Light-emitting element

Abstract

To provide a light-emitting device having a high light extraction efficiency.SOLUTION: A light-emitting device contains a semiconductor structure made of a nitrogen semiconductor containing: an n-side semiconductor layer; a p-side semiconductor layer; and an active layer arranged between the n-side semiconductor layer and the p-side semiconductor layer, and containing a well layer. The p-side semiconductor layer contains, in order from the active layer side: a first layer including Ga, Al and In; a second layer including Ga and Al, and having a thickness thinner than that of the first layer; and a third layer including Ga. A band-gap energy of the second layer is larger than the band-gap energy of the well layer, a p-type impurity concentration of the third layer is higher than the p-type impurity concentration of the first layer. An Al composition ratio of the second layer is larger than the Al composition ratio of the first layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a light-emitting element.

Background Art

[0002] Patent Document 1 discloses a light-emitting element in which layers composed of a plurality of nitride semiconductors are stacked. In such a light-emitting element, it is desirable to improve the light extraction efficiency.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An embodiment of the present invention aims to provide a light-emitting element having high light extraction efficiency.

Means for Solving the Problems

[0005] A light-emitting element according to an embodiment of the present invention includes a semiconductor structure made of a nitride semiconductor including an n-side semiconductor layer, a p-side semiconductor layer, and an active layer including a well layer disposed between the n-side semiconductor layer and the p-side semiconductor layer, wherein the p-side semiconductor layer has, in order from the active layer side, a first layer containing Ga, Al, and In, a second layer containing Ga and Al and thinner than the thickness of the first layer, and a third layer containing Ga, the bandgap energy of the second layer is larger than the bandgap energy of the well layer, the p-type impurity concentration of the third layer is higher than the p-type impurity concentration of the first layer, and the Al composition ratio of the second layer is larger than the Al composition ratio of the first layer.

Effects of the Invention

[0006] According to an embodiment of the present invention, a light-emitting element having high light extraction efficiency can be provided.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2A

Figure 2B

Figure 3

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of a light-emitting element according to the present invention will be described. Note that the drawings referred to in the following description schematically show the present invention, and thus the scale, interval, positional relationship, etc. of each member may be exaggerated, or illustration of a part of the member may be omitted. Further, in the following description, the same names and reference numerals generally denote the same or similar members, and detailed description thereof will be omitted as appropriate.

[0009] FIG. 1 is a schematic cross-sectional view of a light-emitting element 1. FIGS. 2A and 2B are schematic cross-sectional views showing the laminated structure of a p-side semiconductor layer 40. FIG. 3 is a band diagram schematically showing the band structure of an active layer 30 and a p-side semiconductor layer 40.

[0010] As shown in FIG. 1, the light-emitting element 1 has a substrate 10 and a semiconductor structure 100 disposed on the substrate 10. The semiconductor structure 100 includes an n-side semiconductor layer 20, a p-side semiconductor layer 40, and an active layer 30 positioned between the n-side semiconductor layer 20 and the p-side semiconductor layer 40. The light-emitting element 1 has an n electrode 51 electrically connected to the n-side semiconductor layer 20 and a p electrode 52 electrically connected to the p-side semiconductor layer 40.

[0011] As the material of the substrate 10, for example, sapphire, silicon, SiC, GaN, or the like can be used. A buffer layer may be disposed between the substrate 10 and the semiconductor structure 100. As the buffer layer, for example, a layer made of AlGaN or AlN can be used. The substrate 10 may be finally removed.

[0012] The semiconductor structure 100 is a laminate in which a plurality of semiconductor layers made of a nitride semiconductor are laminated. The nitride semiconductor may include semiconductors of all compositions in which the composition ratios x and y are changed within their respective ranges in the chemical formula consisting of In x Al y Ga 1-x-y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1).

[0013] The underlayer 22 is disposed between the substrate 10 and the n-side semiconductor layer 20. The underlayer 22 is, for example, an undoped GaN layer. The thickness of the underlayer 22 can be, for example, 5 μm or more and 10 μm or less. Note that the underlayer 22 may not be disposed. Here, an undoped layer is a layer that is not intentionally doped with n-type impurities or p-type impurities. When an undoped layer is adjacent to a layer intentionally doped with n-type impurities and / or p-type impurities, the undoped layer may contain n-type impurities and / or p-type impurities due to diffusion from the adjacent layer or the like. In the present specification, the thickness of each semiconductor layer is the thickness in the stacking direction of the semiconductor structure 100.

[0014] The n-side semiconductor layer 20 includes one or more n-type semiconductor layers. Examples of the n-type semiconductor layer include semiconductor layers containing n-type impurities such as silicon (Si) and germanium (Ge). The n-type semiconductor layer is, for example, a layer made of GaN containing gallium (Ga) and nitrogen (N), and may contain indium (In) and aluminum (Al). For example, the n-type impurity concentration of an n-type semiconductor layer containing Si as an n-type impurity is 1 × 10 18 / cm 3 or more and 2 × 10 19 / cm 3The following applies. The n-side semiconductor layer 20 only needs to have a function of supplying electrons and may include an undoped layer. Further, the n-side semiconductor layer 20 may include a superlattice layer in which a plurality of semiconductor layers made of different materials are alternately stacked.

[0015] The n-side semiconductor layer 20 has an upper surface on which no other semiconductor layer is disposed. An n-electrode 51 is disposed on the upper surface of the n-side semiconductor layer 20 on which no other semiconductor layer is disposed.

[0016] The active layer 30 is disposed between the n-side semiconductor layer 20 and the p-side semiconductor layer 40. The active layer 30 includes a well layer 31 and a barrier layer 32. The active layer 30 has, for example, a multiple quantum well structure including a plurality of well layers 31 and a plurality of barrier layers 32. As shown in FIG. 3, the bandgap energy of the barrier layer 32 is larger than the bandgap energy of the well layer 31. Light having a wavelength corresponding to the bandgap energy of the well layer 31 is emitted from the well layer 31 included in the active layer 30. For example, layers made of InGaN, GaN, or AlGaN are used for the plurality of well layers 31. For example, layers made of GaN or AlGaN are used for the plurality of barrier layers. The well layer 31 and the barrier layer 32 included in the active layer 30 are, for example, undoped layers. At least a part of the well layer 31 and the barrier layer 32 included in the active layer 30 may contain an n-type impurity and / or a p-type impurity.

[0017] The light emitted from the active layer 30 is, for example, ultraviolet light or visible light. The active layer 30 can emit, for example, blue light or green light as visible light. The emission peak wavelength of the blue light is 430 nm or more and 490 nm or less. The emission peak wavelength of the green light is 500 nm or more and 540 nm or less. The emission peak wavelength of the ultraviolet light is 400 nm or less.

[0018] The p-side semiconductor layer 40 includes one or more p-type semiconductor layers. Examples of the p-type semiconductor layer include a semiconductor layer containing a p-type impurity such as magnesium (Mg). As shown in Fig. 2A, the p-side semiconductor layer 40 includes a first layer 41, a second layer 42, and a third layer 43 in this order from the active layer 30 side. The p-side semiconductor layer 40 further includes a fourth layer 44 disposed between the active layer 30 and the first layer 41, and a fifth layer 45 disposed between the active layer 30 and the fourth layer 44.

[0019] The first layer 41 is a semiconductor layer containing Ga, Al, and In. The second layer 42 is a semiconductor layer containing Ga and Al. The third layer 43 is a semiconductor layer containing Ga. The fourth layer 44 is a semiconductor layer containing Ga. The fifth layer 45 has a semiconductor layer containing Ga and Al. The first layer 41 is, for example, a layer made of AlInGaN. The second layer 42 is, for example, a layer made of AlGaN. The third layer 43 is, for example, a layer made of GaN. The fourth layer 44 is, for example, a layer made of GaN. The fifth layer 45 includes, for example, a layer made of AlGaN or GaN.

[0020] By disposing the first layer 41 made of a semiconductor layer containing Ga, Al, and In on the active layer 30, it becomes easier to fill the V-pits formed on the upper surface of the semiconductor layer after forming the active layer 30. This is presumably because when the first layer 41 is formed, the growth in the V-pits is promoted due to the inclusion of Al and In, and thus the V-pits are more easily filled compared to the case of forming a layer made of, for example, GaN. Note that the V-pits are recesses formed on the upper surface of the semiconductor layer. Since such V-pits are more easily filled, the thermal damage to the active layer 30 caused by the formation of the first layer 41, the second layer 42, and the third layer 43 with the upper surface of the active layer 30 exposed is reduced. As a result, the deterioration of the crystallinity of the active layer 30 is reduced, and the luminous efficiency of the light-emitting element 1 can be increased.

[0021] The p-type impurity concentration of the third layer 43 is higher than that of the first layer 41. By increasing the p-type impurity concentration of the third layer 43, holes can be more easily supplied from the p-side semiconductor layer 40 to the active layer 30, and the luminous efficiency of the light-emitting element 1 can be increased. Further, the p-type impurity concentrations of the second layer 42 and the third layer 43 are preferably higher than that of the first layer 41. Thereby, holes can be more easily supplied from the p-side semiconductor layer 40 to the active layer 30 than in the case where only the third layer 43 is disposed. The p-type impurity concentrations of the second layer 42 and the third layer 43 are, for example, 1×10 20 / cm 3 or more and 5×10 20 / cm 3 or less. The first layer 41 is composed of, for example, an undoped layer. The p-type impurity concentration of the first layer 41 is, for example, 5×10 18 / cm 3 or more and 3×10 19 / cm 3 or less.

[0022] The p-type impurity concentration of the second layer 42 is preferably lower than that of the third layer 43. By reducing the p-type impurity concentration of the second layer 42, a decrease in the light transmittance in the second layer 42 due to the inclusion of p-type impurities at a high concentration can be reduced. Therefore, compared with the case where the p-type impurity concentrations of the second layer 42 and the third layer 43 are the same, absorption of the light emitted from the active layer 30 by the second layer 42 can be reduced, and the light extraction efficiency can be increased. When the p-type impurity concentration of the second layer 42 is lower than that of the third layer 43, for example, the p-type impurity concentration of the second layer 42 can be set to 60% or more and 80% or less of the p-type impurity concentration of the third layer 43. Specifically, the p-type impurity concentration of the second layer 42 can be set to 1×10 20 / cm 3 or more and 3×10 20 / cm 3 or less, and the p-type impurity concentration of the third layer 43 can be set to 3×10 20 / cm 3 or more and 5×10 20 / cm 3 or less.

[0023] The second layer 42 is composed of a semiconductor layer containing Al, and as shown in FIG. 3, has a bandgap energy larger than the bandgap energy of the well layer 31 of the active layer 30. The second layer 42 is, for example, a semiconductor layer having a larger bandgap energy than the well layer 31 made of InGaN, and is less likely to absorb the light emitted by the active layer 30. By disposing such a second layer 42, absorption of the light emitted by the active layer 30 can be reduced, and the light extraction efficiency can be increased. Further, as shown in FIG. 3, it is preferable that the first layer 41 and the second layer 42 have a bandgap energy larger than the bandgap energy of the well layer 31 of the active layer 30. By disposing such a first layer 41, absorption of the light emitted by the active layer 30 can be reduced and the light extraction efficiency can be increased, similarly to the second layer 42 described above. Note that the bandgap energy of the well layer 31 of the active layer 30 is calculated from the emission peak wavelength of the light emitted by the active layer 30. For example, when the emission peak wavelength of the light emitted by the active layer 30 is 450 nm, the bandgap energy of the well layer 31 of the active layer 30 is calculated to be approximately 2.76 eV from bandgap energy [eV] = 1240 / emission peak wavelength [nm]. Further, the bandgap energy of each semiconductor layer is calculated from the composition ratio of the material constituting the semiconductor layer.

[0024] The Al composition ratio of the second layer 42 is larger than the Al composition ratio of the first layer 41. For example, when the first layer 41 is made of In x1 Al y1 Ga 1-x1-y1 N and the second layer 42 is made of In x2 Al y2 Ga 1-x2-y2 N, y1 is larger than y2. Thereby, the bandgap energy of the second layer 42 can be made larger than the bandgap energy of the first layer 41, and absorption of the light emitted by the active layer 30 by the second layer 42 can be reduced.

[0025] The second layer 42 is composed of a semiconductor layer having a higher Al composition ratio than the first layer 41. When forming such a second layer 42, for example, on a GaN layer, lattice relaxation may occur due to the lattice constant difference between the second layer 42 and the GaN layer, and the crystallinity of the second layer 42 may deteriorate. In the present embodiment, by forming the second layer 42 on the first layer 41 having an Al composition ratio lower than that of the second layer 42, the lattice constant difference between the first layer 41 and the second layer 42 is reduced, and the occurrence of lattice relaxation is reduced. Thereby, the crystallinity of the second layer 42 and the third layer 43 disposed on the second layer 42 can be improved.

[0026] It is preferable that the difference between the Al composition ratio of the first layer 41 and the Al composition ratio of the second layer 42 is 5% or more and 10% or less. By setting the difference between the Al composition ratio of the first layer 41 and the Al composition ratio of the second layer 42 to 5% or more, it is easy to reduce the absorption of the light emitted by the active layer 30 by the second layer 42. By setting the difference between the Al composition ratio of the first layer 41 and the Al composition ratio of the second layer 42 to 10% or less, the occurrence of lattice relaxation between the first layer 41 and the second layer 42 can be reduced, and the second layer 42 can be formed with good crystallinity.

[0027] The Al composition ratio of the first layer 41 can be, for example, 1% or more and 4% or less. The Al composition ratio of the second layer can be, for example, 3% or more and 10% or less. For example, the Al composition ratio of the first layer 41 can be about 3%, and the Al composition ratio of the second layer 42 can be about 8%.

[0028] The In composition ratio of the first layer 41 is preferably 1% or more and 3% or less. By setting the In composition ratio of the first layer 41 to 1% or more, the effect of embedding the V-pit formed on the upper surface of the fourth layer 44 by the first layer 41 can be easily obtained. By setting the In composition ratio of the first layer 41 to 3% or less, the deterioration of the crystallinity of the first layer 41 can be reduced.

[0029] The thickness of the second layer 42 is thinner than that of the first layer 41. By disposing the second layer 42, which has a larger Al composition ratio and is more likely to have poor crystallinity than the first layer 41, relatively thinly, the deterioration of the crystallinity of the p-side semiconductor layer 40 can be reduced.

[0030] The thickness of the second layer 42 can be equal to or greater than the thickness of the third layer 43. As shown in FIG. 2B, it is preferable that the thickness of the second layer 42 is greater than the thickness of the third layer 43. Thereby, compared with the case where the second layer 42 and the third layer 43 have the same thickness, the absorption of the light emitted from the active layer 30 can be reduced, so that the light extraction efficiency can be increased. The thickness of the second layer 42 can be, for example, 60% or more and 80% or less of the total thickness of the second layer 42 and the third layer 43. By setting the thickness of the second layer 42 to 60% or more of the total thickness of the second layer 42 and the third layer 43, the light extraction efficiency can be increased. By setting the thickness of the second layer 42 to 80% or less of the total thickness of the second layer 42 and the third layer 43, it is possible to reduce the deterioration of crystallinity due to thickly disposing the second layer 42 containing Al and having a high p-type impurity concentration. The thickness of the second layer 42 can be, for example, 6 nm or more and 10 nm or less. The thickness of the third layer 43 can be, for example, 8 nm or more and 12 nm or less.

[0031] The fourth layer 44 is disposed on the upper surface of the fifth layer 45. It is preferable that the fourth layer 44 is thicker than the first layer 41. The first layer 41 is disposed on the upper surface of the fourth layer 44. The V-pit formed on the upper surface of the semiconductor layer after forming the active layer 30 is filled by the fourth layer 44, and the V-pit formed on the upper surface of the fourth layer 44 is further filled by the first layer 41. Therefore, by disposing the fourth layer 44 containing Ga and thicker than the first layer 41 before disposing the first layer 41, the V-pit formed on the upper surface of the semiconductor layer after forming the active layer 30 can be filled more easily than in the case where only the first layer 41 is disposed. The thickness of the first layer 41 can be, for example, 15 nm or more and 25 nm or less. The thickness of the fourth layer 44 can be, for example, 20 nm or more and 40 nm or less. Note that the fourth layer 44 may not be disposed.

[0032] The fourth layer 44 is, for example, a layer made of undoped GaN. The p-type impurity concentration of the fourth layer 44 is, for example, 5×10 18 / cm 3 or more and 3×10 19 / cm 3 or less. Note that the fourth layer 44 may not be disposed.

[0033] The fifth layer 45 is disposed on the upper surface of the active layer 30. The fifth layer 45 is a layer disposed to confine carriers in the active layer 30. The fifth layer 45 can have, for example, a stacked structure including a GaN layer containing p-type impurities and an AlGaN layer containing p-type impurities. The p-type impurity concentration of the fifth layer 45 is preferably higher than the p-type impurity concentrations of the first layer 41, the second layer 42, and the third layer 43. The p-type impurity concentration of the fifth layer 45 is, for example, 5×10 19 / cm 3 or more and 3×10 20 / cm 3 or less. Note that the fifth layer 45 may not be disposed.

[0034] The Al composition ratio of the AlGaN layer included in the fifth layer 45 is higher than the Al composition ratio of the first layer 41 and the Al composition ratio of the second layer 42. Thereby, carriers can be confined in the active layer 30 and the light emission efficiency can be improved. As shown in FIG. 3, the band gap energy of the fifth layer 45 is larger than the band gap energy of the second layer 42. The Al composition ratio of the AlGaN layer included in the fifth layer 45 is preferably, for example, 30% or more and 40% or less. The thickness of the fifth layer 45 can be, for example, 10 nm or more and 20 nm or less.

[0035] The n electrode 51 is disposed on the n-side semiconductor layer 20 and is electrically connected to the n-side semiconductor layer 20. The p electrode 52 is disposed on the third layer 43 of the p-side semiconductor layer 40 and is electrically connected to the p-side semiconductor layer 40. As the materials of the n electrode 51 and the p electrode 52, for example, metals such as Ag, Al, Ni, Rh, Au, Cu, Ti, Pt, Pd, Mo, Cr, W, or alloys mainly composed of these metals can be used. The n electrode 51 and the p electrode 52 can have, for example, a stacked structure including a Ti layer and an Au layer.

[0036] When a forward voltage is applied between the n electrode 51 and the p electrode 52, a forward voltage is applied between the p-side semiconductor layer 40 and the n-side semiconductor layer 20, and holes and electrons are supplied to the active layer 30, so that the active layer 30 emits light.

[0037] As described above, according to the light-emitting element of the present embodiment, by disposing the first layer 41 and the second layer 42 having a larger bandgap energy than the well layer 31, the light extraction efficiency can be increased. Further, the first layer 41 makes it easier to fill the V-pits formed on the upper surface of the semiconductor layer after forming on the active layer 30, thereby reducing the thermal damage to the active layer 30 and increasing the light emission efficiency of the light-emitting element 1.

[0038] As described above, the embodiments of the present invention have been described with reference to specific examples. However, the present invention is not limited to these specific examples. Based on the above-described embodiments of the present invention, all forms that can be appropriately designed and implemented by those skilled in the art also belong to the scope of the present invention as long as they include the gist of the present invention. In addition, within the scope of the idea of the present invention, those skilled in the art can conceive of various modification examples and correction examples, and those modification examples and correction examples also belong to the scope of the present invention.

Explanation of reference numerals

[0039] 1 Light-emitting element 10 Substrate 20 n-side semiconductor layer 22 Underlayer 30 Active layer 31 Well layer 32 Barrier layer 40 p-side semiconductor layer 41 First layer 42 Second layer 43 Third layer 44 Fourth layer 45 Fifth layer 51 n electrode 52 p electrode 100 Semiconductor structure

Claims

1. A light-emitting device including a semiconductor structure made of a nitride semiconductor including an n-side semiconductor layer, a p-side semiconductor layer, and an active layer including a well layer disposed between the n-side semiconductor layer and the p-side semiconductor layer, wherein the p-side semiconductor layer has, in order from the active layer side, a fifth layer containing Ga and Al, a first layer containing Ga, Al, and In, a second layer containing Ga and Al and thinner than the first layer, and a third layer containing Ga and having a p electrode disposed thereon, wherein the bandgap energy of the second layer is larger than the bandgap energy of the well layer, wherein the bandgap energy of the fifth layer is larger than the bandgap energy of the second layer, wherein the p-type impurity concentration of the third layer is higher than the p-type impurity concentration of the second layer and the p-type impurity concentration of the first layer, and wherein the Al composition ratio of the second layer is larger than the Al composition ratio of the first layer.

2. The light-emitting device according to claim 1, wherein the bandgap energy of the first layer is larger than the bandgap energy of the well layer.

3. The light-emitting device according to claim 1 or 2, wherein the p-type impurity concentration of the second layer is higher than the p-type impurity concentration of the first layer.

4. wherein the p-side semiconductor layer is disposed between the active layer and the first layer and further includes a fourth layer containing Ga, and wherein the thickness of the fourth layer is thicker than the first layer.

5. The light-emitting device according to any one of claims 1 to 4, wherein the difference between the Al composition ratio of the first layer and the Al composition ratio of the second layer is 5% or more and 10% or less.

6. The light-emitting device according to any one of claims 1 to 5, wherein the thickness of the second layer is 60% or more and 80% or less of the total thickness of the second layer and the third layer.

7. The light-emitting device according to any one of claims 1 to 6, wherein the emission peak wavelength of the light emitted by the active layer is 430 nm or more and 490 nm or less.

8. The light-emitting device according to any one of claims 1 to 7, having an n electrode electrically connected to the n-side semiconductor layer.

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