CN110060932B - Lanthanum aluminate/strontium titanate heterojunction and preparation method thereof - Google Patents
Lanthanum aluminate/strontium titanate heterojunction and preparation method thereof Download PDFInfo
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- CN110060932B CN110060932B CN201910337602.9A CN201910337602A CN110060932B CN 110060932 B CN110060932 B CN 110060932B CN 201910337602 A CN201910337602 A CN 201910337602A CN 110060932 B CN110060932 B CN 110060932B
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- 238000002360 preparation method Methods 0.000 title claims abstract description 10
- -1 Lanthanum aluminate Chemical class 0.000 title description 4
- 229910052746 lanthanum Inorganic materials 0.000 title description 4
- VEALVRVVWBQVSL-UHFFFAOYSA-N strontium titanate Chemical compound [Sr+2].[O-][Ti]([O-])=O VEALVRVVWBQVSL-UHFFFAOYSA-N 0.000 title description 4
- 229910002244 LaAlO3 Inorganic materials 0.000 claims abstract description 78
- 229910002370 SrTiO3 Inorganic materials 0.000 claims abstract description 65
- 239000000758 substrate Substances 0.000 claims abstract description 54
- 238000000034 method Methods 0.000 claims abstract description 35
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 18
- 239000001301 oxygen Substances 0.000 claims abstract description 18
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 18
- 238000001816 cooling Methods 0.000 claims abstract description 17
- 229910002367 SrTiO Inorganic materials 0.000 claims abstract description 16
- 238000010438 heat treatment Methods 0.000 claims abstract description 16
- 238000001451 molecular beam epitaxy Methods 0.000 claims abstract description 10
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 10
- 238000004506 ultrasonic cleaning Methods 0.000 claims description 9
- 238000007781 pre-processing Methods 0.000 claims description 6
- 239000002904 solvent Substances 0.000 claims description 5
- 238000004140 cleaning Methods 0.000 claims description 3
- 239000000463 material Substances 0.000 abstract description 5
- 239000004065 semiconductor Substances 0.000 abstract description 4
- 238000000407 epitaxy Methods 0.000 description 10
- 230000000052 comparative effect Effects 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 2
- 239000013077 target material Substances 0.000 description 2
- 230000033228 biological regulation Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 238000009987 spinning Methods 0.000 description 1
- 230000005533 two-dimensional electron gas Effects 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02367—Substrates
- H01L21/0237—Materials
- H01L21/02414—Oxide semiconducting materials not being Group 12/16 materials, e.g. ternary compounds
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02518—Deposited layers
- H01L21/02521—Materials
- H01L21/02565—Oxide semiconducting materials not being Group 12/16 materials, e.g. ternary compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02612—Formation types
- H01L21/02617—Deposition types
- H01L21/02631—Physical deposition at reduced pressure, e.g. MBE, sputtering, evaporation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/24—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only semiconductor materials not provided for in groups H01L29/16, H01L29/18, H01L29/20, H01L29/22
Abstract
The invention discloses LaAlO3/SrTiO3A heterojunction and a preparation method thereof, the LaAlO3/SrTiO3The heterojunction has SrTiO3Substrate layer, inner layerLaAlO3Epitaxial layer and outer layer LaAlO3An epitaxial layer; the LaAlO3/SrTiO3The heterojunction is prepared by adopting the following two-step epitaxial method: inner LaAlO3Epitaxial layer and outer layer LaAlO3The temperature of the laser molecular beam epitaxy equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, and the oxygen atmosphere pressure is 10 DEG‑8～10‑1Torr, laser energy of 0.8 to 2.5J/cm2SrTiO with laser frequency of 1-10 Hz3Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the inner layer or the outer layer LaAlO is prepared3And (5) cooling to room temperature at the speed of 10-40 ℃/min after the epitaxial layer is formed. LaAlO prepared by the method3/SrTiO3The heterojunction has high carrier concentration (≧ 10)14cm‑2) High mobility ≧ 104cm2Vs), etc., can replace the conventional semiconductor material to meet the use requirements of electronic devices such as transistors, electron spin devices, etc.
Description
Technical Field
The invention belongs to the technical field of semiconductors, and particularly relates to LaAlO with high carrier concentration and high electron mobility3/SrTiO3A heterojunction and a method of fabricating the same.
Background
LaAlO3(LAO, lanthanum aluminate) with SrTiO3(STO, strontium titanate) are wide bandgap insulators with perovskite structures, LAO is a polar material, STO is a nonpolar material, and interface conductivity, namely a two-dimensional electron gas phenomenon, is observed due to discontinuous polarization at the interface of the LAO and the STO. By adopting different preparation processes and through the regulation and control technology of interface electrons, LaAlO with greatly improved carrier concentration and electron mobility is expected to be obtained3/SrTiO3The heterojunction lays a foundation for the application of electronic devices such as transistors, electron spinning devices and the like.
LaAlO commonly reported3/SrTiO3Heterojunction with electron mobility of-10 at its interface3cm2Vs, carrier concentration of 1013～1014cm-2. In order to improve the electron mobility of the interface, different processes including defect scattering control, surface control, doping control, and even growth processes with different parameters are used to prepare the LAO epitaxial layer, although these processes are in progressThe electron mobility is improved to a certain extent, but the highest reported electron mobility is only 10 so far4cm2Vs, however, its carrier concentration is generally low, only 1012～1013cm-2It is difficult to satisfy the application of electronic devices such as transistors and electron spin devices.
Disclosure of Invention
The invention aims to provide a method for preparing LaAlO3/SrTiO3A method for preparing LaAlO (lanthanum aluminate/strontium titanate) heterojunction by a two-step epitaxial method3The epitaxial layer specifically comprises the following steps:
step S1 for SrTiO3Carrying out ultrasonic cleaning and pretreatment on the substrate;
step S2 of preparing inner LaAlO3Epitaxial layer, inner LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, and the pressure of the oxygen atmosphere is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2SrTiO with laser frequency of 1-10 Hz3Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the inner layer LaAlO is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min;
step S3 of preparing outer LaAlO3Epitaxial layer, outer layer LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, preferably 30-50 ℃/min, and the pressure of the oxygen atmosphere is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2The laser frequency is 1-10 Hz, and the SrTiO obtained in the step S23Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the outer LaAlO layer is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min to finally obtain LaAlO3/SrTiO3A heterojunction.
LaAlO obtained by the two-step epitaxy method3/SrTiO3The heterojunction has high carrier concentration and high electron mobility coefficientThe step epitaxy method has simple process and originality, can replace the conventional preparation method, and meets the use requirements of the field of electronic device semiconductors such as transistors and the like.
In step S1, the SrTiO3The crystallographic orientation of the substrate is (100) or (111) or (110); SrTiO3And ultrasonically cleaning the surface of the substrate for 5-10 minutes by using an isopropanol solvent until the surface is clean and has no residue.
In step S1, the preprocessing specifically includes: SrTiO after ultrasonic cleaning3The substrate is placed into laser molecular beam epitaxy equipment and is pretreated for 10-60 min, preferably 30min at 700-900 ℃, preferably 850 ℃.
LaAlO3The total thickness of the epitaxial layer is 2 nm-0.1 μm. The inner layer LaAlO of the invention3Thickness of epitaxial layer and outer layer LaAlO3The thickness of the epitaxial layer can be 20-80%: 80% to 20%, preferably 50%: 50 percent.
Step S2 of preparing inner LaAlO3Epitaxial layer and step S3 of preparing outer LaAlO3In the epitaxial layer, the temperature of the laser molecular beam epitaxial equipment is set to be 850 ℃, the heating rate is 30-50 ℃/min, and the oxygen atmosphere pressure is 10 DEG-5～10-3Torr, laser energy of 1.2 to 2.0J/cm2The laser frequency is 2-5 Hz, SrTiO3Substrate isolated LaAlO3The distance between the targets is 5-10 cm, and LaAlO is prepared3And (5) cooling to room temperature at the speed of 20-30 ℃/min after the epitaxial layer is formed.
Another objective of the invention is to provide a LaAlO3/SrTiO3A heterojunction of said LaAlO3/SrTiO3The heterojunction has SrTiO3A substrate layer and a layer of SrTiO3LaAlO on a substrate layer3Epitaxial layer of said LaAlO3An epitaxial layer is formed on the SrTiO3Inner LaAlO on substrate layer3Epitaxial layer and LaAlO positioned in the inner layer3Outer layer LaAlO on epitaxial layer3An epitaxial layer; LaAlO of the invention3/SrTiO3LaAlO of heterojunction3The total thickness of the epitaxial layer is 2 nm-0.1 μm;
the LaAlO3/SrTiO3The heterojunction adopts the followingThe two-step epitaxial method is used for preparing the following components:
step S1 for SrTiO3Carrying out ultrasonic cleaning and pretreatment on the substrate;
step S2 of preparing inner LaAlO3Epitaxial layer, inner LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, and the pressure of the oxygen atmosphere is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2SrTiO with laser frequency of 1-10 Hz3Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the inner layer LaAlO is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min;
step S3 of preparing outer LaAlO3Epitaxial layer, outer layer LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, preferably 30-50 ℃/min, and the pressure of the oxygen atmosphere is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2The laser frequency is 1-10 Hz, and the SrTiO obtained in the step S23Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the outer LaAlO layer is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min to finally obtain LaAlO3/SrTiO3A heterojunction.
The positive progress effects of the invention are as follows: LaAlO obtained by the two-step epitaxial method3/ SrTiO3The interface of the heterojunction has the characteristics of high carrier concentration, high electron mobility coefficient and the like. LaAlO prepared by the method3/SrTiO3The heterojunction has high carrier concentration and high electron mobility coefficient at the interface of not less than 1014cm-2≧ 104cm2the/Vs can be expected to satisfy the characteristics of use in the semiconductor field of electronic devices such as transistors.
Drawings
FIG. 1 shows LaAlO prepared by a conventional method in comparative example 13/SrTiO3Carrier concentration and electron mobility curves of heterojunctionsAnd (6) line drawing. The abscissa is temperature in deg.C and the ordinate is the carrier concentration in cm-2Electron mobility in cm2/Vs。
FIG. 2 shows LaAlO obtained by the two-step epitaxy method of the present invention in example 13/SrTiO3Transmission image of electron microstructure of heterojunction high magnification.
FIG. 3 shows LaAlO obtained by the two-step epitaxy method of the present invention in example 13/SrTiO3A plot of carrier concentration and electron mobility of a heterojunction. The abscissa is temperature in deg.C and the ordinate is the carrier concentration in cm-2Electron mobility in cm2/Vs。
FIG. 4 is LaAlO prepared by the two-step epitaxy method of the present invention in example 23/SrTiO3A plot of carrier concentration and electron mobility of a heterojunction. The abscissa is temperature in deg.C and the ordinate is the carrier concentration in cm-2Electron mobility in cm2/Vs。
FIG. 5 is LaAlO prepared by the two-step epitaxy method of the present invention in example 33/SrTiO3A plot of carrier concentration and electron mobility of a heterojunction. The abscissa is temperature in deg.C and the ordinate is the carrier concentration in cm-2Electron mobility in cm2/Vs。
Detailed Description
Comparative example 1
Selecting a substrate material: the substrate adopted is SrTiO3And the substrate has a crystallographic orientation of (100), and the surface of the substrate is ultrasonically cleaned for 5-10 minutes by using an isopropanol solvent.
Pretreatment of the substrate: putting the substrate into laser molecular beam epitaxy equipment, controlling the temperature to be 700-900 ℃ and the oxygen atmosphere pressure to be 10-8Torr～10-1And (5) Torr for 10-60 min, and carrying out pretreatment on the substrate to remove residual organic matters on the surface of the substrate.
Preparing an LAO epitaxial layer: firstly, setting the specific preparation conditions of 700-900 ℃ and LThe temperature rate is 20 ℃/min to 60 ℃/min, the oxygen atmosphere pressure is 10 DEG C-8Torr～10-1Torr, laser energy 0.8J/cm2～2.5J/cm2The laser frequency is 1Hz-10Hz, the distance between the substrate and the target material is preferably 2-15 cm, and LaAlO with the thickness of 2 nm-0.1 mu m is directly prepared at one time by a laser molecular beam epitaxy method3The temperature reduction rate of the epitaxial layer is 10-40 ℃/min.
As shown in FIG. 1, LaAlO prepared by a conventional method was used in comparative example 13/SrTiO3A plot of carrier concentration and electron mobility of a heterojunction. As shown in the figure, the electron mobility at the interface thereof is up to-10 with the change in temperature3cm2Vs, carrier concentration 2.7 × 1013cm-2。
Examples 1 to 3
Selecting a substrate material: the substrate adopted is SrTiO3The substrate, and the crystallographic orientation of the substrate is (100), the substrate surface needs to be ultrasonically cleaned with isopropanol solvent for t0 minutes.
Pretreatment of the substrate: and (3) putting the substrate into laser molecular beam epitaxy equipment, controlling the temperature to be T1, the heating rate to be V1, the oxygen atmosphere pressure to be P1 and the time to be T1, preprocessing the substrate, and removing residual organic matters on the surface of the substrate.
And preparing the LAO epitaxial layer by adopting a two-step epitaxial method. Firstly, setting the preparation conditions of temperature T2, heating rate V2, oxygen atmosphere pressure P2, laser energy W2, laser frequency F2, distance d2 between the substrate and the target material and cooling rate V3. Preparation of an inner LaAlO layer of thickness D13Epitaxial layer and then cooling to room temperature. Then according to the inner LaAlO3Outer layer LaAlO preparation through parameter setting of epitaxial layer3Parameters of epitaxial layer an outer layer of LaAlO with a thickness of D2 was prepared according to the same conditions3And (5) carrying out epitaxial layer and finally cooling to room temperature. The LaAlO of the invention is obtained3/SrTiO3A heterojunction.
TABLE 1 Process parameters for examples 1-3
As shown in FIG. 2, LaAlO prepared by two-step epitaxy method for example 1 is shown3/SrTiO3Transmission electron microstructure of the heterojunction clearly shows the LAO epitaxial layer of controlled thickness prepared by laser molecular beam epitaxy.
As shown in FIG. 3, LaAlO prepared by two-step epitaxy method for example 1 is shown3/SrTiO3The graph shows that the electron mobility at the interface is up to 3.8 × 10 with the change of temperature4cm2Vs, carrier concentration of 4.14 × 1014cm-2。
As shown in FIG. 4, LaAlO prepared by two-step epitaxy method in example 2 was used3/SrTiO3The electron mobility at the interface is shown to be up to 3.0 × 10 as a function of temperature4cm2Vs, carrier concentration of 2.4 × 1014cm-2。
As shown in FIG. 5, LaAlO prepared by two-step epitaxy for example 33/SrTiO3The graph shows that the electron mobility at the interface is 2.8 × 10 or more4cm2Vs, carrier concentration 1.3 × 1015cm-2。
Claims (15)
1. Preparation of LaAlO3/SrTiO3Method of heterojunction, characterized in that
The method is a two-step epitaxial method for preparing LaAlO3The epitaxial layer specifically comprises the following steps:
step S1 for SrTiO3Carrying out ultrasonic cleaning and pretreatment on the substrate;
step S2 of preparing inner LaAlO3EpitaxyLayer, inner layer LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, and the pressure of the oxygen atmosphere is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2SrTiO with laser frequency of 1-10 Hz3Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the inner layer LaAlO is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min;
step S3 of preparing outer LaAlO3Epitaxial layer, outer layer LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, and the pressure of the oxygen atmosphere is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2The laser frequency is 1-10 Hz, and the SrTiO obtained in the step S23Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the outer LaAlO layer is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min to finally obtain LaAlO3/SrTiO3A heterojunction.
2. The method of claim 1, wherein: step S3 of preparing outer LaAlO3Epitaxial layer, outer layer LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 30-50 ℃/min, and the oxygen atmosphere pressure is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2The laser frequency is 1-10 Hz, and the SrTiO obtained in the step S23Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the outer LaAlO layer is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min to finally obtain LaAlO3/SrTiO3A heterojunction.
3. The method of claim 1, wherein: in step S1, the SrTiO3The crystallographic orientation of the substrate is (100) or (111) or (110); SrTiO3SubstrateAnd ultrasonically cleaning the surface for 5-10 minutes by using an isopropanol solvent until the surface is clean and has no residue.
4. The method of claim 1, wherein: in step S1, the preprocessing specifically includes: SrTiO after ultrasonic cleaning3And (3) putting the substrate into laser molecular beam epitaxy equipment, and pretreating for 10-60 min at 700-900 ℃.
5. The method of claim 4, wherein: in step S1, the preprocessing specifically includes: SrTiO after ultrasonic cleaning3The substrate is put into a laser molecular beam epitaxy device and pretreated for 30min at 850 ℃.
6. The method of claim 1, wherein: LaAlO3The total thickness of the epitaxial layer is 2 nm-0.1 μm; inner LaAlO3Thickness of epitaxial layer and outer layer LaAlO3The thickness ratio of the epitaxial layer is 20-80%: 80 to 20 percent.
7. The method of claim 6, wherein: LaAlO3The total thickness of the epitaxial layer is 2 nm-0.1 μm; inner LaAlO3Thickness of epitaxial layer and outer layer LaAlO3Thickness ratio of epitaxial layer is 50%: 50 percent.
8. The method of claim 1, wherein: step S2 of preparing inner LaAlO3Epitaxial layer and step S3 of preparing outer LaAlO3In the epitaxial layer, the temperature of the laser molecular beam epitaxial equipment is set to be 850 ℃, the heating rate is 30-50 ℃/min, and the oxygen atmosphere pressure is 10 DEG-5～10-3Torr, laser energy of 1.2 to 2.0J/cm2The laser frequency is 2-5 Hz, SrTiO3Substrate isolated LaAlO3The distance between the targets is 5-10 cm, and LaAlO is prepared3And (5) cooling to room temperature at the speed of 20-30 ℃/min after the epitaxial layer is formed.
9. LaAlO3/SrTiO3Heterojunction, anLaAlO as described3/SrTiO3The heterojunction has SrTiO3A substrate layer and a layer of SrTiO3LaAlO on a substrate layer3An epitaxial layer characterized by: the LaAlO3An epitaxial layer is formed on the SrTiO3Inner LaAlO on substrate layer3Epitaxial layer and LaAlO positioned in the inner layer3Outer layer LaAlO on epitaxial layer3An epitaxial layer; the LaAlO3The total thickness of the epitaxial layer is 2 nm-0.1 mu m, and the inner layer LaAlO3Thickness of epitaxial layer and outer layer LaAlO3The thickness ratio of the epitaxial layer is 20-80%: 80% -20%;
the LaAlO3/SrTiO3The heterojunction is prepared by adopting the following two-step epitaxial method:
step S1 for SrTiO3Carrying out ultrasonic cleaning and pretreatment on the substrate;
step S2 of preparing inner LaAlO3Epitaxial layer, inner LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, and the pressure of the oxygen atmosphere is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2SrTiO with laser frequency of 1-10 Hz3Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the inner layer LaAlO is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min;
step S3 of preparing outer LaAlO3Epitaxial layer, outer layer LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 20-60 ℃/min, and the pressure of the oxygen atmosphere is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2The laser frequency is 1-10 Hz, and the SrTiO obtained in the step S23Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the outer LaAlO layer is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min to finally obtain LaAlO3/SrTiO3A heterojunction.
10. According to claim 9The LaAlO3/SrTiO3A heterojunction, characterized in that: inner LaAlO3Thickness of epitaxial layer and outer layer LaAlO3Thickness ratio of epitaxial layer is 50%: 50 percent.
11. LaAlO according to claim 93/SrTiO3A heterojunction, characterized in that: step S3 of preparing outer LaAlO3Epitaxial layer, outer layer LaAlO3The thickness of the epitaxial layer is 1 nm-0.05 μm, the specific conditions are that the temperature of the laser molecular beam epitaxial equipment is set to be 700-900 ℃, the heating rate is 30-50 ℃/min, and the oxygen atmosphere pressure is 10-8～10-1Torr, laser energy of 0.8 to 2.5J/cm2The laser frequency is 1-10 Hz, and the SrTiO obtained in the step S23Substrate isolated LaAlO3The distance between the targets is 2-15 cm, and the outer LaAlO layer is prepared3After the epitaxial layer is formed, cooling to room temperature at the speed of 10-40 ℃/min to finally obtain LaAlO3/SrTiO3A heterojunction.
12. LaAlO according to claim 93/SrTiO3A heterojunction, characterized in that: in step S1, the SrTiO3The crystallographic orientation of the substrate is (100) or (111) or (110); SrTiO3And ultrasonically cleaning the surface of the substrate for 5-10 minutes by using an isopropanol solvent until the surface is clean and has no residue.
13. LaAlO according to claim 93/SrTiO3A heterojunction, characterized in that: in step S1, the preprocessing specifically includes: SrTiO after ultrasonic cleaning3And (3) putting the substrate into laser molecular beam epitaxy equipment, and pretreating for 10-60 min at 700-900 ℃.
14. LaAlO according to claim 133/SrTiO3A heterojunction, characterized in that: in step S1, the preprocessing specifically includes: SrTiO after ultrasonic cleaning3The substrate is put into a laser molecular beam epitaxy device and pretreated for 30min at 850 ℃.
15. LaAlO according to claim 93/SrTiO3A heterojunction, characterized in that: step S2 of preparing inner LaAlO3Epitaxial layer and step S3 of preparing outer LaAlO3In the epitaxial layer, the temperature of the laser molecular beam epitaxial equipment is set to be 850 ℃, the heating rate is 30-50 ℃/min, and the oxygen atmosphere pressure is 10 DEG-5～10-3Torr, laser energy of 1.2 to 2.0J/cm2The laser frequency is 2-5 Hz, SrTiO3Substrate isolated LaAlO3The distance between the targets is 5-10 cm, and LaAlO is prepared3And (5) cooling to room temperature at the speed of 20-30 ℃/min after the epitaxial layer is formed.
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