High-conductivity and high-mobility n-type diamond thin film and preparation method thereof

Abstract

The present invention discloses a high electrical conductivity and high mobility n-type diamond film and a preparation method thereof. In this method, tantalum atoms entering the film during chemical vapor deposition are doped at the nanoscale interface. This doping method is different from the traditional lattice substitution doping, which well solves the problem of n-type doping in diamond and also provides a new way to solve the doping problems of other wide-bandgap materials.

Description

(1) Technical Field

[0001] The present invention relates to a high - conductivity and high - mobility n - type close - packed nanodiamond film and a preparation method thereof. (2) Background Art

[0002] Diamond has many excellent physical properties such as a wide bandgap, high carrier mobility, and high thermal conductivity. Therefore, it has extremely high application value in electronic devices, especially those used in high - temperature and harsh environments. However, the preparation of n - type conductive diamond is very difficult, which greatly hinders the realization of pn - junctions with good performance. Based on the traditional single - crystal silicon lattice replacement doping theory, researchers have studied various dopants, including nitrogen, sulfur, and phosphorus - doped single - crystal or polycrystalline diamond, but the obtained n - type conductive performance still does not meet the requirements of device development. This indicates that for wide - bandgap materials such as diamond, it is necessary to explore other doping methods and dopants, and even develop doping theories different from the single - crystal silicon system to solve this problem.

[0003] Compared with single - crystal and micro - crystal diamond, the small - size effect and surface effect of nanocrystalline diamond endow it with unique advantages in n - type doping. However, traditional nanodiamond films contain a large amount of amorphous carbon or nanographite, which reduces the conductivity of the film. We developed a new - structure nanodiamond film in CN 201810245815.4, in which nanoscale diamond particles are closely packed with each other without amorphous carbon or nanographite, forming a large number of interfaces between nanoscale diamond grains, called close - packed nanocrystalline diamond films, and achieving a relatively high n - type carrier mobility (generally 100 - 300 cm 2 V -1 S -1 or so). In the patent CN 201810247215.1, we further improved the carrier mobility of the film (generally reaching 400 cm 2 V -1 S -1 or more) by sulfur - ion or oxygen - ion implantation doping of the grain - close - packed nanodiamond film. Although the ion - implanted close - packed nanocrystalline diamond film exhibits good conductivity and mobility, the bombardment of high - energy impurity ions damages the diamond crystal structure. In addition, the complexity of the implantation equipment also leads to the complexity of the corresponding process. Secondly, although interfaces in contact with each other have been formed between the grains of the close - packed nanocrystalline diamond film, the mismatch in the orientation between the grains results in large - angle grain - boundary scattering, which reduces the carrier mobility. (3) Summary of the Invention

[0004] To address these problems, the present invention performs high-temperature annealing on the prepared close-packed nanocrystalline diamond film to adjust and optimize the grain orientation, forming interfaces with more regular structures such as twin boundaries and stacking faults between different grains; and tantalum atoms entering the film during the chemical vapor deposition process are doped at the interfaces under the drive of annealing, providing high conductivity and a mobility as high as 959 cm 2 V -1 s -1 . That is, tantalum atoms are not doped into lattice substitution sites but are incorporated into the interface region of the close-packed nanocrystalline diamond film. The size of this interface is on the nanoscale, so we call it nano-interface doping. This doping method is different from traditional lattice substitution doping, which well solves the problem of n-type doping in diamond and also provides a new way to solve the doping problems of other wide-bandgap materials.

[0005] The technical solution adopted by the present invention is as follows:

[0006] The present invention provides a high-conductivity and high-mobility n-type diamond film, and the high-conductivity and high-mobility n-type diamond film is prepared by the following method:

[0007] (1) Spin-coating solution preparation: Diamond powder with a particle size of 3 nm - 1 μm (preferably 3 - 50 nm), an adhesive, and an activator are uniformly dispersed in an organic solvent to obtain a spin-coating solution; the mass ratio of the diamond powder to the activator is 100:5 - 10 (preferably 100:6); the volume of the organic solvent is 0.3 - 0.5 mL / mg based on the mass of the diamond powder (preferably 0.35 - 0.4 mL / mg, particularly preferably 0.38 mL / mg); the volume ratio of the adhesive to the organic solvent is 1:20 - 40 (preferably 1:38); the activator is one or a mixture of more than two of cetyltrimethylammonium bromide, polydiallyldimethylammonium chloride, glycidol, and octadecyldimethylbenzylammonium chloride;

[0008] (2) Spin-coating of seed crystals: Spin-coat the spin-coating solution described in step (1) on the surface of a single-crystalline silicon wafer. The spin-coating includes 15 - 20 cycles (preferably 20 cycles), and each cycle is spin-coated at 1000 rpm for 10 s and then at 3000 rpm for 30 s; a silicon wafer with a dense layer of seed crystals coated on its surface is obtained;

[0009] (3) Heat treatment: Place the silicon wafer with a dense layer of seed crystals coated on its surface described in step (2) in a tube furnace and perform heat treatment at 500 - 800 °C for 8 - 20 min (preferably heat treatment at 700 °C for 10 min) in an argon protective atmosphere to obtain a heat-treated silicon wafer;

[0010] (4) Use the heat-treated silicon wafer described in step (3) as a substrate, use acetone as a carbon source, and use tantalum wire as a heat source and doping source to perform hot filament chemical vapor deposition; obtain a close-packed nanodiamond film;

[0011] (5) Anneal the close-packed nanodiamond film described in step (4) at a temperature of 900 - 1000 °C for 30 min to obtain the high-conductivity and high-mobility n-type diamond film.

[0012] Further, the diamond powder described in step (1) is generally nanodiamond powder, which are W3 diamond powders (120,000 mesh, particle size of ~36 nm, prepared by crushing method) in the embodiments of the present invention.

[0013] Further, for convenient dispersion and to prevent agglomeration, the adhesive and the surfactant described in step (1) are first dispersed in an organic solvent separately and then mixed.

[0014] Further, the adhesive described in step (1) is one or a mixture of two or more of polyvinyl alcohol, epoxy resin, and polyvinyl acetate, and is epoxy resin in an embodiment of the present invention.

[0015] Further, the surfactant described in step (1) is cetyltrimethylammonium bromide. The surfactant selected in the present invention simultaneously meets two requirements required by the technical solution: 1. It can adsorb on the surface of diamond particles through surfactant molecules, and cause repulsion between the same polarities through the same terminal groups, so as to achieve the purpose of preventing agglomeration of nanodiamond particles; 2. It has poor thermal stability and can decompose and volatilize during subsequent heat treatment.

[0016] Further, the organic solvent described in step (1) is one or a mixed solvent of two or more of dimethyl sulfoxide, acetone, and ethyl lactate, and is acetone in an embodiment of the present invention. The organic solvent selected in the present invention simultaneously meets three requirements required by the technical solution: 1. It has good compatibility with the surfactant and the binder; 2. It can ensure the activity of the surfactant; 3. Finally, it should be completely removed after heat treatment.

[0017] Further, the single-crystalline silicon wafer described in step (2) was also pretreated as follows before spin coating:

[0018] Cut into 20×20 mm size, place it in acetone for ultrasonic cleaning (10 min), and dry it with a nitrogen gun.

[0019] Specifically, the hot filament chemical vapor deposition in step (4) is operated as follows: The acetone is bubbled into the reaction chamber of the hot filament chemical vapor deposition equipment by hydrogen with a flow rate of 60 - 100 sccm (preferably 80 sccm). Meanwhile, pure hydrogen with a flow rate of 100 - 300 sccm (preferably 200 sccm) is also introduced. The growth power is 1800 - 2400 W (preferably 2200 W), the growth pressure is controlled at 1.8 - 2.0 KPa (preferably 2.0 KPa), the growth time is 45 - 60 min (preferably 60 min), and the substrate temperature is maintained at 600 - 700 °C (650 °C in an embodiment of the present invention). After the growth is completed, the carbon source is stopped being introduced, and the power is reduced to 0 at a rate of 1 V / min in a pure hydrogen atmosphere to obtain the closely packed nanodiamond film. The obtained film has a grain size of 10 - 30 nm, and the grains are closely packed to form an interface, with a very low amorphous carbon content.

[0020] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: 1. There is no need to adopt the ion implantation process, and only annealing can greatly improve the n-type conductivity and mobility of the closely packed nanodiamond film, with simple operation; 2. The transition metal element Ta is doped in the interface, developing a new interface doping method different from the doping of single-crystal silicon lattice, which well solves the problem of n-type doping in diamond and also provides a new way to solve the doping problem for other wide-bandgap materials; 3. The film has high n-type conductivity and mobility, which has very important scientific significance and engineering value for realizing its application in the field of semiconductor devices. (IV) BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a field emission electron microscope (FESEM) image of sample W3 - 2.0A900 after vacuum annealing treatment at 900 °C in Example 1 at 50000 times magnification.

[0022] Figure 2 It is a high-resolution transmission electron microscope (HRTEM) image of sample W3 - 2.0A900 after vacuum annealing treatment at 900 °C in Example 1. The inset is the selected area electron diffraction image (SAED) corresponding to this area.

[0023] Figure 3 It is a spherical aberration corrected scanning transmission electron microscopy (AC-STEM) image of sample W3 - 2.0A900 after vacuum annealing treatment at 900 °C in Example 1. The position of the interface is within the white frame, and tantalum atoms are marked with red circles; (a) is a low-magnification AC-STEM image of sample A - 900, and (b), (c) are bright-field images and dark-field images corresponding to the selected area 1 in (a), respectively. (d), (e) are bright-field images and dark-field images corresponding to the selected area 2 in (a), respectively.

[0024] Figure 4 The high-angle annular dark-field (HADDF) image of sample W3-2.0A900 after vacuum annealing treatment at 900 °C in Example 1 and the energy-dispersive spectroscopy (EDS) element mapping images of C and Ta elements.

[0025] Figure 5 The field emission scanning electron microscope (FESEM) image of sample W3-2.0A1000 after vacuum annealing treatment at 1000 °C in Example 2 at 50000 times magnification.

[0026] Figure 6 The AC-STEM image of sample W3-2.0A1000 after vacuum annealing treatment at 1000 °C in Example 2. (a) is the low-magnification AC-STEM image of the sample, (b) and (c) are the high-magnification bright-field image and dark-field image of the sample respectively, and tantalum atoms are marked with red circles; (d) and (e) are the enlarged views of region 1 and region 2 in Figure (b) respectively.

[0027] Figure 7 The field emission electron microscope photograph of sample W3-1.8A900 after vacuum annealing treatment at 900 °C in Example 3 at 50000 times magnification.

[0028] Figure 8 The high-resolution transmission electron microscope image of sample W3-1.8A900 after vacuum annealing treatment at 900 °C in Example 3.

[0029] Figure 9 The AC-STEM image of sample W3-1.8A900 after vacuum annealing treatment at 900 °C in Example 3. The position of the interface is within the white frame; (a) is the bright-field image of the sample, (b) is the dark-field image of the sample, and (c) is the enlarged view of the white square in (b). Tantalum atoms are marked with red circles. (V) Specific implementation manners

[0030] The present invention will be further described below through specific examples, but the protection scope of the present invention is not limited thereto:

[0031] Example 1

[0032] 100 mg of W3 diamond powder (120,000 mesh, particle size ~36 nm) was mixed with 1 ml of adhesive: epoxy resin (Shanghai Macklin Biochemical Co., Ltd., product number E871957) + 9 ml of acetone, and 6 mg of surfactant: cetyltrimethylammonium bromide + 9 ml of acetone and dissolved in 20 ml of acetone. Then the solution was ultrasonically oscillated for 60 min to form a suspension, which was reserved for spin coating; a single crystal silicon wafer was cut into a size of ~20×20 mm with a diamond knife, placed in acetone and ultrasonically cleaned for 10 min, and after cleaning, it was dried with a nitrogen gun; the silicon wafer was placed on a spin coater (purchased from Beijing Saidekaisi Electronics Co., Ltd., model KW-4A) and spin-coated with the seed crystal spin coating solution at a spin speed of 1000 rpm (10 s) + 3000 rpm (30 s), and spin-coated 20 times to coat a dense seed crystal layer on the surface of the silicon wafer.

[0033] The silicon wafer spin-coated with the seed crystal was placed in a tube furnace and heat-treated at 700 °C for 10 min in an argon protection atmosphere to remove the organic matter on the surface of the silicon wafer; then the silicon wafer was placed in a hot filament chemical vapor deposition equipment (the hot filament chemical vapor deposition equipment was purchased from Shanghai Jiaoyou Diamond Coating Co., Ltd., model JUHFCVD001), and acetone was used as the carbon source, and acetone was introduced into the reaction chamber by means of hydrogen bubbling. The flow ratio of hydrogen to acetone was 200:80 sccm, the growth power was 2200 W, the growth pressure was controlled at 2.0 kPa, the growth time was 60 min, and the substrate temperature was maintained at about 650 °C. After the growth was completed, the power was slowly reduced to 0 at a rate of 1 V / min in a hydrogen atmosphere to complete the film preparation process.

[0034] The prepared close-packed nanodiamond film was subjected to a vacuum annealing treatment at 900 °C for 30 minutes, and the high-mobility n-type close-packed nanodiamond film was obtained.

[0035] The annealed film was coated with a conductive silver electrode for electrical property testing. The specific steps were as follows: First, the surface of the sample was cleaned with acetone, and then the sample was ultrasonically cleaned with acetone twice, 1 minute each time, to remove the non-diamond phase on the surface. Four square-arranged conductive silver paints (purchased from CAIG, USA, model CW-200B, surface resistance 0.01 - 0.03 Ω / sq) were coated at the four corners of the film using a capillary, and then the silver electrode was dried at room temperature. The tested film was of n-type conductivity, the Hall mobility was 8.90×10 2 cm 2 V -1 s -1 , the Hall coefficient was -2.44×10 2 cm 3 / C, and the carrier concentration was -2.55×10 16 cm3 , the resistivity is 2.74×10 -1 Ω·cm, compared with the as-grown, unannealed intrinsic film grown at the same pressure (Hall mobility of 4.37×10 2 cm 2 V -1 s -1 , Hall coefficient of -1.06×10 3 cm 3 / C, carrier concentration of -5.88×10 15 cm 3 , resistivity of 2.43×10 0 Ω·cm), it can be seen that both its conductivity and mobility have been greatly improved.

[0036] The surface morphologies of the silicon wafer substrate after spin coating and the deposited film were observed by field emission scanning electron microscopy (FESEM); the microstructure composition of the deposited film samples was observed by high-resolution transmission electron microscopy (HRTEM); the atomic-level structural characteristics of the samples were characterized by aberration-corrected transmission electron microscopy (AC-STEM).

[0037] Figure 1 This is a field emission electron microscope image of sample W3-2.0A900 after vacuum annealing at 900 °C at 50,000 times magnification. It can be seen that the surface is composed of nanodiamond particles, forming a continuous and dense surface morphology by nanocrystals.

[0038] Figure 2 This is a high-resolution transmission electron microscopy image of sample W3-2.0A900 after vacuum annealing at 900 °C. It can be seen that the film shows a structure of slender and narrow grain boundaries enclosing irregular nanocrystals. The diamond grains are closely packed together, showing the characteristics of close packing. As can be seen from the inserted SAED pattern, it mainly shows the (111) and (220) crystal planes of diamond, and there is no diffraction information of amorphous carbon phase, indicating that the grain boundaries of the film do not contain amorphous carbon phase.

[0039] Figure 3 This is the AC-STEM image of the sample. Similar to the HRTEM characterization, we can observe the close packing between irregular grains, and these interfaces correspond to the white interfaces in the HRTEM results. Figure 3 (b), (d) are respectively Figure 3 (a) the high-magnification bright-field images of Region I and Region I. There are bulges at the interfaces, similar to the shape of a mountain ridge; in the corresponding dark-field images, it can be observed that the contrast of these interfaces is relatively low, indicating that the thickness of these interfaces is relatively thin, which may be due to the extrusion between different grains causing the edges between them to warp. In the corresponding dark-field images ( Figure 3(c) and (e)), we can clearly see that there are many bright spots with high contrast, and these bright spots are more distributed at the position of the interface, which means that there are atoms with higher atomic numbers in the thin film, and these atoms come from the escape of tantalum in the Ta wire. Tantalum atoms exist at the grain close-packed interface, realizing interface doping.

[0040] Figure 4 It is the HADDF image of the sample and the EDS element mapping images of C and Ta elements, which confirm the existence of tantalum element.

[0041] Example 2

[0042] Mix 100 mg of W3 diamond powder with the adhesive: 1 ml of epoxy resin + 9 ml of acetone, and the activator: 6 mg of cetyltrimethylammonium bromide + 9 ml of acetone, and dissolve them together in 20 ml of acetone. Then, ultrasonically vibrate the solution for 60 min to form a suspension, which is reserved for spin-coating; Cut the single-crystal silicon wafer into a size of about 20×20 mm with a diamond knife, place it in acetone and ultrasonically clean it for 10 min, and blow it dry with a nitrogen gun after cleaning; Place the silicon wafer on a spin coater (purchased from Beijing Saidekaisi Electronics Co., Ltd., model KW-4A) and spin-coat the seed spin-coating solution. The spin-coating speed is 1000 rpm (10 s) + 3000 rpm (30 s), and spin-coat 20 times to coat a dense seed layer on the surface of the silicon wafer.

[0043] Put the silicon wafer spin-coated with seeds into a tube furnace and perform heat treatment at 700 °C for 10 min in an argon protection atmosphere to remove the organic matter on the surface of the silicon wafer; Then, put the silicon wafer into a hot filament chemical vapor deposition device (the hot filament chemical vapor deposition device is purchased from Shanghai Jiaoyou Diamond Coating Co., Ltd., model JUHFCVD001), use acetone as the carbon source, and introduce acetone into the reaction chamber by means of hydrogen bubbling. The flow ratio of hydrogen to acetone is 200:80 sccm, the growth power is 2200 W, the growth pressure is controlled at 2.0 kPa, the growth time is 60 min, and the substrate temperature is kept at about 650 °C. After the growth is completed, slowly reduce the power to 0 at a rate of 1 V / min in a hydrogen atmosphere to complete the thin film preparation process.

[0044] Perform a 1000 °C vacuum annealing treatment on the prepared close-packed nanodiamond thin film for 30 minutes to obtain the high-conductivity and high-mobility n-type close-packed nanodiamond thin film.

[0045] The annealed film was coated with conductive silver electrodes for electrical property testing. The specific steps were as follows: First, the surface of the specimen was cleaned with acetone, and then the specimen was ultrasonically cleaned with acetone twice for one minute each time to remove the non-diamond phase on the surface. Four conductive silver paints arranged in a square were coated at the four corners of the film using a capillary (purchased from CAIG, USA, model CW-200B, surface resistance 0.01 - 0.03 Ω / sq), and then the silver electrodes were dried at room temperature. The tested film had n-type conductivity, with a Hall mobility of 9.59×10 2 cm 2 V -1 s -1 , a Hall coefficient of -1.37×10 2 cm 3 / C, a carrier concentration of -4.54×10 16 cm 3 , a resistivity of 1.43×10 -1 Ω·cm. Compared with the unannealed intrinsic film grown under the same gas pressure (Hall mobility of 4.37×10 2 cm 2 V -1 s -1 , a Hall coefficient of -1.06×10 3 cm 3 / C, a carrier concentration of -5.88×10 15 cm 3 , and a resistivity of 2.43×10 0 Ω·cm), it can be seen that both its conductivity and mobility have been greatly improved.

[0046] The surface morphology of the sample was observed using a field emission scanning electron microscope (FESEM); the atomic structure characteristics of the sample were characterized using an aberration-corrected transmission electron microscope (AC-STEM).

[0047] Figure 5 This is a field emission scanning electron microscope photo of sample W3-2.0A1000 after vacuum annealing treatment at 1000 °C at 50000 times magnification. It can be seen that the surface is composed of nanodiamond particles, forming a continuous and dense surface morphology by nanograins.

[0048] Figure 6AC-STEM image of sample W3-2.0A1000 after 1000 °C vacuum annealing treatment. (a) Low-magnification AC-STEM image of sample W3-2.0A1000, showing a high density of ridged interfaces in the film. (b) and (c) are the high-magnification bright-field image and dark-field image of the film, respectively. The presence of a large number of planar defects is shown in (b), and a large number of tantalum atoms can be observed in the corresponding dark-field image (circled in red). The detailed structures of regions 1 and 2 are shown in Figs. (d) and (e), respectively. In region 1 (orange box, Fig. (d)), there are a large number of stacking faults with an interplanar spacing of 0.19 nm, and every two layers are evenly separated by these stacking faults. The FFT pattern shows some diffraction spots parallel to the diamond (111) crystal plane but not part of the (111) crystal plane, indicating the formation of stacking faults along the diamond (111) crystal plane. Such stacking faults cover the entire white dotted box in Fig. (b), and some tantalum atoms circled in red are found at the corresponding positions in the dark-field image of Fig. (c), revealing that tantalum atoms are located at the stacking faults. The twin defects of the sample are shown in region 2 (region 2 (green box, Fig. (e))), and we also observe tantalum atoms at the same twin boundary in the corresponding dark-field image. This indicates that in the annealed sample at 1000 °C, tantalum atoms tend to occupy positions near planar defects, such as twin boundaries and stacking faults, achieving interfacial doping.

[0049] Example 3

[0050] Mix 100 mg of W3 diamond powder with an adhesive: 1 ml of epoxy resin + 9 ml of acetone, and an activator: 6 mg of cetyltrimethylammonium bromide + 9 ml of acetone, and dissolve them in 20 ml of acetone. Then, ultrasonically vibrate the solution for 60 min to form a suspension, which is reserved for spin coating; Cut a single-crystal silicon wafer into a size of ~20 × 20 mm with a diamond knife, place it in acetone and ultrasonically clean it for 10 min. After cleaning, dry it with a nitrogen gun; Place the silicon wafer on a spin coater (purchased from Beijing Saidekaisi Electronics Co., Ltd., model KW-4A) and spin coat the seed spin coating solution. The spin coating speed is 1000 rpm (10 s) + 3000 rpm (30 s), and spin coat 20 times to coat a dense seed layer on the surface of the silicon wafer.

[0051] The silicon wafer with spin-coated seed crystals is placed in a tube furnace and heat-treated at 700 °C for 10 min in an argon-protected atmosphere to remove the organic substances on the surface of the silicon wafer. Then, the silicon wafer is placed in a hot filament chemical vapor deposition equipment (the hot filament chemical vapor deposition equipment is purchased from Shanghai Jiaoyou Diamond Coating Company, model JUHFCVD001). Using acetone as the carbon source, acetone is introduced into the reaction chamber by means of hydrogen bubbling. Among them, the flow rate ratio of hydrogen to acetone is 200:80 sccm, the growth power is 2200 W, the growth pressure is controlled at 1.8 kPa, the growth time is 60 min, and the substrate temperature is maintained at about 650 °C. After the growth is completed, the power is slowly reduced to 0 at a rate of 1 V / min in a hydrogen atmosphere to complete the film preparation process.

[0052] The prepared close-packed nanodiamond film is subjected to a vacuum annealing treatment at 900 °C for 30 minutes, and then the high-conductivity and high-mobility n-type close-packed nanodiamond film is obtained.

[0053] The annealed film is coated with a conductive silver electrode for electrical property testing. The specific steps are as follows: First, clean the surface of the specimen with acetone, and then ultrasonically clean the specimen with acetone twice, one minute each time, to remove the non-diamond phase on the surface. Use a capillary to coat four conductive silver paints (purchased from CAIG, USA, model CW-200B, surface resistance 0.01 - 0.03 Ω / sq) arranged in a square at the four corners of the film, and then dry the silver electrode at room temperature. The tested film is of n-type conductivity, the Hall mobility is 5.42×10 2 cm 2 V -1 s -1 , the Hall coefficient is -1.15×10 2 cm 3 / C, the carrier concentration is 5.42×10 16 cm 3 , the resistivity is 2.12×10 -1 Ω·cm. Compared with the unannealed intrinsic film grown under the same gas pressure (Hall mobility is 1.81×10 1 cm 2 V - 1 s -1 , the Hall coefficient is -4.22×10 0 cm 3 / C, the carrier concentration is -1.48×10 18 cm 3 , the resistivity is 2.33×10 -1 Ω·cm), it can be seen that its conductivity is slightly improved, while the mobility is greatly improved.

[0054] The surface morphology of the film after vacuum annealing at 900 °C was observed using a field emission scanning electron microscope (FESEM); the microstructure of the deposited film sample was observed using a high-resolution transmission electron microscope (HRTEM); and the atomic-level structural characteristics of the sample were characterized using an aberration-corrected transmission electron microscope (AC-STEM).

[0055] Figure 7 Figure 4 shows the field emission scanning electron microscope image of sample W3-1.8A1000 after vacuum annealing at 900 °C at 50,000 times magnification. It can be seen that the surface is composed of nanodiamond particles, and the needle-like and flaky nanocrystals form a continuous and dense surface morphology.

[0056] Figure 8 Figure 5 shows the high-resolution transmission electron microscope image of sample W3-1.8A900 after vacuum annealing at 900 °C. It can be seen that the film shows a structure of slender and narrow grain boundaries surrounding irregular nanocrystals. The diamond grains are closely packed together, showing the characteristics of close packing. From the inserted SAED pattern, it can be seen that it mainly shows the (111) and (220) crystal planes of diamond, and there is no diffraction information of amorphous carbon phase. It can be seen that the content of amorphous carbon in the grain boundaries of the film is extremely low, which is a typical grain close-packed structure.

[0057] Figure 9 (a) shows the high-magnification bright-field SACTEM image of sample W3-1.8A900 after vacuum annealing at 900 °C. The interplanar spacing is 0.206 nm, which is the (111) plane of diamond. The white box is the interface of grain close packing. From the dark-field image (b), it can be observed that there are many bright spots with high contrast at the interface position. The same as in Example 1, they are tantalum impurities existing in the hot-filament chemical vapor deposition process. Figure (c) is the enlarged view of the white square in (b), and it can be clearly seen that tantalum atoms are located in the (111) twin boundary of diamond. Tantalum atoms exist at the grain close-packing interface, realizing interface doping.

[0058] Example 4

[0059] 100 mg of W3 diamond powder (120,000 mesh, particle size ~36 nm) was mixed with 1 ml of adhesive: epoxy resin (Shanghai Macklin Biochemical Co., Ltd., product number E871957) + 9 ml of acetone, and 6 mg of surfactant: cetyltrimethylammonium bromide + 9 ml of acetone, and then dissolved in 20 ml of acetone. The solution was then ultrasonically vibrated for 60 min to form a suspension, which was reserved for spin coating. A single crystal silicon wafer was cut into a size of ~20×20 mm with a diamond knife, placed in acetone and ultrasonically cleaned for 10 min, and then dried with a nitrogen gun after cleaning. The silicon wafer was placed on a spin coater (purchased from Beijing Saidekaisi Electronics Co., Ltd., model KW-4A) and spin-coated with the seed crystal spin coating solution at a spin speed of 1000 rpm (10 s) + 3000 rpm (30 s), and spin-coated 20 times to coat a dense seed crystal layer on the surface of the silicon wafer.

[0060] The silicon wafer spin-coated with the seed crystal was placed in a tube furnace and heat-treated at 700 °C for 10 min in an argon protection atmosphere to remove the organic matter on the surface of the silicon wafer. Then the silicon wafer was placed in a hot wire chemical vapor deposition equipment (the hot wire chemical vapor deposition equipment was purchased from Shanghai Jiaoyou Diamond Coating Co., Ltd., model JUHFCVD001), and acetone was used as the carbon source, and acetone was introduced into the reaction chamber by means of hydrogen bubbling. The flow ratio of hydrogen to acetone was 200:80 sccm, the growth power was 2200 W, the growth pressure was controlled at 2.0 kPa, the growth time was 60 min, and the substrate temperature was maintained at about 650 °C. After the growth was completed, the power was slowly reduced to 0 at a rate of 1 V / min in a hydrogen atmosphere to complete the film preparation process.

[0061] The prepared close-packed nanodiamond film was subjected to a vacuum annealing treatment at 800 °C for 30 minutes. The annealed film was coated with a conductive silver electrode for electrical property testing. The specific steps were as follows: First, the surface of the sample was cleaned with acetone, and then the sample was ultrasonically cleaned with acetone twice, 1 minute each time, to remove the non-diamond phase on the surface. Four square-arranged conductive silver paints (purchased from CAIG, USA, model CW-200B, surface resistance 0.01 - 0.03 Ω / sq) were coated at the four corners of the film using a capillary tube, and then the silver electrode was dried at room temperature. The tested film was of n-type conductivity, the Hall mobility was 94.5 cm 2 V -1 s -1 , the Hall coefficient was -2.44×10 2 cm 3 / C, the carrier concentration was -1.80×10 16 cm 3 , the resistivity was 3.66 Ω·cm, compared with the as-grown intrinsic film (Hall mobility 4.37×10 2 cm2 V -1 s -1 The Hall coefficient is -1.06×10 3 cm 3 / C, and the carrier concentration is -5.88×10 15 cm 3 . Compared with the resistivity of 2.43×10 0 Ω·cm), it can be seen that both its conductivity and mobility have decreased to a certain extent. Thus, it can be proved that the high-conductivity and high-mobility n-type close-packed nanodiamond film obtained in the above case cannot be obtained by vacuum annealing treatment at 800°C.

Claims

1. A high electrical conductivity and high mobility n-type diamond film, characterized in that The high-conductivity and high-mobility n-type diamond film is prepared by the following method: (1) Spin-coating solution preparation: Diamond powder with a particle size of 3 nm - 1 μm, an adhesive, and an activator are uniformly dispersed in an organic solvent to obtain a spin-coating solution; the mass ratio of the diamond powder to the activator is 100:5 - 10; the volume of the organic solvent is 0.3 - 0.5 mL / mg based on the mass of the diamond powder; the volume ratio of the adhesive to the organic solvent is 1:20 - 40; the activator is one or a mixture of two or more of cetyltrimethylammonium bromide, poly(diallyldimethylammonium chloride), glycidol, and octadecyldimethylbenzylammonium chloride; (2) Spin-coating of seed crystals: Spin-coat the spin-coating solution described in step (1) on the surface of a single-crystalline silicon wafer. The spin-coating includes 15 - 20 cycles, and each cycle is spin-coated at 1000 rpm for 10 s and then at 3000 rpm for 30 s; a silicon wafer with a dense seed crystal layer coated on its surface is obtained; (3) Heat treatment: Place the silicon wafer with a dense seed crystal layer coated on its surface described in step (2) in a tube furnace and heat-treat it at 500 - 800 °C for 8 - 20 min in an argon protective atmosphere to obtain a heat-treated silicon wafer; (4) Use the heat-treated silicon wafer described in step (3) as a substrate, use acetone as a carbon source, and use tantalum wire as a heat source and doping source for hot-filament chemical vapor deposition; a close-packed nanodiamond film is obtained; (5) Anneal the close-packed nanodiamond film described in step (4) at a temperature of 900 - 1000 °C for 30 min to obtain the high-conductivity and high-mobility n-type diamond film.

2. The high-conductivity and high-mobility n-type diamond thin film according to claim 1, characterized in that: The diamond powder described in step (1) is W3 diamond powder.

3. The high-conductivity and high-mobility n-type diamond film according to claim 1, characterized in that: The adhesive described in step (1) is one or a mixture of two or more of polyvinyl alcohol, epoxy resin, and polyvinyl acetate.

4. The high-conductivity and high-mobility n-type diamond thin film according to claim 3, characterized in that: The adhesive described in step (1) is epoxy resin.

5. The high-conductivity and high-mobility n-type diamond film according to claim 1, characterized in that: The activator described in step (1) is cetyltrimethylammonium bromide.

6. The high-conductivity and high-mobility n-type diamond film according to claim 1, wherein: The organic solvent described in step (1) is one or a mixed solvent of two or more of dimethyl sulfoxide, acetone, and ethyl lactate.

7. The high-conductivity and high-mobility n-type diamond film according to claim 1, characterized in that: The organic solvent described in step (1) is acetone.

8. The high-conductivity and high-mobility n-type diamond thin film according to claim 1, wherein: Before spin-coating, the single-crystalline silicon wafer described in step (2) is also pretreated as follows: Cut into pieces of 20×20 mm size, ultrasonically clean in acetone, and dry with a nitrogen gun.

9. The high-conductivity and high-mobility n-type diamond film according to claim 1, characterized in that The hot-filament chemical vapor deposition described in step (4) is operated as follows: The acetone is bubbled into the reaction chamber of the hot-filament chemical vapor deposition equipment by hydrogen with a flow rate of 60 - 100 sccm, and at the same time, pure hydrogen with a flow rate of 100 - 300 sccm is introduced. The growth power is 1800 - 2400 W, the growth pressure is controlled at 1.8 - 2.0 KPa, and the growth time is 45 - 60 min. After the growth is completed, stop introducing the carbon source and reduce the voltage to 0 at a rate of 1 V / min in a pure hydrogen atmosphere to obtain the close-packed nanodiamond film.

10. The high-conductivity and high-mobility n-type diamond film according to claim 9, characterized in that: The growth power is 2200 W, the growth pressure is 2.0 KPa, and the growth time is 60 min.

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