KR100737821B1 - Light emitting device and the fabrication method thereof - Google Patents

Abstract

A light emitting device and its fabricating method are provided to reduce noncontact resistance using a Ni/Au ohmic transparent electrode, so that carriers supplied from an exterior undergoes uniform current spreading. An N-type semiconductor layer(400), an active layer(500) and a P-type semiconductor layer(600) are formed on a substrate(100), and a Ni metal layer is formed on the P-type semiconductor layer. An Au metal layer is formed on the Ni metal layer, and then a plasma process is performed on the Au metal layer using an oxygen containing gas. The Ni metal layer and the Au metal layer are annealed under oxygen atmosphere to form an ohmic transparent electrode(700) consisting of Ni and Au.

Description

LIGHT EMITTING DEVICE AND THE FABRICATION METHOD THEREOF

1 is a cross-sectional view of a light emitting diode according to an embodiment of the present invention.

2 is a process flowchart illustrating a manufacturing process of a light emitting diode according to an embodiment of the present invention.

3 and 4 are cross-sectional views of the manufacturing process of FIG. 2.

5 is an XRD diffraction peak graph of an ohmic electrode prepared according to a light emitting device manufacturing method according to an embodiment of the present invention.

6 is a graph showing the optical output power of the ohmic transparent electrode according to a comparative example and the ohmic transparent electrode according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100: sapphire substrate 200: buffer layer

300: Undoped GaN layer 400: N-type GaN layer

500: active layer 600: P-type GaN layer

700: ohmic transparent electrode 710: Ni metal layer

720: Au metal layer 800a, 800b: electrode pad

The present invention relates to a light emitting device and a method of manufacturing the same, and more particularly, to a light emitting device having an ohmic transparent electrode that can improve the luminous efficiency and a manufacturing method thereof.

Group III-V compound semiconductors used to fabricate various light emitting devices provide superior performance in applications such as high speed and high temperature electronics, light emitters and photo detectors. Particularly, gallium nitride (GaN) included in gallium nitride compound semiconductors has a bandgap required for a blue laser and a light emitting diode emitting a blue wavelength spectrum. This is increasing. In addition, alloys of aluminum nitride (AlN), indium nitride (InN) and gallium nitride (GaN) provide spectra across the visible range.

In order to implement a light emitting device such as a light emitting diode or a laser diode using a nitride compound semiconductor, for example, gallium nitride (GaN) semiconductor, an ohmic contact structure between the semiconductor and the N-type and P-type electrodes is very important. In particular, the ohmic contact structure between the P-type cladding layer and the electrode is an important technical part so as to influence the performance of the nitride-based light emitting device.

Among such nitride-based light emitting devices, light emitting diodes are classified into top-emitting light emitting diodes (TLEDS) and flip-chip light emitting diodes (FCLEDS).

The top emit light emitting diode is formed such that light is emitted through the P-type ohmic electrode layer in contact with the P-type cladding layer. Therefore, the P-type ohmic electrode layer is required to have high light transmittance and low specific contact resistance and sheet resistance values.

The flip chip type light emitting diode has a structure that emits light to the outside through a transparent insulating substrate. Therefore, the P-type ohmic electrode layer in contact with the P-type cladding layer is required to have high light reflectance and low specific contact resistance and sheet resistance values.

However, most electrode materials have a reverse relationship between optical and electrical characteristics, and due to poor electrical characteristics such as low current injection and current spreading of the P-type cladding layer, It is not easy to develop a P-type ohmic electrode layer suitable for an emitter or flip chip type light emitting diode structure.

Currently, the P-type ohmic electrode layer of the top-emitting type light emitting device is a metal thin film structure based on transition metals such as nickel (Ni) metal, and is oxidized semi-transparent nickel (Ni) / gold (Au) metal. Thin films are widely used.

The metal thin film based on the nickel (Ni) metal is heat-treated in an oxygen (O ₂ ) atmosphere to form a semi-transparent ohmic contact layer having a specific contact resistance of about 10 ⁻³ to 10 ⁻⁴ Ω cm ² . It is reported to form.

This low specific contact resistance is due to the island-like shape of nickel oxide (NiO), which is a P-type semiconductor oxide, at the interface between P-type gallium nitride and nickel (Ni) during heat treatment in an oxygen (O ₂ ) temperature range of 500 ° C to 600 ° C It is formed between the Au formed in the upper portion and the upper layer to reduce the Schottky barrier height (SBH), thereby easily supplying a multi-carrier hole near the P-type gallium nitride surface. To increase the effective carrier concentration near the surface of the P-type gallium nitride.

On the other hand, when nickel (Ni) / gold (Au) is contacted with P-type gallium nitride and heat-treated, Mg-H intermetallic compounds are removed to remove magnesium (Mg) dopant on the P-type gallium nitride surface. Reactivation increases the concentration of these effective carrier concentrations above 10 ^{19 on} the surface of gallium nitride, resulting in tunneling conduction between the gallium nitride and the electrode layer (nickel oxide). It is understood to exhibit conductive properties.

However, the top-emitting type light emitting diode using a translucent electrode thin film formed of oxidized nickel / gold has low light utilization efficiency, making it difficult to realize a high capacity and high brightness light emitting device.

SUMMARY OF THE INVENTION An object of the present invention is to improve the light utilization efficiency of an ohmic transparent electrode in a light emitting device in which an N-type semiconductor layer, an active layer, and a P-type semiconductor layer are stacked and an ohmic transparent electrode made of Ni / Au is formed thereon. It is to let.

According to an aspect of the present invention to achieve these technical problems, the step of sequentially forming an N-type semiconductor layer, an active layer, a P-type semiconductor layer on a substrate, forming a Ni metal layer on the P-type semiconductor layer, Forming an Au metal layer on the Ni metal layer, performing a plasma treatment using an oxygen-containing gas on the Au metal layer, and annealing the Ni metal layer and the Au metal layer in an oxygen atmosphere to form Ni / Au. It provides a method of manufacturing a light emitting device comprising the step of forming an electrode.

The plasma treatment is 50-200 W, O ₂ It may be performed for 30-60 SCCM, 40-240 sec at 70-85 mTorr.

The annealing treatment may be performed for 5-10 minutes in an air atmosphere containing an oxygen-containing gas at a temperature of 350 ℃-700 ℃.

Etching a portion of the P-type semiconductor layer, the active layer, and the N-type semiconductor layer to expose a portion of the N-type semiconductor layer, and forming an electrode on the Ni / Au ohmic transparent electrode and the exposed N-type semiconductor layer It may further comprise the step.

According to another aspect of the invention, there is provided a substrate, an N-type semiconductor layer formed on the substrate, an active layer formed on the N-type semiconductor layer, a P-type semiconductor layer formed on the active layer, and a Ni metal layer on the P-type semiconductor layer; Provided is a light emitting device including a Ni / Au ohmic transparent electrode formed by laminating an Au metal layer and performing a plasma treatment using an oxygen-containing gas and an annealing treatment in an oxygen atmosphere.

The light emitting device exposes a portion of the N-type semiconductor layer by etching a portion of the P-type semiconductor layer, the active layer, and the N-type semiconductor layer, and then is formed on the Ni / Au ohmic transparent electrode and the exposed N-type semiconductor layer. It may further include an electrode.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, lengths, thicknesses, and the like of layers and regions may be exaggerated for convenience. Like numbers refer to like elements throughout.

1 is a cross-sectional view of a light emitting diode according to an embodiment of the present invention.

Referring to FIG. 1, a light emitting diode according to an embodiment of the present invention may include a substrate 100, a buffer layer 200, an undoped GaN layer 300, an N-type GaN layer 400, an active layer 500, and a P. A type GaN layer 600, an ohmic transparent electrode 700 made of Ni / Au, and electrode pads 800a and 800b.

The substrate 100 is made of a sapphire substrate. In addition to the sapphire substrate, the substrate 100 may be a spinel substrate, an Si substrate, a porous Si substrate, an SiC substrate, a ZnO substrate, a GaAs substrate, or a GaN substrate.

Buffer layer 200, Undoped GaN layer 300, N-type GaN layer 400, active layer 500, P-type GaN layer 600 is metal organic chemical vapor deposition (MOCVD), molecular beam growth (MBE) or hydride It may be formed using a gas phase growth (HVPE) method and the like. It can also be formed continuously in the same process chamber.

The buffer layer 200 is interposed to mitigate the lattice mismatch between the substrate 100 and the undoped GaN layer 300. For example, the buffer layer 200 may be Al _x Ga _{1 - x} N (0≤x≤1), which may be metal organic chemical vapor deposition (MOCVD) or hydride vapor phase epitaxy (HVPE). Or molecular beam growth (MBE), metalorganic chemical vapor phase epitaxy (MOCVPE), or the like.

When the buffer layer 200 is formed, trimethyl aluminum (TMAl, Al (CH ₃ ) ₃ ) and trimethyl gallium (TMG, Ga (CH ₃ ) ₃ ) are used as source gases of Al and Ga. Ammonia (NH ₃ ) is used as the reaction gas. These source gases and reaction gases may be introduced into the reaction chamber, and the buffer layer 200 may be formed at 400 to 1200 ° C.

The undoped GaN layer 300 is grown to grow the N-type GaN layer 400 on the buffer layer 200.

The N-type GaN layer 400 may be formed by doping silicon (Si) in GaN.

The active layer 500 is an area where electrons and holes are recombined and includes InGaN / GaN. The emission wavelength emitted from the light emitting diode is determined by the type of material constituting the active layer 500. The active layer 500 may be a multilayer film in which a quantum well layer and a barrier layer are repeatedly formed. A quantum well layer and the barrier layer may be a semiconductor layer 2-to 4 won the compounds represented by the general formula _{Al x In y Ga 1 -x- y} N (0≤x, y, x + y≤1).

The P-type GaN layer 600 may be formed by doping zinc (Zn) or magnesium (Mg) on GaN.

The ohmic transparent electrode 700 is formed on the P-type GaN layer 600. The ohmic transparent electrode 700 transmits light emitted from the active layer 500 to the outside in a plate shape.

The ohmic transparent electrode 700 may be formed of a transparent material such as Ni / Au.

The ohmic transparent electrode 700 is formed by laminating a Ni metal layer and an Au metal layer on the P-type GaN layer 600 and then performing plasma treatment using an oxygen-containing gas and annealing in an oxygen atmosphere.

The ohmic transparent electrode 700 evenly distributes the current input through the electrode pad 800a to increase the luminous efficiency.

The electrode pads 800a and 800b are formed on the ohmic transparent electrode 700 and on the N-type GaN layer 400. The electrode pads 800a and 800b are connected to a lead (not shown) by a wire to receive power from an external power source.

2 is a flowchart illustrating a manufacturing process of a light emitting diode according to an exemplary embodiment of the present invention, and FIGS. 3 to 4 are cross-sectional views illustrating a manufacturing process thereof.

2 and 3 to prepare a sapphire substrate 100 (S1).

A buffer layer 200 is formed on the substrate 100 (S2).

The buffer layer 200 may include metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE) or molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MBE). It can be formed using a method (metalorganic chemical vapor phase epitaxy, MOCVPE) and the like.

The buffer layer 200 may be grown using any one of the above-described crystal growth methods at a pressure of about 10 torr to about 780 torr at 400 to 1200 ° C.

After the buffer layer 200 is formed, an undoped GaN layer 300 having a thickness of 1 μm, an N-type GaN layer 400 having a thickness of 2 μm, an active layer 500 and a P-type GaN layer having a thickness of 0.15 μm are formed on the buffer layer 200. (600) grow in order at 1000 ℃ (S3)

Undoped GaN layer 300, N-type GaN layer 400, active layer 500, P-type GaN layer 600 is a metal organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE) or molecular beam growth method ( MBE) and the like. It can also be formed continuously in the same process chamber.

After the P-type GaN layer 600 is formed, Ni metal layer 710 is formed on the P-type GaN layer 600 by MOCVD (Metal Organic Chemical Vapor Deposition) or PALE (Pused Atomic Layer Epitaxy) method (S4). . The deposition thickness of the Ni metal layer 710 may be, for example, 10 nm.

When the Ni metal layer 710 is formed on the P-type GaN layer 600, the Au metal layer 720 is deposited on the Ni metal layer 710 by MOCVD (Metal Organic Chemical Vapor Deposition) or PALE (Pused Atomic Layer Epitaxy). It forms (S5). The deposition thickness of the Au metal layer 720 may be, for example, 10 nm.

When the Ni metal layer 710 and the Au metal layer 720 are formed on the P-type GaN layer 600, oxygen plasma treatment is performed on the Ni metal layer 710 and the Au metal layer 720 using an oxygen-containing gas (S6). .

Oxygen plasma treatment is an oxygen radical reaction using plasma, and the supply of oxygen is controlled by a mass floe controller (MFC).

Here, the oxygen containing gas may be one or more gases selected from O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ and H ₂ O or a mixed gas containing two or more of these gases. The oxygen containing gas may also be a mixed gas containing at least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ and H ₂ O and at least one inert gas, or O ₂ , It may be a mixed gas containing a mixture of two or more of O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ and H ₂ O and one or more inert gases. In short, oxygen-containing gas means a gas containing oxygen atoms or a gas of molecules containing oxygen atoms.

For example, oxygen plasma treatment is 50-200 W, O ₂ It is carried out at 30-60 SCCM, 70-85 mTorr for 40-240 sec.

When the oxygen plasma treatment is performed on the Au metal layer 720, the surface of the Au metal layer 720 is roughened by oxygen particles. If the surface of the Au metal layer 720 is roughened, when the annealing process is performed in an air atmosphere using an oxygen-containing gas, the probability of encountering Ni and oxygen on the surface of the Au metal layer 720 is further increased to further promote oxidation of Ni. The formation of NiO can be better.

When the oxygen plasma treatment is completed on the Ni metal layer 710 and the Au metal layer 720, annealing is performed on the Ni metal layer 710 and the Au metal layer 720 (S8).

The annealing treatment is performed at a temperature of 350 ° C.-700 ° C., preferably at 530 ° C., for 5-10 minutes in an air atmosphere containing an oxygen-containing gas.

The oxygen containing gas may be one or more gases selected from O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ and H ₂ O, or a mixed gas containing two or more of these gases. The oxygen containing gas may also be a mixed gas containing at least one of O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ and H ₂ O and at least one inert gas, or O ₂ , It may be a mixed gas containing a mixture of two or more of O ₃ , CO, CO ₂ , NO, N ₂ O, NO ₂ and H ₂ O and one or more inert gases. In short, oxygen-containing gas means a gas containing oxygen atoms or a gas of molecules containing oxygen atoms.

Referring to FIGS. 2 and 4, after the ohmic transparent electrode 700 formed of Ni / Au is formed, the ohmic transparent electrode 700, the P-type GaN layer 600, and the active layer ( 500 is patterned or etched to expose a portion of the N-type GaN layer 400 (S6).

 Thereafter, when the electrode pad 800b is formed on the exposed N-type GaN layer 400 and the electrode pad 800a is formed on the transparent electrode 700 (S7), the light emitting diode shown in FIG. 1 is completed. The electrode pads 800a and 800b may be formed using a lift off method.

5 is an XRD diffraction peak graph of an ohmic electrode manufactured according to a light emitting device manufacturing method according to an embodiment of the present invention.

In FIG. 5, XRD diffraction peaks were measured under four comparison conditions in forming an ohmic transparent electrode including a 10 nm Ni metal layer and a 10 nm Au metal layer.

The first comparative example (as-deposited Ni / Au) is a case where the plasma treatment and annealing treatment are not performed while the Ni metal layer and the Au metal layer are deposited. In the second comparative example (annealed), the Ni metal layer and the Au metal layer are deposited. In the state where the annealing treatment is performed, and the third comparative example (plasma treated) is a case where only the plasma treatment is performed without performing the annealing treatment in the state in which the Ni metal layer and the Au metal layer are deposited, an embodiment of the present invention treated & annealed) is a case where the plasma treatment and annealing treatment are performed after the deposition of the Ni metal layer and the Au metal layer.

As shown in FIG. 5, the lattice of Au is deformed by performing annealing after plasma treatment, and the oxidation of Ni is increased to better form NiO.

6 is a graph illustrating optical output power of an ohmic transparent electrode according to an embodiment of the present invention and an ohmic transparent electrode according to a comparative example.

Referring to FIG. 6, when the Ni metal layer and the Au metal layer are deposited according to an embodiment of the present invention, the plasma treatment and the annealing treatment are performed after the deposition of the Ni metal layer and the Au metal layer. It can be seen that the optical transmittance is improved by as much as 20% compared to the case of only treatment (un-treated).

As such, the light transmittance is improved by depositing the Ni metal layer and the Au metal layer, and then performing plasma treatment. The surface of the Au metal layer is subjected to the treatment. Therefore, when Ni is annealed in an air atmosphere using an oxygen-containing gas, As the area of the surface capable of bonding with oxygen increases, oxidation of Ni increases, which results from better freezing of NiO.

The present invention is not limited to the embodiments described above, and various modifications and changes can be made by those skilled in the art, which are included in the spirit and scope of the present invention as defined in the appended claims.

For example, in an embodiment of the present invention, the use of gallium nitride (GaN) in a group III-V compound semiconductor as an N-type semiconductor layer and a P-type semiconductor layer for fabricating a light emitting device has been described.

However, in addition to gallium nitride (GaN), various nitride compound semiconductors such as aluminum nitride (AlN), indium nitride (InN), and alloys thereof may be used as N-type and P-type semiconductor layers for manufacturing light emitting devices. _{Al x in y Ga 1 -x- y} N may be used (0≤x, y, x + y≤1 ). in addition may be used a Group III-V compound semiconductor of GaP and GaAs.

According to the present invention, in the light emitting device, the Ni / Au ohmic transparent electrode lowers the specific contact resistance, and thus, the carrier supplied from the outside can uniformly spread current into the device, and also improve light efficiency to emit light. Photons generated inside the device can be easily escaped to the outside.

That is, in the present invention, when forming the ohmic transparent electrode of the light emitting device, the surface of the Au metal layer is roughened by depositing a Ni metal layer and an Au metal layer on the P-type semiconductor layer and then performing an oxygen plasma treatment.

The Ni metal layer and the Au metal layer were annealed to the Ni metal layer and the Au metal layer in an air atmosphere by using an oxygen-containing gas using an oxygen-containing gas while the surface of the Au metal layer was roughened by oxygen plasma treatment. Oxidation proceeds more easily by oxidation with oxygen on the roughened surface of the Au metal layer and alloyed with the metal layer, resulting in better formation of NiO and photon generated inside the device as NiO improves light transmittance. It will be able to escape well outside.

Therefore, when fabricating a top-emitting light emitting diode using an ohmic transparent electrode formed of oxidized nickel / gold, it is possible to further improve the light utilization efficiency required to realize a large capacity and high brightness light emitting device.

Claims (6)

Sequentially forming an N-type semiconductor layer, an active layer, and a P-type semiconductor layer on the substrate, Forming a Ni metal layer on the P-type semiconductor layer; Forming an Au metal layer on the Ni metal layer; Performing a plasma treatment using an oxygen-containing gas on the Au metal layer; Annealing the Ni metal layer and the Au metal layer in an oxygen atmosphere to form an ohmic transparent electrode made of Ni / Au. The method according to claim 1, The plasma treatment is 50-200 W, O ₂ 30-60 SCCM, 70-85mTorr manufacturing method of a light emitting device, characterized in that performed for 40 to 240 sec. The method according to claim 1, The annealing treatment is a light emitting device manufacturing method characterized in that performed for 5 to 10 minutes in an air atmosphere containing an oxygen-containing gas at a temperature of 350 ℃-700 ℃. The method according to claim 1, Etching a portion of the P-type semiconductor layer, the active layer, and the N-type semiconductor layer to expose a portion of the N-type semiconductor layer; And forming an electrode on the Ni / Au ohmic transparent electrode and the exposed N-type semiconductor layer. Substrate, An N-type semiconductor layer formed on the substrate, An active layer formed on the N-type semiconductor layer, A P-type semiconductor layer formed on the active layer, And a Ni / Au ohmic transparent electrode formed by laminating a Ni metal layer and an Au metal layer on the P-type semiconductor layer and performing plasma treatment using an oxygen-containing gas and annealing in an oxygen atmosphere. The method according to claim 5, And etching the portions of the P-type semiconductor layer, the active layer, and the N-type semiconductor layer to expose a portion of the N-type semiconductor layer, and further comprising electrodes formed on the Ni / Au ohmic transparent electrode and the exposed N-type semiconductor layer. Light emitting device.

Images