JP2023133123A - Surface emitting laser element, detection device, and moving object - Google Patents

Abstract

To provide a surface emitting laser element, a detection device, and a moving object that can obtain high output.SOLUTION: A surface emitting laser element includes a first reflecting mirror and a second reflecting mirror, and a resonator region between the first reflecting mirror and the second reflecting mirror, and the resonator region includes a plurality of active layers containing crystal strain, a tunnel junction layer between the plurality of active layers, and a strain relaxation layer located between the first reflecting mirror and the active layer, between the plurality of active layers, or between the active layer and the second reflecting mirror, and the strain relaxation layer includes crystal strain opposite to that of the active layer.SELECTED DRAWING: Figure 2

Description

The present invention relates to a surface emitting laser element, a detection device, and a moving body.

A vertical cavity surface emitting laser (VCSEL) is a semiconductor laser that emits light in a direction perpendicular to a substrate surface. Compared to edge-emitting semiconductor lasers, surface-emitting lasers are characterized by being low in price, low power consumption, compact, high performance, and easy to integrate two-dimensionally.

A surface emitting laser has a resonator structure including a resonator region including an active layer, and an upper Bragg reflector and a lower Bragg reflector provided above and below the resonator region. Therefore, the resonator region is formed with a predetermined optical thickness so that the light with the wavelength λ resonates in the resonator region in order to obtain the light with the oscillation wavelength λ. The upper Bragg reflector and the lower Bragg reflector are distributed Bragg reflectors (DBR) formed by alternately laminating materials with different refractive indexes, that is, low refractive index materials and high refractive index materials. It is formed by In DBR, in order to obtain a high reflectance at the wavelength λ, the low refractive index material and the high refractive index material are formed so that the optical film thickness is λ/4 considering the refractive index of each material. ing.

Additionally, multi-junction surface emitting lasers are known. A multi-junction surface emitting laser includes a plurality of sets of resonator regions including active layers in the stacking direction. Multi-junction surface-emitting lasers enable high-power laser light output. A multi-junction surface emitting laser is sometimes also called a cascade surface emitting laser. In a multi-junction surface emitting laser, the more active layers there are, the higher the optical output can be. Further, by providing a tunnel junction layer between the active layers, carriers can be injected evenly into each active layer, so that the laser output can be effectively increased.

In semiconductor lasers including surface emitting lasers, by imparting crystal strain in the compressive direction to the active layer, the optical gain during laser operation is improved, making it possible to reduce the oscillation threshold current and increase the optical output. However, in a multi-junction surface emitting laser, if the number of active layers is increased to improve output, crystal strain accumulates accordingly, and crystal strain in the resonator region increases. If the total thickness of the active layer exceeds the critical thickness, crystal defects such as misfit dislocations will occur. For this reason, in conventional surface emitting lasers, it is difficult to achieve high output even if a multi-junction structure is adopted.

Regarding crystal strain, Non-Patent Document 1 includes a description suggesting that the number of active layers is limited by crystal strain. Further, Patent Document 1 describes the use of GaInNAs, GaNAs, GaPSb, etc. for the tunnel junction layer. However, even with these conventional techniques, it is difficult to increase the output of a surface emitting laser element.

An object of the present invention is to provide a surface emitting laser element, a detection device, and a moving object that can obtain high output.

According to one aspect of the disclosed technology, a surface emitting laser device includes a first reflecting mirror, a second reflecting mirror, and a resonator region between the first reflecting mirror and the second reflecting mirror. The resonator region includes a plurality of active layers containing crystal strain, a tunnel junction layer between the plurality of active layers, a region between the first reflecting mirror and the active layer, and a plurality of active layers including the plurality of active layers. a strain relaxation layer located between the active layer and the second reflecting mirror, and the strain relaxation layer includes a crystal strain opposite to that of the active layer.

According to the disclosed technology, high output can be obtained.

FIG. 1 is a cross-sectional view showing a surface emitting laser device according to a first embodiment. 1 is a cross-sectional view showing a main part of a surface emitting laser device according to a first embodiment. FIG. 7 is a cross-sectional view showing a surface emitting laser device according to a third embodiment. FIG. 7 is a cross-sectional view showing main parts of a surface emitting laser device according to a third embodiment. It is a figure showing the distance measuring device concerning a 4th embodiment. It is a figure showing the mobile object concerning a 5th embodiment. FIG. 7 is a diagram illustrating a schematic configuration of an optical inspection device according to a sixth embodiment. It is a figure which illustrates the block structure of the optical inspection apparatus based on 6th Embodiment.

Embodiments of the present disclosure will be described below with reference to the accompanying drawings. Note that, in this specification and the drawings, components having substantially the same functional configurations may be given the same reference numerals to omit redundant explanation.

(First embodiment)
First, a first embodiment will be described. The first embodiment relates to a surface emitting laser element. FIG. 1 is a cross-sectional view showing a surface emitting laser device according to a first embodiment.

The surface emitting laser device 100 according to the first embodiment is a surface emitting laser device with an oscillation wavelength λ of 940 nm. The surface emitting laser device 100 mainly includes a substrate 101, a lower DBR 102, a resonator region 103, an upper DBR 104, a contact layer 105, a lower electrode 106, and an upper electrode 107. The lower DBR 102 is on the substrate 101, the resonator region 103 is on the lower DBR 102, the upper DBR 104 is on the resonator region 103, and the contact layer 105 is on the upper DBR 104. The lower DBR 102, the resonator region 103, the upper DBR 104, and the contact layer 105 are formed by stacking semiconductor layers on the upper surface of the substrate 101. The lower electrode 106 is provided on the back surface of the substrate 101, and the upper electrode 107 is provided on the surface of the contact layer 105. The surface emitting laser element 100 emits laser light upward from the resonator region 103. The surface emitting laser device 100 is a top-emitting vertical cavity surface emitting laser (VCSEL) device.

The substrate 101 is formed of an n-GaAs substrate, which is a semiconductor substrate. The lower DBR 102 has 35.5 pairs of n-Al _0.1 Ga _0.9 As high refractive index layer 102a and n-Al _0.9 Ga _0.1 As low refractive index layer 102a, each layer having an optical thickness of λ/4. It is formed by alternately stacking the index layers 102b (see FIG. 2). That is, the lower DBR 102 includes 36 n-Al _0.1 Ga _0.9 As high refractive index layers 102a and 35 n-Al _0.9 Ga _0.1 As low refractive index layers 102b.

The resonator region 103 has three stacked bodies 10 stacked on each other. The resonator region 103 further includes a tunnel junction layer 20 between adjacent stacked bodies 10 in the thickness direction. The laminate 10 has a lower spacer layer 11 , an active layer 12 , and an upper spacer layer 13 . In stack 10 , active layer 12 is on top of bottom spacer layer 11 and top spacer layer 13 is on top of active layer 12 . The tunnel junction layer 20 has a p-type layer 21 and an n-type layer 22 (see FIG. 2). N-type layer 22 is on top of p-type layer 21.

The lower spacer layer 11 and the upper spacer layer 13 are, for example, Al _0.65 Ga _0.35 As _0.925 P _0.075 layers. The active layer 12 has a quantum well structure including GaInAs quantum well layers and AlGaAs barrier layers stacked alternately. For example, the thickness of the GaInAs quantum well layer is 8 nm. The number of GaInAs quantum well layers included in one active layer 12 is, for example, three. The lattice constant of the active layer 12 having such a composition is larger than the lattice constant of GaAs constituting the substrate 101. On the other hand, the lattice constant of Al _0.65 Ga _0.35 As _0.925 P _0.075 constituting the lower spacer layer 11 and the upper spacer layer 13 is smaller than the lattice constant of GaAs. The thickness of the lower spacer layer 11 and the upper spacer layer 13 is about 80 nm in total, although it depends on the position of the stacked body 10. Although details will be described later, in this embodiment, the GaInAs quantum well layer contains 0.9% crystal strain in the compressive direction with respect to the GaAs substrate. In the first embodiment, the lower spacer layer 11 and the upper spacer layer 13 are examples of strain relaxation layers.

The p-type layer 21 is a p ⁺⁺ -GaAs layer with a p-type impurity concentration of 10 ¹⁹ cm ^-3 or higher, and the n-type layer 22 is an n ⁺⁺ -GaAs layer with an n-type impurity concentration of 10 ¹⁹ cm ^-3 or higher. It is a layer. A tunnel junction is formed by stacking the p-type layer 21 and the n-type layer 22 on each other. Electrons in the conduction band in the n-type layer 22 head toward the valence band in the p-type layer 21, and a tunnel current flows between the bands. The tunnel junction layer 20 converts the polarity of charges carrying current from n-type to p-type.

The upper DBR 104 includes 20 pairs of p-Al _0.1 Ga _0.9 As high refractive index layer 104a and p-Al _0.9 Ga _0.1 As low refractive index layer, each layer having an optical thickness of λ/4. 104b (see FIG. 2). That is, the upper DBR 104 includes 20 p-Al _0.1 Ga _0.9 As high refractive index layers 104a and 20 p-Al _0.9 Ga _0.1 As low refractive index layers 104b.

The surface emitting laser device 100 has a current confinement layer 108 between the uppermost stacked body 10 and the lowermost p-Al _0.1 Ga _0.9 As high refractive index layer 104a. Current confinement layer 108 includes a selective oxidation region 108a and a current confinement region 108b. Current confinement region 108b is surrounded by selective oxidation region 108a. The current confinement layer 108 is formed, for example, by selective oxidation of p-AlAs. A portion of the lower side of the current confinement layer 108 is included in the resonator region 103, and a portion of the upper side of the current confinement layer 108 is included in the upper DBR 104.

Contact layer 105 is made of p ⁺ -GaAs. A mesa 109 is formed in part of the contact layer 105, the upper DBR 104, the resonator region 103, and the lower DBR 102. The surface emitting laser device 100 has a protective layer 151 that covers the side surface of the mesa 109 and the top surface of the lower DBR 102. The protective layer 151 is made of a dielectric material such as SiN, for example. Furthermore, a resin layer 152 is formed by embedding a resin material such as polyimide in the region where the semiconductor layer has been removed to form the mesa 109.

Here, the resonator region 103 will be explained in more detail. FIG. 2 is a cross-sectional view showing essential parts of the surface emitting laser device 100 according to the first embodiment. The waveform shown on the right side of the cross-sectional structure in FIG. 2 schematically shows a normalized longitudinal mode waveform.

In the surface emitting laser device 100, the optical thickness of each of the stacked bodies 10 is λ/2 or less, and the antinode of the normalized longitudinal mode is located in each active layer 12.

Regarding the lowermost stack 10, the total optical thickness of the stack 10 and the p-type layer 21 immediately above the stack 10 is λ/2. A normalized longitudinal mode node is located at the boundary between the stacked body 10 and the lower DBR 102, and the p-type layer 21 and the n-type layer 22 included in the tunnel junction layer 20 directly above the stacked body 10 are located at the boundary between the stacked body 10 and the lower DBR 102. A node is located at the boundary. Therefore, the laminate 10 and the p-type layer 21 directly above the laminate 10 function like one λ/2 resonator.

Regarding the center laminate 10, the total optical thickness of the laminate 10, the n-type layer 22 directly below the laminate 10, and the p-type layer 21 directly above the laminate 10 is λ/2. It is. Then, a node is located at the boundary between the p-type layer 21 and the n-type layer 22 included in the tunnel junction layer 20 directly below the stacked body 10, and the p-type layer included in the tunnel junction layer 20 directly above the stacked body 10 is A node is located at the boundary between layer 21 and n-type layer 22. Therefore, the laminate 10, the n-type layer 22 directly below the laminate 10, and the p-type layer 21 directly above the laminate 10 function like one λ/2 resonator.

For the uppermost stack 10, the total optical thickness of the stack 10, the n-type layer 22 immediately below the stack 10, and a portion of the current confinement layer 108 directly above the stack 10 is It is λ/2. Then, a node is located at the boundary between the p-type layer 21 and the n-type layer 22 included in the tunnel junction layer 20 directly below the stacked body 10, and a node is located in a part of the current confinement layer 108 directly above the stacked body 10. To position. Therefore, the laminate 10, the n-type layer 22 directly below the laminate 10, and a portion of the current confinement layer 108 directly above the laminate 10 function like one λ/2 resonator.

The optical thickness of the resonator region 103 is 3λ/2.

Generally, crystal strain ε _// in a direction parallel to the surface of the substrate (in-plane direction), which occurs in a semiconductor layer epitaxially grown on the surface of the substrate, is expressed by the following equation (1). However, a _epi is the lattice constant of the semiconductor layer, and a _sub is the lattice constant of the substrate.

ε _// =-(a _epi -a _sub )/a _sub ...(1)

When the lattice constant a _epi is larger than the lattice constant a _sub , the crystal strain ε _// is negative. In this case, crystal strain in the compression direction (compressive strain) occurs in the semiconductor layer. On the other hand, when the lattice constant a _epi is smaller than the lattice constant a _sub , the crystal strain ε _// is positive. In this case, crystal strain in the tensile direction (tensile strain) occurs in the semiconductor layer.

In this embodiment, as described above, the lattice constant of the active layer 12 is larger than the lattice constant of GaAs constituting the substrate 101, and the lattice constants of the lower spacer layer 11 and the upper spacer layer 13 are larger than the lattice constant of GaAs. It's also small. Therefore, the active layer 12 contains compressive strain, and the lower spacer layer 11 and the upper spacer layer 13 contain tensile strain. That is, in the in-plane direction, the lower spacer layer 11 and the upper spacer layer 13 include crystal strain in the opposite direction to that of the active layer 12. Therefore, inside each stacked body 10, the crystal strain of the active layer 12 and the crystal strain of the lower spacer layer 11 and the upper spacer layer 13 cancel each other out.

In this embodiment, the GaInAs quantum well layer included in the active layer 12 contains 0.9% crystal strain in the compressive direction and has a thickness of 8 nm. Therefore, when the active layer 12 has three GaInAs quantum well layers, the total compressive strain in the active layer 12 including the three stacked quantum well layers is 3×0.9%×8 nm, which is 21. It is 6%·nm. Therefore, if the lower spacer layer 11 and the upper spacer layer 13 in one laminate 10 contain a total tensile strain of 21.6%·nm, the crystal strain can be canceled out. For example, when the total thickness of the lower spacer layer 11 and the upper spacer layer 13 is 80 nm, if the lower spacer layer 11 and the upper spacer layer 13 contain a total tensile strain of 0.27%, each laminate 10 Within this range, crystal strain can be canceled out. For example, when the lower spacer layer 11 and the upper spacer layer 13 are AlGaAsP layers, crystal strain can be offset if the P composition ratio in the group V elements is 7.5%. Note that since the lattice constant of the AlGaAs barrier layer is approximately the same as that of the GaAs substrate, its crystal strain does not need to be taken into account.

The number of quantum well layers included in the active layer 12 is not limited to three. When the number of quantum well layers included in the active layer 12 is one, the total compressive strain in the active layer 12 including one quantum well layer is 1×0.9%×8 nm, which is 7.2%·nm. It is. Therefore, when the total thickness of the lower spacer layer 11 and the upper spacer layer 13 is 80 nm, if the lower spacer layer 11 and the upper spacer layer 13 contain a total tensile strain of 0.09%, each laminate 10, crystal strain can be canceled out. When the lower spacer layer 11 and the upper spacer layer 13 are AlGaAsP layers, crystal strain can be canceled out if the P composition ratio in the group V elements is 2.5%. Furthermore, when the number of quantum well layers included in the active layer 12 is five, the total compressive strain in the active layer 12 including the five quantum well layers stacked on each other is 5 x 0.9% x 8 nm. It is 36%·nm. Therefore, when the total thickness of the lower spacer layer 11 and the upper spacer layer 13 is 80 nm, if the lower spacer layer 11 and the upper spacer layer 13 contain a total tensile strain of 0.45%, each laminate 10, crystal strain can be canceled out. When the lower spacer layer 11 and the upper spacer layer 13 are AlGaAsP layers, if the P composition ratio in the group V elements is 13%, crystal strain can be offset.

In this manner, according to the first embodiment, accumulation of crystal strain can be suppressed while employing a multi-junction structure. Therefore, according to the first embodiment, high output can be achieved.

Note that when the total amount of crystal strain in the active layer 12 included in the resonator region 103 is ε _active , the total amount of crystal strain in the lower spacer layer 11 and the upper spacer layer 13 included in the resonator region 103 is: It is preferably within the range of -1.1ε _active to -0.9ε _active .

Furthermore, when attempting to compensate for crystal strain with a barrier layer, a quantum well layer containing compressive strain and a barrier layer containing tensile strain are repeatedly laminated while being in direct contact with each other, resulting in a narrow growth window. However, part of the crystal strain may be compensated not only by the lower spacer layer 11 and the upper spacer layer 13 but also by the barrier layer, as long as the influence on the growth window is small. In this case, the amount of tensile strain compensated by the lower spacer layer 11 and the upper spacer layer 13 may be reduced. In this case, assuming that the total amount of crystal strain in the quantum well layers of the active layer 12 included in the resonator region 103 is ε _active , the total amount of crystal strain in the quantum well layers included in the resonator region 103 is equal to It is preferable to fall within the range of -1.1ε _active to -0.9ε _active .

Further, in this embodiment, the active layer 12 is arranged at a pitch of λ/2, and a plurality of parts functioning as λ/2 resonators are provided. Therefore, temperature variations among the active layers 12 can be suppressed. For example, when a heat sink is provided below the lower electrode 106, the uppermost active layer 12 can have the same level of heat dissipation as the lowermost active layer 12. Deterioration of heat dissipation may cause a decrease in gain due to carrier leakage and deterioration of characteristics during continuous driving, etc. Also, temperature variations may cause variations in the contribution of characteristics among the active layers 12, but this According to the embodiment, these can be suppressed. For example, compared to a surface emitting laser element in which active layers are arranged at a pitch of λ and has a plurality of portions functioning as λ resonators, better characteristics in terms of heat dissipation can be obtained. This effect is particularly noticeable when surface-emitting laser elements are arranged in a high-density array.

Furthermore, in the present embodiment, since the pitch of the active layers 12 is λ/2, lateral carrier diffusion can be suppressed even in the active layer 12 farthest from the current confinement layer 108, and each active layer 12 has a high gain can be obtained.

In this embodiment, the resonator region 103 includes a plurality (three) of parts that function as λ/2 resonators, and the uppermost layer of the lower DBR 102 is made of n-Al _0.1 Ga _0.9 As with a high refractive index. The lowermost layer of the upper DBR 104 is a p-Al _0.1 Ga _0.9 As high refractive index layer 104a. Therefore, the resonator region 103 is made of a material that serves as a low refractive index layer as a whole. However, since the material of the active layer 12 is determined by the wavelength of the light to be output, the parts whose refractive index can be adjusted are the lower spacer layer 11 and the upper spacer layer 13.

When the lower spacer layer 11 and the upper spacer layer 13 are AlGaAs layers, the higher the Al composition ratio in the group III elements, the lower the refractive index of the lower spacer layer 11 and the upper spacer layer 13. On the other hand, the higher the Al composition ratio in the group III elements, the more likely non-radiative recombination centers are formed due to trace amounts of oxygen in the AlGaAs layer, which may deteriorate the characteristics and reliability. On the other hand, when the lower spacer layer 11 and the upper spacer layer 13 are AlGaAsP layers, the higher the P composition ratio in the group V elements, the lower the refractive index of the lower spacer layer 11 and the upper spacer layer 13. Therefore, a sufficiently low refractive index can be obtained even if the Al composition ratio in the group III elements is not high. For example, even if the Al composition ratio is 65%, a sufficiently low refractive index can be obtained if the P composition ratio is 7.5%. For example, even if the Al composition ratio is 60%, a sufficiently low refractive index can be obtained if the P composition ratio is 13%. The Al composition ratio in the group III elements constituting the lower spacer layer 11 and the upper spacer layer 13 is preferably 65% or less from the viewpoint of suppressing the formation of non-radiative recombination centers.

Furthermore, when the lower spacer layer 11 and the upper spacer layer 13 are AlGaAsP layers, lateral diffusion of carriers can be more easily reduced than when they are AlGaAs layers. The lower spacer layer 11 and the upper spacer layer 13 may be AlGaInAsP layers.

In this embodiment, all of the spacer layers (lower spacer layer 11, upper spacer layer 13) included in the resonator region 103 are strain relaxation layers containing strain in the opposite direction to the active layer 12, but at least It suffices if part of the layer is a strain relaxation layer. For example, one of the lower spacer layer 11 and the upper spacer layer 13 may contain crystal strain in the direction opposite to that of the active layer, and the other may not contain crystal strain, and one spacer layer may contain crystal strain in the direction opposite to that of the active layer. A form including a layer containing crystal strain and a layer not containing crystal strain may be used. Alternatively, only some of the plurality of stacked bodies 10 may have a strain relaxation layer, and only the lowermost lower spacer layer 11 and the uppermost upper spacer layer 13 in the resonator region 103 have crystal strain. It may also be in the form of including. However, it is effective to form a configuration in which at least a part of the spacer layer included in each laminate 10 has a strain relaxation layer, since the accumulated strain can be further reduced and a plurality of laminates can be stacked.

(Method for manufacturing surface emitting laser device)
Next, a method for manufacturing the surface emitting laser device 100 according to the first embodiment will be described. When manufacturing the surface emitting laser device 100, the semiconductor layer is formed by epitaxial growth using a metal organic chemical vapor deposition (MOCVD) method, an electron beam epitaxy (MBE) method, or the like. Specifically, a lower DBR 102, a resonator region 103, an upper DBR 104, and a contact layer 105 are sequentially formed on a substrate 101 by crystal growth. Note that a p-AlAs layer that becomes the current confinement layer 108 is formed at the boundary between the resonator region 103 and the upper DBR 104.

Next, the semiconductor layer is removed by etching until the side surfaces of the p-AlAs layer are exposed, thereby forming a mesa 109. A dry etching method can be used for etching when forming the mesa 109. The shape of the mesa 109 when viewed from the top surface can be any shape other than a circle, such as an ellipse, a square, or a rectangle.

After the mesa 109 is formed, by heat treatment in water vapor, the p-AlAs layer, which will become the current confinement layer 108 whose side surfaces are exposed, is oxidized from the side surfaces to become an insulator such as Al _x O _y , and the selectively oxidized region 108a is formed. By forming the selective oxidation region 108a in the p-AlAs layer in this way, the central portion of the p-AlAs layer that is not oxidized becomes the current confinement region 108b, and the path of the drive current is restricted to the current confinement region 108b in the central portion. can do. Such a structure is sometimes called a current confinement structure.

Next, a protective layer 151 is formed on the entire surface of the mesa 109 including the side and top surfaces using a dielectric material such as SiN. Further, when forming the mesa 109, the region where the semiconductor layer has been etched is filled with polyimide to flatten it, and a resin layer 152 is formed. Thereafter, the protective layer 151 and resin layer 152 on the contact layer 105 are removed, and an upper electrode 107 serving as a p-side individual electrode is formed around the region on the contact layer 105 from which the laser beam is emitted. Furthermore, a lower electrode 106 serving as an n-side common electrode is formed on the back surface of the substrate 101.

In this embodiment, since the side surfaces of the semiconductor layer exposed by forming the mesa 109 and the bottom surface around the mesa 109 are protected by the protective layer 151, the reliability of the surface emitting laser element 100 can be improved. This is particularly effective when the semiconductor layer is a semiconductor layer containing Al that is easily corroded.

Note that the lowermost p-Al _0.1 Ga _0.9 As high refractive index layer 104a included in the upper DBR 104 is in direct contact with the uppermost spacer layer 13 included in the resonator region 103, resulting in current confinement. The layer 108 may be provided above the lowermost p-Al _0.1 Ga _0.9 As high refractive index layer 104a. In this case, in the surface emitting laser device 100, the normalized longitudinal mode node is p-Al _0.1 Ga by adjusting the optical thickness of the uppermost spacer layer 13 included in the resonator region 103. It is configured to be located at the boundary between the _0.9 As high refractive index layer 104a and the upper spacer layer 13. Furthermore, in this case, the entire current confinement layer 108 is included in the upper DBR 104, and the resonator region 103 does not include the current confinement layer 108.

(Second embodiment)
Next, a second embodiment will be described. The surface emitting laser element according to the second embodiment has a 940 nm tunnel junction VCSEL device structure like the first embodiment, but the material of the tunnel junction layer 20 is different. In the first embodiment, the p-type layer 21 is a p ⁺⁺ -GaAs layer, and the n-type layer 22 is an n ⁺⁺ -GaAs layer, whereas in the second embodiment, the p-type layer 21 is a p ⁺⁺ -GaInAs layer. The n-type layer 22 is an n ⁺⁺ -GaInAs layer. Since the p-type layer 21 is a p ⁺⁺ -GaInAs layer and the n-type layer 22 is an n ⁺⁺ -GaInAs layer, the band gap energy is reduced compared to the first embodiment. Therefore, with the same doping concentration, the electrical resistance of the tunnel barrier is reduced, making it easier for tunnel current to flow. Another way to look at it is to consider that the same tunnel current is fixed, the doping concentration can be further reduced. Reducing the doping concentration can reduce optical absorption loss, which has the advantage of improving laser light output.

Note that when a GaInAs layer is used for the tunnel junction layer 20, there is a risk that compressive strain may accumulate, as described with respect to the active layer 12 in the first embodiment. As described above, in the first embodiment, the total compressive strain in the active layer 12 including three quantum well layers is 21.6%·nm, and the total compressive strain in the active layer 12 including one quantum well layer is 21.6%·nm. The total strain is 7.2%·nm, and the total compressive strain in the active layer 12 including five quantum well layers is 36%·nm.

In the second embodiment, compressive strain of the tunnel junction layer 20 including the GaInAs layer is also taken into consideration. Tunnel junction layer 20 includes two GaInAs layers, a p-type layer 21 and an n-type layer 22. Further, since the maximum In composition is the same as that of the active layer, the maximum value of the strain amount of one quantum well layer is 0.9%. If the In composition is higher than this, the light emitted from the quantum well layer is absorbed by the tunnel junction layer 20, so the maximum In composition is the same as that of the active layer. The thickness of each of the p-type layer 21 and the n-type layer 22 is 10 nm to 20 nm. If the thickness of each of the p-type layer 21 and the n-type layer 22 is 10 nm or more, the tunnel junction function is satisfied. If the thickness of either the p-type layer 21 or the n-type layer 22 exceeds 20 nm, light absorption may occur. Therefore, when there are two sets of tunnel junction layers 20, the maximum total compressive strain is 72%·nm (two sets×0.9%×40 nm).

When the amount of strain in the quantum well layer and the amount of strain in the tunnel junction layer are added together, the maximum total amount is 108%.nm. If the spacer layer has a total thickness of 80 nm, crystal strain can be offset if it contains 1.35% tensile strain.

(Third embodiment)
Next, a third embodiment will be described. The third embodiment differs from the first embodiment mainly in the material system and the oscillation wavelength λ. FIG. 3 is a cross-sectional view showing a surface emitting laser device according to a third embodiment.

The surface emitting laser device 200 according to the third embodiment is a surface emitting laser device with an oscillation wavelength λ of 680 nm. The surface emitting laser device 200 mainly includes a substrate 101, a lower DBR 202, a resonator region 203, an upper DBR 204, a contact layer 105, a lower electrode 106, and an upper electrode 107. The lower DBR 202 is on the substrate 101, the resonator region 203 is on the lower DBR 202, the upper DBR 204 is on the resonator region 203, and the contact layer 105 is on the upper DBR 104. The lower DBR 202, the resonator region 203, the upper DBR 204, and the contact layer 105 are formed by stacking semiconductor layers on the upper surface of the substrate 101. The surface emitting laser element 200 emits laser light upward from the resonator region 203. The surface emitting laser device 200 is a top emission type VCSEL device.

The substrate 101 is formed of an n-GaAs substrate, which is a semiconductor substrate. The lower DBR 202 includes 45 pairs of n-Al _0.5 Ga _0.5 As high refractive index layer 202a and n-Al _0.9 Ga _0.1 As low refractive index layer, each layer having an optical thickness of λ/4. 202b (see FIG. 4). That is, the lower DBR 202 includes 45 n-Al _0.5 Ga _0.5 As high refractive index layers 202a and 45 n-Al _0.9 Ga _0.1 As low refractive index layers 202b.

The resonator region 203 has three stacked bodies 30 stacked on each other. The resonator region 203 further includes a tunnel junction layer 40 between adjacent stacks 30 in the thickness direction. The stacked body 30 has a lower spacer layer 31 , an active layer 32 , and an upper spacer layer 33 . In stack 30 , active layer 32 is on top of bottom spacer layer 31 and top spacer layer 33 is on top of active layer 32 . The tunnel junction layer 40 has a p-type layer 41 and an n-type layer 42 (see FIG. 4). N-type layer 42 is on top of p-type layer 41.

The lower spacer layer 31 and the upper spacer layer 33 are, for example, (Al _0.7 Ga _0.3 ) _0.52 In _0.48 P layers. The active layer 32 has a quantum well structure including GaInP quantum well layers and (Al _0.5 Ga _0.5 ) _0.51 In _0.49 P barrier layers stacked alternately. For example, the thickness of the GaInP quantum well layer is 8 nm. The number of GaInP quantum well layers included in one active layer 32 is, for example, three. The lattice constant of the active layer 32 having such a composition is larger than the lattice constant of GaAs constituting the substrate 101. On the other hand, the lattice constant of (Al _0.7 Ga _0.3 ) _0.52 In _0.48 P forming the lower spacer layer 31 and the upper spacer layer 33 is smaller than that of GaAs. The thickness of the lower spacer layer 31 and the upper spacer layer 33 is about 60 nm in total, although it depends on the position of the stacked body 30. In this embodiment, the GaInP quantum well layer contains 0.5% crystal strain in the compressive direction with respect to the GaAs substrate.

The p-type layer 41 is a p ⁺⁺ -(Al _0.2 Ga _0.8 ) _0.51 In _0.49 P layer with a p-type impurity concentration of 10 ¹⁹ cm ^-3 or more, and the n-type layer 42 is The layer is an n ⁺⁺ -(Al _0.2 Ga _0.8 ) _0.51 In _0.49 P layer with an n-type impurity concentration of 10 ¹⁹ cm ^-3 or more. The p-type layer 41 and the n-type layer 42 are tunnel-junctioned with each other. Electrons in the conduction band in the n-type layer 42 head toward the valence band in the p-type layer 41, and a tunnel current flows between the bands. The tunnel junction layer 40 converts the polarity of charges carrying current from n-type to p-type.

The upper DBR 204 includes 32 pairs of p-Al _0.5 Ga _0.5 As high refractive index layer 204a and p-Al _0.9 Ga _0.1 As low refractive index layer, each layer having an optical thickness of λ/4. 204b (see FIG. 4). That is, the upper DBR 204 includes 32 p-Al _0.5 Ga _0.5 As high refractive index layers 204a and 32 p-Al _0.9 Ga _0.1 As low refractive index layers 204b.

The surface emitting laser device 200 has a current confinement layer 108 between the uppermost stacked body 30 and the lowermost p-Al _0.5 Ga _0.5 As high refractive index layer 204a. Current confinement layer 108 includes a selective oxidation region 108a and a current confinement region 108b. A portion of the lower side of the current confinement layer 108 is included in the resonator region 203, and a portion of the upper side of the current confinement layer 108 is included in the upper DBR 204.

Contact layer 105 is made of p-GaAs. A mesa 209 is formed in part of the contact layer 105, the upper DBR 204, the resonator region 203, and the lower DBR 202. The surface emitting laser element 200 has a protective layer 151 that covers the side surface of the mesa 209 and the upper surface of the lower DBR 202. Furthermore, a resin layer 152 is formed by embedding a resin material such as polyimide in the region where the semiconductor layer has been removed to form the mesa 109.

Here, the resonator region 203 will be explained in more detail. FIG. 4 is a cross-sectional view showing the main parts of a surface emitting laser device 200 according to the third embodiment. The waveform shown on the right side of the cross-sectional structure in FIG. 4 schematically shows a normalized longitudinal mode waveform.

In the surface emitting laser device 200, the optical thickness of each of the stacked bodies 30 is λ/2 or less, and the antinode of the normalized longitudinal mode is located in each active layer 32.

Regarding the lowermost stack 30, the total optical thickness of the stack 30 and the p-type layer 41 directly above the stack 30 is λ/2. A normalized longitudinal mode node is located at the boundary between the stacked body 30 and the lower DBR 202, and the p-type layer 41 and the n-type layer 42 included in the tunnel junction layer 40 directly above the stacked body 30 are located at the boundary between the stacked body 30 and the lower DBR 202. A node is located at the boundary. Therefore, the laminate 30 and the p-type layer 41 directly above the laminate 30 function like one λ/2 resonator.

Regarding the central laminate 30, the total optical thickness of the laminate 30, the n-type layer 42 directly below the laminate 30, and the p-type layer 41 directly above the laminate 30 is λ/2. It is. Then, a node is located at the boundary between the p-type layer 41 and the n-type layer 42 included in the tunnel junction layer 40 directly below the stacked body 30, and the p-type layer included in the tunnel junction layer 40 directly above the stacked body 30 is A node is located at the boundary between layer 41 and n-type layer 42 . Therefore, the laminate 30, the n-type layer 42 directly below the laminate 30, and the p-type layer 41 directly above the laminate 30 function like one λ/2 resonator.

For the uppermost stack 30, the total optical thickness of the stack 30, the n-type layer 42 immediately below the stack 30, and a portion of the current confinement layer 108 directly above the stack 30 is It is λ/2. Then, a node is located at the boundary between the p-type layer 41 and the n-type layer 42 included in the tunnel junction layer 40 directly below the stacked body 30, and a node is located in a part of the current confinement layer 108 directly above the stacked body 30. To position. Therefore, the laminated body 30, the n-type layer 42 directly under the laminated body 30, and a portion of the current confinement layer 108 directly above the laminated body 30 function like one λ/2 resonator.

The optical thickness of the resonator region 203 is 3λ/2.

In this embodiment, as described above, the lattice constant of the active layer 32 is larger than the lattice constant of GaAs constituting the substrate 101, and the lattice constants of the lower spacer layer 31 and the upper spacer layer 33 are larger than the lattice constant of GaAs. It's also small. Therefore, the active layer 32 contains compressive strain, and the lower spacer layer 31 and the upper spacer layer 33 contain tensile strain. That is, in the in-plane direction, the lower spacer layer 31 and the upper spacer layer 33 include crystal strain in the opposite direction to that of the active layer 32. Therefore, inside each stacked body 30, the crystal strain of the active layer 32 and the crystal strain of the lower spacer layer 31 and the upper spacer layer 33 cancel each other out.

In this embodiment, the GaInP quantum well layer included in the active layer 32 contains 0.5% crystal strain in the compressive direction and has a thickness of 8 nm. Therefore, when the active layer 32 has three GaInP quantum well layers, the total compressive strain in the active layer 32 including the three stacked quantum well layers is 3×0.5%×8 nm, which is 12%.・It is nm. Therefore, if the lower spacer layer 31 and the upper spacer layer 33 in one laminate 30 contain a total tensile strain of 12%·nm, the crystal strain can be canceled out. For example, when the total thickness of the lower spacer layer 31 and the upper spacer layer 33 is 60 nm, if the lower spacer layer 31 and the upper spacer layer 33 contain a total tensile strain of 0.2%, each laminate 30 Within this range, crystal strain can be canceled out. For example, when the lower spacer layer 31 and the upper spacer layer 33 are AlGaInP layers, if the In composition ratio in the group III elements is 48%, crystal strain can be offset. Note that since the lattice constant of the (Al _0.5 Ga _0.5 ) _0.51 In _0.49 P barrier layer is approximately the same as that of the GaAs substrate, its crystal strain does not need to be taken into account.

In this way, according to the third embodiment as well, accumulation of crystal strain can be suppressed while employing a multi-junction structure. Therefore, the third embodiment can also achieve high output.

The surface emitting laser device 200 according to the third embodiment can be manufactured by the same method as the surface emitting laser device 100 according to the first embodiment.

In the third embodiment, the active layer 32 can also be made to contain tensile strain by adjusting the In composition ratio in the group III elements in the active layer 32. Further, by adjusting the In composition ratio in the group III elements in the lower spacer layer 31 and the upper spacer layer 33, the lower spacer layer 31 and the upper spacer layer 33 can be made to contain compressive strain. The lower spacer layer 31 and the upper spacer layer 33 may be GaInP layers.

In the present disclosure, the total compressive strain in one active layer is not particularly limited, and is, for example, 36%·nm or less.

Furthermore, the number of stacked bodies included in the resonator region is not limited to three, but may be one or two, or four or more. When the number of stacks is n (n is a natural number), the total optical thickness of the resonator region is nλ/2.

Furthermore, the wavelength of light emitted by the surface emitting laser element is not particularly limited. For example, the surface emitting laser element may emit light having a wavelength of 780 nm, 808 nm, 980 nm, 1060 nm, 1200 nm, 1300 nm, or 1500 nm.

(Fourth embodiment)
Next, a fourth embodiment will be described. The fourth embodiment relates to a distance measuring device. FIG. 5 is a diagram showing a distance measuring device according to a fourth embodiment. A distance measuring device is an example of a detection device.

The distance measuring device 400 according to the fourth embodiment is a distance measuring device using the TOF (Time of Flight) method. Distance measuring device 400 includes a light emitting element 410, a light receiving element 420, and a drive circuit 430. The light emitting element 410 irradiates a light emitting beam (irradiation light 411) toward a distance measurement object 450 for distance measurement. The light receiving element 420 receives reflected light 421 from the object 450 to be measured. The drive circuit 430 drives the light emitting element 410 and detects the time difference between the emission timing of the emitted light beam and the reception timing of the reflected light 421 by the light receiving element 420, thereby determining the round trip distance to the distance measurement target 450. calculate. The drive circuit 430 is an example of a calculation unit.

The light emitting device 410 may include a plurality of surface emitting laser devices 100 according to the first embodiment, a surface emitting laser device according to the second embodiment, or a plurality of surface emitting laser devices 200 according to the third embodiment. The pulse repetition frequency ranges from several kHz to several tens of MHz, for example.

The light receiving element 420 is, for example, a photodiode (PD), an avalanche photodiode (APD), or a single photon avalanche diode (SPAD). The light receiving element 420 may include a plurality of light receiving elements arranged in an array. The light receiving element 420 is an example of a detection section.

In distance measurement using the TOF method, it is important to separate signals from the object to be measured and noise. When measuring a ranging object that is farther away or when measuring a ranging object that has a lower reflectance, it is preferable to use a more sensitive light receiving element to obtain a signal from the object. However, the use of a more sensitive light receiving element increases the possibility of erroneously detecting background light noise or shot noise. In order to separate signals from noise, it is possible to raise the threshold of the received light signal, but unless the peak output of the emitted beam is increased accordingly, it will be difficult to receive the signal light from the object to be measured. Become.

According to the surface-emitting laser device 100 according to the first embodiment, the surface-emitting laser device according to the second embodiment, or the surface-emitting laser device 200 according to the third embodiment, it is possible to output a high-power optical pulse. According to the distance measuring device according to the fourth embodiment, high detection accuracy and long distance can be achieved by using optical pulses with high peak output.

(Fifth embodiment)
Next, a fifth embodiment will be described. The fifth embodiment relates to a moving body. FIG. 6 is a diagram showing a car as an example of a moving object according to the fifth embodiment. The distance measuring device 400 described in the fourth embodiment is provided above the front surface (for example, above the windshield) of an automobile 500 as an example of a moving object according to the fifth embodiment. Distance measuring device 400 measures the distance to objects 502 around automobile 500. The measurement result of the distance measuring device 400 is input to a control unit included in the automobile 500, and the control unit controls the operation of the moving body based on this measurement result. Alternatively, the control unit may display a warning on a display unit provided in the vehicle 500 toward the driver 501 of the vehicle 500 based on the measurement result of the distance measuring device 400.

In this manner, in the fifth embodiment, by providing the distance measuring device 400 in the automobile 500, the position of the object 502 around the automobile 500 can be recognized with high accuracy. Note that the mounting position of the distance measuring device 400 is not limited to the upper front of the automobile 500, but may be mounted on the side or rear. Further, in this example, the distance measuring device 400 is provided in the automobile 500, but the distance measuring device 400 may be provided in an aircraft or a ship. Further, it may be provided in a mobile object that moves autonomously and does not have a driver, such as a drone or a robot.

(Sixth embodiment)
Next, a sixth embodiment will be described. The sixth embodiment relates to an optical inspection device. FIG. 7 is a diagram illustrating a schematic configuration of an optical inspection device according to a sixth embodiment. FIG. 8 is a diagram illustrating a block configuration of an optical inspection apparatus according to a sixth embodiment.

The optical inspection apparatus 600 according to the sixth embodiment is used, for example, in diffuse optical tomography (DOT). DOT is a technique for estimating optical characteristics inside the subject by irradiating light onto a subject (scattering body) such as a living body, detecting the light propagated within the subject. In particular, by detecting blood flow in the brain, it is expected to be used as a differential diagnosis aid for depressive symptoms and as an auxiliary device for rehabilitation.

The optical inspection device 600 includes an optical sensor 610, a control section 620, a calculation section 630, a display section 640, and the like. The optical sensor 610 includes an irradiation system including a plurality of light source modules 611 and a detection system including a plurality of detection modules 612. The irradiation system has a function of irradiating a target object with light, and the detection system has a function of detecting light that is irradiated onto the target object from the irradiation system and propagated within the target object. The plurality of light source modules 611 and the plurality of detection modules 612 are each connected to the control section 620 via electrical wiring.

For example, as shown in FIG. 8, the control section 620 includes a central processing unit 621, a switch section 622, a current control section 623, an A/D conversion section 624, a calculation section 625, a recording section 626, and the like. In the control unit 620, the switch unit 622 is controlled by the information from the central processing unit 621, and the light source module 611 that emits light is selected. At this time, the current supplied to the light source module 611 via the switch section 622 is controlled to a desired value by the current control section 623. The detection result (data) from the detection module 612 is A/D converted by an A/D converter 624, and subjected to calculations such as averaging processing by a calculation unit 625. The calculation results in the calculation unit 625 are sequentially recorded in the recording unit 626.

As the light source of the light source module 611, a surface emitting laser including the surface emitting laser element 100 according to the first embodiment, the surface emitting laser element according to the second embodiment, or the surface emitting laser element 200 according to the third embodiment is used. In this embodiment, it is preferable that the wavelength of the emitted light from the surface emitting laser be selected from either the 780 nm band or the 900 nm band, or from two types of surface emitting lasers, the 780 nm band and the 900 nm band. As described above, the surface-emitting laser device 100 according to the first embodiment, the surface-emitting laser device according to the second embodiment, or the surface-emitting laser device 200 according to the third embodiment has high performance compared to the conventional surface-emitting laser device. This is the output. Therefore, a surface emitting laser including the surface emitting laser element 100 according to the first embodiment, the surface emitting laser element according to the second embodiment, or the surface emitting laser element 200 according to the third embodiment is applied to the optical inspection apparatus 600. This allows for more accurate measurements.

Although the preferred embodiments have been described in detail above, they are not limited to the embodiments described above, and various modifications may be made to the embodiments described above without departing from the scope of the claims. Variations and substitutions can be made.

Aspects of the present disclosure are, for example, as follows.
<1>
a first reflecting mirror and a second reflecting mirror;
a resonator region between the first reflecting mirror and the second reflecting mirror;
has
The resonator region is
multiple active layers containing crystal strain;
a tunnel junction layer between the plurality of active layers;
a strain relaxation layer located between the first reflective mirror and the active layer, between the plurality of active layers, or at least between the active layer and the second reflective mirror;
has
A surface emitting laser device characterized in that the strain relaxation layer includes a crystal strain opposite to that of the active layer.
<2>
The resonator region has a plurality of spacer layers,
The surface emitting laser device according to item <1) above, wherein at least a portion of the plurality of spacer layers is the strain relaxation layer.
<3>
The resonator region has a plurality of laminates,
Each of the laminates includes:
a first spacer layer that is one of the plurality of spacer layers;
a second spacer layer that is another one of the plurality of spacer layers;
the active layer being one of the plurality of active layers and located between the first spacer layer and the second spacer layer;
has
The surface emitting laser device according to <2> above, wherein in the laminate, at least a portion of the first spacer layer and the second spacer layer is the strain relaxation layer.
<4>
When the wavelength of the light emitted from the active layer is λ, and the number of the laminates is n (n is a natural number of 2 or more),
The surface emitting laser device according to <3> above, wherein the entire optical thickness of the resonator region is nλ/2.
<5>
The surface emitting laser device according to <3> above, wherein each of the laminates has an optical thickness of λ/2 or less.
<6>
When the total amount of crystal strain in the active layer included in the resonator region is ε, the total amount of crystal strain in the active layer included in the resonator region is −1.1ε to −0. The surface-emitting laser device according to any one of <1> to <5> above, wherein the surface emitting laser element is within a range of 9ε.
<7>
The surface emitting laser device according to any one of <1> to <6>, wherein the total amount of crystal strain in the active layer and the tunnel junction layer is 108%·nm or less.
<8>
The surface emitting laser device according to any one of <1> to <7>, wherein the amount of crystal strain in the active layer is 36%·nm or less.
<9>
The surface emitting laser device according to any one of <1> to <8>, wherein the strain relaxation layer contains P.
<10>
The surface emitting laser device according to <9> above, wherein the strain relaxation layer is an AlGaAsP layer or an AlGaInAsP layer.
<11>
The surface emitting laser device according to <9> above, wherein the strain relaxation layer is an AlGaInP layer or a GaInP layer.
<12>
The surface emitting laser device according to any one of <1> to <11>, wherein the Al composition ratio in the group III elements constituting the strain relaxation layer is 65% or less.
<13>
The surface emitting laser device according to any one of <1> to <12> above,
a detection unit that detects light emitted from the surface emitting laser element and reflected by a target object;
A detection device comprising:
<14>
The detection device according to <13>, further comprising a calculation unit that calculates a distance to the target object based on a signal from the detection unit.
<15>
A mobile object comprising the detection device according to <14> above.

100, 200 Surface emitting laser element 10, 30 Laminated body 11, 31 Lower spacer layer 12, 32 Active layer 13, 33 Upper spacer layer 20, 40 Tunnel junction layer 21, 41 P type layer 22, 42 N type layer 102, 202 Lower DBR
103, 203 Resonator region 104, 204 Upper DBR
400 Distance measuring device 430 Drive circuit (calculation unit)
500 Automobile (mobile object)
600 Optical inspection equipment

Patent No. 4232334

"Multi-junction vertical-cavity surface-emitting lasers in the 800-1100nm wavelength range", Proc. SPIE 11704, Vertical-Cavity Surface-Emitting Lasers XXV, 117040B (5 March 2021) Semiconductor laser Edited by the Japan Society of Applied Physics Ohmsha

Claims (15)

a first reflecting mirror and a second reflecting mirror;
a resonator region between the first reflecting mirror and the second reflecting mirror;
has
The resonator region is
multiple active layers containing crystal strain;
a tunnel junction layer between the plurality of active layers;
a strain relaxation layer located between the first reflective mirror and the active layer, between the plurality of active layers, or at least between the active layer and the second reflective mirror;
has
A surface emitting laser device characterized in that the strain relaxation layer includes a crystal strain opposite to that of the active layer. The resonator region has a plurality of spacer layers,
2. The surface emitting laser device according to claim 1, wherein at least a portion of the plurality of spacer layers is the strain relaxation layer. The resonator region has a plurality of laminates,
Each of the laminates includes:
a first spacer layer that is one of the plurality of spacer layers;
a second spacer layer that is another one of the plurality of spacer layers;
the active layer being one of the plurality of active layers and located between the first spacer layer and the second spacer layer;
has
3. The surface emitting laser device according to claim 2, wherein in the laminate, at least a portion of the first spacer layer and the second spacer layer is the strain relaxation layer. When the wavelength of the light emitted from the active layer is λ, and the number of the laminates is n (n is a natural number of 2 or more),
4. The surface emitting laser device according to claim 3, wherein the total optical thickness of the resonator region is nλ/2. 4. The surface emitting laser device according to claim 3, wherein the optical thickness of each of the laminates is λ/2 or less. When the total amount of crystal strain in the active layer included in the resonator region is ε, the total amount of crystal strain in the active layer included in the resonator region is −1.1ε to −0. 6. The surface emitting laser device according to claim 1, wherein the surface emitting laser element has a surface emitting laser element within a range of 9ε. 6. The surface emitting laser device according to claim 1, wherein the total amount of crystal strain in the active layer and the tunnel junction layer is 108%·nm or less. 6. The surface emitting laser device according to claim 1, wherein the amount of crystal strain in the active layer is 36%·nm or less. 6. The surface emitting laser device according to claim 1, wherein the strain relaxation layer contains P. 10. The surface emitting laser device according to claim 9, wherein the strain relaxation layer is an AlGaAsP layer or an AlGaInAsP layer. 10. The surface emitting laser device according to claim 9, wherein the strain relaxation layer is an AlGaInP layer or a GaInP layer. 6. The surface emitting laser device according to claim 1, wherein the Al composition ratio in the group III elements constituting the strain relaxation layer is 65% or less. A surface emitting laser device according to any one of claims 1 to 5,
a detection unit that detects light emitted from the surface emitting laser element and reflected by a target object;
A detection device comprising: The detection device according to claim 13, further comprising a calculation unit that calculates a distance to the target object based on a signal from the detection unit. A moving body comprising the detection device according to claim 14.

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