System and method for measuring transient response electroluminescence of light emitting diode

Abstract

The invention discloses a system and a method for measuring transient response electroluminescence of a light emitting diode, the system comprises a computer operation module, a voltage pulse input module, a light output detection module and the light emitting diode, the computer operation module comprises a pulse signal control module and a record memory, the control module is used for controlling the function signal generator and recording light output data; the voltage pulse input module comprises a function signal generator and a digital oscilloscope; the light output detection module comprises a photodiode probe and an electrometer and is used for detecting and collecting light output intensity of the light-emitting diode under different voltage pulses. The charge transfer time is determined according to the relation between the light output signal and the applied voltage pulse, the charge transfer distance is determined according to the thickness of the semiconductor film in the light-emitting diode, and the charge mobility of the semiconductor film can be calculated. No additional test sample needs to be prepared for the light-emitting diode, the charge transfer time and mobility in the device can be directly measured in a nondestructive manner, and the method is more convenient and accurate.

Description

Technical Field

[0001] The invention belongs to the technical field of electroluminescent diode device testing, and in particular relates to a system for measuring the transient response electroluminescence of a light emitting diode. Background Art

[0002] An electroluminescent device is a device that converts electrical energy into light energy by utilizing the property of luminescent materials to generate light under the action of an electric field. Among them, light-emitting diodes, as an important type of electroluminescent device in modern display and lighting, have the advantages of high brightness, high contrast, wide color gamut, and flexibility, and are widely used in many fields such as mobile phone screens, wearable display devices, and lighting.

[0003] The principle of electroluminescence of light-emitting diodes is that under the action of an external voltage, electrons and holes are injected from the cathode and anode respectively, and the injected electrons and holes move toward each other under the drive of the electric field until they meet in the light-emitting semiconductor thin film layer for radiative recombination and emit photons. The charge injection, transmission, and recombination processes in the semiconductor light-emitting layer directly affect the performance of light-emitting diode devices. The difference in charge transfer performance between electrons and holes will cause unbalanced charge transfer, which is one of the important factors leading to low device efficiency. In addition, some inevitable traps inside the light-emitting diode will not only hinder charge transfer, but also cause non-radiative recombination, resulting in device efficiency loss and device instability. Therefore, studying the carrier transport process inside the light-emitting diode will help researchers to have a more comprehensive understanding of important information such as carrier dynamics behavior, charge transport characteristics, trap effects, etc. in devices with different structures, which plays a key role in improving material systems and device engineering and improving device performance. Among them, mobility is a key parameter to characterize the charge transport performance of semiconductor materials.

[0004] At present, the measurement methods of mobility mainly include time-of-flight method, space-confined current method, transient electroluminescence method, etc. Among them, the time-of-flight method requires the thickness of the measured sample to reach the micron level, which has a large demand for samples; although the space-confined current method has a lower requirement for the thickness of the test sample (100-300nm), it needs to meet the prerequisite of ohmic injection. In practical applications, most devices are difficult to meet, especially for wide-bandgap blue light-emitting materials, achieving ohmic injection is a challenge. The above methods all require the preparation of additional test samples, which often cannot truly reflect the charge transfer in the light-emitting diode device. One of the key technologies for directly characterizing the charge transfer inside the light-emitting diode device without the need for additional preparation of test samples is the transient electroluminescence method, and its commonly used methods include time-resolved spectroscopy, high-speed photography, etc. Although these methods can achieve the measurement of transient electroluminescence of electroluminescent devices to a certain extent, there are also some problems and shortcomings. For example, the time-resolved spectroscopy method used in the time-resolved spectroscopy rapid measurement system and method (CN202310436246.2) requires a complex optical system and high-speed data acquisition equipment, which is relatively expensive; the high-speed photography method is limited by factors such as frame rate and resolution, and cannot achieve accurate measurement of weak signals.

[0005] Therefore, in view of the shortcomings of the existing technology, a simpler and more efficient method is needed to non-destructively and accurately measure the transient electroluminescence characteristics of light-emitting diodes and study the charge transfer process within light-emitting diode devices. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a system and method for measuring the transient response electroluminescence of a light-emitting diode. By combining a function signal generator and an electrometer, the light output of the light-emitting diode under a voltage pulse with a duration of microseconds can be accurately obtained, and the direct measurement of the transient response electroluminescence signal and charge transfer time of the light-emitting diode with a nanometer-level thin film layer can be achieved, thereby providing an effective solution for characterizing the mobility of semiconductor materials, effectively solving the problems of high cost and low sensitivity in the current transient electroluminescence test, and providing important technical support for the research and application of light-emitting diodes.

[0007] The present invention is achieved by at least one of the following technical solutions.

[0008] A system for measuring transient response electroluminescence of a light emitting diode, comprising: a computer operation module, a voltage pulse input module, a light output detection module and a light emitting diode;

[0009] The computer operation module includes a pulse signal control module and a recording memory;

[0010] The voltage pulse input module includes a function signal generator and a digital oscilloscope; the function signal generator is connected to the light emitting diode, and a voltage pulse is input to the light emitting diode, so that the light emitting diode performs electroluminescence under the voltage pulse; the digital oscilloscope is connected to the function signal generator;

[0011] The light output detection module includes a photodiode probe and an electrometer. The photodiode probe is placed above the light emitting diode and connected to the electrometer to detect the light output intensity of the light emitting diode under the voltage pulse.

[0012] Furthermore, before the function signal generator is connected to the light-emitting diode, a digital oscilloscope is used to calibrate the voltage pulse output by the function signal generator so that the output waveform conforms to the parameters set by the pulse signal control module in the computer, thereby ensuring the accuracy of the voltage pulse;

[0013] Furthermore, the parameters set by the pulse signal control module in the computer include waveform, frequency, voltage waveform amplitude, pulse width, and cycle period, wherein the waveform represents the shape of the output pulse signal, the frequency represents the number of times the pulse signal repeats per unit time, the voltage waveform amplitude represents the value of the applied voltage, the pulse width represents the duration of the applied voltage, and the cycle period represents the time interval from one starting point to the next identical starting point of the pulse signal.

[0014] Furthermore, the function signal generator and the electrometer are connected to a computer via data cables respectively, and the function signal generator is controlled by using a pulse signal control module in the computer to output square wave voltage pulses with different parameters to the light-emitting diode, thereby controlling the electroluminescence of the light-emitting diode; the electroluminescence signal is collected by a photodiode probe located above the light-emitting diode and transmitted to the electrometer for conversion into light output data, which is then transmitted to the computer, and the data is stored in a recording memory in the computer.

[0015] Furthermore, the light-emitting diode can be directly measured without preparing a test sample separately, and the system will not cause physical damage to the light-emitting diode.

[0016] Furthermore, the positive and negative output lines of the function signal generator are connected to the anode and cathode of the light-emitting diode device respectively, so that the function signal generator and the light-emitting diode form a closed loop, and the output voltage pulse can be transmitted to the light-emitting diode to stimulate the light-emitting diode to perform electroluminescence.

[0017] Furthermore, when the light emitting diode performs electroluminescence under a voltage pulse and its light signal is collected by the photodiode probe directly above, the environment is dark, thus preventing the external light signal from affecting the collected data and enhancing the accuracy of the measurement.

[0018] Furthermore, by changing the voltage pulse width and voltage waveform amplitude V applied to the light-emitting diode by the function signal generator through the pulse signal control module, multiple groups of corresponding light output intensities are obtained, so that the functional relationship between pulse width and light output intensity under different voltage pulses can be plotted.

[0019] The method for implementing the system for measuring the transient response electroluminescence of a light emitting diode comprises the following steps:

[0020] Use a data cable to connect the USB ports of the computer host and the function signal generator respectively, and connect the digital oscilloscope probe to the output port of the function signal generator;

[0021] Enter the pulse signal control module in the computer and set the required voltage pulse parameters, including waveform, frequency, voltage waveform amplitude, pulse width, and cycle period;

[0022] The pulse signal control module controls the function signal generator to continuously input voltage pulses to the digital oscilloscope, and the waveform of the pulse as well as the frequency, waveform amplitude, pulse width, and cycle period information are displayed on the digital oscilloscope;

[0023] By comparing the obtained frequency, waveform amplitude, pulse width, and cycle period information with the parameters set in the pulse signal control module, it is detected whether they are consistent with the preset waveform. If not, check the faults in the pulse signal control module and the function signal generator and repair them; if they are consistent, perform subsequent operations.

[0024] Furthermore, when the pulse width is greater than 40μs, the light output intensity increases linearly with the increase of the pulse width, and the intercept of the linear part with the pulse width axis is the delay time between the application of the voltage pulse and the appearance of the light signal, and the delay time represents the measured value τ of the charge transfer time of the semiconductor film in the light-emitting diode; the charge transfer distance of the light-emitting semiconductor film is the film thickness L, and the average electric field strength E=V / L is obtained, where V represents the voltage waveform amplitude, and the charge mobility of the light-emitting semiconductor film to be tested under different electric fields is calculated according to the mobility calculation formula μ=L / (τE).

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention uses a relatively low-cost instrument for simple and effective connection, and without the need to prepare additional test samples, realizes non-destructive measurement of the transient response electroluminescence of the light-emitting diode, thereby determining the charge transfer time and charge mobility of the semiconductor film. The present invention also uses a digital oscilloscope to calibrate the input voltage pulse before actual measurement to ensure the accuracy of the measurement. In addition, the present invention is very sensitive: at low voltage, even if the device emits very little light, light output data can still be obtained, thereby obtaining the charge transfer time in the light-emitting diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a schematic illustration of the present invention, and the above and other objects and features of the present invention will become more intuitive, wherein:

[0028] Figure 1 It is a schematic diagram of the process of the system for measuring the transient response electroluminescence of a light emitting diode according to the present invention;

[0029] Figure 2 A schematic diagram of the structure of the present invention for implementing the calibration function;

[0030] Figure 3 It is a structural schematic diagram of a system for measuring transient response electroluminescence of a light emitting diode according to the present invention;

[0031] Figure 4 is an exemplary test result of an embodiment of the present invention;

[0032] In the figure: 1-computer operation module, 2-voltage pulse input module, 3-light output detection module. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be described in detail and completely in combination with the embodiments of the present invention and the accompanying drawings. However, it should be noted that the embodiments of the present invention are not limited thereto, and all other embodiments obtained by ordinary technicians in the field based on the embodiments and their various features in the present invention are within the scope of protection of the present invention.

[0034] Figure 1 As shown, the system for measuring the transient response electroluminescence of a light emitting diode in this embodiment includes a computer operation module 1, a voltage pulse input module 2, a light output detection module 3 and a light emitting diode.

[0035] The computer operation module 1 includes a pulse signal control module and a recording memory. The computer pulse signal control module (the pulse signal control module can be downloaded from the download area of ​​the official website of the instrument supplier of the function signal generator, such as MFG-2110, MFG-2120, MFG-2120MA, MFG-2130M and other MFG-2000 series models) and the recording memory are used to control the voltage pulse output of the function signal generator and record and save the light output data of the light-emitting diode under each voltage pulse.

[0036] The voltage pulse input module 2 includes a function signal generator and a digital oscilloscope. The function signal generator is connected to a light-emitting diode, receives a square wave voltage pulse from the function signal generator, and performs electroluminescence under the square wave voltage pulse; the digital oscilloscope is connected to the function signal generator, detects the voltage pulse output by the function signal generator, and observes whether the output waveform displayed in the digital oscilloscope meets the set parameters, thereby ensuring the accuracy of the pulse signal.

[0037] The light output detection module 3 includes a photodiode probe and an electrometer, and the photodiode probe and the electrometer are connected by wires. The photodiode probe is placed above the light-emitting diode and connected to the electrometer to detect the light output intensity of the light-emitting diode under the voltage pulse. The photodiode probe is used to collect electroluminescent signals, convert the optical signals into electrical signals, and transmit them to the electrometer for brightness analysis.

[0038] The method for implementing the system for measuring the transient response electroluminescence of a light emitting diode comprises the following steps:

[0039] Before inputting the voltage pulse into the light-emitting diode, the voltage pulse needs to be calibrated first, such as Figure 2 As shown in the figure, the specific connection method is: use a data cable to connect the USB interface of the computer host and the function signal generator respectively, and connect the digital oscilloscope probe to the output port of the function signal generator. The specific operation steps of calibration are:

[0040] Enter the pulse signal control module in the computer and set the required voltage pulse parameters, including waveform, frequency, voltage waveform amplitude, pulse width, and cycle period. The waveform represents the shape of the output pulse signal, the frequency represents the number of times the pulse signal repeats per unit time, the voltage waveform amplitude represents the value of the applied voltage, the pulse width represents the duration of the applied voltage, and the cycle period represents the time interval from one starting point to the next same starting point of the pulse signal.

[0041] Next, the pulse signal control module controls the function signal generator to continuously input voltage pulses to the digital oscilloscope, and the waveform of the pulse can be displayed in the digital oscilloscope.

[0042] Call the display function key in the digital oscilloscope to obtain the frequency, waveform amplitude, pulse width, and cycle period information.

[0043] By comparing the obtained frequency, waveform amplitude, pulse width, and cycle period information with the parameters set in the pulse signal control module, it is detected whether they are consistent with the preset waveform. If not, the pulse signal control module and the function signal generator are checked for faults and repaired; if consistent, subsequent operations can be performed to ensure that the function signal generator can output the required voltage pulse through computer control, thereby improving the accuracy of the measurement.

[0044] Figure 3 The schematic diagram shows the main instrument structure for transient response electroluminescence measurement after calibration. After the connection in the above calibration operation, disconnect the function signal generator from the digital oscilloscope, connect the positive and negative output lines of the function signal generator to the anode and cathode of the light-emitting diode device respectively, so that the square wave voltage pulse output by the function signal generator can be transmitted to the light-emitting diode to stimulate the light-emitting diode to perform electroluminescence. At the same time, a photodiode probe is placed above the light-emitting area of ​​the light-emitting diode to collect the electroluminescence signal of the device, convert the optical signal into an electrical signal, and transmit it to the electrometer to characterize the electroluminescence characteristics of the device. After the electrometer is connected to the computer using a data cable, the light output intensity data of the electrometer in the current mode can be recorded through the recording memory in the computer.

[0045] By changing the voltage pulse width and voltage waveform amplitude V applied by the function signal generator to the device, i.e., the light emitting diode, multiple groups of corresponding light output intensities are obtained, thereby plotting the functional relationship between pulse width and light output intensity under different voltage pulses.

[0046] As an embodiment, when the pulse width is greater than 40μs, the light output intensity increases linearly with the increase of the pulse width, and the intercept of the linear part with the pulse width axis is the delay time between the application of the voltage pulse and the appearance of the light signal, and the delay time represents the measured value τ of the charge transfer time of the semiconductor film in the light-emitting diode; since the charge transfer distance of the light-emitting semiconductor film is the film thickness L, the average electric field strength E=V / L is obtained, and the charge mobility of the light-emitting semiconductor film to be tested under different electric fields is calculated according to the mobility calculation formula μ=L / (τE).

[0047] As an example, Figure 4As shown in the figure, a transient response electroluminescence measurement is performed on a light-emitting diode. The waveform of the voltage pulse input by the function signal generator is a square wave, the frequency is 2kHz, the voltage waveform amplitude is 7V, the pulse width adjustment range is 2 to 200μs, and the pulse cycle is 500μs. By changing the voltage pulse width applied to the device, multiple groups of corresponding light output intensities are obtained, so that the functional relationship between the two can be plotted. Figure 4 It can be observed that in the region where the pulse width is greater than 40μs, the light output intensity increases linearly with the increase of the pulse width. This is because as the pulse width increases, the light output intensity will also increase rapidly. When the pulse width is much larger than the charge transfer time, the light output missing during the transfer period can be ignored, and the functional relationship between the pulse width and the light output intensity will be close to linear behavior. Extrapolating the linear region to when the light output intensity is 0, the intercept with the pulse width axis, that is, the measured value of the charge transfer time, is about 3.4μs. Based on the charge transfer distance of 40nm film thickness, the average electric field intensity can be calculated to be 1.75×10 8 V / m, and the mobility is 6.72×10 -11 m 2 V -1 s -1 .

[0048] The above are embodiments disclosed in the present invention, and the contents described are only for the purpose of facilitating the understanding of the present invention, and are not intended to limit the present invention. For those skilled in the art, various changes may be made to the embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is limited by the claims and equivalents.

Claims

1. A system for measuring the transient response electroluminescence of a light emitting diode, characterized in that: include: Computer operation module, voltage pulse input module, light output detection module and light emitting diode; The computer operation module includes a pulse signal control module and a recording memory; The voltage pulse input module includes a function signal generator and a digital oscilloscope; the function signal generator is connected to the light emitting diode, and a voltage pulse is input to the light emitting diode, so that the light emitting diode performs electroluminescence under the voltage pulse; the digital oscilloscope is connected to the function signal generator; The light output detection module includes a photodiode probe and an electrometer. The photodiode probe is placed above the light emitting diode and connected to the electrometer to detect the light output intensity of the light emitting diode under the voltage pulse.

2. A system for measuring the transient response electroluminescence of a light emitting diode according to claim 1, characterized in that: Before the function signal generator is connected to the light emitting diode, a digital oscilloscope is used to calibrate the voltage pulse output by the function signal generator so that the output waveform conforms to the parameters set by the pulse signal control module in the computer, thereby ensuring the accuracy of the voltage pulse.

3. A system for measuring the transient response electroluminescence of a light emitting diode according to claim 2, characterized in that: The parameters set by the pulse signal control module in the computer include waveform, frequency, voltage waveform amplitude, pulse width, and cycle period, where the waveform represents the shape of the output pulse signal, the frequency represents the number of times the pulse signal repeats per unit time, the voltage waveform amplitude represents the value of the applied voltage, the pulse width represents the duration of the applied voltage, and the cycle period represents the time interval from one starting point to the next identical starting point of the pulse signal.

4. The system for measuring the transient response electroluminescence of a light emitting diode according to claim 1, characterized in that: The function signal generator and the electrometer are connected to the computer through data lines respectively. The pulse signal control module in the computer is used to control the function signal generator to output square wave voltage pulses with different parameters to the light emitting diode, thereby controlling the electroluminescence of the light emitting diode. The electroluminescence signal is collected by a photodiode probe located above the light emitting diode and transmitted to the electrometer for conversion into light output data, which is then transmitted to the computer and stored in the recording memory in the computer.

5. The system for measuring the transient response electroluminescence of a light emitting diode according to claim 1, characterized in that: The light-emitting diode can be directly measured without preparing test samples separately, and the system will not cause physical damage to the light-emitting diode.

6. The system for measuring the transient response electroluminescence of a light emitting diode according to claim 1, characterized in that: The positive and negative output lines of the function signal generator are connected to the anode and cathode of the light-emitting diode device respectively, so that the function signal generator and the light-emitting diode form a closed loop. The output voltage pulse can be transmitted to the light-emitting diode to stimulate the light-emitting diode to perform electroluminescence.

7. The system for measuring the transient response electroluminescence of a light emitting diode according to claim 1, characterized in that: The light emitting diode emits electroluminescence under the voltage pulse, and its light signal is collected by the photodiode probe directly above it in a dark environment, which prevents the external light signal from affecting the collected data and enhances the accuracy of the measurement.

8. The system for measuring the transient response electroluminescence of a light emitting diode according to claim 1, characterized in that: By changing the voltage pulse width and voltage waveform amplitude V applied to the light-emitting diode by the function signal generator through the pulse signal control module, multiple groups of corresponding light output intensities are obtained, so that the functional relationship between pulse width and light output intensity under different voltage pulses can be plotted.

9. A method for implementing a system for measuring transient response electroluminescence of a light emitting diode as claimed in any one of claims 1 to 8, characterized in that: The following steps are involved: Use a data cable to connect the USB ports of the computer host and the function signal generator respectively, and connect the digital oscilloscope probe to the output port of the function signal generator; Enter the pulse signal control module in the computer and set the required voltage pulse parameters, including waveform, frequency, voltage waveform amplitude, pulse width, and cycle period; The pulse signal control module controls the function signal generator to continuously input voltage pulses to the digital oscilloscope, and the waveform of the pulse as well as the frequency, waveform amplitude, pulse width, and cycle period information are displayed on the digital oscilloscope; By comparing the obtained frequency, waveform amplitude, pulse width, and cycle period information with the parameters set in the pulse signal control module, it is detected whether they are consistent with the preset waveform. If not, the pulse signal control module and the function signal generator are checked for faults and repaired; If they are consistent, proceed with the subsequent operation.

10. The system for measuring the transient response electroluminescence of a light emitting diode according to claim 9, characterized in that: When the pulse width is greater than 40μs, the light output intensity increases linearly with the increase of the pulse width, and the intercept of the linear part with the pulse width axis is the delay time between the application of the voltage pulse and the appearance of the light signal. The delay time represents the measured value τ of the charge transfer time of the semiconductor film in the light-emitting diode; the charge transfer distance of the light-emitting semiconductor film is the film thickness L, and the average electric field strength E=V / L is obtained, where V represents the voltage waveform amplitude. The charge mobility of the light-emitting semiconductor film to be tested under different electric fields is calculated according to the mobility calculation formula μ=L / (τE).

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