JP2006156901A - Semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device in which a light extracting efficiency is high and an unevenness of vibration strength can be suppressed. <P>SOLUTION: In the semiconductor light emitting device 30, an anode electrode (current injecting electrode) 14 is formed on the emission face of light emitted to a direction perpendicular to the surface of a medium by a two-dimensional photonic crystal 2. This anode electrode 14 is formed in a polygonal shape in which a planar contour matches to an orientation of a two-dimensional diffractive lattice of the two-dimensional photonic crystal 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device including a two-dimensional diffraction grating and capable of surface light emission.

  As a semiconductor laser, a laser using a so-called Fabry-Perot resonator type resonator using two laminated mirrors for enclosing a medium capable of amplifying light has been the mainstream. However, the Fabry-Perot type laser has a drawback that it is difficult to use in the field of optical communication because oscillation in a single color is not guaranteed.

  This problem is solved by a distributed feedback (DFB) laser. The DFB laser is a laser that uses a standing wave generated as a result of inducing a coupling between a forward wave and a backward wave by a one-dimensional diffraction grating provided therein. This phenomenon occurs only with light of a specific wavelength that satisfies the Bragg condition for a one-dimensional diffraction grating. Therefore, according to the DFB laser, it is possible to stably oscillate light in which the longitudinal mode (resonance mode in the optical axis direction of the oscillated light) is a single mode.

  On the other hand, in the DFB laser, light in directions other than the direction of the optical axis of the oscillated light (in other words, the direction perpendicular to the diffraction grating) does not become a standing wave even if diffracted by the diffraction grating and is not fed back. . That is, in the DFB laser, light in a direction other than the direction of the optical axis of the oscillated light is lost without being involved in the oscillation, so that there is a disadvantage that the light emission efficiency is lowered accordingly.

  Therefore, in recent years, a two-dimensional photonic crystal laser using a photonic crystal having a periodic refractive index distribution is being developed. The two-dimensional photonic crystal laser diffracts light in various directions existing in the photonic crystal plane to generate standing waves, even if the light is not in the optical axis direction of the oscillated light. Thus, the luminous efficiency can be improved. In addition, since the two-dimensional photonic crystal laser has a feature of emitting light in the direction perpendicular to the main surface of the photonic crystal, the output of the laser light can be increased. A two-dimensional photonic crystal laser capable of such surface emission is disclosed in Non-Patent Document 1, for example.

  FIG. 22 is a schematic perspective view showing the configuration of the two-dimensional photonic crystal laser disclosed in the above document. Referring to FIG. 22, this two-dimensional photonic crystal laser 130 includes two wafers 110 and 120, a cathode electrode 103, and an anode electrode 114.

  The wafer 110 has an n-type InP substrate 101 and an n-type InP clad layer 102 formed on the surface of the InP substrate 101. The wafer 120 has an n-type cladding layer 111 formed so as to form a double heterojunction, an active layer 112, and a p-type cladding layer 113.

  The wafer 110 and the wafer 120 are disposed so that the InP cladding layer 102 and the n-type cladding layer 111 face each other, and are integrated by heating. A cathode electrode 103 is formed on the back surface of the InP substrate 101, and an anode electrode 114 is formed on the p-type cladding layer 113.

  The InP clad layer 102 has a plurality of holes 102a arranged on the surface with a predetermined lattice (for example, a triangular lattice, a square lattice, or the like). As a result, the portion having no hole has a refractive index of InP (n = 3.21), the portion having a hole has a refractive index of air (n = 1), and the main surface of the InP cladding layer 102 has a periodicity. A photonic crystal having a typical refractive index distribution.

In such a two-dimensional photonic crystal laser 130, holes and electrons are injected into the active layer 112 by applying an appropriate voltage between the two electrodes 103 and 114. When holes and electrons are recombined, light having a predetermined wavelength is generated in the active layer 112. This light leaks out of the active layer 112 to become evanescent light, propagates to the photonic crystal, and repeats Bragg reflection at the lattice points of the holes 102a in the photonic crystal. As a result, standing waves are generated between the respective lattice points, and the light has a uniform wavelength and phase. This light is oscillated from a direction perpendicular to the main surface of the photonic crystal. Thereby, surface light emission occurs in the surface light emitting region 115 around the anode electrode 114 on the surface where the anode electrode 114 is formed.
Hikaru Yokoyama et al., "Two-dimensional photonic crystal surface emitting laser", Journal of the Infrared Radiological Society of Japan, 2003, Vol. 12, No. 2, pp. 17-23

  However, in the two-dimensional photonic crystal laser 130 disclosed in the above document, since the anode electrode 114 partially overlaps the surface emitting region 115, light can be extracted only from around the anode electrode 114, and the light extraction efficiency is high. Low.

  Further, since the planar shape of the anode electrode 114 is circular, the light confinement region becomes non-uniform, unevenness in the oscillation light intensity occurs, and it becomes difficult to achieve high power by integration.

  Therefore, an object of the present invention is to provide a semiconductor light emitting device that has high light extraction efficiency and can suppress unevenness in oscillation intensity.

  The semiconductor light emitting device of the present invention includes an active layer, a two-dimensional photonic crystal, and a current injection electrode. The active layer generates light by carrier injection. The two-dimensional photonic crystal has a medium having a first refractive index and a second refractive index portion provided on the surface of the medium so as to form a two-dimensional diffraction grating, and is generated in the active layer It diffracts light and emits light in a direction perpendicular to the surface of the medium. The current injection electrode is formed on the emission surface of light emitted by the two-dimensional photonic crystal in a direction perpendicular to the surface of the medium. The current injection electrode has a unit electrode having a polygonal shape whose planar outer shape is aligned with the orientation of the two-dimensional diffraction grating of the two-dimensional photonic crystal.

  According to the semiconductor light emitting device of the present invention, the planar outer shape of the unit electrode of the current injection electrode is a polygonal shape that matches the orientation of the two-dimensional diffraction grating of the two-dimensional photonic crystal. A rectangular light emitting region having the same intensity can be formed along the line. As a result, the light emitting area becomes wider than in the conventional example, so that the light extraction efficiency is increased. Further, since a rectangular light emitting region having the same intensity can be formed along the side direction, unevenness in oscillation intensity can be suppressed.

  Note that “the planar outer shape is a polygonal shape that matches the orientation of the two-dimensional diffraction grating of the two-dimensional photonic crystal” means that the polygonal shape when the semiconductor light emitting element is viewed in plan view from the current injection electrode side. Means that each of the corners is made of a polygon configured to be located immediately above the second refractive index portion.

  In the above semiconductor light emitting device, the two-dimensional diffraction grating is preferably a triangular diffraction grating, and the planar outer shape of the unit electrode is a hexagonal shape.

  This makes it possible to form a rectangular light emitting region having the same intensity along the side direction.

  In the semiconductor light emitting device described above, the planar shape of the unit electrode is preferably a hollow hexagonal frame shape.

  Thereby, since the unit electrode has a hollow shape, light can be extracted also from the hollow portion, and the light extraction efficiency is further increased.

  In the semiconductor light emitting device described above, preferably, the two-dimensional diffraction grating is a square diffraction grating, and the planar outer shape of the unit electrode is a square shape.

  This makes it possible to form a rectangular light emitting region having the same intensity along the side direction.

  In the semiconductor light emitting device described above, the planar shape of the unit electrode is preferably a hollow square frame.

  Thereby, since the unit electrode has a hollow shape, light can be extracted also from the hollow portion, and the light extraction efficiency is further increased.

  In the semiconductor light emitting device described above, the current injection electrode preferably has a configuration in which a plurality of unit electrodes are arranged.

  As a result, the area of the light emitting region can be increased.

  The semiconductor light emitting device preferably further includes a transparent electrode for electrically connecting a plurality of unit electrodes.

  Thereby, a plurality of unit electrodes can be electrically connected without hindering extraction of light.

  As described above, according to the semiconductor light emitting device of the present invention, the planar outer shape of the unit electrode of the current injection electrode is a polygonal shape that matches the orientation of the two-dimensional diffraction grating of the two-dimensional photonic crystal. Therefore, it is possible to increase the light extraction efficiency and to suppress unevenness in oscillation intensity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a perspective view showing a configuration of a semiconductor laser device using a photonic crystal as an example of the semiconductor light emitting device in the first embodiment of the present invention. FIG. 2 is a schematic sectional view taken along line II-II in FIG.

  Referring to FIGS. 1 and 2, a semiconductor laser device 30 includes, for example, a substrate 1, a photonic crystal 2 as a two-dimensional diffraction grating, a cathode electrode 3, an n-type cladding layer 11, and an active layer 12. And a p-type cladding layer 13 and an anode electrode 14.

  The substrate 1 is made of, for example, n-type GaN (gallium nitride). A photonic crystal 2 as a two-dimensional diffraction grating is formed on the surface of the substrate 1. The photonic crystal 2 includes a medium having a first refractive index and a second refractive index portion provided on the surface of the medium so as to form a two-dimensional diffraction grating. The medium having the first refractive index is, for example, an n-type GaN cladding layer 2 (refractive index: 2.54) formed by epitaxial growth, and the second refractive index portion is a hole 2a (for example, filled with air). Refractive index: 1). The holes 2a are columnar (for example, columnar) spaces, and are arranged on the surface 2b of the GaN cladding layer 2 at lattice points so as to form, for example, a triangular lattice.

  The distances between the centers of the holes 2a and the centers of the six holes 2a closest thereto are equal, the pitch of the holes 2a is 140 nm, for example, and the diameter of the holes 2a is 60 nm, for example.

  On the surface 2b of the photonic crystal 2, an n-type cladding layer 11, an active layer 12, and a p-type cladding layer 13 are sequentially formed.

The active layer 12 is made of a material that generates light by injecting carriers, and is composed of, for example, a multiple quantum well made of Al _x Ga _{1 -xy} In _y N (0 ≦ x, y ≦ 1, 0 ≦ x + y ≦ 1). It may be made of a single semiconductor material.

  The n-type cladding layer 11 is made of, for example, n-type GaN, and the p-type cladding layer 13 is made of, for example, p-type GaN. The n-type cladding layer 11 and the p-type cladding layer 13 function as conductive layers through which carriers to be given to the active layer 12 are conducted. For this reason, the n-type cladding layer 11 and the p-type cladding layer 13 are provided so as to sandwich the active layer 12. Both the n-type cladding layer 11 and the p-type cladding layer 13 function as confinement layers that confine carriers (electrons and holes) in the active layer 12. That is, the n-type cladding layer 11, the active layer 12 and the p-type cladding layer 13 form a double heterojunction, and carriers contributing to light emission can be concentrated in the active layer 12.

  Further, the n-type clad layer 11 may function as a block layer that blocks the entrance of holes into the photonic crystal 2. Thereby, it is possible to suppress the non-radiative recombination of electrons and holes in the photonic crystal 2. In particular, when the diffraction grating point 2a is made of air, non-radiative recombination is likely to occur on the surface of the diffraction grating point 2a, so the function as a block layer is important.

  A cathode electrode 3 is formed on the back surface of the substrate 1 so as to be electrically connected to the substrate 1, and an anode electrode 14 is electrically connected to the p-type cladding layer 13 on the surface of the p-type cladding layer 13. Is formed.

  The anode electrode (current injection electrode) 14 has a unit electrode having a polygonal shape whose planar outer shape matches the orientation of the two-dimensional diffraction grating of the two-dimensional photonic crystal 2. In the present embodiment, the anode electrode 14 is composed of, for example, a unit electrode alone, and has a hexagonal outer shape that matches the orientation of the triangular lattice of the two-dimensional photonic crystal 2. Further, as shown in FIG. 3, the hexagonal shape matching the orientation of the triangular lattice means that each of the six corners is directly above the hole 2a when the semiconductor laser element 30 is viewed in plan from the anode electrode 14 side. It means a hexagon configured to be located.

  Note that conductive elements such as bonding wires 15 and bumps are electrically connected to the anode electrode 14.

  Next, a method for manufacturing the semiconductor laser element 30 in the present embodiment will be specifically described.

  Referring to FIG. 1, an n-type GaN cladding layer 2 is formed on an n-type GaN substrate 1 by epitaxial growth. A photoresist (not shown) is applied on the n-type GaN clad layer 2 and then developed by photolithography to form a plurality of hole patterns in the photoresist. This hole pattern has a diameter of 60 nm and a pitch of 140 nm, and is arranged to form a triangular lattice. By processing the n-type GaN clad layer 2 by etching using this resist pattern as a mask, the n-type GaN clad layer 2 has a diameter of 60 nm, a pitch of 140 nm, and a plurality of arrays arranged to form a triangular lattice. Hole 2a is formed. Thereby, the photonic crystal 2 for forming the light confinement region is formed. Thereafter, the resist pattern is removed by ashing or the like. The wafer 10 having the n-type GaN substrate 1 and the photonic crystal 2 formed in this manner is referred to as a first wafer.

  The other wafer 20 is formed to have a structure in which an active layer 12 having a quantum well structure made of GaN / InGaN is sandwiched between an n-type GaN cladding layer 11 and a p-type GaN cladding layer 12. This wafer 20 is referred to as a second wafer.

  The first wafer 10 and the second wafer 20 are bonded by a bonding technique. An anode electrode 14 is formed on the surface of the p-type GaN 13, and a cathode electrode 3 is formed on the back surface of the n-type GaN substrate 1. The bonded wafer is cleaved in a direction perpendicular to the laser oscillation surface, whereby a photonic crystal surface emitting laser using the GaN substrate 1 is formed.

  Next, a light emitting method of the semiconductor laser element 30 will be described with reference to FIGS.

  When a positive voltage is applied to the anode electrode 14 and a negative voltage is applied to the cathode electrode 3, holes are injected from the p-type cladding layer 13 to the active layer 12, and electrons are injected from the n-type cladding layer 11 to the active layer 12. The When holes and electrons (carriers) are injected into the active layer 12, carrier recombination occurs and light is generated. The wavelength of the generated light is defined by the band gap of the semiconductor layer included in the active layer 12.

  The light generated in the active layer 12 is confined in the active layer 12 by the n-type cladding layer 11 and the p-type cladding layer 13, but a part of the light reaches the photonic crystal 2 as evanescent light. When the wavelength of the evanescent light that has reached the photonic crystal 2 matches the predetermined period of the photonic crystal 2, the phase condition of the light is defined at the wavelength corresponding to the period. The light whose phase is defined by the photonic crystal 2 propagates in a direction perpendicular to the surface 2b of the photonic crystal 2 (in the direction of arrow S in FIG. 1), and stimulates stimulated emission in the active layer 12. The stimulated emission light satisfies the light wavelength and phase conditions defined in the photonic crystal 2. This light propagates again to the photonic crystal 2. In this way, light having a uniform wavelength and phase condition is generated and amplified.

  Such a phenomenon can occur in the region around the electrode 14 and in the vicinity thereof because the active layer 12 and the photonic crystal 2 are two-dimensionally widened. The light having the same wavelength and phase condition is emitted in a direction perpendicular to the surface 2b of the photonic crystal 2 and emitted from the light emitting surface 13a.

  Next, the two-dimensional diffraction grating (photonic crystal layer) 2 will be described with specific examples. Two-dimensional diffraction gratings have the property of overlapping when translated in the same period in at least two directions. Such a two-dimensional lattice is formed by arranging regular triangles, squares, or regular hexagons all over the surface and providing lattice points at each vertex. Here, a lattice formed using a regular triangle is referred to as a triangular lattice, a lattice formed using a square is referred to as a square lattice, and a lattice formed using a regular hexagon is referred to as a hexagonal lattice.

  FIG. 4 is a drawing depicting a triangular grating having a grating interval a as a two-dimensional diffraction grating. The triangular lattice is filled with regular triangles whose side length is a. In FIG. 4, paying attention to arbitrarily selected lattice point A, the direction from lattice point A to lattice point B is called the X-Γ direction, and the direction from lattice point A to lattice point C is the XJ direction. Call it. In the present embodiment, a case where the wavelength of light generated in the active layer 12 corresponds to a lattice period in the X-Γ direction will be described.

The two-dimensional diffraction grating 2 can be considered to include three one-dimensional diffraction grating groups L, M, and N described below. The one-dimensional diffraction grating group L includes one-dimensional gratings L ₁ , L ₂ , L _{3 and the} like provided in the Y-axis direction. The one-dimensional diffraction grating group M is composed of one-dimensional gratings M ₁ , M ₂ , M _{3 and the} like provided with an angle of 120 degrees with respect to the X-axis direction. The one-dimensional diffraction grating group N is composed of one-dimensional gratings N ₁ , N ₂ , N _{3 and the} like provided in a direction of 60 degrees with respect to the X-axis direction. These three one-dimensional diffraction grating groups L, N, and M overlap when rotated at an angle of 120 degrees around an arbitrary grating point. In each one-dimensional diffraction grating group L, N, and M, the interval between the one-dimensional gratings is d, and the interval within the one-dimensional grating is a.

  First, the lattice group L is considered. Light traveling in the direction from the lattice point A to the lattice point B causes a diffraction phenomenon at the lattice point B. The diffraction direction is defined by the Bragg condition 2d · sin θ = mλ (m = 0, ± 1,...). Here, λ is the wavelength of light in the GaN cladding layer 2. When the diffraction grating is formed so as to satisfy the second-order Bragg reflection (m = ± 2), other grating points D, E, F and G are formed at angles of θ = ± 60 ° and ± 120 °. Exists. There are also lattice points A and K at angles θ = 0 and 180 ° corresponding to m = 0.

  For example, light diffracted at the lattice point B in the direction of the lattice point D is diffracted according to the lattice group M at the lattice point D. This diffraction can be considered in the same manner as the diffraction phenomenon according to the grating group L. Next, the light diffracted toward the lattice point H at the lattice point D is diffracted according to the lattice group N. In this way, diffraction is sequentially performed at the lattice point H, the lattice point I, and the lattice point J. The light diffracted from the lattice point J toward the lattice point A is diffracted according to the lattice group N.

  As described above, the light traveling from the lattice point A to the lattice point B reaches the first lattice point A through a plurality of diffractions. For this reason, in the semiconductor laser element 30, light traveling in a certain direction returns to the position of the original lattice point through a plurality of diffractions, so that a standing wave is generated between the lattice points. Therefore, the two-dimensional diffraction grating 2 acts as an optical resonator, that is, a wavelength selector and a reflector.

  In the Bragg condition 2d · sin θ = mλ (m = 0, ± 1,...), The Bragg reflection direction under the condition that m is an odd number is θ = ± 90 °. This means that the diffraction becomes stronger in the direction perpendicular to the surface 2b of the two-dimensional diffraction grating 2 (the direction of the arrow S in FIG. 1). Thereby, light can be emitted (surface emission) in a direction perpendicular to the main surface of the two-dimensional diffraction grating 2, that is, from the light emission surface 13a (FIG. 1).

  Further, in the two-dimensional diffraction grating 2, considering that the above description is performed at an arbitrary lattice point A, the above-described light diffraction can occur at all the two-dimensionally arranged lattice points. For this reason, it is considered that light propagating in each X-Γ direction is two-dimensionally coupled to each other by Bragg diffraction. In the two-dimensional diffraction grating 2, it is considered that the three X-Γ directions are coupled by this two-dimensional coupling to form a coherent state.

  According to the present embodiment, since the anode electrode 14 has a hexagonal outer shape that matches the orientation of the triangular lattice of the two-dimensional photonic crystal 2, the light extraction efficiency can be increased, and the oscillation intensity can be uneven. Can be suppressed. Hereinafter, this will be described in detail in comparison with a conventional example.

  FIG. 5 is a plan view for explaining the light emitting region when the planar shape of the anode electrode in the conventional example is circular. Referring to FIG. 5, the light emission intensity depends on the dimension of anode electrode 114 along the direction in which the lattice is arranged. Specifically, the dimension from the point C11 to the point C12 along the lattice arrangement of the circular anode electrode 114 is shorter than the dimension from the point C13 to the point C14. For this reason, the intensity of light along the grid array from point C11 to point C12 is smaller than the intensity of light along the grid array from point C13 to point C14. As a result, the emission intensity is increased at the arrow indicated by the thick line in the figure, and the emission intensity is reduced at the arrow indicated by the thin line in the figure. As a result, the light emitting region S1b around the circular electrode 114 has a triangular shape when seen in a plan view. Further, the light emission intensity becomes non-uniform along the circular arc of the outer shape of the circular electrode 114.

  In contrast, in the present embodiment, referring to FIG. 3, anode electrode 14 has a hexagonal outer shape that matches the orientation of the triangular lattice of two-dimensional photonic crystal 2. For this reason, the dimension from the point C1 to the point C2 along the lattice arrangement of the hexagonal anode electrode 14 is the same as the dimension from the point C3 to the point C4. Therefore, the light intensity along the lattice arrangement from the point C1 to the point C2 is the same as the light intensity along the lattice arrangement from the point C3 to the point C4. As a result, as indicated by the bold arrows in the figure, the light emission intensity is equal in each portion along each grid array, and the light emitting region S1a generated around each side of the hexagonal electrode 14 is rectangular when viewed in plan. Further, the light emission intensity becomes uniform along each side of the hexagonal electrode 14.

  As described above, according to the present embodiment, since the shape of the light emitting region, which has been a triangle in the past, can be expanded to be a rectangle, more light can be extracted and light extraction efficiency can be improved. it can. Further, since the emission intensity can be made uniform along each side of the hexagonal electrode 14, unevenness in oscillation intensity can be suppressed.

(Embodiment 2)
FIG. 6 is a perspective view showing a structure of a semiconductor laser device using a photonic crystal as an example of the semiconductor light emitting device in the second embodiment of the present invention. Referring to FIG. 6, the configuration of the present embodiment is different in the configuration of photonic crystal 2 and anode electrode (current injection electrode) 14 compared to the configuration of the first embodiment.

  In the photonic crystal 2 of the present embodiment, the second refraction is performed so that a square lattice is formed as a two-dimensional diffraction grating on the surface of the medium having the first refractive index (for example, the n-type GaN cladding layer 2). A rate portion (for example, hole 2a) is provided.

  The distance between the center of each hole 2a and the center of the four holes 2a closest thereto is equal, and the pitch of the holes 2a is 120 nm, for example, and the diameter of the holes 2a is 60 nm, for example.

  The anode electrode (current injection electrode) 14 is made of, for example, a single unit electrode, and has a quadrangular outer shape that matches the orientation of the square lattice of the two-dimensional photonic crystal 2. Here, as shown in FIG. 7, the quadrangular shape aligned with the orientation of the square lattice means that each of the four corners is directly above the hole 2 a when the semiconductor laser element 30 is viewed in plan from the anode electrode 14 side. Means a quadrangle configured to be located in

  The remaining configuration of the present embodiment is substantially the same as the configuration of the first embodiment described above, and therefore the same components are denoted by the same reference numerals and description thereof is omitted. Further, since the manufacturing method of the present embodiment is almost the same as the manufacturing method of the first embodiment, the description thereof is omitted.

  Further, the light emitting method of the semiconductor laser device 30 of the present embodiment is different from that of the first embodiment in that respect because a square lattice is used as the two-dimensional diffraction grating.

  FIG. 8 is a diagram depicting a square lattice having a lattice interval d as a two-dimensional diffraction grating. Referring to FIG. 8, the square lattice is filled with a square whose side is d in length. Focusing on the arbitrarily selected lattice point W, the direction from the lattice point W to the lattice point P is called the X-Γ direction, and the direction from the lattice point W to the lattice point Q is called the XJ direction. Here, the case where the wavelength of the light generated in the active layer 12 corresponds to the grating period in the X-Γ direction will be described.

The two-dimensional diffraction grating (photonic crystal layer) 2 can be considered to include two one-dimensional diffraction grating groups U and V described below. The one-dimensional diffraction grating group U is composed of one-dimensional gratings U ₁ , U ₂ , U _{3 and the} like provided in the Y-axis direction. The one-dimensional diffraction grating group V includes one-dimensional gratings V ₁ , V ₂ , V _{3 and the} like provided in the X-axis direction. These two one-dimensional diffraction grating groups U and V overlap when rotated at an angle of 90 ° about an arbitrary grating point. In each one-dimensional diffraction grating group U and V, the interval between the one-dimensional gratings is d, and the interval within the one-dimensional grating is b.

  First, the lattice group U will be considered. Light traveling in the direction from the lattice point W to the lattice point P causes a diffraction phenomenon at the lattice point P. The diffraction direction is defined by the Bragg condition 2d · sin θ = mλ (m = 0, ± 1,...) As in the case of the triangular grating. When the diffraction grating is formed so as to satisfy the second-order Bragg reflection (m = ± 2), there are other grating points Q and R at an angle θ = ± 90 °, and m = 0. There are also lattice points W and S at corresponding angles θ = 0 and 180 °.

  The light diffracted toward the lattice point Q at the lattice point P is diffracted according to the lattice group V at the lattice point Q. This diffraction can be considered in the same manner as the diffraction phenomenon according to the grating group U. Next, the light diffracted toward the lattice point T at the lattice point Q is diffracted according to the lattice group U. In this way, the light is sequentially diffracted. The light diffracted from the lattice point T toward the lattice point W is diffracted according to the lattice group V.

  As described above, the light traveling from the lattice point W to the lattice point P reaches the first lattice point W through a plurality of diffractions. For this reason, in the semiconductor laser device of the present embodiment, light traveling in a certain direction returns to the position of the original lattice point through a plurality of diffractions, so that a standing wave is generated between the lattice points. Therefore, the two-dimensional diffraction grating 2 acts as an optical resonator, that is, a wavelength selector and a reflector.

  In the Bragg condition 2d · sin θ = mλ (m = 0, ± 1,...), The Bragg reflection direction under the condition that m is an odd number is θ = ± 90 °. This means that the diffraction becomes stronger in the direction perpendicular to the main surface of the two-dimensional diffraction grating 2 (the direction perpendicular to the paper surface in FIG. 15). Thereby, light can be emitted (surface emission) in a direction perpendicular to the main surface of the two-dimensional diffraction grating 2, that is, from the light emission surface 13a (FIG. 1).

  Further, in the two-dimensional diffraction grating 2, considering that the above description is performed at an arbitrary grating point W, the above-described light diffraction can occur at all the two-dimensionally arranged grating points. For this reason, it is considered that light propagating in each X-Γ direction is two-dimensionally coupled to each other by Bragg diffraction. In the two-dimensional diffraction grating 2, it is considered that the two X-Γ directions are coupled by this two-dimensional coupling to form a coherent state.

  According to the present embodiment, as in the first embodiment, since the anode electrode 14 has a quadrangular outer shape that matches the orientation of the square lattice of the two-dimensional photonic crystal 2, the light extraction efficiency is increased. In addition, it is possible to suppress unevenness in oscillation intensity. Hereinafter, this will be described in detail in comparison with a conventional example.

  FIG. 9 is a plan view for explaining the light emitting region when the planar shape of the anode electrode in the conventional example is circular. Referring to FIG. 9, as described in the first embodiment, the light emission intensity depends on the dimension of anode electrode 114 along the grid arrangement direction. For this reason, in the case of the circular anode electrode 114, even when the two-dimensional lattice arrangement is a square lattice, the light emitting region S1b around the circular electrode 114 has a triangular shape when seen in a plan view. Further, the light emission intensity becomes non-uniform along the circular arc of the outer shape of the circular electrode 114.

  In contrast, in the present embodiment, referring to FIG. 7, anode electrode 14 has a quadrangular outer shape that matches the orientation of the square lattice of two-dimensional photonic crystal 2. For this reason, the dimension from the point C21 to the point C22 along the lattice arrangement of the square anode electrode 14 is the same as the dimension from the point C23 to the point C24. Therefore, the light intensity along the lattice arrangement from the point C21 to the point C22 is the same as the light intensity along the lattice arrangement from the point C23 to the point C24. Thereby, the light emission intensity is equal in each of the portions along each grid array, and the light emitting region S2a generated around each side of the square electrode 14 is rectangular when viewed in plan. Further, the light emission intensity becomes uniform along each side of the square electrode 14.

  As described above, according to the present embodiment, since the shape of the light emitting region, which has been a triangle in the past, can be expanded to be a rectangle, more light can be extracted and light extraction efficiency can be improved. it can. In addition, since the emission intensity can be made uniform along each side of the square electrode 14, unevenness in oscillation intensity can be suppressed.

(Embodiment 3)
FIG. 10 is a perspective view showing a structure of a semiconductor laser device using a photonic crystal as an example of the semiconductor light emitting device in the third embodiment of the present invention. Referring to FIG. 10, the configuration of the present embodiment is different from the configuration of the first embodiment in the configuration of anode electrode (current injection electrode) 14.

  The anode electrode (current injection electrode) 14 according to the present embodiment is made of, for example, a unit electrode alone, and has a hollow hexagonal frame shape.

  The remaining configuration of the present embodiment is substantially the same as the configuration of the first embodiment described above, and therefore the same components are denoted by the same reference numerals and description thereof is omitted. Further, the manufacturing method and the light emitting method of the present embodiment are almost the same as the manufacturing method of the first embodiment, and thus the description thereof is omitted.

  According to the present embodiment, referring to FIG. 11, anode electrode 14 has a hexagonal outer shape that matches the orientation of the triangular lattice of two-dimensional photonic crystal 2. For this reason, as in the first embodiment, the light emission intensity is equal in each of the portions along each lattice arrangement, and the light emitting region S3a generated around each side of the hexagonal electrode 14 is rectangular when viewed in plan. Further, the light emission intensity becomes uniform along each side of the hexagonal electrode 14.

  As described above, according to the present embodiment, since the shape of the light emitting region, which has been a triangle in the past, can be expanded to be a rectangle, more light can be extracted and light extraction efficiency can be improved. it can. Further, since the emission intensity can be made uniform along each side of the hexagonal electrode 14, unevenness in oscillation intensity can be suppressed.

  Further, since the hexagonal electrode 14 is formed in a frame shape with a hollow, it is possible to extract light from the central portion with the hollow. As a result, more light can be extracted, and the light extraction efficiency can be further increased.

  Even when the hexagonal electrode 14 is hollowed out, the current injected by the hexagonal electrode 14 spreads to the center of the hexagonal electrode 14. For this reason, the same current injection effect as in the case of the hexagonal solid electrode having no hollow in the first embodiment can be obtained.

  In the above description, the case where the anode electrode 14 is made of a single unit electrode having a hexagonal frame shape with a hollow is described. However, the anode electrode 14 is a mesh formed by connecting a plurality of unit electrodes in combination as shown in FIG. (A honeycomb (honeycomb) shape).

  As shown in FIG. 11, when the anode electrode 14 is made of a single unit electrode having a hexagonal frame shape with a hollow, there is a limit to the spread of current from the anode electrode 14 to the center portion. It is difficult to increase the size of the anode electrode 14. Accordingly, by combining the unit electrodes in a mesh shape as shown in FIG. 12, the anode electrode 14 can be enlarged without increasing the size of the unit electrode itself. Further, in the case of the conventional circular anode electrode, the combination connection cannot be made without a gap, but when the outer shape is a hexagon, the connection can be made without a gap.

(Embodiment 4)
FIG. 13 is a perspective view showing a configuration of a semiconductor laser device using a photonic crystal as an example of the semiconductor light emitting device in the fourth embodiment of the present invention. Referring to FIG. 13, the configuration of the present embodiment is different from the configuration of the second embodiment in the configuration of anode electrode (current injection electrode) 14.

  The anode electrode (current injection electrode) 14 of the present embodiment is made of, for example, a unit electrode alone, and has a hollow rectangular frame shape.

  Since the configuration of the present embodiment other than this is almost the same as the configuration of the second embodiment described above, the same components are denoted by the same reference numerals, and the description thereof is omitted. Further, the manufacturing method and the light emitting method of the present embodiment are almost the same as the manufacturing method of the second embodiment, and thus the description thereof is omitted.

  According to the present embodiment, referring to FIG. 14, anode electrode 14 has a rectangular outer shape that matches the orientation of the square lattice of two-dimensional photonic crystal 2. For this reason, as in the second embodiment, the light emission intensity is equal in each portion along each lattice arrangement, and the light emitting region S4a generated around each side of the square electrode 14 is rectangular when viewed in plan. Further, the light emission intensity becomes uniform along each side of the square electrode 14.

  As described above, according to the present embodiment, since the shape of the light emitting region, which has been a triangle in the past, can be expanded to be a rectangle, more light can be extracted and light extraction efficiency can be improved. it can. In addition, since the emission intensity can be made uniform along each side of the square electrode 14, unevenness in oscillation intensity can be suppressed.

  Further, since the square electrode 14 is formed in a frame shape with a hollow, it is possible to extract light from the central portion with the hollow. As a result, more light can be extracted, and the light extraction efficiency can be further increased.

  Even when the square electrode 14 is hollowed out, the current injected by the square electrode 14 spreads to the center of the square electrode 14. For this reason, the same current injection effect as in the case of the rectangular solid electrode having no hollow in the second embodiment can be obtained.

  In the above description, the case where the anode electrode 14 is formed of a single unit electrode having a rectangular frame shape with a hollowed out portion has been described. However, the anode electrode 14 has a mesh shape by connecting a plurality of unit electrodes as shown in FIG. It may be said.

  As shown in FIG. 14, when the anode electrode 14 is made of a single unit electrode having a rectangular frame shape with a hollow, there is a limit to the spread of current from the anode electrode 14 to the center portion. It is difficult to increase the size of the electrode 14. Accordingly, by combining the unit electrodes in a mesh shape as shown in FIG. 15, the anode electrode 14 can be enlarged without increasing the size of the unit electrode itself. Further, in the case of the conventional circular anode electrode, the combination connection cannot be made without a gap, but when the outer shape is a square shape, the connection can be made without a gap.

(Embodiment 5)
FIG. 16 is a plan view schematically showing a configuration of a semiconductor laser element using a photonic crystal as an example of the semiconductor light emitting element in the fifth embodiment of the present invention. Referring to FIG. 16, the configuration of the present embodiment is different from the configuration shown in FIG. 12 in that bonding pad portion 14a is added. The bonding pad portion 14a is formed so as to extend outward from the outermost peripheral portion of the electrode 14 in which the hollow hexagonal frame-shaped unit electrodes are combined in a mesh shape. Is formed. A bonding wire 15 is electrically connected to the bonding pad portion 14a.

  The remaining configuration of the present embodiment is almost the same as the configuration shown in FIG. 12 described above, and thus the same components are denoted by the same reference numerals and description thereof is omitted.

  According to the present embodiment, it is not necessary to electrically connect the bonding wire 15 to the mesh electrode 14 by providing the bonding pad portion 14a. For this reason, the bonding wire 15 does not shield the light emitting region, and the light extraction efficiency can be further improved.

  In the above description, the case where the bonding pad portion 14a is electrically connected to the electrode formed by combining the hollow hexagonal frame unit electrodes has been described. However, as shown in FIG. The bonding pad portion 14a may be electrically connected to an electrode obtained by combining the unit electrodes in the shape, and in this case, the same effect as described above can be obtained.

(Embodiment 6)
FIG. 17 is a plan view schematically showing a configuration of a semiconductor laser element using a photonic crystal as an example of the semiconductor light emitting element in the sixth embodiment of the present invention. 18 is a schematic cross-sectional view taken along the line XVIII-XVIII in FIG.

  Referring to FIGS. 17 and 18, the configuration of the present embodiment includes a plurality of unit electrodes 14 according to the first embodiment which are separated and arranged, and each unit electrode 14 is covered with a transparent electrode 16 to provide a plurality of unit electrodes 14. The unit electrodes 14 are electrically connected to each other. The transparent electrode 16 has a bonding pad portion 16 a formed so as to extend outward from the outermost peripheral portion and integrally formed with the transparent electrode 16. A bonding wire 15 is electrically connected to the bonding pad portion 16a.

  The remaining configuration of the present embodiment is almost the same as the configuration shown in FIG. 1 described above, and therefore the same components are denoted by the same reference numerals and description thereof is omitted.

  According to the present embodiment, since the plurality of arranged hexagonal unit electrodes 14 can be electrically connected by the transparent electrode 16, the light emitting region can be enlarged. In addition, since the transparent electrode 16 does not need to be an electrode for current injection (that is, does not need to be an ohmic electrode), the degree of freedom in selecting a material is increased, and a material that is transparent to the generated light is selected. Can do.

  In the above description, the case where a plurality of arranged hexagonal unit electrodes 14 are electrically connected by the transparent electrode 16 has been described. However, as shown in FIG. In this case, the same effect as described above can be obtained.

  In the above embodiment, the hexagonal unit electrodes are formed in a positional relationship as shown by dotted lines in FIG. 19 with respect to the triangular lattice, but may be formed in a positional relationship shown by a solid line. Further, in the above embodiment, the rectangular unit electrodes are formed in a positional relationship as shown by the dotted line in FIG. 20 with respect to the square lattice, but may be formed in a positional relationship shown by a solid line.

  In the first to sixth embodiments, the configuration in which the photonic crystal 2 is located on the cathode electrode side with respect to the active layer 12 has been described. However, as shown in FIG. It may be located on the anode electrode 14 side. In this case, the semiconductor laser element 30 includes, for example, an n-type cladding layer 11, an active layer 12, a p-type cladding layer 13, a photonic crystal 2 as a two-dimensional diffraction grating, and a p-type cladding layer on a substrate 1. 21 and the contact layer 22 are sequentially formed, the cathode electrode 3 is formed on the back surface of the substrate 1, and the anode electrode 14 is formed on the surface of the contact layer 22.

  In the above embodiment, n-type GaN has been described as the material of the substrate 1. However, the material of the substrate 1 is not limited to this, and may be conductive SiC, InP, or GaAs. The above-described conductive GaN and conductive SiC are used for light emitting elements in the blue to ultraviolet region, and InP and GaAs are used for light emitting elements in the infrared to red region.

  Moreover, although the case where air was satisfy | filled in the hole 2a was demonstrated, gas other than air may be satisfy | filled and solid may be satisfy | filled. In this case, a silicon nitride film (SiNx) or the like can be used as a material for filling the hole 2a, that is, a dielectric material having a low refractive index. However, in order to increase the difference between the first refractive index and the second refractive index, the hole 2a is in a state in which nothing is embedded (a state where gas, for example, air exists, more strictly, a junction described later) It is preferable that the gas contained in the atmosphere in the process exists. When the difference in refractive index is thus increased, light can be confined in the medium having the first refractive index.

  In the above embodiment, the case where the planar outer shape of the current injection electrode 14 is hexagonal or rectangular has been described. However, the present invention is not limited to this, and the present invention is not limited to two-dimensional photo. The present invention can be applied to all current injection electrodes having a polygonal shape in accordance with the orientation of the two-dimensional diffraction grating of the nick crystal.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be advantageously applied to a semiconductor light emitting device including a two-dimensional diffraction grating and capable of surface emission.

It is a perspective view which divides | segments and shows the structure of the semiconductor laser element using a photonic crystal as an example of the semiconductor light-emitting device in Embodiment 1 of this invention. It is a schematic sectional drawing in alignment with the II-II line of FIG. It is a top view which shows roughly the structure of the semiconductor laser element which used the photonic crystal as an example of the semiconductor light-emitting device in Embodiment 1 of this invention. It is a drawing depicting a triangular lattice having a lattice spacing of a as a two-dimensional diffraction grating. It is a top view for demonstrating the light emission area | region in case the planar shape of the anode electrode in a prior art example is circular. It is a perspective view which divides | segments and shows the structure of the semiconductor laser element which used the photonic crystal as an example of the semiconductor light-emitting device in Embodiment 2 of this invention. It is a top view which shows roughly the structure of the semiconductor laser element which used the photonic crystal as an example of the semiconductor light-emitting device in Embodiment 2 of this invention. It is the figure which drew the square lattice whose lattice space | interval is d as a two-dimensional diffraction grating. It is a top view for demonstrating the light emission area | region in case the planar shape of the anode electrode in a prior art example is circular. It is a perspective view which divides | segments and shows the structure of the semiconductor laser element which used the photonic crystal as an example of the semiconductor light-emitting device in Embodiment 3 of this invention. It is a top view for demonstrating the light emission area | region in case the planar shape of an anode electrode is a hexagonal frame shape by which hollow was carried out. It is a top view which shows the mesh-shaped electrode with which the unit electrode which consists of hexagonal frame shape by which hollow was carried out was combined. It is a perspective view which divides | segments and shows the structure of the semiconductor laser element using a photonic crystal as an example of the semiconductor light-emitting device in Embodiment 4 of this invention. It is a top view for demonstrating the light emission area | region in case the planar shape of an anode electrode is a square frame shape by which hollow was carried out. FIG. 5 is a plan view showing a mesh electrode in which a plurality of unit electrodes each having a hollow rectangular frame shape are combined. It is a top view which shows roughly the structure of the semiconductor laser element which used the photonic crystal as an example of the semiconductor light-emitting device in Embodiment 5 of this invention. It is a top view which shows roughly the structure of the semiconductor laser element which used the photonic crystal as an example of the semiconductor light-emitting device in Embodiment 6 of this invention. It is a schematic sectional drawing which follows the XVIII-XVIII line of FIG. It is a top view for demonstrating the modification of a hexagonal electrode. It is a top view for demonstrating the modification of a square electrode. It is a schematic sectional drawing which shows a structure in case a photonic crystal layer is located in an anode electrode side rather than an active layer. It is a schematic perspective view which shows the structure of the two-dimensional photonic crystal laser disclosed by the nonpatent literature 1.

Explanation of symbols

  1 substrate, 2 photonic crystal, 2a hole, 2b surface, 3 cathode electrode, 10 first wafer, 11 n-type cladding layer, 12 active layer, 13 p-type cladding layer, 13a light emitting surface, 14 anode electrode (current) Electrode for injection), 14a, 16a Bonding pad portion, 15 Bonding wire, 16 Transparent electrode, 20 Second wafer, 21 P-type cladding layer, 22 Contact layer, 30 Semiconductor laser device, S1a, S2a, S3a, S4a Light emitting region .

Claims (7)

An active layer that generates light by carrier injection;
A medium having a first refractive index and a second refractive index portion provided on the surface of the medium so as to form a two-dimensional diffraction grating; and diffracting light generated in the active layer A two-dimensional photonic crystal that emits in a direction perpendicular to the surface of the medium;
An electrode for current injection formed on an emission surface of light emitted in a direction perpendicular to the surface of the medium by the two-dimensional photonic crystal;
The current injection electrode is a semiconductor light emitting device having a unit electrode having a polygonal shape in which a planar outer shape is aligned with an orientation of the two-dimensional diffraction grating of the two-dimensional photonic crystal.   The semiconductor light emitting device according to claim 1, wherein the two-dimensional diffraction grating is a triangular diffraction grating, and the planar outer shape of the unit electrode is a hexagonal shape.   The semiconductor light emitting device according to claim 2, wherein the planar shape of the unit electrode is a hollow hexagonal frame shape.   The semiconductor light emitting device according to claim 1, wherein the two-dimensional diffraction grating is a square diffraction grating, and the planar outer shape of the unit electrode is a square shape.   5. The semiconductor light emitting device according to claim 4, wherein the planar shape of the unit electrode is a hollow square frame.   The semiconductor light emitting device according to claim 1, wherein the current injection electrode has a configuration in which a plurality of unit electrodes are arranged.   The semiconductor light emitting device according to claim 6, further comprising a transparent electrode for electrically connecting the plurality of unit electrodes.

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