Germanium hole spin qubit device and preparation method therefor
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- INST OF SEMICONDUCTORS - CHINESE ACAD OF SCI
- Filing Date
- 2024-11-12
- Publication Date
- 2026-05-21
Smart Images
Figure CN2024131644_21052026_PF_FP_ABST
Abstract
Description
A germanium hole spin qubit device and its fabrication method Technical Field
[0001] This application relates to the field of semiconductor manufacturing technology, and in particular to a germanium hole spin qubit device and its fabrication method. Background Technology
[0002] The realization of electron dipole spin resonance (EDSR) in two-dimensional gated germanium quantum dots relies on linear spin-orbit coupling (SOC), but the bulk phase of germanium does not allow linear Dresselhaus SOC due to the presence of center inversion symmetry. On the other hand, it has been previously believed that linear Rashba SOC does not exist in two-dimensional hole gas due to the absence of light-heavy hole coupling.
[0003] However, recent studies have shown that a linear Rashba SOC with tunable electric field exists in the two-dimensional hole gas of germanium quantum wells along the
[0001] growth direction. This is caused by light-heavy hole coupling due to interface effects, but the intensity of the linear Rashba SOC caused by interface effects is relatively weak. Researchers have attempted several theoretical schemes to enhance the linear Rashba SOC in the hole gas of germanium quantum wells, such as fabricating germanium quantum wells along the
[0110] growth direction, applying a small-scale strongly anisotropic electric field, and applying a gradient shear strain along the growth direction. However, these theoretical schemes are difficult to realize and control experimentally and have not been practically applied to germanium hole-based quantum bit devices.
[0004] Summary of the Invention
[0005] This application aims to at least partially address one of the technical problems in the related art.
[0006] Therefore, the first objective of this application is to provide an ultrafast manipulatory germanium hole spin qubit device and its fabrication method, which can successfully fabricate high-quality and ultrafast manipulatory germanium hole spin qubits.
[0007] To achieve the above objectives, the first aspect of this application provides a method for preparing ultrafast manipulated germanium hole-spin qubits, comprising:
[0008] Provide substrate;
[0009] A germanium quantum well is epitaxially formed on the substrate. The interior of the germanium quantum well includes a first region and a second region. The second region is located on both sides of the first region along a first direction. Silicon elements doped along a predetermined crystal orientation are disposed in the second region.
[0010] A dielectric layer is formed on the germanium quantum well structure;
[0011] At least one set of metal electrodes is formed on the dielectric layer, each set of metal electrodes including a first electrode, a second electrode and a third electrode spaced apart from each other along a second direction, wherein the third electrode is located between the first electrode and the second electrode;
[0012] Two-dimensional gated quantum dots were formed in the germanium quantum well using electric dipole spin resonance technology.
[0013] In some embodiments, the germanium quantum well comprises a structure formed on the substrate using a CMOS process.
[0014] In some embodiments, the substrate includes a silicon substrate.
[0015] In some embodiments, the epitaxial formation of a germanium quantum well on the substrate includes:
[0016] A silicon-germanium buffer layer is formed on the substrate;
[0017] A germanium layer is formed on the buffer layer;
[0018] Silicon element doping with a predetermined crystal orientation is performed at a predetermined position of the germanium layer to form the second region;
[0019] A silicon-germanium barrier layer is formed on the germanium layer.
[0020] In some embodiments, the method for doping silicon elements with a predetermined crystal orientation at a predetermined location of the germanium layer includes thermal diffusion, electrochemical implantation, or ion implantation.
[0021] In some embodiments, the preset crystal orientation of silicon doping in the second interval includes a
[0110] crystal orientation, which is used to provide uniaxial tensile strain of the
[0110] crystal orientation to the two-dimensional gated quantum dot formed in the first interval.
[0022] In some embodiments, the silicon content in the silicon-germanium buffer layer is not higher than 50%.
[0023] In some embodiments, the thickness of the germanium layer ranges from tens of nanometers to hundreds of nanometers, and the thickness of the silicon-germanium buffer layer and the silicon-germanium barrier layer ranges from several nanometers to tens of nanometers.
[0024] In some embodiments, the step of fabricating two-dimensional gated quantum dots in the germanium quantum well using electric dipole spin resonance technology includes:
[0025] An in-plane static magnetic field is provided within the germanium quantum well;
[0026] A first threshold voltage and a second threshold voltage are applied to the first electrode and the second electrode, respectively, to provide a first electric field for the germanium quantum well;
[0027] A third threshold voltage is applied to the third electrode to provide a second electric field for the germanium quantum well, so as to form the two-dimensional gated quantum dot within the first interval; the direction of the second electric field is perpendicular to the surface of the substrate.
[0028] In some embodiments, the dielectric material of the dielectric layer includes either SiO2 or Al2O3, and the thickness of the dielectric layer ranges from tens of nanometers to tens of nanometers.
[0029] In some embodiments, the material of the metal electrode includes either Al or Au, and the thickness of the metal electrode ranges from a few nanometers to tens of nanometers.
[0030] In some embodiments, the vertical projection of the third electrode on the substrate overlaps the vertical projection of the first interval.
[0031] In some embodiments, the diameter of the two-dimensional gated quantum dot ranges from 60 nm to 100 nm.
[0032] In some embodiments, the bulk phase of the germanium material in the germanium quantum well has a crystal structure with tetrahedral covalent bonds.
[0033] In some embodiments, the direction of the first electric field is the same as the direction of the in-plane magnetic field and perpendicular to the direction of the second electric field.
[0034] To achieve the above objectives, a first aspect of this application provides an ultrafast manipulatory germanium hole spin qubit device, comprising:
[0035] Substrate;
[0036] A germanium quantum well is formed on the substrate and includes a silicon-germanium buffer layer, a germanium layer and a silicon-germanium barrier layer stacked sequentially from bottom to top.
[0037] A dielectric layer is formed on the germanium quantum well;
[0038] At least one set of metal electrodes is formed on the dielectric layer, each set of metal electrodes including a first electrode, a second electrode and a third electrode spaced apart from each other along a second direction, wherein the third electrode is located between the first electrode and the second electrode;
[0039] The interface between the germanium layer and the silicon-germanium barrier layer includes a first interval, which is used to form a two-dimensional gated quantum dot. The germanium layer includes two second intervals spaced apart from each other along a first direction. The second intervals contain silicon elements doped along a preset crystal orientation. The first interval is located between the two spaced-apart second intervals. The second intervals are used to provide uniaxial tensile strain in a preset direction for the two-dimensional gated quantum dot formed in the first interval.
[0040] This application provides an ultrafast manipulatory germanium hole-spin qubit device and its fabrication method, including providing a substrate and sequentially forming a germanium quantum well, a dielectric layer, and a metal electrode on the substrate. The germanium quantum well contains a first region and second regions located on either side of the first region. By doping silicon along a predetermined crystal orientation within the second region, the second region can continuously provide the first region with uniaxial tensile strain of a predetermined direction and magnitude. Furthermore, by applying an in-plane static magnetic field to the germanium quantum well and forming two-dimensional gated quantum dots in the first region of the germanium quantum well based on EDSR technology, high-quality ultrafast manipulatory germanium hole-spin qubits can be fabricated.
[0041] Compared to traditional germanium quantum wells without uniaxial strain, this application provides a germanium quantum well with applied uniaxial strain that can increase the linear SOC intensity by two orders of magnitude and provide Rabi frequencies in the GHz range.
[0042] The germanium quantum well provided in this application is highly compatible with existing mature microelectronic CMOS processes and is expected to be used to realize the large-scale integration of qubits.
[0043] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description
[0044] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:
[0045] Figure 1 is a schematic diagram of the structure of a germanium hole spin qubit according to an embodiment of this application.
[0046] Figure 2 is a top view of the germanium hole spin qubit shown in Figure 1.
[0047] Figure 3 is a schematic flowchart illustrating the method for preparing germanium hole spin qubits according to an embodiment of this application.
[0048] Figure 4 is a schematic flowchart illustrating the method for preparing a germanium quantum well according to an embodiment of this application.
[0049] Figure 5 is a schematic flowchart illustrating a two-dimensional gated quantum dot fabrication method according to an embodiment of this application.
[0050] Figure 6 is a schematic diagram of the principle of EDSR caused by linear SOC.
[0051] Figure 7 is a schematic diagram of spin splitting of a germanium quantum well under a uniaxial tensile strain of 0.4% in the
[0110] direction and a gate voltage of 100 kV / cm, according to an embodiment of this application.
[0052] Figure 8 is a schematic diagram showing the change of the linear SOC coefficient of a two-dimensional gated quantum dot with uniaxial strain under a fixed biaxial strain of 0.61% compressive strain, according to an embodiment of this application.
[0053] Figure 9 is a schematic diagram showing the change of the linear SOC coefficient of a two-dimensional gated quantum dot under a uniaxial tensile strain of 0.4% in the
[0110] direction with biaxial strain, according to an embodiment of this application.
[0054] Figure 10 is a schematic diagram showing the relationship between the Rabi frequency of a two-dimensional gated quantum dot and the uniaxial strain in the
[0110] direction under an in-plane magnetic field with a Lamour frequency of 5 GHz, according to an embodiment of this application.
[0055] Figure 11 is a schematic diagram showing the relationship between the linear SOC coefficient of a two-dimensional gated quantum dot under a uniaxial tensile strain of 0.4% in the
[0110] direction and the gate voltage, according to an embodiment of this application.
[0056] 100 Substrate; 200 Germanium quantum well; 201 First interval; 202 Second interval; 210 Silicon-germanium buffer layer; 220 Germanium layer; 230 Silicon-germanium barrier layer; 300 Dielectric layer; 400 Metal electrode; 410 First electrode; 420 Second electrode; 430 Third electrode. Detailed Implementation
[0057] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.
[0058] In view of the shortcomings of the prior art described above, this application provides a germanium hole spin qubit device with uniaxial tensile strain applied in a specific direction, which is deeply compatible with microelectronic complementary metal-oxide-semiconductor (CMOS) technology, and its fabrication method. It is expected that on this basis, the fabrication of high-quality hole spin qubits of single and multiple two-dimensional gated quantum dots can be realized, providing a brand-new solution for semiconductor quantum computing.
[0059] Research has found that the strong SOC of holes in germanium quantum wells can rapidly drive spin flipping of its two-dimensional gated quantum dot qubits. Furthermore, group IV elements, due to their near-zero nuclear spin scattering, can provide a longer spin decoherence time and are deeply compatible with microelectronic CMOS processes, thus enabling the fabrication of high-quality, scalable spin qubits. Currently, high-quality charge manipulation of 4x4 (16) quantum dot arrays has been achieved internationally in germanium quantum wells. However, further development of spin qubits remains limited by relatively slow spin manipulation and short decoherence times.
[0060] The basic units of quantum computing include qubits and quantum logic gates. The preparation of a single qubit state requires applying an external magnetic field to induce the Zeeman effect, generating the two energy levels needed for qubit encoding. The realization of a quantum logic gate relies on the flipping between different spin states (qubits). For holes, the EDSR technique is used, which involves quantum states with different spin components. Since an applied alternating electric field or microwave can only induce coupling between quantum states with the same spin component, the SOC (Spin-Oriented Coupling) is inevitably introduced. Because the spin direction generated by the Zeeman effect is always parallel or antiparallel to the direction of the applied static magnetic field, the combined effect of the SOC and the alternating electric field fundamentally provides the driving force for spin flipping. In the EDSR technique, when the frequency of the applied alternating electric field or microwave is equal to the Lamour precession frequency induced by the applied static magnetic field, the spin state resonates. At this point, the spin orientation exhibits a periodic change, and the corresponding spin flipping frequency is the Rabi frequency.
[0061] Improving the manipulation speed (Rabi frequency) of hole qubits is a core concern for quantum computing, and the key to addressing this concern lies in providing a strong linear SOC. Research indicates that the linear SOC of the two-dimensional hole gas in germanium quantum wells originates from light-heavy hole coupling. However, for a long time, researchers generally believed that linear SOC did not exist in the two-dimensional hole gas of semiconductor quantum wells due to the symmetry prohibition of light-heavy hole coupling. Recent theoretical studies have shown that in germanium / silicon quantum wells along the
[0001] growth direction (referred to as the
[0001] direction), the interface effect-induced light-heavy hole coupling generates a linear Rashba SOC, leading to several schemes to induce linear SOC by reducing the symmetry of the germanium quantum well to induce light-heavy hole coupling. However, existing theoretical schemes are difficult to implement and control experimentally, and therefore insufficient for practical applications. Recent theoretical research has found that applying uniaxial strain, a technique commonly used in the integrated circuit industry for CMOS compatibility, to germanium quantum wells can significantly enhance light-heavy hole coupling, thereby inducing a linear state-of-the-art (SOC) intensity two orders of magnitude larger than that of the two-dimensional hole gas in traditional germanium quantum wells. Consequently, the Rabi frequency will increase to the GHz level. However, this theoretical research has not yet been experimentally verified.
[0062] The core idea of this application is to enhance the spin manipulation rate, which can be characterized by the Rabi frequency, by applying uniaxial tensile strain to a conventional quantum well. This application is compatible with existing mature microelectronic CMOS processes, providing a scheme for fabricating germanium quantum wells with applied uniaxial strain. Utilizing the strong linear SOC in the uniaxially strained quantum well, high-quality hole-spin qubits with GHz-level Rabi frequencies from two-dimensional gated quantum dots are fabricated, paving the way for further development of semiconductor quantum computing.
[0063] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings. In the following example illustrations, the x-direction is the first direction, which is also the
[0110] direction; the y-direction is the second direction, which is also the [-110] direction; and the z-direction is the third direction, which is also the
[0001] direction.
[0064] The first aspect of this application provides a method for fabricating germanium hole spin qubits with ultrafast manipulation compatible with CMOS technology, as shown in Figures 1 to 3, including the following steps:
[0065] S1 provides a substrate 100.
[0066] S2, a germanium quantum well 200 is epitaxially formed on the substrate 100. The interior of the germanium quantum well 200 includes a first interval 201 and a second interval 202. The second interval 202 is located on both sides of the first interval 201 along the first direction. Silicon elements doped along a preset crystal orientation are disposed in the second interval 202.
[0067] The interior of the germanium quantum well 200 includes a first region 201 for forming two-dimensional gated quantum dots and a second region 202 for silicon doping along a preset crystal orientation. The second region 202 is located on both sides of the first region 201 along a first direction.
[0068] S3, a dielectric layer 300 is formed on the germanium quantum well 200.
[0069] S4, at least one set of metal electrodes 400 are formed on the dielectric layer 300. Each set of metal electrodes 400 includes a first electrode 410, a second electrode 420 and a third electrode 430 spaced apart from each other along a second direction. The third electrode 430 is located between the first electrode 410 and the second electrode 420.
[0070] S5 uses EDSR technology to form two-dimensional gated quantum dots in a germanium quantum well.
[0071] It is understood that the technical solution provided in this application forms a germanium quantum well 200 epitaxially on a substrate 100, and forms a first interval 201 and a second interval 202 inside the germanium quantum well 200. The second interval 202 is located on both sides of the first interval 201 along a first direction, so that the silicon element doped in the second interval 202 along a preset crystal orientation can continuously provide a stable uniaxial tensile strain to the first interval 201. In other words, by controlling the doping direction and doping concentration of silicon element in the second interval 202, the direction and magnitude of the uniaxial strain in the first interval 201 of the germanium quantum well 200 can be controlled.
[0072] Therefore, by using EDSR technology to form a two-dimensional gated quantum dot in the first interval 201 of the germanium quantum well 200, and when the frequency of the alternating electric field or microwave is equal to the eigenfrequency of the in-plane static magnetic field, the two-dimensional gated quantum dot formed in the first interval 201 can achieve a strong linear SOC under the action of alternating electric field, external static magnetic field and uniaxial strain in the preset direction provided by the second interval 202, thereby realizing the fabrication of high-quality, ultrafast controllable germanium hole spin qubits with GHz-level Rabi frequency.
[0073] As an example, the alternating electric field includes a vertical electric field and a lateral driving electric field. The lateral driving electric field is applied in the plane of the germanium quantum well 200 through the first electrode 410 and the second electrode 420. The vertical electric field is applied to the germanium quantum well 200 through the third electrode 430, which is located between the first electrode 410 and the second electrode 420. The third electrode 430 provides a binding potential to trap two-dimensional holes and confines the two-dimensional gated quantum dots within the first interval 201. It also provides a controllable gate voltage for the formation of the two-dimensional gated quantum dots, enabling the two-dimensional gated quantum dots to generate and regulate linear Rashba SOCs under the gate voltage control of the third electrode 430. Consequently, the vertical projection of the third electrode 430 on the substrate 100 also overlaps the vertical projection of the first interval 201.
[0074] As an example, the hole mobility in the germanium quantum well 200 can reach 10. 5 cm 2 On the order of / (V·s).
[0075] As an example, the substrate 100 can be made of silicon substrate material, and the germanium quantum well 200 formed epitaxially on the substrate 100 is also a germanium quantum well 200.
[0076] It should be noted that at least one set of metal electrodes 400 in step S4 above means that the formation of metal electrodes 400 on the dielectric layer 300 includes, but is not limited to, one set. In the case that multiple sets of metal electrodes 400 are formed on the dielectric layer 300, multiple first intervals 201 will be formed inside the germanium quantum well 200.
[0077] As shown in Figure 4, in some embodiments, the step of epitaxially forming a germanium quantum well 200 on the substrate 100 may include:
[0078] S21, a silicon-germanium buffer layer 210 is formed on the substrate 100.
[0079] S22, a germanium layer 220 is formed on the silicon-germanium buffer layer 210;
[0080] S23, silicon element doping with a preset crystal orientation is performed at a preset position of germanium layer 220 to form second region 202;
[0081] S24, a silicon-germanium barrier layer 230 is formed on the germanium layer 220.
[0082] The silicon-germanium buffer layer 210 is represented as
[0001] -Ge x Si 1-x , and
[0001] -Ge x Si 1-x The proportion of silicon in the buffer layer should be less than 50%. The silicon-germanium buffer layer 210 can alleviate the lattice mismatch between the silicon substrate and the germanium layer 220, thereby improving the epitaxial quality of the silicon-germanium layer 220. Simultaneously, the lattice mismatch between the silicon-germanium buffer layer 210 and the germanium layer 220 can also provide biaxial strain for the second interval 202, and the magnitude of the biaxial strain can be adjusted by the silicon content and thickness of the silicon-germanium buffer layer 210.
[0083] Furthermore, since the second interval 202 is formed on both sides of the first interval 201 along the first direction, the silicon element doped along a preset crystal orientation within the second interval 202 can provide uniaxial tensile strain along the preset direction to the first interval 201. For example, the direction of silicon element doping at a preset position in the germanium layer 220
[0001] can be along the
[0110] crystal orientation of the germanium layer 220. Thus, the direction of the uniaxial tensile strain provided by the second interval 202 to the first interval 201 is
[0110] , and the greater the silicon element doping concentration inside the second interval 202, the greater the uniaxial tensile strain provided by the second interval 202 to the first interval 201.
[0084] As an example, physical vapor deposition and plasma chemical vapor deposition can be used in the epitaxial method of germanium quantum well 200, and the preparation methods that can be used for metal electrode 400 include electron beam lithography and / or electron beam evaporation.
[0085] As an example, the thickness of the silicon-germanium buffer layer 210 ranges from a few nanometers to tens of nanometers, the thickness of the germanium layer 220 ranges from tens of nanometers to hundreds of nanometers, the thickness of the silicon-germanium barrier layer 230 ranges from a few nanometers to tens of nanometers, the thickness of the dielectric layer 300 ranges from tens of nanometers to tens of nanometers, and the thickness of the metal electrode 400 ranges from tens of nanometers.
[0086] As an example, the dielectric layer 300 is composed of a dielectric material, including but not limited to one of SiO2 or Al2O3; the metal electrode 400 is composed of a metal material with low resistivity, including but not limited to aluminum (Al) or gold (Au).
[0087] As an example, the diameter of the two-dimensional gated quantum dots prepared above ranges from 60 nm to 100 nm, and the bulk phase of the germanium material in the germanium quantum well 200 is a crystal structure with tetrahedral covalent bonds.
[0088] It should be noted that the specific doping direction for silicon doping at the preset position of germanium layer 220 described above is only an example and is not specifically limited in this application. In other embodiments, the silicon doping for providing uniaxial tensile strain can also be in directions other than
[0110] . Specific methods for element doping within the second interval 202 include, but are not limited to, thermal diffusion, electrochemical implantation, or ion implantation.
[0089] Furthermore, the doping elements within the second interval 202 may include, but are not limited to, silicon. Other elements that can be doped within the second interval 202 and provide uniaxial strain to the first interval 201 should also be included within the scope disclosed in this application.
[0090] As shown in Figures 2 and 5, in some embodiments, the step of forming two-dimensional gated quantum dots in the first interval 201 using EDSR technology may include:
[0091] S51 provides an in-plane static magnetic field for the germanium quantum well 200;
[0092] S52, a first threshold voltage and a second threshold voltage are applied to the first electrode 410 and the second electrode 420 respectively to provide a first electric field for the germanium quantum well 200.
[0093] S53, a third threshold voltage is applied to the third electrode 430 to provide a second electric field for the germanium quantum well 200 to form a two-dimensional gated quantum dot within the first interval 201.
[0094] The first electric field is the transverse driving electric field, and the second electric field is the vertical electric field. The direction of the first electric field is the same as the direction of the in-plane magnetic field, and the direction of the second electric field is perpendicular to the surface of the substrate 100.
[0095] Combining Figures 2 and 6, it can be seen that applying an in-plane static magnetic field to the two-dimensional gated quantum dots formed in the germanium quantum well 200 will cause the two-dimensional gated quantum dots to exhibit spin-polarized discrete energy levels under the combined effects of quantum binding and Zeeman effects. The quantum states corresponding to these discrete energy levels are called Fock-Darwin states, which can be represented by three quantum numbers: principal quantum number n, angular momentum quantum number l, and spin quantum number s: |n,l,s>. An external alternating electric field or microwave can only couple adjacent quantum states containing the same spin component, i.e., it requires simultaneously satisfying Δn = ±1 and Δs = 0. Without a state of bounding center (SOC), there is no coupling between quantum states with different spin components, thus spin control of a two-level system cannot be achieved. However, with a linear SOC, adjacent quantum states containing different spin components will couple, i.e., simultaneously satisfying Δn = ±1 and Δs ≠ 0, forming a two-level system where each energy level contains a different spin component. Alternating electric fields or microwaves continuously couple the same spin components in a two-level system, thereby constantly changing the spin components of each level and achieving time-dependent spin flipping and spin manipulation.
[0096] Although linear SOC is key to achieving spin flipping and spin manipulation using EDSR technology, it was generally believed in the past that due to the prohibition of light-heavy hole coupling in quantum wells, heavy holes in quantum wells do not possess linear Rashba SOC, but only cubic Rashba SOC, and the center inversion symmetry of quantum wells also prohibits Dresselhaus SOC. Recent studies have shown that light-heavy hole coupling exists in quantum wells, thus enabling linear SOC. However, since
[0001] the light-heavy hole coupling in quantum wells originates from the contribution of the wave function at the interface, the SOC is relatively weak. Several existing studies have attempted to enhance light-heavy hole coupling, but their schemes are all difficult to achieve and control experimentally.
[0097] The first-principles calculation results of the empirical pseudopotential method for spin splitting are shown in Figure 7. When a gate voltage vertical electric field of 100 kV / cm is applied to the quantum well through the third electrode 430, before and after applying a uniaxial tensile strain of 0.4% in the
[0110] direction, (Ge) 120 / (Ge 0.8 Si 0.2 ) 60 The spin splitting of the quantum well increases significantly and anisotropically near the Γ point. The relationship between the linear SOC coefficients fitted from the band structure and strain is shown in Figures 8 and 9. It can be seen that under 0.4% uniaxial tensile strain, the desired effect can be achieved. The Dresselhaus-type linear SOC coefficients (α1 in the diagram) and The Rashba-like linear SOC coefficient (α2 in the figure) is two orders of magnitude higher than the linear SOC coefficient without uniaxial strain. This is because applying uniaxial strain breaks the symmetry of the quantum well, leading to intrinsic light-heavy hole coupling. Therefore, the light-heavy hole coupling strength in the quantum well after applying uniaxial strain is much greater than that without uniaxial strain.
[0098] Within a certain range, the Rabi frequency is directly proportional to the linear SOC coefficient. Among the quantum wells and two-dimensional gated quantum dots reported so far, the highest Rabi frequency that can be obtained is in the hundreds of MHz range, while the two-dimensional gated quantum dot with applied uniaxial strain designed in this application can obtain a Rabi frequency in the GHz range.
[0099] As an example, a magnetic field is applied in the quantum well plane, and the Lamour frequency of the transverse driving electric field is fixed at 5 GHz. The calculation results of the Rabi frequency are shown in Figure 10. Under a vertical electric field of 100 kV / cm gate voltage, a two-dimensional gated quantum dot subjected to 0.4% uniaxial tensile strain can achieve a Rabi frequency of about 4 GHz, thereby enabling the hole spin Rabi frequency in the two-dimensional gated quantum dot to reach the GHz level.
[0100] Theoretical calculations show that quantum wells with uniaxial strain exhibit larger linear state of charge (SOC) and Rabi frequency compared to those without uniaxial strain. Since the linear SOC can be controlled by the gate voltage, and the uniaxial strain has a wide range of parameters to choose from experimentally, various factors can be considered to select suitable parameters. For example, in the above example, the thickness of the germanium layer 220 is approximately 18 nm, and further increasing the thickness of the germanium layer 220 within a certain range can further improve the Rabi frequency.
[0101] Furthermore, theoretical calculations show that, as shown in Figure 11, when the gate voltage is adjusted, the linear SOC coefficient remains essentially unchanged within the gate voltage range of 200 kV / cm to 250 kV / cm. Theoretically, this characteristic can counteract the charge noise caused by a large linear SOC, further improving the usability of the two-dimensional gated quantum dots in quantum computing according to the embodiments of this application.
[0102] It should be noted that in the above embodiments, the direction of the first electric field and the direction of the in-plane magnetic field are the same as the example. This application does not specifically limit the direction of the first electric field and the direction of the second electric field. That is to say, the in-plane magnetic field and the first electric field can also be other directions besides those in the above embodiments.
[0103] A second aspect of this application provides a germanium hole spin qubit device for ultrafast manipulation using CMOS-compatible technology, as shown in Figure 1. The device includes:
[0104] Substrate 100;
[0105] A germanium quantum well 200 is formed on a substrate 100 and includes a silicon-germanium buffer layer 210, a germanium layer 220 and a silicon-germanium barrier layer 230 stacked sequentially from bottom to top.
[0106] Dielectric layer 300 is formed on germanium quantum well 200;
[0107] At least one set of metal electrodes 400 is formed on the dielectric layer 300. Each set of metal electrodes 400 includes a first electrode 410, a second electrode 420 and a third electrode 430 spaced apart from each other along a second direction. The third electrode 430 is located between the first electrode 410 and the second electrode 420.
[0108] The interface between the germanium layer 220 and the silicon-germanium barrier layer 230 includes a first interval 201, which is used to form two-dimensional gated quantum dots. The germanium layer 220 includes two second intervals 202 that are spaced apart from each other along a first direction. The second intervals 202 contain silicon elements doped along a preset crystal orientation. The first interval 201 is located between the two spaced-apart second intervals 202. The second intervals 202 are used to provide uniaxial tensile strain in a preset direction for the two-dimensional gated quantum dots formed in the first interval 201.
[0109] It should be noted that for details not disclosed in the ultrafast manipulatory germanium hole-spin qubit device provided in the embodiments of this application, please refer to the details disclosed in the ultrafast manipulatory germanium hole-spin qubit preparation method in the embodiments of this application, which will not be repeated here.
[0110] In summary, this application provides a germanium hole spin qubit quantum device compatible with CMOS technology and capable of ultrafast manipulation, and its fabrication method. By locally injecting silicon doping elements into the germanium quantum well 200, uniaxial strain with a fixed direction in a local region is achieved, thereby realizing the fabrication of high-quality two-dimensional gated quantum dots with rapid spin flipping.
[0111] In the foregoing descriptions of the embodiments, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0112] 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. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.
Claims
1. A method of preparation of a germanium hole spin qubit, wherein, include: Provide substrate; A germanium quantum well is epitaxially formed on the substrate. The interior of the germanium quantum well includes a first region and a second region. The second region is located on both sides of the first region along a first direction. Silicon elements doped along a predetermined crystal orientation are disposed in the second region. A dielectric layer is formed on the germanium quantum well structure; At least one set of metal electrodes is formed on the dielectric layer, each set of metal electrodes including a first electrode, a second electrode and a third electrode spaced apart from each other along a second direction, wherein the third electrode is located between the first electrode and the second electrode; Two-dimensional gated quantum dots are formed in the second interval using electric dipole spin resonance technology.
2. The production method according to claim 1, wherein, The germanium quantum well is formed on the substrate using a CMOS process.
3. The production method according to claim 1, wherein, The substrate includes a [001] silicon substrate.
4. The production method according to claim 1, wherein The epitaxial formation of a germanium quantum well on the substrate includes: A silicon-germanium buffer layer is formed on the substrate; A germanium layer is formed on the buffer layer; Silicon element doping with a predetermined crystal orientation is performed at a predetermined position of the germanium layer to form the second region; A silicon-germanium barrier layer is formed on the germanium layer.
5. The method of claim 4, wherein, The methods for doping silicon elements with a predetermined crystal orientation at a predetermined position of the germanium layer include thermal diffusion, electrochemical implantation, or ion implantation.
6. The production method according to claim 4, wherein The preset crystal orientation of silicon doping in the second interval includes the [110] crystal orientation, which is used to provide uniaxial tensile strain of the [110] crystal orientation for the two-dimensional gated quantum dots formed in the first interval.
7. The production method according to claim 4, wherein The silicon content in the silicon-germanium buffer layer is no more than 50%.
8. The production method according to claim 4, wherein The thickness of the germanium layer ranges from tens of nanometers to hundreds of nanometers, and the thickness of the silicon-germanium buffer layer and the silicon-germanium barrier layer ranges from a few nanometers to tens of nanometers.
9. The production method according to claim 1, wherein The step of fabricating two-dimensional gated quantum dots in the germanium quantum well using electric dipole spin resonance technology includes: An in-plane static magnetic field is provided within the germanium quantum well; A first threshold voltage and a second threshold voltage are applied to the first electrode and the second electrode, respectively, to provide a first electric field for the germanium quantum well; A third threshold voltage is applied to the third electrode to provide a second electric field for the germanium quantum well, so as to form the two-dimensional gated quantum dot within the first interval; the direction of the second electric field is perpendicular to the surface of the substrate.
10. The production method according to claim 1, wherein, The dielectric material of the dielectric layer includes either SiO2 or Al2O3, and the thickness of the dielectric layer ranges from tens of nanometers to tens of nanometers.
11. The production method according to claim 1, wherein The material of the metal electrode includes either Al or Au, and the thickness of the metal electrode ranges from a few nanometers to tens of nanometers.
12. The method of producing according to claim 1, wherein, The vertical projection of the third electrode on the substrate overlaps the vertical projection of the first interval.
13. The method of producing according to claim 1, wherein, The diameter of the two-dimensional gated quantum dot ranges from 60 nm to 100 nm.
14. The method of producing according to claim 1, wherein, The bulk phase of the germanium material in the germanium quantum well has a crystal structure with tetrahedral covalent bonds.
15. The method of making according to claim 13, wherein, The direction of the first electric field is the same as the direction of the in-plane magnetic field and perpendicular to the direction of the second electric field.
16. A germanium hole spin qubit device, wherein, include: Substrate; A germanium quantum well is formed on the substrate and includes a silicon-germanium buffer layer, a germanium layer and a silicon-germanium barrier layer stacked sequentially from bottom to top. A dielectric layer is formed on the germanium quantum well; At least one set of metal electrodes is formed on the dielectric layer, each set of metal electrodes including a first electrode, a second electrode and a third electrode spaced apart from each other along a second direction, wherein the third electrode is located between the first electrode and the second electrode; The interface between the germanium layer and the silicon-germanium barrier layer includes a first interval, which is used to form a two-dimensional gated quantum dot. The germanium layer includes two second intervals that are spaced apart from each other along a first direction. The second intervals contain silicon elements doped along a preset crystal orientation. The first interval is located between the two spaced-apart second intervals. The second intervals are used to provide uniaxial tensile strain in a preset direction for the two-dimensional gated quantum dot formed in the first interval.