A large-range NP continuously adjustable graphene doping method

Abstract

The present invention belongs to the field of electronic information materials and components, specifically a method for graphene doping with continuously adjustable n-type and p-type doping over a wide range. This method utilizes the multi-phase coexistence of tin oxide, with each phase having a different doping effect on graphene: the metallic phase induces strong n-type doping, the divalent SnO phase induces weak n-type doping, and the tetravalent SnO₂ phase induces strong p-type doping. By annealing to alter the oxidation degree and control the proportion of each phase, this method achieves continuous and adjustable doping of graphene between strong n-type and strong p-type doping over a wide range. This method overcomes the problems of existing doping methods with a single doping type, a narrow doping control range, and a lack of effective p-type doping control.

Description

Technical Field

[0001] The invention belongs to the field of electronic information materials and components, and in particular relates to a large-range NP continuously adjustable graphene doping method. Background Art

[0002] As the most promising of two-dimensional materials, graphene is considered a promising candidate for next-generation semiconductors due to its superior electrical, optical, and thermodynamic properties. The increasing maturity of chemical vapor deposition (CVD) technology has enabled the large-scale growth of graphene, laying the foundation for its wafer-level applications. However, intrinsic graphene is a zero-bandgap semiconductor or semimetal, requiring more precise control of its electrical properties through doping. This allows doped graphene to exhibit multi-electron or multi-hole properties, resulting in n-type or p-type doped graphene.

[0003] The current methods for doping graphene mainly include substitutional doping and surface charge transfer doping. The substitutional doping method can achieve a stable doping effect, but because impurity atoms are used to replace carbon atoms in the graphene lattice during the doping process, the ordered lattice structure of graphene is destroyed, resulting in a serious decrease in carrier mobility. The surface charge transfer doping method achieves the doping effect by covering the graphene surface with dopants, avoiding the problem of lattice destruction and is more popular. The dopants available for selection are mainly divided into two categories: organic and inorganic. Organic dopants have poor controllability, are unstable in the environment, and there is a risk of cross-contamination of organic matter; among inorganic dopants, metal oxide materials have good stability and are suitable for large-area wafer-level applications, so they have more prominent advantages.

[0004] Among metal oxides, molybdenum oxide MoO3 can achieve strong p-type doping of graphene, that is, as an acceptor, because it has a large work function (>6eV), but it is reported that it has only achieved single p-type doping, and the doping level is fixed. Zinc oxide ZnO can be used as an n-type dopant, that is, a donor, and the doping level can be controlled. The specific experimental plan is: a layer of ZnO film is grown on the surface of graphene by ALD (atomic layer deposition) method, and the graphene doping level is controlled by adjusting the thickness of the ZnO grown by ALD. Figure 1 As shown, the original graphene exhibits p-type doping. As the thickness of the grown ZnO increases, the device's Dirac point shifts toward negative voltages, ultimately achieving continuous control from p-type to n-type. However, fundamentally, graphene's p-type properties are provided by impurities such as oxygen and moisture adsorbed from the air. On this basis, the Dirac point shifts toward negative voltages, gradually exhibiting n-type doping. However, this method has a limited doping range and cannot be expanded to p-type. It also relies heavily on high-precision film thickness control, making technical implementation difficult.

[0005] In general, existing doping technologies all use doping source materials with fixed chemical states (both inorganic and organic), and therefore inevitably have the following limitations: first, they can only serve as a single type of dopant, that is, as a donor or an acceptor; second, even if the doping degree can be regulated through the above-mentioned specific methods, the adjustable range is very limited; finally, there is currently a lack of effective means to regulate metal oxides as p-type dopants, that is, acceptors. Summary of the Invention

[0006] The purpose of the present invention is to provide a graphene doping method with a wide range of continuously adjustable np-type and p-type doping, so as to overcome the problems of the existing doping methods such as single doping type, narrow doping control range and lack of effective p-type doping control.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for graphene doping with a wide range of continuously adjustable np ratios comprises the following steps:

[0009] Step 1: depositing a tin oxide film on the graphene;

[0010] Step 2: annealing the structure obtained in step 1 to obtain doped graphene.

[0011] Furthermore, in step 1, the tin oxide film is deposited by magnetron sputtering.

[0012] Furthermore, in step 1, when the tin oxide film is sputtered by magnetron sputtering, the sputtering power is 50-60 W, the time is 5-6 min, the pressure is 0.43-0.5 Pa, and the gas flow rates of argon and oxygen are 21.2 sccm and 0.8 sccm, respectively; the thickness of the sputtered tin oxide film is 40 nm.

[0013] Furthermore, the detailed process of the annealing treatment in step 2 is as follows:

[0014] Place the structure obtained in step 1 in an annealing furnace, and heat the temperature from room temperature to 225°C to 275°C at a heating rate of 10°C to 30°C / min under a nitrogen, oxygen or air atmosphere, and anneal for 60 minutes.

[0015] The present invention provides a method for graphene doping with a wide range of continuously adjustable n-type and p-type properties. This method utilizes the coexistence of multiple phases of tin oxide, each of which has a different doping effect on graphene: the metallic β-Sn phase, with its lower work function than graphene, injects a large number of electrons into graphene, ultimately inducing strong n-type doping; the divalent polycrystalline SnO phase, with a slightly lower work function than graphene, injects electrons into graphene, inducing weak n-type doping; and the tetravalent amorphous SnO2 phase, with a greater work function than graphene, extracts electrons from graphene, increasing the number of holes and inducing strong p-type doping. Leveraging this characteristic, the oxidation degree of the tin oxide film is altered through annealing in a specific atmosphere, thereby controlling the proportions of each phase in the film and achieving a wide range of continuously adjustable graphene doping between strong n-type and strong p-type properties.

[0016] Compared with the existing technology, this method uses tin oxide (SnO X ) thin film as a surface charge-transfer dopant for graphene. A post-annealing process is used to control the degree of tin oxide oxidation, thereby controlling the type and degree of graphene doping. This overcomes the existing problem of graphene dopants being limited to a single type (donor or acceptor), while significantly broadening the doping control range, ultimately achieving continuous control of graphene doping across a wide range of types, from strong n-type to strong p-type. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the controllable doping of graphene by ALD-ZnO; (a) is a schematic diagram of the growth of ALD-ZnO on the surface of graphene,

[0018] (b) Transfer characteristic curves of transistors with different ZnO doping thicknesses;

[0019] Figure 2 Schematic cross-section of tin oxide film doped graphene in the embodiment:

[0020] Figure 3 is a flow chart for preparing tin oxide thin film doped graphene in an embodiment;

[0021] Figure 4 is a graph showing transistor transfer characteristics of pristine graphene samples, unannealed samples, nitrogen annealed samples, and air annealed samples;

[0022] Reference numerals:

[0023] 1. Si substrate; 2. 300nm SiO2 dielectric layer; 3. Graphene; 4. Tin oxide thin film. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] The present invention provides a method for preparing graphene doping with a wide range of NP continuously adjustable, and the process flow is as follows: Figure 3 As shown, the following steps are included:

[0026] Step 1: Growing a graphene film on copper foil. There are many graphene growth methods disclosed in the prior art, all of which are applicable to this embodiment. Therefore, this embodiment does not provide a detailed description of the graphene growth process.

[0027] Step 2: Use PMMA-assisted wet transfer technology to transfer the graphene obtained in step 1 to the required substrate. According to actual needs, the substrates selected for transferring graphene in this embodiment include silicon substrates and silicon dioxide thermally grown on silicon substrates. Before transfer, the substrate needs to be treated. To ensure the cleanliness and dryness of the substrate surface, first soak the substrate in acetone solution and use ultrasonic cleaning for 20 minutes; repeat twice and place it in alcohol solution and ultrasonicate for 20 minutes; then place it in deionized water and ultrasonicate for 20 minutes, then take it out and replace it with unused deionized water for storage. The detailed process of transfer is as follows:

[0028] Step 2.1: Use oxygen dry etching to remove excess graphene on the back of the copper foil. The dry etching parameters are: power 20-25W, oxygen flow rate 20-25sccm, and etching time 15-20s.

[0029] Step 2.2: Attach the graphene-grown side (front side) of the structure obtained in step 2.1 to a polyester film and seal all edges to prevent PMMA from being applied to the back side of the copper foil in the next step, making it difficult to etch the graphene on the back side.

[0030] Step 2.3: evenly spin-coat the PMMA solution on the graphene surface of the structure obtained in step 2.2, and bake on a hot plate at 100-120° C. for 2-3 minutes to solidify the PMMA and protect the graphene surface;

[0031] Step 2.4: Etch the copper foil of the structure obtained in step 2.3 using FeCl3 solution, rinse with deionized water every 3 minutes, and repeat this step until the copper foil is completely removed;

[0032] Step 2.5: Use a glass slide to transfer the structure obtained in step 2.4 into deionized water to remove the residual FeCl3 solution;

[0033] Step 2.6: Transfer the structure obtained in step 2.5 to a SiO2 wafer on a substrate, and remove the PMMA using acetone and ethanol.

[0034] Step 2.7: Place the structure obtained in step 2.6 on a hot plate and use gradient heating to remove moisture. The temperature gradient is 50°C, 70°C, 90°C, and 110°C. Dry at each temperature for 5 minutes, then increase the temperature and finally blow dry.

[0035] Step 3: A tin oxide film was deposited directly onto the transferred graphene using magnetron sputtering. The sputtering power was 50-60 W, the duration was 5-6 minutes, the pressure was 0.43-0.5 Pa, and the argon and oxygen flow rates were 21.2 sccm and 0.8 sccm, respectively. Ellipsometry analysis revealed a tin oxide film thickness of approximately 40 nm.

[0036] Step 4: Place the sample in an annealing furnace and anneal for 1 hour. The annealing atmosphere includes nitrogen, air, and oxygen, and the annealing temperature is 225°C, 250°C, and 275°C. The final doped graphene results are as follows: Figure 2 According to the annealing conditions, the samples are named as unannealed, 225-N2, 250-N2, 275-N2, 225-Air, 250-Air, and 275-Air.

[0037] The carrier types and carrier concentrations of all samples obtained in the above steps and the Dirac points, carrier concentrations and mobility extracted from transistor devices are shown in Table (1), where the positive and negative signs represent the carrier types, + for holes and - for electrons.

[0038] First, the original graphene sample exhibits weak p-type doping properties, and its carrier concentration is measured to be 2.66×10 12 cm -2 , the mobility is 2532.1cm 2 V -1 s -1 After deposition of the tin oxide film, the unannealed sample transformed into a strong n-type with a carrier concentration of -2.39×10 13 cm -2 , the migration rate is reduced to 317.1cm 2 V-1s -1 The samples annealed in nitrogen all showed n-type doping properties, and as the annealing temperature increased, the carrier concentration gradually decreased and the Hall mobility increased accordingly. Specifically, the carrier concentration of the 225-N2 sample was -3.87×10 12 cm -2 , the Hall mobility is 1652.0 cm 2 V -1 s -1 , the carrier concentration of the 250-N2 sample is -2.38×10 12 cm -2, the Hall mobility is 2486.7 cm 2 V -1 s -1 , the carrier concentration of 275-N2 sample is -6.30×10 12 cm -2 , the Hall mobility is 2992.0 cm 2 V -1 s -1 The samples annealed in air all showed strong p-type doping, and as the annealing temperature increased, the carrier concentration increased and the p-type doping property was enhanced. Specifically, the carrier concentration of the 225-Air sample was 5.00×10 12 cm -2 , the Hall mobility is 928.0 cm 2 V -1 s -1 , the carrier concentration of the 250-Air sample is 1.11×10 13 cm -2 , the Hall mobility is 625.1cm 2 V -1 s -1 , the carrier concentration of the 275-Air sample is -1.90×10 12 cm -2 , the Hall mobility is 560.0 cm 2 V -1 s -1 It should be noted that the carrier concentrations of samples annealed in air were higher than those of pristine graphene samples, indicating that annealing in air can enhance graphene's p-type properties. Samples annealed in oxygen showed similar results and trends to those annealed in air: they all exhibited strong p-type doping, with the doping level increasing with increasing annealing temperature.

[0039]

[0040]

[0041] Table 1

[0042] Figure 4 The transistor transfer characteristics curves of the original graphene sample, the unannealed sample, the nitrogen annealed sample and the air annealed sample are shown. Figure 4 As shown, carrier type, concentration, and mobility can be extracted from this data. The transistor properties are identical to those observed in the Hall effect test. Both the unannealed and nitrogen-annealed samples exhibit negative Dirac points, indicating n-type doping, while the Dirac points of the air-annealed samples are all greater than +100V, indicating strong p-type doping. Furthermore, the carrier concentration extracted from the nitrogen-annealed sample is highly consistent with the Hall effect, and the extracted mobility follows a similar trend: mobility decreases as carrier concentration increases.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for graphene doping with a wide range of np continuously adjustable characteristics, characterized in that: The following steps are involved: Step 1: depositing a tin oxide film on the graphene; Step 2: annealing the structure obtained in step 1. The detailed process of the annealing treatment is as follows: placing the structure obtained in step 1 in an annealing furnace, under a nitrogen, oxygen or air atmosphere, heating the temperature from room temperature to 225°C to 275°C at a heating rate of 10°C to 30°C / min, and annealing for 60 minutes; Doped graphene is obtained by annealing, and the doped graphene can achieve a wide range of continuously adjustable doping between strong n-type and strong p-type.

2. The method for graphene doping with a wide range of np continuously adjustable according to claim 1, characterized in that: In the step 1, the tin oxide thin film is deposited by magnetron sputtering.

3. The method for graphene doping with a wide range of np continuously adjustable according to claim 1, characterized in that: In step 1, when the tin oxide film is sputtered by magnetron sputtering, the sputtering power is 50-60 W, the time is 5-6 minutes, the pressure is 0.43-0.5 Pa, and the gas flow rates of argon and oxygen are 21.2 sccm and 0.8 sccm respectively; the thickness of the sputtered tin oxide film is 40 nm.

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