A tungsten-doped hexagonal tantalum pentoxide single-crystal thin film and a preparation method thereof

Abstract

The present invention discloses a tungsten-doped hexagonal tantalum pentoxide single-crystal thin film and a preparation method thereof. A target material fired by mixing tantalum pentoxide powder and tungsten oxide powder is used as a raw material, and the tungsten-doped hexagonal tantalum pentoxide single-crystal thin film is prepared on a yttrium-stabilized zirconia (YSZ) single-crystal substrate by a pulsed laser deposition method. The tungsten-doped hexagonal tantalum pentoxide thin film of the present invention is an epitaxial material with a single-crystal structure. The thin film material has good semiconductor electrical properties, high single-crystal quality and good stability. It can be used in the fields of transparent semiconductor devices and ultraviolet photodetectors, etc.

Description

Technical Field

[0001] The present invention relates to a tungsten-doped hexagonal tantalum pentoxide single crystal thin film and a preparation method thereof, belonging to the technical field of semiconductor optoelectronic materials. Background Art

[0002] With the continuous development of semiconductor device technology, wide bandgap oxide semiconductor materials have attracted increasing attention and are developing towards wide bandgaps, high breakdown voltages, and high dielectric constants. In recent years, oxides with larger bandgaps such as gallium oxide, hafnium oxide, and tantalum oxide have become popular materials after indium oxide, tin oxide, and zinc oxide. Wide bandgap oxide materials can be used in the manufacture of flat panel displays, thin film solar cells, transparent thin film transistors, photodetectors, and high-voltage power devices, etc.

[0003] Tantalum pentoxide (Ta2O5) commonly has hexagonal, tetragonal, and orthorhombic phase structures, and has advantages such as a wide bandgap (3.9 - 4.5 eV), a high dielectric constant (20 - 22), and good corrosion resistance, and is a very promising multifunctional material. It has been studied and applied in the fields of electrochemistry, biochemical sensors, and photocatalysis, etc. Due to its high dielectric constant, Ta2O5 has very important application value as an insulating dielectric material in thin film transistors, field effect transistors, and supercapacitors, etc.

[0004] The crystalline form of Ta2O5 thin films can be amorphous, polycrystalline, and single crystal structures. For example: amorphous and nanocrystalline Ta2O5 thin films [Optical Materials, 97 (2019) 109404; Journal of Applied Physics, 114, 8 (2013) 083515], hexagonal Ta2O5 epitaxial thin films [Ceramics International, 47 (2021) 5510 - 5514, Materials Science in Semiconductor Processing, 135 (2021) 106065]. Bulk single crystal materials have also been reported, for example: tetragonal Ta2O5 [publication number CN201110257469.X]. Intrinsic Ta2O5 thin films are usually insulating materials and cannot be used as an active layer in semiconductor devices.

[0005] Currently, there are the following problems in the preparation of doped Ta2O5 thin films:

[0006] (1) Most of the current doping studies on Ta2O5 are aimed at improving the photocatalytic and luminescence properties of this material [Visible Light Sensitive Photocatalysts, Nitrogen-Doped Ta2O5 Powders, J. Phys. Chem. B, 108, 40(2004)15803–15807; Fabrication and evaluation of green-light emitting Ta2O5:Er,Ce co-sputtered thin films, Results in Physics, 5(2015)78-79]. However, there are very few research reports on regulating the electrical properties of Ta2O5 single crystal materials through doping.

[0007] (2) The structures of the previously reported doped Ta2O5 thin films are mostly amorphous or polycrystalline, with poor crystallization quality and many defects in the thin films. Therefore, the improvement effect on the electrical properties of the thin films is very small. Therefore, doping the single crystal Ta2O5 thin film with high crystallization quality and few lattice defects is conducive to improving the doping efficiency and enhancing the electrical properties of the thin film. (3) Since tantalum atoms in the Ta2O5 thin film exist in the form of a +5 high valence state, it is generally difficult to obtain good doping effects when doping with elements with a valence lower than 5. Taking tin atoms as an example, if Sn +4 ions exist in the Ta2O5 thin film lattice in a substitutional form, it is acceptor doping. However, if Sn exists in the lattice in the form of interstitial atoms, it is donor doping. Therefore, the self-compensation effect is serious when doping the Ta2O5 thin film with tin.

[0008] (4) Although the structure of the hexagonal Ta2O5 material is similar to that of gallium nitride and silicon carbide, its bandgap width is higher and the breakdown voltage is also higher. Therefore, it is a very promising wide bandgap semiconductor material. However, due to the lack of research on the doping and electrical control of Ta2O5 single crystal thin films, its application in semiconductor devices is limited.

[0009] In summary, finding effective elements suitable for doping Ta2O5 single crystal thin film materials, improving the electrical conductivity of the thin film, and developing and preparing doped Ta2O5 single crystal thin films are of great significance for the preparation of Ta2O5-based semiconductor devices. For this reason, the present invention is proposed. Summary of the Invention

[0010] Aiming at the deficiencies of the prior art, the present invention provides a tungsten-doped hexagonal tantalum pentoxide single crystal thin film and a preparation method thereof.

[0011] Term Explanation:

[0012] PLD: Pulsed Laser Deposition, a conventional technique for preparing epitaxial thin film materials in this field.

[0013] Tungsten doping concentration (%): The atomic ratio of W / (Ta + W), where W is the number of tungsten atoms and Ta is the number of tantalum atoms. Summary of the Invention:

[0015] The present invention prepares tungsten-doped hexagonal tantalum pentoxide (δ-Ta2O5:W) thin films by the pulsed laser deposition (PLD) method. The raw material is a ceramic target, which is a conventional commercially available product. The tungsten-doped Ta2O5 target is prepared by mixing Ta2O5 powder with a purity of 99.99% and WO3 powder according to the required tungsten doping ratio, followed by pressing and high-temperature sintering. The diameter of the target is 5.5 cm. Yttria-stabilized zirconia (YSZ) single crystal material is used as the substrate, and the substrate crystal plane is YSZ(111). The preparation method is to deposit tungsten-doped tantalum pentoxide thin films on the single crystal substrate by irradiating the ceramic target with high-energy pulsed laser in an oxygen atmosphere. Under optimized preparation process conditions, hexagonal tantalum pentoxide single crystal thin films with different tungsten doping concentrations are obtained, where the W doping concentration is 0.2 - 4.0%. The present invention has successfully prepared tungsten-doped hexagonal tantalum pentoxide single crystal semiconductor thin films with good electrical properties by selecting raw materials and single crystal substrates and optimizing the PLD process conditions.

[0016] The technical solution of the present invention is as follows:

[0017] A method for preparing tungsten-doped hexagonal tantalum pentoxide single crystal thin films, the chemical composition of the tungsten-doped hexagonal tantalum pentoxide single crystal thin films prepared by this preparation method is Ta2O5:W, where the tungsten doping concentration is 0.2 - 4.0%, and the single crystal thin film is a single-phase single crystal with a hexagonal structure; the specific preparation method uses the conventional PLD process for preparing oxide thin films.

[0018] The specific preparation method is as follows:

[0019] According to the present invention, preferably, the tungsten-doped hexagonal tantalum pentoxide single crystal thin films are prepared on a single crystal substrate by pulsed laser deposition using Ta2O5 ceramic targets with different tungsten doping concentrations, but not limited thereto.

[0020] According to the present invention, preferably, the doping element of the δ-Ta2O5:W single crystal thin film is tungsten, and the tungsten doping concentration is 0.2 - 4.0%.

[0021] According to the present invention, preferably, the δ-Ta2O5:W single crystal thin film is an n-type semiconductor material, and its carrier concentration is 8.0×10 14 ~5.6×10 16 cm -3 ², and the carrier Hall mobility is 9.8 - 82.1 cm 2V -1 s -1 The corresponding change range of the film resistivity is 11.3 - 95.2 Ω·cm. The resistivity of the obtained δ-Ta2O5:W single-crystal film decreases with the increase of the tungsten doping concentration, and the carrier concentration increases with the increase of the tungsten doping concentration.

[0022] According to the present invention, preferably, the growth substrate of the δ-Ta2O5:W single-crystal film is a YSZ(111) single-crystal wafer, but it is not limited thereto.

[0023] According to the present invention, the δ-Ta2O5:W film obtained by the above preparation method is an epitaxial film material with a hexagonal structure, and the growth plane of the hexagonal Ta2O5 film is δ-Ta2O5(0001).

[0024] According to the present invention, preferably, for the preparation of the tungsten-doped hexagonal tantalum pentoxide single-crystal film by the pulsed laser method, the laser parameters and the reaction chamber process conditions are as follows:

[0025]

[0026] According to the actual requirements of the film thickness, films with the required thickness can be prepared by controlling the preparation parameters and the deposition time.

[0027] According to the present invention, further preferably, for the preparation of the tungsten-doped hexagonal tantalum pentoxide single-crystal film by the pulsed laser method, the laser parameters and the reaction chamber process conditions are as follows:

[0028]

[0029] According to the present invention, most preferably, the laser parameters and the reaction chamber process conditions for the pulsed laser deposition are as follows:

[0030]

[0031] According to the present invention, under the above preparation conditions, the growth rate of the δ-Ta2O5:W film is 0.3 - 4.5 nm / minute.

[0032] According to the present invention, what is obtained under the above preparation process conditions is a δ-Ta2O5:W single-crystal epitaxial film.

[0033] The δ-Ta2O5:W single-crystal film prepared by the present invention has many unique advantages. For example, the electrical properties of the film can be controlled by adjusting the doping ratio of tungsten, and the film has good adhesion and the doping ratio is easy to be accurately controlled, and it has broad application prospects.

[0034] Unless otherwise specifically defined in the present invention, all are implemented according to the existing technologies in the art.

[0035] The tungsten-doped hexagonal Ta2O5 thin film prepared by the present invention has the following excellent effects:

[0036] 1. The δ-Ta2O5:W single crystal thin film of the present invention is an n-type semiconductor material, rather than an insulating material. Due to the high valence state of tungsten atoms, whether they exist in the δ-Ta2O5 thin film lattice in a substitutional form or an interstitial form, donor energy levels will be formed, that is, n-type doping, so there is no self-compensation situation.

[0037] 2. The electrical properties of the δ-Ta2O5:W single crystal thin film of the present invention can be controlled by adjusting the doping concentration of tungsten. When the tungsten doping concentration is 0.2-4.0%, the film resistivity changes from 11.3 to 95.2 Ω·cm, and the carrier concentration changes from 8.0×10 14 to 5.6×10 16 cm -3 , and the carrier Hall mobility is 9.8-82.1 cm 2 V -1 s -1 . This provides material support for the preparation of δ-Ta2O5:W thin film semiconductor devices.

[0038] 3. The δ-Ta2O5:W thin film of the present invention is a single crystal epitaxial thin film with a hexagonal structure. Due to the good lattice matching between the (111) plane of the substrate YSZ and the (0001) plane of δ-Ta2O5, and its lattice mismatch rate is 0.4%, the crystallization quality of the prepared thin film is high, the stability is good, which is conducive to improving the doping efficiency.

[0039] The δ-Ta2O5:W single crystal thin film prepared by the present invention has excellent electrical properties, and its resistivity is more than 4 orders of magnitude lower than that of the undoped δ-Ta2O5 thin film. Therefore, it is a new wide-bandgap oxide semiconductor material for manufacturing Ta2O5-based semiconductor devices and ultraviolet optoelectronic devices. Description of the Drawings

[0040] Figure 1 It is the X-ray diffraction θ-2θ scan pattern of the 2.0% tungsten-doped δ-Ta2O5:W thin film prepared in Example 1 of the present invention. Among them, the abscissa: 2θ (degree), the ordinate: intensity (arbitrary unit).

[0041] Figure 2 It is the rocking curve of the X-ray diffraction peak of the (0001) plane of the 2.0% tungsten-doped δ-Ta2O5:W thin film prepared in Example 1 of the present invention. Among them, the abscissa: ω (degree), the ordinate: intensity (arbitrary unit).

[0042] Figure 3X-ray photoelectron spectra of Ta 4f and W 4f core levels for the preparation of 2.0% tungsten-doped δ-Ta2O5:W thin films in Example 1 of the present invention. Among them, the abscissa: energy (eV), the ordinate: intensity (arbitrary unit).

[0043] Figure 4 Variation of the resistivity of the δ-Ta2O5:W thin films prepared by the present invention with the tungsten doping concentration. Among them, the ordinate: resistivity (Ωcm), the abscissa: Tungsten doping concentration (%). Detailed implementation manners

[0044] The present invention will be further described below in conjunction with examples and comparative examples.

[0045] A preparation method of tungsten-doped hexagonal tantalum pentoxide single crystal thin films, the specific preparation method and process are as follows:

[0046] Step (1): Place the YSZ single crystal substrate into an ultrasonic cleaner, with the water bath temperature at 80°C. After ultrasonic cleaning for 15 minutes, take it out and dry the surface of the substrate with high-purity nitrogen.

[0047] Step (2): Place the ceramic target with the required tungsten doping concentration and the clean YSZ single crystal substrate at the target and substrate positions in the reaction chamber respectively, and close the reaction chamber.

[0048] Step (3): Turn on the high-vacuum PLD equipment and the molecular pump, and pump the reaction chamber into a high-vacuum state with a vacuum degree of 9×10 -5 Pa, and heat the YSZ single crystal substrate base to 700°C - 850°C.

[0049] Step (4): Open the valve of the high-purity oxygen cylinder, introduce oxygen into the reaction chamber, and control the pressure in the reaction chamber to be stable at 1 - 15 Pa by adjusting the gas flow meter and the reaction chamber exhaust valve, and maintain it for 25 minutes.

[0050] Step (5): Turn on the laser, adjust the single-pulse energy of the laser to 150 - 350 mJ, and the laser pulse frequency to 1 - 10 Hz. Start the laser beam for pre-irradiation for 10 minutes to remove the attachments on the surface of the target.

[0051] Step (6): Open the substrate baffle and start growing δ-Ta2O5:W thin films on the YSZ(111) single crystal substrate. The film growth rate is 0.3 - 4.5 nm / minute, and the δ-Ta2O5:W thin film with the required thickness is obtained by controlling the deposition time.

[0052] Step (7): After the reaction is completed, turn off the laser, close the valve of the high-purity oxygen cylinder, turn off the molecular pump, turn off the substrate heating power supply and let it cool naturally. Open the reaction chamber and take out the sample.

[0053] According to the present invention, the above preparation method and process conditions result in δ-Ta2O5:W single crystal thin films. By using ceramic targets with different tungsten doping concentrations, δ-Ta2O5:W single crystal thin films with different tungsten doping concentrations are prepared.

[0054] Example 1:

[0055] Using a double-sided polished YSZ(111) single crystal wafer as the substrate and a Ta2O5 ceramic target with a tungsten doping concentration of 2.0% as the target material, δ-Ta2O5:W thin films are prepared by the PLD method.

[0056] The steps are as follows:

[0057] (1) Place the ceramic target and the clean YSZ(111) substrate at the target and substrate positions in the reaction chamber respectively, and close the reaction chamber;

[0058] (2) Turn on the power supply of the PLD equipment, turn on the molecular pump, and evacuate the reaction chamber to a high vacuum state with a vacuum degree of 9.0×10 - 5 Pa, and heat the substrate to 750 °C;

[0059] (3) Open the valve of the high-purity oxygen cylinder, introduce high-purity oxygen into the reaction chamber, adjust the gas flow meter and the evacuation valve of the reaction chamber, and control the pressure of the reaction chamber to be stable at 5 Pa for 25 minutes;

[0060] (4) Turn on the laser, adjust the single-pulse energy of the laser to 250 mJ, and the laser pulse frequency to 4 Hz. Start the laser for pre-irradiation for 10 minutes to remove the attachments on the surface of the target;

[0061] (5) Open the substrate baffle, and start growing the δ-Ta2O5:W thin film on the YSZ(111) substrate. The film deposition time is 180 minutes, and the film growth rate is 1.8 nm / minute;

[0062] (6) After the deposition reaction is completed, turn off the laser, close the valve of the high-purity oxygen cylinder, turn off the molecular pump, turn off the substrate heating power supply, and after naturally cooling to room temperature, open the reaction chamber and take out the prepared sample.

[0063] The thin film prepared in this Example 1 is a 2.0% tungsten-doped hexagonal Ta2O5 single crystal thin film, and the growth surface of the thin film is hexagonal Ta2O5(0001). The epitaxial relationship between the thin film and the substrate is hexagonal Ta2O5(0001)‖YSZ(111). The resistivity of the thin film is about 14.3 Ωcm, the carrier Hall mobility is about 65.1 cm 2 V -1 s -1 , and the carrier concentration is about 6.6×10 15 cm -3 .

[0064] Figure 1 This is the X-ray diffraction θ~2θ scan pattern of the 2.0% tungsten-doped δ-Ta2O5:W thin film prepared in Example 1. The diffraction peaks of the thin film in the figure are located at 22.80° and 46.61°, corresponding to the first- and second-order diffraction peaks of hexagonal Ta2O5(0001) respectively (JCPDS 19-1299), indicating that the prepared Ta2O5 thin film has a hexagonal structure and the growth plane is (0001).

[0065] Figure 2 This is the rocking curve of the X-ray diffraction peak of the (0001) plane of the 2.0% tungsten-doped Ta2O5 thin film prepared in Example 1. The rocking curve in the figure has good symmetry, and the full width at half maximum of the diffraction peak is 0.078°, indicating that the obtained is a high-quality single-crystal thin film.

[0066] Figure 3 This is the Ta4f and W4f core level spectra of the X-ray photoelectron spectroscopy of the 2.0% tungsten-doped δ-Ta2O5:W thin film prepared in Example 1. Four peaks corresponding to Ta4f 7 / 2 (25.85 eV), Ta4f 5 / 2 (27.75 eV), W 4f 7 / 2 (35.45 eV) and W 4f 5 / 2 (37.35 eV) can be observed. This result shows that the valence state of Ta element in the thin film is +5 and the valence state of W element is +6. It can be calculated that the doping concentration of tungsten in the thin film is consistent with the target used.

[0067] Figure 4 This is the curve of the resistivity of the δ-Ta2O5:W thin film of the present invention varying with the tungsten doping concentration. The resistivity of the δ-Ta2O5:W thin film decreases with the increase of the tungsten doping concentration. When the variation range of the tungsten doping concentration is 0.2~4.0%, the variation range of the thin film resistivity is 11.3~95.2 Ωcm.

[0068] Example 2:

[0069] The δ-Ta2O5:W thin film was prepared by PLD technology. The substrate material used and the thin film preparation process are the same as those in Example 1, except that the tungsten doping concentration of the target used is 1.0%. The prepared δ-Ta2O5:W thin film has a hexagonal structure. The resistivity of the thin film is about 15.9 Ωcm, the carrier Hall mobility is about 78.0 cm 2 V -1 s -1 , and the carrier concentration is about 5.0×10 15 cm -3。Compared with Example 1, the resistivity and carrier Hall mobility of the thin film increase, while the carrier concentration decreases.

[0070] Example 3:

[0071] The δ-Ta2O5:W thin film was prepared by PLD technology. The substrate material and the thin film preparation process used were the same as those in Example 1, except that the tungsten doping concentration of the target used was 4.0%. The prepared δ-Ta2O5:W thin film had a hexagonal phase structure. The resistivity of the thin film was about 11.3 Ωcm, and the carrier Hall mobility was about 9.8 cm 2 V -1 s -1 , and the carrier concentration was about 5.6×10 16 cm -3 . Compared with Example 1, the resistivity and carrier Hall mobility of the thin film decreased, while the carrier concentration increased.

[0072] Example 4:

[0073] The δ-Ta2O5:W thin film was prepared by PLD technology. The substrate material and the thin film preparation process used were the same as those in Example 1, except that the tungsten doping concentration of the target used was 0.0%. The prepared Ta2O5 thin film had a hexagonal phase structure. The thin film showed a high-resistance state, and its resistivity was greater than 10 6 Ωcm.

[0074] Comparative Example 1:

[0075] The substrate material and the thin film preparation process conditions were as described in Example 1. The difference was that the substrate temperature was 650°C. The X-ray test results of the prepared sample showed no obvious thin film diffraction peaks, indicating that 650°C did not reach the crystallization temperature of Ta2O5, and the prepared thin film was an amorphous structure. The thin film was highly resistive, indicating that the doping effect was not obvious.

[0076] Comparative Example 2:

[0077] The δ-Ta2O5:W thin film was prepared by PLD technology. The thin film preparation process conditions were as described in Example 1. The difference was that the single-pulse energy of the pulsed laser was 350 mJ. The laser energy was large, and the growth rate of the thin film was too fast. Under this condition, the prepared δ-Ta2O5:W was a polycrystalline thin film, and the crystallization quality of the thin film decreased significantly.

[0078] Comparative Example 3:

[0079] The δ-Ta2O5:W thin film was prepared by PLD technology. The thin film preparation process conditions were as described in Example 2. The difference was that a YSZ(100) single crystal wafer was used as the substrate material. The prepared Ta2O5 thin film was a polycrystalline structure, and the thin film showed a high-resistance state, indicating that the doping effect was not obvious.

[0080] Comparative Example 4:

[0081] The δ-Ta2O5:W thin film was prepared by the PLD technique. The thin film preparation process conditions were as described in Example 2, except that: a polished MgAl2O4(100) single crystal wafer was used as the substrate, and the prepared Ta2O5 thin film had a polycrystalline structure. The resistivity of the prepared δ-Ta2O5:W thin film was relatively high, indicating that the doping effect was not obvious.

Claims

1. A tungsten-doped hexagonal tantalum pentoxide single crystal thin film, characterized in that, The chemical composition of the thin film is tantalum pentoxide doped with tungsten, which is a single crystal material with a hexagonal structure. Using a target made by mixing tantalum pentoxide powder and tungsten oxide powder and sintering as the raw material, it is prepared on a single crystal substrate of yttrium-stabilized zirconia by pulsed laser deposition to obtain a tungsten-doped hexagonal phase tantalum pentoxide single crystal thin film.

2. The tungsten-doped hexagonal tantalum pentoxide single-crystal thin film according to claim 1, wherein The tungsten doping concentration of the tungsten-doped hexagonal phase tantalum pentoxide single crystal thin film is 0.2 - 4.0 %.

3. The tungsten-doped hexagonal tantalum pentoxide single crystal thin film according to claim 1, wherein The resistivity of the described tungsten-doped hexagonal tantalum pentoxide single-crystal thin film varies in the range of 11.3~95.2 Ωcm, and the carrier Hall mobility varies in the range of 9.8~82.1 cm 2 V -1 s -1 , and the carrier concentration varies in the range of 8.0 10 14 ~5.6 10 16 cm -3 .

4. The tungsten-doped hexagonal tantalum pentoxide single-crystal thin film according to claim 1, characterized in that The tungsten-doped hexagonal phase tantalum pentoxide single crystal thin film is prepared on a single crystal substrate by pulsed laser deposition using Ta2O5 ceramic targets with different tungsten doping concentrations as raw materials.

5. The tungsten-doped hexagonal tantalum pentoxide single-crystal thin film according to claim 4, wherein The single crystal substrate material is yttrium-stabilized zirconia YSZ, and the epitaxial relationship between the tungsten-doped hexagonal phase tantalum pentoxide thin film and the YSZ substrate is δ-Ta2O5 (0001) / / YSZ(111).

6. A method for preparing the tungsten-doped hexagonal phase tantalum pentoxide single crystal thin film according to any one of claims 1 - 5, comprising the following steps: Using Ta2O5 ceramic targets with different tungsten doping concentrations as raw materials, and depositing a tungsten-doped hexagonal phase tantalum pentoxide single crystal thin film on a single crystal substrate by pulsed laser deposition; The single crystal substrate is the (111) crystal plane of cubic structure YSZ; During the pulsed laser deposition process, the parameters of the laser and the reaction chamber are as follows: Single pulse energy of the laser: 150 - 320 mJ; Pulse frequency: 1 - 10 Hz; Reaction chamber pressure: 2 - 15 Pa; Substrate temperature: 700 - 850 °C.

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