JP2020053674A - Vertical cavity surface emitting laser - Google Patents

Abstract

To provide a vertical cavity surface emitting laser having a structure in which a change in differential resistance is less sensitive to variations in the size of a current aperture.SOLUTION: A vertical cavity surface emitting laser includes a first semiconductor layer having a first Al composition, a first stack including a second semiconductor layer having a second Al composition larger than the first Al composition, a current confinement structure including a current aperture and a current blocker, a first compound semiconductor layer adjacent to the current confinement structure, and a second compound semiconductor layer adjacent to the first stack and the first compound semiconductor layer. The first compound semiconductor layer has a first aluminum profile that monotonically changes from the first Al lower limit composition to the first Al upper limit composition within a range larger than the first Al composition and smaller than the second Al composition, from the first stack to the current confinement structure. The second compound semiconductor layer has an Al composition that is greater than the first Al composition and equal to or less than the first Al upper limit composition.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a vertical cavity surface emitting laser.

  Non-Patent Document 1 discloses a surface emitting laser.

Kimiyoshi Fukatsu et al., IEEE Photonics Technology Letters, vol.20, no.11, pp.909-911, 2008.

  Some vertical cavity surface emitting lasers use an oxide confinement structure for confining current. The oxide confinement structure is fabricated as follows: forming a semiconductor post including a semiconductor layer with a high Al composition; oxidizing the semiconductor post in an oxidizing atmosphere to obtain an oxide confinement structure having a current aperture. The oxide confinement structure is formed from a semiconductor layer having the highest Al composition in a semiconductor post. Oxidation of the semiconductor layer in an oxidizing atmosphere is a factor in manufacturing variations during the manufacturing process. In the vertical cavity surface emitting laser, various sizes and shapes are required for the semiconductor posts from the characteristic surface, and various sizes are required for the current aperture.

  An object of one aspect of the present invention is to provide a vertical cavity surface emitting laser having a structure in which a change in differential resistance is not so sensitive to a change in the size of a current aperture.

  A vertical cavity surface emitting laser according to one aspect of the present invention includes: an active layer provided in a semiconductor post; a first stack provided in the semiconductor post for distributed Bragg reflection; a current aperture; A current blocker surrounding the current aperture; a current confinement structure provided in the semiconductor post; and a current confinement structure provided in the semiconductor post, wherein the current confinement structure is provided between the first stack and the current confinement structure. An adjacent first compound semiconductor layer, and a second compound semiconductor provided in the semiconductor post and adjacent to the first stack and the first compound semiconductor layer between the first stack and the first compound semiconductor layer. Wherein the current aperture comprises a III-V compound semiconductor containing aluminum as a group III constituent element, and the current blocker comprises a group III acid. The first stack includes first semiconductor layers and second semiconductor layers alternately arranged, the first semiconductor layer includes a first III-V semiconductor having a first Al composition, and the second The semiconductor layer has a second III-V semiconductor having a second Al composition larger than the first Al composition, and each of the first compound semiconductor layer and the second compound semiconductor layer includes an aluminum element as a group III constituent element; The current constriction from the first stack is changed from a first Al lower limit composition within a range larger than the first Al composition and smaller than the second Al composition to a first Al upper limit composition larger than the first Al lower composition. The second compound semiconductor layer has a first aluminum profile that changes monotonically in the direction of the structure, and the second compound semiconductor layer has a first aluminum profile that is larger than the first Al composition and smaller than the first Al upper composition. Has a composition, said current APA - said III-V compound semiconductor char has a larger Al composition than the first 2Al composition.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the invention, which proceeds with reference to the accompanying drawings.

  As described above, according to one aspect of the present invention, there is provided a vertical cavity surface emitting laser having a structure in which a change in differential resistance is not so sensitive to a change in the size of a current aperture.

FIG. 1 is a drawing showing a vertical cavity surface emitting laser according to the present embodiment. FIG. 2 is a drawing showing a structure of a vertical cavity surface emitting laser according to an experimental example. FIG. 3 is a drawing illustrating the structure of the vertical cavity surface emitting laser according to the first embodiment. FIG. 4 is a drawing illustrating the structure of the vertical cavity surface emitting laser according to the second embodiment. FIG. 5 is a drawing illustrating the structure of the vertical cavity surface emitting laser according to the third embodiment. FIG. 6 is a drawing showing the structure of the vertical cavity surface emitting laser according to the fourth embodiment. FIG. 7 is a drawing showing the structure of the vertical cavity surface emitting laser according to the fifth embodiment. FIG. 8 is a drawing showing the structure of a vertical cavity surface emitting laser according to Example 6. FIG. 9 is a drawing showing the structure of the vertical cavity surface emitting laser according to the seventh embodiment. FIG. 10 is a drawing showing the structure of the vertical cavity surface emitting laser according to Example 8. FIG. 11 is a drawing showing characteristics of the vertical cavity surface emitting lasers according to the experimental example and Examples 1 to 4. FIG. 12 is a drawing showing the results of reliability tests of the vertical cavity surface emitting lasers in the experimental example and Examples 1 to 4. FIG. 13 is a drawing showing the results of a reliability test of the vertical cavity surface emitting lasers in Examples 5 to 8. FIG. 14 is a view showing main steps in a method of manufacturing the vertical cavity surface emitting laser according to the present embodiment. FIG. 15 is a drawing schematically showing a current confinement structure in the first portion and the second portion shown in FIGS. 3 to 6 and 7 to 11. FIG. 16 is a drawing showing the structure of the vertical cavity surface emitting laser according to the ninth embodiment. FIG. 17 is a diagram illustrating characteristics of the vertical cavity surface emitting laser according to the ninth embodiment. FIG. 18 is a drawing showing the structure of the vertical cavity surface emitting laser according to Example 10. FIG. 19 is a drawing illustrating characteristics of the vertical cavity surface emitting laser according to the tenth embodiment. FIG. 20 is a diagram illustrating characteristics of the vertical cavity surface emitting lasers according to the ninth and tenth embodiments.

  Some specific examples will be described.

  A vertical cavity surface emitting laser according to a specific example includes: (a) an active layer provided in a semiconductor post; (b) a first lamination provided in the semiconductor post for distributed Bragg reflection; A current confinement structure provided in the semiconductor post, comprising a current aperture and a current blocker surrounding the current aperture; and (d) the first stack and the current confinement structure provided in the semiconductor post. A first compound semiconductor layer adjacent to the current constriction structure between the first stack and the first stack, and (e) provided in the semiconductor post, between the first stack and the first compound semiconductor layer. A second compound semiconductor layer adjacent to the first compound semiconductor layer, wherein the current aperture includes a III-V compound semiconductor containing aluminum as a group III constituent element. The locker includes a group III oxide, the first stack includes first and second semiconductor layers alternately arranged, and the first semiconductor layer includes a first III-V semiconductor having a first Al composition. The second semiconductor layer has a second III-V semiconductor having a second Al composition larger than the first Al composition, and each of the first compound semiconductor layer and the second compound semiconductor layer is a group III constituent element. The first compound semiconductor layer including an aluminum element, the first compound semiconductor layer has a first Al lower limit composition within a range larger than the first Al composition and smaller than the second Al composition, and a first Al upper limit composition larger than the first Al lower composition, The second compound semiconductor layer has a first aluminum profile that monotonically changes from the stack to the current confinement structure, and the second compound semiconductor layer is larger than the first Al composition. Having Al composition than the upper limit composition, said current APA - said III-V compound semiconductor char has a larger Al composition than the first 2Al composition.

  According to the vertical cavity surface emitting laser, the first compound semiconductor layer adjacent to the current confinement structure has a first Al lower limit composition larger than the first Al composition of the first stack. From this first Al lower limit composition, the first aluminum profile monotonously changes in the direction from the first stack to the current confinement structure. An Al composition larger than the first Al composition and smaller than the first Al upper limit composition is given to the first stacked layer and the second compound semiconductor layer adjacent to the first compound semiconductor layer. The first compound semiconductor layer and the second compound semiconductor layer make it possible to avoid that the differential resistance in the vertical cavity surface emitting laser strongly depends on the variation of the current aperture size.

  In addition, the band gap of a III-V compound semiconductor containing aluminum as a group III constituent element increases with an increase in the Al composition. However, the second compound semiconductor layer having an Al composition larger than the first Al composition is effective for reducing the differential resistance.

  The second compound semiconductor layer can be provided with an Al composition that is greater than the first Al composition and equal to or less than the first Al lower limit composition.

  In the vertical cavity surface emitting laser according to the specific example, the first Al lower limit composition is larger than half the difference between the second Al composition and the first Al composition.

  According to the vertical cavity surface emitting laser, the second compound semiconductor layer having a small composition range in the Al composition gradient of the first compound semiconductor layer and a large Al composition is effective in reducing the differential resistance.

  In the vertical cavity surface emitting laser according to the specific example, the first Al lower limit composition is in a range of 0.25 or more, and the Al composition of the second compound semiconductor layer is the first Al of the first compound semiconductor layer. A lower limit composition, wherein the first aluminum profile has the Al composition of the current aperture at an interface between the current aperture and the first compound semiconductor layer.

  According to the vertical cavity surface emitting laser, a continuous aluminum profile can be provided for the current aperture and the arrangement of the first compound semiconductor layer and the second compound semiconductor layer. Also, the first Al lower limit composition smaller than 0.25 increases the variation of the differential resistance with respect to the size of the current aperture. Moreover, the first Al lower limit composition larger than 0.75 lowers the reflectance in Bragg reflection.

  The difference in Al composition between the current aperture of the current confinement structure and the second compound semiconductor layer is smaller than the difference in Al composition between the first semiconductor layer and the second semiconductor layer in the first stack.

  In a vertical cavity surface emitting laser according to a specific example, the first compound semiconductor layer includes a first portion and a second portion that are sequentially arranged in a direction from the current confinement structure to the first stack. The aluminum profile has a first rate of change and a second rate of change at each point within the first portion and the second portion, wherein the first rate of change is a percentage of the thickness of the first compound semiconductor layer. It has an absolute value smaller than the absolute value of the linear change rate of the difference between the first Al upper limit composition and the first Al lower limit composition, and the absolute value of the first change rate is smaller than the absolute value of the second change rate.

  According to the vertical cavity surface emitting laser, the first compound semiconductor layer can have an aluminum profile that gradually changes near the current confinement structure. When a gradual change rate of the Al composition is given in the vicinity of the current confinement structure, the change in long-term operation characteristics becomes small.

  Specifically, the first change rate has an absolute value smaller than the absolute value of the linear change rate of the difference between the first Al upper limit composition and the first Al lower limit composition with respect to the thickness of the first compound semiconductor layer. The absolute value of the rate is smaller than the absolute value of the second rate of change.

  A vertical cavity surface emitting laser according to a specific example includes a second stack provided in the semiconductor post for the distributed Bragg reflection, and a second stack provided in the semiconductor post and the second stack and the current confinement structure. A third compound semiconductor layer adjacent to the current confinement structure between the second stack and the third compound semiconductor layer, provided in the semiconductor post, between the second stack and the third compound semiconductor layer; And a fourth compound semiconductor layer adjacent to the third compound semiconductor layer, wherein the second stack includes first semiconductor layers and second semiconductor layers alternately arranged, and the first semiconductor layer has a third Al-type third semiconductor layer. V semiconductor, the second semiconductor layer includes a fourth III-V semiconductor having a fourth Al composition larger than the third Al composition, and the third compound semiconductor layer and the fourth compound semiconductor layer are group III structures. The third compound semiconductor layer includes an aluminum element as an element, and the third compound semiconductor layer has a second Al upper limit composition larger than the second Al lower limit composition, the second Al upper limit composition being larger than the third Al composition and smaller than the fourth Al composition. A second aluminum profile monotonously changing in a direction from the second stack to the current confinement structure, wherein the fourth compound semiconductor layer has an Al composition larger than the third Al composition and equal to or smaller than the second Al lower limit composition; Having.

  According to the vertical cavity surface emitting laser, the second compound and the third compound semiconductor layer adjacent to the current confinement structure have a second Al lower limit composition larger than the third Al composition of the second stack. From the second Al lower limit composition, the second aluminum profile in the third compound semiconductor layer monotonously changes in the direction from the second stack to the current confinement structure. An Al composition that is larger than the third Al composition and equal to or less than the second Al lower limit composition is given to the second compound semiconductor layer and the fourth compound semiconductor layer adjacent to the third compound semiconductor layer. The third compound semiconductor layer and the fourth compound semiconductor layer can avoid that the differential resistance of the vertical cavity surface emitting laser strongly depends on the variation of the current aperture size.

  A III-V compound semiconductor containing aluminum as a group III constituent element has a band gap that increases with an increase in the Al composition. However, the fourth compound semiconductor layer having an Al composition larger than the third Al composition is effective for reducing the differential resistance.

  In the vertical cavity surface emitting laser according to the specific example, the second Al lower limit composition is 0.25 or more, and the Al composition of the fourth compound semiconductor layer is the second Al lower limit composition of the third compound semiconductor layer. Wherein the second aluminum profile has the Al composition of the current aperture at an interface between the current aperture and the third compound semiconductor layer.

  According to the vertical cavity surface emitting laser, a continuous aluminum profile can be provided for the current aperture and the arrangement of the first compound semiconductor layer and the second compound semiconductor layer. Also, the differential resistance increases the variation with respect to the size of the current aperture in the first Al lower limit composition smaller than 0.25. The second Al lower limit composition larger than 0.75 lowers the reflectance in Bragg reflection.

  The difference in Al composition between the current aperture of the current confinement structure and the fourth compound semiconductor layer is smaller than the difference in Al composition between the first semiconductor layer and the second semiconductor layer in the second stack.

  In a vertical cavity surface emitting laser according to a specific example, the third compound semiconductor layer includes a first portion and a second portion sequentially arranged in a direction from the current confinement structure to the second lamination. The aluminum profile has a third rate of change and a fourth rate of change at respective points within the first portion and the second portion, wherein the third rate of change is a percentage of the thickness of the third compound semiconductor layer. It has an absolute value smaller than the absolute value of the linear change rate of the difference between the second Al upper limit composition and the second Al lower limit composition, and the absolute value of the third change rate is smaller than the absolute value of the fourth change rate.

  According to the vertical cavity surface emitting laser, the third compound semiconductor layer can have an aluminum profile that gradually changes near the current confinement structure. When a small change rate of the Al composition is given in the vicinity of the current confinement structure, the change in long-term operation characteristics becomes small.

  A vertical cavity surface emitting laser according to a specific example is provided in the semiconductor post, a second stack for distributed Bragg reflection, and provided in the semiconductor post, between the second stack and the current confinement structure. And a third compound semiconductor layer adjacent to the current confinement structure, wherein the second stack includes first and second semiconductor layers alternately arranged, and the first semiconductor layer includes a third Al layer. A third III-V semiconductor having a composition, wherein the second semiconductor layer has a fourth III-V semiconductor having a fourth Al composition larger than the third Al composition, and the third compound semiconductor layer is a group III constituent element The third compound semiconductor layer including an aluminum element, wherein the third compound semiconductor layer moves from the second Al lower limit composition of less than 0.25 to a second Al upper limit composition larger than the second Al lower limit composition, from the second stack to the current confinement structure. A second aluminum profile that varies monotonically in the direction.

  According to the vertical cavity surface emitting laser, the fourth compound semiconductor layer having an Al composition equal to or less than the second Al lower limit composition can increase the change in the refractive index at the interface between the fourth compound semiconductor layer and the second stack.

  The findings of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, an embodiment of a vertical cavity surface emitting laser will be described with reference to the accompanying drawings. Where possible, identical parts are given the same reference numerals.

  FIG. 1 is a partially cutaway view showing a vertical cavity surface emitting laser according to the present embodiment. The vertical cavity surface emitting laser 11 includes an active layer 31, a first stack 33, a current confinement structure 35, a first compound semiconductor layer 37, and a second compound semiconductor layer 39. The active layer 31, the first stack 33, the current confinement structure 35, the first compound semiconductor layer 37, and the second compound semiconductor layer 39 are provided in the post 17. The current confinement structure 35, the first compound semiconductor layer 37, the second compound semiconductor layer 39, and the first stack 33 are arranged in the direction of the first axis Ax1. In the vertical cavity surface emitting laser to be described subsequently, the current confinement structure 35, the first compound semiconductor layer 37, and the second compound semiconductor layer 39 are disposed between the first stack 33 and the active layer 31.

  The first stack 33 includes first and second semiconductor layers 41 and 43 alternately arranged for distributed Bragg reflection. Each of the first semiconductor layers 41 has a first III-V semiconductor having a first Al composition C41AL, and each of the second semiconductor layers 43 has a second III-V semiconductor having a second Al composition C43AL larger than the first Al composition C41AL. .

  The current confinement structure 35 includes a current aperture 35a and a current blocker 35b surrounding the current aperture 35a. The current aperture 35a includes a III-V compound semiconductor including an aluminum element as a group III constituent element. The current blocker 35b includes a group III oxide and surrounds the current aperture 35a. The current aperture 35a has a thickness in the range of 10 to 50 nm.

  The first compound semiconductor layer 37 is in contact with the current confinement structure 35 between the first stack 33 and the current confinement structure 35. The second compound semiconductor layer 39 is in contact with the first stack 33 and the first compound semiconductor layer 37 between the first stack 33 and the first compound semiconductor layer 37. Each of the first compound semiconductor layer 37 and the second compound semiconductor layer 39 contains an aluminum element as a group III constituent element.

  The first compound semiconductor layer 37 has an Al composition C37AL on a first aluminum profile (PF1) defined on a first axis Ax1, and the Al composition C37AL is directed from the first stack 33 to the current confinement structure 35. Then, the first Al lower limit composition C1MN37 monotonously changes to the first Al upper limit composition C1MX37. The first Al lower limit composition C1MN37 is in a range larger than the first Al composition C41AL and smaller than the second Al composition C43AL, and the first Al upper limit composition C1MX37 is larger than the first Al lower limit composition C1MN37.

  The second compound semiconductor layer 39 has an Al composition C39AL that is larger than the first Al composition C41AL and is equal to or less than a first Al upper composition C1MX37, and the Al composition C39AL can be equal to or less than the first Al lower composition C1MN37. In this embodiment, the Al composition C39AL can be substantially constant. The III-V compound semiconductor of the current aperture 35a has an Al composition CAPAL larger than the second Al composition C43AL.

  According to the vertical cavity surface emitting laser 11, a first Al lower limit composition C1MN37 that is larger than the first Al composition C41AL of the first stack 33 is given to the first compound semiconductor layer 37 adjacent to the current confinement structure. From the first Al lower limit composition C1MN37, the first aluminum profile PF1 monotonously changes in the first compound semiconductor layer 37 in the direction from the first stack 33 to the current confinement structure 35. An Al composition C39AL that is greater than the first Al composition C41AL and equal to or less than the first Al lower composition C1MN37 is given to the second compound semiconductor layer 39 adjacent to both the first stack 33 and the first compound semiconductor layer 37. The first compound semiconductor layer 37 and the second compound semiconductor layer 39 can avoid that the differential resistance in the vertical cavity surface emitting laser 11 strongly depends on the variation of the current aperture size.

  The first aluminum profile PF1 has a first Al upper limit composition C1MX37 at the interface between the current aperture 35a and the first compound semiconductor layer 37. The first Al upper limit composition C1MX37 is larger than the Al composition C39AL of the second compound semiconductor layer 39.

  In addition, a III-V compound semiconductor containing aluminum as a group III constituent element has a band gap that increases with an increase in the Al composition, and a large band gap generates a large specific resistance. However, providing the second compound semiconductor layer 39 with an Al composition C39AL larger than the first Al composition C41AL is effective in reducing the differential resistance in the vertical cavity surface emitting laser 11. Specifically, the second compound semiconductor layer 39 having an Al composition C39AL of 0.25 or more gives the vertical cavity surface emitting laser 11 a low differential resistance. Further, the Al composition C39AL of the second compound semiconductor layer 39 can be 0.3 or more.

  The Al composition C39AL of the second compound semiconductor layer 39 is preferably larger than half ((C43AL-C41AL) / 2) of the difference between the second Al composition C43AL and the first Al composition C41AL.

  The first compound semiconductor layer 37 is preferably provided with a first Al lower limit composition C1MN37 of 0.25 or more. In a III-V compound semiconductor containing aluminum as a group III constituent element, the band gap increases as the Al composition increases, and the increase in the band gap increases the specific resistance. However, the first compound semiconductor layer 37 having the first Al lower limit composition C1MN37 of 0.25 or more gives the vertical cavity surface emitting laser 11 a low differential resistance. Further, it is preferable to give 0.3 or more to the first Al lower limit composition C1MN37 of the first compound semiconductor layer 37.

  The first compound semiconductor layer 37 is preferably provided with a first Al lower limit composition C1MN37 of 0.75 or less. According to the first Al lower limit composition C1MN37 of 0.75 or less, the reflectivity of the upper distributed Bragg reflector including the first stack 33, the current confinement structure 35, the first compound semiconductor layer 37, and the second compound semiconductor layer 39 is remarkable. Significant degradation can be avoided. Further, 0.70 or less is preferably given to the first Al lower limit composition C1MN37 of the first compound semiconductor layer 37.

  The first Al lower limit composition C1MN37 of the first compound semiconductor layer 37 is preferably larger than half ((C43AL-C41AL) / 2) of the difference between the second Al composition C43AL and the first Al composition C41AL. According to the vertical cavity surface emitting laser 11, the first compound semiconductor layer 37 having the small Al gradient composition and the second compound semiconductor layer having the large Al composition are effective in reducing the differential resistance.

  Referring to FIG. 1, the first aluminum profile PF1 is continuous in the current confinement structure 35, the first compound semiconductor layer 37, and the second compound semiconductor layer 39 with respect to coordinates on the first axis Ax1. Specifically, the Al composition C39AL of the second compound semiconductor layer 39 may be equal to the first Al lower limit composition C1MN37 of the first compound semiconductor layer 37. The Al composition CAPAL of the current aperture 35a may be equal to the first Al upper limit composition C1MX37 of the first compound semiconductor layer 37. The first aluminum profile PF <b> 1 monotonously changes in the first compound semiconductor layer 37. Specifically, the differential coefficient of the first aluminum profile PF1 is equal to or greater than zero in the first compound semiconductor layer 37, and is greater than zero in at least a portion of the first compound semiconductor layer 37 (or the first aluminum profile PF1 has a differentiating coefficient). The differential coefficient is equal to or smaller than zero in the first compound semiconductor layer 37 and smaller than zero in at least a part of the first compound semiconductor layer 37).

  According to the vertical cavity surface emitting laser 11, a continuous aluminum profile can be provided to the arrangement of the current aperture 35a, the first compound semiconductor layer 37, and the second compound semiconductor layer 39.

  Further, according to the first Al lower limit composition C1MN37 and the Al composition C39AL larger than 0.25, the differential resistance becomes insensitive to the variation in the size of the current aperture.

  In the present embodiment, the absolute value of the Al composition difference (CAPAL-C39AL) between the current aperture 35a of the current constriction structure 35 and the second compound semiconductor layer 39 is equal to the absolute value of the second semiconductor layer 43 in the first stack 33. It is smaller than the absolute value of the difference (C43AL-C41AL) in the Al composition between the first semiconductor layer 41 and the semiconductor layer 41.

  In this embodiment, the first stack 33 has a sharp change in the Al composition at the interface between the first semiconductor layer 41 and the second semiconductor layer 43.

  According to the vertical cavity surface emitting laser 11, the change in the differential resistance with respect to the change in the current aperture size is caused by the large Al composition of the first compound semiconductor layer 39 and the second compound semiconductor layer 39 adjacent to the current constriction structure 35. It is reduced by the gentle composition gradient of the layer 37.

  Referring to FIG. 1, the vertical cavity surface emitting laser 11 further includes a second stack 45, a third compound semiconductor layer 57, and a fourth compound semiconductor layer 59. The second stack 45, the third compound semiconductor layer 57, and the fourth compound semiconductor layer 59 are provided in the post 17. The second stack 45, the fourth compound semiconductor layer 59, the third compound semiconductor layer 57, the current confinement structure 35, the first compound semiconductor layer 37, the second compound semiconductor layer 39, and the first stack 33 have a first axis Ax1. Arranged in a direction.

  The second stack 45 includes first semiconductor layers 51 and second semiconductor layers 53 alternately arranged for distributed Bragg reflection. Each of the first semiconductor layers 51 has a third III-V semiconductor having a third Al composition C51AL, and each of the second semiconductor layers 53 has a fourth III-V semiconductor having a fourth Al composition C53AL larger than the third Al composition C51AL. .

  The third compound semiconductor layer 57 is in contact with the current confinement structure 35 between the second stack 45 and the current confinement structure 35. The fourth compound semiconductor layer 59 is in contact with the second stack 45 and the third compound semiconductor layer 57 between the second stack 45 and the third compound semiconductor layer 57. Each of the third compound semiconductor layer 57 and the fourth compound semiconductor layer 59 contains an aluminum element as a group III constituent element.

  Third compound semiconductor layer 57 has Al composition C57AL defined on first axis Ax1. The Al composition C57AL monotonically changes from the second Al lower limit composition C2MN57 to the second Al upper limit composition C2MX57 in the direction from the second stack 45 to the current confinement structure 35. The second Al upper limit composition C2MX57 is larger than the second Al lower limit composition C2MN57.

  The second aluminum profile PF2 has a second Al upper limit composition C2MX57 at the interface between the current aperture 35a and the third compound semiconductor layer 57, and is equal to the Al composition CAPAL of the current aperture 35a in this embodiment. The second Al upper limit composition C2MX57 is larger than the Al composition C59AL of the fourth compound semiconductor layer 59.

  If possible, the second Al lower limit composition C2MN57 of the third compound semiconductor layer 57 may be 0.25 or more, and the second Al lower limit composition C2MN57 of the third compound semiconductor layer 57 may be 0.75 or less. .

  Further, the third compound semiconductor layer 57 can make contact with the second stack 45.

  Furthermore, the second Al lower limit composition C2MN57 can be made equal to the third Al composition C51AL at the interface between the third compound semiconductor layer 57 and the second stack 45. In the current aperture 53a and the third compound semiconductor layer 57, the second aluminum profile PF2 is continuous.

  If necessary, the second Al lower limit composition C2MN57 can be in a range larger than the third Al composition C51AL and smaller than the fourth Al composition C53AL.

  The fourth compound semiconductor layer 59 has an Al composition C59AL larger than the third Al composition C51AL and equal to or smaller than the second Al lower limit composition C2MN57. The fourth Al composition C53AL is smaller than the Al composition CAPAL of the III-V compound semiconductor of the current aperture 35a.

  According to the vertical cavity surface emitting laser 11, the third compound semiconductor layer 57 adjacent to the current confinement structure 35 is provided with the second lower limit composition C2MN57 larger than the third Al composition C51AL of the second stack 45. From the second Al lower limit composition C2MN57, the second aluminum profile PF2 monotonously changes in the direction from the second stack 45 to the current confinement structure 35. An Al composition C59AL that is larger than the third Al composition C51AL and equal to or less than the second Al lower limit composition C2MN57 is given to the second stacked body 45 and the fourth compound semiconductor layer 59 adjacent to the third compound semiconductor layer 57. In this embodiment, the Al composition C59AL can be substantially constant. The third compound semiconductor layer 57 and the fourth compound semiconductor layer 59 can avoid that the differential resistance in the vertical cavity surface emitting laser 11 strongly depends on the variation of the current aperture size.

  In addition, a III-V compound semiconductor containing aluminum as a group III constituent element has a band gap that increases with an increase in the Al composition, and a large band gap generates a large specific resistance. However, providing the fourth compound semiconductor layer 59 with an Al composition C59AL larger than the third Al composition C51AL is effective in reducing the differential resistance in the vertical cavity surface emitting laser 11. Specifically, the fourth compound semiconductor layer 59 having an Al composition C59AL of 0.25 or more gives the vertical cavity surface emitting laser 11 a low differential resistance. The Al composition C59AL of the fourth compound semiconductor layer 59 can be 0.3 or more.

  The Al composition C59AL of the fourth compound semiconductor layer 59 may be larger than half ((C53AL-C51AL) / 2) of the difference between the third Al composition C51AL and the fourth Al composition C53AL.

  In the present embodiment, the second stack 45 has a sharp change in the Al composition at the interface between the first semiconductor layer 51 and the second semiconductor layer 53.

  The third compound semiconductor layer 57 may be given a second Al lower limit composition C2MN57 of 0.25 or more. In a III-V compound semiconductor containing aluminum as a group III constituent element, the band gap increases as the Al composition increases, and the increase in the band gap increases the specific resistance. However, the third compound semiconductor layer 57 having the second Al lower limit composition C2MN57 of 0.25 or more gives the vertical cavity surface emitting laser 11 a low differential resistance.

  The third compound semiconductor layer 57 may be provided with a second Al lower limit composition C2MN57 of 0.75 or less. According to the second Al lower limit composition C2MN57 of 0.75 or less, the first stack 33, the second compound semiconductor layer 39, the first compound semiconductor layer 37, the current confinement structure 35, the fourth compound semiconductor layer 59, and the third compound semiconductor layer It is possible to avoid a significant decrease in reflectivity of the upper distributed Bragg reflector DBRU including the second stack 45 and the second stack 45.

  The second Al lower limit composition C2MN57 of the third compound semiconductor layer 57 is preferably larger than half ((C53AL-C51AL) / 2) of the difference between the fourth Al composition C53AL and the third Al composition C51AL. According to the vertical cavity surface emitting laser 11, the fourth compound semiconductor layer 59 having a small composition range in the Al composition gradient of the third compound semiconductor layer 57 and a large Al composition is effective in reducing the differential resistance.

  Referring to FIG. 1, the second aluminum profile PF2 is continuous in the current confinement structure 35, the third compound semiconductor layer 57, and the fourth compound semiconductor layer 59 on coordinates on the first axis Ax1. Specifically, the Al composition C59AL of the fourth compound semiconductor layer 59 is equal to the second Al lower limit composition C2MN57 of the third compound semiconductor layer 57. The Al composition CAPAL of the current aperture 35a is equal to the second Al upper limit composition C2MX57 of the third compound semiconductor layer 57. The second aluminum profile PF2 decreases in the third compound semiconductor layer 57 in the direction from the current aperture 35a to the second stack 45. The differential coefficient of the second aluminum profile PF2 is equal to or less than zero in the third compound semiconductor layer 57, and smaller than zero in at least a part of the third compound semiconductor layer 57 (or the differential coefficient of the second aluminum profile PF2 is It is greater than or equal to zero in the three compound semiconductor layers 57 and greater than zero in at least a portion of the third compound semiconductor layer 57).

  According to the vertical cavity surface emitting laser 11, a continuous aluminum profile can be provided to the arrangement of the current aperture 35a, the third compound semiconductor layer 57, and the fourth compound semiconductor layer 59.

  Further, the differential resistance becomes insensitive to the variation in the size of the current aperture 35a due to the second Al lower limit composition C2MN57 larger than 0.25 and the large Al composition C59AL.

  In the present embodiment, the absolute value of the Al composition difference (CAPAL-C59AL) between the current aperture 35a of the current constriction structure 35 and the fourth compound semiconductor layer 59 is equal to the absolute value of the second semiconductor layer 53 in the second stack 45. It is smaller than the absolute value of the difference (C53AL-C51AL) in the Al composition between the first semiconductor layer 51 and the semiconductor layer 51.

  According to the vertical cavity surface emitting laser 11, the change in the differential resistance with respect to the change in the current aperture size is caused by the large Al composition and the third compound semiconductor in the fourth compound semiconductor layer 59 adjacent to the second stack 45 and the current confinement structure 35. It is reduced by the gentle composition gradient of the layer 57.

  Referring to FIG. 1, the vertical cavity surface emitting laser 11 may further include a top contact layer 61 of the post 17. The contact layer 61 includes a III-V compound semiconductor, and the first electrode 21 makes contact.

  The contact layer 61, the first stack 33, the second compound semiconductor layer 39, the first compound semiconductor layer 37, the current confinement structure 35, the third compound semiconductor layer 57, the fourth compound semiconductor layer 59, and the second stack 45 Including a type dopant.

  According to the vertical cavity surface emitting laser 11, the contact layer 61, the first stack 33, the second compound semiconductor layer 39, the first compound semiconductor layer 37, the current confinement structure 35, the third compound semiconductor layer 57, the fourth compound semiconductor The layer 59 and the second stack 45 are located on the path of the hole flow.

  The vertical cavity surface emitting laser 11 may further include a third stack 63, and the active layer 31 is provided between the second stack 45 and the third stack 63. The third stack 63 includes first and second semiconductor layers 71 and 73 alternately arranged for distributed Bragg reflection. Each of the first semiconductor layers 71 has a fifth III-V semiconductor having a first Al composition C71AL, and each of the second semiconductor layers 73 has a sixth III-V semiconductor having a second Al composition C73AL larger than the first Al composition C71AL. . The third stack 63 constitutes a lower distributed Bragg reflector DBRL.

  In the present embodiment, the third stack 63 has a sharp change in the Al composition at the interface between the first semiconductor layer 71 and the second semiconductor layer 73.

  The third stack 63 can include an n-type dopant. According to the vertical cavity surface emitting laser 11, the third stack 63 is located on the path of the electron flow. Third stack 63, active layer 31, second stack 45, fourth compound semiconductor layer 59, third compound semiconductor layer 57, current confinement structure 35, first compound semiconductor layer 37, second compound semiconductor layer 39, first stack 33 and the contact layer 61 are arranged in the direction of the first axis Ax1.

  The active layer 31 may include a quantum well structure MQW, and the quantum well structure MQW may include one or more well layers 31a and one or more barrier layers 31b. If necessary, the active layer 31 can include a first spacer layer 31c and a second spacer layer 31d outside all the well layers 31a of the quantum well structure MQW. The first spacer layer 31c is provided between the quantum well structure MQW and the second stack 45, and the second spacer layer 31d is provided between the quantum well structure MQW and the third stack 63.

  The post 17 includes a first portion 17c and a second portion 17d, and the first portion 17c and the second portion 17d extend in a direction crossing the main surface 13a of the support 13 (for example, in the direction of the first axis Ax1). Exist. The first portion 17c of the post 17 includes a current aperture 35a, and the second portion 17d of the post 17 includes an insulating current blocker 35b. In this embodiment, the first portion 17c of the post 17 is formed of a semiconductor, and the second portion 17d of the post 17 is formed of a semiconductor and an oxide of a constituent element of the semiconductor. The oxide region of the second portion 17d surrounds the semiconductor region of the first portion 17c and the second portion 17d.

  The vertical cavity surface emitting laser 11 includes a support 13, a semiconductor stack 15, a post 17, a first electrode 21, a second electrode 23, and a coating film 25. The support 13 has a semiconductor stack 15 mounted thereon, and the semiconductor stack 15 has a post 17 mounted thereon. The post 17 has an upper surface 17a and a side surface 17b. The coating film 25 covers the upper surface 17 a and the side surface 17 b of the post 17 and the semiconductor stack 15. The first electrode 21 makes contact with the post 17 through the first opening of the coating film 25. The second electrode 23 makes contact with the support 13 or the semiconductor stack 15. The active layer 31 is provided between the upper distributed Bragg reflector DBRU and the lower distributed Bragg reflector DBRL and the support 13.

2 illustrates a vertical cavity surface emitting laser 11.
Support 13: n-type GaAs.
Third laminate 63 (first semiconductor layer 71 / second semiconductor layer 73): Si-doped AlGaAs (Al composition: 0.12) / Si-doped AlGaAs (Al composition: 0.90), steep junction of Al composition.
Active layer 31 oscillation wavelength: 850-910 nm.
Well layer 31a: undoped GaAs.
Barrier layer 31b: undoped AlGaAs.
First spacer layer 31c and second spacer layer 31d: AlGaAs.
Second stack 45 (first semiconductor layer 51 / second semiconductor layer 53): carbon (C) -doped AlGaAs (Al composition: 0.12) / carbon (C) -doped AlGaAs (Al composition: 0.90), Al composition Steep junction.
Third compound semiconductor layer 57: carbon-doped Al composition gradient AlGaAs (Al composition gradient: 0.25 to 0.98)
Fourth compound semiconductor layer 59: carbon-doped AlGaAs (Al composition: Al composition in the range of 0.25 to 75)
Current constriction structure 35 (current aperture 35a / current blocker 35b): carbon-doped AlGaAs (Al composition: 0.98) / group III oxide.
First compound semiconductor layer 37: Al-doped AlGaAs with carbon doping gradient (Al composition gradient: lower limit in the range of 0.25 to 0.75, and upper limit equal to CAPAL (e.g. 0.98)).
Second compound semiconductor layer 39: Al composition in the range of carbon-doped AlGaAs (Al composition: 0.25 to 75).
First laminate 33 (first semiconductor layer 41 / second semiconductor layer 43): carbon-doped AlGaAs (Al composition: 0.12) / carbon-doped AlGaAs (Al composition: 0.90), steep junction of Al composition.
Contact layer 61: carbon-doped GaAs or AlGaAs.
The current aperture 35a of the current confinement structure 35 is, for example, circular in a plane perpendicular to the first axis Ax1.

  Examples 1 to 4 and experimental examples according to the embodiment will be described with reference to FIGS. In Examples 1 to 4, at least one of the first compound semiconductor layer 37 and the third compound semiconductor layer 57 has an aluminum profile that changes linearly, and at least one of the second compound semiconductor layer 39 and the fourth compound semiconductor layer 59 One has an Al composition in the range of 0.25 to 0.75. The aluminum profile is continuous over the second compound semiconductor layer 39, the first compound semiconductor layer 37, the current aperture 35a, the third compound semiconductor layer 57, and the fourth compound semiconductor layer 59.

(Experimental example)
FIG. 2 shows a structure of a vertical cavity surface emitting laser EX according to an experimental example.
The current aperture 35a of the current confinement structure 35: C-doped AlGaAs (Al composition CAPAL: 0.98.
First compound semiconductor layer 37c: C-doped Al composition gradient AlGaAs (Al composition gradient: 0.12 to 0.98), thickness: 18 nm.
Third compound semiconductor layer 57c: C-doped Al composition gradient AlGaAs (composition gradient: 0.12 to 0.98), thickness: 18 nm.
First stack 33 (first semiconductor layer 41 / second semiconductor layer 43): C-doped AlGaAs (Al composition: 0.12) / C-doped AlGaAs (Al composition: 0.90).
Second stack 45 (first semiconductor layer 51 / second semiconductor layer 53): C-doped AlGaAs (Al composition: 0.12) / C-doped AlGaAs (Al composition: 0.90).
The first compound semiconductor layer 37c is adjacent to the first semiconductor layer 41 of the first stack 33, and the third compound semiconductor layer 57c is adjacent to the first semiconductor layer 51 of the second stack 45.
In the experimental example, the first stack 33 and the second stack 45 make contact with the first compound semiconductor layer 37c and the third compound semiconductor layer 57c, respectively.

(Example 1)
FIG. 3 illustrates a structure of the vertical cavity surface emitting laser EM1 according to the first embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.30 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.30), thickness: 15 to 20 nm.
Third compound semiconductor layer 57: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.12 to 0.98), thickness: 15 to 20 nm.
First semiconductor layer 51: carbon-doped AlGaAs (Al composition: 0.12), thickness: 15 to 20 nm.

(Example 2)
FIG. 4 illustrates a structure of a vertical cavity surface emitting laser EM2 according to the second embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.30 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.30), thickness: 15 to 20 nm.
Third compound semiconductor layer 57: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.30 to 0.98), thickness: 15 to 20 nm.
Fourth compound semiconductor layer 59: carbon-doped AlGaAs (Al composition: 0.30), thickness: 15 to 20 nm.

(Example 3)
FIG. 5 shows a structure of a vertical cavity surface emitting laser EM3 according to the third embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.70 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.70), thickness: 15 to 20 nm.
Third compound semiconductor layer 57: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.12 to 0.98), thickness: 15 to 20 nm.
First semiconductor layer 51: carbon-doped AlGaAs (Al composition: 0.12), thickness: 15 to 20 nm.

(Example 4)
FIG. 6 illustrates a structure of a vertical cavity surface emitting laser EM4 according to the fourth embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.70 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.70), thickness: 15 to 20 nm.
Third compound semiconductor layer 57: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.70 to 0.98), thickness: 15 to 20 nm.
Fourth compound semiconductor layer 59: carbon-doped AlGaAs (Al composition: 0.70), thickness: 15 to 20 nm.

  Examples 5 to 8 will be described with reference to FIGS. In Examples 5 to 8, at least one of the first compound semiconductor layer 37 and the third compound semiconductor layer 57 has an aluminum profile that changes according to a quadratic curve, and the second compound semiconductor layer 39 and the fourth compound semiconductor layer 59 Has an Al composition in the range of 0.25 to 0.75. The aluminum profile is continuous over the second compound semiconductor layer 39, the first compound semiconductor layer 37, the current aperture 35a, the third compound semiconductor layer 57, and the fourth compound semiconductor layer 59. The aluminum profile has an upwardly convex shape over the first compound semiconductor layer 37 and the current aperture 35a, the current aperture 35a and the third compound semiconductor layer 57, and the first compound semiconductor layer 37, the current aperture 35a and the third compound semiconductor layer 57. It has a shape.

  Further, for example, the vertex of the quadratic curve indicating the aluminum profile in the first compound semiconductor layer 37 is preferably located at the interface between the first compound semiconductor layer 37 and the current aperture 35a, and the aluminum profile in the third compound semiconductor layer 57 is preferably set. Is preferably located at the interface between the third compound semiconductor layer 57 and the current aperture 35a.

(Example 5)
FIG. 7 shows the structure of the vertical cavity surface emitting laser EM5 according to the fifth embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: carbon-doped Al composition gradient AlGaAs (composition gradient according to quadratic curve: 0.30 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.30), thickness: 15 to 20 nm.
Third compound semiconductor layer 57: Al composition gradient AlGaAs doped with carbon (composition gradient according to quadratic curve: 0.12 to 0.98), thickness: 15 to 20 nm.
First semiconductor layer 51: carbon-doped AlGaAs (Al composition: 0.12), thickness: 15 to 20 nm.

(Example 6)
FIG. 8 shows the structure of the vertical cavity surface emitting laser EM6 according to the sixth embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: carbon-doped Al composition gradient AlGaAs (composition gradient according to quadratic curve: 0.30 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.30), thickness: 15 to 20 nm.
Third compound semiconductor layer 57: carbon-doped Al composition gradient AlGaAs (composition gradient according to quadratic curve: 0.30 to 0.98), thickness: 15 to 20 nm.
Fourth compound semiconductor layer 59: carbon-doped AlGaAs (Al composition: 0.30), thickness: 15 to 20 nm.

(Example 7)
FIG. 9 shows a structure of a vertical cavity surface emitting laser EM7 according to the seventh embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.70 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.70), thickness: 15 to 20 nm.
Third compound semiconductor layer 57: Al composition gradient AlGaAs doped with carbon (composition gradient according to quadratic curve: 0.12 to 0.98), thickness: 15 to 20 nm.
First semiconductor layer 51: carbon-doped AlGaAs (Al composition: 0.12), thickness: 15 to 20 nm.

(Example 8)
FIG. 10 shows the structure of the vertical cavity surface emitting laser EM8 according to the eighth embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: carbon-doped Al composition gradient AlGaAs (composition gradient according to quadratic curve: 0.70 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.70), thickness: 15 to 20 nm.
Third compound semiconductor layer 57: carbon-doped Al composition gradient AlGaAs (composition gradient according to quadratic curve: 0.70 to 0.98), thickness: 15 to 20 nm.
Fourth compound semiconductor layer 59: carbon (C) -doped AlGaAs (Al composition: 0.70), thickness: 15 to 20 nm.

  Aluminum profiles are not limited to linear and parabolic variations. Specifically, referring again to FIGS. 7 to 10, the first compound semiconductor layer 37 includes a first portion 37 a and a second portion 37 b sequentially arranged in the direction from the current confinement structure 35 to the first stack 33. Can be included. The first aluminum profile PF1 has a first rate of change RT1 and a second rate of change RT2 at respective arbitrary points in the first portion 37a and the second portion 37b of the first compound semiconductor layer 37. Each of the first rate of change RT1 and the second rate of change RT2 is defined as a slope at a tangent to the first aluminum profile PF1 at a corresponding point.

  The first portion 37a and the second portion 37b have a first rate of change RT1 and a second rate of change RT2 of the first aluminum profile PF1, respectively. The absolute value of the second rate of change RT2 is equal to or greater than the absolute value of the first rate of change RT1. The first change rate RT1 is a first reference having a linear change rate (C1MX37−C1MN37) / T37 of a difference between the first Al upper limit composition C1MX37 and the first Al lower limit composition C1MN37 with respect to the thickness (T37) of the first compound semiconductor layer 37. It is smaller than the absolute value of the slope of the line R1REF (the one-dot chain line shown in FIGS. 7 to 10). The absolute value of the linear change rate is between the absolute value of the first change rate RT1 and the absolute value of the second change rate RT2, and is smaller than the absolute value of the second change rate. The absolute value of the first rate of change RT1 is smaller than the absolute value of the second rate of change RT2.

  The first reference line R1REF represents a gradient composition of a linear change. The first reference line R1REF is translated so as to be in contact with the first aluminum profile PF1, and a second reference line R2REF is defined. The second reference line R2REF contacts the first aluminum profile PF1 at a point M on the first aluminum profile PF1. The point M divides the first compound semiconductor layer 37 into a first portion 37a and a second portion 37b.

  Similarly to the first compound semiconductor layer 37, the third compound semiconductor layer 57 is associated with a third reference line R3REF representing the gradient composition of the linear change and a fourth reference line R4REF (the contact point at the point M) of the translation. The third compound semiconductor layer 57 may include a first portion 57a and a second portion 57b sequentially arranged in a direction from the current confinement structure 35 to the second stack 45. The second aluminum profile PF2 has a third change rate RT3 and a fourth change rate RT4 at respective arbitrary points in the first portion 57a and the second portion 57b of the third compound semiconductor layer 57. Each of the third rate of change RT3 and the fourth rate of change RT4 is defined as an inclination to a tangent to the second aluminum profile PF2 at a corresponding point.

  The third change rate RT3 is a third reference having a linear change rate (C2MX57−C2MN57) / T57 of a difference between the second Al upper limit composition C2MX57 and the second Al lower limit composition C2MN57 with respect to the thickness (T57) of the third compound semiconductor layer 57. It is smaller than the absolute value of the line R3REF (the one-dot chain line shown in FIGS. 7 to 10). The absolute value of the linear change rate is between the absolute value of the third change rate RT3 and the absolute value of the fourth change rate RT4, and is smaller than the absolute value of the fourth change rate RT4. The absolute value of the third rate of change RT3 is smaller than the absolute value of the fourth rate of change RT4.

  FIG. 11 shows the characteristics of the vertical cavity surface emitting laser EX and the vertical cavity surface emitting lasers EM1 to EM4 according to the experimental example and the first to fourth embodiments. The horizontal axis indicates the size of the current aperture, and the vertical axis indicates the differential resistance.

  The exemplary vertical cavity surface emitting laser EX and the vertical cavity surface emitting laser EM1 to the vertical cavity surface emitting laser EM4 have a dimension (opening diameter) of 8.5 μm or less (experimental examples and examples). The difference in the differential resistance between the first embodiment and the fourth embodiment becomes remarkable.

  The differential resistance of the semiconductor laser according to the experimental example increases with a large slope as the size of the current aperture decreases. This indicates that it is sensitive to variations in the size of the current aperture. On the other hand, the differential resistances of the first to fourth embodiments gradually increase in comparison with the differential resistance of the semiconductor laser according to the experimental example in the range of the size of the current aperture from 10 μm to 5 μm.

  The differential resistance of the semiconductor lasers according to the first and second embodiments is smaller than the differential resistance of the semiconductor laser according to the experimental example in the range of the current aperture from 10 to 5 micrometers. The differential resistances of the semiconductor lasers according to the third and fourth embodiments are set within the range of 10 μm to 5 μm of the current aperture. Less than.

  The differential resistance of the semiconductor laser according to the second embodiment is smaller than the differential resistance of the semiconductor laser according to the first embodiment in a range of 10 μm to 5 μm of the current aperture. Further, the differential resistance of the semiconductor laser according to the fourth embodiment is smaller than the differential resistance of the semiconductor laser according to the third embodiment in the range of the current aperture of 10 μm to 5 μm.

  The current aperture 35a may have a cross-sectional area of 38.5 square micrometers or less at the reference plane REF shown in FIG. Alternatively, the current aperture 35a may have a peripheral length of 22.0 micrometers or less at the reference plane REF. The current aperture 35a and the current blocker 35b are arranged along a reference plane REF crossing the first axis Ax1. This reference plane REF is used for defining the cross-sectional area of the current aperture 35a.

Differential resistance at current aperture diameter (10 micrometers).
Example 1, Example 2, Example 3, Example 4, Experimental Example.
85.1, 84.1, 79.4, 79.1, 86.7.

Differential resistance at current aperture diameter (9.0 micrometers).
Example 1, Example 2, Example 3, Example 4, Experimental Example.
87.3, 86.4, 80.5, 79.8, 89.5.

Differential resistance at current aperture diameter (8.5 micrometers).
Example 1, Example 2, Example 3, Example 4, Experimental Example.
90.6, 88.7, 81.1, 80.1, 94.5.

Differential resistance at current aperture diameter (8.0 micrometers).
Example 1, Example 2, Example 3, Example 4, Experimental Example.
92.1, 92.1, 82.3, 81.9, 104.1.

Differential resistance at current aperture diameter (7.5 micrometers).
Example 1, Example 2, Example 3, Example 4, Experimental Example.
94.7, 93.1, 83.2, 82.2, 108.9.

Differential resistance at current aperture diameter (7.0 micrometers).
Example 1, Example 2, Example 3, Example 4, Experimental Example.
96.8, 95.7, 84.7, 83.9, 112.3.

Differential resistance at current aperture diameter (6.0 micrometers).
Example 1, Example 2, Example 3, Example 4, Experimental Example.
99.5, 98.1, 85.8, 84.2, 119.5.

Differential resistance at current aperture diameter (5.0 micrometers).
Example 1, Example 2, Example 3, Example 4, Experimental Example.
102.4, 101.2, 86.9, 85.8, 123.7.

  12 and 13 show the results of reliability tests of the vertical cavity surface emitting lasers in the experimental example and Examples 1 to 8. In this reliability test, the vertical cavity surface emitting lasers in the experimental examples EX and Examples 1 to 8 were subjected to a constant current of 12 mA in an atmosphere at 130 degrees Celsius (the same composition as the atmosphere). Measure the optical output power of The horizontal axis in FIGS. 12 and 13 indicates the accumulation of the energization time at high temperature, and the vertical axis indicates the change in the output power.

  The life of the vertical cavity surface emitting laser changes at the level of -15%, and the experimental example, the example 1, the example 3, the example 2, the example 4, the example 5, the example 7, the example 6, and the example Example 8 is longer in order.

  When a high Al composition is given to one of the second compound semiconductor layer 39 and the fourth compound semiconductor layer 59, the vertical cavity surface emitting laser can withstand use for a long time.

  When a high Al composition is applied to both sides of the second compound semiconductor layer 39 and the fourth compound semiconductor layer 59, the vertical cavity surface emitting laser can withstand use for a longer time.

  When the Al composition is changed at a small rate in the first compound semiconductor layer 37 or the third compound semiconductor layer 57 near the current aperture 35a as compared with the value at a position away from the current aperture 35a, the vertical cavity surface emitting laser further increases Will withstand long-term use.

  FIG. 14 shows main steps in a method for manufacturing the vertical cavity surface emitting laser according to the present embodiment. A method for manufacturing a vertical cavity surface emitting laser will be described with reference to the process flow 100.

  In step S101 of the manufacturing method, a semiconductor stack including a semiconductor layer for a vertical cavity surface emitting laser is grown on an n-type GaAs wafer by metal organic chemical vapor deposition to form an epitaxial substrate. The semiconductor stack includes, according to the example of the vertical cavity surface emitting laser 11, semiconductor films for the following semiconductor layers: a third stack 63 (first semiconductor layer 71 / second semiconductor layer 73); an active layer 31 (first semiconductor layer 71). 1st spacer layer 31c, well layer 31a / barrier layer 31b, second spacer layer 31d); second stack 45 (first semiconductor layer 51 / second semiconductor layer 53); fourth compound semiconductor layer 59; Tri-compound semiconductor layer 57; semiconductor of current aperture 35a of current confinement structure 35; first compound semiconductor layer 37 having Al composition gradient; second compound semiconductor layer 39; first stack 33 (first semiconductor layer 41 / second semiconductor layer) 43); and contact layer 61.

  When growing the Al composition gradient layer, the flow rate controller of the raw material line in the crystal growth furnace is continuously changed to provide an aluminum profile having a changed composition by changing, for example, the Al raw material gas for the group III constituent element. The aluminum profile has a continuous compositional gradient represented by a single linear function in FIGS. 3 to 6 of Examples 1 to 4, and in FIGS. 7 to 10 of Examples 5 to 8, Has a continuous composition gradient represented by a quadratic function. The aluminum profile can include other compositional gradients with various functions that are substantially upwardly convex.

  In step S102 of the manufacturing method, photolithography and etching are applied to the epitaxial substrate to form semiconductor posts from the semiconductor stack on the epitaxial substrate. Specifically, a mask defining the semiconductor post is formed on the epitaxial substrate, and the semiconductor stack is processed by etching using the mask. In the present embodiment, the semiconductor post includes a series of semiconductor films in a lower portion of the third stack 63.

  In step S103 of the manufacturing method, the semiconductor post having a high Al composition for the current aperture 35a of the current confinement structure 35 is oxidized by placing the semiconductor post in an oxidizing atmosphere (for example, high-temperature steam). This oxidation forms posts 17 from the semiconductor posts. The oxide of the semiconductor film becomes the current blocker 35b, and the remaining semiconductor becomes the current aperture 35a. The Al-containing semiconductor film in the semiconductor post is oxidized at an oxidation rate according to the Al composition.

  In step S104 of the manufacturing method, an inorganic insulating film for the coating film 25 is deposited on the wafer so as to cover the posts 17 by a vapor phase growth method.

  In step S105 of the manufacturing method, after growing the insulating film on the wafer, the contact opening is formed in the inorganic insulating film by processing the inorganic insulating film by photolithography and etching before forming the electrode. Using photolithography and metal deposition, an anode electrode and a cathode electrode are formed over the respective contact openings. Through these steps, a substrate product is completed.

  In step S106 of the manufacturing method, dicing or cleavage is applied to a substrate product to manufacture a semiconductor chip for a vertical cavity surface emitting laser.

  FIG. 15 shows a change in the thickness of the current constriction structure in the first portion 17c and the second portion 17d shown in FIGS. 3 to 6 and FIGS. (A change in thickness).

  The insulator current blocker 35b may include an aluminum oxide layer that gradually increases in thickness from the point on the first axis Ax1 to the side of the post 17 at the second portion 17d of the post 17. The insulator of the second portion 17d is an Al oxide containing aluminum, a constituent element of the semiconductor of the current aperture 35a. According to the surface emitting semiconductor laser, the semiconductor having a high Al composition in the semiconductor layer when epitaxially grown is partially oxidized by oxidation from the side surface of the post 17. The thickness of the aluminum oxide layer changes in the radial direction due to a gentle change in the Al composition of the first compound semiconductor layer and the second compound semiconductor layer in contact with the current blocker 35b. The change in the thickness of the insulator of the second portion 17d can reduce the parasitic capacitance of the mesa and can suppress the stress near the current blocker 35b.

  The first compound semiconductor layer 37 having a gradient of Al composition and the third compound semiconductor layer 57 having a gradient of Al composition have a point on the first axis Ax1 in the first portion 17c in the second portion 17d in accordance with the Al composition. From the side of the post 17. The first compound semiconductor layer 37 and the third compound semiconductor layer 57 have a thickness that changes in the radial direction compared to the individual semiconductor layers when epitaxially grown due to oxidation in an oxidizing atmosphere in the manufacturing process. The second compound semiconductor layer 39 and the fourth compound semiconductor layer 59 are formed by oxidation in an oxidizing atmosphere in a manufacturing process according to their Al compositions, and are surrounded by the respective oxide regions in the second portion 17d. These oxide regions are continuous with the current blocker 35b. In the second portion 17d, the second compound semiconductor layer 39 and the fourth compound semiconductor layer 59 are each formed of a thicker oxide than the low Al composition first semiconductor layers 41 and 51 of the first stack 33 and the second stack 45, respectively. , These oxide regions lead to a current blocker 35b.

  Embodiments 9 and 10 will be described with reference to FIGS. In Examples 9 and 10, the second stack 45 includes a single first semiconductor layer 51 and a single second semiconductor layer 53. The first semiconductor layer 51 is disposed between the fourth compound semiconductor layer 59 and the second semiconductor layer 53. The second semiconductor layer 53 is disposed between the first semiconductor layer 51 and the active layer 31. The second stack 45 includes semiconductor layers 81, 83, 85. The semiconductor layer 81 is disposed between the fourth compound semiconductor layer 59 and the first semiconductor layer 51. The semiconductor layer 81 has an Al composition C81AL defined on the first axis Ax1. The Al composition C81AL monotonically increases in the direction from the second stack 45 to the current confinement structure 35. The semiconductor layer 83 is disposed between the first semiconductor layer 51 and the second semiconductor layer 53. The semiconductor layer 83 has an Al composition C83AL defined on the first axis Ax1. The Al composition C83AL monotonously decreases in the direction from the second stack 45 to the current confinement structure 35. The semiconductor layer 85 is disposed between the second semiconductor layer 53 and the active layer 31. The semiconductor layer 85 has an Al composition C85AL defined on the first axis Ax1. The Al composition C85AL monotonically increases in the direction from the second stack 45 to the current confinement structure 35. In the present embodiment, the semiconductor layer 85, the second semiconductor layer 53, the semiconductor layer 83, the first semiconductor layer 51, and the semiconductor layer 81 are arranged on the first axis Ax1 in the direction from the second stack 45 to the current confinement structure 35, They are arranged in order.

  When the second stack 45 includes a single first semiconductor layer 51 and a single second semiconductor layer 53, and when the second stack 45 includes a plurality of first semiconductor layers 51 and a plurality of second semiconductor layers 53, In comparison, the thickness of the second stack 45 can be reduced. Thereby, the distance between the current confinement structure 35 and the active layer 31 can be reduced. As a result, the current confined in the current confinement structure 35 can be suppressed from spreading before reaching the active layer 31. Therefore, the threshold current density of the vertical cavity surface emitting laser can be reduced. On the other hand, the current confinement structure 35 may have crystal defects caused by the oxidation process. The current and light intensity around the crystal defect are increased by the light absorption by the defect level of the crystal defect, so that the deterioration of the vertical cavity surface emitting laser may be accelerated. In order to suppress such deterioration, it is preferable that the distance between the current confinement structure 35 and the active layer 31 is not too close. When the second stack 45 includes the single first semiconductor layer 51 and the single second semiconductor layer 53, the distance between the current confinement structure 35 and the active layer 31 can be ensured. Degradation can be suppressed.

(Example 9)
FIG. 16 shows the structure of the vertical cavity surface emitting laser EM9 according to the ninth embodiment.
The current aperture 35a of the current confinement structure 35: carbon-doped AlGaAs (Al composition CAPAL: 0.98).
First compound semiconductor layer 37: Al-doped AlGaAs with a carbon doping gradient (composition gradient: 0.16 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.16), thickness: 20 to 30 nm.
Third compound semiconductor layer 57: carbon-doped Al composition gradient AlGaAs (composition gradient according to quadratic curve: 0.60 to 0.98), thickness: 15 to 20 nm.
Fourth compound semiconductor layer 59: carbon-doped AlGaAs (Al composition: 0.60), thickness: 30 to 40 nm.
First semiconductor layer 51: carbon-doped AlGaAs (Al composition: 0.16), thickness: 30 to 50 nm.
Second semiconductor layer 53: carbon-doped AlGaAs (Al composition: 0.88), thickness: 10 to 15 nm.
Semiconductor layer 81: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.60 to 0.16), thickness: 10 to 15 nm.
Semiconductor layer 83: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.16 to 0.88), thickness: 20 to 30 nm.
Semiconductor layer 85: carbon-doped Al composition gradient AlGaAs (composition gradient: 0.88 to 0.30), thickness: 10 to 30 nm.
Active layer 31: thickness of 40 to 60 nm.

FIG. 17 is a diagram illustrating a refractive index distribution of the vertical cavity surface emitting laser EM9 according to the ninth embodiment and an electric field intensity distribution of a standing wave calculated from the refractive index distribution. As shown in FIG. 17, the electric field strength of the standing wave is zero in the current confinement structure 35 including the current aperture 35a. That is, a node of the standing wave light is located in the current confinement structure 35. As a result, scattering loss in the current confinement structure 35 and light absorption at a defect level of a crystal defect can be reduced. Assuming that the oscillation wavelength of the vertical cavity surface emitting laser is λ, the optical path length from the center of the active layer 31 to the center of the current confinement structure 35 on the first axis Ax1 is preferably 3λ / 2 ± 20 nm. For example, it is preferable that the following expression (1) is satisfied.
_{T 31/2 + T 85 +} T 53 + T 83 + T 51 + T 81 + T 59 + T 57 + T 35a / 2 = 3λ / 2 (± 20nm) ··· (1)
T ₃₁ is the optical path length of the active layer _{31, T 85} is the optical path length of the semiconductor layer _{85, T 53} is the optical path length of the second semiconductor layer _{53, T 83} is the optical path length of the semiconductor layer _{83, T 51} is the first semiconductor layer 51 T ₈₁ is the optical path length of the semiconductor layer 81, T ₅₉ is the optical path length of the fourth compound semiconductor layer 59, T ₅₇ is the optical path length of the third compound semiconductor layer 57, and T _35a is the optical path length of the current aperture 35a. Represent.

(Example 10)
FIG. 18 illustrates the structure of the vertical cavity surface emitting laser EM10 according to the tenth embodiment. The vertical cavity surface emitting laser EM10 has the same configuration as the vertical cavity surface emitting laser EM9 except that the first compound semiconductor layer 37 and the second compound semiconductor layer 39 have the following configurations.
First compound semiconductor layer 37: Al composition gradient AlGaAs doped with carbon (composition gradient according to quadratic curve: 0.60 to 0.98), thickness: 15 to 20 nm.
Second compound semiconductor layer 39: carbon-doped AlGaAs (Al composition: 0.60), thickness: 30 to 40 nm.

  FIG. 19 is a diagram illustrating a refractive index distribution of the vertical cavity surface emitting laser EM10 according to the tenth embodiment and an electric field intensity distribution of a standing wave calculated from the refractive index distribution. As in the case of the ninth embodiment, as shown in FIG.

  FIG. 20A shows the calculation result of the current density distribution in the cross section along the first axis Ax1 of the vertical cavity surface emitting laser according to the ninth embodiment. FIG. 20B illustrates a calculation result of a current density distribution in a cross section along the first axis Ax1 of the vertical cavity surface emitting laser according to the tenth embodiment. FIG. 20 shows the radial direction R from the center axis of the post 17 to the side surface along the first axis Ax1, and the current blocker 35b. In FIG. 20, the current density is higher as the color is closer to white, and is lower as the color is closer to black. In FIG. 20A, the current is concentrated in the region above the current blocker 35b (that is, the first compound semiconductor layer 37 and the second compound semiconductor layer 39) near the interface between the current aperture 35a and the current blocker 35b. . On the other hand, in FIG. 20B, the concentration of the current in the region above the current blocker 35b (that is, the first compound semiconductor layer 37 and the second compound semiconductor layer 39) is reduced as compared with FIG. This is because the Al composition of the first compound semiconductor layer 37 and the second compound semiconductor layer 39 in Example 10 is larger than the Al composition of the first compound semiconductor layer 37 and the second compound semiconductor layer 39 in Example 9. is there.

  While the principles of the invention have been illustrated and described in preferred embodiments, those skilled in the art will recognize that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes coming from the scope of the claims and their spirit.

  According to one aspect of the present embodiment, there is provided a vertical cavity surface emitting laser having a structure in which a change in differential resistance is not so sensitive to a change in the size of a current aperture. According to another aspect of the present embodiment, there is provided a vertical cavity surface emitting laser having a structure capable of reducing differential resistance. Still another aspect according to the present invention provides a vertical cavity surface emitting laser having high reliability.

11 vertical cavity surface emitting laser, 13 support, 15 semiconductor stack, 17 post, 21 first electrode, 23 second electrode, 25 coating film, 31 active layer, 33 first Stack, 35: current confinement structure, 37: first compound semiconductor layer, 39: second compound semiconductor layer.

Claims (8)

A vertical cavity surface emitting laser,
An active layer provided in the semiconductor post;
A first stack for distributed Bragg reflection provided in the semiconductor post;
A current constriction structure provided in the semiconductor post, comprising a current aperture and a current blocker surrounding the current aperture;
A first compound semiconductor layer provided in the semiconductor post and adjacent to the current confinement structure between the first stack and the current confinement structure;
A second compound semiconductor layer provided in the semiconductor post and adjacent to the first stack and the first compound semiconductor layer between the first stack and the first compound semiconductor layer;
With
The current aperture includes a III-V compound semiconductor including an aluminum element as a group III constituent element, the current blocker includes a group III oxide,
The first stack includes first semiconductor layers and second semiconductor layers that are alternately arranged, the first semiconductor layer includes a first III-V semiconductor having a first Al composition, and the second semiconductor layer includes: A second III-V semiconductor having a second Al composition larger than the first Al composition,
Each of the first compound semiconductor layer and the second compound semiconductor layer includes an aluminum element as a group III constituent element,
The current constriction from the first stack is changed from a first Al lower limit composition in a range larger than the first Al composition and smaller than the second Al composition to a first Al upper limit composition larger than the first Al lower composition. A first aluminum profile that varies monotonically with the orientation of the structure;
The second compound semiconductor layer has an Al composition larger than the first Al composition and smaller than the first Al upper limit composition;
The vertical cavity surface emitting laser, wherein the III-V compound semiconductor of the current aperture has an Al composition larger than the second Al composition.   The vertical cavity surface emitting laser according to claim 1, wherein the first Al lower limit composition is larger than a half of a difference between the second Al composition and the first Al composition. The first Al lower limit composition is in a range of 0.25 or more,
The Al composition of the second compound semiconductor layer is the first Al lower limit composition of the first compound semiconductor layer,
3. The vertical resonance type according to claim 1, wherein the first aluminum profile has the Al composition of the current aperture at an interface between the current aperture and the first compound semiconductor layer. 4. Surface emitting laser. The first compound semiconductor layer includes a first portion and a second portion sequentially arranged in a direction from the current confinement structure to the first stack,
The first aluminum profile has a first rate of change and a second rate of change at respective points within the first portion and the second portion;
The first change rate has an absolute value smaller than an absolute value of a linear change rate of a difference between the first Al upper limit composition and the first Al lower limit composition with respect to a thickness of the first compound semiconductor layer. 4. The vertical cavity surface emitting laser according to claim 1, wherein the absolute value of the rate is smaller than the absolute value of the second rate of change. 5. A second lamination provided in the semiconductor post for the distributed Bragg reflection;
A third compound semiconductor layer provided in the semiconductor post and adjacent to the current confinement structure between the second stack and the current confinement structure;
A fourth compound semiconductor layer provided in the semiconductor post and adjacent to the second stack and the third compound semiconductor layer between the second stack and the third compound semiconductor layer;
With
The second stack includes first semiconductor layers and second semiconductor layers that are alternately arranged, the first semiconductor layer includes a third III-V semiconductor having a third Al composition, and the second semiconductor layer includes: A fourth III-V semiconductor having a fourth Al composition larger than the third Al composition,
The third compound semiconductor layer and the fourth compound semiconductor layer include an aluminum element as a group III constituent element,
The third compound semiconductor layer is configured such that the current confinement from the second stack is changed from a second Al lower limit composition within a range larger than the third Al composition and smaller than the fourth Al composition to a second Al upper limit composition larger than the second Al lower composition. A second aluminum profile that varies monotonically in the direction to the structure;
5. The vertical cavity surface emitting laser according to claim 1, wherein the fourth compound semiconductor layer has an Al composition larger than the third Al composition and smaller than the second Al upper limit composition. 6. The second Al lower limit composition is 0.25 or more;
The Al composition of the fourth compound semiconductor layer is the second Al lower limit composition of the third compound semiconductor layer,
The vertical cavity surface emitting laser according to claim 5, wherein the second aluminum profile has the Al composition of the current aperture at an interface between the current aperture and the third compound semiconductor layer. The third compound semiconductor layer includes a first portion and a second portion sequentially arranged in a direction from the current confinement structure to the second stack.
The second aluminum profile has a third rate of change and a fourth rate of change at respective points within the first portion and the second portion;
The third change rate has an absolute value smaller than an absolute value of a linear change rate of a difference between the second Al upper limit composition and the second Al lower limit composition with respect to the thickness of the third compound semiconductor layer, and 7. The vertical cavity surface emitting laser according to claim 5, wherein an absolute value of the rate is smaller than an absolute value of the fourth rate of change. A second stack for distributed Bragg reflection provided in the semiconductor post;
A third compound semiconductor layer provided in the semiconductor post and adjacent to the current confinement structure between the second stack and the current confinement structure;
With
The second stack includes first semiconductor layers and second semiconductor layers that are alternately arranged, the first semiconductor layer includes a third III-V semiconductor having a third Al composition, and the second semiconductor layer includes: A fourth III-V semiconductor having a fourth Al composition larger than the third Al composition,
The third compound semiconductor layer includes an aluminum element as a group III constituent element,
The third compound semiconductor layer monotonically changes from the second Al lower limit composition of less than 0.25 to the second Al upper limit composition larger than the second Al lower limit composition in the direction from the second stack to the current confinement structure. 5. The vertical cavity surface emitting laser according to claim 4, having a two aluminum profile.