A full van der Waals room temperature spin light emitting device and its preparation and application method

Abstract

The present invention discloses a full van der Waals room temperature spin light emitting device, which comprises a two-dimensional room temperature ferromagnetic spin injection layer, a first tunneling barrier layer, a two-dimensional valley polarized semiconductor active layer, a second tunneling barrier layer and an electrode layer arranged in sequence from bottom to top, wherein the two-dimensional room temperature ferromagnetic spin injection layer and the graphene electrode layer are respectively provided with conductive electrodes for applying voltage or current. The present invention uses a two-dimensional room temperature ferromagnet as a spin injection layer, a two-dimensional valley polarized semiconductor as an active layer, and combines an improved device preparation process to construct a full van der Waals heterojunction room temperature spin light emitting device; by applying voltage (or current) to the two-dimensional room temperature ferromagnetic spin injection layer and the graphene electrode layer, polarized light emission with a higher polarizability can be obtained under room temperature conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of light-emitting devices, and in particular relates to a full van der Waals room temperature spin light-emitting device and a preparation and application method thereof. Background Art

[0002] Spin diodes are an important type of spin electronics device. They have great application potential in the fields of optical information transmission, quantum cryptography, and three-dimensional display. They are one of the current research hotspots in the field of semiconductors and light-emitting devices. In the early days of spin diodes, paramagnetic semiconductors or magnetic semiconductors were used as spin injection terminals in GaAs-based semiconductor heterojunctions. However, due to the low Curie temperature of magnetic semiconductors, they cannot be effectively spin injected at room temperature. Therefore, research related to spin injection has become a core issue in the research of semiconductor spin diodes. The subsequent improved structure (such as the "ferromagnet / semiconductor" structure) using ferromagnets with higher Curie temperatures as spin injection terminals also has serious conductivity mismatch and cannot achieve high spin injection efficiency.

[0003] In response to the above problems, Rashba proposed the method of using a tunneling barrier layer (Phys. Rev. B 62, R16267 (2000)), that is, inserting a barrier layer between the ferromagnet and the semiconductor to form a "ferromagnet / barrier layer / semiconductor" structure, which solved the conductivity mismatch problem and significantly improved the spin injection efficiency. In 2005, Gerhardt et al. used FeTb with perpendicular magnetic anisotropy as the spin injection end and obtained a 0.7% circularly polarized light polarization rate at zero magnetic field and 90K (Appl. Phys. Lett. 87, 032502 (2005)). After that, Adelmann and other teams used MnGa, FeTb, and CoPt as spin injection terminals, respectively, and successfully prepared spin light-emitting diodes with perpendicular magnetic anisotropy characteristics, but the spin injection efficiency was still low (circular polarization rate was less than 3%) (Appl. Phys. Lett. 89, 112511 (2006). The researchers thought about and designed a more optimized perpendicular magnetic anisotropy spin injection terminal, the higher the spin polarization rate, the better, and the thinner the thickness, the better. In 2014, Liang et al. used the interface-induced perpendicular magnetic anisotropy Ta / CoFeB (1.2nm) / MgO spin injection terminal to construct a spin light-emitting diode, and measured a circularly polarized light polarization rate of 13% at low temperature (10K) and 8% at room temperature under zero field (Phys. Rev. B 90,085310(2014)). In 2018, Cadiz et al. used Ta / CoFeB / MoO with perpendicular magnetic anisotropy as the spin injection end and optimized the active region structure design. They observed a circularly polarized light polarizability of 35% at 9K in zero magnetic field (Nano Lett. 18,2381(2018)), but did not involve the study or optimization of room temperature spin luminescence performance.

[0004] Two-dimensional van der Waals materials have atomic-level surface flatness, continuously adjustable sample thickness, and interface coupling characteristics without lattice matching. Due to their flexible structural design, they have been studied and applied to new spin light-emitting diodes and have shown great application potential. In 2016, Ye Yu et al. used electrical injection to inject spin-polarized holes in GaMnAs into WS2, realizing a spin light-emitting diode based on two-dimensional materials (Nat. Nanotechnol. 11, 598 (2016)). In the same year, Sanchez et al. realized a spin light-emitting diode based on MoS2 / WSe2 heterojunction (Nano Lett. 16, 5792 (2016)). In 2022, Li et al. used Fe3GeTe2 / hBN / WSe2 van der Waals heterojunction to realize spin luminescence at 78K (Nat. Nanotechnol. 17, 721 (2022)). However, although researchers have made significant progress in spin LED research, the research on zero-field room-temperature spin LEDs with high polarizability still faces great challenges. Summary of the invention

[0005] The main purpose of the present invention is to provide a full van der Waals room temperature spin light-emitting device to address the problems and shortcomings of the high difficulty in realizing room temperature spin light-emitting diodes. A two-dimensional room temperature ferromagnetic spin injection layer and a two-dimensional valley polarized semiconductor active layer are used, and a barrier tunneling layer and a graphene electrode layer are combined to construct a full van der Waals heterojunction room temperature spin light-emitting device; by applying voltage (current) to the two-dimensional room temperature ferromagnetic spin injection layer and the graphene electrode layer, polarized light with a higher polarizability can be obtained at room temperature.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A full van der Waals room temperature spin light-emitting device comprises a two-dimensional room temperature ferromagnetic spin injection layer, a first tunneling barrier layer, a two-dimensional valley polarized semiconductor active layer, a second tunneling barrier layer and an electrode layer arranged in sequence from bottom to top, wherein conductive electrodes for applying voltage or current are respectively arranged in the two-dimensional room temperature ferromagnetic spin injection layer and the graphene electrode layer.

[0008] Furthermore, the full van der Waals refers to a full van der Waals room temperature spin light-emitting device in which all functional layers have van der Waals contact interfaces.

[0009] Furthermore, conductive electrodes for applying voltage or current are respectively arranged on the lower surface of the two-dimensional room temperature ferromagnetic spin injection layer and the upper surface of the graphene electrode layer.

[0010] In the above scheme, the two-dimensional room-temperature ferromagnet spin injection layer uses a two-dimensional intrinsic ferromagnet with a Curie temperature of above 300K and strong out-of-plane magnetic anisotropy; specifically, one of the room-temperature two-dimensional ferromagnets such as Fe3GaTe2 (FGT), MnSiTe3, MnGeTe3 and their doped compounds can be selected.

[0011] Furthermore, the two-dimensional room-temperature ferromagnetic spin injection layer is a thin film or a crystal.

[0012] In the above scheme, the material of the two-dimensional valley polarized semiconductor active layer is one of WS2, WSe2, MoS2, MoSe2 and their heterojunctions.

[0013] In the above scheme, the first tunneling barrier layer and the second tunneling barrier layer are made of boron nitride or other two-dimensional van der Waals materials (insulators or semiconductor materials) with higher potential barriers. Preferably, the thickness of the two-dimensional room temperature ferromagnetic spin injection layer is 10-40nm.

[0014] Preferably, the thickness of the first tunneling barrier layer and the second tunneling barrier layer is 0.7-10 nm; and the active region is a single atomic layer WS2 film.

[0015] In the above solution, the electrode layer can be made of a material with good electrical conductivity such as graphene, and its thickness is 5-15 nm.

[0016] In the above solution, the conductive electrode can be made of gold, graphene or platinum.

[0017] Furthermore, the two-dimensional room-temperature ferromagnetic spin injection layer is arranged on a silicon wafer.

[0018] Furthermore, one conductive electrode is arranged on one side of the lower surface of the room-temperature ferromagnetic spin injection layer, and the other conductive electrode is arranged on the opposite side of the upper surface of the graphene electrode layer.

[0019] Furthermore, the FGT film is prepared by mechanical stripping, molecular beam epitaxy or chemical deposition; and the FGT crystal is prepared by chemical vapor transfer.

[0020] In the above solution, the boron nitride barrier layer and the tungsten disulfide active layer are prepared by mechanical stripping.

[0021] In the above scheme, the two-dimensional room temperature ferromagnetic spin injection layer and the boron nitride tunneling barrier layer, the boron nitride tunneling barrier layer and the tungsten disulfide active layer, and the tungsten disulfide active layer and the graphene electrode layer are directly bonded by dry transfer method.

[0022] The method for preparing the above-mentioned all-van der Waals room temperature spin light-emitting device comprises the following steps:

[0023] 1) Prefabricate a set (two) of conductive electrodes on a silicon wafer;

[0024] 2) bonding the two-dimensional room temperature ferromagnetic spin injection layer to one of the conductive electrodes using a dry transfer method;

[0025] 3) bonding the first tunneling barrier layer to the two-dimensional room temperature ferromagnetic spin injection layer by a dry transfer method;

[0026] 4) bonding the two-dimensional valley polarization semiconductor active layer to the first tunneling barrier layer by a dry transfer method;

[0027] 5) transferring the second tunneling barrier layer to the two-dimensional valley polarized semiconductor active layer;

[0028] 6) Transferring the electrode layer onto the second tunneling barrier layer, and disposing another prefabricated conductive electrode at one end of the electrode layer to obtain the full van der Waals room temperature spin light-emitting device.

[0029] During the device preparation process, the surface of each functional layer needs to be kept clean to ensure that the sample functional layer can be effectively coupled after transfer.

[0030] Furthermore, after the full van der Waals room temperature spin light-emitting device is prepared, it is subjected to heat treatment and pressure treatment in sequence to further enhance the effective coupling effect between different layers, improve the carrier transfer efficiency in the device, and effectively ensure the room temperature spin light-emitting performance of the device (otherwise the device cannot emit light, or requires a large current to emit light, and is easily burned).

[0031] Furthermore, the heat treatment step includes: heat treatment at 200-300° C. for 2-3 hours in an inert gas (Ar or N 2 gas, etc.) environment to enhance effective coupling between different layers.

[0032] Furthermore, the pressure treatment adopts a pressure process such as static pressure or laser shock pressure, wherein the static pressure step is static pressure for 5-30 minutes under 2-15GPa conditions; the laser shock pressure adopts Nd:YAG laser; and before processing the sample, a layer of aluminum foil with a thickness of about 10μm is set on the surface of the sample, and a single layer of graphene nanopowder with a diameter of 0.5-5μm and a purity of 99% is set on the aluminum foil, and glass is covered on the graphene powder. The laser is focused on the graphene powder to apply pressure to the sample, and the applied pressure (2-15GPa) is adjusted by adjusting the laser power, thereby improving the coupling strength between different functional layers.

[0033] The application method of the above-mentioned all-van der Waals room-temperature spin light-emitting device is achieved by applying voltage or current to two conductive electrodes; wherein, the room-temperature two-dimensional intrinsic ferromagnetic spin injection layer is used as the negative electrode, and the graphene electrode layer is used as the positive electrode, and then voltage or current is applied, and polarized light emission can be observed.

[0034] Furthermore, in order to change the polarization state of the light-emitting diode, the polarization (magnetization) direction of the room temperature two-dimensional intrinsic ferromagnetic spin injection layer can be regulated by using an external magnetic field.

[0035] In the above scheme, the applied voltage is 1-15V and the current is 0.01-0.5mA.

[0036] In the above scheme, the magnetic field that regulates the magnetization direction of the room temperature two-dimensional intrinsic ferromagnetic spin injection layer is perpendicular to the sample surface and upward or downward.

[0037] In the above scheme, after the room temperature two-dimensional intrinsic ferromagnet spin injection layer is magnetized, if there is no need to regulate the polarized luminescence state, the magnetic field can be stopped and polarized luminescence can be obtained by applying voltage under zero magnetic field.

[0038] In the above scheme, after reversing the magnetization direction of the FGT, applying the same voltage can obtain different polarized luminescence polarization states.

[0039] The principles of the present invention include:

[0040] 1) Spin injection end of room temperature two-dimensional intrinsic ferromagnets; two-dimensional room temperature ferromagnetic materials such as Fe3GaTe2 have a Curie temperature higher than room temperature, and have a magnetization direction perpendicular to the sample surface at room temperature after initial magnetization. Under the same applied voltage conditions, the magnetization direction determines the polarization direction of the polarization current flowing out of the two-dimensional room temperature ferromagnetic material. The magnetization direction of the two-dimensional room temperature ferromagnet can be changed by applying a magnetic field perpendicular to the sample surface; it is also possible to further create a spin-orbit moment on the two-dimensional room temperature ferromagnetic material to use current to control its magnetization direction.

[0041] 2) Active region: The active layer of the present invention adopts a two-dimensional semiconductor material with valley polarization characteristics. Under the action of voltage, polarized electrons (or holes) are injected into a specific energy valley of the two-dimensional valley polarized semiconductor material, further promoting the two-dimensional valley polarized semiconductor to undergo electron-hole recombination to emit left-handed (or right-handed) circularly polarized light.

[0042] 3) The spin injection layer used in the present invention is made of metal materials and the active layers are all made of semiconductor materials. The conductivity mismatch between them will lead to extremely low luminous efficiency. It is necessary to insert a tunnel barrier layer between the spin injection layer and the active layer for conductivity matching.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1) The present invention proposes for the first time a full van der Waals room temperature spin light-emitting diode based on room temperature two-dimensional intrinsic ferromagnet;

[0045] 2) By constructing a van der Waals heterojunction, various functional layers (spin injection end, tunneling barrier layer, active region, etc.) with atomically flat interfaces are used to prepare van der Waals heterojunction devices, and combined with a modified device preparation process, the room temperature polarized luminescence of the device is effectively promoted;

[0046] 3) The light-emitting device of the present invention can realize polarized luminescence at room temperature with zero magnetic field, and change the polarization characteristics of the luminescence by applying an external magnetic field. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic structural diagram of the full van der Waals room temperature spin light-emitting device described in Example 1;

[0048] Figure 2 (a) is a schematic diagram of the structure of the spin light-emitting diode system constructed in Example 1, and (b) to (c) are schematic diagrams comparing the left-handed and right-handed luminescence intensities of the full van der Waals room temperature spin light-emitting device under different magnetic field regulation;

[0049] In the figure: 1-Si substrate, 2-FGT film or crystal, 3-hBN tunneling barrier layer, 4-WS2 active area, 5-hBN tunneling barrier layer, 6-graphene electrode connection layer, 7, 8-gold electrodes, 9-power supply, 10-connecting wires, 11-external magnetic field, 12-emitted light. DETAILED DESCRIPTION

[0050] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples. These descriptions are only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention.

[0051] In the following embodiments, the Si substrate used is a commercially available silicon wafer, and the thickness of its oxide layer (silicon oxide) is 90-300 nm.

[0052] In the following examples, the two-dimensional FGT crystals used were prepared by chemical vapor transfer method. The specific preparation process is referred to Nature Communications 13,5067,2022.

[0053] The WS2 active region layer used was obtained by mechanical stripping and then screened under a microscope; the hBN tunneling barrier layer was obtained by mechanical stripping and then screened by optical microscopy and atomic force microscopy to obtain a sample of the required thickness.

[0054] Example 1

[0055] A full van der Waals room temperature spin light emitting device, such as Figure 1 As shown, the FGT layer 2 is located on the Si substrate 1; the first hBN tunneling barrier layer 3 is located on the FGT layer 2, the WS2 active region 4 functional layer is located on the first tunneling barrier layer 3, the second hBN tunneling barrier layer 5 is located on the WS2 active region 4, and the Gr graphene electrode connection layer 6 is located on the hBN tunneling barrier layer 5;

[0056] An electrode 7 (negative electrode) and an electrode 8 (positive electrode) are respectively arranged on the lower surface of the FGT layer 2 and the upper surface of the Gr graphene electrode connection layer 6, and the two are respectively connected to a power source 9 through a wire 10; the electrode 7 is arranged at the right bottom of the FGT layer 2, and the electrode 8 is arranged at the left top of the Gr graphene electrode connection layer 6; the electrode 7 (negative electrode) and the electrode 8 (positive electrode) are respectively connected to the power source 9 through a wire 10;

[0057] The specific preparation method comprises the following steps:

[0058] (1) On a Si substrate 1 (10 mm×10 mm), a gold electrode 7 is prefabricated by laser writing or electronic book exposure process, and the electrode size is 2-5 microns in width and more than 20 microns in length;

[0059] (2) Preparing an FGT thin sheet 2 on a gold electrode, wherein the FGT thickness is within 20 nm; wherein the two-dimensional FGT crystal is obtained by mechanical exfoliation from an FGT bulk crystal, wherein the specific steps include: taking a small amount of FGT bulk and pasting it on a transparent tape, covering it with another piece of tape and pasting it on the surface of the FGT bulk crystal, and after tearing it off, an FGT wave plate with different layer thicknesses can be obtained, and an FGT thin sheet (thickness of 10-40 nm) is obtained by pasting the tape on a silicon wafer, and then the exfoliated FGT thin sheet is lifted up by PDMS and transferred to a prefabricated gold electrode;

[0060] Note that before placement, the electrode surface must be clean to ensure good contact with the FGT film.

[0061] (3) stacking a tunneling layer 3 on the FGT film by dry transfer technology, with an average thickness of 5 nm;

[0062] (4) stacking an active region layer 4 on the tunnel barrier layer 3 by transfer technology, with an average thickness of 0.7 nm;

[0063] (5) stacking a tunnel barrier layer 5 on the active region layer 4 by dry transfer technology, with an average thickness of 5 nm;

[0064] (6) preparing a Gr graphene electrode connection layer 6 on the tunneling barrier layer 5, the average thickness of which is 10 nm;

[0065] (7) making a gold electrode 8 (with the same specifications as step (1)) on the Gr graphene electrode connecting layer 6 to obtain a full van der Waals assembly;

[0066] (8) heat treating the obtained full van der Waals assembly in an inert gas (N2) environment at 200-300°C for 2-3 hours, and then cooling naturally to room temperature;

[0067] (9) Applying a static pressure of 2-2.5 GP to the component treated in step (8) by using an oil pressure technology and maintaining the pressure for 10 minutes; thus, the full van der Waals room temperature spin light-emitting device is obtained.

[0068] The specific application method of the full van der Waals room temperature spin light emitting device of the present invention includes:

[0069] Structure as Figure 2 a spin light-emitting diode; at room temperature, a forward 1T magnetic field is applied to the spin light-emitting diode based on the FGT and WS2 layers, and the intensities of the left-handed polarized light and the right-handed polarized light of the device are detected. It can be found that the luminous intensity of the right-handed circularly polarized light is about 45% stronger than that of the left-handed circularly polarized light, and the corresponding circularly polarized light polarization is about 19% ( Figure 2 b).

[0070] After the magnetic field is removed (1T-0T), the left-handed and right-handed circularly polarized luminescence intensity and circularly polarized light polarization rate of the spin light emitting diode under zero magnetic field are almost unchanged ( Figure 2 c).

[0071] When a -1T magnetic field (the negative sign indicates the direction) is applied to the spin light emitting diode, the luminous intensity of the left-handed circularly polarized light is stronger than that of the right-handed circularly polarized light, and the corresponding circularly polarized light polarization rate is about 25%.

[0072] The light-emitting storage device of the present invention is a spin light-emitting diode; applying a voltage of about +9V to the device can obtain Figure 2 The polarized light emission shown here corresponds to a current of approximately 0.2 mA.

[0073] correspond Figure 2 In the spin light-emitting diode shown, when -9 V voltage was applied, no polarized luminescence was observed, which is determined by the band structure and electronic state distribution of FGT.

[0074] Comparative Example 1

[0075] A spin light-emitting device, the preparation method of which is substantially the same as that of Example 1, except that FGT is replaced by Fe3GeTe2.

[0076] A voltage of +9 V was applied and the intensities of left-handed circularly polarized and right-handed circularly polarized luminescence were measured. Polarized luminescence could be observed at around 80 K, but room temperature spin luminescence could not be achieved at room temperature.

[0077] Comparative Example 2

[0078] A spin light emitting device, the preparation method of which is substantially the same as that of Example 1, except that the heat treatment and pressure treatment described in steps (8) and (9) are not performed.

[0079] When a voltage of +20V was applied to the resulting spin light-emitting device, no polarized light emission was observed, and further increasing the voltage would burn the sample.

[0080] Comparative Example 3

[0081] A spin light-emitting device, the preparation method of which is substantially the same as that of Example 1, except that the pressure treatment described in step (9) is not performed.

[0082] When a voltage of +20 V was applied to the obtained spin light emitting device, it was observed that the polarization luminescence polarization rate was less than 50% of that of the sample obtained in Example 1.

[0083] The present invention is not limited to the above-mentioned embodiments. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A full van der Waals room temperature spin light emitting device, characterized in that: It includes a two-dimensional room temperature ferromagnetic spin injection layer, a first tunneling barrier layer, a two-dimensional valley polarized semiconductor active layer, a second tunneling barrier layer and an electrode layer which are arranged in sequence from bottom to top, wherein conductive electrodes for applying voltage or current are respectively arranged in the two-dimensional room temperature ferromagnetic spin injection layer and the graphene electrode layer; The material of the two-dimensional room temperature ferromagnetic spin injection layer is Fe3GaTe2, MnSiTe3 or MnGeTe3; The material of the two-dimensional valley polarization semiconductor active layer is one of WS2, WSe2, MoS2, MoSe2 and their heterojunctions; The method for preparing the full van der Waals room temperature spin light-emitting device comprises the following steps: 1) Prefabricate a set of conductive electrodes on a silicon wafer; 2) Laminating the two-dimensional room temperature ferromagnetic spin injection layer onto one of the conductive electrodes using a dry transfer method; 3) Laminating the first tunneling barrier layer onto the two-dimensional room temperature ferromagnetic spin injection layer by dry transfer method; 4) bonding the two-dimensional valley polarized semiconductor active layer to the first tunneling barrier layer by a dry transfer method; 5) transferring the second tunneling barrier layer to the two-dimensional valley-polarized semiconductor active layer; 6) transferring the electrode layer onto the second tunneling barrier layer, and disposing another prefabricated conductive electrode at one end of the electrode layer to obtain the full van der Waals room temperature spin light-emitting device; After the full van der Waals room temperature spin light-emitting device is prepared, heat treatment and pressure treatment are performed in sequence.

2. The full van der Waals room temperature spin light emitting device according to claim 1, characterized in that: The first tunneling barrier layer and the second tunneling barrier layer are made of boron nitride.

3. The all-van der Waals room temperature spin light-emitting device according to claim 1, characterized in that: The thickness of the two-dimensional room temperature ferromagnetic spin injection layer is 10-40nm.

4. The full van der Waals room temperature spin light emitting device according to claim 1, characterized in that: The thickness of the first tunneling barrier layer and the second tunneling barrier layer is 0.7-10 nm; the active region is a single atomic layer WS2 film.

5. The method for preparing the full van der Waals room temperature spin light-emitting device according to any one of claims 1 to 4, characterized in that: The steps include: 1) Prefabricate conductive electrodes on silicon wafers; 2) Laminating a two-dimensional room temperature ferromagnetic spin injection layer onto a conductive electrode; 3) Laminating the first tunneling barrier layer onto the two-dimensional room temperature ferromagnetic spin injection layer; 4) Laminating the two-dimensional valley polarized semiconductor active layer onto the first tunneling barrier layer; 5) transferring the second tunneling barrier layer to the two-dimensional valley-polarized semiconductor active layer; 6) The electrode layer is transferred onto the second tunneling barrier layer, and another conductive electrode is arranged at one end of the electrode layer to obtain the full van der Waals room temperature spin light-emitting device.

6. A method for applying the full van der Waals room temperature spin light-emitting device according to any one of claims 1 to 4, characterized in that: The two-dimensional room temperature ferromagnetic spin injection layer of the full van der Waals room temperature spin light-emitting device is used as a negative electrode, and the electrode layer is used as a positive electrode, and then voltage or current is applied to achieve polarized luminescence.

7. The application method according to claim 6, characterized in that: The applied voltage is 1-15V and the current is 0.01-0.5mA.

8. The application method according to claim 6, characterized in that: During the application of voltage or current, a magnetic field is also introduced.

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