JP2008222760A - Semiconductor fluorescent substance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particulate semiconductor fluorescent substance having not only excellent heat resistance but also electroconductivity, and including nitride particles in good crystallinity, having a quantum well structure and/or a p-n junction. <P>SOLUTION: The particulate semiconductor fluorescent substance is obtained by forming a semiconductor crystal having the p-n junction on the surface of a base material particle. The semiconductor crystal may have a structure having a double hetero junction or a structure having a quantum well structure. The base material particle is preferably a single crystal particle, and more preferably a tabular Al<SB>2</SB>O<SB>3</SB>particle. The semiconductor crystal may be obtained by growing a crystal on the single crystal particle without through a buffer layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a particulate semiconductor phosphor.

  For example, the phosphor constitutes a visible light excitation light emitting element such as a white LED in combination with an LED emitting blue light, or constitutes a near ultraviolet light to blue violet light excitation light emitting element in combination with an LED emitting near ultraviolet to blue violet light. It is used for In addition, UV-excited light-emitting elements such as liquid crystal backlights and fluorescent lamps, vacuum ultraviolet-excited light-emitting elements such as plasma display panels and rare gas lamps, electron-beam-excited light-emitting elements such as cathode ray tubes and FEDs (Field Emission Display), and X-rays It is widely used in combination with various light emitting elements such as an X-ray excited light emitting element such as an imaging device and an electric field excited light emitting element such as an inorganic EL display.

  As described above, when a phosphor is used in combination with another element, the phosphor requires various characteristics depending on the element to be combined, for example, a light emitting element. For example, when combined with a white LED, it is used at a temperature close to 100 ° C. or higher, so that thermal stability and chemical stability are also required. In the case of a combination with FED, it is required to have conductivity in order to prevent charging. An example of a phosphor that can satisfy such various requirements is a nitride phosphor.

Since nitride phosphors are excellent in thermal stability and are conductive, they have been expected to be applied to light emitting devices in which it is difficult to use oxide phosphors or sulfide phosphors. However, in general, synthesis of a nitride phosphor requires high temperature and pressure and requires a special apparatus, which increases costs. In particular, since GaN-based phosphors have a high nitrogen partial pressure at high temperatures and are easily decomposed, it has been difficult to obtain good-quality phosphors. In addition, when a GaN thin film is grown on a sapphire substrate by using chemical vapor deposition, a high-quality phosphor film can be obtained, but the luminance is not good because light is not efficiently extracted from the film. It was enough. Patent Document 1 proposes a method in which a GaN thin film is grown on fine particles by chemical vapor deposition and used as a powder phosphor.
JP-A-11-279550

  The technique proposed in Patent Document 1 is intended to form a fluorescent material on the surface of AlN particles using a CVD method. Therefore, even if the particle diameters of the AlN particles are made uniform, the obtained phosphor has a problem that the luminous efficiency is low and the luminance is inevitably insufficient. Furthermore, this proposed technique is to form a conventional phosphor material on the surface of AlN particles, and to improve the light emission efficiency of a heterostructure and / or a quantum well structure. So far, phosphors contained inside and / or phosphors having a pn junction have not been developed.

  An object of the present invention is to provide a particulate semiconductor light emitter capable of solving the above-mentioned problems in the prior art.

  Another object of the present invention is to provide a particulate semiconductor light-emitting body excellent in luminous efficiency.

  It is another object of the present invention to provide a particulate semiconductor fluorescent material that includes nitride particles having excellent crystallinity having excellent thermal stability and conductivity and also having a quantum well structure and / or a pn junction. To provide a body.

  The inventors of the present invention have focused on improving the crystallinity of a fluorescent material in order to obtain a phosphor having excellent light emission characteristics by forming a nitride-based fluorescent material to be a phosphor on the surface of the particle. The present invention has been made based on the knowledge obtained as a result of extensive research to improve the structure of the phosphor.

  According to the first aspect of the present invention, there is proposed a semiconductor phosphor formed by forming a semiconductor crystal on the surface of a substrate particle, wherein the semiconductor crystal has a heterojunction.

  According to the invention of claim 2, there is proposed a semiconductor phosphor formed by forming a semiconductor crystal on the surface of a substrate particle, wherein the semiconductor crystal has a pn junction.

  According to the invention of claim 3, there is proposed a semiconductor phosphor formed by forming a semiconductor crystal on the surface of a base particle, wherein the semiconductor crystal has a double heterojunction. .

  According to the invention of claim 4, there is proposed a semiconductor phosphor formed by forming a semiconductor crystal on the surface of a base particle, wherein the semiconductor crystal has a quantum well structure.

  According to the invention of claim 5, in the invention of claim 1, 2, 3 or 4, the base particle is a single crystal particle, and the semiconductor crystal is grown on the single crystal particle. A semiconductor phosphor is proposed.

According to the invention of claim 6, in the invention of claim 5, there is proposed a semiconductor phosphor in which the single crystal particles are Al ₂ O ₃ and the semiconductor crystal is a group 3-5 nitride compound semiconductor. The

  According to a seventh aspect of the present invention, there is provided a semiconductor phosphor according to the fifth or sixth aspect, wherein the semiconductor crystal is formed by crystal growth on the single crystal particles without a low-temperature buffer layer. Is done.

  Since the semiconductor phosphor according to the present invention is excellent in thermal stability, it is useful for white LEDs. Further, since the semiconductor phosphor according to the present invention is conductive, it can be used effectively for FED. Furthermore, since the semiconductor phosphor according to the present invention has a good crystallinity and has a quantum well structure and / or a pn junction, it emits light with high luminance and is extremely useful industrially.

  Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the drawings.

In one embodiment of the semiconductor phosphor according to the present invention, a nitride compound semiconductor in the form of a group 3-5 nitride compound semiconductor crystal is formed on the surface of Al ₂ O ₃ particles prepared as base particles. ) Is formed as a whole and is a particulate semiconductor phosphor. The fluorescent layer includes either a heterojunction, a pn junction or a quantum well layer, or a heterojunction, and a plurality or all of a pn junction and a quantum well layer. The formation of the fluorescent layer using a Group 3-5 nitride compound semiconductor crystal is an example, and the present invention is not limited to this. For example, instead of the group 3-5 nitride compound semiconductor crystal, arsenide, phosphide, or a mixed crystal of these group 5 elements can be manufactured in the same manner.

  As the layer structure of the fluorescent layer, for example, a conventional layer structure for a hetero structure, a pn junction structure, or a quantum well structure employed in a conventional compound semiconductor light emitting device can be used as it is.

The crystallinity of the fluorescent layer, that is, the crystallinity of the Group 3-5 nitride compound semiconductor crystal provided on the surface of the Al ₂ O ₃ particles prepared as the base particles is improved. Necessary for good fluorescence properties. If the crystallinity is poor, the luminous efficiency as a phosphor is poor, and it is not possible to obtain fluorescence with sufficient luminance.

The fluorescent layer is formed by growing a Group 3-5 nitride compound semiconductor crystal on the surface of Al ₂ O ₃ particles. That is, a method of growing a high-quality crystal by a method such as HVPE (Hydride Vapor Phase Epitaxy), MOVPE (Metal Organic Vapor Phase Epitaxy), MBE (Molecular Beam Epitaxy), or the like.

In the present embodiment, the Al ₂ O ₃ particles have a hexagonal crystal structure, and crystallinity is improved by growing a group 3-5 nitride compound semiconductor crystal on the C plane. This is preferable for obtaining a Group 3-5 nitride compound semiconductor crystal. A low temperature buffer layer may be formed in advance on the surface of the Al ₂ O ₃ particles, and a required group 3-5 nitride compound semiconductor crystal may be grown on the low temperature buffer layer, but the low temperature buffer layer is formed. Without limitation, a group 3-5 nitride compound semiconductor crystal may be directly formed on the surface of the Al ₂ O ₃ particles.

As described above, when Al ₂ O ₃ particles are used, it is easy to make the particle size uniform so that the particle size falls within a certain range, and the Al ₂ O ₃ particles may have a hexagonal crystal structure. Therefore, the fluorescent layer can be formed on the surface of the Al ₂ O ₃ particles with extremely high crystallinity. As a result, the luminous efficiency of the obtained semiconductor phosphor is greatly improved as compared to conventional particulate and powder phosphors. In the case of the prior art using AlN particles, AlN particles are prepared by pulverization. However, since the crystallized orientation of the pulverized AlN particles is random, a GaN thin film is crystallized on the surface of the AlN particles. It is extremely difficult to grow well. As a result, the obtained phosphor is inefficient and inevitably has insufficient luminance.

  Further, since the fluorescent layer includes a heterojunction and / or a pn junction and / or a quantum well structure, light emission due to recombination of electrons and holes can be expected by applying an electric field from the outside. As a result, the luminance is further improved.

In the description of the above embodiment, an example in which Al ₂ O ₃ particles are used as base particles has been described, and the advantage of using Al ₂ O ₃ particles has also been described. However, a fluorescent layer is formed below. The substrate particles that are the substrates to be described will be described in more detail.

  When forming the light emitting layer as described above on the base particle by the vapor phase growth method, for example, a sapphire substrate is prepared in advance, and a large number of base particles are arranged on the sapphire substrate. After forming the fluorescent layer on the surface, the semiconductor phosphor can be obtained by separating the base particles on which the fluorescent layer is formed from the sapphire substrate.

Therefore, in order to separate the semiconductor phosphor from the substrate, it is desirable that no phosphor layer is formed on the substrate. An example of a substrate on which the fluorescent layer is not formed is an inexpensive quartz substrate, but a substrate in which a SiO ₂ thin film is formed on a sapphire substrate or the like may be used.

The substrate particles used to form the fluorescent layer must be able to withstand the process. That is, as a condition for forming the nitride phosphor, a high temperature close to 1000 ° C. and a reducing atmosphere such as NH ₃ are required. Further, the phosphor needs to be selectively formed on the particles. Examples of the material for the base material particles that satisfy these conditions include Al ₂ O ₃ , Si, SiC, AlN, MgAl ₂ O ₄ , LiTaO _3, etc., preferably Al ₂ O ₃ , Si, and SiC, and more preferably Al ₂ O ₃ and α-alumina is particularly preferred. The shape of the substrate particles is not particularly limited, but is preferably a plate shape.

α-Alumina is sold by Sumitomo Chemical Co., Ltd. under the trade name “Sumicorundum” (diameter: 200 nm to 18 μm). In addition, α-alumina fine particles having diameters of 30 nm, 50 nm, 70 nm, and 100 nm are available as developed products. These fine particles are single crystals, and those having a uniform particle size can be obtained. In general, a group 3-5 nitride compound semiconductor can obtain a single crystal by epitaxial growth after forming a low-temperature buffer layer on a single crystal sapphire substrate, but a crystal lattice with sapphire (α-Al ₂ O ₃ ). Many defects occur due to misfit. On the other hand, high-quality crystals can be obtained without using a low-temperature buffer layer by using α-alumina having a diameter of about 30 nm to 100 nm as a substrate.

  It is important that the substrate particles used in the present invention have a specific crystal structure from the viewpoint of easy formation of the fluorescent layer and that the growth direction is appropriately selected. The crystal structure is preferably hexagonal. In addition, it is desired that the base particles are uniformly distributed without overlapping on a predetermined substrate.

  As a method for forming a fluorescent layer (phosphor) on the surface of the base particle, metal organic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), pulsed laser lamination method (PLD). However, the MOCVD method and the MBE method are preferable.

Next, an embodiment of a method for producing a semiconductor phosphor according to the present invention will be described. First, a quartz substrate is prepared, and base material particles are arranged on the quartz substrate. Examples of the arrangement of the base material particles on the quartz substrate include a method in which the base material particles, which are fine particles, are made into a slurry form with ultrapure water or the like and applied onto the quartz substrate with a spin coater or the like. By such a method, the base particles that are fine particles are arranged on the quartz substrate without overlapping. Moreover, you may carry out by the method of immersing a quartz substrate in the slurry containing a base particle and a medium, or the method of apply | coating or spraying on a slurry quartz substrate. Instead of the quartz substrate, a sapphire substrate or the like on which a SiO ₂ thin film is formed by vapor deposition may be used.

As the substrate particles, Al ₂ O ₃ particles are preferable. More preferably, the Al ₂ O ₃ particles are plate-shaped. In the case of Al ₂ O ₃ particles, any shape can be placed on the quartz substrate with a relatively flat surface by applying the slurry onto the quartz substrate. The medium to be used is water, methanol, ethanol, isopropanol, n-butanol, ethylene glycol, dimethylacetamide, methyl ethyl ketone, methyl isobutyl ketone or the like, preferably water. After drying, the base particles such as Al ₂ O ₃ are fixed to the quartz substrate by intermolecular force.

For example, a MOVPE apparatus is used for the epitaxial growth of a Group 3-5 nitride compound semiconductor crystal for forming a fluorescent layer on the surface of the base particle. For epitaxial growth of a Group 3-5 nitride compound semiconductor crystal, Al ₂ O ₃ particles having a hexagonal crystal structure are preferred as the base particles. The reason is as described above.

An embodiment of epitaxial crystal growth when manufacturing a Group 3-5 compound semiconductor microcrystal including a multiple quantum well layer as a fluorescent layer will be described. First, Al ₂ O ₃ particles are arranged as base particles on a quartz substrate or a substrate such as sapphire deposited with SiO ₂ , and n-type GaN is formed on the surface of the base particles without a buffer layer. A well structure is formed to obtain a semiconductor phosphor.

When manufacturing a group 3-5 compound semiconductor microcrystal including a pn junction as the fluorescent layer, a p-type AlGaN layer and a p-type GaN layer are formed on the phosphor having the multiple quantum well structure laminated as described above. The phosphor fine particles are laminated and have a pn junction. At this time, a tunnel injection layer (thin film n-type layer) may be laminated. In this process, Al ₂ O ₃ single crystal fine particles having a particle diameter of 10 nm or more and 100 nm or less can be used.

  The raw material for the above-described epitaxial crystal growth will be described. As the Group 2 source gas, an organic metal compound of one or more elements selected from the group consisting of Mg, Ca, Sr, Ba, and Zn is mixed and used. Examples of the organometallic group include a dimethyl group, a diethyl group, a biscyclopentadienyl group, a bismethylcyclopentadienyl group, and a bisethylcyclopentadienyl group.

As the gallium source gas, aluminum source gas, and indium source gas, trialkylates or trihydrides in which an alkyl group having 1 to 3 carbon atoms or hydrogen is bonded to each metal atom are usually used. For example, trimethylgallium ((CH ₃ ) ₃ Ga), triethylgallium ((C ₂ H ₅ ) ₃ Ga), or the like can be used as a raw material for Ga.

  As the nitrogen raw material, ammonia is usually used, and examples thereof include hydrazine, methyl hydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, t-butylamine, and ethylenediamine. These can be used alone or in any combination. Among these raw materials, ammonia and hydrazine are preferable because they do not contain carbon atoms in their molecules and thus cause less carbon contamination in the semiconductor.

  As the growth atmosphere gas and the carrier gas for the organometallic raw material, gases such as nitrogen, hydrogen, argon, and helium can be used alone or in combination. In an atmosphere of hydrogen gas or helium gas, pre-decomposition of the raw material is suppressed, which is more preferable.

FIG. 1 shows an outline of an example of a vapor growth semiconductor manufacturing apparatus used for manufacturing a semiconductor phosphor according to the present invention by the MOVPE method. The vapor phase growth semiconductor manufacturing apparatus includes a reaction furnace 2 in which a source gas is supplied through a source supply line 1 from a source supply apparatus (not shown). A susceptor 4 for heating the substrate 3 is provided in the reaction furnace 2. The susceptor 4 is a polygonal column, and a plurality of substrates 3 are attached to the surface thereof. In this case, base material particles (not shown) are uniformly applied on the SiO ₂ layer (not shown) on each surface of the substrate 3 as described above.

  The susceptor 4 has a structure that can be rotated by a rotating device 5. An infrared lamp 6 for heating the susceptor 4 is provided inside the susceptor 4. The substrate 3 can be heated to a desired growth temperature by supplying a heating current from the heating power source 7 to the infrared lamp 6. By this heating, the raw material gas supplied to the reaction furnace 2 through the raw material supply line 1 is thermally decomposed on the substrate 3, and the surface of base material particles (not shown) applied on the substrate 3, preferably only on a predetermined surface. A fluorescent layer is formed by vapor growth of a desired compound. Of the raw material gas supplied to the reaction furnace 2, unreacted raw material gas is discharged from the exhaust port 8 to the outside of the reactor and sent to the exhaust gas treatment device.

Since the fluorescent layer thus grown and formed on the surface of the base material particle on the substrate 3 is placed on the SiO ₂ layer on the surface of the substrate 3, the semiconductor phosphor together with the base material particle by an acid such as hydrofluoric acid. Can be peeled off. The semiconductor phosphor obtained by peeling can be used as it is for various light emitting devices. Further, the semiconductor phosphor may be laminated on the light emitting element by a technique such as laser ablation, magnetron sputtering, plasma CVD or the like without scraping off the substrate. As the layer structure of the fluorescent layer, for example, a conventional layer structure such as a heterojunction structure, a pn junction structure, a quantum well structure, or a double heterojunction structure, which is used as a light emitting layer in a conventional compound semiconductor light emitting device, is used as it is. be able to.

  The semiconductor phosphor of the present invention can be used alone. However, semiconductor phosphors according to the present invention can be prepared in various emission colors, and those having different emission colors can be combined and installed on the light emitting surface of the light emitting element to obtain light emitting devices of various emission colors. The emission color of the fluorescent layer can be adjusted by combining, for example, blue and yellow, red and green, and red, green and blue. In particular, a white light emitting device with high brightness can be manufactured by adjusting the amount of the semiconductor phosphor of each color so that the light of the mixed light emission color becomes white visually and installing it on the light emitting surface of the light emitting element. .

  Hereinafter, although an example and a comparative example explain the present invention still in detail, the present invention is not limited to the following example.

(Example 1)
Quartz was used as the substrate. On this quartz substrate, a plate-like particle of α-alumina (average particle size 70 nm) (developed by Sumitomo Chemical Co., Ltd.) made into a slurry with ultrapure water was applied by a spin coater. The quartz substrate coated with this water slurry was sandwiched between different sapphire substrates, and the latter sapphire substrate was slid to be removed. After drying, the quartz substrate was introduced into a vapor phase growth apparatus. The atmospheric pressure MOVPE method was used for the vapor phase growth on the α-alumina surface. As the growth method, a growth method without using a low-temperature growth buffer layer was used.

  The supply of TMG was temporarily stopped, the temperature was raised to 1090 ° C., and a 200 nm n-type GaN layer was grown on the surface (C-plane) of α-alumina using TMG, ammonia and silane as raw materials and hydrogen as a carrier gas. Thereafter, the supply of silane was stopped, and a 100 nm non-doped GaN layer was grown. After stopping the supply of TMG and silane and lowering the temperature to 785 ° C., a 100 nm GaN layer is grown using TEG and ammonia as raw materials and nitrogen as a carrier gas. Subsequently, carrier gases using TMG, TMI and ammonia as raw materials As shown below, a 3 nm InGaN layer and a 15 nm GaN layer were repeatedly grown 5 times under a pressure of 50 kPa using nitrogen. As a detailed growth procedure, ammonia, TEG, and TMI were supplied to grow an InGaN layer by 3 nm. Thereafter, the supply of TMI and TMG was stopped, only ammonia and carrier gas were supplied, and the growth was interrupted for 15 minutes. Subsequently, a non-doped GaN layer was grown to 15 nm.

  After repeating this procedure five times, TMG and ammonia were continuously supplied to grow a non-doped GaN layer by 3 nm, and the thickness of the non-doped GaN layer was finally 18 nm. However, slm and sccm are units of gas flow rate. 1 slm indicates that a gas having a weight occupying a volume of 1 liter in a standard state flows per minute, and 1000 sccm corresponds to 1 slm.

  In this manner, a group 3-5 nitride compound semiconductor crystal including a quantum well structure was formed as a fluorescent layer on the surface of α-alumina, thereby producing a semiconductor phosphor. In order to examine the emission characteristics of the obtained semiconductor phosphor, photoluminescence using a He—Cd laser (325 nm) as an excitation light source was measured at room temperature. The emission from the well layer was observed as a spectrum having a peak at 454 nm, and the peak intensity was 0.98 relative intensity. The light emission intensity was converted to a value in which the semiconductor phosphor covered the entire surface of the substrate.

(Example 2)
After laminating three layers of the multiple quantum well structure in the same procedure as in Example 1, the temperature was raised to 940 ° C., TMG, TMA, ammonia, and bisethylcyclopentadienylmagnesium as a p-type dopant raw material were supplied, and magnesium doping An AlGaN layer was grown to 30 nm. After stopping the supply of TMG, TMA and bisethylcyclopentadienylmagnesium, the temperature was raised to 1010 ° C., bisethylcyclopentadienylmagnesium was supplied as TMG, ammonia and p-type dopant raw material, and the p-type GaN layer was Grows 100 nm.

  In this way, a semiconductor phosphor in which three layers of a multiple quantum well structure were stacked was manufactured, and the emission characteristics of the obtained semiconductor phosphor were measured at room temperature using photoluminescence using a He-Cd laser (325 nm) as an excitation light source. . The emission from the well layer was observed as a spectrum having a peak at 498 nm, and the peak intensity was 1.44 relative intensity. The emission intensity was converted to a value in which the phosphor particles covered the entire surface of the substrate.

(Comparative Example 1)
A semiconductor phosphor was obtained in the same manner as in Example 1 except that only the sapphire substrate was used. This phosphor was evaluated by an excitation spectrum and an emission spectrum in the same manner as in Example 1.

(Comparative Example 2)
A semiconductor phosphor was obtained in the same manner as in Example 2 except that only the sapphire substrate was used. This phosphor was evaluated by an excitation spectrum and an emission spectrum in the same manner as in Example 2.

The emission wavelengths and relative intensities of the semiconductor phosphors obtained in Examples 1 and 2 and Comparative Examples 1 and 2 are summarized below.
Emission wavelength, nm Relative intensity Example 1 (phosphor 1) 455 0.98
Example 2 (phosphor 2) 498 1.44
Comparative Example 1 (phosphor 3) 476 0.57
Comparative Example 2 (phosphor 4) 488 0.47

The figure which shows the outline of an example of the vapor phase growth semiconductor manufacturing apparatus used in manufacturing the semiconductor fluorescent substance by this invention.

Explanation of symbols

1 Raw material supply line 2 Reactor 3 Substrate 4 Susceptor 5 Rotating device 6 Infrared lamp 7 Power supply for heating 8 Exhaust port

Claims (7)

  A semiconductor phosphor formed by forming a semiconductor crystal on the surface of a substrate particle, wherein the semiconductor crystal has a heterojunction.   A semiconductor phosphor formed by forming a semiconductor crystal on the surface of a substrate particle, wherein the semiconductor crystal has a pn junction.   A semiconductor phosphor formed by forming a semiconductor crystal on the surface of a substrate particle, wherein the semiconductor crystal has a double heterojunction.   A semiconductor phosphor formed by forming a semiconductor crystal on the surface of a substrate particle, wherein the semiconductor crystal has a quantum well structure.   5. The semiconductor phosphor according to claim 1, wherein the base particle is a single crystal particle, and the semiconductor crystal is grown on the single crystal particle. The semiconductor phosphor according to claim 5, wherein the single crystal particles are Al ₂ O ₃ , and the semiconductor crystal is a group 3-5 nitride compound semiconductor.   The semiconductor phosphor according to claim 5 or 6, wherein the semiconductor crystal is formed by crystal growth on the single crystal particle without a low-temperature buffer layer.

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