JP2011049453A - Nitride semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor light emitting element which has high light extraction efficiency and high light emission efficiency. <P>SOLUTION: The nitride semiconductor light emitting element includes a nitride semiconductor layer, a conductive first oxide layer, and an insulating second oxide layer, and the first oxide layer and second oxide layer are made of oxide materials of the same kind. It is preferred that titanium in a titanium dioxide forming the first oxide layer is doped with one of niobium, tantalum, molybdenum, arsenic, antimony, aluminum, and tungsten by 1 to 10% in terms of mol ratio, and titanium in a titanium dioxide forming the second oxide layer is doped with one of niobium, tantalum, molybdenum, arsenic, antimony, aluminum, and tungsten by <1% in terms of mol ratio. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor light emitting device, and more particularly to a nitride semiconductor light emitting device having high light extraction efficiency and high light emission efficiency.

  Since a nitride semiconductor has a high refractive index of 2.5, total reflection is likely to occur at the interface between the nitride semiconductor and another material (for example, a substrate or a translucent electrode layer). For this reason, the light emitted from the active layer undergoes total internal reflection inside the nitride semiconductor light emitting device, which contributes to a decrease in the light emission efficiency of the nitride semiconductor light emitting device.

  As an attempt to suppress such a decrease in light emission efficiency, for example, Patent Document 1 discloses a technique for improving the light emission efficiency of a nitride semiconductor light emitting element by using titanium dioxide as a material used for the light transmissive electrode layer. It is disclosed.

The technique of Patent Document 1 will be described. Although the nitride semiconductor made of Al _x Ga _y In _1-xy N has a relatively high refractive index of about 2.5, the refractive index of titanium dioxide is the same. Is about 2.5. For this reason, the refractive index of a nitride semiconductor layer and a translucent electrode layer can be matched by using a titanium dioxide for a translucent electrode layer. Thereby, it becomes difficult to totally reflect at the interface between the nitride semiconductor layer and the translucent electrode layer, and the light emission efficiency of the nitride semiconductor light emitting device can be improved.

JP 2008-294306 A

  As described above, since the refractive index of titanium dioxide and the refractive index of the nitride semiconductor are almost the same, almost no total reflection occurs at the interface between the nitride semiconductor and the translucent electrode layer, and light is transmitted. .

  However, since the refractive index of air is approximately 1.0, the difference between the refractive index of air and the refractive index of the translucent electrode layer is large. For this reason, if the interface between the translucent electrode layer and air (or phosphor) is flat, total reflection at the interface tends to occur, and the light emission efficiency tends to decrease.

  Therefore, in order to prevent total reflection from occurring at the interface between the two layers having greatly different refractive indexes, it is effective to make the interface uneven. In the prior art, by forming irregularities at the interface between air and the translucent electrode layer, light can be transmitted while being scattered, and thus the light transmittance can be improved.

  Here, titanium dioxide is used as the translucent electrode layer, and further, a metal such as niobium is doped into titanium dioxide. Thereby, although the translucency of the light of a translucent electrode layer falls, the resistivity of a translucent electrode layer can be made low. If the thickness of such a translucent electrode layer is increased to such an extent that irregularities of 1 or more times the emission wavelength can be formed on the surface, the translucent electrode layer prevents light transmission, and light emission of the nitride semiconductor light emitting device There is a problem that efficiency decreases.

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a nitride semiconductor light emitting device having high light extraction efficiency and high light emission efficiency.

  The nitride semiconductor light emitting device of the present invention includes a nitride semiconductor multilayer body, a conductive first oxide layer, and an insulating second oxide layer, and includes a first oxide layer and a second oxide layer. Are made of the same type of oxide material.

  The oxide material preferably has a refractive index of 2.3 or more, and is preferably made of titanium dioxide.

  The nitride semiconductor multilayer body, the first oxide layer, and the second oxide layer are preferably formed on the anode side in this order.

  Niobium, tantalum, molybdenum, arsenic, antimony, aluminum or tungsten is doped in a molar ratio of 1% to 10% with respect to titanium in the titanium dioxide constituting the first oxide layer, and the second oxide layer It is preferable that any one of niobium, tantalum, molybdenum, arsenic, antimony, aluminum, or tungsten is doped in a molar ratio of less than 1% with respect to titanium in the titanium dioxide constituting the material. The first oxide layer made of titanium dioxide is preferably anatase type.

  The second oxide layer preferably has a thickness of 100 nm or more, more preferably has irregularities on the surface, and more preferably has irregularities with a height of 100 nm or more on the surface.

  The second oxide layer is preferably patterned into one of a mesh shape, a cone shape, a columnar shape, a pyramid shape, or a prism shape.

  A conductive oxide layer is formed between the nitride semiconductor stacked body and the first oxide layer, and the conductive oxide layer has a thickness equal to or less than a quarter of the emission wavelength of the nitride semiconductor light emitting device. And it is preferably made of an oxide other than titanium dioxide.

The conductive oxide layer is preferably made of Sn-doped indium oxide.
It is preferable that a nitride semiconductor layer containing In be included between the nitride semiconductor multilayer body and the first oxide layer, and the nitride semiconductor layer containing In can be made of Al _x In _y Ga _1-xy N (x > 0, y> 0), and more preferably, the In mixed crystal ratio y of Al _x In _y Ga _1-xy N is larger than the Al mixed crystal ratio x.

The thickness of the nitride semiconductor layer containing In is more preferably 5 nm or more.
It is preferable that the metal electrode is formed so as to extend in a branch shape from the pad electrode on the anode side or the cathode side.

  According to the present invention, it is possible to provide a nitride semiconductor light emitting device having high light extraction efficiency and high light emission efficiency.

It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is a schematic top view of a preferable example of the configuration of the nitride semiconductor light emitting device of the present invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is a schematic top view of a preferable example of the configuration of the nitride semiconductor light emitting device of the present invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is a schematic top view of a preferable example of the configuration of the nitride semiconductor light emitting device of the present invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is a schematic top view of a preferable example of the configuration of the nitride semiconductor light emitting device of the present invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is a schematic top view of a preferable example of the configuration of the nitride semiconductor light emitting device of the present invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is a schematic top view of a preferable example of the configuration of the nitride semiconductor light emitting device of the present invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is a schematic top view of a preferable example of the configuration of the nitride semiconductor light emitting device of the present invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is typical sectional drawing of a preferable example of the structure of the nitride semiconductor light-emitting device of this invention. It is a schematic top view of a preferable example of the configuration of the nitride semiconductor light emitting device of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The configurations shown in the drawings and the following description are merely examples, and the scope of the present invention is not limited to those shown in the drawings and the following description. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts. In the drawings of the present application, the dimensional relationships such as length, width, and thickness are appropriately changed for clarity and simplification of the drawings and do not represent actual dimensional relationships.

(Embodiment 1)
<Nitride semiconductor light emitting device>
Hereinafter, the nitride semiconductor light emitting device of the present embodiment will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing a preferred example of the nitride semiconductor light emitting device of the present invention.

  In the nitride semiconductor light emitting device of the present embodiment, a nitride semiconductor multilayer body 10, a first oxide layer 5, and a second oxide layer 6 are formed on a substrate 1 in this order. Here, the nitride semiconductor multilayer body 10 is composed of an n-type nitride semiconductor layer 2, a light emitting layer 3, and a p-type nitride semiconductor layer 4 in order from the substrate 1, and each of these layers is a nitride semiconductor. It consists of

In the present invention, “nitride semiconductor” typically means a semiconductor represented by Al _x Ga _y In _1-xy N (where x and y are each 0 or more and 1 or less). It is not limited to the above, but includes those added with any element for n-type or p-type conversion.

  The nitride semiconductor light-emitting device of the present invention is formed as a single oxide layer in the conventional nitride semiconductor light-emitting device, but is replaced with a conductive first oxide layer 5 and an insulating second oxide layer 6. The first oxide layer 5 and the second oxide layer 6 are made of the same type of oxide material.

  Here, the “same kind of oxide material” means that the same kind of oxide material is used even if it is doped with any dopant as long as the material composition of the oxide constituting the same is the same. That is, for example, titanium dioxide doped with niobium at 1% by mole and titanium dioxide doped with molybdenum at 5% by mole are the same type of oxide material. Since titanium dioxide has a wide gap and a low resistivity, it is preferably used as the first oxide layer and the second oxide layer in the nitride semiconductor light emitting device of the present invention.

  Since the oxide layer used in the conventional nitride semiconductor light emitting device is not divided into a two-layer structure as in the present invention, the surface of the oxide layer is compatible with both conductivity and translucency in one oxide layer. It was necessary to form irregularities having a size of about 1/4 or more of the emission wavelength. However, since the oxide that constitutes the oxide layer has a trade-off relationship between improving conductivity and improving translucency, it is highly compatible between conductivity and translucency. Was difficult.

  Therefore, the present inventors have studied a structural approach of forming a two-layer structure of a first oxide layer and a second oxide layer as a method for achieving both high conductivity and translucency. did.

  As a result, the inventors of the present invention have a case where the required film thickness is ensured by only one layer having conductivity, and a first oxide layer having high conductivity and a second oxide layer having high translucency. In combination with the two-layer structure, the latter has been found to have higher overall translucency. That is, by dividing into two layers of the conductive first oxide layer 5 and the insulating second oxide layer 6, both conductivity and translucency can be highly compatible, and light extraction efficiency can be achieved. Can be improved.

  Specifically, current diffusion can be caused in the first oxide layer 5 by using a material having high conductivity for the first oxide layer 5. On the other hand, the second oxide layer 6 is made of an insulating and highly light-transmitting material, and unevenness is formed on the surface of the second oxide layer 6 so that the nitride semiconductor light emitting device emits light. The light extraction efficiency can be increased by emitting to the outside.

  Here, although the same type of oxide material is used for the first oxide layer 5 and the second oxide layer 6, the difference in the characteristics is that the composition and amount of the dopant introduced into the first oxide layer 5 and the second oxide layer 6 are different. Because. The composition and amount of the dopant will be described later.

  The oxide material is preferably a material having a refractive index of 2.3 or more. By using a high refractive index material having a refractive index of 2.3 or more for the first oxide layer 5, total reflection is hardly caused at the interface between the p-type nitride semiconductor layer 4 and the first oxide layer 5. Can do. Thereby, the transmittance can be increased, and thus the light extraction efficiency can be increased.

  The oxide material is preferably one or more selected from the group consisting of titanium dioxide and strontium titanium dioxide, and titanium dioxide is used as an oxide material having both high refractive index, conductivity, and translucency. It is more preferable. Titanium dioxide has a refractive index of about 2.5, and has a refractive index substantially equal to that of the p-type nitride semiconductor layer 4. For this reason, by using titanium dioxide for the first oxide layer 5, total reflection at the interface between the p-type nitride semiconductor layer 4 and the first oxide layer 5 can be made difficult to occur. The extraction efficiency can be increased.

  Further, the titanium dioxide showing the conductivity of the first oxide layer 5 may be either a rutile type or an anatase crystal type, but is preferably anatase type in order to obtain high conductivity.

  Here, the nitride semiconductor multilayer body 10, the first oxide layer 5, and the second oxide layer 6 are preferably formed on the anode side in this order. An oxide material generally has a high work function and a resistivity lower than that of a nitride semiconductor layer. For this reason, current diffusion can be efficiently performed by forming the nitride semiconductor stacked body 10, the first oxide layer 5, and the second oxide layer 6 in this order on the anode side.

  In the present embodiment, as the substrate 1, an insulating substrate such as sapphire or a conductive substrate such as GaN or SiC can be used. When a conductive substrate such as GaN or SiC is used as the substrate 1, it is preferable to provide an n electrode on the bottom surface side of the substrate 1 and a p electrode on the top surface side of the second oxide layer 6.

  The n-type nitride semiconductor layer 2 and the p-type nitride semiconductor layer 4 are preferably made of a nitride semiconductor. Examples of the n-type dopant used for the n-type nitride semiconductor layer 2 include Si and Ge, and examples of the p-type dopant used for the p-type nitride semiconductor layer 4 include Mg and Zn.

<First oxide layer>
The first oxide layer 5 is provided as a transparent electrode on the side in contact with the p-type nitride semiconductor layer 4 and has conductivity. The first oxide layer 5 is preferably made of an oxide material. Here, “conductive” means that the resistivity is less than 1 × 10 ⁴ Ωcm.

  As described above, the use of a material mainly composed of titanium dioxide for the first oxide layer 5 makes it difficult for total reflection to occur at the interface between the first oxide layer 5 and the p-type nitride semiconductor layer 4. Can do. Thereby, the transmittance can be increased, and thus the light extraction efficiency can be increased.

  When the oxide material constituting the first oxide layer 5 is titanium dioxide, the titanium in the titanium dioxide constituting the first oxide layer 5 is made of niobium, tantalum, molybdenum, arsenic, antimony, aluminum or tungsten. Any of them is preferably doped in a molar ratio of 1% or more and 10% or less. By doping the dopant at such a ratio, the conductivity of the first oxide layer 5 is increased, and the current diffusibility can be increased. Note that increasing the doping amount of the dopant often increases the conductivity and decreases the translucency.

<Second oxide layer>
The second oxide layer 6 is an insulating material and is characterized by using the same type of oxide material as that used for the first oxide layer 5. By using the same type of oxide material for the material of the first oxide layer 5 and the material of the second oxide layer 6, total reflection can be made difficult to occur at the interface between them, and thus the light extraction efficiency can be reduced. Loss can be reduced. Here, “insulating” means that the resistivity is 1 × 10 ⁴ Ωcm or more.

  Such a second oxide layer 6 does not necessarily have to be conductive like the first oxide layer 5 and may be insulative, but preferably has high translucency. That is, by increasing the translucency of the second oxide layer 6, it is possible to suppress a decrease in light extraction efficiency.

  It is preferable that any of niobium, tantalum, molybdenum, arsenic, antimony, aluminum, or tungsten is doped in a molar ratio of less than 1% with respect to titanium in the titanium dioxide constituting the second oxide layer 6 and includes a dopant. More preferably not. The translucency of the 2nd oxide layer 6 can be improved, so that the dopant amount of titanium dioxide is reduced. Incidentally, titanium dioxide containing no dopant is an insulator and has high translucency.

  Such a second oxide layer 6 preferably has a thickness of ¼ or more of the emission wavelength, and more preferably has a thickness of one or more times of the emission wavelength. By setting the second oxide layer 6 to such a thickness, desired irregularities can be formed on the surface of the second oxide layer 6.

  The second oxide layer 6 is also a layer for forming irregularities. By forming irregularities on the surface of the second oxide layer, total reflection at the interface between the second oxide layer 6 and air can be made difficult to occur, and thus light extraction of the nitride semiconductor light emitting device can be prevented. Efficiency can be improved.

  It is preferable that the 2nd oxide layer 6 has the unevenness | corrugation of 100 nm or more in the surface. Such unevenness of height corresponds to a length of about one quarter of the emission wavelength of the nitride semiconductor light emitting device. By having the unevenness at such a height, it is possible to make it difficult to cause total reflection of light even at an interface having a large difference in refractive index. Here, “the height of the unevenness” means the length from the unevenness of the second oxide layer 6 to the recess.

  Here, in order to form desired unevenness in the second oxide layer 6, the thickness is preferably thick, and more preferably 100 nm or more. If the thickness of the second oxide layer 6 is less than 100 nm, it is not preferable because irregularities having a height of 100 nm or more cannot be formed on the surface.

  The second oxide layer 6 also functions as a protective layer for the nitride semiconductor light emitting device. Conventional nitride semiconductor light emitting devices use silicon dioxide as a protective layer, but titanium dioxide has a refractive index matching that of the first oxide layer 5 rather than silicon dioxide, so that the light extraction efficiency is less likely to decrease. There is a merit.

<Conductive oxide layer>
In the present invention, it is preferable to form a conductive oxide layer (not shown) between the p-type nitride semiconductor layer 4 and the first oxide layer 5. By forming the conductive oxide layer at this position, the contact resistance between the p-type nitride semiconductor layer 4 and the first oxide layer 5 can be lowered, and thus the luminous efficiency can be increased.

  Such a conductive oxide layer preferably has a thickness of ¼ or less of the emission wavelength of the nitride semiconductor light emitting device. With the conductive oxide layer having such a thickness, light tunnels (transmits) through the conductive oxide layer, so that total reflection can hardly occur, and loss of light extraction efficiency can be reduced. Can do.

  Here, the conductive oxide layer is preferably Sn-doped indium oxide (ITO). Since ITO has a refractive index of around 2.0, it has a lower refractive index than a nitride semiconductor. However, if the thickness is ¼ wavelength or less with respect to the emission wavelength, light can tunnel (transmit) through the conductive oxide layer without total reflection of light at the interface. Loss of take-out efficiency can be reduced.

<Nitride semiconductor layer containing In>
In the present embodiment, a nitride semiconductor layer (not shown) containing In is preferably included between the nitride semiconductor stacked body 10 and the first oxide layer 5. By setting the thickness of the nitride semiconductor layer containing In to a critical thickness or more, the strain of the nitride semiconductor layer containing In is relaxed and dislocation occurs. By this dislocation, a current path is generated, and the contact resistance between the nitride semiconductor multilayer body 10 and the first oxide layer 5 can be lowered. In order to make the nitride semiconductor layer containing In more than the critical thickness, the nitride semiconductor layer containing In is formed thick, or the In mixed crystal ratio contained in the nitride semiconductor layer containing In is increased. Can be used.

  Here, the nitride semiconductor layer containing In preferably has a thickness of 5 nm or more. By forming a nitride semiconductor layer containing In having such a thickness, the nitride semiconductor layer containing In becomes thicker than the critical thickness, and the distortion of the nitride semiconductor layer containing In is relaxed and dislocation occurs. . By this dislocation, a current path is generated, and the contact resistance between the p-type nitride semiconductor layer 4 and the first oxide layer 5 can be lowered.

As described above, by increasing the thickness of the nitride semiconductor layer containing In, the light-transmitting property of the nitride semiconductor layer containing In decreases, and the light extraction efficiency of the nitride semiconductor light-emitting element decreases. There is. Therefore, Al is further added to the nitride semiconductor layer containing In, and the nitride semiconductor layer containing In is made of a quaternary mixed crystal of Al _x In _y Ga _1-xy N (x> 0, y> 0). preferable. By adding Al to the nitride semiconductor layer containing In in this manner, the band gap can be increased without greatly changing the lattice constant that governs the critical film thickness. Thereby, the translucency of the nitride semiconductor layer containing In can be improved, and thus the light extraction efficiency can be maintained.

The Al _x In _y Ga _{1 -xy} N constituting the nitride semiconductor layer containing In preferably has an In mixed crystal ratio y larger than the Al mixed crystal ratio x. By setting the In mixed crystal ratio y to the Al mixed crystal ratio x or more, the nitride semiconductor layer containing In can be formed to a thickness greater than the critical film thickness.

  In the first embodiment, a conductive substrate such as GaN or SiC is used as the substrate 1. In the following second to eighth embodiments, an insulating substrate such as sapphire is used as the substrate. When an insulating substrate is used like sapphire, p-electrode 7 and n-electrode 8 can be formed in a chip shape as shown in FIGS. 2 to 15 by mesa etching from the anode side. Here, FIGS. 2 to 15 are cross-sectional views or top views schematically showing a preferred example of the nitride semiconductor light emitting device of the second to eighth embodiments. Embodiments 2 to 8 will be described below.

(Embodiment 2)
The present embodiment is characterized in that sapphire is used as a substrate as an insulating substrate as shown in FIG. Thus, when sapphire is used for the substrate, the second oxide layer 6 is preferably formed avoiding the p-electrode 7.

(Embodiments 3 to 7)
The nitride semiconductor light emitting devices of Embodiments 3 to 7 are characterized in that the unevenness formed in the second oxide layer 6 is patterned into a mesh shape, a cone shape, a columnar shape, a pyramid shape, or a prism shape. To do.

  4 and 5 correspond to a cross-sectional view and a top view of the nitride semiconductor light emitting device of the third embodiment. The third embodiment is characterized in that mesh-like irregularities are formed in the second oxide layer 6 as shown in FIGS. 4 and 5 by using a photolithography technique.

  A sectional view of the nitride semiconductor light emitting device of the fourth embodiment is shown in FIG. 6, and a top view thereof is shown in FIG. Embodiment 4 is characterized in that conical irregularities are formed in the second oxide layer 6 by reducing the selectivity between the oxide and the resist by using a photolithography technique.

  A sectional view of the nitride semiconductor light emitting device of the fifth embodiment is shown in FIG. 8, and a top view thereof is shown in FIG. Embodiment 5 is characterized in that columnar irregularities are formed by removing the taper angle in the resist shape after increasing the selectivity of the oxide and the resist by using a photolithography technique. .

  A cross-sectional view of the nitride semiconductor light emitting device of the sixth embodiment is shown in FIG. 10, and a top view thereof is shown in FIG. In Embodiment 6, pyramidal irregularities are formed on the second oxide layer 6 by reducing the selectivity between the oxide and the resist using photolithography technology and then performing anisotropic etching by wet etching or the like. It is characterized by forming.

  A sectional view of the nitride semiconductor light emitting device of the seventh embodiment is shown in FIG. 12, and a top view thereof is shown in FIG. Embodiment 7 is characterized in that a prismatic unevenness is formed by eliminating the taper angle in the resist shape after increasing the selectivity between the oxide and the resist by using a photolithography technique. .

  As in the third to seventh embodiments, by forming pattern irregularities on the second oxide layer 6, the second oxide layer 6 is spatially divided (isolated). By dividing the second oxide layer 6, current diffusion does not occur in the second oxide layer 6. Therefore, the second oxide layer 6 does not need to be conductive and can improve translucency. it can.

(Embodiment 8)
14 and 15 are a cross-sectional view and a top view of the nitride semiconductor light emitting device of the present embodiment. In the nitride semiconductor light emitting device of the present embodiment, the second oxide layer 6 is formed so as to cover a part of the side surface of the nitride semiconductor light emitting device, and the metal electrode 7 extends from the electrode pad so as to branch. 8 is formed. The branches extending from the electrode pads are not limited to the example shown in FIG.

  As shown in FIG. 15, by forming the metal electrodes 7 and 8 so as to extend in a branch shape from the pad electrode on the anode side or the cathode side, current can be easily diffused in the plane. Thus, the current diffusibility can be improved. In this case, even if the first oxide layer 5 is formed thin, the current diffusion performance is unlikely to be insufficient. Therefore, by forming the first oxide layer 5 thin, Translucency can be improved.

  In this example, a nitride semiconductor light-emitting diode element (hereinafter, also simply referred to as “LED element”) having the configuration shown in FIG. 16 is manufactured. First, a substrate 11 made of sapphire is prepared, and the substrate 11 is set in a reactor of an MOCVD apparatus. Then, the surface (C surface) of the substrate 11 is cleaned by raising the temperature of the substrate 11 to 1050 ° C. while flowing hydrogen into the reaction furnace.

  Next, the n-type nitride semiconductor layer 12 was formed on the surface (C surface) of the substrate 11 by MOCVD. The n-type nitride semiconductor layer 12 includes a buffer layer, an n-type nitride underlayer, and an n-type nitride contact layer, and is specifically manufactured by the following procedure.

  In reducing the temperature of the substrate 11 to 510 ° C., hydrogen as a carrier gas and ammonia and trimethyl gallium (TMG) as a source gas are allowed to flow into the reaction furnace while GaN is formed on the surface (C surface) of the substrate 11. A buffer layer made of is laminated with a thickness of about 20 nm.

Then, the temperature of the substrate 11 is increased to 1050 ° C., while hydrogen as a carrier gas, ammonia and TMG as source gases, and silane as an impurity gas flow into the reactor, the carrier concentration is 1 × 10 ¹⁸ on the buffer layer. An n-type nitride semiconductor underlayer made of GaN doped with Si so as to be / cm ³ is laminated with a thickness of 6 μm.

Subsequently, n is formed of GaN on the n-type nitride semiconductor underlayer by the same method as that of the n-type nitride semiconductor underlayer except that Si is doped so that the carrier concentration becomes 5 × 10 ¹⁸ / cm ^3. A type nitride semiconductor contact layer is formed to a thickness of 0.5 μm. The above is the step of forming the n-type nitride semiconductor layer 12.

Next, the temperature of the substrate 11 is lowered to 700 ° C., nitrogen as a carrier gas, ammonia, TMG and TMI (trimethylindium) as a source gas are flown into the reactor, and 2. on the n-type nitride semiconductor contact layer. A well layer 13a made of In _0.15 Ga _0.85 N having a thickness of 5 nm and a barrier layer 13b made of GaN having a thickness of 10 nm are alternately grown for six periods to form an active layer 13 having a multiple quantum well structure. Needless to say, when the active layer 13 is formed, TMI is not allowed to flow into the reactor when GaN is grown. At this time, one of the well layers 13a formed in six periods functions as a light emitting layer.

  Next, while maintaining the temperature of the substrate 11 at 700 ° C. and flowing nitrogen as a carrier gas and ammonia and TMG as source gases into the reaction furnace, an evaporation preventing layer 14 made of GaN is formed on the light emitting layer 13 with a thickness of 15 nm. It will be formed.

  Next, a p-type nitride semiconductor layer 15 including a first p-type nitride semiconductor layer and a p-type nitride semiconductor contact layer is formed on the evaporation prevention layer 14 by MOCVD. Here, a specific procedure for forming the p-type nitride semiconductor layer 15 is as follows.

First, the temperature of the substrate 11 is raised to 950 ° C., while hydrogen is used as a carrier gas, ammonia, TMG, and trimethylaluminum (TMA) as source gases, and CP ₂ Mg as impurity gases are allowed to flow into the reactor. A first p-type nitride semiconductor layer made of Al _0.20 Ga _0.85 N doped at a concentration of 1 × 10 ²⁰ / cm ³ is formed with a thickness of about 20 nm.

Next, while maintaining the temperature of the substrate 11 at 950 ° C., hydrogen as a carrier gas, ammonia and TMG as source gases, and CP ₂ Mg as an impurity gas are allowed to flow into the reaction furnace, and the first p-type nitride semiconductor layer is formed. Then, a p-type nitride semiconductor contact layer made of GaN doped with Mg at a concentration of 1 × 10 ²⁰ / cm ³ is formed with a thickness of 80 nm. Then, the temperature of the substrate 1 is lowered to 700 ° C., and annealing is performed while flowing nitrogen as a carrier gas into the reaction furnace.

Next, the wafer is taken out from the reaction furnace, and a first oxide layer 16 made of titanium dioxide (TiO ₂ ) doped with niobium at an atomic concentration of 6% is formed on the surface of the p-type nitride semiconductor layer 15 by sputtering. It is formed with a thickness of 300 nm. Then, a second oxide layer 17 made of TiO ₂ containing no 300 nm niobium is formed by the same method.

  Thereafter, a mask patterned into a predetermined shape is formed on the second oxide layer 17. Then, by using a reactive ion etching (RIE) apparatus, the second oxide layer 17, the first oxide layer 16, the p-type nitride semiconductor layer 15, and the evaporation prevention part where the mask is not formed. The surface of the n-type nitride semiconductor layer 12 (n-type nitride semiconductor contact layer) is exposed by removing a part of the layer 14, the light emitting layer 13, and the n-type nitride semiconductor layer 12 by etching.

  Further, a mask patterned into a predetermined shape is formed on the second oxide layer 17. Then, by using the RIE apparatus, a part of the second oxide layer 17 where the mask is not formed is etched to form a pattern on a prism as shown in FIG. Pad electrodes 18 and 19 containing Ti and Al are formed at predetermined positions on the exposed first oxide layer 16 and the exposed n-type nitride semiconductor layer 12, respectively.

  As described above, the LED element of Example 1 is formed. Since the LED element thus fabricated has a small refractive index difference between the p-type nitride semiconductor layer 15 and the first oxide layer 16, it is difficult to reflect at the interface between these layers. For this reason, the light extraction efficiency of the LED element is high and the light emission efficiency can be increased. In addition, since the surface of the second oxide layer 17 is patterned to have a concavo-convex structure, high light extraction efficiency can be realized, and light emission efficiency can be improved.

  In Example 2, the conductive oxide layer 20 is formed between the p-type nitride semiconductor layer 15 and the first oxide layer 16 as shown in FIG. 17 with respect to the LED element of Example 1. Except for this, the LED device of Example 2 is fabricated by the same method as in Example 1.

  Specifically, after the formation of the p-type nitride semiconductor layer 15 in Example 1, the wafer is taken out of the reaction furnace, and the surface of the p-type nitride semiconductor layer 15 is made of ITO (indium tin oxide) using a sputtering method. The conductive oxide layer 20 is formed with a thickness of 50 nm.

  Like the LED element of Example 2, the p-type nitride semiconductor layer 15 is formed by forming the conductive oxide layer 20 made of ITO between the p-type nitride semiconductor layer 15 and the first oxide layer 16. The contact resistance of the contact surface between the first oxide layer 16 and the first oxide layer 16 can be lowered, so that the light extraction efficiency can be increased and the operating voltage can be lowered.

  In Example 3, the nitride semiconductor layer 21 containing In is formed between the p-type nitride semiconductor layer 15 and the first oxide layer 16 as shown in FIG. 18 with respect to the LED element of Example 1. Except for this, the LED element of Example 3 is fabricated by the same method as in Example 1.

Specifically, after the formation of the p-type nitride semiconductor layer 15 in Example 1, the temperature of the substrate is lowered to 700 ° C., the carrier gas is nitrogen, the source gases are ammonia, TMG and TMI, and the impurity gas is CP _2. While flowing Mg into the reaction furnace, the nitride semiconductor layer 21 containing In made of In _0.1 Ga _0.9 N doped with Mg at a concentration of 1 × 10 ²⁰ / cm ³ is formed to a thickness of 20 nm.

As in the LED element of Example 3, the nitride semiconductor layer 21 containing In made of In _0.1 Ga _0.9 N is formed on the p-type nitride semiconductor layer 15, whereby the p-type nitride semiconductor layer 15 and the first nitride semiconductor layer 15 are formed. The contact resistance of the contact surface with the oxide layer 16 can be lowered, the light extraction efficiency can be increased, and the operating voltage can be lowered.

In Example 4, the LED element of Example 4 was fabricated in the same manner as in Example 3 except that the composition of the nitride semiconductor layer 21 containing In in Example 3 was changed to Al _0.05 In _0.15 Ga _0.8 N. Make it.

Specifically, the p-type nitride semiconductor layer 15 is formed in Example 1, the temperature of the substrate is lowered to 700 ° C., nitrogen as a carrier gas, ammonia as a source gas, TMG and TMI, TMA, as an impurity gas While flowing CP ₂ Mg into the reaction furnace, a nitride semiconductor layer 21 containing In composed of Al _0.05 In _0.15 Ga _0.8 N doped with Mg at a concentration of 1 × 10 ²⁰ / cm ³ is formed to a thickness of 20 nm. To do.

As in the LED element of Example 4, the nitride semiconductor layer 21 containing In made of Al _0.05 In _0.15 Ga _0.8 N is formed on the p-type nitride semiconductor layer 15, whereby the p-type nitride semiconductor layer 15 and The contact resistance of the contact surface between the first oxide layer 16 can be lowered, the light extraction efficiency can be increased, and the operating voltage can be lowered.

  In Example 5, compared with Example 1, the pad electrodes 18 and 19 containing Ti and Al are extended in a branch shape as shown in FIG. 19, and the thickness of the first oxide layer 16 is changed to 150 nm. Except for this, the LED device of Example 5 is fabricated by the same method as in Example 1.

  By extending the pad electrode on the branch as in the LED element of Example 5, the current can be sufficiently diffused even if the thickness of the first oxide layer 16 that is the p-side first oxide layer is thin. The operating voltage can be lowered. Further, by reducing the thickness of the first oxide layer 16, the first oxide layer 16 can reduce the light absorption rate from the light emitting layer 13, thereby increasing the light extraction efficiency and emitting light. Efficiency can be improved.

  Although the embodiments and examples of the present invention have been described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  According to the present invention, a nitride semiconductor light emitting device having high light extraction efficiency and high light emission efficiency can be provided.

  1 substrate, 2 n-type nitride semiconductor layer, 3 light emitting layer, 4 p-type nitride semiconductor layer, 5 first oxide layer, 6 second oxide layer, 7, 8 metal electrode, 10 nitride semiconductor laminate, 11 substrate, 12 n-type nitride semiconductor layer, 13 active layer, 14 evaporation prevention layer, 15 p-type nitride semiconductor layer, 16 first oxide layer, 17 second oxide layer 18, 19 pad electrode, 20 conductivity An oxide layer, a nitride semiconductor layer containing 21 In.

Claims (17)

A nitride semiconductor laminate, a conductive first oxide layer, and an insulating second oxide layer;
The nitride semiconductor light emitting device, wherein the first oxide layer and the second oxide layer are made of the same type of oxide material.   The nitride semiconductor light emitting device according to claim 1, wherein the oxide material has a refractive index of 2.3 or more.   3. The nitride semiconductor light emitting device according to claim 1, wherein the nitride semiconductor multilayer body, the first oxide layer, and the second oxide layer are formed on the anode side in this order.   The nitride semiconductor light-emitting element according to claim 1, wherein the oxide material is titanium dioxide. Niobium, tantalum, molybdenum, arsenic, antimony, aluminum or tungsten is doped in a molar ratio of 1% or more and 10% or less with respect to titanium in the titanium dioxide constituting the first oxide layer,
4. The niobium, tantalum, molybdenum, arsenic, antimony, aluminum, or tungsten is doped with a molar ratio of less than 1% with respect to titanium in the titanium dioxide constituting the second oxide layer. Nitride semiconductor light emitting device.   The nitride semiconductor light emitting element according to claim 4 or 5, wherein the first oxide layer made of titanium dioxide is an anatase type.   The nitride semiconductor light-emitting element according to claim 1, wherein the second oxide layer has a thickness of 100 nm or more.   The nitride semiconductor light emitting element according to claim 1, wherein the second oxide layer has irregularities on a surface thereof.   The nitride semiconductor light emitting element according to claim 8, wherein the second oxide layer has irregularities with a height of 100 nm or more on a surface thereof.   The nitride semiconductor light emitting device according to claim 1, wherein the second oxide layer is patterned into any one of a mesh shape, a conical shape, a cylindrical shape, a pyramid shape, or a prism shape. A conductive oxide layer is formed between the nitride semiconductor stack and the first oxide layer,
The conductive oxide layer according to any one of claims 1 to 10, wherein the conductive oxide layer has a thickness of ¼ or less of a light emission wavelength of the nitride semiconductor light-emitting element and is made of an oxide other than titanium dioxide. Nitride semiconductor light emitting device.   The nitride semiconductor light emitting element according to claim 11, wherein the conductive oxide layer is made of Sn-doped indium oxide.   The nitride semiconductor light-emitting device according to claim 1, further comprising a nitride semiconductor layer containing In between the nitride semiconductor stacked body and the first oxide layer.   The nitride semiconductor light emitting device according to claim 13, wherein the nitride semiconductor layer containing In has a thickness of 5 nm or more. The nitride semiconductor light emitting element according to claim 13 or 14, wherein the nitride semiconductor layer containing In is made of Al _x In _y Ga _1-xy N (x> 0, y> 0). The nitride semiconductor light emitting device according to claim 15, wherein an In mixed crystal ratio y of the Al _x In _y Ga _1-xy N is larger than an Al mixed crystal ratio x.   The nitride semiconductor light-emitting device according to claim 1, wherein the metal electrode is formed so as to extend in a branch shape from the pad electrode on the anode side or the cathode side.

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