Surface-emitting laser element

Abstract

The surface-emission laser element of the present disclosure includes a first electrode, a lower cladding layer, an active layer, an upper cladding layer, a relaxation layer, a contact layer having a different band gap from the upper cladding layer, a second electrode, and a photonic crystal layer disposed between the lower cladding layer and the active layer or between the active layer and the upper cladding layer, including a base region and a plurality of regions having different refractive indexes from the base region and distributed two-dimensionally in a plane perpendicular to a thickness direction, and forming a resonance mode of light in the plane. The relaxation layer has a band gap of a size between a band gap of the upper cladding layer and a band gap of the contact layer.

Description

Technical Field

[0001] This disclosure relates to a surface-emitting laser element. Background Technology

[0002] Patent Document 1 discloses a semiconductor laser element. The semiconductor laser element includes a supporting substrate, a first cladding layer, an active layer, a diffraction grating layer, and a second cladding layer. The active layer and the diffraction grating layer are disposed between the first and second cladding layers. The active layer generates light. The second cladding layer has a conductivity type different from that of the first cladding layer. The diffraction grating layer has a two-dimensional photonic crystal structure with a tetragonal lattice configuration.

[0003] Patent Document 2 discloses a semiconductor light-emitting element and a method for manufacturing the same. The semiconductor light-emitting element includes a semiconductor substrate, a first cladding layer, an active layer, a second cladding layer, and a contact layer sequentially disposed on the semiconductor substrate. Furthermore, the semiconductor light-emitting element includes a phase modulation layer located between the first cladding layer and the active layer, or between the active layer and the second cladding layer. The phase modulation layer has a basic region and multiple regions with different refractive indices than the basic region. When an imaginary tetragonal lattice is formed in a plane perpendicular to the thickness direction of the phase modulation layer, the phase modulation layer is configured as follows: The regions with different refractive indices, each assigned to a unit constituting region of the tetragonal lattice, are configured such that their centroids are located away from the lattice point of the corresponding unit constituting region. Each region with different refractive indices has a rotation angle about that lattice point corresponding to the desired light image.

[0004] Patent Document 3 discloses a light-emitting device. The light-emitting device outputs light that forms a light image along the normal direction of the main surface of a substrate, or in an inclined direction intersecting the normal direction, or both the normal direction and the inclined direction. The light-emitting device includes a light-emitting part and a phase modulation layer disposed on the substrate and optically coupled to the light-emitting part. The phase modulation layer includes a basic region and multiple anisotropic regions. The multiple anisotropic regions are disposed in the basic region in a two-dimensional arrangement on a plane perpendicular to the normal direction, and each has a refractive index different from that of the basic region. With an imaginary tetragonal lattice disposed on the aforementioned plane, the centroids of the multiple anisotropic regions are moved away from their corresponding lattice points by a predetermined distance. The rotation angle of the anisotropic regions about the lattice points of the imaginary tetragonal lattice, in other words, the angle of the line segment connecting the centroids of the multiple anisotropic regions to their corresponding lattice points relative to the imaginary tetragonal lattice, is set according to the phase distribution used to form the light image. The lattice spacing 'a' of the hypothetical tetragonal lattice and the emission wavelength 'λ' of the luminescent part are set to satisfy the oscillation condition at point M, which is the symmetric point of the reciprocal lattice space corresponding to the wavenumber space of the phase modulation layer. Among the in-plane wavenumber vectors in the four directions of the reciprocal lattice space formed in the phase modulation layer, at least one in-plane wavenumber vector has a magnitude less than 2π / λ.

[0005] Non-Patent Document 1 discloses a two-dimensional photonic crystal surface-emitting laser that can perform high-output single-mode operation under room temperature and continuous wave conditions by studying the shape of multiple pores constituting the photonic crystal.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-197659

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-198302

[0010] Patent Document 3: International Publication No. 2020 / 045453

[0011] Non-patent literature

[0012] Non-patent literature 1: Kazuyoshi Hirose et al., "Watt-class high-power, high-beam-quality photonic-crystal lasers", Nature Photonics, Volume 8, pp.406-411 (2014)

[0013] Non-patent document 2: Y.Kurosaka et al., "Effects of non-lasing band in two-dimensional photonic-crystal lasers clarified using omnidirectional bandstructure", Opt.Express 20, 21773-21783 (2012) Summary of the Invention

[0014] The technical problem that the invention aims to solve

[0015] As a surface-emitting laser element that emits laser light in a direction intersecting with the main surface of the substrate, there is a photonic crystal surface-emitting laser with an active layer and a photonic crystal layer disposed between two cladding layers. As a surface-emitting laser element with a structure similar to that of a photonic crystal surface-emitting laser, there is a so-called S-iPM (silicon-integrable phase modulating tube) laser, which is said to have a phase modulation layer disposed instead of a photonic crystal layer. In these laser elements, a contact layer is provided on one of the cladding layers, and current is supplied to the active layer from an electrode in ohmic contact with the contact layer via the cladding layer.

[0016] To achieve sufficient laser oscillation with less current, it is desirable to adequately confine the light generated in the active layer to the photonic crystal layer or phase modulation layer. For this, it is desirable to make the refractive index of the cladding sufficiently small compared to the active and phase modulation layers. However, the smaller the refractive index of the cladding, the larger its bandgap becomes. When the cladding bandgap increases, the bandgap difference between the cladding and the contact layer also increases. Furthermore, the potential barrier created by the abrupt change in bandgap at the interface between the cladding and the contact layer causes an increase in resistance. This increased resistance necessitates a higher driving voltage to achieve sufficient laser oscillation. Consequently, power consumption increases, and component reliability decreases.

[0017] The purpose of this disclosure is to achieve sufficient laser oscillation even with low driving voltages in surface-emitting laser elements such as photonic crystal surface-emitting lasers or S-iPM lasers.

[0018] Technical means for solving problems

[0019] The surface-emitting laser element disclosed herein comprises: a first electrode; a first cladding of a first conductivity type electrically connected to the first electrode; an active layer disposed on the first cladding; a second cladding of a second conductivity type disposed on the active layer; a tempering layer of the second conductivity type disposed on the second cladding; a contact layer of the second conductivity type disposed on the tempering layer, having a bandgap different from that of the second cladding; a second electrode disposed on the contact layer, forming an ohmic contact with the contact layer; and a resonant mode forming layer. The resonant mode forming layer is disposed between the first cladding and the active layer, or between the active layer and the second cladding. The resonant mode forming layer includes a base region and multiple anisotropic regions. The multiple anisotropic regions have a refractive index different from that of the base region and are distributed two-dimensionally in a plane perpendicular to the thickness direction. The resonant mode forming layer forms a resonant mode of light in the plane. The tempering layer has a bandgap width between the bandgap width of the second cladding and the bandgap width of the contact layer.

[0020] The effects of the invention

[0021] According to this disclosure, even with a low driving voltage, sufficient laser oscillation can be achieved in surface-emitting laser elements such as photonic crystal surface-emitting lasers or S-iPM lasers. Attached Figure Description

[0022] Figure 1 This is a schematic diagram showing the cross-sectional structure of the surface-emitting laser element of the first embodiment.

[0023] Figure 2 This is a top view of the photonic crystal layer.

[0024] Figure 3 Parts (a) to (g) are diagrams showing examples of the shape of regions with different refractive indices.

[0025] Figure 4 Parts (a) to (k) are diagrams showing examples of the shape of regions with different refractive indices.

[0026] Figure 5 Parts (a) to (k) are diagrams showing examples of the shape of regions with different refractive indices.

[0027] Figure 6 Part (a) is a graph showing the refractive index distribution of a surface-emitting laser element and the distribution of the basic modes generated with the active layer and photonic crystal layer as the center. Figure 6 Part (b) is an enlarged diagram showing the vicinity of the active layer and photonic crystal layer in part (a).

[0028] Figure 7 Part (a) is a graph showing the refractive index distribution and fundamental mode distribution of a surface-emitting laser element without a pacing layer. Figure 7 Part (b) is an enlarged diagram showing the vicinity of the active layer and photonic crystal layer in part (a).

[0029] Figure 8 This is a schematic diagram showing the cross-sectional structure of the surface-emitting laser element of the second embodiment.

[0030] Figure 9 This is a top view of the phase modulation layer.

[0031] Figure 10 This is a magnified image showing a portion of the phase modulation layer.

[0032] Figure 11 It is a diagram used to illustrate the relationship between the optical image obtained by imaging the output beam pattern of an optical device and the rotation angle of the phase modulation layer.

[0033] Figure 12 It is a diagram used to illustrate the coordinate transformation from spherical coordinates to an orthogonal XYZ coordinate system.

[0034] Figure 13 This demonstrates the application within a specific region of the phase modulation layer. Figure 9 A top view of an example of a refractive index structure.

[0035] Figure 14 Parts (a) and (b) are diagrams illustrating points to note when determining the configuration of multiple heterorefringent regions using general discrete Fourier transform or high-speed Fourier transform calculations.

[0036] Figure 15Parts (a) to (d) are diagrams showing examples of beam patterns, or optical images, output from a GaAs-based S-iPM laser in the near-infrared band.

[0037] Figure 16 Part (a) is a graph showing the refractive index distribution of a surface-emitting laser element, the basic mode distribution generated with the active layer and phase modulation layer as the center, and the mode distribution generated with the tempering layer and contact layer as the center. Figure 16 Part (b) is a magnified diagram showing the vicinity of the active layer and phase modulation layer in part (a).

[0038] Figure 17 Part (a) is a graph showing the refractive index distribution and fundamental mode distribution of a surface-emitting laser element without a pacing layer. Figure 17 Part (b) is a magnified diagram showing the vicinity of the active layer and phase modulation layer in part (a).

[0039] Figure 18 This is a top view of the phase modulation layer, which serves as the resonant mode forming layer, provided in the optical device of the third embodiment.

[0040] Figure 19 This is a diagram showing the positional relationship of the heterorefringent regions in the phase modulation layer.

[0041] Figure 20 This is a schematic diagram showing the cross-sectional structure of the surface-emitting laser element of the first modified example.

[0042] Figure 21 This is a schematic diagram showing the cross-sectional structure of the surface-emitting laser element of the second modified example.

[0043] Figure 22 Part (a) is a graph showing the refractive index distribution of a surface-emitting laser element, the basic mode distribution generated with the active layer and photonic crystal layer as the center, and the mode distribution generated with the tempering layer and contact layer as the center. Figure 22 Part (b) is a magnified diagram showing the vicinity of the active layer and photonic crystal layer in part (a).

[0044] Figure 23 Part (a) is a graph showing the refractive index distribution of a surface-emitting laser element, the basic mode distribution generated with the active layer and phase modulation layer as the center, and the mode distribution generated with the tempering layer and contact layer as the center. Figure 23 Part (b) is a magnified diagram showing the vicinity of the active layer and phase modulation layer in part (a).

[0045] Figure 24 This is a schematic diagram showing the cross-sectional structure of the surface-emitting laser element of the third modified example.

[0046] Figure 25 This is a top view showing the reciprocal lattice space of the photonic crystal layer of a PCSEL oscillating at point Γ.

[0047] Figure 26 It is a three-dimensional observation Figure 25 The diagram shows a three-dimensional representation of the inverted lattice space.

[0048] Figure 27 This is a top view showing the reciprocal lattice space of the photonic crystal layer of a PCSEL oscillating at point M.

[0049] Figure 28 This is a top view showing the reciprocal lattice space of the phase modulation layer of an S-iPM laser oscillating at point Γ.

[0050] Figure 29 It is a three-dimensional observation Figure 28 The diagram shows a three-dimensional representation of the inverted lattice space.

[0051] Figure 30 This is a top view showing the reciprocal lattice space of the phase modulation layer of an S-iPM laser oscillating at point M.

[0052] Figure 31 It is a conceptual diagram used to illustrate the operation of adding a diffraction vector with a certain magnitude and direction to the internal wavenumber vector.

[0053] Figure 32 It is a diagram used to schematically illustrate the surrounding structure of a light line.

[0054] Figure 33 This is a diagram that conceptually illustrates an example of the distribution of rotation angles.

[0055] Figure 34 This is a diagram showing an example of the rotation angle distribution of the phase modulation layer.

[0056] Figure 35 It is to zoom in and show Figure 34 The image shown is a partial one.

[0057] Figure 36 This is a diagram showing the far-field image of the multi-point beam formed in the embodiment.

[0058] Figure 37 This is a graph showing the current-light output characteristics of the fabricated surface-emitting laser element.

[0059] Figure 38 This is a graph showing the current-voltage characteristics of the fabricated surface-emitting laser element.

[0060] Figure 39This is a diagram showing a near-field image of an embodiment under low drive current before oscillation. Figure 39 Part (a) shows the case where the drive current is set to 30mA. Figure 39 Section (b) shows the case where the drive current is set to 100mA.

[0061] Figure 40 Part (a) is a graph showing the difference in current-light output characteristics when the thickness of the mitigation layer is varied. Figure 40 Part (b) is a graph showing the difference in current-voltage characteristics when the thickness of the mitigation layer is varied.

[0062] Figure 41 It is a schematic diagram illustrating the fabricated layered structure.

[0063] Figure 42 Parts (a) and (b) are schematic diagrams illustrating the fabricated layered structure. Detailed Implementation

[0064] The surface-emitting laser element disclosed herein comprises: a first electrode; a first cladding of a first conductivity type electrically connected to the first electrode; an active layer disposed on the first cladding; a second cladding of a second conductivity type disposed on the active layer; a tempering layer of the second conductivity type disposed on the second cladding; a contact layer of the second conductivity type disposed on the tempering layer, having a bandgap different from that of the second cladding; a second electrode disposed on the contact layer, forming an ohmic contact with the contact layer; and a resonant mode forming layer. The resonant mode forming layer is disposed between the first cladding and the active layer, or between the active layer and the second cladding. The resonant mode forming layer includes a base region and multiple anisotropic regions. The multiple anisotropic regions have a refractive index different from that of the base region and are distributed two-dimensionally in a plane perpendicular to the thickness direction. The resonant mode forming layer forms a resonant mode of light in the plane. The tempering layer has a bandgap width between the bandgap width of the second cladding and the bandgap width of the contact layer.

[0065] In this surface-emitting laser element, when a voltage is applied between the first and second electrodes, a current flows between them. The active layer converts this current into light. The light output from the active layer is confined between the first and second cladding layers and subjected to diffraction caused by the resonant mode forming layer. In the resonant mode forming layer, resonant modes are formed in an in-plane direction perpendicular to the thickness direction of the resonant mode forming layer, generating laser modes corresponding to the configuration of multiple heterorefringent index regions. The laser travels along the thickness direction of the resonant mode forming layer and exits towards the outside of the surface-emitting laser element.

[0066] This surface-emitting laser element has a moderating layer between the second cladding layer and the contact layer. The moderating layer has a bandgap of the size between the bandgap of the second cladding layer and the bandgap of the contact layer. Therefore, compared to the case without a moderating layer, the rate of change of the bandgap between the cladding and contact layers is moderated, and the potential barrier is lowered. Consequently, the element's resistance is reduced, and sufficient laser oscillation can be achieved even with low driving voltages. As a result, power consumption is reduced, and the reliability of the element is improved.

[0067] In the aforementioned surface-emitting laser element, the resonant mode forming layer can also be a photonic crystal layer with multiple heterorefringent regions arranged periodically. In this case, the light output from the active layer is diffracted by the photonic crystal layer. Within the photonic crystal layer, a resonant mode is formed in the in-plane direction perpendicular to the thickness direction of the photonic crystal layer, and the light oscillates at a wavelength corresponding to the arrangement period of the multiple heterorefringent regions, generating laser light. For example, in a tetragonal lattice crystal where the arrangement period is set to the length of one wavelength of light, a portion of the laser light diffracts in the thickness direction of the photonic crystal layer and exits towards the outside of the surface-emitting laser element.

[0068] The aforementioned surface-emitting laser element can also be a surface-emitting laser element that outputs a light image, i.e., an iPM laser. The centroids of the multiple anisotropic refractive index regions can be respectively arranged away from the corresponding lattice points of an imaginary tetragonal lattice set within the plane of the resonant mode forming layer, having rotation angles about the lattice points corresponding to the light image. The rotation angles of the centroids of at least two anisotropic refractive index regions can be different from each other. Light output from the active layer is diffracted by the resonant mode forming layer. In the resonant mode forming layer, the centroids of the multiple anisotropic refractive index regions have rotation angles about the lattice points of the imaginary tetragonal lattice set for each anisotropic refractive index region. In this case, compared to the case where the centroids of the multiple anisotropic refractive index regions are located at the lattice points of the tetragonal lattice, the light intensity of the light emitted in the thickness direction of the resonant mode forming layer, in other words, in the direction perpendicular to the light-emitting surface of the surface-emitting laser element, i.e., the 0th-order light, decreases. Simultaneously, higher-order light, such as the 1st-order light and -1st-order light, appears emitted in directions inclined relative to this direction. Furthermore, by individually setting the rotation angle of the centroid of each heterorefringent region around the grid point, the phase of the light can be modulated independently for each heterorefringent region, and an arbitrary shape of light image can be output.

[0069] The aforementioned surface-emitting laser element can also be a surface-emitting laser element that outputs a light image, i.e., an iPM laser. When an imaginary tetragonal lattice is set within the plane of the resonant mode forming layer, the centroids of multiple anisotropic refractive index regions can be positioned on a straight line passing through the lattice points of the tetragonal lattice and tilted relative to the tetragonal lattice. The tilt angles of the multiple straight lines corresponding to the multiple anisotropic refractive index regions relative to the tetragonal lattice can also be equal (uniform) within the resonant mode forming layer. Furthermore, the distance between the centroid of each anisotropic refractive index region and its corresponding lattice point can be individually set corresponding to the light image. The distances between the centroids of at least two anisotropic refractive index regions and the lattice points can be different from each other. Light output from the active layer is subjected to diffraction caused by the resonant mode forming layer. In the resonant mode forming layer, the centroids of multiple anisotropic refractive index regions are positioned on a straight line passing through the lattice points of the imaginary tetragonal lattice and tilted relative to the tetragonal lattice. Even in this case, the intensity of light emitted in the direction perpendicular to the light exiting surface, i.e., the 0th-order light, is reduced. Simultaneously, higher-order light, such as first-order light and -1-order light, emerges in a direction tilted relative to this direction. Furthermore, by individually setting the distance between the centroid of each heterorefringent region and the corresponding grid point, the phase of the light can be modulated independently for each heterorefringent region, outputting a light image of arbitrary shape.

[0070] In the aforementioned surface-emitting laser element, the mitigation layer can also be composed of the same constituent elements as the second cladding layer. In this case, after the second cladding layer is grown, the mitigation layer can be grown without changing the raw material supply, thus making it easy to form the mitigation layer.

[0071] In the surface-emitting laser element described above, the bandgap width of the easing layer can also vary continuously from the bandgap width of the second cladding layer to the bandgap width of the contact layer. In this case, since the potential barrier can be effectively reduced, the aforementioned effects caused by the surface-emitting laser element of this disclosure can be obtained more significantly.

[0072] In the aforementioned surface-emitting laser element, the bandgap width of the easing layer can also be varied in stages, approaching the bandgap width of the second cladding layer. Even in this case, the potential barrier can be effectively reduced, thus significantly achieving the aforementioned effects caused by the surface-emitting laser element of this disclosure.

[0073] In the aforementioned surface-emitting laser element, the refractive index of the second cladding layer can also be less than that of the first cladding layer. In this case, the coupling between the modes generated in the contact layer and the resonant mode forming layer is suppressed, thus improving the quality of the output light. Furthermore, the smaller the refractive index of the second cladding layer, the larger its band gap becomes, and therefore the greater the band gap difference between the second cladding layer and the contact layer. The aforementioned surface-emitting laser element is particularly useful in such cases.

[0074] In the aforementioned surface-emitting laser element, the second cladding layer and the buffer layer contain Al as components, and the Al component ratio of the buffer layer can be smaller than that of the second cladding layer. When the second cladding layer contains Al and no buffer layer is provided, the Al in the second cladding layer becomes easily oxidized due to oxygen atoms introduced through the contact layer or exposed from the contact layer. Alternatively, if growth between the second cladding layer and the contact layer is interrupted, the Al in the second cladding layer becomes easily oxidized. In cases where the contact layer requires a high doping concentration due to ohmic contact, the crystal growth conditions of the contact layer differ from those of the second cladding layer. For example, in such cases, growth between the second cladding layer and the contact layer is interrupted. If the Al in the second cladding layer oxidizes, the resistance of the second cladding layer increases, and sufficient laser oscillation cannot be obtained without increasing the driving voltage. As a result, power consumption increases, and the reliability of the element decreases. In this surface-emitting laser element, since a buffer layer with a smaller Al component ratio than that of the second cladding layer is interposed between the contact layer and the second cladding layer, the effects caused by Al oxidation can be reduced. That is, based on this surface-emitting laser element, the increase in resistance caused by Al oxidation can be suppressed, and sufficient laser oscillation can be obtained with a lower driving voltage. As a result, power consumption can be further reduced, and the reliability of the element can be further improved.

[0075] In the aforementioned surface-emitting laser element, the Al composition ratio of the buffer layer can also continuously decrease from the interface of the buffer layer near the second cladding layer to the interface of the buffer layer near the contact layer. In this case, since Al oxidation can be effectively reduced, the aforementioned effects can be obtained more significantly.

[0076] In the aforementioned surface-emitting laser element, the Al composition ratio of the tempering layer can be progressively reduced from the tempering layer interface near the second cladding layer to the tempering layer interface near the contact layer. Even in this case, Al oxidation can be effectively reduced, thus significantly achieving the aforementioned effects.

[0077] In the aforementioned surface-emitting laser element, the second cladding layer and the buffer layer can be AlGaAs layers, and the contact layer can be a GaAs layer. In this case, a surface-emitting laser element in the infrared region can be obtained.

[0078] In the aforementioned surface-emitting laser element, the first cladding layer contains Al as a component, and the Al component ratio of the second cladding layer can also be greater than that of the first cladding layer. In this case, since the refractive index of the second cladding layer becomes less than that of the first cladding layer, it is possible to reduce the higher-order modes generated in the second cladding layer and improve the quality of the output light. Furthermore, when the Al component ratio of the second cladding layer is large, the aforementioned surface-emitting laser element with a mitigation layer is particularly useful.

[0079] In the aforementioned surface-emitting laser element, viewed from the thickness direction, the area of ​​the contact layer is smaller than the area of ​​the buffer layer, and the buffer layer may also be exposed around the contact layer. To efficiently supply current, sometimes the portion of the contact layer other than the part where the second electrode is located is removed. In this case, if the buffer layer is not provided, the second cladding layer is exposed, and the Al in the second cladding layer becomes more susceptible to oxidation. In the aforementioned surface-emitting laser element, since the Al composition ratio is smaller than that of the exposed buffer layer of the second cladding layer, the effects caused by Al oxidation can be reduced.

[0080] In the aforementioned surface-emitting laser element, the thickness of the modulating layer can be less than the thickness of the second cladding layer. In this case, the thickness of the second cladding layer becomes relatively thick, and the modulating layer, which has a higher refractive index than the second cladding layer, is separated from the resonant mode forming layer and the active layer. Therefore, it is possible to suppress the coupling between the modes generated by the modulating layer and the contact layer and the resonant mode forming layer. As a result, the fundamental mode can be stabilized and the quality of the output light can be improved.

[0081] In the aforementioned surface-emitting laser element, the easing layer can also be located at a distance of 1 μm or more from both the resonant mode forming layer and the active layer. In this case, the easing layer, having a refractive index greater than that of the second cladding layer, is separated from both the resonant mode forming layer and the active layer. Therefore, it is possible to suppress the coupling between the mode generated by the easing layer and the contact layer and the resonant mode forming layer. As a result, the fundamental mode can be stabilized and the quality of the output light can be improved.

[0082] Specific examples of the surface-emitting laser element of this disclosure are described below with reference to the accompanying drawings. Furthermore, the invention is not limited to these examples, but is intended to encompass all changes within the scope of the claims and of equivalent meaning. In the following description, the same reference numerals are used for the same elements as in the description of the drawings, and repeated descriptions are omitted.

[0083] [First Implementation]

[0084] Figure 1 This is a schematic diagram illustrating the cross-sectional structure of the surface-emitting laser element 1A according to the first embodiment of this disclosure. The surface-emitting laser element 1A is a photonic crystal surface-emitting laser (PCSEL). For ease of understanding, an orthogonal XYZ coordinate system is defined in the figure as needed. The surface-emitting laser element 1A forms a standing wave in the XY plane and outputs the laser Lout in the Z direction, which is perpendicular to the light emission surface.

[0085] The surface-emitting laser element 1A of this embodiment includes: a semiconductor substrate 8 having a main surface 8a and a back surface 8b; a semiconductor stack 10 disposed on the main surface 8a of the semiconductor substrate 8; a first electrode 21; and a second electrode 22. The semiconductor stack 10 includes an active layer 11, a photonic crystal layer (diffraction grating layer) 12A, a lower cladding layer (first cladding layer) 13, a photoconductive layer 14, an upper cladding layer (second cladding layer) 15, a buffer layer 16A, and a contact layer 17. These layers extend along the XY plane, with the Z direction set as the thickness direction, and are stacked along the Z direction.

[0086] The main surface 8a and the back surface 8b of the semiconductor substrate 8 are flat and parallel to each other. The semiconductor substrate 8 is used for epitaxial growth of multiple semiconductor layers constituting the semiconductor stack 10. When the multiple semiconductor layers constituting the semiconductor stack 10 are GaAs-based semiconductor layers, the semiconductor substrate 8 is, for example, a GaAs substrate. When the multiple semiconductor layers constituting the semiconductor stack 10 are InP-based semiconductor layers, the semiconductor substrate 8 is, for example, an InP substrate. When the multiple semiconductor layers constituting the semiconductor stack 10 are GaN-based semiconductor layers, the semiconductor substrate 8 is, for example, a GaN substrate. The thickness of the semiconductor substrate 8 is, for example, in the range of 50 μm to 1000 μm. The semiconductor substrate 8 has a p-type or n-type conductivity. The planar shape of the main surface 8a is, for example, rectangular or square.

[0087] The lower cladding layer 13 is formed by epitaxial growth on the main surface 8a of the semiconductor substrate 8, and in one example, it contacts the main surface 8a of the semiconductor substrate 8. The lower cladding layer 13 may also be grown directly on the main surface 8a. Alternatively, the lower cladding layer 13 may be grown on the main surface 8a via a buffer layer (not shown) disposed between the main surface 8a and the lower cladding layer 13. The thickness of the lower cladding layer 13 is, for example, in the range of 0.5 μm to 5.0 μm.

[0088] The light-conducting layer 14 is epitaxially grown on the lower cladding layer 13 and, in one example, contacts the lower cladding layer 13. The light-conducting layer 14 is used to adjust the light distribution in the Z direction. In the example shown, the light-conducting layer 14 is disposed only between the lower cladding layer 13 and the active layer 11. If necessary, a light-conducting layer may also be disposed between the active layer 11 and the upper cladding layer 15. When the light-conducting layer is disposed between the active layer 11 and the upper cladding layer 15, the photonic crystal layer 12A is disposed between the upper cladding layer 15 and the light-conducting layer. Alternatively, no light-conducting layer may be disposed between the lower cladding layer 13 and the active layer 11, or between the active layer 11 and the upper cladding layer 15. The light-conducting layer 14 may include a carrier barrier layer for effectively confining carriers within the active layer 11. For example, when the oscillation wavelength is 940 nm, the thickness of the light-conducting layer 14 is in the range of 10 nm to 500 nm. When the photoconductor layer 14 is thick, higher-order modes appear in the thickness direction. If higher-order modes appear in the thickness direction, noise may be generated in the outgoing light. Therefore, the thickness of the photoconductor layer 14 is appropriate within the range that only allows for the fundamental modes in the thickness direction. Even if the thickness of the photoconductor layer 14 is within this range, if the photoconductor layer 14 is relatively thick, the mode will be biased towards the photoconductor layer 14, potentially reducing diffraction efficiency. If the photoconductor layer 14 is relatively thin, the proportion of the resonant mode leaking into the lower cladding layer 13 increases, potentially reducing diffraction efficiency. When a photoconductor layer is also provided between the active layer 11 and the upper cladding layer 15, if this photoconductor layer is relatively thin, the proportion of the resonant mode leaking into the upper cladding layer 15 increases, potentially reducing diffraction efficiency. Therefore, the appropriate thickness of the photoconductor layer 14 and other photoconductor layers can be set considering the mode shape.

[0089] The active layer 11 is epitaxially grown on the lower cladding layer 13. In the example shown, the active layer 11 is epitaxially grown on the photoconductor layer 14. In one example, the active layer 11 is in contact with the photoconductor layer 14. The active layer 11 receives a current supply to generate light. The refractive index of the active layer 11 is greater than that of the lower cladding layer 13 and the upper cladding layer 15, and the band gap of the active layer 11 is smaller than that of the lower cladding layer 13 and the upper cladding layer 15. In one example, the active layer 11 has a multi-quantum-well structure with alternating layers of wells and barrier layers.

[0090] The photonic crystal layer 12A is disposed between the lower cladding layer 13 and the active layer 11, or between the active layer 11 and the upper cladding layer 15. In the example shown, the photonic crystal layer 12A is disposed between the active layer 11 and the upper cladding layer 15, and is in contact with the active layer 11 and the upper cladding layer 15.

[0091] The photonic crystal layer 12A is the resonant mode forming layer in this embodiment. Figure 2This is a top view of the photonic crystal layer 12A. The photonic crystal layer 12A includes a base region 12a and multiple anisotropic regions 12b. The base region 12a is a semiconductor layer composed of a first refractive index medium. The multiple anisotropic regions 12b are composed of a second refractive index medium with a refractive index different from the first refractive index medium and exist within the base region 12a. The anisotropic regions 12b can be voids or can be configured to embed a solid medium within the voids. When the anisotropic regions 12b are voids, the photonic crystal layer 12A may further have a region on the base region 12a for covering the voids. The constituent material of this region may be the same as or different from the constituent material of the base region 12a.

[0092] Multiple anisotropic refractive index regions 12b are arranged in a two-dimensional and periodic manner in a plane perpendicular to the thickness direction of the photonic crystal layer 12A, i.e., in the XY plane. With the equivalent refractive index set to n1, the wavelength λ1 selected by the photonic crystal layer 12A is expressed as λ1 = a1 × n1, where a1 is the lattice spacing. The wavelength λ1 is contained within the emission wavelength range of the active layer 11. The photonic crystal layer 12A forms a resonant mode for light with wavelength λ1 in a plane perpendicular to its thickness direction, i.e., in the XY plane. The arrangement period of the multiple anisotropic refractive index regions 12b is set to cause the light with wavelength λ1 to oscillate at the Γ point. Therefore, the photonic crystal layer 12A can select wavelength λ1 from the emission wavelength of the active layer 11 and diffract in the Z direction.

[0093] Here, an imaginary tetragonal lattice is set in the XY plane of the photonic crystal layer 12A. One side of the tetragonal lattice is parallel to the X-axis, and the other side is parallel to the Y-axis. At this time, a square-shaped unit constitutive region R, centered on the lattice points of the tetragonal lattice, can be set in a two-dimensional manner along multiple columns along the X-axis and multiple rows along the Y-axis. The unit constitutive region R is a region enclosed by straight lines that bisect the lattice points of the imaginary tetragonal lattice. One or more anisotropic regions 12b are set in each unit constitutive region R. The planar shape of the anisotropic regions 12b is, for example, circular. Within each unit constitutive region R, the centroid G of the anisotropic region 12b overlaps with and coincides with each lattice point. The periodic structure of the multiple anisotropic regions 12b is not limited to this; for example, a triangular lattice can be set instead of a tetragonal lattice.

[0094] Figure 2An example is shown where the shape of the anisotropic refractive index region 12b in the XY plane is circular. The anisotropic refractive index region 12b can have shapes other than circular. For example, the shape of the anisotropic refractive index region 12b in the XY plane can have mirror symmetry, i.e., line symmetry. Here, mirror symmetry or line symmetry means that the planar shape of the anisotropic refractive index region 12b sandwiched along a straight line along the XY plane, and located on one side of that line, is mirror-symmetric to the planar shape of the anisotropic refractive index region 12b located on the other side of that line, i.e., line symmetry. Examples of shapes with mirror symmetry or line symmetry include... Figure 3 As shown, the following are examples: (a) a circle, (b) a square, (c) a regular hexagon, (d) a regular octagon, (e) a regular 16-sided polygon, (f) a rectangle, and (g) an ellipse.

[0095] The shape of the anisotropic refractive index region 12b in the XY plane can be a shape that does not have 180° rotational symmetry. For example, such a shape... Figure 4 As shown, examples include (a) an equilateral triangle, (b) a right-angled isosceles triangle, (c) a shape where two circles or parts of an ellipse overlap, (d) an oval shape (i.e., an ellipse deformed such that the dimension along the minor axis near one end of the major axis is smaller than the dimension along the minor axis of the other end), (e) a teardrop shape (i.e., a shape where one end of the ellipse along the major axis is deformed into a pointed end protruding along the major axis), (f) an isosceles triangle, (g) an arrowhead shape (i.e., a rectangle with one side concave into a triangle), (h) a trapezoid, (i) a pentagon, (j) a shape where parts of two rectangles overlap, and (k) a shape where parts of two rectangles overlap and do not have mirror symmetry. Thus, because the shape of the heterorefringent region 12b in the XY plane does not have 180° rotational symmetry, higher light output can be obtained.

[0096] Figure 5 Part (a) to Figure 5 Part (k) is a top view showing another example of the shape of the anisotropic refractive index regions in the XY plane. In this example, multiple other anisotropic refractive index regions 12c, different from the multiple anisotropic refractive index regions 12b, are further provided. Each anisotropic refractive index region 12c is composed of a second refractive index medium having a refractive index different from that of the first refractive index medium of the basic region 12a. Like the anisotropic refractive index regions 12b, the anisotropic refractive index regions 12c can be voids or configured to have a solid medium embedded in the voids. The anisotropic refractive index regions 12c are provided in a one-to-one correspondence with the anisotropic refractive index regions 12b. The centroid G of the combined anisotropic refractive index regions 12b and 12c is located at a lattice point of the unit constitutive region R constituting the imaginary tetragonal lattice. Any anisotropic refractive index regions 12b and 12c are contained within the corresponding unit constitutive region R.

[0097] The planar shape of the anisotropic region 12c is, for example, circular, but like the anisotropic region 12b, it can have various shapes. Figure 5 Part (a) Figure 5 The (k) section shows examples of the shape and relative relationships of the heterorefringent regions 12b and 12c in the XY plane. Figure 5 Part (a) and Figure 5 Part (b) shows the pattern in which the regions 12b and 12c with different refractive indices have the same shape. Figure 5 Part (c) and Figure 5 Part (d) shows the anisotropic refractive index regions 12b and 12c with the same shape, and in such a way that parts of them overlap each other. Figure 5 Part (e) shows a graphic of anisotropic refractive index regions 12b and 12c having the same shape, with the anisotropic refractive index regions 12b and 12c tilted relative to each other. Figure 5 Part (f) shows the pattern in which the regions 12b and 12c with different refractive indexes have different shapes. Figure 5 Part (g) shows a pattern in which the anisotropic refractive index regions 12b and 12c have different shapes from each other, and in a way that the anisotropic refractive index regions 12b and 12c are separated from each other.

[0098] like Figure 5 The (h) part ~ Figure 5 As shown in part (k), the anisotropic region 12b can also be configured as two separate regions 12b1 and 12b2. Furthermore, the distance between the centroid of the merged regions 12b1 and 12b2 and the centroid of the anisotropic region 12c can be arbitrarily set within the unit constitutive region R. The centroid of the merged regions 12b1 and 12b2 is equivalent to the centroid of a single anisotropic region 12b. For example... Figure 5 As shown in part (h), regions 12b1, 12b2 and anisotropic region 12c can have patterns with the same shape. Figure 5 As shown in part (i), two patterns in regions 12b1, 12b2 and anisotropic region 12c can also differ from the other patterns. For example... Figure 5 As shown in part (j), in addition to the angle of the straight line connecting regions 12b1 and 12b2 relative to the X-axis, the angle of the anisotropic region 12c relative to the X-axis can also be arbitrarily set within the unit constitutive region R. For example... Figure 5 As shown in part (k), while regions 12b1, 12b2 and anisotropic region 12c maintain the same relative angle, the angle of the straight line connecting regions 12b1 and 12b2 relative to the X-axis can also be arbitrarily set within the unit constitutive region R.

[0099] Multiple anisotropic regions 12b can be set up for each unit constituting region R. Here, a unit constituting region R refers to the region with the smallest area enclosed by the perpendicular bisecting lines of the grid points of other periodically arranged unit constituting regions relative to a certain unit constituting region R, corresponding to the Wigner-Seitz cell in solid-state physics. In this case, the multiple anisotropic regions 12b contained in a unit constituting region R have the same shape, and their centroids can be separated from each other. The shape of the anisotropic regions 12b in the XY plane can be the same among multiple unit constituting regions R, and can be made to coincide among the unit constituting regions R by translation operations or translation and rotation operations. In this case, the fluctuation of the photon band structure is reduced, and a narrow linewidth spectrum can be obtained. Alternatively, the shape of the anisotropic regions in the XY plane is not necessarily the same among multiple unit constituting regions R, and the shapes can also be different between adjacent unit constituting regions R.

[0100] In the above structure, the anisotropic region 12b is formed by a void. The anisotropic region 12b can also be formed by embedding an inorganic material having a refractive index different from that of the base region 12a into the void. In this case, the void can be formed, for example, by etching in the base region 12a, and the anisotropic region 12b can be formed by embedding the inorganic material into the void using chemical vapor deposition or atomic layer deposition. Alternatively, after embedding the inorganic material into the void of the base region 12a to form the anisotropic region 12b, an inorganic material of the same constituent material as the anisotropic region 12b can be deposited thereon. When the anisotropic region 12b is a void, an inert gas such as argon or nitrogen, or a gas such as hydrogen or air, can be sealed into the void.

[0101] Refer again Figure 1 The upper cladding layer 15 is formed by epitaxial growth on the photonic crystal layer 12A, and in one example, it is in contact with the photonic crystal layer 12A. The thickness of the upper cladding layer 15 is, for example, in the range of 0.5 μm to 5.0 μm. The band gap of the upper cladding layer 15 is larger than that of the active layer 11 and the basic region 12a of the photonic crystal layer 12A, and is constant in the thickness direction. The refractive index of the upper cladding layer 15 is smaller than that of the active layer 11 and the basic region 12a of the photonic crystal layer 12A.

[0102] In this embodiment where the surface-emitting laser element 1A is a PCSEL, the band gap of the upper cladding layer 15 is smaller than that of the lower cladding layer 13. Specifically, when both the lower cladding layer 13 and the upper cladding layer 15 contain Al as a component, the Al component ratio of the upper cladding layer 15 is smaller than that of the lower cladding layer 13. As a result, since the refractive index of the upper cladding layer 15 is relatively higher, the proportion of modes distributed in the photonic crystal layer 12A in the overall mode of the surface-emitting laser element 1A increases, thereby improving diffraction efficiency.

[0103] The mitigation layer 16A is epitaxially grown on and in contact with the upper cladding layer 15. The mitigation layer 16A is provided to mitigate the potential barrier caused by the bandgap difference between the upper cladding layer 15 and the contact layer 17. The mitigation layer 16A is, for example, composed of the same constituent elements as the upper cladding layer 15. The mitigation layer 16A has a bandgap width between the bandgap width of the upper cladding layer 15 and the bandgap width of the contact layer 17. The bandgap width of the mitigation layer 16A monotonically decreases from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. Figure 1 Figure G1 shows the distribution of the bandgap width of the buffer layer 16A in the thickness direction. In Figure G1, the horizontal axis represents the bandgap width, and the vertical axis represents the position in the thickness direction. As shown in Figure G1, in this embodiment, the bandgap width of the buffer layer 16A changes continuously from the bandgap width of the upper cladding layer 15 to the bandgap width of the contact layer 17. In the example shown, since the bandgap width of the contact layer 17 is smaller than the bandgap width of the upper cladding layer 15, the bandgap width of the buffer layer 16A continuously decreases from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. In one example, the bandgap width of the buffer layer 16A changes proportionally to the distance from the interface on the upper cladding layer 15 side. Figure 1 In the diagram, the bandgap width distribution of the buffer layer 16A is represented by the depth of color, with darker areas having larger bandgap widths. The bandgap width of the buffer layer 16A at the interface with the upper cladding layer 15 can be equal to the bandgap width of the upper cladding layer 15. The bandgap width of the buffer layer 16A at the interface with the contact layer 17 can be equal to the bandgap width of the contact layer 17.

[0104] When the upper cladding 15 contains Al as a component, the buffer layer 16A also functions as a layer to inhibit the oxidation of Al in the upper cladding 15. In this case, the buffer layer 16A also contains Al. The buffer layer 16A has an Al component ratio that is between the Al component ratio of the upper cladding 15 and the Al component ratio of the contact layer 17. When the contact layer 17 does not contain Al as a component, the Al component ratio of the contact layer 17 is zero. Furthermore, the Al component ratio of the buffer layer 16A monotonically decreases from the interface on the upper cladding 15 side to the interface on the contact layer 17 side. Figure 1Figure G2 shows the distribution of the Al composition ratio of the buffer layer 16A in the thickness direction. In Figure G2, the horizontal axis represents the Al composition ratio, and the vertical axis represents the position in the thickness direction. As shown in Figure G2, in this embodiment, the Al composition ratio of the buffer layer 16A continuously decreases from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. In one example, the Al composition ratio of the buffer layer 16A decreases proportionally to the distance from the interface on the upper cladding layer 15 side. The Al composition ratio of the buffer layer 16A at the interface on the upper cladding layer 15 side may also be equal to the Al composition ratio of the upper cladding layer 15. The Al composition ratio of the buffer layer 16A at the interface on the contact layer 17 side may also be equal to the Al composition ratio of the contact layer 17. When the Al component ratio of the contact layer 17 is zero, that is, when the contact layer 17 does not contain Al as a component, the Al component ratio at the interface on the contact layer 17 side of the buffer layer 16A is also zero.

[0105] The thickness of the buffer layer 16A is less than the thickness of the upper cladding layer 15. The thickness of the buffer layer 16A is, for example, in the range of 5 nm to 1000 nm. The buffer layer 16A is separated from both the photonic crystal layer 12A and the active layer 11 by more than 1 μm, more preferably by more than 1.5 μm. That is, when only the upper cladding layer 15 is provided between the buffer layer 16A and both the photonic crystal layer 12A and the active layer 11, the thickness of the upper cladding layer 15 is more than 1 μm, more preferably more than 1.5 μm. The sum of the thickness of the upper cladding layer 15 and the thickness of the buffer layer 16A may also be equal to the thickness of the lower cladding layer 13.

[0106] Contact layer 17 is formed by epitaxial growth on buffer layer 16A and contacts buffer layer 16A. Contact layer 17 has a different bandgap width than the upper cladding layer 15. Typically, the bandgap width of contact layer 17 is smaller than the bandgap width of upper cladding layer 15. In one example, the composition of contact layer 17 is the same as that of the base region 12a of photonic crystal layer 12A and the barrier layer of active layer 11. The thickness of contact layer 17 is, for example, in the range of 50 nm to 500 nm.

[0107] The first electrode 21 is a metal electrode disposed on the back surface 8b of the semiconductor substrate 8. The first electrode 21 is electrically connected to the lower cladding layer 13 by forming an ohmic contact with the semiconductor substrate 8. Viewed from a direction perpendicular to the back surface 8b of the semiconductor substrate 8, the first electrode 21 is in the shape of a rectangular frame with an opening 21a for the laser Lout to pass through. The back surface 8b of the semiconductor substrate 8 is exposed from the first electrode 21 through the opening 21a. In the photonic crystal layer 12A, the oscillating laser Lout is output to the outside of the surface-emitting laser element 1A through the opening 21a.

[0108] The second electrode 22 is a metal electrode disposed on the surface of the contact layer 17 in the region of at least the opening 21a of the first electrode 21, i.e., the central region of the semiconductor stack 10. The second electrode 22 forms an ohmic contact with the contact layer 17. The portion of the contact layer 17 that is not in contact with the second electrode 22 can also be removed. The second electrode 22 also has the function of reflecting the light generated in the active layer 11.

[0109] In some examples, the semiconductor substrate 8 is a GaAs substrate, and the active layer 11, photonic crystal layer 12A, lower cladding layer 13, photoconductive layer 14, upper cladding layer 15, buffer layer 16A, and contact layer 17 are made of GaAs-based semiconductors. In one embodiment, the lower cladding layer 13 and photoconductive layer 14 are AlGaAs layers, the active layer 11 has a multi-quantum-well structure, the barrier layer of the multi-quantum-well structure is an AlGaAs layer, the quantum well layers are GaAs layers, and the number of well layers is, for example, three. The basic region 12a of the photonic crystal layer 12A is an AlGaAs layer or a GaAs layer, the anisotropic region 12b is a hole, the upper cladding layer 15 and buffer layer 16A are AlGaAs layers, and the contact layer 17 is a GaAs layer. In this case, the thickness of the semiconductor substrate 8 is, for example, 150 μm. The thickness of the lower cladding layer 13 is, for example, 2000 nm. The thickness of the photoconductive layer 14 is, for example, 80 nm. The thickness of the well and barrier layers of the active layer 11 is, for example, 10 nm. The thickness of the photonic crystal layer 12A is, for example, 300 nm. The thickness of the upper cladding layer 15 is, for example, 1500 nm. The thickness of the buffer layer 16A is, for example, 500 nm. The thickness of the contact layer 17 is, for example, 200 nm. The Al composition ratio of the lower cladding layer 13 is, for example, 70 atomic%. The Al composition ratio of the photoconductive layer 14 is, for example, 15 atomic%. The Al composition ratio of the barrier layer of the active layer 11 is, for example, 15 atomic%. The Al composition ratio of the upper cladding layer 15 is, for example, 43 atomic%. The Al composition ratio of the buffer layer 16A at the interface with the upper cladding layer 15 is, for example, 43 atomic%. The Al composition ratio of the buffer layer 16A at the interface with the contact layer 17 is, for example, 0 atomic%. The Al composition ratio of the contact layer 17 is, for example, 0 atoms.

[0110] The lower cladding layer 13 is given the same conductivity type as the semiconductor substrate 8, i.e., the first conductivity type, while the upper cladding layer 15, the buffer layer 16A, and the contact layer 17 are given the opposite conductivity type to the semiconductor substrate 8, i.e., the second conductivity type. In one example, the semiconductor substrate 8 and the lower cladding layer 13 are n-type, and the upper cladding layer 15, the buffer layer 16A, and the contact layer 17 are p-type. The photonic crystal layer 12A has the same conductivity type as the semiconductor substrate 8 when disposed between the active layer 11 and the lower cladding layer 13, and has the opposite conductivity type to the semiconductor substrate 8 when disposed between the active layer 11 and the upper cladding layer 15. The concentration of the impurity that determines the conductivity type is, for example, 1 × 10⁻⁶. 16 / cm 3~1×10 21 / cm 3 The active layer 11 and the photoconductive layer 14 are intrinsically type I without any intentionally added impurities, but can be endowed with any conductivity type. The intrinsic, type I impurity concentration is 1 × 10⁻⁶. 16 / cm 3 The impurity concentration of the photonic crystal layer 12A can also be intrinsic, i.e., type I, when it is necessary to suppress the effects of light absorption caused by impurity energy levels. The impurity concentration of the buffer layer 16A can be the same as, or greater than, the concentration of the impurities that determine the conductivity type of the upper cladding layer 15.

[0111] The material of the first electrode 21 is appropriately selected based on the constituent material of the semiconductor substrate 8. If the semiconductor substrate 8 is an n-type GaAs substrate, the first electrode 21 may contain, for example, a mixture of Au and Ge. In one example, the first electrode 21 has an AuGe monolayer, or a stacked structure of AuGe layers and Au layers. The material of the second electrode 22 is appropriately selected based on the constituent material of the contact layer 17. If the contact layer 17 is p-type GaAs, the second electrode 22 can be made of, for example, a material containing Au, and at least one of Cr, Ti, and Pt, for example, a stacked structure of Cr layers and Au layers. However, the materials of the first electrode 21 and the second electrode 22 are not limited to those that enable ohmic bonding.

[0112] The surface-emitting laser element 1A of this embodiment, having the above structure, operates as follows: When a driving current is supplied between the first electrode 21 and the second electrode 22, electron-hole recombination occurs within the active layer 11, and light is emitted from the active layer 11. The electrons and holes that contribute to this emission, as well as the generated light, are effectively distributed between the lower cladding layer 13 and the upper cladding layer 15. Since the light emitted from the active layer 11 is distributed between the lower cladding layer 13 and the upper cladding layer 15, it enters the interior of the photonic crystal layer 12A, is confined between the lower cladding layer 13 and the upper cladding layer 15, and is diffracted by the photonic crystal layer 12A. In the photonic crystal layer 12A, a resonant mode is formed in the in-plane direction perpendicular to the thickness direction of the photonic crystal layer 12A, and the light oscillates at a wavelength corresponding to the arrangement period of the plurality of heterorefringent index regions 12b, generating laser light. For example, when the arrangement period of the tetragonal lattice crystal is the length of one wavelength of light, a portion of the laser light is diffracted in the thickness direction of the photonic crystal layer 12A, i.e., the Z direction. Light diffracted from the photonic crystal layer 12A along the Z direction travels in a direction perpendicular to the main surface 8a of the semiconductor substrate 8. This light is output directly from the back surface 8b through the opening 21a to the outside of the surface-emitting laser element 1A, or after being reflected by the second electrode 22, it is output from the back surface 8b through the opening 21a to the outside of the surface-emitting laser element 1A.

[0113] The effects obtained by the surface-emitting laser element 1A of this embodiment described above will be explained. The surface-emitting laser element 1A has a buffer layer 16A between the upper cladding layer 15 and the contact layer 17. The buffer layer 16A has a bandgap width between the bandgap width of the upper cladding layer 15 and the bandgap width of the contact layer 17. Therefore, compared to the case without the buffer layer 16A, the rate of change of the bandgap width between the upper cladding layer 15 and the contact layer 17 is mitigated, and the potential barrier is reduced. Consequently, the resistance of the element is reduced, and sufficient laser oscillation can be obtained even with low driving voltages. As a result, power consumption can be reduced, the reliability of the element can be improved, and the lifespan of the element can be extended.

[0114] As described above, the mitigation layer 16A can also be composed of the same constituent elements as the upper cladding layer 15. In one example, the upper cladding layer 15 and the mitigation layer 16A are both composed of AlGaAs. When the upper cladding layer 15 and the mitigation layer 16A have the same constituent elements, the mitigation layer 16A can be grown without changing the feedstock after the upper cladding layer 15 is grown. Therefore, the mitigation layer 16A can be easily formed.

[0115] like Figure 1 As shown in Figure G1, the bandgap of the buffer layer 16A can also change continuously from the bandgap of the upper cladding layer 15 to the bandgap of the contact layer 17. In this case, since the potential barrier can be effectively reduced, the aforementioned effects achieved by the surface-emitting laser element 1A of this embodiment can be obtained more significantly.

[0116] As in this embodiment, the upper cladding layer 15 and the buffer layer 16A contain Al as a component, and the Al component ratio of the buffer layer 16A can be smaller than that of the upper cladding layer 15. When the upper cladding layer 15 contains Al but the buffer layer 16A is not provided, the Al in the upper cladding layer 15 is easily oxidized due to oxygen atoms passing through the contact layer 17. Alternatively, if growth between the upper cladding layer 15 and the contact layer 17 is interrupted, the Al in the upper cladding layer 15 becomes easily oxidized. If the Al in the upper cladding layer 15 oxidizes, the resistance of the upper cladding layer 15 increases, and sufficient laser oscillation cannot be obtained without increasing the driving voltage. As a result, power consumption increases, and the reliability of the device decreases. In this embodiment, since a buffer layer 16A with an Al component ratio smaller than that of the upper cladding layer 15 is provided between the contact layer 17 and the upper cladding layer 15, the effects caused by Al oxidation can be reduced. That is, according to this embodiment, the increase in resistance caused by Al oxidation can be suppressed, and sufficient laser oscillation can be obtained with a lower driving voltage. As a result, power consumption can be further reduced and the reliability of components can be further improved.

[0117] like Figure 1As shown in Figure G2, the Al composition ratio of the buffer layer 16A can also continuously decrease from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. In this case, since Al oxidation can be effectively reduced, the above-mentioned effects can be obtained more significantly.

[0118] As in this embodiment, the upper cladding layer 15 and the buffer layer 16A can be AlGaAs layers, and the contact layer 17 can be a GaAs layer. In this case, a surface-emitting laser element 1A capable of emitting laser light in the infrared region can be obtained.

[0119] As in this embodiment, the thickness of the moderating layer 16A can also be less than the thickness of the upper cladding layer 15. In this case, the upper cladding layer 15 becomes relatively thick, and the moderating layer 16A, which has a larger refractive index than the upper cladding layer 15, separates from the active layer 11 and the photonic crystal layer 12A. Therefore, it is possible to suppress the coupling of the mode generated by the moderating layer 16A and the contact layer 17 with the photonic crystal layer 12A. As a result, the fundamental mode can be stabilized and the quality of the output light can be improved.

[0120] As shown in this embodiment, the buffer layer 16A can be at least 1 μm or 1.5 μm away from both the photonic crystal layer 12A and the active layer 11. In this case, the buffer layer 16A, having a refractive index greater than that of the upper cladding layer 15, is separated from the active layer 11 and the photonic crystal layer 12A. Therefore, the coupling of the mode generated by the buffer layer 16A and the contact layer 17 with the photonic crystal layer 12A can be suppressed. As a result, the basic mode can be stabilized and the quality of the output light can be improved. In particular, in the surface-emitting laser element 1A, which is a PCSEL, when a higher-order mode in the layer direction is formed, the band end of the higher-order mode is formed. As a result, beam patterns and the like are formed at the anti-crossing point with the band end of the basic mode, and unexpected beam patterns may appear. By separating the buffer layer 16A from both the photonic crystal layer 12A and the active layer 11 by at least 1 μm or 1.5 μm, the formation of higher-order modes in the layer direction can be avoided, and the appearance of unexpected beam patterns can be suppressed.

[0121] Here, an embodiment of the surface-emitting laser element 1A according to this embodiment is shown. Table 1 below shows an embodiment of the composition and thickness of each layer constituting the surface-emitting laser element 1A. In this example, the distance between the tempering layer 16A and the photonic crystal layer 12A is 2 μm. The filling factor refers to the proportion of the anisotropic refractive index region 12b in a unit area of ​​constitutive region R. Figure 6 Part (a) is a graph showing the refractive index distribution G11 of the surface-emitting laser element 1A having the structure of Table 1, the basic mode distribution G12 generated with the active layer 11 and the photonic crystal layer 12A as the center, and the mode distribution G13 generated with the tempering layer 16A and the contact layer 17 as the center. Figure 6Part (b) is enlarged and shown Figure 6 The vicinity of the active layer 11 and the photonic crystal layer 12A in part (a). Figure 7 Part (a) is a graph showing the refractive index distribution G11, the basic mode distribution G12, and the mode distribution G13 of a surface-emitting laser element without the mitigation layer 16A for comparison. Figure 7 Part (b) is enlarged and shown Figure 7 The area near the active layer 11 and photonic crystal layer 12A in part (a). In the figure, interval Tclad1 corresponds to the lower cladding layer 13, interval Tac corresponds to the active layer 11, interval Tpc corresponds to the photonic crystal layer 12A, interval Tclad2 corresponds to the upper cladding layer 15, interval Trelax corresponds to the buffer layer 16A, interval Tcont corresponds to the contact layer 17, and interval Tair corresponds to air.

[0122] Table 1

[0123]

[0124] Reference Figure 6 In parts (a) and (b), the electric field of mode distribution G13 is approximately zero in photonic crystal layer 12A and does not contribute to the diffraction of photonic crystal layer 12A. Furthermore, the coupling coefficient between the fundamental mode distribution G12 and mode distribution G13 is approximately zero. Therefore, by having a mitigation layer 16A with a refractive index greater than that of the upper cladding layer 15, sufficiently separating it from the active layer 11 and photonic crystal layer 12A, mode coupling generated in the mitigation layer 16A and contact layer 17 can be sufficiently suppressed in the fundamental modes generated with the active layer 11 and photonic crystal layer 12A as the center.

[0125] In this embodiment, the case where the refractive index of the upper cladding layer 15 is greater than that of the lower cladding layer 13 has been described, but the embodiment is not limited to this. The refractive index of the upper cladding layer 15 may also be less than that of the lower cladding layer 13. In this case, the coupling between the mode and the fundamental mode generated in the contact layer 17 can be suppressed, thereby improving the quality of the output light. Furthermore, the smaller the refractive index of the lower cladding layer 13, the larger the bandgap width of the lower cladding layer 13 becomes, and the greater the difference between the bandgap width of the lower cladding layer 13 and the bandgap width of the semiconductor substrate 8 becomes. In this case, a bandgap mitigation layer having a bandgap width between that of the lower cladding layer 13 and the semiconductor substrate 8 may be provided between the lower cladding layer 13 and the semiconductor substrate 8. The surface-emitting laser element 1A of this embodiment is particularly useful in such cases.

[0126] Here, the method for fabricating the surface-emitting laser element 1A of this embodiment will be described. First, on the main surface 8a of the semiconductor substrate 8, a base region 12a consisting of a lower cladding layer 13, a photoconductive layer 14, an active layer 11, and a photonic crystal layer 12A is sequentially crystallized using, for example, metal-organic vapor deposition (MOCVD). Next, an electron beam resist is coated on the surface of the base region 12a, and a region with anisotropic refractive index 12b is patterned using electron beam lithography. Furthermore, the pattern of the electron beam resist is transferred to the base region 12a, for example, using inductively coupled plasma (ICP) etching, to form the region with anisotropic refractive index 12b. Thus, a photonic crystal layer 12A having a base region 12a and anisotropic refractive index region 12b is formed. After removing the electron beam resist, an upper cladding layer 15, a buffer layer 16A, and a contact layer 17 are sequentially crystallized on the photonic crystal layer 12A, for example, using MOCVD.

[0127] Next, the back surface 8b of the semiconductor substrate 8 is polished to thin the semiconductor substrate 8, and then mirror polishing is performed on the back surface 8b. Furthermore, a first electrode 21 with an opening 21a is formed on the back surface 8b using photolithography, vacuum evaporation, and a lift-off method. A second electrode 22 is formed on the surface of the contact layer 17 using photolithography, vacuum evaporation, and a lift-off method. The formation of the first electrode 21 and the formation of the second electrode 22 can be performed either way. Afterward, the semiconductor substrate 8 and the layers formed on the semiconductor substrate 8 are diced and cut into chips. Through the above processes, the surface-emitting laser element 1A of this embodiment is manufactured.

[0128] [Second Implementation]

[0129] In the above embodiments, a surface-emitting laser element 1A having a photonic crystal layer 12A with periodically arranged heterochromatic regions 12b has been described. The surface-emitting laser element of this disclosure is not limited to a photonic crystal layer with periodically arranged heterochromatic regions, but can have various resonant mode forming layers. In recent years, a phase-modulated light-emitting element has been studied, which outputs an arbitrary light image by controlling the phase spectrum and intensity spectrum of light emitted from a plurality of light-emitting points arranged in a two-dimensional pattern. Such a phase-modulated light-emitting element is called an S-iPM laser, which outputs a light image of arbitrary shape in space. The resonant mode forming layer can include a structure for such an S-iPM laser.

[0130] Figure 8This diagram schematically illustrates the cross-sectional structure of the surface-emitting laser element 1B according to the second embodiment. The difference between the surface-emitting laser element 1B of this embodiment and the surface-emitting laser element 1A of the first embodiment lies in the structure of the resonant mode forming layer. In this embodiment, the surface-emitting laser element 1B, instead of the photonic crystal layer 12A of the first embodiment, has a phase modulation layer 12B as the resonant mode forming layer.

[0131] Figure 9 This is a top view of the phase modulation layer 12B. The phase modulation layer 12B includes a basic region 12a and multiple anisotropic regions 12b. The basic region 12a is composed of a first refractive index medium. The multiple anisotropic regions 12b are composed of a second refractive index medium with a refractive index different from that of the first refractive index medium. Here, an imaginary tetragonal lattice in the XY plane is set in the phase modulation layer 12B. One side of the square lattice is parallel to the X-axis, and the other side is parallel to the Y-axis. At this time, a square-shaped unit constitutive region R centered on the lattice point O of the tetragonal lattice can be set in two dimensions along multiple columns along the X-axis and multiple rows along the Y-axis. One anisotropic region 12b is provided in each unit constitutive region R. The planar shape of the anisotropic region 12b is the same as in the above embodiment, and can be various shapes such as circles. In each unit constitutive region R, the centroid G of the anisotropic region 12b is arranged away from the lattice point O closest to that anisotropic region 12b.

[0132] like Figure 10 As shown, the angle between the direction from grid point O towards the centroid G and the X-axis is set as... angle This is the rotation angle of the centroid G of the anisotropic refractive index region 15b about lattice point O. x represents the position of the x-th lattice point on the X-axis, and y represents the position of the y-th lattice point on the Y-axis. The rotation angle... With a value of 0°, the direction of the vector connecting lattice point O and the centroid G is aligned with the positive direction of the X-axis. Let the length of the vector connecting lattice point O and the centroid G be r(x,y). In one example, r(x,y) is equal regardless of x and y. In other words, r(x,y) is equal across the entire phase modulation layer 12B.

[0133] like Figure 9 As shown, in phase modulation layer 12B, the rotation angle Corresponding to the desired light image and individually set independently for each unit constituting region R. The rotation angle of the centroid G of at least two heterorefractive index regions 12b. They are different. (Rotation angle) Each position, determined by the values ​​of x and y, has a specific value, but is not necessarily limited to being represented by a specific function. That is, the rotation angle. The distribution is determined by extracting the phase distribution from the complex amplitude distribution obtained by performing an inverse Fourier transform on the desired light image. When the complex amplitude distribution is obtained from the desired light image, the reproducibility of the beam pattern is improved by applying an iterative algorithm such as the Gerchberg-Saxton (GS) method, which is generally used for calculations to generate holograms.

[0134] In this embodiment, the light emitted from the active layer 11 is confined between the lower cladding layer 13 and the upper cladding layer 15, and is diffracted by the phase modulation layer 12B, forming a predetermined pattern corresponding to the internal lattice structure of the phase modulation layer 12B. The laser Lout2, scattered and emitted within the phase modulation layer 12B, passes through the lower cladding layer 13 and the semiconductor substrate 8, and is emitted towards the outside of the surface-emitting laser element 1A. At this time, the 0th-order light is emitted in the thickness direction of the phase modulation layer 12B, i.e., the Z-direction. In contrast, the +1st-order and -1st-order light are emitted in any direction within the space containing the Z-direction and directions inclined relative to the Z-direction.

[0135] Figure 11 This is to illustrate the optical image obtained by projecting the output beam pattern of the surface-emitting laser element 1B of this embodiment and the rotation angle of the phase modulation layer 12B. The relationship between the distributions. The center Q of the output beam pattern is located in the Z direction from the center of the light emitting surface of the surface-emitting laser element 1B. Figure 11 The diagram shows the four quadrants with center Q as the origin. Figure 11 The example shown illustrates the case where the light image is obtained in the first and third quadrants, but it is also possible to obtain the light image in the second and fourth quadrants, or all quadrants. In this embodiment, as... Figure 11 As shown, a point-symmetric light image about the origin is obtained. Figure 11 As an example, we show the cases where the pattern of the letter "A" in the third quadrant is obtained as the +1st order diffraction light, and the pattern of the letter "A" rotated 180 degrees in the first quadrant is obtained as the -1st order diffraction light. When the light image has a rotationally symmetric shape, such as a cross, a circle, or a double circle, the +1st order diffraction light and the -1st order diffraction light overlap and are observed as a single light image.

[0136] The optical image obtained by projecting the output beam pattern of the surface-emitting laser element 1B of this embodiment includes at least one of the following: a light spot, a straight line, a cross, a line drawing, a grid pattern, a photograph, a striped pattern, CG (computer graphics), and text. To obtain the desired optical image, the rotation angle of the heterorefringent region 12b of the phase modulation layer 12B is determined through the following steps. The distribution of .

[0137] An orthogonal XYZ coordinate system is defined by a Z-axis aligned with the normal direction and an XY plane containing mutually orthogonal X and Y axes aligned with a surface of the phase modulation layer 12B containing multiple heterorefringent regions 12b. As a first prerequisite, an imaginary tetragonal lattice consisting of M1×N1 square-shaped unit constituting regions R is defined on its XY plane. M1 and N1 are integers greater than or equal to 1.

[0138] like Figure 12 As shown, the length r of the radius vector and the inclination angle θ from the Z-axis are defined. tilt and the rotation angle θ from the X-axis as determined in the XY plane. rot Defined spherical coordinates (r, θ) rot ,θ tilt As a second prerequisite, the coordinates (ξ,η,ζ) in the XYZ orthogonal coordinate system are relative to the spherical coordinates (r,θ). rot ,θ tilt The coordinates satisfy the relationships shown in the following equations (1) to (3). Figure 12 It is used to explain the relationship between spherical coordinates (r, θ) rot ,θ tilt A diagram showing the coordinate transformation from (ξ, η, ζ) to the XYZ orthogonal coordinate system. The coordinates (ξ, η, ζ) represent the designed light image on a defined plane within the XYZ orthogonal coordinate system, which is the actual space.

[0139]

Mathematical Formula 1

[0140] ξ=r sinθ tilt cosθ rot …(1)

[0141]

Mathematical Formula 2

[0142] η = r sinθ tilt sinθ rot …(2)

[0143]

Mathematical Expression 3

[0144] ζ=r cosθ tilt …(3)

[0145] The beam pattern, equivalent to the light image output from the surface-emitting laser element 1B, is oriented by an angle θ. tilt and θ rot The set of points of illumination in a defined direction. At this point, the angle θ... tilt and θ rot Convert to coordinate value k x and k y Coordinate value k xThe standardized wavenumber is defined by the following formula (4), and is the coordinate value on the Kx-axis corresponding to the X-axis. Coordinate value k y The normalized wavenumber, defined by the following equation (5), is the coordinate value on the Ky axis, which corresponds to the Y-axis and is orthogonal to the Kx-axis. The normalized wavenumber refers to the wavenumber after normalization by taking the wavenumber equivalent to the lattice spacing of an imaginary tetragonal lattice as 1.0. In this case, in the wavenumber space defined by the Kx-axis and Ky-axis, the specific wavenumber range containing the beam pattern equivalent to the light image is composed of M2×N2 image regions FR, which are square in shape. M2 and N2 are integers greater than or equal to 1. The integer M2 does not necessarily have to be the same as the integer M1. The integer N2 does not necessarily have to be the same as the integer N1. Equations (4) and (5) are disclosed, for example, in Y. Kurosaka et al., "Effects of non-lasingband in two-dimensional photonic-crystal lasers clarified using omnidirectional band structure," Opt. Express 20, 21773-21783 (2012).

[0146]

Mathematical Expression 4

[0147]

[0148]

Mathematical Expression 5

[0149]

[0150] a: The lattice constant of a hypothetical tetragonal lattice

[0151] λ: Oscillation wavelength of surface-emitting laser element 1B

[0152] In wavenumber space, the image region FR(k) x ,k y The coordinate components k along the Kx-axis x The coordinate components k along the Ky axis direction y Confirmed. Coordinate component k x It is an integer greater than 0 and less than M²-1. Coordinate component k yIt is an integer greater than 0 and less than N²-1. The unit constitutive region R(x,y) on the XY plane is determined by the coordinate components x in the X-axis direction and y in the Y-axis direction. The coordinate component x is an integer greater than 0 and less than M¹-1. The coordinate component y is an integer greater than 0 and less than N¹-1. As a third prerequisite, the complex amplitude F(x,y) obtained by transforming each two-dimensional inverse discrete Fourier transform of the image region FR(kx,ky) into the unit constitutive region R(x,y) is given by the following equation (6) with j as the imaginary unit. When the amplitude term is A(x,y) and the phase term is P(x,y), the complex amplitude F(x,y) is defined by the following equation (7). As a fourth prerequisite, the unit constitutive region R(x,y) is defined by the s-axis and the t-axis. The s-axis and the t-axis are parallel to the X-axis and the Y-axis, respectively, and are orthogonal to each other at the grid point O(x,y) which is the center of the unit constitutive region R(x,y).

[0153]

Mathematical Expression 6

[0154]

[0155]

Mathematical Expression 7

[0156] F(x,y)=A(x,y)×exp[jP(x,y)]…(7)

[0157] Under the aforementioned conditions 1 to 4, the phase modulation layer 12B is configured to satisfy the following conditions 5 and 6. Condition 5 is that within a unit constitutive region R(x,y), the centroid G is located away from the lattice point O(x,y). Condition 6 is that the length r(x,y) of the line segment from the lattice point O(x,y) to the corresponding centroid G is a common value set in each of the M1 × N1 unit constitutive regions R. Furthermore, the angle between the line segment connecting the lattice point O(x,y) and the corresponding centroid G and the s-axis... The following relationship must be satisfied.

[0158]

[0159] C: Proportionality constant, e.g., 180 / π

[0160] B: Any constant, such as 0

[0161] Figure 13 This demonstrates that the application is limited to a specific region of the phase modulation layer 12B. Figure 9 A top view of an example of a refractive index structure. Figure 13 In the example shown, a refractive index structure for emitting a beam pattern as a target is formed inside the inner region RIN of the square, for example... Figure 9The structure is as follows. On the other hand, in the outer region ROUT surrounding the inner region RIN, circular regions with opposite refractive indices are arranged at the lattice points of the tetragonal lattice, with their centroids aligned. The hypothetical lattice spacing of the tetragonal lattice is the same in both the inner region RIN and the outer region ROUT. With this structure, by distributing light also within the outer region ROUT, the generation of high-frequency noise, i.e., window function noise, caused by abrupt changes in light intensity at the periphery of the inner region RIN can be suppressed. Furthermore, since light leakage in the in-plane direction can be suppressed, the conversion efficiency from light generated in the active layer 11 to laser Lout2 can be improved.

[0162] As a method to derive the intensity and phase distributions from the complex amplitude distribution obtained by Fourier transform, the following methods exist. For example, the intensity distribution I(x,y) can be calculated using the abs function of the numerical analysis software "MATLAB" from MathWorks. The phase distribution P(x,y) can be calculated using the angle function of MATLAB.

[0163] The rotation angle is determined based on the Fourier transform of the light image. When considering the distribution of light and determining the configuration of multiple heterorefringent regions 12b, this section describes considerations for calculations using general Discrete Fourier Transform or Fast Fourier Transform. When the original light image before calculation (the original light image) is as follows... Figure 14 When segmented as in part (a), each segment in the output beam pattern calculated based on the complex amplitude distribution obtained from the inverse Fourier transform is as follows: Figure 14 As in part (b). Figure 14 (a) part and Figure 14 In part (b), the space is divided into four quadrants: A1, A2, A3, and A4. At this point, as... Figure 14 As shown in part (b), in the first quadrant of the output beam pattern, a pattern appears where the third quadrant of the original light image overlaps with a portion of the first quadrant of the original light image rotated 180 degrees. In the second quadrant of the output beam pattern, a pattern appears where the fourth quadrant of the original light image overlaps with a portion of the second quadrant of the original light image rotated 180 degrees. In the third quadrant of the output beam pattern, a pattern appears where the first quadrant of the original light image overlaps with a portion of the third quadrant of the original light image rotated 180 degrees. In the fourth quadrant of the output beam pattern, a pattern appears where the second quadrant of the original light image overlaps with a portion of the fourth quadrant of the original light image rotated 180 degrees. The 180-degree rotated pattern is formed by the -1st order light component.

[0164] Therefore, when using a light image that has a value only in the first quadrant as the light image before Fourier transform, i.e. the original light image, the first quadrant of the original light image appears in the third quadrant of the output beam pattern, and a pattern that rotates the first quadrant of the original light image by 180 degrees appears in the first quadrant of the output beam pattern.

[0165] Figure 15 Part (a) Figure 15 Part (d) shows an example of a beam pattern, or optical image, output from a GaAs-based S-iPM laser in the near-infrared band using the same principle as in this embodiment. The center of each figure is located in the Z direction from the center of the light-emitting surface of the S-iPM laser. As shown in these figures, the S-iPM laser outputs a first-order light comprising a first optical image portion E1, a -1st-order light comprising a second optical image portion E2, and a 0th-order light E3. The first-order light is output in a first direction inclined with respect to an axis extending in the Z direction from the center of the light-emitting surface. The -1st-order light is output in a second direction symmetrical about this axis and the first direction. The second optical image portion E2 is rotationally symmetrical about this axis and the first optical image portion E1. The 0th-order light E3 travels along this axis. The same situation applies to the surface-emitting laser element 1B of this embodiment.

[0166] In this embodiment, the light emitted from the active layer 11 is confined between the lower cladding layer 13 and the upper cladding layer 15 and is diffracted by the phase modulation layer 12B. This light forms a predetermined pattern corresponding to the internal lattice structure of the phase modulation layer 12B. In the phase modulation layer 12B, the centroids of a plurality of anisotropic refractive index regions 12b have rotation angles around lattice points O of an imaginary tetragonal lattice set for each anisotropic refractive index region 12b. This situation is similar to the case where the centroid G of multiple anisotropic refractive index regions 12b is located at a lattice point in a tetragonal lattice (see [reference]). Figure 2 In comparison, the intensity of 0th-order light decreases, while higher-order light, such as 1st-order and -1st-order light, appears. 0th-order light is emitted in the thickness direction of the phase modulation layer 12B, in other words, in the Z direction perpendicular to the light-emitting surface of the surface-emitting laser element 1B. Higher-order light is emitted in a direction inclined relative to this direction. Furthermore, the rotation angle of the centroid G of the different refractive index regions 12b around the lattice point... Individual settings are configured to correspond to the desired light image. Thus, the phase of the light is independently modulated according to each heterorefringence region 12b, and a light image of arbitrary shape in space can be output in the Z direction perpendicular to the light emission surface and in a direction inclined relative to the Z direction. This light image, i.e., laser Lout2, is output to the outside of the surface-emitting laser element 1B through the lower cladding 13 and the semiconductor substrate 8.

[0167] In the first embodiment where the surface-emitting laser element 1A is a PCSEL, the bandgap width of the upper cladding layer 15 is smaller than the bandgap width of the lower cladding layer 13. Conversely, in this embodiment where the surface-emitting laser element 1B is an iPM laser, the bandgap width of the upper cladding layer 15 is set to be larger than the bandgap width of the lower cladding layer 13. This is to ensure that the refractive index of the upper cladding layer 15 is smaller than that of the lower cladding layer 13, thus suppressing the competition between the modes induced by the upper cladding layer 15 and the fundamental modes centered on the active layer 11 and the phase modulation layer 12B. In an iPM laser, modes induced by the upper cladding layer 15 sometimes distribute in the phase modulation layer 12B and form a band structure that crosses back with the band structure of the fundamental modes. This causes noise in the output image. As described above, by making the bandgap width of the upper cladding layer 15 larger than that of the lower cladding layer 13, the competition of these modes can be suppressed, reducing the noise contained in the output image.

[0168] Specifically, when both the lower cladding layer 13 and the upper cladding layer 15 contain Al as a component, the Al component ratio of the upper cladding layer 15 is greater than that of the lower cladding layer 13. In some examples, the semiconductor substrate 8 is a GaAs substrate, and the active layer 11, phase modulation layer 12B, lower cladding layer 13, photoconductive layer 14, upper cladding layer 15, buffer layer 16A, and contact layer 17 are made of GaAs-based semiconductors. In one embodiment, the lower cladding layer 13 and photoconductive layer 14 are AlGaAs layers, the active layer 11 has a multi-quantum-well structure, the barrier layer of the multi-quantum-well structure is made of AlGaAs, the quantum well layers are made of InGaAs, and the number of well layers is, for example, three. The basic region 12a of the phase modulation layer 12B is an AlGaAs layer or a GaAs layer, the anisotropic region 12b is a hole, the upper cladding layer 15 and buffer layer 16A are AlGaAs layers, and the contact layer 17 is a GaAs layer. In this case, the thickness of the semiconductor substrate 8 is, for example, 150 μm. The thickness of the lower cladding layer 13 is, for example, 2000 nm. The thickness of the photoconductor layer 14 is, for example, 80 nm. The thickness of each of the well layer and barrier layer of the active layer 11 is, for example, 10 nm. The thickness of the phase modulation layer 12B is, for example, 300 nm. The thickness of the upper cladding layer 15 is, for example, 1500 nm. The thickness of the buffer layer 16A is, for example, 500 nm. The thickness of the contact layer 17 is, for example, 150 nm. The Al composition ratio of the lower cladding layer 13 is, for example, 43 atomic%. The Al composition ratio of the photoconductor layer 14 is, for example, 15 atomic%. The Al composition ratio of the barrier layer of the active layer 11 is, for example, 15 atomic%. The Al composition ratio of the upper cladding layer 15 is, for example, 70 atomic%. The Al composition ratio of the buffer layer 16A at the interface with the upper cladding layer 15 is, for example, 70 atomic%. The Al composition ratio of the buffer layer 16A at the interface with the contact layer 17 is, for example, 0 atomic. The Al composition of contact layer 17 is, for example, 0 atoms.

[0169] In the surface-emitting laser element 1B of this embodiment, similarly to the embodiment described above, the moderating layer 16A has a bandgap width between the bandgap width of the upper cladding layer 15 and the bandgap width of the contact layer 17. Therefore, the rate of change of the bandgap width between the upper cladding layer 15 and the contact layer 17 is moderated by the moderating layer 16A, and the potential barrier is reduced. Consequently, the resistance of the element is reduced, and sufficient laser oscillation can be obtained even with low driving voltages. As a result, power consumption can be reduced, the reliability of the element can be improved, and the lifespan of the element can be extended. Furthermore, in the surface-emitting laser element 1B, which is an iPM laser, a uniform current supply to the entire active layer 11 is required for high-quality optical imaging. When the anisotropic region 12b is made into a hole, the phase modulation layer 12B becomes relatively high in resistance; however, due to the low voltage caused by the moderating layer 16A, even with low driving currents, the current supply to the entire active layer 11 can be made nearly uniform. The surface-emitting laser element 1B of this embodiment can be manufactured through the same process as the surface-emitting laser element 1A of the first embodiment.

[0170] In this embodiment, the bandgap width of the mitigation layer 16A can also vary continuously from the bandgap width of the upper cladding layer 15 to approximately the bandgap width of the contact layer 17. In this case, since the potential barrier can be effectively reduced, the aforementioned effects achieved by the surface-emitting laser element 1B of this embodiment can be obtained more significantly.

[0171] In this embodiment, the upper cladding layer 15 and the buffer layer 16A may also contain Al as a component. Furthermore, the Al component ratio of the buffer layer 16A may be smaller than that of the upper cladding layer 15. In the case of iPM lasers, sometimes the thickness of the contact layer 17 is set to be smaller than that of the PCSEL in order to reduce the mode caused by the contact layer 17. In this case, oxygen atoms become more likely to pass through the contact layer 17, and without the buffer layer 16A, the Al in the upper cladding layer 15 becomes more easily oxidized. Alternatively, if growth between the upper cladding layer 15 and the contact layer 17 is interrupted, the Al in the upper cladding layer 15 becomes more easily oxidized. Therefore, reducing the effects of Al oxidation by using the buffer layer 16A is particularly useful in iPM lasers like those in this embodiment.

[0172] In this embodiment, the Al composition ratio of the mitigation layer 16A can also continuously decrease from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. In this case, since Al oxidation can be effectively reduced, the above-mentioned effects can be obtained more significantly.

[0173] As described above, the refractive index of the upper cladding 15 can also be less than that of the lower cladding 13. In this case, the coupling between the mode and the fundamental mode generated in the contact layer 17 can be suppressed. As a result, the quality of the output light can be improved, and the noise contained in the output light image can be further reduced. Furthermore, the smaller the refractive index of the upper cladding 15, the larger the bandgap width of the upper cladding 15 becomes, and the larger the bandgap difference between the upper cladding 15 and the contact layer 17 becomes. The surface-emitting laser element 1B of this embodiment, which has a buffer layer 16A between the upper cladding 15 and the contact layer 17, is particularly useful in such cases.

[0174] As described above, when both the lower cladding layer 13 and the upper cladding layer 15 contain Al as a component, the Al component ratio of the upper cladding layer 15 can be greater than that of the lower cladding layer 13. In this case, the refractive index of the upper cladding layer 15 becomes less than that of the lower cladding layer 13. Therefore, as described above, the modes generated in the upper cladding layer 15 can be suppressed, the quality of the output light can be improved, and the noise contained in the output light image can be further reduced. Furthermore, when the Al component ratio of the upper cladding layer 15 is large, the surface-emitting laser element 1B of this embodiment, which has a mitigation layer 16A, is particularly useful.

[0175] Thus, when the Al composition ratio of the upper cladding layer 15 is high, the difference in lattice constant between it and the contact layer 17 increases. Consequently, when the upper cladding layer 15 is in contact with the contact layer 17, the strain of the crystal structure of the contact layer 17 increases. As a result, crystal defects such as dislocations on the element surface increase, becoming a major cause of image quality degradation. In this embodiment, a mitigation layer 16A is provided. The mitigation layer 16A has an Al composition ratio between that of the upper cladding layer 15 and the contact layer 17. This mitigates the strain of the crystal structure of the contact layer 17, reduces crystal defects on the element surface, and suppresses image quality degradation.

[0176] In this embodiment, the thickness of the modulating layer 16A can also be less than the thickness of the upper cladding layer 15. In this case, since the upper cladding layer 15 becomes relatively thick, the modulating layer 16A, which has a higher refractive index than the upper cladding layer 15, separates from the phase modulation layer 12B and the active layer 11. Therefore, the coupling between the mode of the modulating layer 16A and the phase modulation layer 12B can be suppressed. As a result, the fundamental mode can be stabilized and the quality of the output light can be improved, further reducing the noise contained in the output light image.

[0177] In this embodiment, the modulating layer 16A may be located at a distance of 1 μm or more from both the active layer 11 and the phase modulation layer 12B, or at a distance of 1.5 μm or more. In this case, since the modulating layer 16A, with a refractive index greater than that of the upper cladding layer 15, is located away from the active layer 11 and the phase modulation layer 12B, the coupling between the mode of the modulating layer 16A and the phase modulation layer 12B can be suppressed. As a result, the fundamental mode can be stabilized, the quality of the output light can be improved, and the noise contained in the output light image can be further reduced.

[0178] Here, an embodiment of the surface-emitting laser element 1B of this embodiment is shown. Table 2 below shows an embodiment of the composition and thickness of each layer constituting the surface-emitting laser element 1B. In this example, the tempering layer 16A is 1.5 μm away from the phase modulation layer 12B. Figure 16 Part (a) is a graph showing the refractive index distribution G21, the basic mode distribution G22 generated with the active layer 11 and the phase modulation layer 12B as the center, and the mode distribution G23 generated with the tempering layer 16A and the contact layer 17 as the center of the surface-emitting laser element 1B having the structure of Table 2. Figure 16 Part (b) is shown in enlarged form. Figure 16 The vicinity of the active layer 11 and the phase modulation layer 12B in part (a). Figure 17 Part (a) is a graph showing the refractive index distribution G11 and fundamental mode distribution G12 of a surface-emitting laser element without the mitigation layer 16A for comparison. Figure 17 Part (b) is shown in enlarged form. Figure 17 The area near the active layer 11 and phase modulation layer 12B in part (a). In the figure, interval Tclad1 corresponds to the lower cladding 13, interval Tac corresponds to the active layer 11, interval Tpm corresponds to the phase modulation layer 12B, interval Tclad2 corresponds to the upper cladding 15, interval Trelax corresponds to the buffer layer 16A, interval Tcont corresponds to the contact layer 17, and interval Tair corresponds to air.

[0179] Table 2

[0180]

[0181] Reference Figure 16 In parts (a) and (b), the electric field of mode distribution G23 is approximately zero in phase modulation layer 12B, and does not contribute to the diffraction of phase modulation layer 12B. Furthermore, the coupling coefficient between the fundamental mode distribution G22 and mode distribution G23 is approximately zero. Therefore, by having a mitigation layer 16A with a refractive index greater than that of the upper cladding layer 15 sufficiently separated from the active layer 11 and phase modulation layer 12B, the coupling between the modes generated in the mitigation layer 16A and contact layer 17 and the fundamental mode generated with the active layer 11 and phase modulation layer 12B as the center can be effectively suppressed.

[0182] [Third Implementation Method]

[0183] The S-iPM laser is not limited to the structure of the second embodiment described above. For example, even the structure of the phase modulation layer in this embodiment can be appropriately implemented as an S-iPM laser. Figure 18 This is a top view of the phase modulation layer 12C, which serves as a resonant mode forming layer, provided in the optical device of the third embodiment. Figure 19 This is a diagram showing the positional relationship of the heterorefringent region 12b in the phase modulation layer 12C.

[0184] like Figure 18 and Figure 19 As shown, in the phase modulation layer 12C, the centroids G of multiple heterorefringent regions 12b are respectively arranged on multiple straight lines D. Each straight line D is a straight line that passes through the corresponding lattice point O of each unit constituting region R and is inclined relative to each side of the tetragonal lattice. In other words, the straight line D is a straight line inclined relative to both the X-axis and the Y-axis. The inclination angle of the straight line D relative to one side along the X-axis of the tetragonal lattice is θ. The inclination angle θ is equal (uniform) within the phase modulation layer 12C. The inclination angle θ satisfies 0° < θ < 90°, and in one example θ = 45°. Alternatively, the inclination angle θ satisfies 180° < θ < 270°, and in one example θ = 225°. When the inclination angle θ satisfies 0° < θ < 90° or 180° < θ < 270°, the straight line D extends from the first quadrant to the third quadrant of the coordinate plane defined by the X-axis and Y-axis. Alternatively, the inclination angle θ satisfies 90° < θ < 180°, and in one example θ = 135°. Alternatively, the tilt angle θ satisfies 270° < θ < 360°, in one example θ = 315°. When the tilt angle θ satisfies 90° < θ < 180° or 270° < θ < 360°, the line D extends from the second quadrant to the fourth quadrant of the coordinate plane defined by the X and Y axes. Thus, the tilt angle θ is an angle other than 0°, 90°, 180°, and 270°. By tilting the line D relative to the tetragonal lattice, it is possible to make the light output beam contribute to both the light wave traveling along the X-axis and the light wave traveling along the Y-axis. Here, the distance between lattice point O and the centroid G is denoted as r(x,y). x represents the position of the x-th lattice point on the X-axis, and y represents the position of the y-th lattice point on the Y-axis. When the distance r(x,y) is positive, the centroid G is located in the first or second quadrant. When the distance r(x,y) is negative, the centroid G is located in the third or fourth quadrant. When the distance r(x,y) is 0, the centroid G coincides with the lattice point O.

[0185] The distance r(x,y) between the centroid G of each heterorefringent region 12b and the corresponding grid point O of each unit constituting region R corresponds to the desired optical image and is set individually for each heterorefringent region 12b. The distance r(x,y) between the centroid G and grid point O of at least two heterorefringent region 12b is different from each other. The distribution of distance r(x,y) has specific values ​​at each position determined by the values ​​of x and y, but is not limited to being represented by a specific function. The distribution of distance r(x,y) is determined by extracting the phase distribution from the complex amplitude distribution obtained by performing an inverse Fourier transform on the desired optical image. That is, when the phase P(x,y) at a certain coordinate (x,y) is P0, the distance r(x,y) is set to 0. When the phase P(x,y) is π+P0, the distance r(x,y) is set to the maximum value R0. When the phase P(x,y) is -π+P0, the distance r(x,y) is set to the minimum value -R0. Furthermore, for the phase P(x,y) between P0 and π+P0, or between -π+P0 and P0, let r(x,y) = {P (x,y) The distance r(x,y) is set in the manner of -P0}×R0 / π. Here, the initial phase P0 can be set arbitrarily. If the lattice spacing of the tetragonal lattice is set to a, then the maximum value R0 of r(x,y) is, for example, within the range of the following equation (8).

[0186]

Mathematical Expression 8

[0187]

[0188] When the complex amplitude distribution is determined from the desired light image, the reproducibility of the beam pattern is improved by applying an iterative algorithm, such as the GS method, which is generally used for calculations to generate holograms.

[0189] In this embodiment, the desired optical image can be obtained by determining the distribution of the distances r(x,y) of the heterorefringent regions 12b of the phase modulation layer 12C in the following order. Under the first to fourth prerequisites described in the second embodiment, the phase modulation layer 12C is configured to satisfy the following condition: that is, the heterorefringent regions 12b are arranged within the unit constitutive region R(x,y) in such a way that the distances r(x,y) satisfy the following relationship.

[0190] r(x,y)=C×(P(x,y)-P0)

[0191] C: Proportioning constant, for example, R0 / π

[0192] P0: Any constant, for example, 0

[0193] To obtain the desired optical image, an inverse discrete Fourier transform can be performed on the image, supplying the distribution of distances r(x,y) corresponding to the phase P(x,y) of the complex amplitude to multiple heterorefringent regions 12b. The phase P(x,y) and the distance r(x,y) can be proportional to each other.

[0194] In this embodiment, it can also be applied only in a specific region of the phase modulation layer 12C. Figure 18 The refractive index structure. For example, such as Figure 13 The example shown can have a refractive index structure formed inside the inner region RIN of the square for the emitted beam pattern as a target, for example... Figure 18 The structure is as follows. In this case, in the outer region ROUT surrounding the inner region RIN, circular regions with opposite refractive indices are arranged at the lattice points of the tetragonal lattice with the same centroid. The lattice spacing of the hypothetical tetragonal lattice is the same in both the inner region RIN and the outer region ROUT. With this structure, by distributing light also within the outer region ROUT, high-frequency noise, i.e., window function noise, caused by abrupt changes in light intensity at the periphery of the inner region RIN can be suppressed. Furthermore, since light leakage in the in-plane direction can be suppressed, the conversion efficiency from light generated in the active layer 11 to laser Lout2 can be improved.

[0195] As a method for obtaining the intensity and phase distributions based on the complex amplitude distribution obtained from the inverse Fourier transform, there is the following method. For example, the intensity distribution I(x,y) can be calculated using the abs function of the numerical analysis software "MATLAB" from MathWorks. The phase distribution P(x,y) can be calculated using the angle function of MATLAB. When the phase distribution P(x,y) is obtained from the inverse Fourier transform result of the light image and the distance r(x,y) of each heterorefringent region 12b is determined, the points to note when using the general discrete Fourier transform or fast Fourier transform for calculation are the same as those in the second embodiment described above.

[0196] In this embodiment, the light emitted from the active layer 11 is confined between the lower cladding layer 13 and the upper cladding layer 15 and is diffracted by the phase modulation layer 12C. This light forms a predetermined pattern corresponding to the lattice structure inside the phase modulation layer 12C. In the phase modulation layer 12C, the centroids G of multiple anisotropic regions 12b are respectively disposed on multiple straight lines D passing through lattice points O of an imaginary tetragonal lattice and tilted relative to the tetragonal lattice. Furthermore, the distance r(x,y) between the centroid G of each anisotropic region 12b and the corresponding lattice point O is individually set corresponding to the light image. In this case, the case where the centroids G of the multiple anisotropic regions 12b are located at lattice points O of the tetragonal lattice (see...) Figure 2In comparison, the intensity of 0th-order light decreases, and higher-order light, such as 1st-order and -1st-order light, appears. 0th-order light is emitted in the thickness direction of the phase modulation layer 12C, in other words, in the Z direction perpendicular to the light-emitting surface of the surface-emitting laser element. Higher-order light is emitted in a direction inclined relative to this direction. Furthermore, the distance r(x,y) between the centroid G of each heterorefringent region 12b and the corresponding lattice point O is individually set corresponding to the desired light image. Thus, the phase of the light is independently modulated according to each heterorefringent region 12b, enabling the output of a light image of arbitrary shape in space in both the Z direction perpendicular to the light-emitting surface and in a direction inclined relative to the Z direction. This light image, i.e., laser Lout2, is output to the outside of the surface-emitting laser element through the lower cladding layer 13 and the semiconductor substrate 8.

[0197] In the surface-emitting laser element of this embodiment, similar to the embodiments described above, the moderating layer 16A has a bandgap width between the bandgap width of the upper cladding layer 15 and the bandgap width of the contact layer 17. Therefore, the rate of change of the bandgap width between the upper cladding layer 15 and the contact layer 17 is moderated by the moderating layer 16A, reducing the potential barrier. Consequently, the element's resistance is reduced, and sufficient laser oscillation can be achieved even with low driving voltages. As a result, power consumption is reduced, element reliability is improved, and element lifespan is extended. Furthermore, the structure of the surface-emitting laser element of this embodiment is the same as that of the surface-emitting laser element 1B of the second embodiment, except for the phase modulation layer 12C; therefore, the surface-emitting laser element of this embodiment can achieve the same effects as the surface-emitting laser element 1B of the second embodiment. The surface-emitting laser element of this embodiment can be manufactured using the same process as the surface-emitting laser element 1A of the first embodiment.

[0198] [First Variation]

[0199] Figure 20 This is a schematic diagram showing the cross-sectional structure of the surface-emitting laser element 1C of the first modified example. The surface-emitting laser element 1C differs from the second or third embodiment in that, except for the portion of the contact layer 17 where the second electrode 22 is disposed, it is otherwise identical to them. In this modified example, when viewed in the thickness direction, the area of ​​the contact layer 17 is smaller than the area of ​​the buffer layer 16A. The buffer layer 16A is exposed around the contact layer 17. With this structure, the path of the current supplied from the second electrode 22 can be defined, efficiently supplying current to the active layer 11.

[0200] Thus, in conventional surface-emitting laser elements where the upper cladding 15 is in contact with the contact layer 17 (excluding the portion where the second electrode 22 is located), the upper cladding 15 is exposed, without the buffer layer 16A, i.e., without the upper cladding 15 in contact with the contact layer 17. Therefore, the Al in the upper cladding 15 becomes more susceptible to oxidation. In the surface-emitting laser element 1C of this modified example, the Al content is less than that of the exposed buffer layer 16A of the upper cladding 15. This reduces the amount of Al oxide on the exposed surface, mitigating the effects of Al oxidation.

[0201] [Second Variation]

[0202] Figure 21 This diagram schematically illustrates the cross-sectional structure of the surface-emitting laser element 1D of the second modified example. The surface-emitting laser element 1D differs from the first embodiment in that it includes a buffer layer 16B instead of a buffer layer 16A, but is otherwise identical to the first embodiment. The buffer layer 16B is epitaxially grown on the upper cladding layer 15 and is in contact with the upper cladding layer 15. The buffer layer 16B is provided to mitigate the potential barrier caused by the bandgap difference between the upper cladding layer 15 and the contact layer 17. The buffer layer 16B is, for example, composed of the same constituent elements as the upper cladding layer 15. The buffer layer 16B has a bandgap width between the bandgap width of the upper cladding layer 15 and the bandgap width of the contact layer 17. Figure 21 Figure G3 shows the distribution of the bandgap width of the buffer layer 16B in the thickness direction. In Figure G3, the horizontal axis represents the bandgap width, and the vertical axis represents the position in the thickness direction. As shown in Figure G3, in this modified example, the bandgap width of the buffer layer 16B is constant in the thickness direction from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. The difference between the bandgap width at the interface on the upper cladding layer 15 side of the buffer layer 16B and the bandgap width of the upper cladding layer 15 can be equal to the difference between the bandgap width at the interface on the contact layer 17 side of the buffer layer 16B and the bandgap width of the contact layer 17.

[0203] When the upper cladding 15 contains Al as a component, the buffer layer 16B also functions as a layer to inhibit the oxidation of Al in the upper cladding 15. In this case, the buffer layer 16B also contains Al. The buffer layer 16B has an Al component ratio that is between the Al component ratio of the upper cladding 15 and the Al component ratio of the contact layer 17. Figure 21 Figure G4 shows the distribution of the Al composition ratio of the buffer layer 16B in the thickness direction. In Figure G4, the horizontal axis represents the Al composition ratio, and the vertical axis represents the position in the thickness direction. As shown in Figure G4, in this modified example, the Al composition ratio of the buffer layer 16B is constant in the thickness direction from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side.

[0204] The thickness of the buffer layer 16B is less than the thickness of the upper cladding layer 15. The thickness of the buffer layer 16B is within the same range as the thickness of the buffer layer 16A in the first embodiment. The buffer layer 16B is at least 1 μm away from both the photonic crystal layer 12A and the active layer 11, more preferably at least 1.5 μm away from both the photonic crystal layer 12A and the active layer 11. That is, when only the upper cladding layer 15 is provided between the buffer layer 16B and both the photonic crystal layer 12A and the active layer 11, the thickness of the upper cladding layer 15 is at least 1 μm, more preferably at least 1.5 μm. The sum of the thickness of the upper cladding layer 15 and the thickness of the buffer layer 16B may also be equal to the thickness of the lower cladding layer 13.

[0205] As in this modified example, the bandgap width of the mitigation layer 16B can also be constant in the thickness direction. Even in this case, since the mitigation layer 16B has a bandgap width that is between the bandgap width of the upper cladding layer 15 and the bandgap width of the contact layer 17, the rate of change of the bandgap width between the upper cladding layer 15 and the contact layer 17 is mitigated compared to the case without the mitigation layer 16B, thus lowering the potential barrier. Therefore, the resistance of the device is reduced, and sufficient laser oscillation can be obtained even with low driving voltages. As a result, power consumption can be reduced and the reliability of the device can be improved.

[0206] As in this modified example, the Al composition ratio of the mitigation layer 16B can also be constant in the thickness direction. In this case, by having a mitigation layer 16B with an Al composition ratio smaller than that of the upper cladding layer 15 between the contact layer 17 and the upper cladding layer 15, the effects caused by Al oxidation can also be reduced. That is, according to this modified example, the increase in resistance caused by Al oxidation can be suppressed, and sufficient laser oscillation can be obtained with a lower driving voltage. As a result, power consumption can be further reduced, and the reliability of the device can be further improved.

[0207] In addition to the first embodiment, the aforementioned embodiments and modifications can also replace the buffer layer 16A and include the buffer layer 16B of this modification. Thus, the same effect as described above can be achieved.

[0208] An embodiment of the surface-emitting laser element 1D of this modified example is shown. Table 3 below shows the composition and thickness of each layer constituting the surface-emitting laser element 1D in an embodiment. In this example, the buffer layer 16B is 1.5 μm away from the photonic crystal layer 12A. Figure 22 Part (a) is a graph showing the refractive index distribution G31, the basic mode distribution G32 generated with the active layer 11 and the photonic crystal layer 12A as the center, and the mode distribution G33 generated with the tempering layer 16B and the contact layer 17 as the center of the surface-emitting laser element 1D having the structure of Table 3. Figure 22 Part (b) is shown in enlarged form. Figure 22The area near the active layer 11 and photonic crystal layer 12A in part (a). In the figure, interval Tclad1 corresponds to the lower cladding layer 13, interval Tac corresponds to the active layer 11, interval Tpc corresponds to the photonic crystal layer 12A, interval Tclad2 corresponds to the upper cladding layer 15, interval Trelax corresponds to the buffer layer 16B, interval Tcont corresponds to the contact layer 17, and interval Tair corresponds to air.

[0209] Table 3

[0210]

[0211] refer to Figure 22 In parts (a) and (b), the electric field of mode distribution G33 is approximately zero in photonic crystal layer 12A and does not contribute to the diffraction of photonic crystal layer 12A. Furthermore, the coupling coefficient between the fundamental mode distribution G32 and mode distribution G33 is approximately zero. Therefore, by having a mitigation layer 16B with a refractive index higher than that of the upper cladding layer 15, sufficiently separating it from the active layer 11 and photonic crystal layer 12A, the coupling between the modes generated in the mitigation layer 16B and the contact layer 17 and the fundamental mode generated with the active layer 11 and photonic crystal layer 12A as the center can be effectively suppressed.

[0212] Table 4 below shows an embodiment of the composition and thickness of each layer constituting the surface-emitting laser element 1B in which the surface-emitting laser element 1B of the second embodiment replaces the buffer layer 16A and has the buffer layer 16B of this modified example. In this example, the buffer layer 16B is 1.5 μm away from the phase modulation layer 12B. Figure 23 Part (a) is a graph showing the refractive index distribution G41, the basic mode distribution G42 generated with the active layer 11 and the phase modulation layer 12B as the center, and the mode distribution G43 generated with the tempering layer 16B and the contact layer 17 as the center of the surface-emitting laser element with the structure of Table 4. Figure 23 Part (b) is shown in enlarged form. Figure 23 The area near the active layer 11 and the phase modulation layer 12B in part (a). In the figure, interval Tclad1 corresponds to the lower cladding 13, interval Tac corresponds to the active layer 11, interval Tpm corresponds to the phase modulation layer 12B, interval Tclad2 corresponds to the upper cladding 15, interval Trelax corresponds to the buffer layer 16B, interval Tcont corresponds to the contact layer 17, and interval Tair corresponds to air.

[0213] Table 4

[0214]

[0215] Reference Figure 23In parts (a) and (b), the electric field of mode distribution G43 is approximately zero in phase modulation layer 12B, and does not contribute to diffraction of phase modulation layer 12B. Furthermore, the coupling coefficient between fundamental mode distribution G42 and mode distribution G43 is approximately zero. Therefore, by having a tempering layer 16B with a refractive index greater than that of the upper cladding layer 15, sufficiently separating it from the active layer 11 and phase modulation layer 12B, coupling between the modes generated in tempering layer 16B and contact layer 17 and the fundamental modes generated with the active layer 11 and phase modulation layer 12B as centers can be effectively suppressed.

[0216] [3rd Variation]

[0217] Figure 24 This diagram schematically illustrates the cross-sectional structure of the surface-emitting laser element 1E of the third modified example. The surface-emitting laser element 1E differs from the first embodiment in that it has a buffer layer 16C instead of a buffer layer 16A; otherwise, it is consistent with the first embodiment. The buffer layer 16C differs from the buffer layer 16B of the second modified example in the distribution of the bandgap width in the thickness direction and the distribution of the Al composition; otherwise, it is consistent with the buffer layer 16B of the second modified example.

[0218] The buffer layer 16C has a bandgap width that is between the bandgap width of the upper cladding layer 15 and the bandgap width of the contact layer 17. The bandgap width of the buffer layer 16C monotonically decreases from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. Figure 24 Figure G5 shows the distribution of the bandgap width of the buffer layer 16C in the thickness direction. In Figure G5, the horizontal axis represents the bandgap width, and the vertical axis represents the position in the thickness direction. As shown in Figure G5, in this modified example, the bandgap width of the buffer layer 16C changes in stages from the bandgap width of the upper cladding layer 15 to the bandgap width of the contact layer 17. In the example shown, since the bandgap width of the contact layer 17 is smaller than the bandgap width of the upper cladding layer 15, the bandgap width of the buffer layer 16C decreases in stages from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. Figure 24 In this design, the bandgap width distribution of the moderating layer 16C is represented by the depth of color, with darker areas having larger bandgap widths. The number of changes in the bandgap width during these phased changes can be set to any value greater than 1, such as 2 or 3 times. However, the number of changes does not include changes at the interface with the upper cladding layer 15 or the interface with the contact layer 17. Between one change and another, the bandgap width can be constant. Alternatively, between one change and another, the bandgap width can also change continuously in a manner that gradually decreases towards the interface on the contact layer 17 side.

[0219] When the upper cladding layer 15 and the buffer layer 16C contain Al as a component, the buffer layer 16C has an Al component ratio that is between that of the upper cladding layer 15 and the contact layer 17. The Al component ratio of the buffer layer 16C monotonically decreases from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. Figure 24 Figure G6 shows the distribution of the Al composition ratio of the buffer layer 16C in the thickness direction. In Figure G6, the horizontal axis represents the Al composition ratio, and the vertical axis represents the position in the thickness direction. As shown in Figure G6, in this modified example, the Al composition ratio of the buffer layer 16C decreases in stages from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. The number of changes in the staged changes of the Al composition ratio can be set to any value of more than 1, such as 2 or 3 times. However, the number of changes does not include the changes at the interface with the upper cladding layer 15 and the interface with the contact layer 17. Between one change and another, the Al composition ratio can be constant. Alternatively, between one change and another, the Al composition ratio can also change continuously in a manner that gradually decreases towards the interface on the contact layer 17 side.

[0220] As in this modified example, the bandgap width of the mitigation layer 16C can also vary in stages, approaching the bandgap width of the upper cladding layer 15 and the contact layer 17. In this case, since the mitigation layer 16C has a bandgap width between that of the upper cladding layer 15 and the contact layer 17, the rate of change of the bandgap width between the upper cladding layer 15 and the contact layer 17 is mitigated compared to the case without the mitigation layer 16C, thus lowering the potential barrier. Therefore, the resistance of the device is reduced, and sufficient laser oscillation can be obtained even with low driving voltages. As a result, power consumption can be reduced, and the reliability of the device can be improved.

[0221] As in this modified example, the Al composition ratio of the mitigation layer 16C can also gradually decrease from the interface on the upper cladding layer 15 side to the interface on the contact layer 17 side. In this case, by having a mitigation layer 16C with an Al composition ratio lower than that of the upper cladding layer 15 between the contact layer 17 and the upper cladding layer 15, the effects caused by Al oxidation can also be reduced. That is, according to this modified example, the increase in resistance caused by Al oxidation can be suppressed, and sufficient laser oscillation can be obtained with a lower driving voltage. As a result, power consumption can be further reduced, and the reliability of the device can be further improved.

[0222] In addition to the first embodiment and the second modification, the aforementioned embodiments and modifications may also replace the buffer layer 16A and include the buffer layer 16C of this modification. Thus, the same effect as described above can be achieved.

[0223] [4th Variation]

[0224] A modified example of the phase modulation layer 12B according to the second embodiment will be described in detail. In this modified example, the lattice spacing a of the hypothetical tetragonal lattice and the emission wavelength λ of the active layer 11 satisfy the condition for M-point oscillation. Furthermore, considering the reciprocal lattice space, or in other words, considering the wavenumber space, the phase modulation layer 12B has in-plane wavenumber vectors representing standing waves in four directions. The in-plane wavenumber vectors in the four directions are affected by the rotation angle. The distribution of phase modulation, and each includes wavenumber spreads corresponding to the angular spread of the light forming the light image. At least one of these in-plane wavenumber vectors has a magnitude less than 2π / λ. In the following description, the boundary defining the range of in-plane wavenumber vectors with magnitudes less than 2π / λ is referred to as a ray. These points are described in detail below.

[0225] First, for comparison, a photonic crystal laser (PCSEL) oscillating at the Γ point in reciprocal lattice space will be described. The PCSEL has an active layer and a photonic crystal layer. In the photonic crystal layer, multiple heterorefringent regions are arranged periodically in a two-dimensional configuration. In a plane perpendicular to the thickness direction of the photonic crystal layer, the PCSEL forms a standing wave with an oscillation wavelength corresponding to the arrangement period of the heterorefringent regions. Furthermore, the PCSEL outputs laser light along the normal direction of the main surface of the semiconductor substrate. For Γ-point oscillation to occur, the lattice spacing *a* of the hypothetical tetragonal lattice, the emission wavelength *λ* of the active layer 11, and the equivalent refractive index *n* of the mode must satisfy the condition: *λ* = *na*.

[0226] Figure 25 It is a top view showing the reciprocal lattice space of the photonic crystal layer of the PCSEL oscillating at the Γ point; in other words, it is a top view showing the wavenumber space. Figure 25 This diagram illustrates the case where multiple regions of different refractive indices lie on lattice points of a tetragonal crystal. Multiple points P in the diagram represent reciprocal lattice points. Multiple arrows B1 represent fundamental reciprocal lattice vectors. Each of multiple arrows B2 represents a reciprocal lattice vector twice the fundamental reciprocal lattice vector B1. Arrows K1, K2, K3, and K4 represent four in-plane wavenumber vectors. These four in-plane wavenumber vectors K1, K2, K3, and K4 are coupled together through diffraction at 90° and 180°, forming a standing wave state. Here, mutually orthogonal Γ-X and Γ-Y axes are defined in the reciprocal lattice space. The Γ-X axis is parallel to one side of the tetragonal lattice, and the Γ-Y ​​axis is parallel to the other side of the square lattice. An in-plane wavenumber vector is the vector projected onto the Γ-X·Γ-Y plane. That is, in-plane wavenumber vector K1 points towards the positive direction of the Γ-X axis. In-plane wavenumber vector K2 points towards the positive direction of the Γ-Y ​​axis. The in-plane wavenumber vector K3 points towards the negative Γ-X axis. The in-plane wavenumber vector K4 points towards the negative Γ-Y ​​axis. From Figure 25It can be seen that in a PCSEL oscillating at point Γ, the magnitudes of the in-plane wavenumber vectors K1 to K4, i.e. the magnitudes of the standing waves in the in-plane direction, are equal to the magnitude of the basic reciprocal lattice vector B1. The magnitude k of the in-plane wavenumber vectors K1 to K4 is given by the following equation (9).

[0227]

Mathematical Expression 9

[0228]

[0229] Figure 26 It is a three-dimensional observation Figure 25 The diagram shows a three-dimensional representation of the inverted lattice space. Figure 26 The diagram shows the Z-axis, which is orthogonal to the directions of the Γ-X and Γ-Y axes. This Z-axis is... Figure 1 The Z-axis shown is the same. For example... Figure 26 As shown in the figure, in a PCSEL oscillating at point Γ, as indicated by arrow K5, diffraction reduces the wavenumber in the in-plane direction to 0, resulting in diffraction in the direction perpendicular to the plane, i.e., the Z-axis direction. Therefore, the laser output is essentially along the Z-axis direction.

[0230] Next, the PCSEL oscillating at point M will be explained. For oscillation at point M to occur, the hypothetical tetragonal lattice spacing *a*, the emission wavelength *λ* of the active layer 11, and the equivalent refractive index *n* of the mode must satisfy the following conditions: That's all. Figure 27 This is a top view showing the reciprocal lattice space of the photonic crystal layer of the PCSEL oscillating at point M; in other words, it is a top view showing the wavenumber space. Figure 27 This also indicates the case where multiple regions with different refractive indices are located on lattice points of a tetragonal lattice. Figure 27 Multiple points P in the diagram represent reciprocal grid points. Figure 27 The multiple arrows B1 in the image indicate that... Figure 25 The same basic reciprocal lattice vectors. Arrows K6, K7, K8, and K9 represent four in-plane wavenumber vectors. Here, mutually orthogonal Γ-M1 and Γ-M2 axes are defined in the reciprocal lattice space. The Γ-M1 axis is parallel to one diagonal direction of the tetragonal lattice, and the Γ-M2 axis is parallel to the other diagonal direction of the tetragonal lattice. An in-plane wavenumber vector is the vector projected onto the Γ-M1·Γ-M2 plane. That is, the in-plane wavenumber vector K6 points towards the positive direction of the Γ-M1 axis. The in-plane wavenumber vector K7 points towards the positive direction of the Γ-M2 axis. The in-plane wavenumber vector K8 points towards the negative direction of the Γ-1 axis. The in-plane wavenumber vector K9 points towards the negative direction of the Γ-M2 axis. Figure 27 It can be seen that in the PCSEL oscillating at point M, the magnitudes of the in-plane wavenumber vectors K6 to K9, i.e. the magnitudes of the standing waves in the in-plane direction, are smaller than the magnitude of the basic reciprocal lattice vector B1. The magnitudes k of the in-plane wavenumber vectors K6 to K9 are given by the following equation (10).

[0231]

Mathematical Formula 10

[0232]

[0233] Diffraction occurs in the plane, with wavenumber vectors K6 to K9 along the direction of the vector sum of the reciprocal lattice vectors. The magnitude of the reciprocal lattice vector is 2mπ / a, where m is an integer. However, in a PCSEL oscillating at point M, due to diffraction, the wavenumber in the in-plane direction cannot be zero, and diffraction in the direction perpendicular to the plane, i.e., the Z-axis direction, is not generated. Therefore, since no laser is output in the direction perpendicular to the plane, point M oscillation is usually not used in PCSELs.

[0234] Next, the S-iPM laser oscillating at the Γ point will be explained. The conditions for Γ-point oscillation are the same as those for the PCSEL described above. Figure 28 This is a top view showing the reciprocal lattice space of the phase modulation layer of an S-iPM laser oscillating at point Γ. The fundamental reciprocal lattice vector B1 is as follows: Figure 25 The basic reciprocal lattice vector of the PCSEL oscillating at point Γ is the same, but the in-plane wavenumber vectors K1 to K4 are affected by the rotation angle. The phase modulation of the distribution, and each has a wavenumber spread SP corresponding to the spread angle of the optical image. The wavenumber spread SP can be represented as a rectangular region. The rectangular region is centered on the leading edges of the in-plane wavenumber vectors K1 to K4 in the PCSEL oscillating at point Γ. The lengths of the sides of the rectangular region in the x-axis direction and the y-axis direction are 2Δkx, respectively. max and 2Δky max Through this wavenumber extension SP, the in-plane wavenumber vectors K1 to K4 are each extended into a rectangular range of (Kix + Δkx, Kiy + Δky). Here, i = 1 to 4, Kix is ​​the x-direction component of vector Ki, and Kiy is the y-direction component of vector Ki. Δkx is -Δkx max ≤Δkx≤Δkx max The value within the range, Δky is -Δky max ≤Δky≤Δky max The value within the range of Δkx. max and Δky max The size of Δkx is determined correspondingly to the expansion angle of the light image. In other words, Δkx max and Δky max Its size depends on the light image to be represented.

[0235] Figure 29 It is a three-dimensional observation Figure 28 The diagram shows a three-dimensional representation of the inverted lattice space. Figure 29 The diagram shows the Z-axis, which is orthogonal to the directions along the Γ-X axis and the Γ-Y ​​axis, respectively. This Z-axis is... Figure 8 The Z-axis shown is the same. For example... Figure 29 As shown, in the case of an S-iPM laser oscillating at the Γ point, the output has a two-dimensional extended light image (beam pattern) LM that includes not only the 0th order light in the direction perpendicular to the plane, i.e., the Z-axis direction, but also the 1st order light and -1st order light in the direction inclined relative to the Z-axis direction.

[0236] Next, the S-iPM laser oscillating at point M will be explained. The conditions for oscillation at point M are the same as those for the PCSEL described above. Figure 30 This is a top view showing the reciprocal lattice space of the phase modulation layer of an S-iPM laser oscillating at point M. The fundamental reciprocal lattice vector B1 and... Figure 27 The basic reciprocal lattice vector of the PCSEL oscillating at point M is the same, but the in-plane wavenumber vectors K6 to K9 have different values ​​depending on the rotation angle. The wavenumber spread SP of the distribution is the same as that of the Γ-point oscillation described above. In the S-iPM laser, in the case of M-point oscillation, the magnitudes of the in-plane wavenumber vectors K6 to K9, i.e., the magnitudes of the standing waves in the in-plane direction, are also smaller than the magnitude of the basic reciprocal lattice vector B1. Furthermore, due to diffraction, the wavenumber in the in-plane direction cannot be zero, and diffraction in the direction perpendicular to the plane, i.e., the Z-axis direction, is not produced. Therefore, neither the 0th-order light in the direction perpendicular to the plane, i.e., the Z-axis direction, nor both the 1st-order light and the -1st-order light in the direction inclined relative to the Z-axis direction are output.

[0237] In this modified example, the phase modulation layer 12B is subjected to the method described below in the S-iPM laser oscillating at point M. As a result, 0th-order light is not output, but a portion of 1st-order and -1st-order light is output. Specifically, as... Figure 31 As shown, a diffraction vector V with a specific magnitude and direction is added to the in-plane wavenumber vectors K6 to K9. This ensures that at least one of the in-plane wavenumber vectors K6 to K9 (K8 in the figure) has a magnitude less than 2π / λ. In other words, at least one of the in-plane wavenumber vectors K6 to K9 (K8) after adding the diffraction vector V is contained within a circular region of radius 2π / λ, i.e., within the ray LL. Figure 31 The in-plane wavenumber vectors K6 to K9, represented by dashed lines, represent the wavenumber vectors before the addition of the diffraction vector V. The in-plane wavenumber vectors K6 to K9, represented by solid lines, represent the wavenumber vectors after the addition of the diffraction vector V. Since the ray LL corresponds to the condition of total internal reflection, the wavenumber vector contained within the ray LL has a component perpendicular to the plane, i.e., along the Z-axis. In one example, the direction of the diffraction vector V is along the Γ-M1 axis or the Γ-M2 axis, and the magnitude of the diffraction vector V is... arrive Within the range. In one embodiment, the magnitude of the diffraction vector V is...

[0238] The study investigates the magnitude and direction of the diffraction vector V, which contains at least one of the in-plane wavenumber vectors K6 to K9 within the ray LL. The following equations (11) to (14) represent the in-plane wavenumber vectors K6 to K9 before adding the diffraction vector V.

[0239]

Mathematical Expression 11

[0240]

[0241]

Mathematical Expression 12

[0242]

[0243]

Mathematical Expression 13

[0244]

[0245]

Mathematical Expression 14

[0246]

[0247] The in-plane wavenumber vector extensions Δkx and Δky satisfy the following equations (15) and (16), respectively. The maximum value of the in-plane wavenumber vector extension in the x-axis direction is Δkx. max The maximum value of the expansion in the y-axis direction Δky max It is defined by the angular extension of the light that forms the light image in the design.

[0248]

Mathematical Expression 15

[0249] -Δkx max ≤Δkx≤Δkx max …(15)

[0250]

Mathematical Expression 16

[0251] -Δky max ≤Δky≤Δky max …(16)

[0252] The diffraction vector V is expressed as the following equation (17). At this time, the in-plane wavenumber vectors K6 to K9 after adding the diffraction vector V are expressed as the following equations (18) to (21).

[0253]

Mathematical Expression 17

[0254] V=(Vx,Vy)…(17)

[0255]

Mathematical Expression 18

[0256]

[0257]

Mathematical Expression 19

[0258]

[0259]

Mathematical Expression 20

[0260]

[0261]

Mathematical Expression 21

[0262]

[0263] If any one of the in-plane wavenumber vectors K6 to K9 in formulas (18) to (21) is contained within the ray LL, then the following relationship in formula (22) holds.

[0264]

Mathematical Expression 22

[0265]

[0266] That is, by adding the diffraction vector V that satisfies the above equation (22), any one of the in-plane wavenumber vectors K6 to K9 is contained in the light LL, and a portion of the first-order light and the -1st-order light is output.

[0267] The size of the ray LL, i.e. the radius, is set to 2π / λ for the following reasons. Figure 32 This is a diagram used to schematically illustrate the peripheral structure of a light ray LL. The diagram shows the boundary between the device and air as viewed from a direction perpendicular to the Z-axis. The magnitude of the wavenumber vector of light in a vacuum is 2π / λ, however, as... Figure 32 As shown, when light propagates in the device medium, the magnitude of the wavenumber vector Ka in the medium with refractive index n is 2πn / λ. Considering the wavenumber conservation law, for light to propagate at the boundary between the device and air, the wavenumber component parallel to the boundary needs to be continuous. Figure 32 In the case where the wavenumber vector Ka makes an angle β with the Z-axis, the length of the wavenumber vector projected onto the plane, i.e., the in-plane wavenumber vector Kb, is (2πn / λ)sinβ. Generally, since the refractive index n of the medium is greater than 1, if the in-plane wavenumber vector Kb within the medium is changed to an angle β greater than 2π / λ, the wavenumber conservation law does not hold. In this case, total internal reflection occurs, and the light cannot be extracted to the air side. The magnitude of the wavenumber vector corresponding to this total internal reflection condition is the magnitude of the ray LL, i.e., 2π / λ.

[0268] As an example of a specific way to add the diffraction vector V to the in-plane wavenumber vectors K6 to K9, consider the rotation angle distribution corresponding to the second phase distribution independent of the light image. Overlapping with the rotational angle distribution corresponding to the first phase distribution used to form the desired light image In this case, the rotation angle distribution of the phase modulation layer 12B It is expressed in the following manner.

[0269]

[0270] Rotation angle distribution This is equivalent to the phase of the complex amplitude when performing an inverse Fourier transform on the light image as described above. Rotation angle distribution. It is used to add the rotation angle distribution of the diffraction vector V that satisfies the above formula (22). Figure 33 It conceptually illustrates the distribution of rotation angles. An example diagram. (For example...) Figure 33 As shown, in this example, the first phase value and the first phase value The second phase value of different values Arranged in a checkered pattern. That is, the first phase value. and the second phase value They are arranged alternately along two orthogonal directions. In one example, is the phase value. The phase value is 0 (rad). It is π (rad). That is, the first phase value. and the second phase value The difference is π (rad). By arranging these phase values, it is possible to appropriately realize the diffraction vector V along the Γ-M1 axis or the Γ-M2 axis. At the first phase value... and the second phase value When arranged in a checkered pattern as described above, V = (±π / a, ±π / a), therefore the diffraction vector V is... Figure 30 Any one of the in-plane wavenumber vectors K6 to K9 shown cancels out. This achieves the rotational angular distribution of the diffraction vector V. It is represented by the inner product of the diffraction vector V(Vx,Vy) and the position vector r(x,y), and is given by the following equation.

[0271]

[0272] If the diffraction vector V satisfies V = (±π / a, ±π / a), and the position vector is set to r(xa, ya), then the phase values ​​are 0 (rad) and π (rad). x and y are both integers. On the other hand, if the diffraction vector V is at least one of the in-plane wavenumber vectors K6 to K9 entering the range of the ray LL, it can also be shifted from (±π / a, ±π / a).

[0273] In the structure of the second embodiment, if it includes an active layer 11 and a phase modulation layer 12B, the material system, film thickness, and layer structure can be varied. Here, for a so-called tetragonal lattice photonic crystal laser where the perturbation from the hypothetical tetragonal lattice is zero, the scaling rule holds. That is, when the wavelength is a constant α times, the same standing wave state can be obtained by making the entire tetragonal lattice structure α times larger. Similarly, in this modified example, the structure of the phase modulation layer 12B can also be determined according to the scaling rule corresponding to the wavelength.

[0274] The effect obtained by the phase modulation layer 12B in this modified example, as described above, will be explained. In this modified example, the lattice spacing a of the hypothetical tetragonal lattice and the emission wavelength λ of the active layer 11 satisfy the condition for M-point oscillation. Normally, in the standing wave state of M-point oscillation, the light propagating in the phase modulation layer 12B undergoes total internal reflection, suppressing the output of the signal light, i.e., both the first-order light and the -1st-order light and the 0th-order light. However, in this modified example, the in-plane wavenumber vector, which is the reciprocal lattice space formed in the phase modulation layer 12B, and which contains the wavenumber vectors formed by the rotation angle, is... Of the four in-plane wavenumber vectors K6 to K9 obtained from the distribution of wavenumber extension Δk, at least one in-plane wavenumber vector becomes less than 2π / λ, i.e., the magnitude of the ray LL. In S-iPM lasers, for example, by studying the rotation angle... The distribution allows for adjustment of the in-plane wavenumber vectors K6 to K9. Furthermore, when the magnitude of at least one in-plane wavenumber vector is less than 2π / λ, this in-plane wavenumber vector has a component in the Z-axis direction. Therefore, as a result, a portion of the signal light is output from the phase modulation layer 12B. However, the 0th-order light is still confined in-plane in a direction consistent with any of the four in-plane wavenumber vectors (±π / a, ±π / a) forming the standing wave at point M. Therefore, the 0th-order light is not output from the phase modulation layer 12B into the ray LL. That is, according to this modified example, the 0th-order light contained in the output of the S-iPM laser can be removed from the ray LL, and only the signal light is output into the ray LL.

[0275] As in this variation, the rotation angle The distribution can be the rotation angle distribution corresponding to the light image. and rotation angle distribution independent of light image They are formed by overlapping. In this case, the rotation angle distribution... It can be used to, in the reciprocal lattice space of the phase modulation layer 12B, to correlate a diffraction vector V with a certain magnitude and orientation with a diffraction vector distributed by a rotation angle. The resulting distribution of rotation angles is obtained by adding the in-plane wavenumber vectors K6 to K9 in the four directions. Furthermore, by adding the diffraction vector V to the in-plane wavenumber vectors K6 to K9 in the four directions, at least one of the in-plane wavenumber vectors K6 to K9 can become less than 2π / λ. Therefore, it is easy to realize the distribution of rotation angles in the reciprocal lattice space. The distribution of wavenumber extensions Δkx and Δky obtained by the distribution of wavenumber extensions has at least one in-plane wavenumber vector among the four directions K6 to K9 with a magnitude less than 2π / λ, which is the structure of the ray LL.

[0276] As in this variant example, the rotation angle distribution It can also be phase values ​​that are different from each other. A pattern arranged in a checkered pattern. Distributed through this rotational angle. The diffraction vector V described above can be easily achieved.

[0277] Figure 34 This shows the rotation angle of the phase modulation layer 12B. Examples of distributions. Figure 35 It is shown in magnification Figure 34 The diagram shows part S. Figure 34 and Figure 35 In this diagram, the magnitude of the rotation angle is represented by the intensity of the color; darker areas indicate larger rotation angles, i.e., larger phase angles. (See reference...) Figure 35 It can be seen that phase values ​​with different values ​​are arranged in a grid pattern that overlaps.

[0278] In this variation, a pattern that includes a portion along the Z-axis and is symmetrical about the Z-axis can also be output. Since no zero-order light is output, no intensity unevenness of the pattern is produced even along the Z-axis. Examples of such beam patterns include multi-point patterns, mesh patterns, and one-dimensional patterns. By outputting such beam patterns in the visible area, they can be applied, for example, to display applications.

[0279] [5th ​​Variation]

[0280] In this modified example, in the phase modulation layer 12C of the third embodiment, similarly to the fourth modified example, the lattice spacing a of the hypothetical tetragonal lattice and the emission wavelength λ of the active layer 11 satisfy the condition of M-point oscillation. Furthermore, when considering the reciprocal lattice space in the phase modulation layer 12C, at least one of the in-plane wavenumber vectors containing the wavenumber extensions in the four directions obtained by the distribution of distance r(x,y) has a magnitude less than 2π / λ, i.e., the ray LL.

[0281] In detail, in this modified example, in the S-iPM laser oscillating at point M, by implementing the following study in the phase modulation layer 12C, the 0th-order light is not output into the light beam LL, but a portion of the 1st-order and -1st-order light is output. Specifically, as... Figure 31 As shown, a diffraction vector V with a certain magnitude and direction is added to in-plane wavenumber vectors K6 to K9. This makes the magnitude of at least one of the in-plane wavenumber vectors K6 to K9 less than 2π / λ. In other words, at least one of the in-plane wavenumber vectors K6 to K9 after adding the diffraction vector V is contained within the ray LL, which is a circular region with a radius of 2π / λ. That is, by adding the diffraction vector V satisfying the above equation (22), any one of the in-plane wavenumber vectors K6 to K9 is contained within the ray LL, outputting a portion of first-order light and -1-order light.

[0282] In this modified example, the lattice spacing *a* of the hypothetical tetragonal lattice and the emission wavelength *λ* of the active layer 11 satisfy the condition for M-point oscillation. Furthermore, in the reciprocal lattice space of the phase modulation layer 12C, the plane wave forming the standing wave is phase-modulated by the distribution of distances *r*(x,y). At least one of the in-plane wavenumber vectors K6 to K9, which contain the wavenumber extension Δk obtained from the angular expansion of the light image, becomes less than 2π / λ, i.e., the ray LL. Alternatively, by adding the diffraction vector *V* to the portion of the in-plane wavenumber vectors K6 to K9 excluding the wavenumber extension Δk, the magnitude of at least one in-plane wavenumber vector becomes less than the value {(2π / λ)-Δk} minus the wavenumber extension Δk from 2π / λ. Therefore, the 0th-order light contained in the output of the S-iPM laser can be removed from the ray LL, outputting only the signal light.

[0283]

Example

[0284] The inventors actually fabricated and evaluated the surface-emitting laser element of the fourth modified example. In this case, the anisotropic region 12b of the phase modulation layer 12B was set as an octagonal aperture, the lattice constant a was set to 202 nm, the fill factor was set to 28%, and the distance r between the centroid G and the lattice point O was set to 0.08a. Furthermore, multiple anisotropic regions 12b were arranged to form a total of 36 multi-point beams in a 6-row, 6-column configuration in the output light image. The inner region RIN of the phase modulation layer 12B was set as a square with one side of 200 μm, the outer region ROUT was set as a square with one side of 240 μm, the contact portion between the second electrode 22 and the contact layer 17 was set as a square with one side of 200 μm, and the planar shape of the element was set as a square with one side of 800 μm. As in the first modified example, the portion of the contact layer 17 other than the portion where the second electrode 22 is located was removed, exposing the buffer layer 16A.

[0285] Figure 36This is a diagram showing the far-field image of the multi-point beam formed in this embodiment. Figure 37 This is a graph showing the current-light output characteristics of a fabricated surface-emitting laser element during continuous operation at room temperature. Figure 37 In the diagram, the horizontal axis represents current (unit: mA), and the vertical axis represents light output (unit: mW). Figure 38 This is a graph showing the current-voltage characteristics of a fabricated surface-emitting laser element during continuous operation at room temperature. Figure 38 In the diagram, the horizontal axis represents current (unit: mA), and the vertical axis represents voltage (unit: V).

[0286] Reference Figure 37 It can be seen that after the driving current exceeds a certain value (1000mA in this example), the light output increases significantly. (Refer to...) Figure 38 As the driving current increases, the voltage also increases gradually. No sharp increase in voltage caused by high resistance, or kink (i.e., voltage characteristics emphasizing the high-voltage side), is observed. Thus, by setting the buffer layer 16A, current-voltage characteristics can be stabilized, light output improved, and voltage reduced.

[0287] Figure 39 Parts (a) and (b) are diagrams showing the near-field pattern (NFP) of this embodiment under low drive currents (30mA and 100mA) before oscillation. Figure 39 Part (a) shows the case where the drive current is set to 30mA. Figure 39 Part (b) shows the case where the drive current is set to 100 mA. When obtaining these NFPs, a pulsed drive current (pulse width 50 nanoseconds, duty cycle 1%) is supplied between the first electrode 21 and the second electrode 22. The ambient temperature is 25°C.

[0288] Reference Figure 39 In portions (a) and (b), no noise such as dark lines was observed. Furthermore, the regrown surface, i.e., the surface of contact layer 17, exhibited few crystal defects such as dislocations and good morphology. This suggests that the crystal quality of contact layer 17 is improved by intervening with a buffer layer 16A between the upper cladding 15 and contact layer 17.

[0289] Figure 40 Part (a) is a graph showing the difference in current-light output characteristics (IL characteristics) when the thickness of the mitigation layer 16A is varied in this embodiment. Figure 40 Part (b) is a graph showing the difference in current-voltage characteristics (IV characteristics) when the thickness of the mitigation layer 16A is varied. Figure 41 , Figure 42Parts (a) and (b) are schematic diagrams illustrating the fabricated layered structure. The values ​​in the diagrams represent the thickness of each layer. Figure 40 In parts (a) and (b), Figure G7 shows the case where the thickness of the mitigation layer 16A is 50 nm (see reference). Figure 41 Curve G8 is used as a comparative example, such as... Figure 42 As shown in section (a), a 50 nm thick p-type GaAs layer 18 is provided instead of the mitigation layer 16A. Curve G9 is used as a comparative example. Figure 42 As shown in section (b), the upper cladding 15 contacts the contact layer 17 without the buffer layer 16A. (Refer to...) Figure 40 As can be seen from parts (a) and (b), when the thickness of the buffer layer 16A is 50 nm (curve G7), the IL and IV properties are particularly improved.

[0290] The surface-emitting laser element disclosed herein is not limited to the embodiments described above and can be modified in various other ways. For example, in the embodiments described above, the surface-emitting laser element is exemplified as a PCSEL and an S-iPM laser. The surface-emitting laser element is not limited to these; as long as it is a surface-emitting laser element that includes a basic region and a plurality of regions with different refractive indices that are distributed two-dimensionally in a plane perpendicular to the thickness direction, and has a resonance mode forming layer that forms a resonance mode of light in the plane, the structure of this disclosure can be applied to various other surface-emitting laser elements.

[0291] Two structures are illustrated as examples of S-iPM laser structures. One structure has multiple anisotropic refractive index regions whose centroids are arranged away from the lattice points of an imaginary tetragonal lattice, and has rotation angles around the lattice points corresponding to the optical image. The other structure has multiple anisotropic refractive index regions whose centroids are arranged on a straight line passing through the lattice points of the imaginary tetragonal lattice and tilted relative to the tetragonal lattice, and the distance between the centroid of each anisotropic refractive index region and its corresponding lattice point is individually set corresponding to the optical image. The structures disclosed herein can also be applied to S-iPM lasers with different structures.

[0292] In the above embodiments, the case where the bandgap width of the contact layer 17 is smaller than the bandgap width of the upper cladding layer 15 is illustrated. The bandgap width of the contact layer 17 may also be larger than the bandgap width of the upper cladding layer 15. In this case, by having a bandgap width between that of the upper cladding layer 15 and the contact layer 17, the same effect as in the above embodiments can be achieved.

[0293] Industrial availability

[0294] The implementation can be used as a surface-emitting laser element such as a photonic crystal surface-emitting laser or an S-iPM laser, which can achieve sufficient laser oscillation even with low driving voltage.

[0295] Explanation of symbols

[0296] 1A, 1B…Surface-emitting laser element, 8…Semiconductor substrate, 8a…Main surface, 8b…Back surface, 10…Semiconductor stack, 11…Active layer, 12A…Photonic crystal layer, 12a…Base region, 12b, 12c…Heterochromatic refractive index regions, 12B, 12C…Phase modulation layer, 13…Lower cladding, 14…Optical guide layer, 15…Upper cladding, 16A, 16B, 16C…Moderate layer, 17…Contact layer, 21…First electrode, 21a…Opening, 22…Second electrode Pole, D…line, E1…first ray image, E2…second ray image, E3…0th order ray, G…centroid, G11, G21…refractive index distribution, G12, G22…basic mode distribution, G13, G23…mode distribution, K6~K9, Kb…in-plane wavenumber vector, LL…ray, Lout, Lout2…laser, O…grid point, Q…center, R…unit constitutive region, RIN…inner region, ROUT…outer region, S…part, V…diffraction vector.

Claims

1. A surface-emitting laser element, wherein, have: Electrode 1; The first cladding of the first conductivity type is electrically connected to the first electrode; An active layer is disposed on the first cladding layer; A second cladding layer of the second conductivity type is disposed on the active layer; A second conductivity type buffer layer is disposed on the second cladding layer; A second conductive contact layer is disposed on the buffer layer and has a different band gap than the second cladding layer; The second electrode is disposed on the contact layer and forms an ohmic contact with the contact layer; as well as A resonance mode forming layer, disposed between the first cladding layer and the active layer, or between the active layer and the second cladding layer, comprises a basic region and multiple anisotropic regions. The multiple anisotropic regions have refractive indices different from those of the basic region. These multiple anisotropic regions are distributed two-dimensionally within a plane perpendicular to the thickness direction, forming a resonance mode of light within this plane. The buffer layer has a bandgap width that is between the bandgap width of the second cladding layer and the bandgap width of the contact layer. The thickness of the buffer layer is less than the thickness of the second cladding layer.

2. The surface-emitting laser element according to claim 1, wherein, The resonant mode forming layer is a photonic crystal layer with the plurality of different refractive index regions arranged periodically.

3. The surface-emitting laser element according to claim 1, wherein, The surface-emitting laser element is a surface-emitting laser element that outputs a light image. The centroids of the plurality of heterorefringent regions are respectively disposed away from the corresponding lattice points of the imaginary tetragonal lattice set in the plane of the resonance mode forming layer, and have rotation angles around the lattice points corresponding to the light image, wherein the rotation angles of the centroids of at least two of the heterorefringent regions are different from each other.

4. The surface-emitting laser element according to claim 1, wherein, The surface-emitting laser element is a surface-emitting laser element that outputs a light image. When an imaginary tetragonal lattice is set within the plane of the resonance mode forming layer, the centroids of the plurality of anisotropic refractive index regions are arranged on straight lines passing through the lattice points of the tetragonal lattice and inclined relative to the tetragonal lattice. The inclination angles of the plurality of straight lines corresponding to the plurality of anisotropic refractive index regions relative to the tetragonal lattice are equal within the resonance mode forming layer. The centroid of each region of different refractive index and the distance to the grid point corresponding to each region of different refractive index are individually set in relation to the light image, and the distances between the centroid and the grid point of at least two regions of different refractive index are different from each other.

5. The surface-emitting laser element according to any one of claims 1 to 4, wherein, The buffer layer is composed of the same constituent elements as the second cladding layer.

6. The surface-emitting laser element according to any one of claims 1 to 5, wherein, The bandgap width of the buffer layer varies continuously from the bandgap width of the second cladding layer to the bandgap width of the contact layer.

7. The surface-emitting laser element according to any one of claims 1 to 5, wherein, The bandgap width of the buffer layer varies in stages, approaching the bandgap width of the second cladding layer.

8. The surface-emitting laser element according to any one of claims 1 to 7, wherein, The refractive index of the second cladding layer is less than that of the first cladding layer.

9. The surface-emitting laser element according to any one of claims 1 to 5, wherein, The second cladding layer and the buffer layer contain Al as a component. The Al composition ratio of the buffer layer is less than that of the second cladding layer.

10. The surface-emitting laser element according to claim 9, wherein, The Al composition ratio of the buffer layer decreases continuously from the interface of the buffer layer near the second cladding layer to the interface of the buffer layer near the contact layer.

11. The surface-emitting laser element according to claim 9, wherein, The Al composition ratio of the buffer layer decreases in stages from the interface of the buffer layer near the second cladding layer to the interface of the buffer layer near the contact layer.

12. The surface-emitting laser element according to any one of claims 9 to 11, wherein, The second cladding layer and the buffer layer are AlGaAs layers, and the contact layer is a GaAs layer.

13. The surface-emitting laser element according to any one of claims 9 to 12, wherein, The first cladding layer contains Al as a component. The Al composition ratio of the second cladding layer is greater than that of the first cladding layer.

14. The surface-emitting laser element according to any one of claims 1 to 13, wherein, Viewed in the thickness direction, the area of ​​the contact layer is smaller than the area of ​​the buffer layer, and the buffer layer is exposed from the contact layer around the contact layer.

15. The surface-emitting laser element according to any one of claims 1 to 14, wherein, The mitigation layer is more than 1 μm away from both the resonant mode forming layer and the active layer.

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