Application of ultra-sensitive phototransistor based on double photoactivation layers

Abstract

The invention discloses an ultra-sensitive phototransistor based on double photoactivation layers. The photoelectric transistor is composed of a gate electrode (Si), a dielectric layer (HfO2), a light activation ion layer (PbI2), a channel (WSe2) and a source drain electrode (Au) in sequence from bottom to top. The phototransistor shows the advantage of extremely high sensitivity: on one hand, the phototransistor meets the test requirement in an extremely weak light environment, and the light intensity of a dark field detected by the phototransistor is 4 orders of magnitude lower than that of a commercial phototransistor; and on the other hand, the responsivity is four orders of magnitude higher than that of a commercial product. According to the invention, the photoactive ion layer PbI2 is introduced into a traditional photoelectric transistor structure based on a traditional two-dimensional material for the first time, the sensitivity of the device is greatly improved, and a new idea is provided for the development of an extremely dark field detection technology.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric sensing and detection, and innovatively proposes an application of an ultra-sensitive phototransistor based on a double photoactive layer. Background Art

[0002] Phototransistors are core devices of modern optoelectronic technology, which can efficiently convert optical signals into electrical signals. They are widely used in optical communications, optical computing, medical treatment, security, aerospace, environmental monitoring and other fields. With the continuous advancement of science and technology, phototransistors play an irreplaceable role in realizing the accurate detection and efficient transmission of optical signals, and are one of the key factors in promoting the development of optical technology.

[0003] In many application scenarios, the demand for high-sensitivity photoelectric detection is increasing. For example, in the fields of remote sensing and biological imaging, due to the long action 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 poses great challenges to optical system design, signal detection and image recovery. Highly sensitive phototransistors can effectively capture extremely weak light signals, thereby achieving high-quality imaging and signal detection under extremely low signal-to-noise ratio conditions. In addition, phototransistors with high response speeds are also crucial. They can quickly respond to changes in light signals to meet the needs of high-speed imaging and real-time monitoring.

[0004] However, current photoelectric detection technology still has shortcomings in detecting extremely weak light. On the one hand, the sensitivity of existing transistors is difficult to meet the needs of accurate detection of trace substances, and detection sensitivity has become a bottleneck in fields such as mid-infrared systems. On the other hand, the balance between high sensitivity and high response speed is also an issue that needs to be solved urgently. Summary of the invention

[0005] The present invention discloses an application of an ultra-sensitive phototransistor based on a double photoactive layer. The present invention utilizes the photosensitivity effect of ions in a two-dimensional PbI2 / WSe2 heterojunction to achieve a breakthrough in the highly sensitive photosensitivity of the phototransistor. The preparation method of the phototransistor is simple and the cost is low. The transistor can work normally in an extremely weak light environment, and its sensitivity is extremely high, which can meet the harsh environment test requirements that are 4 orders of magnitude lower than the current commercial minimum light level. It meets the requirements of 0.05 nW (1.25 μW / cm 2 ) in an extremely dark field environment, where the dark field light intensity is 4 orders of magnitude lower than that of commercial phototransistors. 11 The high responsivity (A / W) is 4 orders of magnitude higher than that of commercial phototransistors.

[0006] In order to solve the technical problem of the present invention, the technical solution is proposed as follows: an application of an ultra-sensitive phototransistor based on a double photoactive layer, wherein the device structure of the ultra-sensitive phototransistor with a double photoactive layer is, from bottom to top, a gate electrode Si, a dielectric layer HfO2, a photoactive ion layer PbI2, a channel WSe2 and a source-drain electrode Au; the phototransistor is used in the field of image monitoring and biological imaging; the preparation steps of the phototransistor are as follows:

[0007] Step 1: Cleaning the HfO2 / Si substrate: Use acetone, isopropanol and anhydrous ethanol to ultrasonically clean the HfO2 / Si substrate in an ultrasonic machine, and then blow dry with high-purity nitrogen for later use;

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

[0009] Step 3: Preparation of WSe2 / PbI2 heterojunction: In a nitrogen environment, the two-dimensional WSe2 nanosheets are transferred to the surface of the two-dimensional PbI2 nanosheets through the van der Waals integration process to ensure that the interface of the two layers of materials is clean and in close contact;

[0010] Step 4: Prepare source and drain electrodes: Prepare metal electrode Au on the surface of WSe2 material by thermal evaporation coating process through EBL method;

[0011] Preferably, PbI2 material is used as the photoactive layer, which can efficiently capture photons in a weak light environment and significantly reduce the 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, so that the entire device can still maintain stable photoelectric conversion performance under extremely low light conditions.

[0012] Preferably, the transistor meets the requirements of 0.05 nW 1.25 μW / cm 2 The dark field light intensity is 4 orders of magnitude lower than that of commercial phototransistors.

[0013] Preferably, in a dark field detection environment, it still shows 10 11 The high responsivity of A / W is 4 orders of magnitude higher than that of commercial phototransistors. The phototransistor has extremely high detection sensitivity.

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

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

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

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

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

[0019] Step 3: Preparation of WSe2 / PbI2 heterojunction: In a nitrogen environment, the two-dimensional WSe2 nanosheets are transferred to the surface of the two-dimensional PbI2 nanosheets through the van der Waals integration process to ensure that the interface of the two layers of materials is clean and in close contact;

[0020] Step 4: Prepare source and drain electrodes: Use the EBL method combined with Auto CVD software to design an electrode pattern with a reasonable structure and size on the surface of the WSe2 material, and prepare the metal electrode Au through a 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: Align the target WSe2 to the target PbI2 under the microscope field of view and keep it in contact at 90°C for 2-3 minutes;

[0024] Step 3: Obtain WSe2 / PbI2 heterojunction: Lift the thermal release tape to allow WSe2 to fall on the PbI2 film to complete the preparation of the heterojunction.

[0025] Preferably, the steps of the surface Au electrode are as follows:

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

[0027] Step 2: Find the area around the sample in the SEM and draw the alignment marks, develop the exposed alignment marks, and take photos with a microscope to record, locate the sample and draw the pattern;

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

[0029] Step 4: After development, blow dry with a nitrogen gun and evaporate the Au electrode by thermal evaporation.

[0030] Beneficial Effects

[0031] The present invention proposes an ultra-sensitive phototransistor based on a double photoactive layer, which is simple to prepare and inexpensive, and can prepare a PbI2 / WSe2 heterojunction by simple methods such as chemical synthesis and mechanical stripping. The present invention achieves highly sensitive photodetection by constructing a highly sensitive phototransistor based on a two-dimensional metal halide heterojunction and utilizing the ionic activity of PbI2.

[0032] The present invention uses PbI2 material as a photoactive layer, which can efficiently capture photons in a weak 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. The WSe2 material, with its excellent carrier mobility and high light absorption coefficient, further amplifies the photoelectric signal, allowing the entire device to maintain stable photoelectric conversion performance under extremely low light conditions, and can achieve high-sensitivity photoelectric detection. It provides a new method for achieving highly sensitive photoelectric detection, which is expected to promote the application of phototransistors in more fields.

[0033] 1. Highly sensitive response performance

[0034] The present invention achieves a breakthrough in the performance of ultra-sensitive response of phototransistors by introducing an ionic photoactive layer of PbI2 material and the high optical activity of WSe2. Experiments show that the detection threshold of the heterostructure is reduced by 4 orders of magnitude to a level of <0.05 nW, and the photoresponsivity of the device is improved to 10 compared with pure WSe2. 11 A / W, far exceeding the performance of commercial phototransistors.

[0035] 2. Simple and cheap manufacturing process

[0036] The present invention prepares PbI2 nanosheets by thermal evaporation, and the formed nanosheets have regular shapes, high yields, and low costs. The two-dimensional WSe2 nanosheets are prepared by mechanical exfoliation, and the method is simple and easy. Dry transfer accurately constructs heterojunctions, ensuring the repeatability of device preparation and the possibility of mass production. Compared with the phototransistors prepared by complex processes in the prior art, the process of the present invention is simpler and cheaper, and has higher practicality and promotion value.

[0037] 3. Highly sensitive photoelectric response

[0038] like Figure 2 , Figure 3 As shown in the figure, the transistor was tested for its responsiveness to different light intensities at 405nm and 520nm wavelengths. It was found that even at 405nm, the light intensity was 1.25nw / cm 2 The device still has a response curve; it is found that at 520nm, even if the light intensity is 3.75nw / cm 2 The device still has a response curve; the optical power density range of the extremely weak light is usually 10 -9 W / cm² to 10 -6 W / cm². This shows that the device still meets the test requirements in extremely weak light environments, greatly improving the sensitivity of the device and providing new ideas for the development of extremely dark field detection technology.

[0039] 4. Highly sensitive mechanism

[0040] As attached Figure 5 As shown in the figure, the ultra-sensitive response of the present invention mainly comes from the ionic activity of PbI2. As a photoactive layer, PbI2 material can efficiently capture photons in a weak 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. The WSe2 material, with its excellent carrier mobility and high light absorption coefficient, further amplifies the photoelectric signal, allowing the entire device to maintain stable photoelectric conversion performance under extremely low light conditions. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0042] Figure 2 :WSe2 / PbI2 photoelectric-variable power transfer curve at wavelength of 405nm

[0043] Figure 3 :WSe2 / PbI2 photoelectric-variable power transfer curve at wavelength of 520nm

[0044] Figure 4 :Light power density of pure WSe2 and PbI2 / WSe2 heterojunction (μW / cm 2 ) and photoelectric responsivity (A / W)

[0045] Figure 5 :Electron transition mechanism in PbI2 / WSe2 heterojunction DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the embodiments of the invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment proposes an ultra-sensitive phototransistor based on a double photoactive layer and a preparation method thereof, which can work normally in an extremely weak light environment, has extremely high sensitivity, and can meet the harsh environment test requirements that are 4 orders of magnitude lower than the current commercial minimum light level. The specific preparation steps are as follows:

[0049] Step 1: Cleaning the HfO2 / Si substrate (Suzhou Jingsi Electronic Technology): Use acetone, isopropanol and anhydrous ethanol to clean the HfO2 / Si substrate in an ultrasonic machine for 10 minutes each, and then blow dry with high-purity nitrogen for later use.

[0050] Step 2: Preparation of PbI2 by thermal evaporation: Place PbI2 powder in a clean source boat, control the temperature in the boat to 150°C and the pressure to 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 a nitrogen environment: the mechanically exfoliated WSe2 was directly exfoliated onto PDMS (WSe2 crystals were provided by Shanghai Angwei Technology) to obtain WSe2 / PDMS.

[0053] Then transfer WSe2, align the target WSe2 with the target PbI2 under the microscope field of view, and keep the fit at 90°C for 2~3 minutes.

[0054] Finally, lift the thermal release tape to allow WSe2 to fall onto the PbI2 film, completing the preparation of the heterojunction.

[0055] Step 4: The surface of the substrate with the WSe2 / PbI2 heterojunction is spin-coated with photoresists PMMA-A4 and PMMA-A5 in sequence, and baked on a hot plate at 180°C for 90s respectively; find the area around the sample in the scanning electron microscope and draw alignment marks. Develop the exposed alignment marks, take photos and record them with a microscope, locate the sample and draw the pattern; align the marks and expose the sample; blow dry with a nitrogen gun after development, design the structure and the electrode pattern with reasonable size on the surface of the WSe2 / PbI2 heterojunction by the EBL method and combined with the Auto CVD software, and deposit the metal electrode (Au) on the surface of the heterojunction by thermal evaporation coating process; and control the thickness of the Au electrode to 60-80nm.

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

[0057] like Figure 2 As shown, the I ds -V g The relationship is tested, the specific steps are as follows:

[0058] Step 1, device test preparation: perform anti-static treatment and surface cleaning on the measurement samples in advance.

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

[0060] Step 3, device performance measurement: When setting the measurement parameters, the factors that need to be considered are mainly vacuum conditions, ambient temperature, voltage, current range, light wavelength and power, etc. The conditions for the device performance test in this experiment are set as follows: under the conditions of light with a wavelength of 405nm, a fixed gate voltage of ±6V, a bias voltage of 1V and vacuum, the power density of the light wave is adjusted to test the photoelectric response of the device. Under the conditions of light with a wavelength of 405nm, the light power density used is 1.25nw / cm 2 、3.75nw / cm 2 、37.5nw / cm 2 、375nw / cm 2 、3.75μw / cm 2.

[0061] like Figure 2 As shown in the test results, it is found that at 405nm light wave, even if the light power density is 1.25nw / cm 2 The extremely weak light still has a photoelectric response. The light power density range of the extremely weak light is usually 10 -9 W / cm² to 10 -6 W / cm². This shows that the device still meets the test requirements in extremely weak light environments, greatly improving the sensitivity of the device and providing new ideas for the development of extremely dark field detection technology.

[0062] Example 2

[0063] This embodiment proposes an ultra-sensitive phototransistor based on a double photoactive layer and a preparation method thereof. The device structure and preparation process thereof are the same as those in Embodiment 1, except that: Figure 3 As shown, the device is tested using light with a wavelength of 520nm, where the optical power density of the 520nm light wave is as follows: Figure 3 The shown example uses 3.75nw / cm 2 、37.5nw / cm 2 、375nw / cm 2 、3.75μw / cm 2 、37.5μw / cm 2 .

[0064] like Figure 3 As shown in the test results, it is found that at 520nm light wave, even if the light power density is 3.75nw / cm 2 The extremely weak light still has a photoelectric response. The light power density range of the extremely weak light is usually 10 -9 W / cm² to 10 -6 W / cm². This shows that the device still meets the test requirements in extremely weak light environments, greatly improving the sensitivity of the device and providing new ideas for the development of extremely dark field detection technology.

[0065] Comparative Example 1

[0066] The commercial device preparation process of this embodiment is the same as that of Embodiment 1, with the only difference being that when preparing the commercial device, there is no need to thermally evaporate PbI2, and WSe2 only needs to be transferred to the HfO2 / Si substrate.

[0067] Then the R(A / W)-Power Density(μW / cm 2 ) relationship to test, such as Figure 4The PbI2 / WSe2 heterojunction device has a high optical power density (μW / cm 2 ) is 0.00125μW / cm 2 、0.00375μW / cm 2 , 0.0375μW / cm 2 , 0.375μW / cm 2 、3.75μW / cm 2 The photoelectric response R(A / W) of the device was tested and the R(A / W)-Power Density(μW / cm 2 ) relationship fitting curve; at the same time, the pure WSe2 device has a light power density Power Density (μW / cm 2 ) is 5μW / cm 2 、12.5μW / cm 2 , 25μW / cm 2 , 125μW / cm 2 , 250μW / cm 2 、1250μW / cm 2 The photoelectric response R(A / W) of the device was tested and the R(A / W)-Power Density(μW / cm 2 ) relationship fitting curve.

[0068] Test results such as Figure 4 As shown in the figure, the analysis found that the PbI2 / WSe2 heterojunction device has a higher sensitivity in photoelectric response than the pure WSe2 device, and can meet the demanding environmental testing requirements that are 4 orders of magnitude lower than the current commercial minimum light level. 11 The high responsivity of A / W is 4 orders of magnitude higher than that of commercial phototransistors. The phototransistor has extremely high detection sensitivity.

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

Claims

1. An application of an ultra-sensitive phototransistor based on a double photoactive layer, characterized in that: The device structure of the dual-photoactive layer ultra-sensitive phototransistor is, from bottom to top, a gate electrode Si, a dielectric layer HfO2, a photoactive ion layer PbI2, a channel WSe2, and a source-drain electrode Au; the phototransistor is used in the field of image monitoring and biological imaging; the preparation steps of the phototransistor are as follows: Step 1: Cleaning the HfO2 / Si substrate: Use acetone, isopropanol and anhydrous ethanol to ultrasonically clean the HfO2 / Si substrate in an ultrasonic machine, and then blow dry with high-purity nitrogen for later use; Step 2: Preparation of PbI2 by thermal evaporation: PbI2 powder is placed in a clean source boat and prepared by thermal evaporation; Step 3: Preparation of WSe2 / PbI2 heterojunction: In a nitrogen environment, the two-dimensional WSe2 nanosheets are transferred to the surface of the two-dimensional PbI2 nanosheets through the van der Waals integration process to ensure that the interface of the two layers of materials is clean and in close contact; Step 4: Prepare source and drain electrodes: Prepare metal electrode Au on the surface of WSe2 material through EBL method by thermal evaporation coating process.

2. The application of the ultra-sensitive phototransistor based on a double photoactive layer according to claim 1, characterized in that: As a photoactive layer, PbI2 material can efficiently capture photons in weak 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; while WSe2 material, with its excellent carrier mobility and high light absorption coefficient, further amplifies the photoelectric signal, allowing the entire device to maintain stable photoelectric conversion performance under extremely low light conditions.

3. The use of the ultra-sensitive phototransistor based on a double photoactive layer according to claim 1, characterized in that: The transistor meets the requirements of 0.05 nW 1.25 μW / cm 2 It can be used for detection in extremely dark field environment.

4. The use of the ultra-sensitive phototransistor based on a double photoactive layer according to claim 3, characterized in that: In the dark field detection environment, it still shows 10 11 High A / W responsiveness.

5. The application of the ultra-sensitive phototransistor based on double photoactive layers according to claim 1, characterized in that: The phototransistor can be used to monitor extremely weak light images due to its ultra-sensitive photoelectric response.

6. The use of the ultra-sensitive phototransistor based on a double photoactive layer according to claim 5, characterized in that: The optical power density range of the extremely weak light is 10 -9 W / cm² to 10 -6 W / cm².

7. The use of the ultra-sensitive phototransistor based on a double photoactive layer according to claim 1, characterized in that: The thicknesses of the dielectric layer HfO2, the photoactivated ion layer PbI2, the channel WSe2 and the source-drain electrode Au are 8-10 nm, 1-5 nm, 0.7-3.5 nm and 60-80 nm respectively.

8. The application of the ultra-sensitive phototransistor based on double photoactive layers according to claim 1, characterized in that: The phototransistor preparation steps are as follows: Step 1: Cleaning the HfO2 / Si substrate: Use acetone, isopropanol and anhydrous ethanol to clean the HfO2 / Si substrate in an ultrasonic machine for 10 minutes each, and then blow dry with high-purity nitrogen for later use; Step 2: Preparation of PbI2 by thermal evaporation: Place PbI2 powder in a clean source boat, control the temperature in the boat to 150°C and the pressure to 10 -5 -10 -6 PbI2 was prepared by thermal evaporation under a low pressure environment of Pa; Step 3: Preparation of WSe2 / PbI2 heterojunction: In a nitrogen environment, the two-dimensional WSe2 nanosheets are transferred to the surface of the two-dimensional PbI2 nanosheets through the van der Waals integration process to ensure that the interface of the two layers of materials is clean and in close contact; Step 4: Prepare source and drain electrodes: Use the EBL method combined with Auto CVD software to design an electrode pattern with a reasonable structure and size on the surface of the WSe2 material, and prepare the metal electrode Au through a thermal evaporation coating process.

9. The use of the ultra-sensitive phototransistor based on a double photoactive layer according to claim 1, characterized in that: The preparation steps of the WSe2 / PbI2 heterojunction are as follows: Step 1: Preparation of WSe2 nanosheets: Mechanically exfoliated WSe2 is directly exfoliated onto PDMS to obtain WSe2 / PDMS; Step 2: Transfer WSe2: Align the target WSe2 to the target PbI2 under the microscope field of view and keep it in contact at 90°C for 2-3 minutes; Step 3: Obtain WSe2 / PbI2 heterojunction: Lift the thermal release tape to allow WSe2 to fall on the PbI2 film to complete the preparation of the heterojunction.

10. The application of the ultra-sensitive phototransistor based on double photoactive layers according to claim 1, characterized in that: The steps for the surface Au electrode are as follows: Step 1: Spin-coat photoresists PMMA-A4 and PMMA-A5 on the substrate surface with WSe2 / PbI2 heterojunction in sequence and bake them on a hot plate at 180°C for 100 s respectively; Step 2: Find the area around the sample in the SEM and draw the alignment marks, develop the exposed alignment marks, and take photos with a microscope to record, locate the sample and draw the pattern; Step 3: Align the mark and expose the sample; Step 4: After development, blow dry with a nitrogen gun and evaporate the Au electrode by thermal evaporation.

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