Vertical-cavity surface-emitting laser and method for manufacturing same

Abstract

The present invention comprises: a first reflector, a first semiconductor layer, an active layer, and a second semiconductor layer, which are provided on a substrate; and a mesa part which protrudes perpendicularly to the first reflector from any of the layers of the first reflector, the first semiconductor layer, the active layer, and the second semiconductor layer, and which has a current constriction layer, a second reflector, and an emission aperture layer. The mesa part has a cylindrical shape having n substantially same-shaped recesses on the side surface thereof, which are arranged in rotationally symmetrical positions with respect to the central axis at an angle of θ = 360° / n with each other, and expose at least the side surface of the current constriction layer. The current constriction layer is composed of: an n-polygonal current injection part coaxial with the central axis and composed of an Al-containing semiconductor layer; and a current constriction part provided around the current injection part and composed of an oxide of the Al-containing semiconductor layer. The emission aperture layer has a circular light-emitting opening coaxial with the current injection part.

Description

Vertical cavity surface-emitting laser and method for manufacturing the same

[0001] The present invention relates to a vertical cavity surface-emitting laser and a method for manufacturing the same.

[0002] Conventionally, vertical cavity surface-emitting lasers (VCSELs) and other vertical cavity-type light-emitting devices are known, which have a structure that resonates light perpendicular to the substrate surface and emits light in a direction perpendicular to the substrate surface.

[0003] For example, Patent Document 1 discloses a surface-emitting laser element having an oxidation-constricting structure that restricts the path of the drive current to only the unoxidized region (current injection region) in the central part of the mesa.

[0004] Patent No. 5721051

[0005] In surface-emitting laser elements as described above, expanding the current injection aperture (current injection region) results in multimode operation, causing the beam to split into two or more beams or become donut-shaped. Therefore, for example, in red and near-infrared VCSELs, it was necessary to reduce the diameter of the oxidative constriction aperture to 4-5 μm in order to obtain a transverse single mode.

[0006] However, single-mode devices have a smaller aperture area compared to multi-mode devices, resulting in a significant decrease in optical output. Furthermore, VCSELs tend to have unstable polarization of emitted light, leading to performance degradation in applications where polarization characteristics are critical.

[0007] The present invention aims to provide a vertical-cavity surface-emitting laser and a method for manufacturing the same, which maintains transverse single-mode operation even when high current is injected and can obtain high optical output. Furthermore, the present invention aims to provide a vertical-cavity surface-emitting laser and a method for manufacturing the same that have high polarization controllability and good extinction characteristics.

[0008] A vertical-cavity surface-emitting laser according to one embodiment of the present invention comprises: a substrate; a first reflector provided on the substrate; a first semiconductor layer of a first conductivity type provided on the first reflector; an active layer provided on the first semiconductor layer; a second semiconductor layer of a second conductivity type provided on the active layer; and a mesa portion having a current-constricting layer, a second reflector provided on the current-constricting layer, and an exit aperture layer provided on the second reflector, which protrudes perpendicularly from any of the layers of the first reflector, the first semiconductor layer, the active layer, and the second semiconductor layer, wherein the mesa portion has a central axis, and the mesa portion is arranged in a rotationally symmetric position with respect to the central axis at an angle of θ = 360° / n (where n is a natural number of 3 or more), and has a cylindrical shape with n substantially identical recesses on its side surface that expose at least the side surface of the current-constricting layer. The current-constricting layer comprises an n-sided current injection section made of an Al-containing semiconductor layer and coaxial with the central axis, and a current-constricting section made of an oxide of the Al-containing semiconductor layer and provided around the current injection section, and the emission aperture layer has a circular light emission aperture coaxial with the current injection section.

[0009] A vertical-cavity surface-emitting laser according to another embodiment of the present invention comprises a substrate, a first reflector provided on the substrate, a first semiconductor layer of a first conductivity type provided on the first reflector, an active layer provided on the first semiconductor layer, a second semiconductor layer of a second conductivity type provided on the active layer, and a mesa portion having a current-constricting layer, a second reflector provided on the current-constricting layer, and an exit aperture layer provided on the second reflector, which protrudes perpendicularly from any of the layers of the first reflector, the first semiconductor layer, the active layer, and the second semiconductor layer to the first reflector. The mesa portion has a central axis, and the mesa portion is arranged in a rotationally symmetric position with respect to the central axis at an angle of θ = 360° / n (where n is a natural number of 3 or more), and has a cylindrical shape having n substantially identical holes inside that are dug from the upper surface of the mesa portion and expose at least the side surface of the current constriction layer, the current constriction layer consists of an n-sided current injection portion made of an Al-containing semiconductor layer and coaxial with the central axis, and a current constriction portion made of an oxide of the Al-containing semiconductor layer provided around the current injection portion, the emission aperture layer has a circular light emission aperture coaxial with the current injection portion.

[0010] A method for manufacturing a vertical-cavity surface-emitting laser according to another embodiment of the present invention comprises the steps of: forming a laminated structure by epitaxially growing a first reflector, a first semiconductor layer of a first conductivity type, an active layer, a second semiconductor layer of a second conductivity type, an Al-containing semiconductor layer, a second reflector, and a contact layer on a substrate in this order; etching the laminated structure from the upper surface of the laminated structure to any of the layers of the first reflector, the first semiconductor layer, the active layer, and the second semiconductor layer to form a cylindrical mesa portion that protrudes perpendicularly to the first reflector; and forming an output electrode on the contact layer, wherein the step of forming the mesa portion comprises forming n recesses on the side surface of the mesa portion that are arranged in rotationally symmetric positions with respect to the central axis of the mesa portion at an angle of θ = 360° / n, have substantially the same shape, and expose at least the side surface of the Al-containing semiconductor layer. The process includes: performing steam treatment to oxidize the Al-containing semiconductor layer exposed from the n recesses to form a current-constricting layer comprising an n-sided current injection section coaxial with the central axis and a current-constricting section provided around the current injection section and made of an oxide of the Al-containing semiconductor layer; and forming a circular opening in the output electrode coaxial with the current injection section.

[0011] A method for manufacturing a vertical-cavity surface-emitting laser according to yet another embodiment of the present invention comprises the steps of: forming a laminated structure by epitaxially growing a first reflector, a first semiconductor layer of a first conductivity type, an active layer, a second semiconductor layer of a second conductivity type, an Al-containing semiconductor layer, a second reflector, and a contact layer on a substrate in this order; etching the laminated structure from the upper surface of the laminated structure to any of the layers of the first reflector, the first semiconductor layer, the active layer, and the second semiconductor layer to form a cylindrical mesa portion that protrudes perpendicularly to the first reflector; and forming an output electrode on the contact layer, wherein the step of forming the mesa portion comprises: drilling from the upper surface of the mesa portion, arranging in rotationally symmetric positions with respect to the central axis of the mesa portion at an angle of θ = 360° / n, and forming n substantially identical holes inside the mesa portion that expose at least the side surface of the Al-containing semiconductor layer; The process includes: performing steam treatment to oxidize the Al-containing semiconductor layer exposed from the n holes to form a current-constricting layer comprising an n-sided current injection section coaxial with the central axis and a current-constricting section provided around the current injection section and made of an oxide of the Al-containing semiconductor layer; and forming a circular opening in the output electrode coaxial with the current injection section.

[0012] This is a schematic cross-sectional view showing the structure of a vertical-cavity surface-emitting laser according to the first embodiment of the present invention. This is a schematic plan view showing the top surface of the vertical-cavity surface-emitting laser. This is a plan view of a cross section along line A-A in Figure 1, viewed from above. This is a schematic diagram showing the relationship between the aperture diameter of the p electrode and the size of the equilateral triangular current injection section. This is a microscopic image of the top surface of the manufactured vertical-cavity surface-emitting laser. This is a diagram showing the optical output-current characteristics of the vertical-cavity surface-emitting laser at 25°C and CW drive. This is a diagram showing the emission spectrum of the vertical-cavity surface-emitting laser when the optical output is 1 mW. This is a far-field image (FFP) of the vertical-cavity surface-emitting laser when the optical output is 1 mW. This is a diagram showing the optical intensity distribution in the horizontal direction of the far-field image shown in Figure 6. This is a diagram showing the optical intensity distribution in the vertical direction of the far-field image shown in Figure 6. This is a near-field image (NFP) of the vertical-cavity surface-emitting laser when the optical output is 1 mW. This is a diagram showing the optical intensity distribution in the horizontal direction of the near-field image shown in Figure 8. This figure shows the optical intensity distribution in the vertical direction of the near-field image shown in Figure 8. This figure shows the NFP, FFP, and spectrum when the drive current is changed for a vertical-cavity surface-emitting laser. This figure shows the temperature dependence of the optical output characteristics of a vertical-cavity surface-emitting laser. This is a plan view showing the current injection section of Modification Example 1. This is a schematic cross-sectional view showing the structure of the vertical-cavity surface-emitting laser of the second embodiment. This is a schematic plan view showing the top surface of the vertical-cavity surface-emitting laser of the second embodiment. This is a microscopic image of the top surface of the vertical-cavity surface-emitting laser of the second embodiment. This is a schematic top view showing the structure of the vertical-cavity surface-emitting laser of the third embodiment. This figure shows the measurement results of the polarization characteristics of the vertical-cavity surface-emitting laser of the third embodiment. This is a schematic plan view of the current injection section of Modification Example 1 of the third embodiment. This is a schematic plan view of the current injection section of Modification Example 2 of the third embodiment. This is a schematic plan view of the current injection section of Modification Example 3 of the third embodiment. This is a schematic top view showing the structure of the vertical-cavity surface-emitting laser of the fourth embodiment.

[0013] Preferred embodiments of the present invention will be described below, but these may be modified and combined as appropriate. In the following description and accompanying drawings, substantially identical or equivalent parts will be denoted by the same reference numerals.

[0014] [First Embodiment] (1) Structure of a Vertical Cavity Surface Emitting Laser Figure 1 is a schematic cross-sectional view showing the structure of a vertical cavity surface emitting laser 10 according to the first embodiment of the present invention. Figure 2A is a schematic plan view showing the top surface of the vertical cavity surface emitting laser 10, and a cross-section along line B-B in Figure 2B is shown in Figure 1. Figure 2B is a plan view of the cross-section along line A-A in Figure 1 viewed from above (in the -z direction).

[0015] The vertical-cavity surface-emitting laser 10 of this embodiment is, for example, a red-emitting vertical-cavity surface-emitting laser (VCSEL). The vertical-cavity surface-emitting laser (VCSEL) 10 has a laminated structure consisting of a conductive substrate 11, a first reflector 13 sequentially formed on the substrate 11, a first semiconductor layer 14, an active layer 15, a second semiconductor layer 16 having the opposite conductivity to the first semiconductor layer 14, a current-constricting layer 21, a second reflector 25, and a contact layer 27.

[0016] These layers are formed on the substrate 11 by epitaxial growth using the MOCVD (metal-organic vapor deposition) method.

[0017] Furthermore, a metal electrode, the p electrode 28 (exit electrode), is provided on the contact layer 27. Both the contact layer 27 and the p electrode 28 have circular or elliptical openings when viewed from above, and these openings are filled with a light-transmitting film 29. The size of the contact layer 27 is smaller than the size of the p electrode 28. The contact layer 27 and the p electrode 28 function as an exit aperture layer, and the opening of the contact layer 27 functions as a light-emitting aperture 29A. In addition, an n electrode 12 is provided on the back surface of the substrate 11. The n electrode 12 consists of a metal layer, for example, composed of Au / Ge / Ni metal.

[0018] The substrate 11 is made of a GaAs substrate with a crystal growth surface tilted, for example, by 6°. The first reflector 13 and the second reflector 25 are both distributed Bragg reflectors (DBRs), having an optical film thickness of 1 / 4 wavelength, and are formed by alternately stacking layers with different refractive indices.

[0019] The first reflector 13 is an n-type semiconductor DBR (n-DBR), for example, n-Al Ga ０．９５ As layer and n-Al ｘ Ga １－ｘ As (0.9 < x < 0.95) is laminated in 50 to 60 pairs. The second reflector 25 is a p-type semiconductor DBR (p-DBR), and p-Al ０．０５ Ga ０．９５ As layer and p-Al ｘ Ga １－ｘ As (0.9 < x < 0.95) is laminated in 35 to 45 pairs. Since the second reflector 25 is provided on the emission side, it has a structure with a smaller number of laminated pairs than the first reflector 13.

[0020] The vertical cavity surface emitting laser 10 has a mesa portion 20 which is a columnar structure portion protruding in the vertical direction (+z direction) of the first reflector 13 from a part of the surface of the first reflector 13. The mesa portion 20 has a central axis CZ perpendicular to the first reflector 13.

[0021] Specifically, the mesa portion 20 is made of an n-AlGaInP layer, and includes a first semiconductor layer 14 that functions as an n-spacer layer, an active layer 15 that emits light in the wavelength range of red light or near-infrared light, and a second semiconductor layer 16 that is made of a p-AlGaInP layer and functions as a p-spacer layer.

[0022] The active layer 15 has a multiple quantum well (MQW) structure and is composed of a plurality of GaInP well layers and AlGaInP barrier layers. The active layer 15 has, for example, 2 to 5 well layers, and the layer thickness of the active layer 15 is, for example, between 20 and 60 nm. Also, the active layer 15 is formed, for example, as a strained quantum well structure having a compressively strained AlGaInP barrier layer. Note that the active layer 15 may be configured to emit near-infrared light.

[0023] The contact layer 27 is made of p-GaAs, and the light-transmissive film 29 is formed of a dielectric film having light transmissivity with respect to the emission wavelength such as SiN and SiO ２ etc. A circular opening formed from the contact layer 27 filled with the light-transmissive film 29 and the p electrode 28 is formed coaxially with the central axis CZ.

[0024] The first reflector 13 and the second reflector 25 constitute a resonator, and the light emitted from the active layer 15 is emitted from the translucent film 29 (circular aperture) (emitted light LE).

[0025] Furthermore, each of the first semiconductor layer 14 and the second semiconductor layer 16 may be composed of multiple semiconductor layers having different crystal compositions or impurity concentrations, and may also include an undoped layer. Additionally, it may include a composition gradient layer in which the crystal composition changes in the thickness direction. This composition gradient may be implemented particularly at or near the interface of a heterolayer where the Al composition or band gap changes.

[0026] Furthermore, the thicknesses of the first semiconductor layer 14 and the second semiconductor layer 16 can be appropriately adjusted according to the position of the active layer 15 and the current constriction layer 21 relative to the intensity distribution of standing waves within the resonator, and the design value of the resonator length. In order to efficiently confine light in the light emission (vertical) direction, it is preferable to design the active layer 15 to be located in the antinodes of the standing wave intensity distribution. Also, since light is scattered in the regions of the current injection section 21A and the oxide layer 21B, it is preferable to design the active layer 15 to be located in the nodes of the standing wave intensity distribution. The thickness of the current constriction layer 21 is preferably less than 60 nm. Furthermore, the optical distance between the first reflector 13 and the second reflector 25 is preferably λmat × 0.5n (where n is a natural number), where λmat is the wavelength within the medium. In other words, it is preferable that the sum of the optical thicknesses of the first semiconductor layer 14, the active layer 15, the second semiconductor layer 16, and the current constriction layer 21 is λmat × 0.5n, where λmat is the wavelength within the medium.

[0027] (2) Current Constriction Layer Below, the current constriction layer 21 will be described in detail. As shown in Figures 1 and 2B, the current constriction layer 21 consists of a current injection section 21A and an oxide layer 21B. The current injection section 21A is p-Al ｙ Ga １－ｙ The material consists of As, and the oxide layer 21B is a p-AlGaAs oxide layer (AlyOz). The Al composition (y) is preferably 0.9 or greater and 1 or less (0.9 ≤ y ≤ 1). In this case, z is preferably between 0.8 and 1.

[0028] The current injection section 21A of the current constriction layer 21 (oxidation constriction layer) is a layer having an equilateral triangular shape when viewed from above, and functions as an equilateral triangular current injection aperture (region). Furthermore, the outside of the current injection section 21A is formed as an oxide layer 21B by, for example, water vapor oxidation. That is, the oxide layer 21B functions as a constriction section that narrows the current and light. Note that the current injection section 21A may be a triangle with rounded corners at its vertices when viewed from above. Also, it is not necessarily a triangle with sides of equal length.

[0029] More specifically, as shown in Figure 2B, the mesa portion 20 has a shape in which three recesses 20D are formed on the side surface of a cylinder. In this specification, a mesa portion 20 having such a shape is referred to as a cylindrical mesa portion 20.

[0030] More specifically, the mesa portion 20 has a shape in which three recesses 20D are formed in the direction of the central axis CZ, at angles of 120° to each other with respect to the central axis CZ, relative to the hypothetical cylindrical side surface 20C (dashed line). The recesses 20D have a shape that is carved perpendicularly from the top surface to the first reflector 13. That is, the recesses 20D are the parts of the mesa portion 20 that have a curved surface perpendicular to the first reflector 13. It is preferable that the bottom surface 20B of the three recesses 20D is formed to be flat, in order to form an equilateral triangular current injection portion 21A.

[0031] Furthermore, the mesa portion 20 has three protrusions 20G that protrude in the same angular direction, corresponding to the three peaks of the current injection portion 21A. The protrusions 20G correspond to the oxide layer 21B and function as waveguides. By forming the protrusions 20G in the region corresponding to the peaks of the current injection portion 21A, the current injection efficiency is increased and high optical output is obtained.

[0032] The three recesses 20D have the same shape and are provided on the side surface of the mesa portion 20 so as to be 120° rotationally symmetric with respect to the central axis CZ of the mesa portion 20. The equilateral triangular current injection portion 21A is coaxial with the central axis CZ, and each side of the current injection portion 21A is formed parallel to the bottom surface 20B of the recesses 20D. In other words, the equilateral triangular current injection portion 21A and the three recesses 20D are provided aligned with respect to the central axis CZ. Furthermore, each side of the current injection portion 21A is formed parallel to the bottom surface 20B of the recesses 20D, and it is preferable that the length of each side of the bottom surface 20B opposite each side of the current injection portion 21A is longer than the length of each opposite side of the current injection portion 21A. This allows the area of ​​the current injection portion 21A to be increased, thereby increasing the optical output.

[0033] In this specification, "identical" or similar terms regarding the shapes of the current injection section 21A and the recess 20D, etc., include cases where they are substantially identical to the extent obtained through the manufacturing process.

[0034] As shown in Figures 1 and 2A, the circular translucent film 29 filling the openings of the p electrode 28 and the contact layer 27 is provided to be coaxial (central axis CZ) with the equilateral triangular-shaped current injection section 21A. Furthermore, it is preferable that a part of the top of the current injection section 21A protrudes outside the opening of the circular translucent film 29, i.e., the opening of the p electrode 28 (circular aperture), when viewed from above (i.e., when viewed from above, a part of the top is large enough to overlap with the p electrode 28). More specifically, as shown in Figure 2C, it is preferable that the diameter of the light emission aperture 29A, i.e., the aperture diameter of the p electrode 28 (2R), is larger than the diameter of the inscribed circle C1 of the current injection section 21A (2R1) and smaller than the diameter of the circumscribed circle C2 of the current injection section 21A (2R2) (R1 < R < R2). As will be described later, the light intensity during emission is highest at or near the vertices of the triangle, so satisfying the condition R1 < R < R2 is preferable because it increases the luminescence efficiency and improves the light output.

[0035] Further, as shown in FIG. 2A, in the mesa portion 20, a patterned p electrode 28 is formed on the contact layer 27. FIG. 2A shows a case where a pad electrode 28P is provided on the p electrode 28.

[0036] (3) Manufacturing Method of Vertical Cavity Surface Emitting Laser The manufacturing method of the vertical cavity surface emitting laser 10 will be described below.

[0037] (Step S1) Using the MOCVD method (metalorganic chemical vapor deposition method) on a substrate 11 made of GaAs, the first reflector 13 (n-type semiconductor DBR), the first semiconductor layer 14, the active layer 15, the second semiconductor layer 16, a p-AlGaAs layer serving as the current confinement layer 21, the second reflector 25 (p-type semiconductor DBR), and the contact layer 27 were sequentially laminated by epitaxial growth.

[0038] Note that, for the epitaxial growth of the semiconductor layer, a molecular beam epitaxial growth method (MBE method) or the like can also be used.

[0039] (Step S2) A photoresist was applied on the laminated structure grown on the substrate 11 in Step S1. Subsequently, a mask corresponding to the mesa portion 20 (see FIG. 2A) was patterned by photolithography.

[0040] (Step S3) Etching was performed by the ECR (Electron Cyclotron Resonance) plasma etching method to form a mesa portion 20 having three recesses 20D of the same shape arranged at 120° rotationally symmetric positions with respect to the central axis CZ of the mesa portion 20 on the side surface of the mesa portion 20. Subsequently, the resist mask was removed.

[0041] Note that, although a case where the laminated structure is etched to the surface of the first reflector 13 to form the mesa portion 20 will be described as an example, etching may be performed at least to a layer deeper than the current confinement layer 21 to form a mesa portion 20 perpendicular to the first reflector 13. Specifically, etching may be performed to reach any one of the second semiconductor layer 16, the active layer 15, and the first semiconductor layer 14 so that the side surface of the current confinement layer 21 (Al-containing semiconductor layer) is exposed, and a vertically protruding mesa portion 20 may be formed.

[0042] (Step S4) A steam oxidation process was performed by heat treatment in steam. By the steam oxidation process, oxidation progressed from the outer periphery to the inside of the p-AlGaAs layer whose end was exposed in the recess 20D, and a current injection portion 21A (current injection aperture) having a regular triangular shape was formed. An oxide layer 21B was formed around the current injection portion 21A, and the oxide layer 21B functions as a constriction portion that constricts current and light.

[0043] (Step S5) A p electrode 28 was formed on the contact layer 27. For the p electrode 28, a Ti / Pt / Au layer formed in this order of titanium (Ti), platinum (Pt), and gold (Au) was used, but the material used for the p electrode 28 is not limited to this.

[0044] An opening having a circular shape and centered on the central axis CZ was made in the contact layer 27 and the p electrode 28, and a circular aperture (light emission aperture) coaxial with the current injection portion 21A was formed.

[0045] (Step S6) The openings in the contact layer 27 and the p electrode 28 were filled with a light-transmissive film 29, and the manufacturing of the vertical cavity surface emitting laser 10 was completed. Note that a microscope image of the upper surface of the manufactured vertical cavity surface emitting laser 10 is shown in FIG. 3.

[0046] (4) Characteristics of the vertical cavity surface emitting laser The characteristics of the vertical cavity surface emitting laser 10 manufactured by the method described above were evaluated. Note that one side of the regular triangular-shaped current injection portion 21A was 13 μm, and the diameter of the circular aperture of the contact layer 27 and the p electrode 28 was 12 - 14 μm.

[0047] FIG. 4 is a diagram showing the optical output-current characteristics (L-I characteristics) of the vertical cavity surface emitting laser 10 when driven at 25° C. in CW (Continuous Wave), and FIG. 5 is a diagram showing the emission spectrum of the vertical cavity surface emitting laser 10 when the optical output is 1 mW (Po = 1 mW).

[0048] Furthermore, Figure 6 shows the far-field image (FFP) of the vertical-cavity surface-emitting laser 10 when the optical output is 1 mW, and Figures 7A and 7B show the optical intensity distribution in the horizontal (H direction) and vertical (V direction), respectively, of the far-field image shown in Figure 6.

[0049] Furthermore, Figure 8 shows the near-field image (NFP) of the vertical-cavity surface-emitting laser 10 when the optical output is 1 mW, and Figures 9A and 9B show the intensity distribution in the horizontal and vertical directions, respectively, of the near-field image shown in Figure 8.

[0050] As shown in Figures 7A and 7B, the FWHM (full width at half maximum) of the light intensity in the direction parallel to one side of the current injection section 21A was 6.2°, and the FWHM in the perpendicular direction was 4.7°. Furthermore, as shown in Figure 6, a good unimodal far-field image was obtained.

[0051] As shown in Figures 8, 9A, and 9B, the light emission pattern has a triangular shape corresponding to the current injection unit 21A, but in addition to the light emission points corresponding to the three vertices of the current injection unit 21A, there is at least one other light emission point within the light emission pattern. The light intensity is highest in the region at or near the vertices of the triangular light emission pattern, followed by the region on or near the sides of the triangle, and lowest in the region near the centroid of the light emission pattern. All of these multiple light emission points operate in transverse single mode, and as a result of having the same phase direction, a multi-emitting light beam with the same phase at each light emission point in the near-field image is obtained, and a high-power transverse single-mode light beam is obtained.

[0052] Figure 10 shows the NFP, FFP, and spectrum of a vertical-cavity surface-emitting laser 10 when the drive current is varied. Specifically, it shows the operating points A1, A2, and A3 of the L-I characteristics shown in Figure 4. Note that the spectral intensity INT (vertical axis) is shown in arbitrary units.

[0053] As shown in Figure 10, oscillation propagates from the top or near the top of the triangular emission pattern, and as the drive current increases, the number of emission points increases, as does the number of peaks in the spectrum. Furthermore, as the drive current increases, the overall light intensity increases, and the electron and hole concentrations near the center of the emission pattern (each emission point) decrease relatively compared to other regions. Consequently, the FFP angle increases due to a self-focusing phenomenon where the refractive index of the central part increases. Even with these phenomena occurring, each spectrum maintains its unimodality, and the transverse single mode is maintained. Here, in Figure 10, the light intensity at the peak wavelength is stronger for A2 than for A3, because a portion of the drive current contributes to the light intensity at wavelengths other than the peak wavelength.

[0054] In conventional technology, a cutoff condition exists for transverse single-mode operation, and typically, transverse single-mode operation is achieved by reducing the diameter of a circular current-confinement / optical-confinement aperture. That is, a single mode is generated in the center of this circular aperture, and when the diameter is increased (for example, to a diameter of 5 μm or more), the waveguide becomes one in which the first-order mode and higher-order modes can be tolerated in principle. As the optical output increases, higher-order modes rise. Since these higher-order modes are light with different phases from each other, the optical output in the central part of the far-field image becomes low, causing the beam to split and produce a multi-peaked beam or a donut-shaped beam.

[0055] In the vertical-cavity surface-emitting laser 10 of this embodiment, the diameter of the translucent film 29 (light emission aperture) was 12-14 μm, and although the side length of the equilateral triangular current injection section 21A (current injection aperture) was 13 μm, which is a relatively large area (equivalent to the area of ​​a circle with a diameter of 9.6 μm), a unimodal light beam was obtained for the far-field image.

[0056] Thus, because it emits light over a large area, it is possible to achieve a transverse single mode (unimodal beam) with high optical output, and it was found to operate differently from conventional vertical cavity surface-emitting lasers (VCSELs).

[0057] From the above viewpoint, it is preferable that the area of ​​the current injection section 21A is larger than that of a circle with a diameter of 6 μm, and more preferably larger than that of a circle with a diameter of 8 μm.

[0058] Figure 11 shows the temperature dependence of the optical output characteristics (L-I characteristics) of the vertical-cavity surface-emitting laser 10. Oscillation was confirmed at temperatures between 20 and 70°C, and a very high optical output was obtained for a transverse-mode single-mode laser.

[0059] As described above, a single-peak transverse-mode single-mode beam was obtained in the far-field image from a region with a large emission area. In other words, a single-mode beam could be obtained with significantly higher optical output compared to a vertical-cavity surface-emitting laser with a small-area circular emission diameter.

[0060] Therefore, according to this embodiment, it is possible to provide a vertical-cavity surface-emitting laser that maintains transverse single-mode operation even when high current is injected and can obtain high optical output.

[0061] (5) Modification Example 1 of the Current Constriction Layer In the above, the case in which the current injection section 21A has an equilateral triangle shape was described as an example, but it is not limited to this. Figure 12 is a plan view showing the current injection section 31A of modification example 1.

[0062] The current injection section 31A of the modified example 1 has a vertex at the vertex position of an equilateral triangle, and each side is a curve that is monotonically concave inward toward the centroid. In other words, the current injection section 31A has a shape in which three rotationally symmetric curves that are monotonically concave toward the centroid of an equilateral triangle are connected at the vertex position of the equilateral triangle.

[0063] Furthermore, while the above-described example of the mesa portion 20 illustrates the case where the bottom surface 20B of the recess 20D is planar, in the mesa portion 20 having the current injection portion 31A of the modified example 1, the recess 20D may have a bottom surface that is a simple concave shape.

[0064] In this specification, the term "equilateral triangle shape" includes the case where the vertices are located at the vertices of an equilateral triangle, and each side is a curve that is monotonically concave inward toward the centroid. The same applies to the term "regular n-gon shape."

[0065] In addition, in the modified example 1, it is preferable that a part of the top of the current injection section 31A protrudes outside the circular light emission aperture 29A, i.e., the aperture of the p electrode 28, when viewed from above.

[0066] (6) Other Modification Examples In the above description, the case in which the current injection section 21A has an equilateral triangle shape was used as an example, but the current injection section 21A may have a regular n-gon shape (where n is a natural number of 3 or more). Preferably, 3 ≤ n ≤ 6, and most preferably n = 3. Alternatively, the current injection section 21A may have a regular n-gon shape in which each side is a curve that is monotonically concave inward toward the centroid.

[0067] In this case, the mesa portion 20 has n identical recesses 20D on its side surface, which are positioned at rotationally symmetrical positions with respect to the central axis CZ of the mesa portion 20 at an angle θ (θ = 360° / n).

[0068] [Second Embodiment] (1) Structure of a Vertical Cavity Surface Emitting Laser Figure 13 is a schematic cross-sectional view showing the structure of a vertical cavity surface emitting laser 50 according to the second embodiment of the present invention. Figure 14A is a schematic plan view showing the top surface of the vertical cavity surface emitting laser 50. A cross-section along line C-C in Figure 14A is shown in Figure 13. Figure 14B is a microscopic image of the top surface of the manufactured vertical cavity surface emitting laser 50.

[0069] The vertical-cavity surface-emitting laser 50 of the second embodiment has a cylindrical mesa portion 60, and the mesa portion 60 has three holes 60H that are drilled perpendicularly to the first reflector 13 by removing the laminated structure from the upper surface of the mesa portion 60 to the upper surface of the first reflector 13. That is, the vertical-cavity surface-emitting laser 50 has three holes 60H inside the mesa portion 60, and the mesa portion 60 has an annular columnar outer circumference 60C that surrounds the three holes 60H.

[0070] The structure of the laminated structure grown on the substrate 11 is the same as that of the vertical-cavity surface-emitting laser 10 of the first embodiment. That is, the cylindrical mesa portion 60 has a current-constricting layer 21 in which a current-injection portion 21A (current-injection aperture) with an equilateral triangular shape, similar to that of the vertical-cavity surface-emitting laser 10 of the first embodiment, is formed.

[0071] The three holes 60H of the mesa portion 60 have the same shape and are positioned outside the current injection portion 21A, with 120° rotational symmetry with respect to the central axis CZ of the mesa portion 60.

[0072] Furthermore, the holes 60H only need to be formed to a depth greater than the current-constricting layer 21 (Al-containing semiconductor layer) so that the side surface of the current-constricting layer 21 is exposed.

[0073] Furthermore, n identically shaped holes 60H are formed, arranged in rotationally symmetrical positions with respect to the central axis CZ at an angle of θ = 360° / n, and the current injection section 21A may have a regular n-gon shape.

[0074] The vertical-cavity surface-emitting laser 50 of this embodiment can be manufactured by the same method as the vertical-cavity surface-emitting laser 10 of the first embodiment. Specifically,

[0075] (a) A resist mask is patterned and formed on the laminated structure grown on the substrate 11.

[0076] (b) Next, etching is performed by ECR etching or the like to form a cylindrical mesa portion 60 and n holes 60H. The three holes 60H are formed by etching the laminated structure to a layer deeper than at least the current constriction layer 21.

[0077] (c) Next, the steam oxidation process is carried out to oxidize the exposed p-AlGaAs layer from the outer periphery to the interior, forming a triangular-shaped current injection section 21A.

[0078] (d) Next, a p-electrode 28 is formed on the contact layer 27. The contact layer 27 and the p-electrode 28 have a circular shape, and an opening is made in the center of the central axis CZ to form a circular aperture coaxial with the current injection section 21A.

[0079] (e) Next, circular openings are made in the contact layer 27 and the p electrode 28, with the central axis CZ at the center, and the openings in the contact layer 27 and the p electrode 28 are filled with a translucent film 29 to complete the manufacture of the vertical cavity surface-emitting laser 50. Alternatively, n holes 60H (where n is a natural number of 3 or more) may be formed in the mesa portion 60 to form a regular n-gonal current injection portion 21A.

[0080] As described above, the vertical-cavity surface-emitting laser 50 of the second embodiment provides a vertical-cavity surface-emitting laser that maintains lateral single-mode operation during high current injection and obtains high optical output, even when the regular n-gonal shaped current injection section 21A (current injection aperture) has a large area.

[0081] [Third Embodiment] (1) Figure 15, showing the shape and orientation of the current injection section, is a schematic top view illustrating the structure of the vertical-cavity surface-emitting laser 70 according to the third embodiment of the present invention. More specifically, Figure 15 shows a top view of the vertical-cavity surface-emitting laser 70 as seen from a direction perpendicular to the active layer 15. The p electrode 28 is omitted. To the right of the top view, an enlarged view of the current injection section 21A of the current constriction layer 21 is shown.

[0082] The vertical-cavity surface-emitting laser 70 of the third embodiment has the same laminated structure and mesa shape as the vertical-cavity surface-emitting laser 10 of the first embodiment, but in the vertical-cavity surface-emitting laser 70, the orientation of the current injection section 21A when viewed from a direction perpendicular to the active layer 15 is defined. More specifically, the current injection section 21A of the vertical-cavity surface-emitting laser 70 has an equilateral triangle shape when viewed from a direction perpendicular to the active layer 15. Furthermore, the side connecting the vertices P1 and P2 of the equilateral triangle of the current injection section 21A is formed parallel to the <011> direction in the crystal orientation of the mesa section 20. Note that the current injection section 21A is not limited to an equilateral triangle shape, but may have a triangular shape such as an isosceles triangle.

[0083] More specifically, one side is parallel to the [01-1] direction, which is the direction from vertex P1 to vertex P2. In other words, one side is parallel to the [0-11] direction, which is the direction from vertex P2 to vertex P1. The direction perpendicular to this side is the

[011] direction, and vertex P3 is located on the perpendicular bisector of this side.

[0084] Furthermore, the bottom surface 20B of the recess 20D of the mesa portion 20 is planar, similar to the vertical-cavity surface-emitting laser 10 of the first embodiment. However, in the vertical-cavity surface-emitting laser 70, the bottom surface 20B of the recess 20D is formed to be parallel to the [01-1] direction or the [0-11] direction.

[0085] Therefore, the three recesses 20D having a bottom surface 20B allow the central portion 20MC (waveguide portion) of the mesa portion 20 inside the three protruding portions 20G to function as a columnar waveguide structure having three sides (side portions) substantially parallel to the [01-1] direction (or the [0-11] direction).

[0086] Furthermore, in the vertical-cavity surface-emitting laser 70, a compressive-strained quantum well layer is used in the active layer 15. Specifically, the active layer 15 has a laminated structure consisting of 2 to 5 pairs of compressive-strained GaInP well layers / AlGaInP barrier layers. The other configurations of the vertical-cavity surface-emitting laser 70 are the same as those of the vertical-cavity surface-emitting laser 10 of the first embodiment described above.

[0087] (2) Manufacturing Method The manufacturing method for the vertical-cavity surface-emitting laser 70 will be described below. The manufacturing process for the vertical-cavity surface-emitting laser 70 of this embodiment will be described with reference to the manufacturing method for the vertical-cavity surface-emitting laser 10 described above.

[0088] (Step S1) In the vertical-cavity surface-emitting laser 70, a GaAs substrate (offset angle: 10°) was used as the substrate 11, in which the crystal growth plane was tilted 10° in the

[111] direction from the (100) plane. From the viewpoint of crystallinity, the offset angle is preferably in the range of 5 to 12°.

[0089] Furthermore, the active layer 15 has a compressive strain quantum well structure, and the well layer uses a GaInP layer (compressive strain amount 1%) which has a smaller lattice constant than GaAs. The compressive strain amount can be appropriately selected from the viewpoint of desired light emission characteristics such as optical output and oscillation threshold, but from the viewpoint of improving polarization characteristics, it is preferable to be in the range of 0.2 to 0.4%.

[0090] (Steps S2, S3) Dry etching was performed using the ECR plasma etching method to form three identical recesses 20D on the side surface of the mesa portion 20, which were positioned at 120° rotationally symmetrical positions with respect to the central axis CZ of the mesa portion 20. In this embodiment, an etching mask was formed so that the planar bottom surface 20B of the recesses 20D was parallel to the [01-1] direction (or the [0-11] direction). As a result, three recesses 20D were formed in the shape transferred by the mask, and a mesa portion 20 was formed in which the current constriction layer 21 to the first semiconductor layer 14 was etched. It is preferable that the etching is performed so as to reach at least the first semiconductor layer 14.

[0091] (Step S4) The steam oxidation process oxidizes the p-AlGaAs layer exposed from the recess 20D to the interior, forming the equilateral triangular current injection section 21A shown in Figure 15. Note that when forming the current injection section 21A in an n-sided polygon shape (where n is an integer of 3 or more), the sides of the current injection section 21A after the oxidation process may be curved.

[0092] Furthermore, one side of the current injection section 21A was 13 μm, and the diameter of the translucent film 29 (light emission aperture) was 12-14 μm. Steps S5 to S6 were carried out using the same process as the vertical-cavity surface-emitting laser 10 of the first embodiment.

[0093] (3) Polarization Characteristics Figure 16 shows the measurement results of the polarization characteristics of the vertical cavity surface-emitting laser 70. Evaluation was performed on 10 samples (N=10). As shown in Figure 16, it can be seen that the polarization intensity of light in the [01-1] direction and the [01-1] direction is maximized. The variation in polarization angle is extremely small, with an average of -0.05°, and all samples are within ±2°. Since the variation in polarization angle is at the same level as the angle variation during mounting, it can be seen that the polarization angle is well controlled. In addition, the extinction ratio was -14 dB on average. That is, it is possible to provide a vertical cavity surface-emitting laser with high polarization controllability and a good extinction ratio.

[0094] (4) Modified Figure 17 is a schematic plan view of the current injection section 31A of the vertical cavity type surface-emitting laser 70, which is Modified Figure 1 of the third embodiment. The current injection section 31A is shown as viewed from a direction perpendicular to the active layer 15.

[0095] In the modified example 1, the current injection section 31A has vertices P1, P2, and P3 at the vertices of an equilateral triangle, and each side has a shape consisting of a curve that is monotonically concave inward toward the centroid (i.e., the central axis CZ). In addition, the line connecting the adjacent vertices P1 and P2 is formed parallel to the <011> direction in the crystal orientation of the mesa section 20.

[0096] Figure 18 is a schematic plan view of the current injection section 31A of a vertical-cavity surface-emitting laser, which is a modified example 2 of the third embodiment. It shows the current injection section 31A as viewed from a direction perpendicular to the active layer 15. The current injection section 31A of modified example 2 has a rectangular shape (n=4), with one side formed parallel to the <011> direction. In Figure 18, the case where the long side of the current injection section 31A is parallel to the [01-1] direction or the [0-11] direction is shown, but the short side may also be parallel to the [01-1] direction or the [0-11] direction.

[0097] Furthermore, in the vertical-cavity surface-emitting laser of Modification 2, the mesa portion 20 has a rectangular prism-shaped waveguide structure in the center, with four side portions parallel to the <011> direction. Similar to the vertical-cavity surface-emitting laser 70 of Modification 1, the current injection portion 31A of Modification 2 may have a shape consisting of curves where each side is monotonically concave inward toward the centroid (i.e., the central axis CZ).

[0098] Figure 19 is a schematic plan view of the current injection unit 31A of a vertical-cavity surface-emitting laser, which is a modified example 3 of the third embodiment. The current injection unit 31A is shown as viewed from a direction perpendicular to the active layer 15.

[0099] In Modification 3, the current injection section 31A has a regular pentagonal shape (n=5), with one side formed parallel to the <011> direction. Figure 18 shows the case where one side of the current injection section 31A is parallel to the [01-1] direction or the [0-11] direction. In addition, in the vertical-cavity surface-emitting laser of Modification 3, the mesa section 20 has a pentagonal prism-shaped waveguide structure in the center, with five side surfaces parallel to the <011> direction.

[0100] Furthermore, similar to the vertical-cavity surface-emitting laser 70 in Modification 1, the current injection section 31A in Modification 3 may have a shape consisting of curves in which each side is monotonically concave toward the centroid (i.e., the central axis CZ).

[0101] Although the first to third modifications have been described above, the current injection unit 31A may also be configured to have an n-sided polygonal shape (where n is an integer of 3 or more).

[0102] Therefore, according to the vertical-cavity surface-emitting laser 70 of the third embodiment, similar to the vertical-cavity surface-emitting laser 10 of the first embodiment, transverse single-mode operation is maintained even when high current is injected, high optical output is obtained, and a vertical-cavity surface-emitting laser with high polarization controllability and good extinction characteristics can be provided.

[0103] [Fourth Embodiment] (1) The diagram 20 of the shape and orientation of the current injection section is a schematic top view showing the structure of the vertical cavity surface-emitting laser 80 of the fourth embodiment of the present invention. More specifically, it shows a top view of the vertical cavity surface-emitting laser 80 as seen from a direction perpendicular to the active layer 15, and to the right of the top view, it shows an enlarged view of the current injection section 21A of the current constriction layer 21.

[0104] The vertical-cavity surface-emitting laser 80 of the fourth embodiment has the same laminated structure and mesa shape as the vertical-cavity surface-emitting laser 50 of the second embodiment, but in the vertical-cavity surface-emitting laser 70, the orientation of the current injection section 21A when viewed from a direction perpendicular to the active layer 15 is defined.

[0105] More specifically, similar to the case of the vertical-cavity surface-emitting laser 70 of the third embodiment, the current injection section 21A of the vertical-cavity surface-emitting laser 80 has an equilateral triangular shape when viewed from a direction perpendicular to the active layer 15. Furthermore, the current injection section 21A is formed such that one side connecting the vertices P1 and P2 of the equilateral triangle is parallel to the <011> direction in the crystal orientation of the mesa portion 20.

[0106] Furthermore, similar to the case of the vertical-cavity surface-emitting laser 70 of the third embodiment, it is preferable to use a GaAs substrate (offset substrate) as the substrate 11 in which the crystal growth plane is tilted from the (100) plane in the

[111] direction within a range of 5 to 12°. In addition, it is preferable that the active layer 15 has a compression-strain quantum well structure.

[0107] (2) Manufacturing method The vertical-cavity surface-emitting laser 80 can be manufactured by applying the same process as the vertical-cavity surface-emitting laser 50 of the second embodiment. Furthermore, when forming the three holes 60H, the same process as in the case of the vertical-cavity surface-emitting laser 70 of the third embodiment is applied.

[0108] Specifically, in the dry etching process, when the three holes 60H are formed inside the mesa portion 60, the planar inner surface 60B of the mesa portion 60 facing the holes 60H is etched so that it is parallel to the [01-1] direction (or the [0-11] direction). Furthermore, the three holes 60H with inner surfaces 60B allow the central portion 60MC (waveguide portion) of the mesa portion 60 to function as a columnar waveguide structure with its side facing the holes 60H substantially parallel to the [01-1] direction (or the [0-11] direction).

[0109] Then, through a water vapor oxidation process, oxidation is carried out from the p-AlGaAs layer exposed in the pore portion 60H to the interior, forming the equilateral triangular-shaped current injection portion 21A shown in Figure 20. It should be noted that, as with the vertical-cavity surface-emitting laser in the above-described embodiment, the sides of the current injection portion 21A may be curved.

[0110] (3) Modification of the fourth embodiment Modifications can be made in the same way as in the case of the vertical cavity type surface-emitting laser 70 of the third embodiment described above, or modifications can be made in the same way as in the modified examples 1 to 3 of the vertical cavity type surface-emitting laser 70 of the third embodiment.

[0111] Accordingly, the vertical-cavity surface-emitting laser 80 of the fourth embodiment maintains transverse single-mode operation even when high current is injected, similar to the vertical-cavity surface-emitting lasers 10, 50, and 70 of the first to third embodiments, and provides a vertical-cavity surface-emitting laser that can obtain high optical output, as well as have high polarization controllability and good extinction characteristics.

[0112] Furthermore, the polarization characteristics of the vertical-cavity surface-emitting laser 80 can also be controlled by setting the crystal orientation of the substrate 11 to a specific direction. Alternatively, polarization control can be achieved by the crystal state of InGaP (ordered or disordered state).

[0113] In the embodiments described above, the case in which the mesa portion has a cylindrical shape was explained, but it may also have an elliptical or polygonal shape. Also, although the case in which the current injection portion 21A etc. has a regular n-gon shape was explained as an example, it may also have an n-gon shape. Furthermore, in this case, it includes the case in which each side of the n-gonal current injection portion consists of a curve that is monotonically concave inward toward the centroid.

[0114] As described in detail above, this disclosure provides a vertical-cavity surface-emitting laser and a method for manufacturing the same, which maintains transverse single-mode operation even when high current is injected and can obtain high optical output. Furthermore, it is possible to provide a vertical-cavity surface-emitting laser and a method for manufacturing the same that have high polarization controllability and good extinction characteristics.

[0115] 10, 50, 70, 80: Vertical-cavity surface-emitting laser 11: Substrate 12: n-electrode 13: First reflector 14: First semiconductor layer 15: Active layer 16: Second semiconductor layer 20, 60: Mesa portion 20B: Bottom surface 20C: Cylindrical side surface 20D: Recess 20G: Protrusion 20MC, 60MC: Mesa center 21: Current constriction layer 21A: Current injection portion 21B: Oxide layer 25: Second reflector 27: Contact layer 28: p-electrode 28P: Pad electrode 29: Translucent film 29A: Light emission aperture 31A: Current injection portion 60C: Annular columnar outer periphery 60H: Hole CZ: Central axis P1-P3: Axes of the current injection portion

Claims

1. A mesa comprising: a substrate; a first reflector provided on the substrate; a first semiconductor layer of a first conductivity type provided on the first reflector; an active layer provided on the first semiconductor layer; a second semiconductor layer of a second conductivity type provided on the active layer; and a mesa portion having a current-constricting layer, a second reflector provided on the current-constricting layer, and an exit aperture layer provided on the second reflector, the mesa portion having a central axis, and the mesa portion being arranged in rotationally symmetric positions with respect to the central axis at an angle of θ = 360° / n (where n is a natural number of 3 or more), and having a cylindrical shape with n substantially identical recesses on its side surface that expose at least the side surface of the current-constricting layer. The current constriction layer comprises an n-sided current injection section made of an Al-containing semiconductor layer coaxial with the central axis, and a current constriction section provided around the current injection section and made of an oxide of the Al-containing semiconductor layer, and the emission aperture layer has a circular light emission aperture coaxial with the current injection section, in a vertical-cavity surface-emitting laser.

2. The device comprises a substrate, a first reflector provided on the substrate, a first semiconductor layer of a first conductivity type provided on the first reflector, an active layer provided on the first semiconductor layer, a second semiconductor layer of a second conductivity type provided on the active layer, and a mesa portion having a current-constricting layer, a second reflector provided on the current-constricting layer, and an exit aperture layer provided on the second reflector, the mesa portion having a central axis, and the mesa portion being arranged in rotationally symmetric positions with respect to the central axis at an angle of θ = 360° / n (where n is a natural number of 3 or more), and having a cylindrical shape with n substantially identical holes inside, which are dug from the upper surface of the mesa portion and expose at least the side surface of the current-constricting layer. The current constriction layer comprises an n-sided current injection section made of an Al-containing semiconductor layer coaxial with the central axis, and a current constriction section provided around the current injection section and made of an oxide of the Al-containing semiconductor layer, and the emission aperture layer has a circular light emission aperture coaxial with the current injection section, in a vertical-cavity surface-emitting laser.

3. The vertical resonator type surface-emitting laser according to claim 1 or 2, wherein in the n-gon shape, n is in the range of 3 to 6 (3 ≤ n ≤ 6).

4. The vertical-cavity surface-emitting laser according to claim 1 or 2, wherein the mesa portion protrudes perpendicularly from a part of the surface of the first reflector to the first reflector.

5. The vertical cavity type surface-emitting laser according to claim 1 or 2, wherein the current injection section has vertices at the vertex positions of an n-sided polygon and each side is a curve that is monotonically concave inward toward the centroid.

6. The vertical cavity type surface-emitting laser according to claim 1 or 2, wherein the current injection portion of the current-constricting layer has a triangular shape.

7. The vertical-cavity surface-emitting laser according to claim 1 or 2, wherein the current injection section has an area larger than a circle with a diameter of 6 μm.

8. The vertical resonator type surface-emitting laser according to claim 1 or 2, wherein the current injection portion is such that, in a top view, the top of the current injection portion protrudes outside the light emission aperture.

9. The vertical-cavity surface-emitting laser according to claim 1 or 2, wherein the light emitted from the vertical-cavity surface-emitting laser exhibits at least one emission point in addition to the emission point corresponding to the vertices of the n-gon shape in the near-field image, and exhibits a unimodal emission image in the far-field image.

10. The vertical resonator type surface-emitting laser according to claim 9, wherein the at least one light-emitting point is located on the side of the n-sided polygon.

11. The vertical-cavity surface-emitting laser according to claim 1 or 2, wherein the exit aperture layer comprises a contact layer provided on the second reflector and an exit electrode provided on the contact layer and having the light exit aperture, the exit electrode having a circular aperture coaxial with the current injection portion, and the aperture of the contact layer and the light exit aperture of the exit electrode are filled with a translucent film.

12. The vertical cavity surface-emitting laser according to claim 1 or 2, wherein the active layer emits light in the wavelength range of red light or near-infrared light.

13. The process comprises: forming a laminated structure by epitaxially growing a first reflector, a first semiconductor layer of a first conductivity type, an active layer, a second semiconductor layer of a second conductivity type, an Al-containing semiconductor layer, a second reflector, and a contact layer on a substrate in this order; etching the laminated structure from the upper surface of the laminated structure to any of the layers of the first reflector, the first semiconductor layer, the active layer, and the second semiconductor layer to form a cylindrical mesa portion that protrudes perpendicularly to the first reflector; and forming an exit electrode on the contact layer, wherein the process of forming the mesa portion comprises forming n recesses on the side surface of the mesa portion that are arranged in rotationally symmetric positions with respect to the central axis of the mesa portion at an angle of θ = 360° / n, have substantially the same shape, and expose at least the side surface of the Al-containing semiconductor layer. A method for manufacturing a vertical-cavity surface-emitting laser, comprising the steps of: performing steam treatment to oxidize the Al-containing semiconductor layer exposed from the n recesses to form a current-constricting layer comprising an n-sided current injection section coaxial with the central axis and a current-constricting section provided around the current injection section and made of an oxide of the Al-containing semiconductor layer; and forming a circular opening coaxial with the current injection section in the output electrode.

14. The process comprises: forming a laminated structure by epitaxially growing a first reflector, a first semiconductor layer of a first conductivity type, an active layer, a second semiconductor layer of a second conductivity type, an Al-containing semiconductor layer, a second reflector, and a contact layer on a substrate in this order; etching the laminated structure from the upper surface of the laminated structure to any of the layers of the first reflector, the first semiconductor layer, the active layer, and the second semiconductor layer to form a cylindrical mesa portion that protrudes perpendicularly to the first reflector; and forming an exit electrode on the contact layer, wherein the process of forming the mesa portion comprises: drilling from the upper surface of the mesa portion, arranging in rotationally symmetric positions with respect to the central axis of the mesa portion at an angle of θ = 360° / n, and forming n substantially identical holes inside the mesa portion that expose at least the side surface of the Al-containing semiconductor layer; A method for manufacturing a vertical-cavity surface-emitting laser, comprising the steps of: performing steam treatment to oxidize the Al-containing semiconductor layer exposed from the n holes to form a current-constricting layer comprising an n-sided current injection section coaxial with the central axis and a current-constricting section provided around the current injection section and made of an oxide of the Al-containing semiconductor layer; and forming a circular opening coaxial with the current injection section in the output electrode.

15. A method for manufacturing a vertical-cavity surface-emitting laser according to claim 13 or 14, further comprising the steps of: forming a circular opening in the contact layer coaxial with the current injection portion; and filling the opening in the contact layer and the opening in the output electrode with a translucent film.

16. The method for manufacturing a vertical-cavity surface-emitting laser according to claim 13 or 14, wherein the step of forming the current-constricting layer is to perform the steam treatment such that the current injection portion has an area larger than a circle with a diameter of 6 μm.

17. The method for manufacturing a vertical cavity type surface-emitting laser according to claim 13 or 14, wherein the current injection section has vertices at the vertex positions of an n-sided polygon and each side is a curve that is monotonically concave inward toward the centroid.

18. The method for manufacturing a vertical cavity type surface-emitting laser according to claim 13 or 14, wherein the current injection portion of the current-constricting layer has an equilateral triangular shape.

19. The method for manufacturing a vertical cavity type surface-emitting laser according to claim 13 or 14, wherein the current injection unit is sized such that, in a top view, the top of the current injection unit overlaps with the output electrode.

20. The vertical resonator type surface-emitting laser according to claim 1 or 2, wherein one side of the n-sided current injection portion is parallel to the <011> direction in the crystal orientation of the mesa portion.

21. The method for manufacturing a vertical-cavity surface-emitting laser according to claim 13 or 14, wherein the step of forming the n recesses on the side surface of the mesa portion is to form the n recesses such that one side of the n-sided current injection portion is parallel to the <011> direction in the crystal orientation of the mesa portion.

22. The vertical resonator type surface-emitting laser according to claim 20, wherein the mesa portion has a triangular prism-shaped waveguide portion in the center, the side of which is substantially parallel to the <011> direction.

23. The vertical-cavity surface-emitting laser according to claim 20, wherein the current injection section has vertices at the vertex positions of an n-sided polygon and each side is a curve that is monotonically concave inward toward the centroid.

24. The vertical-cavity surface-emitting laser according to claim 21, wherein the current injection section has vertices at the vertex positions of an n-sided polygon and each side is a curve that is monotonically concave inward toward the centroid.

25. The vertical-cavity surface-emitting laser according to claim 20, wherein the light emitted from the vertical-cavity surface-emitting laser has the highest polarization intensity within a range of ±2° from a direction parallel to or parallel to at least one side of the n-sided polygon.

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