CN117949414A - Method for evaluating performance aging of micro-nano light-emitting diode - Google Patents
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Abstract
The invention discloses a method for evaluating performance aging of a micro-nano light-emitting diode, which comprises the following steps: acquiring an atomic level crystal structure diagram of a sample to be measured, and obtaining a crystal structure image before irradiation; irradiating a sample to be detected by adopting laser; acquiring an atomic level crystal structure diagram of a sample to be measured after laser irradiation to obtain an irradiated crystal structure image; carrying out Bragg filtering treatment on the crystal structure image before irradiation and the crystal structure image after irradiation; performing image numerical line scanning statistics on the image subjected to Bragg filtering treatment to obtain image numerical comparison diagrams before and after irradiation; and evaluating the aging degree of the sample before and after irradiation according to the image numerical comparison chart before and after irradiation. According to the method for evaluating the performance aging of the micro-nano light-emitting diode, provided by the invention, the influence of thermal stress and electric stress of the micro-nano light-emitting diode in the working period is simulated by taking laser as an excitation mode, and the method has the advantages of short test time and high efficiency.
Description
Technical Field
The invention belongs to the technical field of performance testing of semiconductor materials, and particularly relates to a method for evaluating performance aging of a micro-nano light-emitting diode.
Background
With the rapid development of technology, the photoelectric technology has made remarkable progress in the display field, particularly the wide application of Liquid Crystal Display (LCD) and Organic Light Emitting Diode (OLED) technology, and provides diversified choices for various display devices. These techniques are not only widely used on conventional display devices, but are increasingly dominant in the marketplace. However, with the rise of emerging technologies such as Virtual Reality (VR) and Augmented Reality (AR), more stringent requirements are placed on display devices, particularly in terms of miniaturization. These new applications require smaller size display devices, such as wearable devices like smartwatches, which require not only high brightness and high reliability of the device, but also excellent display.
Under the promotion of such technical requirements, gallium nitride-based micro/nano-scale light emitting diodes (micro/nano-LEDs) are receiving a great deal of attention from researchers at home and abroad. micro/nano-LEDs have significant advantages in terms of display quality, brightness, resolution and energy efficiency compared to existing LCD and OLED technologies. The light-emitting pixel units of the light-emitting diodes are positioned on the micrometer/nanometer level, so that the light-emitting pixel units become a leading edge technology of the novel display field. Gallium nitride-based LEDs are known for their theoretical lifetime of up to tens of thousands of hours, but in practical applications, their light output performance is inevitably attenuated with increasing use time. This degradation in performance makes assessment of its lifetime and reliability particularly important.
Although micro/nano-LEDs have significant advantages in performance, the prior art has significant limitations in assessing its lifetime and reliability. Currently, most evaluation methods are based on electrical tests, such as current-voltage (I-V) characteristic tests. These methods not only have long testing time, which can take hundreds or even thousands of hours, but also have low testing efficiency. More importantly, the existing testing method is mainly aimed at micro-LED arrays, and cannot provide specific information of a single micro-nano structure.
Therefore, in view of the above technical problems, it is necessary to provide a new solution.
Disclosure of Invention
The invention aims to provide a method for evaluating performance aging of a micro-nano light-emitting diode, which has the advantages of short test time and high efficiency, and can test a single micro-nano scale device structure.
In order to achieve the above purpose, the technical scheme provided by the invention is as follows:
The invention provides a method for evaluating performance aging of a micro-nano light-emitting diode, which comprises the following steps:
Acquiring an atomic level crystal structure diagram of a micro-nano light-emitting diode sample to be detected, and obtaining a crystal structure image before irradiation; irradiating a micro-nano light-emitting diode sample to be detected by adopting laser; acquiring an atomic level crystal structure diagram of a micro-nano light-emitting diode sample to be detected after laser irradiation to obtain an irradiated crystal structure image; carrying out Bragg filtering treatment on the crystal structure image before irradiation and the crystal structure image after irradiation; performing image numerical line scanning statistics on the image subjected to Bragg filtering treatment to obtain image numerical comparison diagrams before and after irradiation; and evaluating the aging degree of the micro-nano light-emitting diode sample before and after irradiation according to the image numerical comparison chart before and after irradiation.
In one or more embodiments, the laser irradiation has an irradiation intensity of 1 to 100mJ/cm 2 and an irradiation time of 5 to 60 minutes.
In one or more embodiments, the manner of the bragg filtering process specifically includes:
Performing fast Fourier transform on the crystal structure image before irradiation and the crystal structure image after irradiation, and converting the images from a space domain to a frequency domain; in the frequency domain, the desired diffraction spots are selected for inverse fourier transformation, converting the image from the frequency domain to the spatial domain.
In one or more embodiments, performing image numerical line scanning statistics on an image after the bragg filter treatment to obtain an image numerical contrast chart before and after irradiation, specifically including:
Selecting at least two strip-shaped areas with preset widths perpendicular to the Bragg filtering stripes on the image subjected to the Bragg filtering treatment; and counting the image values at the positions in the strip-shaped area along the extending direction of the selected strip-shaped area so as to generate an image value comparison chart before and after irradiation.
In one or more embodiments, the method further comprises:
and performing geometric phase analysis on the pre-irradiation crystal structure image and the post-irradiation crystal structure image to obtain a pre-irradiation stress distribution diagram and a post-irradiation stress distribution diagram.
In one or more embodiments, geometric phase analysis is performed on the pre-irradiation crystal structure image and the post-irradiation crystal structure image to obtain a pre-irradiation stress distribution map and a post-irradiation stress distribution map, which specifically include:
Respectively selecting a crystal structure image before irradiation and a stress-free area on the crystal structure image after irradiation as reference areas; performing fast Fourier transform on the crystal structure image before irradiation and the crystal structure image after irradiation to obtain phase information of the crystal structure image before irradiation and the crystal structure image after irradiation; the phase of each region of the crystal structure image before irradiation and the phase of each region of the crystal structure image after irradiation are respectively compared with the phase of the corresponding reference region, so that the phase difference of each region of the crystal structure image before irradiation and the phase difference of each region of the crystal structure image after irradiation relative to the corresponding reference region are obtained; the phase difference is converted to stress values and the stress values are mapped to different colors to generate a pre-irradiation stress profile and a post-irradiation stress profile.
In one or more embodiments, the method further comprises:
Carrying out histogram statistics on the stress distribution diagram before irradiation and the stress distribution diagram after irradiation to generate a stress statistics orthographic comparison diagram before and after irradiation; and evaluating the aging degree of the micro-nano light-emitting diode sample before and after irradiation according to the stress statistics orthographic comparison chart before and after irradiation.
In one or more embodiments, the method further comprises:
Acquiring an element surface distribution diagram before irradiation and an element surface distribution diagram after irradiation of a micro-nano light-emitting diode sample to be detected; and determining the element component change condition before and after irradiation of the surface of the micro-nano light-emitting diode sample to be detected according to the element surface distribution diagram before irradiation and the element surface distribution diagram after irradiation.
In one or more embodiments, determining the element composition change before and after irradiation of the surface of the micro-nano light emitting diode sample to be measured according to the element surface distribution diagram before irradiation and the element surface distribution diagram after irradiation specifically includes:
Performing line scanning statistics on the element surface distribution graph before irradiation and the element surface distribution graph after irradiation to generate element content line scanning statistical graphs before irradiation and after irradiation of the surface of the micro-nano light emitting diode sample to be detected; and comparing element content line scanning statistical graphs before irradiation and after irradiation, and determining element component change conditions before and after irradiation of the surface of the micro-nano light emitting diode sample to be detected.
In one or more embodiments, the method further comprises:
And evaluating the aging degree of the micro-nano LED sample before and after irradiation according to the element component change condition of the surface of the micro-nano LED sample to be tested before and after irradiation.
Compared with the prior art, the method for evaluating the performance aging of the micro-nano light-emitting diode provided by the invention applies stress to the micro-nano light-emitting diode by taking laser as an excitation mode so as to simulate the influence of thermal stress and electric stress of the micro-nano light-emitting diode during the working process, has the advantages of short testing time and high efficiency, and can analyze the conditions of lattice damage and atomic adsorption aiming at a single micro-nano scale device structure; meanwhile, the aging performance of the micro-nano light-emitting diode can be quantitatively analyzed through a specific image processing and quantitative statistical method.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and other drawings may be obtained according to the drawings without inventive effort to those skilled in the art.
FIG. 1 is a flow chart of a method for evaluating performance degradation of a micro-nano LED according to an embodiment of the invention;
FIG. 2 is an image of the crystal structure before irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the invention;
FIG. 3 is a graph showing elemental profiles before irradiation of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the invention;
Fig. 4 is a schematic diagram of a structure of an ultrafast laser continuous irradiation GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) in example 1 of the present invention;
fig. 5 is an image of the crystal structure after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure of example 1 of the present invention;
FIG. 6 is a graph showing elemental surface profiles after irradiation of GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structures in example 1 of the invention;
FIG. 7 is a graph showing Bragg filtering in the horizontal direction before irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the present invention;
fig. 8 is a pre-irradiation vertical bragg filter plot of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the present invention;
Fig. 9 is a graph of a horizontal bragg filter after irradiation of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the present invention;
fig. 10 is a vertical bragg filter plot after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure of example 1 of the present invention;
FIG. 11 is a graph showing the stress distribution in the horizontal direction before irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the invention;
Fig. 12 is a graph showing a stress distribution in a vertical direction before irradiation of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the present invention;
Fig. 13 is a graph showing a post-irradiation horizontal stress distribution of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure according to example 1 of the present invention;
Fig. 14 is a graph showing a post-irradiation vertical stress distribution of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the present invention;
fig. 15 is a graph showing the numerical comparison of images in the horizontal direction before and after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure of example 1 of the present invention;
Fig. 16 is a graph showing the numerical comparison of images in the vertical direction before and after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure of example 1 of the present invention;
FIG. 17 is a graph showing the statistical orthographic comparison of stress in the horizontal direction before and after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the invention;
Fig. 18 is a graph showing the stress statistics in the vertical direction before and after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure of example 1 of the present invention;
FIG. 19 is a line scan statistical plot of elemental content prior to irradiation of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the invention;
Fig. 20 is a line scan statistical plot of elemental content after irradiation of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in example 1 of the present invention.
Detailed Description
In order to make the technical solution of the present invention better understood by those skilled in the art, the technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
Throughout the specification and claims, unless explicitly stated otherwise, the term "comprise" or variations thereof such as "comprises" or "comprising" and the like will be understood to include what is stated, without excluding other matters.
In analyzing the prior art, the inventors recognized that while micro-nano LEDs are of great interest for their excellent display performance, existing aging evaluation methods rely mostly on long-term electrical tests, such as current-voltage (I-V) characteristic tests. These conventional methods are typically time consuming and provide limited macroscopic electrical information, lacking insight into the detailed aging process of individual micro-nano structures.
In view of the limitations of the prior art, the core idea of the invention is to realize the efficient aging evaluation of the micro-nano LED by combining the modern imaging technology with the rapid aging simulation method. The technical implementation idea of the invention is as follows: by laser irradiation, the influence of thermal stress and electric stress on the micro-nano light emitting diode during operation is simulated, so that the crystal structure of the micro-nano light emitting diode is changed, such as lattice distortion, defect generation, quantum well width change and the like. These changes affect the electrical and optical properties of the micro-nano leds, such as current-voltage characteristics, optical power, light efficiency, leakage current, etc. Therefore, the aging degree of the micro-nano light emitting diode can be quantitatively or qualitatively estimated by comparing the crystal structure images before and after irradiation.
Referring to fig. 1, a flowchart of a method for evaluating performance degradation of a micro-nano led according to an embodiment of the invention includes the following steps:
s101: and acquiring an atomic level crystal structure diagram of the micro-nano light-emitting diode sample to be detected, and obtaining a crystal structure image before irradiation.
It should be noted that, the atomic-level crystal structure diagram of the micro-nano LED sample obtained before the laser irradiation is that a baseline or reference point can be provided for subsequent comparison, and can be used as a reference basis for subsequent evaluation, so as to accurately measure the influence of the laser irradiation on the crystal structure, thereby ensuring that the change in the evaluation process is caused by the laser irradiation, rather than the initial irregularity of the sample itself. In addition, it provides the necessary underlying data for subsequent image processing and analysis (e.g., bragg filter processing and line scan statistics).
The Transmission Electron Microscope (TEM) can be used for imaging the micro-nano light-emitting diode sample to be detected, and an atomic-level crystal structure image of the sample can be obtained. TEM is a microscope that transmits a sample with electron beams and enlarges the image, can achieve atomic resolution, and is suitable for observing micro-nano material structures.
The micro-nano LED sample to be detected can be imaged by using a scanning transmission electron microscope (Scanning Transmission Electron Microscopy, STEM) to obtain an atomic-level crystal structure image of the micro-nano LED sample.
And the micro-nano light-emitting diode sample to be detected can be measured by utilizing X-ray diffraction (XRD) to obtain an atomic-level crystal structure image of the sample. XRD is a technology for researching the crystal structure of a substance by utilizing the principle of diffraction of X-rays and crystals, can obtain information such as lattice constant, interplanar spacing, crystal face index and the like of the substance, and is suitable for observing the crystal structure and phase composition of a micro-nano material.
S102: and irradiating the micro-nano light-emitting diode sample to be detected by adopting laser.
It should be noted that, the aging process of the micro-nano light emitting diode can be accelerated by irradiating the micro-nano light emitting diode sample with laser, and the influence of thermal stress and electrical stress of the micro-nano light emitting diode during operation is simulated, so that the crystal structure of the micro-nano light emitting diode is changed, and the aging degree of the micro-nano light emitting diode is evaluated. Laser irradiation simulates in principle the aging phenomenon during long-term use by accelerating the recombination of electron-hole pairs and possibly thermal stresses. This rapid aging method can exhibit structural and performance changes that may result from long-term use in a relatively short period of time.
Specifically, ultra-fast laser can be adopted to continuously irradiate the micro-nano light-emitting diode sample to be detected, the irradiation intensity of the laser irradiation is preferably 1-100 mJ/cm 2, and the irradiation time is preferably 5-60 min.
Ultrafast laser refers to laser with pulse width in picosecond (10 -12 seconds) or femtosecond (10 -15 seconds), has extremely high peak power and extremely short acting time, and can effectively couple energy into the sample without damaging the surface of the sample to generate strong nonlinear effects such as multiphoton absorption, self-focusing, plasma formation and the like. These effects can cause dramatic changes in parameters such as local temperature, pressure, electric field, etc. inside the sample, thereby causing distortion of crystal structure, generation of defects, deformation of quantum wells, etc.
The action time of the ultrafast laser is far less than the thermal relaxation time of the sample, so that thermal diffusion and thermal damage can be avoided, and the integrity and stability of the sample are maintained. Meanwhile, due to the extremely short pulse time, the ultrafast laser can rapidly deposit a large amount of energy in a local area without obviously heating the whole sample. This helps to simulate the effect of the high energy environment on micro-nano LEDs without causing comprehensive thermal damage.
Irradiation intensity refers to the energy density of laser light, i.e., the laser energy per unit area. The magnitude of the irradiation intensity determines the effect of the laser on the sample, and too low an irradiation intensity may not cause significant changes in the sample, and too high an irradiation intensity may cause damage or destruction of the sample. The irradiation intensity is limited to 1-100 mJ/cm 2, which is enough to generate a remarkable stress effect on the micro-nano LED without directly damaging the material.
The irradiation time refers to the time of action of the laser on the sample, i.e. the total duration of continuous irradiation. The irradiation time determines the action degree of the laser on the sample, and too short irradiation time may not simulate the actual working condition of the micro-nano light emitting diode, and too long irradiation time may cause excessive aging or failure of the sample. The irradiation time is limited to 5-60 min in order to simulate the long-term aging process in a controlled range. A shorter time (e.g., 5 minutes) is sufficient to observe the preliminary signs of aging, while a longer time (e.g., 60 minutes) may simulate more severe aging effects.
S103: and acquiring an atomic level crystal structure diagram of the micro-nano light-emitting diode sample to be detected after laser irradiation, and obtaining an irradiated crystal structure image.
By acquiring an image of the crystal structure after irradiation, a lattice change due to laser irradiation can be directly observed. These changes may include stretching of the crystal lattice, formation or addition of dislocations, and other microstructural changes. By comparing with the crystal structure image before irradiation, specific changes caused by irradiation can be definitely determined, so that the aging degree of the LED is quantitatively analyzed.
S104: and carrying out Bragg filtering treatment on the crystal structure image before irradiation and the crystal structure image after irradiation.
The method can improve the quality and the analyzability of the image by the Bragg filtering process, eliminate noise and artifacts in the image, strengthen lattice characteristics in the image, and facilitate the subsequent numerical line scanning statistics of the image, thereby more clearly observing and comparing the changes of lattices before and after irradiation.
In an exemplary embodiment, the manner of the bragg filtering process specifically includes: performing fast Fourier transform on the crystal structure image before irradiation and the crystal structure image after irradiation, and converting the images from a space domain to a frequency domain; in the frequency domain, the desired diffraction spots are selected for inverse fourier transformation, converting the image from the frequency domain to the spatial domain.
The Bragg filtering processing mode is an image processing method for realizing space frequency selection by utilizing Fourier transformation and inverse Fourier transformation, and different space frequency components can be selected or prevented according to Bragg conditions, so that the effect of enhancing the image or reducing the noise is achieved.
Fourier transform is a mathematical method of converting an image from the spatial domain to the frequency domain, and the brightness distribution of the image can be represented as a superposition of sine waves of different spatial frequencies, thereby revealing the frequency characteristics of the image. Spatial frequency refers to how fast the brightness changes in an image, high spatial frequency corresponds to details and edges in the image, and low spatial frequency corresponds to smooth and background in the image.
The inverse fourier transform is a mathematical method of converting an image from the frequency domain back to the spatial domain, and can restore the frequency characteristics of the image to a luminance distribution, thereby reconstructing the spatial characteristics of the image.
The Bragg filtering processing mode has the function of selecting a required diffraction spot to carry out inverse Fourier transform according to Bragg conditions in a frequency domain, so that an enhanced or noise-reduced image is obtained. The bragg condition refers to that when incident light diffracts a crystal, only light waves satisfying the following relationship are reflected or refracted:
nλ＝2dsinθ
where n is an integer, λ is the wavelength of light, d is the interplanar spacing, and θ is the angle of incidence.
Depending on the bragg condition, different interplanar spacings, and thus different spatial frequency components, may be selected according to different wavelengths of light and angles of incidence. For example, if it is desired to enhance lattice features in an image, spatial frequency components that match the lattice period may be selected, and if it is desired to reduce noise and artifacts in the image, spatial frequency components that are independent of noise and artifacts may be selected.
The crystal structure images before and after irradiation can be subjected to customized treatment in a Bragg filtering treatment mode, so that the quality and the analyzability of the images are improved, the subsequent image numerical line scanning statistics is facilitated, and the aging degree of the micro-nano light emitting diode is estimated more accurately.
S105: and carrying out image numerical line scanning statistics on the image subjected to Bragg filtering treatment to obtain image numerical comparison diagrams before and after irradiation.
It should be noted that line scan statistics can provide information about the variation of pixel intensity along a particular path, which can help quantitatively analyze changes in lattice structure, such as lattice distortion, dislocations, or changes in lattice spacing. This method allows analysis of crystal structure changes not only to qualitative observations but also to make quantitative comparisons. Line scan statistics provide a more accurate and intuitive means of analysis, particularly when evaluating microstructural changes in a material.
A specific line scan path may be selected in the crystal structure images before and after irradiation after the bragg filter process. These paths should represent regions of interest in the crystal structure, such as lattice arrangements or defect sites. Along the selected path, the image values (the image values are the real parts of the complex image after Bragg filtering, and the image intensity (state density) and phase (lattice periodicity) are comprehensively reflected), which are usually pixel intensity values (which can be automatically finished by image processing software). Statistical analysis is performed on the collected data, such as calculating intensity distribution, contrast variation, etc. along the scan line. And (5) according to the line scanning statistical result of the images before and after irradiation, making an image numerical comparison chart. These contrast plots can visually show the change in crystal structure before and after irradiation.
In an exemplary embodiment, at least two strip-shaped regions perpendicular to the predetermined width of the bragg filter stripes may be selected on the bragg-filtered image; and counting the image values at the positions in the strip-shaped area along the extending direction of the selected strip-shaped area so as to generate an image value comparison chart before and after irradiation.
And carrying out image numerical value line scanning statistics on the image subjected to Bragg filtering treatment by using the gray level histogram to obtain image numerical value contrast pictures before and after irradiation. Gray level histograms are statistical methods that reflect the frequency of occurrence of each gray level in an image and can describe the gray level distribution and contrast of an image.
S106: and evaluating the aging degree of the micro-nano light-emitting diode sample before and after irradiation according to the image numerical comparison chart before and after irradiation.
The degree of aging can be quantified from the changes displayed in the image numerical comparison map by analyzing the image numerical comparison map before and after irradiation generated in step S105 in detail. By combining quantitative image analysis results with performance characteristics of LEDs, the effect of aging on material and device performance can be more accurately assessed.
In an exemplary embodiment, the method for evaluating performance degradation of a micro-nano light emitting diode provided by the present invention further includes: and performing Geometric Phase Analysis (GPA) on the pre-irradiation crystal structure image and the post-irradiation crystal structure image to obtain a pre-irradiation stress distribution diagram and a post-irradiation stress distribution diagram.
It should be noted that, the displacement field and the strain field of the image can be extracted by GPA, so as to obtain stress distribution diagrams before and after irradiation, so as to quantitatively evaluate the deformation and damage of the micro-nano led crystal structure by the laser irradiation.
And performing geometric phase analysis on the crystal structure images before and after irradiation by using a geometric phase analysis method (GPA) to obtain stress distribution diagrams before and after irradiation. GPA is an image processing method for realizing space frequency selection by utilizing Fourier transform and inverse Fourier transform of an image, and the displacement field and the strain field of the image can be calculated according to different diffraction vectors, so that a stress distribution diagram of the image is obtained.
Specifically, a stress-free region on the crystal structure image before irradiation and a stress-free region on the crystal structure image after irradiation can be selected as reference regions respectively; performing fast Fourier transform on the crystal structure image before irradiation and the crystal structure image after irradiation to obtain phase information of the crystal structure image before irradiation and the crystal structure image after irradiation; the phase of each region of the crystal structure image before irradiation and the phase of each region of the crystal structure image after irradiation are respectively compared with the phase of the corresponding reference region, so that the phase difference of each region of the crystal structure image before irradiation and the phase difference of each region of the crystal structure image after irradiation relative to the corresponding reference region are obtained; the phase difference is converted to stress values and the stress values are mapped to different colors to generate a pre-irradiation stress profile and a post-irradiation stress profile.
Further, histogram statistics can be carried out on the stress distribution diagram before irradiation and the stress distribution diagram after irradiation, and a stress statistics orthographic comparison diagram before and after irradiation is generated; and evaluating the aging degree of the micro-nano light-emitting diode sample before and after irradiation according to the stress statistics orthographic comparison chart before and after irradiation. Histogram statistics and comparison provide an effective way to quantify and visualize changes in stress distribution during aging. This helps to quantify the dynamic change in stress of the material during aging.
In an exemplary embodiment, the method for evaluating performance degradation of a micro-nano light emitting diode provided by the present invention further includes: acquiring an element surface distribution diagram before irradiation and an element surface distribution diagram after irradiation of a micro-nano light-emitting diode sample to be detected; and determining the element component change condition before and after irradiation of the surface of the micro-nano light-emitting diode sample to be detected according to the element surface distribution diagram before irradiation and the element surface distribution diagram after irradiation.
And analyzing whether the element components on the surface of the sample change and the degree and rule of the change by comparing the distribution diagrams of the element surfaces before and after the laser irradiation of the micro-nano light-emitting diode sample so as to evaluate the influence of the irradiation on the micro-nano light-emitting diode sample.
Specifically, line scanning statistics can be carried out on the element surface distribution diagram before irradiation and the element surface distribution diagram after irradiation, so as to generate element content line scanning statistical diagrams before irradiation and after irradiation of the surface of the micro-nano light emitting diode sample to be detected; and comparing element content line scanning statistical graphs before and after irradiation to determine element component change conditions before and after irradiation of the micro-nano light emitting diode sample surface to be detected.
The elemental composition of the material surface can be accurately determined using techniques such as energy dispersive X-ray spectroscopy (EDX). The element content line scanning statistical diagram is a line diagram taking a scanning line as a horizontal axis and taking element content as a vertical axis, and can reflect element content distribution conditions of the sample surface at different positions. The element content line scanning statistical graph before and after irradiation can be horizontally or vertically compared to observe the element content change condition of the sample surface at the same position or different positions.
The method enables quantitative evaluation of chemical changes which can occur in the micro-nano LED material in the laser irradiation process. For example, oxidation or reduction reactions due to laser irradiation may be detected, and these chemical changes may affect the optical and electrical properties of the material.
Furthermore, the aging degree of the micro-nano LED sample before and after irradiation can be estimated according to the element composition change condition of the micro-nano LED sample before and after irradiation.
Based on the obtained profiles of the elemental surfaces before and after irradiation, chemical changes on the material surface, such as increases or decreases in the content of specific elements or the appearance of new elements, can be analyzed. The change in elemental composition is correlated to the degree of aging of the LED, and the elemental composition change is used as an indicator of the degree of aging. For example, an increase in the degree of surface element oxidation may indicate more severe aging.
The invention will be further illustrated with reference to specific examples.
Example 1
Acquiring an atomic resolution High Angle Annular Dark Field (HAADF) image of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure before irradiation to obtain a crystal structure image before irradiation (shown in figure 2); in the annular dark field mode of the scanning transmission electron microscope, a detector with annular design is used for collecting high-angle incoherent scattered electrons, the contrast of the obtained image is related to atomic number, and the change of chemical components at different positions in a sample can be reflected.
A pre-irradiation elemental profile of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure (as shown in fig. 3) was obtained using TEM-EDX, and the number of bright spots represented the content of the corresponding element at that location. The elements tested are Si, O, N, ga, etc.
The GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure was continuously irradiated with an ultrafast laser having an irradiation intensity of 10mJ/cm 2 for 30min. Fig. 4 is a schematic diagram of an ultrafast laser continuous irradiation GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure.
And obtaining an atomic resolution High Angle Annular Dark Field (HAADF) image of the irradiated GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure, and obtaining an irradiated crystal structure image (shown in figure 5). A post-irradiation elemental profile of a GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure was obtained using TEM-EDX (as shown in fig. 6), and the number of bright spots represents the content of the corresponding element at that location. The elements tested are Si, O, N, ga, etc.
The pre-irradiation crystal structure image and the post-irradiation crystal structure image of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure are respectively subjected to Bragg filtering in the horizontal direction and the vertical direction to obtain a pre-irradiation horizontal Bragg filtering diagram (shown in figure 7), a pre-irradiation vertical Bragg filtering diagram (shown in figure 8), a post-irradiation horizontal Bragg filtering diagram (shown in figure 9) and a post-irradiation vertical Bragg filtering diagram (shown in figure 10). As can be seen from fig. 7-10, the filtering stripes of the sample before laser irradiation are uniform and clear, and the uniformity of the stripe contrast after laser irradiation is reduced, the stripes are bent and even dislocation appears, which reflects that the lattice of the GaN nanowire material is damaged after the stress is applied by the laser irradiation.
Geometric Phase Analysis (GPA) is respectively carried out on a pre-irradiation crystal structure image and a post-irradiation crystal structure image of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure in the horizontal direction and the vertical direction to obtain a pre-irradiation horizontal direction stress distribution diagram (shown in figure 11), a pre-irradiation vertical direction stress distribution diagram (shown in figure 12), a post-irradiation horizontal direction stress distribution diagram (shown in figure 13) and a post-irradiation vertical direction stress distribution diagram (shown in figure 14). In GPA processing, the stress-free position on the crystal structure image is selected as a reference area, the color of the stress field distribution diagram is the stress of the corresponding position of the crystal structure image relative to the reference area, the positive value is the tensile stress, the negative value is the compressive stress, and the larger the numerical value is, the larger the stress is, namely the more serious the lattice deformation is. As can be seen from fig. 11 to 14, the stress before laser irradiation is small, the stress after laser irradiation is increased, the lattice is deformed, and the disorder of atomic arrangement occurs, and the dislocation is increased.
Image numerical line scan statistics were performed on bragg filter plots of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure before and after irradiation to generate image numerical comparison plots of the horizontal and vertical directions before and after irradiation (as shown in fig. 15 and 16). The processing method is to select a strip-shaped area perpendicular to the stripes on the graph, and the width of the selected area is 5 pixels, as shown by the areas selected by the red and blue frames in fig. 7-10. The image values in this area are averaged in the width direction to obtain the image value comparison diagrams shown in fig. 15 and 16. The blue lines of fig. 7 and 8 correspond to the blue dotted line in fig. 15, and the red lines of fig. 7 and 8 correspond to the red solid line in fig. 15; the blue lines of fig. 9 and 10 correspond to the blue dotted lines in fig. 16, and the red lines of fig. 9 and 10 correspond to the red solid lines in fig. 16. The dislocation of the extreme values of the red and blue lines in fig. 15 and 16 shows the deformation condition of the crystal lattice. The statistical mode can be used for comparing the Bragg filter fringes more intuitively and easily. And counting the number and offset of extremum dislocation in the images before and after irradiation, wherein the extremum dislocation phenomenon occurs at 15 places in a 17 x 17nm area in the figure, and the damage degree caused by laser irradiation can be estimated according to the number.
Statistical histograms are respectively performed on numerical values in stress distribution diagrams before and after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure to generate stress statistical orthographic comparison diagrams (shown in fig. 17 and 18) of the horizontal direction and the vertical direction before and after irradiation. The absolute value of the horizontal axis in fig. 17 and 18 is closer to 0, indicating that the smaller the stress, the larger the width of the statistical map, and the lower the peak value, the larger the stress, and the more serious the lattice deformation. As can be seen from fig. 17 and 18, the stress in both directions is concentrated near the zero point before the laser irradiation, indicating that the stress is smaller, the points where the stress is larger are increased after the laser irradiation, and the stress statistical histogram is widened. The statistical method can quantitatively show the stress variation degree of the material before and after laser irradiation, and compare the full width at half maximum (FWHM) of the statistical histogram before and after the laser irradiation, for example, in FIG. 18, the FWHM of the statistical histogram before the laser irradiation is 3.87%, the ratio of the FWHM after the irradiation to the FWHM before the irradiation is 1.56, and the numerical value can show the damage degree of the sample under the laser irradiation, and the larger the numerical value is, the more serious the lattice damage degree is.
Line scan statistics (red arrows in fig. 3 and 6 represent scan paths) are performed on the element plane distribution diagram (fig. 3) before irradiation and the element plane distribution diagram (fig. 6) after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure, so as to generate element content line scan statistics diagrams (shown in fig. 19 and 20) before irradiation and after irradiation of the GaN nanowire-Quantum Dot (QD)/Quantum Well (QW) structure surface. The change in element content before and after irradiation can be seen from fig. 19 and 20.
In summary, according to the method for evaluating the performance aging of the micro-nano light emitting diode provided by the invention, the stress is applied to the micro-nano light emitting diode by taking laser as an excitation mode so as to simulate the influence of thermal stress and electric stress suffered by the micro-nano light emitting diode during the working process, and the method has the advantages of short testing time and high efficiency, and can analyze the conditions of lattice damage and atomic adsorption aiming at a single micro-nano scale device structure; meanwhile, the aging performance of the micro-nano light-emitting diode can be quantitatively analyzed through a specific image processing and quantitative statistical method.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.
Claims (10)
1.A method for evaluating performance degradation of a micro-nano light emitting diode, comprising:
Acquiring an atomic level crystal structure diagram of a micro-nano light-emitting diode sample to be detected, and obtaining a crystal structure image before irradiation;
irradiating a micro-nano light-emitting diode sample to be detected by adopting laser;
acquiring an atomic level crystal structure diagram of a micro-nano light-emitting diode sample to be detected after laser irradiation to obtain an irradiated crystal structure image;
Carrying out Bragg filtering treatment on the crystal structure image before irradiation and the crystal structure image after irradiation;
Performing image numerical line scanning statistics on the image subjected to Bragg filtering treatment to obtain image numerical comparison diagrams before and after irradiation;
and evaluating the aging degree of the micro-nano light-emitting diode sample before and after irradiation according to the image numerical comparison chart before and after irradiation.
2. The method for evaluating the performance aging of a micro-nano light emitting diode according to claim 1, wherein the irradiation intensity of the laser irradiation is 1-100 mJ/cm 2 and the irradiation time is 5-60 min.
3. The method for evaluating performance degradation of a micro-nano led according to claim 1, wherein the bragg filter processing method specifically comprises:
Performing fast Fourier transform on the crystal structure image before irradiation and the crystal structure image after irradiation, and converting the images from a space domain to a frequency domain;
in the frequency domain, the desired diffraction spots are selected for inverse fourier transformation, converting the image from the frequency domain to the spatial domain.
4. The method for evaluating performance aging of a micro-nano light emitting diode according to claim 1, wherein the image after bragg filtering is subjected to image numerical line scanning statistics to obtain an image numerical comparison chart before and after irradiation, specifically comprising:
Selecting at least two strip-shaped areas with preset widths perpendicular to the Bragg filtering stripes on the image subjected to the Bragg filtering treatment;
And counting the image values at the positions in the strip-shaped area along the extending direction of the selected strip-shaped area so as to generate an image value comparison chart before and after irradiation.
5. The method of evaluating performance degradation of a micro-nano light emitting diode of claim 1, further comprising:
and performing geometric phase analysis on the pre-irradiation crystal structure image and the post-irradiation crystal structure image to obtain a pre-irradiation stress distribution diagram and a post-irradiation stress distribution diagram.
6. The method for evaluating the performance degradation of a micro-nano light emitting diode according to claim 5, wherein the geometric phase analysis is performed on the pre-irradiation crystal structure image and the post-irradiation crystal structure image to obtain a pre-irradiation stress distribution map and a post-irradiation stress distribution map, and the method specifically comprises:
Respectively selecting a crystal structure image before irradiation and a stress-free area on the crystal structure image after irradiation as reference areas;
Performing fast Fourier transform on the crystal structure image before irradiation and the crystal structure image after irradiation to obtain phase information of the crystal structure image before irradiation and the crystal structure image after irradiation;
The phase of each region of the crystal structure image before irradiation and the phase of each region of the crystal structure image after irradiation are respectively compared with the phase of the corresponding reference region, so that the phase difference of each region of the crystal structure image before irradiation and the phase difference of each region of the crystal structure image after irradiation relative to the corresponding reference region are obtained;
the phase difference is converted to stress values and the stress values are mapped to different colors to generate a pre-irradiation stress profile and a post-irradiation stress profile.
7. The method of evaluating performance degradation of a micro-nano light emitting diode of claim 5, further comprising:
carrying out histogram statistics on the stress distribution diagram before irradiation and the stress distribution diagram after irradiation to generate a stress statistics orthographic comparison diagram before and after irradiation;
And evaluating the aging degree of the micro-nano light-emitting diode sample before and after irradiation according to the stress statistics orthographic comparison chart before and after irradiation.
8. The method of evaluating performance degradation of a micro-nano light emitting diode of claim 1, further comprising:
Acquiring an element surface distribution diagram before irradiation and an element surface distribution diagram after irradiation of a micro-nano light-emitting diode sample to be detected;
And determining the element component change condition before and after irradiation of the surface of the micro-nano light-emitting diode sample to be detected according to the element surface distribution diagram before irradiation and the element surface distribution diagram after irradiation.
9. The method for evaluating the performance aging of a micro-nano led according to claim 8, wherein determining the element composition change before and after the irradiation of the surface of the micro-nano led sample to be tested according to the element profile before the irradiation and the element profile after the irradiation specifically comprises:
performing line scanning statistics on the element surface distribution graph before irradiation and the element surface distribution graph after irradiation to generate element content line scanning statistical graphs before irradiation and after irradiation of the surface of the micro-nano light emitting diode sample to be detected;
And comparing element content line scanning statistical graphs before irradiation and after irradiation, and determining element component change conditions before and after irradiation of the surface of the micro-nano light emitting diode sample to be detected.
10. The method of assessing the performance degradation of a micro-nano led of claim 8, further comprising:
And evaluating the aging degree of the micro-nano LED sample before and after irradiation according to the element component change condition of the surface of the micro-nano LED sample to be tested before and after irradiation.
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