JP5327234B2 - Two-dimensional photonic crystal surface emitting laser and manufacturing method thereof - Google Patents

Abstract

Disclosed is a two-dimensional photonic crystal surface emission laser (100) equipped with a first semiconductor layer (5) in which multiple concave parts (10) are formed as a two-dimensional photonic crystal structure, with the radius of the concave parts (10) gradually changing in the depth direction. The two-dimensional photonic crystal surface emission laser (100) having said structure is manufactured by including a step wherein the concave parts (10) are formed in the first semiconductor layer (5), which is stacked above an active layer (3), to become narrower from the surface opposite the active layer (3) toward the active layer (3).

Description

  The present invention relates to a two-dimensional photonic crystal surface emitting laser that emits a surface by resonating with a two-dimensional photonic crystal and a method for manufacturing the same.

  The surface emitting laser can emit laser light substantially perpendicularly (normal direction) from the substrate surface, can integrate a plurality of laser elements two-dimensionally (two-dimensional array), and each laser. It has various features such as coherent light can be emitted in parallel from the element. For this reason, for example, various applications are expected in various fields such as the storage field, the communication field, and the information processing field, and research and development are progressing.

  In a surface emitting laser, a structure in which an active layer that generates light by carrier injection is sandwiched vertically by a multilayer reflector (DBR) is adopted as a general basic structure. In addition, for example, a two-dimensional photonic crystal is used. There is something to use. Here, the photonic crystal is an optical element that generally has a periodic refractive index distribution that is approximately equal to or smaller than the wavelength of light. Examples of the photonic crystal include a three-dimensional photonic crystal having a three-dimensional refractive index distribution and a two-dimensional photonic crystal having a two-dimensional refractive index distribution. Similar to the phenomenon in which electrons (electron waves) receive black reflections due to the periodic potential of nuclei in semiconductors and band structures are formed in photonic crystals, light waves are subjected to Bragg reflections due to periodic refractive index distribution. A band structure (photonic band structure) is formed. Utilizing this feature, it is expected that various kinds of light can be controlled by the photonic crystal.

  For example, a two-dimensional photonic crystal surface emitting laser includes a photonic crystal periodic structure in which a refractive index period is two-dimensionally arranged in the vicinity of an active layer that emits light by carrier injection, and resonates with the photonic crystal. It emits surface light. For example, Patent Document 1 and the like describe a conventional two-dimensional photonic crystal surface emitting laser. FIG. 22 is a perspective view showing a configuration of a conventional two-dimensional photonic crystal surface emitting laser. More specifically, as shown in FIG. 22, in the two-dimensional photonic crystal surface emitting laser 200, a lower clad layer 102, an active layer 103, and an upper clad layer 104 are roughly stacked on a substrate 101, and the lower clad The layer 102 includes a two-dimensional photonic crystal 120 in the vicinity of the active layer 103.

  The substrate 101 is made of, for example, an n-type InP semiconductor material. The lower cladding layer 102 and the upper cladding layer 104 are, for example, n-type and p-type InP semiconductor layers, respectively, and these have a lower refractive index than the active layer 103. The two-dimensional photonic crystal 120 is configured by forming holes (photonic crystal periodic structure 121) in the lower clad layer 102. Further, SiN or the like may be filled in the holes. Thus, the two-dimensional photonic crystal 120 of the lower cladding layer 102 is composed of a square lattice or a triangular lattice in which media having different refractive indexes are arranged in a two-dimensional cycle. The active layer 103 has a multiple quantum well structure using, for example, an InGaAs / InGaAsP-based semiconductor material, and emits light when carriers are injected. The two-dimensional photonic crystal surface emitting laser 200 forms a double heterojunction with an active layer 103 sandwiched between a lower clad layer 102 and an upper clad layer 104 to confine carriers and concentrate carriers contributing to light emission in the active layer 103. It is like that.

  A lower electrode 106 and an upper electrode 107 made of gold or the like are formed on the bottom surface of the substrate 101 and the upper surface of the upper cladding layer 104. By applying a voltage to the lower electrode 106 and the upper electrode 107, the active layer 103 emits light, and light leaking from the active layer 103 enters the two-dimensional photonic crystal 120. Light whose wavelength matches the lattice spacing of the two-dimensional photonic crystal 120 is amplified by resonance by the two-dimensional photonic crystal 120. As a result, coherent light is surface-emitted from the upper surface of the upper cladding layer 104 (the light emitting region 108 located around the electrode 107).

  Here, the resonance action of the two-dimensional photonic crystal 120 composed of a square lattice as shown in FIG. 23 will be described. FIG. 23 is an explanatory diagram showing the resonance action of the two-dimensional photonic crystal surface emitting laser. The two-dimensional photonic crystal 120 is configured by forming holes 121 in the lower cladding layer 102. A square lattice is formed by forming the holes 121 in two directions orthogonal to each other at the same period. The square lattice has typical directions of the Γ-X direction and the Γ-M direction. If the interval between the holes 121 adjacent to each other in the Γ-X direction is a, a basic lattice E having a square with one side having the hole 121 as a lattice point is formed. Here, when the light L whose wavelength λ matches the lattice interval a of the basic grating E travels in the Γ-X direction, the light L is second-order diffracted at the lattice point. Among these, only the light diffracted in the directions of 0 °, ± 90 °, and 180 ° with respect to the traveling direction of the light L satisfies the Bragg condition. Furthermore, since there are also lattice points in the traveling direction of the light diffracted in the directions of 0 °, ± 90 °, and 180 °, the diffracted light is again in the directions of 0 °, ± 90 °, and 180 ° with respect to the traveling direction. Diffracted into When the light L repeats one or more times of second-order diffraction, the diffracted light returns to the original lattice point, thereby causing a resonance action. Further, light that is first-order diffracted in a direction perpendicular to the paper surface also satisfies the Bragg condition. For this reason, the light amplified by resonance is emitted through the upper clad layer 104 and has a surface emitting function. In addition, since this phenomenon occurs at all lattice points, coherent laser oscillation is possible over the entire surface. Note that Patent Document 1 discloses a method of manufacturing a two-dimensional photonic crystal surface emitting laser by bonding (fusing) a wafer having an active layer formed thereon and a wafer having a two-dimensional photonic crystal 120 formed on the surface thereof. Is described.

  Patent Document 2 describes a method of manufacturing a two-dimensional photonic crystal surface emitting laser without using fusion. Specifically, the manufacturing method described in Patent Document 2 includes a photonic crystal structure step having an epitaxial layer and a dielectric film, and a GaN layer on the dielectric film and the epitaxial layer after the photonic crystal structure step. Forming. According to this manufacturing method, since it is not necessary to use fusion, the device is hardly damaged during manufacturing.

  Patent Document 3 describes a two-dimensional photonic crystal surface emitting laser that forms a photonic crystal by forming a cylindrical recess after forming an upper cladding layer by epitaxial growth. This two-dimensional photonic crystal surface emitting laser has an effect that the threshold current is low and the polarization plane of light is controlled.

  Patent Document 4 describes a two-dimensional photonic crystal surface emitting laser in which the width of the cross-sectional shape with respect to the crystal plane of the photonic crystal structure gradually decreases along the main light emitting direction. Thereby, high light utilization efficiency can be obtained.

  The two-dimensional photonic crystal surface-emitting laser described in Patent Document 1 fuses a wafer on which a photonic crystal is formed and a wafer on which an active layer is disposed immediately above the photonic crystal during manufacturing. By manufacturing. However, it is difficult to fuse the entire wafer surface uniformly, and the yield is poor. In addition, since the optimum fusing conditions are different for each material to be fused, it is necessary to obtain the optimum fusing conditions for each material, and thus the fusing conditions must be changed. The manufacturing method is complicated. Since fusion is usually performed in a reducing or inert atmosphere at a high temperature, damage such as deformation of photonic crystal vacancies may occur during fusion. Further, when warping or waviness is generated in the photonic crystal structure, it becomes difficult to fuse. Therefore, the yield is low.

  The manufacturing method of the two-dimensional photonic crystal surface emitting laser described in Patent Document 2 is possible only when a GaN system is used, and can be realized with a GaAs system or an InP system that is another semiconductor laser material. Can not. In addition, even if the same GaN system is used, when using a plane orientation different from the currently used c-plane, for example, a surface such as a nonpolar plane or a semipolar plane that is being studied with a GaN green laser or LED. When using an azimuth substrate, the growth conditions are different from those on the c-plane. In addition, since it is a special manufacturing method, there is a possibility that the configuration of the two-dimensional photonic crystal laser may be limited.

  Further, in the structure of the two-dimensional photonic crystal surface emitting laser described in Patent Document 3, in order to reduce the threshold value, it is necessary to reduce the diameter of the cylindrical recess to be formed, so that the aspect ratio is high. Become. In order to achieve a configuration that realizes a low threshold value, the aspect ratio becomes too high, and therefore it is actually difficult to form a recess by etching.

  Further, since the two-dimensional photonic crystal surface emitting laser described in Patent Document 4 is manufactured using fusion in the same manner as Patent Document 1, it is the same as the two-dimensional photonic crystal surface emitting laser disclosed in Patent Document 1. There is a problem.

Japanese Patent No. 3989333 JP 2008-130731 A Japanese Patent No. 3613348 Japanese Patent No. 3833953

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a two-dimensional photonic crystal surface emitting laser that can be easily manufactured, has a low cost, and has a high yield, and a method for manufacturing the same. .

  The two-dimensional photonic crystal surface emitting laser of the present invention includes a first semiconductor layer having a plurality of recesses as a two-dimensional photonic crystal structure, and the diameter of the recesses gradually changes along the depth direction. The two-dimensional photonic crystal surface emitting laser having such a configuration is thinned toward the first semiconductor layer stacked on the active layer from the surface opposite to the active layer as it approaches the active layer. It is manufactured by including the process of forming the recessed part which becomes. The two-dimensional photonic crystal surface emitting laser having such a configuration and the method for manufacturing the two-dimensional photonic crystal surface emitting laser can be easily manufactured, have a low cost, and have a high yield.

  The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

It is sectional drawing which shows the structure of the two-dimensional photonic crystal surface emitting laser concerning 1st Embodiment of this invention. It is sectional drawing which shows the model structure of the two-dimensional photonic crystal surface emitting laser used in order to obtain | require coupling coefficient (kappa) and Filling Factor by calculation. It is a graph showing the relationship between coupling coefficient (kappa) calculated | required using the one-dimensional coupled wave theory, and Filling Factor. It is a graph showing the relationship between coupling coefficient (kappa) at the time of changing Al composition of a 1st cladding layer, and Filling Factor. It is sectional drawing which shows the model structure of the laser used in order to obtain | require the relationship between the thickness of a 1st clad layer, and the intensity | strength of optical confinement. It is a graph showing the relationship between the 1st clad layer thickness calculated | required using the transfer matrix method, and the ratio of the light which oozes out to a contact layer. It is a graph showing the relationship between coupling coefficient (kappa) calculated | required using the one-dimensional coupling wave theory and the two-dimensional coupling wave theory, and Filling Factor. It is a graph showing the relationship between coupling coefficient (kappa) and Filling Factor at the time of changing Al composition of the 1st clad layer calculated | required using the two-dimensional coupled wave theory. It is a principal part enlarged view of the two-dimensional photonic crystal surface emitting laser concerning 1st Embodiment of this invention. FIG. 10A is a graph showing calculation results for the surface side FF (Filling Factor) and the active layer side FF (Filling Factor) when the depth of the recess is 0.52 μm, and FIG. 10A is a graph showing the value of the coupling coefficient κ. FIG. 10B is a graph showing the ratio of light that oozes into the contact layer. FIG. 11A is a graph showing calculation results for the surface side FF (Filling Factor) and the active layer side FF (Filling Factor) when the recess depth is 0.92 μm, and FIG. 11A is a graph showing the value of the coupling coefficient κ. FIG. 11B is a graph showing the ratio of light that has oozed into the contact layer. FIGS. 12A to 12E are cross-sectional process diagrams illustrating a manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the first embodiment of the present invention, and FIGS. It is a top view of the resist layer in the state in which the pattern was formed. It is sectional drawing which shows the structure of the two-dimensional photonic crystal surface emitting laser concerning 2nd Embodiment of this invention. It is a principal part enlarged view of the two-dimensional photonic crystal surface emitting laser concerning 2nd Embodiment of this invention. FIGS. 16A to 16D are first cross-sectional process diagrams showing a manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention, and FIGS. . FIGS. 17A to 17D are second cross-sectional process diagrams illustrating a manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention. FIGS. . It is a top view which shows the structure of the electrode of the two-dimensional photonic crystal surface emitting laser in 2nd Embodiment of this invention, Comprising: FIG.18 (A)-FIG.18 (D) show the structure of the electrode of a respectively different shape. It is a top view. FIGS. 19A and 19B are cross-sectional process diagrams for explaining a first manufacturing process as another manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention. ) Is each process drawing. It is sectional process drawing for demonstrating the 2nd manufacturing process as another manufacturing process of the two-dimensional photonic crystal surface emitting laser concerning 2nd Embodiment of this invention. It is sectional drawing which shows the other structure of the two-dimensional photonic crystal surface emitting laser concerning 2nd Embodiment of this invention. It is a perspective view which shows the structure of the conventional two-dimensional photonic crystal surface emitting laser. It is explanatory drawing which shows the resonance effect | action of a two-dimensional photonic crystal surface emitting laser.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a cross-sectional view showing a configuration of a two-dimensional photonic crystal surface emitting laser according to a first embodiment of the present invention. In FIG. 1, a two-dimensional photonic crystal surface emitting laser 100 according to the first embodiment includes a substrate 1, a second cladding layer 2 that is a second semiconductor layer formed on one main surface of the substrate 1, and An active layer 3 formed on the second cladding layer 2, a carrier stop layer 4 formed on the active layer 3, a first cladding layer 5 formed on the carrier stop layer 4, and a first cladding layer 5 Contact layer 6 formed on top, first ring-shaped (ring-shaped, donut-shaped) first electrode 7 formed on contact layer 6, and the other main surface of substrate 1 opposite to the one main surface And the second electrode 8 formed on the entire surface. Note that the portion where the first electrode 7 is not formed on the contact layer 6 is a light emitting surface 9 from which light is emitted. Then, in the first cladding layer 5 and the contact layer 6 made of semiconductor, processing is performed from the main surface on the light emitting surface 9 side (opposite side of the active layer 3), that is, the boundary surface with the first electrode 7, The first cladding layer 5 and the contact layer 6 are formed so that a plurality of recesses 10 are periodically arranged. Thereby, the first semiconductor layer composed of the contact layer 6, the first cladding layer 5, and the carrier stop layer 4 has a two-dimensional photonic crystal structure. Since processing is performed from the first electrode 7 side, the recess 10 is formed at least on the surface of the contact layer 6 on the side in contact with the first electrode 7. This photonic crystal structure selects the wavelength of light that oscillates in the active layer 3. In addition, the diameter of the recessed part 10 is changing gradually along the depth direction. More specifically, in the cross-sectional shape of the surface along the stacking direction, the recess 10 and the semiconductor portion other than the recess 10 have a so-called taper shape.

The substrate 1 is, for example, an n-type GaAs substrate. The second cladding layer 2 is, for example, an n-type semiconductor layer that uses electrons as carriers, and is formed of, for example, n-type Al _0.4 Ga _0.6 As. The carrier stop layer 4 is, for example, a p-type semiconductor layer using holes (holes) as carriers, and is formed of, for example, p-type Al _0.6 Ga _0.4 As. The first cladding layer 5 is also a p-type semiconductor layer using holes (holes) as carriers, for example, and is formed of p-type AlxGa (1-x) As, for example. The contact layer 6 is also a p-type semiconductor layer using holes (holes) as carriers, and is formed of, for example, p + -type GaAs. The conductivity type of each layer in the first semiconductor layer and the second semiconductor layer is not limited to the above. The two-dimensional photonic crystal surface emitting laser 100 has, for example, a structure having p-type and n-type semiconductor layers having different conductivity types in an upper layer of an active layer, such as a buried tunnel junction (BTJ) type. But you can.

  As described above, the active layer 3 is sandwiched between the second semiconductor layer composed of the second cladding layer 2 and the first semiconductor layer composed of the contact layer 6, the first cladding layer 5, and the carrier stop layer 4, Light is generated (emitted) by carrier injection. A carrier stop layer 4 is disposed between the active layer 3 and the first cladding layer 5. The active layer 3 can employ known general materials and structures, and the materials, structures, and the like are selected so as to emit light having a wavelength corresponding to the intended use. The active layer 3 may have a strained quantum well structure constituted by, for example, a three-period InGaAs well layer, a GaAs barrier layer, and a separate confinement layer (SCH (Separate Confinement Heterostructure) layer).

  The first and second cladding layers 5 and 2 are formed of a material having a refractive index lower than that of the active layer 3 and have the functions of the lower and upper cladding layers. The refractive index of the first cladding layer 5 is preferably higher than the refractive index of the second cladding layer 2. As described above, when the refractive index of the first cladding layer 5 is made higher than the refractive index of the second cladding layer 2, the average refractive index of the first cladding layer 5 is formed when a two-dimensional photonic crystal structure is formed. Does not drop too much. This prevents a reduction in the proportion of light distributed in the layer in which the photonic crystal structure is formed, and thus prevents a decrease in the coupling coefficient κ.

  The two-dimensional photonic crystal surface emitting laser 100 forms a double heterojunction with the active layer 3 interposed therebetween, confines carriers, and concentrates carriers contributing to light emission in the active layer 3. The contact layer 6 is disposed between the first electrode 7 and the first clad layer 5 and electrically connects them. The carrier stop layer 4 functions as a potential barrier against electrons traveling from the active layer 3 to the first cladding layer 5 due to carrier overflow. Note that the carrier stop layer 4 may not be disposed between the first cladding layer 5 and the active layer 3. Further, another layer may be interposed between the first cladding layer 5 and the active layer 3.

  The first and second electrodes 7 and 8 are made of, for example, an ITO (Indium Tin Oxide) electrode or a gold electrode, and a voltage is applied between the first electrode 7 and the second electrode 8. As a result, carriers are injected into the active layer 3, and the active layer 3 emits light at a voltage value equal to or higher than a predetermined value. The first and second electrodes 7 and 8 not only have conductivity, but are transparent to the wavelength of the laser light emitted by the two-dimensional photonic crystal surface emitting laser 100 on the light emitting surface side. A transparent electrode using a conductive material is preferable. Therefore, it is preferable to use an ITO electrode. The first electrode 7 provided on the light emitting surface 9 side forms an opening, and the second electrode 8 is formed on the entire surface of the substrate 1. With such a configuration, laser light is selectively emitted from the surface on which the first electrode 7 is formed. The two-dimensional photonic crystal surface emitting laser 100 has a configuration in which a part or all of the first electrode 7 is a transparent electrode, and the first electrode 7 is formed on the entire surface of the light emitting surface 9 without forming an opening. There may be. In such a configuration, laser light is emitted through the transparent electrode.

  In the present embodiment, the upper surface of the first cladding layer 5 is an emission surface (light emitting surface 9) that emits laser light. However, for example, the bottom surface of the substrate 1 can be the light emitting surface. . Specifically, the substrate 1 may be made of a material that is transparent to the wavelength band of light to be extracted, the first electrode 7 may be formed on the entire surface of the contact layer 6, and the opening may be formed in the second electrode 8. Thus, the two-dimensional photonic crystal surface emitting laser 100 can emit laser light from the opening formed in the second electrode 8. Also in this case, in the two-dimensional photonic crystal surface emitting laser 100, a part or all of the second electrode 8 is a transparent electrode, and the second electrode 8 is formed on the entire surface of the substrate 1 without forming an opening. It may be a configuration. Thereby, a laser beam is emitted through the transparent electrode.

  In the two-dimensional photonic crystal structure formed in the first cladding layer 5 and the contact layer 6, the two-dimensional periodic refractive index distribution has a refractive index different from the refractive index of the material forming the first cladding layer 5. Are arranged at predetermined periods (lattice spacing, lattice constant) in two different directions (two linearly independent directions) as lattice points. In the present embodiment, the lattice point is constituted by, for example, a conical recess 10 formed in the first cladding layer 5 and the contact layer 6. The recess 10 may reach not only the contact layer 6 and the first cladding layer 5 but also the carrier stop layer 4, but preferably does not reach the active layer 3. When the recess 10 reaches the active layer 3, that is, when the photonic crystal and the active layer 3 are close to each other, damage to the active layer 3 may occur during etching.

  Here, in the semiconductor and the recess 10 on the upper surface of the contact layer 6, when the ratio of the area occupied by the semiconductor is the front side FF, and a cross section by a plane including the bottom surface of the recess 10 in the first cladding layer 5 is assumed In the semiconductor and the recess 10 in this cross section, the ratio of the area occupied by the semiconductor is defined as the active layer side FF. As described above, since the cross section of the recess 10 is tapered, the surface side FF and the active layer side FF have different values. Thus, since the cross-sectional shape of the concave portion 10 is tapered, the value of the coupling coefficient κ of the two-dimensional photonic crystal is high and the light confinement effect is high. And formation of the recessed part 10 becomes easy. For example, although the recessed part 10 is formed by etching, the formation difficulty can be reduced. The active layer side FF is preferably larger than the surface side FF. That is, the recess 10 has a tapered shape that becomes thinner as the active layer 3 is approached. Therefore, it can be easily manufactured as compared with the concave portion 10 having a tapered shape that becomes thicker as the active layer 3 is approached. Moreover, it is preferable that surface side FF is 0.8 or less, and the said active layer side FF is 0.8 or more. Thereby, a high coupling coefficient κ in the two-dimensional photonic crystal and a high light confinement effect by the first cladding layer 5 can be obtained. And it is easy to manufacture a two-dimensional photonic crystal.

  The thickness of the first cladding layer 5 is preferably about 0.3 μm to 1.0 μm although it depends on the refractive index of the first cladding layer 5. More preferably, it is around 0.5 μm. Thereby, an aspect ratio becomes small, formation of the recessed part 10 is easy, and the light confinement effect can fully be acquired. If the first cladding layer 5 is too thin, light confinement becomes insufficient, and light absorption by the first electrode 7 becomes a problem. On the other hand, if the first cladding layer 5 is too thick, the aspect ratio becomes high and it becomes difficult to form the recess 10.

  In the two-dimensional photonic crystal surface emitting laser 100 according to the above-described embodiment, the active layer 3 emits light when a voltage is applied between the first electrode 7 and the second electrode 8. The light leaking from the active layer 3 enters the two-dimensional photonic crystal structure formed in the contact layer 6 and the first cladding layer 5, and the light whose wavelength matches the lattice spacing is resonated by the two-dimensional photonic crystal. The coherent light is emitted from the light emitting surface 9.

  Here, the coupling coefficient κ of a laser including such a two-dimensional photonic crystal will be described. An important parameter in such a diffraction grating coupled laser is the coupling coefficient κ of the diffraction grating. Here, since the photonic crystal structure is a diffraction grating and the two-dimensional photonic crystal structure is a two-dimensional diffraction grating, the two-dimensional photonic crystal laser is a DFB (distributed feedback laser) using a normal one-dimensional diffraction grating. : Distributed feedback type) laser can be considered in the same way. The coupling coefficient κ is a value indicating the rate at which light is coupled to the diffraction grating. The coupling coefficient κ is expressed by the following equation (1) using a known one-dimensional coupled wave theory in a DFB laser using a one-dimensional diffraction grating (for example, W. Streifer et al., “Coupled Wave Analysis of DFB”). and DBR Lasers ”, IEEE Journal of Quantum Electronics, vol. QE-13, No. 4, pp. 134, 1977).

Here, the direction perpendicular to the diffraction grating is x, and the light propagation direction is z. K ₀ is the wave number in free space, β ₀ is the propagation constant in the z direction, A _q is the q-order component when the square of the refractive index is Fourier-expanded in the z direction, and ε ₀ is the electric field amplitude, ε ₀ ^* (x) is its conjugate complex number, and P is obtained by integrating {ε ₀ (x) ε ₀ ^* (x)} over the entire x direction. When the cross section of the one-dimensional diffraction grating is rectangular, it is represented by the following formula (2) more simply.

Here, n ₁ and n ₂ are the refractive indexes of the materials constituting the one-dimensional diffraction grating, m is the order of Bragg diffraction, and Γ _grating is the proportion of light distributed in the one-dimensional diffraction grating layer (light Confinement factor), w is the width of the groove in the one-dimensional diffraction grating, and Λ is the period of the one-dimensional diffraction grating. As can be seen from the equation (2), the coupling coefficient κ is “the refractive index difference of the material constituting the one-dimensional diffraction grating”, “the ratio of the light distributed in the one-dimensional diffraction grating layer”, “the groove in the one-dimensional diffraction grating”. Width ".

Using Equation (2), the relationship between the coupling coefficient κ in the two-dimensional photonic crystal surface emitting laser 100 and the filling factor (hereinafter referred to as FF), that is, the ratio of the high refractive index portion in the entire two-dimensional photonic crystal structure is calculated. Ask for. The FF is specifically represented by (1-w / Λ). Thus, in the case of a one-dimensional diffraction grating (one-dimensional photonic crystal structure), the value is obtained by subtracting the ratio of the groove to the period in the one-dimensional photonic crystal structure from one, but the two-dimensional photonic crystal structure In this case, when the unit cell of the two-dimensional photonic crystal is considered, the ratio of the area of the recess (low refractive index material) in the unit cell is a value obtained by subtracting from 1. In the calculation, a two-dimensional photonic crystal surface emitting laser having the configuration shown in FIG. 2 is used as the two-dimensional photonic crystal surface emitting laser. FIG. 2 is a cross-sectional view showing a model configuration of a two-dimensional photonic crystal surface emitting laser used for calculating a coupling coefficient κ and a filling factor. In FIG. 2, electrodes are omitted because they are not used in the calculation. In FIG. 2, the substrate 21 is made of GaAs having a refractive index of 3.524 and the thickness is infinite. The second cladding layer 22 was Al _0.4 Ga _0.6 As having a refractive index of 3.306, and the thickness was 2.0 μm. The active layer 23 has an SCH-MQW (Multiple Quantum Well) structure, a refractive index of 3.539, and a thickness of 0.144 μm. The carrier stop layer 24 was made of Al _0.6 Ga _0.4 As having a refractive index of 3.195 and the thickness was 0.04 μm. Further, a portion 25b of the first cladding layer 25 that does not have a photonic crystal structure is Al _0.4 Ga _0.6 As having a refractive index of 3.306, and a thickness of 0.04 μm. Further, the portion 25a having the photonic crystal structure in the first cladding layer 25 is made of Al _0.4 Ga _0.6 As having a refractive index of 3.306 and a material having a refractive index of 1.5. 30 (for example, SiO ₂ ) are alternately and periodically formed as shown in FIG. 2, and the thickness is 1.96 μm. Further, the contact layer 26 is formed by alternately and periodically forming GaAs having a refractive index of 3.5242 and a material 30 (for example, SiO ₂ ) having a refractive index of 1.5 as shown in FIG. The thickness was 0.02 μm. In addition, air having a refractive index of 1.0 is disposed on the contact layer 26 in an infinite thickness. In such a two-dimensional photonic crystal surface emitting laser, the relationship between the coupling coefficient κ and FF was obtained by using Equation (2) assuming that the diffraction order m is 2. As described above, equation (2) is a calculation formula for a one-dimensional diffraction grating (one-dimensional photonic crystal structure), but it can be used as a simple approximation in the calculation for a two-dimensional photonic crystal. Can do. Note that Γ _grating was calculated by the transfer matrix method assuming a slab waveguide. The wavelength of light was assumed to be 980 nm.

The result calculated by equation (2) is shown in FIG. FIG. 3 is a graph showing the relationship between the coupling coefficient κ obtained using the one-dimensional coupled wave theory and the filling factor. Note that the cross-sectional shape of the material 30 (for example, SiO ₂ ) in the photonic crystal structure is first calculated in the case of a rectangular parallelepiped shape rather than the taper shape, that is, the case where the concave portion formed in the photonic crystal is columnar. As shown in FIG. 3, the FF greatly depends on the coupling coefficient κ, and has a maximum value near FF = 0.9. In the two-dimensional photonic crystal surface emitting laser, the larger the coupling coefficient κ, the better the characteristics due to the photonic crystal structure. However, when FF = 0.9, when the one-dimensional photonic crystal structure is used, the groove width is 0.1 with respect to the period. For example, when the period is 300 nm, the groove width is 30 nm. Therefore, since the pattern shape is miniaturized, it is difficult to manufacture. In addition, it is necessary to form a cylindrical recess having a diameter of about 100 nm as a two-dimensional photonic crystal, which is difficult to manufacture because the pattern shape is miniaturized. More specifically, in the case of a one-dimensional photonic crystal structure, an etching depth of about 1.9 μm is required if the thickness of the first cladding layer 25 that is the upper cladding layer is 2 μm as a general laser. Therefore, the aspect ratio is 60, and if the two-dimensional photonic crystal structure is used, the aspect ratio is 20, and a periodic structure with a very high aspect ratio is required. Therefore, the processing difficulty is high.

In general, in a laser having a one-dimensional photonic crystal structure, the coupling coefficient κ is required to be 1000 cm ⁻¹ or more (for example, D. Ohnishi et al., Optics Express, vol. 12, No. .8, pp.1562, 2004). However, since the maximum value shown in FIG. 3 is 500 cm ⁻¹ , favorable characteristics cannot be obtained with the configuration of the two-dimensional photonic crystal surface emitting laser shown in FIG. This is because the two-dimensional photonic crystal surface emitting laser according to the present embodiment forms a photonic crystal structure by processing from the surface of the first cladding layer 25, and thus the first cladding layer 25 which is the upper cladding layer. This is probably because the average refractive index of the entire first cladding layer 25 is lowered and Γ _grating is reduced because the portion filled with the material 30 which is a low refractive index material is formed.

In order to increase the coupling coefficient κ, for example, the refractive index of the first cladding layer 25 is increased by changing the composition of Al in the first cladding layer 25 of Al _0.4 Ga _0.6 As. A method is conceivable. More specifically, for the case where the Al composition is decreased from 40% to 0%, the calculation is performed using Equation (2), and the calculation result is shown in FIG. FIG. 4 is a graph showing the relationship between the coupling coefficient κ and the filling factor when the Al composition of the first cladding layer is changed. As shown in FIG. 4, when the Al composition is 30% or less, the maximum value of the coupling coefficient κ exceeds the required value of 1000 cm ⁻¹ described above. It can also be seen that by further reducing the Al composition, the coupling coefficient κ becomes 5000 cm ⁻¹ or more, which is significantly improved. Thus, a sufficient coupling coefficient κ can be obtained by designing the refractive index of the first cladding layer 25 to be high.

In addition, since the two-dimensional photonic crystal surface emitting laser has a periodic structure with a high aspect ratio, the thickness of the first cladding layer 25 may be reduced in order to improve the difficulty in processing. However, if the thickness is too thin, the light confinement effect of the first cladding layer 25 is weakened, and light absorption by the first electrode 7 is increased, resulting in a problem that the oscillation threshold is increased. Thereby, the problem of not oscillating may also arise. Therefore, the thickness of the first cladding layer 25 having a sufficient light confinement effect was obtained by calculation. For this calculation, a laser having the configuration shown in FIG. 5 was used. FIG. 5 is a cross-sectional view showing a model configuration of a laser used for obtaining the relationship between the thickness of the first cladding layer and the intensity of optical confinement. As shown in FIG. 5, the model used for calculating the optical confinement effect in the second cladding layer was formed of a substrate 31 that is an n-type GaAs substrate and an n-type Al _0.4 Ga _0.6 As. Second cladding layer 32, active layer 33, carrier stop layer 34 formed of p-type Al _0.6 Ga _0.4 As, and first cladding layer formed of p-type Al x Ga (1-x) As 35 and a contact layer 36 made of p + type GaAs are sequentially stacked. Further, the wavelength of light is assumed to be 980 nm as in the previous calculation.

  In the model shown in FIG. 5, when the Al composition of the first cladding layer 35 is 40% that is used in an ordinary laser, the thickness of the first cladding layer 35 and the ratio of light that oozes out to the surface of the contact layer 36 are calculated. And is shown in FIG. Further, when a diffraction grating (one-dimensional or two-dimensional) is formed in the first cladding layer 35 and the contact layer 36 when the Al composition is 0%, the FF is changed to change the first cladding layer 35. The thickness and the percentage of light that oozes into the contact layer 36 are calculated and are shown in FIG. The FF is changed from 0.9 to 0.6. FIG. 6 is a graph showing the relationship between the thickness of the first cladding layer obtained using the transfer matrix method and the ratio of light that leaks into the contact layer. As shown in FIG. 6, in the case of FF = 0.9 where the coupling coefficient κ is an optimum value, the proportion of light that oozes out to the contact layer 36 increases by an order of magnitude or more compared to the case where there is no diffraction grating. It can be seen that the light confinement effect of the first cladding layer 35 is weak. On the other hand, if the FF is 0.8 or less, a light confinement effect stronger than a normal Al composition of 40% can be obtained. In this case, even if the thickness of the first cladding layer 35 is 0.5 to 1 μm or less, which is thinner than the thickness of the upper cladding layer in a normal laser, a sufficiently strong optical confinement effect Is obtained. Therefore, the thickness of the first cladding layer 35 is preferably about 0.3 μm to 1.0 μm. More preferably, it may be about 0.5 μm. This reduces the aspect ratio while obtaining a sufficient light confinement effect. Thereby, formation of a recessed part becomes easy. Specifically, the difficulty of etching processing decreases.

  As described above, a method for increasing the coupling coefficient κ and decreasing the aspect ratio in the two-dimensional photonic crystal surface emitting laser has been calculated. However, Equation (2) used in the above calculation is for a one-dimensional diffraction grating (one-dimensional photonic crystal structure). Even if it is a formula related to the one-dimensional photonic crystal structure, it can be used approximately in the analysis of the two-dimensional photonic crystal structure. Similar calculations are performed using an exact solution of the coupling coefficient κ. For the exact solution in the two-dimensional photonic crystal structure, for example, a two-dimensional coupled wave theory for a known two-dimensional diffraction grating is used. This theory is shown, for example, in “K. Sakai et al.,“ Coupled-wave model for square-lattice two-dimensional photonic crystal with transverse-electric-like mode ”, Applied Physics Letters, vol. 89, 021101 (2006)”. Has been. First, the relationship between the coupling coefficient κ and FF was determined using the model shown in FIG. The refractive index and thickness of each layer are also the same as those described above. Further, assuming that the lattice point shape is a perfect circle, the coupling coefficient κ for diffraction in the 180 ° direction was calculated in both the one-dimensional (1D) and two-dimensional (2D) cases.

FIG. 7 is a graph showing the relationship between the coupling coefficient κ and the filling factor determined using the one-dimensional coupled wave theory and the two-dimensional coupled wave theory. As shown in FIG. 7, the maximum value in the case of the two-dimensional photonic crystal structure (2D calculation) is 0.5 times the maximum value in the case of the one-dimensional photonic crystal structure (1D calculation). It is about. Therefore, as described above, generally, when the coupling coefficient κ of a two-dimensional photonic crystal laser is approximately estimated by the one-dimensional coupled wave theory, a coupling coefficient of 1000 cm ⁻¹ or more is required for low threshold oscillation. κ is required. Here, from the result shown in FIG. 7, when the coupling coefficient of the two-dimensional photonic crystal laser is estimated by the two-dimensional coupled wave theory, it is considered that 500 cm ⁻¹ or more is necessary. Further, using the two-dimensional coupled wave theory, the relationship between the coupling coefficient κ and the filling factor when the Al composition of the first cladding layer 25 is changed was obtained by calculation. In the calculation, the relationship between the coupling coefficient κ and the Filling Factor is calculated under the same conditions as those for obtaining the graph shown in FIG. 4, and the calculation result is shown in FIG. FIG. 8 is a graph showing the relationship between the coupling coefficient κ and the filling factor obtained by changing the Al composition of the first cladding layer, which is obtained using the two-dimensional coupled wave theory. As can be seen from a comparison between FIG. 4 and FIG. 8, there is a slight difference between the two, but both show the same tendency of taking a maximum value at FF = 0.9 to 0.95. Therefore, it can be understood that the analysis of the two-dimensional photonic crystal using the one-dimensional coupled wave theory is an effective approximation.

  From the above calculation results, in the two-dimensional photonic crystal surface emitting laser, the FF of the photonic crystal structure is preferably near 0.9. However, FF is preferably 0.8 or less, more preferably 0.7 or less, from the viewpoint of optical confinement of the cladding layer and processing difficulty. Thus, although the preferable FF values are different, in order to include both of these preferable conditions, the cross-sectional shape of the two-dimensional photonic crystal structure in the two-dimensional photonic crystal surface emitting laser is preferably tapered. . That is, in the concave portion 10 (see FIG. 1), it is preferable that the surface side FF and the active layer side FF are different in cross-sectional shape. FIG. 9 is an enlarged view of a main part of the two-dimensional photonic crystal surface emitting laser according to the embodiment of the present invention. More specifically, FIG. 2 is an enlarged view of a photonic crystal structure portion in the two-dimensional photonic crystal surface emitting laser 100 shown in FIG. In addition, surface side FF means FF in the main surface by the side of a light emission surface among the main surfaces of the contact layer 6. FIG. The active layer side FF is an FF on the surface 10 a along the bottom surface of the recess 10 formed in the first cladding layer 5.

Hereinafter, preferable values of the surface side FF and the active layer side FF are obtained by calculation. For the calculation, the model having the configuration shown in FIG. 2 is used, and the conditions other than the first cladding layer 25 are substantially the same as those described above. The first cladding layer 25 is AlxGa (1-x) As and the Al composition is 0%. Specifically, the portion 25b of the first cladding layer 25 that does not have a photonic crystal structure is Al _0.0 Ga _1.0 As having a refractive index of 3.5242, and the thickness is 0. The thickness was 04 μm. Further, the portion 25a having the photonic crystal structure in the first cladding layer 25 is made of Al _0.0 Ga _1.0 As having a refractive index of 3.5242 and a material having a refractive index of 1.5. 30 are alternately and periodically formed as shown in FIG. 2, and the thickness is 0.5 μm or 0.9 μm. Further, the depths of the recesses in the first cladding layer 25 and the contact layer 26 are also changed. Note that the depth of the recess corresponds to the length of the material 30 in the depth direction. Specifically, the thickness of the entire first cladding layer 25 was calculated as 0.54 μm or 0.94 μm. When the thickness of the entire first cladding layer 25 is 0.54 μm, the thickness of the portion 25 a having the photonic crystal structure is 0.5 μm, and the thickness of the entire first cladding layer 25 is Is 0.94 μm, the thickness of the portion 25 a having the photonic crystal structure is 0.9 μm. Further, since the thickness of the contact layer 26 is 0.02 μm, the recess depth when the thickness of the entire first cladding layer 25 is 0.54 μm is 0.52 μm. When the thickness of the entire cladding layer 25 is 0.94 μm, the recess depth is 0.92 μm.

  For the calculation, a two-dimensional coupled wave theory was used. Then, when the values of the surface side FF and the active layer side FF are changed from 0.0 to 1.0, the diffraction coupling coefficient κ in the 180 ° direction and the ratio of the light oozing out to the contact layer 26 are calculated. It was done. FIG. 10 is a graph showing calculation results for the surface side FF (Filling Factor) and the active layer side FF (Filling Factor) when the depth of the recess is 0.52 μm. FIG. 10A shows the coupling coefficient κ. FIG. 10B is a graph showing the ratio of light that oozes into the contact layer.

From FIG. 10 (A) and FIG. 10 (B), when the depth of the recess is 0.52 μm, the coupling coefficient κ is as follows in a wide range of the surface side FF if the active layer side FF is 0.8 or more. 500 cm ⁻¹ or more. In particular, when the surface side FF is around 0.9, the coupling coefficient κ exceeds 1500 cm ⁻¹ . In addition, if the surface side FF is 0.8 or less, the contact layer is thin although the total thickness of the first cladding layer 25 and the contact layer 26 is about 0.5 μm (more precisely, 0.56 μm). Since the oozing to 26 is 0.01% or less, it can be said that a sufficient light confinement effect is obtained. Therefore, the active layer side FF is preferably 0.8 or more, more preferably 0.9 or more. Moreover, it is preferable that surface side FF shall be 0.8 or less. Thereby, there is an effect that both a high coupling coefficient κ and strong light confinement can be achieved. If the surface-side FF is too small, there is a problem that the semiconductor portion existing between the recesses in the two-dimensional photonic crystal structure becomes thin and structurally weak. Furthermore, the smaller the area of the contact layer 6 in a plan view of the two-dimensional photonic crystal surface emitting laser 100, the smaller the area of the first electrode 7 formed on the contact layer 6, and the higher the electrical resistance. (See FIG. 1). Therefore, it is not preferable that the surface-side FF is too small, and the surface-side FF is preferably 0.4 or more.

  Further, in the two-dimensional photonic crystal surface emitting laser 100 according to the present embodiment, in the manufacture, after stacking semiconductors, a photonic crystal structure is formed by performing etching or the like from the semiconductor surface. Considering the use of such a processing method, it is preferable that the active layer side FF is the same as or larger than the surface side FF from the viewpoint of processing difficulty. That is, in the cross-sectional shape by the plane along the photonic crystal structure lamination direction, the concave portion 10 is preferably a rectangular parallelepiped rather than a tapered shape or a tapered shape that becomes thinner toward the active layer side.

  Next, calculation results for the surface-side FF and the active layer-side FF when the recess depth is 0.92 μm will be described. FIG. 11 is a graph showing the calculation results for the surface side FF (Filling Factor) and the active layer side FF (Filling Factor) when the depth of the recess is 0.92 μm. FIG. It is a graph which shows the value of (kappa), FIG.11 (B) is a graph which shows the ratio of the light which oozed out to the contact layer.

From FIG. 11 (A) and FIG. 11 (B), when the depth of the recess is 0.92 μm, the coupling coefficient κ is 500 cm ⁻¹ or more. In particular, the coupling coefficient κ exceeds 2000 cm ⁻¹ when the surface side FF is around 0.9. Further, if the surface side FF is 0.9 or less, the contact layer is thin although the total thickness of the first cladding layer 25 and the contact layer 26 is as thin as about 1.0 μm (more precisely, 0.96 μm). Since the oozing to 26 is 0.01% or less, it can be said that a sufficient light confinement effect is obtained. Therefore, the active layer side FF is preferably 0.8 or more, more preferably 0.9 or more. Moreover, it is preferable that surface side FF shall be 0.9 or less. As a result, there is an effect that both a high coupling coefficient κ and strong light confinement can be achieved. If the surface-side FF is too small, there is a problem that the semiconductor portion existing between the recesses in the two-dimensional photonic crystal structure becomes thin and structurally weak. Furthermore, the smaller the area of the contact layer 6 in a plan view of the two-dimensional photonic crystal surface emitting laser 100, the smaller the area of the first electrode 7 formed on the contact layer 6, and the higher the electrical resistance. (See FIG. 1). Therefore, it is not preferable that the surface-side FF is too small, and the surface-side FF is preferably 0.4 or more.

  Further, in the two-dimensional photonic crystal surface emitting laser 100 according to the present embodiment, in the manufacture, after stacking semiconductors, a photonic crystal structure is formed by performing etching or the like from the semiconductor surface. Considering the use of such a processing method, it is preferable that the active layer side FF is the same as or larger than the surface side FF from the viewpoint of processing difficulty.

In the above calculation, the Al composition of the first cladding layer 25 made of AlxGa (1-x) As is set to 0%, and the thicknesses are set to 0.54 μm and 0.94 μm. Here, if the Al composition is increased and the average refractive index of the first cladding layer 25 is increased, a sufficient optical confinement effect can be obtained even if the thickness of the first cladding layer 25 is about 0.3 μm or less. Can do. Therefore, the processing difficulty can be further reduced. If the processing is possible even if the processing difficulty level is increased, the thickness of the first cladding layer 25 is set to be thicker than 0.54 μm, for example, 0.75 μm to 1.0 μm. As can be seen from the comparison, the value of the coupling coefficient κ can be increased as a whole, and the proportion of the light leaking into the contact layer 26 can be reduced. As a result, the range of the FF in which the coupling coefficient κ can obtain a value larger than 500 cm ⁻¹ can be widened, and the leakage of light to the contact layer 26 can be further reduced, and the absorption of light at the upper electrode can be further increased. It turns out that it can suppress.

  As described above, in the two-dimensional photonic crystal surface emitting laser 100 (see FIG. 1) according to the present embodiment, a two-dimensional photonic crystal structure is formed in the first semiconductor layer including the first cladding layer 5. As a result, the average refractive index of the first cladding layer 5 can be made significantly lower than that of the active layer 3. Therefore, the first cladding layer 5 can be made of a material having a composition having a higher refractive index than that of a normal semiconductor laser. Furthermore, a sufficient light confinement effect can be obtained even if the thickness of the first cladding layer 5 is thinner than that of a normal semiconductor laser. For example, in a 980 nm band laser, when AlxGa (1-x) As is used as the first cladding layer 5, the Al composition is generally 40% to 60%. The thickness of the first cladding layer 5 is generally about 1.5 to 2.0 μm. However, in the two-dimensional photonic crystal surface emitting laser 100 according to the present embodiment, the Al of the first cladding layer 5 is If the composition is 0% to 20% and the thickness is 0.5 to 1.0 μm, a sufficient light confinement effect can be obtained.

  Therefore, since the aspect ratio and depth of the two-dimensional photonic crystal structure can be reduced, the processing difficulty is lowered. Specifically, the recess 10 can be easily formed by etching. Further, since the Al composition is low, the problem of device deterioration due to the oxidation of Al, which is a problem particularly in a material containing Al, is reduced. Moreover, since the Al composition is low, the electrical resistance and thermal resistance of the first cladding layer 5 are lowered, and the device characteristics are improved. Further, when a GaN-based material is used for the first clad layer 5, the deterioration of crystallinity can be avoided in addition to the above because the Al composition is lowered. Further, when AlGaN is used for the first cladding layer 5, GaN having a lower Al composition and having an Al composition of zero can be used as the first cladding layer. Thereby, the problem that it is difficult to make p-type, which is a general problem with AlGaN-based materials, can also be avoided.

  Next, a manufacturing method of the two-dimensional photonic crystal surface emitting laser according to the present embodiment will be described with reference to the drawings. FIG. 12 is a cross-sectional process diagram illustrating a manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the embodiment of the present invention, and FIGS. 12A to 12E are process diagrams. . Specifically, a manufacturing method of a 980 nm band two-dimensional photonic crystal surface emitting laser using InGaAs as an active layer on a GaAs substrate will be described. It should be noted that other wavelength band material systems such as InGaAsP-based materials on InP substrates, InGaN on GaN substrates, and AlGaN systems can be manufactured in the same manner.

As shown in FIG. 12A, first, an organic metal vapor phase epitaxy (MOVPE) method, a molecular beam epitaxy (MBE) method, or the like is formed on a substrate 1 formed of n-type GaAs. Thus, the semiconductor laser structure is grown sequentially. More specifically, a second cladding layer 2 (thickness 2.0 μm) formed of n-type Al _0.4 Ga _0.6 As on the substrate 1, an additive-free InGaAs / GaAs quantum well active layer 3, Carrier stop layer 4 (thickness 40 nm) formed of p-type Al _0.6 Ga _0.4 As, first cladding layer 5 (thickness 0.5 μm) formed of p-type GaAs, formed of p + -type GaAs The contact layers 6 (thickness 20 nm) are sequentially stacked. Here, the active layer 3 is a strained quantum well structure composed of three periods of an InGaAs well layer (thickness 8 nm), a GaAs barrier layer (thickness 20 nm), and a separate confinement layer (SCH layer) (thickness 20 nm). The quantum well emission wavelength is designed to be 980 nm. In the present embodiment, the above-described crystal growth process may be performed once, so that a two-dimensional photonic crystal surface emitting laser can be easily manufactured.

Next, as shown in FIG. 12B, SiO ₂ (which may be SiN or metal (Ni, Cr, Ti, etc.)) is formed on the contact layer 6 by plasma CVD, sputtering, vapor deposition or the like as the etching mask layer 11. Then, a resist layer 12 (electron beam resist, imprint material or the like) is formed thereon by a method such as spin coating.

Thereafter, as shown in FIG. 12C, a two-dimensional photonic crystal structure pattern is formed on the resist layer 12 by using an electron beam drawing method or a nanoimprint method, and the pattern formed on the resist layer 12 is changed to RIE ( reactive ion etching: ICP (Inductively)
It is transferred to the etching mask layer 11 by dry etching such as coupled plasma. More specifically, the pattern is, for example, a cylindrical recess 13. When surface emitting light having a wavelength of 980 nm, the period of the two-dimensional photonic crystal structure pattern is about 290 nm, and the diameter of the concave portion 13 that is the pattern is about 50 to 200 nm. FIG. 13 is a plan view of the resist layer in a state where a pattern is formed. As shown in FIG. 13, the columnar recesses 13 are regularly arranged in a range of 20 μm square or more. The array region of the recesses 13 may be a square shape, a rectangular shape, a circular shape, or the like.

  In the present embodiment, the two-dimensional photonic crystal structure has a structure in which square lattice points are arranged in a square lattice. However, the lattice point shape is not limited to this, for example, a triangular shape. Alternatively, a known shape such as an ellipse or a V shape may be used. Furthermore, the arrangement is not limited to this, and a known structure such as a triangular lattice arrangement, a composite type of lattice points having different sizes, or a photonic quasicrystal may be used. Such lattice point shapes and arrangements are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2003-23193, 2007-273730, 2006-59864, and 2004-296538.

  Next, as shown in FIG. 12D, the recess 10 is formed by etching the contact layer 6 and the first cladding layer 5 by dry etching such as ICP or RIE using the etching mask layer 11 as a mask. As the etching gas, methane / hydrogen gas, chlorine gas, iodine gas, bromine gas, or the like generally used for dry etching of III-V semiconductors is used. During etching, the cross section of the two-dimensional photonic crystal structure may be formed in a tapered shape. More specifically, the active layer side FF may be made larger than the surface side FF. An etching method in this case will be described. First, in the first method, a hole having a small diameter is formed as a pattern (concave portion 13) at the beginning of etching, and the mask pattern is gradually reduced by utilizing the receding of the mask as the etching proceeds. This is a method in which the upper and lower diameters of the recess 10 are made different by spreading them out. The second method is a method of setting an etching condition that strengthens the sidewall protection of the recess 10 formed by etching. That is, an etching condition is used in which a protective film is deposited on the side wall with the etching and the hole diameter is reduced. Further, when the property that the etching rate by the etching gas is greatly changed by the Al composition is used, the carrier stop layer 4 can also be used as the etching stop layer.

  In the recess 10 formed by etching, the active layer side FF is preferably 0.8 or more, more preferably 0.9 or more. Moreover, it is preferable that surface side FF shall be 0.8 or less. Thereby, there is an effect that both a high coupling coefficient κ and strong light confinement can be achieved. If the surface-side FF is too small, there is a problem that the semiconductor portion existing between the recesses in the two-dimensional photonic crystal structure becomes thin and structurally weak. Furthermore, in order to prevent the problem that the electrical resistance is increased because the area of the first electrode 7 is reduced, the surface side FF is preferably set to 0.4 or more.

  The etching needs to be stopped before reaching the active layer 3. More specifically, the etching is stopped halfway without etching all of the first cladding layer 5. Thereby, the damage to the active layer 3 by the said etching can be suppressed, and the fall of luminous efficiency can be avoided. More specifically, the etching is preferably stopped at any position from 50 nm before the active layer 3 to immediately before the active layer 3. The closer the bottom surface of the recess 10 formed by etching is to the active layer 3, the larger the coupling coefficient κ of the photonic crystal structure, but if it is too close, the active layer 3 may be damaged by plasma.

Here, an example of specific conditions for making the cross-sectional shape of the above-described photonic crystal a tapered shape will be described. As described above, the etching mask layer 11 is dry-etched by using the RIE apparatus for the contact layer 6 formed of p + type GaAs and the first cladding layer 5 formed of p type GaAs as SiO _2. . The etching gas was BCl ₃ , the gas flow rate was 2 sccm, the pressure was 5 mTorr, the RF power was 100 W, and the etching time was 3 minutes. As a result, a recess having a period of 290 nm and a depth of 400 nm could be formed. The surface-side FF was 0.65 and the active layer-side FF was 0.84, and a two-dimensional photonic crystal structure having a tapered shape in the cross section could be formed.

  Next, as shown in FIG. 12E, the first electrode 7 is formed only on the upper surface of the contact layer 6 by removing the etching mask layer 11 with buffered hydrofluoric acid and then depositing metal from an oblique direction. Is done. By forming the first electrode 7 in this manner, it is possible to prevent metal from being deposited on the bottom surface of the recess 10. If a metal is deposited on the bottom surface of the recess 10, the light generated in the active layer 3 is absorbed by the metal, leading to an increase in threshold value and a decrease in luminous efficiency, which is not preferable. The first electrode 7 is not formed on the entire upper surface of the contact layer 6 but is selectively formed to form the light emitting surface 9. Furthermore, by forming the second electrode 8 on the bottom surface of the substrate 1, the two-dimensional photonic crystal surface emitting laser 100 according to the present embodiment is manufactured.

  In the manufacturing method of the two-dimensional photonic crystal surface emitting laser 100 according to the present embodiment, as described above, since it is manufactured without using fusion, it is highly likely to occur by performing fusion. There is no damage, and there is almost no possibility of defective products during manufacturing. Furthermore, although there is a problem that fusion cannot be performed if the device has warpage or undulation, the method of manufacturing the two-dimensional photonic crystal surface emitting laser 100 according to the present embodiment uses fusion. Therefore, the possibility of defective products is low, the yield is high, and manufacturing can be performed easily. Further, the material used is not particularly limited, and the two-dimensional photonic crystal surface emitting laser 100 can be easily manufactured using a commonly used material.

  Next, another embodiment will be described.

(Second Embodiment)

  FIG. 14 is a cross-sectional view showing a configuration of a two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention. FIG. 15 is an enlarged view of a main part of a two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention. In FIG. 14, a two-dimensional photonic crystal surface emitting laser 200 according to the second embodiment includes a substrate 1, a second cladding layer 2 that is a second semiconductor layer formed on one main surface of the substrate 1, and An active layer 3 formed on the second cladding layer 2, a carrier stop layer 4 formed on the active layer 3, a first cladding layer 5 formed on the carrier stop layer 4, and a first cladding layer 5 Contact layer 6 formed on top, insulating layer 14 formed on contact layer 6, and annular (ring-shaped, donut-shaped) first electrode that penetrates insulating layer 14 and makes ohmic contact with contact layer 6 7 and the second electrode 8 formed on the entire surface on the other main surface of the substrate 1 opposite to the one main surface. In addition, the location where the 1st electrode 7 is not formed on the insulating layer 14 is the light emission surface 9 from which light is emitted. In addition, the first cladding layer 5 and the contact layer 6 are embedded with the embedding material 10b in the recess 10 formed by processing from the first electrode 7 side (opposite side of the active layer 3). In the layer 5 and the contact layer 6, a plurality of embedding materials 10b are formed so as to be periodically arranged. Thereby, the first semiconductor layer composed of the contact layer 6, the first cladding layer 5, and the carrier stop layer 4 has a two-dimensional photonic crystal structure. Since processing is performed from the first electrode 7 side, the embedding material 10b is formed at least on the surface of the contact layer 6 on the side in contact with the first electrode 7. This photonic crystal structure selects the wavelength of light that oscillates in the active layer 3. In addition, the diameter of the recessed part 10 is changing gradually along the depth direction. Accordingly, the diameter of the embedding material 10b gradually changes along the depth direction. More specifically, in the cross-sectional shape of the surface along the stacking direction, the semiconductor material other than the embedded material 10b and the embedded material 10b has a so-called tapered shape.

  As described above, the two-dimensional photonic crystal surface-emitting laser 200 of the second embodiment is different from the two-dimensional photonic crystal surface-emitting laser 100 of the first embodiment in that the embedding material 10 b is embedded in the recess 10. The main difference is that the insulating layer 14 is further provided due to this difference.

  In the two-dimensional photonic crystal structure formed in the first cladding layer 5 and the contact layer 6, the two-dimensional periodic refractive index distribution is embedded in a refractive index different from the refractive index of the material forming the first cladding layer 5. The material 10b is formed by arranging the material 10b as lattice points in two different directions (linearly independent two directions) with a predetermined period (lattice interval, lattice constant). In the present embodiment, the lattice point is constituted by, for example, a conical embedding material 10 b formed in the first cladding layer 5 and the contact layer 6. The embedding material 10 b may reach not only the contact layer 6 and the first cladding layer 5 but also the carrier stop layer 4, but preferably does not reach the active layer 3. If the embedding material 10b reaches the active layer 3, that is, if the photonic crystal and the active layer 3 are close to each other, damage to the active layer 3 may occur during etching.

Note that a transparent insulating material is used as the embedding material 10b because it is necessary to transmit light from the active layer 3. For example, the embedding material 10b is made of a material that is transparent and electrically insulative at the oscillation wavelength of the laser, such as SiO ₂ , SiN, SOG (spinon glass), polyimide, BCB (benzocyclobutene), etc. It is a heat-resistant material that can withstand the heating in the electrode alloying process. Further, since the insulating layer 14 formed on the contact layer 6 forms the light emitting surface 9 and needs to transmit light from the active layer 3 in the same manner as the embedded material 10b, the material used for the embedded material 10b. Formed with. The filling material 10b and the insulating layer 14 may be the same material or different materials. In the two-dimensional photonic crystal surface emitting laser 200 according to the present embodiment, since the embedding material 10b is embedded in the recess 10 formed in the contact layer 6, the surface on the first electrode 7 side of the contact layer 6 is flat. It has become. For this reason, formation of the 1st electrode 7 is easy. Further, since the filling material 10b is buried in the contact layer 6 and the first cladding layer 5, they are not exposed. That is, since the contact layer 6 and the first cladding layer 5 are not exposed to air, element deterioration due to oxidation can be prevented.

  Here, in the second embodiment, as shown in FIG. 15, the surface side FF described above is a ratio of the area occupied by the semiconductor in the semiconductor and the embedded material 10 b on the upper surface of the contact layer 6, and the active layer side FF is In the first clad layer 5, when a cross section by a plane including the bottom surface of the embedding material 10 is assumed, the ratio of the area occupied by the semiconductor in the semiconductor and the embedding material 10 b in this cross section is set. The two-dimensional photonic crystal surface emitting laser 200 of the second embodiment has the same analysis as the analysis of the coupling coefficient κ described in the first embodiment, and the two-dimensional photonic crystal surface emitting laser 100 of the first embodiment The same effect is produced. The depth of the recess 10 is also the depth of the embedding material 10b. That is, as described above, since the cross section of the embedding material 10b is tapered, the surface side FF and the active layer side FF have different values. As described above, since the cross-sectional shape of the embedding material 10b is tapered, the value of the coupling coefficient κ of the two-dimensional photonic crystal is high, and the light confinement effect can be easily increased. And it becomes easy to form the recessed part 10 which embeds the embedding material 10b. For example, the recess 10 is formed by etching, but the formation difficulty can be reduced. The active layer side FF is preferably larger than the surface side FF. That is, it is preferable that the recess 10 and the embedding material 10 b have a tapered shape that becomes thinner as the active layer 3 is approached. The concave portion 10 having a tapered shape that becomes thinner as it approaches the active layer 3 can be easily manufactured as compared with the concave portion 10 that has a tapered shape that becomes thicker as the active layer 3 is approached. Therefore, the concave portion 10 can be easily manufactured. . Further, the surface side FF is preferably 0.8 or less, and the active layer side FF is preferably 0.8 or more. Thereby, a high coupling coefficient κ in the two-dimensional photonic crystal and a high light confinement effect by the first cladding layer 5 can be obtained. And it is easy to manufacture a two-dimensional photonic crystal.

  The thickness of the first cladding layer 5 is preferably about 0.3 μm to 1.0 μm although it depends on the refractive index of the first cladding layer 5. More preferably, it may be about 0.5 μm. Thereby, an aspect ratio becomes small, formation of the recessed part 10 is easy, and the light confinement effect can fully be acquired. If the first cladding layer 5 is too thin, light confinement becomes insufficient, and light absorption by the first electrode 7 becomes a problem. On the other hand, if the first cladding layer 5 is too thick, the aspect ratio becomes high and the concave portion 10 is difficult to form.

  In the two-dimensional photonic crystal surface emitting laser 200 according to the second embodiment described above, the active layer 3 emits light when a voltage is applied between the first electrode 7 and the second electrode 8. The light leaking from the active layer 3 enters the two-dimensional photonic crystal structure formed in the contact layer 6 and the first cladding layer 5, and the light whose wavelength matches the lattice spacing is resonated by the two-dimensional photonic crystal. The coherent light is emitted from the light emitting surface 9.

  Next, a manufacturing method of the two-dimensional photonic crystal surface emitting laser according to the second embodiment will be described with reference to the drawings. FIG. 16 is a first cross-sectional process diagram illustrating a manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention, and FIG. 16 (A) to FIG. It is process drawing. FIG. 17 is a second cross-sectional process diagram illustrating a manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention, and FIG. 17 (A) to FIG. It is process drawing. FIG. 17 is a process diagram after the process shown in FIG. Specifically, a manufacturing method of a 980 nm band two-dimensional photonic crystal surface emitting laser using InGaAs as an active layer on a GaAs substrate will be described. It should be noted that other wavelength band material systems such as an InGaAsP material on an InP substrate, InGaN on a GaN substrate, or AlGaN can be manufactured in the same manner as described below.

As shown in FIG. 16A, first, a metal organic vapor phase epitaxy (MOVPE) method, a molecular beam epitaxy (MBE) method, or the like is formed on a substrate 1 formed of n-type GaAs. Thus, the semiconductor laser structure is grown sequentially. More specifically, a second cladding layer 2 (thickness 2.0 μm) formed of n-type Al _0.4 Ga _0.6 As on the substrate 1, an additive-free InGaAs / GaAs quantum well active layer 3, Carrier stop layer 4 (thickness 40 nm) formed of p-type Al _0.6 Ga _0.4 As, first cladding layer 5 (thickness 0.5 μm) formed of p-type GaAs, formed of p + -type GaAs The contact layers 6 (thickness 20 nm) are sequentially stacked. Here, the active layer 3 is a strained quantum well structure composed of three periods of an InGaAs well layer (thickness 8 nm), a GaAs barrier layer (thickness 20 nm), and a separate confinement layer (SCH layer) (thickness 20 nm). The quantum well emission wavelength is designed to be 980 nm. In the present embodiment, since the above-described crystal growth process may be performed once, a two-dimensional photonic crystal surface emitting laser can be easily manufactured.

Next, as shown in FIG. 16B, SiO ₂ (which may be SiN or metal (Ni, Cr, Ti, etc.)) is formed on the contact layer 6 as an etching mask layer 11 by plasma CVD, sputtering, vapor deposition, or the like. Then, a resist layer 12 (electron beam resist, imprint material or the like) is formed thereon by a method such as spin coating.

  Thereafter, as shown in FIG. 16C, a two-dimensional photonic crystal structure pattern is formed on the resist layer 12 by using an electron beam drawing method or a nanoimprint method, and the pattern formed on the resist layer 12 is formed by RIE (reactive ion). Etching is transferred to the etching mask layer 11 by dry etching such as reactive ion etching (ICP) or ICP (Inductively Coupled Plasma). Specifically, the pattern is a cylindrical recess 13. When surface emitting light having a wavelength of 980 nm, the period of the two-dimensional photonic crystal structure pattern may be about 290 nm, and the diameter of the concave portion 13 that is the pattern may be about 50 to 200 nm. Similar to FIG. 13 described above, the cylindrical recesses 13 are arranged with regularity in a range of, for example, 20 μm square or more. The array region of the recesses 13 may be a square shape, a rectangular shape, a circular shape, or the like.

  In the present embodiment, the two-dimensional photonic crystal structure has a structure in which square lattice points are arranged in a square lattice. However, the lattice point shape is not limited to this, and a triangular shape, A known shape such as an ellipse or a V shape may be used. Furthermore, the arrangement is not limited to this, and a known structure such as a triangular lattice arrangement, a composite type of lattice points having different sizes, or a photonic quasicrystal may be used.

  Next, as shown in FIG. 16D, the recess 10 is formed by etching the contact layer 6 and the first cladding layer 5 by dry etching such as ICP or RIE using the etching mask layer 11 as a mask. As an etching gas, a methane / hydrogen gas, a chlorine gas, an iodine gas, a bromine gas, or the like generally used for dry etching of a group III-V semiconductor is used. During the etching, the cross section of the two-dimensional photonic crystal structure may be tapered. More specifically, the active layer side FF may be made larger than the surface side FF. An etching method in this case will be described. First, in the first method, a hole having a small diameter is formed as a pattern (concave portion 13) at the beginning of etching, and the mask pattern is gradually reduced by utilizing the receding of the mask by proceeding with the etching. There is a method of making the upper and lower diameters of the recesses 10 different by spreading. The second method is a method of setting etching conditions that strengthen the side wall protection of the recess 10 formed by etching. That is, an etching condition is used in which a protective film is deposited on the side wall with the etching and the hole diameter is reduced. Further, when the property that the etching rate by the etching gas is greatly changed by the Al composition is used, the carrier stop layer 4 can also be used as the etching stop layer.

  In the recess 10 formed by etching, the active layer side FF is preferably 0.8 or more, more preferably 0.9 or more. Moreover, it is preferable that surface side FF shall be 0.8 or less. Thereby, there is an effect that both a high coupling coefficient κ and strong light confinement can be achieved. If the surface-side FF is too small, there is a problem that the semiconductor portion existing between the recesses 10 in the two-dimensional photonic crystal structure becomes thin and structurally weak. Furthermore, in order to prevent the problem that the electrical resistance is increased because the area of the first electrode 7 is reduced, the surface side FF is preferably set to 0.4 or more.

  The etching needs to be stopped before reaching the active layer 3. More specifically, the etching is stopped halfway without etching all of the first cladding layer 5. Thereby, the damage to the active layer 3 by the said etching can be suppressed, and the fall of luminous efficiency can be avoided. More specifically, the etching is preferably stopped at any position from 50 nm before the active layer 3 to immediately before the active layer 3. The closer the bottom surface of the recess 10 formed by etching is to the active layer 3, the larger the coupling coefficient κ of the photonic crystal structure, but if it is too close, the active layer 3 may be damaged by plasma.

Here, an example of specific conditions for making the cross-sectional shape of the above-described photonic crystal a tapered shape will be described. As described above, the etching mask layer 11 is dry-etched by using the RIE apparatus for the contact layer 6 formed of p + type GaAs and the first cladding layer 5 formed of p type GaAs as SiO _2. . The etching gas was BCl ₃ , the gas flow rate was 2 sccm, the pressure was 5 mTorr, the RF power was 100 W, and the etching time was 3 minutes. As a result, the period was 290 nm, and a recess 10 a having a depth of 400 nm could be formed. The surface-side FF was 0.65 and the active layer-side FF was 0.84, and a two-dimensional photonic crystal structure having a tapered shape in the cross section could be formed.

Next, as shown in FIG. 17A, after the etching mask layer 11 is removed with buffered hydrofluoric acid or the like, an embedding material 10 b is embedded in the recess 10. For example, as described above, the filling material 10b is transparent and electrically insulating at the oscillation wavelength of the laser, such as SiO ₂ , SiN, SOG (spin on glass), polyimide, BCB (benzocyclobutene), and the like. A heat resistant material that can withstand the heating in the electrode alloying process at the time of electrode formation is used as a certain material. As the embedding method, a chemical vapor volume (CVD) method such as plasma CVD (Chemical Vapor Deposition) or LPCVD (Low Pressure Chemical Vapor Deposition), a sputtering method, a spin coating method, or the like is used. Thus, by embedding the embedding material 10 b in the recess 10, the upper surface of the contact layer 6 becomes flat, and it becomes easy to form an electrode on the upper surface of the contact layer 6. In addition, since the recess 10 of the contact layer 6 and the first cladding layer 5 is not exposed, the two-dimensional photonic crystal surface emitting laser 200 is not easily subjected to element deterioration due to oxidation.

  Next, as shown in FIG. 17B, by using etching (wet etching or dry etching), the embedded material 10b formed on the contact layer 6 is removed, and the contact layer 6 is exposed. Although the filling material 10b is etched, the contact layer 6 can be prevented from being etched by selecting the method and conditions so that the contact layer 6 is not etched.

Next, as shown in FIG. 17C, an insulating layer 14 is formed on the entire surface of the device. Note that the material and the deposition method of the insulating layer 14 are the same as those in the case of depositing the embedding material 10b shown in FIG. That is, SiO ₂ , SiN, SOG (spin on glass), polyimide, BCB (benzocyclobutene), etc. are plasma CVD (Chemical Vapor Deposition), LPCVD (Low
The film is formed by a chemical vapor volume (CVD) method such as Pressure Chemical Vapor Deposition), a sputtering method, or a spin coating method. Depending on the thickness of the insulating layer 14, the insulating layer 14 functions as an antireflection layer when laser light is extracted by surface emission. At this time, the thickness of the insulating layer 14 is adjusted. Next, as shown in FIG. 17D, photolithography and dry etching are performed to form the opening 14a in the insulating layer 14 where the first electrode 7 is to be formed. At this time, it is also possible to selectively remove the insulating layer 14 by selecting different materials for the embedding material 10b and the insulating layer 14 and appropriately selecting the etching conditions. Thereby, even if the etching is performed excessively when the insulating layer 14 is etched, the embedded material 10b can be prevented from being etched.

  Next, as shown in FIG. 17E, the first electrode 7 is formed by photolithography and lift-off. The first electrode 7 may be any material that is in ohmic contact with the contact layer 6 that is p + type GaAs. A part of the two-dimensional photonic crystal structure formation region (light emitting surface 9) is not covered by the first electrode 7. Thereby, the light diffracted by the two-dimensional photonic crystal structure and radiated in the vertical direction can be extracted from the light emitting surface 9 to the outside. FIG. 18 is a plan view showing the configuration of the electrodes of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention, and FIGS. 18 (A) to 18 (D) are electrodes having different shapes. It is a top view which shows the structure of these. As shown in FIGS. 18A to 18D, an electrode 28 is disposed in the photonic crystal structure formation region 27 in the two-dimensional photonic crystal surface emitting laser. The shape of the electrode 28 is, for example, a circle or a rectangle. The electrode 28 may have a shape in which no electrode is formed in the central portion of the electrode 28 (see FIGS. 18A and 18B), for example, a donut shape, etc. The shape may be smaller than that of the photonic crystal structure formation region 27 (see FIGS. 18C and 18D). Thereby, in the photonic crystal structure formation region 27, there is a portion where the electrode 28 is not formed, and light can be extracted from the portion.

  Furthermore, by forming the second electrode 8 on the bottom surface of the substrate 1, the two-dimensional photonic crystal surface emitting laser 200 according to the second embodiment is manufactured.

  Further, another manufacturing method of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention will be described. FIG. 19 is a cross-sectional process diagram for explaining a first manufacturing process as another manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention. FIG. 19B is a process diagram. In this manufacturing method, after the step shown in FIG. 17A, as shown in FIG. 19A, the contact layer 6 is formed by forming an opening 10c in a part of the embedded material 10b by photolithography and etching. Is exposed. Then, as shown in FIG. 19B, the first electrode 7 is formed in the opening 10c. Then, the two-dimensional photonic crystal surface emitting laser 200 is manufactured by forming the second electrode on the bottom surface of the substrate 1. Accordingly, there is no need to form the insulating layer 14 as shown in FIG. 17C, and the manufacturing process is shortened.

  Furthermore, still another method for manufacturing the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention will be described. FIG. 20 is a cross-sectional process diagram for explaining a second manufacturing process as another manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention. In this manufacturing method, in the step of FIG. 17A, when the embedding material 10b is embedded in the recess 10 as shown in FIG. The filling material 10b is buried so as to leave the holes 10d). More specifically, when the embedding method uses a CVD method or sputtering, such an embedding method is possible by adjusting the film forming conditions. Further, when the embedding method is spin coating, for example, such embedding can be performed by using a material having a high viscosity as the embedding material 10. First, the embedding material 10 may be embedded partway through the recess 10 by forming the embedding material 10 on another substrate by spin coating and pressing the embedding material 10b against the device in which the recess 10 is formed. . Note that the depth of the hole 10d in the recess 10 is, for example, 0.1 μm or more and may be a depth obtained by subtracting 0.1 μm from the entire depth of the recess 10. That is, the amount of the embedding material 10b embedded is between a state in which only 0.1 μm is embedded in the recess 10 and a state in which the bottom of the recess 10 is only 0.1 μm. After embedding the embedding material 10b, the steps shown in FIG. 17B and subsequent steps are performed. Thereby, it is possible to manufacture a two-dimensional photonic crystal surface emitting laser that includes air in a part of the embedding material 10b. Since the refractive index of air is generally low, in this two-dimensional photonic crystal surface emitting laser, the difference in refractive index between the two-dimensional photonic crystal structures formed in the first cladding layer 5 and the contact layer 6 is increased. be able to. This improves the diffraction efficiency of the two-dimensional photonic crystal structure. This leads to lower threshold and higher efficiency of the two-dimensional photonic crystal surface emitting laser. A gas such as an inert gas may be left in the recess 10 instead of air by embedding the embedding material 10b in a state where an inert gas or the like is injected into the recess 10. Moreover, the hole 10d may be in a vacuum state. Thereby, it can prevent that the recessed part 10 deteriorates by oxidation.

  In the manufacturing method of the two-dimensional photonic crystal surface emitting laser 200 according to the second embodiment, as described above, since the manufacturing is performed without using the fusion, it is highly likely that the fusion occurs to the device. There is no damage, and there is almost no possibility of defective products during manufacturing. Furthermore, there is a problem that the fusion cannot be performed if there is warping or undulation in the device. However, in the manufacturing method of the two-dimensional photonic crystal surface emitting laser 200 according to the present embodiment, fusion is used. Therefore, the possibility of defective products is low, the yield is high, and manufacturing can be performed easily. Further, the material used is not particularly limited, and the two-dimensional photonic crystal surface emitting laser 200 can be easily manufactured using a commonly used material. In addition, since the embedding material 10b is embedded in the recess 10 and the upper surface of the first semiconductor layer (contact layer) is planarized, it is possible to easily form an electrode on the first semiconductor layer (contact layer).

  The two-dimensional photonic crystal surface emitting laser 200 according to the second embodiment of the present invention may be configured to extract light from the substrate 1 side as shown in FIG. FIG. 21 is a cross-sectional view showing another configuration of the two-dimensional photonic crystal surface emitting laser according to the second embodiment of the present invention. More specifically, the material is transparent with respect to the wavelength band of light extracted by the substrate 1. For example, after the step shown in FIG. 17B, the second electrode 8 is formed on the entire surface of the contact layer 6, and is a material transparent to the wavelength band of the light to be extracted on the bottom surface of the substrate 1. An insulating layer 14 is formed, and a first electrode 7 penetrating the insulating layer 14 and contacting the substrate 1 is formed. Thereby, a two-dimensional photonic crystal surface emitting laser 200A in which the light emitting surface 9 is formed on the substrate 1 side is realized. In FIG. 21, the two-dimensional photonic crystal surface emitting laser 200 </ b> A is configured to have an opening without forming the first electrode 7 on the entire surface of the light emitting surface 9, and to emit laser light from the opening. It was said. However, the present invention is not limited to such a configuration, and other configurations may be used. For example, a part or all of the first electrode 7 is a transparent electrode, and an emission surface is formed without forming an opening. The first electrode 7 may be formed on the entire surface of 9. Thereby, a laser beam is emitted through the transparent electrode.

  The present specification discloses various aspects of the technology as described above, and the main technologies are summarized below.

  The two-dimensional photonic crystal surface emitting laser according to one aspect includes an active layer sandwiched between first and second semiconductor layers, the first semiconductor layer, and the second semiconductor layer and generating light by carrier injection. The first semiconductor layer has a plurality of recesses formed from a main surface of the first semiconductor layer opposite to the active layer side, so that at least a part of the first semiconductor layer is two-dimensional. It has a photonic crystal structure, and the diameter of the recess changes along the depth direction. Preferably, the diameter of the recess gradually changes along the depth direction, and preferably, in a cross-sectional shape by a surface along the photonic crystal structure lamination direction in the first semiconductor layer, The recess and the semiconductor other than the recess have a so-called tapered shape.

  According to this configuration, since the two-dimensional photonic crystal surface emitting laser can be manufactured without using fusion, the two-dimensional photonic crystal surface emitting laser can be easily manufactured, and the possibility that a defective product is generated at the time of manufacturing is low. Therefore, according to this configuration, a two-dimensional photonic crystal surface emitting laser that can be manufactured at low cost and has a high yield can be realized. In addition, since the diameter of the concave portion is gradually changed along the depth direction, the coupling coefficient κ of the two-dimensional photonic crystal is increased, the light confinement effect is improved, and the concave portion is easily formed. Can be done. Thereby, it is possible to easily reduce the threshold, increase the efficiency, shorten the wavelength, and the like.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, preferably, the first semiconductor layer includes a first cladding layer, and the second semiconductor layer includes a second cladding layer. And the refractive index of the first cladding layer is higher than the refractive index of the second cladding layer.

  According to this configuration, even if a two-dimensional photonic crystal structure is formed by making the refractive index of the first cladding layer higher than that of the second cladding layer, the average refractive index of the first cladding layer is lowered. Don't do too much. Thereby, since the reduction of the ratio of the light distributed in the photonic crystal layer is prevented, it is possible to prevent the coupling coefficient from being lowered.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, the thickness of the first cladding layer is preferably 0.3 μm to 1.0 μm.

  According to this configuration, since the first cladding layer is not too thick, it has a photonic crystal structure with a small aspect ratio. Therefore, it is easy to process the recesses formed in the first cladding layer. More specifically, the difficulty of etching is low.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, preferably, the concave portion does not reach the active layer.

  When the recess reaches the active layer, that is, when the photonic crystal and the active layer are close to each other, damage to the active layer due to plasma may occur, but according to this configuration, the recess does not reach the active layer. There is no such problem.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, the ratio of the area occupied by the semiconductor in the light emitting surface side main surface of the first semiconductor layer is preferably a surface side FF, and the first When a plane including the bottom surfaces of the plurality of recesses is hypothesized in one semiconductor layer, the ratio of the area occupied by the semiconductor in the hypothetical plane is defined as an active layer side FF, and the surface side FF and the active layer side FF are It is a different value.

  According to this configuration, in the cross-sectional shape of the surface along the photonic crystal structure lamination direction in the first semiconductor layer, the recess and the semiconductor other than the recess have a so-called tapered shape. Therefore, the two-dimensional photonic crystal surface emitting laser having such a configuration can increase the coupling coefficient κ of the two-dimensional photonic crystal and improve the light confinement effect by the first cladding layer. . Further, the recess can be easily processed. More specifically, the difficulty of etching the recesses is low.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, preferably, the active layer side FF is larger than the surface side FF.

  According to this structure, in the cross-sectional shape by the surface along the photonic crystal structure lamination direction in a 1st semiconductor layer, it has a taper shape where a recessed part becomes thin, so that it approaches the active layer side. For this reason, the two-dimensional photonic crystal surface emitting laser having such a configuration can be easily manufactured as compared with the tapered shape in which the concave portion becomes thicker as it approaches the active layer side.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, preferably, the surface-side FF is 0.8 or less, and the active layer-side FF is 0.8 or more. That is.

  The two-dimensional photonic crystal surface emitting laser having such a configuration can improve the light confinement effect due to the high coupling coefficient κ and the first cladding layer in the two-dimensional photonic crystal. Further, the recess can be easily processed. More specifically, the difficulty of etching the recesses is low.

  According to another aspect of the method of manufacturing a two-dimensional photonic crystal surface emitting laser, an active layer is stacked on a second semiconductor layer, the first semiconductor layer is stacked on the active layer, and then the first semiconductor layer is stacked. In one semiconductor layer, a two-dimensional photonic crystal structure is formed on at least a part of the first semiconductor layer by forming a concave portion that becomes thinner from the surface opposite to the active layer toward the active layer. Is to form.

  According to this configuration, a two-dimensional photonic crystal surface emitting laser can be manufactured without using fusion, a special buried regrowth method, and the like. However, the yield is high and the cost can be reduced.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, it is preferable that an embedding material is embedded in the plurality of recesses of the first semiconductor layer.

  Even with such a configuration, the two-dimensional photonic crystal surface emitting laser can be manufactured without using fusion, so that it can be easily manufactured, and the possibility that a defective product is generated at the time of manufacturing is low. Therefore, according to this configuration, a two-dimensional photonic crystal surface emitting laser that can be manufactured at low cost and has a high yield can be realized. In addition, since the diameter of the recess (embedding material) is gradually changed along the depth direction, the coupling coefficient κ of the two-dimensional photonic crystal is increased, and the optical confinement effect is improved. The concave portion can be easily formed. Thereby, it is possible to easily reduce the threshold, increase the efficiency, shorten the wavelength, and the like. In addition, since the embedding material is embedded in the recess, the upper surface of the first semiconductor layer is flattened, so that the electrode can be easily formed on the first semiconductor layer. Moreover, since the embedding material is embedded in the recess, the recess in the first semiconductor layer is not exposed to the atmosphere. Thereby, the first semiconductor layer is difficult to be oxidized, and deterioration of the two-dimensional photonic crystal surface emitting laser can be prevented.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, preferably, the plurality of recesses of the first semiconductor layer are formed with vacancies (holes). That is, the embedding material is embedded halfway in the depth direction. Note that air or a gas other than air may be enclosed in the void. Further, the inside of the holes may be in a vacuum state.

  According to this configuration, a part of the embedding material contains a gas such as air. A gas such as air generally has a lower refractive index, so the refractive index of air is lower than the refractive index of the embedding material. Therefore, the refractive index difference of the two-dimensional photonic crystal structure formed in the first semiconductor layer can be increased. As a result, the diffraction efficiency of the two-dimensional photonic crystal structure is improved, and the two-dimensional photonic crystal surface emitting laser can reduce the threshold and increase the efficiency. In addition, although the inside of a void | hole is good also as a vacuum, in that case, the refractive index is substantially the same as air.

  In another aspect, in the above-described two-dimensional photonic crystal surface emitting laser, preferably, the ratio of the area occupied by the semiconductor on the main surface of the first semiconductor layer opposite to the active layer side is the surface. When the plane including the bottom surfaces of the plurality of recesses in the first semiconductor layer is assumed in the first semiconductor layer, the ratio of the area occupied by the semiconductor in the virtual plane is defined as the active layer side FF, and the surface side FF and the The value is different from that of the active layer side FF.

  According to this configuration, in the cross-sectional shape of the first semiconductor layer along the surface along the photonic crystal structure stacking direction, the recess, the embedded material, and the semiconductor other than the recess have a so-called tapered shape. Therefore, the two-dimensional photonic crystal surface emitting laser having such a configuration can increase the coupling coefficient κ of the two-dimensional photonic crystal and improve the light confinement effect by the first cladding layer. . Further, the recess can be easily processed. More specifically, the difficulty of etching the recesses is low.

  In another aspect, the above-described method for manufacturing a two-dimensional photonic crystal surface emitting laser preferably further includes a step of embedding an embedding material in the plurality of recesses.

  According to this configuration, a two-dimensional photonic crystal surface emitting laser can be manufactured without using fusion, a special buried regrowth method, and the like. However, the yield is high and the cost can be reduced. In addition, according to this configuration, since the embedding material is embedded in the recess and the upper surface of the first semiconductor layer is planarized, it is possible to easily form the electrode on the first semiconductor layer.

  This application is based on Japanese Patent Application Japanese Patent Application No. 2009-0117148 filed on Jan. 28, 2009 and Japanese Patent Application No. 2009-0117179 filed on Jan. 28, 2009. The contents thereof are included in the present application.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

  According to the present invention, a two-dimensional photonic crystal surface emitting laser and a manufacturing method thereof can be provided.

Claims (11)

First and second semiconductor layers;
An active layer sandwiched between the first semiconductor layer and the second semiconductor layer and generating light by carrier injection;
The first semiconductor layer has a two-dimensional photonic crystal structure in which at least a part of the first semiconductor layer is formed by forming a plurality of recesses from a main surface of the first semiconductor layer opposite to the active layer side. A two-dimensional photonic crystal surface emitting laser that emits light of a selected wavelength by resonating light generated from the active layer with the two-dimensional photonic crystal structure,
The plurality of recesses are formed with a period of the two-dimensional photonic crystal structure that matches the selected wavelength, and a refractive index in the recesses is smaller than a refractive index of the first semiconductor , and the recesses The two-dimensional photonic crystal surface is characterized in that the diameter of the first semiconductor layer decreases from the main surface of the first semiconductor layer opposite to the active layer as it approaches the active layer along the depth direction. Light emitting laser. The first semiconductor layer has a first cladding layer,
The second semiconductor layer has a second cladding layer;
2. The two-dimensional photonic crystal surface emitting laser according to claim 1, wherein a refractive index of the first cladding layer is higher than a refractive index of the second cladding layer. 3. The two-dimensional photonic crystal surface emitting laser according to claim 1, wherein a thickness of the first cladding layer is 0.3 μm to 1.0 μm. The two-dimensional photonic crystal surface emitting laser according to any one of claims 1 to 3, wherein the concave portion does not reach the active layer. The ratio of the area occupied by the semiconductor in the light emitting surface side main surface of the first semiconductor layer is the surface side FF
In the first semiconductor layer, when a plane including the bottom surfaces of the plurality of recesses is assumed, the ratio of the area occupied by the semiconductor in the virtual plane is defined as an active layer side FF,
The two-dimensional photonic crystal surface emitting laser according to any one of claims 1 to 4, wherein the active layer side FF is larger than the surface side FF . The two-dimensional photonic crystal surface emitting laser according to claim 5 , wherein the surface-side FF is 0.8 or less and the active layer-side FF is 0.8 or more. A method of manufacturing a two-dimensional photonic crystal surface-emitting laser that emits light of a selected wavelength by resonating light generated from an active layer with a two-dimensional photonic crystal structure,
Laminating the active layer on the second semiconductor layer;
After laminating the first semiconductor layer on the active layer,
In the first semiconductor layer, a plurality of recesses that become thinner toward the active layer from the surface opposite to the active layer at a period of the two-dimensional photonic crystal structure that matches the selected wavelength. To form the two-dimensional photonic crystal structure in at least a part of the first semiconductor layer. 2. A method of manufacturing a two-dimensional photonic crystal surface-emitting laser, comprising: The two-dimensional photonic crystal surface emitting laser according to claim 1, wherein an embedding material is embedded in the plurality of recesses of the first semiconductor layer. 2. The two-dimensional photonic according to claim 1, wherein an embedding material is embedded in the plurality of recesses of the first semiconductor layer halfway in a depth direction so as to form voids. Crystal surface emitting laser. The ratio of the area occupied by the semiconductor on the main surface opposite to the active layer side of the first semiconductor layer is defined as a surface side FF,
In the first semiconductor layer, when a plane including the bottom surfaces of the plurality of recesses is assumed, the ratio of the area occupied by the semiconductor in the virtual plane is defined as an active layer side FF,
The active layer side FF is two-dimensional photonic crystal surface emitting laser according to claim 8 or claim 9 and greater than the surface FF. The method for manufacturing a two-dimensional photonic crystal surface emitting laser according to claim 7 , further comprising a step of embedding an embedding material in the plurality of recesses.

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