Light-emitting device

Abstract

[Problem] To provide a light-emitting device that comprises a dielectric reflecting mirror and can facilitate polarization control. [Solution] This light-emitting device comprises a first reflecting mirror that is formed by layering a plurality of types of semiconductor materials that have different refractive indices and has a first surface and a second surface that is on the reverse side from the first surface, a second reflecting mirror that is formed by layering a plurality of types of dielectric materials that have different refractive indices and has a third surface and a fourth surface that is on the reverse side from the third surface, an active layer that is provided between the first surface of the first reflecting mirror and the fourth surface of the second reflecting mirror and emits light when electric power is applied thereto, and an uneven layer that is formed from a dielectric material, is provided on the third surface of the second reflecting mirror, and has an uneven shape at a light emission surface that emits light from the active layer.

Description

Light-emitting device

[0001] The present disclosure relates to a light emitting device.

[0002] Light-emitting devices such as vertical-cavity surface-emitting lasers (VCSELs) are used as light sources for distance measurement sensors, etc. In GaAs-based light-emitting devices, providing a grating on the surface of a semiconductor distributed Bragg reflector (DBR) has been considered to control polarization (Patent Document 1, Non-Patent Document 1).

[0003] Japanese Patent Application Publication No. 5-021889

[0004] Fundamental, technology and applications of Vertical-Cavity Surface-Emitting Lasers, Michalzik (2013)

[0005] On the other hand, the refractive index of a dielectric is smaller than that of a semiconductor, and the difference in refractive index between the dielectric and air is small. For this reason, even if a grating is provided on the surface of the dielectric DBR used in an InP-based light-emitting device, it has been difficult to control the polarization of the light-emitting device.

[0006] Therefore, the present disclosure provides a light emitting device that can easily control polarization using a dielectric reflecting mirror.

[0007] A light emitting device according to one aspect of the present disclosure includes: a first reflecting mirror formed by stacking a plurality of types of semiconductor materials with different refractive indices and having a first surface and a second surface opposite the first surface; a second reflecting mirror formed by stacking a plurality of types of dielectric materials with different refractive indices and having a third surface and a fourth surface opposite the third surface; an active layer disposed between the first surface of the first reflecting mirror and the fourth surface of the second reflecting mirror and emitting light when electric power is applied; and a concavo-convex layer formed by a dielectric material and disposed on the third surface of the second reflecting mirror and having a concavo-convex shape on the light emitting surface from which light from the active layer is emitted.

[0008] The uneven layer has a refractive index equal to or higher than that of the plurality of types of dielectric material layers that form the second reflecting mirror.

[0009] The refractive index of the dielectric material that forms the uneven layer is 2 or more.

[0010] The concave-convex layer is made of the same material as the dielectric material layer having the highest refractive index among the plurality of types of dielectric material layers that make up the second reflecting mirror.

[0011] The dielectric material constituting the uneven layer is TiO ２ , Ta ２ O ５ , either SiN or amorphous silicon.

[0012] Among the multiple types of dielectric material layers constituting the second reflecting mirror, the dielectric material layer with a low refractive index is SiO ２ Or MgO.

[0013] The uneven shape of the uneven layer is composed of a plurality of grooves extending in a first direction within the light emitting surface, and the period of the uneven shape arranged in a second direction within the light emitting surface perpendicular to the first direction is equal to or less than the wavelength of light emitted from the light emitting surface.

[0014] The height of the convex portions of the concave-convex shape of the concave-convex layer is 200 nm±60 nm.

[0015] The side surfaces between the recesses and protrusions of the uneven shape of the uneven layer are substantially perpendicular or inclined to the light exit surface.

[0016] The active layer is made of AlGaInAs, and the wavelength of light emitted from the active layer is 1.2 μm to 2 μm.

[0017] The semiconductor device further includes a plurality of tunnel junction layers provided between the active layer and the second reflecting mirror and divided with respect to the active layer, and the plurality of concave-convex shapes of the concave-convex layer are provided corresponding to the plurality of tunnel junction layers.

[0018] In a plan view seen from the stacking direction of the plurality of types of dielectric materials, the plurality of concave and convex shapes overlap the plurality of tunnel junction layers, respectively.

[0019] In a plan view seen from the stacking direction of the plurality of types of dielectric materials, the plurality of concave and convex shapes and the plurality of tunnel junction layers have a substantially circular, substantially elliptical, or substantially polygonal shape.

[0020] The first reflecting mirror further includes a substrate containing InP, the substrate being provided on the second surface side of the first reflecting mirror, and the first reflecting mirror has a layered structure of InP and AlGaInAs.

[0021] The first reflecting mirror further includes a substrate containing GaAs, the substrate being provided on the second surface side of the first reflecting mirror, and the first reflecting mirror has a layered structure of GaAs and AlGaAs or AlAs.

[0022] 1. A cross-sectional view showing an example of the configuration of the light emitting device according to the first embodiment. A plan view showing an example of the configuration of the light emitting device according to the first embodiment. A cross-sectional view showing an example of the configuration of a second reflecting mirror and a grating layer. A plan view showing the relationship between the grating and the BTJ. A plan view showing the relationship between the grating and the BTJ. A plan view showing the relationship between the grating and the BTJ. A plan view showing the relationship between the grating and the BTJ. A graph showing the relationship between the refractive index ngr of the grating layer 95 and the reflectivity R and the reflectivity difference ΔR. A graph showing the relationship between the grating height and the reflectivity and the reflectivity difference. A cross-sectional view showing an example of the configuration of a grating layer and a second reflecting mirror according to the second embodiment. A cross-sectional view showing an example of the configuration of a grating layer and a second reflecting mirror according to the third embodiment. A cross-sectional view showing an example of the configuration of a light emitting device according to the fourth embodiment. A plan view showing an example of the configuration of a light emitting device according to the fourth embodiment. A cross-sectional view showing an example of the manufacturing method of the light emitting device according to the above embodiments. A cross-sectional view showing an example of the manufacturing method of the light emitting device following FIG. 14. A cross-sectional view showing an example of the manufacturing method of the light emitting device following FIG. 15. A cross-sectional view showing an example of the manufacturing method of the light emitting device following FIG. 16. A cross-sectional view showing an example of the manufacturing method of the light emitting device following FIG. 17. 21. A cross-sectional view showing an example of a method for manufacturing a light-emitting device, following FIG. 18. A cross-sectional view showing an example of a method for manufacturing a light-emitting device, following FIG. 19. A cross-sectional view showing an example of a method for manufacturing a light-emitting device, following FIG. 20. A cross-sectional view showing an example of a method for manufacturing a light-emitting device, following FIG. 21. A cross-sectional view showing an example of a configuration of a light-emitting device according to a fifth embodiment. A cross-sectional view showing an example of a configuration of a light-emitting device according to a sixth embodiment. A block diagram showing an example of a schematic configuration of a vehicle control system. An explanatory diagram showing an example of the installation positions of an outside vehicle information detection unit and an imaging unit.

[0023] Hereinafter, specific embodiments to which the present technology is applied will be described in detail with reference to the drawings. The drawings are schematic or conceptual, and the proportions of each part are not necessarily the same as those in reality. In the specification and drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0024] (First embodiment) Fig. 1 is a cross-sectional view showing an example of the configuration of a light emitting device according to a first embodiment. Fig. 2 is a plan view showing an example of the configuration of a light emitting device according to the first embodiment. Fig. 1 shows a cross section taken along line 1-1 in Fig. 2.

[0025] The light-emitting device 1 includes a substrate 10, a first reflecting mirror 20, a first semiconductor layer 30, an active layer 40, a second semiconductor layer 50, a third semiconductor layer 60, a fourth semiconductor layer 70, a fifth semiconductor layer 80, a second reflecting mirror 90, a grating layer 95, a first electrode 100, a second electrode 110, and a protective film 120. The light-emitting device 1 is a semiconductor light-emitting device such as a VCSEL. The light-emitting device 1 emits light by applying power between the first electrode 100 and the second electrode 110, injecting electrons and holes from the first and second semiconductor layers 30, 50 into the active layer 40 and recombining the electrons and holes in the active layer 40. The light is reflected and resonates between the first reflecting mirror 20 and the second reflecting mirror 90, and is emitted as laser light from the second reflecting mirror 90 side.

[0026] The substrate 10 may be, for example, a semiconductor substrate such as an n-type InP substrate.

[0027] The first reflecting mirror 20 is a so-called DBR (Distributed Bragg Reflector) and is configured by alternately stacking multiple materials with different refractive indices. For example, the first reflecting mirror 20 has a layered structure of multiple types of semiconductor materials with different refractive indices (e.g., a layered structure of n-type InP and n-type AlGaInAs) epitaxially grown on the substrate 10. The first reflecting mirror 20 has a first surface F1 and a second surface F2 located on the opposite side of the first surface F1.

[0028] The first semiconductor layer 30 is located between the first reflecting mirror 20 and the second reflecting mirror 90, and is a spacer layer provided on the first reflecting mirror 20. The first semiconductor layer 30 is made of n-type InP or an n-type material lattice-matched to InP (e.g., n-type InGaAsP, n-type AlGaInAs, etc.). The first semiconductor layer 30 may be a single layer of any of the above materials, or may be a stacked film of multiple materials selected from the above materials.

[0029] The active layer 40 is provided between the first semiconductor layer 30 and the second semiconductor layer 50. The active layer 40 receives power from the first and second semiconductor layers 30, 50 and emits light by internally recombining electrons from the first semiconductor layer 30 and holes from the second semiconductor layer 50. The active layer 40 has a multiple quantum well (MQW) structure made of, for example, AlGaInAs, InGaAs, or InGaAsP, and generates light with a wavelength of 1.2 μm to 2 μm.

[0030] The second semiconductor layer 50 is a spacer layer located between the first reflecting mirror 20 and the second reflecting mirror 90 and provided on the active layer 40. The second semiconductor layer 50 is made of p-type InP, which is the opposite conductivity type to the first semiconductor layer 30. Therefore, by applying a negative voltage to the first electrode 100 and a positive voltage to the second electrode 110, electrons are supplied from the first semiconductor layer 30 to the active layer 40, and holes are supplied from the second semiconductor layer 50 to the active layer 40. The p-type impurity concentration of the second semiconductor layer 50 is, for example, 5×10 １７ ~1 x 10 １８ / cm －３ is.

[0031] The third semiconductor layer 60 is provided on the second semiconductor layer 50. The third semiconductor layer 60 is located between the second reflecting mirror 90 and the second semiconductor layer 50. The third semiconductor layer 60 is made of a p-type semiconductor, for example, p ＋ The third semiconductor layer 60 is made of p-type AlGaInAs. The p-type impurity concentration of the third semiconductor layer 60 is higher than that of the second semiconductor layer 50, and is, for example, 5×10 １９ / cm －３ is.

[0032] The fourth semiconductor layer 70 is provided on the third semiconductor layer 60. The fourth semiconductor layer 70 is also located between the second reflecting mirror 90 and the second semiconductor layer 50. The fourth semiconductor layer 70 is made of an n-type semiconductor, for example, ＋ The n-type impurity concentration of the fourth semiconductor layer 70 is higher than that of the fifth semiconductor layer 80, and is, for example, 5×10 １９ / cm －３ is.

[0033] The third and fourth semiconductor layers 60 and 70 form a buried tunnel junction (BTJ) with a high impurity concentration. Hereinafter, the third and fourth semiconductor layers 60 and 70 are also referred to as BTJs 60 and 70. The current between the electrodes 100 and 110 flows concentratedly in the BTJs 60 and 70 and is constricted. This allows the BTJs 60 and 70 to promote light emission in the active layer 40 directly below them.

[0034] 2, when viewed from the stacking direction (Z direction), the multiple BTJs 60, 70 overlap with the multiple gratings GR of the second reflecting mirror 90. The stacking direction (Z direction) is also the direction in which current flows through the BTJs 60, 70 and the direction in which light resonates between the first reflecting mirror 20 and the second reflecting mirror 90.

[0035] 2, a plurality of divided BTJs 60, 70 are provided for one active layer 40, and laser light is emitted from each of the BTJs 60, 70 via a grating GR (multi-emitter structure). In FIG. 2, six BTJs 60, 70 are provided, but the number of BTJs 60, 70 is not limited.

[0036] 1, the fifth semiconductor layer 80 is provided on the second semiconductor layer 50 and the BTJs 60 and 70. The fifth semiconductor layer 80 covers the BTJs 60 and 70. The fifth semiconductor layer 80 is made of an n-type semiconductor, for example, n-type InP. The n-type impurity concentration of the fifth semiconductor layer 80 is lower than that of the fourth semiconductor layer 70, for example, 5×10 １７ ~1 x 10 １８ / cm －３When a negative voltage is applied to the first electrode 100 and a positive voltage is applied to the second electrode 110, a reverse bias is applied to the pn junction between the fifth semiconductor layer 80 and the second semiconductor layer 50. Therefore, no current flows through the pn junction between the fifth semiconductor layer 80 and the second semiconductor layer 50.

[0037] The second reflecting mirror 90 is provided above (in the Z direction) the BTJs 60 and 70. The second reflecting mirror 90 is a dielectric DBR, and is configured by alternately laminating multiple types of dielectric materials with different refractive indices. For example, the second reflecting mirror 90 has a laminated structure of multiple dielectric materials (e.g., SiO ２ , MgO and TiO ２ , Ta ２ O ３ , SiN, or amorphous silicon). That is, the second reflecting mirror 90 is a dielectric DBR containing a dielectric material. The dielectric material in this disclosure is a dielectric material other than a single-crystal semiconductor obtained by epitaxial growth on a semiconductor substrate such as GaAs or InP, and is, for example, SiO ２ , TiO ２ , Ta ２ O ３ , SiN, MgO, amorphous semiconductor materials, etc. The second reflecting mirror 90 also has a third surface F3 and a fourth surface F4 located on the opposite side of the third surface F3.

[0038] A grating layer 95 as a concave-convex layer is provided on the third surface F3 of the second reflecting mirror 90. The grating layer 95 has a refractive index equal to or higher than that of the plurality of dielectric materials constituting the second reflecting mirror 90. Furthermore, the grating layer 95 is preferably made of a material with a refractive index of 2 or more. The material of the grating layer 95 may be the same as the dielectric material with the higher refractive index among the dielectric materials constituting the second reflecting mirror 90. For example, if the second reflecting mirror 90 is made of SiO ２ and TiO ２ When the grating layer 95 is a laminated film of TiO ２ The material of the grating layer 95 may be different from the dielectric material that constitutes the second reflecting mirror 90. For example, if the second reflecting mirror 90 is made of SiO ２ and TiO２ When the grating layer 95 is a laminated film of amorphous silicon, the grating layer 95 may be made of amorphous silicon.

[0039] The grating layer 95 has a concave-convex shape (hereinafter referred to as a grating) GR on its surface F5. The surface F5 of the grating layer 95 is a light emission surface from which the laser light is emitted. The grating GR is provided at a position from which the laser light is emitted, and the laser light passes through the grating GR and is emitted to the outside. A more detailed configuration of the grating GR will be described later.

[0040] In this embodiment, light is generated by applying power to the active layer 40 provided between the first surface F1 of the first reflecting mirror 20 and the fourth surface F4 of the second reflecting mirror 90. The light oscillates in the resonator between the first reflecting mirror 20 and the second reflecting mirror 90, and is emitted as laser light from the surface F5 of the second reflecting mirror 90. At this time, the polarization of the laser light can be controlled to one direction by the grating GR.

[0041] The first electrode 100 is provided on the first semiconductor layer 30 and is electrically connected to the first semiconductor layer 30. The first electrode 100 is made of a conductive metal such as Ti, Pt, or Au, a laminated film of AuGe / Ni / Au, or a laminated film of PdGe / Ni / Au. The first electrode 100 is provided around the active layer 40 via a protective film 120. The first electrode 100 is electrically insulated from components other than the first semiconductor layer 30 by the protective film 120.

[0042] The second electrode 110 is provided on the fifth semiconductor layer 80 and is electrically connected to the fourth semiconductor layer 70 via the fifth semiconductor layer 80. The second electrode 110 is also made of a conductive metal such as Ti, Pt, or Au, a laminated film of AuGe / Ni / Au, or a laminated film of PdGe / Ni / Au. The second electrode 110 may be made of the same material as the first electrode 100. The second electrode 110 is provided around the second reflecting mirror 90. The second electrode 110 may be in contact with the second reflecting mirror 90. The second electrode 110 is electrically insulated from components other than the fifth semiconductor layer 80 by a protective film 120.

[0043] When viewed from the Z direction, the first and second electrodes 100 and 110 do not overlap with the BTJs 60 and 70. Therefore, the first and second electrodes 100 and 110 do not block the laser light emitted from the second reflecting mirror 90.

[0044] The protective film 120 covers the side surfaces of the active layer 40, the second semiconductor layer 50, and the fifth semiconductor layer 80, and also covers a portion of the top surface of the fifth semiconductor layer 80. This allows the protective film 120 to protect the structure of the active layer 40, the second semiconductor layer 50, and the fifth semiconductor layer 80, and to prevent the first and second electrodes 100, 110 from short-circuiting to unintended components. The protective film 120 is made of, for example, SiO ２ The insulating material is SiN or the like.

[0045] FIG. 3 is a cross-sectional view showing an example of the configuration of the second reflecting mirror 90 and the grating layer 95. As shown in FIG.

[0046] The second reflecting mirror 90 is a laminated film of a first material 91 and a second material 92. The first material 91 is, for example, a low refractive index dielectric material having a refractive index of less than 2 (for example, SiO ２ The second material 92 is made of, for example, a high refractive index material having a refractive index of 2 or more (for example, TiO ２ , Ta ２ O ３ , SiN or amorphous silicon).

[0047] The grating layer 95 is provided on the first material 91 and is made of a high refractive index material (e.g., TiO ２ , Ta ２ O ３ , SiN, or amorphous silicon) The grating GR is an uneven shape provided on the surface F5 of the grating layer 95.

[0048] The uneven shape of the grating GR is formed by providing a plurality of grooves on the surface F5 of the grating layer 95. The plurality of grooves extend in the Y direction of the surface F5 of the grating layer 95.

[0049] 4 to 7 are plan views showing the relationship between the grating GR and the BTJ. The grating GR is configured with a plurality of grooves extending in the Y direction and arranged at approximately equal intervals in the X direction. Therefore, the uneven shape of the grating GR appears periodically and repeatedly in the X direction. The region where the grating GR is provided has a shape that overlaps with the BTJs 60 and 70 in a plan view seen from the Z direction. For example, the outer shapes of the grating GR and the BTJs 60 and 70 may be approximately circular. The outer shapes of the grating GR and the BTJs 60 and 70 are not particularly limited and may be approximately elliptical or approximately polygonal.

[0050] Furthermore, as shown in FIG. 4, in plan view in the Z direction, the area of ​​the grating GR may be approximately the same size as the corresponding BTJs 60 and 70.

[0051] Also, as shown in FIG. 5, the area of ​​the grating GR may be larger than the corresponding BTJs 60 and 70 in plan view in the Z direction.

[0052] 6, in a plan view seen from the Z direction, the area of ​​the grating GR may be slightly smaller than the corresponding BTJs 60 and 70. The area of ​​the grating GR only needs to cover half or more of the central portion of the corresponding BTJs 60 and 70.

[0053] 7, the grating GR may be composed of gratings GR1 and GR2 with different periods. In a plan view seen from the Z direction, the grating GR1 is provided in the center of the BTJs 60 and 70 where the laser light intensity is high. The grating GR2 is provided around the grating GR1 where the laser light intensity is low. The period (pitch) of the concave-convex pattern of the grating GR1 is wider than the period (pitch) of the concave-convex pattern of the grating GR2.

[0054] The extension direction (Y direction) of the grooves of the grating GR may be any direction, but is preferably, for example, the crystal direction

[011] or the crystal direction [01-1] of the substrate 10 .

[0055] 3 is equal to or less than the wavelength λ of the laser light generated by the light-emitting device 1 and emitted from the surface F5. For example, if the light-emitting device 1 is an InP-based VCSEL with an oscillation wavelength of 1450 nm, the period Pgr of the grating GR is set to, for example, 700 nm. This suppresses diffraction of the laser light at the grating GR, enabling the laser light to be extracted with high efficiency.

[0056] 8 is a graph showing the relationship between the refractive index ngr of the grating layer 95, the reflectance R, and the reflectance difference ΔR. In this graph, Rx represents the reflectance of the grating layer 95 for light polarized in the X direction. Ry represents the reflectance of the grating layer 95 for light polarized in the Y direction. ΔR represents the reflectance difference Ry-Rx. The larger ΔR is, the larger the difference in threshold gain of laser oscillation for the polarization components of the laser light in the X and Y directions becomes. This means that the larger ΔR is, the more advantageous it is to control the polarization of the laser light.

[0057] From this graph, it was found that the greater the refractive index of the grating layer 95, the greater the ΔR. In other words, it was found that the greater the refractive index of the grating layer 95, the more advantageous it is for controlling the polarization of laser light. Conversely, it was found that when the refractive index of the grating layer 95 approaches the refractive index of air, which is 1, it becomes disadvantageous for controlling the polarization of laser light.

[0058] Typically, the threshold gain of a VCSEL is about 1%. The ΔR required for polarization control is preferably about 1%, but it is considered preferable to set it to at least half of that, 0.5% or more. Referring to FIG. 8, in order for ΔR to be 0.5% or more, the refractive index ngr of the grating layer 95 is preferably 2 or more.

[0059] The grating layer 95 is made of SiO ２ When the grating layer 95 is made of TiO (n=1.45), ΔR is 0.06%, and it is considered that it is difficult to control the polarization of the laser light. ２ When configured with (n=2.25), ΔR is approximately 0.9%, and the difference with the refractive index of air is large, which is thought to facilitate polarization control of laser light.

[0060] 8 was created by a wave optics simulation using the finite element method. In the simulation, the fifth semiconductor layer 80 was made of n-type InP. The second reflecting mirror 90 was made of SiO ２ and TiO with a film thickness of λ / 4n ２ The wavelength λ was set to 1450 nm, and n is the refractive index of each material at λ. The grating layer 95 is a TiO ２ The grating GR had a period Pgr of 700 nm and a height of 200 nm. The widths of the recesses and protrusions of the grating GR were approximately equal, and the duty of the uneven shape (the ratio of the width of the recesses to the width of the protrusions) was 50%.

[0061] 9 is a graph showing the relationship between the grating height Hgr, the reflectance R, and the reflectance difference ΔR. This graph was created by a simulation under the same conditions as the simulation in FIG. 8. This graph shows that ΔR becomes small when the grating GR height Hgr is too low or too high. The grating GR height Hgr at which ΔR becomes maximum is approximately 200 nm. If the ΔR required for polarization control is 0.5%, it can be seen that the grating GR height Hgr is preferably approximately 140 nm to 260 nm (200 nm ± 60 nm).

[0062] As described above, the grating layer 95 is preferably made of a material with a refractive index of 2 or higher. Furthermore, the period of the irregularities of the grating GR is preferably equal to or less than the wavelength λ of the laser light. Furthermore, the height Hgr of the convex portions of the grating GR (depth of the concave portions) is preferably 200 nm±60 nm. This allows the light-emitting device 1 to effectively control the polarization of the laser light in one direction (for example, the Ry direction).

[0063] Second Embodiment FIG. 10 is a cross-sectional view showing an example configuration of a grating layer and a second reflecting mirror according to a second embodiment. The side surfaces of the concave or convex portions of the grating GR may be perpendicular to the surface F5, or may be inclined as shown in FIG. 10 . Even if the side surfaces of the concave or convex portions of the grating GR are formed in a forward tapered shape, the effect of the present technology is not lost. By forming the side surfaces of the concave or convex portions of the grating GR in a tapered shape in the process of forming the grating GR, in-plane variation in the shape of the grating GR is suppressed, and yield is improved. The other configurations of the second embodiment may be similar to those of the first embodiment. Therefore, the second embodiment can also achieve the same effects as the first embodiment.

[0064] (Third Embodiment) FIG. 11 is a cross-sectional view showing an example of the configuration of a grating layer and a second reflecting mirror according to a third embodiment. In the third embodiment, the inclination of the taper of the side surface of the grating GR is opposite to that of the second embodiment. That is, the side surface of the concave or convex portion of the grating GR is formed in an inverse tapered shape. In this way, even if the inclination of the taper of the side surface of the grating GR is opposite to that of the second embodiment, the effect of the present technology is not lost. The other configurations of the third embodiment may be the same as those of the second embodiment. Therefore, the third embodiment can obtain the same effect as that of the second embodiment.

[0065] (Fourth Embodiment) Fig. 12 is a cross-sectional view showing an example of the configuration of a light-emitting device according to a fourth embodiment. Fig. 13 is a plan view showing an example of the configuration of a light-emitting device according to the fourth embodiment. In the fourth embodiment, one BTJ 60, 70 and one grating GR are provided for one active layer 40 (jingle emitter structure). The other configurations of the fourth embodiment may be the same as those of the first embodiment. Therefore, the fourth embodiment can achieve the same effects as the first embodiment. The number of BTJs 60, 70 and the number of gratings GR provided for one active layer 40 are not limited.

[0066] (Method for Manufacturing Light-Emitting Device) Next, a method for manufacturing the light-emitting device 1 according to the above embodiment of the present disclosure will be described.

[0067] 14 to 22 are cross-sectional views showing an example of a method for manufacturing the light emitting device according to the above embodiment.

[0068] First, as shown in FIG. 14, an n-type InP buffer layer (not shown), a first reflecting mirror 20 (for example, a stacked film of n-type InP and n-type AlGaInAs), a first semiconductor layer 30 (n-type InP), an active layer (for example, a multi-quantum well layer with well layers of AlGaInAs and barrier layers of AlGaInAs) 40, a second semiconductor layer (for example, p-type InP) 50, a third semiconductor layer (for example, p ＋ type AlGaInAs) 60, a fourth semiconductor layer (n ＋ The layer 70 is epitaxially grown in this order.

[0069] The thickness of each layer of the first reflecting mirror 20 is, for example, λ / (4n). Here, when λ = 1450 nm, the refractive indices of InP and AlGaInAs are 3.18 and 3.45, respectively. Therefore, the thicknesses of the n-type InP layer and the n-type AlGaInAs layer are, for example, 114 nm and 105 nm. Silicon is used as the n-type impurity, and magnesium is used as the p-type impurity. The active layer 40 (e.g., an AlGaInAs / AlGaInAs multiple quantum well) has well and barrier layers whose compositions and thicknesses are designed to achieve an emission wavelength of 1450 nm. Introducing opposing strains of approximately 0.5% into the well and barrier layers is preferable for improving device characteristics. The impurity of the third semiconductor layer 60 constituting the BTJ is preferably carbon, which is difficult to diffuse. The impurity concentrations of the third and fourth semiconductor layers 60 and 70 are each 5×10 １９ cm －３ The impurity concentration of the other semiconductor layers is 5×10 １７ cm －３ ~1 x 10 １８ cm －３ That's fine.

[0070] Next, as shown in FIG. 15 , the material of the BTJs 60 and 70 is processed using lithography and wet etching. In the etching process, the BTJs 60 and 70 are wet-etched using a mixed aqueous solution containing sulfuric acid and hydrogen peroxide. The shape of the BTJs 60 and 70 as viewed from the Z direction may be circular, elliptical, or polygonal. For example, if the BTJs 60 and 70 are circular as viewed from the Z direction, their diameter is approximately 10 μm. The spacing between the multiple BTJs 60 and 70 is preferably 50 μm or more to suppress thermal interference. While two BTJs 60 and 70 are formed in FIG. 15 , the number of BTJs 60 and 70 per active layer 40 is not limited, as described above.

[0071] 16, a fifth semiconductor layer 80 is formed on the second semiconductor layer 50 and the fourth semiconductor layer 70 by MOCVD. The fifth semiconductor layer 80 is, for example, n-type InP, and has a thickness of 1×10 １８ cm －３ The impurity concentration is

[0072] Next, as shown in FIG. 17, lithography and dry etching are used to expose a portion of the upper surface of the first semiconductor layer 30 and the substrate 10 .

[0073] 18 , a material for the protective film 120 is deposited by CVD so as to cover the top surfaces of the fifth semiconductor layer 80 and the first semiconductor layer 30, as well as the side surfaces of the fifth semiconductor layer 80, the second semiconductor layer 50, the active layer 40, the first semiconductor layer 30, and the first reflecting mirror 20. The material for the protective film 120 is, for example, a silicon nitride film.

[0074] Next, the material of the protective film 120 is processed using lithography and etching techniques, thereby forming openings in regions where the first electrode 100, the second electrode 110, and the second reflecting mirror 90 are to be formed.

[0075] Next, the material of the first and second electrodes 100, 110 is deposited on the first semiconductor layer 30, the fifth semiconductor layer 80, and the protective film 120. The material of the first and second electrodes 100, 110 is, for example, a conductive metal such as Ti, Pt, or Au.

[0076] Next, the material of the first and second electrodes 100, 110 is processed using lithography and etching techniques. As a result, as shown in Fig. 18, the first electrode 100 is formed on the first semiconductor layer 30, and the second electrode 110 is formed on the fifth semiconductor layer 80. At this time, the material of the second electrode 110 in the region where the second reflector 90 is to be formed is removed.

[0077] Next, as shown in FIG. 19 , the material of the second reflector 90 (for example, SiO ２ and Ti ２ O ２ A laminated film with SiO ２ Film and Ti ２ O ２ The thickness of each film is λ / (4n). Here, if λ=1450 nm, then SiO ２ and Ti ２ O ２ The refractive indices of SiO are 1.45 and 2.15, respectively. ２ Film and Ti ２ O ２ The respective thicknesses of the films are, for example, 250 nm and 169 nm.

[0078] Next, the material of the grating layer 95 (for example, TiO ２ ) is epitaxially grown to a thickness of λ / (2n). Here, if λ=1450 nm, TiO ２ The refractive index of the grating layer 95 is 2.25. Therefore, the thickness of the grating layer 95 is, for example, 337 nm.

[0079] Next, using lithography, a resist film ER for electron beam lithography is applied onto the grating layer 95. Next, using an electron beam lithography device, an electron beam is irradiated onto the recessed areas where the grating GR will be formed. Next, the resist film ER is developed, and the resist film ER in the recessed areas of the grating GR is removed, as shown in FIG.

[0080] 21 , the grating layer 95 is processed by dry etching using the resist film ER as a mask. The depth of the grooves in the recesses of the grating layer 95 may be, for example, about 200 nm. The grooves may be limited to the grating layer 95 or may extend to the second reflecting mirror 90.

[0081] 22, the resist film ER is removed. The substrate 10 is then diced into individual semiconductor chips, which are then mounted on a heat sink or a wiring board. Metal wires are bonded to the first and second electrodes 100, 110, completing the light emitting device 1.

[0082] Fifth Embodiment Fig. 23 is a cross-sectional view showing an example of the configuration of a light-emitting device according to a fifth embodiment. In the fifth embodiment, the substrate 11 is made of, for example, GaAs. In this case, the first reflecting mirror 21 is made of, for example, a laminated film of GaAs and AlAs. The other configurations of the fifth embodiment may be the same as those of the first embodiment. Therefore, the fifth embodiment can achieve the same effects as the first embodiment.

[0083] In the fifth embodiment, a sacrificial layer (for example, an n-type InGaAs layer) (not shown) is epitaxially grown on the InP substrate 10. Each layer above the first semiconductor layer 30 according to the first embodiment is epitaxially grown on the sacrificial layer.

[0084] Separately, a first reflecting mirror (for example, a laminated film of GaAs and AlGaAs or AlAs) 21 is epitaxially grown on the GaAs substrate 11 .

[0085] Next, the InP substrate 10 and the sacrificial layer are removed.

[0086] Next, the layers above the first semiconductor layer 30 according to the first embodiment are attached onto the GaAs substrate 11 and the first reflecting mirror 21 .

[0087] Thereafter, the light emitting device 1 according to the fifth embodiment is completed through the steps described with reference to FIGS.

[0088] Sixth Embodiment FIG. 24 is a cross-sectional view showing a configuration example of a light-emitting device according to a sixth embodiment. In the sixth embodiment, instead of defining the light-emitting region by processing the BTJs 60 and 70, the light-emitting region is defined by forming a non-conductive region 140 in a portion of the third semiconductor layer 60, the fourth semiconductor layer 70, and the active layer 40. The non-conductive region 140 is formed by ion implantation of impurity ions (e.g., hydrogen ions, helium ions, or boron ions) into a portion of the third semiconductor layer 60, the fourth semiconductor layer 70, and the active layer 40. The non-conductive region 140 is non-conductive, and current flows intensively in the active layer 40 other than the non-conductive region 140. In this way, the non-conductive region 140 functions as a current confinement layer, concentrating the laser light at the position of the grating GR. As a result, polarization control of the laser light is facilitated.

[0089] Other configurations of the sixth embodiment may be the same as those of the first embodiment, and therefore the sixth embodiment can achieve the same effects as the first embodiment.

[0090] (Application Example to a Mobile Body) The technology according to the present disclosure (the present technology) can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of mobile body, such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, or a robot.

[0091] FIG. 25 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile object control system to which the technology according to the present disclosure can be applied.

[0092] The vehicle control system 12000 includes a plurality of electronic control units connected via a communication network 12001. In the example shown in Fig. 25, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an outside-vehicle information detection unit 12030, an inside-vehicle information detection unit 12040, and an integrated control unit 12050. Also shown as functional components of the integrated control unit 12050 are a microcomputer 12051, an audio / video output unit 12052, and an in-vehicle network I / F (Interface) 12053.

[0093] The drivetrain control unit 12010 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 12010 functions as a control device for a drive force generating device for generating a drive force of the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting the drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating a braking force of the vehicle.

[0094] The body system control unit 12020 controls the operation of various devices equipped in the vehicle body according to various programs. For example, the body system control unit 12020 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as headlamps, backup lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves transmitted from a portable device that serves as a key or signals from various switches can be input to the body system control unit 12020. The body system control unit 12020 receives these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

[0095] The outside-vehicle information detection unit 12030 detects information outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the outside-vehicle information detection unit 12030. The outside-vehicle information detection unit 12030 causes the imaging unit 12031 to capture images outside the vehicle and receives the captured images. The outside-vehicle information detection unit 12030 may perform object detection processing or distance detection processing for people, cars, obstacles, signs, characters on the road surface, etc. based on the received images.

[0096] The imaging unit 12031 is an optical sensor that receives light and outputs an electrical signal corresponding to the amount of light received. The imaging unit 12031 can output the electrical signal as an image or as distance measurement information. The light received by the imaging unit 12031 may be visible light or invisible light such as infrared light.

[0097] The in-vehicle information detection unit 12040 detects information inside the vehicle. For example, a driver state detection unit 12041 that detects the state of the driver is connected to the in-vehicle information detection unit 12040. The driver state detection unit 12041 includes, for example, a camera that captures an image of the driver, and the in-vehicle information detection unit 12040 may calculate the degree of fatigue or concentration of the driver based on the detection information input from the driver state detection unit 12041, or may determine whether the driver is dozing off.

[0098] The microcomputer 12051 can calculate control target values ​​for the driving force generating device, steering mechanism, or braking device based on the information inside and outside the vehicle acquired by the outside-vehicle information detection unit 12030 or the inside-vehicle information detection unit 12040, and output control commands to the drive system control unit 12010. For example, the microcomputer 12051 can perform cooperative control aimed at realizing the functions of an ADAS (Advanced Driver Assistance System), including vehicle collision avoidance or impact mitigation, following driving based on the distance between vehicles, maintaining vehicle speed, vehicle collision warning, vehicle lane departure warning, etc.

[0099] In addition, the microcomputer 12051 can perform cooperative control for the purpose of autonomous driving, which allows the vehicle to travel autonomously without relying on driver operation, by controlling the driving force generating device, steering mechanism, braking device, etc. based on information about the surroundings of the vehicle obtained by the outside vehicle information detection unit 12030 or the inside vehicle information detection unit 12040.

[0100] Furthermore, the microcomputer 12051 can output a control command to the body system control unit 12020 based on the information outside the vehicle acquired by the outside information detection unit 12030. For example, the microcomputer 12051 can control the headlamps according to the position of a preceding vehicle or an oncoming vehicle detected by the outside information detection unit 12030, and perform cooperative control aimed at preventing glare, such as switching from high beams to low beams.

[0101] The audio / video output unit 12052 transmits at least one of audio and video output signals to an output device capable of visually or audibly notifying the passengers of the vehicle or the outside of the vehicle of information. In the example of Fig. 25, the output devices are exemplified by an audio speaker 12061, a display unit 12062, and an instrument panel 12063. The display unit 12062 may include, for example, at least one of an on-board display and a head-up display.

[0102] FIG. 26 is a diagram showing an example of the installation position of the imaging unit 12031.

[0103] In FIG. 26, the imaging unit 12031 includes imaging units 12101, 12102, 12103, 12104, and 12105.

[0104] The imaging units 12101, 12102, 12103, 12104, and 12105 are provided, for example, at positions such as the front nose, side mirrors, rear bumper, back door, and the top of the windshield inside the vehicle cabin of the vehicle 12100. The imaging unit 12101 provided on the front nose and the imaging unit 12105 provided on the top of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 provided on the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 provided on the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The imaging unit 12105 provided on the top of the windshield inside the vehicle cabin is mainly used to detect preceding vehicles, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc.

[0105] 26 shows an example of the imaging ranges of the imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of the imaging unit 12101 provided on the front nose, imaging ranges 12112 and 12113 indicate the imaging ranges of the imaging units 12102 and 12103 provided on the side mirrors, respectively, and imaging range 12114 indicates the imaging range of the imaging unit 12104 provided on the rear bumper or back door. For example, by overlaying the image data captured by the imaging units 12101 to 12104, an overhead image of the vehicle 12100 viewed from above can be obtained.

[0106] At least one of the image capturing units 12101 to 12104 may have a function of acquiring distance information. For example, at least one of the image capturing units 12101 to 12104 may be a stereo camera made up of multiple image capturing elements, or may be an image capturing element having pixels for phase difference detection.

[0107] For example, based on the distance information obtained from the imaging units 12101 to 12104, the microcomputer 12051 can calculate the distance to each three-dimensional object within the imaging ranges 12111 to 12114 and the change in this distance over time (relative speed with respect to the vehicle 12100), thereby extracting as a preceding vehicle, in particular, the three-dimensional object that is the closest three-dimensional object on the path of the vehicle 12100 and traveling in approximately the same direction as the vehicle 12100 at a predetermined speed (e.g., 0 km / h or higher). Furthermore, the microcomputer 12051 can set a vehicle-to-vehicle distance to be maintained in advance in front of the preceding vehicle, and perform automatic braking control (including follow-up stop control), automatic acceleration control (including follow-up start control), etc. In this way, cooperative control can be performed for the purpose of autonomous driving, which allows the vehicle to travel autonomously without relying on driver operation.

[0108] For example, the microcomputer 12051 classifies and extracts three-dimensional object data regarding three-dimensional objects into two-wheeled vehicles, ordinary vehicles, large vehicles, pedestrians, utility poles, and other three-dimensional objects based on distance information obtained from the imaging units 12101 to 12104, and can use the data for automatic obstacle avoidance. For example, the microcomputer 12051 distinguishes obstacles around the vehicle 12100 into obstacles that are visible to the driver of the vehicle 12100 and obstacles that are difficult to see. The microcomputer 12051 then determines a collision risk that indicates the risk of collision with each obstacle, and when the collision risk is equal to or greater than a set value and a collision is possible, the microcomputer 12051 can provide driving assistance for collision avoidance by outputting an alarm to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or avoidance steering via the drive system control unit 12010.

[0109] At least one of the image capturing units 12101 to 12104 may be an infrared camera that detects infrared rays. For example, the microcomputer 12051 can recognize a pedestrian by determining whether a pedestrian is present in the images captured by the image capturing units 12101 to 12104. Such pedestrian recognition is performed, for example, by extracting feature points from the images captured by the image capturing units 12101 to 12104 as infrared cameras and performing pattern matching on a series of feature points that indicate the outline of an object to determine whether the object is a pedestrian. When the microcomputer 12051 determines that a pedestrian is present in the images captured by the image capturing units 12101 to 12104 and recognizes the pedestrian, the audio / image output unit 12052 controls the display unit 12062 to superimpose a rectangular outline on the recognized pedestrian for emphasis. The audio / image output unit 12052 may also control the display unit 12062 to display an icon or the like indicating the pedestrian at a desired position.

[0110] The above describes an example of a vehicle control system to which the technology according to the present disclosure can be applied. The technology according to the present disclosure can be applied to, for example, a laser oscillator device for distance measurement used in the image capture unit 12031, etc., among the above-described configurations.

[0111] The present technology can be configured as follows.

[0112] (1) A light emitting device comprising: a first reflecting mirror formed by laminating a plurality of types of semiconductor materials having different refractive indices, and having a first surface and a second surface opposite the first surface; a second reflecting mirror formed by laminating a plurality of types of dielectric materials having different refractive indices, and having a third surface and a fourth surface opposite the third surface; an active layer provided between the first surface of the first reflecting mirror and the fourth surface of the second reflecting mirror, and emitting light when electric power is applied; and a concavo-convex layer formed of a dielectric material, provided on the third surface of the second reflecting mirror, and having a concavo-convex shape on a light emitting surface from which light from the active layer is emitted.

[0113] (2) The light emitting device according to (1), wherein the concavo-convex layer has a refractive index equal to or higher than that of the plurality of types of dielectric material layers constituting the second reflecting mirror.

[0114] (3) The light-emitting device according to (1) or (2), wherein the refractive index of the dielectric material constituting the uneven layer is 2 or more.

[0115] (4) The light-emitting device according to (2), wherein the uneven layer is made of the same material as the dielectric material layer having the highest refractive index among the plurality of types of dielectric material layers constituting the second reflecting mirror.

[0116] (5) The dielectric material constituting the uneven layer is TiO ２ , Ta ２ O ５ , SiN, or amorphous silicon.

[0117] (6) Among the plurality of types of dielectric material layers constituting the second reflecting mirror, the dielectric material layer having a low refractive index is made of SiO ２ or MgO.

[0118] (7) The light-emitting device according to any one of (1) to (6), wherein the uneven shape of the uneven layer is formed by a plurality of grooves extending in a first direction in the light-emitting surface, and the period of the uneven shape arranged in a second direction perpendicular to the first direction in the light-emitting surface is equal to or less than the wavelength of light emitted from the light-emitting surface.

[0119] (8) The light-emitting device according to any one of (1) to (7), wherein the height of the convex portions of the concave-convex shape of the concave-convex layer is 200 nm±60 nm.

[0120] (9) The light emitting device according to any one of (1) to (8), wherein a side surface between the concave and convex portions of the concave-convex shape of the concave-convex layer is substantially perpendicular or inclined to the light emitting surface.

[0121] (10) The light emitting device according to any one of (1) to (9), wherein the active layer is made of AlGaInAs, and the wavelength of light from the active layer is 1.2 μm to 2 μm.

[0122] (11) The light-emitting device according to any one of (1) to (10), further comprising a plurality of tunnel junction layers provided between the active layer and the second reflecting mirror and divided with respect to the active layer, wherein the plurality of uneven shapes of the uneven layer are provided corresponding to the plurality of tunnel junction layers.

[0123] (12) The light emitting device according to (11), wherein the plurality of concave and convex shapes overlap the plurality of tunnel junction layers in a plan view seen from the stacking direction of the plurality of types of dielectric materials.

[0124] (13) The light-emitting device according to (11) or (12), wherein the plurality of concave-convex shapes and the plurality of tunnel junction layers have a substantially circular, substantially elliptical, or substantially polygonal shape in a plan view seen from a stacking direction of the plurality of types of dielectric materials.

[0125] (14) The light emitting device according to any one of (1) to (13), further comprising a substrate including InP provided on the second surface side of the first reflecting mirror, wherein the first reflecting mirror has a layered structure of InP and AlGaInAs.

[0126] (15) The light-emitting device according to any one of (1) to (13), further comprising a substrate including GaAs provided on the second surface side of the first reflecting mirror, wherein the first reflecting mirror has a layered structure of GaAs and AlGaAs or AlAs.

[0127] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present disclosure. Furthermore, the effects described in this specification are merely examples and are not intended to be limiting, and other effects may also be obtained.

[0128] REFERENCE SIGNS LIST 1 Light emitting device 10 Substrate 20 First reflecting mirror 30 First semiconductor layer 40 Active layer 50 Second semiconductor layer 60 Third semiconductor layer 70 Fourth semiconductor layer 80 Fifth semiconductor layer 90 Second reflecting mirror 95 Grating layer 100 First electrode 110 Second electrode 120 Protective film GR Grating

Claims

1. A light emitting device comprising: a first reflecting mirror constructed by laminating multiple types of semiconductor materials with different refractive indices and having a first surface and a second surface opposite the first surface; a second reflecting mirror constructed by laminating multiple types of dielectric materials with different refractive indices and having a third surface and a fourth surface opposite the third surface; an active layer provided between the first surface of the first reflecting mirror and the fourth surface of the second reflecting mirror and emitting light when power is applied; and a concavo-convex layer made of a dielectric material and provided on the third surface of the second reflecting mirror and having a concavo-convex shape on the light emitting surface from which light from the active layer is emitted.

2. The light emitting device according to claim 1, wherein the uneven layer has a refractive index equal to or higher than that of the plurality of types of dielectric material layers constituting the second reflecting mirror.

3. The light emitting device according to claim 1, wherein the refractive index of the dielectric material constituting the uneven layer is 2 or more.

4. The light emitting device according to claim 2, wherein the uneven layer is made of the same material as the dielectric material layer having the highest refractive index among the plurality of types of dielectric material layers constituting the second reflector.

5. The dielectric material constituting the uneven layer is TiO ２ , Ta ２ O ５ 2. The light emitting device of claim 1, wherein the insulating layer is made of either SiN or amorphous silicon.

6. The low refractive index dielectric material layer among the plurality of types of dielectric material layers constituting the second reflecting mirror is made of SiO ２ The light-emitting device according to claim 1 , wherein the material is selected from the group consisting of fluorine, methyl methacrylate ...

7. The light-emitting device according to claim 1, wherein the uneven shape of the uneven layer is constituted by a plurality of grooves extending in a first direction within the light-emitting surface, and the period of the uneven shape arranged in a second direction perpendicular to the first direction within the light-emitting surface is equal to or less than the wavelength of light emitted from the light-emitting surface.

8. The light emitting device according to claim 1, wherein the height of the convex portions of the concave-convex shape of the concave-convex layer is 200 nm±60 nm.

9. The light emitting device according to claim 1, wherein the side surface between the recesses and protrusions of the uneven shape of the uneven layer is substantially perpendicular or inclined to the light emitting surface.

10. The light emitting device according to claim 1, wherein the active layer is made of AlGaInAs, and the wavelength of light from the active layer is 1.2 μm to 2 μm.

11. The light emitting device according to claim 1, further comprising a plurality of tunnel junction layers provided between the active layer and the second reflecting mirror and separated from the active layer, wherein the plurality of uneven shapes of the uneven layer are provided corresponding to the plurality of tunnel junction layers.

12. The light emitting device according to claim 11, wherein, in a plan view seen from the stacking direction of the plurality of types of dielectric materials, the plurality of concave and convex shapes overlap the plurality of tunnel junction layers, respectively.

13. The light-emitting device according to claim 11, wherein, in a plan view seen from the stacking direction of the plurality of types of dielectric materials, the plurality of uneven shapes and the plurality of tunnel junction layers have a substantially circular, substantially elliptical, or substantially polygonal shape.

14. The light emitting device according to claim 1, further comprising a substrate containing InP provided on the second surface side of the first reflecting mirror, wherein the first reflecting mirror has a layered structure of InP and AlGaInAs.

15. The light emitting device according to claim 1, further comprising a substrate containing GaAs provided on the second surface side of the first reflecting mirror, wherein the first reflecting mirror has a layered structure of GaAs and AlGaAs or AlAs.

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