JP2008034478A - Surface-emitting laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-emitting laser element that can easily achieve high output and basic lateral mode oscillation. <P>SOLUTION: The surface-emitting laser element 10 includes a first reflecting layer 12, an n-type spacer layer 13, an active layer 14, and a p-type spacer layer 15 that have been laminated sequentially. On this p-type spacer layer, a first tunnel junction structure 18 and a second tunnel junction structure 19 isolated from the first tunnel junction structure are provided. These tunnel junction structures are covered with the n-type spacer layer 25 provided on the second spacer layer. A second reflecting layer 28 is formed on this n-type spacer layer. Each tunnel junction structure includes a p-type lower layer 20 and an n-type upper layer 21. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface emitting laser element having a tunnel junction structure.

Non-Patent Document 1 below discloses a surface emitting laser element in which a tunnel junction structure is embedded in a pn junction structure. When current is injected in the opposite direction to the pn junction structure, current flows only in the tunnel junction structure and flows into the active layer. Since the refractive index of the tunnel junction structure is higher than that of the surrounding layers, the tunnel junction structure functions as a core of the optical waveguide. The light generated in the active layer repeatedly reciprocates in the optical resonator through this optical waveguide and causes laser oscillation.
Nishiyama and five others, “High efficiency long wavelength VCSEL on InP grown by MOCVD (MOCVD), Electronics Letters, Vol. 39, No. 5, 437-439, March 6, 2003

  For surface emitting laser elements, both high output and fundamental transverse mode oscillation (lateral single mode oscillation) are desired. In order to increase the output, it is preferable to increase the diameter of the tunnel junction surface so that more current can be injected into the active layer. In the surface emitting laser element described above, fundamental transverse mode oscillation can be realized when the diameter of the tunnel junction surface is 5 μm. However, when the diameter is made larger, not only the fundamental transverse mode but also higher order transverse modes cause laser oscillation.

  Accordingly, an object of the present invention is to provide a surface emitting laser element that can easily achieve both high output and fundamental transverse mode oscillation.

  A surface-emitting laser device according to the present invention includes a first reflective layer, a first spacer layer provided on the first reflective layer, an active layer provided on the first spacer layer, and an active layer. A second spacer layer provided on the second spacer layer; a first tunnel junction structure provided on the second spacer layer; and a second spacer layer provided on the second spacer layer and spaced apart from the first tunnel junction structure. Two tunnel junction structures and a second spacer layer provided on the second spacer layer, covering the first and second tunnel junction structures and having the first conductivity type, and on the third spacer layer And a second reflective layer provided. Each of the first and second tunnel junction structures includes a lower layer provided on the second spacer layer and having a second conductivity type, and an upper layer provided on the lower layer and having the first conductivity type. Is included.

  When a current flows through the first and second tunnel junction structures during the operation of the surface emitting laser element, not only the first tunnel junction structure but also the second tunnel junction structure generates heat. For this reason, the thermal gradient in the direction from the first tunnel junction structure to the second tunnel junction structure becomes gentler than that in the case where the first tunnel junction structure is provided alone. Accordingly, the refractive index gradient also becomes gentle, so that the convergence of the thermal lens effect in that direction can be suppressed. As a result, the high-order transverse mode is less likely to cause laser oscillation, so that even if the area of the tunnel junction surface in the first tunnel junction structure is increased, transverse multimode oscillation is unlikely to occur. Therefore, this surface emitting laser element can easily achieve both high output and fundamental transverse mode oscillation.

  The second tunnel junction structure may be an annular body surrounding the first tunnel junction structure.

  By surrounding the first tunnel junction structure with the second tunnel junction structure, the thermal gradient and the refractive index gradient are moderated in any direction from the first tunnel junction structure toward the outside thereof. As a result, the converging action of the thermal lens effect is greatly suppressed, and the high-order transverse mode becomes extremely difficult to cause laser oscillation, so that both high output and fundamental transverse mode oscillation are made easier.

  The first tunnel junction structure may have an elliptical planar shape. The second tunnel junction structure may be an annular body that surrounds the first tunnel junction structure in an elliptical shape.

  Since the first tunnel junction structure is elliptical, it becomes possible to generate linearly polarized laser light. By surrounding the first tunnel junction structure with the second tunnel junction structure, the thermal gradient and the refractive index gradient are moderated in any direction from the first tunnel junction structure toward the outside thereof. As a result, even when linearly polarized laser light is generated, the convergence effect of the thermal lens effect is suppressed, and both high output and fundamental transverse mode oscillation can be easily achieved.

  The surface emitting laser element of the present invention may further include a third tunnel junction structure provided on the second spacer layer and spaced apart from the first and second tunnel junction structures. The third tunnel junction structure may include a lower layer provided on the second spacer layer and having the second conductivity type, and an upper layer provided on the lower layer and having the first conductivity type. Good. The first tunnel junction structure has a circular planar shape, and the second and third tunnel junction structures have a first straight line passing through the center of the planar shape of the first tunnel junction structure. These tunnel junction structures may be arranged so as to be sandwiched from both sides thereof.

  When heat flows due to current flowing through the first to third tunnel junction structures, the heat distribution and the refractive index distribution differ between the direction in which the second and third tunnel junction structures are arranged and the direction perpendicular to the direction. become. For this reason, a difference occurs in the group velocity between two polarized light beams generated in the active layer and orthogonal to each other. As a result, a gain difference is generated between these orthogonally polarized lights, so that only one polarized light can be laser-oscillated if the dimensions and arrangement of the first to third tunnel junction structures are appropriately set. As described above, the surface emitting laser element can generate linearly polarized laser light even though the first tunnel junction structure is circular.

  According to the present invention, it is possible to provide a surface-emitting laser element that can easily achieve both high output and fundamental transverse mode oscillation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

First Embodiment FIG. 1 is a longitudinal sectional view showing a surface emitting laser element 10 according to a first embodiment of the present invention, wherein (a) shows the entire surface emitting laser element 10 and (b) ) Shows enlarged tunnel junction structures 18 and 19 included in the surface emitting laser element 10. FIG. 2 is a cross-sectional view of the surface emitting laser element 10 taken along the line II-II in FIG. The laser element 10 is a vertical cavity surface emitting laser (VCSEL) element.

  The surface-emitting laser element 10 has a substrate 11 made of an n-type semiconductor, and a distributed Bragg reflector (hereinafter referred to as “DBR”) is provided as a reflective layer on one main surface, that is, the upper surface of the substrate 11. ]) 12 is provided. The substrate 11 is made of n-type GaAs. The DBR 12 has a structure in which 33 layers of a laminated body in which an AlGaAs layer (Al composition ratio is 0.9) is stacked on a GaAs layer doped with Si as an n-type dopant.

  On the upper surface of the DBR 12, a spacer layer 13, an active layer 14, and a spacer layer 15 are sequentially stacked. The spacer layer 13 is made of an n-type semiconductor, and the spacer layer 15 is made of a p-type semiconductor. Specifically, the spacer layer 13 is made of GaAs doped with Si. The active layer 14 is made of InGaAs (In composition ratio is 0.2) and has a triple quantum well (TQW) structure. The spacer layer 15 is made of AlGaAs doped with C as a p-type dopant (Al composition ratio is 0.2).

  Two tunnel junction structures 18 and 19 are provided on the upper surface of the p-type spacer layer 15. As shown in FIG. 2, the tunnel junction structure 18 has a circular planar shape, and the tunnel junction structure 19 has an annular planar shape surrounding the tunnel junction structure 18. These tunnel junction structures 18 and 19 are arranged coaxially with each other. The height (thickness) of each tunnel junction structure is 30 nm. As shown in FIG. 1B, each tunnel junction structure includes a lower layer 20 directly formed on the upper surface of the p-type spacer layer 15 and an upper layer 21 directly formed on the upper surface of the lower layer 20. The interface between the lower layer 20 and the upper layer 21 forms a tunnel junction 40. The lower layer 20 is made of a p-type semiconductor, and the upper layer 21 is made of an n-type semiconductor. In particular, the lower layer 20 is made of InGaAs doped with C as a p-type dopant (the composition ratio of In is 0.1), and the upper layer 21 is made of InGaAs doped with Si as an n-type dopant ( The composition ratio of In is 0.1).

  Further, a spacer layer 25 made of an n-type semiconductor is directly formed on the upper surface of the p-type spacer layer 15 so as to cover the tunnel junction structures 18 and 19. The n-type spacer layer 25 is made of GaAs doped with Si. The interface between the p-type spacer layer 15 and the n-type spacer layer 25 forms a pn junction.

  A contact layer 26 and an upper electrode 27 are sequentially formed on the upper surface of the n-type spacer layer 25. A lower electrode 30 is formed on the main surface opposite to the upper surface of the substrate 11, that is, on the entire bottom surface. The upper electrode 27 is an anode, and the lower electrode 30 is a cathode. The contact layer 26 is made of GaAs doped with Si. As shown in FIG. 2, the contact layer 26 and the upper electrode 27 have an annular planar shape.

On the upper surface of the n-type spacer layer 25, a DBR 28 is further provided as a reflective layer. The openings of the contact layer 26 and the upper electrode 27 are filled with the DBR 28. The DBR 28 has a structure in which a laminated body in which an amorphous Si layer is stacked on an Al ₂ O ₃ layer is stacked for four periods.

  The lower DBR 12 and the upper DBR 28 form an optical resonator. This optical resonator has an optical axis perpendicular to the main surface of the substrate 11. When the DBR 28 is viewed from above along a direction perpendicular to the main surface of the substrate 11, the tunnel junction structures 18 and 19 are disposed below the DBR 28 and covered with the DBR 28. The DBR 28 is disposed coaxially with the tunnel junction structures 18 and 19. Therefore, the optical axis of the optical resonator, the central axis of the tunnel junction structure 18, and the central axis of the opening of the tunnel junction structure 19 are arranged on the same straight line. The optical axis of the optical resonator intersects with the tunnel junction structure 18 but does not intersect with the tunnel junction structure 19.

  When a current is passed through the surface emitting laser element 10 through the upper electrode 27 and the lower electrode 30, laser light is emitted from the DBR 28. Since this current is supplied in the opposite direction to the pn junction composed of the p-type spacer layer 15 and the n-type spacer layer 25, it is blocked by this pn junction, but passes through the tunnel junction structures 18 and 19 by the tunnel effect. Can do. As described above, the surface emitting laser element 10 has a current confinement structure in which a current flows only through the tunnel junction structures 18 and 19 in the n-type spacer layer 25.

  When carriers are injected into the active layer 14, light is generated in the active layer 14. Since the tunnel junction structures 18 and 19 have a higher refractive index than the n-type spacer layer 25, they also have a function as a core of the optical waveguide. Therefore, light generated in the active layer 14 mainly passes through the tunnel junction structures 18 and 19 in the n-type spacer layer 25. This light is repeatedly reflected by the DBRs 12 and 28 and passes through the active layer 14 where it is amplified. As a result, laser oscillation finally occurs.

  Below, the manufacturing method of the surface emitting laser element 10 is demonstrated, referring FIG. 3 and FIG. First, as shown in FIG. 3A, the lower DBR layer 12, the n-type spacer layer 13, the active layer 14, the p-type spacer layer 15, the p-type InGaAs layer 20a, Then, the n-type InGaAs layer 21a is sequentially formed. The layers 20 a and 21 a form a continuous tunnel junction structure 22 that covers the entire top surface of the p-type spacer layer 15, and serves as a base material for the tunnel junction structures 18 and 19.

  Next, the substrate 11 is taken out from the reactor, and a resist 24 is applied to the entire upper surface of the n-type InGaAs layer 21. As shown in FIG. 3B, the resist 24 is patterned by photolithography so as to have the same planar shape as the tunnel junction structures 18 and 19 (see FIG. 2).

  Subsequently, as shown in FIG. 3C, the tunnel junction structure 22 is wet-etched using the patterned resist 24 as a mask to form tunnel junction structures 18 and 19. Thereafter, the substrate 11 is washed and then carried into the reactor again, and as shown in FIG. 4D, the n-type spacer layer 25 is formed using the MOVPE method, and further, the entire upper surface of the n-type spacer layer 25 is formed. A contact layer 26a is formed. Subsequently, an annular upper electrode 27 having an opening 27 a is formed on the upper surface of the contact layer 26 a, and a lower electrode 30 is formed on the entire lower surface of the substrate 11.

  Next, as shown in FIG. 4E, only the portion of the contact layer 26a exposed from the opening 27a of the upper electrode 27 is removed by wet etching to obtain the annular contact layer 26. Thereafter, DBR is deposited so as to fill the openings of the contact layer 26 and the upper electrode 27, and the DBR on the upper electrode 27 is removed by a lift-off method to form the DBR 28. Thus, the surface emitting laser element 10 is completed.

  The inventor manufactured the surface-emitting laser element 10 and also manufactured a surface-emitting laser element for comparison, and examined the characteristics of each. As shown in FIG. 7A described later, the comparative laser element 50 has a structure in which the tunnel junction structure 19 is removed from the surface emitting laser element 10. In each laser element, the tunnel junction structure 18 has a diameter D of 7 μm. The tunnel junction structure 19 is a ring with an inner diameter of 11 μm and an outer diameter of 15 μm, and its width W is 2 μm.

  FIG. 5 shows current-light output characteristics of the surface emitting laser element 10 and the comparative laser element 50 at room temperature. Here, the solid line indicates the characteristics of the surface emitting laser element 10, and the broken line indicates the characteristics of the comparative laser element 50. The maximum light output at room temperature of the comparative laser element 50 is 3.0 mW, whereas the maximum light output of the surface emitting laser element 10 is 4.9 mW. The reason why the output of the surface emitting laser element 10 is larger is that the area of the tunnel junction is larger by the amount of the tunnel junction structure 19 and the current injection area is increased accordingly. As a result, more carriers are injected into the active layer 14. It is to be done.

  FIG. 6 shows the change of the transverse mode suppression ratio with respect to the current of the surface emitting laser element 10 and the comparative laser element 50. Here, the circle mark and the triangle mark indicate the transverse mode suppression ratios of the surface emitting laser element 10 and the comparative laser element 50 measured under various currents, respectively. In the comparative laser element 50, it can be seen that the transverse mode suppression ratio does not reach 30 dB at any current value, and multimode oscillation is performed. On the other hand, in the surface emitting laser element 10, the transverse mode suppression ratio is maintained at 30 dB or more even under a current value at which thermal saturation is observed in the output, and fundamental transverse mode oscillation is performed at any current value. ing.

  Thus, although the surface emitting laser element 10 has a larger current injection area than the comparative laser element 50, the fundamental transverse mode oscillation is ensured. Hereinafter, this reason will be described with reference to FIGS. Here, FIG. 7A is a longitudinal sectional view of the surface emitting laser element 50, and FIG. 7B is a schematic diagram showing the heat distribution in the surface emitting laser element 50 corresponding to FIG. 7A. FIG. FIG. 8A is a longitudinal sectional view of the surface emitting laser element 10, and FIG. 8B is a schematic view showing the heat distribution in the surface emitting laser element 10 corresponding to FIG. 8A. .

  In a surface emitting laser element having a current confinement structure using a tunnel junction, a current flows through the tunnel junction structure. However, since the tunnel junction structure is a resistor, heat is generated when a current flows. In the comparative laser element 50, this heat generation forms a Gaussian heat distribution (temperature distribution) 50 a as shown in FIG. 7B along the radial direction of the tunnel junction structure 18. Since the peripheral portion of the tunnel junction structure 18 is in contact with a region where no current flows, the temperature is lower than that of the central portion of the tunnel junction structure 18. Even in a region outside the tunnel junction structure 18, the temperature decreases as the distance from the central axis of the tunnel junction structure 18 increases.

  The refractive index of the comparative laser element 50 changes according to the heat distribution 50a. That is, 50a in FIG. 7B also represents the refractive index distribution of the comparative laser element 50. The refractive index of the comparative laser element 50 decreases with increasing distance from the central axis of the tunnel junction structure 18 corresponding to the heat distribution 50a. Thus, a Gaussian refractive index distribution 50a is formed. The refractive index distribution 50a causes a phenomenon called “thermal lens effect” to converge light propagating in the optical resonator. This thermal lens effect converges not only the fundamental transverse mode but also the higher order transverse mode 42. As a result, in the comparative laser element 50, the loss difference between the fundamental transverse mode and the higher order transverse mode is reduced, and it is considered that not only the fundamental transverse mode but also the higher order transverse mode caused laser oscillation.

  On the other hand, in the surface emitting laser element 10, in addition to the tunnel junction structure 18, another tunnel junction structure 19 provided outside thereof generates heat due to current. For this reason, the thermal gradient becomes gentle in an arbitrary direction from the tunnel junction structure 18 to the tunnel junction structure 19, and the refractive index gradient becomes gentle accordingly. Since the tunnel junction structure 19 is separated from the tunnel junction structure 18, the refractive index of the surface emitting laser element 10 once decreases as the distance from the central axis of the tunnel junction structure 18 increases. However, as the temperature approaches the tunnel junction structure 19, the temperature rises and the refractive index increases accordingly. Therefore, as shown in FIG. 8B, the thermal distribution and refractive index distribution 10a of the surface emitting laser element 10 are not Gaussian.

  The refractive index distribution 10 a has a peak on the central axis of the tunnel junction structure 18 and also has a peak at a radial position corresponding to the tunnel junction structure 19. Since the fundamental transverse mode has a Gaussian optical power distribution having a peak on the central axis of the tunnel junction structure 18, it is sufficiently converged by the refractive index distribution 10a and causes laser oscillation. However, the higher-order transverse mode is relatively strongly affected by the refractive index peak corresponding to the tunnel junction structure 19 because the peak of the optical power is shifted in the radial direction from the central axis of the tunnel junction structure 18. For this reason, the converging action of the thermal lens effect is suppressed for the high-order transverse mode, and the diffraction loss of the high-order transverse mode 42 increases as shown in FIG. 8B. As a result, the higher-order transverse mode does not lead to laser oscillation, and as a result, it is considered that the fundamental transverse mode oscillation is maintained despite having the same tunnel junction structure 18 as the comparative laser element 50.

ここで、「主トンネル」は、光共振器の光軸上に配置されたトンネル接合構造１８を表し、「副トンネル」は、光共振器の光軸からずらして配置されたトンネル接合構造１９を表している。一つの主トンネルの直径値に対して副トンネルの内径値を２通り用意し、各内径値に対して副トンネルの幅を２通り用意した。したがって、主トンネルの各直径値に対して面発光レーザ素子を４個ずつ作製した。 In addition, when a surface emitting laser element in which the planar shape dimensions of the tunnel junction structures 18 and 19 were set as shown in the following table was manufactured, fundamental transverse mode oscillation was obtained in both cases.

Here, the “main tunnel” represents the tunnel junction structure 18 arranged on the optical axis of the optical resonator, and the “sub-tunnel” represents the tunnel junction structure 19 arranged offset from the optical axis of the optical resonator. Represents. Two inner diameter values of the sub-tunnel were prepared for one main tunnel diameter value, and two widths of the sub-tunnel were prepared for each inner diameter value. Therefore, four surface emitting laser elements were manufactured for each diameter value of the main tunnel.

  As described above, in the present embodiment, by disposing another tunnel junction structure 19 outside the tunnel junction structure 18, the current injection area (tunnel junction area) is increased and the power of the laser beam is increased. Basic transverse mode oscillation can be maintained. Therefore, it is possible to easily realize both high output by expanding the current injection area and basic transverse mode oscillation (single transverse mode oscillation).

  In particular, in this embodiment, since the tunnel junction structure 19 is an annular body surrounding the tunnel junction structure 18, the refractive index gradient is relaxed in an arbitrary direction from the tunnel junction structure 18 to the tunnel junction structure 19, and the thermal lens effect is achieved. The convergence effect on the higher order transverse mode can be greatly suppressed. This makes it very difficult for the high-order transverse mode to cause laser oscillation, so that both high output and basic transverse mode oscillation are more easily achieved. Therefore, the surface emitting laser element 10 can perform fundamental transverse mode oscillation despite having the tunnel junction structure 18 having a large area enough to cause transverse multimode oscillation by itself.

Second Embodiment A surface-emitting laser element according to a second embodiment of the present invention is different from the first embodiment in the planar shape of a tunnel junction structure. Other configurations of the second embodiment are the same as those of the first embodiment. FIG. 9 is a cross-sectional view of the surface emitting laser element according to the present embodiment and shows tunnel junction structures 31 and 32. This figure corresponds to FIG. 2 for the first embodiment.

  The tunnel junction structure 31 is disposed coaxially with the DBR 28 and has an elliptical planar shape. The tunnel junction structure 32 has an annular planar shape that surrounds the tunnel junction structure 31 in an elliptical shape and is separated from the tunnel junction structure 31. As shown in FIG. 9, when the DBR 28 is viewed from above along a direction perpendicular to the main surface of the substrate 11 (a direction perpendicular to the paper surface of FIG. 9), the tunnel junction structures 31 and 32 are disposed below the DBR 28. , Covered by DBR28.

  Since the tunnel junction structure 31 is elliptical, the output laser light can be linearly polarized. When current flows through the tunnel junction structure 31 and heat is generated, the refractive index distribution differs between the major axis direction and the minor axis direction of the elliptical shape of the tunnel junction structure 31. For this reason, a difference in group velocity occurs between two polarized light beams generated in the active layer 14 and orthogonal to each other. As a result, a gain difference occurs between these orthogonally polarized lights, and as a result, only one polarized light causes laser oscillation and is output. Thus, the laser light polarized in one direction is emitted from the surface emitting laser element of the present embodiment.

  The tunnel junction structure 32 functions to prevent transverse multimode oscillation in such a surface emitting laser element that emits linearly polarized light. Since the tunnel junction structure 32 is arranged outside the tunnel junction structure 31 so as to be separated from the tunnel junction structure 31, the convergence action of the thermal lens effect on the high-order transverse mode can be suppressed as in the first embodiment. Therefore, the fundamental transverse mode oscillation can be maintained while increasing the current injection area by the tunnel junction structure 32 and increasing the power of the laser beam. Particularly in this embodiment, since the tunnel junction structure 32 is an annular body surrounding the tunnel junction structure 31, the refractive index gradient is relaxed in an arbitrary direction from the tunnel junction structure 31 to the tunnel junction structure 32, and the thermal lens effect is improved. The convergence effect on the high-order transverse mode can be greatly suppressed. This makes it easier to achieve both high output and fundamental transverse mode oscillation, so fundamental transverse mode oscillation is ensured even if the tunnel junction area in the tunnel junction structure 31 is large enough to cause transverse multimode oscillation alone. can do.

Third Embodiment A surface-emitting laser element according to a third embodiment of the present invention is different from the first and second embodiments in the planar shape of a tunnel junction structure. Other configurations of the third embodiment are the same as those of the first embodiment. FIG. 10 is a cross-sectional view of the surface emitting laser element according to the present embodiment and shows tunnel junction structures 35, 36 and 37. This figure corresponds to FIG. 2 for the first embodiment.

  The tunnel junction structure 35 is disposed coaxially with the DBR 28 and has a circular planar shape. The tunnel junction structures 36 and 37 have a circular planar shape having the same diameter that is smaller than the diameter of the tunnel junction structure 35. The tunnel junction structures 36 and 37 are arranged on both sides of the tunnel junction structure 35 on an extension line of one diameter of the tunnel junction structure 35 and are separated from the tunnel junction structure 35. That is, the centers of the circular planar shapes of the tunnel junction structures 35 to 37 are arranged on one straight line 45. As shown in FIG. 10, when the DBR 28 is viewed from above along a direction perpendicular to the main surface of the substrate 11 (a direction perpendicular to the paper surface of FIG. 10), the tunnel junction structures 35 to 37 are disposed below the DBR 28. , Covered by DBR28.

  Since the tunnel junction structures 36 and 37 are arranged outside the tunnel junction structure 35 so as to be separated from the tunnel junction structure 35, the convergence action of the thermal lens effect on the high-order transverse mode can be suppressed as in the above embodiment. Therefore, the fundamental transverse mode oscillation can be ensured while increasing the current injection area by the tunnel junction structures 36 and 37 and increasing the power of the laser beam.

  Furthermore, in the present embodiment, the output laser light can be linearly polarized although the tunnel junction structure 35 is circular. When current flows through tunnel junction structures 35 to 37 and heat is generated, the refractive index distribution is different between the direction in which tunnel junction structures 36 and 37 are aligned (the direction along line 45 in FIG. 10) and the direction perpendicular to that direction. To be different. For this reason, there is a difference in group velocity between the two orthogonally polarized lights generated in the active layer 14, so that a gain difference occurs between these orthogonally polarized lights. As a result, only one linearly polarized light causes laser oscillation. Is output. Thus, the laser light polarized in one direction is emitted from the surface emitting laser element of the present embodiment.

  The present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

  Another p-type spacer layer having a higher band gap than these layers 14 and 15 may be added between the active layer 14 and the p-type spacer layer 15. This additional spacer layer is made of, for example, AlGaAs doped with C as a p-type dopant. By providing such an additional spacer, carriers are efficiently confined in the active layer 14, so that the current-light output characteristics of the surface emitting laser element can be improved.

  In the present invention, the second tunnel junction structure separated from the first tunnel junction structure may be single or plural as in the third embodiment. When a plurality of second tunnel junction structures are provided, it is not always necessary to arrange the second tunnel junction structures on a straight line as in the third embodiment, from the viewpoint of preventing laser oscillation of higher-order transverse modes. You may arrange irregularly. In order to prevent high-order transverse mode laser oscillation, the planar shapes of the second tunnel junction structures do not have to be the same.

  In the above embodiment, the substrate 11, the spacer layer 13, the upper layer 21, and the spacer layer 25 are n-type, and the spacer layer 15 and the lower layer 20 are p-type, but the conductivity types of these layers are reversed. May be. The spacer layer 13 may be a non-doped layer.

It is a longitudinal cross-sectional view which shows the surface emitting laser element of 1st Embodiment. It is a cross-sectional view along the II-II line of FIG. It is process drawing which shows the manufacturing method of a surface emitting laser element. It is process drawing which shows the manufacturing method of a surface emitting laser element. It is a figure which shows the electric current-light output characteristic of embodiment and a comparative example. It is a figure which shows the electric current-lateral mode suppression ratio characteristic of embodiment and a comparative example. It is the schematic showing the heat distribution of a comparative example. It is the schematic showing the heat distribution of embodiment. It is a cross-sectional view showing a surface emitting laser element according to a second embodiment. It is a cross-sectional view showing a surface emitting laser element according to a third embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Surface emitting laser element, 11 ... Substrate, 12 ... Lower DBR, 13 ... N-type spacer layer, 14 ... Active layer, 15 ... P-type spacer layer, 25 ... N-type spacer layer, 27 ... Upper electrode, 28 ... Upper DBR, 30 ... lower electrode, 18, 19, 31, 32, 35-37 ... tunnel junction structure, 50 ... comparative laser element.

Claims (4)

A first reflective layer;
A first spacer layer provided on the first reflective layer;
An active layer provided on the first spacer layer;
A second spacer layer provided on the active layer;
A first tunnel junction structure provided on the second spacer layer;
A second tunnel junction structure provided on the second spacer layer and spaced apart from the first tunnel junction structure;
A third spacer layer provided on the second spacer layer, covering the first and second tunnel junction structures and having a first conductivity type;
A second reflective layer provided on the third spacer layer;
With
Each of the first and second tunnel junction structures has a lower layer provided on the second spacer layer and having a second conductivity type, and has the first conductivity type provided on the lower layer. Including upper layer,
Surface emitting laser element.   The surface emitting laser element according to claim 1, wherein the second tunnel junction structure is an annular body surrounding the first tunnel junction structure. The first tunnel junction structure has an elliptical planar shape,
2. The surface emitting laser element according to claim 1, wherein the second tunnel junction structure is an annular body that surrounds the first tunnel junction structure in an elliptical shape. 2. The surface-emitting laser device according to claim 1, further comprising a third tunnel junction structure provided on the second spacer layer and spaced apart from the first and second tunnel junction structures.
The third tunnel junction structure includes: a lower layer provided on the second spacer layer and having the second conductivity type; and an upper layer provided on the lower layer and having the first conductivity type. Including
The first tunnel junction structure has a circular planar shape,
The second and third tunnel junction structures are arranged so as to sandwich the first tunnel junction structure from both sides thereof on one straight line passing through the center of the planar shape of the first tunnel junction structure. The surface emitting laser element according to claim 1.

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