JP2009231773A - Photonic crystal face emission laser element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photonic crystal face emission laser capable of oscillating at room temperature and having a high reliability, and to provide a method of manufacturing the same. <P>SOLUTION: An emission element 1 includes: a quantum cascade active layer 4 being an active layer using the intersubband transition; an n-type buffer layer 3 and an n-type guide layer 5 as first conduction-type semiconductor layers; and a photonic crystal layer 7 as a two-dimensional diffraction grating. The n-type buffer layer 3 and the n-type guide layer 5 are arranged so as to interpose the quantum cascade active layer 4. The photonic crystal layer 7 is stacked on the n-type buffer layer 3 and the n-type guide layer 5, and is independent of the quantum cascade active layer 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In recent years, quantum cascade lasers using intersubband transitions have been proposed as laser elements that emit laser light in a long wavelength range from the mid-infrared to the terahertz band (see, for example, Non-Patent Document 1 and Non-Patent Document 2). ). 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, “InAs Quantum Cascade Laser Research”, [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.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a highly reliable photonic crystal surface emitting laser element capable of oscillating even at room temperature and a method for manufacturing the same. Is to provide.

  A photonic crystal surface emitting laser element according to the present invention includes an active layer using intersubband transition, a first conductivity type semiconductor layer, and a two-dimensional diffraction grating. The semiconductor layer is disposed so as to sandwich the active layer. The two-dimensional diffraction grating is laminated with the semiconductor layer and independent of the active layer.

  In this way, since the two-dimensional diffraction grating, which is a photonic crystal layer, is formed independently of the active layer, the recesses (air holes) that constitute the two-dimensional diffraction grating reach the active layer. As in the case, the active layer is not damaged or exposed to the air due to the formation of the recess. Therefore, non-radiative bonding of carriers is less likely to occur than when the concave portion of the two-dimensional diffraction grating reaches the active layer, so that sufficient light emission at room temperature can be realized in the active layer. Further, by using a two-dimensional diffraction grating, it is possible to easily oscillate laser light having a single wavelength (single mode).

  Furthermore, since surface emission is performed using a two-dimensional diffraction grating, unlike the laser element shown in Non-Patent Document 2, the possibility of an end face destruction phenomenon is low, and high reliability can be realized.

  In the photonic crystal surface emitting laser element, the active layer and the two-dimensional diffraction grating are preferably separated by 1 μm or more. In this case, since the active layer and the two-dimensional diffraction grating are disposed sufficiently apart from each other, the influence of the two-dimensional diffraction grating on the active layer can be suppressed and a highly reliable laser element can be realized.

  In the photonic crystal surface emitting laser element, the active layer has a superlattice structure in which thin films made of semiconductors are stacked, and may include a quantum cascade structure having a plurality of stepped subband structures. In this way, a step-like potential can be formed in the active layer, and the oscillation wavelength of the laser light can be controlled by controlling the composition and thickness of the thin film.

  In the photonic crystal surface emitting laser element, the emitted laser light may be emitted in a direction perpendicular to the main surface of the active layer.

  In the photonic crystal surface emitting laser element, the wavelength of the emitted laser light is preferably 1.6 μm or more and 1 mm or less (that is, the emitted laser light is an infrared region or a terahertz laser beam). In this case, the laser element according to the present invention using the active layer using the intersubband transition is particularly excellent as a laser element that emits laser light having the above-described wavelength (that is, oscillation with high reliability at room temperature). Therefore, it is excellent as a light source for laser light in the wavelength region described above.

  In the photonic crystal surface emitting laser element, the two-dimensional diffraction grating may be exposed on the outermost surface. In this case, the manufacturing process of the laser element can be simplified as compared with the case where the two-dimensional diffraction grating is arranged in the central portion of the semiconductor laminated structure. For this reason, the increase in the manufacturing cost of a laser element can be suppressed.

  In the photonic crystal surface emitting laser element, the two-dimensional diffraction grating may have a low refractive index portion and a high refractive index portion having a refractive index higher than the refractive index of the low refractive index portion. The high refractive index portion may be made of a semiconductor, and the low refractive index portion may be a hole formed in the high refractive index portion.

  The two-dimensional diffraction grating having such a configuration can be formed by a relatively simple process of forming a semiconductor layer to be a high refractive index portion and forming a hole by etching or the like. For this reason, the manufacturing process of a laser element can be simplified and a low-cost laser element can be realized.

  In the photonic crystal surface emitting laser element, the two-dimensional diffraction grating may have a low refractive index portion and a high refractive index portion having a refractive index higher than that of the low refractive index portion. The high refractive index portion may be made of a metal, and the low refractive index portion may be made of a semiconductor.

  In this case, if the metal constituting the high refractive index portion is used as an electrode, the structure of the laser element can be simplified as compared with the case where the electrode is formed separately from the two-dimensional diffraction grating.

  The photonic crystal surface emitting laser element may further include a layer made of metal or semiconductor that is in contact with the two-dimensional diffraction grating. The semiconductor may be a first conductivity type semiconductor. In this way, a photonic crystal surface emitting laser element according to the present invention having a structure in which a two-dimensional diffraction grating is embedded in a laminated structure can be obtained. In this case, for example, a conventionally known process such as a fusion method can be used to connect the semiconductor layer to the two-dimensional diffraction grating.

  The photonic crystal surface emitting laser element may further include a substrate in which an active layer, a first conductivity type semiconductor layer, and a two-dimensional diffraction grating are stacked on a main surface. The active layer may be located farther than the two-dimensional diffraction grating when viewed from the substrate. In this case, after the two-dimensional diffraction grating is formed on the substrate, the active layer and the first conductivity type semiconductor layer formed on another substrate are fused on the two-dimensional diffraction grating. A crystal surface emitting laser element can be manufactured.

  In the method of manufacturing a photonic crystal surface emitting laser element according to the present invention, a step of forming an active layer using intersubband transition is performed. A step of forming a semiconductor layer constituting a two-dimensional diffraction grating is performed on the active layer. In the semiconductor layer, a step of periodically forming a plurality of recesses that are arranged periodically and do not reach the active layer is performed. A step of forming an electrode in contact with the semiconductor layer is performed. In this case, since the electrodes are formed directly on the semiconductor layer constituting the two-dimensional diffraction grating, the laser element can be manufactured by a simpler process than the structure in which the two-dimensional diffraction grating is sandwiched between other semiconductor layers. it can.

  In the method of manufacturing the photonic crystal surface emitting laser element, in the step of forming the electrode, the electrode may be formed using a plating method. In this case, the thickness of the electrode can be increased relatively easily by using a plating method.

  In the method of manufacturing a photonic crystal surface emitting laser element according to the present invention, a step of forming an active layer using intersubband transition is performed. A step of forming a semiconductor layer constituting a two-dimensional diffraction grating is performed on the active layer. In the semiconductor layer, a step of periodically forming a plurality of recesses that are arranged periodically and do not reach the active layer is performed. A step of forming an electrode that contacts the semiconductor layer and covers the recess is performed.

  In this case, since the electrode acts as a support member that retains the shape of the recess in the semiconductor layer constituting the two-dimensional diffraction grating, a more reliable photonic crystal surface emitting laser element can be obtained. In the method of manufacturing the photonic crystal surface emitting laser element, the electrode may be formed using a plating method in the step of forming the electrode covering the recess. Also in this case, the thickness of the electrode can be increased relatively easily by using a plating method.

  Thus, according to the present invention, a photonic crystal surface emitting laser element capable of oscillating at room temperature can be obtained.

  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.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a first embodiment of a light emitting device according to the present invention. FIG. 2 is a schematic perspective view showing a photonic crystal layer included in the light-emitting element shown in FIG. FIG. 3 is a schematic plan view showing an n-type surface electrode of the light emitting device shown in FIG. With reference to FIGS. 1-3, Embodiment 1 of the light emitting element by this invention is demonstrated.

  The inventors have used the concept of the photonic crystal surface emitting laser element disclosed in Patent Document 1 and have a frequency ranging from the mid-infrared region to the terahertz (THz) band (specifically, the wavelength is 1.6 μm or more) A quantum cascade surface emitting laser (light emitting element 1) as shown in FIGS. 1 to 3 that can oscillate laser light (which is 1 mm or less) was successfully formed. Specifically, referring to FIGS. 1 to 3, a light emitting device 1 according to the present invention is a two-dimensional photonic crystal quantum cascade surface emitting laser device, and is formed on a substrate 2 and an upper surface of the substrate 2. N-type buffer layer 3, quantum cascade active layer 4 formed on n-type buffer layer 3, n-type guide layer 5 formed on quantum cascade active layer 4, and formed on n-type guide layer 5 Photonic crystal layer 7, n-type surface electrode 10 formed on photonic crystal layer 7, and n formed on the back surface of substrate 2 opposite to the surface on which n-type buffer layer 3 is formed. A mold back electrode 9 is provided. As the substrate 2, an n-type substrate can be used. Further, as the material of the substrate 2, for example, indium phosphide (InP) can be used. As the composition of the n-type buffer layer 3, a layer made of n-type InGaAs can be used. The side walls of the holes 8 formed in the photonic crystal layer 7 are exposed on the upper surface of the light emitting element 1. That is, the photonic crystal layer 7 is exposed on the outermost surface of the light emitting element 1.

  As the quantum cascade active layer 4, for example, a superlattice structure is formed by alternately laminating barrier layers made of AlInAs and well layers made of InGaAs. The quantum cascade active layer 4 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 4, for example, when the barrier layer is made of AlInAs (Al composition 0.48) and the well layer is made of InGaAs (Ga composition 0.47), on the high bias side. A structure in which barrier layers / (well layers) / barrier layers / (well layers) /... Are alternately laminated from an n-type front electrode 10 side toward an n-type back electrode 9 on the low bias side. it can. 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 repeated a plurality of times (for example, 10 to 100 periods). Can be configured. In the thickness display described above, the value of the thickness enclosed in parentheses indicates the thickness of the well layer.

  As the n-type guide layer 5, for example, a layer made of InGaAs can be used. As the photonic crystal layer 7, for example, a structure in which holes 8 as periodic recesses are formed in a layer made of n-type indium phosphide (InP) can be used. As a material for the n-type front electrode 10 and the n-type back electrode 9, any metal can be used. The photonic crystal layer 7 and the quantum cascade active layer 4 are separated by 1 μm or more.

  In the photonic crystal layer 7, holes 8 that are air holes are arranged in a triangular lattice shape. As a result, the hole 8 becomes the low refractive index portion 72, and the surrounding InP layer becomes the high refractive index portion 71. As shown in FIG. 3, the n-type surface electrode 10 has a hole having the same planar shape as the planar shape of the hole 8 in a portion overlapping the hole 8 that is an air hole in the photonic crystal layer 7. . The n-type back electrode 9 is formed so as to cover the entire back surface of the substrate 2.

  Referring to FIG. 2, the photonic crystal layer 7 has a high refractive index portion 71 and a low refractive index portion 72 (that is, hole 8). The low refractive index portion 72 (hole 8) has a refractive index lower than that of the high refractive index portion 71. There are a plurality of low refractive index portions 72 (holes 8), and they are uniformly distributed inside the high refractive index portion 71. In FIG. 2, the photonic crystal layer 7 constitutes a two-dimensional diffraction grating in the form of a triangular grating. Each of the low refractive index portions 72 (holes 8) 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.

Next, the light emission principle of the light emitting element 1 shown in FIGS. 1 to 3 will be briefly described.
When a voltage is applied to the n-type front electrode 10 and the n-type back electrode 9, electrons are injected into the quantum cascade active layer 4. 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 4, 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 4.

  Light generated in the quantum cascade active layer 4 is confined in the quantum cascade active layer 4 by the n-type buffer layer 3 and the n-type guide layer 5, but part of the light is evanescent light in the photonic crystal layer 7. To reach. Here, since the structure of the quantum cascade active layer 4 is defined so that the light generated in the quantum cascade active layer 4 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 light emitting device 1 shown in FIG. 1, even if the distance between the photonic crystal layer 7 and the quantum cascade active layer 4 is, for example, 1 μm or more, the photonic crystal layer 7 is sufficiently evanescent from the quantum cascade active layer 4. The light reaches. When the wavelength of the evanescent light that reaches the photonic crystal layer 7 coincides with the predetermined period of the photonic crystal layer 7, a standing wave is induced at the wavelength corresponding to the period.

  Such a phenomenon can occur in a region immediately above the n-type back electrode 9 because the quantum cascade active layer 4 and the photonic crystal layer 7 are two-dimensionally spread. Laser oscillation can be caused by the feedback effect of standing waves.

  The photonic crystal layer 7 (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. 4 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. 4, paying attention to a lattice point A arbitrarily selected from a plurality of lattice points (holes 8), the direction from the lattice point A to the lattice point B is referred to as the X-Γ direction, and the lattice point A to the lattice point The direction toward point C is called the XJ direction. Here, the case where the wavelength of the light generated in the quantum cascade active layer 4 (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 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 high refractive index portion 71 (FIG. 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 θ at angles of θ = ± 60 °, ± 120 °, and G 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. As a result, light is emitted in a direction perpendicular to the main surface of the two-dimensional diffraction grating (main surface of the quantum cascade active layer 4), that is, the light emission surface, in the direction indicated by the arrow 11 in FIG. ).

  Further, in this two-dimensional diffraction grating, considering that the above description is made at an arbitrary grating point A, 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 this two-dimensional diffraction grating, it is considered that the three X-Γ directions are coupled by the two-dimensional coupling to form a coherent state.

  FIG. 5 is a perspective view schematically showing another configuration of the photonic crystal layer in the first embodiment of the present invention. In FIG. 5, the photonic crystal layer 7 constitutes a two-dimensional diffraction grating in the form of a square lattice. Each of the low refractive index portions 72 is a hole 8 formed at a position that becomes a lattice point of a square lattice, in other words, at a position of a square apex. The distances between the center of one lattice point (hole 8) and the centers of the eight lattice points adjacent to this lattice point are all equal.

  FIG. 6 is a diagram for explaining light diffraction in a square lattice. The square lattice is filled with squares whose side length is d. In FIG. 6, 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, the case where the wavelength of the light generated in the quantum cascade active layer 4 (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 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 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. 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, this two-dimensional diffraction grating acts as an optical resonator, that is, a wavelength selector and a reflector.

  Here, in the light emitting device 1 as the photonic crystal surface emitting laser device shown in FIGS. 1 to 3, a quantum cascade active layer 4 that is an active layer using intersubband transition, and a first conductivity type semiconductor layer N-type buffer layer 3 and n-type guide layer 5, and a photonic crystal layer 7 as a two-dimensional diffraction grating. The n-type buffer layer 3 and the n-type guide layer 5 are arranged so as to sandwich the quantum cascade active layer 4. The photonic crystal layer 7 is stacked on the n-type guide layer 5 and is independent of the quantum cascade active layer 4. By providing such a configuration, in the light emitting device 1 shown in FIGS. 1 to 3, the quantum cascade active layer 4 emits light by controlling the structure (lattice constant and air filling rate) of the photonic crystal layer 7. It is possible to oscillate in only one mode by feeding back only light of an arbitrary wavelength among the light to be transmitted into the quantum cascade active layer 4. That is, the oscillation wavelength is not a multimode in which a large number of wavelengths are mixed, as in a normal quantum cascade laser using a conventional Fabry-Perot resonator, and the light emitting device 1 according to the present invention has an arbitrary single wavelength. Oscillation is possible. Further, it becomes possible to emit laser light having a single wavelength in a direction perpendicular to the main surface of the quantum cascade active layer 4 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 structure of the light emitting element 1 as the photonic crystal surface emitting laser element shown in FIGS. 1 to 3, the emission surface can be an area having a very large area on the surface side. As a result, in the light emitting device 1 according to the present invention, a breakdown phenomenon (COD: sudden breakdown: due to light concentration) which is a problem with a laser whose emission surface must be a narrow region, such as a Fabry-Perot laser or a defective photonic crystal laser. The possibility of causing a phenomenon that the exit surface melts is extremely low. That is, the reliability as a laser light source is also improved.

  1 to 3, the photonic crystal layer 7 is formed at a position separated from the quantum cascade active layer 4 (for example, a position separated by 1 μm or more), and evanescent oozed out from the active layer. It is possible to use optical coupling between light and the photonic crystal layer 7. For this reason, it is not necessary to form the hole which reaches an active layer unlike the past. This is because the resonator of the light-emitting element 1 shown in FIGS. 1 to 3 does not require strong localized mode confinement, and has the same optical coupling strength as a normal one-dimensional DFB laser (Distributed feedback laser). This is because it is sufficient. Therefore, since the quantum cascade active layer 4 of the light emitting device 1 shown in FIGS. 1 to 3 is not exposed to the outside, the surface recombination rate does not increase even at room temperature. As a result, the light emitting device 1 shown in FIGS. 1 to 3 can easily realize light emission and oscillation at room temperature.

  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, since the light emitting element 1 shown in FIGS. 1 to 3 oscillates laser light from mid-infrared light to THz band (2 μm or more and 1000 μm or less in wavelength), the region where the evanescent light spreads is very wide. Thus, the distance between the photonic crystal layer 7 and the quantum cascade active layer 4 can be greatly separated. Therefore, as shown in FIG. 1, it is possible to adopt a configuration in which the photonic crystal layer 7 is formed on the surface portion of the light emitting element 1. As a result, for the light-emitting element 1 according to the present invention, it is not essential to use a troublesome manufacturing method such as a fusion method or a regrowth method.

  Further, since the processing position of the hole 8 in the photonic crystal layer 7 and the distance of the quantum cascade active layer 4 are separated, the processing damage to the quantum cascade active layer 4 accompanying the processing when forming the hole 8 hardly occurs. . Similarly, the influence of stress and strain generated when the photonic crystal layer 7 is formed is also reduced with respect to the quantum cascade active layer 4. For this reason, it is also easy to adopt a dielectric column embedded photonic crystal structure, which is sometimes difficult to adopt in other short wavelength photonic crystal surface emitting laser elements due to the strength of residual stress. As a result, the degree of structural freedom has been greatly expanded. That is, the light-emitting element 1 illustrated in FIGS. 1 to 3 has a highly reliable oscillation frequency controlled to an arbitrary single wavelength, and can operate at room temperature, from the mid-infrared region to the THz band. It is a light source capable of emitting laser light having a frequency. Moreover, the light emitting element 1 shown in FIGS. 1 to 3 can be produced by a simple process as will be described later.

  Next, a method for manufacturing the light emitting device shown in FIGS. 1 to 3 will be described. 7-11 is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. 1-3. With reference to FIGS. 7-11, the manufacturing method of the light emitting element shown in FIGS. 1-3 is demonstrated.

  First, the substrate 2 is prepared as shown in FIG. As the substrate 2, for example, an n-type InP substrate can be used as described above.

  Next, the n-type buffer layer 3, the quantum cascade active layer 4, the n-type guide layer 5, and the n-type semiconductor layer 17 are sequentially stacked on the main surface of the substrate 2 using an epitaxial growth method. As a result, a structure as shown in FIG. 8 is obtained.

  Next, the conductor layer 18 is formed on the upper surface of the n-type semiconductor layer 17 by vapor deposition. Further, the n-type back electrode 9 is also formed on the back side of the substrate 2 (the back side opposite to the surface on which the n-type buffer layer 3 is formed) by vapor deposition. In this way, a structure as shown in FIG. 9 is obtained.

  Next, a resist 19 having a pattern is formed on the upper surface of the conductor layer 18 by using a photolithography method. In this resist 19, an opening pattern is formed on the region where the hole 8 (air hole) of the photonic crystal layer 7 shown in FIGS. The planar shape of the opening pattern is the same as the planar shape of the hole 8 and can be, for example, a circular shape. In this way, a structure as shown in FIG. 10 is obtained.

  Next, the conductor layer 18 and the n-type semiconductor layer 17 are partially removed by etching using the resist 19 as a mask, thereby forming the hole 8 as a recess. As a result, a structure as shown in FIG. 11 is obtained.

  Thereafter, the resist 19 is removed. As a result, the light emitting element shown in FIGS. 1 to 3 can be obtained.

  FIG. 12 is a schematic cross-sectional view showing a first modification of the light emitting device shown in FIGS. With reference to FIG. 12, the 1st modification of Embodiment 1 of the light emitting element by this invention shown in FIGS. 1-3 is shown.

  The light-emitting element 1 shown in FIG. 12 basically has the same structure as the light-emitting element shown in FIGS. 1 to 3, but the structure of the photonic crystal layer 7 is partially different. Specifically, in the photonic crystal layer 7, the inside of the hole 8 is filled with a silicon oxide film 20 as an insulating film. The refractive index of the silicon oxide film 20 is lower than that of the n-type semiconductor layer 17 (see FIG. 8) constituting the photonic crystal layer 7. Further, the upper surface of the silicon oxide film 20 constituting the photonic crystal layer 7 is exposed on the outermost surface of the light emitting element 1. Even with such a structure, the same effects as those of the light-emitting element 1 shown in FIGS. 1 to 3 can be obtained.

  Next, a method for manufacturing the light emitting element shown in FIG. 12 will be described. FIG. 13 is a schematic cross-sectional view for explaining a method for manufacturing the light-emitting element shown in FIG. With reference to FIG. 13, the manufacturing method of the light emitting element 1 shown in FIG. 12 is demonstrated.

  In the method for manufacturing the light emitting device shown in FIG. 12, after performing the steps shown in FIGS. 8 to 11, the resist 19 remains so that the inside of the hole 8 is filled as shown in FIG. In this state, the silicon oxide film 20 is formed. The silicon oxide film 20 is formed using, for example, a vapor deposition method. As a result, a silicon oxide film 20 is formed on the upper surface of the resist 19 and inside the hole 8 as shown in FIG.

  Thereafter, the silicon oxide film 20 formed on the resist 19 is removed together with the resist 19 (lift-off). As a result, the light emitting element shown in FIG. 12 can be obtained.

  FIG. 14 is a schematic cross-sectional view showing a second modification of the light emitting device shown in FIGS. Referring to FIG. 14, a second modification of the first embodiment of the light emitting device according to the present invention will be described.

  The light emitting device 1 shown in FIG. 14 basically has the same structure as that of the light emitting device 1 shown in FIGS. 1 to 3, but the configuration of the n-type surface electrode 10 is the light emission shown in FIGS. It is different from the element 1. That is, in the light emitting element 1 shown in FIG. 14, the thickness of the n-type surface electrode 10 is thicker than the thickness of the n-type surface electrode 10 in the light emitting element 1 shown in FIGS. Even with such a configuration, the same effects as those of the light-emitting element 1 shown in FIGS. 1 to 3 can be obtained.

  Next, a method for manufacturing the light emitting element shown in FIG. 14 will be described. First, after illustrating the steps shown in FIGS. 8 to 11, the resist 19 shown in FIG. 11 is removed using a chemical such as a stripping solution. As a result, the upper surface of the n-type surface electrode 10 is exposed as shown in FIG. A conductor film is further formed on the exposed upper surface of the n-type surface electrode 10 by plating. As a result, a thick n-type surface electrode 10 (see FIG. 14) is formed. Thus, the light emitting element 1 shown in FIG. 14 can be obtained.

(Embodiment 2)
FIG. 15 is a schematic cross-sectional view showing a second embodiment of a light emitting device according to the present invention. 16 is a schematic perspective view showing a photonic crystal layer constituting the light emitting device shown in FIG. FIG. 17 is a schematic plan view showing an n-type surface electrode formed on the upper surface of the light emitting device shown in FIG. FIG. 18 is a schematic plan view showing the n-type back electrode 9 formed on the back side of the light emitting element shown in FIG. A second embodiment of the light emitting device according to the present invention will be described with reference to FIGS.

  Referring to FIGS. 15 to 18, light emitting element 1 basically has the same structure as the light emitting element shown in FIGS. 1 to 3, but includes n-type surface electrode 10, photonic crystal layer 7, and n. The structure of the mold back electrode 9 is different. That is, in the light emitting element 1 shown in FIGS. 15 to 18, the n-type back electrode 9 is located on the back surface of the substrate 2 (the back surface opposite to the surface on which the n-type buffer layer 3 is formed). Are arranged in a ring shape. As shown in FIG. 18, the n-type back electrode 9 has a configuration in which an opening 13 is formed at the center. Further, as can be seen from FIGS. 17 and 18, the n-type front electrode 10 has a rectangular planar shape so as to have substantially the same planar shape as the opening 13 formed in the n-type back electrode 9. . In the photonic crystal layer 7, the hole 8 is filled with a metal column 21 as a high refractive index portion. The portion surrounding the metal column 21 in the photonic crystal layer 7 is constituted by a semiconductor layer as a low refractive index portion. The metal column 21 is connected to the n-type surface electrode 10. In the light emitting element 1 shown in FIG. 15, light (laser light) is emitted in the direction shown by the arrow 11 (see FIG. 15). Even with such a configuration, the same effect as that of the light-emitting element 1 shown in FIGS. 1 to 3 can be obtained.

  Next, a method for manufacturing the light-emitting element 1 shown in FIGS. 15 to 18 will be described. 19 to 21 are schematic cross-sectional views for explaining a method for manufacturing the light emitting element shown in FIGS. 15 to 18. With reference to FIGS. 19-21, the manufacturing method of the light emitting element 1 shown in FIGS. 15-18 is demonstrated.

  First, steps similar to those shown in FIGS. 7 and 8 are performed. As a result, as shown in FIG. 8, the n-type semiconductor to be the n-type buffer layer 3, the quantum cascade active layer 4, the n-type guide layer 5 and the photonic crystal layer 7 (see FIG. 15) on the upper surface of the substrate 2. Layer 17 is formed. Thereafter, as shown in FIG. 19, an n-type back electrode 9 is formed on the back surface of the substrate 2. Specifically, a resist pattern (not shown) having the same planar shape as the opening 13 (see FIG. 18) of the n-type back electrode 9 is formed on the back surface of the substrate 2. Then, a conductor film (not shown) to be the n-type back electrode 9 (see FIG. 15) is formed on the resist pattern and on the back surface of the substrate 2. Thereafter, by removing the resist, it is possible to obtain the n-type back electrode 9 in which an opening is formed in a region to be the opening 13. In this way, a structure as shown in FIG. 19 is obtained.

  Next, a resist 19 (see FIG. 20) having a pattern is formed on the n-type semiconductor layer 17. In this way, a structure as shown in FIG. 20 is obtained. The opening pattern formed in the resist 19 has the same planar shape and arrangement as the holes 8 filled with the metal pillars 21 of the photonic crystal layer 7.

  Next, using the resist 19 described above as a mask, the n-type semiconductor layer 17 is partially removed by etching. In this way, the hole 8 (see FIG. 15) is formed. Thereafter, the resist 19 is removed using a stripping solution or the like. As a result, a structure as shown in FIG. 21 is obtained.

  Next, a resist (not shown) is formed on the photonic crystal layer 7 in which the holes 8 are formed by using a photolithography method. In this resist, as shown in FIGS. 15 and 17, an opening pattern is formed in a region where the n-type surface electrode 10 is to be formed. Then, a conductor film (not shown) to be the n-type surface electrode 10 is formed on the upper surface of the resist, the exposed upper surface of the photonic crystal layer 7, and the inside of the hole 8. Form. This conductor film is formed by vapor deposition so as to fill the inside of the hole 8 and to have a film thickness sufficient for constituting the n-type surface electrode 10. Thereafter, the resist film described above is removed together with the conductor film formed on the resist film (lift-off). As a result, the light emitting device 1 shown in FIGS. 15 to 18 can be obtained.

(Embodiment 3)
FIG. 22 is a schematic sectional view showing Embodiment 3 of the light emitting device according to the present invention. FIG. 23 is a schematic diagram showing a planar shape of the n-type back electrode 9 of the light emitting device shown in FIG. With reference to FIG. 22 and FIG. 23, Embodiment 3 of the light emitting element by this invention is demonstrated.

  The light-emitting element 1 shown in FIGS. 22 and 23 basically has the same structure as the light-emitting element 1 shown in FIGS. 15 to 18, but the shapes of the n-type back electrode 9 and the n-type front electrode 10 are the same. The photonic crystal layer 7 is different in structure. That is, in the light emitting element 1 shown in FIGS. 22 and 23, the n-type surface electrode 10 is formed so as to cover the entire upper surface of the photonic crystal layer 7. In addition, the n-type back electrode 9 is also annularly arranged along the outer peripheral portion of the back surface of the substrate 2 from the viewpoint of securing a wider light emitting region.

  In the photonic crystal layer 7, air is present inside the hole 8 and is not filled with an insulating film or the like. The n-type surface electrode 10 is formed so as to cover the entire upper part of the photonic crystal layer 7. Also with the light emitting element 1 having such a configuration, the same effects as those of the light emitting element 1 shown in FIGS. 15 to 18 can be obtained.

  Next, a method for manufacturing the light-emitting element 1 shown in FIGS. 22 and 23 will be described with reference to FIGS. 24 to 27 are schematic cross-sectional views for describing a method for manufacturing the light-emitting element shown in FIGS. 22 and 23.

  First, the same steps as those in FIGS. 7 and 8 described above are performed. Thereafter, a conductor layer 18 (see FIG. 24) to be an electrode is formed on the n-type semiconductor layer 17 (see FIG. 24) to be the photonic crystal layer 7. Further, the n-type back electrode 9 (see FIG. 24) is formed so as to be positioned on the outer peripheral portion on the back side of the substrate 2. Specifically, in order to form the opening 13 of the n-type back electrode 9, a resist is formed in advance on the region of the back surface of the substrate 2 where the opening 13 is to be formed. Then, a conductor film to be the n-type back electrode 9 is formed on the upper surface of the resist and on the exposed portion of the back surface of the substrate 2. A portion of the conductor film formed on the resist is removed together with the resist (lift-off) to obtain a structure as shown in FIG.

  Next, a resist 19 having a pattern (see FIG. 25) is formed on the conductor layer 18 by photolithography. In this way, a structure as shown in FIG. 25 is obtained. The opening pattern formed in the resist 19 is located on the position of the hole 8 to be formed in the photonic crystal layer 7 (see FIG. 22) and has the same planar shape as the planar shape of the hole 8. It is formed.

  Next, the conductor layer 18 and the n-type semiconductor layer 17 are partially removed using the resist 19 as a mask. As a result, the hole 8 is formed as shown in FIG.

  Next, the resist 19 is removed. As a result, a structure as shown in FIG. 27 is obtained. That is, the photonic crystal layer 7 in which the hole 8 is formed and the conductor film portion 22 having an opening on the hole 8 are formed.

  Next, a metal film to be the n-type surface electrode 10 is formed on the conductor film portion 22 by plating. As a result, the hole 8 is maintained in the presence of air, and a conductor film is formed so as to block the upper portion of the hole 8. In this way, the n-type surface electrode 10 (see FIG. 22) is formed. As a result, the light emitting device 1 as shown in FIGS. 22 and 23 can be obtained.

  FIG. 28 is a schematic cross-sectional view illustrating a modification of the light emitting device illustrated in FIGS. 22 and 23. With reference to FIG. 28, a modification of the light-emitting element shown in FIGS. 22 and 23 will be described.

  The light-emitting element 1 shown in FIG. 28 basically has the same structure as the light-emitting element 1 shown in FIGS. 22 and 23, but the structure of the photonic crystal layer 7 is different. That is, in the photonic crystal layer 7, the inside of the hole 8 is filled with the silicon oxide film 20 which is a low refractive index material having a refractive index lower than that of the n-type semiconductor layer constituting the photonic crystal layer 7. ing. Even with such a configuration, the same effect as that of the light-emitting element 1 shown in FIGS. 22 and 23 can be obtained.

  29 and 30 are schematic cross-sectional views for explaining a method for manufacturing the light-emitting element shown in FIG. With reference to FIG. 29 and FIG. 30, the manufacturing method of the light emitting element 1 shown in FIG. 28 is demonstrated.

  First, the steps shown in FIGS. 24 to 26 are performed. Thereafter, with the resist 19 remaining, a silicon oxide film 20 is formed so as to fill the upper surface of the resist 19 and the inside of the hole 8 as shown in FIG. As a result, a structure as shown in FIG. 29 is obtained.

  Thereafter, the silicon oxide film 20 formed on the resist 19 together with the resist 19 is removed (lifted off) to obtain a structure as shown in FIG.

  Thereafter, an n-type surface electrode 10 (see FIG. 28) is formed by forming a conductor film on the conductor film portion 22 (see FIG. 30) by plating. In this way, the light emitting element shown in FIG. 28 can be obtained.

(Embodiment 4)
FIG. 31 is a schematic cross-sectional view showing Embodiment 4 of the light emitting device according to the present invention. 32 is a schematic plan view showing an n-type surface electrode of the light emitting element shown in FIG. With reference to FIG. 31 and FIG. 32, Embodiment 4 of the light emitting element by this invention is demonstrated.

  The light emitting device 1 shown in FIGS. 31 and 32 basically has the same structure as the light emitting device shown in FIGS. 1 to 3, but on the shape of the n-type surface electrode 10 and the photonic crystal layer 7. The difference is that the n-type contact layer 41 is formed. That is, in the light emitting device 1 shown in FIGS. 31 and 32, the n-type buffer layer 3, the quantum cascade active layer 4, the n-type guide layer 5 and the photonic crystal layer 7 are stacked on the upper surface of the substrate 2, An n-type contact layer 41 is formed on the upper surface of the photonic crystal layer 7. As the n-type contact layer 41, for example, a layer made of n-type InP can be used. An n-type back electrode 9 is formed so as to cover the back side of the substrate 2, and on the upper surface of the n-type contact layer 41, the n-type surface electrode 10 having a circular planar shape at the substantially central portion of the light-emitting element 1. Is formed. In the light emitting element 1 shown in FIGS. 31 and 32, light is emitted in the direction indicated by the arrow 11. Even with such a configuration, the same effects as those of the light-emitting element 1 shown in FIGS. 1 to 3 can be obtained.

  Next, a method for manufacturing the light-emitting element shown in FIGS. 31 and 32 will be described with reference to FIGS. 33 to 37 are schematic cross-sectional views for explaining a method for manufacturing the light-emitting element shown in FIGS. 31 and 32.

  First, after performing the same steps as shown in FIGS. 7 and 8, as shown in FIG. 33, a resist having a pattern on the n-type semiconductor layer 17 to be the photonic crystal layer 7 (see FIG. 31). 19 is formed. The opening pattern formed in the resist 19 is formed on a region where the hole 8 is to be formed in the photonic crystal layer 7 of the light emitting element 1 shown in FIG. The planar shape of the opening pattern is the same as the planar shape of the hole 8 in the photonic crystal layer 7.

  Next, the n-type semiconductor layer 17 is partially removed by etching using the resist 19 as a mask. As a result, holes 8 are formed in the n-type semiconductor layer 17 as shown in FIG.

  Thereafter, by removing the resist 19, the photonic crystal layer 7 in which the holes 8 are formed can be obtained as shown in FIG.

  On the other hand, as shown in FIG. 36, another substrate 42 is prepared, and an n-type contact layer 41 is formed on the main surface of the substrate 42 by using, for example, an epitaxial growth method. Then, the substrate 42 on which the n-type contact layer 41 is formed is inverted so that the n-type contact layer 41 faces the photonic crystal layer 7 shown in FIG. 35, and the photo shown in FIG. The nick crystal layer 7 is brought into contact with the upper surface. Further, the photonic crystal layer 7 and the n-type contact layer 41 in contact with each other are fused by heating. Thereafter, the substrate 42 is removed from the n-type contact layer 41. As a result, as shown in FIG. 37, a structure in which the n-type contact layer 41 is arranged on the photonic crystal layer 7 is obtained.

  Thereafter, the n-type back electrode 9 (see FIG. 31) and the n-type front electrode 10 (see FIG. 32) are formed using a conventionally known vapor deposition method or the like. As a result, the light emitting device 1 shown in FIGS. 31 and 32 can be obtained.

  FIG. 38 is a schematic cross-sectional view illustrating a modification of the light emitting device illustrated in FIGS. 31 and 32. With reference to FIG. 38, the modification of the light emitting element shown to FIG. 31 and FIG. 32 is demonstrated.

  As shown in FIG. 38, the light-emitting element 1 basically has the same structure as that of the light-emitting element 1 shown in FIGS. 31 and 32, but the inside of the hole 8 in the photonic crystal layer 7 is the silicon oxide film 20. The difference is that it is filled with. Even with such a structure, the same effects as those of the light-emitting element 1 shown in FIGS. 31 and 32 can be obtained.

  The method for manufacturing the light emitting device shown in FIG. 39 to 41 are schematic cross-sectional views for explaining a method for manufacturing the light-emitting element shown in FIG.

  First, after performing the steps shown in FIGS. 33 to 34, a silicon oxide film 20 is formed so as to fill the upper surface of the resist 19 and the inside of the hole 8 as shown in FIG. The silicon oxide film 20 can be formed using, for example, a vapor deposition method.

  Thereafter, together with the resist 19, the silicon oxide film 20 formed on the resist 19 is removed (lifted off) to obtain a structure as shown in FIG. That is, as shown in FIG. 40, the photonic crystal layer 7 in which the silicon oxide film 20 is filled in the hole 8 can be obtained by the above-described steps.

  Thereafter, the n-type contact layer 41 is formed by performing epitaxial growth again on the photonic crystal layer 7. As a result, a structure as shown in FIG. 41 is obtained. That is, a structure in which the n-type contact layer 41 is disposed on the photonic crystal layer 7 is obtained.

  Thereafter, the n-type back electrode 9 and the n-type front electrode 10 are formed using a conventionally known method, whereby the light emitting device 1 shown in FIG. 38 can be obtained.

(Embodiment 5)
FIG. 42 is a schematic cross-sectional view showing Embodiment 5 of the light-emitting element according to the present invention. With reference to FIG. 42, an embodiment of a light emitting device according to the present invention will be described. As shown in FIG. 42, the light-emitting element 1 includes a substrate 2, an n-type buffer layer 3 formed on the upper surface of the substrate 2, a photonic crystal layer 7 formed on the n-type buffer layer 3, An n-type guide layer 5 formed on the photonic crystal layer 7, a quantum cascade active layer 4 formed on the n-type guide layer 5, and an n-type contact layer 41 formed on the quantum cascade active layer 4. , N-type surface electrode 10 formed on n-type contact layer 41 and n formed on the back surface of substrate 2 (the back surface located on the opposite side of substrate 2 from the upper surface on which n-type buffer layer 3 is formed). A mold back electrode 9 is provided. When viewed from the substrate 2, the quantum cascade active layer 4 is located farther than the photonic crystal layer 7 as a two-dimensional diffraction grating. The planar shape of the n-type back electrode 9 is the same as the planar shape of the n-type back electrode 9 shown in FIG. The planar shape of the n-type surface electrode 10 is the same as the planar shape of the n-type surface electrode 10 shown in FIG.

  As the substrate 2, for example, an n-type gallium arsenide (GaAs) substrate can be used. Further, as the material constituting the n-type buffer layer 3, the n-type guide layer 5, and the n-type contact layer 41, the above-described GaAs can be used. Also in such a light emitting element 1, the effect similar to the light emitting element 1 shown in FIGS. 1-3 can be acquired.

  Next, a method for manufacturing the light-emitting element shown in FIG. 42 will be described. 43 to 48 are schematic cross-sectional views for explaining a method for manufacturing the light-emitting element shown in FIG. A method for manufacturing the light emitting device shown in FIG. 42 will be described with reference to FIGS.

  First, the n-type buffer layer 3 (see FIG. 42) and the n-type semiconductor layer 17 (see FIG. 43) to be the photonic crystal layer 7 (see FIG. 42) are formed on the upper surface of the substrate 2. In this way, a structure as shown in FIG. 43 is obtained.

  Thereafter, a resist 19 (see FIG. 44) having a pattern is formed on the n-type semiconductor layer 17. The pattern in the resist 19 is an opening pattern and is formed at a position overlapping the hole 8 formed in the photonic crystal layer 7. The planar shape of the opening pattern is the same as the planar shape of the hole 8 to be formed. In this way, the structure shown in FIG. 44 is obtained.

  Then, by using resist 19 as a mask, n-type semiconductor layer 17 is partially removed to form hole 8 as shown in FIG.

  Thereafter, the resist 19 is removed. In this way, a structure as shown in FIG. 46 is obtained. That is, as shown in FIG. 46, the photonic crystal layer 7 having the holes 8 is formed on the n-type buffer layer 3.

  47, a separate substrate 42 is prepared, and a structure in which the n-type contact layer 41, the quantum cascade active layer 4, and the n-type guide layer 5 are sequentially stacked on the substrate 42 is prepared. Then, the substrate 42 is inverted, and the substrate 42 is disposed on the substrate 2 so that the n-type guide layer 5 is in contact with the photonic crystal layer 7. Then, the photonic crystal layer 7 and the n-type guide layer 5 are fused by heating. Thereafter, the substrate 42 is peeled off from the n-type contact layer 41. As a result, a structure as shown in FIG. 48 is obtained. Then, by forming the n-type back electrode 9 and the n-type front electrode 10 by a conventionally known method, the light emitting device 1 shown in FIG. 42 can be obtained.

  FIG. 49 is a schematic cross-sectional view showing a modification of the light emitting device shown in FIG. A modification of the light emitting element shown in FIG. 42 will be described with reference to FIG.

  The light emitting element 1 shown in FIG. 49 basically has the same structure as the light emitting element 1 shown in FIG. 42, but the silicon oxide film 20 is filled in the hole 8 in the photonic crystal layer 7. The point is different. Even if it does in this way, the effect similar to the light emitting element 1 shown in FIG. 42 can be acquired.

  Next, a method for manufacturing the light-emitting element 1 shown in FIG. 49 will be described. 50 to 52 are schematic cross-sectional views for explaining a method for manufacturing the light-emitting element 1 shown in FIG. With reference to FIGS. 50-52, the manufacturing method of the light emitting element 1 shown in FIG. 49 is demonstrated.

  First, the steps shown in FIGS. 43 to 45 are performed. Thereafter, as shown in FIG. 50, silicon oxide film 20 is formed so as to fill the upper surface of resist 19 and the inside of hole 8. As a result, a structure as shown in FIG. 50 is obtained.

  Thereafter, the resist 19 is removed to remove the silicon oxide film 20 located on the resist 19 at the same time (lift-off). As a result, as shown in FIG. 51, the photonic crystal layer 7 in which the silicon oxide film 20 is filled in the hole 8 can be obtained.

  Thereafter, epitaxial growth is performed again on the upper surface of the photonic crystal layer 7 to form the n-type guide layer 5, the quantum cascade active layer 4, and the n-type contact layer 41. As a result, a structure as shown in FIG. 52 is obtained. Thereafter, the n-type back electrode 9 and the n-type front electrode 10 are formed by a conventionally known method, whereby the light emitting device 1 as shown in FIG. 49 can be obtained.

Example 1
In order to confirm the effect of the light emitting device according to the present invention, a sample having an open hole surface photonic crystal-forming QC (quantum cascade) laser structure was prepared, and laser pulse oscillation at room temperature was confirmed. Specifically, the light emitting elements A to C having the structures shown in FIGS. 1 to 3, 12, and 14 were formed as samples.

(Sample manufacturing method)
Regarding the light emitting element A:
An n-type (001) plane InP substrate was prepared. Then, using molecular beam epitaxy (MBE), from the InP substrate side, the lattice-matched n-type InGaAs buffer layer (100 nm) / quantum cascade (QC) active layer / lattice-matched n-type InGaAs guide layer (500 nm) / n An epitaxial wafer (substrate with an epitaxial layer) having a structure of a type InP layer (1 μm) was produced. The quantum cascade active layer has a structure in which the barrier layer is AlInAs (Al composition 0.48), the well layer is InGaAs (Ga composition 0.47), and the n-type surface electrode 10 side, which is the high bias side, has a low bias. A structure 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 a structure in which this period is repeated 30 periods is adopted. As a result, the thickness of the quantum cascade active layer was about 1440 nm. In the thickness display described above, the value of the thickness enclosed in parentheses indicates the thickness of the well layer.

  The n-type InP layer is an n-type semiconductor layer to be a photonic crystal layer. An n-type surface electrode was formed on the outermost surface (on the upper surface of the n-type InP layer), and an n-type back electrode was formed on the back side. Each of these electrodes was a gold-germanium-nickel alloy (Au—Ge—Ni alloy) having a thickness of 300 nm. Further, a resist pattern was formed on the n-type surface electrode on the surface side by photolithography. A plurality of opening patterns were formed in the resist. Using the resist as a mask, holes were made in the n-type surface electrode and the n-type InP layer by dry etching. In this way, a photonic crystal layer is constituted by the n-type InP layer. The holes in the photonic crystal layer are located at the lattice points of the triangular lattice, the lattice constant is 1.8 μm, and the air filling rate is 15%. The plane shape of the hole (air hole) was a circular shape having a diameter of 730 nm. The depth of the hole in the vertical direction was 1 μm. The in-plane region size of the photonic crystal layer was 1 mm square. In this manner, a light-emitting element A, which is a sample having the structure shown in FIGS.

Regarding light-emitting element B:
Of the manufacturing method of the light-emitting element A described above, the process up to the step of forming holes in the n-type surface electrode and the n-type InP layer by dry etching was performed. For this reason, the configuration of the quantum cascade active layer is the same as that of the light emitting element A. Thereafter, in order to protect the surface, a silicon oxide film (SiO ₂ ) having a thickness of 1 μm was deposited on the inside of the hole and the upper surface of the resist while leaving the resist remaining. Then, the silicon oxide film other than the inside of the hole was removed together with the resist by the lift-off method. In this way, a light emitting device B having the structure shown in FIG. 12 was obtained.

Regarding light-emitting element C:
After carrying out the manufacturing method of the light-emitting element A described above, in order to further reduce the series resistance component, gold is plated on the n-type surface electrode by electroplating to increase the thickness of the n-type surface electrode to 1 μm. did. At this time, the holes (air holes) in the photonic crystal layer remained open. Thus, the light emitting device C having the structure shown in FIG. 14 was manufactured. The configuration of the quantum cascade active layer is the same as that of the light emitting element A.

(Measurement)
When a current was passed through the above-described three types of light emitting devices A to C under an appropriate bias and observed from above, room temperature pulse oscillation was confirmed at a threshold current density of 1.2 kA / cm ² . The oscillation wavelength of the oscillated laser beam was a single wavelength of 5 μm.

(Example 2)
In order to confirm the effect of the light emitting device according to the present invention, a metal / semiconductor surface photonic crystal-formed QC laser structure sample was prepared, and laser pulse oscillation at room temperature was confirmed. Specifically, a light emitting element D having the structure shown in FIG. 15 was formed as a sample.

(Sample manufacturing method)
Regarding the light emitting element D:
Similar to Example 1, an n-type (001) plane InP substrate was prepared. Then, using the metal organic chemical vapor deposition method (MOCVD method), the lattice matched n-type InGaAs buffer layer (100 nm) / quantum cascade (QC) active layer / lattice matched n-type InGaAs from the InP substrate side as in the first embodiment. An epi wafer (substrate with an epitaxial layer) having a structure of a guide layer (500 nm) / n-type InP layer (1 μm) was produced. The configuration of the quantum cascade active layer was the same as the configuration of the quantum cascade active layer of the light emitting device A in Example 1. And the n-type back electrode in which the window of 500 micrometers square was formed in the back surface side of the board | substrate was formed. Further, a resist pattern was formed on the n-type InP layer by photolithography using a double-sided mask aligner. A plurality of opening patterns were formed in the resist. Then, a hole was made by partially removing the n-type InP layer by a dry etching method using the resist as a mask. The holes are positioned at the lattice points of the triangular lattice, and the region where the holes are formed overlaps the window region of the n-type back electrode.

  Specifically, the region in which the hole was formed was a 500 μm square shape. In a photonic crystal layer composed of an n-type InP layer in which such holes are formed, the triangular lattice has a lattice constant of 1.8 μm and an air filling rate of 22%. The planar shape of the hole was a circular shape having a diameter of 890 nm. The depth of the hole in the vertical direction was 1 μm.

  Then, an n-type surface electrode having a thickness of 2 μm was formed on the photonic crystal layer by a direct vapor deposition method. As a result, as shown in FIG. 15, the hole was filled with the metal material constituting the n-type surface electrode.

(Measurement)
When a current was passed through the light emitting element D under an appropriate bias and observed from the back side, room temperature pulse oscillation was achieved at a threshold current density of 4 kA / cm ² . The wavelength of the oscillated laser beam was a single wavelength of 5.15 μm.

(Example 3)
In order to confirm the effect of the light emitting device according to the present invention, a sample having a surface-side photonic crystal embedded QC laser structure was prepared, and laser oscillation at room temperature was confirmed. Specifically, light emitting elements E and F having the structure shown in FIGS. 22 and 28 were formed as samples.

(Sample manufacturing method)
Regarding light-emitting element E:
Similar to Example 1, an n-type (001) plane InP substrate was prepared. Then, using the MBE method, from the InP substrate side, the structure of n-type InP buffer layer (2 μm) / quantum cascade (QC) active layer / lattice-matched n-type InGaAs guide layer (1 μm) / n-type InP layer (2 μm) An epiwafer was prepared. Here, the configuration of the quantum cascade active layer is high when the barrier layer is made of AlInAs (Al composition 0.48) and the well layer is made of InGaAs (Ga composition 0.47), similar to the light emitting element A described above. Barrier layers / (well layers) / barrier layers / (well layers) /... Were alternately laminated from the n-type front surface electrode 10 on the bias side to the n-type back electrode 9 on the low bias side. Adopted the configuration. The thicknesses of these layers are 4 nm / (2 nm) / 1 nm / (7.5 nm) /1.5 nm / (5.5 nm) /2.5 nm / (4.5 nm) /1.5 nm / (3.5 nm ) /1.2 nm / (3.5 nm) / 2 nm / (4 nm), a laminated structure composed of 14 layers is defined as one cycle, and this cycle is repeated 50 cycles. As a result, the thickness of the quantum cascade active layer was about 2200 nm. In the thickness display described above, the value of the thickness enclosed in parentheses indicates the thickness of the well layer.

  An n-type surface electrode was formed on the surface of this n-type InP layer. Further, an n-type back electrode having a window (opening) formed on the back side of the InP substrate was formed. Each of these electrodes was an Au-Ge-Ni alloy having a thickness of 300 nm.

  Subsequently, a resist pattern was formed on the n-type surface electrode by photolithography. A plurality of opening patterns were formed in the resist. Holes were formed in the n-type surface electrode and the n-type InP layer by a dry etching method using the resist as a mask. In this way, a photonic crystal layer is constituted by the n-type InP layer. The holes in the photonic crystal layer are located at the lattice points of the triangular lattice, the lattice constant is 2.8 μm, and the air filling rate is 15%. The planar shape of the hole (air hole) is a circular shape having a diameter of 1.14 μm. The depth of the air holes in the vertical direction was 1.5 μm.

  The region size in the plane of the photonic crystal (the size of the planar shape of the region where the hole was formed (photonic crystal region)) was 1 mm square. In addition, the n-type back electrode is assumed to have a 1 mm square window opened directly below the photonic crystal region.

  Finally, gold was plated on the n-type surface electrode by electroplating to make the thickness of the n-type surface electrode about 2 μm. In addition, the gold film formed by this plating method closed the upper surface of the hole while maintaining the void inside the hole. In this way, a light-emitting element E which is a sample having the structure shown in FIG. 22 was produced.

Regarding the light emitting element F:
Similar to the manufacturing method of the light-emitting element E, the process up to the step of forming holes in the n-type surface electrode and the n-type InP layer was performed by dry etching. The structure of the quantum cascade active layer was the same as that of the quantum cascade active layer of the light emitting element F. Thereafter, with the resist remaining, a silicon oxide film (SiO ₂ ) having a thickness of 1.5 μm was deposited inside the hole and on the upper surface of the resist. Then, the silicon oxide film other than the inside of the hole was removed together with the resist by the lift-off method. Further, gold was deposited on the entire upper surface of the n-type surface electrode by a vapor deposition method. In this way, a light-emitting element E which is a sample having the structure shown in FIG. 28 was produced.

(Measurement)
When current was applied to the two light-emitting elements E and F produced under an appropriate bias and observed from the back side, the light-emitting element E having an air hole structure had a threshold current density of ² kA / cm ^{2 and} room temperature pulse oscillation. Was confirmed. In addition, in the light-emitting element F having a SiO ₂ pillar structure, room temperature continuous oscillation was achieved at a threshold current density of 2.7 kA / cm ² . The oscillation wavelength of the oscillated laser beam was a single wavelength of 8 μm.

Example 4
In order to confirm the effect of the light emitting device according to the present invention, a sample having a surface-side photonic crystal embedded QC laser structure was prepared, and laser oscillation at room temperature was confirmed. Specifically, light emitting elements G and H having structures similar to those shown in FIGS. 31 and 38 were formed as samples.

(Sample manufacturing method)
Regarding the light emitting element G:
Similar to Example 1, an n-type (001) plane InP substrate was prepared. Then, using the MBE method, from the InP substrate side, n-type InP buffer layer (2 μm) / quantum cascade (QC) active layer / lattice-matched n-type InGaAs guide layer (1 μm) / n-type InP layer (1.5 μm) An epi-wafer with the structure was fabricated. Note that the configuration of the quantum cascade active layer was the same as the configuration of the quantum cascade active layer in the light-emitting element E described above. A resist pattern was formed on the surface of the n-type InP layer by photolithography. A plurality of opening patterns were formed in the resist. A plurality of holes were formed in the n-type InP layer by dry etching using the resist as a mask. In this way, a photonic crystal layer is constituted by the n-type InP layer. The holes in the photonic crystal layer are located at the lattice points of the triangular lattice, the lattice constant is 2.8 μm, and the air filling rate is 15%. The planar shape of the hole (air hole) is a circular shape having a diameter of 1.14 μm. The depth in the vertical direction of the hole was 1.5 μm. The in-plane region size of the photonic crystal (photonic crystal region in which holes are formed) was a circular shape having a diameter of 1 mm.

  Subsequently, an InP substrate (separate substrate) in which an n-type InGaAs contact layer having a thickness of 1 μm and an n-type InP layer having a thickness of 0.5 μm are epitaxially grown on the surface is prepared separately. Then, the n-type InP layer is fused to the photonic crystal layer by inverting the other substrate and bringing the n-type InP layer into contact with the photonic crystal layer (n-type InP layer) and then heating. Thereafter, the InP substrate as another substrate was removed by a selective etching method.

  Finally, an n-type surface electrode was formed on the outermost surface of the n-type InGaAs contact layer, and an n-type back electrode was formed on the back side of the InP substrate. Each of these electrodes was an Au-Ge-Ni alloy having a thickness of 300 nm.

About the light emitting element H:
Similar to the manufacturing method of the light-emitting element G, the process up to the step of forming a hole in the n-type InP layer by dry etching was performed. Note that the configuration of the quantum cascade active layer was the same as the configuration of the quantum cascade active layer in the light-emitting element E described above. Thereafter, with the resist remaining, a silicon oxide film (SiO ₂ ) having a thickness of 1.5 μm was deposited inside the hole and on the upper surface of the resist. Then, the silicon oxide film other than the inside of the hole was removed together with the resist by the lift-off method. Then, epitaxial growth is again performed by MOCVD on the photonic crystal layer in which the silicon oxide film is filled in the hole, thereby forming a 0.5 μm thick n-type InP layer and a 1 μm thick n-type InGaAs contact layer. To do. Then, an n-type surface electrode was formed on the outermost surface of the n-type InGaAs contact layer, and an n-type back electrode was formed on the back side of the InP substrate.

(Measurement)
When an electric current was applied to the two light emitting elements G and H produced under an appropriate bias and observed from above, the light emitting element G having an air hole structure exhibited room temperature pulse oscillation at a threshold current density of ² kA / cm ² . confirmed. In addition, the light emitting element H having a SiO ₂ pillar structure achieved continuous room temperature oscillation at a threshold current density of 2.7 kA / cm ² . The oscillation wavelength of the oscillated laser beam was a single wavelength of 8 μm.

(Example 5)
In order to confirm the effect of the light-emitting element according to the present invention, a substrate-side photonic crystal embedded QC laser structure sample was prepared, and laser oscillation at liquid nitrogen temperature was confirmed. Specifically, light-emitting elements I and J having the structures shown in FIGS. 42 and 49 were formed as samples.

(Sample manufacturing method)
Regarding the light emitting element I:
First, an n-type (001) plane GaAs substrate was prepared. Then, an epi-wafer of n-type GaAs buffer layer (1 μm) / n-type GaAs layer (3 μm) was produced from the GaAs substrate side using MOCVD. Then, a resist pattern was formed on the surface of the n-type GaAs layer by photolithography. A plurality of opening patterns were formed in this resist. Using the resist as a mask, holes were formed in the n-type GaAs layer by dry etching. In this way, a photonic crystal layer is constituted by the n-type GaAs layer. The holes of the photonic crystal layer are located at lattice points of a square lattice, the lattice constant is 21.1 μm, and the air filling rate is 15%. The planar shape of the hole (air hole) is a circular shape having a diameter of 8.5 μm. The vertical depth of the hole was 3 μm. The in-plane region size of the photonic crystal (photonic crystal region in which holes are formed) was a square shape of 2 mm square.

  Subsequently, a GaAs substrate (separate substrate) obtained by epi-growing a 2 μm thick n-type GaAs contact layer, a quantum cascade (QC) active layer, and a 2 μm thick n-type GaAs guide layer is separately prepared. As the configuration of the quantum cascade active layer, the barrier layer was AlGaAs (Al composition 0.15), and the well layer was GaAs. The barrier layer / (well layer) / barrier layer / (well layer) /... Are alternately laminated from the n-type front electrode 10 side, which is the high bias side, to the n-type back electrode 9, which is the low bias side. Was adopted. The thicknesses of these layers are 3 nm / (18.5 nm) / 1 nm / (15.5 nm) /0.5 nm / (13.5 nm) /2.5 nm / (13 nm) / 2 nm / (12 nm) / 2. A laminated structure composed of 14 layers of 5 nm / (11 nm) / 3 nm / (10.5 nm) was defined as one cycle, and this cycle was repeated 100 cycles. As a result, the thickness of the quantum cascade active layer was about 10.8 μm. In the thickness display described above, the value of the thickness enclosed in parentheses indicates the thickness of the well layer.

  Then, the n-type GaAs layer is fused to the photonic crystal layer by reversing another substrate and bringing the n-type GaAs guide layer into contact with the photonic crystal layer (n-type GaAs layer) and then heating. . Thereafter, the GaAs substrate, which is another substrate on the fused side, was removed by a selective etching method.

  Finally, an n-type surface electrode was formed on the outermost surface of the n-type GaAs contact layer, and an n-type back electrode was formed on the back side of the GaAs substrate. The size of the planar shape of the n-type surface electrode was 2 mm square. This n-type surface electrode is formed so as to overlap the above-described photonic crystal region. The n-type back electrode is assumed to have a 2 mm square window (opening) directly below the photonic crystal region.

About light emitting element J:
Similar to the manufacturing method of the light-emitting element I, the process up to the step of forming a hole in the n-type GaAs layer by dry etching was performed. As a result, the configuration of the quantum cascade active layer in the light emitting device J is the same as the configuration of the quantum cascade active layer in the light emitting device I. Thereafter, a silicon oxide film (SiO ₂ ) having a thickness of 3 μm was deposited inside the hole and on the upper surface of the resist with the resist remaining. Then, the silicon oxide film other than the inside of the hole was removed together with the resist by the lift-off method. Then, the epitaxial growth is again performed by MOCVD on the photonic crystal layer in which the silicon oxide film is filled in the hole, the 2 μm thick n-type GaAs guide layer, the QC active layer, and the 2 μm thick n-type GaAs contact. Form a layer.

  Thereafter, an n-type front electrode having the same size as that of the light emitting element I was formed on the surface of the n-type GaAs contact layer, and an n-type back electrode was formed on the back side of the GaAs substrate.

(Measurement)
The two light-emitting elements I and J thus prepared were cooled to liquid nitrogen temperature (77 K), and when current was passed through these light-emitting elements under an appropriate bias and observed from above, the light-emitting element I having an air hole structure was observed. Low temperature pulse oscillation was confirmed at a threshold current density of 3 kA / cm ² . In addition, the light-emitting element J having a SiO ₂ pillar structure achieved low-temperature pulse oscillation at a threshold current density of 4.3 kA / cm ² . All of the oscillated laser beams had a single wavelength of 70 μm (4.3 THz).

  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 present invention is particularly advantageously applied to a light-emitting element that emits laser light in a long wavelength range from the mid-infrared to the terahertz band.

It is a cross-sectional schematic diagram which shows Embodiment 1 of the light emitting element according to this invention. FIG. 2 is a schematic perspective view illustrating a photonic crystal layer included in the light emitting element illustrated in FIG. 1. It is a plane schematic diagram which shows the n-type surface electrode of the light emitting element shown in FIG. It is a figure for demonstrating the diffraction of the light in a triangular lattice. It is a perspective view which shows typically the other structure of the photonic crystal layer in Embodiment 1 of this invention. It is a figure for demonstrating the diffraction of the light in a square lattice. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram which shows the 1st modification of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG. It is a cross-sectional schematic diagram which shows the 2nd modification of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram which shows Embodiment 2 of the light emitting element by this invention. FIG. 16 is a schematic perspective view showing a photonic crystal layer constituting the light emitting element shown in FIG. 15. FIG. 16 is a schematic plan view showing an n-type surface electrode formed on the upper surface of the light emitting device shown in FIG. 15. FIG. 16 is a schematic plan view showing an n-type back electrode 9 formed on the back side of the light emitting element shown in FIG. 15. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIGS. It is a cross-sectional schematic diagram which shows Embodiment 3 of the light emitting element by this invention. It is a schematic diagram which shows the planar shape of the n-type back surface electrode 9 of the light emitting element shown in FIG. FIG. 24 is a schematic cross-sectional view for describing a method for manufacturing the light-emitting element shown in FIGS. 22 and 23. FIG. 24 is a schematic cross-sectional view for describing a method for manufacturing the light-emitting element shown in FIGS. 22 and 23. FIG. 24 is a schematic cross-sectional view for describing a method for manufacturing the light-emitting element shown in FIGS. 22 and 23. FIG. 24 is a schematic cross-sectional view for describing a method for manufacturing the light-emitting element shown in FIGS. 22 and 23. It is a cross-sectional schematic diagram which shows the modification of the light emitting element shown to FIG. 22 and FIG. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG. It is a cross-sectional schematic diagram which shows Embodiment 4 of the light emitting element by this invention. FIG. 32 is a schematic plan view showing an n-type surface electrode of the light emitting element shown in FIG. 31. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG.31 and FIG.32. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG.31 and FIG.32. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG.31 and FIG.32. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG.31 and FIG.32. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG.31 and FIG.32. FIG. 33 is a schematic cross-sectional view showing a modification of the light emitting device shown in FIGS. 31 and 32. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element shown in FIG. It is a cross-sectional schematic diagram which shows Embodiment 5 of the light emitting element by this invention. FIG. 43 is a schematic cross-sectional view for illustrating the method for manufacturing the light emitting element shown in FIG. 42. FIG. 43 is a schematic cross-sectional view for illustrating the method for manufacturing the light emitting element shown in FIG. 42. FIG. 43 is a schematic cross-sectional view for illustrating the method for manufacturing the light emitting element shown in FIG. 42. FIG. 43 is a schematic cross-sectional view for illustrating the method for manufacturing the light emitting element shown in FIG. 42. FIG. 43 is a schematic cross-sectional view for illustrating the method for manufacturing the light emitting element shown in FIG. 42. FIG. 43 is a schematic cross-sectional view for illustrating the method for manufacturing the light emitting element shown in FIG. 42. FIG. 43 is a schematic cross-sectional view showing a modification of the light emitting device shown in FIG. 42. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element 1 shown in FIG. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element 1 shown in FIG. It is a cross-sectional schematic diagram for demonstrating the manufacturing method of the light emitting element 1 shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Light emitting element, 2,42 n-type substrate, 3 n-type buffer layer, 4 quantum cascade active layer, 5 n-type guide layer, 7 photonic crystal layer, 8 hole, 9 n-type back electrode, 10 n-type surface electrode, 11 arrow, 13 opening, 17 n-type semiconductor layer, 18 conductor layer, 19 resist, 20 silicon oxide film, 21 metal pillar, 22 conductor film part, 41 n-type contact layer, 71 high refractive index part, 72 low Refractive index part.

Claims (13)

An active layer using intersubband transition;
A first conductivity type semiconductor layer disposed so as to sandwich the active layer;
A photonic crystal surface emitting laser element comprising a two-dimensional diffraction grating laminated with the semiconductor layer and independent of the active layer.   The photonic crystal surface emitting laser element according to claim 1, wherein the active layer and the two-dimensional diffraction grating are separated from each other by 1 μm or more.   3. The photonic crystal surface emitting laser element according to claim 1, wherein the active layer has a superlattice structure in which thin films made of semiconductors are stacked, and includes a quantum cascade structure having a plurality of stepped subband structures.   The photonic crystal surface emitting laser element according to any one of claims 1 to 3, wherein an emission direction of the emitted laser light is a direction perpendicular to a main surface of the active layer.   The photonic crystal surface emitting laser element according to any one of claims 1 to 3, wherein the wavelength of the emitted laser light is 1.6 µm or more and 1 mm or less.   The photonic crystal surface emitting laser element according to claim 1, wherein the two-dimensional diffraction grating is exposed on the outermost surface. The two-dimensional diffraction grating has a low refractive index portion and a high refractive index portion having a refractive index higher than the refractive index of the low refractive index portion,
The high refractive index portion is made of a semiconductor,
The photonic crystal surface emitting laser element according to claim 6, wherein the low refractive index portion is a hole formed in the high refractive index portion. The two-dimensional diffraction grating has a low refractive index portion and a high refractive index portion having a refractive index higher than the refractive index of the low refractive index portion,
The high refractive index portion is made of metal,
The photonic crystal surface emitting laser element according to claim 6, wherein the low refractive index portion is made of a semiconductor.   The photonic crystal surface emitting laser element according to claim 1, further comprising a layer made of a metal or a semiconductor that is in contact with the two-dimensional diffraction grating. A substrate in which the active layer, the semiconductor layer of the first conductivity type, and the two-dimensional diffraction grating are stacked on a main surface;
6. The photonic crystal surface emitting laser element according to claim 1, wherein the active layer is located farther than the two-dimensional diffraction grating when viewed from the substrate. 7. Forming an active layer using intersubband transition;
Forming a semiconductor layer constituting a two-dimensional diffraction grating on the active layer;
Forming a plurality of recesses that are periodically disposed in the semiconductor layer and do not reach the active layer by etching;
Forming an electrode in contact with the semiconductor layer, and a method of manufacturing a photonic crystal surface emitting laser element. Forming an active layer using intersubband transition;
Forming a semiconductor layer constituting a two-dimensional diffraction grating on the active layer;
Forming a plurality of recesses that are periodically disposed in the semiconductor layer and do not reach the active layer by etching;
Forming an electrode that contacts the semiconductor layer and covers the recess, and a method for manufacturing a photonic crystal surface-emitting laser element.   The method of manufacturing a photonic crystal surface emitting laser element according to claim 11 or 12, wherein, in the step of forming the electrode, the electrode is formed using a plating method.

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