JP2017139265A - Ultraviolet light-emitting element and device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the contact resistance between an n-type nitride semiconductor layer and an n-electrode of an ultraviolet light-emitting element.SOLUTION: An ultraviolet light-emitting element comprises: a substrate 10; and a laminate formed on the substrate 10. The laminate is arranged by laminating a first n-type nitride semiconductor layer 20, a light-emitting layer 50, a second n-type nitride semiconductor layer 30 provided between the first n-type nitride semiconductor layer 20 and the light-emitting layer 50, and having a band gap larger than that of the first n-type nitride semiconductor layer 20, and a film thickness smaller than that of the first n-type nitride semiconductor layer 20, and a p-type nitride semiconductor layer 60. In the ultraviolet light-emitting element, the second n-type nitride semiconductor layer 30 restrains holes injected into the light-emitting layer 50 from leaking into the first n-type nitride semiconductor layer 20. The contact resistance between the first n-type nitride semiconductor layer 20 and an n-electrode is reduced by making smaller the band gap of the first n-type nitride semiconductor layer 20. Thus, the contact resistance is reduced while suppressing the reduction in light emission efficiency.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultraviolet light emitting element and an apparatus including the same.

  Ultraviolet light emitting devices are applied in various fields by taking advantage of their small size and low power consumption. As disclosed in Patent Document 1, generally, an ultraviolet light emitting element includes a stacked portion including an n-type nitride semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer. This ultraviolet light-emitting element is formed from the light-emitting layer by power supplied through one electrode portion provided on the n-type nitride semiconductor layer and the other electrode portion provided on the p-type nitride semiconductor layer. Ultraviolet light is emitted.

International Publication No. 2012/144046 Pamphlet JP 2015-43468 A

By the way, from the viewpoint of further reducing the power consumption by reducing the forward voltage Vf of the ultraviolet light emitting element, it is important to reduce the contact resistance between the laminated portion and the electrode portion provided in the laminated portion. is there.
However, the conventional ultraviolet light emitting element has a problem that the contact resistance is not sufficiently reduced. In particular, the fact is that little attention has been paid to the contact resistance between the n-type nitride semiconductor layer and the electrode portion provided thereon.

  For example, in Patent Document 1, a four-layer metal layer of titanium Ti / aluminum Al / titanium Ti / gold Au is sequentially deposited with a film thickness of 20 nm / 100 nm / 50 nm / 100 nm, and RTA (rapid thermal annealing) method is used. A method of forming an n-electrode on an n-type nitride semiconductor layer by applying a heat treatment is disclosed. Further, in Patent Document 2, four metal layers of Ti / Al / Ti / Au are sequentially deposited with a thickness of 20 nm / 100 nm / 20 nm / 200 nm, and heat treatment by RTA treatment (900 ° C., 1 minute) is added. Thus, a method for forming an n-electrode is disclosed. However, it cannot be said that the contact resistance between the n-type nitride semiconductor layer and the n electrode of the ultraviolet light-emitting device obtained by this method is sufficiently low.

As another method of reducing the contact resistance between the n-type nitride semiconductor layer and the n-electrode, there is a method of reducing the contact resistance by reducing the band gap of the n-type nitride semiconductor layer. However, when the band gap of the n-type nitride semiconductor layer is reduced, holes injected into the light emitting layer leak to the n type nitride semiconductor layer, resulting in a problem that the light emission efficiency itself decreases.
Accordingly, the present invention has been made in view of such circumstances, and provides an ultraviolet light emitting element capable of reducing contact resistance between an n-type nitride semiconductor layer and an n electrode and an apparatus including the same. It is an object.

An ultraviolet light-emitting element according to one embodiment of the present invention includes a substrate and a stacked body formed over the substrate, and the stacked body includes a first n-type nitride semiconductor layer, a light-emitting layer, The first n-type nitride semiconductor layer is provided between the first n-type nitride semiconductor layer and has a larger band gap than the first n-type nitride semiconductor layer and a film thickness of the first n-type nitride semiconductor layer. The second n-type nitride semiconductor layer, which is thinner than the film thickness, and the p-type nitride semiconductor layer are stacked.
An apparatus according to one embodiment of the present invention includes the ultraviolet light-emitting element according to the above embodiment.

  According to one embodiment of the present invention, contact resistance between an n-type nitride semiconductor layer and an n electrode can be reduced without reducing light emission efficiency, and power consumption can be reduced.

It is sectional drawing which shows an example of the ultraviolet light emitting element which concerns on one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the same reference numerals are given to portions corresponding to each other in the drawings to be described below, and description of the overlapping portions will be omitted as appropriate. In addition, the present embodiment exemplifies a configuration for embodying the technical idea of the present invention, and does not specify the material, shape, structure, arrangement, dimensions, and the like of each part as follows. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

<Ultraviolet light emitting device>
FIG. 1 is a cross-sectional view schematically showing a configuration example of an ultraviolet light emitting device 100 according to an embodiment of the present invention.
As shown in FIG. 1, the ultraviolet light emitting device 100 includes a substrate 10, a first n-type nitride semiconductor layer 20, a second n-type nitride semiconductor layer 30, an n electrode 40, and a light emitting layer 50. And a p-type nitride semiconductor layer 60. On the substrate 10, a stacked body including the first n-type nitride semiconductor layer 20, the second n-type nitride semiconductor layer 30, the light emitting layer 50, and the p-type nitride semiconductor layer 60 is arranged in this order. The first n-type nitride semiconductor layer 20 is laminated, and a part of the laminated portion including the second n-type nitride semiconductor layer 30, the light emitting layer 50, and the p-type nitride semiconductor layer 60 is removed by etching or the like. It is formed in a so-called mesa structure in which a part of is exposed. Then, an n electrode 40 is formed on the exposed portion of the first n-type nitride semiconductor layer 20.

Here, as shown in FIG. 1, a first n-type nitride semiconductor layer 20, a second n-type nitride semiconductor layer 30, a light emitting layer 50, and p-type nitridation are formed on a substrate 10. The physical semiconductor layer 60 is laminated in this order, but the present invention is not limited to this. For example, a p-type nitride semiconductor layer 60, a light emitting layer 50, a second n-type nitride semiconductor layer 30, and a first n-type nitride semiconductor layer 20 are stacked on the substrate 10 in this order. May be.
Moreover, although the ultraviolet light emitting element 100 in one Embodiment of this invention shown in FIG. 1 is a horizontal type ultraviolet light emitting element of a mesa structure, the ultraviolet light emitting element in this invention is not restricted to this, For example, a vertical type The ultraviolet light emitting element may be used. In the case of a vertical ultraviolet light emitting device, a structure in which the substrate is peeled off is preferable from the viewpoint of improving the light emission efficiency. A p-electrode may be further provided on the p-type nitride semiconductor layer.

As a growth method of each layer of the ultraviolet light emitting device 100 according to the embodiment of the present invention, for example, an epitaxial growth technique such as a metal organic chemical vapor deposition method (MOVPE method) can be used. It is not limited. For example, the film may be formed using a hydride vapor phase epitaxy method (HVPE method), a molecular beam epitaxy method (MBE method), or the like.
Hereinafter, each component constituting the ultraviolet light emitting element 100 will be described with specific examples.

<Board>
The material of the substrate 10 is not particularly limited. Specifically, sapphire, silicon Si, silicon carbide SiC, magnesium oxide MgO, digallium trioxide Ga ₂ O ₃ , zinc oxide ZnO, gallium nitride GaN, indium nitride InN, nitride An example is aluminum AlN or a mixed crystal substrate thereof. In the case where the first n-type nitride semiconductor layer 20 is formed directly on the substrate 10, the lattice constant difference from the first n-type nitride semiconductor layer 20 is small, and the threading dislocation is grown by growing in a lattice matching system. On a single crystal substrate having a bulk of a nitride semiconductor such as gallium nitride GaN, aluminum nitride AlN, aluminum gallium nitride AlGaN, or on a certain material from the viewpoint of reducing the lattice strain for generating the hole gas It is preferable to use a grown nitride semiconductor layer (also referred to as a template) such as GaN, AlN, or AlGaN as a substrate. Further, impurities may be mixed in the substrate.
As a method for producing the substrate 10, a general substrate growth method such as a gas phase growth method such as a sublimation method or an HVPE method or a liquid phase growth method can be applied.

<First n-type nitride semiconductor layer>
The film thickness of the first n-type nitride semiconductor layer 20 is D1. Examples of the material of the first n-type nitride semiconductor layer 20 include, but are not limited to, gallium nitride GaN, aluminum nitride AlN, indium nitride InN, and mixed crystals thereof.
The first n-type nitride semiconductor layer 20 may be formed directly on the substrate 10 as shown in FIG. 1, or a layer other than the first n-type nitride semiconductor layer 20 may be formed on the substrate 10. The first n-type nitride semiconductor layer 20 may be formed thereon. For example, a buffer layer is formed on the substrate 10, a first n-type nitride semiconductor layer 20 is formed on the buffer layer, and a second n-type nitride semiconductor layer 30 is formed thereon. Also good. In addition, as an ultraviolet light emitting element according to another embodiment, the first n-type nitride semiconductor layer 20 may be indirectly formed on the light emitting layer 50. That is, the p-type nitride semiconductor layer 60 and the light emitting layer 50 may be stacked in this order on the substrate 10, and the first n-type nitride semiconductor layer 20 may be indirectly formed on the light emitting layer 50.

The first n-type nitride semiconductor layer 20, in terms of realization and high luminous efficiency realized with low contact resistance between the n-electrode _40, in _{Al X Ga 1-X N (} 0.5 ≦ X ≦ 0.8) Preferably there is. When the first n-type nitride semiconductor layer is made of AlGaN and the Al composition X is smaller than 0.5, the emitted light is absorbed by the first nitride semiconductor layer, and the ultraviolet light emitting element Output decreases. Further, when the first n-type nitride semiconductor layer is made of AlGaN and the Al composition X is larger than 0.8, the parasitic resistance of the first n-type nitride semiconductor layer is increased, and the light emission of the ultraviolet light emitting element is performed. Efficiency will decrease. In this case, a group III element such as indium In or a group V element such as phosphorus P, arsenic As, or antimony Sb is used in the range where the same effects as those of the ultraviolet light emitting device 100 according to the embodiment of the present invention are obtained. It is a matter of course that the present invention also includes a case where a slight change is made to the composition of the first n-type nitride semiconductor layer 20 by adding a small amount of other elements, such as adding about several percent. . The same applies to the composition of the other layers.

Examples of the n-type dopant when the first n-type nitride semiconductor layer 20 is n-type doped include silicon Si, tellurium Te, tin Sn, and the like, but are not limited thereto. Other examples of n-type dopants include other group V elements such as phosphorus P, arsenic As, and antimony Sb, and elements such as carbon C, hydrogen H, fluorine F, oxygen O, and magnesium Mg.
The range of the film thickness D1 of the first n-type nitride semiconductor layer 20 is preferably 100 nm or more and 2000 nm or less, more preferably 300 nm or more and 1500 nm, from the viewpoint of reducing the series resistance of the ultraviolet light emitting element 100 and improving the productivity. It is as follows. When the film thickness D1 of the first n-type nitride semiconductor layer is smaller than 100 nm, the parasitic resistance of the first n-type nitride semiconductor layer is increased, and the light emission efficiency of the ultraviolet light-emitting element is lowered. There is a problem that the process window in the mesa etching process for separating the n-type and the n-type becomes narrow and the process controllability is low. Further, when the film thickness D1 of the first n-type nitride semiconductor layer is larger than 2000 nm, there is a problem that the thin film growth time becomes long, the throughput is lowered, and the productivity is deteriorated.

<Second n-type nitride semiconductor layer>
The second n-type nitride semiconductor layer 30 is formed between the first n-type nitride semiconductor layer 20 and the light emitting layer 50. The second n-type nitride semiconductor layer 30 has a larger band gap than the first n-type nitride semiconductor layer 20 and a film thickness smaller than the film thickness of the second n-type nitride semiconductor layer 30. , Smaller than “0.1 × D1”. Note that D1 is the thickness of the first n-type nitride semiconductor layer 20.
By disposing the second n-type nitride semiconductor layer 30 having a band gap larger than that of the first n-type nitride semiconductor layer between the first n-type nitride semiconductor layer 20 and the light emitting layer 50, Leakage of holes injected into the light emitting layer 50 into the first n-type nitride semiconductor layer 20 can be reduced. Further, from the viewpoint of reducing the series resistance of the ultraviolet light emitting element 100 and improving the productivity, the thickness of the second n-type nitride semiconductor layer 30 is preferably smaller than “0.1 × D1”. More preferably, it is smaller than “× D1”. When the film thickness of the second n-type nitride semiconductor layer is “0.1 × D1” or more, it becomes a resistance component when electrons are injected from the first n-type semiconductor into the light-emitting layer. The light emission efficiency of the light emitting element is reduced.

The film thickness of the first n-type nitride semiconductor layer 20 is a cleaved cross section obtained by fluorescent X-ray analysis (XRF), secondary ion mass measurement (SIMS), scanning electron microscope (SEM), or transmission electron microscope (TEM). It is possible to measure by measurement. A similar measurement method can be used for the film thickness of the second n-type nitride semiconductor layer 30.
Examples of the material of the second n-type nitride semiconductor layer 30 include, but are not limited to, gallium nitride GaN, aluminum nitride AlN, indium nitride InN, and mixed crystals thereof. As an example, when the first n-type nitride semiconductor layer 20 is made of aluminum gallium nitride AlGaN, an AlGaN layer having a higher Al composition than the first n-type nitride semiconductor layer 20 is used as the second n-type nitride nitride. By using it as the oxide semiconductor layer 30, the band gap of the second n-type nitride semiconductor layer 30 can be made larger than the band gap of the first n-type nitride semiconductor layer 20.

  The second n-type nitride semiconductor layer 30 may be formed directly on the first n-type nitride semiconductor layer 20 as shown in FIG. 1 or the first n-type nitride semiconductor layer 20. A layer other than the second n-type nitride semiconductor layer 30 such as a composition gradient layer may be formed thereon, and the second n-type nitride semiconductor layer 30 may be formed thereon. Alternatively, the second n-type nitride semiconductor layer 30 may be formed on the light emitting layer 50, and the first n-type nitride semiconductor layer 20 may be formed thereon. That is, the p-type nitride semiconductor layer 60 and the light emitting layer 50 are stacked in this order on the substrate 10, and the second n-type nitride semiconductor layer 30 and the first n-type nitride semiconductor layer are formed on the light emitting layer 50. 20 may be laminated in this order.

The second n-type nitride semiconductor layer 30 suppresses leakage of holes injected into the light-emitting layer 50 into the first n-type nitride semiconductor layer 20, and realizes high light emission efficiency. It is preferable that _Y Ga _1-Y N (0.6 ≦ Y ≦ 1) and X <Y with respect to the Al composition X of the first n-type nitride semiconductor layer 20. When the second n-type nitride semiconductor layer is made of AlGaN and the Al composition Y is smaller than 0.6, the barrier effect against holes is lowered, and the luminous efficiency of the ultraviolet light emitting device is lowered. .
Examples of the n-type dopant when the second n-type nitride semiconductor layer 30 is n-type doped include silicon Si, tellurium Te, tin Sn, and the like, but are not particularly limited thereto. Other examples of n-type dopants include other group V elements such as phosphorus P, arsenic As, and antimony Sb, and elements such as carbon C, hydrogen H, fluorine F, oxygen O, and magnesium Mg.

<Light emitting layer>
The light emitting layer 50 may be formed directly on the second n-type nitride semiconductor layer 30 as shown in FIG. 1, or a layer other than the light emitting layer 50 on the second n-type nitride semiconductor layer 30. And the light emitting layer 50 may be formed thereon, and is not particularly limited. Specifically, the light emitting layer 50 may be formed on the undoped AlGaN layer formed on the second n-type nitride semiconductor layer 30. Unlike the stacking order of FIG. 1, the light emitting layer 50 is formed on the p-type nitride semiconductor layer 60, and the second n-type nitride semiconductor layer 30 and the first n-type nitride are formed on the light emitting layer 50. The semiconductor layer 20 may be formed in this order.

  The light emitting layer 50 is not particularly limited as long as it is a nitride semiconductor, but is preferably a mixed crystal of aluminum nitride AlN, gallium nitride GaN, and indium nitride InN from the viewpoint of realizing high luminous efficiency. In addition to nitrogen N, the light emitting layer 50 is mixed with other group V elements such as phosphorus P, arsenic As, and antimony Sb, and impurities such as carbon C, hydrogen H, fluorine F, oxygen O, magnesium Mg, and silicon Si. Also good. Moreover, although it may be a quantum well structure or a single layer structure, it is desirable to have at least one well structure from the viewpoint of realizing high light emission efficiency.

<P-type nitride semiconductor layer>
The p-type nitride semiconductor layer 60 may be directly formed on the light-emitting layer 50 as shown in FIG. 1, and a layer other than the p-type nitride semiconductor layer 60 is formed on the light-emitting layer 50. A p-type nitride semiconductor layer 60 may be formed thereon. For example, a gradient composition layer in which the ratio of constituent elements changes continuously or discretely may be formed on the light emitting layer 50, and the p-type nitride semiconductor layer 60 may be formed thereon. The formation position of the p-type nitride semiconductor layer 60 is not particularly limited. Alternatively, the p-type nitride semiconductor layer 60 may be formed on the substrate 10 and the light emitting layer 50 may be formed thereon.
The ultraviolet light emitting device 100 according to an embodiment of the present invention may further include a barrier layer having a relatively large band gap between the light emitting layer 50 and the gradient composition layer.
Examples of the p-type dopant when p-type doping is performed on the p-type nitride semiconductor layer 60 include magnesium Mg, zinc Zn, and carbon C, but are not limited thereto. Furthermore, in addition to the p-type dopant, other group V elements such as phosphorus P, arsenic As, and antimony Sb, and impurities such as carbon C, hydrogen H, fluorine F, oxygen O, and silicon Si may be mixed.

<N electrode>
As shown in FIG. 1, the n-electrode 40 has a stacked portion including the second n-type nitride semiconductor layer 30, the light emitting layer 50, and the p-type nitride semiconductor layer 60 of the first n-type nitride semiconductor layer 20. It is formed on a region that is not formed and is electrically connected to the first n-type nitride semiconductor layer 20. By forming the n-electrode 40 on the first n-type nitride semiconductor layer 20 having a band gap smaller than that of the second n-type nitride semiconductor layer 30, the first n-type nitride semiconductor layer 20 and the n-electrode are formed. It is possible to further reduce the contact resistance with 40. Examples of the elements constituting the n-electrode 40 include forms that include generally well-known titanium Ti, aluminum Al, nickel Ni, gold Au, vanadium V and the like as constituent elements, but are not limited thereto. Absent. These electrodes may be heat-treated at a high temperature. Further, a pad electrode for needle contact may be provided on the upper portion of the n electrode 40.

<P electrode>
In the ultraviolet light emitting device 100 according to the embodiment of the present invention, a p-electrode may be further formed on the p-type nitride semiconductor layer 60. From the viewpoint of efficiently injecting holes into the p-type nitride semiconductor layer 60, the p-electrode is a metal having a large work function such as nickel Ni, gold Au, platinum Pt, silver Ag, rhodium Rh, and palladium Pd, or these An alloy or an oxide electrode such as indium tin oxide ITO is desirable but not limited thereto.
The p-electrode is disposed so as to partially overlap with the contact electrode disposed on p-type nitride semiconductor layer 60 and the region on p-type nitride semiconductor layer 60 that is not in contact with the contact electrode in plan view. In addition, a configuration in which the reflectance of light from the light emitting layer 50 is higher than that of the contact electrode is also preferable.

  The reflective layer is preferably a metal such as silver Ag, rhodium Rh, and aluminum Al having a high reflectance at a specific wavelength, a reflective film using a dielectric multilayer film, a fluororesin, etc. from the viewpoint of reflecting light emission. Not as long. The reflective layer may be in direct contact with the p-type nitride semiconductor layer 60, and a transparent or semi-transparent layer with respect to the emission wavelength is sandwiched between the p-type nitride semiconductor layer 60 and the reflective layer. A laminated structure may be used. For example, a transparent ITO layer may be in contact with the p-type nitride semiconductor layer 60 with respect to an emission wavelength of 400 nm, and an Ag layer having a high reflectance may be in contact with the ITO layer.

<Device>
The ultraviolet light emitting device 100 according to an embodiment of the present invention can be applied to various devices.
The ultraviolet light emitting element 100 according to an embodiment of the present invention can be applied to all existing apparatuses in which an ultraviolet lamp is used, and can be replaced. In particular, it can be applied to an apparatus using deep ultraviolet light having a wavelength of 280 nm or less.
The ultraviolet light emitting device 100 according to an embodiment of the present invention can be applied to, for example, devices in the medical and life science fields, the environmental field, the industrial and industrial fields, the life and home appliance fields, the agricultural field, and other fields.

An ultraviolet light emitting device 100 according to an embodiment of the present invention includes a chemical or chemical synthesis or decomposition apparatus, a sterilization apparatus for liquids, gases, and solids (containers, food, medical devices, etc.), a cleaning apparatus such as a semiconductor, and a film. Surface modification devices such as glass and metal, semiconductors, exposure devices for manufacturing electronic products, printing or coating devices, adhesion or sealing devices, transfer or molding devices such as films, patterns and mockups, banknotes, scratches, blood and It can be applied to measurement or inspection equipment for chemical substances.
Examples of liquid sterilizers include automatic ice makers, ice trays, ice storage containers, water tanks for ice machines, freezers, ice makers, humidifiers, dehumidifiers, cold water tanks and hot water tanks for water servers, Channel piping, stationary water purifier, portable water purifier, water heater, water heater, wastewater treatment equipment, disposer, toilet drain trap, washing machine, dialysis water sterilization module, peritoneal dialysis connector sterilizer, disaster water storage system Etc., but not limited to this.

Examples of gas sterilizers include air purifiers, air conditioners, ceiling fans, floor and bedding vacuum cleaners, futon dryers, shoe dryers, washing machines, clothes dryers, indoor sterilization lights, and storage ventilation. Examples include, but are not limited to, systems, shoe boxes, and chests.
Examples of solid sterilizers (including surface sterilizers) include vacuum packers, belt conveyors, medical, dental, barber, and beauty salon hand tool sterilizers, toothbrushes, toothbrush holders, chopstick boxes, and cosmetic pouches. Examples include, but are not limited to, drain groove lids, toilet bowl local washer, toilet bowl lids, and the like.

  Next, the ultraviolet light-emitting device in one embodiment of the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited to each Example demonstrated below.

<Example>
On an AlN substrate (10) obtained from an AlN single crystal, an AlN buffer layer and n-type Al _X Ga _1-X N (X = 0.6) as the first n-type nitride semiconductor layer 20; N _- type Al _Y Ga ₁ -YN (Y = 0.75) as the second n-type nitride semiconductor layer 30, AlGaN multiple quantum well structure as the light emitting layer 50, and an electron blocking layer made of AlGaN The p-type GaN layer as the p-type nitride semiconductor layer 60 was formed in this order by the metal organic chemical vapor deposition method (MOCVD method). In the case of the above Al composition, the band gap of the second n-type nitride semiconductor layer 30 is larger than the band gap of the first n-type nitride semiconductor layer 20.
The Al composition of the first n-type nitride semiconductor layer 20 and the second n-type nitride semiconductor layer 30 was calculated from the measurement of the (0002) plane by the X-ray diffraction method.
As a result of measuring the film thickness of the first n-type nitride semiconductor layer 20 and the second n-type nitride semiconductor layer 30 by the cross-section SEM and the cross-section TEM, the thickness of the first n-type nitride semiconductor layer 20 is 560 nm, The thickness of the second n-type nitride semiconductor layer 30 was 35 nm.

Next, using a resist pattern formed by photolithography, a stacked body of a p-type GaN layer (60), an electron blocking layer, a light emitting layer 50, and a second n-type nitride semiconductor layer 30 with a chlorine-based gas, A portion of the first n-type nitride semiconductor layer 20 was dry etched to expose a portion of the first n-type nitride semiconductor layer 20 to form a mesa structure.
Next, an electrode shape was formed on the exposed portion of the first n-type nitride semiconductor layer 20 by lithography, and Ti 20 nm, Al 200 nm, Ni 30 nm, and Au 60 nm were deposited in this order. After performing the registry shift-off, an n-electrode 40 was formed by heat treatment at 880 ° C. for 120 seconds in a nitrogen atmosphere.
Next, after forming an electrode shape by lithography on the p-type GaN layer (60), Ni 20 nm and Au 35 nm were deposited in this order. After performing the registry shift-off, a p-electrode was formed by heat treatment at 600 ° C. for 180 seconds in an oxygen atmosphere.
Thereafter, Ti 20 nm and Au 1000 nm were deposited in this order on the n-electrode 40 and the p-electrode to form a pad electrode.

<Comparative Example 1>
On an AlN substrate (10) obtained from an AlN single crystal, an AlN buffer layer, n-type Al _X Ga _1-X N (X = 0.6) as the first n-type nitride semiconductor layer 20, and a light emitting layer A multi-quantum well structure of AlGaN as 50, an electron block layer made of AlGaN, and a p-type GaN layer as the p-type nitride semiconductor layer 60 were formed in this order by metal organic chemical vapor deposition (MOCVD). . The second n-type nitride semiconductor layer 30 was not provided.
The Al composition of the first n-type nitride semiconductor layer 20 was calculated from the measurement of the (0002) plane by the X-ray diffraction method.
It was 570 nm as a result of measuring the thickness of the 1st n-type nitride semiconductor layer 20 by cross-sectional SEM.
Thereafter, an n electrode 40, a p electrode, and a pad electrode were formed by the same method and conditions as in the example.

<Comparative example 2>
On the AlN substrate (10) obtained from the AlN single crystal, the AlN buffer layer, the n-type Al _X Ga _1-X N (X = 0.6) as the first n-type nitride semiconductor layer 20, the second N _- type Al _Y Ga _1-Y N (Y = 0.75) as the n-type nitride semiconductor layer 30, multiple quantum well structure of AlGaN as the light emitting layer 50, an electron blocking layer made of AlGaN, p-type nitride A p-type GaN layer as the semiconductor layer 60 was formed in this order by a metal organic chemical vapor deposition method (MOCVD method). In the case of the above Al composition, the band gap of the second n-type nitride semiconductor layer 30 is larger than the band gap of the first n-type nitride semiconductor layer 20.

The Al composition of the first n-type nitride semiconductor layer 20 and the second n-type nitride semiconductor layer 30 was calculated from the measurement of the (0002) plane by the X-ray diffraction method.
As a result of measuring the thickness of the first n-type nitride semiconductor layer 20 and the second n-type nitride semiconductor layer 30 by the cross-section SEM and the cross-section TEM, the thickness of the first n-type nitride semiconductor layer 20 is 540 nm, The thickness of the second n-type nitride semiconductor layer 30 was 60 nm.
Thereafter, an n electrode 40, a p electrode, and a pad electrode were formed by the same method and conditions as in the example.
Table 1 shows the results of measuring the light emission output and the drive voltage at a constant current of 100 mA for the ultraviolet light-emitting devices prepared by the methods and conditions of the above-mentioned Examples, Comparative Examples 1 and 2.

  As shown in Table 1, there is a second n-type nitride semiconductor layer 30 having a band gap larger than that of the first n-type nitride semiconductor layer 20 as in the embodiment, and the thickness thereof is the first It was confirmed that an ultraviolet light-emitting element having both high light output and low drive voltage can be obtained when it is smaller than 1/10 of the n-type nitride semiconductor layer 20.

10 substrate 20 first n-type nitride semiconductor layer 30 second n-type nitride semiconductor layer 40 n-electrode 50 light-emitting layer 60 p-type nitride semiconductor layer 100 ultraviolet light-emitting element

Claims (6)

A substrate,
A laminate formed on the substrate,
The laminate is
A band gap is provided between the first n-type nitride semiconductor layer, the light-emitting layer, and the first n-type nitride semiconductor layer provided between the first n-type nitride semiconductor layer and the light-emitting layer. An ultraviolet light emitting element in which a second n-type nitride semiconductor layer and a p-type nitride semiconductor layer, which are larger and thinner than the first n-type nitride semiconductor layer, are stacked. When the film thickness of the first n-type nitride semiconductor layer is D1,
2. The ultraviolet light emitting element according to claim 1, wherein a film thickness of the second n-type nitride semiconductor layer is smaller than 0.1 × D <b> 1.   The ultraviolet light emitting element according to claim 1, further comprising an n electrode in contact with the first n-type nitride semiconductor layer. The first n-type nitride semiconductor layer includes Al _X Ga _1-X N (0.5 ≦ X ≦ 0.8),
4. The second n-type nitride semiconductor layer includes Al _Y Ga _1-Y N (0.6 ≦ Y ≦ 1), and X <Y. 5. Ultraviolet light emitting element.   The ultraviolet light emitting element according to any one of claims 1 to 4, wherein the film thickness D1 is not less than 100 nm and not more than 2000 nm.   An apparatus comprising the ultraviolet light emitting element according to any one of claims 1 to 5.

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