JP5117028B2 - Surface emitting laser element and surface emitting laser element array - Google Patents

Description

  The present invention includes a surface emitting laser having a mesa post in which a plurality of semiconductor layers including an active layer are stacked and formed in a column shape, and emitting laser light in a direction perpendicular to the active layer from an aperture provided on the mesa post The present invention relates to an element and a surface emitting laser element array.

  A vertical cavity surface emitting laser (VCSEL) is a direction perpendicular to a stacked surface of a plurality of semiconductor layers including an active layer stacked on a substrate. The laser beam is emitted by resonating light. Unlike the conventional edge-emitting laser element, such a surface-emitting laser element does not require cleaving to provide a mirror as a resonator. Therefore, a large number of elements are arranged one-dimensionally or two-dimensionally on the same substrate. Can be easily arranged. In addition, the active layer volume is very small, laser oscillation is possible with an extremely low threshold current, and oscillation is possible with low power consumption. For this reason, surface emitting laser elements are attracting attention as various light sources for optical communication such as optical interconnection or other various application devices.

  Generally, a surface emitting laser element has a mesa post in which a plurality of semiconductor layers including an active layer stacked on a substrate are formed in a columnar shape by etching or the like, and emits laser light from an aperture provided on the mesa post. Usually, the mesa post is formed in a columnar shape or a truncated cone shape standing in the resonance direction of light, and the aperture is circular (see, for example, Patent Document 1). For this reason, the surface emitting laser element has a problem that the polarization direction of the emitted laser light is not determined in a predetermined direction, and polarization switching easily occurs when the operating current is changed. For example, in an optical communication system, excessive noise is generated, the operation becomes unstable, and it is difficult to increase the communication speed.

On the other hand, Patent Document 2 discloses a surface emitting laser element in which linearly polarized light polarized in a predetermined direction is emitted as laser light by applying different stresses in two orthogonal directions to the active layer. In this surface emitting laser element, an insulating film (SiNx film, SiO ₂ film, etc.) is formed at different temperatures in two directions perpendicular to a mesa post formed in a truncated quadrangular pyramid shape and having a rectangular aperture. The active layer is subjected to different stresses in two directions due to the difference in stress generated according to the difference in thermal expansion between the two directions.

JP 2004-319643 A Japanese Patent Publication No. 7-73139

  However, in the surface emitting laser element according to Patent Document 2, it is necessary to form two-direction insulating films that generate different stresses in different processes, which requires a lot of labor and time in the semiconductor wafer process. There was a problem that productivity was impaired. In addition, since the polarization direction of linearly polarized light emitted as laser light is limited to a direction perpendicular to any side of the rectangular aperture provided on the mesa post, the degree of freedom in selectivity of the polarization mode is impaired. There was a problem.

  The present invention has been made in view of the above, and includes a surface-emitting laser element and a surface-emitting laser element array that can be manufactured by a simple process and can emit laser light polarized in a desired direction. The purpose is to provide.

In order to solve the above-described problems and achieve the object, a surface emitting laser element according to the present invention has a mesa post in which a plurality of semiconductor layers including an active layer are stacked and formed in a columnar shape, and the mesa post is formed on the mesa post. In a surface-emitting laser element that emits laser light in a direction perpendicular to the active layer from a provided aperture, the surface-emitting laser element is integrally formed within a predetermined range including the aperture, and is in a predetermined direction within the stacked surface with respect to the active layer It is characterized by comprising a stress-applying film that applies stress to the.

In the surface emitting laser element according to the present invention as set forth in the invention described above, the stress applying film is most widely formed in the predetermined direction.

The surface emitting laser element according to the present invention is characterized in that, in the above-described invention, the stress applying film has optical transparency to the laser beam and is formed on the aperture.

In the surface emitting laser element according to the present invention as set forth in the invention described above, the stress applying film is a dielectric film.

In the surface-emitting laser device according to the present invention as set forth in the invention described above, the stress applying film is a dielectric multilayer film in which a plurality of dielectric layers having different compositions are laminated.

In the surface emitting laser element according to the present invention , in the above invention, the stress applying film is formed using at least one of SiO, SiN, a-Si, AlO, MgF, ITO, or TiO. Features.

A surface emitting laser element array according to the present invention includes a plurality of the surface emitting laser elements according to any one of the above inventions on the same substrate.

Further, in the surface emitting laser element array according to the present invention , in the above invention, the plurality of surface emitting laser elements are each subjected to stress in the same direction in the stacked surface with respect to the active layer by the stress applying film. It is characterized by being able to.

  According to the present invention, it is possible to provide a surface emitting laser element and a surface emitting laser element array that can be manufactured by a simple process and can emit laser light polarized in a desired direction.

  Exemplary embodiments of a surface emitting laser element and a surface emitting laser element array according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments. Moreover, in description of drawing, the same code | symbol is attached | subjected and shown to the same part.

(Embodiment 1)
First, the surface emitting laser element and the surface emitting laser element array according to the first embodiment of the present invention will be described. 1 to 3 are diagrams showing a main configuration of the surface emitting laser element 100 according to the first embodiment. FIG. 1 is a plan view, and FIGS. 2 and 3 are cross-sectional views taken along lines II-II and III-III shown in FIG. 1, respectively. As shown in these drawings, the surface emitting laser element 100 includes a lower DBR (Distributed Bragg Reflector) mirror 2, an N clad layer 3, an active layer 4, a current confinement layer 5, which are stacked on a semi-insulating substrate 1. A P clad layer 6, an upper DBR mirror 7, a P electrode 8 and an N electrode 9 are provided. Among these, the active layer 4, the current confinement layer 5, the P clad layer 6, and the upper DBR mirror 7 stacked on the N clad layer 3 are configured as mesa posts 10 formed in a columnar shape by an etching process or the like.

The lower DBR mirror 2 is formed as a semiconductor multilayer mirror in which a plurality of composite layers made of, for example, AlAs / GaAs are stacked. The thickness of each layer constituting the composite layer is λ / 4n (λ: oscillation wavelength, n: Refractive index). On the other hand, the upper DBR mirror 7 is formed, for example, as a dielectric multilayer mirror having a light transmittance of a predetermined transmittance as a whole by laminating a plurality of SiO ₂ and SiN _x as dielectric films.

  The current confinement layer 5 includes an opening 5a and a selective oxidation layer 5b. The current confinement layer 5 is formed of an Al-containing layer made of, for example, AlAs, and the selective oxidation layer 5b is formed on the annular zone by oxidizing the Al-containing layer by a predetermined range along the laminated surface from the outer peripheral portion. . The selective oxidation layer 5b has an insulating property, constricts the current injected from the P electrode 8 and concentrates it in the opening 5a, and increases the current density in the opening 5a.

  The active layer 4 has a three-layer quantum well structure made of, for example, GaInNAs / GaAs, and generates spontaneous emission light according to the current injected from the P electrode 8 and confined by the current confinement layer 5. The generated spontaneous emission light is amplified by being resonated in the vertical direction with respect to each layer including the active layer 4 between the lower DBR mirror 2 and the upper DBR mirror 7 and then provided on the upper surface portion of the upper DBR mirror 7. The laser beam is emitted from the aperture 7a serving as an emission window (transmission window). Here, the aperture 7 a is a circular region immediately above the opening 5 a in the upper surface portion of the upper DBR mirror 7.

  The P electrode 8 is laminated on the P clad layer 6 in a ring shape so as to surround a part of the upper DBR mirror 7 laminated immediately above the opening 5a along the laminated surface. On the other hand, the N electrode 9 is laminated on the N clad layer 3 in a C shape so as to surround the mesa post 10 along the laminated surface. These P electrode 8 and N electrode 9 are electrically connected to an external circuit (current supply circuit) (not shown) by a P extraction electrode 11 and an N extraction electrode 12 (see FIG. 1), respectively.

  Next, the upper DBR mirror 7 formed on the upper part of the mesa post 10 will be described in detail. As shown in FIG. 1, the upper DBR mirror 7 is formed by laminating an oval shape integrally with a mesa post 10 having a circular cross section in the stacking surface direction within a predetermined range including the aperture 7a. . As shown in FIG. 3, the end portion in the major axis direction of the oval upper DBR mirror 7 is formed from the upper surface portion of the P electrode 8 to the upper surface portion of the N cladding layer 3 through the side surface of the mesa post 10. ing. As a result, the upper DBR mirror 7 applies stress to the active layer 4 as a stress applying film in a predetermined direction within the laminated surface.

  Here, the stress that the upper DBR mirror 7 applies to the active layer 4 in a predetermined direction means the maximum stress in the asymmetric stress that the upper DBR mirror 7 exerts on the active layer 4 in the direction of the laminated surface. Corresponds to the stress exerted by the upper DBR mirror 7 in the direction in which the upper (longest) film is formed within the film forming range. That is, the upper DBR mirror 7 formed in an oval shape applies a maximum stress to the active layer 4 in the major axis direction of the oval shape, and generates a strain biased in the major axis direction. As a result, in the surface-emitting laser element 100, the laser light resonated through the active layer 4 is linearly polarized in the strain direction generated in the active layer 4 or polarized in the direction perpendicular to the strain direction. Are emitted as linearly polarized light.

  Whether the polarization direction is a strain direction or a direction perpendicular to the strain direction is determined by whether the stress applied to the active layer 4 by the upper DBR mirror 7 is a tensile stress or a compressive stress. In general, laser light is polarized in a direction perpendicular to the compression direction due to strain generated in the active layer. Therefore, the laser light emitted from the surface emitting laser element 100 is polarized in a direction perpendicular to the stress direction when the stress applied to the active layer 4 from the upper DBR mirror 7 is a compressive stress, and is a tensile stress, Polarized in the stress direction. The stress applied to the active layer 4 can be controlled to be either a compressive stress or a tensile stress depending on various film forming conditions such as a film forming material of the upper DBR mirror 7 and a film forming temperature. That is, in the surface emitting laser element 100, the polarization direction of the laser light can be controlled according to the film forming conditions of the upper DBR mirror 7.

  Further, in the surface emitting laser element 100, it is possible to set the major axis direction of the upper DBR mirror 7 formed into an oval shape in a desired direction along the laminated surface with respect to the substrate 1. Thus, the polarization direction of the laser light can be set to a desired direction. At this time, the lead-out directions of the P lead electrode 11 and the N lead electrode 12 can also be appropriately set according to the major axis direction of the upper DBR mirror 7.

  For example, the upper DBR mirror 7 as the stress applying film is formed on the entire surface of the element from the N clad layer 3 after laminating each layer from the active layer 4 to the P electrode 8 as the mesa post 10. 1 is formed by performing an etching process while leaving the oval portion shown in FIG. In other words, the upper DBR mirror 7 can be formed by performing a series of film formation processes combining film formation and etching once, and can be formed as an insulating film in the surface emitting laser element according to Patent Document 2 described above. Compared to the case where the film forming process is required more than once, it can be manufactured by a simple process. For this reason, the efficiency and throughput of device fabrication in the surface emitting laser device 100 are greatly improved.

  FIG. 4 is a diagram showing the surface emitting laser element array 200 according to the first embodiment. In the surface emitting laser element array 200, a plurality of surface emitting laser elements 100 are arranged in common with the substrate 1 in common. The P extraction electrode 11 and the N extraction electrode 12 of each surface emitting laser element 100 are individually or commonly electrically connected to an external current supply circuit, and emit light individually or simultaneously according to the injection current from the current supply circuit. Be controlled.

  Here, the upper DBR mirrors 7 of the surface emitting laser elements 100 in the surface emitting laser element array 200 are arranged with the major axis direction aligned in a predetermined direction (vertical direction in FIG. 4). As a result, in each surface emitting laser element 100, stress is applied to the active layer 4 in the same direction in the laminated surface, and the laser light that is linearly polarized light polarized in that direction is perpendicular to the substrate 1 Is injected into. In addition, the polarization direction of each surface emitting laser element 100 in the surface emitting laser element array 200, that is, the major axis direction of each upper DBR mirror 7 does not necessarily need to be aligned in the same direction, and should be set in any direction individually. You can also.

(Embodiment 2)
Next, a surface emitting laser element and a surface emitting laser element array according to a second embodiment of the present invention will be described. FIG. 5 is a cross-sectional view showing a configuration of the surface emitting laser element 300 according to the second embodiment, and shows a configuration in a cross section corresponding to the III-III section of the surface emitting laser element 100 shown in FIG. ing. As shown in this figure, the surface emitting laser element 300 includes an upper DBR mirror 13 instead of the upper DBR mirror 7 based on the configuration of the surface emitting laser element 100, and includes a protective film 14 that is a dielectric film. Further prepare.

  Here, the upper DBR mirror 13 is laminated on the P clad layer 6 in place of the upper DBR mirror 7 and the P electrode 8, and the P electrode 8 is laminated on the upper DBR mirror 13 in a ring shape. The protective film 14 is stacked on the upper DBR mirror 13 and is formed in an oval shape in the same manner as the upper DBR mirror 7 in the surface emitting laser element 100. In the surface emitting laser element 300, a region surrounded by the ring-shaped P electrode 8 on the upper surface portion of the upper DBR mirror 13 is provided as an aperture 13a serving as an emission window. Further, a stacked portion from the active layer 4 to the protective film 14 stacked on the N clad layer 3 is configured as a mesa post 15 formed in a columnar shape. Other configurations are the same as those of the surface emitting laser element 100, and the same components are denoted by the same reference numerals.

The upper DBR mirror 13 is formed, for example, as a semiconductor multilayer mirror in which a plurality of composite layers made of AlAs / GaAs are stacked. The thickness of each layer constituting the composite layer is λ / 4n (λ: oscillation wavelength, n: Refractive index). The protective film 14 is formed of a single-layer or multi-layer dielectric film made of, for example, SiO ₂ , SiN _x or the like, and has light transmittance with a predetermined transmittance at least in a region on the aperture 13a.

  Similar to the upper DBR mirror 7 described in the first embodiment, the protective film 14 is formed in an oval shape integrally with the mesa post 15 having a circular cross section in the stacking surface direction within a predetermined range including the aperture 13a. The long-axis direction end portions are formed from the upper surface portion of the P electrode 8 to the upper surface portion of the N clad layer 3 through the side surface portion of the mesa post 15. As a result, the protective film 14 applies stress to the active layer 4 as a stress applying film in a predetermined direction in the laminated surface, that is, the major axis direction.

  As a result, in the surface emitting laser element 300, like the surface emitting laser element 100, linearly polarized light polarized in the major axis direction of the protective film 14 or in a direction perpendicular to the major axis direction is emitted as laser light. Which direction the polarization direction of the emitted laser light is is determined by the film forming conditions such as the film forming material and the film forming temperature of the protective film 14, in other words, the film forming conditions. It is controlled by. Further, the major axis direction of the protective film 14 can be set to a desired direction along the laminated surface similarly to the upper DBR mirror 7, thereby setting the polarization direction of the laser light to a desired direction. can do.

  Further, the protective film 14 as a stress applying film can be formed by performing a series of film forming processes combining film formation and etching once as in the case of the upper DBR mirror 7. Compared to the case where two or more steps are required, such as an insulating film in such a surface emitting laser element, it can be manufactured by a simple process. For this reason, the efficiency and throughput of device fabrication in the surface emitting laser device 300 are greatly improved.

  Note that, in the surface-emitting laser element array according to the second embodiment, a plurality of surface-emitting laser elements 300 are arrayed and formed integrally with the substrate 1 in the same manner as the surface-emitting laser element array 200 described above. The polarization direction of the laser light emitted from each surface emitting laser element 300 in this surface emitting laser element array can be aligned in the same direction according to the major axis direction of each protective film 14, but is set individually. It is also possible to do.

  So far, the best mode for carrying out the present invention has been described as the first and second embodiments. However, the present invention is not limited to the above-described first and second embodiments, and may be within the scope of the present invention. Various modifications are possible.

  For example, in the first and second embodiments described above, the upper DBR mirror 7 or the protective film 14 has been described as being formed from the upper surface portion of the mesa post to the bottom surface portion (N clad layer 3) via the side surface. It is not necessary to extend the film range to the bottom surface, and as long as sufficient stress can be applied to the active layer 4 in a predetermined direction, the film can be formed up to the side surface of the mesa post or only on the top surface of the mesa post. Good.

  In the second embodiment, the protective film 14 is formed on the aperture 13a. However, the protective film 14 is not necessarily formed on the aperture 13a. For example, the entire film is formed integrally. If so, the region on the aperture 13a may be removed later by etching or the like. Furthermore, as long as the protective film 14 can apply sufficient stress in a predetermined direction to the active layer 4 as a whole, a desired portion in the oval film-forming range can be removed by etching or the like. . Thereby, the magnitude of the stress applied from the protective film 14 to the active layer 4 can be controlled. This can be similarly applied to the upper DBR mirror 7 in the first embodiment. That is, as long as sufficient stress can be applied to the active layer 4 in a predetermined direction, the upper DBR mirror 7 can be appropriately removed from the region other than the aperture 7a portion in the oval film-forming range. In addition, the film-forming range of the upper DBR mirror 7 and the protective film 14 is not limited to an oval shape, and may be, for example, a rectangular shape or other shapes.

In the first and second embodiments described above, the dielectric film constituting the upper DBR mirror 7 and the protective film 14 has been described as being formed using, for example, SiO ₂ , SiN _x or the like. It is not necessary to interpret the limitation to these two, and a film formed using at least one of SiO, SiN, a-Si, AlO, MgF, ITO, or TiO may be used in appropriate combination in a single layer or multiple layers. Can do. Furthermore, although it has been described that the semiconductor composite layer constituting the lower DBR mirror 2 and the upper DBR mirror 13 is formed on the basis of a semiconductor composite layer represented by AlAs / GaAs, generally, Al _x Ga _x-1 As / Any semiconductor composite layer represented by Al _y Ga _y-1 As (0 ≦ x, y ≦ 1) may be used.

  In the first and second embodiments described above, the surface emitting laser elements 100 and 300 have been described as having an intracavity structure in which an injection current does not flow to at least one of the upper DBR mirror or the lower DBR mirror. However, the present invention is not limited to this, and a configuration may be employed in which a P electrode is provided above the upper DBR mirror and an N electrode is provided below the lower DBR mirror. Further, in the surface emitting laser elements 100 and 300, the P electrode 8 is provided on the upper side with respect to the active layer 4, and the N electrode 9 is provided on the lower side. However, the polarities of the upper and lower electrodes are described. May be replaced. In this case, the lower DBR mirror and the upper DBR mirror are appropriately doped with p-type or n-type impurities.

  In the first and second embodiments described above, the surface emitting laser element array according to the present invention has been described as being configured by arranging a plurality of surface emitting laser elements 100 or 300 in one direction. There is no need for limitation, and a two-dimensional array may be used. At this time, the polarization direction of the laser light emitted from each of the surface emitting laser elements 100 or 300 to be arranged is set individually in accordance with the major axis direction of the upper DBR mirror 7 or the protective film 14. You can also

  Each layer provided on the substrate 1 of the surface emitting laser elements 100 and 300 described above is formed by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or the like. However, the present invention is not limited to these two film forming methods, and various film forming methods can be appropriately selected and used.

It is a top view which shows the structure of the surface emitting laser element concerning Embodiment 1 of this invention. It is sectional drawing which shows the II-II cross section shown in FIG. It is sectional drawing which shows the III-III cross section shown in FIG. It is a top view which shows the arrangement structure of the surface emitting laser element array concerning Embodiment 1 of this invention. It is sectional drawing which shows the structure of the surface emitting laser element concerning Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower DBR mirror 3 N clad layer 4 Active layer 5 Current confinement layer 5a Opening 5b Selective oxidation layer 6 P clad layer 7 Upper DBR mirror 7a Aperture 8 P electrode 9 N electrode 10 Mesa post 11 P lead electrode 12 N lead electrode 13 Upper DBR mirror 13a Aperture 14 Protective film 15 Mesa post 100,300 Surface emitting laser element 200 Surface emitting laser element array

Claims (6)

A lower DBR mirror, a plurality of semiconductor layers including an active layer, a mesa post formed in a columnar shape, and an upper DBR mirror formed on the mesa post; and the upper DBR mirror In a surface emitting laser element that emits laser light from an aperture provided on the upper surface portion of
The upper DBR mirror is formed of a dielectric multilayer film having optical transparency to the laser beam,
The cross section of the upper DBR mirror in the stacking surface direction has an elongated shape having a major axis in a predetermined direction with respect to the circular mesa post, and is formed from the upper surface portion to the side surface of the mesa post in the major axis direction. A surface emitting laser element characterized by comprising:   The surface emitting according to claim 1, wherein the upper DBR mirror applies compressive stress to the active layer, and the laser beam is polarized in a direction perpendicular to the direction of the major axis. Laser element. 2. The surface emitting laser element according to claim 1, wherein the upper DBR mirror applies a tensile stress to the active layer, and the laser light is polarized in the direction of the major axis.   A surface-emitting laser element array comprising a plurality of the surface-emitting laser elements according to claim 1 on the same substrate.   5. The surface emitting laser element according to claim 4, wherein the plurality of surface emitting laser elements are arranged with the major axis direction of the upper DBR mirror of each surface emitting laser element being aligned in a certain direction. array.   The plurality of surface emitting laser elements are arranged with the major axis direction of the upper DBR mirror of each surface emitting laser element being individually set to an arbitrary direction. Surface emitting laser element array.

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