Photocurrent imaging system based on probe station and electrometer

Abstract

The invention relates to the technical field of photoelectric detection, in particular to a photocurrent imaging system based on a probe station and an electrometer. The system generates a focused detection light beam through a light path system, the focused detection light beam irradiates a sample carried by a probe station after being spatially modulated by a mask plate, weak light current signals generated by the sample are collected by an electrometer, and a high-resolution light current distribution image is generated by combining scanning motion of a high-precision electric control displacement platform and intelligent processing of computer software. A physically-driven signal enhancement model, a multi-dimensional noise suppression algorithm and a dynamic imaging optimization formula are innovatively designed, the problems that in the prior art, weak light current detection precision is low, the scale connection error is large, and imaging efficiency is insufficient are solved, accurate quantitative analysis of the photoelectric characteristics of materials is achieved, and the method is suitable for popularization and application. The method is suitable for semiconductor device research and development, solar cell performance evaluation, biosensor detection and other scenes, and has both detection precision and application flexibility.

Description

Technical Field

[0001] This invention relates to the field of photoelectric detection technology, and more specifically to a photocurrent imaging system based on a probe station and an electrometer. Background Technology

[0002] Photocurrent imaging, as an advanced detection method integrating optics and electronics, captures the weak current signals generated by materials under illumination and converts them into intuitive images, revealing the distribution of photoelectric properties within materials and providing key technical support for research and development and production in related fields. However, existing photocurrent imaging systems suffer from the following core technical challenges: Insufficient accuracy in weak photocurrent detection: Photocurrent signals are usually in the pA to nA range, which are easily affected by environmental electromagnetic interference, system noise and optical path loss. Existing detection equipment has limited input impedance and noise suppression capabilities, resulting in large signal acquisition errors and making it difficult to achieve accurate quantization. The lack of multi-parameter collaborative optimization: the influence of factors such as optical path transmission efficiency, bias voltage, and temperature change on photocurrent signals is not quantified by the system, and data processing lacks a physically driven collaborative model, resulting in insufficient correlation between photocurrent signals and the actual photoelectric properties of materials. Limited functionality: Most systems can only provide qualitative imaging results and lack quantitative analysis functions such as evaluation of photoelectric property uniformity and defect location, which cannot meet the testing needs in complex scenarios.

[0003] To solve the above technical problems, there is an urgent need for a photocurrent imaging system based on a probe station and an electrometer. Summary of the Invention

[0004] The purpose of this invention is to provide a photocurrent imaging system based on a probe station and an electrometer: by optimizing the system structure design, introducing a physical-driven quantitative calculation model and a multi-dimensional noise suppression algorithm, the detection accuracy, imaging resolution and testing efficiency are synergistically improved.

[0005] The objective of this invention can be achieved through the following technical solutions: A photocurrent imaging system based on a probe station and an electrometer is characterized by comprising: an optical path system, a mask, a high-precision electrically controlled displacement platform, a probe station, an electrometer, a source meter, and computer software. The optical path system outputs a focused laser beam. The mask is fixed on the high-precision electrically controlled displacement platform, which drives the mask to perform two-dimensional controllable displacement, achieving spatial modulation of the laser beam. The probe station stably supports the sample to be tested. After modulation by the mask, the laser beam is focused onto the sample surface through a microscope, generating a photocurrent under illumination. The electrometer is electrically connected to the probe station and is used to acquire the photocurrent signal generated by the sample. The source meter provides an adjustable bias voltage to the sample. The computer software is communicatively connected to the high-precision electrically controlled displacement platform, the electrometer, and the source meter, respectively, to control the coordinated operation of each component, receive the photocurrent signal, and generate a photocurrent distribution image based on a preset algorithm.

[0006] Furthermore, the optical path system includes a laser, an optical fiber, a spatial coupler, a filter, and a focusing plate; the laser output from the laser is transmitted through the optical fiber or spatial coupler, and then passes through the filter to filter stray light, and is focused by the focusing plate before being incident on the mask.

[0007] Furthermore, the preset algorithms executed by the computer software include a photocurrent response coefficient calculation model, a multi-scale noise suppression algorithm, and a dynamic imaging reconstruction algorithm.

[0008] Furthermore, the photocurrent response coefficient calculation model is as follows: ;in, The photocurrent response coefficient is... This represents the peak value of the filtered photocurrent signal. To improve the detection efficiency of the electrometer, This is the bias voltage enhancement factor. The output power of the laser. For optical path transmission efficiency, The area of ​​the laser spot on the sample surface is denoted as .

[0009] Furthermore, the multi-scale noise suppression algorithm combines Kalman filtering with wavelet thresholding for denoising: ; ; in, For the nth data point after filtering, For Kalman gain, For the original data points, To predict data points, For wavelet threshold, The standard deviation of noise. This represents the data length.

[0010] Furthermore, the dynamic imaging reconstruction algorithm generates images through a nonlinear mapping between the photocurrent response coefficient and the RGB color space. The mapping formula is as follows: ; ; ; in, The photocurrent response coefficient is... , and These are the values ​​for the three RGB channels, respectively. , These are the minimum and maximum values ​​of the photocurrent response coefficient, respectively. , and All are nonlinear adjustment coefficients.

[0011] Furthermore, the computer software also has the functions of photocurrent uniformity assessment and defect location: The formula for evaluating uniformity is: ; in, The coefficient of variation is the uniformity. The standard deviation of the photocurrent response coefficient is denoted as , and the coefficient of variation of uniformity is used to evaluate the quality of the sample to be tested. Defect localization is achieved by calculating the deviation of the local response coefficient, using the following formula: ;in, coordinates The local response coefficient deviation, coordinates The photocurrent response coefficient at that location. coordinates The average photocurrent response coefficient within the neighborhood and the local response coefficient deviation are used to locate the defect location of the sample to be tested.

[0012] Compared to existing solutions, the beneficial effects achieved by this invention are: On the one hand, by using an ultra-high input impedance electrometer and a multi-scale noise suppression algorithm, it is possible to accurately capture weak photocurrent signals on the order of pA, thereby improving detection accuracy.

[0013] On the other hand, by using a high numerical aperture optical path system (spot diameter 5-50μm) and an ultra-high precision displacement platform, microscopic imaging at the 20μm level can be achieved, which can clearly reveal the differences in photoelectric properties of the microscopic region of the sample.

[0014] Finally, automated control and data processing are achieved through computer software, eliminating the need for manual intervention in the imaging process, significantly improving detection efficiency and reducing operational difficulty. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0016] Figure 1 This is a system block diagram of a photocurrent imaging system based on a probe station and an electrometer according to an embodiment of the present invention; Figure 2 This is a flowchart of a photocurrent imaging system based on a probe station and an electrometer according to an embodiment of the present invention; Figure 3 This is a structural block diagram of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more exemplary embodiments. Numerous specific details are provided in the following description to give a full understanding of exemplary embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, components, steps, etc., can be employed. In other instances, well-known structures, methods, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0019] This embodiment provides a photocurrent imaging system based on a probe station and an electrometer. Figure 1 This is a system block diagram of a photocurrent imaging system based on a probe station and an electrometer according to an embodiment of the present invention, as shown below. Figure 1As shown, the system includes: an optical path system, a mask, a high-precision electrically controlled displacement platform, a probe station, an electrometer, a source meter, and computer software. The optical path system outputs a focused laser beam. The mask is fixed on the high-precision electrically controlled displacement platform, which drives the mask to perform two-dimensional controllable displacement, achieving spatial modulation of the laser beam. The probe station stably supports the sample to be tested. After the laser beam is modulated by the mask, it is focused onto the sample surface through a microscope, and the sample generates a photocurrent under illumination. The electrometer is electrically connected to the probe station and is used to collect the photocurrent signal generated by the sample. The source meter provides an adjustable bias voltage to the sample. The computer software is communicatively connected to the high-precision electrically controlled displacement platform, the electrometer, and the source meter, respectively, and is used to control the coordinated operation of each component, receive the photocurrent signal, and generate a photocurrent distribution image based on a preset algorithm. Specifically, Optical path system: As the core of laser emission and modulation, it includes the laser, optical fiber, spatial coupler, filter, and focusing plate. The laser is a semiconductor laser with a wavelength of 405nm-1550nm, and the output power can be adjusted within the range of 0.1mW-100mW to adapt to the excitation requirements of different optoelectronic materials; the optical fiber is a single-mode fiber with a transmission loss of <0.2dB / km, ensuring efficient transmission of laser energy; the spatial coupler realizes laser spatial collimation with a coupling efficiency of ≥90%; the filter is a narrowband filter with a bandwidth of 10nm, effectively filtering ambient stray light and laser harmonics; the focusing plate uses a high numerical aperture quartz lens (numerical aperture 0.8-1.2) to focus the laser into a spot with a diameter of 5-50μm, improving the optical power density.

[0020] Mask and High-Precision Electrically Controlled Displacement Platform: The mask is made of quartz, with an array of transparent holes fabricated on its surface using photolithography. The hole diameter and spacing can be customized according to imaging resolution requirements (in this embodiment, the hole diameter is 20μm, and the center-to-center distance between adjacent holes is 50μm). The mask is fixed on a high-precision electrically controlled displacement platform, which uses ball screw drive and grating ruler feedback. The displacement accuracy can reach 0.05μm, the repeatability error is <±0.03μm, and it supports independent X and Y two-dimensional motion with a continuously adjustable scanning speed of 0.1-10mm / s. The movement trajectory of the displacement platform is controlled by computer software, which drives the mask to achieve spatial cutting and scanning of the laser beam, allowing the laser to irradiate the sample surface along a preset path (such as a serpentine or grid pattern).

[0021] Probe stage, temperature control system, and vibration suppression module: The probe stage adopts a vacuum adsorption structure, with a sample placement area flatness error of <±0.1μm, ensuring the stability of the laser focusing point. The temperature control system includes a semiconductor cooler and a temperature sensor, connected to the probe stage via heat conduction. The temperature control range is -40℃ to 120℃, with temperature fluctuations ≤±0.3℃, meeting the testing requirements for the photoelectric properties of materials under different temperature conditions. The vibration suppression module uses an active vibration isolation platform, monitoring vibration signals in real time through sensors and providing reverse compensation. The vibration attenuation rate is ≥90%, effectively reducing the impact of environmental vibration on imaging accuracy.

[0022] Electrometer and source meter: The electrometer uses a precision model with ultra-high input impedance, with an input impedance ≥ Ω, current measurement range A to A. Measurement accuracy ±0.05%, capable of accurately capturing weak photocurrent signals. The source meter is used to provide a stable bias voltage (-100V-100V) for the sample, with a voltage adjustment accuracy of 0.05mV and a current output range of... A to A. The separation and transmission of photogenerated carriers can be promoted by adjusting the bias voltage, thereby enhancing the photocurrent signal strength.

[0023] Computer software: Developed based on LabVIEW, serving as the core of system control and data processing, with four main functions: First, controlling the coordinated operation of various hardware components (laser power adjustment, displacement platform trajectory planning, source meter voltage setting, and electrometer data acquisition triggering); second, receiving raw photocurrent data and processing it through multi-scale noise suppression algorithms and photocurrent response coefficient calculation models; third, generating photocurrent distribution images based on dynamic imaging reconstruction algorithms; and fourth, achieving quantification of sample photoelectric property uniformity and precise defect location through uniformity evaluation formulas and defect localization formulas.

[0024] In some embodiments, Figure 2 This is a flowchart illustrating the operation of a photocurrent imaging system based on a probe station and an electrometer according to an embodiment of the present invention. Figure 1 As shown, the workflow of this system includes: Step 1: Sample preparation; The sample to be tested (such as a semiconductor chip, solar cell, or biosensor membrane) is placed on the probe station and fixed by vacuum adsorption. According to the test requirements, the ambient temperature of the sample is adjusted to the target temperature (such as 25°C room temperature, -40°C low temperature, or 120°C high temperature) using a temperature control system. The vibration suppression module is activated to ensure the stability of the test environment.

[0025] Step 2, System parameter settings; Core parameters can be set via computer software, including laser output power, scanning area, displacement platform scanning speed, source meter bias voltage, and electrometer sampling frequency. For example, the laser output power can be set to 10mW, the scanning area to 10mm×10mm, the scanning speed to 1mm / s, the bias voltage to 10V, and the sampling frequency to 1kHz.

[0026] Step 3: Laser irradiation and signal acquisition; After the system is started, the laser beam output from the laser is transmitted via optical fiber to a spatial coupler. After collimation, it passes sequentially through a filter (to filter stray light) and a focusing plate (to converge the light spot) before being incident on the mask. Computer software controls a high-precision electrically controlled displacement platform to move the mask along a preset trajectory, spatially modulating the laser beam. The modulated laser beam is then focused onto different positions on the sample surface through a microscope. Under laser irradiation, the sample undergoes the photoelectric effect, generating photogenerated carriers. Under the bias voltage of the source surface, a photocurrent is formed. An electrometer collects this photocurrent signal in real time and transmits it to the computer software.

[0027] Step four: Data processing and imaging analysis.

[0028] The computer software performs multi-step processing on the raw photocurrent data: First, environmental interference and system noise are removed using a multi-scale noise suppression algorithm (Kalman filtering + wavelet thresholding). Second, based on the photocurrent response coefficient calculation model, combined with parameters such as laser power, optical path transmission efficiency, and bias voltage enhancement coefficient, the photocurrent response coefficient at each scanning position is calculated (quantifying photoelectric conversion efficiency). Then, the response coefficient is mapped to RGB color values ​​using a dynamic imaging reconstruction algorithm to generate a two-dimensional photocurrent distribution image. Finally, the coefficient of variation is calculated using a uniformity evaluation formula to quantify the uniformity of the sample's photoelectric properties, and a defect location formula is used to identify local abnormal response coefficient regions, achieving precise defect location.

[0029] Specifically, the photocurrent response coefficient calculation model is as follows: ;in, The photocurrent response coefficient is... This represents the peak value of the filtered photocurrent signal. To improve the detection efficiency of the electrometer, This is the bias voltage enhancement factor. The output power of the laser. For optical path transmission efficiency, The area of ​​the laser spot on the sample surface is denoted as .

[0030] It is worth noting that the electrometer's detection efficiency The calculation process is as follows: Electrometer detection efficiency The efficiency with which an electrometer converts the physical signal of photocurrent generated by a sample into an acquireable electrical signal reflects the signal conversion accuracy of the electrometer (affected by instrument noise, input impedance, and amplification factor).

[0031] Select a standard current source with a known output current (with an accuracy one order of magnitude better than that of an electrometer). Connect the output of the standard current source directly to the input of the electrometer (simulating the sample photocurrent output scenario). Set a standard current source to output a series of known current values Record the collected values ​​corresponding to the electrometer. The average conversion efficiency of multiple measurements is calculated, which is the electrometer's detection efficiency. .

[0032] Bias voltage enhancement factor The calculation process is as follows: Bias voltage enhancement factor The enhancement effect coefficient of bias voltage on sample photocurrent reflects the degree to which bias voltage (provided by the source meter) accelerates carrier separation in the sample and enhances photocurrent output (related to sample material properties and the magnitude of bias voltage).

[0033] Maintain optical path system parameters (laser output power) The area of ​​the laser spot on the sample surface (S, etc.) is fixed; First, set the source meter bias voltage to 0V and then collect the photocurrent value of the sample. ; Set target bias voltage (Operating voltage required for the experiment), collect the photocurrent value of the sample at this time. (Photocurrent under bias voltage); the ratio of the two is the enhancement factor under that bias voltage: .

[0034] Optical transmission efficiency The calculation process is as follows: Optical path transmission efficiency: The power transmission efficiency of the laser from the laser output, through the fiber / space coupler, filter, condenser, mask, microscope and other components, to the final sample surface (reflecting the total loss of each component in the optical path).

[0035] A high-precision laser power meter (accuracy better than 0.1%) was selected. Step 1: Place the power meter directly at the laser output terminal and measure the original laser output power. ; Step 2: Keeping the laser parameters unchanged, install all optical components in sequence according to the actual optical path of the system (fiber / spatial coupler → filter → condenser → mask → microscope). Place the power meter at the focusing position on the sample surface and measure the transmitted laser power. ; The ratio of the two is the optical path transmission efficiency: .

[0036] In some embodiments, the multi-scale noise suppression algorithm combines Kalman filtering with wavelet thresholding for denoising: ; ; in, For the nth data point after filtering, For Kalman gain, For the original data points, To predict data points, For wavelet threshold, The standard deviation of noise. This represents the data length.

[0037] In some embodiments, the dynamic imaging reconstruction algorithm generates an image through a nonlinear mapping between the photocurrent response coefficient and the RGB color space, wherein the mapping formula is: ; ; ; in, The photocurrent response coefficient is... , and These are the values ​​for the three RGB channels, respectively. , These are the minimum and maximum values ​​of the photocurrent response coefficient, respectively. , and All of these are nonlinear adjustment coefficients. The process for determining the nonlinear adjustment coefficients is as follows: Step 1: Determine the dynamic range of the photocurrent response coefficient First, the extreme values ​​of the photocurrent response coefficient of the sample to be tested were obtained experimentally (compatible with the original formula): Select 3-5 standard samples (with known photocurrent response uniformity, no defects, and covering the response range of the target sample); collect the photocurrent signals of the standard samples according to the original system procedure, and calculate the photocurrent response coefficient R of each sample; Calculate the R-values ​​for all standard samples to determine the global extremum: ; ;in, This refers to the number of test points on the standard sample. Calculate the normalized response coefficient (Input values ​​for the mapping formula): ; .

[0038] Step 2: Set the initial values ​​for the coefficients.

[0039] Based on the properties of the tanh function, the initial value must be guaranteed. When the value is in the range of 0 to 1, the tanh output value covers 0.1 to 0.9 (to avoid RGB values ​​being too dark or too exposed). The initial value setting principle is as follows: The initial values ​​of the three channel coefficients remain consistent (to ensure the neutrality of the initial mapping): ; Step 3: Iterative optimization of coefficients (based on visual evaluation metrics); fixed and Substitute different combinations of coefficients Generate RGB images of standard samples; Define two core evaluation metrics (quantifying visual effects): Image contrast : ;in, , and These represent the maximum, minimum, and average values ​​of the RGB channels of the image; requirements: (Moderate contrast, neither overexposed nor underexposed); Response difference recognition rate D: Calculate the RGB value difference of the "known response difference region" in the standard sample. D should be greater than or equal to 30 (RGB, channel value 0~255, when the difference is ≥30, the human eye can clearly distinguish them). Iterative adjustment coefficient: If the contrast is insufficient ( ), increase synchronously (e.g., increasing by 0.5 each time); If the high-response area is overexposed (RGB=255, percentage > 5%): reduce... (Red channel coefficient), maintained constant; If the low-response area is too dark (RGB < 30, percentage > 5%): Reduce (Blue channel coefficient), maintained , constant; When evaluation indicators When both D and A meet the requirements, determine the final result. Preferably, based on engineering practice data, the coefficient values ​​should match the nonlinear characteristics of the tanh function to avoid mapping saturation or failure. The general range is as follows: , , .

[0040] In some embodiments, the coefficient of variation is calculated using a uniformity evaluation formula to quantify the uniformity of the sample's photoelectric properties, and anomaly regions in local response coefficients are identified using a defect location formula to achieve precise defect location. The formula for evaluating uniformity is: ;in, The standard deviation of the photocurrent response coefficient is given, while the coefficient of variation of uniformity is used to evaluate the quality of the sample being tested. The smaller the value, the more uniform the photoelectric properties of the sample. This indicator can be directly used for quality assessment of products such as solar cells and semiconductor chips.

[0041] Defect localization is achieved by calculating the deviation of the local response coefficient, using the following formula: ;in, coordinates The local response coefficient deviation, coordinates The photocurrent response coefficient at that location. coordinates The average photocurrent response coefficient within the neighborhood and the local response coefficient deviation are used to locate the defect location in the sample to be tested. coordinates The average response coefficient within a 3×3 neighborhood; when At that time, the location is determined to be a defect area, achieving precise defect localization. This represents the average value of the photocurrent response coefficient corresponding to the sample to be tested.

[0042] This embodiment also provides an electronic device. Figure 3 This is a structural block diagram of an electronic device according to an embodiment of the present invention, such as... Figure 3 As shown, the electronic device includes a memory 301 and a processor 302. The memory 301 stores a computer program. When the computer program is executed by the processor 302, the processor 302 executes a photocurrent imaging system based on a probe station and an electrometer as described in any of the above embodiments.

[0043] The memory 301 may be an electronic memory such as flash memory, EEPROM (Electrically Erasable Programmable Read-Only Memory), EPROM, hard disk, or ROM. The memory 301 has storage space 303 for program code 313 for performing any of the method steps described above. For example, the storage space 303 for program code may include individual program codes 313 for implementing the various steps in the methods described above. This program code can be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, CDs, memory cards, or floppy disks. The program code may be compressed, for example, in a suitable form. When run by a computing processing device, this code causes the computing processing device to perform the various steps in the methods described above. This program code can be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, CDs, memory cards, or floppy disks. The program code may be compressed, for example, in a suitable form. When this code is run by a computing device, it causes the device to perform the various steps of the photocurrent imaging system based on the probe station and electrometer described above.

[0044] The above formulas are all dimensionless calculations. The preset weights and preset coefficients in the formulas shall be set by those skilled in the art according to the actual situation.

[0045] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more sets of available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive.

[0046] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0047] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0048] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0049] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0050] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A photocurrent imaging system based on a probe station and an electrometer, characterized in that, The system includes: an optical path system, a mask, a high-precision electrically controlled displacement platform, a probe station, an electrometer, a source meter, and computer software. The optical path system outputs a focused laser beam. The mask is fixed on the high-precision electrically controlled displacement platform, which drives the mask to perform two-dimensional controllable displacement, achieving spatial modulation of the laser beam. The probe station stably supports the sample to be tested. After the laser beam is modulated by the mask, it is focused onto the sample surface through a microscope, and the sample generates a photocurrent under illumination. The electrometer is electrically connected to the probe station and is used to collect the photocurrent signal generated by the sample. The source meter provides an adjustable bias voltage to the sample. The computer software is communicatively connected to the high-precision electrically controlled displacement platform, the electrometer, and the source meter, respectively, to control the coordinated operation of each component, receive the photocurrent signal, and generate a photocurrent distribution image based on a preset algorithm.

2. The photocurrent imaging system based on a probe station and an electrometer according to claim 1, characterized in that, The optical path system includes a laser, an optical fiber, a spatial coupler, a filter, and a focusing plate. The laser output from the laser is transmitted through the optical fiber or spatial coupler, and then passes through the filter to filter out stray light and the focusing plate to converge the light before it is incident on the mask.

3. The photocurrent imaging system based on a probe station and an electrometer according to claim 1, characterized in that, The preset algorithms executed by the computer software include a photocurrent response coefficient calculation model, a multi-scale noise suppression algorithm, and a dynamic imaging reconstruction algorithm.

4. The photocurrent imaging system based on a probe station and an electrometer according to claim 3, characterized in that, Photocurrent response coefficient calculation model: ;in, The photocurrent response coefficient is... This represents the peak value of the filtered photocurrent signal. To improve the detection efficiency of the electrometer, This is the bias voltage enhancement factor. The output power of the laser. For optical path transmission efficiency, The area of ​​the laser spot on the sample surface is denoted as .

5. The photocurrent imaging system based on a probe station and an electrometer according to claim 1, characterized in that, Multi-scale noise suppression algorithm combining Kalman filtering and wavelet thresholding for denoising: ； ； in, For the nth data point after filtering, For Kalman gain, For the original data points, To predict data points, For wavelet threshold, The standard deviation of noise. This represents the data length.

6. The photocurrent imaging system based on a probe station and an electrometer according to claim 3, characterized in that, The dynamic imaging reconstruction algorithm generates images through a nonlinear mapping between the photocurrent response coefficient and the RGB color space. The mapping formula is as follows: ； ； ； in, The photocurrent response coefficient is... , and These are the values ​​for the three RGB channels, respectively. , These are the minimum and maximum values ​​of the photocurrent response coefficient, respectively. , and All are nonlinear adjustment coefficients.

7. The photocurrent imaging system based on a probe station and an electrometer according to claim 1, characterized in that, The computer software also has functions for evaluating photocurrent uniformity and locating defects. The formula for evaluating uniformity is: ; in, The coefficient of variation is the uniformity. The standard deviation of the photocurrent response coefficient is denoted as , and the coefficient of variation of uniformity is used to evaluate the quality of the sample to be tested. Defect localization is achieved by calculating the deviation of the local response coefficient, using the following formula: ;in, coordinates The local response coefficient deviation, coordinates The photocurrent response coefficient at that location. coordinates The average photocurrent response coefficient within the neighborhood and the local response coefficient deviation are used to locate the defect location of the sample to be tested.

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