阅读说明：本技术 一种外延高电导bfco光电固溶薄膜的制备方法及所得产品 (Preparation method of epitaxial high-conductivity BFCO photoelectric solid-solution film and obtained product ) 是由 杨锋 刘芬 林延凌 季凤岐 于 2019-09-23 设计创作，主要内容包括：本发明公开了一种外延高电导BFCO光电固溶薄膜的制备方法及所得产品,步骤包括：配制前驱体溶液,在衬底上采用层层退火工艺制备薄膜,每层薄膜制备时的温度为70-90℃,甩膜时的湿度为11-15%,退火气氛为氮气。本发明对实验设备没有太高的要求,可精确控制原料化学计量比,工艺简单操作方便,所得薄膜即具有较高的电导又具有较好的铁电性,对于其在铁电调控逻辑器件以及阻性存储器应用方面有着很好的应用前景。(The invention discloses a preparation method of an epitaxial high-conductivity BFCO photoelectric solid solution film and an obtained product, and the preparation method comprises the following steps: preparing a precursor solution, preparing films on a substrate by adopting a layer-by-layer annealing process, wherein the temperature of each layer of film during preparation is 70-90 ℃, the humidity of each layer of film during spinning is 11-15%, and the annealing atmosphere is nitrogen. The method has no high requirement on experimental equipment, can accurately control the stoichiometric ratio of the raw materials, has simple process and convenient operation, and the obtained film has high conductivity and good ferroelectricity, thereby having good application prospect in the application aspects of ferroelectric regulating logic devices and resistive memories.)

1. A preparation method of an epitaxial high-conductivity BFCO photoelectric solid-solution film is characterized by comprising the following steps:

(1) stirring and mixing bismuth salt, ferric salt, cobalt salt, a regulator and a mixed solvent uniformly to obtain a precursor solution;

(2) in SrTiO₃Or Nb SrTiO₃Coating a precursor solution on a substrate, and preparing a single-layer film by adopting a spin-coating method, wherein the temperature during film spinning is 70-90 ℃, and the humidity during film spinning is 11-15%;

(3) coating the SrTiO with a single-layer film in the previous step₃Or Nb SrTiO₃The substrate is at 250 DEG 300 DEG^oC, carrying out heat treatment for 5-10 minutes, and then annealing in a quartz tube furnace, wherein the annealing procedure is as follows: maintaining N in the furnace₂The flow is 0.1-1L/min, the temperature is increased from room temperature to 480 ℃ of 400-;

(4) repeating the steps (2) and (3) until the final film thickness meets the requirement to obtain the BiFe_0.7Co_0.3O_3-δAnd the film is a BFCO photoelectric solid solution film.

2. The method of claim 1, wherein: the regulator is mixture of polyethylene glycol 20000, polyethylene glycol 400 and acetylacetone, BiFe_0.7Co_0.3O₃The molar ratio of polyethylene glycol 20000 to polyethylene glycol 400 to acetylacetone is 1: 0.005-0.015%: 0.005-0.015%: 0.5-1.5.

3. The method of claim 1, wherein: BiFe_0.7Co_0.3O_3-δThe thickness of the photoelectric solid solution film is 90 ~ 105 nm.

4. A method according to claim 1, 2 or 3, characterized by: when preparing the first layer of film, spinning the film at 6000-7000rpm, wherein the film spinning time is 1.5-2 minutes; when preparing the 2 nd-3 rd film, throwing the film at the speed of 4000-; when preparing other layers of films, the films are spun at the speed of 5000 plus 6000rpm, and the film spinning time is 1-2 minutes.

5. The method of claim 1, wherein: when preparing the first layer of film, SrTiO is firstly used₃Or Nb SrTiO₃The substrate is pretreated at 650-750 ℃.

6. The method of claim 1, further comprising: in the step (3), the SrTiO coated with the single-layer film in the previous step is subjected to₃Or Nb SrTiO₃The substrate is at 280^oC, carrying out heat treatment for 5 minutes, and then annealing in a quartz tube furnace, wherein the annealing procedure is as follows: maintaining N in the furnace₂The flow is 0.5L/min, the temperature is increased to 450 ℃ from the room temperature at the speed of 5 ℃/min, the temperature is preserved for 30min, then the temperature is increased to 680 ℃ at the speed of 40 ℃/min, the temperature is preserved for 30min, and the substrate is taken out after the furnace temperature is naturally cooled to the room temperature.

7. The method of claim 1, further comprising: the bismuth salt is bismuth nitrate, the ferric salt is ferric nitrate, and the cobalt salt is cobalt nitrate; bismuth salt: iron salt: the molar ratio of the cobalt salt is 1: 0.7: 0.3.

8. the method of claim 1 or 7, wherein: BiFe in precursor solution_0.7Co_0.3O₃The concentration is 0.1 mol/L ~ 0.3.3 mol/L, more preferably 0.2 mol/L.

9. The method of claim 1, further comprising: the mixed solvent is a mixture of glacial acetic acid, glycol and glycol methyl ether, wherein the molar ratio of bismuth salt to glacial acetic acid is 1:5-8, the volume ratio of the glycol to the glycol methyl ether is 1:1, and the dosage of the glycol and the glycol methyl ether ensures that the precursor solution has the required concentration.

10. The BFCO photoelectric solid solution film prepared by the preparation method of the epitaxial high-conductivity BFCO photoelectric solid solution film according to any one of claims 1-9.

Technical Field

The invention relates to high-quality epitaxially grown high-conductivity BFCO (BiFe)_0.7Co_0.3O_3-δ) A method for photoelectric solid solution film, in particular to a method for preparing high-quality epitaxial growth high-conductivity BiFe with the assistance of high polymer_0.7Co_0.3O_3-δPhotoelectric solid solution film method and BiFe obtained by same_0.7Co_0.3O_3-δPhotoelectric solid solution film product.

Background

The ferroelectric photovoltaic effect has attracted much attention due to its potential for applications in energy conversion, optoelectronics, information storage, and the like. Compared with the conventional oneCompared with the photovoltaic effect of a p-n junction interface solar cell, the ferroelectric perovskite oxide has the special property that the non-centrosymmetric structure provides a unique path for spontaneously separating charge carriers (namely the photovoltaic effect), the ultra-band gap extremely-large open-circuit voltage is realized in a single-phase ferroelectric material, and the energy conversion efficiency (PCE) exceeding the limit of Shockley-Queisser can be expected to be obtained. The ferroelectric material has spontaneous electric polarization, and can realize electric field regulation and control of photovoltaic current direction. In addition, inorganic ferroelectric metal oxides have higher stability under ambient conditions than organic-inorganic hybrid perovskite photovoltaic devices that are currently being investigated for are relatively hot. Despite the many advantages and promising application prospects, it is also recognized that at the present stage it still has many disadvantages, most of the conventional ferroelectric oxides having perovskite structure generally absorb light in the ultraviolet energy range (band gap)E _g= 3-4eV, much greater than the ideal value of the maximum PCE of ~ 1.4.4 eV), the photocurrent that can be produced is still relatively low.

Lowering the band gap E_gAnd maintaining ferroelectric properties is an effective way to obtain photovoltaic devices with higher PCEs. Inorganic ferroelectric perovskite ABO₃Ferroelectric materials have a wide band gap (wide band gap is due to a large difference in electronegativity between transition metal cation (B) and oxygen), so that photocurrent is at a low level that is hardly practical. Altering inorganic ferroelectric ABO₃The nature of the B-O bond in the perovskite may allow for the effective tuning of the band gap of the material. Among the various methods of adjusting Eg, chemical composition regulation appears to be one of the most successful. Using this method, Bi₂FeCrO₆The PCE in the multilayer structure reaches 8.1%. Although ferroelectric perovskite oxides are rapidly evolving, there are still some important fundamental problems to be investigated. In particular, there is a need to develop new material compositions to reduce the bandgap and enhance the electrical polarization through cost effective and scalable processing methods. Chemical solution deposition is a well established low cost route for the preparation of high quality polycrystalline oxides with various structural phases, including metastable materials. Thus, the chemical solution process produces ferroelectric oxide filmsThe film is very attractive.

The reduction of the band gap can effectively increase the conductance of the material, thereby having important significance for increasing the current density. However, considering that the detection of the ferroelectric polarization is based on the integration of the polarization current, the leakage current will affect the polarization measurement, and the increase in the conductance will further reduce the ferroelectric polarization of the material. Therefore, how to prepare a ferroelectric thin film material with good ferroelectricity and good semiconductor transport characteristics is a difficult problem in the scientific research field at present.

BiFeO₃(BFO) is one of the most attractive lead-free perovskite oxide materials that can be used as photoactive layers in ferroelectric photovoltaic devices. For BiFeO at present₃The research on how to improve the ferroelectricity is less focused on how to improve the semiconductor transport characteristics while maintaining the ferroelectricity.

Disclosure of Invention

The invention aims to provide epitaxial high-conductivity BFCO (namely BiFe)_0.7Co_0.3O_3-δThe same applies below) preparation method of photoelectric solid solution film and the obtained product, the method is (100) SrTiO₃Or (100) Nb SrTiO₃High-conductivity BiFe deposited on substrate by using polymer-assisted method_0.7Co_0.3O_3-δThe photoelectric solid solution film is simple and convenient to operate, has low requirements on experimental equipment, can accurately control the stoichiometric ratio of raw materials, is epitaxially grown by selecting and optimizing process conditions, has greatly improved ferroelectricity and semiconductor transport performance, can be used for research and development of ferroelectric photovoltaic devices, and can be easily used for research on other high-precision devices.

The invention uses (100) SrTiO₃Or (100) Nb SrTiO₃As a substrate, high-conductivity BiFe is epitaxially grown by a polymer-assisted method_0.7Co_0.3O_3-δThe photoelectric solid solution film is prepared by selecting and optimizing precursor solution and film deposition process in the deposition process to ensure high-conductivity BiFe_0.7Co_0.3O_3-δPhotoelectric solid solution film is formed on (100) SrTiO₃Or (100) Nb SrTiO₃Crystal epitaxially grown on substrateThe grain crystallinity is high, and the arrangement is regular, so that the solid solution film with low band gap, high electric conductivity and good ferroelectricity is prepared.

The epitaxial high-conductivity BiFe_0.7Co_0.3O_3-δThe preparation method of the photoelectric solid solution film (namely BFCO, the same below) comprises the following steps:

(1) stirring and mixing bismuth salt, ferric salt, cobalt salt, a regulator and a mixed solvent uniformly to obtain a precursor solution;

(2) in SrTiO₃Or Nb SrTiO₃Coating a precursor solution on a substrate, and preparing a single-layer film by adopting a spin-coating method, wherein the temperature during film spinning is 70-90 ℃, and the humidity during film spinning is 11-15%;

(3) coating the SrTiO with a single-layer film in the previous step₃Or Nb SrTiO₃The substrate is at 250 DEG 300 DEG^oC, carrying out heat treatment for 5-10 minutes, and then annealing in a quartz tube furnace, wherein the annealing procedure is as follows: maintaining N in the furnace₂The flow is 0.1-1L/min, the temperature is increased from room temperature to 480 ℃ of 400-;

(4) repeating the steps (2) and (3) until the final film thickness meets the requirement to obtain the BiFe_0.7Co_0.3O_3-δAnd the film is a BFCO photoelectric solid solution film.

Further, in the step (1), the mixed solvent is a mixture of glacial acetic acid, ethylene glycol and ethylene glycol monomethyl ether. Wherein the molar ratio of the bismuth salt to the glacial acetic acid is 1:5-8, and the volume ratio of the ethylene glycol to the ethylene glycol monomethyl ether is 1: 1. The amounts of ethylene glycol and ethylene glycol methyl ether are such that the final precursor solution has the desired concentration.

Further, the bismuth salt is bismuth nitrate, the ferric salt is ferric nitrate, and the cobalt salt is cobalt nitrate. The adding sequence of the bismuth salt, the ferric salt, the cobalt salt, the regulator and the mixed solvent can be randomly selected, for example, the bismuth salt and the glacial acetic acid are mixed firstly, the temperature is raised to form a uniform solution, and then the ferric salt, the cobalt salt, the regulator and the other two solvents are added; or mixing the solvents, adding bismuth salt into the mixed solvent, mixing uniformly, and then adding the ferric salt, the cobalt salt and the regulator.

Further, in the step (1), the bismuth salt: iron salt: the cobalt salt was mixed in a ratio of 1: 0.7: 0.3 molar ratio, since BiFe according to the invention_0.7Co_0.3O_3-δFor epitaxial growth, therefore, no bismuth loss exists, and the bismuth salt does not need to be added excessively.

Further, BiFe is added into the precursor solution prepared in the step (1)_0.7Co_0.3O₃Meter, BiFe_0.7Co_0.3O₃The concentration in the final precursor solution is 0.1 mol/L ~ 0.3.3 mol/L, preferably 0.2 mol/L.

Further, in the step (1), the regulator is a mixture of polyethylene glycol 20000, polyethylene glycol 400 and acetylacetone, or BiFe_0.7Co_0.3O₃Polyethylene glycol 20000, polyethylene glycol 400 and acetylacetone in a molar ratio of 1: 0.005-0.015%: 0.005-0.015%: 0.5-1.5. One function of the regulator is to regulate the viscosity of the precursor solution, the viscosity of the final precursor solution is 2-4 mPa.s, and the other function is to assist epitaxial growth.

Furthermore, the invention adopts a layer-by-layer annealing process to prepare the film, and the obtained film epitaxially grows BiFe under the adjustment and control of precursor solution and preparation process_0.7Co_0.3O_3-δPhotoelectric solid solution film. The single-layer film is prepared by adopting a spin-coating method, the preparation process needs to strictly control the process conditions, the film spinning temperature is kept at 70-90 ℃, the film spinning humidity is 11-15%, and the long BiFe with epitaxial growth and high quality can be obtained under the cooperation of the process conditions and other conditions_0.7Co_0.3O_3-δPhotoelectric solid solution film. After a single-layer film is prepared each time, the next layer of film is prepared after annealing, nitrogen is used as atmosphere during annealing to form oxygen vacancy, the carrier transport performance of the film is improved, and BiFe in each layer of film is ensured by controlling the heating rate, the nitrogen flow and the annealing temperature_0.7Co_0.3O_3-δAnd (4) epitaxial growth. Preferably, during layer-by-layer annealingThe annealing procedure of each layer of film is as follows: maintaining N in the furnace₂The flow is 0.5L/min, the temperature is increased to 450 ℃ from the room temperature at the speed of 5 ℃/min, the temperature is preserved for 30min, then the temperature is increased to 680 ℃ at the speed of 40 ℃/min, the temperature is preserved for 30min, and the substrate is taken out after the furnace temperature is naturally cooled to the room temperature. Under the preferred conditions, the formation of high-quality epitaxial growth films is facilitated.

Further, it was found through experiments that the quality of epitaxial growth is closely related to the thickness of each thin film. The invention researches and finds that when the thickness of the first layer film is smaller than that of other layers, and the thickness of the 4 th layer and above films is smaller than that of the 2 nd to 3 rd layers, the obtained film has better performance.

Furthermore, the invention provides the optimal process conditions for preparing each layer of film, namely when preparing the first layer of film, spinning the film at 6000-7000rpm, wherein the spinning time is 1.5-2 minutes; when preparing the 2 nd-3 rd film, throwing the film at the speed of 4000-; when preparing other layers of films, the films are spun at the speed of 5000 plus 6000rpm, and the film spinning time is 1-2 minutes.

Preferably, the first layer of film is spun at 6500rpm for 2 minutes; the 2 nd to 3 rd layer films are spun off at the speed of 4500rpm for 1 minute; the other film was spun off at 5500rpm for 1 minute. Under the condition of the preferred spinning, the obtained film has better performance.

Further, the substrate used in the present invention is (100) SrTiO₃Or (100) Nb SrTiO₃Is a substrate that facilitates the formation of an epitaxially grown thin film. Before use, the substrate needs to be pretreated to remove impurities on the surface and other components affecting the growth of the thin film. The pretreatment is carried out at 650-750 ℃ for 25-35 min.

Further, the final BiFe of the invention_0.7Co_0.3O_3-δThe thickness of the film was 90 ~ 105 nm.

According to the invention, the epitaxially grown BiFe is obtained through the synergy and the collocation of the precursor solution, the preparation process and other conditions_0.7Co_0.3O_3-δPhotoelectric solid solution film. Under the preferred conditions, the resulting filmThe ferroelectric property and the semiconductive property are better, and BiFe is found through XRD test_0.7Co_0.3O_3-δThe photoelectric solid solution film has higher epitaxial degree.

The invention discovers the influence of proper combination of conditions such as high molecular polymer, concentration and viscosity of precursor solution, film-making environment humidity, single-layer film thickness, annealing atmosphere and the like on epitaxial growth of a thin film and semiconducting of the thin film for the first time. Under the guidance of the mechanism, the invention adopts a macromolecule auxiliary method, and the crystal grain epitaxial growth meets the required requirements by matching the steps of preparation of a precursor solution, preparation of a single-layer film, heat treatment and the like, particularly optimizing the precursor solution, the single-layer spin coating and the heat treatment process, and the like, and the (100) SrTiO crystal grain has the advantages of high purity, high yield and high yield₃Or (100) Nb SrTiO₃BiFe capable of being epitaxially grown on a substrate_0.7Co_0.3O_3-δThe photoelectric solid solution film improves the performance of the film better. The film obtained by the invention has high epitaxial degree, good crystallinity, excellent ferroelectric polarization performance and good carrier transport property, and can meet the research and development requirements of high-end electronic devices.

The invention uses a low-cost polymer auxiliary method to dope and modify BiFe by epitaxially growing oxygen vacancies_{1- x}Co_xO_3-δThe phase has great significance in that the low band gap, the high conductivity and the strong ferroelectric property exist in a single-phase material at the same time. The method does not need high-standard experimental equipment and complex operation process, can accurately control the stoichiometric ratio of the raw materials, and the obtained photoelectric solid solution film has good ferroelectricity and high conductivity, reduces the band gap of the energy band, and has good development potential in ferroelectric regulated logic devices and resistive memory devices.

Drawings

FIG. 1 is an XRD pattern of the thin film obtained in example 1.

FIG. 2 is a graph showing the hysteresis loop of the film obtained in example 1.

FIG. 3 shows a film obtained in example 1J-VCurve line.

Detailed Description

The present invention is further illustrated by the following examples, which are intended to be illustrative only and are not intended to be limiting.