JP2019197933A - Surface emission quantum cascade laser - Google Patents

Abstract

To provide a surface emission quantum cascade laser which is enhanced in heat dissipation property, and reduced in leak of light from a chip side face.SOLUTION: A surface emission quantum cascade laser comprises an active layer and a first semiconductor layer. The first semiconductor layer is provided on the active layer, and has a first face. The first face includes: an internal region where first pits form first two-dimensional grid; and an outer peripheral region where second pits form a second two-dimensional grid. A grid spacing of the first pits is m times that of the second pits. The two-dimensional shape of the first pits is asymmetric with respect to a line which runs through a center of mass of the first two-dimensional shape and which is in parallel with at least one side of the first two-dimensional grid. The two-dimensional shape of the second pits is symmetric with respect to each of lines which run through a center of mass of the two-dimensional shape and which are in parallel with all of sides of the second two-dimensional grid. A laser beam has an emission wavelength corresponding to the grid spacing of the second pits and is emitted from the internal region mostly in a vertical direction to the active layer.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to surface emitting quantum cascade lasers.

  The surface emitting quantum cascade laser oscillates in a TM mode and emits laser light having a terahertz wavelength from infrared rays.

  The optical resonator can be composed of a two-dimensional photonic crystal provided close to the active layer.

  A surface emitting quantum cascade laser having a two-dimensional photonic crystal operates as a surface emitting type capable of emitting laser light in a direction perpendicular to the surface of the active layer.

  However, if the operating current is increased to obtain a high output, the chip operating temperature increases and light leakage from the side surface of the chip increases.

JP 2014-197659 A

  Provided is a surface-emitting quantum cascade laser with improved heat dissipation and reduced light leakage from a side surface of a chip.

  The surface emitting quantum cascade laser according to the embodiment includes an active layer, a first semiconductor layer, an insulator layer, an upper electrode, and a lower electrode. The active layer is formed by laminating a plurality of quantum well layers and can emit laser light by intersubband transition. The first semiconductor layer is a first semiconductor layer provided on the active layer and having a first surface, wherein the first surface has a first two-dimensional lattice formed by a first pit. The inner area to be configured and the second pit include an outer peripheral area that forms the second two-dimensional lattice, and the outer peripheral area surrounds the inner area. The insulator layer covers a side surface and a bottom surface of the first pit, a side surface and a bottom surface of the second pit, and a portion of the internal region where the first pit is not provided. The upper electrode covers a portion of the outer peripheral region where the second pit is not provided, and fills the first pit and the second pit through the insulator layer. The lower electrode is a lower electrode provided on the surface of the active layer opposite to the surface on which the first semiconductor layer is provided, and having an opening at the center. In a plan view, a part of the inner region is included in the opening. The first planar shape of the opening end of the first pit is asymmetric with respect to a line passing through the center of gravity of the first planar shape and parallel to at least one side of the first two-dimensional lattice.

1 is a schematic perspective view of a surface emitting quantum cascade laser according to a first embodiment. 2A is a partial schematic plan view of the surface emitting quantum cascade laser according to the first embodiment, and FIG. 2B is a schematic plan view of the first pit. 3A is a schematic cross-sectional view taken along the line AA in FIG. 2A, and FIG. 3B is a schematic cross-sectional view taken along the line BB. FIG. 4A is a schematic cross-sectional view of an inner region according to a first modification of the first embodiment, and FIG. 4B is a schematic cross-sectional view of an outer peripheral region. FIG. 5A is a graph showing the temperature distribution of the surface emitting quantum cascade laser according to the first embodiment, and FIG. 5B is a graph showing the temperature distribution of the surface emitting quantum cascade laser according to the comparative example. is there. It is a model perspective view of the surface emitting quantum cascade laser concerning 2nd Embodiment. It is a partial schematic top view of the surface emitting quantum cascade laser concerning 2nd Embodiment. 8A is a schematic cross-sectional view taken along the line AA in FIG. 7, and FIG. 8B is a schematic cross-sectional view taken along the line BB. FIG. 9A is a schematic cross-sectional view of an internal region according to a first modification of the second embodiment, and FIG. 9B is a schematic cross-sectional view of an outer peripheral region. It is a model perspective view of the surface emitting quantum cascade laser concerning 3rd Embodiment. FIG. 11A is a schematic cross-sectional view taken along the line CC of the third embodiment, FIG. 11B is a schematic cross-sectional view taken along the line DD of FIG. 10, and FIG. FIG. 11 is a schematic cross-sectional view taken along the line DD of FIG. It is a graph explaining the temperature distribution of the surface emitting quantum cascade laser concerning 3rd Embodiment. FIGS. 13A to 13C are schematic cross-sectional views of a surface emitting quantum cascade laser according to the fourth embodiment. FIG. 14A is a schematic plan view of a surface emitting quantum cascade laser according to the fifth embodiment, and FIG. 14B is a schematic plan view of an internal region including a regular triangular lattice. It is a schematic plan view of the surface emitting quantum cascade laser according to the sixth embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic perspective view of the surface emitting quantum cascade laser according to the first embodiment.
2A is a partial schematic plan view of the surface-emitting quantum cascade laser according to the first embodiment except for the upper electrode, and FIG. 2B is a schematic plan view of the first pit.

  A surface emitting quantum cascade laser (Surface Emitting Quantum Cascade Laser) 5 includes an active layer 20 and a first semiconductor layer 30. The active layer 20 is formed by laminating a plurality of quantum well layers, and can emit laser light 80 by intersubband transition. The first semiconductor layer 30 is provided on the active layer 20 and has a first surface 32. The first surface 32 includes an inner region 33 in which the first pits 61 constitute a first two-dimensional lattice and an outer peripheral region 34 in which the second pits 64 constitute a second two-dimensional lattice. The first semiconductor layer 30 can include a cladding layer on the active layer 20 side. As shown in FIG. 2A, it is preferable that the first pit 61 and the second pit 64 do not overlap. The two-dimensional lattice shown in FIG. 2 is a square lattice, but may be a rectangular lattice.

  The lattice interval P 1 of the first pit 61 is twice the lattice interval P 2 of the second pit 64, and the outer peripheral region 34 surrounds the inner region 33.

  The planar shape of the opening end of the first pit 61 is asymmetric with respect to a line (50 or 51) passing through the center of gravity G1 of the planar shape and parallel to at least one side of the first two-dimensional lattice. The planar shape of the opening end of the second pit 64 is symmetric with respect to a line passing through the planar center of gravity G2 and parallel to all the sides (52 and 53) of the second two-dimensional lattice. The laser beam 80 is emitted from the inner region 33 in a direction substantially perpendicular to the active layer 20. In the present specification, the substantially vertical direction is 81 ° or more and 99 ° or less with respect to the surface of the active layer 20.

  The planar shape of the opening end of the first pit 61 can include a plurality of point-symmetric shapes. For example, as shown in FIG. 2B, the first pit 61 is obtained by cutting three cylinders 61 a, 61 b, 61 c from the first surface 32. In FIG. 2B, the three cylinders 61a, 61b, 61c are provided so as to be inscribed in a right-angled isosceles triangle 61d in plan view. However, the embodiment of the present invention is not limited to this. For example, the cylinders do not need to touch each other in plan view. If they act as grating points of the diffraction grating at a predetermined wavelength, they may be separated from each other or overlap each other. Further, the second pit 64 may be a cylinder (a planar shape is a circle) or the like.

  The surface emitting quantum cascade laser 5 includes an upper electrode 35 provided in a portion of the inner region 33 where the first pit 61 is not provided and a portion of the outer peripheral region 34 where the second pit 64 is not provided, an active layer 20, the second semiconductor layer 39 provided on the surface opposite to the surface on which the first semiconductor layer 30 is provided, and the active layer 20 among the surfaces of the second semiconductor layer 39. And a lower electrode 90 provided on the surface on the opposite side to the other side. The second semiconductor layer 39 can include a cladding layer 39a, a substrate 39b, and the like.

  When the first semiconductor layer 30 and the second semiconductor layer 39 each include an n-type layer, carriers that cause an intersubband transition are electrons. The thickness of the first semiconductor layer 30 can be several μm, the thickness of the second semiconductor layer 39 can be several μm, and the like.

  The carriers pass through the quantum well layer by the electric field applied to the upper electrode 35 and the lower electrode 90, thereby causing intersubband transition, and emitting single mode laser light having a wavelength of 2 μm to 100 μm.

  The lattice interval P 1 of the first pit 61 and the lattice interval P 2 of the second pit 64 are set to about the wavelength in the medium of the laser beam 80.

  For reference, in the case of a one-dimensional grating, the laser beam extraction direction will be described. The quantum cascade laser device mainly emits TM (Transverse Magnetic) waves. In the waveguide, when the diffraction angle by the diffraction grating is θ, the order of the diffraction grating is M (integer), and the diffraction order is m (integer), the following equation holds.

cos θ = 1 ± 2 m / M Equation (1)

  In the case of the first-order diffraction grating, according to the equation (1), the m = 0 mode emits in the 0 ° direction and the m = 1 mode emits in the 180 ° direction, but not in the vertical direction.

  In the case of the second-order diffraction grating, the mode of m = 1 is scattered in the ± 90 ° direction with respect to the waveguide according to the equation (1). Since the mode of m = 0 and m = 2 is scattering in the direction parallel to the waveguide, the substantially emitted light is only in the ± 90 ° direction.

  3A is a schematic cross-sectional view taken along the line AA in FIG. 2A, and FIG. 3B is a schematic cross-sectional view taken along the line BB.

  As shown in FIG. 3A, the first pits 61 are arranged in a two-dimensional lattice pattern in the internal region 33 including the second-order diffraction grating. The current injected into the active layer 20 causes the intersubband transition of carriers. Laser light 82 is generated using the second-order diffraction grating as a resonator, and TM waves linearly polarized in a predetermined direction on a plane parallel to the surface of the active layer 20 propagate.

  In the first pit 61, even if the electric field (or magnetic field) in the horizontal plane is integrated, it does not become zero. For this reason, TM waves leak in the vertical direction of the active layer 20. The TM wave is emitted in a substantially vertical direction with respect to the active layer 20 while being linearly polarized in a predetermined direction in a horizontal plane. At this time, the light emitted from the respective pits is strengthened by the two-dimensional grating and emitted in the vertical direction. If the planar shape of the first pit 61 is symmetrical with respect to a line passing through the center of gravity and parallel to all the sides of the two-dimensional lattice (for example, a circle), the electric field in the horizontal plane in the first pit 61 is assumed. The integral value becomes zero, and TM waves leaking in the vertical direction are reduced. That is, when the first pit 61 forms a second-order diffraction grating, diffracted light can be efficiently emitted in the ± 90 ° direction.

As shown in FIG. 3B, in the outer peripheral region 34 including the first-order diffraction grating, the second pits 64 are arranged in a two-dimensional lattice shape. The first lattice interval P1 is twice the second lattice interval P2. For example, if the periphery of the second pit 64 is InP, the lattice interval P2 is 1.467 μm and the in-vacuum wavelength λ ₀ is 4.771 μm. In the outer peripheral region 34, the diffraction direction is only the direction parallel to the surface of the active layer 20. For this reason, no light emitted in the direction perpendicular to the first surface 32 can exist in the outer peripheral region 34.

  The outer peripheral region 34 is generated in the active layer 20, propagates in the outer peripheral region 34 in a direction parallel to the surface of the active layer 20, and reflects the laser beam 82 directed toward the side surface of the chip by the first-order diffraction grating. It functions as a distributed reflector (DBR) that returns toward the front. In the outer peripheral region 34, the light intensity of the laser light 82 from the inner region 33 side toward the outer side surface S rapidly decreases as it goes toward the chip side surface S. For this reason, the laser beam leaking outside from the chip side surface S can be reduced. As a result, the luminous efficiency can be increased and unnecessary radiation can be suppressed to increase safety. If the leakage light is large, the emission mode is likely to change, which is not preferable.

  The depth of the first pit 61 shown in FIG. 3A is D1, and the depth of the second pit 64 shown in FIG. 3B is also D1. The depth of the pit reaches the active layer 20, and a recess is provided on the upper surface side of the active layer 20. If the concave portion of the active layer 20 is too deep, optical coupling with the photonic crystal becomes dense, but this is not preferable because the number of stacked quantum well layers decreases.

  The active layer 20 has a configuration in which intersubband transition light-emitting regions composed of quantum well layers including well layers and barrier layers and relaxation regions are alternately stacked. The quantum well includes, for example, a well layer doped with Si and made of In0.669Ga0.331As and a barrier layer doped with Si and made of In0.362Al0.638As. The quantum well layer may further include, for example, 50 to 200 layers of a multi-quantum well (MQW) structure, which is a unit structure in which at least two well layers and a plurality of barrier layers are alternately stacked. preferable. The thickness of the active layer 20 can be set to 1 to 4 μm, for example. The relaxation region can also include a quantum well layer. The second semiconductor layer 39 can further include a substrate 39b made of InP, GaAs, or the like.

FIG. 4A is a schematic cross-sectional view of an inner region according to a first modification of the first embodiment, and FIG. 4B is a schematic cross-sectional view of an outer peripheral region.
The depth of the first pit 61 in the inner region 33 shown in FIG. 4A is D2, and the depth of the second pit 64 in the outer peripheral region 34 shown in FIG. 4B is also D2. In this modification, the pit depth D2 is smaller than the thickness of the first semiconductor layer 30, and the bottom surfaces of the first pit 61 and the second pit 64 do not reach the active layer 20. If the distance between the bottom surface of the first pit 61 (61a, 61b, 61c) and the surface of the active layer 20 and the distance between the bottom surface of the second pit 64 and the active layer 20 are several μm or less, for example, Optical coupling between the layer 20 and the two-dimensional grating is possible.

FIG. 5A is a graph showing the temperature distribution of the surface emitting quantum cascade laser according to the first embodiment, and FIG. 5B is a graph showing the temperature distribution of the surface emitting quantum cascade laser according to the comparative example. is there.
5A and 5B, the vertical axis represents temperature, and the horizontal axis represents the horizontal position in the chip cross section. As shown in FIG. 5B, the surface-emitting quantum cascade laser 105 according to the comparative example has a photonic crystal constituting a second-order diffraction grating arranged in a two-dimensional lattice. The planar shape of the pits of the secondary diffraction grating is asymmetric with respect to a line passing through the center of gravity of the planar shape and parallel to at least one side of the two-dimensional grating.

  It is assumed that the injection current I1 of the first embodiment and the injection current I2 of the comparative example 105 are equal, and the extracted laser light outputs are substantially equal. In the first embodiment, since the outer peripheral region 34 is provided so as to surround the inner region 33 that is a light extraction region, the area of the active layer 20 is larger than the area of the active layer of the comparative example 105. The thermal resistance of the first embodiment is lower than the thermal resistance of the comparative example 105, and the peak temperature T1 in the active layer 20 can be lower than the peak temperature T2 in the active layer of the comparative example 105. For this reason, the refractive index change in the active layer 20 can be reduced, and the oscillation mode is stabilized. Further, efficiency reduction and failure rate increase due to temperature rise are suppressed.

  Laser light traveling downward from the active layer is reflected by the lower electrode 90 and is emitted from above as laser light 80 together with laser light traveling upward from the active layer 20.

FIG. 6 is a schematic perspective view of the surface emitting quantum cascade laser according to the second embodiment.
FIG. 7 is a partial schematic plan view excluding the upper electrode of the surface emitting quantum cascade laser according to the second embodiment.

  The surface emitting quantum cascade laser 5 includes an active layer 20 and a first semiconductor layer 30. The first surface 32 includes an inner region 33 in which the first pit 63 constitutes a first two-dimensional lattice and an outer peripheral region 34 in which the second pit 64 constitutes a second two-dimensional lattice. As shown in FIG. 7, it is preferable that the first pit 63 and the second pit 64 do not overlap.

  The lattice interval P 1 of the first pit 63 is twice the lattice interval P 2 of the second pit 64, and the outer peripheral region 34 surrounds the inner region 33.

  The planar shape of the open end of the first pit 63 is asymmetric with respect to a line (50 or 51) passing through the center of gravity G1 of the planar shape and parallel to at least one side of the first two-dimensional lattice. The planar shape of the open end of the second pit 64 is symmetric with respect to a line passing through the planar center of gravity G2 and parallel to all the sides (52 and 53) of the second two-dimensional lattice. The laser beam 80 is emitted from the inner region 33 in a direction substantially perpendicular to the active layer 20.

  6 and 7, the first pit 63 is a right triangular prism (planar shape is a right isosceles triangle), and the second pit 64 is a cylinder (planar shape is a circle). However, the planar shape of the first pit 63 is not limited to a right-angled isosceles triangle and may be asymmetric.

  When the two-dimensional lattice is a square lattice or a rectangular lattice, the first planar shape (not limited to a circle or a triangle) of the opening end of the first pit 63 passes through the center of gravity G1 of the first planar shape and the first It is more preferable to make it asymmetric with respect to the lines (50 and 51) parallel to the two sides of the two-dimensional lattice because the optical anisotropy is further increased.

  The surface emitting quantum cascade laser 5 includes an upper electrode 35 provided in a portion of the inner region 33 where the first pit 63 is not provided and a portion of the outer peripheral region 34 where the second pit 64 is not provided, an active layer 20, the second semiconductor layer 39 provided on the surface opposite to the surface on which the first semiconductor layer 30 is provided, and the active layer 20 among the surfaces of the second semiconductor layer 39. And a lower electrode 90 provided on the surface on the opposite side to the other side.

  The lattice interval P 1 of the first pit 63 and the lattice interval P 2 of the second pit 64 are set to about the wavelength in the medium of the laser beam 80.

  8A is a schematic cross-sectional view taken along the line AA in FIG. 7, and FIG. 8B is a schematic cross-sectional view taken along the line BB.

  In the internal region 33 including the second-order diffraction grating, the first pits 63 are arranged in a two-dimensional lattice shape. The current injected into the active layer 20 causes the intersubband transition of carriers. Laser light 82 is generated using the second-order diffraction grating as a resonator, and TM waves linearly polarized in a predetermined direction on a plane parallel to the surface of the active layer 20 propagate.

FIG. 9A is a schematic cross-sectional view of an internal region according to a first modification of the second embodiment, and FIG. 9B is a schematic cross-sectional view of an outer peripheral region.
The depth of the first pit in the internal region 33 shown in FIG. 9A is D2, and the depth of the second pit in the outer peripheral region 34 shown in FIG. 9B is also D2. In this modification, the depth D2 of the first pit 63 and the second pit 64 is smaller than the thickness of the first semiconductor layer 30, and the bottom surfaces of the first pit 63 and the second pit 64 are the active layer. 20 is not reached. If the distance between the bottom surface of the first pit 63 and the surface of the active layer 20 and the distance between the bottom surface of the second pit 64 and the active layer 20 are several μm or less, for example, the active layer 20 and the two-dimensional lattice Can be optically coupled.

FIG. 10 is a schematic perspective view of a surface emitting quantum cascade laser according to the third embodiment.
11A is a schematic cross-sectional view taken along the line CC in FIG. 10, FIG. 11B is a schematic cross-sectional view taken along the line DD in FIG. 10, and FIG. FIG. 11 is a schematic cross-sectional view taken along the line DD of FIG.

It is assumed that the first surface 32 of the first semiconductor layer 30 is the same as the first surface 32 shown in FIG. As shown in FIG. 11A, insulation is performed so as to cover the inner surface (side surface and bottom surface) of the first pit 63 in the inner region 33 and the inner surface (side surface 64b and bottom surface) of the second pit 64 in the outer peripheral region 34. The body layer 50 is provided, and the upper electrode 36 is provided so as to cover the portion of the first surface 32 of the first semiconductor layer 30 that is not covered by the insulator layer 50 and the surface of the insulator layer 50. In this case, the internal region 33 functions as a periodic structure for surface light emission. The insulator layer 50 can be Si ₃ N ₄ , SiO ₂ , ZnSe, CdTe, or the like.

  An opening 90 a is provided in the lower electrode 90 so as to overlap with a part of the inner region 33 in plan view. Therefore, the laser light 80 emitted from the photonic crystal constituting the two-dimensional lattice is reflected by the upper electrode 36, passes through the active layer 20 again, and directly travels from the active layer 20 toward the opening 90a. At the same time, the laser beam 80 is emitted from the opening 90a in a substantially vertical direction.

  The first electrode pit 63 and the second pit 64 are filled with the upper electrode 36 via the insulator layer 50. For this reason, the generated heat can be easily discharged from the upper electrode 36 to the outside through a heat sink or the like. For this reason, the peak temperature in the active layer 20 is further reduced.

  FIG. 11C is a modification of the second pit, and shows a trench structure in which a part of the groove of the second pit 64 in the outer peripheral region 34 is deep. For example, when the wavelength is 5 [mu] m and the groove depth D4 is 5 to 10 [mu] m, the reflectance is increased and the optical loss is increased. Even if the number of the second regions 34 arranged along the direction toward the chip side surface of the two-dimensional grating is reduced to several, the reflectance can be increased, and the chip size can be reduced.

FIG. 12 is a graph illustrating the temperature distribution in the active layer of the surface emitting quantum cascade laser according to the third embodiment.
The vertical axis represents temperature, and the horizontal axis represents the horizontal position. Assuming that the opening 90a is provided at the center of the lower electrode 90, the injected current in the internal region 33 in the injected current I3 can be reduced from the injected current in the outer peripheral region 34. As a result, the heat generated in the internal region 33 is reduced and the heat source can be dispersed outward, so that the temperature distribution can be made closer to the bimodality and the temperature increase in the internal region 33 can be further suppressed. When the injection current I3 is equal to the injection current I1 of the first embodiment, the peak temperature T3 can be lower than the peak temperature T1 in FIG. 5A (T2>T1> T3). Of the laser light generated in the active layer, the light directed upward is reflected by the upper electrode 36 and emitted from the opening 90 a as the laser light 80.

FIG. 13A is a schematic cross-sectional view of the inner region of the fourth embodiment, FIG. 13B is a schematic cross-sectional view of the outer peripheral region of the fourth embodiment, and FIG. 13C is the fourth embodiment. It is a schematic cross section of the outer periphery area | region of a modification.
FIG. 13A is a schematic cross-sectional view taken along the line CC in FIG. FIGS. 13B and 13C are schematic cross-sectional views along the line DD in FIG.

It is assumed that the first surface 32 of the first semiconductor layer 30 is the same as the first surface 32 shown in FIG. As shown in FIG. 13A, the inner surface (side surface and bottom surface) of the first pit 63 in the inner region 33, the inner surface (side surface and bottom surface) of the second pit 64 in the outer peripheral region 34, and the first semiconductor An insulator layer 50 is provided so as to cover the portion of the first surface 32 of the layer 30. Furthermore, an upper electrode 36 is provided so as to cover the surface of the insulator layer 50. In this case, the internal region 33 functions as a periodic structure for surface light emission. The insulator layer 50 can be Si ₃ N ₄ , SiO ₂ , ZnSe, CdTe, or the like.

  An opening 90a is provided in a portion of the lower electrode 90 including a part of the inner region 33 in plan view. For this reason, the laser light 80 emitted from the photonic crystal constituting the two-dimensional lattice is reflected by the upper electrode 36, passes through the active layer 20 again, and is lasered together with the laser light directed from the active layer 20 toward the opening 90a. Light 80 is emitted from the opening 90a in a substantially vertical direction.

  The first electrode pit 63 and the second pit 64 are filled with the upper electrode 36 via the insulator layer 50. For this reason, the generated heat can be easily discharged from the upper electrode 36 to the outside through a heat sink or the like. For this reason, the peak temperature in the active layer 20 is further reduced.

  FIG. 13C shows a trench structure in which a part of the second pit 64 in the outer peripheral region 34 is deep. For example, when the wavelength is 5 [mu] m and the groove depth D4 is 5 to 10 [mu] m, the reflectance is increased and the optical loss is increased. Even if the number of the second regions 34 arranged along the direction toward the chip side surface of the two-dimensional grating is reduced to several, the reflectance can be increased, and the chip size can be reduced.

  The light emitting layer of a conventional pn junction laser diode (LD) that emits light by recombination of electrons and holes acts as a light absorption layer for the emission wavelength when the current injection density is low. For this reason, if there is a region where current injection is not performed in the light emitting layer, the region becomes a light absorption region, which causes a decrease in performance such as an increase in laser threshold current. On the other hand, the light absorption layer of the quantum cascade laser has very little light absorption with respect to the emission wavelength even when no current is injected, and light absorption in a region where no current is injected does not deteriorate the performance. For this reason, even if it is used for light extraction without performing current injection in the inner region 33 as in the present embodiment, and the current injection is performed in the outer peripheral region 34, the performance does not deteriorate.

  In this structure, the laser light generated in the outer peripheral region 34 can be collected in a region where the mode control of the inner region 33 is easy and can be extracted from the inner region 33 as single mode light. The light density is increased by collecting light, but since no current is injected, the temperature rise and temperature difference are smaller than in the current injection region, and stable laser oscillation can be expected. Since the area of the outer peripheral region 34 that generates light can be made larger than the area of the inner region 33 that is mode-controlled and light can be extracted, current density in the outer peripheral region can be reduced and heat dissipation can be improved. For this reason, the operation at a high output is remarkably stable as compared with the conventional pn junction laser diode.

FIG. 14A is a schematic plan view of a surface emitting quantum cascade laser according to the fifth embodiment, and FIG. 10B is a schematic plan view of an internal region including a regular triangular lattice.
In the internal region 33, a second-order diffraction grating is formed by the first pits 63 having a regular triangular plane shape. The first pits 63 are arranged so as to be asymmetric with respect to straight lines 54, 55, and 56 that pass through the planar center of gravity G3 and are parallel to the three sides of the equilateral triangular lattice. The planar shape of the first pit 63 may not be a regular triangle. The outer peripheral region 34 is a regular triangular lattice in which the second pits 64 have a circular plane shape. Further, the lattice interval P3 of the inner region 63 is set to be twice the lattice interval P4 of the outer peripheral region 34. Laser light can be emitted in a direction substantially perpendicular to the inner region 33.

FIG. 15 is a partial schematic plan view of a surface emitting quantum cascade laser according to a sixth embodiment.
The planar shape of the first pit 63 is asymmetric with respect to a line (50 or 51) passing through the gravity center G1 of the planar shape and parallel to at least one side of the first two-dimensional lattice. The planar shape of the second pit 64 is symmetric with respect to a line passing through the center of gravity G2 of the planar shape and parallel to all the sides (50 and 51) of the second two-dimensional lattice.

  In this modification, the two-dimensional lattice is a square lattice. The lattice interval P1 of the second pit 64 is the same as the lattice interval P1 of the first pit 63, and both act as a photonic crystal of the first-order diffraction grating. The internal region 33 emits laser light in a direction substantially perpendicular to the active layer by the first-order diffraction grating using the asymmetry of the first pit 33. The outer peripheral region 34 uses the symmetry of the second pit 64 to reflect the laser beam emitted from the inner region 33 toward the outer peripheral region 34 by the outer peripheral region 34 in a plane parallel to the active layer. It can be returned to the internal area 33.

  According to the first to sixth embodiments and the modifications associated therewith, a surface-emitting quantum cascade laser with improved heat dissipation and reduced light leakage from the side surface of the chip is provided. These surface-emitting quantum cascade lasers can be widely used in environmental analysis devices, hazardous material detection devices, laser processing devices, and the like.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

5 surface emitting quantum cascade laser, 20 active layer, 30 first semiconductor layer, 32 first surface, 33 inner region, 34 outer peripheral region, 35, 36 upper electrode, 39 second semiconductor layer, 50 insulator layer, 61, 63 1st pit, 64 2nd pit, 80, 82 laser beam, 90 lower electrode, 90a (lower electrode) opening, P1, P3 (first pit) lattice spacing, P2, P4 ( Lattice spacing, G1 (first pit) center of gravity, G2 (second pit) center of gravity, G3 (regular triangle pit) center of gravity, D1, D2, D3, D4 Pit depth

Claims (13)

An active layer in which a plurality of quantum well layers are stacked and capable of emitting laser light by intersubband transition;
A first semiconductor layer provided on the active layer and having a first surface, wherein the first surface includes an inner region in which a first pit constitutes a first two-dimensional lattice and a second surface A first semiconductor layer, wherein the pit includes an outer peripheral region constituting a second two-dimensional lattice, and the outer peripheral region surrounds the inner region;
An insulating layer covering the side and bottom surfaces of the first pit, the side and bottom surfaces of the second pit, and the portion of the internal region where the first pit is not provided;
An upper electrode that covers a portion of the outer peripheral region where the second pit is not provided and fills the first pit and the second pit via the insulator layer;
A lower electrode provided on the surface of the active layer opposite to the surface on which the first semiconductor layer is provided and having an opening at a central portion thereof in plan view; A lower electrode, wherein a portion of an internal region is contained within the opening; and
With
The surface emitting quantum cascade laser wherein the first planar shape of the opening end of the first pit is asymmetric with respect to a line passing through the center of gravity of the first planar shape and parallel to at least one side of the first two-dimensional grating .   The surface emitting quantum cascade laser according to claim 1, wherein no current is injected into the internal region. An active layer in which a plurality of quantum well layers are stacked and capable of emitting laser light by intersubband transition;
A first semiconductor layer provided on the active layer and having a first surface, wherein the first surface includes an inner region in which a first pit constitutes a first two-dimensional lattice and a second surface A first semiconductor layer, wherein the pit includes an outer peripheral region constituting a second two-dimensional lattice, and the outer peripheral region surrounds the inner region;
An insulating layer covering the side and bottom surfaces of the first pit and the side and bottom surfaces of the second pit;
Covering the portion of the inner region where the first pit is not provided and the portion of the outer peripheral region where the second pit is not provided, and the first pit via the insulator layer An upper electrode filling the inside and the second pit;
A lower electrode provided on the surface of the active layer opposite to the surface on which the first semiconductor layer is provided and having an opening at a central portion thereof in plan view; A lower electrode, wherein a portion of an internal region is contained within the opening; and
With
The surface emitting quantum cascade laser wherein the first planar shape of the opening end of the first pit is asymmetric with respect to a line passing through the center of gravity of the first planar shape and parallel to at least one side of the first two-dimensional grating .   The surface emitting quantum cascade laser according to claim 3, wherein an injection current into the inner region is lower than an injection current into the outer peripheral region.   The lattice interval of the first pit is the same as the lattice interval of the second pit or is an integer multiple of the lattice interval of the second pit. Surface emitting quantum cascade laser. The second planar shape of the open end of the second pit is symmetrical with respect to a line passing through the center of gravity of the second planar shape and parallel to all sides of the second two-dimensional lattice;
The laser beam has an emission wavelength corresponding to the lattice spacing of the second pit and is emitted from the internal region through the opening in a direction substantially perpendicular to the active layer. The surface emitting quantum cascade laser as described in any one of -5.   The surface emitting quantum cascade laser according to any one of claims 1 to 6, wherein a depth of the second pit is larger than a depth of the first pit.   The surface emitting quantum cascade laser according to claim 7, wherein the depth of the second pit is larger than a wavelength of the laser light.   The surface emitting quantum cascade laser according to any one of claims 1 to 8, wherein a depth of the first pit reaches the inside of the active layer.   10. The surface emitting quantum cascade laser according to claim 1, wherein a depth of the second pit reaches the inside of the active layer or penetrates the active layer. 11.   11. The surface-emitting quantum cascade laser according to claim 1, wherein the first pit and the second pit do not overlap in a plan view.   The surface emitting quantum cascade laser according to claim 1, wherein the first planar shape includes a plurality of point-symmetric shapes. The two-dimensional lattice of the first pit is a square lattice or a rectangular lattice;
The first planar shape of the open end of the first pit is asymmetric with respect to a line passing through the center of gravity of the first planar shape and parallel to each of two sides of the first two-dimensional lattice. The surface emitting quantum cascade laser according to any one of 1 to 12.

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