Quantum cascade laser device and method for manufacturing quantum cascade laser device

Abstract

The quantum cascade laser device according to the present disclosure comprises a semiconductor substrate, a cascade laser region and a difference frequency waveguide stacked on the semiconductor substrate, and a grating coupling region, the grating coupling region being configured to couple light emitted from the cascade laser region in a direction tilted with respect to an upper surface of the semiconductor substrate to a guided mode of the difference frequency waveguide.

Description

[Technical field]

[0001] The present disclosure relates to quantum cascade laser devices and methods for manufacturing quantum cascade laser devices. [Background technology]

[0002] Patent Document 1 discloses a terahertz nonlinear quantum cascade laser (THz-nonlinear-QCL) device. This quantum cascade laser includes a semiconductor substrate and an optical waveguide formed on a first surface of the semiconductor substrate. The optical waveguide has a first region and a second region located on one side of the first region in the optical guiding direction. The first region generates a first light of a first wavelength, and the second region generates a second light of a second wavelength. The optical waveguide generates output light having a frequency according to the difference between the first wavelength and the second wavelength by difference frequency generation. In the quantum cascade laser, the output light is emitted from an inclined surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-153286 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the quantum cascade laser device described in Patent Document 1, the nonlinear optical effect of crystals such as InP and GaAs is utilized to generate a difference frequency f, which is the absolute value of the difference between the frequencies f1 and f2. T Generates the difference frequency f Tare terahertz (THz) waves, and are emitted by Cherenkov radiation. Here, in the quantum cascade laser device of Patent Document 1, it is necessary to process the substrate obliquely after the wafer process is completed. This makes manufacturing difficult. In addition, the emission direction of the THz waves depends on the angle of the substrate oblique grinding. This requires precise processing accuracy.

[0005] An object of the present disclosure is to provide a quantum cascade laser device that can be easily manufactured and a method for manufacturing the quantum cascade laser device. [Means for solving the problem]

[0006] The quantum cascade laser device according to the present disclosure includes a semiconductor substrate; The above The present invention comprises a cascade laser region and a first difference frequency waveguide stacked on a semiconductor substrate, and a first grating coupling region, the cascade laser region having a first cladding layer, a plurality of stages provided on the first cladding layer, and a second cladding layer provided on the plurality of stages, each of the plurality of stages having an active region and an injector region configured to inject carriers into the active region, each of the active region and the injector region having a barrier layer and a well layer alternately provided, the first difference frequency waveguide having a third cladding layer, a first core layer provided on the third cladding layer, and a fourth cladding layer provided on the first core layer, and the first grating coupling region is configured to couple light emitted from the cascade laser region in a direction inclined with respect to an upper surface of the semiconductor substrate to a waveguide mode of the first difference frequency waveguide.

[0007] The method for manufacturing a quantum cascade laser device according to the present disclosure includes stacking a cascade laser region and a difference frequency waveguide on a semiconductor substrate, and forming a cascade laser region between the cascade laser region and the difference frequency waveguide or inside the difference frequency waveguide. Nigua grating coupling region, the cascade laser region having a first cladding layer, a plurality of stages provided on the first cladding layer, and a second cladding layer provided on the plurality of stages, each of the plurality of stages having an active region and an injector region configured to inject carriers into the active region, each of the active region and the injector region having alternating barrier layers and well layers; the difference frequency waveguide having a third cladding layer, a first core layer provided on the third cladding layer, and a fourth cladding layer provided on the first core layer, and the grating coupling region couples light emitted from the cascade laser region in a direction inclined with respect to the top surface of the semiconductor substrate to a guided mode of the difference frequency waveguide. Effect of the Invention

[0008] In the quantum cascade laser device and the method for manufacturing the quantum cascade laser device according to the present disclosure, the grating coupling region couples light emitted from the cascade laser region in a direction inclined with respect to the upper surface of the semiconductor substrate to the guided mode of the difference frequency waveguide. This allows light to be emitted from the difference frequency waveguide, making oblique grinding of the substrate unnecessary. Therefore, the quantum cascade laser device can be easily manufactured. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a quantum cascade laser device according to a first embodiment. [Diagram 2] 1 is a cross-sectional view of a quantum cascade laser device according to a first embodiment. [Diagram 3] FIG. 4 is a diagram showing a band structure of a conduction band of one stage according to the first embodiment. [Figure 4] 2 is a diagram showing a quantum well structure of one stage according to the first embodiment and the square of a wave function at each energy level. FIG. [Diagram 5] FIG. 4 is a diagram illustrating an example of the wavelength dependence of gain according to the first embodiment. [Figure 6]FIG. 2 is a perspective view of a quantum cascade laser device according to a modification of the first embodiment. [Figure 7A] 3A to 3C are diagrams illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment. [Figure 7B] 3A to 3C are diagrams illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment. [Figure 7C] 3A to 3C are diagrams illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment. [Figure 7D] 3A to 3C are diagrams illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment. [Figure 7E] 3A to 3C are diagrams illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment. [Figure 7F] 3A to 3C are diagrams illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment. [Figure 7G] 3A to 3C are diagrams illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment. [Figure 7H] 3A to 3C are diagrams illustrating a method for manufacturing the quantum cascade laser device according to the first embodiment. [Figure 8] FIG. 11 is a perspective view of a quantum cascade laser device according to a second embodiment. [Figure 9] FIG. 11 is a cross-sectional view of a quantum cascade laser device according to a second embodiment. [Figure 10] FIG. 11 is a perspective view of a quantum cascade laser device according to a third embodiment. [Figure 11] FIG. 11 is a cross-sectional view of a quantum cascade laser device according to a third embodiment. [Figure 12] FIG. 11 is a perspective view of a quantum cascade laser device according to a fourth embodiment. [Figure 13] FIG. 11 is a cross-sectional view of a quantum cascade laser device according to a fourth embodiment. [Figure 14A] 11A to 11C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a fourth embodiment. [Figure 14B] 11A to 11C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a fourth embodiment. [Figure 14C] 11A to 11C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a fourth embodiment. [Figure 14D] 11A to 11C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a fourth embodiment. [Figure 14E] 11A to 11C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a fourth embodiment. [Figure 14F] 11A to 11C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a fourth embodiment. [Figure 14G] 11A to 11C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a fourth embodiment. [Figure 14H] 11A to 11C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a fourth embodiment. [Figure 15] FIG. 13 is a perspective view of a quantum cascade laser device according to a fifth embodiment. [Figure 16] FIG. 11 is a cross-sectional view of a quantum cascade laser device according to a fifth embodiment. [Figure 17] FIG. 13 is a perspective view of a quantum cascade laser device according to a sixth embodiment. [Figure 18] FIG. 13 is a cross-sectional view of a quantum cascade laser device according to a sixth embodiment. [Figure 19] FIG. 13 is a perspective view of a quantum cascade laser device according to a seventh embodiment. [Figure 20] FIG. 13 is a cross-sectional view of a quantum cascade laser device according to a seventh embodiment. [Figure 21A] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. [Figure 21B] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. [Figure 21C] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. [Figure 21D] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. [Figure 21E] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. [Figure 21F] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. [Figure 21G] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. [Fig. 21H] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventh embodiment. [Figure 22] FIG. 13 is a perspective view of a quantum cascade laser device according to an eighth embodiment. [Figure 23] FIG. 13 is a cross-sectional view of a quantum cascade laser device according to an eighth embodiment. [Figure 24] FIG. 13 is a perspective view of a quantum cascade laser device according to a ninth embodiment. [Diagram 25] FIG. 13 is a cross-sectional view of a quantum cascade laser device according to a ninth embodiment. [Figure 26] FIG. 23 is a perspective view of a quantum cascade laser device according to a tenth embodiment. [Figure 27] FIG. 23 is a cross-sectional view of a quantum cascade laser device according to a tenth embodiment. [Figure 28A] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. [Figure 28B] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. [Figure 28C] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. [Figure 28D] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. [Figure 28E] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. [Figure 28F] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. [Figure 28G] 13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. [Fig. 28H]13A to 13C are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a tenth embodiment. [Figure 29] FIG. 23 is a perspective view of a quantum cascade laser device according to an eleventh embodiment. [Diagram 30] FIG. 23 is a cross-sectional view of a quantum cascade laser device according to an eleventh embodiment. [Diagram 31] FIG. 23 is a perspective view of a quantum cascade laser device according to a twelfth embodiment. [Diagram 32] FIG. 23 is a cross-sectional view of a quantum cascade laser device according to a twelfth embodiment. [Diagram 33] FIG. 23 is a perspective view of a quantum cascade laser device according to a thirteenth embodiment. [Diagram 34] FIG. 23 is a perspective view of a quantum cascade laser device according to a modification of the thirteenth embodiment. [Diagram 35] 23 is a diagram for explaining the arrangement of a diffraction grating according to the fourteenth embodiment. FIG. [Diagram 36] FIG. 23 is a cross-sectional view of a quantum cascade laser device according to a fifteenth embodiment. [Figure 37] FIG. 23 is a perspective view of a quantum cascade laser device according to a fifteenth embodiment. [Figure 38] FIG. 23 is a cross-sectional view of a quantum cascade laser device according to a sixteenth embodiment. [Figure 39] FIG. 23 is a perspective view of a quantum cascade laser device according to a sixteenth embodiment. [Diagram 40] FIG. 21 is a cross-sectional view of a quantum cascade laser device according to a seventeenth embodiment. [Diagram 41] FIG. 23 is a perspective view of a quantum cascade laser device according to a seventeenth embodiment. [Figure 42A] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Figure 42B] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Figure 42C] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Fig.42D]23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Figure 42E] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Fig.42F] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Figure 42G] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Fig. 42H] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Fig.42I] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. [Fig.42J] 23A to 23D are diagrams illustrating a method for manufacturing a quantum cascade laser device according to a seventeenth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A quantum cascade laser device and a method for manufacturing a quantum cascade laser device according to each embodiment will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repeated description may be omitted.

[0011] Embodiment 1 FIG. 1 is a perspective view of a quantum cascade laser device 100 according to a first embodiment. The quantum cascade laser device 100 is a buried ridge type THz nonlinear QCL device with a cavity length L and a ridge width W. Hereinafter, the difference frequency between a first fundamental wave and a second fundamental wave, which will be described later, may be referred to as a THz wave or THz light. In addition, the wavelength λ of the difference frequency is T is sometimes called the THz wave wavelength or the difference frequency wavelength. The quantum cascade laser device 100 includes a substrate 2, which is a semiconductor substrate formed of, for example, n-type InP. An n-type electrode 1 is provided on the back surface of the substrate 2, and an n-type electrode 14 is provided on the top surface of the substrate 2.

[0012] On the substrate 2, a layer having a thickness of 3.5 μm and a difference frequency wavelength λT The refractive index at n c1Q T A cladding layer 3 made of n-type InP is provided on the cladding layer 3. A layer of n-type Ga 0.47 In 0.53 A guide layer 5 made of GaAs is provided. x In 1-x In addition, current blocking layers 4 made of InP doped with Fe are provided on both sides of the guide layer 5 on the cladding layer 3.

[0013] On the guide layer 5, a plurality of stages 35, 6, are provided. The stage 35 will be described later. On the stage 35, a guide layer 7 having a layer thickness of 230 nm and made of n-type GaInAs is provided. On the guide layer 7, a layer having a layer thickness of 3.5 μm and a difference frequency wavelength λ T The refractive index at n c2Q T A cladding layer 8 made of n-type InP is provided on the cladding layer 8. A grating coupling region 9 having a thickness of 1.0 μm and made of n-type GaInAs is provided on the cladding layer 8.

[0014] Above the grating coupling region 9, a layer with a thickness of d c1 T , difference frequency wavelength λ T The refractive index at n c1T T A cladding layer 10 made of n-type InP is provided on the cladding layer 10. a T , difference frequency wavelength λ T The refractive index at n aT T A core layer 11 made of n-type GaInAs is provided on the core layer 11. c2 T , difference frequency wavelength λ T The refractive index at n c2T TA cladding layer 12 made of n-type InP is provided on the cladding layer 12. A contact layer 13 having a thickness of 300 nm made of n-type GaInAs is provided on the cladding layer 12.

[0015] The cladding layer 3, the guide layers 5, 35, the stage 6, the guide layer 7 and the cladding layer 8 are collectively called a QCL waveguide or a cascade laser region. The cladding layer 10, the core layer 11 and the cladding layer 12 are collectively called a THz waveguide or a difference frequency waveguide. That is, a cascade laser region and a difference frequency waveguide are laminated on the substrate 2. In this embodiment, a cascade laser region is provided on the substrate 2, and a difference frequency waveguide is provided on the cascade laser region. The cascade laser region has a cladding layer 3, a plurality of stages 6 provided on the cladding layer 3, and a cladding layer 8 provided on the plurality of stages 6. The difference frequency waveguide has a cladding layer 10, a core layer 11 provided on the cladding layer 10, and a cladding layer 12 provided on the core layer 11.

[0016] FIG. 2 is a cross-sectional view of the quantum cascade laser device 100 according to the first embodiment. a -z b The cross section is obtained by cutting along a straight line. The guide layer 7 has a length L1 Q and the period is Λ1 Q The guide layer 7 further includes a diffraction grating 15 having a length L2 Q and the period is Λ2 Q A diffraction grating 16 is provided.

[0017] In FIG. 2, wavelength λ1 Q , frequency f1 Q , propagation constant β1 Q QCL guided mode 17 propagating in the cascade laser region at wavelength λ2 Q , frequency f2 Q , propagation constant β2 Q The QCL guided mode 18 propagating in the cascade laser region at wavelength λ1 is shown in schematic form. Q The QCL guided mode 17 is the first fundamental wave, with wavelength λ2Q The QCL guided mode 18 of the second fundamental wave is sometimes called the second fundamental wave. In other words, the cascade laser region is divided into two regions by the diffraction gratings 15 and 16, and the frequency f1 Q The first fundamental wave and frequency f2 Q The wavelength can be expressed as λ=c / f, where c is the speed of light.

[0018] 2 also shows THz light 19, 20 emitted from the cascade laser region in a direction tilted with respect to the upper surface of the substrate 2. The THz light 19 is inclined from the xz plane in the y direction at an angle -θ cm Cherenkov radiation occurs in an inclined direction, f1 Q -f2 Q The absolute value of frequency f T The THz light 20 is incident on the xz plane in the y direction at an angle θ cp Cherenkov radiation occurs in an inclined direction, with a frequency of f T Hereinafter, -θ cm Absolute value of and θ cp When the values ​​are the same, they are -θ c and θ c In addition, in Figure 2, the wavelength λ T , frequency f T , propagation constant β T The THz guided mode 21 propagating through the difference frequency waveguide at frequency f1 is shown in schematic form. Q and frequency f2 Q The waveguide mode corresponds to the difference frequency of

[0019] The grating coupling region 9 is provided between the cascade laser region and the difference frequency waveguide. The grating coupling region 9 has a length L T and the period is Λ T A diffraction grating 22 having a THz waveguide mode 21 is provided. A THz guided mode 21 from the difference frequency waveguide is emitted as THz light 24 from an emission end face 23, which is the front end face of the quantum cascade laser device 100. The emission end face 23 of the difference frequency waveguide is perpendicular to the upper surface of the substrate 2. A rear end face 25 is provided on the side of the substrate 2 opposite to the emission end face 23.

[0020] 3 is a diagram showing the band structure of the conduction band of one stage 50 according to the first embodiment. As an example, FIG. 3 shows a band structure of 5.0×10 6 1 shows the band structure of the conduction band in one stage 50 of 35 stages 6 when an electric field of 1000 V / m is applied. This structure is disclosed in Non-Patent Document 1 "J. Kim et. al., "Theoretical and experimental study of optical gain and linewidth enhancement factor of type-I quantum-cascade lasers," IEEE J. Quantum. Electron., vol. 40, no. 12, pp. 1663-1674, Dec. 2004".

[0021] Each of the multiple stages 6 includes an active region 48 and an injector region 49 configured to inject carriers into the active region 48. Each of the active region 48 and the injector region 49 includes alternating barrier layers and well layers.

[0022] In the active region 48, a barrier layer 31, a well layer 32, a barrier layer 33, a well layer 34, a barrier layer 35, a well layer 36, and a barrier layer 37 are stacked in this order. In the injector region 49, a barrier layer 37, a well layer 38, a barrier layer 39, a well layer 40, a barrier layer 41, a well layer 42, a barrier layer 43, a well layer 44, a barrier layer 45, a well layer 46, and a barrier layer 47 are stacked in this order.

[0023] The barrier layer 31 has a thickness of 2.4 nm and is made of undoped Al 0.48 In 0.52 It is formed by As. From now on, Al x In 1-xAs may be abbreviated as AlInAs. Well layer 32 has a thickness of 6.5 nm and is made of undoped GaInAs. Barrier layer 33 has a thickness of 0.9 nm and is made of undoped AlInAs. Well layer 34 has a thickness of 6.6 nm and is made of undoped GaInAs. Barrier layer 35 has a thickness of 1.5 nm and is made of undoped AlInAs. Well layer 36 has a thickness of 3.2 nm and is made of undoped GaInAs.

[0024] The barrier layer 37 has a thickness of 4.0 nm and is made of undoped AlInAs. The well layer 38 has a thickness of 4.1 nm and is made of undoped GaInAs. The barrier layer 39 has a thickness of 1.7 nm and is made of undoped AlInAs. The well layer 40 has a thickness of 3.7 nm and is made of undoped GaInAs. The barrier layer 41 has a thickness of 1.2 nm and is made of undoped AlInAs.

[0025] The well layer 42 is made of GaInAs doped to n-type and has a thickness of 3.4 nm. The barrier layer 43 is made of AlInAs doped to n-type and has a thickness of 1.1 nm. The well layer 44 is made of GaInAs doped to n-type and has a thickness of 3.4 nm. The barrier layer 45 is made of undoped AlInAs and has a thickness of 1.1 nm. The well layer 46 is made of undoped GaInAs and has a thickness of 2.9 nm. The barrier layer 47 is made of undoped AlInAs and has a thickness of 2.4 nm.

[0026] The active region 48 is a region that emits light by electrons transitioning between subbands formed in the active region 48. The injector region 49 is a region that injects electrons into the active region 48. In this embodiment, the active region 48 is configured with three wells. The doping amounts of the well layer 42, the barrier layer 43, and the well layer 44 in this embodiment are, for example, 2.5×10 17 cm -3 In this embodiment, as an example, 35 stages 6 are configured by vertically connecting 35 stages 50 .

[0027] FIG. 4 is a diagram showing the quantum well structure of one stage 50 according to the first embodiment and the square of the wave function at each energy level. The square of the wave function represents the probability of the electrons existing. There are ten energy levels allowed in one stage 50. In FIG. 4, the levels where electrons exist mainly in the active region 48 are indicated by solid lines, and the levels where electrons exist mainly in the injector region 49 are indicated by dashed lines. The five levels where electrons exist mainly in the active region 48 are #1, #2, #4, #7, and #9, and the five levels where electrons exist mainly in the injector region 49 are #3, #5, #6, #8, and #10.

[0028] Calculation of the electron density revealed that, among the levels where electrons exist mainly in the active region 48, the electron density at energy level #4 is higher than that at energy level #2. In other words, it was found that the population inversion required for laser oscillation has been achieved.

[0029] 5 is a diagram showing an example of the wavelength dependence of gain according to the first embodiment. In FIG. 5, in the quantum cascade laser device 100 having a resonator length L=2.0 mm and a ridge width W=10 μm, the wavelength dependence of gain is shown when an electric field is applied from the electrode 14 to the electrode 1 and a current of 360 mA is injected. p Maximum gain g at 9.47 μm p =21.86cm -1 and the gain exists over the range from 8.0 μm to 12.0 μm.

[0030] Suppose the wavelength of the first fundamental wave is λ1 Q and the wavelength of the second fundamental wave, λ2 Q are 8.80 μm and 10.46 μm, respectively. In this case, the corresponding frequency f1 Q and f2 Q are 3.407x10 13 Hz and 2.866x10 13 Hz. Therefore, the wavelength of the difference frequency is λ T and frequency f T =(f1 Q -f2 Q) are 55.45μm and 5.406x10 12 Hz=5.406THz.

[0031] The refractive indices of InP, AlAs, GaAs, and InAs in the first and second fundamental waves were obtained from Non-Patent Document 2 "SH Wemple et. al., "Behavior of the Electronic Dielectric Constant in Covalent and Ionic Materials," Phys. Rev. B, vol. 3, no. 4, pp. 1338-1351, February 1971," Non-Patent Document 3 "Iga, ed., "Semiconductor Lasers," pp. 36, Ohmsha (October 25, 1994)," and Non-Patent Document 4 "MA Afromowitz, "Refractive Index of Ga1-xAlxAs," Solid State Comm., vol. 15, pp. 59-63, 1974." The refractive indices of GaInAs and AlInAs, which are ternary mixed crystals, were calculated using Non-Patent Document 5, "S. Adachi, "Material parameter of In1-xGaxAsyP1-y," J. Appl. Phys., vol.53, No.12, pp. 8775-8792, 1982." T The refractive indices of InP, GaAs, and InAs for THz waves of =55.45 μm were calculated with reference to Non-Patent Document 6, "ED Palik, "Handbook of Optical Constants of Solids III," 1998," and the refractive index of GaInAs was calculated using Non-Patent Document 5. The results are shown in Table 1.

[0032] [Table 1]

[0033] Using the refractive indices shown in Table 1, the propagation constant β1 for the first fundamental wave in the cascade laser region is Q and the effective refractive index n ef1Q =β1 Q / [2π / λ1 Q ] are 2.27131x10 6 m -1 and 3.18111. Similarly, the propagation constant β2 for the second fundamental wave is Q and the effective refractive index n ef2 Q =β2 Q / [2π / λ2 Q ] are 1.89965x10 6 m -1 and 3.16246.

[0034] The diffraction gratings 15 and 16 provided in the guide layer 7 may be high-order diffraction gratings, but first-order is preferable from the viewpoint of high feedback. Q is the wavelength λ1 in the waveguide Q / n ef1 Q Similarly, the period Λ2 of the first-order diffraction grating 16 for the second fundamental wave is 1.305 μm. Q is the wavelength λ2 in the waveguide Q / n ef2 Q In this embodiment, as an example, the period Λ1 is set to 1.657 μm, which is half of the period Λ1 Q = 1.305 μm and length L1 Q = 800 μm diffraction grating 15 and period Λ2 Q = 1.657 μm and length L2 Q = 800 μm. This allows the wavelength λ Q = 8.80 μm and wavelength λ2 Q = 10.46 μm. Note that the ratio of convex and concave portions of each diffraction grating is preferably 1:1, but can be selected arbitrarily.

[0035] THz Wavelength λ T The refractive index of the cladding layer 3 at 55.45 μm c1Q T and the refractive index n of the cladding layer 8 c2Q Tis 3.6300, and the effective refractive index of the first fundamental wave, n ef1 Q = 3.18111 and the effective refractive index of the second fundamental wave, n ef2 Q = 3.16246. Therefore, Cherenkov radiation occurs in the cladding layers 3 and 8. That is, from the cascade laser region, the resonance direction and the angle θ cp and angle -θ cm The light is emitted in a direction that forms a line.

[0036] Cherenkov radiation angle from cladding layer 3 -θ cm and the Cherenkov radiation angle θ from the cladding layer 8 cp can be expressed by equations (1) and (2) according to Non-Patent Document 7 "Z.-S. Suh, "Simple analytical solution of Cerenkov-type Terahertz wave generation via difference frequency generation in dielectric waveguides," J. Lightw. Technol., vol.37, No.17, pp. 4236-4243, 2019". In addition, k0 T is expressed by equation (3).

[0037]

number

[0038]

number

[0039]

number

[0040] Here, since the cladding layers 3 and 8 are both InP, the refractive index n c1Q T =n c2Q T=3.6300. Therefore, the Cherenkov radiation angle is θ cm =θ cp =θ c =25.37°.

[0041] Also, as can be seen from Table 1, the difference frequency wavelength λ T The refractive index of GaInAs at 55.45 μm is higher than that of InP. Therefore, if GaInAs is used as the core and InP is used as the cladding, a THz waveguide, which is a waveguide at the difference frequency, can be formed. The waveguide can be multimode, but from the viewpoint of using the emitted light, it is preferable that it is a simple mode.

[0042] Therefore, in this embodiment, the thickness d of the cladding layer 10 is c1 T and the thickness d of the cladding layer 12 c2 T 20 μm, and the thickness of the core layer 11 d a T In this case, the wavelength λ T Propagation constant β of difference frequency waveguide for THz waves at 55.45 μm T and the effective refractive index n ef T are 4.58629x10 respectively. 5 m -1 and 4.04751. From Non-Patent Document 8 "A. Yariv et. al., "Periodic structures for integrated optics," IEEE J. Quantum. Electron., vol. QE-13, no. 4, pp. 233-253, Apr. 1977", the angle θ c The light incident at and propagating through the waveguide with a propagation constant β T In order for light propagating at the grating 22 in the grating coupling region 9 to be coupled, the period Λ T must satisfy equation (4).

[0043]

number

[0044] m is an integer other than zero. When formula (4) is applied to this embodiment with m=1, the period Λ of the diffraction grating 22 is T is 72.25μm. T The ratio of convex portions to concave portions of the diffraction grating 22 is preferably 1:1, but is not limited to this and may be selected arbitrarily.

[0045] In view of the above, in this embodiment, as an example, a period Λ is provided in the grating coupling region 9. T = 72.25 μm and length L T = 1000 μm. This allows the angle θ c= θ cp The THz light radiated by Cherenkov radiation at 20 is T 4. The THz light 24 can be coupled to the THz guided mode 21 propagating in the difference frequency waveguide at a wavelength of 100 nm. As a result, the THz light 24 is emitted perpendicularly to the emission end face 23 of the quantum cascade laser device 100.

[0046] Also, -θ cm A portion of the THz light 19 emitted by Cherenkov radiation at the -θ cm The THz light 19 emitted by the Cherenkov radiation can also be extracted outside the device.

[0047] From the above, the grating coupling region 9 is configured to couple the THz lights 19, 20 to the THz guided mode 21 of the difference frequency waveguide. Specifically, the grating coupling region 9 has a diffraction grating 22 configured to couple the THz lights 19, 20 to the THz guided mode 21 of the difference frequency waveguide. This allows the THz light 24 to be emitted from the difference frequency waveguide, making it unnecessary to perform, for example, oblique grinding of the substrate 2 after the completion of the wafer process. Therefore, the quantum cascade laser device 100 can be easily manufactured.

[0048] The difference frequency waveguide of this embodiment can be considered as a three-layer slab waveguide in which the core layer 11 is sandwiched between the clad layers 10 and 12. Therefore, the light intensity distribution of the difference frequency waveguide is a Lorentz type similar to that of a normal optical waveguide. Therefore, the THz light 24 can be coupled with an external optical system with high efficiency.

[0049] 6 is a perspective view of a quantum cascade laser device 200 according to a modification of the first embodiment. The quantum cascade laser device 200 differs from the quantum cascade laser device 100 in that an insulating film 26, such as SiON, is provided between the current blocking layer 4 and the electrode 14. The other structures are similar to those of the quantum cascade laser device 100. By inserting the insulating film 26, it is possible to further suppress the current flowing outside the ridge of width W. The insulating film 26 may also be provided in the following embodiments.

[0050] Next, a method for manufacturing the quantum cascade laser device 100 will be described. Figures 7A to 7H are diagrams for explaining the method for manufacturing the quantum cascade laser device 100 according to the first embodiment. First, as shown in Figure 7A, the cladding layer 3, the guide layer 5, the stage 6, and the guide layer 7 are crystal-grown in this order on the substrate 2. For the crystal growth, a molecular beam epitaxy (MBE) method, a metal organic chemical vapor deposition (MOCVD) method, or the like can be used.

[0051] Next, as shown in FIG. 7B, a period Λ1 is formed in the guide layer 7 by photolithography and etching. Q Diffraction grating 15 and period Λ2 Q The diffraction grating 15 has a length L1 Q , width is W g > W, depth d g Q is 0 <d g Q ≦230 nm. The length of the diffraction grating 16 is L2 Q , width is W g> W, depth d g Q is 0 <d g Q ≦230 nm.

[0052] 7C, the cladding layer 8 and the grating coupling region 9 are grown in this order on the guide layer 7 by MBE, MOCVD or the like. Next, as shown in FIG. 7D, a period Λ is formed in the grating coupling region 9 by photolithography and etching. T The diffraction grating 22 has a length L T , width is W g T > W, depth d g T is 0 <d g T ≦1.0 μm.

[0053] Next, as shown in Fig. 7E, the cladding layer 10, core layer 11, cladding layer 12 and contact layer 13 are crystal-grown in this order on the grating coupling region 9 by MBE, MOCVD or the like. As a result, the cascade laser region and the difference frequency waveguide are laminated on the substrate 2, and the grating coupling region 9 is formed between the cascade laser region and the difference frequency waveguide. Next, as shown in Fig. 7F, both sides of the ridge with width W are etched away to the middle of the cladding layer 3 by photolithography and etching.

[0054] Next, as shown in Fig. 7G, current blocking layer 4 is embedded and grown on both sides of the ridge to cover both sides of core layer 11 by MBE method, MOCVD method, etc. Next, as shown in Fig. 7H, electrode 1 is formed on the back surface of substrate 2, and electrode 14 is formed on contact layer 13 and current blocking layer 4.

[0055] The dimensions, materials, concentrations, etc. of each layer described above are merely examples and may be changed. In addition, in this embodiment, the number of stages is 35. The number of stages is not limited to this, and may be selected as desired as necessary. The structure of the active region 48 and the injector region 49 constituting one stage 50 is not limited to the structure exemplified in this embodiment. In addition, in this embodiment, a GaInAs / AlInAs-based QCL device using an InP substrate is exemplified. This embodiment is not limited to this, and can also be applied to a GaAs / AlGaAs-based QCL device using a GaAs substrate and an InGaN / AlGaN-based QCL device using a GaN substrate. Furthermore, the QCL device of this embodiment is lattice-matched with the substrate. This embodiment is not limited to this, and can also be applied to a lattice-mismatched system having a lattice constant larger or smaller than that of the substrate, that is, a strain-introducing system.

[0056] The above-mentioned modifications can be appropriately applied to the quantum cascade laser devices and the manufacturing methods of the quantum cascade laser devices according to the following embodiments. Note that the quantum cascade laser devices and the manufacturing methods of the quantum cascade laser devices according to the following embodiments have many points in common with the first embodiment, so the differences from the first embodiment will be mainly described.

[0057] Embodiment 2 FIG. 8 is a perspective view of the quantum cascade laser device 300 according to the second embodiment. FIG. 9 is a cross-sectional view of the quantum cascade laser device 300 according to the second embodiment. a -z b The cross section is obtained by cutting along a straight line. In this embodiment, the grating coupling region 9 is provided inside the cladding layer below the core layer 11 of the difference frequency waveguide. The grating coupling region 9 is separated from the cascade laser region. The other configurations are the same as those of the first embodiment.

[0058] Specifically, in the quantum cascade laser device 300, a layer having a thickness of d c1A TA cladding layer 51 made of n-type InP is provided. A grating coupling region 9 is provided on the cladding layer 51. A layer having a thickness of d c1B T and a cladding layer 52 made of n-type InP is provided. c1A T +d c1B T =d c1 T It is.

[0059] By providing the grating coupling region 9 in the cladding layer of the difference frequency waveguide, the THz light 20 can be easily coupled to the difference frequency waveguide, and the output of the THz light 24 can be increased.

[0060] Embodiment 3 FIG. 10 is a perspective view of a quantum cascade laser apparatus 400 according to the third embodiment. FIG. 11 is a cross-sectional view of the quantum cascade laser apparatus 400 according to the third embodiment. a -z b The cross section is obtained by cutting along a straight line. In this embodiment, the grating coupling region is provided at the interface between the core layer 11 and the cladding layer 10 below the core layer 11 in the difference frequency waveguide. Specifically, the grating coupling region is formed by providing a diffraction grating 22 on the upper surface of the cladding layer 10 and burying the diffraction grating 22 in the core layer 11. The other configurations are the same as those of the first embodiment.

[0061] According to this configuration, it is possible to make it easier to couple the THz light 20 to the difference frequency waveguide, and to increase the power of the THz light 24. In addition, since there is no need to add a layer as a grating coupling region, the manufacturing process of the quantum cascade laser device 400 can be simplified.

[0062] Embodiment 4 FIG. 12 is a perspective view of a quantum cascade laser device 500 according to the fourth embodiment. FIG. 13 is a cross-sectional view of the quantum cascade laser device 500 according to the fourth embodiment. a-z b The cross section obtained by cutting along a straight line is shown. This embodiment is different from the first embodiment in that a difference frequency waveguide is provided on the substrate 2, and a cascade laser region is provided on the difference frequency waveguide. The other concepts are the same as the structure of the first embodiment.

[0063] Specifically, a cladding layer 10, a core layer 11, and a cladding layer 12 are laminated in this order on a substrate 2. A grating coupling region 9, a cladding layer 3, guide layers 5, 35 stages 6, a guide layer 7, and a cladding layer 8 are laminated in this order on the cladding layer 12. The grating coupling region 9 is provided between the cascade laser region and the difference frequency waveguide.

[0064] In this embodiment, as in the first embodiment, the resonance direction and the angle θ cp and angle -θ cm The THz light 19 and 20 are emitted in a direction that forms an angle θ cp and angle -θ cm satisfy equations (5) and (6), respectively.

[0065]

number

[0066]

number

[0067] Period Λ of the diffraction grating 22 in the grating coupling region 9 T satisfies formula (7). m is an integer other than zero.

[0068]

number

[0069] In this embodiment as well, the grating coupling region 9 can couple the THz light 19, 20 to the THz guided mode 21 of the difference frequency waveguide. Moreover, the difference frequency waveguide may have a relatively rough control of the layer thickness. For this reason, it is also possible to use a liquid phase epitaxial (LPE) device with a high growth rate. That is, in this embodiment in which the difference frequency waveguide is first formed on the substrate 2, the quantum cascade laser device 500 can be manufactured easily and inexpensively.

[0070] Next, a method for manufacturing the quantum cascade laser device 500 will be described. Figs. 14A to 14H are diagrams for explaining a method for manufacturing the quantum cascade laser device 500 according to the fourth embodiment. First, as shown in Fig. 14A, the cladding layer 10, the core layer 11, the cladding layer 12, and the grating coupling region 9 are crystal-grown in this order on the substrate 2. The crystal growth can be performed by the LPE method, the MBE method, the MOCVD method, or the like. Next, as shown in Fig. 14B, a pattern with a period Λ is formed in the grating coupling region 9 by photolithography and etching. T The diffraction grating 22 has a length L T , width is W g T > W, depth d g T is 0 <d g T ≦1.0 μm.

[0071] Next, as shown in FIG. 14C, the cladding layer 3, the guide layers 5, 35, the stage 6, and the guide layer 7 are crystal-grown in this order on the grating coupling region 9 by MBE, MOCVD, or the like. Next, as shown in FIG. 14D, a period Λ1 is formed in the guide layer 7 by photolithography and etching. Q Diffraction grating 15 and period Λ2 Q The diffraction grating 15 has a length L1 Q , width is W g > W, depth d g Q is 0 <d g Q ≦230 nm. The length of the diffraction grating 16 is L2 Q, width is W g > W, depth d g Q is 0 <d g Q ≦230 nm.

[0072] Next, as shown in Fig. 14E, cladding layer 8 and contact layer 13 are crystal-grown in this order on guide layer 7 by MBE, MOCVD or the like. Next, as shown in Fig. 14F, both sides of the ridge of width W are etched away partway through cladding layer 10 by photolithography and etching.

[0073] Next, as shown in Fig. 14G, current blocking layers 4 are embedded and grown on both sides of the ridge by MBE, MOCVD, etc. Next, as shown in Fig. 14H, an electrode 1 is formed on the back surface of the substrate 2, and an electrode 14 is formed on the contact layer 13 and the current blocking layer 4.

[0074] Embodiment 5. FIG. 15 is a perspective view of a quantum cascade laser device 600 according to the fifth embodiment. FIG. 16 is a cross-sectional view of the quantum cascade laser device 600 according to the fifth embodiment. a -z b The cross section obtained by cutting along a straight line is shown. In this embodiment, the grating coupling region 9 is provided inside the cladding layer above the core layer 11 of the difference frequency waveguide. The grating coupling region 9 is separated from the cascade laser region. The other structures are the same as those of the fourth embodiment.

[0075] Specifically, a layer having a thickness of d on the core layer 11 is c2A T A cladding layer 61 made of n-type InP is provided. A grating coupling region 9 is provided on the cladding layer 61. A layer having a thickness of d c2B T and a cladding layer 62 made of n-type InP is provided. c2A T +d c2B T =d c2T On the cladding layer 62, the cladding layer 3 is provided.

[0076] In this embodiment, by providing the grating coupling region 9 in the cladding layer of the difference frequency waveguide, it is possible to easily couple the THz light 19 to the difference frequency waveguide, and the output of the THz light 24 can be increased.

[0077] Embodiment 6 FIG. 17 is a perspective view of a quantum cascade laser apparatus 700 according to the sixth embodiment. FIG. 18 is a cross-sectional view of the quantum cascade laser apparatus 700 according to the sixth embodiment. a -z b A cross section obtained by cutting along a straight line is shown. In this embodiment, the grating coupling region is provided at the interface between the core layer 11 and the cladding layer 12 above the core layer 11 in the difference frequency waveguide. Specifically, the grating coupling region can be formed by providing a diffraction grating 22 on the upper surface of the core layer 11 and embedding it in the cladding layer 12. The other structures are similar to those of the fourth embodiment.

[0078] In this embodiment, by providing a grating coupling region at the interface between the core layer 11 and the cladding layer 12, it is possible to further facilitate coupling of the THz light 19 to the difference frequency waveguide, thereby increasing the output of the THz light 24. In addition, since there is no need to add a layer as the grating coupling region, the manufacturing process of the quantum cascade laser device 700 can be simplified.

[0079] Embodiment 7 FIG. 19 is a perspective view of a quantum cascade laser device 800 according to the seventh embodiment. FIG. 20 is a cross-sectional view of the quantum cascade laser device 800 according to the seventh embodiment. a -z b The cross section obtained by cutting along a straight line is shown. In this embodiment, the wavelength λ1 of the first fundamental wave Q and the wavelength of the second fundamental wave, λ2 Q The corresponding frequencies f1 are 8.30 μm and 10.48 μm, respectively.Q and f2 Q are 3.612x10 13 Hz and 2.861x10 13 Hz. Difference frequency wavelength λ T and the difference frequency f T =f1 Q -f2 Q are 39.90μm and 7.513x10 respectively. 12 Hz=7.513THz.

[0080] In the quantum cascade laser device 800, a guide layer 71 having a thickness of 230 nm and made of n-type GaInAs is provided on the stage 6. A cladding layer 8 is provided on the guide layer 71. A cladding layer 8 having a thickness of d c1 T , difference frequency wavelength λ T The refractive index at n c1T T On the cladding layer 72, a layer having a thickness of d a T , difference frequency wavelength λ T The refractive index at n aT T A core layer 73 made of n-type InP is provided on the core layer 73. c2 T , difference frequency wavelength λ T The refractive index at n c2T T and a cladding layer 74 made of n-type GaInAs is provided.

[0081] The current blocking layer 4 covers both sides of the cascade laser region from the cladding layer 3 to the cladding layer 8. The difference frequency waveguide including the cladding layer 72, the core layer 73 and the cladding layer 74 is exposed from the current blocking layer 4.

[0082] The guide layer 71 has a length L1 Q , with period Λ1 Q Diffraction grating 75 with length L2 Q , with period Λ2 QIn addition, in FIG. 20, a diffraction grating 76 having a wavelength λ1 Q , frequency f1 Q , propagation constant β1 Q The QCL guided mode 77 propagates through the cascade laser region at wavelength λ2 Q , frequency f2 Q , propagation constant β2 Q 10, a QCL waveguide mode 78 propagating in the cascade laser region is shown. In this embodiment, the QCL waveguide mode 77 is a first fundamental wave, and the QCL waveguide mode 78 is a second fundamental wave.

[0083] 20 also shows THz light 79, 80 emitted from the cascade laser region in a direction tilted with respect to the upper surface of the substrate 2. The THz light 79 is inclined from the xz plane in the y direction at an angle -θ cm Cherenkov radiation occurs in an inclined direction, with a frequency of f T =f1 Q -f2 Q The THz light 80 is incident on the xz plane in the y direction at an angle θ cp Cherenkov radiation occurs in an inclined direction, with a frequency of f T has.

[0084] Furthermore, in FIG. T , frequency f T , propagation constant β T The THz guided mode 81 propagating through the difference frequency waveguide is shown in schematic form. T , the period is Λ T The diffraction grating 82 is formed by etching away the cladding layer 8 to a depth of about 1 μm from the upper surface and burying it with the cladding layer 72. In this manner, the grating coupling region of this embodiment is provided between the cascade laser region and the difference frequency waveguide. The period of the diffraction grating 82 will be described later. THz light 83 is emitted from the emission end face 23.

[0085] As in the first embodiment, the refractive indices of InP, AlAs, GaAs, and InAs in the first fundamental wave and the second fundamental wave were obtained from Non-Patent Documents 2, 3, and 4. The refractive indices of GaInAs and AlInAs, which are ternary mixed crystals, were calculated using Non-Patent Document 5. T The refractive indices of InP, GaAs, and InAs at THz waves of =39.90 μm were calculated with reference to Non-Patent Document 6, and the refractive index of GaInAs was calculated using Non-Patent Document 5. The results are shown in Table 2.

[0086] [Table 2]

[0087] From the refractive indices shown in Table 2, the propagation constant β1 for the first fundamental wave in the cascade laser region is Q and the effective refractive index n ef1 Q =β1 Q / [2π / λ1 Q ] are 2.41324x10 6 m -1 and 3.18785. Similarly, the propagation constant β2 for the second fundamental wave is Q and the effective refractive index n ef2 Q =β2 Q / [2π / λ2 Q ] are 1.89592x10 6 m -1 and 3.16228.

[0088] The diffraction gratings 75 and 76 may be higher-order diffraction gratings, but from the viewpoint of high feedback, the first-order diffraction grating is preferable. Q is the wavelength λ1 in the waveguide Q / n ef1 Q Similarly, the period Λ2 of the first-order diffraction grating for the second fundamental wave is Q is the wavelength λ2 in the waveguide Q / n ef2 QTherefore, for example, the period Λ1 Q = 1.302 μm and length L1 Q = 800 μm diffraction grating 75 and period Λ2 Q = 1.657 μm and length L2 Q If a diffraction grating 76 with a wavelength of λ1 is provided, Q = 8.30 μm and wavelength λ2 Q = 10.48 μm.

[0089] In addition, the difference frequency wavelength λ T The refractive index of the cladding layer 3 at 39.90 μm c1Q T and the refractive index n of the cladding layer 8 c2Q T is 4.2000, and the effective refractive index of the first fundamental wave, n ef1 Q = 3.18785 and the effective refractive index of the second fundamental wave, n ef2 Q = 3.16228. Therefore, Cherenkov radiation occurs in the cladding layers 3 and 8. As in the first embodiment, from the formulas (1) to (3), the Cherenkov radiation angle −θ cm and the Cherenkov radiation angle θ at the cladding layer 8 cp In this embodiment, θ cm =θ cp =θ c =38.54°.

[0090] Also, as can be seen from Table 2, the difference frequency wavelength λ T The refractive index of InP at wavelength d = 39.90 μm is higher than that of GaInAs. Therefore, by using InP as the core and GaInAs as the cladding, a waveguide at the difference frequency, that is, a difference frequency waveguide, can be formed. The waveguide may be multimode, but from the viewpoint of using the emitted light, a simple mode is preferable. Therefore, in this embodiment, the layer thickness d c1 T and the thickness d of the cladding layer 74 c2 T 16 μm, and the thickness of the core layer 73 da T In this case, the wavelength λ T Propagation constant β of difference frequency waveguide for THz waves at 39.90 μm T and the effective refractive index n ef T are 6.13845x10 respectively. 5 m -1 and the result is 3.89818.

[0091] Using equation (4) as in the first embodiment, the angle θ c The light incident at and propagating through the waveguide with a propagation constant β T To couple light propagating at T In other words, for example, the period Λ is set to 65.09 μm at the interface between the cladding layers 8 and 72. T = 65.09 μm and length L T If a diffraction grating of 1000 μm is provided, the angle θ c =θ cp The THz light emitted by Cherenkov radiation at T As a result, THz light 83 is emitted perpendicularly to the emission facet 23.

[0092] In the current blocking layer 4 of this embodiment, the cladding layers 3 to 8 are buried on both sides of the ridge, and the difference frequency waveguide is not buried. This is because if the ridge portion of the difference frequency waveguide is buried with Fe-doped InP, which has a high refractive index, the THz waves will not be confined in the ridge portion, and there is a possibility that it will become an anti-waveguide. Although not shown, both sides of the ridge of the difference frequency waveguide and the top of the current blocking layer 4 may be covered with an insulating film such as SiON.

[0093] Next, a method for manufacturing the quantum cascade laser device 800 will be described. FIGS. 21A to 21H are diagrams for explaining a method for manufacturing the quantum cascade laser device 800 according to the seventh embodiment. First, as shown in FIG. 21A, the cladding layer 3, the guide layers 5 and 35, the stage 6, and the guide layer 71 are crystal-grown in this order on the substrate 2 by MBE, MOCVD, or the like. Next, as shown in FIG. 21B, a periodic structure having a period of Λ1 is formed in the guide layer 71 by photolithography and etching. Q , length L1 Q , width is W g > W, depth d g Q is 0 <d g Q Similarly, a diffraction grating 75 having a period of Λ2 is formed in the guide layer 71. Q , length L2 Q , width is W g > W, depth d g Q is 0 <d g Q A diffraction grating 76 of ≦230 nm is formed.

[0094] 21C, the cladding layer 8 is grown on the guide layer 71 by MBE, MOCVD, or the like. Next, as shown in FIG. 21D, a periodic .LAMBDA. T , length L T , width is W g T > W, depth d g T is 0 <d g T A diffraction grating 82 of ≦1.0 μm is formed. Next, as shown in Fig. 21E, on the cladding layer 8, a cladding layer 72, a core layer 73, a cladding layer 74, and a contact layer 13 are crystal-grown in this order by MBE, MOCVD or the like.

[0095] Next, as shown in Fig. 21F, photolithography and etching are used to etch away both sides of the ridge to a point halfway through the cladding layer 3. Next, as shown in Fig. 21G, a current blocking layer 4 is grown by MBE, MOCVD or the like to a height that embeds the cladding layer 8 on both sides of the ridge. Next, as shown in Fig. 21H, an electrode 1 is formed on the back surface of the substrate 2, and an electrode 14 is formed on the contact layer 13.

[0096] Embodiment 8 FIG. 22 is a perspective view of a quantum cascade laser apparatus 900 according to the eighth embodiment. FIG. 23 is a cross-sectional view of the quantum cascade laser apparatus 900 according to the eighth embodiment. a -z b The cross section is obtained by cutting along a straight line. This embodiment differs from the seventh embodiment in that the grating coupling region is provided inside the cladding layer below the core layer 73 of the difference frequency waveguide. The other configurations are the same as those of the seventh embodiment.

[0097] In the quantum cascade laser device 900, a layer having a thickness of d c1A T A cladding layer 91 made of n-type GaInAs is provided on the cladding layer 91. A grating coupling region 92 made of n-type InP is provided on the cladding layer 91 and has a thickness of 1.0 μm. c1B T and a cladding layer 93 made of n-type GaInAs is provided. c1A T +d c1B T =d c1 T It is.

[0098] If the grating coupling region 92 is provided in the cladding layer of the difference frequency waveguide, it becomes easier to couple the THz light 80 to the difference frequency waveguide, and the output of the THz light 83 can be increased.

[0099] Embodiment 9 FIG. 24 is a perspective view of the quantum cascade laser apparatus 1000 according to the ninth embodiment. FIG. 25 is a cross-sectional view of the quantum cascade laser apparatus 1000 according to the ninth embodiment. a -z b In this embodiment, the grating coupling region is provided at the interface between the cladding layer 72 and the core layer 73 of the difference frequency waveguide. The grating coupling region is a 100 mm long 100 mm thick 110 mm thick 120 mm thick 130 mm thick 140 mm thick 150 mm thick 160 mm thick 170 mm thick 180 mm thick 190 mm thick 200 mm thick 210 mm thick 220 mm thick 230 mm thick 240 mm thick 250 mm thick 260 mm thick 270 mm thick 280 mm thick 290 mm thick 300 mm thick T and the period is Λ T This is accomplished by providing a diffraction grating 94 and embedding it in a core layer 73. The other configurations are the same as those of the seventh embodiment.

[0100] By providing the grating coupling region at the interface between the cladding layer 72 and the core layer 73, it is possible to easily couple the THz light 80 to the difference frequency waveguide, thereby increasing the output of the THz light 83. In addition, since there is no need to add a layer as the grating coupling region, the fabrication process can be simplified.

[0101] Embodiment 10 FIG. 26 is a perspective view of a quantum cascade laser apparatus 1100 according to the tenth embodiment. FIG. 27 is a cross-sectional view of the quantum cascade laser apparatus 1100 according to the tenth embodiment. a -z b The cross section obtained by cutting along a straight line is shown. This embodiment differs from the seventh embodiment in that a difference frequency waveguide is provided on a substrate 2, and a cascade laser region is provided on the difference frequency waveguide.

[0102] That is, cladding layer 72, core layer 73, and cladding layer 74 are laminated in this order on substrate 2. Cladding layer 3, guide layers 5 and 35, stage 6, guide layer 71, and cladding layer 8 are laminated in this order on cladding layer 74. Also, diffraction grating 94 constituting the grating coupling region is formed by etching away cladding layer 74 to a depth of about 1 μm from the top surface, and burying it with cladding layer 3.

[0103] The quantum cascade laser device 1100 also includes a current blocking layer 4 covering both sides of the cascade laser region. The current blocking layer 4 is provided on the upper surface of the cladding layer 74. The side surface of the core layer 73 of the difference frequency waveguide is exposed from the current blocking layer 4.

[0104] The difference frequency waveguide may have a relatively rough control of the layer thickness. Therefore, it is possible to form the difference frequency waveguide using an LPE device with a high growth rate. Therefore, according to the present embodiment in which the difference frequency waveguide is first formed on the substrate 2, the quantum cascade laser device 1100 can be manufactured easily and at low cost.

[0105] Next, a method for manufacturing the quantum cascade laser device 1100 will be described. Figs. 28A to 28H are diagrams for explaining a method for manufacturing the quantum cascade laser device 1100 according to the tenth embodiment. First, as shown in Fig. 28A, crystals of cladding layer 72, core layer 73, and cladding layer 74 are grown in this order on substrate 2 by LPE, MBE, MOCVD, or the like. Next, as shown in Fig. 28B, a periodic region having a length of Λ is formed in cladding layer 74 by photolithography and etching. T , length L T , width is W g T > W, depth d g T is 0 <d g T A diffraction grating 94 of ≦1.0 μm is formed.

[0106] Next, as shown in Fig. 28C, the cladding layer 3, the guide layers 5, 35, the stage 6, and the guide layer 71 are crystal-grown in this order on the cladding layer 74 by MBE, MOCVD, or the like. Next, as shown in Fig. 28D, a periodic Λ1 Q , length L1 Q , width is W g > W, depth d g Q is 0 <d g Q Similarly, a diffraction grating 75 having a period of Λ2 Q , length L2Q , width is W g > W, depth d g Q is 0 <d g Q A diffraction grating 76 of ≦230 nm is formed.

[0107] Next, as shown in Fig. 28E, cladding layer 8 and contact layer 13 are crystal-grown in this order on guide layer 71 by MBE, MOCVD, or the like. Next, as shown in Fig. 28F, both sides of the ridge are etched away down to cladding layer 74 by photolithography and etching. Next, as shown in Fig. 28G, current blocking layers 4 are embedded and grown on both sides of the ridge by MBE, MOCVD, or the like. Next, as shown in Fig. 28H, an electrode 1 is formed on the back surface of substrate 2, and an electrode 14 is formed on contact layer 13 and current blocking layer 4.

[0108] Embodiment 11 FIG. 29 is a perspective view of a quantum cascade laser apparatus 1200 according to the eleventh embodiment, and FIG. 30 is a cross-sectional view of the quantum cascade laser apparatus 1200 according to the eleventh embodiment. a -z b The cross section is obtained by cutting along a straight line. This embodiment is different from the tenth embodiment in that the grating coupling region 92 is provided inside the cladding layer above the core layer 73 of the difference frequency waveguide. The grating coupling region 92 has a length L T and the period is Λ T The other configurations are the same as those of the tenth embodiment.

[0109] In this embodiment, by providing the grating coupling region 92 in the cladding layer of the difference frequency waveguide, it is possible to facilitate coupling of the THz light 79 to the difference frequency waveguide, and the output of the THz light 83 can be increased.

[0110] Embodiment 12 FIG. 31 is a perspective view of a quantum cascade laser apparatus 1300 according to the twelfth embodiment. FIG. 32 is a cross-sectional view of the quantum cascade laser apparatus 1300 according to the twelfth embodiment. a -z b The present embodiment is different from the tenth embodiment in that a diffraction grating 94 constituting the grating coupling region is provided at the interface between the cladding layer 74 and the core layer 73. T , the period is Λ T The diffraction grating 94 is formed by removing a depth of about 1 μm from the upper surface of the core layer 73 by etching and burying it with the cladding layer 74. The other configuration is the same as in the tenth embodiment.

[0111] According to this embodiment, since there is no need to add a layer as a grating coupling region, the fabrication process can be simplified.

[0112] Embodiment 13 33 is a perspective view of a quantum cascade laser device 1400 according to embodiment 13. The quantum cascade laser device 1400 differs from embodiment 1 in that it includes a highly reflective film 102 that covers the rear facet 25 opposite to the emission facet 23. The other configurations are similar to those of embodiment 1.

[0113] For example, the highly reflective film 102 is formed on the rear facet 25 with 450 nm of alumina (Al2O3), 15 nm of Ti, and 100 nm of Au. The highly reflective film 102 can eliminate or reduce the first fundamental wave and the second fundamental wave emitted from the rear facet. Therefore, the output of the THz wave can be increased.

[0114] 34 is a perspective view of a quantum cascade laser device 1500 according to a modification of the thirteenth embodiment. The quantum cascade laser device 1500 is different from the quantum cascade laser device 1400 in that a portion of the emission end face 23 corresponding to the difference frequency waveguide is exposed, and a highly reflective film 102 is further provided to cover a portion corresponding to the cascade laser region. As a result, the first fundamental wave and the second fundamental wave remain within the resonator and are not emitted outside the device. This makes it possible to further increase the output of the THz wave.

[0115] The highly reflective film 102 is expected to have high reflectance not only for the first fundamental wave and the second fundamental wave, but also for the THz light 24. The highly reflective film 102 is not limited to the quantum cascade laser device of the first embodiment, and may be applied to devices of other embodiments.

[0116] Embodiment 14 FIG. 35 is a diagram for explaining the arrangement of the diffraction gratings 15 and 16 according to the fourteenth embodiment. Up to now, the diffraction gratings corresponding to the first fundamental wave and the second fundamental wave have been arranged in cascade in the resonator direction. That is, the diffraction gratings corresponding to the first fundamental wave and the second fundamental wave have been provided at the same height. In this embodiment, the diffraction grating 15 corresponding to the first fundamental wave and the diffraction grating 16 corresponding to the second fundamental wave are provided at positions shifted in a direction perpendicular to the upper surface of the substrate 2. In the example of FIG. 35, the diffraction grating 15 and the diffraction grating 16 are provided on the upper surface and the lower surface of the guide layer 7, respectively. The other configurations are the same as those of any of the first to thirteenth embodiments.

[0117] According to this embodiment, the lengths L1 and L2 of the diffraction gratings 15 and 16 can be freely set within the range of the resonator length L. In other words, the lengths L1 and L2 can be set to lengths such that the diffraction gratings 15 and 16 partially overlap in a planar view. Here, as the length of the diffraction grating increases, the spectral linewidth can be narrowed. Therefore, according to this embodiment, it is possible to narrow the linewidth of the wavelengths of the first fundamental wave and the second fundamental wave.

[0118] Embodiment 15 FIG. 36 is a perspective view of a quantum cascade laser device 1600 according to the fifteenth embodiment. FIG. 37 is a cross-sectional view of the quantum cascade laser device according to the fifteenth embodiment. a -z b The cross section is shown by cutting along a straight line. In the above-mentioned embodiments, the diffraction grating corresponding to the first fundamental wave and the diffraction grating corresponding to the second fundamental wave are provided above the 35 stage 6 in the cascade laser region, that is, in the guide layer 7. In contrast, in this embodiment, the diffraction grating 15 corresponding to the first fundamental wave and the diffraction grating 16 corresponding to the second fundamental wave are provided below the 35 stage 6 in the cascade laser region, that is, in the guide layer 5.

[0119] In this case as well, it is possible to obtain the THz light 19, 20 in the same manner as in the previous embodiments. The arrangement of the diffraction gratings 15, 16 in this embodiment may be applied to any of the embodiments.

[0120] Embodiment 16 FIG. 38 is a perspective view of a quantum cascade laser apparatus 1700 according to the sixteenth embodiment. FIG. 39 is a cross-sectional view of the quantum cascade laser apparatus 1700 according to the sixteenth embodiment. a -z b The cross section is obtained by cutting along a straight line. This embodiment is different from the first embodiment in that difference frequency waveguides are provided at two locations, between the electrode 1 and the cascade laser region, and between the cascade laser region and the electrode 14. In other words, it can be said that the quantum cascade laser device 100 of the first embodiment further includes a difference frequency waveguide and a grating coupling region provided between the substrate 2 and the cascade laser region.

[0121] In the quantum cascade laser device 1700, a layer having a thickness of d c1 T , difference frequency wavelength λ T The refractive index at n c1T T On the cladding layer 201, a layer having a thickness of d a1T , difference frequency wavelength λ T The refractive index at n a1T T A core layer 202 made of n-type GaInAs is provided on the core layer 202. c2 T , difference frequency wavelength λ T The refractive index at n c2T T and a cladding layer 203 made of n-type InP is provided. The cladding layer 201, the core layer 202 and the cladding layer 203 form a first difference frequency waveguide.

[0122] A grating coupling region 204 having a layer thickness of 1.0 μm and made of n-type GaInAs is provided on the cladding layer 203. A cascade laser region is provided on the grating coupling region 204. The structure of the cascade laser region is the same as that of the first embodiment. A grating coupling region 205 having a layer thickness of 1.0 μm and made of n-type GaInAs is provided on the cascade laser region.

[0123] Above the grating coupling region 205, a layer having a thickness of d c3 T , difference frequency wavelength λ T The refractive index at n c3T T On the cladding layer 206, a layer having a thickness of d a2 T , difference frequency wavelength λ T The refractive index at n a2T T A core layer 207 made of n-type GaInAs is provided on the core layer 207. c4 T , difference frequency wavelength λ T The refractive index at n c4T T and a cladding layer 208 made of n-type InP is provided. The cladding layer 206, the core layer 207 and the cladding layer 208 form a second difference frequency waveguide.

[0124] In Fig. 39, the wavelength λ T , frequency f T , propagation constant β T FIG. 39 also shows a THz guided mode 209 propagating through the first difference frequency waveguide at a wavelength λ T , frequency f T , propagation constant β T The grating coupling region 204 has a length L1 T , with period Λ1 T In addition, a diffraction grating 211 having a length of L2 is formed in the grating coupling region 205. T , with period Λ2 T A diffraction grating 212 having the above structure is formed. THz light 213 is emitted from the first difference frequency waveguide. THz light 214 is emitted from the second difference frequency waveguide.

[0125] Cerenkov radiation angle at cladding layer 3 -θ cm and the Cherenkov radiation angle θ at the cladding layer 8 cp can be calculated using the formulas (1) to (3) in the same manner as in the first embodiment. T can be calculated from equation (8) using an integer m other than zero.

[0126]

number

[0127] Also, the period Λ of the diffraction grating 212 in the grating coupling region 205 T can be obtained from equation (9) using an integer j other than zero.

[0128]

number

[0129] In this embodiment, since the cladding layers 3 and 8 are both InP, the Cherenkov radiation angle is θ cm=θ cp =θ c = 25.37°. In addition, since the grating coupling region 204 and the grating coupling region 205 are both made of GaInAs, the period of the diffraction gratings 211 and 212 is Λ T = Λ2 T =Λ T =72.25mm.

[0130] From the above, the grating coupling region 204 allows the THz light 19 emitted from the cascade laser region in a direction tilted with respect to the upper surface of the substrate 2 to be coupled to the THz waveguide mode 209 of the first difference frequency waveguide. Also, the grating coupling region 205 allows the THz light 20 emitted from the cascade laser region in a direction tilted with respect to the upper surface of the substrate 2 to be coupled to the THz waveguide mode 210 of the second difference frequency waveguide.

[0131] In this embodiment, the difference frequency waveguides are provided at two locations, above and below the cascade laser region, so that the THz lights 213 and 214 emitted from the emission end face 23 can be approximately twice as much as in embodiment 1. The structure of this embodiment in which the difference frequency waveguides are provided at two locations may be applied to any of the embodiments.

[0132] Embodiment 17 FIG. 40 is a cross-sectional view of a quantum cascade laser apparatus 1800 according to the seventeenth embodiment. FIG. 41 is a perspective view of the quantum cascade laser apparatus 1800 according to the seventeenth embodiment. a -z b The cross section is obtained by cutting along a straight line. In this embodiment, the grating coupling region 221 and the cladding layers 222, 224 and core layer 223 of the difference frequency waveguide are undoped, that is, doped intentionally. Also, a voltage is applied only to the cascade laser region. This allows the operating voltage to be reduced and the THz output to be increased.

[0133] In the quantum cascade laser device 1800, a contact layer 13 is provided on the cladding layer 8. A grating coupling region 221 and a difference frequency waveguide are provided on the contact layer 13. Specifically, a grating coupling region 221 having a layer thickness of 1.0 μm and made of undoped GaInAs is provided on the contact layer 13. A layer having a layer thickness of d c1 T , difference frequency wavelength λ T The refractive index at n c1T T On the cladding layer 222, a layer having a thickness of d a T , difference frequency wavelength λ T The refractive index at n aT T On the core layer 223, a layer having a thickness of d c2 T , difference frequency wavelength λ T The refractive index at n c2T T and a cladding layer 224 made of undoped InP is provided.

[0134] In this embodiment, the ridge width W Q and the ridge width W of the difference frequency waveguide T However, the present invention is not limited to this, and both may have the same width as in the other embodiments.

[0135] The electrode 14 is provided on the contact layer 13, avoiding the difference frequency waveguide. A voltage is applied only to the electrode 1, the substrate 2, the cladding layer 3, the guide layers 5 and 35, the stage 6, the guide layer 7, the cladding layer 8, the contact layer 13 and the electrode 14. In other words, no voltage is applied to the grating coupling region 221, the cladding layer 222, the core layer 223 and the cladding layer 224. This allows the operating voltage to be reduced.

[0136] In addition, the grating coupling region 221, the cladding layer 222, the core layer 223, and the cladding layer 224 are undoped layers that are not intentionally doped. This reduces the optical absorption of the THz light, and therefore increases the output of the THz light 24.

[0137] Next, a method for manufacturing the quantum cascade laser device 1800 will be described. Figs. 42A to 42J are diagrams for explaining a method for manufacturing the quantum cascade laser device 1800 according to the seventeenth embodiment. First, as shown in Fig. 42A, the cladding layer 3, the guide layers 5, 35, the stage 6, and the guide layer 7 are crystal-grown in this order on the substrate 2 by MBE, MOCVD, or the like. Next, as shown in Fig. 42B, a region with a period of Λ1 is formed in the guide layer 7 by photolithography and etching. Q , length L1 Q , width is W g >W Q , depth d g Q is 0 <d g Q Similarly, a diffraction grating 15 having a period of Λ2 Q , length L2 Q , width is W g >W Q , depth d g Q is 0 <d g Q A diffraction grating 16 of ≦230 nm is formed.

[0138] Next, as shown in FIG. 42C, a cladding layer 8 is grown on the guide layer 7 by MBE, MOCVD, or the like. Next, as shown in FIG. 42D, the cladding layer 3 is partially removed by etching using photolithography and etching to form a cladding layer with a width W Q Next, as shown in Fig. 42E, current blocking layers 4 are grown on both sides of the ridge by MBE, MOCVD or the like.

[0139] Next, as shown in Fig. 42F, the contact layer 13 and the grating coupling region 221 are crystal-grown on the cladding layer 8 and the current blocking layer 4 by MBE, MOCVD, or the like. Next, as shown in Fig. 42G, a lattice pattern having a period Λ is formed in the grating coupling region 221 by photolithography and etching. T , length L T , width is W g T >W T , depth d g T is 0 <d g T A diffraction grating 22 of ≦1.0 μm is formed.

[0140] Next, as shown in FIG. 42H, a cladding layer 222, a core layer 223, and a cladding layer 224 are crystal-grown in this order on the grating coupling region 221 by MBE, MOCVD, or the like. Next, as shown in FIG. 42I, the grating coupling region 221 is etched away by photolithography and etching to form a layer of width W T 42J, an electrode 1 is formed on the back surface of the substrate 2, and an electrode 14 is formed on the contact layer 13.

[0141] It should be noted that the above-mentioned difference frequencies of 5.406 THz (wavelength 55.45 μm) and 7.513 THz (wavelength 39.90 μm) are merely examples, and each embodiment can be applied to any THz wave.

[0142] The technical features described in each embodiment may be used in appropriate combination. [Explanation of symbols]

[0143] 1 electrode, 2 substrate, 3 cladding layer, 4 current blocking layer, 5 guide layer, 6 35 stage, 7 guide layer, 8 cladding layer, 9 grating coupling region, 10 cladding layer, 11 core layer, 12 cladding layer, 13 contact layer, 14 electrode, 15 diffraction grating, 16 diffraction grating, 17 QCL guided mode, 18 QCL guided mode, 19 THz light, 20 THz light, 21 THz guided mode, 22 diffraction grating, 23 emission facet, 24 THz light, 25 rear facet, 26 insulating film, 31 barrier layer, 32 well layer, 33 barrier layer, 34 well layer, 35 barrier layer, 36 well layer, 37 barrier layer, 38 well layer, 39 barrier layer, 40 well layer, 41 barrier layer, 42 well layer, 43 Barrier layer, 44 Well layer, 45 Barrier layer, 46 Well layer, 47 Barrier layer, 48 Active region, 49 Injector region, 50 Stage, 51 Cladding layer, 52 Cladding layer, 61 Cladding layer, 62 Cladding layer, 71 Guide layer, 72 Cladding layer, 73 Core layer, 74 Cladding layer, 75 Diffraction grating, 76 Diffraction grating, 77 QCL guided mode, 78 QCL guided mode, 79 THz light, 80 THz light, 81 THz guided mode, 82 Diffraction grating, 83 THz light, 91 Cladding layer, 92 Grating coupling region, 93 Cladding layer, 94 Diffraction grating, 100 Quantum cascade laser device, 101 Diffraction grating, 102 Highly reflective film, 200 Quantum cascade laser device, 201 Cladding layer, 202 Core layer, 203 Cladding layer, 204 Grating coupling region, 205 Grating coupling region, 206 Cladding layer, 207 Core layer, 208 Cladding layer, 209 THz guided mode, 210 THz guided mode, 211 Diffraction grating, 212 Diffraction grating, 213 THz light, 214 THz light, 221 Grating coupling region, 222 Cladding layer, 223 Core layer, 224 Cladding layer, 300 Quantum cascade laser device, 400 Quantum cascade laser device, 500 Quantum cascade laser device, 600 Quantum cascade laser device, 700 Quantum cascade laser device, 800 Quantum cascade laser device, 900 Quantum cascade laser device, 1000 Quantum cascade laser device, 1100 Quantum cascade laser device, 1200Quantum cascade laser device, 1300 quantum cascade laser device, 1400 quantum cascade laser device, 1500 quantum cascade laser device, 1600 quantum cascade laser device, 1700 quantum cascade laser device, 1800 quantum cascade laser device

Claims

1. Semiconductor substrate and A cascade laser region and a first difference frequency waveguide stacked on a semiconductor substrate, The first grating bonding region, Equipped with, The cascade laser region comprises a first cladding layer, a plurality of stages provided on the first cladding layer, and a second cladding layer provided on the plurality of stages. Each of the aforementioned stages has an active region and an injector region configured to inject a carrier into the active region. Each of the active region and the injector region has alternating barrier layers and well layers. The first differential frequency waveguide comprises a third cladding layer, a first core layer provided on the third cladding layer, and a fourth cladding layer provided on the first core layer. The quantum cascade laser apparatus is characterized in that the first grating coupling region is configured to couple light emitted from the cascade laser region in a direction inclined with respect to the upper surface of the semiconductor substrate to the waveguide mode of the first difference frequency waveguide.

2. The quantum cascade laser apparatus according to claim 1, characterized in that the exit end face of the first difference frequency waveguide is perpendicular to the upper surface of the semiconductor substrate.

3. The cascade laser region is configured such that oscillation occurs with a first fundamental wave of a first frequency and a second fundamental wave of a second frequency. The first difference frequency waveguide has the waveguide mode corresponding to the difference frequency between the first frequency and the second frequency, The quantum cascade laser apparatus according to claim 1 or 2, characterized in that the first grating coupling region has a diffraction grating configured to couple light emitted from the cascade laser region in a direction inclined with respect to the upper surface of the semiconductor substrate to the waveguide mode of the first difference frequency waveguide.

4. The cascade laser region is provided on the semiconductor substrate. The quantum cascade laser apparatus according to claim 3, characterized in that the first difference frequency waveguide is provided on the cascade laser region.

5. From the aforementioned cascade laser region, the resonance direction and angle θ ｃｐ and angle -θ ｃｍ The light is emitted in a direction that makes this, Angle θ ｃｐ and angle -θ ｃｍ Each [Math 1] and [Math 2] Satisfying the conditions, Period Λ of the diffraction grating in the first grating coupling region Ｔ teeth, [Math 3] Satisfying the conditions, β １ Ｑ This is the propagation constant of the cascade laser region for the first fundamental wave, β ２ Ｑ is the propagation constant of the cascade laser region with respect to the second fundamental wave, β Ｔ This is the propagation constant of the first difference frequency waveguide with respect to the difference frequency between the first fundamental wave and the second fundamental wave, λ Ｔ This is the wavelength of the difference frequency, n ｃ１Ｑ Ｔ The wavelength λ of the first cladding layer is Ｔ This is the refractive index in which n ｃ２Ｑ Ｔ The wavelength λ of the second cladding layer is Ｔ This is the refractive index in which n ｃ１Ｔ Ｔ The wavelength λ of the third cladding layer is Ｔ This is the refractive index in which The quantum cascade laser apparatus according to claim 4, characterized in that m is an integer other than zero.

6. The quantum cascade laser apparatus according to claim 4, characterized in that the first grating coupling region is provided between the cascade laser region and the first difference frequency waveguide.

7. The quantum cascade laser apparatus according to claim 4, characterized in that the first grating coupling region is provided inside the third cladding layer and is separated from the cascade laser region.

8. The quantum cascade laser apparatus according to claim 4, characterized in that the first grating coupling region is provided at the interface between the third cladding layer and the first core layer.

9. The quantum cascade laser apparatus according to claim 4, further comprising current-blocking layers covering both sides of the first core layer.

10. The cascade laser region is provided with a current blocking layer covering both sides thereof. The quantum cascade laser apparatus according to claim 4, characterized in that the first core layer is exposed from the current blocking layer.

11. The first differential frequency waveguide is provided on the semiconductor substrate. The quantum cascade laser apparatus according to claim 3, characterized in that the cascade laser region is provided on the first difference frequency waveguide.

12. From the aforementioned cascade laser region, the resonance direction and angle θ ｃｐ and angle -θ ｃｍ Light is emitted in the direction that makes this shape. Angle θ ｃｐ and angle -θ ｃｍ Each [Math 4] and [Math 5] Satisfying the conditions, Period Λ of the diffraction grating in the first grating coupling region Ｔ teeth, [Math 6] Satisfying the conditions, β １ Ｑ This is the propagation constant of the cascade laser region for the first fundamental wave, β ２ Ｑ This is the propagation constant of the cascade laser region for the second fundamental wave, β Ｔ This is the propagation constant of the first difference frequency waveguide with respect to the difference frequency, λ Ｔ This is the wavelength of the difference frequency between the first fundamental wave and the second fundamental wave, n ｃ１Ｑ Ｔ The wavelength λ of the first cladding layer is Ｔ This is the refractive index in which n ｃ２Ｑ Ｔ The wavelength λ of the second cladding layer is Ｔ This is the refractive index in which n ｃ２Ｔ Ｔ The wavelength λ of the fourth cladding layer is Ｔ This is the refractive index in which The quantum cascade laser apparatus according to claim 11, characterized in that m is an integer other than zero.

13. The quantum cascade laser apparatus according to claim 11, characterized in that the first grating coupling region is provided between the cascade laser region and the first difference frequency waveguide.

14. The quantum cascade laser apparatus according to claim 11, characterized in that the first grating coupling region is provided inside the fourth cladding layer and is separated from the cascade laser region.

15. The quantum cascade laser apparatus according to claim 11, characterized in that the first grating coupling region is provided at the interface between the fourth cladding layer and the first core layer.

16. The quantum cascade laser apparatus according to claim 11, further comprising current-blocking layers covering both sides of the first core layer.

17. The cascade laser region is provided with a current blocking layer covering both sides thereof. The quantum cascade laser apparatus according to claim 11, characterized in that the first core layer is exposed from the current blocking layer.

18. The quantum cascade laser apparatus according to claim 1 or 2, further comprising a first highly reflective film covering the rear end face opposite to the output end face of the quantum cascade laser apparatus.

19. The quantum cascade laser apparatus according to claim 1 or 2, characterized in that it includes a second highly reflective film that exposes a portion of the output end face of the quantum cascade laser apparatus corresponding to the first difference frequency waveguide and covers the portion corresponding to the cascade laser region.

20. The cascade laser region has a diffraction grating corresponding to the first fundamental wave and a diffraction grating corresponding to the second fundamental wave. The quantum cascade laser apparatus according to claim 3, characterized in that the diffraction grating corresponding to the first fundamental wave and the diffraction grating corresponding to the second fundamental wave are provided at positions offset in a direction perpendicular to the upper surface of the semiconductor substrate.

21. The cascade laser region has a diffraction grating corresponding to the first fundamental wave and a diffraction grating corresponding to the second fundamental wave. The quantum cascade laser apparatus according to claim 3, characterized in that the diffraction grating corresponding to the first fundamental wave and the diffraction grating corresponding to the second fundamental wave are provided on the plurality of stages in the cascade laser region.

22. The cascade laser region has a diffraction grating corresponding to the first fundamental wave and a diffraction grating corresponding to the second fundamental wave. The quantum cascade laser apparatus according to claim 3, characterized in that the diffraction grating corresponding to the first fundamental wave and the diffraction grating corresponding to the second fundamental wave are provided below the plurality of stages in the cascade laser region.

23. A second differential frequency waveguide is provided between the semiconductor substrate and the cascade laser region, The second grating bonding region, Equipped with, The aforementioned second difference frequency waveguide comprises a fifth cladding layer, a second core layer provided on the fifth cladding layer, and a sixth cladding layer provided on the second core layer. The quantum cascade laser apparatus according to claim 4, characterized in that the second grating coupling region is configured to couple light emitted from the cascade laser region in a direction inclined with respect to the upper surface of the semiconductor substrate to the waveguide mode of the second difference frequency waveguide.

24. The cascade laser region has a contact layer provided on the second cladding layer, The first difference frequency waveguide is provided on the contact layer, The quantum cascade laser apparatus according to claim 4, characterized in that the upper electrode of the quantum cascade laser apparatus is provided on the contact layer, avoiding the first difference frequency waveguide.

25. The quantum cascade laser apparatus according to claim 24, characterized in that the third cladding layer, the first core layer, the fourth cladding layer, and the first grating coupling region are undoped.

26. A cascade laser region and a differential frequency waveguide are stacked on a semiconductor substrate. The grating coupling region is formed between the cascade laser region and the difference frequency waveguide, or inside the difference frequency waveguide. The cascade laser region comprises a first cladding layer, a plurality of stages provided on the first cladding layer, and a second cladding layer provided on the plurality of stages. Each of the aforementioned stages has an active region and an injector region configured to inject a carrier into the active region. Each of the active region and the injector region has alternating barrier layers and well layers. The differential frequency waveguide comprises a third cladding layer, a first core layer provided on the third cladding layer, and a fourth cladding layer provided on the first core layer. The method for manufacturing a quantum cascade laser apparatus is characterized in that the grating coupling region couples light emitted from the cascade laser region in a direction inclined with respect to the upper surface of the semiconductor substrate to the waveguide mode of the difference frequency waveguide.

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