Light-emitting element

Abstract

To provide a light-emitting element capable of further improving luminous efficiency.SOLUTION: A light-emitting element includes: a substrate; and a light-emitting layer provided on the first main surface of the substrate and extending in a horizontal direction parallel to the first main surface. The light-emitting layer includes a quantum well layer containing AlaGa1-aN and AlbGa1-bN, in which the AlaGa1-aN is laterally sandwiched between the AlbGa1-bN in the horizontal direction, and a barrier layer containing AlcGa1-cN. The AlcGa1-cN vertically sandwiches at least a part of the AlaGa1-aN in a vertical direction perpendicular to the first main surface (0≤a<b<c≤1).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] AlGaN mixed crystals using a mixed crystal of Al and Ga as a group III raw material and N as a group V raw material are used in light-emitting devices, power conversion devices, light-receiving devices, etc. A light-emitting device using this AlGaN as a material for a light-emitting layer, for example, an LED (Light Emitting Diode) or a laser diode, is used as a light-emitting device that emits ultraviolet light. Since the energy of the light emitted by an AlGaN-LED is large, the development of a device with high luminous efficiency has become an issue. In order to improve the luminous efficiency of an AlGaN-LED, a light-emitting layer as described in Patent Document 1 is formed of several nm of Al , ,

[0003] , , , , 1-p , ،

[0004] , , , , , Ga 1-o N well layers and several nm of Al p Ga 1-p N (p<o) barrier layers are periodically laminated on a substrate, and a quantum well structure is widely used.

[0003] This is to sandwich the well layer with the barrier layer and create an energy barrier in carrier conduction between the well layer and the barrier layer, thereby efficiently confining the injected electrons and holes in the well layer to improve the luminous efficiency. In Patent Document 2, further, segregation of Ga is caused in the light-emitting layer and the semiconductor layer that is the base of the light-emitting layer to create a locally low-energy region, thereby intentionally creating a region where electrons or holes are easily transported. In this structure, electrons and holes concentrate in a region with a low group III composition ratio of Al (Al / (Al+Ga) molar ratio, hereinafter referred to as the Al ratio), improving the luminous efficiency.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] To improve the luminous efficiency of AlGaN-LEDs, creating a region with a lower energy potential than the surrounding area is effective in confining electrons or holes. However, the luminous efficiency of AlGaN-LEDs is still low at less than 10%, and design technology based on this guideline is still under development, leaving room for further improvement.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light-emitting element that can further improve the light-emitting efficiency. [Means for solving the problem]

[0007] In order to solve the above problems, a light-emitting element according to one aspect of the present invention includes a substrate and a light-emitting layer provided on a first major surface of the substrate and extending in a horizontal direction parallel to the first major surface. a Ga 1-a N and Al b Ga 1-b N, and the Al a Ga 1-a N and Al b Ga 1-b N is sandwiched horizontally adjacently in the quantum well layer, and Al c Ga 1-c and a barrier layer containing N. c Ga 1-c N is the Al a G a1-a At least a part of N is sandwiched between adjacent ones of the first main surface in a vertical direction perpendicular to the first main surface (0≦a <b<c≦1)。 [Effects of the Invention]

[0008] According to one embodiment of the present invention, a light-emitting element whose emission efficiency can be further improved can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an example of the configuration of an LED using AlGaN according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view showing an example of the configuration of a mesa structure of an LED using AlGaN according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings referred to in the following description, identical or similar parts are designated by identical or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc., may differ from the actual ones. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. Furthermore, it goes without saying that the drawings may include parts with different dimensional relationships and ratios.

[0011] Furthermore, the definitions of directions such as up and down in the following explanation are merely for the convenience of explanation and do not limit the technical idea of ​​the present invention. For example, if an object is rotated 90 degrees and observed, up and down are converted to left and right and read as such, and if it is rotated 180 degrees and observed, up and down are obviously read as reversed.

[0012] FIG. 1 is a cross-sectional view showing an example of the configuration of an LED (hereinafter, referred to as an AlGaN-LED) 1 using AlGaN according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing an example of the configuration of a mesa structure of an AlGaN-LED 1 according to an embodiment of the present invention. The AlGaN-LED 1 shown in FIGS. 1 and 2 is an example of a "light-emitting element" according to the present invention. As shown in FIGS. 1 and 2, the AlGaN-LED 1 has a substrate 11 and a multilayer thin film provided on a surface 11a of the substrate 11. The multilayer thin film has a structure in which, from the substrate 11 side, a first conductivity-type semiconductor layer (e.g., an n-AlGaN layer 12), an AlGaN light-emitting layer 13, an AlGaN electron blocking layer 14, a second conductivity-type semiconductor layer (e.g., a p-AlGaN layer 15), and a p-GaN (contact) layer 16 are stacked in this order.

[0013] The AlGaN light-emitting layer 13 has a multi-quantum well structure in which AlGaN quantum well layers 131 and AlGaN barrier layers 132 are repeatedly stacked. The AlGaN quantum well layers 131 are formed by stacking AlGaN quantum well layers 131 in a direction parallel to the surface 11a of the substrate 11 (hereinafter referred to as the horizontal direction). a Ga 1-a N, Al b Ga 1-b N, Al d Ga 1-d In Figure 1, Al a Ga 1-a N, Al b Ga 1-b N, Al d Ga 1-d To distinguish N, Al a Ga 1-a N is represented by the symbol "a" and Al b Ga 1-b N is indicated by the symbol "b", and Al d Ga 1-d The AlGaN barrier layer 132 is made up of Al GaN layers arranged side by side in the horizontal direction. c Ga 1-c N, Al f Ga 1-f N, Al e Ga 1-e In Figure 1, Al c Ga 1-c N, Al f Ga1-f N, Al e Ga 1-e To distinguish N, Al c Ga 1-c N is represented by the symbol "c" and Al f Ga 1-f N is indicated by the symbol "f" and Al e Ga 1-e N is indicated by the symbol "e".

[0014] The AlGaN quantum well layer 131 is Al a Ga 1-a N and Al b Ga 1-b The AlGaN light emitting layer 13 has a structure in which N is sandwiched between adjacent AlGaN quantum well layers 131 in a direction perpendicular to the surface 11a of the substrate 11 (hereinafter referred to as the perpendicular direction). a Ga 1-a At least a part of N is substituted by Al of the AlGaN barrier layer 132. c Ga 1-c It has a structure in which N is sandwiched between adjacent Al. a Ga 1-a N, Al b Ga 1-b N, Al c Ga 1-c The relationship between the composition ratios a, b, and c of Al with respect to N is 0≦a <b<c≦1、である。

[0015] Each layer will be described in detail below. <Substrate> The substrate (e.g., substrate 11) of the embodiment has a first main surface (e.g., front surface 11a) and a second main surface (e.g., back surface) opposite the first main surface, and is not particularly limited as long as it is possible to dispose a first-conductivity-type semiconductor layer on the first main surface. Specific examples of the substrate include an aluminum nitride substrate, a sapphire substrate, and a GaN substrate. From the viewpoint of disposing a highly crystalline AlGaN layer on the substrate, the substrate is preferably an aluminum nitride substrate, and more preferably a single-crystal aluminum nitride substrate. Here, in the description of the AlGaN-LED of the embodiment, "disposing B on A" refers to both a form in which B is disposed directly on the surface of A and a form in which B is disposed indirectly from the surface of A via another substance. For example, the first-conductivity-type semiconductor layer may be disposed indirectly from the surface of the substrate via another substance (e.g., an aluminum nitride (AlN) layer).

[0016] The substrate is not particularly limited in shape, as long as it is capable of disposing an AlGaN multilayer thin film including a light-emitting layer on its first main surface. Light is emitted in the direction of the second main surface of the substrate opposite the light-emitting layer. The thickness of the substrate is not particularly limited as long as the purpose is to laminate an AlGaN layer on top, but it is preferably between 20 micrometers and 1 millimeter. The substrate is used for the purposes of supporting the upper thin film, improving crystallinity, and dissipating heat to the outside. For this reason, it is preferable to use an AlN substrate, which can grow AlGaN with high quality and is a material with high thermal conductivity. There are no particular restrictions on the crystalline quality of the substrate, but in order to form an element thin film with high light-emitting efficiency on the upper layer, it is preferable to use an AlN substrate with a threading dislocation density of 1 x 10 7 cm -2 Less than 1×10 is preferred 6 cm -2 The following is more preferable: The growth surface of the substrate is preferably the commonly used +c-plane AlN because of its low cost, but it may also be -c-plane AlN, a semi-polar plane substrate, or a non-polar plane substrate.

[0017] From the viewpoint of reducing the dislocation density of the laminated thin film, the root mean square (RMS) height (root mean square height Rq) of the first main surface side of the substrate is preferably less than about 1 nm for an area of ​​10 μm × 10 μm. Also, in order to form a flat and uniform thin film surface, the root mean square (RMS) height of the second main surface side of the LED substrate is preferably less than about 10 nm for an area of ​​10 μm × 10 μm.

[0018] <Layered thin film> The laminated thin film is not particularly limited as long as it includes a light-emitting layer and is disposed on the first main surface of the substrate. From the viewpoint of improving light-emitting efficiency, the laminated thin film preferably further includes a first conductivity type semiconductor layer and a second conductivity type semiconductor layer sandwiching the light-emitting layer. Here, "first conductivity type" and "second conductivity type" refer to semiconductors exhibiting mutually different conductivities, and when one has n-type conductivity, the other has p-type conductivity. Generally, an n-type semiconductor layer is present between the light-emitting layer and the substrate, but this embodiment is not limited thereto.

[0019] As a layer other than the first conductivity type semiconductor layer, the light emitting layer, and the second conductivity type semiconductor layer, for example, a layer for blocking electrons or holes may be provided between the light emitting layer and at least one of the first conductivity type semiconductor layer and the second conductivity type semiconductor layer. Furthermore, from the viewpoint of improving the crystallinity of the multilayer thin film, it may be preferable to further provide a buffer layer on the surface of the multilayer thin film that contacts the substrate. Furthermore, from the viewpoint of efficiently supplying power to the light emitting layer, a first conductivity type electrode in contact with the first conductivity type semiconductor layer and a second conductivity type electrode in contact with the second conductivity type semiconductor layer may be provided.

[0020] Furthermore, the laminated thin film may have a mesa structure with a convex shape that includes a light-emitting layer in a part thereof, as shown in FIG. 2. The laminated thin film can be formed by, for example, MOCVD (Metal Organic Chemical Vapor Deposition). Other methods include stacking by MBE (Molecular Beam Epitaxy) or sputtering. The laminated thin film having a mesa structure can be formed by forming the thin film layers that constitute the laminated thin film by the above-mentioned MOCVD method or the like, and then etching the desired region. The laminated thin film is made of Al, which is a mixed crystal of Al, Ga, and N. x Ga 1-x It is composed of N (0≦x≦1).

[0021] The laminated thin film may contain AlN in a layer in contact with the substrate. As an example, the AlN layer is formed on the entire surface of the substrate. In this example, the AlN layer has a thickness of several micrometers (e.g., 1.6 μm), but this value is not limited to this. Specifically, the film thickness of the AlN layer is preferably thicker than 10 nm and thinner than 10 μm. An AlN layer thicker than 10 nm allows for the production of AlN with high crystallinity, and an AlN layer thinner than 10 μm allows for crack-free crystal growth across the entire wafer surface. The AlN layer preferably has a film thickness of more than 50 nm and thinner than 5 μm.

[0022] When the thickness of the AlN layer is greater than 50 nm, AlN with high crystallinity can be produced with good reproducibility, and when the thickness of the AlN layer is less than 5 μm, crystal growth with a low probability of cracking is possible. When AlN is used as the material for forming the substrate 11, the difference between the AlN layer and the substrate is the same material, so the boundary between the AlN layer and the substrate becomes unclear. In this embodiment, if the substrate is made of AlN, the AlGaN-LED is considered to have an AlN layer even if an AlN layer is not stacked on the substrate.

[0023] The AlN layer is formed thinner than the first nitride semiconductor layer, but it is not limited to this. When the first nitride semiconductor layer is thicker than the AlN layer, by making the first nitride semiconductor layer as thick as possible within the range of suppressing cracks, the in-plane resistance of the thin film stack of the first nitride semiconductor layer is reduced, and a low-voltage-driven AlGaN-LED can be realized. When low-voltage driving of the AlGaN-LED is realized, it becomes possible to further suppress breakdown under high current density driving due to heat generation. When the base of the first-conductive-type AlGaN layer is an AlN layer, the lattice constant difference and the thermal expansion coefficient difference with the first-conductive-type AlGaN layer are small, and a thin film of AlGaN with few defects can be grown on the AlN layer, which is preferable.

[0024] Furthermore, by using the AlN layer, the first nitride semiconductor layer can be grown under compressive stress, and the generation of cracks in the first nitride semiconductor layer can be suppressed. When the substrate is formed of a nitride semiconductor such as GaN, AlN, or AlGaN, a nitride semiconductor layer with few defects can be grown on the substrate for the above reasons. Therefore, when the substrate is formed of a nitride semiconductor such as GaN, AlN, or AlGaN, the AlN layer may not be provided. Also, on other substrates, high-quality AlGaN can be directly formed on the substrate without having AlN. The AlN layer may contain impurities such as carbon, silicon, iron, and magnesium.

[0025] (First-conductive-type semiconductor layer) The first-conductive-type semiconductor layer is Al i Ga 1-i N (0 < i ≤ 1) is used as a material. As shown in FIG. 2, the GaN-LED1 of the present embodiment has a first stacked region formed by removing a part of the first-conductive-type semiconductor layer (for example, the n-AlGaN layer 12) and a second stacked region located on the first stacked region and constituting a mesa structure.

[0026] When the first-conductive-type semiconductor constituting the first-conductive-type semiconductor layer is an n-type semiconductor, for example, Si is used as the first-conductive-type semiconductor at 1 × 10 19 cm -3AlGaN doped at the concentration of can be used. Further, as the conductive semiconductor, AlGaN n-type doped by the polarization doping method of continuously changing the mixed crystal composition ratio of the polar mixed crystal semiconductor may also be used.

[0027] When the first conductive semiconductor constituting the first conductive semiconductor layer is a p-type semiconductor, for example, AlGaN doped with Mg at a concentration of 3×10 19 cm -3 can be used. Further, as the conductive semiconductor, AlGaN p-type doped by the polarization doping method of continuously changing the mixed crystal composition ratio of the polar mixed crystal semiconductor may also be used.

[0028] As shown in FIGS. 1 and 2, the Al i Ga 1-i N of this embodiment may be sandwiched by Al j Ga 1-j N (0 < i < j ≦ 1) in the horizontal direction parallel to the surface of the substrate. In the case where Al i Ga 1-i N is n-AlGaN doped with Si, by locally creating a site with a low Al composition, the activation energy of Si can be pseudo-reduced, the electron density can be increased, the resistance of the LED can be reduced, and the driving voltage can be reduced. Further, when Al i Ga 1-i N is sandwiched by Al j Ga 1-j N (0 < i < j ≦ 1) in the horizontal direction, during the thin film growth, the dopant Si can be selectively increased in concentration in the low Al composition Al i Ga 1-i N, and due to the subsequent thermal diffusion during the LED fabrication and the current diffusion during the LED driving, the diffusion of Si into Al j Ga 1-j N occurs, and the Si concentration in Al j Ga 1-j N can be increased.

[0029] Thus, Al i Ga 1-i N is Al j Ga 1-jThe structure sandwiched and adjacent to N(0 < i < j ≤ 1) can be formed by, for example, the following method. Al i Ga 1-i On the surface of the substrate for growing N (AlN in this embodiment), form minute uneven shapes, preferably with a height difference of the unevenness of 1 μm or less, more preferably 200 nm or less, and even more preferably 5 nm or less. With the unevenness present, grow Al i Ga 1-i N. The unevenness can use a shape in which the concave and convex portions repeat in the horizontal plane direction. <​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​N may be grown again in a thin film growth apparatus.

[0031] In this case, Al remaining after etching i Ga 1-i On the upper surface of the convex portion of AlGaN, a mask such as SiO2 is formed, and when AlGaN fills the concave portion, it is taken out from the growth apparatus, and SiO2 is dissolved with hydrofluoric acid, so that AlGaN is sandwiched horizontally by AlGaN (0 < i < j ≦ 1), and a structure with a flat upper surface can be formed. A subsequent light emitting layer can be formed on this flat upper surface. j Ga 1-j When AlGaN fills the concave portion, it is taken out from the growth apparatus, and SiO2 is dissolved with hydrofluoric acid, so that AlGaN is sandwiched horizontally by AlGaN (0 < i < j ≦ 1), and a structure with a flat upper surface can be formed. A subsequent light emitting layer can be formed on this flat upper surface. i Ga 1-i AlGaN j Ga 1-j AlGaN (0 < i < j ≦ 1), and a structure with a flat upper surface can be formed. A subsequent light emitting layer can be formed on this flat upper surface.

[0032] Note that AlGaN may be sandwiched by AlGaN at all positions in the stacking direction of the thin film, or only a part thereof may be sandwiched by AlGaN. Preferably, in order to form a good interface with the underlying layer (AlN in this embodiment) where defects are likely to be generated, on the upper layer of AlN, there is a portion where AlGaN is formed without irregularities, and on this flat AlGaN, there is a structure where AlGaN is sandwiched horizontally by AlGaN (0 < i < j ≦ 1). i Ga 1-i AlGaN j Ga 1-j AlGaN j Ga 1-j AlGaN. Preferably, in order to form a good interface with the underlying layer (AlN in this embodiment) where defects are likely to be generated, on the upper layer of AlN, there is a portion where AlGaN is formed without irregularities, and on this flat AlGaN, there is a structure where AlGaN is sandwiched horizontally by AlGaN (0 < i < j ≦ 1). i Ga 1-i AlGaN is formed without irregularities, and on this flat AlGaN, there is a structure where AlGaN is sandwiched horizontally by AlGaN (0 < i < j ≦ 1). i Ga 1-i AlGaN i Ga 1-i AlGaN j Ga 1-j AlGaN (0 < i < j ≦ 1).

[0033] Note that in this example, the case where the first conductive type semiconductor layer is n-AlGaN is taken as an example, but the first conductive type semiconductor layer may be p-AlGaN. In this case, the dopant for AlGaN is changed from Si to Mg, and in the same manner, AlGaN is sandwiched horizontally by AlGaN (0 < i < j ≦ 1). i Ga 1-i AlGaN s j Ga 1-jA structure sandwiched adjacent to N(0 < i < j ≦ 1) can be formed.

[0034] As shown in FIG. 2, the first-conductivity-type semiconductor layer may have a region (for example, the first region AR1) where the first-conductivity-type electrode 21 contacts the upper part, and a region (for example, the second region AR2) where the light-emitting layer, the second-conductivity-type semiconductor layer, and the second-conductivity-type electrode 22 are laminated on the upper part. The presence of the first region AR1 and the second region AR2 is preferable because the electrode of the GaN-LED is formed on the first main surface (for example, the surface 11a) side of the substrate, so that when light is extracted to the second main surface (for example, the back surface 11b) side of the substrate, the electrode does not block the light.

[0035] [[ID=<<MASK_BEGIN>>8]]As shown in FIG. 1, when there is no first region AR1 and second region AR2 and the light-emitting layer is formed on the upper layer over the entire surface of the first-conductivity-type semiconductor layer, the first-conductivity-type electrode can be formed, for example, on the second main surface (for example, the back surface 11b) of the substrate. In this case, the substrate needs to be a conductive substrate because it is necessary to electrically connect the first-conductivity-type semiconductor layer and the first-conductivity-type electrode. Such substrates include, for example, GaN containing Si as an impurity.

[0036] (Light-emitting layer) The light-emitting layer emits light corresponding to the bandgap of the light-emitting layer when power is applied to the light-emitting layer. In particular, it emits light corresponding to the bandgap of AlGaN with the smallest Al composition in the quantum well layer. The light-emitting layer is above the first-conductivity-type semiconductor layer. For example, in the mesa structure shown in FIG. 2, the light-emitting layer is above the first-conductivity-type semiconductor layer in the second region AR2. The light-emitting layer has a quantum well structure. This is because a quantum well structure in which AlGaN layers with different composition ratios of Al and Ga (different bandgaps) are laminated can be adopted. More preferably, a multiple quantum well in which AlGaN layers with different composition ratios (different bandgaps) are multilayered can be adopted. As a more specific structure, three well layers (thickness 1 nm) with a composition of Al 0.87 Ga 0.13 N and three layers with a composition of Al 0.97 Ga [[ID=<<MASK_END>>21]] 0.03Examples include a triple quantum well structure in which two barrier layers of N (thickness: 5 nm) are alternately stacked. The quantum well layers extend in the plane direction (i.e., the horizontal direction) of the substrate surface.

[0037] The light-emitting layer is Al a Ga 1-a N is horizontally sandwiched between Al b Ga 1-b N, and at least a part of Al a Ga 1-a N is vertically sandwiched between Al c Ga 1-c N (0 ≤ a < b < c ≤ 1). By horizontally sandwiching Al a Ga 1-a N between Al b Ga 1-b N, an energy barrier can be formed at the interface between Al a Ga 1-a N and Al b Ga 1-b N, and electrons and holes injected into the light-emitting layer can be efficiently confined in Al a Ga 1-a N. By vertically sandwiching Al a Ga 1-a N between Al c Ga 1-c N, an energy barrier can be formed between Al a Ga 1-a N and Al c Ga 1-c N, and electrons and holes injected into the light-emitting layer can be efficiently confined in Al a Ga 1-a N. It is not necessary for all quantum well layers and barrier layers in the light-emitting layer to have a relationship in which Al a Ga 1-a N is vertically sandwiched between Al c Ga 1-c N. It is sufficient if at least a part of the light-emitting layer has a relationship in which Al a Ga 1-a N is vertically sandwiched between Al c Ga 1-c N.

[0038] In an embodiment of the present invention, Ala Ga 1-a N is horizontally sandwiched by Al b Ga 1-b N is adjacent and sandwiched, and Al a Ga 1-a N is vertically sandwiched by Al c Ga 1-c N is adjacent and sandwiched (0 ≦ a < b < c ≦ 1). Therefore, in both the horizontal and vertical directions, Al a Ga 1-a N with a lower Al composition is sandwiched by AlGaN with a higher Al composition, so electrons and holes can be efficiently confined in Al a Ga 1-a N, and the light emission efficiency of the AlGaN-LED can be increased. The difference between a and b is preferably within 0.05, and more preferably within 0.03. By setting the composition difference between a and b within this range, the stress in the quantum well layer can be reduced, and the generation of cracks that cause the AlGaN-LED to fracture can be suppressed.

[0039] Also, by reducing the stress, the generation of non-light-emitting defects that reduce the light emission efficiency can be suppressed. As another effect, when the difference between a and b is within this range, an increase in the element resistance in the light-emitting layer can be suppressed. Although a and b have a difference to form an energy barrier, on the other hand, when this difference becomes large, the element resistance of Al b Ga 1-b N with a high Al composition becomes high. Therefore, the driving voltage for driving the element becomes high. To suppress this increase in the driving voltage, the difference between a and b is preferably within the above range.

[0040] The difference between b and c is preferably greater than 0.03, greater than 0.05, and not more than 0.2. If the difference between b and c is 0.03 or less, it becomes difficult to efficiently confine electrons and holes because the energy barrier is small. If the difference between b and c is 0.05 or less, when producing Al d Ga 1-d N, the composition difference between c and d becomes small, and Al d Ga 1-d N to Al c Ga 1-cElectrons and holes cannot be confined efficiently because of the diffusion of electrons and holes into N. If the difference between b and c is 0.2 or more, Al c Ga 1-c N and Al a Ga 1-a N or Al b Ga 1-b The difference in lattice constant with N becomes large, and defects are generated in the quantum well layer, resulting in a decrease in light emission efficiency.

[0041] Al a Ga 1-a N is Al b Ga 1-b There are several ways to create a structure sandwiched between N. The first method is to adjust the V / III ratio, which is the molar ratio of the V and III gases used as raw materials, when forming a quantum well structure using the MOCVD method. Specifically, Al is used as a barrier layer. c Ga 1-c After growing a thin film of N on the first conductivity type semiconductor layer, Al is grown under film formation conditions with a low V / III ratio. a Ga 1-a Grow N. Al a Ga 1-a N is Al c Ga 1-c In order to create a nucleus on N and achieve three-dimensional growth, Al is partially c Ga 1-c The surface of N is Al a Ga 1-a Then, Al is deposited under high V / III ratio conditions. b Ga 1-b When N is grown, Al a Ga 1-a The grooves not covered with N are Al b Ga 1-b N grows to fill in the gap. After that, the surface is flattened to remove any unevenness.

[0042] This planarization process can be achieved by mechanical polishing after removing the thin film once. However, a more preferred method is to perform heat treatment by raising the temperature to 1200-1400 °C in the thin film growth furnace of MOCVD for planarization. At this time, filling the growth furnace with hydrogen promotes surface etching and accelerates the planarization process. Al a Ga 1-a N is Al b Ga 1-b On the quantum well layer of the light-emitting layer that spreads in the plane direction of the substrate surface sandwiched by Al c Ga 1-c N, by growing a thin film of Al a Ga 1-a N, Al b Ga<000025>N can be adjacent and sandwiched, and a structure where Al a Ga 1-a N is adjacent and sandwiched vertically (0 ≦ a < b < c ≦ 1) can be fabricated.

[0043] As another method, grow an Al c Ga 1-c N thin film on Al b Ga 1-b N. With an etching mask having a part opened on this Al b Ga 1-b N, by performing etching treatment on Al b Ga 1-b N, a structure where Al c Ga 1-c N is partially formed on Al b Ga 1-b N can be fabricated. Then, after growing Al a Ga 1-a N, remove the etching mask. If the opening pattern of the etching mask is designed such that Al b Ga 1-b N is sandwiched by the openings, a quantum well layer of the light-emitting layer that spreads in the plane direction of the substrate surface sandwiched by Al a Ga 1-a N and Al b Ga 1-b N can be formed. On the upper layer of this layer, Al c Ga​​​​1-c By growing N into a thin film, Al a Ga 1-a N can be horizontally sandwiched between Al b Ga 1-b N, and Al a Ga 1-a N can be vertically sandwiched between Al c Ga 1-c N to create a structure where they are adjacent and sandwiched (0 ≦ a < b < c ≦ 1).

[0044] In this method, Al b Ga 1-b N is grown first and then Al a Ga 1-a N is grown. However, in a similar method, Al a Ga 1-a N can be grown first and then Al b Ga 1-b N can be grown. As another method, with a growth mask such as SiO2 formed on Al c Ga 1-c N, Al b Ga 1-b N can be grown. In this case, the growth mask such as SiO2 can be designed to sandwich the Al b Ga 1-b N where the non - opening part grows. After removing SiO2, by growing Al[[ID=5o]] a Ga 1-a N into a thin film, a structure where Al a Ga 1-a N is horizontally sandwiched between Al b Ga 1-b N can be formed. Then, after going through the planarization process already described in this paragraph, by growing Al c Ga 1-c N into a thin film, a structure where Al a Ga 1-a N is horizontally sandwiched between Al b Ga 1-b N and Al a Ga 1-a N is vertically sandwiched between Al c Ga 1-c N to create a structure where they are adjacent and sandwiched (0 ≦ a < b < c ≦ 1) can be fabricated.

[0045] In this method, Al b Ga 1-b N is grown first and then Al a Ga 1-a N is grown. However, by the same method, Al a Ga 1-a N can be grown first, and then Al b Ga 1-b N can also be grown.

[0046] Also, before removing the growth mask of SiO2, a growth mask different from SiO2 (for example, Ni) is formed after growing Al b Ga 1-b N. Then, if the growth mask of SiO2 is removed, only the growth mask of Ni can be left on the top of Al b Ga 1-b N. In this case, Al a Ga 1-a N can be grown without a planarization process, and the process can be simplified.

[0047] Al a Ga 1-a After growing N, Ni is dissolved with a mixed acid of concentrated hydrochloric acid and concentrated nitric acid in a molar ratio of 3:1, so that a structure in which Al a Ga 1-a N sandwiches Al b Ga 1-b N horizontally can be formed. Then, by growing a thin film of Al c Ga 1-c N, a structure in which Al a Ga 1-a N sandwiches Al b Ga 1-b N horizontally and Al a Ga 1-a N sandwiches Al c Ga 1-c N vertically (0 ≦ a < b < c ≦ 1) can be fabricated without a planarization process.

[0048] Note that "adjacent" means the case where they are directly in contact without any other different substances sandwiched between them. Al a Ga 1-a N is adjacent to Alb Ga 1-b When Al is sandwiched by GaN, a Ga 1-a Al is adjacent to GaN in both one direction and the opposite direction. b Ga 1-b When GaN is adjacent, it means that Al a Ga 1-a GaN may be partially sandwiched and adjacent to Al b Ga 1-b GaN, or may be sandwiched and adjacent to Al GaN on both entire surfaces of one side and the opposite side. b Ga 1-b GaN may be sandwiched and adjacent.

[0049] Also, Al c Ga 1-c GaN may be in contact with Al a Ga 1-a GaN over the entire area or locally in contact on the contact surface in the vertical up and down direction of Al GaN. In this case, when Al c Ga 1-c GaN is sandwiched by Al a Ga 1-a GaN from the vertical up and down direction, it means that on the axis in the vertical direction, Al c Ga 1-c GaN, Al a Ga 1-a GaN, Al c Ga 1-c GaN are preferably formed in this order for the light emitting layer, but there may be portions where they are not formed in the order of Al c Ga 1-c GaN, Al a Ga 1-a GaN, Al c Ga 1-c GaN in this order.

[0050] Furthermore, in the quantum well layer of the light emitting layer, when Al d Ga 1-d GaN is adjacent in the horizontal direction and sandwiched by Al b Ga 1-b GaN, and Al d Ga 1-d GaN is adjacent in the vertical direction and sandwiched by Al c Ga 1-c GaN (0 ≦ b < d < c ≦ 1) structure, Ala Ga 1-a The efficiency of confining electrons and holes to N is further improved. b Ga 1-b It also diffuses into N, but Al b Ga 1-b N has a larger Al composition d Ga 1-d Since it is also adjacent to N, Al b Ga 1-b This is because the diffusion of Al into N is suppressed. a Ga 1-a N, Al b Ga 1-b N, Al d Ga 1-d N transports electrons and holes more easily in this order, and Al a Ga 1-a This makes it easier to confine electrons and holes to N, improving the luminous efficiency of AlGaN-LEDs. a Ga 1-a N, Al b Ga 1-b N, Al d Ga 1-d N, Al b Ga 1-b N, Al a Ga 1-a N, Al b Ga 1-b N, Al d Ga 1-d N. That is, Al a Ga 1-a N, Al b Ga 1-b N, Al d Ga 1-d N, Al b Ga 1-b If a layer with N arranged horizontally in this order is considered to be one unit, then this unit is arranged repeatedly in a horizontal line.

[0051] Here, in the vertical direction, Al c Ga 1-c N, Al a Ga 1-a N, Al c Ga 1-cThe parts arranged in the order of N, Al c Ga 1-c N, Al b Ga 1-b N, Al c Ga 1-c The parts arranged in the order of N, Al c Ga 1-c N, Al d Ga 1-d N, Al c Ga 1-c In other words, the light-emitting layer is a Ga 1-a At least a part of N is vertically connected to Al c Ga 1-c The structure where N is sandwiched between adjacent Al b Ga 1-b At least a part of N is vertically connected to Al c Ga 1-c The structure where N is sandwiched between adjacent Al d Ga 1-d At least a part of N is vertically connected to Al c Ga 1-c N has a structure sandwiched between adjacent N atoms.

[0052] b <cであるため、Al b Ga 1-b N is perpendicular to Al c Ga 1-c When sandwiched between N, an energy barrier occurs b Ga 1-b N and Al c Ga 1-c All quantum well layers and barrier layers in the light-emitting layer are made of Al. b Ga 1-b N in the vertical direction and Al c Ga 1-c It is not necessary for N to sandwich Al. b Ga 1-b N in the vertical direction and Al c Ga 1-c It's fine as long as N is in the middle.

[0053] Furthermore, d <cであるため、Al d Ga 1-dN is perpendicular to Al c Ga 1-c When sandwiched between N, an energy barrier occurs d Ga 1-d N and Al c Ga 1-c All quantum well layers and barrier layers in the light-emitting layer are made of Al. d Ga 1-d N in the vertical direction and Al c Ga 1-c It is not necessary for N to sandwich Al. d Ga 1-d N in the vertical direction and Al c Ga 1-c It's fine as long as N is in the middle.

[0054] The quantum well layer has a low Al composition in both the horizontal and vertical directions. a Ga 1-a N efficiently transports electrons and holes, and the structure is easy to confine them. The difference between b and d is preferably within 0.05, and more preferably within 0.03. By keeping the composition difference between b and d within this range, the stress in the quantum well layer can be reduced, and the occurrence of cracks that cause AlGaN-LEDs to fracture and break can be suppressed. Furthermore, by reducing the stress, the occurrence of non-luminescent defects that reduce luminous efficiency can be suppressed. Another effect is that when the difference between b and d is within this range, an increase in device resistance in the luminescent layer can be suppressed. The difference between b and d is set to form an energy barrier, but on the other hand, if this difference becomes large, the AlGaN-LED, which has a high Al composition, becomes weak. d Ga 1-d The resistance of the N element becomes high, which in turn increases the drive voltage required to drive the element.

[0055] To suppress this increase in driving voltage, the difference between b and d is preferably within the above range. The difference between d and c is preferably greater than 0.01, greater than 0.03, and less than 0.2. If the difference between d and c is less than 0.01, the energy barrier is small, making it extremely difficult to confine electrons and holes efficiently. If the difference between d and c is less than 0.03, the energy barrier is small, making it difficult to confine electrons and holes efficiently. If the difference between d and c is more than 0.2, Al c Ga 1-c N and Al a Ga 1-a N or Al b Ga 1-b The difference in lattice constant between Al and N becomes large, and defects are generated in the quantum well layer, resulting in a decrease in luminous efficiency. d Ga 1-d N is Al b Ga 1-b The following methods can be used to create a structure sandwiched between N. a Ga 1-a N is Al b Ga 1-b After forming a quantum well layer of the light-emitting layer that spreads in the surface direction of the substrate surface sandwiched between N, an etching mask with a partial opening is formed on the quantum well layer, and then Al b Ga 1-b N etching treatment is performed.

[0056] This allows Al c Ga 1-c Al on N b Ga 1-b A structure with partially formed N can be fabricated. d Ga 1-d After growing N, the etching mask is removed. The opening pattern of the etching mask is b Ga 1-b If you design it so that N is sandwiched between Al d Ga 1-d N is Al b Ga 1-b A quantum well layer of the light-emitting layer can be formed on the surface of the substrate sandwiched between N. c Ga 1-c By growing a thin film of N, Ald Ga 1-d N is horizontally adjacent to Al b Ga 1-b N is sandwiched, and Al d Ga 1-d N is vertically adjacent to Al c Ga 1-c a structure in which N is sandwiched (0 ≦ b < d < c ≦ 1) can be fabricated.

[0057] In this method, Al b Ga 1-b N is grown first and then Al d Ga 1-d N is grown. However, by the same method, Al d Ga 1-d N can be grown first, and then Al b Ga 1-b N can be grown. However, in that case, the etching mask must be designed so that Al b Ga 1-b N sandwiches Al a Ga 1-a N adjacent to it on both sides. As another method, with a growth mask such as SiO2 formed on Al c Ga 1-c N, Al b Ga 1-b N can be grown. In this case, the growth mask such as SiO2 can be designed so that the non-opening part sandwiches Al b [[ID=�3]]Ga 1-b N. After removing SiO2, with a growth mask of SiO2 attached again, Al a Ga 1-a N is grown as a thin film to form a structure in which Al a Ga 1-a N is horizontally sandwiched by Al b Ga 1-b N adjacent to it on both sides. At this time, the pattern of the growth mask coating part is designed so that Al b Ga 1-b N sandwiches it adjacent to it on both sides.

[0058] Al a Ga<000055S>After the thin film growth of Al d Ga1-d By growing N, Al d Ga 1-d N can be made to sandwich Al b Ga 1-b N in a horizontally adjacent structure. After that, after undergoing the planarization process described above, Al c Ga 1-c N is grown into a thin film. In the quantum well layer of the light-emitting layer, Al d Ga 1-d N can be made to sandwich Al b Ga 1-b N horizontally, and Al d Ga 1-d N can be made to sandwich Al c Ga 1-c N vertically to form a structure (0 ≦ b < d < c ≦ 1).

[0059] In this method, Al b Ga 1-b N is grown first and then Al[[ID=3S]] d Ga 1-d N is grown. However, with a similar method, Al d Ga 1-d N can be grown first, and then Al b Ga 1-b N can be grown. However, in that case, an etching mask must be designed so that Al b Ga 1-b [[ID=S3]]N sandwiches Al a Ga 1-a N adjacently.

[0060] Also, before removing the growth mask of SiO2, a growth mask different from SiO2 (for example, Ni) is deposited after growing Al b Ga 1-b N. Then, if the growth mask of SiO2 is removed, a Ni growth mask can be left only on the top of Al b Ga 1-b N (and Al a Ga 1-a N). In this case, Al d Ga 1-d N can be grown without a planarization process, simplifying the process. Al[[ID= / 8]] d Ga1-d After growing N, Ni is dissolved in a mixed acid with a molar ratio of 3:1 of concentrated hydrochloric acid and concentrated nitric acid to dissolve Al d Ga 1-d N can form a structure in which Al b Ga 1-b N is sandwiched adjacent to each other in the horizontal direction. <C <C

[0061] <C After that, by growing a thin film of Al c Ga 1-c N, in the quantum well layer of the light-emitting layer, Al d Ga) 1-d N can be sandwiched adjacent to each other in the horizontal direction by Al b Ga 1-b N, and in the vertical direction by Al c Ga 1-c N (0 ≦ b < d < c ≦ 1) can be fabricated without a planarization process. <C <C

[0062] <C The barrier layer sandwiching the quantum well layer of the light-emitting layer is Al c Ga 1-c N. Here, in the barrier layer of the light-emitting layer that spreads in the plane direction of the substrate surface, Al e Ga 1-e N can be sandwiched adjacent to each other in the horizontal direction by Al c Ga 1-c N, and Al e Ga 1-e N can be sandwiched adjacent to each other in the vertical direction by Al a Ga 1-a N (0 ≦ a < e < c ≦ 1). In the case of a structure in which Al e Ga 1-e N is sandwiched adjacent to each other in the horizontal direction by Al c Ga 1-c N, and Al e Ga 1-e N is sandwiched adjacent to each other in the vertical direction by Al a Ga 1-a N is sandwiched, in the case of the structure, Al e Ga 1-e N has a locally low Al composition in the barrier layer and a low energy potential, so it becomes a region where electrons and holes are easily transported.<C <C

[0063] <C Generally, a barrier layer is used for the purpose of forming an energy barrier to confine electrons and holes in a quantum well layer. However, in the present invention, this energy barrier is formed at the interface between Al a Ga 1-a N and the adjacent Al c Ga 1-c N or between Al e Ga 1-e N. The preferred height of the energy barrier at the interface between Al a Ga 1-a N and the adjacent barrier layer is different from the preferred height of the energy barrier at the interface between Al b Ga 1-b N and the adjacent barrier layer. That is, it is preferable to use Al a Ga 1-a N with an Al composition ratio lower than that of Al c Ga 1-c N as the barrier layer adjacent to Al e Ga 1-e N. Thus, Al b Ga 1-b Nw with an Al composition ratio higher than that of Al e Ga 1-e N can be adjacent to the barrier layer. Since the design of the adjacent barrier layer can be carried out according to the Al composition ratio of AlGaN in the quantum well layer, the light emission efficiency can be increased.

[0064] Furthermore, by using Al e Ga 1-e N with a low Al composition in the barrier layer, the resistance when electrons and holes are transported from the barrier layer to each quantum well of the multiple quantum wells can be reduced, the resistance of the LED can be lowered, and the driving voltage can be lowered. Also, due to the relationship of a < b < e < c, considering the energy potential, the electrons and holes transported into Al c Ga 1-c N will go from Al c Ga 1-c N to Al b Ga 1-b N via Al a Ga 1-a N, or to Al c ​​​​Ga 1-c N to Al e Ga 1-e N, Al b Ga 1-b Al through N a Ga 1-a The difference between e and c is preferably within 0.05, and more preferably within 0.03. By keeping the compositional difference between e and c within this range, stress within the quantum well layer can be reduced, and the occurrence of cracks that cause AlGaN-LEDs to fracture and break can be suppressed. Furthermore, by reducing stress, the occurrence of non-luminescent defects that reduce luminous efficiency can be suppressed.

[0065] Another effect is that when the difference between e and c is within this range, an increase in device resistance in the light-emitting layer can be suppressed. The difference between e and c is set to form an energy barrier, but on the other hand, if this difference becomes large, the Al content of the high Al composition increases. c Ga 1-c The element resistance of N becomes high. As a result, the driving voltage for driving the element becomes high. To suppress this increase in driving voltage, it is preferable that the difference between e and c be within the above range.

[0066] The difference between a and e is preferably greater than 0.01, greater than 0.03, and less than 0.2. If the difference between a and e is less than 0.01, the energy barrier is small, making it extremely difficult to confine electrons and holes efficiently. If the difference between a and e is less than 0.03, the energy barrier is small, making it difficult to confine electrons and holes efficiently. If the difference between a and e is more than 0.2, Al e Ga 1-e N and Al a Ga 1-a N or Al b Ga 1-b The difference in lattice constant with N becomes large, and defects are generated in the quantum well layer, resulting in a decrease in light emission efficiency.

[0067] Furthermore, the barrier layer of the light-emitting layer is Al f Ga 1-f Al is placed horizontally next to N. c Ga 1-cN sandwiches, Al f Ga 1-f Al is adjacent to N in the vertical direction d Ga 1-d A structure in which N sandwiches (0 ≦ d < c < f ≦ 1) may be used. Al f Ga 1-f Al is adjacent to N in the horizontal direction c Ga 1-c N sandwiches, Al f Ga 1-f Al is adjacent to N in the vertical direction d Ga 1-d In the case of a structure where N sandwiches, Al c Ga 1-c N is in the barrier layer and Al f Ga 1-f has a lower Al composition than N and a lower energy potential, so it becomes a region where electrons and holes are easily transported. In this case, in the horizontal direction, Al e Ga 1-e N, Al c Ga 1-c N, Al f Ga 1-f N, Al c Ga 1-c N, Al e Ga 1-e N, Al c Ga 1-c N, Al f Ga 1-f N ··· are arranged in this order. That is, Al e Ga 1-e N, Al c Ga 1-c N, Al f Ga 1-f N, Al c Ga 1-c If a layer in which N is arranged in this order horizontally is taken as one unit, this unit is arranged repeatedly in the horizontal direction.

[0068] In the vertical direction, Al a Ga 1-a N, Al e Ga 1-e N, Al a Ga 1-a At the location where N, Al b Ga 1-b N, Al c Ga1-c N, Al b Ga 1-b The part arranged in the order of N, Al d Ga 1-d N, Al f Ga 1-f N, Al d Ga 1-d There is a part arranged in the order of N.

[0069] Al in the quantum well layer d Ga 1-d N is Al f Ga 1-f The Al composition is lower than that of N and the energy potential is lower, so it becomes a region where electrons and holes are easily transported. Generally, the barrier layer is used for the purpose of forming an energy barrier to confine electrons and holes in the quantum well layer. However, in the present invention, this energy barrier is formed at the interface between Al d Ga<0,`000742>Al adjacent to N c Ga 1-c N, or Al f Ga 1-f and N.

[0070] Here, Al d Ga<00,`00748>The preferable height of the energy barrier between N and the barrier layer is different from the height of the energy barrier at the interface between Al a Ga 1-a N or Al b Ga 1-b and the barrier layer adjacent to N. That is, between Al d Ga 1-d N and the barrier layer, Al c Ga 1-c Al with a higher Al composition than N f Ga 1-f N is preferably used, and thereby the light emission efficiency can be increased.

[0071] Also, due to the relationship of a < b < d < c < f, considering the energy potential, the electrons and holes transported into Al f Ga 1-f N are Al f Ga 1-fN to Al d Ga 1-d Al through N b Ga 1-b N or Al a Ga 1-a The difference between c and f is preferably within 0.05, and more preferably within 0.03. By keeping the composition difference between c and f within this range, the stress in the quantum well layer can be reduced, and the occurrence of cracks that cause AlGaN-LEDs to fracture and break can be suppressed. Furthermore, by reducing the stress, the occurrence of non-luminescent defects that reduce luminous efficiency can be suppressed. Another effect is that when the difference between c and f is within this range, an increase in device resistance in the luminescent layer can be suppressed. The difference between c and f is set to form an energy barrier, but on the other hand, if this difference becomes large, the AlGaN-LED with a high Al composition will be degraded. f Ga 1-f The element resistance of N becomes high. As a result, the driving voltage for driving the element becomes high. To suppress this increase in driving voltage, it is preferable that the difference between c and f be in the above range.

[0072] The difference between d and f is preferably greater than 0.01, greater than 0.03, and less than 0.2. If the difference between d and f is less than 0.01, the energy barrier is small, making it extremely difficult to confine electrons and holes efficiently. If the difference between d and f is less than 0.03, the energy barrier is small, making it difficult to confine electrons and holes efficiently. If the difference between d and f is greater than 0.2, Al f Ga 1-f N and Al d Ga 1-d N or Al b Ga 1-b The difference in lattice constant with N becomes large, and defects are generated in the quantum well layer, resulting in a decrease in light emission efficiency.

[0073] Furthermore, e ≤ d may also be possible. When e ≤ d, the vertical diffusion is promoted more than the horizontal diffusion in the transport of electrons and holes, reducing the resistance. Also, when using multiple quantum wells, it has the effect of suppressing the concentration of electrons and holes in one quantum well layer and dispersing them in many quantum wells. As a result, it has the effects of improving the light emission efficiency and suppressing device breakdown due to carrier concentration.

[0074] (p-type semiconductor layer) The p-type semiconductor layer is Al k Ga 1-k N (0 < k ≤ 1) is used as the material. When the p-type semiconductor constituting the p-type semiconductor layer is an n-type semiconductor, for example, Al 19 cm -3 doped with a concentration of Si of 1 × 10 k Ga 1-k N can be used. Also, as the p-type semiconductor, AlGaN n-type doped by the polarization doping method in which the mixed crystal composition ratio of the polar mixed crystal semiconductor is continuously changed may be used.

[0075] When the p-type semiconductor constituting the p-type semiconductor layer is a p-type semiconductor, for example, Al 19 cm -3 doped with a concentration of Mg of 3 × 10 k Ga 1-k N can be used. Also, as the p-type semiconductor, AlGaN p-type doped by the polarization doping method in which the mixed crystal composition ratio of the polar mixed crystal semiconductor is continuously changed may be used.

[0076] Furthermore, a barrier layer with a large band gap may be provided on the light-emitting layer side of the second conductivity-type semiconductor layer to suppress the movement of electrons and holes that reduce light emission efficiency. Furthermore, a contact layer heavily doped with impurities may be provided on the second conductivity-type electrode side of the second conductivity-type semiconductor layer to reduce contact resistance with the electrode. The thickness of the second conductivity-type semiconductor layer is not particularly limited, but is preferably 5 nm to 1000 nm to achieve high light output. A thinner second conductivity-type semiconductor layer is preferable because it can suppress light absorption. However, if the thickness is less than 5 nm, the effect of compositional variations in the thin film stack surface becomes significant, making it difficult to inject uniform current. If the thickness of the second conductivity-type semiconductor layer is greater than 1000 nm, the time required for thin film formation increases, resulting in higher costs.

[0077] The Al composition ratio is uniform in the horizontal direction above the light-emitting layer. g Ga 1-g N (0≦g≦1) layers may be present. Since the light-emitting layer has a non-uniform composition in the horizontal direction, when a thin film is laminated on top of it, the Al composition ratio may not be uniform when laminating an AlGaN mixed crystal depending on the composition and surface shape of the base. Here, if a layer with a uniform composition is placed on top of the light-emitting layer, g Ga 1-g By stacking an N layer, the compositional non-uniformity in the second conductivity type semiconductor layer due to the horizontal compositional non-uniformity of the light emitting layer can be alleviated. It is preferable to stack AlN or GaN, which are binary mixed crystals and therefore do not cause compositional non-uniformity in the Al composition ratio. Furthermore, it is preferable to stack this AlN or GaN adjacent to the light emitting layer on top of it. The thickness of the AlN or GaN is preferably 5 nm or more from the viewpoint of covering the lower layers including the light emitting layer without leaving any exposed portions, and furthermore, it is preferably 1 μm or less from the viewpoint of suppressing the occurrence of cracks. From the viewpoint of efficiently transporting electrons or holes from the second conductivity type semiconductor to the light emitting layer, the thickness of the AlN or GaN is preferably 50 nm or less.

[0078] Al g Ga 1-gWhen N is a ternary mixed crystal of Al, Ga, and N, the film thickness is preferably 5 nm or more, more preferably 10 nm or more, so as to prevent the composition and surface shape of the base from being reflected in the upper layer. From the viewpoint of suppressing the occurrence of cracks, the film thickness is preferably 1 μm or less, and from the viewpoint of efficiently transporting electrons or holes from the second conductivity type semiconductor to the light-emitting layer, the film thickness is more preferably 50 nm or less.

[0079] The top layer of the AlGaN thin film has a uniform Al composition ratio in the horizontal direction. h Ga 1-h It is preferable that there is an N (0≦h≦1) layer. The uppermost layer of the thin film has a second conductivity type electrode adjacent to it, and has the function of injecting electrons or holes from the electrode into the thin film and transporting them further to the light-emitting layer side. In order to efficiently transport electrons or holes from the second conductivity type electrode to the AlGaN thin film, it is necessary to use an AlGaN thin film with a uniform Al composition ratio. h Ga 1-h It is preferable that N contacts the second conductivity type electrode rather than a non-uniform AlGaN contact. h Ga 1-h The presence of N has the effect of homogenizing the Al composition unevenness in the layers above the light-emitting layer, which is caused by the non-uniformity of the Al composition in the horizontal direction of the light-emitting layer, and reducing the unevenness of the thin film surface.

[0080] <First conductivity type electrode, second conductivity type electrode> The first conductivity type electrode and the second conductivity type electrode are preferably made of a material that provides ohmic contact with the semiconductor layer in contact therewith.

[0081] The first conductivity type electrode is in contact with, for example, the n-type semiconductor layer. Examples of materials constituting the electrode in contact with the n-type semiconductor layer include Ti, Al, Ni, Au, Cr, V, Zr, Hf, Nb, Ta, Mo, W, or alloys thereof, and ITO, and materials containing aluminum and nickel are more preferred from the viewpoint of reducing contact resistance.

[0082] The second conductivity type electrode is in contact with, for example, the p-type semiconductor layer. Examples of materials constituting the electrode in contact with the p-type semiconductor layer include Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, and alloys thereof, and ITO. When the p-type semiconductor layer is a nitride semiconductor layer, Ni, Au, or alloys thereof, or ITO, which have low contact resistance with the nitride semiconductor layer, are preferred.

[0083] For connection, the electrodes may be formed by successively depositing metal layers such as Au, Al, Cu, Ag, and W, and it may be desirable to use Au, which has high conductivity. Furthermore, to improve adhesion, the electrodes may further contain Ti at the interface with the laminated thin film.

[0084] An insulating layer may be provided to protect the surface of the nitride semiconductor layer from air, water, static electricity, physical shock, etc. Examples of materials for the insulating layer include oxides or nitrides such as SiO2, SiN, SiON, and Al2O3. SiO2 or SiN is particularly preferred because of its simple formation process. The insulating layer may be a single layer or a multilayer structure in which multiple materials are stacked.

[0085] The electrodes or insulating layers can be formed using general semiconductor manufacturing equipment, such as a plasma chemical vapor deposition (CVD) system that decomposes raw material gases in a plasma atmosphere to form an insulating layer on a nitride semiconductor thin film, a sputtering system that forms a film by sputtering raw materials, or an evaporation system that vaporizes raw materials using heat or an electron beam to form a film.

[0086] <Measurement method> The thickness of each layer of the AlGaN-LED of this embodiment can be measured by cutting out a predetermined cross section perpendicular to the main surface of the substrate, observing this cross section with a transmission electron microscope (TEM), and using the TEM length measurement function.

[0087] The composition of each layer of the AlGaN-LED of this embodiment can be measured by reciprocal space mapping (RSM) using X-ray diffraction (XRD). Specifically, the Al composition can be determined by analyzing reciprocal space mapping data near the diffraction peak obtained using an asymmetric plane as the diffraction plane. Examples of the diffraction plane include the (10-15) plane and the (20-24) plane.

[0088] Additionally, for layers that do not provide sufficient reflection intensity using XRD, such as quantum well layers and graded layers, measurements can be performed using X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and electron energy-loss spectroscopy (EELS).

[0089] EELS analyzes the composition of a sample by measuring the energy lost when an electron beam passes through the sample. Specifically, for example, in a thin-sectioned sample used in TEM observation, the energy loss spectrum of the transmitted electron beam intensity is measured and analyzed. The position of the peak that appears around 20 eV of energy loss varies depending on the composition of each layer, and the composition can be determined from the peak position.

[0090] XPS allows for depth profile evaluation by performing XPS measurements while performing sputter etching using an ion beam. While Ar+ is typically used as the ion beam, other ion species, such as Ar cluster ions, can also be used as long as they can be irradiated with the etching ion gun installed in the XPS instrument. The depth profile of the Al composition in each layer can be obtained by measuring and analyzing the XPS peak intensities of Al, Ga, and N. Instead of sputter etching, the LED can be polished at an angle so that a cross section perpendicular to the main surface of the substrate is enlarged and exposed, and the exposed cross section can then be measured using XPS.

[0091] The composition of each layer can be measured not only by XPS but also by Auger Electron Spectroscopy (AES). In this case, the composition can be measured by Auger Electron Spectroscopy on a cross section exposed by sputter etching or angled polishing. The composition of each layer can also be measured by SEM-EDX measurement of a cross section exposed by angled polishing. The number of repetition periods of the multiple quantum well structure of the AlGaN-LED of this embodiment is defined by the number of quantum well layers, and can be measured by TEM observation as above.

[0092] <Other embodiments> As described above, the present disclosure has been described using the embodiments shown in FIGS. 1 and 2 and explanations of each layer, but the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operational techniques will become apparent to those skilled in the art from this disclosure. It goes without saying that the present technology includes various embodiments not described herein. Various omissions, substitutions, and / or modifications of components may be made without departing from the spirit of the above-described embodiments and explanations of each layer. Furthermore, the effects described in this specification are merely exemplary and not limiting, and other effects may also be present. [Explanation of symbols]

[0093] 2. Barrier Layer 3. Well layer 11 Circuit Board 11a surface 11b Back side 12 n-AlGaN layer 13 AlGaN light-emitting layer 14 AlGaN electron blocking layer 15 p-AlGaN layer 16 p-GaN (contact) layer 21 1st conductivity type electrode 22 Second conductivity type electrode 41 LED board 131 AlGaN quantum well layer 132 AlGaN barrier layer AR1 1st area AR2 2nd area

Claims

1. A substrate; a light-emitting layer provided on a first main surface of the substrate and extending in a horizontal direction parallel to the first main surface, The light-emitting layer is Al ａ Ga １－ａ N and Al ｂ Ga １－ｂ N, and the Al ａ Ga １－ａ N is replaced with Al ｂ Ga １－ｂ N horizontally sandwiching adjacent quantum well layers; Al ｃ Ga １－ｃ a barrier layer containing N, The Al ｃ Ga １－ｃ N is the Al ａ Ga １－ａ N are sandwiched adjacently in a vertical direction perpendicular to the first main surface (0≦a<b<c≦1).

2. The quantum well layer is Al ｄ Ga １－ｄ further comprising N, The Al ｂ Ga １－ｂ N, the Al ａ Ga １－ａ N, the Al ｂ Ga １－ｂ N, the Al ｄ Ga １－ｄ N, the Al ｂ Ga １－ｂ N, the Al ａ Ga １－ａ N, the Al ｂ Ga １－ｂ N, the Al ｄ Ga １－ｄ They are arranged in the order of N... The Al ｃ Ga １－ｃ N is the Al ｂ Ga １－ｂ The light-emitting device of claim 1 , wherein at least a portion of N are sandwiched between adjacent ones of the N in the vertical direction (0≦b<d<c≦1).

3. The barrier layer is made of Al ｅ Ga １－ｅ further comprising N, The Al ｃ Ga １－ｃ N is the Al ｅ Ga １－ｅ N is sandwiched adjacently, The Al ａ Ga １－ａ N is the Al ｅ Ga １－ｅ The light-emitting device according to claim 2 , wherein at least a portion of N are sandwiched between adjacent ones of the N in the vertical direction (0≦a<e<c≦1).

4. The barrier layer is made of Al ｆ Ga １－ｆ further comprising N, The Al ｅ Ga １－ｅ N, the Al ｃ Ga １－ｃ N, the Al ｆ Ga １－ｆ N, the Al ｃ Ga １－ｃ N, the Al ｅ Ga １－ｅ N, the Al ｃ Ga １－ｃ N, the Al ｆ Ga １－ｆ N, the Al ｃ Ga １－ｃ They are arranged in the order of N... The Al ｄ Ga １－ｄ N is the Al ｆ Ga １－ｆ The light-emitting device according to claim 3 , wherein at least a portion of N are sandwiched between adjacent ones of the N in the vertical direction (0≦d<c<f≦1).

5. an Al film having a uniform Al composition ratio in the horizontal direction provided on the light-emitting layer; ｇ Ga １－ｇ The light-emitting device according to claim 1 , comprising an N-layer.

6. The Al ｇ Ga １－ｇ an AlGaN thin film provided on the N layer; The top layer of the AlGaN thin film is an AlGaN thin film having a uniform Al composition ratio in the horizontal direction. ｈ Ga １－ｈ The light-emitting device according to claim 5 , which is an N-layer (0≦h≦1).

7. The light-emitting device further includes a conductive layer provided under the light-emitting layer, The conductive layer is Al ｉ Ga １－ｉ N and Al ｊ Ga １－ｊ N, and the Al ｉ Ga １－ｉ N is replaced with Al ｊ Ga １－ｊ The light-emitting element according to claim 1 , wherein N adjacent elements sandwich the element in the horizontal direction (0<i<j≦1).

8. 4. The light-emitting device according to claim 3, wherein e≦d.

Images