Method for strain regulating abnormal negative diffusion of carrier in semiconductor thin film and application thereof

Abstract

The present application belongs to the technical field of carrier transport observation, and particularly relates to a method for strain regulation and control of carrier abnormal negative diffusion of semiconductor thin film and application thereof, which can realize experimental determination and quantitative characterization of the carrier "negative diffusion" phenomenon in two-dimensional semiconductors, and actively regulate the initial negative diffusion intensity by applying strain. The present application fills the gap in experimental observation and definition of the phenomenon by the standardized method for experimental determination and quantitative characterization of the carrier "negative diffusion" phenomenon in two-dimensional semiconductors, reveals the physical law that uniaxial tensile strain has specific and significant amplification effect on the negative diffusion constant, and establishes a quantitative correlation model between strain and negative diffusion coefficient. A kind of abnormal carrier dynamics behavior, i.e. the initial negative diffusion phenomenon, observed in two-dimensional semiconductors is actively regulated by applying strain.

Description

Technical Field

[0001] This invention belongs to the field of carrier transport observation technology, specifically relating to a method for strain-controlled anomalous negative diffusion of carriers in semiconductor thin films and its application. Background Technology

[0002] Currently, two-dimensional transition metal sulfides generally possess good stability, optoelectronic and mechanical properties, and excellent carrier transport performance. Among them, molybdenum disulfide, tungsten disulfide, and tin disulfide have been proven to exhibit good carrier transport performance and high flexibility. In semiconductor physics, carrier diffusion typically follows Fick's law, characterized by the movement of carriers from high-concentration regions to low-concentration regions, with the mean square displacement increasing linearly with time, described by the positive diffusion coefficient. Traditional research on strain engineering of two-dimensional materials presupposes and observes the modulation effect of strain on the positive diffusion coefficient. However, in some strongly correlated or non-equilibrium quantum systems, theoretically, "negative diffusion" transport behavior is predicted, where particles aggregate towards regions of higher concentration. Currently, no clear negative diffusion phenomenon has been experimentally reported in conventional semiconductors such as two-dimensional transition metal sulfides. Whether external strain can serve as a controllable means to trigger, regulate, or even amplify this unconventional transport behavior remains unknown. Summary of the Invention

[0003] In view of this, the present invention provides a method for strain-controlled anomalous negative diffusion of charge carriers in semiconductor thin films and its application, which enables standardized experimental determination and quantitative characterization of the "negative diffusion" phenomenon of charge carriers in two-dimensional semiconductors.

[0004] To achieve the objectives of this invention, the following technical solutions are provided.

[0005] A method for strain-controlled anomalous negative diffusion of carriers in a semiconductor thin film includes:

[0006] Provide few-layer two-dimensional semiconductor thin films; A uniaxial tensile strain is applied to the film; Pump-probe transient absorption spectroscopy was performed on the strained thin film to obtain broadband transient absorption data, and the characteristic detection wavelength of the charge carriers was determined based on the peak position of the excited-state absorption positive signal. Transient absorption microscopy was performed on the strained thin film at the characteristic detection wavelength to obtain the spatial distribution of carriers under different pump-probe delay times. Two-dimensional Gaussian fitting was performed on the spatial distribution of carriers at each delay time to obtain the relationship between the Gaussian variance and the delay time. During the initial delay period, the presence of negative diffusion is determined based on the monotonically decreasing behavior of the Gaussian variance with the delay time, and the negative diffusion constant is calculated from the time rate of change of the variance using a two-dimensional diffusion model. The negative diffusion constant can be controlled by changing the magnitude of the uniaxial tensile strain applied to the film.

[0007] The few-layer two-dimensional semiconductor thin film is a transition metal sulfide thin film; the transition metal sulfide is tin disulfide, molybdenum disulfide or tungsten disulfide.

[0008] The method of applying uniaxial tensile strain to the thin film is as follows: a few-layer two-dimensional semiconductor thin film is transferred or directly grown on a flexible substrate, and the thin film is subjected to uniaxial tensile strain by pre-bending the flexible substrate and fixing both ends.

[0009] The flexible substrate is a PET film.

[0010] The pump-probe transient absorption spectroscopy measurement employs a supercontinuum white light transmission pump-probe system with a pump wavelength of 500 nm and a detection wavelength range of 350 nm to 800 nm.

[0011] Specifically, determining the characteristic detection wavelength of the charge carrier based on the peak position of the positive signal absorbed in the excited state includes: identifying the positive signal contributed by the excited state absorption of the charge carrier in the transient absorption spectrum, and using the wavelength corresponding to its peak value as the characteristic detection wavelength.

[0012] The two-dimensional Gaussian fitting uses the following formula:

[0013] Where t is the delay time; The carrier density function represents the spatial location of the Gaussian distribution at a specific time t; while the carrier density function... This describes the carrier distribution at different coordinates and time points; N is the fitting coefficient. and The variances of the Gaussian curves in the x and y directions are described separately; using the equations The spatial distribution of charge carriers at different times is described, where D is the carrier diffusion coefficient, derived from... It is given that when the Gaussian variance decreases with the delay time, the resulting D is negative, which is the negative diffusion constant.

[0014] The initial delay time period is the period in which the pump-probe delay time is in the range of 0 to 4 ps.

[0015] Specifically, changing the magnitude of the uniaxial tensile strain applied to the film includes applying 0% and 1.0% uniaxial tensile strain to the same film, respectively, and when 1.0% uniaxial tensile strain is applied, the absolute value of the measured negative diffusion constant increases by at least 20% compared to when no strain is applied.

[0016] The application of the method described in this invention in the evaluation of carrier transport performance of two-dimensional semiconductor materials is used for basic research and performance evaluation of flexible electronic or optoelectronic materials and devices.

[0017] Beneficial effects 1. This invention is the first to experimentally discover the "negative diffusion" phenomenon of charge carriers in conventional semiconductors such as two-dimensional TMDs, breaking through the cognitive framework of traditional semiconductor transport theory. In the method of this invention, strain is a powerful means to control this quantum anomalous effect, and a quantitative "strain-negative diffusion intensity" correlation model has been established, opening up a new path for the control of material properties.

[0018] 2. The method of this invention is applicable to various two-dimensional transition metal sulfide materials and other photoactive two-dimensional semiconductor materials, and has broad application prospects in the basic research and performance evaluation of flexible electronics, optoelectronic materials and devices. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the transient absorption spectrum of tin disulfide in an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of the dynamic curve of the characteristic signal in the transient absorption spectrum in an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram illustrating the function of pump-probe delay time provided in an embodiment of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] This embodiment provides a method for strain-controlled anomalous negative diffusion of carriers in a semiconductor thin film, comprising the following steps: Step 1: Grow or transfer few-layer two-dimensional transition metal sulfide samples on conventional and flexible substrates; In this embodiment, a few-layer tin disulfide is grown onto a sapphire substrate (rigid substrate) using CVD and then transferred onto a clean PET film (flexible substrate). By pre-bending the PET substrate and fixing its ends, the tin disulfide film on top is subjected to a uniaxial tensile strain of approximately 1.0%. A conventional substrate can also be a transparent silicon dioxide substrate; the flexible substrate used is a PET flexible substrate, which allows for the transmission pump detection experiment in step two.

[0024] Step 2: Using supercontinuous white light transmission-pumped detection, strain-controlled few-layer two-dimensional transition metal sulfides were tested to obtain broadband transient absorption data.

[0025] In this embodiment, a supercontinuum white light transient absorption system is used to test the sample. The supercontinuum white light transient absorption system uses a femtosecond laser as the laser source and consists of a pump beam and a probe beam. The pump beam is used to excite the material, and the probe beam is used to detect the sample absorption change caused by the pump light. The delays of the pump beam and probe beam are controlled by an electric translation stage. The probe beam, through focusing onto a YAG crystal, undergoes a nonlinear effect to generate supercontinuum white light covering the ultraviolet to near-infrared range, thus enabling the acquisition of the sample's transient response at different wavelengths. The pump wavelength used is 500 nm (photon energy approximately 2.48 electron volts), and the probe wavelength is 350 nm–800 nm. The transient absorption spectrum of tin disulfide is shown below. Figure 1 As shown in Figure a, the strain modulation method used was uniaxial tensile strain. Similarly, transient absorption spectroscopy was performed on a tin disulfide film subjected to approximately 1.0% uniaxial tensile strain, with a pump wavelength of 500 nm and a detection wavelength of 350 nm–800 nm. The transient absorption spectrum of strain-modulated tin disulfide is shown in Figure a. Figure 1 As shown in b.

[0026] Step 3: Perform signal attribution analysis on the transient absorption spectrum obtained in Step 2. The positive signal is mainly contributed by the excited state absorption of charge carriers. The characteristic detection wavelength of charge carriers is obtained based on the signal peak of the positive signal.

[0027] Among them, under strain-free conditions, a positive signal due to excited-state absorption exists at 412 nm. This signal is closely related to the basic electronic structure of the material and can be used to identify and study carrier dynamics and transport characteristics in the material. Under the condition of applying approximately 1.0% uniaxial tensile strain, a characteristic signal exists at 430 nm. This is a result of strain causing band structure contraction in the material, which is then reflected in the transient absorption spectrum. Extracting the characteristic signal from the transient absorption spectrum yields its dynamic curve, such as... Figure 2 As shown, Figure 2 a represents the dynamic curve of the sample under strain-free control. Figure 2 b is the kinetic curve of the sample under the condition of applying approximately 1.0% uniaxial tensile strain.

[0028] Step 4: Use a transient absorption microscopy system to detect strain-controlled few-layer two-dimensional transition metal sulfides, where the detection wavelength is selected as the characteristic wavelength in step 3, to obtain the carrier spatial distribution under different time delays.

[0029] In this embodiment, the pump wavelength is 500 nm and the detection wavelength is 412 nm for samples without strain control, and the pump wavelength is 500 nm and the detection wavelength is 430 nm for samples with approximately 1.0% uniaxial tensile strain control.

[0030] Step 5: Perform a two-dimensional Gaussian fitting on the spatial distribution of photogenerated carriers obtained in Step 4. That is, fit the spatial distribution of photogenerated carriers at different time delays obtained in the transient absorption microscopy experiment using a two-dimensional Gaussian distribution. The fitting formula is:

[0031] Where t is the delay time; The carrier density function represents the spatial location of the Gaussian distribution at a specific time t; while the carrier density function... This describes the carrier distribution at different coordinates and time points; N is the fitting coefficient. and The variances of the Gaussian curves in the x and y directions are described separately; using the equations The spatial distribution of charge carriers at different times is described, where D is the carrier diffusion coefficient, derived from... Provided.

[0032] Plot the relationship between the fitted variance and the delay time, and obtain the carrier diffusion coefficient using a two-dimensional diffusion model. The variance of the two-dimensional Gaussian distribution is shown in the figure. This can reflect the spatial distribution of charge carriers at different times. When charge carriers diffuse outwards, It will increase. Plotted as a function of pump-probe delay time, such as Figure 3 As shown, Figure 3 Figure 'a' shows the relationship between the variance of the two-dimensional Gaussian fit and the time delay under different time delays without strain control. Figure 3 b is a graph showing the relationship between the variance of the two-dimensional Gaussian fit and the time delay under different time delays under the condition of applying a uniaxial tensile strain of approximately 1.0%.

[0033] Step Six: By analyzing the change of the spatial distribution variance over time, it was observed that the variance monotonically decreases over time, confirming the existence of negative diffusion, and the negative diffusion constant D was calculated; specifically, by solving the diffusion model:

[0034] And according to:

[0035] The carrier diffusion constant D can be obtained. The first characteristic time during which the negative diffusion phenomenon persists is also considered. Within the initial 4ps range.

[0036] Step 7: Comparing the values ​​of D obtained under different strain conditions, it was found that after applying a 1.0% uniaxial tensile strain, the absolute value of the negative diffusion constant D increased by at least 20% compared to the zero strain state. The negative diffusion phenomenon and its strain amplification effect are related to the following microscopic physical changes in the material: strain-induced singularities in the electronic density of states of specific valleys in the Brillouin zone; and the opening or enhancement of intervalve electron-phonon scattering channels caused by strain, leading to the accumulation of charge carriers in specific regions of momentum space.

[0037] In this embodiment, the negative diffusion constant D1 of the sample under zero strain control in the first stage is -217.8 cm⁻¹. 2 s -1 The diffusion constant D2 for the second stage is 1.36 cm⁻². 2 s -1 For the sample subjected to 1.0% uniaxial tensile strain control, the negative diffusion constant D1 in the first stage is -441.2 cm⁻¹. 2 s -1 The diffusion constant D2 for the second stage is 4.61 cm⁻². 2 s -1 It can be observed that after applying a uniaxial tensile strain of 1.0%, the absolute value of the negative diffusion constant D1 increases by approximately 102.5% compared to the zero strain state. This fully confirms the specific amplification effect of strain on negative diffusion.

[0038] The method described in this invention can be applied to the evaluation of carrier transport performance in two-dimensional semiconductor materials, especially for basic research and performance evaluation of flexible electronic or optoelectronic materials and devices.

[0039] This invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered within the scope of protection of this invention.

Claims

1. A method for strain-controlled anomalous negative diffusion of carriers in a semiconductor thin film, characterized in that, include: Provide few-layer two-dimensional semiconductor thin films; A uniaxial tensile strain is applied to the film; Pump-probe transient absorption spectroscopy was performed on the strained thin film to obtain broadband transient absorption data, and the characteristic detection wavelength of the charge carriers was determined based on the peak position of the excited-state absorption positive signal. Transient absorption microscopy was performed on the strained thin film at the characteristic detection wavelength to obtain the spatial distribution of carriers under different pump-probe delay times. Two-dimensional Gaussian fitting was performed on the spatial distribution of carriers at each delay time to obtain the relationship between the Gaussian variance and the delay time. During the initial delay period, the presence of negative diffusion is determined based on the monotonically decreasing behavior of the Gaussian variance with the delay time, and the negative diffusion constant is calculated from the time rate of change of the variance using a two-dimensional diffusion model. The negative diffusion constant can be controlled by changing the magnitude of the uniaxial tensile strain applied to the film.

2. The method according to claim 1, characterized in that, The few-layer two-dimensional semiconductor thin film is a transition metal sulfide thin film; the transition metal sulfide is tin disulfide, molybdenum disulfide or tungsten disulfide.

3. The method according to claim 1, characterized in that, The method of applying uniaxial tensile strain to the thin film is as follows: a few-layer two-dimensional semiconductor thin film is transferred or directly grown on a flexible substrate, and the thin film is subjected to uniaxial tensile strain by pre-bending the flexible substrate and fixing both ends.

4. The method according to claim 3, characterized in that, The flexible substrate is a PET film.

5. The method according to claim 1, characterized in that, The pump-probe transient absorption spectroscopy measurement employs a supercontinuum white light transmission pump-probe system with a pump wavelength of 500 nm and a detection wavelength range of 350 nm to 800 nm.

6. The method according to claim 1, characterized in that, Determining the characteristic detection wavelength of the carrier based on the peak position of the positive signal absorbed in the excited state specifically includes: identifying the positive signal contributed by the excited state absorption of the carrier in the transient absorption spectrum, and taking the wavelength corresponding to its peak value as the characteristic detection wavelength.

7. The method according to claim 1, characterized in that, The two-dimensional Gaussian fitting uses the following formula: Where t is the delay time; The carrier density function represents the spatial location of the Gaussian distribution at a specific time t; while the carrier density function... This describes the carrier distribution at different coordinates and time points; N is the fitting coefficient. and The variances of the Gaussian curves in the x and y directions are described separately; using the equations The spatial distribution of charge carriers at different times is described, where D is the carrier diffusion coefficient, derived from... It is given that when the Gaussian variance decreases with the delay time, the resulting D is negative, which is the negative diffusion constant.

8. The method according to claim 1, characterized in that, The initial delay time period is the period in which the pump-probe delay time is in the range of 0 to 4 ps.

9. The method according to claim 1, characterized in that, The change in the magnitude of the uniaxial tensile strain applied to the film specifically includes: applying 0% and 1.0% uniaxial tensile strain to the same film respectively, and when 1.0% uniaxial tensile strain is applied, the absolute value of the measured negative diffusion constant increases by at least 20% compared to when no strain is applied.

10. The application of the method according to any one of claims 1-9 in the evaluation of carrier transport performance in two-dimensional semiconductor materials, characterized in that, Used for fundamental research and performance evaluation of flexible electronic or optoelectronic materials and devices.

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