Testing system and characterization method for electroluminescent characteristics of device

Abstract

The invention discloses a device electroluminescence characteristic test system comprising an AC voltage signal source for providing an AC voltage signal; the conductive test bench comprises a base station and a contact probe, the base station is made of a conductive material and is used for placing a sample to be tested, the contact probe comprises a conductive material and is used for forming electric contact with the sample to be tested, and during testing, the sample to be tested is placed on the base station, and the contact probe is used for forming electric contact with the sample to be tested. AC voltage generated by the AC voltage signal source is applied to a to-be-tested sample through the contact probe, and the AC voltage is large enough to drive the to-be-tested sample to emit light; the series resistors are used for forming series connection with a sample to be tested; and a detection instrument. According to the method, the problems of etching damage and complicated operation caused by metal contact in a traditional EL detection method and the problem of inaccurate spectrum test in a PL detection method are solved, a simple and efficient novel EL characterization means without pretreatment is realized, and the method is suitable for rapid test and performance evaluation of various material systems and luminescent devices.

Description

Technical Field

[0001] The present invention relates to a test system and a characterization method for the electroluminescence characteristics of a device, belonging to the field of optoelectronic technology. Background Art

[0002] Gallium nitride (GaN)-based micro-LEDs are widely regarded as an important breakthrough in the field of display technologies such as flat panel displays, virtual reality (VR), and augmented reality (AR) due to their excellent characteristics such as high pixel density, high brightness, and long operating life. To achieve a high-quality micro-LED display effect, it is necessary 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 process is easily affected by factors such as high dislocation density, film stress, and microsystem defects, resulting in a decline in material quality and inevitable deviations in the wavelength and brightness of individual chips during mass production.

[0003] Existing methods for detecting the optoelectronic properties of semiconductor light-emitting device wafers mainly include photoluminescence (PL) detection and electroluminescence (EL) detection. Among them, as a non-destructive detection method, PL detection uses short-wavelength lasers to excite multiple quantum well (MQW) layers to analyze their luminescence properties. However, the spectral signals obtained by PL measurement come from all quantum well layers, rather than specific electron or hole injection regions. Therefore, for semiconductor light-emitting devices with pre-layers or multi-well systems, PL measurement may lead to spectral information deviation. In addition, PL detection is easily interfered by ambient light, affecting the accuracy and consistency of the measurement.

[0004] In contrast, EL detection can directly evaluate the electrical and optical properties of semiconductor light-emitting devices, and the obtained test results are more representative. However, traditional EL detection requires techniques such as indium pressing, laser ablation, and electrode evaporation to form electrodes on the wafer, and then apply a voltage through a microelectrical probe to inject carriers. These processes may cause local mechanical damage to the wafer, affecting the luminescence characteristics and reliability of the device. At the same time, the preparation of n-type or p-type electrodes adds additional processing steps, making the detection process more complex and somewhat destructive.

[0005] To overcome the limitations of traditional EL testing, an alternating-current-driven non-destructive electroluminescence detection method has been proposed in recent years. This method uses alternating current to drive, and through charge induction, electrons drift to the MQW region under the action of an alternating electric field to achieve non-destructive EL measurement. However, the existing alternating-current-driven EL testing technology is still in the exploratory stage. The correlation between the EL luminescence characteristics in the alternating-current-driven mode and traditional direct-current EL testing is not clear, and its applicability in different material systems and light-emitting device systems has not been fully established, which limits the practical application of this technology in the field of semiconductor light-emitting device wafer detection. Therefore, there is an urgent need for a non-destructive, efficient, and accurate wafer optoelectronic performance detection method applicable to various semiconductor light-emitting devices to overcome the deficiencies of the existing technology and improve the reliability and consistency of LED wafer optoelectronic performance detection. Summary of the Invention

[0006] The present invention discloses a test system for the electroluminescence characteristics of a device to solve the above problems existing in the prior art.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A test system for the electroluminescence characteristics of a device, comprising:

[0009] An alternating voltage signal source for providing an alternating voltage signal;

[0010] A conductive test bench, including a conductive base and contact probes. The conductive base is made of a sheet-like, thin-film, or layered metal electrode and is used to place the sample to be tested. The contact probes usually adopt metal probes such as tungsten probes, beryllium copper probes, tungsten rhenium alloy probes, and gold probes to form electrical contact with the sample to be tested. It can also be an ITO film grown on the wafer. During testing, the sample to be tested is placed on the base, and the alternating voltage generated by the alternating voltage signal source is applied to the sample to be tested through the contact probes. The magnitude of the alternating voltage is sufficient to drive the sample to be tested to emit light;

[0011] A series resistor, one end of which is electrically connected to the conductive base and the other end is connected to the alternating voltage signal source, for forming a series connection with the sample to be tested;

[0012] A waveform detection device for monitoring the input alternating voltage of the sample to be tested and the voltage of the voltage division circuit of the series resistor;

[0013] A spectral analysis device for detecting the emission spectrum and peak wavelength of the sample to be tested under alternating-current drive;

[0014] A luminescence intensity detection device for analyzing the time-resolved electroluminescence intensity of the sample to be tested.

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

[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 test system in measuring the electroluminescence characteristics of a device.

[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 radiative recombination layer, and a hole injection layer, such as semiconductor light-emitting device wafers such as GaN LEDs, GaAs LEDs, perovskite LEDs, and OLEDs, or can also be a semiconductor photoelectric conversion device with light absorption characteristics and capable of generating photo-generated 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 base, and use an arbitrary waveform generator to apply a preset AC voltage signal to the sample to be tested through a high-voltage amplifier via a contact probe. For example, a sine wave, square wave, triangular wave, or custom waveform can be used.

[0023] (2) The waveform detection device monitors the input AC voltage of the sample to be tested and the voltage V probe (t) of the voltage division circuit of the series resistor, and calculates the instantaneous AC current density of the sample to be tested. In addition to analyzing the current-voltage characteristics by dividing the measured input AC voltage, it also prepares data for studying the variation law of the electroluminescence intensity and spectral characteristics of the sample with the driving voltage, calculating the external quantum efficiency, and inferring the dynamic response, and is also convenient for monitoring and protection.

[0024] The spectral analysis device measures the emission spectrum of the sample to be tested at different AC current densities and records its peak wavelength.

[0025] The luminous intensity detection device collects the instantaneous optical power of the sample to be tested.

[0026] (3) Calculate the ratio of the instantaneous optical power to the instantaneous AC current density to characterize the external quantum efficiency of the sample to be tested at this AC current density.

[0027] Among them, a waveform detection device is used to monitor the input AC voltage of the sample to be measured. This is not only for analyzing the voltage-current characteristics of the sample, but also includes the following: 1. Analyzing the law of the electroluminescence intensity and spectral characteristics of the sample changing with the driving voltage. 2. The external quantum efficiency can be calculated through the input voltage, instantaneous current density, and output optical power. 3. Measuring the input voltage to analyze the capacitance effect, and combining the instantaneous current density can infer influencing factors such as parasitic resistance and capacitance. 4. At the same time, it also plays a role in monitoring and protection to avoid damage to the sample caused by excessive voltage.

[0028] Preferably, the calculation formula for the instantaneous AC current density is: Where V probe (t) is the instantaneous voltage on the series resistance measured by the waveform detection device, R s is the series resistance value, A is the effective light-emitting area of the sample to be measured. The effective light-emitting area refers to the area where the device actually participates in light emission, and can be determined by observing the local light emission situation with a near-field scanning optical microscope.

[0029] Preferably, the calculation formula for the external quantum efficiency is: Where P opt (t) is the instantaneous optical power measured by the light intensity detection device, A is the effective light-emitting area of the sample to be measured, q is the electron charge 1.602×10 -19 C, h is the Planck constant 6.626×10 -34 J·s, v is the photon frequency, which can be calculated obtained, where c is the speed of light in a vacuum, and the standard value is 3×10 8 m / s, λ is the peak wavelength measured by the spectral analysis device.

[0030] Based on the measured current density, peak wavelength, and external quantum efficiency, the light-emitting performance of the sample to be measured under different driving conditions can be analyzed.

[0031] The beneficial effects of the present invention are as follows:

[0032] (1) The present invention adopts an AC driving method to realize the electroluminescence test of a semiconductor light-emitting device wafer with direct carrier injection without carriers through the charge induction effect, avoiding the physical electrode preparation process for the wafer in the traditional test method, thus effectively reducing the damage to the semiconductor light-emitting device wafer and improving the repeatability of the test and the reliability of the device.

[0033] (2) The test method of the present invention only needs to place the light-emitting device wafer on the metal bottom plate of the conductive test bench and directly apply an AC voltage signal through the contact probe to perform the electroluminescence test without additional electrode preparation, greatly simplifying the detection process, improving the detection efficiency, and being suitable for the rapid screening and evaluation of large-scale semiconductor light-emitting device wafers.

[0034] (3) This test system is compatible with a variety of semiconductor light-emitting devices, has a wide range of applications, can support a variety of drive waveforms, realizes flexible testing, and provides rich experimental data support for the design optimization of different material systems and device systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic cross-sectional view of the micro-LED wafer to be tested in the electroluminescence test system based on GaN-based micro-LEDs of the present invention;

[0036] Figure 2 It is a schematic diagram of the test system of the electroluminescence test system based on GaN-based micro-LEDs of the present invention;

[0037] Figure 3 In the electroluminescence characterization method based on GaN-based micro-LEDs of the present invention, it is a schematic diagram of the lighting of micro-LEDs in the AC drive mode and its corresponding voltage and current density characteristic curves;

[0038] Figure 4 In the electroluminescence characterization method based on GaN-based micro-LEDs of the present invention, it is a comparison chart of the peak wavelengths of blue and green micro-LEDs in the DC and AC drive modes;

[0039] Figure 5 In the electroluminescence characterization method based on GaN-based micro-LEDs of the present invention, it is a comparison chart of the external quantum efficiency (EQE) of blue and green micro-LEDs in the DC and AC drive modes. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The present invention will be further described below in conjunction with embodiments, but the description of the embodiments does not impose any limitation on the protection scope of the present invention.

[0041] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. Additionally, although this document may provide examples containing specific values of parameters, it should be understood that the parameters do not necessarily exactly equal the corresponding values, but may approximate the corresponding values within an acceptable error tolerance or design constraint. The directional terms mentioned in the embodiments, such as "up", "down", "front", "rear", "left", "right", etc., are only with reference to the directions of the drawings. Therefore, the directional terms used are for illustration rather than to limit the protection scope of the present invention.

[0042] The substances or instruments used in the following examples can be obtained from conventional commercial channels if not specified otherwise.

[0043] Example 1: A test system for rapidly measuring GaN-based micro-LED wafers and its characterization method:

[0044] (1) Refer to Figure 1 , a schematic cross-sectional structure diagram of the micro-LED wafer to be measured. An InGaN / GaN green and blue LED wafer grown on a 450-μm sapphire substrate 1 by metalorganic chemical vapor deposition (MOCVD), including an InGaN layer 2, an n-GaN layer 3, a multi-quantum well (MQW) layer 4, and a p-GaN layer 5, is used as the test sample.

[0045] (2) Refer to Figure 2 , a schematic diagram of the test system. The LED wafer is placed on a metal bottom plate 6 in the central area of a cleaned conductive test bench, and the metal bottom plate 6 serves as the bottom electrode. The metal bottom plate 6 is made of a copper substrate and undergoes an anti-oxidation treatment and a conductive coating treatment on the surface to ensure good conductivity and stable grounding conditions. A 1000-Ω series voltage-dividing circuit is connected through a coaxial cable to protect the circuit and facilitate the measurement of the passing current. First, the electrical characteristics of the AC-driven LED are detected. A sinusoidal AC voltage with a frequency of 100 kHz is applied between the p-GaN layer 1 and the bottom electrode 6 through a probe 7. This AC voltage is generated by an arbitrary waveform generator 8 and amplified to different amplitudes by a high-voltage amplifier 9.

[0046] (3) Refer to Figure 3 , a schematic diagram of the lighting of the micro-LED in the AC-driven mode and its corresponding voltage and current density characteristic curves. A dual-channel oscilloscope is used to monitor the applied AC voltage, the voltage amplitude and phase of the 1000-Ω resistor. The voltage of the 1000-Ω 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 I-V characteristics of traditional DC-driven LEDs.

[0047] (4) A sinusoidal AC voltage with a frequency of 200 kHz and an amplitude of 40 V is applied between the p-GaN layer 1 and the bottom electrode 6. Channel <1> of the dual-channel oscilloscope 10 is connected to the output terminal of the high-voltage amplifier 9, and channel <2> is connected to the bottom electrode 6. At this time, the oscilloscope displays the applied AC voltage and the voltage signal passing through the LED, which is also the current density waveform of the LED through calculation. The current phase leads the voltage, and the LED as a whole exhibits capacitive characteristics. Multiple groups of detections are carried out. In each group, 10 different regions are randomly selected for luminescence detection, and multi-region sampling is used to overcome the measurement errors caused by local non-uniformity. The EL spectrum is analyzed using a high-precision optical spectrometer 12, and the integration time is set to 100 ms, which is significantly longer than the AC voltage period (5 μs) at this time.

[0048] (5) See Figure 4 , the comparison chart of the peak wavelengths of blue and green micro-LEDs in DC and AC drive modes. DC drive means that under the same epitaxial structure, one more photolithography is performed, and a 20 / 20 nm Ti / Au thin film is evaporated on the sample surface by electron beam evaporation EBE to fabricate the metal electrode. After that, it is measured by the traditional method. For the green and blue LED wafers driven by AC voltage and DC voltage, as the current density increases, the peak wavelength will undergo a blue shift. 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, effectively proving the accuracy and consistency of the characterization method of the present invention.

[0049] (6) A photodetector 11 is used for time-resolved measurement of the instantaneous electroluminescence intensity, and 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, for the effective luminescence area required in the calculation of the instantaneous current density, the sample surface is subjected to fluorescence scanning using a fluorescence microscope, that is, by collecting the local luminescence image signal of the LED and performing image analysis. The light intensity data of each scanned point is collected, and the 5% of the maximum light intensity value is used as the threshold for the luminescent area to determine the effective luminescence area and the non-luminescent area, and the area of the effective luminescence area is calculated.

[0050] (7) See Figure 5 , the comparison chart of the external quantum efficiency (EQE) of blue and green micro-LEDs in DC and AC drive modes. The values and change trends of the EQE obtained under AC voltage and DC voltage are basically the same.

[0051] Example 2 A test system for rapidly measuring GaN-based micro-LED wafers and its characterization method:

[0052] (1) InGaN / GaN green and blue LED wafers grown on a 450 μm sapphire substrate by metalorganic chemical vapor deposition (MOCVD) successively include an InGaN layer, an n-GaN layer, a multi-quantum well (MQW) layer, and a p-GaN layer. This wafer is used as a test sample. For easy demonstration, a 100 nm thick transparent conductive indium tin oxide (ITO) film is deposited on the micro-LED GaN epitaxial layer by magnetron sputtering (MS), and a 200 nm thick silicon oxide layer is deposited by a plasma-enhanced chemical vapor deposition equipment (PECVD) for photolithography. The photolithography mask is a designed square pattern with different sizes. After undergoing two-step etching of reactive ion etching technology (RIE) and inductively coupled plasma etching technology (ICP), the pattern is transferred to the ITO film, and the GaN is etched to the n-GaN layer with an etching depth of 1 μm to define the light-emitting mesa. After cleaning to remove the residual photoresist and silicon oxide layer, the remaining patterned ITO film serves as the contact electrode.

[0053] (2) Place the LED wafer treated with ITO on the metal bottom plate in the central area of the cleaned conductive test bench. The metal bottom plate serves as the bottom electrode. The metal bottom plate uses a copper substrate and undergoes anti-oxidation treatment and conductive coating treatment on the surface to ensure good conductivity and stable grounding conditions. Connect a 1000 Ω series voltage-dividing circuit through a coaxial cable, which plays a role in protecting the circuit and facilitating the measurement of the passing current. Test is carried out with a 100 μm × 100 μm patterned ITO film as the contact electrode. First, detect the electrical characteristics of the AC-driven LED. Apply a sinusoidal AC voltage with a frequency of 100 kHz 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.

[0054] (3) Schematic diagram of the lighting of the micro-LED in the AC-driven mode and its corresponding voltage and current density characteristic curves. Use a dual-channel oscilloscope to monitor the applied AC voltage, the voltage amplitude and phase of the 1000 Ω resistor. The voltage of the 1000 Ω 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 I-V characteristics of traditional DC-driven LEDs.

[0055] (4) Apply a sinusoidal AC voltage with a frequency of 200 kHz and an amplitude of 40 V between the contact electrode and the bottom electrode. Channel <1> of the dual-channel oscilloscope is connected to the output terminal of the high-voltage amplifier, and channel <2> is connected to the bottom electrode. At this time, the oscilloscope displays the applied AC voltage and the voltage signal passing through the LED, and by calculation, it is also the current density waveform of the LED. The current phase leads the voltage, and the LED as a whole exhibits capacitive characteristics. Conduct multiple groups of detections. For each group, randomly select 10 different 100 μm × 100 μm regions for detection, and use multi-region sampling to overcome the measurement error caused by local non-uniformity. Analyze the EL spectrum using a high-precision optical spectrometer, and set the integration time to 100 ms, which is significantly greater than the AC voltage period (5 μs) at this time.

[0056] (5) Use a photodetector to perform time-resolved measurement of the 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.

[0057] (6) Calculate the external quantum efficiency (EQE) of blue and green micro-LEDs in DC and AC drive modes, where the effective light-emitting area of the sample to be measured is the area of the patterned ITO film with a size of 100 μm × 100 μm. The values and change trends of the EQE obtained under AC voltage and DC voltage are basically the same.

[0058] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A device electroluminescent property testing system, characterized in that include: An AC voltage signal source, providing an AC voltage signal; A conductive test bench, comprising a conductive base and a contact probe, wherein the conductive base is used to place a sample to be tested, and the contact probe is used to form an electrical contact with the sample to be tested. During the test, 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, and the magnitude of the AC voltage is sufficient to drive the sample to be tested to emit light; A series resistor, one end of which is electrically connected to the conductive base, and the other end of which is connected to the AC voltage signal source, and is used to form a series connection with the sample to be tested; Waveform detection equipment, used to monitor the input AC voltage of the sample to be tested, and the voltage of the voltage divider circuit of the series resistor; Spectral analysis equipment, used to detect the emission spectrum and peak wavelength of the sample under AC drive; Luminescence intensity detection equipment, analyzes the time-resolved electroluminescence intensity of the sample to be tested.

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

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

4. The test system according to claim 3, characterized in that: The spectrum analysis device is a spectrometer.

5. The test system according to any one of claims 1 to 4, characterized in that: The luminous intensity detection device is a photoelectric detector.

6. Use of the test system according to any one of claims 1 to 5 in measuring electroluminescent properties of a device.

7. The use according to claim 6, characterized in that The device is a semiconductor device which at least comprises 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 use according to claim 7, characterized in that The steps include: (1) placing the sample to be tested on a conductive base, using an arbitrary waveform generator, and applying 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 to be tested and the voltage V of the voltage divider circuit of the series resistor probe (t), the instantaneous AC current density of the sample to be tested 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 variation of the electroluminescent intensity and spectral characteristics of the sample with the driving voltage, the calculation of the external quantum efficiency and the inference of the dynamic response, and is convenient for monitoring and protection; The spectrum analysis equipment measures the emission spectrum of the sample under test at different AC current densities and records its peak wavelength; The luminous intensity detection device collects the instantaneous optical power of the sample to be tested; (3) Calculate the ratio of instantaneous optical power to instantaneous AC current density to characterize the external quantum efficiency of the sample under test at the AC current density.

9. The use according to claim 8, characterized in that: The calculation formula of the instantaneous AC current density is: Where V probe (t) is the instantaneous voltage on the series resistor measured by the waveform detection device, R s is the series resistance value, and A is the effective luminous area of ​​the sample to be tested.

10. The use according to claim 8, characterized in that: The calculation formula of the external quantum efficiency is: Where P opt (t) is the instantaneous optical power measured by the luminous intensity detection device, A is the effective luminous area of ​​the sample to be tested, and q is the electron charge 1.602×10 -19 C,h is Planck's constant 6.626×10 -34 J·s, v is the photon frequency, which can be calculated from the wavelength We get: where c is the speed of light in a vacuum, which is taken as a standard value of 3×10 8 m / s, λ is the peak wavelength measured by the spectrum analysis device.

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