A method for obtaining polarization of single-domain ferroelectric semiconductor single crystals

Abstract

This invention relates to a polarization method for obtaining a single-domain ferroelectric semiconductor single crystal, comprising the following steps: 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 materials is T. g S200: Heat the raw materials to a first preset temperature T1, T c <T1<T g The raw material is kept at a first preset temperature T1 for a first preset time S1 to ensure that the raw material is heated evenly. S300: After the heat preservation in step S200 is completed, the temperature of the raw material is reduced to room temperature. At the same time, light is introduced during the entire cooling process. The light intensity is within a first preset range. After the light is irradiated, a single-domain ferroelectric semiconductor single crystal is obtained.

Description

Technical Field

[0001] This invention relates to the field of ferroelectric crystal technology, and more particularly to a method for obtaining polarization of single-domain ferroelectric semiconductor single crystals. Background Technology

[0002] Ferroelectric semiconductor materials, due to their excellent ferroelectric, piezoelectric, nonlinear optical, photorefractive, electro-optic, and semiconductor properties, have significant application value in fields such as information storage and memory, smart sensors, pyroelectric infrared detection, photodetectors, ferroelectric photocatalysis, and ferroelectric photovoltaic devices. Regions in ferroelectric materials with the same polarization direction are called ferroelectric domains, and the regions separating different domains are called domain walls. Although multi-domain ferroelectric crystals have a large piezoelectric coefficient, the scattering effect of numerous disordered domain walls significantly reduces optical transmittance, limiting their application in electro-optic devices and transparent sensors. Conversely, single-domain ferroelectric single crystals, due to their superior optical and electro-optic properties, have significant application value in fields such as surface acoustic wave filters, solid-state self-frequency doubling lasers, and electro-optic devices.

[0003] Currently, the main polarization methods for single-domain ferroelectric single crystals include electric field polarization, optically assisted electric field polarization, and all-optical polarization. Among these, electric field polarization is the most commonly used method; however, it is limited by high energy consumption, susceptibility to cracking, and complex circuit design and construction. Compared to electric field polarization, optically assisted electric field polarization effectively reduces the electric field required for polarization by utilizing light illumination; however, this method still requires electrode fabrication and a complex DC bias device. All-optical polarization is simple in process and does not require an external electric field, giving it a significant advantage in single-domain polarization of ferroelectric semiconductor single crystals. However, this polarization method requires a laser, and the thermal effect caused by light absorption from high-energy lasers can easily induce irreversible structural phase transitions and surface damage in the single crystal. Furthermore, all-optical polarization is limited by the wavelength of visible light; during polarization, the ferroelectric single crystal can only absorb and utilize low-wavelength light, which greatly limits the all-optical polarization range of ferroelectric single crystals. Summary of the Invention

[0004] Based on the above analysis, the embodiments of the present invention aim to provide a method for obtaining polarization of a single-domain ferroelectric semiconductor single crystal, which can at least solve one of the above problems.

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

[0006] S100: Provides the raw material to be polarized, the Curie temperature of which is T. c The growth temperature of the raw materials is T. g ;

[0007] S200: Heat the raw material to a first preset temperature T1, T c <T1<Tg The raw material is kept at a first preset temperature T1 for a first preset time S1 to ensure that the raw material is heated evenly throughout.

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

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

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

[0011] Furthermore, the polarization method can process multiple raw materials simultaneously.

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

[0013] Furthermore, 70℃≤T1≤90℃.

[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℃ / min to 2℃ / min.

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

[0017] Furthermore, the first preset range is 1mW / cm². 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 during annealing to polarize the single crystal, 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 a few single-crystal samples at a time, resulting in low polarization efficiency. The polarization method provided by this invention is not limited by the number of single-crystal samples and can polarize multiple single-crystal samples simultaneously.

[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, and realizes the all-optical polarization of ferroelectric semiconductor single crystals with advantages such as low energy consumption, no damage and full visible light absorption.

[0023] (5) This invention obtains stable single-domain ferroelectric semiconductor single crystals through this polarization method.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 This is a photograph of a Sn2P2S6 single crystal before it was polarized in a specific embodiment.

[0027] Figure 2 This is a microscope image of a Sn2P2S6 single crystal before polarization in a specific embodiment.

[0028] Figure 3 The diagram shows the ferroelectric domain structure and local piezoelectric response of the Sn2P2S6 single crystal before polarization in the specific embodiment.

[0029] Figure 4 This is a photograph of a single-domain Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in a specific implementation embodiment.

[0030] Figure 5 This is a microscope image of a single-domain Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in a specific embodiment.

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

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

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

[0034] in, Figure 3 and Figures 6-8 In the figure, (a) is a diagram of the ferroelectric domain structure, and (b) is a diagram of the local piezoelectric response. Detailed Implementation

[0035] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which 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 intended 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 explicitly specified and limited, the term "connected" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0037] Throughout the text, the terms “top,” “bottom,” “above,” “below,” and “on top” refer to the relative positions of components of the device, such as the relative positions of the top and bottom substrates within the device. It is understood that the device is multifunctional and independent of its spatial orientation.

[0038] The working surface of this invention can typically be a plane or a curved surface, and can be inclined or horizontal. For ease of explanation, the embodiments of this invention are placed on a horizontal surface and used on a horizontal surface, thereby defining "height" and "vertical".

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

[0040] S100: Provides the raw material to be polarized, the Curie temperature of which is T. c The growth temperature of the raw materials is T. g ;

[0041] S200: Heat the raw material to a first preset temperature T1, T c <T1<T g The raw material is kept at a first preset temperature T1 for a first preset time S1 to ensure that the raw material is heated evenly throughout.

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

[0043] In step S100, the raw material is a raw bulk single crystal, specifically a multi-domain raw 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 must have a clean surface.

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

[0045] The growth temperature of the raw material refers to the ambient temperature that needs to be precisely controlled during the growth process. The growth temperature has a significant impact on the crystal growth rate, the integrity of the crystal structure, the formation of defects, and the final electrical properties. There is no absolutely fixed value for the crystal growth temperature, as it is influenced by various factors, such as the growth method, the purity of the raw material, the growth rate, and the equipment conditions.

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

[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 stage is increased from room temperature (25±5℃) to the first preset temperature T1 at a heating rate of 3℃ / min to 5℃ / min, so as to ensure that all parts of the ferroelectric crystal are heated uniformly, avoid local overheating or excessive temperature gradient, and make the crystal heated uniformly and reduce thermal stress.

[0049] Preferably, 70℃≤T1≤90℃. 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℃ / min to 2℃ / 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 excessive temperature change.

[0051] The introduced illumination can be visible light, sunlight, or simulated sunlight. For ease of control, simulated sunlight is preferred. The light source is a xenon lamp (Zhongke Microenergy, CME-Xe150P), with a wavelength range of 380nm to 780nm. The preferred first preset range is 1mW / cm². 2 ~5mW / cm 2 The diameter of the light spot is 3cm to 5cm.

[0052] The polarization method of this invention can solve the problems of high energy consumption, the need for DC bias devices, narrow full-optical polarization range, and easy sample damage in existing ferroelectric material polarization methods. This invention provides a method for simulating solar radiation to polarize single-domain ferroelectric semiconductor single crystals, which can achieve single-domain polarization of ferroelectric semiconductor single crystals without the need for complex DC bias devices, with low energy consumption, no damage, and polarization across the entire visible light spectrum.

[0053] The polarization method of this invention does not require a complex DC bias device, has low energy consumption, is non-destructive, and can polarize across the entire visible light spectrum. It is simple and efficient, can ensure a high degree of single-domain polarization of ferroelectric semiconductor single crystals, and does not exhibit crystal cracking after polarization, thus promoting the application of single-domain ferroelectric semiconductor single crystals.

[0054] This invention relates to a polarization method for obtaining a single-domain ferroelectric semiconductor single crystal. The steps are to heat the naturally grown ferroelectric semiconductor crystal to a temperature higher than the Curie temperature of the crystal but much lower than the growth temperature, hold it at the temperature, and then slowly cool the crystal to room temperature. During the cooling process, low-energy simulated sunlight is introduced to obtain the single-domain ferroelectric crystal.

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

[0056] S100: Obtain the raw material to be polarized, i.e., the raw material is a multi-domain bulk Sn2P2S6 ferroelectric semiconductor single crystal, Curie temperature T c Sn₂P₂S₆ single crystals were grown at 66℃ using the chemical vapor transport method. g The temperature is 600–650℃.

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

[0058] S300: After the heat preservation period, the temperature of the heating platform is reduced from 70℃ to room temperature at a rate of 0.5℃ / min. During the entire cooling process, a light intensity of 5mW / cm² is introduced. 2Simulated sunlight with a spot diameter of 3cm was used to treat the raw materials, and after the illumination was completed, a single-domain Sn2P2S6 ferroelectric semiconductor single crystal was obtained.

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

[0060] S100: Obtain the raw material to be polarized, i.e., the raw material is a multi-domain bulk Sn2P2S6 ferroelectric semiconductor single crystal, Curie temperature T c Sn₂P₂S₆ single crystals were grown at 66℃ using the chemical vapor transport method. g The temperature is 600–650℃.

[0061] S200: Use tweezers to gently place multiple raw materials on the heating stage, cover with a transparent bell jar, and raise the temperature of the heating stage from room temperature to 80℃ at a rate of 4℃ / min, and hold at 80℃ for 50 minutes to ensure uniform heating of the single crystal.

[0062] S300: After the heat preservation period, the temperature of the heating platform is reduced from 80℃ to room temperature at a rate of 1℃ / min. During the entire cooling process, a light intensity of 3mW / cm² is introduced. 2 Simulated sunlight with a spot diameter of 4cm was used to treat the raw materials, and after the illumination was completed, a single-domain Sn2P2S6 ferroelectric semiconductor single crystal was obtained.

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

[0064] S100: Obtain the raw material to be polarized, i.e., the raw material is a multi-domain bulk Sn2P2S6 ferroelectric semiconductor single crystal, Curie temperature T c Sn₂P₂S₆ single crystals were grown at 66℃ using the chemical vapor transport method. g The temperature is 600–650℃.

[0065] S200: Use tweezers to gently place multiple raw materials on the heating stage, cover with a transparent bell jar, and raise the temperature of the heating stage from room temperature to 90℃ at a rate of 5℃ / min, and hold at 90℃ for 30 minutes to ensure uniform heating of the single crystal.

[0066] S300: After the heat preservation period, the temperature of the heating platform is reduced from 90℃ to room temperature at a rate of 2℃ / min. During the entire cooling process, a light intensity of 1mW / cm² is introduced. 2 Simulated sunlight with a spot diameter of 5cm was used to treat the raw materials, and after the illumination was completed, a single-domain Sn2P2S6 ferroelectric semiconductor single crystal was obtained.

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

[0068] Figure 1 These are photographs of Sn2P2S6 single crystals before they were polarized, from Example 1 to Example 3.

[0069] Figure 2 These are microscopic images of Sn2P2S6 single crystals before polarization in Examples 1 to 3, taken using a Zeiss microscope (AZEISS, Imager. A2m). The microscopic images from the three microscopes are not significantly different. Figure 2 Microscopic images of the Sn2P2S6 single crystal before polarization in Example 2 are shown only as an example.

[0070] Figure 3 The ferroelectric multidomain structure of Sn2P2S6 single crystals before polarization (size 80×80μm) in Examples 1 to 3. 2 ) and local piezoelectric response diagram.

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

[0072] Figure 5 The images shown are microscopic images of single-domain Sn2P2S6 ferroelectric semiconductor single crystals obtained after polarization in Examples 1 to 3. The microscopes used in this invention are from Zeiss (AZEISS, Imager. A2m). The microscopic images of the three are not significantly different, and none of the crystals showed cracking after polarization. Figure 5 Microscopic images of a single-domain Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization in Example 1 are shown only as examples.

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

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

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

[0076] Characterization methods such as piezoelectric microscopy and local polarization reversal verified that the unpolarized Sn2P2S6 single crystal is a ferroelectric multidomain structure with good ferroelectric properties, such as... Figure 3 As shown.

[0077] The ferroelectric single-domain structure and local piezoelectric response of Sn2P2S6 ferroelectric semiconductor single crystal obtained after polarization [Example 1] were characterized by piezoelectric microscopy at a driving frequency of 350 kHz and a driving voltage of 1.0 V. (See figure). Figure 6 As shown. Figure 6 The ferroelectric domain structure of the Sn2P2S6 single crystal within an 80μm × 80μm range was observed, with no phase contrast difference, indicating it is a single-domain Sn2P2S6 single crystal, and no cracking was observed. Furthermore, 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 using a local polarization reversal characterization technique. The phase loop of the polarized Sn2P2S6 single crystal exhibited good hysteresis characteristics, further verifying that the polarized single crystal exhibits a ferroelectric single-domain structure.

[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 shown below. Figure 7 As shown, no phase contrast difference was observed in the phase diagram, indicating that it is a single-domain Sn2P2S6 single crystal. Moreover, the phase loop of the polarized Sn2P2S6 single crystal exhibits good hysteresis characteristics, further verifying that the polarized single crystal exhibits 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 shown below. Figure 8 As shown, no phase contrast difference was observed in the phase diagram, indicating that it is a single-domain Sn2P2S6 single crystal. Moreover, the phase loop of the polarized Sn2P2S6 single crystal exhibits good hysteresis characteristics, further verifying that the polarized single crystal exhibits a ferroelectric single-domain structure.

[0080] Reducing or even eliminating depolarization energy is an effective method for forming ferroelectric single-domain structures. There are generally two mechanisms for reducing depolarization energy: free charge compensation or the formation of striped domains with opposite polarization orientations. Ferroelectric semiconductor Sn₂P₂S₆ single crystals possess advantages such as high surface charge density, full visible light absorption, and photoinduced ion valence changes, allowing their interaction with sunlight to generate novel and controllable physical and chemical properties. This provides an important foundation for low-energy sunlight-induced modulation of large-area ferroelectric single domains. Therefore, when the temperature rises to T… cAt the above temperature, the ferroelectric domains of Sn2P2S6 single crystal disappear. During a slow cooling process above the Curie temperature, simulated sunlight is introduced, triggering a disproportionation reaction (reaction formula: Sn...). 2+ +hv=Sn 3+ +e;2Sn 3+ =Sn 2+ +Sn 4+ This process generates a large number of positively charged charges that accumulate on the crystal surface, compensating for the opposite-signed bound charges on the upper and lower surfaces of the crystal. This shields the depolarization field, reduces the depolarization energy, and prevents the formation of 180° domain walls in the Sn₂P₂S₆ single crystal, resulting in a final ferroelectric domain configuration of single-domain states. This invention utilizes this unique photoinduced ion valence change to significantly reduce the energy required for polarization of ferroelectric semiconductor single crystals.

[0081] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for obtaining polarization in a single-domain ferroelectric semiconductor single crystal, characterized in that, Includes the following steps: S100: Provides a multi-domain bulk Sn2P2S6 ferroelectric semiconductor single crystal as the raw material to be polarized, wherein the Curie temperature of the raw material is T. c The growth temperature of the raw materials is T. g ; S200: The raw material is placed on a heating stage with a transparent bell jar for heating. The temperature of the heating stage is increased from room temperature to a first preset temperature T1 at a rate of 3℃ / min to 5℃ / min, so as to heat the raw material to the first preset temperature T1. c <T1<T g 70℃≤T1≤90℃, keep the raw material at the first preset temperature T1 for a first preset time S1, 30min≤S1≤60min, so that the raw material is heated evenly. S300: After the heat preservation in step S200 is completed, the temperature of the heating table is reduced from T1 to room temperature at a cooling rate of 0.5℃ / min to 2℃ / min to lower the temperature of the raw materials to room temperature. Simultaneously, light is introduced during the entire cooling process, with the light intensity within the first preset range of 1mW / cm². 2 ~5mW / cm 2 After the illumination period, a single-domain Sn2P2S6 ferroelectric semiconductor single crystal was obtained.

2. The polarization method according to claim 1, characterized in that, It can process multiple raw materials at the same time.

3. The polarization method according to any one of claims 1 or 2, characterized in that, In step S300, the introduced illumination is visible light, sunlight, or simulated sunlight.

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