WO2022181432A1 - Rare-earth-doped nitride semiconductor element and manufacturing method therefor, semiconductor led, and semiconductor laser - Google Patents

Rare-earth-doped nitride semiconductor element and manufacturing method therefor, semiconductor led, and semiconductor laser Download PDF

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WO2022181432A1
WO2022181432A1 PCT/JP2022/006333 JP2022006333W WO2022181432A1 WO 2022181432 A1 WO2022181432 A1 WO 2022181432A1 JP 2022006333 W JP2022006333 W JP 2022006333W WO 2022181432 A1 WO2022181432 A1 WO 2022181432A1
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rare earth
earth element
nitride semiconductor
semiconductor device
added
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French (fr)
Japanese (ja)
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康文 藤原
修平 市川
敦志 竹尾
潤 舘林
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国立大学法人大阪大学
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/20—Deposition of semiconductor materials on a substrate, e.g. epitaxial growth solid phase epitaxy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/20—Deposition of semiconductor materials on a substrate, e.g. epitaxial growth solid phase epitaxy
    • H01L21/2003—Deposition of semiconductor materials on a substrate, e.g. epitaxial growth solid phase epitaxy characterised by the substrate
    • H01L21/2015—Deposition of semiconductor materials on a substrate, e.g. epitaxial growth solid phase epitaxy characterised by the substrate the substrate being of crystalline semiconductor material, e.g. lattice adaptation, heteroepitaxy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/26—Materials of the light emitting region
    • H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
    • H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
    • H01S5/323—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser

Definitions

  • the present invention relates to a rare earth-added nitride semiconductor device, a method for manufacturing the same, and a semiconductor LED and a semiconductor laser using the rare earth-added nitride semiconductor device.
  • the In composition is increased to further increase the emission wavelength. Consideration is being given to increasing the wavelength.
  • the deterioration of crystallinity due to the high In composition and the decrease in luminous efficiency due to the piezoelectric field effect are serious problems.
  • the present inventor found that by applying a rare earth element-doped nitride semiconductor thin film to an optical device, it is possible to realize a wavelength stable light source associated with the 4f intra-shell transition of a rare earth element.
  • a red-light emitting semiconductor device in which an Eu-doped GaN layer controlled at the atomic level is formed as an active layer using a chemical vapor deposition method (Patent Document 1).
  • the emission intensity is still about 1.3 mW in the case of a red light emitting semiconductor device, and semiconductor LEDs, semiconductor lasers, etc. In order to put them into practical use, there is a demand for higher brightness and improved light emission characteristics.
  • an object of the present invention is to provide a technique for fabricating a rare earth element-added nitride element that uses a rare earth element-added nitride semiconductor layer as an active layer and has higher luminance and improved light emission characteristics than conventional ones.
  • a method for manufacturing a rare earth element-added nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more thereof comprising: Using an organometallic vapor phase epitaxial method, Under a temperature condition of 800 to 1000° C., GaN, InN, AlN, or a mixed crystal of any two or more of these is used as a matrix material on a non-polar substrate to replace Ga, In, or Al constituting the matrix material.
  • a rare earth element to form an active layer
  • the invention according to claim 2 2.
  • the invention according to claim 9, 9. The method for manufacturing a rare earth element-added nitride semiconductor device according to claim 1, wherein oxygen is added together with said rare earth element to form said active layer.
  • the invention according to claim 14 A rare earth element-added nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more of these as a base material, An active layer doped with a rare earth element is formed on a non-polar substrate so as to replace Ga, In or Al constituting the base material,
  • the rare earth element-added nitride semiconductor device is characterized in that the existence ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 is 0.10 or more.
  • the invention according to claim 16, 16 16.
  • a semiconductor LED comprising the rare earth element-added nitride semiconductor device according to any one of claims 14 to 17.
  • a semiconductor laser comprising the rare earth element-added nitride semiconductor device according to any one of claims 14 to 17.
  • the present invention it is possible to provide a technique for fabricating a rare-earth-element-added nitride element that uses a rare-earth-element-added nitride semiconductor layer as an active layer and has higher luminance and improved light-emitting characteristics than conventional ones.
  • FIG. 4 is a diagram showing the formation of multiple types of luminescent centers; It is a figure which shows the abundance ratio of each luminescent center.
  • FIG. 3 is a diagram explaining major luminescent centers in luminescence under indirect excitation. It is a figure explaining an emission line width. It is a figure explaining the fall of an optical gain. It is a figure explaining the symmetry of the atomic arrangement around a rare-earth ion.
  • FIG. 10 is a diagram for explaining how multiple types of luminescent centers that are depleted of impurities remain.
  • FIG. 4 is a diagram showing the emission intensity of OMVPE7 observed in Eu-doped GaN formed on AlN/AlGaN superlattice structure (SLs) layers with varying Al concentrations formed on the substrate c-plane. It is a figure explaining the crystal growth conditions in this invention. It is a figure explaining a polar surface and a non-polar surface.
  • 1 is a diagram showing the basic structure of an Eu-added nitride semiconductor device fabricated in an experimental example of the present invention
  • FIG. FIG. 10 is a diagram showing a growth sequence when fabricating an Eu-added nitride semiconductor device in an experimental example of the present invention
  • FIG. 2 is a diagram showing photoluminescence spectra of Eu-added nitride semiconductor devices obtained in one experimental example of the present invention and comparative experimental examples;
  • FIG. 4 is a diagram showing the relationship between wavelength and PL intensity in an Eu-doped nitride semiconductor device obtained in an experimental example of the present invention;
  • FIG. 5 is a graph showing the relationship between wavelength and PL intensity in the Eu-added nitride semiconductor device obtained in Comparative Experimental Example.
  • FIG. 17 is a diagram showing the relationship between emission intensity and excitation intensity based on FIGS. 15 and 16;
  • FIG. 4 shows CEES mapping obtained from one experimental example of the present invention;
  • FIG. 4 shows CEES mapping obtained from a comparative example;
  • FIG. 5 is a diagram showing the relationship between the Eu luminescence center and the concentration for an experimental example of the present invention and a comparative experimental example.
  • FIG. 10 is a diagram showing the relationship between emission energy and PL intensity for a comparative experimental example;
  • FIG. 5 is a diagram showing the relationship between emission energy and PL intensity in an experimental example of the present invention;
  • Rare earth elements which are a generic term for elements, generally have the common property of causing splitting in the 4f electron level due to spin-orbital interaction and crystal field effects, so they are not limited to Eu, but other rare earth elements Elements can be considered in the same way.
  • FIG. 1 is a diagram for explaining the emission mechanism in an Eu-doped nitride semiconductor device. As shown in FIG . 1 , Eu ions excited to the 5D0 state undergo a transition within the 4f shell to move to the ground state 7F2 state, thereby emitting light and emitting light.
  • this 4f intra-shell transition is a forbidden transition, it is necessary to reduce the symmetry of the peripheral local structure of Eu ions in the crystal field in order to increase the luminescence transition probability and obtain high luminescence intensity.
  • FIG. 2 is a diagram showing the formation of multiple types of luminescent centers, in which an Eu-doped nitride is grown on the c-plane, that is, the (0001) plane of the substrate by the organometallic vapor phase epitaxial method (OMVPE method).
  • OMVPE method organometallic vapor phase epitaxial method
  • OMVPE 1-8 there are at least eight types of luminescent centers (OMVPE 1-8) with different peripheral local structures.
  • the abundance ratio of each luminescent center is plotted as shown in FIG. 3.
  • OMVPE4 which cannot be said to have high energy transport efficiency, accounts for about 80% of the total, and is considered to have the highest energy transport efficiency.
  • OMVPE7 is present in only a few percent.
  • OMVPE4 and OMVPE7 are the main luminescence centers, as shown in FIG.
  • FIG. 6 is a diagram explaining this decrease in optical gain.
  • an increase in the emission line width means that there is a variation in the energy level. emission) does not occur.
  • stimulated emission occurs as indicated by circles in the figure, so that a sufficient optical gain can be obtained. That is, from FIG. 6, in order to sufficiently increase the optical gain, the emission line width is narrowed and sharpened by appropriately controlling the formation of the peripheral local structure so as not to cause a large distribution in the emission wavelength. i know i need it.
  • FIG. 7 is a diagram for explaining the symmetry of atomic arrangement around rare earth ions. In the case of a highly symmetrical arrangement as shown in FIG. 7A, the luminous efficiency is low, and the luminous efficiency increases as the symmetry decreases.
  • the doping concentration is limited to about 2.5% of the Eu concentration.
  • FIG. 9 shows OMVPE7 measured in an Eu-doped GaN layer formed on an AlN/AlGaN superlattice structure (SLs) layer formed on the c-plane of a substrate with varying Al concentrations. Emission intensity is shown.
  • (a) is a diagram showing the emission spectrum when the Al concentration (x) is changed
  • (b) is the in-plane compressive strain ( ⁇ ) and the PL integrated intensity (I OMVPE7 ), and the measurement was performed in an atmosphere at a temperature of 10K using a He—Cd laser as an excitation light source. From FIG.
  • peripheral local structure can be controlled to some extent only by crystal growth on the nonpolar plane of the substrate, it is still not sufficient. , it was found that a new study is required for the crystal growth conditions.
  • a rare earth element-added nitride semiconductor device can be manufactured.
  • OMVPE4 and OMVPE7 in the present invention Eu ions are excited using light having an excitation energy corresponding to the energy difference between the 5D0 level and 7F0 of trivalent Eu ions at a measurement temperature of 10 K or lower.
  • OMVPE4 is the Eu luminescence center that exhibits the strongest luminescence at an excitation energy of 2.1045 ⁇ 0.0003 eV, and the Eu emission exhibits the strongest luminescence at an excitation energy of 2.1070 ⁇ 0.0003 eV.
  • the center is OMVPE7.
  • the growth temperature described above is more preferably 850 to 950°C, more preferably 890 to 910°C.
  • the present invention it is possible to provide a rare earth element-added nitride semiconductor device with improved emission intensity and a sharpened emission line width, so that it is possible to realize a semiconductor LED that emits light with high brightness. becomes.
  • a high optical gain can be obtained by sharpening the emission line width, it is possible to greatly contribute to the development of semiconductor lasers.
  • the non-polar plane refers to a plane other than the (0001) plane (c-plane), specifically, the (10-12) plane (r-plane) and the (11-22) plane. , (20-21) plane, and nonpolar planes such as (10-10) plane (m-plane) and (11-20) plane (a-plane) (Fig. 11 ), but is not strictly limited to these planes, and there may be some deviation in the angle.
  • the specific inclination angle with respect to the (0001) plane (c plane) is preferably 3 to 90°, more preferably 30 to 90°, and even more preferably 60 to 90°.
  • the base material is not limited to GaN, and even so-called GaN-based nitrides such as InN, AlN, or mixed crystals thereof (InGaN, AlGaN, etc.) may have chemical properties equivalent to GaN. , so it can be used as a base material as well.
  • GaN-based nitrides such as InN, AlN, or mixed crystals thereof (InGaN, AlGaN, etc.) may have chemical properties equivalent to GaN. , so it can be used as a base material as well.
  • the rare earth element-added nitride semiconductor layer which is the active layer, is formed between the p-type layer and the n-type layer.
  • the formation of and the formation of the p-type layer and the n-type layer are performed in a series of formation steps, that is, each layer is sequentially formed in the reaction vessel in the order of the p-type layer, the active layer, and the n-type layer without taking out from the reaction vessel in the middle.
  • the n-type layer and the p-type layer do not necessarily have to be in contact with the active layer, and for example, a carrier block layer or the like may be provided between them.
  • the thickness of the active layer is preferably 0.1 nm or more.
  • the amount of the rare earth element such as Eu added in the active layer is preferably 0.001 to 10 at%, more preferably 0.01 to 10 at%, and 0.1 to 10 at%. More preferred.
  • the Eu raw material (Eu organic raw material) that supplies Eu is preferably an Eu compound that has a high vapor pressure and can be efficiently added, but Eu[C 5 (CH 3 ) 4 R] 2 (R: alkyl group) (bis(tetramethylmonoalkylcyclopentadienyl)europium) is more preferable, and among these, bis(normal-propyltetramethylcyclopentadienyl ) europium (EuCp pm 2 ) is preferred.
  • (bis(tetramethylmonoalkylcyclopentadienyl)europium) has a relatively low melting point (for example, EuCp pm 2 is 49° C.) and is a liquid at the operating temperature, so it can be stabilized by bubbling. can supply.
  • sapphire is usually used as the substrate on which the active layer is formed, it is not limited to this, and for example, Si, GaN, GaAs, etc. can also be used.
  • the present inventor conducted further experiments and studies, and found that when impurities are intentionally added during crystal growth, the emission intensity can be further improved and the emission line width can be further sharpened. .
  • the impurities to be added are preferably oxygen, magnesium, and aluminum.
  • rare earth elements By being added (co-doped) with rare earth elements, these elements are selectively placed in the vicinity of rare earth element ions to dramatically change the peripheral local structure, thereby reducing the types of luminescent centers formed. can be made
  • the specific addition concentration of oxygen is preferably 1 ⁇ 10 17 to 1 ⁇ 10 20 cm ⁇ 3 , more preferably 1 ⁇ 10 19 to 1 ⁇ 10 20 cm ⁇ 3 .
  • a specific amount of magnesium to be added is preferably 1 ⁇ 10 18 to 1 ⁇ 10 20 cm ⁇ 3 , more preferably 5 ⁇ 10 18 to 5 ⁇ 10 19 cm ⁇ 3 .
  • the specific amount of aluminum to be added is preferably more than 0 atomic % and not more than 40 atomic %, more preferably 15 to 35 atomic %.
  • FIG. 12 shows the basic structure of the Eu-added nitride semiconductor device fabricated in this experimental example.
  • a GaN template in which an undoped GaN buffer layer (20-21) plane (6 ⁇ m thick) was formed on the (22-43) plane of a sapphire substrate was used.
  • an Eu-doped nitride semiconductor is formed.
  • the Eu-added nitride semiconductor device shown in FIG. 12 was manufactured according to the growth sequence shown in FIG.
  • an undoped GaN layer (thickness: 1.8 ⁇ m) was grown on the undoped GaN buffer layer of the GaN template under a temperature condition of 1020° C. using the metal organic vapor phase epitaxy method (OMVPE method).
  • OMVPE method metal organic vapor phase epitaxy method
  • n-layer (not shown) (2500 nm thick) was formed on the undoped GaN layer.
  • an Eu-added GaN layer was grown at a growth rate of 1.0 ⁇ m/h under growth conditions of a temperature of 900° C. and a pressure of 100 kPa to form an active layer with a thickness of 400 nm.
  • an undoped GaN layer (20 nm thick) was laminated as a cap layer on the active layer.
  • TMGa trimethylgallium
  • Ammonia (NH 3 ) was used as the N raw material, and the supply amount was 4.0 slm.
  • EuCp pm 2 bubbled with a carrier gas hydrogen gas: H 2
  • the supply amount was 1.5 slm (supply temperature: 132.5° C.).
  • the supply temperature of the Eu raw material was kept at a sufficiently high temperature of 115 to 135°C by changing the piping valve of the OMVPE equipment from the normal specification (heat resistant temperature 80 to 100°C) to the high temperature special specification. to supply a sufficient amount of Eu to the reaction tube.
  • each layer was performed in a series of steps so that the growth was not interrupted without removing the sample from the reaction tube in the middle.
  • the vertical axis is the PL intensity (arbitrary unit, arb.units), and the horizontal axis is the wavelength (nm).
  • FIG. 15 shows an emission spectrum normalized by the peak intensity obtained by measuring the relationship between the wavelength and the PL intensity in the Eu-added nitride semiconductor device obtained in the experimental example at four levels of excitation intensity. is the PL intensity (arbitrary unit, arb.units), and the horizontal axis is the wavelength (nm).
  • FIG. 16 shows an emission spectrum obtained by similarly measuring the Eu-added nitride semiconductor device obtained in Comparative Experimental Example.
  • FIG. 17 is a diagram plotting the relationship between the emission intensity obtained by integrating the PL intensity of the emission spectra obtained in FIGS. 15 and 16 and the excitation intensity. units), and the horizontal axis is the excitation intensity (mW).
  • the emission intensity is significantly saturated under the strong excitation condition, whereas in the experimental example, the saturation of the emission intensity is remarkably suppressed even under the strong excitation condition.
  • the slope of the emission intensity is also more than twice as high, and by constructing a semiconductor LED using the rare earth element-added nitride semiconductor device according to the present invention, it is possible to provide a semiconductor LED with significantly improved performance. It was confirmed that it is possible.
  • the performance was greatly improved due to the characteristics essential for the development of the semiconductor laser, such as ultra-stability and narrow line width. It was confirmed that it is possible to provide a semiconductor laser.
  • FIG. 18 shows the CEES mapping obtained from the experimental example
  • FIG. 19 shows the CEES mapping obtained from the comparative experimental example.
  • 18 and 19 (a) is a diagram showing the relationship between emission energy (eV) and excitation energy (eV) measured using a dye laser (measurement temperature: 10 K). And (b) is a diagram showing the relationship between emission energy (eV), excitation energy (eV), and PL intensity (arbitrary unit, arb.units) measured using a dye laser (measurement temperature: 10 K). .
  • FIGS. the relationship between the concentration and the PL intensity of the emission center OMVPE4 and the emission center OMVPE7.
  • both OMVPE4 and OMVPE7 have higher PL intensities. It can be seen that the PL intensity is overwhelmingly higher when the Eu-doped GaN layer is formed on the (20-21) plane than when the Eu-doped GaN layer is formed on the (0001) plane.

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Abstract

The present invention provides a technology for producing a rare-earth-element-doped nitride element having higher brightness and better light-emitting characteristics compared to the prior art, in which a rare-earth-element-doped nitride semiconductor layer is an active layer.　A method for manufacturing a rare-earth-element-doped nitride semiconductor element in which, using GaN, InN, AlN, or a mixed crystal of two or more of these as a parent material, a rare earth element is added using organometallic vapor phase epitaxy to form an active layer on a non-polar substrate at a temperature of 800 to 1000°C so that the Ga, In or Al that constitutes the parent material will be replaced. A rare-earth-element-doped nitride semiconductor element in which GaN, InN, AlN or a mixed crystal of two or more of these is used as a parent material, wherein an active layer to which a rare earth element is added is formed on a non-polar substrate so that the Ga, In or Al that constitutes the parent material will be replaced.

Description

希土類添加窒化物半導体素子とその製造方法、半導体ＬＥＤ、半導体レーザーRare-earth-doped nitride semiconductor device and its manufacturing method, semiconductor LED, semiconductor laser
　本発明は、希土類添加窒化物半導体素子とその製造方法、および、前記希土類添加窒化物半導体素子を用いた半導体ＬＥＤ、半導体レーザーに関する。 The present invention relates to a rare earth-added nitride semiconductor device, a method for manufacturing the same, and a semiconductor LED and a semiconductor laser using the rare earth-added nitride semiconductor device.
　近年、窒化物半導体を用いた青色・緑色発光ダイオード（ＬＥＤ）と、赤色ＬＥＤとを組み合わせた大画面フルカラーＬＥＤディスプレイが至る箇所で見掛けられるが、窒化物半導体を用いた赤色ＬＥＤの開発に対する要求はますます強くなっている。 In recent years, large-screen full-color LED displays that combine blue and green light-emitting diodes (LEDs) using nitride semiconductors with red LEDs have been seen everywhere. It's getting stronger.
　その理由として、従来のＩｎｘＧａｙＡｌ１－ｘ－ｙＰ／ＧａＡｓ系の赤色ＬＥＤでは、デバイスとしての安定性に問題があることや、青色ＬＥＤや緑色ＬＥＤと同一の材料による光の三原色発光を揃えることにより、同一基板上での集積化が可能となり、小型で高精細なフルカラーＬＥＤディスプレイや、現在の白色ＬＥＤには含まれていない赤色領域の発光が加えられたＬＥＤ照明などの実現が期待されることなどが挙げられる。 The reason for this is that conventional In x Gay Al 1-x-y P /GaAs-based red LEDs have problems with device stability, and that the three primary colors of light are made from the same materials as blue and green LEDs. By aligning the light emission, it becomes possible to integrate them on the same substrate, realizing compact, high-definition full-color LED displays and LED lighting with the addition of light emission in the red region, which is not included in current white LEDs. is expected.
　この要求に応えるため、青色ＬＥＤや緑色ＬＥＤにおいて既に実用化されているＩｎｘＧａ１―ＸＮ／ＧａＮ多重量子井戸構造の発光層に基づき、Ｉｎ組成をより高くして、発光波長の更なる長波長化を図ることが検討されている。しかしながら、高Ｉｎ組成に起因する結晶性劣化やピエゾ電界効果による発光効率の低下が大きな問題となっている。 In order to meet this demand, based on the light-emitting layer of the In x Ga 1-x N/GaN multiple quantum well structure that has already been put into practical use in blue LEDs and green LEDs, the In composition is increased to further increase the emission wavelength. Consideration is being given to increasing the wavelength. However, the deterioration of crystallinity due to the high In composition and the decrease in luminous efficiency due to the piezoelectric field effect are serious problems.
　このような状況下、本発明者は、希土類添加窒化物半導体薄膜を光デバイスに応用することにより、希土類元素の４ｆ殻内遷移に伴う波長安定な光源が実現可能であることを見出し、世界に先駆けて、化学気相成長法を用いて原子レベルで制御されたＥｕ添加ＧａＮ層が活性層として形成された赤色発光半導体素子を開発した（特許文献１）。 Under such circumstances, the present inventor found that by applying a rare earth element-doped nitride semiconductor thin film to an optical device, it is possible to realize a wavelength stable light source associated with the 4f intra-shell transition of a rare earth element. For the first time, we have developed a red-light emitting semiconductor device in which an Eu-doped GaN layer controlled at the atomic level is formed as an active layer using a chemical vapor deposition method (Patent Document 1).
　しかしながら、このＥｕなどの希土類元素の４ｆ殻内遷移に伴う発光機構は、その空間対称性に大きく依存することが分かったため、さらなる実験と検討を行い、母体ＧａＮに対してＥｕ以外の不純物、例えば、酸素（Ｏ）、マグネシウム（Ｍｇ）、アルミニウム（Ａｌ）などを添加した場合、希土類元素イオン（Ｅｕイオンなど）の周辺局所構造の形成を制御して、発光強度の向上が図れることを見出した（特許文献２、３）。 However, it was found that the emission mechanism associated with the 4f intra-shell transition of rare earth elements such as Eu is highly dependent on its spatial symmetry. , Oxygen (O), magnesium (Mg), aluminum (Al), etc., can control the formation of a peripheral local structure of rare earth element ions (Eu ions, etc.) to improve the emission intensity. (Patent Documents 2 and 3).
特許第５３８８０４１号公報Japanese Patent No. 5388041 特許第６２２２６８４号公報Japanese Patent No. 6222684 特許第６４５００６１号公報Japanese Patent No. 6450061
　しかしながら、上記のように周辺局所構造の形成を制御したとしても、その発光強度（Ｅｍｉｓｓｉｏｎ　Ｉｎｔｅｎｓｉｔｙ）は、赤色発光半導体素子の場合、未だ、１．３ｍＷ程度に留まっており、半導体ＬＥＤや半導体レーザーなどの実用化に向け、さらなる高輝度化や発光特性の向上が求められている。 However, even if the formation of the peripheral local structure is controlled as described above, the emission intensity is still about 1.3 mW in the case of a red light emitting semiconductor device, and semiconductor LEDs, semiconductor lasers, etc. In order to put them into practical use, there is a demand for higher brightness and improved light emission characteristics.
　そこで、本発明は、希土類元素添加窒化物半導体層を活性層とし、従来よりも高輝度化や発光特性が向上した希土類元素添加窒化物素子の作製技術を提供することを課題とする。 Therefore, an object of the present invention is to provide a technique for fabricating a rare earth element-added nitride element that uses a rare earth element-added nitride semiconductor layer as an active layer and has higher luminance and improved light emission characteristics than conventional ones.
　本発明者は、鋭意検討の結果、以下の各請求項に示す発明により、上記の課題が解決できることを見出し、本発明を完成するに至った。 As a result of diligent studies, the inventor found that the above problems can be solved by the inventions shown in the following claims, and completed the present invention.
　請求項１に記載の発明は、
　ＧａＮ、ＩｎＮ、ＡｌＮまたはこれらのいずれか２つ以上の混晶を用いた希土類元素添加窒化物半導体素子の製造方法であって、
　有機金属気相エピタキシャル法を用い、
　８００～１０００℃の温度条件下、非極性基板上に、ＧａＮ、ＩｎＮ、ＡｌＮまたはこれらのいずれか２つ以上の混晶を母体材料として、前記母体材料を構成するＧａ、ＩｎあるいはＡｌと置換するように、希土類元素を添加して活性層を形成して、
　発光中心ＯＭＶＰＥ４に対する発光中心ＯＭＶＰＥ７の存在比率が、０．１０以上である希土類元素添加窒化物半導体素子を製造することを特徴とする希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 1,
A method for manufacturing a rare earth element-added nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more thereof, comprising:
Using an organometallic vapor phase epitaxial method,
Under a temperature condition of 800 to 1000° C., GaN, InN, AlN, or a mixed crystal of any two or more of these is used as a matrix material on a non-polar substrate to replace Ga, In, or Al constituting the matrix material. By adding a rare earth element to form an active layer,
A method for manufacturing a rare earth element-doped nitride semiconductor device, wherein the existence ratio of the luminescent center OMVPE7 to the luminescent center OMVPE4 is 0.10 or more.
　請求項２に記載の発明は、
　前記活性層をｐ型層とｎ型層の間に形成するに際して、前記活性層の形成とｐ型層およびｎ型層の形成とを、一連の形成工程において形成することを特徴とする請求項１に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 2,
2. The method according to claim 1, wherein when forming the active layer between the p-type layer and the n-type layer, the formation of the active layer and the formation of the p-type layer and the n-type layer are formed in a series of forming steps. 2. A method for manufacturing a rare earth element-added nitride semiconductor device according to 1.
　請求項３に記載の発明は、
　ｃ面に対して３～９０°傾斜した非極性基板上で、前記活性層を形成することを特徴とする請求項１または請求項２に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 3,
3. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 1, wherein the active layer is formed on a non-polar substrate inclined from 3 to 90° with respect to the c-plane. .
　請求項４に記載の発明は、
　前記活性層における前記希土類元素の添加量が、０．００１～１０ａｔ％であることを特徴とする請求項１ないし請求項３のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 4,
4. The method for manufacturing a rare earth element-added nitride semiconductor device according to claim 1, wherein the amount of the rare earth element added in the active layer is 0.001 to 10 at %. is.
　請求項５に記載の発明は、
　前記活性層の厚みが０．１ｎｍ以上となるように制御して、前記活性層を形成することを特徴とする請求項１ないし請求項４のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 5,
5. The rare earth element-added nitride semiconductor according to any one of claims 1 to 4, wherein the active layer is formed by controlling the thickness of the active layer to be 0.1 nm or more. A device manufacturing method.
　請求項６に記載の発明は、
　前記母体材料に添加される前記希土類元素としてＥｕを用いて、赤色発光の希土類元素添加窒化物半導体素子を製造することを特徴とする請求項１ないし請求項５のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 6,
6. The rare earth element according to any one of claims 1 to 5, wherein Eu is used as the rare earth element added to the base material to manufacture a red light-emitting rare earth element-added nitride semiconductor device. A method for manufacturing an element-doped nitride semiconductor device.
　請求項７に記載の発明は、
　Ｅｕ原料として、（ビス（テトラメチルモノアルキルシクロペンタジエニル）ユーロピウム）を用いることを特徴とする請求項６に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 7,
7. The method for producing a rare earth element-doped nitride semiconductor device according to claim 6, wherein (bis(tetramethylmonoalkylcyclopentadienyl)europium) is used as the Eu raw material.
　請求項８に記載の発明は、
　発光中心が２～６種類となるように制御して、前記活性層を形成することを特徴とする請求項１ないし請求項７のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 8,
8. The production of a rare earth element-added nitride semiconductor device according to claim 1, wherein the active layer is formed by controlling 2 to 6 types of luminescent centers. The method.
　請求項９に記載の発明は、
　前記希土類元素と共に酸素を添加して、前記活性層を形成することを特徴とする請求項１ないし請求項８のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 9,
9. The method for manufacturing a rare earth element-added nitride semiconductor device according to claim 1, wherein oxygen is added together with said rare earth element to form said active layer.
　請求項１０に記載の発明は、
　前記酸素の添加濃度を、１×１０１７～１×１０２０ｃｍ－３に制御して、前記活性層を形成することを特徴とする請求項９に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 10,
10. The manufacture of a rare earth element-doped nitride semiconductor device according to claim 9, wherein the active layer is formed by controlling the doping concentration of the oxygen to 1×10 17 to 1×10 20 cm −3 . The method.
　請求項１１に記載の発明は、
　前記希土類元素と共にマグネシウムまたはアルミニウムを添加して、前記活性層を形成することを特徴とする請求項１ないし請求項８のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 11,
9. The method for manufacturing a rare earth element-added nitride semiconductor device according to claim 1, wherein magnesium or aluminum is added together with said rare earth element to form said active layer. .
　請求項１２に記載の発明は、
　前記マグネシウムの添加量を１×１０１８～１×１０２０ｃｍ－３に制御して、前記活性層を形成することを特徴とする請求項１１に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 12,
12. The method of manufacturing a rare earth element-doped nitride semiconductor device according to claim 11, wherein the active layer is formed by controlling the amount of magnesium added to 1×10 18 to 1×10 20 cm −3 . is.
　請求項１３に記載の発明は、
　前記アルミニウムの添加量を０原子％を超え４０原子％を超えないように制御して、前記活性層を形成することを特徴とする請求項１１に記載の希土類元素添加窒化物半導体素子の製造方法である。 The invention according to claim 13,
12. The method of manufacturing a rare earth element-added nitride semiconductor device according to claim 11, wherein the active layer is formed by controlling the amount of aluminum to be added so as not to exceed 0 atomic % and not to exceed 40 atomic %. is.
　請求項１４に記載の発明は、
　ＧａＮ、ＩｎＮ、ＡｌＮまたはこれらのいずれか２つ以上の混晶を母体材料とする希土類元素添加窒化物半導体素子であって、
　非極性基板上に、前記母体材料を構成するＧａ、ＩｎあるいはＡｌと置換するように、希土類元素が添加された活性層が形成されており、
　発光中心ＯＭＶＰＥ４に対する発光中心ＯＭＶＰＥ７の存在比率が、０．１０以上であることを特徴とする希土類元素添加窒化物半導体素子である。 The invention according to claim 14,
A rare earth element-added nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more of these as a base material,
An active layer doped with a rare earth element is formed on a non-polar substrate so as to replace Ga, In or Al constituting the base material,
The rare earth element-added nitride semiconductor device is characterized in that the existence ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 is 0.10 or more.
　請求項１５に記載の発明は、
　前記活性層が、ｐ型層とｎ型層とに挟まれていることを特徴とする請求項１４に記載の希土類元素添加窒化物半導体素子である。 The invention according to claim 15,
15. The rare earth element-added nitride semiconductor device according to claim 14, wherein said active layer is sandwiched between a p-type layer and an n-type layer.
　請求項１６に記載の発明は、
　前記活性層に形成された発光中心が、２～６種類であることを特徴とする請求項１４または請求項１５に記載の希土類元素添加窒化物半導体素子である。 The invention according to claim 16,
16. The rare earth element-added nitride semiconductor device according to claim 14 or 15, wherein 2 to 6 types of luminescent centers are formed in the active layer.
　請求項１７に記載の発明は、
　前記母体材料に添加される前記希土類元素としてＥｕが用いられた赤色発光の希土類元素添加窒化物半導体素子であることを特徴とする請求項１４ないし請求項１６のいずれか１項に記載の希土類元素添加窒化物半導体素子である。 The invention according to claim 17,
17. The rare earth element according to any one of claims 14 to 16, wherein the rare earth element-doped nitride semiconductor device emits red light and uses Eu as the rare earth element added to the base material. It is an additive nitride semiconductor device.
　請求項１８に記載の発明は、
　請求項１４ないし請求項１７のいずれか１項に記載の希土類元素添加窒化物半導体素子を用いて構成されていることを特徴とする半導体ＬＥＤである。 The invention according to claim 18,
A semiconductor LED comprising the rare earth element-added nitride semiconductor device according to any one of claims 14 to 17.
　請求項１９に記載の発明は、
　請求項１４ないし請求項１７のいずれか１項に記載の希土類元素添加窒化物半導体素子を用いて構成されていることを特徴とする半導体レーザーである。 The invention according to claim 19,
A semiconductor laser comprising the rare earth element-added nitride semiconductor device according to any one of claims 14 to 17.
　本発明によれば、希土類元素添加窒化物半導体層を活性層とし、従来よりも高輝度化や発光特性が向上した希土類元素添加窒化物素子の作製技術を提供することができる。 According to the present invention, it is possible to provide a technique for fabricating a rare-earth-element-added nitride element that uses a rare-earth-element-added nitride semiconductor layer as an active layer and has higher luminance and improved light-emitting characteristics than conventional ones.
Ｅｕ添加窒化物半導体素子における発光機構を説明する図である。It is a figure explaining the light emission mechanism in an Eu addition nitride semiconductor element. 複数種類の発光中心の形成を示す図である。FIG. 4 is a diagram showing the formation of multiple types of luminescent centers; 各発光中心の存在比率を示す図である。It is a figure which shows the abundance ratio of each luminescent center. 間接励起下での発光における主要な発光中心を説明する図である。FIG. 3 is a diagram explaining major luminescent centers in luminescence under indirect excitation. 発光線幅を説明する図である。It is a figure explaining an emission line width. 光利得の低下を説明する図である。It is a figure explaining the fall of an optical gain. 希土類イオン周辺の原子配置の対称性を説明する図である。It is a figure explaining the symmetry of the atomic arrangement around a rare-earth ion. 不純物が欠乏した複数種類の発光中心の残存を説明する図である。FIG. 10 is a diagram for explaining how multiple types of luminescent centers that are depleted of impurities remain. 基板ｃ面上に形成されたＡｌ濃度を変化させたＡｌＮ／ＡｌＧａＮ超格子構造（ＳＬｓ）層上に形成されたＥｕ添加ＧａＮにおいて観測されたＯＭＶＰＥ７の発光強度を示す図である。FIG. 4 is a diagram showing the emission intensity of OMVPE7 observed in Eu-doped GaN formed on AlN/AlGaN superlattice structure (SLs) layers with varying Al concentrations formed on the substrate c-plane. 本発明における結晶成長条件を説明する図である。It is a figure explaining the crystal growth conditions in this invention. 極性面、無極性面を説明する図である。It is a figure explaining a polar surface and a non-polar surface. 本発明の一実験例において作製したＥｕ添加窒化物半導体素子の基本的な構造を示す図である。1 is a diagram showing the basic structure of an Eu-added nitride semiconductor device fabricated in an experimental example of the present invention; FIG. 本発明の一実験例におけるＥｕ添加窒化物半導体素子を作製する際の成長シーケンスを示す図である。FIG. 10 is a diagram showing a growth sequence when fabricating an Eu-added nitride semiconductor device in an experimental example of the present invention; 本発明の一実験例および比較実験例で得られたＥｕ添加窒化物半導体素子のフォトルミネッセンススペクトルを示す図である。FIG. 2 is a diagram showing photoluminescence spectra of Eu-added nitride semiconductor devices obtained in one experimental example of the present invention and comparative experimental examples; 本発明の一実験例で得られたＥｕ添加窒化物半導体素子における波長とＰＬ強度との関係を示す図である。FIG. 4 is a diagram showing the relationship between wavelength and PL intensity in an Eu-doped nitride semiconductor device obtained in an experimental example of the present invention; 比較実験例で得られたＥｕ添加窒化物半導体素子における波長とＰＬ強度との関係を示す図である。FIG. 5 is a graph showing the relationship between wavelength and PL intensity in the Eu-added nitride semiconductor device obtained in Comparative Experimental Example. 図１５および図１６に基づく発光強度と、励起強度との関係を示す図である。FIG. 17 is a diagram showing the relationship between emission intensity and excitation intensity based on FIGS. 15 and 16; 本発明の一実験例から得られたＣＥＥＳマッピングを示す図である。FIG. 4 shows CEES mapping obtained from one experimental example of the present invention; 比較実験例から得られたＣＥＥＳマッピングを示す図である。FIG. 4 shows CEES mapping obtained from a comparative example; 本発明の一実験例と比較実験例について、Ｅｕ発光中心と濃度との関係を示す図である。FIG. 5 is a diagram showing the relationship between the Eu luminescence center and the concentration for an experimental example of the present invention and a comparative experimental example. 比較実験例について、発光エネルギーとＰＬ強度との関係を示す図である。FIG. 10 is a diagram showing the relationship between emission energy and PL intensity for a comparative experimental example; 本発明の一実験例について、発光エネルギーとＰＬ強度との関係を示す図である。FIG. 5 is a diagram showing the relationship between emission energy and PL intensity in an experimental example of the present invention;
　以下、本発明を実施の形態に基づいて説明する。なお、以下では、希土類元素として、Ｅｕを用いたＥｕ添加窒化物半導体素子を例に挙げて説明しているが、ほぼ同等の化学的特性を有するＳｃ、Ｙ、およびＬａからＬｕまでのランタノイド系元素を総称した希土類元素は、スピン－軌道相互作用や結晶場の効果により、４ｆ電子準位に分裂を生じるという共通の性質を一般的に有しているため、Ｅｕに限定されず他の希土類元素にも同様に考えることができる。 The present invention will be described below based on embodiments. In the following description, an Eu-added nitride semiconductor device using Eu as a rare earth element will be described as an example. Rare earth elements, which are a generic term for elements, generally have the common property of causing splitting in the 4f electron level due to spin-orbital interaction and crystal field effects, so they are not limited to Eu, but other rare earth elements Elements can be considered in the same way.
［１］Ｅｕ添加窒化物半導体素子の現状と問題点
　具体的な実施の形態の説明に先立って、本発明に対する理解を容易にするために、Ｅｕ添加窒化物半導体素子の現状と問題点について、発光強度および発光線幅の観点から説明する。 [1] Current Status and Problems of Eu-Added Nitride Semiconductor Devices Before describing specific embodiments, in order to facilitate understanding of the present invention, the current status and problems of Eu-added nitride semiconductor devices are as follows. Description will be made from the viewpoint of emission intensity and emission line width.
１．発光強度の観点からの現状と問題点
　図１は、Ｅｕ添加窒化物半導体素子における発光機構を説明する図である。図１に示すように、５Ｄ０状態まで励起されたＥｕイオンが、４ｆ殻内を遷移して基底状態である７Ｆ２状態へと移動することにより、光が放出されて、発光する。 1. Current Situation and Problems from the Viewpoint of Emission Intensity FIG. 1 is a diagram for explaining the emission mechanism in an Eu-doped nitride semiconductor device. As shown in FIG . 1 , Eu ions excited to the 5D0 state undergo a transition within the 4f shell to move to the ground state 7F2 state, thereby emitting light and emitting light.
　しかしながら、この４ｆ殻内遷移は禁制遷移であるため、発光遷移確率を高めて、高い発光強度を得るためには、結晶場におけるＥｕイオンの周辺局所構造の対称性を低下させる必要がある。 However, since this 4f intra-shell transition is a forbidden transition, it is necessary to reduce the symmetry of the peripheral local structure of Eu ions in the crystal field in order to increase the luminescence transition probability and obtain high luminescence intensity.
　しかし、単にＥｕを添加した場合には、Ｅｕイオンの周辺局所構造が励起効率や遷移確率が様々に異なった状態で同時に形成されて、対称性の低下が一様とはならないため、多くの種類の発光中心が形成されて、発光波長が分布したブロードな発光スペクトルとなり、発光強度を十分に向上させることができない。 However, when Eu is simply added, peripheral local structures of Eu ions are simultaneously formed with various different excitation efficiencies and transition probabilities. is formed, resulting in a broad emission spectrum with a distribution of emission wavelengths, and the emission intensity cannot be sufficiently improved.
　図２は、この複数種類の発光中心の形成を示す図であり、有機金属気相エピタキシャル法（ＯＭＶＰＥ法）により、基板のｃ面、即ち、（０００１）面上にＥｕ添加窒化物を成長させたサンプルについて、ＣＥＥＳ（Ｃｏｍｂｉｎｅｄ　Ｅｘｃｉｔａｔｉｏｎ－Ｅｍｉｓｓｉｏｎ　Ｓｐｅｃｔｒｏｓｃｏｐｙ）マッピングした結果を示している。ＣＥＥＳは周辺局所構造の異なるＥｕイオンを個別に励起させることができるため、各発光中心を区別することができる。なお、図２において、横軸は発光エネルギー（ｅＶ）、縦軸は励起エネルギー（ｅＶ）である。 FIG. 2 is a diagram showing the formation of multiple types of luminescent centers, in which an Eu-doped nitride is grown on the c-plane, that is, the (0001) plane of the substrate by the organometallic vapor phase epitaxial method (OMVPE method). The results of CEES (Combined Excitation-Emission Spectroscopy) mapping are shown for the samples obtained. Since CEES can individually excite Eu ions with different peripheral local structures, each emission center can be distinguished. In FIG. 2, the horizontal axis is emission energy (eV), and the vertical axis is excitation energy (eV).
　図２に示すように、この場合には周辺局所構造が異なる、少なくとも８種類（ＯＭＶＰＥ１～８）の発光中心が存在している。そして、各発光中心の存在比率をプロットすると、図３に示すようになり、エネルギー輸送効率が高いとは言えないＯＭＶＰＥ４が全体の８０％程度を占めており、エネルギー輸送効率が最も高いと考えられるＯＭＶＰＥ７は数％しか存在していない。 As shown in FIG. 2, in this case, there are at least eight types of luminescent centers (OMVPE 1-8) with different peripheral local structures. The abundance ratio of each luminescent center is plotted as shown in FIG. 3. OMVPE4, which cannot be said to have high energy transport efficiency, accounts for about 80% of the total, and is considered to have the highest energy transport efficiency. OMVPE7 is present in only a few percent.
　そして、間接励起下での発光の場合、図４に示すように、ＯＭＶＰＥ４およびＯＭＶＰＥ７が主要な発光中心となっている。 In the case of luminescence under indirect excitation, OMVPE4 and OMVPE7 are the main luminescence centers, as shown in FIG.
　以上の点を考慮すると、発光強度のさらなる向上を図るためには、エネルギー輸送効率がより優れたＯＭＶＰＥ７などの発光中心が増加されるように、周辺局所構造の形成を適切に制御する必要があることが分かる。 Considering the above points, in order to further improve the emission intensity, it is necessary to appropriately control the formation of peripheral local structures so that the number of emission centers such as OMVPE7, which has better energy transport efficiency, is increased. I understand.
２．発光線幅の観点からの現状と問題点
　レーザーにおいて大きなエネルギーの光を得るためには、図５に示す発光線幅を狭くして、高い光利得の発光を得ることが重要である。しかしながら、前記したように、基板のｃ面上にＥｕ添加窒化物を成長させた場合、周辺局所構造が異なる複数種類の発光中心が形成されるため、発光波長に分布が生じてブロード、即ち、発光線幅が増大した発光スペクトルしか得られず、レーザーに必要な十分な光利得を得ることができない。 2. Current Situation and Problems from the Viewpoint of Emission Linewidth In order to obtain high-energy light in a laser, it is important to narrow the emission linewidth shown in FIG. 5 to obtain light emission with high optical gain. However, as described above, when the Eu-added nitride is grown on the c-plane of the substrate, a plurality of types of emission centers with different peripheral local structures are formed, so that the emission wavelength is distributed and broad, that is, Only an emission spectrum with an increased emission linewidth can be obtained, and a sufficient optical gain necessary for a laser cannot be obtained.
　図６は、この光利得の低下を説明する図である。図６に示すように、発光線幅の増大はエネルギー順位にばらつきがあることを意味しており、エネルギー順位のばらつきは、図中に×印で示すように、誘導放出（位相が揃った光の放出）が発生しない。これに対して、エネルギー順位が揃っている場合には、図中に丸印で示したように、誘導放出が発生するため、十分な光利得を得ることができる。即ち、図６より、十分に光利得を増大させるためには、発光波長に大きな分布が生じないように、周辺局所構造の形成を適切に制御して、発光線幅を狭くして先鋭化させる必要があることが分かる。 FIG. 6 is a diagram explaining this decrease in optical gain. As shown in FIG. 6, an increase in the emission line width means that there is a variation in the energy level. emission) does not occur. On the other hand, when the energy levels are aligned, stimulated emission occurs as indicated by circles in the figure, so that a sufficient optical gain can be obtained. That is, from FIG. 6, in order to sufficiently increase the optical gain, the emission line width is narrowed and sharpened by appropriately controlling the formation of the peripheral local structure so as not to cause a large distribution in the emission wavelength. i know i need it.
３．従来の周辺局所構造制御
　上記したように、発光強度のさらなる向上、および発光線幅の先鋭化を図るためには、周辺局所構造の形成を適切に制御する必要がある。 3. Conventional Peripheral Local Structure Control As described above, in order to further improve the emission intensity and sharpen the emission line width, it is necessary to appropriately control the formation of the peripheral local structure.
　この周辺局所構造とは、希土類イオン周辺の原子配置を示しており、この原子配置の対称性によって、発光効率が変化する。図７は、希土類イオン周辺の原子配置の対称性を説明する図である。図７（ａ）に示すような対称性が高い配置の場合には発光効率が低く、対称性が低くなるにつれて発光効率が上昇する。 This peripheral local structure indicates the atomic arrangement around the rare earth ion, and the luminous efficiency changes depending on the symmetry of this atomic arrangement. FIG. 7 is a diagram for explaining the symmetry of atomic arrangement around rare earth ions. In the case of a highly symmetrical arrangement as shown in FIG. 7A, the luminous efficiency is low, and the luminous efficiency increases as the symmetry decreases.
　対称性を低下させる具体的な手法として、図７（ｂ）に示す意図的な不純物の共添加や、図７（ｃ）に示す意図的なひずみの導入が考えられる。 As a specific method for reducing the symmetry, intentional co-doping of impurities shown in FIG. 7(b) and intentional introduction of strain shown in FIG. 7(c) are conceivable.
　しかしながら、従来の製法に基づいて、意図的な不純物の共添加や意図的なひずみの導入を行ったところ、発光強度を十分に高めることができず、発光強度のさらなる向上および発光線幅の先鋭化が図れないことが分かった。 However, when intentional co-doping of impurities and intentional introduction of strain were performed based on the conventional manufacturing method, the emission intensity could not be sufficiently increased, and the emission intensity was further improved and the emission line width was sharpened. It turned out that it could not be changed.
　即ち、意図的な不純物の共添加の場合には、添加濃度に限界がある。具体的な一例として、基板ｃ面上に酸素（Ｏ）が共添加されたＥｕ添加活性層を形成しようとしても、その添加濃度はＥｕ濃度の２．５％程度が限界であり、図８に示すように、不純物としてのＯが欠乏した複数種類の発光中心が残存しているため、発光強度の向上が十分に図られているとは言えない。 That is, in the case of intentional co-doping of impurities, there is a limit to the doping concentration. As a specific example, even if an Eu-doped active layer co-doped with oxygen (O) is formed on the c-plane of the substrate, the doping concentration is limited to about 2.5% of the Eu concentration. As shown, since a plurality of kinds of luminescent centers lacking O as an impurity remain, it cannot be said that the luminescent intensity is sufficiently improved.
　また、意図的なひずみの導入の場合には、結晶性の悪化を招いてしまう。具体的な一例として、図９に、Ａｌ濃度を変化させて基板ｃ面上に形成されたＡｌＮ／ＡｌＧａＮ超格子構造（ＳＬｓ）層の上に形成されたＥｕ添加ＧａＮ層において測定されたＯＭＶＰＥ７の発光強度を示す。なお、図９において、（ａ）はＡｌ濃度（ｘ）を変化させたときの発光スペクトルを示す図であり、（ｂ）は、Ａｌ濃度（ｘ）の変化に伴うＯＭＶＰＥ７の面内圧縮ひずみ（ε）とＰＬ積分強度（ＩＯＭＶＰＥ７）との関係を示す図であり、測定は、Ｈｅ－Ｃｄレーザーを励起光源として温度１０Ｋの雰囲気下で行った。図９より、面内圧縮ひずみが大きくなるに従って、ＯＭＶＰＥ７のＰＬ積分強度が大きくなることが分かる。しかしながら、面内圧縮ひずみを導入した際にも、得られる発光スペクトルは複数種類の発光中心からなり、発光強度の向上に十分に寄与しているとは言えない。 In addition, the intentional introduction of strain leads to deterioration of crystallinity. As a specific example, FIG. 9 shows OMVPE7 measured in an Eu-doped GaN layer formed on an AlN/AlGaN superlattice structure (SLs) layer formed on the c-plane of a substrate with varying Al concentrations. Emission intensity is shown. In FIG. 9, (a) is a diagram showing the emission spectrum when the Al concentration (x) is changed, and (b) is the in-plane compressive strain ( ε) and the PL integrated intensity (I OMVPE7 ), and the measurement was performed in an atmosphere at a temperature of 10K using a He—Cd laser as an excitation light source. From FIG. 9, it can be seen that the PL integrated intensity of OMVPE7 increases as the in-plane compressive strain increases. However, even when the in-plane compressive strain is introduced, the obtained emission spectrum consists of a plurality of types of emission centers, and it cannot be said that the emission intensity is sufficiently improved.
　以上、従来の製法に基づいて、意図的な不純物の共添加や意図的なひずみの導入を行っても、発光強度を十分に高めることができないため、発光強度のさらなる向上および発光線幅の先鋭化を図るためには、新たな結晶成長技術について検討する必要があることが分かった。 As described above, even if the intentional co-doping of impurities or the intentional introduction of strain is performed based on the conventional manufacturing method, the emission intensity cannot be sufficiently increased. It was found that it is necessary to study a new crystal growth technology in order to achieve this.
［２］本発明の基本的な考え方
　本発明者は、新たな結晶成長技術について、従来の製法に捉われることなく、鋭意検討を行った。その結果、従来は基本的に使用されていなかった面方位の異なる基板を用いて、結晶成長を行った場合、周辺局所構造の形成を適切に制御できるという驚くべき知見を得た。そして、併せて、不純物の添加を行わなくても、ＯＭＶＰＥ７の存在比率を上昇させることができ、発光強度のさらなる向上および発光線幅の先鋭化が可能であることを見出した。 [2] Basic Idea of the Present Invention The present inventors have earnestly studied new crystal growth techniques without being bound by conventional manufacturing methods. As a result, we obtained a surprising finding that the formation of peripheral local structures can be appropriately controlled when crystal growth is performed using substrates with different plane orientations, which have not been used in the past. In addition, the present inventors have found that the ratio of OMVPE7 can be increased without adding impurities, and that the emission intensity can be further improved and the emission line width can be sharpened.
　即ち、従来のＥｕ添加窒化物の結晶成長に際しては、極性面である（０００１）面（ｃ面）が最も安定な面方位であることから、極性基板上での結晶成長が一般的であり、不安定な面方位である非極性面上での結晶成長は、ＧａＮ／ＩｎＧａＮ／ＧａＮヘテロ成長での内部電界の低減など、特別な理由がない限り、行われていなかったが、本発明者は、非極性面上で結晶成長させた場合、非対称性を反映した非等方的なひずみを導入することができるため、対称性の低い発光中心を選択的に形成してＯＭＶＰＥ７など、高効率な発光中心を形成できる可能性があると考えた。 That is, in the conventional crystal growth of Eu-added nitride, since the (0001) plane (c-plane), which is a polar plane, is the most stable plane orientation, crystal growth is generally performed on a polar substrate. Crystal growth on a non-polar plane, which is an unstable plane orientation, has not been performed unless there is a special reason such as a reduction in the internal electric field in GaN/InGaN/GaN hetero-growth. , when the crystal is grown on a nonpolar plane, an anisotropic strain reflecting the asymmetry can be introduced. We thought that it might be possible to form a luminescent center.
　しかしながら、単に、基板の非極性面上での結晶成長だけでは、周辺局所構造の形成をある程度は制御できるものの、未だ、十分とは言えず、基板の非極性面上での結晶成長に加えて、結晶成長条件についても新たな検討が必要なことが分かった。 However, although the formation of the peripheral local structure can be controlled to some extent only by crystal growth on the nonpolar plane of the substrate, it is still not sufficient. , it was found that a new study is required for the crystal growth conditions.
　そして、さらに検討を行ったところ、成長温度の制御が重要であることを見出した。具体的に、当初は、従来の製法に従って、９００～１１００℃（最も好ましくは９６０℃）の温度条件下で結晶成長を制御していたが、結晶性が悪化した。そこで、さらに種々の実験と検討を行ったところ、従来よりも低い８００～１０００℃の温度条件下で結晶成長させた場合（図１０参照）には、結晶性の悪化を招くことなく、非極性面上での結晶成長が可能であり、周辺局所構造の形成を十分に制御して、２～６種類の発光中心を形成することにより、発光強度の向上が図れると共に、従来に比べて１／２以下という発光線幅の先鋭化が図れることが分かった。 After further investigation, we found that controlling the growth temperature is important. Specifically, initially, crystal growth was controlled under temperature conditions of 900 to 1100° C. (most preferably 960° C.) according to the conventional manufacturing method, but the crystallinity deteriorated. Therefore, as a result of further various experiments and studies, it was found that when the crystal was grown under a temperature condition of 800 to 1000 ° C., which is lower than the conventional temperature (see FIG. 10), the crystallinity was not deteriorated, and the non-polar Crystal growth on the surface is possible, and by sufficiently controlling the formation of the peripheral local structure and forming 2 to 6 types of luminescent centers, the luminous intensity can be improved, and at the same time, it is 1/1 compared to the conventional method. It was found that the emission line width of 2 or less can be sharpened.
　具体的には、上記のように結晶成長させることにより、後述する図１８（ｂ）から読み取れ、後述する表１に明示したように発光中心ＯＭＶＰＥ４に対する発光中心ＯＭＶＰＥ７の存在比率が、０．１０以上である希土類元素添加窒化物半導体素子を製造することができる。 Specifically, by growing the crystal as described above, the existence ratio of the luminescent center OMVPE7 to the luminescent center OMVPE4 as shown in FIG. A rare earth element-added nitride semiconductor device can be manufactured.
　ここにおいて、本発明におけるＯＭＶＰＥ４およびＯＭＶＰＥ７については、測定温度１０Ｋ以下において３価のＥｕイオンの5Ｄ0準位と7Ｆ0のエネルギー差に相当する励起エネルギーを有する光を用いてＥｕイオンを励起した場合に、図２から読み取れるように励起エネルギー２．１０４５±０．０００３ｅＶで最も強い発光を示すＥｕ発光中心がＯＭＶＰＥ４であり、励起エネルギー２．１０７０±０．０００３ｅＶで最も強い発光を示すＥｕ発光中心がＯＭＶＰＥ７である。 Here, for OMVPE4 and OMVPE7 in the present invention, Eu ions are excited using light having an excitation energy corresponding to the energy difference between the 5D0 level and 7F0 of trivalent Eu ions at a measurement temperature of 10 K or lower. As can be read from FIG. 2, OMVPE4 is the Eu luminescence center that exhibits the strongest luminescence at an excitation energy of 2.1045±0.0003 eV, and the Eu emission exhibits the strongest luminescence at an excitation energy of 2.1070±0.0003 eV. The center is OMVPE7.
　なお、前記した成長温度は、８５０～９５０℃であるとより好ましく、８９０～９１０℃であるとさらに好ましい。 The growth temperature described above is more preferably 850 to 950°C, more preferably 890 to 910°C.
　このように、本発明によれば、発光強度の向上および発光線幅の先鋭化が図られた希土類元素添加窒化物半導体素子を提供することができるため、高輝度発光の半導体ＬＥＤの実現が可能となる。また、発光線幅の先鋭化により高い光利得を得ることができるため、半導体レーザーの開発にも大きく寄与することができる。 As described above, according to the present invention, it is possible to provide a rare earth element-added nitride semiconductor device with improved emission intensity and a sharpened emission line width, so that it is possible to realize a semiconductor LED that emits light with high brightness. becomes. In addition, since a high optical gain can be obtained by sharpening the emission line width, it is possible to greatly contribute to the development of semiconductor lasers.
　なお、本発明において、非極性面とは、（０００１）面（ｃ面）以外の面を指しており、具体的には、（１０－１２）面（ｒ面）、（１１－２２）面、（２０－２１）面のような半極性面や、（１０－１０）面（ｍ面）、（１１－２０）面（ａ面）のような無極性面を挙げることができる（図１１参照）が、厳密にこれらの面に限定されるものではなく、角度に多少のずれがあってもよい。（０００１）面（ｃ面）に対する具体的な傾斜角度としては、３～９０°が好ましく、３０～９０°であるとより好ましく、６０～９０°であるとさらに好ましい。 In the present invention, the non-polar plane refers to a plane other than the (0001) plane (c-plane), specifically, the (10-12) plane (r-plane) and the (11-22) plane. , (20-21) plane, and nonpolar planes such as (10-10) plane (m-plane) and (11-20) plane (a-plane) (Fig. 11 ), but is not strictly limited to these planes, and there may be some deviation in the angle. The specific inclination angle with respect to the (0001) plane (c plane) is preferably 3 to 90°, more preferably 30 to 90°, and even more preferably 60 to 90°.
　そして、本発明において、母材としてはＧａＮに限定されず、ＩｎＮ、ＡｌＮまたはこれらの混晶（ＩｎＧａＮ、ＡｌＧａＮなど）などのいわゆるＧａＮ系の窒化物であっても、ＧａＮと同等の化学的特性を有しているため、同様に母材として使用することができる。 In the present invention, the base material is not limited to GaN, and even so-called GaN-based nitrides such as InN, AlN, or mixed crystals thereof (InGaN, AlGaN, etc.) may have chemical properties equivalent to GaN. , so it can be used as a base material as well.
　そして、本発明に係る希土類元素添加窒化物半導体素子の製造においては、活性層である希土類元素添加窒化物半導体層を、ｐ型層とｎ型層の間に形成するが、その際、活性層の形成とｐ型層およびｎ型層の形成とを、一連の形成工程、即ち、途中で反応容器から取り出すことなく、反応容器内において各層を、ｐ型層、活性層、ｎ型層の順、又は、ｎ型層、活性層、ｐ型層の順で形成することが好ましい。 In manufacturing the rare earth element-added nitride semiconductor device according to the present invention, the rare earth element-added nitride semiconductor layer, which is the active layer, is formed between the p-type layer and the n-type layer. The formation of and the formation of the p-type layer and the n-type layer are performed in a series of formation steps, that is, each layer is sequentially formed in the reaction vessel in the order of the p-type layer, the active layer, and the n-type layer without taking out from the reaction vessel in the middle. Alternatively, it is preferable to form the n-type layer, the active layer, and the p-type layer in this order.
　これにより、活性層、ｐ型層、ｎ型層の各層間に界面準位が存在せず、キャリアを効率的に注入できるため、数Ｖ程度の低電圧動作での発光が可能となる。なお、前記した途中で反応容器から取り出さないという観点から、ｎ型層、ｐ型層もＯＭＶＰＥ法により形成することが好ましいが、他の成長法を排除するものではない。また、ｎ型層、ｐ型層は活性層に必ずしも接している必要はなく、例えば、活性層との間にキャリアブロック層などが設けられていてもよい。なお、活性層の厚みは、０．１ｎｍ以上に形成されていることが好ましい。 As a result, there is no interface state between the active layer, the p-type layer, and the n-type layer, and carriers can be efficiently injected, enabling light emission at a low voltage operation of about several volts. From the viewpoint of avoiding removal from the reaction vessel during the process described above, it is preferable to form the n-type layer and the p-type layer by the OMVPE method, but other growth methods are not excluded. Also, the n-type layer and the p-type layer do not necessarily have to be in contact with the active layer, and for example, a carrier block layer or the like may be provided between them. The thickness of the active layer is preferably 0.1 nm or more.
　また、活性層において添加されるＥｕなどの希土類元素の量は、０．００１～１０ａｔ％であることが好ましく、０．０１～１０ａｔ％であるとより好ましく、０．１～１０ａｔ％であるとさらに好ましい。 Further, the amount of the rare earth element such as Eu added in the active layer is preferably 0.001 to 10 at%, more preferably 0.01 to 10 at%, and 0.1 to 10 at%. More preferred.
　なお、上記したＥｕ添加窒化物半導体の製造に際して、Ｅｕを供給するＥｕ原料（Ｅｕ有機原料）としては、蒸気圧が高く、効率的な添加を行うことができるＥｕ化合物が好ましいが、Ｅｕ［Ｃ５（ＣＨ３）４Ｒ］２（Ｒ：アルキル基）で示される（ビス（テトラメチルモノアルキルシクロペンタジエニル）ユーロピウム）がより好ましく、この内でも、ビス（ノルマルプロピルテトラメチルシクロペンタジエニル）ユーロピウム（ＥｕＣｐｐｍ ２）が好ましい。 In the production of the above-described Eu-added nitride semiconductor, the Eu raw material (Eu organic raw material) that supplies Eu is preferably an Eu compound that has a high vapor pressure and can be efficiently added, but Eu[C 5 (CH 3 ) 4 R] 2 (R: alkyl group) (bis(tetramethylmonoalkylcyclopentadienyl)europium) is more preferable, and among these, bis(normal-propyltetramethylcyclopentadienyl ) europium (EuCp pm 2 ) is preferred.
　即ち、例えば、Ｅｕ（Ｃ１１Ｈ１９Ｏ２）３やＥｕ（Ｃ５Ｈ７Ｏ２）３などの化合物は比較的蒸気圧が高いため、従来よりＥｕ供給源（Ｅｕ有機原料）として一般的に使用されているが、使用温度である１５０℃付近で固体であるため、供給時の安定性に問題がある。 That is, for example, compounds such as Eu(C 11 H 19 O 2 ) 3 and Eu(C 5 H 7 O 2 ) 3 have relatively high vapor pressures, and thus have been commonly used as Eu supply sources (Eu organic raw materials). However, since it is a solid at around 150°C, which is the operating temperature, there is a problem with its stability during supply.
　これに対して、（ビス（テトラメチルモノアルキルシクロペンタジエニル）ユーロピウム）は、融点が比較的低く（例えば、ＥｕＣｐｐｍ ２は４９℃）、使用温度において液体であるため、バブリングにより安定的に供給することができる。 In contrast, (bis(tetramethylmonoalkylcyclopentadienyl)europium) has a relatively low melting point (for example, EuCp pm 2 is 49° C.) and is a liquid at the operating temperature, so it can be stabilized by bubbling. can supply.
　そして、活性層が形成される基板としては、通常サファイアが用いられるが、これに限定されるものではなく、例えば、Ｓｉ、ＧａＮ、ＧａＡｓなどを用いることもできる。 Although sapphire is usually used as the substrate on which the active layer is formed, it is not limited to this, and for example, Si, GaN, GaAs, etc. can also be used.
　さらに、本発明者は、さらに、実験と検討を行い、結晶成長に際して、さらに、意図的に不純物を添加した場合、発光強度のさらなる向上、および発光線幅のさらなる先鋭化が図れることを見出した。 Furthermore, the present inventor conducted further experiments and studies, and found that when impurities are intentionally added during crystal growth, the emission intensity can be further improved and the emission line width can be further sharpened. .
　添加する不純物としては、酸素、マグネシウム、アルミニウムが好ましい。 The impurities to be added are preferably oxygen, magnesium, and aluminum.
　これらの元素は、希土類元素と共に添加（共添加）されることにより、希土類元素イオンの近傍に選択的に配置されて周辺局所構造を劇的に変化させて、形成される発光中心の種類を低減させることができる。 By being added (co-doped) with rare earth elements, these elements are selectively placed in the vicinity of rare earth element ions to dramatically change the peripheral local structure, thereby reducing the types of luminescent centers formed. can be made
　なお、酸素の具体的な添加濃度としては、１×１０１７～１×１０２０ｃｍ－３であることが好ましく、１×１０１９～１×１０２０ｃｍ－３であるとより好ましい。そして、マグネシウムの具体的な添加量としては、１×１０１８～１×１０２０ｃｍ－３であることが好ましく、５×１０１８～５×１０１９ｃｍ－３であるとより好ましい。また、アルミニウムの具体的な添加量としては、０原子％を超え４０原子％を超えないことが好ましく、１５～３５原子％であるとより好ましい。 Note that the specific addition concentration of oxygen is preferably 1×10 17 to 1×10 20 cm −3 , more preferably 1×10 19 to 1×10 20 cm −3 . A specific amount of magnesium to be added is preferably 1×10 18 to 1×10 20 cm −3 , more preferably 5×10 18 to 5×10 19 cm −3 . Further, the specific amount of aluminum to be added is preferably more than 0 atomic % and not more than 40 atomic %, more preferably 15 to 35 atomic %.
［３］具体的な実施の形態
　以下、具体的な実施の形態として、Ｅｕ添加窒化物半導体素子を作製する実験例を挙げ、本発明をより詳細に説明する。 [3] Specific Embodiments Hereinafter, the present invention will be described in more detail with reference to experimental examples for fabricating Eu-added nitride semiconductor devices as specific embodiments.
１．本実験例におけるＥｕ添加窒化物半導体素子
　図１２に、本実験例において作製したＥｕ添加窒化物半導体素子の基本的な構造を示す。本実験例においては、図１２に示すように、サファイア基板の（２２－４３）面上に、（２０－２１）面のアンドープＧａＮバッファ層（厚さ６μｍ）が形成されたＧａＮテンプレートを用いて、Ｅｕ添加窒化物半導体を形成させている。 1. Eu-Added Nitride Semiconductor Device in this Experimental Example FIG. 12 shows the basic structure of the Eu-added nitride semiconductor device fabricated in this experimental example. In this experimental example, as shown in FIG. 12, a GaN template in which an undoped GaN buffer layer (20-21) plane (6 μm thick) was formed on the (22-43) plane of a sapphire substrate was used. , an Eu-doped nitride semiconductor is formed.
　具体的には、図１３に示す成長シーケンスに従って、図１２に示すＥｕ添加窒化物半導体素子を作製した。 Specifically, the Eu-added nitride semiconductor device shown in FIG. 12 was manufactured according to the growth sequence shown in FIG.
　すなわち、最初に、ＧａＮテンプレートのアンドープＧａＮバッファ層上に、有機金属気相成長法（ＯＭＶＰＥ法）を用いて１０２０℃の温度条件下、アンドープＧａＮ層（厚さ１．８μｍ）を成長させた。 That is, first, an undoped GaN layer (thickness: 1.8 μm) was grown on the undoped GaN buffer layer of the GaN template under a temperature condition of 1020° C. using the metal organic vapor phase epitaxy method (OMVPE method).
　次に、アンドープＧａＮ層上に、図示しないｎ層（厚さ２５００ｎｍ）を形成した。 Next, an n-layer (not shown) (2500 nm thick) was formed on the undoped GaN layer.
　次に、ｎ層上に、温度９００℃、圧力１００ｋＰａの成長条件下、成長速度１．０μｍ／ｈでＥｕ添加ＧａＮ層を成長させて、厚さ４００ｎｍの活性層を積層した。 Next, on the n-layer, an Eu-added GaN layer was grown at a growth rate of 1.0 μm/h under growth conditions of a temperature of 900° C. and a pressure of 100 kPa to form an active layer with a thickness of 400 nm.
　次に、活性層上に、キャップ層としてのアンドープＧａＮ層（厚さ２０ｎｍ）を積層した。 Next, an undoped GaN layer (20 nm thick) was laminated as a cap layer on the active layer.
　最後に、アンドープＧａＮ層（キャップ層）上に、図示しないｐ層（厚さ７０ｎｍ）を積層した。 Finally, an unillustrated p-layer (70 nm thick) was laminated on the undoped GaN layer (cap layer).
　なお、本実験例において、Ｇａ原料としてはトリメチルガリウム（ＴＭＧａ）を用い、供給量は５．３ｓｃｃｍとした。 In addition, in this experimental example, trimethylgallium (TMGa) was used as the Ga raw material, and the supply amount was set to 5.3 sccm.
　また、Ｎ原料としてはアンモニア（ＮＨ３）を用い、供給量は４．０ｓｌｍとした。 Ammonia (NH 3 ) was used as the N raw material, and the supply amount was 4.0 slm.
　また、Ｅｕ原料としては、キャリアガス（水素ガス：Ｈ２）でバブリングしたＥｕＣｐｐｍ ２を用い、供給量は１．５ｓｌｍとした（供給温度：１３２．５℃）。 As the Eu source material, EuCp pm 2 bubbled with a carrier gas (hydrogen gas: H 2 ) was used, and the supply amount was 1.5 slm (supply temperature: 132.5° C.).
　このとき、ＯＭＶＰＥ装置の配管バルブなどを通常仕様のもの（耐熱温度８０～１００℃）から高温特殊仕様のものに変更することにより、Ｅｕ原料の供給温度を１１５～１３５℃の十分高い温度に保って、十分な量のＥｕが反応管に供給できるようにした。 At this time, the supply temperature of the Eu raw material was kept at a sufficiently high temperature of 115 to 135°C by changing the piping valve of the OMVPE equipment from the normal specification (heat resistant temperature 80 to 100°C) to the high temperature special specification. to supply a sufficient amount of Eu to the reaction tube.
　なお、各層の形成は、途中で試料を反応管より取り出すことなく、成長の中断がないように一連の工程で行った。 The formation of each layer was performed in a series of steps so that the growth was not interrupted without removing the sample from the reaction tube in the middle.
２．比較実験例
　別途、比較のために、サファイア基板の（０００１）面上に、（０００１）面のアンドープＧａＮバッファ層（厚さ６μｍ）が形成されたＧａＮテンプレートを用い、Ｅｕ添加ＧａＮ層を、温度９６０℃、圧力１００ｋＰａの成長条件下で形成したこと以外は、上記と同じ条件で、Ｅｕ添加ＧａＮ層を活性層として積層したＥｕ添加窒化物半導体素子（比較実験例）を作製した。 2. Comparative Experimental Example Separately, for comparison, a GaN template in which an undoped GaN buffer layer (6 μm in thickness) of the (0001) plane was formed on the (0001) plane of a sapphire substrate was used. An Eu-doped nitride semiconductor device (comparative experiment example) in which an Eu-doped GaN layer was laminated as an active layer was fabricated under the same conditions as described above, except that the growth conditions were 960° C. and a pressure of 100 kPa.
３．発光特性
　次に、実験例および比較実験例で得られた各Ｅｕ添加窒化物半導体素子について、Ｈｅ－Ｃｄレーザーを用いて、各活性層からのフォトルミネッセンススペクトル（ＰＬスペクトル）を測定した（測定温度：室温）。 3. Emission Characteristics Next, for each Eu-doped nitride semiconductor device obtained in Experimental Example and Comparative Experimental Example, a photoluminescence spectrum (PL spectrum) from each active layer was measured using a He—Cd laser (measurement temperature :room temperature).
　図１４に結果を示す。なお、図１４において、縦軸はＰＬ強度（任意単位、ａｒｂ．ｕｎｉｔｓ）であり、横軸は波長（ｎｍ）である。 The results are shown in Fig. 14. In FIG. 14, the vertical axis is the PL intensity (arbitrary unit, arb.units), and the horizontal axis is the wavelength (nm).
　図１４に示すように、非極性面上にＥｕ添加ＧａＮ層を形成させた実験例では、赤色発光する波長６２１ｎｍ付近に高いピークが出現しており、その発光線幅も劇的に先鋭化している一方、極性面上にＥｕ添加ＧａＮ層を形成させた比較実験例では、波長６２１ｎｍ付近でもさほど高いピークが出現せず、その発光線幅も広くなっていることが分かる。 As shown in FIG. 14, in the experimental example in which the Eu-doped GaN layer was formed on the non-polar plane, a high peak appeared near a wavelength of 621 nm for red light emission, and the emission line width was sharpened dramatically. On the other hand, in the comparative experimental example in which the Eu-doped GaN layer was formed on the polar plane, a not so high peak appeared even around the wavelength of 621 nm, and the emission line width was widened.
　そして、このＰＬ強度を積分して求められる積分ＰＬ強度、即ち、発光強度についても、約２倍となっており、発光強度も劇的に増大していることが分かった。 Then, it was found that the integrated PL intensity obtained by integrating this PL intensity, that is, the luminous intensity was also approximately doubled, and the luminous intensity was also dramatically increased.
　次に、実験例および比較実験例で得られた各Ｅｕ添加窒化物半導体素子の発光強度（積分ＰＬ強度）と励起強度（励起電力）との関係について、Ｈｅ－Ｃｄレーザーを用いて測定を行った（測定温度：室温）。結果を、図１５、図１６、図１７に示す。 Next, the relationship between the emission intensity (integrated PL intensity) and the excitation intensity (excitation power) of each Eu-added nitride semiconductor device obtained in Experimental Example and Comparative Experimental Example was measured using a He—Cd laser. (Measurement temperature: room temperature). The results are shown in FIGS. 15, 16 and 17. FIG.
　なお、図１５は、実験例で得られたＥｕ添加窒化物半導体素子における波長とＰＬ強度との関係を、４段階の励起強度において測定し、ピーク強度で規格化した発光スペクトルであり、縦軸はＰＬ強度（任意単位、ａｒｂ．ｕｎｉｔｓ）であり、横軸は波長（ｎｍ）である。そして、図１６は、比較実験例で得られたＥｕ添加窒化物半導体素子について、同様に測定して得られた発光スペクトルである。 In addition, FIG. 15 shows an emission spectrum normalized by the peak intensity obtained by measuring the relationship between the wavelength and the PL intensity in the Eu-added nitride semiconductor device obtained in the experimental example at four levels of excitation intensity. is the PL intensity (arbitrary unit, arb.units), and the horizontal axis is the wavelength (nm). FIG. 16 shows an emission spectrum obtained by similarly measuring the Eu-added nitride semiconductor device obtained in Comparative Experimental Example.
　また、図１７は、図１５および図１６で得られた発光スペクトルのＰＬ強度を積分して求められた発光強度と、励起強度との関係をプロットした図であり、縦軸は発光強度（任意単位、ａｒｂ．ｕｎｉｔｓ）であり、横軸は励起強度（ｍＷ）である。 Further, FIG. 17 is a diagram plotting the relationship between the emission intensity obtained by integrating the PL intensity of the emission spectra obtained in FIGS. 15 and 16 and the excitation intensity. units), and the horizontal axis is the excitation intensity (mW).
　図１５に示すように、非極性面上にＥｕ添加ＧａＮ層を形成させた実験例では、励起強度の大小に左右されることなく、類似した発光スペクトルが得られ、発光線幅１．３３ｎｍで先鋭なピークが維持されていることが分かる。 As shown in FIG. 15, in the experimental example in which the Eu-doped GaN layer was formed on the non-polar plane, similar emission spectra were obtained regardless of the magnitude of the excitation intensity, and the emission line width was 1.33 nm. It can be seen that a sharp peak is maintained.
　これに対して、極性面上にＥｕ添加ＧａＮ層を形成させた比較実験例では、図１６に示すように、励起強度の大小によって発光スペクトルが変化し、発光線幅も３．０３ｎｍと２倍以上となっていることが分かる。 On the other hand, in the comparative experimental example in which the Eu-doped GaN layer was formed on the polar plane, as shown in FIG. It can be seen that the above is the case.
　そして、図１７より、比較実験例では、強励起条件で発光強度に顕著な飽和が見られるのに対し、実験例では、強励起条件でも発光強度の飽和が著しく抑制されており、励起強度に対する発光強度の傾き（ＳＬＯＰＥ）も２倍以上であることが分かり、本発明に係る希土類元素添加窒化物半導体素子を用いて半導体ＬＥＤを構成させることにより、大幅に性能が向上した半導体ＬＥＤの提供が可能であることが確認できた。 Further, from FIG. 17, in the comparative experimental example, the emission intensity is significantly saturated under the strong excitation condition, whereas in the experimental example, the saturation of the emission intensity is remarkably suppressed even under the strong excitation condition. It can be seen that the slope of the emission intensity (SLOPE) is also more than twice as high, and by constructing a semiconductor LED using the rare earth element-added nitride semiconductor device according to the present invention, it is possible to provide a semiconductor LED with significantly improved performance. It was confirmed that it is possible.
　また、図１５より、本発明に係る希土類元素添加窒化物半導体素子を用いて半導体レーザーを構成させることにより、超安定・狭線幅という半導体レーザーの開発に不可欠な特性により大幅に性能が向上した半導体レーザーの提供が可能であることが確認できた。 Further, from FIG. 15, by constructing a semiconductor laser using the rare earth element-added nitride semiconductor device according to the present invention, the performance was greatly improved due to the characteristics essential for the development of the semiconductor laser, such as ultra-stability and narrow line width. It was confirmed that it is possible to provide a semiconductor laser.
　図１８に実験例から得られたＣＥＥＳマッピングを、図１９に比較実験例から得られたＣＥＥＳマッピングを示す。なお、図１８、図１９において、（ａ）は、色素レーザーを用いて測定（測定温度：１０Ｋ）した発光エネルギー（ｅＶ）と励起エネルギー（ｅＶ）との関係を示す図である。そして、（ｂ）は、色素レーザーを用いて測定（測定温度：１０Ｋ）した発光エネルギー（ｅＶ）、励起エネルギー（ｅＶ）、ＰＬ強度（任意単位、ａｒｂ．ｕｎｉｔｓ）間の関係を示す図である。 FIG. 18 shows the CEES mapping obtained from the experimental example, and FIG. 19 shows the CEES mapping obtained from the comparative experimental example. 18 and 19, (a) is a diagram showing the relationship between emission energy (eV) and excitation energy (eV) measured using a dye laser (measurement temperature: 10 K). And (b) is a diagram showing the relationship between emission energy (eV), excitation energy (eV), and PL intensity (arbitrary unit, arb.units) measured using a dye laser (measurement temperature: 10 K). .
　図１８、図１９より、非極性面上にＥｕ添加ＧａＮ層を形成させることにより、非対称性を反映した異方的なひずみが導入されて、発光中心の選択的形成が行われ、ＯＭＶＰＥ７による発光強度が増加していることが分かる。 From FIGS. 18 and 19, by forming the Eu-doped GaN layer on the non-polar plane, anisotropic strain reflecting the asymmetry is introduced, selective formation of the luminescent center is performed, and light emission by OMVPE7 It can be seen that the intensity increases.
　上記に示した実験例、比較実験例から得られた結果に基づき、図２０～図２２および表１に、（０００１）面と（２０－２１）面のそれぞれにＥｕ添加ＧａＮ層を形成した場合の、発光中心ＯＭＶＰＥ４と発光中心ＯＭＶＰＥ７の濃度およびＰＬ強度の関係を示す。 Based on the results obtained from the experimental examples and comparative experimental examples described above, FIGS. , the relationship between the concentration and the PL intensity of the emission center OMVPE4 and the emission center OMVPE7.
　図２０より、（０００１）面にＥｕ添加ＧａＮ層を形成した場合と、（２０－２１）面にＥｕ添加ＧａＮ層を形成した場合とを比較すると、発光中心ＯＭＶＰＥ４の濃度については大きな相違はないが、発光中心ＯＭＶＰＥ７の濃度については、（２０－２１）面にＥｕ添加ＧａＮ層を形成した場合の方がはるかに大きいことが分かる。 As shown in FIG. 20, when the Eu-doped GaN layer formed on the (0001) plane and the Eu-doped GaN layer formed on the (20-21) plane are compared, there is no significant difference in the concentration of the emission center OMVPE4. However, it can be seen that the concentration of the emission center OMVPE7 is much higher when the Eu-doped GaN layer is formed on the (20-21) plane.
　そして、ＰＬ強度を比較した場合、図２１、図２２より、（２０－２１）面にＥｕ添加ＧａＮ層を形成した場合の方が、ＯＭＶＰＥ４、ＯＭＶＰＥ７共にＰＬ強度が大きく、特に、発光中心ＯＭＶＰＥ７のＰＬ強度については、（２０－２１）面にＥｕ添加ＧａＮ層を形成した場合の方が、（０００１）面にＥｕ添加ＧａＮ層を形成した場合に比べて、圧倒的に大きいことが分かる。 21 and 22, when the Eu-added GaN layer is formed on the (20-21) plane, both OMVPE4 and OMVPE7 have higher PL intensities. It can be seen that the PL intensity is overwhelmingly higher when the Eu-doped GaN layer is formed on the (20-21) plane than when the Eu-doped GaN layer is formed on the (0001) plane.
　そして、表１に示す通り、発光中心ＯＭＶＰＥ４に対する発光中心ＯＭＶＰＥ７の存在比率が、（０００１）面にＥｕ添加ＧａＮ層を形成した場合には、０．００２と小さいが、（２０－２１）面にＥｕ添加ＧａＮ層を形成した場合には、０．１６２と圧倒的に発光中心ＯＭＶＰＥ４に対する発光中心ＯＭＶＰＥ７の存在比率が、高いことが分かる。 Then, as shown in Table 1, when the Eu-doped GaN layer is formed on the (0001) plane, the existence ratio of the emission center OMVPE7 to the emission center OMVPE4 is as small as 0.002, but on the (20-21) plane It can be seen that when the Eu-doped GaN layer is formed, the existence ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 is overwhelmingly high at 0.162.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　以上、本発明を実施の形態に基づいて説明したが、本発明は上記の実施の形態に限定されるものではない。本発明と同一および均等の範囲内において、上記の実施の形態に対して種々の変更を加えることができる。 Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiment within the same and equivalent scope of the present invention.

Claims (19)

  1. 　ＧａＮ、ＩｎＮ、ＡｌＮまたはこれらのいずれか２つ以上の混晶を用いた希土類元素添加窒化物半導体素子の製造方法であって、
    　有機金属気相エピタキシャル法を用い、
    　８００～１０００℃の温度条件下、非極性基板上に、ＧａＮ、ＩｎＮ、ＡｌＮまたはこれらのいずれか２つ以上の混晶を母体材料として、前記母体材料を構成するＧａ、ＩｎあるいはＡｌと置換するように、希土類元素を添加して活性層を形成して、
    　発光中心ＯＭＶＰＥ４に対する発光中心ＯＭＶＰＥ７の存在比率が、０．１０以上である希土類元素添加窒化物半導体素子を製造することを特徴とする希土類元素添加窒化物半導体素子の製造方法。     A method for manufacturing a rare earth element-added nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more thereof, comprising:
    Using an organometallic vapor phase epitaxial method,
    Under a temperature condition of 800 to 1000° C., GaN, InN, AlN, or a mixed crystal of any two or more of these is used as a matrix material on a non-polar substrate to replace Ga, In, or Al constituting the matrix material. By adding a rare earth element to form an active layer,
    A method for producing a rare earth element-added nitride semiconductor device, wherein the existence ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 is 0.10 or more.
  2. 　前記活性層をｐ型層とｎ型層の間に形成するに際して、前記活性層の形成とｐ型層およびｎ型層の形成とを、一連の形成工程において形成することを特徴とする請求項１に記載の希土類元素添加窒化物半導体素子の製造方法。 2. The method according to claim 1, wherein when forming the active layer between the p-type layer and the n-type layer, the formation of the active layer and the formation of the p-type layer and the n-type layer are formed in a series of forming steps. 2. A method for producing a rare earth element-added nitride semiconductor device according to 1.
  3. 　ｃ面に対して３～９０°傾斜した非極性基板上で、前記活性層を形成することを特徴とする請求項１または請求項２に記載の希土類元素添加窒化物半導体素子の製造方法。 The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 1 or claim 2, wherein the active layer is formed on a non-polar substrate inclined at 3 to 90° with respect to the c-plane.
  4. 　前記活性層における前記希土類元素の添加量が、０．００１～１０ａｔ％であることを特徴とする請求項１ないし請求項３のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法。 4. The method for manufacturing a rare earth element-added nitride semiconductor device according to claim 1, wherein the amount of the rare earth element added in the active layer is 0.001 to 10 at %. .
  5. 　前記活性層の厚みが０．１ｎｍ以上となるように制御して、前記活性層を形成することを特徴とする請求項１ないし請求項４のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法。 5. The rare earth element-added nitride semiconductor according to any one of claims 1 to 4, wherein the active layer is formed by controlling the thickness of the active layer to be 0.1 nm or more. A method for manufacturing an element.
  6. 　前記母体材料に添加される前記希土類元素としてＥｕを用いて、赤色発光の希土類元素添加窒化物半導体素子を製造することを特徴とする請求項１ないし請求項５のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法。 6. The rare earth element according to any one of claims 1 to 5, wherein Eu is used as the rare earth element added to the base material to manufacture a red light-emitting rare earth element-added nitride semiconductor device. A method for manufacturing an element-added nitride semiconductor device.
  7. 　Ｅｕ原料として、（ビス（テトラメチルモノアルキルシクロペンタジエニル）ユーロピウム）を用いることを特徴とする請求項６に記載の希土類元素添加窒化物半導体素子の製造方法。 (Bis(tetramethylmonoalkylcyclopentadienyl)europium) is used as the Eu raw material.
  8. 　発光中心が２～６種類となるように制御して、前記活性層を形成することを特徴とする請求項１ないし請求項７のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法。 8. The production of a rare earth element-added nitride semiconductor device according to claim 1, wherein the active layer is formed by controlling 2 to 6 types of luminescent centers. Method.
  9. 　前記希土類元素と共に酸素を添加して、前記活性層を形成することを特徴とする請求項１ないし請求項８のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法。 The method for manufacturing a rare earth element-added nitride semiconductor device according to any one of claims 1 to 8, characterized in that oxygen is added together with the rare earth element to form the active layer.
  10. 　前記酸素の添加濃度を、１×１０１７～１×１０２０ｃｍ－３に制御して、前記活性層を形成することを特徴とする請求項９に記載の希土類元素添加窒化物半導体素子の製造方法。 10. The manufacture of a rare earth element-doped nitride semiconductor device according to claim 9, wherein the active layer is formed by controlling the doping concentration of the oxygen to 1×10 17 to 1×10 20 cm −3 . Method.
  11. 　前記希土類元素と共にマグネシウムまたはアルミニウムを添加して、前記活性層を形成することを特徴とする請求項１ないし請求項８のいずれか１項に記載の希土類元素添加窒化物半導体素子の製造方法。 The method for manufacturing a rare earth element-added nitride semiconductor device according to any one of claims 1 to 8, characterized in that magnesium or aluminum is added together with the rare earth element to form the active layer.
  12. 　前記マグネシウムの添加量を１×１０１８～１×１０２０ｃｍ－３に制御して、前記活性層を形成することを特徴とする請求項１１に記載の希土類元素添加窒化物半導体素子の製造方法。 12. The method of manufacturing a rare earth element-doped nitride semiconductor device according to claim 11, wherein the active layer is formed by controlling the amount of magnesium added to 1×10 18 to 1×10 20 cm −3 . .
  13. 　前記アルミニウムの添加量を０原子％を超え４０原子％を超えないように制御して、前記活性層を形成することを特徴とする請求項１１に記載の希土類元素添加窒化物半導体素子の製造方法。 12. The method of manufacturing a rare earth element-added nitride semiconductor device according to claim 11, wherein the active layer is formed by controlling the amount of aluminum to be added so as not to exceed 0 atomic % and not to exceed 40 atomic %. .
  14. 　ＧａＮ、ＩｎＮ、ＡｌＮまたはこれらのいずれか２つ以上の混晶を母体材料とする希土類元素添加窒化物半導体素子であって、
    　非極性基板上に、前記母体材料を構成するＧａ、ＩｎあるいはＡｌと置換するように、希土類元素が添加された活性層が形成されており、
    　発光中心ＯＭＶＰＥ４に対する発光中心ＯＭＶＰＥ７の存在比率が、０．１０以上であることを特徴とする希土類元素添加窒化物半導体素子。     A rare earth element-added nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more of these as a base material,
    An active layer doped with a rare earth element is formed on a non-polar substrate so as to replace Ga, In or Al constituting the base material,
    A rare-earth element-added nitride semiconductor device, characterized in that the existence ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 is 0.10 or more.
  15. 　前記活性層が、ｐ型層とｎ型層とに挟まれていることを特徴とする請求項１４に記載の希土類元素添加窒化物半導体素子。 The rare earth element-added nitride semiconductor device according to claim 14, wherein the active layer is sandwiched between a p-type layer and an n-type layer.
  16. 　前記活性層に形成された発光中心が、２～６種類であることを特徴とする請求項１４または請求項１５に記載の希土類元素添加窒化物半導体素子。 The rare earth element-doped nitride semiconductor device according to claim 14 or 15, characterized in that 2 to 6 kinds of luminescent centers are formed in the active layer.
  17. 　前記母体材料に添加される前記希土類元素としてＥｕが用いられた赤色発光の希土類元素添加窒化物半導体素子であることを特徴とする請求項１４ないし請求項１６のいずれか１項に記載の希土類元素添加窒化物半導体素子。 17. The rare earth element according to any one of claims 14 to 16, wherein the rare earth element-doped nitride semiconductor device emits red light and uses Eu as the rare earth element added to the base material. Additive nitride semiconductor device.
  18. 　請求項１４ないし請求項１７のいずれか１項に記載の希土類元素添加窒化物半導体素子を用いて構成されていることを特徴とする半導体ＬＥＤ。 A semiconductor LED characterized by being constructed using the rare earth element-added nitride semiconductor device according to any one of claims 14 to 17.
  19. 　請求項１４ないし請求項１７のいずれか１項に記載の希土類元素添加窒化物半導体素子を用いて構成されていることを特徴とする半導体レーザー。 A semiconductor laser comprising the rare earth element-added nitride semiconductor device according to any one of claims 14 to 17.
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