JP4867414B2 - Nitride semiconductor light emitting diode - Google Patents

Description

The present invention relates to a nitride semiconductor light-emitting diode having an electrode for an n-type nitride semiconductor suitable for making electrical connection with an external electrode through solder.

In recent years, a nitride semiconductor light emitting diode having a pn junction type light emitting diode element structure made of a nitride semiconductor has been developed and put into practical use. A nitride semiconductor is a compound semiconductor represented by the general formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), GaN, InGaN , AlGaN, AlInGaN, AlN, InN, etc. In the above chemical formula, a part of the group 3 element is substituted with B (boron), Tl (thallium), etc., and a part of N (nitrogen) is P (phosphorus), As (arsenic), Sb (antimony) Those substituted with Bi (bismuth) or the like are also included in the nitride semiconductor. Hereinafter, the nitride semiconductor light emitting diode is also referred to as “GaN-based LED”. The n-type nitride semiconductor layer is also simply referred to as “n-type layer”, and the p-type nitride semiconductor layer is also simply referred to as “p-type layer”. In addition, with reference to the pn junction serving as the light emitting portion, an electrode provided on the p-type layer side is also referred to as a p-side electrode, and an electrode provided on the n-type layer side is also referred to as an n-side electrode.

An n-type layer in which an n-type layer, a light-emitting layer made of InGaN, and a p-type layer are grown and stacked in this order on a substrate made of sapphire and the like, and a part of the light-emitting layer and the p-type layer are removed and exposed. A GaN-based LED configured by forming an n-side electrode on a layer and forming a p-side electrode on a p-type layer is known (Patent Document 1).

Further, an n-type layer, a light-emitting layer made of InGaN, and a p-type layer are grown and stacked in this order on a substrate made of an n-type nitride semiconductor by a MOVPE (organometallic compound vapor phase epitaxy) method. A GaN-based LED configured by forming an n-side electrode on the back surface and a p-side electrode on the surface of the p-type layer is known (Patent Document 2).

A first n-type layer, a light-emitting layer made of InGaN, a p-type layer, and a second n-type layer are grown and stacked in this order on a substrate made of sapphire or the like to form a first n-type layer. A GaN-based LED configured by forming an n-side electrode and a p-side electrode in a second n-type layer is known (Patent Document 3 and Patent Document 4).

In addition, an n-type layer, a light emitting layer made of InGaN, and a p-type layer are grown and laminated in this order on a crystal growth substrate. The growth substrate is removed from the nitride semiconductor layer, and a separately prepared conductive substrate is bonded to the exposed n-type layer, and then the support substrate is peeled off to form a p-side electrode on the surface of the p-type layer. A GaN-based LED configured by this is known (Patent Document 5).

As an electrode for an n-type nitride semiconductor, an electrode that essentially contains a Ti—W alloy, Ge, and Rh is known (Patent Document 6).

JP 2006-59933 A JP 2005-44954 A JP 2002-9335 A JP 2004-179369 A JP 2005-217112 A Japanese Patent Laid-Open No. 11-8410 Japanese Patent Laid-Open No. 5-295531 JP-A-4-193947 JP-A-4-293770

Patent Document 1 describes an electrode made of an Al single layer film (hereinafter also referred to as “Al single layer electrode”) as an electrode for an n-type nitride semiconductor. Since Al has a high light reflectance, an Al single layer electrode is suitable as an electrode for LED. However, since Al reacts with molten solder to cause alloying, LED chip electrodes and external electrodes (lead frame and circuit serving as a support for the LED chip, such as LEDs for flip chip mounting). An Al single layer electrode cannot be used for an LED that uses solder for connection to an electrode provided on a substrate, a submount, or the like. This is because there is a problem that the contact resistance between the electrode and the n-type nitride semiconductor increases due to alloying. There is also a problem that the reflectance of the alloy generated by the reaction with solder is significantly lower than that of Al alone. In order to improve this problem, Patent Document 1 discloses an electrode configured by laminating an Au (gold) layer on an Al layer via a barrier layer made of a metal having a high melting point. However, even in this electrode, since the thermal expansion coefficient of Al is extremely large compared to nitride semiconductors and other metals, large thermal stress is likely to be generated inside, and therefore characteristics when the electrode is heated. There is a problem that it is likely to fluctuate. Further, when the barrier layer is damaged by the thermal stress, the barrier function of the barrier layer is lowered, and an alloying reaction may occur between the Al layer and the Au layer or solder.

The present invention has been made in view of such circumstances, and provides a GaN-based LED including an n-type nitride semiconductor electrode suitable for electrical connection with an external electrode via solder. Objective. Another object of the present invention is to provide a GaN-based LED that includes such an electrode and compensates for a decrease in light emission output caused thereby.

The present inventors have found that the Ti—W alloy exhibits a low contact resistance with the n-type nitride semiconductor without using Ge or Rh together, and thus the present invention has been made. Here, the Ti—W alloy is an alloy substantially consisting of Ti (titanium) and W (tungsten). In order to achieve the above object, the present invention provides a nitride semiconductor light emitting diode having the following characteristics.

(1) A nitride semiconductor light-emitting diode having an n-type nitride semiconductor layer and an electrode formed on the n-type nitride semiconductor layer, the electrode being electrically connected to an external electrode through solder A nitride semiconductor light-emitting diode, wherein the electrode includes a Ti—W alloy layer in contact with the n-type nitride semiconductor layer.
(2) The nitride semiconductor light emitting diode according to (1), wherein the Ti concentration of the Ti—W alloy layer is 5 wt% to 50 wt%.
(3) The nitride semiconductor light-emitting diode according to (1) or (2), wherein the electrode includes a metal layer stacked on the Ti—W alloy layer.
(4) The nitride semiconductor light-emitting diode according to (3), wherein the metal layer includes an Au layer laminated directly on the Ti—W alloy layer.
(5) The nitride semiconductor light-emitting diode according to (3) or (4), wherein the uppermost layer of the metal layer is a layer made of Au, a platinum group element, Sn, or solder.
(6) The nitride semiconductor light-emitting diode according to any one of (1) to (5), wherein the electrode does not contain Rh.
(7) In a nitride semiconductor light-emitting diode including a nitride semiconductor layer including a light-emitting layer and an n-type contact layer directly or indirectly stacked on the light-emitting layer, a part on the n-type contact layer An electrode formed so as to be in contact with the region, and a reflective film that reflects light generated in the light-emitting layer formed in a region other than the region in contact with the electrode on the n-type contact layer, The nitride semiconductor light-emitting diode, wherein the electrode includes a Ti-W alloy layer in contact with the n-type contact layer.
(8) The nitride semiconductor light emitting diode according to (7), wherein the n-type contact layer is a substrate made of an n-type nitride semiconductor.
(9) The nitride semiconductor light-emitting diode according to (7), wherein a p-type nitride semiconductor layer is provided between the light-emitting layer and the n-type contact layer.
(10) The nitride semiconductor light-emitting diode according to any one of (7) to (9), wherein the reflective film includes a light-transmitting layer having a lower refractive index than the n-type contact layer.
(11) The nitride semiconductor light-emitting diode according to any one of (7) to (10), wherein the reflective film includes a dielectric multilayer type reflective layer.
(12) The nitride semiconductor light-emitting diode according to any one of (7) to (11), wherein the reflective film includes a metal layer.
(13) The nitride semiconductor light-emitting diode according to any one of (7) to (12), wherein a part of the Ti—W alloy layer is formed so as to cover a surface of the reflective film.
(14)
The nitride semiconductor light-emitting diode according to any one of (7) to (13), wherein the electrode includes a bonding layer formed from above the Ti—W alloy layer.
(15) The nitride semiconductor light-emitting diode according to (14), wherein a part of the Ti—W alloy layer separates the reflective film and the bonding layer.
(16) The nitride semiconductor light-emitting diode according to (7), further including a conductive substrate provided so as to sandwich the electrode and the reflective film with the n-type contact layer.

A nitride semiconductor light emitting diode according to a preferred embodiment of the present invention includes an n-type nitride semiconductor layer and an electrode formed on the n-type nitride semiconductor layer, and the electrode is the n-type nitride. A Ti—W alloy layer in contact with the semiconductor layer is included. Ti-W alloy is an alloy with good heat resistance and does not react even when it comes into contact with molten solder. In this light emitting diode, the element side electrode and the external electrode are connected via solder. When mounted, the problem that the operating voltage after mounting becomes higher than before mounting is prevented.

A nitride semiconductor light emitting diode according to another preferred embodiment of the present invention includes a nitride semiconductor layer including a light emitting layer and an n-type contact layer laminated directly or indirectly on the light emitting layer. And an electrode formed so as to be in contact with a part of the region on the n-type contact layer and light generated in the light-emitting layer formed in a region other than the region on the n-type contact layer in contact with the electrode. The electrode includes a Ti—W alloy layer in contact with the n-type contact layer. In this nitride semiconductor light emitting diode, the electrode formed on the n-type contact layer and the external electrode can be suitably connected via solder. Ti-W alloy has a relatively low light reflectivity. In this nitride semiconductor light emitting diode, a Ti-W alloy is used as an electrode by providing a reflective film in addition to the electrode on the n-type contact layer. This compensates for a decrease in light emission output.

The GaN-based LED according to the present invention has an n-type contact layer, which is an n-type layer on which an electrode is formed, and an electrode formed on the n-type contact layer, and the electrode is an n-type contact layer. A Ti—W alloy layer in contact with the substrate.

The composition of the nitride semiconductor constituting the n-type contact layer is arbitrary, but is preferably Al _x Ga _1-x N (0 ≦ x ≦ 0.2). This is because a nitride semiconductor containing no In can be grown at a high temperature (900 ° C. or more in the case of the MOVPE method), so that a semiconductor having good crystallinity, that is, a semiconductor having good conductivity is manufactured. This is because it is easy to do. In addition, the nitride semiconductor having a lower Al composition has better crystallinity. As long as the n-type contact layer exhibits n-type conductivity, it may be undoped or doped with impurities, but the carrier is used so that the contact resistance with the electrode is lowered. The concentration is preferably 1 × 10 ¹⁸ cm ⁻³ or more, and more preferably 3 × 10 ¹⁸ cm ⁻³ or more. The type of n-type impurity used for controlling the carrier concentration is not limited, and any known n-type impurity such as Si (silicon) or Ge (germanium) can be used. The n-type contact layer may be produced by any method, and is grown by a vapor phase method such as MOVPE method, HVPE (hydride vapor phase epitaxy) method, MBE (molecular beam epitaxy) method, etc. Alternatively, it may be grown by a method other than the gas phase method such as a high pressure method or a liquid phase method. The n-type contact layer is not limited to a layer epitaxially grown on the substrate, and may be a substrate made of an n-type nitride semiconductor.

The electrode formed on the n-type contact layer may be composed of a single layer film of Ti—W alloy, or another metal layer may be formed on the Ti—W alloy layer in contact with the n-type contact layer. It may be laminated. In the latter case, the type of metal laminated on the Ti—W alloy layer is arbitrary, and it may be a simple substance or an alloy. The metal layer may be a single layer or have a multilayer structure. You may do it. When laminating a metal layer for the purpose of reducing the resistance of the electrode, the metal layer preferably includes a layer made of a highly conductive metal such as Ag, Cu (copper), Au, or Al. For the purpose of making the surface of the electrode easy to wet with solder, the metal layer preferably includes a layer made of Au or a platinum group element as the uppermost layer. Since Au and platinum group elements hardly form an oxide film on the surface, the surface of the layer made of Au or platinum group elements is easily wetted by solder. In order to improve the bonding property between the electrode and the solder, the uppermost layer may be formed of Sn (tin) or solder. Here, Sn is a metal frequently used as a solder component. In order to reduce the thermal stress applied to the Ti—W alloy layer due to the lamination of another metal layer on the Ti—W alloy layer, the laminated metal layer is made of an Au layer or an Au layer and another metal. It is preferable to make a laminated body with the layer which consists of. Particularly preferably, the layer immediately above the Ti—W alloy layer is an Au layer. This is because Au is a soft and easily deformable metal. By reducing the thermal stress applied to the Ti—W alloy layer, problems such as electrode deformation and peeling and instability of the contact state between the electrode and the n-type contact layer can be suppressed. From the viewpoint of electrode stability, it is the Al layer that is not preferably laminated on the Ti—W alloy layer (particularly immediately above). This is because Al has a particularly large coefficient of thermal expansion, and when an Al layer is laminated, the thermal stress received by the Ti—W alloy layer increases.

There is no limitation in the formation method of a Ti-W alloy layer, The conventionally well-known formation method of a Ti-W alloy thin film can be used suitably. Preferably, the Ti—W alloy layer is formed by a sputtering method using a Ti—W target. For details of the Ti-W target, Patent Document 7, Patent Document 8, Patent Document 9, and other known documents can be referred to. The Ti—W alloy layer formed using the Ti—W target contains impurities inevitably contained in the target in addition to Ti and W, but such impurities that are difficult to remove from the raw material. Is allowed to be contained in the Ti-W alloy layer. The film thickness of the Ti—W alloy layer can be, for example, 0.01 μm to 1 μm, and preferably 0.05 to 0.5 μm. The Ti concentration of the Ti—W alloy layer is not particularly limited, but when formed by sputtering, if the content of the Ti component in the Ti—W target is less than 5 wt%, the formed Ti—W alloy thin film is peeled off. It becomes easy (patent document 7). Since the Ti concentration of the Ti—W alloy layer formed by sputtering is lower than the Ti content of the target, the Ti concentration of the Ti—W alloy layer is preferably 5 wt% or more. In addition, the higher the Ti concentration of the Ti—W alloy layer, the lower the heat resistance of the electrode. Therefore, the Ti concentration of the Ti—W alloy layer is preferably 50 wt% or less, and preferably 25 wt% or less. More preferred is 10 wt% or less.

An electrode that is in contact with the n-type contact layer with a Ti—W alloy layer formed by a sputtering method has a contact resistance with the n-type contact layer that is low enough that there is no practical problem without performing heat treatment. Therefore, it is not necessary to perform heat treatment for the purpose of reducing the contact resistance. From this, after forming the Ti—W alloy layer, it is possible to continuously stack an Sn layer or a solder layer having a low melting point. When the Ti concentration of the Ti—W alloy layer is 10% or less, the roughness of the electrode surface associated with the heat treatment is reduced. Therefore, it is preferable to stabilize the electrode state by the heat treatment before use. When heat treatment is performed, components of the n-type contact layer (elements constituting the nitride semiconductor crystal, impurities added for imparting conductivity, etc.) diffuse into the Ti—W alloy layer, or n The component of the Ti—W alloy layer may diffuse inside the mold contact layer, but is allowed as long as the effect of the present invention is not impaired.

Next, specific embodiments of the present invention will be described with reference to the drawings. In the following, for convenience, the surface on the side of the substrate on which the nitride semiconductor layer is formed is referred to as the “front surface”, and the surface on which the nitride semiconductor layer is not formed is referred to as the “back surface”. I will call it.

(First embodiment)
FIG. 1 is a cross-sectional view showing the structure of a GaN-based LED according to the first embodiment of the present invention. This GaN-based LED has a substrate 110 made of sapphire and a nitride semiconductor layer 120 epitaxially grown thereon via a buffer layer (not shown). The nitride semiconductor layer 120 includes a substrate 110. In order from the side, an n-type GaN layer 121, an InGaN light emitting layer 122, and a p-type GaN layer 123 are included. The n-type GaN layer 121 is an n-type contact layer, and an n-side electrode P110 is formed on the partially exposed n-type GaN layer 121. A p-side electrode P120 having no translucency is formed on almost the entire surface of the p-type GaN layer P123. The n-side electrode P110 is a laminate including a Ti—W alloy layer P111 (thickness: 100 nm) in contact with the n-type GaN layer 121 and an Au layer P112 (thickness: 200 nm) laminated thereon. The p-side electrode P120 includes an Rh (rhodium) layer P121 (thickness 20 nm), a Pt (platinum) layer P122 (thickness 100 nm), and an Au layer P123 (thickness 200 nm) in this order from the side in contact with the p-type GaN layer 123. After forming the laminated body containing, it heat-processes. This GaN-based LED is flip-chip mounted with the front side of the substrate facing the support in order to extract light generated in the InGaN light emitting layer 122 from the back side of the substrate 110.

Next, a method for manufacturing the GaN-based LED shown in FIG. 1 will be described.
First, on a substrate 110 made of sapphire, a buffer layer (not shown) made of GaN or the like, an n-type GaN layer 121, an InGaN light emitting layer 122 using a vapor phase epitaxial growth method such as MOVPE method, HVPE method, MBE method or the like. The p-type GaN layer 123 is sequentially grown and laminated to form the nitride semiconductor layer 120. Changes in the composition of the nitride semiconductor constituting each layer included in this laminate, changes in each layer to a multilayer film structure, changes to add various functional layers such as a high-temperature buffer layer, cladding layer, strain relaxation layer, etc. This can be appropriately carried out with reference to a known technique.

Next, after an Rh layer, a Pt layer, and an Au layer are sequentially formed and stacked on the surface of the p-type GaN layer 123 by using an electron beam evaporation method, heat treatment is performed at 500 ° C. for 1 minute using an RTA apparatus. To form the p-side electrode P120. Next, using a reactive ion etching method, etching is performed from the surface side of the p-type GaN layer 123 to a depth reaching the n-type GaN layer 121, and a part of the p-type GaN layer 123 and the InGaN light emitting layer 122. And the surface of the n-type GaN layer 121 is partially exposed. Next, an n-side electrode P110 is formed by forming and laminating a Ti—W alloy layer and an Au layer in this order on the exposed surface of the n-type GaN layer 121 using RF sputtering. The Ti—W alloy layer is formed by RF sputtering using a Ti—W target (manufactured by Mitsubishi Materials Corporation, product name: 4N W-10 wt% Ti target) as a target, and Ar (argon) as a sputtering gas, and RF power: It can be performed under the conditions of 200 W and sputtering gas pressure: 1.0 × 10 ⁻¹ Pa. The n-side electrode P110 may be heat-treated. For example, the wafer on which the n-side electrode is formed is heat-treated at 500 ° C. for 1 minute in a nitrogen atmosphere using an RTA apparatus. This heat treatment may be performed after the formation of an insulating protective film described later.

Next, an insulating protective film (not shown) made of silicon oxide and having a thickness of 300 nm is formed on the exposed portion of the nitride semiconductor layer 120 without being covered with the electrode, using a plasma CVD method. Finally, the wafer is cut using a well-known method in this field such as dicing, scribing, laser cutting, etc., and the GaN-based LED is formed into a chip shape.

(Second Embodiment)
In the GaN-based LED according to the second embodiment of the present invention, a substrate made of an n-type nitride semiconductor is used as a contact layer. FIG. 2 is a structural diagram of the GaN-based LED according to the second embodiment, FIG. 2 (a) is a top view, and FIG. 2 (b) is a cross section taken along line XY of FIG. 2 (a). FIG. This GaN-based LED includes a substrate 210 made of n-type GaN, and a nitride semiconductor layer 220 epitaxially grown thereon via a buffer layer (not shown). The nitride semiconductor layer 220 includes: In order from the substrate 210 side, an n-type GaN layer 221, an InGaN light emitting layer 222, and a p-type GaN layer 223 are included. On the back surface of the substrate 210, a reflective film P230 that is a single layer film (thickness: 100 nm) of Ag (silver) is formed. The reflective film P230 has a circular opening at the center. FIG. 3 is a top view illustrating only the reflective film P230. On the back surface of the substrate 210, an n-side electrode P210 is further formed so as to cover the reflective film P230. The n-side electrode P210 is made of a single layer film (thickness: 200 nm) of Ti—W alloy, and is in contact with the back surface of the substrate 210 through the opening of the reflective film P230. A p-side electrode P220 is formed on the p-type GaN layer 223. The p-side electrode P220 includes a translucent ohmic electrode P221 (thickness 600 nm) made of ITO (indium tin oxide) formed so as to cover substantially the entire surface of the p-type GaN layer 223, and an upper surface thereof. The bonding pad P222 is formed in part. The bonding pad P222 is composed of a Ti (titanium) layer P222a (thickness 30 nm) and an Au layer P222b (thickness 400 nm) laminated thereon, above the opening provided in the reflective film P230. Is located. An insulating current barrier layer B made of silicon oxide is formed in a region on the p-type layer 223 including the projected portion of the bonding pad P222, thereby preventing contact between the ohmic electrode P221 and the p-type layer 223.

The GaN-based LED shown in FIG. 2 is fixed to the surface of the external electrode by joining an n-side electrode P210 provided on the back side of the substrate 210 and an external electrode (negative electrode) via solder. Can do. The electrical connection between the p-side electrode P220 and the external electrode (positive electrode) is performed by connecting the bonding pad 222 and the external electrode via a bonding wire. Light generated in the light emitting layer 222 is radiated to the outside of the chip through the translucent ohmic electrode P221. A part of the light traveling from the light emitting layer 222 toward the back surface of the substrate 210 is reflected by the n-side electrode P210 made of a Ti—W alloy, while the other part is a reflective film P230 made of Ag having a high reflectance. Therefore, the light emission output of the LED is improved as compared with the case where the reflective film P230 is not provided. In addition, since the current barrier layer B is provided on the shortest path connecting the portion where the n-side electrode P210 is in contact with the substrate 210 and the bonding pad P222, current concentration on the path is suppressed, Light emission from the projected portion of the bonding pad P222, which is blocked by the bonding pad P222 and hardly radiated out of the chip, is suppressed.

In the GaN-based LED shown in FIG. 2, the shape, number, position, and the like of the openings provided in the reflective film P230 can be arbitrarily set. The n-side electrode P210 may be configured to be in contact with the substrate 210 in a region around the reflective film P230, and FIG. 4 is a cross-sectional view of the GaN-based LED configured as such. In the GaN-based LED shown in FIG. 4, a reflective film P230 having no opening is formed on the back surface of the substrate 210 made of n-type GaN, and from above, the end face of the reflective film P230 is covered so that Ti− An n-side electrode P210 made of a W alloy single layer film is formed. The n-side electrode P210 is in contact with the back surface of the substrate 210 around the reflective film P230.

In the GaN-based LED shown in FIGS. 2 and 4, a part of the Ti—W alloy layer constituting the n-side electrode P210 is formed so as to cover the surface of the reflective film P230. With this configuration, since the solder bonded to the n-side electrode P210 is prevented from coming into contact with the reflective film P230, the reflectance of the reflective film P230 due to the combination of Ag constituting the reflective film P230 with the solder Is prevented.

In the GaN-based LED according to the second embodiment, the n-side electrode may be composed of a Ti—W alloy layer in contact with the n-type contact layer and a bonding layer formed thereon. Here, the bonding layer is a metal layer to which solder is bonded during mounting. The bonding layer preferably includes a layer made of Au, a platinum group element, Sn, or solder as a surface layer. FIG. 5 shows a cross-sectional view of a GaN-based LED having such an n-side electrode. In the example shown in FIG. 5A, the entire n-side electrode P210 formed on the back side of the substrate 210 made of n-type GaN has a two-layer structure composed of a Ti—W alloy layer P211 and a bonding layer P212. A part of the Ti—W alloy layer P211 is in contact with a part of the back surface of the substrate 210. With this configuration, the bonding layer P212 and the reflective film P230 are separated from each other by the Ti—W alloy layer P211. Therefore, particularly when the P230 is a metallic reflective film, the bonding layer P212 is configured. There is an effect that an undesirable alloying reaction between the metal and the metal constituting the reflective film P230 is prevented. In the example of FIG. 5B, the Ti—W alloy layer P211 constituting the n-side electrode P210 is not formed so as to extend to the surface of the reflective film P230, and the bonding layer P212 is the Ti—W alloy layer P211. And the reflective film P230.

(Third embodiment)
The GaN-based LED according to the third embodiment of the present invention is in contact with the p-type layer as a p-side contact layer, in addition to the n-type layer and the p-type layer that form the pn junction that becomes the light-emitting portion. One n-type layer is included. FIG. 6 is a cross-sectional view of such a GaN-based LED according to the third embodiment. This GaN-based LED has a substrate 310 made of sapphire and a nitride semiconductor layer 320 epitaxially grown thereon via a buffer layer (not shown). The nitride semiconductor layer 320 includes a substrate 310. In order from the side, a first n-type GaN layer 321, an InGaN light emitting layer 322, a p-type GaN layer 323, and a second n-type GaN layer 324 are included. Here, the first n-type GaN layer 321 is an n-side contact layer, and the second n-type GaN layer 324 is a p-side contact layer. Both contact layers are n-type contact layers. A reflective film P330 that is a single layer film of Ag is formed on the second n-type layer 324, and a p-side electrode P320 is formed to cover the reflective film P330. The p-side electrode P320 is made of a single layer film (thickness: 200 nm) of a Ti—W alloy and is in contact with the second n-type GaN layer 324 around the opening provided in the reflective film P330 and the reflective film P330. Yes. Further, on the surface of the first n-type layer 321 exposed by removing a part of the light-emitting layer 322, the p-type GaN layer 323, and the second n-type layer 324, a single layer film of Ti—W alloy ( An n-side electrode P310 having a thickness of 200 nm is formed. This GaN-based LED is flip-chip mounted with the front surface side of the substrate facing the support in order to extract light generated in the InGaN light emitting layer 322 from the back surface side of the substrate 310.

In the third embodiment, when a light-transmitting semiconductor substrate made of GaN, AlGaN, SiC, GaP, ZnO or the like imparted with n-type conductivity is used as the substrate 310, a GaN-based LED shown in FIG. In addition, a configuration in which the n-side electrode P310 is provided on a part of the back surface of the substrate 310 can be employed. Here, the n-side electrode P310 can be, for example, a stacked body in which an Au layer is stacked on a Ti layer. In the case where the substrate 310 is made of an n-type nitride semiconductor, the layer in contact with the substrate is preferably a Ti—W alloy layer. In the example shown in FIG. 7, the p-side electrode P320 is composed of a Ti—W alloy layer P321 in contact with the n-type contact layer (second n-type layer 324) and a bonding layer P322 formed thereon. ing. In the GaN-based LED shown in FIG. 7, the bonding layer P322 and the external electrode (positive electrode) are bonded to each other through solder, so that fixing of the chip and electrical connection between the electrodes can be performed simultaneously. The electrical connection between the n-side electrode P310 and the external electrode (negative electrode) is performed by connecting these electrodes via a bonding wire.

(Fourth embodiment)
In the GaN-based LED according to the fourth embodiment of the present invention, an n-type layer, a light emitting layer, and a p-type layer are grown and stacked in this order on a crystal growth substrate, and then the crystal growth substrate is used as a nitride semiconductor. It is manufactured by bonding a conductive substrate to an exposed n-type layer through an n-side electrode. FIG. 8 is a cross-sectional view showing the structure of a GaN-based LED according to the fourth embodiment. A substrate 410 made of CuW and a nitride semiconductor layer 420 bonded on the substrate 410 via an n-side electrode P410 are shown. have. The nitride semiconductor layer 420 includes an n-type GaN layer 421, an InGaN light emitting layer 422, and a p-type GaN layer 423 in this order from the substrate 410 side. On the lower surface (surface on the substrate 410 side) of the n-type GaN layer 421 that is an n-type contact layer, a reflective film P430 that is a single layer film (thickness 100 nm) of Ag is formed, and the n-side electrode P410 is The lower surface of the n-type GaN layer 421 is in contact with an opening provided in the central portion of the reflective film P430. The n-side electrode P410 has a laminated structure including a Ti—W alloy layer P411 in contact with the n-type GaN layer 421 and a solder layer P412 that bonds the Ti—W alloy layer 411 and the substrate 410 together. A p-side electrode P420 is formed on the p-type GaN layer 423. The p-side electrode P420 is formed on a part of the upper surface of the translucent ohmic electrode P421 made of ITO (indium tin oxide), which is formed so as to cover substantially the entire surface of the p-type GaN layer 423. It is comprised from the bonding pad P422. The bonding pad P422 includes a Ti (titanium) layer P422a and an Au layer 422b laminated thereon, and is located above the opening provided in the reflective film P430. An insulating current barrier layer B made of silicon oxide is formed in a region on the p-type layer 423 including the projected portion of the bonding pad P422, thereby preventing contact between the ohmic electrode P421 and the p-type GaN layer 423.

The GaN-based LEDs according to the second to fourth embodiments have a reflective film in contact with the n-type contact layer. In the above, each embodiment has been described with an example in which the reflective film is a single Ag film, but the reflective film is not limited to this, and promotes reflection of light on the surface of the n-type contact layer. Any film may be used as long as it is a film to be used. Therefore, the reflective film may be a metal layer other than Ag (however, a reflectance higher than that of the Ti—W alloy layer) or a dielectric multilayer type reflective layer. Preferred metals when the reflective film is a metal layer include Al and platinum group elements (Rh, Pt, etc.) in addition to Ag. Further, the reflective film may be a translucent layer made of an insulating transparent material having a lower refractive index than that of the n-type contact layer, such as silicon oxide, aluminum oxide, and spinel. At the interface between the reflective film made of such a light-transmitting layer and the n-type contact layer, a component of which incident angle is larger than the total reflection critical angle among the light incident from the n-type contact layer side undergoes total reflection. This is because the loss associated with the total reflection is smaller than the loss associated with the reflection by the surface of the Ti—W alloy. The reflective film is also a translucent layer having a lower refractive index than the n-type contact layer, a dielectric multilayer film type reflective layer and a metal layer, or a combination of these three. Also good. In this case, the light transmitting layer, the dielectric multilayer reflective layer, and the metal layer are preferably used in this order from the n-type contact layer side on which light is incident.

It is sectional drawing which shows the structure of the nitride semiconductor light-emitting diode which concerns on embodiment of this invention. FIG. 2 is a structural diagram of a nitride semiconductor light emitting diode according to an embodiment of the present invention, in which FIG. 2A is a top view and FIG. 2B is a cross-sectional view. FIG. 3 is a top view illustrating a reflection film extracted from the nitride semiconductor light emitting diode illustrated in FIG. 2. It is sectional drawing which shows the structure of the nitride semiconductor light-emitting diode which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the nitride semiconductor light-emitting diode which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the nitride semiconductor light-emitting diode which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the nitride semiconductor light-emitting diode which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the nitride semiconductor light-emitting diode which concerns on embodiment of this invention.

Explanation of symbols

110, 210, 310, 410 Substrate 120, 220, 320, 420 Nitride semiconductor layers 121, 221, 321, 421 N-type nitride semiconductor layers 122, 222, 322, 422 Light emitting layers 123, 223, 323, 423 p-type Nitride semiconductor layers P110, P210, P310, P410 n-side electrodes P120, P220, P320, P420 p-side electrodes P230, P330, P430 Reflective film B Current barrier layer

Claims (5)

A nitride semiconductor light-emitting diode comprising a nitride semiconductor layer,
The nitride semiconductor layer includes a light emitting layer and an n-type contact layer laminated directly or indirectly on the light emitting layer,
The n-type contact layer has a first main surface on the side opposite to the light emitting layer side,
A reflective film for reflecting light generated in the light emitting layer is formed on a part of the first main surface of the n-type contact layer;
An electrode is formed on the first main surface of the n-type contact layer so as to be in contact with a region other than the region where the reflective film is formed;
The electrode includes a Ti—W alloy layer in contact with the n-type contact layer,
A first metal layer is laminated on the Ti-W alloy layer,
The first metal layer is a solder layer or a metal layer to which solder is joined,
The reflective film has a second metal layer having a higher reflectance than the Ti-W alloy layer,
The Ti-W alloy layer and the first metal layer have a portion covering the reflective film, and the first metal layer and the second metal layer are separated by the Ti-W alloy layer in the portion. This prevents the alloying reaction between the first metal layer and the second metal layer.
A nitride semiconductor light emitting diode characterized by the above. The nitride semiconductor light-emitting diode according to claim 1 , wherein the n-type contact layer is a substrate made of an n-type nitride semiconductor. The reflective film is between the n-type contact layer and the second metal layer comprises a light-transmitting layer having a lower refractive index than the n-type contact layer, the nitride according to claim 1 or 2 Semiconductor light emitting diode. 4. The nitride semiconductor light emitting diode according to claim 3 , wherein the reflective film includes a dielectric multilayer film type reflective layer between the second metal layer and the translucent layer . 5. The nitride semiconductor light-emitting diode according to claim 1, wherein the second metal layer is an Ag layer or an Al layer.