阅读说明：本技术 一种全氧化物铁电光电二极管及其制备方法 (Full-oxide ferroelectric photodiode and preparation method thereof ) 是由 杨锋 刘芬 林延凌 季凤岐 岳炳臣 于 2019-09-23 设计创作，主要内容包括：本发明公开了一种全氧化物铁电光电二极管及其制备方法,其包括基底,所述基底上覆有LSMO层,所述LSMO层上覆有BFCO层,所述BFCO层上覆有ITO层。其中,所述LSMO层为外延生长的La<Sub>0.7</Sub>Sr<Sub>0.3</Sub>MnO<Sub>3</Sub>薄膜,所述BFCO层为外延生长的BiFe<Sub>0.7</Sub>Co<Sub>0.3</Sub>O<Sub>3-δ</Sub>薄膜。本发明利用铁电极化与电极之间肖特基结区势垒的耦合作用,促进器件中光生电子空穴对的分离和高效收集,增强了光电流响应和铁电极化对二极管电流的调制性,兼具了铁电性和半导性的优点,具有大的光电流响应,且具有很好的极化可调性。(The invention discloses a full-oxide ferroelectric photodiode and a preparation method thereof. Wherein the LSMO layer is La grown epitaxially 0.7 Sr 0.3 MnO 3 A film, wherein the BFCO layer is epitaxially grown BiFe 0.7 Co 0.3 O 3‑δ A film. The invention utilizes the coupling effect of the Schottky junction region potential barrier between the ferroelectric polarization and the electrode to promote the separation and the high-efficiency collection of the photo-generated electron hole pair in the device, thereby enhancing the light current responseThe method has the advantages of good modulation of diode current due to ferroelectric polarization, good ferroelectric and semiconducting properties, large photocurrent response, and good polarization adjustability.)

1. An all-oxide ferroelectric photodiode comprising a substrate, characterized in that: the substrate is covered with an LSMO layer, the LSMO layer is covered with a BFCO layer, and the BFCO layer is covered with an ITO layer; the LSMO layer is La grown epitaxially_0.7Sr_0.3MnO₃A film, wherein the BFCO layer is epitaxially grown BiFe_0.7Co_0.3O_3-δA film.

2. The all-oxide ferroelectric photodiode of claim 1, further comprising:

preferably, the substrate is (100) oriented single crystal SrTiO₃；

Preferably, the thickness of the LSMO layer is 10-20 nm;

preferably, the thickness of the BFCO layer is 90-120 nm;

preferably, the thickness of the ITO layer is 100-600 nm.

3. A preparation method of a full-oxide ferroelectric photodiode is characterized by comprising the following steps:

(1) epitaxially growing an LSMO thin film on the substrate by adopting a polymer auxiliary method to obtain an LSMO/substrate;

(2) taking the LSMO/substrate obtained in the step (1) as a substrate, and epitaxially growing a BFCO film on the LSMO/substrate by adopting a high-molecular auxiliary method to obtain the BFCO/LSMO/substrate;

(3) depositing ITO on the BFCO/LSMO/substrate obtained in the step (2) by using an ITO target by adopting a pulse laser deposition method to form ITO/BFCO/LSMO/substrate;

(4) and (4) carrying out rapid heat treatment on the ITO/BFCO/LSMO/substrate obtained in the step (3) in a nitrogen atmosphere at the temperature of 300-600 ℃ to obtain the full-oxide ferroelectric photodiode.

4. The method of claim 3, wherein: the preparation method of the LSMO thin film comprises the following steps:

a. according to the molar ratio La: sr: mn = 7: 3: weighing (CH)₃COOH)₃La、(CH₃COOH)₂Sr and (CH)₃COOH)₂Mn, mixing the Mn, polyethyleneimine, ethylenediamine tetraacetic acid, glacial acetic acid and water to prepare a precursor solution with the LSMO concentration of 0.05mol/L ~ 0.15.15 mol/L;

b. putting the substrate into a spin coater, controlling the humidity at 30-50% and the temperature at 70-80%^oC, coating the precursor solution on a substrate, firstly spinning the film at 500rpm for 5s, and then spinning the film at 5000-6000rpm until the thickness of the film meets the requirement;

c. the substrate coated with the thin film in the previous step is processed at 250-300^oC, heat treatment for 5-10 min, then annealing in a quartz tube furnace, firstly from room temperature by 1-5^oThe rate of C/min is increased to 400-^oC, heat preservation 20-40 min; raising the temperature to 900-1000 ℃ at the speed of 40-50 ℃/min, and preserving the heat for 2-3 h; o in the furnace₂The flow rate is 0.5-1L/min; and taking out the substrate after the furnace temperature is naturally cooled to room temperature to obtain the LSMO/substrate.

5. The method according to claim 4, wherein:

preferably, the mass ratio of the polyethyleneimine to the ethylenediamine tetraacetic acid is 1:1, and the concentrations of the polyethyleneimine and the ethylenediamine tetraacetic acid in the precursor solution are both 0.02-0.04 g/ml;

preferably, the volume ratio of glacial acetic acid to water is 1: 1.

6. The method according to claim 4, wherein:

preferably, the concentration of the LSMO precursor solution is 0.1 mol/L;

preferably, when the single-layer LSMO thin film is prepared, the humidity is controlled to be 40%;

preferably, when the single-layer LSMO thin film is prepared, the rotating speed of the spin coater is 6000 rpm;

preferably, O in the furnace is used for preparing a single layer LSMO thin film₂The flow rate was 0.7L/min.

7. The method of claim 3, wherein: the preparation method of the BFCO film comprises the following steps:

a. the molar ratio Bi: fe: co = 10: 7: 3 weighing bismuth nitrate, ferric nitrate and cobalt nitrate, uniformly stirring and mixing the bismuth nitrate, ferric nitrate and cobalt nitrate with a regulator and a mixed solvent to prepare BiFe_0.7Co_0.3O₃Precursor solution with the concentration of 0.1 mol/L ~ 0.3.3 mol/L;

b. putting the LSMO/substrate into a spin coater, controlling the humidity at 11-15% and the temperature at 70-90 ℃, then coating the precursor solution on the LSMO/substrate, and preparing a single-layer film by adopting a spin coating method; 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, spinning the films at the speed of 5000 plus 6000rpm for 1-2 minutes;

c. after the single layer film was applied, the samples were tested at 250 ℃ to 300-^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-;

d. and (c) repeating the steps b and c, and preparing each layer of film by adopting a layer-by-layer annealing process until the final film thickness is 90 ~ 120 nm, so as to obtain the BFCO/LSMO/substrate.

8. The method of claim 7, wherein:

preferably, when preparing BFCO thin films, 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;

preferably, when the BFCO thin film is prepared, the mixed solvent is a mixture of glacial acetic acid, ethylene glycol and ethylene glycol methyl ether, wherein the molar ratio of bismuth salt to glacial acetic acid is 1:5-8, the volume ratio of ethylene glycol and ethylene glycol methyl ether is 1:1, and the ethylene glycol and ethylene glycol methyl ether are used in an amount to make the precursor solution have the required concentration.

9. The method of claim 7, wherein:

preferably, when preparing BFCO thin films, BiFe_0.7Co_0.3O₃The concentration is 0.2 mol/L;

preferably, when the BFCO film is prepared, the first layer of film is subjected to film spinning at the speed of 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 films are spun off at a speed of 5500rpm for 1 minute;

preferably, when preparing the BFCO film, after coating the single-layer film, the sample is heat-treated at 280 ℃ for 5 minutes and then annealed 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.

10. The method of claim 3, wherein: in the step (3), during pulsed laser deposition, the BFCO/LSMO/substrate and the ITO target material are placed into a vacuum chamber of pulsed laser deposition equipment, and the vacuum chamber is vacuumized until the vacuum degree reaches 4 multiplied by 10^-5Below Torr, the temperature of the vacuum chamber is adjusted to 100 ~ 180 deg.C, the BFCO/LSMO/substrate and ITO target are rotated, and the oxygen pressure is adjusted to 1 × 10^-2～6×10^-2Torr and laser energy density of 2-3J/cm²。

Technical Field

The invention relates to an all-oxide ferroelectric photodiode and a preparation method thereof, belonging to the technical field of lead-free ferroelectric photodiode devices.

Background

Under two opposite ferroelectric polarization states, the ferroelectric diode presents a high-conductivity state and a low-conductivity state, bipolar switching can be realized between the two states, and further nondestructive reading of binary information can be realized. The device has an ultra-fast operating speed (1-2 ps, depending on the polarization switching time) and an ultra-high switching ratio (up to 1: 3000). However, most ferroelectrics are wide bandgap semiconductors which limit the maximum diode current to ≈ 20mA cm^-2The storage logic state is difficult to be stably detected using the sense amplifier in the existing circuit, so that one has to develop a semiconductive ferroelectric material having both excellent ferroelectric and semiconductor transport properties.

Another important aspect of ferroelectric diodes is their strong photoelectric response, especially the induced photovoltage under light is still much larger than the band gap of the material. This is not achievable with conventional PN junction solar cells. The only unsatisfactory is that the photocurrent induced under illumination is still relatively small, which as mentioned above can improve the photocurrent response by adjusting the band gap of the ferroelectric material. BiFeO₃Has good room temperature ferroelectric property, is a material with the smallest gap in the ferroelectric material, and is hopeful to be made into a high-conductivity ferroelectric semiconductor material by further modifying the material. However, even with good ferroelectric semiconductor materials, there is a great distance from a good device, and it is not easy to integrate the ferroelectric, the electrode, and the substrate.

Disclosure of Invention

The invention provides a full-oxide ferroelectric photodiode, which is composed of a substrate, an epitaxial growth LSMO layer and an epitaxial growth BFCO layer attached to the substrate, has narrow band gap, and utilizes the coupling effect of Schottky junction region barrier between ferroelectric polarization and electrodes to promote the separation and high-efficiency collection of photo-generated electron hole pairs in a device, thereby enhancing the photocurrent response and the modulation of the ferroelectric polarization on diode current.

The invention also provides a preparation method of the full-oxide ferroelectric photodiode, the ferroelectric photodiode is prepared by adopting a polymer auxiliary method, the cost is low, the industrial production is convenient, and the appeal of dreaming in the industry is solved.

So far, no device report such as the structure of the invention exists, and no report of adopting a macromolecule assisted method to epitaxially prepare the product of the invention exists. The polymer-assisted method is a method in which a polymer is added to a precursor solution for preparing a thin film, and the thin film is epitaxially grown with the aid of the polymer. The device is composed of full oxide, and how to realize high-quality epitaxially grown electrodes on a substrate and epitaxially grow high-crystallinity and high-performance BFCO ferroelectric semiconductor films on the electrodes are important points influencing the performance of the device. The technical scheme of the invention is described in detail below.

A full-oxide ferroelectric photodiode comprises a substrate, wherein an LSMO layer is coated on the substrate, a BFCO layer is coated on the LSMO layer, and an ITO (indium tin oxide) layer is coated on the BFCO layer. Wherein the LSMO layer is La grown epitaxially_0.7Sr_0.3MnO₃A film, wherein the BFCO layer is epitaxially grown BiFe_0.7Co_0.3O_3-δA film.

Further, the substrate is (100) oriented single crystal SrTiO₃Abbreviated as STO.

Further, the thickness of the LSMO layer is 10-20 nm, preferably 10 nm.

Further, the BFCO layer is BiFe doped with oxygen vacancy_0.7Co_0.3O_3-δThe layer has a narrow band gap, both ferroelectric and good semiconductor transport properties, and a thickness of 90-120 nm.

Furthermore, the ITO layer is a transparent electrode layer, and the thickness of the ITO layer is 100-600 nm.

The invention also provides a preparation method of the full-oxide ferroelectric photodiode, which comprises the following steps:

(1) epitaxially growing an LSMO thin film on the substrate by adopting a polymer auxiliary method to obtain an LSMO/substrate;

(2) taking the LSMO/substrate obtained in the step (1) as a substrate, and epitaxially growing a BFCO film on the LSMO/substrate by adopting a high-molecular auxiliary method to obtain the BFCO/LSMO/substrate;

(3) depositing ITO on the BFCO/LSMO/substrate obtained in the step (2) by using an ITO target by adopting a pulse laser deposition method to form ITO/BFCO/LSMO/substrate;

(4) and (4) carrying out rapid thermal treatment (RTA) on the ITO/BFCO/LSMO/substrate obtained in the step (3) in a nitrogen atmosphere at the temperature of 300-600 ℃ to obtain the full-oxide ferroelectric photodiode.

Further, before growing the LSMO thin film on the substrate, the substrate is cleaned.

Further, a polymer-assisted method is adopted to epitaxially grow the LSMO thin film on the substrate, and the process is as follows:

a. according to the molar ratio La: sr: mn = 7: 3: weighing (CH)₃COOH)₃La、(CH₃COOH)₂Sr and (CH)₃COOH)₂Mn, and then mixing the Mn and the Mn with Polyethyleneimine (PEI), Ethylene Diamine Tetraacetic Acid (EDTA), glacial acetic acid and water to prepare a precursor solution with the LSMO concentration of 0.05mol/L ~ 0.15.15 mol/L;

b. putting the substrate into a spin coater, controlling the humidity at 30-50% and the temperature at 70-80%^oC, coating the precursor solution on a substrate, firstly spinning the film at 500rpm for 5s, and then spinning the film at 5000-6000rpm until the thickness of the film meets the requirement;

c. the substrate coated with the thin film in the previous step is processed at 250-300^oC, heat treatment for 5-10 min, then annealing in a quartz tube furnace, firstly from room temperature by 1-5^oThe rate of C/min is increased to 400-^oC, preserving heat for 20-40 min; raising the temperature to 900-1000 ℃ at the speed of 40-50 ℃/min, and preserving the heat for 2-3 h; o in the furnace₂The flow rate is 0.5-1L/min; naturally cooling to room temperature, and takingAnd (4) taking out the substrate to obtain the LSMO/substrate. According to the preparation method, the obtained LSMO thin film is epitaxially grown.

Furthermore, the concentration of the precursor solution, the selection and content of the high molecules, the humidity of the spin coating and the annealing process conditions are the keys for ensuring the high-quality epitaxial growth of the LSMO thin film.

Preferably, the mass ratio of the polyethyleneimine to the ethylenediamine tetraacetic acid is 1:1, and the concentrations of the polyethyleneimine and the ethylenediamine tetraacetic acid in the precursor solution are the same and are 0.02 to 0.04 g/ml. The polyethyleneimine and the ethylene diamine tetraacetic acid have the function of assisting epitaxial growth.

Preferably, the volume ratio of glacial acetic acid to water is 1: 1.

Preferably, the concentration of the LSMO precursor solution is 0.1 mol/L.

Preferably, the humidity is controlled at 40% when preparing a single layer LSMO thin film.

Preferably, the spin speed of the spin coater is 6000rpm when preparing the single layer LSMO thin film.

Preferably, O in the furnace is used for preparing a single layer LSMO thin film₂The flow rate was 0.7L/min.

When the preferable process conditions are adopted, the obtained LSMO thin film has better crystallinity and better epitaxial growth.

Further, a BFCO film is epitaxially grown on the LSMO/substrate by a polymer-assisted method, and the process is as follows:

a. the molar ratio Bi: fe: co = 10: 7: 3 weighing bismuth nitrate, ferric nitrate and cobalt nitrate, uniformly stirring and mixing the bismuth nitrate, ferric nitrate and cobalt nitrate with a regulator and a mixed solvent to prepare BiFe_0.7Co_0.3O₃Precursor solution with the concentration of 0.1 mol/L ~ 0.3.3 mol/L;

b. putting the LSMO/substrate into a spin coater, controlling the humidity at 11-15% and the temperature at 70-90 ℃, then coating the precursor solution on the LSMO/substrate, and preparing a single-layer film by adopting a spin coating method; 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, spinning the films at the speed of 5000 plus 6000rpm for 1-2 minutes;

c. after the single-layer film is coated, the sample is thermally treated at the temperature of 250-300 ℃ for 5-10 minutes and then is annealed in a quartz tube furnace, wherein the annealing procedure comprises the following steps: maintaining N in the furnace₂The flow is 0.1-1L/min, the temperature is increased from room temperature to 480 ℃ of 400-;

d. and (c) repeating the steps b and c, and preparing each layer of film by adopting a layer-by-layer annealing process until the final film thickness is 90 ~ 120 nm, so as to obtain the BFCO/LSMO/substrate.

Further, when preparing the BFCO film, 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.

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

Further, when the BFCO film is prepared, the ratio of bismuth nitrate to ferric nitrate to cobalt nitrate is 10: 7: 3, since the BiFe of the invention is added_0.7Co_0.3O_3-δFor epitaxial growth, therefore, no bismuth loss exists, and the bismuth salt does not need to be added excessively.

Furthermore, the selection of the regulator, the concentration of the precursor solution, the humidity of the spin coating, the spin coating condition and the annealing process condition are the keys for ensuring the high-quality epitaxial growth of the BFCO film.

Preferably, when preparing BFCO thin films, BiFe_0.7Co_0.3O₃The concentration is 0.2 mol/L.

Preferably, when the BFCO film is prepared, the first layer of film is subjected to film spinning at the speed of 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.

Preferably, when preparing the BFCO film, after coating the single-layer film, the sample is heat-treated at 280 ℃ for 5 minutes and then annealed 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.

Further, in the step (3), during pulsed laser deposition, the BFCO/LSMO/substrate and the ITO target material are placed into a vacuum chamber of pulsed laser deposition equipment, and vacuum pumping is carried out until the vacuum degree reaches 4 multiplied by 10^-5Below Torr, the temperature of the vacuum chamber is adjusted to 100 ~ 180 deg.C, the BFCO/LSMO/substrate and ITO target are rotated, and the oxygen pressure is adjusted to 1 × 10^-2～6×10^-2Torr and laser energy density of 2-3J/cm²。

Further, in the step (4), the ITO film obtained by deposition is subjected to rapid RTA heat treatment at the temperature of 600 ℃ and 300 ℃ in a nitrogen atmosphere for 10-15 minutes to further crystallize the ITO layer.

The invention has the beneficial effects that:

1. the invention skillfully utilizes the regulation and control function of the iron polarization on the Schottky barrier of the interface between the upper electrode and the lower electrode to control the high-low resistance state of the current of the ferroelectric diode, and can realize the application of the ferroelectric diode in a resistive memory. When light exists, the ferroelectric layer is used as an absorption layer, the separation of a photoproduction electron hole pair is effectively promoted by the synergistic action of a depolarization electric field and Schottky barriers between the absorption layer and upper and lower electrodes, the photoelectric conversion performance of a device is improved, the photocurrent response and the modulation of ferroelectric polarization on diode current are enhanced, and the device has the advantages of ferroelectricity and semiconductivity and expands the application of the device in the photovoltaic field and photoelectric memories.

2. The invention prepares the epitaxial LSMO electrode film with good conductivity on the substrate by a macromolecule assisted method, so that the epitaxial growth is extended to the preparation of the BFCO film, the BFCO ferroelectric semiconductor film with high crystallization quality/narrow band gap is obtained, the visible light absorption is effectively improved, the carrier recombination is reduced, and the photocurrent and dark current response are improved.

3. The method is a polymer-assisted method, has low requirements on experimental equipment, can accurately control the stoichiometric ratio of the raw materials, and is simple and convenient in process operation and easy to produce.

Drawings

FIG. 1 is a schematic structural diagram of a full oxide ferroelectric photodiode according to the present invention.

FIG. 2 is an XRD test pattern of the BFCO/LSMO/STO structure prepared in example 1.

FIG. 3 shows the positive and negative remanent polarization of the fully-oxide ferroelectric photodiode prepared in example 1 under no lightJ - VCurve line.

FIG. 4 shows the illumination of the fully-oxide ferroelectric photodiode prepared in example 1 under positive and negative remanent polarizationJ - VCurve line.

Detailed Description

The present invention is further illustrated by the following specific examples, which are provided for purposes of illustration only and are not intended to be limiting.