Polarization method for obtaining single-domain ferroelectric semiconductor single crystal

Abstract

The invention relates to a polarization method for obtaining a single-domain ferroelectric semiconductor single crystal, which comprises the following steps: S100: providing a raw material to be polarized, the Curie temperature of the raw material being Tc, and the growth temperature of the raw material being Tg; s200, the temperature of the raw material is increased to a first preset temperature T1, T1 is larger than Tc and smaller than Tg, the raw material is subjected to heat preservation for a first preset duration S1 at the first preset temperature T1, and all the positions of the raw material are evenly heated; and S300, after heat preservation in the step S200 is finished, the temperature of the raw material is reduced to the room temperature, meanwhile, illumination is introduced in the whole cooling process, the illumination intensity is located in a first preset range, and the single domain ferroelectric semiconductor single crystal is obtained after illumination is finished.

Description

Technical Field

[0001] The invention relates to the technical field of ferroelectric crystals, and in particular to a polarization method for obtaining a single-domain ferroelectric semiconductor single crystal. Background Art

[0002] Ferroelectric semiconductor materials have important application value in the fields of information storage and memory, intelligent sensors, pyroelectric infrared detection, photodetectors, ferroelectric photocatalysis, ferroelectric photovoltaic devices, etc. due to their good ferroelectric, piezoelectric, nonlinear optical, photorefractive, electro-optical and semiconductor properties. The regions with the same polarization direction in ferroelectric materials are called ferroelectric domains, and the regions that separate different domains are called domain walls. Although multi-domain ferroelectric crystals have huge piezoelectric coefficients, the scattering effect of a large number of disordered domain walls on light greatly reduces the optical transmittance, which restricts their application in the fields of electro-optical devices and transparent sensors. On the contrary, single-domain ferroelectric single crystals have important application value in the fields of surface acoustic wave filters, solid-state self-frequency doubling lasers, electro-optical devices, etc. due to their excellent optical and electro-optical properties.

[0003] At present, the main polarization methods for single-domain ferroelectric single crystals include electric field polarization, light-assisted electric field polarization, and all-optical polarization. Among them, electric field polarization is the most commonly used single-domain ferroelectric polarization method, but it is limited by factors such as high energy consumption, easy cracking, and cumbersome circuit design and construction. Compared with electric field polarization, light-assisted electric field polarization effectively reduces the electric field required for polarization with the help of light, but this polarization method still requires the preparation of electrodes and complex DC bias devices. The all-optical polarization process is simple and does not require an external electric field. It has outstanding advantages in the single-domain polarization of ferroelectric semiconductor single crystals. However, this polarization method requires lasers. The thermal effect caused by light absorption caused by high-energy lasers can easily induce irreversible structural phase changes and surface damage in single crystals. In addition, all-optical polarization is limited by the wavelength of visible light. During polarization, ferroelectric single crystals can only absorb and utilize low-band light, which greatly limits the all-optical polarization range of ferroelectric single crystals. Summary of the invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a polarization method for obtaining a single-domain ferroelectric semiconductor single crystal, which can at least solve one of the above problems.

[0005] The present invention provides a polarization method for obtaining a single-domain ferroelectric semiconductor single crystal, comprising the following steps:

[0006] S100: Providing a raw material to be polarized, wherein the Curie temperature of the raw material is T c , the growth temperature of the raw material is T g ;

[0007] S200: Heating the temperature of the raw material to a first preset temperature T1, T c <T1<Tg , keeping the raw material at a first preset temperature T1 for a first preset time S1, so that the raw material is heated evenly at all locations;

[0008] S300: After the heat preservation of step S200 is completed, the temperature of the raw material is lowered to room temperature, and light is introduced during the entire cooling process. The light intensity is within a first preset range, and a single-domain ferroelectric semiconductor single crystal is obtained after the light exposure.

[0009] Furthermore, the raw material is a multi-domain original bulk ferroelectric semiconductor single crystal.

[0010] Furthermore, in step S200, the raw materials are placed on a heating table with a transparent bell jar for heating.

[0011] Furthermore, the polarization method is capable of processing multiple pieces of raw materials simultaneously.

[0012] Furthermore, the temperature of the heating stage is increased from room temperature to a first preset temperature T1 at a heating rate of 3° C. / min to 5° C. / min.

[0013] Furthermore, 70°C≤T1≤90°C.

[0014] Furthermore, 30min≤S1≤60min.

[0015] Furthermore, in step S300, the temperature of the heating stage is reduced from T1 to room temperature at a cooling rate of 0.5°C / min to 2°C / min.

[0016] Furthermore, in step S300, the introduced light is visible light, sunlight or simulated sunlight.

[0017] Furthermore, the first preset range is 1 mW / cm 2 ~5mW / cm 2 .

[0018] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0019] (1) By introducing visible light, sunlight or simulated sunlight to polarize the single crystal during annealing, a single-domain ferroelectric semiconductor single crystal is obtained. This method can significantly reduce the energy consumption required for polarization;

[0020] (2) Compared with electric field polarization, the present invention does not require the use of a complex DC bias device, and there is no crystal cracking after polarization;

[0021] (3) Traditional polarization methods can only polarize one or several single crystal samples at a time, and the polarization efficiency is low. The polarization method provided by the present invention is not limited by the number of single crystal samples and can polarize multiple single crystal samples at the same time;

[0022] (4) The all-optical polarization method of the present invention is not limited by the wavelength of visible light. It uses low-energy visible light, sunlight or simulated sunlight to replace the commonly used high-energy laser to achieve all-optical polarization of ferroelectric semiconductor single crystals, which has the advantages of low energy consumption, no damage, and full visible light absorption;

[0023] (5) The present invention obtains a stable single-domain ferroelectric semiconductor single crystal through this polarization method.

[0024] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0026] Figure 1 is a photograph of a Sn2P2S6 single crystal before being polarized in a specific embodiment;

[0027] Figure 2 This is a microscope image of a Sn2P2S6 single crystal before being polarized in a specific embodiment;

[0028] Figure 3 The ferroelectric domain structure diagram and local piezoelectric response diagram of the Sn2P2S6 single crystal before being polarized in a specific implementation manner;

[0029] Figure 4 A photograph of a single-domain Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in a specific implementation manner;

[0030] Figure 5 A microscope image of a single-domain Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in a specific implementation manner;

[0031] Figure 6 The ferroelectric domain structure diagram and local piezoelectric response diagram of the Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in the specific implementation method [Example 1];

[0032] Figure 7 The ferroelectric domain structure diagram and local piezoelectric response diagram of the Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in the specific implementation method [Example 2];

[0033] Figure 8The ferroelectric domain structure diagram and local piezoelectric response diagram of the Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in the specific implementation method [Example 3];

[0034] in, Figure 3 and Figure 6 to Figure 8 In the figure, (a) is the ferroelectric domain structure diagram, and (b) is the local piezoelectric response diagram. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0036] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the term "connected" should be understood in a broad sense, for example, it can be a fixed connection, or a detachable connection, or an integral connection, which can be a mechanical connection, or an electrical connection, which can be a direct connection, or can be indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] The terms "top", "bottom", "above", "lower", and "on" used throughout the description are relative to the relative positions of components of a device, such as the relative positions of the top and bottom substrates within a device. It is understood that devices are multifunctional regardless of their orientation in space.

[0038] The common working surface of the present invention can be a plane or a curved surface, can be inclined, or can be horizontal. For the convenience of description, the embodiment of the present invention is placed on a horizontal plane and used on the horizontal plane, and "high and low" and "up and down" are defined in this way.

[0039] A specific embodiment of the present invention discloses a polarization method for obtaining a single-domain ferroelectric semiconductor single crystal, comprising the following steps:

[0040] S100: Providing a raw material to be polarized, wherein the Curie temperature of the raw material is T c , the growth temperature of the raw material is T g ;

[0041] S200: Heating the temperature of the raw material to a first preset temperature T1, T c <T1<T g , keeping the raw material at a first preset temperature T1 for a first preset time S1, so that the raw material is heated evenly at all locations;

[0042] S300: After the heat preservation of step S200 is completed, the temperature of the raw material is lowered to room temperature, and light is introduced during the entire cooling process. The light intensity is within a first preset range, and a single-domain ferroelectric semiconductor single crystal is obtained after the light exposure.

[0043] In step S100, the raw material is an original bulk single crystal, that is, a multi-domain original bulk ferroelectric semiconductor single crystal. The surface of the raw material needs to be cleaned before processing, that is, the raw material to be polarized is a raw material with a clean surface.

[0044] The Curie temperature of the raw material refers to the critical temperature at which the raw material changes from a ferroelectric phase to a paraelectric phase, also known as the ferroelectric phase transition temperature.

[0045] The growth temperature of the raw materials is the ambient temperature that needs to be precisely controlled during the growth of the raw materials. The growth temperature has a significant impact on the growth rate of the crystal, the integrity of the crystal structure, the formation of defects, and the final electrical properties. The growth temperature of the crystal does not have an absolute fixed value because it is affected by many factors, such as the growth method, raw material purity, growth rate, and equipment conditions.

[0046] In step S200, the raw material is placed on a heating platform with a transparent bell jar for heating. Specifically, the multi-domain original block single crystal is gently placed on the heating platform and covered with a transparent bell jar. The polarization method of the present invention can process multiple raw materials at the same time.

[0047] T1 is much smaller than T g , that is, T c <T1<<T g , preferably, T1<0.15*T g .

[0048] Preferably, the temperature of the heating platform rises from room temperature (25±5°C) to a first preset temperature T1 at a heating rate of 3°C / min to 5°C / min to ensure that all parts of the ferroelectric crystal are heated evenly, avoid local overheating or excessive temperature gradient, and heat the crystal evenly and reduce thermal stress.

[0049] Preferably, 70°C≤T1≤90°C and 30min≤S1≤60min.

[0050] In step S300, the temperature of the heating stage is reduced from T1 to room temperature at a cooling rate of 0.5°C / min to 2°C / min. The slow cooling provides sufficient time for the diffusion of solute atoms in the crystal, making the composition distribution of the crystal more uniform while avoiding thermal stress caused by rapid temperature changes.

[0051] The introduced light can be visible light, sunlight or simulated sunlight. For ease of control, simulated sunlight is preferably used. The light source is a xenon light source (Zhongke Micro Energy, CME-Xe150P), and the wavelength range of the light is 380nm to 780nm. The preferred first preset range is 1mW / cm 2 ~5mW / cm 2 , the spot diameter is 3cm~5cm.

[0052] The polarization method of the present invention can solve the problems of high energy consumption, need to use a DC bias device, narrow full-light polarization range, and easy damage to samples in the existing ferroelectric material polarization. The present invention provides a method for polarizing a single-domain ferroelectric semiconductor single crystal by simulating sunlight, which can achieve single-domain polarization of a ferroelectric semiconductor single crystal without using a complex DC bias device, with low energy consumption and no damage, and can be polarized within the full visible light band.

[0053] The polarization method of the present invention does not require the use of a complex DC bias device, has low energy consumption, is damage-free, and polarizes within the entire visible light band. It is simple and efficient, can ensure a high degree of monodomainization of ferroelectric semiconductor single crystals, and has no crystal cracking after polarization, thus promoting the application of monodomain ferroelectric semiconductor single crystals.

[0054] The present invention relates to a polarization method for obtaining a single-domain ferroelectric semiconductor single crystal, the steps of which are to heat a naturally grown ferroelectric semiconductor crystal to a temperature higher than the Curie temperature of the crystal but much lower than the growth temperature, to slowly cool the crystal to room temperature after heat preservation, and to introduce low-energy simulated sunlight during the cooling process, thereby obtaining a single-domain ferroelectric crystal.

[0055] [Example 1] A polarization method for obtaining a single-domain Sn2P2S6 ferroelectric semiconductor single crystal is provided, comprising the following steps:

[0056] S100: Obtain the raw material to be polarized, that is, the raw material is a multi-domain bulk Sn2P2S6 ferroelectric semiconductor single crystal with a Curie temperature T c The growth temperature of Sn2P2S6 single crystal is 66℃, and the chemical vapor transport method is used to grow the Sn2P2S6 single crystal. g 600~650℃;

[0057] S200: Use tweezers to gently place multiple raw materials on the heating table, cover with a transparent bell jar, and raise the temperature of the heating table from room temperature to 70°C at a heating rate of 3°C / min, and keep it at 70°C for 60 minutes to ensure that the single crystal is heated evenly.

[0058] S300: After the insulation is completed, the temperature of the heating platform is reduced from 70°C to room temperature at a cooling rate of 0.5°C / min. During the entire cooling process, the light intensity introduced is 5mW / cm 2The raw materials were irradiated with simulated sunlight with a spot diameter of 3 cm, and single-domain Sn2P2S6 ferroelectric semiconductor single crystals were obtained after the irradiation.

[0059] [Example 2] A polarization method for obtaining a single-domain Sn2P2S6 ferroelectric semiconductor single crystal is provided, comprising the following steps:

[0060] S100: Obtain the raw material to be polarized, that is, the raw material is a multi-domain bulk Sn2P2S6 ferroelectric semiconductor single crystal with a Curie temperature T c The growth temperature of Sn2P2S6 single crystal is 66℃, and the chemical vapor transport method is used to grow the Sn2P2S6 single crystal. g 600~650℃;

[0061] S200: Use tweezers to gently place multiple raw materials on the heating table, cover with a transparent bell jar, and raise the temperature of the heating table from room temperature to 80°C at a heating rate of 4°C / min, and keep it at 80°C for 50 minutes to ensure that the single crystal is heated evenly;

[0062] S300: After the insulation is completed, the temperature of the heating platform is reduced from 80°C to room temperature at a cooling rate of 1°C / min. During the entire cooling process, the light intensity introduced is 3mW / cm 2 The raw materials were irradiated with simulated sunlight with a spot diameter of 4 cm, and single-domain Sn2P2S6 ferroelectric semiconductor single crystals were obtained after the irradiation.

[0063] [Example 3] A polarization method for obtaining a single-domain Sn2P2S6 ferroelectric semiconductor single crystal is provided, comprising the following steps:

[0064] S100: Obtain the raw material to be polarized, that is, the raw material is a multi-domain bulk Sn2P2S6 ferroelectric semiconductor single crystal with a Curie temperature T c The growth temperature of Sn2P2S6 single crystal is 66℃, and the chemical vapor transport method is used to grow the Sn2P2S6 single crystal. g 600~650℃;

[0065] S200: Use tweezers to gently place multiple raw materials on the heating table, cover with a transparent bell jar, and raise the temperature of the heating table from room temperature to 90°C at a heating rate of 5°C / min, and keep it at 90°C for 30 minutes to ensure that the single crystal is heated evenly.

[0066] S300: After the insulation is completed, the temperature of the heating platform is reduced from 90°C to room temperature at a cooling rate of 2°C / min. During the entire cooling process, the light intensity introduced is 1mW / cm 2 The raw materials were irradiated with simulated sunlight with a spot diameter of 5 cm, and single-domain Sn2P2S6 ferroelectric semiconductor single crystals were obtained after the irradiation.

[0067] The ferroelectric domain structure of Sn2P2S6 single crystal before and after polarization was verified by piezoelectric force microscopy and local polarization reversal.

[0068] Figure 1 These are photos of Sn2P2S6 single crystals before polarization from [Example 1] to [Example 3].

[0069] Figure 2 The microscope images of Sn2P2S6 single crystals before polarization in [Example 1] to [Example 3] were taken using a Zeiss microscope (AZEISS, Imager.A2m). The microscope images of the three are not much different. Figure 2 The microscope image of the Sn2P2S6 single crystal of Example 2 before being polarized is shown only as an example.

[0070] Figure 3 Ferroelectric multi-domain structure of Sn2P2S6 single crystal before polarization (size 80×80μm) in [Example 1] to [Example 3] 2 ) and local piezoelectric response diagram.

[0071] Figure 4 These are photos of single-domain Sn2P2S6 ferroelectric semiconductor single crystals obtained after polarization of [Example 1] to [Example 3].

[0072] Figure 5 These are microscope images of single-domain Sn2P2S6 ferroelectric semiconductor single crystals obtained after polarization in [Example 1] to [Example 3]. The present invention uses a microscope from Zeiss (AZEISS, Imager.A2m). There is little difference between the microscope images of the three, and no cracking occurs in the crystals after polarization. Figure 5 The microscope image of the single-domain Sn2P2S6 ferroelectric semiconductor single crystal obtained after poling in Example 1 is shown only as an example.

[0073] Figure 6 The ferroelectric single domain structure of Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in [Example 1] (size 80×80μm 2 ) and local piezoelectric response diagram.

[0074] Figure 7 The ferroelectric single domain structure of Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in Example 2 (size 80×80μm 2 ) and local piezoelectric response diagram.

[0075] Figure 8 The ferroelectric single domain structure of Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in [Example 3] (size 80×80μm 2 ) and local piezoelectric response diagram.

[0076] Through characterization methods such as piezoelectric force microscopy and local polarization reversal, it was verified that the Sn2P2S6 single crystal before polarization has a ferroelectric multi-domain structure and has good ferroelectric properties, such as Figure 3 shown.

[0077] By using piezoelectric force microscopy, the ferroelectric single domain structure and local piezoelectric response diagram of the Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization at a driving frequency of 350kHz and a driving voltage of 1.0V [Example 1] are shown in Figure 1. Figure 6 shown. Figure 6 The ferroelectric domain structure of the Sn2P2S6 single crystal within the range of 80μm×80μm was not observed. No phase contrast difference was observed, indicating that it was a single-domain Sn2P2S6 single crystal, and the crystal did not crack. Moreover, the local piezoelectric response of the single-domain Sn2P2S6 ferroelectric semiconductor single crystal obtained in [Example 1] was tested at a driving voltage of 6.0V through the local polarization reversal characterization technology. The phase loop of the Sn2P2S6 single crystal after polarization showed good hysteresis characteristics, which further verified that the single crystal showed a ferroelectric single domain structure after polarization.

[0078] Under the same test conditions, the ferroelectric single domain structure and local piezoelectric response diagram of the Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in [Example 2] are as follows: Figure 7 As shown. No phase contrast difference was observed in the phase image, indicating that it was a single-domain Sn2P2S6 single crystal. Moreover, the phase loop of the Sn2P2S6 single crystal after poling showed good hysteresis characteristics, further verifying that the single crystal after poling showed a ferroelectric single-domain structure.

[0079] Under the same test conditions, the ferroelectric single domain structure and local piezoelectric response diagram of the Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in [Example 3] are as follows: Figure 8 As shown. No phase contrast difference was observed in the phase image, indicating that it was a single-domain Sn2P2S6 single crystal. Moreover, the phase loop of the Sn2P2S6 single crystal after poling showed good hysteresis characteristics, further verifying that the single crystal after poling showed a ferroelectric single-domain structure.

[0080] Reducing or even eliminating the depolarization energy is an effective way to form a ferroelectric single domain structure. There are usually two mechanisms to reduce the depolarization energy: free charge compensation or the formation of stripe domains with opposite polarization orientations. Ferroelectric semiconductor Sn2P2S6 single crystals have advantages such as high surface charge density, full visible light absorption characteristics, and photoinduced ion valence change, so that the process of its interaction with sunlight can derive novel and controllable physical and chemical properties, providing an important basis for low-energy sunlight regulation of large-area ferroelectric single domains. Therefore, when the temperature rises to T cWhen the temperature is above the Curie temperature, the ferroelectric domain of the Sn2P2S6 single crystal disappears. When the simulated sunlight is introduced into the slow cooling process above the Curie temperature, a disproportionation reaction occurs (the reaction formula is: Sn 2+ +hv=Sn 3+ +e;2Sn 3+ =Sn 2+ +Sn 4+ ) generates a large number of positive negative charge carriers that gather on the crystal surface, compensating for the opposite bound charges on the upper and lower surfaces of the crystal, thereby shielding the depolarization field, reducing the depolarization energy, and preventing the Sn2P2S6 single crystal from forming a 180° domain wall, resulting in the final ferroelectric domain configuration being a single domain state. The present invention utilizes this unique photoinduced ion valence change to greatly reduce the energy required for the polarization of the ferroelectric semiconductor single crystal.

[0081] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for obtaining a polarization of a single-domain ferroelectric semiconductor single crystal, characterized in that: The following steps are involved: S100: Providing a raw material to be polarized, wherein the Curie temperature of the raw material is T c , the growth temperature of the raw material is T g ; S200: Heating the raw material to a first preset temperature T1, T c <T1<T g , keeping the raw material at a first preset temperature T1 for a first preset time S1, so that the raw material is heated evenly at all locations; S300: After the heat preservation of step S200 is completed, the temperature of the raw material is lowered to room temperature, and light is introduced during the entire cooling process. The light intensity is within a first preset range, and a single-domain ferroelectric semiconductor single crystal is obtained after the light exposure.

2. The polarization method according to claim 1, characterized in that: The raw material is a multi-domain original bulk ferroelectric semiconductor single crystal.

3. The polarization method according to claim 1, characterized in that: In step S200, the raw material is placed on a heating table with a transparent bell jar for heating.

4. The polarization method according to claim 3, characterized in that: Capable of processing multiple pieces of raw material simultaneously.

5. The polarization method according to claim 3, characterized in that: The temperature of the heating stage is increased from room temperature to a first preset temperature T1 at a heating rate of 3° C. / min to 5° C. / min.

6. The polarization method according to claim 5, characterized in that: 70℃≤T1≤90℃。 7. The polarization method according to claim 1, characterized in that: 30min≤S1≤60min.

8. The polarization method according to claim 3, characterized in that: In step S300, the temperature of the heating stage is reduced from T1 to room temperature at a cooling rate of 0.5°C / min to 2°C / min.

9. The polarization method according to any one of claims 1 to 8, characterized in that: In step S300, the introduced light is visible light, sunlight or simulated sunlight.

10. The polarization method according to claim 9, characterized in that: The first preset range is 1mW / cm 2 ~5mW / cm 2 .

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