Nitride semiconductor light-emitting element

Abstract

To provide a nitride semiconductor light-emitting element capable of improving optical output.SOLUTION: A nitride semiconductor light-emitting element 1 comprises a substrate 2 having a growth surface 21 as its c plane, a buffer layer 3 formed on the growth surface 21, an n type semiconductor layer 4 formed on the buffer layer 3, an active layer 6 formed on the n type semiconductor layer 4 and emitting ultraviolet light of 365 nm or less in center wavelength, and a p type semiconductor layer 8 formed on the active layer 6. The buffer layer 3 has a film thickness larger than 500 nm. The mean value of oxygen concentration of the buffer layer 3 is 4.5×1021 atoms / cm3.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 attempts to improve the crystallinity of each semiconductor layer formed on a buffer layer by devising the distribution of the oxygen concentration in the buffer layer in a semiconductor light-emitting device having an emission peak wavelength of 380 nm or more and 425 nm or less.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a nitride semiconductor light-emitting device that emits ultraviolet light having a center wavelength of 365 nm or less, a new problem has been found that the oxygen contained in the buffer layer can cause a decrease in light output due to absorption of ultraviolet light.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a nitride semiconductor light-emitting device capable of improving light output.

Means for Solving the Problems

[0006] To achieve the above object, the present invention includes a substrate having a c-plane as a growth surface, a buffer layer formed on the growth surface, an n-type semiconductor layer formed on the buffer layer, an active layer formed on the n-type semiconductor layer and emitting ultraviolet light having a center wavelength of 365 nm or less, and a p-type semiconductor layer formed on the active layer. The film thickness of the buffer layer is greater than 500 nm, and the average value of the oxygen concentration in the buffer layer is 4.5×10 21 atoms / cm3 Provided is a nitride semiconductor light-emitting device that satisfies the following.

Advantages of the Invention

[0007] According to the present invention, it becomes possible to provide a nitride semiconductor light-emitting device capable of improving light output.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0009] [Embodiment] An embodiment of the present invention will be described with reference to FIG. 1. Note that the embodiment described below is shown as a preferred specific example for carrying out the present invention, and although there are parts that specifically exemplify various technically preferable technical matters, the technical scope of the present invention is not limited to this specific aspect.

[0010] (Nitride Semiconductor Light-Emitting Device 1) FIG. 1 is a schematic diagram schematically showing the configuration of the nitride semiconductor light-emitting element 1. In FIG. 1, the dimensional ratio in the stacking direction of each semiconductor layer of the nitride semiconductor light-emitting element 1 (hereinafter, also simply referred to as "light-emitting element 1") does not necessarily match the actual one. Hereinafter, the stacking direction of each semiconductor layer of the light-emitting element 1 is referred to as the vertical direction. Also, on one side in the vertical direction, the side on the substrate 2 where each semiconductor layer is grown (for example, the upper side in FIG. 1) is defined as the upper side, and the opposite side (for example, the lower side in FIG. 1) is defined as the lower side. Note that the expressions of up and down are for convenience and do not limit the posture of the light-emitting element 1 with respect to the vertical direction when the light-emitting element 1 is in use, for example.

[0011] The light-emitting element 1 constitutes, for example, a light-emitting diode (LED: Light Emitting Diode) or a semiconductor laser (LD: Laser Diode). In this embodiment, the light-emitting element 1 constitutes a light-emitting diode that emits light having a wavelength in the ultraviolet region. In particular, the light-emitting element 1 of this embodiment emits ultraviolet light having a central wavelength of 240 nm or more and 365 nm or less. The light-emitting element 1 can be used, for example, in fields such as sterilization (for example, air purification, water purification, etc.), medical treatment (for example, phototherapy, measurement / analysis, etc.), and UV curing.

[0012] The light-emitting element 1 sequentially includes a buffer layer 3, an n-type semiconductor layer 4, a composition gradient layer 5, an active layer 6, an electron blocking layer 7, and a p-type semiconductor layer 8 on the substrate 2. The light-emitting element 1 also includes an n-side electrode 11 provided on the n-type semiconductor layer 4 and a p-side electrode 12 provided on the p-type semiconductor layer 8.

[0013] As the semiconductor constituting the light-emitting element 1, for example, Al a Ga b In 1-a-b N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), a ternary to quaternary group III nitride semiconductor can be used. In this embodiment, as the semiconductor constituting the light-emitting element 1, Al c Ga 1-cA binary or ternary group-III nitride semiconductor represented by N (0 ≦ c ≦ 1) is used. Some of these group-III elements may be replaced with boron (B), thallium (Tl), etc. Also, some of the nitrogen may be replaced with phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), etc.

[0014] The substrate 2 is made of a material that transmits the light emitted by the active layer 6. In this embodiment, the substrate 2 is a sapphire (Al2O3) substrate. The growth surface 21 formed on the upper surface of the substrate 2 is the c-plane. This c-plane may have an off-angle. The off-angle of the substrate 2 is preferably 0.6° or more. When the off-angle of the substrate 2 is less than 0.6°, the terrace width of the step-terrace structure formed on the upper surface of the substrate 2 becomes wider, and hillocks are likely to be formed on the upper surface of the buffer layer 3. As a result, oxygen is likely to be incorporated into the buffer layer 3. The off-angle of the substrate 2 is more preferably 0.9° or more and 1.1° or less. Also, as the substrate 2, for example, an aluminum nitride (AlN) substrate or an aluminum gallium nitride (AlGaN) substrate may be used.

[0015] The buffer layer 3 is formed on the substrate 2. In this embodiment, the buffer layer 3 includes, in order from the substrate 2 side, an AlN layer 31 formed of undoped aluminum nitride and an undoped Al p Ga 1-pIt is composed of two layers including an AlGaN layer 32 formed by N (0 ≦ p ≦ 1). An undoped semiconductor layer means a semiconductor layer in which impurities are not intentionally added during the formation of the semiconductor layer, and a semiconductor layer containing a trace amount of unavoidably contained impurities is also regarded as an undoped semiconductor layer. The total film thickness of the buffer layer 3 is greater than 500 nm. Thereby, it is easy to relax the lattice mismatch between the substrate 2 and the semiconductor layer formed on the buffer layer 3, and the crystallinity of the semiconductor layer formed on the buffer layer 3 can be improved. From the viewpoint of suppressing the occurrence of cracks in the buffer layer 3, the total film thickness of the buffer layer 3 is preferably 5 μm or less. The film thickness of the AlN layer 31 is greater than the film thickness of the AlGaN layer 32. For example, the film thickness of the AlN layer 31 is 380 nm or more and 2200 nm or less, and the film thickness of the AlGaN layer 32 is 80 nm or more and 120 nm or less. The Al composition ratio p of the AlGaN layer 32 is, for example, 45% or more and 65% or less. By interposing the AlGaN layer 32 between the AlN layer 31 and the n-type semiconductor layer 4, the difference in the Al composition ratio between the buffer layer 3 and the n-type semiconductor layer 4 is reduced, and as a result, the propagation of dislocations to the n-type semiconductor layer 4 is suppressed, and the conductivity of the n-type semiconductor layer 4 is improved.

[0016] In the light-emitting element 1 that emits ultraviolet light with a central wavelength of 365 nm or less, if the average value of the oxygen concentration unavoidably contained as an impurity in the buffer layer 3 is high, the ultraviolet light emitted from the active layer 6 is absorbed by the oxygen in the buffer layer 3, and the light output of the light-emitting element 1 decreases. Therefore, in the light-emitting element 1 of the present embodiment, the average value of the oxygen concentration of the buffer layer 3 is 4.5×10 21 atoms / cm 3 or less. Hereinafter, the average value of the oxygen concentration of the buffer layer 3 means a value obtained by averaging the oxygen concentrations at each position in the vertical direction of the buffer layer 3. The average value of the oxygen concentration of the buffer layer 3 is preferably 1.0×10 21 atoms / cm 3 or less, more preferably 3.5×10 20 atoms / cm 3 or less, and even more preferably 3.0×10 20 atoms / cm 3The following is even more preferable. The method for adjusting the oxygen concentration of the buffer layer 3 can be realized, for example, by devising manufacturing conditions as described later.

[0017] Here, the sapphire substrate as the substrate 2 contains oxygen as its constituent element. Preferably, the average value of the oxygen concentration of the buffer layer 3 is smaller than the average value of the oxygen concentration of the sapphire substrate. The ratio of the average value of the oxygen concentration of the buffer layer 3 to the average value of the oxygen concentration of the substrate 2 is preferably 3 / 20 or less, more preferably 13 / 100 or less, even more preferably 13 / 1000 or less, and still more preferably 1 / 100 or less.

[0018] Note that the buffer layer 3 may be a single layer or three or more layers. When the substrate 2 is an aluminum nitride substrate or an aluminum gallium nitride substrate, the buffer layer 3 may be composed of, for example, only the AlGaN layer 32.

[0019] The n-type semiconductor layer 4 is formed on the buffer layer 3. The n-type semiconductor layer 4 is, for example, an n-type cladding layer formed of Al q Ga 1-q N (0≦q≦1). In this embodiment, silicon (Si) is used as the n-type impurity. The same applies to semiconductor layers containing n-type impurities other than the n-type semiconductor layer 4. Note that germanium (Ge), selenium (Se), tellurium (Te), or the like may be used as the n-type impurity. The Al composition ratio q of the n-type semiconductor layer 4 is, for example, 45% or more and 65% or less. The n-type semiconductor layer 4 may have a single-layer structure or a multilayer structure.

[0020] The composition gradient layer 5 is formed on the n-type semiconductor layer 4. The composition gradient layer 5 is composed of Al r Ga 1-r N (0≦r≦1). The Al composition ratio at each position in the vertical direction of the composition gradient layer 5 increases as the position is higher. Note that the composition gradient layer 5 may include a region where the Al composition ratio does not increase as it goes upward in, for example, an extremely small part of the region in the vertical direction (for example, a region of 5% or less of the entire vertical direction of the composition gradient layer 5).

[0021] The compositional gradient layer 5 preferably has an Al composition ratio at its lower end that is substantially the same as (e.g., within a 5% difference) the Al composition ratio at the upper end of the n-type semiconductor layer 4 adjacent to the lower side of the compositional gradient layer 5. Also, the compositional gradient layer 5 preferably has an Al composition ratio at its upper end that is substantially the same as (e.g., within a 5% difference) the Al composition ratio at the lower end of the barrier layer 61 adjacent to the upper side of the compositional gradient layer 5.

[0022] The active layer 6 is formed on the compositional gradient layer 5. The active layer 6 in this embodiment has a multiple quantum well structure having a plurality of well layers 621, 622. The bandgap of the active layer 6 is adjusted so that it can emit ultraviolet light with a central wavelength of 240 nm or more and 365 nm or less. When the active layer 6 has a multiple quantum well structure as in this embodiment, from the viewpoint of improving the light output, the central wavelength of the ultraviolet light emitted by the active layer 6 is preferably 250 nm or more and 320 nm or less, and more preferably 260 nm or more and 290 nm or less. In this embodiment, the active layer 6 has three barrier layers 61 and three well layers 621, 622, and the barrier layers 61 and the well layers 621, 622 are alternately laminated. In the active layer 6, a barrier layer 61 is located at the lower end, and a well layer 622 is located at the upper end.

[0023] Each barrier layer 61 is formed of Al s Ga 1-s N (0 < s ≤ 1). The Al composition ratio s of each barrier layer 61 is, for example, 75% or more and 95% or less. Also, the film thickness of each barrier layer 61 is, for example, 2 nm or more and 50 nm or less.

[0024] The well layers 621, 622 are formed of Al t Ga 1-t N (0 < t < 1). The Al composition ratio t of each well layer 621, 622 is smaller than the Al composition ratio s of the barrier layer 61 (i.e., t < s).

[0025] The three well layers 621 and 622 are composed of the bottom well layer 621, which is the bottommost well layer arranged at the lowermost side, and the upper well layers 622, which are the other two well layers than the bottom well layer 621, and have different configurations. For example, the film thickness of the bottom well layer 621 is 1 nm or more greater than the respective film thicknesses of the two upper well layers 622, and the Al composition ratio of the bottom well layer 621 is 2% or more greater than the respective Al composition ratios of the two upper well layers 622. In this embodiment, the upper well layer 622 has a film thickness of 2 nm or more and 4 nm or less and an Al composition ratio of 25% or more and 45% or less, and the bottom well layer 621 has a film thickness of 4 nm or more and 6 nm or less and an Al composition ratio of 35% or more and 55% or less. The difference in the film thickness between the bottom well layer 621 and each upper well layer 622 can be 2 nm or more and 4 nm or less.

[0026] By making the Al composition ratio of the bottom well layer 621 larger than the Al composition ratio of the upper well layer 622, the crystallinity of the bottom well layer 621 is improved. This is because the difference in the Al composition ratio between the bottom well layer 621 and the n-type semiconductor layer 4 becomes smaller. By improving the crystallinity of the bottom well layer 621, the crystallinity of each semiconductor layer of the active layer 6 formed upward from the bottom well layer 621 is also improved. As a result, the mobility of carriers in the active layer 6 is improved and the light output is improved. Such an effect is more remarkable as the film thickness of the bottom well layer 621 increases, but the film thickness of the bottom well layer 621 is designed to be equal to or less than a predetermined value from the viewpoint of suppressing an increase in the electrical resistance value of the entire light-emitting element 1.

[0027] In this embodiment, an example in which the active layer 6 has a multiple quantum well structure with three well layers 621 and 622 has been shown, but the present invention is not limited thereto, and a multiple quantum well structure with two or four or more well layers 621 and 622 may be used. Further, the active layer 6 may have a single quantum well structure having only one well layer 621 and 622.

[0028] The electron blocking layer 7 is formed on the active layer 6. The electron blocking layer 7 has a role of improving the electron injection efficiency into the active layer 6 by suppressing the occurrence of an overflow phenomenon in which electrons leak from the active layer 6 to the p-type semiconductor layer 8 side (hereinafter also referred to as the electron blocking effect). The electron blocking layer 7 has a stacked structure in which a first layer 71 and a second layer 72 are stacked in order from the bottom side.

[0029] The first layer 71 is provided on the active layer 6. The first layer 71 is made of, for example, Al u Ga 1-u N (0 ≤ u ≤ 1). The Al composition ratio u of the first layer 71 is, for example, 90% or more, and in this embodiment, it is made of aluminum nitride. The film thickness of the first layer 71 is, for example, 0.5 nm or more and 5.0 nm or less.

[0030] The second layer 72 is made of, for example, Al v Ga 1-v N (0 < v < 1). The Al composition ratio v of the second layer 72 is smaller than the Al composition ratio u of the first layer 71 (that is, u > v), and is, for example, 70% or more and 90% or less. The film thickness of the second layer 72 is larger than the film thickness of the first layer 71, and is, for example, 15 nm or more and 100 nm or less.

[0031] Since a semiconductor layer with a larger Al composition ratio has a larger electrical resistance value, if the film thickness of the first layer 71 with a relatively high Al composition ratio is made too large, it will cause an excessive increase in the overall electrical resistance value of the light-emitting element 1. Therefore, it is preferable to make the film thickness of the first layer 71 somewhat smaller. On the other hand, if the film thickness of the first layer 71 is made smaller, the probability that electrons tunnel through the first layer 71 from the bottom side to the top side can increase. Therefore, in the light-emitting element 1 of this embodiment, by forming the second layer 72 on the first layer 71, the electrons from passing through the entire electron blocking layer 7 are suppressed.

[0032] Each of the first layer 71 and the second layer 72 can be an undoped layer, a layer containing n-type impurities, a layer containing p-type impurities, or a layer containing both n-type and p-type impurities. As the p-type impurity, magnesium (Mg) can be used, but in addition to magnesium, zinc (Zn), beryllium (Be), calcium (Ca), strontium (Sr), barium (Ba), carbon (C), etc. may also be used. The same applies to semiconductor layers containing other p-type impurities. When each electron blocking layer 7 contains impurities, the impurities contained in each electron blocking layer 7 may be contained in the whole of each electron blocking layer 7 or may be contained in a part of each electron blocking layer 7.

[0033] The p-type semiconductor layer 8 is formed on the electron blocking layer 7. The p-type semiconductor layer 8 has a smaller Al composition ratio than the electron blocking layer 7 and is Al doped with p-type impurities w Ga 1-w formed by N (0 ≦ w ≦ 1). In this embodiment, the p-type semiconductor layer 8 has a laminated structure in which a first p-type clad layer 81, a second p-type clad layer 82, and a p-type contact layer 83 are laminated in order from the bottom.

[0034] The first p-type clad layer 81 is provided so as to be in contact with the second layer 72. The first p-type clad layer 81 is composed of Al x Ga 1-x formed by N (0 < x ≦ 1). The Al composition ratio x of the first p-type clad layer 81 is, for example, 45% or more and 65% or less. The film thickness of the first p-type clad layer 81 is, for example, 15 nm or more and 35 nm or less.

[0035] The second p-type clad layer 82 is composed of Al containing p-type impurities y Ga 1-y formed by N (0 < y ≦ 1). The Al composition ratio at each position in the vertical direction of the second p-type clad layer 82 becomes smaller as the position is higher. Note that the second p-type clad layer 82 may include a region where the Al composition ratio does not become smaller as it goes upward in a very small region in the stacking direction (for example, a region of 5% or less of the whole stacking direction of the second p-type clad layer 82).

[0036] The second p-type clad layer 82 preferably has an Al composition ratio at its lower end that is substantially the same as that of the first p-type clad layer 81 (for example, the difference is within 5%), and an Al composition ratio at its upper end that is substantially the same as that of the p-type contact layer 83 (for example, the difference is within 5%). The film thickness of the second p-type clad layer 82 can be, for example, 2 nm or more and 4 nm or less.

[0037] The p-type contact layer 83 is a layer to which the p-side electrode 12 described later is connected and is doped with a high concentration of p-type impurities. The p-type contact layer 83 is configured such that the Al composition ratio is low (for example, 10% or less) in order to achieve an ohmic contact with the p-side electrode 12, and from this perspective, it is preferably formed of p-type gallium nitride (GaN). The film thickness of the p-type contact layer 83 is, for example, 10 nm or more and 25 nm or less. Note that the p-type semiconductor layer 8 may be a single layer or a plurality of layers.

[0038] The n-side electrode 11 is formed on the exposed surface 41 of the n-type semiconductor layer 4 that is exposed upward from the active layer 6. The n-side electrode 11 can be, for example, a multilayer film in which titanium (Ti), aluminum, titanium, and titanium nitride (TiN) are sequentially laminated on the n-type semiconductor layer 4. Further, when the light-emitting element 1 is flip-chip mounted as described later, the n-side electrode 11 may be formed of a material capable of reflecting the ultraviolet light emitted by the active layer 6.

[0039] The p-side electrode 12 is formed on the upper surface of the p-type semiconductor layer 8. The p-side electrode 12 can be composed of, for example, rhodium (Rh). In this embodiment, the p-side electrode 12 is a reflective electrode having a reflectivity of 50% or more, preferably 60% or more, at the central wavelength of the light emitted by the active layer 6, but is not limited thereto.

[0040] The light-emitting element 1 is used by being flip-chip mounted on a package substrate (not shown). That is, the light-emitting element 1 has the side on which the n-side electrode 11 and the p-side electrode 12 are provided in the vertical direction facing the package substrate side, and each of the n-side electrode 11 and the p-side electrode 12 is mounted on the package substrate via a connection member such as a gold bump. Light is extracted from the light-emitting element 1 flip-chip mounted from the substrate 2 side (i.e., the lower side).

[0041] (Method for manufacturing nitride semiconductor light-emitting element 1) Next, an example of the method for manufacturing the light-emitting element 1 of the present embodiment will be described. In the present embodiment, a buffer layer 3, an n-type semiconductor layer 4, a composition gradient layer 5, an active layer 6, an electron blocking layer 7, and a p-type semiconductor layer 8 are sequentially epitaxially grown on a disk-shaped substrate 2 by metalorganic chemical vapor deposition (MOCVD). That is, in the present embodiment, a disk-shaped substrate 2 is installed in the chamber, and each semiconductor layer is formed on the substrate 2 by introducing the source gas of each semiconductor layer formed on the substrate 2 into the chamber. As the source gas for epitaxially growing each semiconductor layer, trimethylaluminum (TMA) can be used as the aluminum source, trimethylgallium (TMG) as the gallium source, ammonia (NH3) as the nitrogen source, tetramethylsilane (TMSi) as the silicon source, and biscyclopentadienylmagnesium (Cp2Mg) as the magnesium source.

[0042] Note that the MOCVD method is sometimes referred to as the Metal Organic Vapor Phase Epitaxy (MOVPE) method. From the perspective of forming the buffer layer 3 with a film thickness greater than 500 nm on the substrate 2, it is preferable to use an epitaxial growth method such as the MOCVD method, the Hydride Vapor Phase Epitaxy (HVPE) method, or the Physical Vapor Transport (PVT) method. In this embodiment, the buffer layer 3 grown by the sputtering method is excluded. It is difficult to form a buffer layer 3 with a film thickness greater than 500 nm using the sputtering method. However, if it is possible to form a buffer layer 3 with a film thickness greater than 500 nm by the sputtering method, the sputtering method may be used.

[0043] In the manufacturing method of the light-emitting element 1 of this embodiment, the manufacturing conditions are designed so that the oxygen concentration of the buffer layer 3 becomes low as described above. For example, before forming each semiconductor layer on the substrate 2, evacuation of the chamber is performed so that the degree of vacuum in the chamber becomes relatively high, making it difficult for oxygen to be contained in the formed buffer layer 3. Also, depending on the material of the wall surface of the chamber facing the space inside the chamber, oxygen may be generated from the wall surface in the high-temperature environment of the film formation temperature of the buffer layer. Therefore, the material of the wall surface of the chamber can also affect the oxygen concentration of the buffer layer 3. As exemplified above, by appropriately designing the manufacturing conditions that can affect the oxygen concentration of the buffer layer 3, the oxygen concentration of the buffer layer 3 can be adjusted.

[0044] After forming each semiconductor layer on the disk-shaped substrate 2, a mask is formed on a part of the p-type semiconductor layer 8, that is, on a part other than the exposed surface 41 of the n-type semiconductor layer 4. Then, the region where the mask is not formed is removed by etching from the upper surface of the p-type semiconductor layer 8 to the middle of the n-type semiconductor layer 4 in the vertical direction. As a result, an exposed surface 41 that is exposed upward is formed in the n-type semiconductor layer 4. After the formation of the exposed surface 41, the mask is removed.

[0045] Next, an n-side electrode 11 is formed on the exposed surface 41 of the n-type semiconductor layer 4, and a p-side electrode 12 is formed on the p-type semiconductor layer 8. The n-side electrode 11 and the p-side electrode 12 may be formed by a well-known method such as an electron beam evaporation method or a sputtering method. By cutting the thus completed one into desired dimensions, a plurality of light-emitting elements 1 as shown in FIG. 1 are manufactured from one wafer.

[0046] (Operation and Effect of Embodiment) In the light-emitting element 1 of this embodiment, the active layer 6 emits ultraviolet light having a central wavelength of 365 nm or less, and the film thickness of the buffer layer 3 is greater than 500 nm. In such a premise configuration, although the relatively large film thickness of the buffer layer 3 easily relaxes the lattice mismatch between the substrate 2 and the n-type semiconductor layer 4, the problem that the light output of the light-emitting element 1 is significantly reduced due to oxygen contained in the buffer layer 3 absorbing ultraviolet light becomes prominent. Therefore, in this embodiment, the average value of the oxygen concentration in the buffer layer 3 is set to 4.5×10 21 atoms / cm 3 or less. Thereby, the light output of the light-emitting element 1 can be improved. This numerical value is supported by the experimental examples described later. Further, since the growth surface 21 of the substrate 2 is the c-plane, the oxygen concentration in the buffer layer 3 formed on the substrate 2 is reduced as compared with the r-plane or the like.

[0047] Further, the average value of the oxygen concentration in the buffer layer 3 further satisfies 1.0×10 21 atoms / cm 3 or less. Thereby, the light output of the light-emitting element 1 can be further improved.

[0048] Further, the substrate 2 is a sapphire substrate, and the average value of the oxygen concentration in the buffer layer 3 is smaller than the average value of the oxygen concentration in the substrate 2. In this way, by making the average value of the oxygen concentration in the buffer layer 3 smaller than the average value of the oxygen concentration in the sapphire substrate containing oxygen as a constituent element, the light output of the light-emitting element 1 can be further improved.

[0049] In addition, the ratio of the average value of the oxygen concentration in the buffer layer 3 to the average value of the oxygen concentration in the substrate 2 satisfies 3 / 20 or less. Thereby, further improvement of the light output of the light-emitting element 1 can be achieved.

[0050] The ratio of the average value of the oxygen concentration in the buffer layer 3 to the average value of the oxygen concentration in the substrate 2 further satisfies 13 / 100 or less. Thereby, further improvement of the light output of the light-emitting element 1 can be achieved.

[0051] As described above, according to this embodiment, a nitride semiconductor light-emitting element capable of improving the light output can be provided.

[0052] [Experimental Example] This experimental example is an example in which the relationship between the average value of the oxygen concentration in the buffer layer and the light output of the wafer was evaluated. Among the names of the components used in this experimental example, those that are the same as the names used in the previous embodiments represent the same components as those in the previous embodiments unless otherwise specified.

[0053] First, the wafers according to Samples 1 to 4 will be described using Table 1. Samples 1 to 4 are wafers having the same basic configuration as the light-emitting element in the embodiment unless otherwise specified.

[0054]

Table 1

[0055] As shown in Table 1, Samples 1 to 4 are those in which the average value of the oxygen concentration in the buffer layer and the film thickness of the AlN layer in the buffer layer are changed from each other. Note that the average values of the oxygen concentrations in the substrates of Samples 1 to 4 are slightly different from each other, but this is not intentionally changed and is within the range of individual differences.

[0056] In Table 1, for the configurations common to Samples 1 to 4, they are shown without distinguishing Samples 1 to 4. For each of the film thickness of the AlN layer, the average value of the oxygen concentration of the substrate, and the average value of the oxygen concentration of the AlN layer, they are shown for each of Samples 1 to 4. The Al composition ratio of each layer described in Table 1 is a value estimated from the secondary ion intensity of Al measured by secondary ion mass spectrometry (SIMS). Also, in the column of the composition gradient layer in Table 1, it shows that the Al composition ratio at each position in the vertical direction of the composition gradient layer gradually increases from 55% to 85% from the lower end to the upper end of the composition gradient layer. Also, in the column of the second p-type cladding layer in Table 1, it shows that the Al composition ratio at each position in the vertical direction of the second p-type cladding layer gradually decreases from 55% to 0% from the lower end to the upper end of the second p-type cladding layer.

[0057] The average value of the oxygen concentration of each layer described in Table 1 is calculated from the measurement values of SIMS. The oxygen concentrations of the substrate and the AlN layer in each sample were measured using wafers grown up to the AlN layer under manufacturing conditions equivalent to those during the manufacturing of each sample. Also, the measurement values of the oxygen concentrations of each layer of the wafers by SIMS are the results when the wafers were measured from the upper side. Note that for the AlGaN layer constituting the buffer layer, its film thickness is small and it is difficult to obtain an accurate oxygen concentration, but it is expected to be equivalent to the oxygen concentration of the AlN layer. As described above, the oxygen concentration of the buffer layer can vary depending on its manufacturing environment (i.e., the temperature inside the chamber, the material of the chamber wall, etc.). In this experimental example, the AlN layer and the AlGaN layer of each sample were manufactured in the same manufacturing environment, and it was considered that the oxygen concentration of the AlN layer and the oxygen concentration of the AlGaN layer are the same. That is, in this experimental example, the oxygen concentration of the AlN layer described in Table 1 was regarded as the oxygen concentration of the entire buffer layer.

[0058] Then, in each of Samples 1 to 4, a current of 20 mA was passed in the on-wafer state, and the optical output was measured. The optical output of each sample was measured by a photodetector installed on the lower side (i.e., the substrate side) of each sample. The results are shown in Fig. 2. Fig. 2 is a graph showing the relationship between the average value of the oxygen concentration in the buffer layer and the optical output.

[0059] As can be seen from Fig. 2, when the average value of the oxygen concentration in the buffer layer increases, the optical output gradually decreases until the average value of the oxygen concentration in the buffer layer reaches 4.5×10 21 atoms / cm 3 However, when the average value of the oxygen concentration exceeds 4.5×10 21 atoms / cm 3 it can be seen that the optical output decreases rapidly. Therefore, the average value of the oxygen concentration in the buffer layer is preferably 4.5×10 21 atoms / cm 3 or less. Also, as can be seen from Fig. 2, from the viewpoint of improving the optical output, the average value of the oxygen concentration in the buffer layer is preferably 1.0×10 21 atoms / cm 3 or less, more preferably 3.5×10 20 atoms / cm 3 or less, and even more preferably 3.0×10 20 atoms / cm 3 or less.

[0060] Also, using Table 2 and Fig. 3, the results of Fig. 2 are examined from another perspective. Table 2 shows the average value of the oxygen concentration in the substrate, the average value of the oxygen concentration in the buffer layer, the ratio of the average value of the oxygen concentration in the buffer layer to the average value of the oxygen concentration in the substrate (hereinafter referred to as the "oxygen concentration ratio"), and the optical output results for each sample. Fig. 3 is a diagram showing the relationship between the oxygen concentration ratio and the optical output.

[0061]

Table 2

[0062] As can be seen from Table 2 and FIG. 3, the oxygen concentration ratio is preferably 0.150 or less (i.e., 3 / 20 or less), more preferably 0.130 or less (i.e., 13 / 100 or less), still more preferably 0.013 or less (i.e., 13 / 1000 or less), and even more preferably 0.010 or less (i.e., 1 / 100 or less).

[0063] (Summary of Embodiments) Next, the technical idea grasped from the embodiments described above will be described by referring to the reference numerals and the like in the embodiments. However, each reference numeral and the like in the following description are not limited to the members and the like that specifically show the components in the claims in the embodiments.

[0064] [1] The first embodiment of the present invention includes a substrate 2 whose c-plane is a growth surface 21, a buffer layer 3 formed on the growth surface 21, an n-type semiconductor layer 4 formed on the buffer layer 3, an active layer 6 that is formed on the n-type semiconductor layer 4 and emits ultraviolet light having a central wavelength of 365 nm or less, and a p-type semiconductor layer 8 formed on the active layer 6. The film thickness of the buffer layer 3 is greater than 500 nm, and the average value of the oxygen concentration of the buffer layer 3 is 4.5×10 21 atoms / cm 3 The nitride semiconductor light-emitting device 1 satisfies the following conditions. Thereby, the light output of the nitride semiconductor light-emitting device 1 can be improved.

[0065] [2] The second embodiment of the present invention is that, in the first embodiment, the average value of the oxygen concentration of the buffer layer 3 further satisfies the following condition: 1.0×10 21 atoms / cm 3 or less. Thereby, the light output of the nitride semiconductor light-emitting device 1 can be further improved.

[0066] [3] The third embodiment of the present invention is that, in the first or second embodiment, the substrate 2 is a sapphire substrate, and the average value of the oxygen concentration of the buffer layer 3 is smaller than the average value of the oxygen concentration of the substrate 2. Thereby, further improvement in the light output of the nitride semiconductor light-emitting device 1 can be achieved.

[0067] [4] A fourth embodiment of the present invention is that, in the third embodiment, the ratio of the average value of the oxygen concentration of the buffer layer 3 to the average value of the oxygen concentration of the substrate 2 satisfies 3 / 20 or less. Thereby, further improvement in the light output of the nitride semiconductor light-emitting device 1 can be achieved.

[0068] [5] A fifth embodiment of the present invention is that, in the fourth embodiment, the ratio of the average value of the oxygen concentration of the buffer layer 3 to the average value of the oxygen concentration of the substrate 2 further satisfies 13 / 100 or less. Thereby, further improvement in the light output of the nitride semiconductor light-emitting device 1 can be achieved.

[0069] (Supplementary Note) Although the embodiments of the present invention have been described above, the above-described embodiments do not limit the invention according to the claims. Also, it should be noted that not all combinations of the features described in the embodiments are essential means for solving the problems of the invention. Further, the present invention can be appropriately modified and implemented without departing from its gist.

Explanation of Reference Numerals

[0070] 1... Nitride semiconductor light-emitting device 2... Substrate 21... Growth surface 3... Buffer layer 4... n-type semiconductor layer 6... Active layer 8... p-type semiconductor layer

Claims

1. A substrate with a c-plane as the growth plane, A buffer layer formed on the growth plane, An n-type semiconductor layer formed on the buffer layer, An active layer that is formed on the n-type semiconductor layer and emits ultraviolet light with a central wavelength of 365 nm or less, A p-type semiconductor layer formed on the active layer, comprising: The film thickness of the buffer layer is greater than 500 nm, The average value of the oxygen concentration of the buffer layer is 4.5×10 ２１ atoms / cm ３ satisfying the following, A nitride semiconductor light-emitting device.

2. The average value of the oxygen concentration of the buffer layer further satisfies ２１ 1.0×10 ３ atoms / cm or less, The nitride semiconductor light-emitting device according to Claim 1.

3. The substrate is a sapphire substrate, The average value of the oxygen concentration of the buffer layer is smaller than the average value of the oxygen concentration of the substrate, The nitride semiconductor light-emitting device according to Claim 1 or 2.

4. The ratio of the average value of the oxygen concentration of the buffer layer to the average value of the oxygen concentration of the substrate satisfies 3 / 20 or less, The nitride semiconductor light-emitting device according to Claim 3.

5. The ratio of the average value of the oxygen concentration of the buffer layer to the average value of the oxygen concentration of the substrate further satisfies 13 / 100 or less, The nitride semiconductor light-emitting device according to Claim 4.

Images