JP2021034509A - Ultraviolet light-emitting element - Google Patents

Abstract

To increase the robustness to wavelength deviation of emission spectrum while suppressing the decrease in emission intensity.SOLUTION: An ultraviolet light-emitting element 1 comprises: a substrate 2 made of an Al-containing nitride semiconductor; a first conductivity-type nitride semiconductor layer 3 formed on the substrate, having conductivity and containing Al and Ga; a light-emitting layer 4 formed on the first conductivity-type nitride semiconductor layer and having a multi-quantum well structure arranged by laminating a plurality of quantum well layers containing Al, Ga and N; an electronic barrier layer 5 formed on the light-emitting layer and containing Al and N; and a second conductivity-type nitride semiconductor layer 7 formed on the electronic barrier layer and differing from the first conductivity-type nitride semiconductor layer in conductivity type. The quantum well layers have a thickness of 2.5 to 8.0 nm, and a half-value width of emission spectrum is 10 nm or larger and 17 nm or smaller.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an ultraviolet light emitting device.

The ultraviolet light emitting element can control the emission wavelength by controlling the bandgap energy of the light emitting layer, and has a long life and high reliability. Therefore, it is used for various purposes such as lighting, a light source for measuring instruments, and a light source for sterilization. A general ultraviolet light emitting device has a PIN structure in which a light emitting layer is sandwiched between a p-type nitride semiconductor and an n-type nitride semiconductor on a substrate.

In particular, in the case of a sterilizing light source, if the light emitting output (light emitting intensity) of the light emitting element is high, the sterilizing effect can be strengthened, and the object can be sterilized in a shorter time. Therefore, in order to increase the light emitting output, a technique for improving the luminous efficiency of the light emitting element has been required. For example, Patent Document 1 describes a technique for improving luminous efficiency by forming a quantum barrier layer between an active layer (light emitting layer) and a p-type nitride semiconductor layer and adjusting the bandgap energy of each layer. It is disclosed.

Japanese Unexamined Patent Publication No. 2010-114403

Here, it is possible to increase the light emitting output of the light emitting element by thinning the quantum well layer of the light emitting layer and confining the carriers. However, by thinning the quantum well layer, the half width of the emission spectrum of the light emitting device is generally narrowed.

For example, when the light emitting element is a light source for sterilization, it is preferable to irradiate a wavelength effective for sterilization (for example, 265 nm). The light emitting element, which is a light source for sterilization, is designed so that such a wavelength is the center of the light emission spectrum. However, when the center wavelength is deviated due to, for example, a manufacturing error, if the half width is narrow, a wavelength effective for sterilization may not be included. That is, if the half width of the emission spectrum is narrow, the robustness against wavelength shift is lowered, and for example, a state in which the wavelength having a high sterilizing effect is not included and the sterilizing efficiency is lowered is likely to occur.

An object of the present disclosure is to provide an ultraviolet light emitting element capable of enhancing robustness against a wavelength shift of an emission spectrum while suppressing a decrease in emission intensity.

The ultraviolet light emitting element according to the present disclosure includes a substrate made of a nitride semiconductor containing Al, a first conductive nitride semiconductor layer formed on the substrate, having conductivity, and containing Al and Ga, and the first conductive type nitride semiconductor layer. 1 A light emitting layer having a multiple quantum well structure formed on a conductive nitride semiconductor layer and having a plurality of quantum well layers containing Al, Ga and N laminated, and electrons formed on the light emitting layer and containing Al and N. A barrier layer and a second conductive nitride semiconductor layer formed on the electron barrier layer and having a conductivity different from that of the first conductive nitride semiconductor layer are provided, and the thickness of the quantum well layer is determined. It is 2.5 nm or more and 8.0 nm or less, and the half-value width of the emission spectrum is 10 nm or more and 17 nm or less.

According to the present disclosure, it is possible to provide an ultraviolet light emitting device capable of enhancing robustness against a wavelength shift of an emission spectrum while suppressing a decrease in emission intensity.

It is sectional drawing which shows the structure of the ultraviolet light emitting element which concerns on one Embodiment. It is sectional drawing which shows the periodic structure of a light emitting layer. It is a figure for demonstrating the robustness with respect to the wavelength shift of an emission spectrum. It is a figure which shows the wavelength deviation of the emission spectrum in the comparative example.

<Structure of ultraviolet light emitting element>
As shown in FIG. 1, the ultraviolet light emitting element 1 of the present embodiment includes a substrate 2 and a nitride semiconductor laminate 11 formed on the substrate 2. The nitride semiconductor laminate 11 includes a first conductive type nitride semiconductor layer 3, a light emitting layer 4, an electron barrier layer 5, a composition gradient layer 6, and a second conductive type nitride semiconductor layer 7. That is, the ultraviolet light emitting element 1 includes a substrate 2, a first conductive nitride semiconductor layer 3, a light emitting layer 4, an electron barrier layer 5, a composition gradient layer 6, and a second conductive nitride semiconductor layer 7. , Equipped with. The ultraviolet light emitting element 1 may further include an electrode.

(substrate)
The substrate 2 is made of a nitride semiconductor containing Al. The nitride semiconductor containing Al is, for example, AlN. Here, the wording "contains" in the expression "the substrate 2 includes a nitride semiconductor" means that the nitride semiconductor is mainly contained in the layer, but this expression also includes other elements. included. Specifically, a small amount of other elements (for example, when Al and N are the main elements, elements such as Ga, In, As, P, and Sb are added in a small amount or less) are added to the composition of this layer. This expression also includes the case of making various changes. In the expression of the composition of other layers, the word "contains" has the same meaning. Further, the small amount of elements contained is not limited to the above specific example.

For example, when a nitride semiconductor single crystal substrate such as AlN is used, the difference in lattice constant with the nitride semiconductor layer formed on the upper side of the substrate 2 becomes small, and dislocations, particularly, are caused by growing the nitride semiconductor layer in a lattice matching system. Penetration dislocations penetrating one or more layers can be reduced.

Further, the substrate 2 may be doped into n-type or p-type by donor impurities or acceptor impurities.

As a method for producing the substrate 2, a vapor phase growth method such as a sublimation method or an HVPE method and a general substrate growth method such as a liquid phase growth method can be applied. Further, the thickness of the substrate 2 may be 100 μm or more and 600 μm or less as an example. Further, the plane orientation includes c-plane (0001), a-plane {11-20}, m-plane {10-10}, r-plane {01-12}, and the like, but a c-plane substrate is more preferable.

(First Conductive Nitride Semiconductor Layer)
The first conductive type nitride semiconductor layer 3 is a layer of a nitride semiconductor having conductivity and containing Al and Ga. The first conductive nitride semiconductor layer 3 is formed on the substrate 2. Here, for example, in the expression "the first conductive nitride semiconductor layer 3 is formed on the substrate 2", the word "on" means that the first conductive nitride semiconductor layer 3 is formed on the substrate 2. However, the case where another layer is further present between the substrate 2 and the first conductive nitride semiconductor layer 3 is also included in this expression. The word "above" has the same meaning in the relationships between other layers. For example, even when another layer (for example, a composition gradient layer 6) is provided directly above the electron barrier layer 5 and the second conductive nitride semiconductor layer 7 is formed directly above the other layer, the “second conductive type” is also formed. The nitride semiconductor layer 7 is formed on the electron barrier layer 5. "

The nitride semiconductor included in the first conductive type nitride semiconductor layer 3 is, for example, Al _x Ga _(1-x) N (0 <x <1). When a material corresponding to the bandgap energy in the deep ultraviolet region is formed as the light emitting layer 4, the crystallinity thereof can be enhanced and the luminous efficiency can be improved. From the viewpoint of achieving high luminous efficiency, the nitride semiconductor included in the first conductive nitride semiconductor layer 3 is preferably a mixed crystal of AlN and GaN. In addition to N, the nitride semiconductor of the first conductive type nitride semiconductor layer 3 contains group V elements other than N such as P, As and Sb, and impurities such as C, H, F, O, Mg and Si. It may be mixed, but the type of impurity element is not limited to this.

Further, the first conductive type nitride semiconductor layer 3 and the second conductive type nitride semiconductor layer 7 are layers of nitride semiconductors having different conductivitys from each other. In general, n-type semiconductors are more crystalline than p-type semiconductors and have less influence on the light emitting layer 4. Therefore, it is preferable that the first conductive nitride semiconductor layer 3 is n-type and the second conductive nitride semiconductor layer 7 is p-type.

Further, the first conductive nitride semiconductor layer 3 preferably has a thickness within a predetermined range from the viewpoint of lattice relaxation. When the thickness of the first conductive nitride semiconductor layer 3 is thin, the lattice relaxation is not performed, but the resistance increases, which leads to deterioration of the threshold resistance. Further, when the thickness of the first conductive type nitride semiconductor layer 3 is thick, the lattice is relaxed and through-shifting occurs, which causes a decrease in light emission intensity. The predetermined range is, for example, 500 nm or more and 1000 nm or less. Further, when the first conductive nitride semiconductor layer 3 contains Al _x Ga _(1-x) N (0 <x <1), it is preferable to have an Al composition ratio within a predetermined range from the viewpoint of lattice relaxation. The Al composition ratio in the predetermined range is 0.6 or more and 0.8 or less.

(Light emitting layer)
The light emitting layer 4 is a layer of a nitride semiconductor containing Al and Ga. The light emitting layer 4 is formed on the first conductive nitride semiconductor layer 3. The nitride semiconductor included in the light emitting layer 4 preferably contains, for example, a mixed crystal of AlN and GaN from the viewpoint of realizing high luminous efficiency. In addition to N, the light emitting layer 4 may contain group V elements other than N such as P, As, and Sb, and impurities such as C, H, F, O, Mg, and Si. The type is not limited to this. The light emitting layer 4 has at least one well structure in order to realize high luminous efficiency.

Further, when the emission wavelength of the light emitting element 20 is desired to be a wavelength in the deep ultraviolet region (280 nm or less), the nitride semiconductor included in the light emitting layer 4 preferably contains Al, Ga and N. Further, from the viewpoint of increasing the luminous efficiency, as shown in FIG. 2, the light emitting layer 4 has a multiple quantum well structure (MQW) in which the quantum well layer 41 and the quantum barrier layer 42 are periodically multilayered. Is preferable. That is, it is preferable that a plurality of quantum well layers 41 are laminated with the quantum barrier layer 42 sandwiched between them. In the following, the i-period stacking of the quantum well layer 41 and the quantum barrier layer 42 means stacking the quantum well layer 41 of the i layer with the quantum barrier layer 42 sandwiched between them. However, i is an integer of 2 or more. The quantum well layer 41 contains, for example, Al, Ga and N. Further, the quantum barrier layer 42 contains Al and N. The quantum barrier layer 42 may be a layer of a nitride semiconductor containing the same elements as the quantum well layer 41. As an example, when the quantum well layer 41 _{contains Al x} Ga _(1-x) N (0 <x <1), the quantum barrier layer 42 contains Al _y Ga _(1-y) N (0 <y <1). May include. Here, the Al composition ratio x is different from the Al composition ratio y. As another example, the quantum barrier layer 42 may contain AlN.

Here, as shown in FIG. 2, the quantum well layer 41 has a thickness t _w . Further, the quantum barrier layer 42 has a thickness t _b . Further, the electron barrier layer 5 may be laminated directly above the quantum well layer 41 which is laminated at the top, that is, at the position farthest from the substrate 2. For example, the thickness t _b of the quantum barrier layer 42 may be set to 1/3 to 1/2 times the thickness of the electron barrier layer 5. As an example, when the thickness of the electron barrier layer 5 is 18.0 nm, the thickness t _b of the quantum barrier layer 42 may be 6.0 nm.

(Electronic barrier layer)
The electron barrier layer 5 is a layer of a nitride semiconductor containing Al and N. The electron barrier layer 5 is formed on the light emitting layer 4. As an example, the electron barrier layer 5 may have the same composition as the quantum barrier layer 42. As another example, when the quantum barrier layer 42 _{contains Al y} Ga _(1-y) N (0 <y <1), the electron barrier layer 5 contains Al _q Ga _(1-q) N (0). <Q <1) may be included. Here, the Al composition ratio q is different from the Al composition ratio y. As yet another example, the electron barrier layer 5 may contain AlN.

(Composition inclined layer)
The composition gradient layer 6 is _{a layer of a nitride semiconductor containing Al z} Ga _(1-z) N (0 <z <1). The composition gradient layer 6 is formed between the electron barrier layer 5 and the second conductive nitride semiconductor layer 7. In the composition gradient layer 6, the Al composition ratio z becomes smaller as the electron barrier layer 5 approaches the second conductive nitride semiconductor layer 7. That is, the composition inclined layer 6 is configured so that the Al composition ratio z has an inclination with respect to the stacking direction. Even if the acceptor is not doped, the composition gradient layer 6 produces holes due to the internal electrolysis and the piezo electrolysis generated by the composition gradient, which has the effect of increasing the efficiency of carrier injection and improving the emission intensity.

(Second conductive nitride semiconductor layer)
The second conductive type nitride semiconductor layer 7 is a layer of a nitride semiconductor having a conductivity different from that of the first conductive type nitride semiconductor layer 3. The second conductive nitride semiconductor layer 7 is formed on the electron barrier layer 5. In the example of FIG. 1, the second conductive nitride semiconductor layer 7 is formed on the electron barrier layer 5 via the composition gradient layer 6. The nitride semiconductor included in the second conductive type nitride semiconductor layer 7 is, for example, GaN, AlN or InN, and a mixed crystal containing them. In addition to N, the nitride semiconductor of the second conductive type nitride semiconductor layer 7 includes group V elements other than N such as P, As, and Sb, C, H, F, O, Mg, Si, Be, and the like. Impurities may be mixed. However, as described above, it is preferable that the conductivity of the first conductive type nitride semiconductor layer 3 is n-type and the conductivity of the second conductive type nitride semiconductor layer 7 is p-type.

(electrode)
The ultraviolet light emitting element 1 may further include an electrode. The electrode can be at least one of an n-type electrode and a p-type electrode.

The n-type electrode is a metal such as Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zr, and these. Mixed crystals, or conductive oxides such as _{ITO or Ga 2} O _{3 can be used.} Further, the n-type electrode is preferably formed so as to be in contact with the layer having n-type conductivity among the first conductive type nitride semiconductor layer 3 and the second conductive type nitride semiconductor layer 7.

The p-type electrode is a metal such as Ni, Au, Pt, Ag, Rh, Pd, Pt, Cu, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Co, Ir, Zr, etc. These mixed crystals, or conductive oxides such as _{ITO or Ga 2} O _{3 can be used.} Further, the p-type electrode is preferably formed so as to be in contact with the layer having p-type conductivity among the first conductive type nitride semiconductor layer 3 and the second conductive type nitride semiconductor layer 7.

Examples of the electrode forming method include, but are not limited to, resistance heating vapor deposition, electron gun vapor deposition, sputtering, and the like. The electrodes can be monolayer. Also, the electrodes can be laminated. Further, the electrode may be heat-treated in oxygen, nitrogen, an air atmosphere or the like after the formation of the layer.

(Ultraviolet light emitting element)
The ultraviolet light emitting element 1 can be applied to devices in, for example, a medical / life science field, an environmental field, an industrial / industrial field, a living / home appliance field, an agricultural field, and other fields. The ultraviolet light emitting element 1 is a chemical or chemical substance synthesis / decomposition device, a liquid / gas / solid (container, food, medical equipment, etc.) sterilizer, a semiconductor cleaning device, a film / glass / metal surface modification device. , Exposure equipment for semiconductor / FPD / PCB / other electronic product manufacturing, printing / coating equipment, adhesion / sealing equipment, transfer / molding equipment for films / patterns / mockups, measurement of banknotes / scratches / blood / chemical substances, etc. -Applicable to inspection equipment.

Examples of liquid sterilizers include automatic ice makers in refrigerators, ice trays and ice storage containers, water tanks for ice makers, freezers, ice makers, humidifiers, dehumidifiers, cold water tanks for water servers, hot water tanks, and flow paths. Piping, stationary water purifiers, portable water purifiers, water dispensers, water heaters, wastewater treatment equipment, disposers, toilet drain traps, washing machines, dialysis water sterilization modules, peritoneal dialysis connector sterilizers, disaster water storage systems, etc. It can be mentioned, but this is not the case.

Examples of gas sterilizers include air purifiers, air conditioners, ceiling fans, floor or bedding vacuum cleaners, futon dryers, shoe dryers, washing machines, clothes dryers, indoor germicidal lamps, and storage ventilation. Examples include systems, shoe boxes, and tons, but this is not the case.

Examples of solid sterilizers (including surface sterilizers) include vacuum packers, conveyor belts, hand tool sterilizers for medical / dental / barber / beauty salons, toothbrushes, toothbrush holders, chopstick boxes, cosmetic pouches, etc. Examples include, but are not limited to, drainage ditch lids, toilet bowl local cleaners, toilet bowl lids, and the like.

<Manufacturing method>
The ultraviolet light emitting element 1 is manufactured through a step of forming each layer on the substrate 2. This step is carried out, for example, by molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), or metalorganic vapor deposition (MOCVD) organic vapor deposition. be able to.

Here, among the layers formed on the substrate 2, the nitride semiconductor layer is, for example, an Al raw material containing trimethylaluminum (TMAl), for example, a Ga raw material containing trimethylgallium (TMGa), triethylgallium (TEGa), or the like, for example. It can be formed using N raw materials containing ammonia (NH _3).

The ultraviolet light emitting element 1 is manufactured through a step of removing unnecessary portions of each layer formed on the substrate 2 by etching. This step can be performed, for example, by inductively coupled plasma (ICP) etching.

Further, the ultraviolet light emitting element 1 can be manufactured through a step of forming an electrode. This step can be performed by various methods such as depositing a metal by an electron beam deposition (EB) method.

Here, the ultraviolet light emitting element 1 is manufactured by dividing the substrate 2 on which each layer is formed through the above steps into individual pieces by dicing. For products such as the ultraviolet light emitting element 1 that can include a stochastic element in the manufacturing process, evaluation (evaluation step) of an intermediate is generally included in the manufacturing process. That is, the characteristics of the final product can be predicted based on the evaluation result of the intermediate product in the evaluation process, and the selection of the intermediate product, the selection or addition of the process, and the like can be carried out.

The intermediates in the manufacture of the ultraviolet light emitting element 1 are, for example, the substrate 2 and the nitride semiconductor laminate 11 before forming the electrodes. Further, as an example of the evaluation process included in the manufacturing process, there is a measurement of the dislocation density at the interface between the substrate 2 and the nitride semiconductor laminate 11. The dislocation density can be observed using, for example, a cross-sectional TEM (Transmission Electron Microscope, transmission electron microscope). Further, as another example of the evaluation process included in the manufacturing process, there is a measurement of the relaxation rate of the substrate 2 and the nitride semiconductor laminate 11. The relaxation rate can be measured, for example, by performing reciprocal lattice mapping on the (20-24) plane using XRD (X-ray diffraction, X-ray diffraction). More specifically, using X'pert / MRD manufactured by PANalytical Co., Ltd., using a radiation source parallelized with a dicrystal Ge (220) in a state where the tube is 45 kV / 40 mA, an incident solar slit is formed. At 0.04 °, the detector slit is set to 1/16 mm, and the shaft is erected with respect to the (20-24) plane peak of the substrate 2. After that, the 2θ / ω scan was performed in the range of 34 ° to 37 ° with a measurement interval of 0.02 ° and an integration time of 0.3 seconds, and ω was 0.05 in the range of ± 1.5 °. Repeat the 2θ / ω scan, changing at ° intervals. Qx and Qy are calculated from the above measurements, and the relaxation rate for the substrate 2 is calculated.

Further, as yet another example of the evaluation process included in the manufacturing process, there is a measurement of the thickness (film thickness) of each of the substrate 2 and the nitride semiconductor laminate 11. The thickness of each layer can be measured by cutting out a predetermined cross section perpendicular to the substrate 2, observing this cross section with a transmission electron microscope (TEM), and using the length measuring function of the TEM.

As this measurement method, first, a TEM is used to observe a cross section of the ultraviolet light emitting element perpendicular to the main surface of the substrate 2. Specifically, for example, the observation width is 2 μm or more in the TEM image showing the cross section perpendicular to the main surface of the substrate 2 of the ultraviolet light emitting element 1. Then, within this observation width range, contrast occurs between layers having different compositions. The thickness to the interface is observed in a continuous observation region having a width of 200 nm. The average value of the thickness of the electron barrier layer included in the observation region having a width of 200 nm is calculated from 5 samples arbitrarily extracted.

The emission spectrum and emission intensity are calculated by an integrating sphere and a spectroscope. The fragmented ultraviolet light emitting element is connected to the current voltage source by a prober. The wavelength at which the maximum emission intensity is obtained is defined as the peak wavelength, and the emission intensity at that time is defined as the peak emission intensity. Regarding the half-value width, the wavelength interval at an intensity that is 1/2 of the peak emission intensity is defined as the wavelength half-value width. When there are a plurality of peaks, the peak wavelength, emission intensity, and full width at half maximum are calculated in the same manner as above using the waveform determined by Gaussian fitting.

<Preferable form>
As a result of examination based on the above-mentioned manufacturing process of the ultraviolet light emitting element 1, the inventor suppresses a decrease in light emission intensity by satisfying a predetermined relationship between the values relating to the substrate 2 and the first conductive nitride semiconductor layer. However, it has been found that the robustness to the wavelength shift of the emission spectrum can be enhanced.

Ultraviolet light emitting device 1 having the above-mentioned hierarchical structure, the ultraviolet light-emitting element 1, it is preferable that the thickness t _w of the quantum well layer 41 is 2.5nm or more and 8.0nm or less. In general, for example, in the light emitting device using a sapphire substrate, leading to that the thickness t _w of the quantum well layer 41 confine carriers in a thin multi-quantum well of less than 2.5nm enhance the emission intensity. However, in the light emitting device using a substrate made of nitride semiconductor containing Al, the thickness t _w of the quantum well layer 41 is even more and 8.0nm thick or less 2.5 nm, the emission intensity is not reduced. In addition, the full width at half maximum of the emission spectrum becomes wider as the thickness of the multiple quantum well increases. Therefore, the ultraviolet light emitting element 1 using the substrate 2 made of a nitride semiconductor containing Al can widen the half width of the light emission spectrum without lowering the light emission intensity.

Further, in the ultraviolet light emitting element 1, it is preferable that the half width of the light emission spectrum adjusted by the thickness of the multiple quantum well as described above is 10 nm or more and 17 nm or less. At this time, the robustness against the wavelength shift of the emission spectrum is improved. Within the range of the above half-value width, this wavelength shift is usually about 5 nm. For example, even if the center wavelength shifts by 5 nm, 66% or more of the case where the target original center wavelength light does not shift. It is possible to irradiate.

Further, it is more preferable that the ultraviolet light emitting element 1 has a dislocation density of 1 × 10 ⁶ cm ^{-3 or less at the interface between the substrate 2 and the first conductive nitride semiconductor layer 3.} As described above, dislocations are suppressed by using a single crystal AlN substrate in the substrate 2. By setting the dislocation density to 1 × 10 ⁶ cm ^-3 or less, it is possible to increase the electrical conductivity of the first conductive nitride semiconductor layer 3 and increase the light emission intensity of the light emitting layer 4.

The ultraviolet light emitting elements of Examples 1-8 and Comparative Example 1-5 having the same layer structure as the ultraviolet light emitting element 1 of the above embodiment were produced. That is, the ultraviolet light emitting devices of Examples 1-8 and Comparative Example 1-5 are the substrate 2, the first conductive nitride semiconductor layer 3, the light emitting layer 4, the electron barrier layer 5, the composition gradient layer 6 and the second conductive type. A nitride semiconductor layer 7 is provided. Further, the ultraviolet light emitting elements of Examples 1-8 and Comparative Example 1-5 include an n-type electrode and a p-type electrode.

[Example 1]
The c-plane AlN substrate having a thickness of 550 μm was annealed using an organometallic vapor phase growth (MOCVD) apparatus. Next, the AlN layer, which is a homoepitaxial layer, was formed at 1150 ° C. with a thickness of 500 nm. At this time, the V / III ratio was 1000. The degree of vacuum was 50 mbar. The growth rate was 1 μm / hr. Further, trimethylaluminum (TMAl) was used as the Al raw material. In addition, ammonia (NH ₃ ) was used as the N raw material.

The first conductive nitride semiconductor layer was formed on the AlN layer formed as described above. The first conductive nitride semiconductor layer is an n-type AlGaN layer (Al: 70%) using Si as a dopant impurity, that is, Al _0.70 Ga _0.30 N. The n-type AlGaN layer was formed with a thickness of 500 nm at a temperature of 1080 ° C. under the condition that the degree of vacuum was set to 50 mbar and the V / III ratio was 4000. The growth rate at this time was 0.3 μm / hr. Further, trimethylaluminum (TMAl) was used as the Al raw material. Further, triethyl gallium (TEGa) was used as a Ga raw material. In addition, ammonia (NH ₃ ) was used as the N raw material. Further, monosilane (SiH ₄ ) was used as a Si raw material.

A light emitting layer was formed on the n-type AlGaN layer formed as described above. As the light emitting layer, a quantum well layer and a quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 3.0 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. The light emitting layer was formed under the condition that the degree of vacuum was set to 50 mbar and the V / III ratio was 4000. The growth rate of the quantum well layer at this time was 0.12 μm / hr. The growth rate of the quantum barrier layer was 0.1 μm / hr.

A composition gradient layer was formed on the light emitting layer formed as described above. The composition gradient layer is Al _z Ga _(1-z) N, and the range of z is 0.2 to 0.75. In the composition inclined layer, z takes a maximum value of 0.75 on the substrate side, that is, a portion in contact with the electron barrier layer, and the value of z decreases toward the second conductive nitride semiconductor layer, so that the second conductive nitride semiconductor Z has a minimum value of 0.2 at the portion in contact with the layer. In addition, a second conductive nitride semiconductor layer was formed on the composition gradient layer. The second conductive nitride semiconductor layer is a p-type GaN layer. In this way, the nitride semiconductor laminate was formed on the AlN substrate.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was less than 1 × 10 ⁶ cm ^-3.

Further, a part of the n-type AlGaN layer was exposed by dry etching the obtained nitride semiconductor laminate. An alloy electrode containing Ti, Al, Ni and Au (corresponding to an n-type electrode) was formed on the exposed n-type AlGaN layer. Further, an alloy electrode containing Ni and Au (corresponding to the p-type electrode) was formed on the p-type GaN layer (second conductive type nitride semiconductor layer). The AlN substrate was ground to a thickness of 100 μm and then divided into individual pieces of an ultraviolet light emitting element by dicing. When the obtained ultraviolet light emitting element was driven by a current of 500 mA in a measurement system using an integrating sphere and a spectroscope, the drive voltage was 6.5 V and the emission intensity at a peak wavelength of 265 nm was 40 mW. The half width of the emission spectrum was 10.5 nm.

[Example 2]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 4.0 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, the ultraviolet light emitting device was obtained by the same method as in Example 1 using the same conditions as in Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was less than 1 × 10 ⁶ cm ^-3.

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 6.5 V and the light emission intensity at a peak wavelength of 265 nm was 55 mW. The full width at half maximum of the emission spectrum was 12 nm.

[Example 3]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 4.5 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, the ultraviolet light emitting device was obtained by the same method as in Example 1 using the same conditions as in Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was less than 1 × 10 ⁶ cm ^-3.

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 6.5 V and the light emission intensity at a peak wavelength of 265 nm was 60 mW. The full width at half maximum of the emission spectrum was 13 nm.

[Example 4]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 5.0 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, the ultraviolet light emitting device was obtained by the same method as in Example 1 using the same conditions as in Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was less than 1 × 10 ⁶ cm ^-3.

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 6.5 V and the light emission intensity at a peak wavelength of 265 nm was 65 mW. The full width at half maximum of the emission spectrum was 13.5 nm.

[Example 5]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 6.0 nm and contains AlGaN (Al: 55%), that is, Al _0.55 Ga _0.45 N. One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, the ultraviolet light emitting device was obtained by the same method as in Example 1 using the same conditions as in Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was less than 1 × 10 ⁶ cm ^-3.

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 6.5 V and the light emission intensity at a peak wavelength of 265 nm was 60 mW. The full width at half maximum of the emission spectrum was 14 nm.

[Example 6]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 7.0 nm and contains AlGaN (Al: 55%), that is, Al _0.55 Ga _0.45 N. One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, the ultraviolet light emitting device was obtained by the same method as in Example 1 using the same conditions as in Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was less than 1 × 10 ⁶ cm ^-3.

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 6.5 V and the light emission intensity at a peak wavelength of 265 nm was 45 mW. The full width at half maximum of the emission spectrum was 15.5 nm.

[Example 7]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 2.5 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, the ultraviolet light emitting device was obtained by the same method as in Example 1 using the same conditions as in Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was less than 1 × 10 ⁶ cm ^-3.

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 7.2 V and the light emission intensity at a peak wavelength of 265 nm was 25 mW. The half width of the emission spectrum was 10 nm.

[Example 8]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 8.0 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, the ultraviolet light emitting device was obtained by the same method as in Example 1 using the same conditions as in Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was less than 1 × 10 ⁶ cm ^-3.

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 6.5 V and the light emission intensity at a peak wavelength of 265 nm was 27 mW. The full width at half maximum of the emission spectrum was 17 nm.

[Comparative Example 1]
A c-plane sapphire substrate having a thickness of 450 μm was annealed using a MOCVD apparatus. Next, the AlN layer was formed at 1200 ° C. with a thickness of 2000 nm. At this time, the V / III ratio was 100. The degree of vacuum was 50 mbar. The growth rate was 1 μm / hr. Further, trimethylaluminum (TMAl) was used as the Al raw material. In addition, ammonia (NH ₃ ) was used as the N raw material.

A structure similar to that of Example 1 was formed on the AlN / sapphire substrate formed as described above. In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 0.5 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. An ultraviolet light emitting device was obtained by the same method as in Example 1 using the same conditions as in Example 1 except for the substrate and the light emitting layer.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was 1 × 10 ⁹ cm ^-3 .

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 7.2 V and the light emission intensity at a peak wavelength of 265 nm was 3.3 mW. The full width at half maximum of the emission spectrum was 9 nm.

[Comparative Example 2]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 1.0 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, an ultraviolet light emitting device was obtained by the same method as in Comparative Example 1 using the same conditions as in Comparative Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was 1 × 10 ⁹ cm ^-3 .

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 7.2 V and the light emission intensity at a peak wavelength of 265 nm was 4 mW. The full width at half maximum of the emission spectrum was 9 nm.
[Comparative Example 3]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 1.5 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, an ultraviolet light emitting device was obtained by the same method as in Comparative Example 1 using the same conditions as in Comparative Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was 1 × 10 ⁹ cm ^-3 .

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 7.2 V and the light emission intensity at a peak wavelength of 265 nm was 5.5 mW. The full width at half maximum of the emission spectrum was 9 nm.

[Comparative Example 4]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 2.0 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, an ultraviolet light emitting device was obtained by the same method as in Comparative Example 1 using the same conditions as in Comparative Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was 1 × 10 ⁹ cm ^-3 .

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 7.2 V and the light emission intensity at a peak wavelength of 265 nm was 5 mW. The full width at half maximum of the emission spectrum was 9.6 nm.

[Comparative Example 5]
In the formation of the light emitting layer, the quantum well layer and the quantum barrier layer were laminated for 5 cycles. Here, one quantum well layer has a thickness of 2.5 nm and contains _{AlGaN (Al: 55%), that is, Al 0.55} Ga _{0.45 N.} One quantum barrier layer is 6.0 nm thick and contains AlGaN (Al: 75%), i.e. Al _0.75 Ga _0.25 N. Other than that, an ultraviolet light emitting device was obtained by the same method as in Comparative Example 1 using the same conditions as in Comparative Example 1.

When the nitride semiconductor laminate formed as described above was observed using a cross-sectional TEM, the dislocation density at the interface between the AlN layer (substrate) and the n-type AlGaN layer (first conductive type nitride semiconductor layer) was found. It was 1 × 10 ⁹ cm ^-3 .

When the obtained ultraviolet light emitting element was driven with a current of 500 mA, the drive voltage was 7.2 V and the light emission intensity at a peak wavelength of 265 nm was 3.5 mW. The full width at half maximum of the emission spectrum was 10.2 nm.

The above manufacturing conditions and evaluation results for the ultraviolet light emitting devices of Examples 1-8 and Comparative Example 1-5 are summarized in Table 1 below.

The ultraviolet light emitting device of Example 1-8 includes a substrate (AlN substrate) made of a nitride semiconductor containing Al, and the thickness of the quantum well layer is 2.5 nm or more and 8.0 nm or less, which is half of the emission spectrum. The price range is 10 nm or more and 17 nm or less. The ultraviolet light emitting device of Example 1-8 has a high light emission intensity of 25 mW or more, and suppresses a decrease in light emission intensity even if the thickness of the multiple quantum well structure is large. Since the ultraviolet light emitting device of Example 1-8 has a large half-value width of 10 nm or more, it is possible to enhance the robustness against the wavelength shift of the light emission spectrum. As shown in FIG. 3, when the center wavelength of the ultraviolet light emitting element of Example 1-8 _{is designed to be the first wavelength λ 1} , the center wavelength is the second wavelength λ due to, for example, a manufacturing error. It may shift to _2. At this time, since the ultraviolet light emitting device of Example 1-8 has a large half-value width, it may include _{the first wavelength λ 1 which is the original center wavelength.} Further, in the ultraviolet light emitting device of Example 1-8, the dislocation density at the interface between the substrate and the first conductive nitride semiconductor layer is smaller than ^{1 × 10 6} cm ^-3.

In the ultraviolet light emitting device of Comparative Example 1-4, the thickness of the quantum well layer is smaller than 2.5 nm, and the half width of the light emission spectrum is also smaller than 10 nm. Since the ultraviolet light emitting element of Comparative Example 1-4 has a smaller full width at half maximum than that of Example 1-8, when the center wavelength shifts to _{the second wavelength λ 2 due to, for example, a manufacturing error, as shown in FIG. , The first wavelength λ 1} , which is the original center wavelength, may not be included. Further, as the ultraviolet light emitting element of Comparative Example 1-5, a sapphire substrate on which an AlN layer is formed is used. That is, the substrate of the ultraviolet light emitting element of Comparative Example 1-5 is different from the AlN substrate. For example, in Comparative Example 5, the thickness of the quantum well layer is 2.5 nm, the half width of the emission spectrum is 10.2 nm, and the robustness against wavelength deviation is higher than that of other Comparative Examples, but the substrate is not an AlN substrate. The dislocation density is 1 × 10 ⁶ cm ^-3 or more, and the emission intensity is as low as 3.5 mW. The emission intensity of Comparative Example 1-5 is in the range of 3.3 to 5.5 mW, which is less than the emission intensity (25 mW or more) of the ultraviolet light emitting element of Example 1-8. As is clear from the above comparison, the ultraviolet light emitting device of Example 1-8 can enhance the robustness against the wavelength shift of the light emission spectrum while suppressing the decrease in the light emission intensity.

Here, in the ultraviolet light emitting device of Example 1-6, the thickness of the quantum well layer is 3.0 nm or more and 7.0 nm or less, and the half width of the emission spectrum is 10.5 nm or more and 15.5 nm or less. .. The ultraviolet light emitting element of Example 1-6 has an even higher light emission intensity of 40 mW or more. Since the ultraviolet light emitting element of Example 1-6 has a large half-value width of 10.5 nm or more, the robustness against wavelength deviation of the light emission spectrum can be further enhanced.

Here, in the ultraviolet light emitting device of Example 2-5, the thickness of the quantum well layer is 4.0 nm or more and 6.0 nm or less, and the half width of the emission spectrum is 12 nm or more and 14 nm or less. The ultraviolet light emitting element of Example 2-5 has an even higher light emission intensity of 55 mW or more. Since the ultraviolet light emitting device of Example 2-5 has a large half-value width of 12 nm or more, the robustness against wavelength deviation of the light emission spectrum can be further enhanced.

Further, in the ultraviolet light emitting device of Example 3-5, the thickness of the quantum well layer is 4.5 nm or more and 6.0 nm or less, and the half width of the emission spectrum is 13 nm or more and 14 nm or less. The ultraviolet light emitting element of Example 3-5 has an even higher light emission intensity of 60 mW or more. Since the ultraviolet light emitting device of Example 3-5 has a large half-value width of 13 nm or more, the robustness against wavelength deviation of the light emission spectrum can be further enhanced.

(Other)
The present disclosure is not limited to the embodiments and modifications described above. It is possible to make design changes, etc. to each embodiment based on the knowledge of those skilled in the art, and aspects of such changes, etc. are included in the scope of the present disclosure.

1 Ultraviolet light emitting element 2 Substrate 3 First conductive type nitride semiconductor layer 4 Light emitting layer 5 Electron barrier layer 6 Composition gradient layer 7 Second conductive type nitride semiconductor layer 41 Quantum well layer 42 Quantum barrier layer 11 Nitride semiconductor laminate

Claims (9)

A substrate made of a nitride semiconductor containing Al and
A first conductive nitride semiconductor layer formed on the substrate, having conductivity, and containing Al and Ga,
A light emitting layer formed on the first conductive nitride semiconductor layer and having a multiple quantum well structure in which a plurality of quantum well layers containing Al, Ga and N are laminated.
An electron barrier layer formed on the light emitting layer and containing Al and N,
A second conductive nitride semiconductor layer formed on the electron barrier layer and having a conductivity different from that of the first conductive nitride semiconductor layer is provided.
The thickness of the quantum well layer is 2.5 nm or more and 8.0 nm or less.
The half width of the emission spectrum is 10 nm or more and 17 nm or less.
Ultraviolet light emitting element. The ultraviolet light emitting device according to claim 1, wherein the dislocation density at the interface between the substrate and the first conductive nitride semiconductor layer is ^{smaller than 1 × 10 6} cm ^-3. The thickness of the quantum well layer is 3.0 nm or more and 7.0 nm or less.
The ultraviolet light emitting device according to claim 1 or 2, wherein the half width of the emission spectrum is 10.5 nm or more and 15.5 nm or less. The thickness of the quantum well layer is 4.0 nm or more and 6.0 nm or less.
The ultraviolet light emitting device according to claim 3, wherein the half width of the emission spectrum is 12 nm or more and 14 nm or less. The thickness of the quantum well layer is 4.5 nm or more and 6.0 nm or less.
The ultraviolet light emitting device according to claim 4, wherein the half width of the emission spectrum is 13 nm or more and 14 nm or less. The ultraviolet light emitting device according to any one of claims 1 to 5, wherein the first conductive nitride semiconductor layer has a thickness of 500 nm or more and 1000 nm or less. The ultraviolet light emitting device according to any one of claims 1 to 6, wherein the first conductive nitride semiconductor layer has an Al composition ratio of 0.6 or more and 0.8 or less. _{A composition gradient layer containing Al z} Ga _(1-z) N (0 <z <1) is provided between the electron barrier layer and the second conductive nitride semiconductor layer.
The ultraviolet light emitting device according to any one of claims 1 to 7, wherein the composition gradient layer has an Al composition ratio z that decreases as the electron barrier layer approaches the second conductive nitride semiconductor layer. The first conductive nitride semiconductor layer has n-type conductivity and has n-type conductivity.
The ultraviolet light emitting device according to any one of claims 1 to 8, wherein the second conductive nitride semiconductor layer has p-type conductivity.

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