JP2013004530A - Light emitting element and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element that emits light with high efficiency and is suitably designed to be thin.SOLUTION: A light emitting element 1 comprises an ultraviolet light radiation portion 15 and a phosphor layer 21. An ultraviolet light emission layer 11 formed of a semiconductor material containing ZnO as a base material and added with Ga and P and a p-type semiconductor layer 12 containing ZnO as a base material are subjected to pn-junction, and a first electrode 13 is connected to the ultraviolet light emission layer 11 while a second electrode 14 is connected to the p-type semiconductor layer 12. A voltage is applied between the first electrode 13 and the second electrode, whereby ultraviolet light having a peak wavelength of 400 nm or less is emitted from the ultraviolet light emission layer 11. The phosphor layer 21 absorbs ultraviolet light emitted from the ultraviolet light radiation portion 15 and converts the ultraviolet light to visible light. The visible light is transmitted through a substrate 22 and emitted to the outside.

Description

  The present invention relates to a semiconductor light emitting element and an image display device including the semiconductor light emitting element.

A light-emitting element using a semiconductor is used in a lamp, an image display device, and the like, and it is required to realize a light-emitting element that is light and thin and can efficiently emit visible light.
In addition, an image display apparatus is required that has a large screen size, is light and thin, and can display images with excellent image quality. It is quite difficult to satisfy all these requirements sufficiently, but development is progressing with the aim of realizing a new image display device.

For example, Patent Document 1 describes a surface conduction electron-emitting device (SED), which is a kind of field emission device (field emission device FED), as a next-generation lightweight and thin display device.
The SED disclosed in Patent Document 1 includes a first substrate and a second substrate that are arranged to face each other at a predetermined interval, and these substrates are vacuum-bonded by bonding peripheral portions to each other via rectangular side walls. An envelope is configured, and phosphor layers of three colors are formed on the inner surface of the first substrate, and a large number of electron-emitting devices are arranged on the inner surface of the second substrate as electron emission sources that excite the phosphor. ing. A plurality of spacers are disposed between the two substrates in order to support the atmospheric pressure load acting between the first substrate and the second substrate and maintain a gap between the substrates.

In addition, a plurality of electron beam passage holes through which the electron beams emitted from the electron-emitting devices pass are formed in the substrate.
It is considered that such an FED can realize an increase in size and definition of the image display device.

JP 2006-93036 A

However, the FED is a mechanism that emits electrons into a vacuum by field emission and collides with a phosphor to emit light, and therefore, in manufacturing, a vacuum envelope is provided and the process of evacuating the inside is required. It becomes. Also, the materials used in the vacuum envelope are limited in order to maintain a constant state within the vacuum envelope.
Therefore, it is also desired that the image display device be increased in size and definition without using a vacuum envelope.

  The present invention has been made in view of the above problems, and has an object to provide a light-emitting element that is lightweight, thin, and has excellent light emission efficiency. Further, in an image display device, a high-quality and large-screen image display device is realized. For the purpose.

  In order to achieve the above object, a light emitting device according to the present invention includes an ultraviolet light emitter made of an ultraviolet light emitting semiconductor material, and a first electrode and a second electrode electrically connected to the ultraviolet light emitter. The phosphor is disposed in the ultraviolet light emitting portion where the ultraviolet light emitter emits ultraviolet light by applying a voltage between the first electrode and the second electrode, and in the ultraviolet light emitting region from the ultraviolet light emitting portion. Thus, a phosphor part that converts the wavelength of ultraviolet light emitted from the ultraviolet light emitting part and emits it is provided.

Here, “ultraviolet light” refers to electromagnetic waves having a peak wavelength in the spectrum of 400 nm or less.
The ultraviolet emitter is preferably formed of a semiconductor material based on zinc oxide.
Specifically, the ultraviolet light emitter is formed by stacking an ultraviolet light emitting layer made of an n-type semiconductor based on zinc oxide and a p-type semiconductor layer based on zinc oxide, and the first electrode is a p-type. The second electrode is preferably connected to the ultraviolet light emitting layer side on the semiconductor layer side.

Here, the ultraviolet light emitting layer is preferably formed of a material in which an additive containing an element selected from aluminum, gallium, and indium and an additive containing phosphorus are added to a zinc compound.
An image display device can be configured by arranging a plurality of the light emitting elements on a substrate.
In order to achieve the above object, an image display device according to the present invention includes a plurality of first electrodes extending in a stripe shape on a substrate, and a three-dimensional structure extending in a stripe shape with respect to the first electrode. A plurality of second electrodes arranged in an intersecting manner are provided, and an ultraviolet light emitting layer formed by molding an ultraviolet light emitting semiconductor material is interposed at each location where the first electrode and the second electrode intersect three-dimensionally, By arranging a phosphor layer for the phosphor and applying a voltage between the first electrode and the second electrode, the ultraviolet emitter emits ultraviolet light, and the corresponding phosphor layer emits ultraviolet light. An image is displayed by emitting after wavelength conversion.

A light-emitting panel can be formed by providing one or more light-emitting elements on a substrate.
The light emitting element package can be formed by sealing the light emitting element with a sealing body.

According to the light emitting device of the present invention, when a voltage is applied between the first electrode and the second electrode in the ultraviolet light emitting portion, ultraviolet light having a peak wavelength of 400 nm or less is emitted from the ultraviolet light emitter. And in a fluorescent substance part, the ultraviolet light radiated | emitted from the ultraviolet light emission part is wavelength-converted into visible light etc. with a fluorescent substance, and is radiated | emitted. Visible light refers to electromagnetic waves having a wavelength of 400 nm to 780 nm.
Here, since the ultraviolet light emitter is formed by molding a semiconductor material that emits ultraviolet light, a vacuum envelope is not required, and a light-weight and thin light-emitting element can be realized.

Further, the emission color can be changed by changing the type of phosphor used in the phosphor portion.
In addition, a light-weight and thin image display device can be realized by arranging a plurality of the light-emitting elements on a substrate.
Further, the image display device includes a plurality of first electrodes extending in a stripe shape on a substrate, and a plurality of second electrodes extending in a stripe shape and three-dimensionally intersecting the first electrode, An ultraviolet light-emitting layer formed by molding an ultraviolet light-emitting semiconductor material is interposed at each location where the second electrode is three-dimensionally crossed, and a phosphor layer is disposed for each ultraviolet light-emitting body. By applying a voltage between the electrodes, the ultraviolet emitter emits ultraviolet light, and by configuring the image to be displayed by converting the wavelength of the ultraviolet light emitted by the corresponding phosphor layer, A lightweight and thin image display device can be realized.

By providing one or more light emitting elements on the substrate, a light and thin light emitting panel can be realized.
Further, a light emitting element package can be realized by sealing the light emitting element with a resin body.
In the light-emitting element, the ultraviolet light emitter can be satisfactorily realized by being formed of a semiconductor material based on zinc oxide. Specifically, the ultraviolet light emitter is formed by stacking an ultraviolet light emitting layer made of an n-type semiconductor based on zinc oxide and a p-type semiconductor layer based on zinc oxide, and the first electrode is a p-type. By connecting the second electrode to the ultraviolet light emitting layer side on the semiconductor layer side, it is possible to realize an ultraviolet light emitter having good ultraviolet light emitting characteristics.
Here, the ultraviolet light emitting layer is formed of a material in which an additive containing an element selected from aluminum, gallium, and indium and an additive containing phosphorus are added to a zinc compound, thereby improving ultraviolet light emission characteristics. Can do.

It is a figure which shows typically schematic structure of the image display apparatus concerning embodiment. FIG. 3 is a diagram showing energy levels of the ultraviolet light emitting layer 11 and the p type semiconductor layer 12 in an element in which the ultraviolet light emitting layer 11 and a p-type semiconductor layer 12 made of Zn1-xNixO are heterojunctioned. It is a figure which shows one form of the method of forming a p-type semiconductor layer in an ultraviolet light emitter. 1 is a plan view schematically showing main parts of an image display device 2 according to Example 1. FIG. 2 is a view showing a cross section of the image display device 2. FIG. FIG. 6 is a diagram illustrating an appearance and a structure of a flat light-emitting panel 3 according to Example 2. 6 is a schematic cross-sectional view showing the structure of a bullet-type light emitting element 4 according to Example 3. FIG. It is a figure which shows the result of having measured the spectrum of PL light emission about the zinc oxide which has not added the additive, and ZnO which added Ga and P with respect to Zn.

[Basic structure of light emitting element]
The basic configuration and effect of the light emitting element 1 will be described.
FIG. 1 is a cross-sectional view illustrating a schematic configuration of the light-emitting element 1.
An ultraviolet light emitting layer 11 formed by molding an n-type semiconductor material based on ZnO on a substrate 10 and a p-type semiconductor layer 12 formed immediately above the ultraviolet light emitting layer 11 are provided. A first electrode 13 and a second electrode 14 are provided so as to sandwich the p-type semiconductor layer 12 to form an ultraviolet light emitting portion 15, and a driving voltage is applied between the first electrode 13 and the second electrode 14. Thus, ultraviolet light is emitted from the ultraviolet light emitting layer 11. This ultraviolet light is an electromagnetic wave having a peak wavelength in the spectrum of 400 nm or less.

The first electrode 13 is made of, for example, Al, and the second electrode is made of, for example, ITO. An electron injection layer may be provided between the ultraviolet light emitting layer 11 and the first electrode 13.
In the light emitting element 1, a phosphor layer 21 is formed adjacent to the ultraviolet light emitting portion 15, and the phosphor layer 21 is covered with a transparent substrate 22.
The phosphor layer 21 receives the ultraviolet light from the ultraviolet light emitting section 15 and changes to visible light and emits it. The emitted visible light passes through the substrate 22 and is emitted to the outside.

[Material of ultraviolet light emitting layer 11]
For the ultraviolet light emitting layer 11, an n-type ultraviolet light emitting material based on ZnO is used. This material will be described.
As a result of adding various compound powders to normal ZnO powders alone or in combination and heat-treating them under various conditions and evaluating their emission characteristics, by adding specific elements in combination to ZnO, no addition It has been found that the ultraviolet emission characteristics are remarkably improved as compared with the ZnO powder. Based on the knowledge, the material of the ultraviolet emission layer 11 is based on zinc oxide, and the first additive is aluminum, gallium, indium. One or more types and the addition of phosphorus as the second additive were used.

The first additive suppresses green light emission in zinc oxide and improves ultraviolet light emission to some extent. Moreover, a 1st additive reduces the electrical resistivity of zinc oxide. This is considered to be because a donor level is formed in the forbidden band directly under the conductor by replacing the divalent zinc site of zinc oxide with trivalent aluminum, gallium, and indium.
Therefore, aluminum, gallium, and indium, which are the first additives, need to be replaced with zinc in zinc oxide, and an effect of improving ultraviolet light emission characteristics is not recognized with a simple mixture.

Zinc oxide thus substituted is suitable for a light-emitting element because its electrical resistivity is one to several orders of magnitude lower than that of ordinary zinc oxide.
Among these three types of elements, gallium is most easily substituted for zinc, and aluminum and indium are hardly substituted. In this respect, gallium is desirable because the effect of improving the characteristics is most apparent. On the other hand, aluminum is the cheapest in terms of cost, and gallium and indium are rare and expensive compared to aluminum. Therefore, aluminum is most desirable in terms of cost. Compared to gallium and aluminum, there are few advantages of using indium.

Even if the first additive is added alone, the effect of improving the ultraviolet emission luminance is small. However, in addition to the first additive, phosphorous, which is the second additive, is added to dramatically increase the ultraviolet emission. Brightness is improved.
The mechanism for improving the luminance of light emission due to the addition of phosphorus is not clear, but the addition of phosphorus alone has little effect on improving the luminance, and the addition of phosphorus promotes the substitution of aluminum, gallium, and indium to Zn sites. As a result, aluminum, gallium, and indium prevent electrical neutral breakdown caused by substituting Zn sites for phosphorus by substituting the oxygen sites of ZnO as phosphorus anions. It is considered that the substitution of gallium and indium is promoted to improve the ultraviolet emission luminance.

The first additive and the second additive are additives that improve the ultraviolet emission luminance of zinc oxide, and the main component is zinc oxide (zinc and oxygen). That is, zinc is 80% or more in the cation, oxygen is 80% or more in the anion, and more preferably 90% or more.
The total amount of aluminum, gallium and indium as the first additive is 0.03 at% or more and 3.0 at% or less with respect to zinc. However, this is because no further improvement in luminance is recognized, which is a waste. However, even if the total amount is less than 0.03 at% or more than 3 at%, the luminance improvement effect can be obtained.

The reason why the amount of phosphorus added to zinc is preferably 0.03 at% or more and 3.0 at% or less is also the same. From the above consideration, it is considered that the amount of phosphorus added is preferably the same as the total amount of aluminum, gallium, and indium.
In addition to the first additive and the second additive described above, tungsten may be used in combination as a third additive. By using tungsten together, green light emission is suppressed and the light emission luminance in the ultraviolet region is further improved. However, the mechanism for improving the luminance by adding tungsten oxide is not clear at present.

  Tungsten oxide is also known as an additive that has the effect of improving the luminance of green light emission and preventing the deterioration of luminance even in a ZnO: Zn phosphor that emits green light. It is considered to prevent the zinc surface from being contaminated by carbon dioxide gas or moisture, which is completely opposite to the effect of the present embodiment that suppresses green light emission and improves ultraviolet light emission.

In addition, as a result of the study by the present inventors, when firing in nitrogen containing no carbon dioxide gas or moisture, no improvement in luminance was observed even when tungsten was added. However, it shows that the green light emission of ZnO: Zn is improved by preventing contamination with carbon dioxide gas or moisture.
According to the results examined by the present inventors, it is considered that the presence of tungsten oxide expresses an action effect when synthesizing the ultraviolet light emitting phosphor.

One of the effects of tungsten oxide during the synthesis is that the tungsten is a metal having a high hexavalent value and a high valence, and the valence is likely to fluctuate, and at the same time the diffusion rate is high. It is thought that it works as.
In addition, as an effect, when an alkali metal oxide such as lithium oxide, sodium oxide, or potassium oxide is present during synthesis, the alkali metal oxide is substituted and dissolved in zinc oxide to suppress the ultraviolet emission. However, since tungsten oxide has a high diffusion rate and easily forms a compound with an alkali metal oxide, it is considered that there is an action to prevent the alkali metal oxide from being substituted and dissolved in zinc oxide.

Thus, the effect of adding tungsten is different from the effect of adding aluminum, gallium, indium, and phosphorus. In order to obtain this effect, tungsten does not need to be dissolved in zinc oxide, and in fact, there is no evidence of solid solution.
It is preferable that the amount of tungsten added to zinc is 0.01 at% or more and 1.0 at% or less. If less than 0.01 at%, the effect of improving the luminance of ultraviolet light emission is not remarkable, and if it exceeds 1.0 at%, ultraviolet light is emitted. This is because the luminance starts to decrease. The decrease in luminance is considered to be because tungsten is easily concentrated on the surface.

The ultraviolet light-emitting material may contain zinc oxide and the above-described two or three kinds of additives, but may contain other components within the range not impairing the characteristics.
For example, magnesium oxide dissolves in a small amount in zinc oxide and has the effect of increasing its band gap (that is, shifting the emission wavelength to the short wavelength side), but this zinc oxide-magnesium oxide solid solution system is also effective. By using the above-mentioned two or three kinds of additives, there is an effect of suppressing the green light emission and improving the ultraviolet light emission intensity. In this case, the amount of cation as the main component is the total amount of zinc and magnesium.

FIG. 8 is a diagram showing the results of measuring PL emission spectra for A (ZnO added with Ga and P by 1.0 at% each with respect to Zn) and B (ZnO with no additive added). .
As shown in the figure, A (ZnO doped with Ga and P) has a strong emission peak in the vicinity of 380 nm. On the other hand, B (undoped ZnO) has a large emission peak in the vicinity of 500 nm.

Thus, it can be seen that ZnO doped with Ga and P efficiently emits ultraviolet light having an emission peak at 400 nm or less.
[Method for synthesizing ultraviolet light emitting material, method for forming ultraviolet light emitting layer 11]
The starting materials for synthesizing the ultraviolet light emitting material are a zinc compound, a compound of an element selected from aluminum, gallium, and indium as a first additive, and a phosphorus compound as a second additive.

As for the zinc compound, zinc oxide ZnO, zinc hydroxide Zn (OH) ₂ , zinc carbonate ZnCO ₃ or the like may be used, and generally ZnO may be used.
As for the compound of the first additive (one or more of aluminum, gallium, and indium), oxides, hydroxides, carbonates and the like may be used as starting materials, respectively, and generally oxides may be used.

As for the compound of the second additive (phosphorus), an oxide can be used as a starting material. However, a general phosphorus oxide P ₂ O ₅ is highly hygroscopic and reacts violently with moisture. Phosphorates such as diammonium hydrogen phosphate and ammonium dihydrogen phosphate may be used. When these ammonium salts are heated, ammonia and water are released at a low temperature to become P ₂ O ₅ , so that the same effect as using P ₂ O ₅ directly can be obtained.

Even if phosphorus oxide or salt is used, the phosphorus oxide itself is sublimable, and if heated to react with ZnO, it may sublime before reaction, and the desired material composition is obtained. In order to prevent this, in order to prevent this, a method in which phosphorus is added excessively more than the necessary amount, or zinc phosphate, which is a compound of phosphorus and zinc in advance, may be synthesized and used.
More desirably, a compound containing both the first additive and the second additive is preferably used. Specific examples thereof include aluminum phosphide AlP, gallium phosphide GaP, and indium phosphide InP.

However, since these phosphorus compounds are generally expensive and may react with moisture to generate highly toxic hydrogen phosphide, more preferable compounds include aluminum phosphate, gallium phosphate, and indium phosphate. Is mentioned.
Thus, when the compound containing the 1st additive and the 2nd additive is used, a brightness improvement will become remarkable even with a comparatively small amount of additives. This is presumably because the evaporation of phosphorus is suppressed and the presence of phosphorus in the nearest vicinity of aluminum, gallium, and indium promotes the solid solution in ZnO.

As a form of synthesizing an ultraviolet luminescent material from the above starting material and forming a film, there are a solid phase method, a liquid phase method, and a gas phase method.
In the solid phase method, a raw material powder (metal oxide, metal carbonate, etc.) containing each metal is mixed, and the mixture is subjected to a heat treatment at a temperature of a certain level or more to react, whereby an ultraviolet light emitting material based on ZnO is obtained. obtain. Then, the ultraviolet light emitting layer 11 is formed by dispersing this material in a solvent and applying the dispersion onto the second electrode 14.

In the liquid phase method, a solution containing each metal is made, and a solid phase is precipitated from this solution. Then, the ultraviolet light emitting layer 11 is formed by applying the obtained solid phase onto the first electrode 13.
Alternatively, the ultraviolet light emitting layer 11 is formed by a method in which a solution containing each metal is applied and then dried and subjected to a heat treatment or the like at a temperature of a certain level to obtain a solid phase.
In the vapor phase method, the mixture of the raw material powders is formed into a thin film on the second electrode 14 by a method such as vapor deposition, sputtering, or CVD.

Any of the above methods may be used. However, when the ultraviolet light emitting layer 11 is formed of a material in a powder form, the use of the solid phase method is relatively inexpensive and easy to manufacture in large quantities. Suitable for.
When an ultraviolet light emitting material is synthesized by a solid phase method, a mixture of raw materials is reacted by heat treatment. Also, even when synthesized by a liquid phase method or a gas phase method, it is often better to perform heat treatment in order to improve the crystallinity and further improve the ultraviolet emission luminance.

At this time, if the heat treatment is performed in an atmosphere containing a large amount of oxygen, the ultraviolet emission intensity is difficult to improve, so that the neutrality of nitrogen gas, argon gas, helium gas, etc. is not present in an oxidizing atmosphere containing a large amount of oxygen. It is desirable to perform heat treatment in an atmosphere.
Usually, heat treatment may be performed in an inexpensive nitrogen gas. The concentration of oxygen contained in the nitrogen gas is preferably 100 ppm or less, and more preferably 10 ppm or less.

As another method for synthesizing the ultraviolet light emitting material, there is a method of producing ZnO particles to which Ga and P are added by injecting Ga and P into the ZnO particles.
And the ultraviolet light emitting layer 11 can also be formed by apply | coating the particle | grains of the ultraviolet light emitting material manufactured by this method on the 1st electrode 13. FIG.
Furthermore, as another method of forming the ultraviolet light emitting layer 11, a thin film of ZnO is formed on the first electrode 13, and Ga and P are injected into the ZnO film, thereby forming an ultraviolet made of ZnO to which Ga and P are added. There is also a method of forming the light emitting layer 11.

[Material of p-type semiconductor layer 12]
The p-type semiconductor layer 12 is formed of a p-type semiconductor material composed of Zn, M, and O (M is an element having 3d electrons in the outermost shell and having a higher energy level of 3d orbitals than 4s orbitals. Specifically, they are Ni and Cu).
Since this p-type semiconductor material is excellent in film formability at a low temperature, a low-resistance thin film can be formed on a substrate or an n-type semiconductor layer even at a relatively low temperature of 500 ° C. or lower.

Then, by stacking the p-type semiconductor material on the ZnO layer, an element in which the p-type semiconductor material layer and the n-type ZnO layer are heterojunction can be formed. A light emitting element can be formed.
In order to form a thin film of p-type semiconductor material, a mixed material of ZnO and MO may be sputtered on a substrate or a ZnO layer as a sputtering target.

Note that since this thin film formation is likely to be n-type when performed in a reducing atmosphere, it is preferable to form a p-type semiconductor film in an oxidizing atmosphere.
The material having the above composition has the property of a p-type semiconductor because an element having 3d electrons in the outermost shell and having a higher energy level in the 3d orbit than the 4s orbital is mixed with ZnO so that a hole is formed in the 4s orbital. It is thought that this is easy to form.

The p-type semiconductor material has a composition of Zn _1-x M _x O (where M is an element having 3d electrons in the outermost shell and having a higher energy level in the 3d orbital than the 4s orbital, 0 <x <1). Is preferred. Zn _1-x M _x O is an oxide in which ZnO and MO are mixed, and x is the ratio of the number of moles of M to the total number of moles of Zn and M.
The p-type semiconductor material may be in an amorphous state, but is desirably a crystalline compound in order to obtain excellent characteristics.

In the case of a crystalline compound, it may be a mixed crystal in which Zn in the ZnO crystal is partially replaced with M, or a mixed crystal in which M in the MO crystal is partially replaced with Zn, or the ZnO crystal and the MO crystal are mixed. It may be a crystal mixture.
As specific examples of the material for forming the p-type semiconductor layer 12, (1) Zn1-xNixO and (2) Zn1-xCuxO will be described below.

(1) Zn _1-x Ni _x O is an oxide in which ZnO and NiO are mixed, and x is the ratio of the number of moles of Ni to the total number of moles of Zn and Ni.
Zn _1-x Ni _x O can also be referred to as a compound in which Zn in ZnO is partially replaced with Ni, or a compound in which Ni in NiO is partially replaced with Zn.
The crystal form of Zn _1-x Ni _x O may be a mixed form in which a ZnO crystal (Wurtz type) and a NiO crystal (NaCl type) are mixed, a mixed crystal having a ZnO crystal structure, or A mixed crystal having a crystal structure of NiO may be used.

The Zn _1-x Ni _x O-based material is a p-type semiconductor capable of forming a thin film at a low temperature, and can form an excellent heterojunction on the ZnO layer.
FIG. 2 shows energy levels of the ultraviolet light emitting layer 11 and the p type semiconductor layer 12 in an element in which a p-type semiconductor layer 12 made of Zn _1-x Ni _x O and an ultraviolet light emitting layer 11 made of n-type ZnO are heterojunctioned. FIG.

The energy level of the valence band top of the p-type semiconductor layer 12 is higher than the valence band top of the ultraviolet light emitting layer 11 (the valence band top is offset). Here, as the value of x in Zn _1-x Ni _x O constituting the p-type semiconductor layer 12 is increased, this offset amount is also increased.
When this offset amount increases, the hole injection efficiency and the reverse bias withstand voltage in the pn junction element decrease. Therefore, the value of x is set to 0.65 or less, and the offset amount of the valence band top is within 1 eV. It is preferable to suppress it, and it is preferable that the value of x is small.

On the other hand, considering that the electric conduction type is p-type and electric resistance is kept low, the value of X in Zn1-XNi _x O is preferably 0.13 or more.
(2) Zn _1-x CuxO is an oxide in which ZnO and CuO are mixed, and x is the ratio of the number of moles of Cu to the total number of moles of Zn and Cu.
Zn _1-x Cu _x O can also be said to be a compound in which Zn in ZnO is partially replaced by Cu.

The crystal form of Zn _1-x Cu _x O may be a mixed form in which a ZnO crystal and a CuO crystal are mixed, a mixed crystal having a ZnO crystal structure, or a mixed crystal having a CuO crystal structure. It may be a crystal.
The Zn _1-x Cu _x O material is a p-type semiconductor capable of forming a thin film at a low temperature, and can form an excellent heterojunction on the ZnO layer.

In the Zn _1-x Cu _x O material, as the value of x increases, the offset amount of the valence band top with respect to ZnO increases, and when a ZnO layer and a pn junction element are formed, the hole injection efficiency and the reverse bias withstand voltage are reduced. descend. In addition, the Zn _1-x Cu _x O material has a narrower band gap as the value of x increases.
Therefore, it is preferable to set the value of x to 0.10 or less from the viewpoint of maintaining these in good condition, and to suppress the offset amount of the valence band top with respect to ZnO within 1 eV, and it is preferable that the value of x is small.

On the other hand, considering that the electric conduction type is p-type and the electric resistance is reduced, the value of X in Zn _1-x Cu _x O is preferably 0.05 or more.
The material of the p-type semiconductor layer 12 is preferably formed of a ZnO-based p-type semiconductor material, but is a p-type semiconductor material such as GaN having a valence band top offset amount of 1 eV or less. It doesn't matter.

In addition, even in a light-emitting element in which a p-type semiconductor material such as NiO having an offset amount at the top of the valence band of 1 eV or more and an n-type semiconductor material based on ZnO are formed, the hole injection efficiency and the light emission efficiency are reduced. However, light emission can be confirmed.
[Method of forming p-type semiconductor layer 12]
As described above, after the ultraviolet light emitting layer 11 is formed by applying particles or forming a thin film, the p-type semiconductor layer 12 is laminated on the ultraviolet light emitting layer 11. A method for forming the p-type semiconductor layer 12 is also available. There are a method of forming a thin film of a p-type semiconductor material by a method such as sputtering, and a method of applying and drying a liquid in which a p-type semiconductor material is dispersed in a solvent.

In addition, as described below, there is a method of forming the p-type semiconductor layer 12 by ion implantation.
3A and 3B are views for explaining a method of forming the p-type semiconductor layer 12 by ion implantation.
As shown in FIG. 3A, a first electrode 13 is formed on a substrate 10, and an ultraviolet light emitting material (ZnO containing aluminum, gallium, and indium as a first additive is formed on the first electrode 13. The ultraviolet light emitting material layer 11a is formed by applying particles of a compound and a phosphorus compound as the second additive). Alternatively, the ultraviolet light emitting material layer 11a is formed by forming a thin film of an ultraviolet light emitting material.

Then, M (Ni or Cu) is ion-implanted into the surface portion of the formed ultraviolet light emitting material layer 11a as shown in FIG. As a result, as shown in FIG. 3B, a part of Z of ZnO in the surface portion of the ultraviolet light emitting material layer 11a is partially replaced with M, and the p-type semiconductor layer 12 is formed.
In the formed p-type semiconductor layer 12, aluminum, gallium, and indium as the first additive and phosphorus as the second additive are added to Zn _1-x M _x O.

Moreover, the area | region except the surface part into which M was inject | poured among the ultraviolet light emitting material layers 11a becomes the ultraviolet light emitting layer 11.
When the ultraviolet light emitting material layer 11a is formed by a method of applying particles of the ultraviolet light emitting material, the p-type semiconductor layer 12 is also formed in a form in which the particles are aggregated, and the ultraviolet light emitting material layer 11a is formed by a thin film forming method. In this case, the p-type semiconductor layer 12 is also formed in a thin film form.

Then, by forming the second electrode 14 or the like on the p-type semiconductor layer 12, the light emitting element 1 can be manufactured.
[Effects of Light-Emitting Element 1]
The light emitting element 1 has an ultraviolet light emitting portion 15 having a structure in which a p-type semiconductor layer 12 is pn heterojunctioned to an ultraviolet light emitting layer 11 based on ZnO, and can emit light in the ultraviolet region with high efficiency. .

In particular, the ultraviolet light emitting layer 11 is formed of a material obtained by adding a first additive (one or more types of aluminum, gallium, and indium) and a second additive (phosphorus) to ZnO, and the p-type semiconductor layer 1212 is made of ZnO. By forming the base p-type semiconductor material, ultraviolet light can be emitted with high efficiency.
Since this ultraviolet light is converted into visible light by the phosphor layer, visible light of a wide range of colors can be emitted depending on the type of phosphor layer used.

Further, by suppressing the offset amount of the valence band top of the p-type semiconductor layer 12 with respect to the valence band top of the ultraviolet light emitting layer 11 within 1 eV, the driving voltage is kept low, and the hole injection efficiency and the light emission efficiency are kept good. The breakdown voltage against the bias can also be improved.
In addition, each layer included in the light-emitting element 1 can be formed at a low temperature of 500 ° C. or lower, and thus a glass substrate can be used as the substrate 10. Therefore, the light-emitting element 1 is suitable for a large-area element.

[Form in which p-type semiconductor layer is formed on the surface of each ZnO particle]
As shown in FIG. 1, the p-type semiconductor layer 12 is preferably formed by being laminated on the ultraviolet light emitting layer 11. However, the p type semiconductor layer 12 surrounds the surface of each ZnO particle constituting the ultraviolet light emitting layer 11. A form in which a semiconductor layer is formed is also conceivable.
That is, as shown in FIG. 3C, a particle powder made of an ultraviolet light emitting material based on ZnO is prepared, and a p-type semiconductor layer 12a is formed on the surface of each ultraviolet light emitting particle 11c. As a method of forming the p-type semiconductor layer 12a, a thin film is formed on the surface of each ultraviolet light emitting particle 11c by sputtering a powder bulk based on ZnO with a p-type semiconductor material Zn _1-x M _x O. Alternatively, the p-type semiconductor layer 12a may be formed on the surface of each ultraviolet light emitting particle 11c by a method of ion-implanting M (Ni or Cu) into the powder bulk.

Then, the ultraviolet light-emitting particles 11c having the p-type semiconductor layer 12a formed on the surface are coated on the first electrode 13, so that the ultraviolet light-emitting particles with the p-type semiconductor layer 12a are applied as shown in FIG. An ultraviolet light emitting layer 16 made of 11c is formed.
By forming the second electrode 14 or the like on the ultraviolet light emitting layer 16, the light emitting element 1 can be manufactured.

A hole transport layer may be provided between the ultraviolet light-emitting layer 11, the p-type semiconductor layer 12, and the first electrode 13, and an electron transport layer may be provided between the ultraviolet light-emitting layer 11 and the second electrode.
Also when providing a hole transport layer and an electron transport layer, these layers may be composed of fine particles (powder) or may be formed.
Instead of forming the p-type semiconductor layer 12 on the ultraviolet light emitting layer 11, the periphery of the particles made of the ultraviolet light emitting material is coated with Zn _1-x M _x O, and the coated particles are coated with the second electrode 14. By coating on and sintering, an ultraviolet light emitting layer formed of particles made of an ultraviolet light emitting material coated with Zn _1-x M _x O can be obtained.

[Modification in which the ultraviolet light emitting layer 11 also serves as a substrate]
In the light-emitting element 1 shown in FIG. 1, ZnO particles (a first additive added with aluminum, gallium, indium, and a second additive phosphorus) as a material of the ultraviolet light-emitting layer 11 are formed in a substrate shape. If molded, the ultraviolet light emitting layer 11 also serves as a substrate, so that the substrate 10 can be omitted.

For example, the ZnO particles containing the first additive and the second additive are pressed and then sintered to form a plate shape.
The ultraviolet light emitting portion 15 may be formed by forming the first electrode 13 on the back surface of the substrate-like ultraviolet light emitting layer 11 thus fabricated and forming the p-type semiconductor layer 12 and the second electrode 14 on the upper surface. it can.

Embodiment 1 in which the light emitting element 1 is applied to an image display device, Embodiment 2 in which the light emitting element 1 is applied to a flat light emitting panel, and Embodiment 3 in which the light emitting element package is applied are introduced below.
[Example 1] Image display device Configuration of image display device 2:
FIG. 4 is a plan view schematically showing the main part of the image display device 2 according to the first embodiment, in which the phosphor layer is omitted.

FIG. 5 is a view showing a cross section of the image display device 2.
The image display device 2 is provided with a second electrode 34 extending in a horizontal direction on a substrate 30 in a stripe shape, and a stripe-shaped first electrode 33 extending in a direction perpendicular to the second electrode 34. An ultraviolet light emitting layer 31 and a p-type semiconductor layer 32 are interposed in the gap.
In this way, the ultraviolet light emitting portion 35 including the ultraviolet light emitting layer 31, the p-type semiconductor layer 32, the first electrode 33, and the second electrode 34 is arranged on the substrate 30 in a matrix.

Similarly to the ultraviolet light emitting layer 11, the ultraviolet light emitting layer 31 is formed of a semiconductor material based on ZnO, in which one or more kinds of aluminum, gallium, and indium are added as the first additive and phosphorus is added as the second additive. Form.
The p-type semiconductor layer 32 is formed by forming a p-type semiconductor material based on ZnO in the same manner as the p-type semiconductor layer 12.

In addition, a second electrode 14 laminated on the p-type semiconductor layer 12 and a first electrode 13 laminated on the ultraviolet light emitting layer 11 are provided. The first electrode 33 is formed, for example, by forming a film of Al by a vacuum process, and the second electrode 34 is formed, for example, by forming a film of ITO by a vacuum process.
Then, by applying a driving voltage between the first electrode 13 and the second electrode 14, the ultraviolet light emitting layer 11 emits ultraviolet light having a wavelength of 400 nm or less.

As shown in FIG. 5, a phosphor layer 41 that covers the ultraviolet light emitting portion 35 is provided.
The phosphor layer 41 is provided with any of a plurality of types of phosphors (for example, three types of blue, green, and red).
That is, a phosphor that emits red light, a phosphor that emits green light, or a phosphor that emits blue light is sequentially arranged for each column of ultraviolet light emitting elements arranged in a matrix.

Examples of each color phosphor include the following.
Blue BaMgA ₁₁ O ₁₇ : Eu ²⁺
Green BaO.6Al ₂ O ₃ : Mn
Red (Y, Gd) BO ₃ : Eu
A set of three ultraviolet light emitting layers 31 and three color phosphor layers constitutes a pixel as a basic unit of an image.

The substrate 30 is formed of a non-conductive material, for example, a hard material such as synthetic quartz glass or transparent plastic. What is necessary is just to set the magnitude | size, thickness, shape, etc. of the board | substrate 30 according to the objective of an image display apparatus.
The cover substrate 42 is formed of a light-transmitting material and covers each phosphor layer 41. The cover substrate 42 is provided with partition walls 42a for partitioning adjacent phosphor layers 41, and the periphery of each phosphor layer 41 is surrounded by the partition walls 42a.

Driving method of the image display device 2:
A drive unit (not shown) is connected to the first electrode 33 and the second electrode 34 of the image display device 2, and when the image display device 2 is driven, the drive unit performs the second operation based on the input image data. Matrix driving is performed by selectively applying a positive voltage to the plurality of first electrodes 33 while sequentially applying a negative voltage to the electrodes 34.

Accordingly, in the image display device 2, ultraviolet light is radiated from the ultraviolet light emitting layer 31 of each pixel and converted into visible light by the phosphor layer 41 based on the image data, and visible light of each color is emitted. Is done. In this way, in the image display device 2, image display is performed by emitting light of each color in each pixel.
Method for manufacturing image display device 2:
A first electrode 33 is formed on the substrate 30, and an ultraviolet light emitting portion 35 is formed thereon by sequentially forming an ultraviolet light emitting layer 31, a p-type semiconductor layer 32, and a second electrode 34.

A phosphor layer 41 is formed so as to cover each ultraviolet light emitting portion 35.
The phosphor layer 41 can be formed by applying a paste of each color phosphor on each ultraviolet emitting portion 35 by a screen printing method, an ink jet method or the like and drying.
By covering and bonding the cover substrate 42 over the phosphor layer 41, the image display device 2 is completed.

In the above manufacturing method, the phosphor layer 41 is formed on the ultraviolet light emitting portions 35 by the method of applying the phosphor paste and the cover substrate 42 is covered, but the phosphor paste is applied to the back surface of the cover substrate 42. The phosphor layer 41 is formed by the method described above, and the image display device 2 can be manufactured by the method of covering the phosphor layer 41 on the ultraviolet light emitting portion 35 on the substrate 30.
Effects of the image display device 2:
According to the image display device 2, since the ultraviolet light emitter is formed of the ultraviolet light emitting semiconductor material in each pixel, an envelope is not required, and a large screen, light weight, and thin image display device can be realized.

Further, since the ultraviolet light emitting portion 35 is formed by laminating a layer made of an n-type semiconductor based on ZnO and a p-type semiconductor layer based on ZnO, the ultraviolet light emission characteristics are good, Good image display can be realized.
Example 2 Flat Light Emitting Panel FIGS. 6A and 6B are views showing the appearance and structure of a flat light emitting panel 3 according to Example 2. FIG.

  In the flat light emitting panel 3, a metal electrode 53 made of Al or the like, an ultraviolet light emitting layer 51, a p-type semiconductor layer 52, and a transparent electrode 54 made of ITO or the like are sequentially laminated on a substrate 50 made of glass or resin. A radiation portion 55 is formed, and a transparent sealing cover 56 that covers the ultraviolet light radiation portion 55 is provided. A phosphor layer 57 is disposed on the inner surface of the sealing cover 56.

Similar to the ultraviolet light emitting layer 11, the ultraviolet light emitting layer 51 is formed by forming a semiconductor material based on ZnO and adding one or more kinds of aluminum, gallium, and indium as the first additive and phosphorus as the second additive. Similarly to the p-type semiconductor layer 12, the p-type semiconductor layer 52 is formed by depositing a p-type semiconductor material based on ZnO.
The sealing cover 56 covers the transparent electrode 54, the ultraviolet light emitting layer 51, the p-type semiconductor layer 52, and the metal electrode 53, and seals them. Conductive lead layers 58 and 59 extending outward from the metal electrode 53 and the transparent electrode 54 are formed on the outer peripheral portion of the sealing cover 56, and transparent to the metal electrode 53 from the outside via the conductive lead layers 58 and 59. Electric power can be supplied between the electrodes 54. The conductive lead layers 58 and 59 can be formed on the surface of the sealing cover 56 by plating or evaporating a metal material.

The phosphor layer 57 is a layer formed by applying a phosphor to the inner surface of the sealing cover 56 and receives ultraviolet light emitted from the ultraviolet light emitting layer 51 to emit visible light of various emission colors. .
As a phosphor forming the phosphor layer 57, a mixture of a red phosphor, a green phosphor, and a blue phosphor may be used to emit white light, or a monochromatic phosphor may be used. May be.

In order to reinforce the flat light-emitting panel 3, a resin or metal frame may be provided on the periphery or the back side of the substrate 50.
Operation and effect of the flat panel 3:
In the flat light emitting panel 3, when a voltage is applied between the conductive lead layer 58 and the conductive lead layer 59 from a lighting circuit (not shown), ultraviolet light is radiated from the ultraviolet light radiating unit 55 and becomes visible light by the phosphor layer 57. Converted and emitted.

According to the flat light emitting panel 3, since the ultraviolet light emitting portion 55 is formed of an ultraviolet light emitting semiconductor material, a light and thin flat light emitting panel can be realized.
Further, in the ultraviolet light emitting portion 55, an ultraviolet light emitting layer 51 made of an n-type semiconductor based on ZnO and a p-type semiconductor layer 52 based on ZnO are laminated, so that the ultraviolet light emitting characteristics are good. In addition, it is possible to realize a light emitting panel with good characteristics.

Variations of the flat panel 3:
In the flat light emitting panel 3, one light emitting element is formed on one substrate, but a plurality of light emitting elements may be arranged in a matrix on one substrate.
In that case, the same color may be emitted using a common phosphor in a plurality of light emitting elements, but different colors may be emitted in each light emitting element. For example, each light emitting element may emit red light, green light, or blue light to emit white light as a whole.

In the case of providing a plurality of light emitting elements, the plurality of elements can be connected in series with each other, and the lighting circuit unit can collectively turn on the plurality of light emitting elements to light them.
[Example 3] Light emitting device package
A bullet-type light emitting element will be described as an example of the light emitting element package.
FIG. 7 is a schematic cross-sectional view illustrating the structure of a bullet-type light emitting element 4 according to the third embodiment.

As shown in FIG. 7, the bullet-type light emitting element 4 includes lead wires 61 and 62, and a reflection cup portion 61 a is formed on the top of the lead wire 61.
And the ultraviolet light radiation | emission part 60 is mounted | worn in the recessed part of this reflective cup part 61a.
The ultraviolet light emitting portion 65 is an LED chip having the same structure as the ultraviolet light emitting portion 15 described above, and is configured by sandwiching an ultraviolet light emitting layer based on ZnO and a p-type semiconductor layer between a pair of electrodes. ing.

One electrode of the ultraviolet light radiation portion 65 is electrically connected to the reflection cup portion 61 a by the bonding wire 63, and the other electrode is electrically connected to the lead wire 62 by the bonding wire 64.
A sealing portion 66 is formed in the concave portion of the reflection cup portion 61a by being filled with a transparent resin in which a phosphor is dispersed. The sealing portion 66 entirely covers the periphery of the ultraviolet light emitting portion 65.

Further, a sealing portion 67 is provided so as to cover the upper part of the reflection cup portion 61 a, the sealing portion 66, and the lead wire 62. The sealing portion 67 is made of a transparent resin molded into a bullet shape, and has a lens shape at the tip.
As the sealing body for forming the sealing portions 66 and 67, a silicone resin is preferable, but a resin such as a polycarbonate resin and an epoxy resin or a transparent material such as glass may be used. It is preferable to use the same kind of resin for the sealing portions 66 and 67 in terms of ease of manufacture and adhesiveness.

Effects of the bullet-type light emitting element 4:
When a voltage is applied between the lead wires 61 and 62, ultraviolet light is radiated from the ultraviolet light radiating unit 60, converted into visible light by the phosphor layer 57, and radiated out of the bullet-type light emitting element 4.
According to this bullet-type light emitting element 4, the ultraviolet light emitting portion 65 is configured by laminating a layer made of an n-type semiconductor based on ZnO and a p-type semiconductor layer based on ZnO. The ultraviolet light emission characteristics are good, and the light emission characteristics of the bullet-type light emitting element 4 are also good.

  As described above, the light-emitting element according to the present invention can be used for an image display device, a flat light-emitting panel, a bullet-type light-emitting element, and the like. In particular, when applied to an image display device, a device that can display an image with a light weight, a large screen, a thin shape, and a high quality image can be realized.

DESCRIPTION OF SYMBOLS 1 Light emitting element 2 Image display apparatus 3 Flat light emission panel 4 Bullet-type light emitting element 10 Substrate 11 Ultraviolet light emitting layer 11a Ultraviolet light emitting material layer 11c Ultraviolet light emitting particle 12 P-type semiconductor layer 13 First electrode 14 Second electrode 15 Ultraviolet light emission part 30 Substrate 31 Ultraviolet light emitting layer 32 P-type semiconductor layer 33 First electrode 34 Second electrode 35 Ultraviolet light emitting portion 41 Phosphor layer 42 Cover substrate 42a Partition 50 Substrate 51 Ultraviolet light emitting layer 52 P-type semiconductor layer 53 Metal electrode 54 Transparent electrode 55 Ultraviolet light radiation part 56 Sealing cover 57 Phosphor layer 60 Ultraviolet light radiation part 61, 62 Lead wire 61a Reflection cup part 65 Ultraviolet light radiation part 66, 67 Sealing part

Claims (8)

An ultraviolet light emitter made of an ultraviolet light-emitting semiconductor material, a first electrode and a second electrode electrically connected to the ultraviolet light emitter, and a voltage between the first electrode and the second electrode An ultraviolet light emitting part that emits ultraviolet light by applying an ultraviolet light,
A light emitting device comprising: a phosphor disposed in a radiation region from the ultraviolet light emitting portion, and a phosphor portion that radiates ultraviolet light emitted from the ultraviolet light emitting portion by converting the wavelength. The ultraviolet emitter is
A p-type semiconductor layer and an ultraviolet light-emitting layer made of an n-type semiconductor material based on zinc oxide are stacked,
The light emitting device according to claim 1, wherein the first electrode is connected to the p-type semiconductor layer side, and the second electrode is connected to the n-type semiconductor layer side.   The light emitting device according to claim 2, wherein the ultraviolet light emitting layer is formed of a material in which an additive containing an element selected from aluminum, gallium, and indium and an additive containing phosphorus are added to an oxide compound. The p-type semiconductor layer is
The light emitting device according to claim 2, wherein the light emitting device is formed of a p-type semiconductor material based on zinc oxide.   An image display device in which a plurality of the light emitting elements according to claim 1 are arranged on a substrate. A plurality of first electrodes arranged in a striped manner on a substrate; and a plurality of second electrodes arranged in a three-dimensional crossing with respect to the first electrodes and arranged in a striped shape;
An ultraviolet light-emitting layer formed by molding an ultraviolet light-emitting semiconductor material is interposed at each location where the first electrode and the second electrode intersect three-dimensionally, and a phosphor layer is disposed for each ultraviolet light emitter.
By applying a voltage between the first electrode and the second electrode, the ultraviolet emitter emits ultraviolet light, and the corresponding phosphor layer displays the image by converting the wavelength of the ultraviolet light and emitting it. An image display device.   A light-emitting panel comprising one or more light-emitting elements according to claim 1 provided on a substrate.   The light emitting element package by which the light emitting element in any one of Claims 1-4 is sealed with the sealing body.

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