Semiconductor light-emitting element

Abstract

The objective is to provide a semiconductor light-emitting element with reduced ripple in FFP. [Solution] A semiconductor light-emitting element comprising a GaN substrate, a first nitride semiconductor portion provided on the substrate and containing n-type impurities, a second nitride semiconductor portion provided on the first nitride semiconductor portion and containing n-type impurities, and a third nitride semiconductor portion provided on the second nitride semiconductor portion and containing n-type impurities, wherein the n-type impurity concentration in the first nitride semiconductor portion is greater than the n-type impurity concentration in the third nitride semiconductor portion, the n-type impurity concentration in the second nitride semiconductor portion is greater than the n-type impurity concentration in the third nitride semiconductor portion, the Al composition ratio of the second nitride semiconductor portion is greater than the Al composition ratio of the first nitride semiconductor portion, and the Al composition ratio of the third nitride semiconductor portion is greater than the Al composition ratio of the first nitride semiconductor portion.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor light-emitting device.

Background Art

[0002] Conventionally, as a blue semiconductor light-emitting device, a technique of growing an n-type semiconductor layer on a GaN substrate is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Some GaN substrates have poor flatness. When an n-type semiconductor layer is grown thereon, the poor flatness is inherited by the n-type semiconductor layer, and ripples may occur in the far-field pattern (hereinafter referred to as "FFP") of the obtained semiconductor light-emitting device. An object of the present disclosure is to provide a semiconductor light-emitting device with reduced FFP ripple.

Means for Solving the Problems

[0005] A semiconductor light-emitting element according to one embodiment of the present disclosure comprises a GaN substrate, a first nitride semiconductor portion provided on the substrate and containing n-type impurities, a second nitride semiconductor portion provided on the first nitride semiconductor portion and containing n-type impurities, and a third nitride semiconductor portion provided on the second nitride semiconductor portion and containing n-type impurities, wherein the n-type impurity concentration in the first nitride semiconductor portion is greater than the n-type impurity concentration in the third nitride semiconductor portion, the n-type impurity concentration in the second nitride semiconductor portion is greater than the n-type impurity concentration in the third nitride semiconductor portion, the Al composition ratio of the second nitride semiconductor portion is greater than the Al composition ratio of the first nitride semiconductor portion, and the Al composition ratio of the third nitride semiconductor portion is greater than the Al composition ratio of the first nitride semiconductor portion. [Effects of the Invention]

[0006] According to one embodiment of the present disclosure, it is possible to provide a semiconductor light-emitting element in which the ripple of the FFP is reduced. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic cross-sectional view showing a semiconductor light-emitting element of an embodiment. [Figure 2] This is a schematic cross-sectional view showing the n-side semiconductor layer 2 of the embodiment. [Figure 3] This graph shows the SIMS results in the depth direction from the n-side semiconductor layer to the substrate of the semiconductor light-emitting element in the example. [Figure 4] This graph shows the FFP characteristics of the examples and comparative examples. [Modes for carrying out the invention]

[0008] Hereinafter, a semiconductor light-emitting element according to an embodiment of the present invention will be described with reference to the drawings. In the following description, terms indicating specific directions or positions (e.g., "up," "down," and other terms including these terms) will be used as needed. However, the use of these terms is for the purpose of facilitating the understanding of the invention with reference to the drawings, and the meaning of these terms does not limit the technical scope of the present invention. Parts with the same reference numerals appearing in multiple drawings indicate the same or equivalent parts or components. The embodiments described below illustrate light-emitting devices and the like that embody the technical concept of the present invention, and do not limit the present invention to the following. Unless otherwise specified, the dimensions, materials, shapes, relative arrangements, etc., of the components described below are intended to be illustrative and not to limit the scope of the present invention to them alone. The contents described in one embodiment are applicable to other embodiments or modifications. The size and positional relationships of the members shown in the drawings may be exaggerated to clarify the explanation. To avoid the drawings becoming excessively complex, schematic diagrams that omit the illustration of some elements or end faces that show only the cross-section as cross-sectional views may be used. In this specification, the direction from the n-side semiconductor layer to the p-side semiconductor layer may be referred to as up or upward, and the opposite direction may be referred to as down or downward.

[0009] Embodiment 1 As shown in Figure 1, the semiconductor light-emitting device according to this embodiment has, in this order, a substrate 1, n-side semiconductor layers 2 provided on the substrate 1 and each made of nitride semiconductors, an active layer 3, and a p-side semiconductor layer 4. In particular, the n-side semiconductor layer 2 includes a first nitride semiconductor portion 2A provided on the substrate 1, a second nitride semiconductor portion 2B provided on the first nitride semiconductor portion 2A, and a third nitride semiconductor portion 2C provided on the second nitride semiconductor portion 2B, and further an n-type semiconductor layer 2D containing n-type impurities is disposed on the third nitride semiconductor portion 2C. Here, the semiconductor light-emitting device is, for example, a semiconductor laser element.

[0010] (Circuit board 1) The substrate 1 is a nitride semiconductor substrate made of, for example, GaN. The main surface of the substrate 1 is, for example, the +c plane ((0001) plane). The main surface of the substrate 1 may include having an off-angle of ±1 degree or less. Using a substrate with the +c plane as the main surface provides excellent mass productivity. The thickness of the substrate 1 is, for example, 400 μm or more and 500 μm or less. Substrate 1 contains, for example, Ge. In this case, the Ge concentration is 1 × 10⁻⁶. 18 cm -3 The above 5 x 10 18 cm -3 The following are listed:

[0011] (n-side semiconductor layer 2) The n-side semiconductor layer 2 includes, in part, a first nitride semiconductor portion 2A, a second nitride semiconductor portion 2B, and a third nitride semiconductor portion 2C provided on the substrate 1. Preferably, the substrate 1 is in contact with the first nitride semiconductor portion 2A, the first nitride semiconductor portion 2A is in contact with the second nitride semiconductor portion 2B, and the second nitride semiconductor portion 2B is in contact with the third nitride semiconductor portion 2C. This configuration allows for a reduction in the thickness of the n-side semiconductor layer 2. The first nitride semiconductor portion 2A, the second nitride semiconductor portion 2B, and the third nitride semiconductor portion 2C contain n-type impurities. Examples of n-type impurities include Si and Ge. The first nitride semiconductor portion 2A may or may not contain Al in its composition. The second nitride semiconductor portion 2B and the third nitride semiconductor portion 2C contain Al in their composition. The second nitride semiconductor portion 2B and the third nitride semiconductor portion 2C are, for example, AlGaN. The Al composition ratio of the second nitride semiconductor portion 2B is greater than that of the first nitride semiconductor portion 2A, and the Al composition ratio of the third nitride semiconductor portion 2C is greater than that of the first nitride semiconductor portion 2A. Preferably, the Al composition ratio in the second nitride semiconductor portion 2B is the same as that in the third nitride semiconductor portion 2C. This makes the lattice constants of the second nitride semiconductor portion 2B and the third nitride semiconductor portion 2C closer together. The third nitride semiconductor portion 2C is the base portion for the n-type semiconductor layer 2D, the active layer 3, and the p-side semiconductor layer 4, and therefore requires high crystallinity. For this reason, it is desirable to grow the third nitride semiconductor portion 2C while the substrate 1 is at a high temperature. However, when heating the substrate 1, the surface of the substrate may become rough due to thermal desorption. This surface roughness is not resolved as the material grows and is reflected even in the portion stacked above the substrate 1. As a result, the light confinement performance decreases, and light generated in the active layer 3 leaks into the substrate 1. Then, the leaked light reinforces at a distance, which can cause ripple in the FFP. Therefore, by providing a first nitride semiconductor portion 2A and a second nitride semiconductor portion 2B containing a high concentration of n-type impurities between the substrate 1 and the third nitride semiconductor portion 2C, the diffusion rate of atoms in the in-plane direction increases during the growth of the nitride semiconductor, and surface roughness can be reduced. Thus, with these configurations, ripple in the FFP of the semiconductor light-emitting element can be reduced. Furthermore, the n-type impurity concentration in the first nitride semiconductor portion 2A is greater than that in the third nitride semiconductor portion 2C. The n-type impurity concentration in the second nitride semiconductor portion 2B is also greater than that in the third nitride semiconductor portion 2C. The presence of n-type impurities increases the diffusion rate of atoms in the in-plane direction during the growth of the nitride semiconductor, thereby reducing surface roughness. Therefore, these configurations allow for flatter first nitride semiconductor portion 2A and second nitride semiconductor portion 2B. In addition, since the Al composition ratio differs between the first nitride semiconductor portion 2A and the second nitride semiconductor portion 2B, surface roughness is likely to occur at the boundary between these nitride semiconductors. Therefore, by adding n-type impurities to the first nitride semiconductor portion 2A and the second nitride semiconductor portion 2B, surface roughness at the boundary can be reduced. As a result, ripple in the FFP of the semiconductor light-emitting element can be reduced. The n-type impurity concentration contained in the first nitride semiconductor portion 2A is, for example, 10 times or more, and specifically 50 times or less, than the n-type impurity concentration contained in the third nitride semiconductor portion 2C. The n-type impurity concentration contained in the second nitride semiconductor portion 2B is 10 times or more than the n-type impurity concentration contained in the third nitride semiconductor portion 2C. Specifically, the n-type impurity concentration contained in the first nitride semiconductor portion 2A is 5×10 19 cm -3 or more, and specifically 5×10 20 cm -3 or less. The n-type impurity concentration contained in the second nitride semiconductor portion 2B is 5×10 19 cm -3 or more, and specifically 5×10 20 cm -3 or less. By setting these numerical ranges, the conductivity of the semiconductor light-emitting device can be made suitable. In the examples, the n-type impurity concentration contained in the second nitride semiconductor portion 2B is greater than the n-type impurity concentration contained in the first nitride semiconductor portion 2A. As a result, the resistance of the atoms in the in-plane direction during semiconductor growth due to Al contained in the second nitride semiconductor portion 2B can be canceled out by the n-type impurities, and surface roughness can be reduced. As a result, the ripple in the FFP of the semiconductor light-emitting device can be reduced. The thickness of the first nitride semiconductor portion 2A is 2 nm or more and 10 nm or less. The thickness of the second nitride semiconductor portion 2B is 2 nm or more and 10 nm or less. The thickness of the third nitride semiconductor portion 2C is 1000 nm or more and 1500 nm or less. In particular, the total thickness of the first nitride semiconductor portion 2A and the second nitride semiconductor portion 2B may be thicker, thinner, or equal to the thickness of either the GaN substrate 1 or the third nitride semiconductor portion 2C, but is preferably thinner. Among these, the total thickness of the first nitride semiconductor portion 2A and the second nitride semiconductor portion 2B is preferably 5 nm or more and 30 nm or less. By setting this value, it is possible to minimize the optical loss of the semiconductor light-emitting device due to impurities and obtain the effect of reducing ripple.

[0012] An n-type semiconductor layer 2D is provided on the third nitride semiconductor portion 2C, which constitutes the n-side semiconductor layer 2 other than the first nitride semiconductor portion 2A, the second nitride semiconductor portion 2B, and the third nitride semiconductor portion 2C. The n-type semiconductor layer 2D provided on the third nitride semiconductor portion 2C can be one or more layers made of a nitride semiconductor such as GaN, InGaN, or AlGaN.

[0013] The n-side semiconductor layer 2 has, for example, the stacked structure shown in Figure 2. That is, the n-side semiconductor layer 2 has, in order from the substrate 1 side, a first nitride semiconductor portion 2A and a second nitride semiconductor portion 2B, and a third nitride semiconductor portion 2C as an underlayment on the second nitride semiconductor portion 2B. An n-type semiconductor layer 2D is provided on the third nitride semiconductor portion 2C. The n-type semiconductor layer 2D has, for example, a first n-side cladding layer, a crack prevention layer, an intermediate layer, a second n-side cladding layer, a first n-side optical guide layer, a second n-side optical guide layer, and a hole block layer. The hole block layer has a first hole block layer and a second hole block layer. In other words, a crack prevention layer is included between the third nitride semiconductor portion 2C and any of the n-side semiconductor layers. The first n-side cladding layer has a larger bandgap energy than the n-side optical guide layer. Although not as significant as p-type impurities, n-type impurities also contribute to light absorption; therefore, it is preferable that the n-side optical guide layer is undoped or has a lower n-type impurity concentration than the first n-side cladding layer. Each of these nitride semiconductor n-type semiconductor layers 2D contains a semiconductor layer containing one or more n-type impurities. Examples of n-type impurities include Si and Ge. For example, n-type impurities are added from the first n-side cladding layer to the first n-side optical guide layer. The first n-side cladding layer has a larger bandgap energy than the third nitride semiconductor portion 2C and is a layer to which n-type impurities are added. The crack prevention layer is made of, for example, InGaN, and its bandgap energy is smaller than that of the well layer in the active layer 3. By providing a crack prevention layer, the probability of cracks occurring can be reduced. The intermediate layer has a lattice constant between the crack prevention layer and the second n-side cladding layer and is made of, for example, GaN. When the crack prevention layer is an InGaN layer, it is preferable to form an intermediate GaN layer before growing the second n-side cladding layer. If the second n-side cladding layer is grown in contact with the upper surface of the crack prevention layer, a part of the crack prevention layer may decompose, affecting the growth of the active layer 3, but by providing an intermediate layer, the probability of such decomposition occurring can be reduced. The intermediate layer is preferably formed with a thinner film thickness than, for example, the crack prevention layer. The second n-side cladding layer is, for example, a layer with a larger bandgap energy than the third nitride semiconductor portion 2C, and may be the same as the first n-side cladding layer. The first n-side cladding layer and the second n-side cladding layer are made of, for example, AlGaN. Either or both of the first n-side cladding layer and the second n-side cladding layer may have the largest bandgap energy in the n-side semiconductor layer 2. The composition and / or n-type impurity concentration of the first n-side cladding layer and the second n-side cladding layer may be the same. The n-side cladding layer may be a single layer, in which case the crack prevention layer may not be provided, or may be provided above or below the n-side cladding layer. The first n-side optical guide layer is a layer with a smaller bandgap energy and a smaller n-type impurity concentration than the first n-side cladding layer and the second n-side cladding layer. The first n-side optical guide layer is made of, for example, GaN. The bandgap energy of the second n-side optical guide layer is greater than that of the well layer in the active layer 3 and smaller than that of the first n-side optical guide layer. Since the second n-side optical guide layer is located closer to the active layer 3 than the first n-side optical guide layer, it is preferable for it to have a smaller n-type impurity concentration than the first n-side optical guide layer in order to reduce optical absorption loss. The second n-side optical guide layer is made of, for example, undoped InGaN. The second n-side optical guide layer may be a compositional gradient layer in which the bandgap energy decreases as it approaches the active layer 3. When a compositional gradient layer is provided as the n-side optical guide layer, the layer should have a gradually changing composition such that the refractive index increases as it approaches the active layer 3. This continuously forms an optical waveguide barrier in the n-side compositional gradient layer, thereby strengthening optical confinement to the active layer 3. The average value of the compositional gradient layer can be used as a criterion for determining the relative magnitudes of the bandgap energy and impurity concentration of the compositional gradient layer with those of other layers. The average value of the compositional gradient layer refers to the sum of the product values ​​of the bandgap energy, etc., of each sublayer constituting the compositional gradient layer and the film thickness, divided by the total film thickness. Preferably, the hole-blocking layer contains n-type impurities in at least a portion of it. This allows for more efficient hole blocking. For example, the first hole-blocking layer is made of GaN, and the second hole-blocking layer is made of InGaN.

[0014] (active layer 3) The active layer 3 can be a multilayer structure consisting of nitride semiconductor layers such as GaN and InGaN. The active layer 3 has a single quantum well structure or a multiple quantum well structure. The multiple quantum well structure is considered to be more likely to obtain sufficient gain than the single quantum well structure. When the active layer 3 has a multiple quantum well structure, it has multiple well layers and an intermediate barrier layer sandwiched between the well layers. For example, the active layer 3 includes a well layer, an intermediate barrier layer, and a well layer in order from the n-side semiconductor layer 2 side. An n-side barrier layer may be provided between the well layer closest to the n-side semiconductor layer 2 and the n-side semiconductor layer 2. The n-side barrier layer may function as part of the hole block layer. The n-side barrier layer may be omitted, and a hole block layer or an n-side optical guide layer (second n-side optical guide layer) may function as the n-side barrier layer. Similarly, a p-side barrier layer may be provided between the well layer closest to the p-side semiconductor layer 4 and the p-side semiconductor layer 4. If this p-side barrier layer is not provided or is thin, a part of the p-side semiconductor layer 4 may function as the p-side barrier layer. When a p-side barrier layer is provided in the active layer 3, the thickness of the p-side barrier layer can be, for example, 5 nm or less. In other words, the shortest distance between the p-side semiconductor layer 4 and the well layer in the active layer 3 is, for example, 5 nm or less. Also, as mentioned above, since the addition of p-type impurities increases the light absorption loss, it is preferable to form the active layer 3 without adding p-type impurities. Each layer of the active layer 3 is, for example, an undoped layer. In the case where the semiconductor light-emitting element is a semiconductor laser element with an oscillation wavelength of 530 nm or higher, x Ga 1-x The In composition ratio x of the N well layer varies slightly depending on the layer structure other than the active layer 3, but for example, it can be 0.25 or higher. An upper limit for the In composition ratio x of the well layer can be 0.50 or lower. In this case, the oscillation wavelength of the semiconductor laser element is considered to be around 600 nm or less.

[0015] (p-side semiconductor layer 4) The p-side semiconductor layer 4 can be a multilayer structure made of nitride semiconductors such as GaN, InGaN, or AlGaN. The p-side semiconductor layer 4 may have a p-side cladding layer and a p-side optical guide layer, and may also include other layers. If a translucent conductive film is provided as the p-electrode 6 on the p-side semiconductor layer 4, this can function as a cladding layer, so a cladding layer does not need to be provided in the p-side semiconductor layer 4. The p-side semiconductor layer 4 includes one or more p-type semiconductor layers. Examples of p-type semiconductor layers include layers made of nitride semiconductors containing p-type impurities such as Mg. The p-side semiconductor layer 4 includes, for example, an undoped or low-concentration doped layer 41, an electron barrier layer 42, and a doped layer 43.

[0016] The undoped or low-doped layer 41 is preferably a portion that does not contain a p-type semiconductor layer. The thickness of the undoped or low-doped layer 41 is preferably 400 nm or more. The upper limit of the thickness of the undoped or low-doped layer 41 can be 660 nm or less. Furthermore, the undoped or low-doped layer 41 can reduce the probability of electron overflow occurring due to the band gap difference between it and the electron barrier layer 42. For this reason, the undoped or low-doped layer 41 preferably has a band gap energy smaller than that of the electron barrier layer 42 as the layer in contact with the electron barrier layer 42. When the undoped or low-concentration doped layer 41 is a low-concentration doped layer, it is preferable that the p-type impurity concentration throughout the entire layer be lower than the p-type impurity concentration of the electron barrier layer 42. Furthermore, the n-type impurity concentration of the low-concentration doped layer is 2 × 10⁻⁶. 18 / cm 3 Examples include those less than or equal to n-type impurities, and preferably those that are substantially free of n-type impurities. When the undoped or low-concentration doped layer 41 is a low-concentration doped layer, the undoped or low-concentration doped layer 41 may include a p-side composition gradient layer and a p-side intermediate layer. When a p-side composition gradient layer is present, optical confinement to the active layer 3 can be enhanced. As a result, the threshold current density of laser oscillation can be reduced. The p-side composition gradient layer is a layer in which the band gap energy increases as it moves upward. The p-side intermediate layer may be a single layer of a single composition or a multilayer structure. The electron barrier layer 42 contains p-type impurities such as Mg. Preferably, the band gap energy of the electron barrier layer 42 is greater than the band gap energy of the undoped or low-concentration doped layer 41. By having a large band gap energy, the electron barrier layer 42 can function as a barrier against electrons overflowing from the active layer 3. The doped layer 43 has one or more p-type semiconductor layers containing p-type impurities. The concentration of p-type impurities in the p-type semiconductor layers of the doped layer 43 is, for example, 1 × 10⁻⁶ 18 / cm 3 The above points can be raised. The p-side semiconductor layer 4 is provided with an upwardly protruding ridge 4a. Preferably, the lower end of the ridge 4a is located in the undoped or low-concentration doped layer 41. In this manner, an n-type semiconductor layer 2D, an active layer 3, and a p-side semiconductor layer 4 are stacked on top of the third nitride semiconductor portion 2C. Because the third nitride semiconductor portion 2C is flat, the flatness of the n-type semiconductor layer 2D, active layer 3, and p-side semiconductor layer 4 stacked on top of it is also improved.

[0017] (Insulating film 5, n electrode 8, p electrode 6, p-side pad electrode 7) The insulating film 5 can be formed by a single-layer or multi-layer film of an oxide or nitride such as Si, Al, Zr, Ti, Nb, or Ta. The n-electrode 8 is provided, for example, over almost the entire lower surface of the n-type substrate 1. The p electrode 6 is provided on the upper surface of the ridge 4a. If the width of the p electrode 6 is narrow, a p-side pad electrode 7 wider than the p electrode 6 can be provided on top of the p electrode 6, and a wire or the like can be connected to the p-side pad electrode 7. The material of each electrode can be a single layer or multilayer film of a conductive oxide containing, for example, at least one selected from metals or alloys such as Ni, Rh, Cr, Au, W, Pt, Ti, Al, Zn, In, and Sn. Examples of conductive oxides include ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), and GZO (Gallium-doped Zinc Oxide). The thickness of the electrode can usually be any thickness that allows it to function as an electrode of a semiconductor light-emitting element. For example, it can be about 0.1 μm to 2 μm. The p electrode 6 is preferably a translucent conductive film having a refractive index smaller than that of the active layer 3. This allows it to function as a cladding layer. Furthermore, the p electrode 6 is preferably a translucent conductive film having a refractive index smaller than that of the doped layer 43. This allows for a greater light confinement effect.

[0018] (Examples) As an example, a semiconductor light-emitting element 10 shown in Figure 1 was fabricated by growing an n-side semiconductor layer 2, an active layer 3, and a p-side semiconductor layer 4 on an n-type GaN substrate 1 with a thickness of 400 μm and the +c plane facing upwards. MOCVD equipment was used to fabricate the epitaxial wafers that would become the semiconductor light-emitting elements 10. The raw materials used were trimethylgallium (TMG), triethylgallium (TEG), trimethylaluminum (TMA), trimethylindium (TMI), ammonia (NH3), silane gas, and bis(cyclopentadienyl)magnesium (Cp2Mg). First, on the GaN substrate 1, a GaN layer with a thickness of 30 nm and Si doped as part of the n-side semiconductor layer 2, and an Al layer with a thickness of 1.25 μm and Si doped. 0.018 Ga 0.982 A portion containing an N layer was formed. The first nitride semiconductor portion 2A, the second nitride semiconductor portion 2B, and the third nitride semiconductor portion 2C are included in this portion. Here, the GaN substrate 1 has a Ge concentration of 3 × 1018 cm -3 The Si concentration contained in the first nitride semiconductor portion 2A was set to 1 × 10⁻⁶. 20 cm -3 The Si concentration contained in the second nitride semiconductor portion 2B was set to 2.5 × 10⁻⁶. 20 cm -3 The Si concentration contained in the third nitride semiconductor portion 2C was set to 4 × 10⁻⁶. 18 cm -3 That's what I decided. Next, on the third nitride semiconductor portion 2C, an n-type semiconductor layer 2D with a film thickness of 250 nm, containing Si, is added. 0.08 Ga 0.92 N layer (first n-side cladding layer 22) and In layer with Si doped, 150 nm thick 0.04 Ga 0.96 The structure consists of an N layer (crack prevention layer 23), a GaN layer with a thickness of 10 nm and Si doped (intermediate layer 24), and an Al layer with a thickness of 650 nm and Si doped. 0.08 Ga 0.92 An N layer (second n-side cladding layer 25), a GaN layer with Si doping and a thickness of 200 nm (first n-side optical guide layer 26), a composition gradient layer with Si doping and a thickness of 230 nm (second n-side optical guide layer 27), a GaN layer with Si doping and a thickness of 1.2 nm (first hole block layer 281), and an In layer with Si doping and a thickness of 44 nm 0.045 Ga 0.955 The N-layer (second hole block layer 282) was grown in this order. The second n-side optical guide layer 27 started with GaN and ended with In 0.045 Ga 0.955 As N, the In composition ratio was increased substantially monotonically in 120 steps so that the composition gradient was almost linear. Next, a Si-doped GaN layer (n-side barrier layer), an undoped In0.25Ga0.75N layer (well layer), an undoped GaN layer (intermediate barrier layer), and an undoped In 0.25 Ga 0.75 An active layer 3 was grown containing an N layer (well layer) and an undoped GaN layer (p-side barrier layer) in that order. Next, as the p-side semiconductor layer 4, there is an undoped first composition gradient layer with a thickness of 180 nm, an undoped second composition gradient layer with a thickness of 150 nm, an undoped AlGaN layer with a thickness of 200 nm, and an Al GaN layer with a thickness of 3.9 nm with Mg added. 0.10 Ga 0.90 The structure consists of an N layer, a third composition gradient layer with a thickness of 7 nm and Mg doped, and an Al layer with a thickness of 100 nm and Mg doped. 0.04 Ga 0.96 An N layer and a 16 nm thick GaN layer with Mg doping were grown in this order. The first composition gradient layer was grown with the starting point in In 0.045 Ga 0.955 The first layer was grown with N at the beginning and GaN at the end of the growth cycle, and the In composition ratio was substantially monotonically decreased in 120 steps so that the composition gradient was almost linear. The second composition gradient layer was grown with GaN at the beginning and Al at the end of the growth cycle. 0.04 Ga 0.96 As the N layer, the Al composition ratio was substantially monotonically increased in 80 steps so that the composition gradient was almost linear. The third composition gradient layer was grown with Al at the beginning of its growth. 0.24 Ga 0.76 Let's make it an N-layer structure, and end the growth with Al 0.17 Ga 0.83 As the N layer, the Al composition ratio was substantially monotonically decreased in 10 steps so that the compositional gradient was almost linear. The epitaxial wafer, on which the above layers were formed, was removed from the MOCVD apparatus, and a ridge 4a, insulating film 5, p electrode 6, p-side pad electrode 7, and n electrode 8 were formed. The depth of the ridge 4a was approximately 270 nm. In addition, an ITO film with a thickness of 200 nm was formed as the p electrode 6. Next, the semiconductor light-emitting element 10 was formed into a bar, and then reflective films were formed on the light-emitting end face and the light-reflecting end face, respectively. After that, it was separated into individual pieces to obtain the semiconductor light-emitting element 10. For a sample in which a third nitride semiconductor portion 2C was grown on a substrate 1 in the same manner as for the semiconductor light-emitting element 10, the SIMS results in the depth direction from the outermost surface to the substrate 1 were measured by secondary ion mass spectrometry. As a result, the profile shown in Figure 3 was obtained. In Figure 3, the profiles of the third nitride semiconductor portion 2C, the second nitride semiconductor portion 2B, the first nitride semiconductor portion 2A, and the substrate 1 are shown in order from left to right. First, the leftmost region has a Si concentration of 4 × 10⁻⁶. 18 cm -3 degree of Al 0.018 Ga 0.982 This shows the N-3 nitride semiconductor portion 2C. Furthermore, the region to the right of the 3 nitride semiconductor portion 2C has a Si concentration of 2.5 × 10⁻⁶. 20 cm -3 It corresponds to the second nitride semiconductor portion 2B, which is of a certain degree and has an Al composition ratio of about 1.8%, and has a high Si concentration Al 0.018 Ga 0.982 This portion consists of N. The region to the right of the second nitride semiconductor portion 2B has a Si concentration of 1 × 10⁻⁶. 20 cm -3 This corresponds to the first nitride semiconductor portion 2A, where the Al composition ratio is lower than that of the second nitride semiconductor portion 2B, and is composed of GaN with a high Si concentration. Furthermore, the region where both the Al composition ratio and Si concentration are lower and constant than the first region indicates substrate 1. In the profile of Figure 3, the Si values ​​are measured values, while the Al and Ga intensities were detected and the relative Al composition ratios were compared. In addition, a maximum value appears in the Al intensity at a depth of 0.22 μm, but since the uneven distribution of Al could not be confirmed by analysis using STEM, this is considered to be due to error, etc.

[0019] (Comparative example) As a comparative example, a semiconductor light-emitting device was fabricated. The semiconductor light-emitting device in the comparative example had a GaN layer with a thickness of 3 nm and Si doped as part of the n-side semiconductor layer, and an Al layer with a thickness of 3 nm and Si doped. 0.018 Ga 0.982 Al with a thickness of 1.25 μm, without forming an N layer and with Si added. 0.018 Ga 0.982 The semiconductor light-emitting element 10 was fabricated in the same manner as the example, except that the N layer was formed directly on the GaN substrate.

[0020] The peak wavelength of the laser light emitted by the obtained semiconductor light-emitting element 10 was approximately 525 nm. Furthermore, when multiple semiconductor light-emitting elements were fabricated according to both the example and the comparative example, and the presence or absence of ripple was measured, the probability of ripple occurrence was lower in the example. As shown in Figure 4, ripple occurrence was infrequent in the example sample, while ripple occurred at a high rate in the comparative example sample. The reasons for this are as follows. In semiconductor light-emitting devices like the comparative example, the difference in in-plane lattice constants at the point where the Al composition ratio changes can easily destabilize the semiconductor layer growth mode, potentially inducing surface roughness. This can lead to ripple generation in some substrates, resulting in a lower yield of the resulting semiconductor light-emitting devices. On the other hand, in the semiconductor light-emitting element 10 as in the embodiment, portions containing high concentrations of n-type impurities, such as a first nitride semiconductor portion 2A and a second nitride semiconductor portion 2B, are arranged on the GaN substrate 1, and a third nitride semiconductor portion 2C is arranged on the second nitride semiconductor portion 2B. In other words, the second nitride semiconductor portion 2B containing a high concentration of n-type impurities is arranged between the first nitride semiconductor portion 2A (a portion containing a relatively high composition ratio of Al) containing a high concentration of n-type impurities and the third nitride semiconductor portion 2C (a portion containing a relatively low composition ratio of Al) containing a low concentration of n-type impurities. By arranging a semiconductor portion containing a high concentration of n-type impurities in the region where the Al composition ratio changes, the growth of the semiconductor layer in the region where the Al composition ratio changes becomes more two-dimensional, and surface roughness can be reduced. Therefore, a flat semiconductor stacked structure can be obtained, and a semiconductor light-emitting element with good flatness can be formed. As a result, ripple in the FFP of the semiconductor light-emitting element can be reduced.

[0021] This specification discloses the following technical details: (1) GaN substrate and A first nitride semiconductor portion containing n-type impurities is provided on the substrate, A second nitride semiconductor portion containing n-type impurities is provided on the first nitride semiconductor portion, The second nitride semiconductor portion is provided on the third nitride semiconductor portion, which contains n-type impurities, The n-type impurity concentration in the first nitride semiconductor portion is greater than the n-type impurity concentration in the third nitride semiconductor portion, and the n-type impurity concentration in the second nitride semiconductor portion is greater than the n-type impurity concentration in the third nitride semiconductor portion. A semiconductor light-emitting device in which the Al composition ratio of the second nitride semiconductor portion is greater than the Al composition ratio of the first nitride semiconductor portion, and the Al composition ratio of the third nitride semiconductor portion is greater than the Al composition ratio of the first nitride semiconductor portion. (2) The n-type impurity concentration contained in the first nitride semiconductor portion is 5 × 10 19 cm -3 The semiconductor light-emitting device described in (1) above. (3) The n-type impurity concentration contained in the second nitride semiconductor portion is 5 × 10 19 cm -3 The semiconductor light-emitting device described in (1) or (2) above. (4) The semiconductor light-emitting element according to any one of (1) to (3), wherein the n-type impurity concentration contained in the first nitride semiconductor portion is 10 times or more the n-type impurity concentration contained in the third nitride semiconductor portion. (5) The semiconductor light-emitting element according to any one of (1) to (4), wherein the n-type impurity concentration contained in the second nitride semiconductor portion is 10 times or more the n-type impurity concentration contained in the third nitride semiconductor portion. (6) The semiconductor light-emitting element according to any one of (1) to (5), wherein the total thickness of the first nitride semiconductor portion and the second nitride semiconductor portion is 5 nm or more and 30 nm or less. (7) The semiconductor light-emitting element according to any one of (1) to (6), wherein the total thickness of the first nitride semiconductor portion and the second nitride semiconductor portion is thinner than the thickness of either the GaN substrate or the third nitride semiconductor portion. (8) The semiconductor light-emitting element according to any one of (1) to (7), wherein the Al composition ratio y in the second nitride semiconductor portion is the same as the Al composition ratio z in the third nitride semiconductor portion. (9) The semiconductor light-emitting element according to any one of (1) to (8), further comprising an n-type semiconductor layer, an active layer, and a p-side semiconductor layer on the third nitride semiconductor portion in this order. (10) The semiconductor light-emitting element according to (9), further comprising a crack prevention layer between the third nitride semiconductor portion and the n-type semiconductor layer. (11) The semiconductor light-emitting element according to any one of (1) to (10), wherein the GaN substrate contains Ge. [Explanation of Symbols]

[0022] 1 circuit board 2 n-side semiconductor layer 2A First nitride semiconductor portion 2B Second nitride semiconductor portion 2C Third Nitride Semiconductor Portion 2D n-type semiconductor layer 3 Active layer 4 p-side semiconductor layer 4a Ridge 41 Low-concentration doped layer 42 Electron barrier layer 43 Dope Layer 5. Insulating film 6p electrode 7 p-side pad electrode 8n electrode 10 Semiconductor light-emitting element

Claims

1. GaN substrate and A first nitride semiconductor portion containing n-type impurities is provided on the substrate, A second nitride semiconductor portion containing n-type impurities is provided on the first nitride semiconductor portion, The second nitride semiconductor portion is provided on the third nitride semiconductor portion containing n-type impurities, The n-type impurity concentration in the first nitride semiconductor portion is greater than the n-type impurity concentration in the third nitride semiconductor portion, and the n-type impurity concentration in the second nitride semiconductor portion is greater than the n-type impurity concentration in the third nitride semiconductor portion. A semiconductor light-emitting element in which the Al composition ratio of the second nitride semiconductor portion is greater than the Al composition ratio of the first nitride semiconductor portion, and the Al composition ratio of the third nitride semiconductor portion is greater than the Al composition ratio of the first nitride semiconductor portion.

2. The n-type impurity concentration contained in the first nitride semiconductor portion is 5 × 10 １９ cm －３ The semiconductor light-emitting element according to claim 1, as described above.

3. The n-type impurity concentration contained in the second nitride semiconductor portion is 5 × 10 １９ cm －３ The semiconductor light-emitting element according to claim 1, as described above.

4. The semiconductor light-emitting element according to claim 1, wherein the n-type impurity concentration contained in the first nitride semiconductor portion is 10 times or more the n-type impurity concentration contained in the third nitride semiconductor portion.

5. The semiconductor light-emitting element according to claim 1, wherein the n-type impurity concentration contained in the second nitride semiconductor portion is 10 times or more the n-type impurity concentration contained in the third nitride semiconductor portion.

6. The semiconductor light-emitting element according to claim 1, wherein the total thickness of the first nitride semiconductor portion and the second nitride semiconductor portion is 5 nm or more and 30 nm or less.

7. The semiconductor light-emitting element according to claim 1, wherein the combined thickness of the first nitride semiconductor portion and the second nitride semiconductor portion is thinner than the thickness of either the GaN substrate or the third nitride semiconductor portion.

8. The semiconductor light-emitting element according to claim 1, wherein the Al composition ratio y in the second nitride semiconductor portion is the same as the Al composition ratio z in the third nitride semiconductor portion.

9. Furthermore, the semiconductor light-emitting element according to claim 1 further comprises an n-type semiconductor layer, an active layer, and a p-side semiconductor layer on the third nitride semiconductor portion in this order.

10. Furthermore, the semiconductor light-emitting element according to claim 9 further includes a crack-preventing layer between the third nitride semiconductor portion and the n-type semiconductor layer.

11. The semiconductor light-emitting element according to claim 1, wherein the GaN substrate contains Ge.

Images