980nm single-mode laser with asymmetric coupling waveguide structure and preparation method thereof

Abstract

The invention relates to a 980nm single-mode laser with an asymmetric coupling waveguide structure and a preparation method of the 980nm single-mode laser. Passive coupling waveguide layers are inserted into limiting layers on the two sides of a strain compensation quantum well respectively, an asymmetric epitaxial structure and a step doping mode are adopted, the P-side optical limiting capacity is improved, a fundamental mode limiting factor is increased, and light field loss is further reduced; and meanwhile, a fundamental mode light field is widened, a far-field divergence angle is reduced, and the single-mode output capability of the laser is improved.

Description

Technical Field

[0001] This invention belongs to the field of single-mode semiconductor laser technology, specifically relating to a 980nm single-mode laser with an asymmetric coupled waveguide structure and its fabrication method. Background Technology

[0002] With the rapid development of ultra-high-speed and ultra-high-capacity optical fiber communication, the coupling problem between pump lasers and optical fibers has attracted increasing attention. In optical fiber communication systems, single-mode semiconductor lasers serve as the core pump source, and their performance plays a decisive role in the coupling effect. The core objective of coupling is to efficiently and stably inject the laser output light into the optical fiber. The main challenge lies in matching the laser beam characteristics with the fiber parameters. A laser operating in its fundamental mode is fundamental to ensuring coupling with single-mode fiber. Further structural design can reduce the divergence angle and improve beam symmetry. Lowering the vertical divergence angle of the semiconductor laser can improve coupling efficiency and reduce coupling losses and shaping difficulties. However, the output beam mode of existing GaAs-based 980nm semiconductor lasers is not stable enough, and the energy distribution is uneven, resulting in a very large vertical divergence angle. This causes the far-field beam spot of the laser to be elliptical, reducing the pump efficiency of the 980nm semiconductor laser and the fiber coupling efficiency. Reducing the vertical divergence angle of semiconductor lasers and improving single-mode output capability can expand their application range and has significant practical implications.

[0003] The waveguide layer in the epitaxial structure serves as a key functional layer. Its special design allows for the selective accommodation of different lateral modes, widening the near-field spot size, reducing the far-field divergence angle, and achieving good single-mode output capability. The paper *Journal of Applied Physics*, 144, 013104 (2022) proposes a narrow waveguide structure design. By reducing the waveguide layer thickness, the equivalent spot size is increased. However, optical catastrophic damage (COD) is prone to occur at high power, making practical application of this design difficult. The paper *IEEE Journal of Quantum Electronics*, 17(6): 1715–1722 (2021) reports an asymmetric large-cavity wide waveguide structure that effectively widens the near-field spot size while maintaining high power output. However, the increased waveguide layer thickness leads to an increase in optical field modes, and mode competition easily occurs when the injected current increases.

[0004] CN107147005A discloses an asymmetric waveguide 980nm single-mode laser. The laser includes a substrate and, from bottom to top, a buffer layer, a lower confinement layer, a lower waveguide layer, a quantum well layer, an upper waveguide layer, a first upper confinement layer, an etch stop layer, a second upper confinement layer, and an ohmic contact layer grown on the substrate. The etch stop layer is made of highly doped p-type GaInP material. This single-mode laser uses an AlGaAs asymmetric waveguide based on a symmetric structure, and inserts an etch stop layer to prevent carrier leakage, ensuring high electro-optic conversion efficiency and other device performance. However, this type of single-mode laser has a large fast-axis divergence angle, and its single-mode output performance needs further improvement.

[0005] In summary, existing GaAs-based 980nm single-mode semiconductor lasers have numerous design and performance shortcomings, failing to meet the evolving needs of various fields. Therefore, developing a GaAs-based 980nm single-mode semiconductor laser that overcomes these problems and possesses superior performance is of paramount practical significance, hence this application. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a 980nm single-mode laser with an asymmetric coupled waveguide structure and its fabrication method, which can significantly improve the single-mode performance of single-mode semiconductor lasers.

[0007] One of the technical problems to be solved by this invention is how to provide an asymmetric waveguide 980nm single-mode laser that can broaden the fundamental mode optical field, reduce the far-field divergence angle, and achieve good single-mode output.

[0008] The second technical problem to be solved by this invention is how to effectively reduce carrier loss, increase output power, and improve the optoelectronic performance of the asymmetric waveguide 980nm single-mode laser.

[0009] Terminology Explanation:

[0010] Strain-compensated quantum well: In this field, a quantum well and the barriers on both sides are generally referred to as a strain-compensated quantum well.

[0011] MOCVD refers to metal-organic chemical vapor deposition; MO refers to metal-organic compounds.

[0012] Confinement layer: also known as cladding layer in the art. In this specification, cladding layer and confinement layer are synonymous.

[0013] Passive coupled waveguide layer: also known as coupled waveguide layer.

[0014] Active waveguide layer: also known as waveguide layer, is a conventional waveguide.

[0015] The present invention achieves its objective through the following technical solutions.

[0016] A 980nm laser with an asymmetric coupled waveguide structure is disclosed. The laser epitaxial wafer utilizes a GaAsP / InGaAs / GaAsP strain-compensated quantum well, with passive coupled waveguide layers inserted into the confinement layers on both sides of the strain-compensated quantum well. An asymmetric epitaxial structure is employed, with asymmetric thicknesses of the N-side and P-side confinement layers, asymmetric thicknesses of the N-side and P-side waveguide layers, and asymmetric composition and thicknesses of the N-side and P-side coupled waveguide layers. A stepped doping method is used: the doping concentration of the N-side confinement layer and the passive coupled waveguide layer is lower closer to the quantum well, and the doping concentration of the P-side confinement layer and the passive coupled waveguide layer is also lower closer to the quantum well.

[0017] A further technical solution is a 980nm laser with an asymmetric coupled waveguide structure. The laser includes a substrate and, from bottom to top, a buffer layer, a first N-side confinement layer, an N-side coupled waveguide layer, a second N-side confinement layer, an N-side waveguide layer, an N-side barrier layer, a quantum well layer, a P-side barrier layer, a P-side waveguide layer, a first P-side confinement layer, a P-side coupled waveguide layer, a second P-side confinement layer, and an ohmic contact layer. The thickness of the first N-side confinement layer is greater than the thickness of the second P-side confinement layer, the thickness of the N-side waveguide layer is greater than the thickness of the P-side waveguide layer, and the thickness of the N-side coupled waveguide layer is greater than the thickness of the P-side coupled waveguide layer. The composition of the N-side coupled waveguide layer is asymmetric to that of the P-side coupled waveguide layer. The doping ratio of the second N-side confinement layer is lower than that of the N-side coupled waveguide layer, the doping ratio of the N-side coupled waveguide layer is lower than that of the first confinement layer, the doping ratio of the first P-side confinement layer is lower than that of the P-side coupled waveguide layer, and the doping ratio of the P-side coupled waveguide layer is lower than that of the second confinement layer, forming a stepped doping structure.

[0018] Preferably, the substrate is made of GaAs material; the buffer layer is formed on the upper surface of the substrate and is also made of GaAs material.

[0019] Preferably, the first N-side confinement layer is formed on the upper surface of the buffer layer, using Al x1 Ga 1-x1 Made of As material;

[0020] Preferably, the N-side coupled waveguide layer is formed on the upper surface of the first N-side confinement layer; it is Al. x2 Ga 1-x2 Made of As material;

[0021] Preferably, the second N-side confinement layer is formed on the upper surface of the N-side coupled waveguide layer, using Al x3 Ga 1-x3 Made of As material;

[0022] Preferably, the N-side waveguide layer is formed on the upper surface of the second N-side confinement layer, using Al x4 Ga 1-x4Made of As material;

[0023] Preferably, the N-side barrier layer is formed on the upper surface of the second N-side waveguide layer and is made of GaAs. y1 P 1-y1 Material preparation;

[0024] Preferably, the quantum well layer is formed on the upper surface of the N-side barrier layer, using In... y2 Ga 1-y2 Made of As material;

[0025] Preferably, the P-side barrier layer is formed on the upper surface of the quantum well layer and is made of GaAs. y3 P 1-y3 Made of P material;

[0026] Preferably, the P-side waveguide layer is formed on the upper surface of the P-side barrier layer, using Al x7 Ga 1-x7 Made of As material;

[0027] Preferably, the first P-side confinement layer is formed on the upper surface of the P-side waveguide layer, using Al x8 Ga 1-x8 Made of As material;

[0028] Preferably, the P-side coupling waveguide layer is formed on the upper surface of the first P-side confinement layer, using Al x9 Ga 1-x9 Made of As material;

[0029] Preferably, the second P-side confinement layer is formed on the upper surface of the P-side coupled waveguide layer, using Al x10 Ga 1-x10 Made of As material;

[0030] Preferably, the ohmic contact layer is formed on the upper surface of the second P-side confinement layer and is made of GaAs material.

[0031] Furthermore, the GaAs buffer layer has a thickness of 350-450 nm and a doping concentration of 2E18-6E18 atoms / cm². 3 ;

[0032] Furthermore, the first N-side confinement layer Al x1 Ga 1-x1 As, with a thickness of 0.5-0.9 μm (thicker than the second P-side confinement layer), 0.4 ≤ x1 ≤ 0.6; doping concentration of 1E18-3E18 atoms / cm² 3 ;

[0033] Furthermore, the N-side coupled waveguide layer Al x2 Ga 1-x2As, thickness 0.3-0.5 μm; 0.35 ≤ x2 ≤ 0.55, and x2 ≠ x9; doping concentration 7E17-2E18 atoms / cm³ 3 And the doping concentration is lower than that of the first N-side confinement layer;

[0034] Furthermore, the second N-side confinement layer Al x3 Ga 1-x3 As, thickness 0.1-0.3 μm; 0.4 ≤ x3 ≤ 0.6, doping concentration 6E17-1.2E18 atoms / cm² 3 Furthermore, the doping concentration is lower than that of the N-side coupled waveguide layer and the first N-side confinement layer;

[0035] Furthermore, the N-side waveguide layer Al x4 Ga 1-x4 As, thickness 0.2-0.4µm; 0.15≤x4≤0.35, unintentional doping;

[0036] Furthermore, the N-side barrier layer GaAs y1 P 1-y1 Thickness is 10-30nm; 0.15≤y1≤0.35, unintentional doping;

[0037] Furthermore, the In y2 Ga 1-y2 As quantum well, with a thickness of 6-10 nm and 0.1 ≤ y² ≤ 0.3; unintentionally doped;

[0038] Furthermore, the P-side barrier layer GaAs y3 P 1-y3 Thickness is 10-30nm, 0.5≤y3≤0.8; unintentional doping;

[0039] Furthermore, the P-side waveguide layer Al x7 Ga 1-x7 As, with a thickness of 0.1-0.3 μm and less than the thickness of the N-side waveguide layer; 0.15 ≤ x7 ≤ 0.35, unintentionally doped;

[0040] Furthermore, the first P-side confinement layer Al x8 Ga 1-x8 As, thickness 0.1-0.3 μm; 0.45 ≤ x8 ≤ 0.65, doping concentration 6E17-2E18 atoms / cm² 3 Furthermore, the doping concentration is lower than that of the P-side coupled waveguide layer.

[0041] Furthermore, the P-side coupled waveguide layer Al x9 Ga 1-x9As, with a thickness of 0.1-0.28 μm; 0.25 ≤ x9 ≤ 0.45, and x9 ≠ x2, and a doping concentration of 1E18-2E18 atoms / cm². 3 The doping concentration is lower than that of the second P-side confinement layer.

[0042] Furthermore, the second P-side confinement layer Al x10 Ga 1-x10 As, with a thickness of 0.2-0.4 μm; 0.45 ≤ x 10 ≤ 0.65, and a doping concentration of 1.2E18-3E18 atoms / cm². 3 ;

[0043] Furthermore, the GaAs ohmic contact layer has a thickness of 200-400 nm and a doping concentration of 2E19-6E19 atoms / cm². 3 .

[0044] This invention also provides a method for fabricating a 980nm laser with an asymmetric coupled waveguide structure, which utilizes MOCVD technology to sequentially epitaxially grow a buffer layer, a first N-side confinement layer, an N-side coupled waveguide layer, a second N-side confinement layer, an N-side waveguide layer, an N-side barrier layer, a quantum well layer, a P-side barrier layer, a P-side waveguide layer, a first P-side confinement layer, a P-side coupled waveguide layer, a second P-side confinement layer, and an ohmic contact layer on a substrate.

[0045] Technical features and beneficial effects of the present invention

[0046] Traditional semiconductor laser epitaxial structure designs employ separate confinement structures in the vertical direction of the laser, utilizing the refractive index difference between the waveguide layer and the cladding (confinement layer) for optical field confinement. Increasing the waveguide layer thickness accommodates more modes, easily leading to mode competition issues. Although using asymmetric waveguides or reducing cladding thickness can increase the mode loss difference between the fundamental mode and higher-order modes to some extent, and improve the single-mode operating waveguide thickness, this does not bring substantial improvement. This invention abandons the above approach of existing technologies, taking a different approach to optimize the single-mode output capability of the laser by differentiating gain and loss. Increasing loss is achieved by increasing the loss of higher-order modes, increasing the overlap between higher-order modes and the absorption layer in the epitaxial structure, thus preventing higher-order modes from lasing. Increasing gain is achieved by adjusting the position of the active layer, ensuring that only the fundamental mode has a high optical confinement factor, further increasing the fundamental mode confinement factor, and guaranteeing the fundamental mode lasing of the semiconductor laser.

[0047] The core technology of this invention is to insert passive coupled waveguide structures at different positions in the confinement layer, thereby reducing the loss of specific higher-order modes and extending the optical field of the selected mode to different positions, thus preventing the higher-order modes from lasing. Simultaneously, it broadens the fundamental mode optical field, reduces the far-field divergence angle, and ensures single-mode lasing. Using a GaAsP / InGaAs / GaAsP strain-compensated quantum well, passive coupled waveguide layers are inserted in the confinement layers on both sides. The co-directional coupling effect between adjacent conventional waveguides and coupled waveguides causes the selected higher-order modes in the conventional waveguides to be coupled and broadened into the P-side passive coupled waveguide. The presence of highly doped holes on the P-side increases the carrier loss of the higher-order modes, preventing lasing due to the reduced optical confinement factor and increased optical loss. Inserting a coupled waveguide layer in the N-side confinement layer broadens the fundamental mode optical field, increases the near-field spot size of the fundamental mode, and reduces the far-field divergence angle. The overall epitaxial structure adopts an asymmetric design, increasing the Al composition difference on the P-side (increasing the Al composition difference between the P-side confinement layer and the waveguide layer) to improve confinement capability. This biases the overall optical field towards the active region and the N-side, increasing the optical confinement factor in the active region and reducing optical loss caused by holes on the P-side, further reducing optical field loss. A stepped doping method is used to optimize carrier transport by adjusting the potential field, reducing carrier loss and improving the device's optoelectronic performance. The conventional active waveguide in this invention employs a large-cavity, wide-waveguide structure design to ensure the equivalent spot size of the fundamental mode. The synergistic effect with the coupled waveguide structure further facilitates single-mode lasing. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of a 980nm single-mode semiconductor laser with an asymmetric coupled waveguide structure according to an embodiment of the present invention; wherein, 1. GaAs substrate, 2. GaAs buffer layer, 3. Al x1 Ga 1-x1 As the first N-side confinement layer, 4. is Al x2 Ga 1-x2 As N-side coupled waveguide layer, 5.Al x3 Ga 1-x3 As the second N-side confinement layer, 6.Al x4 Ga 1-x4 As N-side waveguide layer, 7.GaAs y1 P 1-y 1N side barrier layer, 8.In y2 Ga 1-y2 As quantum well, 9.GaAs y3 P 1-y3 P-side barrier layer, 10.Al x7 Ga 1-x7 As P-side waveguide layer, 11.Al x8 Ga 1- x8 As the first P-restricted layer, 12.Al x9 Ga1-x9 As P-side coupled waveguide layer, 13.Al x10 Ga 1-x10 As second P-side confinement layer, 14. GaAs ohmic contact layer.

[0049] Figure 2 This is a schematic diagram of a conventional 980nm single-mode semiconductor laser. The components are: 21. GaAs substrate, 22. GaAs buffer layer, 23. N-side confinement layer, 24. N-side waveguide layer, 25. N-side barrier layer, 26. quantum well, 27. P-side barrier layer, 28. P-side waveguide layer, 29. P-confinement layer, and 30. GaAs ohmic contact layer. Detailed Implementation

[0050] The present invention will be further described below with reference to embodiments and accompanying drawings, but is not limited thereto. The described embodiments are some embodiments of the present invention. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this invention and simplifying the description, and should not be construed as limiting this invention. In addition, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0052] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified in the embodiments of the present invention, all techniques existing in the art can be used.

[0053] In this embodiment, the N-type doping source is Si₂H₆; the P-type doping source is CBr₄. The Al, Ga, As, and P sources in this embodiment are derived from TMAl (trimethylaluminum), TMGa (trimethylgallium), AsH₃ (arsine), and PH₃ (phosphine), respectively.

[0054] This invention discloses an epitaxial wafer for a 980nm single-mode semiconductor laser with an asymmetric coupled waveguide structure and its fabrication method.

[0055] This invention utilizes MOCVD technology to grow epitaxial materials on GaAs substrates, such as epitaxial wafers for 980nm single-mode semiconductor lasers with asymmetric coupled waveguide structures. Figure 1 As shown, GaAs buffer layer 2 and Al are grown sequentially from bottom to top on GaAs substrate 1. x1 Ga 1-x1 As the first N-side confinement layer 3, Al x2 Ga 1-x2As N-side coupled waveguide layer 4, Al x3 Ga 1-x3 As the second N-side confinement layer 5, Al x4 Ga 1-x4 As N-side waveguide layer 6, GaAs y1 P 1-y1 First N-side barrier layer 7, In y2 Ga 1-y2 As quantum well 8, GaAs y3 P 1-y3 P-side barrier layer 9, Al x7 Ga 1-x7 As P-side waveguide layer 10, Al x8 Ga 1-x8 As first P-restriction layer 11, Al x9 Ga 1-x9 As P-side coupling waveguide layer 12, Al x10 Ga 1-x10 As second P-side confinement layer 13, GaAs ohmic contact layer 14.

[0056] This invention inserts passive coupled waveguide layers into the confinement layers on both sides of a GaAsP / InGaAs / GaAsP strain-compensated quantum well. The co-directional coupling effect between two adjacent parallel waveguides causes selected higher-order modes in the conventional waveguide to be coupled and broadened into the passive waveguide on the P-side. The presence of highly doped holes on the P-side increases the free carrier loss of the higher-order modes, preventing lasing due to the reduced optical confinement factor and increased optical loss. Due to different positions, the optical field of the fundamental mode is coupled and broadened to the N-side. The loss caused by free carriers on the N-side is lower, ensuring that the optical field broadening of the fundamental mode does not result in excessive loss, increasing the near-field beam size of the fundamental mode and reducing the far-field divergence angle. The epitaxial structure employs an asymmetric structure, increasing the optical confinement capability on the P-side and pressing the overall optical field towards the active region and the N-side, increasing the fundamental mode confinement factor while further reducing optical field loss. Furthermore, by adjusting the growth interface and using a doping gradient (lower doping concentration in layers closer to the quantum well on the same side) to optimize carrier transport, the overall performance of the device is further improved. By adjusting the quantum well position through asymmetric thickness adjustment on both sides of the N-side and P-side waveguide layers, and by adjusting the barrier height through changes in the composition difference between the quantum well and the barrier layer, and between the barrier layer and the waveguide layer, the abrupt interface change is mitigated, carrier transport is optimized, carrier leakage and waste heat generation are reduced, and the overall optoelectronic performance of the device is further improved.

[0057] This invention provides a method for fabricating a 980nm single-mode semiconductor laser with a coupled waveguide structure, comprising the following steps:

[0058] 1. Place GaAs substrate 1 in the MOCVD reaction chamber, heat the H2 environment to 400-500℃, then introduce AsH3, raise the temperature to 790-810℃ for heat treatment for 25-35 minutes to create an arsine environment for the subsequent epitaxial growth reaction. The purpose of the high-temperature heat treatment is to bake GaAs substrate 1 at high temperature to remove water and oxygen impurities on the substrate surface.

[0059] 2. Control the temperature of the reaction chamber to slowly decrease to 680℃-695℃, with a cooling rate not exceeding 50℃ / min. Then, introduce MO source TMGa and AsH3 to grow a GaAs buffer layer 2 with a thickness of 350-450nm on GaAs substrate 1.

[0060] In a preferred embodiment of the present invention, the doping concentration in step 2 is 2E18-6E18 atoms / cm². 3 The N-type doping source is Si2H6.

[0061] 3. The reaction chamber temperature is raised to 700℃-715℃, with a heating rate not exceeding 40℃ / min. TMAl, TMGa, and AsH3 are introduced to grow Al on the GaAs buffer layer 2 described in step 2. x1 Ga 1-x1 As the first N-side confinement layer 3, the thickness is 0.5-0.9 μm; 0.4 ≤ x1 ≤ 0.6;

[0062] In a preferred embodiment of the present invention, the doping concentration in step 3 is 1E18-3E18 atoms / cm³. 3 The doping source is Si2H6.

[0063] 4. Maintain the reaction chamber temperature at 700℃-715℃. After step 3 is completed, introduce TMAl, TMGa, and AsH3 to grow Al. x2 Ga 1-x2 As N-side coupling waveguide layer 4, thickness is 0.3-0.5 μm; 0.35 ≤ x2 ≤ 0.55;

[0064] In a preferred embodiment of the present invention, the doping source in step 4 is Si2H6, and the doping concentration is 5E17-2E18 atoms / cm³. 3 ;

[0065] 5. Maintain the reaction chamber temperature at 700℃-715℃. After step 4 is completed, introduce TMAl, TMGa, and AsH3 to grow Al. x3 Ga 1-x3 As the second N-side confinement layer 5, the thickness is 0.1-0.3 μm; 0.4 ≤ x3 ≤ 0.6;

[0066] In a preferred embodiment of the present invention, the doping source in step 5 is Si₂H₆, and the doping concentration is 6E¹⁷-1.2E¹⁸ atoms / cm². 3 ;

[0067] 6. The reaction chamber temperature is reduced to 680℃-695℃ at a rate not exceeding 50℃ / min. TMAl, TMGa, and AsH3 are introduced to grow Al on the substrate from step 5. x4 Ga 1-x4 As N-side waveguide layer 6, thickness 0.2-0.4µm; 0.15≤x4≤0.35, unintentionally doped;

[0068] 7. Maintain the reaction chamber temperature at 680℃-695℃, and introduce TMGa, AsH3, and PH3 to grow GaAs on the substrate from step 6. y1 P 1-y1 N-side barrier layer 7, thickness 10-30 nm; 0.15≤y1≤0.35, 0.15≤y1≤0.35; N-side barrier layer is not intentionally doped;

[0069] 8. Maintain the reaction chamber temperature at 680℃-695℃. After step 7 is completed, introduce TMGa, TMIn, and AsH3 to grow In. y2 Ga 1-y2 As quantum well 8, with a thickness of 6-10 nm, 0.1 ≤ y2 ≤ 0.3, unintentionally doped;

[0070] 9. Maintain the reaction chamber temperature at 680℃-695℃. After the growth in step 8 is completed, introduce TMGa, PH3, and AsH3 to grow GaAs. y3 P 1-y3 P-side barrier layer 9, with a thickness of 10-30 nm and 0.5 ≤ y3 ≤ 0.8, the P-side barrier layer is not intentionally doped;

[0071] 10. Maintain the reaction chamber temperature at 680℃-695℃, and introduce TMAl, TMGa, and AsH3 to grow Al on the substrate from step 9. x7 Ga 1-x7 As P-side waveguide layer 10, with a thickness of 0.1-0.3 μm, 0.15 ≤ x7 ≤ 0.35, is not intentionally doped;

[0072] 11. The reaction chamber temperature is raised to 730℃-750℃, with a heating rate not exceeding 50℃ / min. TMAl, TMGa, and AsH3 are introduced to grow Al on the substrate from step 10. x8 Ga 1-x8 As the first P-side confinement layer 11, 0.45≤x8≤0.65, with a thickness of 0.1-0.3um;

[0073] In a preferred embodiment of the present invention, the doping source in step 11 is CBr4, and the doping concentration is 6E17-2E18 atoms / cm³. 3 ;

[0074] 12. Maintain the reaction chamber temperature at 730℃-750℃, and introduce TMAl, TMGa, and AsH3 to grow Al on the substrate from step 11. x9 Ga 1-x9 As P-side coupled waveguide layer 12, thickness is 0.1-0.3um; 0.25≤x9≤0.45.

[0075] In a preferred embodiment of the present invention, the doping source in step 12 is CBr4, and the doping concentration is 1E18-2E18 atoms / cm³. 3 .

[0076] 13. Maintain the reaction chamber temperature at 730℃-750℃, and introduce TMAl, TMGa, and AsH3 to grow Al on the substrate from step 12. x10 Ga 1-x10 As the second P-side confinement layer 13, the thickness is 0.2-0.4um; 0.45≤x10≤0.65.

[0077] In a preferred embodiment of the present invention, the doping source in step 13 is CBr4, and the doping concentration is 1.2E18-3E18 atoms / cm³. 3 .

[0078] 14. Control the temperature of the reaction chamber to drop to 530-550℃, introduce TMGa and AsH3, and grow a GaAs ohmic contact layer 14 with a thickness of 200-400nm on step 13.

[0079] In a preferred embodiment of the present invention, the doping source in step 14 is CBr4, and the doping concentration is 2E19-6E19 atoms / cm³. 3 .

[0080] Based on the above preferred embodiments, a further optimal embodiment is provided:

[0081] Example 1: A method for fabricating a 980nm single-mode semiconductor laser with an asymmetric coupled waveguide structure. An epitaxial layer is grown on a GaAs substrate 1 using MOCVD technology. The epitaxial structure of the semiconductor laser is as follows: Figure 1 As shown, the preparation steps are as follows:

[0082] (1) GaAs substrate 1 is placed in the MOCVD reaction chamber, the H2 environment is heated to 450°C, AsH3 is introduced, and the temperature is raised to 800°C for high-temperature heat treatment for 30 minutes.

[0083] (2) The temperature of the reaction chamber is slowly reduced to 690℃ at a rate not exceeding 50℃ / min. Then, MO source TMGa and AsH3 are introduced to grow a GaAs buffer layer 2 on GaAs substrate 1. The thickness of GaAs buffer layer 2 is 400nm and the doping concentration is 4E18 atoms / cm². 3 The N-type doping source is Si2H6;

[0084] (3) The reaction chamber temperature is raised to 710℃, with a heating rate not exceeding 40℃ / min. TMAl, TMGa, and AsH3 are introduced to grow Al on the GaAs buffer layer 2. x1 Ga 1-x1 As the first N-side confinement layer 3, the thickness is 0.8 μm; x1 = 0.5, and the doping concentration is 2E18 atoms / cm. 3 The doping source is Si2H6.

[0085] (4) The reaction chamber temperature is maintained at 710℃, and TMAl, TMGa and AsH3 are introduced to grow Al. x2 Ga 1-x2 As N-side coupled waveguide layer 4, thickness 0.4 μm; x2 = 0.45, doping concentration 1E18 atoms / cm² 3 The doping source is Si2H6.

[0086] (5) The reaction chamber temperature was maintained at 710℃, and TMAl, TMGa and AsH3 were introduced to grow Al. x3 Ga 1-x3 As the second N-side confinement layer 5, with a thickness of 0.2 μm, x3 = 0.5, and a doping concentration of 8E17 atoms / cm². 3 The doping source is Si2H6.

[0087] (6) The chamber temperature should be reduced to 690℃ at a rate not exceeding 50℃ / min. TMAl, TMGa, and AsH3 should be introduced to grow Al. x4 Ga 1-x4 As N-side waveguide layer 6, with a growth thickness of 0.3 μm and x4 = 0.25, is not intentionally doped;

[0088] (7) The reaction chamber temperature was maintained at 690℃, and TMGa, AsH3 and PH3 were introduced to grow GaAs. y1 P 1-y1 N-side barrier layer 7, with a growth thickness of 20 nm, y1 = 0.25, unintentionally doped;

[0089] (8) The reaction chamber temperature is maintained at 690℃, and TMGa, TMIn and AsH3 are introduced to grow In. y2 Ga 1-y2As quantum well 8, with a growth thickness of 7.5 nm and y2 = 0.2;

[0090] (9) Maintain the reaction chamber temperature at 690℃, introduce TMGa, PH3 and AsH3 to grow GaAs. y3 P 1-y3 P-side barrier layer 9, with a growth thickness of 20 nm and y3 = 0.65;

[0091] (10) The reaction chamber temperature was maintained at 690℃, and TMAl, TMGa and AsH3 were introduced to grow Al. x7 Ga 1-x7 As P-side waveguide layer 10, with a growth thickness of 0.2 μm, x7 = 0.25, the P-side waveguide layer is not intentionally doped;

[0092] (11) The reaction chamber temperature is raised to 740℃, with a heating rate not exceeding 50℃ / min. TMAl, TMGa and AsH3 are introduced to grow Al. x8 Ga 1-x8 The first P-side confinement layer 11 has a growth thickness of 0.2 μm, x8 = 0.55, and a doping concentration of 9E17 atoms / cm². 3 The doping source is CBr4;

[0093] (12) The reaction chamber temperature was maintained at 740℃, and TMAl, TMGa and AsH3 were introduced to grow Al. x9 Ga 1-x9 As P-side coupled waveguide layer 12, with a growth thickness of 0.2 μm, x9 = 0.35, and a doping concentration of 1.5E18 atoms / cm². 3 The doping source is CBr4;

[0094] (13) The reaction chamber temperature was maintained at 740℃, and TMAl, TMGa and AsH3 were introduced to grow Al. x10 Ga 1-x10 The second P-side confinement layer 13 (As) has a growth thickness of 0.3 μm, x 10 = 0.55, and a doping concentration of 2E18 atoms / cm². 3 The doping source is CBr4;

[0095] (14) The reaction chamber temperature was lowered to 540℃, and TMGa and AsH3 were introduced to grow a GaAs ohmic contact layer 14 with a thickness of 300 nm and a doping concentration of 4E19 atoms / cm². 3 The doping source is CBr4.

[0096] Comparative Example 1: Conventional 980nm Single-Mode Laser

[0097] A conventional 980nm single-mode laser, referencing Figure 2From bottom to top, the structure includes a GaAs substrate 21, a GaAs buffer layer 22, an N-side confinement layer 23, an N-side waveguide layer 24, an N-side barrier layer 25, a quantum well 26, a P-side barrier layer 27, a P-side waveguide layer 28, a P-side confinement layer 29, and a GaAs ohmic contact layer 30. The GaAs substrate 21 has a thickness of 4500 nm and is doped with Si₂H₆ at a doping concentration of 3E¹⁸ atoms / cm². 3 The GaAs buffer layer is 500 nm thick and doped with Si2H6 at a concentration of 2E18 atoms / cm². 3 N-side confinement layer 23, component Al 0.4 Ga 0.6 As, thickness 1200nm, doped with Si2H6, doping concentration 5E17 atoms / cm² 3 N-side waveguide layer 24, composition Al 0.3 Ga 0.7 As, 250 nm thick, unintentionally doped; N-side barrier layer 25, GaAsP, 50 nm thick, unintentionally doped; quantum well 26, InGaAs, 6 nm thick, unintentionally doped; P-side barrier layer 27, GaAsP, 50 nm thick, unintentionally doped; P-side waveguide layer 28, Al... 0.3 Ga 0.7 As, 250 nm thick, unintentionally doped; P confinement layer 29, Al composition. 0.5 Ga 0.5 As, 1000 nm thick, doped with CBr4, doping concentration 1E18 atoms / cm² 3 The GaAs ohmic contact layer is 30mm thick, 150nm thick, and doped with CBr4 at a doping concentration of 5E19 atoms / cm². 3 .

[0098] Table 1 below compares the relevant parameters obtained by testing the conventional structure laser device of Comparative Example 1 and the laser device described in Example 1 of the present invention under the same process conditions, with a test condition of 300mA.

[0099] Table 1

[0100]

[0101] As shown in Table 1, the 980nm single-mode semiconductor laser with the asymmetric coupled waveguide structure of this invention has a lower threshold current and higher slope efficiency. Under the same current, its output power is greater than that of the conventional structure laser in Comparative Example 1. Both the fast-axis divergence angle and the slow-axis divergence angle are smaller than those in Comparative Example 1. This indicates that the 980nm single-mode semiconductor laser with the asymmetric coupled waveguide structure of this invention effectively increases the loss of higher-order modes, widens the fundamental mode optical field, reduces the far-field divergence angle, realizes single-mode lasing, and improves the single-mode output capability of the laser.

Claims

1. A 980nm laser of asymmetrically coupled waveguide structure, the laser epitaxial wafer comprising: using GaAsP / InGaAs / GaAsP strain-compensated quantum wells, passive coupling waveguide layers are inserted in the confining layers on both sides of the strain-compensated quantum wells; using an asymmetric epitaxial structure, the thickness of the N-side confining layer and the P-side confining layer is asymmetric, the thickness of the N-side waveguide layer and the P-side waveguide layer is asymmetric, and the composition and thickness of the N-side coupling waveguide layer and the P-side coupling waveguide layer are asymmetric; using a step doping method: the doping concentration of the N-side confining layer and the passive coupling waveguide layer is lower closer to the quantum well part, and the doping concentration of the P-side confining layer and the passive coupling waveguide layer is lower closer to the quantum well part.

2. The 980 nm asymmetrically coupled waveguide structure laser of claim 1, wherein, The laser comprises a substrate and, sequentially grown on the substrate from bottom to top, a buffer layer, a first N-side confining layer, an N-side coupling waveguide layer, a second N-side confining layer, an N-side waveguide layer, an N-side barrier layer, a quantum well layer, a P-side barrier layer, a P-side waveguide layer, a first P-side confining layer, a P-side coupling waveguide layer, a second P-side confining layer, and an ohmic contact layer, wherein the thickness of the first N-side confining layer is greater than the thickness of the second P-side confining layer, the thickness of the N-side waveguide layer is greater than the thickness of the P-side waveguide layer, the thickness of the N-side coupling waveguide layer is greater than the thickness of the P-side coupling waveguide layer, and the composition of the N-side coupling waveguide layer is asymmetric to the composition of the P-side coupling waveguide layer; the doping ratio of the second N-side confining layer is lower than that of the N-side coupling waveguide layer, the doping ratio of the N-side coupling waveguide layer is lower than that of the first confining layer, the doping ratio of the first P-side confining layer is lower than that of the P-side coupling waveguide layer, the doping ratio of the P-side coupling waveguide layer is lower than that of the second confining layer, forming a step doping.

3. The 980 nm asymmetrically coupled waveguide structure laser of claim 1, wherein, One or more of the following conditions are included: a. The substrate is made of GaAs material; the buffer layer is formed on the upper surface of the substrate and is made of GaAs material; b. The first N-side confinement layer is formed on the upper surface of the buffer layer, and the first N-side confinement layer is Al x1 Ga 1-x1 As material; c. the N-side coupling waveguide layer is formed on the upper surface of the first N-side confinement layer; the N-side coupling waveguide layer is AlGaAs material x2 Ga 1-x2 As material; d. The second N-side confinement layer is formed on the upper surface of the N-side coupled waveguide layer, and the second N-side confinement layer is Al x3 Ga 1-x3 As material; e. The N-side waveguide layer is formed on the upper surface of the second N-side confinement layer, and the N-side waveguide layer is an Al x4 Ga 1-x4 As material; f. The N-side barrier layer is formed on the upper surface of the second N-side waveguide layer, and the N-side barrier layer is GaAs y1 P 1-y1 material; g. The quantum well layer is formed on the upper surface of the N-side barrier layer, and the quantum well layer is an In y2 Ga 1-y2 As material; h. The P-side barrier layer is formed on the upper surface of the quantum well layer, and the P-side barrier layer is GaAs y3 P 1-y3 P material; i. The P-side waveguide layer is formed on the upper surface of the P-side barrier layer, and the P-side waveguide layer is an Al x7 Ga 1-x7 As material; j. The first P-side confinement layer is formed on the upper surface of the P-side waveguide layer, and the first P-side confinement layer material is Al x8 Ga 1-x8 As; k. The P-side coupling waveguide layer is formed on the upper surface of the first P-side confinement layer, and the material of the P-side coupling waveguide layer is Al x9 Ga 1- x9 As; l. The second P-side confinement layer is formed on the upper surface of the P-side coupled waveguide layer, and the material of the second P-side confinement layer is Al x10 Ga 1- x10 As material; m. The ohmic contact layer is formed on the upper surface of the second P-side confining layer, and the material of the ohmic contact layer is GaAs.

4. The 980 nm asymmetrically coupled waveguide structure laser of claim 3, wherein, One or more of the following conditions are also included: a. The GaAs buffer layer thickness is in the range of 350-450 nm, with a doping concentration of 2E18-6E18 atoms / cm 3 ; b. the first N-side confinement layer Al x1 Ga 1-x1 As, thickness 0.5-0.9um, 0.4≤x1≤0.6; doping concentration 1E18-3E18 atoms / cm 3 ; c. the N-side coupling waveguide layer Al x2 Ga 1-x2 As, with a thickness of 0.3-0.5um; 0.35≤x2≤0.55, and x2≠x9; a doping concentration of 7E17-2E18 atoms / cm 3 , and a doping concentration lower than that of the first N-side confinement layer; d. the second N-side confinement layer Al x3 Ga 1-x3 As, thickness 0.1-0.3um; 0.4 < x3 < 0.6, with a doping concentration of 6E17-1.2E18 atoms / cm 3 and a doping concentration lower than that of the N-side coupled waveguide layer and the first N-side confinement layer. e. the N-side waveguide layer Al x4 Ga 1-x4 As, 0.2-0.4um thick; 0.15≤x4≤0.35, unintentional doping; f. the N-side barrier layer GaAs y1 P 1-y1 , thickness 10-30 nm; 0.15≤y1≤0.35, unintentionally doped; g. the In y2 Ga 1-y2 As quantum well, 6-10 nm thick, 0.1≤y2≤0.3 atoms / cm2; unintentionally doped; h. the P-side barrier layer GaAs y3 P 1-y3 , thickness 10-30 nm, 0.5≤y3≤0.8; unintentionally doped; i. the P-side waveguide layer Al x7 Ga 1-x7 As, 0.1-0.3 um thick and less than the N-side waveguide layer thickness; 0.15≤x7≤0.35, unintentionally doped; j. the first P-side confinement layer Al x8 Ga 1-x8 As, 0.1-0.3um thick; 0.45 < x8 < 0.65, with a doping concentration of 6E17 - 2E18 atoms / cm 3 ; and a doping concentration lower than that of the P-side coupled waveguide layer; k. the P-side coupler waveguide layer Al x9 Ga 1-x9 As, 0.1-0.28um thick; 0.25 < x9 < 0.45, and x9 ≠ x2, with a doping concentration of 1E18 - 2E18 atoms / cm 3 ; a doping concentration lower than that of the second P-side confinement layer l. The second P-side confinement layer Al x10 Ga 1-x10 As, 0.2-0.4um thick; 0.45 < x10 < 0.65, and a doping concentration of 1.2E18 - 3E18 atoms / cm 3 ; m. The GaAs ohmic contact layer thickness is in the range of 200-400 nm; doping concentration is in the range of 2E19-6E19 atoms / cm 3 .

5. A method for preparing the 980nm laser of asymmetrically coupled waveguide structure according to any one of claims 1-4, using MOCVD technology to sequentially epitaxially grow a buffer layer, a first N-side confining layer, an N-side coupling waveguide layer, a second N-side confining layer, an N-side waveguide layer, an N-side barrier layer, a quantum well layer, a P-side barrier layer, a P-side waveguide layer, a first P-side confining layer, a P-side coupling waveguide layer, a second P-side confining layer, and an ohmic contact layer on a substrate.

6. The method of claim 5, wherein the asymmetrically coupled waveguide structure is formed by a process comprising: The steps include: ​ S1. Place the GaAs substrate in the MOCVD reaction chamber, heat to 400-500℃ in a H2 environment, then introduce AsH3, heat to 790-810℃ for heat treatment for 25-35 minutes; S2. Control the temperature of the reaction chamber to decrease to 680-695℃ at a rate not higher than 50℃ / min, then introduce TMGa and AsH3 to grow a GaAs buffer layer with a thickness of 350-450nm on the GaAs substrate; S3. The temperature of the reaction chamber is raised to 700-715°C at a rate of no more than 40°C / min, TMAl, TMGa and AsH3 are introduced, and Al x1 Ga 1-x1 As a first N-side confining layer 3, 0.5-0.9um thick; 0.4≤x1≤0.6； S4. The temperature of the reactor chamber is maintained at 700-715°C. After completion of step 3, TMAl, TMGa and AsH3 are introduced and Al x2 Ga 1-x2 As N-side coupled waveguide layer 4, thickness 0.3-0.5um; 0.35≤x2≤0.55; S5. The temperature of the reaction chamber is kept at 700-715°C. After step 4 is completed, TMAl, TMGa and AsH3 are introduced, and Al x3 Ga 1-x3 As a second N-side confining layer 5, 0.1-0.3 um thick; 0.4≤x3≤0.6； S6. The temperature of the reaction chamber is reduced to 680-695°C at a rate of no more than 50°C / min, and TMAl, TMGa, and AsH3are introduced, growing Al x4 Ga 1-x4 As N-side waveguide layer 6, 0.2-0.4um thick; 0.15≤x4≤0.35, unintentional doping; S7. The temperature of the reaction chamber is kept at 680-695 °C, TMGa, AsH3 and PH3 are introduced, and GaAs is grown on step 6 y1 P 1-y1 N-side barrier layer 7, thickness 10-30 nm; 0.15≤y1≤0.35, 0.15≤y1≤0.35; S8. The temperature of the reactor chamber is maintained at 680-695°C. After step 7 is completed, TMGa, TMIn and AsH3 are introduced, and In y2 Ga 1- y2 As quantum well 8, 6-10 nm thick, 0.1≤y2≤0.3, unintentionally doped; S9. The temperature of the reaction chamber is kept at 680-695 °C. After the growth of step 8 is completed, TMGa, PH3 and AsH3 are introduced to grow GaAs y3 P 1-y3 P-side barrier layer 9, thickness 10-30 nm, 0.5≤y3≤0.8, the P-side barrier layer is unintentionally doped; S10. The temperature of the reactor chamber is maintained at 680-695°C, TMAl, TMGa, and AsH3are introduced, and Al x7 Ga 1-x7 AsP side waveguide layer 10, thickness 0.1-0.3um, 0.15≤x7≤0.35, unintentionally doped; S11. The temperature of the reaction chamber is raised to 730-750°C at a rate of no more than 50°C / min, TMAl, TMGa, and AsH3are introduced, and Al x8 Ga 1-x8 As a first P-side confining layer 11, 0.45≤x8≤0.65, and having a thickness of 0.1-0.3um; S12. The temperature of the reaction chamber is kept at 730-750 °C, TMAl, TMGa, and AsH3are introduced, and Al x9 Ga 1- x9 As P-side coupling waveguide layer 12, thickness 0.1-0.3 um; 0.25≤x9≤0.45； S13. The temperature of the reaction chamber is kept at 730-750°C, TMAl, TMGa, and AsH3are introduced, and Al x10 Ga 1-x10 As the second P-side confining layer 13, with a thickness of 0.2-0.4um; 0.45≤x10≤0.65； S14. Control the temperature of the reaction chamber to decrease to 530-550°C, introduce TMGa and AsH3, and grow an ohmic contact layer with a thickness of 200-400 nm on the layer of step 13.

7. The method for fabricating a 980nm laser with an asymmetric coupled waveguide structure as described in claim 6, characterized in that, Also included is one or more of the following conditions: i. The doping source of S2 uses Si2H6, and the doping concentration is 2E18-6E18 atoms / cm 3 ; ii. The doping source of S3 uses Si2H6, and the doping concentration is 1E18-3E18 atoms / cm 3 ; iii. The doping source of S4 uses Si2H6, and the doping concentration is 7E17-2E18 atoms / cm3 3 ; iv. The doping source of S5 uses Si2H6, and the doping concentration is 6E17-1.2E18 atoms / cm3 3 ; v. The doping source of S11 uses CBr4, and the doping concentration is 6E17-2E18 atoms / cm 3 ; vi. The doping source of S12 uses CBr4, and the doping concentration is 1E18-2E18 atoms / cm 3 ; vii. The doping source of S13 uses CBr4, and the doping concentration is 1.2E18-3E18 atoms / cm 3 ; viii. The doping source of S14 uses CBr4, and the doping concentration is 2E19-6E19 atoms / cm 3 .

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