JP2007149875A - Semiconductor light-emitting element, and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further improve light extraction efficiency by deeply engraving a reflecting mirror when improving the light extraction efficiency by engraving up to an nGaN layer so as to form the reflecting mirror, in a semiconductor light-emitting element composed by laminating at least the nGaN layer, a light-emitting layer, and a pGaN layer. <P>SOLUTION: A groove 19 as the reflecting mirror is arranged dispersedly in a plane direction of a substrate 12 so as not to make it into a closed loop. Accordingly, it is possible to secure a current pathway from one end side with an n-type electrode 17 formed thereto to the other end side in the nGaN layer while preventing the nGaN layer, light-emitting layer, and pGaN layer from being separated from each other in the plane direction (in a state of not being separated in a columnar shape). The groove 19 can be deeply engraved, namely, the reflecting mirror can be made high while being in a low-resistance state. By this, it is possible to improve the light extraction efficiency while increasing components hitting the reflecting mirror. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device that generates light by combining electrons and holes in a semiconductor and a method for manufacturing the same.

  In recent years, III-N compounds (hereinafter referred to as "nitrides") are used to form quantum wells, and an electric current is applied from outside to generate electrons by combining electrons and holes in these quantum wells. The development of semiconductor solid state light emitting devices is remarkable. The nitride GaN is most frequently used as the III-V compound. The refractive index of nitride, including this GaN, is larger than 1, and there is a problem in extracting light into the atmosphere. . Taking the case of GaN as an example, the refractive index is about 2.5, which is 23.6 degrees with respect to the normal of the boundary between GaN and the atmosphere (hereinafter referred to as 23.6 degrees with respect to this normal). Light incident on the boundary at a larger angle (conical region formed by a small region is called an escape cone) is not emitted into the atmosphere, but is totally reflected at the boundary surface and confined in GaN.

  Part of the confined light is reabsorbed by the light-emitting layer and contributes to re-emission due to electron-hole pair generation and recombination, but the re-emitted light is also emitted in some escape cones. The light emitted outside the escape cone is confined in GaN again. Then, the confined light is reabsorbed by the crystal and the electrode material and changed into heat. For this reason, a flat GaN layer has a problem that it is difficult to improve the light emission efficiency due to the total reflection due to the refractive index.

  Thus, for such a problem, for example, in Patent Document 1, by forming a rectangular unevenness on the light extraction surface, when light is reflected on the light extraction surface, the concave portion and the convex portion respectively. It is devised that the reflected light cancels each other out by λ / 2 of the phase of each other, the reflection is reduced, and as a result, the light extraction efficiency is improved.

  However, the conventional technology has a problem that unevenness is formed in the vicinity of the surface, so that light emitted from the light emitting layer in the surface direction cannot be easily captured by the unevenness. Therefore, Patent Document 2 has been proposed for such a problem.

FIG. 6 is a sectional view showing the structure of the light-emitting diode 1 according to Patent Document 2. As shown in FIG. The light emitting diode 1 is, generally, the above substrate 2, such as sapphire _(Al 2 _{O 3),} n-type buffer layer 3, The InGaN layer 4, the light emitting layer 5, pGaN layer 6 are formed in this order, the light emitting layer 5 This is a flip-chip (face-down) type light emitting diode that takes out the light generated in step 1 from the sapphire substrate 2 side. A part of the light emitting layer 5 and the pGaN layer 6 are removed on the nGaN layer 4 to form an n-type electrode 7, and a p-type electrode 8 is formed on the pGaN layer 6.

It should be noted in this prior art that a groove 9 reaching the nGaN layer 4 from the pGaN layer 6 to the light emitting layer 5 is formed, and a transparent insulating film 10 is formed on the inner surface of the groove 9. By forming the mold electrode 8, the portion 8 a of the p-type electrode 8 on the inner surface of the groove 9 becomes a reflecting mirror. By forming this reflecting mirror, for example, as indicated by an arrow F1, light emitted in a plane direction as described above from a distant position of the light emitting layer 5 is reflected in the direction of the substrate 2 to convert the angle. The light extraction efficiency is improved by allowing the light to enter the air layer or the escape cone of the substrate 2 from GaN.
JP-A-7-202257 JP-T-2004-506331

  In the above-described prior art, the deeper the groove 9 is formed, the higher the efficiency of extracting light generated in the light emitting layer 5. However, as shown in FIG. 7, for example, the groove 9 is formed in a polygonal shape in plan view. Therefore, the nGaN layer 4, the light emitting layer 5, and the pGaN layer 6 are separated in the plane direction, that is, separated into columns, for each section surrounded by the groove 9. For this reason, the deeper the groove 9 is formed from the relatively low resistance nGaN layer 4 toward the medium resistance n-type buffer layer 3, the n n layers formed at the end portions from the respective portions of the nGaN layer 4. As indicated by the arrow F2, the resistance to the current flowing in the surface direction of the nGaN layer 4 increases, and the amount of light emitted from the light emitting layer 5 decreases, canceling the improvement in the light extraction efficiency. There's a problem. Note that the pGaN layer 6 has a relatively high resistance.

  An object of the present invention is to provide a semiconductor light emitting device and a method for manufacturing the same, in which a groove can be deeply carved in an n-type nitride semiconductor layer while a current path in a plane direction has a low resistance.

  The semiconductor light emitting device of the present invention is formed by sequentially laminating at least an n-type nitride semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer, from the p-type nitride semiconductor layer side to the n-type nitride semiconductor layer side. In a semiconductor light emitting device in which a reaching groove is formed and a reflecting mirror is formed on the inner surface of the groove, a current flows in the surface direction in the n-type nitride semiconductor layer so that the groove does not form a closed loop. , And a plurality of them are discretely engraved in the plane direction.

  The method for manufacturing a semiconductor light-emitting device according to the present invention includes at least an n-type nitride semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer that are sequentially stacked. In the method of manufacturing a semiconductor light emitting device in which a plurality of grooves are formed, a plurality of grooves are formed discretely in a plane direction so as not to form a closed loop from the p-type nitride semiconductor layer side to the n-type nitride semiconductor layer side. And a step of forming a reflecting mirror on the inner surface of the groove.

  According to the above configuration, it is realized as a light emitting diode or the like, and at least an n-type nitride semiconductor (nGaN) layer, a light emitting layer (active layer), and a p-type nitride semiconductor (pGaN) layer are sequentially stacked on the substrate. Or by removing the substrate after growth, and forming a reflecting mirror on the inner surface of the groove reaching (engraved) from the p-type nitride semiconductor layer side to the n-type nitride semiconductor layer side, The light emitted from the light emitting layer is directly incident on the reflecting mirror, or is incident after multiple reflection, so that the reflected light is incident on the n-type nitride semiconductor layer side below the critical angle and can be taken out to the outside. Thus, in the semiconductor light emitting device in which the light extraction efficiency is improved, the n-type electrode is formed at one end in the surface direction of the semiconductor light emitting device, or formed at the center, so that the n-type nitriding is performed. Inside the semiconductor layer If the current flows in the direction, the groove, so as not to form a closed loop, the plurality is engraved so as to discretely from each other in said surface direction.

  Therefore, by not forming a closed loop, the n-type nitride semiconductor layer, the light-emitting layer, and the p-type nitride semiconductor layer are not separated in the plane direction (so as not to be separated into columns), and in the n-type nitride semiconductor layer A current path can be secured from one end side to the other end side, and the groove can be deeply carved, that is, the reflecting mirror can be made high with low resistance. Thereby, the component which hits a reflecting mirror can be increased, and light extraction efficiency can be improved.

  Furthermore, in the semiconductor light emitting device of the present invention, the groove has a tapered surface.

  According to said structure, compared with a groove | channel with a rectangular cross-sectional shape, light extraction efficiency can be improved.

  In addition, the semiconductor light emitting device of the present invention has a structure in which the n-type nitride semiconductor layer, the light emitting layer, and the p-type nitride semiconductor layer are grown on a substrate and then the substrate is peeled off. .

  According to the above configuration, after the n-type nitride semiconductor layer, the light emitting layer, and the p-type nitride semiconductor layer are grown, the light extraction efficiency can be further improved by peeling the growth substrate.

  As described above, the semiconductor light-emitting device and the method for manufacturing the same according to the present invention are realized as a light-emitting diode or the like. At least an n-type nitride semiconductor (nGaN) layer, a light-emitting layer (active layer), and a p-type nitride are formed on a substrate. A semiconductor (pGaN) layer is sequentially stacked, or the substrate is removed after growth, and a groove reaching (engraved) from the p-type nitride semiconductor layer side to the n-type nitride semiconductor layer side is formed. By forming the reflecting mirror on the inner surface, the light emitted from the light emitting layer is directly incident on the reflecting mirror or incident by multiple reflection, so that the reflected light is critical to the n-type nitride semiconductor layer side. In a semiconductor light emitting device that is incident at an angle or less and can be extracted to the outside so that the light extraction efficiency is improved, the n-type electrode is formed at one end in the surface direction of the semiconductor light emitting device, etc. n-type nitriding If the current flows through the semiconductor layer in the plane direction, the groove, so as not to form a closed loop, the plurality is engraved so as to discretely from each other in said surface direction.

  Therefore, the n-type nitride semiconductor layer, the light emitting layer, and the p-type nitride semiconductor layer are not separated in the plane direction (not separated into columns), and the current flows from one end side to the other end side in the n-type nitride semiconductor layer. The path can be secured, and the groove can be deeply carved, that is, the reflecting mirror can be made high with low resistance. Thereby, the component which hits a reflecting mirror can be increased, and light extraction efficiency can be improved.

[Embodiment 1]
FIG. 1 is a sectional view showing a structure of a light emitting diode 11 according to an embodiment of the present invention. The light emitting diode 11 is, generally, the above substrate 12 such as sapphire _(Al 2 _{O 3),} n-type buffer layer 13, The InGaN layer 14, the light emitting layer 15, pGaN layer 16 are formed in this order, the light emitting layer 15 This is a flip-chip (face-down) type light emitting diode that takes out the light generated in step 1 from the sapphire substrate 12 side. A part of the light emitting layer 15 and the pGaN layer 16 are removed on the nGaN layer 14 to form an n-type electrode 17, and a p-type electrode 18 is formed on the pGaN layer 16.

  Needless to say, the substrate 12 is not limited to the sapphire, and may be any material having translucency with respect to the emission wavelength. A manufacturing method of this type of light emitting diode can be realized by using a MOCVD method known to those skilled in the art, and a detailed description thereof will be omitted here.

  Before forming the electrodes 17, 18, a tapered groove 19 reaching the nGaN layer 14 from the pGaN layer 16 to the light emitting layer 15 is formed, and a transparent insulating film 20 is formed on the inner surface of the groove 19. Is formed. Thereafter, the p-type electrode 18 is formed, so that the portion 18a of the p-type electrode 18 on the inner surface of the groove 19 becomes a reflecting mirror. By forming this reflecting mirror, light emitted in a plane direction from a distant position of the light emitting layer 15 can be reflected in the direction of the substrate 12 and angle-converted, and the air layer or the escape of the substrate 12 can be converted from GaN. It can enter into a cone and can improve the light extraction efficiency. The above configuration is the same as that of the light-emitting diode 1 shown in FIG.

  It should be noted that in the present embodiment, as shown in FIG. 2, the n-type electrode 17 is formed at one end in the surface direction of the light emitting diode 11, and a current flows in the nGaN layer 14 in the surface direction. On the other hand, a plurality of the grooves 19 are engraved discretely in the plane direction (disposed independently) so as not to form a closed loop. In the present invention, the n-type electrode 17 may be formed in the center of the light-emitting diode 11 and may be locally formed so that a current flows in the plane direction in the nGaN layer 14. That's fine.

  In the example of FIG. 2, as shown in FIG. 3, the groove 19 is formed by superimposing three types of hexagonal patterns so as to overlap each other, and in each pattern, two sides facing each other are formed as the groove 19. It is a thing. The more polygonal the pattern is, the more light can be captured from many directions, but the circle is not suitable because it forms the closed loop.

  FIG. 4 is a diagram for explaining a manufacturing process of the light-emitting diode 11 configured as described above. In the present embodiment, the groove 19 is produced by a nanoimprint lithography method.

  First, when the groove 19 is formed, a mold 30 having the inverted shape of the groove 19 as shown in FIG. For example, an electron beam lithography method can be used to create the mold 30. Specifically, a resist pattern for the grooves 19 is created by irradiating an electron beam resist formed on a silicon wafer by spin coating with an electron beam. The pattern height can be changed corresponding to the taper shape of the groove 19 by changing the dose amount of the electron beam. If the dose amount is large, the photosensitive depth of the electron beam resist becomes deep, and the dose amount is increased. If the amount is small, the exposure depth of the electron beam resist becomes shallow. In this way, resist patterns having different heights can be created. By adopting Ni electroforming of the resist pattern, a press die 30 can be created.

  After the respective layers 13 to 16 are formed on the substrate 12 as shown in FIG. 4A by using the MOCVD method or the like, the substrate 12 of the light emitting diode 11 in the wafer state is formed as shown in FIG. A resist 31 is spin-coated on the surface, and the mold 30 is pressed as shown in FIG. 4C to transfer the shape. The material of the resist 31 may be either organic or inorganic, but it needs to have good transferability and high dry etching resistance. For example, spin-on glass can be used. As shown in FIG. 4D, the pattern of the mold 30 is transferred to the resist 31 after the mold release. By performing reactive ion etching using chlorine gas using the resist 31 after the transfer as a mask, the pattern of the mold 30 is inverted on the surface of the substrate 12 of the light emitting diode 11 as shown in FIG. Thus, the groove 19 can be formed. Thereafter, after the transparent insulating film 20 is formed by a known method, the electrodes 17 and 18 are formed.

  By manufacturing in this way, the groove 19 is not a closed loop, so that the nGaN layer 14, the light emitting layer 15 and the pGaN layer 16 are not separated in the plane direction (so as not to be separated into pillars), and in the nGaN layer 14, A current path can be secured from one end side to the other end side where the n-type electrode 17 is formed, and the groove 19 can be deeply carved, that is, the reflecting mirror can be made high with low resistance. Thereby, the component which hits a reflecting mirror can be increased, and light extraction efficiency can be improved. Further, since the groove 19 has a tapered surface, the light extraction efficiency can be improved as compared with a groove having a rectangular cross-sectional shape.

[Embodiment 2]
FIG. 5 is a sectional view showing the structure of a light emitting diode 41 according to another embodiment of the present invention. The light-emitting diode 41 is similar to the light-emitting diode 11 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. It should be noted that in the light emitting diode 41, the sapphire substrate 12 is removed after the grooves 19 to the electrodes 17 and 18 are formed.

In this case, it is necessary to peel off the substrate 12 from the nGaN layer 14, and generally an ultraviolet laser is used. Specifically, a KrF excimer laser (λ = 248 nm, irradiation intensity: 0.3 J / cm ² ) is incident from the substrate 12 (sapphire) side. Since the laser passes through the transparent crystal substrate 12 and is absorbed by the nGaN layer 14, ablation occurs at the interface, and as a result, the substrate 12 peels from the nGaN layer 14.

  In this way, after the nGaN layer 14, the light emitting layer 15 and the pGaN layer 16 are grown on the substrate 12, the substrate 12 is peeled off so that the nGaN layer 14 becomes a light extraction surface, and the light extraction efficiency is further increased. Can be improved.

It is sectional drawing which shows the structure of the light emitting diode which concerns on one Embodiment of this invention. It is a top view of the light emitting diode shown in FIG. It is a top view for demonstrating the formation pattern of the groove | channel in the light emitting diode shown in FIG. It is a figure for demonstrating the manufacturing process of the light emitting diode shown in FIG. It is sectional drawing which shows the structure of the light emitting diode which concerns on the other embodiment of this invention. It is sectional drawing which shows the structure of the light emitting diode of a prior art. It is a top view of the light emitting diode shown in FIG.

Explanation of symbols

11, 41 Light-emitting diode 12 Substrate 13 Buffer layer 14 nGaN layer 15 Light-emitting layer 16 pGaN layer 17 n-type electrode 18 p-type electrode 19 groove 20 transparent insulating film 30 type 31 resist

Claims (4)

At least an n-type nitride semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer are sequentially stacked, and a groove is formed from the p-type nitride semiconductor layer side to the n-type nitride semiconductor layer side. In the semiconductor light-emitting device in which the reflecting mirror is formed on the inner surface of the groove,
A current flows in the plane direction in the n-type nitride semiconductor layer,
A plurality of grooves are engraved discretely in the plane direction so as not to form a closed loop.   The semiconductor light emitting element according to claim 1, wherein the groove has a tapered surface.   3. The semiconductor light emitting device according to claim 1, wherein the n type nitride semiconductor layer, the light emitting layer and the p type nitride semiconductor layer are grown on the substrate and then the substrate is peeled off. . In a method for manufacturing a semiconductor light emitting device, comprising at least an n-type nitride semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer sequentially stacked, wherein a current flows in a plane direction in the n-type nitride semiconductor layer.
Reaching the n-type nitride semiconductor layer side from the p-type nitride semiconductor layer side and forming a plurality of grooves discretely in the plane direction so as not to form a closed loop;
And a step of forming a reflecting mirror on the inner surface of the groove.

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