# Patent

## Title
Light emitting diode chip having electrode pad

## Abstract

Disclosed herein in an LED chip including electrode pads. The LED chip includes a semiconductor stack including a first conductive type semiconductor layer, a second conductive type semiconductor layer on the first conductive type semiconductor layer, and an active layer interposed between the first conductive type semiconductor layer and the second conductive type semiconductor layer, a first electrode pad located on the second conductive type semiconductor layer opposite to the second conductive type semiconductor layer; a first electrode extension extending from the first electrode pad and connected to the first conductive type semiconductor layer; a second electrode pad electrically connected to the second conductive type semiconductor layer; and an insulation layer interposed between the first electrode pad and the second conductive type semiconductor layer. The LED chip includes the first electrode pad on the second conductive type semiconductor layer, thereby increasing a light emitting area.

## Background
CROSS-REFERENCE TO RELATED APPLICATION(S)
This application is a continuation of and, claims the benefits and priorities to U.S. patent application Ser. No. 13/885,777, filed on May 16, 2013, which is the National Stage entry of International Application PCT/KR2011/001385, filed on Feb. 28, 2011, and claims priorities from and the benefits of Korean Patent Application No. 10-2010-0114747, filed on Nov. 18, 2010, and Korean Patent Application No. 10-2010-0114748, filed on Nov. 18, 2010, which are incorporated herein by reference for all purposes as if fully set forth herein.


BACKGROUND
1. Field
The present invention relates to a light emitting diode chip and, more particularly, to a light emitting diode chip having electrode pads.
2. Background
Gallium nitride (GaN) based light emitting diodes (LEDs) have been used in a wide range of applications including natural color LED displays, LED traffic lights, white LEDs, etc. In recent years, a highly efficient white LED is expected to replace fluorescent lamps and, in particular, efficiency of the white LED approaches efficiency of typical fluorescent lamps.
The GaN-based LED is generally formed by growing epitaxial layers on a substrate, for example, a sapphire substrate, and includes an n-type semiconductor layer, a p-type semiconductor layer and an active layer interposed between the n-type semiconductor layer and the p-type semiconductor layer. Further, an n-electrode pad is formed on the n-type semiconductor layer and a p-electrode pad is formed on the p-type semiconductor layer. The LED is electrically connected to and operated by an external power source through these electrode pads. Here, electric current is directed from the p-electrode pad to the n-electrode pad through the semiconductor layers.
To assist current spreading in the LED, the LED includes extensions extending from electrode pads. For example, U.S. Pat. No. 6,650,018 discloses an LED which includes a plurality of extensions extending in opposite directions from electrode contact portions, that is, electrode pads to enhance current spreading. The use of the extensions extending from the electrode pads may result in improvement in efficiency of the LED through current spreading.
However, an n-electrode pad and n-electrode extensions are generally formed on the n-type semiconductor layer exposed by etching the p-type semiconductor layer and the active layer. Accordingly, the formation of the n-electrode pad and the n-electrode extensions results in a reduction in light emitting area, causing deterioration in light emitting efficiency.
Meanwhile, since the electrode pads and the electrode extensions are formed of metal, the electrode pads and the electrode extensions absorb light generated in the active layer, thereby causing optical loss. Further, although the use of the electrode extensions enhances current spreading, current crowding still occurs at regions near the electrode extensions, causing electrode extension induced optical loss. In addition, since the electrode pads and the electrode extensions use a material such as Cr, which exhibits low reflectivity, as an underlying layer, optical loss becomes sever due to optical absorption by bottom portions of the electrode pads and/or the electrode extensions.
Furthermore, as the size of the LED increases, the likelihood of a defect being present in the LED increases. For example, defects such as threading dislocations and pin-holes, provide a path through which electric current flows rapidly, thereby disturbing current spreading in the LED.
Moreover, when a large LED of 1 mm2 is operated at a current of about 200 mA or more, the current crowds through such defects or through a certain position and the LED suffers a severe reduction in external quantum efficiency relating to current density, which is referred to as a droop phenomenon.
SUMMARY
Exemplary embodiments of the invention provide light emitting diode chips configured to prevent a reduction in light emitting area resulting from formation of electrode pads and/or electrode extensions.
Exemplary embodiments of the invention provide light, emitting diode chips which permit uniform current spreading over a wide area by relieving current crowding near electrode pads and electrode extensions.
Exemplary embodiments of the invention provide light emitting diode chips capable of preventing optical loss due to electrode pads and electrode extensions.
Exemplary embodiments of the invention provide light emitting diode chips that may prevent current crowding at a certain position during operation at high current, thereby enhancing external quantum efficiency.
In accordance with one aspect, a light emitting diode (LED) chip includes: a semiconductor stack including a first conductive type semiconductor layer, a second conductive type semiconductor layer on the first conductive type semiconductor layer, and an active layer interposed between the first conductive type semiconductor layer and the second conductive type semiconductor layer; a first electrode pad located on the second conductive type semiconductor layer opposite to the first conductive type semiconductor layer; a first electrode extension extending from the first electrode pad and connected to the first conductive type semiconductor layer; a second electrode pad electrically connected to the second conductive type semiconductor layer; and an insulation layer interposed between the first electrode pad and the second conductive type semiconductor layer. Since the first electrode pad is located on the second conductive type semiconductor layer, it is possible to prevent a reduction in light emitting area due to the formation of the first electrode pad.
The LED chip may further include a substrate and the semiconductor stack may be located on the substrate. In this case, the first conductive type semiconductor layer is located closer to the substrate than the second conductive type semiconductor layer. In addition, the second electrode pad may also be located on the second conductive type semiconductor layer.
The insulation layer may include a distributed Bragg reflector. A reflector may also be interposed between the insulation layer and the second conductive type semiconductor layer. The reflector may be a distributed Bragg reflector or a metal reflector.
In some exemplary embodiments, a transparent conductive layer may be interposed between the insulation layer and the second conductive type semiconductor layer. The transparent conductive layer under the insulation layer assists supply of electric current to the active layer under the insulation layer. Alternatively, the reflector may be in direct contact with the second conductive type semiconductor layer under the first electrode pad, thereby reducing optical loss by the transparent conductive layer.
In some exemplary embodiments, the LED chip may further include a dot pattern interposed between the first electrode extension and the first conductive type semiconductor layer along the first electrode extension such that the first electrode extension is partially separated from the first conductive type semiconductor layer by the dot pattern. The dot pattern may relieve current crowding around the first electrode extension and permits current spreading over a wider area.
The dot pattern may be formed of an insulation material. The dot pattern may include a reflector, for example, a metal reflector or a distributed Bragg reflector.
In some exemplary embodiments, the semiconductor stack may further include a plurality of through-holes extending through the second conductive type semiconductor layer and the active layer to expose the first conductive type semiconductor layer. The plurality of through-holes may be arranged along the first electrode extension and the first electrode extension may be connected to the first conductive type semiconductor layer through the through-holes.
Since the first electrode extension is connected to the first conductive type semiconductor layer through the through-holes, it is possible to achieve current spreading over a wide area by relieving current crowding around the first electrode extension.
An insulation layer may be interposed between the first electrode extension and the second conductive type semiconductor layer, so that the first electrode extension may be insulated from the second conductive type semiconductor layer by the insulation layer.
In addition, the insulation layer under the first electrode extension may extend to a sidewall of the through-holes to insulate the first electrode extension from the sidewall of through-holes.
The insulation layer under the first electrode extension may include a distributed Bragg reflector. In addition, the distributed Bragg reflector under the first electrode extension may extend to a sidewall of the through-holes to insulate the first electrode extension from the sidewall of the through-holes.
In some exemplary embodiments, the LED chip may further include a transparent conductive layer interposed between the insulation layer under the first electrode extension and the second conductive type semiconductor layer. The transparent conductive layer allows electric current to be supplied to the active layer under the first electrode extension.
In other exemplary embodiments, the insulation layer may be in direct contact with the second conductive type semiconductor layer under the first electrode extension. In other words, the transparent conductive layer is not located under the first electrode extension, thereby preventing optical loss due to the transparent conductive
The LED chip may further include a second electrode extension extending from the second electrode pad, and a transparent conductive layer located on the second conductive type semiconductor layer. The second electrode pad and the second electrode extension may be electrically connected to the second conductive type semiconductor layer through the transparent conductive layer.
In some exemplary embodiments, a current blocking layer may be interposed between the transparent conductive layer and the second conductive type semiconductor layer along the second electrode extension. The current blocking layer may be arranged in a line shape or in a dot pattern. With this structure, it is possible to relieve current crowding around the second electrode extension. The current blocking layer may further be disposed under the second electrode pad.
In addition, the current blocking layer may include a reflector. Therefore, it is possible to prevent light directed towards the second electrode extension from being absorbed and lost into the second electrode extension.
In other exemplary embodiments, the current blocking layer may be arranged in a dot pattern between the transparent conductive layer and the second electrode extension along the second electrode extension. The second electrode extension is connected to the second conductive type semiconductor layer through the transparent conductive layer between the dot regions.
Further, an exemplary embodiment of the invention provides an LED chip that has a dot pattern of contact regions at which the first electrode extension and/or second electrode extension are electrically connected to the semiconductor stack to permit current spreading over a wide area of the LED chip.
For example, the first electrode extension may be connected to the first conductive type semiconductor layer in a plurality of dot regions. Here, the plurality of dot regions may include first dot regions closer to the first electrode pad than the second electrode pad and second dot regions closer to the second electrode pad than the first electrode pad. In addition, the first dot regions may increase in size as the distance between the first dot regions and the first electrode pads increases. Further, the second dot regions may decrease in size as the distance between the second dot regions and the first electrode pad increases.
The LED chip may further include a second electrode extension extending from the second electrode pad and a transparent conductive layer interposed between the second electrode extension and the second conductive type semiconductor layer. In addition, the second electrode extension may be connected to the second conductive type semiconductor layer through the transparent conductive layer in a plurality of dot regions, and the plurality of dot regions arranged along the second electrode extension may include third dot regions closer to the second electrode pad than the first electrode pad and fourth dot regions closer to the first electrode pad than the second electrode pad. The third dot regions may increase in size as the distance between the third dot regions and the second electrode pad increases. Further, the fourth dot regions may decrease in size as the distance between the fourth dot regions and the second electrode pad increases.
In addition, the first to fourth dot regions may increase in size as the distance from the first to fourth dot regions to a line crossing the first electrode pad and the second electrode pad increases.
In accordance with another aspect, an LED chip includes: a first conductive type semiconductor layer; a plurality of mesa structures arranged on the first conductive type semiconductor layer and each including a second conductive type semiconductor layer and an active layer interposed between the first conductive type semiconductor layer and the second conductive type semiconductor layer, a first electrode pad, at least a part of which is located on the second conductive type semiconductor layer opposite to the first conductive type semiconductor layer; a first electrode extension extending from the first electrode pad and connected to the first conductive type semiconductor layer; a second electrode pad electrically connected to the second conductive type semiconductor layer; and an insulation layer interposed between the first electrode pad and the second conductive type semiconductor layer. Since the first electrode pad is formed on the second conductive type semiconductor layer, it is possible to prevent a reduction in light emitting area due to the formation of the first electrode pad. Further, since the LED chip employs the plurality of mesa structures, the LED chip may achieve current spreading to the plurality of mesa structures and prevent a rapid increase in current density in a certain position of the LED chip, thereby improving external quantum efficiency.
The LED chip may further include a substrate and the first conductive type semiconductor layer may be located on the substrate. In this case, the first conductive type semiconductor layer is located closer to the substrate than the second conductive type semiconductor layer. In addition, the second electrode pad may also be located on the second conductive type semiconductor layer.
The second electrode pad may include plurality of electrode pads located on the plurality of mesa structures, respectively. In addition, the first electrode pad may include a plurality of electrode pads located on the plurality of mesa structures, respectively.
The plurality of mesa structures may be separated from each other by a separation region exposing the first conductive type semiconductor layer. As a result, a surface of the first conductive type semiconductor layer is exposed at the separation region.
In an exemplary embodiment, the first electrode extension may include an electrode extension connected to the first conductive type semiconductor layer in the separation region. In addition, a dot pattern may be interposed between the electrode extension and the first conductive type semiconductor layer along the electrode extension in separation region to partially separate the electrode extension from the first conductive type semiconductor layer. The dot pattern may be formed of an insulation material and may include a distributed Bragg reflector. The dot pattern may relieve current crowding around the electrode extension and permit current spreading over a wider area.
The insulation layer interposed between the first electrode pad and the second conductive type semiconductor layer may include a distributed Bragg reflector. Further, a reflector may be interposed between the insulation layer and the second conductive type semiconductor layer. The reflector may be a distributed Bragg reflector or a metal reflector.
Further, the first electrode pad may include an electrode pad partially located in the separation region.
In some exemplary embodiments, a transparent conductive layer may be interposed between the insulation layer and the second conductive type semiconductor layer. The transparent conductive layer under the insulation layer assists supply of electric current to the active layer under the insulation layer. Alternatively, the reflector may be in direct contact with the second conductive type semiconductor layer in a region under the first electrode pad, thereby reducing optical loss by the transparent conductive layer.
Each of the mesa structures may include a plurality of through-holes extending through the second conductive type semiconductor layer and the active layer to expose the first conductive type semiconductor layer. Further, the first electrode extension may include an electrode extension connected to the first conductive type semiconductor layer through the plurality of through-holes. The plurality of through-holes is arranged along the electrode extension. Since the electrode extension is connected to the first conductive type semiconductor layer through the through-holes, it is possible to achieve current spreading over a wider area by relieving current crowding around the electrode extension.
In addition, an insulation layer is interposed between the second conductive type semiconductor layer and the electrode extension connected to the first conductive type semiconductor layer through the plurality of through-holes. The electrode extension may be insulated from the second conductive type semiconductor layer by the insulation layer.
Further, the insulation layer interposed between the electrode extension and the second conductive type semiconductor layer may include a distributed Bragg reflector. With this structure, it is possible to prevent optical loss of light generated in the mesa structure by the electrode extension.
Further, the insulation layer interposed between the electrode extension and the second conductive type semiconductor layer may extend to a sidewall of the through-holes to insulate the first electrode extension from the sidewall of the through-holes.
In addition, a transparent conductive layer may be interposed between the insulation layer under the electrode extension and the second conductive type semiconductor layer. The transparent conductive layer may assist supply of electric current to the active layer wider the electrode extension. Alternatively, the insulation layer may be in direct contact with second conductive type semiconductor layer under the electrode extension. In other words, the transparent conductive layer is not located under the electrode extension, thereby reducing optical loss by the transparent conductive layer.
The LED chip may further include a second electrode extension extending from the second electrode pad; and a transparent conductive layer formed on the second conductive type semiconductor layer. The second electrode pad and the second electrode extension may be electrically connected to the second conductive type semiconductor layer through the transparent conductive layer.
In some exemplary embodiments, a current blocking layer may be interposed between the transparent conductive layer and the second conductive type semiconductor layer along the second electrode extension. The current blocking layer may be arranged in a line shape or in a dot pattern. With this structure; it is possible to relieve current crowding around the second electrode extension. The current blocking layer may further be disposed under the second electrode pad.
In addition, the current blocking layer may include a reflector, for example, a distributed Bragg reflector. Therefore, it is possible to prevent light directed towards the second electrode extension from being absorbed and lost into the second electrode extension.
In other exemplary embodiments, the current blocking layer may be arranged in a dot pattern between the transparent conductive layer and the second electrode extension along the second electrode extension. The second electrode extension is connected to the second conductive type semiconductor layer through the transparent conductive layer between the dots.
According to exemplary embodiments, an LED chip includes an electrode pad formed on a semiconductor stack, thereby preventing a reduction in light emitting area due to the formation of the electrode pad. In addition, electrode extensions are connected to a semiconductor layer via through-holes, thereby preventing a reduction in light emitting area due to the formation of the electrode extension.
Further, the first electrode extension may be connected to the semiconductor layer in dot regions, thereby relieving current crowding around the electrode extension while achieving current spreading over a wide area. Furthermore, a current blocking layer is disposed under a second electrode pad and second electrode extensions, thereby relieving current crowding around the second electrode pad and second electrode extensions.
Moreover, reflectors are disposed between semiconductor stacks and the electrode pad and/or the electrode extensions, thereby preventing optical loss due to the electrode pad and/or the electrode extension. In addition, a light emitting region is divided by a plurality of mesa structures, thereby preventing a reduction in external quantum efficiency under high current due to current crowding at a certain position.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain the principles of the invention.
FIG. 1 is a schematic plan view of an LED chip according to one exemplary embodiment of the invention;
FIGS. 2a, 2b and 2c are sectional views taken along lines A-A, B-B and C-C of FIG. 1, respectively;
FIG. 3 is a schematic plan view of an LED chip according to another exemplary embodiment of the invention;
FIGS. 4a, 4b and 4c are sectional views taken along lines A-A, B-B and C-C of FIG. 3, respectively;
FIGS. 5a, 5b and 5c are sectional views of an LED chip according to a further exemplary embodiment of the invention, respectively;
FIGS. 6a, 6b and 6c are sectional views of an LED chip according to yet another exemplary embodiment of the invention;
FIG. 7 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention;
FIG. 8 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention;
FIG. 9 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention;
FIG. 10 is a plan view of an LED chip according to yet another exemplary embodiment of the invention,
FIG. 11 is a schematic plan view of an LED chip according to yet another exemplary embodiment of the invention;
FIGS. 12a, 12b, 12c and 12d are sectional views taken along lines A-A, B-B, C-C and D-D of FIG. 11 respectively;
FIG. 13 is a schematic plan view of an LED chip according to yet another exemplary embodiment of the invention,
FIGS. 14a, 14b, 14c and 14d are sectional views taken along lines A-A, B-B, C-C and D-D of FIG. 13, respectively;
FIGS. 15a, 15b and 15c are sectional views of an LED chip according to yet another exemplary embodiment of the invention;
FIGS. 16a, 16b and 16c are sectional views of an LED chip according to yet another exemplary embodiment of the invention, respectively;
FIG. 17 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention;
FIG. 18 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention;
FIGS. 19(a) and 19(b) are schematic plan views of an LED chip according to yet another exemplary embodiment of the invention: and
FIGS. 20(a) and 20(b) are plan views illustrating light emitting patterns for explaining enhancement of light emitting characteristics when adopting a plurality of mesa structures.



DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
The invention is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure is thorough and will fully convey the scope of the invention to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements.
It will be understood that-when-an element such as a layer, film, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening dements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.
FIG. 1 is a schematic plan view of an LED chip according to one exemplary embodiment of the invention, and FIGS. 2a, 2b and 2c are sectional views taken along lines A-A, B-B and C-C of FIG. 1, respectively.
Referring to FIGS. 1, 2a, 2b and 2c, the LED chip may include a semiconductor stack 30, a first electrode pad 37, a second electrode pad 39, first electrode extensions 37a, second electrode extensions 39a, and a protective insulation layer 35. The LED chip may further include a substrate 21, a buffer layer 23, a first functional layer 31a, a second functional layer 31b, a transparent conductive layer 33, a lower reflector 45, and a metal layer 47. The semiconductor stack 30 may include a first conductive type semiconductor layer 25, an active layer 27, and a second conductive type semiconductor layer 29.
The substrate 21 may be, for example, a sapphire substrate, a SiC substrate or a Si substrate, but is not limited thereto, The substrate 21 may be a growth substrate for growing a gallium nitride based compound semiconductor layer thereon.
The first conductive type semiconductor layer 25 is located on the substrate 21 and the second conductive type semiconductor layer 9 is located on the first conductive type semiconductor layer 25 with the active layer 27 interposed between the first and second conductive type-semiconductor layers. The first conductive type semiconductor layer 25, active layer 27 and second conductive type semiconductor layer 29 may be formed of, but are not limited to, a GaN-based compound semiconductor material such as (Al, In, Ga)N. The active layer 27 is composed of elements to emit light at desired wavelengths, for example, UV or visible light.
The first conductive type semiconductor layer 25 may be an n-type nitride semiconductor layer and the second conductive type semiconductor layer 29 may be a p-type nitride semiconductor layer, or vice versa.
The first conductive type semiconductor layer 25 and/or the second conductive type semiconductor layer 29 may have a single layer structure or a multilayer structure. Further, the active layer 27 may have a single quantum well structure or a multi-quantum well structure. The light emitting diode may further include a buffer layer 23 such as GaN or AlN between the substrate 21 and the first conductive type semiconductor layer 25. These semiconductor layers 25, 27, 29 may be formed by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).
The semiconductor stack 30 has a plurality of through-holes 30a extending through the second conductive type semiconductor layer 29 and the active layer 27 to expose the first conductive type semiconductor layer 25. The plurality of through-holes 30a is linearly arranged along first electrode extensions 37a, as shown in FIG. 1.
The transparent conductive layer 33 may be formed on the second conductive type semiconductor layer 29. The transparent conductive layer 33 may be formed of indium tin oxide (ITO) or Ni/Au and forms an ohmic contact with the second conductive type semiconductor layer 29.
As clearly shown in FIG. a, the first electrode pad 37 is located on the second conductive type semiconductor layer 29 of the semiconductor stack 30. The first electrode extensions 37a extend from the first electrode pad 37. The first electrode pad 37 is insulated from the semiconductor stack 30 and electrically connected to the first Conductive type semiconductor layer 25 through the first electrode extensions 37a. The first electrode-extensions 37a are connected to the first conductive type semiconductor layer 25 exposed through the plurality of through-holes 30a. 
The second electrode pad 39 may be located on the transparent conductive layer 33 and second electrode extensions 39a may extend from the second electrode pad 39. The second electrode pad 39 and the second electrode extensions 39a may be connected to the transparent conductive layer 33.
Meanwhile, a protective insulation layer 35 is located on the semiconductor stack 30 to cover the semiconductor stack 30. The protective insulation layer 35 may cover the transparent-conductive layer 33. In addition, the protective insulation layer 35 is interposed between the first electrode pad 37 and the second conductive type semiconductor layer 29 to separate the first electrode pad 37 from the second conductive type semiconductor layer 29, and between the first electrode extensions 37a and the second conductive type semiconductor layer 29 to separate the first electrode extensions 37a from the second conductive type semiconductor layer 29. Further, the protective insulation layer 35 covers side walls of the plurality of through-holes 30a to insulate the first electrode extensions 37a from the sidewalls.
The first functional layer 31a may be interposed in a pattern of dots between the protective insulation layer 35 and the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a. The first functional layer 31a may be a reflector having a reflectivity of 50% or more, for example, a distributed Bragg reflector. The distributed Bragg reflector may be formed by alternately stacking insulation layers having difference indices of refraction, for example, SiO2/TiO2 or SiO2/Nb2O5. When the first functional layer 31a constitutes the reflector having a reflectivity of 50% or more, the first functional layer 31a may reflect light directed towards the first electrode pad 37 and the first electrode extensions 37a, thereby reducing optical loss. In addition, when the first functional layer 31a constitutes the distributed Bragg-reflector, both the first functional layer 31a and the protective insulation layer 35 may serve to insulate the first electrode pad 37 from the semiconductor stack 30.
Further, the second functional layer 31b may be located between the transparent conductive layer 33 and the second conductive type semiconductor layer 29. The second functional layer 31b may be restrictively located under the second electrode pad 39 and the second electrode extensions 39a, and the transparent conductive layer 33 is connected to the second conductive type semiconductor layer 29 while covering the second functional layer 31b. 
The second functional layer 31b may serve as a current blocking layer and/or a reflector. For example, the second functional layer 31b may be formed of an insulation material and shield electric current which flows from the second electrode pad 39 and the second electrode extensions 39a to the second conductive type semiconductor layer 29 directly disposed under the second functional layer 31b through the transparent conductive layer 33. As a result, the second functional layer 31b relieves current crowding around the second electrode pad 39 and the second electrode extensions 39a, thereby enhancing current spreading. The second functional layer 31b may also be formed of a reflector having a reflectivity of 50% or more. Here, the reflector may include a metal reflector or a distributed Bragg reflector. For example, when the second functional layer 31b constitutes a distributed Bragg reflector formed by alternately stacking insulation layers having different indices of refraction, the second functional layer 31b may serve as both the current blocking layer and the reflector. Furthermore, the second functional layer 31b may be formed of the same material as that of the first functional layer 31a. 
The lower reflector 45 may be a distributed Bragg reflector. The lower distributed Bragg reflector 45 is formed by alternately stacking insulation materials having different indices of refraction and exhibits a relatively high reflectivity, preferably a reflectivity of 90% or more, not only with respect to light in a blue wavelength range, for example, light generated in the active layer 27, but also with respect to light in a yellow wavelength range or in a green and/or red wavelength range. In addition, the lower distributed Bragg reflector 45 may have a reflectivity of 90% or more in a wavelength range of, for example 490-700 nm.
The lower distributed Bragg reflector 45 having a relatively high reflectivity over a wide wavelength range is formed by controlling the optical thickness of each of the material layers repeatedly stacked one above another. The lower distributed Bragg reflector 45 may be formed, for example, by alternately stacking a first SiO2 layer and a second TiO2 layer, or by alternately stacking a first SiO2 layer and a second Nb2O5 layer. Since Nb2O5 exhibits a lower optical absorption rate than TiO2, it is more advantageous that the lower distributed Bragg reflector 45 is formed by alternately stacking the first SiO2 layer and the second Nb2O5 layer. As the number of first and second layers increases, the distributed. Bragg reflector 45 exhibits more stable reflectivity. For example, the distributed Bragg reflector 40 may be composed of fifty or more layers, that is, 25 pairs or more.
It is not necessary for the first layers or second layers to have the same thickness. The thickness of the first layers or the second layers is selected to provide relatively high reflectivity not only with respect to light generated in the active layer 27 but also with respect to light having different wavelengths in the visible spectrum. Further, the lower distributed Bragg reflector 45 may be formed by stacking a plurality of distributed Bragg reflectors exhibiting high reflectivity in different wavelength ranges.
The use of the distributed Bragg reflector 45 in the LED chip results in reflection and discharge not only of light generated in the active layer 27 but also of external light entering the substrate 21.
Further, the metal layer 47 may be located under the lower distributed Bragg reflector 45. The metal layer 47 may be formed of a reflective metal such as aluminum to reflect light passing through the lower distributed Bragg reflector 45. Of course, the metal layer 47 may be formed of other metals instead of the reflective metal. Moreover, the metal layer 47 assists dissipation of heat from the stack 30, thereby enhancing heat dissipation of the LED chip 102.
In the present embodiment, the first electrode pad 37 is located above the second conductive type semiconductor layer 29 of the semiconductor stack 30. Accordingly, there is no need to etch the second conductive type semiconductor layer 29 and the active layer 27 to form the first electrode pad 37, thereby preventing a reduction in light emitting area. In addition, since the first electrode extensions 37a are connected to the first conductive type semiconductor layer 25 through the plurality of through-holes 30a, it is possible to relieve a reduction in the light emitting area due to the formation of the first electrode extensions 37a. Furthermore, since first electrode extensions 37a are connected in the dot pattern to the first conductive type semiconductor layer 25 instead of being continuously connected thereto, it is possible to relieve current crowding around the first electrode extensions 37a. 
Next, a method of fabricating the LED chip will be described.
First, epitaxial layers 25, 27, 29 are grown on a substrate 21. A buffer layer 23 may be further formed before forming the epitaxial layers. Then, a second conductive type semiconductor layer 29 and an active layer 27 are patterned to form a semiconductor stack 30 having a mesa structure. At this time, a plurality of through-holes 30a is also formed therein.
Then a first functional layer 31a and a second functional layer 31b are formed on the second conductive type semiconductor layer 29. The first functional layer 31a may be formed in a dot pattern on a region to be formed with a first electrode pad 37 and on regions of the second conductive type semiconductor layer between the plurality of through-holes 30a. The second functional layer 31b is formed along regions where a second electrode pad 39 and second electrode extensions 39a will be formed. Both the first functional layer 31a and the second functional layer 31b may be formed of an insulation material or a reflective material. Further, the first and second functional layers 31a and 31b may be formed as distributed Bragg reflectors. The first and second functional layers 31a, 31b may be formed before the formation of the semiconductor stack 30 of the mesa structure.
Then, a transparent conductive layer 33 is formed. The transparent conductive layer 33 is connected to the second conductive type semiconductor layer 29 and covers the second functional layer 31b. At this time, the first functional layer 31a is exposed, instead of being covered with the transparent conductive layer 33.
Then, a protective insulation layer 35 is formed to cover the transparent conductive layer 33, the first functional layer 31a and the plurality of through-holes 30a. Meanwhile, the protective insulation layer 35 in the plurality of through-holes 30a is etched to expose the first conductive type semiconductor layer 25. In addition, the protective insulation layer 35 above the second functional layer 31b is etched to expose the transparent conductive layer 33.
Next, the first electrode pad 37, the second electrode pad 39, first electrode extensions 37a and second electrode extensions 39a are formed. The first electrode pad 37 is formed on the protective insulation layer 35 and may be formed above the first functional layer 31a. Meanwhile, the first electrode extensions 37a covers the plurality of through-holes 30a, which are linearly arranged, and are connected to the first conductive type semiconductor layer 25. Further, the second electrode pad 19 and the second electrode extensions 39a are formed on the transparent conductive layer 33 above the second functional layer 31b. 
Then, a lower reflector 45 and a metal layer 47 are formed under the substrate 21, and then the substrate 21 is divided into individual LED chips, thereby finishing preparation of the LED chips.
FIG. 3 is schematic plan view of an LED chip according to another exemplary embodiment of the invention, and FIGS. 4a, 4b and 4c are sectional views taken along lines A-A, B-B and C-C of FIG. 3, respectively.
Referring to FIGS. 3, 4a, 4b and 4c, the LED chip according to this embodiment is generally similar to the LED chip of the above embodiment, and detailed description of the same components will thus be omitted herein.
Referring to FIG. 4a, a first electrode pad 37 is formed on a first functional layer 51a. In other words, the protective insulation layer 35 between the first electrode pad 37 and the first functional layer 51a is eliminated in this embodiment. Further, the protective insulation layer 35 between the first electrode extensions 37a and the semiconductor stack 30 is also eliminated in this embodiment, Herein, the first functional layer 51a is formed of an insulation material and may constitute a distributed Bragg reflector. A second functional layer 31b may be formed of the same material as that of the first functional layer 51a by the same process.
Meanwhile, the first electrode extensions 37a a plurality of through-holes 30a are separated from sidewalls in the through-holes 30a by the first functional layer 51a. Specifically, the first functional layer 51a located on the second conductive type semiconductor layer 29 in regions between the plurality of through-holes 30a extends into the plurality of through-holes 30a and covers the sidewalls of the through-holes 30a. Meanwhile, some of the sidewalls, that is, sidewalls located at opposite sides of the first electrode extensions 37a in the plurality of through-holes 30a, may be covered with the protective insulation layer 35.
In the above embodiment, openings formed on the protective insulation layer 35 include regions exposing the transparent conductive layer 33 and regions exposing the first conductive type semiconductor layer in the plurality of through-holes 30a. Among these regions, the regions exposing the transparent conductive layer 33 correspond to regions at which the second electrode pad 39 and the second electrode extensions 39a are formed, but the regions exposing the first conductive type semiconductor layer do not correspond to the first electrode pad 37 and the first electrode extensions 37a. Accordingly, When the first and second electrode pads 37, 39 and the first and second electrode extensions 37a, 39a are simultaneously formed by lift-off, a pattern of openings is first formed on the protective insulation layer 35 using a photomask, and the first and second electrode pads 37, 39 and the first and second electrode extensions 37a, 39a are formed using another photomask.
According to the present embodiment, however, since the shapes of the first and second electrode pads 37, 39 and the shapes of the first and second electrode extensions 37a, 39a correspond to the pattern of openings formed on the protective insulation layer 35, the first and second electrode pads 37, 39 and the first and second electrode extensions 37a, 39a may be formed using the same photomask as that used to pattern the protective insulation layer 35. In addition, after forming the pattern of openings on the protective insulation layer 35 using a photoresist, the photoresist may be continuously used to form the first and second electrode pads 37, 39 and the first and second electrode extensions 37a, 39a. Accordingly, it is possible to reduce the number of photomasks for fabrication of LED chips, so that the number of photolithography and developing processes for forming the photoresist pattern can be reduced.
FIGS. 5a, 5b and 5c are sectional views of an LED chip according to a further exemplary embodiment of the invention. The respective figures correspond to sectional views taken along lines A-A, B-B and C-C of FIG. 1.
Referring to FIGS. 5a, 5b and 5c, the LED chip according to this embodiment is generally similar to the LED chip described with reference to FIGS. 1 and 2. In this embodiment, however, a transparent conductive layer 33 extends to a region between a first electrode pad 37 and a second conductive type semiconductor layer 29 and to regions between first electrode extensions 37a and the second conductive type semiconductor layer 29.
Specifically, in the previous embodiments, the transparent conductive layer 33 is not formed on regions of the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a, whereas the transparent conductive layer 33 is also formed on these regions in this embodiment. Since the transparent conductive layer 33 is connected to the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a, electric current can be supplied to the semiconductor stack 30 in these regions.
The first electrode pad 37 and the first electrode extensions 37a are insulated from the transparent conductive layer 33 by the protective insulation layer 35, and a first functional layer 61a may be located between the protective insulation layer 35 and the transparent conductive layer 33.
In this embodiment, the first functional layer 61a and a second functional layer 31b are formed by separate processes. Specifically, after the transparent conductive layer 33 is formed to cover the second functional layer 31b, the first functional layer 61a is formed again on the transparent conductive layer 33.
FIGS. 6a, 6b and 6c are sectional views of an LED chip according to yet another exemplary embodiment of the invention. The respective figures correspond to sectional views taken along lines A-A, B-B and C-C of FIG. 3.
Referring to FIGS. 6a, 6b and 6c, the LED chip of this embodiment is generally similar to the LED chip described with reference to FIGS. 3 and 4. In this embodiment, however, a transparent conductive layer 33 extends to a region between a first electrode pad 37 and a second conductive type semiconductor layer 29 and to regions between first electrode extensions 37a and the second conductive type semiconductor layer 29.
Specifically, in the embodiment of FIG. 3, the transparent conductive layer 33 is not formed on regions of the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a, whereas the transparent conductive layer 33 is located on these regions in the present embodiment. Since the transparent conductive layer 33 is connected to the region of the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a, electric current can be supplied to the semiconductor stack 30 in these regions.
The first electrode pad 37 and the first electrode extensions 37a are insulated from the transparent conductive layer 33 by a first functional layer 71a. 
In this embodiment, the first functional layer 71a and a second functional layer 31b are formed by separate processes. Specifically, after the transparent conductive layer 33 is formed to cover the second functional layer 31b, the first functional layer 71a is formed again on the transparent conductive layer 33.
FIG. 7 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention.
Referring to FIG. 7, the LED chip according to this embodiment is generally similar to the LED chip described with reference to FIGS. 1 and 2. In this embodiment, however, a second functional layer 71b is arranged in a pattern of dots along a second electrode pad 39 and second electrode extensions 39a. 
Specifically, the second functional layer 71b is arranged in the pattern of dots instead of being lineally arranged. In this embodiment; the transparent conductive layer 33 covers the second functional layer 71b and is connected to the second conductive type semiconductor layer 29 in regions between the dots.
Arrangement of the second functional layer 71b in the dot pattern may be applied not only to the embodiment shown in FIGS. 1 and 2, but also to the embodiments shown in FIGS. 3 to 6.
FIG. 8 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention.
Referring to FIG. 8, the LED chip according to this embodiment is generally similar to the LED chip described with reference to FIGS. 1 and 2. In this embodiment, however, a second functional layer 81b is arranged in a pattern of dots along a second electrode pad 39 and second electrode extensions 39a on a transparent conductive layer 33.
Specifically, the second functional layer 81b is arranged in the pattern of dots between a transparent conductive layer 33 and a second electrode pad 30 and between the transparent conductive layer 33 and the second electrode extensions 39a. The second electrode extensions 39a are connected to the transparent conductive layer 33 in regions between the dots.
The second functional layer 81b according to this embodiment may be applied not only to the exemplary embodiment shown in FIGS. 1 and 2, but also to the exemplary embodiments shown in. FIGS. 3 to 6. Furthermore, when the second functional layer 81b is applied to the exemplary embodiments of FIGS. 5 and 6, the first functional layers 61a, 71a and the second functional layer 81b may be formed on the transparent conductive layer 33 by the same process.
FIG. 9 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention. FIG. 9 corresponds to the sectional view taken along line C-C of FIG. 1.
Referring to FIG. 9, the LED chip of this embodiment is generally similar to the LED Chips described above. In this embodiment, however, grooves are linearly formed on a semiconductor stack 30 instead of the plurality of through-holes 30a. The grooves expose a first conductive type semiconductor layer 25 and first electrode extensions 37a are connected to the first conductive type semiconductor layer 25 in the grooves. In this embodiment, the dot pattern formed of an insulation material is located between the first conductive type semiconductor layer 25 and first electrode extensions 37a and partially separates the first electrode extensions 37a from the first conductive type semiconductor layer 25.
Since the dot pattern allows the first electrode extensions 37a to be connected to the first conductive type semiconductor layer 25 in a plurality of dot regions separated from each other instead of being continuously connected thereto, it is possible to relieve current crowding around the first electrode extensions 37a. 
FIG. 10 is a plan view of an LED chip according to yet another exemplary embodiment of the invention.
Referring to FIG. 10, first electrode extensions 37a are connected to a first conductive type semiconductor layer 25 in a plurality of dot regions 37b. The plurality of dot regions 37b may correspond, for example, to the regions where the first electrode extensions 37a are connected to the first conductive type semiconductor layer 25 in the plurality of through-holes 30a in the LED chip described with reference to FIGS. 1 and 2; or to the regions where the first electrode extensions 37a are connected to the first conductive type semiconductor layer 25 in the grooves in the LED chip described with reference to FIG. 9.
Further, second electrode extensions 39a are connected to the second conductive type semiconductor layer 29 through a transparent conductive layer 33 in a plurality of dot regions 39b: The plurality of dot regions 39b may correspond, for example, to the regions where the second electrode extensions 39a are connected to the transparent conductive layer 33 between the dots of the second functional layer 71b in the LED chip described with reference to FIG. 7, or to the regions where the second electrode extensions 39a are connected to the transparent conductive layer 33 between the dots of the second functional layer 81b in the grooves in the LED chip described with reference to FIG. 8.
The dot regions 37b, 39b may have different sizes and current spreading of the LED chip may be improved by adjusting the sizes of the dot regions. The sizes of the dot regions 37b may be controlled by adjusting the sizes of the through-holes 30a or the size of the dot pattern 91a (see FIG. 9a), and the sizes of the dot regions 39b may be controlled by adjusting the size of the second functional layer 71b or 81b. 
For example, the dot regions 37b in the first electrode extensions 37a may be divided into first dot regions closer to the first electrode pad 37 than the second electrode pad 39 and second dot regions closer to the second electrode pad than the first electrode pad. The sizes of the first dot regions may increase as the distance between the first dot regions and the first electrode pad 37 increases and the sizes of the second dot regions may decrease as the distance between the second dot regions and the first electrode pad 37 increases.
Further, the dot regions 39b in the second electrode extensions 39a may be divided into third dot regions closer to the second electrode pad 39 than the first electrode pad 37 and fourth dot regions closer to the first electrode pad than the second electrode pad. The sizes of the third dot regions may increase as the distance between the third dot regions and the second electrode pad 39 increases and the sizes of the fourth dot regions may decrease as the distance between the fourth dot regions and the second electrode pad 39 increases.
Generally, since electric current tends to crowd around the first electrode pad 37 or the second electrode pad 39, the LED chip is configured to have relatively small dot regions formed in regions near these electrode pads 37, 39 and relatively large dot region formed in regions distant from these electrode pads, thereby enhancing current spreading.
in addition, the sizes of the dot regions may increase as the distance between the dot regions and a line crossing the first electrode pad 37 and the second electrode pad 39 increases, thereby preventing current crowding at a central region of the LED chip.
FIG. 11 is a schematic plan view of an LED-chip according to yet another exemplary embodiment of the invention, and FIGS. 12a, 12b, 12c and 12d are sectional views taken along lines A-A, B-B, C-C and D-D of FIG. 11, respectively.
Referring to FIG. 11 and FIGS. 12a, 12b, 12c and 12d, the LED chip may include a semiconductor stack 30, a plurality of mesa structures M1, M2, a separation region SR, a first electrode pad 37, a second electrode pad 39, first electrode extensions 37a, 37b, 37c, second electrode extensions 39a, and a protective insulation layer 35. The LED chip may further include a substrate 21, a buffer layer 23, a first functional layer 31a, a second functional layer 31b, a transparent conductive layer 33, a lower reflector 45, and a metal layer 47. Meanwhile, the semiconductor stack 30 includes a first conductive type semiconductor layer 25, an active layer 27, and a second conductive type semiconductor layer 29.
The substrate 21, first conductive type semiconductor layer 25, active layer 25 and second conductive type semiconductor layer 29 of the LED chip according to this embodiment are similar to those of the LED chip described with reference to FIGS. 1, 2a, 2b and 2c, and detailed descriptions thereof will thus be omitted herein.
The semiconductor stack 30 includes the plurality of mesa structures M1, M2 separated from each other by the separation region SR. Each of the mesa structures M1, M2 includes the second conductive type semiconductor layer 29 and the active layer 27 interposed between the first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 29. Namely, the second conductive type semiconductor layer 29 and the active layer 27 are separated by the separation region SR, thereby forming the plurality of mesa structures M1, M2. An upper surface of the first conductive type semiconductor layer 25 is exposed by the separation region SR.
The plurality of mesa structures M1, M2 may have the same shapes. For example, as shown in FIG. 11, two mesa structures M1, M2 may have symmetrical structures with respect to the separation region SR. In this embodiment, the LED chip is illustrated as including the two mesa structures M1, M2, but the invention is not limited thereto. It should be understood that the LED chip according to the invention may have two or more mesa structures.
Each of the mesa structures M1, M2 has a plurality of through-holes 30a extending through second conductive type semiconductor layer 29 and the active layer 27 to expose the first conductive type semiconductor layer 25. The plurality of through-holes 30a is linearly arranged along first electrode extensions 37a, as shown in FIG. 11.
The transparent conductive layer 33 may be formed on the second conductive type semiconductor layer 29. The transparent conductive layer 33 may be formed of indium tin oxide (ITO) or Ni/Au and forms an ohmic contact with the second conductive type semiconductor layer 29.
As clearly shown in FIG. 12a, the first electrode pad 37 is located on the second conductive type: semiconductor layer 29 of the semiconductor stack 30. The first electrode pad 37 may include a plurality of electrode pads 37 located on the mesa structures M1, M2, respectively. These electrode pads may be connected to each other by, for example, the electrode extension 37c. The first electrode extensions 37a extend from the first electrode pad 37. The first electrode pad 37 is insulated from the semiconductor stack 30 and electrically connected to the first conductive type semiconductor layer 25 through the first electrode extensions 37a. The first electrode extensions 37a are connected to the first conductive type semiconductor layer 25 exposed through the plurality of through-holes 30a. 
Meanwhile, the first electrode extension 37b may be connected to the first conductive type semiconductor layer 25 exposed on the separation region SR. The first electrode extension 37b is electrically connected to the first electrode pad 37.
As clearly shown in FIG. 12d, the first conductive type semiconductor layer 25 is exposed through the separation region SR and the first electrode extension 37b is connected to the first conductive type semiconductor layer 25 in the separation region SR. Meanwhile, a dot pattern 31c formed of an insulation material is located between the first conductive type semiconductor layer 25 and the first electrode extension 37b such that the first electrode extension 37b can be partially separated from the first conductive type semiconductor layer 25. The dot pattern 31c allows the first electrode extension 37b to be connected to the first conductive type semiconductor layer 25 in a plurality of dot region separated from each other instead of being continuously connected thereto, thereby relieving current crowding around the first electrode extension 37b. 
The second electrode pad 39 may be located on the transparent conductive layer 33. The second electrode pad 39 may include a plurality of electrode pads 39 located on the mesa structures M1, M2, respectively, Further, the second electrode extensions 39a may extend from the second electrode pad 39. The second electrode pad 39 and the second electrode extensions 39a may be connected to the transparent conductive layer 33.
Meanwhile, a protective insulation layer 35 is located on the semiconductor stack 30 to cover the semiconductor stack 30. The protective insulation layer 35 may cover the transparent conductive layer 33. In addition, the protective insulation layer 35 is interposed between the first electrode pad 37 and the second conductive type semiconductor layer 29 to separate the first electrode pad 37 from the second conductive type semiconductor layer 29, and between the first electrode extensions 37a and the second conductive type semiconductor layer 29 to separate the first electrode extensions 37a from the second conductive type semiconductor layer 29. Further, the protective insulation layer 35 covers side walls of the plurality of through-holes 30a to insulate the first electrode extensions 37a from the sidewalls. The protective insulation layer 35 may also separate the first electrode extension 37b from the second conductive type semiconductor layer 79.
The first functional layer 31a may be interposed in a pattern of dots between the protective insulation layer 35 and the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a. Further, the second functional layer 31b may be located between the transparent conductive layer 33 and the second conductive type semiconductor layer 29. The first functional layer 31a and the second functional layer 31b are similar to the first functional layer 31a and the second functional layer 31b described with reference to FIGS. 1, 2a, 2b and 2c, and detailed descriptions thereof will thus be omitted herein. The second functional layer 31b may be formed of the same material as that of the first functional layer 31a and the dot pattern 31c may also be formed of the same material as that of the functional layers 31a 31b. 
In this embodiment, the lower reflector 45 is located under the substrate 21 and the metal layer 47 may be located under the lower reflector 45. The lower reflector and the metal layer 47 are similar to the lower reflector 45 and the metal layer 47 described with reference to FIG. 1, FIGS. 2a, 2b and 2c, and detailed descriptions thereof will be omitted herein.
According to this embodiment, the plurality of mesa structures M1, M2 are separated from each other and located on the first conductive type semiconductor layer 25. Therefore, when the LED chip is operated at high electric current, the electric current spreads to and flows through the respective mesa structures M1, M2. Thus, it is possible to prevent a reduction in external quantum efficiency due to current crowding at a certain position of the semiconductor stack 30. In particular, if a certain mesa structure has a defect, the LED chip may prevent flow of high electric current through the defect, thereby preventing a reduction in external quantum efficiency of a large LED chip.
Next, a method of fabricating the LED chip will be described.
First, epitaxial layers 25, 27, 29 are grown on a substrate 21. A buffer layer 23 may further be formed before forming the epitaxial layers. Then, a second conductive type semiconductor layer 29 and an active layer 27 are patterned to form a semiconductor stack 30 having a plurality of mesa structures M1, M2. At this time, a plurality of through-holes 30a is also formed therein and a separation region SR is formed to divide the mesa structures M1, M2 from each other.
Then, a first functional layer 31a and a second functional layer 31b are formed on the second conductive type semiconductor layer 29. Further, a dot pattern 31c may be formed together therewith. The first functional layer 31a may be formed in a dot pattern on a region to be formed with a first electrode pad 37 and on regions of the second conductive type semiconductor layer between tire plurality of through-holes 30a. The second functional layer 31b is formed along regions where a second electrode pad 39 and second electrode extensions 39a will be formed. The dot pattern 31c is formed on regions of the first conductive type semiconductor layer 25 exposed by the separation region SR. Both the first functional layer 31a and the second functional layer 31b may be formed of an insulation material or a reflective material. Further, the first and second functional layers 31a, 31b may be formed as distributed Bragg reflectors. The first and second functional layers 31a, 31b may be formed before the formation of the semiconductor stack 30 of the mesa structures.
Then, a transparent conductive layer 33 is formed on the second conductive type semiconductor layer 29. The transparent conductive layer 33 is connected to the second conductive type semiconductor layer 29 and covers the second functional layer 31b. At this time, the first functional layer 31a is exposed, instead of being covered with the transparent conductive layer 33.
Then, a protective insulation layer 35 is formed to cover the transparent conductive layer 33, the first functional layer 31a and the plurality of through-holes 30a. Meanwhile, the protective insulation layer 35 in the plurality of through-holes 30a is etched to expose the first conductive type semiconductor layer 25. In addition, the protective insulation layer 35 above the second functional layer 31b is etched to expose the transparent conductive layer 33. Further, the protective insulation layer 35 may cover sidewalls of the mesa structures M1, M2 located at opposite sides of the separation region SR.
Next, the first electrode pad 37, the second electrode pad 39, first electrode extensions 37a, 37b, 37c, and second electrode extensions 39a are formed. Meanwhile, the first electrode extensions 37a covers the plurality of through-holes 30a linearly arranged and are connected to the first conductive type semiconductor layer 25. Meanwhile the first electrode extension 37b is formed in the separation region SR and covers the dot pattern 31c. The first electrode extensions 37a, 37b may be connected to the first electrode pad 37 through the first electrode extensions 37c, and the plurality of electrode pads are respectively located on the mesa structures M1, M2 to be connected to each other through the first electrode extensions 37c. The first electrode extensions 37c may be arranged along edges of the mesa structures M1, M2. In this case, the first electrode extensions 37c may also be partially connected to the first conductive type semiconductor layer 25. The first electrode extensions 37c may be connected to the first conductive type semiconductor layer at portions on the edges of the mesa structures M1, M2 having the second conductive type semiconductor layer 29 and the active layer 27 removed therefrom, instead of being connected thereto in through-holes 30a. In other words, portions of the through-holes 30a having the first electrode extensions 37c connected to the first conductive type semiconductor layer 25 may be exposed to the outside of the mesa structures M1, M2.
Further, the second electrode pad 39 and the second electrode extensions 39a are formed on the transparent conductive layer 33 above the second functional layer 31b. 
Then, a lower reflector 45 and a metal layer 47 are formed under the substrate 21, and then the substrate 21 is divided into individual LED chips, thereby finishing preparation of the LED chips.
In this embodiment the dot pattern 31c is formed by the same process as that used to form the first functional layer 31a and the second functional layer 31b. However, the dot pattern 31c may be omitted from the LED chip. In this case, after a protective insulation layer 35 is formed to cover the separation region SR, the protective insulation layer 35 in the separation region SR is partially etched to form a plurality of openings through which the first conductive type semiconductor layer 25 is exposed, thereby forming an insulation pattern that partially separates the first electrode extension 37b from the first conductive type semiconductor layer 25.
FIG. 13 is a schematic plan view of an LED chip according to yet another exemplary embodiment of the invention, and FIGS. 14a, 14b, 14c and 14d are sectional views taken along lines A-A, B-B, C-C and D-D of FIG. 13, respectively.
Referring to FIGS. 13, 14a, 14b, 14c and 14d, the LED chip according to this embodiment is generally similar to the LED chip of the above exemplary embodiment described with reference to FIGS. 11, 12a,12b, 12c and 12d, and detailed descriptions of identical components will thus be omitted herein.
First, as shown in FIG. 14a, a first electrode pad 37 is directly located on a first functional layer 51a. Namely, the protective insulation layer 35 is removed from between the first electrode pad 37 and the first functional layer 51a. Further, the protective insulation layer 35 is also removed from between the first electrode extensions 37a and the semiconductor stack 30. Here, the first functional layer 51a is formed of an insulation material and may constitute a distributed Bragg reflector. A second functional layer 31b may also be formed of the same material as that of the first functional layer 51a by the same process.
Meanwhile, the first electrode extensions 37a in a plurality of through-holes 30a are separated from sidewalls in the through-holes 30a by the first functional layer 51a. Specifically, the first functional layer 51a located on the second conductive type semiconductor layer 29 in regions between the plurality of through-holes 30a extends into the plurality of through-holes 30a and covers the sidewalls of the through-holes 30a. Meanwhile, some of the sidewalls, that is, sidewalls located at opposite sides of the first electrode extensions 37a in the plurality of through-holes 30a, may be covered with the protective insulation layer 35.
In the previous exemplary embodiment, openings formed on the protective insulation layer 35 include regions exposing the transparent conductive layer 33 and regions exposing the first conductive type semiconductor layer 25 in the plurality of through-holes 30a and the separation region SR. Among these regions, the regions exposing the transparent conductive layer 33 correspond to regions at which the second electrode pad 39 and the second electrode extensions 39a are formed, but the regions exposing the first conductive type semiconductor layer do not correspond to the first electrode pad 37 and the first electrode extensions, 37a, 37b. Accordingly, when the first and second electrode pads 37, 39 and the first and second electrode extensions 37a, 37b, 37c, 39a are simultaneously formed by lift-off, the pattern of openings is first formed on the protective insulation layer 35 using a photomask, and the first and second electrode pads 37, 39 and the first and second electrode extensions 37a, 37b, 37c, 39a are formed using another photomask.
According to the present embodiment, however, since the shapes of the first and second electrode pads 37, 39 and the shapes of the first and second electrode extensions 37a, 37b, 37c, 39a correspond to the pattern of openings formed on the protective insulation layer 35, the first and second electrode pads 37, 39 and the first and second electrode extensions 37a, 37b, 37c, 39a may be formed using the same photomask as that for patterning the protective insulation layer 35. In addition, after forming the pattern of openings on the protective insulation layer 35 using a photoresist, the photoresist may be continuously used to form the first and second electrode pads 37, 39 and the first and second electrode extensions 37a, 37b, 37c, 39a. Accordingly, it is possible to reduce the number of photomasks for fabrication of LED chips, so that the number of photolithography and developing processes for forming the photoresist pattern can be reduced.
FIGS. 15a, 15b and 15c are sectional views of an LED chip according to yet another exemplary embodiment of the invention. The respective figures correspond to sectional views taken along lines A-A, B-B and C-C of FIG. 11. Further, in this embodiment, the sectional view taken along line D-D of FIG. 11 is the same as the corresponding sectional view of the present embodiment and is thus omitted herein.
Referring to FIGS. 15a, 15b and 15c, the LED chip according to this embodiment is generally similar to the LED chip described with reference to FIGS. 11 and 12. In this embodiment, however, a transparent conductive layer 33 extends to a region between a first electrode pad 37 and a second conductive type semiconductor layer 29 and to regions between first electrode extensions 37a and the second conductive type semiconductor layer 29. The transparent conductive layer 33 may also extend to regions between a first electrode extension 37c and the second conductive type semiconductor layer 29.
Specifically, in the exemplary embodiment of FIG. 11, the transparent conductive layer 33 is not formed on regions of the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a, 37c, whereas the transparent conductive layer 33 is also formed on these regions in this embodiment. Since the transparent conductive layer 33 is connected to the regions of the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a, 37c, electric current can be supplied to the semiconductor stack 30 in these regions.
The first electrode pad 37 and the first electrode extensions 37a, 37c are insulated from the transparent conductive layer 33 by the protective insulation layer 35, and first functional layer 61a may be located between the protective insulation layer 35 and the transparent conductive layer 33.
In this embodiment, the first functional layer 61a and a second functional layer 31b are formed by separate processes. Specifically, after the transparent conductive layer 33 is formed to cover the second functional layer 31b, the first functional layer 61a is formed again on the transparent conductive layer 33.
FIGS. 16a, 16b and 16c are sectional views of an LED chip according to yet another exemplary embodiment of the invention. The respective figures correspond to sectional views taken along lines A-A, B-B and C-C of FIG. 13. Further, in this embodiment, the sectional view taken along line D-D of FIG. 13 is the same as the corresponding sectional view of the present embodiment and is thus omitted herein.
Referring to FIGS. 16a, 16b and 16c, the LED chip of this embodiment is generally similar to the LED chip described with reference to FIGS. 13 and 14. In this embodiment, however, a transparent conductive layer 33 extends to a region between a first electrode pad 37 and a second conductive type semiconductor layer 29 and to regions between first electrode extensions 37a and the second conductive type semiconductor layer 29. The transparent conductive layer 33 may also extend to regions between a first electrode extension 37c and the second conductive type semiconductor layer 29.
Specifically, in the exemplary embodiment of FIG. 13, the transparent conductive layer 33 is not formed on regions of the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a, 37c, whereas the transparent conductive layer 33 is located on these regions in the present embodiment. Since the transparent conductive layer 33 is connected to the regions of the second conductive type semiconductor layer 29 under the first electrode pad 37 and the first electrode extensions 37a, 37c, electric current can be supplied to the semiconductor stack 30 in these regions.
The first electrode pad 37 and the first electrode extensions 37a, 37c are insulated from the transparent conductive layer 33 by a first functional layer 71a. 
In this embodiment, the first functional layer 71a and a second functional layer 31b are formed by separate processes. Specifically, after the transparent conductive layer 33 is formed to cover the second functional layer 31b, the first functional layer 71a is formed again on the transparent conductive layer 33.
FIG. 17 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention.
Referring to FIG. 17, the LED chip according to this embodiment is generally similar to the LED chip described with reference to FIGS. 11 and 12. In this embodiment, however, a second functional layer 71b is arranged in a pattern of dots along a second electrode pad 39 and second electrode extensions 39a. 
Specifically, the second functional layer 71b is arranged in the pattern of dots instead of being linearly arranged. In this embodiment, the transparent conductive layer 33 covers the second functional layer 71b and is connected to the second conductive type semiconductor layer 29 in regions between the dots.
Arrangement of the second functional layer 71b in the dot pattern may be applied not only to the exemplary embodiment shown in FIGS. 11, and 12, but also to the exemplary embodiments shown in FIGS. 13 to 16.
FIG. 18 is a sectional view of an LED chip according to yet another exemplary embodiment of the invention.
Referring to FIG. 18, the LED chip according to this embodiment is generally similar to the LED chip described with reference to FIGS. 11 and 12. In this embodiment, however, a second functional layer 81b is arranged in pattern of dots along a second electrode pad 39 and second electrode extensions 39a on a transparent conductive layer 33.
Specifically, the second functional layer 81b is arranged in the pattern of dots between a transparent conductive layer 33 and a second electrode pad 30 and between the transparent conductive layer 33 and the second electrode extensions 39a. The second electrode extensions 39a are connected to the transparent conductive layer 33 in regions between the dots.
The second functional layer 81b according to this embodiment may be applied not only to the exemplary embodiment shown in FIGS. 11 and 12, but also to the exemplary embodiments shown in FIGS. 13 to 16. Furthermore, when the second functional layer 81b is applied to the exemplary embodiments of FIGS. 15 and 16, the first functional layers 61a, 71a and the second functional layer 81b may be formed on the transparent conductive layer 33 by the same process.
FIGS. 19(a) and 19(b) are schematic plan views of an LED chip according to yet another exemplary embodiment of the invention.
Referring to FIG. 19(a), differing from the above exemplary embodiments, the LED chip according to this embodiment includes first electrode pads 37, which are electrically separated from each other. Specifically, in the above exemplary embodiments, the first electrode pads 37 respectively located on the mesa structures M1, M2 are electrically connected to each other by the first electrode extensions 37c, whereas the first electrode pads 37 are electrically separated from each other in this embodiment.
Referring to FIG. 1.9(b), in the LED chip according to this embodiment, a part of the first electrode pad 37 is located in the separation region SR. The remaining portion of the first electrode pad 37 is located on the mesa structures M1 and M2. In this embodiment, two mesa structures M1 and M2 may share the first electrode pad 37, thereby reducing the number of first electrode pad 37. Further, the first electrode extension 37b in the separation region SR may be directly connected to the first electrode pad 37.
Various exemplary embodiments and modifications including two or more mesa structures M1, M2 may also be realized. Each of the mesa structures includes a first electrode pad and a second electrode pad thereon. In this case, the first electrode pads may be electrically separated from each other and the second electrode pads may also be separated from each other.
FIG. 20 is plan views illustrating light emitting patterns for explaining enhancement of light emitting characteristics when adopting a plurality of mesa structures. Here, FIG. 20(a) shows a light emitting pattern of an LED chip having first electrode extensions and second electrode extensions on a single mesa structure, and FIG. 20(b) is a light emitting pattern of an LED chip having mesa structures M1, M2 which are completely separated into two regions by a separation region SR. Further, a certain region approaching a dark grey shade indicates that the region emits large amounts of light a certain region approaching a light grey shade indicates that the region emits small amounts of light, and a black shade indicates that the corresponding region does not emit light.
The LED chip of FIG. 20(a) has a single mesa structure which is not separated into two or more regions, and the LED chip of FIG. 20(b) includes mesa structures which are separated from each other by the separation region SR. Although both LED chips have a similar arrangement of electrode pads 37, 39 and electrode extensions 37a, 37b therein, it can be ascertained that the LED chip of FIG. 20(b) having two mesa structures M1, M2 completely separated from each other exhibits a more uniform light emitting pattern and emits more light than the LED chip of FIG. 20(a).
Although the invention has been illustrated with reference to some exemplary embodiments in conjunction with the drawings, it will be apparent to those skilled in the art that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention. Therefore, it should be understood that the exemplary embodiments are provided by way of illustration only and are given to provide complete disclosure of the invention and to provide thorough understanding of the invention to those skilled in the art. Thus, it is intended that the invention covers the modifications and variations provided they fall within the scope of the appended claims and their equivalents.

## Claims

1. A light emitting diode (LED) comprising:
a substrate having a first edge, a second edge opposite to the first edge, a third edge connecting the first edge to the second edge, and a fourth edge opposite to the third edge;
a semiconductor stack disposed over a first surface of the substrate, the semiconductor stack comprising:
a first conductivity-type semiconductor layer, a second conductivity-type semiconductor layer, and an active layer interposed between the first conductivity-type semiconductor layer and the second conductivity-type semiconductor layer;

a first electrode pad electrically connected to the first conductivity-type semiconductor layer and disposed over the second conductivity-type semiconductor layer and on at least a portion of the first edge of the substrate;
a first electrode extension extending from the first electrode pad along at least a portion of the first edge and at least a portion of the third edge, the first electrode extension electrically connected to the first conductivity-type semiconductor layer;
a second electrode pad electrically connected to the second conductivity-type semiconductor layer, wherein the second electrode pad is disposed over the second conductively-type semiconductor layer and on at least a portion of the second edge of the substrate;
a first insulation layer interposed between the first electrode pad and the second conductivity-type semiconductor layer;
a second insulation functional layer interposed between the second electrode pad and the second conductivity type semiconductor layer; and
a transparent conductive layer disposed over the second conductivity-type semiconductor layer and between the second electrode extension and the second conductivity type semiconductor layer, wherein the transparent conductive layer is separated from the first insulation layer.

2. The LED of claim 1, wherein the first insulation layer comprises opening regions to expose the first conductivity-type semiconductor layer.

3. The LED of claim 2, wherein the first electrode extension is in ohmic contact with the first conductivity-type semiconductor layer through the opening regions.

4. The LED of claim 1, wherein the transparent conductive layer is configured to cover a side surface of second insulation layer.

5. The LED of claim 1, further comprising:
a lower reflector disposed on a second surface of the substrate and opposite to the first surface of the substrate,
wherein the lower reflector includes alternately stacked insulation materials having different indices of refraction.

6. The LED of claim 1, wherein the first insulation layer and the second insulation layer include a reflective material.

7. The LED of claim 1, wherein the first edge, second edge, third edge and fourth edge define structural boundaries of the substrate.

8. The LED of claim 1, wherein the transparent layer includes indium tin oxide (ITO).

9. The LED of claim 1, wherein the substrate includes sapphire.

10. The LED of claim 1, wherein:
the first conductivity-type semiconductor layer includes a p-type nitride semiconductor layer; and
the second conductivity-type semiconductor layer includes an n-type nitride semiconductor layer.

11. The LED of claim 1, wherein the transparent conductive layer is disposed over the second conductivity-type semiconductor layer to include through-holes that expose a portion of the second conductivity-type semiconductor layer.

12. The LED of claim 1, wherein the second insulating layer is interposed between the second electrode extension and the second conductive type semiconductor layer.

13. The LED of claim 1, wherein:
the second insulating layer is patterned between the transparent conductive layer and the second electrode extension to provide an electrical connection between the second electrode extension and the second conductive type semiconductor layer.

14. The LED of claim 1 wherein:
the second conductivity-type semiconductor layer includes through-holes under at least a portion of the first electrode extension to provide an electrical connection to the first conductive type semiconductor layer.

15. The LED of claim 1, wherein the second electrode extension is disposed to extend from the second electrode pad along at least a portion of the fourth edge.

16. The LED of claim 1, wherein:
the first electrode extension is disposed to extend from the first electrode pad towards the second edge; and
the second electrode extension is disposed to extend from the second electrode pad towards the first edge.

17. A light emitting diode (LED) comprising:
a substrate;
a semiconductor stack disposed over a surface of the substrate, the semiconductor stack including:
a first conductivity-type semiconductor layer, a second conductivity-type semiconductor layer, and an active layer interposed between the first conductivity-type semiconductor layer and the second conductivity-type semiconductor layer,
wherein the semiconductor stack is disposed to include a plurality of through-holes extending through the second conductivity-type semiconductor layer to expose a portion of the first conductivity-type semiconductor layer;

a first electrode pad disposed over the second conductivity-type semiconductor layer and electrically connected to the first conductivity-type semiconductor layer through at least one of the through-holes of the semiconductor stack;
a second electrode pad disposed over and electrically connected to the second conductively-type semiconductor layer, wherein the second electrode pad and the first electrode pad are disposed on opposing regions on the surface of the substrate;
a first electrode extension extending from the first electrode pad towards the second electrode pad, wherein the first electrode extension is electrically connected to the first conductivity-type semiconductor layer through at least some of the through-holes of the semiconductor stack; and
a second electrode extension extending from the second electrode pad towards the first electrode pad.

18. The LED of claim 17, comprising:
a first insulation layer interposed between the first electrode pad and the second conductivity-type semiconductor layer;
a second insulation layer interposed between the second electrode pad and the second conductivity type semiconductor layer; and
a transparent conductive layer disposed over the second conductivity-type semiconductor layer, wherein the transparent conductive layer is separated from the first insulation layer.

19. The LED of claim 18, wherein the transparent conductivity layer is disposed between the second electrode pad and the second insulation layer.

20. The LED of claim 17, further comprising:
a lower reflector disposed under the substrate, wherein the lower reflector includes alternately stacked insulation materials having different indices of refraction.

21. The LED of claim 17, wherein the first electrode extension includes a plurality of portions extending from the first electrode pad.

22. The LED of claim 17, wherein the second electrode extension includes a plurality of portions extending from the second electrode pad.

23. The LED of claim 17, wherein:
the first conductivity-type semiconductor layer includes a p-type nitride semiconductor layer; and
the second conductivity-type semiconductor layer includes an n-type nitride semiconductor layer.

24. A light emitting diode (LED) comprising:
a substrate;
a semiconductor stack disposed over a surface of the substrate, the semiconductor stack including:
a first conductivity-type semiconductor layer, a second conductivity-type semiconductor layer, and an active layer interposed between the first conductivity-type semiconductor layer and the second conductivity-type semiconductor layer,
wherein the semiconductor stack is disposed to include means for providing electrical connections to the first conductivity-type semiconductor layer through the second conductivity-type semiconductor layer;

a transparent conductive layer disposed over a portion of the second conductivity-type semiconductor layer;
a first electrode pad disposed over the second conductivity-type semiconductor layer and electrically connected to the first conductivity-type semiconductor layer through the means for providing electrical connections to the first conductivity-type semiconductor layer;
a second electrode pad disposed over the transparent conductive layer and electrically connected to the second conductively-type semiconductor layer, wherein the second electrode pad and the first electrode pad are disposed on opposing regions on the surface of the substrate;
a first electrode extension extending from the first electrode pad towards the second electrode pad;
a second electrode extension extending from the second electrode pad towards the first electrode pad;
a first insulation means interposed between the first electrode pad and the second conductivity-type semiconductor layer; and
a second insulation means interposed between the transparent conductive layer and the second conductivity type semiconductor layer.

25. The LED of claim 24, wherein the transparent conductive layer is separated from the first insulation means.

26. The LED of claim 24, wherein the means for means for providing electrical connections to the first conductivity-type semiconductor layer through the second conductivity-type semiconductor layer include through-holes extending through the second conductivity-type semiconductor layer.

27. The LED of claim 24, wherein:
at least one of the first insulation means and the second insulation means include SiO2.