Nitride semiconductor ultraviolet light emitting element

Abstract

The nitride semiconductor ultraviolet light-emitting element has a light-emitting element structure portion in which an n-type layer, an active layer, and a p-type layer including a wurtzite-structured AlGaN-based semiconductor are stacked in the vertical direction. The peak emission wavelength is in the range of 300 nm to 327 nm. The n-type layer is composed of an n-type AlGaN-based semiconductor and includes one or more well layers composed of a GaN-based semiconductor. The p-type layer is composed of a p-type AlGaN-based semiconductor. Each semiconductor layer in the n-type layer and the active layer is an epitaxial growth layer having a surface formed with a multi-step terrace parallel to the (0001) plane. The n-type layer has a plurality of first Ga-rich regions including n-type AlGaN regions containing Al1Ga1N2 in which the AlGaN composition ratio is an integer ratio. The first Ga-rich regions are layered regions with a locally low AlN mole fraction that are evenly dispersed in the n-type layer. The AlN mole fraction in the n-type main region other than the layered regions in the n-type layer is in the range of 54% to 66%.

Description

[0001] Technical Area

[0002] The present invention relates to a nitride semiconductor ultraviolet light emitting element having a peak emission wavelength in the range of 300nm to 327nm and comprising a light emitting element structure having an n-type layer, an active layer and a p-type layer of an AlGaN-based semiconductor having a wurtzite structure stacked in the vertical direction. 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. 1-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.13The 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.13 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 AlxGal-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 due to drift of a crystal growth apparatus etc. is suppressed and which can be stably produced.

[0021] -Methods for solving technical problems-

[0022] In order to achieve the above-mentioned object, the present invention provides 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 and having a peak emission wavelength in the range of 300nm to 327nm, characterized in that:

[0023] The n-type layer is composed of 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 composed of a GaN-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 in which the AlN mole fraction is locally low and is evenly dispersed in the n-type layer and contains AlGaN having an integer composition ratio. 1 Ga 1 N 2 n-type AlGaN region,

[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 AlN mole fraction of the n-type body region other than the layered region in the n-type layer is in the range of 54% to 66%.

[0030] Furthermore, 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 configured to include 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 an up-and-down direction, and the peak emission wavelength is within a range of 300 nm to 327 nm, wherein the manufacturing method is characterized by:

[0031] 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;

[0032] A second step of epitaxially growing the active layer of a quantum well structure including a well layer composed of one or more GaN-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

[0033] a third step of forming the p-type layer of a p-type AlGaN-based semiconductor on the active layer by epitaxial growth,

[0034] In the first step, the target value of the AlN mole fraction of the n-type layer is set within a range of 54% to 66%, and a plurality of first Ga-rich regions are grown extending obliquely upward, the first Ga-rich regions being layered regions evenly dispersed in the n-type layer, having a locally low AlN mole fraction and containing AlGaN having an integer composition ratio. 1 Ga 1 N 2 n-type AlGaN region.

[0035] 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.

[0036] 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.

[0037] 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 first utilizing the quasi-stable AlGaN described later formed in the first Ga-rich region of the n-type layer and second utilizing the well layer composed of GaN semiconductor, the characteristic fluctuation caused by drift of the crystal growth device, etc., can be suppressed, and it can be expected that the nitride semiconductor ultraviolet light-emitting element with a peak emission wavelength in the range of 300nm to 327nm can be stably produced.

[0038] First, “quasi-stable AlGaN” represented by a given integer ratio of AlGaN composition ratio will be described.

[0039] 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, since the covalent bond radius of Al and Ga is different, the one with a higher symmetry of the atomic arrangement of Al and Ga in the crystal structure generally becomes a stable structure.

[0040] 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.

[0041] In this periodic symmetrical arrangement structure, only a slight increase in the amount of Ga supplied to the crystal growth surface can achieve an energetically stable mixed crystal mole fraction due to high symmetry, which can prevent the proliferation of places where Ga is extremely increased, which is prone to 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 due to drift of the crystal growth device, the change in the mixed crystal mole fraction in 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.

[0042] Next, the composition ratio of AlGaN in which Al and Ga are arranged periodically and symmetrically in the (0001) plane will be described.

[0043] 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.

[0044] 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 illustrated. 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 atoms (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 atoms (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.

[0045] Figure 2 The 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.

[0046] 1) Al 1 Ga 5 N 6 ,

[0047] 2) Al 2 Ga 4 N 6 (=Al 1 Ga 2 N 3 ),

[0048] 3) Al 3 Ga 3 N 6 (=Al 1 Ga1 N 2 ),

[0049] 4) Al 4 Ga 2 N 6 (=Al 2 Ga 1 N 3 ),

[0050] 5)Al 5 Ga 1 N 6 .

[0051] 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.

[0052] for Figure 3 Al shown in (A) 1 Ga 5 N 6 When Ga is arranged at the six vertices of the A3 surface, the six vertices of the B3 surface, and one central portion, and Al is arranged at one central portion of the A3 surface.

[0053] Figure 3 (B) shows Al 1 Ga 2 N 3 When Ga is arranged at three vertices and one central portion of the A3 and B3 surfaces, Al is arranged at three vertices of the A3 and B3 surfaces.

[0054] for Figure 3 Al shown in (C) 1 Ga 1 N 2 When Ga is arranged at the three vertices and one center portion of the A3 surface and the three vertices of the B3 surface, Al is arranged at the three vertices of the A3 surface and the three vertices and one center portion of the B3 surface.

[0055] for Figure 3 (D) shows Al 2 Ga 1 N 3 When , 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 (B) shows Al 1 Ga 2 N 3 The positions of Al and Ga at that time.

[0056] for Figure 3 Al shown in (E) 5 Ga 1 N 6 When , Ga is placed at the center of the A3 surface, and Al is placed at the six vertices of the A3 surface and the six vertices and one center of the B3 surface. Figure 3 Al shown in (A) 1 Ga 5 N 6 The positions of Al and Ga at that time.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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 x1 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.

[0061] 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.

[0062] 6) Al 1 Ga 11 N 12 (=GaN+Al 1 Ga 5 N 6 ),

[0063] 7) Al 3 Ga 9 N 12 (=Al 1 Ga 3 N 4 =Al 1 Ga 5 N 6 +Al 1 Ga 2 N 3 ),

[0064] 8) Al 5 Ga 7 N 12 (=Al 1 Ga 2 N 3 +Al 1 Ga 1 N 2 ),

[0065] 9)Al 7 Ga 5 N 12 (=Al 1 Ga 1 N 2 +Al 2 Ga 1 N 3 ),

[0066] 10) Al 9 Ga 3 N 12 (=Al 3 Ga 1 N 4 =Al 2 Ga 1 N3 +Al 5 Ga 1 N 6 ),

[0067] 11) Al 11 Ga 1 N 12 (=Al 5 Ga 1 N 6 +AlN).

[0068] 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 -x2 N 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".

[0069] 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.

[0070] Therefore, even for quasi-stable AlGaN, the Al 1 Ga 5 N 6 、Al in 6) above 1 Ga 11 N 12 , and Al in 7) above 1 Ga 3 N 4The AlN mole fraction 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.

[0071] Next, the "first Ga-rich region" will be explained. In the nitride semiconductor ultraviolet light-emitting element and the method for manufacturing the nitride semiconductor ultraviolet light-emitting element having the above characteristics, the n-type layer and each semiconductor layer in the active layer are epitaxially grown layers having a surface forming a multi-stepped platform parallel to the (0001) plane. Therefore, 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 molar fraction than the platform region. This boundary region extends obliquely upward relative to the (0001) plane along with the epitaxial growth of the n-type AlGaN layer of the n-type layer, and layered regions with locally low AlN molar fractions are evenly dispersed in the n-type layer. Here, when the mass movement of Ga is large enough, the layered region becomes a region containing AlGaN with a composition ratio of AlN of AlGaN of AlGaN of AlGaN of AlGaN. 1 Ga 1 N 2 The first Ga-rich region of the n-type AlGaN region of the quasi-stable AlGaN.

[0072] Specifically, since the AlN mole fraction of the n-type body region of the n-type layer (approximately the target value of the AlN mole fraction of the n-type layer) is in the range of 54% to 66%, the closest quasi-stable AlGaN that can be included in the layered region formed by the mass migration of Ga from the n-type body region is the AlGaN composition ratio of Al 1 Ga 1 N 2 The difference between the AlN mole fractions in the n-type main region and the layered region is 5% or more. Therefore, in the n-type layer, the mass transfer of Ga is large enough to stably form a layer containing AlGaN with a composition ratio of Al 1 Ga 1 N 2 The first Ga-rich region is the first Ga-rich region of the n-type AlGaN region of the quasi-stable AlGaN. That is, the first Ga-rich region is mainly present in the layered region, and as a result, it is evenly dispersed in the n-type layer. Since the crystal growth of AlGaN is a random process, the mass transfer amount of Ga also varies randomly. Therefore, in the layered region, there is no AlGaN composition ratio of Al 1 Ga 1 N 2 An n-type AlGaN region of quasi-stable AlGaN, that is, a region where the AlN mole fraction is locally low and the AlN mole fraction is greater than 50%, is formed.

[0073] In the first Ga-rich region, due to the presence of AlGaN with a composition ratio of Al 1 Ga 1 N 2 The quasi-stable AlGaN in the first Ga-rich region absorbs the change in the Ga supply in the first Ga-rich region. That is, in the first Ga-rich region, when the Ga supply increases, the quasi-stable AlGaN increases, and when the Ga supply decreases, the quasi-stable AlGaN decreases. As a result, the change in the AlN mole fraction in the first Ga-rich region is suppressed. Therefore, in the first Ga-rich region, the change in the Ga supply caused by the drift of the crystal growth device is absorbed, and the AlGaN composition ratio is stably formed. 1 Ga 1 N 2 That is, the variation of the AlN mole fraction in the first Ga-rich region can be suppressed with respect to the variation of the Ga supply amount.

[0074] As mentioned above, in the crystal growth of AlGaN, a random asymmetric arrangement state and a regular symmetric arrangement state can usually coexist. Therefore, in the first Ga-rich region, a region of quasi-stable AlGaN with a regular symmetric arrangement state of 50% AlN mole fraction is stably formed, and a region where the AlN mole fraction varies slightly from 50% (for example, 0 to 3%) is mixed. Therefore, the AlN mole fraction in the first Ga-rich region is concentrated in the region where the AlGaN composition ratio is Al 1 Ga 1 N 2 Near the AlN mole fraction (50%) of the quasi-stable AlGaN.

[0075] In addition, since the AlN mole fraction of the n-type main region of the n-type layer is within the range of 54% to 66%, the difference in AlN mole fraction between the first Ga-rich region and the n-type main region is stably maintained at 4% or more. Therefore, the carriers in the n-type layer are locally distributed 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 flow preferentially and stably into the first Ga-rich region, thereby suppressing the characteristic variation of the nitride semiconductor ultraviolet light-emitting element. However, as described above, since a region having an AlN mole fraction greater than 50% but having a locally low AlN mole fraction that does not reach the first Ga-rich region is also formed in a part of the layered region, when the difference in AlN mole fraction between this region and the n-type main region is 4% or more, the carriers in the n-type layer are also fully locally distributed in this region, and the current can flow in this region in the same manner as in the first Ga-rich region.

[0076] Next, the "well layer" is explained. Since the n-type layer and each semiconductor layer in the active layer have an epitaxial growth layer on the surface of a multi-step platform parallel to the (0001) plane, the boundary area between adjacent platforms of the multi-step platform of the well layer becomes an inclined area inclined relative to the (0001) plane connecting the adjacent platforms (refer to the above-mentioned non-patent documents 1 and 2). However, this inclined area 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 terrace surface of the stepped (0001) plane and the multi-step platform exposed in the inclined area.

[0077] 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. As a result, the band gap energy of the inclined region is smaller than that of the terrace region, and it is easy to produce local distribution of carriers, just like the first Ga-rich region of the n-type layer. For this reason, the luminescence of the well layer becomes more significant in the inclined region than in the terrace region. The above-mentioned non-patent documents 1 and 2 report the same content for the well layer of AlGaN-based semiconductors. However, in addition to the above-mentioned film thickness modulation, the well layer of the AlGaN-based semiconductor also produces composition modulation, and the band gap energy is smaller than that of the terrace region. The same local distribution of carriers is produced in the well layer of the GaN-based semiconductor that does not produce composition modulation. However, each terrace region of the well layer and the barrier layer is a region sandwiched by the terrace on the upper surface and the terrace on the lower surface of each layer in the c-axis direction. Therefore, the region outside each terrace region of the well layer and the barrier layer becomes the boundary region (inclined region) of each layer.

[0078] 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.

[0079] 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 50% is stably formed, which can stably supply carriers to the inclined region of the well layer, thereby suppressing the variation in the characteristics of the nitride semiconductor ultraviolet light-emitting element.

[0080] In addition, since the upper limit of the AlN mole fraction of the n-type body region of the n-type layer and the upper limit of the target value of the AlN mole fraction of the n-type layer are set to 66%, the AlGaN composition ratio of Al2O3 is not dominantly formed in the n-type layer. 2 Ga 1 N 3If the upper limit is 67% or more, AlGaN is stably formed in the n-type main region. 2 Ga 1 N 3 Quasi-stable AlGaN is difficult to form in the first Ga-rich region. 2 Ga 1 N 3 The quasi-stable AlGaN is fully supplied for the stable formation of Al 1 Ga 1 N 2 The Ga in the quasi-stable AlGaN causes the AlN mole fraction of the n-type AlGaN-based semiconductor formed in the first Ga-rich region to vary randomly, and the desired effect cannot be achieved.

[0081] Furthermore, since the AlN molar fraction of almost the entire n-type layer is above 50%, ultraviolet light with a peak emission wavelength of 300nm to 327nm emitted in the well layer of the active layer passes through the n-type layer, an element structure can be obtained in which ultraviolet light is extracted from the n-type layer side.

[0082] However, in order to achieve a peak emission wavelength of 300nm to 327nm, a method is generally adopted in which the AlGaN-based semiconductor is used to form a well layer and the AlN mole fraction is adjusted to a range of, for example, less than 33%. However, since the composition ratio of Ga is large at this time, the composition variation caused by Ga segregation is large, and the variation of the emission wavelength, the broadbandization of the emission spectrum, the separation of the peak wavelength, and other emission characteristics become problematic, making it difficult to stably achieve the desired peak emission wavelength.

[0083] According to the nitride semiconductor ultraviolet light emitting element of the above characteristics, since the well layer is composed of GaN-based semiconductor, there will be no composition change caused by Ga segregation, so it is possible to suppress characteristic changes caused by drift of the crystal growth device, etc. That is, it is possible to suppress characteristic changes in the emission wavelength.

[0084] In addition, the nitride semiconductor ultraviolet light-emitting element with the above characteristics is preferably set so that the thickness of the boundary region between adjacent platforms of the multi-stepped platforms of the well layer is in the range of 2 unit cells to 4 unit cells in the c-axis direction, the AlN mole fraction of the two AlGaN-based semiconductor layers adjacent to the well layer in the up and down directions is in the range of 50% to 100%, and the peak emission wavelength is in the range of 300nm to 327nm.

[0085] Furthermore, the manufacturing method of the nitride semiconductor ultraviolet light-emitting element with the above characteristics is preferably set so that the thickness of the boundary region between the adjacent platforms of the multi-stepped platforms of the well layer is in the range of 2 unit cells to 4 unit cells in the c-axis direction, the AIN mole fraction of the two AlGaN-based semiconductor layers adjacent to the well layer in the upper and lower directions is in the range of 50% to 100%, and the peak emission wavelength is in the range of 300nm to 327nm,

[0086] In the second step, the well layer is grown, and in at least one of the first step, the second step, and the third step, two AlGaN-based semiconductor layers adjacent to the well layer in the vertical direction are grown.

[0087] According to these preferred embodiments, the well layer is formed of GaN-based semiconductors, and a peak emission wavelength of 300 nm to 327 nm is specifically achieved.

[0088] In addition, when the active layer is composed of only one well layer, two AlGaN-based semiconductor layers adjacent to each other in the vertical direction relative to the well layer are equivalent to an n-type layer and a p-type layer. For example, when the p-type layer is composed of multiple p-type AlGaN-based semiconductors with different AlN mole fractions, it is equivalent to the p-type AlGaN-based semiconductor layer connected to the well layer. In addition, when the active layer includes one or more well layers and a barrier layer connected to the n-type layer side or the p-type layer side of the one or more well layers, or when the active layer includes two or more well layers and a barrier layer inserted between the two adjacent well layers, the barrier layer is equivalent to at least one of the above-mentioned two AlGaN-based semiconductor layers. Furthermore, when there are more than one well layer, in the case where the n-type layer is connected to the well layer close to the n-type layer, the n-type layer has Al in the first Ga-rich region, which is an integer ratio of AlGaN composition. 1 Ga 1 N 2 Since the n-type AlGaN region is formed, the AlN mole fraction satisfies the condition in the range of 50% to 100%.

[0089] However, in such preferred embodiments, the range of 2 to 4 unit cells in the c-axis direction for the thickness of the boundary region of the well layer and the range of 50% to 100% of the AlN mole fraction of the two AlGaN-based semiconductor layers adjacent to the well layer in the vertical direction show that by appropriately setting the thickness of the boundary region of the well layer and the AlN mole fraction of the two AlGaN-based semiconductor layers within the range, a peak emission wavelength within the range of 300nm to 327nm can be achieved, but it is not guaranteed that the peak emission wavelength within the range of 300nm to 327nm can be achieved in the entire region within each individual range. This point will be described later.

[0090] 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.

[0091] 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 GaN-based semiconductors and the barrier layer composed of AlGaN-based semiconductors 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.

[0092] 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.

[0093] Furthermore, the nitride semiconductor ultraviolet light-emitting element with the above characteristics is more preferably, wherein the barrier layer is composed of an AlGaN-based semiconductor having an AlN mole fraction in the range of 50% to 90%, and a boundary region between adjacent platforms of at least the multi-stepped platforms of the barrier layer closest to the p-type layer in the barrier layer located between the two well layers becomes a second Ga-rich region where the AlN mole fraction is locally low also in the barrier layer.

[0094] Furthermore, the method for manufacturing a nitride semiconductor ultraviolet light-emitting element having the above characteristics is more preferably, in the second step, the target value of the AlN molar fraction of the barrier layer is set in the range of 55% to 90%, and a second 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 in the barrier layer located between the two well layers.

[0095] According to such preferred embodiments, in the barrier layer, local distribution of carriers can be generated in the second Ga-rich region similarly to the first Ga-rich region of the n-type layer. Therefore, when carriers (electrons) are supplied from the n-type layer to the boundary region (inclined region) between adjacent terraces where light emission is concentrated in the well layer, the supply can be effectively performed through the first Ga-rich region of the n-type layer and the second Ga-rich region of the barrier layer.

[0096] Here, in a multi-quantum well structure with more than two well layers, the luminescence efficiency is high in the well layer closest to the p-type layer. Therefore, by forming a second Ga-rich region in the barrier layer on the n-type layer side of the well layer, the above-mentioned carrier supply to the well layer can be carried out more efficiently.

[0097] In the nitride semiconductor ultraviolet light emitting device of the above preferred embodiment, it is preferred that an AlGaN composition ratio of an integer ratio exists in the second Ga-rich region of the barrier layer. 1 Ga 1 N 2 、Al 2 Ga 1 N 3 、Al 3 Ga 1 N 4 , or Al 5 Ga 1 N 6 AlGaN region.

[0098] 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,

[0099] 1) The target value of the AlN mole fraction of the barrier layer is set within the range of 51% to 66%, and the AlGaN composition ratio is set to an integer ratio of Al in the second Ga-rich region. 1 Ga 1 N 2 AlGaN region growth; or

[0100] 2) The target value of the AlN mole fraction of the barrier layer is set within the range of 68% to 74%, and the AlGaN composition ratio is made an integer ratio of Al in the second Ga-rich region. 2 Ga 1 N 3 AlGaN region growth; or

[0101] 3) The target value of the AlN mole fraction of the barrier layer is set within the range of 76% to 82%, and the AlGaN composition ratio is made an integer ratio of Al in the second Ga-rich region. 3 Ga 1 N 4 AlGaN region growth; or

[0102] 4) The target value of the AlN mole fraction of the barrier layer is set within the range of 85% to 90%, and the AlGaN composition ratio is made an integer ratio of Al in the second Ga-rich region. 5 Ga 1 N 6 The AlGaN region is grown.

[0103] According to these preferred embodiments, the presence of quasi-stable AlGaN in the second Ga-rich region of the barrier layer can suppress the variation of the AlN mole fraction in the second Ga-rich region in the same manner as in the first Ga-rich region of the n-type layer, and stably form the quasi-stable AlGaN region in the second Ga-rich region. Therefore, the effect exerted by the second Ga-rich region of the barrier layer can be more stably achieved.

[0104] 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.

[0105] 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.

[0106] -Effects of the Invention-

[0107] According to the nitride semiconductor ultraviolet light emitting element and the manufacturing method of the nitride semiconductor ultraviolet light emitting element with the above characteristics, a nitride semiconductor ultraviolet light emitting element with a peak emission wavelength in the range of 300nm to 327nm can be stably provided, which suppresses characteristic fluctuations caused by drift of the crystal growth device, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Figure 1 It is a diagram schematically showing the wurtzite crystal structure of AlGaN.

[0109] Figure 2 It is shown from Figure 1 A 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.

[0110] 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.

[0111] 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.

[0112] Figure 5 It is schematically shown Figure 41 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.

[0113] Figure 6 This is a graph showing the relationship between the emission wavelength of a quantum well structure including a GaN well layer and an AlGaN barrier layer, the film thickness of the well layer, and the AlN mole fraction of the barrier layer.

[0114] Figure 7 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.

[0115] Figure 8 This is a HAADF-STEM image showing the cross-sectional structure inside the n-type cladding layer.

[0116] Fig. 9 It is shown in Figure 8 The HAADF-STEM image shown is a diagram of five measurement areas A to E where cross-sectional TEM-EDX line analysis was performed in the n-type cladding layer.

[0117] Fig. 10A It is shown Fig. 9 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.

[0118] Fig. 10B It is shown Fig. 9 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.

[0119] Fig. 10C It is shown Fig. 9 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.

[0120] Fig. 10D It is shown Fig. 9 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.

[0121] Fig. 10E It is shown Fig. 9 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.

[0122] Fig.11This is a SEM image showing a measurement region of the AlN mole fraction in the n-type cladding layer by the CL method.

[0123] Fig.12 It is shown from Fig.11 The diagram shows the first and second CL spectra calculated from the CL spectra at 10 points measured in each measurement area.

[0124] Fig.13 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

[0125] 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.

[0126] [First embodiment]

[0127] <Element Structure of Light Emitting Element>

[0128] 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".

[0129] 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.

[0130] The AlN layer 12 is composed of AlN crystals epitaxially grown from the main surface of the sapphire substrate 11, and the AlN crystals have an epitaxial crystal orientation relationship with respect to the main surface 11a of the sapphire substrate 11. Specifically, for example, the AlN crystals are grown so that the c-axis direction ( <0001> direction) 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 the present 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.

[0131] 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.

[0132] 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.

[0133] 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 4As 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 .

[0134] 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 AlN mole fraction is locally low and is evenly dispersed. As described above, the layered region is dominated by AlGaN with an AlGaN composition ratio in an integer ratio. 1 Ga 1 N 2 The first Ga-rich region 21 a is an n-type AlGaN region (ie, n-type quasi-stable AlGaN having an AlN mole fraction of 50%). 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.

[0135] In this embodiment, the AlN mole fraction of the n-type main region 21b is adjusted to be within the range of 54% to 66%. 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 AlGaN. 1 Ga 1 N 2 The n-type AlGaN region of the quasi-stable AlGaN is conveniently referred to as the "quasi-stable n-type region". In addition, the region slightly changed from 50% (half) of the AlN mole fraction 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 plurality of layered first Ga-rich regions 21a, but may exist intermittently by being interrupted by the quasi-stable near n-type region.

[0136] The active layer 22 is a multi-quantum well structure having two or more well layers 220 composed of GaN-based semiconductors and one or more barrier layers 221 composed of AlGaN-based semiconductors or AlN-based semiconductors alternately stacked. The barrier layer 221 does not necessarily need to be provided between the bottom well layer 220 and the n-type cladding layer 21. In addition, the barrier layer 221 may be provided between the top well layer 220 and the electron blocking layer 23, 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.

[0137] exist Figure 5 Schematically shows an example of a stacked 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.

[0138] In this embodiment, the thickness of the boundary region (inclined region) between adjacent platforms of the multi-stepped platforms of the well layer 220 is set in the range of 2 to 4 unit cells in the c-axis direction, and the AlN molar fraction of the barrier layer 221 is adjusted to be in the range of 50% to 100%, so that the peak emission wavelength of the ultraviolet light from the well layer 220 is in the range of 300nm to 327nm.

[0139] Figure 6 This is a quantum well structure model in which the well layer is GaN and the barrier layer is AlGaN or AlN. For two cases where the AlN mole fraction of the barrier layer is 66.7% (AlGaN) and 100% (AlN), the simulation results of the emission wavelength (equivalent to the peak emission wavelength) obtained by varying the film thickness of the well layer in the range of 4ML (single atomic layer) to 10ML are graphed.

[0140] pass Figure 6 It can be seen that when the film thickness of the well layer is in the range of 4ML to 8ML (2 unit cells to 4 unit cells), the greater the AlN mole fraction of the barrier layer, or the smaller the film thickness of the well layer, the greater the quantum confinement effect on the well layer, and the shorter the wavelength of light emission. In addition, it can be seen that within this range, the light emission wavelength varies in the range of approximately 270nm to 325nm. Therefore, when the light emission wavelength is slightly longer than 325nm to 327nm, it can be achieved by making the AlN mole fraction of the barrier layer slightly less than 66.7%. By Figure 6 It can be seen that by adjusting the thickness of the inclined region of the well layer 220 within the range of 2 to 4 unit cells and adjusting the AlN mole fraction of the barrier layer 221 within the range of 50% to 100%, a peak emission wavelength within the range of 300nm to 327nm can be achieved.

[0141] Since the ultraviolet light emission of the well layer 220 is significantly generated in the boundary region (inclined region) BA between adjacent terraces T, it is important to satisfy the film thickness condition of the well layer 220 in the inclined region BA. However, similarly to the inclined region BA, it is preferred to adjust the film thickness of the terrace region TA of the well layer 220 within the range of 2 to 4 unit cells, but in a part of the terrace T, there are hexagonal micro-protrusions (hills), etc., and the film thickness may partially exceed 4 unit cells. In addition, the film thickness of the barrier layer 221 is preferably adjusted within the range of 6nm to 8nm, including the terrace region TA and the inclined region BA.

[0142] As described above, the barrier layer 221 has a surface with multi-step terraces parallel to the (0001) plane, similarly to the n-type cladding layer 21 and the well layer 220, and is further composed of an AlGaN-based semiconductor, similarly to the n-type cladding layer 21. Here, the barrier layer 221 may be composed of an AlN-based semiconductor with an AlN mole fraction of 100%, or may be composed of an AlGaN-based semiconductor with an AlN mole fraction of non-100%, depending on the peak emission wavelength and the film thickness of the inclined region of the well layer 220. Therefore, Figure 5 As schematically shown, when the barrier layer 221 is composed of an AlGaN-based semiconductor whose AlN mole fraction is not 100%, similarly to the n-type cladding layer 21, a second Ga-rich region 221a in which the AlN mole fraction is locally low in the barrier layer 221 can be formed in or near the boundary region (inclined region) BA between adjacent terraces T of the barrier layer 221. Here, for convenience, the region other than the second Ga-rich region 221a in the barrier layer 221 is 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 barrier layer 221 including the second Ga-rich region 221a is within the range of 50% to 90% of the above-mentioned range of 50% to 100%, in order to fully ensure the local distribution effect of carriers in the second Ga-rich region 221a, it is preferred that the difference in the AlN mole fraction between the second Ga-rich region 221a and the barrier main body region 221b is 4 to 5% or more, but even if it is about 1%, the effect of local distribution of carriers can be expected. Therefore, in this embodiment, the AlN mole fraction of the barrier main body region 221b is set to be within the range of 51% to 90%.

[0143] 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.

[0144] 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 shapes 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 .

[0145] In this embodiment, if Figure 7 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 7 of examples.

[0146] 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.

[0147] 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 various layers of the 1st Ga-enriched region 21a are schematically illustrated as parallel lines (double lines), the inclination angle formed by the extension direction and the lateral direction is not necessarily the same between the various 1st Ga-enriched regions 21a, and may vary due to the location within the same 1st Ga-enriched region 21a. Therefore, the 1st Ga-enriched 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-enriched region 21a can also intersect with other 1st Ga-enriched regions 21a or branch from other 1st Ga-enriched regions 21a on the first plane. The points where the inclination angle formed by the extension direction of the 1st Ga-enriched region 21a and the lateral direction varies depending on the location and the points where the 1st Ga-enriched region 21a is evenly dispersed in the n-type cladding layer 21 are clearly shown. Figure 8 HAADF-STEM image shown.

[0148] 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, multiple first Ga-rich regions 21a can be observed in stripes on multiple second planes in the n-type cladding layer 21.

[0149] 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.

[0150] 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.

[0151] 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 50% 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 migration 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.

[0152] 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.

[0153] <Method for manufacturing light-emitting element>

[0154] Next, Figure 4 An example of a method for manufacturing the illustrated light emitting device 1 will be described.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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, and even for the first quasi-stable AlGaN, it is difficult to stably form a quasi-stable AlGaN with an AlN mole fraction of 50%, because the AlN mole fraction is prone to random fluctuations. Therefore, it is not preferred. As for the growth pressure, 75 Torr or less is preferably a good growth condition for AlGaN, and as a control limit for the film forming device, 10 Torr or more is actually preferred. The donor impurity concentration is 1×10 18 ~5×10 18 cm -3However, 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.

[0160] 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 (=54% to 66%), 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 50% and the quasi-stable near n-type region with an AlN mole fraction slightly higher than 50% exist is Xc (>50%). 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.

[0161] A quasi-stable n-type region with an AlN mole fraction of 50% stably exists 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 54% to 66%, the difference (Xb-50%) 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 4%, 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 66%, a region with an AlGaN composition ratio of AlGaN is not dominantly formed in the n-type main region 21b. 2 Ga 1 N 3 If the upper limit of the target value Xa is 67% or more, AlGaN is stably formed in the n-type body region 21b. 2 Ga 1 N 3 The quasi-stable AlGaN in the first Ga-rich region is 2 Ga 1 N 3 It is difficult to provide sufficient quasi-stable AlGaN for stable formation of Al 1 Ga 1 N 2 Therefore, by setting the upper limit of the target value Xa to 66%, a quasi-stable n-type region with an AlN mole fraction of 50% can be stably formed in the first Ga-rich region 21a.

[0162] 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 -3 The thickness of the low impurity concentration layer is preferably greater than 0 nm and less than 200 nm, more preferably greater than 10 nm and less than 100 nm, and further preferably greater than 20 nm and less than 50 nm. In addition, the donor impurity concentration of the low impurity concentration layer can be lower than the above-mentioned set concentration, and a part of the low impurity concentration layer may also include an undoped layer (0 cm -3 ) In addition, it is preferred that part or all of the low impurity concentration layer exists in an upper region within a depth of 100 nm from the upper surface of the n-type cladding layer 21 to the lower side.

[0163] When the n-type cladding layer 21 having the first Ga-rich region 21a and the n-type main region 21b is formed by the above-mentioned method, an active layer 22 (well layer 220, barrier layer 221), an electron blocking layer 23, a p-type cladding layer 24 and a p-type contact layer 25 are formed on the entire upper surface of the n-type cladding layer 21 by a well-known epitaxial growth method such as organic metal compound vapor phase deposition (MOVPE) method.

[0164] In the formation of the active layer 22, the film thickness is set in advance within the range of 2 to 4 unit cells in the c-axis direction, so that the peak emission wavelength of ultraviolet light is within the range of 300 nm to 327 nm, and the well layer 220 is grown under the growth conditions that are easy to expose the multi-step terrace without supplying TMA gas. Furthermore, the barrier layer 221 is grown under the growth conditions that are easy to expose the multi-step terrace in the same manner as the n-type cladding layer 21, with the AlN mole fraction (51% to 90% or 100%) set for the barrier main body region 221b as the target value.

[0165] Next, the second region R2 of the nitride semiconductor layers 21 to 25 stacked in the above manner is selectively etched by a known etching method such as reactive ion etching until the upper surface of the n-type cladding layer 21 is exposed, thereby partially exposing the second region R2 of the upper surface of the n-type cladding layer 21. Then, by a known film forming 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, a heat treatment may be performed by a known heat treatment method such as RTA (transient thermal annealing).

[0166] However, as an example, after the light-emitting element 1 is flip-chip mounted on a base such as a pedestal, it is used in a state of being encapsulated with a given resin such as silicone resin or amorphous fluororesin (for example, a resin in a lens shape).

[0167] <Cross-sectional Observation and Composition Analysis Results of n-Type Cladding Layer>

[0168] Next, a specimen for cross-sectional observation of the n-type cladding layer 21 is fabricated. From this specimen, a specimen piece having a cross-section perpendicular (or slightly perpendicular) to the upper surface of the n-type cladding layer 21 is processed by focused ion beam (FIB). The results of observing this specimen piece with a scanning transmission electron microscope (STEM) will be described with reference to the attached drawings.

[0169] This specimen is fabricated by sequentially stacking an n-type cladding layer 21, an active layer 22, an AlGaN layer having a higher AlN mole fraction than the n-type cladding layer 21, an AlGaN layer for protecting the specimen surface, and a protective resin film on a base portion 10 including the above-mentioned sapphire substrate 11 and AlN layer 12 according to the above-mentioned manufacturing method of the n-type cladding layer 21 and the like. However, in the fabrication of this specimen, the base portion 10 is used, and the main surface of the base portion uses a sapphire substrate 11 having an inclination angle with respect to the (0001) plane and having a stepped platform exposed on the surface of the AlN layer 12. However, in the fabrication of this specimen, the film thickness of the n-type cladding layer 21 is set to 2 μm, and the target value of the AlN mole fraction of the n-type cladding layer 21 is 58%. In addition, the donor impurity concentration is made about 3×10 18 cm -3 , and the implantation amount of the donor impurity (Si) is controlled.

[0170] In Figure 8 A high-angle annular dark field (HAADF)-STEM image of the cross-section of the above specimen piece is shown. Figure 8 It is a HAADF-STEM image for observing the whole of the n-type cladding layer 21 from the upper part of the AlN layer 12 of the specimen piece to the upper surface of the n-type cladding layer 21.

[0171] The HAADF-STEM image can obtain a contrast proportional to the atomic weight, and heavy elements are shown brightly. 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 having a lower AlN mole fraction is shown more brightly than the n-type main region 21b. The HAADF-STEM image is more suitable for observing the difference in AlN mole fraction than a normal STEM image (bright field image).

[0172] By Figure 8It 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 Figure 8 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.

[0173] 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).

[0174] In the composition analysis based on the EDX method (EDX measurement), first, Figure 8 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.

[0175] 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. 9 As shown in FIG. 1 , five measurement areas A to F having a substantially square shape (approximately 420 nm×approximately 420 nm) are set within the entire measurement area. Fig. 9 exist Figure 8 The HAADF-STEM image is overlapped with rectangular frames representing the measurement areas A to E. Each of the 5 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 E (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. 9In each measurement area A to E, for the convenience of explanation, 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. Among them, an arrow is attached to the vertical line indicating the scanning direction to indicate the direction of the AlN layer 12. In addition, the scanning position is set in the range of 49 to 88 points in total in the vertical direction at intervals of about 5 nm according to each measurement area A to E, sandwiching the above-mentioned origin on the central vertical line.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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 n-type cladding layer 21 is a low or high value.

[0180] At Figures 10A to 10E , showing that the line analysis measured by EDX was performed Fig. 9 The results of the composition analysis in the n-type cladding layer 21 at six measurement areas A to E are shown. Figures 10A to 10E The graph of the composition analysis results of each measurement area A to E shown in the figure shows that 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-rich 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.

[0181] 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 10A to 10E The AlN mole fraction and the GaN mole fraction in the measurement regions A to E shown are results of the calibration.

[0182] pass Fig. 10AIt can be confirmed that in the measurement area A, the first Ga-rich region 21a exists in the area A1 of about -131nm to about -92nm at the scanning position and the area A2 of about -5nm to about 10nm at the scanning position. The AlN mole fraction of the 9 scanning positions in the area A1 is 49.4% to 52.8% (6 points in 49% to 52%, 3 points in 49% to 51%), and the area A1 also includes a scanning position with an AlN mole fraction of 50.0%. The AlN mole fraction of the 4 scanning positions in the area A2 is 51.3% to 52.8% (2 points in 50% to 52%).

[0183] pass Fig. 10B It can be confirmed that in the measurement area B, the first Ga-rich region 21a exists in the area B1 of about -116nm to about -73nm at the scanning position and the area B2 of about -5nm to about 5nm at the scanning position. The AlN mole fraction at the scanning position of 10 points in the area B1 is 51.3% to 52.8% (4 points are within 50% to 52%). The AlN mole fraction at the scanning position of 3 points in the area B2 is 50.5% to 51.9% (3 points are within 50% to 52%).

[0184] pass Fig. 10C It can be confirmed that in the measurement area C, the first Ga-rich region 21a exists in the area C1 of about -140nm to about -111nm at the scanning position and the area C2 of about -10nm to about 48nm at the scanning position. The AlN mole fraction at the scanning position of 7 points in the area C1 is 51.1% to 52.7% (4 points are within 50% to 52%). The AlN mole fraction at the scanning position of 13 points in the area C2 is 51.1% to 52.7% (9 points are within 50% to 52%).

[0185] pass Fig. 10DIt can be confirmed that in the measurement area D, the first Ga-rich region 21a exists in the area D1 of about -160nm to about -140nm at the scanning position, the area D2 of about -73nm to about -58nm at the scanning position, the area D3 of about 0nm to about 15nm at the scanning position, and the area D4 of about 97nm to about 106nm at the scanning position. The AlN mole fraction at the scanning positions of the 5 points in the area D1 is 49.1% to 52.3% (3 points within 49% to 52%), and the area D1 also includes a scanning position with an AlN mole fraction of 49.8%. The AlN mole fraction at the scanning positions of the 4 points in the area D2 is 51.4% to 52.7% (3 points within 50% to 52%). The AlN mole fraction at the scanning positions of the 4 points in the area D3 is 51.6% to 52.2% (2 points within 50% to 52%). The AlN mole fraction at three scanning positions in region D4 was 51.0% to 51.3% (three points were within the range of 50% to 52%).

[0186] pass Fig. 10E It can be confirmed that in the measurement area E, the first Ga-rich area 21a exists in the area E1 of about -169nm to about -97nm at the scanning position and the area E2 of about -5nm to about 5nm at the scanning position. The AlN mole fraction at the scanning position of 16 points in the area E1 is 50.5% to 52.5% (11 points within 50% to 52%, 6 points within 50% to 51%). The AlN mole fraction at the scanning position of 3 points in the area E2 is 50.8% to 52.6% (2 points within 50% to 52%).

[0187] 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 in the first Ga-rich region 21a is higher than the AlN mole fraction of the quasi-stable n-type region, it can be confirmed that there is a quasi-stable n-type region with an AlN mole fraction of 50% in the first Ga-rich region 21a of each of the measurement regions A1, A2, B1, B2, C1, C2, D1 to D4, E1, and E2 of the measurement regions A to E. 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 region C at the center, and the measurement regions D and E at the lower part close to the AlN layer 12, and is evenly dispersed in the n-type cladding layer 21.

[0188] In addition, through Figures 10A to 10E, it can be confirmed that the AlN mole fraction in the n-type main body region 21b adjacent to each of the measurement regions A to E, A1, A2, B1, B2, C1, C2, D1 to D4, E1, and E2, is within the range of about 55% to about 58%. 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 58%, 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 10A to 10E The AlN mole fraction of the n-type body region 21 b is shown with high accuracy.

[0189] 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. Figure 8 The sample piece used for observation of the HAADF-STEM image shown was prepared in the same manner.

[0190] Fig.11 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 d) surrounded by dotted lines in the cross section show the incident areas of the electron beams irradiated for the respective measurements. The measurement areas a and b are located at a distance of about 1000nm from the upper surface of the AlN layer 12, and the measurement areas c and d are located at a distance of about 350nm 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.

[0191] Fig.12 The first CL spectrum of two CL spectra with an average wavelength distribution close to short wavelengths and the second CL spectrum of two CL spectra with an average wavelength distribution close to long wavelengths among the 10 CL spectra of each measurement area (a to d) are classified and shown for each measurement area (a to d).

[0192] Since the separation distance between the two ends of the 10 electron beam centers in the measurement area (a to d) is 450nm, 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, the width of the cross section perpendicular to the extension direction of the first Ga-rich region 21a is about 20nm on average, so the n-type main region 21b is partially included in the irradiation range of the beam diameter of 50nm. 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.

[0193] 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.

[0194] First, the first CL spectra of each measurement area (a to d) are examined. In measurement area a, the peak of the emission wavelength exists at about 260nm. In measurement area b, the moderate peak of the emission wavelength exists at two locations, about 260nm and about 269nm. In measurement area c, the peak of the emission wavelength exists at about 259nm. In measurement area d, the peak of the emission wavelength exists at about 258nm.

[0195] When the peak wavelength of about 258 nm to about 260 nm in each measurement region (a to d) is converted into AlN mole fraction, it is equivalent to about 59% to about 61%. Considering the measurement error of about ±3% in terms of conversion into AlN mole fraction, the CL wavelength of the first CL spectrum and the average AlN mole fraction Xb ( The target value is 58%).

[0196] In addition, in the first CL spectra of the measurement areas a, c, and d, the long-wavelength components above the peak wavelength of about 258 nm to about 260 nm are more than the short-wavelength components less than the peak wavelength, and it can be seen that the mass transfer of Ga occurs in the two irradiation ranges corresponding to the first CL spectra of each measurement area. In addition, when the peak wavelength of about 269 nm of the first CL spectrum of the measurement area b is converted into the AlN mole fraction, it is equivalent to about 53%±3%, which is roughly consistent with the CL wavelength from the quasi-stable near n-type region where the AlN mole fraction is slightly higher than 50% existing in the first Ga-enriched region 21a, and it can be seen that a part of the two irradiation ranges corresponding to the first CL spectrum in the measurement area b contains the first Ga-enriched region 21a formed by the mass transfer of Ga.

[0197] Next, the second CL spectrum of each measurement area (a~d) is reviewed. In measurement area a, the relaxation peak of the emission wavelength exists in two places near about 262nm and about 270nm. In measurement area b, the relaxation peak of the emission wavelength exists in the range of about 270nm to about 273nm. In measurement area c, the relaxation peak of the emission wavelength exists in the range of about 266nm to about 269nm, and the plateau-like peak area extends to the range of about 261nm to about 270nm as a whole. In measurement area d, the relaxation peak of the emission wavelength exists in the range of about 259nm and about 268nm, and the plateau-like peak area extends to the range of about 258nm to about 269nm as a whole.

[0198] When the peak wavelength of about 270nm to about 273nm in each measurement area a and b is converted into AlN mole fraction, it is equivalent to about 51% to about 53%. Considering the measurement error of about ±3% in terms of conversion into AlN mole fraction, it is roughly consistent with the CL wavelength (about 275nm) corresponding to the quasi-stable n-type region with an AlN mole fraction of 50% existing in the first Ga-rich region 21a. In addition, in the second CL spectrum of the measurement areas a and b, the CL wavelength of about 275nm corresponding to the quasi-stable n-type region is included with a luminescence intensity of about 72 to 78% of the peak intensity. Among them, the peak wavelength of about 270nm to about 273nm is about 2 to 5nm shorter than the CL wavelength (about 275nm) corresponding to the quasi-stable n-type region. Furthermore, in each second CL spectrum of the measurement areas a and b, the moderate peak or shoulder (fluctuation) of the luminescence wavelength exists near about 262nm. The second CL spectra of the measurement regions a and b shown here are shown as composite spectra of the CL spectra of the quasi-stable n-type region and the quasi-stable near n-type region having 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. Furthermore, in the second CL spectrum of the measurement region a, the proportion of the CL spectrum of the n-type main region 21b occupying the composite spectrum becomes larger than that in the measurement region b.

[0199] On the other hand, in the second CL spectra of the measurement areas c and d, the long wavelength end of the plateau-shaped peak region is about 269nm to about 270nm, which is equivalent to about 53% to about 54% when converted to the AlN mole fraction. Considering the measurement error of about ±3% converted to the AlN mole fraction, it is roughly consistent with the CL wavelength (about 275nm) corresponding to the quasi-stable n-type region with an AlN mole fraction of 50% existing in the first Ga-rich region 21a. In addition, in the second CL spectra of the measurement areas c and d, the CL wavelength of about 275nm corresponding to the quasi-stable n-type region is included with a luminescence intensity of about 49 to 55% of the peak intensity. This shows that each second CL spectrum of the measurement areas c and d appears as a composite spectrum of the CL spectra of the quasi-stable n-type region and the quasi-stable near-n-type region in the first Ga-rich region 21a, and the CL spectrum of the n-type main region 21b, similarly to the measurement areas a and b. Furthermore, in the second CL spectrum of measurement regions c and d, the proportion of the CL spectrum of the n-type body region 21b occupying the synthetic spectrum and the proportion of the quasi-stable near n-type region in the first Ga-rich region 21a become larger than those in measurement regions a and b.

[0200] Above, through Fig.12From the first CL spectra of each measurement area a to d shown, it can be seen that the AlN mole fraction of the n-type main region 21b is almost consistent with the target value of 58% of the AlN mole fraction of the n-type cladding layer 21. In addition, from the second CL spectra of each measurement area a to d, it can be seen that in the first Ga-rich region 21a, while including a quasi-stable n-type region with an AlN mole fraction of 50%, there is a quasi-stable near n-type region with an AlN mole fraction higher than that of the quasi-stable n-type region. Fig.12 The analysis results shown in the first and second CL spectra of each measurement area a to d are different from those shown in FIG. Figures 10A to 10E The results of the EDX analysis are quite consistent with those of the

[0201] However, from Fig.12 The second CL spectra of each measurement area a to d 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.

[0202] 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 .

[0203] [Second embodiment]

[0204] 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 second Ga-rich region 221a is made within the range of 50% to 90%, and the AlN mole fraction of the barrier main region 221b is made within the range of 51% to 90%. In order to ensure the local distribution effect of carriers in the second Ga-rich region 221a, the difference in AlN mole fractions between the second Ga-rich region 221a and the barrier main region 221b is made greater than 1%.

[0205] In the second embodiment, similarly to the first Ga-rich region 21a of the n-type cladding layer 21 in the first embodiment, the second Ga-rich region 221a of the barrier layer 221 is preferably composed of quasi-stable AlGaN. Here, since the AlN mole fraction of the entire barrier layer 221 is within the range of 50% to 90%, the first quasi-stable AlGaN applicable to the second Ga-rich region 221a is AlGaN with an AlGaN composition ratio of an integer ratio. 1 Ga 1 N2、Al 2 Ga 1 N 3 , or Al 5 Ga 1 N 6 In addition, the Al of the second quasi-stable AlGaN 7 Ga 5 N 12 With Al 3 Ga 1 N 4 , although it can also be applied to the second Ga-rich region 221a, if it is to be used, the more stable Al 3 Ga 1 N 4 However, the Al 11 Ga 1 N 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, making it difficult to apply to the second Ga-enriched region 221a.

[0206] AlGaN 2 Ga 1 N 3 、Al 3 Ga 1 N 4 , and Al 5 Ga1 N 6 When forming the second Ga-rich region 221a, the AlN mole fraction of the barrier body region 221b preferably corresponds to the four AlN mole fractions of the second Ga-rich region 221a, and is preferably in the range of 51% to 66%, 68% to 74%, 76% to 82%, or 85% to 90%. 5 Ga 1 N 6 In order to prevent the low stability of Al 11 Ga i N 12 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%.

[0207] The manufacturing method of the second 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.

[0208] In the second Ga-rich region 221a, Al as the first quasi-stable AlGaN is 1 Ga 1 N 2 During the growth, the target value Xd of the AlN mole fraction of the barrier layer 221 is set in the range of 51% to 66% similarly to the target value Xa of the AlN mole fraction of the n-type cladding layer 21. In the same manner, the AlN mole fraction of the first quasi-stable AlGaN is set in the second Ga-rich region 221a. 2 Ga 1 N 3 During the growth, the target value Xd of the AlN mole fraction of the barrier layer 221 is set within the range of 68% to 74%, and the AlN as the second quasi-stable AlGaN is made to 3 Ga 1 N 4 During the growth, the target value Xd of the AlN mole fraction of the barrier layer 221 is set within the range of 76% to 82%, and the AlN as the first quasi-stable AlGaN is made to 5 Ga 1 N 6 During the growth, the target value Xd of the AlN mole fraction of the barrier layer 221 is set within a range of 85% to 90%.

[0209] 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 second 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 second Ga-rich region 221a, the difference in AlN mole fraction between the second Ga-rich region 221a and the barrier main body region 221b is ensured to be 1% or more, and the carriers in the barrier layer 221 are locally distributed in the second Ga-rich region 221a having a smaller band gap energy than the barrier main body region 221b.

[0210] By forming the second Ga-rich region 221a with highly stable quasi-stable AlGaN, the variation of the mixed crystal mole fraction due to drift of the crystal growth device is suppressed, and the second 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 second Ga-rich region 221a, and the variation of the characteristics of the light-emitting element 1 can be further suppressed.

[0211] [Other embodiments]

[0212] Hereinafter, modified examples of the above-mentioned first and second embodiments will be described.

[0213] (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 GaN-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.

[0214] (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.

[0215] (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.

[0216] (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.

[0217] (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.

[0218] -Industrial Availability-

[0219] The present invention can be used for a nitride semiconductor ultraviolet light emitting element having a quantum well structure in which an active layer includes one or more well layers composed of a GaN-based semiconductor and having a peak emission wavelength in the range of 300 nm to 327 nm.

[0220] -Explanation of symbols-

[0221] 1: Nitride semiconductor ultraviolet light emitting element

[0222] 10: Base

[0223] 11: Sapphire substrate

[0224] 11a: Main surface of sapphire substrate

[0225] 12: AlN layer

[0226] 20: Light-emitting element structure

[0227] 21: n-type cladding layer (n-type layer)

[0228] 21a: 1st Ga-rich region (n-type layer)

[0229] 21b: n-type main region (n-type layer)

[0230] 22: Active layer

[0231] 220: Well layer

[0232] 221: Barrier layer

[0233] 221a: 2Ga-enriched region

[0234] 221b: Barrier main area

[0235] 23: Electron blocking layer (p-type layer)

[0236] 24: p-type cladding layer (p-type layer)

[0237] 25: p-type contact layer (p-type layer)

[0238] 26: p electrode

[0239] 27: n electrode

[0240] 100: Substrate

[0241] 101: AlGaN semiconductors

[0242] 102: Template

[0243] 103: n-type AlGaN semiconductor layer

[0244] 104: Active layer

[0245] 105: p-type AlGaN semiconductor layer

[0246] 106: p-type contact layer

[0247] 107: n electrode

[0248] 108: p electrode

[0249] BL: Boundary between area 1 and area 2

[0250] BA: Boundary area (sloping area)

[0251] R1: Area 1

[0252] R2: Area 2

[0253] T: Platform

[0254] TA: Platform area.

Claims

1. A nitride semiconductor ultraviolet light emitting element, comprising an n-type layer, an active layer and a p-type layer of an AlGaN-based semiconductor having a wurtzite structure stacked on a light emitting element structure in a vertical direction, and having a peak emission wavelength in the range of 300 nm to 327 nm, 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 a GaN-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 Al1Ga1N2 having an AlGaN composition ratio in 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 AlN mole fraction of the n-type body region outside the layered region in the n-type layer is in the range of 54% to 66%.

2. The nitride semiconductor ultraviolet light emitting element according to claim 1, characterized in that: It is set as follows: the thickness of the boundary area between adjacent platforms of the multi-stepped platforms of the well layer is in the range of 2 unit cells to 4 unit cells in the c-axis direction, the AlN mole fraction of the two AlGaN-based semiconductor layers adjacent to the well layer in the up and down directions is in the range of 50% to 100%, and the peak emission wavelength is in the range of 300nm to 327nm.

3. 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.

4. The nitride semiconductor ultraviolet light emitting element according to claim 3, characterized in that: The barrier layer is composed of an AlGaN-based semiconductor having an AlN mole fraction in the range of 50% to 90%. At least the boundary region between adjacent terraces of the multi-step terraces of the barrier layer closest to the p-type layer in the barrier layer between the two well layers becomes a second Ga-rich region where the AlN mole fraction is locally low similarly in the barrier layer.

5. The nitride semiconductor ultraviolet light emitting element according to claim 4, characterized in that: In the second Ga-rich region of the barrier layer, there exists an AlGaN region of Al1Ga1N2, Al2Ga1N3, Al3Ga1N4, or Al5Ga1N6 in which the AlGaN composition ratio is an integer ratio.

6. 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 tilted 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.

7. A method for manufacturing a nitride semiconductor ultraviolet light emitting element, wherein the nitride semiconductor ultraviolet light emitting element comprises an n-type layer, an active layer and a p-type layer of an AlGaN-based semiconductor having a wurtzite structure stacked on a light emitting element structure portion in a vertical direction and has a peak emission wavelength in the range of 300 nm to 327 nm, 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 GaN-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, the target value of the AlN molar fraction of the n-type layer is set within the range of 54% to 66%, and a plurality of first Ga-rich regions are grown extending obliquely upward. The first Ga-rich regions are layered regions with locally low AlN molar fractions that are evenly dispersed in the n-type layer and contain n-type AlGaN regions of Al1Ga1N2 with an AlGaN composition ratio in an integer ratio.

8. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 7, characterized in that: The thickness of the boundary region between the adjacent platforms of the multi-stepped platforms of the well layer is within the range of 2 unit cells to 4 unit cells in the c-axis direction, the AlN mole fraction of the two AlGaN-based semiconductor layers adjacent to the well layer in the up-down direction is within the range of 50% to 100%, and the peak emission wavelength is within the range of 300nm to 327nm, In the second step, the well layer is grown. In at least one of the first step, the second step, and the third step, two AlGaN-based semiconductor layers adjacent to each other in the vertical direction with respect to the well layer are grown.

9. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 7 or 8, characterized in that: In the second step, the well layer composed of GaN-based semiconductors and the barrier layer composed of AlGaN-based semiconductors are alternately stacked by epitaxial growth to form the active layer of a multi-quantum well structure in which the well layer with multi-stepped platforms parallel to the (0001) plane is exposed on each surface of the barrier layer and the well layer and includes more than two layers of the well layer.

10. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 9, characterized in that: In the second step, the target value of the AlN molar fraction of the barrier layer is set within the range of 55% to 90%, and a second Ga-rich region having a locally low AlN molar fraction 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 in the barrier layer located between the two well layers.

11. The method for manufacturing a nitride semiconductor ultraviolet light emitting element according to claim 10, 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 51% to 66%, and growing an AlGaN region of Al1Ga1N2 with an AlGaN composition ratio of an integer ratio in the second Ga-rich region; or 2) 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 second Ga-rich region; or 3) 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 second Ga-rich region; or 4) 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 second Ga-rich region.

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