Quantum cascade laser and preparation method thereof

Abstract

The invention relates to the technical field of lasers, and discloses a quantum cascade laser and a preparation method thereof. The quantum cascade laser comprises a substrate layer, a laser main body and a reflection structure, wherein the laser main body comprises a first electrode, an epitaxial structure, a substrate layer and a second electrode which are stacked; the first cavity surface and the second cavity surface are oppositely arranged along a first direction, and laser is emitted from the first cavity surface; the reflecting structure is arranged on one side of the second cavity surface of the laser main body, is spaced from the second cavity surface, and comprises a reflecting part with reflecting bulges and grooves which are alternately arranged along the first direction. The reflection structures suitable for the long-wave quantum cascade laser are adopted, the reflection structures and the laser main body are packaged and fixed on the substrate layer, and the reflection structures are arranged on one side of the second cavity surface of the laser main body at intervals, so that light absorption is effectively reduced, and catastrophic optical damage caused by temperature rise of the second cavity surface is prevented; and the light output, service life and reliability of the laser are ensured.

Description

Technical Field

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

[0002] Quantum Cascade Laser (QCL) is a semiconductor laser that can emit 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 the stages are connected in series. The spectral range covers the mid-infrared to far-infrared bands. 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 laser in the related art, an anti-reflection film (AR film) is set on the front cavity surface of the device to ensure light emission, and a high-reflection film (HR film) is set on the rear cavity surface of the device to form a resonant cavity structure. Among them, the anti-reflection film on the front cavity surface adopts an yttrium trioxide dielectric film to adjust the reflectivity of the front cavity surface, while the high-reflection film on the rear cavity surface adopts a composite film system of yttrium trioxide + gold + yttrium trioxide to provide a reflectivity of more than 90%. However, the materials used in the cavity film system (including AR film and HR film) of the front and rear cavity surfaces, such as yttrium trioxide, aluminum oxide, zirconium dioxide, etc., have strong light absorption in the mid-infrared band. The cavity film system is prone to temperature rise during operation, which causes catastrophic optical mirror damage (COMD) on the front and rear cavity surfaces and failure, ultimately leading to the failure of the quantum cascade laser, affecting its service life and reliability. 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, which affects the service life and reliability.

[0005] In the first aspect, the present invention provides a quantum cascade laser, comprising a substrate layer and a laser body and a reflective structure arranged on the same side surface of the substrate layer, the laser body comprising a first electrode, an epitaxial structure, a substrate layer and a second electrode arranged in a stacked manner; the laser body also comprises a first cavity facet and a second cavity facet arranged opposite to each other along a first direction, and the laser is suitable for being emitted from the first cavity facet; the reflective structure is arranged on one side of the second cavity facet of the laser body and is spaced apart from the second cavity facet to reflect the laser; the reflective structure comprises a reflective portion, and the reflective portion comprises reflective protrusions and grooves alternately arranged along the first direction.

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

[0007] In an optional embodiment, the reflective structure also includes a substrate and a mounting portion located on the substrate, the substrate is arranged relatively far away from the base layer, one end of the mounting portion away from the substrate is connected to the base layer, the mounting portion and the reflective portion are adjacently arranged on the substrate along a first direction, and the reflective portion is relatively close to one side of the laser body.

[0008] Beneficial effects: The substrate, reflecting part and mounting part of the reflecting structure are integrally formed, the substrate connects the reflecting part and the mounting part into a whole, the mounting part and the reflecting part are adjacently arranged along a first direction, the reflecting part is close to the laser body to realize reflection of the laser transmitted from the laser body, the mounting part is used to realize fixation with the base layer and realize efficient heat dissipation at the same time, there is no fixing material between the reflecting part and the base layer, which effectively guarantees the reflection performance of the reflecting part to the laser.

[0009] In an optional embodiment, the mounting portion 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 reflective protrusion relatively far from the substrate, and the groove is arranged adjacent to the mounting protrusion.

[0010] Beneficial effect: The surfaces of the reflective protrusion and the mounting protrusion are flush. When the reflective structure is inverted and the lower surface of the mounting protrusion is fixed to the base layer, the presence of fixing materials such as colloid or solder causes a tiny gap to exist between the small surface of the reflective protrusion and the upper surface of the base layer, which not only ensures that the reflective part fully covers the laser output from the second cavity surface, but also avoids the reflective part from contacting the base layer and affecting the reflection performance.

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

[0012] Beneficial effect: In the first direction, the geometric length of the mounting protrusion is greater than the geometric length of the reflective protrusion, which facilitates efficient heat transfer from the reflective structure to the heat sink base layer, and also enables reliable fixation of the reflective structure on the base layer.

[0013] In an optional implementation, the optical length of the reflective 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] Beneficial effect: The optical lengths of the reflective protrusions and grooves in the first direction are set to be 1 / 4 of the laser wavelength, which can ensure that the laser is transmitted in the light field and realize effective reflection of the laser by the reflective part.

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

[0016] Beneficial effect: The optical distance between a reflective protrusion on the far right of the reflective structure and the left cavity surface of the laser body is set to one-quarter of the laser wavelength, ensuring that the laser output from the second cavity surface of the laser body can be effectively transmitted between the laser body and the reflective structure, reducing light transmission loss.

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

[0018] Beneficial effect: The depth of the groove in the direction perpendicular to the surface of the substrate is set to be greater than or equal to 20 μm, ensuring that the reflective structure fully covers the laser in the vertical direction, and the reflective part can fully reflect the laser, thereby improving the light output efficiency.

[0019] In an optional implementation, in a plane parallel to the surface of the base layer, the width of the reflective structure in the second direction ranges from 100 μm to 400 μm, and the second direction is perpendicular to the first direction.

[0020] Beneficial effect: In the horizontal plane, the geometric width of the reflective structure in the second direction is limited to between 100 μm and 400 μm, ensuring that the reflective structure fully covers the laser in the second direction. The reflective part can fully reflect the laser and improve the light output efficiency.

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

[0022] Beneficial effect: The semi-insulating material mentioned above basically does not absorb mid-infrared light, thereby ensuring sufficient reflection of the laser output from the second cavity surface, so as to improve the laser lasing of the quantum cascade laser on the first cavity surface.

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

[0024] Beneficial effect: When setting the first electrode, it is retracted a certain distance compared to the edge of the epitaxial structure in the first direction to form a gap space, so that when the laser body is fixed to the base layer, the packaging materials such as colloid or solder used for fixing can enter the gap space, thereby avoiding the overflow of the packaging material to affect the packaging reliability.

[0025] In an optional implementation, it also includes: A first welding layer is arranged between the mounting portion and the base layer; The second welding layer is arranged between the laser body and the base layer, and the thickness of the first welding layer is smaller than the thickness of the second welding layer.

[0026] Beneficial effects: The laser body and the reflective structure are fixed to the base layer by welding, and the welding connection is stable and can ensure good conductivity. The first welding layer is arranged between the lower surface of the mounting protrusion and the base layer, and the second welding layer is arranged 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 smaller than the thickness of the second welding layer. The second welding layer is set thicker to ensure efficient current injection of the laser body, and at the same time, the laser emission of the laser body is adjusted to fully reach the reflective part to avoid unnecessary laser loss.

[0027] 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, which are sequentially arranged from one side of the substrate layer toward a side away from the substrate layer, and the first electrode is arranged on the second confinement layer; The epitaxial structure is formed with a ridge structure, which includes a second restriction layer, a second waveguide layer, an active layer, a first waveguide layer and a first restriction layer of partial thickness; in a second direction perpendicular to the first direction, a first isolation structure and a second isolation structure are respectively arranged on both sides of the ridge structure.

[0028] Beneficial effect: Semi-insulating materials, such as semi-insulating iron-doped indium phosphide, are filled in the two side areas of the single ridge structure extending along the Y-axis direction to form a first isolation structure and a second isolation structure for electrical isolation and optical confinement, thereby preventing the laser from escaping in the second direction and ensuring the laser output effect.

[0029] In a second aspect, the present invention further provides a method for preparing a quantum cascade laser, which is used to prepare the above-mentioned quantum cascade laser, comprising: Forming a laser body, the laser body comprising a first electrode, an epitaxial structure, a substrate layer and a second electrode arranged in a stacked manner; the laser body also comprises a first cavity facet and a second cavity facet arranged opposite to each other along a first direction, and the laser is suitable for emitting from the first cavity facet; forming a reflective structure, the reflective structure comprising a reflective portion, the reflective portion comprising reflective protrusions and grooves alternately arranged along a first direction to reflect laser light; The laser body and the reflective structure are fixed on one side surface of the base layer. The reflective structure is arranged on one side of the second cavity surface of the laser body and is spaced apart from the second cavity surface.

[0030] Beneficial effects: The quantum cascade laser obtained by the above preparation method adopts a reflective structure suitable for a long-wave quantum cascade laser, and is packaged and fixed with the laser body on the same side surface of a substrate layer; the laser is emitted from the first cavity surface side of the laser body, and the reflective structure is arranged on the second cavity surface side of the laser body opposite to the first cavity surface, and is spaced apart from the laser body, replacing the composite film system (HR film) with large light absorption for mid-infrared light in the conventional scheme, effectively reducing light absorption, inhibiting the temperature rise of the second cavity surface, preventing catastrophic optical damage from occurring on the second cavity surface, and ensuring the efficient light output, service life and reliability of the quantum cascade laser.

[0031] In an optional embodiment, forming 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 a ridge structure on a side of the epitaxial structure away from the substrate layer, wherein the ridge structure includes a second confinement layer, a second waveguide layer, an active layer, a first waveguide layer, and a first confinement layer of a partial thickness; A first isolation structure and a second isolation structure are respectively arranged on both sides of the ridge structure in the second direction; A first electrode is arranged on a side of the epitaxial structure away from the substrate layer, and a second electrode is arranged on a side of the substrate layer away from the epitaxial structure; the first electrode is suitable for being arranged toward a side of the base layer.

[0032] Beneficial effects: By means such as setting a mask layer and wet etching, a single ridge structure extending in the first direction is formed simply and efficiently. The sidewall of the ridge structure formed by wet etching has a certain inclination, but because the sidewall surface is not on the light-emitting side and because an isolation structure is set up later, there is no need to overly demand accuracy for the process of forming the ridge structure. By means of growth techniques such as metal organic chemical vapor deposition, 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 in the second direction to form a first isolation structure and a second isolation structure for electrical isolation and optical confinement, to avoid the escape of the laser in the second direction and ensure 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 to enhance the electrical excitation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 is a schematic structural diagram of a quantum cascade laser according to an embodiment of the present invention; Figure 2 is a schematic structural diagram of a reflective structure according to an embodiment of the present invention; Figure 3 is a front structural schematic diagram of a laser body according to an embodiment of the present invention; Figure 4 is a schematic diagram of the side structure of a laser body according to an embodiment of the present invention; Figure 5 is a schematic flow chart of a method for preparing a quantum cascade laser according to an embodiment of the present invention; Figure 6 is a schematic structural diagram of an embodiment of the present invention after an epitaxial structure is formed on a substrate layer; Figure 7 is a schematic structural diagram of an epitaxial structure after a ridge structure is formed in an embodiment of the present invention; Figure 8 It is a schematic structural diagram of an embodiment of the present invention after a first isolation structure and a second isolation structure are arranged on both sides of a ridge structure along a second direction.

[0035] Description of reference numerals: 100. mask layer; 1. Basal layer; 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; 3. Reflection structure; 31. Reflection part; 311. Reflection protrusion; 312. Groove; 32. Base; 33. Mounting part; 41. First welding layer; 42. Second welding layer. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only some structures related to the present invention are shown in the accompanying drawings, rather than all structures. In the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified for the purpose of clear expression, and some details may be omitted. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships between them are only exemplary, and may be deviated due to manufacturing tolerances or technical limitations in practice, and those skilled in the art may additionally 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 may be directly on the other layer / element, or there may be an intermediate layer / element between them. In addition, if one layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0037] In the quantum cascade laser in the related art, the front cavity surface is provided with an anti-reflection film to ensure light emission, and the rear cavity surface is provided with a high-reflection film to form a resonant cavity structure, wherein the anti-reflection film of the front cavity surface is usually made of yttrium trioxide dielectric film, and the high-reflection film of the rear cavity surface is made of a composite film system of yttrium trioxide + gold + yttrium trioxide. However, the materials used in the cavity film system of the front and rear cavity surfaces, such as yttrium trioxide, aluminum oxide, zirconium dioxide, etc., have strong light absorption in the mid-infrared band, which makes the cavity film system prone to temperature rise during operation, and then causes catastrophic optical damage to the front and rear cavity surfaces and failure. Even if the material or structure of the cavity film system is improved, it is impossible to avoid damage and failure of the front and rear cavity surfaces during long-term use, and the light output efficiency, service life and reliability of the quantum cascade laser are difficult to guarantee.

[0038] Based on this, the present embodiment provides a quantum cascade laser and a preparation method thereof. The front and rear cavity surfaces are not provided with a fitted cavity surface film system, the front cavity surface is a dielectric film structure, and a specially designed reflective structure 3 is arranged at intervals on one side of the rear cavity surface to efficiently reflect the laser generated in the laser body 2, while avoiding laser failure caused by cavity surface temperature rise, thereby ensuring the light output efficiency, service life and reliability of the quantum cascade laser structure.

[0039] refer to Figures 1 to 4A quantum cascade laser provided in this embodiment includes: a substrate layer 1, a laser body 2 and a reflection structure 3 arranged on the same side surface of the substrate layer 1, the laser body 2 includes a first electrode 23, an epitaxial structure 22, a substrate layer 21 and a second electrode 24 arranged in a stacked manner; the laser body 2 also includes a first cavity surface 26 and a second cavity surface 27 arranged opposite to each other along a first direction, and the laser is suitable for emitting from the first cavity surface 26; the reflection structure 3 is arranged 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 part 31, and the reflection part 31 includes reflection protrusions 311 and grooves 312 alternately arranged along the first direction.

[0040] This embodiment is described by taking a quantum cascade laser structure with a laser wavelength of 9 μm as an example. Exemplarily, the base layer 1 uses a heat sink base, such as aluminum nitride, silicon carbide, etc., and is fixed with the laser body 2 and the reflective structure 3 to achieve good heat dissipation. The substrate layer 21 of the laser body 2 can be an indium phosphide substrate, and multiple 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 arranged on the exposed side surface of the epitaxial structure 22, and a second electrode 24 is arranged on the exposed side surface of the substrate layer 21. The first electrode 23 and the second electrode 24 are respectively used as positive and negative electrodes of the quantum cascade laser to form the laser body 2. Exemplarily, the laser body 2 can be inverted, and the first electrode 23 can be fixed to the upper surface of the base layer 1 to achieve the fixation of the laser body 2 on the base layer 1. Of course, it is not excluded that the laser body 2 is fixed to the upper surface of the base layer 1 by the second electrode 24 to achieve the upright position of the laser body 2. In this embodiment, the inverted mode 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 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, which is used to set the reflection structure 3 to achieve the 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 2The reflective structure 3 of this embodiment includes a reflective portion 31 having reflective protrusions 311 and grooves 312 arranged alternately, that is, a distributed Bragg reflector (DBR) structure with a peak and valley structure is formed; illustratively, the reflective protrusion 311 can be a semi-insulating material, and the space of the groove 312 is air, forming a semi-insulating material / air / semi-insulating material / air... Such a repeated alternating multi-layer DBR reflector structure, the wavelength corresponding to its reflection curve is exactly the laser wavelength, which is equivalent to setting a DBR reflector with a bandgap width consistent with the laser wavelength on one side of the reflective cavity surface of the laser body 2, and the reflectivity can easily reach more than 90%, and the semi-insulating material and air do not absorb mid-infrared light. In addition, there is a certain distance from the second cavity surface 27 of the laser body 2, and while achieving efficient laser reflection on one side of the second cavity surface 27 of the laser body 2, it also avoids causing the temperature rise of the second cavity surface 27 of the laser body 2, and finally ensures the light output efficiency, performance and reliability of the quantum cascade laser.

[0041] In summary, the quantum cascade laser of this embodiment adopts a reflective structure 3 suitable for a long-wave quantum cascade laser, and packages and fixes it with 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 1 As shown in the lateral y direction, the laser is emitted from the right side of the laser body 2, and the reflective structure 3 is arranged on the left side of the laser body 2. It is spaced apart from the laser body 2, replacing the composite film system (HR film) with large light absorption for mid-infrared light in the conventional scheme, effectively reducing light absorption, inhibiting the temperature rise of the second cavity surface 27, preventing catastrophic optical damage to the second cavity surface 27, and ensuring the efficient light output, service life and reliability of the quantum cascade laser.

[0042] In addition, the laser body 2 of this embodiment does not have a dielectric film on the first cavity surface 26, i.e., the light-emitting cavity surface, which effectively reduces the light absorption of the light-emitting cavity surface and ensures the cavity surface performance. Of course, it is not excluded to set a very thin dielectric film on the first cavity surface 26, such as a dielectric film with a thickness of less than 30nm, to reduce the light absorption of the dielectric film.

[0043] In one embodiment, reference Figure 1 and Figure 2 The reflective structure 3 also includes a substrate 32 and a mounting portion 33 located on the substrate 32. The substrate 32 is arranged relatively far away from the base layer 1. One end of the mounting portion 33 away from the substrate 32 is connected to the base layer 1. The mounting portion 33 and the reflective portion 31 are adjacently arranged on the substrate 32 along the first direction, and the reflective portion 31 is relatively close to one side of the laser body 2.

[0044] In this embodiment, the base 32, the reflecting portion 31 and the mounting portion 33 of the reflecting structure 3 are integrally formed, and the base 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 along the first direction, that is, Figure 1 As shown, the reflecting portion 31 is arranged adjacent to the laser body 2 in the y-axis direction, and is close to the laser body 2 to reflect the laser transmitted from the laser body 2. The mounting portion 33 is used to fix with the base layer 1 and realize efficient heat dissipation. There is no direct connection and fixation between the reflecting portion 31 and the base layer 1, which effectively ensures the reflection performance of the reflecting portion 31 to the laser.

[0045] Further, refer to Figure 1 and Figure 2 The above-mentioned mounting portion 33 includes a mounting protrusion protruding from the surface of the base 32; one end of the mounting protrusion relatively far away from the base 32 is flush with one end of the reflective protrusion 311 relatively far away from the base 32, and the groove 312 is arranged adjacent to the mounting protrusion.

[0046] The reflective structure 3 of this embodiment is first formed into an overall structure, and then fixed on the surface of the base layer 1. Figure 2 For example, multiple strip grooves and protrusions extending along the x-axis direction can be formed on the upper surface of the complete reflective material by etching, etc., wherein a protrusion on the left side is used as a mounting protrusion of the mounting portion 33 for fixing with the base layer 1; multiple protrusions on the right side that are spaced apart from each other form a reflective protrusion 311, and the surfaces of the reflective protrusion 311 and the mounting protrusion are naturally flush. Figure 1 As 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 colloid or solder allows a small gap to exist between the small surface of the reflective protrusion 311 and the upper surface of the base layer 1, which not only ensures that the reflective part 31 fully covers the laser output from the second cavity surface 27, but also avoids the reflective part 31 from contacting the base layer 1 and affecting the reflection performance.

[0047] Furthermore, if Figure 1 and Figure 2 As shown, the geometric length of the above-mentioned mounting protrusion in the first direction is greater than the geometric length of the reflecting protrusion 311 in the first direction.

[0048] 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 efficient heat transfer from the reflective structure 3 to the heat sink base layer 1, and also enables 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 be more than 100 μm.

[0049] On the basis of 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.

[0050] In this embodiment, in order to achieve 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. The optical length here can be understood as the optical path rather than a simple geometric length. Optical length = geometric length × real part of the medium refractive index. 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.

[0051] Furthermore, in this embodiment, the optical distance between a reflective protrusion 311 adjacent to the laser body 2 and the second cavity facet 27 of the laser body 2 is set to be one quarter of the laser wavelength.

[0052] Similarly, reference Figure 1 Similarly, the optical distance between the rightmost reflective protrusion 311 of the reflective structure 3 and the left cavity surface of the laser body 2 is set to be one quarter of the laser wavelength, and the geometric distance corresponding to the optical distance is set to be L3, then L3= , ensuring that the laser output from the second cavity surface 27 of the laser body 2 can be effectively propagated between the laser body 2 and the reflective structure 3, thereby reducing the transmission loss of the laser.

[0053] In one embodiment, the depth of the groove 312 in the direction perpendicular to the surface of the substrate 32 is greater than or equal to 20 μm. At this depth, the reflective structure 3 can fully cover the laser in the vertical direction, i.e., the z-axis direction, and the reflective portion 31 can fully reflect the laser.

[0054] On this basis, in a plane parallel to the surface of the base layer 1 , the width of the reflective structure 3 in the second direction is in the range of 100 μm to 400 μm, and the second direction is perpendicular to the first direction.

[0055] That is, in the horizontal plane formed by the x-axis and the y-axis, the geometric width of the reflective structure 3 in the second direction, i.e., the x-axis direction, ranges from 100 μm to 400 μm, to ensure that the reflective structure 3 fully covers the laser in the x-axis direction, and the reflective portion 31 can fully reflect the laser.

[0056] In one embodiment, the material of the reflective 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 sufficient reflection of the laser output from the second cavity surface 27 to improve the laser lasing of the quantum cascade laser on the first cavity surface 26.

[0057] In one embodiment, reference Figure 1 and Figure 4 , the first electrode 23 of the laser body 2 is relatively close to the substrate layer 1 and fixed to the substrate layer 1; in the first direction, there is a spacing between the two side edges of the projection of the first electrode 23 on the substrate layer 1 and the two side edges of the projection of the epitaxial structure 22 on the substrate layer 1.

[0058] That is, when the first electrode 23 is set, it is retracted a certain distance from the edge of the epitaxial structure 22 in the first direction to form a gap space, so that when the laser body 2 is fixed to the base layer 1, the packaging materials such as colloid or solder used for fixing can enter the gap space, thereby avoiding overflow of the packaging material to affect the packaging reliability.

[0059] As a preferred implementation, the retraction distance in this embodiment is set to 50 μm, which does not affect the reliable fixation of the first electrode 23 and the base layer 1 , and can ensure sufficient gap space.

[0060] refer to Figure 1 The quantum cascade laser of this embodiment also includes a first welding layer 41 and a second welding layer 42. The first welding layer 41 is arranged between the mounting portion 33 and the base layer 1; the second welding layer 42 is arranged between the laser body 2 and the base layer 1, and the thickness of the first welding layer 41 is less than the thickness of the second welding layer 42.

[0061] That is, in this embodiment, the laser body 2 and the reflective structure 3 are fixed to the base layer 1 by welding, and the welding connection is stable and can ensure good electrical conductivity. The first welding layer 41 is arranged between the lower surface of the mounting protrusion and the base layer 1, and the second welding layer 42 is arranged 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 the thickness of the second welding layer 42. The second welding layer 42 is set to be thicker to ensure efficient current injection of the laser body 2. At the same time, the laser emission of the laser body 2 is adjusted to fully reach the reflective portion 31, avoiding unnecessary laser loss.

[0062] Furthermore, the first welding layer 41 and the second welding layer 42 should be as thin as possible, for example, less than 2 μm, and no solder is provided between the reflective portion 31 of the reflective structure 3 and the base layer 1 to prevent the solder from affecting light field transmission.

[0063] refer to Figure 3 and 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 arranged in sequence from one side of the substrate layer 21 to the side away from the substrate layer 21, and the first electrode 23 is arranged 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 first confinement layer 221 with a partial thickness; in a second direction perpendicular to the first direction, a first isolation structure 28 and a second isolation structure 29 are respectively arranged on both sides of the ridge structure 25.

[0064] For example, the substrate layer 21 may be an indium phosphide substrate, and the first confinement layer 221 may be a substrate having a thickness of 4 μm and a doping concentration of 2×10 16 cm -3 The first waveguide layer 222 has a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3 GaAs; an active layer 223 with a thickness of 2 μm; a second waveguide layer 224 with a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3 The second confinement layer 225 has a thickness of 5 μm and a doping concentration of 2×10 16 cm -3 Indium phosphide; in addition, an indium phosphide contact layer (not shown in the figure) is formed on the side of the upper limiting layer away from the substrate layer 21, which has a thickness of 1 μm and a doping concentration of 5×10 18 cm -3 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 along the Y-axis direction is formed, and then by a growth technique such as metal-organic chemical vapor deposition (MOCVD), 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 the first electrode 23 and the second electrode 24.

[0065] refer to Figures 1 to 8 This embodiment also provides a method for preparing a quantum cascade laser, which is used to prepare the above-mentioned quantum cascade laser. Figure 5The schematic diagram of the preparation method is shown in FIG. 1 , and the preparation method comprises the following steps: 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 which are stacked, and the first electrode 23 faces the side of the substrate layer 1; the laser body 2 also includes a first cavity face 26 and a second cavity face 27 which are arranged opposite to each other along a first direction, and the laser is suitable for emitting from the first cavity face 26.

[0066] Exemplarily, the substrate layer 21 of the laser body 2 may be an indium phosphide substrate, on which multiple structural layers including an active layer 223 are sequentially epitaxially grown to form an epitaxial structure 22, a first electrode 23 is disposed on the exposed side surface of the epitaxial structure 22, and a second electrode 24 is disposed on the exposed side surface of the substrate layer 21, and the first electrode 23 and the second electrode 24 serve as positive and negative electrodes of the quantum cascade laser, respectively, to form the laser body 2. The laser body 2 has a first cavity facet 26 and a second cavity facet 27 opposite to each other in the first direction, and the first direction of this embodiment is Figure 1 In the y-axis direction shown in the figure, 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, which is used to set the reflection 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.

[0067] Step S502 : forming a reflective structure 3 , wherein the reflective structure 3 comprises a reflective portion 31 , wherein the reflective portion 31 comprises reflective protrusions 311 and grooves 312 alternately arranged along a first direction to reflect laser light.

[0068] refer to Figure 1 and Figure 2 The reflective structure 3 of this embodiment includes a reflective portion 31 having reflective protrusions 311 and grooves 312 arranged alternately, that is, a distributed Bragg reflector (DBR) structure with a peak and valley structure is formed; illustratively, the reflective protrusion 311 can be a semi-insulating material, and the space of the groove 312 is air, forming a semi-insulating material / air / semi-insulating material / air... Such a repeated alternating multi-layer DBR reflector structure, the wavelength corresponding to its reflection curve is exactly the laser wavelength, which is equivalent to setting a DBR reflector with a bandgap width consistent with the laser wavelength on one side of the reflective cavity surface of the laser body 2, and the reflectivity can easily reach more than 90%, and the semi-insulating material and air do not absorb mid-infrared light. In addition, there is a certain distance from the second cavity surface 27 of the laser body 2, and while achieving efficient laser reflection on one side of the second cavity surface 27 of the laser body 2, it also avoids causing the temperature rise of the second cavity surface 27 of the laser body 2, and finally ensures the light output efficiency, performance and reliability of the quantum cascade laser.

[0069] Step S503 , fixing the laser body 2 and the reflective structure 3 on one side surface of the substrate layer 1 , wherein the reflective structure 3 is disposed on one side of the second cavity facet 27 of the laser body 2 and is spaced apart from the second cavity facet 27 .

[0070] Will Figure 3 and Figure 4 As shown, after the laser body 2 is inverted, the laser body 2 is fixed on the base layer 1 by fixing the first electrode 23 to the upper surface of the base layer 1. Figure 2 The reflective structure 3 is inverted and fixed on the base layer 1 at a certain distance from the laser body 2. The base layer 1 of this embodiment can be a heat sink structure made of materials such as aluminum nitride, silicon carbide, etc.

[0071] The quantum cascade laser obtained by the above preparation method adopts a reflective structure 3 suitable for a long-wave quantum cascade laser, and packages and fixes it with 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 1 As shown in the lateral y direction, the laser is emitted from the right side of the laser body 2, and the reflective structure 3 is arranged on the left side of the laser body 2. It is spaced apart from the laser body 2, replacing the composite film system (HR film) with large light absorption for mid-infrared light in the conventional scheme, effectively reducing light absorption, inhibiting the temperature rise of the second cavity surface 27, preventing catastrophic optical damage to the second cavity surface 27, and ensuring the efficient light output, service life and reliability of the quantum cascade laser.

[0072] In one embodiment, the step S501 of forming the laser body 2 includes: Step S5011 provides a substrate layer 21 .

[0073] Exemplarily, the substrate layer 21 mentioned above may be an indium phosphide substrate.

[0074] Step S50212 , epitaxially growing 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 in sequence on the substrate layer 21 to form an epitaxial structure 22 .

[0075] refer to Figure 6 The first confinement layer 221 has a thickness of 4 μm and a doping concentration of 2×10 16 cm -3 The first waveguide layer 222 has a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3 GaAs; an active layer 223 with a thickness of 2 μm; a second waveguide layer 224 with a thickness of 0.1 μm and a doping concentration of 2×10 16 cm-3 The second confinement layer 225 has a thickness of 5 μm and a doping concentration of 2×10 16 cm -3 Indium phosphide; in addition, an indium phosphide contact layer (not shown in the figure) is formed on the side of the upper limiting layer away from the substrate layer 21, which has a thickness of 1 μm and a doping concentration of 5×10 18 cm -3 The contact layer helps to enhance the ohmic contact with the second confinement layer 225, thereby ensuring the current injection effect.

[0076] Step S5013 , etching to form a ridge structure 25 on the side of the epitaxial structure 22 away from the substrate layer 21 , the ridge structure 25 including a second confinement layer 225 , a second waveguide layer 224 , an active layer 223 , a first waveguide layer 222 and a partial thickness of the first confinement layer 221 .

[0077] refer to Figure 7 A single ridge structure 25 extending along the y-axis direction is simply and efficiently formed by methods such as setting a mask layer 100 and wet etching. The side wall of the ridge structure 25 formed by wet etching has a certain inclination, but because the side wall surface is not the light-emitting side and because an isolation structure is subsequently set, there is no need to excessively require precision in the process of forming the ridge structure 25.

[0078] Step S5014 , a first isolation structure 28 and a second isolation structure 29 are respectively disposed on both sides of the ridge structure 25 in the second direction.

[0079] refer to Figure 8 By using a growth technique such as metal-organic chemical vapor deposition (MOCVD), 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.

[0080] Step S5015 , disposing a first electrode 23 on a side of the epitaxial structure 22 away from the substrate layer 21 , and disposing a second electrode 24 on a side of the substrate layer 21 away from the epitaxial structure 22 ; the first electrode 23 is suitably disposed toward a side of the base layer 1 .

[0081] refer to Figure 3 and Figure 4Finally, 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 away from the substrate layer 21, and the second electrode 24 is set on the surface of the substrate layer 21 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 substrate layer 1 to achieve the fixation of the laser body 2 on the substrate layer 1.

[0082] In this embodiment, when the first electrode 23 is set, it is retracted by a certain distance compared to the edge of the epitaxial structure 22 in the first direction to form a gap space, so that when the laser body 2 is fixed to the base layer 1, the packaging material such as colloid or solder used for fixing can enter the gap space, thereby preventing the packaging material from overflowing and affecting the packaging reliability. For example, setting the retraction distance to 50μm does not affect the reliable fixation of the first electrode 23 and the base layer 1, and can ensure sufficient gap space.

[0083] In one embodiment, before the first electrode 23 is provided on the side of the epitaxial structure 22 away from the substrate layer 21, the method further includes: forming a protective layer on the surface of the side of the epitaxial structure 22 away from the substrate layer 21, the protective layer covers the first isolation structure 28 and the second isolation structure 29, and has a window that exposes at least the surface of the ridge structure 25, so as to achieve current injection. The protective layer is usually made of silicon oxide material, and a window is formed on the ridge structure 25, and other areas are insulated and protected to limit the current injection range and improve the current injection effect.

[0084] The further functional description of each of the above modules is the same as that of the above corresponding embodiments and will not be repeated here.

[0085] In the above description, the technical details of 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. of desired shapes. In addition, in order to form the same structure, those skilled in the art can also design methods that are not completely the same as the methods described above. In addition, although the various embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage.

[0086] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A quantum cascade laser, characterized in that: It comprises a base layer, and a laser body and a reflective structure arranged on the same side surface of the base layer; The laser body comprises a first electrode, an epitaxial structure, a substrate layer and a second electrode which are stacked; the laser body also comprises a first cavity facet and a second cavity facet which are arranged opposite to each other along a first direction, and the laser is suitable for emitting from the first cavity facet; The reflective structure is arranged on one side of the second cavity surface of the laser body and is spaced apart from the second cavity surface to reflect the laser; the reflective structure includes a reflective portion, and the reflective portion includes reflective protrusions and grooves alternately arranged along the first direction.

2. The quantum cascade laser according to claim 1, characterized in that The reflective structure also includes a substrate and a mounting portion located on the substrate, the substrate is arranged relatively far away from the base layer, one end of the mounting portion away from the substrate is connected to the base layer, the mounting portion and the reflective portion are adjacently arranged on the substrate along the first direction, and the reflective portion is relatively close to one side of the laser body.

3. The quantum cascade laser according to claim 2, characterized in that The mounting portion comprises 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 reflective protrusion relatively far from the substrate, and the groove is arranged adjacent to the mounting protrusion.

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

5. The quantum cascade laser according to claim 4, characterized in that An optical length of the reflective protrusion in the first direction and an optical length of the groove in the first direction are both one quarter of the laser wavelength.

6. The quantum cascade laser according to claim 5, characterized in that An optical distance between one of the reflective protrusions adjacent to the laser body and the second cavity surface of the laser body is one quarter of the laser wavelength.

7. The quantum cascade laser according to claim 6, characterized in that The depth of the groove in a direction perpendicular to the surface of the substrate is greater than or equal to 20 μm.

8. The quantum cascade laser according to claim 7, characterized in that In a plane parallel to the surface of the base layer, the width of the reflective structure in a second direction ranges from 100 μm to 400 μm, and the second direction is perpendicular to the first direction.

9. The quantum cascade laser according to claim 8, characterized in that The material of the reflective structure includes: semi-insulating iron-doped indium phosphide, or semi-insulating gallium arsenide, or semi-insulating zinc selenide.

10. The quantum cascade laser according to claim 9, characterized in that 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 distance 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.

11. The quantum cascade laser according to any one of claims 2 to 10, characterized in that: Also includes: A first welding layer, disposed between the mounting portion and the base layer; The second welding layer is arranged between the laser body and the base layer, and the thickness of the first welding layer is smaller than the thickness of the second welding layer.

12. The quantum cascade laser according to claim 11, characterized in that The epitaxial structure comprises a first restriction layer, a first waveguide layer, an active layer, a second waveguide layer, and a second restriction layer which are sequentially arranged from one side of the substrate layer toward a side away from the substrate layer, and the first electrode is arranged on the second restriction layer; The epitaxial structure is formed with a ridge structure, which includes a second limiting layer, a second waveguide layer, an active layer, a first waveguide layer and a first limiting layer of partial thickness; in a second direction perpendicular to the first direction, a first isolation structure and a second isolation structure are respectively arranged on both sides of the ridge structure.

13. A method for preparing a quantum cascade laser, for preparing the quantum cascade laser according to any one of claims 1 to 12, characterized in that: include: Forming a laser body, the laser body comprising a first electrode, an epitaxial structure, a substrate layer, and a second electrode which are stacked; the laser body further comprising a first cavity facet and a second cavity facet which are arranged opposite to each other along a first direction, and the laser is suitable for emitting from the first cavity facet; forming a reflective structure, the reflective structure comprising a reflective portion, the reflective portion comprising reflective protrusions and grooves alternately arranged along the first direction to reflect laser light; The laser body and the reflective structure are fixed on one side surface of the substrate layer. The reflective structure is arranged on one side of the second cavity surface of the laser body and is spaced apart from the second cavity surface.

14. The method for preparing a quantum cascade laser according to claim 13, characterized in that: The forming of the laser body comprises: 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 a ridge structure on a side of the epitaxial structure away from the substrate layer, wherein the ridge structure includes the second confinement layer, the second waveguide layer, the active layer, the first waveguide layer, and a partial thickness of the first confinement layer; A first isolation structure and a second isolation structure are respectively provided on both sides of the ridge structure in the second direction; A first electrode is arranged on a side of the epitaxial structure away from the substrate layer, and a second electrode is arranged on a side of the substrate layer away from the epitaxial structure; the first electrode is suitable for being arranged toward a side of the base layer.

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