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

Abstract

The quantum cascade laser device (500) of the present disclosure includes at least an active region (38) in which barrier layers and well layers are alternately formed, and a core region (10) in which a plurality of stages (40) are formed, each having an injector region (39) for injecting electrons into the active region (38). qcl The wavelength width between the two points where the gain is maximum and the gain value drops by a preset percentage from the maximum gain value is defined as Δλ qcl In this case, the wavelength λ qcl λ is a wavelength that is a preset wavelength away from cot A low reflectance film (6) is provided, which has a minimum reflectance at mir The wavelength width between the two points where the mirror loss value occurs when a preset loss value is subtracted from the maximum value of mir In this case, Δλ mir is Δλ qcl It is characterized by being smaller than

Description

[Technical field]

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

[0002] Conventional terahertz nonlinear quantum cascade laser devices (THz-nonlinear-QCL, hereinafter referred to as THz nonlinear QCL devices) are designed so that two emission transitions occur in one element, as described in Non-Patent Document 1, for example. Therefore, it is possible to oscillate at two different frequencies ω1 and ω2, and output a difference frequency ω1-ω2 by utilizing the nonlinear optical effect of crystals such as InP or GaAs. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] K. Fujita et.al., “Recent progress in terahertz difference-frequency quantum cascade laser sources,” Nanophotonics, vol.7, no.11, pp.1795-1817, Sept.2018 [Non-Patent Document 2] 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 [Non-Patent Document 3] I.Ladany et.al., “Al2O3 half-wave films for long-life cw lasers,” Appl.Phys.Lett., vol.30, no.2, pp.87-88, 1977 [Non-Patent Document 4] K. Fujita et.al., “High-performance, homogeneous broad-gain quantum cascade lasers based on dual-upper-state,” Appl.Phys.Lett., vol.96, 241107, 2010 [Non-Patent Document 5] K. Fujita et.al., “Broad gain (Δλ / λ0~0.4), temperature-insensitive (T0~510K) quantum cascade lasers,” Opt.Express, vol.19, no.3, pp.2694-2701, 2011 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional THz nonlinear QCL devices, it was extremely difficult to design a quantum well structure so that two luminescence transitions would occur within a single element, and the laser output from these two luminescence transitions had to be made nearly equal. Furthermore, to stably oscillate at two different frequencies, ω1 and ω2, it was necessary to strictly control the thickness and composition of the well and barrier layers in the quantum well structure.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a quantum cascade laser device that can easily realize terahertz oscillation 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 comprises: A semiconductor substrate; a first cladding layer of a first conductivity type formed on the semiconductor substrate; a core region formed on the first cladding layer, the core region including a plurality of stages each including an active region in which a barrier layer and a well layer are alternately formed, and an injector region for injecting electrons into the active region; a second cladding layer of a first conductivity type formed on the core region; The cavity length is L, and when current is injected, the wavelength λ qcl The gain is maximum at Δλ, and the wavelength width between two points where the gain value is lower than the maximum gain value by a preset percentage is defined as qcl In this case, on one end Within the wavelength range between the two points above wavelength λ qcl λ is a wavelength that is a preset wavelength away from cot a low reflectance film is provided, which has a minimum reflectance at The reflectance of the other end face R r The wavelength width between two points where the mirror loss value occurs when a preset loss value is subtracted from the maximum mirror loss calculated by L is defined as Δλ mir In this case, the Δλ mir is the above Δλ qcl It is characterized by being smaller than

[0007] A method for manufacturing a quantum cascade laser device according to the present disclosure includes: A method for manufacturing the quantum cascade laser device described above, comprising the steps of: cleaving the wafer after the wafer process is completed to create cleaved bars; The wavelength dependence of the gain of the quantum cascade laser device is measured by driving the cleavage bar, and the wavelength at which the gain becomes maximum is determined. λ qcl and obtaining a band of gain; The maximum gain value The wavelength width between two points where the gain value is reduced by a preset percentage is defined as Δλ qcl In this case, the above-mentioned wavelength λ qcl A wavelength that is a preset wavelength away from λ cot A step of designing a low reflectance film having a minimum reflectance at forming the low reflectance film on a front end surface of the quantum cascade laser device; Equipped with. Effect of the Invention

[0008] According to the quantum cascade laser device and the method for manufacturing the quantum cascade laser device of the present disclosure, a low-reflectivity film optimally designed for generating terahertz light is formed on the front end face of the quantum cascade laser device, thereby making it possible to easily obtain a quantum cascade laser device that can output terahertz light, and also achieving the effect of easily manufacturing such a quantum cascade laser device. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic view of a quantum cascade laser device according to a first embodiment. [Diagram 2] 2 is a cross-sectional view taken along the line ya-yb in FIG. 1 in the quantum cascade laser device according to the first embodiment. [Diagram 3] 4 is a schematic diagram showing a band structure of a conduction band in one stage when an electric field is applied in the quantum cascade laser device according to the first embodiment. FIG. [Figure 4] 2 is a schematic diagram showing a quantum well structure of one stage of the quantum cascade laser device according to the first embodiment and the square of a wave function at each energy level. FIG. [Diagram 5] 4 is a diagram showing an example of the wavelength dependence of gain in the quantum cascade laser device according to the first embodiment. FIG. [Figure 6] 4 is a schematic diagram showing a case where a single-layer coating film is replaced with a three-layer coating film in the quantum cascade laser device according to the first embodiment. FIG. [Figure 7] 4 is a schematic diagram showing a film configuration in which a coating film is inserted between an end face and a first coating film of the quantum cascade laser device according to the first embodiment. FIG. [Figure 8] 5 is a diagram showing the wavelength dependence of the reflectance of a coating film in the quantum cascade laser device according to the first embodiment. FIG. [Figure 9] 3 is a schematic diagram for explaining a method of designing a low reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first embodiment. FIG. [Figure 10] 4 is a diagram showing the wavelength dependence of the reflectance of a coating film provided on an end face of the quantum cascade laser device according to the first embodiment and the wavelength dependence of mirror loss. FIG. [Figure 11] 4 is a diagram showing the wavelength dependence of gain and the wavelength dependence of total loss of the quantum cascade laser device according to the first embodiment. FIG. [Figure 12] 2 is a cross-sectional view taken along line xa-xb in FIG. 1 in the quantum cascade laser device according to the first embodiment. [Figure 13] FIG. 11 is a cross-sectional view of a quantum cascade laser device according to a second embodiment. [Figure 14] 13 is a schematic diagram showing a quantum well structure of one stage and the square of a wave function at each energy level in a quantum cascade laser device according to the third embodiment. FIG. [Figure 15] 13 is a schematic diagram showing a quantum well structure of one stage and the square of a wave function at each energy level in a quantum cascade laser device according to a fourth embodiment. FIG. [Figure 16] 13 is a schematic diagram of a film configuration in which a coating film is inserted between an end face and a first coating film of a quantum cascade laser device according to a fifth embodiment, and a further coating film is provided on a third coating film. FIG. [Figure 17] 13 is a diagram showing the wavelength dependence of the reflectance of a coating film provided on the front end face of the quantum cascade laser device according to the fifth embodiment. FIG. [Figure 18] 13 is a schematic diagram for explaining a method of designing a low reflectance film having an extremely small reflectance of a quantum cascade laser device according to the fifth embodiment. FIG. [Figure 19] 13 is a diagram comparing the wavelength dependence of the reflectance of a coating film provided on the front end face of a quantum cascade laser device according to a fifth embodiment with that of the first embodiment. FIG. [Figure 20]1 is a schematic diagram for explaining a method of designing a low reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Figure 21] 13 is a diagram showing the wavelength dependence of the reflectance of a low-reflectance film designed by a design method for a low-reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Figure 22] 1 is a schematic diagram for explaining a method of designing a low reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Diagram 23] 1 is a schematic diagram for explaining a method of designing a low reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Figure 24] 13 is a diagram showing the wavelength dependence of the reflectance of a low-reflectance film designed by a design method for a low-reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Diagram 25] 1 is a schematic diagram for explaining a method of designing a low reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Figure 26] 13 is a diagram showing the wavelength dependence of the reflectance of a low-reflectance film designed by a design method for a low-reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Figure 27] 1 is a schematic diagram for explaining a method of designing a low reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Figure 28] 13 is a diagram showing the wavelength dependence of the reflectance of a low-reflectance film designed by a design method for a low-reflectance film having an extremely small reflectance of the quantum cascade laser device according to the first and fifth embodiments. FIG. [Figure 29] FIG. 13 is a schematic view of a quantum cascade laser device according to a sixth embodiment. [Diagram 30] 29 in a quantum cascade laser device according to a sixth embodiment. FIG. [Diagram 31] FIG. 13 is a schematic view of a quantum cascade laser device according to a seventh embodiment. [Diagram 32] 32 is a cross-sectional view taken along the line ya-yb in FIG. 31 in the quantum cascade laser device according to the seventh embodiment. [Figure 33A] FIG. 2 is a diagram showing a process of a manufacturing method of the quantum cascade laser device according to the first to seventh embodiments. [Figure 33B] FIG. 2 is a diagram showing a process of a manufacturing method of the quantum cascade laser device according to the first to seventh embodiments. [Figure 33C] FIG. 2 is a diagram showing a process of a manufacturing method of the quantum cascade laser device according to the first to seventh embodiments. [Figure 33D] FIG. 2 is a diagram showing a process of a manufacturing method of the quantum cascade laser device according to the first to seventh embodiments. [Figure 33E] FIG. 2 is a diagram showing a process of a manufacturing method of the quantum cascade laser device according to the first to seventh embodiments. [Figure 33F] FIG. 2 is a diagram showing a process of a manufacturing method of the quantum cascade laser device according to the first to seventh embodiments. [Figure 33G] FIG. 2 is a diagram showing a process of a manufacturing method of the quantum cascade laser device according to the first to seventh embodiments. [Fig. 33H] FIG. 2 is a diagram showing a process of a manufacturing method of the quantum cascade laser device according to the first to seventh embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Embodiment 1 FIG. 1 is a schematic diagram showing a quantum cascade laser device 500 according to the first embodiment. FIG. 2 is a schematic diagram showing the y-axis of the quantum cascade laser device 500 according to the first embodiment. a -y b Quantum cascade laser device 500 has a cavity length L and a ridge width W. Quantum cascade laser device 500 has a buried ridge type waveguide structure.

[0011] As shown in FIGS. 1 and 2, the quantum cascade laser device 500 includes an n-type first electrode 1, an n-type InP substrate 2, an n-type InP first cladding layer 3, an Fe-doped InP current blocking layer 4, an n-type second electrode 5, a front end facet coating film 6, a rear end facet coating film 7, a terahertz light extraction surface 8, and an n-type Ga 0.47 In 0.53 1, an n-type GaInAs first optical confinement layer 9; a core region 10; an n-type GaInAs second optical confinement layer 11; an n-type InP second cladding layer 12; and an n-type GaInAs contact layer 13. ,of The n-type conductivity is also called the first conductivity type.

[0012] As shown in the cross-sectional view of FIG. 2, the quantum cascade laser device 500 is composed of an n-type GaInAs first optical confinement layer 9, a core region 10 which is a stacked structure (35 stages) in which 35 stages 40 each consisting of an active region 38 and an injector region 39 are stacked, an n-type GaInAs second optical confinement layer 11, an n-type InP second cladding layer 12, an n-type GaInAs contact layer 13, and an n-type second electrode 5.

[0013] FIG. 3 shows a 5.0×10 6 3 is a schematic diagram showing the band structure of the conduction band of one stage 40 when an electric field of 1000 V / m is applied. Such a band structure is disclosed in, for example, Non-Patent Document 2. As shown in FIG. 3, the stage 40 is composed of an active region 38 and an injector region 39.

[0014] The active region 38 is a 2.4 nm thick undoped Al 0.48 In 0.52The semiconductor layer is composed of an As (hereinafter abbreviated as AlInAs) barrier layer (undoped AlInAs barrier layer 21), an undoped GaInAs well layer 22 having a thickness of 6.5 nm, an undoped AlInAs barrier layer 23 having a thickness of 0.9 nm, an undoped GaInAs well layer 24 having a thickness of 6.6 nm, an undoped AlInAs barrier layer 25 having a thickness of 1.5 nm, an undoped GaInAs well layer 26 having a thickness of 3.2 nm, and a part of an undoped AlInAs barrier layer 27 having a thickness of 4.0 nm.

[0015] The injector region 39 is composed of the remainder of the 4.0 nm-thick undoped AlInAs barrier layer 27, an undoped GaInAs well layer 28 with a thickness of 4.1 nm, an undoped AlInAs barrier layer 29 with a thickness of 1.7 nm, an undoped GaInAs well layer 30 with a thickness of 3.7 nm, an undoped AlInAs barrier layer 31 with a thickness of 1.2 nm, an n-type GaInAs well layer 32 with a thickness of 3.4 nm and doped to be n-type, an n-type AlInAs barrier layer 33 with a thickness of 1.1 nm and doped to be n-type, an n-type GaInAs well layer 34 with a thickness of 3.4 nm and doped to be n-type, an undoped AlInAs barrier layer 35 with a thickness of 1.1 nm, an undoped GaInAs well layer 36 with a thickness of 2.9 nm, and an undoped AlInAs barrier layer 37 with a thickness of 2.4 nm.

[0016] The active region 38 is a region where electrons emit light by transitioning between subbands formed in the active region 38. The injector region 39 is a region where electrons are injected into the active region 38. In the first embodiment, the total number of well layers constituting the active region 38 is three, that is, three layers of GaInAs well layers 22, 24, and 26 are illustrated as an example. In the first embodiment, the doping concentrations of the n-type GaInAs well layer 32, the n-type AlInAs barrier layer 33, and the n-type GaInAs well layer 34 in the injector region 39 are, for example, 2.5×10 17 cm -3 Let us assume that.

[0017] 2, in the first embodiment, the total number of stages 40 is 35. Since 35 identical stages are connected in series, analysis of the laser characteristics using one stage 40 is sufficient.

[0018] 4 is a schematic diagram showing the quantum well structure of one stage of the quantum cascade laser device according to the embodiment 1 and the square of the wave function at each energy level. In other words, FIG. 4 shows the probability of electron existence.

[0019] There are a total of 10 energy levels allowed in one stage 40, and the energy levels in which electrons exist mainly in the active region 38 are indicated by solid lines, and the energy levels in which electrons exist mainly in the injector region 39 are indicated by dashed lines. The energy levels in which electrons exist mainly in the active region 38 are five, energy level #1, energy level #2, energy level #4, energy level #7, and energy level #9, and the energy levels in which electrons exist mainly in the injector region 39 are five, energy level #3, energy level #5, energy level #6, energy level #8, and energy level #10.

[0020] Calculation of the electron density in the stage 40 reveals that, among the energy levels in which electrons exist mainly in the active region 38, the electron density at energy level #4 is higher than the electron density at energy level #2, and thus a population inversion necessary for laser oscillation is formed.

[0021] 5 is a diagram showing an example of the wavelength dependence of gain in the quantum cascade laser device 500 according to the first embodiment. FIG. 5 shows the wavelength dependence of gain when an electric field is applied from the n-type second electrode 5 to the n-type first electrode 1 and a current of 137 mA is injected in the quantum cascade laser device 500 having a resonator length L of 1.36 mm and a ridge width W of 14 μm. qcl ) At 9.466 μm, the maximum gain value g p As a result, 20.09 cm -1 The maximum gain value g pThe total wavelength width Δλ between the two gain values ​​that occurs when the gain value decreases by 10% from qcl is calculated to be 1.00 μm.

[0022] Next, the loss of the quantum cascade laser device 500 will be considered. The total loss α t As shown in the following formulas (1) and (2), the loss (α wc ) and mirror loss (α mir ) can be expressed as the sum of

[0023]

number

[0024] In formula (2), R f , R r and L are the front end facet reflectance, the rear end facet reflectance, and the cavity length, respectively. In the first embodiment, the front end facet reflectance R f is designed as follows assuming that it has wavelength dependency. On the other hand, the rear facet reflectance R r The rear end face is coated with gold (Au) or other material to achieve a reflectivity of nearly 100%, and is said to be independent of wavelength.

[0025] Also, if α wc 5 cm -1 Considering the asymmetry of the gain distribution, the wavelength λ cot = 9.461μm, total loss α t is the maximum, i.e. 24.79cm -1 If the loss band is narrower than the gain band, it is estimated that it is possible to oscillate at two wavelengths. cot At α = 9.461 μm, the reflectivity is 0.459%, and the mirror loss α mir The maximum value is 19.79 cm. -1 is equivalent to. Therefore, the desired wavelength λ cotThe desired minimum reflectance R0 of 0.459% is realized at the desired wavelength λ cot The desired minimum reflectivity R0 is the maximum gain value g of the quantum cascade laser device. p , the wavelength λ at which the gain is maximum qcl The design method will be described later.

[0026] As disclosed in Non-Patent Document 3, the wavelength λ cot Refractive index n c A quantum cascade laser device with a refractive index of n f When a single-layer coating made of Al2O3 with a reflectance of 1.72 is applied, the reflectance changes periodically with the thickness of the coating. f is λ cot / (4n f The minimum reflectance R0 in this case is expressed by the following formula (3) and is uniquely determined.

[0027]

number

[0028]

number

[0029] The same is true when applied to a quantum cascade laser device. As is clear from equation (4), in order to obtain the desired minimum reflectance R0 with a single-layer coating film, the refractive index (n fl ,n fh ) needs to be changed, but so far no material has been found that has this refractive index and is substantially free of absorption in the mid-infrared light emission wavelength range of quantum cascade laser devices. Therefore, the minimum reflectance R0 of the single-layer coating is replaced with a multi-layer coating made of multiple materials that do not absorb mid-infrared light.

[0030] High refractive index fh In the first embodiment, the case of n fl The effective refractive index n c is 3.2, and the desired minimum reflectance R0 of the single-layer coating is R0 = 0.00459 (0.459%), the refractive index n fl is calculated as 1.67150083 from equation (4).

[0031] At least one of the single-layer coatings has a refractive index of n fl and at least one of the materials has a refractive index n fl Consider replacing the material with a three-layer coating of three materials with known refractive indices, each of which has a higher refractive index than the other material.

[0032] Figure 6 shows the refractive index n fl and the film thickness d fl is λ cot / (4n fl ) are respectively formed by dividing the single-layer coating film 42 into two layers, one with a refractive index of n1 and a thickness of d1, one with a refractive index of n2 and a thickness of d2, and one with a refractive index of n3 and a thickness of d4. n 6 is a schematic diagram showing the case where the effective refractive index n c The refractive index n fl (=1.67150083) and the film thickness d fl = λ cot / (4n fl ), a first coating film 43 having a refractive index n1 and a thickness d1, a second coating film 44 having a refractive index n2 and a thickness d2, and a n 3 and the third coating film 45 having a thickness d3. If the single-layer coating film 42 can be replaced with a three-layer coating film, the characteristic matrices of the two become equal, as expressed by the following formula (5).

[0033]

number

[0034]

number

[0035] In formula (5), the refractive index n1 , refractive index n 2 and refractive index n Since 3 is known, the unknowns are the film thicknesses d1, d2, and d3, and each film thickness can be calculated by solving equation (5).

[0036] wavelength λ cot = 9.461 μm, the first coating film 43 has a refractive index of n fl The second coating film 44 is made of YF3 having a refractive index n1=1.40 lower than that of the first coating film 44. fl ZnSe, which has a refractive index n2=2.41 higher than that of the third coating film 45, is used as the third coating film 45. fl Using CeF3, which has a refractive index n1=1.45 lower than that of the first coating film 43, as an example, the following equation (5) is solved: d1=609.328 nm, d2=183.785 nm, and d3=697.248 nm. In order to narrow the reflectance band, a 1000 nm thick fluorine-containing layer having a refractive index n a and the film thickness d a is λ cot / (2n a ) may be inserted.

[0037] 7 is a schematic diagram showing the film configuration of the four-layer coating film according to the first embodiment. In FIG. 7, the coating film 46 has a refractive index of n a and the film thickness d a is λ cot / (2n a The characteristic matrix of the four-layer coating membrane is expressed by the following equation (7).

[0038]

number

[0039]

number

[0040]

number

[0041] An example of the material of the inserted coating film 46 is a material having a refractive index n a The thickness of the coating film 46 is set to 1.70. cot = 9.461 μm a = λ cot / (2n a )=2782.60 nm. In a quantum cascade laser device having a three-layer coating film with thicknesses d1=609.328 nm, d2=183.785 nm, and d3=697.248 nm, when a coating film 46 is inserted between the end face of the quantum cascade laser device 41 and the first coating film 43, the wavelength dependence of the reflectance is as shown by the dashed line 47 in FIG. 8. min = 9.449 μm, the minimum reflectance value R of the four-layer coating min 0 is 0.4576%. In this disclosure, R min and R min 0 The meanings are as follows: (1)R min : The minimum reflectance of a multilayer coating when the set reflectance R1 of a single-layer coating is replaced by a multilayer coating (2)R min 0: The minimum reflectance of a multilayer coating when the desired minimum reflectance R0 of a single-layer coating is replaced by a multilayer coating

[0042] The minimum reflectance R0 of the desired single-layer coating is R0 = 0.459%, whereas the minimum reflectance R0 of the four-layer coating is min 0 The reflectance of the four-layer coating is 0.4576%, which is lower than the minimum reflectance R0 of the single-layer coating. min In order to achieve the desired minimum reflectance R0, the set reflectance R1 is set high at 0.460388%. The guideline for the increment in reflectance ΔR0 is R0-R min 0 = 0.0014%, and adjust the increment ΔR0 until it coincides with the desired minimum reflectance R0. In the first embodiment, the increment ΔR0 = 0.00139%.

[0043]

number

[0044]

number

[0045] By solving equation (12) to calculate the thickness of each coating film, d1=609.407 nm, d2=183.660 nm, and d3=697.402 nm are calculated. a is 1.70 and the film thickness d a The wavelength dependency of reflectance when a coating film 46 having a wavelength λ of 2782.60 nm is inserted is shown by a two-dot chain line 48 in FIG. min = 9.449μm, the minimum reflectance of the three-layer coating min Therefore, the desired minimum reflectance R0 of 0.459% can be obtained.

[0046] Next, each film thickness is expressed as λ cot / λ min Double that, d a The wavelength dependence of the reflectance in this case is shown by a solid line 49 in FIG. cot At 9.461 μm, the minimum reflectance R0 is 0.459%. For reference, the refractive index n fl (=1.67150083) and the film thickness d fl The wavelength dependence of the reflectance of a single coating film with a reflectance of 0.1 nm is shown by dashed line 50 in FIG.

[0047] The above-mentioned replacement method will be explained with reference to FIG. (1) The desired wavelength (λ cot In order to replace the desired minimum reflectance (R0) of the single-layer coating film at the wavelength (dotted line 50a for the reflectance dependence on wavelength), with the three-layer coating film, the thickness of each layer of the three-layer coating film is determined so that the characteristic matrices of both are equal. Next, a and the film thickness d a is λ cot / (2n a The wavelength dependence of the reflectance of the four-layer coating film with the coating film 46 having a refractive index of n a and the film thickness is λ cot / (2n a ) the coating film 46 has a wavelength λ cot Since it has no effect on the reflectance at wavelength λ cot The minimum reflectance at is R0, but the minimum reflectance value of the four-layer coating film (minimum reflectance value R min 0 ) and the wavelength at which the reflectance becomes minimum (λ min ) deviates from the normal. The wavelength dependency of the reflectance in this case is represented by the dashed line 47a in FIG. (2) The set reflectance R1 of the single-layer coating film is R1 = R0 + ΔR0 (wavelength dependence of reflectance is dashed line 50b), and the thickness of each of the three-layer coating films that has the same characteristic matrix is ​​calculated. a and the film thickness d a is λ cot / (2n aThe wavelength dependence of the reflectance of the four-layer coating film with the coating film 46 inserted is calculated. min The minimum reflectance at the desired minimum reflectance R min =Minimum reflectance R0. The wavelength dependency of the reflectance in this case is represented by a two-dot chain line 48a in FIG. (3) Wavelength λ cot The thickness of each of the four coating layers is set to λ so that the minimum reflectance R0 is obtained at cot / λ min The wavelength dependency of the reflectance in this case is represented by a solid line 49a in FIG.

[0048] 10 is a diagram showing the wavelength dependence of the reflectance of the coating film and the wavelength dependence of the mirror loss shown in FIG. 8. In FIG. 10, a dotted line 51 shows the reflectance R f , and the solid line 52 represents the mirror loss α mir The other end face (rear end face) is coated with gold (Au) to achieve a reflectance of R r The mirror loss α mir is calculated using the above formula (2).

[0049] Mirror loss α mir is the maximum value of 19.79 cm. -1 and a 10% reduction in maximum mirror loss (Δλ mir ) is 0.387 μm, and the full width of the wavelength between the two gain values, Δλ qcl As mentioned above, the loss α that is almost independent of the wavelength, such as the waveguide loss and carrier absorption, wc 5 cm -1 Then, the total loss α t The maximum value is 24.79 cm -1 It becomes.

[0050] Figure 11 shows the wavelength dependence of gain and total loss α t In FIG. 11, the dotted line 61 indicates the wavelength dependence of the gain, and the solid line 62 indicates the total loss α t The wavelength dependence of the gain and total loss αt is equal at two points, λ1 and λ2. In general, a laser has a gain and a total loss α t Since oscillation occurs when the wavelengths λ1 and λ2 are equal, one quantum cascade laser device 500 oscillates at two wavelengths. The wavelength λ1 of the first laser oscillation is 8.802 μm, and the wavelength λ2 of the second laser oscillation is 10.151 μm. The angular frequency ω1 is 2.14005×10 14 Hz and ω2 are 1.85564×10 14 Hz.

[0051] Due to the nonlinear optical effect of the InP crystal, the difference angular frequency is ω1-ω2=2.8441×10 13 Hz, difference frequency f1-f2=4.52656×10 12 Hz (4.53 THz) can be obtained. The wavelength corresponding to the difference frequency f1-f2 is 66.230 μm.

[0052] FIG. 12 is a diagram showing a quantum cascade laser device 500 according to the first embodiment, in which the x a -x b A cross-sectional view taken along the line. The terahertz wave (ω1-ω2) is emitted in the direction of the Cherenkov angle (θ) that satisfies the phase matching condition. Normally, the Cherenkov angle θ is about 20°, so when the laser light reaches the end face, it satisfies the total reflection condition and cannot be extracted to the outside of the quantum cascade laser device 500. Therefore, the end face is inclined obliquely by polishing or the like, and the laser light is extracted to the outside of the quantum cascade laser device 500. Note that the total number of stages 40 of the quantum cascade laser device 500, 35, is an example and is not limited to this, and can be changed according to the required characteristics.

[0053] The features of the quantum cascade laser device 500 according to the first embodiment are summarized below. The quantum cascade laser device 500 according to the first embodiment includes an n-type InP substrate 2, an n-type InP first cladding layer 3 of a first conductivity type (n-type) formed on the n-type InP substrate 2, a core region 10 formed on the n-type InP first cladding layer 3 and including a plurality of stages 40 each having an active region 38 in which barrier layers and well layers are alternately formed, and an injector region 39 for injecting electrons into the active region, and an n-type InP second cladding layer 12 of the first conductivity type formed on the core region 10. The resonator length is L, and a wavelength λ qcl The wavelength width between the two points where the gain is maximum and the gain value drops to a preset percentage of the maximum gain value is defined as Δλ qcl In this case, the wavelength λ qcl λ is a wavelength that is a preset wavelength away from cot A low-reflectance film (front end surface coating film 6) is provided at the front end surface, and the reflectance of the other end surface R r and the mirror loss α calculated from the cavity length L mir The wavelength width between the two points where the mirror loss value occurs when a preset loss value is subtracted from the maximum value of mir In this case, Δλ mir is Δλ qcl It is characterized by being smaller than

[0054] In the first embodiment, the mirror loss α mir The wavelength λ at which cot (9.461 μ m) is the wavelength λ at which the gain is maximum. qcl (9.466μm), but the total loss band is the mirror loss α mir If the bandwidth is wider than λ and the total loss and gain are equal at two wavelengths, then cot is λ qcl It may be the same as.

[0055] In addition, a desired wavelength (λ cotThe low reflectance film having the desired minimum reflectance (R0) at 100 nm utilizes the concept of the design method of the low reflectance film of the first embodiment, and it is not necessary for each coating film of the multilayer coating film to strictly match the values ​​shown in the first embodiment in manufacturing. In other words, the mirror loss α mir If the band is narrower than the gain band of the quantum cascade laser device, the function will be fully exhibited.

[0056] <Advantages of the First Embodiment> As described above, according to the quantum cascade laser device according to the first embodiment, the wavelength λ qcl The gain is maximum at Δλ, and the wavelength width between two points where the gain value is lower than the maximum gain value by a preset percentage is defined as qcl In this case, the wavelength λ qcl λ is a wavelength that is a preset wavelength away from cot A low reflectance film is provided, which has a minimum reflectance at the mirror loss α mir The wavelength width between the two points where the mirror loss value occurs when a preset loss value is subtracted from the maximum value of mir In this case, Δλ mir is Δλ qcl Since the distance is set to be smaller than the distance t1, it is possible to obtain a quantum cascade laser device that can easily realize terahertz oscillation.

[0057] Embodiment 2 13 is a cross-sectional view of a quantum cascade laser apparatus 600 according to the second embodiment. The quantum cascade laser apparatus 600 according to the second embodiment includes a temperature adjustment device 71. That is, in the quantum cascade laser apparatus 600 according to the second embodiment, a quantum cascade laser apparatus 74 is installed on a temperature adjustment device 71 such as a Peltier element. The quantum cascade laser apparatus 74 is the same as the quantum cascade laser apparatus 500 according to the first embodiment.

[0058] 13, quantum cascade laser device 74 according to the second embodiment includes temperature adjustment device 71, metal block 72 bonded onto temperature adjustment device 71, submount 73 bonded to metal block 72, and quantum cascade laser device 74 bonded onto submount 73. In order to reduce thermal resistance, quantum cascade laser device 74 is bonded to submount 73 with the epitaxial crystal growth layer side facing down (Epi-side down).

[0059] Mirror loss α mir , the total loss α t The distribution of the λ / 2 wavelength is almost independent of temperature, whereas the gain distribution depends on temperature and shifts to longer wavelengths as the temperature increases.

[0060] When a current is injected into the quantum cascade laser device 74 to increase the gain, and the temperature control device 71 is driven to change the temperature of the quantum cascade laser device 74, the gain peak wavelength and the mirror loss α mir Even if the maximum wavelength of the gain is adjusted relatively roughly in advance, the gain and total loss α t Since it is possible to make these values ​​equal, terahertz oscillation can be easily performed.

[0061] In addition, even if the gain distribution fluctuates over time during operation, resulting in single-wavelength oscillation and causing the terahertz oscillation to stop, the oscillation can be easily restored to two-wavelength oscillation by adjusting the amount of current injected into quantum cascade laser device 74 and the temperature using temperature control device 71, making it easy to restore the terahertz oscillation.

[0062] <Advantages of the second embodiment> As described above, the quantum cascade laser device according to the second embodiment has an effect of providing a quantum cascade laser device in which the terahertz oscillation can be easily restored by adjusting the temperature of the quantum cascade laser device using the temperature adjustment device.

[0063] Embodiment 3 The quantum cascade laser device of the present disclosure has a gain band that is smaller than the mirror loss αmir The third embodiment is characterized by a wider gain band than the first embodiment. Therefore, in the third embodiment, an example of a quantum cascade laser device with a wider gain band is shown. FIG. 14 shows the quantum well structure of one stage 106 in the quantum cascade laser device according to the third embodiment and the square of the wave function at each energy level, which is the structure described in Non-Patent Document 4.

[0064] As shown in FIG. 14, one stage 106 is composed of an active region 104 and an injector region 105 .

[0065] The active region 104 is composed of an undoped AlInAs barrier layer 81 having a thickness of 1.8 nm, an undoped GaInAs well layer 82 having a thickness of 5.2 nm, an undoped AlInAs barrier layer 83 having a thickness of 1.5 nm, an undoped GaInAs well layer 84 having a thickness of 5.8 nm, an undoped AlInAs barrier layer 85 having a thickness of 0.7 nm, an undoped GaInAs well layer 86 having a thickness of 7.5 nm, an undoped AlInAs barrier layer 87 having a thickness of 2.7 nm, an undoped GaInAs well layer 88 having a thickness of 3.1 nm, and a part of an undoped AlInAs barrier layer 89 having a thickness of 3.7 nm.

[0066] The injector region 105 is made up of the remainder of the 3.7 nm-thick undoped AlInAs barrier layer 89, an undoped GaInAs well layer 90 having a thickness of 3.3 nm, an undoped AlInAs barrier layer 91 having a thickness of 2.8 nm, an undoped GaInAs well layer 92 having a thickness of 3.4 nm, an undoped AlInAs barrier layer 93 having a thickness of 2.3 nm, an undoped GaInAs well layer 94 having a thickness of 3.4 nm, an n-type AlInAs barrier layer 95 having a thickness of 2.0 nm that is doped to be n-type, and an undoped GaInAs well layer 96 having a thickness of 3.4 nm that is doped to be n-type. 1.7 nm thick n-type GaInAs well layer 96, 1.7 nm thick n-type AlInAs barrier layer 97 doped to be n-type, 3.5 nm thick n-type GaInAs well layer 98 doped to be n-type, 1.6 nm thick undoped AlInAs barrier layer 99, 3.8 nm thick undoped GaInAs well layer 100, 1.5 nm thick undoped AlInAs barrier layer 101, 4.1 nm thick undoped GaInAs well layer 102, and 1.8 nm thick undoped AlInAs barrier layer 103.

[0067] There are two upper energy levels that contribute to light emission, energy level #3 and energy level #4, and one lower energy level, energy level #2. To quickly extract electrons from the lower energy levels, there is a ground energy level #1 below the lower energy levels. This structure is called a dual-upper-state to single-lower-state transition (DAU / SS), and has a wider gain band than those with a single transition process.

[0068] <Advantages of the Third Embodiment> As described above, according to the quantum cascade laser device of the third embodiment, the gain band of the quantum cascade laser device is wider than the band of the mirror loss derived from the reflective film provided on the end face, thereby achieving the effect of easily oscillating terahertz waves.

[0069] Embodiment 4 The quantum cascade laser device of the present disclosure has a gain band that is smaller than the mirror loss α mir Therefore, in the fourth embodiment, an example in which the gain bandwidth of a quantum cascade laser device is widened is shown.

[0070] FIG. 15 shows the quantum well structure of one stage 136 in the quantum cascade laser device according to the fourth embodiment and the square of the wave function at each energy level, and is the structure described in Non-Patent Document 5.

[0071] As shown in FIG. 15, one stage 136 is composed of an active region 134 and an injector region 135 .

[0072] The active region 134 is composed of an undoped AlInAs barrier layer 111 having a thickness of 1.5 nm, an undoped GaInAs well layer 112 having a thickness of 4.1 nm, an undoped AlInAs barrier layer 113 having a thickness of 1.2 nm, an undoped GaInAs well layer 114 having a thickness of 5.2 nm, an undoped AlInAs barrier layer 115 having a thickness of 1.0 nm, an undoped GaInAs well layer 116 having a thickness of 5.8 nm, an undoped AlInAs barrier layer 117 having a thickness of 0.9 nm, an undoped GaInAs well layer 118 having a thickness of 7.5 nm, an undoped AlInAs barrier layer 119 having a thickness of 2.7 nm, an undoped GaInAs well layer 120 having a thickness of 3.1 nm, and a part of an undoped AlInAs barrier layer 121 having a thickness of 3.7 nm.

[0073] The injector region 135 is made up of the remainder of the 3.7 nm-thick undoped AlInAs barrier layer 121, an undoped GaInAs well layer 122 with a thickness of 3.3 nm, an undoped AlInAs barrier layer 123 with a thickness of 2.8 nm, an undoped GaInAs well layer 124 with a thickness of 3.4 nm, an undoped AlInAs barrier layer 125 with a thickness of 2.3 nm, an undoped GaInAs well layer 126 with a thickness of 3.4 nm, and an n-type AlInAs barrier layer 127 with a thickness of 2.0 nm that is doped to be n-type. The semiconductor device is made up of an n-type AlInAs barrier layer 129 doped to be n-type and having a thickness of 3.5 nm, an n-type GaInAs well layer 130 doped to be n-type and having a thickness of 3.5 nm, an undoped AlInAs barrier layer 131 having a thickness of 1.6 nm, an undoped GaInAs well layer 132 having a thickness of 3.8 nm, and an undoped AlInAs barrier layer 133 having a thickness of 1.5 nm.

[0074] The upper energy levels that contribute to light emission are energy level #3 and energy level #4, and the lower energy level is a miniband #2mb consisting of four subbands. In order to quickly extract electrons from the lower energy levels, a ground level #1mb consisting of three subbands exists below the lower energy levels. This structure is called a dual-upper-state to multiple-lower-state transition (DAU / MS), and can widen the gain band more than the DAU / SS of the third embodiment.

[0075] <Advantages of the Fourth Embodiment> As described above, according to the quantum cascade laser device of the fourth embodiment, the gain band of the quantum cascade laser device is wider than the band of mirror losses derived from the reflective film provided on the end face, thereby achieving the effect of making it even easier to oscillate terahertz waves.

[0076] Embodiment 5. In the quantum cascade laser device according to the fifth embodiment, the gain band of the quantum cascade laser device is mir In the third and fourth embodiments, examples of widening the gain band of the quantum cascade laser device are shown, but in the fifth embodiment, the mirror loss α mir An example of narrowing the bandwidth is shown below.

[0077] 16 is a schematic diagram showing a part of a quantum cascade laser device according to the fifth embodiment, in which a coating film 141 is added to the outside of the third coating film 45 in FIG. 7 showing the first embodiment. In FIG. 16, the coating film 141 has a refractive index of n b and the film thickness d b is λ cot / (2n b The characteristic matrix of the five-layer coating film is expressed by the following equation (13).

[0078]

number

[0079]

number

[0080] As an example, the additional coating film 141 may be formed with a refractive index of n b If the thickness of the film is ZnS with a wavelength of λ cot = 9.461 μm b = λ cot / (2n b ) = 2150.20 nm.

[0081] The aforementioned film thickness d aThe wavelength dependency of reflectance when a coating film 141 is provided as the final layer of each coating film of wavelength λ = 2782.600 nm, d1 = 609.328 nm, d2 = 183.785 nm, and d3 = 697.248 nm (double-dashed line 48 in FIG. 8) is shown by a dashed line 142 in FIG. min = 9.458 μm, the minimum reflectance value R of the five-layer coating min 0 is 0.4600%.

[0082] Minimum reflectance R0 of a single-layer coating a : 0.460388%, the minimum reflectance value R of the five-layer coating min 0 The minimum reflectance R0 of the single-layer coating is 0.4600%. a However, it is higher than the desired minimum reflectance R0. Therefore, the minimum reflectance R min In order to obtain the desired minimum reflectance R0, if the set reflectance R1 of the single-layer coating film is set to 0.459324% in equation (11), the refractive index n fl 1 is calculated as 1.6714607.

[0083] By solving equation (12) to calculate the thickness of each coating film, the following values ​​are calculated: d1 = 609.347 nm, d2 = 183.756 nm, and d3 = 697.284 nm. a is 1.70 and the film thickness d a The coating film 46 having a refractive index of 2782.60 nm was inserted as the final coating film. b is 2.20 and the film thickness d b The wavelength dependency of reflectance when a coating film 141 having a reflectance of 2150.20 nm is provided is shown by a two-dot chain line 143 in FIG. min is the wavelength λ min = 9.458 μm, the desired minimum reflectance R0 of 0.459% can be obtained.

[0084] Next, each film thickness is expressed as λ cot / λ min Double that, d a=2783.4826nm, d1=609.5403nm, d2=183.8143nm, d3=697.5052nm, d b The wavelength dependency of the reflectance in this case is shown by a solid line 144 in FIG. cot It can be seen that the minimum reflectance is 0.459% at = 9.461 μm.

[0085] The above-mentioned replacement method will be explained with reference to FIG. (1) The dashed line 50a in FIG. 18 represents the desired wavelength λ cot The dashed line 48a in FIG. 18 represents the wavelength dependence of the reflectance of the single-layer coating film having the minimum reflectance R0. a This shows the wavelength dependence of reflectance for d1 = 2782.600 nm, d1 = 609.328 nm, d2 = 183.785 nm, and d3 = 697.248 nm (double-dashed line 48) in FIG. 8). (2) The wavelength dependence of the reflectance of a five-layer coating film in which a coating film 141 is provided on the final layer of the four-layer coating film described above is represented by a two-dot chain line 142a in FIG. b and the film thickness is d b = λ cot / (2n b ) so the wavelength λ cot There is no effect on reflectance at wavelength λ cot The reflectance of the five-layer coating at is the same as the set reflectance of the four-layer coating, R0 a = 0.460388%. The minimum reflectance value R min 0 is 0.4600%. Wavelength λ cot At minimum reflectance R0 a (=0.460388%), the refractive index of the single-layer coating fl 1 is 1.67132893 for the four-layer coating film described above, and the wavelength dependency of the reflectance of the single-layer coating film is shown by the dashed line 50b in FIG. cot At minimum reflectance R0 a A single-layer coating film (whose reflectance depends on wavelength: 50b) with a refractive index of n a and the film thickness is d a = λcot / (2n a ) and the refractive index n b and the film thickness is d b = λ cot / (2n b ), the wavelength dependence of the reflectance is represented by the two-dot chain line 142a in FIG. 18, and the wavelength λ min The minimum reflectance value R of the five-layer coating is min 0 It becomes.

[0086] (3) Minimum reflectance R0 of a single-layer coating a : 0.460388%, the minimum reflectance value R of the five-layer coating min 0 The minimum reflectance R0 of the single-layer coating is 0.4600%. a However, it is higher than the desired minimum reflectance R0. Therefore, the minimum reflectance R min In order to obtain the desired minimum reflectance R0, if the set reflectance R1 of the single-layer coating film is set to 0.459324% in equation (11), the refractive index n fl 1 The thickness of each coating film is calculated by solving equation (12), and the refractive index n a and the film thickness d a The coating film 46 having a refractive index of n b and the film thickness d b Then, the wavelength dependency of the reflectance is calculated (two-dot chain line 143a in FIG. 18). min The desired minimum reflectance R0 is obtained. (4) Wavelength λ cot The thickness of each of the five coating layers is set to λ so that the minimum reflectance R0 is obtained at cot / λ min In this case, the wavelength dependency of the reflectance is shown by a solid line 144a in FIG.

[0087] In addition, a desired wavelength (λ cot) a low reflectance film having a desired minimum reflectance (R0) utilizes the concept of the design method of the low reflectance film of the fifth embodiment, and in manufacturing, each coating film of the multilayer coating film does not have to strictly match the value shown in the fifth embodiment. In other words, the mirror loss α mir If this band is narrower than the gain band of the quantum cascade laser device, the function of the fifth embodiment can be sufficiently exhibited.

[0088] FIG. 19 shows the reflectance and mirror loss α mir 19 is a graph showing the wavelength dependence of the reflectance in comparison with the first embodiment. In FIG. 19, the dotted line 145 indicates the wavelength dependence of the reflectance, and the solid line 146 indicates the mirror loss α mir 19 shows the wavelength dependence of the reflectance and the mirror loss distribution, respectively. From FIG. 19, it can be seen that the minimum reflectance and the maximum mirror loss do not change, but the reflectance distribution and the mirror loss distribution become narrower. The full width (Δλ mir ) is 0.184 μm, which is about half the value achieved in the first embodiment.

[0089] <Advantages of the Fifth Embodiment> As described above, according to the quantum cascade laser device according to the fifth embodiment, the mirror loss α mir Since a state in which the gain band is narrower than the gain band can be easily achieved, the effect is that the oscillation of terahertz waves can be more easily performed.

[0090] The present disclosure provides a method for detecting a desired wavelength (λ cot ) and thus obtaining the desired minimum reflectivity (R0) at the desired wavelength. Therefore, the method for achieving the desired minimum reflectivity at the desired wavelength is described in detail below.

[0091] Effective refractive index is n c The quantum cascade laser device 211 is cot The refractive index is n f and the film thickness is λ cot / (4n f), the reflectance of the single-layer coating film becomes the minimum reflectance R0, which is the minimum value. The minimum reflectance R0 is expressed by the above formula (3).

[0092] Conversely, from equation (3), the refractive index n of the coating film to achieve the desired minimum reflectance R0 is fl , and the refractive index n fh is calculated using equation (4) above.

[0093] For example, the effective refractive index n c is 3.2 and the minimum reflectance R0 = 0.005 (0.5%), the refractive index n fl and the refractive index n fh are calculated to be 1.666535 and 1.920152, respectively. However, in terms of reliability and cost, there are currently no materials constituting the coating film that have these refractive index values ​​and are applicable to quantum cascade laser devices. Therefore, in the present disclosure, the above-mentioned refractive index values ​​are realized by replacing them with known materials.

[0094] First, the refractive index n fl = 1.666535. A single-layer coating film with a refractive index of n fl and materials with a refractive index lower than n fl Consider replacing the material with a three-layer coating of two materials, one of which has a higher refractive index than the other.

[0095] Figure 20 shows the refractive index n fl and the film thickness d fl is λ cot / (4n fl 20 is a schematic diagram showing a case where the single-layer coating film 212 having an effective refractive index n1 and a thickness d1, a three-layer coating film having an effective refractive index n2 and a thickness d2, and a three-layer coating film having an effective refractive index n1 and a thickness d3, respectively. c and wavelength λ cot The refractive index n fl (=1.66535) and the film thickness d fl = λ cot / (4n fl) is replaced with a three-layer coating film consisting of a first coating film 213 with a refractive index n1 and a thickness d1, a second coating film 214 with a refractive index n2 and a thickness d2, and a third coating film 215 with a refractive index n1 and a thickness d3. If the single-layer coating film 212 can be replaced with a three-layer coating film, the characteristic matrices of both become equal, as expressed by the following equation (16).

[0096]

number

[0097]

number

[0098] In equation (16), the refractive indexes n1 and n2 are known, so there are three unknowns: film thicknesses d1, d2, and d3. Each film thickness can be calculated by solving equation (16).

[0099] wavelength λ cot = 10 μm, the first coating film 213 and the third coating film 215 have a refractive index of n fl The second coating film 214 is made of YF3 having a refractive index n1=1.40 lower than that of the first coating film 214. fl When equation (16) is solved using ZnS, which has a higher refractive index n2=2.20 than that of ZnS, as an example, the thicknesses of the coating films are d1=654.371 nm, d2=277.806 nm, and d3=654.371 nm, respectively. The wavelength dependence of the reflectance in this case is shown by the dashed dotted line 222 in FIG. 21. The reflectance is 0.5% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R min 0 is 0.4857%.

[0100] The minimum reflectance of a single-layer coating is R0:0.5%, whereas the minimum reflectance of a three-layer coating is R min 0The reflectance of the three-layer coating is 0.4857%, which is lower than the minimum reflectance R0 of the single-layer coating. min In order to achieve the desired minimum reflectance R0, the set reflectance R1 is set high. The guideline for the reflectance increment ΔR0 is R0-R min 0 = 0.0143%, and adjust the increment ΔR0 until it coincides with the desired minimum reflectance R0. In the sixth embodiment, the increment ΔR0 = 0.0146%, and the set reflectance R1 is 0.51460%. From the following equation (18), the refractive index n fl 1 is calculated as 1.6648189.

[0101]

number

[0102] In other words, from equation (18), the refractive index n of the single-layer coating film to achieve R1 = 0.51460% is fl 1 is calculated as 1.6648189. By solving the following equation (19), the thickness of each coating film is calculated as d1 = 655.839 nm, d2 = 276.062 nm, and d3 = 655.839 nm, respectively.

[0103]

number

[0104] The wavelength dependence of the reflectance in this case is shown by the two-dot chain line 223 in FIG. min is the wavelength λ min = 9.876 μm, the desired minimum reflectance of 0.5% can be obtained.

[0105] Next, the wavelength λ at which the reflectance becomes minimum min , the desired wavelength λ cot The thickness of each coating film is set to λ cot / λ minMultiplying by 1, the results are d1 = 664.074 nm, d2 = 279.528 nm, and d3 = 664.074 nm. The wavelength dependence of the reflectance in this case is shown by the solid line 224 in FIG. 21. cot It can be seen that the reflectance reaches a minimum of 0.5% at 10 μm.

[0106] In addition, the dashed line 221 in FIG. fl and the film thickness is λ cot / (4n fl 21 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.1 μm / cm2 (wherein the reflectance is 0.1 μm / cm2). Although the solid line 224 and the dashed line 221 in Fig. 21 do not completely match, they show almost the same wavelength dependence of reflectance, and the minimum reflectance and the wavelength at which the minimum reflectance is obtained are completely the same.

[0107] Minimum reflectance R0=0.5% and wavelength λ cot In the above example, YF3 is used for the first coating film 213 and the third coating film 215, and ZnS is used for the second coating film 214, but the present invention is not limited to these examples. fl and n fl 1 At least one material with a refractive index higher than n fl and n fl 1 There must be at least one ingredient that is lower than , and the order of ingredients can be chosen arbitrarily. From the above, it can be seen that a desired minimum reflectance at a desired wavelength can be achieved by using a material with a known refractive index.

[0108] FIG. 22 shows the wavelength λ cot The refractive index n at which the reflectance R0 is minimum fl and the film thickness is λ cot / (4n fl 22 is a schematic diagram showing a method of replacing a single-layer coating film having a refractive index n fl and the film thickness λ cot / (4n fl ) represents the wavelength dependence of the reflectance of a single-layer coating film, and the wavelength λ cotIt shows a minimum reflectance R0 at

[0109] The above substitution method is explained below. (1) In order to replace the single-layer coating film (dashed line 221a) with a three-layer coating film, the thicknesses of the three-layer coating film are determined so that the characteristic matrices of both are equal. In this case, the wavelength λ cot The minimum reflectance R0 is reached at the three-layer coating film. min 0 ) and the wavelength λ at which the reflectance becomes minimum min The wavelength dependency of the reflectance in this case is represented by the dashed line 222a in FIG. (2) The set reflectance R1 of the single-layer coating film is set as R1 = R0 + ΔR0 (dashed line 221b), and the thicknesses of the three-layer coating film that make the characteristic matrix equal are calculated, and the wavelength λ min The minimum reflectance value R of a three-layer coating is desired. min =Minimum reflectance R0. The wavelength dependency of the reflectance in this case is represented by the two-dot chain line 223a in FIG. (3) Wavelength λ cot The thickness of each of the three coating layers is set to λ so that the minimum reflectance R0 is obtained at cot / λ min The wavelength dependency of the reflectance in this case is represented by a solid line 224a in FIG.

[0110] The method for setting the set reflectance R1 will be described in more detail below. The minimum reflectance of the three-layer coating film at the first substitution is R min 0(0) If R0 is not satisfied, the difference between the desired minimum reflectance R0 and the reflectance ΔR0 (0) is ΔR0 (0) =R0-R min 0(0) Next, the set reflectance R1 of the single-layer coating for the first loop (1) , R1 (1) =R0+ΔR0 (0) Then, the three-layer coating is replaced to minimize the reflectance R min 0(1) Calculate the result, R min 0(1)If =R0, the calculation ends here. In this case, ΔR0=ΔR0 (0) , R1=R1 (1) It becomes.

[0111] R min 0(1) If R0, the process moves to the second loop. The difference between the desired minimum reflectance R0 and the actual reflectance ΔR0 (1) is ΔR0 (1) =R0-R min 0(1) The set reflectance R1 of the single-layer coating (2) , R1 (2) =R0+ΔR0 (1) Then, the three-layer coating is replaced to minimize the reflectance R min 0(2) Calculate.

[0112] The calculated result is R min 0(2) If =R0, the calculation ends here. In this case, ΔR0 = ΔR0 (1) , R1=R1 (2) It becomes. R min 0(2) If ≠ R0, the process moves to the third loop and the calculation is repeated in the same way. min 0(k) By looping k times until R1 = R0, the set reflectance R1 = R1 (k) can be determined. The above is the method for setting the set reflectance R1.

[0113] Similarly, the refractive index n fh = 1.920152. A single-layer coating film with a refractive index of n fh and materials with a refractive index lower than n fh Consider replacing the material with a triple coating of at least two materials with a higher refractive index than the material ...

[0114] Figure 23 shows the refractive index n fh and the film thickness d fh is λ cot / (4n fh23 is a schematic diagram showing a case where the single-layer coating film 231 having an effective refractive index n1 and a thickness d1, the refractive index n2 and a thickness d2, and the refractive index n1 and a thickness d3 are respectively replaced with a three-layer coating film having an effective refractive index n c Wavelength λ cot The refractive index n fh (=1.920152) and the film thickness d fh = λ cot / (4n fh The single-layer coating film 231, which has a refractive index of n1 and a thickness of d1, the second coating film 233, which has a refractive index of n2 and a thickness of d2, and the third coating film 234, which has a refractive index of n1 and a thickness of d3, are replaced with a three-layer coating film. fl This is the same as in the case of (1), and is carried out by solving the following equation (20).

[0115]

number

[0116] wavelength λ cot = 10 μm, the first coating film 232 and the third coating film 234 have a refractive index of n fh The second coating film 233 is made of YF3 having a refractive index n1=1.40 lower than that of the first coating film 233. fh Taking ZnS, which has a higher refractive index n2=2.20, as an example, solving equation (20) gives d1=434.257 nm, d2=547.934 nm, and d3=434.257 nm, respectively. The wavelength dependence of reflectance in this case is shown by the dashed line 236 in FIG. 24. The reflectance is 0.5% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R of the reflectance of the three-layer coating film. min 0 is 0.4715%.

[0117] The minimum reflectance of a single-layer coating is R0:0.5%, whereas the minimum reflectance of a three-layer coating is R min 0is 0.4715%, which is lower than the minimum reflectance R0 of the single-layer coating. fl As in the case of min In order to obtain the desired reflectance R0, the set reflectance R1 is set to a high value of 0.53032%. From the following formula (21), the refractive index n of the single-layer coating film to realize the set reflectance R1 = 0.53032% is fh 1 calculates to 1.9243333.

[0118]

number

[0119]

number

[0120] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 237 in FIG. min is the wavelength λ min = 10.174 μm, the desired minimum reflectance of 0.5% can be obtained.

[0121] Next, the wavelength λ at which the reflectance becomes minimum min The desired wavelength λ cot The thickness of each of the three coating layers is set to λ cot / λ min Multiplying by 1, the calculated values ​​are d1=423.150 nm, d2=543.247 nm, and d3=423.150 nm. The wavelength dependency of the reflectance in this case is shown by a solid line 238 in FIG. 24. cot It can be seen that the reflectance reaches a minimum of 0.5% at 10 μm.

[0122] In addition, the dashed line 235 in FIG. fh and the film thickness is λ cot / (4nfh 24 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.1 μm / cm2 (where 0.1 μm / cm2) and a reflectance of 0.1 μm / cm2 (where 0.1 μm / cm2) in the wavelength dependence of reflectance. Although the solid line 238 and the dashed line 235 in Fig. 24 do not match perfectly, they show almost the same reflectance dependence on wavelength, and the minimum reflectance and the wavelength at which the minimum reflectance is obtained match perfectly.

[0123] Minimum reflectance R0=0.5% and wavelength λ cot = 10 μm is an example, and is not limited thereto, and can be set to a desired value. In the above example, YF3 is used for the first coating film 232 and the third coating film 234, and ZnS is used for the second coating film 233, but the present invention is not limited thereto, and any other suitable material may be used as long as the refractive index is n fh and n fh 1 At least one material with a refractive index higher than n fh and n fh 1 There must be at least one ingredient that is lower than , and the order of ingredients can be chosen arbitrarily. From the above, it can be seen that a desired minimum reflectance at a desired wavelength can be achieved with a material having a known refractive index.

[0124] As described above, according to the design method of the reflectance coating according to the first and fifth embodiments, by replacing the single-layer coating film with a three-layer multilayer coating film by utilizing the characteristic matrix, it is possible to design a low-reflectance coating in which the reflectance is controlled to a desired minimum reflectance at a desired wavelength.

[0125] Next, we will show a case where the multilayer coating is made of three different materials. As a method for designing a low reflectance coating in this case, we will show an example of a minimum reflectance R0 = 0.01 (1%). The effective refractive index n c If we set the value to 3.2, then from the above formula (4), n fl and n fh are calculated as 1.618080 and 1.977653, respectively.

[0126] First, the refractive index n fl = 1.618080. At least one single-layer coating film has a refractive index n flThe material has a lower refractive index than fl Consider replacing the material with a three-layer coating made of three materials, each of which has a higher refractive index than the other material.

[0127] Figure 25 shows the refractive index n fl and the film thickness d fl is λ cot / (4n fl 25 is a schematic diagram showing a case where a single-layer coating film 241 having an effective refractive index n1 and a thickness d1, a three-layer coating film having an effective refractive index n2 and a thickness d2, and a three-layer coating film having an effective refractive index n3 and a thickness d3. c and wavelength λ cot The refractive index n fl (=1.618080) and the film thickness d fl = λ cot / (4n fl ) is replaced with a three-layer coating film consisting of a first coating film 242 with a refractive index n1 and a thickness d1, a second coating film 243 with a refractive index n2 and a thickness d2, and a third coating film 244 with a refractive index n3 and a thickness d3. If the single-layer coating film 241 can be replaced with a three-layer coating film, the characteristic matrices of both become equal, as expressed by the following equation (23).

[0128]

number

[0129]

number

[0130] In equation (23), the refractive indexes n1, n2, and n3 are known, so there are three unknowns: film thicknesses d1, d2, and d3. By solving equation (23), the film thickness of each coating film can be calculated.

[0131] wavelength λ cot = 10 μm, the first coating film 242 has a refractive index of nfl The second coating film 243 is YF3 having a refractive index n1=1.40 lower than that of the first coating film 242. fl The third coating film 244 is made of ZnS with a refractive index n2=2.20 higher than that of the first coating film 241. fl When equation (23) is solved using CeF3 with n3=1.45, which is lower than the above, as an example, the thicknesses of the coating films are d1=640.642 nm, d2=206.894 nm, and d3=763.646 nm, respectively. The wavelength dependency of the reflectance in this case is shown by the dashed line 246 in FIG. 26. The reflectance is 1.0% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R of the reflectance of the three-layer coating film. min 0 is 0.9836%.

[0132] The minimum reflectance of a single-layer coating is R0:1.0%, whereas the minimum reflectance of a three-layer coating is R min 0 The reflectance of the three-layer coating is 0.9836%, which is lower than the minimum reflectance R0 of the single-layer coating. min In order to make R0 the desired minimum reflectance, the set reflectance R1 is set to a high value of 1.01648%. In this case, from equation (18), fl 1 By solving the following equation (25) to calculate the thickness of each coating film, the following values ​​are obtained: d1 = 641.123 nm, d2 = 205.474 nm, d3 = 765.332 nm.

[0133]

number

[0134] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 247 in FIG. min As the wavelength λ min = 9.864 μm, the desired minimum reflectance of 1.0% can be obtained.

[0135] Next, the wavelength λ at which the reflectance becomes minimum min , the desired wavelength λ cot Each film thickness is set to λcot / λ min Multiplying by 1, the calculated values ​​are d1=649.962 nm, d2=208.307 nm, and d3=775.884 nm. The wavelength dependency of the reflectance in this case is shown by a solid line 248 in FIG. 26. cot It can be seen that the minimum reflectance is 1.0% at the refractive index n fl and the film thickness is λ cot / (4n fl 26 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.1 μm / cm2 (where 0.1 μm / cm2) at wavelength 0.25 ...

[0136] Minimum reflectance R0 = 1.0% and wavelength λ cot The refractive index is not limited to 10 μm, but may be set to a desired value. In addition, YF3 is used for the first coating film 242, ZnS is used for the second coating film 243, and CeF3 is used for the third coating film 244, but the present invention is not limited to these, and any other suitable material may be used as long as the refractive index is n fl and n fl 1 At least one material with a refractive index higher than n fl and n fl 1 There must be at least one ingredient that is lower than , and the order of ingredients can be chosen arbitrarily. From the above, it can be seen that a desired minimum reflectance at a desired wavelength can be achieved by using a material with a known refractive index.

[0137] Similarly, n fh = 1.977653. At least one single-layer coating film has a refractive index n fh At least one of the materials has a refractive index lower than n fh Consider replacing the material with a three-layer coating of three materials, each of which has a higher refractive index than the other.

[0138] Figure 27 shows the refractive index n fh and the film thickness d fh is λ cot / (4n fh27 is a schematic diagram showing a case where the single-layer coating film 249 having an effective refractive index n1 and a thickness d1, the refractive index n2 and a thickness d2, and the refractive index n3 and a thickness d3 are respectively replaced with a three-layer coating film having an effective refractive index n c and wavelength λ cot The refractive index n fh (=1.977653) and the film thickness d fh = λ cot / (4n fh ) is replaced with a three-layer coating film consisting of a first coating film 250 with a refractive index n1 and a thickness d1, a second coating film 251 with a refractive index n2 and a thickness d2, and a third coating film 252 with a refractive index n3 and a thickness d3. The method of replacing the single-layer coating film with the three-layer coating film is the same as in the case of the low refractive index described above, and is performed by solving the following equation (26).

[0139]

number

[0140] wavelength λ cot = 10 μm, the first coating film 250 has a refractive index of n fl The second coating film 251 is YF3, which has a refractive index n1=1.40 lower than that of the first coating film 251. fl The third coating film 252 is made of ZnS, which has a refractive index n2=2.20 higher than that of the first coating film 251. fl Taking CeF3, which has n3=1.45, lower than the above, as an example, solving equation (26) gives d1=370.115 nm, d2=607.246 nm, and d3=395.897 nm, respectively. The wavelength dependence of reflectance in this case is shown by the dashed line 254 in FIG. 28. The reflectance is 1.0% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R of the reflectance of the three-layer coating film. min 0 is 0.94561%.

[0141] The minimum reflectance of a single-layer coating is R0:1.0%, whereas the minimum reflectance of a three-layer coating is R min 0 is 0.94561%, which is lower than the minimum reflectance R0 of the single-layer coating.min In order to obtain the desired minimum reflectance R0, the set reflectance R1 is set high at 1.057485%. The refractive index n of the single-layer coating film to realize the set reflectance R1 = 1.057485% is fh 1 From equation (21), n fh 1 By solving the following equation (27) to calculate the thickness of each coating film, the thicknesses are calculated to be d1 = 364.825 nm, d2 = 614.601 nm, and d3 = 390.009 nm, respectively.

[0142]

number

[0143] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 255 in FIG. min is the wavelength λ min = 10.243 μm, the desired minimum reflectance of 1.0% can be obtained.

[0144] Next, the wavelength λ at which the reflectance becomes minimum min , the desired wavelength λ cot The thickness of each coating film is set to λ cot / λ min Multiplying by 1, we get d1 = 356.170 nm, d2 = 600.021 nm, and d3 = 380.757 nm. The wavelength dependency of the reflectance in this case is shown by the solid line 256 in FIG. 28. cot It can be seen that the minimum reflectance is 1.0% at

[0145] In addition, the dashed line 253 in FIG. fh and the film thickness is λ cot / (4n fh 28 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.1 μm / cm2 (where 0.1 μm / cm2) at wavelength ...

[0146] Minimum reflectance R0 = 1.0% and wavelength λ cot = 10 μm is an example, and is not limited to these, and can be set to a desired value. In addition, YF3 is used for the first coating film 250, ZnS is used for the second coating film 251, and CeF3 is used for the third coating film 252, but the present invention is not limited to these, and the refractive index may be n fh and n fh 1 At least one material with a refractive index higher than n fh and n fh 1 There must be at least one ingredient that is lower than , and the order of ingredients can be chosen arbitrarily. From the above, it can be seen that a desired minimum reflectance at a desired wavelength can be achieved by using a material with a known refractive index.

[0147] <Advantages of the Fifth Embodiment> As described above, according to the method for designing a low-reflectance coating according to the fifth embodiment, by replacing a single-layer coating film with a three-layer multilayer coating film by utilizing a characteristic matrix, it is possible to design a low-reflectance coating whose reflectance is controlled to a desired minimum reflectance at a desired wavelength.

[0148] In addition, as for a multilayer coating film of four or more layers made of four or more materials, it can be designed in a similar manner by setting the film thickness of the coating film having more than three layers in advance, as described in the first and second embodiments.

[0149] Embodiment 6 29 is a schematic diagram showing a quantum cascade laser apparatus 700 according to the sixth embodiment. The quantum cascade laser apparatus 700 has a cavity length L and a ridge width W. The quantum cascade laser apparatus 700 has a buried ridge type waveguide structure.

[0150] 29, the quantum cascade laser device 700 includes an n-type first electrode 153, a semi-insulating InP substrate 151, an n-type InP first cladding layer 3, an Fe-doped InP current blocking layer 4, an n-type GaInAs current injection layer 152, an n-type second electrode 5, a front end facet coating film 6, a rear end facet coating film 7, and a terahertz light extraction surface 8. FIG. 30 shows the quantum cascade laser device 700 in FIG. a -y b FIG.

[0151] The quantum cascade laser apparatus 700 of the sixth embodiment differs from the quantum cascade laser apparatus 500 of the first embodiment in that a semi-insulating InP substrate 151 is used instead of the n-type InP substrate 2 constituting the quantum cascade laser apparatus 500 of the first embodiment, that an n-type GaInAs current injection layer 152 is provided on the semi-insulating InP substrate 151 to perform current injection, and that an n-type first electrode 153 is provided on the n-type GaInAs current injection layer 152.

[0152] The semi-insulating InP substrate 151 has a smaller absorption of terahertz waves than the n-type InP substrate 2. Therefore, the quantum cascade laser device 700 can realize higher output terahertz waves.

[0153] <Advantages of the Sixth Embodiment> As described above, the quantum cascade laser device according to the sixth embodiment uses a semi-insulating InP substrate as the semiconductor substrate, and therefore has the effect of providing a quantum cascade laser device capable of realizing a higher output terahertz wave.

[0154] Embodiment 7 31 is a schematic diagram showing a quantum cascade laser device 800 according to the seventh embodiment. The quantum cascade laser device 800 has a cavity length L and a ridge width W. The quantum cascade laser device 800 has a buried ridge type waveguide structure. FIG. 32 shows the y-axis direction of the quantum cascade laser device 800 in FIG. a -y b FIG.

[0155] A quantum cascade laser device 800 according to the seventh embodiment differs from the quantum cascade laser device 700 according to the sixth embodiment in that a Si substrate 154 is used instead of the semi-insulating InP substrate 151. The Si substrate 154 has a smaller absorption of terahertz waves than an n-type InP substrate. This makes it possible to obtain high-output terahertz waves. The Si substrate 154 and the n-type GaInAs current injection layer 152 are bonded together by lamination.

[0156] <Advantages of the Seventh Embodiment> As described above, according to the quantum cascade laser device of the seventh embodiment, since a Si substrate is used as a semiconductor substrate, it is possible to obtain an effect of obtaining a quantum cascade laser device capable of realizing a higher output terahertz wave.

[0157] Embodiment 8 33A to 33H are diagrams showing steps of the method for manufacturing the quantum cascade laser device according to the embodiments 1 to 7. The method for manufacturing the quantum cascade laser device will be described with reference to the diagrams. (1) Prepare a wafer 161 that has undergone wafer processing (FIG. 33A). (2) After dividing the wafer 161 into rectangular blocks, cleavage bars 162 are produced by cleavage (FIG. 33B). (3) Power is supplied to each element of the quantum cascade laser device by a probe 163 or the like, and the gain distribution (wavelength dependence of gain) is measured (FIG. 33C). (4) Based on the measured gain distribution, a front facet coating film 6 is designed that provides a predetermined minimum reflectance at a desired wavelength (FIG. 33D). (5) The front end facet is coated with front end facet coating film 6 made of the multilayer coating designed in (4) above, and the rear end facet is coated with rear end facet coating film 7, which is a high reflectivity film (FIG. 33E). (6) The front end face side of the quantum cascade laser device element is polished to form a terahertz light extraction surface 8 so that terahertz waves can be extracted (FIG. 33F). (7) Divide into individual quantum cascade laser device 74 elements (Figure 33G). (8) After bonding the quantum cascade laser device 74, the submount 73, and the metal block 72, they are mounted on a temperature adjustment device 71 such as a Peltier element (FIG. 33H).

[0158] In the eighth embodiment, polishing for extracting terahertz waves is performed after end face coating, but polishing may also be performed after cleavage.

[0159] <Advantages of the Eighth Embodiment> As described above, according to the manufacturing method of the quantum cascade laser device of the eighth embodiment, the gain distribution of the quantum cascade laser device is measured in advance, and the extremely small reflectivity is designed based on the measured gain distribution, and then the front end face coating film (low reflectivity film) is coated, thereby achieving the effect of easily manufacturing a quantum cascade laser device capable of easily achieving terahertz oscillation with a high yield.

[0160] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.

[0161] Therefore, countless modifications not exemplified are assumed within the scope of the technology of the present disclosure, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment. [Explanation of symbols]

[0162] 1, 153 n-type first electrode, 2 n-type InP substrate, 3 n-type InP first cladding layer, 4 Fe-doped InP current blocking layer, 5 n-type second electrode, 6 front end facet coating film, 7 rear end facet coating film, 8 terahertz light extraction surface, 9 n-type GaInAs first optical confinement layer, 10 core region, 40, 106, 136 stage, 38, 104, 134 active region, 39, 105, 135 injector region, 11 n-type GaInAs second optical confinement layer, 12 n-type InP second cladding layer, 13 n-type GaInAs contact layer, 21, 23, 25, 27, 29, 31, 35, 37, 81, 83, 85, 87, 89, 91, 93, 99, 101, 103, 111, 113, 115, 117, 119, 121, 123, 125, 131, 133 Undoped AlInAs barrier layer, 22, 24, 26, 28, 30, 36, 82, 84, 86, 88, 90, 92, 94, 100, 102, 112, 114, 116, 118, 120, 122, 124, 126, 132 Undoped GaInAs well layer, 32, 34, 96, 98, 128, 130 N-type GaInAs well layer, 33, 95, 97, 127, 129 N-type AlInAs barrier layer, 42, 212, 231, 241, 249 Single layer coating film, 43, 213, 232, 242, 250 First coating film, 44, 214, 233, 243, 251 Second coating film, 45, 215, 234, 244, 252 Third coating film, 46, 141 Covering film, 47, 47a, 48a, 142, 222, 222a, 236, 246, 254 Dot-dashed line, 48, 142a, 143, 143a, 223, 223a, 237, 247, 255 Two-dot chain lines, 49, 49a, 52, 62, 144, 144a, 146, 224, 224a, 238, 248, 256 Solid lines, 50, 50a, 50b, 221, 221a, 221b, 235, 245, 253 Dashed lines, 51, 61, 145 Dotted lines, 41, 74, 211, 500, 600, 700, 800 Quantum cascade laser device, 71 Temperature control device, 72 Metal block, 73 Submount, 151 Semi-insulating InP substrate, 152 n-type GaInAs current injection layer, 154 Si substrate, 161 Wafer, 162 Cleaved bar, 163 Probe

Claims

1. A semiconductor substrate, A first cladding layer of a first conductivity type formed on the semiconductor substrate, A core region in which a plurality of stages are formed, the stages having an active region in which a barrier layer and a well layer are alternately formed, and an injector region for injecting electrons into the active region, formed on the first cladding layer, A second cladding layer of a first conductivity type formed on the core region, The resonator length is L, and at a wavelength λ qcl when the gain becomes the maximum gain value and a gain value reduced by a preset ratio with respect to the maximum gain value occurs, the width of the wavelength between two points where the gain value occurs is Δλ qcl When this is the case, on one end face, a low reflectivity film having a reflectivity minimum at a wavelength λ qcl separated from the preset wavelength by a preset wavelength is provided, cot and the reflectivity R of the other end face and the width of the wavelength between two points where the mirror loss value occurs when a preset loss value is subtracted from the maximum value of the mirror loss calculated by the L is Δλ r When this is the case, the Δλ mir is smaller than the Δλ mir A quantum cascade laser device characterized by this. qcl

2. A contact layer of a first conductivity type is provided on the second cladding layer, A first electrode of a first conductivity type is provided on the back side of the semiconductor substrate, and a second electrode of a first conductivity type is provided on the contact layer. The quantum cascade laser device according to claim 1, characterized by this.

3. The semiconductor substrate is a semiconductor substrate of a first conductivity type, a semi-insulating semiconductor substrate, or a silicon substrate. The quantum cascade laser device according to claim 1 or 2, characterized by this.

4. The gain value of the preset ratio is a gain value of 10% of the maximum gain value. The quantum cascade laser device according to claim 1, characterized by this.

5. The quantum cascade laser device according to any one of claims 1, 2, and 4, characterized in that it is mounted on a temperature adjustment device.

6. The quantum cascade laser device according to any one of claims 1, 2, and 4, characterized in that electrons transition between two upper energy levels and one lower energy level in the active region.

7. The quantum cascade laser device according to any one of claims 1, 2, and 4, characterized in that electrons transition between two upper energy levels and a plurality of lower energy levels in the active region.

8. The gain value for a preset ratio is a gain value of 10% of the maximum gain value, and the quantum cascade laser device according to claim 2 is characterized in that.

9. The gain value for a preset ratio is a gain value of 10% of the maximum gain value, and the quantum cascade laser device according to claim 3 is characterized in that.

10. A method for manufacturing a quantum cascade laser device according to any one of claims 1 to 4 and 8, A step of cleaving a wafer after the wafer process is completed to create a cleaving bar; A step of measuring the wavelength dependence of the gain of the quantum cascade laser device by driving the cleaving bar to obtain the wavelength at which the maximum gain value is obtained and the gain band; A step of designing a low reflectivity film having a minimum reflectivity at a wavelength separated from the wavelength at which the maximum gain value is obtained by a preset wavelength; A step of forming the low reflectivity film on the front end face of the quantum cascade laser device; A method for manufacturing a quantum cascade laser device comprising.

11. A step of polishing the end face of the semiconductor substrate of the quantum cascade laser device; The method for manufacturing a quantum cascade laser device according to claim 10, further comprising a step of separating the cleaving bar into individual elements. Claim 12 The method for manufacturing a quantum cascade laser device according to claim 11, further comprising a step of bonding the element to a temperature adjusting device via a submount and a metal block.

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