Test system and characterization method for electroluminescence characteristics of micro-led device

Abstract

Disclosed in the present invention are a test system for electroluminescence (EL) characteristics of a micro-LED device. The test system comprises: an alternating-current voltage signal source, which provides an alternating-current voltage signal; a conductive test stage, which comprises a base and a contact probe, wherein the base is made of a conductive material and is configured to place a sample to be tested, the contact probe contains a conductive material and is configured to form electrical contact with said sample, and during testing, said sample is placed on the base, and an alternating-current voltage generated by the alternating-current voltage signal source is applied to said sample by means of the contact probe, the magnitude of the alternating-current voltage being sufficient to drive said sample to emit light; a set of series resistors, which is configured to be connected in series with said sample; and a detection instrument. The present invention overcomes the problems of etching damage and complex operations caused by metal contact in a conventional EL detection method and the problem of inaccurate spectral testing in a PL detection method, achieves a new EL characterization means that requires no pretreatment and is simple and efficient, and is applicable to rapid testing and performance evaluation of a plurality of material systems and light-emitting devices.

Description

Testing System and Characterization Method for Electroluminescence Properties of Micro-LED Devices Technical Field

[0001] This invention relates to a testing system and characterization method for the electroluminescence properties of Micro-LED devices, belonging to the field of optoelectronic technology. Background Technology

[0002] Gallium nitride (GaN)-based micro-LEDs are widely considered a significant breakthrough in display technologies such as flat panel displays, virtual reality (VR), and augmented reality (AR) due to their superior characteristics, including high pixel density, high brightness, and long lifespan. To achieve high-quality micro-LED displays, it is essential to ensure a high degree of consistency in the wavelength and brightness of the LED chips. However, due to the physical properties of GaN materials, their epitaxial growth is susceptible to factors such as high dislocation density, thin film stress, and microsystem defects, leading to a decline in material quality and unavoidable deviations in wavelength and brightness of individual chips during mass production.

[0003] Existing methods for measuring the photoelectric performance of semiconductor light-emitting device wafers mainly include photoluminescence (PL) detection and electroluminescence (EL) detection. PL detection, as a non-destructive method, utilizes short-wavelength lasers to excite multiple quantum well (MQW) layers to analyze their luminescence performance. However, the spectral signal obtained by PL measurement originates from all quantum well layers, rather than specific electron or hole injection regions. Therefore, for semiconductor light-emitting devices with pre-layered or multi-well systems, PL measurement may lead to spectral information deviations. Furthermore, PL detection is susceptible to ambient light interference, affecting the accuracy and consistency of the measurement.

[0004] In contrast, EL (electroluminescent) detection can directly evaluate the electrical and optical performance of semiconductor light-emitting devices, and the test results are more representative. However, traditional EL detection requires techniques such as indium embrittlement, laser ablation, and electrode evaporation to form electrodes on the wafer, followed by applying voltage through a micro-electrical probe to inject charge carriers. These processes can cause localized mechanical damage to the wafer, affecting the device's light-emitting characteristics and reliability. Furthermore, the fabrication of n-type or p-type electrodes adds extra processing steps, making the detection process more complex and somewhat destructive.

[0005] To overcome the limitations of traditional electroluminescence (EL) testing, AC-driven non-destructive EL detection methods have been proposed in recent years. This method uses AC drive, utilizing charge induction to cause electrons to drift to the MQW region under the influence of an AC electric field, thus achieving non-destructive EL measurement. However, existing AC-driven EL testing technology is still in the exploratory stage. The correlation between the EL luminescence characteristics in AC-driven mode and traditional DC EL testing is unclear, and its applicability to different material systems and light-emitting device systems has not been fully established, limiting its practical application in the field of semiconductor light-emitting device wafer inspection. Therefore, there is an urgent need for a non-destructive, efficient, and accurate wafer optoelectronic performance testing method applicable to various semiconductor light-emitting devices to overcome the shortcomings of existing technologies and improve the reliability and consistency of LED wafer optoelectronic performance testing. Technical issues

[0006] This invention discloses a testing system for the electroluminescence properties of a device, in order to solve the aforementioned problems existing in the prior art. Technical solutions

[0007] The technical solution adopted in this invention is as follows:

[0008] A testing system for the electroluminescence properties of a device, comprising:

[0009] An AC voltage signal source provides an AC voltage signal;

[0010] A conductivity test stage includes a conductive substrate and contact probes. The conductive substrate is made of sheet-like, thin-film, or layered metal electrodes and is used to place the sample to be tested. The contact probes are typically metal probes such as tungsten probes, beryllium copper probes, tungsten-rhenium alloy probes, and gold probes, used to form electrical contact with the sample to be tested. Alternatively, they can be ITO films grown on wafers. During testing, the sample to be tested is placed on the substrate, and an AC voltage generated by an AC voltage signal source is applied to the sample to be tested through the contact probes. The magnitude of the AC voltage is sufficient to drive the sample to emit light.

[0011] A series resistor, one end of which is electrically connected to a conductive substrate, and the other end is connected to an AC voltage signal source, is used to form a series connection with the sample to be tested;

[0012] Waveform detection equipment is used to monitor the input AC voltage of the sample under test, as well as the voltage of the voltage divider circuit of the series resistor;

[0013] Spectroscopic analysis equipment is used to detect the emission spectrum and peak wavelength of a sample under AC drive.

[0014] A luminescence intensity detection device to analyze the time-resolved electroluminescence intensity of a sample.

[0015] Preferably, the AC voltage signal source includes an arbitrary waveform generator and a voltage amplifier connected in signal connection.

[0016] Preferably, the waveform detection device is a dual-channel oscilloscope.

[0017] Preferably, the spectral analysis device is a spectrometer.

[0018] Preferably, the luminous intensity detection device is a photodetector.

[0019] The present invention also discloses the application of the above-mentioned testing system in measuring the electroluminescence characteristics of devices.

[0020] Preferably, the device has the characteristic of emitting light under a certain voltage, and can be a semiconductor device including at least an electron injection layer, a radiation recombination layer, and a hole injection layer, such as GaN LED, GaAs LED, perovskite LED, OLED and other semiconductor light-emitting device wafers, or a semiconductor photoelectric conversion device with light absorption characteristics that can generate photogenerated carriers under illumination, such as silicon-based solar cells, GaAs-based solar cells, perovskite solar cells or organic solar cells.

[0021] Preferably, the steps include:

[0022] (1) Place the sample to be tested on a conductive substrate, and use an arbitrary waveform generator to apply a preset AC voltage signal to the sample to be tested through a contact probe via a high voltage amplifier. For example, a sine wave, square wave, triangle wave or custom waveform can be used.

[0023] (2) The waveform detection equipment monitors the input AC voltage of the sample under test and the voltage of the voltage divider circuit of the series resistor. The instantaneous AC current density of the sample under test is obtained by calculation. The measured input AC voltage is used not only to analyze the current-voltage characteristics, but also to prepare data for the study of the change law of electroluminescence intensity and spectral characteristics of the sample with driving voltage, the calculation of external quantum efficiency and the inference of dynamic response, and to facilitate monitoring and protection.

[0024] The spectral analysis equipment measures the emission spectrum of the sample under different alternating current densities and records its peak wavelength;

[0025] The luminescence intensity detection device collects the instantaneous luminous power of the sample under test;

[0026] (3) Calculate the ratio of instantaneous light power to instantaneous alternating current density to characterize the external quantum efficiency of the sample under test at the alternating current density.

[0027] The use of waveform detection equipment to monitor the input AC voltage of the sample serves several purposes. First, it allows for the analysis of the sample's voltage-current characteristics. Second, it enables the analysis of how the sample's electroluminescence intensity and spectral characteristics change with the driving voltage. Third, it allows for the calculation of the external quantum efficiency using the input voltage, instantaneous current density, and output optical power. Fourth, it allows for the analysis of the capacitance effect by measuring the input voltage, and by combining this with the instantaneous current density, it allows for the deduction of influencing factors such as parasitic resistance and capacitance. Fifth, it also serves a monitoring and protection function, preventing damage to the sample due to excessive voltage.

[0028] Preferably, the formula for calculating the instantaneous alternating current density is: ,in The instantaneous voltage across the series resistor as measured by the waveform detection equipment. This is the series resistance value. The effective luminescent area of ​​the sample to be tested refers to the area where the device actually participates in luminescence, which can be determined by observing the local luminescence using a near-field scanning optical microscope.

[0029] Preferably, the formula for calculating the external quantum efficiency is: ,in The instantaneous photopower measured by the luminous intensity detection device. The effective luminescent area of ​​the sample to be tested. For electron charge , Planck's constant , The photon frequency can be calculated from the wavelength. Received, among which It is the speed of light in a vacuum, and its standard value is taken as 1. It is the peak wavelength measured by the spectral analysis equipment.

[0030] Based on the measured current density, peak wavelength, and external quantum efficiency, the luminescence performance of the sample under different driving conditions can be analyzed. Beneficial effects

[0031] (1) The present invention adopts an AC driving method to realize electroluminescence testing of semiconductor light-emitting device wafers without direct carrier injection through charge induction effect, avoiding the physical electrode preparation process of wafers in traditional testing methods, thereby effectively reducing damage to semiconductor light-emitting device wafers and improving the repeatability of testing and device reliability.

[0032] (2) The testing method of the present invention only requires placing the light-emitting device wafer on the metal base plate of the conductive test stage and applying an AC voltage signal directly through the contact probe to perform electroluminescence testing. No additional electrode preparation is required, which greatly simplifies the detection process and improves the detection efficiency. It is suitable for rapid screening and evaluation of large-scale semiconductor light-emitting device wafers.

[0033] (3) The test system is compatible with a variety of semiconductor light-emitting devices, has a wide range of applications, can support a variety of driving waveforms, realize flexible testing, and provide rich experimental data support for the design optimization of different material systems and device systems. Attached Figure Description

[0034] Figure 1 is a schematic diagram of the cross-sectional system of the micro-LED wafer under test in the electroluminescence testing system based on GaN-based micro-LED of the present invention;

[0035] Figure 2 is a schematic diagram of the testing system of the electroluminescence testing system based on GaN-based micro-LED of the present invention;

[0036] Figure 3 shows the illumination diagram of the micro-LED in AC driving mode and its corresponding voltage and current density characteristic curves in the electroluminescence characterization method based on GaN micro-LED of the present invention.

[0037] Figure 4 is a comparison of the peak wavelengths of blue and green micro-LEDs in DC and AC driving modes in the electroluminescence characterization method based on GaN micro-LED of the present invention.

[0038] Figure 5 is a comparison of the external quantum efficiency (EQE) of blue and green micro-LEDs in DC and AC driving modes in the electroluminescence characterization method based on GaN micro-LEDs of the present invention. The best embodiment of the present invention

[0039] The present invention will be further described below with reference to the embodiments, but the description of the embodiments does not limit the scope of protection of the present invention in any way.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. Furthermore, while this document provides examples of parameters containing specific values, it should be understood that the parameters need not be exactly equal to the corresponding values, but can approximate the corresponding values ​​within acceptable error tolerances or design constraints. Directional terms mentioned in the embodiments, such as “up,” “down,” “front,” “back,” “left,” “right,” etc., are only for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the scope of protection of this invention.

[0041] Unless otherwise specified, all substances or instruments used in the following examples can be obtained from conventional commercial sources. Embodiments of the present invention

[0042] Example 1: A rapid measurement test system and characterization method for GaN-based micro-LED wafers:

[0043] (1) Referring to Figure 1, a schematic diagram of the cross-sectional structure of the micro-LED wafer under test. InGaN / GaN green and blue LED wafers grown on a 450μm sapphire substrate 1 by metal-organic chemical vapor deposition (MOCVD) contain an InGaN layer 2, an n-GaN layer 3, a multiple quantum well (MQW) layer 4, and a p-GaN layer 5. This wafer is used as the test sample.

[0044] (2) Refer to Figure 2, a schematic diagram of the test system. The LED wafer is placed on the metal base plate 6 in the center area of ​​the cleaned conductive test platform, with the metal base plate 6 serving as the bottom electrode. The metal base plate 6 is made of copper substrate and has been treated with anti-oxidation and conductive coating to ensure good conductivity and stable grounding conditions. A 1000Ω series voltage divider circuit is connected via a coaxial cable to protect the circuit and facilitate the measurement of the current. First, the electrical characteristics of the AC-driven LED are tested. A sinusoidal AC voltage with a frequency of 100kHz is applied between the p-GaN layer 1 and the bottom electrode 6 through the probe 7. This AC voltage is generated by the arbitrary waveform generator 8 and amplified to different amplitudes by the high-voltage amplifier 9.

[0045] (3) Referring to Figure 3, the schematic diagram of the micro-LED being lit in AC drive mode and its corresponding voltage and current density characteristic curves are shown. The amplitude and phase of the applied AC voltage and the voltage across the 1000Ω resistor are monitored using a dual-channel oscilloscope. The voltage across the 1000Ω resistor divided by the resistance value can be regarded as the instantaneous current value passing through the micro-LED wafer. The frequency of the applied AC voltage is fixed at 100 kHz. As the amplitude increases, the peak current density increases linearly, which is significantly different from the IV characteristics of traditional DC-driven LEDs.

[0046] (4) Apply a sinusoidal AC voltage with a frequency of 200kHz and an amplitude of 40V between the p-GaN layer 1 and the bottom electrode 6. (Channels of the dual-channel oscilloscope 10) <1> Connect to the output terminal of high voltage amplifier 9, channel <2> Connect the bottom electrode 6. The oscilloscope displays the applied AC voltage and the voltage signal passing through the LED. The current density waveform of the LED is calculated. The current phase leads the voltage, and the LED exhibits capacitive characteristics. Multiple sets of tests are performed, with 10 different regions randomly selected for each set for emission detection. Multi-region sampling overcomes measurement errors caused by local non-uniformity. The EL spectrum is analyzed using a high-precision optical spectrometer 12, with an integration time set to 100ms, significantly longer than the AC voltage period (5μs).

[0047] (5) Refer to Figure 4, a comparison of peak wavelengths of blue and green micro-LEDs under DC and AC driving modes. DC driving refers to the process of adding another photolithography step under the same epitaxial structure, using electron beam evaporation to deposit a 20 / 20 nm Ti / Au thin film on the sample surface to achieve metal electrode preparation, and then measuring the peak wavelength using traditional methods. For green and blue LED wafers driven by AC and DC voltages, the peak wavelength will blue shift with the increase of current density. The maximum deviation of the average peak wavelength of the green LED epitaxial wafer is 0.9 nm, and the minimum deviation is 0.1 nm. The maximum deviation of the average peak wavelength of the blue LED epitaxial wafer is 0.7 nm, and the minimum deviation is 0 nm, which effectively proves the accuracy and consistency of the characterization method of this invention.

[0048] (6) A time-resolved measurement of the instantaneous electroluminescence intensity is performed using a photodetector 11. A dual-channel oscilloscope 10 is used to detect and calculate the voltage and instantaneous current in the circuit to accurately obtain the external quantum efficiency of the LED epitaxial wafer. In this embodiment, the effective luminescent area required for the instantaneous current density calculation is determined by fluorescence scanning of the sample surface using a fluorescence microscope, i.e., by collecting local luminescence image signals of the LED and performing image analysis. The light intensity data of each scanning point is collected, and the effective luminescent area and non-luminescent area are determined by using 5% of the maximum light intensity value as a threshold. The area of ​​the effective luminescent area is then calculated.

[0049] (7) See Figure 5, a comparison of the external quantum efficiency (EQE) of blue and green micro-LEDs under DC and AC driving modes. The EQE values ​​and trends obtained under AC and DC voltages are basically the same.

[0050] Example 2: A rapid measurement test system and characterization method for GaN-based micro-LED wafers:

[0051] (1) Green and blue InGaN LED wafers grown on a 450 μm sapphire substrate by metal-organic chemical vapor deposition (MOCVD) consist of an InGaN layer, an n-GaN layer, a multiple quantum well (MQW) layer, and a p-GaN layer, and are used as test samples. For demonstration purposes, a 100 nm thick transparent conductive indium tin oxide (ITO) film was deposited on the micro-LED GaN epitaxial layer by magnetron sputtering (MS), and a 200 nm thick silicon oxide layer was deposited by plasma-enhanced chemical vapor deposition (PECVD). The photolithography mask was a square pattern of different sizes designed. The pattern was transferred to the ITO film by two steps of etching: reactive ion etching (RIE) and inductively coupled plasma etching (ICP). The GaN was then etched to the n-GaN layer to a depth of 1 μm, thus defining the light-emitting mesa. After cleaning away the residual photoresist and silicon oxide layer, the remaining patterned ITO film serves as the contact electrode.

[0052] (2) The ITO-treated LED wafer is placed on a cleaned metal base plate in the center of a conductive test bench, which serves as the bottom electrode. The metal base plate is made of copper substrate and has been treated with anti-oxidation and conductive coating to ensure good conductivity and stable grounding conditions. A 1000Ω series voltage divider circuit is connected via a coaxial cable to protect the circuit and facilitate the measurement of the current. A 100μm×100μm patterned ITO film is used as the contact electrode for testing. First, the electrical characteristics of the AC-driven LED are tested. A sinusoidal AC voltage with a frequency of 100kHz is applied between the contact electrode and the bottom electrode. This AC voltage is generated by an arbitrary waveform generator and amplified to different amplitudes by a high-voltage amplifier.

[0053] (3) A schematic diagram of the micro-LED being lit in AC drive mode and its corresponding voltage and current density characteristic curves. The amplitude and phase of the applied AC voltage and the voltage across the 1000Ω resistor were monitored using a dual-channel oscilloscope. The voltage across the 1000Ω resistor divided by the resistance value can be considered as the instantaneous current value passing through the micro-LED wafer. The frequency of the applied AC voltage was fixed at 100 kHz. As the amplitude increased, the peak current density increased linearly, which is significantly different from the IV characteristics of traditional DC-driven LEDs.

[0054] (4) Apply a sinusoidal AC voltage with a frequency of 200kHz and an amplitude of 40V between the contact electrode and the bottom electrode. (Channels of a dual-channel oscilloscope) <1> Connect to the output terminal of the high-voltage amplifier, channel <2> Connect the bottom electrode. The oscilloscope then displays the applied AC voltage and the voltage signal passing through the LED. Calculations show the LED's current density waveform. The current phase leads the voltage, indicating the LED exhibits capacitive characteristics. Multiple tests are performed, with 10 different 100μm × 100μm regions randomly selected for each test. Multi-region sampling overcomes measurement errors caused by local inhomogeneities. The EL spectrum is analyzed using a high-precision optical spectrometer with an integration time set to 100ms, significantly longer than the AC voltage period (5μs).

[0055] (5) Use a photodetector to perform time-resolved measurement of instantaneous electroluminescence intensity, and use a dual-channel oscilloscope to detect and calculate the voltage and instantaneous current in the circuit to accurately obtain the external quantum efficiency of the LED epitaxial wafer.

[0056] (6) Calculate the external quantum efficiency (EQE) of blue and green micro-LEDs under DC and AC driving modes, where the effective emitting area of ​​the sample is the area of ​​the patterned ITO film of 100 μm × 100 μm. The EQE values ​​and trends obtained under AC and DC voltages are basically consistent.

[0057] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A testing system for the electroluminescence properties of a device, characterized in that... include: An AC voltage signal source provides an AC voltage signal; A conductivity test stage includes a conductive base and a contact probe. The conductive base is used to place the sample to be tested, and the contact probe is used to form an electrical contact with the sample to be tested. During testing, the sample to be tested is placed on the conductive base, and an AC voltage generated by an AC voltage signal source is applied to the sample to be tested through the contact probe. The magnitude of the AC voltage is sufficient to drive the sample to emit light. A series resistor, one end of which is electrically connected to a conductive substrate, and the other end is connected to an AC voltage signal source, is used to form a series connection with the sample to be tested; Waveform detection equipment is used to monitor the input AC voltage of the sample under test, as well as the voltage of the voltage divider circuit of the series resistor; Spectroscopic analysis equipment is used to detect the emission spectrum and peak wavelength of a sample under AC drive. A luminescence intensity detection device to analyze the time-resolved electroluminescence intensity of a sample.

2. The testing system according to claim 1, characterized in that: The AC voltage signal source includes an arbitrary waveform generator and a voltage amplifier connected in signal connection.

3. The testing system according to claim 1, characterized in that: The waveform detection device is a dual-channel oscilloscope.

4. The testing system according to claim 3, characterized in that: The spectral analysis equipment is a spectrometer.

5. The testing system according to any one of claims 1-4, characterized in that: The light intensity detection device is a photodetector.

6. The application of the test system according to any one of claims 1-5 in measuring the electroluminescence properties of a device.

7. The application according to claim 6, characterized in that... The device is a semiconductor device comprising at least an electron injection layer, a radiation recombination layer, and a hole injection layer, and has the characteristic of emitting light under a certain voltage.

8. The application according to claim 7, characterized in that... The steps include: (1) Place the sample to be tested on a conductive substrate, and use an arbitrary waveform generator to apply a preset AC voltage signal to the sample to be tested through a contact probe via a high voltage amplifier. (2) The waveform detection equipment monitors the input AC voltage of the sample under test and the voltage of the voltage divider circuit of the series resistor. The instantaneous AC current density of the sample under test is obtained by calculation. The measured input AC voltage is used not only to analyze the current-voltage characteristics, but also to prepare data for the study of the change law of electroluminescence intensity and spectral characteristics of the sample with driving voltage, the calculation of external quantum efficiency and the inference of dynamic response, and to facilitate monitoring and protection. The spectral analysis equipment measures the emission spectrum of the sample under different alternating current densities and records its peak wavelength; The luminescence intensity detection device collects the instantaneous luminous power of the sample under test; (3) Calculate the ratio of instantaneous light power to instantaneous alternating current density to characterize the external quantum efficiency of the sample under test at the alternating current density.

9. The application according to claim 8, characterized in that: The formula for calculating the instantaneous alternating current density is: ,in The instantaneous voltage across the series resistor as measured by the waveform detection equipment. This is the series resistance value. The effective luminescent area of ​​the sample to be tested.

10. The application according to claim 8, characterized in that: The formula for calculating the external quantum efficiency is as follows: ,in The instantaneous photopower measured by the luminous intensity detection device. The effective luminescent area of ​​the sample to be tested. For electron charge , Planck's constant , The photon frequency can be calculated from the wavelength. Received, among which It is the speed of light in a vacuum, and its standard value is taken as 1. , It is the peak wavelength measured by the spectral analysis equipment.

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