A nonlinear waveguide structure and method of growing the same

Abstract

The application relates to a nonlinear waveguide structure and a growth method thereof. In the growth process, the composition is controlled by continuously changing parameters, so that the composition realizes continuous nonlinear change, and then the refractive index changes nonlinearly with the waveguide thickness, thereby obtaining the nonlinear waveguide structure. The nonlinear waveguide structure can be an InGaN waveguide layer with continuous In composition or an InGaN / GaN superlattice waveguide layer. Under the same conditions, compared with linear waveguides and constant refractive index waveguides, the nonlinear waveguide of the application can effectively reduce the laser threshold current, improve the optical power and the service life, and improve the comprehensive performance. In the case of growing the same thickness, the nonlinear waveguide of the application has better optical confinement performance than the linear waveguide, requires shorter time, can realize continuous and rapid growth, can save the growth time of the epitaxial structure, improve the production efficiency, and reduce the production cost.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology, specifically relating to a nonlinear waveguide structure and its growth method. Background Technology

[0002] Semiconductor lasers are crucial optoelectronic devices, boasting advantages such as high power, small size, high efficiency, and a wide wavelength range, making them essential for applications in laser cutting, laser welding, laser display, laser lighting, laser communication, and laser detection. GaN-based semiconductor lasers, in particular, can emit wavelengths covering the visible light spectrum from ultraviolet to green light, exhibiting exceptionally high luminous efficiency—the highest photoelectric conversion efficiency among all light-emitting devices—thus securing their irreplaceable applications in numerous fields. Although GaN-based lasers have been commercialized, with companies like Sharp in Japan and Osram in Germany already producing GaN laser products, research into their structure and performance is far from over. The industry continuously strives for higher luminous efficiency, greater luminous power, and a wider wavelength range, with new technologies being invented every year, demonstrating the ongoing advancements in human understanding of this field. The main feature of this invention is the optimized design and implementation of the laser's waveguide structure, achieving superior performance and further enhancing the capabilities of GaN-based lasers.

[0003] To generate laser light, three basic conditions are typically required: 1. The working medium must achieve population inversion; 2. The pump source must provide the energy for particles to transition to higher energy levels; 3. An optical resonator must be available to generate optical gain. Common semiconductor side-emitting laser structures are designed as follows: Figure 1 As shown. The active region (multi-quantum-well heterojunction) is the working medium. Under external power supply or light source pumping, holes in the P-region and electrons in the N-region recombine in the active region to generate photons. When the pump energy exceeds a threshold, the condition for population inversion is met, making it the core light-emitting region. To meet the conditions of an optical resonant cavity, two parallel smooth surfaces are typically designed in the light-emitting direction to act as the resonant cavity, such as... Figure 1As shown in (a). To obtain gain, it is also necessary to confine the light in two other axes perpendicular to the emission direction to reduce light dissipation and improve the gain of the resonant cavity. In edge-emitting stripe semiconductor lasers, different optical confinement methods are usually used in the two axes perpendicular to the emission direction, mainly gain waveguides and refractive index waveguides. The gain waveguide structure uses a limited contact area to localize the injected carriers, mainly concentrating them along the entire cavity length below the contact area. The refractive index changes in the region with current injection, becoming slightly higher than in the region without injection, thus playing a role in optical confinement. The final effect is that optical gain is only generated in this region with carrier injection, and the light is also confined to this region to a certain extent. However, the refractive index change caused by carrier injection is very small. Therefore, the optical confinement capability of a simple gain waveguide is poor, and a large amount of light field will leak into the non-gain region and be absorbed, resulting in a high laser threshold. The combination of refractive index waveguides and gain waveguides is more common to achieve better optical confinement. Refractive index waveguides confine light by controlling the refractive index through the design and manipulation of the material composition. For compound semiconductor lasers (such as GaAs and GaN), it's impossible to alter the local material composition using ion implantation. Therefore, refractive index control is achieved by growing materials with different compositions during epitaxial growth or by etching away material in certain areas before growing other materials. Due to fabrication limitations of semiconductor lasers, the light-confining waveguides in the left and right directions of edge-emitting semiconductor lasers are typically created by etching away material on both sides and then depositing an insulating dielectric film (such as SiO2) with a refractive index lower than that of the semiconductor material, forming a waveguide structure like... Figure 1 As shown in (a), the ridge structure has a low equivalent refractive index on both sides, and the current is injected only from above the ridge. Therefore, transverse light is confined to the region below the ridge, which is the effect of combining a gain waveguide and a refractive index waveguide. In the other axis, perpendicular to the plane, a refractive index waveguide is achieved by controlling the composition of the grown material during epitaxial growth, such as... Figure 1As shown in (b), the upper and lower waveguide layers confine light within the active region. This confines light in four directions (up, down, left, and right), allowing light to exit from the resonant cavity surfaces at the front and rear, forming a laser beam. The upper and lower waveguides are located on either side of the active region, close to the core area, and are therefore crucial structures. The design parameters for the upper and lower waveguide layers mainly include waveguide layer thickness, refractive index structure, crystal quality, doping concentration, and stress distribution. These parameters are critical to improving laser performance. Specifically, the refractive index and waveguide layer thickness jointly determine the waveguide layer's ability to confine light emitted from the active region; crystal quality and doping concentration determine the amount of light absorbed; and stress distribution alters the polarization state and band structure of the quantum well, affecting the emission wavelength and laser lifetime. Various design approaches and implementation methods exist for these parameters of the upper and lower waveguide layers. This invention focuses on the design optimization and implementation methods for the thickness and refractive index structure of the upper and lower waveguide layers. The refractive index waveguides in the left and right directions are a matter of manufacturing processes and are not the focus of this invention. Unless otherwise specified, waveguides in this article will specifically refer to... Figure 1 (b) shows the upper and lower waveguide structures.

[0004] The refractive index structure of a waveguide layer refers to the change in its refractive index as the waveguide layer's thickness varies; that is, the functional relationship between the refractive index and the waveguide thickness. There are two common waveguide refractive index structures, such as... Figure 2 As shown, one type is a constant refractive index structure, where the refractive index remains constant with the waveguide thickness, and the other type is a structure where the refractive index changes linearly with the waveguide thickness.

[0005] The refractive index of the waveguide layer in a semiconductor laser is related to its composition; therefore, the refractive index can be controlled by adjusting the composition ratio during growth. Taking a GaN-based blue-green edge-emitting laser as an example, the quantum well is typically InGaN with a high In content and a low refractive index. The matching waveguide layer is typically InGaN with a low In content. During growth, by adjusting the growth parameters to reduce the In content, a waveguide structure with a higher refractive index than the active region can be grown.

[0006] In existing technologies, the advantage of constant refractive index structures is their simple growth method; a constant waveguide structure can be achieved by maintaining fixed parameters during the growth of the upper and lower waveguides. The advantage of linear waveguide structures is the relative ease of calculating the average refractive index, making it easier to evaluate the relationship between optical confinement capability and waveguide thickness. Comparing the two, with equal average refractive indices, linear refractive index waveguides offer better optical confinement capability and reduce mismatch stress. Under the same conditions, linear refractive index waveguide structures have lower threshold current and higher optical power.

[0007] The disadvantages of existing technology are:

[0008] 1) For waveguides of the same thickness, the light confinement capability of a constant refractive index waveguide is not as good as that of a graded waveguide with an average refractive index equal to a constant refractive index.

[0009] 2) Controlling the growth of linearly graded waveguides is quite difficult. A common approach is to divide the waveguide thickness into multiple thin layers. The parameters are fixed during the growth of each layer, and the growth conditions are slightly adjusted towards the design values ​​when growing the next layer, until all the designed thin layers have been grown. Finally, through large-scale approximation, a waveguide structure approaching a linear refractive index distribution is obtained, such as... Figure 3 As shown, it is clear that the more slices there are, the closer the distribution approximates to linearity. Therefore, to obtain a good linear waveguide, it is usually necessary to perform hundreds of thin-layer segmentation. Thus, the growth process of this method is very cumbersome, difficult to control, and has low production efficiency.

[0010] 3) Constant composition (refractive index) waveguides: Because the refractive index of the waveguide is significantly higher than that of the active region, the composition difference is also large. This leads to a large lattice mismatch at the interface, resulting in not only significant mismatch stress and polarization charge, affecting the band structure of the quantum well, but also generating more dislocations and shortening the laser lifetime. In InGaN waveguides, the higher the refractive index, the lower the In content. When the In content drops to zero, it becomes GaN material. The growth temperature of low-In-content InGaN is higher than that of high-In-content InGaN because higher temperatures reduce the incorporation of In atoms. Therefore, the waveguide layer growth temperature is higher than that of the active region. Furthermore, high-In-content InGaN is unstable at high temperatures, easily decomposing or undergoing compositional segregation, forming In clusters and reducing the luminous efficiency of the quantum well. Therefore, for the growth of constant refractive index waveguides, when growing a quantum well with high In composition (In composition 15-30%) and then growing an InGaN waveguide with low In composition (In composition 1-10%), the growth temperature needs to be increased by tens of degrees Celsius, which can easily cause the quantum well performance to degrade.

[0011] 4) While linear waveguides, by dividing themselves into a sufficiently large number of thin layers, minimize parameter variations between adjacent layers, thus reducing mismatch stress and dislocations, the large number of layers also leads to numerous interfaces between these layers. These interfaces are typically regions with many point defects; hundreds of thin-layer interfaces can generate a significant number of point defects, increasing optical absorption loss and hindering laser performance. Furthermore, the numerous interfaces result in greater roughness, which also increases light absorption. Summary of the Invention

[0012] To address the above-mentioned problems, this invention provides a nonlinear waveguide structure and its growth method.

[0013] The technical solution adopted in this invention is as follows:

[0014] A nonlinear waveguide structure is disclosed, wherein the refractive index of the nonlinear waveguide structure varies nonlinearly with the waveguide thickness, and the nonlinear variation of the refractive index is achieved through nonlinear variation of the components.

[0015] Furthermore, the nonlinear change of the components is achieved by adjusting the components through continuously changing parameters during the growth process, thereby enabling continuous changes in the components.

[0016] Furthermore, the continuously changing parameters include at least one of the following: temperature and gas source flow rate.

[0017] Furthermore, the nonlinear change in refractive index is a parabolic nonlinear change.

[0018] Furthermore, the nonlinear waveguide structure is an InGaN waveguide layer with continuously varying In composition or an InGaN / GaN superlattice waveguide layer.

[0019] Furthermore, the mass fraction of In component in the InGaN waveguide layer or InGaN / GaN superlattice waveguide layer starts at 0%-10% and ends at 0%-10%; the thickness of the InGaN waveguide layer or InGaN / GaN superlattice waveguide layer is 25nm-500nm.

[0020] A method for growing a nonlinear waveguide structure involves continuously varying parameters to control the composition during the growth process, thereby enabling continuous nonlinear changes in the composition and causing the refractive index to change nonlinearly with the waveguide thickness, thus obtaining a nonlinear waveguide structure.

[0021] Furthermore, the continuous nonlinear variation of the components through continuously changing parameters is achieved using one of the following three methods:

[0022] 1) Variable flow growth: The temperature is kept constant during the growth process, and the gas flow rate is adjusted;

[0023] 2) Variable temperature growth: During the growth process, the gas supply flow rate is kept constant, and the temperature is regulated;

[0024] 3) Synergistic growth: During the growth process, both temperature and air flow are regulated so that temperature and air flow change simultaneously.

[0025] A semiconductor laser includes a waveguide layer, wherein the waveguide layer employs the nonlinear waveguide structure of the present invention.

[0026] Furthermore, the waveguide layer of the semiconductor laser includes an upper waveguide layer and a lower waveguide layer located on both sides of the active region; the upper waveguide layer and the lower waveguide layer are InGaN waveguide layers or InGaN / GaN superlattice waveguide layers with continuously varying In composition, and the region near the active region has a high In composition content.

[0027] The core innovation of this invention is the proposal of a structural design and implementation method for a nonlinear waveguide, the main objectives of which are as follows:

[0028] 1) The upper waveguide layer is generally unintentionally doped, meaning Mg is not intentionally added as a p-type dopant to reduce absorption. However, this results in relatively poor conductivity in the waveguide layer, increasing the series resistance of the laser, raising the turn-on voltage, generating more heat, and shortening the device's lifetime. Reducing the waveguide layer thickness without compromising its optical confinement capability would improve device performance. For waveguides of the same thickness and average refractive index, nonlinear waveguides can provide better optical confinement than linear and constant refractive index waveguides. Therefore, while achieving the desired optical confinement capability, the waveguide layer thickness can be further reduced, thereby lowering the series resistance, reducing heat generation, and increasing lifetime.

[0029] 2) The nonlinear waveguide designed in this invention has a relatively high In composition in a large area near the active region. Therefore, when growing low In composition at high temperature, the active region is already covered by a thick waveguide layer, which is beneficial to protect the quantum well, reduce the degradation of the quantum well, and thus improve the performance of the quantum well.

[0030] 3) Nonlinear waveguides, due to their continuous growth without obvious growth interfaces, reduce the number of point defects formed at the interfaces, improve surface smoothness, reduce light absorption, reduce heat generation, and increase lifetime. They also lower the laser threshold and increase power. Therefore, nonlinear waveguides can achieve comprehensive performance improvements in multiple aspects.

[0031] To achieve the above objectives, the main innovation of this invention is to transform linear In-component graded InGaN into parabolic linear InGaN.

[0032] The beneficial effects of this invention are as follows:

[0033] 1. Under the same conditions, the nonlinear waveguide of the present invention can effectively reduce the threshold current of the laser, improve the optical power and lifetime, and enhance the overall performance of the laser compared with linear waveguides and constant refractive index waveguides.

[0034] 2. When growing the same thickness, the nonlinear waveguide of the present invention requires less time than the linear waveguide. This is because there is no need to wait for the parameters to stabilize during the process of parameter changes, so continuous and rapid growth can be achieved. This saves the growth time of epitaxial structures, improves production efficiency, and reduces production costs. Attached Figure Description

[0035] Figure 1It is an edge-emitting strip semiconductor laser; (a) schematic diagram of its external shape, (b) schematic diagram of its epitaxial structure.

[0036] Figure 2 These are common waveguide refractive index structures; (a) constant refractive index waveguide, (b) linearly graded refractive index waveguide.

[0037] Figure 3 This is a schematic diagram of an approximate linear distribution of refractive index using a slice method.

[0038] Figure 4 This is a schematic diagram showing the relationship between TMIn flow rate and In composition during the variable flow rate growth process.

[0039] Figure 5 This is a schematic diagram showing the relationship between temperature and In composition during variable-temperature growth.

[0040] Figure 6 This is a schematic diagram showing the relationship between temperature, TMIn flow rate, and In composition during the synergistic growth process.

[0041] Figure 7 The test results are for linear In-component varying InGaN waveguides and nonlinear In-component varying InGaN waveguides; (a) Secondary ion mass spectrum (SIMS) of In atoms in the actual grown linear In-component varying InGaN waveguide laser, (b) Secondary ion mass spectrum (SIMS) of In atoms in the actual grown nonlinear In-component varying InGaN waveguide laser, (c) Laser performance test LIV plot of the linear waveguide, and (d) Laser performance test LIV plot of the nonlinear waveguide. Detailed Implementation

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0043] Taking MOCVD growth of InGaN as an example, lower growth temperatures are more conducive to the incorporation of In atoms, and higher In source (trimethylindium™In) flux also favors In atom incorporation. In other words, to obtain InGaN with a higher In composition, it is necessary to lower the temperature or increase the In source flux, or both. To obtain InGaN with a lower In composition, the opposite is true. However, the In composition does not change linearly with temperature or In source flux; both temperature and In source flux have nonlinear effects on the In composition of InGaN. Based on this knowledge, this invention designs three methods for growing nonlinear InGaN waveguide layers:

[0044] 1. Maintaining a constant temperature while adjusting the In flow rate is called variable flow rate growth.

[0045] 2. With a constant In flux, the temperature decreases in the regions of the waveguides near the quantum well on both sides; this method is called variable-temperature growth.

[0046] 3. Temperature and In flow rate change simultaneously. During the growth process, both temperature and In flow rate are adjusted. This method is called synergistic growth.

[0047] The following describes three methods for growing nonlinear waveguides, where all percentages representing component content are mole fractions. The first method is the variable flow rate growth method, using the growth of InGaN waveguides with 5% to 0% In content as an example. First, the initial growth conditions must be selected: 5% In content, a temperature of 780°C, and a TMIn flow rate of 520 sccm. The flow rates of the carrier gas and other sources are not the focus of this invention; parameters matching these conditions are sufficient. Maintaining the growth temperature at 780°C, the variable In flow rate is set to the time required to grow the desired InGaN waveguide thickness. Since the growth temperature is constant and the In content is relatively small, changes in the In flow rate have little impact on the InGaN growth rate. The required growth time can be calculated based on the growth rate of InGaN with an average In content of 2.5% at 780°C. For example, under the experimental settings of this invention, growing a 300 nm thick InGaN waveguide with an average In content of 2.5% requires 20 minutes. The equipment supports a linear variation mode, where the time for the In source flow rate to ramp from 520 sccm to 0 sccm is set to 20 minutes. Figure 4 As shown, in this mode, as the In flux decreases, the In composition of InGaN exhibits a parabolic nonlinear variation with waveguide thickness.

[0048] The second method is variable-temperature growth. Taking the realization of InGaN waveguides with 5% to 0% In composition as an example, the initial conditions are 5% In composition, a temperature of 780℃, and a TMIn flow rate of 520 sccm. A key difference between variable-temperature and variable-flow-rate growth is that variable-temperature growth significantly affects the overall growth rate. Within a certain temperature range, increasing the temperature makes the organometallic source more prone to decomposition, thus accelerating the growth rate of InGaN. Growing a 300nm InGaN nonlinear waveguide only requires approximately 18 minutes. On the other hand, increasing the temperature increases the migration rate of In atoms, thereby reducing the incorporation of In atoms. Under the combined effect of these two factors, the decrease in In composition accelerates with increasing temperature, resulting in a nonlinear change in composition. For example... Figure 5As shown, under the experimental conditions, when the temperature rises to 900℃, the In composition is essentially close to zero, thus achieving the growth of a nonlinear waveguide. A significant advantage of the variable-temperature growth method is that the crystal quality of the waveguide layer improves with increasing temperature, which helps reduce light absorption and enhance the device's light-emitting performance.

[0049] The third method is the co-growth method. Taking the realization of InGaN waveguides with 5% to 0% In composition as an example, the initial conditions are 5% In composition growth, a temperature set at 780℃, and a TMIn flow rate set at 520 sccm. Co-growth, where the temperature and flow rate are combined, adjusts the shape of the nonlinear curve. Ramping the TMIn flow rate from 520 sccm to 0 and the temperature from 780℃ to 900℃, it takes approximately 18 minutes to grow a 300 nm thick InGaN waveguide. Figure 6 As shown, in this case, the In composition in InGaN changes faster in the initial stage and slower towards the end with the thickness, thus achieving the goal of adjusting the shape of the nonlinear curve and enriching the means of composition control. Furthermore, the temperature of the synergistic growth method also increases, and the crystal quality of the waveguide layer is improved.

[0050] To illustrate the advantages of nonlinear waveguides, this invention describes the growth and fabrication of lasers with linear and nonlinear waveguide structures. To ensure comparability, the structures and fabrication processes are identical except for the growth method of the InGaN waveguide. The nonlinear waveguide was grown using a co-growth method. By designing the rate of change of In flux, an InGaN nonlinear waveguide with an In composition close to a parabola was grown, reaching a thickness of 300 nm and taking approximately 18 minutes. The linear InGaN waveguide layer was grown using a conventional thin-layer slicing method. Flux and temperature were kept stable within each thin layer. The 300 nm InGaN waveguide layer was sliced ​​into 150 thin layers, with an average thickness of 2 nm per layer. Because it required waiting for temperature and flux to stabilize, the overall time was increased; growing a 300 nm thick linear InGaN waveguide took approximately 50 minutes. Since the laser structure requires two waveguide layers to confine the light, the overall time for growing the linear waveguide was approximately 64 minutes longer than that for the nonlinear waveguide. For lasers grown using both methods, this invention uses secondary ion mass spectrometry (SIMS) to obtain the compositional distribution of In atoms in the InGaN waveguide, such as... Figure 7 As shown in (a) and (b), the results demonstrate that the present invention yields InGaN waveguides with good linearly graded In composition and InGaN waveguides with parabolic In composition, indicating that the method achieves the expected design. Performance tests were performed on both types of lasers, as follows: Figure 7As shown in (c) and (d), using the same maximum current of 0.1A, the threshold current of the linear waveguide laser was 0.045A, and the optical power was 75mW, while the threshold current of the parabolic waveguide was 0.04A, and the optical power was 93mW. Compared to the linear waveguide laser, the parabolic waveguide laser has a threshold current that is about 11% lower and an optical power that is about 22% higher. This is because the parabolic waveguide layer has more functional advantages, which significantly improves the laser performance.

[0051] Compared with linear waveguides, the parabolic waveguide of this invention has the following key functional advantages:

[0052] 1. With the same average In composition, nonlinear waveguides have better optical confinement capabilities, thereby reducing optical field leakage, reducing optical loss, lowering the threshold, and increasing optical output power.

[0053] 2. Nonlinear gradients facilitate stress release in the quantum well, reduce the quantum confinement Stark effect (QCSE) of the quantum well, thereby reducing the change in wavelength with the injection current and making the spectrum more stable.

[0054] 3. The higher In content near the quantum well region helps reduce the generation of mismatched dislocations between the waveguide layer and the confinement layer, thereby reducing the number of penetrating dislocations entering the quantum well. This reduces leakage current, which in turn reduces heat generation and improves lifetime.

[0055] 4. When growing thick InGaN films, using parabolic composition can make the surface smoother and flatter, which is beneficial to the growth of subsequent structures, improves crystal quality, and thus reduces absorption.

[0056] In addition to the solutions described in the above embodiments, the following alternative solutions can also be used to achieve the same objective of the present invention:

[0057] 1. Nonlinear lines can have many variations; the parabola is just one of them.

[0058] 2. The starting point of the In composition in nonlinear InGaN can be 0%-10%, and the ending point can be 0%-10%;

[0059] 3. The thickness of InGaN waveguides can vary from 25nm to 500nm;

[0060] 4. The upper InGaN waveguide can be undoped or Mg-doped (1E18-1E20), and the lower waveguide can be undoped or Si-doped (1E17-5E19).

[0061] 5. InGaN can be replaced with an InGaN / GaN superlattice, such as a 10nm InGaN superlattice. 0.04 Ga 0.96 N is equivalent to 5nmIn0.08 Ga 0.92 Since N / 5nm GaN superlattices can be used, InGaN waveguides can be replaced with InGaN / GaN superlattices with graded In composition. The period of the superlattice can also be a variable, and the thinnest superlattice can be as long as 2nm / 2nm.

[0062] 6. The nonlinear waveguide implementation scheme of this invention is mainly aimed at metal-organic chemical vapor deposition (MOCVD), but is not limited to MOCVD growth equipment with various configurations. One of its features is that the In composition in the InGaN waveguide layer can be continuously varied by continuously changing parameters (temperature, gas source flow rate). However, there are other ways to implement nonlinear waveguides, because there are other methods for growing GaN, such as molecular beam epitaxy (MBE). Therefore, nonlinear waveguides can also be grown using MBE, but the specific implementation method may differ from the three methods mentioned above. However, this does not prevent nonlinear waveguides from improving the optical performance of lasers.

[0063] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A nonlinear waveguide structure, characterized in that, The refractive index of the nonlinear waveguide structure varies nonlinearly with the waveguide thickness. This nonlinear variation in refractive index is achieved through nonlinear variations in the composition. The nonlinear variations in the composition are achieved by continuously varying parameters during the growth process to enable continuous nonlinear changes in the composition. This continuous nonlinear variation in the composition is achieved through one of the following three methods: 1) Variable flow growth: The temperature is kept constant during the growth process, and the gas flow rate is adjusted; 2) Variable temperature growth: During the growth process, the gas supply flow rate is kept constant, and the temperature is regulated; 3) Synergistic growth: During the growth process, both temperature and air flow are regulated, so that temperature and air flow change simultaneously; The variable flow rate growth includes growing InGaN waveguides with an In composition ranging from 5% to 0%. The steps include: first, selecting initial growth conditions, growing with an In composition of 5%, setting the temperature to 780℃, and setting the TMIn flow rate to 520 sccm; keeping the growth temperature constant at 780℃, setting the variable In flow rate according to the time required to grow the required InGaN waveguide thickness, calculating the required growth time based on the growth rate of InGaN with an average In composition of 2.5% under 780℃ conditions, and setting the time for the In source flow rate to continuously change from 520 sccm to 0 sccm as the growth time. As the In flow rate decreases, the In composition of InGaN exhibits a parabolic nonlinear change with the waveguide thickness. The variable-temperature growth involves growing InGaN waveguides with an In composition ranging from 5% to 0%. The steps include: initial conditions of 5% In composition, a temperature set to 780°C, and a TMIn flow rate set to 520 sccm. Increasing the temperature makes the organometallic source easier to decompose, thus accelerating the growth rate of InGaN. On the other hand, the increased temperature also increases the migration rate of In atoms. Under the combined effect of these two factors, the decrease in In composition accelerates with increasing temperature, resulting in a nonlinear change in composition. When the temperature rises to 900°C, the In composition is essentially close to zero, achieving the growth of a nonlinear waveguide. The synergistic growth includes growing InGaN waveguides with 5% to 0% In composition. The steps include: initial conditions of 5% In composition growth, temperature set to 780℃, and TMIn flow rate set to 520 sccm; adjusting the shape of the nonlinear curve by superimposing the two factors of temperature and flow rate; continuously changing the TMIn flow rate from 520 sccm to 0 and the temperature from 780℃ to 900℃. The In composition in InGaN changes with thickness, accelerating in the initial stage and slowing down at the end, thereby achieving the purpose of adjusting the shape of the nonlinear curve.

2. A method for growing the nonlinear waveguide structure according to claim 1, characterized in that, During the growth process, the composition is continuously adjusted by changing parameters, which makes the composition continuously nonlinear, and thus the refractive index changes nonlinearly with the waveguide thickness, thereby obtaining a nonlinear waveguide structure. The continuous nonlinear variation of components by adjusting the parameters through continuous changes can be achieved using one of the following three methods: 1) Variable flow growth: The temperature is kept constant during the growth process, and the gas flow rate is adjusted; 2) Variable temperature growth: During the growth process, the gas supply flow rate is kept constant, and the temperature is regulated; 3) Synergistic growth: During the growth process, both temperature and gas flow rate are regulated so that temperature and gas flow rate change simultaneously.

3. A semiconductor laser, comprising a waveguide layer, characterized in that, The waveguide layer adopts the nonlinear waveguide structure described in claim 1.

4. The semiconductor laser according to claim 3, characterized in that, The waveguide layer includes an upper waveguide layer and a lower waveguide layer located on both sides of the active region; the upper and lower waveguide layers are InGaN waveguide layers with continuously varying In composition, and the region near the active region has a high In composition content.

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