A method and apparatus for characterizing carrier recombination and diffusion processes under the action of an electric field

Abstract

The application discloses a kind of electric field effect download carrier recombination and diffusion process characterization method and device, belong to time-resolved spectroscopy test technical field.The method for realizing of the present application is: preset time delay sequence, time delay refers to the interval of laser emission time and image acquisition time;According to the time delay sequence of step one preset, the transient fluorescence image of sample is sequentially collected;According to transient fluorescence image, diffusion rate D is obtained by numerical method fitting, and the characterization of carrier diffusion process is realized based on diffusion rate D.The characterization device for realizing the characterization method of the electric field effect download carrier recombination and diffusion process, including pump laser, dichroic mirror, objective, sample, reflector, optical filter, plano-convex lens, gated image intensifier detector, control module, host computer and voltage source.The present application can realize the characterization of electric field effect download carrier recombination and diffusion process, and the detection window of transient fluorescence imaging is greatly expanded to the scale of seconds.

Description

TECHNICAL FIELD

[0001] The application relates to a method and device for characterizing carrier recombination and diffusion processes under the action of an electric field, and belongs to the technical field of time-resolved spectroscopy. BACKGROUND

[0002] The carrier recombination and diffusion capability of a semiconductor material directly affects the efficiency of a corresponding device. Accurate characterization of the recombination and diffusion processes of long-lived carriers, especially those with a time scale of seconds, is of great significance for the development of high-efficiency optoelectronic materials. In addition, the drift motion and diffusion motion of carriers under the action of an electric field are directly related, and the development of a carrier recombination and diffusion observation method under the action of an electric field is conducive to the research and development of new optoelectronic materials. SUMMARY

[0003] The application aims to provide a method and device for characterizing carrier recombination and diffusion processes under the action of an electric field, which can realize the characterization of carrier recombination and diffusion processes under the action of an electric field and greatly expand the detection window of transient fluorescence imaging to a time scale of seconds. The application can improve the performance test precision, range and efficiency of optoelectronic materials.

[0004] The application aims to achieve the above-mentioned purposes by the following solutions.

[0005] In one aspect of the application, a method for characterizing carrier recombination and diffusion processes under the action of an electric field is disclosed, which comprises the following steps:

[0006] Step one, presetting a time delay sequence, wherein the time delay refers to the interval between the laser emission time and the image acquisition time;

[0007] Step two, sequentially acquiring the transient fluorescence images of the sample according to the time delay sequence preset in step one;

[0008] Step three, obtaining the diffusion rate D by numerical fitting based on the images obtained in step two, and realizing the characterization of the carrier diffusion process based on the diffusion rate D;

[0009] Under the action of an electric field, the initial spatial distribution of sample carriers generated by pump laser with a Gaussian distribution of spatial intensity satisfies formula (1):

[0010]

[0011] Wherein, n(x,0) is the spatial distribution of carriers at the initial moment, x is the spatial position, N is a fitting parameter related to the carrier density, and sigma0 is the width of the Gaussian distribution at the initial moment.

[0012] With the increase of time t, the recombination and spatial diffusion process of carriers in the x direction is represented as:

[0013]

[0014] wherein n(x,t) is the spatial distribution of the carriers at time t, D represents the diffusion rate of the carriers, μ represents the carrier mobility, E represents the electric field strength, f[n(x,t)] nr represents the rate of the decrease of the number of carriers at this point due to non-radiative recombination; f[n(x,t)] r represents the rate of the decrease of the number of carriers at this point due to radiative recombination, which is obtained by formula (3);

[0015] The spatial distribution I(x,t) of the transient fluorescence image detected in step two satisfies formula (3):

[0016] I(x,t)∝f[n(x,t)] r (3)

[0017] The diffusion rate D of the carriers is obtained according to formula (1) to formula (3), and is obtained by fitting the spatial distribution of the transient fluorescence image under different time delays.

[0018] Another aspect of the present application also discloses a device for characterizing the carrier recombination and diffusion process under the action of an electric field, which is used to realize the method for characterizing the carrier recombination and diffusion process under the action of an electric field. The device for characterizing the carrier recombination and diffusion process under the action of an electric field comprises a pump laser, a dichroic mirror, an objective lens, a sample, a mirror, a filter, a plano-convex lens, a gated image intensifier detector, a control module, an upper computer and a voltage source.

[0019] The pump laser emitted by the pump laser is introduced into the objective lens through the dichroic mirror and focused on the surface of the sample.

[0020] The fluorescence emitted by the sample is collimated by the objective lens, passes through the dichroic mirror, the mirror, the filter and the plano-convex lens, and is imaged on the gated image intensifier detector.

[0021] The control module is connected with the pump laser, the gated image intensifier detector and the upper computer, and is used to collect transient sample fluorescence images under different time delays.

[0022] The control module is also connected with the voltage source.

[0023] Further, the pump laser is a single-color pulsed laser with adjustable repetition frequency, and can output a synchronous output electrical signal of the laser.

[0024] Further, the cut-off wavelength of the dichroic mirror is greater than the wavelength of the emitted laser of the pump laser, so that the emitted pump laser can only be reflected into the objective lens, and cannot be transmitted through the dichroic mirror into the gated image intensifier, thereby preventing the gated image intensifier from being irradiated by the intense pump laser.

[0025] Further, the filter is a band-pass filter for selecting the required fluorescent wavelength for transient fluorescence imaging.

[0026] Further, the synchronization output signal of the pump laser is connected to the control module and is output after a specific time delay, for triggering the gated image intensifier to acquire the transient fluorescence image.

[0027] Further, the control module is used to adjust the time delay of the synchronization output signal of the pump laser in units of 1 nanosecond.

[0028] Further, the control module is used to control the voltage source to apply different intensity electric fields to the sample surface.

[0029] Beneficial effects:

[0030] 1. The disclosed method for characterizing the carrier recombination and diffusion process under electric field action provides a method for characterizing the carrier diffusion under electric field action by fitting the transient fluorescence image, which can obtain the diffusion constant D through numerical fitting, and can serve the semiconductor diffusion mechanism research under working conditions.

[0031] 2. The disclosed device for characterizing the carrier recombination and diffusion process under electric field action uses a high-time-resolution gated image intensifier, which can characterize the transient photoluminescence image of the sample under electric field action with a time resolution of nanoseconds, thereby serving the semiconductor diffusion mechanism research under working conditions, and greatly expanding the detection window of the carrier recombination and diffusion process to a time scale of seconds. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a schematic diagram of a device for characterizing the carrier recombination and diffusion process under electric field action according to an embodiment of the present application.

[0033] Figure 2 is a flowchart of a method for characterizing the carrier recombination and diffusion process under electric field action according to an embodiment of the present application.

[0034] Figure 3 is a timing diagram of a method for characterizing the carrier recombination and diffusion process under electric field action according to an embodiment of the present application.

[0035] wherein,Figure 1 The application discloses a characterization device for carrier recombination and diffusion process under electric field effect, wherein each component can be represented as: 1-pump laser, 2-dichroic mirror, 3-objective lens, 4-sample, 5-reflection mirror, 6-filter, 7-plano-convex lens, 8-gated image intensifier detector, 9-control module, 10-upper computer and 11-voltage source. DETAILED DESCRIPTION

[0036] In order to better illustrate the purpose and advantages of the application, the application content is further illustrated below in combination with the drawings and examples.

[0037] Embodiment 1

[0038] The embodiment discloses a characterization method for carrier recombination and diffusion process under electric field effect, and the specific implementation steps are as follows:

[0039] Step one, presetting a time delay sequence, wherein the time delay refers to the interval between laser emission time and image acquisition time;

[0040] Step two, sequentially acquiring transient fluorescence images of the sample according to the time delay sequence preset in step one;

[0041] Step three, obtaining the diffusion rate D through a numerical method fitting according to the images obtained in step two, so as to realize characterization of the carrier diffusion process;

[0042] Under the action of the electric field, the initial spatial distribution of the sample carrier generated by the pump laser with Gaussian distribution of spatial intensity distribution should satisfy:

[0043]

[0044] Wherein, n(x, 0) is the spatial distribution of the carrier at the initial moment, x is the spatial position, N is a fitting parameter related to the carrier density, and σ0 is the width of the Gaussian distribution at the initial moment.

[0045] With the increase of time t, the recombination and spatial diffusion process of the carrier in the x direction is represented as:

[0046]

[0047] Wherein, n(x, t) is the spatial distribution of the carrier at the t moment, D represents the diffusion rate of the carrier, μ represents the carrier mobility, E represents the electric field intensity, f[n(x, t)] nr represents the rate of decrease of the number of carriers at the point due to non-radiative recombination; f[n(x, t)] r represents the rate of decrease of the number of carriers at the point due to radiative recombination, which is obtained through equation (3);

[0048] The spatial distribution I(x, t) of the transient fluorescence image probed in step two should satisfy:

[0049] I(x, t)∝f[n(x, t)] r (3)

[0050] The diffusion rate D of the carriers is obtained according to formula (1) to formula (3) by fitting the spatial distribution of the transient fluorescence image at different time delays.

[0051] The embodiment also discloses a device for characterizing the carrier recombination and diffusion process under the action of an electric field, which is used to realize the method for characterizing the carrier recombination and diffusion process under the action of an electric field. In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the present application.

[0052] Figure 1 Fig. 1 is a schematic diagram of a device for characterizing the carrier recombination and diffusion process under the action of an electric field. As shown in the figure, the device comprises: 1 a pump laser, 2 a dichroic mirror, 3 an objective lens, 4 a sample, 5 a mirror, 6 a filter, 7 a plano-convex lens, 8 a gated intensified detector, 9 a control module, 10 an upper computer, and 11 a voltage source. Figure 1

[0053] The pump laser emitted by the pump laser is introduced into the objective lens through the dichroic mirror and focused on the surface of the sample. The fluorescence emitted by the sample is collimated through the objective lens, and then imaged on the gated intensified detector after passing through the dichroic mirror, the mirror, the filter and the plano-convex lens.

[0054] The control module is connected with the pump laser, the gated intensified detector and the upper computer, and is used to collect the transient sample fluorescence images at different time delays. The control module is also connected with the voltage source, and is used to apply an external electric field to the sample.

[0055] The pump laser is a monochromatic pulsed laser, the repetition frequency of which is adjustable, and the pump laser can output a synchronous output electrical signal of the laser. Exemplarily, the pump laser can be a nanosecond pulsed laser with a wavelength of 400 nm and a repetition frequency of 10 Hz.

[0056] ​The cut-off wavelength of the dichroic mirror should be greater than the wavelength of the emitted laser of the pump laser, so that the emitted pump laser can only be reflected into the objective lens, but cannot be transmitted through the dichroic mirror into the gated intensified detector, thereby preventing the gated intensified detector from being irradiated by the intense pump laser; for example, the dichroic mirror can select a dichroic mirror with a cut-off wavelength of 450 nm;

[0057] The filter is a band-pass filter for selecting the required fluorescent wavelength for transient fluorescence imaging; for example, a band-pass filter with a wavelength of 550±10 nm can be selected;

[0058] The exposure gate width of the gated intensified detector can generally reach 1 nanosecond, thereby realizing high time resolution transient fluorescence imaging;

[0059] The synchronization output signal of the pump laser is connected to the control module and is output after a specific time delay, which is used to trigger the gated intensified detector to acquire a transient fluorescence image; for example, the acquisition time of the gated intensified detector can be fixed as 1 nanosecond, and the working mode is set as external triggering;

[0060] The control module should be able to adjust the time delay of the synchronization output signal of the pump laser at a high time resolution, generally not more than 1 nanosecond;

[0061] The control module can control the voltage source to apply different intensity electric fields to the sample surface;

[0062] In another aspect of the present application, a method for characterizing the carrier recombination and diffusion process under an electric field is provided, and the test method comprises:

[0063] As shown in Figure 3 The time delay sequence is preset to change the time delay between the emitted laser of the pump laser and the acquisition of the transient fluorescence image by the gated intensified detector; for example, the time delay sequence can be set as {0, 1, 2, 3, …, 999, 1000} (0 to 1000, unit interval is 1, unit is nanosecond).

[0064] The intensity of the electric field acting on the sample is changed; for example, the voltage can be preset to 0 V;

[0065] The transient fluorescence images of the sample are acquired in sequence according to the preset time delay sequence and the preset voltage action sequence; in order to realize better transient fluorescence imaging effect, the acquisition should be repeated multiple times according to the above-mentioned time delay sequence;

[0066] The diffusion constant under no electric field is obtained by numerical fitting;

[0067] Further, the time delay sequence is kept unchanged, and the electric field intensity acting on the sample is changed; for example, the voltage can be preset to 1V;

[0068] The transient fluorescence images of the sample are collected according to the preset time delay sequence and the preset voltage action sequence in sequence, and in order to achieve a better transient fluorescence imaging effect, the collection should be repeated multiple times according to the time delay sequence.

[0069] The diffusion constant under the electric field is obtained by numerical fitting.

[0070] The above specific description further describes the purpose, technical scheme and beneficial effects of the application, and it should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. A method of characterizing the recombination and diffusion of charge carriers in an electric field, comprising: It comprises the following steps, Step one, presetting a time delay sequence, the time delay refers to the interval between the laser emission time and the image acquisition time; Step two, sequentially acquiring the transient fluorescence images of the sample according to the time delay sequence preset in step one; Step three, obtaining the diffusion rate D by fitting the images obtained in step two through a numerical method, and realizing the characterization of the carrier diffusion process based on the diffusion rate D; Under the action of an electric field, the initial spatial distribution of the sample carriers generated by the pump laser with a Gaussian spatial intensity distribution satisfies formula (1): Wherein, n(x, 0) is the spatial distribution of the carriers at the initial moment, x is the spatial position, N is a fitting parameter related to the carrier density, and σ0 is the width of the Gaussian distribution at the initial moment; With the increase of time t, the recombination and spatial diffusion process of the carriers in the x direction is represented as: where n(x, t) is the spatial distribution of carriers at time t, D represents the diffusion rate of the carriers, μ represents the carrier mobility, E represents the electric field intensity, f[n(x, t)] nr represents the rate of decrease in the number of carriers at this point due to non-radiative recombination; f[n(x, t)] r represents the rate of decrease in the number of carriers at this point due to radiative recombination, obtained by equation (3); The spatial distribution I(x, t) of the transient fluorescence image detected in step two satisfies formula (3): I(x, t) ∝ f[n(x, t)] r (3) The diffusion rate D of the carriers is obtained according to formula (1) to formula (3), and is obtained by fitting the spatial distribution of the transient fluorescence image under different time delays.

2. Apparatus for implementing the method of claim 1, characterized in that: It comprises a pump laser, a dichroic mirror, an objective lens, a sample, a mirror, a filter, a plano-convex lens, a gated intensified detector, a control module, an upper computer and a voltage source. The pump laser emitted by the pump laser is introduced into the objective lens through the dichroic mirror and focused on the surface of the sample. The fluorescence emitted by the sample is collimated through the objective lens, and then imaged on the gated intensified detector after passing through the dichroic mirror, the mirror, the filter and the plano-convex lens. The control module is connected with the pump laser, the gated intensified detector and the upper computer, and is used to acquire the transient sample fluorescence images under different time delays. The control module is also connected with the voltage source.

3. The apparatus of claim 2, wherein: The pump laser is a single-color pulse laser with adjustable repetition frequency, and can output a synchronous output signal of the laser.

4. The apparatus of claim 2, wherein: The cutoff wavelength of the dichroic mirror is greater than the wavelength of the laser emitted by the pump laser, so that the emitted pump laser can only be reflected into the objective lens, but cannot be transmitted through the dichroic mirror and enter the gated intensified detector, thereby preventing the gated intensified detector from being irradiated by the intense pump laser.

5. The apparatus of claim 2 wherein: The filter is a band-pass filter used to select the required fluorescence wavelength for transient fluorescence imaging.

6. The apparatus of claim 2, wherein: The synchronous output signal of the pump laser is connected to the control module, and is output after a predetermined time delay, which is used to trigger the gated intensified detector to acquire the transient fluorescence image.

7. The apparatus of claim 2 wherein: The control module is used to adjust the time delay of the synchronous output signal of the pump laser in units of 1 nanosecond.

8. The apparatus of claim 2, wherein: The control module is used to control the voltage source, so as to apply different intensity electric fields to the surface of the sample.

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