Lead iodide nanosheet with superlattice structure, silicon-based device and preparation method
By preparing lead iodide nanosheets with a superlattice structure and utilizing the band difference between the 2H/4H phases, the problem of low carrier transport efficiency at the lead iodide interface was solved, realizing a photodetector with a wide-band optical response and breaking through the optical response range limitation of traditional materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-17
- Publication Date
- 2026-03-06
Smart Images
Figure CN121609360A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, and in particular to a lead iodide nanosheet with a superlattice structure, a silicon-based device, and a method for its fabrication. Background Technology
[0002] Photodetectors are devices that convert optical signals into electrical signals. They have a huge market in both defense and civilian applications, and have therefore attracted widespread attention. Currently, besides pursuing high optical response sensitivity, photodetectors also face extremely high demands in terms of optical response wavelength range and optical polarization state detection. Wideband photodetectors are currently a research hotspot due to their enormous application prospects and market demand in imaging, communication, and medicine. Furthermore, broadband photodetectors can be used in wavelength-selective photodetector applications. Traditional silicon-based, germanium-based, and mercury cadmium telluride-based detectors face insurmountable problems such as large device size and limited integration. High-performance broadband photodetectors covering the ultraviolet, visible, and infrared bands still face significant challenges. Currently commercially available detectors require complex material growth and / or manufacturing technologies and have high operating temperature requirements. Thermal detectors can achieve broadband detection to some extent, but their response speed is slow. Therefore, exploring new strategies to achieve high-sensitivity broadband photodetectors is urgently needed.
[0003] Currently, photodetectors using two-dimensional materials as photoelectric conversion materials have attracted widespread attention. Compared with traditional bulk photoelectric materials, two-dimensional materials can theoretically solve the integration problem faced by photodetectors to a certain extent, and have very high theoretical photoresponsivity. However, lead iodide prepared by existing methods, as a two-dimensional material, suffers from low interfacial carrier transport efficiency, resulting in a narrow detection band and poor performance when used in photodetectors.
[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention
[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a superlattice structured lead iodide nanosheet, a silicon-based device, and a preparation method thereof, in order to solve the problem of low interfacial carrier transport efficiency of lead iodide prepared by existing methods.
[0006] The technical solution of the present invention is as follows: A method for preparing lead iodide nanosheets with a superlattice structure, wherein the lead iodide nanosheets with the superlattice structure are hexagonal and are composed of three 2H phases and three 4H phases alternately distributed along the center of the hexagonal structure; The preparation method of the superlattice structured lead iodide nanosheets includes the following steps: Lead iodide powder is mixed with water and then heated to obtain a supersaturated solution of lead iodide. A supersaturated solution of lead iodide was dropped onto the surface of a substrate to remove moisture, resulting in lead iodide nanosheets. The lead iodide nanosheets were subjected to thermal annealing to obtain the lead iodide nanosheets with the superlattice structure.
[0007] The method for preparing lead iodide nanosheets with superlattice structure, wherein the heating treatment temperature is 80℃-120℃ and the heating treatment time is 50min-70min.
[0008] The method for preparing lead iodide nanosheets with superlattice structure, wherein the thermal annealing treatment is carried out under an inert atmosphere; the temperature of the thermal annealing treatment is 200℃-450℃, and the time of the thermal annealing treatment is 10min-60min.
[0009] The method for preparing lead iodide nanosheets with superlattice structure, wherein the temperature of the thermal annealing treatment is 400℃ and the time of the thermal annealing treatment is 10 min.
[0010] A lead iodide nanosheet with a superlattice structure, prepared by the method for preparing lead iodide nanosheets with the superlattice structure; And / or, the lead iodide nanosheets of the superlattice structure are hexagonal structures, and the lead iodide nanosheets of the superlattice structure are composed of three 2H phases and three 4H phases alternately distributed along the center of the hexagonal structure.
[0011] A silicon-based device includes a lead iodide nanosheet of the superlattice structure, a first electrode layer connected to the 2H phase of the lead iodide nanosheet of the superlattice structure, a second electrode layer connected to the 4H phase of the lead iodide nanosheet of the superlattice structure, and a silicon substrate layer for supporting the lead iodide nanosheet of the superlattice structure, the first electrode layer, and the second electrode layer.
[0012] The silicon-based device wherein the thickness of the first electrode layer is 25nm-55nm; and the thickness of the second electrode layer is 25nm-55nm.
[0013] The silicon-based device wherein the first electrode layer is composed of a Cr metal layer and an Au metal layer, wherein the Cr layer is connected to the 2H; and the second electrode layer is composed of a Cr metal layer and an Au metal layer, wherein the Cr layer is connected to the 4H.
[0014] A method for fabricating a silicon-based device, comprising the following steps: Provides a silicon substrate layer; A first electrode layer is deposited on the surface of the silicon substrate using photomask lithography. The lead iodide nanosheets of the superlattice structure were transferred to the first electrode layer using a dry directional transfer method, so that the first electrode layer was connected to the 2H phase of the lead iodide nanosheets of the superlattice structure. Align the photomask with the lead iodide nanosheet of the superlattice structure, so that the cutout area of the photomask is aligned with the 4H phase of the lead iodide nanosheet of the superlattice structure, and deposit the second electrode layer to obtain the silicon-based device.
[0015] Beneficial Effects: This invention provides a superlattice structure of lead iodide nanosheets, a silicon-based device, and a preparation method thereof. The preparation method of the superlattice structure of lead iodide nanosheets includes the following steps: mixing lead iodide powder with water and heating the mixture to obtain a supersaturated solution of lead iodide; dropping the supersaturated solution of lead iodide onto a substrate surface to obtain lead iodide nanosheets; and subjecting the lead iodide nanosheets to thermal annealing to obtain 2H / 4H superlattice structured lead iodide nanosheets. This invention utilizes a solution-crystallization method to prepare a periodic 2H / 4H superlattice structure of lead iodide, achieving periodic control of the phase structure in a single hexagonal lead iodide nanosheet. Specifically, by controlling the structure of lead iodide, a periodic superlattice structure of lead iodide with a two-dimensional structure was obtained. Due to the different arrangement rules of the Pb-I atomic chains, a 4H phase structure also exists in this two-dimensional lead iodide material in addition to the common 2H phase structure. At the same time, due to the difference in energy bands between the 2H and 4H phases of lead iodide, a potential difference exists at the 2H / 4H homojunction interface, which realizes efficient interfacial carrier transport and can effectively expand the photoelectric detection performance of the material. In particular, it has made breakthrough progress in expanding the optical response range, breaking through the limitation of the photosensitive material's energy band on the optical response range in semiconductor photodetectors. Attached Figure Description
[0016] Figure 1 This is a schematic flowchart of a method for preparing lead iodide nanosheets with a superlattice structure according to the present invention. Figure 2 This is a schematic diagram of the planar structure of a silicon-based device according to the present invention; Figure 3 This is a side view of a silicon-based device according to the present invention. Figure 4 Optical and fluorescence micrographs of lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 400℃ for 10 min. Figure 5 Transmission electron microscope images of the 2H and 4H regions of lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 250℃ for 60 min. Figure 6The photoluminescence spectra of different regions of lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 350℃ for 30 min are shown at 300K and 80K. Figure 7 The photocurrent response of a silicon-based device fabricated from lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 450℃ for 10 min is shown under 405 nm ultraviolet light irradiation. Figure 8 The photocurrent response of a silicon-based device fabricated from lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 300℃ for 20 min is shown under visible light irradiation at 520 nm and 638 nm. Figure 9 The photocurrent response diagrams of silicon-based devices based on lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 450℃ for 10 min are shown for silicon-based detectors with lead iodide structures of different thicknesses under 1064 nm near-infrared light irradiation. Detailed Implementation
[0017] This invention provides a lead iodide nanosheet with a superlattice structure, a silicon-based device, and a method for its fabrication. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.
[0018] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.
[0019] Among numerous two-dimensional materials, two-dimensional lead iodide has wide applications in X-ray detection, ultraviolet light detection, and other fields. Because lead iodide has a band gap of approximately 2.5 eV, it only responds to light with wavelengths less than 500 nanometers. However, lead iodide prepared by existing methods suffers from low interfacial carrier transport efficiency.
[0020] Based on this, the present invention provides a method for preparing lead iodide nanosheets with a superlattice structure, wherein the lead iodide nanosheets with the superlattice structure are hexagonal and are composed of three 2H phases and three 4H phases alternately distributed along the center of the hexagonal structure. like Figure 1 As shown, the method for preparing the superlattice structured lead iodide nanosheets includes the following steps: Step S10: Mix lead iodide powder with water and heat to obtain a supersaturated solution of lead iodide; Step S20: Drop the supersaturated solution of lead iodide onto the substrate surface to remove moisture and obtain lead iodide nanosheets; Step S30: The lead iodide nanosheets are subjected to thermal annealing to obtain the lead iodide nanosheets with the superlattice structure.
[0021] In this embodiment, a periodic 2H / 4H superlattice structure of lead iodide was prepared using a solution-crystallization method, achieving periodic control of the phase structure in a single hexagonal lead iodide nanosheet. Specifically, by controlling the structure of lead iodide, a periodic superlattice structure of two-dimensional lead iodide was obtained. Due to the different arrangement rules of the Pb-I atomic chains, this two-dimensional lead iodide material exhibits both a common 2H phase structure and a 4H phase structure. Simultaneously, due to the difference in the energy bands of the 2H and 4H phases of lead iodide, a potential difference exists at the 2H / 4H homojunction interface, enabling efficient interfacial carrier transport and effectively expanding the photoelectric detection performance of the material. This represents a breakthrough in extending the photoresponse range, overcoming the limitation imposed by the energy band structure of photosensitive materials on the photoresponse range in semiconductor photodetectors. Furthermore, this preparation method is simple to operate, uses low-cost raw materials, and is highly reproducible.
[0022] Specifically, this invention utilizes the band structure differences between different phases of the 2H / 4H superlattice structure of lead iodide nanosheets to achieve wide-bandgap detection in wide-bandgap semiconductor materials, overcoming the limitation of the material's band structure on its optical detection response band. When the lead iodide superlattice structure is used in a photodetector, it serves as a photosensitive material for photoelectric conversion. Two sets of electrodes are connected to the 2H and 4H phases of the periodic lead iodide 2H / 4H superlattice structure, respectively. Photogenerated carriers generated through photoelectric conversion are transported to the two sets of electrodes and form a photocurrent through an external circuit. This achieves a wide-band optical response from ultraviolet to near-infrared, improving the device's optical detection performance and expanding its application scenarios.
[0023] In some embodiments, the heat treatment temperature is 80℃-120℃, and the heat treatment time is 50min-70min. This heat treatment allows the lead iodide powder to disperse in water to form a supersaturated solution, which is beneficial for subsequent crystallization on the substrate surface to form lead iodide nanosheets.
[0024] In a preferred embodiment, the heat treatment temperature is 100°C and the heat treatment time is 60 minutes.
[0025] In some embodiments, step S10 specifically includes: dispersing lead iodide powder in deionized water, heating it thoroughly in an oil bath to obtain a supersaturated solution of lead iodide. Then, the supernatant is collected and placed in a water bath for insulation. Preferably, the temperature of the water bath is 50°C, and the insulation time is 30 minutes.
[0026] In some embodiments, step S20 specifically includes: dropping the supernatant onto a clean substrate, allowing it to stand, absorbing excess moisture with absorbent paper, and drying the surface with a nitrogen gun to obtain lead iodide hexagonal sheets, i.e., lead iodide nanosheets, on the substrate; preferably, the temperature of the substrate is 20℃-25℃, and the standing time is 30s-40s. Lead iodide nanosheets with a hexagonal structure are formed on the substrate surface through natural crystallization.
[0027] In some embodiments, the thermal annealing treatment is performed under an inert atmosphere; the temperature of the thermal annealing treatment is 200℃-450℃, and the time of the thermal annealing treatment is 10min-60min. By thermally annealing the lead iodide nanosheets, a periodic lead iodide 2H / 4H superlattice structure can be obtained. During the growth of the lead iodide nanosheets, due to the limitations of surface energy differences and crystal symmetry, lead atoms and iodine atoms will periodically appear on the six edges of the hexagonal lead iodide sheets. Compared to lead atoms, iodine atoms are more reactive. During the heat treatment, the regions with iodine atoms at the edges are more prone to atomic rearrangement, achieving a phase transition from the 2H phase to the 4H phase, thereby growing a periodic lead iodide 2H / 4H superlattice structure in the prepared hexagonal lead iodide nanosheets.
[0028] In some embodiments, the heating rate of the heat annealing treatment is 15°C / min to 25°C / min; preferably, the heating rate of the heat annealing treatment is 20°C / min.
[0029] In a preferred embodiment, the heat annealing is performed under an argon atmosphere; the temperature of the heat annealing is 400°C, and the time of the heat annealing is 10 minutes.
[0030] In some embodiments, in step S30, the prepared lead iodide nanosheets are placed in the center of a tube furnace and subjected to thermal annealing to prepare lead iodide with a 2H / 4H superlattice structure. Specifically, this includes: raising the temperature of the tube furnace to 200-450°C (heating rate 20°C / min) and holding it at that temperature for 10-60 min, then rapidly cooling the furnace to room temperature (ambient temperature approximately 25°C) by opening the furnace's protective cover. During the heat treatment, the tube furnace is maintained at atmospheric pressure (one atmosphere), and the tube is filled with argon gas for protection (gas flow rate 30 sccm).
[0031] In addition, the present invention also provides a lead iodide nanosheet with a superlattice structure, which is prepared by the method for preparing the lead iodide nanosheet with the superlattice structure. And / or, the lead iodide nanosheets of the superlattice structure are hexagonal structures, and the lead iodide nanosheets of the superlattice structure are composed of three 2H phases and three 4H phases alternately distributed along the center of the hexagonal structure.
[0032] In this embodiment, a periodic 2H / 4H superlattice structure of lead iodide was prepared using a solution-crystallization method, achieving periodic control of the phase structure in a single hexagonal lead iodide nanosheet. Due to the difference in energy bands between the 2H and 4H phases of lead iodide, a potential difference exists at the 2H / 4H homojunction interface, enabling efficient interfacial carrier transport and effectively expanding the photoelectric detection performance of the material. In particular, it represents a breakthrough in extending the photoresponse range, overcoming the limitation imposed by the energy band structure of photosensitive materials on the photoresponse range in semiconductor photodetectors.
[0033] In some embodiments, the lead iodide nanosheets of the superlattice structure are hexagonal, and the lead iodide in the superlattice structure is composed of three 2H phases and three 4H phases alternately distributed along the center of the hexagonal structure. By utilizing the band differences between the different phases of the lead iodide 2H / 4H superlattice structure, wide-bandgap detection is achieved in wide-bandgap semiconductor materials, overcoming the limitation of the material's band structure on its optical detection response band.
[0034] In addition, such as Figure 2 and Figure 3 As shown, the present invention also provides a silicon-based device, comprising the lead iodide nanosheet 10 of the superlattice structure, a first electrode layer 20 connected to the 2H phase of the lead iodide nanosheet 10 of the superlattice structure, a second electrode layer 30 connected to the 4H phase of the lead iodide nanosheet 10 of the superlattice structure, and a substrate layer 40 for supporting the lead iodide nanosheet 10 of the superlattice structure, the first electrode layer 20 and the second electrode layer 30.
[0035] In this embodiment, two sets of electrodes are connected to the 2H and 4H phases of a periodic lead iodide 2H / 4H superlattice structure, respectively. Photogenerated carriers generated through photoelectric conversion are transported to the two sets of electrodes and form a photocurrent through an external circuit. This enables a wide-band optical response from ultraviolet to near-infrared, improving the device's photodetector performance and expanding its application scenarios. Furthermore, the thickness of each layer in the photodetector is unlimited; by selecting different substrate layers, the device can be realized as a solid-state or flexible photodetector. In addition, this photodetector can produce a good optical response in the ultraviolet (405nm) to near-infrared (2400nm) band at room temperature.
[0036] In some embodiments, the thickness of the first electrode layer is 25nm-55nm; the thickness of the second electrode layer is 25nm-55nm.
[0037] In some embodiments, the first electrode layer consists of a Cr metal layer and an Au metal layer, wherein the Cr layer is connected to the 2H layer; the second electrode layer consists of a Cr metal layer and an Au metal layer, wherein the Cr layer is connected to the 4H layer. The thickness of the Cr metal layer is 5 nm, and the thickness of the Au metal layer is 45 nm.
[0038] Finally, the present invention also provides a method for fabricating a silicon-based optical device, comprising the following steps: Step S100: Provide a base layer; Step S200: Deposit the first electrode layer on the surface of the substrate layer using photomask lithography; Step S300: Transfer the superlattice-structured lead iodide nanosheets onto the first electrode layer using a dry directional transfer method, so that the first electrode layer is connected to the 2H phase of the superlattice-structured lead iodide nanosheets; Step S400: Align the mask with the lead iodide nanosheet of the superlattice structure, so that the cutout area of the mask is aligned with the 4H phase of the lead iodide nanosheet of the superlattice structure, and deposit the second electrode layer to obtain the silicon-based device.
[0039] In this embodiment, the electrode configuration of the device can be varied by selecting different material sizes. Compared to broadband detectors based on heterojunctions, this device has a simpler fabrication process, milder material preparation conditions, lower energy consumption, and is suitable for mass production. It can be rapidly fabricated on silicon substrates, which is beneficial for expanding the application of two-dimensional silicon-based optoelectronic devices.
[0040] Specifically, the first electrode layer and the second electrode layer may be distributed on the same side of the lead iodide, or they may be distributed on opposite sides of the lead iodide.
[0041] In some implementations, such as Figure 2 As shown, the first electrode layer consists of electrodes 1, 3, and 5 corresponding to three 2H electrodes, and the width of the first electrode is 1μm-5μm; the second electrode layer consists of electrodes 2, 4, and 6 corresponding to three 4H electrodes, and the width of the second electrode is 1μm-5μm.
[0042] As an example, the method for fabricating the silicon-based device includes the following steps: 1) Fabrication of the bottom electrode: A 1cm × 1cm Si / SiO2 substrate was selected as the substrate, and metal electrodes were deposited on its surface using photolithography. Figure 2Electrodes 1, 3, 5 or 2, 4, 6 shown. The electrode material is a Cr / Au bilayer metal, where the Cr thickness is 5 nm, the Au thickness is 45 nm, and the electrode width is 5 μm.
[0043] 2) Transfer of intermediate photosensitive material: The periodic lead iodide 2H / 4H superlattice structure prepared above was transferred to the bottom electrode using a dry directional transfer method.
[0044] 3) Fabrication of the upper electrode: Using the lead iodide 2H / 4H superlattice structure on the surface of electrodes 1, 3, 5 or electrodes 2, 4, 6 as the substrate, the mask and the lead iodide 2H / 4H superlattice structure are aligned using a microscope alignment system, keeping the cutout areas of the mask aligned. Figure 2 In the regions shown by electrodes 2, 4, 6 or electrodes 1, 3, 5, metal electrodes are directly vapor-deposited on the surface of the lead iodide 2H / 4H superlattice structure. The electrode material is a Cr / Au bilayer metal, with a Cr thickness of 5 nm, an Au thickness of 45 nm, and an electrode width of 5 μm.
[0045] In this device, a periodic lead iodide 2H / 4H superlattice structure serves as the photosensitive material to achieve photoelectric conversion. Two sets of electrodes are respectively in contact with the upper and lower surfaces of the periodic lead iodide 2H / 4H superlattice structure. The photogenerated carriers generated by photoelectric conversion are transported to the two electrodes and form a photocurrent through an external circuit.
[0046] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.
[0047] Example 1 This embodiment provides a lead iodide nanosheet with a superlattice structure, specifically comprising the following: 1) Mix 0.1g of lead iodide powder with 10ml of deionized water and heat it in an oil bath at 100℃ for 60min to obtain a supersaturated solution of lead iodide. Then take the supernatant and place it in a water bath at 50℃ for 30min for later use. 2) Take 20 μL and drop it onto a clean substrate surface (substrate temperature is 20℃). After standing for 30 seconds, use absorbent paper to remove excess water and blow the surface dry with a nitrogen gun to obtain lead iodide nanosheets (i.e. lead iodide hexagonal sheets) on the substrate. 3) The prepared lead iodide nanosheets were placed in the center of a tube furnace and subjected to thermal annealing under different parameters. The heating rate was 20 °C / min, and then the protective cover of the tube furnace was opened to rapidly cool down to room temperature (ambient temperature approximately 25 °C), yielding lead iodide nanosheets with a 2H / 4H superlattice structure. During the thermal annealing process, the tube furnace was maintained at atmospheric pressure (one atmosphere), and the tube was filled with argon gas for protection (gas flow rate 30 sccm).
[0048] The lead iodide nanosheets with a 2H / 4H superlattice structure obtained after heat annealing at 400℃ for 10 min are shown in (a) optical microscope images and (b) fluorescence microscope images (dark areas represent the 2H region, and bright areas represent the 4H region). Figure 4 As shown in the images, the optical microscope reveals that the prepared lead iodide nanosheets exhibit a relatively regular hexagonal shape with a smooth surface and almost no obvious defects or adhering substances. This demonstrates that even after annealing, the lead iodide nanosheets retain their intact morphology. Under a fluorescence microscope, it is clearly visible that the fluorescence of the lead iodide nanosheets displays a distinct periodic alternation of light and dark.
[0049] Lead iodide nanosheets with a 2H / 4H superlattice structure were obtained by thermal annealing at 250℃ for 60 min. Transmission electron microscopy images of the (a) 2H region and (b) 4H region are shown below. Figure 5 As shown, transmission electron microscopy observation of different regions of lead iodide nanosheets reveals that the bright fluorescent regions exhibit a regular atomic arrangement, displaying the structural characteristics of the 2H phase lead iodide. Conversely, the dark fluorescent regions show an atomic arrangement consistent with the structural characteristics of the 4H phase lead iodide. This demonstrates that the alternating changes in fluorescence intensity within the prepared lead iodide nanosheets originate from the periodic variations in the crystal structure.
[0050] Lead iodide nanosheets with a 2H / 4H superlattice structure were obtained by thermal annealing at 350℃ for 30 min. The photoluminescence spectra of different regions of these nanosheets at (a) 300 K and (b) 80 K (excitation light 405 nm) are shown below. Figure 6As shown, lead iodide exhibits only free exciton fluorescence emission at approximately 506 nm at room temperature, while at low temperatures, in addition to the free exciton fluorescence emission peak, a certain intensity of free exciton fluorescence emission peak is also observed near approximately 600 nm. Due to the difference in phase structure, the fluorescence display in the two regions shows significant differences. At room temperature (300 K), the 2H phase exhibits stronger free exciton fluorescence emission, and at a low temperature (80 K), the free exciton fluorescence of 2H is even stronger. However, the 4H phase shows stronger luminescence of self-trapped excitons at low energies. Since the emission peak of self-trapped excitons mainly originates from the combined effect of exciton-phonon coupling and transient distortion of the crystal structure, this also demonstrates that in the prepared lead iodide, the 4H phase is more prone to lattice distortion than the 2H phase, resulting in a stronger binding effect on free excitons and significantly enhanced self-trapped luminescence.
[0051] Example 2 This embodiment provides a silicon-based device, specifically including the following: 1) Fabrication of the bottom electrode: A 1cm × 1cm Si / SiO2 substrate was selected as the substrate, and metal electrodes were deposited on its surface using photolithography. Figure 2 Electrodes 1, 3, and 5 are shown in the diagram. The electrode material is a Cr / Au bilayer metal, with a Cr thickness of 5 nm, an Au thickness of 45 nm, and an electrode width of 5 μm.
[0052] 2) Transfer of intermediate photosensitive material: Using a dry directional transfer method, periodic lead iodide 2H / 4H superlattice structures with different thermal annealing treatments were transferred to different bottom electrodes.
[0053] 3) Fabrication of the upper electrode: The lead iodide 2H / 4H superlattice structure on the surface of electrodes 2, 4, and 6 is used as the substrate. The mask and the lead iodide 2H / 4H superlattice structure are aligned using a microscope alignment system, keeping the cutout areas of the mask aligned. Figure 2 In the regions shown by electrodes 2, 4, and 6, metal electrodes are directly deposited on the surface of the lead iodide 2H / 4H superlattice structure. The electrode material is a Cr / Au bilayer metal, with a Cr thickness of 5 nm, an Au thickness of 45 nm, and an electrode width of 5 μm, thus obtaining a silicon-based device.
[0054] A silicon-based device based on lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 450℃ for 10 min is shown in the photocurrent response diagram under 405nm ultraviolet light irradiation. Figure 7As shown, using a 405nm continuous laser (with a 150µm diameter Gaussian spot) as the ultraviolet excitation source to irradiate the device, the current between electrode 1 and electrode 4 is detected. A clear photocurrent signal can be observed. Even at a laser intensity of 2nW, a very significant photocurrent can still be detected. The on / off ratio of the device under 2nW laser irradiation is approximately 50. Since the band gap of lead iodide is approximately 2.5eV, it exhibits a significant photoresponse for light signals below 500nm due to the intrinsic light absorption of the material.
[0055] The photocurrent response diagrams of silicon-based devices fabricated from lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 300℃ for 20 min under visible light irradiation at 520 nm and 638 nm are shown below. Figure 8 As shown, continuous laser beams at 520 nm and 638 nm (with a Gaussian spot diameter of 150 μm) are used as visible excitation sources to irradiate the device, detecting the current between electrodes 1 and 6. The current-voltage characteristic curve shows that the device has a significant photoresponse to visible light, proving that the device can be used for visible light detection. In fact, the intrinsic bandgap absorption cutoff wavelength of the lead iodide structure is around 500 nm. In this embodiment, the photoresponse in the 520 nm and 638 nm bands is due to photon absorption below the bandgap energy, which excites photogenerated carriers. This absorption is mainly achieved by sub-bandgap light absorption generated by the self-trapped energy level.
[0056] Silicon-based devices were fabricated using lead iodide nanosheets with a 2H / 4H superlattice structure obtained by thermal annealing at 450℃ for 10 min. The photocurrent response diagrams of silicon-based detectors with periodic lead iodide structures of different thicknesses (30 nm, 55 nm, 160 nm) under 1064 nm near-infrared light illumination are shown below. Figure 9 As shown, a 1064 nm continuous laser (with a 150 μm diameter Gaussian spot) was used as the near-infrared excitation source to irradiate the device, and the current between electrode 1 and electrode 2 was detected. The on / off ratio showed that the device had a significant photoresponse to near-infrared light, proving that the device can be used for near-infrared light detection. When testing with lead iodide nanosheets of different thicknesses, it was observed that increasing the thickness significantly enhanced the photocurrent of the device. This is mainly due to the effect of thickness variation on the light absorption of the photosensitive medium. The response to near-infrared light is primarily due to the absorption of photons below the bandgap energy caused by the interlayer exciton transition induced by the band difference between the 2H and 4H phases.
[0057] In summary, this invention provides a superlattice-structured lead iodide nanosheet, a silicon-based device, and a fabrication method. The fabrication method of the superlattice-structured lead iodide nanosheet includes the following steps: mixing lead iodide powder with water and heating the mixture to obtain a supersaturated lead iodide solution; dropping the supersaturated lead iodide solution onto a substrate surface to obtain lead iodide nanosheets; and subjecting the lead iodide nanosheets to thermal annealing to obtain 2H / 4H superlattice-structured lead iodide nanosheets. This invention utilizes a solution-crystallization method to prepare a periodic 2H / 4H lead iodide superlattice structure, achieving periodic control of the phase structure in a single hexagonal lead iodide nanosheet. Specifically, by controlling the structure of lead iodide, a periodic superlattice structure of lead iodide with a two-dimensional structure was obtained. Due to the different arrangement rules of the Pb-I atomic chains, a 4H phase structure also exists in this two-dimensional lead iodide material in addition to the common 2H phase structure. At the same time, due to the difference in energy bands between the 2H and 4H phases of lead iodide, a potential difference exists at the 2H / 4H homojunction interface, which realizes efficient interfacial carrier transport and can effectively expand the photoelectric detection performance of the material. In particular, it has made breakthrough progress in expanding the optical response range, breaking through the limitation of the photosensitive material's energy band on the optical response range in semiconductor photodetectors.
[0058] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
Claims
1. A method of preparing a lead iodide nanoplatelet of superlattice structure, characterized by, The lead iodide nanosheet of the superlattice structure is a hexagonal structure, and the lead iodide nanosheet of the superlattice structure is composed of three 2H phases and three 4H phases alternately distributed along the center of the hexagonal structure. The preparation method of the lead iodide nanosheet of the superlattice structure comprises the following steps: Lead iodide powder is mixed with water, and a supersaturated solution of lead iodide is obtained through heating treatment; The supersaturated solution of lead iodide is dropped on the surface of a substrate, and water is removed to obtain lead iodide nanosheets; The lead iodide nanosheets are subjected to thermal annealing treatment to obtain the lead iodide nanosheet of the superlattice structure.
2. The method of claim 1, wherein the lead iodide nanosheets of the superlattice structure are prepared by the method comprising: The temperature of the heating treatment is 80-120°C, and the time of the heating treatment is 50-70 min.
3. The method of claim 1, wherein the lead iodide nanosheets of superlattice structure are prepared by the method comprising: The thermal annealing treatment is carried out in an inert atmosphere, the temperature of the thermal annealing treatment is 200-450°C, and the time of the thermal annealing treatment is 10-60 min.
4. The method of claim 3, wherein the lead iodide nanosheets of superlattice structure are prepared by the method comprising: The temperature of the thermal annealing treatment is 400°C, and the time of the thermal annealing treatment is 10 min.
5. A lead iodide nanoplatelet of superlattice structure, characterized in that, The preparation method of the lead iodide nanosheet of the superlattice structure is prepared by the method according to any one of claims 1-4. The lead iodide nanosheet of the superlattice structure is a hexagonal structure, and the lead iodide nanosheet of the superlattice structure is composed of three 2H phases and three 4H phases alternately distributed along the center of the hexagonal structure.
6. A silicon-based device, characterized by, The silicon substrate layer for loading the lead iodide nanosheet of the superlattice structure, the first electrode layer connected with the 2H phase of the lead iodide nanosheet of the superlattice structure, and the second electrode layer connected with the 4H phase of the lead iodide nanosheet of the superlattice structure.
7. The silicon-based device of claim 6, wherein, The thickness of the first electrode layer is 25-55 nm, and the thickness of the second electrode layer is 25-55 nm.
8. The silicon-based device of claim 6, wherein, The first electrode layer is composed of a Cr metal layer and an Au metal layer, and the Cr layer is connected with the 2H phase; the second electrode layer is composed of a Cr metal layer and an Au metal layer, and the Cr layer is connected with the 4H phase.
9. A method of fabricating a silicon-based device as claimed in any one of claims 6-8, characterized in that, The method comprises the following steps: A silicon substrate layer is provided; A first electrode layer is evaporated on the surface of the silicon substrate layer by using a mask lithography technology; The lead iodide nanosheet of the superlattice structure is transferred onto the first electrode layer by using a dry directional transfer method, so that the first electrode layer is connected with the 2H phase of the lead iodide nanosheet of the superlattice structure; The mask is aligned with the lead iodide nanosheet of the superlattice structure, so that the hollow area of the mask is aligned with the 4H phase of the lead iodide nanosheet of the superlattice structure, a second electrode layer is evaporated, and a silicon device is prepared.