A method for preparing a hole spin qubit

Abstract

The application provides a preparation method of a hole spin quantum bit, which comprises the following two steps: preparing a tilted quantum well structure based on a CMOS process, and realizing growth of a quantum well in a [110] direction by controlling a tilt angle, wherein the quantum well structure is a P-type doped germanium quantum well; and preparing a two-dimensional gate-controlled quantum dot in the quantum well structure based on an electric dipole spin resonance (EDSR) technology, so as to realize a high-quality hole spin quantum bit. Compared with a traditional quantum well grown in a [100] direction, the quantum well in the [110] growth direction has the largest linear Rashba spin-orbit coupling effect and can provide the fastest Rabi spin flip. The application overcomes the difficulty of directly growing the [110] quantum well on a plane by designing the tilted quantum well, and provides a brand-new solution for realizing the high-quality hole spin quantum bit.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, specifically to the fabrication of a high-quality spin qubit of a semiconductor two-dimensional gate-controlled

[110] quantum dot compatible with microelectronic CMOS technology, with the aim of promoting the development of semiconductor quantum computing. Background Technology

[0002] In recent years, quantum computing has become a hot topic in basic research and technological breakthroughs both domestically and internationally due to its exponentially growing computing power. Among various approaches, semiconductor gated quantum dots (SQDs) have attracted significant attention due to their deep compatibility with mature microelectronic CMOS processes. In SQD schemes, the spin of charge carriers within the quantum dot can serve as the carrier for constructing qubits. Currently, four qubits have been manipulated in a hole-spin system of two-dimensional gated germanium quantum dots. Compared to electron spin, germanium hole spin has the following four advantages: 1. Holes possess a p-type wavefunction, significantly reducing the probability of scattering by nuclear spin, and germanium can further improve spin decoherence time through isotope purification; 2. Germanium holes exhibit a strong tunable spin-orbit coupling (SOC) effect, thereby increasing spin manipulation speed; 3. Germanium holes are free from valley degeneracy and valley scattering interference; 4. Germanium holes have a relatively small effective mass, and since the size and effective mass of a quantum dot are inversely proportional when the two-dimensional bound electric potential is fixed, larger gated quantum dots can be fabricated, making spin manipulation easier.

[0003] Rabi spin-flipping frequency can be used to characterize the speed of spin manipulation. Achieving hole spin manipulation in a two-dimensional gated germanium quantum dot system requires EDSR (Electro-Electro-Spin Resonance) technology. The principle of EDSR is as follows: 1. Apply an out-of-plane or in-plane static magnetic field to the two-dimensional gated quantum dot, causing Zeeman spin splitting of the energy levels. The spins on the two split sublevels of each energy level are opposite, parallel or antiparallel to the direction of the applied magnetic field; 2. Apply an in-plane alternating electric field or microwave to couple quantum states with the same spin in adjacent lower energy levels of the two-dimensional gated quantum dot; 3. Apply an out-of-plane electrostatic field to generate a linear Rashba spin-orbit coupling effect, providing electric dipole transitions to couple quantum states with different spins in adjacent lower energy levels, forming a two-level system with different spin states, thus causing spin resonance, where each resonant spin state is a qubit. Compared to electron spin resonance (ESR) technology, hole-based EDSR technology does not require the design of intricate gradient micromagnetic structures in low-dimensional systems to provide a magnetic field for spin flipping. Instead, it utilizes an equivalent magnetic field generated by electrically controlled spin-orbit coupling. This electrical control, replacing magnetic control, further expands the application prospects of semiconductor quantum dot quantum computing based on hole spin.

[0004] The realization of EDSR technology in two-dimensional gated germanium quantum dots relies on the linear Rashba spin-orbit coupling effect or the cubic Dresselhaus spin-orbit coupling effect. However, the Dresselhaus effect does not exist in germanium due to the bulk-center inversion symmetry. On the other hand, it was previously believed that the linear Rashba effect did not exist in two-dimensional hole gas due to the absence of light-heavy hole coupling. However, recent studies have shown that an electric field-tunable linear Rashba effect exists in the hole gas of the

[100] -oriented quantum well, caused by light-heavy hole coupling induced by the interface. Even a weak effect can induce a Rabi frequency of 100 MHz, enabling rapid spin flipping. Furthermore, research has found that the Rashba effect in the hole gas of the

[110] -oriented germanium quantum well is one to two orders of magnitude larger than that in the

[100] -oriented quantum well, thus enabling GHz-level Rabi frequencies in two-dimensional gated

[110] quantum dots. This points the way forward for faster spin flipping and higher-quality spin qubits.

[0005] Despite the promising application prospects of germanium quantum wells in the

[110] orientation, no quantum well structure in this crystal orientation has been successfully fabricated experimentally to date, which seriously hinders the development of semiconductor quantum dot quantum computing. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the technical problems in the related art.

[0007] The purpose of this invention is to provide a fabrication scheme for high-quality hole spin qubits of semiconductor two-dimensional gate-controlled

[110] quantum dots that are compatible with microelectronic CMOS processes, so as to solve the problem that it is impossible to fabricate

[110] quantum wells experimentally and further improve the speed of hole spin qubit manipulation.

[0008] One embodiment of this application proposes a method for preparing hole spin qubits, including:

[0009] Provide substrate;

[0010] A germanium quantum well is formed on the substrate, wherein the germanium quantum well is an inclined quantum well structure grown along the

[110] direction, and the germanium quantum well is formed by CMOS process;

[0011] Two-dimensional gated quantum dots were prepared in the germanium quantum well.

[0012] In some embodiments, a germanium quantum well is formed on the substrate, including:

[0013] An alloy layer is formed on the substrate;

[0014] A

[100] germanium layer is formed on the alloy layer, wherein the

[100] germanium layer is p-type doped.

[0015] A bevel is formed on the

[100] germanium layer by etching.

[0016] In some embodiments, it also includes:

[0017] A dielectric layer is formed on the

[100] germanium layer;

[0018] Electrodes are formed on the dielectric layer.

[0019] In some embodiments, the inclination angle of the inclined plane is 45 degrees to the horizontal direction.

[0020] In some embodiments, the diameter of the two-dimensional gated quantum dot is 60 to 100 nm.

[0021] In some embodiments, the substrate is a

[100] silicon substrate.

[0022] In some embodiments, the alloy layer is a

[100] germanium-silicon alloy layer, wherein the thickness of the

[100] germanium-silicon alloy layer is between a few nanometers and tens of nanometers, and the proportion of silicon in the

[100] germanium-silicon alloy layer is less than 50%.

[0023] In some embodiments, the thickness of the

[100] germanium layer is from tens of nanometers to hundreds of nanometers.

[0024] In some embodiments, the dielectric material of the dielectric layer is SiO2 or Al2O3, and the thickness of the dielectric layer is between tens of nanometers and hundreds of nanometers.

[0025] In some embodiments, the electrode is a metal electrode, the material of which is Al or Au, and the thickness of the metal electrode is on the order of tens of nanometers.

[0026] In some embodiments, the method of P-type doping of the

[100] germanium layer includes thermal diffusion, electrochemical implantation or ion implantation.

[0027] In some embodiments, the bulk phase of the germanium material in the germanium quantum well has a crystal structure with tetrahedral covalent bonds.

[0028] In some embodiments, the mobility of the germanium quantum well reaches 10-10. 5 cm 2 On the order of / (V·s).

[0029] In some embodiments, the hole spin Rabi flipping frequency in the two-dimensional gated quantum dot reaches the GHz level and the quality factor is greater than 10. 4 .

[0030] In some embodiments, the two-dimensional gated quantum dot is prepared in a germanium quantum well using an electric dipole moment spin resonance technique.

[0031] In some embodiments, a back-gate binding electric field, an in-plane alternating electric field or microwave, a vertical electrostatic field on the inclined plane, and an in-plane or vertical static magnetic field on the inclined plane are applied to the germanium quantum well to generate Rabi spin flips, wherein the direction of the in-plane static magnetic field is not perpendicular to the direction of the in-plane alternating electric field or microwave.

[0032] In some embodiments, the frequency of the alternating electric field or microwave within the inclined plane is equal to the natural frequency of the static magnetic field within the inclined plane or perpendicular to the inclined plane.

[0033] Another embodiment of this application proposes a semiconductor structure, including:

[0034] Substrate;

[0035] A germanium quantum well is formed on the substrate, wherein the germanium quantum well is an inclined quantum well structure grown along the

[110] direction;

[0036] Two-dimensional gated quantum dots prepared in the germanium quantum well.

[0037] In some embodiments, the substrate includes, from bottom to top, a substrate, an alloy layer, a

[100] germanium layer, a dielectric layer and an electrode, wherein the

[100] germanium layer is p-type doped and a slope is formed on the

[100] germanium layer.

[0038] In some embodiments, the inclination angle of the inclined plane is 45 degrees to the horizontal direction.

[0039] In some embodiments, the size of the two-dimensional gated quantum dot is 60 to 100 nm.

[0040] In some embodiments, the substrate is a

[100] silicon substrate.

[0041] In some embodiments, the alloy layer is a

[100] germanium-silicon alloy layer, wherein the thickness of the

[100] germanium-silicon alloy layer is between a few nanometers and tens of nanometers, and the proportion of silicon in the

[100] germanium-silicon alloy layer is less than 50%.

[0042] In some embodiments, the thickness of the

[100] germanium layer is from tens of nanometers to hundreds of nanometers.

[0043] In some embodiments, the dielectric material of the dielectric layer is SiO2 or Al2O3, and the thickness of the dielectric layer is between tens of nanometers and hundreds of nanometers.

[0044] In some embodiments, the electrode is a metal electrode, the material of which is Al or Au, and the thickness of the metal electrode is on the order of tens of nanometers.

[0045] In some embodiments, the bulk phase of the germanium material in the germanium quantum well has a crystal structure with tetrahedral covalent bonds.

[0046] The beneficial effects of this invention are as follows:

[0047] 1. This invention points out that holes in two-dimensional gated

[110] germanium quantum dots can provide GHz-level Rabi spin flips, realizing the preparation of high-quality hole spin qubits.

[0048] 2. This invention proposes a method to obtain the

[110] crystal plane by using a 45-degree inclined plane in the

[100] direction, which solves the problem of the difficulty in growing germanium quantum wells in the

[110] direction.

[0049] 3. The germanium quantum well of the present invention

[110] is deeply compatible with existing mature microelectronic CMOS processes and is expected to be used for large-scale integration of qubits.

[0050] Additional aspects and advantages of the invention 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 the invention. Attached Figure Description

[0051] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0052] in:

[0053] Figure 1 is a three-dimensional and two-dimensional cross-sectional schematic diagram of the

[110] quantum well and two-dimensional gated quantum dot of an embodiment of the present invention, wherein:

[0054] Figure 1a This is a schematic diagram of the three-dimensional structure of a quantum well and a two-dimensional gated quantum dot

[110] .

[0055] Figure 1b A schematic diagram of a two-dimensional cross-section of a quantum well and a two-dimensional gated quantum dot

[110] ;

[0056] Figure 2 is a schematic diagram of the

[100] crystal plane and the

[110] crystal plane in an embodiment of the present invention, wherein:

[0057] Figure 2a This is a schematic diagram of the

[100] crystal plane.

[0058] Figure 2b This is a schematic diagram of the

[110] crystal plane;

[0059] Figure 3This is a schematic diagram illustrating the principle of electric dipole moment spin resonance (EDSR) induced by the linear Rashba spin-orbit coupling effect in an embodiment of the present invention.

[0060] Figure 4 shows an embodiment of the present invention with

[110] -(Ge). 40 / (Si) 20 Quantum wells and

[100] -(Ge) 40 / (Si) 20 A schematic diagram of spin splitting in a quantum well at 30 kV / cm (where subscripts represent single atomic layers), wherein:

[0061] Figure 4a

[110] -(Ge) 40 / (Si) 20 Schematic diagram of spin splitting of a quantum well at 30 kV / cm.

[0062] Figure 4b

[100] -(Ge) 40 / (Si) 20 Schematic diagram of spin splitting of a quantum well at 30 kV / cm;

[0063] Figure 5 is a schematic diagram showing the relationship between the Rabi frequency of

[110] germanium quantum dots and

[100] germanium quantum dots under an in-plane magnetic field of 1.65T and the alternating electric field or microwave, according to an embodiment of the present invention.

[0064] Figure 5a The diagram shows the relationship between the Rabi frequency of

[110] germanium quantum dots under a 1.65T in-plane magnetic field and alternating electric field or microwave.

[0065] Figure 5b A schematic diagram showing the relationship between the Rabi frequency of

[100] germanium quantum dots and alternating electric field or microwave under a 1.65T in-plane magnetic field;

[0066] Figure 6 This is a schematic diagram showing the relationship between the Rabi frequency and the linear Rashba parameter of the germanium quantum dot

[110] under a 1.65T in-plane magnetic field as a function of gate voltage in an embodiment of the present invention.

[0067] Figure label:

[0068] 1-

[100] Silicon substrate; 2-

[100] Germanium-silicon alloy layer; 3-

[100] Germanium layer; 4- Dielectric layer; 5- Metal electrode; 6- Two-dimensional gated quantum dot. Detailed Implementation

[0069] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0070] In view of the shortcomings of the prior art described above, the present invention provides a method for fabricating a

[110] germanium quantum well that is deeply compatible with CMOS technology, which is expected to realize the fabrication of high-quality hole spin qubits of single and multiple two-dimensional gated quantum dots, providing a brand-new solution for semiconductor quantum computing.

[0071] Studies have found that the strong spin-orbit coupling effect of holes in germanium quantum wells can rapidly drive the spin flipping of their gated quantum dot qubits. Furthermore, group IV elements, due to their near-zero nuclear spin scattering, can provide a long spin decoherence time and are deeply compatible with microelectronic CMOS processes, thus enabling the fabrication of high-quality scalable spin qubits. Currently, high-quality spin manipulation of four qubits has been achieved internationally in germanium quantum wells. However, spin qubits are still limited by slow spin manipulation and fast decoherence time. The core idea of ​​this invention is to improve the spin manipulation rate by growing a tilted structure on a conventional quantum well

[110] to fabricate quantum wells and gated quantum dots, which can be characterized by the Rabi frequency. Time-dependent spin flipping is achieved in spin resonance. For holes, electric dipole moment spin resonance (EDSR) technology is used, involving quantum states with different spin components. Since an external alternating electric field or microwave can only induce coupling between quantum states with the same spin component, it is inevitable to introduce the Zeeman effect and spin-orbit coupling (SOC) effect. Because the spin direction generated by the Zeeman effect is always parallel or antiparallel to the direction of the applied static magnetic field, the spin-orbit coupling effect fundamentally provides the driving force for spin reversal. In EDSR technology, when the frequency of the applied alternating electric field or microwave is equal to the eigenfrequency of the applied static magnetic field, the spin state resonates and exhibits periodic changes with time; the corresponding spin reversal frequency is the Rabi frequency.

[0072] Improving the Rabi frequency of hole qubits is a core concern in quantum computing, and the key to addressing this concern lies in providing a strong spin-orbit coupling effect. Recent research indicates that the linear Rashba spin-orbit coupling effect of holes in germanium quantum wells is the source of rapid spin-flipping. For a long time, it was believed that the linear Rashba effect did not exist in semiconductor quantum well hole systems due to the prohibition of light-heavy hole coupling. However, recent theoretical studies have shown that the light-heavy hole coupling caused by boundary effects in

[100] germanium quantum wells induces a linear Rashba effect, and the presence of intrinsic light-heavy hole coupling in

[110] quantum wells produces a linear Rashba effect one to two orders of magnitude larger than that in

[100] quantum wells. The linear Rashba effect in

[100] quantum wells has successfully explained, both qualitatively and quantitatively, the Rabi frequency of hole spin qubits in experimentally

[100] gated quantum dots, while the

[110] quantum well, with its stronger linear Rashba effect, can provide qubits with even higher Rabi frequencies. However, due to various reasons, high-quality

[110] quantum wells have not yet been successfully fabricated in experiments, let alone high-quality

[110] quantum dot qubits, which seriously hinders the further development of semiconductor quantum computing.

[0073] This invention is compatible with existing mature microelectronic CMOS processes, proposes a scheme for fabricating

[110] quantum wells, and utilizes the strong linear Rashba spin-orbit coupling effect in the

[110] quantum wells to fabricate high-quality hole spin qubits with GHz-level Rabi frequencies of

[110] gated quantum dots, paving the way for the further development of semiconductor quantum computing.

[0074] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0075] One embodiment of this application proposes a method for fabricating high-quality hole-spin qubits of semiconductor two-dimensional gate-controlled

[110] quantum dots that are compatible with CMOS technology, comprising the following two steps:

[0076] I: Based on CMOS technology, a tilted germanium quantum well structure is prepared. By controlling the tilt angle, a germanium quantum well in the growth direction

[110] is achieved. The germanium quantum well structure is a P-type doped germanium quantum well.

[0077] II: Two-dimensional gated quantum dots 6 were fabricated in germanium quantum well structures based on electric dipole moment spin resonance (EDSR) technology to realize high-quality hole spin qubits.

[0078] Figure 1a and Figure 1bThis is a schematic diagram of the tilted

[110] germanium quantum well and the two-dimensional gated

[110] germanium quantum dots in an embodiment of the present invention. The preparation method of the tilted

[110] germanium quantum well includes the following steps:

[0079] S1, A

[100] germanium-silicon alloy layer 2 is grown on a

[100] silicon substrate 1 to alleviate the lattice mismatch between germanium and silicon. The

[100] germanium-silicon alloy layer

[100] -Ge x Si 1-x The proportion of silicon should be less than 50%, and the thickness of the germanium-silicon alloy layer 2 is between a few nanometers and tens of nanometers.

[0080] S2, a

[100] germanium layer 3 of tens to hundreds of nanometers is epitaxially grown on the

[100] germanium-silicon alloy layer 2, and the

[100] germanium layer 3 is P-type doped by ion implantation and other methods to obtain

[100] -P type Ge.

[0081] S3, a bevel is etched on the

[100] germanium layer 3 using dry or wet etching methods, such that the bevel angle θ is 45 degrees to the horizontal direction. The 45-degree bevel angle ensures that the germanium on the bevel of the quantum well has a

[110] crystal orientation, thereby fabricating a

[110] quantum well. A schematic diagram of the

[100] crystal orientation is shown below. Figure 2a As shown, the crystal orientation diagram of

[110] is as follows. Figure 2b As shown.

[0082] S4, a dielectric layer 4 is grown on the inclined surface of the quantum well. As a preferred option, the dielectric material of the dielectric layer 4 can be SiO2 or Al2O3, and the thickness is between tens of nanometers and hundreds of nanometers.

[0083] S5, Multiple metal electrodes 5 are fabricated on the dielectric layer 4. Preferably, the metal electrode 5 can be made of Al or Au, and its thickness is on the order of tens of nanometers. Figure 1a and Figure 1b As shown, the metal electrode 5 includes P1, P2, P3, P4, G1, G2 and TG electrodes, and the two-dimensional gated quantum dot 6 includes quantum dots Q1 and Q2. The P1, P2, P3 and P4 electrodes provide the binding potential to trap two-dimensional holes, the G1 and G2 electrodes provide the gate voltage to regulate quantum dots Q1 and Q2 to generate and regulate the Rashba spin-orbit coupling effect, and the TG electrode provides the potential to separate or couple quantum dots Q1 and Q2.

[0084] Specifically, P1, P2, P3, P4, G1, G2 and TG electrodes are arranged in a row, with the number of electrodes in each row being equal.

[100] The left and right sides of the germanium layer 3 form opposing inclined surfaces, with a plane between the tops of the two inclined surfaces. The dielectric layer 4 forms the same inclined surface and plane as the

[100] germanium layer. The TG electrodes are evenly distributed longitudinally on the plane of the dielectric layer 4. The P1, G1 and P2 electrodes are distributed on one side of the inclined surface of the dielectric layer 4, and the P3, G2 and P4 electrodes are distributed on the other side of the inclined surface of the dielectric layer 4. The G1 electrode is located between the P1 and P2 electrodes and corresponds to the Q1 quantum dot. The G2 electrode is located between the P3 and P4 electrodes and corresponds to the Q2 quantum dot. The Q1 quantum dot and the Q2 quantum dot are located within the inclined surface of the

[100] germanium layer.

[0085] In a sloping quantum well structure, both single and double qubits can be generated along the y-direction, while multiple qubits can be generated simultaneously along the z-direction. The coupling strength between qubits can be adjusted using appropriate electrodes to meet different needs. The size of the qubits ranges from tens of nanometers to 100 nanometers. Therefore, as a preferred embodiment, the length L in the y-direction of the sloping quantum well structure... y The length L in the z-direction can be between 800 nanometers and 1200 nanometers. z It can then be freely adjusted according to needs.

[0086] The principle of EDSR technology for manipulating hole spin qubits is as follows: Figure 3 As shown. When an in-plane or out-of-plane static magnetic field is applied to a gated quantum dot formed in a quantum well, spin-polarized discrete energy levels appear in the quantum dot under the combined effects of the quantum binding effect and the Zeeman effect. 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., Δn = ±1 and Δs = 0 must be satisfied simultaneously. In the absence of spin-orbit coupling, there is no coupling between quantum states with different spin components, so spin control of a two-level system cannot be achieved. When the linear Rashba spin-orbit coupling effect exists, it will cause coupling between adjacent quantum states containing different spin components, i.e., Δn = ±1 and Δs ≠ 0 must be satisfied simultaneously, 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 the two-level system, thereby continuously changing the spin components of each energy level and achieving time-dependent spin flipping and spin manipulation.

[0087] Although the linear Rashba effect is key to achieving spin flipping and spin manipulation using EDSR (Electronic Spinning Reversal) technology, it was previously generally believed that due to the prohibition of light-heavy hole coupling in quantum wells, heavy holes in quantum wells would only exhibit a cubic Rashba effect, not a linear one. Recent studies have shown that light-heavy hole coupling exists in quantum wells, thus enabling a linear Rashba effect. First-principles calculations using the empirical pseudopotential method for spin splitting are shown below. Figure 4a and Figure 4b As shown, when a vertical electric field of 30 kV / cm is applied,

[110] -(Ge) 40 / (Si) 20 Quantum wells and

[100] -(Ge) 40 / (Si) 20 The Rashba spin splitting of the quantum well near the Γ point exhibits a linear relationship with the wave vector, and the linear Rashba parameter α R The values ​​are 30.7 meV and 0.8 meV, respectively. It is not difficult to find that the

[110] quantum well has a Rashba parameter that is two orders of magnitude larger than that of the

[100] quantum well. This is because the light-heavy hole coupling in the

[100] quantum well is entirely caused by the boundary effect, while the light-heavy hole coupling in the

[110] quantum well includes not only the part caused by the boundary effect, but also the intrinsic light-heavy hole coupling caused by the breaking of axisymmetry under the specific orientation of the quantum well. Therefore, the light-heavy hole coupling strength in the

[110] quantum well is much greater than that in the

[100] quantum well, thus exhibiting a stronger linear Rashba effect.

[0088] It should be noted that, in order to exclude the influence of Dresselhaus spin splitting caused by the alloy during the calculation, we used a pure Si barrier; however, in the experiment, only GeSi alloy barriers can be grown because there is a 4% lattice mismatch between Ge and Si, so Ge ​​cannot be grown directly on Si. The calculation illustrates the essential issue of the magnitude relationship of the Rashba effect, but in actual experiments, GeSi alloy must be used.

[0089] The Rabi frequency is directly proportional to the linear Rashba parameter. Currently reported quantum wells and two-dimensional gated quantum dots are grown along the

[100] direction, achieving Rabi frequencies in the hundreds of MHz range. However, the

[110] quantum dot designed in this invention can achieve Rabi frequencies in the GHz range. As a preferred embodiment, a 1.65T magnetic field is applied within the quantum well plane, and the Rabi frequency is calculated as follows: Figure 5a and Figure 5bAs shown, at a gate voltage of 30 kV / cm, by adjusting the amplitude of the alternating electric field or microwave,

[110] quantum dots can achieve a Rabi frequency of approximately 4 GHz, compared to approximately 100 MHz for

[100] quantum dots. In 5a and Figure 5b In the calculation, the quantum dot radius is taken as 50 nm, the in-plane g factor is 0.39, and the effective masses of the

[110] and

[100] quantum dots obtained by first-principles calculation are 0.135 and 0.132 electron masses, respectively.

[0090] Figure 4a , Figure 4b , Figure 5a and Figure 5b Theoretical calculations show that the

[110] quantum well has a larger linear Rashba effect and Rabi frequency compared to the

[100] quantum well. Since the linear Rashba effect can be modulated by the gate voltage, the gate voltage can also modulate the Rabi frequency. Figure 6 As shown, when the gate voltage varies within the range of 100 kV / cm, the linear Rashba parameter can reach 80 meV, and the Rabi frequency can reach 11 GHz. Since the thickness of the 40 monolayer germanium layers in the calculated system is approximately 6 nm, further increasing the germanium layer thickness within a certain range can further improve the Rabi frequency.

[0091] In summary, this invention provides a method for fabricating high-quality hole spin qubits of semiconductor gate-controlled

[110] germanium quantum dots compatible with CMOS technology. By tilting the etching of the

[100] germanium layer to obtain a

[110] crystal plane quantum well, a high-quality gate-controlled quantum dot with fast spin flipping is realized.

[0092] In some specific embodiments, the diameter of the two-dimensional gated quantum dot 6 is 60 to 100 nm.

[0093] In some specific embodiments, P-type doping methods include thermal diffusion, electrochemical implantation, or ion implantation.

[0094] In some specific embodiments, the bulk phase of the germanium material in the germanium quantum well is a crystal structure with tetrahedral covalent bonds.

[0095] In some specific embodiments, physical vapor deposition and plasma-chemical vapor deposition can be used in the preparation method of germanium quantum wells.

[0096] In some specific embodiments, the method of etching a bevel on the germanium layer 3

[100] may include dry etching and / or wet etching.

[0097] In some specific embodiments, the preparation methods that can be used to prepare the metal electrode 5 include electron beam exposure and / or electron beam evaporation.

[0098] In some specific embodiments, the mobility of the germanium quantum well reaches 102. 5 cm 2 On the order of / (V·s).

[0099] In some specific embodiments, the hole spin Rabi flipping frequency in the two-dimensional gated quantum dot 6 reaches the GHz level and the quality factor is greater than 10. 4 .

[0100] In some specific embodiments, the germanium quantum well is subjected to a quantum binding effect in the

[110] direction.

[0101] In some specific embodiments, the substrate may not be limited to a silicon substrate.

[0102] In some specific embodiments, the tilt angle θ of the quantum well is not limited to 45 degrees. When θ is 45 degrees, the crystal orientation on the tilt is

[110] , which has the maximum Rashba effect and Rabi frequency, which is the most ideal case; however, strictly controlling the tilt angle to 45 degrees in experiments may have errors or difficulties, and a slight deviation in the tilt angle can also achieve the technical effect of this case.

[0103] EDSR technology requires the application of a back-gate binding electric field, an in-plane alternating electric field or microwave, a vertical electrostatic field, and an in-plane or vertical static magnetic field to a germanium quantum well to generate Rabi spin flips. The direction of the in-plane static magnetic field must not be perpendicular to the direction of the in-plane alternating electric field or microwave. The frequency of the in-plane alternating electric field or microwave is equal to the natural frequency of the in-plane or vertical static magnetic field.

[0104] Due to the strong tunable spin-orbit coupling (SOC) effect of germanium holes, their near-independence from nuclear spin scattering, and the potential for further spin decoherence time through isotope purification, along with their immunity to valley scattering, high mobility among all known semiconductors, and deep compatibility with traditional CMOS processes, germanium quantum dots have become an important carrier for semiconductor quantum computing. Compared to traditional quantum wells grown in the

[100] direction, quantum wells grown in the

[110] direction exhibit the largest linear Rashba spin-orbit coupling effect, providing the fastest Rabi spin flip. This invention overcomes the difficulty of directly growing

[110] quantum wells on a plane by designing a tilted quantum well, providing a novel solution for realizing high-quality hole spin qubits.

[0105] Another embodiment of this application proposes a semiconductor structure, such as Figure 1a and Figure 1bAs shown, the structure includes, from bottom to top, a

[100] silicon substrate 1, a

[100] germanium-silicon alloy layer 2, a

[100] germanium layer 3, a dielectric layer 4, and a metal electrode 5. The

[100] germanium layer 3 is p-type doped, and a slope is formed on the

[100] germanium layer 3. Two-dimensional gated quantum dots 6 are embedded in the slope of the

[100] germanium layer 3. The tilt angle θ of the slope is 45 degrees to the horizontal direction.

[0106] In some specific embodiments, the size of the two-dimensional gated quantum dot 6 is 60 to 100 nm.

[0107] In some specific embodiments, the thickness of the germanium-silicon alloy layer 2 is between a few nanometers and tens of nanometers, and the proportion of silicon is less than 50%.

[0108] In some specific embodiments, the thickness of the germanium layer 3 is from tens of nanometers to hundreds of nanometers.

[0109] In some specific embodiments, the dielectric material of dielectric layer 4 is SiO2 or Al2O3, and the thickness of dielectric layer 4 is between tens of nanometers and hundreds of nanometers.

[0110] In some specific embodiments, the metal electrode 5 is made of Al or Au, and the thickness of the metal electrode 5 is on the order of tens of nanometers.

[0111] In some specific embodiments, the bulk phase of the germanium material in the germanium quantum well is a crystal structure with tetrahedral covalent bonds.

[0112] In some specific embodiments, the substrate may not be limited to a silicon substrate.

[0113] In some specific embodiments, the tilt angle θ of the quantum well is not limited to 45 degrees. When θ is 45 degrees, the crystal orientation on the tilt is

[110] , which has the maximum Rashba effect and Rabi frequency, which is the most ideal case; however, strictly controlling the tilt angle to 45 degrees in experiments may have errors or difficulties, and a slight deviation in the tilt angle can also achieve the technical effect of this case.

[0114] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0115] 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 invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0116] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0117] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0118] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. 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.

[0119] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing hole-spin qubits, characterized in that, include: Provide substrate; A germanium quantum well is formed on the substrate, wherein the germanium quantum well is an inclined quantum well structure grown along the [110] direction, and the germanium quantum well is formed by CMOS process; Two-dimensional gated quantum dots were fabricated in the germanium quantum well; Forming a germanium quantum well on the substrate includes: An alloy layer is formed on the substrate, the alloy layer being a [100] germanium-silicon alloy layer; A [100] germanium layer is formed on the alloy layer, wherein the [100] germanium layer is p-type doped. An inclined surface is formed on the [100] germanium layer by etching, and the inclined surface has an inclination angle of 45 degrees with the horizontal direction; A dielectric layer is formed on the [100] germanium layer; Electrodes are formed on the dielectric layer. The electrodes are metal electrodes, including P1, P2, P3, P4, G1, G2, and TG electrodes. The two-dimensional gated quantum dots include quantum dots Q1 and Q2. Electrodes P1, P2, P3, and P4 provide the binding potential for trapping two-dimensional holes. Electrodes G1 and G2 provide the gate voltage for regulating quantum dots Q1 and Q2 to generate and regulate the Rashba spin-orbit coupling effect. Electrode TG provides the potential for separating or coupling quantum dots Q1 and Q2. Opposing slopes are formed on the left and right sides of the [100] germanium layer, with the tops of the two slopes... The dielectric layer is a plane, and the dielectric layer forms the same inclined plane as the [100] germanium layer. The TG electrodes are evenly distributed on the plane of the dielectric layer along the longitudinal direction. The P1, G1 and P2 electrodes are distributed on the inclined plane on one side of the dielectric layer, and the P3, G2 and P4 electrodes are distributed on the inclined plane on the other side of the dielectric layer. The G1 electrode is located between the P1 and P2 electrodes and corresponds to the Q1 quantum dot. The G2 electrode is located between the P3 and P4 electrodes and corresponds to the Q2 quantum dot. The Q1 quantum dot and the Q2 quantum dot are located in the inclined plane of the [100] germanium layer.

2. The preparation method according to claim 1, characterized in that, The two-dimensional gated quantum dot has a size of 60 to 100 nm.

3. The preparation method according to claim 1, characterized in that, The substrate is a [100] silicon substrate.

4. The preparation method according to claim 1, characterized in that, The thickness of the [100] germanium-silicon alloy layer is between a few nanometers and tens of nanometers, and the proportion of silicon in the [100] germanium-silicon alloy layer is less than 50%.

5. The preparation method according to claim 1, characterized in that, The thickness of the [100] germanium layer is from tens of nanometers to hundreds of nanometers.

6. The preparation method according to claim 1, characterized in that, The dielectric material of the dielectric layer is SiO2 or Al2O3, and the thickness of the dielectric layer is between tens of nanometers and hundreds of nanometers.

7. The preparation method according to claim 1, characterized in that, The electrode is a metal electrode, and the material of the metal electrode is Al or Au. The thickness of the metal electrode is on the order of tens of nanometers.

8. The preparation method according to claim 1, characterized in that, Methods for P-type doping of the [100] germanium layer include thermal diffusion, electrochemical implantation, or ion implantation.

9. The preparation method according to any one of claims 1-8, characterized in that, The bulk phase of the germanium material in the germanium quantum well has a crystal structure with tetrahedral covalent bonds.

10. The preparation method according to claim 1, characterized in that, The germanium quantum well has a mobility of 10. 5 cm 2 / (V (s) magnitude.

11. The preparation method according to claim 1, characterized in that, The hole spin Rabi flipping frequency in the two-dimensional gated quantum dot reaches the GHz level and the quality factor is greater than 10. 4 .

12. The preparation method according to claim 1, characterized in that, The two-dimensional gated quantum dot was prepared in a germanium quantum well using electric dipole moment spin resonance technology.

13. The preparation method according to claim 1, characterized in that, Apply the following to the germanium quantum well: A: Back-grid bound electric field; and B: Alternating electric field or microwaves within the inclined plane; and C: The inclined plane is perpendicular to the electrostatic field; and D: A static magnetic field inside or perpendicular to the inclined plane to generate Rabi spin flipping, wherein the direction of the static magnetic field inside the inclined plane is not perpendicular to the direction of the alternating electric field or microwave inside the inclined plane.

14. The preparation method according to claim 13, characterized in that, The frequency of the alternating electric field or microwave within the inclined plane is equal to the natural frequency of the static magnetic field within the inclined plane or perpendicular to the inclined plane.

15. A semiconductor structure, characterized in that, The semiconductor structure is prepared using the method for preparing hole-spin qubits as described in any one of claims 1-14, and comprises: Substrate; A germanium quantum well is formed on the substrate, wherein the germanium quantum well is an inclined quantum well structure grown along the [110] direction; Two-dimensional gated quantum dots prepared in the germanium quantum well.

16. The semiconductor structure according to claim 15, characterized in that, It includes a substrate, an alloy layer, a [100] germanium layer, a dielectric layer and an electrode formed sequentially from bottom to top. The [100] germanium layer is P-type doped and has a bevel formed on it.

17. The semiconductor structure according to claim 16, characterized in that, The inclination angle of the inclined plane is 45 degrees with respect to the horizontal direction.

18. The semiconductor structure according to claim 15, characterized in that, The diameter of the two-dimensional gated quantum dot is 60 to 100 nm.

19. The semiconductor structure according to claim 15, characterized in that, The substrate is a [100] silicon substrate.

20. The semiconductor structure according to claim 16, characterized in that, The alloy layer is a [100] germanium-silicon alloy layer, wherein the thickness of the [100] germanium-silicon alloy layer is between a few nanometers and tens of nanometers, and the proportion of silicon in the [100] germanium-silicon alloy layer is less than 50%.

21. The semiconductor structure according to claim 16, characterized in that, The thickness of the [100] germanium layer is from tens of nanometers to hundreds of nanometers.

22. The semiconductor structure according to claim 16, characterized in that, The dielectric material of the dielectric layer is SiO2 or Al2O3, and the thickness of the dielectric layer is between tens of nanometers and hundreds of nanometers.

23. The semiconductor structure according to claim 16, characterized in that, The electrode is a metal electrode, and the material of the metal electrode is Al or Au. The thickness of the metal electrode is on the order of tens of nanometers.

24. The semiconductor structure according to claim 16, characterized in that, The bulk phase of the germanium material in the germanium quantum well has a crystal structure with tetrahedral covalent bonds.

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