Nitride semiconductor light-emitting element

Abstract

Provided is a nitride semiconductor light-emitting element capable of improving light emission output. The nitride semiconductor light-emitting element includes: an active layer including at least one well layer; a p-type semiconductor layer on one side of the active layer; and an electron blocking layer stack between the active layer and the p-type semiconductor layer. The electron blocking layer stack includes: a first electron blocking layer; and a second electron blocking layer located on the p-type semiconductor layer side of the first electron blocking layer and having an Al composition ratio smaller than that of the first electron blocking layer. When the total number of well layers in the active layer is N, the film thickness of the first electron blocking layer is d [nm], and the Al composition ratio of the second electron blocking layer is x [%], the film thickness d of the first electron blocking layer satisfies the relationship 0.1N+0.9 ≤ d ≤ 0.2N+2.0, and the Al composition ratio x of the second electron blocking layer satisfies the relationship 10N+40 ≤ x ≤ 10N+60.

Description

TECHNICAL FIELD

[0001] The present application relates to a nitride semiconductor light-emitting element. BACKGROUND

[0002] Patent Document 1 discloses a nitride semiconductor light-emitting element including a first electron blocking layer disposed on an active layer, and a second electron blocking layer disposed on the first electron blocking layer. The second electron blocking layer is configured so as to have an Al composition ratio smaller than an Al composition ratio of the first electron blocking layer.

[0003] Prior art documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-027194 SUMMARY

[0006] Problems to be solved by the invention

[0007] In the nitride semiconductor light-emitting element described in Patent Document 1, there is room for improvement in terms of improving light-emitting output.

[0008] The present application has been achieved in view of the foregoing, and aims to provide a nitride semiconductor light-emitting element capable of improving light-emitting output.

[0009] Solution to the problem

[0010] To achieve the above object, the present application provides a nitride semiconductor light-emitting element including an active layer including at least one well layer, a p-type semiconductor layer on one side of the active layer, and an electron blocking layer stack between the active layer and the p-type semiconductor layer, the electron blocking layer stack having a first electron blocking layer, and a second electron blocking layer disposed on a position closer to the p-type semiconductor layer than the first electron blocking layer, and having an Al composition ratio smaller than an Al composition ratio of the first electron blocking layer, wherein, when the total number of the well layers in the active layer is denoted as N, the film thickness of the first electron blocking layer is denoted as film thickness d [nm], and the Al composition ratio of the second electron blocking layer is denoted as Al composition ratio x [%], the film thickness d of the first electron blocking layer satisfies the relationship of 0.1N + 0.9 ≤ d ≤ 0.2N + 2.0, and the Al composition ratio x of the second electron blocking layer satisfies the relationship of 10N + 40 ≤ x ≤ 10N + 60.

[0011] Effects of the invention

[0012] According to the present invention, a nitride semiconductor light-emitting element capable of improving light output can be provided. Attached Figure Description

[0013] Figure 1 This is a schematic diagram that schematically illustrates the configuration of the nitride semiconductor light-emitting element in the first embodiment.

[0014] Figure 2 This is a schematic diagram that schematically illustrates the configuration of the nitride semiconductor light-emitting element in the second embodiment.

[0015] Figure 3 This is a coordinate graph showing the relationship between the thickness d of the first electron blocking layer and the light output of each sample in Experimental Example 1.

[0016] Explanation of reference numerals

[0017] 1…nitride semiconductor light-emitting element

[0018] 6…Active layer

[0019] 62… well layer

[0020] 621…Lowermost well layer (farthest well layer)

[0021] 7… Electron blocking stack

[0022] 71…First Electron Blocking Layer

[0023] 72…Second Electron Blocking Layer

[0024] 8…p-type semiconductor layer. Detailed Implementation

[0025] [First Implementation]

[0026] Reference Figure 1 The first embodiment of the present invention will be described below. Furthermore, the embodiments described below are shown as preferred specific examples for carrying out the present invention. Although various technically preferred aspects are also specifically illustrated, the scope of the present invention is not limited to these specific solutions.

[0027] (Nitride semiconductor light-emitting element 1)

[0028] Figure 1 This is a schematic diagram that schematically illustrates the configuration of the nitride semiconductor light-emitting element 1 in this embodiment. Furthermore, in Figure 1 In the process, the aspect ratio of each layer of the nitride semiconductor light-emitting element 1 (hereinafter also referred to as "light-emitting element 1") in the stacking direction is not necessarily consistent with the actual aspect ratio.

[0029] The light-emitting element 1 of this embodiment is a light-emitting element 1 having a well layer 62 with a single quantum well structure. The light-emitting element 1 is, for example, a light-emitting diode (LED) or a semiconductor laser (LD). In this embodiment, the light-emitting element 1 is a light-emitting diode (LED) that emits light in the ultraviolet region. Specifically, the light-emitting element 1 of this embodiment is a deep ultraviolet LED that emits deep ultraviolet light with a center wavelength of 200 nm or more and 365 nm or less. The light-emitting element 1 of this embodiment can be used, for example, in fields such as sterilization (e.g., air purification, water purification), medical applications (e.g., phototherapy, measurement / analysis), and UV curing.

[0030] The light-emitting element 1 comprises, sequentially on a substrate 2, a buffer layer 3, an n-type cladding layer 4, a tilting layer 5, an active layer 6, an electron blocking stack 7, and a p-type semiconductor layer 8. Each layer on the substrate 2 can be formed using well-known epitaxial growth methods such as Metal-Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), and Hydride Vapor Phase Epitaxy (HVPE). Furthermore, the light-emitting element 1 includes an n-side electrode 11 disposed on the n-type cladding layer 4 and a p-side electrode 12 disposed on the p-type semiconductor layer 8.

[0031] The following describes the stacking directions of substrate 2, buffer layer 3, n-type cladding layer 4, tilted layer 5, active layer 6, electron blocking stack 7, and p-type semiconductor layer 8. Figure 1 The vertical direction is referred to as the vertical direction. Additionally, the side on which each layer of the light-emitting element 1 is stacked relative to the substrate 2 (i.e., Figure 1 The upper side is called the upper side, and its opposite side (i.e. Figure 1 The lower side (the side below the light-emitting element) is referred to as the lower side. The use of "up" and "down" is for convenience and is not intended to limit, for example, the orientation of the light-emitting element 1 relative to the vertical direction when using it. In this embodiment, each layer constituting the light-emitting element 1 has a thickness in the vertical direction.

[0032] As a semiconductor constituting the light-emitting element 1, for example, Al can be used. a Ga b In 1-a-bN (0 ≤ a ≤ 1, 0 ≤ b ≤ 1, 0 ≤ a + b ≤ 1) indicates a binary to quaternary group-III nitride semiconductor. Further, in a deep ultraviolet LED, a semiconductor of an aluminum gallium nitride (AlGaN) system not containing indium is often used. Here, "AlGaN" is a ternary mixed crystal whose ratio of the composition of group-III elements (i.e., the total composition of aluminum (Al) and gallium (Ga)) to the composition of nitrogen (N) is 1:1, and the composition ratio of aluminum and the composition ratio of gallium are arbitrarily set. In addition, a part of these group-III elements can be substituted with boron (B), thallium (Tl), or the like. In addition, a part of nitrogen can be substituted with phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), or the like. Hereinafter, each constituent element of the light emitting element 1 will be described.

[0033] (Substrate 2)

[0034] The substrate 2 includes a material that transmits light (in the present embodiment, deep ultraviolet light) emitted from the active layer 6. The substrate 2 is, for example, a sapphire (Al2O3) substrate. In addition, as the substrate 2, for example, an aluminum nitride (AlN) substrate or an aluminum gallium nitride substrate, or the like can be used.

[0035] (Buffer layer 3)

[0036] The buffer layer 3 is formed on the substrate 2. In the present embodiment, the buffer layer 3 is formed of aluminum nitride. Further, in the case where the substrate 2 is an aluminum nitride substrate or an aluminum gallium nitride substrate, the buffer layer 3 can not necessarily be provided.

[0037] (n-type cladding layer 4)

[0038] The n-type cladding layer 4 is formed on the buffer layer 3. The n-type cladding layer 4 includes, for example, Al q Ga 1-q N (0 ≤ q ≤ 1). The subscript q in the composition Al q Ga 1-q N indicates the Al composition ratio (also referred to as the AlN mole fraction). The Al composition ratio q of the n-type cladding layer 4 is, for example, 20% or more, and is preferably set to 25% or more and 70% or less. In the case where the well layer 62 is formed in such a manner as to become a single quantum well structure as in the present embodiment, the Al composition ratio of the n-type cladding layer 4 is preferably set to 40% or more and 60% or less.

[0039] The n-type cladding layer 4 has a film thickness of 1 μm or more and 4 μm or less. In the case where the active layer 6 is a single quantum well structure (SQW), the film thickness of the n-type cladding layer 4 is preferably about 3 μm. In the case where the active layer 6 is a single quantum well structure, the n-type cladding layer 4 is preferably provided as one in which lattice relaxation has occurred, and in the case where the film thickness of the n-type cladding layer 4 is a certain value or more, lattice relaxation is likely to occur in the n-type cladding layer 4. In the case where the active layer 6 is a multi quantum well structure (MQW), the film thickness of the n-type cladding layer 4 is preferably about 2 μm. In the case where the active layer 6 is a multi quantum well structure, the n-type cladding layer 4 is preferably provided as one in which coherent growth has been performed, and in the case where the film thickness of the n-type cladding layer 4 is a certain value or less, coherent growth is likely to be promoted. The n-type cladding layer 4 can be a single layer structure or a multi layer structure. In the present embodiment, silicon (Si) is used as the n-type impurity doped into the n-type cladding layer 4. The same applies to a semiconductor layer containing an n-type impurity other than the n-type cladding layer 4. In addition, germanium (Ge), selenium (Se), tellurium (Te), or the like can also be used as the n-type impurity.

[0040] (the composition gradient layer 5)

[0041] The composition gradient layer 5 is formed on the n-type cladding layer 4. The composition gradient layer 5 includes Al r Ga 1-r N (0 < r < 1). The Al composition ratio at each position in the up-down direction of the composition gradient layer 5 is greater at a position on the upper side. In addition, the composition gradient layer 5 can include a region in which the Al composition ratio does not increase toward the upper side in a very small portion of the up-down direction (for example, a region of 5% or less of the entire up-down direction of the composition gradient layer 5).

[0042] It is preferable that the Al composition ratio of the lower end portion of the composition gradient layer 5 be substantially the same as (for example, differ by 5% or less from) the Al composition ratio of the n-type cladding layer 4, and that the Al composition ratio of the upper end portion of the composition gradient layer 5 be substantially the same as (for example, differ by 5% or less from) the Al composition ratio of the first barrier layer 611. By providing the composition gradient layer 5, it is possible to prevent a sudden change in the Al composition ratio between the first barrier layer 611 and the n-type cladding layer 4 adjacent to the composition gradient layer 5 in the up-down direction. Thereby, it is possible to suppress the occurrence of dislocations caused by lattice mismatch. As a result, the non-light-emitting recombination rate of electrons and holes in the active layer 6 decreases, and the light emitted from the active layer 6 increases. The film thickness of the composition gradient layer 5 can be set to, for example, 5 nm or more and 20 nm or less. In the present embodiment, the composition gradient layer 5 contains silicon as the n-type impurity, but is not limited thereto.

[0043] (the active layer 6)

[0044] The active layer 6 is formed on the compositionally graded layer 5. In the present embodiment, the active layer 6 is formed in a manner to become a single quantum well structure. The active layer 6 has, in order from the n-type cladding layer 4 side, a first barrier layer 611, a second barrier layer 612, and a well layer 62. Hereinafter, in the case where the first barrier layer 611 and the second barrier layer 612 are not particularly distinguished, they are simply referred to as "barrier layers 61".

[0045] The first barrier layer 611 includes Al s1 Ga 1-s1 N (0 < s1 < 1). In the present embodiment, the Al composition ratio s1 of the first barrier layer 611 is 100%. That is, in the present embodiment, the first barrier layer 611 includes AlN. The first barrier layer 611 has a function of suppressing the injection of electrons below a prescribed energy to the well layer 62. The first barrier layer 611 has, for example, a film thickness of 1.0 nm or more and 5.0 nm or less.

[0046] The second barrier layer 612 includes Al s2 Ga 1-s2 N (0 < s2 < 1). The Al composition ratio s2 of the second barrier layer 612 can be set to an Al composition ratio between the Al composition ratio t of the well layer 62 described later and the Al composition ratio s1 of the first barrier layer 611. The Al composition ratio s2 of the second barrier layer 612 can be set to, for example, 55% or more and 75% or less. The second barrier layer 612 has, for example, a film thickness of 5 nm or more and 20 nm or less.

[0047] The well layer 62 includes Al t Ga 1-t N (0 < t < 1). The Al composition ratio t of the well layer 62 is smaller than each of the Al composition ratios s1, s2 of the barrier layers 61. In the present embodiment, the Al composition ratio t of the well layer 62 is 10% or more and 30% or less. The well layer 62 preferably has, for example, a film thickness of 1 nm or more and 10 nm or less, and particularly preferably has a film thickness of 2 nm or more and 4 nm or less.

[0048] In the present embodiment, the first barrier layer 611, the second barrier layer 612, and the well layer 62 each contain silicon as an n-type impurity. The silicon concentration at each position in the vertical direction in the active layer 6 becomes a maximum value in the first barrier layer 611 or the second barrier layer 612. The maximum value is larger than the silicon concentration at each position in the vertical direction in the compositionally graded layer 5. Further, for example, at least one of the first barrier layer 611, the second barrier layer 612, and the well layer 62 can be set to an undoped layer.

[0049] The active layer 6 recombines electrons and holes within the single quantum well structure to generate light of a prescribed wavelength. In the present embodiment, the active layer 6 is configured to have a band gap of 3.4 eV or more for outputting deep ultraviolet light having a wavelength of 365 nm or less. In particular, in the present embodiment, the active layer 6 is configured to be capable of generating deep ultraviolet light having a center wavelength of 200 nm or more and 365 nm or less. Further, in the case where the active layer 6 is a single quantum well structure as in the present embodiment, the center wavelength of the ultraviolet light emitted by the active layer 6 is preferably 295 nm or more and 365 nm or less from the viewpoint of improving the light emission output.

[0050] (Electron blocking layer stack 7)

[0051] The electron blocking layer stack 7 has an effect of improving the electron injection efficiency into the active layer 6 by suppressing the occurrence of an overflow phenomenon of electrons leaking from the active layer 6 toward the p-type semiconductor layer 8 side (hereinafter, also referred to as an electron blocking effect). The electron blocking layer stack has a stacked structure in which the first electron blocking layer 71 and the second electron blocking layer 72 are stacked in order from the lower side. Hereinafter, in the case where the first electron blocking layer 71 and the second electron blocking layer 72 are not particularly distinguished, it is simply referred to as an "electron blocking layer". The electron blocking layer is a layer in which the Al composition ratio becomes 50% or more among the layers formed on the active layer 6.

[0052] The first electron blocking layer 71 is provided on the active layer 6 (in the present embodiment, the well layer 62). The first electron blocking layer 71 includes, for example, Al u Ga 1-u N (0 < u < 1). The Al composition ratio u of the first electron blocking layer 71 is preferably set to, for example, 80% or more and 100% or less, and further preferably set to 90% or more and 100% or less. The greater the Al composition ratio, the higher the electron blocking effect of suppressing the passage of electrons. Therefore, by forming the first electron blocking layer 71 having a large Al composition ratio at a position adjacent to the active layer 6, a high electron blocking effect can be obtained at a position close to the active layer 6, and it is easy to secure the probability of presence of electrons in the well layer 62.

[0053] The film thickness of the first electron-blocking layer 71 is 1.0 nm or more and 2.2 nm or less. It is preferable that the film thickness of the first electron-blocking layer 71 be smaller than the film thickness of the well layer 62. The larger the Al composition ratio of a semiconductor layer, the larger the resistance value thereof, and therefore, if the film thickness of the first electron-blocking layer 71 having a large Al composition ratio u is excessively large, the resistance value of the entire light-emitting element 1 can excessively increase. Therefore, it is preferable that the film thickness of the first electron-blocking layer 71 be small to some extent. On the other hand, if the film thickness of the first electron-blocking layer 71 is small, the probability of electrons passing through the first electron-blocking layer 71 from the lower side to the upper side due to a tunneling effect can increase. Therefore, in the light-emitting element 1 of the present embodiment, the second electron-blocking layer 72 is formed over the first electron-blocking layer 71, whereby the penetration of electrons through the electron-blocking layer stack 7 is suppressed.

[0054] The second electron-blocking layer 72 includes Al x Ga 1-x N (0 < x < 1). The Al composition ratio x of the second electron-blocking layer 72 is smaller than the Al composition ratio u of the first electron-blocking layer 71. In the present embodiment, the Al composition ratio x of the second electron-blocking layer 72 is 50% or more and 70% or less. Details will be described later, but by setting the Al composition ratio x of the second electron-blocking layer 72 to be 50% or more and 70% or less and setting the film thickness of the first electron-blocking layer 71 to be 1.0 nm or more and 2.2 nm or less as described above, an increase in the light-emitting output of the light-emitting element 1 can be achieved. The film thickness of the second electron-blocking layer 72 can be set to be, for example, 5 nm or more and 100 nm or less, and is preferably set to be 10 nm or more and 30 nm or less. The film thickness of the second electron-blocking layer 72 is larger than each of the film thickness of the well layer 62 and the film thickness of the first electron-blocking layer 71.

[0055] Each of the electron-blocking layers can be an undoped layer, a layer containing an n-type impurity, a layer containing a p-type impurity, or a layer containing both an n-type impurity and a p-type impurity. 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), or carbon (C) or the like can be used. In the case where each of the electron-blocking layers contains an impurity, the impurity contained in each of the electron-blocking layers can be contained in the entirety of each of the electron-blocking layers or can be contained in a part of each of the electron-blocking layers.

[0056] (p-type semiconductor layer 8)

[0057] The p-type semiconductor layer 8 is formed over the second electron-blocking layer 72. The p-type semiconductor layer 8 is a semiconductor layer having an Al composition ratio of less than 50%. In the present embodiment, the p-type semiconductor layer 8 includes a p-type contact layer 81. The p-type contact layer 81 is a layer to which the p-side electrode 12 is connected, and includes Al u Ga 1-uN (0 ≤ u ≤ 1). In the present embodiment, as the p-type impurity, magnesium is used. In addition, as the p-type impurity, zinc, beryllium, calcium, strontium, barium, or carbon, or the like can also be used. The p-type contact layer 81 is configured in a manner in which the Al composition ratio is low in order to achieve ohmic contact with the p-side electrode 12, and from this viewpoint, it is preferable to be formed of p-type gallium nitride (GaN).

[0058] (n-side electrode 11)

[0059] The n-side electrode 11 is formed on the surface of the n-type cladding layer 4 that is exposed on the upper side. The n-side electrode 11 can be provided, for example, as a multilayer film in which titanium (Ti), aluminum, titanium, and gold (Au) are sequentially layered on the n-type cladding layer 4.

[0060] (p-side electrode 12)

[0061] The p-side electrode 12 is formed on the p-type contact layer 81. The p-side electrode 12 can be provided, for example, as a multilayer film in which nickel (Ni) and gold are sequentially layered on the p-type contact layer 81.

[0062] In the present embodiment, the light emitting element 1 is mounted to a packaging substrate, not shown, in a flip chip manner. That is, the light emitting element 1 is such that the side on which the n-side electrode 11 and the p-side electrode 12 are provided in the upward and downward directions faces the packaging substrate side, and the n-side electrode 11 and the p-side electrode 12 are mounted to the packaging substrate via gold bumps or the like, respectively. The light emitting element 1 mounted in the flip chip manner extracts light from the substrate 2 side, that is, the lower side. In addition, the light emitting element 1 can also be mounted to the packaging substrate by wire bonding or the like, without being limited thereto. In the present embodiment, the light emitting element 1 is provided as a so-called horizontal light emitting element in which the n-side electrode 11 and the p-side electrode 12 are both provided on the upper side in the light emitting element 1, but is not limited thereto, and can also be a vertical light emitting element. The vertical light emitting element is a light emitting element in which the active layer is sandwiched by the n-side electrode and the p-side electrode. In addition, in the case where the light emitting element is provided as a vertical light emitting element, it is preferable that the substrate and the buffer layer be removed by laser lift-off or the like.

[0063] (Regarding the film thickness of the first electron blocking layer 71 and the Al composition ratio of the second electron blocking layer 72)

[0064] The greater the film thickness and the Al composition ratio of each electron blocking layer, respectively, the greater the electron blocking effect of each electron blocking layer, and the greater the probability of the existence of electrons in the well layer 62. However, there is a limit to the number of electrons that can be injected into one well layer 62. Therefore, merely making the film thickness and the Al composition ratio of the electron blocking layer greater, respectively, does not result in a high light emission output. As evidenced by Experimental Example 1 described later, the appropriate values of the film thickness of the first electron blocking layer 71 and the Al composition ratio of the second electron blocking layer 72 differ depending on the total number of well layers 62 in the active layer 6.

[0065] Here, the total number of the well layers 62 in the active layer 6 is set to N, the film thickness of the first electron blocking layer 71 is set to a film thickness d [nm], and the Al composition ratio of the second electron blocking layer 72 is set to x [%] as described above. At this time, by making the film thickness d of the first electron blocking layer 71 satisfy the relation of 0.1N + 0.9 ≤ d ≤ 0.2N + 2.0, and making the Al composition ratio x of the second electron blocking layer 72 satisfy the relation of 10N + 40 ≤ x ≤ 10N + 60, a high light emission output can be obtained in the light emitting element 1. That is, the more the total number N of the well layers 62 in the active layer 6, the larger the film thickness d of the first electron blocking layer 71 and the Al composition ratio x of the second electron blocking layer 72. In the present mode, the total number N of the well layers 62 in the active layer 6 is 1, and therefore the film thickness d of the first electron blocking layer 71 satisfies the relation of 1.0 ≤ d ≤ 2.2, and the Al composition ratio x of the second electron blocking layer 72 satisfies the relation of 50 ≤ x ≤ 70. These numerical ranges will be confirmed in the experimental examples described later.

[0066] In addition, from the viewpoint of improving the light emission output of the light emitting element 1, the total number N of the well layers 62 in the active layer 6 is preferably 5 or less, and more preferably 4 or less. In particular, as in the second embodiment described later, the total number N of the well layers 62 is further preferably 3.

[0067] In addition, from the viewpoint of improving the light emission output of the light emitting element 1, it is preferable to adjust the Al composition ratio of the n-type cladding layer 4 in accordance with the total number N of the well layers 62. Specifically, the Al composition ratio of the n-type cladding layer 4 is preferably set to (5N + 75) / 2 [%] or more, and (5N + 115) / 2 [%] or less. That is, in the case where, for example, N = 1, the Al composition ratio of the n-type cladding layer 4 is preferably 40% or more, and 60% or less, and in the case where, for example, N = 3, the Al composition ratio of the n-type cladding layer 4 is preferably 45% or more, and 65% or less. In the case of a multiple quantum well structure in which the total number N of the well layers 62 is large, it is preferable to make the film thickness of the n-type cladding layer 4 small so that the n-type cladding layer 4 grows coherently. On the other hand, in the case where the total number N of the well layers 62 is small, it is preferable to make the film thickness of the n-type cladding layer 4 large so that the n-type cladding layer 4 undergoes lattice relaxation.

[0068] (Action and Effect of the First Embodiment)

[0069] In the present embodiment, the film thickness d of the first electron-blocking layer 71 satisfies the relation of 0.1N+0.9≤d≤0.2N+2.0, and the Al composition ratio x of the second electron-blocking layer 72 satisfies the relation of 10N+40≤x≤10N+60. In the present embodiment, the total number N of the well layers 62 is 1, the film thickness d of the first electron-blocking layer 71 satisfies the relation of 1.0≤d≤2.2, and the Al composition ratio x of the second electron-blocking layer 72 satisfies the relation of 50≤x≤70. Thus, in the light-emitting element 1, a high light-emitting output can be obtained. Further, as to the numerical values, it will be confirmed in Experimental Examples to be described later.

[0070] As described above, according to the present embodiment, a nitride semiconductor light-emitting element capable of improving a light-emitting output can be provided.

[0071] [2nd Embodiment]

[0072] The present embodiment is a light-emitting element 1 having an active layer 6 with a multiple quantum well structure. Figure 2 is a schematic view showing the configuration of the light-emitting element 1 in the present embodiment.

[0073] The active layer 6 has three barrier layers 61 and three well layers 62, and is formed by alternately stacking the barrier layers 61 and the well layers 62. In the active layer 6, the barrier layers 61 are located at the lower end, and the well layers 62 are located at the upper end.

[0074] Each barrier layer 61 includes Al v Ga 1-v N (0 < v < 1). The Al composition ratio of each barrier layer 61 is preferably 75% or more and 95% or less. In addition, each barrier layer 61 has a film thickness of 2 nm or more and 12 nm or less.

[0075] Among the three well layers 62, the lowermost well layer 621 (also referred to as the farthest well layer) that is the well layer 62 formed at the position farthest from the p-type semiconductor layer 8 is different in constitution from the upper well layers 622 that are the two well layers 62 other than the lowermost well layer 621. That is, the film thickness of the lowermost well layer 621 is 1 nm or more greater than the film thickness of each of the two upper well layers 622, and the Al composition ratio of the lowermost well layer 621 is 2% or more greater than the Al composition ratio of each of the two upper well layers 622. In the present embodiment, the upper well layers 622 have a film thickness of 2 nm or more and 4 nm or less and have an Al composition ratio of 25% or more and 45% or less, and the lowermost well layer 621 has a film thickness of 4 nm or more and 6 nm or less and has an Al composition ratio of 35% or more and 55% or less. The difference between the film thickness of the lowermost well layer 621 and the film thickness of each of the upper well layers 622 can be 2 nm or more and 4 nm or less. The film thickness of the lowermost well layer 621 can be 2 times or more and 3 times or less of the film thickness of the upper well layers 622. Further, the difference between the Al composition ratio of the lowermost well layer 621 and the Al composition ratio of each of the upper well layers 622 can be 10% or more and 30% or less. The Al composition ratio of the lowermost well layer 621 can be 1.4 times or more and 2.2 times or less of the Al composition ratio of the upper well layers 622.

[0076] By making the Al composition ratio of the lowermost well layer 621 greater than the Al composition ratio of the other well layers 62 (i.e., the upper well layers 622), the crystallinity of the lowermost well layer 621 is improved. This is because the difference between the Al composition ratio of the lowermost well layer 621 and the Al composition ratio of the n-type clad layer 4 is smaller. As a result of the improvement in the crystallinity of the lowermost well layer 621, the propagation of dislocations from the lowermost well layer 621 to the upper side is suppressed.

[0077] Further, as a result of the improvement in the crystallinity of the lowermost well layer 621, the crystallinity of each layer of the active layer 6 formed on the lowermost well layer 621 is also improved. As a result, the mobility of carriers in the active layer 6 is improved, and the emission intensity of the output light is improved. The greater the film thickness of the lowermost well layer 621, the more significant this effect is, but from the viewpoint of suppressing an increase in the resistance value of the light-emitting element 1 as a whole, the film thickness of the lowermost well layer 621 is designed to be equal to or smaller than a prescribed value. Furthermore, the plurality of well layers 62 can also be configured such that the farther the well layer 62 is on the lower side, the greater the Al composition ratio is.

[0078] Further, for example, the lowermost well layer 621 can be doped with silicon as an n-type impurity. As a result, the formation of V-shaped pits in the active layer 6 is induced, and the V-shaped pits function to suppress the development of dislocations from the n-type clad layer 4 side. Furthermore, the upper well layers 622 can also contain an n-type impurity such as silicon.

[0079] In the case where the active layer 6 is a multiple quantum well structure as in the present embodiment, from the viewpoint of improving the emission of ultraviolet light, the center wavelength of the ultraviolet light emitted from the active layer 6 is preferably 250 nm or more and 295 nm or less.

[0080] Also, as with the first embodiment, the film thickness d of the first electron blocking layer 71 satisfies the relationship of 0.1N+0.9≤d≤0.2N+2.0, and the Al composition ratio x of the second electron blocking layer 72 satisfies the relationship of 10N+40≤x≤10N+60. That is, in the present embodiment, the total number N of the well layers 62 is 3, and therefore the film thickness d of the first electron blocking layer 71 is 1.2 nm or more and 2.6 nm or less, and the Al composition ratio x of the second electron blocking layer 72 is 70% or more and 90% or less. Thus, the light emission output of the light emitting element 1 can be improved. As to these values, this will be confirmed in Experimental Examples to be described later.

[0081] Also, by making the film thickness of the lowermost well layer 621 larger than the film thickness of the upper well layer 622, the lowermost well layer 621 is planarized, and the planarity of each layer of the active layer 6 formed on the lowermost well layer 621 is also improved. Thus, the deviation of the Al composition ratio in each layer of the active layer 6 can be suppressed, and the monochromaticity of the output light can be improved. Also, the planarity of each electron blocking layer formed on the active layer 6 is also improved. Thus, the film thickness of each electron blocking layer can be uniformized. Therefore, the electron blocking effect can be prevented from varying depending on the position in the plane direction orthogonal to the vertical direction. As a result, the effect of improving the light emission output resulting from adjusting the film thickness d of the first electron blocking layer 71 and the Al composition ratio x of the second electron blocking layer 72 as described above is further easily obtained.

[0082] Also, in the case where the total number N of the well layers 62 is 3, the Al composition ratio of the n-type clad layer 4 is preferably 45% or more and 65% or less.

[0083] The other is the same as the first embodiment.

[0084] Further, the same reference numerals are used for the same components as those of the described embodiments among the reference numerals used in the second embodiment and subsequent embodiments, unless specifically indicated otherwise.

[0085] (Action and Effect of the Second Embodiment)

[0086] In this mode as well, the film thickness d of the first electron-blocking layer 71 satisfies the relation of 0.1N+0.9≤d≤0.2N+2.0, and the Al composition ratio x of the second electron-blocking layer 72 satisfies the relation of 10N+40≤x≤10N+60. In this mode, the total number N of the well layers 62 is 3, the film thickness d of the first electron-blocking layer 71 satisfies the relation of 1.2≤d≤2.6, and the Al composition ratio x of the second electron-blocking layer 72 satisfies the relation of 70≤x≤90. Thereby, in the light-emitting element 1, a high light-emitting output can be obtained. Further, as to the numerical values, it will be confirmed in the experimental examples to be described later.

[0087] Further, the film thickness of the lowermost well layer 621 is larger than that of each of the upper well layers 622 by 1 nm or more, and the Al composition ratio of the lowermost well layer 621 is larger than that of each of the upper well layers 622 by 2% or more. Thereby, the crystallinity and planarity of each layer constituting the active layer 6 are improved, and the improvement of the light-emitting output and the monochromaticity of the light-emitting element 1 can be achieved.

[0088] (EXPERIMENTAL EXAMPLE 1)

[0089] This experimental example is an example in which the light-emitting output was measured in Samples 1 to 4 and Samples 5 to 12, wherein Samples 1 to 4 are samples in which the film thickness d of the first electron-blocking layer was changed in a light-emitting element of a single quantum well structure (SQW: Single Quantum Well), and Samples 5 to 12 are samples in which the film thickness d of the first electron-blocking layer was changed in a light-emitting element of a multi quantum well structure (MQW: Multi Quantum Well). Samples 1 to 4 are light-emitting elements having the same basic structure as the first embodiment, and Samples 5 to 12 are light-emitting elements having the same basic structure as the second embodiment. The detailed structures of Samples 1 to 4, which are light-emitting elements of a single quantum well structure, are shown in Table 1, and the detailed structures of Samples 5 to 12, which are light-emitting elements of a multi quantum well structure, are shown in Table 2. "3QW" in Table 2 means a multi quantum well structure in which the number of well layers is 3.

[0090] [Table 1]

[0091]

[0092] [Table 2]

[0093]

[0094] The film thicknesses listed in Tables 1 and 2 were determined using transmission electron microscopy. Furthermore, the Al composition ratios for each layer listed in Tables 1 and 2 were estimated from the secondary ion intensities of Al determined by secondary ion mass spectrometry (SIMS). In Table 1, the film thickness of the first electron blocking layer, 1.0–2.3 nm, refers to various variations in the film thickness of the first electron blocking layer in samples 1–4, ranging from 1.0 nm to 2.3 nm. In Table 2, the film thickness of the first electron blocking layer, 0.7–3.0 nm, refers to various variations in the film thickness of the first electron blocking layer in samples 5–12, ranging from 0.7 nm to 3.0 nm. In addition, the column for the inclined layer in Table 1 shows that the Al composition ratio at each position in the vertical direction of the inclined layer varies from 50% to 100% from the bottom to the top, and the column for the inclined layer in Table 2 shows that the Al composition ratio at each position in the vertical direction of the inclined layer varies from 55% to 85% from the bottom to the top.

[0095] In samples 1 to 4 with single quantum well structures, the Al composition ratio x of the second electron blocking layer is between 50% and 70%. In samples 5 to 12 with multi-quantum well structures (N=3), the Al composition ratio x of the second electron blocking layer is between 70% and 90%. That is, the Al composition ratio x of the second electron blocking layer satisfies the relationship 10N+40≤x≤10N+60.

[0096] In this experimental example, the light emission output of each of the samples 1 to 12 was measured. The light emission output of each sample was the light emission output when a current of 20 mA flowed through each sample in its wafer state. The light emission output was measured using a photodetector located on the underside of each of the samples 1 to 12. Table 3 shows the total number of well layers N, the film thickness d of the first electron blocking layer, the Al composition ratio x of the second electron blocking layer, the emission wavelength, and the light emission output in samples 1 to 12. The unit of the measured light emission output values ​​is set to an arbitrary unit [au].

[0097] Table 3

[0098]

[0099] In addition, the relationship between the thickness d of the first electron blocking layer and the light emission output of each sample is shown in... Figure 3 It is shown in the middle. Figure 3 In the diagram, samples 1 to 4, with a total number of trap layers N equal to 1, are plotted using circular symbols, while samples 5 to 12, with a total number of trap layers N equal to 3, are plotted using diamond symbols. Additionally, in... Figure 3In this case, the approximate curve of the circular plots and the approximate curve of the diamond plots are shown.

[0100] From Table 3 and Figure 3 It is known that, in the case where the total number N of the well layers is 1, in the samples 1 to 3 where the Al composition ratio x of the second electron blocking layer satisfies 50% or more and 70% or less and the film thickness d of the first electron blocking layer satisfies 1.0 nm or more and 2.2 nm or less, a high luminous output is obtained. On the other hand, it is known that, in the case where the total number N of the well layers is 1, in the sample 4 where the film thickness d of the first electron blocking layer deviates from the numerical range of 1.0 nm or more and 2.2 nm or less, the luminous output is reduced. That is, in the case where the total number N of the well layers is 1, it is preferable that the Al composition ratio x of the second electron blocking layer satisfies 50% or more and 70% or less and the film thickness d of the first electron blocking layer satisfies 1.0 ≤ d ≤ 2.2. In addition, in the case where the total number N of the well layers is 1, the film thickness d of the first electron blocking layer is preferably 1.1 ≤ d ≤ 2.1, more preferably 1.2 ≤ d ≤ 2.0, and further preferably 1.3 ≤ d ≤ 1.8. In addition, in the case where the total number N of the well layers is 1, the Al composition ratio x of the second electron blocking layer is preferably 55% or more and 65% or less, and more preferably 60% or more and 65% or less.

[0101] In addition, from Table 3 and Figure 3 It is known that, in the case where the total number N of the well layers is 3, in the samples 6 to 11 where the Al composition ratio x of the second electron blocking layer satisfies 70% or more and 90% or less and the film thickness d of the first electron blocking layer satisfies 1.2 nm or more and 2.6 nm or less, a high luminous output is obtained. On the other hand, it is known that, in the case where the total number N of the well layers is 3, in the samples 5 and 12 where the film thickness d of the first electron blocking layer deviates from the numerical range of 1.2 nm or more and 2.6 nm or less, the luminous output is reduced. That is, in the case where the total number N of the well layers is 3, it is preferable that the Al composition ratio x of the second electron blocking layer satisfies 70% or more and 90% or less and the film thickness d of the first electron blocking layer satisfies 1.2 ≤ d ≤ 2.6. In addition, in the case where the total number N of the well layers is 3, the film thickness d of the first electron blocking layer is preferably 1.3 ≤ d ≤ 2.5, more preferably 1.5 ≤ d ≤ 2.4, and further preferably 1.7 ≤ d ≤ 2.1. In addition, in the case where the total number N of the well layers is 3, the Al composition ratio x of the second electron blocking layer is preferably 70% or more and 80% or less, and more preferably 70% or more and 75% or less.

[0102] (Experimental Example 2)

[0103] This experiment example is an experiment example showing that the luminous output is improved by making the film thickness of the lowermost well layer (the farthest well layer) 1 nm or more greater than the film thickness of each upper well layer and making the Al composition ratio of the lowermost well layer 2% or more greater than the Al composition ratio of each upper well layer as in the second embodiment.

[0104] In this experiment example, a light emitting element of an embodiment having the same configuration as the second embodiment in which the film thickness of the lowermost well layer is made 1 nm or more greater than the film thickness of each upper well layer and the Al composition ratio of the lowermost well layer is made 2% or more greater than the Al composition ratio of each upper well layer was prepared. Also, a light emitting element of a comparative example in which the film thickness is made the same and the Al composition ratio is made the same in all well layers was prepared. The light emitting element of the embodiment is the same as the samples 5 to 12 in the aforementioned experiment example 1 in the basic structure, and the film thickness d of the first electron blocking layer is 1.9 ± 0.2 nm. The light emitting element of the comparative example is the same as the embodiment except that the film thickness is made 3 ± 1 nm and the Al composition ratio is made 35 ± 10% in all well layers, and the composition gradient layer present in the light emitting element of the embodiment is omitted. The film thickness and the Al composition ratio of each layer of the embodiment are shown in Table 4, and the film thickness and the Al composition ratio of each layer of the comparative example are shown in Table 5.

[0105] [Table 4]

[0106]

[0107] [Table 5]

[0108]

[0109] Then, in each sample, the luminous output was measured as in experiment example 1. As a result, the measurement result of the luminous output of the light emitting element of the embodiment was 1.29 [a.u.], and the measurement result of the luminous output of the light emitting element of the comparative example was 0.56 [a.u.]. That is, it was found that the luminous output is improved by making the film thickness of the lowermost well layer 1 nm or more greater than the film thickness of each upper well layer and making the Al composition ratio of the lowermost well layer 2% or more greater than the Al composition ratio of each upper well layer.

[0110] (Summary of Embodiments)

[0111] Next, the technical ideas grasped from the above-described embodiments will be described using reference numerals and the like in the embodiments. However, each reference numeral and the like in the following description is not intended to limit the components in the claims to the members and the like specifically shown in the embodiments.

[0112] [1] The first embodiment of the present application is a nitride semiconductor light-emitting element (1) comprising: an active layer (6) comprising at least one well layer (62); a p-type semiconductor layer (8) on one side of the active layer (6); and an electron-blocking layer stack (7) between the active layer (6) and the p-type semiconductor layer (8), the electron-blocking layer stack (7) comprising: a first electron-blocking layer (71); and a second electron-blocking layer (72) on the p-type semiconductor layer (8) side of the first electron-blocking layer (71) and having an Al composition ratio smaller than that of the first electron-blocking layer (71), wherein, when the total number of the well layers (62) in the active layer (6) is denoted by N, the film thickness of the first electron-blocking layer (71) is denoted by d [nm], and the Al composition ratio of the second electron-blocking layer (72) is denoted by x [%], the film thickness d of the first electron-blocking layer (71) satisfies the relationship 0.1N + 0.9 ≤ d ≤ 0.2N + 2.0, and the Al composition ratio x of the second electron-blocking layer (72) satisfies the relationship 10N + 40 ≤ x ≤ 10N + 60.

[0113] Thus, in the nitride semiconductor light-emitting element, a high light-emitting output can be obtained.

[0114] [2] The second embodiment of the present application is, in the first embodiment, the active layer (6) has a plurality of well layers (62), and when a well layer (62) formed at the position farthest from the p-type semiconductor layer (8) among the plurality of well layers (62) is denoted by the farthest well layer (621), the film thickness of the farthest well layer (621) is greater than the film thickness of each of the well layers (62) other than the farthest well layer (621) among the plurality of well layers (62) by 1 nm or more, and the Al composition ratio of the farthest well layer (621) is greater than the Al composition ratio of each of the well layers (62) other than the farthest well layer (621) among the plurality of well layers (62) by 2% or more.

[0115] Thus, the crystallinity and planarity of each layer constituting the active layer are improved, and the light-emitting output and monochromaticity of the nitride semiconductor light-emitting element can be improved.

[0116] [3] The third embodiment of the present application is, in the first or second embodiment, the total number N of the well layers (62) is 3, and the film thickness d of the first electron-blocking layer (71) is 1.7 nm or more and 2.1 nm or less.

[0117] Thus, in the nitride semiconductor light-emitting element, a higher light-emitting output can be obtained.

[0118] [4] The fourth embodiment of the present application is that, in the third embodiment, the Al composition ratio x of the second electron-blocking layer (72) is 65% or more and 75% or less.

[0119] Thus, in the nitride semiconductor light-emitting element, a higher light-emitting output can be obtained.

[0120] [5] The fifth embodiment of the present application is that, in the first or second embodiment, the total number N of the well layer (62) is 1, and the film thickness d of the first electron-blocking layer (71) is 1.3 nm or more and 1.8 nm or less.

[0121] Thus, in the nitride semiconductor light-emitting element, a higher light-emitting output can be obtained.

[0122] [6] The sixth embodiment of the present application is that, in the fifth embodiment, the Al composition ratio x of the second electron-blocking layer (72) is 55% or more and 65% or less.

[0123] Thus, in the nitride semiconductor light-emitting element, a higher light-emitting output can be obtained.

[0124] [7] The seventh embodiment of the present application is that, in any one of the first to sixth embodiments, the Al composition ratio of the first electron-blocking layer (71) is 80% or more, and the film thickness of the second electron-blocking layer (72) is 10 nm or more and 30 nm or less.

[0125] Thus, in the nitride semiconductor light-emitting element, a higher light-emitting output can be obtained.

[0126] (Postscript)

[0127] The above describes embodiments of the present application, but the above-described embodiments do not limit the application covered by the claims. Note that all combinations of the features described in the embodiments are not necessarily essential to the solution of the problem of the application. In addition, the present application can be implemented in a modified form without departing from the spirit of the application.

Claims

1. A nitride semiconductor light-emitting element, characterized in that, Possessing: an active layer possessing at least one well layer; a p-type semiconductor layer on one side of the active layer; and an electron-blocking layer stack between the active layer and the p-type semiconductor layer, the electron-blocking layer stack has a first electron-blocking layer and a second electron-blocking layer positioned on the p-type semiconductor layer side of the first electron-blocking layer and having an Al composition ratio less than that of the first electron-blocking layer, when the total number of well layers in the active layer is N, the film thickness of the first electron-blocking layer is film thickness d [nm], and the Al composition ratio of the second electron-blocking layer is Al composition ratio x [%], the film thickness d of the first electron-blocking layer satisfies the relationship 0.1N + 0.9 ≤ d ≤ 0.2N + 2.0, and the Al composition ratio x of the second electron-blocking layer satisfies the relationship 10N + 40 ≤ x ≤ 10N + 60, the active layer has a plurality of well layers, when the well layer formed at the position farthest from the p-type semiconductor layer among the plurality of well layers is the farthest well layer, the film thickness of the farthest well layer is 1 nm or more greater than the film thickness of each of the well layers other than the farthest well layer among the plurality of well layers, and the Al composition ratio of the farthest well layer is 2% or more greater than the Al composition ratio of each of the well layers other than the farthest well layer among the plurality of well layers, the total number N of well layers is 3, the film thickness d of the first electron-blocking layer is 1.7 nm or more and 2.1 nm or less, the Al composition ratio x of the second electron-blocking layer is 65% or more and 75% or less, the Al composition ratio of the first electron-blocking layer is 80% or more, the film thickness of the second electron-blocking layer is 10 nm or more and 30 nm or less.

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