Hafnium oxide-based ultrathin phototransistors based on two-dimensional channels

Abstract

The application discloses a hafnium oxide-based ultrathin optoelectronic transistor based on a two-dimensional channel, which comprises, from bottom to top, a substrate, a hafnium oxide-based ferroelectric back gate dielectric layer covering the substrate, wherein the hafnium oxide-based ferroelectric back gate dielectric layer adopts an aluminum-doped hafnium oxide ferroelectric film, and a source-drain composite electrode metal layer arranged at two ends of the hafnium oxide-based ferroelectric back gate dielectric layer and a two-dimensional semiconductor channel arranged on the surface of the hafnium oxide-based ferroelectric back gate dielectric layer. The application utilizes a ferroelectric residual polarization field as a floating gate to realize the regulation and control of the two-dimensional semiconductor electron transport characteristics, and does not need to apply an external gate voltage during operation. The application has the advantages of high sensitivity, rapid response and low power consumption in the detection of visible light, and adopts a standardized process to achieve an ultrathin thickness, thereby realizing mass production of large-scale and high-integration micro-nano sensing arrays.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic sensor materials technology, specifically to a hafnium oxide-based ultrathin phototransistor with a two-dimensional channel. Background Technology

[0002] Since the advent of graphene in 2004, two-dimensional materials have attracted widespread attention due to their unique physicochemical properties. They exhibit strong light-matter interactions and show great promise in the field of photoelectric detection, with new device structures constantly emerging. Transition metal sulfides, represented by molybdenum disulfide (MoS2), have only atomic-level thickness, which is beneficial for device miniaturization and easily modulated by external fields. Simultaneously, their bandgap is thickness-dependent, allowing for changes from indirect to direct bandgap from bulk materials to monolayers, facilitating efficient broadband photoelectric detection. Furthermore, the layers are bound together by van der Waals forces, and there are no dangling bonds on the surface, allowing for stacking at arbitrary angles, resulting in flexible structures and broad performance tuning potential. Currently, optoelectronic devices based on two-dimensional materials have been extensively studied, achieving high-sensitivity and fast-response visible light detection. However, devices often require high gate voltage to control the channel carrier concentration, which not only results in poor dark current suppression but also easily leads to leakage between the gate and source, generating high power consumption. In addition, two-dimensional optoelectronic devices are mostly fabricated using mechanical stripping methods, which makes their thickness and size uncontrollable and cannot be applied to the fabrication of large-scale arrays. These factors have become important obstacles to the development of two-dimensional optoelectronic devices.

[0003] Currently, the fabrication of two-dimensional optoelectronic devices mostly utilizes polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)) and lead zirconate titanate (PZT). However, these common commercial organic ferroelectric thin films require a thickness of hundreds of nanometers to achieve optimal ferroelectric performance, making it impossible to simultaneously achieve high responsivity, low power consumption, fast response speed at room temperature, and high integration. Their thickness and size cannot be further optimized. Therefore, how to fabricate ultrathin field-effect phototransistors is of great significance to the field of visible light sensors and has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide an ultrathin hafnium oxide-based phototransistor based on a two-dimensional channel to overcome the defects of the prior art. This invention utilizes the ferroelectric residual polarization field as a floating gate to achieve the control of the electronic transport characteristics of the two-dimensional semiconductor. No external gate voltage is required during operation. It has the advantages of high sensitivity, fast response and low power consumption in the detection of visible light. Furthermore, it adopts a standardized process to achieve ultrathin thickness, thereby realizing the mass production of large-scale, highly integrated micro-nano sensing arrays.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A hafnium oxide-based ultrathin phototransistor with a two-dimensional channel, comprising, from bottom to top:

[0007] Substrate;

[0008] A hafnium oxide-based ferroelectric back gate dielectric layer covering the substrate, wherein the hafnium oxide-based ferroelectric back gate dielectric layer is an aluminum-doped hafnium oxide ferroelectric thin film;

[0009] The hafnium oxide-based ferroelectric back gate dielectric layer includes source / drain composite electrode metal layers at both ends and a two-dimensional semiconductor channel on the surface of the hafnium oxide-based ferroelectric back gate dielectric layer.

[0010] Furthermore, the substrate is a p-type doped silicon substrate with the following crystal orientation: <100> ±0.5°, the thickness of the substrate is 500±15μm, and the thickness of the oxide layer of the substrate is 300±30nm.

[0011] Furthermore, the aluminum-doped hafnium oxide ferroelectric thin film was prepared by atomic layer deposition.

[0012] Furthermore, the aluminum doping concentration of the aluminum-doped hafnium oxide ferroelectric thin film is 7 mol%.

[0013] Furthermore, the thickness of the aluminum-doped hafnium oxide ferroelectric thin film is 10 nm.

[0014] Furthermore, the residual polarization field of the aluminum-doped hafnium oxide ferroelectric thin film acts on the two-dimensional semiconductor channel instead of the externally applied gate voltage, thereby constructing a floating gate structure.

[0015] Furthermore, the aluminum-doped hafnium oxide ferroelectric thin film is modulated into an upward polarization or a downward polarization state.

[0016] Furthermore, the two-dimensional semiconductor channel employs a single layer of molybdenum disulfide.

[0017] Furthermore, the two-dimensional semiconductor channel is prepared by atmospheric pressure chemical vapor deposition.

[0018] Furthermore, the source / drain composite electrode metal layer adopts a Ti / Au composite electrode, wherein the thickness of Ti is 5nm and the thickness of Au is 40nm.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] This invention designs an ultrathin hafnium oxide-based phototransistor based on a two-dimensional channel. By using an aluminum-doped hafnium oxide ferroelectric thin film as the dielectric layer of the device, compared to commonly used organic ferroelectric thin films which require a thickness of hundreds of nanometers to achieve optimal ferroelectric performance, the aluminum-doped hafnium oxide ferroelectric thin film can maintain a high remanent polarization intensity at a thickness of only 10 nm. Furthermore, it exhibits good compatibility with complementary metal-oxide two-dimensional semiconductors, effectively reducing device size and realizing ultrathin photodetectors. This also lays the foundation for wearable flexible sensing. When the gate voltage of the field-effect phototransistor is removed, the remanent polarization field of the aluminum-doped hafnium oxide ferroelectric thin film will continuously and stably act on the two-dimensional channel, constructing a floating gate structure. The channel characteristics are modulated using the electrostatic field effect, suppressing dark current, reducing power consumption, and achieving high integration, which helps to break the limits of Moore's Law. The two-dimensional channel-based hafnium oxide-based ultrathin phototransistor described in this invention meets the advantages of high responsivity, low power consumption, fast response speed, and high integration at room temperature, which is conducive to the mass production of large-scale, highly integrated micro-nano sensing arrays.

[0021] Furthermore, the aluminum-doped hafnium oxide ferroelectric thin film was prepared by atomic layer deposition to form a novel high-performance Al:HfO2 nano-ferroelectric thin film with a thickness of 10 nm. Compared with commercial organic ferroelectric thin films such as P(VDF-TrFE) and PZT, which require a thickness of hundreds of nanometers to exhibit ferroelectric performance, Al:HfO2 can maintain a high remanent polarization intensity at a thickness of 10 nm. As a gate dielectric material, it will effectively reduce device power consumption, improve device integration, and meet the application requirements of flexible wearable devices.

[0022] Furthermore, the residual polarization field of the aluminum-doped hafnium oxide ferroelectric thin film replaces the applied gate voltage on the two-dimensional semiconductor channel to form a floating gate structure, and the aluminum-doped hafnium oxide ferroelectric thin film is modulated into an upward polarization or downward polarization state. This invention targets the ferroelectric dielectric layer of a back-gate structure. Periodic bipolar pulses are applied between the gate and source to modulate the remanent polarization characteristics of the Al:HfO2 ferroelectric thin film. Therefore, no external gate voltage is required during device testing. By controlling the channel transport characteristics and metal-semiconductor contact barrier through the remanent polarization of the Al:HfO2 ferroelectric thin film, the device can be modulated into an upward or downward polarized state. The ultrathin ferroelectric back-gate dielectric layer acts as a floating gate, regulating the carrier transport characteristics of the two-dimensional channel. Compared to traditional field-effect phototransistors that apply a constant gate voltage to improve the photoelectric on / off ratio, the floating gate effectively suppresses dark current and gate-source leakage, improves photoelectric response sensitivity, and reduces device power consumption. This enables ultrathin visible light sensors with high sensitivity, fast response speed, and low power consumption, laying the foundation for the commercial application of novel intelligent sensing. Attached Figure Description

[0023] The accompanying drawings are provided to further understand the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0024] Figure 1 This is a schematic diagram of the structure of the hafnium oxide-based ultrathin phototransistor based on a two-dimensional channel according to the present invention;

[0025] Figure 2 This is a flowchart illustrating the fabrication process of a hafnium oxide-based ultrathin phototransistor based on a two-dimensional channel, as described in this embodiment of the invention.

[0026] Figure 3 This is a characterization diagram of the hysteresis loop test of the Al:HfO2 ferroelectric thin film in an embodiment of the present invention;

[0027] Figure 4 These are scanning electron microscope (SEM) images of the ultrathin phototransistor in an embodiment of the present invention.

[0028] Figure 5 The output characteristic curves of the hafnium oxide-based ultrathin phototransistor with a wavelength of 530 nm obtained in the embodiments of the present invention are shown at different optical powers.

[0029] In the figure, 1 is the substrate, 2 is the hafnium oxide-based ferroelectric back gate dielectric layer, 3 is the source-drain composite electrode metal Ti, 4 is the source-drain composite electrode metal Au, and 5 is the two-dimensional semiconductor channel. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0032] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0033] Example 1

[0034] This invention provides a hafnium oxide-based ultrathin phototransistor with a two-dimensional channel, such as... Figure 1 As shown, the phototransistor comprises, from bottom to top:

[0035] Substrate 1;

[0036] A hafnium oxide-based ferroelectric back gate dielectric layer 2 covering the substrate, wherein the hafnium oxide-based ferroelectric back gate dielectric layer 2 is an aluminum-doped hafnium oxide ferroelectric thin film;

[0037] The hafnium oxide-based ferroelectric back gate dielectric layer 2 has source-drain composite electrode metal layers at both ends and a two-dimensional semiconductor channel 5 on the surface of the hafnium oxide-based ferroelectric back gate dielectric layer 2.

[0038] This invention designs an ultrathin hafnium oxide-based phototransistor based on a two-dimensional channel. By using an aluminum-doped hafnium oxide ferroelectric thin film as the dielectric layer of the device, compared to commonly used organic ferroelectric thin films which require a thickness of hundreds of nanometers to achieve optimal ferroelectric performance, the aluminum-doped hafnium oxide ferroelectric thin film can maintain a high remanent polarization intensity at a thickness of only 10 nm. Furthermore, it exhibits good compatibility with complementary metal-oxide two-dimensional semiconductors, effectively reducing device size and realizing ultrathin photodetectors. This also lays the foundation for wearable flexible sensing. When the gate voltage of the field-effect phototransistor is removed, the remanent polarization field of the aluminum-doped hafnium oxide ferroelectric thin film will continuously and stably act on the two-dimensional channel, constructing a floating gate structure. The channel characteristics are modulated using the electrostatic field effect, suppressing dark current, reducing power consumption, and achieving high integration, which helps to break the limits of Moore's Law. The two-dimensional channel-based hafnium oxide-based ultrathin phototransistor described in this invention meets the advantages of high responsivity, low power consumption, fast response speed, and high integration at room temperature, which is conducive to the mass production of large-scale, highly integrated micro-nano sensing arrays.

[0039] Preferably, the substrate 1 is a p-type doped silicon substrate with the following crystal orientation: <100> ±0.5°, the thickness of substrate 1 is 500±15μm, and the thickness of oxide layer of substrate 1 is 300±30nm.

[0040] Furthermore, the two-dimensional semiconductor channel 5 is made of a single layer of molybdenum disulfide (MoS2), which is controllably prepared by atmospheric pressure chemical vapor deposition (CVD).

[0041] Furthermore, the preparation of the monolayer molybdenum disulfide (MoS2) in this invention includes the following steps:

[0042] Using Si / SiO2 as the substrate, sulfur powder as the sulfur source, molybdenum trioxide powder as the molybdenum source, sodium chloride as the precursor for molten salt-assisted growth, and argon as the carrier gas, MoS2 crystals on a SiO2 substrate, i.e. MoS2 / SiO2, can be controlledly prepared in a face-down structure in a self-built dual-temperature zone tube furnace using atmospheric pressure chemical vapor deposition (CVD).

[0043] Furthermore, the fabrication of the two-dimensional semiconductor channel 5 in this invention includes the following steps:

[0044] Polymethyl methacrylate (PMMA) was spin-coated onto the surface of MoS2 / SiO2 grown by chemical vapor deposition. MoS2 was attached to the surface of the PMMA film and transferred to an Al:HfO2 ferroelectric substrate using a wet chemical etching technique. The process included spin-coating, baking, alkaline etching, deionized water cleaning, transfer to a new substrate, baking, and resist removal.

[0045] This invention prepares MoS2 crystals with controllable size and number of layers using atmospheric pressure chemical vapor deposition (CVD). These crystals can be used as channel materials to further fabricate large-scale arrays of field-effect transistors. This method is highly reliable, simplifies the process flow, and can be effectively integrated into the current semiconductor device production chain, which is conducive to the mass production of sensors.

[0046] Preferably, the thickness of the two-dimensional semiconductor channel 5 is 0.65 nm.

[0047] Preferably, the aluminum doping concentration in the aluminum-doped hafnium oxide ferroelectric thin film (Al:HfO2) is 7 mol%, and the thickness of the aluminum-doped hafnium oxide ferroelectric thin film is 10 nm.

[0048] Furthermore, the preparation of the aluminum-doped hafnium oxide ferroelectric thin film (Al:HfO2) described in this invention includes the following steps:

[0049] Using tetra(dimethylamino)hafnium as the hafnium source, trimethylaluminum as the aluminum source, and water vapor as the oxygen source, Al:HfO2 ferroelectric thin films were deposited on silicon wafers by atomic layer deposition by adjusting the HfO2:Al2O3:HfO2 deposition cycle ratio. Subsequently, the crystal structure of the ferroelectric thin film was transformed to orthorhombic ferroelectric phase by a rapid annealing (RTA) process, thus preparing an Al:HfO2 ferroelectric thin film with a doping concentration of 7 mol% and a thickness of 10 nm on a silicon substrate.

[0050] This invention prepares a novel high-performance Al:HfO2 nano-ferroelectric thin film with a thickness of 10 nm using atomic layer deposition. Compared with commercial organic ferroelectric thin films such as P(VDF-TrFE) and PZT, which require a thickness of hundreds of nanometers to exhibit ferroelectric properties, Al:HfO2 can maintain a high remanent polarization intensity at a thickness of 10 nm. As a gate dielectric material, it will effectively reduce device power consumption, improve device integration, and meet the application requirements of flexible wearable devices.

[0051] Furthermore, a floating gate structure is constructed based on the remanent polarization characteristics of the aluminum-doped hafnium oxide ferroelectric thin film (Al:HfO2), and its fabrication includes the following steps:

[0052] For the hafnium oxide-based ferroelectric back gate dielectric layer 2 of the back gate structure, periodic bipolar pulses are applied between the gate and the source to modulate the residual polarization characteristics of the aluminum-doped hafnium oxide ferroelectric thin film (Al:HfO2), so that the device is modulated into an upward polarization or downward polarization state. The hafnium oxide-based ferroelectric back gate dielectric layer 2 will act as a floating gate, regulate the channel transport characteristics, and improve the optoelectronic performance of the device.

[0053] This invention utilizes the residual polarization field of an Al:HfO2 ferroelectric thin film to construct a floating gate structure and modulate the carrier transport characteristics of the MoS2 channel. Compared to traditional field-effect phototransistors that rely on externally applied constant gate voltage to improve the photoelectric on / off ratio, this invention achieves a floating gate effect by controlling the channel transport characteristics and metal-semiconductor contact barrier through the residual polarization of the ferroelectric thin film. The floating gate effectively suppresses dark current and gate-source leakage, enabling a high-sensitivity, fast-response, and low-power ultrathin visible light sensor, laying the foundation for the commercial application of novel intelligent sensing.

[0054] Furthermore, the source / drain composite electrode metal layer adopts a Ti / Au composite electrode, wherein the thickness of Ti is 5nm and the thickness of Au is 40nm.

[0055] Furthermore, the preparation of the source-drain composite electrode metal layer in this invention includes the following steps:

[0056] Patterned source and drain electrodes are deposited on the transferred MoS2 surface using standard ultraviolet lithography and electron beam evaporation processes, including spin coating of photoresist, pre-baking, ultraviolet exposure, post-baking, ultraviolet bare exposure, development, electron beam evaporation, and photoresist removal. The source and drain electrodes are Ti / Au (5nm / 40nm) composite electrodes to form good ohmic contact between the metal and the semiconductor channel.

[0057] Example 2

[0058] This embodiment provides an ultrathin phototransistor with a CVD-grown monolayer MoS2 channel and a 10nm thick Al:HfO2 ferroelectric thin film as the back gate dielectric layer. The device structure diagram is shown below. Figure 1 As shown.

[0059] The phototransistor consists of the following components from bottom to top: substrate 1, hafnium oxide-based ferroelectric back gate dielectric layer 2, source-drain composite electrode metal Ti 3, source-drain composite electrode metal Au 4, and two-dimensional semiconductor channel 5.

[0060] In this embodiment, substrate 1 is a P-type doped silicon substrate with a 300 nm thick oxide layer covering its surface; hafnium oxide-based ferroelectric back gate dielectric layer 2 is an aluminum-doped hafnium oxide ferroelectric thin film with a thickness of 10 nm and an aluminum doping concentration of 7 mol%, prepared by atomic layer deposition; the source-drain composite electrode metal Ti3 has a thickness of 5 nm; the source-drain composite electrode metal Au4 has a thickness of 40 nm, and the patterned source-drain composite electrode is prepared by standard ultraviolet lithography and electron beam evaporation technology; the two-dimensional semiconductor channel 5 is a monolayer MoS2 channel grown by CVD, which is transferred from the growth substrate to the ferroelectric substrate by wet method.

[0061] In this embodiment, the ultrathin phototransistor based on a two-dimensional channel and an ultrathin ferroelectric back gate dielectric layer is characterized by scanning electron microscopy as follows: Figure 4 As shown, the transferred MoS2 surface has a good morphology and uniform thickness, with no obvious wrinkles or damage, good contact between the channels and electrodes, and no obvious residual adhesive on the device surface.

[0062] like Figure 5 The figure shows the photoelectric response characteristics of the ultrathin phototransistor device. It can be seen that applying a polarization pulse between the gate and source results in a stable residual polarization field acting on the channel, suppressing the dark current to a few picoamperes. Removing the gate pulse voltage and applying a 1V bias voltage between the source and drain, for incident light with a wavelength of 530nm, as the optical power increases from 0μW to 1.204μW, the source and drain currents increase accordingly. The output characteristic curve of the device is symmetrical about the origin, proving that the introduction of metallic Ti effectively improves the metal-semiconductor contact; furthermore, the device photocurrent reaches the microampere level, and the photoelectric on / off ratio is at least 10. 5It exhibits extremely high photoelectric response sensitivity; in addition, the device does not require an external gate voltage input during operation, effectively reducing power consumption.

[0063] The results above demonstrate that the hafnium oxide-based ultrathin phototransistor disclosed in this invention, based on a two-dimensional channel, exhibits excellent photoelectric conversion performance, high sensitivity, low power consumption, rapid response, and small size (only tens of nanometers thick), making it highly commercially viable. Furthermore, its fabrication process boasts high reliability, making it suitable for industrial production and laying the foundation for the fabrication of large-scale flexible sensing arrays.

[0064] The following is in conjunction with the appendix Figure 2 This embodiment provides a detailed explanation of how the hafnium oxide-based ultrathin phototransistor with a two-dimensional channel is fabricated.

[0065] 1. Controlled CVD preparation of MoS2 crystals

[0066] Step 1: Introduce a mixed carrier gas of Ar@200sccm / O2@5sccm into the growth system and maintain it at 800℃ for 20 minutes to clean the quartz tube;

[0067] Step 2: Cut the heavily p-doped silicon wafer (oxide layer thickness of 300nm) into 1cm×1cm pieces, sonicate them in acetone and isopropanol for 15min in sequence, and then clean them with deionized water.

[0068] Step 3: Weigh 200mg of sulfur powder and place it in a quartz boat in a low-temperature tube furnace. Weigh 3mg of molybdenum trioxide powder and 1mg of sodium chloride, mix them evenly, and place them in the quartz boat. Place the cleaned silicon wafer with the oxide layer facing down on top of the molybdenum trioxide and sodium chloride mixture. The center of the mixture should be about 0.5cm away from the upstream edge of the first silicon wafer. The other two silicon wafers are arranged closely downstream of the first silicon wafer. Then place the quartz boat in a high-temperature tube furnace.

[0069] Step 4: Wrap a heating tape around the quartz tube of the tubular furnace between the two temperature zones, and control the temperature at 137-140℃ to prevent the quartz tube between the two tube furnaces from being exposed to the air when sulfur vapor is transported from the carrier gas to the downstream high-temperature growth zone, which would cause the temperature to drop and sublimate on the tube wall.

[0070] Step 5: After the precursor and substrate are placed in the tube furnace, 10 sccm of argon gas is introduced to observe the bubbling of the tail gas treatment device and confirm the airtightness of the growth system.

[0071] Step 6: Introduce argon gas at 450 sccm into the system for 30 minutes to remove impurity gases;

[0072] Step 7: The system enters the heating stage: the high-temperature tube furnace is heated from room temperature to 750°C at a rate of 18°C / min, and the low-temperature tube furnace is heated to 160°C at a rate of 12°C / min after being kept at room temperature for 30 minutes. During the heating stage, the argon flow rate is controlled at 150 sccm.

[0073] Step 8: The system enters the growth stage: the high-temperature tube furnace is maintained at 750℃, the low-temperature tube furnace is maintained at 160℃, the argon flow rate is maintained at 60 sccm, and the growth time is 10 min;

[0074] Step 9: After growth is complete, wait for the furnace temperature to drop to 500°C, then open the tube furnace lid and allow it to cool naturally to room temperature before removing the substrate and turning off the airflow.

[0075] Step 10: The crystal quality, surface morphology, thickness, and uniformity of the CVD-grown MoS2 were characterized using optical microscopy (OM), scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence spectroscopy (PL), and atomic force microscopy (AFM).

[0076] 2. Preparation of Al:HfO2 ferroelectric thin films

[0077] Step 1: The heavily p-doped silicon wafer (oxide layer thickness of 300nm) was ultrasonically cleaned in anhydrous ethanol and deionized water for 15 minutes in sequence.

[0078] Step 2: Prepare a 55 mL solution of hydrofluoric acid and deionized water at a volume ratio of 1:10. Immerse the cleaned silicon wafer in the solution for about 10 seconds to etch SiO2. Then rinse the silicon wafer with deionized water and dry it with nitrogen.

[0079] Step 3: Place the silicon wafer with the oxide layer removed into an atomic layer deposition (ALD) apparatus. Use tetra(dimethylamino)hafnium as the hafnium source and trimethylaluminum as the aluminum source. Introduce water vapor as the oxygen source. Deposit for 4 cycles at a HfO2:Al2O3:HfO2 cycle ratio of 12:2:12. The deposition rate is [missing information].

[0080] Step 4: After deposition, the sample is not covered with the top electrode. It is rapidly annealed at 750°C for 30s in an oxygen atmosphere to promote the transformation of Al:HfO2 to the orthogonal ferroelectric phase. Finally, an Al:HfO2 ferroelectric thin film with a doping concentration of 7mol% and a thickness of 10nm is obtained on the silicon substrate.

[0081] Step 5: Perform transmission electron microscopy (TEM) on the ferroelectric thin film to characterize its surface morphology, film thickness, doping quality, etc.; then cut a portion of the sample and perform surface sputtering with gold to prepare a capacitor structure, and then test its hysteresis loop to characterize the ferroelectric properties such as remanent polarization and coercive voltage, etc. Figure 3As shown, the Al:HfO2 ferroelectric thin film exhibits a high C / cm² temperature at a thickness of 10 nm. 2 The residual polarization intensity is high, and the coercive voltage of the thin film is only about 10V, which can construct a stable residual polarization field.

[0082] 3. Wet transfer of MoS2 crystals

[0083] Step 1: Spin-coat PMMA photoresist (Micro-Chem A4) onto the CVD-grown MoS2 surface. The specific spin coating parameters are: 500 r / min @ 10 s for the low-speed stage and 8000 r / min @ 50 s for the high-speed stage. Then, bake the sample on a hot stage at 180°C for 90 s to cure.

[0084] Step 2: Sand the edges of the silicon wafer with sandpaper to fully expose the SiO2 layer. The width of the SiO2 portion is about 2mm. Then blow away the debris with argon gas and wipe the silicon wafer with a cotton swab dipped in isopropanol.

[0085] Step 3: Prepare a 1 mol / L KOH solution, place the silicon wafer in it to fully etch SiO2, place the culture dish containing the silicon wafer and KOH solution on a hot plate and keep it at a constant temperature of 45°C to promote the reaction, replace the KOH solution every 30 minutes, so that MoS2 adheres to the PMMA film and detaches from the growth substrate.

[0086] Step 4: Lift the MoS2 / PMMA film onto a glass slide and transfer it to deionized water for washing. Repeat this process three times to remove residual KOH impurities. During this process, ensure that the film is always facing upwards.

[0087] Step 5: Use an Al:HfO2 ferroelectric substrate to lift the film. During this process, try to ensure that the film is flat and wrinkle-free and avoid air bubbles. Then dry the sample in a fume hood overnight, and then bake it on a hot stage at 150°C for 15 minutes to enhance the bonding force between the ferroelectric substrate and the two-dimensional material.

[0088] Step 6: Using self-locking tweezers, vertically immerse the sample in acetone to remove PMMA impurities. Place the beaker containing acetone on a hot stage and heat at a constant temperature of 45°C. Replace the acetone every 6 hours, repeating the process three times, and finally obtain the MoS2 crystal transferred onto the ferroelectric substrate.

[0089] 4. Fabrication of patterned source and drain electrodes

[0090] Step 1: Spin coat ROL-7133 photoresist onto the MoS2 surface transferred to the ferroelectric substrate. The specific spin coating parameters are: 600 r / min @ 5s at low speed, 4000 r / min @ 30s at high speed, and the photoresist thickness is about 2 μm. Then, cure it on a hot stage at 95°C for 90s.

[0091] Step 2: Install the photomask on the lithography machine, adjust its position and align it, then immerse it in ultraviolet light at a wavelength of 265nm for 5.5s for dissolution exposure;

[0092] Step 3: Bake the sample on a hot stage at 110°C for 90 seconds, then remove the mask and expose it to UV light for 55 seconds.

[0093] Step 4: Develop the sample in alkaline developer for 25 seconds, wash the sample with deionized water, and dry it with nitrogen to obtain MoS2 with patterned photoresist on the surface.

[0094] Step 5: Place the photolithographically etched sample into an electron beam evaporation apparatus, using 99.99% pure gold particles and titanium pillars as the gold and titanium sources, respectively. A 5nm thick layer of metallic Ti was deposited at a high speed as an interface improvement layer. A 40nm thick layer of metallic Au was deposited at a high speed as an electrode;

[0095] Step 6: After removing the sample from the electron beam evaporation system, use self-locking tweezers to vertically place the sample in acetone and sonicate at 10W power and 40℃ for 3 minutes to remove the photoresist. Finally, an ultrathin visible light photoelectric sensor is obtained with CVD-grown MoS2 as the channel, Al:HfO2 ferroelectric thin film as the back gate dielectric layer, and Ti / Au composite electrode as the source and drain electrode.

[0096] 5. Testing Scheme for Ultrathin Visible Light Sensors Based on Al:HfO2 Ferroelectric Substrates and Monolayer MoS2 Channels

[0097] Step 1: Place the prepared sample on the probe stage, and use a tungsten needle to connect the gate, source, and drain to the semiconductor tester. The source-drain voltage V ds Maintain 1V, gate voltage V gs The device's transfer characteristic curve is obtained by periodically scanning from -1V to around 10V to open the hysteresis window of the ferroelectric thin film.

[0098] Step 2: Apply a bipolar pulse between the gate and the source, with the pulse amplitude gradually increasing until it is maintained at the coercive voltage. The ferroelectric thin film can be modulated into two states, upward polarization and downward polarization, depending on the direction of the gate voltage.

[0099] Step 3: In order to effectively suppress dark current and improve the photoelectric switching ratio, the ferroelectric thin film is modulated to a downward polarization state according to the back gate structure to deplete the intrinsic carriers in the channel. After removing the gate voltage, the residual polarization field is used as a floating gate to control the channel characteristics.

[0100] Step 4: Further test the output characteristic curves, photoelectric switching characteristics, response time, etc. under different optical powers to obtain the photoelectric response performance parameters of the device. The residual polarization field perpendicular to the two-dimensional channel downwards effectively depletes intrinsic carriers, and the dark current is suppressed to the order of picoamperes. When visible light of a certain power is incident, the source-drain current increases with the increase of optical power, exhibiting a high photoelectric switching ratio, especially showing high sensitivity for weak light.

[0101] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A two-dimensional channel-based hafnium oxide-based ultra-thin optoelectronic transistor, characterized in that, The phototransistor comprises, from bottom to top, in order: a substrate (1); a hafnium oxide-based ferroelectric back gate dielectric layer (2) covering the substrate (1), wherein the hafnium oxide-based ferroelectric back gate dielectric layer (2) is made of an aluminum-doped hafnium oxide ferroelectric thin film; a source-drain composite electrode metal layer arranged at two ends of the hafnium oxide-based ferroelectric back gate dielectric layer (2), and a two-dimensional semiconductor channel (5) arranged on the surface of the hafnium oxide-based ferroelectric back gate dielectric layer (2); the remanent polarization field of the aluminum-doped hafnium oxide ferroelectric thin film acts on the two-dimensional semiconductor channel (5) instead of an externally applied gate voltage, thereby constructing a floating gate structure; the aluminum-doped hafnium oxide ferroelectric thin film is modulated to be in an upward polarization state or a downward polarization state; the two-dimensional semiconductor channel (5) is made of a single-layer molybdenum disulfide; the aluminum element doping concentration of the aluminum-doped hafnium oxide ferroelectric thin film is 7 mol%; the thickness of the aluminum-doped hafnium oxide ferroelectric thin film is 10 nm.

2. The two-dimensional channel based hafnium oxide based ultra-thin phototransistor according to claim 1, wherein, The substrate (1) is a P-type doped silicon substrate, the crystal direction of which is <100>±0.5°, the thickness of the substrate (1) is 500±15 μm, and the thickness of the oxide layer of the substrate (1) is 300±30 nm.

3. The two-dimensional channel based hafnium oxide based ultra-thin phototransistor according to claim 1, wherein, The aluminum-doped hafnium oxide ferroelectric thin film is prepared by an atomic layer deposition method.

4. The two-dimensional channel based hafnium oxide based ultra-thin phototransistor according to claim 1, wherein, The two-dimensional semiconductor channel (5) is prepared by an atmospheric pressure chemical vapor deposition method.

5. The two-dimensional channel-based hafnium oxide-based ultra-thin phototransistor of claim 1, wherein, The source-drain composite electrode metal layer is made of a Ti / Au composite electrode, wherein the thickness of Ti is 5 nm, and the thickness of Au is 40 nm.

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