Magnetic semiconductor thin film and method for manufacturing the same

Abstract

The application provides a method for preparing a magnetic semiconductor thin film, which comprises the following steps: (1) placing a polycrystalline magnetic semiconductor target into a thin film deposition chamber; (2) placing K single element and Mn single element as beam source materials into two beam source furnaces respectively; (3) cleaning a substrate, and then mounting the cleaned substrate on a substrate table; (4) then, heating the substrate table and the substrate; (5) controlling the air pressure of the thin film deposition chamber to be 6-100 Pa by means of a non-reactive gas, and then using a molecular beam assisted pulsed laser deposition method to epitaxially grow a thin film on the substrate; and (6) after the thin film is grown, adjusting the air pressure of the thin film deposition chamber and cooling the substrate, so as to obtain a magnetic semiconductor thin film (Ba 1‑x K x )(Zn 1‑y Mn y )2As2, wherein 0.08

Description

Technical Field

[0001] This invention belongs to the field of magnetic semiconductors. Specifically, this invention relates to magnetic semiconductor thin films in which spin doping and charge doping are separated, and methods for preparing the same. Background Technology

[0002] Semiconductor thin films and magnetic thin films are two major categories of fundamental materials in modern information science and technology. Semiconductor thin films based on charge physics properties are the material basis for integrated circuits, solid-state microwave and laser devices, while magnetic thin films based on spin physics properties are the material basis for information storage devices and spintronic devices.

[0003] As the feature size of semiconductor photolithography continues to shrink, approaching the physical limits of the nanoscale, the sustainability of the current technological system based on existing physical effects is being challenged. Researchers are actively seeking breakthroughs in new materials, including various quantum materials capable of quantum computing, and magnetic semiconductor materials that possess both semiconductor properties and magnetism. With the development of information science and technology, there is an urgent need to prepare and study thin film materials for this new material.

[0004] Research on magnetic semiconductors began in the 1960s and has gone through several typical material research stages, including concentrated magnetic semiconductors represented by Eu and Cr sulfides, and dilute magnetic semiconductors of groups II-VI, III-V, and dilute magnetic oxides caused by magnetic element doping.

[0005] For the aforementioned types of dilute magnetic semiconductor materials doped with magnetic elements, a common characteristic is that the doping of the magnetic element itself introduces spin doping. While introducing magnetism into the material, this inevitably leads to changes in the material's charge doping level. It is believed that a better balance must be struck between spin doping and charge doping in the material.

[0006] In recent years, the emergence of doped zinc arsenide-based dilute magnetic semiconductor materials has provided a novel materials research platform for studying spin doping and charge doping control separately within a single material (Nat. Commun. 2 422 (2011)), among which (Ba 1-x K x (Zn) 1-y Mn y The 2As2 polycrystalline system further raises the paramagnetic-ferromagnetic transition temperature (Tc) to 230K (Chin.Sci.Bull.59,2524(2014)), exceeding the record of 200K Curie temperature in the (Ga,Mn)As system (Nano.Letters.11, 2584(2011)).

[0007] Currently, (Ba1-x K x (Zn) 1-y Mn y The 2As2 thin film was prepared by pulsed laser deposition (PLD) (AIPAdvance 7,045017 (2017)). This research currently faces the following obstacles: the Mn content is relatively low, less than or equal to 15%; the K content is relatively low, less than or equal to 8%. Low Mn doping concentration means low magnetic ion concentration, which will directly affect the sample's magnetism; while low K doping concentration means low carrier concentration, which may also affect the sample's ferromagnetism. Both ultimately lead to (Ba... 1-x K x (Zn) 1-y Mn y The Tc of the 2As2 thin film is below 10K, and its magnetization is also very weak, which greatly limits the potential of (Ba) thin films. 1- x K x (Zn) 1-y Mn y The application prospects of Ba2As2 thin films. Therefore, how to control the doping content of K and Mn, and how to increase their content to improve Tc, has become a key issue. 1-x K x (Zn) 1-y Mn y The key points and difficulties in the research of 2As2 dilute magnetic semiconductors.

[0008] Therefore, there is an urgent need for a method that can improve (Ba 1-x K x (Zn) 1-y Mn y Methods for determining the K and Mn content in As2 thin films. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing (Ba 1-x K x (Zn) 1-y Mn y The present invention discloses a method for preparing As2 thin films, which increases the K and Mn content in the film, thereby increasing the paramagnetic-ferromagnetic transition temperature (Tc). Specifically, the thin film material prepared by the method of the present invention can increase the Tc of existing thin film materials from 9K to 160K. Another object of the present invention is to provide a thin film material prepared by the method of the present invention.

[0010] The above-mentioned objective of the present invention is achieved through the following technical solution.

[0011] In the context of the present invention, the deposition equipment of the present invention may adopt the equipment already disclosed in the prior art, such as the deposition equipment disclosed in CN202576547U. The thin film deposition equipment includes a thin film deposition chamber, and the thin film deposition chamber includes: a chamber housing that encloses the chamber of the thin film deposition chamber; a target holder disposed in the middle of the chamber for placing a target made of component A; a substrate stage disposed in the middle of the chamber and opposite to the target holder; a laser entrance port disposed on the side of the chamber housing and obliquely opposite to the target holder for incident laser to bombard the target on the target holder to generate a plasma plume; a beam source furnace interface disposed on the side of the chamber housing and obliquely opposite to the substrate stage for incident molecular beam current composed of component B; the laser entrance port and the beam source furnace interface incident laser and molecular beam current simultaneously.

[0012] On the one hand, the present invention provides a method for preparing a magnetic semiconductor thin film, which includes the following steps:

[0013] (1) Place a polycrystalline magnetic semiconductor target in the thin film deposition chamber.

[0014] (2) Place elemental K and elemental Mn as beam source materials in two beam source furnaces respectively.

[0015] (3) Clean the substrate, and then mount the cleaned substrate on the substrate stage.

[0016] (4) Then, heat the substrate stage to heat the substrate.

[0017] (5) Control the air pressure in the thin film deposition chamber to be 6 - 100 Pa, preferably 15 - 75 Pa, with a non-reactive gas, and then epitaxially grow a thin film on the substrate by a molecular beam assisted pulsed laser deposition method.

[0018] (6) After the thin film growth is completed, adjust the air pressure in the thin film deposition chamber and cool the substrate to obtain a magnetic semiconductor thin film (Ba 1-x K x )(Zn 1-y Mn y )2As2, where 0.08 < x ≤ 0.40, 0.15 < y ≤ 0.30; preferably, 0.18 ≤ x ≤ 0.40, 0.23 ≤ y ≤ 0.30.

[0019] The inventors of this application unexpectedly discovered that, in the preparation of magnetic semiconductor thin films, using a non-reactive gas to control the pressure of the deposition chamber during film growth, and employing elemental K and Mn as beam source materials, can increase the K and Mn content in the obtained thin film material, thereby increasing Tc. This discovery, not wishing to be bound by theory, is likely due to the fact that adjusting the pressure of the deposition chamber during film growth can better confine the plasma plume obtained from pulsed laser bombardment of the target between the target and the substrate, increasing deposition efficiency and reducing the escape of elements from the plasma plume. Furthermore, elemental K and Mn can increase the K and Mn content in the plasma plume, thereby increasing the content of doped elements in the thin film, even exceeding the range of the target material content, as in Example 2 of this invention, where the target material composition is Ba. 0.7 K 0.3 (Zn 0.85 Mn 0.15 )2As2, while the composition of the thin film is Ba 0.67 K 0.33 (Zn 0.75 Mn 0.25 )2As2, it can be clearly seen that the content of doped elements in the thin film is higher than that in the target material.

[0020] In one specific embodiment of the present invention, the adjustment of the gas pressure in the thin film deposition chamber and the cooling of the substrate in step (6) are carried out by a method including the following steps: introducing a non-reactive gas into the thin film deposition chamber to adjust the gas pressure in the thin film deposition chamber to 0.1-0.8 atmospheres, then cooling the substrate to 250-300°C and holding it for 10-30 minutes, and then allowing it to cool naturally to room temperature.

[0021] Preferably, in the method described in this invention, the composition of the polycrystalline magnetic semiconductor target is represented by the following chemical formula: Ba 1-m K m (Zn 1-n Mn n )2As2, where 0.10≤m≤0.30, 0.10≤n≤0.30; preferably, 0.25≤m≤0.30, 0.15≤n≤0.20.

[0022] Preferably, in the method described in this invention, after step (3) and before step (4), the method further includes the following steps:

[0023] Adjust the stage height to make the distance between the target and the substrate 2-4 cm; and evacuate the thin film deposition chamber to make the vacuum level inside the thin film deposition chamber higher than 1×10⁻⁶. -6 Pa.

[0024] Preferably, in the method of the present invention, the heating of the substrate stage in step (4) is performed by heating the substrate to 500-550°C at a heating rate of 10-30°C / min.

[0025] Preferably, in the method described in this invention, after step (4) and before step (5), the method further includes the following steps:

[0026] The substrate is blocked by a baffle, and the surface of the target material is then treated with a pulsed laser, with 600-1200 pulses; and two beam source furnaces are heated.

[0027] Preferably, in the method described in this invention, the heating of the two beam source furnaces is performed by heating the temperature of the beam source furnace containing K to 100-300°C and the temperature of the beam source furnace containing Mn to 600-950°C.

[0028] Preferably, in the method described in this invention, the substrate is selected from (001) oriented SrTiO3 single crystal substrate, (001) oriented Si single crystal substrate, (001) oriented MgAl2O4 single crystal substrate, or (001) oriented (La) single crystal substrate. 0.272 Sr 0.728 (Al) 0.648 Ta 0.352 O3 single crystal substrate.

[0029] Preferably, in the method described in this invention, the epitaxial growth of the thin film in step (5) is carried out under the following conditions: the energy density of the pulsed laser is 120-160 mJ / mm². 2 The laser repetition frequency is 1-5Hz.

[0030] Preferably, in the method described in this invention, the non-reactive gas is selected from one or more of argon, helium, and nitrogen.

[0031] On the other hand, the present invention provides a magnetic semiconductor thin film prepared by the method of the present invention, the composition of which is represented by the following chemical formula: (Ba 1-x K x (Zn) 1-y Mn y )2As2, where 0.08 <x≤0.40, 0.15<y≤0.30。

[0032] The present invention has the following beneficial effects:

[0033] The method of this invention can prepare high-quality single-phase, c-axis unidirectional epitaxial thin films, increasing the K and Mn content in the films, thereby increasing the paramagnetic-ferromagnetic transition temperature (Tc), which can reach up to 160K. The materials prepared by this invention have potential applications in electronic devices. Attached Figure Description

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0035] Figure 1 A schematic diagram of the crystal structure of a thin film material prepared according to a specific embodiment of the present invention. Figure 1 The crystal structure shown satisfies space group I4 / mmm and has the chemical formula AB2C2. Corresponding to the material of this invention, the A-site is a Ba atom, substituting for a K atom; the B-site is a Zn atom, substituting for a Mn atom; and the C-site is an As atom.

[0036] Figure 2 The image shows the full X-ray diffraction pattern of the dilute magnetic semiconductor thin film prepared according to Example 1 of the present invention.

[0037] Figure 3 The image shows the MT curve of the dilute magnetic semiconductor thin film prepared according to Example 1 of the present invention; wherein the applied external field is 1000 Oe.

[0038] Figure 4 The X-ray diffraction full spectrum of the dilute magnetic semiconductor thin film prepared according to Example 2 of the present invention is shown.

[0039] Figure 5 The image shows the MT curve of the dilute magnetic semiconductor thin film prepared according to Example 2 of the present invention; wherein the applied external field is 1000 Oe.

[0040] Figure 6 The X-ray diffraction full spectrum is shown for the dilute magnetic semiconductor thin film prepared according to Example 3 of the present invention.

[0041] Figure 7 The image shows the MT curve of the dilute magnetic semiconductor thin film prepared according to Example 3 of the present invention; wherein the applied external field is 1000 Oe.

[0042] Figure 8 The X-ray diffraction full spectrum of the dilute magnetic semiconductor thin film prepared according to Comparative Example 1 of the present invention is shown.

[0043] Figure 9 The image shows the MT curve of the dilute magnetic semiconductor thin film prepared according to Comparative Example 1 of the present invention; wherein the applied external field is 1000 Oe.

[0044] Figure 10The X-ray diffraction full spectrum is shown for the dilute magnetic semiconductor thin film prepared according to Comparative Example 2 of the present invention.

[0045] Figure 11 The image shows the MT curve of the dilute magnetic semiconductor thin film prepared according to Comparative Example 2 of the present invention; wherein the applied external field is 1000 Oe.

[0046] Figure 12 The image shows the full X-ray diffraction pattern of the dilute magnetic semiconductor thin film prepared according to Comparative Example 3 of the present invention. Detailed Implementation

[0047] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0048] Example 1

[0049] (1) Prepare polycrystalline Ba 0.7 K 0.3 (Zn 0.85 Mn 0.15 The 2As2 target is fixed on the target holder, and then the target holder is installed into the thin film deposition chamber.

[0050] (2) The beam source material composed of K and Mn elements is placed into two beam source furnaces respectively.

[0051] (3) Prepare a (001) oriented SrTiO3 single crystal substrate. Clean it ultrasonically with acetone and alcohol for 5 minutes, then dry it with compressed nitrogen. Install the cleaned substrate on the substrate stage through the feed port, and then adjust the position of the substrate stage so that the target is directly below the substrate. The distance between the target and the substrate should be controlled at about 2 cm.

[0052] (4) Turn on the multi-stage vacuum pump until the vacuum level in the chamber is better than 1×10⁻⁶. -6 When Pa, the substrate stage is heated, and the substrate temperature is raised to 540°C at a heating rate of 30°C / min.

[0053] (5) When the vacuum level of the vacuum chamber is better than 2×10 -5 At a pressure of 15 Pa, the valve between the chamber and the molecular pump is closed, and Ar gas is introduced through the gas filling system until the chamber pressure reaches 15 Pa. The substrate is blocked by a baffle, and then the target surface is pre-sputtered with a pulsed laser for approximately 600 pulses. Simultaneously, two beam source furnaces, each containing K and Mn beam source materials respectively, are heated.

[0054] (6) After pre-sputtering, remove the baffle so that the plasma plume obtained by the pulsed laser bombarding the target and the K and Mn beams obtained by the heated beam source furnace are deposited on the substrate. That is, the molecular beam-assisted pulsed laser deposition method is used to grow a thin film on the substrate. The number of deposition pulses is 1200 and the deposition time is 5 min.

[0055] (7) After the film growth is complete, Ar gas is introduced until the pressure in the film deposition chamber is 0.1 atmospheres. The substrate temperature is reduced to 300°C at a cooling rate of 10°C / min and held for 30 min. Then the heater is turned off and the substrate is allowed to cool naturally to room temperature.

[0056] The dilute magnetic semiconductor thin film prepared in this embodiment is a single-phase, epitaxially grown (Ba) film with a single orientation along the c-axis. 0.82 K 0.18 (Zn) 0.70 Mn 0.30 )2As2 thin film, its XRD diffraction is as follows Figure 2 As shown, its MT test results are as follows: Figure 3 As shown. Figure 2 The sample is shown to be a single-phase, single-orientation epitaxially grown (Ba) material grown on a (001) oriented SrTiO3 substrate. 1-x K x (Zn) 1-y Mn y )2As2 thin film. Figure 3 The paramagnetic-ferromagnetic transition temperature of the sample is shown to be 120K.

[0057] Example 2

[0058] (1) Prepare polycrystalline Ba 0.7 K 0.3 (Zn 0.85 Mn 0.15 The 2As2 target is fixed on the target holder, and then the target holder is installed into the thin film deposition chamber.

[0059] (2) The beam source material composed of K and Mn elements is placed into two beam source furnaces respectively.

[0060] (3) Prepare a (001) oriented MgAl2O4 single crystal substrate. Clean it ultrasonically with acetone and alcohol for 5 minutes, then dry it with compressed nitrogen. Install the cleaned substrate on the substrate stage through the feed port, and then adjust the position of the substrate stage so that the target is directly below the substrate. The distance between the target and the substrate should be controlled at about 2.5 cm.

[0061] (4) Turn on the multi-stage vacuum pump until the vacuum level in the chamber is better than 1×10⁻⁶. -6When Pa, the substrate stage is heated, and the substrate temperature is raised to 550°C at a heating rate of 20°C / min.

[0062] (5) When the vacuum level of the vacuum chamber is better than 2×10 -5 At pressure Pa, the valve between the chamber and the molecular pump is closed, and Ar gas is introduced through the gas filling system until the chamber pressure reaches 45 Pa. The substrate is blocked by a baffle, and then the target surface is pre-sputtered with a pulsed laser for approximately 600 pulses. Simultaneously, two beam source furnaces, each containing K and Mn beam source materials respectively, are heated.

[0063] (6) After pre-sputtering is completed, the baffle is removed so that the plasma plume obtained by the pulsed laser bombarding the target and the K and Mn beam obtained by the heated beam source furnace are deposited on the substrate. That is, the thin film is grown on the substrate by the molecular beam assisted pulsed laser deposition method. The deposition pulse number is 600 and the deposition time is 5 min.

[0064] (7) After the film growth is complete, Ar gas is introduced until the pressure in the film deposition chamber is 0.1 atmospheres. The substrate temperature is reduced to 300°C at a cooling rate of 10°C / min and held for 30 min. Then the heater is turned off and the substrate is allowed to cool naturally to room temperature.

[0065] The dilute magnetic semiconductor thin film prepared in this embodiment is a single-phase, epitaxially grown (Ba) film with a single orientation along the c-axis. 0.67 K 0.33 (Zn) 0.75 Mn 0.25 )2As2 thin film, its XRD diffraction is as follows Figure 4 As shown, its MT test results are as follows: Figure 5 As shown. Figure 4 This sample is shown to be a single-phase, single-orientation epitaxially grown (Ba) material on a (001) oriented MgAl2O4 substrate. 1-x K x (Zn) 1-y Mn y )2As2 thin film. Figure 5 The paramagnetic-ferromagnetic transition temperature of the sample is shown to be 160K.

[0066] Example 3

[0067] (1) Prepare polycrystalline Ba 0.7 K 0.3 (Zn 0.85 Mn 0.15 The 2As2 target is fixed on the target holder, and then the target holder is installed into the thin film deposition chamber.

[0068] (2) The beam source material composed of K and Mn elements is placed into two beam source furnaces respectively.

[0069] (3) Prepare a (001) oriented Si single crystal substrate. Clean it ultrasonically with acetone and alcohol for 5 minutes, dry it with compressed nitrogen, and then soak it in a 2% HF solution for 20 seconds. Finally, wash away the residual HF solution with deionized water and alcohol. Mount the cleaned substrate on the substrate stage through the feed port, and then adjust the position of the substrate stage so that the target is directly below the substrate, and the distance between the target and the substrate is controlled at about 2.0 cm.

[0070] (4) Turn on the multi-stage vacuum pump until the vacuum level in the chamber is better than 1×10⁻⁶. -6 When Pa, the substrate stage is heated, and the substrate temperature is raised to 540°C at a heating rate of 20°C / min.

[0071] (5) When the vacuum level of the vacuum chamber is better than 2×10 -5 At pressure Pa, the valve between the chamber and the molecular pump is closed, and Ar gas is introduced through the gas filling system until the chamber pressure reaches 75 Pa. The substrate is blocked by a baffle, and then the target surface is pre-sputtered with a pulsed laser for approximately 600 pulses. Simultaneously, two beam source furnaces, each containing K and Mn beam source materials respectively, are heated.

[0072] (6) After pre-sputtering, remove the baffle so that the plasma plume obtained by the pulsed laser bombarding the target and the K and Mn beams obtained by the heated beam source furnace are deposited on the substrate. That is, the molecular beam-assisted pulsed laser deposition method is used to grow a thin film on the substrate. The number of deposition pulses is 1200 and the deposition time is 5 min.

[0073] (7) After the film growth is complete, Ar gas is introduced until the pressure in the film deposition chamber is 0.1 atmospheres. The substrate temperature is reduced to 300°C at a cooling rate of 10°C / min and held for 30 min. Then the heater is turned off and the substrate is allowed to cool naturally to room temperature.

[0074] The dilute magnetic semiconductor thin film prepared in this embodiment is a single-phase, epitaxially grown (Ba) film with a single orientation along the c-axis. 0.60 K 0.40 (Zn) 0.77 Mn 0.23 )2As2 thin film, its XRD diffraction is as follows Figure 6 As shown, its MT test results are as follows: Figure 7 As shown. Figure 6 The sample is shown to be a single-phase, single-orientation epitaxially grown (Ba) material grown on a (001) oriented Si substrate. 1-x K x (Zn) 1- y Mn y )2As2 thin film. Figure 7 The paramagnetic-ferromagnetic transition temperature of the sample is shown to be 120K.

[0075] Comparative Example 1

[0076] (1) Prepare polycrystalline Ba 0.7 K 0.3 (Zn 0.85 Mn 0.15 The 2As2 target is fixed on the target holder, and then the target holder is installed into the thin film deposition chamber.

[0077] (2) Prepare a (001) oriented SrTiO3 single crystal substrate. Clean it with acetone and alcohol for 5 minutes in succession, and then dry it with compressed nitrogen. Then install the substrate on the substrate stage through the feed port. Then adjust the position of the substrate stage so that the target is directly below the substrate. The distance between the target and the substrate is controlled at about 2cm.

[0078] (4) Turn on the multi-stage vacuum pump until the vacuum level in the chamber is better than 1×10⁻⁶. -6 When Pa, the substrate stage is heated, and the substrate temperature is raised to 540°C at a heating rate of 30°C / min.

[0079] (5) When the vacuum level of the vacuum chamber is better than 2×10 -5 At pressure Pa, close the valve between the chamber and the molecular pump, and introduce Ar gas through the gas filling system until the chamber pressure reaches 5 Pa. Block the substrate with a baffle, and then pre-sputter the target surface with a pulsed laser for approximately 600 pulses.

[0080] (6) After pre-sputtering is completed, remove the baffle to allow the plasma plume obtained by the pulsed laser bombarding the target to be deposited on the substrate. The number of deposition pulses is 1200 and the deposition time is 5 min.

[0081] (7) After the film growth is complete, Ar gas is introduced until the pressure in the film deposition chamber is 0.1 atmospheres. The substrate temperature is reduced to 300°C at a cooling rate of 10°C / min and held for 30 min. Then the heater is turned off and the substrate is allowed to cool naturally to room temperature.

[0082] The dilute magnetic semiconductor thin film prepared in this comparative example is a single-phase, single-epitaxially grown (Ba) film along the c-axis. 0.91 K 0.09 (Zn) 0.85 Mn 0.15 )2As2 thin film, its XRD diffraction is as follows Figure 8 As shown, its MT test results are as follows: Figure 9 As shown. Figure 8 The sample is shown to be a single-phase, single-orientation epitaxially grown (Ba) material grown on a (001) oriented SrTiO3 substrate. 1-x K x (Zn) 1-y Mny )2As2 thin film. Figure 9 The paramagnetic-ferromagnetic transition temperature of the sample is shown to be 9K. This comparative example shows that if the growth pressure is not within the range required by this invention and no beam source material is used, the paramagnetic-ferromagnetic transition temperature of the prepared sample is only 9K.

[0083] Comparative Example 2

[0084] (1) Prepare polycrystalline Ba 0.7 K 0.3 (Zn 0.85 Mn 0.15 The 2As2 target is fixed on the target holder, and then the target holder is installed into the thin film deposition chamber.

[0085] (2) Prepare a (001) oriented MgAl2O4 single crystal substrate. Clean it ultrasonically with acetone and alcohol for 5 minutes, then dry it with compressed nitrogen. Install the cleaned substrate on the substrate stage through the feed port, and then adjust the position of the substrate stage so that the target is directly below the substrate. The distance between the target and the substrate should be controlled at about 2.5 cm.

[0086] (4) Turn on the multi-stage vacuum pump until the vacuum level in the chamber is better than 1×10⁻⁶. -6 When Pa, the substrate stage is heated, and the substrate temperature is raised to 550°C at a heating rate of 20°C / min.

[0087] (5) When the vacuum level of the vacuum chamber is better than 2×10 -5 At a pressure of 40 Pa, close the valve between the chamber and the molecular pump, and introduce Ar gas through the gas filling system until the chamber pressure reaches 40 Pa. Block the substrate with a baffle, and then pre-sputter the target surface using a pulsed laser for approximately 600 pulses.

[0088] (6) After pre-sputtering is completed, remove the baffle to allow the plasma plume obtained by the pulsed laser bombarding the target to be deposited on the substrate. The number of deposition pulses is 600 and the deposition time is 5 min.

[0089] (7) After the film growth is complete, Ar gas is introduced until the pressure in the film deposition chamber is 0.1 atmospheres. The substrate temperature is reduced to 300°C at a cooling rate of 10°C / min and held for 30 min. Then the heater is turned off and the substrate is allowed to cool naturally to room temperature.

[0090] The dilute magnetic semiconductor thin film prepared in this comparative example is a single-phase, single-epitaxially grown (Ba) film along the c-axis. 0.85 K 0.15 (Zn) 0.85 Mn 0.15 )2As2 thin film, its XRD diffraction is as follows Figure 10 As shown, its MT test results are as follows: Figure 11 As shown. Figure 10 This sample is shown to be a single-phase, c-axis unidirectional epitaxially grown (Ba) material on a (001) oriented MgAl2O4 substrate. 1-x K x (Zn) 1- y Mn y )2As2 thin film. Figure 11 The sample is shown to have a paramagnetic-ferromagnetic transition temperature of 70 K. This comparative example shows that even when the growth pressure is within the range required by this invention, the paramagnetic-ferromagnetic transition temperature of the prepared sample will not be too high if no beam source material is used.

[0091] Comparative Example 3

[0092] (1) Prepare Ba 0.7 K 0.3 (Zn 0.85 Mn 0.10 The 2As2 target (polycrystalline) is fixed on the target support, and then the target support is installed into the thin film deposition chamber.

[0093] (2) Prepare a (001) oriented SrTiO3 single crystal substrate. Clean it with acetone and alcohol for 5 minutes in succession, and then dry it with compressed nitrogen. Then install the substrate on the substrate stage through the feed port. Adjust the position of the substrate stage so that the target is directly below the substrate. The distance between the target and the substrate is controlled at about 2.5cm.

[0094] (4) Turn on the multi-stage vacuum pump until the vacuum level in the chamber is better than 1×10⁻⁶. -6 When Pa, the substrate stage is heated, and the substrate temperature is raised to 540°C at a heating rate of 20°C / min.

[0095] (5) When the vacuum level of the vacuum chamber is better than 2×10 -5 At a pressure of 110 Pa, close the valve between the chamber and the molecular pump, and introduce Ar gas through the gas filling system until the chamber pressure reaches 110 Pa. Block the substrate with a baffle, and then pre-sputter the target surface using a pulsed laser for approximately 600 pulses.

[0096] (6) After pre-sputtering is completed, remove the baffle to allow the plasma plume obtained by the pulsed laser bombarding the target to be deposited on the substrate. The number of deposition pulses is 1200 and the deposition time is 5 min.

[0097] (7) After the film growth is complete, Ar gas is introduced until the pressure in the film deposition chamber is 0.1 atmospheres. The substrate temperature is reduced to 300°C at a cooling rate of 10°C / min and held for 30 min. Then the heater is turned off and the substrate is allowed to cool naturally to room temperature.

[0098] The dilute magnetic semiconductor thin film prepared in this comparative example contains impurity phases (Ba). 1-x K x (Zn) 1-y Mn y )2As2 thin film, its XRD diffraction is as follows Figure 12 As shown. From Figure 12 It can be seen that the impurity phase in this sample is (Ba) along the (103) crystal orientation. 1-x K x (Zn) 1- y Mn y )2As2 thin film. This comparative example shows that if the growth pressure exceeds the range required by the present invention, the prepared sample contains impurity phases.

Claims

1. A method for preparing a magnetic semiconductor thin film, comprising the following steps: (1) Place the polycrystalline magnetic semiconductor target into the thin film deposition chamber; (2) Place the K and Mn elements, which are used as beam source materials, into two beam source furnaces respectively; (3) Clean the substrate, and then mount the cleaned substrate on the substrate stage; (4) Then, the substrate stage is heated to heat the substrate; (5) The pressure of the thin film deposition chamber is controlled to be 6-100 Pa by non-reactive gas, and then a thin film is epitaxially grown on the substrate by molecular beam assisted pulsed laser deposition. (6) After the thin film growth is complete, adjust the gas pressure in the thin film deposition chamber and cool the substrate to obtain a magnetic semiconductor thin film (Ba). 1-x K x (Zn) 1-y Mn y )2As2, where, 0.08 <x≤0.40,0.15<y≤0.30。 2. The method according to claim 1, wherein, The composition of the polycrystalline magnetic semiconductor target is represented by the following chemical formula: Ba 1-m K m (Zn 1-n Mn n )2As2, where 0.10≤m≤0.30, 0.10≤n≤0.

30.

3. The method according to claim 1, wherein, After step (3) and before step (4), the method further includes the following steps: Adjust the stage height to make the distance between the target and the substrate 2-4 cm; and evacuate the thin film deposition chamber to make the vacuum level inside the thin film deposition chamber higher than 1×10⁻⁶. -6 Pa.

4. The method according to claim 1, wherein, The heating of the substrate stage in step (4) is performed by heating the substrate to 500-550°C at a heating rate of 10-30°C / min.

5. The method according to claim 1, wherein, After step (4) and before step (5), the method further includes the following steps: The substrate is blocked by a baffle, and the surface of the target material is then treated with a pulsed laser, with 600-1200 pulses; and two beam source furnaces are heated.

6. The method according to claim 5, wherein, The heating of the two beam source furnaces is carried out by heating the temperature of the beam source furnace containing K to 100-300°C and the temperature of the beam source furnace containing Mn to 600-950°C.

7. The method according to claim 1, wherein, The substrate is selected from (001) oriented SrTiO3 single crystal substrate, (001) oriented Si single crystal substrate, (001) oriented MgAl2O4 single crystal substrate, or (001) oriented (La) single crystal substrate. 0.272 Sr 0.728 (Al) 0.648 Ta 0.352 O3 single crystal substrate.

8. The method according to claim 1, wherein, The epitaxial growth of the thin film in step (5) is carried out under the following conditions: the energy density of the pulsed laser is 120-160 mJ / mm. 2 The laser repetition frequency is 1-5Hz.

9. The method according to claim 1, wherein, The non-reactive gas is selected from one or more of argon, helium, and nitrogen.

10. A magnetic semiconductor thin film prepared by any one of claims 1-9, the composition of which is represented by the following chemical formula: (Ba 1-x K x (Zn) 1-y Mn y )2As2, where, 0.08 <x≤0.40,0.15<y≤0.30。

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