UV-emitting element

Abstract

A UV-emitting element (1) has a layered structure comprising, in order: an active layer (13) containing a Group III-V nitride semiconductor; a p-AlGaN layer (15); a UV transparent electrode layer (16); and a p-type contact electrode (17).

Description

ultraviolet light emitting element

[0001] The present invention relates to an ultraviolet light-emitting device, and more particularly to a light-emitting device having an emission wavelength in the deep ultraviolet region.

[0002] In ultraviolet light-emitting devices (UV-LEDs), it is possible to generate light with a short wavelength by adjusting the composition of the semiconductor that forms the light-emitting layer. For example, when an AlGaN semiconductor is used, adjusting the Al composition ratio allows the LED to emit light with a wavelength in the range of 210 nm to 365 nm (ultraviolet to deep ultraviolet region).

[0003] In order to improve the efficiency of an ultraviolet light emitting device, it is necessary to efficiently extract light generated in the light emitting layer to the outside of the LED. ｘ Ga １－ｘ Between the n-contact layer made of N material (0.7≦x≦1.0) and the n-side electrode, Al ｙ Ga １－ｙ A nitride semiconductor light-emitting device is disclosed in which an intermediate layer made of an N material (0≦y≦0.5) is formed to prevent absorption of ultraviolet light generated in the light-emitting layer in the n-contact layer.

[0004] JP 2010-161311 A

[0005] In order to increase the output of ultraviolet light-emitting devices, further improvement in light extraction efficiency is required. One of the objects of the present invention is to improve the luminous efficiency of light-emitting devices having an emission wavelength in the deep ultraviolet region.

[0006] According to the present invention, the following ultraviolet light-emitting devices are provided: 1. An ultraviolet light-emitting device having a layered structure including, in this order, an active layer containing a III-V nitride semiconductor, a p-AlGaN layer, an ultraviolet-transparent electrode layer, and a p-type contact electrode. 2. The ultraviolet light-emitting device according to 1, which has a p-GaN layer between the p-AlGaN layer and the ultraviolet-transparent electrode layer. 3. The ultraviolet light-emitting device according to 1 or 2, which has an AlN layer between the active layer and the p-AlGaN layer. 4. The ultraviolet light-emitting device according to any one of 1 to 3, in which ultraviolet light generated in the active layer is extracted from the ultraviolet-transparent electrode layer side. 5. The ultraviolet light-emitting device according to any one of 1 to 3, in which ultraviolet light generated in the active layer is extracted from the side opposite the p-type contact electrode. 6. The ultraviolet light-emitting device according to any one of 1 to 5, in which the ultraviolet-transparent electrode layer contains magnesium oxide and zinc oxide as main components, and contains at least one element X selected from trivalent and tetravalent metal elements other than the magnesium and zinc. 7. 8. The ultraviolet light-emitting device according to 6, wherein the molar ratio of the element X to all metal elements [element X / total metal elements] is 0.0001 or more and 0.20 or less. 9. The ultraviolet transparent electrode layer has a conductivity of 1.0×10 －１ 9. The ultraviolet light-emitting element according to any one of 1 to 7, wherein the carrier concentration of the ultraviolet transparent electrode layer is 1.0×10 S / cm or more. １８ cm －３ That's it, 1.0 x 10 ２２ cm －３ 10. The ultraviolet light-emitting device according to any one of 1 to 8, wherein the carrier concentration of the ultraviolet transparent electrode layer is 1.0×10 or less. １９ cm －３ 10. The ultraviolet light-emitting device according to 9 above.

[0007] According to the present invention, the luminous efficiency of the ultraviolet light emitting element can be improved.

[0008] 1 is a diagram illustrating an example of a layer structure of an ultraviolet light-emitting element according to an embodiment. 2 is a diagram illustrating a layer structure of an ultraviolet light-emitting element fabricated in an example.

[0009] An ultraviolet light-emitting device according to one embodiment of the present invention has a layered structure including, in this order, an active layer containing a III-V nitride semiconductor, a p-AlGaN layer, an ultraviolet transparent electrode layer, and a p-type contact electrode.

[0010] 1 is a diagram illustrating an example of the layer configuration of an ultraviolet light-emitting element according to this embodiment. The ultraviolet light-emitting element 1 has a layered structure including, in this order, a substrate 11, an n-type contact layer 12, an active layer 13 (sometimes referred to as a light-emitting layer), a p-AlGaN layer 15, an ultraviolet transparent electrode layer 16, and a p-type contact electrode 17. An n-type contact electrode 18 is formed on a portion of the n-type contact layer 12 where the active layer 13 is not formed.

[0011] In this embodiment, holes are injected from the p-type contact electrode 17 and electrons are injected from the n-type contact electrode 18, and the holes recombine in the active layer 13, thereby emitting light. Of the light generated in the active layer 13, light that is emitted in the direction of the p-type contact electrode 17 is reflected by the p-type contact electrode 17 and extracted from the substrate 11. In the light-emitting element 1, the light extraction efficiency can be improved by forming the ultraviolet transparent electrode layer 16 and the p-type contact electrode 17. Furthermore, for example, by providing the ultraviolet transparent electrode layer 16 with a layer having an MgZnO-based composition, which will be described later, the applied voltage can be reduced, thereby improving the luminous efficiency.

[0012] The ultraviolet light-emitting device of this embodiment may have a layered structure including, in this order, an active layer 13, a p-AlGaN layer 15, an ultraviolet transparent electrode layer 16, and a p-type contact electrode 17, and the other layers are not limited and may be any known layer. For example, a buffer layer may be provided between the substrate and the n-type contact layer. Furthermore, an electron blocking layer and / or a hole blocking layer may be formed to trap holes or electrons in the light-emitting layer. Each layer constituting the light-emitting device may be a single layer or may have a layered structure of two or more layers.

[0013] In one embodiment, the ultraviolet light emitting device has a p-GaN layer and a p-AlGaN layer between the p-AlGaN layer and the ultraviolet transparent electrode layer. ＋ The p-GaN layer and the p-GaN layer ＋ The p-GaN layer may have only one of the p-GaN layer and the p-GaN layer. ＋ -GaN layer, ＋When only the p-GaN layer is provided, the efficiency of hole injection into the p-GaN layer can be improved. ＋ -p when only the GaN layer is included ＋ The efficiency of hole injection into the p-GaN layer can be improved. ＋ The thickness of the -GaN layer is preferably 1 nm or more and 50 nm or less, and more preferably 5 nm or more and 20 nm or less.

[0014] In one embodiment, the ultraviolet light-emitting device has an AlN layer between the active layer and the p-AlGaN layer. The AlN layer functions as an electron blocking layer, thereby improving the light-emitting efficiency. The thickness of the AlN layer is preferably 0.5 nm to 10 nm, and more preferably 0.5 nm to 5 nm.

[0015] In the ultraviolet light-emitting device of this embodiment, the direction from which light (ultraviolet rays) is extracted is not particularly limited. The ultraviolet light-emitting device 1 extracts light from the substrate 11 side (the opposite side of the p-type contact electrode 17) (face down), making it suitable as a light-emitting device for flip-chip mounting. In flip-chip mounting, the p-type contact electrode 17 and the n-type contact electrode 18 are connected to the positive and negative electrodes, respectively, via wiring on the substrate on which the device is mounted. In this case, it is preferable to use a light-reflecting layer such as a metal for the p-type contact electrode 17.

[0016] On the other hand, for example, by forming the p-type contact electrode 17 in a lattice-like shape with gaps, it is possible to extract light from the p-type contact electrode 17 side (face up). In this case, a light-opaque material can be used for the substrate 11. In one embodiment, the ultraviolet light-emitting element can extract ultraviolet light from both the substrate side 11 and the p-type contact electrode 17 side.

[0017] The configuration of the light-emitting device fabricated in the examples of the present application will be illustrated below, and each component will be described in detail. Figure 2 is a diagram illustrating the layer configuration of the ultraviolet light-emitting device fabricated in the examples. The same numbers are used for layers that are the same as those in the ultraviolet light-emitting device 1. The ultraviolet light-emitting device 2 comprises a sapphire substrate as the substrate 11, an AlN layer and a u-AlGaN layer as the buffer layer 21, an n-AlGaN layer as the n-type contact layer 12, an AlGaN-based layer as the active layer 13, an AlN layer as the electron blocking layer 22, a p-AlGaN layer 15, and a p-GaN layer and p-AlGaN layer. ＋ The buffer layer 21 has a structure in which a -GaN layer 23, an ultraviolet transparent electrode layer 16, and a p-type contact electrode 17 are stacked in this order. An n-type contact electrode 18 is connected to a part of the surface of the buffer layer 21 facing the active layer 13, in a region where the active layer 13 is not provided.

[0018] (Substrate 11) The substrate is not particularly limited, and known materials used in this technical field can be used. In the case of a face-down type ultraviolet light-emitting element, a material capable of transmitting deep ultraviolet light (360 nm or less) is used for the substrate. Examples of materials capable of transmitting deep ultraviolet light include sapphire, AlGaN, AlN, InAlGaN, and SiC. Among these, a sapphire substrate is preferred. The thickness of the sapphire substrate can be, for example, 430 μm or more and 1000 μm or less. When the emission wavelength is 260 nm or more, the crystal growth surface of the substrate is preferably the c-plane (0001). When the emission wavelength is 260 nm or less, a crystal plane other than the c-plane may be used.

[0019] In the case of a face-up type ultraviolet light emitting element, in addition to the above-mentioned substrate, Si, ScAlMg, ZnO, LiGaO ２ , LiAlO ２ etc. can be used.

[0020] (Buffer Layer 21) When a thin film of a different crystal is stacked on a substrate, the buffer layer reduces differences in the crystal structure and atomic arrangement between the materials. The buffer layer may allow a thin film with fewer defects to be grown. The buffer layer may be a single layer or a stacked structure of two or more layers. The buffer layer may have, for example, an AlN composition or an AlGaN composition. The total thickness of the buffer layer is not particularly limited and may be, for example, 1000 nm or more, 1500 nm or more, or 2000 nm or more, and 5000 nm or less, 4500 nm or less, or 4000 nm or less. The thickness of each layer constituting the buffer layer is, for example, 50 nm or more and 500 nm or less, preferably 70 nm or more and 300 nm or less, and more preferably 80 nm or more and 150 nm or less.

[0021] (N-type Contact Layer 12) The n-type contact layer functions as, for example, an electron transport layer. The n-type contact layer has an AlGaN-based composition. The AlGaN-based composition is not particularly limited, and can be, for example, Al ａ Ga １－ａ N (where a is 0.5 or more, 0.55 or more, or 0.6 or more, and 0.95 or less, 0.9 or less, or 0.8 or less). The n-type contact layer is n-doped. As a dopant used for n-type doping, Si is preferred when the Al composition is 60% or more, and Ge is preferred when the Al composition is 60% or less. The dopant concentration in the n-type contact layer is, for example, 8×10 １８ cm －３ ~4 x 10 １９ cm －３ In the present application, "Al composition: %" refers to the proportion of Al atoms in an AlGaN-based composition [Al / (Al+Ga): atomic %]. The thickness of the n-type contact layer is not particularly limited, and is, for example, 500 nm or more, 700 nm or more, or 900 nm or more, and is 4000 nm or less, 3000 nm or less, or 2000 nm or less.

[0022] (Active layer 13) The active layer is a light-emitting layer that emits light in the ultraviolet region. The active layer is a layer containing a group III-V nitride semiconductor. The active layer may have, for example, an AlGaN-based composition and a multiple quantum well (MQW) structure. The active layer may include a plurality of well layers and a plurality of barrier layers having a band gap larger than that of the well layers. Here, the plurality of well layers and the plurality of barrier layers are each made of Al ｂ Ga １－ｂ N (b is 0.35 or more, 0.5 or more, or 0.6 or more, and 0.5 or less, 0.7 or less, or 0.8 or less). This composition (the value of b) may be the same for each layer or may be different. The thickness of each well layer is, for example, 1 to 6 nm, and the thickness of each barrier layer is, for example, 3 to 15 nm. The configuration of the active layer is not limited to this. For example, the active layer may not have a multiple quantum well structure. For example, the active layer may have a single quantum well structure, or may be composed of a single layer.

[0023] (AlN Layer 22) The AlN layer functions as, for example, an electron blocking layer. The thickness of the AlN layer is preferably 0.5 nm to 10 nm, and more preferably 0.5 nm to 5 nm.

[0024] (p-AlGaN layer 15) The p-AlGaN layer has, for example, a function of improving hole injection efficiency and a function of transmitting ultraviolet light, and has an AlGaN-based composition. The p-AlGaN layer is p-type doped. Dopants used for p-type doping include known metal elements such as Mg. The Mg concentration in the p-AlGaN layer is 1×10 １８ cm －３ That's it, 1 x 10 ２０ cm －３ Preferably, it is less than 5 × 10 １８ cm －３ That's it, 5 x 10 １９ cm －３ The p-AlGaN layer can be a single layer or can have a multi-layer structure formed of multiple layers, and its thickness is preferably 1 nm or more and less than 100 nm.

[0025] (p-GaN layer and p＋ -GaN layer 23) p-GaN layer and p ＋ The GaN layer has the function of improving hole injection efficiency. ＋ The dopant concentration (e.g., Mg concentration) of the -GaN layer is higher than that of the p-GaN layer. For example, the Mg concentration of the p-GaN layer is 5×10 １８ cm －３ That's it, 2 x 10 ２０ cm －３ Preferably, it is equal to or less than 1×10 １９ cm －３ That's it, 1 x 10 ２０ cm －３ The following is true: ＋ - The Mg concentration in the GaN layer is 1×10 １９ cm －３ That's it, 5 x 10 ２０ cm －３ Preferably, it is equal to or less than 1×10 ２０ cm －３ That's it, 3 x 10 ２０ cm －３ The p-GaN layer and p ＋ The p-GaN layer is preferably formed thinly to absorb deep ultraviolet rays. ＋ The thickness of each of the p-GaN layers is preferably 1 nm or more and 50 nm or less, and more preferably 5 nm or more and 20 nm or less. ＋ Both of the -GaN layers may be provided, or only one of them may be provided.

[0026] Buffer layer, n-type contact layer, active layer, p-AlGaN layer, p-GaN layer and p ＋ The method for forming the GaN layer is not particularly limited, and metal organic vapor phase epitaxy (MOVPE) or the like can be used.

[0027] (Ultraviolet-Transparent Electrode Layer 16) The ultraviolet-transparent electrode layer transmits ultraviolet light, for example, light having an emission wavelength in the range of 200 to 350 nm, and transfers holes between the p-GaN layer and the p ＋The ultraviolet transparent electrode layer 16 has a function of injecting ions into a layer adjacent to the active layer 13 side of the ultraviolet transparent electrode layer 16, such as a GaN layer. Examples of the ultraviolet transparent electrode layer include an ITO (Indium Tin Oxide) layer, a layer having a MgZnO-based composition, a Ga ２ O ３ Layer having a composition of the system, InGaO ３ A layer having the composition of the system can be used.

[0028] In one embodiment, the ultraviolet-transparent electrode layer preferably contains magnesium oxide and zinc oxide as its main components, i.e., a layer having an MgZnO-based composition. Layers having an MgZnO-based composition have high ultraviolet transmittance and can be made thicker than ITO and other materials. For example, if the p-type contact electrode 17 is provided directly on the p-AlGaN layer 15, annealing to reduce contact resistance can result in a loss of surface smoothness for the p-type contact electrode 17, making it difficult to achieve specular reflection from the deep-UV-reflective metal. In contrast, using a layer having an MgZnO-based composition as the ultraviolet-transparent electrode layer 16 allows for the formation of a thick film. Therefore, the ultraviolet-transparent electrode layer 16 maintains the surface smoothness of the p-type contact electrode 17 during annealing, thereby stably maintaining specular reflection from the deep-UV-reflective metal. The p-type contact electrode 17 can efficiently reflect deep ultraviolet light due to the specular reflection from the deep-UV-reflective metal.

[0029] The ultraviolet-transparent electrode layer containing magnesium oxide and zinc oxide as main components means, for example, that the element ratio of magnesium and zinc (Mg+Zn) to all metal elements contained in the ultraviolet-transparent electrode layer is 0.500 or more, 0.600 or more, or 0.750 or more.

[0030] The composition of the MgZnO system is Mg ｘ Zn ｙPreferably, the composition is 0 (x is 0.2 to 0.8, y is 0.2 to 0.8). Here, the relationship y = 1 - x may or may not be satisfied. Note that "MgZnO-based composition" means that the constituent elements include Mg, Zn, and O, and does not mean a solid solution of these three elements. The ultraviolet-transparent electrode layer preferably contains magnesium oxide (MgO, etc.) and zinc oxide (ZnO, etc.) as the MgZnO-based composition. Note that the MgZnO-based composition may or may not contain a solid solution of Mg, Zn, and O in addition to magnesium oxide and zinc oxide.

[0031] The ultraviolet-transparent electrode layer preferably contains at least one element X selected from trivalent and tetravalent metal elements other than Mg and Zn. This allows for a reduction in the applied voltage, thereby improving luminous efficiency. The molar ratio of element X to all metal elements [element X / total metal elements] is preferably 0.0001 to 0.200, more preferably 0.001 to 0.100. In particular, when the molar ratio of element X to all metal elements [element X / total metal elements] is 0.010 to 0.100, the conductivity of the ultraviolet-transparent electrode layer is improved. When the molar ratio of element X to all metal elements [element X / total metal elements] is 0.020 to 0.050, the conductivity of the ultraviolet-transparent electrode layer is significantly improved. Note that the total metal elements correspond to Mg + Zn + element X. Examples of element X include B, Al, Ga, In, Tl, C, Si, Ge, Sn, and Pb. Preferably, B, Al, or Ga.

[0032] In one embodiment, the total atomic ratio of Mg, Zn, and element X to all metal elements contained in the ultraviolet-transparent electrode layer is 0.900 or more, 0.950 or more, or 0.990 or more. Furthermore, all metal elements contained in the ultraviolet-transparent electrode layer may be substantially only Mg, Zn, and element X. In this case, unavoidable impurities may be contained.

[0033] In one embodiment, the conductivity of the ultraviolet transparent electrode layer is 1.0×10 －１The conductivity of the ultraviolet-transparent electrode layer is preferably 1.0 S / cm or more, and more preferably 10.0 S / cm or more. The upper limit is not particularly limited, but is usually 100 S / cm or less. The conductivity of the ultraviolet-transparent electrode layer is measured by the method shown in the examples.

[0034] In one embodiment, the carrier concentration of the ultraviolet transparent electrode layer is 1.0×10 １８ cm －３ That's it, 1.0 x 10 ２２ cm －３ This allows the driving voltage of the ultraviolet light-emitting device to be reduced. The carrier concentration of the ultraviolet transparent electrode layer is 5.0×10 or less. １８ cm －３ That's it, 1.0 x 10 １９ cm or more, or 5.0 x 10 １９ cm －３ It can be 5.0 × 10 or more. ２１ cm －３ or less, or 5.0 x 10 ２０ cm －３ The carrier concentration of the ultraviolet transparent electrode layer is measured by the method shown in the examples.

[0035] The thickness of the ultraviolet-transparent electrode layer is not particularly limited. In the case of a face-down type element, the thickness of the ultraviolet-transparent electrode layer is, for example, 80 nm or less, 60 nm or less, or even 50 nm or less. This suppresses absorption of deep ultraviolet light by the ultraviolet-transparent electrode layer, thereby further improving the efficiency of extracting deep ultraviolet light from the light-emitting element. Furthermore, by making the thickness of the ultraviolet-transparent electrode layer 1 nm or more, 5 nm or more, or even 15 nm or more, the conductivity of the ultraviolet-transparent electrode layer can be improved. From these viewpoints, the thickness of the ultraviolet-transparent electrode layer is preferably 1 to 80 nm, 5 to 60 nm, or even 15 to 50 nm.

[0036] In the case of a face-up element, the thickness of the ultraviolet-transparent electrode layer may be 2000 nm or less, 1500 nm or less, or 1000 nm or less. It may also be 50 nm or more, 100 nm or more, or 200 nm or more. To increase the efficiency of extracting ultraviolet light from the p-type contact electrode (p-PAD), the thickness of the ultraviolet-transparent electrode layer is preferably 500 nm or more. The thickness of the ultraviolet-transparent electrode layer can be measured by observing the cross section with a transmission electron microscope (TEM).

[0037] The ultraviolet-transparent electrode layer can be formed by sputtering, molecular beam epitaxy (MBE), vacuum deposition, ion plating, or the like. For example, when forming the ultraviolet-transparent electrode layer by sputtering, the composition of the ultraviolet-transparent electrode layer can be controlled by adjusting the composition of the sputtering target. Alternatively, it can be controlled by adjusting the film formation rate of each of a magnesium oxide sintered target, a zinc oxide sintered target, and optionally a sintered target containing element X in co-sputtering. For other film formation methods, the composition of the ultraviolet-transparent electrode layer can also be controlled by adjusting the composition of the raw materials, such as the evaporation source. Note that when forming the ultraviolet-transparent electrode layer by sputtering or evaporation, the composition of the sputtering target and evaporation source and the composition of the ultraviolet-transparent electrode layer are approximately the same. The molar ratio of each element in the ultraviolet-transparent electrode layer (for example, the above-mentioned Mg ｘ Zn ｙ The x and y in O can be measured, for example, by secondary ion mass spectrometry.

[0038] The ultraviolet-transparent electrode layer can be formed, for example, by forming a film on a semiconductor layer that forms an ultraviolet light-emitting element. The surface temperature of the semiconductor layer during deposition of the ultraviolet-transparent electrode layer (e.g., during sputtering) is not particularly limited, and is, for example, 20°C or higher, 40°C or higher, 60°C or higher, 80°C or higher, 100°C or higher, 120°C or higher, 140°C or higher, 160°C or higher, 170°C or higher, or 180°C or higher. The higher this temperature, particularly 180°C or higher, the more favorably the transmittance of the ultraviolet-transparent electrode layer to deep ultraviolet light can be improved. The upper limit is not particularly limited, and for example, 600°C or lower is preferable, and 300°C or lower is more preferable.

[0039] The formed ultraviolet-transparent electrode layer is preferably subjected to a heat treatment. The treatment temperature is preferably 600°C or higher, more preferably 650°C or higher, and particularly preferably 700°C or higher. The heat treatment causes aggregation and separation of oxides, resulting in the formation of a zinc oxide network, which favorably exhibits conductivity, while the aggregation of magnesium oxide in the gaps of the zinc oxide network is thought to favorably improve the transmittance of deep ultraviolet light. The upper limit of the heat treatment temperature is not particularly limited, and is, for example, 1200°C or lower.

[0040] (p-type contact electrode 17) The p-type contact electrode is a positive electrode. In the case of a face-down type element, it is configured to be able to reflect light from the ultraviolet transparent electrode layer side back to the ultraviolet transparent electrode layer side. The p-type contact electrode can be a layer made of a metal capable of reflecting deep ultraviolet light, a dielectric multilayer film, or the like. It preferably includes a layer made of a metal capable of reflecting deep ultraviolet light. Examples of metals capable of reflecting deep ultraviolet light include metals such as Al, Pt, Ni, Au, Rh, Mo, W, and Cr, and alloys of these metals. Among these, Al, Rh, Mo, W, or Cr are preferred, and Al is more preferred because it has excellent deep ultraviolet light reflection. Nd, Ni, etc. may be added to Al.

[0041] The thickness of the p-type contact electrode is not particularly limited and is, for example, 200 nm or more, 100 nm or more, or 50 nm or more, and 2000 nm or less, 1000 nm or less, or 500 nm or less. The p-type contact electrode may be a single layer or a laminate of two or more layers.

[0042] (n-type contact electrode 18) The n-type contact electrode is a negative electrode and is connected to, for example, a pad electrode. The n-type contact electrode can be made of a conductive material. Examples of conductive materials include metals. Examples of metals include one metal or an alloy of two or more metals selected from the group consisting of V, Al, Ti, Pt, Au, In, and Sn.

[0043] The n-type contact electrode may be a single layer or may have a laminated structure of two or more layers. The thickness (total thickness) of the n-type contact electrode is not particularly limited, and is, for example, 100 to 1000 nm, preferably 100 to 500 nm.

[0044] The method for forming the p-type contact electrode and the n-type contact electrode is not particularly limited, and for example, evaporation can be used.

[0045] In the ultraviolet light-emitting device of this embodiment, when holes and electrons recombine in the active layer 13, deep ultraviolet rays are emitted from the active layer 13. The deep ultraviolet rays emitted from the active layer 13 toward the substrate 11 side are transmitted through the substrate 11 and emitted to the outside of the light-emitting device. In the case of a face-down type element, the deep ultraviolet rays emitted from the active layer 13 toward the ultraviolet transparent electrode layer 16 side are efficiently reflected by the p-type contact electrode 17, transmitted through the substrate 11, and emitted to the outside of the light-emitting device. This has the effect of improving the light extraction efficiency of a light-emitting device having an emission wavelength in the deep ultraviolet region.

[0046] The ultraviolet light-emitting element according to this embodiment has an emission wavelength in the deep ultraviolet region. Specifically, the emission wavelength is in the region of 200 to 350 nm, preferably in the region of 210 to 310 nm, and more preferably in the region of 220 to 290 nm. The applications of the ultraviolet light-emitting element are not particularly limited, and it can be used in a wide variety of fields. For example, it can be used in sterilization, virus inactivation, detection devices, skin treatment, light sources for resin curing, etc.

[0047] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0048] [Face-down Light-Emitting Element] Example 1 A device having the same layer structure as the ultraviolet light-emitting element 2 shown in Figure 2 was fabricated. Specifically, an AlN layer (2000 nm thick) serving as a buffer layer was formed on the c-plane of a sapphire substrate by metalorganic chemical epitaxy (MOVPE). Next, an undoped AlGaN (u-AlGaN) layer (100 nm thick) and an Si-doped AlGaN layer (2000 nm thick) with an Al composition of 60% as an n-AlGaN layer were stacked in this order on the buffer layer.

[0049] Next, an active layer was formed on the n-AlGaN layer by MOVPE. The active layer was formed by stacking a first barrier layer (thickness 11 nm), a first well layer (thickness 2.5 nm), a second barrier layer (thickness 11 nm), a second well layer (thickness 2.5 nm), and a third barrier layer (thickness 5.5 nm) in this order. All were AlGaN layers, and the growth conditions for each layer were, for example, a growth temperature of 975°C and a growth pressure of 400 mbar. The Al composition of the first to third barrier layers was 55 at%, and the Al composition of the first and second well layers was 40 at%. The Si concentration in the third barrier layer was 5.0 × 10 －１８ cm －３ and the others are 9.0 x 10 －１８ cm －３ It was decided.

[0050] Next, an AlN layer (2 nm thick) was formed on the active layer as an electron blocking layer by MOCVD. Next, a p-AlGaN layer was formed on the AlN layer by MOCVD to a thickness of 25 nm. Next, a p-GaN layer was formed on the p-AlGaN layer by MOCVD to a thickness of 15 nm. Next, a p-GaN layer was formed on the p-GaN layer by MOCVD. ＋ The p-GaN layer was formed to a thickness of 5 nm. ＋ The -GaN layer was formed so that the Mg concentration was higher than that of the p-GaN layer.

[0051] To activate the p-type semiconductor layer formed up to this point, it was annealed in a nitrogen atmosphere at 700°C for 5 minutes. Next, to form an n-type contact electrode, a portion of the stack was mesa-etched by photolithography. The etching conditions were as follows: Method: Inductively Coupled Plasma (ICP) Etching Bias Power: 15 W Antenna Power: 150 W Cl Gas: 30 sccm

[0052] Subsequently, after photolithography for lift-off, MgZnO (Mg:Zn=1:2) was deposited as an ultraviolet transparent electrode layer by radio frequency (RF) sputtering. ＋ A mask (50 nm thick) was formed on the GaN layer. After lift-off, the formed MgZnO film was lamp annealed in a nitrogen atmosphere at 850° C. for 5 minutes.

[0053] Next, on a portion of the n-AlGaN layer where the active layer was not provided, V / Al / Ni / Au films (thicknesses: 20 nm / 10 nm / 30 nm / 60 nm) were deposited in this order to form an n-type contact electrode. Next, Al / Ti / Au films (thicknesses: 100 nm / 20 nm / 60 nm) were deposited in this order by sputtering on the ultraviolet transparent electrode layer to form a p-type contact electrode, thereby producing an ultraviolet light-emitting device. The ultraviolet light-emitting device produced in Example 1 was a face-down type device, and for example, the p-type contact electrode and n-type contact electrode could be flip-chip connected to a substrate on which the device was mounted.

[0054] Example 2 An ultraviolet light-emitting device was fabricated in the same manner as in Example 1, except that a layer was formed in which Ga was added to MgZnO (Mg:Zn = 1:2) in an atomic ratio of 0.18 (Ga / (Ga + Mg + Zn) = 0.18) instead of MgZnO (Mg:Zn = 1:2) as the ultraviolet transparent electrode layer. ２ O ３ A film was formed by sputtering a sintered target having a composition of MgO:ZnO=9.0:30.3:60.7 (molar ratio).

[0055] Example 3 An ultraviolet light-emitting device was fabricated in the same manner as in Example 1, except that a layer of MgZnO (Mg:Zn=1:2) to which Ga was added at an atomic ratio of 0.05 (Ga / (Ga+Mg+Zn)=0.05) was formed as the ultraviolet transparent electrode layer instead of MgZnO (Mg:Zn=1:2).

[0056] Example 4 An ultraviolet light-emitting device was fabricated in the same manner as in Example 1, except that a layer of MgZnO (Mg:Zn=1:2) to which Al was added at an atomic ratio of 0.03 (Al / (Al+Mg+Zn)=0.03) was formed as the ultraviolet transparent electrode layer instead of MgZnO (Mg:Zn=1:2). ２ O ３ The film was formed by sputtering a sintered target having a molar ratio of MgO:ZnO=1.5:32.8:65.7.

[0057] Example 5 An ultraviolet light-emitting device was fabricated in the same manner as in Example 1, except that a layer of MgZnO (Mg:Zn=1:2) to which Ga was added at an atomic ratio of 0.02 (Ga / (Ga+Mg+Zn)=0.02) was formed as the ultraviolet transparent electrode layer instead of MgZnO (Mg:Zn=1:2).

[0058] Example 6 An ultraviolet light-emitting device was fabricated in the same manner as in Example 1, except that a layer was formed in which MgZnO (Mg:Zn=1:2) was replaced with Ga added to MgZnO (Mg:Zn=1:2) at an atomic ratio of 0.0001 (Ga / (Ga+Mg+Zn)=0.0001) as the ultraviolet transparent electrode layer.

[0059] Comparative Example 1 An ultraviolet light-emitting device was fabricated in the same manner as in Example 1, except that no ultraviolet transparent electrode layer was formed and Ni / Au was laminated in this order as the p-type contact electrode instead of Al / Ti / Au.

[0060] [Face-up Light-Emitting Element] Example 7 An ultraviolet light-emitting element was fabricated in the same manner as in Example 1, except that a p-type contact electrode formed by sequentially stacking Ni / Au (thicknesses of 20 nm / 150 nm) in a lattice pattern was formed, and the thickness of the MgZnO (Mg:Zn = 1:2) layer serving as the ultraviolet transparent electrode layer was changed to 1000 nm. The lattice-shaped p-type contact electrode was formed by a lift-off process using photolithography. The ultraviolet light-emitting element fabricated in Example 7 was capable of extracting light not only from the substrate side but also from the p-type contact electrode side.

[0061] Example 8 An ultraviolet light-emitting device was fabricated in the same manner as in Example 7, except that a layer of MgZnO (Mg:Zn=1:2) to which Ga was added at an atomic ratio of 0.02 (Ga / (Ga+Mg+Zn)=0.02) was formed as the ultraviolet transparent electrode layer instead of MgZnO (Mg:Zn=1:2). The ultraviolet transparent electrode layer was formed by sputtering.

[0062] The ultraviolet light-emitting device was evaluated as follows. The results are shown in Table 1. (1) Turn-on voltage (Vf) IV measurement was performed using a semiconductor parameter analyzer, and the voltage was measured at a current of 5 A / cm. ２ The voltage at this time was defined as the rising voltage (Vf(V)).

[0063] (2) Output (mW) The ultraviolet light emission output was measured using an integrating sphere. When the ultraviolet light emitting element emitted light (output) at 50 mA, it was evaluated as ◯ if it was 10 mW or more, and evaluated as × if it was less than 10 mW.

[0064] (3) Composition of the UV-Transparent Electrode Layer With the UV-light-emitting device set in an X-ray photoelectron spectroscopy (XPS) device, the region of the p-type contact electrode was etched with Ar ions. Etching was continued until the constituent elements of the UV-transparent electrode layer were observed. From the point where the constituent elements of the UV-transparent electrode layer were observed, the constituent elements were etched a further 30 nm, and the composition ratio of the metal elements was determined from the spectral intensity.

[0065] (4) Conductivity and Carrier Concentration of the Ultraviolet-Transparent Electrode Layer A Hall effect element was fabricated, and the conductivity and carrier concentration of the ultraviolet-transparent electrode layer were measured using the element. (i) Fabrication of Hall Effect Element As in Example 1, an AlN layer and a u-AlGaN layer serving as buffer layers were formed on a sapphire substrate by metalorganic chemical epitaxy (MOVPE). As in each example, an ultraviolet-transparent electrode layer was formed on the buffer layer, and lamp annealing (heat treatment) was performed in a nitrogen atmosphere for 5 minutes at 850°C to fabricate a Hall effect element. (ii) Measurement of Conductivity and Carrier Concentration The Hall effect element was set in a resistivity / Hall measurement system (Toyo Corporation: ResiTest 8300), and the carrier concentration n of the ultraviolet-transparent electrode layer was measured at 23°C. Furthermore, the conductivity of a sample in which a wiring layer was formed on the ultraviolet-transparent electrode layer was measured by a four-terminal method at 25°C. In Table 1, "E+XX" means "×10 ＋ＸＸ For example, 4.84E+18 means 4.84 x 10 １８ is.

[0066]

[0067] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention. Accordingly, these numerous modifications are within the scope of the present invention. The contents of all documents cited in this specification and of the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims

1. An ultraviolet light-emitting device having a layered structure including, in this order, an active layer containing a III-V nitride semiconductor, a p-AlGaN layer, an ultraviolet transparent electrode layer, and a p-type contact electrode.

2. The ultraviolet light emitting element according to claim 1, further comprising a p-GaN layer between said p-AlGaN layer and said ultraviolet transparent electrode layer.

3. The ultraviolet light emitting device according to claim 1 or 2, further comprising an AlN layer between the active layer and the p-AlGaN layer.

4. The ultraviolet light emitting element according to any one of claims 1 to 3, wherein ultraviolet light generated in said active layer is extracted from said ultraviolet transparent electrode layer side.

5. The ultraviolet light emitting element according to any one of claims 1 to 3, wherein ultraviolet light generated in the active layer is extracted from the opposite side of the p-type contact electrode.

6. The ultraviolet light-emitting device according to any one of claims 1 to 5, wherein the ultraviolet transparent electrode layer contains magnesium oxide and zinc oxide as main components, and contains at least one element X selected from trivalent and tetravalent metal elements other than the magnesium and zinc.

7. The ultraviolet light-emitting device according to claim 6, wherein the molar ratio of the element X to the total metal elements [element X / total metal elements] is 0.0001 or more and 0.20 or less.

8. The electrical conductivity of the ultraviolet transparent electrode layer is 1.0×10 －１ The ultraviolet light-emitting element according to any one of claims 1 to 7, wherein the electrical conductivity is 1 S / cm or more.

9. The carrier concentration of the ultraviolet transparent electrode layer is 1.0×10 １８ cm －３ That's it, 1.0 x 10 ２２ cm －３ The ultraviolet light-emitting device according to any one of claims 1 to 8, wherein:

10. The carrier concentration of the ultraviolet transparent electrode layer is 1.0×10 １９ cm －３ The ultraviolet light-emitting element according to claim 9 .