Photonic crystal surface-emitting laser and method for manufacturing same

Abstract

This photonic crystal surface-emitting laser comprises an active layer, a photonic crystal layer, and a first semiconductor layer, wherein: the photonic crystal layer has a base material and a plurality of holes periodically arranged in the base material; the holes extend from one surface of the photonic crystal layer to the opposite surface of the photonic crystal layer; the first semiconductor layer is provided on the one surface of the photonic crystal layer; and the lengths of the holes in the <110> direction of the photonic crystal layer are smaller than the lengths of the holes in the <1-10> direction of the photonic crystal layer.　

Description

Photonic crystal surface-emitting laser and method for manufacturing the same

[0001] This disclosure relates to a photonic crystal surface-emitting laser and a method for manufacturing the same. This disclosure claims priority to Japanese Application No. 2022-121596, filed July 29, 2022, and incorporates by reference all of the contents of said Japanese application.

[0002] Photonic-crystal surface-emitting lasers (PCSELs) have been used, in which a photonic crystal and an active layer having optical gain are stacked (see, for example, Patent Documents 1 to 3). Photonic crystals include a periodic structure with a refractive index different from that of the base material. By diffracting light within the plane of the photonic crystal, light is oscillated at a wavelength based on the period and emitted in the direction normal to the plane. Because the resonator extends within a plane, PCSELs are superior to edge-emitting lasers in terms of single-mode operation and high output.

[0003] JP 2007-180120 A JP 2008-243962 A WO 2017 / 150387 A

[0004] The photonic crystal surface-emitting laser according to the present disclosure comprises an active layer, a photonic crystal layer, and a first semiconductor layer, wherein the photonic crystal layer has a base material and a plurality of voids periodically arranged in the base material, the voids extending from one surface of the photonic crystal layer to the opposite surface of the photonic crystal layer, the first semiconductor layer being provided on the one surface of the photonic crystal layer, and the length of the voids in the <110> direction of the photonic crystal layer being shorter than the length of the voids in the <1-10> direction of the photonic crystal layer.

[0005] The method for manufacturing a photonic crystal surface-emitting laser according to the present disclosure includes the steps of forming a plurality of periodically arranged voids in a base material of a photonic crystal layer, the voids extending from one surface of the photonic crystal layer to the opposite surface, forming a first semiconductor layer on the one surface of the photonic crystal layer, and forming an active layer, wherein the length of the voids in the <110> direction of the photonic crystal layer is smaller than the length of the voids in the <1-10> direction of the photonic crystal layer.

[0006] FIG. 1 is a cross-sectional view illustrating a photonic crystal surface-emitting laser according to the first embodiment. FIG. 2A is a top view illustrating a photonic crystal surface-emitting laser. FIG. 2B is a bottom view illustrating a photonic crystal surface-emitting laser. FIG. 3 is an enlarged cross-sectional view of the photonic crystal surface-emitting laser. FIG. 4A is a plan view of a photonic crystal layer. FIG. 4B is an enlarged view of the photonic crystal layer. FIG. 5A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. FIG. 5B is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. FIG. 6A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. FIG. 6B is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. FIG. 7A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. FIG. 7B is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. FIG. 8A is a plan view illustrating a photonic crystal surface-emitting laser according to Comparative Example 1. FIG. 8B is a plan view illustrating a photonic crystal surface-emitting laser according to Comparative Example 2. FIG. 9 is a cross-sectional view illustrating a photonic crystal surface-emitting laser according to a modified example. Fig. 10 is a plan view illustrating a photonic crystal surface-emitting laser according to a second embodiment. Fig. 11 is a plan view illustrating a photonic crystal surface-emitting laser according to a third embodiment. Fig. 12 is a plan view illustrating a photonic crystal surface-emitting laser according to a fourth embodiment. Fig. 13 is a plan view illustrating a photonic crystal surface-emitting laser according to a fifth embodiment. Fig. 14 is a plan view illustrating a photonic crystal surface-emitting laser according to a sixth embodiment.

[0007] [Problem to be Solved by the Present Disclosure] Holes are provided in the base material of a photonic crystal layer. The refractive index of the holes differs from that of the base material, allowing for diffraction of light. However, dislocations occur in the semiconductor layer provided on the photonic crystal layer with the holes. Dislocations reduce the crystallinity of the semiconductor layer, degrading the characteristics of the PCSEL. Therefore, an object of the present disclosure is to provide a photonic crystal surface-emitting laser capable of suppressing dislocations in the semiconductor layer, and a method for manufacturing the same.

[0008] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a photonic crystal surface-emitting laser capable of suppressing deterioration of characteristics, and a method for manufacturing the same.

[0009] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0010] One aspect of the present disclosure provides a photonic crystal surface-emitting laser (PCL) including: an active layer, a photonic crystal layer, and a first semiconductor layer; the photonic crystal layer has a base material and a plurality of periodically arranged voids in the base material, the voids extending from one surface of the photonic crystal layer to the opposite surface of the photonic crystal layer; the first semiconductor layer is provided on the one surface of the photonic crystal layer; and the length of the voids in the <110> direction of the photonic crystal layer is shorter than the length of the voids in the <1-10> direction of the photonic crystal layer. The growth rate of the first semiconductor layer in the <110> direction is higher than the growth rate in the <1-10> direction. Rapid growth of the first semiconductor layer in the <110> direction results in rapid closure of the voids. Closure of the voids suppresses dislocations. Degradation of the characteristics of the PCL is suppressed. (2) In (1) above, the planar shape of the air holes may have a first axis of symmetry and a second axis of symmetry, the length of the air holes in the direction of the first axis of symmetry may be smaller than the length of the air holes in the direction of the second axis of symmetry, and the angle between the first axis of symmetry and the <110> direction of the photonic crystal layer may be 30° or less. Since the angle between the first axis of symmetry and the <110> direction is 30°, the air holes are shortened in the <110> direction. The first semiconductor layer grows rapidly in the <110> direction. Since the air holes are closed rapidly, dislocations are suppressed, and deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed. (3) In (1) or (2) above, the first axis of symmetry may be parallel to the <110> direction. The air holes are shortened in the <110> direction. The first semiconductor layer grows rapidly in the <110> direction. Since the air holes are closed rapidly, dislocations are suppressed, and deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed. (4) In any of (1) to (3) above, the planar shape of the voids may be elliptical, and the minor axis of the voids may be parallel to the <110> direction. The voids become shorter in the <110> direction. The first semiconductor layer grows rapidly in the <110> direction. Because the voids are closed quickly, dislocations are suppressed, and deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed. (5) In any of (1) to (4) above, the photonic crystal layer, the first semiconductor layer, and the photonic crystal layer may be stacked in this order.The voids are closed by the first semiconductor layer. The first semiconductor layer can be made thinner, and the active layer can be brought closer to the photonic crystal layer. Optical coupling between the active layer and the photonic crystal layer is strengthened. Diffraction of light facilitates laser oscillation at a desired wavelength. (6) In any of (1) to (4) above, the active layer, the photonic crystal layer, and the first semiconductor layer may be stacked in this order. Deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed. (7) In any of (1) to (6) above, the multiple voids may be arranged in a square lattice pattern within the plane of the photonic crystal layer, and the ratio of the voids to the area of ​​the square lattice may be 3% or more and 30% or less. Deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed. (8) In any of (1) to (7) above, the photonic crystal layer may have a plurality of first voids and a plurality of second voids, the plurality of first voids and the plurality of second voids being periodically arranged in the base material, and the length of at least one of the first voids and the second voids in the <110> direction of the photonic crystal layer may be shorter than the length of the photonic crystal layer in the <1-10> direction. The first semiconductor layer grows rapidly in the <110> direction. Since at least one of the first voids and the second voids is closed quickly, dislocations are suppressed, and deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed. (9) In any of (1) to (8) above, the photonic crystal layer may contain indium gallium arsenide phosphide or aluminum indium gallium arsenide, and the first semiconductor layer may contain indium phosphide. The voids are provided in the indium gallium arsenide phosphide. The indium phosphide first semiconductor layer grows rapidly in the <110> direction, and the voids are closed. Deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed. (10) A method for manufacturing a photonic crystal surface-emitting laser, comprising the steps of: forming a plurality of voids in a base material of a photonic crystal layer, the voids being periodically arranged and extending from one surface of the photonic crystal layer to the opposite surface; forming a first semiconductor layer on the one surface of the photonic crystal layer; and forming an active layer, wherein the length of the voids in the <110> direction of the photonic crystal layer is shorter than the length of the voids in the <1-10> direction of the photonic crystal layer.The growth rate of the first semiconductor layer in the <110> direction is higher than the growth rate in the <1-10> direction. The rapid growth of the first semiconductor layer in the <110> direction results in rapid closure of vacancies. Closure of vacancies suppresses dislocations. Deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed.

[0011] [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.

[0012] <First Embodiment> (Photonic Crystal Surface Emitting Laser) Fig. 1 is a cross-sectional view illustrating a photonic crystal surface emitting laser 100 according to a first embodiment. Fig. 2A is a top view illustrating the photonic crystal surface emitting laser 100, and Fig. 2B is a bottom view.

[0013] As shown in FIG. 1, a photonic crystal surface-emitting laser (PCSEL) 100 includes a substrate 10 , a cladding layer 12 , a photonic crystal layer 14 , a cladding layer 16 (first semiconductor layer), an active layer 18 , a cladding layer 20 , and a contact layer 22 .

[0014] 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 extends parallel to the XY plane. The X, Y, and Z axes are perpendicular to each other.

[0015] A groove 23 is provided in the contact layer 22 and the cladding layer 20. The groove 23 extends from the upper surface of the contact layer 22 to partway through the cladding layer 20. The bottom surface of the groove 23 is recessed below the upper surfaces of the contact layer 22 and the cladding layer 20. As shown in Fig. 2A, the planar shape of the groove 23 is, for example, a ring.

[0016] 1, an insulating film 24 is provided on the upper surface of the contact layer 22. The insulating film 24 covers the upper surface of the contact layer 22 and is also provided inside the groove 23. The insulating film 24 is made of, for example, silicon nitride (SiN) or silicon oxide (SiO ２ ) is an insulator. The insulating film 24 has openings 24a and 24b. The contact layer 22 is exposed from the openings 24a and 24b. As shown in FIG. 2A , the opening 24a has a planar shape of, for example, a ring. The opening 24a is located outside the groove 23. The opening 24b has a planar shape of, for example, a circle. The opening 24b is located inside the groove 23.

[0017] As shown in FIG. 1 , an electrode 26 is provided on the insulating film 24. The electrode 26 is a p-type electrode and may be formed of, for example, titanium (Ti), platinum (Pt), or gold (Au), or may be formed of other metals. The electrode 26 is provided over the entire upper surface of the insulating film 24 and contacts the upper surface of the contact layer 22 inside the opening 24 a. In other words, the electrode 26 is electrically connected to the contact layer 22. As shown in FIGS. 1 and 2A , the edge (outer periphery) of the electrode 26 is provided at the same position as the edge of the opening 24 a.

[0018] An electrode 28 is provided on the surface of the substrate 10 opposite to the surface on which the cladding layer 12 is provided. The electrode 28 is an n-type electrode and may be formed of, for example, gold (Au), germanium (Ge), nickel (Ni), or other metals. The electrode 28 has an opening 28a in the center of the XY plane. As shown in FIG. 2B , the planar shape of the opening 28a is, for example, circular. The substrate 10 is exposed through the opening 28a. The opening 28a functions as a light-emitting portion (aperture).

[0019] The substrate 10 and the cladding layers 12 and 16 are made of, for example, n-type indium phosphide (n-InP). The n-type dopant is, for example, silicon (Si). The cladding layer 12 has a thickness of, for example, 500 nm. The cladding layer 16 has a thickness of, for example, 100 nm.

[0020] The cladding layer 20 is made of, for example, p-type indium phosphide (p-InP). The contact layer 22 is made of, for example, p-type indium gallium arsenide (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.

[0021] The 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.

[0022] 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 above materials are examples, and each layer may be formed of other materials or a combination of the above materials with other materials.

[0023] 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, which is the base material of photonic crystal layer 14, is higher than those of cladding layers 12, 16, and 20, for example, 3.4.

[0024] FIG. 3 is an enlarged cross-sectional view of the photonic crystal surface-emitting laser 100, showing the cladding layer 12 to the cladding layer 20. As shown in FIG. 3, the photonic crystal layer 14 has a plurality of air holes 30. The air holes 30 extend from the surface of the photonic crystal layer 14 on which the cladding layer 16 is provided (the upper surface in FIG. 3) toward the opposite surface of the photonic crystal layer 14 (the lower surface in FIG. 3), and extend, for example, halfway through the photonic crystal layer 14. The inside of the air holes 30 is air. The refractive index of the air holes 30 differs from the refractive index of the base material of the photonic crystal layer 14.

[0025] 4A and 4B are plan views of the photonic crystal layer 14. FIG. 4A illustrates a plane including multiple air holes. FIG. 4B illustrates a single air hole. In FIGS. 4A and 4B, the <110> direction of the photonic crystal layer 14 faces upward. The <1-10> direction faces right. The <100> direction is tilted at 45° with respect to the <110> direction and the <1-10> direction.

[0026] As shown in Figure 4A, the plurality of air holes 30 are arranged periodically on the upper surface of the photonic crystal layer 14. The plurality of air holes 30 are arranged in a square lattice pattern. In Figure 4A, the square lattice is indicated by dotted lines. The sides of the square lattice are inclined at 45° with respect to the <110> direction and the <1-10> direction and point in the <100> direction. The air holes 30 and the square lattice are arranged periodically in the <100> direction. The number of air holes 30 is, for example, several tens or several hundreds.

[0027] The distance a (period) between the centers of adjacent holes 30 is equal to the length of one side of a square lattice. The distance a is determined according to the oscillation wavelength. For example, when the oscillation wavelength is 1300 nm, the distance a is about 400 nm.

[0028] 4B, the voids 30 are elliptical and have a short axis 32 (first axis of symmetry) and a long axis 34 (second axis of symmetry). The voids 30 are line-symmetric about the short axis 32 and line-symmetric about the long axis 34. The short axis 32 is parallel to the <110> direction. The long axis 34 is parallel to the <1-10> direction. The short axis 32 and the long axis 34 are tilted at 45° from the <100> direction.

[0029] The length L1 of the minor axis 32 is smaller than the length L2 of the major axis 34. The length L1 of the minor axis 32 is, for example, 60 nm or more and 150 nm or less, e.g., 120 nm. The length L2 of the major axis 34 is, for example, 100 nm or more and 355 nm or less, e.g., 280 nm.

[0030] Area of ​​one square lattice a ２ The ratio of the area of ​​one hole 30 to the total area (area filling rate) is, for example, 3% or more and 30% or less.

[0031] A voltage is applied to the photonic crystal surface-emitting laser 100 via electrodes 26 and 28. The active layer 18 has optical gain and generates light when carriers are injected into it. The photonic crystal layer 14 has a plurality of periodically arranged holes 30, so the refractive index also changes periodically. Light is Bragg diffracted within the plane of the photonic crystal layer 14. Light having a wavelength corresponding to the period of the holes 30 is amplified and laser oscillation occurs. The laser light is emitted in the normal direction (Z-axis direction) of the photonic crystal layer 14. In the example of FIG. 1 , the bottom surface of the electrode 26 is mirror-finished to reflect light. The opening 28 a in the electrode 28 serves as a light emission portion (aperture), and light is emitted from the aperture.

[0032] 5A to 7B are cross-sectional views illustrating a method for manufacturing photonic crystal surface-emitting laser 100. As shown in Fig. 5A, 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, the base material (InGaAsP) of photonic crystal layer 14 is formed, but voids 30 are not formed.

[0033] 5B to 6B are enlarged views similar to those in FIG. 3. As shown in FIG. 5B, a mask 31 is provided on the upper surface of the photonic crystal layer 14. The mask 31 is made of an insulator such as SiN. An insulating film is formed on the upper surface of the photonic crystal layer 14. A resist pattern is formed using an electron beam or the like, and the resist pattern is transferred to the insulating film to form the mask 31. The mask 31 has a plurality of openings 31a. The upper surface of the photonic crystal layer 14 is exposed through the openings 31a. The planar shape of the openings 31a is an ellipse corresponding to the voids 30. The minor axis of the openings 31a is oriented in the <110> direction. The major axis is oriented in the <1-10> direction.

[0034] As shown in Fig. 6A, a plurality of holes 30 are formed in the photonic crystal layer 14 by reactive ion etching (RIE) or the like. The etching proceeds, for example, partway through the photonic crystal layer 14, but does not reach the bottom surface of the photonic crystal layer 14. The holes 30 have an elliptical shape corresponding to the openings 31a (see Figs. 4A and 4B). After etching is completed, the mask 31 is removed.

[0035] 6B, cladding layer 16, active layer 18, cladding layer 20, and contact layer 22 are epitaxially grown on photonic crystal layer 14. Air holes 30 are closed by cladding layer 16. The inside of air holes 30 is not filled by cladding layer 16 and becomes a cavity.

[0036] The growth rate of the cladding layer 16 in the <110> direction is greater than the growth rate in the <100> direction and the growth rate in the <1-10> direction. As shown in FIG. 4B , the minor axes 32 of the holes 30 are parallel to the <110> direction. The cladding layer 16 grows rapidly in the direction of the minor axes 32 of the holes 30. The cladding layer 16 grown in the <110> direction blocks the upper sides of the holes 30. The active layer 18, the cladding layer 20, and the contact layer 22 are grown on the cladding layer 16.

[0037] 7A, an insulating film 24 is formed by, for example, plasma CVD. Grooves 23 are formed in the insulating film 24 by resist patterning (resist pattern not shown) and etching.

[0038] 7B, an electrode 26 is provided on the contact layer 22 by, for example, vacuum deposition and lift-off. An electrode 28 is provided on the lower surface of the substrate 10. Through the above steps, the photonic crystal surface-emitting laser 100 is formed.

[0039] FIG. 8A is a plan view illustrating a photonic crystal surface-emitting laser according to Comparative Example 1, illustrating a portion of the photonic crystal layer 14 including one air hole 30R1. As shown in FIG. 8A, the major axis 34 of the air hole 30R1 faces in the <100> direction. In other words, the air hole 30R1 faces in a direction rotated 45° to the left from the air hole 30 in FIG. 3B. As in the examples of FIGS. 4A and 4B, the air holes 30 are arranged in a square lattice with sides of 400 nm. The length L3 of the air hole 30R1 in the <110> direction is 170 nm, which is longer than the length L1 of the minor axis 32 of the air hole 30 in FIG. 4B.

[0040] FIG. 8B is a plan view illustrating a photonic crystal surface-emitting laser according to Comparative Example 2, illustrating a portion of the photonic crystal layer 14 including one air hole 30R2. As shown in FIG. 8B, the major axis 34 of the air hole 30R1 faces in the <110> direction. In other words, the air hole 30R2 faces in a direction rotated 90° to the left from the air hole 30 in FIG. 3B. As in the examples of FIGS. 4A and 4B, the air holes 30 are arranged in a square lattice with sides of 400 nm. The length L4 of the air hole 30R2 in the <110> direction is equal to the length of the major axis 34, e.g., 280 nm, and is greater than the length L1 of the minor axis 32 of the air hole 30 in FIG. 4B.

[0041] Crystal growth of the semiconductor layer on the vacancies progresses from the edge of the vacancies toward the top of the vacancies, closing the vacancies. III-V semiconductors, such as InP-based and GaAs-based semiconductors, have a low growth rate in the <1-10> direction and a high growth rate in the <110> direction due to their atomic structure. When growing a GaAs-based semiconductor layer on a vacancy with a long and short axis, a difference in growth rate between the long and short axes is likely to cause crystal defects (dislocations). When growing a GaAs-based semiconductor layer on the vacancies (30R1), the difference between the growth rate along the long axis and the growth rate along the short axis is small. Therefore, a cladding layer with few dislocations can be grown. In other words, the vacancies (30R1) can be closed by a good GaAs-based semiconductor layer with few dislocations. However, the inventors discovered that the crystal growth behavior differs for semiconductor layers other than GaAs-based semiconductors due to differences in materials. For example, in InP-based semiconductors, closing voids in a short time is more effective in suppressing crystal defects in the cladding layer than reducing the difference between the growth rate along the major axis and the growth rate along the minor axis. For example, an InP cladding layer 16 has a low growth rate in the <1-10> direction and a high growth rate in the <110> direction. The length L3 in the <110> direction in the example of FIG. 8A is greater than the length L1 in the example of FIG. 4. The length L4 in the <110> direction in the example of FIG. 8B is greater than the length L1. It takes a long time for the voids to close. In experiments using InP-based semiconductors, dislocations may have occurred in the cladding layer 16 above the voids 30R1 and the cladding layer 16 above the voids 30R2. Dislocations in the cladding layer 16 may degrade the characteristics of the photonic crystal surface-emitting laser.

[0042] According to the first embodiment, the photonic crystal layer 14 has a plurality of voids 30. The length L1 of the voids 30 in the <110> direction is smaller than the length L2 in the <1-10> direction. The growth rate of the cladding layer 16 in the <110> direction is higher than the growth rate in the <100> direction and the growth rate in the <1-10> direction. The cladding layer 16 grows faster in the <110> direction, which allows the voids 30 to be closed quickly by the cladding layer 16. Closing the voids 30 reduces the likelihood of dislocations occurring in the cladding layer 16. Deterioration of the characteristics of the photonic crystal surface-emitting laser 100 due to dislocations is suppressed. Suppressing dislocations improves the crystallinity of the cladding layer 16 and layers above the cladding layer 16 (such as the active layer 18). The characteristics of the photonic crystal surface-emitting laser 100 are improved. For example, it is possible to reduce the threshold current and increase the output power. Long-term reliability is also improved.

[0043] As shown in FIG. 4B , the planar shape of the air holes 30 is elliptical and has two axes of symmetry (a minor axis 32 and a major axis 34). The length L1 of the air holes 30 along the minor axis 32 is smaller than the length L2 of the air holes 30 along the major axis 34. The minor axis 32 is parallel to the <110> direction. Because the direction in which the growth rate of the cladding layer 16 is high is parallel to the orientation of the minor axis 32 of the air holes 30, the cladding layer 16 grows faster along the minor axis 32 than in other directions. The cladding layer 16 quickly closes the air holes 30. This can suppress dislocations in semiconductor layers such as the cladding layer 16. Suppressing dislocations improves the characteristics of the photonic crystal surface-emitting laser 100.

[0044] As shown in Figure 1, a photonic crystal layer 14, a cladding layer 16, and an active layer 18 are stacked in this order. The voids 30 in the photonic crystal layer 14 are closed by the cladding layer 16. The active layer 18 is grown on the cladding layer 16. Because the voids 30 are closed quickly, dislocations are less likely to occur in the cladding layer 16 and active layer 18 above the photonic crystal layer 14. The surface of the cladding layer 16 is flatter than the surface of the photonic crystal layer 14. Because the active layer 18 is grown on a flat surface, it has high crystallinity.

[0045] The cladding layer 16 grows rapidly and closes the voids 30, thereby suppressing the occurrence of dislocations in the cladding layer 16. Even if the cladding layer 16 is thinned to, for example, 50 nm or more and 200 nm or less, the occurrence of dislocations is suppressed. By thinning the cladding layer 16, the distance between the active layer 18 and the photonic crystal layer 14 is reduced. Optical coupling between the active layer 18 and the photonic crystal layer 14 is strengthened. Light generated in the active layer 18 is strongly affected by the photonic crystal layer 14. Diffraction of light facilitates laser oscillation at the desired wavelength. In other words, the output power of the laser light is increased.

[0046] As shown in Fig. 4A, the plurality of holes 30 are arranged in a square lattice pattern. The ratio of the area of ​​the holes 30 to the area of ​​one square lattice is 5% or more and 20% or less. Laser oscillation is possible by diffracting light. The ratio of the area of ​​the holes 30 may be, for example, 3% or more, 10% or more, 15% or less, or 30% or less.

[0047] When the resonant wavelength is 1300 nm, the length a of one side of the square lattice is 400 nm. The length L1 of the minor axis 32 of the hole 30 is 60 nm or more and 150 nm or less. The length L2 of the major axis 34 is 100 nm or more and 355 nm or less. The length L1 of the minor axis 32 is within the above range and is smaller than the length L2. The above dimensions may be changed depending on the resonant wavelength.

[0048] The photonic crystal layer 14 is formed of, for example, InGaAsP or AlInGaAs. The photonic crystal layer 14 is a semiconductor layer containing the above-mentioned compound semiconductor. The cladding layer 16 contains InP, and is formed of, for example, n-type InP. The growth rate varies depending on the crystal direction. The cladding layer 16 has a high growth rate in the <110> direction. By orienting the short axis 32 of the voids 30 in the <110> direction, the voids 30 can be quickly closed by the cladding layer 16. By growing a semiconductor having a high growth rate in the <110> direction, such as InP, on the photonic crystal layer 14, the voids 30 can be quickly closed.

[0049] The holes 30 may extend partway through the photonic crystal layer 14 as shown in FIG. 2, or may extend all the way through the photonic crystal layer 14 to the cladding layer 12 .

[0050] (Modification) Fig. 9 is a cross-sectional view illustrating a photonic crystal surface-emitting laser 110 according to a modification. Description of the same configuration as in the first embodiment will be omitted. As shown in Fig. 9, a substrate 10, a cladding layer 12, an active layer 18, a cladding layer 16, a photonic crystal layer 14, and a cladding layer 20 are stacked in this order. The active layer 18 is provided between the cladding layer 12 and the photonic crystal layer 14.

[0051] As shown in Figures 4A and 4B, the photonic crystal layer 14 has elliptical voids 30 with their minor axes 32 pointing in the <110> direction. The voids 30 can be closed quickly, suppressing the occurrence of dislocations. This improves the characteristics of the photonic crystal surface-emitting laser 110.

[0052] Second Embodiment Fig. 10 is a plan view illustrating a photonic crystal surface-emitting laser according to a second embodiment, showing an enlarged view of the air holes 30 in the photonic crystal layer 14. The same configuration as in the first embodiment will not be described. The air holes 30 and square lattice in Fig. 10 are positioned at an angle θ rotated to the left from the air holes 30 and square lattice in Fig. 4B. The minor axes 32 of the air holes 30 are inclined with respect to the <110> direction. The angle θ between the minor axes 32 and the <110> direction is, for example, 30° or less.

[0053] 4A and 4B, the holes 30 are arranged in a square lattice with a side length of 400 nm. The length L5 of the holes 30 in the <110> direction in FIG. 10 is 139 nm, which is shorter than the length L6 in the <1-10> direction.

[0054] According to the second embodiment, the length L5 of the air holes 30 in the <110> direction is smaller than the length L6 in the <1-10> direction. The cladding layer 16 grows rapidly in the <110> direction, thereby closing the air holes 30. Closing the air holes 30 makes it difficult for dislocations to occur in the cladding layer 16. This suppresses deterioration of the characteristics of the photonic crystal surface-emitting laser.

[0055] The angle θ between the minor axis 32 and the <110> direction is, for example, 30° or less. By setting the angle θ to 30° or less, the length L5 becomes smaller. The cladding layer 16 can close the holes 30 more quickly. The angle θ may be, for example, 35° or less, 20° or less, 10° or less, or 5° or less. The smaller the angle θ, the closer the minor axis 32 is to the <110> direction. The smaller the angle θ, the smaller the length L5 shown in FIG. 10 becomes. If the angle θ is 0°, the minor axis 32 is parallel to the <110> direction as shown in FIG. 4B. At θ = 0°, the length L5 is equal to the length L1 in FIG. 4B. The smaller the length L5, the faster the holes 30 can be closed.

[0056] The shape of the voids 30 is determined by the shape of the openings 31a of the mask 31 used for etching. By making the openings 31a elliptical, the voids 30 also become elliptical. By making the minor axes of the openings 31a parallel to the <110> direction, the minor axes 32 of the voids 30 also become parallel to the <110> direction, as shown in FIG. 4B. By tilting the minor axes of the openings 31a from the <110> direction by an angle θ, the minor axes 32 of the voids 30 also become tilted by an angle θ from the <110> direction, as shown in FIG. 10.

[0057] 10, the minor axis 32 is oriented in a direction rotated counterclockwise by an angle θ from the <110> direction. The minor axis 32 may be oriented in a direction rotated clockwise by an angle θ from the <110> direction.

[0058] 11 is a plan view illustrating a photonic crystal surface-emitting laser according to a third embodiment, showing one square lattice of the photonic crystal layer 14. The same configuration as in the first embodiment will not be described. Two air holes 30 (first air holes) and two air holes 36 (second air holes) are provided in one square lattice. The planar shapes of the air holes 30 and the air holes 36 are each elliptical.

[0059] The voids 36 are smaller than the voids 30 and similar to the voids 30. The minor axes 32 of the voids 30 and the minor axes 37 of the voids 36 are parallel to the <110> direction. The major axes 34 of the voids 30 and the major axes 38 of the voids 36 are parallel to the <1-10> direction. The voids 30 have the same shape as the example in FIG. 4B , for example. The minor axis 37 of the voids 36 is shorter than the minor axis 32 of the voids 30. The major axis 38 of the voids 36 is shorter than the major axis 34 of the voids 30.

[0060] According to the third embodiment, the minor axes of the voids 30 and 36 are parallel to the <110> direction. The cladding layer 16 has a high growth rate in the <110> direction. The voids 30 and 36 are quickly closed by the cladding layer 16. Dislocations are suppressed, and deterioration of the characteristics of the photonic crystal surface-emitting laser is suppressed.

[0061] The photonic crystal layer 14 has two holes 30 and two holes 36 in one square lattice. The number of holes provided in one square lattice may be two or more, for example, three or more, or four or more. In at least one hole, the length in the <110> direction is shorter than the length in the <1-10> direction. For example, the planar shape of at least one hole among the plurality of holes is elliptical. The minor axis of the elliptical hole is oriented within an angle θ or less from the <110> direction.

[0062] 11, both of the two holes 30 and the hole 36 are elliptical. One or both of the two holes 30 and the hole 36 may have a shape other than an ellipse. The shape other than an ellipse may be a polygon as shown in the fourth to sixth embodiments.

[0063] 12 is a plan view illustrating a photonic crystal surface-emitting laser according to a fourth embodiment, illustrating one square lattice in the photonic crystal layer 14. Description of the same configuration as in the first embodiment will be omitted.

[0064] Air holes 40 are provided in the photonic crystal layer 14. The planar shape of the air holes 40 is rectangular. The air holes 40 have a minor axis 41 and a major axis 42. The minor axis 41 is shorter than the major axis 42. The minor axis 41 is parallel to the <110> direction. The major axis 42 is parallel to the <1-10> direction.

[0065] According to the fourth embodiment, the minor axes 41 of the holes 40 are parallel to the <110> direction. As the cladding layer 16 grows rapidly in the <110> direction, the holes 40 are quickly closed by the cladding layer 16. Closing the holes 40 makes it difficult for dislocations to occur in the cladding layer 16. Suppressing dislocations suppresses deterioration of the characteristics of the photonic crystal surface-emitting laser.

[0066] 13 is a plan view illustrating a photonic crystal surface-emitting laser according to a fifth embodiment, illustrating one square lattice in the photonic crystal layer 14. Description of the same configuration as in the first embodiment will be omitted.

[0067] Air holes 44 are provided in the photonic crystal layer 14. The planar shape of the air holes 44 is a rhombus. The air holes 44 have a minor axis 45 and a major axis 46. The minor axis 45 is shorter than the major axis 46. The minor axis 45 is parallel to the <110> direction. The major axis 46 is parallel to the <1-10> direction.

[0068] According to the fifth embodiment, the minor axes 45 of the holes 44 are parallel to the <110> direction. As the cladding layer 16 grows rapidly in the <110> direction, the holes 44 are quickly closed by the cladding layer 16. Closing the holes 44 makes it difficult for dislocations to occur in the cladding layer 16. Suppressing dislocations suppresses deterioration of the characteristics of the photonic crystal surface-emitting laser.

[0069] In the first to fifth embodiments, the holes have two axes of symmetry. The holes are line-symmetric with respect to each of the two axes of symmetry. The holes may be strictly line-symmetric, or may deviate from line symmetry within the range of manufacturing tolerances, for example. The shape of the holes is determined by the etching precision, etc. The holes may deviate slightly from line symmetry depending on the etching precision, etc.

[0070] 14 is a plan view illustrating a photonic crystal surface-emitting laser according to a sixth embodiment, illustrating one square lattice in the photonic crystal layer 14. Description of the same configuration as in the first embodiment will be omitted.

[0071] A hole 50 is provided in the photonic crystal layer 14. The planar shape of the hole 50 is a triangle. One side 51 of the hole 50 is parallel to the <110> direction. Of the vertices of the hole 50, the vertex opposite the side 51 is defined as vertex 52. A line segment that passes through vertex 52 and bisects the side 51 is defined as line segment 53. Line segment 53 is parallel to the <1-10> direction. Side 51 is shorter than line segment 53.

[0072] According to the sixth embodiment, the sides 51 of the holes 50 are parallel to the <110> direction and shorter than the line segments 53 in the <1-10> direction. The cladding layer 16 grows rapidly in the <110> direction, and the holes 50 are quickly closed by the cladding layer 16. The closure of the holes 50 makes it difficult for dislocations to occur in the cladding layer 16. The suppression of dislocations suppresses deterioration of the characteristics of the photonic crystal surface-emitting laser.

[0073] As shown in the first embodiment, the planar shape of the holes may be elliptical. As shown in the fourth to sixth embodiments, the planar shape of the holes may be polygonal. The vertices of the polygon may include curved lines.

[0074] 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 changes are possible within the scope of the gist of the present disclosure described in the claims.

[0075] REFERENCE SIGNS LIST 10 substrate 12, 16, 20 cladding layer 14 photonic crystal layer 18 active layer 22 contact layer 23 groove 24 insulating film 24a, 24b, 28a, 31a opening 26, 28 electrode 31 mask 30, 30R1, 30R2, 36, 40, 50 hole 32, 37, 45 minor axis 34, 38, 46 major axis 51 side 52 vertex 53 line segment 100, 110 photonic crystal surface-emitting laser

Claims

1. An active layer; a photonic crystal layer; A first semiconductor layer, the photonic crystal layer has a base material and a plurality of holes periodically arranged in the base material; the holes extend from one surface of the photonic crystal layer to an opposite surface of the photonic crystal layer; the first semiconductor layer is provided on the one surface of the photonic crystal layer; A photonic crystal surface emitting laser in which the length of the air hole in the <110> direction of the photonic crystal layer is smaller than the length of the air hole in the <1-10> direction of the photonic crystal layer.

2. the planar shape of the hole has a first axis of symmetry and a second axis of symmetry, a length of the hole in the direction of the first axis of symmetry is smaller than a length of the hole in the direction of the second axis of symmetry; 2. The photonic crystal surface emitting laser according to claim 1, wherein the angle between the first symmetry axis and the <110> direction of the photonic crystal layer is 30 degrees or less.

3. The photonic crystal surface emitting laser according to claim 2 , wherein the first symmetry axis is parallel to the <110> direction.

4. The planar shape of the hole is elliptical, 4. The photonic crystal surface emitting laser according to claim 3, wherein the minor axis of the hole is parallel to the <110> direction.

5. 3. The photonic crystal surface emitting laser according to claim 1, wherein the photonic crystal layer, the first semiconductor layer, and the active layer are stacked in this order on a substrate.

6. 3. The photonic crystal surface emitting laser according to claim 1, wherein the active layer, the first semiconductor layer, and the photonic crystal layer are stacked in this order on a substrate.

7. the plurality of holes are arranged in a square lattice pattern within a plane of the photonic crystal layer, 3. The photonic crystal surface emitting laser according to claim 1, wherein a ratio of an area of ​​the holes to an area of ​​the square lattice is 3% or more and 30% or less.

8. the photonic crystal layer has a plurality of first holes and a plurality of second holes; the plurality of first voids and the plurality of second voids are periodically arranged in the base material, 3. The photonic crystal surface-emitting laser according to claim 1, wherein, in at least one of the first holes and the second holes, the length in the <110> direction of the photonic crystal layer is shorter than the length in the <1-10> direction of the photonic crystal layer.

9. the photonic crystal layer comprises indium gallium arsenide phosphide or aluminum indium gallium arsenide; 3. The photonic crystal surface emitting laser according to claim 1, wherein the first semiconductor layer contains indium phosphide.

10. forming a plurality of periodically arranged holes in a base material of a photonic crystal layer, the holes extending from one surface of the photonic crystal layer to an opposite surface of the photonic crystal layer; forming a first semiconductor layer on the one surface of the photonic crystal layer; forming an active layer; A method for manufacturing a photonic crystal surface emitting laser, wherein the length of the air hole in the <110> direction of the photonic crystal layer is smaller than the length of the air hole in the <1-10> direction of the photonic crystal layer.