A semiconductor structure and a manufacturing method thereof

Abstract

The present invention relates to a semiconductor structure and a manufacturing method in the field of semiconductor technology, comprising a substrate layer and an epitaxial layer, wherein the epitaxial layer is arranged on one end face of the substrate layer, a main waveguide is arranged on one end face of the epitaxial layer away from the substrate layer, a first coupling waveguide and a second coupling waveguide are also arranged on one end face of the epitaxial layer away from the substrate layer, and the first coupling waveguide is located on one side of the main waveguide, and the second coupling waveguide is located on the other side of the main waveguide, and the main waveguide, the first coupling waveguide and the second coupling waveguide are all curved waveguides, thereby solving the problem of how to improve the single transverse mode output power of a semiconductor device.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a semiconductor structure and a manufacturing method. Background Art

[0002] High-power single-transverse mode semiconductor optical amplifier (SOA) / semiconductor laser (SL) is widely used in fiber laser, fiber communication, space optical communication, material processing, pump source, detection and medical fields. Its basic structure is an optical waveguide with an active area. The transverse mode in the waveguide refers to the light intensity distribution of the light transmitted in the waveguide on the waveguide cross section. A single transverse mode (i.e., only the fundamental mode is transmitted) waveguide can bring higher output brightness and better beam quality to a single device, which is crucial for applications such as optical coupling amplification, detection and optical communication.

[0003] The ridge waveguide structure is a widely used index-guided waveguide that can achieve high beam quality (close to the diffraction-limited beam). The general single-transverse mode ridge waveguide suppresses or cuts off the high-order transverse mode through a narrow waveguide width, but the narrow waveguide width limits the volume of the active area, thereby limiting the output power. It also leads to higher thermal resistance and smaller light mode size and light-emitting aperture. The former will cause power saturation due to heat accumulation, and the latter will cause the light field intensity at the end face of the laser to be too high, resulting in catastrophic optical mirror damage, which will greatly reduce the laser output. Therefore, the output power of a general single-transverse mode ridge waveguide is relatively limited.

[0004] In order to solve the above problems, it is necessary to increase the active area volume and light mode size by increasing the waveguide width, while reducing thermal resistance. In order to ensure the single transverse mode operation of the waveguide while increasing the waveguide width, it is necessary to make the refractive index difference between the waveguide core (higher refractive index region) and the periphery (lower refractive index region) smaller. However, a smaller refractive difference will make the waveguide very sensitive to the refractive index change caused by thermal effects and carrier injection, resulting in mode instability. Especially when the operating current is much higher than the threshold current (general working conditions of high-power lasers), the spatial hole burning effect and thermal lens effect will make the high-order transverse mode easier to excite. Therefore, in order to increase the single transverse mode output power of the laser, a new method is needed to increase the threshold current of the high-order transverse mode relative to the fundamental mode. Summary of the invention

[0005] The present invention aims at the shortcomings of the prior art, provides a semiconductor structure and a manufacturing method, and solves the problem of how to improve the single transverse mode output power of a semiconductor device.

[0006] In order to solve the above technical problems, the present invention is solved by the following technical solutions:

[0007] A semiconductor structure comprises a substrate layer and an epitaxial layer, wherein the epitaxial layer is arranged on one end face of the substrate layer, a main waveguide is arranged on the end face of the epitaxial layer away from the substrate layer, a first coupling waveguide and a second coupling waveguide are also arranged on the end face of the epitaxial layer away from the substrate layer, and the first coupling waveguide is located on one side of the main waveguide, and the second coupling waveguide is located on the other side of the main waveguide, and the main waveguide, the first coupling waveguide and the second coupling waveguide are all curved waveguides.

[0008] Optionally, the direction from the second coupled waveguide to the first coupled waveguide is the first direction, the length direction of the epitaxial layer is the second direction, and the first direction is perpendicular to the second direction, the first direction and the second direction constitute a top-view plane, and the curve equation of any edge curve of the main waveguide, the first coupled waveguide, and the second coupled waveguide on the top-view plane is: 0≤x≤L, where y is the length in the first direction, x is the length in the second direction, is the end phase of the edge curve, L is the length of the main waveguide / first coupled waveguide / second coupled waveguide in the second direction, MinR is the minimum curvature radius of the edge curve, and θ is the initial phase of the edge curve.

[0009] Optionally, the edge curves of the main waveguide, the first coupled waveguide, and the second coupled waveguide are equidistant lines from each other, and based on the reference curve and the spacing between the equidistant lines, the curve equations of the edge curves of the main waveguide, the first coupled waveguide, and the second coupled waveguide except the reference curve are set.

[0010] Optionally, the width of the main waveguide is set to support at most a second-order transverse mode.

[0011] Optionally, the widths of the first coupling waveguide and the second coupling waveguide are set to satisfy a condition that the fundamental modes of the first coupling waveguide and the second coupling waveguide are phase-matched with the first-order transverse mode of the main waveguide.

[0012] Optionally, the width of the first coupling waveguide is set to satisfy a condition that the fundamental mode of the first coupling waveguide is phase-matched with the first-order transverse mode of the main waveguide; the width of the second coupling waveguide is set to satisfy a condition that the first-order transverse mode of the second coupling waveguide is phase-matched with the second-order transverse mode of the main waveguide.

[0013] Optionally, the distances between the first coupling waveguide and the second coupling waveguide and the main waveguide are respectively set to meet the condition that the difference between the fundamental mode loss and the high-order transverse mode loss of the main waveguide is maximized.

[0014] Optionally, a back electrode is provided on the substrate layer, and a first waveguide electrode is provided on the main waveguide, and a forward bias voltage is applied to the main waveguide through the first waveguide electrode.

[0015] Optionally, a second waveguide electrode 1 is arranged on the first coupling waveguide, and the second waveguide electrode 1 is grounded / suspended, or the second waveguide electrode 1 is used to apply a reverse bias voltage to the first coupling waveguide; a second waveguide electrode 2 is arranged on the second coupling waveguide, and the second waveguide electrode 2 is grounded / suspended, or the second waveguide electrode 2 is used to apply a reverse bias voltage to the second coupling waveguide.

[0016] Optionally, the contact area between the back electrode and the substrate layer is opposite to the position of the main waveguide on the epitaxial layer.

[0017] A method for manufacturing a semiconductor structure, wherein the method for manufacturing a semiconductor structure is used to prepare a semiconductor structure as described in any one of the above.

[0018] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0019] 1. A first coupled waveguide and a second coupled waveguide are respectively arranged on both sides of the main waveguide (a wide ridge waveguide with current injection) and are narrower and adjacent to the main waveguide. The modes of the first coupled waveguide and the second coupled waveguide are phase-matched with the high-order transverse mode in the main waveguide, so that the high-order transverse mode in the main waveguide can be coupled to the first coupled waveguide and the second coupled waveguide, while the fundamental mode of the main waveguide is basically unaffected. Since there is no current injection in the first coupled waveguide and the second coupled waveguide, their active regions have strong absorption of light, thereby effectively increasing the loss of the high-order transverse mode of the main waveguide;

[0020] 2. The main waveguide, the first coupling waveguide and the second coupling waveguide are all set as curved waveguides. Since the high-order transverse mode field is more distributed outside the waveguide core, the high-order transverse mode has a greater leakage loss in the curved waveguide. The continuous change of the curvature radius of the cosine / sine type curved waveguide can avoid the fundamental mode loss caused by the curvature radius jump. In addition, the curved waveguide can also increase the coupling efficiency of the high-order transverse mode, and the curved waveguides are equidistantly arranged adjacent to each other to ensure the consistency of the coupling and improve the stability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 A three-dimensional diagram of a semiconductor structure proposed in the first embodiment;

[0023] Figure 2 A cross-sectional view of a semiconductor structure proposed in the first embodiment;

[0024] Figure 3 A top view of a semiconductor structure proposed in the first embodiment;

[0025] Figure 4 This is a waveguide mode effect diagram of a semiconductor structure proposed in the first embodiment;

[0026] Figure 5 It is a cross-sectional view of a semiconductor structure proposed in the second embodiment.

[0027] Figure numerals: 1. substrate layer; 2. epitaxial layer; 3. main waveguide; 4. first coupling waveguide; 5. second coupling waveguide; 6. back electrode; 7. first waveguide electrode; 8. second waveguide electrode one; 9. second waveguide electrode two. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with embodiments. The following embodiments are for explanation of the present invention but the present invention is not limited to the following embodiments.

[0029] Embodiment 1

[0030] like Figure 1 and Figure 2 As shown, a semiconductor structure includes a substrate layer 1 and an epitaxial layer 2, wherein the epitaxial layer 2 is arranged on one end face of the substrate layer 1, a main waveguide 3 is arranged on the end face of the epitaxial layer 2 away from the substrate layer 1, and a first coupling waveguide 4 and a second coupling waveguide 5 are also arranged on the end face of the epitaxial layer 2 away from the substrate layer 1, and the first coupling waveguide 4 is located on one side of the main waveguide 3, and the second coupling waveguide 5 is located on the other side of the main waveguide 3, and the main waveguide 3, the first coupling waveguide 4 and the second coupling waveguide 5 are all curved waveguides. It should be noted that the semiconductor structure in this embodiment can be a laser or an optical amplifier, etc.

[0031] Among them, the direction from the second coupling waveguide 5 to the first coupling waveguide 4 is the first direction y, the length direction of the epitaxial layer 2 is the second direction x, and the first direction is perpendicular to the second direction, the first direction and the second direction constitute a top-down plane, and the height direction of the main waveguide 3 is the third direction, and the third direction is perpendicular to both the first direction and the second direction.

[0032] like Figure 3 As shown, the edge curve of the main waveguide 3 is Figure 3 f3, f4 in the figure, the edge curve of the first coupling waveguide 4 is Figure 3The edge curve of the second coupling waveguide 5 is as follows: Figure 3 In f5 and f6, the distance between the edge curve of the main waveguide 3 and the first coupling waveguide 4 is d1, that is, the distance between f2 and f3 is d1, the distance between the edge curve of the main waveguide 3 and the second coupling waveguide 5 is d2, that is, the distance between f4 and f5 is d3, the width of the first coupling waveguide 4 is w1, that is, the distance between f1 and f2 is w1, and the ridge height of the first coupling waveguide 4 is h1; the width of the main waveguide 3 is w, that is, the distance between f3 and f6 is w; the ridge height of the main waveguide 3 is h; the width of the second coupling waveguide 5 is w2, that is, the distance between f5 and f6 is w2, and the ridge height of the second coupling waveguide 5 is h2.

[0033] Furthermore, a back electrode 6 is provided on the substrate layer 1, a first waveguide electrode 7 is provided on the main waveguide 3, a forward bias voltage is applied to the main waveguide 3 through the first waveguide electrode 7, a second waveguide electrode 8 is provided on the first coupling waveguide 4, the second waveguide electrode 8 is grounded / suspended, or the second waveguide electrode 8 is used to apply a reverse bias voltage to the first coupling waveguide 4; a second waveguide electrode 29 is provided on the second coupling waveguide 5, the second waveguide electrode 29 is grounded / suspended, or the second waveguide electrode 29 is used to apply a reverse bias voltage to the second coupling waveguide 5. Specifically, the first waveguide electrode 7 is connected to the positive pole, the back electrode 6 is grounded, the current is injected from the main waveguide 3, flows through the active area below the main waveguide 3 and is grounded through the back electrode 6, the second waveguide electrode 18 and the second waveguide electrode 29 are grounded or suspended or reverse biased, and no current is injected. The electrode connection conditions of the first waveguide electrode 18 and the second waveguide electrode 29 can be the same or different.

[0034] In this embodiment, the back electrode 6 contacts the entire end face of the substrate layer 1. At this time, when current is injected, the active area below the main waveguide 3 is a gain area, which can perform light amplification, and the active area below the first coupling waveguide 4 and the second coupling waveguide 5 is an absorption area, which has a strong absorption effect on light. Therefore, after the high-order transverse mode in the main waveguide 3 is coupled to the first coupling waveguide 4 and the second coupling waveguide 5, its loss is greatly increased; on the other hand, the active area below the first coupling waveguide 4 and the second coupling waveguide 5 absorbs photons and generates photoelectrons. By grounding or reverse biasing the second waveguide electrode 1 8 and the second waveguide electrode 2 9, the extraction of photoelectrons can be accelerated to ensure the efficiency of continuous absorption of light.

[0035] The curve equation of any edge curve of the main waveguide 3, the first coupling waveguide 4 and the second coupling waveguide 5 on the top-view plane is: 0≤x≤L, and the selected edge curve is the reference curve, where y is the length in the first direction, x is the length in the second direction, is the end phase of the edge curve, L is the length of the main waveguide 3 / the first coupled waveguide 4 / the second coupled waveguide 5 in the second direction, MinR is the minimum radius of curvature of the edge curve, θ is the initial phase of the edge curve, the edge curves of the main waveguide 3, the first coupled waveguide 4 and the second coupled waveguide 5 are equidistant lines from each other, and based on the reference curve and the spacing between the equidistant lines, the curve equations of the edge curves of the main waveguide 3, the first coupled waveguide 4 and the second coupled waveguide 5 except the reference curve are set.

[0036] Specifically, since the radius of curvature of the cosine / sine waveguide changes continuously, the fundamental mode loss of the waveguide caused by the jump of the radius of curvature can be avoided. Therefore, any edge curve in the main waveguide 3, the first coupling waveguide 4 and the second coupling waveguide 5 is set to a cosine / sine type, and the formed curved waveguide is a cosine / sine curved waveguide, and the edge curve spacing is always kept equal, thereby ensuring the coupling consistency of the high-order transverse mode in the curved waveguide. On the other hand, since the high-order transverse mode field is more distributed outside the waveguide core, the high-order transverse mode has a larger leakage loss in the curved waveguide. In addition, the curved waveguide can also increase the coupling efficiency of the high-order transverse mode.

[0037] Specifically, Figure 3 As shown, taking f1 as the reference curve, the curve equation is: 0≤x≤L. Where k=φ / L, φ is the phase at the end of the curve; MinR is the minimum radius of curvature of the curve; θ is the initial phase of the curve. Therefore, the curve f1 is determined by four parameters: θ, φ, L and MinR, where L determines the distance between the two end faces of the device, that is, the length of the device, MinR determines the curvature of the curve, the smaller the MinR, the greater the curvature of the curve, which can adjust the leakage loss of the waveguide mode; θ determines the direction of the waveguide tangent at x=0, and φ determines the direction of the waveguide tangent at the other end of the device (x=L), which can meet the needs of some designs that require a waveguide with a specific output angle.

[0038] Further, in Figure 3 In the design shown, θ=0, φ=π, and taking f1 as the reference, the equidistant lines f2 to f6 can be determined by the following parametric equations: Xn=x-y'Dn / (1+(y')^2)^0.5, Yn=y+Dn / (1+(y')^2)^0.5, y' is the first-order derivative of y with respect to x, Dn is the distance between curve fn and curve f1, which can be obtained from w1, w2, d1, d2, w, n=2, 3, 4, 5, 6, 0≤x≤L.

[0039] Furthermore, the width of the main waveguide 3 is set to support at most the second-order transverse mode. At this time, there are two situations. When the main waveguide 3 supports two transverse modes, the fundamental mode and the first-order transverse mode, the width of the first coupling waveguide 4 and the second coupling waveguide 5 is set to meet the condition that the fundamental membrane of the first coupling waveguide 4 and the second coupling waveguide 5 is phase-matched with the first-order transverse mode of the main waveguide 3. The distance between the first coupling waveguide 4 and the second coupling waveguide 5 and the main waveguide 3 is set to meet the condition that the difference between the fundamental mode loss and the high-order transverse mode loss of the main waveguide 3 is maximized.

[0040] On the other hand, when the main waveguide 3 supports three transverse modes, namely, the fundamental mode, the first-order transverse mode and the second-order transverse mode, the width of the first coupling waveguide 4 is set to satisfy the phase matching condition between the fundamental mode of the first coupling waveguide 4 and the first-order transverse mode of the main waveguide 3, and the width of the second coupling waveguide 5 is set to satisfy the phase matching condition between the first-order transverse mode of the second coupling waveguide 5 and the second-order transverse mode of the main waveguide 3.

[0041] like Figure 4 As shown in FIG. 1 , it is an example of waveguide cross-section design. Assuming the operating wavelength is 1550 nm, the ridge height h2 of the second coupled waveguide 5 determines the refractive index difference Δn between the waveguide core and the periphery. To ensure the stability of the device under current injection and heating conditions, Δn can be set to 0.004 (it should be noted that the actual value of Δn can be set to other values ​​according to actual conditions, and 0.004 is only an example in this embodiment). The specific value of h2 can be determined by scanning the ridge height and calculating Δn using the numerical simulation method commonly used in waveguide design.

[0042] Then the width of the main waveguide 3 is designed, wherein the main waveguide 3 supports three transverse modes, namely the fundamental mode, the first-order transverse mode and the second-order transverse mode. In this embodiment, only the transverse electric mode is considered, because the quantum well in the active region has a much higher gain for the transverse electric mode polarization. In order to maximize the width of the main waveguide 3, the width of the main waveguide 3 can be set to just cut off the third-order transverse mode; then the width of the first coupling waveguide 4 is designed, and the width of the first coupling waveguide 4 is scanned by numerical simulation and its transverse mode is calculated, so that its fundamental mode and the first-order transverse mode of the main waveguide 3 are phase-matched, that is, The two have the same equivalent refractive index, so the width of the first coupling waveguide 4 can be determined, so that the width of the first coupling waveguide 4 is narrow and only supports fundamental mode transmission; finally, the width of the second coupling waveguide 5 is designed, and the same method is used to make the first-order transverse mode in the second coupling waveguide 5 and the second-order transverse mode in the main waveguide 3 phase-matched, so the width of the second coupling waveguide 5 can be determined, so that the second coupling waveguide 5 supports the fundamental mode and the first-order transverse mode, and its fundamental mode and the fundamental mode in the main waveguide 3 are not phase-matched, so they will not couple with each other.

[0043] On the other hand, the settings of d1 and d2 can be determined by numerical simulation to calculate the transverse modes of the overall three-waveguide structure, ensuring that the fundamental mode in the main waveguide 3 is stable and the high-order transverse modes are effectively coupled. The specific design optimization condition is to maximize the difference between the fundamental mode loss and the high-order transverse mode loss. The transverse modes in the final structure are as follows: Figure 4 As shown, it can be seen that the fundamental mode of the main waveguide 3 is basically unaffected, while the first-order transverse mode and the second-order transverse mode of the main waveguide 3 are coupled to the two coupling waveguides respectively, and their losses are greatly increased.

[0044] Embodiment 2

[0045] like Figure 5 As shown, the difference between this embodiment and the first embodiment is that the contact area between the back electrode 6 and the substrate layer 1 in this embodiment is relative to the position of the main waveguide 3 on the epitaxial layer 2, that is, the back electrode 6 only contacts the area of ​​the substrate layer 1 directly below the main waveguide 3, so that the current diffused to both sides from the main waveguide 3 to the active area below the first coupling waveguide 4 and the second coupling waveguide 5 can be reduced, thereby reducing the decrease in light absorption capacity caused by the diffusion current. It should be noted that, in this embodiment, only the contact area of ​​the back electrode 6, the first waveguide electrode 7, the second waveguide electrode 1 8 and the second waveguide electrode 2 9 is emphasized, and no specific limitation is made to the actual electrode size and shape.

[0046] On the other hand, the ridge height of each ridge waveguide can be increased so that the active area is truncated, thereby cutting off the current diffusing from the main waveguide 3 to the first coupling waveguide 4 and the active area below the second coupling waveguide 5. In this case, the second waveguide electrode 1 8 and the second waveguide electrode 2 9 can also be connected to a negative voltage, that is, a reverse bias voltage, to further accelerate the extraction of photoelectrons generated after the active area below the first coupling waveguide 4 and the second coupling waveguide 5 absorbs photons.

[0047] Embodiment 3

[0048] A method for manufacturing a semiconductor laser structure, the method for manufacturing a semiconductor laser device structure is used to prepare the semiconductor laser structure as described in any one of the first embodiments, specifically as follows:.

[0049] S1. Epitaxial growth: firstly, an epitaxial layer is grown on the substrate layer;

[0050] S2. Waveguide structure manufacturing: The waveguide etching area is defined by photolithography, and then the epitaxial layer of the corresponding area is etched away by conventional semiconductor process steps such as etching to complete the manufacturing of the waveguide structure;

[0051] S3, electrical isolation: grow a dielectric film on the chip surface to isolate the electrodes;

[0052] S4, opening a window in the electrode contact area: defining the electrode contact area by photolithography, and then etching away the dielectric film in the corresponding area by conventional semiconductor process steps such as etching to expose the electrode contact area;

[0053] S5. P electrode (positive electrode) manufacturing: the electrode area is defined by photolithography, and the P electrode (positive electrode) is manufactured in the corresponding area by conventional semiconductor process steps such as metal evaporation and stripping. Due to electrical isolation, the electrode only contacts the electrode contact area defined in the previous step;

[0054] S6, back side thinning and polishing: thinning and polishing the back side of the wafer;

[0055] S7, manufacturing of back N-electrode (negative electrode): manufacturing of N-electrode (negative electrode) on the back of wafer by conventional semiconductor process steps such as metal evaporation, and finally performing rapid thermal annealing to make all electrodes form ohmic contact;

[0056] S8, cleavage, coating and cutting: First, the processed wafer is cleaved into Bar strips, then the end surfaces of the Bar strips are coated, and finally the Bar strips are further cut into single chips.

[0057] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and evolutions of the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A semiconductor structure, characterized in that: The invention comprises a substrate layer and an epitaxial layer, wherein the epitaxial layer is arranged on one end face of the substrate layer, a main waveguide is arranged on one end face of the epitaxial layer away from the substrate layer, a first coupling waveguide and a second coupling waveguide are also arranged on one end face of the epitaxial layer away from the substrate layer, and the first coupling waveguide is located on one side of the main waveguide, and the second coupling waveguide is located on the other side of the main waveguide, the main waveguide, the first coupling waveguide and the second coupling waveguide are all curved waveguides, the direction from the second coupling waveguide to the first coupling waveguide is the first direction, the length direction of the epitaxial layer is the second direction, and the first direction is arranged perpendicular to the second direction, the first direction and the second direction constitute a top-view plane, and the curve equation of any one edge curve of the main waveguide, the first coupling waveguide and the second coupling waveguide on the top-view plane is: And the selected edge curve is the reference curve, where y is the length in the first direction, x is the length in the second direction, is the end phase of the edge curve, L is the length of the main waveguide / first coupled waveguide / second coupled waveguide in the second direction, MinR is the minimum curvature radius of the edge curve, and θ is the initial phase of the edge curve.

2. A semiconductor structure according to claim 1, characterized in that: The edge curves of the main waveguide, the first coupled waveguide, and the second coupled waveguide are equidistant lines from each other, and based on the reference curve and the spacing between the equidistant lines, curve equations of the edge curves of the main waveguide, the first coupled waveguide, and the second coupled waveguide except the reference curve are set.

3. A semiconductor structure according to claim 1, characterized in that: The width of the main waveguide is set to support at most the second-order transverse mode.

4. A semiconductor structure according to claim 1, characterized in that: The widths of the first coupling waveguide and the second coupling waveguide are set to meet the phase matching condition of the fundamental modes of the first coupling waveguide and the second coupling waveguide and the first-order transverse mode of the main waveguide.

5. A semiconductor structure according to claim 1, characterized in that: The width of the first coupled waveguide is set to satisfy the phase matching condition between the fundamental mode of the first coupled waveguide and the first-order transverse mode of the main waveguide; the width of the second coupled waveguide is set to satisfy the phase matching condition between the first-order transverse mode of the second coupled waveguide and the second-order transverse mode of the main waveguide.

6. A semiconductor structure according to claim 1, characterized in that: The distances between the first coupling waveguide and the second coupling waveguide and the main waveguide are respectively set to meet the condition that the difference between the fundamental mode loss and the high-order transverse mode loss of the main waveguide is maximized.

7. A semiconductor structure according to claim 1, characterized in that: A back electrode is disposed on the substrate layer, and a first waveguide electrode is disposed on the main waveguide. A forward bias voltage is applied to the main waveguide through the first waveguide electrode.

8. The semiconductor structure according to claim 1, characterized in that: A second waveguide electrode 1 is arranged on the first coupling waveguide, and the second waveguide electrode 1 is grounded / suspended, or the second waveguide electrode 1 is used to apply a reverse bias voltage to the first coupling waveguide; a second waveguide electrode 2 is arranged on the second coupling waveguide, and the second waveguide electrode 2 is grounded / suspended, or the second waveguide electrode 2 is used to apply a reverse bias voltage to the second coupling waveguide.

9. A semiconductor structure according to claim 7, characterized in that: The back electrode is in contact with the substrate layer and the main waveguide is located on the epitaxial layer.

10. A method for manufacturing a semiconductor structure, characterized in that: The method for manufacturing the semiconductor structure is used to prepare the semiconductor structure as claimed in any one of claims 1 to 9.

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