Quantum cascade laser with barrel-shaped waveguide and preparation method thereof

Abstract

The invention relates to a quantum cascade laser with a cylindrical waveguide and a preparation method thereof, and belongs to the field of photoelectron, the quantum cascade laser comprises a laminated structure, the laminated structure is provided with two waveguide grooves, a ridge waveguide is formed between the two waveguide grooves, the waveguide grooves are hyperbolic, and the ridge waveguide is cylindrical; the bottom and side wall areas of the waveguide groove are subjected to mechanochemical grinding treatment and filled with InP: Fe, then mechanochemical grinding is carried out again, and then an insulating film layer material is evaporated; due to the unique cylindrical shape of the ridge waveguide, the photon density can be effectively improved, and the output characteristic of laser is optimized; and meanwhile, the mode distribution of light can be better controlled, and excellent laser characteristics are realized by utilizing optical reflection and interference effects. According to the invention, before secondary epitaxy, a mechanochemical grinding method is adopted to carry out surface treatment on the double channels, so that waveguide loss after secondary epitaxy of InP: Fe can be effectively reduced, the threshold current density is further reduced, and the output power and the slope efficiency are increased.

Description

Technical Field

[0001] The invention relates to a quantum cascade laser with a barrel-shaped waveguide and a preparation method thereof, belonging to the technical field of optoelectronics. Background Art

[0002] Quantum Cascade Laser (QCL) is an innovative laser based on the principles of quantum mechanics. It has important applications in gas composition detection, medical diagnosis, remote sensing of dangerous goods, free space communication, directional infrared countermeasures, etc. Since it was first proposed in 1994, QCL has developed rapidly in the field of infrared laser technology. Because it can achieve flexible wavelength control and high power output, it has become one of the hot spots in laser technology research. The stimulated emission process of QCL only involves electrons. Its lasing principle is to use the population inversion between separated electronic states caused by the quantum confinement effect in the semiconductor heterojunction thin layer. Electrons interact with multiple quantum well barrier layers to repeatedly excite and emit photons, thereby forming continuous laser output. This structure allows QCL to operate within a specific wavelength range, and by properly designing the material and thickness of the quantum well, laser emission of multiple wavelengths can be achieved.

[0003] The waveguide structure of the QCL laser has a crucial influence on its performance. The waveguide must not only guide the laser effectively, but also have good coupling efficiency and scattering characteristics at different wavelengths. In recent years, research on QCL waveguide structures has gradually deepened. Researchers have tried different geometric shapes and material combinations to improve the output performance of the laser. In addition to the traditional rectangular waveguide, many waveguide forms have been explored, such as stepped waveguides and photonic crystal waveguides. The introduction of these new waveguides has promoted the development of QCL technology, especially in the fields of multi-wavelength lasers and high-power output.

[0004] The research on the waveguide structure of QCL has important theoretical and application significance. By exploring new waveguide forms, we can break through some limitations of current QCL technology, improve the beam quality and performance of lasers, and further promote the development of laser technology.

[0005] In addition, current high-performance QCLs often use secondary epitaxy to selectively epitaxially grow semi-insulating InP:Fe on both sides of the chip ridge waveguide to form a buried heterojunction. This can provide better heat dissipation for the chip as well as better lateral light field and current limitation. The double grooves on both sides of the ridge waveguide are obtained by wet etching or dry etching, and the unavoidable roughness of the double groove surface will inevitably lead to photon absorption at the interface where the InP:Fe after secondary epitaxy contacts the chip main structure, resulting in large waveguide losses. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a quantum cascade laser with a cylindrical waveguide and a preparation method thereof. Due to its unique cylindrical geometric shape, it can effectively improve the photon density and optimize the output characteristics of the laser; at the same time, this waveguide form can better control the mode distribution of light, and use optical reflection and interference effects to achieve excellent laser characteristics. The present invention uses a mechanical chemical grinding method before secondary epitaxy to perform surface treatment on the double channel, which can effectively reduce the waveguide loss after secondary epitaxy InP:Fe, thereby reducing the threshold current density and increasing the output power and slope efficiency.

[0007] The technical solution of the present invention is as follows:

[0008] A quantum cascade laser with a barrel-shaped waveguide, comprising a stacked structure, wherein the stacked structure comprises, from bottom to top, an N-type InP substrate, an N-type InP buffer layer, an N-type InP lower waveguide layer, an N-type GaInAs lower confinement layer, a multi-period active region structure, an N-type GaInAs upper confinement layer, an N-type InP upper waveguide layer, and an N-type highly doped InP ohmic contact layer;

[0009] The stacked structure is provided with two waveguide grooves, a ridge waveguide is formed between the two waveguide grooves, and the ridge waveguide extends along a first direction of the quantum cascade laser chip, the first direction being the extension direction of the chip cavity length, that is, the light emitting direction;

[0010] The waveguide groove is in a hyperbolic shape, and the ridge waveguide is in a cylindrical shape that is narrow in the middle and wide at both ends in the first direction; the waveguide groove is etched to the upper part of the N-type GaInAs lower confinement layer, and is prepared by completely removing the N-type highly doped InP ohmic contact layer, the N-type InP upper waveguide layer, the N-type GaInAs upper confinement layer, the multi-period active area structure and part of the N-type GaInAs lower confinement layer; the bottom and sidewall areas of the waveguide groove are processed by mechanical chemical grinding, and InP:Fe is filled, and the InP:Fe filled area is mechanically chemically ground again, and then the insulating film layer material is evaporated;

[0011] An electric injection region is arranged on the ridge waveguide, the electric injection region extends along a first direction of the chip, and is formed on the N-type highly doped InP ohmic contact layer.

[0012] Preferably, the center of the single chip is the origin, the first direction of the chip is the x-axis, the second direction of the chip is the y-axis, and a coordinate system is established, wherein the second direction of the chip is perpendicular to the extension direction of the chip cavity length; the waveguide groove follows the equation: The units of the x-axis and y-axis are μm, and a and b are constants.

[0013] Preferably, the chip cavity length is 6000 μm, and the x value at the maximum width of the ridge waveguide groove along the second direction corresponding to y=3000 μm is twice the absolute value, that is, 2|x|; the x value at the minimum width of the waveguide groove along the second direction corresponding to y=0 μm is twice the absolute value, that is, 2|x|, at which time the waveguide groove width is

[0014] Preferably, the minimum value of the waveguide groove width ridge waveguide width is 40 μm, that is, a=50, at which time the ridge waveguide width is the maximum, which is 10 μm. Only by adjusting the value of b, the opening degree and the maximum width of the arc in the waveguide groove hyperbola are adjusted, thereby adjusting the shape of the cylindrical ridge waveguide. When the minimum width of the cylindrical ridge waveguide along the second direction is y=3000 μm, 50-|2x|.

[0015] Preferably, an upper electrode metal layer is deposited above the insulating film layer and the N-type highly doped InP ohmic contact layer; and a lower electrode metal layer is provided below the N-type InP substrate.

[0016] Preferably, the electrical injection region is rectangular in shape and has a width of 0.5 μm.

[0017] Preferably, the insulating film layer is made of SiO2 and has a thickness of 300 nm.

[0018] Preferably, the thickness of the N-type highly doped InP ohmic contact layer is 500 nm.

[0019] Preferably, the upper electrode metal layer is a Ti / Au metal layer with a thickness of 40 / 250 nm; the lower electrode metal layer is an Au metal layer with a thickness of 4 μm.

[0020] A method for preparing the above-mentioned quantum cascade laser with a barrel-shaped waveguide comprises the following steps:

[0021] (1) epitaxially depositing an N-type InP buffer layer, an N-type InP lower waveguide layer, an N-type GaInAs lower confinement layer, a multi-period active region structure, an N-type GaInAs upper confinement layer, an N-type InP upper waveguide layer and an N-type highly doped InP ohmic contact layer on an N-type InP substrate in sequence by using a MOCVD process to form a stacked structure;

[0022] (2) The stacked structure is patterned, and the N-type InP lower waveguide layer is wet-etched to form a hyperbolic waveguide groove, and a barrel-shaped ridge waveguide structure is formed through the waveguide groove, and a ridge waveguide is formed between the two waveguide grooves;

[0023] (3) First, evaporate a 100nm SiO2 thin film layer on the surface of the ridge waveguide, and then evaporate a 200nm Cr metal layer;

[0024] (4) Mechanical chemical grinding of the wafer, the polishing liquid used is SiO2 with an average particle size of 4nm, and the polishing film layer needs to be made of ultra-flexible materials such as felt, woolen cloth, velvet, etc.; during grinding, the Cr metal layer can protect the ridge waveguide from being damaged, and the waveguide groove that has been wet-etched is polished to reduce its roughness;

[0025] (5) Using a wet etching method, a diluted nitric acid solution is used to remove the Cr metal layer on the surface of the ridge waveguide, and the remaining SiO2 insulating film layer is used to protect the ridge waveguide during the secondary epitaxy. Subsequently, the wafer is subjected to secondary epitaxy, and semi-insulating InP:Fe is selectively epitaxially grown on both sides of the ridge waveguide. Finally, the SiO2 film layer is removed using a HF:NH4F:H2O=3:6:9 solution.

[0026] (6) performing mechanical chemical grinding on the wafer after secondary epitaxy to grind to an N-type highly doped InP ohmic contact layer;

[0027] (7) A SiO2 insulating thin film layer is evaporated on the surface of the chip, and a current injection window is opened on the thin film layer of the ridge waveguide. Then, the Ti / Au (40 / 250nm) upper electrode metal layer is uniformly evaporated on the chip surface using electron beam evaporation technology (the part entering the current injection window during the Ti / Au evaporation forms an electric injection zone, and the electric injection zone is made of the same material as the upper electrode metal layer). The Ti layer is a wetting layer, which allows Au to better contact with the surface of the semiconductor sample.

[0028] (8) The chip thickness is thinned and a 4 μm lower electrode Au metal layer is deposited under the substrate.

[0029] Anything not described or limited in the above technical solution shall be carried out with reference to the prior art.

[0030] The beneficial effects of the present invention are:

[0031] The present invention provides a novel cylindrical waveguide structure. Compared with the traditional rectangular waveguide, by regulating the curvature of the waveguide side wall along the second direction of the ridge waveguide, the probability of photons leaking to the outside of the waveguide can be effectively controlled, the wandering time of photons in the optical cavity can be increased, and the photon density in the optical cavity can be improved. The increase in photon density can further reduce the threshold current density of the chip. In addition, the design of the cylindrical ridge waveguide is more conducive to the heat dissipation of the chip in the continuous wave mode, reduces the optical absorption of free electrons, reduces the optical power loss, thereby increasing the output power of photons and increasing the stability and reliability of the chip. In addition, it is well known that when light is transmitted in a waveguide, reflection occurs at the interface of the waveguide due to the different refractive indices of the medium. The present invention adopts a cylindrical ridge waveguide structure, and the wall surface of the waveguide has a large curvature, which helps to increase the number of reflections of photons, so that light can be transmitted over long distances in the waveguide, and increases the probability of interaction between photons and excitons, thereby improving the electro-optical conversion efficiency. Furthermore, light waves in the waveguide structure will experience interference effects during propagation, resulting in interference enhancement or suppression of the light field. By adjusting the side wall curvature of the cylindrical waveguide, the lateral propagation of light waves can be effectively controlled, thereby affecting the mode distribution of light and realizing multi-transverse mode controllable output of QCL.

[0032] In addition, by introducing mechanical chemical grinding before the secondary epitaxial semi-insulating InP:Fe, the rough hyperbolic waveguide groove can be surface polished, greatly reducing the photon absorption at the contact interface between the chip main structure and InP:Fe, thereby reducing the scattering loss of the waveguide, and further enabling the photons to obtain greater gain in the optical cavity. The increase in gain further optimizes the output characteristics of the chip, including reducing the threshold current density, increasing the output power and slope efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0034] Figure 1 A top view of the stacked structure after wet etching to the N-type InP lower waveguide layer in step (2) of the present invention and a front view along the first direction;

[0035] Figure 2 A top view and a front view along the first direction of the stacked structure after evaporating SiO2 and Cr layers in step (3) of the present invention;

[0036] Figure 3 It is a front view of the stacked structure along the first direction after the double grooves are mechanically and chemically polished in step (4) of the present invention;

[0037] Figure 4This is a front view of the stacked structure along the first direction after the semi-insulating InP:Fe is selectively epitaxially grown on both sides of the ridge waveguide in step (5) of the present invention;

[0038] Figure 5 The wafer after secondary epitaxy is subjected to mechanical chemical grinding in step (6) of the present invention, and a main view of the stacked structure along the first direction after grinding to the N-type highly doped InP ohmic contact layer;

[0039] Figure 6 It is a schematic diagram of the complete chip structure of the present invention;

[0040] Figure 7 is a flow chart of the method of the present invention;

[0041] Figure 8 It is a performance comparison chart of Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2.

[0042] In the figure: 1-N-type InP substrate, 2-N-type InP buffer layer, 3-N-type InP lower waveguide layer, 4-N-type GaInAs lower confinement layer, 5-multi-period active area structure, 6-N-type GaInAs upper confinement layer, 7-N-type InP upper waveguide layer, 8-N-type highly doped InP ohmic contact layer, 9-ridge waveguide, 10-waveguide groove, 11-Cr metal layer, 12-SiO2 thin film layer, 13-upper electrode metal layer, 14-electric injection region, 15-lower electrode metal layer. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described, but not limited to this. Anything not fully described in the present invention shall be based on conventional techniques in the art.

[0044] Example 1

[0045] A quantum cascade laser with a barrel-shaped waveguide, such as Figure 1 ~such as Figure 6 As shown, the stacked structure includes, from bottom to top, an N-type InP substrate 1, an N-type InP buffer layer 2, an N-type InP lower waveguide layer 3, an N-type GaInAs lower confinement layer 4, a multi-period active region structure 5, an N-type GaInAs upper confinement layer 6, an N-type InP upper waveguide layer 7, and an N-type highly doped InP ohmic contact layer 8;

[0046] The stacked structure is provided with two waveguide grooves 10, and a ridge waveguide 9 is formed between the two waveguide grooves. The ridge waveguide 9 extends along a first direction of the quantum cascade laser chip, and the first direction is the extension direction of the chip cavity length, that is, the light emitting direction;

[0047] The waveguide groove 10 is in a hyperbolic shape, and the ridge waveguide 9 is in a cylindrical shape with a narrow middle and wide ends in the first direction; the waveguide groove 10 is etched to the upper part of the N-type GaInAs lower confinement layer, and is prepared by completely removing the N-type highly doped InP ohmic contact layer, the N-type InP upper waveguide layer, the N-type GaInAs upper confinement layer, the multi-period active area structure and part of the N-type GaInAs lower confinement layer; the bottom and sidewall areas of the waveguide groove are processed by mechanical chemical grinding, and filled with InP:Fe, and the InP:Fe filled area is mechanically chemically ground again, and then the insulating film layer material is evaporated;

[0048] An electric injection region 14 is disposed on the ridge waveguide 9 . The electric injection region 14 extends along a first direction of the chip and is formed on the N-type highly doped InP ohmic contact layer.

[0049] The center of the single chip is the origin, the first direction of the chip is the x-axis, and the second direction of the chip is the y-axis. A coordinate system is established, wherein the second direction of the chip is perpendicular to the extension direction of the chip cavity length; the waveguide groove follows the equation: The units of the x-axis and y-axis are μm, and a and b are constants.

[0050] The chip cavity length is 6000 μm. When the width of the ridge waveguide groove is the largest along the second direction, the value of x is twice the absolute value when y=3000 μm, that is, 2|x|; when the width of the waveguide groove is the smallest along the second direction, the value of x is twice the absolute value when y=0 μm, that is, 2|x|. At this time, the width of the waveguide groove is

[0051] The minimum value of the ridge waveguide width of the waveguide slot 10 is 40 μm, that is, a=50. At this time, the width of the ridge waveguide 9 is the maximum, which is 10 μm.

[0052] The maximum width of the waveguide slot 10 along the second direction is 44 μm, and at this time, b=5500000;

[0053] The ridge waveguide is determined by the size of the hyperbolic waveguide groove, and the minimum width along the second direction is 6 μm.

[0054] An upper electrode metal layer 13 is deposited above the insulating film layer and the N-type highly doped InP ohmic contact layer; and a lower electrode metal layer 15 is disposed below the N-type InP substrate.

[0055] The electrical injection region is rectangular in shape and has a width of 0.5 μm.

[0056] The insulating film layer material is SiO2, and the thickness is 300nm.

[0057] The thickness of the N-type highly doped InP ohmic contact layer is 500nm.

[0058] The upper electrode metal layer is a Ti / Au metal layer with a thickness of 40 / 250 nm; the lower electrode metal layer is an Au metal layer with a thickness of 4 μm.

[0059] Example 2

[0060] A quantum cascade laser with a cylindrical waveguide, as described in Example 1, except that the maximum width of the waveguide groove 10 along the second direction is 42 μm, in which case b=11000000;

[0061] The ridge waveguide 9 is determined by the size of the hyperbolic waveguide groove, and the minimum width along the second direction is 8 μm.

[0062] Example 3

[0063] A quantum cascade laser with a barrel-shaped waveguide, as described in Example 1, except that the maximum width of the waveguide groove 10 along the second direction is 41 μm, in which case b=22000000;

[0064] The ridge waveguide 9 is determined by the size of the hyperbolic waveguide groove, and the minimum width along the second direction is 9 μm.

[0065] Embodiment 4:

[0066] A method for preparing a quantum cascade laser having a barrel-shaped waveguide, such as Figure 7 As shown, the following steps are included:

[0067] (1) epitaxially depositing an N-type InP buffer layer 2, an N-type InP lower waveguide layer 3, an N-type GaInAs lower confinement layer 4, a multi-period active region structure 5, an N-type GaInAs upper confinement layer 6, an N-type InP upper waveguide layer 7 and an N-type highly doped InP ohmic contact layer 8 on an N-type InP substrate 1 in sequence by using a MOCVD process to form a stacked structure;

[0068] (2) The stacked structure is patterned, and the N-type InP lower waveguide layer is wet-etched to form a hyperbolic waveguide groove, and a barrel-shaped ridge waveguide structure is formed through the waveguide groove, and a ridge waveguide is formed between the two waveguide grooves;

[0069] (3) First, a 100nm thick SiO2 thin film layer 12 is evaporated on the surface of the ridge waveguide, and then a 200nm thick Cr metal layer 11 is evaporated;

[0070] (4) Mechanical chemical grinding of the wafer, the polishing liquid used is SiO2 with an average particle size of 4nm, and the polishing film layer needs to be made of ultra-flexible materials such as felt, woolen cloth, velvet, etc.; during grinding, the Cr metal layer can protect the ridge waveguide from being damaged, and the waveguide groove that has been wet-etched is polished to reduce its roughness;

[0071] (5) Using a wet etching method, the Cr metal layer 11 on the surface of the ridge waveguide is removed with a diluted nitric acid solution, and the remaining SiO2 insulating film layer is used to protect the ridge waveguide during the secondary epitaxy; then the wafer is subjected to secondary epitaxy, and semi-insulating InP:Fe is selectively epitaxially grown on both sides of the ridge waveguide, and finally the SiO2 film layer is removed with a HF:NH4F:H2O=3:6:9 solution;

[0072] (6) performing mechanical chemical grinding on the wafer after the secondary epitaxy to grind to an N-type highly doped InP ohmic contact layer;

[0073] (7) A SiO2 insulating thin film layer is evaporated on the surface of the chip, and a current injection window is opened on the thin film layer of the ridge waveguide. Then, the Ti / Au (40 / 250nm) upper electrode metal layer is uniformly evaporated on the chip surface using electron beam evaporation technology (the part entering the current injection window during the Ti / Au evaporation forms an electric injection zone, and the electric injection zone is made of the same material as the upper electrode metal layer). The Ti layer is a wetting layer, which allows Au to better contact with the surface of the semiconductor sample.

[0074] (8) The chip thickness is thinned and a 4 μm lower electrode Au metal layer is deposited under the substrate.

[0075] Comparative Example 1

[0076] A quantum cascade laser, as described in Example 1, except that the ridge waveguide uses a traditional rectangular waveguide.

[0077] Comparative Example 2

[0078] A quantum cascade laser with a barrel-shaped waveguide is as described in Example 1, except that the waveguide groove is not subjected to mechanochemical grinding before secondary epitaxial InP:Fe filling.

[0079] The performance of Example 1, Example 2, Example 3 and Comparative Example 1 was compared under the same conditions. Figure 8 As shown (the Chinese characters corresponding to the horizontal and vertical axes are current and output power, respectively). Compared with comparative example 1, the output power and slope efficiency of Example 1, Example 2 and Example 3 are relatively high, and the threshold current density is relatively low, indicating that the introduction of the barrel-shaped waveguide significantly improves the performance of the chip; compared with Example 1 and Example 3, the power of Example 2 is relatively high, and the threshold current density is relatively low, indicating that the size of the barrel-shaped waveguide has an effect on the photon density. Preferably, when the minimum width of the barrel-shaped waveguide along the second direction is 8μm, the performance of the chip is more significantly improved. The performance of Example 2 and Comparative Example 2 is compared with that under the same conditions, as shown in FIG. Figure 8Compared with comparative example 2, the output power and slope efficiency of example 2 are relatively high, indicating that mechanochemical grinding of the hyperbolic waveguide groove before secondary epitaxial InP:Fe filling is helpful to reduce waveguide transmission loss.

[0080] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A quantum cascade laser having a barrel-shaped waveguide, characterized in that: The invention comprises a stacked structure, wherein the stacked structure comprises, from bottom to top, an N-type InP substrate, an N-type InP buffer layer, an N-type InP lower waveguide layer, an N-type GaInAs lower confinement layer, a multi-period active region structure, an N-type GaInAs upper confinement layer, an N-type InP upper waveguide layer and an N-type highly doped InP ohmic contact layer; The stacked structure is provided with two waveguide grooves, a ridge waveguide is formed between the two waveguide grooves, and the ridge waveguide extends along a first direction of the quantum cascade laser chip, the first direction being the extension direction of the chip cavity length, that is, the light emitting direction; The waveguide groove is in a hyperbolic shape, and the ridge waveguide is in a cylindrical shape that is narrow in the middle and wide at both ends in the first direction; the waveguide groove is etched to the upper part of the N-type GaInAs lower confinement layer, and is prepared by completely removing the N-type highly doped InP ohmic contact layer, the N-type InP upper waveguide layer, the N-type GaInAs upper confinement layer, the multi-period active area structure and part of the N-type GaInAs lower confinement layer; the bottom and sidewall areas of the waveguide groove are processed by mechanical chemical grinding, and InP:Fe is filled, and the InP:Fe filled area is mechanically chemically ground again, and then the insulating film layer material is evaporated; An electric injection region is arranged on the ridge waveguide, the electric injection region extends along a first direction of the chip, and is formed on the N-type highly doped InP ohmic contact layer.

2. The quantum cascade laser with a barrel-shaped waveguide according to claim 1, characterized in that: The center of the single chip is the origin, the first direction of the chip is the x-axis, and the second direction of the chip is the y-axis. A coordinate system is established, wherein the second direction of the chip is perpendicular to the extension direction of the chip cavity length; the waveguide groove follows the equation: The units of the x-axis and y-axis are μm, and a and b are constants.

3. The quantum cascade laser with a barrel-shaped waveguide according to claim 2, characterized in that: The chip cavity length is 6000 μm. When the width of the ridge waveguide groove is the largest along the second direction, the value of x is twice the absolute value when y=3000 μm, that is, 2|x|; when the width of the waveguide groove is the smallest along the second direction, the value of x is twice the absolute value when y=0 μm, that is, 2|x|. At this time, the width of the waveguide groove is 4. The quantum cascade laser with a barrel-shaped waveguide according to claim 3, characterized in that: The minimum value of the waveguide groove width ridge waveguide width is 40 μm, that is, a=50, at which time the ridge waveguide width is the maximum, which is 10 μm.

5. The quantum cascade laser with a barrel-shaped waveguide according to claim 4, characterized in that: An upper electrode metal layer is deposited above the insulating film layer and the N-type highly doped InP ohmic contact layer; and a lower electrode metal layer is arranged below the N-type InP substrate.

6. The quantum cascade laser with a barrel-shaped waveguide according to claim 5, characterized in that: The electrical injection region is rectangular in shape and has a width of 0.5 μm.

7. The quantum cascade laser with a barrel-shaped waveguide according to claim 6, characterized in that: The insulating film layer material is SiO2, and the thickness is 300nm.

8. The quantum cascade laser with a barrel-shaped waveguide according to claim 7, characterized in that: The thickness of the N-type highly doped InP ohmic contact layer is 500 nm.

9. The quantum cascade laser with a barrel-shaped waveguide according to claim 8, characterized in that The upper electrode metal layer is a Ti / Au metal layer with a thickness of 40 / 250 nm; the lower electrode metal layer is an Au metal layer with a thickness of 4 μm.

10. A method for preparing a quantum cascade laser having a barrel-shaped waveguide according to claim 9, characterized in that: The steps include: (1) epitaxially depositing an N-type InP buffer layer, an N-type InP lower waveguide layer, an N-type GaInAs lower confinement layer, a multi-period active region structure, an N-type GaInAs upper confinement layer, an N-type InP upper waveguide layer and an N-type highly doped InP ohmic contact layer on an N-type InP substrate in sequence by using a MOCVD process to form a stacked structure; (2) The stacked structure is patterned, and the N-type InP lower waveguide layer is wet-etched to form a hyperbolic waveguide groove, and a barrel-shaped ridge waveguide structure is formed through the waveguide groove, and a ridge waveguide is formed between the two waveguide grooves; (3) First, evaporate a 100nm SiO2 thin film layer on the surface of the ridge waveguide, and then evaporate a 200nm Cr metal layer; (4) Mechanical chemical grinding of the wafer, the polishing liquid used is SiO2 with an average particle size of 4 nm, and the polishing film layer is made of ultra-flexible material; (5) Using a wet etching method, a diluted nitric acid solution is used to remove the Cr metal layer on the surface of the ridge waveguide, and the remaining SiO2 insulating film layer is used to protect the ridge waveguide during the secondary epitaxy. Subsequently, the wafer is subjected to secondary epitaxy, and semi-insulating InP:Fe is selectively epitaxially grown on both sides of the ridge waveguide. Finally, the SiO2 film layer is removed using a HF:NH4F:H2O=3:6:9 solution. (6) performing mechanical chemical grinding on the wafer after the secondary epitaxy to grind to an N-type highly doped InP ohmic contact layer; (7) Evaporating a SiO2 insulating thin film layer on the surface of the wafer, and opening a current injection window on the thin film layer of the ridge waveguide, and then using electron beam evaporation technology to uniformly evaporate a Ti / Au upper electrode metal layer on the chip surface; (8) The chip thickness is thinned and a 4 μm lower electrode Au metal layer is deposited under the substrate.

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