JP2005197670A - Gallium nitride base compound semiconductor light emitting element and its negative electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gallium nitride base compound semiconductor light emitting element provided with a negative electrode capable of obtaining satisfactory ohmic contacts with an n-type gallium nitride base compound semiconductor layer and having resistance to a deterioration in characteristics due to heating. <P>SOLUTION: A light emitting element comprises an n-type semiconductor layer of a gallium nitride base compound semiconductor, a light emitting layer, and a p-type semiconductor layer on a substrate in this order and provided with a negative electrode and a positive electrode in the n-type semiconductor layer and the p-type semiconductor layer, respectively. The negative electrode comprises at least a contact metal layer contacting with the n-type semiconductor layer and a bonding pad layer. The contact metal layer of the gallium nitride base compound semiconductor light emitting element is made of chromium or chromium alloys formed by a sputtering method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gallium nitride compound semiconductor light emitting device, and more particularly to a flip chip type gallium nitride compound semiconductor light emitting device including a negative electrode having excellent characteristics and productivity.

In recent years, a gallium nitride-based compound semiconductor represented by Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1) has been developed from an ultraviolet region to a blue or green light emitting diode (LED). It is attracting attention as a material. By using a compound semiconductor of such a material, it has become possible to emit ultraviolet light, blue light, green light, and the like with high light emission intensity, which has been difficult until now. Since such a gallium nitride compound semiconductor is generally grown on a sapphire substrate which is an insulating substrate, an electrode cannot be provided on the back surface of the substrate unlike a GaAs light emitting device. For this reason, it is necessary to form both the negative electrode and the positive electrode on the side of the crystal grown semiconductor layer.

  In particular, in the case of a semiconductor device using a gallium nitride compound semiconductor, since the sapphire substrate has translucency with respect to the emission wavelength, the electrode surface is mounted on the lower side and light is extracted from the sapphire substrate side. Flip chip type is attracting attention.

  FIG. 1 is a schematic view showing an example of a general structure of a light emitting device of this type. That is, in the light-emitting element, the buffer layer 2, the n-type semiconductor layer 3, the light-emitting layer 4, and the p-type semiconductor layer 5 are crystal-grown on the substrate 1, and a part of the light-emitting layer 4 and the p-type semiconductor layer 5 is etched away. The n-type semiconductor layer 3 is exposed, and the positive electrode 10 is formed on the p-type semiconductor layer 5 and the negative electrode 20 is formed on the n-type semiconductor layer 3. Such a light-emitting element is mounted, for example, on a lead frame with the electrode formation surface facing, and then bonded.

  Therefore, in the case of a flip chip type light emitting element, the negative electrode is heated at several hundred degrees Centigrade during mounting. For this reason, the negative electrode of the flip-chip type light emitting element is required to be able to suppress deterioration of characteristics due to heating.

  A negative electrode obtained by depositing Al, Cr, and Ti on an n-type gallium nitride compound semiconductor layer is known as a negative electrode that obtains good ohmic contact with a gallium nitride compound semiconductor (see, for example, Patent Document 1). However, this negative electrode is deteriorated by heating. An underlayer made of at least one metal selected from the group consisting of V, Nb, Zr and Cr or an alloy containing this metal and another metal on the underlayer on the n-type gallium nitride compound semiconductor layer A negative electrode is known in which a main electrode layer made of the above is formed by vapor deposition and heat-treated (see, for example, Patent Document 2). However, this method is inferior in productivity because it includes a heat treatment step after electrode formation.

JP-A-5-291621 Japanese Patent Laid-Open No. 10-112555

  An object of the present invention is to provide a negative electrode that can obtain good ohmic contact with an n-type gallium nitride-based compound semiconductor layer and has resistance to deterioration of characteristics due to heating. It is also an object of the present invention to provide a gallium nitride compound semiconductor light emitting device having such a negative electrode.

The present invention provides the following inventions.
(1) An n-type semiconductor layer made of a gallium nitride-based compound semiconductor, a light emitting layer, and a p-type semiconductor layer are included in this order on a substrate, and a negative electrode and a positive electrode are provided in the n-type semiconductor layer and the p-type semiconductor layer, respectively. In the light emitting device, the negative electrode includes at least a contact metal layer and a bonding pad layer in contact with the n-type semiconductor layer, and the contact metal layer is Cr or a Cr alloy formed by a sputtering method. Semiconductor light emitting device.

(2) The gallium nitride compound semiconductor light-emitting element according to (1) above, wherein the Cr alloy is an alloy of Cr and a metal element having a work function of 4.5 eV or less.

(3) The metal element having a work function of 4.5 eV or less was selected from the group consisting of Al, Ti, Si, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Hf, Ta, W, and V The gallium nitride-based compound semiconductor light-emitting element according to the above item (2), which is one or more metal elements.

(4) Item (3) above, wherein the metal element having a work function of 4.5 eV or less is one or more metal elements selected from the group consisting of Al, V, Nb, Mo, W and Mn. 2. A gallium nitride-based compound semiconductor light emitting device according to 1.

(5) The gallium nitride-based compound semiconductor light-emitting element according to any one of (1) to (4), wherein a Cr ratio in the Cr alloy is 1% by mass or more and less than 100% by mass.

(6) The gallium nitride compound semiconductor light-emitting element according to the above (5), wherein the ratio of Cr in the Cr alloy is 10% by mass or more.

(7) The gallium nitride-based compound semiconductor light-emitting element according to any one of (1) to (6), wherein the contact metal layer has a thickness of 1 to 500 nm.

(8) The gallium nitride-based compound semiconductor light-emitting element according to (7) above, wherein the contact metal layer has a thickness of 10 nm or more.

(9) The bonding pad layer is a metal selected from the group consisting of Au, Al, Ni and Cu, or an alloy containing the metal, according to any one of (1) to (8) above The gallium nitride-based compound semiconductor light-emitting device described.

(10) The gallium nitride-based compound semiconductor light-emitting element according to any one of (1) to (9) above, wherein the bonding pad layer has a thickness of 100 to 1000 nm.

(11) The gallium nitride compound semiconductor light-emitting element according to (10) above, wherein the bonding pad layer has a thickness of 200 to 500 nm.

(12) The gallium nitride-based compound semiconductor light-emitting element according to any one of (1) to (11) above, wherein a layer made of an Au—Sn alloy is provided on the bonding pad layer.

(13) The gallium nitride compound semiconductor light-emitting element according to (12) above, wherein the Au—Sn alloy layer has a thickness of 200 nm or more.

(14) The gallium nitride-based compound semiconductor light-emitting element according to any one of (1) to (11), wherein a lead-free solder layer is provided on the bonding pad layer.

(15) The gallium nitride-based compound semiconductor light-emitting element according to (14) above, wherein the lead-free solder layer has a thickness of 200 nm or more.

(16) The gallium nitride compound semiconductor light emitting device as described in any one of (1) to (15) above, wherein an adhesive layer made of Ti is provided between the contact metal layer and the bonding pad layer. element.

(17) The gallium nitride-based compound semiconductor light-emitting element according to the above (16), wherein the adhesive layer has a thickness of 1 to 100 nm.

(18) The gallium nitride-based compound semiconductor light-emitting element according to the above (17), wherein the adhesive layer has a thickness of 10 nm or more.

(19) The gallium nitride compound semiconductor light-emitting element according to any one of (1) to (15) above, wherein a barrier layer is provided between the contact metal layer and the bonding pad layer.

(20) The gallium nitride as described in any one of (12) to (18) above, wherein a barrier layer is provided between the bonding pad layer and the Au—Sn alloy layer or the lead-free solder layer. Compound semiconductor light emitting device.

(21) A metal selected from the group consisting of Ti, Zr, Hf, Ta, W, Re, Os, Ir, Pt, Fe, Co, Ni, Ru, Rh and Pd, or an alloy containing the metal The gallium nitride-based compound semiconductor light-emitting device according to item (19) or (20), wherein

(22) The gallium nitride-based compound semiconductor light-emitting element according to the above (21), wherein the barrier layer is a metal selected from the group consisting of Ti, Ta, W, and Pt or an alloy containing the metal. .

(23) The gallium nitride-based compound semiconductor light-emitting element according to any one of (19) to (22) above, wherein the barrier layer has a thickness of 10 to 500 nm.

(24) The gallium nitride-based compound semiconductor light-emitting element according to the above (23), wherein the barrier layer has a thickness of 50 to 300 nm.

(25) The gallium nitride compound semiconductor light emitting device according to any one of (1) to (24) above, wherein the gallium nitride compound semiconductor light emitting device is a flip chip type.

(26) A negative electrode for a gallium nitride-based compound semiconductor device, comprising at least a contact metal layer and a bonding pad layer in contact with an n-type semiconductor layer, wherein the contact metal layer is Cr or a Cr alloy formed by sputtering. A negative electrode for a gallium nitride compound semiconductor light emitting device.

(27) The negative electrode for a gallium nitride-based compound semiconductor light-emitting device according to the above (26), wherein the gallium nitride-based compound semiconductor light-emitting device is a flip chip type.

(28) An n-type semiconductor layer made of a gallium nitride compound semiconductor, a light emitting layer, and a p-type semiconductor layer are included on the substrate in this order, a positive electrode is provided on the p-type semiconductor layer, and a bonding pad layer and Cr or Cr alloy A method of manufacturing a gallium nitride-based compound semiconductor light-emitting device in which a negative electrode having at least a contact metal layer made of is provided on the n-type semiconductor layer, wherein the contact metal layer is formed on the n-type semiconductor layer by a sputtering method And producing a gallium nitride-based compound semiconductor light emitting device, wherein the ohmic contact is performed without annealing.
(29) A lamp comprising the light emitting device according to any one of (1) to (25) above.

  The negative electrode of the present invention using Cr or Cr alloy formed by sputtering as a contact metal layer can obtain good ohmic contact with the n-type gallium nitride compound semiconductor layer, and causes deterioration of characteristics by heating. There is no. In addition, since a good ohmic contact between the negative electrode of the present invention and the n-type gallium nitride compound semiconductor layer is achieved without annealing treatment, the gallium nitride compound semiconductor light emitting device of the present invention is excellent in productivity.

As the gallium nitride compound semiconductor laminated on the substrate in the present invention, as shown in FIG. 1, a buffer layer 2, an n-type semiconductor layer 3, a light emitting layer 4 and a p-type semiconductor layer 5 are crystal-grown on the substrate 1. Conventionally known ones can be used without any limitation. Conventionally known materials such as sapphire and SiC are used for the substrate without any limitation, and the general formula Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y) is used for the gallium nitride compound semiconductor. A conventionally known gallium nitride compound semiconductor represented by ≦ 1) is used without any limitation.

  For example, as shown in FIG. 2, a buffer layer 2 made of an AlN layer is stacked on a sapphire substrate 1, a contact layer 3a made of an n-type GaN layer thereon, and a lower portion made of an n-type GaN layer. It is possible to use a clad layer 3b, a light emitting layer 4 made of an InGaN layer, an upper clad layer 5b made of a p-type AlGaN layer, and a contact layer 5a made of a p-type GaN layer in this order. As the positive electrode 10 provided on the contact layer 5a, a positive electrode having a conventionally known composition and structure such as Al can be used without any limitation.

  A part of the contact layer 5a, upper clad layer 5b, light emitting layer 4 and lower clad layer 3b of such a gallium nitride compound semiconductor is removed by etching, and the negative electrode 20 is provided on the contact layer 3a. The negative electrode 20 includes a contact metal layer 21, an adhesive layer 22, and a bonding pad layer 23.

  In the present invention, the negative electrode includes at least two layers of a contact metal layer that forms ohmic contact with the n-type semiconductor layer and a bonding pad layer for electrical connection with a circuit board or a lead frame, and the contact metal layer is formed by a sputtering method. It consists of formed Cr or Cr alloy. By forming the contact metal layer using a sputtering method, alloying between the n-type GaN and the contact metal layer proceeds, so that a low contact resistance can be obtained after the contact metal layer is formed without annealing.

  The thickness of the contact metal layer is preferably 1 nm or more. In particular, the thickness of 5 nm or more is desirable because low resistance can be obtained. Furthermore, if it is 10 nm or more, a stable low resistance can be obtained, which is more desirable. Since productivity deteriorates even if it is too thick, 500 nm or less is preferable. More preferably, it is 200 nm or less.

  As the Cr alloy, an alloy with a metal element having a work function of 4.5 eV or less is preferable because of its low contact specific resistance. Examples of the metal element having a work function of 4.5 eV or less include Al, Ti, Si, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Hf, Ta, W, and V. Among these, Al, V, Nb, Mo, W and Mn are particularly preferable.

  The Cr content of the Cr alloy is preferably 1% by mass or more and less than 100% by mass. In particular, in order to suppress deterioration of characteristics due to heating of the light emitting element, it is desirable that the Cr content is 10% by mass or more. Furthermore, in order to suppress characteristic deterioration stably, it is desirable to set it as 20 mass% or more. Moreover, since the reflectance of Cr is improved by applying heat at 300 ° C., it is desirable that the Cr content is high.

Sputtering can be carried out by appropriately selecting conventionally known conditions using a conventionally known sputtering apparatus. A substrate in which a gallium nitride compound semiconductor layer is stacked and a part of the n-type semiconductor layer is exposed by etching is accommodated in a chamber, and the substrate temperature is set in a range of room temperature to 500 ° C. Preferably, it is around room temperature. The chamber is evacuated until the degree of vacuum is 10 ⁻⁴ to 10 ⁻⁷ Pa. As the sputtering gas, He, Ne, Ar, Kr, Xe, or the like can be used. Ar is desirable because of availability. One of these gases is introduced into the chamber and the discharge is performed after the pressure is set to 0.1 to 10 Pa. Preferably it sets to the range of 0.2-5Pa. The supplied power is preferably in the range of 0.2 to 2.0 kW. At this time, the thickness of the layer to be formed can be adjusted by adjusting the discharge time and supply power. The oxygen content of the required target used for sputtering is preferably 10,000 ppm or less because the oxygen content in the formed layer is reduced. More preferably, it is 6000 ppm or less. When forming an alloy layer, it is preferable to prepare an alloy having a target composition in advance and then sputtering the alloy layer having the same composition using the alloy as a target.

  For good contact resistance between the contact metal layer and the n-type GaN semiconductor layer, the removal state of the natural oxide film on the surface of the n-type GaN semiconductor layer greatly affects. The surface of the GaN semiconductor layer is oxidized in the atmosphere to form a natural oxide film. Even if the oxide film is once removed by etching or the like, the surface is oxidized again if it is exposed to the atmosphere before electrode formation. Since the film in which GaN is oxidized is an insulator, the contact resistance at the electrode / GaN interface increases if the entire GaN surface is covered with the oxide film. Therefore, it is important to remove the oxide film on the surface of the n-type semiconductor layer before sputtering.

  The bonding pad layer is preferably formed of a metal selected from the group consisting of Au, Al, Ni, and Cu or an alloy containing the metal because of good adhesion to the bumps. The thickness of the bonding pad is preferably 100 to 1000 nm because of excellent productivity. More preferably, it is 200-800 nm. Especially preferably, it is 200-500 nm.

  An adhesive layer made of Ti is preferably interposed between the contact metal layer and the bonding pad layer in order to improve the adhesion between the two layers. When providing an adhesive layer, the thickness is preferably 1 to 100 nm. If it is less than 1 nm, a sufficient adhesive effect cannot be obtained. If the thickness exceeds 100 nm, the Ti film may be oxidized when the light emitting element is heated, and the electrical characteristics may be deteriorated. If it is 5 nm or more, a stable adhesive effect can be obtained, which is more preferable. Especially preferably, it is 10 nm or more.

  An Au—Sn alloy layer or a lead-free solder layer can be provided on the bonding pad layer. The Au—Sn alloy layer or the lead-free solder layer preferably has a thickness of 200 nm or more in order to serve as an adhesive layer when the light emitting element is attached to the submount. Moreover, it is preferable that it is 5 micrometers or less from a viewpoint of productivity.

  Even when an Au—Sn alloy layer or a lead-free solder layer is provided, heat of 300 to 400 ° C. is required for several minutes or more when the light emitting element is mounted. At this time, Cr in the contact metal layer may diffuse into the bonding pad layer, the Au—Sn alloy layer, or the lead-free solder layer. Therefore, it is preferable to provide a barrier layer between the contact metal layer and the bonding pad layer or between the bonding pad layer and the Au—Sn alloy layer (or lead-free solder layer) in order to prevent Cr from diffusing.

The barrier layer is a metal selected from the group consisting of Ti, Zr, Hf, Ta, W, Re, Os, Ir, Pt, Fe, Co, Ni, Ru, Rh, and Pd or an alloy containing the metal. Is desirable. In particular, Ti, Ta, W, and Pt are preferable. If the thickness of the barrier layer is too thin, a uniform single film cannot be obtained. Therefore, the thickness is preferably 10 nm or more, and is preferably 500 nm or less from the viewpoint of productivity. More preferably, it is 50-300 nm.
When the adhesive layer made of Ti described above is provided, this adhesive layer also serves as a barrier layer.

  As a method for forming the bonding pad layer, the adhesive layer, and the barrier layer, conventionally known methods such as sputtering and vapor deposition can be used without any limitation. However, since the contact metal layer is formed by the sputtering method, it is preferable that the contact metal layer is formed by the sputtering method subsequent to the formation of the contact metal layer because the process is simplified. As a method for forming the Au—Sn alloy layer or the lead-free solder layer, a conventionally known method such as a vapor deposition method, a plating method, and a coating method using a paste can be used without any limitation.

  Moreover, the light emitting element of the present invention can be provided with a cover having a fluorescent agent as necessary to form a lamp.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. Table 1 shows the negative electrode material and the forming method used in this example and the comparative example, and the evaluation results immediately after the film formation and after the heating test, but the present invention is not limited to these examples.

FIG. 2 is a schematic view of the gallium nitride compound semiconductor light emitting device manufactured in this example.
The used gallium nitride-based compound semiconductor has a buffer layer 2 made of an AlN layer stacked on a sapphire substrate 1, a contact layer 3a made of an n-type GaN layer, a lower cladding layer 3b made of an n-type GaN layer, and InGaN. A light emitting layer 4 made of layers, an upper cladding layer 5b made of a p-type AlGaN layer, and a contact layer 5a made of a p-type GaN layer are sequentially laminated. The contact layer 3a is an n-type GaN layer doped with Si 7 × 10 ¹⁸ / cm ³ , and the lower cladding layer 3b is an n-type GaN layer doped with Si 5 × 10 ¹⁸ / cm ³ , and the structure of the light emitting layer 4 Is a single quantum well structure, and the composition of InGaN is In _0.95 Ga _0.05 N. The upper clad layer 5b is p-type AlGaN doped with 1 × 10 ¹⁸ / cm ³ of Mg, and its composition is Al _0.25 Ga _0.75 N. The contact layer 5a is a p-type GaN layer doped with 5 × 10 ¹⁹ / cm ³ of Mg. Lamination of these layers was performed by MOCVD under normal conditions well known in the art.

  The gallium nitride compound semiconductor was provided with the positive electrode 10 and the negative electrode 20 in the following procedure to produce a flip-chip gallium nitride compound semiconductor light emitting device.

  First, this gallium nitride compound semiconductor element was treated for 10 minutes in concentrated HCl boiled for the purpose of removing the oxide film on the surface of the contact layer 5a.

  Next, Al was formed on the contact layer 5 a as the positive electrode 10. The formation procedure is as follows. After uniformly applying a resist on the entire surface, the resist in the positive electrode forming region was removed by a known lithography technique. After immersing in buffered hydrofluoric acid (BHF) at room temperature for 1 minute, a positive electrode was formed with a vacuum sputtering apparatus. The operating conditions for forming by sputtering are as follows.

The chamber was evacuated until the degree of vacuum was 10 ⁻⁶ Pa. The substrate was accommodated in the chamber, Ar gas was introduced into the chamber as a sputtering gas, and after 0.5 Pa, discharge was performed. The supplied power was 0.25 kW. At this time, the thickness of the layer to be formed was adjusted to 100 nm by adjusting the discharge time and the supplied power. After taking out from the sputtering apparatus, the metal film other than the positive electrode region was removed together with the resist using a lift-off technique.

Next, the negative electrode 20 was formed on the contact layer 3a. The formation procedure is as follows.
First, an etching mask was formed on the positive electrode 10. The formation procedure is as follows. After the resist was uniformly applied on the entire surface, the resist was removed from a region that was slightly larger than the positive electrode region using a known lithography technique. It was set in a vacuum deposition apparatus, and Ni and Ti were laminated by an electron beam method at a pressure of 4 × 10 ⁻⁴ Pa or less so that the film thicknesses were about 50 nm and 300 nm, respectively. Thereafter, the metal film other than the positive electrode region was removed together with the resist by a lift-off technique. This etching mask is a layer for protecting the positive electrode from plasma damage of reactive ion dry etching.

  Next, the contact layer 3a was exposed, and the negative electrode 20 was formed thereon. The formation procedure is as follows. Etching was carried out by reactive ion dry etching until the contact layer 3a was exposed, then taken out from the dry etching apparatus, and the etching mask was removed with nitric acid and hydrofluoric acid.

  Next, after uniformly applying a resist on the entire surface, using a known lithography technique, the resist is removed from the exposed contact layer 3a region, and then the contact metal layer 21 made of Cr and Ti are formed by the sputtering method described above. The adhesive layer 22 and the bonding pad layer 23 made of Au were formed with thicknesses of 100 nm, 20 nm, and 300 nm, respectively. Thereafter, the metal film other than the negative electrode portion was removed together with the resist, and the gallium nitride compound semiconductor light emitting device of the present invention was produced.

  Furthermore, a gallium nitride-based compound semiconductor light-emitting element was fabricated in the same manner as described above using a contact metal layer, an adhesive layer, and a bonding pad layer made of the materials shown in Table 1. The contact specific resistance of the obtained light emitting device was measured by a circular TLM method, and the results are also shown in Table 1.

The “evaporation” in the forming method of Table 1 is a method in which a negative electrode is formed by a vapor deposition method for comparison. The substrate was placed in a furnace, and a negative electrode was formed by vapor deposition in a vacuum of 10 ⁻⁴ Pa or less. “SPT” means a sputtering method. In the heating test, heating was performed at 300 ° C. for 1 minute in the atmosphere using an RTA furnace.

  When the contact metal layer is formed by a vapor deposition method, it has ohmic characteristics after the film formation, but the contact characteristics become Schottky after the heating test, and the resistance value is remarkably deteriorated. On the other hand, in the present invention formed by the sputtering method, it has ohmic characteristics after film formation and after a heat test, and maintains low resistance. When a contact metal layer is formed by sputtering, this characteristic is maintained when a Cr—Al alloy is used even if the Cr ratio is 20%. When a Cr—Mo alloy is used, the resistance is further reduced, and the low resistance is maintained even after the heating test.

  The flip chip type gallium nitride compound semiconductor light emitting device provided by the present invention is useful as a material for light emitting diodes and lamps.

It is the schematic which shows the general structure of the conventional flip chip type compound semiconductor light-emitting device. It is the schematic which shows an example of the flip chip type gallium nitride compound semiconductor light emitting element of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 N-type semiconductor layer 4 Light emitting layer 5 P-type semiconductor layer 10 Positive electrode 20 Negative electrode 21 Contact metal layer 22 Adhesive layer 23 Bonding pad layer

Claims (29)

  In a light-emitting element including an n-type semiconductor layer made of a gallium nitride-based compound semiconductor, a light-emitting layer, and a p-type semiconductor layer in this order on a substrate, and a negative electrode and a positive electrode provided in the n-type semiconductor layer and the p-type semiconductor layer, respectively The gallium nitride-based compound semiconductor light-emitting device, wherein the negative electrode includes at least a contact metal layer and a bonding pad layer in contact with the n-type semiconductor layer, and the contact metal layer is Cr or a Cr alloy formed by a sputtering method .   2. The gallium nitride compound semiconductor light-emitting element according to claim 1, wherein the Cr alloy is an alloy of Cr and a metal element having a work function of 4.5 eV or less.   One or more metal elements having a work function of 4.5 eV or less selected from the group consisting of Al, Ti, Si, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Hf, Ta, W, and V The gallium nitride-based compound semiconductor light-emitting element according to claim 2, wherein the gallium nitride-based compound semiconductor light-emitting element is a metal element.   The gallium nitride according to claim 3, wherein the metal element having a work function of 4.5 eV or less is one or more metal elements selected from the group consisting of Al, V, Nb, Mo, W and Mn. Compound semiconductor light emitting device.   5. The gallium nitride-based compound semiconductor light-emitting element according to claim 1, wherein a Cr ratio in the Cr alloy is 1% by mass or more and less than 100% by mass.   6. The gallium nitride compound semiconductor light-emitting element according to claim 5, wherein a Cr ratio in the Cr alloy is 10% by mass or more.   The gallium nitride-based compound semiconductor light-emitting device according to claim 1, wherein the contact metal layer has a thickness of 1 to 500 nm.   The gallium nitride-based compound semiconductor light-emitting element according to claim 7, wherein the contact metal layer has a thickness of 10 nm or more.   The gallium nitride compound according to any one of claims 1 to 8, wherein the bonding pad layer is a metal selected from the group consisting of Au, Al, Ni and Cu or an alloy containing the metal. Semiconductor light emitting device.   The gallium nitride-based compound semiconductor light-emitting device according to claim 1, wherein the bonding pad layer has a thickness of 100 to 1000 nm.   The gallium nitride-based compound semiconductor light-emitting device according to claim 10, wherein the bonding pad layer has a thickness of 200 to 500 nm.   The gallium nitride-based compound semiconductor light-emitting element according to claim 1, wherein a layer made of an Au—Sn alloy is provided on the bonding pad layer.   The gallium nitride-based compound semiconductor light-emitting element according to claim 12, wherein the Au-Sn alloy layer has a thickness of 200 nm or more.   The gallium nitride-based compound semiconductor light-emitting element according to claim 1, wherein a lead-free solder layer is provided on the bonding pad layer.   The gallium nitride-based compound semiconductor light-emitting element according to claim 14, wherein the lead-free solder layer has a thickness of 200 nm or more.   The gallium nitride compound semiconductor light-emitting element according to claim 1, wherein an adhesive layer made of Ti is provided between the contact metal layer and the bonding pad layer.   The gallium nitride compound semiconductor light-emitting element according to claim 16, wherein the adhesive layer has a thickness of 1 to 100 nm.   The gallium nitride-based compound semiconductor light-emitting element according to claim 17, wherein the adhesive layer has a thickness of 10 nm or more.   The gallium nitride-based compound semiconductor light-emitting element according to claim 1, wherein a barrier layer is provided between the contact metal layer and the bonding pad layer.   The gallium nitride-based compound semiconductor light-emitting device according to any one of claims 12 to 18, wherein a barrier layer is provided between the bonding pad layer and the Au-Sn alloy layer or the lead-free solder layer.   The barrier layer is a metal selected from the group consisting of Ti, Zr, Hf, Ta, W, Re, Os, Ir, Pt, Fe, Co, Ni, Ru, Rh, and Pd or an alloy containing the metal. The gallium nitride-based compound semiconductor light-emitting device according to claim 19 or 20.   The gallium nitride-based compound semiconductor light-emitting element according to claim 21, wherein the barrier layer is a metal selected from the group consisting of Ti, Ta, W, and Pt or an alloy containing the metal.   The gallium nitride-based compound semiconductor light-emitting element according to any one of claims 19 to 22, wherein the barrier layer has a thickness of 10 to 500 nm.   24. The gallium nitride compound semiconductor light-emitting element according to claim 23, wherein the barrier layer has a thickness of 50 to 300 nm.   The gallium nitride-based compound semiconductor light-emitting element according to claim 1, wherein the gallium nitride-based compound semiconductor light-emitting element is a flip chip type.   A negative electrode for a gallium nitride compound semiconductor device, comprising at least a contact metal layer and a bonding pad layer in contact with an n-type semiconductor layer, wherein the contact metal layer is Cr or a Cr alloy formed by a sputtering method A negative electrode for a gallium nitride-based compound semiconductor light emitting device.   27. The negative electrode for a gallium nitride compound semiconductor light emitting device according to claim 26, wherein the gallium nitride compound semiconductor light emitting device is of a flip chip type.   A n-type semiconductor layer made of a gallium nitride compound semiconductor, a light-emitting layer, and a p-type semiconductor layer are arranged in this order on a substrate, a positive electrode is provided on the p-type semiconductor layer, and a contact made of a bonding pad layer and Cr or Cr alloy A method for manufacturing a gallium nitride-based compound semiconductor light-emitting device in which a negative electrode having at least a metal layer is provided on the n-type semiconductor layer, wherein the contact metal layer is formed on the n-type semiconductor layer by a sputtering method and annealed A method for manufacturing a gallium nitride-based compound semiconductor light-emitting device, characterized in that ohmic contact is performed without any contact.   A lamp comprising the light emitting device according to any one of claims 1 to 25.

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