JP2010098135A - Surface light emitting device and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light emitting device including a quantum cascade laser element oscillating at a single wavelength at room temperature and operated stably, and to provide a method of manufacturing the surface light emitting device. <P>SOLUTION: The surface light emitting device 1 includes a heat sink 80 and a surface light emitting element 2. The surface light emitting element 2 includes an n-InP substrate 10, a quantum cascade active layer 30, an n-InGaAs buffer layer 20 and an n-InGaAs guide layer 40, a photonic crystal layer 50 laminated with the n-InGaAs buffer layer 20 and the n-InGaAs guide layer 40 and made independent of the quantum cascade active layer 30, a surface electrode 60 formed so as to be laminated with the quantum cascade active layer 30, and a metal pad 70 connected to the surface electrode 60. Then, by connecting the metal pad 70 and the heat sink 80 through a solder layer 91, the surface light emitting element 2 is loaded on the heat sink 80. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface emitting device and a manufacturing method thereof, and more particularly to a surface emitting device including a quantum cascade laser element including an active layer using intersubband transition and a manufacturing method thereof.

  In recent years, quantum cascade laser elements using intersubband transition have been proposed as laser elements that emit laser light in a long wavelength range from the mid-infrared to the terahertz band (for example, Non-Patent Document 1 and Non-Patent Document 2). reference). In the above-described quantum cascade laser, a superlattice structure made of two or more kinds of semiconductor materials can be created, and laser light in a long wavelength region can be obtained using intersubband transition formed in the superlattice structure. It is said that.

  For example, Non-Patent Document 1 discloses a quantum cascade laser that uses a Fabry-Perot resonator as a laser resonator.

  Further, in Non-Patent Document 2, a photonic crystal structure in which air holes penetrating from the element surface to the active layer are periodically arranged with respect to a quantum cascade laser structure using a superlattice structure made of two or more kinds of semiconductor materials. An element in which is formed has been proposed. The element introduces lattice defects due to air hole defects in the photonic crystal structure, and uses the modes localized in the lattice defects to cause laser oscillation in a direction perpendicular to the surface of the element. A defect-type photonic crystal quantum cascade laser.

Moreover, as a surface emitting laser element using the above-mentioned photonic crystal structure, it is disclosed by patent document 1, for example.
Japanese Patent No. 3989333 Keita Otani, “Research on InAs Quantum Cascade Laser”, [online], Marubun Research Foundation, [March 19, 2008 search], Internet (http://www.marubun-zaidan.jp/pdf/ h16_ootani.pdf) Raffaele Colombelli et al., SCIENCE, “Quantum Cascade Surface-Emitting Photonic Crystal Laser”, 21 November 2003, Vol. 302, p.1374-1377

  The laser element disclosed in Non-Patent Document 1 described above is a multimode oscillation element because it uses a Fabry-Perot resonator, and it is difficult to control the oscillation wavelength of the laser to a single value.

  Further, since the laser element disclosed in Non-Patent Document 2 described above needs to confine the localized mode strongly in the defect portion, the light emission in the active layer and the optical coupling strength of the photonic crystal are maximized. Since it is necessary, the photonic crystal has air holes reaching the active layer. As a result, laser light oscillation occurs only in an extremely low temperature environment, and it is difficult to oscillate laser light, for example, at room temperature. This is because there are many exposed side walls of air holes in the active layer, and at room temperature, non-radiative recombination of carriers is very likely to occur on the exposed surface (surface recombination rate is very fast). It is. For this reason, in order to realize light emission and oscillation in the laser element disclosed in Non-Patent Document 2, it is necessary to cool the entire element to an extremely low temperature of about the liquid helium temperature (4K) in order to reduce the surface recombination speed. There is. For this reason, the laser element disclosed in Non-Patent Document 2 is difficult to use at room temperature and is difficult to be applied in practice.

  Further, in the case of the defect type photonic crystal quantum cascade laser disclosed in Non-Patent Document 2, in order to confine the localized mode strongly in the defect part, it is necessary to minimize the volume of the defect part itself to the wavelength level. For this reason, since it is difficult to increase the amount of localized light, high-power laser oscillation is considered difficult. Even when high-power oscillation is successful, the emitted light is emitted from a very narrow defect surface, so that light concentration occurs on this defect surface and an end face destruction phenomenon (sudden death phenomenon called COD) Can easily cause. For this reason, it has been difficult to produce a highly reliable element.

  Furthermore, in the quantum cascade laser element, although the efficiency (quantum efficiency) per number of carriers injected into the active layer can be increased, a relatively large bias is required, so that the effective power conversion efficiency is not necessarily high. I can't say that. For this reason, there is a tendency for heat generation during operation to increase, and there is a possibility that the operation may become unstable if sufficient heat dissipation from the element cannot be ensured.

  The present invention has been made to solve the above-described problems. That is, an object of the present invention is to provide a surface emitting device including a quantum cascade laser element that can oscillate at a single wavelength at room temperature and can operate stably, and a method of manufacturing the same.

  A surface light emitting device according to the present invention includes a heat sink body and a surface light emitting element mounted on the heat sink body. The surface light emitting element is disposed so as to sandwich the active layer on the main surface of the substrate, the first conductivity type substrate, the active layer formed on the main surface of the substrate using the intersubband transition, and the substrate. A semiconductor layer of the first conductivity type, laminated with the semiconductor layer on the main surface of the substrate, formed to be laminated with the active layer on the main surface of the substrate, and a two-dimensional diffraction grating independent of the active layer. And a conductive pad connected to the electrode. Then, the surface-emitting element is mounted on the heat sink body by connecting the conductor pad and the heat sink body via the connecting material layer.

  In the surface light emitting device, since the two-dimensional diffraction grating is formed independently of the active layer, as in the case where the recesses (such as air holes) constituting the two-dimensional diffraction grating reach the active layer, The active layer is not damaged or exposed to the air due to the formation of the recess. Therefore, non-radiative recombination of carriers is less likely to occur than when the concave portion of the two-dimensional diffraction grating reaches the active layer, and sufficient light emission at room temperature can be realized. In addition, by using a two-dimensional diffraction grating, not only can a single wavelength (single mode) laser oscillation be easily realized, but also an end face destruction phenomenon like the laser element shown in Non-Patent Document 2 occurs. It is unlikely to happen and can achieve high reliability.

  Further, in the surface light emitting device of the present invention, the conductor is not on the side of the substrate having a small thickness (on the side opposite to the substrate), but on the side of the substrate having a large thickness as viewed from the active layer that becomes a heat generating region during the operation of the surface emitting element. The surface light emitting element is mounted on the heat sink body so as to connect the conductor pad and the heat sink body. Therefore, it is possible to efficiently dissipate the heat generated in the active layer to the heat sink body, and the temperature rise of the surface light emitting element can be suppressed. As a result, the surface light emitting device can be stably operated.

  As described above, according to the surface emitting device of the present invention, it is possible to provide a surface emitting device including a quantum cascade laser element that can oscillate at a single wavelength at room temperature and can operate stably. Can do.

  In the surface light emitting device, preferably, the conductor pad has a planar shape larger than the planar shape of the electrode.

  Accordingly, it is possible to dissipate heat generated in the active layer over a wide area and then dissipate heat to the heat sink body, and the conductor pad can function as a heat spreader. As a result, the temperature rise of the surface light emitting element can be further suppressed, and the surface light emitting device can be operated more stably.

  In the surface light emitting device, preferably, the material constituting the heat sink body has a thermal conductivity of 150 W / mK or more. Thereby, the temperature rise of the surface light emitting element can be further suppressed, and the operation of the surface light emitting device can be more reliably stabilized.

  Preferably, in the surface light emitting device, the center of gravity of the electrode and the center of gravity of the conductor pad are aligned in a direction perpendicular to the surface of the heat sink body to which the connecting material layer is connected. Thereby, when the heat generated in the light emitting layer flows into the conductor pad via the electrode, it can be efficiently diffused in many directions, and thus the temperature rise of the surface light emitting element can be further suppressed.

  In the surface light emitting device, the thickness of the conductor pad is preferably 1 μm or more. Thereby, the heat spread effect of the conductor pad is further increased, and the surface light emitting device can be operated more stably. If the thickness of the conductor pad exceeds 20 μm, there is a possibility that cracks may occur on the conductor pad or the semiconductor layer side due to the problem of stress. Therefore, the thickness of the conductor pad is preferably 20 μm or less.

  A method for manufacturing a surface light emitting device according to the present invention includes a step of forming a surface light emitting element and a step of mounting the surface light emitting element on a heat sink body. The step of forming the surface light emitting element includes a step of preparing a first conductivity type substrate, a step of forming an active layer and a semiconductor layer, a step of forming a two-dimensional diffraction grating, a step of forming an electrode, Forming a conductive pad. In the step of forming the active layer and the semiconductor layer, an active layer using intersubband transition and a first conductivity type semiconductor layer disposed so as to sandwich the active layer are formed on the main surface of the substrate. The In the step of forming the two-dimensional diffraction grating, a two-dimensional diffraction grating independent of the active layer is formed by being laminated with the semiconductor layer on the main surface of the substrate. In the step of forming the electrode, the electrode is formed so as to be laminated with the active layer on the main surface of the substrate. In the step of forming the conductor pad, the conductor pad connected to the electrode is formed. In the step of mounting the surface light emitting element on the heat sink body, the conductor pads and the heat sink body in the surface light emitting element are connected via the connecting material layer.

  According to the method for manufacturing a surface emitting device of the present invention, it is possible to manufacture a surface emitting device including a quantum cascade laser element that can oscillate at a single wavelength at room temperature and can operate stably. .

  In the surface light emitting device of the present invention, preferably, in the step of forming the conductor pad, a conductor pad having a planar shape larger than the planar shape of the electrode is formed.

  Thereby, the surface light-emitting device which can suppress a temperature rise further by making a conductor pad function as a heat spreader, and can operate | move more stably can be manufactured.

  In the surface light emitting device of the present invention, preferably, the step of forming the conductor pad includes the step of forming the conductor pad using a plating method.

  Thereby, it is possible to easily increase the thickness of the conductor pad, and it is possible to easily manufacture a surface light emitting device that can operate stably.

  As is apparent from the above description, the surface light emitting device and the manufacturing method thereof according to the present invention include a quantum cascade laser element that can oscillate at a single wavelength at room temperature and can operate stably. A flat surface light emitting device and a method for manufacturing the same can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a schematic cross-sectional view showing a configuration of a surface light emitting device according to an embodiment of the present invention. FIG. 2 is a schematic perspective view showing a part of the configuration of the photonic crystal layer included in the surface light emitting device of FIG. FIG. 3 is a schematic plan view showing the configuration of the surface electrodes, metal pads, and heat sink included in the surface light emitting device of FIG. FIG. 4 is a schematic plan view showing the configuration of the n-InP substrate and the back electrode included in the surface light emitting device of FIG.

  With reference to FIG. 1, the surface light emitting device 1 according to the present embodiment includes a heat sink 80 and a surface light emitting element 2 mounted on the heat sink 80. The surface light emitting element 2 is a quantum cascade laser capable of oscillating laser light having a frequency ranging from the mid-infrared region to the terahertz (THz) band (specifically, the wavelength is 1.6 μm or more and 1 mm or less).

  The surface light emitting element 2 includes an n-InP substrate 10 whose conductivity type is n-type (first conductivity type), and a first conductivity type semiconductor layer disposed on one main surface of the n-InP substrate 10. n-InGaAs buffer layer 20, quantum cascade active layer 30 disposed on n-InGaAs buffer layer 20, and n-InGaAs guide layer as a first conductivity type semiconductor layer disposed on quantum cascade active layer 30 40, a photonic crystal layer 50 as a two-dimensional diffraction grating disposed on the n-InGaAs guide layer 40, a surface electrode 60 disposed on a region where the hole 51 is formed in the photonic crystal layer 50, An insulating layer 95 disposed so as to surround the outer peripheral surface of the surface electrode 60; a metal pad 70 as a conductor pad disposed on the surface electrode 60 and the insulating layer 95; and n-I. And a back electrode 92 formed on the main surface opposite to the side on which the n-InGaAs buffer layer 20 is disposed in the P substrate 10. Further, a gold wire 94 that is a wiring is connected to the back electrode 92.

  And the surface emitting element 2 is mounted in the heat sink 80 by connecting the metal pad 70 and the heat sink 80 via the solder layer 91 as a connection material layer.

  The n-InP substrate 10 is made of InP (indium phosphide) and includes an n-type impurity, so that the conductivity type is n-type (first conductivity type). The n-InGaAs buffer layer 20 is made of InGaAs (indium gallium arsenide) and contains n-type impurities, so that the conductivity type is n-type.

  The quantum cascade active layer 30 has a superlattice structure in which barrier layers made of, for example, AlInAs (aluminum indium arsenide) and well layers made of InGaAs are alternately stacked. The quantum cascade active layer 30 is formed so that the intersubband transition region and the injection region repeat a plurality of periods, that is, a quantum cascade structure having a plurality of stepped subband structures.

  Specifically, as a configuration example of the quantum cascade active layer 30, for example, when the barrier layer is AlInAs (Al composition 0.48) and the well layer is InGaAs (Ga composition 0.47), A structure in which barrier layers / (well layers) / barrier layers / (well layers) /... Are alternately laminated from a certain surface electrode 60 side toward a back electrode 92 on the low bias side can be employed. The thickness of each layer is, for example, 5 nm / (1 nm) /1.5 nm / (4.5 nm) / 2 nm / (4 nm) / 3 nm / (2.5 nm) /2.5 nm / (2.2 nm) / A laminated structure composed of 18 layers of 2.2 nm / (2 nm) / 2 nm / (2 nm) /2.2 nm / (2 nm) / 3 nm / (2 nm) is defined as one period, and this period is plural (10 to 100 periods, For example, 30 cycles can be repeated. In the thickness display described above, the value of the thickness enclosed in parentheses indicates the thickness of the well layer.

  The n-InGaAs guide layer 40 is made of InGaAs and has an n-type conductivity by including an n-type impurity.

  Referring to FIG. 2, the photonic crystal layer 50 has a structure in which holes 51 as periodic recesses are formed in a base layer 52 made of, for example, n-type InP. More specifically, in the photonic crystal layer 50, holes 51 that are air holes are arranged in a triangular lattice pattern. As a result, the hole 51 becomes a low refractive index portion, and the surrounding base layer 52 made of InP becomes a high refractive index portion having a higher refractive index than the low refractive portion. Each of the holes 51 is formed at a position that becomes a lattice point of a triangular lattice, in other words, at a vertex position of an equilateral triangle. The distances between the center of one lattice point and the centers of the six lattice points adjacent to this lattice point are all equal. Note that the photonic crystal layer 50 and the quantum cascade active layer 30 are separated by, for example, 1 μm or more.

The surface electrode 60 is made of, for example, an Au—Ge—Ni (gold-germanium-nickel) alloy. The insulating layer 95 surrounding the surface electrode 60 is made of, for example, SiO ₂ (silicon dioxide). The metal pad 70 is made of, for example, Au (gold). Furthermore, the back electrode 92 is made of, for example, an Au—Ge—Ni alloy, similarly to the front electrode 60.

  As a material constituting the heat sink 80, a material having high thermal conductivity, more specifically, a material having a thermal conductivity of 150 W / mK or more is preferably adopted. For example, a Cu—W (copper-tungsten) alloy, A copper-diamond composite material, a copper-carbon fiber composite material, AlN (aluminum nitride), CVD diamond, graphite, SiC, or the like can be employed.

  Referring to FIG. 3, surface electrode 60, metal pad 70, and heat sink 80 are arranged so as to overlap in plan view. The planar shape of the surface electrode 60 and the metal pad 70 is a point-symmetric shape (square in the present embodiment) with respect to the center of gravity (center). Further, the center of gravity of the surface electrode 60 and the metal pad 70 is positioned so as to overlap when seen in a plan view. That is, the center of gravity of the surface electrode 60 and the center of gravity of the metal pad 70 are aligned in a direction perpendicular to the surface of the heat sink 80 to which the solder layer 91 is connected. As a result, the center of gravity of the gain region (light emitting region) determined according to the shape of the surface electrode 60 and the center of gravity of the metal pad 70 are aligned in a direction perpendicular to the surface of the heat sink 80 to which the solder layer 91 is connected. ing.

  On the other hand, referring to FIGS. 1 and 4, window electrode 92 </ b> A that is a through hole is formed in back electrode 92. The n-InP substrate 10 is exposed from the window 92A.

  Next, operation | movement of the surface emitting device 1 in this Embodiment is demonstrated easily. Referring to FIG. 1, when a voltage is applied between front surface electrode 60 and back surface electrode 92, electrons are injected into quantum cascade active layer 30. Then, electrons transition between subbands in the transition region generated in the conduction band of the quantum well structure in the quantum cascade active layer 30, but by tilting the band by applying a voltage (bias) to the electrode, Electron transitions between subbands occur continuously. As a result, light (for example, mainly having a long wavelength of 2 μm or more) is generated. Note that the wavelength of the generated light is defined by the configuration of the quantum cascade active layer 30.

  The light generated in the quantum cascade active layer 30 is confined in the quantum cascade active layer 30 by the n-InGaAs buffer layer 20 and the n-InGaAs guide layer 40, but a part of the light is evanescent light as the photonic crystal layer 50. To reach. Here, since the structure of the quantum cascade active layer 30 is defined so that the light generated in the quantum cascade active layer 30 changes from mid-infrared light to terahertz (THz) light, the region where the evanescent light spreads becomes wide. . This is because the spread of evanescent light is proportional to the wavelength of the light. Therefore, in the surface emitting device 1 shown in FIG. 1, even if the distance between the photonic crystal layer 50 and the quantum cascade active layer 30 is, for example, 1 μm or more, the photonic crystal layer 50 is sufficiently separated from the quantum cascade active layer 30. Evanescent light arrives. When the wavelength of the evanescent light that has reached the photonic crystal layer 50 matches the predetermined period of the photonic crystal layer 50, a standing wave is induced at the wavelength corresponding to the period.

  Such a phenomenon can occur in a region immediately above the surface electrode 60 because the quantum cascade active layer 30 and the photonic crystal layer 50 are formed to expand two-dimensionally. Laser oscillation can be caused by the feedback effect of the standing wave.

  The photonic crystal layer 50 (two-dimensional diffraction grating) has a property of overlapping when translated in the same period in at least two directions. Such a two-dimensional diffraction grating is formed by arranging regular triangles, squares, or regular hexagons all over the surface and providing a lattice point 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. 5 is a diagram for explaining light diffraction in a triangular lattice. The triangular lattice is filled with regular triangles whose side length is a. In FIG. 5, focusing on a lattice point A arbitrarily selected from a plurality of lattice points (holes 51), a direction from the lattice point A toward the lattice point B is referred to as an X-Γ direction. The direction toward point C is called the XJ direction. Here, a case where the wavelength of light generated in the quantum cascade active layer 30 (see FIG. 1) corresponds to the lattice period in the X-Γ direction will be described.

The two-dimensional diffraction grating 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 in the direction of 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 base layer 52 (see FIG. 2), which is a high refractive index portion. 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, 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, this two-dimensional diffraction grating 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 also in the direction perpendicular to the main surface of the two-dimensional diffraction grating. Thereby, referring to FIG. 1, light travels in a direction perpendicular to the main surface of the two-dimensional diffraction grating (main surface of photonic crystal layer 50), and arrow α passes through window portion 92A that defines the light emission surface. Light is emitted along the direction of.

  Further, in this two-dimensional diffraction grating, the above-described light diffraction can occur at all the two-dimensionally arranged grating points. Therefore, light propagating in the X-Γ direction is two-dimensionally coupled to each other by Bragg diffraction, and a coherent state is formed. As described above, the surface emitting device 1 in the present embodiment can function as a surface emitting laser device.

  FIG. 6 is a schematic perspective view showing another configuration of the photonic crystal layer. Referring to FIG. 6, photonic crystal layer 50 constitutes a two-dimensional diffraction grating having a square lattice form. Each of the holes 51 is formed at a position serving as a lattice point of a square lattice, in other words, at a vertex position of a square. The distances between the center of one lattice point (hole 51) and the centers of the eight lattice points adjacent to this lattice point are all equal.

  FIG. 7 is a view for explaining light diffraction in a square lattice. The square lattice is filled with squares whose side length is d. In FIG. 7, paying attention to 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 the XJ direction. Call. Here, a case where the wavelength of light generated in the quantum cascade active layer 30 (see FIG. 1) corresponds to the lattice period in the X-Γ direction will be described.

The two-dimensional diffraction grating can be considered to include two one-dimensional diffraction grating groups U and V described below. The one-dimensional diffraction grating group U includes 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 also d.

  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. The light that is sequentially diffracted in this way and diffracted from the lattice point T toward the lattice point W is further 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, this two-dimensional diffraction grating acts as an optical resonator, that is, a wavelength selector and a reflector. Accordingly, even when the photonic crystal layer 50 described based on FIGS. 6 and 7 is used instead of the photonic crystal layer 50 described based on FIG. 2, the surface light emitting device 1 in the present embodiment is It can function as a surface emitting laser device.

  Here, the surface light emitting element 2 included in the surface light emitting device 1 includes an n-InP substrate 10 as a first conductivity type substrate and an intersubband transition formed on the main surface of the n-InP substrate 10. A n-InGaAs buffer layer 20 as a first conductivity type semiconductor layer disposed so as to sandwich the quantum cascade active layer 30 on the main surface of the n-InP substrate 10 and The n-InGaAs guide layer 40 and the n-InGaAs buffer layer 20 and the n-InGaAs guide layer 40 are stacked on the main surface of the n-InP substrate 10, and serve as a two-dimensional diffraction grating independent of the quantum cascade active layer 30. Photonic crystal layer 50 and a surface formed so as to be stacked with quantum cascade active layer 30 on the main surface of n-InP substrate 10 A pole 60, and a metal pad 70 of the conductor pads connected to the surface electrode 60. And the surface emitting element 2 is mounted in the heat sink 80 by connecting the metal pad 70 and the heat sink 80 via the solder layer 91 as a connection material layer.

  By providing the surface light emitting element 2 having such a configuration, in the surface light emitting device 1 in the present embodiment, by controlling the structure (lattice constant and air filling rate) of the photonic crystal layer 50, the quantum Of the light emitted from the cascade active layer 30, only light having an arbitrary wavelength can be fed back into the quantum cascade active layer 30 and oscillated in only one mode. That is, it is not a multimode in which a large number of wavelengths are mixed in the oscillation wavelength as in a conventional quantum cascade laser using a conventional Fabry-Perot resonator, and the surface light emitting device 1 according to the present embodiment uses any single unit. Oscillation at a wavelength is possible. In addition, a single wavelength laser beam can be emitted in a direction perpendicular to the main surface of the quantum cascade active layer 30 by a diffraction effect. It is very significant that a laser light source having an arbitrary wavelength can be obtained from the mid-infrared region to the THz band where a light source having a high intensity has not existed.

  Further, in the surface light emitting device 1 according to the present embodiment, it is possible to make the emission surface a region having a very large area on the surface side. As a result, in the surface light emitting device 1 according to the present embodiment, a breakdown phenomenon (COD: abrupt breakdown: which is a problem with a laser whose output surface must be a narrow region, such as a Fabry-Perot laser or a defective photonic crystal laser, is required. The possibility of causing the exit surface to melt due to light concentration is extremely low. That is, the reliability as a laser light source is also improved.

  Further, in the surface light emitting device 1 according to the present embodiment, the photonic crystal layer 50 is formed at a position separated from the quantum cascade active layer 30 (for example, a position separated by 1 μm or more) and exudes from the quantum cascade active layer 30. The optical coupling between the evanescent light and the photonic crystal layer 50 can be used. Therefore, it is not necessary to form a hole that reaches the active layer as in the prior art. This is because the resonator of the surface light emitting device 1 does not require confinement of a strong localized mode, and an optical coupling strength comparable to that of a normal one-dimensional DFB (Distributed Feedback) laser is sufficient. Therefore, since the quantum cascade active layer 30 of the surface light emitting device 1 is not exposed to the outside, the surface recombination rate does not increase even at room temperature. As a result, in the surface light emitting device 1 in the present embodiment, light emission and oscillation at room temperature can be easily realized.

  Note that the photonic crystal surface emitting laser element disclosed in Patent Document 1 described above is premised on a laser from near infrared light to visible light (wavelength: 0.4 μm to 1.5 μm). In this case, the region where the evanescent light spreads (the width is proportional to the wavelength) is small, and the photonic crystal layer needs to be formed in the vicinity of the active layer. Therefore, in Patent Document 1, an element is formed by using a fusion method or a regrowth method. However, in the surface light emitting device 1 according to the present embodiment, laser light in the range from mid-infrared light to THz band (2 μm or more and 1000 μm or less in wavelength) is targeted for oscillation, so the region where the evanescent light spreads becomes very wide. Therefore, the distance between the photonic crystal layer 50 and the quantum cascade active layer 30 can be greatly separated. Therefore, as shown in FIG. 1, it is possible to adopt a configuration in which the photonic crystal layer 50 is formed adjacent to the surface electrode 60. As a result, in the surface light emitting device 1 according to the present embodiment, it is not essential to use a troublesome manufacturing method such as a fusion method or a regrowth method.

  Further, since the distance between the processing position of the hole 51 in the photonic crystal layer 50 and the quantum cascade active layer 30 is large, the processing damage to the quantum cascade active layer 30 accompanying the processing when forming the hole 51 is almost all. Does not occur. Similarly, the stress and strain generated when forming the photonic crystal layer 50 have less influence on the quantum cascade active layer 30. For this reason, it is also easy to adopt a dielectric column embedded photonic crystal structure, which has been difficult to employ in other short wavelength photonic crystal surface emitting laser elements due to the strength of residual stress. . As a result, the degree of freedom of structure is greatly expanded.

  Furthermore, in the surface light emitting device 1 according to the present embodiment, the thickness of the surface light emitting device 1 is small as opposed to the thick n-InP substrate 10 side as viewed from the quantum cascade active layer 30 that becomes a heat generation region during the operation of the surface light emitting element 2. A metal pad 70 is disposed on the side (opposite to the n-InP substrate 10), and the surface light emitting element 2 is mounted on the heat sink 80 so as to connect the metal pad 70 and the heat sink 80. Therefore, the heat generated in the quantum cascade active layer 30 can be efficiently radiated to the heat sink 80, and the temperature rise of the surface light emitting element 2 is suppressed.

  In the surface light emitting device 1 of the present embodiment, the metal pad 70 has a larger planar shape than the planar shape of the surface electrode 60. As a result, the heat generated in the quantum cascade active layer 30 can be diffused over a wide area and then dissipated to the heat sink 80. Therefore, the temperature rise of the surface light emitting element 2 is further suppressed. As a result, the surface light emitting device 1 can be stably operated.

  As described above, the surface emitting device 1 according to the present embodiment is a surface emitting device including a quantum cascade laser element that can oscillate at a single wavelength at room temperature and can operate stably. Yes.

  Here, the thermal conductivity of the material constituting the heat sink 80 is preferably 150 W / mK or more. Thereby, the temperature rise of the surface light emitting element 2 can be further suppressed, and the operation of the surface light emitting device 1 can be more reliably stabilized.

  In the surface light emitting device 1, the center of gravity of the surface electrode 60 and the center of gravity of the metal pad 70 are preferably aligned in a direction perpendicular to the surface of the heat sink 80 to which the solder layer 91 is connected. Thereby, when the heat generated in the quantum cascade active layer 30 flows into the metal pad 70 through the surface electrode 60, the heat can be efficiently diffused in many directions, thereby further suppressing the temperature rise of the surface light emitting device 1. it can. The planar shape of the metal pad 70 is preferably such that the center of gravity of the metal pad 70 overlaps the center of gravity of the planar shape of the surface electrode 60 in a plan view and has a shape that is pointed with respect to the center of gravity. More specifically, for example, when the planar shape of the surface electrode 60 is a square or regular hexagon, it is preferable that the center of gravity of the surface electrode 60 has a square or circular shape overlapping the square or regular hexagon when viewed in plan. The planar shape of the metal pad 70 may be a similar enlargement of the planar shape of the surface electrode 60. In addition, if the area of the planar shape of the metal pad 70 is 3 times or more than the area of the planar shape of the surface electrode 60, an effective heat spread effect is exhibited. On the other hand, if it exceeds 100 times, the chip area increases. Since there is a possibility that the problem of high cost may arise, it is preferable to set it to 3 times or more and 100 times or less.

  Furthermore, the thickness of the metal pad 70 is preferably 1 μm or more. Thereby, the heat spread effect of the metal pad 70 is further increased, and the surface light emitting device 1 can be operated more stably.

  Next, the manufacturing method of the surface emitting device in one embodiment of the present invention will be described. FIG. 8 is a flowchart showing an outline of a method of manufacturing the surface light emitting device in one embodiment of the present invention. 9 to 16 are schematic cross-sectional views for explaining the method for manufacturing the surface light emitting device in one embodiment of the present invention.

  Referring to FIG. 8, in the method for manufacturing the surface light emitting device in the present embodiment, a substrate preparation step is first performed as a step (S10). Specifically, referring to FIG. 9, n-InP substrate 10 made of, for example, InP and having an n-type conductivity is prepared. In addition to InP, GaAs, GaSb, InAs, or the like can be used as a material for the substrate constituting the surface light emitting device of the present invention.

  Next, a buffer layer forming step is performed as a step (S20). In this step (S20), referring to FIG. 10, one main surface ((001) plane) of n-InP substrate 10 prepared in step (S10) is made of, for example, InGaAs, and the conductivity type is n. An n-InGaAs buffer layer 20 that is a mold is formed. The n-InGaAs buffer layer 20 can be formed by epitaxially growing an InGaAs layer containing an n-type impurity on the n-InP substrate 10. As the material of the buffer layer constituting the surface light emitting device of the present invention, for example, InGaAs can be adopted when the substrate is InP, and when the substrate is GaAs, GaAs or AlGaAs is used, and the substrate is GaSb. In this case, GaSb or InAs can be used, and in the case where InAs is used as the substrate, InAs or GaSb can be used.

  Next, an active layer forming step is performed as a step (S30). In this step (S30), the quantum cascade active layer 30 is formed on the n-InGaAs buffer layer 20. Specifically, referring to FIG. 10, on the n-InGaAs buffer layer 20 formed in the step (S20), for example, a barrier layer made of, for example, AlInAs and a well layer made of InGaAs are alternately provided a plurality of times (for example, 30). Epitaxial growth is repeated repeatedly. The barrier layer and the well layer are undoped (a state in which no conscious impurity is added) except for a part thereof. As the combination of the barrier layer / well layer material constituting the surface light emitting device of the present invention, for example, AlInAs / InGaAs can be adopted when the substrate is InP, and AlGaAs / GaAs when the substrate is GaAs. When the substrate is made of GaSb or InAs, AlSb / InAs, AlGaSb / InAs, GaSb / InAs, or the like can be employed.

  Next, a guide layer forming step is performed as a step (S40). In this step (S40), referring to FIG. 10, on the quantum cascade active layer 30 formed in step (S30), an n-InGaAs guide layer 40 made of, for example, InGaAs and having an n-type conductivity is formed. Is done. The n-InGaAs guide layer 40 can be formed by epitaxially growing an InGaAs layer containing an n-type impurity on the quantum cascade active layer 30. As the material of the guide layer constituting the surface light emitting device of the present invention, for example, InGaAs can be adopted when the substrate is InP, and when the substrate is GaAs, GaAs or the like is used, and the substrate is GaSb or InAs. In this case, InAs, GaSb, or the like can be used.

  Next, an n-InP layer forming step is performed as a step (S50). In this step (S50), referring to FIG. 10, an n-InP layer 55 to be the base layer 52 (see FIGS. 1 and 2) of the photonic crystal layer 50 is formed on the n-InGaAs guide layer 40. Is done. Specifically, an InP layer containing n-type impurities is formed by epitaxial growth on the n-InGaAs guide layer 40 formed in the step (S40). The base layer material of the photonic crystal layer constituting the surface light emitting device of the present invention is InP, InGaAs, etc. when the substrate is InP, GaAs, AlGaAs, etc. when the substrate is GaAs, InAs, GaSb, AlSb, AlGaSb, etc. can be employed when GaSb or InAs is used. Moreover, the said process (S20)-(S50) can be implemented by MBE (Molecular Beam Epitaxy; molecular beam epitaxy) method, for example.

  Next, an electrode formation step is performed as a step (S60). In this step (S60), referring to FIG. 11, surface electrode 60 having a square planar shape, for example, is formed on n-InP layer 55 formed in step (S50). Further, a back electrode 92 is formed on the main surface of the n-InP substrate 10 opposite to the side where the n-InGaAs buffer layer 20 is formed. A window portion 92A is formed on the back surface electrode 92 using a double-sided mask aligner so as to be located immediately below the region where the front surface electrode 60 is formed. Both the front electrode 60 and the back electrode 92 can be formed by evaporating a layer made of, for example, an Au—Ge—Ni alloy.

  Next, a through hole forming step is performed as a step (S70). In this step (S <b> 70), a through hole to be a hole 51 (see FIGS. 1 and 2) of the photonic crystal layer 50 is formed in the n-InP layer 55. Specifically, first, a resist is applied on n-InP layer 55 and surface electrode 60 formed in steps (S50) and (S60). Thereafter, exposure and development are performed to form a mask layer made of resist and having holes in desired regions where through holes are to be formed. Then, for example, by performing dry etching using the mask layer as a mask, a through hole penetrating the surface electrode 60 and the n-InP layer 55 is formed with reference to FIG.

  Next, a through-hole sealing step is performed as a step (S80). In this step (S80), the through-hole formed in the n-InP layer 55 is sealed by closing the through-hole formed in the surface electrode 60 in the step (S70). Specifically, referring to FIG. 13, for example, by performing plating, the through hole formed in surface electrode 60 is closed. Thereby, the through hole formed in the n-InP layer 55 is sealed, and the photonic crystal layer 50 having the hole 51 is completed.

Next, an insulating layer forming step is performed as a step (S90). In this step (S90), referring to FIG. 14, an insulating layer 95 made of, for example, SiO ₂ is formed so as to surround the surface electrode 60 in a planar manner. The insulating layer 95 can be formed by, for example, a CVD (Chemical Vapor Deposition) method. As the material constituting the insulating layer 95, in addition to SiO _{2, Si} 3 _{N 4} (silicon nitride), can be employed as TiO ₂ (titanium oxide).

  Next, a metal pad vapor deposition step is performed as a step (S100). In this step (S100), referring to FIG. 15, metal pad 70 made of, for example, gold (Au) is formed on surface electrode 60 so as to be in contact with surface electrode 60. Specifically, a film made of gold is formed on the surface electrode 60 by vapor deposition. In addition, as a raw material which comprises the metal pad 70, silver, copper, platinum, nickel, palladium etc. other than gold | metal | money, and those laminated structures are employable.

  Next, a metal pad plating step is performed as a step (S110). In this step (S110), the metal pad 70 formed in the step (S100) is thickened by performing plating. This step (S110) can be omitted by forming the metal pad 70 having a sufficient film thickness in the previous step (S100), for example, by vapor deposition. However, by forming only a part of the thickness of the metal pad 70 in the step (S100) and then increasing the thickness of the metal pad 70 using a plating method, the thick metal pad 70 is efficiently formed. Can do. Through the above steps, the surface light-emitting element 2 constituting the surface light-emitting device 1 in the present embodiment is completed (see FIG. 1).

  Next, an element mounting step is performed as a step (S120). In this step (S120), referring to FIG. 16, a separately prepared heat sink 80 and metal pads 70 of surface light emitting element 2 formed in the above steps (S10) to (S110) are used, for example, with solder. By joining, the surface light emitting element 2 is mounted on the heat sink 80. That is, in the step (S120), the side opposite to the n-InP substrate 10 as viewed from the quantum cascade active layer 30, that is, the side of the layer formed by epitaxial growth as viewed from the n-InP substrate 10 is bonded to the heat sink 80. Thus, the surface light emitting element 2 is mounted on the heat sink 80. Thereafter, with reference to FIG. 1, wire bonding is performed to form gold wire 94 which is a wiring, and is placed on stem 93, so that surface light emitting device 1 in the present embodiment can be obtained. Complete.

  By performing the steps (S10) to (S120) as described above, the surface light emitting device 1 according to the present embodiment can be easily manufactured without using a complicated fusion method or an embedding method by epi-regrowth. can do.

  Embodiment 1 of the present invention will be described below. In the surface light-emitting device of the present invention, a simulation test was performed to confirm the effect of the mounting mode of the surface light-emitting elements included in the surface light-emitting device on the heat sink body. The test procedure is as follows.

  FIG. 17 is a schematic perspective view showing the simulation conditions assuming the mounting mode of the surface light emitting device of the present invention. FIG. 18 is a schematic perspective view showing the conditions of the simulation assuming the mounting mode of the surface light emitting element outside the scope of the present invention.

Referring to FIG. 17, under the simulation conditions assuming the mounting mode of the surface light emitting device of the embodiment within the scope of the present invention, the bottom surface has a square shape with a side of 1200 μm, the heat sink 103 with a thickness of 300 μm, and the thickness of 2 μm. It was assumed that the Au layer 102, the 0.1 μm thick SiO ₂ layer 104, and the 100 μm thick surface light emitting device 101 were sequentially stacked in a rectangular parallelepiped shape. In the mounting mode of the embodiment, the light emitting layer 109 (heat generating layer) disposed in the surface light emitting element 101 is connected to the heat sink body on the side opposite to the substrate when viewed from the quantum cascade active layer. The SiO ₂ layer 104 is disposed at a distance of 2 μm. The shape of the light emitting layer 109 was a square shape having a 100 μm side and a thickness of 1 μm.

  On the other hand, referring to FIG. 18, under the simulation conditions assuming the mounting mode of the surface light emitting device of the comparative example that is outside the scope of the present invention, the heat sink 103 having a square shape with a bottom surface of 1200 μm on one side and a thickness of 300 μm, It was assumed that an Au layer 102 having a thickness of 2 μm and a surface light emitting device 101 having a thickness of 100 μm were sequentially stacked in a rectangular parallelepiped shape. In the mounting mode of the comparative example, the light emitting layer 109 (heat generation layer) disposed in the surface light emitting element 101 is connected to the Au layer 102 by connecting the substrate side to the heat sink body as viewed from the quantum cascade active layer. It is arranged at a distance of 2 μm from the surface on the opposite side. In addition, the shape of the light emitting layer 109 was set to a square shape with a 100 μm side and a thickness of 1 μm as in the case of the example.

Then, in both the examples and the comparative examples, the heat generation density was 4.2 × 10 ⁹ W / cm ³ and the current density was 10 kA / cm ² , and the temperature distribution during the operation of the surface light emitting device was obtained.

  FIG. 19 is a diagram illustrating test results of the example in Example 1. FIG. 20 is an enlarged view showing a main part of FIG. FIG. 21 is a diagram showing the test results of the comparative example in Example 1. FIG. 22 is an enlarged view showing a main part of FIG. In FIG. 19 and FIG. 21, a plurality of connected rectangular figures displayed at the bottom of the rectangular parallelepiped figure indicate the legend of the temperature distribution. The hatched area of the same shape as the rectangle in the legend indicates that the temperature is between the numerical values (unit: ° C.) described on both ends of the rectangle. FIGS. 19 and 21 show temperature distributions of the system in which FIGS. 17 and 18 are cut by two planes perpendicular to the bottom surface and orthogonal to the center of gravity of the bottom surface, respectively. That is, the ridge line extending in the thickness direction at the left end in FIGS. 19 and 21 matches the straight line perpendicular to the bottom surface as the center of gravity in the planar shape of the light emitting layer 109 in FIGS. 17 and 18.

  With reference to FIGS. 19 to 22, when the mounting mode of the embodiment is adopted, a region where the temperature is rising greatly spreads inside the heat sink body, and the temperature of the region where the temperature is highest is 55 ° C. It was. On the other hand, when the mounting mode of the comparative example is adopted, the spread of the region where the temperature is rising to the inside of the heat sink body is small, and the temperature of the region where the temperature is highest is 150 ° C. .

  This is because the heat dissipation path from the planar heat generation area must be one-dimensional, but by adopting the mounting mode of the embodiment, the heat from the heat generation layer is efficiently dissipated to the heat sink body, and the temperature rises. This is considered to be because of the suppression.

  From the above results, it is possible to efficiently dissipate the heat generated in the heat generating layer to the heat sink body by adopting the mounting aspect of the surface light emitting element in the above embodiment which is the configuration of the present invention to the heat sink body, It was confirmed that the temperature rise of the surface light emitting device can be suppressed.

  Next, a second embodiment of the present invention will be described. In the surface light emitting device of the present invention, a simulation test was conducted to investigate the relationship between the thermal conductivity of the heat sink body included in the surface light emitting device and the temperature rise of the surface light emitting element. The test procedure is as follows.

FIG. 23 is a schematic perspective view showing simulation conditions. Referring to FIG. 23, in the simulation in Example 2, a system in which a rectangular parallelepiped AuSn layer 202, a SiO ₂ layer 204, and a surface light emitting element 201 including a quantum cascade active layer are sequentially stacked on a rectangular parallelepiped heat sink body 203. Was assumed. Inside the surface light emitting device 201, a heat generating layer having a bottom surface of a square shape with a side of 100 μm and a thickness of 1 μm was disposed. Then, the thermal conductivity of the sheet sink body was changed in the range of 100 to 1000 W / mK, and the temperature of the surface light emitting element (element maximum temperature) during the operation of the surface light emitting device was investigated.

  FIG. 24 is a diagram showing test results in Example 2. 24, the horizontal axis represents the thermal conductivity of the heat sink body, and the vertical axis represents the temperature of the surface light emitting element during the operation of the surface light emitting device. In the drawing, a broken line parallel to the horizontal axis indicates the maximum temperature (continuous oscillation limit) at which the quantum cascade active layer included in the surface issuing device can continue laser oscillation.

  Referring to FIG. 24, in the system of Example 2 described in FIG. 23, the surface light emitting device of the present invention can continuously oscillate because the heat conductivity of the material constituting the heat sink body is 150 W / mK or more. It turns out that. From this, in the surface light emitting device of the present invention, it can be said that the thermal conductivity of the material constituting the heat sink body is preferably 150 W / mK or more.

  Next, Embodiment 3 of the present invention will be described. A surface light emitting device employing a heat sink body made of various materials was actually fabricated, and an experiment was conducted to investigate the influence of the material of the heat sink body on whether continuous oscillation is possible. The experimental procedure is as follows.

  First, a surface light emitting device having the same configuration as that of the above embodiment was manufactured. Specifically, first, on a n-InP substrate (001) surface, a lattice-matched n-InGaAs buffer layer having a thickness of 100 nm, a quantum cascade active layer, a lattice-matched n-InGaAs guide layer having a thickness of 500 nm, and an n-InP having a thickness of 1 μm. The layer was epitaxially grown by the MBE method. In the quantum cascade active layer, the barrier layer is made of AlInAs (Al composition 0.48), the well layer is made of InGaAs (Ga composition 0.47), and the surface electrode side on the high bias side is directed to the back electrode on the low bias side. Thus, a configuration in which barrier layers / (well layers) / barrier layers / (well layers) /. The thicknesses of these layers are 5 nm / (1 nm) /1.5 nm / (4.5 nm) / 2 nm / (4 nm) / 3 nm / (2.5 nm) /2.5 nm / (2.2 nm) / 2. A laminated structure composed of 18 layers of 2 nm / (2 nm) / 2 nm / (2 nm) /2.2 nm / (2 nm) / 3 nm / (2 nm) is defined as one period, and this period is plural (for example, 10 to 100 periods, For example, 30 cycles). In the thickness display described above, the value of the thickness enclosed in parentheses indicates the thickness of the well layer. As a result, the thickness of the quantum cascade active layer was about 1440 nm.

  A surface electrode having a square shape with a planar shape of 100 μm on one side was formed on the n-InP layer of the epi-wafer thus fabricated. On the other hand, a back electrode was formed on the main surface opposite to the side where the n-InGaAs buffer layer was formed on the n-InP substrate. A window portion 92A was formed on the back surface electrode using a double-sided mask aligner so as to be located immediately below the region where the front surface electrode was formed. Both the front electrode and the back electrode were formed by evaporating a layer made of, for example, an Au—Ge—Ni alloy.

Then, a photonic crystal layer having holes constituting a triangular lattice having a lattice constant of 1.8 μm and an air filling ratio of 15% (air holes are circular with a diameter of 730 nm) was manufactured in the same procedure as in the above embodiment. . The depth of the hole was 1 μm. In addition, the planar shape of the region where the hole is formed in the photonic crystal layer was a square shape having a side of 100 μm. Then, the periphery of the surface electrode was covered with a SiO ₂ film, and a metal pad made of gold having a side of 400 μm and a thickness of 1 μm was formed thereon by a vapor deposition method to complete a surface light emitting device. Thereafter, the surface light emitting device was mounted on the heat sink by bonding the metal pad and the heat sink with Au—Sn (gold-tin) solder according to the configuration of the present invention.

  As the heat sink, (1) a silicon heat sink (thermal conductivity: 140 W / mK) having a 1 mm side cube shape subjected to gold plating, and (2) a copper shape having a 1 mm side cube shape subjected to gold plating Three types of heat sinks made of tungsten alloy (thermal conductivity: 180 W / mK) and (3) heat sink made of aluminum nitride having a 1 mm side cubic shape with gold plating (thermal conductivity: 230 W / mK) are used. did.

  Then, a current was passed under an appropriate bias to the surface light emitting element of the surface light emitting device employing the above three types of heat sinks. As a result, the surface light-emitting devices employing the heat sinks (2) and (3) oscillated continuously at room temperature, whereas the surface light-emitting devices employing the heat sink (1) were only pulsed. In addition, the oscillation wavelength of the surface emitting device employing the heat sinks (2) and (3) was a single wavelength of 5 μm.

  From the above experimental results, it was confirmed that it is preferable to employ a material having a thermal conductivity of 150 W / mK as the material constituting the heat sink.

  Next, a fourth embodiment of the present invention will be described. An experiment was conducted to investigate the effect of the shape of the conductor pad on the temperature of the quantum cascade active layer during the operation of the surface emitting device. The experimental procedure is as follows.

  First, a surface light emitting device was prepared in the same manner as in Example 3 described above, and mounted on a heat sink made of aluminum nitride having a 1 mm side cubic shape subjected to gold plating to produce a surface light emitting device. Here, the material constituting the conductor pad (metal pad) was gold, and only the shape of the metal pad was changed as follows.

  FIGS. 25 to 27 are schematic plan views showing the shapes of the metal pads in the fourth embodiment. 28 to 30 are schematic cross-sectional views showing the shape of the metal pad in Example 4.

  Referring to FIGS. 25 to 30, in this embodiment, the metal pads are shaped as follows: (1) a square shape having a 200 μm side, a thickness of 1 μm (see FIGS. 25 and 28), and (2) a planar shape being vertical. A rectangular shape of 800 μm, a width of 200 μm, a thickness of 1 μm (see FIGS. 26 and 28), (3) a square shape having a planar shape of 400 μm on one side, a thickness of 1 μm (see FIGS. 27 and 28), and a (4) a planar shape having a side of 400 μm. A square shape with a thickness of 0.3 μm (see FIGS. 27 and 29) and (5) a square shape with a 400 μm side and a thickness of 5 μm (see FIGS. 27 and 30) were adopted. Then, each surface light emitting device was energized while changing the environmental temperature, and the temperature change of the oscillation threshold was investigated to estimate the temperature of the quantum cascade active layer when the same power was applied.

  As a result, when the temperature of the quantum cascade active layer of the sample in which the shape of the metal pad is (3) is 50 ° C., the shape of (1) and (4) is 57 ° C., the shape of (2) is 54 ° C., The shape of (5) was 45 ° C.

  From the above experimental results, in the surface light emitting device of the present invention, the planar shape of the conductor pad is enlarged to a similar shape to the planar shape of the surface electrode, and the thickness of the conductor pad is increased. As a result, it was confirmed that the heat spread effect is increased and the heat dissipation can be improved.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. 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 surface emitting device and the manufacturing method thereof according to the present invention are particularly advantageously applied to a surface emitting device including a quantum cascade laser element including an active layer using intersubband transition and a manufacturing method thereof.

It is a schematic sectional drawing which shows the structure of the surface emitting device in one embodiment of this invention. It is a schematic perspective view which shows a part of structure of the photonic crystal layer contained in the surface emitting device of FIG. It is a schematic plan view which shows the structure of the surface electrode, metal pad, and heat sink which are included in the surface emitting device of FIG. It is a schematic plan view which shows the structure of the n-InP board | substrate and back electrode which are included in the surface emitting device of FIG. It is a figure for demonstrating the diffraction of the light in a triangular lattice. It is a schematic perspective view which shows the other structure of a photonic crystal layer. It is a figure for demonstrating the diffraction of the light in a square lattice. It is a flowchart which shows the outline of the manufacturing method of the surface emitting device in one embodiment of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of a surface emitting device. It is a schematic sectional drawing for demonstrating the manufacturing method of a surface emitting device. It is a schematic sectional drawing for demonstrating the manufacturing method of a surface emitting device. It is a schematic sectional drawing for demonstrating the manufacturing method of a surface emitting device. It is a schematic sectional drawing for demonstrating the manufacturing method of a surface emitting device. It is a schematic sectional drawing for demonstrating the manufacturing method of a surface emitting device. It is a schematic sectional drawing for demonstrating the manufacturing method of a surface emitting device. It is a schematic sectional drawing for demonstrating the manufacturing method of a surface emitting device. It is a schematic perspective view which shows the conditions of the simulation supposing the mounting aspect of the surface emitting element of this invention. It is a schematic perspective view which shows the conditions of the simulation which assumed the mounting aspect of the surface emitting element outside the range of this invention. It is a figure which shows the test result of the Example in Example 1. FIG. It is a figure which expands and shows the principal part of FIG. 6 is a diagram showing test results of a comparative example in Example 1. FIG. It is a figure which expands and shows the principal part of FIG. It is a schematic perspective view which shows the conditions of simulation. It is a figure which shows the test result in Example 2. FIG. 6 is a schematic plan view showing the shape of a metal pad in Example 4. FIG. 6 is a schematic plan view showing the shape of a metal pad in Example 4. FIG. 6 is a schematic plan view showing the shape of a metal pad in Example 4. FIG. It is a schematic sectional drawing which shows the shape of the metal pad in Example 4. It is a schematic sectional drawing which shows the shape of the metal pad in Example 4. It is a schematic sectional drawing which shows the shape of the metal pad in Example 4.

Explanation of symbols

1 surface emitting device, 2 surface emitting element, 10 n-InP substrate, 20 n-InGaAs buffer layer, 30 quantum cascade active layer, 40 n-InGaAs guide layer, 50 photonic crystal layer, 51 hole, 52 base layer, 55 n-InP layer, 60 surface electrode, 70 metal pad, 80 heat sink, 91 solder layer, 92 back electrode, 92A window, 93 stem, 94 gold wire, 95 insulating layer, 101, 201 surface light emitting element, 102 Au layer, 103 heat sink, 104, 204 SiO ₂ layer, 109 light emitting layer, 202 AuSn layer, 203 heat sink body.

Claims (8)

A surface light emitting device comprising a heat sink body and a surface light emitting element mounted on the heat sink body,
The surface light emitting element is
A first conductivity type substrate;
An active layer formed on the main surface of the substrate using intersubband transition;
A first conductivity type semiconductor layer disposed on the main surface of the substrate so as to sandwich the active layer;
A two-dimensional diffraction grating laminated with the semiconductor layer on the main surface of the substrate and independent of the active layer;
An electrode formed on the main surface of the substrate so as to be laminated with the active layer;
A conductor pad connected to the electrode,
The surface light emitting device in which the surface light emitting element is mounted on the heat sink body by connecting the conductor pad and the heat sink body via a connecting material layer.   The surface issuing device according to claim 1, wherein the conductor pad has a planar shape larger than a planar shape of the electrode.   The surface light-emitting device according to claim 1, wherein the material constituting the heat sink body has a thermal conductivity of 150 W / mK or more.   The center of gravity of the electrode and the center of gravity of the conductor pad are aligned in a direction perpendicular to the surface of the heat sink body to which the connection material layer is connected. Surface light emitting device.   The surface emitting device according to claim 1, wherein the conductor pad has a thickness of 1 μm or more. Forming a surface light emitting element;
Mounting the surface light emitting element on a heat sink body,
The step of forming the surface light emitting element includes:
Preparing a first conductivity type substrate;
Forming, on the main surface of the substrate, an active layer using intersubband transition, and a first conductivity type semiconductor layer disposed so as to sandwich the active layer;
Laminating with the semiconductor layer on the main surface of the substrate, forming a two-dimensional diffraction grating independent of the active layer;
Forming an electrode on the main surface of the substrate so as to be laminated with the active layer;
Forming a conductive pad connected to the electrode,
In the step of mounting the surface light emitting element on a heat sink body, the method of manufacturing a surface light emitting device, wherein the conductor pad and the heat sink body in the surface light emitting element are connected via a connecting material layer.   The method for manufacturing a surface light emitting device according to claim 6, wherein in the step of forming the conductor pad, the conductor pad having a planar shape larger than a planar shape of the electrode is formed.   The method of manufacturing a surface light emitting device according to claim 6, wherein the step of forming the conductor pad includes a step of forming the conductor pad using a plating method.

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