 33 extends from the upper electrode 31 to correspond to the second lower electrode extension 23, and is formed on the transparent electrode layer 19. The upper electrode 31, the first upper electrode extension 32, and the second upper electrode extension 33 may be formed by the same material and the same process.

3 and 4 and FIGS. 6 and 7 compare the contact resistance and the current distribution in the light emitting diode according to the prior art and the light emitting diode according to the embodiment of the present invention.

First, in FIGS. 3 and 4, the lower electrode 121 and the electrode extensions 122 and 123 are formed on the same height of the lower semiconductor layer 113. In this case, the current paths flowing into the lower semiconductor layer 113 through the lower electrode 121 are the same in the current passing paths flowing into the lower semiconductor layer 113 through the electrode extensions 122 and 123. In this situation, as the electrode extensions 122 and 123 have their own resistance, the current spraying property from the electrode extensions 122 and 123 to the lower semiconductor layer 113 is lowered from the lower electrode 121 to the lower semiconductor layer ( Compared to the current spraying characteristic to 113).

However, in FIGS. 6 and 7, the lower electrode 21 and the electrode extensions 22 and 23 are formed in the lower semiconductor layer 13 with a step. That is, the electrode extensions 22 and 23 are formed in the portion 13a having the first height of the lower semiconductor layer 13, and the lower electrode 21 is the portion having the second height of the lower semiconductor layer 13. It is formed in 13b. Accordingly, a current passage path leading to the lower electrode 21, the lower semiconductor layer 13, the active layer 15, the upper semiconductor layer 17, the transparent electrode layer 19, and the upper electrode 31 may extend through the electrode extension part 22,. 23, the lower semiconductor layer 13, the active layer 15, the upper semiconductor layer 17, the transparent electrode layer 19, the longer than the current passing path to the upper electrode 31. In other words, the length of the current passage path differs by the step between the first height and the second height.

In this situation, even if the electrode extensions 22 and 23 have their own resistance, the current spraying characteristics from the electrode extensions 22 and 23 to the lower semiconductor layer 13 due to the compensation action of the shortening of the current passage path. As compared with the current spraying characteristic from the lower electrode 21 to the lower semiconductor layer 13, it can be effectively compensated for.

8 is a plan view illustrating a light emitting diode having an electrode extension structure for current distribution according to another embodiment of the present invention. Another embodiment of the present invention illustrated in FIG. 8 has a modified position of the upper electrode and the lower electrode compared to the embodiment described with reference to FIGS. 5 to 7, and thus forms the first lower extension and the second lower extension. It can be seen that is modified. Other technical matters may be applied with the same or appropriate modifications. Here, although the upper electrode extension is not separately formed, the present invention is not limited thereto, and the upper electrode extension shown in FIGS. 5 to 7 may be appropriately modified.

Referring to FIG. 8, in the light emitting diode having the electrode extension structure for current distribution according to another embodiment of the present invention, a lower electrode 21a is formed at one edge of the substrate on the exposed lower semiconductor layer 13. The first lower electrode extension part 22a and the second lower electrode extension part 23a are formed adjacent to each side adjacent to each other via the corner. In this case, the widths of the lower electrode extension part 22a and the second lower electrode extension part 23a may be the same. On the other hand, the upper electrode 31 is formed in the corner portion located in the diagonal direction of the corner where the lower electrode 21a is formed.

9 is a plan view illustrating a light emitting diode having an electrode extension structure for current distribution according to another embodiment of the present invention.

9, the widths of the first lower electrode extension 22b and the second lower electrode extension 23b are deformed compared to the embodiment described with reference to FIG. 8. have. Other technical matters may be applied with the same or appropriate modifications. That is, the widths of the first lower electrode extension part 22b and the second lower electrode extension part 23b are wider as they move away from the lower electrode 31b. As the width of the lower electrode extensions 22b and 23b increases as the distance from the lower electrode 21 increases, the current density is concentrated on the lower electrode 21b as the self-resistance decreases as the distance from the lower electrode 21b increases. Can be prevented. In addition, the lower electrode extension parts 22b and 23b may be formed to be wider as they move away from the lower electrode 21b and to be spaced apart from the upper semiconductor layer.

10 to 15 are cross-sectional views corresponding to FIG. 6 for describing a light emitting diode according to various embodiments of the present disclosure.

Referring to FIGS. 10 to 15, various modifications of the lower electrode and the lower semiconductor layer in which lower electrode extensions are formed, which have been described with reference to FIG. 6, are illustrated. These modifications are provided via the lower semiconductor layer 13 from the lower electrode extensions 22 and 23 formed on the partial region 13a of the lower semiconductor layer 13 by various steps formed in the lower semiconductor layer 13. The length of the current passing path leading to the active layer 15 is the current from the lower electrode 21 formed on the other partial region 13b of the lower semiconductor layer 13 to the active layer 15 via the lower semiconductor layer 13. It shows structural characteristics that are shortened compared to the length of the passage path.

10, the region 13c adjacent to the region 13b in which the lower electrode 21 is formed is compared with the region 13a having the first height in which the lower electrode extensions 22 and 23 are formed. It is located lower and the same or similar for other things.

11, the region 13b in which the lower electrode 21 is formed is positioned at the same height as the region 13a in which the lower electrode extensions are formed. The other matters are the same or similar.

12, the region 13b in which the lower electrode 21 is formed is positioned at the same height as the region 13a having the first height in which the lower electrode extensions 22 and 23 are formed. The matter is the same or similar.

FIG. 13 illustrates a region in which the region 13b in which the lower electrode 21 is formed and the adjacent region 13c are located at the same height as each other, and have a first height in which the lower electrode extensions 22 and 23 are formed. It is located lower than the region 13a having a, and the same or similar for other matters.

In FIG. 14, the region 13b in which the lower electrode 21 and the adjacent region 13c are positioned at the same height, and the region 13a having the first height in which the lower electrode extensions 22 and 23 are formed. ) Is lower than that of FIG. 13, and the region 13a having the first height where the lower electrode extensions 22 and 23 are formed is lower than that of FIG. 13, and is otherwise the same or similar.

In FIG. 15, the region 13b in which the lower electrode 21 is formed is located lower than in FIG. 6, and the other matters are the same or similar.

While some embodiments of the present invention have been described by way of example, those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential features thereof. Therefore, the embodiments described above should not be construed as limiting the technical spirit of the present invention but merely for better understanding. The scope of the present invention is not limited by these embodiments, and should be interpreted by the following claims, and the technical spirit within the scope equivalent thereto should be interpreted as being included in the scope of the present invention.

For example, as a modification of the present invention, the positions of the upper electrode and the lower electrode may be modified in comparison with the embodiment described with reference to FIG. 5. That is, the lower electrode 21 may be positioned closer to the left edge side by deflecting to the left side as compared to FIG. 5, and the upper electrode 31 may be positioned closer to the right edge side to the right side as compared to FIG. 5. .

As another modified example, a third lower electrode extension part and a third upper electrode extension part may be formed on the upper electrode and the lower electrode, respectively, as compared with the embodiment described with reference to FIG. 5. In this case, the third lower electrode extension part and the third upper electrode extension part may be formed at positions corresponding to each other, and the third lower electrode extension part may be the first lower electrode extension part 22 or the second lower electrode extension part 23. The third upper electrode extension part may be formed in the first upper electrode extension part 32 or the second upper electrode extension part 33.

In addition, as another modification of the present invention, the impurity doping structure of the lower semiconductor layer may be modified as compared with the embodiment described with reference to FIG. 5.

That is, deformation may be applied to the impurity doping structure of the lower semiconductor layer 13 illustrated in FIG. 5. For example, the impurity doping concentration of the portion 13a having the first height of the lower semiconductor layer 13 on which the lower electrode extensions 22 and 23 are to be formed is determined by the lower semiconductor layer 13 of the lower electrode 21. By making the doping concentration higher than the impurity doping concentration of the portion 13b having the second height, the ohmic resistance characteristic between the lower electrode extensions 22 and 23 and the lower semiconductor layer 13 is lowered to the lower electrode 21 and the lower semiconductor layer 13. The current spreading can be adjusted by having a relatively improved value compared to the ohmic resistance characteristic between the?

In addition, in the above-described embodiments of the present invention, it has been described that the lower semiconductor layer has at least some of the edge regions exposed, and electrode extensions are formed in at least some of the exposed edge regions. However, in another modification, the lower semiconductor layer may expose at least a portion of the central regions, and the electrode extension may be modified to be formed in at least a portion of the central regions.

In addition, in the above-described embodiments of the present invention, the material of the lower electrode and the electrode extension parts has been described with the same material, but in another modification, the material of the electrode extension parts may be compared with the material of the lower electrode. It can be implemented with a high material.

In addition, in another modification, the width of the electrode extension part may be adjusted according to the height so that the upper part thereof is narrower than the lower part. For example, the width | variety of the part which contact | connects a lower semiconductor layer can also be made narrower as it goes upward. This allows the electrode extension to be inclined laterally so that the light emitted from the active layer can be effectively reflected to the outside.

Further, in other modifications, the lower electrode or the electrode extensions may be formed to be lower than the active layer.

Claims (8)

A first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer formed on the substrate;
A first electrode formed on the first region of the first conductivity type semiconductor layer;
An electrode extension formed on a second region different from the first region of the first conductivity type semiconductor layer, and connected to the first electrode,
And a first ohmic resistance between the first conductive semiconductor and the first electrode and a second ohmic resistance between the first conductive semiconductor and the electrode extension portion have different sizes. The method according to claim 1,
And a predetermined step is formed between the first region and the second region of the first conductivity type semiconductor layer. The method according to claim 1,
The size of the first ohmic resistor is larger than the size of the second ohmic resistor. The method according to claim 1,
The size of the first ohmic resistor and the second ohmic resistor is formed by varying the concentration of impurities in the first conductivity type semiconductor layer. The method according to claim 1,
The size of the first ohmic resistor and the second ohmic resistor is a light emitting diode, characterized in that formed by different materials of the first electrode and the electrode extension. The method according to claim 1,
And the electrode extension portion is formed to be wider as it is farther from the first region. The method according to claim 1,
The distance that the electrode extension is spaced apart from the second conductivity type semiconductor layer is a light emitting diode. The method according to claim 1,
The electrode extension portion of the light emitting diode, characterized in that the upper portion is narrower than the lower.

Images