JP2009111167A - Surface-emitting semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-emitting semiconductor laser element using a photonic crystal structure and capable of efficiently outputting a laser beam. <P>SOLUTION: The surface-emitting semiconductor laser element 10 comprises: a substrate 12; an active layer 16 provided on the main surface 12a of the substrate 12; a photonic crystal layer 20 optically coupled with the active layer 16; a beam output plane S for outputting a laser beam generated by the semiconductor laser element 10; and an electrode 28 provided on the beam output plane S. The photonic crystal layer 20 has a two-dimensional photonic crystal structure for partially diffracting the beam having the predetermined wavelength included in the beam generated by the active layer to the beam output plane side and confining the other part of the beam having the predetermined wavelength to the plane in approximately parallel with the main surface. The predetermined wavelength is the wavelength of the laser beam, the electrode has at least one edge part 28a, 28b, and phase shift parts 36x, 36y are formed under vicinity of the edge part of the photonic crystal layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface emitting semiconductor laser element using a photonic crystal.

  Conventionally, as a technology in this field, a surface emitting semiconductor laser element described in Patent Document 1 is known. The surface emitting semiconductor laser element described in the above document includes an active layer, a photonic crystal layer (photonic band layer) optically coupled to the active layer, and a main surface of the substrate on the main surface of the substrate. And a light emission surface for outputting laser light generated in the surface emitting semiconductor laser element. The photonic crystal layer provided in the surface emitting semiconductor laser element has a two-dimensional photonic crystal structure composed of a two-dimensional periodic refractive index change. In the surface-emitting semiconductor laser device, an optical resonator in the surface-emitting semiconductor laser device is realized by utilizing the two-dimensional optical confinement and the two-dimensional optical feedback action in the photonic crystal structure. The surface emission operation is realized by utilizing the diffraction phenomenon caused by the periodic refractive index change constituting the photonic crystal structure.

In the surface emitting semiconductor laser device having a photonic crystal layer as described in the above document, when the light generated in the active layer reaches the photonic crystal layer, the photonic crystal structure of the reached light Light with a defined wavelength and phase condition reaches the active layer and promotes stimulated emission. The stimulated emission light satisfies the light wavelength and phase conditions defined by the photonic crystal structure. This stimulated emission light reaches the photonic crystal layer again. In this way, light having a uniform wavelength and phase condition is generated and amplified, and laser light is generated in the surface emitting semiconductor laser element. The generated laser light is output to the light emitting surface side by the diffraction phenomenon, so that the laser light is output from the surface emitting semiconductor laser element. Patent Document 1 exemplifies introducing a phase shift structure into a photonic crystal layer for the purpose of unifying wavelengths.
JP 2000-332351 A

  In a conventional surface emitting semiconductor laser element using a photonic crystal as described in Patent Document 1, light confinement in a photonic crystal layer that functions as an optical resonator is strong. The laser beam extraction efficiency tends to decrease.

  Accordingly, an object of the present invention is to provide a surface emitting semiconductor laser element using a photonic crystal structure and capable of efficiently outputting laser light.

  The present invention relates to a surface emitting semiconductor laser element, which is provided on a main surface of a substrate, an active layer provided on the main surface of the substrate and generating light when carriers are injected, and The photonic crystal layer that is optically coupled to the active layer, and located on the opposite side of the substrate from the photonic crystal layer in a direction substantially perpendicular to the main surface, is generated in the surface emitting semiconductor laser element described above A photonic crystal layer is provided on the light output surface, and is provided on the light output surface. The electrode provides carriers to the active layer. It has a two-dimensional photonic crystal structure that diffracts a part of the light of the wavelength to the light output surface side and confines another part of the light of the predetermined wavelength in a plane substantially parallel to the main surface. The wavelength of the laser beam, and the electrodes are few Both have one edge, the photonic crystal layer, according to the surface-emitting type semiconductor laser element, wherein a phase shift portion is formed in the vicinity just below the edge.

  In the surface emitting semiconductor laser device according to the present invention, when the light generated in the active layer reaches the photonic crystal layer, a part of the light having the predetermined wavelength is diffracted to the light output surface side by the photonic crystal structure. Thus, the surface emission operation is realized. In addition, light satisfying the phase condition is confined in the photonic crystal layer in the other part of the light having the predetermined wavelength that has reached the photonic crystal layer from the active layer. Since the photonic crystal layer is optically coupled to the active layer, stimulated emission is promoted in the active layer by light confined in the photonic crystal layer. The stimulated emission satisfies the phase condition in the light having a predetermined wavelength defined by the photonic crystal structure, and reaches the photonic crystal layer again. In this way, light having a uniform wavelength and phase condition is generated and amplified, so that laser light is generated. As described above, the surface emitting operation is enabled by the diffraction to the light output surface side in the photonic crystal layer, so that the laser light generated in the surface emitting semiconductor laser element is output from the light output surface. Will be.

  In the surface emitting semiconductor laser device having the above configuration, since the phase shift portion is introduced at the above position in the photonic crystal layer, light from the photonic crystal layer reaches a region that does not overlap the electrode on the light output surface. Easy to do. As a result, the laser light generated in the surface emitting semiconductor laser element is not easily blocked by the electrode, and light can be efficiently output from the surface emitting semiconductor laser element.

  In the surface-emitting type semiconductor laser device according to the present invention, the plurality of lattice points of the photonic crystal structure constitute two or more diffraction grating groups, and each diffraction grating group extends in a different direction. The grating points constituting each of the grating groups are arranged in the same arrangement relation along the extending direction of each diffraction grating group among the diffraction grating groups, and each diffraction grating group is phase-shifted in the vicinity immediately below the edge. It is preferable to have a part.

  In this configuration, the photonic crystal structure is a two-dimensional diffraction grating composed of two or more diffraction grating groups extending in different directions, and a two-dimensional diffraction grating in which a phase shift portion is introduced in the vicinity immediately below the edge of the electrode. Can be considered. In each diffraction grating group, it can be formed by shifting the interval between adjacent grating points near the edge of the electrode from the period of each diffraction grating group.

  In the surface-emitting type semiconductor laser device according to the present invention, the plurality of lattice points of the photonic crystal structure are the first diffraction grating group and the second diffraction grating extending in the first and second directions orthogonal to each other. The grating points constituting each of the first and second diffraction grating groups have the same arrangement relationship along the first and second directions in the first and second diffraction grating groups. The electrodes have a substantially square shape in plan view, and the electrodes have a pair of first edges facing each other and a pair of second edges facing each other, and the first and second , And the first and second diffraction grating groups are phase-shifted in the vicinity immediately below the pair of first edges and the pair of second edges, respectively. It is preferable to have a part.

  In this configuration, the photonic crystal structure can be regarded as a two-dimensional diffraction grating composed of first and second diffraction grating groups in which phase shift portions are formed in the vicinity immediately below the first and second edges. Also in this case, the first and second diffraction grating groups are formed by shifting the interval between adjacent grating points near the edge of the electrode from the period of the first and second diffraction grating groups. Can do.

  When the electrode has a pair of first edges and a pair of second edges extending in the first and second directions as described above, the pair of first edges and the pair of second edges Each phase shift portion corresponding to the edge portion may be extended in the first and second directions.

  According to the present invention, it is possible to provide a surface emitting semiconductor laser element using a photonic crystal and capable of efficiently outputting light from a light output surface.

  Hereinafter, embodiments of a surface emitting semiconductor laser device according to the present invention will be described with reference to the drawings. In the following description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted. Further, the dimensional ratios and the like in the drawings do not necessarily match those described.

  FIG. 1 is a perspective view of an embodiment of a surface emitting semiconductor laser device (hereinafter simply referred to as “semiconductor laser device”) according to the present invention. In FIG. 1, a part of the surface emitting semiconductor laser element 10 is notched for the sake of explanation. FIG. 2 is a cross-sectional view taken along the line II-II in FIG.

  A semiconductor laser element 10 shown in FIGS. 1 and 2 is a surface-emitting photonic crystal laser element using a two-dimensional photonic crystal structure.

  The semiconductor laser element 10 has a substrate 12 such as a semiconductor substrate of a first conductivity type (in this embodiment, n-type as an example). An example of the material of the substrate 12 is GaN. On the main surface 12 a of the substrate 12, a first conductivity type cladding layer 14, an active layer 16, a buffer layer 18, a photonic crystal layer 20, a guide layer 22, a second conductivity type (in this embodiment, p-type as an example) The cladding layer 24 and the contact layer 26 are stacked in this order. In the following description, as shown in FIGS. 1 and 2, the direction orthogonal to the main surface 12a of the substrate 12 is referred to as the z-axis direction, and the two directions substantially orthogonal to the z-axis direction are respectively the x-axis direction (first axis). Direction) and y-axis direction (second direction).

  In the semiconductor laser device 10, when carriers are given to the active layer 16, laser light is generated by the action of the active layer 16 and the photonic crystal layer 20 based on the light generated in the active layer 16, and the laser light is converted into the contact layer 26. Is output from the surface 26a. Thus, in the semiconductor laser element 10, the surface 26a of the contact layer 26 functions as the light output surface S of the laser light.

  On the surface 26a of the contact layer 26, a square electrode 28 smaller than the light output surface S in plan view is provided in order to supply carriers to the active layer 16. The planar view shape of the electrode 28 is not limited to a square shape, and examples thereof include a circular shape, another quadrangular shape (for example, a rectangular shape), and a hexagonal shape. A pair of opposite edges (second edge) 28a, 28a of the electrode 28 extend in the y-axis direction, and a pair of opposite edges (first edge) 28b of the electrode 28, 28b extends in the x-axis direction. An electrode 30 is provided on almost the entire back surface 12b on the back surface 12b, which is the surface facing the main surface 12a of the substrate 12. An example of the material of the electrodes 28 and 30 is gold.

  The clad layers 14 and 24 increase the photon density in the region sandwiched between the clad layers 14 and 24, more specifically, the photon density of the active layer 16 and the photonic crystal layer 20 to increase the efficiency of laser light. It is for generating. The clad layers 14 and 24 are made of a semiconductor having a refractive index lower than that of the active layer 16. The buffer layer 18 and the guide layer 22 function as a spacer layer for appropriately adjusting the distance between the cladding layers 14 and 24 in order to increase the photon density in the region sandwiched between the cladding layers 14 and 24. Further, as will be described later, for example, the buffer layer 18 can be used as an etching stop layer when the photonic crystal layer 20 is formed by etching.

  The active layer 16 emits light when carriers are injected. Since carriers are mainly injected into the region immediately below the electrode 28 in the active layer 16, the region immediately below the electrode 28 in the active layer 16 functions as a gain region. Examples of the active layer 16 include those including an InGaN-based multiple quantum well (MQW) structure. The active layer 16 can also be composed of a multiple quantum well structure made of another semiconductor material. Moreover, the active layer 16 can also be comprised from a single quantum well structure instead of a multiple quantum well structure. Furthermore, the active layer 16 may be composed of a single semiconductor material.

The photonic crystal layer 20 is provided on the active layer 16 with the buffer layer 18 interposed therebetween, and is optically coupled to the active layer 16. The photonic crystal layer 20 is a layer having a two-dimensional photonic crystal structure that defines the wavelength of laser light to be generated by the semiconductor laser element 10 (hereinafter referred to as laser wavelength). In the photonic crystal layer 20, a plurality of columnar portions 34 having a refractive index different from the refractive index of the semiconductor layer 32 (for example, a lower refractive index) are the same in the x-axis direction and the y-axis direction. They are arranged in an array relationship. Each columnar part 34 is each lattice point in the photonic crystal structure, and a photonic band is formed by the spatial arrangement relationship of the columnar part 34 and the difference in refractive index between the semiconductor layer 32 and the columnar part 34. . An example of the material of the semiconductor layer 32 is GaN, and an example of the material of the columnar portion 34 is SiO ₂ . In addition, the columnar part 34 can also be made into a hole, for example. As shown in FIG. 1, the shape of the columnar portion 34 in plan view is exemplified by a circle, but may be a polygon such as a triangle or a quadrangle. In the photonic crystal structure of the photonic crystal layer 20, a phase shift unit 36x and a phase shift unit 36y are introduced in the vicinity of a pair of edge portions 28a, 28a and a pair of edge portions 28b, 28b of the electrode 28. Yes.

  FIG. 3 is a schematic diagram showing the arrangement relationship of lattice points in a photonic crystal layer having a square lattice structure. In order to explain the positional relationship between the phase shifters 36x and 36y and the electrode 28, the position of the electrode 28 is shown for convenience in FIG. 3 using a solid line.

  As shown in FIG. 3, the photonic crystal structure in which the phase shift portions 36x and 36y are introduced is a diffraction grating group extending in the x-axis direction (first direction) and includes two phase shifts in the x-axis direction. A diffraction grating group (first diffraction grating group) Lx having a portion 36x and a diffraction grating group extending in the y-axis direction (second direction) orthogonal to the x-axis, and having two phase shifts in the y-axis direction It can be regarded as a two-dimensional diffraction grating composed of a diffraction grating group (second diffraction grating group) Ly having a portion 36y. The diffraction grating group Lx includes a one-dimensional diffraction grating lx having a period d1 extending in the x-axis direction and arranged in parallel in the y-axis direction. The diffraction grating group Ly extends in the y-axis direction and is in the x-axis direction. A plurality of primary diffraction gratings ly having the same period d1 as the diffraction gratings lx of the diffraction grating group Lx. The period d1 of each one-dimensional diffraction grating lx, ly defines the laser wavelength. Further, the phase of light is defined by a two-dimensional diffraction grating composed of a plurality of columnar portions 34 constituting the photonic crystal, and the phases of the light diffracted by the plurality of two-dimensional diffraction gratings are phase-matched and To the extent that waves can exist, the period d1 of each one-dimensional diffraction grating lx, ly has the same period with respect to the laser wavelength. Each of the one-dimensional diffraction gratings lx and ly is provided with a phase shift structure that constitutes the phase shift portions 36x and 36y in the vicinity immediately below the pair of edge portions 28a and 28a and the pair of edge portions 28b and 28b of the electrode 28. Has been.

  As shown in FIG. 3, the phase shift portions 36x and 36y have a lattice interval d2 that is a distance between the columnar portions 34 adjacent to each other in the x-axis direction and the y-axis direction near the edges 28a and 28b of the electrode 28. It can be formed by shifting from the period d1 by a predetermined amount. Thus, when the phase shift parts 36x and 36y are formed, the phase shift amount is defined by the difference between the grating interval d2 and the period d1. For example, when the grating interval d2 is d1 / 2, the phase shift amount is π. When the phase shift portions 36x and 36y are formed by shifting the grating interval d2 from the period d1, the photonic crystal structure includes a diffraction grating group including a plurality of one-dimensional diffraction gratings having a period d1 extending in the x-axis direction. A plurality of two-dimensional diffraction gratings composed of a plurality of one-dimensional diffraction gratings having a period d1 extending in the y-axis direction are arranged in the x-axis direction and the y-axis direction at the introduction positions of the phase shift portions 36x and 36y. It can also be considered that they are arranged at an interval d2.

  Here, the case where the phase shift portions 36x and 36y are formed by shifting the lattice interval is illustrated, but the phase shift portions 36x and 36y are formed by the columnar portions 34 as lattice points immediately below the edges 28a and 28b. You may form by shifting conditions, such as a refractive index and planar view shape, from the conditions of the columnar part 34 of another area | region. It can also be formed by forming a lattice defect in the vicinity immediately below the edge portions 28a, 28b.

  The semiconductor laser element 10 shown in FIG. 1 is manufactured as follows, for example. First, the clad layer 14, the active layer 16 and the buffer layer 18 are formed on the substrate 12, and then a columnar portion forming layer made of a material constituting the columnar portion 34 is formed on the surface of the buffer layer 18. Then, after forming a plurality of columnar portions 34 by applying, for example, a photolithography method and an etching method to the columnar portion forming layer, the columnar portions 34 are different in refractive index from the columnar portions 34 to be the semiconductor layers 34. The photonic crystal layer 20 is formed by embedding with a semiconductor including Next, the guide layer 22, the cladding layer 24, and the contact layer 26 are formed on the photonic crystal layer 20. Thereafter, the electrode 28 is formed on the contact layer 26 and the electrode 30 is formed on the back surface of the substrate 12, whereby the semiconductor laser device 10 can be manufactured.

Examples of materials and thicknesses (length in the z-axis direction) of the substrate 12, the cladding layers 14 and 24, the active layer 16, the buffer layer 18, the guide layer 22, and the contact layer 26 in the semiconductor laser device 10 shown in FIG. It is as Table 1.

  In the semiconductor laser device 10 having the above configuration, when carriers are applied to the active layer 16 by applying a signal from the electrode 28, light is generated in the active layer 16, and the light generated in the active layer 16 is optically applied to the active layer 16. To the photonic crystal layer 20 bonded to.

  Since the photonic crystal layer 20 has a photonic crystal structure that functions as a second-order two-dimensional diffraction grating, most of the light having a laser wavelength that reaches the photonic crystal layer 20 is photonic due to the photonic crystal structure. It is confined in the crystal layer 20. More specifically, when two-dimensional standing waves are propagated in the photonic crystal layer 20 when the diffraction by the plurality of columnar portions 34 is repeated to propagate through a predetermined closed path and the phase condition is satisfied in the closed path. Is formed and confined in the photonic crystal layer 20. In this case, the photonic crystal layer 20 functions as an optical resonator in the semiconductor laser element 10. The light confined in the photonic crystal layer 20 interacts with the active layer 16 to cause stimulated emission, thereby causing laser oscillation. Further, since the photonic crystal structure is also a secondary diffraction grating, a part of the light having a laser wavelength is also diffracted in the z-axis direction by a diffraction phenomenon. Therefore, the surface emitting operation can be performed in the semiconductor laser element 10.

  Then, light having a laser wavelength whose light intensity is increased by laser oscillation propagates to the light output surface S side by the diffraction phenomenon and is output from the light output surface S, so that the laser light is output from the semiconductor laser element 10. The That is, the semiconductor laser device 10 including the photonic crystal layer 20 is a distributed feedback surface emitting semiconductor laser device using second-order diffraction in a photonic crystal structure, and utilizes the diffraction phenomenon in the photonic crystal layer 20. This corresponds to a semiconductor laser device realizing surface emitting operation.

  In the semiconductor laser element 10, more light can be extracted from the light output surface S by introducing the phase shift portions 36 x and 36 y immediately below the edges 28 a and 28 b of the electrode 28 in the photonic crystal layer 20. Is possible. This point will be described using simulation results.

  First, basic conditions for simulation will be described. 4 is a schematic diagram of a basic configuration model for simulation of the semiconductor laser device shown in FIG. 1, and corresponds to a cross-sectional configuration of a cross section orthogonal to the x-axis direction or the y-axis direction in FIG.

  In the semiconductor laser device 10M having the simulation model structure shown in FIG. 4, as in the case of the semiconductor laser device 10 shown in FIGS. 1 and 2, the cladding layer 14M, the active layer 16M, and the buffer are formed on the substrate 12M. The layer 18M, the photonic crystal layer 20M, the guide layer 22M, the cladding layer 24M, and the contact layer 26M are laminated in this order, and the electrode 28M and the electrode 30M are provided on the contact layer 26M and the back surface of the substrate 12M, respectively. ing. Also in the semiconductor laser element 10M, the surface of the contact layer 26M functions as the light output surface S.

  In the following description, the substrate 12M, the cladding layer 14M, the active layer 16M, the buffer layer 18M, the photonic crystal layer 20M, the guide layer 22M, the cladding layer 24M, and the contact layer 26M are the semiconductor shown in FIG. 1 unless otherwise specified. It corresponds to the substrate 12, the cladding layer 14, the active layer 16, the buffer layer 18, the photonic crystal layer 20, the guide layer 22, the cladding layer 24, and the contact layer 26 of the laser element 10. For convenience, the direction toward the side surface 10b with respect to the side surface 10Ma of the semiconductor laser element 10M shown in FIG. 4 corresponds to the x-axis direction shown in FIG. The direction in which the layer 16M, the buffer layer 18M, the photonic crystal layer 20M, the guide layer 22M, the cladding layer 24M, and the contact layer 26M are stacked is the z-axis direction as in the case of FIG.

  The length D1 in the x-axis direction of the substrate 12M is 300 μm, and the length D2 in the x-axis direction of the electrode 28M is 100 μm. It is assumed that the center position of the electrode 28M in the x-axis direction and the center position of the substrate 12M in the x-axis direction coincide. Further, it is assumed that the semiconductor laser element 10M outputs laser light having a laser wavelength of 400 nm.

  The materials and thicknesses of the substrate 12M, the clad layer 14M, the active layer 16M, the buffer layer 18M, the guide layer 22M, the clad layer 24M, and the contact layer 26M are those shown in Table 1.

Similar to the photonic crystal layer 20, the photonic crystal layer 20M is configured such that columnar portions 34M having a refractive index smaller than the refractive index of the semiconductor layer 32M are arranged in a square lattice pattern on the semiconductor layer 32M. . Similar to the case shown in Table 1, the thickness of the photonic crystal layer 20M is 40 nm. The semiconductor layer 32M and the columnar part 34M correspond to the semiconductor layer 32 and the columnar part 34 in the semiconductor laser element 20. The hatching in FIG. 4 is for showing the semiconductor layer 32M. The material of the semiconductor layer 32M was GaN having a refractive index of 2.54, and the material of the columnar part 34M was SiO ₂ having a refractive index of 1.42. Further, the columnar portion 34M is a cylinder having a circular shape in plan view, and its diameter is 48 nm. The interval between adjacent columnar portions 34M, that is, the period d1 in the photonic crystal structure was 160 nm. The introduction position of the phase shift portion in the photonic crystal layer 20M will be described sequentially when the simulation results are described. At this time, the phase shift unit to be introduced is also referred to as a phase shift unit 36M. The phase shift unit 36M is introduced by shifting the interval between the adjacent columnar parts 34M and 34M from the period d1.

  Further, as described above, the semiconductor laser element using the photonic crystal structure corresponds to the distributed feedback semiconductor laser element using the second-order diffraction that realizes the surface emission operation using the diffraction phenomenon. The simulation was carried out based on the coupled wave equation and the rate equation used for the analysis of the distributed feedback semiconductor laser device. In this case, two coupling constants indicating the strength of feedback appear in the coupled wave equation. Of these two coupling constants, the coupling constant h2 exhibiting second-order diffraction determines the photon density distribution in the photonic crystal layer 20M, that is, the optical resonator of the semiconductor laser device 10M, and the photons in the photonic crystal layer 20M. The coupling constant h1 indicating the density distribution and the diffraction phenomenon determines the photon density distribution output from the photonic crystal layer 20M to the light output surface S. In the following description, for convenience, the electrode 28M side with respect to the substrate 12M will be described as the “up” direction.

  Next, the point that the amount of light output from the photonic crystal layer 20M upward is changed by introducing a phase shift portion into the photonic crystal layer 20M using FIGS. .

  FIG. 5 is a diagram showing the power density of light output from the photonic crystal layer 20M to the light output surface S side and the photon density distribution in the photonic crystal layer when the phase shift portion is not introduced as in the prior art. is there. Specifically, FIG. 5A shows the power density distribution at the position of the light output surface S of the light output from the photonic crystal layer 20M, and FIG. 5B shows the photonic crystal layer. The photon density distribution within 20M is shown. The horizontal axes in FIGS. 5A and 5B indicate the position in the x-axis direction with the side surface 10Ma of the semiconductor laser element 10M shown in FIG. 4 as a reference (origin position). The vertical axis in FIG. 5A indicates the photon density, and the vertical axis in FIG. 5B indicates the power density.

  FIG. 6 shows the power density distribution of light output from the photonic crystal layer 20M to the light output surface S side and the photonic crystal layer 20M when one phase shift portion is introduced directly below the center of the electrode 28. It is drawing which shows inside photon density distribution. Specifically, FIG. 6A shows the power density distribution at the position of the light output surface S of the light output from the photonic crystal layer 20M, and FIG. 6B shows the photonic crystal layer. The photon density distribution within 20M is shown. The horizontal axis in FIGS. 6A and 6B indicates the position in the x-axis direction as in FIGS. 5A and 5B. The vertical axis in FIG. 6A indicates the photon density, and the vertical axis in FIG. 6B indicates the power density.

  5 and 6, the region of 100 to 200 μm corresponds to the region directly below the electrode 28M at the position indicated on the horizontal axis, and the region immediately below the electrode 28M in the active layer 16M is assumed to be the gain region.

  FIG. 5B shows that the photon density is high in the central portion of the photonic crystal layer 20M, and photons are confined in the central portion. On the other hand, FIG. 5A shows that the photon density at the central portion where the photon density is high inside the optical resonator is hardly output to the light output surface S side. This phenomenon is considered to occur because the phases of light output from the photonic crystal layer 20M to the light output surface S side weaken each other. In this case, it is not possible to efficiently extract photons from the central part having a high photon density upward.

  Further, FIG. 6B shows that even when the phase shift part is introduced into the central part, the photon density is high in the central part of the photonic crystal layer 20M, and the photons are confined in the central part. 6A that the power density distribution similar to the photon density distribution in the photonic crystal layer 20M can be realized even in the light output surface S when the phase shift portion is introduced in the central portion.

  As shown in FIGS. 5 and 6, the phase weakening described above can be avoided by introducing the phase shift portion 36M into the photonic crystal layer 20M. However, when the phase shift portion 36M is provided immediately below the center portion of the electrode 28, the power density distribution on the light output surface S has a sharp peak at the center portion as shown in FIG. In this case, most of the light output from the light output surface S is blocked by the electrode 28M and does not contribute to the light output from the semiconductor laser element 10M.

  From the above, increasing the light output from the light output surface S makes the phase shift unit 36M appropriate so that the proportion of photons output from the portion not overlapping the electrode 28M on the light output surface S is increased. It can be realized by placing it at a location.

Next, the difference in light extraction efficiency according to the introduction position of the phase shift unit 36M will be described using FIGS. 7 to 9 while changing the introduction position of the phase shift unit 36M in the photonic crystal layer 20M. Here, the extraction efficiency is defined as follows.
(Extraction efficiency) = (photons emitted outside the semiconductor laser element) / (all photons incident on the light output surface)
7 to 9, it is assumed that the entire region of the active layer 16M is a gain region in order to appropriately perform the simulation even when the phase shift portion is introduced outside the edge 28Ma of the electrode 28M. . The edge portion 28Ma in the electrode 28M corresponds to the edge portion 28a in the electrode 28.

  7 and 8 are diagrams showing a change in extraction efficiency with respect to a change in the distance between two phase shift portions introduced at a predetermined position in the x-axis direction. 7 and 8, the phase shift portions 36M and 36M are provided at positions symmetrical with respect to the center position of the electrode 28M in the x-axis direction. 7 and 8, the horizontal axis indicates the distance D3 between the phase shift portions, and the case where the two phase shift portions are overlapped at the center position in the x-axis direction of the electrode 28M is 0. It is said. The vertical axis represents the extraction efficiency.

  Further, FIG. 7 shows a change in extraction efficiency when the phase shift amounts by the two phase shift units 36M and 36M are the same Φ, and Φ is changed to 0.25π, 0.35π, and 0.50π. . On the other hand, in FIG. 8, the phase shift amounts by the two phase shift units 36M and 36M are different Φ1 and Φ2, and a set of Φ1 and Φ2, that is, (Φ1, Φ2) is (0.50π, 0.50π), ( This shows the change in extraction efficiency when the values are changed to 0.40π, 0.60π) and (0.30π, 0.70π).

  FIG. 9 is also a diagram showing a change in extraction efficiency with respect to a change in the distance between the phase shift portions. However, FIG. 9 shows a simulation result in the case where the phase shift portion 36M is further arranged at the center position in the x-axis direction of the electrode 28M in the same configuration of the semiconductor laser element 10M as in FIG. In this case, three phase shift units 36M, 36M, and 36M are introduced in the x-axis direction. The phase shift amounts of the three phase shift units 36M, 36M, and 36M all employ 0.5π. The distance between the phase shift portions on the horizontal axis shown in FIG. 9 indicates the distance between the phase shift portions on both sides arranged with the central phase shift portion interposed therebetween.

  As shown in the simulation results shown in FIGS. 7 to 9, when the distance between the phase shift portions 36M and 36M is larger than 50 μm, that is, in the x-axis direction of the electrode 28M on the basis of directly below the edge portion 28Ma. When the phase shift units 36M and 36M are respectively introduced outside the inner position by about 1/4 of the length (100 μm in the model configuration of FIG. 4), the phase shift unit 36M is disposed only at the center. The extraction efficiency is higher than that. Further, it can be seen that the peak of extraction efficiency is located at a position immediately below the edge portions 28Ma and 28Ma of the electrode 28M, that is, in a region where the distance D3 is near 100 μm, for example, 80 μm to 140 μm.

  In the above simulation, the x-axis direction shown in FIG. 4 is the x-axis direction shown in FIG. 1, and unless otherwise specified, the edge portion 28Ma and the phase shift portion 36M are used as the edge portion 28a and the phase shift portion 36x in the semiconductor laser device 10. Although described, the direction from the side surface 10Ma toward the side surface 10Mb is the y-axis direction shown in FIG. 1, and the edge portion 28Ma and the phase shift portion 36M are the edge portion 28b and the phase shift portion 36x in the semiconductor laser element 10, respectively. It is the same.

  Accordingly, as described with reference to FIGS. 1 to 3, the light extraction efficiency from the light output surface S can be obtained by introducing the phase shift portions 36 x and 36 y in the vicinity immediately below the edge portions 28 a and 28 b of the electrode 28. Can be improved. Further, from the results of FIGS. 7 to 9, since the extraction efficiency tends to show a peak value immediately below the edge portions 28Ma and 28Ma of the electrode 28M, the position of the phase shift portions 36x and 36y is set to the edge portion 28a of the electrode 28. , 28b is more preferable.

  In addition, as a two-dimensional arrangement example of the phase shift unit 36M with respect to the photonic crystal layer 20M when performing the simulation obtained from the simulation result of FIG. 9, the form shown in FIG. 10 is exemplified. That is, when three phase shift portions 36M, 36M, and 36M are introduced in the photonic crystal layer 20M along the x-axis direction and the y-axis direction, they are respectively directly below the center line of the electrode 28M with respect to the x-axis direction and the y-axis direction. If phase shift units 36M and 36M are introduced and phase shift units 36M and 36M are respectively introduced on both sides of phase shift units 36M and 36M provided immediately below the center line of electrode 28M in the x-axis direction and the y-axis direction. Good. In FIG. 10, the phase shift portion 36 </ b> M is schematically shown by a one-dot chain line, and the columnar portions (lattice points) 34 are omitted. Further, in order to show the positional relationship between the phase shift unit 36M and the electrode 28M, the electrode 28M is schematically shown by a broken line. In the arrangement example of the phase shift unit 36M shown in FIG. 10, the simulation result of FIG. 9 shows that the two phase shifts at both ends in the three phase shift units 36M, 36M, 36M provided in the x-axis direction or the y-axis direction, respectively. The distance between the parts 36M and 36M is D3, and the change in the extraction efficiency when D3 is appropriately changed corresponds to the result obtained by calculation.

  As mentioned above, although the embodiment of the surface emitting semiconductor laser device of the present invention has been described, the present invention is not limited to the above embodiment. The semiconductor laser device 10 shown in FIG. 1 includes a cladding layer 14, an active layer 16, a buffer layer 18, a photonic crystal layer 20, a guide layer 22, a cladding layer 24, and a contact layer 26 on a main surface 12 a of a substrate 12. In addition, the light output surface S is provided, and the electrode 28 is provided on the light output surface S. However, the semiconductor laser device includes at least the active layer 16 and the photonic crystal layer 28 on the substrate 12, and has a light output surface S in a direction orthogonal to the main surface 12a, and the electrode 28 is disposed on the light output surface S. What is necessary is just to be provided. In particular, the buffer layer 18 is not necessarily provided when the photonic crystal layer 20 is not formed by etching.

  Further, although the active layer 16 and the photonic crystal layer 20 are provided in this order on the main surface 12a of the substrate 12, the photonic crystal layer 20 and the active layer 16 are provided in this order on the main surface 12a. May be.

  Moreover, the phase shift part should just be formed according to the planar view shape of the electrode 28. FIG. For example, if the shape of the electrode 28 in a plan view is circular, the shape of the region immediately below the edge is also circular. Therefore, the phase shift portion may be formed along a circular curve or a closed curve close to a circle. In this case, one phase shift portion is formed for the electrode 28.

  Further, the semiconductor laser device 10 has been described as having two phase shift portions 36x and 36y in the x-axis direction and the y-axis direction, respectively, as shown in FIG. 3, but in the vicinity immediately below the edges 28a and 28b of the electrode 28. If the phase shift units 36x and 36y are provided, the number of the phase shift units 36x and 36y is not particularly limited. Further, as shown in FIG. 3, even if the phase shift portions 36x and 36y are not formed so as to extend in the y-axis direction and the x-axis direction, for example, a closed curve is formed according to the planar view shape of the electrode 28. In this manner, the phase shift portion may be formed.

  Furthermore, in the embodiment, the columnar part 34 included in the photonic crystal layer 20 constitutes two diffraction grating groups Lx and Ly extending in the first and second directions orthogonal to each other, and each diffraction grating group Lx, In Ly, the arrangement of the columnar portions 34 is the same. However, the columnar portion 34 as a grating point may constitute two or more diffraction grating groups extending in different directions, and the arrangement state of the grating points in each diffraction grating group may be the same. In other words, when the columnar portions 34 as lattice points constitute a diffraction grating group extending in the first and second directions orthogonal to each other, the lattice points can be regarded as being arranged in a square lattice shape. The invention is not limited to this, and the lattice points may be arranged in a triangular lattice shape or a hexagonal lattice shape, and two or more diffraction grating groups extending in different directions may be configured. As described above, since the phase shift portion is formed according to the planar view shape of the electrode 28, it is possible to associate the planar view shape of the electrode 28 with the arrangement state of the lattice points in the vicinity immediately below the edge portion of the electrode 28. It is more preferable from the viewpoint of disposing the phase shift portion. For example, as shown in the embodiment, when the planar view shape of the electrode 28 is a square shape, the lattice points of the photonic crystal layer 20 are preferably arranged in a square lattice shape.

1 is a perspective view of an embodiment of a surface-emitting type semiconductor laser device according to the present invention. It is sectional drawing along the II-II line of FIG. FIG. 2 is a schematic diagram showing an arrangement relationship of lattice points in a photonic crystal layer of the surface emitting semiconductor laser element shown in FIG. 1. It is a schematic diagram which shows the basic composition for simulation of the surface emitting semiconductor laser element shown in FIG. It is drawing which shows the power density of the light output to the light output surface side from the photonic crystal layer in case the phase shift part is not introduce | transduced, and the photon density distribution in a photonic crystal layer. It is a schematic diagram showing the power density distribution of light output from the photonic crystal layer to the light output surface side and the photon density distribution in the photonic crystal layer when one phase shift portion is introduced in the center. FIG. 5 is a diagram showing a change in extraction efficiency with respect to a change in distance between phase shift portions when phase shift portions having the same phase shift amount are introduced at two locations in the x-axis direction shown in FIG. 4. FIG. 5 is a diagram showing a change in extraction efficiency with respect to a change in distance between phase shift portions when phase shift portions having different phase shift amounts are introduced at two locations in the x-axis direction shown in FIG. 4. FIG. 5 is a diagram illustrating a change in extraction efficiency with respect to a change in distance between two phase shift portions at both ends when phase shift portions are introduced at three positions in the x-axis direction illustrated in FIG. 4. It is drawing which shows the example of arrangement | positioning of the phase shift part with respect to an electrode at the time of introducing three phase shift parts in a x-axis direction and a y-axis direction.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Surface emitting semiconductor laser element, 12 ... Board | substrate, 12a ... Main surface, 16 ... Active layer, 20 ... Photonic crystal layer, 28 ... Electrode, 28a, 28a ... A pair of edge part (2nd edge part) ), 28b, 28b ... a pair of edges (first edge) of the electrode, 34 ... columnar parts (grating points), 36x, 36y ... phase shift parts, Lx, Ly ... diffraction grating groups, S ... light output surface .

Claims (4)

A surface emitting semiconductor laser element,
A substrate,
An active layer provided on the main surface of the substrate and generating light when carriers are injected;
A photonic crystal layer provided on the major surface of the substrate and optically coupled to the active layer;
A light output surface that outputs laser light generated by the surface-emitting semiconductor laser element, located on the opposite side of the substrate as viewed from the photonic crystal layer in a direction substantially orthogonal to the main surface;
An electrode provided on the light output surface and supplying the carrier to the active layer;
With
The photonic crystal layer diffracts a part of light having a predetermined wavelength included in the light generated in the active layer to the light output surface side, and another part of the light having the predetermined wavelength is substantially formed on the main surface. It has a two-dimensional photonic crystal structure confined in parallel planes,
The predetermined wavelength is a wavelength of the laser beam,
The electrode has at least one edge;
The surface-emitting type semiconductor laser device, wherein a phase shift portion is formed in the photonic crystal layer in the vicinity immediately below the edge portion. The plurality of grating points of the photonic crystal structure constitutes two or more diffraction grating groups,
Each of the diffraction grating groups extends in a different direction,
The grating points constituting each of the diffraction grating groups are arranged in the same arrangement relationship along the direction in which the diffraction grating groups extend between the diffraction grating groups,
2. The surface-emitting type semiconductor laser device according to claim 1, wherein each of the diffraction grating groups has the phase shift portion in the vicinity immediately below the edge portion. The plurality of lattice points of the photonic crystal structure constitute a first diffraction grating group and a second diffraction grating group extending in first and second directions orthogonal to each other,
The grating points constituting each of the first and second diffraction grating groups are arranged in the same arrangement relationship along the first and second directions in the first and second diffraction grating groups. And
The shape of the electrode in plan view is a substantially square shape, and the electrode has a pair of first edges facing each other and a pair of second edges facing each other.
The first and second edges extend in the first and second directions, respectively;
The said 1st and 2nd diffraction grating group has the said phase shift part in the immediate vicinity of each of a pair of said 1st edge part and a pair of said 2nd edge part, respectively. Surface emitting semiconductor laser device.   The phase shift portions corresponding to the pair of first edge portions and the pair of second edge portions extend in the first and second directions, respectively. Surface emitting semiconductor laser element.

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