Germanium-silicon quantum well material, and preparation method therefor and use thereof

Abstract

Disclosed in the present application are a germanium-silicon quantum well material, and a preparation method therefor and the use thereof. The germanium-silicon quantum well material sequentially comprises, from bottom to top: a germanium-silicon substrate layer, a germanium-silicon buffer layer, a first barrier layer, a potential well layer and a second barrier layer, wherein the component contents of germanium and silicon in at least one of the first barrier layer, the potential well layer and the second barrier layer are respectively in a gradual change state, with the gradual change state comprising gradually increasing from bottom to top, gradually decreasing from bottom to top, and / or fluctuating changes. The germanium-silicon quantum well material of the present application can be used in precise quantum devices, and can effectively solve the problem of surface charge accumulation during the grid control process of a germanium-silicon quantum device, thereby optimizing the performance of various germanium-silicon grid control quantum devices.

Description

A germanium-silicon quantum well material, its preparation method and application Technical Field

[0001] This application relates to the field of quantum well materials technology, specifically to a germanium-silicon quantum well material and its preparation method and application. Background Technology

[0002] Germanium-silicon quantum wells, due to their excellent material properties, are widely used in quantum devices such as two-dimensional electron (hole) gases, high-mobility field-effect transistors, gated quantum dots, and qubits. Germanium-silicon / silicon / germanium-silicon quantum well materials have well-developed micro- and nano-fabrication processes, and quantum devices fabricated from them exhibit good scalability and integrability. After isotopic purification... 72 germanium 28 In silicon quantum wells, the interaction between carrier spin and material nuclear spin is extremely weak, making silicon a promising candidate material for semiconductor quantum computing chips. On the other hand, germanium-silicon / germanium / germanium-silicon quantum wells exhibit strong spin-orbit coupling, enabling the construction of electrically controllable hole-type qubits and achieving ultrafast qubit manipulation. They can also be combined with superconducting materials to realize novel topological quantum devices. However, the performance of these quantum devices is limited by surface charge accumulation. During gate control, carriers tunnel to the material surface and accumulate charge, disrupting the stable energy states of these quantum devices. The academic community has long focused on techniques to suppress or completely eliminate surface charge accumulation, with exploration of new technologies primarily involving optimization of device fabrication processes and material optimization.

[0003] Previous optimization schemes for germanium-silicon quantum well-related quantum devices have often focused on the fabrication process of the gate dielectric, material growth process, and changes in the quantum well structure. Optimizing the fabrication and growth processes of the gate dielectric can effectively reduce the defect state density on the material surface, thereby reducing charge accumulation. However, optimization schemes for the quantum well material structure only focus on the fixed composition and thickness of each layer of material, changing the distance between the surface charge and the functional regions of the device to reduce the impact of charge accumulation on device performance. However, the above methods cannot eliminate the charge accumulation problem. With the increase of the gate electric field and the accumulation of gate control time, the gradually enriched surface charge will still degrade the device stability.

[0004] To further develop high-fidelity qubits and other precision quantum devices, it is necessary to develop other technical methods to suppress or eliminate surface charge. Summary of the Invention

[0005] To address the aforementioned deficiencies in this field, this application aims to provide a germanium-silicon quantum well material, its preparation method, and its applications.

[0006] According to one aspect of this application, a germanium-silicon quantum well material is provided, comprising, from bottom to top: a germanium-silicon substrate layer, a germanium-silicon buffer layer, a first barrier layer, a potential well layer, and a second barrier layer;

[0007] Among them, the content of germanium and silicon elements in at least one of the first barrier layer, the potential well layer, and the second barrier layer are in a gradual state.

[0008] The gradual change includes a gradual increase or decrease from bottom to top, and / or a fluctuating change.

[0009] According to some embodiments of this application, the crystal planes of the germanium-silicon quantum well material include (001), (110) and (111) crystal planes.

[0010] According to some embodiments of this application, the gradient states include:

[0011] The germanium content in the first barrier layer, the well layer, and the second barrier layer varies from 0% to 100%, corresponding to a silicon content variation from 100% to 0%.

[0012] According to some embodiments of this application, the gradient states include: continuous gradient, stepped gradient, and periodic gradient.

[0013] According to some embodiments of this application, the thickness of the first barrier layer and the second barrier layer is 1-150 nm;

[0014] The thickness of the potential well layer is 1-50 nm.

[0015] According to some embodiments of this application, the first barrier layer and the second barrier layer are doped with one or more of the elements boron, aluminum, gallium, indium, phosphorus, arsenic and antimony;

[0016] According to some embodiments of this application, the doping concentration is 0-1×10⁻⁶. 18 cm -3 .

[0017] According to some embodiments of this application, a spacer layer and a modulation doping layer are further provided between the first barrier layer and the potential well layer, and / or between the potential well layer and the second barrier layer.

[0018] The spacer layer is located between the modulation doped layer and the potential well layer.

[0019] According to some embodiments of this application, the thickness of the modulation doped layer is 0-50 nm;

[0020] Optionally, the modulation doped layer is doped with one or more of the elements boron, aluminum, gallium, indium, phosphorus, arsenic and antimony;

[0021] Further, optionally, the doping concentration of the modulation doped layer is 1×10⁻⁶. 16-5×10 20 cm -3 .

[0022] According to some embodiments of this application, the thickness of the spacer layer is 0-60 nm;

[0023] Optionally, the germanium and silicon elements in the spacer layer are in a gradient state, with the gradient range being 0%-100%.

[0024] According to another aspect of this application, a method for preparing the above-mentioned germanium-silicon quantum well material is also provided, comprising:

[0025] Pre-treatment of the germanium-silicon substrate layer;

[0026] A germanium-silicon buffer layer is epitaxially grown on the first surface of the pretreated germanium-silicon substrate;

[0027] A first barrier layer is epitaxially grown on the surface of the germanium-silicon buffer layer away from the germanium-silicon substrate layer;

[0028] A potential well layer is epitaxially grown on the surface of the first barrier layer away from the germanium-silicon buffer layer.

[0029] A second barrier layer is epitaxially grown on the surface of the potential well layer away from the first barrier layer;

[0030] In this process, the ratio of germanium and silicon growth rates is dynamically adjusted during the growth of at least one of the first barrier layer, the potential well layer, and the second barrier layer.

[0031] According to some embodiments of this application, it further includes: an epitaxially grown spacer layer and a modulation doped layer;

[0032] The spacer layer is located between the modulation doped layer and the potential well layer.

[0033] According to some embodiments of this application, epitaxial growth includes molecular beam epitaxy, chemical vapor deposition, and physical vapor deposition.

[0034] According to another aspect of this application, a germanium-silicon quantum well material as described above is provided, and / or the germanium-silicon quantum well material prepared by the above-described preparation method is used in precision quantum devices;

[0035] Among them, precision quantum devices include: qubits, two-dimensional electron (hole) gas, field-effect transistors, and gated quantum dots.

[0036] Compared with the prior art, this application has at least the following beneficial effects:

[0037] This application provides a germanium-silicon quantum well material and its preparation method. Based on band engineering design, the material exhibits germanium-silicon composition and doping concentration that gradually vary with sample depth. The germanium-silicon quantum well material of this application can be applied to precision quantum devices, effectively solving the surface charge accumulation problem during the gate control process of germanium-silicon quantum devices. This optimizes the performance of various germanium-silicon gate-controlled quantum devices, such as improving the decoherence time of germanium-silicon qubits, enhancing the transport performance of two-dimensional carrier gas, and improving the energy stability of gate-controlled quantum dots, field-effect transistors, and other devices. This facilitates the precise construction of quantum systems and contributes to the development of quantum technology. Attached Figure Description

[0038] Figure 1 is a schematic diagram of the germanium-silicon quantum well material of Example Embodiment 1 of this application.

[0039] Figure 2 shows the X-ray diffraction surface scan pattern (XRD-mapping) of the germanium-silicon quantum well material of Example Embodiment 1 of this application.

[0040] Figure 3 is an atomic force microscope image of the surface of the germanium-silicon quantum well material in Example Embodiment 1 of this application.

[0041] Figure 4 shows the secondary ion mass spectrometry (SIMS) spectrum of the germanium-silicon quantum trap material in Example 1 of this application.

[0042] Figure 5 is a schematic diagram of the band structure simulation of the germanium-silicon quantum well material in Example Embodiment 1 of this application when a voltage is applied.

[0043] Figure 6 shows the X-ray diffraction pattern of the germanium-silicon quantum well material of Comparative Example 1 of this application.

[0044] Figure 7 is a schematic diagram of the band structure of the germanium-silicon quantum well material of Comparative Example 1 of this application when a voltage is applied.

[0045] Figure 8 is an image of the planar quantum Hall device of Example Embodiment 2 of this application taken under an optical microscope.

[0046] Figure 9 shows the curve of the turn-on voltage (Vt.o.) of the planar quantum Hall device in Example Embodiment 2 of this application as a function of the gate control voltage (Vmin).

[0047] Figure 10 shows the curve of the turn-on voltage (Vt.o.) of the planar quantum Hall device of Comparative Example 2 of this application as a function of the gate control voltage (Vmin).

[0048] Figure 11 is a schematic diagram of the band structure of the germanium-silicon quantum well material in Example Embodiment 3 of this application when a voltage is applied. Detailed Implementation

[0049] The technical solution of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] It should be particularly noted that similar substitutions and modifications made to this application are obvious to those skilled in the art, and they are all considered to be included in this application. Those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0051] Unless otherwise specified, this application shall be made in accordance with conventional conditions or conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, whose manufacturers are not specified, are all conventional products that can be obtained commercially.

[0052] The following is a detailed description of this application.

[0053] In the context of this application, a "potential well layer" refers to a material layer in which charge carriers accumulate under quantum confinement.

[0054] In the context of this application, a "barrier layer" refers to a material layer that provides quantum confinement for charge carriers.

[0055] In the context of this application, "spacer layer" refers to a material layer used to separate the potential well layer and the doped layer in the case of modulation doping.

[0056] In the context of this application, "composition gradient" refers to the gradual change in the content ratio of germanium and silicon elements with different depths from the material surface, including continuous gradient with depth, step gradient, and periodic gradient.

[0057] In the context of this application, "doping" includes the doping of elements such as boron, aluminum, gallium, indium, phosphorus, arsenic, and antimony in germanium-silicon materials.

[0058] In the context of this application, a "germanium-silicon virtual substrate" refers to a substrate with a specific germanium-silicon content ratio obtained by epitaxial growth on a silicon or germanium wafer, wherein the substrate surface structure has a constant germanium-silicon content and is stress-relaxed.

[0059] In the context of this application, "epitaxy growth" includes molecular beam epitaxy, chemical vapor deposition, and physical vapor deposition.

[0060] High-quality germanium-silicon quantum well materials are fundamental for constructing novel germanium-silicon quantum devices. Currently, the main technical approaches for preparing germanium-silicon quantum well materials are as follows: Using molecular beam epitaxy or chemical vapor deposition, a first barrier layer, a potential well layer, and a second barrier layer with fixed germanium-silicon composition are sequentially grown on a germanium-silicon virtual substrate to form a germanium-silicon quantum well structure. Further optimization of material properties is achieved by controlling the growth temperature, growth rate, or the thickness of each layer in the quantum well structure.

[0061] Currently, the performance of quantum devices is limited by the surface charge accumulation effect. During gate control, charge carriers tunnel to the material surface and accumulate charge, thereby disrupting the stable energy states of these quantum devices.

[0062] To address the existing technical problems in this field, this application provides a germanium-silicon quantum well material. Unlike conventional materials with fixed component content designs, this material is based on band engineering design and has germanium-silicon component content and doping concentration that gradually change with depth. This application also provides a method for preparing the above-mentioned germanium-silicon quantum well material, comprising: epitaxially growing a germanium-silicon buffer layer on a germanium-silicon virtual substrate; and epitaxially growing a barrier layer, a potential well layer, a modulation doping layer, and a spacer layer on the germanium-silicon buffer layer, spaced apart, to obtain a quantum well structure.

[0063] The germanium-silicon quantum well material of this application can solve the problem of surface charge accumulation in the gate control process of germanium-silicon quantum devices, thereby optimizing the performance of various germanium-silicon gate-controlled quantum devices.

[0064] The germanium-silicon quantum well material of this application comprises, from bottom to top: a germanium-silicon substrate layer, a germanium-silicon buffer layer, a first barrier layer, a potential well layer, and a second barrier layer;

[0065] Among them, the content of germanium and silicon elements in at least one of the first barrier layer, the potential well layer, and the second barrier layer are in a gradual state.

[0066] The gradual change state is characterized by a gradual increase or decrease from bottom to top, or by a fluctuating change.

[0067] Optionally, the first and second barrier layers are doped with one or more of the elements boron, aluminum, gallium, indium, phosphorus, arsenic and antimony.

[0068] Optionally, a spacer layer and a modulation doped layer are further provided between the first barrier layer and the potential well layer, and / or between the potential well layer and the second barrier layer;

[0069] The spacer layer is located between the modulation doped layer and the potential well layer.

[0070] The crystal planes of the material include (001), (111), and (110) crystal planes.

[0071] The thickness of the barrier layer ranges from 1 to 150 nm. The germanium content in the barrier layer varies from 0% to 100%, corresponding to a silicon content variation range of 100% to 0%. The doping concentration of the barrier layer varies from 0 to 1 × 10⁻⁶. 18 cm -3 .

[0072] The thickness of the potential well layer is 1-50 nm. The germanium content of the potential well layer varies from 0% to 100%, corresponding to a silicon content variation of 100% to 0%.

[0073] The thickness of the spacer layer is 0-60 nm. The germanium content of the spacer layer varies from 0% to 100%, corresponding to a silicon content variation of 100% to 0%.

[0074] The thickness of the modulation doped layer ranges from 0 to 50 nm. The doping concentration of the modulation doped layer varies from 1 × 10⁻⁶. 16 -5×10 20 cm -3 .

[0075] The method for preparing germanium-silicon quantum well material of this application includes: epitaxially growing a germanium-silicon buffer layer on a germanium-silicon virtual substrate; and epitaxially growing a barrier layer, a potential well layer, a modulation doping layer and a spacer layer on the germanium-silicon buffer layer at intervals to obtain a quantum well structure.

[0076] The epitaxial growth of a germanium-silicon buffer layer on a germanium-silicon virtual substrate includes:

[0077] The germanium-silicon virtual substrate was immersed in a diluted hydrogen fluoride solution, then removed and placed in a growth chamber for high-temperature pretreatment. Subsequently, a germanium-silicon buffer layer with the same germanium-silicon composition as the substrate surface was epitaxially grown on the germanium-silicon virtual substrate. The growth temperature was 320-550℃, and the growth rate was 0.05-1 nm / s.

[0078] Specifically, a quantum well structure is obtained by epitaxially growing a barrier layer, a well layer, a modulation doping layer, and a spacer layer on a germanium-silicon buffer layer at intervals, including:

[0079] First, the first barrier layer of the quantum well is epitaxially grown on a germanium-silicon buffer layer at 320-550℃ and a growth rate of 0.05-1 nm / s. As the growth progresses, the ratio of germanium to silicon growth rates is dynamically adjusted to achieve gradual changes in the germanium-silicon composition at different depths of the barrier layer.

[0080] A potential well layer is epitaxially grown on the barrier layer at a growth temperature of 320-500℃ and a growth rate of 0.05-1 nm / s. The ratio of germanium to silicon growth rates is dynamically adjusted as growth progresses to achieve gradual changes in germanium-silicon composition at different depths of the potential well layer.

[0081] A second barrier layer was epitaxially grown on the potential well layer at a growth temperature of 310-550℃ and a growth rate of 0.05-1 nm / s. The ratio of germanium to silicon growth rates was dynamically adjusted as growth progressed to achieve gradual changes in the germanium-silicon composition at different depths of the second barrier layer.

[0082] In some embodiments of this application, the ratio of germanium to silicon growth rates is dynamically adjusted during the growth of at least one of the first barrier layer, the potential well layer, and the second barrier layer.

[0083] Optionally, between the epitaxial growth steps of the first barrier layer, the well layer, and the second barrier layer, the epitaxial growth of the modulation doped layer and the spacer layer can be selectively inserted.

[0084] Optionally, the growth temperature of the modulated doped layer is 320-550℃, and the growth rate is 0.05-1 nm / s. Doping is achieved by simultaneously depositing impurity elements during the epitaxial growth process.

[0085] Optionally, the growth temperature of the spacer layer is 320-550℃, and the growth rate is 0.05-1 nm / s. The ratio of germanium to silicon growth rates is dynamically adjusted as growth progresses to achieve gradual changes in the germanium-silicon composition at different depths of the spacer layer.

[0086] Applications of the germanium-silicon quantum well material described above or the germanium-silicon quantum well material prepared by the above method in precision quantum devices such as quantum bits, two-dimensional electron (hole) gas, high mobility field-effect transistors, and gated quantum dots.

[0087] The technical solution of this application will be further described below with reference to specific embodiments.

[0088] Example 1

[0089] The germanium-silicon quantum well material of this application was prepared.

[0090] (1) A germanium-silicon buffer layer with a fixed germanium content of 79% was epitaxially grown on a germanium-silicon (001) virtual substrate using molecular beam epitaxy:

[0091] A germanium-silicon (001) virtual substrate was selected, with a fixed germanium-silicon content of 79% on the surface and stress relaxation. The substrate was immersed in a diluted hydrogen fluoride solution for 1 min; it was then removed and placed in the growth chamber of a molecular beam epitaxy (MBE) apparatus for high-temperature pretreatment at 650 °C. A 300 nm thick germanium-silicon buffer layer was epitaxially grown at 450 °C, with a germanium growth rate of 0.079 nm / s and a silicon growth rate of 0.021 nm / s, for a total material growth rate of 0.1 nm / s.

[0092] (2) A compositionally graded germanium-silicon quantum well material was epitaxially grown on the germanium-silicon buffer layer using molecular beam epitaxy:

[0093] A first barrier layer with a thickness of 100 nm was epitaxially grown on a germanium-silicon buffer layer at 450 °C. The growth rate of germanium in the first barrier layer was 0.079 nm / s, and the growth rate of silicon was 0.021 nm / s, for a total material growth rate of 0.1 nm / s. A potential well layer with a thickness of 15 nm was epitaxially grown on the first barrier layer at 450 °C. This potential well layer had a germanium content of 100%, with a germanium growth rate of 0.079 nm / s and a silicon growth rate of 0 nm / s. Subsequently, a second barrier layer with a thickness of 35 nm was epitaxially grown on the potential well layer at 390 °C. During the growth of the second barrier layer, the germanium growth rate gradually decreased from 0.079 nm / s to 0.01 nm / s, the silicon growth rate gradually increased from 0.021 nm / s to 0.04 nm / s, and the total growth rate gradually decreased from 0.1 nm / s to 0.05 nm / s. The germanium content of the resulting second barrier layer varies with thickness, gradually decreasing from 79% to 20%, corresponding to a silicon content that gradually decreases from 21% to 80%.

[0094] Example 2

[0095] Application of germanium-silicon quantum well material in Example 1 of this application.

[0096] The germanium-silicon quantum well material from Example 1 was fabricated into a planar quantum Hall device using micro-nano fabrication techniques:

[0097] First, the planar Hall device structure was etched onto the germanium-silicon quantum well material using ultraviolet (UV) lithography and reactive ion etching. Then, palladium electrodes were fabricated on the source / drain and voltage measurement regions of the planar Hall device structure using UV lithography, electron beam evaporation, and thermal annealing. Next, an alumina gate dielectric layer was fabricated using atomic layer deposition (ALD). Finally, the titanium top gate of the planar Hall device was fabricated using UV lithography and electron beam evaporation.

[0098] Figure 8 is an image of the planar quantum Hall device prepared in Example 2 of this application, taken under an optical microscope. The area marked by the dashed line in Figure 8 shows the region where gate-controlled two-dimensional hole gas is formed.

[0099] Figure 9 shows the turn-on voltage of the planar quantum Hall device prepared in Example 2 of this application as a function of the gate control voltage. Figure 9 illustrates the energy stability of the planar quantum Hall device prepared in Example 2. Within the gate control voltage range of -0.2V to -0.7V, the turn-on voltage of the planar quantum Hall device remains stable, indicating that no charge surface accumulation occurs within the gate control range of -0.2V to -0.7V.

[0100] Example 3

[0101] This embodiment is used to illustrate the germanium-silicon quantum well material and its preparation method of this application.

[0102] (1) A germanium-silicon buffer layer with a fixed germanium content of 20% was epitaxially grown on a germanium-silicon (001) virtual substrate using molecular beam epitaxy:

[0103] A germanium-silicon (001) virtual substrate was selected, with a fixed germanium-silicon content of 20% on the surface and under stress relaxation. The substrate was immersed in a diluted hydrogen fluoride solution for 1 min; it was then removed and placed in the growth chamber of a molecular beam epitaxy (MBE) device for high-temperature pretreatment at 650 °C. A 300 nm thick germanium-silicon buffer layer was then epitaxially grown at 450 °C, with a germanium growth rate of 0.020 nm / s and a silicon growth rate of 0.080 nm / s, for a total material growth rate of 0.1 nm / s.

[0104] (2) A compositionally graded germanium-silicon quantum well material was epitaxially grown on the germanium-silicon buffer layer using molecular beam epitaxy:

[0105] First, a 20 nm thick modulation doped layer is epitaxially grown on the germanium-silicon buffer layer at 450 °C. The impurity element in the modulation doped layer is phosphorus, and the doping concentration is 1 × 10⁻⁶. 17 cm -3 Subsequently, a 20 nm thick spacer layer was epitaxially grown on the modulation-doped layer at 450 °C. During the growth of this spacer layer, the growth rate of germanium gradually increased from 0.020 nm / s to 0.050 nm / s, while the growth rate of silicon gradually decreased from 0.080 nm / s to 0.050 nm / s. The total growth rate remained constant at 0.10 nm / s. The germanium content of the resulting spacer layer varied with thickness, gradually increasing from 20% to 50%, and the silicon content gradually decreased from 80% to 50%. Then, a 15 nm thick potential well layer was epitaxially grown on the spacer layer at 450 °C. This potential well layer had a germanium content of 0% and a silicon content of 100%, with a silicon growth rate of 0.050 nm / s. Subsequently, a 35 nm thick second barrier layer was epitaxially grown on the potential well layer at 390 °C. During the growth of this barrier layer, the growth rate of germanium gradually increased from 0.050 nm / s to 0.1 nm / s, while the growth rate of silicon gradually decreased from 0.050 nm / s to 0 nm / s, with the total growth rate remaining at 0.10 nm / s. The germanium content of the resulting second barrier layer varied with thickness, gradually increasing from 50% to 100%, corresponding to a silicon content that gradually decreased from 50% to 0%.

[0106] Comparative Example 1

[0107] This comparative example prepares a conventional germanium-silicon quantum well material without compositional gradients to illustrate that the germanium-silicon quantum well material of this application solves the problem of surface charge accumulation under gate control.

[0108] (1) A germanium-silicon buffer layer with a fixed germanium content of 79% was epitaxially grown on a germanium-silicon (001) virtual substrate using molecular beam epitaxy:

[0109] A germanium-silicon (001) virtual substrate was selected, with a fixed germanium-silicon content of 79% on the surface and under stress relaxation. The substrate was immersed in a diluted hydrogen fluoride solution for 1 min. It was then removed and placed in the growth chamber of a molecular beam epitaxy (MBE) apparatus for high-temperature pretreatment at 650 °C. A 300 nm thick germanium-silicon buffer layer was then epitaxially grown at 450 °C, with a growth rate of 0.079 nm / s for germanium and 0.021 nm / s for silicon, for a total material growth rate of 0.1 nm / s.

[0110] (2) A germanium-silicon quantum well material with a constant composition content was epitaxially grown on the germanium-silicon buffer layer using molecular beam epitaxy:

[0111] First, a 100 nm thick first barrier layer is epitaxially grown on the germanium-silicon buffer layer at 450 °C. The growth rate of germanium in this barrier layer is 0.079 nm / s, and the growth rate of silicon is 0.021 nm / s, for a total material growth rate of 0.1 nm / s. Then, a 15 nm thick potential well layer is epitaxially grown on the first barrier layer at 450 °C. This potential well layer has a germanium content of 100%, with a germanium growth rate of 0.079 nm / s and a silicon growth rate of 0 nm / s. Subsequently, a 35 nm thick second barrier layer is epitaxially grown on the potential well layer at 390 °C. The growth rate of germanium in this barrier layer is 0.079 nm / s, and the growth rate of silicon is 0.021 nm / s, for a total material growth rate of 0.1 nm / s. The germanium content in this second barrier layer is fixed at 79%.

[0112] Comparative Example 2

[0113] Application of conventional germanium-silicon quantum well material without compositional gradient in Comparative Example 1.

[0114] The hole gas quantum device in Example 2 is used for comparison to illustrate that it solves the problem of charge surface accumulation.

[0115] Planar quantum Hall devices were fabricated using micro-nano fabrication techniques on the germanium-silicon quantum well material of Comparative Example 1:

[0116] First, the planar Hall device structure was etched onto the germanium-silicon quantum well material using ultraviolet (UV) lithography and reactive ion etching. Then, palladium electrodes were fabricated on the source / drain and voltage measurement regions of the planar Hall device structure using UV lithography, electron beam evaporation, and thermal annealing. Next, an alumina gate dielectric layer was fabricated using atomic layer deposition (ALD). Finally, the titanium top gate of the planar Hall device was fabricated using UV lithography and electron beam evaporation.

[0117] Figure 10 shows the turn-on voltage of the planar quantum Hall device prepared in Comparative Example 2 as a function of the gate control voltage. Figure 10 illustrates that the energy stability of the planar quantum Hall device prepared in Comparative Example 2 is weaker than that of the planar quantum Hall device in Example 2. Within the range of gate control voltage from -0.25V to -0.4V, the turn-on voltage of the planar quantum Hall device changes by -0.08V, indicating that charge surface accumulation occurs when the gate control range exceeds -0.25V.

[0118] Experimental Example

[0119] 1. Comparative test of germanium-silicon quantum well materials of Example 1 and Comparative Example 1 of this application.

[0120] Figure 1 is a schematic diagram of the structure of the germanium-silicon quantum well material prepared in Example 1 of this application.

[0121] Figure 2 is the X-ray diffraction pattern (XRD-mapping) of the germanium-silicon quantum well material prepared in Example 1 of this application. The intensity peaks marked with triangles in Figure 2 indicate that a germanium-silicon buffer layer with a germanium content of 79% was prepared in step (1) of Example 1. The intensity peaks marked with triangles in Figure 2 also indicate that a first barrier layer with a germanium content of 79% was prepared in step (2) of Example 1. The intensity signals marked with dashed boxes in Figure 2 indicate that a second barrier layer with a graded composition was prepared in step (2) of Example 1.

[0122] Figure 3 is an atomic force microscope image of the surface of the germanium-silicon quantum well material prepared in Example 1 of this application. Figure 3 shows that steps (1) and (2) of Example 1 enable the germanium-silicon material to grow in a two-dimensional layered manner, and finally prepare a quantum well material with a flat surface and a root mean square (RMS) surface roughness of 0.94 nm.

[0123] Figure 4 shows the secondary ion mass spectrometry (SIMS) spectrum of the germanium-silicon quantum well material prepared in Example 1 of this application. Figure 4 shows that the germanium and silicon content of the germanium-silicon quantum well material prepared in Example 1 varies with depth. As the depth decreases from the outermost layer of the material to the potential well layer, the germanium content decreases continuously from 79% to 20%.

[0124] Figure 5 is a schematic diagram of the band structure of the germanium-silicon quantum well material prepared in Embodiment 1 of this application when a voltage is applied. Figure 5 shows that the germanium-silicon quantum well material solves the problem of surface charge accumulation under gate control. When a voltage of -0.5V is applied to the surface of the material, the hole energy level in the potential well layer crosses the Fermi level, forming hole filling in the quantum well. At the same time, the hole energy level on the material surface is below the Fermi level, and holes cannot tunnel from the potential well layer to the material surface, thus preventing surface charge accumulation.

[0125] Figure 6 is an X-ray diffraction pattern of the germanium-silicon quantum well material prepared in Comparative Example 1 of this application. The intensity peaks marked with triangles in Figure 6 indicate that step (1) of Comparative Example 1 yielded a germanium-silicon buffer layer with a germanium content of 79%. The intensity peaks marked with triangles in Figure 5 also indicate that step (2) of Comparative Example 1 yielded a first barrier layer and a second barrier layer with a fixed composition of 79% germanium content.

[0126] Figure 7 is a schematic diagram of the band structure simulation of the germanium-silicon quantum well material prepared in Comparative Example 1 of this application when a voltage is applied. Figure 7 shows that the germanium-silicon quantum well material in Comparative Example 1 has the problem of surface charge accumulation under gate control. When a voltage of -0.5V is applied to the surface of the material, the hole energy level on the surface of the material crosses the Fermi level, and the holes will tunnel from the potential well layer to the surface of the material under the electric field, resulting in surface charge accumulation.

[0127] 2. Numerical simulation of the germanium-silicon quantum well material of Example 3 of this application.

[0128] Figure 11 is a schematic diagram of the band structure of the germanium-silicon quantum well material prepared in Embodiment 3 of the present invention when a voltage is applied. Figure 11 shows that the germanium-silicon quantum well material solves the problem of surface charge accumulation under gate control. When a voltage of +0.65V is applied to the surface of the material, the electronic energy levels in the potential well layer cross the Fermi level, forming an electron filling within the quantum well. At the same time, the electronic energy levels on the material surface are above the Fermi level, and electrons cannot tunnel from the potential well layer to the material surface, thus preventing surface charge accumulation.

[0129] Based on the test results of the above embodiments and comparative examples of this application, it can be seen that the germanium-silicon quantum well material provided by this application has material layers with gradually changing composition in bandgap engineering design. Unlike previous germanium-silicon quantum wells, when a strong electric field is applied to this material, charge carriers no longer tunnel to the material surface. This material can effectively solve the problem of surface charge accumulation in germanium-silicon gated quantum devices, improve the decoherence time of germanium-silicon qubits, improve the electrical transport performance of two-dimensional carrier gas, and improve the energy stability of devices such as gated quantum dots and field-effect transistors.

[0130] The germanium-silicon gate-controlled quantum devices prepared using the materials provided in this application have better gate control tunability, improved chemical potential adjustment range of the device functional region, expanded energy scale range of device operation, and increased potential application scenarios for related devices.

[0131] This application uses compositional gradients and modulation doping to precisely plan the band structure of materials. For germanium-silicon qubits and gated quantum dot devices, the spatial position and energy of specific electronic (hole) states can be precisely controlled, which is conducive to the precise construction of quantum systems and helps the development of quantum technology.

[0132] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A germanium-silicon quantum well material, characterized in that, The germanium-silicon quantum well material comprises, from bottom to top: a germanium-silicon substrate layer, a germanium-silicon buffer layer, a first barrier layer, a potential well layer, and a second barrier layer; The germanium and silicon content in at least one of the first barrier layer, the potential well layer, and the second barrier layer varies gradually. The gradual change includes a gradual increase or decrease from bottom to top, and / or a fluctuating change.

2. The germanium-silicon quantum well material according to claim 1, characterized in that, The gradual transition states include: The germanium content in the first barrier layer, the potential well layer, and the second barrier layer varies from 0% to 100%, corresponding to a silicon content variation range of 100% to 0%. Optionally, the gradient states include: continuous gradient, stepped gradient, and periodic gradient.

3. The germanium-silicon quantum well material according to claim 1, characterized in that, The thicknesses of the first barrier layer and the second barrier layer are 1-150 nm; The thickness of the potential well layer is 1-50 nm.

4. The germanium-silicon quantum well material according to claim 3, characterized in that, The first barrier layer and the second barrier layer are doped with one or more of the elements boron, aluminum, gallium, indium, phosphorus, arsenic and antimony; Optionally, the doping concentration is 0-1×10⁻⁶. 18 cm -3 .

5. The germanium-silicon quantum well material according to any one of claims 1-4, characterized in that, Between the first barrier layer and the potential well layer, and / or between the potential well layer and the second barrier layer, there is also a spacer layer and a modulation doping layer; The spacer layer is located between the modulation doped layer and the potential well layer.

6. The germanium-silicon quantum well material according to claim 5, characterized in that, The thickness of the modulation doped layer is 0-50 nm; Optionally, the modulation doped layer is doped with one or more of the elements boron, aluminum, gallium, indium, phosphorus, arsenic and antimony; Further optionally, the doping concentration of the modulation doped layer is 1×10⁻⁶. 16 -5×10 20 cm -3 .

7. The germanium-silicon quantum well material according to claim 5, characterized in that, The thickness of the spacer layer is 0-60 nm; Optionally, the germanium and silicon elements in the spacer layer are in a gradient state, with the germanium content ranging from 0% to 100% and the silicon content ranging from 100% to 0%.

8. A method for preparing the germanium-silicon quantum well material according to any one of claims 1-7, characterized in that, include: Pre-treatment of the germanium-silicon substrate layer; A germanium-silicon buffer layer is epitaxially grown on the first surface of the pretreated germanium-silicon substrate; A first barrier layer is epitaxially grown on the surface of the germanium-silicon buffer layer away from the germanium-silicon substrate layer; A potential well layer is epitaxially grown on the surface of the first barrier layer away from the germanium-silicon buffer layer; A second barrier layer is epitaxially grown on the surface of the potential well layer away from the first barrier layer; The ratio of germanium and silicon growth rates is dynamically adjusted during the growth of at least one of the first barrier layer, the potential well layer, and the second barrier layer.

9. The preparation method according to claim 8, characterized in that, Also includes: Epitaxial growth of spacer layers and modulation doped layers; The spacer layer is located between the modulation doped layer and the potential well layer.

10. The germanium-silicon quantum well material according to any one of claims 1-7, and / or the germanium-silicon quantum well material prepared by the preparation method according to any one of claims 8-9, in precision quantum devices; in, The precision quantum devices include: qubits, two-dimensional electron (hole) gas, field-effect transistors, and gated quantum dots.

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