Semiconductor laser and method for manufacturing the same

Abstract

The application provides a semiconductor laser and a preparation method thereof. The semiconductor laser comprises a substrate, a germanium waveguide layer and a germanium-tin epitaxial structure which are arranged in layers. The side of the germanium waveguide layer away from the substrate comprises a second waveguide part and a third waveguide part which are connected to each other. The width of the second waveguide part gradually decreases from the side close to the third waveguide part to the side away from the third waveguide part. The germanium-tin epitaxial structure is formed on the third waveguide part, and a Bragg grating is arranged on the third waveguide part. The mass fraction of Sn component in the active layer of the germanium-tin epitaxial structure is controlled to be between 9% and 13% so that the germanium-tin epitaxial structure can output infrared light of a preset wavelength when being electrically excited. The Bragg grating reflects and oscillates the light as a resonant cavity, and then couples the light into the second waveguide part, thereby realizing single-longitudinal-mode stable light output of the semiconductor laser. Finally, the infrared light output by the single-longitudinal-mode is shaped by the second waveguide part with a gradually changing width, thereby improving the coupling efficiency of the infrared light and the external optical fiber.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor lasers, and particularly relates to a semiconductor laser and a preparation method thereof. BACKGROUND

[0002] Silicon-based optoelectronic integration technology is a technology of integrating photonic components and electronic devices on a silicon-based substrate. The technology realizes wafer-level integration of lasers, modulators, detectors, waveguides, couplers and other passive optical components and electronic devices by using the infrastructure of CMOS process. The technology originated in the mid-1980s and has developed rapidly by drawing on electronic industry technology. Due to its compatibility with CMOS process, the technology has become the best choice for mass production of photonic integrated circuits at low cost, and is leading the development of chip technology in the post-Moore era. With the rapid development of 5G networks, data centers, artificial intelligence and other technologies, the demand for high-performance lasers is increasing in the field of optoelectronic integration. A major bottleneck of monolithic silicon photonic integrated circuits is the lack of CMOS-compatible lasers.

[0003] Although III-V lasers are widely used in optoelectronic integration, their non-compatible process with CMOS leads to complex integration and high manufacturing cost on silicon chips. Methods for integrating III-V lasers with passive devices include wafer bonding, flip-chip soldering and micro-transfer printing, and problems such as thermal mismatch, low alignment accuracy and poor integration need to be solved. The complex manufacturing process results in low yield and high cost. As a new type of group IV semiconductor material, GeSn has successfully prepared an electrically pumped infrared laser, but there is no on-chip coupling scheme for GeSn lasers and silicon waveguides.

[0004] Therefore, how to provide a new semiconductor laser and a preparation method thereof, which can reduce the manufacturing cost and integration difficulty of the semiconductor laser and improve the laser output coupling efficiency, has become one of the technical problems to be solved by those skilled in the art. SUMMARY

[0005] The present application aims to at least partly solve one of the technical problems in the related art.

[0006] To this end, the present application aims to provide a semiconductor laser and a preparation method thereof, which can reduce the manufacturing cost and integration difficulty of the semiconductor laser and improve the laser output coupling efficiency.

[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a semiconductor laser, comprising:

[0008] a substrate;

[0009] A germanium waveguide layer includes a first waveguide section on the substrate, and a second waveguide section and a third waveguide section on the first waveguide section, the second waveguide section and the third waveguide section are connected to each other, the width of the second waveguide section gradually decreases from the side close to the third waveguide section to the side away from the third waveguide section; the third waveguide section is formed with a Bragg grating on the side away from the substrate;

[0010] A germanium tin epitaxial structure is on the third waveguide section and covers the Bragg grating; the germanium tin epitaxial structure includes a lower cladding layer, an upper cladding layer, and an active layer between the two, the mass fraction of Sn component in the active layer is between 9% and 13%.

[0011] Optionally, the Bragg grating includes a plurality of grooves formed on the side of the third waveguide section away from the substrate, and a SiO2 filling layer filled in each of the grooves.

[0012] Optionally, the duty cycle of the Bragg grating is between 45% and 60%.

[0013] Optionally, the active layer includes a GeSn material layer or a multi-quantum well structure composed of a GeSn / SiGeSn periodic layer stack.

[0014] Optionally, the Bragg grating is a λ / 4 phase shift Bragg grating.

[0015] Optionally, the germanium tin epitaxial structure further includes an N-type contact layer and a P-type contact layer, the N-type contact layer is on the third waveguide section and completely covers the surface of the third waveguide layer away from the substrate, and the lower cladding layer is on the N-type contact layer; the P-type contact layer is on the upper cladding layer and completely covers the surface of the upper cladding layer away from the active layer.

[0016] Optionally, the N-type contact layer includes an N-type heavily doped SiGeSn material layer, the P-type contact layer includes a P-type heavily doped SiGeSn material layer; the lower cladding layer and the upper cladding layer include an undoped intrinsic SiGeSn material layer.

[0017] Optionally, the semiconductor laser further includes a first electrode and a second electrode, the first electrode is formed on the N-type contact layer and is spaced apart from the stack composed of the lower cladding layer, the active layer and the upper cladding layer; the second electrode is formed on the P-type contact layer.

[0018] Optionally, the germanium tin epitaxial structure is used to excite infrared light with an output wavelength range between 2 μm and 3 μm.

[0019] The first aspect embodiment of the present application provides a preparation method of a semiconductor laser, which is used for preparing the semiconductor laser described in any one of the above aspects, and the method comprises the following steps:

[0020] providing a substrate;

[0021] forming a germanium epitaxial layer on the substrate, the germanium epitaxial layer comprising a first waveguide part located on the substrate, and a second waveguide part and a third waveguide part located on the first waveguide part;

[0022] etching a plurality of equidistant grooves on the third waveguide part, and filling SiO2 in the grooves to form a Bragg grating on a side of the third waveguide part away from the substrate;

[0023] forming a germanium-tin epitaxial structure on the third waveguide part, the germanium-tin epitaxial structure comprising an N-type contact layer, a lower cladding layer, an active layer, an upper cladding layer and a P-type contact layer which are stacked on one side;

[0024] forming a first electrode and a second electrode on the germanium-tin epitaxial structure, the first electrode being formed on the N-type contact layer and spaced apart from the lower cladding layer, and the second electrode being formed on the P-type contact layer.

[0025] The semiconductor laser and the preparation method thereof provided by the present application at least have the following beneficial effects:

[0026] The present application provides a semiconductor laser and a preparation method thereof, which comprises a substrate, a germanium waveguide layer and a germanium-tin epitaxial structure which are arranged in a stack, the side of the germanium waveguide layer away from the substrate comprises a second waveguide part and a third waveguide part which are connected to each other, the width of the second waveguide part gradually decreases from the side close to the third waveguide part to the side away from the third waveguide part, the germanium-tin epitaxial structure is formed on the third waveguide part, and the third waveguide part is provided with a Bragg grating. By controlling the mass fraction of Sn component in the active layer of the germanium-tin epitaxial structure to be between 9% and 13%, the germanium-tin epitaxial structure can output infrared light of a preset wavelength when being electrically excited, the Bragg grating reflects and oscillates the light as a resonant cavity, and then the light is coupled into the second waveguide part, thereby realizing single-longitudinal-mode stable light output of the semiconductor laser, and finally the infrared light output by the single-longitudinal-mode is beam-shaped by the second waveguide part with gradually changing width, thereby improving the coupling efficiency of the infrared light and the external optical fiber.

[0027] Additional aspects and advantages of the present application will be made apparent from the following description, which, taken in conjunction with the accompanying drawings, which are shown by way of illustration, not limitation. BRIEF DESCRIPTION OF DRAWINGS

[0028] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which:

[0029] Figure 1 A structure schematic diagram of a semiconductor semiconductor laser according to an embodiment of the present application.

[0030] Figures 2 to 6 A preparation flow structure schematic diagram of a semiconductor semiconductor laser according to an embodiment of the present application. Figure 1 A preparation flow structure schematic diagram of a semiconductor semiconductor laser according to an embodiment of the present application.

[0031] Figure 7 A preparation flow structure schematic diagram of a semiconductor semiconductor laser according to an embodiment of the present application.

[0032] 110 substrate; 120 germanium waveguide layer; 121 first waveguide part; 122 second waveguide part; 123 third waveguide part; 124 Bragg grating; 130 germanium tin epitaxial structure; 131 N-type contact layer; 132 lower cladding layer; 133 active layer; 134 upper cladding layer; 135 P-type contact layer; 141 first electrode; 142 second electrode. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described below in detail, examples of which are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary, and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0034] The four-group material germanium (Ge) is an indirect bandgap structure, and the indirect bandgap structure of the laser can be converted into a direct bandgap structure by various means, for example, applying biaxial tensile strain to the germanium, or forming an alloy of germanium and tin elements, and the basic structure of the laser can be realized through the combination of the two. However, the existing GeSn bar-shaped laser is a common F-P cavity resonant edge-emitting laser, and the quality and efficiency of light emission need to be improved.

[0035] Based on the above problems, the embodiments of the present application provide a semiconductor laser and a preparation method thereof, by providing a germanium tin epitaxial structure, and regulating the mass fraction of the Sn component of the active layer in the germanium tin epitaxial structure, to convert the GeSn material in the active layer from an indirect bandgap to a direct bandgap, and at the same time, a germanium waveguide layer is added, to perform light reflection resonance and light emission coupling, thereby realizing the high emission efficiency requirement and wavelength coverage requirement of the laser.

[0036] According to an aspect of the present application, a semiconductor laser is provided, as shown in the figure, which includes a substrate 110, a germanium waveguide layer 120 formed on the substrate 110, and a germanium tin epitaxial structure 130 formed on the germanium waveguide layer 120. Figure 1

[0037] ​The germanium waveguide layer 120 includes a first waveguide part 121 located on the substrate 110, and a second waveguide part 122 and a third waveguide part 123 located on the first waveguide part 121. The second waveguide part 122 and the third waveguide part 123 are connected to each other, and the width of the second waveguide part 122 gradually decreases from the side close to the third waveguide part 123 to the side away from the third waveguide part 123; and the side of the third waveguide part away from the substrate 110 is formed with a Bragg grating 124.

[0038] A germanium tin epitaxial structure 130 is located on the third waveguide part 123 and covers the Bragg grating 124; the germanium tin epitaxial structure 130 includes a lower cladding layer 132, an upper cladding layer 134, and an active layer 133 located therebetween, and the mass fraction of Sn component in the active layer 133 is between 9% and 13%.

[0039] It can be understood that when the content of Sn component in the germanium tin material exceeds a certain proportion (about 8%), the germanium tin material will change from an indirect band gap to a direct band gap, which meets the band requirement of laser. The mass fraction of Sn component in the active layer 133 in the present application is between 9% and 13%, so that the material of the active layer 133 is a direct band gap material, which can be excited to output infrared light outward, and the wavelength range of the infrared light output outward is between 2 μm and 3 μm.

[0040] Since the germanium tin epitaxial structure 130 is epitaxially formed on the third waveguide layer, the infrared light excited and generated by the germanium tin epitaxial structure 130 can be coupled by the third waveguide part 123, and then output outward through the second waveguide part 122, thereby realizing on-chip coupling and infrared light output of the group IV laser.

[0041] Since the third waveguide part 123 is further formed with the Bragg grating 124 on the side away from the substrate 110, and the germanium tin epitaxial structure 130 is formed on the third waveguide part 123 and covers the Bragg grating 124, when the infrared light excited and output by the germanium tin epitaxial structure 130 is coupled to the third waveguide part 123, the infrared light will be reflected and oscillated in the grating structure periodically arranged in the Bragg grating 124, thereby realizing the effect of a resonant cavity, and further realizing the infrared light output outward by the second waveguide part 122 with strong feedback and threshold gain. At the same time, the Bragg grating 124 can realize longitudinal mode selection, reduce the relative intensity noise introduced by longitudinal mode competition, and realize stable light output in a single longitudinal mode.

[0042] Since the width of the second waveguide part 122 gradually decreases from the side close to the third waveguide part 123 to the side away from the third waveguide part 123, the cross-sectional structure of the second waveguide part 122 is tapered. Therefore, after the infrared light output by the third waveguide part 123 is incident on the second waveguide part 122 with a tapered cross section, the light beam will be gradually shaped and converged along the direction of propagation of the infrared light, thereby improving the coupling efficiency of the infrared light output by the laser and the optical fiber.

[0043] As an example, the Bragg grating 124 can be composed of a plurality of periodically arranged grooves formed on the side of the third waveguide section 123 away from the substrate 110, a germanium waveguide layer 120 between the grooves, and a SiO2layer filled in the grooves. Due to the different refractive indices between the SiO2and the germanium waveguide layer 120, the infrared light will repeatedly reflect and oscillate in the Bragg grating 124 after being coupled into the third waveguide section 123.

[0044] Since the diffraction period A, the Bragg wavelength λ b The effective refractive index n eff of the Bragg grating 124 satisfy A = λ b / 2n eff , the grating period, the grating depth, and the duty cycle of the Bragg grating 124 will have different degrees of influence on the coupling coefficient of the third coupling section, and the Bragg grating 124 has the maximum reflectivity at the Bragg wavelength λ b . Therefore, by controlling the duty cycle of the Bragg grating 124 and making it between 45% and 60%, the coupling efficiency of the infrared light excited by the germanium-tin epitaxial structure 130 on the third coupling section can be controlled to a certain extent. At the same time, increasing the etching depth of the groove corresponding to the grating will also increase the infrared light coupling efficiency of the third coupling section, but further increasing the groove depth will lead to the generation of a multimode. Therefore, in combination with the influence of the etching depth of the grating groove on the refractive index and reflectivity of the infrared light, the etching depth range of the grating groove should not be higher than 0.2 μm.

[0045] As an example, the Bragg grating 124 formed on the side of the third waveguide section 123 away from the substrate 110 is a first-order λ / 4 phase shift Bragg grating, and the grating period is 250 nm, the duty cycle is 50%, and the etching depth of the grating groove is 80 nm.

[0046] In some embodiments, the substrate 110, as the growth substrate of the germanium waveguide layer 120 and the germanium-tin epitaxial structure 130, can be made of a conductive material or an insulating material or a light-transmitting material with excellent heat conduction performance, such as any one of a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, a zinc oxide substrate, a silicon substrate, a gallium arsenide substrate, or a gallium phosphide substrate, wherein the silicon substrate is the preferred substrate material for the growth of the germanium waveguide layer 120 and the germanium-tin epitaxial structure 130.

[0047] The germanium-tin epitaxial structure 130 is the main laser emission body of the semiconductor laser, and the main material components are germanium and tin. Therefore, the germanium-tin epitaxial structure 130 is formed on the germanium waveguide layer 120 by the method of epitaxial deposition, which can further improve the epitaxial quality of the germanium-tin epitaxial structure 130 and reduce the internal defect density of the germanium-tin epitaxial structure 130. That is, the germanium waveguide layer 120 here can also play a role as a buffer layer, thereby reducing the problem of lattice mismatch between the germanium-tin epitaxial structure 130 and the substrate 110. The above-mentioned germanium waveguide layer 120 and germanium-tin epitaxial structure 130 are formed by selective epitaxy.

[0048] Specifically, the germanium-tin epitaxial structure 130 can include an N-type contact layer 131, a lower cladding layer 132, an active layer 133, an upper cladding layer 134, and a P-type contact layer 135, which are sequentially stacked from bottom to top. The N-type contact layer 131 is formed on the third waveguide layer and completely covers the surface of the third waveguide layer away from the substrate 110, used to contact the cathode of the electrode structure and provide a conductive channel for electron injection into the germanium-tin epitaxial structure 130. The P-type contact layer 135 is formed on the upper cladding layer 134, contacts the anode of the electrode structure, and provides a conductive channel for hole injection into the germanium-tin epitaxial structure 130. The lower cladding layer 132, the active layer 133, and the upper cladding layer 134 are sequentially stacked on the N-type contact layer 131, so that electrons and holes are injected into the active layer 133 of the germanium-tin epitaxial structure 130 from different directions, respectively, and recombine in the active layer 133 to radiate photons outward. The lower cladding layer 132 and the upper cladding layer 134 are arranged on both sides of the active layer 133, which not only keeps the active layer 133 apart from other semiconductor material layers, but also provides physical support and protection for the active layer 133 to some extent, and can limit the holes from passing through the lower cladding layer 132 into the N-type contact layer 131 and limit the electrons from passing through the upper cladding layer 134 into the P-type contact layer 135, thereby improving the recombination efficiency of electrons and holes in the active layer 133 and increasing the light emission efficiency of the laser.

[0049] As an example, the main formation material of the N-type contact layer 131 is an N-type doped SiGeSn material layer, the main formation material of the P-type contact is a P-type doped SiGeSn material layer, the main formation material of the lower cladding layer 132 is an intrinsic SiGeSn material layer or an N-type doped SiGeSn material layer; the main formation material of the upper cladding layer 134 is an intrinsic SiGeSn material layer or a P-type doped SiGeSn material layer, and the main formation material of the active layer 133 is a GeSn material layer or a multi-quantum well structure composed of periodically stacked GeSn / SiGeSn material layers.

[0050] Further, the GeSn epitaxial structure 130 also forms a first electrode 141 and a second electrode 142. The first electrode 141 is formed on the N-type contact layer 131 and is spaced apart from the lower cladding layer 132 also on the N-type contact layer 131. The first electrode 141 corresponds to the cathode of the semiconductor laser and is used to be connected to the negative output terminal of the external circuit and inject electrons into the GeSn epitaxial structure 130. The second electrode 142 is formed on the P-type contact layer 135 and corresponds to the anode of the semiconductor laser and is used to be connected to the positive output terminal of the external circuit and inject holes into the GeSn epitaxial structure 130.

[0051] The material of the first electrode 141 and the second electrode 142 includes a conductive metal material, including but not limited to chromium (Cr), titanium (Ti), tungsten (W), gold (Au), aluminum (Al), indium (In), tin (Sn), nickel (Ni), platinum (Pt), and the like, or an alloy of the above-mentioned materials.

[0052] According to a second aspect of the present application, a preparation method of a semiconductor laser is provided, as shown in the following. Figures 2 to 7 The method is used to prepare the semiconductor laser of any of the above-mentioned embodiments and can specifically include the following steps:

[0053] S1, providing a substrate 110;

[0054] S2, epitaxially forming a Ge epitaxial layer on the substrate 110, the Ge epitaxial layer including a first waveguide part 121 on the substrate 110, and a second waveguide part 122 and a third waveguide part 123 on the first waveguide part 121;

[0055] S3, etching a plurality of equidistant grooves on the third waveguide part 123 and filling SiO2 in the grooves to form a Bragg grating 124 on the side of the third waveguide part 123 away from the substrate 110;

[0056] S4, epitaxially forming a GeSn epitaxial structure 130 on the third waveguide part 123, the GeSn epitaxial structure 130 including an N-type contact layer 131, a lower cladding layer 132, an active layer 133, an upper cladding layer 134, and a P-type contact layer 135 stacked on one side, and the mass fraction of Sn in the active layer 133 is controlled to be between 9% and 13%;

[0057] S5, forming a first electrode 141 and a second electrode 142 on the GeSn epitaxial structure 130, the first electrode 141 being formed on the N-type contact layer 131 and being spaced apart from the lower cladding layer 132, and the second electrode 142 being formed on the P-type contact layer 135.

[0058] In step S2, the step of epitaxially forming the germanium epitaxial layer on the substrate 110 can specifically include the following steps: firstly, epitaxially forming a complete germanium tin epitaxial material layer on the substrate 110; and then, performing a dry or wet etching process on the surface of the germanium tin epitaxial material layer to obtain the first waveguide part 121 at the bottom, the second waveguide part 122 and the third waveguide part 123 connected to the first waveguide part 121, and the width of the second waveguide part 122 gradually decreasing from the side close to the third waveguide part 123 to the side away from the third waveguide part 123.

[0059] In step S3, as shown in Figure 3 and Figure 4 After the step of filling SiO2 in the groove, the step of etching the SiO2 covering the third waveguide layer by using an ICP dry etching process is further included to make the SiO2 exist only in each groove and expose the upper surface of the third waveguide layer.

[0060] It should be noted that the germanium waveguide layer 120 and the germanium tin epitaxial structure 130 can be epitaxially formed by a selective epitaxy method. The selective epitaxy method can include, but is not limited to, any one or a combination of multiple methods such as molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD).

[0061] In summary, the present application provides a semiconductor laser and a preparation method thereof. The semiconductor laser includes a substrate 110, a germanium waveguide layer 120 and a germanium tin epitaxial structure 130 arranged in layers. The side of the germanium waveguide layer 120 away from the substrate 110 includes a second waveguide part 122 and a third waveguide part 123 connected to each other. The width of the second waveguide part 122 gradually decreases from the side close to the third waveguide part 123 to the side away from the third waveguide part 123. The germanium tin epitaxial structure 130 is formed on the third waveguide part 123, and the third waveguide part 123 is provided with a Bragg grating 124. By controlling the mass fraction of Sn component in the active layer 133 of the germanium tin epitaxial structure 130 to be between 9% and 13%, the germanium tin epitaxial structure 130 can output infrared light of a preset wavelength when being electrically excited. The Bragg grating 124 reflects and oscillates the light as a resonant cavity, and then couples the light into the second waveguide part 122, thereby realizing single longitudinal mode stable light output of the semiconductor laser. Finally, the width-gradually-changing second waveguide part 122 is used to perform beam shaping output on the single longitudinal mode output infrared light, thereby improving the coupling efficiency of the infrared light and the external optical fiber.

[0062] In the foregoing detailed description, reference is made to the terms "one embodiment", "some embodiments", "an example", "a specific example" or "some examples" etc. which describe a particular feature, structure, material, or characteristic included in at least one embodiment or example of the application. The illustrative discussion of these terms are not intended to teach that there are any, notwithstanding the fact that the terms so refer to a particular embodiment or example. Moreover, these terms can be used interchangeably to signify that a particular feature, structure, material, or characteristic is included in at least one embodiment or example. Additionally, the description can use perspective-based adjectives such as "first", "second", "third", etc. to describe a particular name, characteristic, property, or the like, but these adjectives are used merely for description and do not imply or suggest any relative importance or an implied reference to the number of the indicated technical features. Thus, a feature defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "a plurality" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0063] Furthermore, the terms "first", "second", etc. are used herein only to describe various features, and do not imply or suggest relative importance or an implied reference to the number of the indicated technical features. Thus, a feature defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "a plurality" is at least two, for example, two, three, etc., unless otherwise specifically limited.

Claims

1. A semiconductor laser, characterized in that include: substrate; a germanium waveguide layer comprising a first waveguide portion located on the substrate, and a second waveguide portion and a third waveguide portion located on the first waveguide portion, wherein the second waveguide portion and the third waveguide portion are connected to each other, and the width of the second waveguide portion gradually decreases from a side close to the third waveguide portion to a side away from the third waveguide portion; a Bragg grating is formed on a side of the third waveguide away from the substrate; A germanium-tin epitaxial structure is located on the third waveguide portion and covers the Bragg grating; the germanium-tin epitaxial structure includes a lower cladding layer, an upper cladding layer and an active layer located therebetween, and the mass fraction of the Sn component in the active layer is between 9% and 13%.

2. The semiconductor laser according to claim 1, wherein The Bragg grating includes a plurality of grooves formed on a side of the third waveguide portion away from the substrate, and a SiO2 filling layer filled in each of the grooves.

3. The semiconductor laser according to claim 2, wherein The duty cycle of the Bragg grating is between 45% and 60%.

4. The semiconductor laser according to claim 1, wherein The Bragg grating is a λ / 4 phase-shifted Bragg grating.

5. The semiconductor laser according to claim 1, wherein The active layer includes a GeSn material layer or a multi-quantum well structure composed of GeSn / SiGeSn periodically stacked layers.

6. The semiconductor laser according to claim 1, wherein The germanium-tin epitaxial structure also includes an N-type contact layer and a P-type contact layer. The N-type contact layer is located on the third waveguide portion and completely covers the surface of the third waveguide portion away from the substrate. The lower cladding layer is located on the N-type contact layer; the P-type contact layer is located on the upper cladding layer and completely covers the surface of the upper cladding layer away from the active layer.

7. The semiconductor laser according to claim 6, characterized in that The N-type contact layer includes an N-type heavily doped SiGeSn material layer, and the P-type contact layer includes a P-type heavily doped SiGeSn material layer; the lower cladding layer and the upper cladding layer include undoped intrinsic SiGeSn material layers.

8. The semiconductor laser according to claim 6, wherein The semiconductor laser further includes a first electrode and a second electrode, wherein the first electrode is formed on the N-type contact layer and is spaced apart from the stack consisting of the lower cladding layer, the active layer and the upper cladding layer; and the second electrode is formed on the P-type contact layer.

9. The semiconductor laser according to claim 1, wherein The germanium-tin epitaxial structure is used to excite infrared light with an output wavelength ranging from 2 μm to 3 μm.

10. A method for preparing a semiconductor laser, for preparing the semiconductor laser according to any one of claims 1 to 9, characterized in that: The method comprises: providing a substrate; forming a germanium epitaxial layer on the substrate by epitaxial growth, wherein the germanium epitaxial layer includes a first waveguide portion located on the substrate, and a second waveguide portion and a third waveguide portion located on the first waveguide portion; Etching a plurality of grooves with equal spacing on the third waveguide portion, and filling the grooves with SiO2 to form a Bragg grating on a side of the third waveguide portion away from the substrate; forming a germanium-tin epitaxial structure on the third waveguide portion, wherein the germanium-tin epitaxial structure includes an N-type contact layer, a lower cladding layer, an active layer, an upper cladding layer, and a P-type contact layer stacked on one side; A first electrode and a second electrode are formed on the germanium-tin epitaxial structure, wherein the first electrode is formed on the N-type contact layer and is spaced apart from the lower cladding layer, and the second electrode is formed on the P-type contact layer.

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