An epitaxial method for InGaAs layered linear gradient variation buffer layers based on molecular beam epitaxy

Abstract

This invention discloses an epitaxial method for InGaAs layered linear gradient variation buffer layers based on molecular beam epitaxy, comprising the following steps: S1: Determine the total variation range of the specific In composition and the total thickness of the linear variation of In, and calculate the retreat composition of the retreat layer based on the variation rate of the In composition; S2: Design the InGaAs linear gradient buffer layer in layers and determine the thickness of the entire layer; S3: Determine the value of the In composition after actual epitaxy, and adjust the In composition and thickness in step S2 according to the value after actual epitaxy; S4: Determine the growth rate of each gradient layer of InGaAs; S5: Epitaxially construct the InGaAs layered linear gradient variation buffer layer based on the layer thickness and the growth rate of each gradient layer of InGaAs. This invention realizes the InGaAs layered linear gradient variation buffer layer. x Ga 1‑x As linear gradient buffer layer, the linear change of In composition in As reduces the influence of source furnace temperature changes on the uncertainty of In and Ga growth rate changes.

Description

Technical Field

[0001] This invention relates to the field of epitaxial technology, and more specifically, to an epitaxial method for InGaAs layered linear gradient variation buffer layers based on molecular beam epitaxy. Background Technology

[0002] InGaAs materials are widely used in optoelectronic materials and device research. In III-V semiconductor systems, heterogeneous mismatch epitaxy is typically required to combine different material systems. Researchers have been conducting extensive research on InGaAs metamorphic material growth techniques since 1970. GaAs-based high electron mobility transistors and heterojunction bipolar transistors based on InGaAs metamorphic material growth techniques have seen rapid development. In recent years, GaAs-based quantum well lasers and detectors fabricated using InGaAs metamorphic epitaxy have been frequently reported, achieving experimental results comparable to InP-based lattice-matched materials. Furthermore, InGaAs metamorphic epitaxy is considered an important way to improve the quality of 1.3μm-1.55μm optoelectronic devices.

[0003] However, InGaAs metamorphic materials inevitably face many challenges in material growth and device fabrication, the main problem being the significant lattice mismatch between the epitaxial layer and the substrate. This lattice mismatch creates dangling bonds at the interface between the two semiconductor materials, introducing interface states and resulting in numerous mismatch dislocations and defects, significantly degrading material quality and severely impacting device performance. The metamorphic buffer layer is a crucial transition layer for adjusting the lattice mismatch between the active region material and the substrate material. In InGaAs metamorphic gradient layers, as the In composition increases, the accumulated strain becomes increasingly large, making it difficult to maintain surface flatness during epitaxy. Furthermore, how to better avoid or reduce the occurrence of threading dislocations in the metamorphic buffer layer is also a problem that needs to be solved in the epitaxy of metamorphic buffer layers. These challenges greatly limit the quality of high-quality InGaAs metamorphic material epitaxy.

[0004] In the design of variable buffer layers, there are two common methods for designing gradient buffer layers: linear-graded and step-graded buffer layers (see [reference]). Figure 1Both of these design methods have been widely used in the research of materials and devices. Among them, the linear gradient variation buffer layer is considered to be a method that can effectively reduce the density of penetrating dislocations, thereby improving the quality of the variation material. The main reasons why the compositional gradient variation buffer layer can reduce the density of penetrating dislocations are: (1) The linear variation variation buffer layer has a large residual strain on the surface, which will exert a force on the penetrating dislocations in the variation layer, thereby causing the penetrating dislocations to bend towards the sidewall instead of penetrating upward into the active region structure; (2) The compositional gradient buffer layer extends the strain interface to the entire buffer layer, and the strain in the gradient buffer layer is greatly reduced, which to a certain extent prevents the formation of dislocation loops, and also facilitates the sliding of penetrating dislocations towards the sidewall to release strain, thereby reducing the upward extension of dislocations.

[0005] According to the classical J. Tersoff theory, for a linearly graded buffer layer, a setback layer needs to be introduced in the actual growth of heterogeneous materials to match the lattice of the setback layer and the heterogeneous transition layer, thereby eliminating the influence of residual strain on the growth of the active region material. x Ga 1-x When As is used as a variable buffer layer, the magnitude of the residual strain is determined by the rate of change of the In composition. (See [reference needed]) Figure 2 As shown. Currently, the epitaxial growth method using a gradient-and-reverse-composition buffer layer is considered the best method for effectively suppressing dislocation penetration into the active region and is widely used in optoelectronic devices, such as quantum lasers. However, for achieving linear compositional changes, most researchers achieve linear changes in the growth rates of In and Ga by linearly altering the source furnace temperatures of the In and Ga sources, ultimately realizing linear compositional changes. See [reference needed]. Figure 3 As shown. Theoretically, this method can achieve a linear change in In composition. However, in actual MBE epitaxy, the growth rates of In and Ga are not strictly proportional to the source furnace temperature. When the source furnace temperature changes in the low-temperature range, the growth rates of In and Ga change slowly, while in the high-temperature range, their growth rates change rapidly. This results in a non-linear change in In composition, thus limiting the quality of the anomalous epitaxial layer.

[0006] To address the aforementioned issues, existing technologies have employed methods starting with the Arrhenius equation to analyze the relationship between temperature and growth rate. Through mathematical modeling, Molly code is incorporated into the MBE control program to control the source furnace temperature, achieving more precise linear gradients in In composition. While this method can control the linear gradient of In composition with relatively high accuracy, the epitaxial method is complex and requires mathematical modeling for analysis, significantly increasing the complexity and difficulty of device epitaxy. Furthermore, not all MBE devices support external program control of the source furnace temperature. Therefore, this method cannot be widely applied. Summary of the Invention

[0007] This invention provides an epitaxial method for InGaAs layered linear gradient variation buffer layers based on molecular beam epitaxy, realizing the InGaAs layered linear gradient variation buffer layer. x Ga 1-x As the linear gradient buffer layer, the In composition changes linearly, while the temperature of the Ga furnace is kept constant to maintain the growth rate of Ga. The In composition is changed by changing the temperature of the In furnace, which reduces the influence of the uncertainty of the growth rate of In and Ga caused by the change of the source furnace temperature.

[0008] The primary objective of this invention is to solve the aforementioned technical problems. The technical solution of this invention is as follows:

[0009] An epitaxial method for InGaAs layered linear gradient variation buffer layers based on molecular beam epitaxy includes the following steps:

[0010] S1: Determine the total variation range of the specific In component and the total thickness of the linear variation of In, and calculate the retreat component of the retreat layer based on the variation rate of the In component;

[0011] S2: Design the InGaAs linear gradient buffer layer in layers and determine the thickness of the entire layer;

[0012] S3: Determine the value of the In component after actual epitaxy, and adjust the In component and thickness in step S2 according to the value after actual epitaxy;

[0013] S4: Determine the growth rate of each gradient layer in InGaAs;

[0014] S5: Based on the thickness of the layers and the growth rate of each gradient layer in InGaAs, an epitaxial InGaAs layer with linear gradient variation buffer layer is formed.

[0015] Furthermore, the total variation range of the specific In component and the total thickness with linear In variation were designed using J. Tersoff's theory.

[0016] Furthermore, the specific process of step S2 is as follows: the In component linear gradient layer is divided into layers to ensure that the In component in each layer changes to a preset value, and then the thickness of the entire layer is determined according to the amount of gradient In component.

[0017] Furthermore, the In component in each layer is varied to a preset value of 0.1.

[0018] Furthermore, the specific process of step S3 is as follows:

[0019] First, the node values ​​of the In component in step S2 are subjected to step-gradient epitaxy. That is, by keeping the Ga beam current constant, the In beam current is changed to change the proportion of the In component. The InGaAs epitaxy of each In component has a preset thickness. The higher the In component, the lower the temperature required during epitaxy.

[0020] Next, the epitaxial InGaAs stepped gradient layer was characterized by XRD and SEM to determine its actual In composition and epitaxial thickness.

[0021] Finally, the In composition and thickness designed in step S2 are adjusted based on the actual values.

[0022] Furthermore, the epitaxial thickness is preset to be 300nm.

[0023] Furthermore, the epitaxial rate of each InGaAs component can be calculated using the SEM data from step S3.

[0024] Furthermore, In 0.4-0.5 Ga 0.6-0.5 The growth rate of the gradient layer of As is (V 0.4 +V 0.5 ) / 2, V 0.4 and V 0.5 In 0.4 Ga 0.6 As and In 0.5 Ga 0.5 As growth rate.

[0025] Furthermore, in In composition graded epitaxy, the epitaxial rate of each graded layer is the average of the epitaxial rate of the lowest composition InGaAs and the epitaxial rate of the highest composition InGaAs.

[0026] Furthermore, the specific process of step S5 is as follows: the Ga beams of each layer are kept consistent, and the In source furnace of each layer ensures the linear change of In composition by using the linear temperature change that can be set by the MBE equipment itself according to the change of In composition; finally, after all InGaAs layered linear buffer layers are epitaxially completed, another InGaAs layer with In composition return is epitaxially epitaxially based on the calculated percentage of returned composition; at this point, the InGaAs layered linearly gradient buffer layer is completed.

[0027] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0028] This invention achieves a more precise linear change in the In composition of the InxGa1-xAs linear gradient buffer layer through layered linear epitaxy. Fewer dislocations or defects in the epitaxial InGaAs anisotropic buffer layer penetrate to the surface, resulting in lower surface roughness. By keeping the Ga furnace temperature constant, the growth rate of Ga remains constant. The In composition is changed by altering the In furnace temperature, reducing the influence of uncertain changes in the growth rates of In and Ga caused by variations in the source furnace temperature. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a linear gradient buffer layer and a gradient gradient buffer layer according to an embodiment of the present invention.

[0030] Figure 2 This is a graph showing the relationship between the In component and the linear change rate of In according to an embodiment of the present invention.

[0031] Figure 3 The graphs show the linear changes in the growth rates of In and Ga and the linear changes in the In composition in embodiments of the present invention.

[0032] Figure 4 This is an epitaxial diagram of the InGaAs layered linear gradient and the InGaAs linear gradient variant buffer layer in an embodiment of the present invention.

[0033] Figure 5 This is a flowchart illustrating the epitaxial growth process of the InGaAs layered linear gradient aberration buffer layer according to an embodiment of the present invention.

[0034] Figure 6 This is a diagram of the InGaAs stepped gradient epitaxial structure according to an embodiment of the present invention.

[0035] Figure 7 This is a stepped gradient XRD characterization diagram of an embodiment of the present invention.

[0036] Figure 8 This is a step-gradient SEM characterization image of an embodiment of the present invention.

[0037] Figure 9The images show the XRD characterization of the InGaAs layered linearly gradient aberration buffer layer and the original linearly gradient aberration buffer layer in this embodiment of the invention.

[0038] Figure 10 This is an AFM characterization diagram of the linearly gradient InGaAs a heterogeneous buffer layer according to an embodiment of the present invention.

[0039] Figure 11 This is an AFM characterization diagram of the InGaAs layered linear gradient aberration buffer layer according to an embodiment of the present invention. Detailed Implementation

[0040] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0041] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0042] Example 1

[0043] like Figure 1 As shown, an epitaxial method for InGaAs layered linear gradient mutation buffer layers based on molecular beam epitaxy divides the linearly gradient portion of InGaAs into several independent InGaAs linearly gradient layers, and then performs linear epitaxy on each InGaAs layer individually. The advantage of this epitaxial method is that it can transform InGaAs layers with large In composition variations into several InGaAs layers with small In composition variations. Because the In composition variation in each layer is small, the source furnace temperature change is small, thus greatly reducing the problem of non-linear In composition variation caused by large source furnace temperature changes. In the embodiments of this invention, the InGaAs mutation buffer layer comprises multiple layers, with the In composition variation in each layer being approximately 0.1. The epitaxial thickness of each layer should be strictly proportional to the amount of In composition variation. (See reference...) Figure 4 As shown in (a). This includes the following steps:

[0044] S1: Determine the total variation range of the specific In component and the total thickness of the linear variation of In, and calculate the retreat component of the retreat layer based on the variation rate of the In component;

[0045] In a specific embodiment, the total variation range of the In component and the total thickness with linear In variation are designed using J. Tersoff theory. Then, based on... Figure 2The curve is used to calculate the retreating component of the retreating layer based on the rate of change of the In component.

[0046] S2: Design the InGaAs linear gradient buffer layer in layers and determine the thickness of the entire layer;

[0047] It should be noted that after determining the total thickness, the linearly gradient In component layer is divided into layers, ensuring that the In component variation in each layer is the preset value. The thickness of the entire layer is then determined based on the amount of gradient In component. (See [reference needed]). Figure 4 (a). The In component of each layer changes to a preset value of 0.1.

[0048] S3: Determine the value of the In component after actual epitaxy, and adjust the In component and thickness in step S2 according to the value after actual epitaxy;

[0049] The specific process is as follows:

[0050] First, the node values ​​of each In component in step S2 are subjected to step-gradient epitaxy. That is, by keeping the Ga beam current constant, the In beam current is changed to change the In component ratio. The InGaAs epitaxial thickness of each In component is 300nm. The higher the In component, the lower the temperature required for epitaxy.

[0051] Next, the epitaxial InGaAs stepped gradient layer was characterized by XRD and SEM to determine its actual In composition and epitaxial thickness. (See [reference needed]). Figures 6-8 ;

[0052] Finally, the In composition and thickness designed in step S2 are adjusted based on the actual values.

[0053] S4: Determine the growth rate of each gradient layer in InGaAs;

[0054] The epitaxial rate of each InGaAs component can be calculated using the SEM data from step S3.

[0055] Furthermore, in In composition graded epitaxy, the epitaxial rate of each graded layer is the average of the epitaxial rate of the lowest composition InGaAs and the epitaxial rate of the highest composition InGaAs. For example, In... 0.4-0.5 Ga 0.6-0.5 The growth rate of the gradient layer of As is (V 0.4 +V 0.5 ) / 2, V 0.4 and V 0.5 In 0.4 Ga 0.6 As and In 0.5 Ga 0.5 The growth rate of As. The same applies to setting the growth temperature.

[0056] S5: Based on the thickness of the layers and the growth rate of each gradient layer in InGaAs, an epitaxial InGaAs layer with linear gradient variation buffer layer is formed.

[0057] The specific process is as follows: The Ga beam current remains consistent across all layers. For each layer's In source furnace, the linear temperature change of the In composition is ensured by adjusting the temperature within the MBE device itself, based on the variation in In composition. Finally, after the epitaxy of all InGaAs layered linear buffer layers is completed, another InGaAs layer with the returned In composition is epitaxially layered according to the calculated percentage of returned composition. At this point, the epitaxy of the InGaAs layered linearly gradient buffer layers is complete. See the epitaxy process documentation. Figure 5 .

[0058] Example 2

[0059] This embodiment is described in detail with reference to the accompanying drawings. Figure 1 To illustrate the relationship between the lattice mismatch degree of linear gradient buffer layers and stepped gradient buffer layers and the epitaxial thickness, this invention achieves the linear gradient buffer layer shown in the figure by linearly changing the proportion of In composition in InGaAs.

[0060] Figure 2 This is a graph showing the relationship between the setback layer and the linear change rate of In. According to J. Tersoff's theory, after the In component completes a linear gradient, there will be a large residual strain on the surface. The In component of the setback layer, introduced to eliminate this residual strain, is determined by the rate of linear change of the In component, and the relationship is as follows: Figure 2 As shown. Therefore, after completing the linear gradient of the In component, this invention will, according to... Figure 2 The relationship diagram shown introduces a retreat layer of In component to eliminate residual strain.

[0061] Figure 3 This figure shows the linear variation of In and Ga growth rates and the linear variation of In composition. It illustrates existing epitaxial methods for achieving linear gradients in In composition. In current techniques, linear variations in the growth rates of Ga and In are achieved by controlling the linear temperature changes of the Ga and In source furnaces, while simultaneously maintaining the same overall growth rate for both Ga and In. Since the In composition percentage is... (V In and V Ga (These are the growth rates of In and Ga, respectively), so the change in the In composition will be linear at this time.

[0062] Figure 4(a) is a structural diagram of the InGaAs layered linear gradient gradient aberration buffer layer designed and epitaxially constructed according to the scheme of this invention. The structure consists of three parts: a GaAs substrate, an InGaAs layered linear gradient layer, and an InGaAs retreat layer. In the InGaAs layered linear gradient layer, the In composition, ranging from 0.02 to 0.5, is divided into five layers, and the thickness and growth rate of each layer are calculated separately. The total thickness of the gradient layer is 650 nm. Based on the rate of change of the In composition in the gradient layer, a 12% In retreat layer is finally introduced. 0.38 Ga 0.62 As the return layer.

[0063] Figure 4 (b) is a structural diagram of the existing InGaAs anisotropic buffer layer with direct linear gradient. The linear gradient of the In composition is achieved through... Figure 3 The method described in the text directly transitions the composition from 0.02 to 0.5, with the same thickness of 650 nm, and finally epitaxially layers In. 0.38 Ga 0.62 The retreat layer of As. The characterization results of the epitaxy in this figure will be the same as... Figure 4 (a) Compare the characterization results of the extension.

[0064] Figure 5 This is a flowchart illustrating the epitaxial process for InGaAs with a layered, linearly graded variation buffer layer. The main epitaxial approach is to first determine the epitaxial rate and thickness of InGaAs at each In component node by using a step-by-step, linearly graded buffer layer. Then, the epitaxy is performed based on the actual epitaxial conditions. Figure 4 (b) InGaAs layered linearly gradient aberration buffer layer.

[0065] Figure 6 For the stepped gradient extensional structure diagram and Figure 7 For step-gradient XRD characterization, and Figure 8 The image shows a stepped gradient SEM representation. Before epitaxially growing the linearly gradient aberration buffer layer, it is necessary to epitaxially grow InGaAs at each In node to determine the thickness and growth rate of the linearly gradient layer. Figure 6 The extension of In was respectively 0.067 In 0.216 In 0.4 and In 0.016 In 0.3 In 0.5 Two InGaAs layers with six In components each, arranged in a stepped gradient, were used. The actual epitaxial thickness was determined using SEM, which then allowed for the determination of the actual epitaxial rate of each In component. XRD patterns were used to determine the actual percentage of In component in each InGaAs layer.

[0066] Figure 9XRD characterization images of the InGaAs layered linearly graded variation buffer layer and the original linearly graded variation buffer layer. In the XRD characterization image of the InGaAs layered linearly graded variation buffer layer epitaxially generated by the present invention, the substrate peak and In 0.38 Ga 0.62 Between As peaks and In 0.38 Ga 0.62 The XRD intensity curve after the As peak is flatter, which indicates that the gradient of the In component in the linear gradient buffer layer of InGaAs epitaxial layer of the present invention is close to linear.

[0067] Figure 10 for Figure 4 (b) AFM characterization of the linearly graded InGaAs aberrant buffer layer. The AFM characterization shows a classic cross-hatched pattern, with a clearly defined three-dimensional island structure, wide horizontal and vertical stripes, and a relatively rough RMS of 4.42 nm. This indicates that even with the introduction of the retreat layer, significant surface stress remains, suggesting that the effect of the linearly graded InGaAs layer is not particularly ideal.

[0068] Figure 11 for Figure 4 (a) AFM characterization of the InGaAs layered linearly graded cross-hatched anomalous buffer layer. The characterization shows that the surface still exhibits the classic cross-hatched pattern, but compared to… Figure 10 , Figure 11 The AFM image shows finer horizontal and vertical stripes, less surface undulation, and an RMS of only 2.37 nm, indicating a smoother surface. This suggests that the In composition variation in the InGaAs layered linearly gradient InGaAs anisotropic buffer layer epitaxially constructed using the present invention is closer to linear, resulting in surface residual strain close to the theoretical value. Furthermore, the addition of the retreat layer further eliminates the residual strain, leading to a smoother surface and a lower RMS.

[0069] By using the epitaxial method of this invention, the In composition in the obtained InGaAs heterogeneous buffer layer will exhibit a more accurate linear variation. This is because the present invention divides the variation of In composition into several small intervals for independent solution using a layered linear epitaxial method. This method utilizes the concept of calculus to avoid the problem of non-linear growth of In composition due to the non-linear relationship between the source furnace temperature and the growth rates of Ga and In. Through the scheme of this invention, an InGaAs heterogeneous buffer layer epitaxial wafer with a gradually varying In composition was epitaxially produced, with the In composition linearly varying layer by layer to 0.5 and then retreating to 0.38. See the detailed structural diagram. Figure 4 (a) Simultaneously, using existing technology, a direct linear gradient epitaxial wafer was epitaxially generated; see the structural diagram. Figure 4(b) XRD characterization was performed on both epitaxial wafers simultaneously; the results are shown in [reference needed]. Figure 9 .Depend on Figure 9 It can be seen that the XRD curve between the two peaks of InGaAs epitaxially produced using the method of this invention is flatter than that of InGaAs with a direct linear gradient. This indicates that the thickness of InGaAs per unit In composition is basically the same in layered epitaxy, which means that the change of In is closer to linear.

[0070] Because the change in In composition is more linear after adopting the present invention, fewer dislocations or defects in the epitaxial InGaAs anisotropic buffer layer of the present invention penetrate to the surface, resulting in lower surface roughness. AFM characterization was performed on the InGaAs layered linearly graded epitaxial wafer; the results are shown in [reference needed]. Figure 11 Compared to the AFM plot of a directly linearly gradient buffer layer, see [reference needed]. Figure 10 The surface roughness (RMS) of the buffer layer using the method of this invention is only 2.37 nm, which is less than the 4.43 nm of the buffer layer with direct linear gradient. Moreover, according to the AFM plot, both epitaxial methods have obvious cross-hatched patterns. However, the buffer layer with layered gradient epitaxy has finer and denser horizontal and vertical stripes, and the surface is smoother.

[0071] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An epitaxial method for InGaAs layered linearly graded metamorphic buffer layer based on molecular beam epitaxy, characterized in that, The method comprises the following steps: S1: determining the total variation range of the In component and the total thickness of the In linear variation, and calculating the rollback component of the rollback layer according to the variation rate of the In component; S2: layering the InGaAs linearly graded buffer layer, and determining the thickness of the entire layering; S3: determining the value of the In component after actual epitaxy, and adjusting the In component and the thickness in step S2 according to the value after actual epitaxy; S4: determining the growth rate of each InGaAs layering; S5: epitaxying the InGaAs layering linearly graded buffer layer according to the thickness of the layering and the growth rate of each InGaAs layering; The specific process of step S2 is: layering the In component linearly graded layer, ensuring that the In component of each layer changes by a preset value, and then determining the thickness of the entire layering according to the number of the In component that is graded; The specific process of step S3 is: First, the node values of the In component in step S2 are step-graded epitaxied, that is, by fixing the Ga beam unchanged and changing the In beam to change the proportion of the In component, the InGaAs of each In component is epitaxied by a preset thickness, and the higher the In component, the lower the temperature during epitaxy; Then, the step-graded epitaxied InGaAs layer is characterized by XRD and SEM to determine the actual In component and the epitaxied thickness; Finally, the In component and the thickness designed in step S2 are adjusted according to the actual value; The specific process of step S5 is: the Ga beam of each layering remains unchanged, the In source furnace of each layering changes according to the variation of the In component, the linear temperature change of the MBE equipment itself is set to ensure the linear change of the In component, and finally, an InGaAs layer with a rollback component is epitaxied according to the percentage of the rollback component calculated; thus, the InGaAs layering linearly graded buffer layer is epitaxied.

2. The method of claim 1, wherein the InGaAs graded layer is formed by molecular beam epitaxy. The total variation range of the In component and the total thickness of the In linear variation are designed by J. Tersoff theory.

3. The method of claim 1, wherein the InGaAs graded layer is formed by molecular beam epitaxy. Each layer of the In component changes by a preset value of 0.

1.

4. The method of claim 1, wherein the InGaAs graded layer is formed by molecular beam epitaxy. The epitaxied preset thickness is 300 nm.

5. The method of claim 1, wherein the InGaAs graded layer is formed by molecular beam epitaxy. The epitaxied rate of each component InGaAs can be calculated through the SEM data in step S3.

6. The method of claim 1, wherein the InGaAs graded layer is formed by molecular beam epitaxy. In 0.4-0.5 Ga 0.6-0.5 As of the graded layer is (V 0.4 + V 0.5 ) / 2, V 0.4 and V 0.5 are growth rates of In 0.4 Ga 0.6 As and In 0.5 Ga 0.5 As, respectively.

7. The method of claim 6, wherein the InGaAs graded layer is formed by molecular beam epitaxy. In the In component graded epitaxy, the epitaxied rate of each layer is the average value of the InGaAs epitaxied rate of the lowest component and the InGaAs epitaxied rate of the highest component.

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