Nitride semiconductor light emitting device

In a nitride semiconductor LED having a light emitting structure, an n-doped semiconductor layer has a first region and a second region surrounding the first region, an active layer is formed on the second region of the n-doped semiconductor layer, and a p-doped nitride semiconductor layer is formed on the active layer. A p-electrode is formed on the p-doped semiconductor layer. An n-electrode is formed on the first region of the n-doped nitride semiconductor layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nitride semiconductor light emitting diode, and more particularly, a large-sized high efficiency nitride semiconductor light emitting diode which can be used suitably in a high power lighting system.

2. Description of the Related Art

As well known in the art, nitride semiconductors in the form of III-V group semiconductor crystals such as GaN, InN and AlN are widely used in Light Emitting Diodes (LEDs) for emitting single wavelength light (e.g., ultraviolet ray and green light), in particular, blue light. Because a nitride semiconductor LED is fabricated on an insulation substrate such as a sapphire substrate and a SiC substrate satisfying lattice matching conditions for crystal growth, it necessarily has a planar structure in which two electrodes connected to p- and n-doped nitride semiconductor layers are arranged substantially horizontally on the top of a light emitting structure.

A planar LED has drawbacks that an effective light emitting area is not sufficient and luminous efficiency per light emitting area is low because the flow of electric current is not uniformly distributed across the light emitting area unlike a vertical LED in which both electrodes are arranged on the top and the bottom of its light emitting structure. An example of the planar LED and the restricted luminous efficiency will be described with reference toFIGS. 1aand1b.

FIGS. 1aand1billustrate an example of a conventional nitride semiconductor LED10.

The nitride semiconductor LED10shown inFIG. 1ahas p- and n-electrodes19and18both of which are arranged in diagonal corners on the top of a substantially rectangular LED body. Then, the conventional nitride semiconductor LED10has a planar structure with the p- and n-electrodes19and18being horizontally arranged side by side.

Describing it in more detail with reference toFIG. 1billustrating a longitudinal section taken across a line A–A′ inFIG. 1a, the nitride semiconductor LED10has an n-doped nitride semiconductor layer12, an active layer14and a p-doped nitride semiconductor layer16formed on the substrate11one atop another in their order on a sapphire substrate11. As in this illustration, the p-doped nitride semiconductor layer16may be covered with a transparent electrode layer17such as tin-doped indium oxide or Indium Tin Oxide (ITO) in order to improve contact resistance.

Because the sapphire substrate11in use for the formation or growth of the nitride semiconductor layers is electrically insulated as described above, both the p-doped nitride semiconductor layer16and the active layer14are partially removed to form the n-electrode18that is to be connected to the n-doped nitride semiconductor layer12. Owing to the electrical insulation of the substrate for growing the nitride semiconductor, the nitride semiconductor LED10has the planar structure with the p- and n-electrodes19and18being arranged on the same side.

In the planar semiconductor LED10shown inFIGS. 1aand1b, current flow is concentrated on the shortest path between the both electrodes to narrow the current path which current density is concentrated on unlike the vertical LED allowing vertical current flow. Also, the current flow is directed laterally to increase drive voltage owing to large series resistance, resultantly reducing actual light emitting area. That is, the nitride semiconductor LED has drawbacks of low current density per unit area originated from limitations of the planar structure as well as low area efficiency owing to small light emitting area. As a result, it has been regarded very difficult to obtain a high power LED in use for lighting systems by a large-size (e.g., 1000×1000 μm).

In order to alleviate these problems, various forms of conventional approaches such as p- and n-electrode configurations and arrangements for raising current density and area efficiency have been developed as shown inFIGS. 2 to 3b.

FIG. 2is a plan view of an LED having an n-doped nitride semiconductor22, an active layer and a p-doped nitride semiconductor layer (not shown) which are laid on a substrate one atop another in their order. On the top of the LED, p- and n-electrodes29and28are formed, connected to the p-doped nitride semiconductor layer (or a transparent electrode layer27if any) and the n-doped nitride semiconductor layer22. The n-electrode28includes two contact pads28aand a number of electrode fingers28bextended from the contact pads28a, respectively, and the p-electrode29includes two contact pads29aand a number of electrode fingers29bextended from the contact pads29a, respectively, in which the n-electrode fingers28balternate with the p-electrode fingers29b. This electrode structure can provide separate current paths through the electrode fingers28band29bto reduce the lateral mean distance between the electrodes. This as a result can reduce series resistance, improve the uniformity of electric density across the whole area as well as ensure a sufficient light emitting area to the entire top surface even in case of a large-sized LED.

However, there is a problem that distal ends of the respective electrode fingers28band29bshow a lower optical power than other proximal portions thereof because they are placed substantially away from the contact pads28aand29athrough which electric current is introduced.

FIGS. 3aand3billustrate a nitride semiconductor LED30having another conventional electrode structure. Referring toFIG. 3a, a p-electrode39includes a contact pad39aformed in a substantially central area on the top of the LED30and four electrode fingers39bextended from the contact pad39ain diagonal directions. An n-electrode38includes a contact pad38aformed adjacent to a corner on the top of the LED30, an extension38bextended from the contact pad38aalong adjacent to the outer periphery to surround the p-electrode39and four electrode fingers38cextended from the extension38btoward the p-electrode contact pad39a.

As shown inFIG. 3b, the nitride semiconductor LED30has a light emitting structure which includes an n-doped nitride semiconductor layer32, an active layer34and a p-doped nitride semiconductor layer36formed on a substrate31one atop another in their order. On the top of the light emitting structure, a transparent electrode37may be formed on the p-doped nitride semiconductor36to improve the contact resistance with the p-electrode38. Herein, both the n-electrode contact pad38aand the n-electrode extension and38bare formed on the n-doped nitride semiconductor layer32exposed along the outer periphery of the LED30, and both the p-electrode contact pad39aand the p-electrode fingers39bare formed on the transparent electrode37and electrically connected to a p-doped nitride cladding layer37.

In the nitride semiconductor LED30shown inFIGS. 3aand3b, because the contact pads and terminals of other electrode regions are formed shorter than in the structure shown inFIG. 2and the both electrodes are distributed at a uniform gap across the entire area, series resistance can be reduced to improve luminous efficiency and current density can be distributed uniformly.

However, because the active layer is removed by a considerable amount in order to form the n-electrode, this electrode structure also has drawbacks in that actual light emitting area is remarkably reduced with respect to the whole size of the originally grown light emitting structure and luminous efficiency per unit area is degraded on the contrary according to the size growth of the LED.

As a consequence, novel electrode structures and arrangements for ensuring higher power to large-sized nitride semiconductor LEDs have been incessantly searched in the art.

SUMMARY OF THE INVENTION

Therefore the present invention has been made to solve the foregoing problems of the prior art.

It is an object of the present invention to provide a nitride semiconductor LED which has an n-electrode arranged in an inner area on the top of the LED and a p-electrode arranged surrounding the n-electrode in order to realize a geometry capable of ensuring larger effective light emitting area while ensuring more effective current distribution.

According to an aspect of the invention for realizing the object, there is provided a nitride semiconductor LED comprising: a light emitting structure including an n-doped semiconductor layer having a first region and a second region surrounding the first region on a top thereof, an active layer formed on the second region of the n-doped semiconductor layer and a p-doped nitride semiconductor layer formed on the active layer; a p-electrode formed on the p-doped semiconductor layer; and an n-electrode formed on the first region of the n-doped nitride semiconductor layer.

Preferably, the first region on the top of the n-doped nitride semiconductor layer may correspond to a substantially central area of the n-doped nitride semiconductor layer, and the n-electrode may be formed in the central area.

The nitride semiconductor LED may further comprise a transparent electrode layer for reducing the contact resistance between the p-doped nitride semiconductor layer and the p-electrode.

Preferably, the p-electrode may have at least one contact pad and at least one extension extended from the contact pad along an outer periphery of the p-doped nitride semiconductor layer, and the p-electrode may be formed to surround the n-electrode.

According to a more preferred embodiment, the light emitting structure may have four corners and four sides each for connecting adjacent corners on the top thereof, and the p-electrode may have at least one contact pad placed adjacent to at least one of the four corners and an extension extended from the contact pad along the four sides.

In this embodiment, the p-electrode can be modified into various forms. That is, the p-electrode may further comprise at least one p-electrode finger extended from the contact pad and/or the extension toward the n-electrode. Also, the p-electrode further may have an electrode bar extended in a lateral direction from a terminal of at least one of the p-electrode finger to a predetermined length.

Similarly, the n-electrode of the invention can be modified into various forms.

Preferably, the n-electrode may include a contact pad formed on a substantially central area of the n-doped nitride semiconductor layer and at least one n-electrode finger extended outward from the contact pad on the n-doped nitride semiconductor layer.

In an embodiment that the light emitting structure has four corners and four sides each for connecting adjacent corners on the top thereof, the n-electrode finger may comprise four electrode fingers extended toward four corners, respectively. Also, the n-electrode may further have an electrode bar formed in a lateral direction at a terminal of at least one of the n-electrode finger at a predetermined length.

According to another aspect of the invention for realizing the object, there is provided a nitride semiconductor LED comprising: a light emitting structure including an n-doped nitride semiconductor layer, an active layer and a p-doped semiconductor layer which are laid one atop another in their order; a p-electrode including at least one contact pad formed in a predetermined area on the p-doped nitride semiconductor layer and an extension extended from the contact pad along the outer periphery on the n-doped nitride semiconductor layer; and an n-electrode including at least one contact pad formed in a predetermined area on the n-doped nitride semiconductor layer surrounded by the p-electrode.

In this embodiment, the area on the n-doped nitride semiconductor layer surrounded by the p-electrode may be divided into a plurality of equal-sized sub-areas, and the contact pad of the n-electrode may comprise a plurality of contact pads which are arranged in substantially central portions of the plurality of sub-areas, respectively. Then, the n-electrode may further include an extension extended between the contact pads and/or from the contact pads toward the p-electrode. Also, the n-electrode extension may connect at least some of the n-electrode contact pads together.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 4aand4bare plan and side sectional views illustrating a nitride semiconductor LED according to an embodiment of the invention.

Referring toFIG. 4a, it is depicted an LED40having an n-electrode48and a p-electrode49formed on the top thereof. The n-electrode48is formed on a predetermined area of an n-doped nitride semiconductor layer42. The predetermined area for the n-electrode48is defined to an inner area of the n-doped semiconductor layer42surrounded by the active layer44and the p-doped nitride semiconductor layer46. The n-electrode48may preferably be of a contact pad formed on a central area of the n-doped nitride semiconductor layer42as in this embodiment.

The p-electrode49is formed on the p-doped nitride semiconductor layer46, and includes a contact pad49aformed at a corner of the p-doped nitride semiconductor layer46and an extension49bextended from the contact pad49aalong adjacent to the outer periphery of the top. In particular, the extension49bof the p-electrode49may be so formed to completely surround the n-electrode48as shown inFIG. 4a. While this embodiment illustrates that the p-electrode49is in direct contact on the p-doped nitride semiconductor layer46, a transparent electrode layer for reducing contact resistance may be formed between the p-electrode49and the p-doped nitride semiconductor layer46in a number of actual applications. The p-electrode49is also called a p-bonding electrode.

Like this, the nitride semiconductor LED40of the invention provides a novel electrode arrangement of the n-electrode48formed in the inner area on the n-doped nitride semiconductor layer42and the p-electrode49formed on the nitride semiconductor layer46surrounding the n-electrode48.

The inventors found that the n- and p-electrodes48and49arranged reversely to the electrode structure shown inFIG. 3acan reduce the removal of the active area, which is induced from the geometry of the electrode structure inFIG. 3a, to increase actual light emitting area as well as improve current distribution effect and forward voltage characteristics thereby raising actual luminous efficiency.

Describing it in more detail, the light emitting area of the invention can be increased based upon a novel geometric arrangement structure obtained by placing the n-electrode in an inner area to reduce the removal of the active layer, which is necessary for the formation of the n-electrode, and the p-electrode around the n-electrode. That is, in the nitride semiconductor LED, both the p-doped nitride semiconductor layer and the active layer are to be selectively removed from predetermined areas, in which the n-electrode will be formed, by smaller amounts if the n-electrode is placed inside rather than outside in view of the geometric structure, thereby reducing the area of the active layer to be removed. Improved forwarding voltage characteristics and entire luminous efficiency enhanced thereby as another effects of the invention will be described later in more detail with reference toFIGS. 9ato12c.

The LED structure of this embodiment shown inFIG. 4amay adopt various electrode structure modifications within the scope of the invention as set forth above in order to distribute current more uniformly between the both electrodes.

FIGS. 5ato5care plan and side sectional views illustrating a nitride semiconductor LED according to an alternate embodiment of the invention, in which an n-electrode is modified to realize more effective current distribution.

Referring toFIG. 5a, it is depicted an LED50having an n-electrode58and a p-electrode59formed on the top thereof. The n-electrode58includes a contact pad58aformed on a central area of an n-doped nitride semiconductor layer52and four electrode fingers58bextended from the contact pad58a. The p-electrode59includes two contact pad59aformed at two opposed corners and extensions59bformed along adjacent to the outer periphery of the top. As shown inFIGS. 5band5c, the n-electrode58is formed in the central area of the n-doped nitride semiconductor layer52, and the p-electrode59is formed along adjacent to the outer periphery of the p-doped nitride semiconductor56. In the LED50of this embodiment, although the both contact pads59amay be connected to an external circuit via wire bonding or flip chip bonding, one of the contact pads59amay be selectively connected to the external circuit.

The extensions59bof the p-electrodes59may be formed to surround the n-electrode58completely as shown inFIG. 5a. In this embodiment shown inFIG. 5a, the n-electrode fingers58bare extended from the n-electrode contact pad58atoward central portions of four sides of the extensions58bof the p-electrode59. The n-electrode fingers58bare used as means for shortening the current path between the p-electrode59and the n-electrode58to decrease series resistance while ensuring more uniform current distribution across the whole light emitting area.

Because the n-electrode58is arranged on the central portion of the n-doped nitride semiconductor layer52, the p-electrode59is arranged to surround the n-electrode58, and the n-electrode fingers58bare further formed in the n-electrode59to extend toward the sides of the light emitting structure, the current distribution effect can be further enhanced. The n-electrode can be modified into various forms in order to enhance the current distribution effect.FIGS. 6ato6care plan views illustrating various examples of n-electrode structures.

FIG. 6aillustrates an n-electrode structure similar to that shown inFIG. 5aexcept that electrode bars68care extended in lateral directions from terminals of n-electrode fingers68b, respectively, to a predetermined length.

As shown inFIG. 6a, a nitride semiconductor LED60of this embodiment has an n-electrode68connected to an n-doped nitride semiconductor layer62and a p-electrode69connected to a p-doped nitride semiconductor layer66on the top thereof. The p-electrode69has two contact pad69aformed at two opposed corners, respectively, and extensions69bextended from the contact pads69aalong adjacent to the outer periphery of the top. The n-electrode68includes a contact pad68aformed in a central area of the n-doped nitride semiconductor layer62, four electrode fingers68bextended from the contact pad68aand electrode bars68cextended in lateral directions from terminals of the electrode fingers68b, respectively, to a predetermined length. The n-electrode bars68ccan be used as means for realizing uniform current distribution across the entire light emitting area while shortening the current path between the n- and p-electrodes68and69as the electrode fingers68b.

FIG. 6billustrates an n-electrode structure having four n-electrode fingers78bsimilar to those shown inFIG. 5aexcept that the electrode fingers78bhave different orientations.

A nitride semiconductor LED70shown inFIG. 6bhas an n-electrode78connected to an n-doped nitride semiconductor layer72and a p-electrode79connected to a p-doped nitride semiconductor layer76on the top thereof. The p-electrode79includes two contact pads79aformed at two opposed corners, respectively, and extensions79bextended from the contact pads79aalong adjacent to the outer periphery on the top. The n-electrode78includes a contact pad78aformed in a central area of the n-doped nitride semiconductor layer72and four electrode fingers78bextended from the contact pad78atoward the corners. The n-electrode fingers78bextended toward the corners on the p-doped nitride semiconductor layer76can be adopted as means for realizing uniform current distribution across the entire light emitting area while shortening the current path as the p-electrode fingers59bshown inFIG. 5b. As in this embodiment, the n-electrode fingers78bextended toward the corners of p-nitride semiconductor layer76may be of different lengths. In view of more uniform current distribution, one pair of the n-electrode fingers78bdirected toward the p-electrode contact pads79aare preferably formed shorter than the other pair of the n-electrode fingers78b.

FIG. 6cillustrates an n-electrode structure modified from that shown inFIG. 6b, in which electrode bars88care formed in lateral directions at terminals of n-electrode fingers88bat a predetermined length.

A nitride semiconductor LED80shown inFIG. 6chas an n-electrode88connected to an n-doped nitride semiconductor layer82and a p-electrode89connected to a p-doped nitride semiconductor layer86on the top thereof. The p-electrode89includes two contact pads89aformed at two opposed corners, respectively, and extensions89bextended from the contact pads89aalong adjacent to the upper outer periphery of the p-doped nitride semiconductor layer86. The n-electrode88includes a contact pad88aformed in a central area of the n-doped nitride semiconductor layer82, four electrode fingers88bextended from the contact pad88aand the electrode bars88cformed in lateral directions at terminals of the electrode fingers88b, respectively, at a predetermined length.

Alternatively, the present invention can modify the p-electrode structure in replacement of the n-electrode structure.FIGS. 7aand7billustrate another alternative embodiment of the invention with a modified p-electrode structure.

FIG. 7aillustrates an LED structure having four p-electrode fingers98bextended toward an n-electrode98placed in the center.

A nitride semiconductor LED90shown inFIG. 7ahas an n-electrode98connected to an n-doped nitride semiconductor layer92and a p-electrode99connected to a p-doped nitride semiconductor layer96on the top thereof. The n-electrode98is constituted of only a contact pad formed in a central area of the n-doped nitride semiconductor layer92, whereas the p-electrode includes two contact pads99aformed at two opposed corners, respectively, extensions99bextended from the contact pads99aalong adjacent to the upper outer periphery of the p-doped nitride semiconductor layer96and four electrode fingers99cextended from the corners toward the n-electrode98, respectively. In this embodiment, the p-electrode fingers99care used as means for more uniformly distributing electric current across the entire light emitting area while shortening the current path as the afore-described n-electrode fingers.

A nitride semiconductor LED100shown inFIG. 7bhas an n-electrode108connected to an n-doped nitride semiconductor layer102and a p-electrode109connected to the p-doped nitride semiconductor layer106on the top thereof. The n-electrode108is constituted of only a contact pad formed in a central area of the n-doped nitride semiconductor layer102, whereas the p-electrode109includes two contact pads109aformed in two opposed corners, extensions109bextended from the contact pads109along adjacent to the upper outer periphery of the p-doped nitride semiconductor layer106and four electrode fingers109cextended from central portions of four sides of the extensions109btoward the n-electrode108. The p-electrode fingers109calso have p-electrode bars109dformed in lateral directions at terminals thereof, respectively, at a predetermined length. The electrode bars109dcan increase the current density between the n- and p-electrodes108and109at the terminals of the p-electrode fingers109cto further enhance the overall luminous efficiency.

The present invention may provide additional embodiments by combining the two afore-described structures, that is, the n-electrode structure and the p-electrode structure.FIGS. 8aand8bare plan views illustrating further another alternate embodiments with improved p- and n-electrode structures.

In a nitride semiconductor LED110shown inFIG. 8a, an n-electrode118includes a contact pad118aformed in a central area of an n-doped nitride semiconductor layer112, four electrode fingers118bdirected from the contact pad118atoward central portions of sides, respectively, and electrode bars118cformed in lateral directions at terminals of the electrode fingers118, respectively. Also, a p-electrode119connected to a p-doped nitride semiconductor layer116includes two contact pads119aformed in two opposed corners, extensions119bextended from the contact pads119aalong adjacent to the upper outer periphery of the p-doped nitride semiconductor layer116and four electrode fingers119cextended from the corners, respectively, toward the n-electrode contact pad118a.

Describing the electrode structure of this embodiment in top view of a substantially rectangular light emitting structure, the p-electrode119has the electrode fingers119carranged in diagonal directions, and the n-electrode118has the electrode fingers118bcrossed into separate areas defined between the p-electrode fingers119c. The n-electrode118also has electrode bars118cformed in lateral directions at terminals of the electrode fingers118, respectively, to shorten the current path to the p-electrode119.

In a nitride semiconductor LED120shown inFIG. 8b, the n-electrode128includes a contact pad128aformed in a central area of an n-doped nitride semiconductor layer122, four electrode fingers128barranged from the contact pad128atoward corners, respectively, and electrode bars128cformed in lateral directions at terminals of the electrode fingers128b. Further, a p-electrode129connected to a p-doped nitride semiconductor layer126includes two contact pads129aformed at two opposed corners, respectively, extensions129bextended from the contact pads129aalong adjacent to the outer periphery of the p-doped nitride semiconductor layer126and four electrode fingers129cextended from the central portions of sides toward the n-electrode contact pads128a, respectively.

Describing the electrode structure of this embodiment in top view of a substantially rectangular light emitting structure, the p-electrode129has the electrode fingers129c, which are arranged in the form of a cross, and the n-electrode128includes the electrode fingers128b, which are arranged in diagonal directions in separate areas defined between the p-electrode fingers129c. Further, the n-electrode128also has the electrode bars128cformed in lateral directions at the terminals of the electrode fingers128b, respectively, to shorten the current path to the p-electrode129.

EXAMPLE

In order to examine those improved characteristics of the nitride semiconductor LED of the invention, three nitride semiconductor LED structures were fabricated with same component and thickness on rectangular sapphire substrates of approximately 1000×1000 μm size.

First two of the LED structures were fabricated into the nitride semiconductor LEDs of the electrode structures illustrated inFIGS. 2 and 3a, respectively. The conventional nitride semiconductor LEDs fabricated like this are illustrated inFIGS. 9aand9b, respectively. The rest of the LED structures was fabricated to have the same electrode structure as inFIG. 8a. The nitride semiconductor LED of the invention fabricated like this is illustrated inFIG. 9c.

Although the LED of the invention shown inFIG. 9chas electrode patterns similar to those of the conventional LED shown inFIG. 9b, it has an n-electrode formed on a central area and a p-electrode formed on the upper outer periphery to surround the n-electrode to the contrary of that shown inFIG. 9b.

A predetermined value of voltage was applied to the LEDs shown inFIGS. 9ato9cthrough wire bonding on any one of the p- and n-electrode contact pads. Then, the respective LEDs were measured of current to determine their forward voltage characteristics, and then observed of brightness. Resultant forward voltage characteristics and current-brightness characteristics are drawn as graphs inFIGS. 10aand10b. For reference, characteristics of a conventional nitride semiconductor LED (of 350×350 μm size) are indicated with the reference symbol s together with the high power LEDs for illumination.

First, referring toFIG. 10a, the forward voltage characteristics of the LEDs shown inFIGS. 9ato9care indicated with the reference symbols a to c, respectively. FromFIG. 10a, it can be understood that the LED inFIG. 9chas more excellent forward voltage characteristics over the conventional LEDs inFIGS. 9aand9b.

In particular, the LED inFIG. 9chas the electrode structure of substantially same size and similar configuration as the LED inFIG. 9b, but the p- and n-electrodes of the LED inFIG. 9cexchanged their positions with each other from those of the LED inFIG. 9b. According to the result inFIG. 10a, it can be understood that the forward voltage characteristics can be improved by placing the n-electrode inside but the p-electrode around the n-electrode as in the LED inFIG. 9c.

Next,FIG. 10billustrates optical power variations according to current in the LEDs shown inFIGS. 9ato9c. As shown inFIG. 10b, it can be understood that the LED inFIG. 9cshows the highest brightness and thus has the most excellent optical power.

In order to compare different optical powers of the nitride semiconductor LEDs inFIGS. 9ato9cwith the naked eye,FIGS. 11ato11candFIGS. 12ato12cillustrate photographs of the nitride semiconductor LEDs operating at currents of 100 mA and 300 mA, respectively. As shown inFIGS. 11ato11candFIGS. 12ato12c, it can be observed that the LEDs inFIGS. 11cand12caccording to the invention show most excellent optical power at the input currents as above.

In particular, the LEDs inFIGS. 9band9cshow more different optical power characteristics than expectable from different forward voltage characteristics. The improvement in the optical power characteristics was made since the LED inFIG. 9chas a more advantageous geometric configuration for achieving a larger light emitting area than the LED inFIG. 9b.

That is, because the LED as shown inFIG. 9cwith the n-electrode being arranged inside can more decrease the area necessary for forming the n-electrode than the LED as shown inFIG. 9bwith the n-electrode being arranged along the outer periphery, the LED inFIG. 9cis more advantageous for ensuring a larger light emitting area.

The LED of the invention can be advantageously applied to high power LEDs generally in use for illumination. Although the high power LEDs for illumination can be provided through combination of several small-sized LEDs, they are generally provided as large sized LEDs of at least 1000×1000 μm. The present invention can be more advantageously applied to this type of large-sized high power LEDs. In particular, in case that the LED size is increased in order to ensure higher optical power, contact pads connected to an external power source via connection means such as wires can be further provided to realize uniform current distribution. For example, as shown inFIGS. 6ato8b, the p-electrode may have two contact pads placed at two opposed corners, or four contact pads at corners. Positions of the plurality of contact pads are not limited to the corners, but the contact pads may be preferably arranged at a uniform spacing.

Similarly, the n-electrode structure can be provided as a plurality of contact pads also in order to realize uniform current distribution in a larger area.

FIGS. 13ato13care plan views illustrating nitride semiconductor LEDs having n-electrode structures of a plurality of contact pads, respectively.

In a nitride semiconductor LED130shown inFIG. 13a, a p-electrode139includes a contact pad139aformed at a corner and an extension139bformed along the outer periphery of a p-doped nitride semiconductor layer136. An n-electrode132has four n-electrode contact pads138aconnected to an n-doped nitride semiconductor layer132. The n-electrode contact pads138aare formed at central portions of four quarters of the whole light emitting area, respectively, in order to realize uniform current distribution across a large area.

In a nitride semiconductor LED140shown inFIG. 13b, an electrode has four n-electrode contact pads148aconnected to an n-nitride semiconductor layer142similar to that inFIG. 13a, whereas a p-electrode149may have a contact pad149aformed at a corner, an extension formed along the outer periphery of a p-doped nitride semiconductor layer146and four electrode fingers149cextended from central portions of four sides of the extension into between the n-electrode contact pads.

In a nitride semiconductor LED150shown inFIG. 13c, a p-electrode159includes a contact pad159aformed at a corner, an extension159bformed along the outer periphery of a p-doped nitride semiconductor layer156and four electrode fingers159cextended from central portions of four sides of the extension159binto between n-electrode contact pads158a. An n-electrode158may include the four n-electrode contact pads158aand a crossed extension158bconnecting the n-electrode contact pads158awithout interference with the p-electrode159.

The LED of the invention may be modified or varied in forms so that contact pads of each electrode can be suitably increased in number in order to realize sufficient uniform current distribution effect even in large-sized LEDs. In addition to the above modifications obtained by increasing the number of the contact pads, other embodiments may be modified variously while maintaining the basic structure of the invention having an n-electrode arranged inside on the top of a light emitting structure, surrounded by a p-doped nitride semiconductor layer of the light emitting structure, and a p-electrode formed along the upper outer periphery of the p-doped nitride semiconductor layer to surround the n-electrode.

While the present invention has been described with reference to the particular illustrative embodiments and the accompanying drawings, it is not to be limited thereto but will be defined by the appended claims. It is to be appreciated that those skilled in the art can substitute, change or modify the embodiments into various forms without departing from the scope and spirit of the present invention.

As set forth above, the present invention can embody a novel electrode arrangement of an n-electrode formed in an inner area and a p-electrode arranged around the n-electrode to minimize the reduction of an active region from the formation of the n-electrode as well as improve forward voltage characteristics thereby remarkably raising overall luminous efficiency.