WO2019148760A1 - 具有绝缘保护层的拓扑绝缘体结构及其制备方法 - Google Patents

具有绝缘保护层的拓扑绝缘体结构及其制备方法 Download PDF

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WO2019148760A1
WO2019148760A1 PCT/CN2018/093183 CN2018093183W WO2019148760A1 WO 2019148760 A1 WO2019148760 A1 WO 2019148760A1 CN 2018093183 W CN2018093183 W CN 2018093183W WO 2019148760 A1 WO2019148760 A1 WO 2019148760A1
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topological insulator
quantum well
protective layer
well film
insulating protective
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PCT/CN2018/093183
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English (en)
French (fr)
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何珂
姜高源
薛其坤
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清华大学
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Publication of WO2019148760A1 publication Critical patent/WO2019148760A1/zh
Priority to US16/984,151 priority Critical patent/US20200365805A1/en

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N99/00—Subject matter not provided for in other groups of this subclass
    • H10N99/05—Devices based on quantum mechanical effects, e.g. quantum interference devices or metal single-electron transistors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N52/00—Hall-effect devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/80—Constructional details
    • H10N50/85—Magnetic active materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N52/00—Hall-effect devices
    • H10N52/01—Manufacture or treatment

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  • the present application relates to the field of condensed matter physics, and relates to a topological insulator structure having an insulating protective layer and a preparation method thereof.
  • Magnetically doped topological insulators are the only material system that has achieved quantum anomalous Hall effects to date and have been validated by several experimental groups around the world.
  • Professor Tokura of the Japan Institute of Physical and Chemical Research, Wang Kanglong's research group at the University of California, Los Angeles, and the Nitin Samarth research group at Pennsylvania State University also implemented the quantum anomalous Hall effect in chromium-doped (Bi, Sb) 2 Te 3 And at the Massachusetts Institute of Technology's Jagadeesh S.
  • Moodera research group Tsui Tsui first achieved the quantum anomalous Hall effect of the larger coercive field in vanadium-doped (Bi,Sb) 2 Te 3 .
  • Samples that implement the quantum anomalous Hall effect are generally relatively thin, and can be quantized to a thickness of 4 nm to 10 nm.
  • a relatively thick protective layer is generally deposited thereon to allow the sample to be stored for a longer period of time.
  • the method reported now is to grow relatively thin metal aluminum and then naturally oxidize to form a dense oxide protective layer, and the other method is to deposit a thicker Te protective layer, both methods need to adjust the growth temperature to room temperature or lower. .
  • the other is to deposit alumina as a protective layer in an ultra-high vacuum external atomic layer deposition system, but this method requires the sample to be transferred to another system for deposition, and is no longer ultra-high vacuum conditions, while the atomic layer deposition system The deposition rate is generally slower.
  • a topological insulator structure having an insulating protective layer comprising: an insulating substrate, a topological insulator quantum well film, and an insulating protective layer, wherein the topological insulator quantum well film and the insulating protective layer are sequentially stacked on the surface of the insulating substrate to form a different a junction structure
  • the insulating protective layer is selected from the group consisting of a wurtzite structure CdSe, a sphalerite structure ZnTe, a sphalerite structure CdSe, a sphalerite structure CdTe, a sphalerite structure HgSe, and a sphalerite structure. At least one of HgTe.
  • the insulating protective layer molecular beam is epitaxially grown on the surface of the topological insulator quantum well film.
  • the topological insulator quantum well film is formed by doping a first element and a second element at a Sb site of Sb 2 Te 3 , the first element including Cr, Ti, Fe, Mn, and V.
  • the first element including Cr, Ti, Fe, Mn, and V.
  • the material of the topological insulator quantum well film is represented by the chemical formula M y N z (Bi x Sb 1-x ) 2-yz Te 3 , where 0 ⁇ x ⁇ 1, 0 ⁇ y, 0 ⁇ z, and 0 ⁇ y + z ⁇ 2, M and N are respectively Cr, Ti, Fe, Mn or V.
  • a topological insulator structure having an insulating protective layer comprising: an insulating substrate, a topological insulator quantum well film, and an insulating protective layer, wherein the insulating protective layer is lattice-matched with the topological insulator quantum well film, and is sequentially stacked on the insulating layer
  • a heterojunction structure is formed on the surface of the substrate.
  • the topological insulator quantum well film has a first lattice constant
  • the insulating protective layer has a second lattice constant
  • a ratio of the first lattice constant to the second lattice constant It is 1:1.1 to 1.1:1.
  • the insulating protective layer molecular beam is epitaxially grown on the surface of the topological insulator quantum well film.
  • the molecular beam epitaxial growth temperature of the insulating protective layer is within a range of a molecular beam epitaxial growth temperature of the topological insulator quantum well film of ⁇ 100 °C.
  • a method for preparing a topological insulator structure having an insulating protective layer comprising:
  • topological insulator quantum well film by molecular beam epitaxy on the surface of the insulating substrate having a first temperature
  • the insulating protective layer is grown by molecular beam epitaxy on the surface of the topological insulator quantum well film having a second temperature.
  • the second temperature is within a range of the first temperature ⁇ 100 °C.
  • the first temperature is from 150 °C to 250 °C and the second temperature is from 50 °C to 350 °C.
  • the insulating protective layer of the topological insulator of the present application is lattice-matched with the topological insulator quantum well film, thereby sequentially superposing a surface of the insulating substrate to form a heterojunction structure to better protect the topological insulator.
  • the quantum well film is not destroyed, improving the quality of the topological insulator structure.
  • FIG. 1 is a schematic view showing the structure of a Sb 2 Te 3 lattice according to an embodiment of the present invention, wherein (a) is a perspective view, (b) is a plan view, (c) is a lattice structure diagram in the [110] direction, and (d) is [ 210] a lattice structure diagram of the direction;
  • FIG. 2 is a schematic view showing a structure of a CdSe lattice according to an embodiment of the present invention, wherein (a) is a perspective view, (b) is a plan view, (c) is a lattice structure diagram in the [110] direction, and (d) is a [210] direction.
  • Lattice structure diagram
  • FIG. 3 is a schematic diagram of a lattice matching structure of Sb 2 Te 3 and CdSe according to an embodiment of the present invention, wherein (a) is a front view and (b) is a side view;
  • FIG. 4 is a schematic structural view of an MBE reaction chamber according to an embodiment of the present application.
  • FIG. 5 is a schematic structural view of a multi-channel topological insulator of a single-layer, two-layer, and three-layer magnetic doped topological insulator quantum well film according to an embodiment of the present application;
  • FIG. 6 is a schematic structural view of an electrical device according to an embodiment of the present application.
  • FIG. 7 is a topographical view and a RHEED fringe pattern of a multi-layer topological insulator of different layers according to an embodiment of the present invention, wherein (a)(b)(c) are only one layer of magnetically doped topological insulator quantum well film.
  • (d) (e)(f) are the RHEED stripes corresponding to (a)(b)(c);
  • FIG. 8 is a TEM diagram of a multi-channel topological insulator according to an embodiment of the present invention, wherein (a) is a super-lattice structure formed by a 4-layer magnetic doped topological insulator quantum well film and a 3-layer CdSe spacer layer, and (b) is ( a) partial enlargement;
  • FIG. 9 is an XRD diagram of a multi-channel topological insulator structure according to an embodiment of the present application.
  • FIG. 10A-10C are Hall graphs of multi-channel topological insulators of FIG. 5 at different back gate voltages according to an embodiment of the present invention, wherein FIG. 10A is a single-layer magnetic doped topological insulator quantum well film, FIG. 10B a magnetic doped topological insulator quantum well film having two layers of the same coercive field, FIG. 10C is a three-layer magnetic doping topological insulator quantum well film having the same coercive field;
  • FIG. 11A-11C are magnetic resistance curves of the multi-channel topological insulator of FIG. 5 at different back gate voltages according to an embodiment of the present invention, wherein FIG. 11A is a single-layer magnetic doped topological insulator quantum well film, FIG. 11B a magnetically doped topological insulator quantum well film having two layers of the same coercive field, and FIG. 11C is a three-layer magnetic doping topological insulator quantum well film having the same coercive field;
  • FIG. 13 is an angular resolution photoelectron spectrum and a second-order differential diagram of a CdSe-covered topological insulator of different thicknesses according to an embodiment of the present invention, wherein (a) is a 6QL magnetic doped topological insulator quantum well film without CdSe coverage. (b) is 0.5 nm CdSe coverage, (c) is 1 nm CdSe coverage, (d) is 1.5 nm CdSe coverage angular resolution photoelectron spectroscopy; (e) (f) (g) (h) respectively Is the second-order differential map of (a)(b)(c)(d).
  • topological insulator structure with an insulating protective layer of the present application and a preparation method thereof will be further described in detail below by way of embodiments and with reference to the accompanying drawings. It is understood that the specific embodiments described herein are merely illustrative of the application and are not intended to be limiting.
  • an embodiment of the present application first provides a topological insulator structure having an insulating protective layer, including: an insulating substrate 10 , a topological insulator quantum well film 20 , and an insulating protective layer 30 , and the insulating protective layer 30 and the topology
  • the lattice matching of the insulator quantum well film 20, the topological insulator quantum well film 20 and the insulating protective layer 30 are sequentially superposed on the surface of the insulating substrate 10 to form a heterojunction structure of 20-30.
  • the insulating protective layer 30 has a similar crystal structure and similar atomic spacing with the topological insulator quantum well film 20 to form a matching lattice relationship, thereby forming a heterojunction structure and better protecting the topological insulator quantum.
  • the well film 20 is not damaged, improving the quality of the topological insulator structure.
  • the topological insulator quantum well film 20 is grown on the insulating substrate 10 by molecular beam epitaxy.
  • Molecular beam epitaxy refers to a method of evaporating a coating at a slow deposition rate of 0.1 to 1 nm/s under an ultra-high vacuum of the order of 10 -10 mbar.
  • the insulating protective layer 30 is continuously grown by molecular beam epitaxy on the surface of the topological insulator quantum well film 20.
  • the topological insulator quantum well film 20 and the insulating protective layer 30 are continuously grown by molecular beam epitaxy to form a structurally uniform heterojunction structure.
  • Thin film samples of topological insulators generally have a relatively low growth temperature, and heating for a long time in a vacuum tends to cause desorption of Te, causing the sample to deviate from the original charge neutral point. At the same time, too high a temperature can easily decompose the film sample and destroy the sample.
  • the molecular beam epitaxial growth temperature of the material of the insulating protective layer 30 is close to the molecular beam epitaxial growth temperature of the material of the topological insulator quantum well film 20.
  • the molecular beam epitaxial growth temperature of the insulating protective layer 30 is within a range of a molecular beam epitaxial growth temperature of the topological insulator quantum well film 20 of ⁇ 100 ° C, such that the insulating protective layer 30 is grown.
  • the structure of the topological insulator quantum well film 20 that has been formed is not destroyed, and the quantum effect and performance are not affected by the formation process of the insulating protective layer 30.
  • the topological insulator quantum well film 20 and the insulating protective layer 30 have close lattice constants, which can lower the lattice mismatch ratio and make the lattice matching more uniform.
  • the topological insulator quantum well film 20 has a first lattice constant
  • the insulating protective layer 30 has a second lattice constant
  • the first lattice constant and the second lattice constant The ratio is 1:1.1 to 1.1:1.
  • the topological insulator quantum well film 20 has a hexagonal close-packed surface having a first lattice constant in the hexagonal close-packed surface
  • the insulating protective layer 30 has a hexagonal close-packed surface
  • the hexagonal close-packed surface has a second lattice constant
  • the ratio of the first lattice constant to the second lattice constant is 1:1.1 to 1.1:1.
  • the topological insulator quantum well film 20 is a magnetically doped topological insulator quantum well film 20 formed by doping a first element and a second element at the Sb site of Sb 2 Te 3 .
  • the first element is for providing a magnetic element
  • the second element is for introducing electrons into the topological insulator quantum well film 20 to cause holes introduced in the topological insulator quantum well film 20 and the topological insulator
  • the electrons introduced in the quantum well film 20 substantially cancel each other, that is, the carrier concentration of the magnetic doped topological insulator quantum well film 20 is adjusted when the voltage is not applied through the top gate electrode or the back gate electrode.
  • the topological insulator quantum well film 20 is preferably a quaternary (containing four elements) or a quinary material (containing five elements).
  • the first element comprises one or more elements selected from the group consisting of Cr, Ti, Fe, Mn, and V, and the second element includes Bi.
  • the material of the topological insulator quantum well film 20 is represented by the chemical formula M y N z (Bi x Sb 1-x ) 2-yz Te 3 , where 0 ⁇ x ⁇ 1, 0 ⁇ y, 0 ⁇ z, and 0 ⁇ y +z ⁇ 2, M and N are Cr, Ti, Fe, Mn or V, respectively.
  • the M and N may be the same or different elements.
  • the M is Cr and the N is V.
  • the thickness of the topological insulator quantum well film 20 is preferably 5QL to 10QL.
  • the thickness of the insulating protective layer 30 is preferably greater than 0.35 nm and can be grown to an infinite thickness.
  • the material of the insulating protective layer 30 preferably has a hexagonal close-packed (hcp) plane so as to form a hexagonal close-pack in the superposition direction when superposed with the doped Sb 2 Te 3 topological insulator quantum well film 20.
  • the (001) plane of the wurtzite structure or the (111) plane of the zinc blende structure of the material of the insulating protective layer 30 is a hexagonal close-packed surface.
  • the insulating protective layer 30 is selected from the group consisting of a wurtzite structure CdSe, a sphalerite structure ZnTe, a sphalerite structure CdSe, a sphalerite structure CdTe, a sphalerite structure HgSe, and a sphale zinc. At least one of the HgTe of the ore structure.
  • the material of the insulating protective layer 30 is close to the epitaxial growth temperature of the magnetically doped Sb 2 Te 3 topological insulator quantum well film 20, and can be epitaxially grown on the surface of the topological insulator quantum well film 20, and the insulating protection
  • the layer 30 and the topological insulator quantum well film 20 have a lattice constant close to each other, lattice matching, and a heterojunction structure can be formed.
  • the lattice constant of the magnetically doped topological insulator quantum well film 20 is between the lattice constants of Sb 2 Te 3 ((001) in-plane 0.426 nm) and Bi 2 Te 3 ((001) in-plane 0.443 nm) .
  • the lattice constant gradually becomes close to 0.443 nm from approximately 0.426 nm.
  • the in-plane lattice constants of the CdSe (111) plane of the zinc blende structure are 0.457 nm, 0.424 nm, 0.456 nm, 0.431 nm and 0.430 nm, respectively, as an optional lattice-matched insulating protective layer 30 material.
  • the in-plane lattice constant of the (001) plane of the cdSe structure of the wurtzite structure is 0.430 nm, which closely matches the lattice constant of the magnetic topological insulator (about 3% of the lattice mismatch with Bi2Te3) The lattice mismatch with Sb2Te3 is about 1%). Therefore, in the present embodiment, the wurtzite structure of CdSe may be an optional insulating protective layer 30 material.
  • Sb2Te3 is a layered material belonging to the trigonal system and the space group is For the specific lattice structure, please refer to FIG. 1.
  • each layer of Sb and Te atoms has a hexagonal close-packed structure (ie, a surface perpendicular to the c-axis is a hexagonal close-packed surface), and is perpendicular to ab.
  • the c-axis direction of the plane is distributed in layers, and each of the five atomic layers constitutes a "Quintuple layer" (QL).
  • the topological insulator quantum well film 20 is a magnetically doped topological insulator quantum well film 20, and the five atomic layers are respectively a first Te atomic layer (Te1) and a magnetically doped layer.
  • An Sb atomic layer (Sb), a second Te atomic layer (Te2), a magnetically doped second Sb atomic layer (Sb'), and a third Te atomic layer (Te1') within a single QL, the atoms are common A valence-ion type chemical bond; between adjacent QLs, a van der Waals interaction between the Te1 atomic layer and the Te1' atomic layer forms an interface that is easily cleaved.
  • the wurtzite structure of cadmium selenide belongs to the hexagonal crystal system.
  • the CdSe of the wurtzite structure is alternately stacked by Cd and Se along the [001] direction (ie, the c-axis). It is made of ⁇ and has a hexagonal close-packed surface on the (001) side.
  • the lattice matching relationship between the CdSe insulating protective layer 30 and the magnetic doped topological insulator quantum well film 20Sb 2 Te 3 see FIG.
  • Se in Sb 2 Te 3 and Se in CdSe each form a hexagonal structure, and their six
  • the lattice structure of the edge structure is close to each other, and a hexagonal close-pack can be formed to form an epitaxial structure that matches the lattice to form a heterojunction structure.
  • the molecular beam epitaxy temperature of the CdSe thin film is close to the molecular beam epitaxial growth temperature of the magnetically doped Sb 2 Te 3 topological insulator quantum well film 20.
  • the CdSe thin film material can be continuously grown in the molecular beam epitaxy cavity at substantially the same growth temperature as the insulating of the magnetic doped topological insulator quantum well film 20.
  • the protective layer 30 ensures maximum protection of the topological insulator quantum well film 20 from environmental pollution and improves product quality and performance.
  • the material of the insulating substrate 10 is conventional, preferably indium phosphide, gallium arsenide, barium titanate, aluminum oxide or single crystal silicon.
  • the material of the insulating substrate 10 may be selected to have a material having a dielectric constant greater than 5,000 at a low temperature of less than or equal to 10 Kelvin (K), such as barium titanate (STO). Since a large abnormal anomalous Hall resistance is obtained, even if a quantum anomalous Hall effect (QAHE) is realized, a voltage is applied to the magnetic doped topological insulator quantum well film 20 for chemical potential regulation, specifically by forming a top gate electrode.
  • K barium titanate
  • the back gate electrode realizes a loading voltage, and the chemical potential of the magnetic doped topological insulator quantum well film 20 is regulated by field effect.
  • the insulating substrate 10 having a large dielectric constant at a low temperature, the insulating substrate 10 can still have a large capacitance at a large thickness, so that the insulating substrate 10 can directly function as a back gate electrode and
  • the dielectric layer between the magnetically doped topological insulator quantum well film 20 is used to realize back gate voltage regulation at a low temperature, and the chemical potential of the magnetic doped topological insulator quantum well film 20 is controlled to realize QAHE.
  • the magnetic doped topological insulator quantum well film 20 is preferably grown on the surface of the (111) crystal plane of the STO.
  • the STO substrate may have a thickness of 0.1 mm to 1 mm. Since the dielectric constants of other base materials other than STO are relatively small, it is impossible to form a back gate on their back surfaces.
  • alumina, zirconia, boron nitride, or the like may be used to form a top gate structure for regulation, or an ionic liquid may be used for the magnetic doped topological insulator quantum well film 20.
  • the chemical potential is subjected to electrostatic field regulation.
  • the present application further provides a method for preparing a topological insulator structure having an insulating protective layer 30, including:
  • the insulating protective layer 30 is grown by molecular beam epitaxy on the surface of the topological insulator quantum well film 20 having a second temperature.
  • the insulating substrate 10 has an atomized level surface.
  • the STO substrate can be specifically cut into the surface of the (111) crystal plane and heated in deionized water of less than 100 ° C (such as 70 ° C), and in an oxygen and argon atmosphere. Burning at 800 ° C to 1200 ° C (eg 1000 ° C). The heating time in deionized water may be 1 to 2 hours, and the burning time may be 2 to 3 hours in an oxygen and argon atmosphere.
  • step S200 the barium titanate substrate is heated and a beam of the topological insulator quantum well film 20 material or elements is simultaneously formed in the molecular beam epitaxy cavity, thereby being in the insulating substrate 10
  • the surface forms a topological insulator quantum well film 20.
  • the material of the topological insulator quantum well film 20 is represented by the chemical formula M y N z (Bi x Sb 1-x ) 2-yz Te 3 .
  • the molecular beam epitaxy reaction chamber is provided with independent solid Bi, Sb, M, N and Te evaporation sources, and the beams of Bi, Sb, M, N and Te are heated to be in the base of the barium titanate substrate.
  • the magnetic doped topological insulator quantum well film 20 is formed on the surface, and the ratio between Bi, Sb, M, N, and Te is controlled by controlling the flow rates of the beams of Bi, Sb, M, N, and Te, so that M and N are
  • M is Cr
  • N is V
  • T Bi 491 ° C
  • T Sb 358 ° C
  • T Cr 941 ° C
  • T V 1557 ° C
  • the first temperature T sub 150 ° C to 250 ° C.
  • an evaporation source of the material of the insulating protective layer 30 is further disposed in the MBE reaction chamber.
  • a beam current of the material of the insulating protective layer 30 may be formed by heating an evaporation source of the material of the insulating protective layer 30.
  • the flow rate of the beam current of the material of the insulating protective layer 30 is controlled to grow the insulating protective layer 30 in situ on the topological insulator quantum well film 20 to form a topological insulator structure having the insulating protective layer 30.
  • the temperature of the surface of the topological insulator quantum well film 20 when the insulating protective layer 30 is grown is a second temperature.
  • the growth temperature of the insulating protective layer 30 is close to the growth temperature of the topological insulator quantum well film 20, and the insulating protective layer 30 can be grown after the topological insulator quantum well film 20 is epitaxially grown. And the topological insulator quantum well film 20 that has been formed is not damaged or the performance is not affected.
  • the second temperature is from 50 ° C to 350 ° C.
  • the second temperature is within a range of the first temperature ⁇ 100 ° C.
  • the second temperature is from 150 °C to 250 °C.
  • the insulating protective layer 30 is a wurtzite structure CdSe, and the evaporation source of the insulating protective layer 30 is a bulk CdSe.
  • the insulating protective layer 30 When heated, the insulating protective layer 30 is formed as a CdSe molecule.
  • the flow of the beam in the form of a beam is easier to control, making it easier to form a lattice-matched heterojunction structure.
  • an embodiment of the present application further provides a multi-channel topological insulator structure, including an insulating substrate 10 , a plurality of topological insulator quantum well films 20 , and a plurality of insulating spacer layers 40 , and the plurality of topological insulator quantum well films 20 .
  • a plurality of insulating spacer layers 40 are alternately superposed on the surface of the insulating substrate 10, and two adjacent topological insulator quantum well films 20 are spaced apart by one of the insulating spacer layers 40.
  • the insulating protective layer 30 in the previous embodiment has a lattice relationship matched with the topological insulator quantum well film 20, and the insulating protective layer 30 can be continuously grown as a topological insulator quantum well film as the insulating spacer layer 40 in this embodiment. 20, forming a multi-channel topological insulator.
  • a plurality of topological insulator quantum well films 20 can be independently connected to external circuitry for use as separate electrical components.
  • a plurality of topological insulator quantum well films 20 can be connected in parallel by electrodes. When connected in parallel, the contact resistance between the entire topological insulator structure and the electrodes can be significantly reduced, thereby reducing energy consumption.
  • the adjacent insulating spacer layer 40 and the topological insulator quantum well film 20 have a matching lattice structure, and the plurality of topological insulator quantum well films 20 are spaced apart by the insulating spacer layer 40, thereby forming a super Multi-channel topological insulator of lattice structure.
  • each of the topological insulator quantum well film 20 is preferably 5QL to 10QL.
  • the thickness of the insulating spacer 40 is preferably 0.35 nm to 20 nm.
  • the lattice constants of the adjacent topological insulator quantum well film 20 and the insulating spacer layer 40 are close to each other, which can lower the lattice mismatch ratio and make the lattice matching more uniform.
  • the ratio of the lattice constants of the adjacent topological insulator quantum well film 20 and the insulating spacer layer 40 is between 1:1.1 and 1.1:1.
  • the insulating spacer layer 40 is epitaxially grown on the surface of the topological insulator quantum well film 20, and the insulating spacer layer 40 and the topological insulator quantum well film 20 are each formed by molecular beam epitaxial growth.
  • the difference between the temperatures, and the difference between the molecular beam epitaxial growth temperatures of any two of the insulating spacer layers 40 are less than or equal to 100 °C.
  • the topological insulator quantum well film 20 and the insulating spacer layer 40 can be continuously epitaxially grown while the temperature conditions are substantially the same, and the topological insulator quantum well film 20 that has been formed is not formed when the subsequent insulating spacer layer 40 is formed. destroyed.
  • the topological insulator quantum well film 20 is magnetically doped to form a magnetic doped topological insulator quantum well film 20, which can form a multi-channel quantum anomalous Hall effect under the action of an applied electric field and a magnetic field.
  • the materials of the magnetically doped topological insulator quantum well film 20 of different layers in the multi-channel topological insulator structure may be the same or different, as long as the lattice structure of each layer between the insulating layers can be matched to form a multi-channel quantum anomalous Hall effect. Just fine.
  • the material of the topological insulator quantum well film 20 is represented by the chemical formula M y N z (Bi x Sb 1-x ) 2-yz Te 3 , where 0 ⁇ x ⁇ 1, 0 ⁇ y, 0 ⁇ z, and 0 ⁇ y + z ⁇ 2, M or N is a doped magnetic element selected from Cr, Ti, Fe, Mn or V. M or N may be the same or different elements, and the assignment of the magnetically doped topological insulator quantum well film 20, M or N and the corresponding x, y and z of the different layers may be the same or different.
  • each of the topological insulator quantum well films 20 is of the same material and is capable of forming a plurality of multi-channel topological insulators in parallel with the same Hall resistance.
  • the chemical formula of the material of each of the topological insulator quantum well films 20 has the same M, N, x, y, and z, respectively.
  • the insulating protective layer 30 can serve as the insulating spacer layer 40.
  • the insulating protective layer 30 may be selected from a wurtzite structure of CdSe, a sphalerite structure of ZnTe, a sphalerite structure of CdSe, a sphalerite structure of CdTe, a sphalerite structure of HgSe or a sphalerite structure of HgTe.
  • the wadite structure CdSe has a better lattice matching relationship with the magnetically doped Sb2Te3 topological insulator quantum well film 20 and a better matching relationship with the growth temperature, and is an optional insulating spacer layer 40.
  • the multi-channel topological insulator structure further includes an insulating protective layer 30 finally superimposed on the topmost insulating insulator quantum well film 20 to protect the top-mounted topological insulator quantum well film 20 from being destroyed.
  • the insulating layer serves as the insulating protective layer 30.
  • an insulating protective layer 30 may be further laminated.
  • the insulating protective layer 30 includes a wurtzite structure of CdSe, a sphalerite structure of ZnTe, a sphalerite structure of CdSe, a sphalerite structure of CdTe, a sphalerite structure of HgSe, and a sphalerite structure of HgTe.
  • the materials of the insulating protective layer 30 and the plurality of insulating spacer layers 40 may be the same or different, preferably the same, to simplify the evaporation source required for growth.
  • the embodiment of the present application further provides a method for fabricating the multi-channel topology insulator structure, including:
  • the molecular beam epitaxial growth temperature of the insulating spacer layer 40 is close to the molecular beam epitaxial growth temperature of any of the topological insulator quantum well films 20.
  • the topological insulator quantum well film 20 and the insulating protective layer 30 can be continuously epitaxially grown while the temperature conditions are substantially the same, and the top insulating insulator quantum well film 20 that has been formed is not formed when the subsequent insulating spacer layer 40 is formed. destroyed.
  • the topological insulator quantum well film 20 has a growth temperature of 150 ° C to 250 ° C
  • the insulating spacer 40 has a growth temperature of 50 ° C to 350 ° C.
  • the plurality of topological insulator quantum well films 20 and the plurality of insulating spacer layers 40 each have a growth temperature of 150 ° C to 250 ° C.
  • an embodiment of the present application further provides an electrical device including the multi-channel topological insulator structure, wherein the topological insulator quantum well film 20 of the multi-channel topological insulator structure is a magnetically doped topological insulator quantum.
  • the electrical device includes a gate electrode (eg, a back gate electrode or a top gate electrode) and two energization electrodes 1 and 4 (ie, a source and a drain).
  • the gate electrode is used to regulate the chemical potential of the magnetically doped topological insulator quantum well film 20.
  • the two energization electrodes 1 , 4 are spaced apart from each other and electrically connected to the topological insulator quantum well film 20 , respectively.
  • the direction from one energized electrode 1 to the other energized electrode 4 is a first direction (ie, a longitudinal resistance direction), and a direction perpendicular to the first direction is a second direction.
  • the two current-carrying electrodes 1 and 4 are respectively disposed at two ends of the multi-channel topological insulator in a first direction for introducing a current in the first direction to the multi-channel topological insulator structure.
  • each of the energized electrodes 1 or 4 is electrically coupled to all of the topological insulator quantum well films 20, respectively, such that the plurality of topological insulator quantum well films 20 are connected in parallel.
  • the two energization electrodes 1, 4 may be strip-shaped, have a longer length, and the length direction is disposed along the second direction.
  • the length of the energized electrodes 1, 4 may be equal to the length of the multi-channel topological insulator structure in the second direction.
  • the electrical device may further include three output electrodes (2, 3, and 5, respectively), and the three output electrodes 2, 3, and 5 are spaced apart from each other and electrically connected to the topological insulator quantum well film 20, respectively. And outputting the multi-path topological insulator structure in the first direction of resistance (ie, longitudinal resistance) and the second direction of resistance (ie, Hall resistance).
  • the direction from the output electrodes 2 to 3 is the first direction (i.e., the longitudinal resistance direction), and the direction from the output electrodes 3 to 5 is the second direction (i.e., the direction of the Hall resistance).
  • the output electrodes 2, 3, 5 may be respectively disposed at two ends of the multi-channel topology insulator in a second direction, for example, the output electrodes 2 and 3 are disposed at one end of the multi-channel topology insulator in the second direction, and output The electrode 5 is disposed at the other end of the multi-channel topological insulator in the second direction.
  • the three output electrodes may all be point electrodes.
  • each of the output electrodes is electrically coupled to all of the topological insulator quantum well films 20, such that the plurality of topological insulator quantum well films 20 are connected in parallel.
  • the longitudinal resistance and the Hall resistance are parallel resistances formed by a plurality of the magnetically doped topological insulator quantum well films 20.
  • the insulating substrate 10 has opposite first and second surfaces; the plurality of magnetically doped topological insulator quantum well films 20 and the plurality of insulating spacers 40 are disposed on the first surface.
  • the back gate electrode is disposed on the second surface.
  • the two energized electrodes and the four output electrodes are spaced apart from each other on a surface of the multi-channel topological insulator to be electrically connected to the multi-channel topological insulator. All of the above electrodes may be formed by an electron beam evaporation (E-beam) method, and the material may be gold or titanium having good conductivity, or may be directly applied to the surface of the sample as an electrode by using indium or silver paste.
  • E-beam electron beam evaporation
  • the electrical device may further have a fourth output electrode 6 similar to the output electrodes 2, 3, 5, the output electrode 6 and the output electrodes 2, 3, 5 being spaced apart from each other, and respectively disposed at the A multi-channel topological insulator structure is formed at both ends in the second direction.
  • the output electrodes 2 and 3 are disposed at one end of the multi-channel topological insulator in the second direction
  • the output electrodes 5 and 6 are disposed at the other end of the multi-channel topological insulator in the second direction.
  • Parallel Hall resistance and parallel longitudinal resistance can be formed by connecting the plurality of magnetically doped topological insulator quantum well films 20 in parallel.
  • the topological insulator has a non-dissipative edge state, there is a hot spot at the current end, and the hot spot has heat dissipation, and the multi-channel quantum anomalous Hall effect formed by the multi-channel topological insulator structure can reduce the current end by parallel connection.
  • the contact resistance between the energized electrode and the magnetically doped topological insulator quantum well film 20 reduces energy dissipation.
  • the superlattice structure formed by the multi-channel topological insulator makes it possible to realize the foreign semi-metallic state.
  • the thickness of the magnetically doped topological insulator quantum well film 20 By adjusting the thickness of the magnetically doped topological insulator quantum well film 20, the coupling strength between the upper and lower surfaces of the magnetically doped topological insulator quantum well film 20 can be changed, and changing the magnetic doping amount of each layer can change the size of the magnetic exchange interaction.
  • the thickness of the insulating spacer layer 40 the coupling strength of the surface states between the layers of the adjacent magnetically doped topological insulator quantum well film 20 can be adjusted.
  • the foreign semi-metallic state can be realized when the three quantities of the multi-channel topological insulator are regulated to satisfy certain conditions. This is a potential application of the multi-channel topological insulator superlattice structure.
  • the embodiment of the present application further provides a dual-channel topological insulator structure, including: an insulating substrate 10, a first topological insulator quantum well film 20, an insulating spacer layer 40, and a second topology.
  • An insulator quantum well film 20, the first topological insulator quantum well film 20, the insulating spacer layer 40, and the second topological insulator quantum well film 20 are sequentially stacked on the insulating substrate 10, and the insulating spacer layer 40 is sequentially stacked.
  • the first topological insulator quantum well film 20 and the second topological insulator quantum well film 20 are spaced apart.
  • the lattice matching of the first topological insulator quantum well film 20, the insulating spacer layer 40, and the second topological insulator quantum well film 20 is sequentially superposed on the surface of the insulating substrate 10 to form a heterojunction structure.
  • the first topological insulator quantum well film 20 has a first lattice constant
  • the insulating spacer layer 40 has a second lattice constant
  • the second topological insulator quantum well film 20 has a third lattice constant
  • the first The ratio of a lattice constant to the second lattice constant is 1:1.1 to 1.1:1
  • the ratio of the second lattice constant to the third lattice constant is 1:1.1 to 1.1:1.
  • the insulating spacer layer 40 is epitaxially grown on the surface of the first topological insulator quantum well film 20, and the molecular beam epitaxial growth temperature of the insulating spacer layer 40 is molecular beam epitaxy of the first topological insulator quantum well film 20.
  • the molecular beam epitaxial growth temperature of the second topological insulator quantum well film 20 is within a range of the molecular beam epitaxial growth temperature of the insulating spacer layer 40 within a range of ⁇ 100 ° C in the range of the growth temperature ⁇ 100 ° C.
  • the materials of the first topological insulator quantum well film 20 and the second topological insulator quantum well film 20 may be the same or different.
  • the magnetically doped topological insulator quantum well film 20 has a coercive field.
  • the coercive field refers to the electric field or magnetic field strength in which the material is in an electric or magnetic field such that spontaneous polarization or magnetization disappears, that is, the intensity of an electric or magnetic field generated by polarization or magnetization inside the material.
  • Different magnetically doped topological insulators have different coercive fields, and different topological insulators can obtain different coercive fields by doping different proportions or different kinds of magnetic elements.
  • the first topological insulator quantum well film 20 has a first coercive field (Hc1)
  • the second topological insulator quantum well film 20 has a second coercive field (Hc2).
  • Hc1 first coercive field
  • Hc2 second coercive field
  • the first coercive field is equal to the second coercive field when an arbitrary magnetic field is applied
  • the current formed by the second magnetically doped topological insulator quantum well film 20 and the first magnetically doped topological insulator quantum well film 20 have the same chiral edge state, both clockwise or counterclockwise .
  • the first coercive field is larger or smaller than the second Coercive field.
  • the applied magnetic field (H) is between the second coercive field (Hc2) and the first coercive field (Hc1) (ie, Hc1 ⁇ H ⁇ Hc2)
  • the two-channel topological insulator can be made 1.
  • the current formed by the second topological insulator quantum well film 20 has opposite chiral edge states, forming a clockwise and a counterclockwise spiral edge current, respectively, to achieve a quantum spin Hall effect (QSHE).
  • the magnetic doping of the materials of the first topological insulator quantum well film 20 and the second topological insulator quantum well film 20 is different by adjusting the ratio of the magnetic doping elements, thereby making the A coercive field is greater or smaller than the second coercive field.
  • the material of the first topological insulator quantum well film 20 is represented by a chemical formula of M y N z (Bi x Sb 1-x ) 2-yz Te 3
  • the magnetic doping of the materials of the first topological insulator quantum well film 20 and the second topological insulator quantum well film 20 is different by adjusting the kind of the magnetic doping element, thereby causing the The first coercive field is larger or smaller than the second coercive field.
  • the material of the first topological insulator quantum well film 20 is represented by a chemical formula of M y N z (Bi x Sb 1-x ) 2-yz Te 3
  • the insulating spacer layer 40 and the lattice structure of the first and second topological insulator quantum well films 20 are matched with each other.
  • the material of the topological insulator quantum well film 20 is magnetically doped Sb 2 Te 3
  • the The insulating spacer layer 40 is preferably one of a wurtzite structure of CdSe, a zinc blende structure of ZnTe, a sphalerite structure of CdSe, a sphalerite structure of CdTe, a sphalerite structure of HgSe, and a sphalerite structure of HgTe.
  • the dual channel topological insulator structure further includes an insulating protective layer 30 superimposed on the second topological insulator quantum well film 20.
  • the insulating protective layer 30 can continue to grow on the second topological insulator quantum well film 20 to protect the second topological insulator quantum well film 20 from being damaged.
  • a layer of the insulating spacer layer 40 may be further laminated on the second topological insulator quantum well film 20 as the insulating protective layer 30, including a wurtzite structure of CdSe and sphalerite structure.
  • the embodiment of the present application further provides a method for preparing the dual-channel topological insulator structure, including:
  • the first topological insulator quantum well film 20 is grown by molecular beam epitaxy on the surface of the insulating substrate 10 having a first temperature
  • the second topological insulator quantum well film 20 is grown by molecular beam epitaxy on the surface of the insulating spacer layer 40 having a third temperature.
  • the second temperature is within a range of the first temperature ⁇ 100 °C
  • the third temperature is within a range of the first temperature ⁇ 100 °C.
  • the first topological insulator quantum well film 20, the insulating protective layer 30 and the second topological insulator quantum well film 20 can be continuously epitaxially grown while the temperature conditions are substantially the same, and the subsequent insulating spacer layer 40 is formed.
  • the first topological insulator quantum well film 20 that has been formed is not destroyed.
  • the first temperature is from 150 ° C to 250 ° C
  • the second temperature is from 50 ° C to 350 ° C
  • the third temperature is from 150 ° C to 250 ° C.
  • the first temperature, the second temperature, and the third temperature are both 150 ° C to 250 ° C.
  • the first and second topological insulator quantum well films 20 can be made by adjusting the magnetic doping element type or the doping ratio of the first and second topological insulator quantum well films 20 in steps S200 and S400. Have different coercive fields.
  • the material of the first topological insulator quantum well film 20 is represented by a chemical formula Cr y V z (Bi x Sb 1-x ) 2-yz Te 3
  • the second topological insulator quantum well film 20 The material is represented by the chemical formula Cr y' V z' (Bi x' Sb 1-x' ) 2-y'-z' Te 3 , in one embodiment, 0.05 ⁇ x ⁇ 0.5, 0 ⁇ y ⁇ 0.3, 0 ⁇ z ⁇ 0.3 and 0.05 ⁇ x' ⁇ 0.5, 0 ⁇ y' ⁇ 0.3, 0 ⁇ z' ⁇ 0.3.
  • Different magnetic doping of the first and second topological insulator quantum well films 20 is achieved by adjusting the ratios of x, y, and z and
  • the present application example also provides a method of generating a quantum spin Hall effect (QSHE), comprising:
  • the first topological insulator quantum well film 20 having a first coercive field
  • the second topological insulator quantum well film 20 having a second coercive field
  • the field is larger or smaller than the second coercive field
  • a field voltage and a magnetic field between the first coercive field and the second coercive field are applied to the dual channel topological insulator.
  • first and second topological insulator quantum well films 20 of the dual-channel topological insulator have different magnetic doping, have unequal coercive fields, and the applied magnetic field is between the first coercive field and the second coercive field. Between the first and second topological insulator quantum well films 20 generate opposite edge currents, thereby achieving a quantum spin Hall effect.
  • the magnetically doped topological insulator quantum well film 20 has resistances R xx and R yx in different directions, wherein R xx is a resistance (ie, a longitudinal resistance) along the constant current direction (ie, the first direction), and the R yx is perpendicular to The resistance in the constant current direction (ie, the second direction) (ie, the Hall resistance).
  • the chemical potential of the magnetically doped topological insulator quantum well film 20 is voltage modulated by a top gate electrode or a back gate electrode as needed during measurement.
  • the top gate voltage is V t and the back gate voltage is V b .
  • the magnetic properties of the magnetic doped topological insulator quantum well film 20 were investigated by a low temperature strong magnetic field transport measurement system. The test results are as described in the following examples.
  • R yx R A M(T, H) + R N H.
  • R A is the anomalous Hall coefficient
  • M(T, H) is the magnetization
  • R N is the normal Hall coefficient.
  • R A M(T,H) is an anomalous Hall resistance, which is related to the magnetization M(T,H) and plays a major role in the low magnetic field.
  • the second normal Hall resistance indicates that R yx is high.
  • R N determines the carrier concentration n 2D and the carrier type.
  • (a) (b) (c) are respectively a magnetically doped topological insulator quantum well film 20, a magnetically doped topological insulator quantum well film 20 covering a CdSe insulating protective layer 30 of about 1 nm, and two layers of magnetically doped topological insulator quantum wells. A surface topography of the CdSe insulating spacer layer 40 of 1 nm is sandwiched between the films 20.
  • (d) (e)(f) are their corresponding RHEED stripes, respectively.
  • FIG. (a) The result of super-lattice structure formed by covering four layers of about 6 QL of magnetically doped topological insulator quantum well film 20 and three layers of about 3.5 nm of CdSe protective layer, and (b) is the result of an enlarged local range. It can be seen that the magnetic doped topological insulator quantum well film 20 and the CdSe protective layer have a good lattice epitaxial growth matching relationship to form a superlattice structure.
  • the 6QL magnetic doped topological insulator quantum well film 20 can be well wrapped in the middle of the CdSe insulating protective layer 30 to form a capsule structure, which can form a good protection for the topological insulator.
  • XRD analysis was performed on the topological insulator having the CdSe insulating protective layer 30.
  • 003, 006, 00 15 , 00 18 and 00 21 are XRD peaks of the magnetic doped topological insulator quantum well film 20
  • 002 is a characteristic peak of CdSe
  • 111 is a characteristic peak of a barium titanate substrate STO.
  • a satellite peak with a distinct superlattice structure can be seen on the peak of 002 of CdSe and the 0018 peak of the magnetically doped topological insulator quantum well film 20, and the upper right corner is the result of a small range of amplification of the satellite peak.
  • the XRD results show that the grown multi-channel topological insulators are of high quality.
  • the magnetic doped topological insulator quantum well film 20 of the present embodiment has Cr 0.02 V 0.16 (Bi 0.34 Sb 0.66 ) 1.82 Te 3 and a thickness of 6 QL, the insulating substrate 10 is an STO substrate, and the thickness of the CdSe layer is 3.5 nm.
  • topological insulator samples having the same magnetic doped topological insulator quantum well film 20 (having the same coercive field) of 1 (a), 2 (b), and 3 (c), respectively, are in different backs.
  • the Hall curve at the gate voltage is analyzed.
  • the Hall resistivity ⁇ yx of the sample changes as a function of the back gate voltage (V b ).
  • the Hall curve in Figure 10 also exhibits hysteresis and the sample has very good ferromagnetism.
  • ⁇ 0 H is the magnetic field strength
  • ⁇ 0 is the vacuum permeability
  • the unit T is Tesla
  • ⁇ yx is the Hall resistivity.
  • the three samples form 1 times, 1/2 times, and 1/3 times of the Hall platform, respectively, which are equivalent to one, two and three conductive edges, which are nearly 1 times, 1/2 times, respectively.
  • /3 times the quantum Hall resistance which indicates that the three samples are one channel, two channels, and three channels of quantum anomalous Hall effect samples.
  • the magnetoresistance curves of the samples of Example 4 at different back gate voltages were analyzed. Please refer to Figure 11. Under different V b , the magnetoresistance curves are all "butterfly type", and the samples are also very good from one side. Ferromagnetic. It can be seen that the reluctance peaks of the one-channel, two-channel, three-channel quantum anomalous Hall effect samples have substantially no change, indicating that the magnetic coercive field of each layer has no change.
  • This embodiment is a topological insulator sample with a 3.5 nm CdSe insulating spacer layer 40 sandwiched between two layers of magnetically doped topological insulator quantum well film 20.
  • the first magnetically doped topological insulator quantum well film 20 is Cr 0.02 V 0.16 (Bi 0.34 Sb 0.66 ) 1.82 Te 3 , and has a thickness of 6 QL;
  • the insulating substrate 10 is an STO substrate; and the thickness of the CdSe insulating spacer 40 is 3.5 nm;
  • the two-layer magnetic doped topological insulator quantum well film 20 is Cr 0.10 V 0.08 (Bi 0.44 Sb 0.56 ) 1.82 Te 3 and has a thickness of 6 QL.
  • the first and second layers of the magnetically doped topological insulator quantum well film 20 have different first and second coercive fields.
  • ⁇ xx also appeared a platform, close to 1.25h/e 2 , deviating from the perfect quantum spin Hall effect 0.5h/e under the same measurement mode. 2 , but the ⁇ yx curve also has a bend at zero, indicating that the Hall voltages in the opposite direction of the upper and lower magnetic topological insulator layers cancel each other out, and the Hall resistances are close to zero, that is, they can be regarded as a whole. It is considered that the Hall effect does not exist at this time, but there is a spin Hall effect, and the spiral edge state exists only because some of the upper and lower layers have some residual resistance deviating from the quantized value.
  • the coercive field Hc2 of the first layer Hc1 and the second layer may be changed, respectively, when the applied magnetic field
  • the quantum spin Hall effect occurs between Hc1 and Hc2.
  • the coercive field of the first layer is about 0.8T
  • the coercive field of the second layer is about 0.2T.
  • the so-called artificial quantum spin can occur under the magnetic field of 0.2T-0.8T. Effect.
  • This embodiment achieves an effect close to the quantum spin Hall effect in the range of 0.4T-0.6T.
  • This embodiment is an angular resolution photoelectron spectroscopy characterization and corresponding second-order differential characterization of a topological insulator sample having CdSe insulating protective layers 30 of different thicknesses.
  • the magnetic doped topological insulator quantum well film is 6QL Cr 0.02 V 0.16 (Bi 0.34 Sb 0.66 ) 1.82 Te 3 .
  • FIG. 13 wherein (a) is a topological insulator sample without CdSe grown, (b) is a topological insulator sample with 0.5 nm CdSe, (c) is a topological insulator sample with 1 nm CdSe, (d) Characterization of the angular fractional photoelectron spectroscopy of a topological insulator sample with 1.5 nm CdSe. (e) (f) (g) (h) are the second-order differential maps corresponding to the samples of (a), (b), (c) and (d), respectively.
  • the growth of the protective layer on the quantum anomalous Hall effect magnetic doped topological insulator quantum well film 20 tends to cause a pn-type change of the magnetic doped topological insulator quantum well film 20, while the poor quality sample interface may cause the resistance of the sample itself. Become bigger.
  • the comparison diagrams of (a), (b) and (e), (f) of the embodiments of the present application show that the 0.5 nm CdSe-covered magnetic doped topological insulator quantum well film 20 can see the following magnetic doped topological insulator quantum well
  • the film 20 can have no movement, that is, the increase of CdSe does not cause charge transfer or pn-type change to the magnetic doped topological insulator quantum well film 20 below, indicating that the increase of CdSe does not interfere with the anomalous Hall effect, which is Protecting the quantum anomalous Hall effect is of great significance.
  • the surface state is in the energy gap of CdSe.

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Abstract

本申请公开了一种具有绝缘保护层的拓扑绝缘体结构，包括：绝缘基底、拓扑绝缘体量子阱薄膜和绝缘保护层，其特征在于，所述拓扑绝缘体量子阱薄膜和所述绝缘保护层依次叠加在所述绝缘基底表面形成一异质结结构，所述绝缘保护层选自纤锌矿结构的CdSe、闪锌矿结构ZnTe、闪锌矿结构的CdSe、闪锌矿结构的CdTe、闪锌矿结构的HgSe和闪锌矿结构的HgTe中的至少一种。本申请还公开了一种具有绝缘保护层的拓扑绝缘体结构的制备方法。

Description

具有绝缘保护层的拓扑绝缘体结构及其制备方法
相关申请
本申请要求2018年2月5日申请的，申请号为201810113604.5，名称为“具有绝缘保护层的拓扑绝缘体结构及其制备方法”的中国专利申请的优先权，在此将其全文引入作为参考。
技术领域
本申请涉及凝聚态物理领域，涉及一种具有绝缘保护层的拓扑绝缘体结构及其制备方法。
背景技术
1879年，美国物理学家霍尔发现在通电的导体上加上一个垂直于电流方向的磁场，则在垂直于电流和磁场的方向就会产生电势差。这个电势差是由洛伦兹力导致的，也叫霍尔电压，由霍尔电压可以得到霍尔电阻。在正常霍尔效应下，霍尔电阻的大小和所加磁场B具有线性关系：Rxy＝R H*B，其中R H是霍尔系数。但是紧接着1880年，霍尔发现在磁性材料中，霍尔效应会比非磁性样品的霍尔效应大很多，随着磁场不是单纯的线性关系，这个效应叫做反常霍尔效应。1980年，德国物理学家冯·克利青等在强磁场下的二维电子气系统中发现了整数霍尔效应。1982年，美籍华裔物理学家崔琦发现了具有分数个量子电阻的分数霍尔效应。但是反常霍尔效应的量子化版本一直没有实现。直到2013年由薛其坤院士领导的团队在铬掺杂(Bi,Sb) 2Te 3中首先实现了零磁场下的量子反常霍尔效应。
磁性掺杂的拓扑绝缘体是目前为止实现量子反常霍尔效应的唯一的一个材料体系，并被世界上多个实验小组验证。日本理化研究所的Tokura教授研究组，加州大学洛杉矶分校的王康隆研究组，宾夕法尼亚州立大学的Nitin Samarth研究组也在铬掺杂的(Bi,Sb) 2Te 3中实现了量子反常霍尔效应，并且在麻省理工大学的Jagadeesh S.Moodera研究组的常翠祖首先在钒掺杂的(Bi,Sb) 2Te 3实现了更大矫顽场的量子反常霍尔效应。实现量子反常霍尔效应的样品一般来说是比较薄的，厚度4nm～10nm都能实现量子化。为了能更好的保护量子反常霍尔效应的薄膜样品，一般在上面沉积比较厚的保护层，使样品能更长时间的存放。现在报道的方法是生长比较薄的金属铝然后自然氧化形成致密的氧化物保护层，另一种方法是沉积较厚Te保护层，这两种方法需要把生长温度调节到室温或者更低的温度。另外一 种是在超高真空外用原子层沉积系统沉积氧化铝作为保护层，但是这种方法生长需要把样品转移到另外的系统进行沉积，并且不再是超高真空条件，同时原子层沉积系统的沉积速率一般比较慢。
发明内容
基于此，有必要提供一种具有绝缘保护层的拓扑绝缘体结构及其制备方法。
一种具有绝缘保护层的拓扑绝缘体结构，包括：绝缘基底、拓扑绝缘体量子阱薄膜和绝缘保护层，所述拓扑绝缘体量子阱薄膜和所述绝缘保护层依次叠加在所述绝缘基底表面形成一异质结结构，所述绝缘保护层选自纤锌矿结构的CdSe、闪锌矿结构ZnTe、闪锌矿结构的CdSe、闪锌矿结构的CdTe、闪锌矿结构的HgSe和闪锌矿结构的HgTe中的至少一种。
在其中一个实施例中，所述绝缘保护层分子束外延生长在所述拓扑绝缘体量子阱薄膜表面。
在其中一个实施例中，所述拓扑绝缘体量子阱薄膜通过在Sb 2Te 3的Sb位掺杂第一元素和第二元素形成，所述第一元素包括从Cr、Ti、Fe、Mn和V中选择的一种或多种元素，所述第二元素包括Bi。
在其中一个实施例中，所述拓扑绝缘体量子阱薄膜的材料由化学式M yN z(Bi xSb 1-x) 2-y-zTe 3表示，其中0<x<1，0≤y，0≤z，且0<y+z<2，M和N分别为Cr、Ti、Fe、Mn或V。
一种具有绝缘保护层的拓扑绝缘体结构，包括：绝缘基底、拓扑绝缘体量子阱薄膜和绝缘保护层，所述绝缘保护层与所述拓扑绝缘体量子阱薄膜的晶格匹配，依次叠加在所述绝缘基底表面形成一异质结结构。
在其中一个实施例中，所述拓扑绝缘体量子阱薄膜具有第一晶格常数，所述绝缘保护层具有第二晶格常数，所述第一晶格常数和所述第二晶格常数的比值为1:1.1～1.1:1。
在其中一个实施例中，所述绝缘保护层分子束外延生长在所述拓扑绝缘体量子阱薄膜表面。
在其中一个实施例中，所述绝缘保护层的分子束外延生长温度在所述拓扑绝缘体量子阱薄膜的分子束外延生长温度±100℃的区间范围内。
一种所述的具有绝缘保护层的拓扑绝缘体结构的制备方法，包括：
在分子束外延反应腔体中提供所述绝缘基底；
在具有第一温度的所述绝缘基底表面通过分子束外延生长所述拓扑绝缘体量子阱薄膜；
在具有第二温度的所述拓扑绝缘体量子阱薄膜表面通过分子束外延生长所述绝缘保护层。
在其中一个实施例中，所述第二温度在所述第一温度±100℃的区间范围内。
在其中一个实施例中，所述第一温度为150℃至250℃，所述第二温度为50℃至350℃。
本申请的所述拓扑绝缘体的所述绝缘保护层与所述拓扑绝缘体量子阱薄膜的晶格匹配，从而依次叠加在所述绝缘基底表面形成一异质结结构，更好的保护所述拓扑绝缘体量子阱薄膜不被破坏，提高拓扑绝缘体结构的质量。
附图说明
图1为本申请一实施例的Sb 2Te 3晶格结构示意图，其中(a)为立体图，(b)为俯视图，(c)为[110]方向的晶格结构图，(d)为[210]方向的晶格结构图；
图2为本申请一实施例的CdSe晶格结构示意图，其中(a)为立体图，(b)为俯视图，(c)为[110]方向的晶格结构图，(d)为[210]方向的晶格结构图；
图3为本申请一实施例的Sb 2Te 3和CdSe的晶格匹配结构示意图，其中(a)为主视图，(b)为侧视图；
图4为本申请一实施例的MBE反应腔体结构示意图；
图5为本申请一实施例的单层、两层和三层磁性掺杂拓扑绝缘体量子阱薄膜的多通道拓扑绝缘体结构示意图；
图6为本申请一实施例的电学器件的结构示意图；
图7为本申请一实施例的不同层数的多通道拓扑绝缘体的表面形貌图和RHEED条纹图，其中(a)(b)(c)分别为仅一层磁性掺杂拓扑绝缘体量子阱薄膜、覆盖约1nm的CdSe的磁性掺杂拓扑绝缘体量子阱薄膜、两层磁性掺杂拓扑绝缘体量子阱薄膜中间夹一层CdSe薄膜的拓扑绝缘体的表面形貌图。(d)(e)(f)则分别为(a)(b)(c)对应的RHEED条纹；
图8为本申请一实施例的多通道拓扑绝缘体的TEM图，其中(a)为4层磁性掺杂拓扑绝缘体量子阱薄膜和3层CdSe间隔层形成的超晶格结构，(b)为(a)局部放大图；
图9为本申请一实施例的多通道拓扑绝缘体结构的XRD图；
图10A至图10C为本申请一实施例的图5对应的多通道拓扑绝缘体在不同背栅极电压下的霍尔曲线图，其中图10A为单层磁性掺杂拓扑绝缘体量子阱薄膜，图10B为两层相同矫顽场的磁性掺杂拓扑绝缘体量子阱薄膜，图10C为三层相同矫顽场的磁性掺杂拓扑绝缘体量子阱薄膜；
图11A至图11C为本申请一实施例的图5对应的多通道拓扑绝缘体在不同背栅极电压下的磁阻曲线图，其中图11A为单层磁性掺杂拓扑绝缘体量子阱薄膜，图11B为两层相同矫顽场的磁性掺杂拓扑绝缘体量子阱薄膜，图11C为三层相同矫顽场的磁性掺杂拓扑绝缘体量子阱薄膜；
图12为本申请一实施例的不同矫顽场的双通道拓扑绝缘体在不同背栅极电压下的霍尔电阻曲线(a)和霍尔电导曲线(b)；
图13为本申请一实施例的不同厚度的CdSe覆盖的拓扑绝缘体的角分辨光电子能谱图和二阶微分图，其中，(a)为没有CdSe覆盖的6QL的磁性掺杂拓扑绝缘体量子阱薄膜，(b)为0.5nm的CdSe覆盖，(c)为1nm的CdSe覆盖，(d)为1.5nm的CdSe覆盖的角分辨光电子能谱图；(e)(f)(g)(h)分别为(a)(b)(c)(d)的二阶微分图。
具体实施方式
为了使本申请的目的、技术方案及优点更加清楚明白，以下通过实施例，并结合附图，对本申请的具有绝缘保护层的拓扑绝缘体结构及其制备方法进行进一步详细说明。应当理解，此处所描述的具体实施例仅用以解释本申请，并不用于限定本申请。
本文所使用的术语“垂直的”、“水平的”、“左”、“右”以及类似的表述只是为了说明的目的。实施例附图中各种不同对象按便于列举说明的比例绘制，而非按实际组件的比例绘制。
请参阅图5，本申请实施例首先提供一种具有绝缘保护层的拓扑绝缘体结构，包括：绝缘基底10、拓扑绝缘体量子阱薄膜20和绝缘保护层30，所述绝缘保护层30与所述拓扑绝缘体量子阱薄膜20的晶格匹配，所述拓扑绝缘体量子阱薄膜20和所述绝缘保护层30依次叠加在所述绝缘基底10表面，形成20-30的异质结结构。
所述绝缘保护层30与所述拓扑绝缘体量子阱薄膜20有相似的晶体结构和相近的原子间距，形成匹配的晶格关系，从而能够形成异质结结构，更好的保护所述拓扑绝缘体量子阱薄膜20不被破坏，提高拓扑绝缘体结构的质量。
在一实施例中，所述拓扑绝缘体量子阱薄膜20通过分子束外延生长在所述绝缘基底10上。分子束外延(molecular beam epitaxy,MBE)，是指在数量级为10 -10mbar的超高真空下以0.1～1nm/s的慢沉积速率蒸发镀膜的一种方法。在一实施例中，生长形成所述拓扑绝缘体量子阱薄膜20后，在所述拓扑绝缘体量子阱薄膜20的表面继续通过分子束外延生长所述绝缘保护层30。通过分子束外延连续生长所述拓扑绝缘体量子阱薄膜20和所述绝缘保护层30，形成结构整齐的异质结结构。
拓扑绝缘体的薄膜样品一般生长温度比较低，在真空中长时间加热容易导致Te的脱附，使得样品偏离原来的电荷中性点。同时，温度过高还容易使薄膜样品分解，破坏样品。在一实施例中，所述绝缘保护层30的材料的分子束外延生长温度和所述拓扑绝缘体量子阱薄膜20的材料的分子束外延生长温度接近。在一实施例中，所述绝缘保护层30的分子束外延生长温度在所述拓扑绝缘体量子阱薄膜20的分子束外延生长温度±100℃的区间范围内，使得所述绝缘保护层30生长时，已经形成的所述拓扑绝缘体量子阱薄膜20结构不被破坏，量子效应和性能不因绝缘保护层30的形成过程受到影响。
所述异质结结构中，所述拓扑绝缘体量子阱薄膜20和所述绝缘保护层30的晶格常数接近，能够使晶格失配率降低，晶格匹配更整齐。在一实施例中，所述拓扑绝缘体量子阱薄膜20具有第一晶格常数，所述绝缘保护层30具有第二晶格常数，所述第一晶格常数和所述第二晶格常数的比值为1:1.1～1.1:1。在一实施例中，所述拓扑绝缘体量子阱薄膜20具有六角密排面，在所述六角密排面内具有第一晶格常数，所述绝缘保护层30具有六角密排面，在所述六角密排面内具有第二晶格常数，所述第一晶格常数和所述第二晶格常数的比值为1:1.1～1.1:1。
在一实施例中，所述拓扑绝缘体量子阱薄膜20是通过在Sb 2Te 3的Sb位掺杂第一元素和第二元素形成的磁性掺杂拓扑绝缘体量子阱薄膜20。所述第一元素用于提供磁性元素，所述第二元素用于在所述拓扑绝缘体量子阱薄膜20中引入电子，使所述拓扑绝缘体量子阱薄膜20中引入的空穴与所述拓扑绝缘体量子阱薄膜20中引入的电子基本相互抵消，也就是使得所述磁性掺杂拓扑绝缘体量子阱薄膜20在未通过顶栅电极或背栅电极加电压进行调控时的载流子浓度就已经降到1×10 13cm -2以下，从而保证应用所述拓扑绝缘体结构的器件实现量子化反常霍尔效应时顶栅电极或背栅电极调节的有效性。所述拓扑绝缘体量子阱薄膜20优选是四元(含有四种元素)或五元材料(含有五种元素)。在一实施例中，所述第一元素包括从Cr、Ti、Fe、Mn和V中选择的一种或多种元素，所述第二元素包括Bi。所述拓扑绝缘体量子阱薄膜20的材料由化学式M yN z(Bi xSb 1-x) 2-y-zTe 3表示，其中0<x<1,0≤y，0≤z，且0<y+z<2，M和N分别为Cr、Ti、Fe、Mn或V。所述M和N可以为同种或不同种元素。在一实施例中，所述M为Cr，且所述N为V。
所述拓扑绝缘体量子阱薄膜20的厚度优选为5QL至10QL。所述绝缘保护层30的厚度优选大于0.35nm，并可以生长至无限厚度。
所述绝缘保护层30的材料优选具有六角密排(hcp)面，从而与掺杂的Sb 2Te 3拓扑绝缘体量子阱薄膜20叠加时在叠加方向形成六角密排。在一实施例中，所述绝缘保护层30的材料的纤锌矿结构的(001)面或闪锌矿结构的(111)面为六角密排面。在一实施例中，所述绝 缘保护层30选自纤锌矿结构的CdSe、闪锌矿结构ZnTe、闪锌矿结构的CdSe、闪锌矿结构的CdTe、闪锌矿结构的HgSe和闪锌矿结构的HgTe中的至少一种。
所述绝缘保护层30的材料与所述磁性掺杂的Sb 2Te 3拓扑绝缘体量子阱薄膜20的外延生长温度接近，能够外延生长在所述拓扑绝缘体量子阱薄膜20表面，并且所述绝缘保护层30和所述拓扑绝缘体量子阱薄膜20的晶格常数接近，晶格匹配，能够形成异质结结构。所述磁性掺杂拓扑绝缘体量子阱薄膜20的晶格常数介于Sb 2Te 3((001)面内0.426nm)和Bi 2Te 3((001)面内0.443nm)的晶格常数之间。随着Bi的逐渐掺入，晶格常数从接近0.426nm逐渐变得接近0.443nm。所述绝缘保护层30中，闪锌矿结构的CdTe的(111)面、闪锌矿结构的HgSe的(111)面、闪锌矿结构的HgTe、闪锌矿结构的ZnTe的(111)面以及闪锌矿结构的CdSe(111)面的面内晶格常数分别为0.457nm、0.424nm、0.456nm、0.431nm和0.430nm，作为可选的晶格匹配的绝缘保护层30材料。在一实施例中，纤锌矿结构的CdSe的(001)面的面内晶格常数为0.430nm，与所述磁性拓扑绝缘体的晶格常数非常匹配(与Bi2Te3的晶格失配约3％，与Sb2Te3的晶格失配约1％)，因此，在本实施例中纤锌矿结构的CdSe可以为一种可选的绝缘保护层30材料。
Sb2Te3是一种层状材料，隶属于三方晶系，空间群为
Figure PCTCN2018093183-appb-000001
具体晶格结构请参阅图1，在图1中的ab平面上每层的Sb和Te原子均具有六角密排的结构(即垂直于c轴的面为六角密排面)，沿垂直于ab平面的c轴方向呈层状分布，每五个原子层组成1个“五原子层”(Quintuple layer，QL)。在一实施例中，所述拓扑绝缘体量子阱薄膜20为磁性掺杂拓扑绝缘体量子阱薄膜20，所述五个原子层分别是依次排列的第一Te原子层(Te1)、磁性掺杂的第一Sb原子层(Sb)、第二Te原子层(Te2)、磁性掺杂第二Sb原子层(Sb’)、第三Te原子层(Te1’)，在单个的QL之内，原子以共价-离子型化学键结合；在相邻的QL之间，Te1原子层与Te1’原子层之间是范德瓦耳斯力相互作用，从而形成易于解理的界面。
所述纤锌矿结构的硒化镉(CdSe)属于六方晶系，具体晶格结构请参阅图2，纤锌矿结构的CdSe是由Cd与Se沿[001]方向(即c轴)交替堆垛而成，在(001)面具有六角密排面。CdSe绝缘保护层30和磁性掺杂拓扑绝缘体量子阱薄膜20Sb 2Te 3的晶格匹配关系请参阅图3，Sb 2Te 3的Te和CdSe中的Se各自形成六边形结构，并且他们的六边形结构的晶格常数接近，能够形成六角密排，从而形成互相匹配晶格的外延结构，形成异质结结构。
并且，CdSe薄膜的分子束外延生成温度与磁性掺杂的Sb 2Te 3拓扑绝缘体量子阱薄膜20的分子束外延生长温度接近。在形成磁性掺杂Sb 2Te 3拓扑绝缘体量子阱薄膜20后，能够在基本相同的生长温度下，在分子束外延反应腔体内继续生长CdSe薄膜材料作为磁性 掺杂拓扑绝缘体量子阱薄膜20的绝缘保护层30，最大限度的保障拓扑绝缘体量子阱薄膜20不会受到环境污染，提高产品的质量和性能。
所述绝缘基底10的材料为现有的，优选为磷化铟、砷化镓、钛酸锶、三氧化二铝或单晶硅。在一实施例中，所述绝缘基底10的材料可以选择为在小于或等于10开尔文(K)的低温下具有大于5000的介电常数的材料，如钛酸锶(STO)。由于在获得较大的反常霍尔电阻，甚至实现量子反常霍尔效应(QAHE)时需要对所述磁性掺杂拓扑绝缘体量子阱薄膜20加电压以进行化学势调控，具体可以通过形成顶栅电极和/或背栅电极实现加载电压，通过场效应调控所述磁性掺杂拓扑绝缘体量子阱薄膜20的化学势。通过采用在低温下具有较大的介电常数的绝缘基底10，使所述绝缘基底10在较大厚度时仍然可以具有较大电容，从而使所述绝缘基底10可以直接作为背栅电极与所述磁性掺杂拓扑绝缘体量子阱薄膜20之间的介电层使用，从而实现在低温下的背栅压调控，实现对磁性掺杂拓扑绝缘体量子阱薄膜20的化学势进行调控，从而实现QAHE。当所述绝缘基底10的材料为STO时，所述磁性掺杂拓扑绝缘体量子阱薄膜20优选是在所述STO的(111)晶面的表面上生长的。所述STO基底的厚度可以为0.1毫米至1毫米。由于除了STO之外的其他基底材料的介电常数相对较小，因此不能在它们的背面形成背栅。当需要利用静电场进行化学势调控时，可以使用氧化铝、氧化锆、氮化硼等制作成顶栅结构以进行调控，或者可以使用离子液体对所述磁性掺杂拓扑绝缘体量子阱薄膜20的化学势进行静电场调控。
请参阅图4，本申请还提供一种所述的具有绝缘保护层30的拓扑绝缘体结构的制备方法，包括：
S100，在分子束外延反应腔体中提供所述绝缘基底10；
S200，在具有第一温度的所述绝缘基底10表面通过分子束外延生长所述拓扑绝缘体量子阱薄膜20；以及
S300，在具有第二温度的所述拓扑绝缘体量子阱薄膜20表面通过分子束外延生长所述绝缘保护层30。
在步骤S100中，所述绝缘基底10具有原子级平整的表面。当所述绝缘基底10为STO时，具体可将所述STO基底切割出(111)晶面的表面，并在小于100℃(如70℃)的去离子水中加热，并在氧气和氩气氛围中800℃至1200℃(如1000℃)灼烧。在去离子水中加热时间可以为1至2小时，在氧气和氩气氛围中灼烧时间可以为2至3小时。
在步骤S200中，加热所述钛酸锶基底并在所述分子束外延反应腔体中同时形成所述拓扑绝缘体量子阱薄膜20材料或所含元素的束流，从而在所述绝缘基底10的所述表面形成拓扑绝缘体量子阱薄膜20。在一实施例中，所述拓扑绝缘体量子阱薄膜20的材料由化 学式M yN z(Bi xSb 1-x) 2-y-zTe 3表示。所述分子束外延反应腔体中设置有独立的固体Bi、Sb、M、N及Te蒸发源，加热Bi、Sb、M、N及Te的束流，从而在所述钛酸锶基底的所述表面形成磁性掺杂拓扑绝缘体量子阱薄膜20，通过控制Bi、Sb、M、N及Te的束流的流量从而控制Bi、Sb、M、N及Te之间的比例，使M和N在所述磁性掺杂拓扑绝缘体量子阱薄膜20中引入的空穴型载流子与Bi在所述磁性掺杂拓扑绝缘体量子阱薄膜20中引入的电子型载流子基本相互抵消。在一实施例中，M为Cr，N为V，各蒸发源温度分别为T Te＝258℃，T Bi＝491℃，T Sb＝358℃，T Cr＝941℃，T V＝1557℃，第一温度T sub＝150℃至250℃。
在步骤S300中，所述MBE反应腔体内还设置有绝缘保护层30的材料的蒸发源。可通过加热绝缘保护层30的材料的蒸发源形成所述绝缘保护层30材料的束流。控制所述绝缘保护层30材料的束流的流量从而在所述拓扑绝缘体量子阱薄膜20上原位生长绝缘保护层30，形成具有绝缘保护层30的拓扑绝缘体结构。所述绝缘保护层30生长时所述拓扑绝缘体量子阱薄膜20表面的温度为第二温度。在一实施例中，所述绝缘保护层30的生长温度和所述拓扑绝缘体量子阱薄膜20的生长温度接近，能够外延生长形成所述拓扑绝缘体量子阱薄膜20之后继续生长所述绝缘保护层30，并且已经形成的所述拓扑绝缘体量子阱薄膜20不被破坏或性能不受影响。所述第二温度为50℃至350℃。可选的，所述第二温度在所述第一温度±100℃的区间范围内。在一实施例中，所述第二温度为150℃至250℃。在一实施例中，所述绝缘保护层30为纤锌矿结构的CdSe，所述绝缘保护层30的蒸发源为块状CdSe，加热时，形成的所述绝缘保护层30束流为CdSe分子束流，分子形式的束流的流量更容易控制，形成晶格匹配的异质结结构更容易。在步骤S300中，所述绝缘基底10的加热温度T sub＝150℃至250℃，CdSe蒸发源温度T CdSe＝520℃。
请参阅图5，本申请实施例还提供一种多通道拓扑绝缘体结构，包括绝缘基底10、多个拓扑绝缘体量子阱薄膜20和多个绝缘间隔层40，所述多个拓扑绝缘体量子阱薄膜20和多个绝缘间隔层40交替的叠加在所述绝缘基底10表面，相邻的两个所述拓扑绝缘体量子阱薄膜20之间通过一个所述绝缘间隔层40间隔。
在上一实施例中的绝缘保护层30具有与拓扑绝缘体量子阱薄膜20匹配的晶格关系，可以将所述绝缘保护层30作为本实施例中的绝缘间隔层40继续生长拓扑绝缘体量子阱薄膜20，形成多通道拓扑绝缘体。多个拓扑绝缘体量子阱薄膜20可以独立的与外部电路连接，从而作为独立的电学元件使用。多个拓扑绝缘体量子阱薄膜20之间可以通过电极并联，当为并联关系，可以明显的降低拓扑绝缘体结构整体与电极之间的接触电阻，从而降低能耗。
相邻的所述绝缘间隔层40与所述拓扑绝缘体量子阱薄膜20具有匹配的晶格结构，通 过所述绝缘间隔层40将所述多个拓扑绝缘体量子阱薄膜20间隔开，从而共同形成超晶格结构的多通道拓扑绝缘体。
每个所述拓扑绝缘体量子阱薄膜20的厚度优选为5QL至10QL。所述绝缘间隔层40的厚度优选为0.35nm～20nm。
所述超晶格结构中，相邻的所述拓扑绝缘体量子阱薄膜20和所述绝缘间隔层40的晶格常数接近，能够使晶格失配率降低，晶格匹配更整齐。在一实施例中，相邻的所述拓扑绝缘体量子阱薄膜20和所述绝缘间隔层40的晶格常数的比值为1:1.1～1.1:1。
所述绝缘间隔层40分子束外延生长在所述拓扑绝缘体量子阱薄膜20表面，所述绝缘间隔层40和所述拓扑绝缘体量子阱薄膜20均通过分子束外延生长形成。任一所述绝缘间隔层40的分子束外延生长温度和任一所述拓扑绝缘体量子阱薄膜20的分子束外延生长温度之间的差异，任意两个拓扑绝缘体量子阱薄膜20的分子束外延生长温度之间的差异，以及任意两个绝缘间隔层40的分子束外延生长温度之间的差异均小于或等于100℃。能够在温度条件基本相同时，连续交替外延生长所述拓扑绝缘体量子阱薄膜20和所述绝缘间隔层40，并且形成后续的绝缘间隔层40时，已经形成的所述拓扑绝缘体量子阱薄膜20不被破坏。
所述拓扑绝缘体量子阱薄膜20通过磁性掺杂形成磁性掺杂拓扑绝缘体量子阱薄膜20，在外加电场和磁场作用下，从而能够形成多通道量子反常霍尔效应。所述多通道拓扑绝缘体结构中不同层的磁性掺杂拓扑绝缘体量子阱薄膜20的材料可以相同或不同，只要能够和所述绝缘间各层的晶格结构匹配，形成多通道量子反常霍尔效应即可。在一实施例中，所述拓扑绝缘体量子阱薄膜20的材料由化学式M yN z(Bi xSb 1-x) 2-y-zTe 3表示，其中0<x<1，0≤y，0≤z，且0<y+z<2，M或N为掺杂的磁性元素，选自Cr、Ti、Fe、Mn或V。M或N可以为相同或不同元素，并且，不同层的磁性掺杂拓扑绝缘体量子阱薄膜20，M或N以及对应的x、y和z的赋值可以相同或不同。在一实施例中，每个所述拓扑绝缘体量子阱薄膜20的材料相同，能够形成多个相同霍尔电阻并联的多通道拓扑绝缘体。在一实施例中，每个所述拓扑绝缘体量子阱薄膜20的材料的所述化学式具有分别相同的M、N、x、y和z。在施加电场和磁场时，每个所述拓扑绝缘体量子阱薄膜20产生的边态电流相同，从而形成多通道量子反常霍尔效应。
所述绝缘保护层30可以作为所述绝缘间隔层40。所述绝缘保护层30可以选自纤锌矿结构的CdSe、闪锌矿结构的ZnTe、闪锌矿结构的CdSe、闪锌矿结构的CdTe、闪锌矿结构的HgSe或闪锌矿结构的HgTe。纤锌矿结构的CdSe，与所述磁性掺杂的Sb2Te3拓扑绝缘体量子阱薄膜20的晶格结构关系和生长温度关系匹配度更好，是一种可选的绝缘间隔 层40。
所述多通道拓扑绝缘体结构，还包括最后叠加在最上层的所述拓扑绝缘体量子阱薄膜20上的绝缘保护层30，保护最后叠加的所述拓扑绝缘体量子阱薄膜20不被破坏。当最后一层叠加的为所述绝缘间隔层40时，所述绝缘层作为所述绝缘保护层30。当最后叠加的为所述拓扑绝缘体量子阱薄膜20时，可以再叠加一层绝缘保护层30。所述绝缘保护层30包括纤锌矿结构的CdSe、闪锌矿结构的ZnTe、闪锌矿结构的CdSe、闪锌矿结构的CdTe、闪锌矿结构的HgSe和闪锌矿结构的HgTe中的一种。绝缘保护层30以及多个绝缘间隔层40的材料可以相同或不同，优选为相同，以简化生长时所需的蒸发源。
本申请实施例还提供一种所述的多通道拓扑绝缘体结构的制备方法，包括：
S100，在分子束外延反应腔体中提供所述绝缘基底10；
S200，在所述绝缘基底10表面通过分子束外延交替生长所述多个拓扑绝缘体量子阱薄膜20和所述多个绝缘间隔层40。
在一实施例中，所述绝缘间隔层40的分子束外延生长温度和任一所述拓扑绝缘体量子阱薄膜20的分子束外延生长温度接近。能够在温度条件基本相同时，连续交替外延生长所述拓扑绝缘体量子阱薄膜20和所述绝缘保护层30，并且形成后续的绝缘间隔层40时，已经形成的所述拓扑绝缘体量子阱薄膜20不被破坏。可选的，所述拓扑绝缘体量子阱薄膜20的生长温度均为150℃至250℃，所述绝缘间隔层40的生长温度均为50℃至350℃。更在一实施例中，所述多个拓扑绝缘体量子阱薄膜20和所述多个绝缘间隔层40的生长温度均为150℃至250℃。
请参阅图6，本申请实施例还提供一种电学器件，包括所述的多通道拓扑绝缘体结构，所述多通道拓扑绝缘体结构的所述拓扑绝缘体量子阱薄膜20为磁性掺杂的拓扑绝缘体量子阱薄膜20。进一步地，所述电学器件包括一栅电极(例如背栅电极或顶栅电极)及两个通电电极1和4(即源极和漏极)。所述栅电极用于调控所述磁性掺杂拓扑绝缘体量子阱薄膜20的化学势。所述两个通电电极1、4相互间隔并分别与所述拓扑绝缘体量子阱薄膜20电连接。从一通电电极1至另一通电电极4的方向为第一方向(即纵向电阻方向)，与所述第一方向垂直的方向为第二方向。所述两个通电电极1、4分别设置在所述多通道拓扑绝缘体沿第一方向的两端，用于给所述多通道拓扑绝缘体结构通入沿第一方向的电流。在一实施例中，每个通电电极1或4分别与所有的拓扑绝缘体量子阱薄膜20电连接，从而使所述多个拓扑绝缘体量子阱薄膜20并联。所述两个通电电极1、4可以为条带状，具有较长的长度，且长度方向沿所述第二方向设置。所述通电电极1、4的长度可以与所述多通道拓扑绝缘体结构在第二方向上的长度相等。
所述电学器件可进一步包括三个输出电极(分别为2、3及5)，所述三个输出电极2、3、5相互间隔并分别与所述拓扑绝缘体量子阱薄膜20电连接，分别用于输出所述多通道拓扑绝缘体结构在在第一方向的电阻(即纵向电阻)及第二方向的电阻(即霍尔电阻)。从所述输出电极2至3的方向为所述第一方向(即纵向电阻方向)，从所述输出电极3至5的方向为所述第二方向(即霍尔电阻方向)。所述输出电极2、3、5可以分别设置在所述多通道拓扑绝缘体沿第二方向的两端，例如，输出电极2和3设置在所述多通道拓扑绝缘体沿第二方向的一端，输出电极5设置在多通道拓扑绝缘体沿第二方向的另一端。所述三个输出电极可均为点状电极。在一实施例中，每个输出电极分别与所有的拓扑绝缘体量子阱薄膜20电连接，从而使所述多个拓扑绝缘体量子阱薄膜20并联。所述纵向电阻和所述霍尔电阻为多个所述磁性掺杂拓扑绝缘体量子阱薄膜20形成的并联电阻。
在一实施例中，所述绝缘基底10具有相对的第一表面及第二表面；所述多个磁性掺杂拓扑绝缘体量子阱薄膜20和多个绝缘间隔层40设置在所述第一表面，所述背栅电极设置在所述第二表面。所述两个通电电极以及四个输出电极相互间隔的设置在所述多通道拓扑绝缘体表面，从而与所述多通道拓扑绝缘体电连接。上述所有电极均可用电子束蒸镀(E-beam)法形成，材料可以是导电性较好的金或钛等，也可以采用铟或银胶直接涂抹到样品表面作为电极。
另外，所述电学器件可进一步具有与输出电极2、3、5相似的第四个输出电极6，所述输出电极6与所述输出电极2、3、5相互间隔，且分别设置在所述多通道拓扑绝缘体结构沿第二方向的两端。例如所述输出电极2和3设置在所述多通道拓扑绝缘体沿第二方向的一端，输出电极5和6设置在多通道拓扑绝缘体沿第二方向的另一端。
将所述多个磁性掺杂拓扑绝缘体量子阱薄膜20并联，可以形成并联霍尔电阻和并联纵向电阻。虽然拓扑绝缘体具有无耗散的边态，但是在电流端会存在热点，热点就具有热耗散，而多通道拓扑绝缘体结构形成的多通道的量子反常霍尔效应可以通过并联的方式降低电流端的通电电极和磁性掺杂拓扑绝缘体量子阱薄膜20之间的接触电阻，从而降低能量耗散。
另外，多通道拓扑绝缘体形成的超晶格结构，有可能实现外尔半金属态。通过调控磁性掺杂拓扑绝缘体量子阱薄膜20的厚度可以改变磁性掺杂拓扑绝缘体量子阱薄膜20上下两个表面的耦合强度，而改变每一层的磁性掺杂量可以改变磁性交换相互作用的大小，通过调控绝缘间隔层40的厚度可以调控相邻磁性掺杂拓扑绝缘体量子阱薄膜20层之间的表面态的耦合强度。当把所述多通道拓扑绝缘体的这三个量调控到满足一定条件时就可以实现外尔半金属态。这是所述多通道拓扑绝缘体超晶格结构的一种潜在应用。
在所述多通道拓扑绝缘体结构的基础上，本申请实施例进一步还提供一种双通道拓扑绝缘体结构，包括：绝缘基底10、第一拓扑绝缘体量子阱薄膜20、绝缘间隔层40和第二拓扑绝缘体量子阱薄膜20，所述第一拓扑绝缘体量子阱薄膜20、所述绝缘间隔层40和所述第二拓扑绝缘体量子阱薄膜20在所述绝缘基底10上依次叠加，所述绝缘间隔层40将所述第一拓扑绝缘体量子阱薄膜20和所述第二拓扑绝缘体量子阱薄膜20间隔。
所述第一拓扑绝缘体量子阱薄膜20、所述绝缘间隔层40和所述第二拓扑绝缘体量子阱薄膜20的晶格匹配，依次叠加在所述绝缘基底10表面共同形成一异质结结构。所述第一拓扑绝缘体量子阱薄膜20具有第一晶格常数，所述绝缘间隔层40具有第二晶格常数，所述第二拓扑绝缘体量子阱薄膜20具有第三晶格常数，所述第一晶格常数和所述第二晶格常数的比值为1:1.1～1.1:1，所述第二晶格常数和所述第三晶格常数的比值为1:1.1～1.1:1。
所述绝缘间隔层40分子束外延生长在所述第一拓扑绝缘体量子阱薄膜20表面，所述绝缘间隔层40的分子束外延生长温度在所述第一拓扑绝缘体量子阱薄膜20的分子束外延生长温度±100℃的区间范围内，所述第二拓扑绝缘体量子阱薄膜20的分子束外延生长温度在所述绝缘间隔层40的分子束外延生长温度±100℃的区间范围内。
所述第一拓扑绝缘体量子阱薄膜20和所述第二拓扑绝缘体量子阱薄膜20的材料可以相同或不同。磁性掺杂的拓扑绝缘体量子阱薄膜20具有矫顽场。矫顽场指的是材料在电场或磁场中，使得自发极化或者磁化消失的电场或磁场强度，也就是材料内部的极化或磁化而产生的电场或磁场的强度。不同磁性掺杂的拓扑绝缘体具有不同的矫顽场，不同的拓扑绝缘体可以通过掺杂不同比例或不同种类的磁性性元素获得不同的矫顽场。所述第一拓扑绝缘体量子阱薄膜20具有第一矫顽场(Hc1)，所述第二拓扑绝缘体量子阱薄膜20具有第二矫顽场(Hc2)。所述第一拓扑绝缘体量子阱薄膜20和所述第二拓扑绝缘体量子阱薄膜20的材料的磁性掺杂相同时，所述第一矫顽场等于所述第二矫顽场，当施加任意磁场(H)后，所述第二磁性掺杂拓扑绝缘体量子阱薄膜20和所述第一磁性掺杂拓扑绝缘体量子阱薄膜20形成的电流具有相同手性的边态，都为顺时针或逆时针。所述第一拓扑绝缘体量子阱薄膜20和所述第二拓扑绝缘体量子阱薄膜20的材料的磁性掺杂的种类和/或比例不同时，所述第一矫顽场大于或小于所述第二矫顽场。在施加的磁场(H)介于第二矫顽场(Hc2)和第一矫顽场(Hc1)之间(即Hc1<H<Hc2)时，时，可以使所述双通道拓扑绝缘体的第一、第二拓扑绝缘体量子阱薄膜20形成的电流具有相反手性的边态，分别形成一个顺时针和一个逆时针的螺旋边态电流，从而实现量子自旋霍尔效应(QSHE)。
在一实施例中，通过调节磁性掺杂元素的比例，使所述第一拓扑绝缘体量子阱薄膜20和所述第二拓扑绝缘体量子阱薄膜20的材料的磁性掺杂不同，从而使所述第一矫顽场大 于或小于所述第二矫顽场。所述第一拓扑绝缘体量子阱薄膜20的材料由化学式M yN z(Bi xSb 1-x) 2-y-zTe 3表示，所述第二拓扑绝缘体量子阱薄膜20的材料由化学式M y’N z’(Bi x’Sb 1-x’) 2-y’-z’Te 3表示，其中M，M’，N，N’独立的选自Cr、Ti、Fe、Mn和V中的一种；0<x<1，0≤y，0≤z，且0<y+z<2；0<x’<1，0≤y’，0≤z’且0<y’+z’<2；x≠x’和/或y≠y’和/或z≠z’。
在另一实施例中，通过调节磁性掺杂元素的种类，使所述第一拓扑绝缘体量子阱薄膜20和所述第二拓扑绝缘体量子阱薄膜20的材料的磁性掺杂不同，从而使所述第一矫顽场大于或小于所述第二矫顽场。所述第一拓扑绝缘体量子阱薄膜20的材料由化学式M yN z(Bi xSb 1-x) 2-y-zTe 3表示，所述第二拓扑绝缘体量子阱薄膜20的材料由化学式M y’N z’(Bi x’Sb 1-x’) 2-y’-z’Te 3表示，其中M，M’，N，N’独立的选自Cr、Ti、Fe、Mn和V中的一种，且M≠M’和/或N≠N’；0<x<1，0≤y，0≤z，且0<y+z<2；0<x’<1，0≤y’，0≤z’且0<y’+z’<2。
所述绝缘间隔层40与所述第一、第二拓扑绝缘体量子阱薄膜20的晶格结构相互匹配，所述拓扑绝缘体量子阱薄膜20的材料为磁性掺杂的Sb 2Te 3时，所述绝缘间隔层40优选为纤锌矿结构的CdSe、闪锌矿结构的ZnTe、闪锌矿结构的CdSe、闪锌矿结构的CdTe、闪锌矿结构的HgSe和闪锌矿结构的HgTe中的一种。
在一实施例中，所述双通道拓扑绝缘体结构还包括叠加在所述第二拓扑绝缘体量子阱薄膜20上的绝缘保护层30。所述绝缘保护层30能够在所述第二拓扑绝缘体量子阱薄膜20上继续生长，保护所述第二拓扑绝缘体量子阱薄膜20不被破坏。在一实施例中，可以在所述第二拓扑绝缘体量子阱薄膜20上再叠加一层所述绝缘间隔层40作为所述绝缘保护层30，包括纤锌矿结构的CdSe、闪锌矿结构的ZnTe、闪锌矿结构的CdSe、闪锌矿结构的CdTe、闪锌矿结构的HgSe和闪锌矿结构的HgTe中的一种。
本申请实施例还提供一种所述的双通道拓扑绝缘体结构的制备方法，包括：
S100，在分子束外延反应腔体中提供所述绝缘基底10；
S200，在具有第一温度的所述绝缘基底10表面通过分子束外延生长所述第一拓扑绝缘体量子阱薄膜20；
S300，在具有第二温度的所述第一拓扑绝缘体量子阱薄膜20表面通过分子束外延生长所述绝缘间隔层40；以及
S400，在具有第三温度的所述绝缘间隔层40表面通过分子束外延生长所述第二拓扑绝缘体量子阱薄膜20。
所述第二温度在所述第一温度±100℃的区间范围内，所述第三温度在所述第一温度±100℃的区间范围内。能够在温度条件基本相同时，连续交替外延生长所述第一拓扑绝缘 体量子阱薄膜20、所述绝缘保护层30和所述第二拓扑绝缘体量子阱薄膜20，并且形成后续的绝缘间隔层40时，已经形成的所述第一拓扑绝缘体量子阱薄膜20不被破坏。在一实施例中，所述第一温度为150℃至250℃，所述第二温度为50℃至350℃，所述第三温度为150℃至250℃。在一实施例中，所述第一温度、第二温度和第三温度均为150℃至250℃。
其中，在步骤S200和S400中，通过调节所述第一、第二拓扑绝缘体量子阱薄膜20的磁性掺杂元素种类或掺杂比例，可以使所述第一、第二拓扑绝缘体量子阱薄膜20具有不同的矫顽场。在一实施例中，所述第一拓扑绝缘体量子阱薄膜20的材料由化学式Cr yV z(Bi xSb 1-x) 2-y-zTe 3表示，所述第二拓扑绝缘体量子阱薄膜20的材料由化学式Cr y’V z’(Bi x’Sb 1-x’) 2-y’-z’Te 3表示，在一实施例中，0.05<x<0.5，0<y<0.3，0<z<0.3且0.05<x’<0.5，0<y’<0.3，0<z’<0.3。通过调节x、y和z以及x’、y’和z’的比例，实现所述第一、第二拓扑绝缘体量子阱薄膜20的不同磁性掺杂。
本申请实例还提供一种产生量子自旋霍尔效应(QSHE)的方法，包括：
提供所述的的双通道拓扑绝缘体，所述第一拓扑绝缘体量子阱薄膜20具有第一矫顽场，所述第二拓扑绝缘体量子阱薄膜20具有第二矫顽场，所述第一矫顽场大于或小于所述第二矫顽场；以及
对所述双通道拓扑绝缘体施加场电压和介于第一矫顽场和所述第二矫顽场之间的磁场。
由于所述双通道拓扑绝缘体的第一、第二拓扑绝缘体量子阱薄膜20的磁性掺杂不同，具有不相等的矫顽场，在施加的磁场介于第一矫顽场和第二矫顽场之间时，所述第一、第二拓扑绝缘体量子阱薄膜20产生相反的边态电流，从而实现量子自旋霍尔效应。
实验测试
以不同的磁性掺杂拓扑绝缘体量子阱薄膜20形成上述电学器件，在低温下通过该两个通电电极对该磁性掺杂拓扑绝缘体量子阱薄膜20通入恒定电流，并通过该三个输出电极测试该磁性掺杂拓扑绝缘体量子阱薄膜20不同方向上的电阻R xx及R yx，其中R xx为沿该恒定电流方向(即第一方向)的电阻(即纵向电阻)，该R yx为垂直于该恒定电流方向(即第二方向)的电阻(即霍尔电阻)。在测量时根据需要通过顶栅电极或背栅电极对磁性掺杂拓扑绝缘体量子阱薄膜20的化学势进行电压调制。其中顶栅电压为V t，背栅电压为V b。另外，通过低温强磁场输运测量系统对磁性掺杂拓扑绝缘体量子阱薄膜20的磁性性质进行了研究。测试结果如下述实施例所述。
在磁性材料中，一般定义：R yx＝R AM(T,H)+R NH。其中，R A为反常霍尔系数，M(T,H)为磁化强度，R N为正常霍尔系数。定义反常霍尔电阻R AH的大小为零磁场下霍尔电阻的大小，(R AH＝R AM(T,H＝0))。式中第一项R AM(T,H)为反常霍尔电阻，与磁化强度M(T,H)有关， 在低磁场下占主要作用；第二项正常霍尔电阻表示R yx在高场下的线性部分，R N决定了载流子的浓度n 2D和载流子类型。以下实验均在低于铁磁转变温度以下进行研究，体系中载流子浓度较低，可以把零磁场下的R yx近似等于R AH。通过换算得到纵向电阻率ρ xx和霍尔电阻率ρ yx。
实施例1
对生长样品的表面形貌和RHEED条纹进行分析，请参阅图7。(a)(b)(c)分别为磁性掺杂拓扑绝缘体量子阱薄膜20、覆盖约1nm的CdSe绝缘保护层30的磁性掺杂拓扑绝缘体量子阱薄膜20，两层磁性掺杂拓扑绝缘体量子阱薄膜20中间夹1nm的CdSe绝缘间隔层40的表面形貌图。(d)(e)(f)则分别为它们对应的RHEED条纹。
(a)(b)对比说明在磁性掺杂拓扑绝缘体量子阱薄膜20上生长CdSe之后，样品的表面形貌基本没有变化。从(d)(e)RHEED条纹对比可以看出生长CdSe之后样品在面内的晶格常数也基本没有变化，说明它们有很好的晶格匹配关系。从(c)(f)可以看出在CdSe上可以继续生长量子反常霍尔效应的薄膜，形貌也没有明显变化，依然可以看到量子反常霍尔效应薄膜上面的岛，RHEED条纹也说明在CdSe上依然可以继续生长高质量的磁性掺杂拓扑绝缘体量子阱薄膜20。
实施例2
对具有CdSe绝缘保护层30的拓扑绝缘体的晶格结构进行TEM分析，请参阅图8。(a)为覆盖4层约6QL的磁性掺杂拓扑绝缘体量子阱薄膜20和3层约3.5nm的CdSe保护层形成的超晶格结构的结果，(b)是放大的局部范围的结果。可以看到磁性掺杂拓扑绝缘体量子阱薄膜20和CdSe保护层具有很好的晶格外延生长匹配关系，形成超晶格结构。6QL的磁性掺杂拓扑绝缘体量子阱薄膜20可以被很好的包裹在CdSe绝缘保护层30中间，形成胶囊结构，对拓扑绝缘体可以形成很好的保护作用。
实施例3
对具有CdSe绝缘保护层30的拓扑绝缘体进行XRD分析。请参阅图9，003、006、00 15、00 18和00 21为磁性掺杂拓扑绝缘体量子阱薄膜20的XRD峰，002为CdSe的特征峰，111为钛酸锶衬底STO的特征峰。在CdSe的002的峰和磁性掺杂拓扑绝缘体量子阱薄膜20的0018峰上可以看到明显超晶格结构的卫星峰，右上角是卫星峰放大的小范围的结果。
XRD结果说明生长的多通道拓扑绝缘体具有很高的质量。在超晶格的生长方向具有严格的周期性，从超晶格的卫星峰上可以计算超晶格的周期d为磁性掺杂拓扑绝缘体量子阱薄膜20的厚度d1和CdSe的厚度d2之和，d＝d1+d2，并且在大范围内都没有杂相。
实施例4
本实施例的磁性掺杂拓扑绝缘体量子阱薄膜20为Cr 0.02V 0.16(Bi 0.34Sb 0.66) 1.82Te 3，厚度为6QL，绝缘基底10为STO基底，CdSe层的厚度为3.5nm。
请参阅图10，对分别具有1层(a)、2层(b)、3层(c)相同的磁性掺杂拓扑绝缘体量子阱薄膜20(具有相同矫顽场)的拓扑绝缘体样品在不同背栅极电压下的霍尔曲线进行分析。
在温度为30毫开(mK)，样品的霍尔电阻率ρ yx随背栅电压(V b)的变化而变化。图10中霍尔曲线也出现磁滞现象，样品具有非常好的铁磁性。其中μ 0H中H是磁场强度，而μ 0是真空导磁率，单位T为特斯拉；ρ yx为霍尔电阻率。
通过调节栅极电压，可以看到霍尔电阻的变化。三个样品分别形成1倍，1/2倍，1/3倍的霍尔平台，分别相当于有一个，两个和三个的导电边态，分别具有接近1倍，1/2倍，1/3倍的量子霍尔电阻，这说明这三个样品分别是一个通道，两个通道，三个通道的量子反常霍尔效应样品。
实施例5
对实施例4的样品在不同背栅极电压下的磁阻曲线进行分析，请参阅图11，不同V b下，磁阻曲线均为“蝴蝶型”，从一个侧面也说明样品具有非常好的铁磁性。可以看出一通道，两通道，三通道的量子反常霍尔效应的样品的磁阻峰位基本没有变化，说明各层的磁性矫顽场没有变化。
实施例6
本实施例为两层磁性掺杂拓扑绝缘体量子阱薄膜20中间夹一层3.5nm CdSe绝缘间隔层40的拓扑绝缘体样品。第一层磁性掺杂拓扑绝缘体量子阱薄膜20为Cr 0.02V 0.16(Bi 0.34Sb 0.66) 1.82Te 3，厚度为6QL；绝缘基底10为STO基底；CdSe绝缘间隔层40的厚度为3.5nm；第二层磁性掺杂拓扑绝缘体量子阱薄膜20为Cr 0.10V 0.08(Bi 0.44Sb 0.56) 1.82Te 3，厚度为6QL。第一、二层的磁性掺杂拓扑绝缘体量子阱薄膜20具有不相同的第一、第二矫顽场。
对样品在不同背栅极电压下的霍尔曲线和磁阻曲线进行分析。请参阅图12，从图中可以看出，在施加的电场为(底栅电压Vb＝-150V)～(顶栅电压Vt＝5V)，磁场约为(0.4T)～(0.6T)时，可以看到霍尔电导σ yx在零处出现一个平台，说明此时霍尔电导σ yx近似为零，是螺旋边态出现的一个证明。同时，在相同的底栅和顶栅电压和相同的磁场范围下，ρ xx也出现了一个平台，接近1.25h/e 2,偏离完美量子自旋霍尔效应相同测量方式下的0.5h/e 2，但ρ yx曲线也在零处有一个弯折，说明此时上下磁性拓扑绝缘体层的相反方向边态的霍尔电压相互抵消，霍尔电阻接近为零，即把它们看成一个整体可以认为霍尔效应此时不存在，而存在自旋霍尔效应，螺旋边态存在，只是由于上下两层有一些剩余电阻偏离了量子化的数值。当调节底栅和顶栅电压偏离Vb＝-150V，Vt＝5V时，霍尔电导σ yx和霍尔电阻ρ yx的平台都会偏离零，并且平台变得倾斜，调节化学势可以使体系逐渐远离量子自旋霍尔效应的态。当所施加的磁场较大超过第一层和第二层的矫顽场，两层的边态变成相同方向的，相 当于两通道的量子反常霍尔效应并联，霍尔电阻ρ yx会接近量子化的数值0.5h/e 2，霍尔电导会接近量子化的数值2e 2/h。
当调节第一层的磁性拓扑绝缘体薄膜和第二层的磁性拓扑绝缘体薄膜中Cr和V的掺杂量，可以分别改变第一层Hc1和第二层的矫顽场Hc2，则当所施加的磁场位于Hc1和Hc2之间时会出现量子自旋霍尔效应。在上面的样品，第一层的矫顽场约为0.8T，第二层的矫顽场约为0.2T,在理想情况下会在0.2T-0.8T磁场下出现所谓的人工量子自旋霍尔效应。本实施例在0.4T-0.6T范围达到了接近量子自旋霍尔效应的效果。
实施例7
本实施例为具有不同厚度的CdSe绝缘保护层30的拓扑绝缘体样品的角分辨光电子能谱表征和对应的二阶微分图表征。磁性掺杂拓扑绝缘体量子阱薄膜为6QL的Cr 0.02V 0.16(Bi 0.34Sb 0.66) 1.82Te 3。
请参阅图13，其中，(a)为生长的没有CdSe的拓扑绝缘体样品，(b)为具有0.5nm的CdSe的拓扑绝缘体样品，(c)为具有1nm的CdSe的拓扑绝缘体样品，(d)为具有1.5nm的CdSe的拓扑绝缘体样品的角分表光电子能谱表征。(e)(f)(g)(h)分别为(a)(b)(c)(d)样品对应的的二阶微分图。
在量子反常霍尔效应的磁性掺杂拓扑绝缘体量子阱薄膜20上生长保护层容易导致磁性掺杂拓扑绝缘体量子阱薄膜20的p-n型变化，同时质量较差的样品界面有可能使样品本身的电阻变大。本申请实施例的(a)、(b)和(e)、(f)的对比图说明，0.5nm的CdSe覆盖磁性掺杂拓扑绝缘体量子阱薄膜20可以看到下面磁性掺杂拓扑绝缘体量子阱薄膜20能带没有移动，也就是CdSe的增加不会对下面的磁性掺杂拓扑绝缘体量子阱薄膜20带来电荷转移或者p-n型的改变，说明CdSe的增加不会干扰反常霍尔效应，这对于保护量子反常霍尔效应具有重要意义。1nm CdSe或者1.5nm的CdSe覆盖之后，表面态位于CdSe的能隙中。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本申请的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对本申请专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本申请构思的前提下，还可以做出若干变形和改进，这些都属于本申请的保护范围。因此，本申请专利的保护范围应以所附权利要求为准。

Claims (11)

  1. 一种具有绝缘保护层的拓扑绝缘体结构，包括：绝缘基底、拓扑绝缘体量子阱薄膜和绝缘保护层，其特征在于，所述拓扑绝缘体量子阱薄膜和所述绝缘保护层依次叠加在所述绝缘基底表面形成一异质结结构，所述绝缘保护层选自纤锌矿结构的CdSe、闪锌矿结构ZnTe、闪锌矿结构的CdSe、闪锌矿结构的CdTe、闪锌矿结构的HgSe和闪锌矿结构的HgTe中的至少一种。
  2. 根据权利要求1所述的具有绝缘保护层的拓扑绝缘体结构，其特征在于，所述绝缘保护层分子束外延生长在所述拓扑绝缘体量子阱薄膜表面。
  3. 根据权利要求1所述的具有绝缘保护层的拓扑绝缘体结构，其特征在于，所述拓扑绝缘体量子阱薄膜通过在Sb 2Te 3的Sb位掺杂第一元素和第二元素形成，所述第一元素包括从Cr、Ti、Fe、Mn和V中选择的一种或多种元素，所述第二元素包括Bi。
  4. 根据权利要求1所述的具有绝缘保护层的拓扑绝缘体结构，其特征在于，所述拓扑绝缘体量子阱薄膜的材料由化学式M yN z(Bi xSb 1-x) 2-y-zTe 3表示，其中0<x<1，0≤y，0≤z，且0<y+z<2，M和N分别为Cr、Ti、Fe、Mn或V。
  5. 一种具有绝缘保护层的拓扑绝缘体结构，包括：绝缘基底、拓扑绝缘体量子阱薄膜和绝缘保护层，其特征在于，所述绝缘保护层与所述拓扑绝缘体量子阱薄膜的晶格匹配，依次叠加在所述绝缘基底表面形成一异质结结构。
  6. 根据权利要求5所述的具有绝缘保护层的拓扑绝缘体结构，其特征在于，所述拓扑绝缘体量子阱薄膜具有第一晶格常数，所述绝缘保护层具有第二晶格常数，所述第一晶格常数和所述第二晶格常数的比值为1:1.1～1.1:1。
  7. 根据权利要求5所述的具有绝缘保护层的拓扑绝缘体结构，其特征在于，所述绝缘保护层分子束外延生长在所述拓扑绝缘体量子阱薄膜表面。
  8. 根据权利要求7所述的具有绝缘保护层的拓扑绝缘体结构，其特征在于，所述绝缘保护层的分子束外延生长温度在所述拓扑绝缘体量子阱薄膜的分子束外延生长温度±100℃的区间范围内。
  9. 一种如权利要求1至8任一项所述的具有绝缘保护层的拓扑绝缘体结构的制备方法，包括：
    在分子束外延反应腔体中提供所述绝缘基底；
    在具有第一温度的所述绝缘基底表面通过分子束外延生长所述拓扑绝缘体量子阱薄膜；以及
    在具有第二温度的所述拓扑绝缘体量子阱薄膜表面通过分子束外延生长所述绝缘保 护层。
  10. 根据权利要求9所述的具有绝缘保护层的拓扑绝缘体结构的制备方法，其特征在于，所述第二温度在所述第一温度±100℃的区间范围内。
  11. 根据权利要求9所述的具有绝缘保护层的拓扑绝缘体结构的制备方法，其特征在于，所述第一温度为150℃至250℃，所述第二温度为50℃至350℃。
PCT/CN2018/093183 2018-02-05 2018-06-27 具有绝缘保护层的拓扑绝缘体结构及其制备方法 WO2019148760A1 (zh)

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