Nitride-based light-emitting device and method of manufacturing the same

A nitride-based light-emitting device capable of suppressing reduction of the light output characteristic as well as reduction of the manufacturing yield is provided. This nitride-based light-emitting device comprises a conductive substrate at least containing a single type of metal and a single type of inorganic material having a lower linear expansion coefficient than the metal and a nitride-based semiconductor element layer bonded to the conductive substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nitride-based light-emitting device and a method of manufacturing the same, and more particularly, it relates to a nitride-based light-emitting device comprising a nitride-based semiconductor element layer and a method of manufacturing the same.

2. Description of the Background Art

A nitride-based light-emitting device such as a nitride-based light-emitting diode device comprising a nitride-based semiconductor element layer consisting of a nitride-based semiconductor is actively developed at present. In order to employ a nitride-based light-emitting diode device as the light source for a lighting fixture, improvement of the light output characteristic of the nitride-based light-emitting diode device and increase of an applied current have recently been developed in particular. In order to form such a nitride-based light-emitting diode device, a nitride-based semiconductor element layer is grown on a sapphire substrate requiring a more reasonable cost than a high-priced nitride-based semiconductor substrate of GaN or the like.

FIG. 35is a sectional view showing the structure of a conventional nitride-based light-emitting diode device. Referring toFIG. 35, a buffer layer102, an underlayer103, an n-type contact layer104, an n-type cladding layer105and an active layer106are successively formed on an insulating sapphire substrate101in the conventional nitride-based light-emitting diode device. A cap layer107, a p-type cladding layer108and a p-type contact layer109are successively formed on the active layer106. The n-type contact layer104, the n-type cladding layer105, the active layer106, the cap layer107, the p-type cladding layer108and the p-type contact layer109constitute a nitride-based semiconductor element layer100.

A prescribed region of the nitride-based semiconductor element layer100is removed between the upper surface of the p-type contact layer109and a portion of an intermediate depth of the n-type contact layer104, for partially exposing the n-type contact layer104. A p-side electrode110is formed on the p-type contact layer109, while an n-side electrode111is formed on a prescribed region of the exposed surface of the n-type contact layer104.

In the conventional nitride-based light-emitting diode device shown inFIG. 35, as hereinabove described, the p-side electrode110and the n-side electrode11are taken out from the surface of the nitride-based semiconductor element layer100opposite to the sapphire substrate101. In order to increase the emission area for improving the light output characteristic, therefore, light must be emitted from the side of the sapphire substrate101formed with neither the p-side electrode110nor the n-side electrode111. Therefore, flip chip bonding is employed for mounting the conventional nitride-based light-emitting diode device shown inFIG. 35to a base (not shown) from the side of the p-side electrode110and the n-side electrode111.

However, the conventional nitride-based light-emitting diode device shown inFIG. 35has a step between the p-side electrode110formed on the p-type contact layer109and the n-side electrode111formed on the exposed surface of the n-type contact layer104. In order to assemble the conventional nitride-based light-emitting diode device shown inFIG. 35by flip chip bonding, therefore, it is necessary to provide the base with a step portion corresponding to the step between the p-side electrode110and the n-side electrode111with precise position control for attaining coincidence between the positions of the step portion and the p-side electrode110and the n-side electrode111. Therefore, the manufacturing yield is disadvantageously reduced. Further, the thermal conductivity of the sapphire substrate101of the conventional nitride-based light-emitting diode device shown inFIG. 35is so low that it is disadvantageously difficult to sufficiently radiate heat generated in the nitride-based semiconductor element layer100.

Therefore, generally proposed is a nitride-based light-emitting diode device formed by growing a nitride-based semiconductor element layer on a sapphire substrate and thereafter bonding a cleavable conductive substrate of GaAs or the like to the nitride-based semiconductor element layer and removing the sapphire substrate, as disclosed in Japanese Patent Laying-Open No. 9-8403 (1997), for example. In the aforementioned nitride-based light-emitting diode device disclosed in Japanese Patent Laying-Open No. 9-8403, a p-side electrode and an n-side electrode can be oppositely arranged through the nitride-based semiconductor element layer due to the employment of the conductive substrate. Therefore, the nitride-based light-emitting diode device may not be assembled by flip chip bonding requiring precise position control dissimilarly to the case of employing the insulating sapphire substrate, whereby the manufacturing yield can be improved.

In the aforementioned nitride-based light-emitting diode device disclosed in Japanese Patent Laying-Open No. 9-8403, however, the thermal conductivity of the conductive substrate of GaAs or the like is so insufficient that it is disadvantageously difficult to sufficiently radiate heat generated in the nitride-based semiconductor element layer, similarly to the case of employing the sapphire substrate. Consequently, the light output characteristic is disadvantageously reduced by heat when a high current is fed to the nitride-based light-emitting diode device. Further, difference between the linear expansion coefficients of the conductive substrate of GaAs or the like and the nitride-based semiconductor element layer of GaN or the like is so large that the nitride-based light-emitting diode device is warped in the manufacturing process due to the difference between the linear expansion coefficients. Consequently, the manufacturing yield is disadvantageously reduced due to the warping of the diode device.

SUMMARY OF THE INVENTION

The present invention has been proposed in order to solve the aforementioned problems, and an object of the present invention is to provide a nitride-based light-emitting device capable of suppressing reduction of the light output characteristic as well as reduction of the manufacturing yield.

Another object of the present invention is to provide a method of manufacturing a nitride-based light-emitting device capable of suppressing reduction of the light output characteristic as well as reduction of the manufacturing yield.

In order to attain the aforementioned objects, a nitride-based light-emitting device according to a first aspect of the present invention comprises a conductive substrate at least containing a single type of metal and a single type of inorganic material having a lower linear expansion coefficient than the metal and a nitride-based semiconductor element layer bonded to the conductive substrate.

In the nitride-based light-emitting device according to the first aspect, as hereinabove described, the conductive substrate is so constituted as to contain at least a single type of metal and a single type of inorganic material having a lower linear expansion coefficient than the metal, whereby the conductive substrate can be provided with high thermal conductivity similar to that of the metal. When a high current is fed to the nitride-based light-emitting device, therefore, heat generated in the nitride-based semiconductor element layer can be sufficiently radiated toward the conductive substrate, whereby reduction of the light output characteristic caused by heat can be suppressed. Consequently, the nitride-based light-emitting device can be provided with a high rated output. Further, the linear expansion coefficient of the conductive substrate can be approached to that of the nitride-based semiconductor element layer by adjusting the mixing ratio between the metal and the inorganic material through the function of the inorganic material having a low linear expansion coefficient contained in the conductive substrate, whereby the difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer can be reduced. Thus, the nitride-based light-emitting device can be inhibited from warping or cracking resulting from large difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor layer in the manufacturing process, whereby reduction of the manufacturing yield can be suppressed. Further, the conductive substrate is so employed that two electrodes can be oppositely arranged through the nitride-based semiconductor element layer. Thus, the emission area can be increased as compared with a nitride-based light-emitting device employing an insulating substrate having two electrodes arranged only on one side of a nitride-based semiconductor element layer, whereby the light output characteristic can be improved. In addition, the nitride-based light-emitting device may not be assembled by flip chip bonding requiring precise position control for improving the light output characteristic, whereby reduction of the manufacturing yield can be suppressed also by this.

In the aforementioned nitride-based light-emitting device according to the first aspect, the inorganic material preferably includes a metal oxide. According to this structure, the linear expansion coefficient of the conductive substrate containing the metal and the inorganic material (metal oxide) can be easily rendered lower than that of a conductive substrate consisting of only a metal.

In the aforementioned nitride-based light-emitting device according to the first aspect, the conductive substrate and the nitride-based semiconductor element layer are preferably bonded to each other through at least either an electrode or a conductive material. According to this structure, the conductive substrate can be easily bonded to the nitride-based semiconductor element layer.

In this case, the conductive substrate and the nitride-based semiconductor element layer are preferably bonded to each other through the electrode. According to this structure, the conductive substrate and the nitride-based semiconductor element layer can be easily bonded to each other through the electrode.

In the aforementioned structure having the conductive substrate and the nitride-based semiconductor element layer bonded to each other through the electrode, a surface of the electrode closer to the nitride-based semiconductor element layer is preferably textured, and the nitride-based semiconductor element layer is preferably formed on the textured surface of the electrode. According to this structure, light incident upon the interface between the electrode and the nitride-based semiconductor element layer is easily reflected due to the textured surface of the electrode. Thus, the reflected light is emitted from a surface (light-emitting surface) of the nitride-based semiconductor element layer opposite to the conductive substrate, whereby the light output characteristic can be improved.

In the aforementioned structure having the conductive substrate and the nitride-based semiconductor element layer bonded to each other through the electrode, a surface of the conductive substrate closer to the electrode is preferably textured, and the electrode is preferably bonded to the textured surface of the conductive substrate. According to this structure, the contact area between the conductive substrate and the electrode is so increased that heat radiation toward the conductive substrate can be further improved.

The aforementioned nitride-based light-emitting device according to the first aspect preferably further comprises a protective film covering the side surface of the nitride-based semiconductor element layer. According to this structure, the protective film can protect the nitride-based semiconductor element layer.

In the aforementioned nitride-based light-emitting device according to the first aspect, the metal preferably includes copper. According to this structure, the conductive substrate can be easily provided with high thermal conductivity similar to that of copper through the function of copper.

In the aforementioned nitride-based light-emitting device according to the first aspect, the inorganic material preferably includes copper oxide. According to this structure, the linear expansion coefficient of the conductive substrate can be easily approached to that of the nitride-based semiconductor element layer through the function of copper oxide, whereby the difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer can be reduced.

In the aforementioned nitride-based light-emitting device according to the first aspect, the metal preferably includes copper, and the inorganic material preferably includes copper oxide. The conductive substrate containing such materials has a linear expansion coefficient close to that of a nitride-based semiconductor such as GaN used for a light-emitting device and high thermal conductivity, whereby warping of the nitride-based light-emitting device resulting from large difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer can be easily suppressed while sufficiently radiating heat generated in the nitride-based semiconductor element layer toward the conductive substrate.

In the aforementioned nitride-based light-emitting device according to the first aspect, the conductive substrate preferably has thermal conductivity of at least about 100 W/m·K. According to this structure, heat generated in the nitride-based semiconductor element layer can be easily sufficiently radiated toward the conductive substrate. This point has already been experimentally confirmed.

In the aforementioned nitride-based light-emitting device according to the first aspect, the conductive substrate preferably has a Young's modulus of not more than about 120 GPa. According to this structure, the conductive substrate can be inhibited from deformation under stress. Thus, the nitride-based semiconductor element layer bonded to the conductive substrate can be inhibited from deformation under stress resulting from deformation under stress of the conductive substrate when the same is separated from a growth substrate. Therefore, the nitride-based semiconductor element layer can be inhibited from cracking, whereby reduction of the manufacturing yield resulting from cracking of the nitride-based light-emitting device can be suppressed. This point has also been already experimentally confirmed.

In the aforementioned nitride-based light-emitting device according to the first aspect, the conductive substrate preferably has a linear expansion coefficient of not more than about 18×10−6/K. According to this structure, the difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer can be easily reduced. Thus, the nitride-based light-emitting device can be inhibited from warping resulting from large difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer. This point has also been already experimentally confirmed.

A method of manufacturing a nitride-based light-emitting device according to a second aspect of the present invention comprises steps of growing a nitride-based semiconductor element layer on a growth substrate, bonding a conductive substrate at least containing a single type of metal and a single type of inorganic material having a lower linear expansion coefficient than the metal to the nitride-based semiconductor element layer and removing the growth substrate from the nitride-based semiconductor element layer to which the conductive substrate is bonded.

In the method of manufacturing a nitride-based light-emitting device according to the second aspect, as hereinabove described, the conductive substrate at least containing a single type of metal and a single type of inorganic material having a lower linear expansion coefficient than the metal is bonded to the nitride-based semiconductor element layer provided on the growth substrate and the growth substrate is thereafter removed from the nitride-based semiconductor element layer, whereby the conductive substrate can be provided with high thermal conductivity similar to that of the metal through the function of the metal contained in the conductive substrate. When a high current is fed to the nitride-based light-emitting device, therefore, heat generated in the nitride-based semiconductor element layer can be sufficiently radiated toward the conductive substrate, whereby reduction of the light output characteristic caused by heat can be suppressed. Consequently, it is possible to form a nitride-based light-emitting device having a high rated output. Further, the linear expansion coefficient of the conductive substrate can be approached to that of the nitride-based semiconductor element layer by adjusting the mixing ratio between the metal and the inorganic material through the function of the inorganic material having a low linear expansion coefficient contained in the conductive substrate, whereby the distance between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer can be reduced. Thus, the nitride-based light-emitting device can be inhibited from warping or cracking resulting from large difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer in the manufacturing process, whereby reduction of the manufacturing yield can be suppressed. Further, the conductive substrate is so employed that two electrodes can be oppositely arranged through the nitride-based semiconductor element layer. Thus, the emission area can be increased as compared with a nitride-based light-emitting device employing an insulating substrate having two electrodes arranged only on one side of a nitride-based semiconductor element layer, whereby a nitride-based light-emitting device capable of improving the light output characteristic can be formed. In addition, the nitride-based light-emitting device may not be assembled by flip chip bonding requiring precise position control for improving the light output characteristic, whereby reduction of the manufacturing yield can be suppressed also by this.

In the aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect, the inorganic material preferably includes a metal oxide. According to this structure, the linear expansion coefficient of the conductive substrate containing the metal and the inorganic material (metal oxide) can be easily rendered lower than that of a conductive substrate consisting of only a metal.

In the aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect, the step of bonding the conductive substrate to the nitride-based semiconductor element layer preferably includes a step of bonding the conductive substrate to the nitride-based semiconductor element layer through at least either an electrode or a conductive material. According to this structure, the conductive substrate can be easily bonded to the nitride-based semiconductor element layer.

In this case, the step of bonding the conductive substrate to the nitride-based semiconductor element layer preferably includes a step of bonding the conductive substrate to the nitride-based semiconductor element layer through the electrode. According to this structure, the conductive substrate and the nitride-based semiconductor element layer can be easily bonded to each other through the electrode.

In the aforementioned structure including the step of bonding the conductive substrate to the nitride-based semiconductor element layer through the electrode, the step of bonding the conductive substrate to the nitride-based semiconductor element layer through the electrode preferably includes steps of texturing a surface of the nitride-based semiconductor element layer, forming the electrode on the textured surface of the nitride-based semiconductor element layer and bonding the conductive substrate to a surface of the electrode opposite to the nitride-based semiconductor element layer. According to this structure, light incident upon the interface between the electrode and the nitride-based semiconductor element layer is easily reflected due to the textured surface of the electrode. Thus, the reflected light is emitted from a surface (light-emitting surface) of the nitride-based semiconductor element layer opposite to the conductive substrate, whereby the light output characteristic can be improved.

In the aforementioned structure including the step of bonding the conductive substrate to the nitride-based semiconductor element layer through the electrode, the step of forming the electrode on the textured surface of the nitride-based semiconductor element layer preferably includes a step of forming the electrode on the textured surface of the nitride-based semiconductor element layer to have a textured surface reflecting the texture on the surface of the nitride-based semiconductor element, and the step of bonding the conductive substrate to the surface of the electrode opposite to the nitride-based semiconductor element layer preferably includes steps of texturing a surface of the conductive substrate and bonding the conductive substrate to the surface of the electrode opposite to the nitride-based semiconductor element layer so that the positions of projecting and recess portions of the electrode and the positions of recess and projecting portions of the conductive substrate coincide with each other. According to this structure, the contact area between the conductive substrate and the electrode is so increased that heat radiation toward the conductive substrate can be further improved.

The aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect preferably further comprises a step of forming a protective film to cover the side surface of the nitride-based semiconductor element layer in advance of the step of bonding the conductive substrate to the nitride-based semiconductor element layer. According to this structure, the protective film can protect the nitride-based semiconductor element layer.

In the aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect, the metal may include copper. According to this structure, the conductive substrate can be easily provided with high thermal conductivity similar to that of copper through the function of copper.

In the aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect, the inorganic material may include copper oxide. According to this structure, the linear expansion coefficient of the conductive substrate can be easily approached to that of the nitride-based semiconductor element layer through the function of copper oxide, whereby the difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer can be reduced.

In the aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect, the metal may include copper, and the inorganic material may include copper oxide. The conductive substrate containing such materials has a linear expansion coefficient close to that of a nitride-based semiconductor such as GaN used for a light-emitting device and high thermal conductivity, whereby warping of the nitride-based light-emitting device resulting from large difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer can be easily suppressed while sufficiently radiating heat generated in the nitride-based semiconductor element layer toward the conductive substrate.

In the aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect, the conductive substrate may have thermal conductivity of at least about 100 W/m·K. According to this structure, heat generated in the nitride-based semiconductor element layer can be easily sufficiently radiated toward the conductive substrate. This point has already been experimentally confirmed.

In the aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect, the conductive substrate may have a Young's modulus of not more than about 120 GPa. According to this structure, the conductive substrate can be inhibited from deformation under stress. Thus, the nitride-based semiconductor element layer bonded to the conductive substrate can be inhibited from deformation under stress resulting from deformation under stress of the conductive substrate when the same is separated from the growth substrate. Therefore, the nitride-based semiconductor element layer can be inhibited from cracking, whereby reduction of the manufacturing yield resulting from cracking of the nitride-based light-emitting device can be suppressed. This point has also been already experimentally confirmed.

In the aforementioned method of manufacturing a nitride-based light-emitting device according to the second aspect, the conductive substrate may have a linear expansion coefficient of not more than about 18×10−6/K. According to this structure, the difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer can be easily reduced. Thus, the nitride-based light-emitting device can be inhibited from cracking resulting from large difference between the linear expansion coefficients of the conductive substrate and the nitride-based semiconductor element layer. This point has also been already experimentally confirmed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

The structure of a nitride-based light-emitting diode device according to a first embodiment of the present invention is described with reference toFIG. 1.

In the nitride-based light-emitting diode device according to the first embodiment, a nitride-based semiconductor element layer10is formed on a conductive substrate1through a p-side electrode2, as shown inFIG. 1. According to the first embodiment, the conductive substrate1has a thickness of about 50 μm to about 2 mm, and contains copper and copper oxide mixed with each other at a ratio of 20:80.

More specifically, the p-side electrode2prepared by successively forming an Au layer having a thickness of about 100 nm and a Pd layer having a thickness of about 300 nm from the side closer to the conductive substrate1is bonded to the conductive substrate1. The p-side electrode2is an example of the “electrode” in the present invention. A p-type contact layer3of GaN, AlGaN or InGaN doped with Mg, having a thickness of about 1 nm to about 1 μm, is formed on the p-side electrode2. A p-type cladding layer4of AlGaN (Al composition ratio≦50%) doped with Mg, having a thickness of about 1 nm to about 1 μm, is formed on the p-type contact layer3. A cap layer5of Mg-doped or undoped GaN or AlGaN having a thickness of about 10 nm to about 40 nm is formed on the p-type cladding layer4. An active layer6including a well layer of InGaN having a thickness of about 3 nm and a barrier layer of InGaN or GaN having a thickness of about 10 nm is formed on the cap layer5. This active layer6has a multiple quantum well (MQW) structure including a plurality of well layers and a plurality of barrier layers or a single quantum well (SQW) structure including a single well layer and a single barrier layer.

An n-type cladding layer7of AlGaN (Al composition ratio≦50%) doped with Si or Ge, having a thickness of about 1 nm to about 1 μn, is formed on the active layer6. An n-type contact layer8of GaN or AlGaN doped with Si or Ge, having a thickness of about 10 nm to about 5 μm, is formed on the n-type cladding layer7. The p-type contact layer3, the p-type cladding layer4, the cap layer5, the active layer6, the n-type cladding layer7and the n-type contact layer8constitute a nitride-based semiconductor element layer10. An n-side electrode9is formed on a prescribed region of the n-type contact layer8constituting the nitride-based semiconductor element layer10. This n-side electrode9is constituted of an Al layer having a thickness of about 10 nm, a Pd layer having a thickness of about 10 nm and an Au layer having a thickness of about 100 nm in ascending order.

A manufacturing process for the nitride-based light-emitting diode device according to the first embodiment is now described with reference toFIGS. 1 to 7.

As shown inFIG. 2, a buffer layer12of GaN or AlGaN having a thickness of about 10 nm to about 100 nm is grown on the (0001) plane of a sapphire substrate11having a thickness of about 400 μm for serving as a growth substrate by MOCVD (metal organic chemical vapor deposition). Then, an underlayer13of undoped GaN or AlGaN having a thickness of about 1 μm is grown on the buffer layer12. Then, the nitride-based semiconductor element layer10consisting of the layers3to8having the aforementioned compositions and thicknesses is grown on the underlayer13. At this time, the n-type contact layer8, the n-type cladding layer7, the active layer6, the cap layer5, the p-type cladding layer4and the p-type contact layer3are grown in this order for forming the nitride-based semiconductor element layer10. Thereafter heat treatment or electron beam irradiation is so performed as to convert the p-type cladding layer4and the p-type contact layer3to the p type.

As shown inFIG. 3, the p-side electrode2is formed on the p-type contact layer3by vacuum evaporation or the like. In order to form the p-side electrode2, the Pd layer having the thickness of about 300 nm and the Au layer having the thickness of about 100 nm are formed in this order.

As shown inFIG. 4, the conductive substrate1having the thickness of about 50 μm to about 2 mm and containing copper and copper oxide mixed with each other at the ratio of 20:80 is boned to the upper surface of the p-side electrode2. At this time, the conductive substrate1may be bonded to the upper surface of the p-side electrode2through solder of Au—Sn or Pd—Sn or through conductive paste of Ag. The solder or the conductive paste is an example of the “conductive material” in the present invention. Alternatively, the conductive substrate1may be directly pasted onto the upper surface of the p-side electrode2and pressurized under a temperature condition of about 400° C. to about 1000° C., to be bonded to the upper surface of the p-side electrode2. Further alternatively, the conductive substrate1may be bonded to the upper surface of the p-side electrode2by anodic bonding applying an electric field to the conductive substrate1. Thereafter the sapphire substrate11is removed by polishing or laser irradiation. Thereafter the buffer layer12and the underlayer13are removed by dry etching through CF4gas or the like or wet etching through a hot phosphoric acid solution or the like. Thus, the surface of the n-type contact layer8is exposed as shown inFIG. 5.

As shown inFIG. 6, the n-side electrode9is formed on the prescribed region of the exposed surface of the n-type contact layer8by vacuum evaporation or the like. At this time, the Al layer having the thickness of about 10 nm, the Pd layer having the thickness of about 10 nm and the Au layer having the thickness of about 100 nm are formed in this order for forming the n-side electrode9.

As shown inFIG. 7, the device is separated from an adjacent device along a separation region10a. At this time, the separation region10amay be notched through dicing, for separating the device from the adjacent device along the notch. Alternatively, the separation region10amay be notched through etching, for separating the device from the adjacent device along the notch. Further alternatively, the separation region10aof the conductive substrate1may be notched through dicing while notching the separation region10aof the nitride-based semiconductor element layer10through etching, for separating the device from the adjacent device along the notches formed through dicing and etching respectively. When dicing and etching are combined with each other in the aforementioned manner, no cutting tool comes into contact with the nitride-based semiconductor element layer10, and hence damage on the nitride-based semiconductor element layer10is reduced. Thus, the nitride-based light-emitting diode device according to the first embodiment is formed as shown inFIG. 1.

According to the first embodiment, as hereinabove described, the conductive substrate1is so formed as to contain copper and copper oxide mixed with each other at the ratio of 20:80, whereby the conductive substrate1can be provided with high thermal conductivity similar to that of copper. When a high current is fed to the nitride-based light-emitting diode device, therefore, heat generated in the nitride-based semiconductor element layer10bonded to the conductive substrate1can be sufficiently radiated toward the conductive substrate1, whereby reduction of the light output characteristic caused by heat can be suppressed. Consequently, the nitride-based light-emitting diode device can be provided with a high rated output. Further, the linear expansion coefficient of the conductive substrate1can be so approached to that of the nitride-based semiconductor element layer10that the difference between the linear expansion coefficients of the conductive substrate1and the nitride-based semiconductor element layer10can be reduced. Thus, the nitride-based light-emitting diode device can be inhibited from warping or cracking resulting from large difference between the linear expansion coefficients of the conductive substrate1and the nitride-based semiconductor element layer10in the manufacturing process, whereby reduction of the manufacturing yield can be suppressed. In addition, the conductive substrate1is so employed that the p-side electrode2and the n-side electrode9can be oppositely arranged through the nitride-based semiconductor element layer10. Thus, the emission area can be increased as compared with a nitride-based semiconductor light-emitting diode device employing an insulating substrate having two electrodes arranged only on one side of a nitride-based semiconductor element layer, whereby the light output characteristic can be improved. Further, the nitride-based light-emitting diode device may not be assembled by flip chip bonding requiring precise position control for improving the light output characteristic, whereby reduction of the manufacturing yield can be suppressed also by this.

Second Embodiment

Referring toFIG. 8, a nitride-based light-emitting diode device according to a second embodiment of the present invention employs a conductive substrate21containing copper and copper oxide mixed with each other at a ratio of 70:30, dissimilarly to the aforementioned first embodiment.

In the nitride-based light-emitting diode device according to the second embodiment, a p-side electrode2having a composition and a thickness similar to those in the aforementioned first embodiment is bonded to the conductive substrate21containing copper and copper oxide mixed with each other at the ratio of 70:30, as shown inFIG. 8. Further, a nitride-based semiconductor element layer10constituted of layers3to8having compositions and thicknesses similar to those in the aforementioned first embodiment respectively is formed on the p-side electrode2. An n-side electrode9having a composition and a thickness similar to those in the aforementioned first embodiment is formed on a prescribed region of the n-type contact layer8constituting the nitride-based semiconductor element layer10.

A manufacturing process for the nitride-based light-emitting diode device according to the second embodiment is now described with reference toFIGS. 8 to 12.

As shown inFIG. 9, a buffer layer12and an underlayer13having compositions and thicknesses similar to those in the aforementioned first embodiment are successively grown on the (0001) plane of a sapphire substrate11serving as a growth substrate by MOCVD, similarly to the aforementioned first embodiment. Thereafter an isolation layer (gap layer)14of InGaN or AlGaN having a thickness of about 1 nm to about 1 μm and including spaces therein is formed on the underlayer13. At this time, the spaces may be formed in the isolation layer14by anodic oxidation or etching, or the isolation layer14may be formed as a porous or amorphous layer inferior in crystallinity (having a large number of cracks). The porous isolation layer14can be formed by adjusting growth conditions, or implanting ions. The amorphous isolation layer14can be formed by low-temperature growth. Alternatively, the isolation layer14may be formed by a metal film or an insulating film having clearances. The isolation layer14formed by a metal film or an insulating film having clearances can also be employed as a mask for laterally growing the nitride-based semiconductor element layer10. Then, the n-type contact layer8, the n-type cladding layer7, the active layer6, the cap layer5, the p-type cladding layer4and the p-type contact layer3having the compositions and the thicknesses similar to those in the aforementioned first embodiment are successively grown on the isolation layer14, and the p-type cladding layer4and the p-type contact layer3are thereafter converted to the p type.

As shown inFIG. 10, the p-type electrode2having the composition and the thickness similar to those in the aforementioned first embodiment is formed on the p-type contact layer3by vacuum evaporation or the like, and the conductive substrate21containing copper and copper oxide mixed with each other at the ratio of 70:30 is bonded onto the upper surface of the p-side electrode2through a process similar to that of the first embodiment shown inFIG. 4. Thereafter the nitride-based semiconductor element layer10located on the isolation layer14is isolated from the layers (the sapphire substrate11, the buffer layer12and the underlayer13) located under the isolation layer14. At this time, the isolation layer14may be removed by wet etching through a mixture of an HF solution and an HNO3solution, or by externally applying physical force. Alternatively, the nitride-based semiconductor element layer10located on the isolation layer14and the layers (11to13) located under the isolation layer14may be pulled in opposite directions, to be isolated from each other. Further alternatively, the isolation layer14may be removed by heating and melting the same by a method such as laser irradiation. Thus, the surface of the n-type contact layer8is exposed as shown inFIG. 11.

As shown inFIG. 12, the n-side electrode9having the composition and the thickness similar to those in the aforementioned embodiment is formed on the prescribed region of the exposed surface of the n-type contact layer8by vacuum evaporation or the like, and the device is separated from an adjacent device along a separation region10athrough a process similar to that of the first embodiment shown inFIG. 7. Thus, the nitride-based light-emitting diode device according to the second embodiment is formed as shown inFIG. 8.

According to the second embodiment, as hereinabove described, the conductive substrate21is so formed as to contain copper and copper oxide mixed with each other at the ratio of 70:30, whereby the conductive substrate21can be provided with high thermal conductivity similar to that of copper while the linear expansion coefficient of the conductive substrate21can be approached to that of the nitride-based semiconductor element layer10. The conductive substrate21employed in the second embodiment has a higher percentage of copper and a lower percentage of copper oxide as compared with the conductive substrate1containing copper and copper oxide mixed with each other at the ratio of 20:80 in the aforementioned first embodiment. In the conductive substrate21employed in the second embodiment, therefore, the thermal conductivity as well as the linear expansion coefficient are higher than those in the conductive substrate1employed in the aforementioned first embodiment. Thus, heat generated in the nitride-based semiconductor element layer10bonded to the conductive substrate21can be further sufficiently radiated toward the conductive substrate21as compared with the aforementioned first embodiment, whereby reduction of the light output characteristic caused by heat can be more suppressed as compared with the first embodiment. In the second embodiment, on the other hand, the difference between the linear expansion coefficients of the conductive substrate21and the nitride-based semiconductor element layer10is larger than that in the aforementioned first embodiment, and hence an effect of inhibiting the nitride-based light-emitting diode device from warping is reduced as compared with that in the first embodiment.

The remaining effects of the second embodiment are similar to those of the aforementioned first embodiment.

Third Embodiment

Referring toFIG. 13, a nitride-based light-emitting diode device according to a third embodiment of the present invention employs a conductive substrate31having thermal conductivity of about 170 W/m·K and containing copper and copper oxide mixed with each other at a ratio of 60:40, dissimilarly to the aforementioned first and second embodiments.

In the nitride-based light-emitting diode device according to the third embodiment, a p-side electrode32having a composition and a thickness similar to those of the p-side electrode2in the aforementioned first embodiment with a width smaller than that of the conductive substrate31is bonded to the conductive substrate31having the thermal conductivity of about 170 W/m·K and containing copper and copper oxide mixed with each other at the ratio of 60:40, as shown inFIG. 13. The p-side electrode32is an example of the “electrode” in the present invention. A p-type contact layer33, a p-type cladding layer34, a cap layer35, an active layer36, an n-type cladding layer37and an n-type contact layer38each having a width smaller than that of the conductive substrate31and larger than that of the p-side electrode32are successively formed on the p-side electrode32. The p-type contact layer33, the p-type cladding layer34, the cap layer35, the active layer36, the n-type cladding layer37and the n-type contact layer38have compositions and thicknesses similar to those of the p-type contact layer3, the p-type cladding layer4, the cap layer5, the active layer6, the n-type cladding layer7and the n-type contact layer8in the aforementioned first embodiment respectively. The p-type contact layer33, the p-type cladding layer34, the cap layer35, the active layer36, the n-type cladding layer37and the n-type contact layer38constitute a nitride-based semiconductor element layer30. A protective film39of SiO2, SiN, TiO2or ZrO having a thickness of about 300 nm is formed to cover regions other than the upper surface of the nitride-based semiconductor element layer30(the n-type contact layer38). An n-side electrode9having a composition and a thickness similar to those in the aforementioned first embodiment is formed on a prescribed region of the n-type contact layer38constituting the nitride-based semiconductor element layer30.

A manufacturing process for the nitride-based light-emitting diode device according to the third embodiment is now described with reference toFIGS. 13 to 19.

As shown inFIG. 14, a buffer layer42and an underlayer43are successively grown on an SiC substrate41serving as a growth substrate by MOCVD. The buffer layer42and the underlayer43have compositions and thicknesses similar to those of the buffer layer12and the underlayer13in the aforementioned first embodiment respectively. Thereafter an isolation layer44of InGaN having a high In composition ratio capable of efficiently absorbing a laser beam having a prescribed wavelength (InxGax-1N (X≦0.2) when employing a second harmonic YAG laser beam (wavelength: 532 nm), for example) is formed on the underlayer43. Then, the n-type contact layer38, the n-type cladding layer37, the active layer36, the cap layer35, the p-type cladding layer34and the p-type contact layer33are successively grown on the isolation layer44, and the p-type cladding layer34and the p-type contact layer33are thereafter converted to the p type.

As shown inFIG. 15, a trench having a depth reaching the SiC substrate41is formed in a separation region30athrough etching, thereby parting the nitride-based semiconductor element layer30through the trench. Alternatively, the trench formed in the separation region30amay not reach the SiC substrate41. Thereafter the protective film39is formed by CVD to cover the nitride-based semiconductor element layer30, the isolation layer44, the buffer layer42and the underlayer43.

As shown inFIG. 16, a prescribed region of the protective film39located on the upper surface of the p-type contact layer33constituting the nitride-based semiconductor element layer30is removed, and the p-side electrode32is thereafter formed on the exposed upper surface of the p-type contact layer33by vacuum evaporation or the like.

As shown inFIG. 17, the conductive substrate31having the thermal conductivity of about 170 W/m·K and containing copper and copper oxide mixed with each other at the ratio of 60:40 is bonded onto the upper surface of the p-side electrode32through a process similar to that of the first embodiment shown inFIG. 4. Thereafter the nitride-based semiconductor element layer30located on the isolation layer44is isolated from the layers (the SiC substrate41, the buffer layer42and the underlayer43) located under the isolation layer44. At this time, a laser beam is applied through a high-output laser such as a YAG laser, a KrF excimer laser, a DPSS laser (semiconductor laser excited solid-state laser) or a nitrogen laser from the side of the SiC substrate41, so that the isolation layer44absorbs light. Thus, the isolation layer44is so thermally decomposed as to isolate the nitride-based semiconductor element layer30located thereon from the layers (41to43) located under the same.

According to the third embodiment, the isolation layer44is made of In0.5Ga0.5N, and a second harmonic laser beam (wavelength: 532 nm) is applied through a YAG laser from the side of the SiC substrate41so that the isolation layer44absorbs the laser beam transmitted through the SiC substrate41, the buffer layer42and the underlayer43. Thus, isolation through the isolation layer44can be simplified by properly designing the band gap of the isolation layer44and the wavelength of the applied laser beam. Among the semiconductor layers shown inFIG. 17, therefore, the isolation layer44can most efficiently absorb the laser beam, so that isolation can be easily performed through the isolation layer44. Thus, the surface of the n-type contact layer38is exposed as shown inFIG. 18.

As shown inFIG. 19, the n-side electrode9having the composition and the thickness similar to those in the aforementioned first embodiment is formed on the prescribed region of the exposed surface of the n-type contact layer38by vacuum evaporation or the like, and the device is separated from an adjacent device along a separation region30athrough a process similar to that of the first embodiment shown inFIG. 7. Thus, the nitride-based light-emitting diode device according to the third embodiment is formed as shown inFIG. 13.

Results of investigation of the relation between an applied current and the light output as to a sample of the nitride-based light-emitting diode device according to the third embodiment prepared in practice along the aforementioned manufacturing process are now described. The relation between applied currents and light outputs was also investigated as to samples of nitride-based light-emitting diode devices employing conductive substrates having thermal conductivity of about 100 W/m·K and thermal conductivity of about 80 W/m·K respectively, in addition to the sample of the nitride-based light-emitting diode device according to the third embodiment employing a conductive substrate having thermal conductivity of about 170 W/m·K. In these samples, the thermal conductivity of about 100 W/m·K and the thermal conductivity of about 80 W/m·K of the conductive substrates were adjusted by adjusting mixing ratios between copper and copper oxide respectively.

FIG. 20shows the relation between the applied currents and the light outputs in the samples of the nitride-based light-emitting diode devices employing the three types of conductive substrates different in thermal conductivity from each other. Referring toFIG. 20, the axis of ordinates shows the light outputs of an arbitrary unit (a.u.), and the axis of abscissas shows the applied currents (A).

Referring toFIG. 20, it has been proved that the light output is increased in proportion to the applied current in the sample of the nitride-based light-emitting diode device according to the third embodiment employing the conductive substrate having the thermal conductivity of about 170 W/m·K also when the applied current exceeds 1.0 A. It has also been proved that the light output is increased in proportion to the applied current also in the sample of the nitride-based light-emitting diode device employing the conductive substrate having the thermal conductivity of about 100 W/m·K similarly to the aforementioned sample of the nitride-based light-emitting diode device according to the third embodiment until the applied current reaches a value close to 1.0 A. On the other hand, it has been proved that the light output cannot keep proportional relation to the applied current in the sample of the nitride-based light-emitting diode device employing the conductive substrate having the thermal conductivity of about 80 W/m·K when the applied current exceeds about 0.5 A. It is conceivable from these results that the light output is increased in proportion to the applied current also when the applied current exceeds 0.5 A, if the thermal conductivity of the conductive substrate is at least about 100 W/m·K.

According to the third embodiment, as hereinabove described, the conductive substrate31is so formed as to contain copper and copper oxide mixed with each other at the ratio of 60:40, whereby heat generated in the nitride-based semiconductor element layer30bonded to the conductive substrate31can be easily sufficiently radiated toward the conductive substrate31when a high current of at least 0.5 A is fed to the nitride-based light-emitting diode device by setting the thermal conductivity of the conductive substrate31to about 170 W/m·K and hence reduction of the light output characteristic caused by heat can be easily suppressed. Consequently, the nitride-based light-emitting diode device can be provided with a high rated output.

The remaining effects of the third embodiment are similar to those of the aforementioned first embodiment.

Fourth Embodiment

Referring toFIG. 21, a nitride-based light-emitting diode device according to a fourth embodiment of the present invention employs a conductive substrate51having a Young's modulus of about 50 GPa and containing copper and copper oxide mixed with each other at a ratio of 45:55.

In the nitride-based light-emitting diode device according to the fourth embodiment, a p-side electrode52having a textured surface with a width smaller than that of the conductive substrate51is bonded to the conductive substrate51containing copper and copper oxide mixed with each other at the ratio of 45:55, as shown inFIG. 21. The p-side electrode52has a composition and a thickness similar to those of the p-side electrode2in the aforementioned first embodiment. The width of portions between the centers of adjacent projecting and recess portions of the textured surface of the p-side electrode52is about 0.1 μm to about 50 μm, and the height of the projecting portions with reference to the bottoms of the recess portions is about 1 nm to about 2 μm. The p-side electrode52is an example of the “electrode” in the present invention. A p-type contact layer53having a function for serving as a cladding layer is formed on the p-side electrode52to fill up the recess portions on the surface of the p-side electrode52. This p-type contact layer53consists of GaN, AlGaN or InGaN doped with Mg, and has a thickness of about 1 nm to about 1 μm. A cap layer54, an active layer55, an n-type cladding layer56and an n-type contact layer57are successively formed on the p-type contact layer53. The cap layer54, the active layer55, the n-type cladding layer56and the n-type contact layer57have compositions and thicknesses similar to those of the cap layer5, the active layer6, the n-type cladding layer7and the n-type contact layer8in the aforementioned first embodiment respectively. The p-type contact layer53, the cap layer54, the active layer55, the n-type cladding layer56and the n-type contact layer57constitute a nitride-based semiconductor element layer50. A protective film58having a composition and a thickness similar to those of the protective film39in the aforementioned third embodiment is formed on the side surfaces of the nitride-based semiconductor element layer50. An n-side electrode9having a composition and a thickness similar to those in the aforementioned first embodiment is formed on a prescribed region of the n-type contact layer57constituting the nitride-based semiconductor element layer50.

A manufacturing process for the nitride-based light-emitting diode device according to the fourth embodiment is now described with reference toFIGS. 21 to 27.

As shown inFIG. 22, a buffer layer62and an underlayer63are successively grown on an Si substrate61serving as a growth substrate by MOCVD. The buffer layer62and the underlayer63have compositions and thicknesses similar to those of the buffer layer12and the underlayer13in the aforementioned first embodiment respectively. Then, the p-type contact layer57, the n-type cladding layer56, the active layer55, the cap layer54and the p-type contact layer53are successively grown on the underlayer63, and the p-type contact layer53is thereafter converted to the p type.

As shown inFIG. 23, a trench having a depth reaching the Si substrate61is formed in a separation region50aby etching, thereby parting the nitride-based semiconductor element layer50through the trench. Thereafter the protective film58is formed by CVD to cover the nitride-based semiconductor element layer50, the buffer layer62and the underlayer63.

As shown inFIG. 24, the portion of the protective film58located on the upper surface of the p-type contact layer53is removed, and the exposed surface of the p-type contact layer53is thereafter textured by photolithography and dry etching. At this time, the surface of the p-type contact layer53is so textured that the width of the portions between the centers of the adjacent projecting and recess portions of the textured surface of the p-type contact layer53is about 0.1 μm to about 50 μm and the height of the projecting portions with reference to the bottoms of the recess portions is about 1 nm to about 2 μm. Thereafter the p-side electrode52is formed by vacuum evaporation or the like to fill up the recess portions on the surface of the p-type contact layer53.

As shown inFIG. 25, the conductive substrate51having the Young's modulus of about 50 GPa and containing copper and copper oxide mixed with each other at the ratio of 45:55 is bonded onto the upper surface of the p-side electrode52through solder (not shown) of Au—Sn. Thereafter the Si substrate61, the buffer layer62and the underlayer63are removed by wet etching through a hot phosphoric acid solution or the like. Thus, the surface of the n-type contact layer57is exposed as shown inFIG. 26.

As shown inFIG. 27, the n-side electrode9having the composition and the thickness similar to those in the aforementioned first embodiment is formed on the prescribed region of the exposed surface of the n-type contact layer57by vacuum evaporation or the like, and the device is separated from an adjacent device along the separation region50athrough a process similar to that of the first embodiment shown inFIG. 7. Thus, the nitride-based light-emitting diode device according to the fourth embodiment is formed as shown inFIG. 21.

Table 1 shows results of an experiment for investigating presence/absence of cracks on nitride-based semiconductor element layers with reference to five conductive substrates having different Young's moduli (about 100 GPa, about 110 GPa, about 120 GPa, about 130 GPa and about 140 GPa) respectively. The Young's moduli of about 100 GPa, about 110 GPa, about 120 GPa, about 130 GPa and about 140 GPa were adjusted by adjusting the mixing ratios of copper and copper oxide contained in the conductive substrates respectively. Further, the Young's moduli of about 130 GPa and about 140 GPa were adjusted by employing other conductive metals.

Referring to Table 1, it has been proved that no cracks were formed on the nitride-based semiconductor element layers bonded to the conductive substrates having the Young's moduli of about 100 GPa, about 110 GPa and about 120 GPa respectively. On the other hand, it has been proved that the nitride-based semiconductor element layers bonded to the conductive substrates having the Young's moduli of about 130 GPa and about 140 GPa respectively were cracked. It is conceivable from these results that the nitride-based semiconductor element layer can be inhibited from cracking when the Young's modulus of the conductive substrate is not more than about 120 GPa.

According to the fourth embodiment, the conductive substrate51has the Young's modulus of about 50 GPa, whereby the nitride-based semiconductor element layer50can conceivably be inhibited from cracking.

According to the fourth embodiment, as hereinabove described, the conductive substrate51is so formed as to contain copper and copper oxide mixed with each other at the ratio of 45:55, whereby the conductive substrate51having the Young's modulus set to about 50 GPa can be inhibited from deformation under stress. When the nitride-based semiconductor element layer50bonded to the conductive substrate51is separated from the Si substrate61, therefore, the nitride-based semiconductor element layer50can be inhibited from deformation under stress caused by deformation under stress of the conductive substrate51. Thus, the nitride-based semiconductor element layer50can be inhibited from cracking, whereby the manufacturing yield can be inhibited from reduction resulting from cracks formed in the nitride-based light-emitting diode device.

According to the fourth embodiment, further, the surface of the p-type contact layer53is so textured that light incident upon the interface between the p-type contact layer53and the p-side electrode52is easily reflected by the textured surface of the p-type contact layer53. Thus, the reflected light is emitted from the n-side, whereby the light output characteristic can be improved.

The remaining effects of the fourth embodiment are similar to those of the aforementioned first embodiment.

Fifth Embodiment

Referring toFIG. 28, a nitride-based light-emitting diode device according to a fifth embodiment of the present invention employs a conductive substrate71having a linear expansion coefficient of about 9.5×10−6/K and containing copper and copper oxide mixed with each other at a ratio of 50:50.

According to the fifth embodiment, a p-side electrode72having a width smaller than that of the conductive substrate71is bonded to the conductive substrate71containing copper and copper oxide mixed with each other at the ratio of 50:50, as shown inFIG. 28. The conductive substrate71has a textured surface. The width of portions between the centers of adjacent projecting and recess portions of the textured surface of the conductive substrate71is about 0.1 μm to about 50 μm, and the height of the projecting portions with reference to the bottoms of the recess portions is about 1 nm to about 2 μm. The upper and lower surfaces of the p-side electrode72are textured similarly to the textured surface of the conductive substrate71. Further, the positions of the recess portions (projecting portions) of the conductive substrate71coincide with the positions of the projecting portions (recess portions) of the p-side electrode72. The p-side electrode72has a composition and a thickness similar to those of the p-side electrode2in the aforementioned first embodiment. The p-side electrode72is an example of the “electrode” in the present invention.

A p-type contact layer73is formed on the p-side electrode72to fill up the recess portions on the textured surface of the p-side electrode72. A p-type cladding layer74, a cap layer75and an active layer76are successively formed on the p-type contact layer73. The p-type contact layer73, the p-type cladding layer74, the cap layer75and the active layer76have compositions and thicknesses similar to those of the p-type contact layer3, the p-type cladding layer4, the cap layer5and the active layer6in the aforementioned first embodiment respectively. An n-type cladding layer77having a function for serving as a contact layer is formed on the active layer76. This n-type cladding layer77consists of AlGaN (Al composition ratio≦50%) doped with Si or Ge, and has a thickness of about 1 nm to about 1 μm. The p-type contact layer73, the p-type cladding layer74, the cap layer75, the active layer76and the n-type cladding layer77constitute a nitride-based semiconductor element layer70. A protective film78having a composition and a thickness similar to those of the protective film39in the aforementioned third embodiment is formed on the side surfaces of the nitride-based semiconductor element layer70. An n-side electrode9having a composition and a thickness similar to those in the aforementioned first embodiment is formed on a prescribed region of the n-type cladding layer77constituting the nitride-based semiconductor element layer70.

A manufacturing process for the nitride-based light-emitting diode device according to the fifth embodiment is now described with reference toFIGS. 28 to 34.

As shown inFIG. 29, an isolation layer (gap layer)82having spaces therein is formed on a GaN substrate81serving as a growth substrate by MOCVD. The isolation layer82has a composition and a thickness similar to those of the isolation layer14in the aforementioned second embodiment. Then, the n-type cladding layer77, the active layer76, the cap layer75, the p-type cladding layer74and the p-type contact layer73are successively grown on the isolation layer82, and the p-type cladding layer74and the p-type contact layer73are thereafter converted to the p type.

As shown inFIG. 30, a trench having a depth reaching the GaN substrate81is formed in a separation region70aby etching, thereby parting the nitride-based semiconductor element layer70through the trench. Thereafter the protective film78is formed by CVD to cover the nitride-based semiconductor element layer70and the isolation layer82.

As shown inFIG. 31, the portion of the protective film78located on the upper surface of the p-type contact layer73constituting the nitride-based semiconductor element layer70is removed, and the exposed surface of the p-type contact layer73is thereafter textured by photolithography and dry etching. At this time, the surface of the p-type contact layer73is so textured that the width of the portions between the centers of the adjacent projecting and recess portions of the textured surface of the p-type contact layer53is about 0.1 μm to about 50 μm and the height of the projecting portions with reference to the bottoms of the recess portions is about 1 nm to about 2 μm. Thereafter the p-side electrode72is formed by vacuum evaporation or the like to fill up the recess portions on the surface of the p-type contact layer73. At this time, the p-side electrode72is provided with the textured surfaces reflecting the texture on the surface of the p-type contact layer73.

As shown inFIG. 32, the surface of the conductive substrate71having the linear expansion coefficient of about 9.5×10−6/K and containing copper and copper oxide mixed with each other at the ratio of 50:50 is textured similarly to the textured surfaces of the p-side electrode72by embossing or the like. Thereafter the conductive substrate71is bonded onto the upper surface of the p-side electrode72through a process similar to that of the first embodiment shown inFIG. 4. At this time, the conductive substrate71is so is bonded onto the upper surface of the p-side electrode72that the positions of the recess portions (projecting portions) of the conductive substrate71coincide with the positions of the projecting portions (recess portions) of the p-side electrode72. Thereafter the nitride-based semiconductor element layer70located on the isolation layer82is isolated from the GaN substrate81located under the isolation layer82through a process similar to that of the second embodiment shown inFIG. 10. Thus, the surface of the n-type cladding layer77is exposed as shown inFIG. 33.

As shown inFIG. 34, the n-side electrode9having the composition and the thickness similar to those in the aforementioned first embodiment is formed on the prescribed region of the exposed surface of the n-type cladding layer77by vacuum evaporation or the like, and the device is thereafter separated from an adjacent device along the separation region70athrough a process similar to that of the first embodiment shown inFIG. 7. Thus, the nitride-based light-emitting diode device according to the fifth embodiment is formed as shown inFIG. 28.

Table 2 shows results of an experiment for investigating warping of a sample of the nitride-based light-emitting diode device according to the fifth embodiment prepared in practice according to the aforementioned manufacturing process and presence/absence of cracks on a nitride-based semiconductor element layer. Also as to samples of nitride-based light-emitting devices employing conductive substrates having linear expansion coefficients of about 12×10−6/K, about 18×10−6/K, about 20×10−6/K and about 25×10−6/K respectively, warping of the light-emitting diode devices and presence/absence of cracks formed on nitride-based semiconductor element layers were investigated in addition to the sample of the nitride-based light-emitting diode device according to the fifth embodiment having the linear expansion coefficient of about 9.5×10−6/K. The linear expansion coefficients of about 12×10−6/K, about 18×10−6/K, about 20×10−6/K and about 25×10−6/K were adjusted by adjusting the mixing ratios of copper and copper oxide contained in the conductive substrates respectively. Referring to Table 2, “warping of device” is defined as the difference between the maximum and minimum thicknesses of the portion between the lower surface of the conductive substrate and the upper surface of the nitride-based semiconductor element layer in each sample.

Referring to Table 2, it has been proved that the sample of the nitride-based light-emitting diode device according to the fifth embodiment employing the conductive substrate having the linear expansion coefficient of about 9.5×10−6/K was extremely slightly warped by about 5 μm and the nitride-based semiconductor element layer thereof was not cracked. It has also been proved that the nitride-based light-emitting diode device having the linear expansion coefficient of about 12×10−6/K was slightly warped by about 17 μm and the nitride-based semiconductor element layer thereof was not cracked. It has further been proved that the nitride-based light-emitting diode device having the linear expansion coefficient of about 18×10−6/K was slightly warped by about 30 μm and the nitride-based semiconductor element layer thereof was not cracked. On the other hand, it has been proved that the nitride-based light-emitting diode devices having the linear expansion coefficients of about 20×10−6/K and about 25×10−6/K respectively were remarkably warped by about 80 μm and about 130 μm respectively and the nitride-based semiconductor element layers thereof were cracked. It is conceivable from these results that warping of the nitride-based light-emitting diode device can be reduced and the nitride-based semiconductor element layer can be inhibited from cracking when the linear expansion coefficient of the conductive substrate is not more than about 18×10−6/K.

According to the fifth embodiment, as hereinabove described, the conductive substrate71is so formed as to contain copper and copper oxide mixed with each other at the ratio of 50:50 thereby setting the linear expansion coefficient of the conductive substrate71to about 9.5×10−6/K, whereby the difference between the linear expansion coefficients of the conductive substrate71and the nitride-based semiconductor element layer70can be reduced. Thus, the nitride-based light-emitting diode device can be easily inhibited from warping or cracking resulting from large difference between the linear expansion coefficients of the conductive substrate71and the nitride-based semiconductor element layer70in the manufacturing process, whereby the manufacturing yield can be easily inhibited from reduction.

According to the fifth embodiment, further, the surface of the p-type contact layer73is so textured that the textured surface of the p-type contact layer73can easily reflect light similarly to that in the aforementioned fourth embodiment. Thus, the reflected light is emitted from the n side, whereby the light output characteristic can be improved. In addition, the surface of the conductive substrate71is textured similarly to the textured surfaces of the p-side electrode72formed on the p-type contact layer73while the conductive substrate71and the p-side electrode72are so bonded to each other that the positions of the recess portions (projecting portions) of the conductive substrate71coincide with the positions of the projecting portions (recess portions) of the p-side electrode72, whereby the contact area between the conductive substrate71and the p-side electrode72is increased and heat radiation toward the conductive substrate71can be further improved.

For example, while the conductive substrate containing copper and copper oxide is employed in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but a conductive substrate containing a metal other than copper and a metal oxide other than copper oxide may alternatively be employed. For example, a conductive substrate containing aluminum and aluminum oxide may be employed. Further alternatively, a conductive substrate containing copper and aluminum oxide or aluminum and copper oxide may be employed. In place of copper or aluminum, gold, silver, molybdenum or tungsten may conceivably be employed as the metal constituting the conductive substrate.

While the sapphire, SiC, Si or GaN substrate is employed as the growth substrate in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but a GaAs, MgO, ZnO, LAO(LaAlO3), Ga2O3, ZrB2or spinel substrate may alternatively be employed as the growth substrate.

While the p-side electrode consists of the lower Au layer (closer to the conductive substrate) having the thickness of about 100 nm and the upper Pd layer having the thickness of about 300 nm in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but the p-side electrode may alternatively consist of a plurality of metal layers other than the Au and Pd layers. For example, the p-side electrode may conceivably be constituted of an Al layer having a thickness of about 300 nm and a Pd layer having a thickness of about 10 nm, an Ag layer having a thickness of about 300 nm, a Ti layer having a thickness of about 10 nm and a Pt layer having a thickness of about 10 nm, an Ag layer having a thickness of about 300 nm and a Pd layer having a thickness of about 30 nm, an Al layer having a thickness of about 200 nm, an Ni layer having a thickness of about 50 nm, an Ag layer having a thickness of about 300 nm and a Ti layer having a thickness of about 1 nm, an Al layer having a thickness of about 200 nm, an Ni layer having a thickness of about 50 nm, an Ag layer having a thickness of about 300 nm and an Ni layer having a thickness of about 0.5 nm, an Al layer having a thickness of about 200 nm, an Ni layer having a thickness of about 50 nm, an Ag layer having a thickness of about 300 nm and an Al layer having a thickness of about 0.5 nm or a Ti layer having a thickness of about 20 nm, an Ag layer having a thickness of about 300 nm and an Al layer having a thickness of about 0.3 nm in ascending order, in place of the Au layer and the Pd layer. Further, the p-side electrode may be entirely or only partially formed on the surface of the nitride-based semiconductor element layer closer to the conductive substrate. When the p-side electrode is only partially formed on the surface of the nitride-based semiconductor element layer closer to the conductive substrate, a layer for reflecting light is preferably formed on a region other than that formed with the p-side electrode. Further, a pad electrode is preferably formed between the p-side electrode and the conductive substrate, in order to increase the bonding power therebetween. The pad electrode may conceivably be constituted of an Au layer, a Pd layer and a Ti layer, an Au layer, a Pt layer and a Ti layer or an Au layer, an Mo layer and a Ti layer in ascending order from the side closer to the conductive substrate, for example. When solder is employed for bonding the p-side electrode to the conductive substrate, a barrier metal layer of Pt or Pd is preferably formed as a protective film for the p-side electrode.

While the p-side electrode consists of the lower Au layer (closer to the conductive substrate) having the thickness of about 100 nm and the upper Pd layer having the thickness of about 300 nm in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but the thicknesses of and the materials for the metal layers constituting the p-side electrode may alternatively be changed to reduce the quantity of light absorption in the p-side electrode in response to the emission wavelength.

While the p-side electrode consists of the lower Au layer (closer to the conductive substrate) and the upper Pd layer in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but an Al layer having higher light reflectance than the Au or Pd layer may alternatively be employed for increasing the quantity of emitted reflected light, thereby further improving the light output characteristic. For example, the light output characteristic can be further improved by providing an electrode layer of a transparent material between the Al layer and the nitride-based semiconductor element layer.

While the n-side electrode consisting of the Au layer, the Pd layer and the Al layer and having the thickness incapable of transmitting light is employed in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but an electrode consisting of a metal, a transparent material and a translucent material or the like having a thickness capable of transmitting light can alternatively be employed. A pad electrode is preferably formed on the n-side electrode, in order to connect a gold wire thereto.

While the nitride-based semiconductor element layer includes the layer of GaN, AlGaN or InGaN in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but the nitride-based semiconductor element layer may alternatively include a layer other than the layer of GaN, AlGaN or InGaN. For example, a group III-V nitride semiconductor such as AlN (aluminum nitride), InN (indium nitride), BN (boron nitride) or TiN (thallium nitride) or a mixed crystal of the group III-V nitride semiconductor may conceivably be employed as a nitride-based semiconductor other than GaN, AlGaN or InGaN. Further, a mixed crystal prepared by introducing at least one element of As, P and Sb into the aforementioned group III-V nitride semiconductor or the mixed crystal is also conceivable.

While the surface of the n-type contact layer is not finely worked in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but the surface of the n-type contact layer may alternatively be textured by fine working. In this case, the quantity of light totally reflected on the surface of the n-type contact layer is reduced, whereby the light output characteristic can be improved. When an SiO2film or an SiN film having a textured surface is formed on a region of the surface of the n-type contact layer other than that formed with the n-side electrode, an effect of improving the light output characteristic can be attained.

While the conductive substrate and the nitride-based semiconductor element layer are bonded to each other through the electrode in each of the aforementioned first to fifth embodiments, the present invention is not restricted to this but the conductive substrate and the nitride-based semiconductor element layer may alternatively be bonded to each other through a conductive material other than the electrode. Further alternatively, the conductive substrate and the nitride-based semiconductor element layer may be boned to each other through both of the electrode and the conductive material.

While the isolation layer of In0.5Ga0.5N is formed between the growth substrate and the nitride-based semiconductor element layer and the isolation layer is thereafter thermally decomposed by absorption of a laser beam thereby isolating the growth substrate and the nitride-based semiconductor element layer from each other in the aforementioned third embodiment, the present invention is not restricted to this but the isolation layer may alternatively be formed by a thin metal film or a thin insulating film absorbing a laser beam. The metal film absorbing a laser beam may be formed by a Ti film, an Al film, a Pd film, an Ni film or an Hf film. The insulating film absorbing a laser beam may be formed by a TiO2film, an SiO2film, a ZrO2film or an SiN film. Further alternatively, the isolation layer may be formed by stacking the aforementioned metal and insulating films with each other.

While the conductive substrate has the thermal conductivity of about 170 W/m·K in the aforementioned third embodiment, the present invention is not restricted to this but an effect similar to the above can be attained so far as the thermal conductivity of the conductive substrate is at least about 100 W/m·K.

While the conductive substrate has the Young's modulus of about 50 GPa in the aforementioned fourth embodiment, the present invention is not restricted to this but an effect similar to the above can be attained so far as the Young's modulus of the conductive substrate is not more than about 120 GPa.

While the conductive substrate has the linear expansion coefficient of about 9.5×10−6/K in the aforementioned fifth embodiment, the present invention is not restricted to this but an effect similar to the above can be attained so far as the linear expansion coefficient of the conductive substrate is not more than about 18×10−6/K.