Rare earth-doped nitride semiconductor elements and their manufacturing methods, semiconductor LEDs, semiconductor lasers

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

[Technical Field]

[0001] The present invention relates to a rare earth-doped nitride semiconductor device, a method for manufacturing the same, and a semiconductor LED and a semiconductor laser that use the rare earth-doped nitride semiconductor device. [Background technology]

[0002] 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 become commonplace, and there is growing demand for the development of red LEDs using nitride semiconductors.

[0003] The reason for this is that the conventional In x Ga y Al 1-x-y P / GaAs-based red LEDs have problems with device stability, and by emitting the three primary colors of light using the same materials as blue and green LEDs, it will be possible to integrate them on the same substrate, which is expected to lead to the realization of small, high-resolution full-color LED displays and LED lighting that emits light in the red range, which is not included in current white LEDs.

[0004] To meet this demand, we have developed In, which is already in practical use in blue and green LEDs. x Ga 1―X Based on an N / GaN multiple quantum well structure light-emitting layer, studies are being conducted to further increase the In composition to further extend the emission wavelength. However, significant problems have arisen, such as deterioration of crystallinity due to the high In composition and reduced emission efficiency due to the piezoelectric field effect.

[0005] Under these circumstances, the inventors discovered that by applying rare-earth-doped nitride semiconductor thin films to optical devices, it is possible to realize a wavelength-stable light source associated with the intra-4f shell transition of rare-earth elements, and developed a world-first red light-emitting semiconductor element in which an Eu-doped GaN layer controlled at the atomic level is formed as an active layer using chemical vapor deposition (Patent Document 1).

[0006] However, it was found that the emission mechanism associated with the transition within the 4f shell of rare earth elements such as Eu is highly dependent on their spatial symmetry. As a result of further experiments and investigations, it was found that when impurities other than Eu, such as oxygen (O), magnesium (Mg), and aluminum (Al), are added to the host GaN, the formation of the local structure around the rare earth element ions (such as Eu ions) can be controlled, thereby improving the emission intensity (Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5388041 [Patent Document 2] Patent No. 6222684 [Patent Document 3] Patent No. 6450061 Summary of the Invention [Problem to be solved by the invention]

[0008] However, even if the formation of the peripheral local structure is controlled as described above, the emission intensity of a red light-emitting semiconductor element is still limited to about 1.3 mW. Therefore, further improvements in brightness and light-emitting properties are required for practical use in semiconductor LEDs, semiconductor lasers, etc.

[0009] Therefore, an object of the present invention is to provide a technique for fabricating a rare earth element-doped nitride element that uses a rare earth element-doped nitride semiconductor layer as an active layer and has higher brightness and improved light emission characteristics than conventional elements. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that the above problems can be solved by the inventions set forth in the following claims, and have completed the present invention.

[0011] The invention described in claim 1 is A method for manufacturing a rare earth element-doped nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of two or more of these, comprising: Using metal organic vapor phase epitaxy, Under temperature conditions of 800 to 1000°C, The tilt angle to the (0001) plane (c-plane) is 30 to 90 degrees. non-polar having a surface substrate The non-polar plane of An active layer is formed on the substrate by adding rare earth elements to GaN, InN, AlN or a mixed crystal of two or more of these as a base material so as to replace Ga, In or Al constituting the base material. , rare The present invention relates to a method for producing a rare earth element-doped nitride semiconductor device, characterized in that the rare earth element-doped nitride semiconductor device is produced. The invention described in claim 2 is 2. The method for manufacturing a rare-earth-element-doped nitride semiconductor device according to claim 1, wherein the nonpolar plane is any one of a (10-12) plane (r-plane), a (11-22) plane, a (20-21) plane, a (10-10) plane (m-plane), and a (11-20) plane (a-plane).

[0012] Claim 3 The invention described in 2. A method for forming an active layer between a p-type layer and an n-type layer, comprising the steps of forming the active layer, the p-type layer, and the n-type layer in a single step. or claim 2 1. A method for manufacturing the rare earth element-doped nitride semiconductor device according to claim 1.

[0013] Claim 4 The invention described in The method for manufacturing a rare earth element-doped nitride semiconductor device according to any one of claims 1 to 3, characterized in that a rare earth element-doped nitride semiconductor device is manufactured in which the abundance ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 in the active layer is 0.10 or more.

[0014] Claim 5 The invention described in 3. The active layer according to claim 1, wherein the amount of the rare earth element added is 0.001 to 10 at %. 4 1 is a method for producing the rare earth element-doped nitride semiconductor device according to any one of the above items.

[0015] Claim 6 The invention described in 10. The method of claim 1, wherein the thickness of the active layer is controlled to be 0.1 nm or more.5 1 is a method for producing the rare earth element-doped nitride semiconductor device according to any one of the above items.

[0016] Claim 7 The invention described in 10. A rare earth element-doped nitride semiconductor device that emits red light is manufactured by using Eu as the rare earth element to be doped into the base material. 6 1 is a method for producing the rare earth element-doped nitride semiconductor device according to any one of the above items.

[0017] Claim 8 The invention described in The Eu source is characterized by using bis(tetramethylmonoalkylcyclopentadienyl)europium. 7 1. A method for manufacturing the rare earth element-doped nitride semiconductor device according to claim 1.

[0018] Claim 9 The invention described in 2. The active layer is formed by controlling the number of luminescence centers to be 2 to 6. 8 1 is a method for producing the rare earth element-doped nitride semiconductor device according to any one of the above items.

[0019] Claim 10 The invention described in 10. The active layer according to claim 1, wherein oxygen is added together with the rare earth element. 9 1 is a method for producing the rare earth element-doped nitride semiconductor device according to any one of the above items.

[0020] Claim 11 The invention described in The concentration of added oxygen is 1×10 17 ~1×10 20 cm -3 and forming the active layer by controlling the temperature to a value higher than the predetermined value. 10 1. A method for manufacturing the rare earth element-doped nitride semiconductor device according to claim 1.

[0021] Claim 12 The invention described in 10. The active layer according to claim 1, wherein magnesium or aluminum is added together with the rare earth element. 11 1 is a method for producing the rare earth element-doped nitride semiconductor device according to any one of the above items.

[0022] Claim 13 The invention described in The amount of magnesium added is 1×10 18 ~1×10 20 cm -3 and forming the active layer by controlling the temperature to a value higher than the predetermined value. 12 1. A method for manufacturing the rare earth element-doped nitride semiconductor device according to claim 1.

[0023] Claim 14 The invention described in 3. The active layer is formed by controlling the amount of aluminum added to be greater than 0 atomic % but not greater than 40 atomic %. 12 1. A method for manufacturing the rare earth element-doped nitride semiconductor device according to claim 1. The invention described in claim 15 is A method for manufacturing a rare earth element-doped nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of two or more of these, comprising: Using metal organic vapor phase epitaxy, A method for producing a rare-earth-element-doped nitride semiconductor device, characterized in that an active layer is formed on a non-polar surface of a substrate having a non-polar surface selected from the (10-12) plane (r-plane), (11-22) plane, (20-21) plane, (10-10) plane (m-plane), and (11-20) plane (a-plane) at a temperature of 800 to 1000°C, using GaN, InN, AlN, or a mixed crystal of any two or more of these as a host material, by adding a rare-earth element to substitute for Ga, In, or Al constituting the host material. The invention described in claim 16 is 16. The method for producing a rare earth element-doped nitride semiconductor device according to claim 15, wherein a rare earth element-doped nitride semiconductor device is produced in which the abundance ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 in the active layer is 0.10 or more.

[0024] Claim 17 The invention described in A rare earth element-doped nitride semiconductor device having GaN, InN, AlN, or a mixed crystal of two or more of these as a base material, The tilt angle to the (0001) plane (c-plane) is 30 to 90 degrees. non-polar having a surface substrate The non-polar plane of An active layer is formed on the substrate, to which rare earth elements are added so as to replace Ga, In or Al constituting the base material. There are The rare earth element-doped nitride semiconductor device is characterized by the above. The invention described in claim 18 is 18. The rare-earth-element-doped nitride semiconductor device according to claim 17, wherein the nonpolar plane is any one of the (10-12) plane (r-plane), the (11-22) plane, the (20-21) plane, the (10-10) plane (m-plane), and the (11-20) plane (a-plane). The invention described in claim 19 is 19. The rare-earth-element-doped nitride semiconductor device according to claim 17 or 18, wherein in the active layer, the abundance ratio of the luminescence centers OMVPE7 to the luminescence centers OMVPE4 is 0.10 or more.

[0025] Claim 20 The invention described in The active layer is sandwiched between a p-type layer and an n-type layer. Any one of claims 17 to 19 1. A rare earth element-doped nitride semiconductor device according to claim 1.

[0026] Claim 21 The invention described in The active layer has two to six types of luminescence centers. Any one of claims 17 to 20 1. A rare earth element-doped nitride semiconductor device according to claim 1.

[0027] Claim 22 The invention described in The rare earth element added to the base material is Eu, which is a rare earth element-added nitride semiconductor element that emits red light. 17 or claims 21 1. A rare earth element-doped nitride semiconductor device according to any one of claims 1 to 9. The invention described in claim 23 is A rare earth element-doped nitride semiconductor device having GaN, InN, AlN, or a mixed crystal of two or more of these as a base material, The rare-earth-element-doped nitride semiconductor device is characterized in that an active layer to which a rare-earth element is added is formed on a nonpolar surface of a substrate having any of the (10-12) plane (r-plane), (11-22) plane, (20-21) plane, (10-10) plane (m-plane), and (11-20) plane (a-plane), so as to replace Ga, In, or Al constituting the base material. The invention described in claim 24 is 24. The rare-earth-element-doped nitride semiconductor device according to claim 23, wherein in the active layer, the abundance ratio of the luminescence centers OMVPE7 to the luminescence centers OMVPE4 is 0.10 or more.

[0028] Claim 25 The invention described in Claim 17 or claims 24 1. A semiconductor LED characterized by being configured using the rare earth element-doped nitride semiconductor element according to any one of claims 1 to 9.

[0029] Claim 26 The invention described in Claim 17 or claims 241. A semiconductor laser characterized by being configured using the rare earth element-doped nitride semiconductor element according to any one of the above. [Effects of the Invention]

[0030] According to the present invention, it is possible to provide a technique for fabricating a rare earth element-doped nitride device that uses a rare earth element-doped nitride semiconductor layer as an active layer and has higher brightness and improved light emission characteristics than conventional devices. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram illustrating the light emission mechanism in an Eu-doped nitride semiconductor device. [Figure 2] FIG. 1 is a diagram showing the formation of multiple types of luminescence centers. [Figure 3] FIG. 2 is a diagram showing the abundance ratio of each luminescence center. [Figure 4] FIG. 1 is a diagram illustrating the main luminescence centers in luminescence under indirect excitation. [Figure 5] FIG. 10 is a diagram illustrating an emission line width. [Figure 6] FIG. 10 is a diagram illustrating a decrease in optical gain. [Figure 7] FIG. 2 is a diagram illustrating the symmetry of the atomic arrangement around a rare earth ion. [Figure 8] 1A and 1B are diagrams illustrating the remaining of multiple types of luminescence centers when impurities are depleted. [Figure 9] FIG. 1 shows the photoluminescence 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. [Figure 10] FIG. 2 is a diagram illustrating the crystal growth conditions in the present invention. [Figure 11] FIG. 2 is a diagram illustrating a polar plane and a non-polar plane. [Figure 12] FIG. 1 is a diagram showing the basic structure of an Eu-doped nitride semiconductor device fabricated in an experimental example of the present invention. [Figure 13]FIG. 2 is a diagram showing a growth sequence for fabricating an Eu-doped nitride semiconductor device in an experimental example of the present invention. [Figure 14] FIG. 1 is a diagram showing photoluminescence spectra of Eu-doped nitride semiconductor devices obtained in an experimental example of the present invention and a comparative experimental example. [Figure 15] FIG. 1 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. [Figure 16] FIG. 10 is a graph showing the relationship between wavelength and PL intensity in an Eu-doped nitride semiconductor device obtained in a comparative experiment. [Figure 17] FIG. 17 is a diagram showing the relationship between emission intensity and excitation intensity based on FIGS. 15 and 16. [Figure 18] FIG. 1 shows CEES mapping obtained from an experimental example of the present invention. [Figure 19] FIG. 10 shows CEES mapping obtained from a comparative experiment. [Figure 20] FIG. 1 is a diagram showing the relationship between Eu luminescence centers and concentrations for an experimental example of the present invention and a comparative experimental example. [Figure 21] FIG. 10 is a diagram showing the relationship between emission energy and PL intensity for a comparative experimental example. [Figure 22] FIG. 1 is a diagram showing the relationship between emission energy and PL intensity for an experimental example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will be described below based on embodiments. Note that, although the following description will be given taking as an example an Eu-doped nitride semiconductor device using Eu as a rare earth element, rare earth elements, which collectively refer to Sc, Y, and the lanthanoid elements from La to Lu, which have almost the same chemical properties, generally share the property of causing splitting in the 4f electron level due to the effects of spin-orbit interaction and crystal field, and therefore, the present invention is not limited to Eu and can be applied to other rare earth elements as well.

[0033] [1] Current status and problems of Eu-doped nitride semiconductor devices Before describing specific embodiments, the current state and problems of Eu-doped nitride semiconductor devices will be described from the perspective of emission intensity and emission linewidth in order to facilitate understanding of the present invention.

[0034] 1. Current status and issues from the viewpoint of luminescence intensity FIG. 1 is a diagram illustrating the light emission mechanism in an Eu-doped nitride semiconductor device. As shown in FIG. 5 The Eu ion excited to the D0 state transitions within the 4f shell to the ground state. 7 By moving to the F2 state, light is released and light is emitted.

[0035] However, since this intra-4f shell transition is forbidden, in order to increase the radiative transition probability and obtain high luminescence intensity, it is necessary to reduce the symmetry of the local structure around the Eu ion in the crystal field.

[0036] However, when Eu is simply added, local structures around the Eu ions are simultaneously formed with various excitation efficiencies and transition probabilities, and the reduction in symmetry is not uniform. As a result, many types of luminescence centers are formed, resulting in a broad emission spectrum with a distribution of emission wavelengths, and the emission intensity cannot be sufficiently improved.

[0037] Figure 2 shows the formation of these multiple types of luminescence centers, showing the results of combined excitation-emission spectroscopy (CEES) mapping of a sample in which Eu-doped nitride was grown on the c-plane, i.e., the (0001) plane, of a substrate by organometallic vapor phase epitaxy (OMVPE). CEES can individually excite Eu ions with different surrounding local structures, making it possible to distinguish between the various luminescence centers. In Figure 2, the horizontal axis represents luminescence energy (eV), and the vertical axis represents excitation energy (eV).

[0038] As shown in Figure 2, in this case, there are at least eight types of luminescence centers (OMVPE1 to 8) with different surrounding local structures. When the abundance ratio of each luminescence center is plotted, as shown in Figure 3, OMVPE4, which cannot be said to have a high energy transport efficiency, accounts for about 80% of the total, while OMVPE7, which is thought to have the highest energy transport efficiency, is present in only a few percent.

[0039] In the case of emission under indirect excitation, OMVPE4 and OMVPE7 are the main emission centers, as shown in Figure 4.

[0040] Considering the above points, it is clear that in order to further improve the luminescence intensity, it is necessary to appropriately control the formation of surrounding local structures so as to increase the number of luminescence centers such as OMVPE7, which have better energy transport efficiency.

[0041] 2. Current status and issues 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 Figure 5 and obtain emission with high optical gain. However, as mentioned above, when a Eu-doped nitride is grown on the c-plane of a substrate, multiple types of emission centers with different surrounding local structures are formed, which causes a distribution in the emission wavelength, resulting in only a broad emission spectrum with an increased emission linewidth, and it is not possible to obtain sufficient optical gain required for a laser.

[0042] Figure 6 illustrates this decrease in optical gain. As shown in Figure 6, an increase in the emission linewidth indicates variations in the energy levels, and variations in the energy levels do not result in stimulated emission (emission of light with a coherent phase), as indicated by the cross marks in the figure. In contrast, when the energy levels are coherent, stimulated emission occurs, as indicated by the circle marks in the figure, and sufficient optical gain can be obtained. In other words, Figure 6 shows that in order to sufficiently increase the optical gain, it is necessary to narrow and sharpen the emission linewidth by appropriately controlling the formation of the peripheral local structure so as to prevent a large distribution in the emission wavelength.

[0043] 3. Conventional control of peripheral local structure As described above, in order to further improve the emission intensity and sharpen the emission linewidth, it is necessary to appropriately control the formation of the peripheral local structure.

[0044] This peripheral local structure refers to the atomic arrangement around the rare-earth ion, and the luminous efficiency changes depending on the symmetry of this atomic arrangement. Figure 7 is a diagram explaining the symmetry of the atomic arrangement around the rare-earth ion. In the case of a highly symmetric arrangement as shown in Figure 7(a), the luminous efficiency is low, and as the symmetry decreases, the luminous efficiency increases.

[0045] Specific methods for reducing symmetry include intentional co-doping of impurities as shown in Figure 7(b) and intentional introduction of strain as shown in Figure 7(c).

[0046] However, when intentional co-doping of impurities or intentional introduction of strain was performed based on conventional manufacturing methods, it was found that the emission intensity could not be sufficiently increased, and further improvement of the emission intensity and sharpening of the emission linewidth could not be achieved.

[0047] In other words, when intentionally co-doping an impurity, there is a limit to the doping concentration. As a specific example, even if an attempt is made to form an Eu-doped active layer co-doped with oxygen (O) on the c-plane of a substrate, the doping concentration is limited to about 2.5% of the Eu concentration. As shown in Figure 8, multiple types of luminescence centers deficient in O as an impurity remain, so it cannot be said that the luminescence intensity is sufficiently improved.

[0048] Furthermore, intentional introduction of strain leads to deterioration of crystallinity. As a specific example, Figure 9 shows the photoluminescence intensity of OMVPE7 measured in a Eu-doped GaN layer formed on an AlN / AlGaN superlattice structure (SLs) layer formed on the c-plane of a substrate with varying Al concentration. In Figure 9, (a) shows the photoluminescence spectrum when the Al concentration (x) is changed, and (b) shows the relationship between the in-plane compressive strain (ε) and the integrated PL intensity (I OMVPE7) and the measurements were performed in an atmosphere at a temperature of 10 K using a He-Cd laser as the excitation light source. Figure 9 shows that the integrated PL intensity of OMVPE7 increases as the in-plane compressive strain increases. However, even when in-plane compressive strain is introduced, the resulting emission spectrum consists of multiple types of emission centers, and it cannot be said that this strain contributes sufficiently to improving the emission intensity.

[0049] As described above, even if intentional co-doping of impurities or intentional introduction of strain is performed based on conventional manufacturing methods, it is not possible to sufficiently increase the emission intensity. Therefore, it was found that in order to further improve the emission intensity and sharpen the emission linewidth, it is necessary to consider new crystal growth techniques.

[0050] [2] Basic concept of the present invention The inventors have conducted extensive research into new crystal growth techniques, without being bound by conventional manufacturing methods. As a result, they have made the surprising discovery 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. Furthermore, they have discovered that the abundance ratio of OMVPE7 can be increased without the addition of impurities, thereby enabling further improvement of the emission intensity and sharpening of the emission linewidth.

[0051] In other words, in conventional crystal growth of Eu-doped nitrides, crystal growth is generally performed on polar substrates because the polar (0001) plane (c-plane) is the most stable plane orientation. Crystal growth on nonpolar planes, which are unstable plane orientations, has not been performed unless there is a special reason, such as reducing the internal electric field in GaN / InGaN / GaN heteroepitaxy. However, the inventors believed that when crystals are grown on nonpolar planes, anisotropic strain reflecting asymmetry can be introduced, which may enable the selective formation of low-symmetry luminescence centers and the formation of highly efficient luminescence centers, such as those produced by OMVPE.

[0052] However, although crystal growth on the nonpolar surface of the substrate alone can control the formation of peripheral local structures to some extent, it is still not sufficient. It was found that in addition to crystal growth on the nonpolar surface of the substrate, new consideration is needed regarding the crystal growth conditions.

[0053] Further investigation revealed that controlling the growth temperature is important. Specifically, initially, crystal growth was controlled at temperatures of 900 to 1100°C (most preferably 960°C) according to conventional manufacturing methods, but this resulted in a deterioration in crystallinity. Further experiments and investigations revealed that, when crystal growth was performed at temperatures lower than conventional conditions of 800 to 1000°C (see FIG. 10), crystal growth on nonpolar planes was possible without causing a deterioration in crystallinity, and by sufficiently controlling the formation of peripheral local structures and forming two to six types of luminescence centers, it was possible to improve the luminescence intensity and sharpen the emission linewidth to half or less compared to conventional methods.

[0054] Specifically, by growing the crystal as described above, it is possible to manufacture a rare earth element-doped nitride semiconductor device in which the abundance ratio of the luminescent center OMVPE7 to the luminescent center OMVPE4 is 0.10 or more, as can be seen from Figure 18(b) described below and shown in Table 1 described below.

[0055] Here, for OMVPE4 and OMVPE7 in the present invention, the amount of trivalent Eu ions was 10 K or less. 5 D0 level and 7 When Eu ions are excited using light with an excitation energy equivalent to the energy difference of F0, as can be seen from Figure 2, the Eu luminescence center that exhibits the strongest luminescence at an excitation energy of 2.1045±0.0003 eV is OMVPE4, and the Eu luminescence center that exhibits the strongest luminescence at an excitation energy of 2.1070±0.0003 eV is OMVPE7.

[0056] The growth temperature is more preferably 850 to 950°C, and even more preferably 890 to 910°C.

[0057] As described above, the present invention can provide a rare-earth-element-doped nitride semiconductor device with improved emission intensity and a sharpened emission linewidth, thereby enabling the realization of semiconductor LEDs with high luminance. Furthermore, the sharpened emission linewidth allows for high optical gain, which can greatly contribute to the development of semiconductor lasers.

[0058] In the present invention, the term "nonpolar plane" refers to a plane other than the (0001) plane (c-plane), and specifically includes semi-polar planes such as the (10-12) plane (r-plane), (11-22) plane, and (20-21) plane, as well as non-polar planes such as the (10-10) plane (m-plane) and (11-20) plane (a-plane) (see FIG. 11). However, the plane is not strictly limited to these planes, and some deviation in angle is acceptable. The specific tilt angle relative to the (0001) plane (c-plane) is preferably 3 to 90°, more preferably 30 to 90°, and even more preferably 60 to 90°.

[0059] In the present invention, the base material is not limited to GaN, and so-called GaN-based nitrides such as InN, AlN, or mixed crystals thereof (InGaN, AlGaN, etc.) can also be used as the base material because they have chemical properties equivalent to those of GaN.

[0060] In the manufacture of the rare-earth-element-doped nitride semiconductor device according to the present invention, the rare-earth-element-doped nitride semiconductor layer, which is the active layer, is formed between the p-type layer and the n-type layer. In this case, it is preferable to form the active layer and the p-type and n-type layers in a single formation process, i.e., to form the layers in the reaction vessel in the order of p-type layer, active layer, and n-type layer, or in the order of n-type layer, active layer, and p-type layer, without removing the reaction vessel from the vessel midway.

[0061] This eliminates the interface states between the active layer, p-type layer, and n-type layer, allowing for efficient carrier injection, enabling light emission at low voltage operation of approximately several volts. From the viewpoint of not removing the layer from the reaction vessel during the process, it is preferable to form the n-type and p-type layers by OMVPE, but other growth methods are not excluded. Furthermore, the n-type and p-type layers do not necessarily need to be in contact with the active layer; for example, a carrier blocking layer may be provided between them and the active layer. The active layer is preferably formed to a thickness of 0.1 nm or more.

[0062] The amount of rare earth elements such as Eu added to the active layer is preferably 0.001 to 10 at %, more preferably 0.01 to 10 at %, and even more preferably 0.1 to 10 at %.

[0063] In the production of the above-mentioned Eu-doped nitride semiconductor, the Eu source material (Eu organic source material) for supplying Eu is preferably an Eu compound that has a high vapor pressure and can be efficiently doped. However, (bis(tetramethylmonoalkylcyclopentadienyl)europium) represented by Eu[C5(CH3)4R]2 (R: alkyl group) is more preferred, and among these, bis(normalpropyltetramethylcyclopentadienyl)europium (EuCp pm 2) is preferred.

[0064] That is, for example, Eu(C 11 H 19 Compounds such as Eu(C5H7O2)3 and Eu(C5H7O2)3 have a relatively high vapor pressure and have been commonly used as Eu sources (organic Eu raw materials). However, because they are solid at the operating temperature of around 150°C, there are problems with stability during supply.

[0065] In contrast, (bis(tetramethylmonoalkylcyclopentadienyl)europium) has a relatively low melting point (e.g., EuCp pm Since 2 is a liquid at the operating temperature (49°C), it can be supplied stably by bubbling.

[0066] The substrate on which the active layer is formed is usually made of sapphire, but is not limited to this and may be made of, for example, Si, GaN, GaAs, or the like.

[0067] Furthermore, the present inventors have conducted further experiments and studies and found that if impurities are intentionally added during crystal growth, the emission intensity can be further improved and the emission linewidth can be further sharpened.

[0068] The impurities to be added are preferably oxygen, magnesium, and aluminum.

[0069] When these elements are added together with rare earth elements (co-doping), they are selectively placed in the vicinity of the rare earth element ions, dramatically changing the surrounding local structure and reducing the number of types of luminescence centers that are formed.

[0070] The specific concentration of oxygen added is 1×10 17 ~1×10 20 cm -3 Preferably, it is 1×10 19 ~1×10 20 cm -3 It is more preferable that the amount of magnesium added is 1×10 18 ~1×10 20 cm -3 Preferably, it is 5 x 10 18 ~5×10 19 cm -3 The specific amount of aluminum added is preferably more than 0 atomic % and not more than 40 atomic %, and more preferably 15 to 35 atomic %.

[0071] [3] Specific implementation form The present invention will be described in more detail below by way of an experimental example in which an Eu-doped nitride semiconductor device is fabricated as a specific embodiment.

[0072] 1. Eu-doped nitride semiconductor device in this experimental example The basic structure of the Eu-doped nitride semiconductor device fabricated in this experimental example is shown in Figure 12. In this experimental example, as shown in Figure 12, a Eu-doped nitride semiconductor was grown using a GaN template in which an undoped GaN buffer layer (6 μm thick) of the (20-21) plane was formed on the (22-43) plane of a sapphire substrate.

[0073] Specifically, the Eu-doped nitride semiconductor device shown in FIG. 12 was fabricated according to the growth sequence shown in FIG.

[0074] First, an undoped GaN layer (thickness 1.8 μm) was grown on the undoped GaN buffer layer of the GaN template at a temperature of 1020°C by using organometallic vapor phase epitaxy (OMVPE).

[0075] Next, an n-layer (2500 nm thick) (not shown) was formed on the undoped GaN layer.

[0076] Next, a Eu-doped GaN layer was grown on the n-layer at a growth rate of 1.0 μm / h under growth conditions of a temperature of 900° C. and a pressure of 100 kPa, thereby forming an active layer with a thickness of 400 nm.

[0077] Next, an undoped GaN layer (thickness: 20 nm) was deposited on the active layer as a cap layer.

[0078] Finally, a p-layer (70 nm thick) (not shown) was laminated on the undoped GaN layer (cap layer).

[0079] In this experimental example, trimethylgallium (TMGa) was used as the Ga source material, and the supply amount was set to 5.3 sccm.

[0080] Ammonia (NH3) was used as the N raw material, and the supply amount was 4.0 slm.

[0081] The Eu source was EuCp bubbled with carrier gas (hydrogen gas: H2). pm2 was used, and the supply amount was 1.5 slm (supply temperature: 132.5°C).

[0082] At this time, the piping valves of the OMVPE equipment were changed from standard specifications (heat-resistant temperature 80-100°C) to special high-temperature specifications, which allowed the supply temperature of the Eu raw material to be kept at a sufficiently high temperature of 115-135°C, ensuring that a sufficient amount of Eu could be supplied to the reaction tube.

[0083] The formation of each layer was carried out in a series of steps without removing the sample from the reaction tube during the process, so as to prevent interruption of growth.

[0084] 2. Comparative experiment example Separately, for comparison, a Eu-doped nitride semiconductor device (comparative experimental example) was fabricated using a GaN template in which an undoped GaN buffer layer (6 μm thick) of the (0001) plane was formed on the (0001) plane of a sapphire substrate, and in which an Eu-doped GaN layer was stacked as an active layer under the same conditions as above, except that the Eu-doped GaN layer was grown at a temperature of 960°C and a pressure of 100 kPa.

[0085] 3. Luminous properties Next, for each of the Eu-doped nitride semiconductor devices obtained in the 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).

[0086] The results are shown in Figure 14. In Figure 14, the vertical axis represents PL intensity (arbitrary units, arb. units) and the horizontal axis represents wavelength (nm).

[0087] As shown in Figure 14, in the experimental example in which the Eu-doped GaN layer was formed on a nonpolar surface, a high peak appeared at a wavelength of around 621 nm, where red light was emitted, and the emission linewidth was also dramatically sharpened. On the other hand, in the comparative experimental example in which the Eu-doped GaN layer was formed on a polar surface, no such high peak appeared even at a wavelength of around 621 nm, and the emission linewidth was also broadened.

[0088] Furthermore, the integrated PL intensity, i.e., the luminescence intensity, calculated by integrating this PL intensity, was found to be approximately doubled, indicating a dramatic increase in luminescence intensity.

[0089] Next, the relationship between the emission intensity (integrated PL intensity) and excitation intensity (excitation power) of each Eu-doped nitride semiconductor device obtained in the experimental example and comparative experimental example was measured using a He—Cd laser (measurement temperature: room temperature). The results are shown in Figures 15, 16, and 17.

[0090] 15 shows the relationship between wavelength and PL intensity in the Eu-doped nitride semiconductor device obtained in the experimental example, measured at four levels of excitation intensity and normalized by peak intensity, with the vertical axis representing PL intensity (arbitrary units, arb. units) and the horizontal axis representing wavelength (nm). Figure 16 shows the emission spectrum obtained by similar measurement for the Eu-doped nitride semiconductor device obtained in the comparative experimental example.

[0091] Figure 17 is a plot of the relationship between the emission intensity, calculated by integrating the PL intensities of the emission spectra obtained in Figures 15 and 16, and the excitation intensity, where the vertical axis represents the emission intensity (arbitrary units, arb.units) and the horizontal axis represents the excitation intensity (mW).

[0092] As shown in Figure 15, in the experimental example in which a Eu-doped GaN layer was formed on a nonpolar plane, similar emission spectra were obtained regardless of the excitation intensity, and a sharp peak was maintained with an emission linewidth of 1.33 nm.

[0093] In contrast, in a comparative experiment in which a Eu-doped GaN layer was formed on the polar plane, as shown in Figure 16, the emission spectrum changed depending on the excitation intensity, and the emission linewidth was 3.03 nm, more than double that of the original.

[0094] Furthermore, as can be seen from Figure 17, in the comparative experimental example, significant saturation of the emission intensity was observed under strong excitation conditions, whereas in the experimental example, the saturation of the emission intensity was significantly suppressed even under strong excitation conditions, and the slope of the emission intensity with respect to the excitation intensity (SLOPE) was more than twice as large. This confirms that by constructing a semiconductor LED using the rare earth element-doped nitride semiconductor element according to the present invention, it is possible to provide a semiconductor LED with significantly improved performance.

[0095] Furthermore, from FIG. 15, it was confirmed that by constructing a semiconductor laser using the rare-earth element-doped nitride semiconductor element according to the present invention, it is possible to provide a semiconductor laser with significantly improved performance due to the characteristics essential for the development of semiconductor lasers, namely, ultrastability and narrow linewidth.

[0096] Figure 18 shows the CEES mapping obtained from an experimental example, and Figure 19 shows the CEES mapping obtained from a comparative experimental example. In Figures 18 and 19, (a) shows the relationship between the emission energy (eV) and excitation energy (eV) measured using a dye laser (measurement temperature: 10 K). And (b) shows the relationship between the emission energy (eV), excitation energy (eV), and PL intensity (arbitrary units, arb. units) measured using a dye laser (measurement temperature: 10 K).

[0097] 18 and 19, it can be seen that by forming a Eu-doped GaN layer on a nonpolar plane, anisotropic strain reflecting the asymmetry is introduced, leading to the selective formation of luminescence centers and an increase in the luminescence intensity by OMVPE7.

[0098] Based on the results obtained from the experimental examples and comparative experimental examples described above, Figures 20 to 22 and Table 1 show the relationship between the concentrations of the emission centers OMVPE4 and OMVPE7 and the PL intensity when Eu-doped GaN layers are formed on the (0001) plane and the (20-21) plane, respectively.

[0099] From Figure 20, when comparing the case where the Eu-doped GaN layer is formed on the (0001) plane with the case where the Eu-doped GaN layer is formed on the (20-21) plane, it can be seen that there is not much difference in the concentration of the luminescence center OMVPE4, but the concentration of the luminescence center OMVPE7 is much higher when the Eu-doped GaN layer is formed on the (20-21) plane.

[0100] When comparing the PL intensities, Figures 21 and 22 show that the PL intensity is higher when the Eu-doped GaN layer is formed on the (20-21) plane for both OMVPE4 and OMVPE7. In particular, the PL intensity of the emission center OMVPE7 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.

[0101] As shown in Table 1, when the Eu-doped GaN layer is formed on the (0001) plane, the abundance ratio of the OMVPE7 luminescence center to the OMVPE4 luminescence center is small at 0.002, but when the Eu-doped GaN layer is formed on the (20-21) plane, the abundance ratio of the OMVPE7 luminescence center to the OMVPE4 luminescence center is overwhelmingly high at 0.162.

[0102] [Table 1]

[0103] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-described embodiments. Various modifications can be made to the above-described embodiments within the scope of the same or equivalent to the present invention.

Claims

1. A method for manufacturing a rare earth element-doped nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of two or more of these, comprising: Using metal organic vapor phase epitaxy, A method for producing a rare-earth-element-doped nitride semiconductor device, comprising the steps of: forming an active layer on a non-polar surface of a substrate having a non-polar surface with an inclination angle of 30 to 90 degrees with respect to a (0001) plane (c-plane) under a temperature condition of 800 to 1000°C, using GaN, InN, AlN or a mixed crystal of any two or more of these as a host material; and adding a rare-earth element to substitute for Ga, In or Al constituting the host material.

2. The method for manufacturing a rare earth element-doped nitride semiconductor device described in claim 1, characterized in that the nonpolar plane is any one of the (10-12) plane (r-plane), (11-22) plane, (20-21) plane, (10-10) plane (m-plane), and (11-20) plane (a-plane).

3. 3. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 1, wherein when the active layer is formed between a p-type layer and an n-type layer, the formation of the active layer and the formation of the p-type layer and the n-type layer are performed in a single formation process.

4. A method for manufacturing a rare earth element-doped nitride semiconductor element described in any one of claims 1 to 3, characterized in that a rare earth element-doped nitride semiconductor element is manufactured in which the abundance ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 in the active layer is 0.10 or more.

5. 5. The method for manufacturing a rare earth element-doped 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 %.

6. 6. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 1, wherein the active layer is formed by controlling the thickness of the active layer to be 0.1 nm or more.

7. 7. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 1, wherein Eu is used as the rare earth element to be doped into the base material, and a red light-emitting rare earth element-doped nitride semiconductor device is manufactured.

8. 8. The method for producing a rare earth element-doped nitride semiconductor device according to claim 7, wherein (bis(tetramethylmonoalkylcyclopentadienyl)europium) is used as the Eu raw material.

9. 9. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 1, wherein the active layer is formed by controlling the number of luminescence centers to be two to six.

10. 10. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 1, wherein oxygen is added together with the rare earth element to form the active layer.

11. The concentration of added oxygen is 1×10 １７ ~1 x 10 ２０ cm －３ 11. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 10, wherein the active layer is formed by controlling the temperature to be higher than the temperature of the nitride semiconductor layer.

12. 12. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 1, wherein the active layer is formed by adding magnesium or aluminum together with the rare earth element.

13. The amount of magnesium added was 1×10 １８ ~1 x 10 ２０ cm －３ 13. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 12, wherein the active layer is formed by controlling the temperature to be higher than the temperature of the nitride semiconductor layer.

14. 13. The method for manufacturing a rare earth element-doped nitride semiconductor device according to claim 12, wherein the active layer is formed by controlling the amount of aluminum added to be greater than 0 atomic % but not greater than 40 atomic %.

15. A method for manufacturing a rare earth element-doped nitride semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more of these, comprising: Using metal organic vapor phase epitaxy, A method for producing a rare-earth-element-doped nitride semiconductor device, characterized in that, under a temperature condition of 800 to 1000°C, a substrate having a nonpolar plane selected from a (10-12) plane (r-plane), a (11-22) plane, a (20-21) plane, a (10-10) plane (m-plane), and a (11-20) plane (a-plane) is formed on the nonpolar plane by adding a rare-earth element to a base material of GaN, InN, AlN, or a mixed crystal of any two or more of these, so as to substitute for Ga, In, or Al constituting the base material, thereby producing a rare-earth-element-doped nitride semiconductor device.

16. A method for manufacturing a rare earth element-doped nitride semiconductor element as described in claim 15, characterized in that a rare earth element-doped nitride semiconductor element is manufactured in which the abundance ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 in the active layer is 0.10 or more.

17. A rare earth element-doped nitride semiconductor device having a base material of GaN, InN, AlN, or a mixed crystal of two or more of these, A rare-earth-element-doped nitride semiconductor device, characterized in that an active layer is formed on a non-polar surface of a substrate having a non-polar surface with an inclination angle of 30 to 90 degrees with respect to a (0001) plane (c-plane), to which a rare-earth element is added so as to substitute for Ga, In, or Al constituting the base material.

18. The rare earth element-doped nitride semiconductor element described in Claim 17, characterized in that the nonpolar plane is any one of the (10-12) plane (r-plane), (11-22) plane, (20-21) plane, (10-10) plane (m-plane), and (11-20) plane (a-plane).

19. A rare earth element-doped nitride semiconductor device according to claim 17 or claim 18, characterized in that in the active layer, the abundance ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 is 0.10 or more.

20. 20. The rare earth element-doped nitride semiconductor device according to claim 17, wherein the active layer is sandwiched between a p-type layer and an n-type layer.

21. 21. The rare earth element-doped nitride semiconductor device according to claim 17, wherein the number of types of luminescence centers formed in the active layer is 2 to 6.

22. 22. The rare earth element-doped nitride semiconductor device according to claim 17, wherein the rare earth element is Eu as the rare earth element added to the base material, and the rare earth element-doped nitride semiconductor device is a red-light emitting rare earth element-doped nitride semiconductor device.

23. A rare earth element-doped nitride semiconductor device having GaN, InN, AlN, or a mixed crystal of any two or more of these as a base material, A rare-earth-element-doped nitride semiconductor device, characterized in that an active layer to which a rare-earth element is added is formed on a non-polar surface of a substrate having any one of a (10-12) plane (r-plane), a (11-22) plane, a (20-21) plane, a (10-10) plane (m-plane), and a (11-20) plane (a-plane), so as to substitute for Ga, In, or Al constituting the base material.

24. The rare earth element-doped nitride semiconductor device according to claim 23, characterized in that in the active layer, the abundance ratio of the luminescence center OMVPE7 to the luminescence center OMVPE4 is 0.10 or more.

25. 25. A semiconductor LED comprising the rare earth element-doped nitride semiconductor element according to claim 17.

26. 25. A semiconductor laser comprising the rare earth element-doped nitride semiconductor device according to claim 17.

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