Photonic crystal surface emitting laser and method of manufacturing the same

Abstract

To provide a photonic crystal surface emitting laser capable of contributing to oscillation in a single mode, and to provide a method of manufacturing the same.SOLUTION: A first semiconductor layer, an active layer stacked on the first semiconductor layer, a photonic crystal layer stacked on the active layer, a second semiconductor layer provided on a side opposite to the first semiconductor layer of the photonic crystal layer, a first electrode electrically connected to the first semiconductor layer, and a second electrode electrically connected to the second semiconductor layer, wherein the photonic crystal layer includes a first region and a plurality of second regions having a refractive index different from that of the first region, and the second semiconductor layer includes a plurality of ring portions; Wherein the plurality of ring portions form a multiple ring structure.SELECTED DRAWING: Figure 3B

Description

[Technical Field]

[0001] The present disclosure relates to a photonic crystal surface-emitting laser and a method for manufacturing the same. [Background technology]

[0002] Photonic-crystal surface-emitting lasers (PCSELs) are known, in which a photonic crystal and an active layer having optical gain are stacked. Research is being conducted into techniques for operating PCSELs in a single mode (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 031966 Summary of the Invention [Problem to be solved by the invention]

[0004] A voltage is applied to the electrodes to inject carriers into the semiconductor layer. The carrier density injected near the periphery is sometimes higher than the carrier density near the center. Higher-order modes are easily excited, making single-mode oscillation difficult. Therefore, the objective of this study is to provide a photonic crystal surface-emitting laser that can contribute to single-mode oscillation, and a method for manufacturing the same. [Means for solving the problem]

[0005] The photonic crystal surface-emitting laser according to the present disclosure comprises a first semiconductor layer, an active layer stacked on the first semiconductor layer, a photonic crystal layer stacked on the active layer, a second semiconductor layer provided on the opposite side of the active layer from the first semiconductor layer, a first electrode electrically connected to the first semiconductor layer, and a second electrode electrically connected to the second semiconductor layer, wherein the photonic crystal layer has a first region and a plurality of second regions having a refractive index different from that of the first region, and the second semiconductor layer has a plurality of ring portions, and the plurality of ring portions form a multiple ring structure. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide a photonic crystal surface-emitting laser capable of contributing to single-mode oscillation and a method for manufacturing the same. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view illustrating a photonic crystal surface-emitting laser according to the first embodiment. [Figure 2A] FIG. 2A is a plan view illustrating an example of a photonic crystal layer. [Figure 2B] FIG. 2B is an enlarged plan view of the photonic crystal layer region. [Figure 2C] FIG. 2C is an enlarged cross-sectional view of the photonic crystal layer. [Figure 3A] FIG. 3A is a bottom view illustrating a photonic crystal surface-emitting laser. [Figure 3B] FIG. 3B is a top view illustrating a photonic crystal surface-emitting laser. [Figure 4A] FIG. 4A is a schematic diagram illustrating the distribution of light. [Figure 4B] FIG. 4B is a schematic diagram illustrating the distribution of light. [Figure 5] FIG. 5 is a cross-sectional view illustrating a photonic crystal surface-emitting laser according to a comparative example. [Figure 6A] FIG. 6A is a schematic diagram illustrating the carrier density. [Figure 6B] FIG. 6B is a schematic diagram illustrating the carrier density. [Figure 7] FIG. 7 is a diagram illustrating an example of the carrier density distribution. [Figure 8] FIG. 8 is a diagram illustrating a multiple ring structure. [Figure 9A] FIG. 9A is a diagram showing the calculation results of the width of the annular portion. [Figure 9B] FIG. 9B is a diagram showing the calculation results of the width of the annular portion. [Figure 10] FIG. 10 is a diagram illustrating an example of the carrier density distribution. [Figure 11A] FIG. 11A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 11B] FIG. 11B is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 11C] FIG. 11C is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 12A] FIG. 12A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 12B] FIG. 12B is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 13A] FIG. 13A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 13B] FIG. 13B is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0009] One aspect of the present disclosure is a photonic crystal surface-emitting laser (SPEL) including: (1) a first semiconductor layer; an active layer stacked on the first semiconductor layer; a photonic crystal layer stacked on the active layer; a second semiconductor layer provided on the active layer opposite the first semiconductor layer; a first electrode electrically connected to the first semiconductor layer; and a second electrode electrically connected to the second semiconductor layer, wherein the photonic crystal layer has a first region and a plurality of second regions having a refractive index different from that of the first region; the second semiconductor layer has a plurality of ring portions; and the plurality of ring portions form a multiple ring structure. The carrier density is higher near the center of the multiple ring structure and lower near the periphery. Higher-order modes are suppressed, and the fundamental mode is easily excited. This can contribute to single-mode oscillation. (2) In the above (1), the ring portions closer to the center of the multi-ring structure may be thicker and the ring portions closer to the periphery of the multi-ring structure may be thinner. The carrier density is higher closer to the center and lower toward the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. This can contribute to single-mode oscillation. (3) In the above (1) or (2), the plurality of ring portions may have widths determined based on a Gaussian function. The carrier density is higher near the center and lower toward the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. This can contribute to single-mode oscillation. (4) In any one of the above (1) to (3), the second electrode may cover the plurality of ring portions. Since the second electrode reflects light, the light output can be increased. (5) In any of (1) to (4) above, the second semiconductor layer may have a central portion, the width of the central portion being greater than the width of the ring portions, the multiple ring portions surrounding the central portion, and the second electrode covering the central portion and the multiple ring portions. The carrier density is higher closer to the center and lower toward the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. This can contribute to single-mode oscillation. (6) In the above (5), the planar shape of the central portion may be circular, the planar shapes of the multiple ring portions may be annular, and the central portion and the multiple ring portions may be arranged concentrically. The carrier density is high at the center and low near the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. Circular light can be emitted. (7) In any of the above (1) to (6), an insulating film may be provided between the plurality of ring portions. This can separate the ring portions. This can change the carrier density distribution. (8) In any one of (1) to (7) above, the plurality of second regions of the photonic crystal layer may be periodically arranged over a wider range than the multiple ring structure of the second semiconductor layer. Depending on the carrier density distribution, higher-order modes are suppressed and the fundamental mode is easily excited. (9) In any of the above (1) to (8), a third semiconductor layer may be provided between the active layer and the second semiconductor layer, the first semiconductor layer having an n-type conductivity, and the second semiconductor layer and the third semiconductor layer having a p-type conductivity. Since a pin junction is formed, carriers can be injected into the active layer. (10) A method for fabricating a semiconductor device, comprising the steps of: stacking an active layer on a first semiconductor layer; forming a photonic crystal layer; forming a second semiconductor layer opposite to the first semiconductor layer of the active layer; forming a multiple ring structure in the second semiconductor layer; forming a first electrode electrically connected to the first semiconductor layer; and forming a second electrode electrically connected to the second semiconductor layer, wherein the photonic crystal layer has a first region and a plurality of second regions having a refractive index different from that of the first region; The second semiconductor layer has a plurality of ring portions, and the plurality of ring portions form the multi-ring structure. This is a method for manufacturing a photonic crystal surface-emitting laser. The carrier density is higher near the center of the multi-ring structure and lower near the periphery. Higher-order modes are suppressed, and the fundamental mode is easily excited. This can contribute to single-mode oscillation.

[0010] [Details of the embodiments of the present disclosure] Specific examples of photonic crystal surface-emitting lasers and methods for manufacturing the same according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0011] <Embodiment> (Photonic crystal surface-emitting laser) Fig. 1 is a cross-sectional view illustrating a photonic crystal surface-emitting laser 100 according to the first embodiment. As shown in Fig. 1, the photonic crystal surface-emitting laser (PCSEL) 100 includes a substrate 10, a cladding layer 12 (first semiconductor layer), a photonic crystal layer 14, a cladding layer 16 (first semiconductor layer), an active layer 18, a cladding layer 20 (third semiconductor layer), a contact layer 22 (second semiconductor layer), an electrode 24 (first electrode), and an electrode 26 (second electrode).

[0012] The semiconductor layers are stacked along the Z axis. A cladding layer 12, a photonic crystal layer 14, a cladding layer 16, an active layer 18, a cladding layer 20, and a contact layer 22 are stacked in this order on a substrate 10. The surface of each layer is parallel to the XY plane. The X, Y, and Z axes are perpendicular to one another. The dashed-dotted line in Figure 1 represents the center C of the photonic crystal surface-emitting laser 100 in the XY plane.

[0013] The contact layer 22 has a multiple ring structure, as will be described later. An insulating film 23 is provided between the rings of the contact layer 22. The upper surface of the contact layer 22 is exposed from the insulating film 23. An electrode 26 is provided on the contact layer 22 and the insulating film 23. The electrode 26 is electrically connected to the contact layer 22. The electrode 24 contacts the lower surface of the substrate 10 and is electrically connected to the substrate 10 and the cladding layer 12.

[0014] The substrate 10, the cladding layer 12, and the cladding layer 16 are formed of, for example, n-type indium phosphide (n-InP). The n-type dopant is, for example, silicon (Si). The thickness of the cladding layer 12 is, for example, 500 nm. The thickness of the cladding layer 16 is, for example, 100 nm.

[0015] Photonic crystal layer 14 is made of, for example, n-type indium gallium arsenide phosphide (InGaAsP) or aluminum indium gallium arsenide (AlInGaAs), and has a thickness of, for example, 300 nm.

[0016] The active layer 18 includes multiple well layers and barrier layers, and has a multi-quantum well (MQW) structure. The well layers and barrier layers are formed of, for example, undoped indium gallium arsenide phosphide (InGaAsP) or aluminum gallium indium arsenide (AlGaInAs). The active layer 18 has optical gain.

[0017] The cladding layer 20 is formed of, for example, p-type indium phosphide (p-InP). The contact layer 22 includes, for example, p-type indium gallium arsenide phosphide (p-InGaAsP) and p-type indium gallium arsenide (p-InGaAs). A p-InGaAsP layer is stacked on the surface of the cladding layer 20, and a p-InGaAs layer is stacked on the p-InGaAsP layer. The surface of the contact layer 22 is p-InGaAs. The p-type dopant is, for example, zinc (Zn). The cladding layer 20 has a thickness of, for example, 3 μm. The contact layer 22 has a thickness of, for example, 300 nm. The insulating film 23 is formed of an insulator such as silicon nitride (SiN). The above materials are examples, and each layer may be formed of other materials or a combination of the above materials with other materials.

[0018] The refractive index of active layer 18 is, for example, 3.5. The refractive index of each of cladding layers 12, 16, and 20 is, for example, 3.2. The refractive index of InGaAsP, the base material of photonic crystal layer 14, is higher than those of cladding layers 12, 16, and 20, for example, 3.4.

[0019] 2A is a plan view illustrating photonic crystal layer 14. The lengths of one side, L1 and L2, are, for example, 1000 μm. Region 15 of photonic crystal layer 14 is located at the center of photonic crystal layer 14. Region 15 has a circular planar shape. Region 15 has a diameter D1 of, for example, 300 μm. Air holes are provided in region 15.

[0020] FIG. 2B is an enlarged plan view of region 15 of photonic crystal layer 14. FIG. 2C is an enlarged cross-sectional view of photonic crystal layer 14, showing a cross section along line AA in FIG. 2B. Photonic crystal layer 14 has base material 30 (first region), voids 32, and voids 34 (second region). Base material 30 is an InGaAsP layer or the like, as described above. A plurality of voids 32 and a plurality of voids 34 are provided in base material 30.

[0021] As shown in FIG. 2B, the plurality of voids 32 and voids 34 are arranged two-dimensionally. The plurality of voids 32 are arranged in a square lattice pattern. The plurality of voids 34 are arranged in a square lattice pattern. The plurality of voids 32 and voids 34 are arranged periodically in the X-axis direction and the Y-axis direction. The lattice constant is, for example, 400 nm. That is, the distance between adjacent voids 32 and the distance between adjacent voids 34 in the X-axis direction and the Y-axis direction is 400 nm. The planar shape of the voids 32 is elliptical. The major and minor axes of the voids 32 are inclined from the direction in which the plurality of voids 32 are arranged. The planar shape of the voids 34 is circular.

[0022] As shown in FIG. 2C , the air holes 32 and 34 extend in the Z-axis direction. One end of each of the air holes 32 and 34 is located on one surface of the photonic crystal layer 14. The other end of each of the air holes 32 and 34 is located midway through the photonic crystal layer 14. The air holes 32 and 34 may extend through the photonic crystal layer 14 to the cladding layer 12. The air holes 32 are longer than the air holes 34. The interiors of the air holes 32 and 34 are filled with air. The refractive index of the air holes 32 and 34 is different from the refractive index of the base material 30. The refractive index varies periodically within the plane of the photonic crystal layer 14.

[0023] 3A is a bottom view illustrating a photonic crystal surface-emitting laser 100. As shown in FIG. 3A, an opening 25 is provided in the electrode 24. The opening 25 has a circular planar shape. The diameter D2 of the opening 25 is, for example, 340 μm. The opening 25 penetrates the electrode 24, and the substrate 10 is exposed through the opening 25. The opening 25 functions as an aperture for emitting light.

[0024] The electrode 24 is an n-type electrode and is in contact with the surface of the substrate 10. The electrode 24 is made of metal, and is formed, for example, by stacking nickel (Ni), germanium (Ge), and gold (Au) from the side closest to the substrate 10.

[0025] 3B is a top view illustrating the photonic crystal surface-emitting laser 100, with the electrode 26 being seen through. In FIG. 3B, the hatched portion is the contact layer 22. The non-hatched portion is the insulating film 23. The line L will be described later.

[0026] The contact layer 22 has a central portion 40 and multiple annular portions 42 (ring portions). The planar shape of the central portion 40 is circular. The planar shape of the annular portions 42 is annular. The central portion 40 and the annular portions 42 are arranged concentrically. The central portion 40 is located at the center of the photonic crystal surface-emitting laser 100. One annular portion 42 surrounds the central portion 40. This annular portion 42 is surrounded by another annular portion 42. Similarly, further annular portions 42 are arranged on the outside. In other words, the contact layer 22 has a multiple annular structure. The central portion 40 and the annular portion 42 are spaced apart. The multiple annular portions 42 are spaced apart from each other. Annular insulating films 23 are provided between the central portion 40 and the annular portion 42 and between the multiple annular portions 42.

[0027] The centers of central portion 40 and annular portion 42 of contact layer 22 coincide with center C in Figure 1. The center of region 15 of photonic crystal layer 14, the center of opening 25 of electrode 24, and the centers of central portion 40 and annular portion 42 of contact layer 22 coincide and overlap in the Z-axis direction. Central portion 40 and annular portion 42 of contact layer 22 overlap region 15 of photonic crystal layer 14 and opening 25 of electrode 24.

[0028] The diameter D3 of the outermost of the multiple annular portions 42 is smaller than the diameter D1 of the region 15 and the diameter D2 of the opening 25, and is, for example, 200 μm. The distance from the center C of the photonic crystal surface-emitting laser to the outermost annular portion 42 is defined as the radius R0 of the multiple annular structure.

[0029] Of the multiple annular portions 42, the thicker ones are located near the center of the multiple annular structure. The thinner ones are located farther from the center and closer to the outer periphery. The diameter of the central portion 40 is larger than the width of any of the annular portions 42. The radius Rc of the central portion 40 is, for example, several tens of μm.

[0030] The sizes of the central portion 40 and the annular portions 42 and the number of the annular portions 42 can be determined depending on the characteristics required of the photonic crystal surface-emitting laser 100. The number of the annular portions 42 may be expressed as the number N of divisions of the multiple ring structure.

[0031] 3B and covers the central portion 40 and the multiple annular portions 42 of the contact layer 22. The electrode 26 is in contact with the upper surface of the central portion 40 and the upper surfaces of the multiple annular portions 42, and is electrically connected to the central portion 40 and the multiple annular portions 42. The electrode 26 is a p-type electrode and is formed, for example, by stacking titanium (Ti), platinum (Pt), and gold (Au) from the side closest to the contact layer 22.

[0032] The operation of the photonic crystal surface-emitting laser 100 will now be described. A voltage is applied to the photonic crystal surface-emitting laser 100 through the electrodes 24 and 26. Light is generated when carriers are injected into the active layer 18. The light is diffracted and scattered within the plane of the photonic crystal layer 14, and light having a wavelength corresponding to the period of the air holes 32 and 34 is amplified, resulting in laser oscillation. The wavelength of the laser light is, for example, in the 1.3 μm band or the 1.5 μm band.

[0033] The laser light is emitted in the Z-axis direction. Light propagating downward in FIG. 1 is emitted from opening 25 in electrode 24. Light propagating upward is reflected by the lower surface of electrode 26, propagates downward, and is emitted from opening 25.

[0034] It is desirable to operate the photonic crystal surface-emitting laser 100 in a single mode (fundamental mode), but higher-order modes may be excited along with the fundamental mode.

[0035] Figures 4A and 4B are schematic diagrams illustrating the distribution of light. Figure 4A shows the fundamental mode. Figure 4B shows higher-order modes. Light is shown by dotted lines. As shown in Figure 4A, the fundamental mode is strongly distributed in the center and becomes weaker toward the outside. As shown in Figure 4B, the higher-order modes are distributed to the outside. To achieve single-mode oscillation, it is sufficient to oscillate the fundamental mode and suppress the higher-order modes.

[0036] 5 is a cross-sectional view illustrating a photonic crystal surface-emitting laser 110 according to a comparative example. The contact layer 22 does not have a multiple ring structure but is a single layer. The planar shape of the contact layer 22 is circular. The electrode 26 is provided on the contact layer 22 and the insulating film 23 and is electrically connected to the contact layer 22.

[0037] 6A and 6B are schematic diagrams illustrating carrier density. The horizontal axis represents the position within the photonic crystal surface-emitting laser, along the Y-axis direction. C represents the center of the photonic crystal surface-emitting laser. The vertical axis represents carrier density. The dotted line represents the carrier density injected into the active layer 18. The dashed line represents the carrier density consumed. The solid line represents the carrier density after oscillation.

[0038] Figure 6A shows the carrier density in the comparative example. Compared to the injected carrier density at the center C, the injected carrier density near the periphery is higher. The position of high carrier density corresponds to the vicinity of the periphery of region 15 of contact layer 22 and photonic crystal layer 14. The consumed carrier density is higher towards the center and decreases towards the periphery. The post-oscillation carrier density is high near the periphery and low at the center. Because the post-oscillation carrier density is high near the periphery, higher-order modes are more likely to be excited.

[0039] Figure 6B shows the carrier density in this embodiment. The injected carrier density and consumed carrier density are higher in the center and lower toward the periphery. The carrier density after oscillation is nearly flat. Higher-order modes are suppressed, and the fundamental mode is easily excited.

[0040] Photonic crystal surface-emitting laser 100 is designed so that the carrier density shown in FIG. 6B is realized.

[0041] FIG. 7 is a diagram illustrating an example of a carrier density distribution. The horizontal axis represents the distance from the center C of the photonic crystal surface-emitting laser, with 0 representing the position of the center C. The larger the value on the horizontal axis, the closer it is to the outer periphery of the photonic crystal surface-emitting laser. The 100 μm position is near the edge of the multiple circular ring structure of the contact layer 22. The diameter of the central portion 40 of the contact layer 22 is 50 μm.

[0042] The vertical axis in Fig. 7 represents carrier density (electron density). The dashed line represents a comparative example. The solid line represents an example in which the number of divisions of the multiple ring structure is 5 (N = 5) in the embodiment. The dotted line represents an example in which the number of divisions of the multiple ring structure is 20 (N = 20) in the embodiment.

[0043] As shown by the dashed line in FIG. 7, in the comparative example, the carrier density near the periphery (near 100 μm) of the contact layer 22 is higher than the carrier density at the center. As shown by the solid and dotted lines, according to the embodiment, the carrier density near the periphery is lower than the carrier density at the center. The range from 0 μm to 50 μm on the horizontal axis corresponds to the central portion 40 of the contact layer 22. In the embodiment, the carrier density at the central portion 40 is almost flat. The carrier density decreases from the central portion 40 toward the periphery. Corresponding to the multiple ring structure, the carrier density pulsates. In the example of N=5 shown by the solid line, the amplitude of the carrier density is large. In the example of N=20 shown by the dotted line, the amplitude is small and changes in a step-like manner.

[0044] Next, a design example of a multiple ring structure will be described. FIG. 8 is a diagram illustrating an example of a multiple ring structure, showing a cross section along line L in FIG. 3B. The number of divisions is N. The contact layer 22 has a central portion 40 and N ring portions. From the side closest to the central portion 40, the ring portions are designated as ring portion 42-1, ring portion 42-2, ..., ring portion 42-N. Ring portion 42-2 surrounds ring portion 42-1. The outer ring portion surrounds the inner ring portion.

[0045] The insulating film 23 is divided into N annular portions. The annular portions of the insulating film 23 are designated, from the side closest to the central portion 40, as an annular portion 23-1, an annular portion 23-2, . . . , an annular portion 23-N. An annular portion 23-1 of the insulating film 23 is provided between the central portion 40 and annular portion 42-1 of the contact layer 22. An annular portion 23-2 is provided between annular portions 42-1 and 42-2. The annular portions of the contact layer 22 and the annular portions of the insulating film 23 are arranged alternately. An annular portion 42-N of the contact layer 22 is located outside annular portion 23-10 of the insulating film 23.

[0046] Two adjacent annular portions are defined as a unit. An annular portion 42-1 of the contact layer 22 and an annular portion 23-1 of the insulating film 23 form a unit U1. An annular portion 42-2 and an annular portion 23-2 form a unit U2. N units are formed.

[0047] As shown in Figure 4B, in order to increase the carrier density at the center and decrease it at the periphery, the dimensions of the contact layer 22 are set to appropriate values. The widths of the annular portions of the contact layer 22 are defined as w1, w2, ... wN. The widths of the annular portions of the insulating film 23 are defined as s1, s2, ... sN. The radius Rc of the central portion 40 of the contact layer 22 is larger than any of the widths w1 to wN of the annular portions. Of the multiple annular portions 42-1 to 42-N, the closer they are to the central portion 40, the thicker they are, and the farther they are, the thinner they are.

[0048] As an example, the width can be determined based on a Gaussian function. The width wk of the annular portion of the contact layer 22 is calculated by the following equation:

number

[0049] The coefficient A in Equation 1 is expressed by the following equation, for example.

number

[0050] The width of the annular portion of the insulating film 23 is calculated by the following formula.

number

[0051] (R0-Rc) / N in Equations 2 and 3 represents the width of one unit. The width of the unit is a constant value, and is divided into the width wk of the annular portion 42 of the contact layer 22 and the width sk of the annular portion of the insulating film 23.

[0052] In the following example, R0 = 100 μm, Rc = 10 μm, and N = 10. The width of one unit is 9 μm. From equation 2, A is calculated as 7.

[0053] 9A and 9B are diagrams showing the calculation results for the width of the annular portion. The horizontal axis represents the distance from the center of the photonic crystal surface-emitting laser. The vertical axis represents the widths wk and sk. The black circle represents the width wk of the annular portion of the contact layer 22. The white circle represents the width sk of the annular portion of the insulating film 23. The dashed line represents the width wk calculated using the Gaussian function of Equation 1.

[0054] FIG. 9A shows an example where σ=160 in Equation 1. FIG. 9B shows an example where σ=20 in Equation 1. As shown in FIGS. 9A and 9B, the width wk of the annular portion of the contact layer 22 varies according to a Gaussian function, being larger closer to the center and smaller closer to the periphery. The width sk of the annular portion of the insulating film 23 is smaller closer to the center and larger closer to the periphery. As in the example of FIG. 9A, when the parameter σ is large, the width wk varies gradually. As in the example of FIG. 9B, when the parameter σ is small, the width wk varies rapidly.

[0055] When σ=20, the width w1 of the annular portion 42-1 of the contact layer 22 is 7.177 μm, and the width s1 of the annular portion 23-1 of the insulating film 23 is 1.823 μm. The width w2 of the annular portion 42-2 is 5.481 μm, and the width s2 of the annular portion 23-2 is 3.519 μm. The width w3 of the annular portion 42-3 is 3.668 μm, and the width s3 of the annular portion 23-3 is 5.332 μm. The width w4 of the annular portion 42-4 is 2.304 μm, and the width s4 of the annular portion 23-4 is 6.696 μm. The width w5 of the annular portion 42-5 is 1.523 μm, and the width s5 of the annular portion 23-5 is 7.477 μm. The width w6 of the annular portion 42-6 is 1.172 μm, and the width s6 of the annular portion 23-6 is 7.828 μm. The width w7 of the annular portion 42-7 is 1.047 μm, and the width s7 of the annular portion 23-7 is 7.953 μm. The width w8 of the annular portion 42-8 is 1.010 μm, and the width s8 of the annular portion 23-8 is 7.990 μm. The width w9 of the annular portion 42-9 is 1.002 μm, and the width s9 of the annular portion 23-9 is 7.998 μm. The width w10 of the annular portion 42-10 is 1.000 μm, and the width s10 of the annular portion 23-10 is 8.000 μm.

[0056] 10 is a diagram illustrating an example of the carrier density distribution. The horizontal axis represents the distance from the center of the photonic crystal surface-emitting laser, and the vertical axis represents the carrier density.

[0057] The thin dashed line represents a comparative example. The other lines represent embodiments. The thick solid line represents an example where σ=160. The dotted line represents an example where σ=80. The thick dashed line represents an example where σ=60. The dot-dash line represents an example where σ=40. The thin solid line represents an example where σ=20.

[0058] According to the embodiment, the carrier density near the periphery can be lowered compared to the comparative example. As σ is made smaller, the carrier density decreases more rapidly from the center to the periphery. That is, the carrier density is higher in the center and lower on the periphery.

[0059] (Manufacturing method) 11A to 13B are cross-sectional views illustrating a method for manufacturing photonic crystal surface-emitting laser 100. As shown in Fig. 11A, cladding layer 12 and photonic crystal layer 14 are epitaxially grown in this order on substrate 10, for example, by metal organic chemical vapor deposition (MOCVD). In this step, base material 30 (InGaAsP) of photonic crystal layer 14 is formed, but no voids are formed.

[0060] 11B and 11C are enlarged views of photonic crystal layer 14. As shown in FIG. 11B, a mask 50 is provided on the upper surface of photonic crystal layer 14. Mask 50 is made of an insulator such as SiN. An insulating film is formed on the upper surface of photonic crystal layer 14. A resist pattern is formed using an electron beam (EB) or the like, and the resist pattern is transferred to the insulating film to form mask 50. Mask 50 has openings 51 and 52. The upper surface of base material 30 is exposed through openings 51 and 52. A plurality of openings 51 and 52 are arranged two-dimensionally.

[0061] As shown in FIG. 11C, holes 32 and 34 are formed in photonic crystal layer 14 by reactive ion etching (RIE) or the like. The etching proceeds, for example, partway through photonic crystal layer 14, but does not reach the bottom surface of photonic crystal layer 14. Holes 32 are formed at positions overlapping with openings 51 in mask 50. Holes 34 are formed at positions overlapping with openings 52. The planar shapes of holes 32 and 34 are determined by the planar shapes of openings 51 and 52. By making openings 51 elliptical and openings 52 circular, elliptical holes 32 and circular holes 34 are formed, as shown in FIG. 3B. After etching is completed, mask 50 is removed.

[0062] 12A, cladding layer 16, active layer 18, cladding layer 20, and contact layer 22 are epitaxially grown on photonic crystal layer 14. Air holes 32 and 34 are blocked by cladding layer 16. The inside of the air holes is not filled with cladding layer 16, and becomes a cavity. Active layer 18, cladding layer 20, and contact layer 22 are formed on flat cladding layer 16.

[0063] As shown in Fig. 12B, the contact layer 22 is subjected to dry etching or the like to form a multiple annular structure. As shown in Fig. 4A, a central portion 40 and annular portions 42 are formed in the contact layer 22. The cladding layer 20 is exposed between the annular portions 42, etc. The width of the contact layer 22 can be set to a desired size by determining the dimensions of a mask (not shown) used for etching based on a Gaussian function, for example, as shown in Equation 1.

[0064] 13A, the insulating film 23 is formed by, for example, plasma CVD, and the portion of the insulating film 23 that overlaps the contact layer 22 is removed by etching.

[0065] 13B, an electrode 26 is provided on the contact layer 22 by, for example, vacuum deposition and lift-off. The electrode 26 covers the central portion 40 and the multiple annular portions 42 of the contact layer 22. An electrode 24 is provided on the lower surface of the substrate 10. The electrode 24 has an opening 25. Through the above steps, the photonic crystal surface-emitting laser 100 is formed.

[0066] According to this embodiment, the contact layer 22 has a multiple ring structure, including a central portion 40 and multiple ring portions 42, as shown in FIG. 3B. The electrode 26 covers the central portion 40 and the multiple ring portions 42. When a voltage is applied to the electrode 26, carriers are injected. Because the contact layer 22 has a multiple ring structure, the carrier density is higher closer to the center of the multiple ring structure and lower toward the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. This can contribute to single-mode oscillation.

[0067] The contact layer 22 has, for example, ten annular portions 42-1 to 42-10. Annular portion 42-1 is located on the innermost side. Annular portion 42-10 is located on the outermost side. The annular portions closer to the center are thicker, and the annular portions closer to the periphery are thinner. The carrier density is higher closer to the center and lower toward the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. This can contribute to single-mode oscillation.

[0068] As in the example of Equation 1, the width wk of the multiple annular portions can be determined based on a Gaussian function. The closer to the center the wider the width, and the further away from the center the narrower the width. The carrier density is higher in the center and lower near the periphery. Higher-order modes are suppressed, and the fundamental mode is more easily excited.

[0069] As shown in Figures 9A and 9B, the width increases at the center and decreases toward the periphery. As shown in Figure 10, the difference in carrier density distribution can be increased from the center to the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. To design the width, a Gaussian function including coefficients different from those in Equation 1 may be used, or a function other than a Gaussian function may be used.

[0070] The electrode 26 covers the central portion 40 and the multiple annular portions of the contact layer 22. The area of ​​the electrode 26 is similar to that of the comparative example. Light emitted from the active layer 18 is reflected by the lower surface of the electrode 26. Since the area of ​​the electrode 26 does not need to be reduced, high output power is possible.

[0071] As shown in FIG. 3B, the contact layer 22 has a central portion 40 and multiple annular portions 42. The multiple annular portions 42 surround the central portion 40. The electrode 26 covers the central portion 40 and the multiple annular portions 42. Carriers can be injected from the entire contact layer 22. The width (diameter) of the central portion 40 is larger than the width wk of the annular portions 42. The carrier density is high at the center and low near the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. Since the area of ​​the electrode 26 does not need to be small, high output is possible.

[0072] The number of divisions N may be 2 or more, 5 or more, 10 or more, or 20 or more. The multiple annular portions 42 may include portions with the same width. For example, the contact layer 22 may have 10 or more annular portions 42, and two adjacent annular portions 42 may have the same width.

[0073] The planar shape of the central portion 40 is circular. The planar shape of the annular portion 42 is annular. The central portion 40 and the multiple annular portions 42 are arranged concentrically. The carrier density is high at the center and low near the periphery. Higher-order modes are suppressed, making it easier to excite the fundamental mode. Circular light can be emitted in accordance with the shape of the contact layer 22.

[0074] The central portion 40 and the annular portions 42 do not have to be arranged concentrically. The centers of the multiple annular portions 42 may be offset. The center of the central portion 40 may be offset from the center of the annular portions 42.

[0075] The contact layer 22 may have a multiple ring structure and include multiple ring portions. In the example of FIG. 3B, the multiple ring structure is a multiple circular ring structure, and the ring portion is a circular ring portion 42. The ring portion may have a shape other than a circle, such as an ellipse, a closed curve, or a polygon. The central portion 40 may have a shape other than a circle, such as an ellipse or a polygon. The contact layer 22 may not have a central portion 40 and may only have a circular ring portion 42. The thickest circular ring portion 42 is located in the center. Carrier density is high in the center and low near the periphery.

[0076] The insulating film 23 is provided between the plurality of annular portions 42, and between the central portion 40 and the annular portion 42. The plurality of annular portions 42 are separated from each other. The central portion 40 and the annular portion 42 are separated from each other. This allows for variation in the carrier density distribution.

[0077] Diameter D1 of region 15 of photonic crystal layer 14 is larger than diameter D3 of the multiple ring structure. Multiple air holes 32 and 34 are periodically arranged over a wider range than the multiple ring structure. Active layer 18 generates light upon carrier injection. The light undergoes repeated diffraction and scattering within the plane of photonic crystal layer 14, resulting in laser oscillation. Depending on the carrier density distribution, higher-order modes are suppressed and the fundamental mode is easily excited.

[0078] The center of region 15 of photonic crystal layer 14, the center of opening 25 in electrode 24, and center C of the multiple ring structure of contact layer 22 are aligned. Depending on the carrier density distribution, higher-order modes are suppressed and the fundamental mode is easily excited. Laser light is emitted from opening 25. Light in the fundamental mode can be extracted.

[0079] The center of region 15, the center of opening 25 in electrode 24, and the center C of the multiple ring structure of contact layer 22 do not have to coincide. When region 15, opening 25, and the multiple ring structure overlap in the Z-axis direction, laser light is generated and emitted.

[0080] The substrate 10, cladding layer 12, photonic crystal layer 14, and cladding layer 16 have n-type conductivity. The active layer 18 is an undoped layer. The cladding layer 20 and contact layer 22 have p-type conductivity. Stacking these layers forms a pin junction (positive-intrinsic-negative), allowing carriers to be injected into the active layer 18. The conductivity types may be reversed. An n-type layer is provided on one side of the active layer 18, and a p-type layer is provided on the other side.

[0081] Although two types of holes are used in the embodiment, one type or three or more types may be used. The planar shape of the holes may be elliptical, circular, or polygonal. Photonic crystal layer 14 is periodically provided with regions having a refractive index different from that of base material 30. These regions may be holes or may be made of a material different from base material 30. Photonic crystal layer 14 may be provided between cladding layer 12 and active layer 18, or between active layer 18 and cladding layer 20.

[0082] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present disclosure as described in the claims. [Explanation of symbols]

[0083] 10 Substrate 12, 16, 20 cladding layers 14 Photonic crystal layer 15 areas 18 Active layer 22 Contact layer 23 insulating film 23-1~23-N, 42, 42-1~42-N Annular section 24, 26 electrodes 25, 51, 52 openings 30 Base material 32, 34 Vacancies 40 Central part 50 Mask 100, 110 Photonic crystal surface-emitting laser U1~UN Unit

Claims

1. a first semiconductor layer; an active layer stacked on the first semiconductor layer; a photonic crystal layer stacked on the active layer; a second semiconductor layer provided opposite the first semiconductor layer of the active layer; a first electrode electrically connected to the first semiconductor layer; a second electrode electrically connected to the second semiconductor layer, the photonic crystal layer has a first region and a plurality of second regions having a refractive index different from that of the first region; the second semiconductor layer has a plurality of ring portions; The photonic crystal surface emitting laser, wherein the plurality of ring portions form a multi-ring structure.

2. 2. The photonic crystal surface-emitting laser according to claim 1, wherein the ring portions closer to the center of the multiple ring structure are thicker and the ring portions closer to the outer periphery of the multiple ring structure are thinner.

3. 3. The photonic crystal surface-emitting laser according to claim 1, wherein the plurality of ring portions have widths determined based on a Gaussian function.

4. 3. The photonic crystal surface emitting laser according to claim 1, wherein the second electrode covers the plurality of ring portions.

5. the second semiconductor layer has a central portion; the width of the central portion is greater than the width of the ring portion; the plurality of ring portions surround the central portion; 3. The photonic crystal surface-emitting laser according to claim 1, wherein the second electrode covers the central portion and the plurality of ring portions.

6. The planar shape of the central portion is circular, the plurality of ring portions have a plane shape that is annular, The photonic crystal surface-emitting laser according to claim 5 , wherein the central portion and the plurality of ring portions are concentrically arranged.

7. 3. The photonic crystal surface emitting laser according to claim 1, further comprising an insulating film provided between the plurality of ring portions.

8. 3. The photonic crystal surface-emitting laser according to claim 1, wherein the plurality of second regions of the photonic crystal layer are periodically arranged over a range wider than the multiple ring structure of the second semiconductor layer.

9. a third semiconductor layer provided between the active layer and the second semiconductor layer; the first semiconductor layer has n-type conductivity; 3. The photonic crystal surface-emitting laser according to claim 1, wherein the second semiconductor layer and the third semiconductor layer have p-type conductivity.

10. depositing an active layer on the first semiconductor layer; forming a photonic crystal layer; forming a second semiconductor layer opposite the first semiconductor layer of the active layer; forming a multi-ring structure in the second semiconductor layer; forming a first electrode electrically connected to the first semiconductor layer; forming a second electrode electrically connected to the second semiconductor layer; the photonic crystal layer has a first region and a plurality of second regions having a refractive index different from that of the first region; the second semiconductor layer has a plurality of ring portions; A method for manufacturing a photonic crystal surface-emitting laser, wherein the plurality of ring portions form the multi-ring structure.

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