Method for producing an epitaxial structure

Abstract

A preparation method of an epitaxial structure, comprising: selecting a substrate; growing a first Ga compound layer on the substrate by limiting migration of Ga atoms at a first temperature, the first Ga compound layer being formed in an island shape in a three-dimensional growth mode; growing a second Ga compound layer on the first Ga compound layer by promoting fusion of Ga compound islands at a second temperature higher than the first temperature, the second Ga compound layer being formed in a continuous film in a three-dimensional to two-dimensional complete or incomplete conversion growth mode; and growing a third Ga compound layer on the second Ga compound layer in a two-dimensional growth mode by accelerating migration ability and threading dislocation movement of Ga atoms at a third temperature higher than the second temperature. By setting the second Ga compound layer, a buffering effect is achieved, fusion between GaAs islands is promoted, a continuous film is formed on the GaAs surface as early as possible, surface roughness is reduced, and a two-dimensional planar growth mode is achieved as soon as possible.

Description

Technical Field

[0001] This invention belongs to the field of silicon-based optoelectronic materials and devices in the field of semiconductor technology, and in particular, a method for preparing an epitaxial structure. Background Technology

[0002] With the explosive growth of data traffic, data centers, as hubs of data flow, face increasingly higher demands on information processing, storage, and transmission capabilities. Low-cost, low-power, and high-bandwidth Si-based optoelectronic integrated circuits hold significant application value in high-speed optical interconnect networks within data centers and other applications. Based on CMOS technology, combining existing microelectronics and optoelectronics technologies fully leverages the advantages of mature microelectronic processes, high integration, low cost, and the high transmission rate, low power consumption, and anti-interference capabilities of photons, elevating modern electronic information technology and industry to new heights. However, due to silicon's indirect bandgap semiconductor and low luminous efficiency, it is difficult to use as the efficient and reliable light source required in silicon-based optoelectronic integrated chips. Introducing high-gain III-V group semiconductors on silicon substrates to fabricate efficient laser sources can effectively solve this problem. Currently, heteroepitaxial InAs / GaAs quantum dot lasers (QD-LDs) on silicon substrates are a promising silicon-based light source integration solution. However, it is necessary to overcome the defects introduced into the epitaxial layer by polarity mismatch, lattice mismatch, and thermal expansion coefficient mismatch between GaAs materials and silicon substrates, such as antiphase domains, penetrating dislocations, and microcracks.

[0003] Heteroepitaxy of GaAs on Si or SOI substrates using metal-organic chemical vapor deposition (MOCVD) is a novel method for preparing silicon-based heteroepitaxial materials. Currently, molecular beam epitaxy (MBE) is commonly used to grow GaAs on Si, but this method is slow, has low yield, and is difficult to transition to InP material systems. MOCVD overcomes these difficulties. In a hydrogen atmosphere, Si(001) can form two-atom steps, overcoming the polarity mismatch between GaAs and Si and effectively suppressing reverse domains generated at the GaAs-Si interface, providing favorable growth conditions for heteroepitaxial GaAs compound semiconductors. By optimizing the growth conditions of the GaAs epitaxial layer, high-quality GaAs single-crystal thin films can be obtained. On one hand, InAs / GaAs quantum dot materials can be grown on this basis as O-band light sources; on the other hand, InP materials can be heteroepitaxially grown on this GaAs epitaxial film, providing a good transition buffer layer for 1.55-micron silicon-based quantum dot lasers. Currently, most methods for growing GaAs layers on Si substrates employ a two-temperature growth method. Although this method can form continuous single-crystal thin films, the GaAs / Si surface has high roughness and poor lattice quality, which makes it difficult to epitaxially grow subsequent multilayer heterostructures (quantum wells, superlattices). Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing an epitaxial structure, in order to at least partially solve at least one of the above-mentioned technical problems.

[0005] This invention provides a method for preparing an epitaxial structure, comprising:

[0006] S1: Select a substrate;

[0007] S2: On the above substrate, a first Ga compound layer is grown at a first temperature by restricting the migration of Ga atoms. The first Ga compound layer is formed as an island in a three-dimensional growth mode.

[0008] S3: On the first Ga compound layer, a second Ga compound layer is grown at a second temperature higher than the first temperature by promoting the fusion of Ga compound islands. The second Ga compound layer is formed as a continuous thin film in a growth mode of complete or incomplete conversion from three-dimensional to two-dimensional.

[0009] S4: On the second Ga compound layer described above, at a third temperature higher than the second temperature, a third Ga compound layer is grown in a two-dimensional growth mode by accelerating the migration ability of Ga atoms and the movement of penetrating dislocations.

[0010] According to one embodiment of the present invention, the substrate includes one of Si(001) substrate, SOI substrate, Si beveled substrate, GaP / Si pseudo-substrate, Ge / Si pseudo-substrate, and GaAs / Si pseudo-substrate.

[0011] According to one embodiment of the present invention, the substrate is subjected to cleaning and deoxidation treatments sequentially before the growth of the first Ga compound layer.

[0012] According to one embodiment of the present invention, the growth methods in the above steps S2, S3 and S4 are all metal-organic chemical vapor deposition.

[0013] According to one embodiment of the present invention, the thickness of the first Ga compound layer is 1 to 100 nm, and the first growth temperature is 350 to 550 °C.

[0014] According to one embodiment of the present invention, the first Ga compound layer comprises: GaAs, Al x Ga 1-x As or In x Ga 1- x AsyP 1-y .

[0015] According to one embodiment of the present invention, the second Ga compound layer comprises GaAs, wherein the thickness of the second Ga compound layer comprises 1 to 500 nm, and the second growth temperature comprises 400 to 650 °C.

[0016] According to one embodiment of the present invention, the growth mode of the second Ga compound layer, which involves a complete or incomplete conversion from three-dimensional to two-dimensional, is related to the growth thickness of the second Ga compound layer.

[0017] According to one embodiment of the present invention, when the growth thickness of the second Ga compound layer is 1 to 200 nm, the growth mode of the second Ga compound layer is an incomplete conversion from three-dimensional to two-dimensional; when the growth thickness of the second Ga compound layer is 201 to 500 nm, the growth mode of the second Ga compound layer is a complete conversion from three-dimensional to two-dimensional.

[0018] According to one embodiment of the present invention, the third Ga compound layer may include GaAs, wherein the thickness of the third Ga compound layer is 200-2000 nm, and the third growth temperature is 500-750 °C.

[0019] According to the method for preparing the epitaxial structure described above in the embodiments of the present invention, the second Ga compound layer acts as a buffer, promoting the fusion between GaAs islands, enabling the formation of a continuous thin film on the GaAs surface as early as possible, reducing surface roughness, and achieving a two-dimensional planar growth mode as quickly as possible. This avoids the situation where, due to excessively high temperatures, Ga atoms preferentially deposit on the islands, forming clusters that affect roughness and crystal quality. Attached Figure Description

[0020] Figure 1 This is a cross-sectional schematic diagram of the extensional structure according to an embodiment of the present invention;

[0021] Figure 2 To illustrate the atomic force microscopy (AFM) comparison images of 200 nm thick GaAs surfaces generated using different epitaxial growth methods according to embodiments of the present invention;

[0022] Figure 3 To illustrate the atomic force microscopy (AFM) comparison images of a 500 nm thick GaAs surface generated using different biological elongation methods according to embodiments of the present invention;

[0023] Figure 4 To illustrate the present invention, an electron tunneling contrast imaging (ECCI) comparison image of a 500 nm thick GaAs surface generated using different epitaxial growth methods is presented.

[0024] Figure 5This is a comparison of X-ray diffraction (XRD) rocking curves of GaAs generated using different external elongation methods according to an embodiment of the present invention.

[0025] Explanation of reference numerals in the attached figures

[0026] 1: Substrate;

[0027] 2: First Ga compound layer;

[0028] 3: Second Ga compound layer;

[0029] 4: Third Ga compound layer. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0031] This invention provides a method for preparing an epitaxial structure. By introducing a three-temperature growth method (i.e., introducing a second Ga compound layer at a second growth temperature between the first Ga compound layer and the third Ga compound layer), the obtained epitaxial layer can achieve lower surface roughness and higher crystal quality while remaining relatively thin.

[0032] This invention provides a method for preparing an epitaxial structure, comprising:

[0033] S1: Select a substrate;

[0034] S2: On the above substrate, a first Ga compound layer is grown at a first temperature by restricting the migration of Ga atoms. The first Ga compound layer is formed as an island in a three-dimensional growth mode.

[0035] S3: On the first Ga compound layer, a second Ga compound layer is grown at a second temperature higher than the first temperature by promoting the fusion of Ga compound islands. The second Ga compound layer is formed as a continuous thin film in a growth mode of complete or incomplete conversion from three-dimensional to two-dimensional.

[0036] S4: On the second Ga compound layer described above, at a third temperature higher than the second temperature, a third Ga compound layer is grown in a two-dimensional growth mode by accelerating the migration ability of Ga atoms and the movement of penetrating dislocations.

[0037] In some embodiments of the present invention, the substrate includes one of the following: Si(001) substrate, SOI substrate, Si beveled substrate, GaP / Si pseudo-substrate, Ge / Si pseudo-substrate, and GaAs / Si pseudo-substrate.

[0038] In some embodiments of the present invention, the substrate is subjected to cleaning and deoxidation treatments sequentially before the growth of the first Ga compound layer.

[0039] In some embodiments of the present invention, the growth methods in steps S2, S3, and S4 can all be metal-organic chemical vapor deposition.

[0040] In some embodiments of the present invention, the thickness of the first Ga compound layer includes 1 to 100 nm, for example, 1 nm, 15 nm, 35 nm, 68 nm, 100 nm, and the first growth temperature includes 350 to 550 °C, for example, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C.

[0041] In some embodiments of the present invention, the first Ga compound layer includes: GaAs, Al x Ga 1-x As or In x Ga 1- x AsyP 1-y .

[0042] In some embodiments of the present invention, the second Ga compound layer comprises GaAs, the thickness of the second Ga compound layer comprises 1 to 500 nm, for example, 1 nm, 88 nm, 250 nm, 380 nm, 500 nm, and the second growth temperature comprises 400 to 650 °C, for example, 400 °C, 450 °C, 500 °C, 600 °C, 650 °C.

[0043] In some embodiments of the present invention, the growth mode of the second Ga compound layer, which involves a complete or incomplete conversion from three-dimensional to two-dimensional, is related to the growth thickness of the second Ga compound layer.

[0044] In some embodiments of the present invention, when the growth thickness of the second Ga compound layer is 1 to 200 nm, for example, 1 nm, 50 nm, 100 nm, 150 nm, or 200 nm, the growth mode of the second Ga compound layer is an incomplete conversion from three-dimensional to two-dimensional; when the growth thickness of the second Ga compound layer is 201 to 500 nm, for example, 201 nm, 250 nm, 300 nm, 450 nm, or 500 nm, the growth mode of the second Ga compound layer is a complete conversion from three-dimensional to two-dimensional.

[0045] In some embodiments of the present invention, the third Ga compound layer may include GaAs, the thickness of the third Ga compound layer includes 200 to 2000 nm, for example 200 nm, 600 nm, 900 nm, 1500 nm, 2000 nm, and the third growth temperature includes 500 to 750 °C, for example 500 °C, 550 °C, 600 °C, 650 °C, 750 °C.

[0046] Figure 1 This is a cross-sectional schematic diagram of the extensional structure according to an embodiment of the present invention.

[0047] The method for preparing an epitaxial structure according to an exemplary embodiment of the present invention includes steps S1-S4.

[0048] S1: Select a substrate, the GaP / Si pseudo-substrate 1 used, with crystal orientation (100) and no oblique cut. Ultrasonically clean the substrate 1 in acetone and ethanol solution to remove organic matter on the surface. Then use the standard RCA-1 standard cleaning method to remove inorganic impurities and metal particle impurities on the surface of the substrate 1.

[0049] S2: On the substrate 1, a first Ga compound layer 2 is grown by metal-organic chemical vapor deposition at a temperature of 450°C by restricting the migration of Ga atoms. The first Ga compound layer 2 is formed in a three-dimensional growth mode as an island. The thickness of the first Ga compound layer 2 is 30 nm, the ratio of V / III (group V source flux As to group III source flux Ga) is 70, and the growth rate is 0.03 nm / s.

[0050] S3: On the first Ga compound layer 2, a second Ga compound layer 3 is grown at a temperature of 550°C by promoting the fusion of Ga compound islands. The second Ga compound layer 3 is formed as a continuous thin film in a growth mode of complete conversion from three-dimensional to two-dimensional. The growth thickness of the second Ga compound layer 3 is 170 nm, the ratio of V / III (group V source flux As to group III source flux Ga) is 50, and the growth rate is 0.21 nm / s.

[0051] S4: On the second Ga compound layer 3, at a temperature of 650°C, a third Ga compound layer 4 is grown in a two-dimensional growth mode by accelerating the migration ability of Ga atoms and the movement of penetrating dislocations. The growth thickness of the third Ga compound layer 4 is 300 nm, the ratio of V / III (group V source flux As to group III source flux Ga) is 45, and the growth rate is 1.17 nm / s.

[0052] Figure 2 To illustrate the atomic force microscopy (AFM) comparison images of 200 nm thick GaAs surfaces generated using different epitaxial growth methods according to embodiments of the present invention.

[0053] In a comparative example of the present invention, epitaxial wafers were prepared using the two-temperature method and the three-temperature method of the present invention, respectively, and compared.

[0054] Figure 2 The left side of the middle section (a) is a morphology diagram obtained by the traditional two-temperature method, that is, after the low-temperature seed layer is deposited, a 200nm thick high-temperature epitaxial layer is grown at high temperature. Figure 2 Part (b) on the right side of the image is a morphology diagram obtained by the preparation method of the present invention, that is, after growing a first Ga compound layer at a first growth temperature, a second Ga compound layer with a thickness of 200 nm is grown at a second growth temperature higher than the first growth temperature.

[0055] As can be seen from the comparison images, introducing a second Ga compound layer after growing the first Ga compound layer can significantly improve the surface morphology of GaAs. Compared to the high-temperature epitaxial layer of the traditional two-temperature method, the growth temperature of the introduced second Ga compound is slightly lower, the surface mobility of Ga atoms is lower, the resulting GaAs film has a more uniform distribution in the horizontal direction, and the size of unmerged pits on the surface is significantly reduced, thus lowering the surface roughness. This indicates that the introduction of the second Ga compound is beneficial for reducing the size and depth of pores, enabling the transition from three-dimensional to two-dimensional epitaxial film growth to be achieved earlier.

[0056] Figure 3 To illustrate the atomic force microscopy (AFM) comparison images of 500 nm thick GaAs surfaces generated using different epitaxial growth methods according to embodiments of the present invention;

[0057] Figure 4 To illustrate the present invention, an electron tunneling contrast imaging (ECCI) comparison image of a 500 nm thick GaAs surface is generated using different epitaxial growth methods.

[0058] Figure 5 This is a comparison of X-ray diffraction (XRD) rocking curves of GaAs generated using different epitaxial growth methods according to embodiments of the present invention. In another comparative example of the present invention, Figure 3 Part (a) on the left shows the surface morphology of a 500 nm thick epitaxial structure grown using the traditional two-temperature growth method. It can be seen that the sample surface has significant undulations, with a roughness of 1.01 nm within a 5 μm × 5 μm surface testing range; while Figure 3 The rightmost part (b) shows the surface morphology of a 500 nm thick epitaxial structure grown using the growth method of the present invention. Not only are more obvious atomic steps obtained, but the details of the step morphology are also clearer, and the roughness is reduced to 0.72 nm, a reduction of 28.7%.

[0059] Electron tunneling contrast imaging (ECCI) was used to observe the density of penetrating dislocations on the sample surface. After employing the growth method of this invention, a significant reduction in the density of penetrating dislocations was observed. Figure 4 The left side of the middle section (a) shows the traditional two-temperature growth method with a growth rate of 2.45 × 10⁻⁶. 9 cm -2 Reduce to Figure 4 The rightmost part (b) uses the 2.01 × 10⁻⁶ method of the present invention. 9 cm -2 It decreased by approximately 18%.

[0060] Furthermore, the XRD rocking curve test results of the epitaxial structures obtained by the above two growth methods are as follows: Figure 5 As shown, the full width at half maximum (FWHM) of the XRD rocking curve is reduced and the diffraction intensity is stronger after using the growth method of the present invention, which indicates that the epitaxial layer grown under this condition has higher crystal quality.

[0061] This is because the first Ga compound layer deposited on the GaP / Si substrate is grown using the SK growth mode: the GaAs epitaxial layer first grows layer by layer. When stress accumulates to a certain level (or the deposition thickness reaches a critical thickness), the GaAs epitaxial layer forms a large number of islands to release stress. As the epitaxial thickness increases, the GaAs islands continue to grow and further release stress by generating dislocations and defects. At this point, the growth mode is three-dimensional, resulting in poor surface smoothness. If high-temperature epitaxy is used directly at this stage, i.e., the traditional two-temperature growth method, the surface mobility of Ga atoms will be very high, and the newly deposited GaAs will be distributed in clusters, which is not conducive to the transition from three-dimensional to two-dimensional growth. Two-dimensional growth is conducive to the full sliding of penetrating dislocations, and when they meet, they will undergo fusion or annihilation reactions to reduce dislocations. Therefore, achieving two-dimensional growth with the epitaxial layer as thin as possible helps to reduce the density of penetrating dislocations. In the three-temperature growth method, a second Ga compound layer is inserted. The Ga atoms deposited at a second growth temperature, which is higher than the first growth temperature and lower than the third growth temperature, have a more uniform distribution in the horizontal direction, which is conducive to achieving two-dimensional growth more quickly. Finally, when epitaxy is performed at the third growth temperature, the epitaxial layer has achieved a two-dimensional planar growth mode. Ga atoms have strong transport capabilities between atomic layers, which determines the good uniformity of the epitaxial film in the vertical direction, thus improving the lattice quality and reducing the surface roughness. At the same time, two-dimensional growth means that there is less resistance when through dislocations slip, which helps them meet and disappear, thus reducing the through dislocation density.

[0062] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0063] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an epitaxial structure, comprising the following steps: S1: Select a substrate; the substrate includes one of Si(001) substrate, SOI substrate, Si beveled substrate, GaP / Si pseudo-substrate, Ge / Si pseudo-substrate, and GaAs / Si pseudo-substrate; S2: On the substrate, a first Ga compound layer is grown at a first temperature by restricting the migration of Ga atoms. The first Ga compound layer is formed in a three-dimensional growth mode as an island. The first Ga compound layer includes: GaAs, Al... x Ga 1-x As or In x Ga 1-x As y P 1-y ; S3: On the first Ga compound layer, a second Ga compound layer is grown at a second temperature higher than the first temperature by promoting the fusion of Ga compound islands. The second Ga compound layer is formed as a continuous thin film in a growth mode of complete or incomplete three-dimensional to two-dimensional conversion. The second Ga compound layer includes GaAs. The second temperature includes 400~650℃. The growth mode of complete or incomplete three-dimensional to two-dimensional conversion of the second Ga compound layer is related to the growth thickness of the second Ga compound layer. The thickness of the second Ga compound layer is 1~500nm. When the growth thickness of the second Ga compound layer is 1~200nm, the growth mode of the second Ga compound layer is incomplete three-dimensional to two-dimensional conversion. When the growth thickness of the second Ga compound layer is 201~500nm, the growth mode of the second Ga compound layer is complete three-dimensional to two-dimensional conversion. S4: On the second Ga compound layer, at a third temperature higher than the second temperature, a third Ga compound layer is grown in a two-dimensional growth mode by accelerating the migration ability of Ga atoms and penetrating dislocation movement, the third Ga compound layer comprising GaAs; The growth methods in steps S2, S3, and S4 are all metal-organic chemical vapor deposition.

2. The preparation method according to claim 1, wherein, The substrate is subjected to cleaning and deoxidation treatments sequentially before the first Ga compound layer is grown.

3. The preparation method according to claim 1, wherein, The thickness of the first Ga compound layer ranges from 1 to 100 nm, and the first temperature ranges from 350 to 550 °C.

4. The preparation method according to claim 1, wherein, The thickness of the third Ga compound layer is 200~2000 nm, and the third temperature is 500~750 °C.

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