Quantum cascade laser structure and preparation method thereof

Abstract

The invention relates to the technical field of lasers, and discloses a quantum cascade laser structure and a preparation method thereof. The preparation method comprises the following steps: forming an epitaxial structure comprising a lower limiting layer, a lower waveguide layer, an active layer, an upper waveguide layer and an upper limiting layer on a substrate layer; a ridge structure comprising an upper limiting layer, an upper waveguide layer, an active layer, a lower waveguide layer and a part of lower limiting layer is formed in the epitaxial structure, the ridge structure comprises a first surface and a second surface which are oppositely arranged in the first direction, and the first surface is a surface used for emitting light; and forming an isolation structure comprising a first isolation layer and a second isolation layer on the outer wall surface of the ridge structure to respectively cover the first surface and the second surface. The first isolation layer and the second isolation layer effectively reduce light absorption, so that the failure risk caused by cavity surface temperature rise is reduced, the process tolerance and thickness selection of a cavity surface dielectric film system in the subsequent light emitting direction are reduced, and the light emitting effect and the service life are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and in particular to a quantum cascade laser structure 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 related art, the preparation process of quantum cascade lasers is to first etch the epitaxial structure into a single ridge structure; then, the left and right sides of the ridge structure are filled with iron-doped indium phosphide using a secondary epitaxial growth technique, and its good electrical insulation and thermal conductivity properties ensure the heat dissipation capacity and optical confinement of the device; then, the front and rear cavity surfaces of the device are cleaved and coated, an anti-reflection film (AR film) is evaporated on the front cavity surface of the device to ensure light output, and a high-reflection film (HR film) is evaporated on the rear cavity surface, finally forming a resonant cavity structure, wherein the anti-reflection film on the front cavity surface adopts an yttrium trioxide dielectric film to adjust the reflectivity of the front cavity surface, and the high-reflection film adopts a composite film system of yttrium trioxide + gold + yttrium trioxide to provide a reflectivity of more than 90%.

[0004] 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, which makes the cavity film system prone to temperature rise during operation, and then causes catastrophic optical mirror damage (COMD) on the front and rear cavity surfaces; in addition, in order to ensure the electrical isolation effect, the insulating layer of the composite film system of the HR film is often increased in thickness, and the increase in thickness will further lead to enhanced light absorption, thereby increasing the probability of catastrophic optical damage to the rear cavity surface, and the increase in film thickness will also increase the risk of falling off, thereby increasing the risk of cavity surface failure of the quantum cascade laser structure, and affecting the light output efficiency, service life and reliability. Summary of the invention

[0005] In view of this, the present invention provides a quantum cascade laser structure and a preparation method thereof to solve the problem that the existing quantum cascade laser structure is prone to cavity surface failure, which affects the light output efficiency, service life and reliability.

[0006] In a first aspect, the present invention provides a method for preparing a quantum cascade laser structure, comprising: forming an epitaxial structure on the substrate layer, the epitaxial structure comprising a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer and an upper confinement layer formed in sequence; A ridge structure is formed on a side of the epitaxial structure away from the substrate layer, the ridge structure comprising an upper confinement layer, an upper waveguide layer, an active layer, a lower waveguide layer and a portion of the lower confinement layer, and the ridge structure comprises a first surface and a second surface arranged opposite to each other in a first direction, the first direction being a light emitting direction; An isolation structure is formed on the outer wall surface of the ridge structure. The isolation structure includes a first isolation layer and a second isolation layer. The first isolation layer covers the first surface, and the second isolation layer covers the second surface.

[0007] Beneficial effects: Compared with the conventional scheme, only the two side surfaces (such as the left and right side surfaces) of the epitaxial structure which are parallel to the light emitting direction and opposite to each other are etched to form a ridge structure, and then material filling is performed to limit the laser emission on these two sides; when etching the epitaxial structure, the present invention partially etches and removes the epitaxial structure in the light emitting direction to form a ridge structure, and then covers the first surface and the second surface of the ridge structure opposite to each other along the light emitting direction (such as the front and back direction) with a first isolation layer and a second isolation layer respectively. The first isolation layer and the second isolation layer can effectively reduce the light absorption in the light emitting direction, that is, on one side of the front and back cavity surfaces, when the laser is output, and the first isolation layer and the second isolation layer constitute part of the outer wall surface in the light emitting direction, which can have a certain isolation and insulation effect, effectively reduce the temperature increase of the cavity surface, and then reduce the process tolerance and thickness selection of the cavity surface dielectric film system in the subsequent light emitting direction, and finally reduce the cavity surface failure risk of the quantum cascade laser structure, and ensure the light emitting effect and service life.

[0008] In an optional embodiment, a ridge structure is formed on a side of the epitaxial structure facing away from the substrate layer, including: etching the side of the epitaxial structure facing away from the substrate layer to form a plurality of ridge structures spaced apart from each other, the plurality of ridge structures being arranged in a rectangular array, the ridge structure also including a third surface and a fourth surface arranged relative to each other along a second direction, the second direction forming a preset angle with the first direction; the isolation structure also including a third isolation layer and a fourth isolation layer, the third isolation layer covering the third surface of the ridge structure, and the fourth isolation layer covering the fourth surface of the ridge structure.

[0009] Beneficial effects: Forming multiple ridge structures on the epitaxial structure is conducive to the mass production of quantum cascade laser structures; and multiple ridge structures are arranged in a rectangular array, which is convenient for subsequent cleavage and cutting to form multiple quantum cascade laser structures. Each quantum cascade laser structure includes a substrate layer, a lower confinement layer with the same area as the substrate layer, and a ridge structure with a projected area smaller than the substrate layer and the lower confinement layer. The isolation structure realizes all-round insulation isolation of the side wall surface of the ridge structure.

[0010] In an optional implementation, the thickness of the first isolation layer and the second isolation layer in the first direction ranges from 0.2 μm to 5 μm.

[0011] Beneficial effect: The thickness of the first isolation layer and the second isolation layer is controlled between 0.2μm and 5μm, and preferably set close to 0.2μm, which can not only ensure effective insulation isolation and reduce light absorption effect, avoid leakage current causing short circuit of laser structure, but also ensure efficient light transmission in the resonant cavity and the reflection performance of the cavity surface, ultimately ensuring the light output efficiency and performance of the quantum cascade laser.

[0012] In an optional embodiment, the isolation structure is annular and integrally formed on the outer wall surface of the ridge structure; the thickness of the third isolation layer and the fourth isolation layer in the second direction is equal to the thickness of the first isolation layer and the second isolation layer in the first direction.

[0013] Beneficial effects: The isolation structure is formed into an integrated annular column, which is simple to prepare and has good structural performance. Its inner wall is close to the outer wall of the ridge structure, and the thickness of the annular column is consistent, which helps to achieve uniform electrical isolation and insulation effect at various parts of the ridge structure and ensure the light output effect.

[0014] In an optional embodiment, after a ridge structure is formed on a side of the epitaxial structure facing away from the substrate layer and before an isolation structure is formed on an outer wall surface of the ridge structure, the preparation method further includes: forming a first cleavage groove and a second cleavage groove on a surface of the lower restriction layer facing away from the substrate layer, wherein projection areas of the first cleavage groove and the second cleavage groove on the substrate layer are relatively isolated from projection areas of the ridge structure on the substrate layer; the first cleavage groove is arranged on both sides of the ridge structure along the first direction and extends along the second direction; the second cleavage groove is arranged between two adjacent ridge structures along the second direction and extends along the first direction.

[0015] Beneficial effects: In the first direction, a first cleavage groove is etched on the lower restriction layer between each two adjacent ridge structures, and the two cavity surfaces of the ridge structure in the light output direction are precisely cleaved by controlling the width of the first cleavage groove; in the second direction, a second cleavage groove is etched between two adjacent ridge structures, so that the separation between the ridge structures in the second direction is simply and quickly achieved, without the need for precise cleavage and etching to the third isolation layer and the fourth isolation layer, and the process requirements are relatively low.

[0016] In an optional embodiment, in the first direction, two adjacent ridge structures include two first cleavage grooves, and the distance between the two first cleavage grooves is greater than or equal to 0.5 mm.

[0017] Beneficial effect: Compared with a first cleavage groove that simultaneously realizes the cleavage of the cavity surfaces of the two ridge structures on both sides, each ridge structure of the present invention includes a separately configured first cleavage groove on both sides of the first direction, so as to accurately realize the cleavage of the cavity surfaces on both sides of the ridge structure in the light-emitting direction, and the ridge structures close to one of them can be applied to epitaxial structures with various ridge structure spacing distances, and the application range is wide. In the first direction, the width of the sacrificial area between the two first cleavage grooves between the two adjacent ridge structures is greater than or equal to 0.5mm, so as to ensure the smooth completion of the cleavage steps of the two adjacent first cleavage paths.

[0018] In an optional embodiment, the depth of the first cleavage groove ranges from 0.5 μm to 2 μm, and the width of the first cleavage groove in the first direction ranges from 0.5 μm to 5 μm; the depth of the second cleavage groove ranges from 0.2 μm to 2 μm, and the width of the second cleavage groove in the second direction ranges from 2 μm to 10 μm.

[0019] Beneficial effect: The etching width and etching depth of the first cleavage groove and the second cleavage groove are set to ensure that the epitaxial structure is cleaved and divided into multiple separate quantum cascade laser structures with high precision, thereby improving the cavity surface performance of the quantum cascade laser structure.

[0020] In an optional embodiment, forming an isolation structure on the outer wall surface of the ridge structure includes: forming the isolation structure using hydride vapor phase epitaxy technology, wherein the first isolation layer and the second isolation layer of the isolation structure respectively cover two first cleavage grooves located on both sides of the ridge structure along the first direction.

[0021] Beneficial effects: The hydride vapor phase epitaxy (HVPE) technology is used to selectively grow an isolation structure outside the ridge structure formed after etching, which is used for electrical isolation and optical confinement to achieve the filling of steep side walls. The first isolation layer and the second isolation layer of the isolation structure cover the first cleavage groove to ensure that when cleavage etching is performed at the position of the first cleavage groove, the cavity surface formed after etching includes the isolation structure, and at least the cavity surface on the side where the laser emerges has the isolation structure, ensuring that the isolation structure effectively reduces the absorption of the outgoing laser.

[0022] In an optional embodiment, after forming an isolation structure on the outer wall surface of the ridge structure, the preparation method further includes: cutting the epitaxial structure and the substrate layer at the first cleavage groove and the second cleavage groove to cleave to form a plurality of quantum cascade laser structures, any quantum cascade laser structure includes a first cavity surface and a second cavity surface arranged opposite to each other along a first direction, the first cavity surface is coplanar with the outer wall surface of the first isolation layer, and the second cavity surface is coplanar with the outer wall surface of the second isolation layer.

[0023] Beneficial effects: The second cleavage groove extending in the first direction and the first cleavage groove extending in the second direction cut the lower restriction layer and the substrate layer, separate the ridge structures arranged in a rectangular array, and form a plurality of separate quantum cascade laser structures, and at least the cutting along the second direction in the first cleavage groove contacts the first isolation layer and the second isolation layer, and a group of opposite outer wall surfaces formed in the first direction of the quantum cascade laser structure form a first cavity surface and a second cavity surface, the first cavity surface includes the outer wall surface of the first isolation layer, and the second cavity surface includes the outer wall surface of the second isolation layer, so that when the dielectric film system is set on the first cavity surface and the second cavity surface, it is directly in contact with the first isolation layer and the second isolation layer, reducing the risk of the dielectric film system falling off, ensuring that the isolation structure fully reduces the light absorption on the first cavity surface and the second cavity surface in the first direction, thereby avoiding cavity surface failure.

[0024] In an optional embodiment, after forming the isolation structure on the outer wall surface of the ridge structure and before cutting the epitaxial structure and the substrate layer at the first cleavage groove and the second cleavage groove, the method further includes: Thinning a surface of the substrate layer facing away from the epitaxial structure; A first electrode is formed on the surface of the ridge structure facing away from the substrate layer, and a second electrode is formed on the surface of the substrate layer facing away from the first electrode; cutting the epitaxial structure and the substrate layer at the first cleavage groove and the second cleavage groove also includes: cutting the second electrode.

[0025] Beneficial effects: Before cutting to form multiple individual quantum cascade laser structures, the lower surface of the substrate layer is first thinned to form a better conductive path after the second electrode is formed; then the first electrode is arranged on the upper surface of the ridge structure, and the second electrode is arranged on the lower surface of the substrate layer. Both the first electrode and the second electrode are made of metal materials with good conductive properties, such as gold, silver, aluminum, etc., and have a small contact resistance with the substrate layer and the surface of the structure. When cleavage cutting is performed later, the second electrode layer on the lower surface of the substrate layer is cut at the same time.

[0026] In an optional embodiment, after the epitaxial structure and the substrate layer are cut at the first cleavage groove and the second cleavage groove, the method further includes: Forming an anti-reflection film layer on the first cavity surface, wherein the anti-reflection film layer includes a single-layer structure formed by the first insulating layer; A high-reflection film layer is formed on the second cavity surface, wherein the high-reflection film layer comprises a composite structure formed by stacking a second insulating layer, a reflective layer and a third insulating layer in sequence.

[0027] Beneficial effects: On the first cavity surface for emitting laser, an yttrium trioxide insulating single layer material is used to form an anti-reflection film layer (AR film), and a structure combining a first isolation layer and an anti-reflection film layer is provided on one side of the first cavity surface, which can not only make the laser fully emitted, but also further reduce the thickness of the anti-reflection film layer, and reduce the temperature rise of the cavity surface while also reducing the risk of the anti-reflection film layer falling off, and greatly increase the reliability, light output efficiency and service life of the cavity surface. A multi-layer composite structure is arranged on the second cavity surface for reflecting laser, wherein the reflective layer adopts a gold layer to achieve high reflection of laser, especially mid-infrared light, and a second insulating layer and a third insulating layer are respectively arranged on both sides of the reflective layer to achieve an electrical isolation effect, and the second insulating layer and the third insulating layer are both made of the same yttrium trioxide material as the first insulating layer. A structure combining a second isolation layer and a high-reflection film layer is adopted on one side of the second cavity surface. The second isolation layer formed by iron-doped indium phosphide (Fe:InP) can effectively reduce the thickness of the second insulating layer and the third insulating layer. As the thickness decreases, the absorption of laser by the second insulating layer and the third insulating layer is also significantly reduced. Therefore, the temperature rise of the second cavity surface will be effectively suppressed, and the catastrophic optical damage threshold of the second cavity surface will be ultimately increased to ensure the performance of the second cavity surface. The dielectric film system on the first cavity surface and the second cavity surface of the quantum cascade laser structure in the light output direction is improved, and the light output efficiency, service life and reliability of the quantum cascade laser structure are ultimately improved.

[0028] In an optional implementation manner, the thickness of the second insulating layer is equal to that of the third insulating layer, and the thickness of the second insulating layer and the third insulating layer is 30 nm.

[0029] Beneficial effect: The thickness of the second insulating layer and the third insulating layer in the high-reflective film layer is set to be the same, which is convenient for achieving consistent electrical isolation on both sides of the reflective layer. The setting of the second isolation layer can reduce the thickness of the second insulating layer and the third insulating layer from 200nm in the conventional solution to around 30nm, which greatly reduces the thickness of the second insulating layer and the third insulating layer. As the thickness decreases, the absorption of the laser by the second insulating layer and the third insulating layer is significantly reduced, and the temperature rise on the second cavity surface will be effectively suppressed, ultimately increasing the catastrophic optical damage threshold of the second cavity surface and ensuring the performance of the second cavity surface. Through the setting of the isolation structure, the cavity surface dielectric film system is improved as a whole, thereby effectively improving the optical output power, service life and reliability of the quantum cascade laser structure.

[0030] In a second aspect, the present invention further provides a quantum cascade laser structure, which is manufactured by the manufacturing method of the above-mentioned quantum cascade laser structure, and includes: a substrate layer, an epitaxial structure and an isolation structure; the epitaxial structure is arranged on one side surface of the substrate layer, and the side of the epitaxial structure away from the substrate layer has a ridge structure, the ridge structure includes an upper confinement layer, an upper waveguide layer, an active layer, a lower waveguide layer and a part of the lower confinement layer, and the ridge structure includes a first surface and a second surface arranged opposite to each other in a first direction, and the first surface is a surface for emitting light; the isolation structure is arranged on the outer wall surface of the ridge structure, the isolation structure includes a first isolation layer and a second isolation layer, the first isolation layer covers the first surface, and the second isolation layer covers the second surface.

[0031] Beneficial effects: In the quantum cascade laser structure of the present invention, the first surface and the second surface of the ridge structure opposite to each other along the light-emitting direction are respectively covered with the first isolation layer and the second isolation layer. In the light-emitting direction, the laser output first passes through the isolation structure and then reaches the dielectric film system at the cavity surface. The first isolation layer and the second isolation layer are arranged on the outer surface of the ridge structure, which can effectively reduce the light absorption of the dielectric film system directly output to the cavity surface by the laser, effectively reduce the temperature rise of the cavity surface, and can form a certain insulation isolation in the laser cavity surface, which helps to reduce the thickness of the dielectric film system on the cavity surface, thereby reducing the risk of cavity surface failure caused by the shedding of the dielectric film system. The process tolerance and thickness selection of the dielectric film system on the cavity surface in the subsequent light-emitting direction are reduced, and finally the cavity surface failure risk of the quantum cascade laser structure is reduced, ensuring the light-emitting effect and service life. In addition, the isolation structure also reduces the probability of the active layer material contacting the dielectric film system on the cavity surface and the air, reduces the possibility of oxidation failure of the active layer material, and further improves the device life and reliability.

[0032] In an optional implementation, it also includes: A first electrode is arranged on a surface of the ridge structure facing away from the substrate layer; A second electrode is arranged on a surface of the substrate layer facing away from the first electrode; An anti-reflection film layer is arranged on the first cavity surface, and the anti-reflection film layer includes a single-layer structure formed by a first insulating layer; A high-reflection film layer is arranged on the second cavity surface, and the high-reflection film layer includes a composite structure in which a second insulating layer, a reflective layer and a third insulating layer are stacked in sequence; the first cavity surface and the second cavity surface are a group of outer wall surfaces of the quantum cascade laser structure that are arranged opposite to each other in the first direction, the first cavity surface includes the outer surface of the first isolation layer in a direction perpendicular to the first direction and a partial surface on one side of the epitaxial structure, and the second cavity surface includes the outer surface of the second isolation layer in a direction perpendicular to the first direction and a partial surface on the other side of the epitaxial structure.

[0033] Beneficial effects: A first electrode is arranged on the upper surface of the ridge structure, and a second electrode is arranged on one side of the lower surface of the substrate layer. Both the first electrode and the second electrode are made of metal materials with good conductive properties, such as gold, silver, aluminum, etc., and have a small contact resistance with the substrate layer and the surface of the contact structure. An anti-reflection film layer (AR film) is formed by using an insulating single layer of yttrium trioxide material on the first cavity surface for emitting laser. The present invention has a structure combining a first isolation layer and an anti-reflection film layer on one side of the first cavity surface, which can not only make the laser fully emitted, but also further reduce the thickness of the anti-reflection film layer, while reducing the temperature rise of the cavity surface, but also reducing the risk of the anti-reflection film layer falling off, and greatly increasing the reliability, light output efficiency and service life of the cavity surface. A multi-layer composite structure is arranged on the second cavity surface for reflecting laser, wherein the reflective layer adopts a gold layer to achieve high reflection of laser, especially mid-infrared light, and a second insulating layer and a third insulating layer are respectively arranged on both sides of the reflective layer to achieve an electrical isolation effect. The second insulating layer and the third insulating layer are both made of the same yttrium trioxide material as the first insulating layer. A structure combining a second isolation layer and a high-reflection film layer is adopted on one side of the second cavity surface. The second isolation layer formed by iron-doped indium phosphide (Fe:InP) can effectively reduce the thickness of the second insulating layer and the third insulating layer. As the thickness decreases, the absorption of laser by the second insulating layer and the third insulating layer is also significantly reduced. Therefore, the temperature rise of the second cavity surface will be effectively suppressed, and the catastrophic optical damage threshold of the second cavity surface will be ultimately increased to ensure the performance of the second cavity surface. The dielectric film system on the first cavity surface and the second cavity surface of the quantum cascade laser structure in the light output direction is improved, and the light output efficiency, service life and reliability of the quantum cascade laser structure are ultimately improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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.

[0035] Figure 1 is a schematic flow chart of a method for preparing a quantum cascade laser structure according to an embodiment of the present invention; Figure 2 is a schematic structural diagram of an embodiment of the present invention after an epitaxial structure is formed on a substrate layer; Figure 3 is a schematic structural diagram of a ridge structure formed on an epitaxial structure according to an embodiment of the present invention; Figure 4 is a schematic structural diagram of an embodiment of the present invention after first cleavage grooves are formed on both sides of the ridge structure in the first direction; Figure 5is a schematic diagram of a structure after an isolation structure is formed on the outer wall surface of the ridge structure according to an embodiment of the present invention; Figure 6 is a schematic diagram of the structure after the substrate layer is thinned and the first electrode and the second electrode are formed in an embodiment of the present invention; Figure 7 is a schematic top view of an embodiment of the present invention after forming a first electrode and a second electrode; Figure 8 is a schematic structural diagram of an embodiment of the present invention after cleavage cutting is performed at a first cleavage groove and a second cleavage groove; Fig. 9 It is a schematic structural diagram of a quantum cascade laser structure after an anti-reflection film layer is arranged on a first cavity surface and a high-reflection film layer is arranged on a second cavity surface according to an embodiment of the present invention.

[0036] Description of reference numerals: 1. substrate layer; 2. lower limiting layer; 3. lower waveguide layer; 4. active layer; 5. upper waveguide layer; 6. upper limiting layer; 7. ridge structure; 701. first surface; 702. second surface; 703. third surface; 704. fourth surface; 8. isolation structure; 801. first isolation layer; 802. second isolation layer; 803. third isolation layer; 804. fourth isolation layer; 9. first cleavage groove; 10. second cleavage groove; 11. first cavity surface; 12. second cavity surface; 13. first electrode; 14. second electrode; 15. anti-reflection film layer; 16. high reflection film layer; 1601. second insulating layer; 1602. reflection layer; 1603. third insulating layer; 100. Mask layer. DETAILED DESCRIPTION

[0037] 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.

[0038] In the related art, the materials used in the cavity film system (including AR film and HR film) of the front and rear cavity surfaces of the quantum cascade laser structure, such as yttrium trioxide, aluminum oxide, zirconium dioxide, etc., all 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 mirror damage (COMD) on the front and rear cavity surfaces; in order to ensure the electrical isolation effect of the composite film system of the HR film, the insulating layer is often increased in thickness, and the increase in thickness will further lead to enhanced light absorption, thereby increasing the probability of catastrophic optical damage to the rear cavity surface, and ultimately causing the cavity surface of the quantum cascade laser structure to fail, affecting its performance and life.

[0039] It should be noted that the structure of a conventional quantum cascade laser is similar to that of a conventional edge-emitting laser, with differences in the dielectric film system settings on the front and rear cavity surfaces. However, there are two main reasons why conventional edge-emitting lasers do not need to consider cavity surface failure: on the one hand, the laser wavelength of a conventional edge-emitting laser is usually 2μm, and the conventional multilayer dielectric films used in its AR film and HR film, such as silicon dioxide, aluminum oxide, titanium dioxide, etc., will not have obvious light absorption in the 2μm band, and there will be no problem of cavity surface temperature rise failure; on the other hand, when using a multilayer dielectric film, the total thickness of the required dielectric film material is positively correlated with the laser wavelength, that is, the shorter the laser wavelength, the smaller the total thickness of the required dielectric film, the simpler the dielectric film manufacturing process, and the less likely it is to have problems such as film layer shedding, that is, there is no need to consider the problem of cavity surface failure. On the one hand, the quantum cascade laser structure has light absorption in this band due to the laser wavelength usually being above 3.5μm. The longer the laser wavelength, the more serious the absorption of the dielectric film. Especially when the laser wavelength is higher than 9μm, severe light absorption will increase the temperature rise of the cavity surface, leading to cavity surface failure. On the other hand, when a multi-layer dielectric film structure is used, the thickness of the dielectric film required for the quantum cascade laser structure is much higher than that of the conventional edge-emitting laser structure, which makes it more likely for the dielectric film to fall off, causing the cavity surface failure of the quantum cascade laser structure. Therefore, a quantum cascade laser structure and a preparation method thereof are urgently needed to avoid cavity surface failure of the quantum cascade laser structure, which affects the light output effect and service life.

[0040] Based on this, see Figures 1 to 9 This embodiment provides a method for preparing a quantum cascade laser structure. Figure 1 The preparation method is a schematic flow chart, and the preparation method comprises the following steps: Step S101 , forming an epitaxial structure on a substrate layer 1 , the epitaxial structure comprising a lower confinement layer 2 , a lower waveguide layer 3 , an active layer 4 , an upper waveguide layer 5 and an upper confinement layer 6 which are formed in sequence.

[0041] refer to Figure 2 , exemplarily, the substrate layer 1 is an indium phosphide substrate; the layers of the epitaxial structure are sequentially grown on the indium phosphide substrate, and the lower limiting layer 2 is 4 μm thick and has a doping concentration of 2×10 16 cm -3 Indium phosphide; the lower waveguide layer 3 has a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3 The active layer 4 has a thickness of 2 μm and includes a multilayer quantum well composed of a GaAs barrier layer and an InAs Al spacer layer; the upper waveguide layer 5 has a thickness of 0.1 μm and a doping concentration of 2×10 16 cm -3The upper limiting layer 6 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 is formed on the side of the upper limiting layer 6 away from the substrate layer 1, and the thickness of the indium phosphide contact layer is 1 μm and the doping concentration is 5×10 18 cm -3 The contact layer helps to enhance the ohmic contact with the upper confinement layer 6, thereby ensuring the current injection effect.

[0042] Step S102, forming a ridge structure 7 on the side of the epitaxial structure away from the substrate layer 1, the ridge structure 7 includes an upper confinement layer 6, an upper waveguide layer 5, an active layer 4, a lower waveguide layer 3 and a portion of the lower confinement layer 2, and the ridge structure 7 includes a first surface 701 and a second surface 702 arranged opposite to each other in a first direction, and the first surface 701 is a surface for emitting light.

[0043] refer to Figure 3 , by arranging a patterned mask layer 100 on the side of the epitaxial structure away from the substrate layer 1, the exposed part of the epitaxial structure is dry-etched to a depth of up to a part of the lower confinement layer 2, for example, etching the lower confinement layer 2 of about 1 μm, so as to form a ridge structure 7 protruding from the unetched lower confinement layer 2. The first direction of this embodiment is the light-emitting direction of the quantum cascade laser structure with sidewall light emission, that is, Figure 3 The direction perpendicular to the first surface 701 and the second surface 702 in the horizontal direction. The first surface 701 and the second surface 702 of the ridge structure 7, which are arranged opposite to each other in the first direction, can be used as the front cavity surface side and the back cavity surface side of the laser structure, respectively, for light extraction and setting a reflective film layer; in addition, the angle deviation of the side wall of the ridge structure 7 formed by etching from the vertical direction should be less than 2°, and the roughness of the side wall surface should be less than 100nm, so as to ensure the light extraction efficiency of the ridge structure 7. The formation of the above-mentioned mask layer 100 includes: using plasma enhanced chemical vapor deposition (Plasma Enhanced Chemical Vapor Deposition, referred to as PECVD) technology to deposit a 300nm silicon dioxide layer on the surface of the epitaxial structure; then performing photolithography, and using inductively coupled plasma etching (Inductively Coupled Plasma Etching, referred to as ICPE) technology to selectively etch the silicon dioxide layer; then removing the glue to obtain a patterned mask layer 100.

[0044] Step S103 , forming an isolation structure 8 on the outer wall surface of the ridge structure 7 , the isolation structure 8 comprising a first isolation layer 801 and a second isolation layer 802 , the first isolation layer 801 covers the first surface 701 , and the second isolation layer 802 covers the second surface 702 .

[0045] Exemplarily, the ridge structure 7 of this embodiment is formed into a rectangular parallelepiped, and the isolation structure 8 is made of iron-doped indium phosphide material, which has the characteristics of semi-insulation and low light absorption efficiency. When the isolation structure 8 is formed on the outer wall surface of the ridge structure 7 formed by etching, the isolation structure 8 at least covers the two opposite side walls of the ridge structure 7 in the light-emitting direction, that is, the first isolation layer 801 of the isolation structure 8 covers the first surface 701, and the second isolation layer 802 covers the second surface 702. In the light-emitting direction, the laser output first passes through the isolation structure 8, and then reaches the dielectric film system at the cavity surface. The first isolation layer 801 and the second isolation layer 802 are arranged on the outer surface of the ridge structure 7, which can effectively reduce the light absorption of the dielectric film system directly output to the cavity surface by the laser, and can form a certain insulation isolation in the laser cavity surface, which helps to reduce the thickness of the dielectric film system on the cavity surface, thereby reducing the risk of cavity surface failure caused by the shedding of the dielectric film system. In addition, the isolation structure 8 also reduces the probability of the active layer 4 material contacting the dielectric film system and air on the cavity surface, reduces the possibility of oxidation failure of the active layer 4 material, and is conducive to improving the device life and reliability.

[0046] In the preparation method of the quantum cascade laser structure of the present embodiment, when etching the epitaxial structure, it is ensured that a portion of the epitaxial structure is etched away in the light emitting direction to form a ridge structure 7, and then the first isolation layer 801 and the second isolation layer 802 are respectively covered on the first surface 701 and the second surface 702 opposite to each other in the light emitting direction of the ridge structure 7, and the first isolation layer 801 and the second isolation layer 802 can effectively reduce the light absorption of the laser output, and the first isolation layer 801 and the second isolation layer 802 constitute part of the outer wall surface in the light emitting direction, which can have a certain isolation and insulation effect, effectively reduce the wall surface temperature increase, and further reduce the process tolerance and thickness selection of the cavity surface dielectric film system in the subsequent light emitting direction, and finally reduce the cavity surface failure risk of the quantum cascade laser structure, and ensure the light emitting effect and service life.

[0047] In one embodiment, the above-mentioned step S101 of forming a ridge structure 7 on the side of the epitaxial structure away from the substrate layer 1 includes: etching the side of the epitaxial structure away from the substrate layer 1 to form a plurality of ridge structures 7 spaced apart from each other, the plurality of ridge structures 7 are arranged in a rectangular array, the ridge structure 7 also includes a third surface 703 and a fourth surface 704 arranged relative to each other along a second direction, and the second direction forms a preset angle with the first direction; the isolation structure 8 also includes a third isolation layer 803 and a fourth isolation layer 804, the third isolation layer 803 covers the third surface 703 of the ridge structure 7, and the fourth isolation layer 804 covers the fourth surface 704 of the ridge structure 7.

[0048] refer to Figure 7, forming multiple ridge structures 7 on the epitaxial structure is conducive to the mass production of quantum cascade laser structures; and multiple ridge structures 7 are arranged in a rectangular array, which is convenient for subsequent cleavage and cutting to form multiple quantum cascade laser structures. Each quantum cascade laser structure includes a substrate layer 1, a lower confinement layer 2 with the same area as the substrate layer 1, and a ridge structure 7 with a projected area smaller than the substrate layer 1 and the lower confinement layer 2; the cutting can be only for the lower confinement layer 2 and the substrate layer 1, or it can be cut by contacting the isolation structure 8, but the cutting needs to be perpendicular to the surface of the substrate layer 1 to ensure the verticality of the cavity surface of the formed quantum cascade laser structure in the light output direction. The ridge structure 7 is formed as a rectangular parallelepiped, including a first surface 701 and a second surface 702 arranged opposite to each other in the first direction, and a third surface 703 and a fourth surface 704 arranged opposite to each other in the second direction. Correspondingly, the isolation structure 8 also includes a third isolation layer 803 covering the third surface 703 and a fourth isolation layer 804 covering the fourth surface 704. The isolation structure 8 realizes all-round insulation isolation of the side wall surface of the ridge structure 7. In this embodiment, the first direction is preferably perpendicular to the second direction, that is, the second direction is a direction parallel to the first surface 701 and the second surface 702 in the horizontal direction.

[0049] In one embodiment, the thickness of the first isolation layer 801 and the second isolation layer 802 in the first direction ranges from 0.2 μm to 5 μm.

[0050] If the thickness of the first isolation layer 801 and the second isolation layer 802 is less than 0.2μm, the insulation isolation effect is not obvious, and leakage current may be generated. For example, the injected current may pass through the second isolation layer 802 and the thinner second insulation layer 1601, and directly transmit downward from the metal reflection layer 1602 in the middle of the high reflection film layer 16 on the second cavity surface 12, causing the laser structure to short-circuit; but if the thickness of the first isolation layer 801 and the second isolation layer 802 exceeds 5μm, it will affect the light transmission of the resonant cavity of the quantum cascade laser structure, resulting in a weakening of the cavity surface reflection performance, and ultimately affecting the performance of the laser structure. Therefore, the thickness of the first isolation layer 801 and the second isolation layer 802 is controlled between 0.2μm and 5μm, and preferably set close to 0.2μm, which can not only ensure effective insulation isolation and reduce light absorption effect, but also ensure efficient light transmission in the resonant cavity and the reflection performance of the cavity surface, and ultimately ensure the light output efficiency and performance of the quantum cascade laser.

[0051] In this embodiment, the above-mentioned limited thickness is the thickness of the first isolation layer 801 and the second isolation layer 802 in the laser structure after final cleavage. The thickness of the initially grown isolation structure 8 can be greater than the above-mentioned limited thickness. The final thickness control is achieved through the cleavage position and the cleavage etching width.

[0052] Further, see Figure 7The isolation structure 8 is annular and integrally formed on the outer wall surface of the ridge structure 7; the thickness of the third isolation layer 803 and the fourth isolation layer 804 in the second direction is equal to the thickness of the first isolation layer 801 and the second isolation layer 802 in the first direction.

[0053] In this embodiment, the isolation structure 8 is formed as an integrated annular column, which is simple to prepare and has good structural performance. Its inner wall surface is close to the outer wall surface of the ridge structure 7, and the thickness of the annular column is consistent at all locations, which helps to achieve uniform electrical isolation and insulation effects at all locations of the ridge structure 7 and ensure the light output effect.

[0054] On the basis of the above scheme, after step S102 of forming a ridge structure 7 on the side of the epitaxial structure away from the substrate layer 1, and before step S103 of forming an isolation structure 8 on the outer wall surface of the ridge structure 7, the preparation method also includes: forming a first cleavage groove 9 and a second cleavage groove 10 on the surface of the lower restriction layer 2 on the side away from the substrate layer 1, and the projection areas of the first cleavage groove 9 and the second cleavage groove 10 on the substrate layer 1 are relatively isolated from the projection area of ​​the ridge structure 7 on the substrate layer 1; the first cleavage groove 9 is arranged on both sides of the ridge structure 7 along the first direction; the second cleavage groove 10 is arranged between two adjacent ridge structures 7 along the second direction, and extends along the first direction.

[0055] refer to Figure 2 and Figure 7 In the first direction, a first cleavage groove 9 is etched on the lower restriction layer 2 between each two adjacent ridge structures 7. By controlling the width of the first cleavage groove 9, the two cavity surfaces of the ridge structure 7 in the light emitting direction are precisely cleaved, and the first cleavage groove 9 extends along the second direction; a second cleavage groove 10 is etched between two adjacent ridge structures 7 in the second direction, so as to simply and quickly separate the ridge structures 7 in the second direction without the need for precise cleavage etching to the third isolation layer 803 and the fourth isolation layer 804, and the process requirements are relatively low. The second cleavage groove 10 extends along the first direction, and the first cleavage groove 9 and the second cleavage groove 10 of this embodiment both extend to the edge of the lower restriction layer 2 to facilitate cleavage etching positioning.

[0056] Further, in the first direction, two adjacent ridge structures 7 include two first cleavage grooves 9 , and the distance between the two first cleavage grooves 9 is greater than or equal to 0.5 mm.

[0057] In the epitaxial structure of this embodiment, a plurality of ridge structures 7 are formed at least in the first direction, and each ridge structure 7 includes a first cleavage groove 9 configured separately on both sides of the first direction, so as to accurately realize the cleavage of the cavity surfaces on both sides of the ridge structure 7 in the light-emitting direction. Compared with one first cleavage groove 9 that realizes the cleavage of the cavity surfaces of the two ridge structures 7 on both sides simultaneously, in this embodiment, two first cleavage grooves 9 are arranged between the adjacent ridge structures 7 in the first direction, and are respectively close to one of the ridge structures 7, which can be applied to epitaxial structures with various spacing distances of the ridge structures 7, and has a wide range of applications. In the first direction, the area between the two first cleavage grooves 9 between the two adjacent ridge structures 7 is a sacrificial area, and the width of the area should be greater than or equal to 0.5 mm to ensure the smooth completion of the cleavage steps of the two adjacent first cleavage paths.

[0058] In one embodiment, the depth of the first cleavage groove 9 is in the range of 0.5 μm to 2 μm, and the width of the first cleavage groove 9 in the first direction is in the range of 0.5 μm to 5 μm; the depth of the second cleavage groove 10 is in the range of 0.2 μm to 2 μm, and the width of the second cleavage groove 10 in the second direction is in the range of 2 μm to 10 μm.

[0059] refer to Figure 7 The etching width and etching depth of the first cleavage groove 9 and the second cleavage groove 10 are set to ensure that the epitaxial structure is cleaved and divided into a plurality of separate quantum cascade laser structures with high precision, thereby improving the cavity surface performance of the quantum cascade laser structure.

[0060] Specifically, see Figure 5 and Figure 7 As shown, the above-mentioned isolation structure 8 formed on the outer wall surface of the ridge structure 7 includes: using hydride vapor phase epitaxy technology to form the isolation structure 8, and the first isolation layer 801 and the second isolation layer 802 of the isolation structure 8 respectively cover the first cleavage groove 9 located on both sides of the ridge structure 7 along the first direction.

[0061] The annular region outside the ridge structure 7 formed after etching by the hydride vapor phase epitaxy (HVPE) technology can also be referred to as the selective growth region to form an isolation structure 8 for electrical isolation and optical confinement. The width of the annular region is greater than the width of the isolation structure 8 layer. This step can only be regrown by HVPE to achieve the filling of the steep sidewalls. The first isolation layer 801 and the second isolation layer 802 of the isolation structure 8 cover the first cleavage groove 9 to ensure that when cleavage etching is performed at the position of the first cleavage groove 9, the cavity surface formed after etching includes the isolation structure 8, and at least the cavity surface on the side where the laser emerges has the isolation structure 8, so as to ensure that the isolation structure 8 effectively reduces the absorption of the emitted laser. In this embodiment, the width of the annular region outside the ridge structure 7 is limited to 20μm~40μm, and the thickness in the first direction and the second direction is as close as possible, preferably consistent.

[0062] In one embodiment, reference Figure 7 and Figure 8 After step S103 of forming the isolation structure 8 on the outer wall surface of the ridge structure 7, the method further includes the following steps: Step S104, cutting the epitaxial structure and the substrate layer 1 at the first cleavage groove 9 and the second cleavage groove 10 to cleave to form a plurality of quantum cascade laser structures, any quantum cascade laser structure includes a first cavity surface 11 and a second cavity surface 12 arranged opposite to each other along a first direction, the first cavity surface 11 is coplanar with the outer wall surface of the first isolation layer 801, and the second cavity surface 12 is coplanar with the outer wall surface of the second isolation layer 802.

[0063] The second cleavage groove 10 extending along the first direction and the first cleavage groove 9 extending in the second direction cut the lower confinement layer 2 and the substrate layer 1, separate the ridge structures 7 arranged in a rectangular array, and form a plurality of separate quantum cascade laser structures. At least the cutting along the second direction in the first cleavage groove 9 contacts the first isolation layer 801 and the second isolation layer 802. A set of opposite outer wall surfaces formed in the first direction of the quantum cascade laser structure form a first cavity surface 11 and a second cavity surface 12. The first cavity surface 11 includes the outer wall surface of the first isolation layer 801, and the second cavity surface 12 includes the outer wall surface of the second isolation layer 802, so that when a dielectric film system is set on the first cavity surface 11 and the second cavity surface 12, it is directly in contact with the first isolation layer 801 and the second isolation layer 802, thereby reducing the risk of the dielectric film system falling off, and ensuring that the isolation structure 8 sufficiently reduces the light absorption on the first cavity surface 11 and the second cavity surface 12 in the first direction, thereby avoiding cavity surface failure.

[0064] refer to Figure 6, after step S103 of forming an isolation structure 8 on the outer wall surface of the ridge structure 7, and before step S104 of cutting the epitaxial structure and the substrate layer 1 at the first cleavage groove 9 and the second cleavage groove 10, it also includes: thinning the side surface of the substrate layer 1 away from the epitaxial structure; forming a first electrode 13 on the side surface of the ridge structure 7 away from the substrate layer 1, and forming a second electrode 14 on the side surface of the substrate layer 1 away from the substrate layer 1; cutting the epitaxial structure and the substrate layer 1 at the first cleavage groove 9 and the second cleavage groove 10 also includes: cutting the second electrode 14.

[0065] Before cutting to form multiple individual quantum cascade laser structures, the lower surface of the substrate layer 1 is first thinned to form a better conductive path after the second electrode 14 is formed; then the first electrode 13 is set on the upper surface of the ridge structure 7, and the second electrode 14 is set on the lower surface of the substrate layer 1. The first electrode 13 and the second electrode 14 are both made of metal materials with good conductive properties, such as gold, silver, aluminum, etc., and have a small contact resistance with the substrate layer 1 and the surface of the structure. When cleavage cutting is performed later, the second electrode 14 layer on the lower surface of the substrate layer 1 is cut at the same time.

[0066] In one embodiment, reference Fig. 9 After the epitaxial structure and the substrate layer 1 are cut at the first cleavage groove 9 and the second cleavage groove 10, the preparation method further comprises the following steps: Step S105 , forming an anti-reflection film layer 15 on the first cavity surface 11 , wherein the anti-reflection film layer 15 includes a single-layer structure formed by a first insulating layer.

[0067] The first cavity surface 11 of the present embodiment is used for emitting laser light, and therefore an anti-reflection film layer 15 (AR film) is formed on the first cavity surface 11 using a single layer of yttrium trioxide insulating material. The single layer of yttrium trioxide cooperates with the first isolation layer 801, which greatly reduces the absorption of laser light on the first cavity surface 11, thereby ensuring sufficient emission of the laser light and reducing the temperature rise of the cavity surface, thereby reducing the risk of failure of the first cavity surface 11.

[0068] In conventional solutions, in order to avoid catastrophic optical damage (COMD), a dielectric film-free uncoating structure is usually adopted for the first cavity surface 11. In simple terms, the first cavity surface 11 adopts a natural cleavage surface as a reflective surface, and does not additionally evaporate the anti-reflection film layer 15, that is, the anti-reflection film layer 15 is not plated after cleavage; or an anti-reflection film layer 15 with a thickness of less than 30nm is evaporated to reduce the light absorption of the anti-reflection film layer 15 on the first cavity surface 11. The structure of the first isolation layer 801 and the anti-reflection film layer 15 on one side of the first cavity surface 11 in this embodiment can not only realize sufficient laser emission, but also further reduce the thickness of the anti-reflection film layer 15, thereby greatly reducing the risk of the anti-reflection film layer 15 falling off, and greatly increasing the light extraction efficiency and service life.

[0069] Step S106 , forming a high reflection film layer 16 on the second cavity surface 12 , wherein the high reflection film layer 16 comprises a composite structure formed by stacking a second insulating layer 1601 , a reflective layer 1602 and a third insulating layer 1603 in sequence.

[0070] The second cavity surface 12 of this embodiment is used to reflect the laser so that the laser is emitted from the second cavity surface 12. A multi-layer stacked composite structure is set on the second cavity surface 12, wherein the reflective layer 1602 adopts a gold layer to achieve high reflection of the laser, especially mid-infrared light, but the high conductivity of gold easily leads to short circuit of the device, so a second insulating layer 1601 and a third insulating layer 1603 are respectively set on both sides of the reflective layer 1602 to achieve electrical isolation effect, and the second insulating layer 1601 and the third insulating layer 1603 are both made of the same yttrium trioxide material as the first insulating layer. In the conventional scheme, in order to achieve effective electrical isolation of the reflective layer 1602, the thickness of the second insulating layer 1601 and the third insulating layer 1603 on both sides of the reflective layer 1602 is usually not less than 200nm, the light absorption is large, and the thickness of the overall high-reflective film layer 16 is very thick, which is very easy to fall off and cause the second cavity surface 12 to fail. In the present solution, a second isolation layer 802 and a high-reflection film layer 16 are combined on one side of the second cavity surface 12. The second isolation layer 802 formed by iron-doped indium phosphide (Fe:InP) can effectively reduce the thickness of the second insulating layer 1601 and the third insulating layer 1603. As the thickness decreases, the absorption of the laser by the second insulating layer 1601 and the third insulating layer 1603 is also significantly reduced. Therefore, the temperature rise of the high-reflection cavity surface, that is, the second cavity surface 12, will be effectively suppressed, and ultimately the catastrophic optical damage threshold of the second cavity surface 12 will be improved, thereby ensuring the performance of the second cavity surface 12.

[0071] Specifically, the thickness of the second insulating layer 1601 and the third insulating layer 1603 are equal, and the thickness of the second insulating layer 1601 and the third insulating layer 1603 is 30 nm.

[0072] In this embodiment, the second insulating layer 1601 and the third insulating layer 1603 in the high reflective film layer 16 are set to have the same thickness, which is convenient for achieving consistent electrical isolation on both sides of the reflective layer 1602. In addition, due to the setting of the second isolation layer 802, the thickness of the second insulating layer 1601 and the third insulating layer 1603 can be reduced from 200nm in the conventional solution to about 30nm, which greatly reduces the thickness of the second insulating layer 1601 and the third insulating layer 1603. With the reduction of thickness, the absorption of laser by the second insulating layer 1601 and the third insulating layer 1603 is significantly reduced, and the temperature rise on the second cavity surface 12 will be effectively suppressed, and finally the catastrophic optical damage threshold of the second cavity surface 12 is improved, and the performance of the second cavity surface 12 is guaranteed. Through the setting of the isolation structure 8, the cavity surface dielectric film system is improved as a whole, thereby effectively improving the optical output power, service life and reliability of the quantum cascade laser structure.

[0073] like Figure 8 and Fig. 9 As shown, this embodiment also provides a quantum cascade laser structure, which is manufactured by the above-mentioned method for manufacturing the quantum cascade laser structure, and includes: a substrate layer 1, an epitaxial structure and an isolation structure 8; the epitaxial structure is arranged on one side surface of the substrate layer 1, and the side of the epitaxial structure away from the substrate layer 1 has a ridge structure 7, the ridge structure 7 includes an upper confinement layer 6, an upper waveguide layer 5, an active layer 4, a lower waveguide layer 3 and a part of the lower confinement layer 2, and the ridge structure 7 includes a first surface 701 and a second surface 702 arranged opposite to each other in a first direction, and the first surface 701 is a surface for emitting light; the isolation structure 8 is arranged on the outer wall surface of the ridge structure 7, and the isolation structure 8 includes a first isolation layer 801 and a second isolation layer 802, the first isolation layer 801 covers the first surface 701, and the second isolation layer 802 covers the second surface 702.

[0074] In the quantum cascade laser structure of this embodiment, the first surface 701 and the second surface 702 of the ridge structure 7 opposite to each other in the light-emitting direction are respectively covered with a first isolation layer 801 and a second isolation layer 802. In the light-emitting direction, the laser output first passes through the isolation structure 8, and then reaches the dielectric film system at the cavity surface. The first isolation layer 801 and the second isolation layer 802 are arranged on the outer surface of the ridge structure 7, which can effectively reduce the light absorption of the dielectric film system directly output to the cavity surface by the laser, effectively reduce the temperature rise of the cavity surface, and can form a certain insulation isolation in the laser cavity surface, which helps to reduce the thickness of the dielectric film system of the cavity surface, thereby reducing the risk of cavity surface failure caused by the shedding of the dielectric film system. The process tolerance and thickness selection of the dielectric film system of the cavity surface in the subsequent light-emitting direction are reduced, and finally the cavity surface failure risk of the quantum cascade laser structure is reduced, and the light-emitting effect and service life are guaranteed. In addition, the isolation structure 8 also reduces the probability of the active layer 4 material contacting the dielectric film system and air on the cavity surface, reduces the possibility of oxidation failure of the active layer 4 material, and further improves the device life and reliability.

[0075] In one embodiment, reference Fig. 9 The quantum cascade laser structure of this embodiment further includes: a first electrode 13, a second electrode 14, an anti-reflection film layer 15 and a high-reflection film layer 16, wherein the first electrode 13 is arranged on a side surface of the ridge structure 7 away from the substrate layer 1; the second electrode 14 is arranged on a side surface of the substrate layer 1 away from the first electrode 13; the anti-reflection film layer 15 is arranged on the first cavity surface 11, and the anti-reflection film layer 15 includes a single-layer structure formed by a first insulating layer; the high-reflection film layer 16 is arranged on the second cavity surface 12, and the high-reflection film layer 16 includes a composite structure in which a second insulating layer 1601, a reflective layer 1602 and a third insulating layer 1603 are stacked in sequence; the first cavity surface 11 and the second cavity surface 12 are a group of outer wall surfaces of the quantum cascade laser structure arranged opposite to each other in the first direction, the first cavity surface 11 includes an outer surface of the first isolation layer 801 perpendicular to the first direction and a partial surface of one side of the epitaxial structure, and the second cavity surface 12 includes an outer surface of the second isolation layer 802 perpendicular to the first direction and a partial surface of the other side of the epitaxial structure.

[0076] A first electrode 13 is arranged on the upper surface of the ridge structure 7, and a second electrode 14 is arranged on one side of the lower surface of the substrate layer 1. The first electrode 13 and the second electrode 14 are both made of metal materials with good electrical conductivity, such as gold, silver, aluminum, etc., and have a small contact resistance with the substrate layer 1 and the surface of the contact structure. An anti-reflection film layer 15 (AR film) is formed on the first cavity surface 11 for emitting laser using an insulating single layer of yttrium trioxide material. This embodiment has a structure combining a first isolation layer 801 and an anti-reflection film layer 15 on one side of the first cavity surface 11, which can not only make the laser fully emitted, but also further reduce the thickness of the anti-reflection film layer 15, while reducing the cavity surface temperature rise, but also reducing the risk of the anti-reflection film layer 15 falling off, and greatly improving the cavity surface reliability, light extraction efficiency and service life. Fig. 9The arrow on the right side indicates the emitted laser. A multilayer composite structure is arranged on the second cavity surface 12 for reflecting the laser, wherein the reflective layer 1602 is made of a gold layer to achieve high reflection of the laser, especially the mid-infrared light, and a second insulating layer 1601 and a third insulating layer 1603 are respectively arranged on both sides of the reflective layer 1602 to achieve an electrical isolation effect, and the second insulating layer 1601 and the third insulating layer 1603 are both made of the same yttrium trioxide material as the first insulating layer. A structure combining a second isolation layer 802 and a high-reflection film layer 16 is adopted on one side of the second cavity surface 12. The second isolation layer 802 formed by iron-doped indium phosphide (Fe:InP) can effectively reduce the thickness of the second insulating layer 1601 and the third insulating layer 1603. As the thickness decreases, the absorption of laser by the second insulating layer 1601 and the third insulating layer 1603 is also significantly reduced. Therefore, the temperature rise of the second cavity surface 12 will be effectively suppressed, and the catastrophic optical damage threshold of the second cavity surface 12 will be finally improved to ensure the performance of the second cavity surface 12. The dielectric film system on the first cavity surface 11 and the second cavity surface 12 in the light output direction of the quantum cascade laser structure is improved, and the light output efficiency, service life and reliability of the quantum cascade laser structure are finally improved.

[0077] 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.

[0078] 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 method for preparing a quantum cascade laser structure, characterized in that: include: forming an epitaxial structure on the substrate layer, wherein the epitaxial structure comprises a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer and an upper confinement layer formed in sequence; A ridge structure is formed on a side of the epitaxial structure away from the substrate layer, the ridge structure comprising an upper confinement layer, an upper waveguide layer, an active layer, a lower waveguide layer and a portion of the lower confinement layer, and the ridge structure comprises a first surface and a second surface arranged opposite to each other in a first direction, the first surface being a surface for emitting light; An isolation structure is formed on the outer wall surface of the ridge structure, wherein the isolation structure includes a first isolation layer and a second isolation layer, wherein the first isolation layer covers the first surface, and the second isolation layer covers the second surface.

2. The method for preparing a quantum cascade laser structure according to claim 1, characterized in that: The step of forming a ridge structure on a side of the epitaxial structure away from the substrate layer comprises: The side of the epitaxial structure facing away from the substrate layer is etched to form a plurality of ridge structures spaced apart from each other, wherein the plurality of ridge structures are arranged in a rectangular array, wherein the ridge structure further comprises a third surface and a fourth surface arranged opposite to each other along a second direction, wherein the second direction forms a preset angle with the first direction; the isolation structure further comprises a third isolation layer and a fourth isolation layer, wherein the third isolation layer covers the third surface of the ridge structure, and the fourth isolation layer covers the fourth surface of the ridge structure.

3. The method for preparing a quantum cascade laser structure according to claim 2, characterized in that: The thickness of the first isolation layer and the second isolation layer in the first direction ranges from 0.2 μm to 5 μm.

4. The method for preparing a quantum cascade laser structure according to claim 3, characterized in that: The isolation structure is annular and integrally formed on the outer wall surface of the ridge structure; the thickness of the third isolation layer and the fourth isolation layer in the second direction is equal to the thickness of the first isolation layer and the second isolation layer in the first direction.

5. The method for preparing a quantum cascade laser structure according to any one of claims 2 to 4, characterized in that: After forming a ridge structure on a side of the epitaxial structure away from the substrate layer and before forming an isolation structure on an outer wall surface of the ridge structure, the preparation method further includes: A first cleavage groove and a second cleavage groove are formed on the surface of the lower limiting layer on the side away from the substrate layer, and the projection areas of the first cleavage groove and the second cleavage groove on the substrate layer are relatively isolated from the projection area of ​​the ridge structure on the substrate layer; the first cleavage groove is arranged on both sides of the ridge structure along the first direction and extends along the second direction; the second cleavage groove is arranged between two adjacent ridge structures along the second direction and extends along the first direction.

6. The method for preparing a quantum cascade laser structure according to claim 5, characterized in that: In the first direction, two adjacent ridge structures include two first cleavage grooves, and a distance between the two first cleavage grooves is greater than or equal to 0.5 mm.

7. The method for preparing a quantum cascade laser structure according to claim 6, characterized in that: The depth of the first cleavage groove ranges from 0.5 μm to 2 μm, and the width of the first cleavage groove in the first direction ranges from 0.5 μm to 5 μm; the depth of the second cleavage groove ranges from 0.2 μm to 2 μm, and the width of the second cleavage groove in the second direction ranges from 2 μm to 10 μm.

8. The method for preparing a quantum cascade laser structure according to claim 7, characterized in that: The forming of the isolation structure on the outer wall surface of the ridge structure includes: forming the isolation structure by using hydride vapor phase epitaxy technology, wherein the first isolation layer and the second isolation layer of the isolation structure respectively cover two first cleavage grooves located on both sides of the ridge structure along the first direction.

9. The method for preparing a quantum cascade laser structure according to claim 8, characterized in that: After forming an isolation structure on the outer wall surface of the ridge structure, the preparation method further comprises: The epitaxial structure and the substrate layer are cut at the first cleavage groove and the second cleavage groove to form a plurality of quantum cascade laser structures by cleavage, wherein any of the quantum cascade laser structures comprises a first cavity surface and a second cavity surface arranged opposite to each other along the first direction, wherein the first cavity surface is coplanar with an outer wall surface of the first isolation layer, and the second cavity surface is coplanar with an outer wall surface of the second isolation layer.

10. The method for preparing a quantum cascade laser structure according to claim 9, characterized in that: After forming an isolation structure on the outer wall surface of the ridge structure and before cutting the epitaxial structure and the substrate layer at the first cleavage groove and the second cleavage groove, the method further includes: Thinning a surface of the substrate layer facing away from the epitaxial structure; A first electrode is formed on a surface of the ridge structure facing away from the substrate layer, and a second electrode is formed on a surface of the substrate layer facing away from the first electrode; cutting the epitaxial structure and the substrate layer at the first cleavage groove and the second cleavage groove also includes: cutting the second electrode.

11. The method for preparing a quantum cascade laser structure according to claim 10, characterized in that: After cutting the epitaxial structure and the substrate layer at the first cleavage groove and the second cleavage groove, the method further includes: forming an anti-reflection film layer on the first cavity surface, wherein the anti-reflection film layer includes a single-layer structure formed by a first insulating layer; A high reflection film layer is formed on the second cavity surface, wherein the high reflection film layer comprises a composite structure formed by stacking a second insulating layer, a reflective layer and a third insulating layer in sequence.

12. The method for preparing a quantum cascade laser structure according to claim 11, characterized in that: The second insulating layer and the third insulating layer have the same thickness, and the thickness of the second insulating layer and the third insulating layer is 30 nm.

13. A quantum cascade laser structure, characterized in that: The method for preparing a quantum cascade laser structure according to any one of claims 1 to 12 comprises: substrate layer; An epitaxial structure is arranged on one side surface of the substrate layer; a side of the epitaxial structure away from the substrate layer has a ridge structure, the ridge structure includes an upper confinement layer, an upper waveguide layer, an active layer, a lower waveguide layer and a portion of the lower confinement layer, and the ridge structure includes a first surface and a second surface arranged opposite to each other in a first direction, the first surface is a surface for emitting light; The isolation structure is arranged on the outer wall surface of the ridge structure, and the isolation structure includes a first isolation layer and a second isolation layer. The first isolation layer covers the first surface, and the second isolation layer covers the second surface.

14. The quantum cascade laser structure according to claim 13, characterized in that: Also includes: A first electrode is arranged on a surface of the ridge structure facing away from the substrate layer; A second electrode is disposed on a surface of the substrate layer facing away from the first electrode; An anti-reflection film layer is arranged on the first cavity surface, and the anti-reflection film layer includes a single-layer structure formed by a first insulating layer; A high-reflection film layer is arranged on the second cavity surface, and the high-reflection film layer includes a composite structure in which a second insulating layer, a reflective layer and a third insulating layer are stacked in sequence; the first cavity surface and the second cavity surface are a group of outer wall surfaces of the quantum cascade laser structure that are arranged opposite to each other in the first direction, the first cavity surface includes the outer surface of the first isolation layer in a direction perpendicular to the first direction and a partial surface on one side of the epitaxial structure, and the second cavity surface includes the outer surface of the second isolation layer in a direction perpendicular to the first direction and a partial surface on the other side of the epitaxial structure.

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