JP2014027310A - Light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element which is improved in reliability while its light output is increased.SOLUTION: The light-emitting element comprises: a light-emitting layer capable of emitting emission light; a first electrode; a first layer provided between the light-emitting layer and the first electrode; a second layer provided between the first layer and the first electrode; and a clad layer provided between the first layer and the light-emitting layer. The first layer has a first impurity density of a first conductivity type, and is arranged so that carriers injected thereinto from the first electrode can be diffused in an in-plane direction of the light-emitting layer. The second layer has a second impurity density of the first conductivity type which is higher than the first impurity density. The second layer is in contact with the first layer at a first face. The second layer has a second face on the side opposite to the first face, and it has, in the second face, a formation region for forming the first electrode and a non-formation region. In the light-emitting element, protrusions in a net-like form or island-like forms are provided on the non-formation region, and have an average pitch equal to or smaller than the wavelength of the emission light. Further, the clad layer has the first conductivity type.

Description

  Embodiments described herein relate generally to a light emitting device.

  Increasing output is increasingly required for light-emitting elements used in lighting devices, display devices, traffic lights, and the like.

  When a high-concentration current diffusion layer is provided between the light emitting layer and the first electrode, carriers injected from the first electrode are spread in the plane of the light emitting layer, and it becomes easy to emit a high light output.

  Moreover, if minute irregularities are formed on the surface of the current diffusion layer on the light emission side, the light extraction efficiency can be improved and the light output can be increased. If a dry etching method is used as a method for forming the minute unevenness, the minute unevenness having a size equal to or smaller than the wavelength of the emitted light can be reliably formed with good productivity.

  However, when the dry etching method is used, a crystal defect or the like is generated in the processing region, and the light output may be lowered by long-time operation.

JP 2006-128227 A

  A light-emitting element with improved light output and improved reliability is provided.

A light emitting layer capable of emitting emitted light; a first electrode; a first layer provided between the light emitting layer and the first electrode; and between the first layer and the first electrode. There is provided a light emitting device including a provided second layer. The first layer has a first impurity concentration of the first conductivity type. The second layer has an impurity concentration of 1.5 × 10 ¹⁸ cm ⁻³ or more, includes a plurality of convex portions on at least a part of the upper surface, and has crystal defects.

FIG. 1A is a schematic plan view of the light emitting device according to the first embodiment, and FIG. 1B is a schematic cross-sectional view taken along the line AA. 2A is a schematic cross-sectional view of a first conductivity type layer provided with a convex portion, and FIG. 2B is a partially enlarged view of the convex portion. 3A is a light output remaining rate of the light emitting device of the second embodiment, FIG. 3B is a light output remaining rate of the first comparative example, and FIG. 3C is a light output remaining rate of the second comparative example. FIG. 3D is a graph showing the light output remaining ratio of the third comparative example. FIG. 4A is a schematic plan view of a light emitting element according to a first comparative example, and FIG. 4B is a schematic cross-sectional view taken along the line BB. FIG. 5A is a graph showing the dependence of the relative emission intensity on the impurity concentration of the first layer, and FIG. 5B is a graph showing the dependence of the relative emission intensity on the thickness of the first layer. 6A is an SEM photograph of the top surface of the island-shaped convex portion, FIG. 6B is an SEM photograph of the island-shaped convex portion seen from obliquely above, and FIG. 6C is a schematic perspective view of the net-shaped convex portion. . 7A and 7B are SEM photographs of the upper surface of the convex portion formed by the wet etching method, and FIG. 7C is an SEM photograph of the cross section thereof. It is a graph of the dependence of relative light emission intensity with respect to the number of MQW wells. FIG. 9A shows the relative emission intensity dependence on the impurity concentration of the p-type contact layer, and FIG. 9B shows the dependence of the forward voltage on the impurity concentration of the p-type contact layer. FIG. 10A is a schematic plan view of the light emitting device according to the third embodiment, and FIG. 10B is a schematic cross-sectional view taken along the line CC.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1A is a schematic plan view of a light emitting device according to the first embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view taken along the line AA. The light emitting element includes a stacked body 32, a first electrode 50 provided on the stacked body 32, a second electrode 40 provided under the stacked body 32, the substrate 10, and the like.

  The stacked body 32 includes a light emitting layer 22, a first conductivity type layer 30 provided on the light emitting layer 22, and a second conductivity type layer 20 provided below the light emitting layer 22. The first conductivity type layer 30 includes at least a first layer 25 provided on the light emitting layer 22 and a second layer 26 provided on the first layer 25. In addition, it is more preferable that the first conductivity type layer 30 has the contact layer 28 on the second layer 26 because a good ohmic contact can be formed with the first electrode 50. Furthermore, it is more preferable that the first conductivity type layer 30 has the cladding layer 24 in contact with the light emitting layer 22 because light can be effectively confined in the light emitting layer 22 and the light emission efficiency can be increased.

  Both the second layer 26 and the first layer 25 have the first conductivity type, and the first impurity concentration of the first layer 25 is the second impurity concentration of the second layer 26. Lower than. The first surface 26a is in contact with the first layer 25, and the second surface of the second layer 26 opposite to the first surface 26a is formed between the formation region 26b and the non-formation region 26c of the first electrode 50. And have. A convex portion 27 is provided in the non-formation region 26c. The average pitch of the protrusions 27 is preferably smaller than the wavelength of the emitted light. The average pitch of the convex portions 27 will be described in detail later.

  Further, the light emitting element may be provided in contact with a part of the surface of the second conductivity type layer 20 on the side opposite to the light emitting layer 22, and may have a current blocking layer 42 whose outer edge protrudes from the first electrode 50. Good. In this case, the second electrode 40 includes a surface of the current block layer 42 opposite to the second conductivity type layer 20 and a region of the surface of the second conductivity type layer 20 that is not in contact with the current block layer 42. , To be in contact with. A part of the light emitted downward from the light emitting layer 22 is transmitted through the protruding region of the current blocking layer 42 made of a transparent insulating film, reflected by the second electrode 40, and transmitted again through the current blocking layer 42 upward. Contains the emitted light GL. If the protruding area of the current blocking layer 42 is widened, the light output can be further increased. For example, the diameter DE of the first electrode 50 is 120 μm, and the diameter DB of the current blocking layer 42 is 220 μm.

FIG. 2A is a schematic cross-sectional view of a first conductivity type layer provided with island-shaped convex portions, and FIG. 2B is a partially enlarged view of a C portion.
The thickness of the second layer 26 is T2, and the thickness of the first layer 25 is T1. Further, the convex portion 27 is provided on the second surface of the second layer 26. When the convex portion 27 has a plurality of island shapes, the height H is made smaller than the thickness T2 of the second layer 26 so that the bottom portion 27b around the convex portion 27 does not reach the first surface 26a. To do. Further, the convex portion 27 may be formed in a net shape, and a bottom portion may be provided around the convex portion 27. The net-like convex portion 27 will be described later.

  In the case of a plurality of island-shaped convex portions 27, the shortest distances among the distances to the surrounding islands as viewed from one island are defined as pitches P1, P2, and the like. When the island shape is random, the distance is replaced with a circle of equal area and the distance between the centers is set. The average value of each pitch is defined as the average pitch of the island-shaped convex portions 27.

  When the external refractive index is lower than the refractive index of the second layer 26, the refractive index of the second layer 26 provided with the island-shaped convex portions 27 is changed from the refractive index of the second layer 26 to the external refraction. It has a refractive index gradient (Graded Index) that decreases toward the index. For this reason, the light extraction efficiency can be increased. Moreover, the island-shaped convex part 27 acts as a diffraction grating, and a part of n-th order diffracted light (n = ± 1, ± 2,...) Can be extracted, and the light extraction efficiency can be further increased.

  The carrier flow F1, F2, F3, F4, etc. injected from the first electrode 50 provided on the first electrode formation region 26b of the second layer 26 is the second layer having the second impurity concentration N2. 26 and flows into the first layer 25. Since the convex portion 27 is provided in the non-formation region 26 c of the first electrode 50 of the second layer 26, the carrier flow F <b> 5 is generated between the bottom portion 27 b provided around the convex portion 27 and the second layer 26. It flows into the first layer 25 while spreading in the horizontal plane direction between the first surface 26a. That is, a part of the first layer 25 and the second layer 26 functions as a current spreading layer. When the impurity concentration of the current diffusion layer is increased, the current can be diffused in the plane of the light emitting layer 22 to increase the light output. Even if the current diffusion layer is thickened, the current can be diffused in the plane of the light emitting layer 22 to increase the light output.

  On the other hand, when the impurity concentration of the current diffusion layer exceeds a predetermined range, impurity energy levels are formed in the band gap. For this reason, light absorption may increase and light output may decrease.

  The convex portions 27 having an average pitch smaller than the wavelength of the emitted light can be formed by using a dry etching method such as RIE (Reactive Ion Etching) using, for example, a self-organized pattern of a block copolymer as a mask.

  First, a block copolymer can be prepared by mixing, for example, equal amounts of polystyrene (PS) -polymethyl methacrylate (PMMA) and PMMA homopolymer, and using PS homopolymer and propylene glycol monoether acetate (PGMEA) as a solvent. . After applying the block copolymer to a uniform thickness on the wafer using, for example, a spin coater, heat treatment such as baking or annealing can be performed to separate the phase into PS and PMMA. That is, PS and PMMA are aggregated in a self-organizing manner to form a particulate PS layer. In this case, changing the composition ratio of PS and PMMA can change the particle size of the PS layer, the occupation ratio of the particles, and the like. Subsequently, when RIE is performed, the PMMA is removed by selective etching, and the PS layer remains as an island-shaped convex portion in an average pitch range of, for example, 10 nm to 300 nm. Further, by forming a mask of, for example, a SiO2 film using the PS layer pattern as a mask, and using the dry etching method with the SiO2 film as a mask, a desired convex portion 27 can be formed. Note that a dry etching method may be used with the resist pattern as a mask.

  However, in the dry etching process, damage such as crystal defects may occur depending on processing conditions, and the light output may decrease with time due to energization. The inventors have found that when the convex portion is formed by the dry etching method, this damage can be reduced by increasing the impurity concentration in the processed region.

  Based on this knowledge, in the present embodiment, the second impurity concentration N2 of the second layer 26 is set to a predetermined concentration or more, and the convex portion 27 is formed on the second layer 26 using a dry etching method. . Further, by making the first impurity concentration N1 of the first layer 25 lower than the second impurity concentration N2 of the second layer 26 and not less than a predetermined concentration, light absorption is maintained while maintaining the current diffusion effect. The increase can be suppressed. Thereby, the influence of the processing damage of the convex part 27 can be reduced, spreading an electric current in the surface of the light emitting layer 22. FIG.

Note that the stacked body 32 including the light-emitting layer 22 is In _x (Ga _y Al _1-y ) _1-x P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), or Al _x Ga _1-x As. (0 ≦ x ≦ 1) can be included. Further, for example, each light-emitting layer 22, the cladding layer 24, the _{In x (Ga y Al 1-} y) 1-x P ( where, 0 ≦ x ≦ 1,0 ≦ y ≦ 1) consists, first layer 25 and at least one of the second layers 26 is made of Al _x Ga _1-x As (0 ≦ x ≦ 1) and the other (both are Al _x Ga _1-x As (0 ≦ x ≦ 1)) except) can be made of _{in x (Ga y Al 1-} y) 1-x P ( where, 0 ≦ x ≦ 1,0 ≦ y ≦ 1). Further, the stacked body 32 may include In _x Ga _y Al _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1).

Next, the case where the laminate 32 is _{In x (Ga y Al 1-} y) 1-x P ( where, 0 ≦ x ≦ 1,0 ≦ y ≦ 1) is a InGaAlP-based material represented by a composition formula, the The second embodiment is used. 1A and 1B, the laminated body 32 is formed in this order using, for example, a MOCVD (Metal Organic Chemical Vapor Deposition) method or MBE (Molecular Beam Epitaxy) method on a GaAs substrate (not shown). The first conductivity type layer 30, the light emitting layer 22, and the second conductivity type layer 20 that are crystal-grown in FIG.

The first conductivity type layer 30 includes a GaAs contact layer 28 (impurity concentration 1.0 × 10 ¹⁸ cm ⁻³ , thickness 0.1 μm), In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P A first layer 25 made of, a second layer 26 made of In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P, and a cladding layer 24 made of In _0.5 Al _0.5 P ( Impurity concentration of 4 × 10 ¹⁷ cm ⁻³ and thickness of 0.6 μm).

The light emitting layer 22 is, for example, a well layer (thickness 8 nm) made of In _0.5 (Ga _0.9 Al _0.1 ) _0.5 P and In _0.5 (Ga _0.4 Al _0.6 ) _{0. It} has a MQW (Multi Quantum Well) structure including a barrier layer made of ₅ P (thickness 5 nm). For example, the number of wells is in the range of 30-60. In that case, the number of barriers is one more than the number of wells.

The second conductivity type layer 20 includes, for example, a cladding layer 18 (impurity concentration 3 × 10 ¹⁷ cm ⁻³ , thickness 0.6 μm) made of In _0.5 Al _0.5 P, In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P current diffusion layer 16 (impurity concentration 4 × 10 ¹⁷ cm ⁻³ , thickness 0.2 μm), and Al _0.5 Ga _0.5 As contact layer 14 (impurities Concentration 9 × 10 ¹⁸ cm ⁻³ , thickness 0.2 μm).

  The first electrode 50 is provided on the contact layer 28, and the contact layer 28 is removed in the non-formation region 26c except under the first electrode 50. That is, the second surface of the second layer 26 is The non-formation region 26c of the first electrode 50 is exposed, and the non-formation region 26b provided with the contact layer 28 and the first electrode 50 is not exposed. A convex portion 27 is formed in the non-formation region 26c.

  The second electrode 40 is bonded to the substrate first electrode 12 provided on the substrate 10 made of conductive Si or the like in a wafer state, and then the GaAs substrate is removed. A substrate second electrode 13 is provided on the back surface of the substrate 10.

3A is a light output remaining rate of the light emitting device of the second embodiment, FIG. 3B is a light output remaining rate of the first comparative example, and FIG. 3C is a light output remaining rate of the second comparative example. FIG. 3D shows the light output remaining rate of the third comparative example.
The vertical axis represents the optical output remaining rate (%), and the horizontal axis represents the energization time (h). The light output remaining rate (%) represents the ratio of the light output that has changed due to energization, where the light output before energization is 100%. The operating current was 50 mA for all.

FIG. 3A shows the remaining optical output rate of the InGaAlP-based light-emitting element according to the second embodiment. The second layer 26 has n-type In _0.5 (Ga _0.6 Al _0.4 ) _0. consists _.5 P, the second impurity concentration N2 30 × ¹⁰ 17 ^{cm -3,} thickness T2 was 1 [mu] m, and. The first layer 25 is made of n-type In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P, and the first impurity concentration N1 is 8 × 10 ¹⁷ cm ⁻³ and the thickness T1. Was 3 μm. Furthermore, the height H of the convex part 27 was 0.5 μm. Even after 1000 hours, the light output hardly decreased.

FIG. 4A is a schematic plan view of a light emitting element according to a first comparative example, and FIG. 4B is a schematic cross-sectional view taken along the line BB.
In the first comparative example, the first conductivity type is n-type and the second conductivity type is p-type. A current diffusion layer 125 is provided between the first electrode 150 and the cladding layer 124. The current diffusion layer 125 is made of In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P, has a thickness of 3 μm, and an impurity concentration of 8 × 10 ¹⁷ cm ⁻³ . In addition, island-shaped convex portions 127 are formed on the upper surface 125 a of the current diffusion layer 125.

  The light emitting layer 122, the cladding layer 124 of the n-type layer 130, the contact layer 128, the p-type layer 120, the first electrode 150, the second electrode 140, and the current blocking layer 142 are the InGaAlP-based layers of the second embodiment. Suppose that it is the same as a light emitting element.

  As shown in FIG. 3B, the light output remaining rate after 168 hours was approximately 50%, and the light output remaining rate after 1000 hours was approximately 40%. In the dry etching process for forming the convex portion 127, crystal defects are generated in the current diffusion layer 125, and the crystal defects are increased by energization, so that the light output is lowered with time.

FIG. 3C shows the light output remaining rate of the second comparative example. The second layer is made of n-type In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P, the second impurity concentration N 2 is 30 × 10 ¹⁷ cm ⁻³ , and the thickness T 2 is 0. The first layer is made of n-type In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P, and the first impurity concentration N1 is 8 × 10 ¹⁷ cm ^{−. 3} and the thickness T1 was 3 μm. The height H of the convex part 27 was 0.5 μm. The light output remaining rate after 168 hours passed was 60 to 63%, and the light output remaining rate after 1000 hours passed was 58 to 61%. In this case, the bottom part around the convex part 27 reaches the first layer. That is, crystal defects occur in the first layer having a low impurity concentration in the dry etching process. When this region is energized, the light output is reduced.

FIG. 5A shows the dependence of the relative emission intensity on the impurity concentration of the first layer, and FIG. 5B shows the dependence of the relative emission intensity on the thickness of the first layer in the second embodiment. FIG.
For example, in FIG. 5A, the thickness T1 of the first layer 25 is 3 μm. The vertical axis represents the relative light emission intensity, and the horizontal axis represents the impurity concentration N1 (× 10 ¹⁷ cm ⁻³ ) of the first layer 25. When the impurity concentration N1 is 5 × 10 ¹⁷ cm ⁻³ or more, the injected current spreads sufficiently in the first layer 25 and increases the light that is reflected by the second electrode 40 and can be extracted without being blocked by the first electrode 50. To do. For this reason, it can be made about 1.5 times the light emission intensity when the impurity concentration N1 of the first layer 25 is 4 × 10 ¹⁷ cm ⁻³ . In addition, since the activation rate is about 1 when Si is added to the InGaAlP-based material to form n-type, the impurity concentration represents the carrier concentration.

In FIG. 5B, the impurity concentration N1 is set to 5 × 10 ¹⁷ cm ⁻³ . The vertical axis represents the relative light emission intensity, and the horizontal axis represents the thickness T1 (μm) of the first layer 25. When the thickness T1 of the first layer 25 is 2 μm or more, the injected current is sufficiently spread by the first layer 25, reflected by the second electrode 40, and light that can be extracted without being blocked by the first electrode 50. Increase. For this reason, it can be as high as about 1.5 times the emission intensity when the thickness of the current diffusion layer is 1 μm.

  Therefore, in the second embodiment which is an InGaAlP-based light emitting element, the impurity concentration N1 of the first layer 25 is more preferably in the range of the formula (1).

5 × 10 ¹⁷ ≦ N1 (1 / cm ³ ) Formula (1)

If the impurity concentration N1 is higher than 30 × 10 ¹⁷ cm ⁻³ , the donor concentration is too high and an impurity energy level is formed in the band gap to absorb light. For this reason, the light output decreases. That is, the impurity concentration N1 is more preferably 30 × 10 ¹⁷ cm ⁻³ or less.

  Further, when the thickness T1 of the first layer 25 is larger than 5 μm, the quality of the growth film is lowered due to an increase in crystal defects and the light output is lowered. In other words, the thickness T1 of the first layer 25 is more preferably in the range of the formula (2).

2 ≦ T1 (μm) ≦ 5 Formula (2)

  When the height H of the convex portion 27 is brought close to the thickness T2 of the second layer 26, the current spreading effect in the lower region of the second layer 26 is reduced. In this case, it is more preferable to perform the current diffusion required in the first layer 25.

FIG. 3D shows the light output residual ratio of the third comparative example. The second layer is made of n-type In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P, the second impurity concentration N2 is 1 × 10 ¹⁸ cm ⁻³ , and the thickness T2 is 1 μm. The first layer is made of n-type In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P, and the first impurity concentration N1 is 8 × 10 ¹⁷ cm ⁻³ , The thickness T1 is 3 μm. The height H of the convex portion is 0.5 μm. The remaining light output after 168 hours was 56 to 64%, and the remaining light output after 1000 hours was 55 to 62%. In this case, the bottom of the convex portion does not reach the second layer, but the impurity concentration of the second layer is too low at 1 × 10 ¹⁸ cm ⁻³ , indicating that crystal defects increase. That is, it has been found that the impurity concentration N2 capable of reducing damage in the dry etching process is more preferable when it is within the range of the formula (3). Equation (3) can also be applied to the case where the first layer and the second layer are each made of Al _x Ga _1-x As (0 ≦ x ≦ 1).

1.5 × 10 ¹⁸ ≦ N2 (1 / cm ³ ) Formula (3)

Note that if the second impurity concentration N2 of the second layer 26 becomes too high, light absorption may increase due to the impurity energy level formed in the band gap. That is, it is more preferable that the second impurity concentration N2 is 50 × 10 ¹⁷ cm ⁻³ or less.

6A is an SEM photograph of the top surface of an island-shaped convex portion made of InGaAlP, FIG. 6B is an SEM photograph of the island-shaped convex portion seen from obliquely above, and FIG. 6C is a mesh-shaped convex portion. It is a model perspective view.
When a dry etching method is used with a block copolymer as a mask, fine convex portions 27 having a random shape as shown in SEM (Scanning Electron Microscope) photographs of FIGS. 6A and 6B can be formed. FIG. 6B is an SEM photograph corresponding to the schematic cross-sectional view of FIG. The convex portion 27 including a plurality of island shapes can be formed in a columnar shape having a flat region on the upper surface 27a, and the bottom portion 27b provided around the convex portion 27 can be inclined.

  As shown in FIG. 6C, the net-like convex portion 27 has a flat region on the upper surface 27c, and a plurality of bottom portions 27d are provided around it. Such a net-like convex portion 27 can be formed by increasing the relative composition ratio of PS to PMMA in the block copolymer. In the case of the net-like convex part 27, the shortest distances among the distances from the center of one bottom part 27d provided around the convex part 27 are the pitches P4, P5, etc. . In this way, the average value of the respective pitches P is defined as the average pitch of the net-like convex portions 27.

  The average pitch of the convex portions 27 in FIGS. 6A and 6B is smaller than the wavelength range of 610 to 700 nm of red light. The column diameter is distributed in a range of 100 to 200 nm, the depth H of the recess 27 is 200 to 600 nm, and the like. It is also possible to form the convex portions 27 having a regular shape using a photoresist mask.

  6, a refractive index gradient is provided in the depth direction from the surface of the second layer 26, and diffracted light can be extracted upward, so that high light extraction efficiency can be obtained.

7A and 7B are SEM photographs of the upper portion of the island-shaped convex portion formed by the wet etching method, and FIG. 7C is an SEM photograph of the cross section thereof.
When a frost treatment is performed using a wet etching method or the like, it is difficult to form island-like or net-like convex shapes having a size smaller than the wavelength, and it is difficult to increase the convex portions. Therefore, it is difficult to form the refractive index gradient region with good controllability and to form a diffraction grating. Further, it is difficult to control the upper surface of the convex portion to be flat.

FIG. 8 is a graph showing the dependence of relative emission intensity on the number of MQW wells.
The vertical axis represents relative emission intensity, and the horizontal axis represents the number of MQW wells. A solid line indicates the InGaAlP-based light emitting element according to the second embodiment. The second layer 26 is made of n-type In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P, the second impurity concentration N 2 is 30 × 10 ¹⁷ cm ⁻³ , and the thickness T 2. Is 1 μm. The first layer 25 is made of n-type In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P, and the first impurity concentration N1 is 8 × 10 ¹⁷ cm ⁻³ and the thickness T1. Is 3 μm. Moreover, the height H of the convex part 27 shall be 0.5 micrometer. The light emission intensity of the second embodiment represented by a solid line can be approximately 1.4 times the light emission intensity of SQW (Single Quantum Well) in the range of 30 to 60 wells.

  In the second embodiment, the first layer 25 further spreads the current in the plane of the light emitting layer 22, and even if the number of wells is increased to 30 to 60, the carriers of each well are in the plane of the light emitting layer 22 and Since it can be more uniformly distributed in the vertical direction, the emission intensity can be increased.

FIG. 9A shows the relative emission intensity dependence on the impurity concentration of the p-type contact layer, and FIG. 9B shows the dependence of the forward voltage on the carrier concentration of the p-type contact layer.
As shown in FIG. 9A, when the impurity concentration of the contact layer 14 made of p-type Al _0.5 Ga _0.5 As is higher than 30 × 10 ¹⁸ cm ⁻³ , the emission intensity rapidly decreases. This is because when the impurity concentration increases, the acceptor forms a non-emission level in the band gap and absorbs the emitted light.

On the other hand, as shown in FIG. 9B, when the p-type impurity concentration is lower than 7 × 10 ¹⁸ cm ⁻³ , the contact resistance with the second electrode 40 increases and the forward voltage increases. From these results, when the impurity concentration of the contact layer 14 is 7 to 30 × 10 ¹⁸ cm ⁻³ , it is easy to increase the emission intensity while suppressing an increase in the forward voltage.

Next, in the case where the stacked body 32 is a nitride-based material containing In _x Ga _y Al _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1), It is set as the light emitting element of embodiment.
FIG. 10A is a schematic plan view of the third embodiment, and FIG. 10B is a schematic cross-sectional view taken along the line CC.

The light emitting element includes a substrate 80, a stacked body 89, a first electrode 90, and a second electrode 92.
The laminate 89 includes In _x Ga _y Al _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1), and the emitted light is in the ultraviolet to green wavelength range. And The laminated body 89 is provided on the light emitting layer 84 and the light emitting layer 84, has the first conductivity type, and is provided on the clad layer 85 and the clad layer 85 made of Al _0.2 Ga _0.8 N or the like. A first layer 86 having a first impurity concentration of one conductivity type, a second layer having a second impurity concentration of a first conductivity type provided on the first layer 86 and higher than the first impurity concentration. Layer 88.

The stacked body 89 has a second conductivity type layer 81 including a cladding layer 83 made of Al _0.2 Ga _0.8 N or the like provided under the light emitting layer 84 and a contact layer 82. When the substrate 80 is an insulating sapphire, the second electrode 92 can be provided on the surface of the contact layer 82 opposite to the surface in contact with the substrate 80.

  One surface of the first layer 86 has a formation region and a non-formation region of the first electrode 90. In the non-formation region, a net-like or a plurality of island-like convex portions 97 are provided. The average pitch of the convex portions 97 is smaller than the wavelength of the emitted light in the second layer 88.

  According to the embodiment of the present invention, a light emitting device with improved light output and improved reliability in long-time operation is provided. These light-emitting elements can emit light in the visible light wavelength range and can be widely used in lighting devices, display devices, traffic lights, and the like.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

20, 81 Second conductivity type layer, 22, 84 Light emitting layer, 24, 85 Cladding layer, 25, 86 First layer, 26, 88 Second layer, 27, 97 Convex portion, 40, 92 Second electrode, 42 current blocking layer, 50, 90 first electrode

Claims (10)

A light emitting layer capable of emitting emitted light;
A first electrode;
A first layer of a first conductivity type provided between the light emitting layer and the first electrode;
Provided between the first layer and the first electrode, the impurity concentration of the first conductivity type is 1.5 × 10 ¹⁸ cm ⁻³ or more, and a plurality of protrusions are provided on at least a part of the upper surface A second layer having crystal defects;
A light-emitting element comprising:   The light emitting device according to claim 1, wherein an upper surface of the convex portion has a flat region.   The light emitting device according to claim 1, wherein a bottom portion around the convex portion is located in the second layer.   4. The light-emitting element according to claim 1, wherein the impurity concentration of the first layer is lower than the impurity concentration of the second layer. The _{EML, In x (Ga y Al 1} -y) 1-x P ( However, 0 ≦ x ≦ 1,0 ≦ y ≦ 1) consists,
One of the first layer and the second layer is made of Al _x Ga _1-x As (0 ≦ x ≦ 1), and the other is In _x (Ga _y Al _1-y ) _{1− x} P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), or both the first and second layers are composed of Al _x Ga _1-x As (0 ≦ x ≦ 1). The light emitting device according to claim 1, wherein the light emitting device is a light emitting device.   6. The light emitting device according to claim 5, wherein the first conductivity type impurities of the first layer and the second layer contain Si. The _{EML, In x Ga y Al 1-} x-y N ( However, 0 ≦ x ≦ 1,0 ≦ y ≦ 1, x + y ≦ 1) any one of claims 1 to 4, characterized in that it consists of The light emitting element as described in one. A second electrode;
A second conductivity type layer provided between the second electrode and the light emitting layer;
The light emitting device according to claim 1, further comprising:   The light emitting element according to claim 1, wherein the plurality of convex portions are formed by a reactive ion etching method.   The light emitting device according to claim 9, wherein the crystal defect is formed by the reactive ion etching method.