Preparation method of epitaxial wafer and epitaxial wafer

Abstract

The invention relates to a preparation method of an epitaxial wafer and the epitaxial wafer, and the preparation method of the epitaxial wafer comprises the steps: providing a substrate; executing a molecular beam epitaxial growth process, and repeating a plurality of growth cycles to form an epitaxial laminated structure on the substrate; wherein the epitaxial laminated structure comprises a plurality of groups of laminated units which are stacked along the growth direction, one group of laminated units is formed in each growth period, and each group of laminated units comprises at least two material layers which are stacked along the growth direction; wherein the material of the material layer comprises a III-V group compound; and in the process of repeating a plurality of growth cycles, the inflow of the V-group atomic beam flow is in a descending trend along with the growth cycles. Therefore, the stability of air pressure in the growth chamber is guaranteed, and the quality of the epitaxial wafer is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, and in particular to a preparation method of an epitaxial wafer and the epitaxial wafer. BACKGROUND

[0002] Molecular beam epitaxy (MBE) is a thin film epitaxial growth technology based on an ultrahigh vacuum environment. MBE is achieved by heating solid source materials to evaporate them into molecular beams, which are then sprayed onto the surface of a substrate at an appropriate temperature to achieve atomic-level deposition layer by layer and form a thin film. MBE technology is widely used in the field of optoelectronic devices due to its extremely low impurity contamination rate, precise beam control capability, and excellent interface steepness.

[0003] Some optoelectronic devices are provided with a laminated structure, which is usually formed by periodically stacking semiconductor materials with different properties. When the laminated structure is prepared using the MBE process, the epitaxial growth time is prolonged with the number of periods, resulting in a thermal accumulation effect in the growth chamber of the MBE equipment due to continuous heating of the source furnace and long-term radiation of the beam. Under the influence of the thermal accumulation effect, the gas pressure in the growth chamber increases with the growth period, affecting the ultrahigh vacuum environment, and then leading to poor quality of the prepared laminated structure.

[0004] Therefore, how to maintain the stability of the gas pressure in the growth chamber when growing multiple period material layers using the MBE process and ensure the growth quality of the laminated structure has become a technical problem to be solved in the field. SUMMARY

[0005] In view of the above, the embodiments of the present application provide a preparation method of an epitaxial wafer and the epitaxial wafer to solve at least one problem in the background art.

[0006] In a first aspect, the embodiments of the present application provide a preparation method of an epitaxial wafer, which comprises:

[0007] providing a substrate;

[0008] performing a molecular beam epitaxial growth process repeatedly for multiple growth periods to form an epitaxial laminated structure on the substrate; wherein the epitaxial laminated structure comprises multiple groups of laminated units stacked along a growth direction, each growth period forms a group of laminated units, and each group of laminated units comprises at least two material layers stacked along the growth direction.

[0009] wherein the material of the material layer comprises a group III-V compound; and during the repeating of the multiple growth periods, the V group atom beam flow input amount shows a downward trend with the growth period.

[0010] In combination with the first aspect of the present application, in an optional implementation, the V-group atom beam flux input amount remains unchanged in a single growth cycle.

[0011] In combination with the first aspect of the present application, in an optional implementation, the V-group atom beam flux input amount decreases by a range of 0.3% to 1.4% between two adjacent growth cycles.

[0012] In combination with the first aspect of the present application, in an optional implementation, the V-group atom beam flux input amount decreases by the same amount between two adjacent growth cycles.

[0013] In combination with the first aspect of the present application, in an optional implementation, the needle valve opening degree of the V-group atom beam flux source decreases with the growth cycle during the repeated multiple growth cycles.

[0014] In combination with the first aspect of the present application, in an optional implementation, the needle valve opening degree of the V-group atom beam flux source decreases by a range of 0.1% to 0.5% between two adjacent growth cycles.

[0015] In combination with the first aspect of the present application, in an optional implementation, the ratio of the V-group atom beam flux input amount to the III-group atom beam flux input amount is less than or equal to 20 in the first growth cycle, and the ratio of the V-group atom beam flux input amount to the III-group atom beam flux input amount is greater than or equal to 10 in the last growth cycle.

[0016] In combination with the first aspect of the present application, in an optional implementation, the material layer includes a first material layer and a second material layer; the V-group atom beam flux includes a first V-group atom beam flux for growing the first material layer and a second V-group atom beam flux for growing the second material layer.

[0017] In combination with the first aspect of the present application, in an optional implementation, the first V-group atom beam flux input amount and / or the second V-group atom beam flux input amount decreases with the growth cycle.

[0018] In combination with the first aspect of the present application, in an optional implementation, the epitaxial superlattice structure includes a Bragg reflector.

[0019] In a second aspect, the embodiments of the present application provide an epitaxial wafer prepared by the preparation method of the epitaxial wafer according to any one of the first aspect.

[0020] The application provides a preparation method of an epitaxial wafer and the epitaxial wafer, and in the process of performing a molecular beam epitaxy growth process, repeating a plurality of growth cycles, and forming an epitaxial laminated structure composed of a group III-V compound on a substrate, the amount of group V atom beam flow is controlled to decrease with the growth cycle, so that the amount of vapor in the growth chamber is reduced, and the gas pressure of the growth chamber is reduced, so as to effectively resist the influence of heat accumulation effect on the gas pressure in the growth chamber, maintain the stability of the gas pressure, and guarantee the growth quality of the epitaxial laminated structure.

[0021] Additional aspects and advantages of the application will be made apparent by the following description. BRIEF DESCRIPTION OF DRAWINGS

[0022] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0023] Figure 1 A flowchart of a preparation method of an epitaxial wafer provided in the embodiments of the application is shown in the figure;

[0024] Figure 2 A cross-sectional structure schematic diagram of an epitaxial wafer is shown in the figure;

[0025] Figure 3 A gas pressure change curve in a growth chamber in an epitaxial growth process in the related art is shown in the figure;

[0026] Figure 4 A gas pressure change curve in a growth chamber in an epitaxial growth process in the embodiments of the application is shown in the figure;

[0027] Figure 5 A surface roughness measurement point schematic diagram of an epitaxial wafer in the embodiments of the application is shown in the figure. DETAILED DESCRIPTION

[0028] The exemplary embodiments of the present application will be described hereinafter with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it is understood that the present application can be embodied in various forms and should not be limited by the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0029] In the following description, numerous specific details are given to provide a thorough understanding of the application. However, it will be apparent that the application can be practiced without one or more of the specific details. In other instances, well-known

[0030] In the drawings, the size of layers, regions, elements, and the like can be exaggerated for clarity. Like reference numerals can represent like elements throughout the several figures.

[0031] It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or connected to the other element or layer or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element, there are no intervening elements or layers present. It will be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the application. Similarly, a second element, component, region, layer or section discussed below could be termed a first element, component, region, layer or section without departing from the teachings of the application.

[0032] Spatially relative terms, such as "beneath", "below", "lower", "under", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" or "over" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0034] For a thorough understanding of the application, detailed descriptions will be made in the following description with specific steps and detailed structures, so as to illustrate the technical solutions of the application. The preferred embodiments of the application are described in detail as follows, however, the application can have other implementation manners in addition to these detailed descriptions.

[0035] Figure 1 The flowchart of the preparation method of the epitaxial wafer provided in the embodiments of the application is shown in the figure, and the preparation method comprises:

[0036] Step S101: providing a substrate;

[0037] Step S102: performing a molecular beam epitaxy growth process and repeating a plurality of growth cycles to form an epitaxial layer structure on the substrate; wherein the epitaxial layer structure comprises a plurality of groups of stacked layer units along a growth direction, each growth cycle forms a group of stacked layer units, and each group of stacked layer units comprises at least two material layers stacked along the growth direction; wherein the material of the material layer comprises a group III-V compound; and during the repeating of the plurality of growth cycles, the V group atom beam flow input amount decreases with the growth cycle.

[0038] Therefore, in the process of performing the molecular beam epitaxy growth process and repeating the plurality of growth cycles to form the epitaxial layer structure on the substrate, the embodiments of the application control the V group atom beam flow input amount to decrease with the growth cycle, so that the vapor amount in the growth chamber is reduced and the gas pressure of the growth chamber is reduced, thereby effectively resisting the influence of the heat accumulation effect on the gas pressure in the growth chamber, maintaining the stability of the gas pressure and the ultrahigh vacuum environment, and guaranteeing the growth quality of the epitaxial layer structure.

[0039] Firstly, step S101 is performed to provide a substrate 100.

[0040] The substrate 100 can be any suitable semiconductor substrate, for example, a bulk silicon substrate, which can also be at least one of the following materials: SiGe, SiC, SiGeC, TnAs, GaAs, InP or other group III and group V compound semiconductors, including multilayer structures formed by these semiconductors, etc., or a silicon-on-insulator (SOI), a silicon-germanium-on-insulator (SiGeOI) and a germanium-on-insulator (GeOI), or a sapphire substrate, etc. The present embodiment is not limited in this regard.

[0041] Before forming the epitaxial stack structure on the substrate 100, refer to Figure 2 The preparation method can further include forming a first buffer layer 200 on the substrate 100. In this way, the lattice mismatch between the epitaxial stack structure and the substrate 100 is reduced. The material of the first buffer layer 200 can be any suitable semiconductor material, and the present embodiment is not limited in this regard. The process of preparing the first buffer layer 200 can be the same as the process of preparing the epitaxial stack structure, and the present embodiment is not limited in this regard.

[0042] In some embodiments, the preparation method can further include forming a sacrificial layer 310 on the first buffer layer 200. It can be understood that in actual applications, the material layers such as the first buffer layer 200 and the substrate 100 in the epitaxial wafer need to be removed, and thus the corresponding material layers can be removed by etching the sacrificial layer 310. Optionally, the material of the sacrificial layer 310 includes Al 0.92 Ga 0.08 As.

[0043] In some embodiments, the preparation method can further include forming a wavelength adjustment layer 320 on the sacrificial layer 310. In this way, the reflection wavelength of the epitaxial stack structure can be adjusted by the wavelength adjustment layer 320. In some embodiments, the stack unit includes a first material layer and a second material layer, and the material of the wavelength adjustment layer 320 is the same as the material of the first material layer. Optionally, the material of the wavelength adjustment layer 320 includes GaAs.

[0044] Next, step S102 is performed, a molecular beam epitaxy growth process is performed, and a plurality of growth cycles are repeated to form an epitaxial stack structure 400 on the substrate 100; wherein the epitaxial stack structure 400 includes a plurality of groups of stack units 410 stacked along the growth direction, each growth cycle forms a group of stack units 410, and each group of stack units 410 includes at least two material layers stacked along the growth direction; wherein the material of the material layer includes a group III-V compound; during the repeating of the plurality of growth cycles, the group V atomic beam current input amount shows a downward trend with the growth cycle.

[0045] It can be understood that in the process of preparing the epitaxial stack structure 400, each growth cycle forms a group of stack units 410, and therefore a plurality of growth cycles are required to prepare a plurality of groups of stack units 410 constituting the epitaxial stack structure 400, and the epitaxial growth time is prolonged with the number of cycles, and a thermal accumulation effect is generated in the growth chamber. In the epitaxial growth process, in addition to the substrate surface, other places in the growth chamber will also adsorb group III atoms and group V atoms to form solid materials, which are evaporated into a gaseous state under the influence of the thermal accumulation effect, so that the amount of vapor in the growth chamber increases, and the gas pressure rises. Therefore, in the process of growing the epitaxial stack structure 400, the amount of group V atom beam current flowing in is reduced with the growth cycle in the embodiments of the present application, so that the amount of vapor in the growth chamber is reduced, and the gas pressure in the growth chamber is reduced. In this way, the influence of the thermal accumulation effect on the gas pressure in the growth chamber can be effectively resisted, the stability of the gas pressure and the ultrahigh vacuum environment can be maintained, and the growth quality of the epitaxial stack structure 400 can be ensured.

[0046] The material of the material layer can be any suitable group III-V compound, for example, it can be a compound formed by B, Al, Ga, In of group III and N, P, As, Sb of group V in the periodic table of elements, and specific examples include group III-V compounds such as GaAs, InGaAs, GaAsP, GaAsPSb, GaAsSb, AlGaAs, AlGaAsSb, AlGaAsP, InAlGaAs, InAlGaP, InGaAsSb, GaPSb and InGaAsP. The embodiments do not limit the material of the material layer.

[0047] Each group of stack units 410 includes at least two material layers having different materials, in other words, each group of stack units 410 includes at least a first material layer 411 and a second material layer 412, and the material of the first material layer 411 and the material of the second material layer 412 are different. In some embodiments, the element composition of the material layers in the stack unit 410 is different, for example, the material of the first material layer 411 is AlGaAs, and the material of the second material layer 412 is GaAs. In some other embodiments, the element composition of the material layers in the stack unit 410 is the same, but the element composition is different, for example, the material of the first material layer 411 is AlGaAs, and the material of the second material layer 412 is AlGaAs. 0.1 Ga 0.9 As, the material of the second material layer 412 is Al 0.3 Ga 0.7 As.

[0048] Please refer to Figure 2In some embodiments, the stack unit 410 can include two material layers stacked along the growth direction, and the material layers include a first material layer 411 and a second material layer 412. Specifically, the stack unit 410 includes the first material layer 411 and the second material layer 412 stacked along the growth direction. At this time, the epitaxial stack structure 400 includes the first material layer 411 and the second material layer 412 alternately and periodically stacked along the growth direction. Understandably, Figure 2 Only taking the case that the stack unit 410 includes two material layers stacked along the growth direction as an example, the present application does not exclude the case that the number of material layers is three or more than three, for example, the stack unit 410 includes three material layers stacked along the growth direction, and the material layers include a first material layer 411, a second material layer 412 and a third material layer; specifically, the stack unit 410 includes the first material layer 411, the second material layer 412 and the third material layer stacked along the growth direction. The present embodiment does not limit the number of material layers in the stack unit 410.

[0049] The epitaxial stack structure can include a Bragg reflector. As a key component in optoelectronic devices, the Bragg reflector (DBR) is usually composed of material layers with different refractive indices alternately and periodically stacked. When light propagates at the interface of materials with different refractive indices, part of the light is reflected. When the working center wavelength of the DBR is λ0and the thickness is d (d = λ0 / (4n)), the light is reflected on the upper and lower surfaces of each material layer, and the optical path difference of the two reflections is 0.5λ, and the half-wave loss brings a phase change of π, so that the reflected light is in phase and superimposed, enhancing the reflection coefficient. The refractive index difference and the number of periods of the material layer determine the reflectivity of the DBR, and the refractive index difference and the center wavelength λ0of the material layer determine the stopband width of the DBR. Compared with a superlattice structure also composed of different material layers alternately and periodically stacked, the thickness of each material layer in the DBR is larger, so that the growth time of the DBR is longer, and the thermal accumulation effect is more likely to occur. The thermal accumulation effect not only affects the surface quality of the DBR, but also affects the wavelength uniformity of the DBR, which has a significant impact on the performance of the DBR.

[0050] Next, the variation trend of the Group V atomic beam flux in the embodiments of the present application will be described in detail.

[0051] It should be noted that, in the embodiments of the present application, the amount of the group V atom beam flux decreases with the growth period, which is the amount of the group V atom beam flux used for preparing all the material layers in a single growth period. It can be understood that the total amount of the group V atom beam flux decreases with the growth period. When the stack unit has multiple material layers, in the group V atom beam fluxes used for preparing the material layers, the amount of any one or more of the group V atom beam fluxes decreases with the growth period, and the amount of the remaining group V atom beam fluxes remains unchanged. In this case, the total amount of the group V atom beam flux in each growth period also decreases.

[0052] In some embodiments, the stack unit includes a first material layer and a second material layer; the group V atom beam flux includes a first group V atom beam flux for growing the first material layer and a second group V atom beam flux for growing the second material layer; and the amount of the first group V atom beam flux and / or the amount of the second group V atom beam flux decreases with the growth period. As described above, when the stack unit has two material layers, the group V atom beam flux includes a first group V atom beam flux for growing the first material layer and a second group V atom beam flux for growing the second material layer. In a single growth period, the amount of the group V atom beam flux is the sum of the amount of the first group V atom beam flux and the amount of the second group V atom beam flux. The amount of at least one of the first group V atom beam flux and the second group V atom beam flux decreases with the growth period, and the amount of the remaining group V atom beam flux remains unchanged. In this case, the amount of the group V atom beam flux decreases with the growth period.

[0053] The first group V atom beam flux and the second group V atom beam flux can be beams of different group V atoms. For example, the material of the first material layer can be GaAs, the first group V atom beam flux is an As beam, and the material of the second material layer can be InAlGaP, and the second group V atom beam flux is a P beam. The present embodiments are not limited in this regard.

[0054] It should also be noted that, when the group V atom beam flux for growing a material layer includes multiple sub-beams, the amount of each sub-beam decreases with the growth period, and the ratio between the amounts of the sub-beams remains unchanged. For example, the material of a material layer is AlGaAsSb, and the group V atom beam flux includes an As beam and an Sb beam. The amount of the As beam decreases with the growth period, the amount of the Sb beam decreases with the growth period, and the ratio between the amount of the As beam and the amount of the Sb beam remains unchanged.

[0055] In some embodiments, the amount of the group V atom beam flux remains unchanged in a single growth period. The amount of the group V atom beam flux is regulated before the start of each growth period, and the amount of the group V atom beam flux is maintained during the growth of the material, so as to avoid the influence of the change in the amount of the group V atom beam flux on the growth of the material layer.

[0056] In this embodiment, the amount of the group V atomic beam flux decreases stepwise with the growth period, or the amount of the group V atomic beam flux decreases stepwise with the growth time. Understandably, if the growth period is taken as the independent variable of the amount of the group V atomic beam flux, the trend of the change of the amount of the group V atomic beam flux is shown in the coordinate system, at this time, the value point of the X axis is the growth period, and the value point of the Y axis is the amount of the group V atomic beam flux, then a plurality of discrete points will be shown in the coordinate system, and the trend of the decrease of the amount of the group V atomic beam flux can be called as the trend that the amount of the group V atomic beam flux decreases stepwise with the growth period. If the growth time is taken as the independent variable of the amount of the group V atomic beam flux, since each growth period corresponds to a growth time, then the discrete points in the coordinate system will be converted into horizontal line segments as the value point of the X axis changes from the growth period to the growth time, and the trend of the decrease of the amount of the group V atomic beam flux can be called as the trend that the amount of the group V atomic beam flux decreases stepwise with the growth time.

[0057] In some embodiments, the decrease range of the amount of the group V atomic beam flux between two adjacent growth periods includes 0.3% to 1.4%. Understandably, if the decrease range of the amount of the group V atomic beam flux is too large, the amount of the group V atomic beam flux decreases continuously with the growth period, and the amount of the group V atomic beam flux is too small at a certain growth period, the ratio of the group V / III atoms in the growth chamber is insufficient, and the material cannot be continuously grown, which forces the epitaxial growth to stop. Therefore, controlling the decrease range of the amount of the group V atomic beam flux in this range is more conducive to achieving the desired effect.

[0058] Alternatively, the decrease range of the amount of the group V atomic beam flux between each two adjacent growth periods is the same. Understandably, the decrease range of the amount of the group V atomic beam flux refers to the ratio of the decrease of the amount of the group V atomic beam flux between the current growth period and the previous growth period to the amount of the group V atomic beam flux in the previous growth period. For example, the decrease range of the amount of the group V atomic beam flux between each two adjacent growth periods is 0.3%; the ratio of the amount of the group V atomic beam flux in the second growth period to the amount of the group V atomic beam flux in the first growth period is 1-0.3%=99.7%, and the ratio of the amount of the group V atomic beam flux in the third growth period to the amount of the group V atomic beam flux in the second growth period is also 1-0.3%=99.7%, at this time, the ratio of the amount of the group V atomic beam flux in the third growth period to the amount of the group V atomic beam flux in the first growth period is (1-0.3%)(1-0.3%) = 99.4009%, and so on.

[0059] In some embodiments, the ratio of the decrease of the amount of the group V atomic beam flux between each two adjacent growth periods to the initial value of the amount of the group V atomic beam flux includes 0.3% to 1.4%; wherein the initial value of the amount of the group V atomic beam flux is the amount of the group V atomic beam flux in the first growth period.

[0060] Optionally, the amount of decrease of the flux of the group V atom beam between each two adjacent growth cycles is the same. For example, the amount of decrease of the flux of the group V atom beam between each two adjacent growth cycles is 0.3% of the initial value of the flux of the group V atom beam; the ratio of the flux of the group V atom beam in the first growth cycle to the initial value is 100%, so that the ratio of the flux of the group V atom beam in the second growth cycle to the initial value is 100% (1-0.3%) = 99.7%, the ratio of the flux of the group V atom beam in the third growth cycle to the initial value is 100% (1-2*0.3%) = 99.4%, and so on.

[0061] It can be understood that, in a conventional MBE device, a needle valve is arranged on a source furnace for generating a group V atom beam, and the flux of the group V atom beam into the growth chamber can be controlled by controlling the opening and closing of the needle valve. In some embodiments, during the repetition of multiple growth cycles, the opening degree of the needle valve of the group V atom beam source decreases with the growth cycle. Thus, by adjusting the opening degree of the needle valve of the group V atom beam source, the flux of the group V atom beam into the growth chamber can be quickly adjusted so that the flux of the group V atom beam into the growth chamber decreases with the growth cycle. Since the change in the opening degree of the needle valve is carried out in a very short time, in actual preparation, the opening degree of the needle valve can be adjusted before the start of each growth cycle, and the opening degree of the needle valve of the group V atom beam source remains unchanged in a single growth cycle, so that the flux of the group V atom beam into the growth chamber remains unchanged in a single growth cycle. It should be noted that the "group V atom beam source" in the embodiments of the present application can be understood as "a source furnace for generating a group V atom beam".

[0062] In some embodiments, the decrease range of the opening degree of the needle valve of the group V atom beam source between each two adjacent growth cycles includes 0.1% to 0.5%. It can be understood that, since the opening degree of the needle valve is usually expressed in percentage (%), which represents the ratio of the current valve passage cross-sectional area to the valve passage cross-sectional area when the valve is fully open, 0% represents that the valve is fully closed, and 100% represents that the valve is fully open. The decrease range of the opening degree of the needle valve can be understood as the ratio of the decrease amount of the opening degree of the needle valve of the group V atom beam source between the current growth cycle and the previous growth cycle to the opening degree of the needle valve of the group V atom beam source in the previous growth cycle.

[0063] It should be noted that, when the decrease range of the opening degree of the needle valve of the group V atom beam source is 0.1%, the decrease range of the flux of the group V atom beam is 0.3% correspondingly; when the decrease range of the opening degree of the needle valve of the group V atom beam source is 0.5%, the decrease range of the flux of the group V atom beam is 1.4% correspondingly.

[0064] Optionally, the needle valve opening of the group V atomic beam source decreases by the same amount between each two adjacent growth cycles. For example, the needle valve opening of the group V atomic beam source decreases by 0.1% between each two adjacent growth cycles; assuming that the needle valve opening of the group V atomic beam source is 100% in the first growth cycle, then the needle valve opening of the group V atomic beam source is 100% (1-0.1%) = 99.9% in the second growth cycle, the needle valve opening of the group V atomic beam source is 99.9% (1-0.1%) = 99.8001% in the third growth cycle, and so on.

[0065] In some embodiments, the needle valve opening of the group V atomic beam source decreases by an amount in the range of 0.3% to 1.4% between each two adjacent growth cycles. It is appreciated that since the needle valve opening is usually expressed in percentage (%), the decrease of the needle valve opening of the group V atomic beam source between each two adjacent growth cycles can also be expressed in percentage.

[0066] It is noted that when the needle valve opening of the group V atomic beam source decreases by 0.1%, the ratio of the decrease of the group V atomic beam flux to the initial value of the group V atomic beam flux is 0.3%; when the needle valve opening of the group V atomic beam source decreases by 0.5%, the ratio of the decrease of the group V atomic beam flux to the initial value of the group V atomic beam flux is 1.4%.

[0067] Optionally, the needle valve opening of the group V atomic beam source decreases by the same amount between each two adjacent growth cycles. For example, the needle valve opening of the group V atomic beam source decreases by 0.1% between each two adjacent growth cycles; assuming that the needle valve opening of the group V atomic beam source is 100% in the first growth cycle, then the needle valve opening of the group V atomic beam source is 99.9% in the second growth cycle, the needle valve opening of the group V atomic beam source is 99.8% in the third growth cycle, and so on.

[0068] It can be understood that in the embodiments of the present application, during the process of repeating multiple growth cycles, the amount of group V atomic beam flux input decreases with the growth cycle, the number of group V atoms input into the growth chamber decreases, and the ratio of group V / III atoms in the growth chamber decreases. Once the ratio is less than the growth requirement, the growth will be stopped, so it is necessary to ensure that the ratio of the amount of group V atomic beam flux input to the amount of group III atomic beam flux input in the last growth cycle can also meet the growth requirement. To achieve this requirement, the ratio of the amount of group V atomic beam flux input to the amount of group III atomic beam flux input in the first growth cycle is relatively large, but a too high ratio will affect the ultrahigh vacuum degree of the growth chamber, and in turn affect the growth quality. Therefore, in some embodiments, the ratio of the amount of group V atomic beam flux input to the amount of group III atomic beam flux input in the first growth cycle is less than or equal to 20; and the ratio of the amount of group V atomic beam flux input to the amount of group III atomic beam flux input in the last growth cycle is greater than or equal to 10. In this way, while ensuring the smooth progress of the growth, the ultrahigh vacuum environment in the growth chamber is avoided from being destroyed, which is more conducive to ensuring the growth quality of the epitaxial layered structure.

[0069] Next, take the substrate material as GaAs; the first buffer layer material is GaAs and the thickness is 5000 angstroms; the second buffer layer includes a first sublayer and a second sublayer stacked along the growth direction, the material of the first sublayer is Al 0.92 Ga 0.08 As and the thickness is 5000 angstroms, and the material of the second sublayer is GaAs and the thickness is 1021.3 angstroms; the layered unit includes a first material layer and a second material layer stacked along the growth direction, the material of the first material layer is Al 0.92 Ga 0.08 As and the thickness is 1190 angstroms, and the material of the second material layer is GaAs and the thickness is 1030 angstroms; the number of growth cycles is 40, i.e., the epitaxial layered structure has 40 groups of layered units as a specific example. During the epitaxial growth process, the change of the gas pressure in the growth chamber is specifically described.

[0070] In the epitaxial growth process of the related art, please refer to Figure 3, the first stage is a preparatory stage for growing the epitaxial stacked structure, in the early stage of the first stage, the GaAs substrate is gradually heated to a suitable growth temperature, and the heating of the GaAs substrate can cause material decomposition of the GaAs substrate, so that an appropriate amount of As beam is introduced into the growth chamber to make up for it, so that the amount of vapor in the growth chamber increases, the pressure increases, and while the GaAs substrate is heated, the growth frame in the growth chamber is also heated, both of which gradually increase the temperature in the growth chamber, and the pressure increases due to the temperature. Then, a buffer layer is grown on the substrate to prepare for the growth of the epitaxial stacked structure. Specifically, a first buffer layer GaAs with a thickness of 5000 angstroms is first grown on the substrate; then a second buffer layer is grown on the first buffer layer GaAs, that is, a first sublayer Al 0.92 Ga 0.08 As with a thickness of 5000 angstroms and a second sublayer GaAs with a thickness of 1021.3 angstroms, when growing Al 0.92 Ga 0.08 As, the group III beam and group V beam introduced into the growth chamber are relatively more, and the gas pressure in the growth chamber rises; when growing GaAs, the group III beam and group V beam introduced into the growth chamber are relatively less, and the gas pressure in the growth chamber decreases. During the growth of the buffer layer, as the beam is continuously introduced into the growth chamber, the growth substrate and the growth frame are continuously heated, and the gas pressure in the growth chamber generally shows an upward trend.

[0071] The second stage is a growth stage of the epitaxial stacked structure, in which 40 growth cycles are repeated on the substrate to grow multiple groups of stacked units stacked in the growth direction to form the epitaxial stacked structure, each group of stacked units includes a first material layer Al 0.92 Ga 0.08 As and a second material layer GaAs. Comparing the pressure changes between adjacent growth cycles, specifically, comparing the pressure value changes after the growth of the first material layer in adjacent growth cycles, the pressure value after the growth of the first material layer in the growth cycle S2 is greater than that in the growth cycle S1; the pressure value after the growth of the first material layer in the growth cycle S3 is greater than that in the growth cycle S2, and the same is true for the remaining growth cycles; it can be found that the pressure gradually increases between adjacent growth cycles as the growth proceeds. It should be noted that Figure 3 Specifically, 5 consecutive growth cycles of the 40 growth cycles are shown, and it can be understood that the pressure change trend in the growth chamber during the entire growth stage of the epitaxial stacked structure, that is, the 40 growth cycles, is the same as the pressure change trend shown by the 5 consecutive growth cycles.

[0072] The third stage is an end-of-growth stage, in which epitaxial growth has been stopped, heating of the substrate and the growth holder is stopped, the temperature in the growth chamber is reduced, and the gas pressure is reduced; and the molecular beam flow into the growth chamber is stopped, the vapor content in the growth chamber is reduced, and the gas pressure is reduced.

[0073] In the epitaxial growth process of the embodiments of the present application, please refer to Figure 4 , the gas pressure change in the first and third stages is basically consistent with the gas pressure change trend shown in Figure 3 , the difference is the gas pressure change in the second stage. By comparing the gas pressure change between adjacent growth periods, specifically, the change of the gas pressure value after the growth of the first material layer in adjacent growth periods can be compared; the gas pressure value after the growth of the first material layer in the growth period S2 is basically consistent with the gas pressure value after the growth of the first material layer in the growth period S1; the gas pressure value after the growth of the first material layer in the growth period S3 is basically consistent with the gas pressure value after the growth of the first material layer in the growth period S2, and the same is true for the remaining growth periods; it can be found that the gas pressure remains stable between adjacent growth periods. It should be noted that Figure 4 , the gas pressure change trend in the 40 growth periods is the same as the gas pressure change trend shown in the 5 continuous growth periods.

[0074] In the process of growing the epitaxial layer structure, keeping the gas pressure in the growth chamber stable is conducive to ensuring the growth quality of the epitaxial layer structure. AFM (Atomic Force Microscope) measurement of the epitaxial layer structure is performed, please refer to Figure 5 , the variance of the surface height distribution of the epitaxial layer structure is calculated, and specifically, three regions of the surface of the epitaxial layer structure (as shown in the block in Figure 5 ) are measured, it is found that the Rq (Root Mean Square Roughness) of the epitaxial layer structure is less than 0.25 nm, the surface roughness is low, and the surface quality is good. As can be seen, in the process of growing the multi-period epitaxial layer structure, by controlling the V-group atomic beam flow input amount to decrease with the growth period, the stability of the gas pressure in the growth chamber can be effectively ensured, and the growth quality of the epitaxial layer structure can be effectively ensured.

[0075] The embodiments of the present application also provide an epitaxial wafer prepared by the preparation method of the epitaxial wafer provided in any of the preceding embodiments. Thus, in the process of epitaxially growing the epitaxial layer structure, the V-group atomic beam flow input amount is controlled to decrease with the growth period, the stability of the gas pressure in the growth chamber is ensured, and the quality of the epitaxial wafer is effectively improved.

[0076] It should be understood that the above examples are exemplary and are not intended to limit the scope of the claims encompassing all possible embodiments. Various modifications and changes can be made thereto without departing from the scope of the present disclosure, which is set forth in the claims. Similarly, each of the individual features of the above examples can be combined with each other to form further embodiments of the present application, which can not be explicitly described. Therefore, the above examples merely express several embodiments of the present application, and do not limit the scope of the patent protection of the present application.

Claims

1. A method for producing an epitaxial wafer, characterized by, The method comprises: providing a substrate; performing a molecular beam epitaxy growth process repeatedly for multiple growth cycles to form an epitaxial stack structure on the substrate; wherein the epitaxial stack structure comprises multiple groups of stack units stacked along a growth direction, each of the growth cycles forms a group of the stack units, and each group of the stack units comprises at least two material layers stacked along the growth direction; wherein the material of the material layers comprises a group III-V compound; and during the repeatedly performing of the multiple growth cycles, a V-group atomic beam flux input amount decreases with the growth cycles.

2. The method according to claim 1, wherein the V-group atomic beam flux input amount remains unchanged during a single one of the growth cycles.

3. The method according to claim 2, wherein a decrease range of the V-group atomic beam flux input amount between two adjacent ones of the growth cycles comprises 0.3% to 1.4%.

4. The method according to any one of claims 1 to 3, wherein the decrease amount of the V-group atomic beam flux input amount between each two adjacent ones of the growth cycles is the same.

5. The method according to claim 1, wherein a needle valve opening degree of a V-group atomic beam flux source decreases with the growth cycles during the repeatedly performing of the multiple growth cycles.

6. The method according to claim 5, wherein a decrease range of the needle valve opening degree of the V-group atomic beam flux source between two adjacent ones of the growth cycles comprises 0.1% to 0.5%.

7. The method according to claim 1, wherein a ratio of the V-group atomic beam flux input amount to a III-group atomic beam flux input amount is less than or equal to 20 during a first one of the growth cycles, and the ratio of the V-group atomic beam flux input amount to the III-group atomic beam flux input amount is greater than or equal to 10 during a last one of the growth cycles.

8. The method according to claim 1, wherein the material layers comprise a first material layer and a second material layer; and the V-group atomic beam flux comprises a first V-group atomic beam flux for growing the first material layer and a second V-group atomic beam flux for growing the second material layer; wherein the first V-group atomic beam flux input amount and / or the second V-group atomic beam flux input amount decreases with the growth cycles.

9. The method according to claim 1, wherein the epitaxial stack structure comprises a Bragg reflector.

10. An epitaxial wafer, characterized by, is prepared by the method according to any one of claims 1 to 9.

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