KR102401334B1 - A method for bandgap engineering of diamond by hybridization with graphene - Google Patents

Abstract

The present invention is a method for controlling the band gap of diamond by controlling the length of graphene formed on diamond, the surface of which is converted into graphene by a predetermined thickness using the steps of preparing a diamond base material and high-density hydrogen plasma There is provided a method for controlling a bandgap of diamond, including a treatment step, and controlling the bandgap of diamond to 3 eV or less by adjusting the length of the graphene.

Description

A method for controlling the bandgap of diamond by hybridization with graphene {A method for bandgap engineering of diamond by hybridization with graphene}

The present invention relates to a next-generation semiconductor material, and more particularly, to a method for controlling a bandgap of diamond by hybridization with graphene.

Although diamond is an insulator with a band gap of 5.45 eV, it has the highest thermal conductivity among existing materials (7.5 and 3.5 times higher than that of GaN and SiC, respectively). can be used as In this case, it is possible to realize not only high output (~ 100 W/cm ³ ) but also low power consumption and miniaturization of electronic devices. In addition, diamond is expected to be an extreme semiconductor that can be used in outer space and nuclear power plants because of its radiation resistance (106~109 Gy) and high temperature stability (~500 ℃) characteristics.

High-temperature and high-pressure method (at 50,000 atmospheres, about 1400°C, high-temperature and high-pressure diamonds are single-crystals with a maximum size of 1x1 cm ² , but since the synthesis process is exposed to the atmosphere, nitrogen in the atmosphere is contained inside the diamond as an electronic material. use is not allowed

In the 1980s, with the development of a vapor phase chemical vapor deposition (CVD) diamond synthesis method that synthesizes diamond by decomposing the gas with heat and plasma using methane gas as a raw material, 'diamond electronics' using diamond as an electronic device substrate 'The possibility of the coming of the era was high.

However, single crystal growth by the CVD method is manufactured using high temperature and high pressure single crystal diamond as a seed, and the size of 1x1 cm ² is limited by the current technology. On the other hand, polycrystalline CVD diamond can be manufactured with a diameter of 4", but there is a problem of low mobility due to polycrystalline nature.

In order for diamond, which is an insulator, to be used as an electronic device, the bandgap must be controlled as in the case of silicon. As a method of controlling the band gap of diamond, research has been conducted to imitate the case of silicon and doping the diamond with boron (B) or nitrogen (N). However, since diamond has strong interatomic bonding force, impurity doping is difficult, and when doping with boron or nitrogen, the plasma environment is changed to deteriorate the crystallinity of diamond. This is the main reason that diamond electronic device has not yet been realized.

The present invention is to solve the problems of the prior art, and to provide a method for controlling the band gap of diamond by adjusting the length of graphene formed on the diamond. However, these problems are exemplary, and the scope of the present invention is not limited thereto.

According to one aspect of the present invention, comprising the steps of preparing a diamond base material and a surface treatment step of converting the surface of the diamond base material to graphene by a certain thickness using high-density hydrogen plasma, and adjusting the graphene length to form a diamond band Provided is a method for controlling a bandgap of diamond that controls the gap to 3 eV or less.

In one embodiment of the present invention, the surface treatment step may be performed by hydrogen plasma treatment.

In an embodiment of the present invention, the hydrogen plasma treatment may be performed in a temperature region where diamond is stable.

In one embodiment of the present invention, the surface treatment step may be performed by laser treatment.

In one embodiment of the present invention, the laser treatment may be performed in a hydrogen gas atmosphere in a vacuum vessel.

In one embodiment of the present invention, the diamond base material may be a single crystal or a polycrystalline.

In one embodiment of the present invention, as the graphene length increases, the band gap of diamond may decrease.

In one embodiment of the present invention, the surface treatment step may include (a) growing the graphene to an effective length or longer, and (b) grinding the graphene to an effective length.

In one embodiment of the present invention, the effective length may be 0.3 to 1.4 nm.

In one embodiment of the present invention, the polishing step may be performed by any one or more methods of a chemical method, a mechanical method, and a plasma etching method.

According to an embodiment of the present invention made as described above, the electronic device of diamond may be possible by controlling the band gap of diamond by precisely adjusting the length of the graphene layer to the nano level. Of course, the scope of the present invention is not limited by these effects.

1 shows a structure in which graphene is formed from the surface of a diamond base material and its density of state (DOS) according to an embodiment of the present invention.
Figure 2 shows the change in the band gap according to the graphene length of the hybrid structure according to the embodiment of the present invention.
3 shows the surface AFM image and SEM photograph of the graphene-diamond hybrid structure prepared according to an embodiment of the present invention.
4 shows a PL curve obtained from a hybrid structure prepared according to an embodiment of the present invention.
5 shows the results of XRD analysis of a hybrid structure prepared according to an embodiment of the present invention.
6 is an AFM image obtained after rubbing the graphene surface of the hybrid structure prepared according to an embodiment of the present invention on sandpaper.
7 is a laser device for manufacturing a hybrid structure according to an embodiment of the present invention.
8 is a schematic diagram illustrating a method for manufacturing a hybrid structure using a laser according to an embodiment of the present invention.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. Examples of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, and the scope of the present invention is as follows It is not limited to an Example. Rather, these embodiments are provided so as to more fully and complete the present disclosure, and to fully convey the spirit of the present invention to those skilled in the art. In addition, in the drawings, the thickness or size of each layer is exaggerated for convenience and clarity of description.

The diamond bandgap control method according to an embodiment of the present invention may be achieved by etching the diamond base material surface using high-density hydrogen plasma to convert a certain thickness of the diamond surface into graphene. As the high-density plasma, a general thermal plasma for CVD diamond synthesis or a laser may be used.

In one embodiment of the present invention, both single crystal and polycrystal may be used as the diamond base material, and may have a powder, film, or plate shape. In one embodiment, HPHT single crystal diamond, CVD single crystal diamond, CVD polycrystalline diamond, or diamond deposited in the form of a thin film on a heterogeneous substrate may be used. The surface of the diamond base material is preferably mirror polished.

In one embodiment of the present invention, the {111} lattice plane cut off from the surface of the diamond base material may be converted into graphene using high-density hydrogen plasma. Two diamond {111} lattice planes can be converted into one graphene. Graphene can be formed vertically on the {111} lattice plane cut off from the diamond surface. Thus, the graphene-diamond hybrid structure according to the embodiment of the present invention may be formed.

Bandgap Control by Thermal Plasma for Diamond Synthesis

In one embodiment of the present invention, the diamond surface may be converted into graphene by a certain thickness by using a plasma apparatus for CVD diamond synthesis. The plasma apparatus for synthesizing diamond may be microwave plasma or DC power plasma. Graphene may be formed on the diamond {111} lattice plane, which is the base material, by 'hydrogen plasma' generated using hydrogen gas in the device. When hydrogen plasma is used, there is an advantage that graphene can be formed as a whole on the diamond base material.

The hydrogen plasma treatment may be performed in a temperature region where diamond is stable. It may be made at a temperature higher than about 800 to 1000° C., which is a typical CVD diamond synthesis temperature. Preferably, it can be carried out at about 1000 ~ 1500 ℃. When the diamond is subjected to hydrogen plasma treatment in a stable temperature region, the sp ² graphite phase is unstable and graphene may be etched. In this way, the length of the graphene layer can be more precisely controlled, and the band gap of diamond can be controlled. In the hydrogen plasma treatment, the pressure and the gas flow rate may be the same as the normal CVD diamond synthesis conditions.

Bandgap control by laser processing of diamonds

In one embodiment of the present invention, a graphene-diamond hybrid structure may be formed using a laser. The laser treatment may be performed in a vacuum vessel capable of maintaining a hydrogen gas atmosphere. A sight glass through which a laser beam passes, a stage on which a sample is placed, and a port for supplying hydrogen gas may be installed in the vacuum container. In this case, the diamond base material is charged on the stage in the vacuum container, the container is brought to a certain vacuum state, hydrogen gas is introduced to maintain a certain pressure, and graphene is produced by irradiating the surface of the diamond base material with a laser through a sight glass. can be formed. When a surface treatment method using a laser is used, graphene can be locally formed on the diamond base material. For example, graphene may be formed in the form of dots, lines, planes, and complexes thereof.

Hereinafter, experimental examples to help the understanding of the present invention will be described. This experimental example is provided to help the understanding of the present invention, and it goes without saying that the present invention is not limited to the present experimental example.

<Example 1>

The band gap of the graphene-diamond hybrid structure was predicted by the simulation technique. 1 (a) shows an atomic model diagram of a graphene-diamond hybrid structure, and FIG. 1 (b) shows a density of state (DOS). As shown in FIG. 1 , the hybrid structure (graphene length of about 0.7 nm) exhibited a band gap of about 1.1 eV.

2 is a graph showing the bandgap change according to the length of the graphene using a simulation technique. The band gap of 5,45 eV of diamond gradually decreases as the graphene length of the hybrid structure according to an embodiment of the present invention increases, and decreases to the values of AA and AA' graphite at 1.4 nm (0.5 and 0.3 eV, respectively). can be known This result shows that the bandgap can be controlled by changing the length of graphene. In particular, it can be seen that when the graphene length is controlled to 0.3 to 1.4 nm (effective length), the band gap of diamond can be controlled to 0.3 to 2 eV. On the other hand, since the diamond bandgap of 5.45 eV was low as about 4.5 eV in this simulation, it is expected to be larger than the bandgap value shown in FIG. 2 in actual measurement.

<Example 2>

A polycrystalline CVD diamond plate (10×10×0.5mm ³ ) polished to a mirror surface on one side is charged into a DC-powered plasma CVD diamond synthesis device, a vacuum is drawn with 2×10 ^-3 Torr, and hydrogen gas is supplied to power on. Plasma was formed. Hydrogen plasma treatment was performed for 10 minutes while maintaining the diamond plate temperature at 1300°C at a pressure of 100 Torr.

3 shows (A) the sample treated as described above, (B) a photograph of the sample observed with an atomic force microscope (AFM), and (C) a scanning electron microscope (SEM) photograph. In the AFM analysis, the length of the graphene layer was about 1 nm. Several patterns shown in the SEM picture show hybrid structuring. The pattern appearing in the SEM picture is due to the non-uniformity of the graphene layer according to the non-uniformity of diamond (twin and grain boundaries).

4 is a result of analyzing the sample with a PL (Photoluminance) device. As shown in FIG. 4 , in the hybrid structure, it can be confirmed that a band gap of about 2.8 eV (a value greater than the simulated value of about 1.8 eV) was formed.

5 is a result of XRD analysis of the sample. 5(a) shows a (110) peak (2θ=22.9°) of stacked graphene along with a diamond (111) peak (2θ=43.8°) and a (220) peak (2θ=75.4°). This shows that AA stacked graphene with an interplanar distance of about 3.9 Å was epitaxially bonded to the diamond base material. 5 (b) is a rocking curve XRD analysis result of this sample. It was confirmed that graphene was oriented at a 60° angle to the diamond surface (ie, (110) plane).

<Example 3>

Treatment was performed in the same manner as in Example 2, except that hydrogen plasma treatment was performed for 1 minute. A scanning electron microscope (SEM) photograph of the treated sample was shown. It was formed showing various patterns on the diamond surface. As a result of AFM analysis, the length of the graphene layer was about 3 nm. As a result of analyzing the sample with a PL (Photoluminance) device, the bandgap was found to be 1.5 eV.

<Example 4>

A 5×5×1 mm ³ single-crystal diamond plate was used as a base material, and plasma treatment was performed under the same conditions as in Example 1 (provided that the substrate temperature was 1320° C. for 30 seconds).

As a result of analyzing the plasma-treated sample by AFM, it was confirmed that a graphene layer with a length of 3 nm or less was formed on the surface of the diamond base material. The band gap of this sample was 1.4 eV.

<Example 5>

Using a 10×10×0.5 mm ³ polycrystalline diamond plate as a base material, plasma treatment was performed under the same conditions as in Example 1 (provided that the substrate temperature was 1350° C. for 2 minutes).

As a result of analyzing the plasma-treated sample by AFM, it was confirmed that a graphene layer with a length of about 10 nm was formed on the diamond surface. To reduce the length of the graphene layer of this sample, the graphene surface was rubbed with silicon carbide sandpaper. As a result of analyzing the graphene surface by AFM, as shown in FIG. 6 , the graphene length was reduced to several nm. The irregular thickness distribution is due to hand rubbing. This result shows that the graphene length can be controlled to the effective length by a polishing process (mechanical, chemical and plasma etching) after growing graphene longer than the effective length.

<Example 6>

A polycrystalline CVD diamond plate (10×10×0.5 mm ³ ) whose upper surface is mirror-polished is placed on a support in a vacuum container, and vacuum is drawn with 2×10 ^-3 Torr, then hydrogen gas is added to make it 300 Torr, and then vacuum The laser was irradiated and scanned into the upper surface of the diamond plate through the vessel sight. 7 shows a state of laser processing in a hydrogen gas atmosphere in a vacuum container. As a result of analyzing the sample with a photo-luminance (PL) device, a band gap was formed. 8 shows the hybrid structuring step by laser treatment. When a surface treatment method using a laser is used, graphene may be formed in the form of dots, lines, planes, and complexes thereof on the diamond base material.

<Example 7>

Using a polycrystalline CVD diamond film (10×10×0.5 mm ³ ) having a polished <110> texture as a base material, it was maintained at about 1400° C. in a vacuum furnace (vacuum furnace without plasma) in a hydrogen atmosphere for 10 minutes. It was heat-treated.

As a result of analyzing the heat-treated sample by HRTEM, the thickness of the AA graphene layer was several nm, and a 2:1 conversion relationship between the diamond {111} lattice plane and graphene was confirmed. Thus, an AA stacked graphene-diamond hybrid film could be obtained.

<Example 8>

A polycrystalline CVD diamond film (10×10×0.5 mm ³ ) having a polished <110> texture was used as a base material, and laser treatment was performed in a hydrogen atmosphere in a vacuum furnace equipped with a laser device. The scan speed of the laser beam was maintained at 1 mm/min.

As a result of analyzing the trajectory of the laser beam with HRTEM, the AA graphene layer was confirmed.

Although the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

Claims (10)

Preparing a diamond base material with a mirror-polished surface; and
a surface treatment step of converting the surface of the diamond base material into graphene by a predetermined thickness using high-density hydrogen plasma;
including,
By adjusting the graphene length, the band gap of diamond is controlled to 3 eV or less,
The surface treatment step is
(a) growing the graphene to an effective length or longer; and
(b) polishing by removing at least a portion of the graphene within an effective length;
The polishing step is
carried out by way of plasma etching,
A method of controlling the bandgap of diamond. The method of claim 1,
The surface treatment step is
performed by thermal plasma treatment for CVD diamond synthesis,
A method of controlling the bandgap of diamond. 3. The method of claim 2,
The thermal plasma treatment for CVD diamond synthesis,
Diamond is performed in a stable temperature region,
A method of controlling the bandgap of diamond. The method of claim 1,
The surface treatment step is
performed by laser processing,
A method of controlling the bandgap of diamond. 5. The method of claim 4,
The laser treatment is
carried out in a hydrogen gas atmosphere in a vacuum vessel,
A method of controlling the bandgap of diamond. The method of claim 1,
The diamond base material is
monocrystalline or polycrystalline;
A method of controlling the bandgap of diamond. The method of claim 1,
As the graphene length increases, the band gap of diamond decreases,
A method of controlling the bandgap of diamond. delete The method of claim 1,
wherein the effective length is 0.3 to 1.4 nm;
A method of controlling the bandgap of diamond. delete

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