WO2004112157A1 - Iii-nitride compound semiconductor light emitting device with mesh type electrode - Google Patents

Iii-nitride compound semiconductor light emitting device with mesh type electrode Download PDF

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Publication number
WO2004112157A1
WO2004112157A1 PCT/KR2004/001318 KR2004001318W WO2004112157A1 WO 2004112157 A1 WO2004112157 A1 WO 2004112157A1 KR 2004001318 W KR2004001318 W KR 2004001318W WO 2004112157 A1 WO2004112157 A1 WO 2004112157A1
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Prior art keywords
ill
nitride semiconductor
electrode layer
mesh
emitting device
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PCT/KR2004/001318
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French (fr)
Inventor
Soo Kun Jeon
Chang Tae Kim
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Epivalley Co., Ltd.
Samsung Electro-Mechanics Co., Ltd
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Publication of WO2004112157A1 publication Critical patent/WO2004112157A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/36—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
    • H01L33/38—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes with a particular shape
    • H01L33/387—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes with a particular shape with a plurality of electrode regions in direct contact with the semiconductor body and being electrically interconnected by another electrode layer

Definitions

  • the present invention relates to a Ill-nitride semiconductor light-emitting device, and more particularly to a Ill-nitride semiconductor light-emitting device in which a mesh-type electrode is included to increase the external quantum efficiency of the device.
  • Ill-nitride semiconductor refers to Al x Gayln ⁇ -x .yN (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1 , x + y ⁇ 1).
  • a semiconductor constituting a light-em ittingdevice has a h igher refractive i ndex than that of external e nvironment (epoxy or a ir layer)
  • most of photons formed by the recombination of electrons and holes remain within the device.
  • Such photons pass through various pathways, including thin films, a substrate and electrodes, before escaping out of the device, and thus, the external quantum efficiency of the device is reduced due to this photon absorption by the components.
  • the external quantum efficiency of the light-emitting device is much influenced by not only the structural shape of the l ight-emitting device b ut also the o ptical p roperties of materials constituting the light-emitting device.
  • a conductive film with a i given thickness is formed on most area of the p-type layer in order to efficiently spread an electric current through the p-type layer. Due to photon absorption by such a conductive film, the external quantum efficiency of the device is reduced. For high efficiency devices, not only conductivity for the uniform current spreading through the entire area but also transparency for high external quantum efficiency must be simultaneously satisfied. However, if the thickness of the conductive film is made thicker in order to increase its conductivity, there will be a problem in that the transparency of the conductive film cannot be ensured.
  • the thickness of the conductive film is made thinner in order to secure its transparency, its resistance becomes too large such that an electric current cannot be uniformly spread on the entire area. Furthermore, if the conductive film is formed on a device having a rough top surface in order to increase the external quantum efficiency of the device, there will be a problem in that the conductive film can be broken.
  • a conventional semi-transparent conductive film consists of Ni/Au-based materials with a thickness of several tens A to several hundreds A, and a photon absorption of about 20-30% occurs by this semi-transparent conductive film.
  • a n a ttempt to o vercome this p roblem
  • a m ethod w as p roposed b y which photon absorption by an conductive film is reduced using a mesh-type electrode with not only high reflectivity but also low contact resistance to p-type GaN, while light efficiently escapes from the portion of p-type GaN surface which is not covered by the mesh-type electrode
  • FIG. 1 is a schematic view illustrating a Ill-nitride semiconductor light-emitting device with a mesh-type electrode according to the prior art.
  • a buffer layer 12 is formed on the top surface of a substrate 11 , and a lower contact layer 13 made of an n-type Ill-nitride semiconductor is formed on the buffer layer 12.
  • an active layer 14 made of a Ill-nitride semiconductor is formed, an upper contact layer 15 made of a p-type Ill-nitride semiconductor is formed on the active layer 14.
  • a reflective film 50 may be formed.
  • a mesh-type electrode layer 17 is formed, and a bonding pad 16 is formed on the mesh-type electrode layer 17.
  • an ohmic contact layer 18 is formed on the exposed surface of the lower contact layer 13, which is not covered by the active layer 14.
  • the size of the mesh-type electrode must be limited. Namely, the minimum size of each opening in the mesh-type electrode must be 1/4 larger than the size of the wavelength of light being escaped, and the maximum size of each opening varies depending on the thickness of the p-type GaN l ayer, b ut must not exceed a bout 1 -4 ⁇ m if the thickness of the p-type
  • GaN layer is larger than 1 ⁇ m. Although the size of each opening needs to be large for the effective escape of light, the current spreading is not sufficiently made since it occurs through t he p-type GaN layer with low conductivity. Thus, in order that the current spreading is sufficiently made, the openings of the mesh-type electrode need to be made fine. However, if the openings are made fine as such, there will be a problem in that light emission to the outside is not sufficiently made, thus reducing the efficiency of the device.
  • the openings n eed to be made fine, but the formation of such a fine pattern causes a problem in the process of forming the mesh-type electrode and reduces the light emission efficiency of the device.
  • the p resent invention has b een m ade to s olve t he a bove-mentioned problems occurring in the prior art, and an object of the present invention is to a Ill-nitride semiconductor light-emitting device in which a mesh-type electrode is included in such a manner that effective current spreading occurs even when the sizes of the openings in the mesh-type electrode are somewhat large, thus increasing the external quantum efficiency of the device.
  • the present invention provides a Ill-nitride semiconductor light-emitting device, which comprises: a lower contact layer formed above the top surface of a substrate and made of an n-type Ill-nitride semiconductor; an active layer formed on a given region of the lower contact layer and made of a Ill-nitride semiconductor; an upper contact layer formed on the active layer and made of a p-type Ill-nitride semiconductor; a transparent electrode l ayer formed on the upper contact layer, the transparent electrode layer having a higher conductivity than that of the upper contact layer; a mesh-type electrode layer formed on the transparent electrode layer in such a manner that the transparent electrode layer is exposed through the openings of the mesh-type electrode layer; and an omhic contact layer formed on an exposed surface of the lower contact layer, which is not covered by the active layer.
  • the present i nvention provides a Ill-nitride semiconductor light-emitting device, which comprises: a lower contact layer formed above the top surface of a substrate and made of an n-type Ill-nitride semiconductor; an active layer formed on a given region of the lower contact layer and made of a Ill-nitride semiconductor; an upper contact layer formed on the active layer and made of a p-type Ill-nitride semiconductor; a mesh-type electrode layer formed on the upper contact layer i n such a m anner that the upper contact l ayer i s exposed through the openings of the mesh-type electrode layer; a transparent electrode layer formed on the mesh-type electrode layer such that it covers the mesh-type electrode layer, the transparent electrode layer having a higher conductivity than that of the upper contact layer; and an omhic contact layer formed on an exposed surface of the lower contact layer, which is not covered by the active layer.
  • the current spreading occurs mainly through the transparent electrode layer rather than the upper contact layer. For this reason, sufficient current spreading can be achieved even when the size of each opening is not small.
  • the present invention provides advantages in that the mesh-type electrode layer does not need to be finely formed as in the prior art, and thus, a portion covered by the mesh-type electrode layer is reduced, resulting in an increase in the external quantum efficiency of the device.
  • the size of each opening may be increased to larger than 4 ⁇ m, so that a complicated patterning process does not need to be carried out.
  • the transparent electrode layer needs to be formed thin in order to ensure its transparency, but a reduction in conductivity caused by this reduction in thickness can be overcome by the presence of the mesh-type electrode layer.
  • FIG. 1 is a schematic view illustrating a Ill-nitride semiconductor light-emitting device with a mesh-type electrode according to a prior art.
  • FIGs. 2 to 4 are drawings illustrating a Ill-nitride semiconductor light-emitting device according to a first embodiment of the present invention.
  • FIG. 5 is a schematic view illustrating a Ill-nitride semiconductor light-emitting d evice according to a s econd e mbodiment of the present
  • FIGS. 2 and 5 the same reference numerals as in FIG. 1 denote components having the same function as in FIG. 1 , and the explanation of the components will be omitted.
  • FIG. 2 is a schematic view illustrating a Ill-nitride semiconductor light-emitting device according to a first embodiment of the present invention.
  • the Ill-nitride semiconductor light-emitting device is characterized in that a transparent electrode layer 26 is formed on an upper contact layer 15 before a mesh-type electrode layer 27 is formed.
  • a transparent electrode layer 26 is formed on an upper contact layer 15 before a mesh-type electrode layer 27 is formed.
  • the n+ o r p+ Ill-nitride semiconductor layer 25 or the supper-lattice layer made of the n-or p-type Ill-nitride semiconductor material is interposed. Through the openings of the mesh-type electrode layer 27, the transparent electrode layer 26 is exposed.
  • the transparent electrode layer 26 and the mesh-type electrode layer 27 are made of either one selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium, or a combination of two or more selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium.
  • the openings of the mesh-type electrode layer 27 may have any shape, such as a circular, oval, rectangular, triangular or hexagonal shape.
  • the reflective layer 50 is made of either one selected from a group consisting of aluminum, silver, nickel, chromium, titanium and rhodium, or a combination of two or more selected from a group consisting of aluminum, silver, nickel, chromium, titanium and rhodium.
  • the reflective film 50 prevents light from escaping through the substrate 11 , thus improving the performance of the device.
  • the transparent electrode layer 26 preferably has such a high transparency that light emitted from the active layer 14 can easily escape to the outside.
  • the transparent electrode layer 26 must be able to uniformly supply an electric current to the entire area of the active layer 14. As the transparency of the transparent electrode layer 26 increases, the absorption rate of light passing through the transparent electrode layer 26 via various pathways reduces. In order to uniformly supply an electric current to the active layer 14, the transparent electrode layer 26 must have low contact resistance to the upper contact layer 15. Of course, if the supper-lattice layer 25 is additionally formed, the transparent electrode layer 26 must have low contact resistance to the supper-lattice layer 25.
  • the mesh-type electrode 27 functions to uniformly transfer an electric current to the transparent electrode layer 26 and may be formed to a relatively larger thickness than that of the transparent electrode 26.
  • a conventional semi-transparent conductive film is made of materials having a thickness of several tens A to several hundreds A, and its thickness influences its transparency and conductivity heavily.
  • the transparent electrode 26 is formed to a thinner thickness of a few A to several tens A. This decrease in the thickness of the transparent electrode 26 can provide a sharp increase of about 10-30% in its transparency as compared to that of the prior art, but results in a reduction in its conductivity, thus making it impossible to spread a current uniformly.
  • the mesh-type electrode layer 27 is formed on the transparent electrode layer 26 such that the mesh-type electrode layer 27 allows an electric current to be uniformly supplied to the transparent electrode layer 26 covering most area of the device.
  • Each of the transparent electrode layer 26 and the mesh-type electrode layer 27 preferably has a thickness of 0.0001-10 ⁇ m.
  • the current spreading will not be sufficiently made since the conductivity of a p-type Ill-nitride semiconductor constituting the upper contact layer 15 is low.
  • the upper contact layer 15 has a thickness of 0.01-2 ⁇ m, the current spreading to the entire area of the device will easily occur and operation voltage will also be reduced, since the transparent electrode layer 26 and/or the supper-lattice layer 25, which has good conductivity, exist below the mesh-type electrode layer 27. For this reason, even when the size of each opening in the mesh-type electrode is not fine, the current spreading can be sufficiently achieved, thus eliminating a need for a finely-patterning process as required in the prior art.
  • the openings of the mesh-type electrode layer 27 preferably have a size of 0.1 ⁇ m-1 mm and the mesh-type electrode 27 preferably has a width of 0.1
  • the total area covered by the mesh-type electrode layer 27 preferably is 10-90% of the surface of the transparent electrode layer 26.
  • FIG. 3 is a drawing illustrating the pathway of current spreading in the device of FIG. 2. As shown in FIG. 3, an electric current is first spread through the mesh-type electrode layer 27 and then spread through the transparent electrode layer 26 and the supper-lattice layer 25 to the remaining portions of the device.
  • the device according to the present invention shows an average of about 15-18% increase in power as compared to that of the prior art, although this increase in power can vary depending on the size of the mesh-type electrode and the thicknesses of the electrodes.
  • FIG. 4 is a schematic view illustrating a Ill-nitride semiconductor light-emitting device according to a second embodiment of the present invention.
  • the device of FIG. 4 has a structure in which a mesh-type electrode layer 27 is first formed, on which the transparent electrode layer 26 is then formed. If the mesh-type electrode layer 27 is formed of a metal with high reflectivity, there will be an advantage in that light absorption by the electrode is reduced since light emitted from the active layer 14 first meets the mesh-type electrode 27 with high reflectivity.

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Abstract

According to the present invention, the current spreading occurs mainly through the transparent electrode layer (27) rather than the upper contact layer (15). For this reason, sufficient current spreading can be achieved even when the size of each opening is not small, and the present invention provides advantages in that the mesh-type electrode layer (27) does not need to be finely formed as in the prior art, and thus, a portion covered by the mesh-type electrode layer (27) is reduced, resulting in an increase in the external quantum efficiency of the device. Particularly, even when the thickness of the upper contact layer (15) is thin (<0.5 µm), the size of each opening in the mesh-type electrode layer (27) may be increased to larger than 4 µm, so that a complicated patterning process does not need to be carried out.

Description

III-NITRIDE COMPOUND SEMICONDUCTOR LIGHT EMITTING DEVICE WITH MESH TYPE ELECTRODE
[Technical Field] The present invention relates to a Ill-nitride semiconductor light-emitting device, and more particularly to a Ill-nitride semiconductor light-emitting device in which a mesh-type electrode is included to increase the external quantum efficiency of the device. As used herein, the term "Ill-nitride semiconductor" refers to AlxGaylnι-x.yN (0 ≤ x < 1, 0 ≤ y < 1 , x + y < 1).
[Background Art]
Generally, since a semiconductor constituting a light-em ittingdevice has a h igher refractive i ndex than that of external e nvironment (epoxy or a ir layer), most of photons formed by the recombination of electrons and holes remain within the device. Such photons pass through various pathways, including thin films, a substrate and electrodes, before escaping out of the device, and thus, the external quantum efficiency of the device is reduced due to this photon absorption by the components. Namely, the external quantum efficiency of the light-emitting device is much influenced by not only the structural shape of the l ight-emitting device b ut also the o ptical p roperties of materials constituting the light-emitting device.
Particularly, in a GaN-based Ill-nitride semiconductor light-emitting device, because of the low conductivity of p-type GaN, a conductive film with a i given thickness is formed on most area of the p-type layer in order to efficiently spread an electric current through the p-type layer. Due to photon absorption by such a conductive film, the external quantum efficiency of the device is reduced. For high efficiency devices, not only conductivity for the uniform current spreading through the entire area but also transparency for high external quantum efficiency must be simultaneously satisfied. However, if the thickness of the conductive film is made thicker in order to increase its conductivity, there will be a problem in that the transparency of the conductive film cannot be ensured. On the other hand, if the thickness of the conductive film is made thinner in order to secure its transparency, its resistance becomes too large such that an electric current cannot be uniformly spread on the entire area. Furthermore, if the conductive film is formed on a device having a rough top surface in order to increase the external quantum efficiency of the device, there will be a problem in that the conductive film can be broken.
A conventional semi-transparent conductive film consists of Ni/Au-based materials with a thickness of several tens A to several hundreds A, and a photon absorption of about 20-30% occurs by this semi-transparent conductive film. In a n a ttempt to o vercome this p roblem, a m ethod w as p roposed b y which photon absorption by an conductive film is reduced using a mesh-type electrode with not only high reflectivity but also low contact resistance to p-type GaN, while light efficiently escapes from the portion of p-type GaN surface which is not covered by the mesh-type electrode [Lester et. al, "Light emitting device having a finely-patterned reflective contact", US Pat No.6,291 ,839].
FIG. 1 is a schematic view illustrating a Ill-nitride semiconductor light-emitting device with a mesh-type electrode according to the prior art. Referring to FIG. 1 , a buffer layer 12 is formed on the top surface of a substrate 11 , and a lower contact layer 13 made of an n-type Ill-nitride semiconductor is formed on the buffer layer 12. On a given region of the lower contact layer 13, an active layer 14 made of a Ill-nitride semiconductor is formed, an upper contact layer 15 made of a p-type Ill-nitride semiconductor is formed on the active layer 14. On the bottom surface of the substrate 11, a reflective film 50 may be formed.
On the upper contact layer 15, a mesh-type electrode layer 17 is formed, and a bonding pad 16 is formed on the mesh-type electrode layer 17. On the exposed surface of the lower contact layer 13, which is not covered by the active layer 14, an ohmic contact layer 18 is formed.
The efficient current spreading in the mesh-type electrode, and the escape of p hotons from the device, must be a chieved, but in order to meet such requirements, the size of the mesh-type electrode must be limited. Namely, the minimum size of each opening in the mesh-type electrode must be 1/4 larger than the size of the wavelength of light being escaped, and the maximum size of each opening varies depending on the thickness of the p-type GaN l ayer, b ut must not exceed a bout 1 -4 μm if the thickness of the p-type
GaN layer is larger than 1 μm. Although the size of each opening needs to be large for the effective escape of light, the current spreading is not sufficiently made since it occurs through t he p-type GaN layer with low conductivity. Thus, in order that the current spreading is sufficiently made, the openings of the mesh-type electrode need to be made fine. However, if the openings are made fine as such, there will be a problem in that light emission to the outside is not sufficiently made, thus reducing the efficiency of the device. Particularly, if the p-type GaN layer has a thin thickness ( <0.5 μm), the openings n eed to be made fine, but the formation of such a fine pattern causes a problem in the process of forming the mesh-type electrode and reduces the light emission efficiency of the device.
[Disclosure] [Technical Problem]
The p resent invention has b een m ade to s olve t he a bove-mentioned problems occurring in the prior art, and an object of the present invention is to a Ill-nitride semiconductor light-emitting device in which a mesh-type electrode is included in such a manner that effective current spreading occurs even when the sizes of the openings in the mesh-type electrode are somewhat large, thus increasing the external quantum efficiency of the device. [Technical Solution]
To achieve the above object, the present invention provides a Ill-nitride semiconductor light-emitting device, which comprises: a lower contact layer formed above the top surface of a substrate and made of an n-type Ill-nitride semiconductor; an active layer formed on a given region of the lower contact layer and made of a Ill-nitride semiconductor; an upper contact layer formed on the active layer and made of a p-type Ill-nitride semiconductor; a transparent electrode l ayer formed on the upper contact layer, the transparent electrode layer having a higher conductivity than that of the upper contact layer; a mesh-type electrode layer formed on the transparent electrode layer in such a manner that the transparent electrode layer is exposed through the openings of the mesh-type electrode layer; and an omhic contact layer formed on an exposed surface of the lower contact layer, which is not covered by the active layer.
In addition, the present i nvention provides a Ill-nitride semiconductor light-emitting device, which comprises: a lower contact layer formed above the top surface of a substrate and made of an n-type Ill-nitride semiconductor; an active layer formed on a given region of the lower contact layer and made of a Ill-nitride semiconductor; an upper contact layer formed on the active layer and made of a p-type Ill-nitride semiconductor; a mesh-type electrode layer formed on the upper contact layer i n such a m anner that the upper contact l ayer i s exposed through the openings of the mesh-type electrode layer; a transparent electrode layer formed on the mesh-type electrode layer such that it covers the mesh-type electrode layer, the transparent electrode layer having a higher conductivity than that of the upper contact layer; and an omhic contact layer formed on an exposed surface of the lower contact layer, which is not covered by the active layer. [Advantageous Effects]
According to the present invention, the current spreading occurs mainly through the transparent electrode layer rather than the upper contact layer. For this reason, sufficient current spreading can be achieved even when the size of each opening is not small.
Accordingly, the present invention provides advantages in that the mesh-type electrode layer does not need to be finely formed as in the prior art, and thus, a portion covered by the mesh-type electrode layer is reduced, resulting in an increase in the external quantum efficiency of the device. Particularly, even when the thickness of the upper contact layer is thin (<0.5 μm), the size of each opening may be increased to larger than 4 μm, so that a complicated patterning process does not need to be carried out.
Furthermore, the transparent electrode layer needs to be formed thin in order to ensure its transparency, but a reduction in conductivity caused by this reduction in thickness can be overcome by the presence of the mesh-type electrode layer.
[Description of Drawings]
FIG. 1 is a schematic view illustrating a Ill-nitride semiconductor light-emitting device with a mesh-type electrode according to a prior art.
FIGs. 2 to 4 are drawings illustrating a Ill-nitride semiconductor light-emitting device according to a first embodiment of the present invention.
FIG. 5 is a schematic view illustrating a Ill-nitride semiconductor light-emitting d evice according to a s econd e mbodiment of the present
invention.
[Mode for Invention] Hereinafter, the present invention will be described in detail with reference to the accompanying figures. In FIGS. 2 and 5, the same reference numerals as in FIG. 1 denote components having the same function as in FIG. 1 , and the explanation of the components will be omitted.
The following embodiments are presented for illustrative purpose only, and many modifications to these embodiments can be made by any person skilled i n the art without departing from the technical concept of the present invention. Thus, these embodiments are not intended to limit the scope of the present invention.
Embodiment 1 FIG. 2 is a schematic view illustrating a Ill-nitride semiconductor light-emitting device according to a first embodiment of the present invention.
The Ill-nitride semiconductor light-emitting device is characterized in that a transparent electrode layer 26 is formed on an upper contact layer 15 before a mesh-type electrode layer 27 is formed. Preferably, between the upper contact layer 15 and the transparent e lectrode I ayer 26, the n+ o r p+ Ill-nitride semiconductor layer 25 or the supper-lattice layer made of the n-or p-type Ill-nitride semiconductor material is interposed. Through the openings of the mesh-type electrode layer 27, the transparent electrode layer 26 is exposed.
Preferably, the transparent electrode layer 26 and the mesh-type electrode layer 27 are made of either one selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium, or a combination of two or more selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium.
The openings of the mesh-type electrode layer 27 may have any shape, such as a circular, oval, rectangular, triangular or hexagonal shape.
On the bottom surface of a substrate 11, a reflective film 50 with a reflectivity of more than 60% to light emitted from an active layer 14.
Preferably, the reflective layer 50 is made of either one selected from a group consisting of aluminum, silver, nickel, chromium, titanium and rhodium, or a combination of two or more selected from a group consisting of aluminum, silver, nickel, chromium, titanium and rhodium. The reflective film 50 prevents light from escaping through the substrate 11 , thus improving the performance of the device.
The transparent electrode layer 26 preferably has such a high transparency that light emitted from the active layer 14 can easily escape to the outside. The transparent electrode layer 26 must be able to uniformly supply an electric current to the entire area of the active layer 14. As the transparency of the transparent electrode layer 26 increases, the absorption rate of light passing through the transparent electrode layer 26 via various pathways reduces. In order to uniformly supply an electric current to the active layer 14, the transparent electrode layer 26 must have low contact resistance to the upper contact layer 15. Of course, if the supper-lattice layer 25 is additionally formed, the transparent electrode layer 26 must have low contact resistance to the supper-lattice layer 25. The mesh-type electrode 27 functions to uniformly transfer an electric current to the transparent electrode layer 26 and may be formed to a relatively larger thickness than that of the transparent electrode 26.
A conventional semi-transparent conductive film is made of materials having a thickness of several tens A to several hundreds A, and its thickness influences its transparency and conductivity heavily. According to the present invention, the transparent electrode 26 is formed to a thinner thickness of a few A to several tens A. This decrease in the thickness of the transparent electrode 26 can provide a sharp increase of about 10-30% in its transparency as compared to that of the prior art, but results in a reduction in its conductivity, thus making it impossible to spread a current uniformly. To solve this problem, according to the present invention, after the transparent electrode layer 26 is formed to a thinner thickness of a few A to several tens A, the mesh-type electrode layer 27 is formed on the transparent electrode layer 26 such that the mesh-type electrode layer 27 allows an electric current to be uniformly supplied to the transparent electrode layer 26 covering most area of the device. Each of the transparent electrode layer 26 and the mesh-type electrode layer 27 preferably has a thickness of 0.0001-10 μm.
If the mesh-type electrode layer 27 is formed just on the upper contact layer 15 as in the prior art, the current spreading will not be sufficiently made since the conductivity of a p-type Ill-nitride semiconductor constituting the upper contact layer 15 is low. However, in the present invention, even when the upper contact layer 15 has a thickness of 0.01-2 μm, the current spreading to the entire area of the device will easily occur and operation voltage will also be reduced, since the transparent electrode layer 26 and/or the supper-lattice layer 25, which has good conductivity, exist below the mesh-type electrode layer 27. For this reason, even when the size of each opening in the mesh-type electrode is not fine, the current spreading can be sufficiently achieved, thus eliminating a need for a finely-patterning process as required in the prior art.
It is not desirable that the mesh-type electrode layer 27 interferes with light emission to lower the external light-emitting efficiency of the device. Thus, the openings of the mesh-type electrode layer 27 preferably have a size of 0.1 μm-1 mm and the mesh-type electrode 27 preferably has a width of 0.1
μm-1 mm. Also, the total area covered by the mesh-type electrode layer 27 preferably is 10-90% of the surface of the transparent electrode layer 26.
FIG. 3 is a drawing illustrating the pathway of current spreading in the device of FIG. 2. As shown in FIG. 3, an electric current is first spread through the mesh-type electrode layer 27 and then spread through the transparent electrode layer 26 and the supper-lattice layer 25 to the remaining portions of the device.
As can be seen in FIG. 5, the device according to the present invention shows an average of about 15-18% increase in power as compared to that of the prior art, although this increase in power can vary depending on the size of the mesh-type electrode and the thicknesses of the electrodes.
Embodiment 2 FIG. 4 is a schematic view illustrating a Ill-nitride semiconductor light-emitting device according to a second embodiment of the present invention. Unlike the device of FIG. 2, the device of FIG. 4 has a structure in which a mesh-type electrode layer 27 is first formed, on which the transparent electrode layer 26 is then formed. If the mesh-type electrode layer 27 is formed of a metal with high reflectivity, there will be an advantage in that light absorption by the electrode is reduced since light emitted from the active layer 14 first meets the mesh-type electrode 27 with high reflectivity.

Claims

1. A Ill-nitride semiconductor light-emitting device comprising: a lower contact layer formed above the top surface of a substrate and made of an n-type Ill-nitride semiconductor; an active layer formed on a given region of the lower contact layer and made of a Ill-nitride semiconductor; an upper contact layer formed on the active layer and made of a p-type Ill-nitride semiconductor; a transparent electrode layer formed on the upper contact layer, the transparent electrode layer having a higher conductivity than that of the upper contact layer; a mesh-type electrode layer having a plurality of openings and formed on the transparent electrode layer in such a manner that the transparent electrode layer is exposed through the plurality of the openings of the mesh-type electrode layer; and an omhic contact layer formed on an exposed surface of the lower contact layer, the exposed surface of the lower contact layer not being covered by the active layer.
2. The Ill-nitride semiconductor light-emitting device of claim 1 further comprising: an n+ or p+ Ill-nitride semiconductor layer or a supper-lattice layer made of the n- or p-type Ill-nitride semiconductor material interposed between the upper contact layer and the transparent electrode layer.
3. The Ill-nitride semiconductor light-emitting device of claim 1 , wherein the transparent electrode layer is made of either one selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium, or a combination of two or more selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium.
4. The Ill-nitride semiconductor light-emitting device of claim 1 , wherein the mesh-type electrode layer is made of either one selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium, or a combination of two or more selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium.
5. The Ill-nitride semiconductor light-emitting device of claim 1 , wherein the transparent electrode layer has a thickness of 0.0001-10 μm.
6. The Ill-nitride semiconductor light-emitting device of claim 1 , wherein the mesh-type electrode layer has a thickness of 0.0001-10 μm.
7. The Ill-nitride semiconductor light-emitting device of claim 1 , wherein the upper contact layer has a thickness of 0.01-2 μm.
8. The Ill-nitride semiconductor light-emitting device of claim 1 , wherein each of the plurality of the openings of the mesh-type electrode layer has a size, the size being in a range of 0.1 μm-1 mm.
9. The Ill-nitride semiconductor light-emitting device of claim 1 , wherein the mesh-type electrode layer has a width of 0.1 μm-1 mm.
10. The Ill-nitride semiconductor light-emitting device of claim 1, wherein the total area covered by the mesh-type electrode layer is 10-90% of the surface of the transparent electrode layer.
11. The Ill-nitride semiconductor light-emitting device of claim 1, wherein the plurality of the openings of the mesh-type electrode layer have a shape, the shape being selected from a group consisting of a circular shape, an oval shape, a rectangular shape, a triangular shape and a hexagonal shape.
12. The Ill-nitride semiconductor light-emitting device of claim 1, further comprising: a reflective film formed on the bottom surface of the substrate, the reflective film made of either one selected from a group consisting of aluminum, silver, nickel, chromium, titanium and rhodium, or a combination of two or more selected from a group consisting of aluminum, silver, nickel, chromium, titanium and rhodium.
13. A Ill-nitride semiconductor light-emitting device comprising: a lower contact layer formed above the top surface of a substrate and made of an n-type Ill-nitride semiconductor; an active layer formed on a given region of the lower contact layer and made of a Ill-nitride semiconductor; an upper contact layer formed on the active layer and made of a p-type Ill-nitride semiconductor; a mesh-type electrode layer having a plurality of openings and formed on the upper contact layer i n s uch a m anner that the upper contact l ayer i s exposed through the plurality of the openings of the mesh-type electrode layer; a transparent electrode layer formed on the mesh-type electrode layer to cover the mesh-type electrode layer, the transparent electrode layer having a higher conductivity than that of the upper contact layer; and an omhic contact layer formed on an exposed surface of the lower contact layer, the exposed surface of the lower contact layer not being covered by the active layer.
14. The Ill-nitride semiconductor light-emitting device of claim 13 further comprising: an n+ or p+ Ill-nitride semiconductor layer or a supper-lattice layer made of the n- or p-type Ill-nitride semiconductor material interposed between the upper contact layer and the mesh-type electrode layer.
15. The Ill-nitride semiconductor light-emitting device of claim 13, wherein the transparent electrode layer is made of either one selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium, or a combination of two or more selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium.
16. The Ill-nitride semiconductor light-emitting device of claim 13, wherein the mesh-type electrode layer is made of either one selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium, or a combination of two or more selected from a group consisting of nickel, gold, silver, platinum, chromium, titanium, aluminum and rhodium.
17. The Ill-nitride semiconductor light-emitting device of claim 13, wherein the transparent electrode layer has a thickness of 0.0001-10 μm.
18. The Ill-nitride semiconductor light-emitting device of claim 13, wherein the mesh-type electrode layer has a thickness of 0.0001-10 μm.
19. The Ill-nitride semiconductor light-emitting device of claim 13, wherein the upper contact layer has a thickness of 0.01-2 μm.
20. The Ill-nitride semiconductor light-emitting device of claim 13, wherein each of the plurality of the openings of the mesh-type electrode layer has a size, the size being in a range of 0.1 μm-1 mm.
21. The Ill-nitride semiconductor light-emitting device of claim 13, wherein the mesh-type electrode layer has a width of 0.1 μm-1 mm.
22. The Ill-nitride semiconductor light-emitting device of claim 13, wherein the mesh-type electrode layer has a surface corresponding to 10-90% of the surface of the transparent electrode layer.
23. The Ill-nitride semiconductor light-emitting device of claim 13, wherein the plurality the openings of the mesh-type electrode layer have a shape, the shape being selected from a group consisting of a circular shape, an oval shape, a rectangular shape, a triangular shape and a hexagonal shape.
24. The Ill-nitride semiconductor light-emitting device of claim 13, further comprising: a reflective film formed on the bottom surface of the substrate, the reflective film made of either one selected from a group consisting of aluminum, silver, nickel, chromium, titanium and rhodium, or a combination of two or more selected from a group consisting of aluminum, silver, nickel, chromium, titanium and rhodium.
PCT/KR2004/001318 2003-06-03 2004-06-03 Iii-nitride compound semiconductor light emitting device with mesh type electrode WO2004112157A1 (en)

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