CN111874891A - Method for preparing periodic pn junction graphene based on high-purity semi-insulating silicon carbide substrate - Google Patents

Method for preparing periodic pn junction graphene based on high-purity semi-insulating silicon carbide substrate Download PDF

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CN111874891A
CN111874891A CN202010713285.9A CN202010713285A CN111874891A CN 111874891 A CN111874891 A CN 111874891A CN 202010713285 A CN202010713285 A CN 202010713285A CN 111874891 A CN111874891 A CN 111874891A
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silicon carbide
graphene
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张福生
杨昆
路亚娟
刘新辉
牛晓龙
崔景光
尚远航
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Hebei Tongguang Semiconductor Co.,Ltd.
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Abstract

The invention discloses a method for preparing periodic pn junction graphene based on a high-purity semi-insulating silicon carbide substrate, and belongs to the technical field of microelectronic materials. According to the method for preparing the graphene by pyrolyzing the silicon carbide, firstly, a regular step is etched on the surface of the silicon carbide substrate by using a hydrogen etching method, and then a structure with a single-layer graphene strip and a buffer layer structure which are alternated grows on the etched silicon carbide surface. And finally, converting the original buffer layer structure into p-type conductive graphene by a hydrogen passivation technology, wherein the original single-layer graphene still keeps n-type conductivity. Therefore, the periodic pn junction graphene can be prepared. The high-quality periodic pn stone graphene prepared by the method can be widely applied to the fields of information electronic devices such as enhanced photodetectors, photosensitive elements, logic operation field effect transistors and the like.

Description

Method for preparing periodic pn junction graphene based on high-purity semi-insulating silicon carbide substrate
Technical Field
The invention belongs to the technical field of microelectronic materials, and particularly relates to a method for preparing periodic pn junction graphene based on a high-purity semi-insulating silicon carbide substrate.
Background
Graphene is a hexagonal honeycomb lattice two-dimensional carbon material formed by closely packing carbon atoms, and the thickness of single-layer graphene is only 0.335nm, so that graphene is the thinnest material in the world at present. Due to the unique structure of graphene, graphene has a relationship between a zero band gap and linear dispersion energy near a Dirac point, so that the graphene shows many excellent properties. Mainly comprises extremely high carrier mobility, high mechanical strength, high thermal conductivity and half-integer quantum Hall effect.
Particularly, graphene is a material with zero band gap (i.e. the conduction band bottom and the valence band top are coincident), so that the graphene has good absorption performance on light of all bands, and shows great application potential in the field of photoelectric detection. The graphene photoelectric detector can show ultra-fast responsivity, ultra-wide spectrum absorption and dynamic photoelectric performance adjusting characteristics. The photoelectric conversion mechanism of graphene mainly includes: photovoltaic effect, photothermal effect, radiative heat effect, photovoltaic gate effect, and surface plasmon assisted effect. In addition, an important photoelectric conversion mechanism is a pn junction effect in a semiconductor, and the pn junction can greatly enhance the photoelectric conversion efficiency in a semiconductor material. The pn junction is also the basis of the current semiconductor logic unit-field effect transistor, and the processing and the storage of information data benefit from the generation of the pn junction. Therefore, the prepared pn-junction graphene has great research value and application potential for preparing enhanced photoelectric detectors and high-speed logic operation units later.
The formation of pn junctions in semiconductor materials is achieved primarily by doping. For example, doping phosphorus or nitrogen donor atoms in a silicon single crystal to provide excess electrons as majority carriers, thereby forming an n region; boron or aluminum acceptor atoms are doped into a silicon single crystal to provide excess holes as carriers, which results in the formation of a p-region. The doping method is mainly to dope into the crystal lattice during the growth process and to hit the inside of the crystal lattice by adopting an ion implantation method after the growth is finished. In any of the doping methods, the crystal lattice of the original crystal itself is affected, and newly formed chemical bonds may be long or short, or defects such as interstitial atoms or voids may be formed.
Chinese patent CN105217604B discloses a method for in-situ epitaxial growth of graphene pn junction on semi-insulating silicon carbide, which mainly comprises the steps of carrying out selective boron ion implantation doping on the silicon surface of the semi-insulating silicon carbide, then carrying out annealing to grow graphene, wherein the boron doping of the graphene grown in the region implanted with boron ions in the selective region is p-type, and the region not implanted is n-type. However, the technology adopts an ion implantation method to damage the atomic layer on the surface layer of the silicon carbide, and the quality of the graphene is seriously reduced by growing the graphene on the damaged atomic layer; in addition, the width of the pn junction band of the graphene prepared by diffusing atoms into the graphene lattice needs to be more than millimeter magnitude, and the purpose cannot be achieved due to the small size, because the diffusion distance of the atoms is long, and the doping concentration is gradually reduced along with the increase of the distance. It follows that this method is not suitable for producing pn junction stripes in the order of microns.
However, a method for realizing periodic pn junction graphene in an undoped mode is not reported. Therefore, how to design a simple, damage-free, and doping-free graphene pn junction characteristic to be effectively adjusted for preparing periodic pn-junction graphene materials becomes a problem to be solved in the field.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for preparing periodic pn junction graphene based on a high-purity semi-insulating silicon carbide substrate, which is characterized in that a method for preparing graphene by pyrolyzing silicon carbide is adopted, the characteristics of thermodynamics and molecular diffusion kinetics of two-dimensional graphene growth and graphene structure formation by pyrolyzing silicon carbide are combined, firstly, a regular step is etched on the surface of the silicon carbide substrate by utilizing a hydrogen etching method, and then a structure with a single-layer graphene strip and a buffer layer structure which are alternated is grown on the etched silicon carbide surface. And finally, the original buffer layer structure is converted into a p-type conductive graphene structure through a hydrogen passivation technology, and the original single-layer graphene still keeps an n-type structure. Therefore, periodic pn-junction graphene can be prepared, and the width of the pn-junction graphene can be adjusted by adjusting the width of the step.
One of the technical schemes of the invention is a method for preparing periodic pn junction graphene based on a high-purity semi-insulating silicon carbide substrate, which comprises the following steps:
(1) cutting, grinding and polishing the high-purity semi-insulating 4H-silicon carbide crystal to obtain a high-purity semi-insulating silicon carbide crystal substrate, and cleaning for later use;
(2) placing the crucible containing the silicon carbide wafer substrate prepared in the step (1) in a chamber of a medium-frequency induction heating furnace for vacuum high-temperature impurity removal;
(3) introducing hydrogen into the furnace chamber, and performing hydrogen etching on the silicon surface of the silicon carbide wafer substrate to obtain a hydrogen-etched high-purity semi-insulating silicon carbide substrate, wherein a regular silicon carbide step structure is formed on the surface of the silicon carbide substrate; under proper etching conditions, the atomic step can generate a coalescence effect, so that the Gibbs free energy of the surface is lowest, and a regular silicon carbide step structure is formed on the surface.
(4) Stopping introducing hydrogen, introducing argon, raising the temperature, pyrolyzing silicon carbide, growing the structure of the graphene strip and the buffer layer strip on the surface of the hydrogen-etched high-purity semi-insulating silicon carbide substrate prepared in the step (3) in a full-covering manner, and cooling to room temperature after the growth is finished to obtain a structural sample substrate in which the graphene and the buffer layer are periodically arranged;
(5) and (3) introducing a mixed gas of hydrogen and argon into the furnace chamber, raising the temperature, and passivating the graphene prepared in the step (4) and the structural sample substrate with the buffer layer in periodic arrangement to obtain periodic pn stone graphene.
Preferably, in the step (1), the thickness of the high-purity semi-insulating silicon carbide wafer substrate is 200-600 μm, the polishing roughness is below 0.5nm, and the flatness is below 10 μm.
Preferably, in step (2), the silicon carbide wafer substrate is placed flat in a graphite crucible with the silicon surface facing upward, and then placed in a chamber of a medium frequency induction heating furnace in which the degree of vacuum is (1.0-8.0) × 10-5mbar, rapidly heating to 1250-.
Preferably, in the step (3), high-purity hydrogen is introduced into the furnace chamber, the pressure is controlled at 800mbar at the temperature of 5-10 ℃/min to 1550-.
Preferably, in the step (4), the pressure of 500-.
Preferably, the mixing ratio of hydrogen and argon in the step (5) is 1:3, the pressure in the furnace is controlled at 600-900mbar, the temperature is rapidly raised to 700-1100 ℃ at the speed of 10-20 ℃/min, the temperature is reduced in the mixed gas atmosphere after being kept for 30-60min, the temperature is reduced to be below 500 ℃, then single argon is introduced, and the temperature is naturally reduced to the room temperature, so that the periodic pn stone graphene is obtained.
The second technical scheme of the invention is as follows: the periodic pn-junction graphene prepared by the method is based on the high-purity semi-insulating silicon carbide substrate.
The third technical scheme of the invention is as follows: the periodic pn-stone graphene is applied to the field of information electronic devices.
Preferably, the periodic pn-junction graphene is applied to an enhanced photoelectric detector, a photosensitive element and a logic operation field effect transistor.
The structure of the graphene strip and the buffer layer strip prepared in the step (4) of the invention is fully covered and grown on the hydrogen-etched high-purity semi-insulating silicon carbide substrate, and the passivation process in the step (5) mainly utilizes the following technical principles:
1. the method for preparing graphene by pyrolyzing silicon carbide is characterized in that a first layer of carbon structure growing on a silicon surface is a buffer layer and is not pure graphene. Although the buffer layer has the same atomic arrangement as graphene, 1/3 carbon atoms are covalently bonded to the silicon atoms on the top layer of the underlying silicon carbide substrate. As the growth proceeds, a new buffer layer appears, and the original buffer layer is converted into a first graphene layer;
2. more chemical bonds are exposed at the edge, and less energy is consumed during action, so that the reaction is easier to occur, so that the growth of graphene is preferentially nucleated at the edge of the step and then expands on the step platform, and a graphene strip structure is preferentially formed at the edge of the step;
3. due to the existence of the buffer layer structure, the silicon carbide substrate can generate an electric polarization effect at an interface, so that the graphene on the surface layer is n-type conductive. In the hydrogen passivation process, because the energy required by hydrogen atoms penetrating through a single-layer atom is lower than that required by double-layer atoms, hydrogen gas can preferentially penetrate through the buffer layer structure, and a carbon-silicon bond between the buffer layer and the substrate is opened, so that the buffer layer is changed into a new graphene layer, and the inserted hydrogen atoms can saturate a silicon dangling bond on the surface layer, so that the polarization between interfaces is reversed, and the graphene layer is represented as p-type conduction. By controlling the step morphology of the silicon carbide substrate, the growth condition of the graphene strip and the hydrogen passivation insertion condition, high-quality periodic pn stone graphene can be prepared.
Description of terms:
high-purity semi-insulating silicon carbide: refers to silicon carbide crystal materials with purity above 99.999% and which achieve semi-insulating properties by virtue of their intrinsic structural features without introducing any compensation.
4H-silicon carbide wafer: 4H-silicon carbide is a conventional shorthand expression for 4H-type silicon carbide.
Buffer layer structure: the graphene is a layer of carbon atom structure which grows on the silicon surface of a silicon carbide substrate and has the same hexagonal atomic ring structure as graphene, but one third of carbon atoms are connected with the substrate through carbon-silicon bonds, and if the connected carbon-silicon bonds are completely opened, the graphene can be converted into a new layer of graphene.
Silicon surface: refers to the surface of a silicon carbide substrate terminated with an atomic layer of silicon in the <0001> direction.
High purity hydrogen/argon: refers to high-purity hydrogen/argon gas with the purity of more than 99.999 percent.
Periodic pn-stone graphene: the graphene is a pn junction graphene structure with adjacent p-type regions and n-type regions which are arranged in a periodically repeated manner by one unit.
Electric polarization effect: the dipolar molecule refers to a molecule in which bound charges are asymmetrically distributed, and the centers of positive charges and negative charges are not coincident, so that the molecule itself forms an electric dipole moment (electric moment for short), or an effect called electric dipole.
Compared with the prior art, the invention has the following beneficial effects:
1. the silicon carbide substrate for preparing the periodic pn stone graphene is a high-purity semi-insulating silicon carbide substrate, the influence of doping inside the substrate on the growth of graphene is eliminated, and the high insulating property of the substrate can reduce the negative influence of the substrate on the carrier transport in the graphene, so that the electrical property of the graphene is better exerted.
2. The periodic pn stone graphene prepared by the invention has no doping element introduced into the graphene structure or is embedded with atoms in an ion implantation mode, and the pn junction characteristic is expressed only by the polarization effect of the substrate, so that the structural integrity of the graphene is ensured, and the transmission characteristic of carriers in the graphene is favorably improved.
3. The width of the periodic pn stone graphene prepared by the invention can be freely adjusted, and the width of the step can be adjusted by adjusting the deflection angle of the substrate and the hydrogen etching condition, for example, the width of the step can be reduced along with the increase of the deflection angle of the substrate; the strip width of the graphene can be adjusted by adjusting the growth conditions of the graphene, so that the expected pn junction graphene width can be effectively adjusted.
4. The periodic pn stone graphene prepared by the method has better photoelectric conversion characteristic and electrical transportation performance, and can be widely applied to the fields of information electronic devices such as enhanced photodetectors, photosensitive elements, logic operation field effect transistors and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
Fig. 1 is a schematic diagram of a method for preparing periodic pn-junction graphene by a silicon carbide pyrolysis method in embodiment 1 of the present invention, and the lower schematic diagram is a schematic diagram of a periodic pn-junction graphene structure. The device comprises a high-purity graphite cylinder, a high-purity graphite cover, a high-purity semi-insulating silicon carbide substrate and a high-purity induction coil, wherein the induction coil 1 is an induction coil, the high-purity graphite cylinder 2 is a high-purity graphite cylinder, the high-purity graphite cover 3 is a high-purity graphite cover, and the high-.
Fig. 2 is a scanning electron microscope image of the periodic arrangement of the graphene and the buffer layer in example 1 of the present invention.
Fig. 3 is a raman scan of the periodic arrangement of graphene and the buffer layer in embodiment 1 of the present invention. Wherein fig. 3(a) is a scanning curve diagram of a 2D peak of graphene, and fig. 3(b) is a scanning spatial distribution diagram of 2D peak intensity of graphene.
Fig. 4 is a scanning electron microscope image of the periodic pn junction graphene prepared in example 2 of the present invention.
Fig. 5 is an enhanced raman test spectrum of different positions of periodic pn junction graphene prepared in embodiment 2 of the present invention.
FIG. 6 is a hole of an atomic force microscope image after hydrogen passivation in a pure hydrogen atmosphere in comparative example 1 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The high-temperature furnace for preparing the periodic pn stone graphene is the prior art, and the used high-temperature furnace is a vertical high-temperature furnace generally sold in the market.
The high-purity hydrogen/argon used in the invention is hydrogen/argon with the purity of more than 99.999 percent; the silicon carbide substrate used was a high-purity semi-insulating silicon carbide substrate having a purity of 99.999% or more.
Example 1
(1) Grinding and polishing a piece of 4-inch high-purity semi-insulating 4H-silicon carbide crystal to obtain a high-purity semi-insulating silicon carbide crystal substrate with the thickness of 350 mu m, so that the roughness of the surface of the high-purity semi-insulating silicon carbide crystal substrate is below 0.5nm and the flatness of the high-purity semi-insulating silicon carbide crystal substrate is 10 mu m, and then cleaning and packaging the surface of the high-purity semi-insulating silicon carbide crystal substrate for later use;
(2) and (2) flatly placing the prepared silicon carbide wafer substrate in the step (1) in a graphite crucible, enabling the silicon surface to face upwards, and pressing a graphite cover tightly. Then placing the mixture in a cavity of a medium-frequency induction heating furnace, wherein the vacuum degree in the cavity is 5.0 multiplied by 10-5mbar, rapidly heating to 1300-;
(3) introducing high-purity hydrogen into the furnace chamber, controlling the pressure at 500mbar, continuously raising the temperature to 1550 ℃, performing hydrogen etching on the silicon surface of the silicon carbide wafer substrate for 10min, forming a regular silicon carbide step structure on the surface, and cooling to room temperature to obtain a hydrogen-etched high-purity semi-insulating silicon carbide substrate;
(4) stopping introducing hydrogen, changing to introducing high-purity argon, heating the furnace chamber to 1650 ℃, preserving the temperature for 20min, completing the structure full-coverage growth of the graphene strip and the buffer layer strip, and cooling to room temperature at a cooling speed of 25 ℃/min after the growth is completed to obtain a structure sample substrate in which the graphene and the buffer layer are periodically arranged;
(5) and (3) carrying out hydrogen passivation treatment on the graphene obtained in the step (4) and the sample with the buffer layer periodically arranged, introducing mixed gas of hydrogen and argon (the volume mixing ratio is 1:3) into the furnace chamber, controlling the pressure at 900mbar, rapidly heating to 850 ℃, and carrying out passivation for 30min to complete the insertion of hydrogen atoms. And after the insertion is finished, reducing the temperature to be below 500 ℃ in the mixed gas atmosphere, then introducing single argon gas, and naturally cooling to room temperature to obtain a complete periodic pn stone graphene sample.
As shown in fig. 2, a scanning electron microscope image of the periodically arranged graphene and the buffer layer prepared in the embodiment shows that the width of the graphene is 2-4 μm, and the width of the buffer layer is 2-4 μm, wherein a dark black region is a single-layer graphene structure and shows n-type conductivity; the bright white region is a buffer layer structure and exhibits an insulating property. Fig. 3 shows a corresponding raman scan distribution diagram, where fig. 3(a) is a scan graph of a graphene 2D peak, and fig. 3(b) is a scan spatial distribution diagram of graphene 2D peak intensity. As can be seen from the figure, the bright white region in fig. 3(b) is a region with a stronger 2D peak corresponding to single-layer graphene, and the dark black region in fig. 3(b) is a region without 2D peak intensity corresponding to the buffer layer structure; according to the distribution of the 2D peak intensity, the distribution condition of the graphene strips can be seen to correspond to the scanning electron microscope image. The prepared periodic pn junction graphene has a complete structure, the width of a p-type region is 2-4 mu m, the width of an n-type region is 2-4 mu m, and the whole periodic width is 5-8 mu m.
Example 2
(1) Grinding and polishing a piece of 4-inch high-purity semi-insulating 4H-silicon carbide crystal to obtain a high-purity semi-insulating silicon carbide crystal substrate with the thickness of 350 mu m, so that the roughness of the surface of the high-purity semi-insulating silicon carbide crystal substrate is below 0.5nm and the flatness of the high-purity semi-insulating silicon carbide crystal substrate is 10 mu m, and then cleaning and packaging the surface of the high-purity semi-insulating silicon carbide crystal substrate for later use;
(2) and (2) flatly placing the prepared silicon carbide wafer substrate in the step (1) in a graphite crucible, enabling the silicon surface to face upwards, and pressing a graphite cover tightly. Then placing the mixture in a cavity of a medium-frequency induction heating furnace, wherein the vacuum degree in the cavity is 5.0 multiplied by 10-5mbar, rapidly heating to 1300-;
(3) introducing high-purity hydrogen into the furnace chamber, controlling the pressure at 500mbar, continuously raising the temperature to 1550 ℃, performing hydrogen etching on the silicon surface of the silicon carbide wafer substrate for 40min, forming a regular silicon carbide step structure on the surface, and cooling to room temperature to obtain a hydrogen-etched high-purity semi-insulating silicon carbide substrate;
(4) stopping introducing hydrogen, changing into introducing argon, heating the furnace chamber to 1650 ℃, preserving the temperature for 20min, completing the structure full-coverage growth of the graphene strip and the buffer layer strip, and cooling to room temperature at a cooling speed of 25 ℃/min after the growth is completed to obtain a structure sample substrate in which the graphene and the buffer layer are periodically arranged;
(5) and (3) carrying out hydrogen passivation treatment on the graphene obtained in the step (4) and the sample with the buffer layer periodically arranged, introducing mixed gas of hydrogen and argon (the mixing ratio is 1:3) into the furnace chamber, controlling the pressure at 900mbar, rapidly heating to 850 ℃, and passivating for 30min to complete the insertion of hydrogen atoms. And after the insertion is finished, reducing the temperature to be below 500 ℃ in the mixed gas atmosphere, then introducing single argon gas, and naturally cooling to room temperature to obtain a complete periodic pn stone graphene sample.
The scanning electron microscope image of the periodically arranged pn-junction graphene prepared in this example is shown in fig. 4, where a relatively bright place is an original single-layer graphene region at a step edge, and a darker place is a graphene region after a buffer layer on a platform is converted, and it can be seen that the periodic pn-junction graphene has a complete structure. After the hydrogen etching time is increased, the whole width of the step is widened, the width of a p-type region of the prepared graphene is expanded to 12-15 mu m, the condition of the graphene is kept unchanged, the width of an n-type region is still 2-4 mu m, and the whole period width is 15-20 mu m, which shows that the hydrogen etching is adjustedThe step width can be adjusted. To verify whether the buffer layer was converted to graphene, we performed an enhanced raman spectroscopy test on the buffer layer, the test result is shown in fig. 5, where 2130cm of graphene marked on the platform is clearly visible by the test point-1There is a peak of silicon-hydrogen bonds, while graphene hitting the edge of the step has no peak of silicon-hydrogen bonds. This indicates that after the hydrogen passivation treatment, only the exposed buffer layer structure is transformed, the underlying silicon bond is saturated by the inserted hydrogen atoms, and the original graphene still maintains the original structure, which indicates that the hydrogen atoms have saturated the silicon dangling bond under the graphene, and the electric polarization direction has been transformed, so that the graphene can show p-type conductivity.
Example 3
(1) Grinding and polishing a piece of 4-inch high-purity semi-insulating 4H-silicon carbide crystal to obtain a high-purity semi-insulating silicon carbide crystal substrate with the thickness of 350 mu m, so that the roughness of the surface of the high-purity semi-insulating silicon carbide crystal substrate is below 0.5nm and the flatness of the high-purity semi-insulating silicon carbide crystal substrate is 10 mu m, and then cleaning and packaging the surface of the high-purity semi-insulating silicon carbide crystal substrate for later use;
(2) and (2) flatly placing the prepared silicon carbide wafer substrate in the step (1) in a graphite crucible, enabling the silicon surface to face upwards, and pressing a graphite cover tightly. Then placing the mixture in a cavity of a medium-frequency induction heating furnace, wherein the vacuum degree in the cavity is 5.0 multiplied by 10-5mbar, rapidly heating to 1300-;
(3) introducing high-purity hydrogen into the furnace chamber, controlling the pressure at 500mbar, continuously raising the temperature to 1550 ℃, performing hydrogen etching on the silicon surface of the silicon carbide wafer substrate for 40min, forming a regular silicon carbide step structure on the surface, and cooling to room temperature to obtain a hydrogen-etched high-purity semi-insulating silicon carbide substrate;
(4) stopping introducing hydrogen, changing into introducing argon, heating the furnace chamber to 1650 ℃, preserving the temperature for 50min, completing the structure full-coverage growth of the graphene strip and the buffer layer strip, and cooling to room temperature at a cooling speed of 25 ℃/min after the growth is completed to obtain a structure sample substrate in which the graphene and the buffer layer are periodically arranged;
(5) and (3) carrying out hydrogen passivation treatment on the graphene obtained in the step (4) and the sample with the buffer layer periodically arranged, introducing mixed gas of hydrogen and argon (the mixing ratio is 1:3) into the furnace chamber, controlling the pressure at 900mbar, rapidly heating to 850 ℃, and passivating for 30min to complete the insertion of hydrogen atoms. And after the insertion is finished, reducing the temperature to be below 500 ℃ in the mixed gas atmosphere, then introducing single argon gas, and naturally cooling to room temperature to obtain a complete periodic pn stone graphene sample.
The width of the p-type region of the periodically arranged pn-junction graphene prepared in this example is 7-12 μm, the width of the n-type graphene region is 8-13 μm, and the overall period width is 15-20 μm, which indicates that the graphene stripe width can be adjusted by adjusting the graphene growth time.
Comparative example 1
The preparation method is the same as that of example 1, except that: and 5, changing the mixed gas of hydrogen and argon in the hydrogen passivation treatment step into single hydrogen.
The height distribution diagram of the periodic pn stone graphene atomic force microscope prepared by the comparative example is shown in fig. 6, and due to the excessively high hydrogen ratio value, the hydrogen generates an etching effect on the graphene on the surface layer, and a plurality of hexagonal etching pits are generated.
Comparative example 2
The preparation method is the same as that of example 1, except that: step 5 the passivation temperature was raised to 1200 c during the hydrogen passivation treatment step.
The periodic pn-junction graphene prepared by the comparative example fails, and the surface layer graphene is completely converted into p-type conduction, because the excessive temperature can provide high energy for hydrogen atoms to penetrate through the single-layer graphene and a transition layer. Therefore, hydrogen atoms are inserted into the lower surface of the entire graphene, and all the graphene exhibits p-type conductivity.
And because passivation requires certain energy, when the temperature is lower than 700 ℃, passivation reaction does not occur.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, are used only for convenience of description of the present invention, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims (9)

1. A method for preparing periodic pn junction graphene based on a high-purity semi-insulating silicon carbide substrate is characterized by comprising the following steps: the method comprises the following steps:
(1) cutting, grinding and polishing the high-purity semi-insulating 4H-silicon carbide crystal to obtain a high-purity semi-insulating silicon carbide crystal substrate, and cleaning for later use;
(2) placing the crucible containing the silicon carbide wafer substrate prepared in the step (1) in a chamber of a medium-frequency induction heating furnace for vacuum high-temperature impurity removal;
(3) introducing hydrogen into the furnace chamber, and performing hydrogen etching on the silicon surface of the silicon carbide wafer substrate to obtain a hydrogen-etched high-purity semi-insulating silicon carbide substrate, wherein a regular silicon carbide step structure is formed on the surface of the silicon carbide substrate;
(4) stopping introducing hydrogen, introducing argon, raising the temperature, enabling the structure of the graphene strip and the buffer layer strip to fully cover and grow on the surface of the hydrogen-etched high-purity semi-insulating silicon carbide substrate prepared in the step (3), and cooling to room temperature after the growth is completed to obtain a structural sample substrate with periodically arranged graphene and buffer layers;
(5) and (3) introducing a mixed gas of hydrogen and argon into the furnace chamber, raising the temperature, and passivating the graphene prepared in the step (4) and the structural sample substrate with the buffer layer in periodic arrangement to obtain periodic pn stone graphene.
2. The method for preparing the periodic pn-junction graphene based on the high-purity semi-insulating silicon carbide substrate as claimed in claim 1, wherein in the step (1), the thickness of the high-purity semi-insulating silicon carbide wafer substrate is 200-600 μm, the roughness of polishing is below 0.5nm, and the flatness is below 10 μm.
3. The method for preparing periodic pn-junction graphene based on high-purity semi-insulating silicon carbide substrate as claimed in claim 1, wherein in the step (2), the silicon carbide wafer substrate is placed in a graphite crucible with the silicon surface facing upwards, and then placed in a chamber of a medium-frequency induction heating furnace, wherein the vacuum degree in the chamber is (1.0-8.0) x 10-5mbar, rapidly heating to 1250-.
4. The method for preparing periodic pn junction graphene based on the high-purity semi-insulating silicon carbide substrate as claimed in claim 1, wherein in the step (3), high-purity hydrogen is introduced into the furnace chamber, the pressure is controlled at 800mbar, the temperature is increased to 1650 ℃ at 5-10 ℃/min, the silicon surface of the silicon carbide substrate is subjected to hydrogen etching for 10-60min, a regular silicon carbide step structure is formed on the surface, and the temperature is reduced to room temperature, so as to obtain the hydrogen-etched high-purity semi-insulating silicon carbide substrate.
5. The method for preparing periodic pn junction graphene based on the high-purity semi-insulating silicon carbide substrate as claimed in claim 1, wherein in the step (4), the pressure of 500-.
6. The method for preparing periodic pn junction graphene based on the high-purity semi-insulating silicon carbide substrate as claimed in claim 1, wherein the mixing ratio of hydrogen and argon in step (5) is 1:3, the pressure in the furnace is controlled at 600-900mbar, the temperature is rapidly raised to 700-1100 ℃ at a speed of 10-20 ℃/min, the temperature is reduced in the mixed gas atmosphere after being maintained for 30-60min, the temperature is reduced to below 500 ℃, then single argon is introduced, and the temperature is naturally reduced to room temperature, so that the periodic pn junction graphene is obtained.
7. A periodic pn-stone graphene prepared according to the method of any one of claims 1-6.
8. Use of the periodic pn-junction graphene according to claim 7 in the field of information electronics.
9. The periodic pn-junction graphene as claimed in claim 8, wherein the periodic pn-junction graphene is applied to enhancement type photoelectric detectors, photosensitive elements and logic operation field effect transistors.
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