Method for detecting surface oxidation of two-dimensional material by using differential electrode configuration and optoelectronic device

Abstract

The application discloses a method for detecting surface oxidation of two-dimensional materials by using differential electrode configuration and a photoelectric device. An embedded electrode is prepared on a silicon substrate with an oxide layer, a MoTe2 film is obtained by mechanical exfoliation and PDMS dry transfer, and bottom-bottom contact is formed between the MoTe2 film and the bottom electrode. Then, a top electrode is evaporated on the surface of the material to construct various differential contact structures. The degree of in-situ oxidation by UVO is judged by testing the output current of the top-top electrode structure and the bottom-bottom electrode structure by using in-situ oxidation by UVO combined with multi-channel electrical real-time testing, and the corresponding photoelectric device is prepared. The embedded electrode solves the deformation defect of the film transfer, realizes in-situ and non-damage tracking of the self-limiting growth of the oxide layer and the evolution of the barrier state, and the prepared photoelectric device realizes unbiased ultrafast self-driven photoelectric detection by relying on the vertical double-competition built-in electric field. In addition, the photoelectric device can rely on photoelectric synergistic regulation to output three-level electrical signals and complete balanced ternary logic encoding.

Description

Technical Field

[0001] This invention relates to the field of semiconductor devices, and more specifically to a method and optoelectronic device for detecting surface oxidation of two-dimensional materials using differentiated electrode configurations. Background Technology

[0002] Molybdenum ditelluride (MoTe2), a typical transition metal chalcogenide, possesses an indirect band gap of approximately 1.1 eV (close to that of bulk silicon), high carrier mobility, and excellent near-infrared light absorption, showing broad application prospects in high-performance field-effect transistors, high-sensitivity photodetectors, and photovoltaic devices. Furthermore, MoTe2 exhibits intrinsic bipolar transport properties, providing a unique material basis for constructing complementary logic circuits and reconfigurable electronic devices.

[0003] Despite its promising prospects, the commercial application of MoTe2 devices still faces significant challenges. The practical application of MoTe2-based devices is constrained by several key issues. Firstly, the lack of dangling bonds on the two-dimensional MoTe2 surface leads to a strong Fermi level pinning effect when metal electrodes contact it, resulting in a significant increase in the Schottky barrier and contact resistance, severely limiting the device's current-driving capability and transconductance performance. Secondly, intrinsic MoTe2 is environmentally sensitive and prone to spontaneous oxidation, and the lack of mature ion implantation methods for precise control of carrier concentration makes improving interfacial transport efficiency a long-standing scientific challenge in the field.

[0004] To address the aforementioned bottlenecks, researchers have attempted to modulate the electronic structure and interfacial properties of MoTe2 through surface chemical modification. Among these, ultraviolet ozone (UVO) or ozone (O3) oxidation technology has attracted considerable attention in two-dimensional material interface engineering in recent years due to its non-destructive nature, low cost, and the fact that it does not require a vacuum environment. The core idea of ​​this technology is to utilize ultraviolet light to excite ozone molecules to generate highly reactive oxygen free radicals, thereby controlling the oxidation of the few-layer MoTe2 surface under mild conditions, resulting in the in-situ generation of a dense layer of MoO with non-stoichiometric properties. X Oxide layer. The introduction of this oxide layer brings multiple benefits: firstly, MoO XThe oxide layer possesses high electron affinity, enabling it to extract electrons from the MoTe2 layer, achieving efficient surface charge transfer doping and resulting in significant p-type conductivity. Secondly, this oxide layer serves as a natural interface modification layer, effectively mitigating the Fermi level pinning effect between the metal electrode and MoTe2, reducing the Schottky barrier height and contact resistance. Furthermore, by precisely controlling the ozone exposure dose, atomic-level layer-by-layer thinning of few-layer MoTe2 can be achieved, thereby adjusting the material thickness to optimize the device's transfer characteristic curve. Based on these mechanisms, successful cases of improving the electrical performance of devices such as MoTe2 field-effect transistors and photodetectors through UVO or O3 treatment have been reported, demonstrating the effectiveness of this technology in improving device on-state current, on / off ratio, and response speed.

[0005] Although the aforementioned oxidation modification strategies have made some progress, existing studies generally adopt a process of "oxidation treatment first, offline characterization second, and fabrication and testing third." This means that after treatment, X-ray photoelectron spectroscopy (XPS) is used to analyze changes in surface chemical states, transmission electron microscopy (TEM) is used to observe the thickness and morphology of the oxide layer, or atomic force microscopy (AFM) is used to assess surface roughness and the number of layers. Finally, samples under different oxidation conditions are fabricated into devices for electrical testing, thereby indirectly inferring the correlation between the oxidation process and device performance. However, this characterization model has significant limitations: XPS, TEM, and AFM are all offline, static detection methods that must be performed separately after oxidation treatment. Furthermore, the sample preparation process for TEM and other methods is destructive, making continuous tracking of the same device impossible. More importantly, these methods cannot obtain in-situ electrical response information during the oxidation process while the device is in operation, resulting in the dynamic evolution of microscopic oxidation depth, interfacial doping gradient, and Schottky barrier remaining in a state of "indirect inference" rather than "real-time observation." This research paradigm, which separates surface oxidation processes from device electrical behavior, lacks direct experimental evidence to support the causal relationship between microscopic chemical modifications and macroscopic device performance. It makes it difficult to reveal the dynamic evolution of charge transport mechanisms with the degree of oxidation and also restricts the precise optimization of oxidation process parameters.

[0006] Therefore, there is an urgent need to develop an in-situ detection method that can convert microscopic surface oxidation behavior into macroscopic electrical characteristics in real time, and use this method to guide the structural design of high-performance optoelectronic devices. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a method and optoelectronic device for detecting surface oxidation of two-dimensional materials using differentiated electrode configurations. This method involves constructing an embedded bottom electrode on a substrate surface, transferring the two-dimensional material onto the substrate, and then constructing a top electrode on the surface of the two-dimensional material. Ultraviolet ozone (UVO) is used to oxidize the two-dimensional surface, and the degree of oxidation of the two-dimensional material is determined by real-time detection of changes in the transport current between the top-top electrode and the bottom-bottom electrode. The present invention also provides a structure for an optoelectronic device fabricated based on this method. This optoelectronic device exhibits good self-driven photoelectric response performance and can implement balanced ternary (Base-3) logic encoding, providing a novel underlying device architecture for developing low-power, integrated sensing and computing high-information-density chips.

[0008] To achieve the above objectives, the present invention first provides a method for detecting surface oxidation of two-dimensional materials using differentiated electrode configurations. The method involves first preparing a stepless embedded bottom electrode on a SiO2 layer on a silicon substrate using plasma technology; then transferring a mechanically exfoliated MoTe2 film to the surface of the embedded bottom electrode using a dry transfer technique; finally preparing a top electrode on the MoTe2 surface to form a differentiated contact structure; and finally oxidizing the MoTe2 surface using ultraviolet ozone (UVO) and detecting the degree of oxidation of the two-dimensional material by monitoring the changes in transport current between the top-top electrode and the bottom-bottom electrode.

[0009] In one embodiment of the present invention, the method for detecting surface oxidation of two-dimensional materials using differentiated electrode configurations includes the following steps: (1) On a silicon substrate with a SiO2 layer, the original SiO2 layer is processed by photolithography and plasma etching techniques, and then metal is deposited by thermal evaporation. After peeling, an embedded bottom electrode flush with the SiO2 surface is obtained. (2) The 2H phase MoTe2 film obtained by mechanical exfoliation is transferred to the substrate surface containing the embedded bottom electrode in step (1) using PDMS dry transfer technology to form a bottom-to-bottom contact structure; (3) Place the sample obtained in step (2) on a maskless photolithography stage and use photolithography and vapor deposition process to prepare the top electrode on the MoTe2 surface, thereby forming bottom-bottom, top-top and top-bottom contact structures on the same channel; (4) Use ultraviolet ozone (UVO) to oxidize the device with top electrode prepared in step (3). By comparing and analyzing the dynamic evolution of the output current under different contact structures in real time, the detection and analysis of the surface oxidation degree and self-confined depth are completed.

[0010] In one embodiment of the present invention, before preparing the embedded bottom electrode in step (1), the silicon substrate needs to be cleaned. The specific cleaning steps include: first, placing the silicon substrate with a 200-350 nm thick SiO2 layer into an acetone solution and ultrasonically cleaning it for 3-10 minutes; then placing it in an anhydrous ethanol solution and ultrasonically cleaning it for 3-10 minutes; then ultrasonically cleaning it in deionized water for 3-10 minutes; finally, taking it out and drying it with a high-pressure nitrogen gun to obtain a clean substrate.

[0011] In one embodiment of the present invention, the plasma etching technology in step (1) specifically involves using a mixture of SF6 / N2 (SF6: 10 ~ 20 sccm and N2: 5 ~ 15 sccm) to etch a patterned SiO2 layer on a silicon substrate. The etching parameters are set as follows: radio frequency power 250 ~ 350 W and reflection power within 80 W, the cavity pressure of the mild plasma reaction chamber is maintained at 20 ~ 40 Pa, and the reaction time is 1 ~ 3 minutes, so that the etching depth is precisely controlled at 40 ~ 60 nm.

[0012] In one embodiment of the present invention, the vapor deposition process described in steps (1) and (3) both include hot vapor deposition of bismuth (Bi) metal and hot vapor deposition of gold (Au) metal; wherein when hot vapor deposition is used to prepare bismuth metal, the vacuum condition of the vapor deposition machine must meet 2×10 -3 Below Pa, the plating rate used is 0.20~0.25 Å / s, the time is 2~8 minutes, and the thickness of the obtained bismuth electrode material is 2~10 nm; when preparing gold metal by thermal evaporation, the vacuum condition of the evaporation machine meets 2×10 -3 For a Pa value below 0.20~0.25 Å / s, the plating rate is 0.20~0.25 Å / s, the time is about 20~50 minutes, and the thickness of the gold electrode material obtained is 40~60 nm.

[0013] In one embodiment of the present invention, the ultraviolet ozone (UVO) treatment in step (4) is carried out using a UV ultraviolet ozone cleaning machine to perform surface oxidation on the device under normal temperature and pressure and equipment power of 50 ~ 100 W.

[0014] In one embodiment of the present invention, the thickness of the MoTe2 film in step (2) is 10~50 nm.

[0015] This invention also provides a method for fabricating a high-performance optoelectronic device, comprising the following steps: S1. On a silicon substrate with a SiO2 layer, the original SiO2 layer is processed using photolithography and plasma etching techniques. Then, metal is deposited by thermal evaporation. After peeling, an embedded bottom electrode flush with the SiO2 surface is obtained. S2. The 2H phase MoTe2 thin film obtained by mechanical peeling is transferred to the substrate surface containing the embedded bottom electrode in step (1) using PDMS dry transfer technology; S3. Perform UVO surface oxidation treatment on the MoTe2 thin film from step S2 to form MoO2 on its surface in situ. x Layers are formed, and p-type doping is induced, constructing upward-growing vertical MoO in the vertical direction. x / MoTe2 structure; S4. Place the sample after surface oxidation treatment in step S3 on a photolithography stage, use photolithography to etch the device structure and deposit the top electrode to obtain the optoelectronic device.

[0016] In one embodiment of the present invention, in step S1, the SiO2 layer on the surface of the silicon substrate has a thickness of 200-350 nm, the width of a single embedded bottom electrode is 2-20 μm, the configuration depth is 40-60 nm, and the spacing between adjacent bottom electrodes is 2-20 μm.

[0017] In one embodiment of the present invention, in step S2, the thickness of the MoTe2 film is 10 ~ 50 nm.

[0018] In one embodiment of the present invention, in step S3, the power of the equipment during UVO surface oxidation treatment is 50-100 W, and the treatment time is 50-160 minutes.

[0019] In one embodiment of the present invention, in step S4, the material of the top electrode is a composite layer of bottom bismuth (Bi) and top gold (Au), wherein the thickness of the bottom bismuth is 2 to 10 nm, the thickness of the top gold is 40 to 60 nm, the width of a single top electrode is 2 to 20 μm, the total thickness of the electrode material is 40 to 80 nm, and the distance between the top electrode and the embedded bottom electrode in the channel direction is 2 to 20 μm.

[0020] In one embodiment of the present invention, step S4, which involves etching the device structure using photolithography, specifically involves aligning the electrode pattern onto the oxidized MoTe2 surface under a microscope, exposing the area to be plated with electrodes, blocking the channel area, and retaining the width of the MoTe2 channel in the range of 2 to 20 μm, and obtaining the device pattern using photolithography.

[0021] The present invention also provides a high-performance optoelectronic device prepared according to the above preparation method.

[0022] In one embodiment of the present invention, the high-performance optoelectronic device includes an asymmetric contact barrier and a hole tunneling-dominated asymmetric directional transport mechanism, and combines the performance of unbiased ultrafast photoelectric response and balanced ternary logic encoding.

[0023] The present invention also provides an application of the above-mentioned high-performance optoelectronic device in the fields of ternary logic calculation and information processing, integrated sensing and computing and edge computing, optical communication and encrypted communication, and low-power high-performance chips.

[0024] Beneficial effects: (1) This invention transforms the dynamic evolution process of two-dimensional material interface oxidation into macroscopic electrical testing by constructing differentiated contact configurations of “bottom-bottom, top-top, and top-bottom”. Compared with destructive, offline physical characterization methods such as XPS and AFM, the method of this invention can detect the self-confined growth law and resistive state evolution of amorphous oxide layers in situ and accurately while the device is in operation.

[0025] (2) This invention innovatively introduces plasma etching technology to prepare an embedded metal bottom electrode that is completely flush with the substrate, thus solving the physical steps generated by the traditional evaporation process. This configuration avoids the mechanical stress, wrinkles and suspended deformation generated during the transfer of two-dimensional thin films, ensuring the purity and extremely high fidelity of the extracted bulk transport parameters.

[0026] (3) This invention constructs an asymmetric contact band and interface barrier in the device by controlling the process sequence of "oxidation first, then evaporation". In the dark state with zero bias, due to the combined effect of band bending and the high barrier at the source, electrons drift unidirectionally towards the drain, forming a stable negative dark current. Under laser irradiation, an efficient photogenerated hole tunneling mechanism is triggered inside the device, which promotes the efficient injection of photogenerated holes into the drain through tunneling. At the same time, photogenerated electrons drift directionally towards the source along the conduction band, realizing ultrafast spatial separation of photogenerated carriers, so that the macroscopic net current instantly changes from negative to positive. This mechanism successfully realizes ultrafast self-driven photoelectric response at the microsecond level (0.8 μs / 2.5 μs) without bias.

[0027] (4) Relying on the optoelectronic synergistic control characteristics of the device, the optoelectronic device prepared by the present invention can break through the limitations of traditional binary logic calculation, undergo a unique polarity reversal, and output three independent level states of negative (-1), zero (0), and positive (1) with extreme stability. This characteristic successfully realizes balanced ternary (Base-3) logic encoding, providing a brand-new underlying device architecture for developing low-power, integrated sensing and computing high information density chips.

[0028] (5) This invention uses ultraviolet ozone (UVO) treatment, with reaction conditions at room temperature and pressure and the depth of action controllable in real time. This self-confined oxidation mechanism preserves the intrinsic lattice of the two-dimensional material bottom layer without damage, avoiding secondary damage to the ultrathin sample by high-energy methods such as ion implantation. The process is simple to operate and highly compatible with modern mainstream CMOS micro-nano fabrication technology, and has extremely strong wafer-level mass production potential.

[0029] (6) This invention constructs a test device with differentiated electrode configurations to extract electrical parameters of charge carriers under the dominance of bulk transport and interfacial transport in two-dimensional materials. The special feature of the substrate of this test device is that an embedded bottom electrode completely flush with the substrate surface is prepared on the SiO2 layer using plasma etching technology, which solves the physical step caused by direct electrode deposition, avoids deformation of the two-dimensional material under mechanical stress during the transfer process, and ensures that the ultraviolet ozone (UVO) treatment only treats the MoTe2 surface. The MoTe2 film and the embedded bottom electrode form a completely fitted bottom-to-bottom contact, which, together with the subsequently prepared top electrode, constitutes a differentiated structure for detecting oxidation behavior in the lateral and longitudinal directions. Through the method of this invention, the interfacial barrier and bulk doping evolution caused by micro-oxidation are utilized to macroscopically output significantly different electrical characteristics. This not only accurately detects the self-confined growth and resistive state evolution of oxidation on the surface of two-dimensional materials, but also, based on the physical laws revealed in the characterization process, extracts the "top-to-bottom" electrode structure to further derive and prepare high-performance optoelectronic devices. Attached Figure Description

[0030] Figure 1 This is a three-dimensional structural diagram of the test device with differentiated electrode configuration in this invention. The diagram intuitively shows the three differentiated transport channels (bottom-bottom electrode, top-bottom electrode, and top-top electrode) formed by the embedded bottom electrode, the MoTe2 thin film, and the top electrode.

[0031] Figure 2 This is a flowchart of the method for detecting surface oxidation of two-dimensional materials using differentiated electrode configuration in Embodiment 1 of the present invention.

[0032] Figure 3 This is a comparison of the dynamic evolution of the transport current of the differentiated electrode structures under different UVO treatment times in Examples 1 and 2. Specifically, (a) shows the three-stage evolution curve of the output current of the differentiated electrode structure in Example 1 as a function of treatment time; (b) shows the ratio of the equivalent resistance (Ri) of electrode structure 1 to electrode structure 3 in Example 1. 电极结构 1 / R 电极结构 3 (c) is the curve showing the change of the output current of the differentiated electrode structure in Example 2 with the processing time in three stages; (d) is the quantitative curve showing the change of the equivalent resistance ratio corresponding to Example 2 with the processing time.

[0033] Figure 4 The curves show the output current of electrode structures 1-3 in Example 1 as a function of processing time.

[0034] Figure 5 This is a flowchart illustrating the fabrication process of the optoelectronic device in Embodiment 3 of the present invention.

[0035] Figure 6 This is a quantitative characteristic diagram showing the evolution of photoelectric responsivity (R) and specific detectivity (D*) of the optoelectronic device prepared in Example 3 with UVO surface oxidation treatment time.

[0036] Figure 7 The images show the transfer characteristic curves (a) of the bottom-bottom electrode structure of the optoelectronic device in Example 3 after untreated and UVO surface oxidation treatment for 120 min, and the transmission electron microscope (TEM) image (b) of the vertical distribution cross-section of the in-situ induced amorphous MoOx oxygen-rich barrier layer and the underlying crystalline MoTe2.

[0037] Figure 8 The test curves of the ultrafast photoelectric response time (rise / fall time) of the optoelectronic device prepared in Example 3 in self-driven mode.

[0038] Figure 9 This is a demonstration diagram of balanced ternary (Base-3) logic encoding and dynamic character decoding implemented by the optoelectronic device prepared in Example 3. Detailed Implementation

[0039] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0040] Test method: UVO treatment: The sample is placed in a UV ozone cleaner and the surface of the device is oxidized under normal temperature and pressure and equipment power of 100 W. The treatment is interrupted and the sample is taken out at multiple preset time points (such as 0 min, 10 min, 30 min to several hours) to obtain test devices with different oxidation degrees.

[0041] Photoelectric performance characterization: The device was excited by light using a self-built optical path system and specific wavelength lasers (such as 520 nm, 532 nm, 640 nm, 1064 nm, etc.). The light / dark current and electrical output / transfer characteristic curves were acquired in real time using a Keithley 2634B test source meter.

[0042] AFM test: The sample is placed under the AFM (Brook Dimension Fastscan) probe and then scanned in semi-contact mode to obtain a surface topography image of the sample.

[0043] Raw materials used in the examples: MoTe2 thin films are prepared by mechanical exfoliation. The specific steps are as follows: First, a portion of the sample is adhered to the surface of the MoTe2 crystal with 3M tape. Then, the tapes are peeled off one by one. This process is repeated about ten times until the sample remaining on the tape turns gray. The MoTe2 thin film is then obtained. The thickness of the film can be determined by AFM testing.

[0044] PDMS dry transfer technology: Apply a tape containing MoTe2 to the surface of PDMS, let it stand for 1-2 hours, then peel off the tape, leaving the MoTe2 sample on the surface of polydimethylsiloxane (PDMS); then attach the treated silicon substrate to the surface of PDMS, let it stand for another 1-2 hours, then peel off the silicon substrate, and the MoTe2 sample has been transferred to the substrate surface.

[0045] The PDMS substrate used was prepared in-house. To prepare it, Dow Corning SYLGARD 184 silicone rubber and curing agent were mixed at a weight ratio of 10:1 and stirred until all the air bubbles disappeared. Then, the mixture was left to stand in a refrigerator at 4°C for 48 hours to solidify into a transparent film.

[0046] The electrodes are prepared by thermal evaporation, specifically including bismuth metal and gold metal prepared by thermal evaporation.

[0047] Example 1 A method for detecting surface oxidation of two-dimensional materials using differentiated electrode configurations includes the following steps: (1) Take a silicon substrate with a 285 nm thick SiO2 layer on the surface, and place it in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning for 5 minutes each. Then use a high-pressure nitrogen gun to dry it to obtain a clean substrate.

[0048] (2) Photoresist was spin-coated onto a silicon substrate and placed on a maskless lithography stage for exposure and development to reveal the bottom electrode and channel pattern (both electrode and channel widths were defined as 10 μm). The substrate was then placed in a mild plasma reaction chamber, and a mixture of SF6 / N2 (SF6: 15 sccm and N2: 7 sccm) was introduced to finely etch the exposed SiO2 region. The core parameters were set as follows: RF power 300 W, reflection power within 60 W, chamber pressure 30 Pa, etching time 1 minute 45 seconds, and a precise etching depth of 55 nm. Subsequently, a thermal evaporation machine was used to etch the substrate under a vacuum of 2 × 10⁻⁶. -3 Under ultra-high vacuum conditions below Pa, 5 nm of bismuth (Bi) metal and 50 nm of gold (Au) metal were sequentially deposited at a low deposition rate of 0.20~0.25 Å / s. After stripping the photoresist, an embedded bottom electrode with a thickness perfectly matching the SiO2 etching depth and a flush surface was obtained.

[0049] (3) Using dry transfer technology, a MoTe2 film with a thickness of about 20 nm was precisely transferred onto the embedded bottom electrode. Since the bottom electrode is embedded and coplanar, the MoTe2 film achieved perfect adhesion when crossing the electrode region and the channel region, avoiding mechanical deformation stress such as suspension and wrinkles. At the same time, it ensured the absolute fidelity of UVO processing only the MoTe2 surface and subsequent bulk parameter extraction.

[0050] (4) Fabrication of the top electrode and differentiated configuration: Photoresist was spin-coated again on the MoTe2 surface and aligned for exposure to expose the top electrode region. The widths of the top electrode, the top-top electrode channel, and the top-bottom electrode channel were all defined as 10 μm. The top electrode was deposited using the same thermal evaporation conditions (5 nm Bi / 50 nm Au) as in step (2) to obtain a semi-finished optoelectronic device. At this point, three differentiated transmission channels were successfully constructed on the same MoTe2 channel: bottom-bottom (extracting pure bulk signals), top-top (extracting surface and interface signals), and top-bottom (mixed signals).

[0051] (5) Dynamic oxidation decoupling detection: The optoelectronic device semi-finished product obtained in step (4) is placed in a UV ozone cleaner and oxidized at room temperature and pressure with a power of 100 W. The output current is tested at different processing times, and the dynamic evolution of the output current of different electrode structures is extracted in real time under a fixed bias voltage.

[0052] The fabrication steps of the optoelectronic device in Example 1 are as follows: Figure 2 As shown. Figure 3 Figures (a) and (b) show the output current of the bottom-bottom electrode structure 1 and the top-top electrode structure 3, as well as the ratio of the equivalent resistance of electrode structure 1 to electrode structure 3, as a function of processing time. From the figures, it can be seen that UVO oxidation can be divided into three stages, which are analyzed as follows: Stage 1 (Early Oxidation Stage): Because the bottom-bottom electrode structure initially forms an ohmic contact with extremely low contact resistance, it can directly convert UVO-induced p-type doping into a rapid increase in current. However, the top-top electrode structure is initially constrained by the strong Fermi pinning effect and the Schottky barrier, and the interface transport obstacles mask the gain brought by the doping. This can be quantified from the equivalent resistance ratio curve (e.g., ...). Figure 3 As shown in b), this stage is characterized by the resistance ratio R. 电极结构 1 / R 电极结构 3 <1, thus the surface oxidation is clearly identified as being in the initial stage 1 by the characteristic that the resistance ratio is less than 1.

[0053] Phase 2 (Interface Barrier Removal Period): As processing continues, the current growth rate of the top-top electrode structure surpasses that of the bottom-bottom electrode structure, reaching peak performance. During this phase, the MoOx interface layer formed on the channel surface and electrode edges achieves the transition from Schottky to ohmic contacts. Through the synergistic effect of interface optimization and bulk p-type doping, device performance is significantly improved; meanwhile, the current growth of the bottom-bottom electrode structure gradually plateaus due to the gradual saturation of bulk doping. Figure 3 On the resistance ratio curve of b, this stage is characterized by a sudden jump in the resistance ratio and a sustained value greater than 1 (R). 电极结构 1 / R 电极结构 3 >1), and at this point, the current in both channels is in the rising phase. As the current in the top-top electrode structure climbs to its highest peak, this is the optimal process node for the subsequent fabrication of high-performance optoelectronic devices.

[0054] Stage 3 (Deep Oxidation Blocking Period): As the processing time further increases, the amorphous MoOx layer on the surface and electrode edges continuously thickens and the oxidation degree deepens (x→3). The high-resistivity components lead to an increase in the equivalent resistance of the interface and channel, and the current in both configurations decreases. Because the top-to-top electrode structure is highly dependent on surface transport, it is more sensitive to the blockage of the high-resistivity oxide layer; therefore, the current decrease is much more drastic than that of the bottom-to-bottom electrode structure, which avoids the high-resistivity top layer. Figure 3 b, although the resistance ratio remains greater than 1 (R 电极结构 1 / R 电极结构 3 Within the range of >1), since both channels' currents show a clear downward / falling trend at this time, the negative correlation between current and time can accurately quantify and distinguish between stage 3 and stage 2.

[0055] Combination Figure 3 It can be seen that when the oxidation stage is in stage 2, i.e., the interface barrier removal period, the oxidation degree of the MoTe2 film is relatively sufficient, and the device performance is optimal at this time. The corresponding UVO treatment time can be used as the preferred time range, which is 50~180 min. This time range can be used as a reference when fabricating corresponding devices in the future. Figure 3 The effect of the curve is used to determine the UVO treatment time.

[0056] In contrast, if a conventional, non-differentiated top-bottom electrode contact structure (electrode structure 2) is used, the transport current is strongly coupled and modulated by the bulk resistance and interface resistance. During the oxidation process, whether the current rises or falls, single-channel data cannot qualitatively decouple whether the current is caused by bulk doping saturation or excessive surface oxidation. The current-time curve is as follows: Figure 4As shown. This confusion caused by the lack of independent reference comparison terms makes it impossible for conventional characterization structures to accurately capture and judge the three-stage characteristic nodes of self-confined growth evolution, thus proving the uniqueness and high accuracy of the proposed method based on the synergistic determination of differential resistance ratio and current evolution trend.

[0057] Example 2 The difference between Example 2 and Example 1 is that the thickness of the MoTe2 film in step (3) is adjusted to 10 nm.

[0058] Compared with Example 1 ( Figure 3 (ab) In comparison, this thin-layer sample also exhibits consistent quantitative characteristics in the early and middle stages of oxidation, and stage 1 and stage 2 can be clearly distinguished by whether the resistance ratio is greater than 1. However, it is worth noting that, as Figure 3 As shown in Figure d, as the processing time enters the deep oxidation stage (stage 3), the resistivity ratio of this thin-layer sample eventually exhibits a unique trend of converging towards 1. The physical mechanism lies in the fact that after prolonged high-dose UVO treatment, the inherent self-confined oxidation depth boundary of the ultrathin two-dimensional material exceeds the material's own spatial physical thickness, resulting in the complete oxidation and breakdown of the extremely thin MoTe2 channels, transforming them in situ into a homogeneous, amorphous, high-resistivity MoO2. x Layer. At this point, the physical difference between the bulk transport channel and the surface transport channel is completely eliminated, causing the equivalent resistance extracted by the differentiated electrode configuration to converge uniformly. This final state result, with a ratio approaching 1, not only does not weaken the effectiveness of the characterization model, but also strongly confirms from the reverse extreme state that the electrical detection method of this invention has extremely high and extremely sensitive quantitative tracking and resolution capabilities for the longitudinal self-confined saturation boundary, loss of thin film crystal integrity, and complete oxidation behavior of two-dimensional materials.

[0059] Based on the experimental data from Examples 1 and 2, it can be seen that when the thickness of the MoTe2 film is within a certain range, such as 10~50 nm, the output current of the bottom-bottom electrode structure 1 and the top-top electrode structure 3 exhibits essentially the same trend with UVO treatment time, differing only in the numerical value of the output current. Therefore, when fabricating corresponding devices, while ensuring that the thickness of the MoTe2 film is not significantly different from that in the examples, it is possible to refer to the examples. Figure 3 The UVO treatment time is used to prepare the corresponding devices.

[0060] Example 3 A method for fabricating a high-performance optoelectronic device includes the following steps: (1)~(3): The preparation steps are the same as in Example 1, except that the thickness of the MoTe2 film is 40nm.

[0061] (4) Place the device semi-finished product obtained in step (3) in a UV ozone cleaner and perform oxidation treatment at room temperature and pressure with a power of 100 W for 120 seconds. (5) After the treatment is completed, photoresist is spin-coated again on the oxidized MoTe2 surface and aligned for exposure to expose the top electrode area. The widths of the top electrode, the top-to-top electrode channel, and the top-to-bottom electrode channel are all defined as 10 μm. The top electrode is deposited using the same thermal evaporation conditions (5 nm Bi / 50 nm Au) as in step (2) to obtain the finished optoelectronic device.

[0062] The process for preparing the optoelectronic device in Example 3 is as follows: Figure 5 As shown. To further verify the accuracy of the UVO oxidation time determined by the methods in Examples 1 and 2, this example prepared optoelectronic devices corresponding to different UVO treatment times. The quantitative characteristic diagram of the evolution of photoresponsivity (R) and specific detectivity (D*) with UVO surface oxidation treatment time is shown in the figure. Figure 6 As shown. From Figure 6 It can be seen that the oxidation degree of MoTe2 film is optimal when the UVO treatment time is in the range of 50~180 min, and more preferably in the range of 80~140 min. Figure 3 The experimental results correspond to those of Examples 1 and 2, which shows that the methods in Examples 1 and 2 can accurately determine the degree of oxidation of MoTe2 thin films by UVO, and the results can provide guidance for subsequent devices.

[0063] Figure 7 (a) shows the transfer characteristic curves of the bottom-bottom electrode structure of the device in Example 3 after untreated and UVO surface oxidation treatment for 120 min. It can be clearly seen from this figure that the polarity of the device reversed after treatment, changing from N-type to P-type. Simultaneously, combined with... Figure 7 (b) It can be seen that UVO treatment generates an amorphous MoOx layer in situ on the surface, and the self-confined characteristics allow the undamaged MoTe2 in the bottom layer to retain its crystalline structure, thereby constructing a heterogeneous curved interface with an asymmetric resistive state distribution in the vertical direction.

[0064] Photoelectric response performance of optoelectronic devices: Figure 8 The ultrafast photoelectric response time (rise / fall time) test curves of the optoelectronic device prepared in Example 3 in self-driven mode are presented. The asymmetric interface band structure reconstructed based on the top-bottom electrode structure and the controlled process timing is described in [reference needed]. Figure 7 In the dark state without an applied bias voltage, due to the significant contact barrier at the Au electrode on the right side of the source terminal, the injection of reverse charge carriers is prevented. Electrons move directionally from right to left towards the Bi electrode at the drain terminal, resulting in a stable negative dark current (I0) output by the device. dark< 0); When excited by laser irradiation, a large number of photogenerated carriers are generated inside the device, triggering an efficient charge transport mechanism. Photogenerated holes successfully cross the interface barrier through tunneling and are injected into the left drain terminal. At the same time, photogenerated electrons flow along the conduction band of MoTe2 to the right towards the source Au electrode. This efficient spatial asymmetric separation and directional drift of photogenerated carriers allows the macroscopic output net current to instantly break free from the dark state limitation and turn from negative to positive (I ph >0). At a modulation frequency of 50 kHz, the measured rise / fall times of the photoelectric response reached extremely fast 0.8 μs / 2.5 μs, respectively.

[0065] Applications of multi-valued logic: Figure 9 Demonstration diagrams of balanced ternary (Base-3) logic encoding and dynamic character decoding implemented by the optoelectronic device prepared in Example 3 are provided. Relying on the unique asymmetric contact barrier and hole tunneling-dominated asymmetric directional transport mechanism, the device exhibits unique optoelectronic dual-control polarity reversal characteristics. In the dark state (negative drift current), small bias voltage (currents cancel each other out to zero), and illumination (positive photocurrent), this single device can serve as a photoelectric co-input terminal, outputting three independent level states, "-1", "0", and "1", with extremely stable and clear output. Based on this transport characteristic, this invention successfully demonstrated balanced ternary dynamic logic encoding and real-time character decoding for characters such as "J", "N", and "U", successfully verifying the device's potential application in the underlying architecture of next-generation low-power, integrated sensing and computing high-information-density chips.

[0066] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for detecting surface oxidation of two-dimensional materials using differentiated electrode configurations, characterized in that, The method involves first fabricating a stepless embedded bottom electrode on a SiO2 layer on a silicon substrate using plasma technology; then transferring a mechanically exfoliated MoTe2 film to the embedded bottom electrode surface using a dry transfer technique; fabricating a top electrode on the MoTe2 surface to form a differentiated contact structure; and finally oxidizing the MoTe2 surface using ultraviolet ozone (UVO) and detecting the degree of oxidation of the two-dimensional material by monitoring the changes in the transport current between the top-top electrode and the bottom-bottom electrode.

2. The method according to claim 1, characterized in that, The method for detecting surface oxidation of two-dimensional materials using differentiated electrode configurations includes the following steps: (1) On a silicon substrate with a SiO2 layer, the original SiO2 layer is processed by photolithography and plasma etching techniques, and then metal is deposited by thermal evaporation. After peeling, an embedded bottom electrode flush with the SiO2 surface is obtained. (2) The 2H phase MoTe2 film obtained by mechanical exfoliation is transferred to the substrate surface containing the embedded bottom electrode in step (1) using PDMS dry transfer technology to form a bottom-to-bottom contact structure; (3) Place the sample obtained in step (2) on a maskless photolithography stage and use photolithography and vapor deposition process to prepare the top electrode on the MoTe2 surface, thereby forming bottom-bottom, top-top and top-bottom contact structures on the same channel; (4) Use ultraviolet ozone (UVO) to oxidize the device with top electrode prepared in step (3). By comparing and analyzing the dynamic evolution of the output current under different contact structures in real time, the detection and analysis of the surface oxidation degree and self-confined depth are completed.

3. The method according to claim 2, characterized in that, The plasma etching technique described in step (1) is as follows: using a mixture of SF6 / N2 gas to etch the patterned SiO2 layer on the silicon substrate. The etching parameters are set as follows: radio frequency power of 250 ~ 350 W and reflection power of less than 80 W, the cavity pressure of the mild plasma reaction chamber is maintained at 20 ~ 40 Pa, and the reaction time is 1 ~ 3 minutes, so that the etching depth is precisely controlled at 40 ~ 60 nm. The flow rate of SF6 is 10 ~ 20 sccm and the flow rate of N2 is 5 ~ 15 sccm.

4. The method according to claim 2, characterized in that, The thickness of the MoTe2 film in step (2) is 10~50nm.

5. The method according to claim 2, characterized in that, The vapor deposition processes described in steps (1) and (3) both include hot vapor deposition of bismuth (Bi) metal and hot vapor deposition of gold (Au) metal; When preparing bismuth metal by thermal evaporation, the vacuum conditions of the evaporation machine must meet 2×10⁻⁶. -3 For bismuth electrode materials with a thickness of 2–10 nm, the plating rate used is 0.20–0.25 Å / s, the time is 2–8 minutes, and the thickness of the resulting bismuth electrode material is 2–10 nm. When preparing gold metal by thermal evaporation, the vacuum conditions of the evaporation machine must meet 2 × 10⁻⁶ Å / s. -3 For a Pa value below 0.20~0.25 Å / s, the plating rate is 0.20~0.25 Å / s, the time is about 20~50 minutes, and the thickness of the gold electrode material obtained is 40~60 nm.

6. The method according to claim 2, characterized in that, The ultraviolet ozone (UVO) treatment in step (4) is carried out using a UV ozone cleaning machine. The device is oxidized at room temperature and pressure with a power of 50 to 100 W.

7. A method for fabricating a high-performance optoelectronic device, characterized in that, Includes the following steps: S1. On a silicon substrate with a SiO2 layer, the original SiO2 layer is processed using photolithography and plasma etching techniques, followed by thermal evaporation to deposit metal. After peeling, an embedded bottom electrode flush with the SiO2 surface is obtained. The thickness of the SiO2 layer on the silicon substrate surface is 200 ~ 350 nm, the width of a single embedded bottom electrode is 2 ~ 20 μm, the configuration depth is 40 ~ 60 nm, and the spacing between adjacent bottom electrodes is 2 ~ 20 μm. S2. The 2H phase MoTe2 film obtained by mechanical exfoliation is transferred to the substrate surface containing the embedded bottom electrode in step (1) using PDMS dry transfer technology; the thickness of the MoTe2 film is 10 ~ 50 nm. S3. Perform UVO surface oxidation treatment on the MoTe2 thin film from step S2 to form MoO2 on its surface in situ. x Layers are formed, and p-type doping is induced, constructing upward-growing vertical MoO in the vertical direction. x / MoTe2 structure; the power of the equipment for UVO surface oxidation treatment is 50 ~ 100 W, and the treatment time is 50 ~ 160 minutes; S4. Place the sample after surface oxidation treatment in step S3 on a photolithography stage, use photolithography to etch the device structure and deposit the top electrode to obtain the optoelectronic device; the material of the top electrode is a composite layer of bottom metal bismuth (Bi) and top metal gold (Au), the thickness of the bottom metal bismuth is 2 ~ 10 nm, the thickness of the top metal gold is 40 ~ 60 nm, the width of a single top electrode is 2 ~ 20 μm, the total thickness of the electrode material is 40 ~ 80 nm, and the distance between the top electrode and the embedded bottom electrode in the channel direction is 2 ~ 20 μm.

8. The preparation method according to claim 7, characterized in that, The specific steps of step S4, which involve using photolithography to etch the device structure, are as follows: under a microscope, the electrode pattern is aligned on the oxidized MoTe2 surface, exposing the area where the electrode needs to be plated while blocking the channel area, retaining the width of the MoTe2 channel in the range of 2 to 20 μm, and then using photolithography to obtain the device pattern.

9. The high-performance optoelectronic device prepared by the preparation method according to claim 7 or 8, wherein the high-performance optoelectronic device comprises an asymmetric contact barrier and an asymmetric directional transport mechanism dominated by hole tunneling, and has the performance of unbiased ultrafast photoelectric response and balanced ternary logic encoding.

10. The high-performance optoelectronic device of claim 9 is applied in the fields of ternary logic computing and information processing, integrated sensing and computing and edge computing, optical communication and encrypted communication, and low-power high-performance chips.

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