Semiconductor laser and preparation method thereof

Abstract

The invention provides a semiconductor laser and a preparation method thereof, and the semiconductor laser comprises a substrate, a germanium waveguide layer and a germanium tin epitaxial structure which are stacked, and one side, far away from the substrate, of the germanium waveguide layer comprises a second waveguide part and a third waveguide part which are connected with each other. The width of the second waveguide part is gradually reduced from one side close to the third waveguide part to one side far 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 the Sn component in the active layer of the germanium-tin epitaxial structure is controlled to be 9%-13%, so that the germanium-tin epitaxial structure can output infrared light with a preset wavelength when being electrically excited, and the Bragg grating serves as a resonant cavity to reflect and oscillate the light and then is coupled into the second waveguide part, so that the wavelength of the infrared light is reduced. Single-longitudinal-mode stable light emitting of the semiconductor laser is achieved, finally, light beam shaping output is conducted on infrared light output by a single longitudinal mode through the second waveguide part with the gradually-changed width, and the coupling efficiency of the infrared light and an external optical fiber is improved.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor lasers, and in particular to a semiconductor laser and a method for preparing the same. Background Art

[0002] Silicon-based optoelectronic integration technology is a technology that integrates photonic components and electronic devices on a silicon-based substrate. It uses the infrastructure of the CMOS process to achieve wafer-level integration of lasers, modulators, detectors, waveguides, couplers and other passive optical components with electronic devices. This technology originated in the mid-1980s and has developed rapidly by drawing on the technology of the electronics industry. Due to its compatibility with the CMOS process, it 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 technologies such as 5G networks, data centers, and artificial intelligence, optoelectronic integration technology has an increasing demand for high-performance lasers. A major bottleneck of monolithic integrated silicon photonic circuits is the lack of CMOS-compatible lasers.

[0003] Although III-V lasers are currently widely used as light sources in the field of optoelectronic integration, their incompatible processes with CMOS have led to complex integration and high manufacturing costs in the silicon chip manufacturing chain. The methods for integrating III-V lasers with passive devices include wafer bonding, flip-chip welding, micro-transfer printing, etc., and at the same time, existing problems need to be solved, such as thermal mismatch, low alignment accuracy, poor integration, etc. The complex manufacturing process leads to low yield and high cost. GeSn, as a new type of IV semiconductor material, has successfully produced infrared band electrically pumped lasers, but there is currently no solution for on-chip coupling of GeSn lasers with silicon waveguides.

[0004] Therefore, how to provide a new semiconductor laser and its preparation method to 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 that technical personnel in this field need to solve urgently. Summary of the invention

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

[0006] To this end, the purpose of this application is to propose 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 embodiment of the present application proposes a semiconductor laser, comprising:

[0008] substrate;

[0009] 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;

[0010] A germanium-tin epitaxial structure is located on the third waveguide portion and covers the Bragg grating; the germanium-tin epitaxial structure comprises 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%.

[0011] Optionally, 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.

[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 consisting of periodically stacked GeSn / SiGeSn layers.

[0014] Optionally, the Bragg grating is a λ / 4 phase-shifted 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 located on the third waveguide portion and completely covers the surface of the third waveguide layer away from the substrate, and 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.

[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 undoped intrinsic SiGeSn material layers.

[0017] Optionally, 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.

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

[0019] In a first aspect, an embodiment of the present application provides a method for preparing a semiconductor laser, which is used to prepare any of the semiconductor lasers described above, and the method comprises:

[0020] providing a substrate;

[0021] epitaxially forming a germanium epitaxial layer on the substrate, 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;

[0022] 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;

[0023] epitaxially 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;

[0024] 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.

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

[0026] The present application provides a semiconductor laser and a preparation method thereof, comprising a stacked substrate, a germanium waveguide layer and a germanium tin epitaxial structure, wherein the side of the germanium waveguide layer away from the substrate comprises a second waveguide portion and a third waveguide portion connected to each other, the width of the second waveguide portion gradually decreases from the side close to the third waveguide portion to the side away from the third waveguide portion, the germanium tin epitaxial structure is formed on the third waveguide portion, and a Bragg grating is arranged on the third waveguide portion. By controlling the mass fraction of the 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 electrically excited, and the Bragg grating acts as a resonant cavity to reflect and oscillate the light, and then couples into the second waveguide portion, thereby realizing the single longitudinal mode stable light output of the semiconductor laser, and finally using the second waveguide portion with a gradually changing width to perform beam shaping and output on the infrared light output in the single longitudinal mode, thereby improving the coupling efficiency of the infrared light with the external optical fiber.

[0027] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0030] Figure 2 to Figure 6 The semiconductor laser according to the embodiment of the present application is shown along Figure 1 Schematic diagram of the preparation process structure of the AA section line.

[0031] Figure 7 It is a schematic diagram of the preparation process of a semiconductor laser according to an embodiment of the present application.

[0032] 110 substrate; 120 germanium waveguide layer; 121 first waveguide portion; 122 second waveguide portion; 123 third waveguide portion; 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] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0034] Germanium (Ge), a Group IV material, has an indirect bandgap structure. Various methods can be used to transform the indirect bandgap structure of the laser into a direct bandgap structure, such as applying biaxial tensile strain to germanium, or forming an alloy of germanium and tin. The basic structure of the laser can be realized by combining the two. However, most of the existing GeSn strip lasers are ordinary FP cavity resonant edge-emitting lasers, and the quality and efficiency of the light output need to be improved.

[0035] Based on the above problems, an embodiment of the present application provides a semiconductor laser and a method for preparing the same. By providing a germanium-tin epitaxial structure and regulating the mass fraction of the Sn component in the active layer of the germanium-tin epitaxial structure, the GeSn material in the active layer is converted from an indirect band gap to a direct band gap. At the same time, a germanium waveguide layer is added to perform light reflection resonance and light output coupling, thereby achieving the high emission efficiency requirements and wavelength coverage requirements of the laser.

[0036] According to one aspect of the present application, a semiconductor laser is provided. Figure 1 As shown, the laser 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 .

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

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

[0039] It is understandable that when the Sn component content 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, achieving the energy band requirements of the laser. The mass fraction of the Sn component in the active layer 133 in the present application is between 9% and 13%, so that the active layer 133 material is a direct band gap material, which can be excited to output infrared light, and the wavelength range of the infrared light output is between 2μm and 3μm.

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

[0041] Since a Bragg grating 124 is formed on the side of the third waveguide portion 123 away from the substrate 110, and a germanium tin epitaxial structure 130 is formed on the third waveguide portion 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 portion 123, it will reflect and oscillate in the grating structure periodically arranged in the Bragg grating 124, achieving the effect of a resonant cavity, thereby achieving the infrared light with strong feedback and anti-threshold gain output from the second waveguide portion 122. 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 portion 122 gradually decreases from the side close to the third waveguide portion 123 to the side away from the third waveguide portion 123, the cross-sectional structure of the second waveguide portion 122 is tapered. Therefore, after the infrared light output by the third waveguide portion 123 is incident on the second waveguide portion 122 with a tapered cross-section, the light beam will be gradually shaped and converged along the propagation direction of the infrared light, thereby improving the coupling efficiency between the infrared light output by the laser and the optical fiber.

[0043] As an example, the Bragg grating 124 may be composed of a plurality of periodically arranged grooves formed on the side of the third waveguide portion 123 away from the substrate 110, a germanium waveguide layer 120 between the plurality of grooves, and a SiO2 layer filled in the grooves. Since SiO2 and the germanium waveguide layer 120 have different refractive indices, the infrared light will repeatedly reflect and oscillate in the Bragg grating 124 after being coupled to the third waveguide portion 123.

[0044] Since the diffraction period Λ and the Bragg wavelength λ of the Bragg grating 124 b The effective refractive index n of the grating eff Satisfy Λ=λ b / 2n eff , so that the grating period, grating depth and duty cycle of the Bragg grating 124 will have different degrees of influence on the coupling coefficient of the third coupling part, and the Bragg grating 124 has a Bragg wavelength λ b The maximum reflectivity is at the place where the Bragg grating 124 has the maximum reflectivity. 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 GeSn epitaxial structure 130 on the third coupling part can be increased 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 part, but further increase in the groove depth will lead to the generation of mixed modes. Therefore, combined 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 0.2μm.

[0045] As an example, the Bragg grating 124 formed on the side of the third waveguide portion 123 away from the substrate 110 is a first-order λ / 4 phase-shifted 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 serves as a growth substrate for the germanium waveguide layer 120 and the germanium tin epitaxial structure 130 and can be made of a conductive material, an insulating material, or a light-transmitting material with excellent thermal conductivity, such as 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, among which a silicon substrate is a 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 laser emission body of the semiconductor laser, and its main material components are germanium and tin. Therefore, the germanium-tin epitaxial structure 130 is stacked and epitaxially formed on the germanium waveguide layer 120 by 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. In other words, the germanium waveguide layer 120 here can also play the role of a buffer layer, thereby reducing the lattice mismatch problem between the germanium-tin epitaxial structure 130 and the substrate 110. Among them, the above-mentioned germanium waveguide layer 120 and the germanium-tin epitaxial structure 130 are both formed by selective epitaxy.

[0048] Specifically, the germanium tin epitaxial structure 130 may 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 stacked in sequence 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, and is 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, and is in contact with 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, whereby electrons and holes are respectively injected into the active layer 133 of the germanium-tin epitaxial structure 130 from different directions, and are recombined 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 can not only keep the active layer 133 separated from other semiconductor material layers and provide a certain degree of physical support and protection for the active layer 133, but also limit holes from passing through the lower cladding layer 132 to enter the N-type contact layer 131, and limit electrons from passing through the upper cladding layer 134 to enter the P-type contact layer 135, thereby improving the recombination efficiency of electrons and holes in the active layer 133, and further increasing the luminous efficiency of the laser.

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

[0050] Furthermore, the germanium tin epitaxial structure 130 is also formed by 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 which is also on the N-type contact layer 131. The first electrode 141 is equivalent to the cathode of the semiconductor laser, which is used to connect to the negative output terminal of the external circuit and inject electrons into the germanium tin epitaxial structure 130. The second electrode 142 structure is formed on the P-type contact layer 135, which is equivalent to the anode of the semiconductor laser, which is used to connect to the positive output terminal of the external circuit and inject holes into the germanium tin epitaxial structure 130.

[0051] Among them, the materials of the first electrode 141 and the second electrode 142 include conductive metal materials, including but not limited to metals such as chromium (Cr), titanium (Ti), tungsten (W), gold (Au), aluminum (Al), indium (In), tin (Sn), nickel (Ni), platinum (Pt) or alloys of the above materials.

[0052] According to a second aspect of the present application, a method for preparing a semiconductor laser is provided, such as Figure 2 to Figure 7 As shown, the method is used to prepare the semiconductor laser described in any of the above embodiments, and may specifically include the following steps:

[0053] S1, providing a substrate 110;

[0054] S2, epitaxially forming a germanium epitaxial layer on the substrate 110, wherein the germanium epitaxial layer includes a first waveguide portion 121 located on the substrate 110, and a second waveguide portion 122 and a third waveguide portion 123 located on the first waveguide portion 121;

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

[0056] S4, epitaxially forming a germanium-tin epitaxial structure 130 on the third waveguide portion 123, wherein the germanium-tin epitaxial structure 130 includes 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 the Sn component 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, wherein the first electrode 141 is formed on the N-type contact layer 131 and is spaced apart from the lower cladding layer 132, and the second electrode 142 is formed on the P-type contact layer 135.

[0058] In step S2, the step of epitaxially forming a germanium epitaxial layer on the substrate 110 can specifically be to pre-epitaxially form a complete germanium-tin epitaxial material layer on the substrate 110, and then use a dry or wet etching process to pattern the surface of the germanium-tin epitaxial material layer to obtain a first waveguide portion 121 located at the bottom, a second waveguide portion 122 and a third waveguide portion 123 connected to the first waveguide portion 121, and the width of the second waveguide portion 122 gradually decreases from a side close to the third waveguide portion 123 to a side away from the third waveguide portion 123.

[0059] In step S3, if Figure 3 and Figure 4 As shown, after the step of filling the groove with SiO2, the SiO2 covering the third waveguide layer should be etched using an ICP dry etching process, so that the SiO2 only exists in each groove and the upper surface of the third waveguide layer is exposed.

[0060] It should be noted that the above-mentioned germanium waveguide layer 120 and germanium tin epitaxial structure 130 can be formed by epitaxy by a selective area epitaxy method, wherein the selective area epitaxy method may include but is not limited to a combination of any one or more 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 method for manufacturing the same, comprising a stacked substrate 110, a germanium waveguide layer 120 and a germanium-tin epitaxial structure 130, wherein the side of the germanium waveguide layer 120 away from the substrate 110 comprises a second waveguide portion 122 and a third waveguide portion 123 connected to each other, the width of the second waveguide portion 122 gradually decreases from a side close to the third waveguide portion 123 to a side away from the third waveguide portion 123, the germanium-tin epitaxial structure 130 is formed on the third waveguide portion 123, and a Bragg grating 124 is arranged on the third waveguide portion 123. By controlling the mass fraction of the 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 electrically excited, and the Bragg grating 124 acts as a resonant cavity to reflect and oscillate the light, and then couples it into the second waveguide portion 122, thereby achieving single longitudinal mode stable light output of the semiconductor laser. Finally, the second waveguide portion 122 with a gradually varying width is used to shape the infrared light output in the single longitudinal mode, thereby improving the coupling efficiency of the infrared light with the external optical fiber.

[0062] In the description of the aforementioned embodiments, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0063] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

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 comprises 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, characterized in that 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, characterized in that The duty cycle of the Bragg grating is between 45% and 60%.

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

5. The semiconductor laser according to claim 1, characterized in that 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, characterized in that 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 layer 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, characterized in that The semiconductor laser also 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 consisting of the lower cladding layer, the active layer and the upper cladding layer. The second electrode is formed on the P-type contact layer.

9. The semiconductor laser according to claim 1, characterized in that 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, used for preparing the semiconductor laser according to any one of claims 1 to 9, characterized in that: The method comprises: providing a substrate; epitaxially forming a germanium epitaxial layer on the substrate, 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; epitaxially 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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