Ferroelectric / semiconductor heterojunction-based photoelectric detector and preparation method thereof

Abstract

The invention belongs to the technical field of photoelectric detectors, discloses a photoelectric detector based on ferroelectric / semiconductor heterojunction and a preparation method thereof, and solves the problems of limited carrier separation efficiency, complex device structure, insufficient interface regulation and control means and the like in the photoelectric detector. The photoelectric detector comprises a substrate, a planar electrode pair arranged on the surface of the substrate, and a two-dimensional heterojunction active layer which covers and is attached to the planar electrode pair and a channel region between the planar electrode pair; wherein the two-dimensional heterojunction active layer is formed by vertically stacking a CuInP2S6 thin film and a GeSe thin film in sequence. By constructing a Van der Waals heterojunction active layer and utilizing a built-in electric field formed on a heterojunction interface by ferroelectric polarization, the generation, separation and transmission processes of photon-generated carriers are effectively regulated and controlled, so that the photoelectric detection performance of the device is improved on the premise of not introducing a complex process.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detector technology, and particularly relates to a photoelectric detector. Background Technology

[0002] With the rapid development of two-dimensional materials in the field of photoelectric detection, two-dimensional heterojunctions based on van der Waals forces have been widely used in the design of novel photoelectric detection devices due to their advantages such as high interface quality, flexible structure, and no need for strict lattice matching. In existing research, various heterojunction structures have been constructed using transition metal sulfides / selenides such as MoS2, WSe2, and ZrSe2, or other layered semiconductors, and photodetection functions in the visible to near-infrared bands have been achieved.

[0003] However, existing two-dimensional heterojunction photodetectors still suffer from some common problems: On the one hand, many reported heterojunctions have band arrangements close to type-I or have small band steps, resulting in a limited built-in electric field at the interface. This makes it difficult for photogenerated electrons and holes to achieve sufficient spatial separation at the interface, leading to a high recombination rate of photogenerated carriers and limiting the photoelectric conversion efficiency and response capability of the device. On the other hand, to compensate for the insufficient interface electric field, existing devices usually require a large external bias voltage or the introduction of gate electrode structures in conjunction with gate voltage modulation. This increases the complexity of the device structure and driving power consumption to some extent, which is not conducive to realizing a simple, low-power photodetector.

[0004] Furthermore, some two-dimensional heterojunction materials still have limitations in terms of light absorption range and optical response modulation capabilities: some materials have weak absorption in the visible or near-infrared bands, making it difficult to achieve both a broad spectral response and a high absorption coefficient; some heterojunction interface modulation methods mainly rely on thickness adjustment or external electrostatic fields, resulting in limited controllability of interface polarization and built-in electric fields, making it difficult to achieve fine modulation of photogenerated carrier behavior. In existing technologies, there is still room for improvement in technical solutions that can effectively enhance the built-in electric field at the interface and improve the carrier separation and transport process while maintaining a simple device structure, thereby improving photoelectric detection performance. Summary of the Invention

[0005] To address the problems of limited carrier separation efficiency, complex device structure, and insufficient interface control methods in existing two-dimensional photodetectors, this invention proposes a photodetector based on a ferroelectric / semiconductor heterojunction (CuInP2S6 / GeSe heterojunction, abbreviated as CIPS-GeSe or CIPS / GeSe) and its fabrication method.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A photodetector based on a ferroelectric / semiconductor heterojunction includes a substrate, a pair of planar electrodes disposed on the surface of the substrate, and a two-dimensional heterojunction active layer covering and adhering to the planar electrode pair and the channel region therebetween; wherein the two-dimensional heterojunction active layer is formed by vertically stacking CuInP2S6 thin films (CIPS) and GeSe thin films in sequence.

[0008] The aforementioned CuInP2S6 and GeSe films are vertically stacked via van der Waals interactions. By vertically stacking CuInP2S6 and GeSe films with ferroelectric polarization characteristics, a van der Waals heterojunction active layer is constructed. The built-in electric field formed at the heterojunction interface by ferroelectric polarization enables effective control of the generation, separation, and transport processes of photogenerated carriers, thereby improving the photoelectric detection performance of the device without introducing complex processes.

[0009] Furthermore, the thickness of the CuInP2S6 thin film in the above-mentioned heterojunction active layer is 10-80 nm, and the thickness of the GeSe thin film is 5-50 nm.

[0010] The lateral dimensions of the active layer of the above-mentioned heterojunction are (10-30) μm × (30-80) μm.

[0011] The aforementioned planar electrode pair includes a first electrode and a second electrode, both of which are metal electrodes. More preferably, the metal electrodes are chromium / gold electrodes.

[0012] In the aforementioned chromium / gold electrode, chromium (Cr) serves as the adhesive layer with a thickness of 5-10 nm; the gold layer serves as the electrode layer with a thickness of 50-200 nm.

[0013] The fabrication method of the above-mentioned photodetector based on ferroelectric / semiconductor heterojunction includes the following steps:

[0014] (1) Substrate cleaning;

[0015] (2) On the substrate cleaned in step (1), a planar electrode pair, namely the first electrode and the second electrode, is prepared by photolithography and electron beam evaporation.

[0016] (3) CuInP2S6 is transferred to the planar electrode pair and the channel region between them by mechanical peeling and dry transfer process to form CuInP2S6 thin film; then GeSe is transferred to the surface of CuInP2S6 thin film by mechanical peeling and dry transfer process to form two-dimensional heterojunction active layer.

[0017] Specifically, the fabrication method of the above-mentioned photodetector based on ferroelectric / semiconductor heterojunction includes the following steps:

[0018] (1) Substrate cleaning. A silicon substrate (SiO2 / Si) with a silicon dioxide layer on its surface was selected as the device substrate. First, the substrate was ultrasonically cleaned in deionized water for 5-10 minutes to remove surface particulate matter and organic contaminants, and then dried with high-purity nitrogen. Next, the substrate was subjected to RCA cleaning (including two steps), and after each cleaning step, it was rinsed with high-purity deionized water for no less than 5 minutes. Finally, the substrate was dried with nitrogen or a spin dryer and stored in a clean environment for later use.

[0019] (2) On the substrate cleaned in step (1), a planar electrode pair, namely the first electrode and the second electrode, is prepared by photolithography and electron beam evaporation.

[0020] First, a photoresist (such as S1813 or AZ 5214) was spin-coated onto the substrate surface using a spin coater at 3000 rpm for 60 s, resulting in a photoresist layer with a thickness of approximately 1.3 μm. This was followed by a soft bake at 90°C for 2 minutes. During the exposure stage, the substrate was aligned with a mask, and exposure was performed using a mask alignment exposure machine. The exposure energy was set to 70-100 mJ / cm², and the exposure time was 2-3 s. After exposure, the substrate was baked at 115°C for 1 minute. For development, the substrate treated in step (1) was immersed in AZ400K developer (mixed with deionized water at a 1:4 ratio) for approximately 60 s, then rinsed with deionized water and dried.

[0021] Subsequently, an electron beam evaporation process was used to deposit metal electrodes: first, a 5-10 nm layer of chromium (Cr) was deposited as an adhesion layer, followed by a 50-200 nm layer of gold (Au) as the electrode layer, with the deposition rate controlled at 0.1-1 Å / s. After deposition, the substrate was immersed in acetone for 20-30 minutes for a stripping process, supplemented by short-duration ultrasonication if necessary, to remove excess metal, ultimately yielding the first and second electrodes.

[0022] (3) CuInP2S6 is transferred to the planar electrode pair and the channel region between them by mechanical peeling and dry transfer process to form CuInP2S6 thin film; then GeSe is transferred to the surface of CuInP2S6 thin film by mechanical peeling and dry transfer process to form two-dimensional heterojunction active layer.

[0023] To further improve the heterojunction interface quality, the device can be subjected to low-temperature annealing in a nitrogen or inert atmosphere. After the GeSe transfer, the device is further annealed at 80-150℃ for 5-20 min in an inert atmosphere to enhance the van der Waals coupling strength and reduce the interface defect density.

[0024] The beneficial effects of this invention are:

[0025] (1) The material combination in this invention has a reasonable interface physical mechanism, which is suitable for constructing a high-efficiency photoelectric detection heterojunction. CuInP2S6 is a room-temperature ferroelectric layered material with a stable spontaneous polarization direction, which can generate a directional built-in electric field at the heterojunction interface; GeSe, as a group IV-VI two-dimensional semiconductor, has a moderate band gap, a high light absorption coefficient and good carrier mobility. The direction of the interface electric field formed after the two are stacked is consistent with the direction of photogenerated carrier separation, which enables the spatial separation of electrons and holes at the interface under conditions of no external bias voltage or extremely low bias voltage.

[0026] (2) This invention achieves excellent photoelectric performance enhancement by inducing a built-in electric field through interface polarization. The polarization electric field of CuInP2S6 forms a 10 Ω·cm polarization field at the heterojunction interface. 5 -10 6 An equivalent built-in field on the order of V / m creates a voltage drop across the GeSe layer's band, causing photogenerated electrons to migrate towards GeSe while holes remain on the CuInP2S6 side, thus significantly reducing the interfacial recombination probability. Optical and device response tests (such as spectral absorption and transient response) show a significant increase in light absorption intensity in the 400–900 nm range (with an enhancement trend from visible to near-infrared); under weak bias conditions, the photogenerated carrier lifetime is extended and the interfacial recombination rate is reduced; and under the same light intensity, the photocurrent is significantly higher than that of the iron-free polarized control heterojunction device.

[0027] (3) The present invention achieves device performance with higher optical gain, higher response speed and lower bias voltage requirement. Since ferropolarization enhances the interface field establishment capability, the device of the present invention can generate significant photocurrent under small bias voltage or even zero bias voltage conditions; in the comparative test, it can be observed that: the responsivity increases significantly with the incident light wavelength, which is significantly improved compared with the non-polarized heterojunction; the optical gain change curve is steep and the gain amplitude is higher; the response speed is faster and the rise / fall time is shortened, reflecting the rapid transport characteristics of charge carriers at the interface.

[0028] (4) The fabrication process of this invention is mature and has good repeatability, making it suitable for subsequent process integration and large-scale expansion. It adopts mature micro-nano fabrication methods such as photolithography, electrode evaporation, mechanical lift-off and dry transfer. The entire process is consistent with existing two-dimensional material devices, with strong equipment versatility and a wide process window. In multiple fabrications, the interface bonding is stable, the heterojunction position alignment is high, and the electrical behavior of the device is reproducible. The material system is well compatible with SiO2 / Si substrate and Au / Cr electrode structure, and has good scalability, process compatibility and integrability, which facilitates the further development of arrayed or on-chip photoelectric detection systems. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the photodetector based on a ferroelectric / semiconductor heterojunction according to the present invention.

[0031] Figure 2 The diagram shows a comparison of the imaginary part ε2(ω) of the dielectric function of CuInP2S6 (Comparative Example 1), the curve of the absorption coefficient as a function of photon energy (b), and the comparison of reflectivity (c) of the CuInP2S6 (Comparative Example 1), GeSe monolayer structure (Comparative Example 2), and CuInP2S6 / GeSe heterojunction (Example 1) used in this invention.

[0032] Figure 3 The partial charge density diagrams of the CuInP2S6 / GeSe heterojunction used in Embodiment 1 of the present invention are shown; where (a) is the electron cloud distribution at the top of the valence band (VBM) and (b) is the electron cloud distribution at the bottom of the conduction band (CBM).

[0033] Figure 4 The following are band structure diagrams: (a) is the band structure diagram of a single-layer CuInP2S6 thin film (used in Comparative Example 1), (b) is the band structure diagram of a single-layer GeSe thin film (used in Comparative Example 2), and (c) is the band structure diagram of the CuInP2S6 / GeSe heterojunction used in Example 1.

[0034] Figure 5 The average charge accumulation distribution Q(z) in the CuInP2S6 / GeSe heterojunction plane used in Example 1.

[0035] Figure 6 This is a schematic diagram of the quantitative type-II band alignment of the CuInP2S6 / GeSe heterojunction used in Example 1 (based on vacuum energy level).

[0036] Figure 7 The image shows a comparison of the band structure of the CuInP2S6 / GeSe heterojunction used in Example 1 under different ferroelectric polarization states (P↑ and P↓).

[0037] Figure 8 The ε2(ω) curves (a) and absorption coefficient α(ω) curves (b) of the CuInP2S6 / GeSe heterojunction used in Example 1 under different polarization states are shown. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] The fabrication method of the photodetector based on ferroelectric / semiconductor heterojunction in this embodiment includes the following steps:

[0041] (1) Substrate cleaning. A silicon substrate (SiO2 / Si) with a silicon dioxide layer on its surface is selected as the device substrate. First, the substrate is ultrasonically cleaned in deionized water for 5-10 minutes to remove surface particulate matter and organic contaminants, and then dried with high-purity nitrogen. Next, the substrate is subjected to RCA cleaning, which includes two steps:

[0042] a. A mixed solution of ammonia, hydrogen peroxide (H2O2), and deionized water in a volume ratio of 5:1:1 was used to treat the substrate at 75°C for 10 minutes to remove organic contaminants and particulates. The substrate was then briefly immersed in a 1.5 wt% dilute hydrofluoric acid (HF) solution to remove the natural oxide layer on the surface while retaining the SiO2 layer.

[0043] b. Use a mixture of hydrochloric acid (37 wt%), hydrogen peroxide (H₂O₂), and deionized water (volume ratio 6:1:1) at 80°C for 10 minutes to remove metal ion contamination. After each cleaning step, rinse with high-purity deionized water for at least 5 minutes. Finally, dry the substrate using nitrogen or a spin dryer and store it in a clean environment.

[0044] (2) Electrode fabrication. Electrodes are fabricated on the clean substrate obtained in step S1 using photolithography and electron beam evaporation.

[0045] First, a negative photoresist (AZ 5214) was spin-coated onto the substrate surface using a spin coater at 4500 rpm for 60 s, resulting in a photoresist layer with a thickness of approximately 1.3 μm. This was followed by a soft bake at 90°C for 2 minutes. During the exposure stage, the substrate and mask were aligned, and exposure was performed using a mask alignment exposure machine with an exposure energy set to 80 mJ / cm². 2The exposure time was 2 seconds. After exposure, the substrate was baked at 115°C for 1 minute. During development, the substrate was immersed in AZ 400K developer (1:4 ratio with deionized water) for approximately 60 seconds, followed by rinsing with deionized water and drying. Electron beam evaporation was then used to deposit metal electrodes. A 7 nm chromium (Cr) layer was deposited first as an adhesion layer, followed by a 100 nm gold (Au) layer as the electrode layer, with the deposition rate controlled at 0.5 Å / s. After deposition, the substrate was immersed in acetone for 20 minutes for stripping, with short-duration ultrasonication if necessary to remove excess metal, ultimately yielding the first and second electrodes.

[0046] (3) Preparation and transfer of CuInP2S6 thin film. CuInP2S6 thin film was prepared using a mechanical exfoliation method. The specific process is as follows: A bulk CuInP2S6 crystal was placed on a 3M blue film tape and peeled off by 15 folds to obtain a thin layer of CuInP2S6. The CuInP2S6 thin film on the blue film tape was then transferred to an organosilicon film (such as PDMS) and allowed to stand for 7 minutes. The PDMS carrying the CuInP2S6 thin film was fixed on a three-dimensional micro-displacement platform, and its position was precisely adjusted under an optical microscope to transfer the CuInP2S6 thin film onto the two electrode pairs and the channel region between them, forming a CuInP2S6 active layer with a thickness controlled at 40 nm.

[0047] (4) GeSe thin film transfer and heterostructure construction. Repeat the transfer method in step (3) to prepare a GeSe thin film. After mechanical exfoliation, the GeSe crystal is transferred onto a PDMS thin film. Under a microscope, a GeSe thin film of suitable size is selected and precisely stacked on the surface of a CuInP2S6 thin film using a three-dimensional micro-displacement platform to form a CuInP2S6 / GeSe vertical heterojunction structure. The thickness of the GeSe thin film is controlled at 20 nm, and it is ensured that the GeSe thin film is in full contact with the CuInP2S6 thin film below, without being directly short-circuited to the electrode below. After the GeSe thin film is transferred, the device is placed in a nitrogen atmosphere and annealed at 150°C for 5 minutes to obtain a photodetector based on a ferroelectric / semiconductor heterojunction (CuInP2S6 / GeSe heterojunction) (wherein, the lateral dimension of the two-dimensional heterojunction active layer is 25 μm × 50 μm). The schematic diagram of the structure of the photodetector based on the ferroelectric / semiconductor heterojunction prepared in this invention is shown below. Figure 1 As shown.

[0048] Example 2

[0049] The fabrication method of the photodetector based on ferroelectric / semiconductor heterojunction in this embodiment includes the following steps:

[0050] (1) Substrate cleaning. A silicon substrate (SiO2 / Si) with a silicon dioxide layer on its surface is selected as the device substrate. First, the substrate is ultrasonically cleaned in deionized water for 5-10 minutes to remove surface particulate matter and organic contaminants, and then dried with high-purity nitrogen. Next, the substrate is subjected to RCA cleaning, which includes two steps:

[0051] a. A mixed solution of ammonia, hydrogen peroxide (H2O2), and deionized water in a volume ratio of 5:1:1 was used to treat the substrate at 80°C for 10 minutes to remove organic contaminants and particulates. The substrate was then briefly immersed in a 1 wt% dilute hydrofluoric acid (HF) solution to remove the natural oxide layer on the surface while retaining the SiO2 layer.

[0052] b. Use a mixture of hydrochloric acid (37 wt%), hydrogen peroxide (H₂O₂), and deionized water (volume ratio 6:1:1) at 75°C for 10 minutes to remove metal ion contamination. After each cleaning step, rinse with high-purity deionized water for at least 5 minutes. Finally, dry the substrate using nitrogen or a spin dryer and store it in a clean environment.

[0053] (2) Electrode fabrication. Electrodes are fabricated on the clean substrate obtained in step S1 using photolithography and electron beam evaporation.

[0054] First, a negative photoresist (AZ 5214) was spin-coated onto the substrate surface using a spin coater at 4500 rpm for 60 s, resulting in a photoresist layer with a thickness of approximately 1.3 μm. This was followed by a soft bake at 90°C for 2 minutes. During the exposure stage, the substrate and mask were aligned, and exposure was performed using a mask alignment exposure machine with an exposure energy set to 70 mJ / cm². 2 The exposure time was 3 seconds. After exposure, the substrate was baked at 115°C for 1 minute. During development, the substrate was immersed in AZ 400K developer (1:4 ratio with deionized water) for approximately 60 seconds, then rinsed with deionized water and dried. Subsequently, metal electrodes were deposited using electron beam evaporation. A 5 nm layer of chromium (Cr) was deposited as an adhesion layer, followed by a 200 nm layer of gold (Au) as the electrode layer, with the deposition rate controlled at 0.1 Å / s. After deposition, the substrate was immersed in acetone for 30 minutes for stripping, with short-duration ultrasonication if necessary to remove excess metal, ultimately yielding the first and second electrodes.

[0055] (3) Preparation and transfer of CuInP2S6 thin film. CuInP2S6 thin film was prepared using a mechanical exfoliation method. The specific process is as follows: A bulk CuInP2S6 crystal was placed on a 3M blue film tape and peeled off by 10 folds to obtain a thin layer of CuInP2S6. The CuInP2S6 thin film on the blue film tape was then transferred to an organosilicon film (such as PDMS) and allowed to stand for 10 minutes. The PDMS containing the CuInP2S6 thin film was fixed on a three-dimensional micro-displacement platform, and its position was precisely adjusted under an optical microscope to transfer the CuInP2S6 thin film onto the two electrode pairs and the channel region between them, forming a CuInP2S6 active layer with a thickness controlled at 80 nm.

[0056] (4) GeSe thin film transfer and heterostructure construction. Repeat the transfer method in step (3) to prepare a GeSe thin film. After mechanical exfoliation, the GeSe crystal is transferred onto a PDMS thin film. Under a microscope, a GeSe thin film of suitable size is selected and precisely stacked on the surface of a CuInP2S6 thin film using a three-dimensional micro-displacement platform to form a CuInP2S6 / GeSe vertical heterojunction structure. The thickness of the GeSe thin film is controlled at 5 nm, and it is ensured that the GeSe thin film is in full contact with the CuInP2S6 thin film below, without being directly short-circuited to the electrode below. After the GeSe thin film is transferred, the device is placed in a nitrogen atmosphere and annealed at 80°C for 20 minutes to obtain a ferroelectric / semiconductor heterojunction (CuInP2S6 / GeSe heterojunction) (wherein, the lateral dimension of the two-dimensional heterojunction active layer is 10 μm × 80 μm).

[0057] Example 3

[0058] The fabrication method of the photodetector based on ferroelectric / semiconductor heterojunction in this embodiment includes the following steps:

[0059] (1) Substrate cleaning. A silicon substrate (SiO2 / Si) with a silicon dioxide layer on its surface is selected as the device substrate. First, the substrate is ultrasonically cleaned in deionized water for 5-10 minutes to remove surface particulate matter and organic contaminants, and then dried with high-purity nitrogen. Next, the substrate is subjected to RCA cleaning, which includes two steps:

[0060] a. A mixed solution of ammonia, hydrogen peroxide (H2O2), and deionized water in a volume ratio of 5:1:1 was used to treat the substrate at 80°C for 10 minutes to remove organic contaminants and particulates. The substrate was then briefly immersed in a 2 wt% dilute hydrofluoric acid (HF) solution to remove the natural oxide layer on the surface while retaining the SiO2 layer.

[0061] b. Use a mixture of hydrochloric acid (37 wt%), hydrogen peroxide (H₂O₂), and deionized water (volume ratio 6:1:1) at 80°C for 10 minutes to remove metal ion contamination. After each cleaning step, rinse with high-purity deionized water for at least 5 minutes. Finally, dry the substrate using nitrogen or a spin dryer and store it in a clean environment.

[0062] (2) Electrode fabrication. Electrodes are fabricated on the clean substrate obtained in step S1 using photolithography and electron beam evaporation.

[0063] First, a positive photoresist (S1813) was spin-coated onto the substrate surface using a spin coater at 3000 rpm for 60 s, resulting in a photoresist layer with a thickness of approximately 1.3 μm. This was followed by a soft bake at 90°C for 2 minutes. During the exposure stage, the substrate and mask were aligned, and exposure was performed using a mask alignment exposure machine with an exposure energy set to 100 mJ / cm². 2 The exposure time was 2 seconds. After exposure, the substrate was baked at 115°C for 1 minute. During development, the substrate was immersed in AZ 400K developer (1:4 ratio with deionized water) for approximately 60 seconds, followed by rinsing with deionized water and drying. Electron beam evaporation was then used to deposit metal electrodes. A 10 nm chromium (Cr) layer was deposited first as an adhesion layer, followed by a 50 nm gold (Au) layer as the electrode layer, with the deposition rate controlled at 1 Å / s. After deposition, the substrate was immersed in acetone for 25 minutes for stripping, with short-duration ultrasonication if necessary to remove excess metal, ultimately yielding the first and second electrodes.

[0064] (3) Preparation and transfer of CuInP2S6 thin film. CuInP2S6 thin film was prepared using a mechanical exfoliation method. The specific process is as follows: A bulk CuInP2S6 crystal was placed on a 3M blue film tape and peeled off by 25 folds to obtain a thin layer of CuInP2S6. The CuInP2S6 thin film on the blue film tape was then transferred to an organosilicon film (such as PDMS) and allowed to stand for 5 minutes. The PDMS containing the CuInP2S6 thin film was fixed on a three-dimensional micro-displacement platform, and its position was precisely adjusted under an optical microscope to transfer the CuInP2S6 thin film onto the two electrode pairs and the channel region between them, forming a CuInP2S6 active layer with a thickness controlled at 10 nm.

[0065] (4) GeSe thin film transfer and heterostructure construction. Repeat the transfer method in step (3) to prepare a GeSe thin film. After mechanical exfoliation, the GeSe crystal is transferred onto a PDMS thin film. Under a microscope, a GeSe thin film of suitable size is selected and precisely stacked on the surface of a CuInP2S6 thin film using a three-dimensional micro-displacement platform to form a CuInP2S6 / GeSe vertical heterojunction structure. The thickness of the GeSe thin film is controlled at 50 nm, and it is ensured that the GeSe thin film is in full contact with the CuInP2S6 thin film below, without being directly short-circuited to the electrode below. After the GeSe thin film is transferred, the device is placed in a nitrogen atmosphere and annealed at 100°C for 10 minutes to obtain a ferroelectric / semiconductor heterojunction (CuInP2S6 / GeSe heterojunction) (wherein, the lateral dimension of the two-dimensional heterojunction active layer is 30 μm × 30 μm).

[0066] Example 4

[0067] The fabrication method of the photodetector based on ferroelectric / semiconductor heterojunction in this embodiment includes the following steps:

[0068] (1) Substrate cleaning. A silicon substrate (SiO2 / Si) with a silicon dioxide layer on its surface is selected as the device substrate. First, the substrate is ultrasonically cleaned in deionized water for 5-10 minutes to remove surface particulate matter and organic contaminants, and then dried with high-purity nitrogen. Next, the substrate is subjected to RCA cleaning, which includes two steps:

[0069] a. A mixed solution of ammonia, hydrogen peroxide (H2O2), and deionized water in a volume ratio of 5:1:1 was used to treat the substrate at 75°C for 10 minutes to remove organic contaminants and particulates. The substrate was then briefly immersed in a 1.5 wt% dilute hydrofluoric acid (HF) solution to remove the natural oxide layer on the surface while retaining the SiO2 layer.

[0070] b. Use a mixture of hydrochloric acid (37 wt%), hydrogen peroxide (H₂O₂), and deionized water (volume ratio 6:1:1) at 80°C for 10 minutes to remove metal ion contamination. After each cleaning step, rinse with high-purity deionized water for at least 5 minutes. Finally, dry the substrate using nitrogen or a spin dryer and store it in a clean environment.

[0071] (2) Electrode fabrication. Electrodes are fabricated on the clean substrate obtained in step S1 using photolithography and electron beam evaporation.

[0072] First, a negative photoresist (AZ 5214) was spin-coated onto the substrate surface using a spin coater at 3000 rpm for 60 s, resulting in a photoresist layer with a thickness of approximately 1.3 μm. This was followed by a soft bake at 90°C for 2 minutes. During the exposure stage, the substrate and mask were aligned, and exposure was performed using a mask alignment exposure machine with an exposure energy set to 80 mJ / cm². 2 The exposure time was 2 seconds. After exposure, the substrate was baked at 115°C for 1 minute. During development, the substrate was immersed in AZ 400K developer (1:4 ratio with deionized water) for approximately 60 seconds, followed by rinsing with deionized water and drying. Electron beam evaporation was then used to deposit metal electrodes. A 7 nm chromium (Cr) layer was deposited first as an adhesion layer, followed by a 100 nm gold (Au) layer as the electrode layer, with the deposition rate controlled at 0.5 Å / s. After deposition, the substrate was immersed in acetone for 20 minutes for stripping, with short-duration ultrasonication if necessary to remove excess metal, ultimately yielding the first and second electrodes.

[0073] (3) Preparation and transfer of CuInP2S6 thin films. CuInP2S6 thin films were prepared by mechanical exfoliation. The specific process is as follows: Bulk CuInP2S6 crystals were placed on 3M blue film tape and peeled off by 15 folds to obtain a thin layer of CuInP2S6. The CuInP2S6 thin film on the blue film tape was then transferred to an organosilicon film (such as PDMS) and left to stand for 7 minutes. The PDMS carrying the CuInP2S6 thin film was fixed on a three-dimensional micro-displacement platform, and its position was precisely adjusted under an optical microscope to transfer the CuInP2S6 thin film onto the two electrode pairs and the channel region between them, forming a CuInP2S6 active layer with a thickness controlled at 50 nm.

[0074] (4) GeSe thin film transfer and heterostructure construction. Repeat the transfer method in step (3) to prepare a GeSe thin film. After mechanical exfoliation, the GeSe crystal is transferred onto a PDMS thin film. Under a microscope, a GeSe thin film of suitable size is selected and precisely stacked on the surface of a CuInP2S6 thin film using a three-dimensional micro-displacement platform to form a CuInP2S6 / GeSe vertical heterojunction structure. The thickness of the GeSe thin film is controlled at 40 nm, and it is ensured that the GeSe thin film is in full contact with the CuInP2S6 thin film below, without being directly short-circuited to the electrode below, thus obtaining a ferroelectric / semiconductor heterojunction (CuInP2S6 / GeSe heterojunction) (wherein, the lateral dimension of the two-dimensional heterojunction active layer is 25 μm × 50 μm).

[0075] Comparative Example 1

[0076] The fabrication method of the photodetector in this comparative example differs from that in Example 1 in that the CuInP2S6 / GeSe heterojunction is replaced with a CuInP2S6 thin film only. The specific steps are as follows:

[0077] (1) Substrate cleaning. A silicon substrate (SiO2 / Si) with a silicon dioxide layer on its surface is selected as the device substrate. First, the substrate is ultrasonically cleaned in deionized water for 5-10 minutes to remove surface particulate matter and organic contaminants, and then dried with high-purity nitrogen. Next, the substrate is subjected to RCA cleaning, which includes two steps:

[0078] a. A mixed solution of ammonia, hydrogen peroxide (H2O2), and deionized water in a volume ratio of 5:1:1 was used to treat the substrate at 75°C for 10 minutes to remove organic contaminants and particulates. The substrate was then briefly immersed in a 1.5 wt% dilute hydrofluoric acid (HF) solution to remove the natural oxide layer on the surface while retaining the SiO2 layer.

[0079] b. Use a mixture of hydrochloric acid (37 wt%), hydrogen peroxide (H₂O₂), and deionized water (volume ratio 6:1:1) at 80°C for 10 minutes to remove metal ion contamination. After each cleaning step, rinse with high-purity deionized water for at least 5 minutes. Finally, dry the substrate using nitrogen or a spin dryer and store it in a clean environment.

[0080] (2) Electrode fabrication. Electrodes are fabricated on the clean substrate obtained in step S1 using photolithography and electron beam evaporation.

[0081] First, a negative photoresist (AZ 5214) was spin-coated onto the substrate surface using a spin coater at 4500 rpm for 60 s, resulting in a photoresist layer with a thickness of approximately 1.3 μm. This was followed by a soft bake at 90°C for 2 minutes. During the exposure stage, the substrate and mask were aligned, and exposure was performed using a mask alignment exposure machine with an exposure energy set to 80 mJ / cm². 2 The exposure time was 2 seconds. After exposure, the substrate was baked at 115°C for 1 minute. During development, the substrate was immersed in AZ 400K developer (1:4 ratio with deionized water) for approximately 60 seconds, followed by rinsing with deionized water and drying. Electron beam evaporation was then used to deposit metal electrodes. A 7 nm chromium (Cr) layer was deposited first as an adhesion layer, followed by a 100 nm gold (Au) layer as the electrode layer, with the deposition rate controlled at 0.5 Å / s. After deposition, the substrate was immersed in acetone for 20 minutes for stripping, with short-duration ultrasonication if necessary to remove excess metal, ultimately yielding the first and second electrodes.

[0082] (3) Preparation and transfer of CuInP2S6 thin film. CuInP2S6 thin film was prepared by mechanical exfoliation. The specific process is as follows: Bulk CuInP2S6 crystal was placed on 3M blue film tape and peeled off by 15 folds to obtain a thin layer of CuInP2S6. Then, the CuInP2S6 thin film on the blue film tape was transferred to an organosilicon film (such as PDMS) and left to stand for 7 minutes. The PDMS carrying the CuInP2S6 thin film was fixed on a three-dimensional micro-displacement platform. The position was precisely adjusted under an optical microscope to transfer the CuInP2S6 thin film onto the two electrode pairs and the channel region between them, forming a CuInP2S6 active layer (thickness of 40 nm), thus obtaining a photodetector (wherein, the lateral dimension of the CuInP2S6 active layer is 25 μm × 50 μm).

[0083] Comparative Example 2

[0084] The fabrication method of the photodetector in this comparative example differs from that in Example 1 in that the CuInP2S6 / GeSe heterojunction is replaced with a GeSe thin film only. The specific steps are as follows:

[0085] The fabrication method of the photodetector based on the CuInP2S6 / GeSe heterojunction in this embodiment includes the following steps:

[0086] (1) Substrate cleaning. A silicon substrate (SiO2 / Si) with a silicon dioxide layer on its surface is selected as the device substrate. First, the substrate is ultrasonically cleaned in deionized water for 5-10 minutes to remove surface particulate matter and organic contaminants, and then dried with high-purity nitrogen. Next, the substrate is subjected to RCA cleaning, which includes two steps:

[0087] a. A mixed solution of ammonia, hydrogen peroxide (H2O2), and deionized water in a volume ratio of 5:1:1 was used to treat the substrate at 75°C for 10 minutes to remove organic contaminants and particulates. The substrate was then briefly immersed in a 1.5 wt% dilute hydrofluoric acid (HF) solution to remove the natural oxide layer on the surface while retaining the SiO2 layer.

[0088] b. Use a mixture of hydrochloric acid (37 wt%), hydrogen peroxide (H₂O₂), and deionized water (volume ratio 6:1:1) at 80°C for 10 minutes to remove metal ion contamination. After each cleaning step, rinse with high-purity deionized water for at least 5 minutes. Finally, dry the substrate using nitrogen or a spin dryer and store it in a clean environment.

[0089] (2) Electrode fabrication. Electrodes are fabricated on the clean substrate obtained in step S1 using photolithography and electron beam evaporation.

[0090] First, a negative photoresist (AZ 5214) was spin-coated onto the substrate surface using a spin coater at 3000 rpm for 60 s, resulting in a photoresist layer with a thickness of approximately 1.3 μm. This was followed by a soft bake at 90°C for 2 minutes. During the exposure stage, the substrate and mask were aligned, and exposure was performed using a mask alignment exposure machine with an exposure energy set to 80 mJ / cm². 2 The exposure time was 2 seconds. After exposure, the substrate was baked at 115°C for 1 minute. During development, the substrate was immersed in AZ 400K developer (1:4 ratio with deionized water) for approximately 60 seconds, followed by rinsing with deionized water and drying. Electron beam evaporation was then used to deposit metal electrodes. A 7 nm chromium (Cr) layer was deposited first as an adhesion layer, followed by a 100 nm gold (Au) layer as the electrode layer, with the deposition rate controlled at 0.5 Å / s. After deposition, the substrate was immersed in acetone for 20 minutes for stripping, with short-duration ultrasonication if necessary to remove excess metal, ultimately yielding the first and second electrodes.

[0091] (3) GeSe thin film preparation and transfer. GeSe thin films were prepared by mechanical exfoliation, and the specific process is as follows: a bulk GeSe crystal was placed on a 3M blue film tape and peeled off by 15 folds to obtain a thin layer of GeSe. The GeSe thin film on the blue film tape was then transferred to an organosilicon thin film (such as PDMS) and left to stand for 7 minutes. The PDMS carrying the GeSe thin film was fixed on a three-dimensional micro-displacement platform, and its position was precisely adjusted under an optical microscope to transfer the GeSe thin film onto the two electrode pairs and the channel region between them, forming a GeSe active layer (thickness of 20 nm), and finally a photodetector was obtained (where the lateral dimension of the GeSe active layer is 25 μm × 50 μm).

[0092] Implementation Results Example

[0093] Figure 2 This is an optical response analysis diagram of CuInP2S6 (Comparative Example 1), GeSe monolayer structure (Comparative Example 2), and CuInP2S6 / GeSe heterojunction (Example 1) in the energy range of 0 to 6 eV. Figure 2 The imaginary part of the dielectric function of α reflects the material's ability to absorb and convert photons. The gray shaded area is marked as the "low-energy enhancement region." It can be seen that the CIPS-GeSe heterojunction exhibits a large peak (close to 120) at extremely low energies (<1 eV), significantly higher than that of single CIPS (approximately 80) and the almost non-responsive GeSe. This indicates that the formation of the heterojunction greatly enhances the material's photoelectric coupling ability in the infrared and low-energy regions. Furthermore, from the absorption spectrum (Absorption... Figure 2As shown in Figure b (blue): In the low-energy region (< 1.5 eV), GeSe material hardly absorbs, but has a very strong absorption peak around 3.2 eV (UV region). CIPS (orange): The absorption of CIPS steadily increases with increasing energy. In the energy range of 0.1 eV to 2.0 eV, the absorption rate of the CIPS-GeSe heterojunction is significantly better than that of its constituent monomer materials. It exhibits relatively stable and high absorption in the visible light region (rainbow band), but the absorption rate begins to decrease and falls below that of the monomer in the high-energy region (>3.5 eV). GeSe has a distinct reflection peak near 3.2 eV, corresponding to its absorption characteristics. CIPS-GeSe has a higher reflectivity in the low-energy region than the other two, but maintains low and stable reflection in the visible and high-energy regions. This helps photons to be absorbed more than reflected. Figure 2 c).

[0094] Depend on Figure 2 It can be observed that the CIPS-GeSe heterojunction produces significant synergistic effects: (1) It broadens the spectral response range, making up for the shortcomings of GeSe in the long-wavelength (low-energy) region. (2) Infrared enhancement applications: The heterojunction's strong dielectric response and absorption characteristics in the low-energy region make it have great application potential in infrared detectors, long-wavelength optoelectronic devices, and more efficient solar cells (capturing long-wavelength photons). (3) Visible light performance: In the visible light range of 1.6-3.1 eV, the heterojunction maintains stable optical activity, making it suitable for full-spectrum optoelectronic applications.

[0095] Figure 3 The partial charge density distribution of the CuInP2S6 / GeSe heterojunction at the band edge states is shown. It can be seen that the valence band top (VBM) and conduction band bottom (CBM) exhibit a clear spatial isolation characteristic: the VBM is mainly contributed by the CuInP2S6 layer, while the CBM is concentrated in the GeSe layer. This Type-II band alignment constructs an effective interfacial potential gradient, which can drive photogenerated electrons and holes to migrate in opposite directions, thereby achieving effective spatial separation of charge carriers and suppressing recombination.

[0096] Figure 4 The band structure evolution of monolayer CuInP2S6, monolayer GeSe, and their heterojunctions is illustrated. Monolayer CuInP2S6 exhibits an indirect bandgap semiconductor with a bandgap of 1.56 eV, and its valence band peak (VBM) is located at Gamma (…). Figure 4 a) such as Figure 4 As shown in b, the monolayer GeSe is an indirect bandgap semiconductor with a bandgap of 0.90 eV ( Figure 4b) When the two are constructed into a heterojunction, the band structure of the heterojunction changes significantly due to the charge redistribution and band alignment effects at the interface. The band gap of the CuInP2S6 / GeSe heterojunction used in Example 1 is reduced to 0.91 eV ( Figure 4 c). From the above Figure 4 It can be seen that the valence band apex of the heterojunction mainly originates from the CuInP2S6 layer, while the conduction band apex is mainly contributed by the GeSe layer, indicating that the valence and conduction band states are concentrated in different material layers. This characteristic facilitates the migration of photogenerated electrons and holes along different directions at the interface, thereby reducing recombination behavior and improving carrier separation efficiency.

[0097] Figure 5 The planar average charge accumulation distribution Q(z) of the CuInP2S6 / GeSe heterojunction in Example 1 is shown. The charge transfer behavior at the CuInP2S6 / GeSe heterojunction interface was quantitatively analyzed, and the planar average charge difference density Δρ(z) and its accumulation distribution Q(z) were calculated. The results show that Q(z) increases significantly with increasing z in the CuInP2S6 layer region, indicating electron accumulation in the CuInP2S6 layer; while Q(z) decreases overall in the GeSe layer region, indicating electron depletion in the GeSe layer. This result clearly demonstrates the transfer of electrons from GeSe to CuInP2S6, forming a built-in electric field at the interface, further verifying that this heterojunction is a typical type-II band-aligned structure.

[0098] Figure 6 This is a schematic diagram (based on vacuum levels) of the quantitative type-II band alignment of the CuInP2S6 / GeSe heterojunction in Example 1. As can be seen from the figure, the conduction band bottom (CBM) level of the GeSe (Donor) monolayer is approximately -3.6 eV, the valence band top (VBM) level is approximately -4.5 eV, and the band gap is approximately 0.9 eV. The conduction band bottom (CBM) level of the CuInP2S6 (CIPS, Acceptor) monolayer is approximately -2.83 eV, the valence band top (VBM) level is approximately -4.43 eV, and the band gap is approximately 1.6 eV. Based on the band edge positions of both, the following interface band shift parameters can be obtained: valence band shift (ΔEV) ≈ 1.44 eV, conduction band shift (ΔEC) ≈ 0.77 eV. Furthermore, the vacuum level difference (electron affinity difference) between the two is approximately: W ≈ 4.7 eV. Figure 6 As can be seen from the band edge positions, the valence band top mainly comes from CuInP2S6, and the conduction band bottom mainly comes from GeSe. The two exhibit a band edge distribution characteristic that is separated from top to bottom on the energy axis, which is conducive to the migration of photogenerated electrons and holes in different directions at the interface, thereby suppressing recombination and improving carrier separation efficiency.

[0099] Figure 7 This is a comparison of the band structure of the CuInP2S6 / GeSe heterojunction in Example 1 under different ferroelectric polarization states (P↑ and P↓). As can be seen from the figure, there is a significant difference in the band gap value of the heterojunction under different polarization directions. The calculated band gap of the P↑ polarization state is approximately 0.915 eV (solid black line), and the calculated band gap of the P↓ polarization state is approximately 0.003 eV (dashed red line), with a band gap difference of approximately ΔEg≈0.912 eV between the two polarization states. Simultaneously, distinguishable changes in the position of the band edge and the local band shape can be observed in both polarization states, indicating that the reversal of the polarization direction has a significant impact on the band edge states of the heterojunction. The differences in the band edge under different polarization states cause changes in the effective mass of charge carriers, band curvature, and energy distribution in the heterojunction. These reversible changes in the band gap and band edge position with polarization direction reflect changes in the interfacial potential environment, which is beneficial for adjusting the electronic transport behavior and optical response characteristics of the device under different bias voltages or illumination conditions.

[0100] Figure 8 The figures show the ε2(ω) curves (a) and absorption coefficient α(ω) curves (b) of the CuInP2S6 / GeSe heterojunction in Example 1 under different polarization states. The figures demonstrate that the ε2(ω) and absorption coefficient α(ω) of the heterojunction exhibit significant differences in the infrared to visible light energy range under different polarization states, proving that the material system of this invention possesses tunable optical response characteristics and can be used to construct polarization-controlled infrared photodetectors.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A photodetector based on a ferroelectric / semiconductor heterojunction, characterized in that, The photodetector includes a substrate, a pair of planar electrodes disposed on the surface of the substrate, and a two-dimensional heterojunction active layer covering and adhering to the planar electrode pair and the channel region therebetween; wherein the two-dimensional heterojunction active layer is formed by vertically stacking CuInP2S6 thin films and GeSe thin films in sequence.

2. The photodetector based on a ferroelectric / semiconductor heterojunction according to claim 1, characterized in that, The CuInP2S6 thin film and GeSe thin film form a vertically stacked structure through van der Waals interaction.

3. The photodetector based on a ferroelectric / semiconductor heterojunction according to claim 2, characterized in that, The thickness of the CuInP2S6 thin film in the active layer of the heterojunction is 10-80 nm.

4. The photodetector based on a ferroelectric / semiconductor heterojunction according to claim 3, characterized in that, The thickness of the GeSe thin film in the 3D heterojunction active layer is 5-50 nm.

5. The photodetector based on a ferroelectric / semiconductor heterojunction according to claim 4, characterized in that, The lateral dimension of the active layer of the heterojunction is (10-30) μm × (30-80) μm.

6. The photodetector based on a ferroelectric / semiconductor heterojunction according to any one of claims 1-5, characterized in that, The planar electrode pair includes a first electrode and a second electrode, both of which are metal electrodes.

7. The photodetector based on a ferroelectric / semiconductor heterojunction according to claim 6, characterized in that, The metal electrode is a chromium / gold electrode.

8. The photodetector based on a ferroelectric / semiconductor heterojunction according to claim 7, characterized in that, The thickness of the chromium layer in the chromium / gold electrode is 5-10 nm, and the thickness of the gold layer is 50-200 nm.

9. The method for fabricating a photodetector based on a ferroelectric / semiconductor heterojunction as described in claim 1, characterized in that, The steps are as follows: (1) Substrate cleaning; (2) On the substrate cleaned in step (1), a planar electrode pair, namely the first electrode and the second electrode, is prepared by photolithography and electron beam evaporation. (3) CuInP2S6 is transferred to the planar electrode pair and the channel region between them by mechanical peeling and dry transfer process to form CuInP2S6 thin film; then GeSe is transferred to the surface of CuInP2S6 thin film by mechanical peeling and dry transfer process to form two-dimensional heterojunction active layer.

10. The method for fabricating a photodetector based on a ferroelectric / semiconductor heterojunction according to claim 9, characterized in that, After the GeSe transfer in step (3), the process also includes annealing at 80-150°C for 5-20 minutes in a nitrogen or inert atmosphere.

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