Application of a dual photo-activation layer based ultra-sensitive phototransistor

Abstract

The application discloses a kind of based on double light activation layer's super-sensitivity phototransistor.The phototransistor described in the application is sequentially composed of gate electrode (Si), dielectric layer (HfO2), photoactive ion layer (PbI2), channel (WSe2) and source-drain electrode (Au) from bottom to top.The phototransistor described in the application exhibits extremely high sensitivity advantage: on the one hand, it meets the test demand in extremely weak light environment, and the dark field light intensity detected by it is lower than that of commercial phototransistor by 4 orders of magnitude;On the other hand, its responsivity is higher than that of commercial product by 4 orders of magnitude.PbI2, a photoactive ion layer, is introduced into the traditional phototransistor structure based on traditional two-dimensional material for the first time, which greatly improves the sensitivity of the device and provides a new idea for the development of extremely dark field detection technology.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photoelectric sensing and detection technology, and innovatively proposes an application of a super-sensitive phototransistor based on a double photoactive layer. BACKGROUND

[0002] A phototransistor is a core device in modern photoelectric technology, which can efficiently convert optical signals into electrical signals. It is widely used in optical communication, optical computing, medical treatment, security and protection, aerospace, environmental monitoring and other fields. With the continuous progress of science and technology, phototransistors play an irreplaceable role in realizing accurate detection and efficient transmission of optical signals, and are one of the key factors to promote the development of optical technology.

[0003] In many application scenarios, there is an increasing demand for high-sensitivity photoelectric detection. For example, in the fields of remote sensing and biological imaging, due to the long distance or low irradiation power, the number of signal photons reaching the detection surface is extremely small, and the signal-to-noise ratio is extremely low, which brings great challenges to optical system design, signal detection and image recovery. A high-sensitivity phototransistor can effectively capture extremely weak optical signals, thereby realizing high-quality imaging and signal detection under extremely low signal-to-noise ratio conditions. In addition, a high-response-speed phototransistor is also crucial, which can quickly respond to changes in optical signals to meet the needs of high-speed imaging and real-time monitoring.

[0004] However, the current photoelectric detection technology still has deficiencies in extremely weak light detection. On the one hand, the sensitivity of existing transistors cannot meet the needs of accurate detection of trace substances, and detection sensitivity has become a bottleneck in the field of mid-infrared systems. On the other hand, the balance between high sensitivity and high response speed is also a problem to be solved. SUMMARY

[0005] The application discloses an application of a super-sensitive phototransistor based on a double photoactive layer. The application utilizes the ion photosensitive effect of a two-dimensional PbI2 / WSe2 heterojunction to break through the high-sensitivity light sensing performance of the phototransistor. The phototransistor has a simple preparation method and low cost. The transistor can work normally in an extremely weak light environment, has extremely high sensitivity, and can meet the stringent environmental test requirements that are 4 orders of magnitude lower than the current lowest light level. It meets the detection application in an extremely dark field environment of 0.05 nW (1.25 μW / cm 2 ), which is 4 orders of magnitude lower than the light intensity of a commercial phototransistor. In the dark field detection environment, it still shows a high response of 10 11 (A / W), which is 4 orders of magnitude higher than that of a commercial phototransistor.

[0006] To solve the technical problem of this invention, the proposed technical solution is as follows: an application of an ultrasensitive phototransistor based on a dual photoactivation layer, wherein the device structure of the ultrasensitive phototransistor with the dual photoactivation layer, from bottom to top, consists of a gate electrode Si, a dielectric layer HfO2, a photoactivated ion layer PbI2, a channel WSe2, and source / drain electrodes Au; the phototransistor is used in image monitoring and bioimaging fields; the fabrication steps of the phototransistor are as follows:

[0007] Step 1: Cleaning HfO2 / Si substrate: The HfO2 / Si substrate was ultrasonically cleaned in an ultrasonic cleaner using acetone, isopropanol and anhydrous ethanol in sequence, and then dried with high-purity nitrogen gas for later use.

[0008] Step 2: Preparation of PbI2 by thermal evaporation: PbI2 powder is placed in a clean source boat and PbI2 is prepared by thermal evaporation.

[0009] Step 3: Fabrication of WSe2 / PbI2 heterojunction: Under nitrogen atmosphere, two-dimensional WSe2 nanosheets are transferred to the surface of two-dimensional PbI2 nanosheets using van der Waals integration process to ensure that the interface between the two materials is clean and in close contact.

[0010] Step 4: Fabrication of source and drain electrodes: Using the EBL method, metal electrodes Au are fabricated on the surface of WSe2 material by thermal evaporation deposition process;

[0011] Preferably, PbI2 material, as a photoactivator layer, can efficiently capture photons in a low-light environment and significantly reduce dark current by enhancing the separation efficiency of photogenerated electron-hole pairs, thereby improving the signal-to-noise ratio of the transistor; while WSe2 material, with its excellent carrier mobility and high light absorption coefficient, further amplifies the photoelectric signal, enabling the entire device to maintain stable photoelectric conversion performance under extremely low light conditions.

[0012] Preferably, the transistor satisfies 0.05 nW 1.25 μW / cm². 2 This technology enables detection applications in extremely dark environments. The light intensity in this dark environment is four orders of magnitude lower than that of commercial phototransistors.

[0013] Preferably, it still exhibits 10 in dark field detection environments. 11 The A / W phototransistor exhibits high responsivity, exceeding that of commercial phototransistors by four orders of magnitude. It also possesses extremely high detection sensitivity.

[0014] Preferably, the phototransistor, due to its ultra-sensitive photoelectric response, can be used for monitoring extremely weak light images. The optical power density of the extremely weak light is in the range of 10. -9 W / cm² up to 10 -6 Between W / cm².

[0015] Preferably, the thicknesses of the dielectric layer HfO2, the photoactivated ion layer PbI2, the channel WSe2, and the source / drain electrodes Au are 8-10 nm, 1-5 nm, 0.7-3.5 nm, and 60-80 nm, respectively.

[0016] Preferably, the phototransistor fabrication steps are as follows:

[0017] Step 1: Cleaning the HfO2 / Si substrate: Clean the HfO2 / Si substrate by ultrasonication for 10 minutes each with acetone, isopropanol and anhydrous ethanol in an ultrasonic machine, and then dry it with high-purity nitrogen gas for later use.

[0018] Step 2: Preparation of PbI2 by thermal evaporation: Place PbI2 powder in a clean source boat, and control the temperature inside the boat at 150℃ and the pressure at 10. -5 -10 -6 PbI2 was prepared by thermal evaporation under a low-pressure environment of Pa.

[0019] Step 3: Fabrication of WSe2 / PbI2 heterojunction: Under nitrogen atmosphere, two-dimensional WSe2 nanosheets are transferred to the surface of two-dimensional PbI2 nanosheets using van der Waals integration process to ensure that the interface between the two materials is clean and in close contact.

[0020] Step 4: Fabrication of source and drain electrodes: Using the EBL method and Auto CVD software, an electrode pattern with a reasonable structure and size is designed on the surface of WSe2 material, and a metal electrode Au is prepared by thermal evaporation coating process.

[0021] Preferably, the preparation steps of the WSe2 / PbI2 heterojunction are as follows:

[0022] Step 1: Preparation of WSe2 nanosheets: Mechanically exfoliated WSe2 is directly exfoliated onto PDMS to obtain WSe2 / PDMS;

[0023] Step 2: Transfer WSe2: Under the microscope, align the target WSe2 with the target PbI2 and keep them in contact at 90°C for 2-3 minutes;

[0024] Step 3: Obtaining the WSe2 / PbI2 heterojunction: Lifting the heat-release tape allows WSe2 to fall onto the PbI2 film, completing the preparation of the heterojunction.

[0025] Preferably, the steps for using a surface Au electrode are as follows:

[0026] Step 1: Spin-coat photoresist PMMA-A4 and PMMA-A5 sequentially on the surface of a substrate with WSe2 / PbI2 heterojunction, and bake them on a hot plate at 180°C for 100 s respectively;

[0027] Step 2: Locate the area around the sample in the scanning electron microscope and delineate alignment marks. Develop the exposed alignment marks and record them with a microscope to locate the sample and delineate the pattern.

[0028] Step 3: Align the markers and expose the sample;

[0029] Step 4: After development, dry with a nitrogen gun and deposit Au electrodes by thermal evaporation.

[0030] Beneficial effects

[0031] This invention proposes an ultrasensitive phototransistor based on a dual photoactivation layer, which is simple and inexpensive to fabricate, requiring only simple methods such as chemical synthesis and mechanical exfoliation to obtain the PbI2 / WSe2 heterojunction. This invention achieves highly sensitive photodetection by constructing a high-sensitivity phototransistor based on a two-dimensional metal halide heterojunction and utilizing the ionic activity of PbI2.

[0032] This invention utilizes PbI2 material as a photoactivator layer, which can efficiently capture photons in low-light environments and significantly reduce dark current by enhancing the separation efficiency of photogenerated electron-hole pairs, thereby improving the signal-to-noise ratio of the transistor. Meanwhile, WSe2 material, with its excellent carrier mobility and high light absorption coefficient, further amplifies the photoelectric signal, enabling the entire device to maintain stable photoelectric conversion performance under extremely low illumination conditions, achieving highly sensitive photoelectric detection. This provides a new method for achieving highly sensitive photoelectric detection and is expected to promote the application of phototransistors in more fields.

[0033] 1. Highly sensitive response performance

[0034] This invention achieves a breakthrough in ultrasensitive response performance of phototransistors by introducing an ionic photoactivator layer of PbI2 material and the high optical activity of WSe2. Experiments show that the detection threshold of this heterostructure is reduced by four orders of magnitude, reaching a level of <0.05 nW, while the photoresponsivity is improved to 10 compared to pure WSe2 devices. 11 A / W, far exceeding the performance of commercial phototransistors.

[0035] 2. The manufacturing process is simple and inexpensive.

[0036] This invention prepares PbI2 nanosheets via thermal evaporation, resulting in nanosheets with regular shapes, high yield, and low cost. Two-dimensional WSe2 nanosheets are prepared via mechanical exfoliation, a simple and easy method. Dry transfer precisely constructs heterojunctions, ensuring reproducibility and mass production feasibility. Compared to existing phototransistors that rely on complex processes, this invention offers a simpler and cheaper process, possessing high practicality and widespread applicability.

[0037] 3. Highly sensitive photoelectric response

[0038] like Figure 2 , Figure 3 As shown, the transistor's responsivity was tested for different light intensities at wavelengths of 405 nm and 520 nm. It was found that even at 405 nm with a light intensity of 1.25 nW / cm², the transistor still exhibited good responsivity. 2 The device still produced a response curve; it was found that even at a light intensity of 3.75 nW / cm² at 520 nm. 2 The device still generates a response curve; the optical power density range of the extremely weak light is typically in the range of 10. -9 W / cm² up to 10 -6 The W / cm² value indicates that the device still meets testing requirements in extremely low light environments, significantly improving its sensitivity and providing new insights for the development of ultra-dark field detection technology.

[0039] 4. Highly sensitive mechanism

[0040] As attached Figure 5 As shown, the ultrasensitive response of this invention mainly originates from the ionic activity of PbI2. As a photoactivator layer, PbI2 material can efficiently capture photons in low-light environments and significantly reduce dark current by enhancing the separation efficiency of photogenerated electron-hole pairs, thereby improving the signal-to-noise ratio of the transistor. Meanwhile, WSe2 material, with its excellent carrier mobility and high light absorption coefficient, further amplifies the photoelectric signal, enabling the entire device to maintain stable photoelectric conversion performance even under extremely low light conditions. Attached Figure Description

[0041] Figure 1 Device structure diagram of a two-dimensional PbI2 / WSe2 heterojunction phototransistor

[0042] Figure 2 Photoelectric-variable power transfer curves of WSe2 / PbI2 at a wavelength of 405nm

[0043] Figure 3 Photoelectric-variable power transfer curves of WSe2 / PbI2 at a wavelength of 520nm

[0044] Figure 4 Optical power density of pure WSe2 and PbI2 / WSe2 heterojunction (μW / cm²) 2 Comparison chart of the relationship between photoelectric responsivity (A / W) and photoelectric responsivity (A / W)

[0045] Figure 5 Electron transition mechanism in PbI2 / WSe2 heterojunction Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments. The described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment proposes an ultrasensitive phototransistor based on a dual-photoactivation layer and its fabrication method. It can operate normally in extremely low light environments and exhibits extremely high sensitivity, meeting stringent environmental testing requirements that are four orders of magnitude lower than the lowest light levels currently available in commercially available light sources. The specific fabrication steps are as follows:

[0049] Step 1: Cleaning the HfO2 / Si substrate (Suzhou Crystal Silicon Electronics Technology): Clean the HfO2 / Si substrate by ultrasonication for 10 minutes each with acetone, isopropanol and anhydrous ethanol in an ultrasonic machine, and then dry it with high-purity nitrogen gas for later use.

[0050] Step 2: Preparation of PbI2 by thermal evaporation: Place PbI2 powder in a clean source boat, and control the temperature inside the boat at 150℃ and the pressure at 10. -5 -10 -6 PbI2 was prepared by thermal evaporation under a low-pressure environment of Pa.

[0051] Step 3: Preparation of WSe2 / PbI2 heterojunction:

[0052] WSe2 nanosheets were prepared under nitrogen atmosphere: mechanically exfoliated WSe2 was directly exfoliated onto PDMS (WSe2 crystals were provided by Shanghai Angwei Technology) to obtain WSe2 / PDMS.

[0053] Then transfer WSe2, and under the microscope, align the target WSe2 with the target PbI2, keeping them in contact at 90°C for 2-3 minutes.

[0054] Finally, the heat-release tape is lifted to allow WSe2 to fall onto the PbI2 film, completing the preparation of the heterojunction.

[0055] Step 4: Spin-coat photoresist PMMA-A4 and PMMA-A5 sequentially onto the substrate surface with the WSe2 / PbI2 heterojunction, and bake them on a hot plate at 180°C for 90 seconds respectively; locate the area around the sample in a scanning electron microscope and scribing alignment marks. Develop the exposed alignment marks and record the image with a microscope to position the sample and scribing the pattern; perform mark alignment and sample exposure; after development, dry with a nitrogen gun; design a reasonably structured and sized electrode pattern on the surface of the WSe2 / PbI2 heterojunction using the EBL method combined with Auto CVD software, and deposit a metal electrode (Au) on the surface of the heterojunction using a thermal evaporation deposition process; control the thickness of the Au electrode to be 60-80 nm.

[0056] The PbI2 / WSe2 heterojunction phototransistor prepared through the above experimental steps has a three-terminal transistor structure, such as... Figure 1 As shown, from bottom to top, the layers are: gate electrode (Si), dielectric layer (HfO2) with a thickness of 8-10 nm, photoactivated ion layer (PbI2) with a thickness of 1-5 nm, channel (WSe2) with a thickness of 0.7-3.5 nm, and source / drain electrode (Au) with a thickness of 60-80 nm.

[0057] like Figure 2 As shown, the I of the device under illumination at a wavelength of 450 nm... ds -V g To test the relationship, the specific steps are as follows:

[0058] Step 1, Device testing preparation: Perform pre-treatment such as anti-static treatment and surface cleaning on the measurement sample.

[0059] Step 2, Device Performance Evaluation: The equipment used is Keithley's 2612B series source meter and Blue Ocean Scientific's low-temperature probe station. Kickstart program control is used to conduct comprehensive testing of the device and determine the test environment such as voltage and light intensity.

[0060] Step 3, Device Performance Measurement: When setting measurement parameters, the main factors to consider include vacuum conditions, ambient temperature, voltage, current range, and light wavelength and power. This experiment sets the device performance testing conditions as follows: under conditions of 405nm wavelength light, fixed gate voltage of ±6V, bias voltage of 1V, and vacuum, the power density of the light wave is adjusted to test the device's photoelectric response. Specifically, under 405nm wavelength light, the light power density used is 1.25 nW / cm². 2 3.75nw / cm 2 37.5nw / cm 2 375nw / cm 2 3.75 μw / cm 2.

[0061] like Figure 2 As shown, the test results revealed that even at a light wavelength of 405nm, with a light power density of 1.25nW / cm², 2 Even extremely weak light still exhibits a photoelectric response. The optical power density of such extremely weak light typically ranges from 10... -9 W / cm² up to 10 -6 The efficiency is between W / cm². This demonstrates that the device still meets testing requirements in extremely low light environments, significantly improving its sensitivity and providing new insights for the development of ultra-dark field detection technology.

[0062] Example 2

[0063] This embodiment proposes an ultrasensitive phototransistor based on a dual photoactivation layer and its fabrication method. Its device structure and fabrication process are the same as in Embodiment 1, except that: Figure 3 As shown, the device was tested using light with a wavelength of 520nm, where the optical power density of the 520nm light wave is as follows. Figure 3 The figure shows a value of 3.75 nw / cm. 2 37.5nw / cm 2 375nw / cm 2 3.75 μw / cm 2 37.5 μw / cm 2 .

[0064] like Figure 3 As shown, the test results revealed that even at a light wavelength of 520nm, with a light power density of 3.75nW / cm², 2 Even extremely weak light still exhibits a photoelectric response. The optical power density of such extremely weak light typically ranges from 10... -9 W / cm² up to 10 -6 The W / cm² value indicates that the device still meets testing requirements in extremely low light environments, significantly improving its sensitivity and providing new insights for the development of ultra-dark field detection technology.

[0065] Comparative Example 1

[0066] The fabrication process for the commercial device in this embodiment is the same as in Embodiment 1. The only difference is that PbI2 does not need to be thermally deposited when fabricating the commercial device. Instead, WSe2 can be transferred onto the HfO2 / Si substrate.

[0067] Then the R(A / W)-Power Density (μW / cm²) of the two devices was analyzed. 2 Test the relationship, such as Figure 4The device shown is based on the PbI2 / WSe2 heterojunction and its power density (μW / cm²). 2 The value is 0.00125 μW / cm. 2 0.00375μW / cm 2 0.0375μW / cm 2 0.375μW / cm 2 3.75 μW / cm 2 The photoelectric response R(A / W) of the device was measured and the R(A / W) - Power Density (μW / cm²) plotted was generated. 2 The relationship fitting curve was used; simultaneously, the power density (μW / cm²) of pure WSe2 devices was compared. 2 ) is 5μW / cm 2 12.5 μW / cm 2 25μW / cm 2 125μW / cm 2 250μW / cm 2 1250μW / cm 2 The photoelectric response R(A / W) of the device was measured and the R(A / W) - Power Density (μW / cm²) plotted was generated. 2 () Relationship fitting curve.

[0068] Test results are as follows Figure 4 As shown, analysis revealed that devices with PbI2 / WSe2 heterojunctions exhibit higher photoelectric response sensitivity than pure WSe2 devices, meeting stringent environmental testing requirements four orders of magnitude lower than the lowest current commercial illumination levels. Even in dark-field detection environments, they still demonstrate a sensitivity of 10... 11 The A / W phototransistor exhibits high responsivity, exceeding that of commercial phototransistors by four orders of magnitude. It also possesses extremely high detection sensitivity.

[0069] This invention is not limited to the specific technical solutions described in the above embodiments. Any modification or equivalent substitution of this invention to achieve the same technical effect is within the scope of protection of this invention.

Claims

1. Application of a dual photo-activated layer based ultra-sensitive phototransistor, characterized in that: the device structure of the dual photo-activated layer based ultra-sensitive phototransistor is gate electrode Si, dielectric layer HfO2, photo-activated ion layer PbI2, channel WSe2 and source-drain electrode Au from bottom to top; the phototransistor is used for image monitoring and biological imaging; the preparation steps of the phototransistor are as follows: Step 1: cleaning HfO2 / Si substrate: clean the HfO2 / Si substrate in an ultrasonic machine with acetone, isopropanol and anhydrous ethanol for 10 minutes respectively, and then blow dry with high-purity nitrogen for standby; Step 2: Preparation of PbI2 by thermal evaporation method: Put PbI2 powder in a clean source boat, control the temperature in the boat to be 150°C, and the pressure to be 10 -5 -10 -6 Prepare PbI2 by thermal evaporation method in a low-pressure environment of 10 Pa Step 3: preparation of WSe2 / PbI2 heterojunction: prepare WSe2 nanosheet in a nitrogen environment: directly exfoliate the mechanically exfoliated WSe2 onto PDMS to obtain WSe2 / PDMS; Then transfer WSe2, under the microscope field of view, align the target WSe2 to the target PbI2, and keep it at 90°C for 2-3 minutes; Finally, lift the heat release tape to make WSe2 fall on the PbI2 film, and complete the preparation of the heterojunction; Step 4: the substrate surface with WSe2 / PbI2 heterojunction is spin-coated with photoresist PMMA-A4 and PMMA-A5 in turn, and is baked at 180°C hot plate for 90s respectively; find the sample surrounding area in the scanning electron microscope and draw the alignment mark; develop the exposed alignment mark and take a photo record with a microscope, position the sample and draw the pattern; align the mark and expose the sample; After development, dry with nitrogen gun, design a structure and size reasonable electrode pattern on the surface of WSe2 / PbI2 heterojunction by EBL method combined with Auto CVD software, and deposit metal electrode Au on the surface of the heterojunction by thermal evaporation film process; and control the thickness of Au electrode to be 60-80 nm; The device structure of the PbI2 / WSe2 heterojunction phototransistor prepared by the above preparation steps is a three-terminal transistor, in which the thickness of the dielectric layer (HfO2) is 8-10 nm, the thickness of the photo-activated ion layer (PbI2) is 1-5 nm, the thickness of the channel (WSe2) is 0.7-3.5 nm, and the thickness of the source-drain electrode (Au) is 60-80 nm; The PbI2 material as a photo-activated layer can efficiently capture photons in a weak light environment, and greatly reduce the dark current by enhancing the separation efficiency of photo-generated electron-hole pairs, thereby improving the signal-to-noise ratio of the transistor; and the WSe2 material further amplifies the photoelectric signal with its excellent carrier mobility and high light absorption coefficient, so that the whole device can still maintain stable photoelectric conversion performance under extremely low light conditions; The phototransistor can be used for extremely weak light image monitoring and biological imaging under extremely weak light conditions with an incident light power density of 10 -9 -10 -6 W / cm², wherein the minimum working light power density can reach 1.25×10 -9 W / cm² under a 405 nm wave band, and the maximum photoelectric responsivity can reach 10 11 A / W.

Images