JP2011108935A - Two-dimensional photonic crystal surface emitting laser and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-dimensional photonic crystal surface emitting laser that facilitates fabrication, without separately providing a current narrowing structure, and to provide a method of manufacturing the laser. <P>SOLUTION: The two-dimensional photonic crystal surface emitting laser includes first and second semiconductor layers and an active layer interposed between the first semiconductor layer and the second semiconductor layer for generating light by carrier injection. The first semiconductor layer has a plurality of protrusions oppositely to the active layer, wherein all or part of the plurality of protrusions form a two-dimensional photonic crystal structure. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a two-dimensional photonic crystal surface emitting laser that resonates and emits light by using a two-dimensional photonic crystal, and a manufacturing method thereof.

  A surface emitting laser can emit laser light substantially perpendicularly from a substrate surface, can integrate a plurality of laser elements in two dimensions (two-dimensional array), and can emit coherent light from each laser element. From various characteristics such as being able to inject in parallel, for example, various applications are expected in various fields such as storage, communication, and information processing, 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. The photonic crystal includes 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 describes a conventional two-dimensional photonic crystal surface emitting laser. FIG. 19 is a perspective view showing a configuration of a conventional two-dimensional photonic crystal surface emitting laser. Specifically, as shown in FIG. 19, the two-dimensional photonic crystal surface-emitting laser 200 is roughly formed by laminating a lower cladding layer 102, an active layer 103, and an upper cladding layer 104 on a substrate 101, thereby forming a lower cladding 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 period. 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. 20 will be described. FIG. 20 is an explanatory diagram showing the resonance action of a 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. The holes 121 are formed in two directions orthogonal to each other at the same period, thereby forming a square lattice. 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 coincides with the lattice interval a of the basic grating E travels in the Γ-X direction, the light L is Bragg diffracted at the lattice point. Of 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 second-order Bragg diffraction 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. Diffraction. When the light L repeats Bragg diffraction once or a plurality of times, the diffracted light returns to the original lattice point, thereby causing a resonance action. The light diffracted in the direction perpendicular to the paper also satisfies the first order Bragg diffraction 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.

Japanese Patent No. 3989333

  However, in Patent Document 1, in the lower clad layer 102, the medium in a portion of the lower clad layer 102 excluding the vacancies (photonic crystal periodic structure 121) is continuous. Will spread. In order to prevent current from flowing in a region where current injection is not required, a current confinement structure (for example, an oxide confinement structure, a proton injection structure, or a structure using buried regrowth) is provided in a two-dimensional photonic crystal surface emitting laser. It is necessary to provide it separately. Providing such a current confinement structure separately increases the number of manufacturing steps when manufacturing a two-dimensional photonic crystal surface emitting laser.

  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 without separately providing a current confinement structure and a method for manufacturing the same. That is.

  As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below.

  That is, the two-dimensional photonic crystal surface emitting laser according to one embodiment of the present invention is sandwiched between the first and second semiconductor layers, the first semiconductor layer, and the second semiconductor layer, and receives light by carrier injection. The first semiconductor layer has a plurality of convex portions on a side opposite to the active layer side, and a two-dimensional photonic is formed by all or a part of the plurality of convex portions. A crystal structure is formed.

  As a result, the convex portion and the convex portion are electrically insulated by the concave portion, so that all or a part of the plural convex portions not only function as a two-dimensional photonic crystal but also as a current confinement structure. Function. Therefore, a two-dimensional photonic crystal surface emitting laser that can be easily manufactured without separately providing a current confinement structure can be realized.

  In the above-described two-dimensional photonic crystal surface emitting laser, the first electrode provided on the opposite side of the first semiconductor layer to the active layer side and the second electrode provided on the active layer side of the second semiconductor layer. An electrode, wherein the first semiconductor layer has a first cladding layer, the second semiconductor layer has a second cladding layer, and the diameter of the convex portion gradually increases along the depth direction. An embedding material having a second refractive index different from the first refractive index of the material forming the convex portion is embedded in the first semiconductor layer other than the convex portion on the side opposite to the active layer side. It is.

  Thus, since the diameter of the convex portion is gradually changed along the depth direction, the value of the coupling coefficient κ of the two-dimensional photonic crystal is increased, the light confinement effect is improved, and the convexity is increased. Part formation can be performed easily. 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 a portion other than the convex portion of the first semiconductor layer, the upper surface of the first semiconductor layer is flattened, so that an electrode can be easily formed on the first semiconductor layer. Can do. Further, since the embedding material is embedded in the portion other than the convex portion of the first semiconductor layer, the convex portion in the first cladding layer is not exposed to the atmosphere. Thereby, the first cladding layer is not easily oxidized, and deterioration of the two-dimensional photonic crystal surface emitting laser can be prevented.

  In the two-dimensional photonic crystal surface emitting laser, the refractive index of the first cladding layer is preferably higher than the refractive index of the second cladding layer.

  Thus, even if a two-dimensional photonic crystal structure is formed by increasing the refractive index of the first cladding layer, the average refractive index of the first cladding layer does not decrease too much. As a result, a decrease in the ratio of light distributed in the photonic crystal layer can be prevented, so that a reduction in coupling coefficient can be prevented.

  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.

  Thereby, since the thickness of 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 convex portion formed in the first cladding layer. For example, when etching is performed, the difficulty of etching is low.

  Further, in the above-described two-dimensional photonic crystal surface emitting laser, 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 defined as a surface side FF, and in the first semiconductor layer, When the plane including the bottom surface of the portion other than the convex portion is hypothesized, the ratio of the area occupied by the semiconductor in the hypothetical plane is the active layer side FF, and the surface side FF and the active layer side FF are different values. It is preferable that

  Thereby, in the two-dimensional photonic crystal surface emitting laser, the value of the coupling coefficient κ of the two-dimensional photonic crystal can be increased, and the light confinement effect by the first cladding layer can be improved. Moreover, the processing of the convex portion is easy.

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

  Thereby, in the cross-sectional shape by the surface along the photonic crystal structure lamination direction in the 1st semiconductor layer, it has a taper shape where a convex part becomes thick, so that it approaches the active layer side. Therefore, it can be easily manufactured as compared with the tapered shape in which the convex portion becomes thinner as it approaches the active layer side.

  In the above-described two-dimensional photonic crystal surface emitting laser, it is preferable that the surface-side FF is 0.8 or less and the active layer-side FF is 0.8 or more.

  Thereby, in the two-dimensional photonic crystal surface emitting laser, it is possible to improve the high coupling coefficient κ in the two-dimensional photonic crystal and the light confinement effect by the first cladding layer. Moreover, the processing of the convex portion is easy.

  According to another aspect of the present invention, there is provided a method for manufacturing a two-dimensional photonic crystal surface emitting laser, comprising: laminating an active layer on a second semiconductor layer; and laminating the first semiconductor layer on the active layer. In the first semiconductor layer, the plurality of protrusions are formed on the side opposite to the active layer side in order to form a two-dimensional photonic crystal structure by all or a part of the plurality of protrusions.

  Thereby, since a two-dimensional photonic crystal surface emitting laser can be manufactured without separately providing a current confinement structure, an increase in manufacturing steps can be prevented.

  According to the present invention, it is possible to provide a two-dimensional photonic crystal surface emitting laser that can be easily manufactured without providing a current confinement structure and a manufacturing method thereof.

It is sectional drawing which shows the structure of the two-dimensional photonic crystal surface emitting laser which concerns on 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 which concerns on 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 embedding material is 0.52 μm. FIG. 10A shows the value of the coupling coefficient κ. FIG. 10B is a graph showing the ratio of light that has oozed 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 depth of the embedding material is 0.92 μm, and FIG. FIG. 11B is a graph showing the ratio of light that oozes into the contact layer. FIGS. 12A to 12D are first cross-sectional process diagrams showing a manufacturing process of a two-dimensional photonic crystal surface emitting laser according to an embodiment of the present invention. FIG. FIG. 13A is a cross-sectional process diagram illustrating a manufacturing process of a two-dimensional photonic crystal surface emitting laser according to an 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. FIG. 15A is a plan view showing a configuration of an electrode of a two-dimensional photonic crystal surface emitting laser according to an embodiment of the present invention, and FIGS. 15A to 15D are plan views showing configurations of electrodes having different shapes. It is. FIGS. 16A and 16B are cross-sectional process diagrams for explaining a manufacturing process of another two-dimensional photonic crystal surface emitting laser according to an embodiment of the present invention, and FIGS. . It is sectional process drawing for demonstrating the manufacturing process of the further another two-dimensional photonic crystal surface emitting laser which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the other two-dimensional photonic crystal surface emitting laser which concerns on 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 according to 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.

  FIG. 1 is a cross-sectional view showing a configuration of a two-dimensional photonic crystal surface emitting laser according to an embodiment of the present invention. In FIG. 1, a two-dimensional photonic crystal surface emitting laser 100 according to an 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, The active layer 3 formed on the two cladding layers 2, the carrier stop layer 4 formed on the active layer 3, the first cladding layer 5 formed on the carrier stop layer 4, and the first cladding layer 5 A contact layer 6 formed on the contact layer 6, an insulating layer 14 formed on the contact layer 6, and an annular (ring-shaped, donut-shaped) first electrode 7 penetrating the insulating layer 14 and in ohmic contact with the contact layer 6. 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. Note that a portion where the first electrode 7 is not formed on the insulating layer 14 is a light emitting 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 10 in the concave portions between the convex portions 10a formed by processing from the first electrode 7 side (the side opposite to the active layer 3). ing. The first cladding layer 5 and the contact layer 6 are formed such that a plurality of convex portions 10a 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 the processing is performed from the first electrode 7 side, the convex portion 10 a 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. Note that the diameter of the concave portion gradually changes along the depth direction. Therefore, the diameter of the convex portion 10a gradually changes along the depth direction. Specifically, in the cross-sectional shape by the surface along the lamination direction, the embedding material 10 other than the convex portion 10a and the convex portion 10a has a so-called tapered 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 using electrons as carriers, and is formed of, for example, n-type Al _0.4 Ga _0.6 As. The carrier stop layer 4 is a p-type semiconductor layer having 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, for example, holes (carriers) as carriers, and is formed of, for example, p-type Al _x Ga _(1-x) As. The contact layer 6 is also a p-type semiconductor layer using, for example, holes (holes) as carriers, and is made 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. For example, a structure having p-type and n-type semiconductor layers having different conductivity types in the upper layer of the active layer, such as a buried tunnel junction (BTJ) type, may be used.

  As described above, the active layer 3 is sandwiched between the second cladding layer 2 (second semiconductor layer) and the first semiconductor layer including 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 provided 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 including, 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. Thus, even if a two-dimensional photonic crystal structure is formed by increasing the refractive index of the first cladding layer 5, the average refractive index of the first cladding layer 5 does not decrease too much. This prevents a decrease in the ratio of light distributed in the layer in which the photonic crystal structure is formed, thereby preventing a decrease in the coupling coefficient κ.

  Then, a double heterojunction is formed across the active layer 3, carriers are confined, and carriers contributing to light emission are concentrated in the active layer 3. The contact layer 6 is provided between the first electrode 7 and the first cladding 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 provided 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 composed of, for example, an ITO (Indium Tin Oxide) electrode or a gold-based electrode, and are activated by applying a voltage between the first and second electrodes 7 and 8. Carriers are injected into the 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 on the light emitting surface side with respect to the wavelength of the laser light emitted by the two-dimensional photonic crystal surface emitting laser 100. In addition, a transparent electrode using a conductive material is preferable. Therefore, for example, an ITO electrode is preferable. 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. Note that a part or all of the first electrode 7 may be a transparent electrode, and the first electrode 7 may be formed on the entire surface of the light emitting surface 9 without forming an opening. 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 convex portion 10 a having a refractive index different from the refractive index of the embedding material 10. Are arranged in two different directions (two linearly independent directions) with a predetermined period (lattice interval, lattice constant). In the present embodiment, the lattice points are constituted by, for example, conical convex portions 10 a formed in the first cladding layer 5 and the contact layer 6. The protrusion 10 a 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 convex portion 10a 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.

  And unlike the conventional two-dimensional photonic crystal structure, in this Embodiment, the optical confinement is implement | achieved by arrange | positioning the convex part 10a which is a semiconductor periodically. In the present embodiment, the two-dimensional photonic crystal structure functions as a light bulb constriction structure that suppresses a current from flowing into a region where it is not necessary. Therefore, according to the present embodiment, it is easy to manufacture a two-dimensional photonic crystal without separately providing a current confinement structure. Furthermore, according to the present embodiment, current can be efficiently injected into the active layer 3 by obtaining a current confinement effect.

In the present embodiment, the convex portion 10a is formed, for example, by processing the first cladding layer 5 by etching, and thus is constituted by the first semiconductor layer of the first cladding layer 5. Further, as the embedding material 10, a transparent insulating material is used because it is necessary to transmit light from the active layer 3. For example, the embedding material 10 is a material that is transparent and electrically insulative at the laser oscillation wavelength, such as SiO ₂ , SiN, SOG (spin on glass), polyimide, BCB (benzocyclobutene), etc. What is necessary is just to use the heat resistant material which can endure the heating of the electrode alloying process in the case of formation. 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 10, the material used for the embedded material 10 and do it. The embedding material 10 and the insulating layer 14 may be the same material or different materials. In the two-dimensional photonic crystal surface emitting laser 100 according to the present embodiment, since the embedding material 10 is embedded in the concave portions between the convex portions 10a, the surface on the first electrode 7 side of the contact layer 6 is planarized. ing. Therefore, it is easy to form the first electrode 7. Moreover, since the filling material 10 is embedded 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. Thus, since the embedding material 10 is an insulating material, the embedding material 10 can confine the injected current, so that the light emission efficiency of the laser can be improved.

  Here, in the semiconductor and the embedded material 10 on the upper surface of the contact layer 6, 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 embedded material 10 in the first cladding layer 5 is assumed. Further, in the semiconductor and the filling material 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 embedding material 10 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 10 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 the formation of the convex part 10a becomes easy. For example, although the convex part 10a is formed by etching, its 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 embedding material 10 has a taper shape that becomes thinner as it approaches the active layer 3. The convex portion 10a having a tapered shape that becomes thicker as it approaches the active layer 3 can be easily manufactured as compared with the convex portion 10a that has a tapered shape that becomes thinner as the active layer 3 is approached. Can be produced. Moreover, it is preferable that surface side FF is 0.8 or less, and 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 may be about 0.5 μm. Thereby, the aspect ratio becomes small, the formation of the convex portion 10a is easy, and the light confinement effect can be sufficiently obtained. If the first clad 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 clad layer 5 is too thick, the aspect ratio becomes high and convex. Formation of the part 10a becomes difficult.

  In the two-dimensional photonic crystal surface emitting laser 100 according to the above-described embodiment, a voltage is applied between the first electrode 7 and the second electrode 8 to cause the injected current to flow into the contact layer 6 and the first cladding. The two-dimensional photonic crystal structure formed in the layer 5 is current-confined, and the active layer 3 emits light. 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 laser (distributed feedback laser) using a normal one-dimensional diffraction grating. This can be considered in the same manner as a distributed feedback laser. 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 one-dimensional coupled wave theory in a DFB laser using a one-dimensional diffraction grating (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, ε ₀ is the electric field amplitude, and ε ₀ ^* (X) is the 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 expressed more simply by the following formula (2).

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 coefficient). ), 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 and the filling factor (hereinafter referred to as FF) in the two-dimensional photonic crystal surface emitting laser, that is, the ratio of the high refractive index portion in the entire two-dimensional photonic crystal structure is calculated. Ask. 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 is made of Al _0.6 Ga _0.4 As having a refractive index of 3.195, and the thickness is 0.04 μm. Further, the 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 the thickness is 0.04 μm. Further, in the first clad layer 25, a portion 25a having a photonic crystal structure has Al _0.4 Ga _0.6 As having a refractive index of 3.306 and a material 30 having a refractive index of 1.5. (For example, SiO ₂ ) are alternately and periodically formed as shown in FIG. 2, and the thickness is 1.96 μm. 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 provided on the contact layer 26 in an infinite thickness. In such a two-dimensional photonic crystal surface emitting laser, assuming that the diffraction order m is 2, the relationship between the coupling coefficient κ and FF is obtained using equation (2). As described above, equation (2) is a calculation formula for a one-dimensional diffraction grating (one-dimensional photonic crystal structure), but it can also be used as a simple approximation in calculations for a two-dimensional photonic crystal. it can. Note that Γ- _grading 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 the 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. In addition, it calculates first about the case where the convex part formed in a photonic crystal is columnar. As shown in FIG. 3, FF greatly depends on the coupling coefficient κ, and has a local 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. Also, a two-dimensional photonic crystal needs to be formed with a cylindrical convex portion having a diameter of about 100 nm, and 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 the two-dimensional photonic crystal structure has an aspect ratio of 20, which requires a periodic structure with a very high aspect ratio. Therefore, the processing difficulty is high.

In general, a laser having a one-dimensional photonic crystal structure requires a coupling coefficient κ of 1000 cm ⁻¹ or more (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, so that the first cladding layer which is the upper cladding layer This is probably because a portion filled with the material 30 that is a low refractive index material is formed in 25, and the average refractive index of the first cladding layer 25 as a whole is lowered and Γ _grating is reduced.

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. Specifically, for the case where the Al composition is decreased from 40% to 0%, 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 is 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 formed of p-type Al _x Ga _(1-x) As The cladding layer 35 and the 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, the thickness of the first cladding layer 35 and the ratio of light that leaks into the contact layer 36 when the Al composition of the first cladding layer 35 is 40% that is used in a normal laser are calculated. As 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 proportion of light that oozes into the contact layer 36 are calculated and 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. Thereby, the aspect ratio becomes small while obtaining a sufficient light confinement effect. Thereby, formation of a convex part becomes easy. Specifically, the difficulty of etching processing decreases.

  As described above, the method of increasing the coupling coefficient κ and decreasing the aspect ratio in the two-dimensional photonic crystal surface emitting laser was obtained by calculation. 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, but in the following, in order to obtain a more exact solution, the coupling in the two-dimensional photonic crystal structure Similar calculations are performed using an exact solution of the coefficient κ. The exact solution for the two-dimensional photonic crystal structure is described 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) ”, the two-dimensional coupled wave theory for the two-dimensional diffraction grating may be used. First, the relationship between the coupling coefficient κ and FF is determined using the model shown in FIG. The refractive index and thickness of each layer are also the same as those described above. Also, 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 determined using the one-dimensional coupled wave theory and the two-dimensional coupled wave theory and the filling factor. 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 is 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, both are slightly different, 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, from the viewpoint of optical confinement of the clad layer and processing difficulty, FF is preferably 0.8 or less, more preferably 0.7 or less. 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. . In other words, in the convex portion 10a (see FIG. 1), it is preferable that the surface side FF and the active layer side FF are different in the 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. Specifically, it 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 b along the bottom surface of the embedding material 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 made of Al _x Ga _(1-x) As and has an Al composition of 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 0.04 μm. did. 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. In addition, the depth of the material 30 in the first cladding layer 25 and the contact layer 26 (depth of the embedding material) is also changed. The depth of the embedding material corresponds to the length of the material 30 in the depth direction. Specifically, the thickness of the entire first cladding layer 25 is 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 In the case of 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 depth of the embedding material when the total thickness of the first cladding layer 25 is 0.54 μm is 0.52 μm, When the thickness of the entire first cladding layer 25 is 0.94 μm, the depth of the filling material is 0.92 μm.

  The calculation is performed using a two-dimensional coupled wave theory. Then, when the values of the surface-side FF and the active layer-side FF are changed from 0.0 to 1.0, respectively, the diffraction coupling coefficient κ in the 180 ° direction and the ratio of the light oozing out to the contact layer 26 are calculated. To do. 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 embedding material is 0.52 μm. FIG. 10 (A) shows the coupling coefficient κ. FIG. 10B is a graph showing the ratio of light that oozes into the contact layer. The depth of the embedding material is the same as the depth of the diffraction grating in which the embedding material is embedded.

From FIG. 10A and FIG. 10B, when the depth of the embedding material is 0.52 μm, the coupling coefficient κ is wide in the 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. In addition, when the surface side FF is too small, the problem that the convex part in a two-dimensional photonic crystal structure becomes thin and becomes structurally weak arises. 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 manufacturing, after stacking the semiconductors, etching and the like are performed from the semiconductor surface to form the convex portions 10a, and then the convex portions and the convex portions A photonic crystal structure is formed by embedding the embedding material 10 in the recesses between the two. 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 surface along the photonic crystal structure lamination direction, it is preferable that the convex part 10a is not a tapered truncated cone or a cylindrical body that becomes thicker as it approaches the active layer side.

  Next, calculation results for the surface-side FF and the active layer-side FF when the depth of the embedding material is 0.9 μm will be described. FIG. 11 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 embedding material is 0.92 μm. FIG. 11A shows the coupling coefficient κ. FIG. 11B is a graph showing the ratio of light that oozes into the contact layer.

From FIG. 11 (A) and FIG. 11 (B), when the depth of the embedding material is 0.92 μm, the coupling coefficient κ is the entire 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 2000 cm ⁻¹ . 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, the semiconductor portion 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 it is preferable to set it to 0.4 or more.

  Further, in the two-dimensional photonic crystal surface emitting laser 100 according to the present embodiment, in manufacturing, after stacking the semiconductors, etching and the like are performed from the semiconductor surface to form the convex portions 10a, and then the convex portions and the convex portions A photonic crystal structure is formed by embedding the embedding material 10 in the recesses between the two. 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 Al _x Ga _(1-x) As is 0%, and the thicknesses are 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 decreased, 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 reduced. 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 conductive layer cladding layer 5. To do. Thereby, the average refractive index of the first cladding layer 5 can be significantly lowered as compared with the active layer 3. Therefore, the first cladding layer 5 can be made of a material 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 Al _x Ga _(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, but 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 convex portion 10a 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. In addition, since the Al composition is low, the electrical resistance and thermal resistance of the first cladding layer 5 are reduced, 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 first 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 12D are process diagrams. is there. FIG. 13 is a second 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. 13A to 13D are process diagrams. is there. FIG. 13 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, and AlGaN may be manufactured in the same manner as described below.

As shown in FIG. 12A, first, an organic metal vapor phase epitaxy (MOVPE) method, a molecular beam epitaxy (MBE) method, etc. are formed on a substrate 1 formed of n-type GaAs. Thus, the semiconductor laser structure is sequentially grown. 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, p A carrier stop layer 4 (thickness 40 nm) formed of type Al _0.6 Ga _0.4 As, a first cladding layer 5 (thickness 0.5 μm) formed of p-type GaAs, and 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. 12B, SiO ₂ (which may be SiN or metal (Ni, Cr, Ti, etc.)) is formed as an etching mask layer 11 on the contact layer 6 by plasma CVD, sputtering, vapor deposition, or the like. Subsequently, a resist layer 12 (electron beam resist, imprint material, etc.) is formed thereon by a method such as spin coating.

  After that, 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 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 columnar convex portion 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 convex portion 13 as a pattern may be about 50 to 200 nm. FIG. 14 is a plan view of the resist layer in a state where a pattern is formed. As shown in FIG. 14, the columnar convex portions 13 are arranged with regularity in a range of, for example, 20 μm square or more. In addition, what is necessary is just to make the arrangement | sequence area | region of the convex part 13 into square shape, a rectangular shape, circular shape.

  In the present embodiment, the two-dimensional photonic crystal structure has a structure in which perfect circular lattice points are arranged in a positive direction, but the lattice point shape may be a triangle, an ellipse, a V shape, or the like. The shape may be used. Furthermore, as the arrangement, a known structure such as a triangular lattice arrangement or a composite type / photonic quasicrystal of lattice points having different sizes may be used (Japanese Patent Laid-Open No. 2003-23193, Japanese Patent Laid-Open No. 2007-273730, (See JP 2006-59864 A, JP 2004-296538 A, etc.).

  Next, as shown in FIG. 12D, the contact layer 6 and the first cladding layer 5 are etched by dry etching such as ICP or RIE using the etching mask layer 11 as a mask to form the convex portion 10a. 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 may be used. During the etching, the cross section of the two-dimensional photonic crystal structure may be tapered. Specifically, the active layer side FF may be made larger than the surface side FF. An etching method in that case will be described. As such a method, at the beginning of etching, a mask pattern (convex portion 13) is formed with a predetermined diameter, and the mask pattern diameter is reduced by utilizing the receding of the mask as the etching proceeds. There is a method of making the upper and lower diameters of the convex portion 10a different by gradually narrowing. Further, the carrier stop layer 4 can be used as an etch stop layer by utilizing the property that the etch rate varies greatly depending on the Al composition depending on the etching gas.

  In the convex portion 10a 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 arises a problem that the convex portion 10a (semiconductor portion) 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 may be 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. Specifically, the etching may be performed from 50 nm before the active layer 3 to immediately before the active layer 3. The closer the bottom surface of the concave portion between the convex portions 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. It is.

Here, the concrete conditions for making the cross-sectional shape of the photonic crystal mentioned above into a taper shape are shown. As described above, the etching mask layer 11 is made of SiO ₂ , and the contact layer 6 formed of p + type GaAs and the first cladding layer 5 formed of p type GaAs are dry-etched using an RIE apparatus. 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 convex part 10a with a period of 290 nm and a depth of 400 nm could be formed. And the surface side FF was 0.65 and the active layer side FF was 0.84, and it was possible to form a two-dimensional photonic crystal structure having a tapered shape in the cross section.

Next, as shown in FIG. 13A, after the etching mask layer 11 is removed with buffered hydrofluoric acid or the like, the embedding material 10 is embedded in the concave portion between the convex portions. For example, as described above, the filling material 10 is transparent and electrically insulative at the oscillation wavelength of the laser, such as SiO ₂ , SiN, SOG (spin on glass), polyimide, BCB (benzocyclobutene), and the like. The material may be a heat-resistant material that can withstand the heating in the electrode alloying process at the time of electrode formation. 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 can be used. Thus, by embedding the embedding material 10 in the recess, the upper surface of the contact layer 6 becomes flat, and the electrode formation on the upper surface of the contact layer 6 becomes easy. In addition, since the contact layer 6 and the convex portion 10a of the first cladding layer 5 are not exposed, the element is not easily deteriorated due to oxidation.

  By configuring in this way, electrons flowing through the convex portion 10a cannot flow into the embedding material 10 embedded in the concave portion between the convex portions, so that a current confinement effect can be obtained.

  Next, as shown in FIG. 13B, the filling material 10 formed on the contact layer 6 is removed by etching (wet or dry) to expose the contact layer 6. Note that the contact layer 6 can be prevented from being etched by selecting the method and conditions so that the embedding material 10 is etched but the contact layer 6 is not etched.

Next, as shown in FIG. 13C, 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 10 shown in FIG. That is, SiO ₂ , SiN, SOG (spin on glass), polyimide, BCB (benzocyclobutene), etc., chemical vapor volume (CVD) such as plasma CVD (Chemical Vapor Deposition), LPCVD (Low Pressure Chemical Vapor Deposition), etc. The film is formed by a method, a sputtering method, a spin coating method, or the like. Depending on the thickness of the insulating layer 14, the insulating layer 14 can function as an antireflection layer when laser light is extracted by surface emission. Therefore, the thickness of the insulating layer 14 may be adjusted at this time. Next, as shown in FIG. 13D, photolithography and dry etching are performed so that a portion of the insulating layer 14 where the first electrode 7 is to be formed is the opening 14a. At this time, it is also possible to selectively etch away the insulating layer 14 by intentionally selecting different materials for the embedding material 10 and the insulating layer 14 and appropriately selecting the etching conditions. Accordingly, even if the etching is performed excessively when the insulating layer 14 is etched, the embedded material 10 can be prevented from being etched.

  Next, as shown in FIG. 13E, 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 emitted in the vertical direction can be extracted from the light emitting surface 9 to the outside. FIG. 15 is a plan view showing the configuration of the electrodes of the two-dimensional photonic crystal surface emitting laser according to the embodiment of the present invention. FIGS. 15A to 15D show the configurations of the electrodes having different shapes. FIG. As shown in FIGS. 15A to 15D, the electrode 28 may be disposed in the photonic crystal structure formation region 27 in the two-dimensional photonic crystal surface emitting laser. The shape of the electrode 28 may be circular or rectangular, for example. A shape where no electrode is formed in the central portion of the electrode 28 (see FIGS. 15A and 15B), for example, a donut shape, or the like may be used, or the electrode 28 may be compared with the photonic crystal structure formation region 27. It is good also as a small shape (refer FIG.15 (C) and FIG.15 (D)). 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 100 according to the present embodiment is manufactured.

  In addition, another method for manufacturing a two-dimensional photonic crystal surface emitting laser according to an embodiment of the present invention will be described. FIG. 16 is a cross-sectional process diagram for explaining another manufacturing process of the two-dimensional photonic crystal surface emitting laser according to the embodiment of the present invention. FIG. 16 (A) and FIG. FIG. In another two-dimensional photonic crystal surface emitting laser manufacturing method according to the embodiment of the present invention, as shown in FIG. 16A, photolithography and etching are performed after the process shown in FIG. Thus, the contact layer 6 is exposed by forming an opening 10c in a part of the embedding material 10. Then, as shown in FIG. 16B, the first electrode 7 is formed in the opening 10c. Then, a second electrode is formed on the bottom surface of the substrate 1 to manufacture a two-dimensional photonic crystal surface emitting laser. Thus, there is no need to form the insulating layer 14 as shown in FIG. 13C, and the manufacturing process is shortened.

  Further, another method for manufacturing a two-dimensional photonic crystal surface emitting laser according to an embodiment of the present invention will be described. FIG. 17 is a cross-sectional process diagram for explaining a manufacturing process of still another two-dimensional photonic crystal surface emitting laser according to the embodiment of the present invention. In another manufacturing method of a two-dimensional photonic crystal surface emitting laser according to the embodiment of the present invention, in the step of FIG. 13A, as shown in FIG. When embedding the embedding material 10, the embedding material 10 is not embedded in all the recesses, but is embedded so that air portions (holes 10 d) remain in the recesses. In the present embodiment, an air layer is formed on the active layer 3 side of the embedding material 10. 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 method is possible by using a material having a high viscosity as the embedding material 10. First, the embedding material 10 is formed on another substrate by spin coating, and the embedding material 10 is pressed against the device on which the convex portion 10a is formed, so that the embedding material 10 is embedded in the middle of the concave portion between the convex portion and the convex portion. The material 10 may be embedded. The depth of the hole 10d in the recess may be 0.1 μm or more, and may be a depth obtained by subtracting 0.1 μm from the entire depth of the recess. In other words, the amount of the embedding material 10 to be embedded may be between a state in which only 0.1 μm is embedded in the recess and a state in which only 0.1 μm is embedded up to the bottom of the recess. After embedding the embedding material 10, the steps shown in FIG. Thereby, a two-dimensional photonic crystal surface emitting laser in which air is contained in a part of the embedding material 10 can be manufactured. Since the refractive index of air is generally low, in this two-dimensional photonic crystal surface emitting laser, the refractive index difference between the two-dimensional photonic crystal structures formed in the first cladding layer 5 and the contact layer 6 is increased. Can do. Thereby, the diffraction efficiency of the two-dimensional photonic crystal structure is improved. This leads to lower threshold and higher efficiency of the two-dimensional photonic crystal surface emitting laser. In addition, an inert gas or the like may remain in the recess instead of air by embedding the embedding material 10 in a state where an inert gas or the like is injected into the recess. Further, the hole 10d may be in a vacuum state. Thereby, it can prevent that a convex part deteriorates by oxidation.

  In the manufacturing method of the two-dimensional photonic crystal surface emitting laser according to the present embodiment, as described above, since the manufacturing is performed without using the fusion, it is highly likely to occur by performing the fusion. No damage occurs and there is almost no possibility of defective products during manufacturing. Furthermore, although there is a problem that fusion cannot be performed if there is warping or undulation in the device, fusion is not used in the manufacturing method of the two-dimensional photonic crystal surface emitting laser according to the present embodiment. Therefore, the possibility that a defective product is generated is low, the yield is high, and the manufacturing can be easily performed. Further, the material to be used is not particularly limited, and a two-dimensional photonic crystal surface emitting laser can be easily manufactured using a commonly used material. In addition, since the upper surface of the first semiconductor layer (contact layer) is flattened by embedding a filling material in the concave portion between the convex portions, it is easy to form an electrode on the first semiconductor layer (contact layer). Can be done.

  The two-dimensional photonic crystal surface emitting laser according to the embodiment of the present invention may be configured to extract light from the substrate 1 side as shown in FIG. FIG. 18 is a cross-sectional view showing the configuration of another two-dimensional photonic crystal surface emitting laser according to an embodiment of the present invention. Specifically, a material transparent to the wavelength band of light extracted by the substrate 1 may be used. For example, after the step shown in FIG. 13B, the second electrode 8 is formed on the entire surface of the contact layer 6 and is made of a material transparent to the wavelength band of the light to be extracted on the bottom surface of the substrate 1. The insulating layer 14 is formed, and the first electrode 7 that contacts the substrate 1 through the insulating layer 14 may be formed. Thereby, a two-dimensional photonic crystal surface emitting laser in which the light emitting surface 9 is formed on the substrate 1 side can be realized. In FIG. 18, the first electrode 7 is not formed on the entire surface of the light emitting surface 9 but has an opening, and a laser beam is emitted from the opening. However, other configurations may be used. For example, a part or all of the first electrode 7 may be a transparent electrode, and the first electrode 7 may be formed on the entire surface of the light emitting surface 9 without forming an opening. . Thereby, a laser beam is emitted through the transparent electrode.

  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.

1, 2, 31 Substrate 2, 22, 32 Second cladding layer 3, 23, 33 Active layer 4, 24, 34 Carrier stop layer 5, 25, 35 First cladding layer 6, 26, 36 Contact layer 7 First electrode 8 Second electrode 9 Light emitting surface 10 Embedding material 10a, 13 Protruding portion 10b Surface 10c, 14a Opening 10d Hole 11 Etching mask layer 12 Resist layer 14 Insulating layers 25a, 25b Location 27 Photonic crystal structure forming region 28 Electrode 30 Material 100 Two-dimensional photonic crystal surface emitting laser 101 Substrate 102 Lower cladding layer 103 Active layer 104 Upper cladding layer 106 Lower electrode 107 Upper electrode 108 Light emitting region 120 Two-dimensional photonic crystal 121 Photonic crystal periodic structure 200 Two-dimensional photonic crystal surface Light emitting laser

Claims (8)

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 plurality of protrusions on the side opposite to the active layer side, and a two-dimensional photonic crystal structure is formed by all or a part of the plurality of protrusions. Two-dimensional photonic crystal surface emitting laser. A first electrode provided on a side opposite to the active layer side in the first semiconductor layer;
A second electrode provided on the active layer side of the second semiconductor layer,
The first semiconductor layer has a first cladding layer,
The second semiconductor layer has a second cladding layer;
The diameter of the convex portion gradually changes along the depth direction,
An embedding material having a second refractive index different from the first refractive index of the material forming the convex portion is embedded in the first semiconductor layer other than the convex portion on the side opposite to the active layer side. The two-dimensional photonic crystal surface emitting laser according to claim 1.   The two-dimensional photonic crystal surface emitting laser according to claim 1 or 2, wherein a refractive index of the first cladding layer is higher than a refractive index of the second cladding layer.   4. 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 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 the plane including the bottom surface of the portion other than the convex portion is assumed, the ratio of the area occupied by the semiconductor in the virtual plane is defined as the active layer side FF,
The two-dimensional photonic crystal surface emitting laser according to any one of claims 1 to 4, wherein the surface side FF and the active layer side FF have different values.   The two-dimensional photonic crystal surface emitting laser according to claim 5, wherein the active layer side FF is larger than the surface side FF.   The two-dimensional photonic crystal surface emitting laser according to claim 6, wherein the surface-side FF is 0.8 or less and the active layer-side FF is 0.8 or more. Laminating an active layer on the second semiconductor layer;
After laminating the first semiconductor layer on the active layer,
In the first semiconductor layer, the plurality of protrusions are formed on the side opposite to the active layer side in order to form a two-dimensional photonic crystal structure by all or part of the plurality of protrusions. A method for manufacturing a photonic crystal surface emitting laser.