Photonic crystal surface emitting laser and method of manufacturing the same

Abstract

To provide a photonic crystal surface emitting laser capable of suppressing deterioration of characteristics, and to provide a method of manufacturing the same.SOLUTION: A photonic crystal layer having a refractive index higher than that of the first semiconductor layer and provided on the first semiconductor layer, and an active layer provided on a side of the photonic crystal layer opposite to the first 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 periodically arranged in a plane of the photonic crystal layer, and the second region includes a plurality of first holes and a plurality of second holes, An area of the second hole in a plane of the photonic crystal layer is larger than an area of the first hole, the first hole and the second hole form a pair, the pair is periodically arranged, and the second hole is deeper than the first hole and extends from the photonic crystal layer to the first semiconductor layer.SELECTED DRAWING: Figure 3

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 used, which are made by stacking a photonic crystal and an active layer with optical gain (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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-180120 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-243962 [Patent Document 3] International Publication No. 2017 / 150387 Summary of the Invention [Problem to be solved by the invention]

[0004] To reduce power consumption, it is possible to miniaturize the PCSEL and lower its threshold current. However, miniaturization can reduce the coupling efficiency of the photonic crystal layer, which can degrade the PCSEL's characteristics. Therefore, the objective of this study is to provide a photonic crystal surface-emitting laser that can suppress this degradation, as well as a method for manufacturing such a laser. [Means for solving the problem]

[0005] The photonic crystal surface-emitting laser according to the present disclosure comprises a first semiconductor layer, a photonic crystal layer having a refractive index higher than that of the first semiconductor layer and provided on the first semiconductor layer, and an active layer provided on the side of the photonic crystal layer opposite the first 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 periodically arranged in the first region within the plane of the photonic crystal layer, the second regions including a plurality of first holes and a plurality of second holes, the area of ​​the second holes within the plane of the photonic crystal layer being larger than the area of ​​the first holes, the first holes and the second holes forming pairs, the pairs being periodically arranged, the second holes being deeper than the first holes and extending from the photonic crystal layer to the first semiconductor layer.

[0006] A method for manufacturing a photonic crystal surface-emitting laser according to the present disclosure includes the steps of: forming a photonic crystal layer on a first semiconductor layer, the photonic crystal layer having a refractive index higher than that of the first semiconductor layer; forming a mask on an upper surface of the photonic crystal layer, the mask having openings corresponding to first holes and second holes; performing dry etching using the mask; and forming an active layer on the photonic crystal layer on the opposite side of the first semiconductor layer, the photonic crystal layer including a first region and a plurality of second regions having a refractive index different from that of the first region and periodically arranged in the first region within the plane of the photonic crystal layer, the second regions including a plurality of the first holes and a plurality of the second holes, the area of ​​the second holes within the plane of the photonic crystal layer being larger than the area of ​​the first holes, the second holes being deeper than the first holes and extending from the photonic crystal layer to the first semiconductor layer. [Effects of the Invention]

[0007] 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. [Brief explanation of the drawings]

[0008] [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 top view illustrating a photonic crystal surface-emitting laser. [Figure 2B] FIG. 2B is a bottom view illustrating a photonic crystal surface-emitting laser. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the photonic crystal surface-emitting laser. [Figure 4A] FIG. 4A is a plan view of the photonic crystal layer. [Figure 4B] FIG. 4B is an enlarged view of the photonic crystal layer. [Figure 5] FIG. 5 is a diagram illustrating the coupling coefficient. [Figure 6A] FIG. 6A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 6B] FIG. 6B is a top view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 7A] FIG. 7A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 7B] FIG. 7B is a top view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 8A] FIG. 8A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 8B] FIG. 8B is a top view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 9A] FIG. 9A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 9B] FIG. 9B is a top view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 10A] FIG. 10A is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 10B] FIG. 10B is a top view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 11] FIG. 11 is a cross-sectional view illustrating a method for manufacturing a photonic crystal surface-emitting laser. [Figure 12] FIG. 12 is a cross-sectional view illustrating a photonic crystal surface-emitting laser according to the second embodiment. [Figure 13] FIG. 13 is a diagram illustrating the electric field intensity. [Figure 14] FIG. 14 is a cross-sectional view illustrating a photonic crystal surface-emitting laser according to the third embodiment. [Figure 15] FIG. 15 is a cross-sectional view illustrating a photonic crystal surface-emitting laser according to the fourth embodiment. [Figure 16A] FIG. 16A is a plan view illustrating a photonic crystal layer of the photonic crystal surface-emitting laser according to the fifth embodiment. [Figure 16B] FIG. 16B is a plan view illustrating the photonic crystal layer of the photonic crystal surface-emitting laser according to the fifth embodiment. [Figure 17] FIG. 17 is a diagram illustrating the coupling coefficient. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the 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 is a photonic crystal surface-emitting laser comprising: a first semiconductor layer; a photonic crystal layer having a refractive index higher than that of the first semiconductor layer and disposed on the first semiconductor layer; and an active layer disposed on the opposite side of the photonic crystal layer from the first 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 periodically arranged in the first region within a plane of the photonic crystal layer, the second regions including a plurality of first holes and a plurality of second holes, the area of ​​the second holes within the plane of the photonic crystal layer being larger than the area of ​​the first holes, the first holes and the second holes forming pairs, the pairs being periodically arranged, the second holes being deeper than the first holes, and extending from the photonic crystal layer to the first semiconductor layer. This can increase the coupling coefficient of the photonic crystal layer and suppress deterioration of characteristics. (2) In the above (1), the first hole and the second hole may extend from the photonic crystal layer to the first semiconductor layer, thereby increasing the coupling coefficient and suppressing deterioration of characteristics. (3) In the above (1), the first hole may extend to the interface between the photonic crystal layer and the first semiconductor layer, thereby increasing the coupling coefficient and suppressing deterioration of characteristics. (4) In the above (1), the first holes may extend partway through the photonic crystal layer in the thickness direction, which can increase the coupling coefficient and suppress deterioration of characteristics. (5) In any one of (1) to (4) above, the plurality of first holes and the plurality of second holes may be arranged to form a square lattice within the plane of the photonic crystal layer, and the ratio d / a of the distance d between the first holes and the second holes to the lattice constant a of the square lattice may be 0.35 or more and 0.45 or less. This can increase the coupling coefficient and suppress deterioration of characteristics. (6) In any one of (1) to (5) above, the plurality of first holes and the plurality of second holes may be arranged to form a square lattice within the plane of the photonic crystal layer, and the depth of the first holes and the depth of the second holes may be equal to or greater than the lattice constant of the square lattice. This can increase the coupling coefficient and suppress deterioration of characteristics. (7) In any one of (1) to (6) above, the plurality of first holes and the plurality of second holes may be arranged to form a square lattice within the plane of the photonic crystal layer, and the depth of the first holes and the depth of the second holes may be five times or less the lattice constant of the square lattice. This can suppress increases in thermal resistance and electrical resistance. (8) In any of the above (1) to (7), a second semiconductor layer may be provided between the photonic crystal layer and the active layer, and the ends of the first hole and the second hole on the active layer side may be located at the interface between the photonic crystal layer and the second semiconductor layer, thereby increasing the coupling coefficient and suppressing deterioration of characteristics. (9) In any of the above (1) to (8), the ends of the first hole and the second hole on the active layer side may be located inside the photonic crystal layer and closer to the first semiconductor layer than the interface between the photonic crystal layer and the active layer, thereby increasing the coupling coefficient and suppressing deterioration of characteristics. (10) In any of (1) to (9) above, a p-type third semiconductor layer may be provided on the active layer, and the first semiconductor layer and the photonic crystal layer may be n-type layers. Since the n-type photonic crystal layer has the first region and the second region, damage to the photonic crystal layer and the first semiconductor layer is unlikely to occur, and changes in electrical resistance are suppressed. (11) In any one of the above (1) to (10), the first semiconductor layer may contain indium phosphide, and the first region of the photonic crystal layer may contain indium gallium arsenide phosphide. This can increase the coupling coefficient and suppress deterioration of characteristics. (12) A method for manufacturing a photonic crystal surface-emitting laser, comprising the steps of: forming a photonic crystal layer on a first semiconductor layer, the photonic crystal layer having a refractive index higher than that of the first semiconductor layer; forming a mask on an upper surface of the photonic crystal layer, the mask having openings corresponding to first holes and second holes, performing dry etching using the mask; and forming an active layer on the side of the photonic crystal layer opposite the first 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 periodically arranged in the first region within the plane of the photonic crystal layer, the second regions including a plurality of the first holes and a plurality of the second holes, the area of ​​the second holes within the plane of the photonic crystal layer being larger than the area of ​​the first holes, the second holes being deeper than the first holes, and extending from the photonic crystal layer to the first semiconductor layer. This method can increase the coupling coefficient of the photonic crystal layer and suppress deterioration of characteristics.

[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. 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 (second semiconductor layer), an active layer 18, a cladding layer 20, and a contact layer 22, which are stacked in this order. The Z-axis direction is the stacking direction of the layers. Each layer extends within the XY plane. The X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other.

[0013] The contact layer 22 is circular in the XY plane and is located at the center of the upper surface of the cladding layer 20. The electrode 26 is a p-type electrode located on the upper surface of the contact layer 22 and may be formed of, for example, titanium (Ti), platinum (Pt), or gold (Au), or may be formed of other metals. As shown in FIG. 2A, the electrode 26 is circular and located at the center of the upper surface of the cladding layer 20. The diameter of the electrode 26 is φ. The electrode 24 is an n-type electrode and may be formed of, for example, gold (Au), germanium (Ge), or nickel (Ni), or may be formed of other metals. As shown in FIG. 2B, the electrode 24 is located at the periphery of the lower surface of the substrate 10, and the portion surrounded by the electrode 24 functions as a light emission portion (aperture). An aperture may be provided on the upper surface of the photonic crystal surface-emitting laser 100.

[0014] The substrate 10 and cladding layers 12 and 16 are formed of, for example, n-type indium phosphide (n-InP). The cladding layer 20 is formed of, for example, p-InP. The contact layer 22 is formed of, for example, p-type indium gallium arsenide (p-InGaAs). The n-type dopant is, for example, silicon (Si). The p-type dopant is, for example, zinc (Zn). The photonic crystal layer 14 is formed of, for example, n-type indium gallium arsenide phosphide (InGaAsP). The active layer 18 includes multiple well layers and barrier layers formed of, for example, undoped indium gallium arsenide phosphide (InGaAsP) or aluminum gallium indium arsenide (AlGaInAs), and has a multi-quantum well (MQW) structure. The above materials are examples, and each layer may be formed of other materials or a combination of the above materials with other materials. The thickness of each layer will be described later.

[0015] The refractive index of active layer 18 is, for example, 3.5. The refractive index 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 that of cladding layers 12, 16, and 20, for example, 3.4.

[0016] FIG. 3 is an enlarged cross-sectional view of photonic crystal surface-emitting laser 100, showing cladding layers 12 to 20. FIG. 4A is a plan view of photonic crystal layer 14. FIG. 4B is an enlarged view of photonic crystal layer 14. As shown in FIGS. 3 and 4B, photonic crystal layer 14 is a two-dimensional photonic crystal layer having hole 30 (first hole) and hole 32 (second hole). As shown in FIG. 3, holes 30 and 32 penetrate photonic crystal layer 14 in the Z-axis direction and extend to cladding layer 12. The bottoms of holes 30 and 32 are formed in cladding layer 12. The ends of holes 30 and 32 on the active layer 18 side are located at the interface between photonic crystal layer 14 and cladding layer 16. Depth D2 of hole 32 is greater than depth D1 of hole 30.

[0017] The insides of holes 30 and 32 are hollow. The refractive index of InGaAsP, which is the base material of photonic crystal layer 14, is different from the refractive index of holes 30 and 32. That is, photonic crystal layer 14 includes the base material InGaAsP (first region) and holes 30 and 32 (second regions) which have a refractive index different from that of the base material.

[0018] As shown in Figure 4A, the holes 30 and the holes 32 are arranged periodically in the X-axis and Y-axis directions in the plane of the photonic crystal layer 14, and are arranged in a square lattice pattern. The period of the holes 30 and 32 in the X-axis and Y-axis directions is a. The period a is equal to the ratio λ / n of the wavelength λ of light to the effective refractive index n. For example, when λ = 1.3 μm and n = 3.25, a = 0.4 μm.

[0019] FIG. 4B is an enlarged view of a square (square lattice) in the photonic crystal layer 14, with one side having a length a and containing one hole 30 and one hole 32 inside. In other words, the lattice constant of the square lattice is a. The direction in which the holes 30 and 32 are aligned is inclined at, for example, 45° with respect to the X-axis direction and the Y-axis direction. The planar shape of the hole 30 is, for example, circular. The planar shape of the hole 32 is, for example, elliptical. The major axis and minor axis of the hole 32 are inclined at, for example, 45° with respect to the X-axis direction and the Y-axis direction. The area a of one square lattice 2The ratio of the area of ​​holes 30 to the total area (area filling rate) is, for example, 4%, and the area filling rate of holes 32 is, for example, 8%. The distance between the center of gravity (center) of hole 30 and the center of gravity (center) of hole 32 in the X-axis direction and the Y-axis direction is defined as d. As described below, the distance d is determined based on the lattice constant a.

[0020] The thickness of each layer and the depth of the holes are also determined based on the lattice constant a. The thickness T2 of the cladding layer 16 and the thickness T3 of the active layer 18 are, for example, 0.25a, ​​and the thickness T4 of the cladding layer 20 is, for example, 7.5a. The thickness T1 of the photonic crystal layer 14 is, for example, a or greater. The depth D3 of the holes 30 projecting into the cladding layer 12 is, for example, 0.25a, ​​and the overall depth D1 of the holes 30 is, for example, 1.25a or greater. The depth D4 of the holes 32 projecting into the cladding layer 12 is, for example, 0.75a, and the overall depth D2 of the holes 32 is, for example, 1.75a or greater. When a=0.4 μm, the depth D1 is 0.5 μm or greater, and the depth D2 is 0.7 μm or greater.

[0021] By applying a voltage to electrodes 24 and 26 and injecting a current into active layer 18, active layer 18 generates light. Photonic crystal layer 14 has a plurality of periodically arranged holes 30 and 32, and therefore the refractive index also changes periodically. Light undergoes diffraction and interference in response to changes in the refractive index within photonic crystal layer 14. Light with a wavelength corresponding to the period of the holes in photonic crystal layer 14 is amplified and emitted in the normal direction (Z-axis direction) of photonic crystal layer 14. In the example of Figure 1, the bottom surface of electrode 26 is mirror-finished, which reflects light downward. The portion of substrate 10 surrounded by electrode 24 shown in Figure 2B is the light emission portion (aperture), and light is emitted from the aperture.

[0022] In order to reduce power consumption, it is important to miniaturize the photonic crystal surface-emitting laser 100 and lower the threshold current. However, miniaturization can lead to a deterioration in characteristics. In the first embodiment, the in-plane coupling coefficient of the photonic crystal layer 14 is improved, thereby suppressing deterioration in characteristics.

[0023] 5 is a diagram illustrating the coupling coefficient. The horizontal axis represents the ratio d / a of the distance d between the centers of gravity of holes 30 and 32 to the lattice constant a. The vertical axis represents the coupling coefficient κ. The thickness T1 of photonic crystal layer 14 shown in FIG. 3 and the lattice constant a shown in FIG. 4B are each, for example, 0.4 μm. The area a of the square lattice 2 The area filling rate of the holes 30 is 4%, and the area filling rate of the holes 32 is 8%.

[0024] The larger the ratio d / a, the higher the coupling coefficient κ. If the ratio is 0.35 or more, the coupling coefficient κ is 800 cm -1 When the ratio is 0.4 or more, the coupling coefficient κ is 1000 cm -1 When the ratio is 0.5, the coupling coefficient κ is 1200 cm -1 reaches.

[0025] As mentioned above, the lattice constant a is determined by the wavelength λ and the effective refractive index n, and is equal to the ratio λ / n. As shown in Figure 5, the coupling coefficient changes depending on the ratio d / a between the distance d and the lattice constant a. Therefore, the distance d can be set so that the coupling coefficient becomes higher. For example, by setting the distance d to 0.35a or more, the coupling coefficient κ becomes approximately 800cm. -1 As the distance d approaches 0.5a, the scattering of light from the photonic crystal layer 14 decreases, resulting in a decrease in optical output. The distance d is set to 0.5a or less, for example, 0.45a or less.

[0026] (Manufacturing method) 6A, 7A, 8A, 9A, 10A, and 11 are cross-sectional views illustrating a method for manufacturing the photonic crystal surface-emitting laser 100. Figures 6B, 7B, 8B, 9B, and 10B are top views illustrating a method for manufacturing the photonic crystal surface-emitting laser 100.

[0027] As shown in FIGS. 6A and 6B, cladding layer 12 and photonic crystal layer 14 are epitaxially grown in this order on the upper surface of substrate 10 by, for example, organometallic vapor phase epitaxy (OMVPE).

[0028] As shown in Figures 7A and 7B, a plurality of holes 30 and 32 are formed. A resist mask 29 is formed on the upper surface of the photonic crystal layer 14 by photolithography. The resist mask 29 has openings corresponding to the holes 30 and 32. The holes 30 and 32 are formed by dry etching the photonic crystal layer 14. The etching progresses faster in the larger openings corresponding to the holes 32 and slower in the smaller openings corresponding to the holes 30. Therefore, the holes 30 and 32 can be formed in a single etching step. The holes 30 and 32 extend from the upper surface of the photonic crystal layer 14 to partway through the cladding layer 12. After etching, the resist mask 29 is removed.

[0029] 8A and 8B, cladding layer 16, active layer 18, cladding layer 20, and contact layer 22 are epitaxially grown in this order on the upper surface of photonic crystal layer 14 by OMVPE or the like. Cladding layer 16 contacts the upper surface of photonic crystal layer 14 and forms a flat surface. Active layer 18, cladding layer 20, and contact layer 22 are formed on flat cladding layer 16. The insides of holes 30 and 32 are not filled with cladding layer 16 and remain hollow.

[0030] As shown in Figures 9A and 9B, the contact layer 22 is formed into a circular shape. For example, a circular resist mask (not shown) is formed on the contact layer 22 by photolithography. The contact layer 22 is shaped by removing the portion of the contact layer 22 that is exposed from the resist mask by dry etching or wet etching. After etching, the cladding layer 20 is exposed outside the contact layer 22. The resist mask is removed.

[0031] 10A and 10B, an electrode 26 is provided on the upper surface of the contact layer 22. For example, a resist mask is provided by photolithography, and a metal layer is formed by vapor deposition or the like. Unnecessary metal layer is removed along with the resist mask, and the electrode 26 is formed from the metal layer on the contact layer 22. An insulating film may be provided on the cladding layer 20, and a pad connected to the electrode 26 may be provided on the insulating film.

[0032] 11, the electrode 24 is provided on the lower surface of the substrate 10 by vapor deposition and lift-off in the same manner as the electrode 26. Through the above steps, the photonic crystal surface-emitting laser 100 is formed.

[0033] According to the first embodiment, as shown in FIG. 3, a cladding layer 12 and a photonic crystal layer 14 having a higher refractive index than the cladding layer 12 are stacked. The holes 30 and 32 in the photonic crystal layer 14 extend from the photonic crystal layer 14 to the cladding layer 12. The coupling coefficient is increased, and light is strongly diffracted by the photonic crystal layer 14. Degradation of characteristics such as threshold current and optical output can be suppressed. The photonic crystal surface-emitting laser 100 can be made compact while maintaining good characteristics. Miniaturization can reduce power consumption. For example, the diameter φ of the electrode 26 shown in FIG. 1 can be reduced to make the photonic crystal surface-emitting laser 100 compact. Lasing is possible even when the diameter φ is reduced to 40 μm or less, for example, 20 μm.

[0034] As shown in FIG. 3 , photonic crystal layer 14 has holes 30 and 32 with a refractive index different from that of the base material, InGaAsP. Both holes 30 and 32 penetrate photonic crystal layer 14 and extend to cladding layer 12. More specifically, one end of holes 30 and 32 is located at the interface between photonic crystal layer 14 and cladding layer 16, and the other end is located in cladding layer 12. This increases the coupling coefficient and strongly diffracts light, thereby suppressing deterioration of characteristics. As will be described in the second embodiment, the configuration of holes 30 and 32 may be modified. Instead of holes, photonic crystal layer 14 may have regions with a refractive index different from that of the base material.

[0035] As shown in Fig. 4A, the multiple holes 30 and 32 are arranged in a square lattice pattern in the XY plane. As shown in Fig. 4B, the ratio d / a of the distance d between the centers of gravity of the holes to the lattice constant a is 0.35 or more and 0.45 or less. By setting the ratio d / a within this range, the coupling coefficient can be increased as shown in Fig. 5, and the photonic crystal surface-emitting laser 100 can be made compact while maintaining good characteristics. The ratio d / a may be, for example, 0.35 or more, 0.4 or more, 0.5 or less, or 0.55 or less.

[0036] The depth D1 of the holes 30 is 1.25a or more, and the depth D2 of the holes 32 is 1.75a or more. Deep holes 30 and 32 increase the coupling coefficient, strongly diffract light, and suppress deterioration of characteristics. To improve the coupling coefficient, it is preferable that the depth of holes 30 and 32 be equal to or greater than the lattice constant a. On the other hand, if holes 30 and 32 are too deep, thermal resistance and electrical resistance increase. An increase in temperature causes deterioration of characteristics. An increase in electrical resistance increases power loss. It is preferable that the depths D1 and D2 are, for example, five times the lattice constant a or less. Increases in thermal resistance and electrical resistance can be suppressed.

[0037] As shown in Fig. 4A, the area of ​​hole 32 in the plane of photonic crystal layer 14 is larger than the area of ​​hole 30, and as shown in Fig. 3, hole 32 is deeper than hole 30. By providing two types of holes 30 and 32 of different sizes in photonic crystal layer 14, it becomes easier to extract light in the normal direction (Z-axis direction). As shown in Figs. 7A and 7B, holes 30 and 32 can be formed simultaneously by providing a resist mask 29 and performing dry etching once. This simplifies the process.

[0038] Larger holes 30 and 32 can strengthen the diffraction of light. On the other hand, larger holes 30 and 32 decrease the effective refractive index of photonic crystal layer 14, which may cause light to leak into other layers. The area filling rate of each of holes 30 and 32 relative to a square lattice is, for example, 15% or less. The sum of the area filling rate of holes 30 and holes 32 is, for example, 10% or more and 20% or less.

[0039] As shown in FIG. 4B, holes 30 are circular and holes 32 are elliptical. The alignment direction of holes 30 and 32 is tilted with respect to the X-axis and Y-axis directions. Light is diffracted and emitted in the normal direction. Holes 30 may be elliptical and holes 32 may be circular. Holes 30 and 32 may have the same shape, for example, both may be circular or both may be elliptical. Holes 30 and 32 may be polygonal, for example, triangular or rectangular. The angle at which holes 30 and 32 are aligned with respect to the X-axis and Y-axis directions may be other than 45°.

[0040] As shown in FIG. 3, photonic crystal layer 14, cladding layer 16, and active layer 18 are laminated in this order. Because active layer 18 is not formed during the process of forming holes 30 and 32 shown in FIGS. 4A and 4B, etching does not damage active layer 18. As shown in FIG. 8A, active layer 18 is formed on cladding layer 16, which is flatter than photonic crystal layer 14, so depressions and the like are unlikely to occur in active layer 18. Photonic crystal layer 14 may be laminated on active layer 18. However, during the process of forming holes 30 and 32, dry etching may progress to active layer 18, potentially damaging active layer 18. By laminating active layer 18 on photonic crystal layer 14 as shown in FIG. 3, damage can be suppressed.

[0041] Damage caused by dry etching may occur around holes 30 and 32 in photonic crystal layer 14 and cladding layer 12. The damaged areas exhibit n-type characteristics. Because photonic crystal layer 14 and cladding layer 12 are n-type layers, electrical resistance is unlikely to increase even if damage occurs. Photonic crystal layer 14 and cladding layer 12 may be p-type layers. However, as described above, damage may occur around holes 30 and 32. If damage exhibiting n-type characteristics occurs in a p-type layer, electrical resistance will increase. By making photonic crystal layer 14 and cladding layer 12 n-type layers, the increase in electrical resistance can be suppressed.

[0042] The cladding layer 12 is made of n-InP. The photonic crystal layer 14 is made of InGaAsP and has a higher refractive index than the cladding layer 12. By providing holes 30 and 32 in these two layers, the coupling coefficient can be increased. The substrate 10, the cladding layers 12, 16, and 20, the photonic crystal layer 14, the active layer 18, and the contact layer 22 may be made of compound semiconductors other than those mentioned above. The photonic crystal layer 14 may be made of, for example, n-type aluminum gallium indium arsenide (n-AlGaInAs).

[0043] For example, substrate 10 and photonic crystal layer 14 may be formed of n-type gallium arsenide (n-GaAs), and cladding layers 12 and 16 may be formed of n-AlGaAs. Cladding layer 20 may be formed of p-AlGaAs, and contact layer 22 may be formed of p-GaAs. Active layer 18 may be formed of a stacked structure of InGaAs / AlGaAs or AlGaInAs.

[0044] Second Embodiment FIG. 12 is a cross-sectional view illustrating a photonic crystal surface-emitting laser 200 according to the second embodiment, and is an enlarged view similar to FIG. 3. Description of the same configuration as in the first embodiment will be omitted. The D-axis direction in FIG. 12 is opposite to the Z-axis direction. As shown in FIG. 12, the lower end of the hole 30 is located at the interface between the cladding layer 12 and the photonic crystal layer 14. The depth D1 of the hole 30 is equal to the thickness T1 of the photonic crystal layer 14. The depth D2 of the hole 32 is greater than the thickness T1 by, for example, 0.5a.

[0045] In the second embodiment, holes 30 penetrate the photonic crystal layer 14. Holes 32 extend from the photonic crystal layer 14 to the cladding layer 12. As in the first embodiment, the coupling coefficient is increased, which can suppress deterioration in the characteristics of the photonic crystal surface-emitting laser 200. The photonic crystal surface-emitting laser 200 can be made both compact and have good characteristics.

[0046] FIG. 13 is a diagram illustrating electric field intensity. The horizontal axis represents the vertical position, normalized by the lattice constant a. 0 on the horizontal axis is the center of the active layer 18, positive values ​​represent the position in the D-axis direction (the position on the substrate 10 side), and negative values ​​represent the position in the Z-axis direction (the position on the cladding layer 20 side). The vertical axis represents electric field intensity. The dashed line represents the calculation result of the electric field intensity for the comparative example, and the solid line represents the calculation result for the second embodiment.

[0047] In the comparative example, neither of holes 30 nor 32 penetrates photonic crystal layer 14, and their lower ends are located above the interface between photonic crystal layer 14 and cladding layer 12. As shown by the dashed lines in Figure 13, light confinement in high-refractive-index photonic crystal layer 14 is strong, and light confinement in active layer 18 is weak.

[0048] On the other hand, in the second embodiment, holes 30 and 32 penetrate photonic crystal layer 14. Compared to the comparative example, light confinement in photonic crystal layer 14 is weaker and light confinement in active layer 18 is stronger. This improves characteristics such as threshold current and optical output.

[0049] <Third embodiment> FIG. 14 is a cross-sectional view illustrating a photonic crystal surface-emitting laser 300 according to the third embodiment, and is an enlarged view similar to FIG. 3. Description of the same configuration as in the first embodiment will be omitted. As shown in FIG. 14, the hole 30 does not penetrate the photonic crystal layer 14 and does not reach the cladding layer 12. The lower end of the hole 30 is located in the photonic crystal layer 14, and the photonic crystal layer 14 forms the bottom surface. The hole 32 penetrates the photonic crystal layer 14 and reaches the cladding layer 12. The depth D1 of the hole 30 is smaller than the thickness T1 of the photonic crystal layer 14 by, for example, 0.25a. The depth D2 of the hole 32 is larger than the thickness T1 by, for example, 0.5a.

[0050] According to the third embodiment, the holes 32 extend from the photonic crystal layer 14 to the cladding layer 12, thereby increasing the coupling coefficient and suppressing deterioration of the characteristics of the photonic crystal surface-emitting laser 300. This makes it possible to achieve both miniaturization and good characteristics of the photonic crystal surface-emitting laser 300.

[0051] <Fourth embodiment> Fig. 15 is a cross-sectional view illustrating a photonic crystal surface-emitting laser 400 according to the fourth embodiment, and is an enlarged view similar to Fig. 3. Description of the same configuration as in the first embodiment will be omitted.

[0052] As shown in FIG. 15 , the photonic crystal surface-emitting laser 400 does not have a cladding layer 16. An active layer 18 is stacked on the upper surface of the photonic crystal layer 14. The thickness T1 of the photonic crystal layer 14 is, for example, larger than the lattice constant a. The holes 30 and 32 do not penetrate from the upper surface to the lower surface of the photonic crystal layer 14. The upper ends of the holes 30 and 32 are located within the photonic crystal layer 14. The photonic crystal layer 14 closes the upper ends of the holes 30 and 32. The lower ends of the holes 30 and 32 are located in the cladding layer 12. The depths of the holes 30 and 32 are, for example, similar to those of the first embodiment. The depth D1 of the hole 30 is, for example, 1.25a, ​​and the protrusion amount D3 from the lower surface of the photonic crystal layer 14 is, for example, 0.25a. The depth D2 of the hole 32 is, for example, 1.75a, and the protrusion amount D4 is, for example, 0.75a.

[0053] The substrate 10 and the photonic crystal layer 14 are made of, for example, n-type gallium nitride (n-GaN). The cladding layer 12 is made of, for example, n-type aluminum gallium nitride (n-AlGaN). The cladding layer 20 is made of, for example, p-AlGaN, and the contact layer 22 is made of, for example, p-GaN. The active layer 18 is made of, for example, indium gallium nitride (InGaN).

[0054] According to the fourth embodiment, the holes 30 and 32 extend from the photonic crystal layer 14 to the cladding layer 12. Since the coupling coefficient is increased, deterioration of the characteristics of the photonic crystal surface-emitting laser 400 can be suppressed. The photonic crystal surface-emitting laser 400 can be made compact while maintaining good characteristics. As in the first to fourth embodiments, it is sufficient that at least one of the two types of holes 30 and 32 extends from the photonic crystal layer 14 to the cladding layer 12.

[0055] Fifth Embodiment 16A and 16B are plan views illustrating the photonic crystal layer 14 of the photonic crystal surface-emitting laser according to the fifth embodiment. Similar to FIG. 4B, FIG. 16B is an enlarged view of one square lattice. Description of the same configuration as in the first embodiment will be omitted. As shown in FIGS. 16A and 16B, the photonic crystal layer 14 has one type of hole 34. The planar shape of the holes 34 is, for example, circular, but they may also be elliptical or other. As shown in FIG. 16A, the multiple holes 34 are arranged at a period a in the X-axis and Y-axis directions. The area filling factor of the holes 34 with respect to the square lattice is, for example, 12%. Similar to the holes 30 and 32 in FIG. 3, the holes 34 penetrate the photonic crystal layer 14 and extend to the cladding layer 12.

[0056] FIG. 17 is a diagram illustrating the coupling coefficient. The horizontal axis represents the ratio T1 / a of the thickness T1 of the photonic crystal layer 14 to the lattice constant a. The vertical axis represents the coupling coefficient κ. The larger the ratio, the higher the coupling coefficient. When the ratio is 1 or more, the coupling coefficient is 800 cm -1 As shown in Fig. 17, in order to increase the coupling coefficient, it is preferable to set the thickness T1 to be equal to or larger than the lattice constant a.

[0057] According to the fifth embodiment, as in the first embodiment, the coupling coefficient is increased, so that deterioration of the characteristics of the photonic crystal surface-emitting laser can be suppressed, and both miniaturization and good characteristics of the photonic crystal surface-emitting laser can be achieved.

[0058] 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]

[0059] 10 Substrate 12, 16, 20 cladding layers 14 Photonic crystal layer 18 Active layer 22 Contact layer 24, 26 electrodes 29 Resist mask 30, 32, 34 holes 100, 200, 300, 400 Photonic crystal surface-emitting laser

Claims

1. a first semiconductor layer; a photonic crystal layer having a refractive index higher than that of the first semiconductor layer and provided on the first semiconductor layer; an active layer provided on the opposite side of the photonic crystal layer from the first semiconductor layer, 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 periodically arranged in the first region within a plane of the photonic crystal layer; the second region includes a plurality of first holes and a plurality of second holes; an area of ​​the second hole in the plane of the photonic crystal layer is larger than an area of ​​the first hole; the first holes and the second holes form pairs, and the pairs are periodically arranged; The second hole is deeper than the first hole and extends from the photonic crystal layer to the first semiconductor layer.

2. The photonic crystal surface-emitting laser according to claim 1 , wherein the first hole and the second hole extend from the photonic crystal layer to the first semiconductor layer.

3. The photonic crystal surface-emitting laser according to claim 1 , wherein the first hole extends to an interface between the photonic crystal layer and the first semiconductor layer.

4. The photonic crystal surface-emitting laser according to claim 1 , wherein the first hole extends partway through the photonic crystal layer in the thickness direction.

5. the plurality of first holes and the plurality of second holes are arranged to form a square lattice in a plane of the photonic crystal layer; 5. The photonic crystal surface-emitting laser according to claim 1, wherein the ratio d / a of the distance d between the first hole and the second hole to the lattice constant a of the square lattice is 0.35 or more and 0.45 or less.

6. the plurality of first holes and the plurality of second holes are arranged to form a square lattice in a plane of the photonic crystal layer; 6. The photonic crystal surface-emitting laser according to claim 1, wherein the depth of the first hole and the depth of the second hole are equal to or greater than the lattice constant of the square lattice.

7. the plurality of first holes and the plurality of second holes are arranged to form a square lattice in a plane of the photonic crystal layer; 7. The photonic crystal surface-emitting laser according to claim 1, wherein the depth of the first hole and the depth of the second hole are five times or less the lattice constant of the square lattice.

8. a second semiconductor layer provided between the photonic crystal layer and the active layer; 8. The photonic crystal surface-emitting laser according to claim 1, wherein the ends of the first hole and the second hole on the active layer side are located at the interface between the photonic crystal layer and the second semiconductor layer.

9. 9. The photonic crystal surface-emitting laser according to claim 1, wherein the ends of the first hole and the second hole on the active layer side are located inside the photonic crystal layer and closer to the first semiconductor layer than the interface between the photonic crystal layer and the active layer.

10. a p-type third semiconductor layer provided on the active layer; 10. The photonic crystal surface-emitting laser according to claim 1, wherein the first semiconductor layer and the photonic crystal layer are n-type layers.

11. the first semiconductor layer comprises indium phosphide; 11. The photonic crystal surface-emitting laser according to claim 1, wherein the first region of the photonic crystal layer contains indium gallium arsenide phosphide.

12. forming a photonic crystal layer on a first semiconductor layer, the photonic crystal layer having a refractive index higher than that of the first semiconductor layer; forming a mask on the upper surface of the photonic crystal layer, the mask having an opening corresponding to the first hole and an opening corresponding to the second hole; performing dry etching using the mask; and forming an active layer on the side of the photonic crystal layer opposite to the first semiconductor layer, 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 periodically arranged in the first region within a plane of the photonic crystal layer; the second region includes a plurality of the first holes and a plurality of the second holes; an area of ​​the second hole in the plane of the photonic crystal layer is larger than an area of ​​the first hole; The method for manufacturing a photonic crystal surface-emitting laser, wherein the second hole is deeper than the first hole and extends from the photonic crystal layer to the first semiconductor layer.

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