Quantum Cascade Laser and Its Manufacturing Method

Abstract

The present invention relates to the technical field of lasers, and discloses a quantum cascade laser and a preparation method thereof. The quantum cascade laser includes a base layer, a laser body, and a reflection structure. The laser body includes a first electrode, an epitaxial structure, a substrate layer, and a second electrode that are stacked; it also includes a first cavity surface and a second cavity surface that are oppositely arranged in a first direction, and laser light exits from the first cavity surface; the reflection structure is arranged on one side of the second cavity surface of the laser body and is spaced from the second cavity surface, and includes a reflection part having reflection protrusions and grooves alternately arranged in the first direction. The present invention adopts a reflection structure suitable for long-wave quantum cascade lasers, which is packaged and fixed on a base layer together with the laser body. The reflection structure is spaced on one side of the second cavity surface of the laser body, effectively reducing light absorption, preventing catastrophic optical damage caused by the temperature rise of the second cavity surface, and ensuring the light output, service life, and reliability of the laser.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and particularly relates to a quantum cascade laser and a preparation method thereof. Background Art

[0002] A quantum cascade laser (QCL for short) is a semiconductor laser capable of emitting lasers in the mid-infrared and far-infrared frequency bands. The output of the previous component in its active region is the input of the next component, and they are connected in series one by one. The spectral range covers the mid-infrared to far-infrared bands, and it can be used in many fields such as trace gas detection and free-space optical communication. It has the advantages of high sensitivity and fast detection speed, and has broad market application prospects.

[0003] In the quantum cascade lasers in the related art, an antireflection film (AR film) is provided on the front cavity surface of the device to ensure light output, and a high-reflection film (HR film) is provided on the rear cavity surface of the device to form a resonant cavity structure. Among them, the antireflection film on the front cavity surface uses a yttrium oxide dielectric film to adjust the reflectivity of the front cavity surface, and the high-reflection film on the rear cavity surface uses a composite film system of yttrium oxide + gold + yttrium oxide to provide a reflectivity of more than 90%. However, the materials used in the cavity film systems (including AR film and HR film) on the front and rear cavity surfaces, such as yttrium oxide, alumina, zirconia, etc., have strong light absorption in the mid-infrared band. The cavity film systems are prone to temperature rise during operation, which further causes catastrophic optical mirror damage (COMD for short) on the front and rear cavity surfaces and fails, ultimately resulting in the failure of the quantum cascade laser, and the service life and reliability are affected. Summary of the Invention

[0004] In view of this, the present invention provides a quantum cascade laser and a preparation method thereof to solve the problem that the cavity surface of the existing quantum cascade laser is prone to failure, affecting the service life and reliability.

[0005] In a first aspect, the present invention provides a quantum cascade laser, including a base layer, a laser body and a reflection structure provided on the same side surface of the base layer. The laser body includes a first electrode, an epitaxial structure, a substrate layer and a second electrode which are stacked; the laser body further includes a first cavity surface and a second cavity surface oppositely arranged along a first direction, and the laser is suitable for emitting from the first cavity surface; the reflection structure is provided on one side of the second cavity surface of the laser body and is spaced from the second cavity surface to reflect the laser; the reflection structure includes a reflection part, and the reflection part includes reflection protrusions and grooves alternately arranged along the first direction.

[0006] Beneficial effects: A reflection structure suitable for long-wave quantum cascade lasers is adopted. The reflection structure includes a reflection part with alternately arranged reflection protrusions and grooves, forming a distributed Bragg reflector (hereinafter referred to as DBR) structure with a peak-valley structure. The wavelength corresponding to its reflection curve is exactly the laser wavelength, ensuring ultra-high reflectivity. The reflection structure and the laser body are encapsulated and fixed on the same side surface of a base layer. The reflection structure is arranged on the second cavity surface of the laser body, that is, on the side of the reflection cavity surface, replacing the composite film system that has a large light absorption for mid-infrared light in the conventional solution, effectively reducing light absorption, suppressing the temperature rise of the second cavity surface, preventing catastrophic optical damage to the second cavity surface, and ultimately ensuring the high-efficiency light output, service life, and reliability of the quantum cascade laser.

[0007] In an alternative embodiment, the reflection structure further includes a substrate and a mounting part located on the substrate. The substrate is arranged relatively far from the base layer. One end of the mounting part away from the substrate is connected to the base layer. The mounting part and the reflection part are arranged adjacent to each other on the substrate along a first direction, and the reflection part is relatively closer to the laser body side.

[0008] Beneficial effects: The substrate, the reflection part, and the mounting part of the reflection structure are integrally formed. The substrate connects the reflection part and the mounting part into a whole. The mounting part and the reflection part are arranged adjacent to each other along the first direction. The reflection part is close to the laser body to reflect the laser transmitted from the laser body. The mounting part is used to be fixed to the base layer and achieve efficient heat dissipation at the same time. There is no fixing material between the reflection part and the base layer, effectively ensuring the reflection performance of the reflection part for the laser.

[0009] In an alternative embodiment, the mounting part includes a mounting protrusion protruding from the surface of the substrate; one end of the mounting protrusion relatively far from the substrate is flush with one end of the reflection protrusion relatively far from the substrate, and the groove is adjacent to the mounting protrusion.

[0010] Beneficial effects: The surfaces of the reflection protrusion and the mounting protrusion are flush. When the lower surface of the mounting protrusion is fixed to the base layer after the reflection structure is inverted, the existence of fixing materials such as colloid or solder makes there be a small gap between the small surface of the reflection protrusion and the upper surface of the base layer, which not only ensures the full coverage of the laser output from the second cavity surface by the reflection part, but also can avoid the contact between the reflection part and the base layer from affecting the reflection performance.

[0011] In an alternative embodiment, the geometric length of the mounting protrusion in the first direction is greater than the geometric length of the reflection protrusion in the first direction.

[0012] Beneficial effects: In the first direction, the geometric length of the mounting protrusion is greater than the geometric length of the reflection protrusion, which is convenient for realizing the efficient heat transfer of the reflection structure to the heat sink base layer, and can also realize the reliable fixation of the reflection structure on the base layer.

[0013] In an alternative embodiment, the optical length of the reflection protrusion in the first direction and the optical length of the groove in the first direction are both one - quarter of the laser wavelength.

[0014] Advantageous effects: By setting the optical lengths of the reflection protrusion and the groove in the first direction to be both one - quarter of the laser wavelength, it can ensure the transmission of the laser within the optical field and achieve the effective reflection of the laser by the reflection part.

[0015] In an alternative embodiment, the optical distance between a reflection protrusion adjacent to the laser body and the second cavity surface of the laser body is one - quarter of the laser wavelength.

[0016] Advantageous effects: By setting the optical distance between the right - most reflection protrusion of the reflection structure and the left - hand cavity surface of the laser body to be one - quarter of the laser wavelength, it can ensure the effective propagation of the laser output from the second cavity surface of the laser body between the laser body and the reflection structure, reducing the optical transmission loss.

[0017] In an alternative embodiment, the depth of the groove in the direction perpendicular to the surface of the substrate is greater than or equal to 20 μm.

[0018] Advantageous effects: By setting the depth of the groove in the direction perpendicular to the surface of the substrate to be greater than or equal to 20 μm, it can ensure the full coverage of the laser by the reflection structure in the vertical direction, enabling the reflection part to fully reflect the laser and improving the light output efficiency.

[0019] In an alternative embodiment, in a plane parallel to the surface of the base layer, the width range of the reflection structure in the second direction is 100 μm - 400 μm, and the second direction is perpendicular to the first direction.

[0020] Advantageous effects: In the horizontal plane, by limiting the geometric width of the reflection structure in the second direction to be between 100 μm and 400 μm, it can ensure the full coverage of the laser by the reflection structure in the second direction, enabling the reflection part to fully reflect the laser and improving the light output efficiency.

[0021] In an alternative embodiment, the material of the reflection structure includes: semi - insulating iron - doped indium phosphide, or semi - insulating gallium arsenide, or semi - insulating zinc selenide.

[0022] Advantageous effects: The above - mentioned semi - insulating materials have little absorption of mid - infrared light, ensuring the full reflection of the laser output from the second cavity surface, so as to improve the lasing of the quantum cascade laser on the first cavity surface.

[0023] In an alternative embodiment, the first electrode of the laser body is relatively close to the base layer and fixed to the base layer; in the first direction, there is a spacing between the two side edges of the projection of the first electrode on the base layer and the two side edges of the projection of the epitaxial structure on the base layer.

[0024] Beneficial effects: When setting the first electrode, it retracts a certain distance from the edge of the epitaxial structure in the first direction to form a gap space. When the laser body is fixed to the base layer, encapsulation materials such as colloids or solders for fixing can enter the gap space, thus preventing the encapsulation materials from overflowing and affecting the encapsulation reliability.

[0025] In an optional embodiment, it further includes:

[0026] A first welding layer, disposed between the installation part and the base layer;

[0027] A second welding layer, disposed between the laser body and the base layer, and the thickness of the first welding layer is less than that of the second welding layer.

[0028] Beneficial effects: The laser body and the reflection structure are fixed to the base layer by welding. The welding connection has strong stability and can ensure good electrical conductivity. The first welding layer is disposed between the lower surface of the installation protrusion and the base layer, and the second welding layer is disposed between the lower surface of the first electrode of the inverted laser body and the base layer. The thickness of the first welding layer is set to be less than that of the second welding layer. The relatively thick second welding layer can ensure the efficient current injection of the laser body, and at the same time adjust the laser emission of the laser body to fully reach the reflection part, avoiding unnecessary laser loss.

[0029] In an optional embodiment, the epitaxial structure includes a first confinement layer, a first waveguide layer, an active layer, a second waveguide layer, and a second confinement layer sequentially arranged from one side of the substrate layer towards the side away from the substrate layer, and the first electrode is disposed on the second confinement layer;

[0030] The epitaxial structure is formed with a ridge structure, and the ridge structure includes the second confinement layer, the second waveguide layer, the active layer, the first waveguide layer, and a part of the thickness of the first confinement layer; in a second direction perpendicular to the first direction, a first isolation structure and a second isolation structure are respectively disposed on both sides of the ridge structure.

[0031] Beneficial effects: Semi-insulating materials, such as semi-insulating iron-doped indium phosphide, are filled in the areas on both sides of the single ridge structure extending in the Y-axis direction to form the first isolation structure and the second isolation structure for electrical isolation and optical confinement, preventing the laser from escaping in the second direction and ensuring the laser output effect.

[0032] In a second aspect, the present invention further provides a preparation method of a quantum cascade laser for preparing the above-mentioned quantum cascade laser, including:

[0033] Form a laser body, which includes a first electrode, an epitaxial structure, a substrate layer, and a second electrode that are stacked; the laser body further includes a first cavity surface and a second cavity surface that are oppositely arranged in a first direction, and laser light is adapted to exit from the first cavity surface;

[0034] Form a reflection structure, which includes a reflection part, and the reflection part includes reflection protrusions and grooves that are alternately arranged in the first direction to reflect laser light;

[0035] Fix the laser body and the reflection structure on one side surface of the base layer. The reflection structure is arranged on one side of the second cavity surface of the laser body and is spaced from the second cavity surface.

[0036] Beneficial effects: The quantum cascade laser obtained by the above preparation method adopts a reflection structure suitable for a long-wave quantum cascade laser and packages and fixes it on the same side surface of a base layer together with the laser body; the laser light exits from one side of the first cavity surface of the laser body, and the reflection structure is arranged on the second cavity surface side opposite to the first cavity surface of the laser body and is spaced from the laser body, replacing the composite film system (HR film) that has a large light absorption for mid-infrared light in the conventional solution, effectively reducing light absorption, suppressing the temperature rise of the second cavity surface, preventing catastrophic optical damage on the second cavity surface, and ensuring the high-efficiency light output, service life, and reliability of the quantum cascade laser.

[0037] In an optional implementation manner, forming the laser body includes:

[0038] Provide a substrate layer;

[0039] Epitaxially grow a first confinement layer, a first waveguide layer, an active layer, a second waveguide layer, and a second confinement layer in sequence on the substrate layer to form an epitaxial structure;

[0040] Etch to form a ridge structure on the side of the epitaxial structure away from the substrate layer. The ridge structure includes the second confinement layer, the second waveguide layer, the active layer, the first waveguide layer, and a part of the thickness of the first confinement layer;

[0041] Respectively arrange a first isolation structure and a second isolation structure on both sides of the ridge structure in a second direction;

[0042] Arrange a first electrode on the side of the epitaxial structure facing away from the substrate layer, and arrange a second electrode on the side of the substrate layer facing away from the epitaxial structure; the first electrode is adapted to be arranged facing the base layer side.

[0043] Beneficial effects: By means such as setting a mask layer and wet etching, a single ridge structure extending in the first direction can be simply and efficiently formed. Although the side walls of the ridge structure formed by wet etching have a certain inclination, since the side wall surfaces are not the light-emitting sides and an isolation structure is subsequently provided, there is no excessive requirement for the precision of the process for forming the ridge structure. By means such as metal organic chemical vapor deposition growth technology, a semi-insulating material, such as semi-insulating iron-doped indium phosphide, is filled in the etching regions on both sides of the ridge structure in the second direction to form a first isolation structure and a second isolation structure for electrical isolation and optical confinement, avoiding the escape of laser light in the second direction and ensuring the laser output effect; the laser body is inverted on the base layer in a manner that the first electrode is connected to the base layer, enhancing the electrical excitation effect. Description of the Drawings

[0044] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0045] Figure 1 It is a schematic structural diagram of the quantum cascade laser according to an embodiment of the present invention;

[0046] Figure 2 It is a schematic structural diagram of the reflection structure according to an embodiment of the present invention;

[0047] Figure 3 It is a schematic front view structural diagram of the laser body according to an embodiment of the present invention;

[0048] Figure 4 It is a schematic side view structural diagram of the laser body according to an embodiment of the present invention;

[0049] Figure 5 It is a schematic flow chart of the preparation method of the quantum cascade laser according to an embodiment of the present invention;

[0050] Figure 6 It is a schematic structural diagram after forming an epitaxial structure on a substrate layer according to an embodiment of the present invention;

[0051] Figure 7 It is a schematic structural diagram after forming a ridge structure in the epitaxial structure according to an embodiment of the present invention;

[0052] Figure 8 It is a schematic structural diagram after setting a first isolation structure and a second isolation structure on both sides of the ridge structure in the second direction according to an embodiment of the present invention.

[0053] Description of the Reference Numerals: [[ID=4,2]]

[0054] 100. Mask layer;

[0055] 1. Substrate layer;

[0056] 2. Laser body; 21. Substrate layer; 22. Epitaxial structure; 221. First confinement layer; 222. First waveguide layer; 223. Active layer; 224. Second waveguide layer; 225. Second confinement layer; 23. First electrode; 24. Second electrode; 25. Ridge structure; 26. First cavity surface; 27. Second cavity surface; 28. First isolation structure; 29. Second isolation structure;

[0057] 3. Reflective structure; 31. Reflective portion; 311. Reflective protrusion; 312. Groove; 32. Substrate; 33. Mounting portion;

[0058] 41. First welding layer; 42. Second welding layer. Detailed implementation manners

[0059] The present invention will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the sake of description, only parts related to the present invention rather than all structures are shown in the drawings. In the following description, the description of well-known structures and technologies is omitted to avoid unnecessarily confusing the concepts of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the drawings. These figures are not drawn to scale, where for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are only exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element can be directly on the other layer / element, or there can be an intermediate layer / element between them. Additionally, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element can be "under" the other layer / element.

[0060] In a quantum cascade laser in the related art, an antireflection film is provided on the front cavity surface to ensure light output, and a high-reflection film is provided on the rear cavity surface to form a resonant cavity structure. Among them, the antireflection film on the front cavity surface usually uses a yttrium oxide dielectric film, and the high-reflection film on the rear cavity surface uses a composite film system of yttrium oxide + gold + yttrium oxide. However, materials such as yttrium oxide, alumina, and zirconia used in the cavity film systems on the front and rear cavity surfaces have strong light absorption in the mid-infrared band, which makes the cavity film systems prone to temperature rise during operation, and then causes catastrophic optical damage and failure of the front and rear cavity surfaces. Even if the materials or structures of the cavity film systems are improved, it is impossible to avoid the damage and failure of the front and rear cavity surfaces during long-term use, and it is difficult to ensure the light output efficiency, service life, and reliability of the quantum cascade laser.

[0061] Based on this, this embodiment provides a quantum cascade laser and a preparation method thereof. The cavity film systems are not provided on the front and rear cavity surfaces in a fitting manner. The front cavity surface is a structure without a dielectric film, and a specially designed reflection structure 3 is provided at intervals on one side of the rear cavity surface to efficiently reflect the laser generated in the laser body 2, while avoiding the failure of the laser caused by the temperature rise of the cavity surface, and ensuring the light output efficiency, service life, and reliability of the quantum cascade laser structure.

[0062] Reference Figures 1 to 4 Referring to, a quantum cascade laser provided in this embodiment includes: a base layer 1, a laser body 2, and a reflection structure 3 provided on the same-side surface of the base layer 1. The laser body 2 includes a first electrode 23, an epitaxial structure 22, a substrate layer 21, and a second electrode 24 stacked; the laser body 2 further includes a first cavity surface 26 and a second cavity surface 27 oppositely arranged in a first direction, and the laser is suitable for exiting from the first cavity surface 26; the reflection structure 3 is provided on one side of the second cavity surface 27 of the laser body 2 and is spaced from the second cavity surface 27 to reflect the laser; the reflection structure 3 includes a reflection portion 31, and the reflection portion 31 includes reflection protrusions 311 and grooves 312 alternately arranged in the first direction.

[0063] This embodiment is described by taking a quantum cascade laser structure with a laser wavelength of 9 μm as an example. For example, the base layer 1 is a heat sink base, such as aluminum nitride, silicon carbide, etc., which is fixed to the laser body 2 and the reflective structure 3 to achieve good heat dissipation. The base layer 21 of the laser body 2 can be an indium phosphide substrate. A plurality of structural layers including an active layer 223 are sequentially epitaxially grown on the indium phosphide substrate to form an epitaxial structure 22. A first electrode 23 is provided on the exposed side surface of the epitaxial structure 22, and a second electrode 24 is provided on the exposed side surface of the base layer 21. The first electrode 23 and the second electrode 24 serve as the positive and negative electrodes of the quantum cascade laser, respectively, to form the laser body 2. For example, the laser body 2 can be inverted and fixed to the upper surface of the base layer 1 by the first electrode 23. Of course, it is not ruled out that the laser body 2 is fixed to the upper surface of the base layer 1 by the second electrode 24. In this embodiment, the inverted method is preferred. The laser body 2 has a first cavity facet 26 and a second cavity facet 27 opposite to each other in the first direction. The first direction of this embodiment is Figure 1 In the y-axis direction shown in FIG, which is also the cavity length direction of the laser body 2, the first cavity surface 26 is the front cavity surface for laser emission, and the second cavity surface 27 is the rear cavity surface. This side is used to set the reflective structure 3 to achieve reflection of the laser, so that the laser can be emitted from the first cavity surface 26 to the greatest extent. Figure 1 and Figure 2 The reflective structure 3 of this embodiment includes a reflective portion 31 having alternating reflective protrusions 311 and grooves 312, forming a distributed Bragg reflector (DBR) structure with a peak-valley structure. For example, the reflective protrusions 311 can be made of a semi-insulating material, while the grooves 312 contain air, forming a multi-layer DBR reflector structure with a repeated alternation of semi-insulating material / air / semi-insulating material / air... The wavelength corresponding to its reflection curve is exactly the laser wavelength, equivalent to providing a DBR reflector with a bandgap width consistent with the laser wavelength on the reflective cavity facet of the laser body 2. The reflectivity easily reaches over 90%. Furthermore, the semi-insulating material and air do not absorb mid-infrared light. Furthermore, the presence of a certain distance from the second cavity facet 27 of the laser body 2 allows for efficient laser reflection on the second cavity facet 27 of the laser body 2 while preventing temperature rise on the second cavity facet 27 of the laser body 2, ultimately ensuring the optical output efficiency, performance, and reliability of the quantum cascade laser.

[0064] In summary, the quantum cascade laser of this embodiment adopts a reflective structure 3 suitable for a long-wave quantum cascade laser, and packages it and the laser body 2 on the same side surface of a substrate layer 1; the reflective structure 3 is arranged on the side of the second cavity surface 27 of the laser body 2, that is, the side of the reflective cavity surface, that is, Figure 1In the transverse y direction as shown, the laser exits from the right side of the laser body 2, and the reflection structure 3 is arranged on the left side of the laser body 2, which is spaced from the laser body 2. It replaces the composite film system (HR film) with high light absorption for mid-infrared light in the conventional solution, effectively reducing light absorption, suppressing the temperature rise of the second cavity surface 27, preventing catastrophic optical damage to the second cavity surface 27, and ensuring the high-efficiency light output, service life, and reliability of the quantum cascade laser.

[0065] In addition, in the laser body 2 of this embodiment, no dielectric film is arranged on the first cavity surface 26, that is, the light-emitting cavity surface side, effectively reducing the light absorption of the light-emitting cavity surface and ensuring the cavity surface performance. Of course, it is not excluded to arrange a very thin dielectric film on the first cavity surface 26, such as a dielectric film with a thickness less than 30 nm, to reduce the light absorption of the dielectric film.

[0066] In one embodiment, referring to Figure 1 and Figure 2 , the reflection structure 3 further includes a base body 32 and a mounting portion 33 located on the base body 32. The base body 32 is relatively far from the base layer 1. One end of the mounting portion 33 away from the base body 32 is connected to the base layer 1. The mounting portion 33 and the reflecting portion 31 are arranged adjacent to each other on the base body 32 along the first direction, and the reflecting portion 31 is relatively closer to the laser body 2 side.

[0067] In this embodiment, the base body 32, the reflecting portion 31, and the mounting portion 33 of the reflection structure 3 are integrally formed. The base body 32 connects the reflecting portion 31 and the mounting portion 33 into a whole. The mounting portion 33 and the reflecting portion 31 are arranged adjacent to each other along the first direction, that is, Figure 1 the y-axis direction shown. The reflecting portion 31 is close to the laser body 2 to reflect the laser transmitted from the laser body 2. The mounting portion 33 is used to be fixed to the base layer 1 and achieve efficient heat dissipation at the same time. There is no direct connection and fixation between the reflecting portion 31 and the base layer 1, effectively ensuring the reflection performance of the reflecting portion 31 for the laser.

[0068] Furthermore, referring to Figure 1 and Figure 2 , the above-mentioned mounting portion 33 includes a mounting protrusion protruding from the surface of the base body 32; one end of the mounting protrusion relatively far from the base body 32 is flush with one end of the reflecting protrusion 311 relatively far from the base body 32, and the groove 312 is arranged adjacent to the mounting protrusion.

[0069] The reflection structure 3 of this embodiment first completes the overall structure forming, and then fixes it on the surface of the base layer 1. Referring to Figure 2, for example, on the upper surface of the complete reflective material, multiple strip-shaped grooves and protrusions extending in the x-axis direction can be formed by etching or other means. One of the left protrusions serves as the mounting protrusion of the mounting portion 33 for fixing to the base layer 1; multiple spaced-apart protrusions on the right form the reflective protrusions 311, and the surfaces of the reflective protrusions 311 and the mounting protrusion are naturally flush. As Figure 1 shown, when the reflective structure 3 is inverted and the lower surface of the mounting protrusion is fixed to the base layer 1, the presence of fixing materials such as colloids or solders causes a small gap between the small surface of the reflective protrusion 311 and the upper surface of the base layer 1, which not only ensures the full coverage of the laser output from the second cavity surface 27 by the reflective portion 31, but also avoids the contact between the reflective portion 31 and the base layer 1 from affecting the reflection performance.

[0070] Furthermore, as Figure 1 and Figure 2 shown, the geometric length of the above-mentioned mounting protrusion in the first direction is greater than the geometric length of the reflective protrusion 311 in the first direction.

[0071] That is, in the y direction, the geometric length of the mounting protrusion is greater than the geometric length of the reflective protrusion 311, which facilitates the efficient heat transfer from the reflective structure 3 to the heat sink base layer 1 and can also achieve the reliable fixation of the reflective structure 3 on the base layer 1. Exemplarily, the geometric length of the mounting protrusion in the first direction is set to exceed 100 μm.

[0072] Based on the above solution, the optical length of the reflective protrusion 311 in the first direction and the optical length of the groove 312 in the first direction are both one-quarter of the laser wavelength.

[0073] In this embodiment, in order to achieve the effective reflection of the laser by the reflective portion 31, it is necessary to ensure that the optical lengths of the reflective protrusion 311 and the groove 312 in the first direction are both 1 / 4 of the laser wavelength. Here, the optical length can be understood as the optical path rather than simply the geometric length. Optical length = geometric length × real part of the refractive index of the medium. In this embodiment, the geometric length of the reflective protrusion 311 in the first direction is L2, and the geometric length of the groove 312 in the first direction is L1, then L2 = , and L1 = , where λ is the laser wavelength, n2 is the real part of the refractive index of the material of the reflective protrusion 311, and n1 is the real part of the refractive index of air.

[0074] Furthermore, in this embodiment, the optical distance between a reflective protrusion 311 adjacent to the laser body 2 and the second cavity surface 27 of the laser body 2 is set to be one-quarter of the laser wavelength.

[0075] Similarly, referring to Figure 1, similarly, set the optical distance between the rightmost reflection protrusion 311 of the reflection structure 3 and the left cavity surface of the laser body 2 to be one - quarter of the laser wavelength, and set the corresponding geometric distance of this optical distance to be L3, then L3 = , ensure that the laser output from the second cavity surface 27 of the laser body 2 can effectively propagate between the laser body 2 and the reflection structure 3, and reduce the transmission loss of the laser.

[0076] In one embodiment, set the depth of the groove 312 in the direction perpendicular to the surface of the substrate 32 to be greater than or equal to 20 μm. At this depth, it can ensure that the reflection structure 3 fully covers the laser in the vertical direction, that is, the z - axis direction, and the reflection part 31 can achieve full reflection of the laser.

[0077] On this basis, in the plane parallel to the surface of the base layer 1, the width range of the reflection structure 3 in the second direction is 100 μm - 400 μm, and the second direction is perpendicular to the first direction.

[0078] That is, in the horizontal plane formed by the x - axis and the y - axis, the geometric width range of the reflection structure 3 in the second direction, that is, the x - axis direction, is 100 μm - 400 μm, to ensure that the reflection structure 3 fully covers the laser in the x - axis direction, and the reflection part 31 can achieve full reflection of the laser.

[0079] In one embodiment, the material of the above - mentioned reflection structure 3 includes: semi - insulating iron - doped indium phosphide (Fe:InP), or semi - insulating gallium arsenide (GaAs), or semi - insulating zinc selenide (ZnSe). These materials basically do not absorb mid - infrared light, ensuring full reflection of the laser output from the second cavity surface 27, so as to improve the lasing of the quantum cascade laser on the first cavity surface 26.

[0080] In one embodiment, referring to Figure 1 and Figure 4 , the first electrode 23 of the laser body 2 is relatively close to the base layer 1 and fixed to the base layer 1; in the first direction, there are spacings between the two side edges of the projection of the first electrode 23 on the base layer 1 and the two side edges of the projection of the epitaxial structure 22 on the base layer 1.

[0081] That is, when setting the first electrode 23, it retracts a certain distance compared to the edge of the epitaxial structure 22 in the first direction, forming a gap space, so that when the laser body 2 is fixed to the base layer 1, packaging materials such as colloids or solders used for fixing can enter the gap space, thus avoiding the overflow of packaging materials and affecting the packaging reliability.

[0082] As a preferred implementation manner, in this embodiment, the retracted distance is set to 50 μm, which neither affects the reliable fixation of the first electrode 23 to the base layer 1 nor can ensure sufficient gap space.

[0083] Reference Figure 1 Figure 1 , the quantum cascade laser of this embodiment further includes a first welding layer 41 and a second welding layer 42. The first welding layer 41 is disposed between the mounting portion 33 and the base layer 1; the second welding layer 42 is disposed between the laser body 2 and the base layer 1, and the thickness of the first welding layer 41 is less than that of the second welding layer 42.

[0084] That is, in this embodiment, the laser body 2 and the reflection structure 3 are fixed to the base layer 1 by welding. The welding connection has strong stability and can ensure good electrical conductivity. The first welding layer 41 is disposed between the lower surface of the mounting protrusion and the base layer 1, and the second welding layer 42 is disposed between the lower surface of the first electrode 23 of the inverted laser body 2 and the base layer 1. The thickness of the first welding layer 41 is set to be less than that of the second welding layer 42. The relatively thick second welding layer 42 can ensure the efficient current injection of the laser body 2, and at the same time, adjust the laser emission of the laser body 2 to fully reach the reflection portion 31, avoiding unnecessary laser loss.

[0085] Further, the above-mentioned first welding layer 41 and second welding layer 42 should be as thin as possible, for example, less than 2 μm, and no solder is provided between the reflection portion 31 of the reflection structure 3 and the base layer 1 to prevent the solder from affecting the light field transmission.

[0086] Reference Figure 3 and Figure 4 Figure 4 , the epitaxial structure 22 of the quantum cascade laser of this embodiment includes: a first confinement layer 221, a first waveguide layer 222, an active layer 223, a second waveguide layer 224, and a second confinement layer 225, which are sequentially arranged from one side of the substrate layer 21 toward the side away from the substrate layer 21. The first electrode 23 is disposed on the second confinement layer 225; the epitaxial structure 22 is formed with a ridge structure 25, and the ridge structure 25 includes the second confinement layer 225, the second waveguide layer 224, the active layer 223, the first waveguide layer 222, and a part of the first confinement layer 221 with a certain thickness; in the second direction perpendicular to the first direction, a first isolation structure 28 and a second isolation structure 29 are respectively disposed on both sides of the ridge structure 25.

[0087] Exemplarily, the substrate layer 21 can be an indium phosphide substrate, and the first confinement layer 221 is indium phosphide with a thickness of 4 μm and a doping concentration of 2×10 16 cm -3 ; the first waveguide layer 222 is indium gallium arsenide with a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3 ; the active layer 223 with a thickness of 2 μm; the second waveguide layer 224 is indium gallium arsenide with a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3Indium gallium arsenide; the second confinement layer 225 has a thickness of 5 μm and a doping concentration of 2×10 16 cm -3 of indium phosphide; in addition, an indium phosphide contact layer (not shown in the figure) is formed on the side of the upper confinement layer away from the substrate layer 21, which has a thickness of 1 μm and a doping concentration of 5×10 18 cm -3 , and the contact layer helps to enhance the ohmic contact with the second confinement layer 225, thereby ensuring the current injection effect. By means such as setting a mask layer 100 and wet etching, a single ridge structure 25 extending in the Y-axis direction is formed, and then by means such as metal-organic chemical vapor deposition (abbreviated as MOCVD) growth technology, a semi-insulating material, such as semi-insulating iron-doped indium phosphide, is filled in the etched areas on both sides of the ridge structure 25 in the X-axis direction to form a first isolation structure 28 and a second isolation structure 29 for electrical isolation and optical confinement. Finally, the preparation of the complete quantum cascade laser body 2 is completed by cleavage and forming a first electrode 23 and a second electrode 24.

[0088] Reference Figures 1 to 8 , this embodiment also provides a method for preparing a quantum cascade laser for preparing the above-mentioned quantum cascade laser, Figure 5 is a schematic flow chart of the preparation method, and the preparation method includes the following steps:

[0089] Step S501, forming a laser body 2, the laser body 2 includes a first electrode 23, an epitaxial structure 22, a substrate layer 21, and a second electrode 24 stacked, and the first electrode 23 faces the base layer 1 side; the laser body 2 also includes a first cavity surface 26 and a second cavity surface 27 oppositely arranged in a first direction, and the laser is adapted to exit from the first cavity surface 26.

[0090] Exemplarily, the substrate layer 21 of the laser body 2 can be an indium phosphide substrate, and a plurality of structural layers including an active layer 223 are sequentially epitaxially grown on the indium phosphide substrate to form an epitaxial structure 22. A first electrode 23 is provided on the exposed side surface of the epitaxial structure 22, and a second electrode 24 is provided on the exposed side surface of the substrate layer 21. The first electrode 23 and the second electrode 24 are respectively used as the positive and negative electrodes of the quantum cascade laser to form the laser body 2. The laser body 2 has opposite first cavity surface 26 and second cavity surface 27 in a first direction. The first direction in this embodiment is Figure 1 the y-axis direction shown in, that is, the cavity length direction of the laser body 2. The first cavity surface 26 is the front cavity surface for laser emission, and the second cavity surface 27 is the rear cavity surface. A reflection structure 3 is provided on this side to realize the reflection of the laser, so that the laser exits from the first cavity surface 26 to the greatest extent.

[0091] Step S502: Form a reflection structure 3. The reflection structure 3 includes a reflection part 31, and the reflection part 31 includes reflection protrusions 311 and grooves 312 alternately arranged in a first direction to reflect laser light.

[0092] Reference Figure 1 And Figure 2 , the reflection structure 3 of this embodiment includes a reflection part 31 with alternately arranged reflection protrusions 311 and grooves 312, that is, it constitutes a distributed Bragg reflector (hereinafter referred to as DBR) structure with a peak-valley structure; exemplarily, the reflection protrusions 311 can be semi-insulating materials, and the space of the grooves 312 is air, forming a multi-layer DBR mirror structure such as semi-insulating material / air / semi-insulating material / air... repeating alternately. The wavelength corresponding to its reflection curve is exactly the laser wavelength, which is equivalent to setting a DBR mirror with a bandgap width consistent with the laser wavelength on the reflection cavity surface side of the laser main body 2. The reflectivity easily reaches more than 90%. Moreover, the semi-insulating material and air do not absorb mid-infrared light, and with a certain interval from the second cavity surface 27 of the laser, while achieving efficient laser reflection on the second cavity surface 27 side of the laser main body 2, it also avoids causing a temperature rise of the second cavity surface 27 of the laser main body 2, ultimately ensuring the light output efficiency, performance, and reliability of the quantum cascade laser.

[0093] Step S503: Fix the laser main body 2 and the reflection structure 3 on one side surface of the base layer 1. The reflection structure 3 is arranged on the second cavity surface 27 side of the laser main body 2 and is spaced from the second cavity surface 27. [[ID=I3]]

[0094] After Figure 3 And Figure 4 inverting the laser main body 2 as shown, the laser main body 2 is fixed on the base layer 1 by fixing the first electrode 23 to the upper surface of the base layer 1, and Figure 2 after inverting the reflection structure 3 as shown, it is fixed to the base layer 1 at a certain distance from the laser main body 2. The base layer 1 of this embodiment can be a heat sink structure made of materials such as aluminum nitride and silicon carbide.

[0095] The quantum cascade laser obtained by the above preparation method adopts a reflection structure 3 suitable for long-wave quantum cascade lasers and packages and fixes it on the same-side surface of a base layer 1 together with the laser main body 2; the reflection structure 3 is arranged on the second cavity surface 27 side of the laser main body 2, that is, on the reflection cavity surface side, that is Figure 1In the transverse y direction as shown, the laser beam exits from the right side of the laser body 2, and the reflection structure 3 is arranged on the left side of the laser body 2, which is spaced from the laser body 2. It replaces the composite film system (HR film) with a large light absorption for mid-infrared light in the conventional solution, effectively reducing light absorption, suppressing the temperature rise of the second cavity surface 27, preventing catastrophic optical damage to the second cavity surface 27, and ensuring the high-efficiency light output, service life, and reliability of the quantum cascade laser.

[0096] In one embodiment, the above step S501 of forming the laser body 2 includes:

[0097] Step S5011: Provide a substrate layer 21.

[0098] Exemplarily, the above substrate layer 21 can be an indium phosphide substrate.

[0099] Step S50212: Epitaxially grow a first confinement layer 221, a first waveguide layer 222, an active layer 223, a second waveguide layer 224, and a second confinement layer 225 on the substrate layer 21 in sequence to form an epitaxial structure 22.

[0100] Reference Figure 6 , the above first confinement layer 221 is indium phosphide with a thickness of 4 μm and a doping concentration of 2×10 16 cm -3 ; the first waveguide layer 222 is indium gallium arsenide with a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3 ; the active layer 223 has a thickness of 2 μm; the second waveguide layer 224 is indium gallium arsenide with a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3 ; the second confinement layer 225 is indium phosphide with a thickness of 5 μm and a doping concentration of 2×10 16 cm -3 ; in addition, an indium phosphide contact layer (not shown in the figure) is also formed on the side of the upper confinement layer away from the substrate layer 21, which has a thickness of 1 μm and a doping concentration of 5×10 18 cm -3 , and the contact layer helps to enhance the ohmic contact with the second confinement layer 225, thereby ensuring the current injection effect.

[0101] Step S5013: Etch and form a ridge structure 25 on the side of the epitaxial structure 22 away from the substrate layer 21. The ridge structure 25 includes the second confinement layer 225, the second waveguide layer 224, the active layer 223, the first waveguide layer 222, and a part of the thickness of the first confinement layer 221.

[0102] Reference Figure 7By means of, for example, setting a mask layer 100 and wet etching, a single ridge structure 25 extending along the y-axis direction is formed simply and efficiently. The sidewall of the ridge structure 25 formed by wet etching has a certain inclination, but since the sidewall surface is not the light-emitting side and since an isolation structure is subsequently set, there is no need to excessively require precision in the process of forming the ridge structure 25.

[0103] Step S5014 : Dispose a first isolation structure 28 and a second isolation structure 29 on both sides of the ridge structure 25 in the second direction, respectively.

[0104] refer to Figure 8 The etched regions on both sides of the ridge structure 25 in the x-axis direction are filled with a semi-insulating material, such as semi-insulating iron-doped indium phosphide, by a growth technique such as metal-organic chemical vapor deposition (MOCVD), to form a first isolation structure 28 and a second isolation structure 29 for electrical isolation and optical confinement.

[0105] In step S5015 , a first electrode 23 is provided on the side of the epitaxial structure 22 facing away from the substrate layer 21 , and a second electrode 24 is provided on the side of the substrate layer 21 facing away from the epitaxial structure 22 . The first electrode 23 is preferably provided toward the side of the base layer 1 .

[0106] refer to Figure 3 and Figure 4 Finally, the preparation of the complete quantum cascade laser body 2 is completed by cleavage and slicing, and setting the first electrode 23 and the second electrode 24. The first electrode 23 is set on the surface of the epitaxial structure 22 on the side away from the substrate layer 21, and the second electrode 24 is set on the surface of the substrate layer 21 on the side away from the epitaxial structure 22. The first electrode 23 and the second electrode 24 serve as the positive and negative electrodes of the quantum cascade laser, respectively, to form the laser body 2. After the laser body 2 is inverted, the first electrode 23 is fixed to the upper surface of the base layer 1 to achieve the fixation of the laser body 2 on the base layer 1.

[0107] In this embodiment, when the first electrode 23 is provided, it is retracted a certain distance from the edge of the epitaxial structure 22 in the first direction to form a gap space. This allows packaging materials such as colloid or solder used for fixing the laser body 2 to enter the gap space when the laser body 2 is fixed to the base layer 1, thereby preventing the packaging material from overflowing and affecting the packaging reliability. For example, setting the retraction distance to 50 μm does not affect the reliable fixing of the first electrode 23 to the base layer 1, while ensuring sufficient gap space.

[0108] In one embodiment, before the first electrode 23 is disposed on the side of the epitaxial structure 22 facing away from the substrate layer 21, the following steps are further included: forming a protective layer on the surface of the epitaxial structure 22 away from the substrate layer 21, the protective layer covering the first isolation structure 28 and the second isolation structure 29 and having a window that at least exposes the surface of the ridge structure 25 so as to enable current injection. The protective layer is generally made of silicon oxide material, forming a window on the ridge structure 25 and insulating and protecting other regions to limit the current injection range and improve the current injection effect.

[0109] The further function descriptions of the above modules are the same as those in the corresponding embodiments above and will not be elaborated here.

[0110] In the above description, technical details such as the patterning and etching of each layer are not described in detail. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. with the desired shapes. In addition, to form the same structure, those skilled in the art can also design methods that are not exactly the same as the methods described above. In addition, although the above embodiments are described separately, this does not mean that the measures in each embodiment cannot be used in combination advantageously.

[0111] Although the embodiments of the present invention are described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A quantum cascade laser, characterized in that, It includes a base layer and a laser body and a reflection structure encapsulated on the same-side surface of the base layer; The base layer is a heat sink substrate, including aluminum nitride and silicon carbide; The laser body includes a first electrode, an epitaxial structure, a substrate layer, and a second electrode stacked; the laser body further includes a first cavity surface and a second cavity surface oppositely arranged in a first direction, and the laser is adapted to exit from the first cavity surface; The reflection structure is arranged on one side of the second cavity surface of the laser body and is spaced from the second cavity surface to reflect the laser; the bandgap width of the reflection structure is the same as the laser wavelength, the reflection structure includes a reflection part, and the reflection part includes reflection protrusions and grooves alternately arranged in the first direction. The optical length of the reflection protrusions in the first direction and the optical length of the grooves in the first direction are both one-fourth of the laser wavelength, and the optical distance between one of the reflection protrusions adjacent to the laser body and the second cavity surface of the laser body is one-fourth of the laser wavelength; The material of the reflection structure includes: semi-insulating iron-doped indium phosphide, or semi-insulating gallium arsenide, or semi-insulating zinc selenide.

2. The quantum cascade laser according to claim 1, wherein The reflection structure further includes a substrate and a mounting part located on the substrate. The substrate is arranged relatively far from the base layer. One end of the mounting part away from the substrate is connected to the base layer. The mounting part and the reflection part are adjacent to each other in the first direction on the substrate, and the reflection part is relatively close to the laser body side.

3. The quantum cascade laser according to claim 2, wherein The mounting part includes a mounting protrusion protruding from the surface of the substrate; one end of the mounting protrusion relatively far from the substrate is flush with one end of the reflection protrusion relatively far from the substrate, and the groove is adjacent to the mounting protrusion.

4. The quantum cascade laser according to claim 3, characterized in that, The geometric length of the mounting protrusion in the first direction is greater than the geometric length of the reflection protrusion in the first direction.

5. The quantum cascade laser according to claim 4, wherein The depth of the groove in the direction perpendicular to the surface of the substrate is greater than or equal to 20 μm.

6. The quantum cascade laser according to claim 5, wherein In a plane parallel to the surface of the base layer, the width range of the reflection structure in a second direction is 100 μm to 400 μm, and the second direction is perpendicular to the first direction.

7. The quantum cascade laser according to claim 6, wherein The first electrode of the laser body is relatively close to the base layer and is fixed to the base layer; in the first direction, there is a spacing between the two side edges of the projection of the first electrode on the base layer and the two side edges of the projection of the epitaxial structure on the base layer.

8. The quantum cascade laser according to any one of claims 2-7, characterized in that, It further includes: A first welding layer, arranged between the mounting part and the base layer; A second welding layer, arranged between the laser body and the base layer, and the thickness of the first welding layer is less than the thickness of the second welding layer.

9. The quantum cascade laser according to claim 8, wherein, The epitaxial structure includes a first confinement layer, a first waveguide layer, an active layer, a second waveguide layer, and a second confinement layer sequentially arranged from one side of the substrate layer towards the side away from the substrate layer. The first electrode is arranged on the second confinement layer; The epitaxial structure is formed with a ridge structure, and the ridge structure includes a second confinement layer, a second waveguide layer, an active layer, a first waveguide layer, and a first confinement layer with a partial thickness; in a second direction perpendicular to the first direction, a first isolation structure and a second isolation structure are respectively disposed on two sides of the ridge structure.

10. A method for preparing a quantum cascade laser, which is used to prepare the quantum cascade laser according to any one of claims 1-9, characterized in that, Comprising: Forming a laser body, the laser body includes a first electrode, an epitaxial structure, a substrate layer, and a second electrode which are stacked; the laser body further includes a first cavity surface and a second cavity surface which are oppositely disposed along a first direction, and laser is adapted to emit from the first cavity surface; Forming a reflection structure, the reflection structure includes a reflection portion, and the reflection portion includes reflection protrusions and grooves which are alternately disposed along the first direction to reflect laser; the bandgap width of the reflection structure is the same as the laser wavelength, the optical length of the reflection protrusions in the first direction and the optical length of the grooves in the first direction are both one-fourth of the laser wavelength, and the optical distance between one of the reflection protrusions adjacent to the laser body and the second cavity surface of the laser body is one-fourth of the laser wavelength; The material of the reflection structure includes: semi-insulating indium phosphide doped with iron, or semi-insulating gallium arsenide, or semi-insulating zinc selenide; Encapsulating and fixing the laser body and the reflection structure on one side surface of a base layer, the reflection structure is disposed on one side of the second cavity surface of the laser body and is spaced from the second cavity surface; the base layer is a heat sink substrate and includes aluminum nitride and silicon carbide.

11. The method for preparing a quantum cascade laser according to claim 10, wherein The forming of the laser body includes: Providing a substrate layer; Epitaxially growing a first confinement layer, a first waveguide layer, an active layer, a second waveguide layer, and a second confinement layer in sequence on the substrate layer to form an epitaxial structure; Etching on a side of the epitaxial structure away from the substrate layer to form a ridge structure, and the ridge structure includes the second confinement layer, the second waveguide layer, the active layer, the first waveguide layer, and the first confinement layer with a partial thickness; Respectively disposing a first isolation structure and a second isolation structure on two sides of the ridge structure in the second direction; Disposing a first electrode on a side of the epitaxial structure away from the substrate layer, and disposing a second electrode on a side of the substrate layer away from the epitaxial structure; the first electrode is adapted to be disposed towards the side of the base layer.

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