Wavelength conversion element, manufacturing method for wavelength conversion element, and light-emitting device

Abstract

To provide a wavelength conversion element that facilitates control of the thickness of a Group-III nitride semiconductor crystal layer, and facilitates the manufacture by a simple process.SOLUTION: A wavelength conversion element according to the present disclosure includes a first substrate having a first main surface, a second substrate having a second main surface facing the first main surface, and a Group-III nitride semiconductor crystal layer provided between the first main surface and the second main surface. The Group-III nitride semiconductor crystal layer has a polarity inverted structure including a first crystal layer provided on the first main surface and having one polarity of Group-III polarity and nitrogen polarity, and a second crystal layer provided on the second main surface, forming an interface with the first crystal layer, and having the other polarity. In the first crystal layer, two cavities that are depressed from the interface toward the first main surface, penetrating the first crystal layer along the interface, and separated from each other are formed. The first crystal layer and the second crystal layer between the two cavities form a waveguide. The cavity accommodates a material with a smaller refractive index than that of the waveguide.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a wavelength conversion element, a method for manufacturing a wavelength conversion element, and a light emitting device. [Background technology]

[0002] For example, a wavelength conversion element having a quasi-phase matching structure is disclosed in Patent Document 1. The wavelength conversion element of Patent Document 1 has a group III nitride semiconductor crystal layer, and has a polarity inversion structure in the group III nitride semiconductor crystal layer.

[0003] In the wavelength conversion element of Patent Document 1, as shown in Fig. 13(a), a group III nitride semiconductor crystal layer, for example, aluminum nitride (AlN) layers 103a and 103b are formed on sapphire substrates 102a and 102b. As shown in Fig. 13(b) and Fig. 13(c), the two AlN layers 103a and 103b are faced and bonded to form a polarity inversion structure. As shown in Fig. 13(d) to Fig. 13(f), the upper sapphire substrate 102b is peeled off, and the peripheries of the AlN layers 103a and 103b are removed, and then a protective layer 107 is formed to cover the AlN layers 103a and 103b. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7100309 specification Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a demand for controlling the thickness of a group III nitride semiconductor crystal layer with high precision in order to obtain light of a desired wavelength by a wavelength conversion element. However, in the wavelength conversion element of Patent Document 1, when the sapphire substrate is peeled off from the bonded AlN layer, a part of the surface layer of the AlN layer is also removed, and the thickness of the AlN layer may change. Therefore, there is a demand for a wavelength conversion element that suppresses unintended changes in the thickness of the group III nitride semiconductor crystal layer and makes it easy to control the thickness. In addition to the peeling process, a process of removing the outer periphery of the AlN layer and a process of forming a protective layer are necessary, which results in a large number of processes.

[0006] Therefore, an object of the present disclosure is to solve the above problems by providing a wavelength conversion element that facilitates control of the thickness of a Group III nitride semiconductor crystal layer and that can be easily manufactured through simple steps. [Means for solving the problem]

[0007] A wavelength conversion element according to the present disclosure comprises a first substrate having a first main surface, a second substrate having a second main surface opposite to the first main surface, and a Group III nitride semiconductor crystal layer provided between the first and second main surfaces, the Group III nitride semiconductor crystal layer forming a polarity inversion structure having a first crystal layer provided on the first main surface and having one of Group III polarity and nitrogen polarity, and a second crystal layer provided on the second main surface and having the other of nitrogen polarity and Group III polarity forming an interface with the first crystal layer, the first crystal layer having two cavities recessed from the interface toward the first main surface, penetrating the first crystal layer along the interface and spaced apart from one another, the first crystal layer and the second crystal layer between which form a waveguide, the cavity containing a material having a smaller refractive index than the waveguide.

[0008] A manufacturing method of a wavelength conversion element according to the present disclosure is a manufacturing method of a wavelength conversion element including a first substrate, a second substrate, and a Group III nitride semiconductor crystal layer having a first crystal layer and a second crystal layer, the method including the steps of: forming a first crystal layer having one of Group III polarity and nitrogen polarity on the first substrate; forming a second crystal layer having the same polarity as the first crystal layer on the second substrate; forming two grooves having a gap in between in the first crystal layer; bonding the first crystal layer and the second crystal layer having the same polarity as the first crystal layer opposite each other to form a polarity inversion structure, thereby forming a bonded body in which cavities corresponding to the grooves are formed; and cutting the wavelength conversion element from the bonded body so that the cavities are exposed at an end face intersecting the extension direction of the cavities.

[0009] A light emitting device according to the present disclosure includes a wavelength conversion element and a fundamental wave laser light source that irradiates the wavelength conversion element with laser light, and the laser light emitted from the fundamental wave laser light source is irradiated onto a waveguide. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a wavelength conversion element that allows easy control of the thickness of a Group III nitride semiconductor crystal layer and that can be easily manufactured through simple steps. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a side view of a wavelength conversion element according to a first embodiment of the present disclosure. [Diagram 2] 2 is a cross-sectional view of the wavelength conversion element taken along the line AA in FIG. [Figure 3A] FIG. 2 is a top view showing a step of a manufacturing method of the wavelength conversion element according to the first embodiment. [Figure 3B] FIG. 2 is a top view showing a step of a manufacturing method of the wavelength conversion element according to the first embodiment. [Figure 3C] FIG. 2 is a top view showing a step of a manufacturing method of the wavelength conversion element according to the first embodiment. [Figure 3D] FIG. 2 is a top view showing a step of a manufacturing method of the wavelength conversion element according to the first embodiment. [Figure 4A]3 is a cross-sectional view showing a step of a manufacturing method of the wavelength conversion element according to the first embodiment. FIG. [Figure 4B] 3 is a cross-sectional view showing a step of a manufacturing method of the wavelength conversion element according to the first embodiment. FIG. [Figure 4C] 3 is a cross-sectional view showing a step of a manufacturing method of the wavelength conversion element according to the first embodiment. FIG. [Diagram 5] 1 is a schematic diagram of a light emitting device including a wavelength conversion element according to a first embodiment. [Figure 6] 3 is an end view showing a state in which a fundamental laser beam is irradiated onto an end face of the wavelength conversion element according to the first embodiment. FIG. [Figure 7] FIG. 11 is a cross-sectional view of a wavelength conversion element according to a second embodiment of the present disclosure. [Figure 8A] 6 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the second embodiment. [Figure 8B] 6 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the second embodiment. [Figure 8C] 6 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the second embodiment. [Figure 9] FIG. 11 is a cross-sectional view of a wavelength conversion element according to a third embodiment of the present disclosure. [Figure 10A] 11 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the third embodiment. [Figure 10B] 11 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the third embodiment. [Figure 10C] 11 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the third embodiment. [Figure 10D] 11 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the third embodiment. [Figure 10E] 11 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the third embodiment. [Figure 11] FIG. 11 is a cross-sectional view of a wavelength conversion element according to a fourth embodiment of the present disclosure. [Figure 12A] FIG. 11 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the fourth embodiment. [Figure 12B]FIG. 11 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the fourth embodiment. [Figure 12C] FIG. 11 is a cross-sectional view showing a step of a manufacturing method of a wavelength conversion element according to the fourth embodiment. [Figure 13] 1A to 1C are schematic diagrams showing a manufacturing process of a conventional wavelength conversion element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the width direction of the wavelength conversion element 4 is defined as the X direction, the longitudinal direction of the wavelength conversion element 4 perpendicular to the X direction is defined as the Y direction, and the height direction perpendicular to the XY plane is defined as the Z direction.

[0013] [Embodiment 1] <Wavelength conversion element> (Overall composition) Fig. 1 is a side view of a wavelength conversion element 4. As shown in Fig. 1, the wavelength conversion element 4 includes a first substrate 3A, a second substrate 3B, and a group III nitride semiconductor crystal layer 1 sandwiched between the substrates 3A and 3B. The group III nitride semiconductor crystal layer 1 has two crystal layers, group III nitride semiconductor crystal layers 11 and 12, bonded to each other.

[0014] The substrates 3A and 3B are substrates on which the group III nitride semiconductor crystal layers 11 and 12 are formed, respectively. Specifically, the first substrate 3A has a first main surface R1 on which the group III nitride semiconductor crystal layer 11 is formed, and the second substrate 3B has a second main surface R2 on which the group III nitride semiconductor crystal layer 12 is formed. In the manufacturing process of the wavelength conversion element 4, the group III nitride semiconductor crystal layers 11 and 12 are bonded to each other while facing each other. Therefore, in the wavelength conversion element 4, the first main surface R1 and the second main surface R2 face each other, and the group III nitride semiconductor crystal layer 1 is provided between the first main surface R1 and the second main surface R2. In the first embodiment, the first main surface R1 and the second main surface R2 extend along each other and may be parallel to each other.

[0015] The substrates 3A and 3B are, for example, sapphire substrates.

[0016] The group III nitride semiconductor crystal layers 11 and 12 are each a crystal layer whose main component is aluminum nitride (AlN), and may be referred to as an AlN layer.

[0017] The AlN layers 11 and 12 transmit light having a predetermined wavelength, such as a predetermined laser light. The AlN layers 11 and 12 have an end face T1 on one side and an end face T2 on the other side, and the end faces T1 and T2 function as an incident surface and an exit surface, respectively. The end faces T1 and T2 are exposed from other members. The end faces T1 and T2 intersect with the longitudinal direction (Y direction) of the AlN layers 11 and 12, and in the first embodiment, are perpendicular to the longitudinal direction of the AlN layers 11 and 12.

[0018] The first AlN layer 11 is a crystal layer formed on the first substrate 3A and grown in a direction (-Z direction) perpendicular to the first main surface R1. The first AlN layer 11 has a third main surface R3 opposite the first main surface R1. The second AlN layer 12 is a crystal layer formed on the second substrate 3B and grown in a direction (+Z direction) perpendicular to the second main surface R2. The second AlN layer 12 has a fourth main surface R4 opposite the second main surface R2. The main surfaces R3 and R4 are bonded to each other to form an interface 13. The interface 13 may be referred to as a "bonded interface."

[0019] In the film-formed state, the AlN layers 11 and 12 have the same polarity (group III polarity or nitrogen polarity). On the other hand, in the manufacturing process of the wavelength conversion element 4, when the AlN layers 11 and 12 having the same polarity are opposed to each other and the main surfaces R3 and R4 are bonded, the AlN layers 11 and 12 form a polarity-inverted structure. Specifically, when the AlN layers 11 and 12 are opposed to each other, the c-axes of the AlN layers 11 and 12 are inverted by 180 degrees, the polarities of the AlN layers 11 and 12 are inverted to each other, and the AlN layers 11 and 12 are bonded in a polarity-inverted state. That is, in the bonded state, the polarities of the AlN layers 11 and 12 are different above and below the interface 13 (Z direction in FIG. 2). The first AlN layer 11 has one polarity of group III polarity or nitrogen polarity, and the second AlN layer 12 has a polarity of nitrogen polarity or group III polarity different from that of the first AlN layer 11. In the first embodiment, the first AlN layer 11 has group III polarity and the second AlN layer 12 has nitrogen polarity, but they may be reversed.

[0020] In the first embodiment, the principal surfaces R1 and R2 and the interface 13 may extend along each other and be parallel to each other. The interface 13 may extend along the XY plane and be parallel to the XY plane.

[0021] For example, when converting light having a wavelength of 450 nm to 225 nm, the thicknesses of the AlN layers 11 and 12 are almost the same, preferably 100 nm to 200 nm, more preferably about 150 nm.

[0022] Fig. 2 is a cross-sectional view of the wavelength conversion element 4 taken along line AA in Fig. 1. As shown in Fig. 2, the first AlN layer 11 has two cavities 5 recessed from the interface 13 toward the first main surface R1. The two cavities 5 are provided with a gap between them. A part of the first AlN layer 11 is located between the two cavities 5. The two cavities 5 are aligned in the width direction (X direction) along the interface 13.

[0023] The two cavities 5 extend in a penetration direction (Y direction) along the interface 13, which is perpendicular to the width direction (X direction), and penetrate the first AlN layer 11. Therefore, the two cavities 5 are exposed at end faces T1 and T2 (FIG. 1), and each form a through hole that communicates from end face T1 to end face T2. Note that the penetration direction is not limited to the Y direction, and may include an X direction component as long as it is along the interface 13.

[0024] The distance between the two cavities 5 is approximately constant in the penetration direction (Y direction). The two cavities 5 may extend parallel to each other. Furthermore, the cross-sectional shape of each cavity 5 as viewed from the penetration direction (Y direction) is approximately constant in the penetration direction (Y direction). In other words, the two cross-sectional shapes of the cavity 5 defined at any two positions in the penetration direction (Y direction) are approximately the same as each other. Here, "approximately constant" means that it includes errors due to processing, etc. In the first embodiment, the cross-sectional shape of the cavity 5 is rectangular.

[0025] Since they are recessed from the interface 13, the two cavities 5 expose the second AlN layer 12. In the first embodiment, the two cavities 5 penetrate the first AlN layer 11 in the vertical direction (Z direction) and also expose the first substrate 3A.

[0026] The portion of the first AlN layer 11 sandwiched between the left and right cavities 5 forms a waveguide 6 together with the second AlN layer 12 that forms an interface 13 with the portion of the first AlN layer 11. In other words, the AlN layers 11 and 12 between the cavities 5 form the waveguide 6. Since the waveguide 6 has a polarity inversion structure above and below the interface 13, the light propagating within the waveguide 6 is wavelength converted.

[0027] The first AlN layer 11 in the waveguide 6 contacts the left and right cavities 5 and has side surfaces 6A extending in the vertical direction (Z direction) from the interface 13 to the first substrate 3A. The side surfaces 6A define each of the cavities 5 on one side.

[0028] When viewed from the Y direction, the waveguide 6 is located on one side of the cavity 5, and the first AlN layer 11 is located on the other side of the cavity 5. In other words, the cavity 5 does not reach the outer periphery of the wavelength conversion element 4 at most. With this configuration, the first substrate 3A is supported from below by the waveguide 6 on one side of the cavity 5, and is supported from below by the first AlN layer 11 on the other side of the cavity 5. Therefore, the first substrate 3A does not become a cantilever beam, and forms a structure that is stable against external forces.

[0029] The width of the waveguide 6 is determined by the spacing between the cavities 5. Since the waveguide 6 is defined by the cavities 5 having a substantially constant spacing, the width of the waveguide 6 is substantially constant in the penetration direction (Y direction). The width of the waveguide 6 is preferably 0.5 μm to 200 μm, more preferably 0.5 μm to 10 μm. The narrower the width of the waveguide 6, the higher the efficiency of wavelength conversion. The width of the cavities 5 is preferably 0.5 μm to 200 μm, more preferably 0.5 μm to 10 μm. It is preferable that the focused diameter of the laser light irradiated to the waveguide 6 described later has a width dimension approximately equal to the width of the first AlN layer 11 sandwiched between the cavities 5 and a height dimension approximately equal to the combined height of the first AlN layer 11 and the second AlN layer 12. With such dimensions, the wavelength conversion element 4 can efficiently convert the wavelength of the laser light.

[0030] Each numerical value in this specification is appropriately set depending on the wavelength of the incident fundamental wave light and the wavelength of the target wavelength-converted light, etc.

[0031] The cross-sectional shape of the waveguide 6 as viewed from the penetration direction (Y direction) is approximately constant along the penetration direction. In the first embodiment, the cross-sectional shape of the waveguide 6 is a convex shape formed by a combination of the first AlN layer 11 sandwiched between the cavities 5 and the second AlN layer 12 extending beyond the first AlN layer 11. Note that in other embodiments, the cross-sectional shape or width of the cavities 5 or the waveguide 6 may vary along the penetration direction. For example, the cross-sectional shape of the waveguide 6 may gradually change along the penetration direction (i.e., the waveguiding direction).

[0032] When the wavelength conversion element 4 is placed in air, the cavity 5 penetrates the first AlN layer 11 in the Y direction, and therefore air enters the cavity 5. In other words, the cavity 5 contains air and is filled with air. The refractive index varies depending on the wavelength, but at a wavelength of 450 nm, the refractive index of the cavity 5 is the refractive index of air (1.00), which is smaller than the refractive index of the AlN layers 11 and 12 (2.09).

[0033] Furthermore, the refractive index of substrates 3A and 3B (the refractive index of sapphire, 1.77) is smaller than the refractive index of waveguide 6. The light incident on waveguide 6 undergoes wavelength conversion while traveling within waveguide 6.

[0034] (effect) The wavelength conversion element 4 according to the first embodiment can provide the following effects.

[0035] As described above, the wavelength conversion element 4 of the first embodiment includes the first substrate 3A having the first main surface R1, the second substrate 3B having the second main surface R2 facing the first main surface R1, and the group III nitride semiconductor crystal layer 1 provided between the first main surface R1 and the second main surface R2. The group III nitride semiconductor crystal layer 1 forms a polarity inversion structure having a first crystal layer (first AlN layer 11) and a second crystal layer (second AlN layer 12). The first AlN layer 11 is provided on the first main surface R1 and has one polarity of group III polarity or nitrogen polarity. The second AlN layer 12 is provided on the second main surface R2 and has the other polarity of nitrogen polarity or group III polarity, forming an interface 13 with the first AlN layer 11. Two cavities 5 are formed in the first AlN layer 11, recessed from the interface 13 toward the first main surface R1, penetrating the first AlN layer 11 along the interface 13, and spaced apart from each other. The first AlN layer 11 and the second AlN layer 12 between the two cavities 5 form a waveguide 6. The cavity 5 contains a material having a smaller refractive index than the waveguide 6.

[0036] With this configuration, the waveguide 6 can be formed, and there is no need to peel off the first substrate 3A and cover the AlN layers 11, 12 with other members. This suppresses unintended changes in the thickness of the AlN layers 11, 12 caused by peeling off the first substrate 3A, and facilitates control of the thickness of the AlN layers 11, 12 in the wavelength conversion element 4. The AlN layers 11, 12 after bonding can easily maintain the thickness of the AlN layers 11, 12 that was controlled with high precision by CMP or the like before bonding. Furthermore, the manufacturing process of the wavelength conversion element 4 is simplified, making it easier to manufacture.

[0037] In the wavelength conversion element 4 of the first embodiment, the cross-sectional shape of each of the cavities 5 viewed from the penetration direction (Y direction) in which the cavities 5 penetrate the first AlN layer 11 is approximately constant throughout the penetration direction.

[0038] With such a configuration, not only can the cavity 5 be easily processed, but also the cavity 5 can be manufactured through a simple process. Also, it becomes easier to make the cross-sectional shape and width of the waveguide 6 substantially constant along the penetration direction.

[0039] In the wavelength conversion element 4 of the first embodiment, the cavity 5 contains a gas.

[0040] With this configuration, the process of filling the cavity 5 with a solid can be omitted, compared to a structure in which the cavity 5 contains a solid, and therefore the wavelength conversion element 4 can be manufactured more easily.

[0041] In the wavelength conversion element 4 of the first embodiment, the Group III nitride semiconductor crystal layer 1 contains aluminum nitride as a main component.

[0042] With this configuration, a polarity inversion structure can be formed.

[0043] In the wavelength conversion element 4 of the first embodiment, the refractive index of the first substrate 3 A and the second substrate 3 B is smaller than the refractive index of the waveguide 6 .

[0044] With such a configuration, the progression of the incident light through the waveguide 6 can be promoted.

[0045] <Method of manufacturing wavelength conversion element> Here, a method for manufacturing the wavelength conversion element 4 will be described.

[0046] 3A to 3D are top views showing a manufacturing method of the wavelength conversion element 4. Fig. 4A to Fig. 4C are cross-sectional views of one wavelength conversion element 4 showing a manufacturing method of the wavelength conversion element 4.

[0047] (1) As shown in Figures 3A and 4A, AlN layers 11 and 12 are formed on the main surfaces R1 and R2 of the substrates 3A and 3B, respectively. The AlN layers 11 and 12 are formed under the same conditions. Therefore, the AlN layers 11 and 12 have the same polarity in the vertical direction (Z direction). The thickness of the AlN layers 11 and 12 may be adjusted to a desired thickness with high precision by CMP, surface polishing, etc. after the film formation. The thickness of the AlN layers 11 and 12 is 100 nm or more and 200 nm or less, preferably around 150 nm, as described above.

[0048] (2) As shown in Figs. 3B and 4B, the first AlN layer 11, one of the AlN layers 11 and 12, is processed by dry etching or the like to form grooves 2 corresponding to the cavities 5. Specifically, as shown in Fig. 3B, a plurality of pairs of grooves 2 are formed in one first AlN layer 11. By such a process, a plurality of wavelength conversion elements 4 can be manufactured at the same time. The pairs of grooves 2 may extend parallel to each other with a substantially constant interval. In addition, the cross-sectional shape of the grooves 2 is substantially constant throughout the Y direction in which the grooves 2 extend. In Fig. 4B, the grooves 2 may penetrate the first AlN layer 11 and bite into the first substrate 3A.

[0049] (3) As shown in Figs. 3C and 4C, the first AlN layer 11 in which the grooves 2 are formed is bonded to the second AlN layer 12 of the same polarity in the vertical direction (Z direction) to form a polarity inversion structure. When bonding, the AlN layers 11 and 12 may be pressure-bonded at room temperature or an appropriate temperature. In the bonded state, a bonded body 15 is formed between the substrates 3A and 3B and the AlN layers 11 and 12. In the bonded body 15, the substrates 3A and 3B are on the outside, sandwiching the AlN layers 11 and 12 between them. In addition, a cavity 5 corresponding to the grooves 2 is formed inside the bonded body 15. Since the grooves 2 are formed only in the first AlN layer 11 of one of the AlN layers 11 and 12, highly accurate alignment of the grooves 2 is not required in the bonding process, and manufacturing is easy.

[0050] (4) Fig. 3D shows one wavelength conversion element 4 cut out from a bonded body 15 of substrates 3A, 3B and AlN layers 11, 12. One wavelength conversion element 4 is cut out from the bonded body 15 by machining or the like. One wavelength conversion element 4 is cut out from the bonded body 15 so that the cavity 5 is exposed at an end face intersecting with the penetration direction (Y direction). In the first embodiment, the end face of the cut out wavelength conversion element 4 is perpendicular to the penetration direction (Y direction) and includes end faces T1, T2 of the AlN layers 11, 12.

[0051] The surface of the end face of the cut wavelength conversion element 4 may be subjected to additional processes such as polishing and / or cleaning.

[0052] (effect) According to the manufacturing method of the wavelength conversion element 4 according to the first embodiment, the following effects can be achieved.

[0053] The manufacturing method of the wavelength conversion element 4 of the first embodiment is a manufacturing method of the wavelength conversion element 4 including a first substrate 3A, a second substrate 3B, and a group III nitride semiconductor crystal layer 1 having a first AlN layer 11 and a second AlN layer 12. The manufacturing method includes a step of forming a first AlN layer 11 having one of group III polarity and nitrogen polarity on the first substrate 3A, and a step of forming a second AlN layer 12 having the same polarity as the first AlN layer 11 on the second substrate 3B. The manufacturing method further includes a step of forming two grooves 2 with a gap in the first AlN layer 11. The manufacturing method further includes a step of forming a polarity inversion structure by bonding the first AlN layer 11 and the second AlN layer 12 having the same polarity in an opposed manner, and forming a bonded body 15 in which a cavity 5 corresponding to the groove 2 is formed. The manufacturing method further includes a step of cutting the wavelength conversion element 4 from the bonded body 15 so that the cavity 5 is exposed at an end face intersecting the direction in which the cavity 5 extends.

[0054] With this configuration, it is possible to omit the process of peeling off the first substrate 3A and covering the AlN layers 11, 12 with another member. Therefore, unintended changes in the thickness of the AlN layers 11, 12 caused by peeling off the first substrate 3A are suppressed, and it becomes easy to control the thickness of the AlN layers 11, 12 in the wavelength conversion element 4. Furthermore, by omitting the process of peeling off the first substrate 3A and covering the AlN layers 11, 12 with another member, it is possible to reduce the number of processes.

[0055] The manufacturing method of the wavelength conversion element 4 of the first embodiment further includes a step of performing at least one of polishing and cleaning on the end face of the wavelength conversion element 4 where the cavity 5 is exposed.

[0056] With this configuration, irregularities formed on the surface of the end face of the wavelength conversion element 4 and dirt adhering thereto can be removed, and the end face can be treated to be in a good condition as an incident surface for laser light.

[0057] <Light-emitting device including wavelength conversion element> FIG. 5 is a schematic diagram of a light emitting device 100 including a wavelength conversion element 4. The light emitting device 100 is a laser device that irradiates laser light. As shown in FIG. 5, the light emitting device 100 has a fundamental laser light source 7, a condenser lens 9, and a wavelength conversion element 4. The fundamental laser light source 7 emits fundamental laser light 8 having a wavelength of, for example, 450 nm. The condenser lens 9 condenses the emitted fundamental laser light 8. The fundamental laser light 8 condensed by the condenser lens 9 is irradiated onto an end face of the wavelength conversion element 4. In the wavelength conversion element 4, the guide direction of the fundamental laser light 8 is along the Y direction.

[0058] Fig. 6 is an end view showing a state in which the fundamental laser light 8 is irradiated onto the end face of the wavelength conversion element 4. As shown in Fig. 6, the fundamental laser light 8 condensed by the condensing lens 9 is irradiated onto the waveguide 6 including the interface 13 at the end face T1 of the AlN layers 11 and 12. That is, the condensed diameter 8B of the fundamental laser light 8 includes the interface 13 in the waveguide 6.

[0059] The fundamental laser light 8 irradiated onto the waveguide 6 travels in the +Y direction within the waveguide 6 and is wavelength converted.

[0060] A focused diameter 8B of the fundamental laser light 8 may be large enough to be contained within the waveguide 6, or may be larger than the waveguide 6. Regardless of the relationship between the focused diameter 8B and the waveguide 6, the fundamental laser light 8 propagating through the waveguide 6 is wavelength converted.

[0061] Returning to FIG. 5, the fundamental laser light 8 is wavelength-converted and emitted from the opposite end face (end face T2) of the waveguide 6 as wavelength-converted light 10 having a wavelength of 225 nm.

[0062] On the other hand, the condenser lens 9 may be omitted from the configuration of the light emitting device 100. In the light emitting device 100, the fundamental laser light 8 may be directly incident on the wavelength conversion element 4 by direct coupling as used in semiconductor lasers.

[0063] (effect) The light emitting device 100 according to the first embodiment can provide the following advantages.

[0064] The light emitting device 100 of the first embodiment includes a wavelength conversion element 4 and a fundamental laser light source 7 that irradiates laser light to the wavelength conversion element 4. The laser light (fundamental laser light 8) emitted from the fundamental laser light source 7 is irradiated onto the waveguide 6.

[0065] With this configuration, wavelength-converted light 10 can be obtained by irradiating the waveguide 6 including the interface 13 with fundamental laser light 8 .

[0066] The present disclosure is not limited to the above-described embodiment, but can be embodied in various other forms.

[0067] In the first embodiment, the group III nitride semiconductor crystal layer is made of aluminum nitride, but the present invention is not limited to this. For example, the group III nitride semiconductor crystal layer may be mainly made of gallium nitride, aluminum gallium nitride, or aluminum gallium indium nitride.

[0068] In the first embodiment, the substrates 3A and 3B are made of sapphire, but the present invention is not limited to this. The substrates 3A and 3B may be made of a material having a smaller refractive index than the waveguide 6. The substrates 3A and 3B may be made of silicon dioxide having a refractive index of 1.46, for example.

[0069] In the first embodiment, the example in which the cavity 5 contains air has been described, but the present invention is not limited to this. The gas filling the cavity 5 may be any gas having a refractive index smaller than that of the group III nitride semiconductor crystal layer. The gas filling the cavity 5 may be, for example, helium, argon, nitrogen, oxygen, or the like.

[0070] (Embodiment 2) <Wavelength conversion element> A wavelength conversion element according to embodiment 2 of the present disclosure will be described below. Note that in embodiment 2, the same reference numerals are used for configurations that are the same as or similar to those in embodiment 1, and descriptions that overlap with embodiment 1 will be omitted.

[0071] FIG. 7 is a cross-sectional view of a wavelength conversion element 27 according to the second embodiment of the present disclosure.

[0072] The second embodiment differs from the first embodiment in that the side surface 26A of the first AlN layer 11 in the waveguide 26 is inclined with respect to the up-down direction (Z direction).

[0073] 7, in the second embodiment, the side surface 26A is inclined with respect to the up-down direction (Z direction) from the interface 13 to the first main surface R1. Specifically, the side surface 26A is inclined such that the width of the waveguide 26 narrows from the first main surface R1 toward the interface 13. The width of the two cavities 25 increases from the first main surface R1 toward the interface 13. As a result, in a cross section viewed from the penetration direction (Y direction), the cavities 25 and the portion of the first AlN layer 11 in the waveguide 26 have a trapezoidal cross section.

[0074] The angle of the side surface 26A with respect to the up-down direction (Z direction) is defined as the inclination angle θ. When the inclination angle θ is small, it corresponds to a state in which the width of the waveguide 26 is narrowed, and the efficiency of wavelength conversion is improved. Therefore, the inclination angle θ is preferably 45° or less.

[0075] Note that the side surface opposite to the side surface 26A and defining the cavity 25 may be inclined with respect to the vertical direction (Z direction) or may extend in the vertical direction (Z direction).

[0076] <Method of manufacturing wavelength conversion element> 8A to 8C are cross-sectional views of one wavelength conversion element 27 illustrating a manufacturing method of the wavelength conversion element 27 according to the second embodiment.

[0077] (1) As shown in FIG. 8A, AlN layers 11 and 12 of the same polarity are formed on the main surfaces R1 and R2 of the substrates 3A and 3B, respectively.

[0078] (2) As shown in Fig. 8B, the first AlN layer 11 is subjected to processing such as dry etching to form grooves 24 corresponding to the cavities 25. The grooves 24 are defined by side surfaces inclined at an inclination angle θ with respect to the up-down direction (Z direction).

[0079] (3) As shown in FIG. 8C, the first AlN layer 11 in which the grooves 24 are formed is opposed to and bonded to the second AlN layer 12.

[0080] (effect) According to the wavelength conversion element 27 according to the second embodiment, the following effects can be obtained.

[0081] As described above, in the wavelength conversion element 27 of the second embodiment, the waveguide 26 has the side surface 26A extending from the interface 13, and the side surface 26A is inclined with respect to the direction from the interface 13 toward the first main surface R1.

[0082] With such a configuration, in many cases, the side surface of the groove 24 formed by dry etching or the like has an inclination angle θ, so that the groove 24 having an inclined side surface can be easily manufactured. Therefore, the wavelength conversion element 27 can be easily manufactured.

[0083] (Embodiment 3) <Wavelength conversion element> A wavelength conversion element according to embodiment 3 of the present disclosure will be described. In embodiment 3, the same or equivalent configurations as those in embodiment 1 are denoted by the same reference numerals, and descriptions that overlap with embodiment 1 will be omitted.

[0084] FIG. 9 is a cross-sectional view of a wavelength conversion element 37 according to the third embodiment of the present disclosure.

[0085] The third embodiment differs from the first embodiment in that the cavity 35 contains a solid body.

[0086] 9, the cavity 35 contains silicon dioxide (SiO2) and is filled with SiO2. Therefore, the refractive index of the cavity 35 is the refractive index of SiO2 (1.46), which is smaller than the refractive index (2.09) of the AlN layers 11 and 12. The refractive index of SiO2 filling the cavity 35 is smaller than the refractive index of the waveguide 6, and the light traveling through the waveguide 6 is wavelength converted.

[0087] (effect) According to the wavelength conversion element 37 according to the third embodiment, the following effects can be obtained.

[0088] As described above, in the wavelength conversion element 37 of the third embodiment, the cavity 35 contains a solid.

[0089] With this configuration, the possibility of foreign matter entering the cavity 35 can be reduced compared to when the cavity 35 contains a gas. Foreign matter may fall out of the cavity 35 and adhere to other components of the light-emitting device 100, potentially causing a breakdown in the light-emitting device 100. Therefore, by having the cavity 35 contain a solid, the breakdown of the light-emitting device 100 can be reduced.

[0090] <Method of manufacturing wavelength conversion element> 10A to 10E are cross-sectional views of one wavelength conversion element 37, illustrating a manufacturing method of the wavelength conversion element 37.

[0091] (1) As shown in FIG. 10A, AlN layers 11 and 12 of the same polarity are formed on the main surfaces R1 and R2 of the substrates 3A and 3B, respectively.

[0092] (2) As shown in FIG. 10B, the first AlN layer 11 is processed by dry etching or the like to form a groove 34 corresponding to the cavity 35. The groove 34 is filled with SiO2 in a later process. If the aspect ratio defined by the depth / width of the groove 34 is 1 or less, it is generally easy to fill. Here, the film thickness of the first AlN layer 11 is about 150 nm, so the width that is easy to fill is 150 nm or more. With this width, it is easy to fill using a film formation method such as a CVD method or a sputtering method. However, the minimum groove width that is easy to fill varies depending on the film thickness and the material and method used for filling.

[0093] (3) As shown in Fig. 10C, a silicon dioxide (SiO2) layer 32 is formed on the first substrate 3A and the first AlN layer 11 by using a CVD method, a sputtering method, etc. The grooves 34 are filled with SiO2.

[0094] (4) As shown in FIG. 10D, the SiO2 layer 32 is removed by polishing or the like to expose the first AlN layer 11 and the SiO2 filled in the grooves .

[0095] (5) As shown in Fig. 10E, the first AlN layer 11 with the grooves 34 formed therein is bonded to the second AlN layer 12 so as to face each other. The SiO2 filled in the grooves 34 contacts the second AlN layer 12 and forms an interface 13 between the second AlN layer 12 and the SiO2.

[0096] The SiO2 layer 32 may form a recess in the portion where the groove 34 is located. In this case, the SiO2 filled in the groove 34 may form a gap containing air between the second AlN layer 12 and the SiO2. (effect) According to the manufacturing method of the wavelength conversion element 37 according to the third embodiment, the following effects can be obtained.

[0097] The manufacturing method of the wavelength conversion element 37 of the third embodiment further includes a step of forming a solid layer (SiO2 layer 32) having a smaller refractive index than the AlN layers 11, 12 in the grooves .

[0098] With this configuration, the grooves 34 can be easily filled with SiO 2 , which has a smaller refractive index than the AlN layers 11 and 12 .

[0099] In the third embodiment, an example in which the cavity 35 is filled with SiO2 has been described, but the present invention is not limited to this. There may be a gap between the SiO2 in the cavity 35 and the side surface 36A of the first AlN layer 11 in the waveguide 6. In this case, the gap contains a gas or solid having a refractive index smaller than that of the waveguide 6.

[0100] In the third embodiment, an example in which SiO2 is used as the solid contained in the cavity 35 has been described, but the present invention is not limited to this. The solid contained in the cavity 35 may be any material having a refractive index smaller than that of the group III nitride semiconductor crystal layer. When the group III nitride semiconductor crystal layer is AlN, the solid contained in the cavity 35 may be an optical material having a refractive index smaller than that of AlN, such as aluminum oxide (Al2O3) including sapphire, magnesium oxide (MgO), magnesium fluoride (MgF2), or calcium fluoride (CaF2).

[0101] In the third embodiment, an example in which the SiO2 layer 32 is formed on the first substrate 3A and the first AlN layer 11 has been described, but the present invention is not limited to this. For example, a mask may be provided on the region of the first AlN layer 11 other than the grooves 34 so that only the grooves 34 are exposed, and the mask may be removed after the SiO2 layer 32 is formed. With this process, the polishing process after the formation of the SiO2 layer 32 can be omitted, and the thickness of the first AlN layer 11 can be maintained with high precision.

[0102] (Embodiment 4) <Wavelength conversion element> A wavelength conversion element according to embodiment 4 of the present disclosure will be described. In embodiment 4, the same or similar configurations as those in embodiment 1 are denoted by the same reference numerals, and descriptions that overlap with embodiment 1 will be omitted.

[0103] FIG. 11 is a cross-sectional view of a wavelength conversion element 47 according to the fourth embodiment of the present disclosure.

[0104] The fourth embodiment differs from the first embodiment in that the cavity 45 does not expose the first substrate 3A.

[0105] 11, the cavity 45 is defined by the interface 13 and a bottom surface 44 facing the interface 13 in the up-down direction (Z direction), and the bottom surface 44 is spaced apart from the first main surface R1. In other words, the substrate 3A is not exposed in the cavity 45. The depth of the cavity 45 is, for example, ⅓ or more of the thickness of the first AlN layer 11. With this configuration, it is possible to suppress deterioration in the function of the waveguide 46.

[0106] <Method of manufacturing wavelength conversion element> 12A to 12C are cross-sectional views of one wavelength conversion element 47, illustrating a manufacturing method of the wavelength conversion element 47.

[0107] (1) As shown in FIG. 12A, AlN layers 11 and 12 of the same polarity are formed on the main surfaces R1 and R2 of the substrates 3A and 3B, respectively.

[0108] (2) As shown in Fig. 12B, the first AlN layer 11 is processed by dry etching or the like to form a groove 42 corresponding to the cavity 45. The processing is terminated before the first AlN layer 11 is completely removed, and a part of the first AlN layer 11 is left at the bottom of the groove 42 to form an AlN layer remaining portion 43.

[0109] (3) As shown in FIG. 12C, the first AlN layer 11 in which the grooves 42 are formed is bonded to the second AlN layer 12 so as to face each other.

[0110] (effect) According to the wavelength conversion element 47 according to the fourth embodiment, the following effects can be obtained.

[0111] As described above, in the wavelength conversion element 47 of the fourth embodiment, the cavity 45 is defined by the interface 13 and the bottom surface 44 facing the interface 13 in the up-down direction (Z direction), and the bottom surface 44 is spaced apart from the first main surface R1.

[0112] With this configuration, the contact area between the first AlN layer 11 and the first substrate 3A can be increased, improving the adhesion between the first AlN layer 11 and the first substrate 3A. Therefore, it is possible to prevent the portion of the first AlN layer 11 corresponding to the waveguide from being detached independently from the first substrate 3A.

[0113] Although Figures 1 to 12 of embodiments 1 to 4 describe the case where there are two cavities, the configuration may also be such that there are at least three cavities and the fundamental laser light emitted from the fundamental laser light source is irradiated onto two or more waveguides between the cavities.

[0114] A wavelength conversion element in a first aspect includes a first substrate having a first main surface, a second substrate having a second main surface opposite to the first main surface, and a III nitride semiconductor crystal layer provided between the first and second main surfaces, the III nitride semiconductor crystal layer forming a polarity inversion structure having a first crystal layer provided on the first main surface and having one of III polarity and nitrogen polarity, and a second crystal layer provided on the second main surface and having the other of nitrogen polarity and III polarity forming an interface with the first crystal layer, the first crystal layer having two cavities recessed from the interface toward the first main surface, penetrating the first crystal layer along the interface, the first crystal layer having two cavities with a gap therebetween, the first crystal layer and the second crystal layer between which form a waveguide, the cavity containing a material having a smaller refractive index than the waveguide.

[0115] In the wavelength conversion element of the second aspect, in the wavelength conversion element of the first aspect, the cross-sectional shape of each cavity seen from the penetration direction in which the cavities penetrate the first crystal layer is approximately constant throughout the penetration direction.

[0116] As a wavelength conversion element in a third aspect, in the wavelength conversion element in the first or second aspect, the waveguide has a side surface extending from the interface, and the side surface is inclined with respect to a direction from the interface toward the first main surface.

[0117] As the wavelength conversion element in the fourth aspect, in the wavelength conversion element in any one of the first to third aspects, the cavity contains a gas.

[0118] As the wavelength converting element in the fifth aspect, in the wavelength converting element in any one of the first to third aspects, the cavity contains a solid.

[0119] As a wavelength conversion element in a sixth aspect, in the wavelength conversion element in any one of the first to fifth aspects, the cavity is defined by an interface and a bottom surface that is vertically opposite to the interface, and the bottom surface is spaced apart from the first main surface.

[0120] As a wavelength conversion element in a seventh aspect, in the wavelength conversion element in any one of the first to sixth aspects, the Group III nitride semiconductor crystal layer contains any one of aluminum nitride, gallium nitride, aluminum gallium nitride, and aluminum gallium indium nitride as a main component.

[0121] As a wavelength conversion element in an eighth aspect, in the wavelength conversion element in any one of the first to seventh aspects, the refractive indexes of the first and second substrates are smaller than the refractive index of the waveguide.

[0122] A manufacturing method of a wavelength conversion element in a ninth aspect is a manufacturing method of a wavelength conversion element including a first substrate, a second substrate, and a Group III nitride semiconductor crystal layer having a first crystal layer and a second crystal layer, the manufacturing method including the steps of: forming a first crystal layer having one of Group III polarity and nitrogen polarity on the first substrate; forming a second crystal layer having the same polarity as the first crystal layer on the second substrate; forming two grooves having a gap in between in the first crystal layer; bonding the first crystal layer and the second crystal layer having the same polarity as the first crystal layer opposite each other to form a polarity inversion structure, thereby forming a bonded body in which a cavity corresponding to the grooves is formed; and cutting the wavelength conversion element from the bonded body so that the cavity is exposed at an end face intersecting the extension direction of the cavity.

[0123] A tenth aspect of the method for producing a wavelength conversion element is the method for producing a wavelength conversion element according to the ninth aspect, further comprising the step of forming, in the grooves, a solid layer having a refractive index smaller than that of the Group III nitride semiconductor crystal layer.

[0124] In an eleventh aspect, the method for producing a wavelength conversion element in the ninth or tenth aspect further includes a step of performing at least one of polishing and cleaning on an end face of the wavelength conversion element where the cavity is exposed.

[0125] A light emitting device in a twelfth aspect comprises a wavelength conversion element in any one of the first to eighth aspects, and a fundamental wave laser light source that irradiates laser light onto the wavelength conversion element, and the laser light emitted from the fundamental wave laser light source is irradiated onto a waveguide.

[0126] Although the present disclosure has been fully described in connection with the preferred embodiments with reference to the accompanying drawings, various changes and modifications will be apparent to those skilled in the art, and such changes and modifications should be understood to be included within the scope of the present disclosure as defined by the appended claims unless they depart therefrom. [Industrial Applicability]

[0127] The wavelength conversion element, manufacturing method, and light emitting device according to the present disclosure have the effect of efficiently converting fundamental laser light into a desired wavelength, and are particularly useful in an irradiation device that irradiates electromagnetic waves including directional light. The wavelength conversion element, manufacturing method, and light emitting device according to the present disclosure are applicable in various fields such as the processing field, the optical information processing field, and the optical application measurement and control field. [Explanation of symbols]

[0128] 1. III-nitride semiconductor crystal layer 2 grooves 3A 1st board 3B 2nd board 4 Wavelength conversion element 5 hollow 6. Waveguide 6A side 7 Fundamental laser light source 11 1st AlN layer 12 2nd AlN layer 13 Interface 15 Zygote R1 First main surface R2 Second main surface 100 Light emitting device

Claims

1. a first substrate having a first major surface; a second substrate having a second main surface opposite to the first main surface; a Group III nitride semiconductor crystal layer provided between the first major surface and the second major surface; Equipped with the Group III nitride semiconductor crystal layer forms a polarity inversion structure including a first crystal layer provided on the first main surface and having one of Group III polarity and nitrogen polarity, and a second crystal layer provided on the second main surface and having the other polarity of nitrogen polarity and Group III polarity, forming an interface with the first crystal layer; two cavities are formed in the first crystal layer, the cavities being recessed from the interface toward the first main surface, penetrating the first crystal layer along the interface, and spaced apart from each other; The first crystal layer and the second crystal layer between the two cavities form a waveguide; the cavity contains a material having a refractive index less than that of the waveguide; Wavelength conversion element.

2. a cross-sectional shape of each of the cavities as viewed from a penetration direction in which the cavities penetrate the first crystal layer is substantially constant along the penetration direction; The wavelength conversion element according to claim 1 .

3. the waveguide has a side surface extending from the interface; The side surface is inclined with respect to a direction from the interface toward the first main surface. The wavelength conversion element according to claim 1 .

4. The cavity contains a gas. The wavelength conversion element according to claim 1 .

5. The cavity contains a solid. The wavelength conversion element according to claim 1 .

6. the cavity is defined by the interface and a bottom surface that is vertically opposed to the interface, The bottom surface is spaced from the first major surface. The wavelength conversion element according to claim 1 .

7. The Group III nitride semiconductor crystal layer is mainly composed of any one of aluminum nitride, gallium nitride, aluminum gallium nitride, and aluminum gallium indium nitride. The wavelength conversion element according to claim 1 .

8. The refractive index of the first substrate and the second substrate is smaller than the refractive index of the waveguide. The wavelength conversion element according to claim 1 .

9. A method for manufacturing a wavelength conversion element including a first substrate, a second substrate, and a Group III nitride semiconductor crystal layer having a first crystal layer and a second crystal layer, comprising: forming the first crystal layer having one of group III polarity and nitrogen polarity on the first substrate; forming a second crystal layer having the same polarity as the first crystal layer on the second substrate; forming two grooves having an interval in the first crystal layer; a step of bonding the first crystal layer to the second crystal layer having the same polarity as the first crystal layer to form a polarity inversion structure, thereby forming a bonded body having a cavity corresponding to the groove; cutting the wavelength conversion element from the bonded body so that the cavity is exposed at an end surface intersecting a direction in which the cavity extends; A method for manufacturing a wavelength conversion element comprising the steps of:

10. forming a solid layer in the groove, the solid layer having a refractive index smaller than that of the Group III nitride semiconductor crystal layer; The method for producing a wavelength conversion element according to claim 9 .

11. The method further includes a step of polishing or cleaning the end surface of the wavelength conversion element where the cavity is exposed. The method for producing a wavelength conversion element according to claim 9 or 10.

12. A wavelength conversion element according to any one of claims 1 to 8, a fundamental wave laser light source that irradiates the wavelength conversion element with laser light; Equipped with The laser light emitted from the fundamental wave laser light source is irradiated onto the waveguide. Light emitting device.

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