Nitride semiconductor ultraviolet light emitting element and method for manufacturing the same

Abstract

The nitride semiconductor ultraviolet light-emitting device has a light-emitting device structure portion in which an n-type layer, an active layer, and a p-type layer including a wurtzite structure AlGaN-based semiconductor are stacked in the vertical direction. The n-type layer is made of an n-type AlGaN-based semiconductor, the active layer includes one or more well layers made of an AlGaN-based semiconductor, the p-type layer is made of a p-type AlGaN-based semiconductor, and each semiconductor layer in the n-type layer and the active layer has an epitaxial growth layer with a surface forming a multi-step platform parallel to the (0001) plane. The n-type layer has a plurality of first Ga-rich regions, which are layered regions with a locally low AlN mole fraction evenly dispersed in the n-type layer and include Al2Ga1N3-rich regions with an integer ratio of the AlGaN composition ratio. In the second Ga-rich region, there is an AlGaN region of Al1Ga1N2 or Al5Ga7N with an integer ratio of the AlGaN composition ratio. 12 of AlGaN region.

Description

[0001] Technical Area

[0002] The present invention relates to a nitride semiconductor ultraviolet light emitting element having a light emitting element structure in which an n-type layer, an active layer and a p-type layer including an AlGaN-based semiconductor having a wurtzite structure are stacked in an up-and-down direction, and a method for manufacturing the same. Background Art

[0003] Generally speaking, nitride semiconductor light-emitting devices are mostly formed by epitaxial growth on a substrate such as sapphire to form a light-emitting device structure including multiple nitride semiconductor layers. l-x-y Ga x In y It is represented by N(0≤x≤1, 0≤y≤1, 0≤x+y≤1).

[0004] The light-emitting element of the light-emitting diode has a double heterostructure with an active layer composed of a nitride semiconductor layer sandwiched between two cladding layers of an n-type nitride semiconductor layer and a p-type nitride semiconductor layer. When the active layer is an AlGaN-based semiconductor, by adjusting the AlN mole fraction (also known as the Al composition ratio), the band gap energy can be adjusted within the range of the band gap energy that GaN and AlN can take (about 3.4eV and about 6.2eV) as the lower limit and upper limit, respectively, to obtain an ultraviolet light-emitting element with a light emission wavelength from about 200nm to about 365nm. Specifically, by flowing a forward current from the p-type nitride semiconductor layer toward the n-type nitride semiconductor layer, light emission corresponding to the above-mentioned band gap energy generated by the recombination of carriers (electrons and holes) is generated in the active layer. The forward current is supplied from the outside, thereby setting a p-electrode on the p-type nitride semiconductor layer and an n-electrode on the n-type nitride semiconductor layer.

[0005] When the active layer is an AlGaN-based semiconductor, the n-type nitride semiconductor layer and the p-type nitride semiconductor layer sandwiching the active layer are composed of an AlGaN-based semiconductor with a higher AlN mole fraction than the active layer. However, it is difficult for the p-type nitride semiconductor layer with a high AlN mole fraction to form a good ohmic contact with the p-electrode, so a p-type contact layer is generally formed on the top layer of the p-type nitride semiconductor layer, which can make a good ohmic contact with the p-electrode containing a p-type AlGaN-based semiconductor (specifically, p-GaN) with a low AlN mole fraction. The AlN mole fraction of this p-type contact layer is smaller than that of the AlGaN-based semiconductor constituting the active layer, so the ultraviolet rays emitted from the active layer toward the p-type nitride semiconductor layer side are absorbed in the p-type contact layer and cannot be effectively taken out to the outside of the device. For this reason, general ultraviolet light-emitting diodes whose active layers are AlGaN-based semiconductors use Fig.14The device structure schematically shown effectively extracts ultraviolet rays emitted from the active layer toward the n-type nitride semiconductor layer side to the outside of the device (for example, refer to Patent Documents 1 and 2 listed below).

[0006] like Fig.14 As shown, a general ultraviolet light-emitting diode is constructed as follows: an n-type AlGaN-based semiconductor layer 103, an active layer 104, a p-type AlGaN-based semiconductor layer 105, and a p-type contact layer 106 are sequentially deposited on a template 102 formed by depositing an AlGaN-based semiconductor layer 101 (for example, an AlN layer) on a substrate 100 such as a sapphire substrate, the active layer 104, the p-type AlGaN-based semiconductor layer 105, and a portion of the p-type contact layer 106 are etched away until the n-type AlGaN-based semiconductor layer 103 is exposed, and an n-electrode 107 is formed on the exposed surface of the n-type AlGaN-based semiconductor layer 103, and a p-electrode 108 is formed on the surface of the p-type contact layer 106.

[0007] In order to improve the light emission efficiency (internal quantum efficiency) due to carrier recombination in the active layer, the active layer is provided with a multi-quantum well structure, an electron blocking layer is provided on the active layer, and the like.

[0008] On the other hand, it is reported that composition modulation caused by Ga segregation occurs in the cladding layer composed of the n-type AlGaN-based semiconductor layer, and a layered region with a low AlN mole fraction is formed locally extending in an oblique direction relative to the surface of the cladding layer (for example, refer to the following patent document 3, non-patent documents 1, 2, etc.). The band gap energy of the AlGaN-based semiconductor layer with a low AlN mole fraction locally will also be locally reduced. Therefore, in patent document 3, it is reported that the carriers in the cladding layer are easily distributed locally in the layered region, which can provide a low-resistance current path relative to the active layer, and can achieve an improvement in the luminous efficiency of the ultraviolet light-emitting diode.

[0009] [Prior art literature]

[0010] [Patent Document]

[0011] [Patent Document 1] International Publication No. 2014 / 178288

[0012] [Patent Document 2] International Publication No. 2016 / 157518

[0013] [Patent Document 3] International Publication No. 2019 / 159265

[0014] [Non-patent literature]

[0015] [Non-patent document 1] Y. Nagasawa, et al., "Comparison of AlxGa 1-xN multiplequantum wells designed for 265and 285nm deep-ultraviolet LEDs grown on AlNtemplates having macrosteps", Applied Physics Express 12, 064009(2019)

[0016] [Non-patent document 2] K. Kojima, et al., "Carrier localization structure combined with current micropaths in AlGaN quantum wells grown on an AlN template with macrosteps", Applied Physics letter 114, 011102 (2019) Summary of the invention

[0017] -Technical problem to be solved by the invention-

[0018] Ultraviolet light-emitting elements made of AlGaN semiconductors are produced on substrates such as sapphire substrates by well-known epitaxial growth methods such as metal organic vapor phase deposition (MOVPE). However, when producing ultraviolet light-emitting elements, the characteristics of the ultraviolet light-emitting elements (emission wavelength, wall plug efficiency, forward bias, etc.) are affected by the drift of the crystal growth device and vary, so it is not necessarily easy to produce them with a stable yield.

[0019] The drift of the crystal growth device is caused by the attachment of the tray or the wall of the processing chamber, the change of the effective temperature of the crystal growth part, etc. Therefore, in order to suppress the drift, the growth history has been studied in the past. Although some experienced people have made efforts such as subtly changing the set temperature or the composition of the raw material gas or fixing the growth history for a certain period of time, and also performing maintenance such as cleaning at a certain period of time, it is still difficult to completely eliminate the drift.

[0020] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a nitride semiconductor ultraviolet light emitting element in which characteristic variation caused by drift of a crystal growth apparatus is suppressed and which can be stably produced.

[0021] -Methods used to solve technical problems-

[0022] In order to achieve the above-mentioned object, the present invention provides a nitride semiconductor ultraviolet light emitting element, which is composed of a light emitting element structure in which an n-type layer, an active layer, and a p-type layer of an AlGaN-based semiconductor having a wurtzite structure are stacked in a vertical direction, and is characterized in that:

[0023] The n-type layer is composed of an n-type AlGaN-based semiconductor.

[0024] The active layer disposed between the n-type layer and the p-type layer has a quantum well structure including one or more well layers formed of an AlGaN-based semiconductor.

[0025] The p-type layer is composed of a p-type AlGaN-based semiconductor.

[0026] The n-type layer and each semiconductor layer in the active layer are epitaxial growth layers having surfaces with multi-step terraces parallel to the (0001) plane.

[0027] The n-type layer has a plurality of first Ga-rich regions, each of which is a layered region evenly dispersed in the n-type layer, in which the AlN mole fraction is locally low and includes an n-type AlGaN region of Al2Ga1N3 having an AlGaN composition ratio of an integer ratio,

[0028] Each extension direction of the first Ga-rich region on a first plane orthogonal to the upper surface of the n-type layer is inclined relative to an intersection line between the upper surface of the n-type layer and the first plane,

[0029] The boundary region between adjacent terraces of the multi-step terraces of the well layer has a second Ga-rich region where the AlN mole fraction is locally low in the well layer.

[0030] In the second Ga-rich region, there is Al1Ga1N2 or Al5Ga7N with an AlGaN composition ratio of an integer ratio. 12 AlGaN region.

[0031] In addition, in order to achieve the above-mentioned object, the present invention provides a method for manufacturing a nitride semiconductor ultraviolet light emitting element, wherein the nitride semiconductor ultraviolet light emitting element is constituted by a light emitting element structure portion in which an n-type layer, an active layer, and a p-type layer including an AlGaN-based semiconductor having a wurtzite structure are stacked in a vertical direction, and the method is characterized in that:

[0032] A first step of epitaxially growing the n-type layer of an n-type AlGaN-based semiconductor on a base portion including a sapphire substrate having a primary surface tilted at a given angle relative to the (0001) plane so that multi-step terraces parallel to the (0001) plane are exposed on the surface of the n-type layer;

[0033] A second step of epitaxially growing the active layer having a quantum well structure including one or more well layers composed of an AlGaN-based semiconductor on the n-type layer so that multi-step terraces parallel to the (0001) plane are exposed on the surface of the well layer; and

[0034] a third step of forming the p-type layer of a p-type AlGaN-based semiconductor on the active layer by epitaxial growth,

[0035] In the first step, a plurality of first Ga-rich regions are grown extending obliquely upward, the first Ga-rich regions being n-type AlGaN regions evenly dispersed in the n-type layer, having a locally low AlN mole fraction and containing Al2Ga1N3 with an AlGaN composition ratio in an integer ratio,

[0036] In the second step, a second Ga-rich region in which the AlN mole fraction is locally low in the well layer is formed in the boundary region between the adjacent terraces of the multi-step terraces of the well layer, and in the second Ga-rich region, Al1Ga1N2 or Al5Ga7N is formed so that the AlGaN composition ratio becomes an integer ratio. 12 The AlGaN region is grown.

[0037] Furthermore, although AlGaN semiconductors are generally 1-x Ga x N (0≤x≤1), but if the band gap energy is within the range of the lower and upper limits of the band gap energy that GaN and AlN can take, then impurities such as group 3 elements such as B or In or group 5 elements such as P can be contained in trace amounts. In addition, GaN-based semiconductors are nitride semiconductors basically composed of Ga and N, and can also contain impurities such as group 3 elements such as Al, B or In or group 5 elements such as P in trace amounts. In addition, AlN-based semiconductors are nitride semiconductors basically composed of Al and N, and can also contain impurities such as group 3 elements such as Ga, B or In or group 5 elements such as P in trace amounts. Therefore, in the present application, GaN-based semiconductors and AlN-based semiconductors are respectively part of AlGaN-based semiconductors.

[0038] In addition, n-type or p-type AlGaN-based semiconductors are AlGaN-based semiconductors doped with Si or Mg as donor or acceptor impurities. AlGaN-based semiconductors that are not explicitly stated as p-type and n-type in this application refer to undoped AlGaN-based semiconductors, but even if they are undoped, they can contain trace amounts of donor or acceptor impurities that are inevitably mixed in. In addition, the first plane is not an exposed surface specifically formed during the manufacturing process of the n-type layer or a boundary surface with other semiconductor layers, but an imaginary plane extending parallel to the up and down direction in the n-type layer. In addition, in this specification, AlGaN-based semiconductor layers, GaN-based semiconductor layers, and AlN-based semiconductor layers are semiconductor layers composed of AlGaN-based semiconductors, GaN-based semiconductors, and AlN-based semiconductors, respectively.

[0039] According to the nitride semiconductor ultraviolet light-emitting element with the above characteristics or the method for manufacturing the nitride semiconductor ultraviolet light-emitting element with the above characteristics, as described below, by utilizing the quasi-stable AlGaN described later formed in the first Ga-rich region in the n-type layer and the second Ga-rich region in the well layer, respectively, characteristic fluctuations caused by drift of the crystal growth device, etc., can be suppressed, and it can be expected that nitride semiconductor ultraviolet light-emitting elements with desired light-emitting characteristics can be stably produced.

[0040] First, “quasi-stable AlGaN” represented by a given integer ratio of AlGaN composition ratio will be described.

[0041] Generally, ternary mixed crystals such as AlGaN are a crystal state in which group 3 elements (Al and Ga) are randomly mixed, which can be described as "random nonuniformity". However, the covalent bond radius of Al is different from that of Ga, so in the crystal structure, the one with higher symmetry of the atomic arrangement of Al and Ga generally becomes a stable structure.

[0042] There are two types of AlGaN semiconductors with wurtzite structure: random arrangement without symmetry and stable symmetric arrangement. Here, the symmetric arrangement becomes dominant at a certain ratio. In the "quasi-stable AlGaN" represented by the AlGaN composition ratio (composition ratio of Al, Ga and N) described later as a given integer ratio, a periodic symmetric arrangement structure of Al and Ga is found.

[0043] In this periodic symmetrical arrangement structure, the amount of Ga supplied to the crystal growth surface is only slightly increased, and due to the high symmetry, the mixed crystal mole fraction becomes somewhat stable in energy, which can prevent the proliferation of places where Ga is extremely increased, which is easy to move mass (mass transfer). That is, by utilizing the properties of the "quasi-stable AlGaN" formed in the first Ga-rich region in the n-type layer, as an AlGaN-based semiconductor, even if there is a change in the mixed crystal mole fraction caused by drift of the crystal growth device, the change in the mixed crystal mole fraction of the first Ga-rich region that provides a low-resistance current path for the active layer can be partially suppressed as described later. As a result, a stable carrier supply from the n-type layer to the active layer can be achieved, and changes in device characteristics can be suppressed, thereby expecting stable production of nitride semiconductor ultraviolet light-emitting elements that exhibit desired characteristics.

[0044] Next, the composition ratio of AlGaN in which Al and Ga are arranged in a periodic symmetrical manner in the (0001) plane will be described.

[0045] exist Figure 1 In the figure, a schematic diagram showing one unit cell (two monoatomic layers) is shown in the c-axis direction of AlGaN. Figure 1 In the figure, white circles indicate the sites where atoms of the group 3 elements (Al, Ga) are located, and black circles indicate the sites where atoms of the group 5 elements (N) are located.

[0046] exist Figure 1 In the figure, the hexagonal planes of the group 3 elements (A3 plane, B3 plane) and the group 5 elements (A5 plane, B5 plane) are all parallel to the (0001) plane. There are 6 locations of the A3 plane and the A5 plane (collectively referred to as the A plane) at each vertex of the hexagon and 1 location at the center of the hexagon. The same is true for the B3 plane and the B5 plane (collectively referred to as the B plane). Figure 1 In the figure, only three sites that exist in the hexagon of the B surface are shown. The sites of the A surface overlap in the c-axis direction, and the sites of the B surface overlap in the c-axis direction. However, an atom (N) at one site of the B5 surface forms a four-coordinate bond with atoms (Al, Ga) at three sites of the A3 surface located above the B5 surface and an atom (Al, Ga) at one site of the B3 surface located below the B5 surface, and an atom (Al, Ga) at one site of the B3 surface forms a four-coordinate bond with an atom (N) at one site of the B5 surface located above the B3 surface and an atom (N) at three sites of the A5 surface located below the B3 surface. Therefore, as shown in FIG. Figure 1 As shown, the various parts of the A surface and the various parts of the B surface do not overlap in the c-axis direction.

[0047] Figure 2The positional relationship between each part of the A surface and each part of the B surface is illustrated as a top view observed from the c-axis direction. For both the A surface and the B surface, the six vertices of the hexagon are shared by the other two adjacent hexagons, and the center part is not shared with other hexagons, so there are actually three atomic parts in one hexagon. Therefore, in each unit cell, there are 6 parts of atoms of group 3 elements (Al, Ga) and 6 parts of atoms of group 5 elements (N). Therefore, as AlGaN composition ratios expressed as integer ratios other than GaN and AlN, there are the following 5 situations.

[0048] 1)Al1Ga5N6,

[0049] 2) Al2Ga4N6(=Al1Ga2N3),

[0050] 3) Al3Ga3N6(=Al1Ga1N2),

[0051] 4) Al4Ga2N6(=Al2Ga1N3),

[0052] 5)Al5Ga1N6.

[0053] exist Figure 3 , the A3 plane and B3 plane of the above five combinations of Group 3 elements are schematically shown. Ga is shown as a black circle, and Al is shown as a white circle.

[0054] for Figure 3 In the case of Al1Ga5N6 shown in (A), Ga is arranged at the 6 vertices of the A3 surface, the 6 vertices of the B3 surface, and 1 central portion, and Al is arranged at the 1 central portion of the A3 surface.

[0055] for Figure 3 In the case of Al1Ga2N3 shown in (B), Ga is arranged at three vertices of the A3 plane and the B3 plane and one central portion, and Al is arranged at three vertices of the A3 plane and the B3 plane.

[0056] for Figure 3 In the case of Al1Ga1N2 shown in (C), Ga is arranged at the three vertices and one center portion of the A3 surface and the three vertices of the B3 surface, and Al is arranged at the three vertices of the A3 surface and the three vertices and one center portion of the B3 surface.

[0057] for Figure 3 In the case of Al2Ga1N3 shown in (D), Ga is arranged at the three vertices of the A3 and B3 surfaces, and Al is arranged at the three vertices and one center of the A3 and B3 surfaces. This is equivalent to replacing Figure 3 The positions of Al and Ga in Al1Ga2N3 as shown in (B).

[0058] for Figure 3 In the case of Al5Ga1N6 shown in (E), Ga is arranged at one central part of the A3 surface, and Al is arranged at six vertices of the A3 surface and six vertices and one central part of the B3 surface. This is equivalent to replacing Figure 3 The positions of Al and Ga in Al1Ga5N6 as shown in (A).

[0059] exist Figure 3 In each of the figures (A) to (E), it can be seen that if the center is assumed to be moved to any of the six vertices of the hexagon, then the six vertices of Al or Ga on the A3 surface, and the three vertices and one center of Al or Ga on the A3 surface are equivalent, and the one center of Al or Ga on the A3 surface is equivalent to the three vertices of Al or Ga on the A3 surface. The same is true for the B3 surface. In addition, Figure 3 In each of the figures (A), (C) and (E), the A3 surface and the B3 surface may be replaced.

[0060] exist Figure 3 In each of Figures (A) to (E) of FIG. 1 , the atomic arrangement of Al and Ga can maintain symmetry regardless of whether it is the A3 plane or the B3 plane. In addition, even if the center of the hexagon is moved, the atomic arrangement of Al and Ga can maintain symmetry.

[0061] In addition, Figure 3 If the hexagonal planes of the A3 and B3 planes (A) to (E) are repeatedly arranged in a honeycomb shape, when each part is observed in the direction parallel to the (0001) plane, such as the [11-20] direction and the [10-10] direction, Al and Ga are periodically and repeatedly located, or either Al or Ga is continuously located. Therefore, all of them become periodically symmetrical atomic arrangements.

[0062] Here, for convenience of explanation, the AlN mole fraction x1 (x1=1 / 6, 1 / 3, 1 / 2, 2 / 3, 5 / 6) corresponding to the AlGaN composition ratio in 1) to 5) above is denoted as xl Ga 1-xl N is called “first quasi-stable AlGaN.” The first quasi-stable AlGaN is AlGaN in which the atoms of Al and Ga are arranged in a periodic symmetric arrangement and are energetically stable.

[0063] Next, we will Figure 1When the hexagonal planes shown are extended to two unit cells (4 monoatomic layers), there are two planes of group 3 elements (A3 plane, B3 plane) and two planes of group 5 elements (A5 plane, B5 plane), and in every two unit cells, there are 12 sites of atoms of group 3 elements (Al, Ga) and 12 sites of atoms of group 5 elements (N). Therefore, as AlGaN composition ratios expressed as integer ratios other than GaN and AlN, in addition to the AlGaN composition ratios 1) to 5) above, there are the following 6 combinations.

[0064] 6)Al1Ga 11 N 12 (=GaN+Al1Ga5N6),

[0065] 7) Al3Ga9N 12 (=Al l Ga3N4=Al l Ga5N6+Al1Ga2N3)、

[0066] 8)Al5Ga7N 12 (=Al l Ga2N3+Al1Ga1N2)、

[0067] 9)Al7Ga s N 12 (=Al1Ga1N2+Al2Ga1N3),

[0068] 10)Al9Ga3N 12 (=Al3Ga1N4=Al2Ga1N3+Al5Ga l N6)

[0069] 11) Al 11 Ga1N 12 (=Al5Ga1N6+AlN).

[0070] However, since the six AlGaN composition ratios of 6) to 11) are formed by combining the two AlGaN composition ratios in the first quasi-stable AlGaN, GaN, and AlN located before and after them, there is a high possibility that the symmetry in the c-axis direction is disordered. Therefore, although the stability is lower than that of the first quasi-stable AlGaN, the symmetry of the atomic arrangement of Al and Ga in the A3 plane and the B3 plane is the same as that of the first quasi-stable AlGaN, and the stability is higher than that of AlGaN in a random asymmetric arrangement state. Here, for the convenience of explanation, the AlGaN corresponding to the AlN mole fraction x2 (x2 = 1 / 12, 1 / 4, 5 / 12, 7 / 12, 3 / 4, 11 / 12) of the AlGaN composition ratios of 6) to 11) is x2 Ga1 -x2N is called "second quasi-stable AlGaN". According to this, the first and second quasi-stable AlGaN have a stable structure due to the symmetry of the atomic arrangement of Al and Ga in the crystal structure. Hereinafter, the first and second quasi-stable AlGaN are collectively referred to as "quasi-stable AlGaN".

[0071] To grow AlGaN with a certain crystal quality, it is necessary to grow the crystal at a high temperature of 1000°C or higher. However, even if Ga atoms reach the surface of the crystal, they will not move around until the temperature is above 1000°C. On the other hand, unlike Ga, Al is easily adsorbed on the surface, and its movement after entering the surface is somewhat restricted.

[0072] Therefore, even if it is quasi-stable AlGaN, the Al1Ga5N6 in 1) and the Al1Ga 11 N 12 , and Al in 7) above l The AlN molar fraction of Ga3N4 is less than 25%. Due to the high composition ratio of Ga, at the growth temperature around 1000°C, Ga moves violently, the symmetry of the atomic arrangement is disordered, and the atomic arrangement of Al and Ga is close to a random state. The above stability is lower than that of other quasi-stable AlGaN.

[0073] Next, the "first Ga-rich region" is explained. In the nitride semiconductor ultraviolet light-emitting element and the method for manufacturing the nitride semiconductor ultraviolet light-emitting element of the above-mentioned characteristics, since each semiconductor layer in the n-type layer and the active layer is an epitaxial growth layer having a surface forming a multi-step platform parallel to the (0001) plane, in the n-type layer, Ga, which is easy to move in mass, moves on the platform region and concentrates in the boundary region between adjacent platforms, forming a region with a lower AlN mole fraction than the platform region. This boundary region is accompanied by the epitaxial growth of the n-type AlGaN layer of the n-type layer, extending obliquely upward relative to the (0001) plane, and the layered region with a locally low AlN mole fraction is evenly dispersed in the n-type layer. Here, when the mass movement of Ga is large enough, the layered region becomes the first Ga-rich region of the n-type AlGaN region containing quasi-stable AlGaN with an AlGaN composition ratio of Al2Ga1N3.

[0074] In the first Ga-rich region, due to the presence of quasi-stable AlGaN whose AlGaN composition ratio is Al2Ga1N3, the variation of the Ga supply amount in the first Ga-rich region is absorbed by the quasi-stable AlGaN. That is, in the first Ga-rich region, when the Ga supply amount is increased, the quasi-stable AlGaN increases, and when the Ga supply amount is reduced, the quasi-stable AlGaN decreases, and as a result, the variation of the AlN mole fraction in the first Ga-rich region is suppressed. Therefore, in the first Ga-rich region, the variation of the Ga supply amount caused by the drift of the crystal growth device, etc. is absorbed, and the quasi-stable AlGaN whose AlGaN composition ratio is Al2Ga1N3 (the AlN mole fraction is 66.7% (two-thirds)) is stably formed. That is, the variation of the AlN mole fraction in the first Ga-rich region can be suppressed relative to the variation of the Ga supply amount. In this specification, when the two-thirds AlN mole fraction is appropriately expressed as a percentage, it is approximately expressed as 66.7%.

[0075] As described above, in the crystal growth of AlGaN, a random asymmetric arrangement state and a regular symmetric arrangement state can usually be mixed. In the first Ga-rich region, a region of quasi-stable AlGaN with a regular symmetric arrangement state of AlN mole fraction of 66.7% is stably formed, and a region where the AlN mole fraction varies slightly (for example, 0 to 3%) from 66.7% is mixed. Therefore, the AlN mole fraction in the first Ga-rich region is concentrated near the AlN mole fraction (66.7%) of the quasi-stable AlGaN with an AlGaN composition ratio of Al2Ga1N3.

[0076] By stably forming the 1st Ga-rich region in a layered region where the AlN mole fraction is locally low within the n-type layer, the carriers in the n-type layer are locally distributed in the 1st Ga-rich region with a small band gap energy within the n-type layer. In the n-type layer, the current preferentially and stably flows into the 1st Ga-rich region, thereby suppressing the variation in the characteristics of the nitride semiconductor ultraviolet light-emitting element.

[0077] Furthermore, since the variation of the Ga supply amount due to the drift of the crystal growth device is absorbed in the first Ga-rich region, the lower limit of the variation range of the AlN mole fraction in the n-type layer is limited to the vicinity of the AlN mole fraction of the quasi-stable AlGaN (66.7%). That is, since the formation of a region in which the AlN mole fraction in the n-type layer is smaller than the vicinity of 66.7% is suppressed, part of the light emission from the well layer is absorbed in this region, and the reduction of the light emission efficiency can be prevented.

[0078] Next, the "well layer" and the "second Ga-enriched region" are explained. Since the n-type layer and each semiconductor layer in the active layer have an epitaxial growth layer on the surface forming a multi-step platform parallel to the (0001) plane, the boundary region between adjacent platforms of the multi-step platform of the well layer becomes an inclined region inclined relative to the (0001) plane connecting the adjacent platforms (refer to the above-mentioned non-patent documents 1 and 2). However, the inclined region is a structure that combines multiple steps (the step difference of one unit cell) and giant steps (the step difference of multiple unit cells), which can distinguish the stepped (0001) plane exposed in the inclined region from the platform surface of the multi-step platform.

[0079] As the terrace on the upper surface of the well layer moves in the lateral direction relative to the terrace below the well layer during the step flow growth, the film thickness of the inclined region of the well layer is thicker than the film thickness of the terrace region outside the inclined region. In addition, similarly to the formation of the first Ga-rich region with a locally low AlN mole fraction in the n-type layer, the second Ga-rich region with a locally low AlN mole fraction is formed in the inclined region of the well layer. Here, when the mass transfer of Ga is large enough, an AlGaN composition ratio of Al1Ga1N2 or Al5Ga7N is formed in the second Ga-rich region. 12 The AlGaN region of the quasi-stable AlGaN.

[0080] That is, as an appropriate combination of the quasi-stable AlGaN formed in the second Ga-rich region with respect to the quasi-stable AlGaN with an AlN mole fraction of 66.7% stably formed in the first Ga-rich region, the AlGaN composition ratio is Al2O3. l Ga l N2 and Al5Ga7N 12 These two are quasi-stable AlGaN.

[0081] In the 2nd Ga-rich region, due to the presence of AlGaN with a composition ratio of Al1Ga1N2 or Al5Ga7N 12 The quasi-stable AlGaN in the 2nd Ga-rich region absorbs the change in the Ga supply amount in the quasi-stable AlGaN. That is, in the 2nd Ga-rich region, when the Ga supply amount is increased, the quasi-stable AlGaN increases, and when the Ga supply amount is reduced, the quasi-stable AlGaN decreases. As a result, the change in the AlN mole fraction in the 2nd Ga-rich region is suppressed. Therefore, in the 2nd Ga-rich region, the change in the Ga supply amount caused by the drift of the crystal growth device is absorbed, and the AlGaN composition ratio is stably formed to be Al1Ga1N2 (the AlN mole fraction is 50% (half)) or Al5Ga7N 12(AlN mole fraction is 41.7% (5 / 12)) quasi-stable AlGaN. That is, the variation of the AlN mole fraction in the second Ga-rich region is suppressed in response to the variation of the Ga supply amount. In this specification, when the AlN mole fraction of 5 / 12 is expressed as a percentage, it is approximately expressed as 41.7%.

[0082] As described above, in the crystal growth of AlGaN, a random asymmetric arrangement state and a regular symmetric arrangement state are usually mixed. Therefore, in the 2Ga-rich region, a region of quasi-stable AlGaN with a regular symmetric arrangement state of 50% or 41.7% AlN mole fraction is stably formed, while a region in which the AlN mole fraction varies slightly (for example, 0 to 3%) from 50% or 41.7% is mixed.

[0083] As described above, the band gap energy of the inclined region is smaller than that of the platform region, and similarly to the first Ga-rich region of the n-type layer, it is easy to generate local distribution of carriers. For this reason, the luminescence of the well layer becomes more significant in the inclined region than in the platform region. The above-mentioned non-patent documents 1 and 2 report the same content for the well layer of AlGaN-based semiconductors. However, each platform region of the well layer and the barrier layer is a region sandwiched by the platform on the upper surface and the platform on the lower surface of each layer in the c-axis direction. Therefore, the areas outside each platform region of the well layer and the barrier layer become the boundary regions (inclined regions) of each layer.

[0084] In addition, the multi-step terrace formed by the epitaxial growth of the active layer is formed continuously with the multi-step terrace formed by the epitaxial growth of the n-type layer. Therefore, the carriers (electrons) supplied to the well layer along the current path in the first Ga-rich region are concentratedly supplied to the boundary region (inclined region) between adjacent terraces where the light emission in the well layer is concentrated.

[0085] Therefore, in the first Ga-rich region that dominates the layered region of the n-type layer, a quasi-stable AlGaN, i.e., an n-type AlGaN region, with an AlN mole fraction of 66.7% is stably formed. In addition, in the second Ga-rich region in the inclined region of the well layer, a quasi-stable AlGaN, i.e., an AlGaN region, with an AlN mole fraction of 50% or 41.7% is stably formed. This allows for stable carrier supply to the inclined region of the well layer, thereby suppressing variations in the characteristics of the nitride semiconductor ultraviolet light-emitting element.

[0086] Furthermore, since the AlN molar fraction of the n-type layer is 66.7% or more, ultraviolet light emitted from the well layer of the active layer passes through the n-type layer, a device structure can be obtained in which ultraviolet light is extracted from the n-type layer side.

[0087] In the nitride semiconductor ultraviolet light emitting device having the above characteristics, it is preferred that the AlN mole fraction of the n-type body region other than the layered region of the n-type layer is within a range of 69% to 74%.

[0088] In addition, the manufacturing method of the nitride semiconductor ultraviolet light-emitting element with the above characteristics is preferably such that in the first step, the target value of the AlN molar fraction of the n-type layer is set within the range of 69% to 74%, and in the first Ga-rich region, an n-type AlGaN region of Al2Ga1N3 with an AlGaN composition ratio becoming an integer ratio is grown.

[0089] In these preferred embodiments, the AlN mole fraction of the n-type main region outside the layered region of the n-type layer absorbs the variation of the Ga supply amount caused by the drift of the crystal growth device, etc., and is within the range of 69% to 74%, so that the difference in AlN mole fraction between the first Ga-rich region and the n-type main region is stably maintained at 2.3% or more. Therefore, the carriers in the n-type layer are more stably distributed locally in the first Ga-rich region having a smaller band gap energy than the n-type main region, and in the n-type layer, the current can be preferentially and stably flowed into the first Ga-rich region, thereby suppressing the variation of the characteristics of the nitride semiconductor ultraviolet light-emitting element.

[0090] In addition, since the upper limit of the AlN mole fraction in the n-type body region of the n-type layer and the upper limit of the target value of the AlN mole fraction in the n-type layer are set at 74%, the quasi-stable AlGaN with an AlGaN composition ratio of Al3Ga1N4 will not be formed dominantly in the n-type layer. If the upper limit is 75% or more, the quasi-stable AlGaN of Al3Ga1N4 will be stably formed in the n-type body region, and it will be difficult to form Al3Ga1N4 in the first Ga-rich region. l The quasi-stable AlGaN of N4 sufficiently supplies Ga for stably forming the quasi-stable AlGaN of Al2Ga1N3, but the AlN mole fraction of the n-type AlGaN-based semiconductor formed in the first Ga-rich region fluctuates randomly, and the desired effect cannot be obtained.

[0091] Furthermore, the nitride semiconductor ultraviolet light-emitting element with the above characteristics preferably has an AlGaN region of Al1Ga1N2 with an AlGaN composition ratio of an integer ratio in the aforementioned second Ga-rich region, and the AlN mole fraction outside the aforementioned boundary region portion of the aforementioned well layer is in the range of 51% to 54%.

[0092] Furthermore, the manufacturing method of the nitride semiconductor ultraviolet light-emitting element with the above characteristics is preferably such that, in the aforementioned second step, the target value of the AlN mole fraction of the aforementioned well layer is set within the range of 51% to 54%, and an AlGaN region of Al1Ga1N2 with an AlGaN composition ratio becoming an integer ratio is grown in the aforementioned second Ga-rich region.

[0093] Through these preferred embodiments, the variation width of the AlN mole fraction in the well layer is suppressed to within 4%. Furthermore, even if the luminescence peaks caused by the composition modulation generated in the region other than 50% AlN mole fraction overlap, a single-peak quantum well can be virtually formed, thereby avoiding the separation of the luminescence peaks of the luminescence spectrum.

[0094] Furthermore, the nitride semiconductor ultraviolet light emitting element having the above characteristics preferably has Al5Ga7N in which the AlGaN composition ratio is an integer ratio in the second Ga-rich region. 12 In the AlGaN region, the AlN mole fraction outside the boundary region portion of the well layer is in the range of 42% to 45%.

[0095] In the method for manufacturing the nitride semiconductor ultraviolet light emitting element of the above-mentioned characteristics, it is preferred that in the aforementioned second step, the target value of the AlN mole fraction of the aforementioned well layer is set within the range of 42% to 45%, and in the aforementioned second Ga-rich region, the AlGaN composition ratio is made to be an integer ratio of Al5Ga7N 12 AIGaN region growth.

[0096] According to these appropriate embodiments, the variation range of the AlN mole fraction in the well layer is suppressed to within 3.3%. Furthermore, even if the luminescence peaks caused by the composition modulation generated in the region other than 41.7% of the AlN mole fraction overlap, a quantum well with a single peak can be virtually formed, thereby avoiding the separation of the luminescence peaks of the luminescence spectrum.

[0097] In the nitride semiconductor ultraviolet light emitting element having the above characteristics, it is preferred that the active layer has a multi-quantum well structure including two or more well layers, and a barrier layer composed of an AlGaN-based semiconductor exists between the two well layers.

[0098] In addition, the manufacturing method of the nitride semiconductor ultraviolet light-emitting element with the above characteristics is preferably that, in the second step, the well layer composed of AlGaN-based semiconductor and the barrier layer composed of AlGaN-based semiconductor are alternately stacked by epitaxial growth to form the active layer of a multi-quantum well structure in which multi-stepped platforms parallel to the (0001) plane are exposed on the surfaces of the barrier layer and the well layer and the active layer includes more than two layers of the well layer.

[0099] According to these preferred embodiments, the active layer has a multi-quantum well structure, and the light emission efficiency can be expected to be improved compared with the case where there is only one well layer.

[0100] In addition, the nitride semiconductor ultraviolet light-emitting element with the above characteristics is preferably configured such that the barrier layer is composed of an AlGaN-based semiconductor, and the boundary area between adjacent platforms of at least the multi-stepped platforms of the barrier layer closest to the p-type layer among the barrier layers located between the two well layers has a third Ga-rich region in which the AlN mole fraction is locally low.

[0101] In addition, the manufacturing method of the nitride semiconductor ultraviolet light-emitting element with the above characteristics is preferably such that, in the second step, when forming the barrier layer composed of an AlGaN-based semiconductor, a third Ga-rich region in which the AlN molar fraction is locally low is formed in the barrier layer at least in the boundary region between the terraces of the barrier layer closest to the p-type layer among the barrier layers located between the two well layers.

[0102] According to such preferred embodiments, in the barrier layer, similarly to the first Ga-rich region of the n-type layer and the second Ga-rich region of the well layer, local distribution of carriers can be generated in the third Ga-rich region. Therefore, when carriers (electrons) are supplied from the n-type layer to the second Ga-rich region of the boundary region (inclined region) between adjacent terraces where light emission is concentrated in the well layer, the supply can be effectively performed via the first Ga-rich region of the n-type layer and the third Ga-rich region of the barrier layer.

[0103] Here, in a multi-quantum well structure having more than two well layers, the luminous efficiency is high in the well layer closest to the p-type layer. Therefore, by forming a third Ga-rich region in the barrier layer on the n-type layer side of the well layer, the carrier supply to the well layer can be more effective.

[0104] Furthermore, in the above-mentioned preferred embodiment of the nitride semiconductor ultraviolet light emitting element, it is preferred that in the above-mentioned 3Ga-rich region of the above-mentioned barrier layer, there is Al2Ga2N with an AlGaN composition ratio of an integer ratio. l AlGaN region of N3, Al3Ga1N4, or Al5Ga1N6.

[0105] Furthermore, in the method for manufacturing a nitride semiconductor ultraviolet light emitting element according to the above preferred embodiment, it is preferred that in the second step,

[0106] 1) setting the target value of the AlN mole fraction of the barrier layer within the range of 68% to 74%, and growing an AlGaN region of Al2Ga1N3 with an AlGaN composition ratio of an integer ratio in the third Ga-rich region; or

[0107] 2) setting the target value of the AlN mole fraction of the barrier layer to a range of 76% to 82%, and growing an AlGaN region of Al3Ga1N4 with an AlGaN composition ratio of an integer ratio in the third Ga-rich region; or

[0108] 3) The target value of the AlN mole fraction of the barrier layer is set within the range of 85% to 90%, and an AlGaN region of Al5Ga1N6 with an AlGaN composition ratio of an integer ratio is grown in the third Ga-rich region.

[0109] According to these preferred embodiments, in the 3rd Ga-rich region of the barrier layer, due to the presence of quasi-stable AlGaN, the variation of the mole fraction of AlN in the 3rd Ga-rich region is suppressed, similarly to the 1st Ga-rich region of the n-type layer and the 2nd Ga-rich region of the well layer, and the quasi-stable AlGaN region is stably formed in the 3rd Ga-rich region. Therefore, the effect exerted by the 3rd Ga-rich region of the barrier layer can be achieved more stably.

[0110] In addition, the nitride semiconductor ultraviolet light-emitting element with the above characteristics preferably also has a base portion including a sapphire substrate, wherein the sapphire substrate has a main surface inclined at only a given angle relative to the (0001) plane, and the light-emitting element structure is formed above the main surface, and at least each semiconductor layer from the main surface of the sapphire substrate to the surface of the active layer is an epitaxial growth layer having a surface forming a multi-stepped platform parallel to the (0001) plane.

[0111] Through the above-mentioned preferred embodiment, a sapphire substrate with an off-angle can be used for epitaxial growth so that multi-step platforms are exposed on the surface of each layer from the main surface of the sapphire substrate to the surface of the active layer, thereby realizing a nitride semiconductor ultraviolet light-emitting element with the above-mentioned characteristics.

[0112] -Effects of the Invention-

[0113] According to the nitride semiconductor ultraviolet light emitting element and the method for manufacturing the nitride semiconductor ultraviolet light emitting element having the above characteristics, a nitride semiconductor ultraviolet light emitting element having desired light emitting characteristics and suppressing characteristic fluctuations caused by drift of a crystal growth device can be stably provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0114] Figure 1 It is a diagram schematically showing the wurtzite crystal structure of AlGaN.

[0115] Figure 2 It is shown from Figure 1A plan view showing the positional relationship between various parts of the A surface and various parts of the B surface as viewed in the c-axis direction of the wurtzite crystal structure.

[0116] Figure 3 FIG. 1 schematically shows the arrangement of Al and Ga on the A3 plane and the B3 plane for each of five combinations of AlGaN composition ratios expressed as integer ratios.

[0117] Figure 4 This is a cross-sectional view of main parts schematically showing an example of the structure of a nitride semiconductor ultraviolet light emitting element according to an embodiment of the present invention.

[0118] Figure 5 It is schematically shown Figure 4 1 is a cross-sectional view of the main parts of an example of the stacked structure of the active layer of the nitride semiconductor ultraviolet light emitting element shown.

[0119] Figure 6 This is a graph showing the relationship between the emission wavelength of the quantum well structure including the AlGaN well layer and the AlGaN barrier layer, the film thickness of the well layer, and the AlN mole fraction of the barrier layer when the AlN mole fraction of the second Ga rich region 220a is 50%.

[0120] Figure 7 This is a graph showing the relationship between the emission wavelength of the quantum well structure including the AlGaN well layer and the AlGaN barrier layer, the film thickness of the well layer, and the AlN mole fraction of the barrier layer when the AlN mole fraction of the second Ga rich region 220a is 41.7%.

[0121] Figure 8 It is schematically shown from Figure 4 Observation from the upper side Figure 4 A top view of an example of the structure of a nitride semiconductor ultraviolet light emitting element is shown.

[0122] Fig. 9 This is a HAADF-STEM image showing the cross-sectional structure inside the n-type cladding layer.

[0123] Fig.10 It is shown in Fig. 9 The HAADF-STEM image shown is a diagram of six measurement areas A to F where cross-sectional TEM-EDX line analysis was performed in the n-type cladding layer.

[0124] Fig.11A It is shown Fig.10 FIG. 1 is a graph showing the measurement results of the AlN mole fraction and the GaN mole fraction in the n-type cladding layer in the measurement region A by cross-sectional TEM-EDX line analysis.

[0125] Fig. 11B It is shown Fig.10 FIG. 1 is a graph showing the measurement results of the AlN mole fraction and the GaN mole fraction in the n-type cladding layer in the measurement region B by cross-sectional TEM-EDX line analysis.

[0126] Fig. 11C It is shown Fig.10 FIG. 1 is a graph showing the measurement results of the AlN mole fraction and the GaN mole fraction in the n-type cladding layer in the measurement region C by cross-sectional TEM-EDX line analysis.

[0127] Fig.11D It is shown Fig.10 FIG. 1 is a graph showing the measurement results of the AlN mole fraction and the GaN mole fraction in the n-type cladding layer in the measurement region D by cross-sectional TEM-EDX line analysis.

[0128] Fig.11E It is shown Fig.10 FIG. 1 is a graph showing the measurement results of the AlN mole fraction and the GaN mole fraction in the n-type cladding layer in the measurement region E by cross-sectional TEM-EDX line analysis.

[0129] Fig.11F It is shown Fig.10 FIG. 1 is a graph showing the measurement results of the AlN mole fraction and the GaN mole fraction in the n-type cladding layer in the measurement region F by cross-sectional TEM-EDX line analysis.

[0130] Fig.12 This is a SEM image showing a measurement region of the AlN mole fraction in the n-type cladding layer by the CL method.

[0131] Fig.13 It is shown from Fig.12 The diagram shows the first and second CL spectra calculated from the CL spectra at 10 points measured in each measurement area.

[0132] Fig.14 This is a cross-sectional view of main parts schematically showing an example of a device structure of a general ultraviolet light emitting diode. DETAILED DESCRIPTION

[0133] The nitride semiconductor ultraviolet light emitting element (hereinafter referred to as "light emitting element") according to the embodiment of the present invention is described with reference to the accompanying drawings. However, in the schematic diagrams of the accompanying drawings used in the following description, the main parts are emphasized and the invention is schematically shown for easy understanding of the description, so the size of each part may not be the same as the size ratio of the actual element. In the following, in this embodiment, the light emitting element is assumed to be a light emitting diode for description.

[0134] [First embodiment]

[0135] <Element Structure of Light Emitting Element>

[0136] like Figure 4 As shown, the light emitting element 1 of the present embodiment comprises: a base portion 10 including a sapphire substrate 11; and a light emitting element structure portion 20 including a plurality of AlGaN-based semiconductor layers 21 to 25, a p-electrode 26, and an n-electrode 27. On a mounting base (submount) or the like, a light emitting element structure portion 20 is disposed toward the side ( Figure 4 The light emitting element 1 is mounted (flip chip mounting) on ​​the upper side of the figure, and the light extraction direction is the base portion 10 side ( Figure 4 However, in this specification, for the convenience of explanation, the direction perpendicular to the main surface 11a of the sapphire substrate 11 (or the upper surface of the base 10 and each AlGaN-based semiconductor layer 21 to 25) is referred to as the "upper and lower directions" (or "longitudinal directions"), and the direction from the base 10 toward the light-emitting element structure 20 is referred to as the upper direction, and the opposite direction is referred to as the lower direction. In addition, the plane parallel to the upper and lower directions is referred to as the "first plane". In addition, the plane parallel to the main surface 11a of the sapphire substrate 11 (or the upper surface of the base 10 and each AlGaN-based semiconductor layer 21 to 25) is referred to as the "second plane", and the direction parallel to the second plane is referred to as the "lateral direction".

[0137] The base portion 10 is constituted to include a sapphire substrate 11 and an AlN layer 12 formed directly on a main surface 11a of the sapphire substrate 11. The sapphire substrate 11 is a slightly inclined substrate in which the main surface 11a is inclined at an angle (offset angle) within a certain range (e.g., about 0 to 6 degrees) relative to the (0001) plane, and a multi-step terrace is exposed on the main surface 11a.

[0138] The AlN layer 12 is composed of AlN crystals epitaxially grown from the main surface of the sapphire substrate 11, and this AlN crystal has an epitaxial crystal orientation relationship with respect to the main surface 11a of the sapphire substrate 11. Specifically, for example, the AlN crystal grows so that the c-axis direction (<0001> direction) of the sapphire substrate 11 is consistent with the c-axis direction of the AlN crystal. However, the AlN crystal constituting the AlN layer 12 may contain a trace amount of Ga or other impurities, and may also be an AlN-based semiconductor layer. In this embodiment, the film thickness of the AlN layer 12 is assumed to be about 2μm to 3μm. However, the structure of the base 10 and the substrate used are not limited to the above-mentioned structure. For example, between the AlN layer 12 and the AlGaN-based semiconductor layer 21, an AlGaN-based semiconductor layer having an AlN mole fraction greater than the AlN mole fraction of the AlGaN-based semiconductor layer 21 may also be provided.

[0139] The AlGaN-based semiconductor layers 21 to 25 of the light-emitting element structure 20 have a structure in which an n-type cladding layer 21 (n-type layer), an active layer 22, an electron blocking layer 23 (p-type layer), a p-type cladding layer 24 (p-type layer) and a p-type contact layer 25 (p-type layer) are epitaxially grown in sequence from the base 10 side and stacked in order.

[0140] In the present embodiment, the AlN layer 12 of the base portion 10, the n-type cladding layer 21 of the light-emitting element structure 20, and each semiconductor layer in the active layer 22, which are sequentially epitaxially grown from the main surface 11a of the sapphire substrate 11, have a surface formed with a multi-step terrace parallel to the (0001) plane derived from the main surface 11a of the sapphire substrate 11. However, since the electron blocking layer 23, the p-type cladding layer 24, and the p-type contact layer 25 of the p-type layer are formed on the active layer 22 by epitaxial growth, the same multi-step terrace may be formed, but the surface may not have the same multi-step terrace.

[0141] However, if Figure 4 As shown, within the light emitting element structure 20, the active layer 22, the electron blocking layer 23, the p-type cladding layer 24, and the p-type contact layer 25 are formed on the first region R1 of the upper surface of the n-type cladding layer 21 by removing the portion stacked on the second region R2 of the upper surface of the n-type cladding layer 21 through etching or the like. Then, the upper surface of the n-type cladding layer 21 is exposed in the second region R2 excluding the first region R1. Figure 4 As schematically shown, the upper surface of the n-type cladding layer 21 has a different height between the first region R1 and the second region R2 . In this case, the upper surface of the n-type cladding layer 21 is independently defined in the first region R1 and the second region R2 .

[0142] The n-type cladding layer 21 is composed of an n-type AlGaN-based semiconductor. In the n-type cladding layer 21, there is a layered region where the mole fraction of AlN is locally low and is evenly dispersed. As described above, the layered region is dominated by Al2GaN with an AlGaN composition ratio of an integer ratio. l The first Ga-rich region 21 a of the n-type AlGaN region of N3 (ie, n-type quasi-stable AlGaN having an AlN mole fraction of 66.7%). Figure 4 , as an example in which the first Ga-rich region 21a is dominant in the layered region, a case in which the entire layered region is the first Ga-rich region 21a is schematically shown. The region other than the layered region in the n-type cladding layer 21 is referred to as an n-type body region 21b.

[0143] In this embodiment, the AlN mole fraction of the n-type main region 21b is adjusted to be within the range of 69% to 74%. The film thickness of the n-type cladding layer 21 is assumed to be about 1 μm to 2 μm, which is the same as the film thickness used in general nitride semiconductor ultraviolet light-emitting elements, but the film thickness may also be about 2 μm to 4 μm. In the following, for the sake of simplicity, the AlGaN composition ratio present in the first Ga-rich region 21a is set to an integer ratio of Al2Ga l The n-type AlGaN region of the quasi-stable AlGaN of N3 is conveniently referred to as the "quasi-stable n-type region". In addition, the region slightly changed from the AlN mole fraction of 66.7% (two-thirds) outside the quasi-stable n-type region existing in the first Ga-rich region 21a is referred to as the "quasi-stable near n-type region". Here, the quasi-stable n-type region does not necessarily have to exist continuously in layers in the first Ga-rich region 21a in multiple layers, and may also exist intermittently by being interrupted by the quasi-stable near n-type region.

[0144] The active layer 22 is a multi-quantum well structure having two or more well layers 220 composed of AlGaN-based semiconductors and one or more barrier layers 221 composed of AlGaN-based semiconductors or AlN-based semiconductors alternately stacked. It is not necessary to provide the barrier layer 221 between the bottom well layer 220 and the n-type cladding layer 21. In addition, between the top well layer 220 and the electron blocking layer 23, the barrier layer 221 may be provided, or an AlGaN layer or an AlN layer having a high AlN mole fraction may be provided as a thinner film than the barrier layer 221.

[0145] exist Figure 5 Schematically shows an example of a stacked structure (multi-quantum well structure) of the well layer 220 and the barrier layer 221 of the active layer 22 . Figure 5 In FIG. 1 , a case where the well layer 220 has three layers is illustrated. Figure 5 The terraces T of the well layer 220 and the barrier layer 221 shown are grown in a multi-step structure, as disclosed in the above-mentioned non-patent documents 1 and 2, and are well-known structures. As described above, the boundary region BA between adjacent terraces T becomes an inclined region inclined relative to the (0001) plane. In this embodiment, the depth of one terrace T (the distance between adjacent boundary regions BA) is assumed to be several tens of nm to several hundreds of nm.

[0146] like Figure 5 As schematically shown, a second Ga-rich region 220a having a locally low AlN mole fraction is formed in the well layer 220 in the boundary region portion (inclined region) BA between adjacent terraces T of the multi-stepped terraces T in the well layer 220. For convenience, the region other than the second Ga-rich region 220a in the well layer 220 is referred to as a well body region 220b.

[0147] In this embodiment, in the second Ga-rich region 220a, there is Al1GaN with an integer composition ratio. l N2 or Al5Ga7N 12 The quasi-stable AlGaN is AlGaN with an AlN mole fraction of 50% (one-half) or 41.7% (five-twelfths). Furthermore, the AlN mole fraction of the well body region 220b is adjusted to be within the range of 51% to 54% when the quasi-stable AlGaN with an AlN mole fraction of 50% exists in the second Ga-rich region 220a, and is adjusted to be within the range of 42% to 45% when the quasi-stable AlGaN with an AlN mole fraction of 41.7% exists in the second Ga-rich region 220a. The film thickness of the well layer 220, including the terrace region TA and the inclined region BA, is adjusted to be within the range of 2 unit cells to 7 unit cells, for example.

[0148] In order to simplify the description below, the AlGaN composition ratio existing in the second Ga-rich region 220a is assumed to be an integer ratio of Al1Ga1N2 or Al5Ga7N 12 The quasi-stable AlGaN is conveniently referred to as the "quasi-stable well region". In addition, the region slightly changed from 50% (one-half) or 41.7% (five-twelfths) of the AlN mole fraction outside the quasi-stable well region existing in the second Ga-rich region 220a is referred to as the "quasi-stable nearby well region". Here, the quasi-stable well region is not necessarily present continuously along the edge line in the second Ga-rich region 220a formed in the inclined region BA existing along the edge line of the terrace T when viewed from above, and may also exist intermittently by being interrupted by the quasi-stable nearby n-type region.

[0149] As described above, the barrier layer 221 is made of AlGaN-based semiconductors, similarly to the n-type cladding layer 21 and the well layer 220, and has a surface having a multi-step terrace T parallel to the (0001) plane. Here, as an example, the AlN mole fraction of the barrier layer 221 as a whole is assumed to be in the range of 66.7% to 100%. Although the barrier layer 221 includes a case where the AlN mole fraction is 100% and a case where the AlN mole fraction is not 100%, there is also a case where the barrier layer 221 is made of AlGaN-based semiconductors. Therefore, Figure 5As schematically shown, when the barrier layer 221 is composed of an AlGaN-based semiconductor having an AlN mole fraction of not 100%, a third Ga-rich region 221a having a locally low AlN mole fraction in the barrier layer 221 can be formed in a boundary region (inclined region) BA between adjacent terraces T of the barrier layer 221, similarly to the n-type cladding layer 21 and the well layer 220. Here, the region other than the third Ga-rich region 221a in the terrace region in the barrier layer 221 is conveniently referred to as a barrier body region 221b. The barrier body region 221b mainly exists in the terrace region TA in the barrier layer 221. As an example, when the AlN mole fraction of the entire 3rd Ga-rich region 221a including the barrier layer 221 is within the range of 66.7% to 90%, which is a part of the above-mentioned range of 66.7% to 100%, in order to fully ensure the local distribution effect of the carriers in the 3rd Ga-rich region 221a, it is preferred that the difference in the AlN mole fraction between the 3rd Ga-rich region 221a and the barrier main region 221b is 4 to 5% or more, but even if it is about 1%, the local distribution effect of the carriers can be expected. Therefore, in this embodiment, the AlN mole fraction of the barrier main region 221b is within the range of 68% to 90%. In addition, the film thickness of the barrier layer 221 includes the terrace region TA and the inclined region BA, and is preferably adjusted within the range of 6nm to 8nm, for example.

[0150] Figure 6 and Figure 7 For the quantum well structure model composed of AlGaN in the well layer 220 and the barrier layer 221, the simulation results (equivalent to the peak emission wavelength) of the emission wavelength obtained by changing the film thickness of the well layer in the range of 3ML (monoatomic layer) to 14ML (1.5 unit cells to 7 unit cells) are shown in the graph. As the conditions of the above simulation, Figure 6 In the embodiment, the AlN mole fraction of the second Ga-rich region 220a of the well layer 220 is set to 50% (half) of the AlN mole fraction of the quasi-stable well region. Figure 7 In the embodiment, the AlN mole fraction of the second Ga-rich region 220a of the well layer 220 is set to be 41.7% (five-twelfths) of the AlN mole fraction of the quasi-stable well region. Figure 6 and Figure 7 In the embodiment of the present invention, the AlN mole fraction of the third Ga-rich region 221 a of the barrier layer 221 is 66.7%, 75% and 83.3%. Figure 6 and Figure 7 In the simulation results shown, it is assumed that ultraviolet light emission of the well layer 220 occurs significantly in the boundary area (inclined area) BA. Therefore, it is important that the film thickness condition of the well layer 220 is satisfied in the inclined area BA.

[0151] according to Figure 6 and Figure 7 It can be seen that when the thickness of the well layer 220 is within the range of 3ML to 14ML, the smaller the thickness of the well layer 220 is, the greater the quantum confinement effect of the well layer 220 is, and the shorter the wavelength of the emission is. Furthermore, the greater the AlN mole fraction of the barrier layer 221 is, the greater the degree of change in the emission wavelength for the change in the thickness of the well layer 220 is. Figure 6 It can be seen that when the AlN mole fraction of the second Ga-rich region 220a is 50%, within the above range of the film thickness of the well layer 220 and the AlN mole fraction of the barrier layer 221, the emission wavelength changes in the range of approximately 246nm to 295nm. Figure 7 It can be seen that when the AlN mole fraction of the second Ga-rich region 220a is 41.7%, within the above range of the thickness of the well layer 220 and the AlN mole fraction of the barrier layer 221, the emission wavelength changes in the range of approximately 249nm to 311nm. Furthermore, when the barrier layer 221 is made of AlN, the emission wavelength can be further extended. Figure 6 In FIG. 1 , the emission wavelengths 258 nm and 280 nm indicated by the single-dot chain line are the control ranges (lower and upper limits) of the emission wavelengths assumed in the light-emitting element 1 of this embodiment when the AlN mole fraction in the second Ga-rich region 220 a is 50%. Figure 7 In the figure, the emission wavelengths 263 nm and 291 nm indicated by the single-dot chain line are the control ranges (lower and upper limits) of the emission wavelengths assumed by the light-emitting element 1 of this embodiment when the AlN mole fraction in the second Ga-rich region 220a is 41.7%. In the second Ga-rich region 220a of the well layer 220, AlGaN composition ratios of Al1Ga1N2 or Al5Ga7N are dominant. 12 As a result of the quasi-stable AlGaN, as an example, the film thickness of the well layer 220 and the AlN mole fraction of the barrier layer 221 are set in the range of 3ML to 11ML accordingly, and the emission wavelength can be controlled in the range of 258nm to 280nm, or in the range of 263nm to 291nm.

[0152] The electron blocking layer 23 is composed of a p-type AlGaN semiconductor. The p-type cladding layer 24 is composed of a p-type AlGaN semiconductor. The p-type contact layer 25 is composed of a p-type AlGaN semiconductor or a p-type GaN semiconductor. The p-type contact layer 25 is typically composed of GaN. However, the film thickness of each layer such as the active layer 22, the electron blocking layer 23, the p-type cladding layer 24, and the p-type contact layer 25 is appropriately determined according to the emission wavelength characteristics and electrical characteristics of the light-emitting element 1. In addition, since the p-type cladding layer 24 reduces the parasitic resistance of the p-type layer, it is not a problem even if it is omitted.

[0153] The p-electrode 26 is composed of a multilayer metal film such as Ni / Au, and is formed on the upper surface of the p-type contact layer 25. The n-electrode 27 is composed of a multilayer metal film such as Ti / Al / Ti / Au, and is formed on a portion of the exposed surface in the second region R2 of the n-type cladding layer 21. However, the p-electrode 26 and the n-electrode 27 are not limited to the multilayer metal films described above, and the electrode structures such as the metals constituting each electrode, the number of layers, and the order of layers can be appropriately changed. Figure 7 , an example of the shape of the p-electrode 26 and the n-electrode 27 viewed from the upper side of the light emitting element 1 is shown. Figure 7 In FIG. 8 , the line BL between the p-electrode 26 and the n-electrode 27 indicates the boundary between the first region R1 and the second region R2 , and coincides with the outer peripheral side wall surfaces of the active layer 22 , the electron blocking layer 23 , the p-type cladding layer 24 , and the p-type contact layer 25 .

[0154] In this embodiment, if Figure 8 As shown in FIG. 1 , as an example, the plan view shape of the first region R1 and the p-electrode 26 is a comb shape, but the plan view shape and arrangement of the first region R1 and the p-electrode 26 are not limited to the comb shape. Figure 8 of examples.

[0155] When a forward bias is applied between the p-electrode 26 and the n-electrode 27, holes are supplied from the p-electrode 26 toward the active layer 22, and electrons are supplied from the n-electrode 27 toward the active layer 22. The supplied holes and electrons reach the active layer 22, and then bond to each other to emit light. In addition, a forward current flows between the p-electrode 26 and the n-electrode 27.

[0156] Figure 4 In the figure, as shown schematically by double lines, the first Ga-rich region 21a of the n-type cladding layer 21 has multiple layers separated in the vertical direction. In addition, in a first plane parallel to the vertical direction (for example, Figure 4 The extending direction of at least a part of the first Ga-rich region 21a is inclined relative to the lateral direction (the extending direction of the intersection line of the first plane and the second plane). Figure 4On the first plane shown, although the layers of the 1st Ga-rich region 21a are schematically illustrated as parallel lines (double lines), the inclination angle between the extension direction and the lateral direction is not necessarily the same between each 1st Ga-rich region 21a, and may vary due to the location within the same 1st Ga-rich region 21a. Therefore, the 1st Ga-rich region 21a on the first plane is not necessarily limited to extending in a straight line. In addition, the inclination angle varies according to the orientation of the first plane. Therefore, a part of the 1st Ga-rich region 21a can also intersect with other 1st Ga-rich regions 21a or branch from other 1st Ga-rich regions 21a on the first plane. The points where the inclination angle between the extension direction of the 1st Ga-rich region 21a and the lateral direction varies depending on the location and the points where the 1st Ga-rich region 21a is evenly dispersed in the n-type cladding layer 21 are clearly shown. Fig. 9 HAADF-STEM image shown.

[0157] In addition, the first Ga-rich region 21a is Figure 4 Although each is shown as a single line (double line) on the first plane in the figure, it also extends parallel to or obliquely on the second plane in a direction perpendicular to the first plane, and has a two-dimensional extension. Therefore, a plurality of first Ga-rich regions 21a exist in stripes on a plurality of second planes in the n-type cladding layer 21.

[0158] As described above, the first Ga-rich region 21a is a layered region in which the AlN mole fraction is locally low in the n-type cladding layer 21. That is, the AlN mole fraction of the first Ga-rich region 21a is lower than the AlN mole fraction of the n-type body region 21b. In addition, near the boundary between the first Ga-rich region 21a and the n-type body region 21b, when the AlN mole fractions of the two regions are continuous in a diffusive manner, the boundary between the two regions cannot be clearly defined.

[0159] Therefore, in this case, the average AlN mole fraction of the entire n-type cladding layer 21, for example, the AlN mole fraction that will be the premise of the growth conditions of the n-type cladding layer 21 described later (the supply amount and flow rate of the raw material gas or carrier gas used in the organic metal compound vapor deposition method), can be used as a reference, and the portion where the AlN mole fraction is lower than the reference value can be relatively defined as the first Ga-rich region 21a. In addition, in addition to the above-mentioned definition method, for example, based on the HAADF-STEM image described later, the portion with a large brightness change can also be defined as the boundary between the two layers. In the present invention, the definition of the boundary between the two layers itself is not important, and the existence of the first Ga-rich region 21a itself can be fully grasped.

[0160] In fact, since the first Ga-rich region 21a is formed with the mass transfer of Ga from the n-type main region 21b, the average AlN mole fraction in the first Ga-rich region 21a changes according to the supply amount of Ga from the n-type main region 21b, and the AlN mole fraction in the first Ga-rich region 21a is not necessarily average. However, in the present embodiment, since the quasi-stable n-type region is stably formed in the first Ga-rich region 21a, even if there is a slight change in the supply amount of Ga, the change is absorbed by the quasi-stable n-type region, and the change in the AlN mole fraction in the first Ga-rich region 21a can be suppressed. For this reason, the minimum value of the AlN mole fraction in each first Ga-rich region 21a is 66.7% of the AlN mole fraction in the quasi-stable n-type region or a value in the vicinity thereof. As described above, in the first Ga-rich region 21a, along with the quasi-stable n-type region, there is also a quasi-stable nearby n-type region. The quasi-stable nearby n-type region is also formed along with the mass transfer of Ga from the n-type main region 21b. Usually, the AlN mole fraction of the quasi-stable nearby n-type region is higher than the AlN mole fraction of the quasi-stable n-type region, and the average AlN mole fraction in the first Ga-rich region 21a is slightly higher than the AlN mole fraction of the quasi-stable n-type region.

[0161] On the other hand, the n-type body region 21b supplies Ga to the first Ga-rich region 21a, so that the AlN mole fraction of the part after the Ga mass transfer in the n-type body region 21b becomes relatively high. In addition, since the mass transfer of Ga that does not reach the formation of the first Ga-rich region 21a occurs in the n-type body region 21b, the AlN mole fraction in the n-type body region 21b changes to a certain extent. However, as described above, the carriers in the n-type cladding layer 21 are locally distributed in the first Ga-rich region 21a having a smaller band gap energy than the n-type body region 21b, and the current in the n-type cladding layer 21 preferentially flows stably into the first Ga-rich region 21a, even if the AlN mole fraction in the n-type body region 21b changes slightly, the characteristic change of the light-emitting element 1 can be suppressed by the first Ga-rich region 21a.

[0162] Here, the above description of the first Ga-rich region 21a is also directly applied to the second Ga-rich region 220a. That is, in the present embodiment, since the quasi-stable well region is stably formed in the second Ga-rich region 220a, even if the supply amount of Ga mentioned above changes slightly, the change is absorbed by the quasi-stable well region, and the average AlN mole fraction of the second Ga-rich region 220a becomes 50% or a value in the vicinity of the AlN mole fraction of the quasi-stable well region, or 41.7% or a value in the vicinity of the AlN mole fraction of the quasi-stable well region. As described above, in the second Ga-rich region 220a, along with the quasi-stable well region, there is also a quasi-stable near-well region, and since the quasi-stable near-well region is also formed along with the mass transfer of Ga from the well main region 220b, the AlN mole fraction of the quasi-stable near-well region is usually higher than the AlN mole fraction of the quasi-stable well region, and the average AlN mole fraction in the second Ga-rich region 220a is slightly higher than the AlN mole fraction of the quasi-stable well region.

[0163] On the other hand, the well body region 220b supplies Ga to the second Ga-rich region 220a, and the AlN mole fraction of the part after the mass transfer of Ga in the well body region 220b becomes relatively high. In addition, since the mass transfer of Ga that does not reach the formation of the second Ga-rich region 220a occurs in the well body region 220b, the AlN mole fraction in the well body region 220b changes to a certain extent. However, as described above, the carriers in the well layer 220 are locally distributed in the second Ga-rich region 220a having a smaller band gap energy than the well body region 220b, and the current in the well layer 220 preferentially flows into the second Ga-rich region 220a stably, even if the AlN mole fraction in the well body region 220b changes slightly, the characteristic change of the light-emitting element 1 can be suppressed by the second Ga-rich region 220a.

[0164] <Method for manufacturing light-emitting element>

[0165] Next, Figure 4 An example of a method for manufacturing the illustrated light emitting element 1 will be described.

[0166] First, the AlN layer 12 included in the base portion 10 and the nitride semiconductor layers 21 to 25 included in the light emitting element structure portion 20 are sequentially epitaxially grown and stacked on the sapphire substrate 11 by a metal organic vapor phase deposition (MOVPE) method. At this time, Si is doped in the n-type cladding layer 21 as a donor impurity, and Mg is doped in the electron blocking layer 23, the p-type cladding layer 24, and the p-type contact layer 25 as an acceptor impurity.

[0167] In the present embodiment, in order to expose multi-step platforms parallel to the (0001) plane on at least the surfaces of the AlN layer 12, the n-type cladding layer 21 and the active layer 22 (well layer 220, barrier layer 221), the sapphire substrate 11 uses a slightly inclined substrate in which the main surface 11a is inclined at an angle (offset angle) within a certain range (for example, 0 to 6 degrees) relative to the (0001) plane and the multi-step platforms are exposed on the main surface 11a.

[0168] As conditions for epitaxial growth, in addition to the use of the (0001) sapphire substrate 11 as a slightly inclined substrate, for example, a growth rate that easily exposes a multi-step terrace (specifically, such growth rate is achieved by appropriately setting conditions such as growth temperature, supply amount or flow rate of raw material gas or carrier gas, etc.) etc. However, such conditions vary depending on the type or structure of the film forming apparatus, so it is sufficient to actually make several samples in the film forming apparatus and determine such conditions.

[0169] As the growth conditions of the n-type cladding layer 21, immediately after the start of growth, the growth starting point of the first Ga-enriched region 21a is formed by the mass migration of Ga at the step difference portion (boundary region) between the multi-step platforms formed on the upper surface of the AlN layer 12. Then, the growth temperature, growth pressure, and donor impurity concentration are selected so that along with the epitaxial growth of the n-type cladding layer 21, the first Ga-enriched region 21a grows obliquely upward through segregation accompanied by the mass migration of Ga.

[0170] Specifically, the growth temperature is preferably above 1050°C where the mass migration of Ga is easy to occur and below 1150°C where good n-type AlGaN can be modulated. In addition, when the growth temperature exceeds 1170°C, the mass migration of Ga will be excessive. Even for the first quasi-stable AlGaN, since the AlN mole fraction is prone to random fluctuations, it is difficult to stably form a quasi-stable AlGaN with an AlN mole fraction of 66.7%, which is not preferred. As for the growth pressure, 75 Torr or less is preferably a good growth condition for AlGaN. As the control limit of the film forming device, 10 Torr or more is actually preferred. The donor impurity concentration is 1×10 18 ~5×10 18 cm -3 However, the above growth temperature and growth pressure are merely examples, and the optimal conditions may be appropriately determined according to the film forming apparatus to be used.

[0171] The supply amount and flow rate of the raw material gas (trimethylaluminum (TMA) gas, trimethylgallium (TMG) gas, ammonia gas) or carrier gas used in the organic metal compound vapor phase deposition method are specified by taking the average AlN mole fraction Xa of the entire n-type cladding layer 21 as a target value. Here, the average AlN mole fraction of the n-type main region 21b is Xb (=69% to 74%), and the average AlN mole fraction of the first Ga-rich region 21a where the quasi-stable n-type region with an AlN mole fraction of 66.7% and the quasi-stable near n-type region with an AlN mole fraction slightly higher than 66.7% exist is Xc (>66.7%). If the mass transfer of Ga from the n-type main region 21b to the first Ga-rich region 21a is considered, Xb>Xa>Xc, but since the volume ratio of the first Ga-rich region 21a occupying the entire n-type cladding layer 21 is small, it can be approximately set to Xa=Xb.

[0172] A quasi-stable n-type region with an AlN mole fraction of 66.7% exists stably in the first Ga-rich region 21a. Since the target value Xa of the AlN mole fraction of the n-type cladding layer 21 is 69% to 74%, the difference (Xb-66.7%) between the AlN mole fraction of 50% in the quasi-stable n-type region and the average AlN mole fraction Xb of the n-type main region 21b can be stably ensured to be above 2.3%, and the carriers in the n-type layer are locally distributed in the first Ga-rich region 21a with a smaller band gap energy than the n-type main region 21b. In addition, since the upper limit of the target value Xa is 74%, the quasi-stable AlGaN with an AlGaN composition ratio of Al3Ga1N4 will not be dominantly formed in the n-type main region 21b. If the upper limit of the target value Xa is 75% or more, the quasi-stable AlGaN of Al3Ga1N4 is stably formed in the n-type body region 21b, and it is difficult to sufficiently supply Ga for stably forming the quasi-stable AlGaN (quasi-stable n-type region) of Al2Ga1N3 from the quasi-stable AlGaN of Al3Ga1N4 in the first Ga-rich region. Therefore, by setting the upper limit of the target value Xa to 74%, a quasi-stable n-type region with an AlN mole fraction of 66.7% can be stably formed in the first Ga-rich region 21a.

[0173] However, the donor impurity concentration does not necessarily need to be uniformly controlled in the vertical direction with respect to the film thickness of the n-type cladding layer 21. For example, the impurity concentration of a predetermined thin film thickness portion in the n-type cladding layer 21 may be lower than the above-set concentration, for example, controlled to be less than 1×10 18 cm -3 , more preferably 1×10 17 cm -3The following low impurity concentration layer. As the film thickness of this low impurity concentration layer, it is preferably greater than 0 nm and on the order of 200 nm or less, more preferably on the order of 10 nm or more and 100 nm or less, and still more preferably on the order of 20 nm or more and 50 nm or less. In addition, the donor impurity concentration of this low impurity concentration layer may be lower than the above-set concentration, and may also partly include an undoped layer (0 cm- 3 ). In addition, it is preferable that part or all of this low impurity concentration layer exists in the upper layer region at a depth within 100 nm from the upper surface of the n-type cladding layer 21 downward.

[0174] When forming the n-type cladding layer 21 having the first Ga-rich region 21a and the n-type main region 21b in the above-described manner, then, on the entire upper surface of the n-type cladding layer 21, by a known epitaxial growth method such as metalorganic vapor phase epitaxy (MOVPE), an active layer 22 (well layer 220, barrier layer 221), an electron blocking layer 23, a p-type cladding layer 24, a p-type contact layer 25, etc. are formed.

[0175] In the formation of the active layer 22, in the same manner as the n-type cladding layer 21, under growth conditions that are likely to expose the above-described multi-step platform, taking the AlN mole fraction (51% - 54% or 42% - 45%) set for the well main region 220b as the target value, the well layer 220 is grown. In addition, taking the AlN mole fraction (68% - 90% or 100%) set for the barrier main region 221b as the target value, the barrier layer 221 is grown.

[0176] Next, by a known etching method such as reactive ion etching, the second region R2 of the nitride semiconductor layers 21 - 25 stacked in the above-described manner is selectively etched until the upper surface of the n-type cladding layer 21 is exposed, and the second region R2 portion of the upper surface of the n-type cladding layer 21 is exposed. Then, by a known film formation method such as electron beam evaporation, a p electrode 26 is formed on the p-type contact layer 25 in the unetched first region R1, and an n electrode 27 is formed on the n-type cladding layer 21 in the etched second region R2. However, after the formation of one or both of the p electrode 26 and the n electrode 27, heat treatment may be performed by a known heat treatment method such as RTA (rapid thermal annealing).

[0177] However, as an example, after the light-emitting element 1 is flip-chip mounted on a base such as a base, it is used in a state of being sealed with a given resin such as silicone resin or amorphous fluororesin (for example, a resin in a lens shape).

[0178] <Cross-sectional Observation and Composition Analysis Results of the n-Type Cladding Layer>

[0179] Next, a sample for cross-sectional observation of the n-type cladding layer 21 is prepared, and a sample piece having a cross-section perpendicular (or slightly perpendicular) to the upper surface of the n-type cladding layer 21 is processed from the sample using a focused ion beam (FIB). The results of observing the sample piece using a scanning transmission electron microscope (STEM) are explained with reference to the accompanying drawings.

[0180] This sample is produced by sequentially stacking the n-type cladding layer 21, the active layer 22, the AlGaN layer having a higher AlN mole fraction than the n-type cladding layer 21, the AlGaN layer for protecting the sample surface, and the protective resin film on the base 10 including the sapphire substrate 11 and the AlN layer 12 according to the production method of the n-type cladding layer 21, etc. However, in the production of this sample, a base 10 is used, and the main surface of the base uses a sapphire substrate 11 with an off-angle relative to the (0001) plane and exposes multi-step terraces on the surface of the AlN layer 12. However, in the production of this sample, the film thickness of the n-type cladding layer 21 is set to 2μm, and the target value of the AlN mole fraction of the n-type cladding layer 21 is set to 70%. In addition, the donor impurity concentration is set to about 3×10 18 cm -3 , controlling the amount of donor impurities (Si) injected. In addition, although this sample was produced so that the AlN mole fraction of the second Ga-rich region 220a of the well layer 220 was 41.7%, the composition analysis results of the n-type cladding layer can directly correspond even when the AlN mole fraction of the second Ga-rich region 220a is other than 41.7%.

[0181] At Fig. 9 A high-angle annular dark field (HAADF)-STEM image of a cross section of the above-mentioned sample piece is shown. Fig. 9 This is a HAADF-STEM image of the entire n-type cladding layer 21 including the upper layer portion of the AlN layer 12 of the sample, the n-type cladding layer 21 , and the active layer 22 .

[0182] HAADF-STEM images can obtain a contrast ratio that is proportional to the atomic weight, and heavy elements are brightly displayed. Therefore, for the first Ga-rich region 21a and the n-type main region 21b in the n-type cladding layer 21, the first Ga-rich region 21a with a low AlN mole fraction is brighter than the n-type main region 21b. HAADF-STEM images are more suitable for observing the difference in AlN mole fractions than conventional STEM images (bright field images).

[0183] pass Fig. 9It can be seen that within the n-type cladding layer 21, multiple first Ga-enriched regions 21a in layered regions with locally low AlN mole fractions are dispersed in the up-down direction, and each first Ga-enriched region 21a extends in a direction inclined relative to the intersection of the upper surface of the n-type cladding layer 21 and the first plane on the screen of the HAADF-STEM image (the cross section of the sample piece, equivalent to the first plane). Although each first Ga-enriched region 21a extends in a linear upward direction, it does not necessarily extend in a straight line. It can be seen that the inclination angle relative to the above-mentioned intersection will vary depending on the position in the same first Ga-enriched region 21a. In addition, in Fig. 9 In the cross section shown (corresponding to the first plane), it can be observed that a part of the first Ga-rich region 21 a intersects with other first Ga-rich regions 21 a or branches from other first Ga-rich regions 21 a.

[0184] In the present embodiment, the composition analysis in the n-type cladding layer 21 of the above-mentioned sample piece is performed by two analysis methods (line analysis by energy dispersive X-ray spectroscopy (cross-sectional TEM-EDX) and CL (cathodoluminescence) method).

[0185] In the composition analysis based on the EDX method (EDX measurement), first, Fig. 9 In almost the entire measurement area of ​​the HAADF-STEM image shown, the electron beam probe (diameter: about 2 nm) is scanned in the vertical direction (up and down direction) and the horizontal direction (direction parallel to the second plane), and the detection data (corresponding to the X-ray intensity of each composition of Al and Ga) of each probe position distributed at intervals of about 4 nm in the vertical and horizontal directions are obtained in a 512×512 matrix.

[0186] Next, in order to perform line analysis based on EDX measurement on the first Ga-rich regions 21a dispersed throughout the measurement region, as shown in FIG. Fig.10 As shown in FIG. 1 , six measurement areas A to F having a substantially square shape (approximately 420 nm×approximately 420 nm) are set within the entire measurement area. Fig.10 exist Fig. 9 The HAADF-STEM image is overlapped with rectangular frames representing the measurement areas A to F. Each of the 6 measurement areas is set to span at least one first Ga-rich region 21a confirmed on the HAADF-STEM image. In addition, the inclination of each measurement area is set for each measurement area so that the extension direction of at least one first Ga-rich region 21a in the measurement area is orthogonal to the scanning direction of the line analysis. The inclinations of the measurement areas A to F (the angle between the longitudinal direction of the entire measurement area and the longitudinal direction of each measurement area) are approximately equal to 20°, but strictly speaking, they are not necessarily exactly the same. Here, unlike the longitudinal and lateral directions of the entire measurement area, Fig.10In each measurement area A to F, for the sake of convenience, the scanning direction of the line analysis is defined as the vertical direction, and the direction perpendicular to the scanning direction is defined as the horizontal direction. The central vertical line in each measurement area indicates the scanning direction, and the central horizontal line indicates the position where the at least one first Ga-enriched region 21a is assumed to exist, which becomes the origin (0 nm) of the scanning position of the line analysis of the composition analysis result described later. The vertical line indicating the scanning direction is attached with an arrow to indicate the direction of the AlN layer 12. In addition, the scanning position is set in the range of 65 to 72 points in total in the vertical direction at intervals of about 5 nm according to each measurement area A to F, sandwiching the above-mentioned origin on the central vertical line.

[0187] In EDX measurement, the diameter of the electron beam probe used for irradiation is as small as about 2 nm, so although the spatial resolution is high, the X-rays emitted from each probe position are weak. In the line analysis of this embodiment, the detection data obtained from the plurality of probe positions arranged in the horizontal direction are accumulated at each scanning position to form the detection data of each scanning position. However, "arranged in the horizontal direction" means that the irradiation range of the electron beam probe overlaps the horizontal line that intersects the vertical line and extends in the horizontal direction at each scanning position.

[0188] Therefore, when all of the plurality of probe positions arranged in the lateral direction are located in the quasi-stable n-type region of the first Ga-rich region 21a at a certain scanning position, the accumulated detection data can accurately show the AlN mole fraction of the quasi-stable n-type region. Similarly, when all of the plurality of probe positions arranged in the lateral direction are located in the n-type body region 21b at a certain scanning position, the accumulated detection data can accurately show the AlN mole fraction of the n-type body region 21b.

[0189] However, when, at a certain scanning position, the extension direction of the quasi-stable n-type region of the first Ga-rich region 21a is not exactly orthogonal to the scanning direction of the line analysis, or the extension direction of the quasi-stable n-type region of the first Ga-rich region 21a is bent and non-linear, etc., when a part of the multiple probe positions arranged in the horizontal direction or a part of the probe range (diameter of about 2 nm) of each probe position is located in the quasi-stable nearby n-type region outside the quasi-stable n-type region or in the n-type main region 21b, the accumulated detection data shows the average AlN mole fraction of the multiple pin positions, which shows a value higher than the AlN mole fraction of the quasi-stable n-type region.

[0190] Similarly, at a certain scanning position, even if most of the plurality of probe positions arranged in the horizontal direction are located in the n-type body region 21b, a part of the plurality of probe positions or a part of the probe range (about 2 nm in diameter) of each probe position is located in a region where the AlN mole fraction is locally low or high due to the mass migration of Ga in the n-type body region 21b or a region where the AlN mole fraction outside the n-type body region 21b is locally low (a layered region outside the first Ga-rich region 21a, a quasi-stable n-type region or a quasi-stable near-n-type region in the first Ga-rich region 21a), the accumulated detection data shows an average AlN mole fraction of the plurality of probe positions, which is higher than the average AlN mole fraction of the n-type body region 21b ( The target value of the AlN mole fraction of the type cladding layer 21) is a low or high value.

[0191] At Figures 11A to 11F , showing that the line analysis measured by EDX was performed Fig.10 The results of the composition analysis in the n-type cladding layer 21 at six measurement areas A to F are shown. Fig.11A FIG1 is a graph of the composition analysis results of each measurement area A to F, wherein the horizontal axis shows the scanning position along the vertical line in the center of each measurement area, and the vertical axis shows the measurement results of the AlN mole fraction and the GaN mole fraction. The 0nm of the scanning position on the horizontal axis shows the position of the horizontal line in the center of each measurement area (assuming that there is at least one first Ga-enriched region 21a). The scanning position shows that the lower side (AlN layer 12 side) of the origin (0nm) is positive, and the upper side (active layer 22 side) is negative.

[0192] In EDX measurement, as described above, since the X-rays emitted from the probe position are weak, at each scanning position, even if the detection data of the probe position (X-ray intensity of each composition) is accumulated in the horizontal direction, the measurement error is generally large. For example, when the AlN mole fraction (100%) of the AlN layer 12, which has a predetermined AlN mole fraction, is used as a reference for correction, the measurement error of the detection data of each scanning position is about ±2 to 3% near the AlN layer 12, which is the reference, and the measurement accuracy decreases as it moves away from the AlN layer 12. For this reason, in the present embodiment, in order to suppress the measurement error of each scanning position to about ±2 to 3% in the area away from the AlN layer 12, the same sample piece as the sample piece used for EDX measurement is used to perform the composition analysis of Al and Ga in the n-type cladding layer 21 based on the Rutherford backscattering (RBS) analysis method, and the result of the RBS analysis is used to correct the result obtained by the EDX measurement. Figures 11A to 11F The AlN mole fraction and the GaN mole fraction in the measurement regions A to F shown are results of the calibration.

[0193] pass Fig.11A It can be confirmed that in the measurement area A, the first Ga-rich region 21a exists in the area A1 of about -73nm to about -52nm at the scanning position and the area A2 of about -36nm to about 62nm at the scanning position. The AlN mole fraction at the scanning positions of 5 points in the area A1 is 66.1% to 68.4% (4 points within 66.7% ± 2%, 3 points within 66.7% ± 1%). The AlN mole fraction at the scanning positions of 20 points in the area A2 is 66.3% to 68.7% (16 points within 66.7% ± 1%). However, since a part of the upper left corner of the measurement area A overlaps with the upper part of the n-type cladding layer 21 containing the AlGaN layer having a higher AlN mole fraction than the n-type cladding layer 21, the AlN mole fraction exceeds 75% and increases in the scanning position below about -177nm.

[0194] pass Fig. 11B It can be confirmed that in the measurement area B, the first Ga-rich region 21a exists in the area B1 of about -5nm to about 5nm at the scanning position, the area B2 of about 71nm to about 82nm at the scanning position, and the area B3 of about 120nm to about 137nm at the scanning position. The AlN mole fraction at the scanning position of the three points in the area B1 is 67.0% to 67.7%. The AlN mole fraction at the scanning position of the three points in the area B2 is 68.4% to 68.7%. The AlN mole fraction at the scanning position of the four points in the area B3 is 66.6% to 67.7%.

[0195] pass Fig. 11C It can be confirmed that in the measurement area C, the first Ga-rich region 21a exists in the area C1 of about -189nm to about -167nm at the scanning position, the area C2 of about -11nm to about 11nm at the scanning position, and the area C3 of about 156nm to about 167nm at the scanning position. The AlN mole fraction at the scanning position of the 5 points in the area C1 is 65.9% to 68.6% (3 points within 66.7% ± 1%). The AlN mole fraction at the scanning position of the 5 points in the area C2 is 66.1% to 68.0% (4 points within 66.7% ± 1%). The AlN mole fraction at the scanning position of the 3 points in the area C3 is 66.0% to 68.6% (2 points within 66.7% ± 1%).

[0196] pass Fig.11DIt can be confirmed that in the measurement area D, the first Ga-rich region 21a exists in the area D1 of about -184nm to about -163nm at the scanning position, the area D2 of about -115nm to about -100nm at the scanning position, and the area D3 of about -5nm to about 5nm at the scanning position. The AlN mole fraction at the scanning position of 5 points in the area D1 is 67.0% to 68.6% (3 points are within 66.7% ± 1%). The AlN mole fraction at the scanning position of 4 points in the area D2 is 66.4% to 68.9% (3 points are within 66.7% ± 1%). The AlN mole fraction at the scanning position of 3 points in the area D3 is 67.4% to 68.4% (1 point is within 66.7% ± 1%).

[0197] pass Fig.11E It can be confirmed that in the measurement area E, the first Ga-rich area 21a exists in the area E1 of about -26nm to about 21nm at the scanning position and the area E2 of about 154nm to about 159nm at the scanning position. The AlN mole fraction at the scanning positions of 10 points in the area E1 is 65.9% to 68.8% (8 points within 66.7% ± 1%). The AlN mole fraction at the scanning positions of 2 points in the area E2 is 67.9% to 68.0%. However, since a part of the upper right corner of the measurement area E overlaps with the AlN layer 12, the AlN mole fraction exceeds 75% and increases at the scanning positions above about 190nm.

[0198] pass Fig.11F It can be confirmed that in the measurement region F, the first Ga-rich region 21a exists in the region F1 of about -5nm to about 10nm of the scanning position. The AlN mole fraction at the scanning positions of the four points in the region F1 is 67.1% to 68.9% (2 points within 66.7% ± 1%). However, since a part of the upper right corner of the measurement region F overlaps with the AlN layer 12, the AlN mole fraction exceeds 75% and increases at the scanning position above about 160nm.

[0199] As described above, considering the measurement error of ±2 to 3% of each scanning position and the possibility that the average AlN mole fraction of the plurality of probe positions arranged in the horizontal direction is higher than the AlN mole fraction of the quasi-stable n-type region in the first Ga-rich region 21a, it can be confirmed that the first Ga-rich region 21a of each of the measurement regions A1, A2, B1 to B3, C1 to C3, D1 to D3, E1, E2, and F1 of the measurement regions A to F has a quasi-stable n-type region with an AlN mole fraction of 66.7%. In addition, it can be seen that the first Ga-rich region 21a exists in the measurement regions A and B at the upper part close to the upper surface of the n-type cladding layer 21, the measurement regions C and D at the central part, and the measurement regions E and F at the lower part close to the AlN layer 12, and is evenly dispersed in the n-type cladding layer 21.

[0200] In addition, through Figures 11A to 11F It can be confirmed that the majority of the AlN mole fractions in the n-type main body region 21b adjacent to each of the measurement regions A to F, A1, A2, B1 to B3, C1 to C3, D1 to D3, E1, E2, and F1 are within the range of about 70% to about 74%. As described above, since the target value of the AlN mole fraction of the n-type cladding layer 21 of the sample used for the EDX measurement is 70%, considering the measurement error of ±2 to 3% at each scanning position and the possibility that the average AlN mole fraction of a plurality of probe positions arranged in the horizontal direction with respect to the n-type main body region 21b is higher or lower than the average AlN mole fraction of the n-type main body region 21b, it can be known that Figures 11A to 11F The AlN mole fraction of the n-type body region 21 b is shown with high accuracy.

[0201] Next, the results of measuring the AlN mole fraction of the first Ga-rich region 21a and the n-type body region 21b in the n-type cladding layer 21 by CL (cathode luminescence) are described. Fig. 9 The sample piece used for observation of the HAADF-STEM image shown was prepared in the same manner.

[0202] Fig.12 The scanning electron microscope (SEM) image of the cross section in the n-type cladding layer 21 of the above-mentioned sample is shown. The measurement areas (a to f) surrounded by dotted lines in the cross section show the incident areas of the electron beam irradiated for each measurement. The measurement areas a and b are located at a distance of about 1600nm from the upper surface of the AlN layer 12, the measurement areas c and d are located at a distance of about 1000nm from the upper surface of the AlN layer 12, and the measurement areas e and f are located at a distance of about 300nm from the upper surface of the AlN layer 12. In each measurement area, an electron beam with a beam diameter of 50nm (diameter) is moved horizontally, and irradiated once at intervals of 50nm, a total of 10 times, and the CL spectrum of each irradiation is measured.

[0203] Fig.13 Among the 10 CL spectra of each measurement area (a to f), the first CL spectrum obtained by averaging two CL spectra with a wavelength distribution close to a short wavelength and the second CL spectrum obtained by averaging two CL spectra with a wavelength distribution close to a long wavelength are classified and shown for each measurement area (a to f).

[0204] Since the separation distance between the two ends of the 10 electron beam centers in each measurement area (a to f) is 450 nm, both the first Ga-rich region 21a and the n-type main region 21b exist in the 10 irradiation areas. Since the volume ratio of the first Ga-rich region 21a occupying the entire n-type cladding layer 21 is small, the first CL spectrum mainly shows the CL spectrum of the n-type main region 21b. On the other hand, although the second CL spectrum includes the CL spectrum of the first Ga-rich region 21a, since the width of the cross section perpendicular to the extension direction of the first Ga-rich region 21a is about 20 nm on average, the n-type main region 21b is partially included in the irradiation range of the beam diameter of 50 nm. Therefore, the second CL spectrum becomes a composite spectrum of the CL spectrum of the first Ga-rich region 21a and the CL spectrum of the n-type main region 21b. However, even when the center of each electron beam of the two CL spectra with wavelength distribution close to the long wavelength is located in the middle of the width direction of the 1st Ga-rich region 21a, the electron beam in the central part of the irradiation range is concentrated on the 1st Ga-rich region 21a with a low energy level, and there is a high possibility that the 1st Ga-rich region 21a is specifically excited, and the second CL spectrum mainly shows the CL spectrum of the 1st Ga-rich region 21a.

[0205] Here, the reason for setting the first CL spectrum as the average of two CL spectra with wavelength distribution close to the short wavelength and setting the second CL spectrum as the average of two CL spectra with wavelength distribution close to the long wavelength is that the irradiation position of the electron beam in each measurement area is randomly set, and the irradiation range of each CL spectrum close to the shortest wavelength and close to the long wavelength is different in each measurement area. Considering that the measurement results in each measurement area vary greatly, or it is difficult to select each CL spectrum close to the shortest wavelength and close to the long wavelength, in order to suppress the unevenness of each measurement area, two CL spectra with wavelength distribution close to the short wavelength and close to the long wavelength are mechanically selected to obtain an average.

[0206] First, the first CL spectrum of each measurement area (a~f) is studied. In the measurement area a, the high plateau-shaped peak area of ​​the emission wavelength extends to the range of about 247nm~about 255nm. In the measurement area b, the relaxation peak of the emission wavelength exists near about 252nm, and the existence of fluctuations is confirmed near about 247nm and about 254nm on both sides of the peak wavelength. In the measurement area c, the relaxation peak of the emission wavelength exists near about 245nm~248nm. In the measurement area d, the relaxation peak of the emission wavelength exists near about 247nm. In the measurement area e, the peak of the emission wavelength exists near about 248nm. In the measurement area f, the peak of the emission wavelength exists near about 244nm, and the high plateau-shaped peak area of ​​the emission wavelength extends to the range of about 242nm~245nm.

[0207] The peak wavelength and fluctuation of about 247 nm to about 248 nm in the measurement regions a to e are equivalent to about 69% to about 70% when converted into AlN mole fraction. If the measurement error of about ±3% when converted into AlN mole fraction is taken into account, the CL wavelength of the first CL spectrum and the average AlN mole fraction Xb ( The target value is 70%).

[0208] In addition, in the first CL spectra of the measurement areas a to e, the long-wavelength components of about 247 nm to about 248 nm or more are more than the short-wavelength components that are insufficient for the wavelength, and it is known that the mass transfer of Ga occurs in the two irradiation ranges of the first CL spectra corresponding to the measurement areas (a to e). Furthermore, when the peak wavelength of about 252 nm to about 255 nm of the first CL spectra of the measurement areas a and b is converted into the AlN mole fraction, it is equivalent to about 65% to about 67%, and it is known that it overlaps with the CL wavelength (about 253 nm) from the quasi-stable n-type region with an AlN mole fraction of 66.7% existing in the first Ga-enriched region 21a, and the first Ga-enriched region 21a formed by the mass transfer of Ga is included in a part of the two irradiation ranges of the first CL spectra corresponding to the measurement areas a and b.

[0209] When the peak wavelength of about 244 nm in the measurement region f is converted into AlN mole fraction, it is equivalent to about 72%, which is higher than the average AlN mole fraction Xb ( However, considering the measurement error of about ±3% in terms of AlN mole fraction, the value is roughly within the variation range of the AlN mole fraction assumed in the n-type body region 21b.

[0210] Next, the second CL spectrum of each measurement area (a~f) was studied. In measurement area a, the peak of the emission wavelength exists near about 252nm. In measurement area b, the peak of the emission wavelength exists near about 253nm. In measurement area c, the relaxation peak of the emission wavelength exists near about 251nm~252nm. In measurement area d, the peak of the emission wavelength exists near about 252nm. In measurement area e, the high-plateau peak area of ​​the emission wavelength extends to the range of about 249nm~about 252nm. In measurement area f, the relaxation peak of the emission wavelength exists near about 247nm~249nm, and the existence of fluctuations is confirmed near about 244nm and about 252nm on both sides of the peak wavelength.

[0211] The peak wavelength of about 252nm to about 253nm in the measurement regions a to e is equivalent to about 66.7% to about 67% when converted into AlN mole fraction. If the measurement error of about ±3% in terms of conversion into AlN mole fraction is taken into account, it is consistent with the CL wavelength (about 253nm) corresponding to the quasi-stable n-type region with an AlN mole fraction of 66.7% existing in the first Ga-rich region 21a. In addition, the wavelength of about 249nm in the high-table peak region of the measurement region e is equivalent to about 69% when converted into AlN mole fraction. If the measurement error of about ±3% in terms of conversion into AlN mole fraction is taken into account, it is consistent with the average AlN mole fraction Xb ( The peak wavelength of the measurement region f at about 247 nm to 249 nm includes the average AlN mole fraction Xb ( The CL wavelength (about 248 nm) of the target value (70%) fluctuates at about 252 nm, which is roughly consistent with the CL wavelength (about 253 nm) corresponding to the quasi-stable n-type region.

[0212] Depend on Fig.13 As can be seen from the above description, each second CL spectrum of the measurement areas a to f is shown as a composite spectrum of the CL spectra of the quasi-stable n-type region and the quasi-stable nearby n-type region with a slightly higher AlN mole fraction than the quasi-stable n-type region in the first Ga-rich region 21a, and the CL spectrum of the n-type main region 21b. In the measurement areas a to d, the proportion of the CL spectrum of the n-type main region 21b in the composite spectrum is small. On the other hand, in the measurement area e, the proportion of the CL spectrum of the n-type main region 21b in the composite spectrum is larger than that in the measurement areas a to d, and is equivalent to the proportion of the CL spectrum of the quasi-stable n-type region, and further, in the measurement area f, it is larger than that in the measurement area e.

[0213] Above, through Fig.13 The first CL spectra of each measurement area a to f shown in the figure show that the AlN mole fraction of the n-type main region 21b is almost consistent with the target value of 70% of the AlN mole fraction of the n-type cladding layer 21. In addition, the second CL spectra of each measurement area a to f show that in the first Ga-rich region 21a, while including a quasi-stable n-type region with an AlN mole fraction of 66.7%, there is also a quasi-stable near n-type region with an AlN mole fraction higher than that of the quasi-stable n-type region. Fig.13 The analysis results shown in the first and second CL spectra of each measurement area a to f are different from those shown in FIG. Figures 11A to 11F The results of the EDX analysis are quite consistent with those of the

[0214] However, from Fig.13The second CL spectra of each measurement area a~f shown in the figure show that the existence ratio of the quasi-stable n-type region within the first Ga-rich region 21a tends to vary depending on the location within the n-type cladding layer 21, but since there are still many uncertain parts, a detailed review is omitted.

[0215] Here, even if the existence ratio of the quasi-stable n-type region in the region close to the AlN layer 12 in the n-type cladding layer 21 becomes smaller, the effect of the present invention does not necessarily decrease. As described above, the carriers (electrons) in the n-type cladding layer 21 are locally distributed in the first Ga-rich region 21a, and in the n-type cladding layer 21, the current preferentially and stably flows into the first Ga-rich region, which can achieve the suppression of the characteristic variation of the light-emitting element. However, since the active layer 22 in the light-emitting region is located on the upper side of the n-type cladding layer 21, the effect of the above-mentioned local distribution becomes obvious near the upper surface in contact with the active layer 22 of the n-type cladding layer 21. Therefore, in the region close to the AlN layer 12 in the n-type cladding layer 21, even if the above-mentioned local distribution is insufficient, the characteristic variation of the light-emitting element can be suppressed. In addition, Figure 4 In the device structure shown, since more forward current flows to the upper layer side than to the lower layer side in the n-type cladding layer 21 , the influence of the above-mentioned local insufficient distribution hardly exists in the region close to the AlN layer 12 in the n-type cladding layer 21 .

[0216] However, no Figures 11A to 11F and Fig.13 Composition analysis based on the EDX method and the CL method is shown. Since the film thickness of the well layer 220 is extremely thin, ranging from 2 to 7 unit cells, it is basically not suitable for composition analysis based on the EDX method. On the other hand, the part that needs to be paid attention to in the measurement of the CL spectrum of the well layer 220 is different from the composition analysis based on the CL method of the n-type cladding layer 21. The AlN mole fraction of the barrier layer 221, the n-type cladding layer 21, and the electron blocking layer adjacent to the well layer 220 is about 17% higher than the AlN mole fraction (50% or 41.7%) of the inclined region BA (the second Ga-rich region 220a) of the well layer 220. For this reason, the beam diameter of the electron beam irradiated toward the inclined region BA of the well layer 220 is as large as 50nm, and the high-energy electrons in the center of the electron beam are concentrated in the inclined region BA of the well layer 220 with a low energy state, so that the emission wavelength of the inclined region BA of the well layer 220 can be accurately measured using the CL method.

[0217] [Second embodiment]

[0218] In the above-mentioned first embodiment, when the barrier layer 221 is composed of an AlGaN-based semiconductor whose AlN mole fraction is not 100%, as an example, the overall AlN mole fraction of the barrier layer 221 including the third Ga-rich region 221a is made within the range of 66.7% to 90%, and the AlN mole fraction of the barrier main region 221b is made within the range of 68% to 90%. In order to ensure the local distribution effect of carriers in the third Ga-rich region 221a, the difference in AlN mole fractions between the third Ga-rich region 221a and the barrier main region 221b is made greater than 1%.

[0219] In the second embodiment, similarly to the first Ga-rich region 21a of the n-type cladding layer 21 and the second Ga-rich region 220a of the well layer 220 in the first embodiment, the third Ga-rich region 221a of the barrier layer 221 is preferably composed of the first or second quasi-stable AlGaN. Here, since the AlN mole fraction of the barrier layer 221 as a whole is within the range of 66.7% to 90%, the first quasi-stable AlGaN applicable to the third Ga-rich region 221a is Al2Ga1N3 or Al5Ga1N6 in which the AlGaN composition ratio is an integer ratio. In addition, it is considered that Al3Ga1N4 of the second quasi-stable AlGaN can also be applied to the third Ga-rich region 221a. However, the Al content of the second quasi-stable AlGaN is not necessarily greater than 90%. 11 Ga1N 12 Since the Al composition ratio is too high, the easily mobile Ga enters the symmetrically arranged part, and the large amount of Al enters the random part. The possibility that the atomic arrangement of Al and Ga cannot be symmetrically arranged increases. The atomic arrangement of Al and Ga is close to a random state, and the above-mentioned stability is reduced, so it is difficult to apply it to the third Ga-enriched region 221a.

[0220] However, Figure 6 and Figure 7 In the simulation results of the emission wavelength of the well layer 220 shown, the AlN molar fraction of the third Ga-rich region 221a of the barrier layer 221 is assumed to be 66.7%, 75% and 83.3%, but these situations are equivalent to the AlN molar fraction of quasi-stable AlGaN with AlGaN composition ratios of Al2Ga1N3, Al3Ga1N4, and Al5Ga1N6.

[0221] When the third Ga-rich region 221a is composed of quasi-stable AlGaN Al2Ga1N3, Al3Ga1N4, and Al5Ga1N6, the AlN mole fraction of the barrier body region 221b preferably corresponds to the three kinds of AlN mole fractions of the third Ga-rich region 221a, and is in the range of 68% to 74%, 76% to 82%, or 85% to 90%. Here, when the third Ga-rich region 221a is composed of quasi-stable AlGaN Al5Ga1N6, in order to prevent the AlN with low stability from 11 Ga1N l2 The AlN and AlN molecules are randomly mixed and preferably the AlN molar fraction of the barrier body region 221 b is set to not more than 90%.

[0222] The manufacturing method of the 3rd Ga-rich region 221a and the barrier main region 221b of the barrier layer 221 is as described above. The barrier layer 221 is grown under growth conditions that easily expose a multi-step platform, using the same method as the n-type cladding layer 21, with the AlN mole fraction set for the barrier main region 221b as the target value.

[0223] When Al2Ga1N3 as the first quasi-stable AlGaN is grown in the third Ga-rich region 221a, the target value Xd of the AlN mole fraction of the barrier layer 221 is set within the range of 68% to 74%. Similarly, when Al3Ga1N4 as the second quasi-stable AlGaN is grown in the third Ga-rich region 221a, the target value Xd of the AlN mole fraction of the barrier layer 221 is set within the range of 76% to 82%, and when Al5Ga1N6 as the first quasi-stable AlGaN is grown in the third Ga-rich region 221a, the target value Xd of the AlN mole fraction of the barrier layer 221 is set within the range of 85% to 90%.

[0224] Therefore, the target value Xd of the AlN mole fraction of the barrier layer 221 is set to be higher than the AlN mole fraction of the quasi-stable AlGaN (target standard stable AlGaN) formed in the third Ga-rich region 221a by 1% or more and less than the AlN mole fraction of the nearest quasi-stable AlGaN larger than the AlN mole fraction of the target standard stable AlGaN. For this reason, similarly to the first Ga-rich region 21a of the n-type cladding layer 21, along with the stable formation of the target standard stable AlGaN in the third Ga-rich region 221a, the difference in AlN mole fraction between the third Ga-rich region 221a and the barrier body region 221b is ensured to be 1% or more, and the carriers in the barrier layer 221 are locally distributed in the third Ga-rich region 221a having a smaller band gap energy than the barrier body region 221b.

[0225] By forming the third Ga-rich region 221a with highly stable quasi-stable AlGaN, the variation of the mixed crystal mole fraction caused by drift of the crystal growth device is suppressed, and the third Ga-rich region 221a that generates local distribution of carriers in the barrier layer 221 is stably formed with an AlN mole fraction corresponding to the quasi-stable AlGaN used. As a result, in the barrier layer 221, as in the n-type cladding layer 21, the current preferentially and stably flows into the third Ga-rich region 221a, and the variation of the characteristics of the light-emitting element 1 can be further suppressed.

[0226] [Other embodiments]

[0227] Hereinafter, modified examples of the above-mentioned first and second embodiments will be described.

[0228] (1) In the first and second embodiments described above, the active layer 22 is assumed to be composed of a multi-quantum well structure in which two or more well layers 220 composed of AlGaN-based semiconductors and one or more barrier layers 221 composed of AlGaN-based semiconductors or AlN-based semiconductors are alternately stacked. However, the active layer 22 may be a single quantum well structure in which the well layer 220 is only one layer, and may not have a barrier layer 221 (quantum barrier layer). It is also clear that the effect of the n-type cladding layer 21 used in the above-mentioned embodiments can be exerted in the relevant single quantum well structure.

[0229] (2) In the above embodiment, as an example of the growth conditions of the n-type cladding layer 21, the supply amount and flow rate of the raw material gas or carrier gas used in the organic metal compound vapor deposition method are set according to the average AlN mole fraction of the entire n-type AlGaN layer constituting the n-type cladding layer 21. That is, when the average AlN mole fraction of the entire n-type cladding layer 21 is set to a constant value in the vertical direction, it is assumed that the supply amount and flow rate of the above-mentioned raw material gas, etc. are controlled to be constant. However, the supply amount and flow rate of the above-mentioned raw material gas, etc. do not necessarily have to be controlled to be constant.

[0230] (3) In the above embodiment, the plan view shape of the first region R1 and the p-electrode 26 is a comb shape as an example, but the plan view shape is not limited to the comb shape. Alternatively, a plurality of first regions R1 may exist and each of them may be surrounded by one second region R2.

[0231] (4) In the above-mentioned embodiment, although a sapphire substrate 11 having a main surface with an off-angle relative to the (0001) plane is used, and a base portion 10 with a multi-step platform exposed on the surface of the AlN layer 12 is used, the size of the off-angle or the direction of setting the off-angle (specifically, the direction of the inclined (0001) plane, such as the m-axis direction or the a-axis direction, etc.) can be arbitrarily determined as long as the growth starting point of the first Ga-rich region 21a is formed so as to expose the multi-step platform on the surface of the AlN layer 12.

[0232] (5) In the above embodiment, as the light emitting element 1, Figure 1 As illustrated, the light emitting element 1 having the base 10 including the sapphire substrate 11 is illustrated, but the sapphire substrate 11 (and a part or all of the layers included in the base 10) can be removed by lift-off, etc. In addition, the substrate constituting the base 10 is not limited to a sapphire substrate.

[0233] -Industrial Availability-

[0234] The present invention can be used for a nitride semiconductor ultraviolet light emitting element having a light emitting element structure in which an n-type layer, an active layer, and a p-type layer including an AlGaN-based semiconductor having a wurtzite structure are stacked in the vertical direction.

[0235] -Explanation of symbols-

[0236] 1: Nitride semiconductor ultraviolet light emitting element

[0237] 10: Base

[0238] 11: Sapphire substrate

[0239] 11a: Main surface of sapphire substrate

[0240] 12: AlN layer

[0241] 20: Light-emitting element structure

[0242] 21: n-type cladding layer (n-type layer)

[0243] 21a: 1st Ga-rich region (n-type layer)

[0244] 21b: n-type main region (n-type layer)

[0245] 22: Active layer

[0246] 220: Well layer

[0247] 220a: 2Ga-enriched region

[0248] 220b: Well body area

[0249] 221: Barrier layer

[0250] 221a: 3Ga-enriched region

[0251] 221b: Barrier main area

[0252] 23: Electron blocking layer (p-type layer)

[0253] 24: p-type cladding layer (p-type layer)

[0254] 25: p-type contact layer (p-type layer)

[0255] 26: p electrode

[0256] 27: n electrode

[0257] 100: Substrate

[0258] 101: AlGaN-based semiconductor layer

[0259] 102: Template

[0260] 103: n-type AlGaN semiconductor layer

[0261] 104: Active layer

[0262] 105: p-type AlGaN semiconductor layer

[0263] 106: p-type contact layer

[0264] 107: n electrode

[0265] 108: p electrode

[0266] BL: Boundary between area 1 and area 2

[0267] BA: Boundary area (sloping area)

[0268] R1: Area 1

[0269] R2: Area 2

[0270] T: Platform

[0271] TA: Platform area.

Claims

1. A nitride semiconductor ultraviolet light emitting element, comprising a light emitting element structure in which an n-type layer, an active layer and a p-type layer of an AlGaN-based semiconductor having a wurtzite structure are stacked in a vertical direction, The nitride semiconductor ultraviolet light emitting element is characterized in that: The n-type layer is composed of n-type AlGaN-based semiconductor, The active layer disposed between the n-type layer and the p-type layer has a quantum well structure including one or more well layers composed of an AlGaN-based semiconductor. The p-type layer is composed of a p-type AlGaN-based semiconductor. The n-type layer and each semiconductor layer in the active layer are epitaxial growth layers having surfaces with multi-step terraces parallel to the (0001) plane. The n-type layer has a plurality of first Ga-rich regions, each of which is a layered region evenly dispersed in the n-type layer and having a locally low AlN mole fraction and includes an n-type AlGaN region of Al2Ga1N3 in which an AlGaN composition ratio is an integer ratio, Each extension direction of the first Ga-rich region on a first plane orthogonal to the upper surface of the n-type layer is inclined relative to an intersection line between the upper surface of the n-type layer and the first plane, The boundary region between adjacent terraces of the multi-step terraces of the well layer has a second Ga-rich region where the AlN mole fraction is locally low in the well layer. In the second Ga-rich region, there is Al1Ga1N2 or Al5Ga7N with an AlGaN composition ratio of an integer ratio. 12 AlGaN region.

2. The nitride semiconductor ultraviolet light emitting element according to claim 1, characterized in that: The AlN mole fraction of the n-type body region outside the layered region in the n-type layer is in the range of 69% to 74%.

3. The nitride semiconductor ultraviolet light emitting element according to claim 1 or 2, characterized in that: In the second Ga-rich region, there is an AlGaN region of Al1Ga1N2 in which the AlGaN composition ratio is an integer ratio. The AlN mole fraction of the well layer outside the boundary region is in a range of 51% to 54%.

4. The nitride semiconductor ultraviolet light emitting element according to claim 1 or 2, characterized in that: In the second Ga-rich region, there is Al5Ga7N with an integer AlGaN composition ratio. 12 AlGaN region, The AlN mole fraction of the well layer outside the boundary region is in a range of 42% to 45%.

5. The nitride semiconductor ultraviolet light emitting element according to claim 1 or 2, characterized in that: The active layer has a multi-quantum well structure including two or more well layers. A barrier layer made of an AlGaN-based semiconductor exists between the two well layers.

6. The nitride semiconductor ultraviolet light emitting element according to claim 5, characterized in that: The barrier layer is composed of AlGaN-based semiconductor. At least the barrier layer closest to the p-type layer among the barrier layers between the two well layers has a third Ga-rich region where the AlN mole fraction is locally low in the barrier layer, at a boundary region between adjacent terraces of the multi-stepped terraces.

7. The nitride semiconductor ultraviolet light emitting element according to claim 6, characterized in that: In the third Ga-rich region of the barrier layer, there exists an AlGaN region of Al2Ga1N3, Al3Ga1N4 or Al5Ga1N6 in which the AlGaN composition ratio is an integer ratio.

8. The nitride semiconductor ultraviolet light emitting element according to claim 1 or 2, characterized in that: The invention also comprises a base portion including a sapphire substrate, The sapphire substrate has a main surface that is inclined at a given angle relative to the (0001) plane, and the light emitting element structure is formed on the main surface. At least each semiconductor layer from the main surface of the sapphire substrate to the surface of the active layer is an epitaxial growth layer having a surface on which multi-step terraces parallel to the (0001) plane are formed.

9. A method for manufacturing a nitride semiconductor ultraviolet light emitting element, the nitride semiconductor ultraviolet light emitting element comprising a light emitting element structure in which an n-type layer, an active layer, and a p-type layer including an AlGaN semiconductor having a wurtzite structure are stacked in a vertical direction, The method for manufacturing the nitride semiconductor ultraviolet light emitting element is characterized by comprising: A first step of epitaxially growing the n-type layer of an n-type AlGaN-based semiconductor on a base portion including a sapphire substrate having a primary surface tilted at a predetermined angle relative to the (0001) plane, such that multi-step terraces parallel to the (0001) plane are exposed on the surface of the n-type layer; A second step of epitaxially growing the active layer of a quantum well structure including a well layer composed of one or more AlGaN-based semiconductor layers on the n-type layer so that multi-step terraces parallel to the (0001) plane are exposed on the surface of the well layer; and A third step of forming the p-type layer of a p-type AlGaN-based semiconductor on the active layer by epitaxial growth; In the first step, a plurality of first Ga-rich regions are grown extending obliquely upward, the first Ga-rich regions being layered regions with locally low AlN mole fractions evenly dispersed in the n-type layer and containing n-type AlGaN regions of Al2Ga1N3 with an AlGaN composition ratio in an integer ratio, In the second step, a second Ga-rich region having a locally low AlN mole fraction is formed in the well layer at a boundary region between adjacent terraces of the multi-step terraces of the well layer, and Al1Ga1N2 or Al5Ga7N2 having an AlGaN composition ratio of an integer ratio is formed in the second Ga-rich region. 12 The AlGaN region is grown.

10. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 9, characterized in that: In the first step, the target value of the AlN mole fraction of the n-type layer is set within a range of 69% to 74%, and an n-type AlGaN region of Al2Ga1N3 having an AlGaN composition ratio of an integer ratio is grown in the first Ga-rich region.

11. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 9 or 10, characterized in that: In the second step, the target value of the AlN mole fraction of the well layer is set within a range of 51% to 54%, and an AlGaN region of Al1Ga1N2 having an AlGaN composition ratio of an integer ratio is grown in the second Ga-rich region.

12. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 9 or 10, characterized in that: In the second step, the target value of the AlN mole fraction of the well layer is set within a range of 42% to 45%, and the AlGaN composition ratio in the second Ga-rich region is made an integer ratio of Al5Ga7N 12 The AlGaN region is grown.

13. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 9 or 10, characterized in that: In the second step, the well layer composed of AlGaN-based semiconductors and the barrier layer composed of AlGaN-based semiconductors are alternately stacked by epitaxial growth, thereby forming an active layer with a multi-quantum well structure in which multi-stepped platforms parallel to the (0001) plane are exposed on the surfaces of the barrier layer and the well layer and the active layer includes more than two well layers.

14. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 13, characterized in that: In the second step, when the barrier layer composed of AlGaN-based semiconductor is formed, a third Ga-rich region in which the AlN molar fraction is locally low is formed in the boundary area between the terraces of at least the barrier layer closest to the p-type layer among the barrier layers located between the two well layers.

15. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 14, characterized in that: In the second step, 1) setting the target value of the AlN mole fraction of the barrier layer within the range of 68% to 74%, and growing an AlGaN region of Al2Ga1N3 with an AlGaN composition ratio of an integer ratio in the third Ga-rich region; or 2) setting the target value of the AlN mole fraction of the barrier layer within the range of 76% to 82%, and growing an AlGaN region of Al3Ga1N4 with an AlGaN composition ratio of an integer ratio in the third Ga-rich region; or 3) The target value of the AlN mole fraction of the barrier layer is set within a range of 85% to 90%, and an AlGaN region of Al5Ga1N6 having an AlGaN composition ratio of an integer ratio is grown in the third Ga-rich region.

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