JP2017054654A - Deep ultraviolet light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deep ultraviolet light-emitting element excellent in practicality, enabling favorable deep ultraviolet emission, and specifically enabling favorable deep ultraviolet emission at sufficient emission intensity.SOLUTION: In a deep ultraviolet light-emitting element including at least a first electrode 102, a second electrode 103 and a luminous layer 104 that emits ultraviolet light, the luminous layer contains an oxide containing at least gallium and has a quantum well structure in which a first layer and a second layer containing a material different from that of the first layer as a main component are laminated at least alternately by each layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a deep ultraviolet light emitting element, and more specifically to a deep ultraviolet light emitting element that emits light having a wavelength of 280 nm or less.

  Deep ultraviolet light sources are used in various fields such as lighting, sterilization, medical treatment, water purification, and measurement. Deep ultraviolet light mainly means light having a wavelength of about 200 to about 350 nm, and in some cases, includes light having a wavelength of 100 nm to 200 nm. As means for generating deep ultraviolet light, mercury lamps, semiconductor light emitting devices (semiconductor LEDs), excimer lamps, and the like are known.

  On the other hand, nitride-based deep ultraviolet light-emitting elements are known as semiconductor LEDs (see Patent Document 1 below). In the lateral structure element disclosed in Patent Document 1, since the current must flow in the n-type AlGaN layer in the lateral direction, the element resistance is increased, the amount of heat generation is increased, and the carrier injection efficiency is adversely affected. There are disadvantages that arise. Therefore, it is not suitable for high output operation. Further, the chip size cannot be increased.

  As a device for improving this defect, a nitride-based deep ultraviolet light emitting device having a vertical structure is known (see Patent Documents 2 and 3 below). With the vertical structure disclosed in Patent Documents 2 and 3, the element resistance can be reduced, so that driving efficiency can be increased, heat generation can be suppressed, and high output operation is possible.

However, among these conventional deep ultraviolet light generating means, the mercury lamp has a problem of using mercury which is bad for the environment. Further, the mercury lamp has a problem that the wavelength that can be generated is limited, the lifetime is short, a high voltage is required, and it is difficult to use.
In addition, the excimer lamp has a problem that it is limited to a special application because it has a short lamp life and becomes a large-sized device.

  Nitride-based deep ultraviolet light-emitting elements are small in size and are expected to replace mercury lamps, but the nitride-based deep ultraviolet light-emitting elements disclosed in Patent Document 1 have low luminous efficiency and are compatible with high output. There was a problem that could not be done. Although the nitride-based deep ultraviolet light-emitting elements disclosed in Patent Documents 2 and 3 can be reduced in size, there is a problem that in the deep ultraviolet region, the light emission efficiency is low and it is difficult to increase the output. In particular, there is a problem that a multi-layer structure is necessary, doping is necessary, and the level is deep, so that the carrier concentration cannot be increased. In particular, when the wavelength is shortened, it is difficult to reduce the contact resistance of the electrode, it is difficult to increase the external quantum efficiency, and the manufacturing process is complicated.

  In recent years, a microplasma-excited deep ultraviolet light-emitting element (hereinafter also referred to as “MIPE”) has been studied for the above problem (see Patent Document 4 below). MIPE can realize strong light emission in a large area even in a wavelength region that cannot be emitted by a current injection type semiconductor light emitting device. In particular, a light source that can arbitrarily select a wavelength in a wavelength region of 280 nm or less is difficult except for MIPE. Has been. However, the MIPE described in Patent Document 4 is not particularly satisfactory in light emission intensity, and therefore, an acceleration electrode is necessary, and even if an acceleration electrode is provided, it is difficult to say that the light emission intensity is still sufficient. There were many issues in practical use.

  As described above, none of the conventional deep ultraviolet light-emitting elements are satisfactory, and therefore, a new and useful deep ultraviolet light-emitting element that is excellent in practical use and enables good deep ultraviolet light emission has been awaited.

JP-A-11-307811 JP 2006-278554 A JP-T-2006-104063 JP2015-103340A

  It is an object of the present invention to provide a new and useful deep ultraviolet light emitting device that is excellent in practicality and enables good deep ultraviolet light emission.

As a result of intensive studies to achieve the above object, the present inventors have surprisingly found that when a deep ultraviolet light emitting device is produced using an oxide containing at least gallium in the light emitting layer, the obtained deep ultraviolet light is obtained. It has been found that the light-emitting element has excellent practicality and can emit good deep ultraviolet light. In addition, the inventors have variously discovered that such deep ultraviolet light emitting elements emit deep ultraviolet light of 280 nm or less, have sufficient light emission intensity, and excellent light emission efficiency. It was found that it can be solved.
Moreover, after obtaining the said knowledge, the present inventors repeated investigation further, and came to complete this invention.

That is, the present invention relates to the following inventions.
[1] A deep ultraviolet light emitting device having at least a first electrode, a second electrode, and a light emitting layer, wherein the light emitting layer emits deep ultraviolet light, wherein the light emitting layer contains at least gallium oxide A deep ultraviolet light emitting element comprising:
[2] The light emitting layer has a quantum well structure in which a first layer and a second layer containing a material different from the first layer as a main component are alternately stacked at least one layer at a time. [1] The deep ultraviolet light-emitting device according to [1].
[3] The deep ultraviolet light-emitting device according to [2], wherein the main components of the first layer and the second layer are oxides each containing at least gallium.
[4] The deep ultraviolet light-emitting element according to the above [2] or [3], wherein any one of the main components of the first layer and the second layer is an oxide containing at least aluminum.
[5] The deep ultraviolet light-emitting device according to any one of [2] to [4], wherein the main components of the first layer and the second layer are oxides each having a corundum structure.
[6] The first electrode is a reference electrode, and the second electrode is disposed on the opposite side of the reference electrode with the discharge electrode disposed so as to face the reference electrode. From the plasma generated by the gas when a voltage higher than the potential of the reference electrode and the reference electrode is applied, and the gas filled in the space accommodating the reference electrode and the discharge electrode. The light emitting layer is configured to emit deep ultraviolet light when the electrons or positive ions extracted by the extracting means collide with the light emitting layer. The deep ultraviolet light-emitting device according to any one of [1] to [5].
[7] A secondary electron emission material layer disposed on the opposite side of the discharge electrode with the reference electrode interposed therebetween, and when the extraction unit extracts electrons, the positive electrode extracted to the reference electrode side is further provided. The deep ultraviolet light-emitting device according to [6], wherein the secondary electron emission material layer generates electrons when ions collide with the secondary electron emission material layer.
[8] The above [6] or [6], wherein the gas is at least one gas selected from the group consisting of Ne, Xe, He, Ar, H ₂ , D ₂ , N ₂ , XeCl and ArF, or a mixed gas thereof. 7]. A deep ultraviolet light emitting device according to item 7].
[9] The deep ultraviolet light-emitting element according to any one of [6] to [8], wherein the extraction unit includes a pulling electrode disposed between the discharge electrode and the light-emitting layer.
[10] The deep ultraviolet light-emitting element according to any one of [6] to [9], wherein the extraction unit includes an acceleration electrode disposed on the opposite side of the discharge electrode with the light-emitting layer interposed therebetween.
[11] The deep ultraviolet light-emitting device according to [10], wherein the acceleration electrode is exposed to the outside of the deep ultraviolet light-emitting device.
[12] The deep ultraviolet light-emitting element according to [10] or [11], wherein a pulse voltage is sequentially applied in the order of the discharge electrode, the pulling electrode, and the acceleration electrode.
[13] The deep ultraviolet light-emitting element according to [12], wherein each pulse voltage applied to the pulling electrode and the acceleration electrode starts to be applied after a predetermined time has elapsed since the last application of the pulse voltage.

  The deep ultraviolet light-emitting device of the present invention is excellent in practicality and enables good deep ultraviolet light emission, and particularly enables good deep ultraviolet light emission in light emission intensity.

It is a figure which shows typically schematic structure of the deep ultraviolet light emitting element which is one of the embodiments of this invention. It is a figure which shows typically schematic structure of the deep ultraviolet light emitting element which is one of the embodiments of this invention. It is a schematic block diagram of the film-forming apparatus (mist CVD) used in the Example. It is a graph which shows the emission spectrum of the deep ultraviolet light emitting element of an Example.

The deep ultraviolet light emitting device of the present invention has at least a first electrode, a second electrode, and a light emitting layer. The light emitting layer is not particularly limited as long as it contains an oxide containing at least gallium. In the present invention, the light-emitting layer has a quantum well structure in which a first layer and a second layer mainly composed of a material different from the first layer are alternately stacked. It is preferable to have. Moreover, it is preferable that one of the main components of the first layer and the second layer is an oxide containing at least gallium, and the main components of the first layer and the second layer each contain at least gallium. More preferably, it is an oxide. Any of the main components of the first layer and the second layer is an oxide containing at least aluminum (for example, α-Al ₂ O ₃ , α- (Al _x Ga _1-x ) ₂ O ₃ (provided that 1>X> 0), α- (Al Z1 Ga Z2 in Z3) 2 O 3 ( where, 1> Z1, Z2, Z3 > is the also preferably 0, and Z1 + Z2 + Z3 = 1), etc.), each having a corundum structure An oxide is also preferable. The oxide containing at least aluminum preferably has an aluminum / gallium content ratio (atomic ratio) of 1: 0.1 to 1:10, more preferably 1: 0.5 to 1: 5. A ratio of 1: 0.8 to 1: 2 is most preferable. The oxide is preferably a crystal, and the crystal may be a single crystal or a polycrystal. The oxide is preferably a semiconductor. More preferable examples of the oxide include α-Ga ₂ O ₃ , α- (Al _x Ga _1-x ) ₂ O ₃ (where 1>X> 0), α- (In _Y Ga _{1 -Y) 2} O ₃ (where, 1>Y> 0), α- (Al Z1 Ga Z2 In Z3) 2 O 3 ( where, 1> Z1, Z2, Z3 > 0 and Z1 + Z2 + Z3 = 1), and the like . By using such a preferable material, the emission intensity can be further improved. Here, "main component", e.g., the case where the oxide is α-Ga ₂ O _3, gallium atomic ratio α-Ga ₂ O ₃ at a ratio of more than 0.5 in the metal elements of the layer If it is included, that's fine. In the present invention, the atomic ratio of gallium in the metal element in the layer is preferably 0.7 or more, and more preferably 0.8 or more.

  The light emitting layer can be formed by means such as a mist CVD method. Hereinafter, as a preferable light emitting layer forming means in the present invention, means for forming the quantum well structure using mist on a substrate will be described, but the present invention is not limited to these. A single layer structure or a multilayer structure other than the quantum well structure can be formed by the same means.

  Mist or droplets generated by atomizing or dropletizing the raw material solution are transported to the substrate with a carrier gas, and then the mist or droplets are reacted on the substrate to cause oxide or corundum containing gallium. An oxide having a structure or the like can be formed. Further, the quantum well structure in which the first layer and the second layer are alternately stacked by using the raw material solution alternately as the first layer raw material solution and the second layer raw material solution. Can be formed.

(Raw material solution)
The raw material solution is not particularly limited as long as it contains a material that can be atomized or formed into droplets, and may be an inorganic material or an organic material. Preferably, there is one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, cobalt, zinc, magnesium, calcium, silicon, yttrium, strontium and barium. More preferably.

  In the present invention, as the raw material solution, a solution in which the metal is dissolved or dispersed in an organic solvent or water in the form of a complex or a salt can be suitably used. Examples of complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, hydride complexes, and the like. Examples of the salt form include organic metal salts (for example, metal acetates, metal oxalates, metal citrates, etc.), sulfide metal salts, nitrate metal salts, phosphorylated metal salts, metal halide salts (for example, metal chlorides). Salt, metal bromide salt, metal iodide salt, etc.).

Moreover, you may mix additives, such as a hydrohalic acid and an oxidizing agent, with the said raw material solution. Examples of the hydrohalic acid include hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. Among them, hydrobromic acid or hydroiodic acid is preferable. Examples of the oxidizing agent include hydrogen peroxide (H ₂ O ₂ ), sodium peroxide (Na ₂ O ₂ ), barium peroxide (BaO ₂ ), and benzoyl peroxide (C ₆ H ₅ CO) ₂ O _2. Peroxides, hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, organic peroxides such as peracetic acid and nitrobenzene.

The raw material solution may contain a dopant. The dopant is not particularly limited as long as the object of the present invention is not impaired. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium or niobium, or p-type dopants. The concentration of the dopant may usually be about 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²² / cm ³ , and the concentration of the dopant is set to a low concentration of about 1 × 10 ¹⁷ / cm ³ or less, for example. May be. Furthermore, according to the present invention, the dopant may be contained at a high concentration of about 1 × 10 ²⁰ / cm ³ or more.

(Substrate)
The substrate is not particularly limited as long as it can support the film. The material of the substrate is not particularly limited as long as the object of the present invention is not impaired, and may be a known substrate, an organic compound, or an inorganic compound. The shape of the substrate may be any shape and is effective for all shapes, for example, a plate shape such as a flat plate or a disk, a fiber shape, a rod shape, a columnar shape, a prismatic shape, A cylindrical shape, a spiral shape, a spherical shape, a ring shape and the like can be mentioned. In the present invention, a substrate is preferable. The thickness of the substrate is not particularly limited in the present invention.

  The substrate is not particularly limited as long as it is plate-shaped and serves as a support for the crystal film. The substrate may be an insulator substrate, a semiconductor substrate, or a conductive substrate, but the substrate is preferably an insulator substrate, and has a metal film on the surface. A substrate is also preferred. Examples of the substrate include a base substrate containing a substrate material having a corundum structure as a main component, a base substrate containing a substrate material having a β-gallia structure as a main component, and a substrate material having a hexagonal crystal structure as a main component. Examples thereof include a base substrate. Here, the “main component” means that the substrate material having the specific crystal structure is preferably 50% or more, more preferably 70% or more, and still more preferably 90% by atomic ratio with respect to all components of the substrate material. % Or more, meaning that it may be 100%.

The substrate material is not particularly limited as long as the object of the present invention is not impaired, and may be a known material. Examples of the substrate material having the corundum structure include the same materials as those exemplified as the material having the corundum structure. In the present invention, α-Al ₂ O ₃ or α-Ga ₂ O is used. ₃ is preferred. As a base substrate mainly composed of a substrate material having a corundum structure, a sapphire substrate (preferably a c-plane sapphire substrate), an α-type gallium oxide substrate, or the like is given as a suitable example. As a base substrate mainly composed of a substrate material having a β-gallia structure, for example, a β-Ga ₂ O ₃ substrate, or a Ga ₂ O ₃ and Al ₂ O ₃ containing Al ₂ O ₃ content of more than 0 wt% Examples thereof include a mixed crystal substrate of 60 wt% or less. In addition, examples of the base substrate whose main component is a substrate material having a hexagonal crystal structure include a SiC substrate, a ZnO substrate, and a GaN substrate. Note that each layer may be stacked directly or via another layer (for example, a buffer layer) on a base substrate whose main component is a substrate material having a hexagonal crystal structure.

  In the present invention, the substrate is preferably a base substrate mainly composed of a substrate material having a corundum structure, more preferably a sapphire substrate or an α-type gallium oxide substrate, and a c-plane sapphire substrate. Is most preferred.

(Lamination method)
The lamination method is not particularly limited, but preferably the raw material solution is atomized or dropletized (atomization / droplet forming step), and the generated mist or droplet is supplied to the substrate by a carrier gas. Then, the supplied mist or liquid droplets are reacted to form a film on the substrate (film formation process).

  In the atomization / droplet forming step, a raw material solution is prepared, and the raw material solution is atomized or formed into droplets to generate mist. The blending ratio of the metal is not particularly limited, but is preferably 0.0001 mol / L to 20 mol / L with respect to the entire raw material solution. The atomization or droplet formation means is not particularly limited as long as the raw material solution can be atomized or dropletized, and may be a known atomization means or droplet formation means. An atomizing means or a droplet forming means using sound waves is preferable. The mist or the droplet preferably has a zero initial velocity and floats in the air.For example, the mist or the droplet is more preferably a mist that floats in a space and can be transported as a gas instead of being sprayed like a spray. preferable. The droplet size is not particularly limited and may be a droplet of about several mm, but is preferably 50 μm or less, and more preferably 1 to 10 μm.

  In the mist / droplet supplying step, the mist or the droplet is supplied to the substrate by the carrier gas. The type of the carrier gas is not particularly limited as long as the object of the present invention is not impaired. For example, an inert gas such as oxygen, ozone, nitrogen or argon, or a reducing gas such as hydrogen gas or forming gas is preferable. As mentioned. Further, the type of carrier gas may be one type, but may be two or more types, and a diluent gas (for example, a 10-fold diluted gas) whose carrier gas concentration is changed is used as the second carrier gas. Further, it may be used. Further, the supply location of the carrier gas is not limited to one location but may be two or more locations. The flow rate of the carrier gas is not particularly limited, but the linear velocity in the reactor (more specifically, the reactor is at a high temperature and changes depending on the environment. 0.1 m / s to 100 m / s is preferable, and 1 m / s to 10 m / s is more preferable.

  In the film forming step, the mist or the droplet is reacted to form a film on a part or all of the substrate surface. The reaction is not particularly limited as long as it is a reaction in which a film is formed from the mist or the droplet, but in the present invention, a thermal reaction is preferable. The thermal reaction may be performed as long as the mist or the droplet reacts with heat, and the reaction conditions are not particularly limited as long as the object of the present invention is not impaired. In this step, the thermal reaction is usually performed at a temperature not lower than the evaporation temperature of the solvent, but is preferably not higher than the temperature. Further, the thermal reaction may be performed in any atmosphere of a vacuum, a non-oxygen atmosphere, a reducing gas atmosphere, and an oxygen atmosphere as long as the object of the present invention is not impaired. Although the reaction may be performed under reduced pressure or reduced pressure, in the present invention, the reaction is preferably performed under atmospheric pressure from the viewpoint of simplifying the calculation of the evaporation temperature. In the case of a vacuum, the evaporation temperature can be lowered. The film thickness can be set by adjusting the film formation time. In the present invention, the thicknesses of the first layer and the second layer in the quantum well are each preferably 100 nm or less, more preferably 20 nm or less, and most preferably 1 to 10 nm.

  The first electrode and the second electrode may be composed of the same or different electrode materials, and examples of the electrode material include Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, and Ta. , Ti, Au, Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, In, Pd, Nd or Ag, or alloys thereof, tin oxide, zinc oxide, indium oxide, indium tin oxide Examples thereof include metal oxide conductive films such as (ITO) and zinc indium oxide (IZO), organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, and mixtures thereof. The electrode can be formed by a known means such as a vacuum deposition method or a sputtering method.

  In the present invention, the deep ultraviolet light emitting element includes a discharge electrode arranged such that the first electrode is a reference electrode and the second electrode is opposed to the reference electrode, and the discharge electrode is sandwiched between the discharge electrode and the discharge electrode. A light emitting layer disposed on the opposite side of the reference electrode, a gas filled in a space accommodating the reference electrode and the discharge electrode, and a voltage higher than the potential of the reference electrode and the reference electrode were applied. In some cases, a drawing means for drawing out electrons or positive ions from the plasma generated by the gas is provided, and the light emitting layer becomes deep ultraviolet light when the electrons or positive ions drawn out by the drawing means collide with the light emitting layer. It is preferable that it is comprised so that it may emit.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these drawings and the like.

  FIG. 1 is a cross-sectional view showing a schematic configuration of a deep ultraviolet light emitting element (hereinafter also simply referred to as “light emitting element”) 101 which is one of the preferred embodiments of the present invention. The light emitting element 101 includes a reference electrode 102, a discharge electrode 103, a light emitting layer 104, a pulling electrode 105, an acceleration electrode 106, a secondary electron emission material layer 107, a lower transparent substrate 108, a pulse output unit. 109.

The light emitting layer 104 and the secondary electron emission material layer 107 are arranged to face each other, and a space 110 is formed between them. The space 110 is sealed from the outside, and the height thereof, that is, the distance between the light emitting layer 104 and the secondary electron emission material layer 107 is, for example, 0.15 to 5 mm. In the space 110, the gas for generating plasma, for example, at least one gas selected Ne, _Xe, the He, _Ar, from the group consisting of _{H 2, D 2, N 2} , XeCl and ArF, Or the mixed gas is filled. The pressure of the gas filled in the space 110 is, for example, 1 × 10 ¹ to 1 × 10 ⁶ Pa. The space 110 may be an open space where gas can be continuously supplied (flow type).

  In the space 110, the reference electrode 102, the discharge electrode 103, and the pulling electrode 105 are accommodated. The reference electrode 102, the discharge electrode 103, and the pulling electrode 105 are made of Fe, Ni, stainless steel, Ti, Mo, Cu, Au, Ag, Cr, or an alloy thereof.

  The reference electrode 102 is composed of three electrodes provided in the lower part of the space 110. In this embodiment, the reference electrode 102 is grounded, but the potential of the reference electrode 102 is not particularly limited.

  The discharge electrode 103 is composed of six electrodes arranged to face the reference electrode 102. A pulse voltage P1 is applied to the discharge electrode 103 from the pulse output unit 109 at a predetermined timing. The pulse voltage P1 is higher or lower than the potential of the reference electrode 102. By applying the pulse voltage P1, a fluctuating electromagnetic field is formed between the reference electrode 102 and the discharge electrode 103 and is filled in the space 110. The generated gas generates plasma by the electromagnetic field.

  The pulling electrode 105 and the accelerating electrode 106 correspond to the “drawing means”. The pulling electrode 105 includes six electrodes disposed between the discharge electrode 103 and the light emitting layer 104. A pulse voltage P <b> 2 is applied from the pulse output unit 109 to the pulling electrode 105. The acceleration electrode 106 is disposed on the opposite side of the discharge electrode 103 with the light emitting layer 104 interposed therebetween, and is exposed to the outside of the light emitting element 101. A pulse voltage P <b> 3 is applied from the pulse output unit 109 to the acceleration electrode 106. As will be described later, a pulse voltage is sequentially applied from the pulse output unit 109 in the order of the discharge electrode 103, the pulling electrode 105, and the acceleration electrode 106. Thus, the pulling electrode 105 and the acceleration electrode 106 draw electrons or positive ions (electrons in this embodiment) from the plasma and collide with the light emitting layer 104.

The reference electrode 2, the pulling electrode 105, and the acceleration electrode 106 extend linearly from the front of FIG. The light emitting layer 104 is disposed on the surface of the acceleration electrode 106 on the space 110 side. The secondary electron emission material layer 107 is disposed on the opposite side of the discharge electrode 103 with the reference electrode 102 interposed therebetween, and is formed of fine particles made of MgO. Note that BN may be used as the fine particles. A lower transparent substrate 108 is disposed on the surface of the secondary electron emission material layer 107 opposite to the space 110. The lower transparent substrate 108 is transparent to deep ultraviolet light, and is, for example, quartz, CaF ₂ or a single crystal sapphire substrate.

Next, the light emission operation of deep ultraviolet light by the light emitting element 101 will be described.
The pulse voltages P1, P2, P3 are sequentially applied to the discharge electrode 3, the pulling electrode 5, and the acceleration electrode 6. Specifically, the pulse voltage P1 is output at any time T1 to T2, the pulse voltage P2 is output at any time T3 to T4, the pulse voltage P3 is output at any time T5 to T6, Thereafter, this cycle is repeated at a predetermined cycle. The frequency of the cycle, that is, the frequency of each pulse voltage P1 to P3 is, for example, 50 Hz to 100 MHz. The pulse voltages P1, P2, and P3 are, for example, 100 to 5000 V, but at least the pulse voltages P2 and P3 are set higher than the pulse voltage P1. The pulse width of the pulse voltages P1, P2, P3 is, for example, 10 to 50 μs. From time T1 to T2, the pulse voltage P1 is applied to the discharge electrode 3. Thereby, a fluctuating electromagnetic field is formed between the reference electrode 2 and the discharge electrode 3, and the gas filled in the space 110 generates plasma by the electromagnetic field. At this time, the plasma contains equal amounts of electrons and positive ions, and is in a charge neutral state. Subsequently, at time T <b> 3 to T <b> 4, the pulse voltage P <b> 2 is applied to the pulling electrode 5. Thereby, some of the electrons in the plasma are pulled to the light emitting layer 104 side. Along with this, some of the ions in the plasma are extracted to the reference electrode 102 side. Subsequently, at time T <b> 5 to T <b> 6, the pulse voltage P <b> 3 is applied to the acceleration electrode 106. Thereby, the electrons pulled by the pulling electrode 105 are accelerated and collide with the light emitting layer 104. Thereby, the light emitting layer 104 is excited to generate deep ultraviolet light, and the deep ultraviolet light is emitted to the outside through the secondary electron emission material layer 107 and the lower transparent substrate 108. Note that since the secondary electron emission material layer 107 is made of MgO or BN, the light transmittance is very high. In addition, the neutral state of the charge of the plasma partially collapses due to some electrons being pulled out. On the other hand, the ions extracted toward the reference electrode 102 collide with the secondary electron emission material layer 107, and the secondary electron emission material layer 107 generates electrons (secondary electrons). Can be stabilized.

  As described above, the light-emitting element 101 emits deep ultraviolet light by extracting electrons from plasma and causing the electrons to collide with the light-emitting layer 104. Therefore, a light-emitting element with higher light emission efficiency than the conventional one can be provided.

  Further, since the electrons extracted from the plasma can be further accelerated by the acceleration electrode 106, the emission intensity can be increased. Furthermore, since the acceleration electrode 106 is exposed to the outside of the light emitting element 101, it can be cooled by air or liquid. Therefore, a high voltage can be applied to the acceleration electrode 106. Therefore, the acceleration of electrons can be further increased and higher output can be achieved more easily.

  In addition, it is preferable to form a layer made of nano-sized metal fine particles on the surface of the light emitting layer 104. In such a configuration, the electric charge at the portion where the metal fine particles are formed increases due to the plasmon effect, so that the emission intensity can be further increased. Furthermore, the light emission intensity of the light emitting element 101 can be controlled by changing the frequency of the pulse voltages P <b> 1 to P <b> 3 to change the collision frequency of electrons with the light emitting layer 104.

  The pulse voltages P2 and P3 applied to the pulling electrode 105 and the accelerating electrode 106 are applied after a predetermined time has elapsed from the end of applying the pulse voltage immediately before. That is, a waiting time of, for example, 2.5 to 5 μm is provided between the time T2 and the time T3 and between the time T5 and the time T6. At the end of application of the pulse voltages P1 and P2, since the plasma potential is maintained, positive ions are gathered around the electrons. Therefore, even if the next pulse voltage is applied simultaneously with the end of the application of the immediately preceding pulse voltage, electrons cannot be efficiently extracted to the light emitting layer 104 side. Therefore, in this embodiment, the next voltage pulse is applied at the timing when the standby time is provided and the electrons are no longer affected by the positive ions. Thereby, electrons can be efficiently extracted from the plasma.

  As described above, the light-emitting element 101 can achieve high light emission efficiency and can have better light emission intensity. Good deep ultraviolet light having a wavelength of less than 210 nm (about 170 nm) that cannot be sufficiently output by a conventional deep ultraviolet light emitting element can be sufficiently output.

  Furthermore, the wavelength of the deep ultraviolet light can be controlled to an arbitrary wavelength by appropriately selecting a material for forming the light emitting layer 104. The wavelength of deep ultraviolet light can also be changed by making the material forming the light emitting layer 104 a superlattice, adding impurities to the material or the superlattice, or changing the lattice spacing of the superlattice. Can do.

In the light emitting element 1 described above, electrons are extracted from the plasma to the light emitting layer 104 side, but ions may be extracted to the light emitting layer 104 side. In this case, negative pulse voltages P 2 and P 3 are applied to the pulling electrode 105 and the acceleration electrode 106. Thereby, ions are extracted from the plasma and collide with the light emitting layer 104, thereby generating deep ultraviolet light. Since ions have a larger mass than electrons, the intensity of deep ultraviolet light is greater than when electrons collide with the light emitting layer 104. Therefore, the emission intensity can be increased by using a gas having a large mass as a gas for generating plasma. However, if the mass of ions is too large, the light emitting layer 104 is likely to be damaged. Therefore, when emphasizing the light emission lifetime, gases having a small mass such as He, H ₂ , and D ₂ are used as gases for generating plasma. It is preferable to use it.

  Moreover, the schematic structural drawing of the deep ultraviolet light emitting element 101 which is another preferable embodiment of this invention is shown in FIG. The light emitting element 101 includes a reference electrode 102, a discharge electrode 103, a light emitting layer 104, a tensile electrode 105, a secondary electron emission material layer 107, a lower transparent substrate 108, a pulse output unit 109, and an upper transparent element. And a substrate 111. 2, the same members as those in the light emitting element 101 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. That is, the light emitting element 101 has a configuration in which the upper transparent substrate 111 is provided instead of the acceleration electrode 106 in the light emitting element 1 shown in FIG. Similar to the lower transparent substrate 8, the upper transparent substrate 11 may be a single crystal sapphire substrate or the like. In this embodiment, the pulse voltages P1 and P2 are sequentially applied to the discharge electrode 103 and the pulling electrode 5.

  The light emitting operation of the light emitting element 101 is substantially the same as that of the light emitting element 1 shown in FIG. That is, when the pulse voltage P <b> 1 is applied to the discharge electrode 103, plasma is generated in the space 110. Subsequently, when the pulse voltage P <b> 2 is applied to the pulling electrode 5, some of the electrons in the plasma are pulled toward the light emitting layer 104 and collide with the light emitting layer 104. As a result, the light emitting layer 104 is excited to generate deep ultraviolet light. Deep ultraviolet light is emitted downward in the drawing through the secondary electron emission material layer 107 and the lower transparent substrate 108, and also emitted upward in the drawing through the upper transparent substrate 111.

  Thus, since the light emitting element 101 does not include the acceleration electrode, it is possible to irradiate deep ultraviolet light in both directions. In addition, the light emitting element 101 may include two or more rows of pulling electrodes 105 so that electrons are sufficiently accelerated to collide with the light emitting layer 104.

  In the light-emitting element 101 illustrated in FIG. 1, the pulling electrode 105 may be omitted as long as a sufficiently high voltage can be applied to the acceleration electrode 106. Similarly, the acceleration electrode 106 may be omitted if a sufficiently high voltage can be applied to the pulling electrode 105. In other words, the “drawing means” may be constituted by only one of the pulling electrode 105 and the accelerating electrode 106.

  In the above embodiment, a pulse voltage is applied to the discharge electrode 103, the pulling electrode 105, and the acceleration electrode 106 as desired. However, electrons or positive ions can be extracted from the plasma and collide with the light emitting layer. If there is, it is not limited to the pulse voltage. For example, an AC voltage or a DC voltage may be applied to the discharge electrode 103, the pulling electrode 105, and the acceleration electrode 106.

  The light emitting element 101 may be formed in an arbitrary size or may be formed in a curved surface shape. For example, the surfaces of the lower transparent substrate 8 and the upper transparent substrate 11 may be formed in a curved surface shape. The material forming the lower transparent substrate 8 and the upper transparent substrate 11 is not limited to sapphire, but may be any material that has high transparency to deep ultraviolet light. For example, AlN or quartz may be used.

  Since the deep ultraviolet light emitting device of the present invention can emit deep ultraviolet light having a wavelength of 280 nm or less and has very high energy, various fields such as sterilization of pools and hot springs, curing of 3D printer modeling materials, It can be used for decomposition of persistent substances, ozone sensing, medical sterilization, ultraviolet ray treatment, and the like.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

Example 1
1. Film Forming Apparatus The mist CVD apparatus (1) used in this example will be described with reference to FIG. The mist CVD apparatus (1) includes a carrier gas source (2a, 12a) for supplying a carrier gas, and a flow rate adjusting valve (3a, 13a) for adjusting the flow rate of the carrier gas sent from the carrier gas source (2a, 12a). ), A mist generating source (4, 14) in which the raw solution (4a, 14a) is stored, a container (5, 15) containing water (5a, 15a), and a container (5, 15) An ultrasonic transducer (6, 16) attached to the bottom surface, a film formation chamber (7), a supply pipe (9, 19) connecting the mist generation source (4, 14) to the vicinity of the substrate (10), And at least a hot plate (8) installed in the film forming chamber (7). A substrate (10) is placed on the hot plate (8). In addition, there are two types of raw material solutions (4a, 14a), and carrier gas sources (2a, 12a), carrier gas (dilution) sources (2b, 12b), flow control valves (3a, 3b, 13a, 13b), respectively. , A mist generation source (4, 14), a container (5, 15), an ultrasonic transducer (6, 16), and a supply pipe (9, 19).

2. 2. Preparation of raw material solution 2-1. Preparation of first raw material solution Mixing gallium bromide with water to prepare a 0.005M gallium bromide aqueous solution. At this time, hydrobromic acid is contained in a volume ratio of 10%. It was.
2-2. Preparation of Second Raw Material Solution Gallium acetylacetonate (Gaac) and aluminum acetylacetonate (Alac) are mixed with water so that Gaac 0.07M and Alac 0.02M are obtained. 2% by volume was used as a second raw material solution.

3. Preparation of film formation The first raw material solution (4a) obtained in (1) was accommodated in the first mist generation source (4). In addition, the above 2. The second raw material solution (14a) obtained in (1) was accommodated in the second mist generation source (14). Next, a 2-inch c-plane sapphire substrate was placed on the hot plate (8) as the substrate (10), and the hot plate (8) was operated to raise the temperature to 600 ° C. Next, the flow control valves (3a, 13a) are opened, and carrier gas is supplied from the carrier gas supply means (2a, 12a), which is a carrier gas source, into the film formation chamber (7). After sufficiently substituting the atmosphere with a carrier gas, the flow rate of the carrier gas was adjusted to 5 L / min. Note that oxygen was used as a carrier gas.

4). Formation of light emitting layer (quantum well structure) Next, the ultrasonic vibrator (6, 16) is vibrated at 2.4 MHz, and the vibration is propagated to the raw material solution (4a, 14a) through water (5a, 15a). By this, the raw material solution (4a, 14a) was atomized and the mist (4b, 14b) was produced | generated. The mist (4b, 14b) is introduced into the film forming chamber (7) by the carrier gas through the supply pipe (9, 19), and is formed at 600 ° C. under atmospheric pressure at the film forming chamber (7). ) Caused a thermal reaction to form a film on the substrate (10). Regarding the film formation time, after forming the film for 20 seconds using the first raw material solution, the film formation process was stopped for 10 seconds (however, the gas flow rate was 0.5 LPM), and then the second After film formation was performed for 80 seconds using the raw material solution, the film formation process was stopped for 10 seconds (however, the gas flow rate was 0.5 LPM), and this series of processes was repeated. Then, the first layer made of the first raw material solution and the second layer made of the second raw material solution are alternately laminated, and the first layer and the second layer are made into one pair, for a total of 17 pairs. A superlattice structure was obtained. The superlattice structure was confirmed by XRD. The content ratio (atomic ratio) of aluminum and gallium in the second layer was 1: 1. The film thickness was 1 nm for the first layer and 6 nm for the second layer.

5). Evaluation Using the obtained superlattice structure as a light emitting layer, a light emitting device 101 shown in FIG. 2 was manufactured. A sapphire substrate was used as the lower transparent substrate 108 in the same manner as the upper transparent substrate 111. Then, a positive pulse voltage (700 V) was applied to the tension electrode 105, and an emission spectrum was measured when the light emitting layer 104 was excited and emitted by electrons. Note that a pulse voltage of 500 V was applied to the discharge electrode 103 in order to generate plasma. Further, Ne was used as a gas for generating plasma.

  The measured emission spectrum is shown in FIG. From this emission spectrum, it can be seen that the emission intensity is very excellent in the wavelength region of 280 nm or less as compared with the conventional deep ultraviolet light emitting device.

  The deep ultraviolet light emitting device of the present invention has sufficient light emission intensity and can output deep ultraviolet light with high efficiency, and thus can be used for various applications. For example, it can be used for sterilization of pools and hot springs, curing of 3D printer modeling materials, decomposition of hardly decomposable substances, ozone sensing, medical sterilization, ultraviolet ray treatment, and the like.

DESCRIPTION OF SYMBOLS 1 Mist CVD apparatus 2a (First) Carrier gas source 3a (First) Flow control valve 4 (First) Mist generation source 4a (First) Raw material solution 4b (First) Mist 5 (First 5) (First) Water 6 (First) Ultrasonic vibrator 7 Deposition chamber 8 Hot plate 9 (First) Supply tube 10 Substrate 12a (Second) Carrier gas source 13a (Second) (Second) mist generating source 14a (second) raw material solution 14b (second) mist 15 (second) container 15a (second) water 16 (second) Sonic transducer 19 (second) supply pipe

Claims (13)

  In a deep ultraviolet light-emitting element having at least a first electrode, a second electrode, and a light emitting layer, wherein the light emitting layer emits deep ultraviolet light, the light emitting layer includes an oxide containing at least gallium. A deep ultraviolet light emitting device characterized by   2. The light emitting layer has a quantum well structure in which a first layer and a second layer containing a material different from the first layer as a main component are alternately stacked at least one layer. Deep ultraviolet light emitting device.   The deep ultraviolet light-emitting device according to claim 2, wherein the main components of the first layer and the second layer are oxides each containing at least gallium.   4. The deep ultraviolet light-emitting element according to claim 2, wherein one of main components of the first layer and the second layer is an oxide containing at least aluminum.   The deep ultraviolet light-emitting device according to any one of claims 2 to 4, wherein the main components of the first layer and the second layer are oxides each having a corundum structure.   A discharge electrode disposed such that the first electrode is a reference electrode and a second electrode is opposed to the reference electrode; and a light emitting layer disposed on the opposite side of the reference electrode with the discharge electrode interposed therebetween An electron or a gas filled in a space accommodating the reference electrode and the discharge electrode, and a plasma generated by the gas when a voltage higher than the potential of the reference electrode and the reference electrode is applied. The light emitting layer is configured to emit deep ultraviolet light when electrons or positive ions extracted by the extracting means collide with the light emitting layer. 6. The deep ultraviolet light-emitting device according to any one of 5 above.   A secondary electron emission material layer disposed on the opposite side of the discharge electrode with the reference electrode interposed therebetween, and when the extraction means extracts electrons, positive ions extracted toward the reference electrode are The deep ultraviolet light-emitting device according to claim 6, wherein the secondary electron emission material layer generates electrons by colliding with the secondary electron emission material layer. 8. The depth according to claim 6, wherein the gas is at least one gas selected from the group consisting of Ne, Xe, He, Ar, H ₂ , D ₂ , N ₂ , XeCl, and ArF, or a mixed gas thereof. Ultraviolet light emitting element.   The deep ultraviolet light emitting element according to any one of claims 6 to 8, wherein the extraction means includes a pulling electrode disposed between the discharge electrode and the light emitting layer.   The deep ultraviolet light-emitting device according to any one of claims 6 to 9, wherein the lead-out means includes an acceleration electrode disposed on the opposite side of the discharge electrode with the light-emitting layer interposed therebetween.   The deep ultraviolet light emitting element according to claim 10, wherein the acceleration electrode is exposed to the outside of the deep ultraviolet light emitting element.   The deep ultraviolet light-emitting element according to claim 10 or 11, wherein a pulse voltage is sequentially applied in the order of the discharge electrode, the pulling electrode, and the acceleration electrode. The deep ultraviolet light emitting element according to claim 12, wherein each pulse voltage applied to the pulling electrode and the accelerating electrode is started to be applied after a predetermined time has elapsed from the end of the application of the immediately preceding pulse voltage.