Ag-bst based thermoelectric thin film for photothermal electric detector and preparation method and application thereof

Abstract

This invention discloses an Ag-BST-based thermoelectric thin film for photothermal detectors, its preparation method, and its applications. The key feature is that the chemical structural formula of the thin film material is Ag. x (Bi) 0.5 Sb 1.5 Te3) 100‑x The thin film material, in which 6.61 at.% ≤ x ≤ 54.61 at.%, was obtained by dual-target co-sputtering of a BST alloy target and a metallic Ag target in a magnetron sputtering coating system. The nano-AgSbTe2 phase is distributed in the form of discontinuous nano-islands on Bi. 0.5 Sb 1.5 The Te3 matrix also provides the application of Ag-BST-based thermoelectric thin films in the fabrication of photothermal detectors. The advantage is that while maintaining stable conductivity, the Seebeck coefficient of the material is greatly improved. The self-powered photothermal detector successfully fabricated based on this film exhibits excellent voltage response performance in a wide wavelength range of 350-980 nm.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection and thermoelectric energy conversion technology, and in particular relates to an Ag-BST-based thermoelectric thin film for photothermal detectors, its preparation method and application. Background Technology

[0002] Photothermal detectors (PTEs) operate based on the synergistic effect of photothermal and Seebeck effects: incident light is converted into heat by the absorption layer, causing a local temperature rise in the device. This temperature difference is converted into a voltage signal by integrated high-performance thermoelectric materials. Due to their outstanding advantages such as not requiring external bias voltage (self-powered), theoretically having no dark current noise, and a wide response spectrum (from ultraviolet to terahertz), PTE detectors have become the research frontier of next-generation photoelectric detection technology.

[0003] The core performance indicator of a PTE detector is voltage response rate (R). V The specific detectivity (D*) is directly proportional to the Seebeck coefficient (S) of the thermoelectric material. A high Seebeck coefficient means that the device can generate a stronger electrical signal output for weak photothermal signals, thus achieving extremely high detection sensitivity. However, current PTE detectors generally use conventional thermoelectric materials (such as Bi2Te3 and Sb2Te3), whose Seebeck coefficients are limited (usually below 200 μV / K), severely restricting further improvements in detector responsivity.

[0004] Bi 0.5 Sb 1.5 Te3 (BST) bulk exhibits intrinsically high S (>200 μV / K) at room temperature, but when fabricated into a <200 nm thin film, grain boundary scattering leads to degradation of electrical transport properties, with the Seebeck coefficient dropping to 150-200 μV / K, which is insufficient to meet the requirements of high-performance PTE detectors. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an Ag-BST-based thermoelectric thin film for photothermal detectors that significantly improves the Seebeck coefficient of the material while maintaining stable electrical conductivity, as well as its preparation method and its application in self-powered, broadband photothermal detectors.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is: an Ag-BST-based thermoelectric thin film for photothermal detectors, wherein the chemical structural formula of the thin film material is Ag. x (Bi) 0.5 Sb 1.5 Te3) 100-xWhere 6.61 at.% ≤ x ≤ 54.61 at.%, the thin film material is obtained by dual-target co-sputtering in a magnetron sputtering coating system using a BST alloy target and a metallic Ag target.

[0007] Preferably, the thin film material is a nano-AgSbTe2 phase distributed in the form of discontinuous nano-islands on the Bi. 0.5 Sb 1.5 In the Te3 matrix.

[0008] Preferably, the chemical structural formula of the thin film material is Ag. 6.61 (Bi) 0.5 Sb 1.5 Te3) 93.39 .

[0009] Preferably, the chemical structural formula of the thin film material is Ag. 16.79 (Bi) 0.5 Sb 1.5 Te3) 83.21 .

[0010] Preferably, the chemical structural formula of the thin film material is Ag. 25.07 (Bi) 0.5 Sb 1.5 Te3) 74.93 .

[0011] Preferably, the chemical structural formula of the thin film material is Ag. 54.61 (Bi) 0.5 Sb 1.5 Te3) 45.39 .

[0012] This invention also provides a method for preparing the above-mentioned Ag-BST-based thermoelectric thin film for photothermal detectors, comprising the following steps: in a magnetron sputtering system, Bi... 0.5 Sb 1.5 The Te3 target is mounted on a magnetron RF sputtering target, and the Ag target is mounted on a magnetron DC sputtering target, using a quartz wafer or silicon oxide wafer as the substrate; the sputtering chamber is evacuated to a vacuum level ≤6.0×10⁻⁶. -6 Pa, introduce high-purity argon gas at a flow rate of 30 mL / min to the ignition pressure; control Bi 0.5 Sb 1.5 The sputtering power of the Te3 target was 30 W, and the sputtering power of the Ag target ranged from 1 W to 15 W. Sputtering was performed for a total of 600 s at room temperature to deposit an Ag-BST-based thermoelectric thin film on the substrate. The chemical structure of the film is Ag. x (Bi) 0.5 Sb 1.5 Te3) 100-x, where 6.61 at.% ≤ x ≤ 54.61 at.%.

[0013] The present invention also provides the application of the above-mentioned Ag-BST-based thermoelectric thin film in the preparation of photothermoelectric detectors, wherein the Ag-BST thermoelectric thin film serves as the core thermoelectric conversion layer.

[0014] Compared with the prior art, the advantages of the present invention are as follows: The present invention provides an Ag-BST-based thermoelectric thin film for photothermal detectors, its preparation method and application, and constructs an AgSbTe2 (AST) nanophase and Bi... 0.5 Sb 1.5 Multiphase heterostructure thin films composed of Te3 (BST) matrix. In this system, there are two dominant physical mechanisms: 1) when forming nanocrystalline heterostructures, the interfacial energy filtering effect plays a dominant role; 2) when inducing structural amorphization, the dramatic change in carrier mobility caused by strong disorder plays a dominant role. Both mechanisms can effectively screen low-energy carriers, thereby achieving a high Seebeck coefficient over a wide range of process parameters.

[0015] Ag-BST-based thermoelectric thin films are prepared using a magnetron co-sputtering process: BST alloy targets and Ag elemental targets are deposited at room temperature on a quartz sheet or silicon oxide substrate. The AST phase is dispersed in the BST matrix as nanocrystals or ultrathin layers, forming numerous BST / AST heterojunctions. These interfaces effectively scatter low-energy carriers, producing a significant energy filtering effect, thereby significantly improving the Seebeck coefficient of the material while maintaining stable conductivity. The films prepared in this invention have a thickness of 75-175 nm, and the absolute value of the Seebeck coefficient at room temperature can reach 250-731 μV / K, far exceeding that of pure BST films. A self-powered photothermal detector successfully fabricated based on this film exhibits excellent voltage response performance in a wide wavelength range of 350-980 nm. Furthermore, the fabrication process is low-temperature (<50℃), simple, and controllable, and compatible with semiconductor micro / nano fabrication technology. This thin film can serve as a core thermoelectric conversion layer for constructing a self-powered broadband (ultraviolet to terahertz) photothermoelectric detector that requires no external bias, has low noise, and high sensitivity, and has broad application prospects. Attached Figure Description

[0016] Figure 1 The graph shows the Seebeck coefficient of the BST, BST-Ag (1 W), BST-Ag (3 W), BST-Ag (5 W), BST-Ag (15 W), and BST-Ag (20 W) films of the present invention as a function of temperature. Figure 2A comparison chart of Seebeck coefficients at room temperature for the BST, BST-Ag (1 W), BST-Ag (3 W), BST-Ag (5 W), BST-Ag (15 W), and BST-Ag (20 W) films of the present invention; Figure 3 The elemental composition diagram of the BST, BST-Ag (3 W), BST-Ag (5 W), and BST-Ag (15 W) films of the present invention is shown. Figure 4 This is a histogram of the particle size distribution of the BST film of the present invention at room temperature; Figure 5 This is a histogram of the particle size distribution of the BST-Ag (3 W) film of the present invention at room temperature; Figure 6 This is a histogram of the particle size distribution of the BST-Ag (5 W) film of the present invention at room temperature; Figure 7 The transmission electron microscope image (scale bar 100 nm) and electron diffraction pattern (scale bar 10 nm) of the BST thin film of the present invention at room temperature are shown. -1 ); Figure 8 The transmission electron microscope image (scale bar 100 nm) and electron diffraction pattern (scale bar 10 nm) of the BST-Ag (3 W) thin film of the present invention at room temperature are shown. -1 ); Figure 9 The transmission electron microscope image (scale bar 100 nm) and electron diffraction pattern (scale bar 10 nm) of the BST-Ag (5 W) thin film of the present invention at room temperature are shown. -1 ); Figure 10 The transmission electron microscope (TEM) image (scale bar 100 nm) and electron diffraction pattern (scale bar 10 nm) of the BST-Ag (15 W) thin film of the present invention at room temperature are shown. -1 ); Figure 11 The photothermoelectric detector prepared in Example 6 of this invention, using a BST-Ag (5 W) thermoelectric thin film, shows the response spectrum of the photovoltage generated under different wavelength pulsed light irradiation as a function of time. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. I. Specific Implementation Methods In a magnetron sputtering system, Bi 0.5 Sb 1.5 The Te3 target is mounted on a magnetron RF sputtering target, and the Ag target is mounted on a magnetron DC sputtering target, using a quartz wafer or silicon oxide wafer as the substrate; the sputtering chamber is evacuated to a vacuum level ≤6.0×10⁻⁶.-6 Pa, introduce high-purity argon gas at a flow rate of 30 mL / min to the ignition pressure; control Bi 0.5 Sb 1.5 The sputtering power of the Te3 target was 30 W, and the sputtering power of the Ag target was 1 W to 20 W. Sputtering was performed for a total of 600 s at room temperature to deposit an Ag-BST-based thermoelectric thin film on the substrate.

[0019] Example 1: Preparation of Ag-BST thin films with Ag target power of 1 W, the chemical structural formula of which is Ag 6.61 (Bi) 0.5 Sb 1.5 Te3) 93.39 A magnetron sputtering system was used, with a BST target (RF) power of 30 W and an Ag target (DC) power of 1 W. The film was co-sputtered onto a double-sided polished SiO2 / Si substrate, achieving a thickness of approximately 75 nm. The Seebeck coefficient at room temperature was S = 234 μV / K, exhibiting a positive value, indicating that the conductivity type is p-type.

[0020] Example 2: Preparation of Ag-BST thin films with Ag target power of 3 W, the chemical structural formula of which is Ag 16.79 (Bi) 0.5 Sb 1.5 Te3) 83.21 The steps are the same as in Example 1, except that the Ag target power is adjusted to 3 W. The film thickness is approximately 85 nm. The Seebeck coefficient at room temperature is S = 276 μV / K, which is positive, indicating that its conductivity type is P-type.

[0021] Example 3: Preparation of Ag-BST thin films with an Ag target power of 5 W, the chemical structural formula of which is Ag 25.07 (Bi) 0.5 Sb 1.5 Te3) 74.93 The steps are the same as in Example 1, except that the Ag target power is adjusted to 5 W. The film thickness is approximately 111 nm. The room temperature Seebeck coefficient S = -731 μV / K (extremely high), and its negative Seebeck coefficient indicates that its conductivity type is N-type.

[0022] Example 4: Preparation of Ag-BST thin films with Ag target power of 15 W, the chemical formula of which is Ag 54.61 (Bi) 0.5 Sb 1.5 Te3) 45.39 The steps are the same as in Example 1, except that the Ag target power is adjusted to 15 W. The film thickness is approximately 160 nm. The room temperature Seebeck coefficient S = -500 μV / K (extremely high), and its negative Seebeck coefficient indicates that its conductivity type is N-type.

[0023] Example 5: Preparation of Ag-BST thin films with Ag target power of 20 W, the chemical formula of which is Ag 60.46 (Bi) 0.5 Sb 1.5 Te3) 39.54 The steps are the same as in Example 1, except that the Ag target power is adjusted to 20 W. The film thickness is approximately 175 nm. The Seebeck coefficient at room temperature is S = 20 μV / K, which is positive, indicating that its conductivity type is P-type.

[0024] Comparative example: Pure BST film, with the chemical structural formula Bi. 0.5 Sb 1.5 Te3. Thin films with a thickness of approximately 73 nm were prepared by sputtering using only a BST target (RF, 30 W). The Seebeck coefficient at room temperature was S = 151 μV / K. It is speculated that the high power of the Ag target led to metallization of the sample, causing the energy filtering effect to fail and the Seebeck coefficient to decrease significantly. Therefore, this power was not the preferred option.

[0025] Table 1. Seebeck coefficients of BST-based thermoelectric thin films prepared at room temperature under different Ag target sputtering powers.

[0026] II. Analysis of Experimental Results

[0027] Figure 1 This is a graph showing the Seebeck coefficient of the BST, BST-Ag (1 W), BST-Ag (3 W), BST-Ag (5 W), BST-Ag (15 W), and BST-Ag (20 W) films of the present invention as a function of temperature; Figure 1 It can be seen that all samples exhibit significant differences in Seebeck coefficients near room temperature (around 300 K). Among them, BST-Ag (5 W) and BST-Ag (15 W) films have extremely high absolute Seebeck coefficients at room temperature (731 μV / K and 500 μV / K, respectively), which are significantly better than pure BST films (151 μV / K). Although the Seebeck coefficients of each sample show a certain trend with temperature, the core of this study is to achieve a significant increase in the Seebeck coefficient at room temperature through Ag doping. Figure 1 This further demonstrates that, over a wide temperature range, the preferred samples such as BST-Ag (5 W) maintain a high Seebeck coefficient, indirectly confirming the stability of their thermoelectric properties.

[0028] Figure 2This is a comparison chart of the Seebeck coefficients of the BST, BST-Ag (1 W), BST-Ag (3 W), BST-Ag (5 W), BST-Ag (15 W), and BST-Ag (20 W) films of the present invention at room temperature; Figure 2 It can be seen that with the increase of Ag target sputtering power, the Seebeck coefficient of the film first increases and then decreases, reaching a peak at 5 W (-731 μV / K), which is nearly 5 times higher than that of pure BST film (151 μV / K). This indicates that appropriate Ag doping can effectively introduce the AST nanophase, enhance the interfacial energy filtering effect, and thus significantly improve the Seebeck coefficient; however, when Ag doping is excessive (e.g., 20 W), the material tends to metallize, the interfacial effect weakens, and the Seebeck coefficient drops sharply to 20 μV / K. This result clearly demonstrates the controllable adjustment of the Seebeck coefficient by the amount of Ag doping.

[0029] Figure 3 This is a graph showing the elemental composition of the BST, BST-Ag (3 W), BST-Ag (5 W), and BST-Ag (15 W) films of the present invention; Figure 3 It is evident that with increasing Ag target sputtering power, the Ag content in the thin film gradually increases, while the relative proportions of Bi, Sb, and Te change accordingly. At Ag target powers of 5 W and 15 W, the proportion of Ag atoms significantly increases, forming a clear compositional partition with the BST matrix. This provides a compositional basis for the formation of the AST nanophase and the construction of the heterostructure interface. The uniformity of elemental distribution and the degree of phase separation directly affect the interface density and carrier scattering behavior, thereby modulating the synergistic optimization effect of the Seebeck coefficient and conductivity.

[0030] Figure 4 , Figure 5 and Figure 6 The following are histograms of particle size distribution at room temperature for the BST film, BST-Ag (3 W) film, and BST-Ag (5 W) film of the present invention. Figure 4 The pure BST film shown exhibits a relatively uniform grain size distribution. However, after Ag doping, as... Figure 5 , Figure 6 As shown, the particle size distribution of the BST-Ag composite film exhibits a multi-peak characteristic, suggesting the presence of different phases. Structural characterization of the prepared Ag-BST composite film indicates that the morphology and distribution of the second phase in the BST matrix can be effectively controlled by adjusting the Ag target sputtering power.

[0031] Further analysis using transmission electron microscopy (TEM) confirmed the formation of the nanocomposite structure. For example... Figure 7 As shown, pure BST films exhibit a single-phase structure. Figure 8 and Figure 9As shown, in samples with Ag target power of 3 W and 5 W, nanoscale second-phase particles of varying contrast embedded in the BST matrix were clearly observed. Electron diffraction analysis of selected regions (see...) Figure 8 , Figure 9 The right-hand side of the figure confirms that these nanophases are AgSbTe2 (AST).

[0032] The sample from Example 4 was analyzed by transmission electron microscopy, such as... Figure 10 As shown, its diffraction pattern reveals diffuse rings, indicating that the sample exhibits amorphous characteristics under high sputtering power. These AST nanophases, acting as discontinuous second phases, form numerous heterogeneous interfaces with the BST matrix, which is the structural basis for the aforementioned energy filtering effect. Although the long-range ordered grain boundaries decrease at this point, the strong structural disorder introduced by the amorphous state creates a ubiquitous scattering potential field. This potential field also exhibits energy dependence on the scattering of charge carriers, thus maintaining a high Seebeck coefficient (-500 μV / K) even in highly doped regions.

[0033] Using the BST-Ag (5 W) thin film with the highest Seebeck coefficient (-731 μV / K) prepared in Example 3 as the thermoelectric conversion layer, a photothermoelectric detector was fabricated and its performance was verified. A set of metal Au electrodes was fabricated on the substrate coated with this thin film to form a planar device structure. Under conditions without any external bias, the device was irradiated with pulsed lasers of different wavelengths (including 350 nm, 400 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 808 nm, and 980 nm), and the generated open-circuit voltage (photovoltage) was measured in real time.

[0034] Test results are as follows Figure 11 As shown in the spectrum, the device clearly demonstrates that, under zero external bias, it generates significant photovoltage signals across a broad spectral range of 350 nm to 980 nm, confirming its self-powered operation and wide-spectrum detection capability. Photothermoelectric detection is essentially a light-thermal-electric conversion process, and its response spectral width is primarily determined by the light-absorbing material, without any particular dependence on the optical properties of the thermoelectric material itself. Therefore, combining this thin film with different broadband light-absorbing materials (such as metal nanoparticles, two-dimensional materials, and carbon materials) holds promise for achieving broadband and efficient detection from the ultraviolet to the terahertz band.

[0035] Meanwhile, the photovoltage signal can respond and recover rapidly with the light pulse, demonstrating the device's excellent transient characteristics. This directly verifies the effectiveness of the thermoelectric conversion layer with the ultra-high Seebeck coefficient thin film of this invention in constructing a high-performance photothermoelectric detector. The detector achieves high voltage responsivity and excellent detection performance in the visible-near infrared band, while also possessing extremely low noise and high sensitivity.

[0036] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. An Ag-BST-based thermoelectric thin film for use in photothermal detectors, characterized in that: The chemical structural formula of the thin film material is Ag. x (Bi) 0.5 Sb 1.5 Te3) 100-x , wherein 6.61 at.% ≤ x ≤ 54.61 at.%, the thin film material is obtained by dual-target co-sputtering in a magnetron sputtering coating system using a BST alloy target and a metallic Ag target.

2. The Ag-BST-based thermoelectric thin film for photothermoelectric detectors according to claim 1, characterized in that: The thin film material is a nano-AgSbTe2 phase distributed in the form of discontinuous nanoislands on the Bi. 0.5 Sb 1.5 In the Te3 matrix.

3. The Ag-BST-based thermoelectric thin film for photothermoelectric detectors according to claim 1, characterized in that: The chemical structural formula of the thin film material is Ag. 6.61 (Bi) 0.5 Sb 1.5 Te3) 93.39 .

4. The Ag-BST-based thermoelectric thin film for photothermoelectric detectors according to claim 1, characterized in that: The chemical structural formula of the thin film material is Ag. 16.79 (Bi) 0.5 Sb 1.5 Te3) 83.21 .

5. The Ag-BST-based thermoelectric thin film for photothermoelectric detectors according to claim 1, characterized in that: The chemical structural formula of the thin film material is Ag. 25.07 (Bi) 0.5 Sb 1.5 Te3) 74.93 .

6. The Ag-BST-based thermoelectric thin film for photothermoelectric detectors according to claim 1, characterized in that: The chemical structural formula of the thin film material is Ag. 54.61 (Bi) 0.5 Sb 1.5 Te3) 45.39 .

7. A method for preparing an Ag-BST-based thermoelectric thin film for a photothermoelectric detector according to any one of claims 1-6, characterized in that... The steps include: in a magnetron sputtering system, Bi... 0.5 Sb 1.5 The Te3 target is mounted on a magnetron RF sputtering target, and the Ag target is mounted on a magnetron DC sputtering target, using a quartz wafer or silicon oxide wafer as the substrate; the sputtering chamber is evacuated to a vacuum level ≤6.0×10⁻⁶. -6 Pa, introduce high-purity argon gas at a flow rate of 30 mL / min to the ignition pressure; control Bi 0.5 Sb 1.5 The sputtering power of the Te3 target was 30 W, and the sputtering power of the Ag target ranged from 1 W to 15 W. Sputtering was performed for a total of 600 s at room temperature to deposit an Ag-BST-based thermoelectric thin film on the substrate. The chemical structure of the film is Ag. x (Bi) 0.5 Sb 1.5 Te3) 100-x , of which 6.61 at.% ≤ x ≤ 54.61 at.%.

8. The application of the Ag-BST-based thermoelectric thin film according to claim 1 in the fabrication of a photothermal detector, characterized in that: The Ag-BST thermoelectric thin film is used as the core thermoelectric conversion layer.

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