Carrier lifetime testing method for variable excitation intensity time-resolved photoluminescence

Abstract

The variable excitation intensity time-resolved photoluminescence carrier lifetime test method comprises the following steps: S1, pulse excitation time-resolved photoluminescence response is carried out to obtain a time-dependent attenuation curve of the unbalanced carrier concentration of a to-be-tested sample, and S2, according to the attenuation curve, the time-dependent attenuation curve of the unbalanced carrier concentration of the to-be-tested sample is calculated. The carrier lifetime data under different excitation intensities are fitted to obtain the SRH lifetime and the surface composite lifetime of the sample, and the # imgabs0 # SRH composite lifetime, the # imgabs1 # radiation composite lifetime and the # imgabs2 # auger composite lifetime are obtained. The variable excitation intensity time-resolved photoluminescence carrier lifetime test method can accurately measure each component of the carrier lifetime.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-contact testing of semiconductor materials, and particularly relates to a method for testing the carrier lifetime of variable excitation intensity time-resolved photoluminescence. Background Art

[0002] Infrared detection technology uses the infrared radiation of objects to achieve non-contact measurement and imaging, and is widely used in military reconnaissance, medical diagnosis, environmental monitoring, fire warning, security monitoring and other fields, improving the detection efficiency and accuracy, and providing important support for modern technology and social security. With the wide application of infrared detection technology in military, security, medical and other fields, the demand for high-performance infrared detectors is increasing continuously.

[0003] In photovoltaic devices such as solar cells and certain types of infrared detectors, a longer carrier lifetime allows carriers more time to reach the electrodes and complete charge collection, thereby improving the photoelectric conversion efficiency. The carrier lifetime is also closely related to the noise performance of the detector. A longer carrier lifetime helps to reduce the dark current noise of the detector, thereby improving the signal-to-noise ratio and detection sensitivity. The detectivity is one of the important indicators to measure the performance of an infrared detector, which reflects the detection ability of the detector for weak infrared radiation. The carrier lifetime indirectly affects the detectivity by influencing the photoelectric conversion efficiency and noise performance. A longer carrier lifetime usually helps to improve the detectivity. In order to improve the performance of infrared detectors, researchers usually take a series of measures to extend the carrier lifetime, such as optimizing the energy band structure of semiconductor materials, reducing impurities and defects, controlling the doping concentration, etc. In addition, the carrier lifetime and detector performance can be further improved by improving the structural design and process manufacturing process of the detector.

[0004] In summary, a long carrier lifetime is crucial for high-performance infrared detection, and there is an urgent need to study how to accurately characterize the carrier lifetime of detector materials.

[0005] Optical cavity ring-down technique: Chinese invention patent CN103080730A discloses a method and device for measuring carrier lifetime, providing a method and device for measuring the carrier lifetime in materials such as semiconductors, and accurately measuring the effective carrier lifetime of semiconductor materials by measuring the exponential decay time of the probe laser energy emitted from the resonant cavity. However, the effective carrier lifetime consists of three parts, and the SRH recombination lifetime more related to the defect energy level of the recombination center, the radiative recombination lifetime more related to the number of photons emitted by radiative recombination in the laser material, and the Auger recombination lifetime related to temperature-sensitive low-temperature / room-temperature operating materials. For different materials, or for the same material, the three types of lifetimes are also different, and the comparative document cannot achieve such high-precision measurement. SRH recombination lifetime, the radiative recombination lifetime more related to the number of photons emitted by radiative recombination in the laser material radiative recombination lifetime, the Auger recombination lifetime related to temperature-sensitive low-temperature / room-temperature operating materials Auger recombination lifetime. For different materials, or for the same material, the three types of lifetimes are also different, and the comparative document cannot achieve such high-precision measurement.

[0006] Terahertz transient absorption spectroscopy detection system: Chinese invention patent CN108827914A discloses a terahertz transient absorption spectroscopy detection system and a carrier lifetime measurement method. A femtosecond laser with a specific wavelength is used to excite a sample, and the photoinduced response of the sample is detected with a broadband and continuous spectrum to study characteristics such as ground state bleaching and excited state absorption of the material after optical excitation, realizing the detection of the non-equilibrium carrier dynamics process within a time window from nanoseconds to several seconds, with sub-nanosecond time accuracy, high data acquisition rate, relatively low cost, simple optical path, and convenient use. If the surface of the sample is prone to oxidation or reaction with air, such as group III-V materials, the surface recombination rate is extremely fast and the interlayer radiative recombination luminescence efficiency is greater than the internal radiative recombination of the sample. At this time, the fluorescence response is very strong and decays rapidly, which is extremely easy to cover the photoinduced response of the in vivo recombination. Because the decay rate of the fluorescence response is relatively fast, it will cover or interfere with the signal of the in vivo radiative recombination luminescence, making it difficult to accurately separate and analyze them. Although the terahertz transient absorption spectroscopy detection system can measure the bulk recombination process of photo-generated carriers, it cannot accurately distinguish and calculate the luminescence contributions from these two different sources. This application selects quadratic fitting to distinguish these two different lifetimes.

[0007] Therefore, how to accurately measure the components of the carrier lifetime of the bulk material and provide a specific calculation method is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for testing the carrier lifetime of variable excitation intensity time-resolved photoluminescence for the problems in the prior art.

[0009] To this end, the above object of the present invention is achieved through the following technical solutions: A method for testing the carrier lifetime of variable excitation intensity time-resolved photoluminescence includes the following steps: S1, obtaining the decay curve of the non-equilibrium carrier concentration of the sample to be tested with respect to time by pulsed excitation time-resolved photoluminescence response: Fitting the decay curve using a double-exponential function, starting from the maximum value of the response: (8) Wherein, and are function fitting coefficients, is the offset compensation of the response curve, is the long carrier lifetime reflecting the bulk lifetime of the material, is the short carrier lifetime; S2, according to the decay curve, fitting the carrier lifetime data at different excitation intensities to obtain the SRH lifetime and surface recombination lifetime of the sample: Wherein, the carrier fluorescence lifetime Relationship with excess carrier concentration: (10) Wherein, is the SRH recombination coefficient, is the radiative recombination coefficient, is the photon recycling factor, a parameter reflecting the process of repeated absorption of photons emitted by radiative recombination, is the Auger recombination coefficient, excess carrier concentration, is the SRH recombination lifetime, is the radiative recombination lifetime, is the Auger recombination lifetime; Plot image. Under low injection conditions, for long carrier lifetimes perform fitting according to Equation (10). Take the reciprocal of the intercept obtained from the fitting to obtain the SRH lifetime of the sample; Plot image. At high injection, the short carrier lifetime remains stable. Select the short carrier lifetime at this time as the surface recombination lifetime of the material.

[0010] While adopting the above technical solution, the present invention can also adopt or combine the following technical solutions: As a preferred technical solution of the present invention: Step S1 specifically includes the following steps: In the pulsed excitation time-resolved photoluminescence response technology, by building a test system and selecting a pulsed laser with an appropriate wavelength to irradiate the surface of the sample, the decay curve of the non-equilibrium carrier concentration of the sample over time can be measured. The following is a detailed analysis of this process: S1.1, Excitation and generation of non-equilibrium carriers: Use a pulsed laser capable of exciting the sample to undergo intrinsic absorption. After passing through the optical system, it irradiates the surface of the sample to be measured; after the surface of the sample is irradiated by light, valence band electrons inside absorb photons with energy greater than Eg at a certain rate and are excited to the conduction band, generating non-equilibrium carriers in the conduction band and valence band respectively; S1.2, Diffusion and relaxation: After the relaxation time, the non-equilibrium carriers diffuse in the conduction band / valence band and simultaneously relax to lower energy states near the bottom of the conduction band / top of the valence band in the form of thermal radiation; S1.3, Recombination and release: The electrons and holes after relaxation undergo radiative recombination in the form of photon release, so that the electrons optically excited to the conduction band return to the valence band again; Use a detector to collect the photons released during the radiative recombination of electrons and holes, that is, the fluorescence signal, and display it on an oscilloscope; S1.4, Calculation and analysis: The calculation of the non-equilibrium carrier concentration excited in the sample involves factors such as the laser generation rate, laser pulse time, loss of the laser passing through the optical system to reach the sample surface, laser power, sample reflectivity, absorption coefficient of the sample for this laser, sample thickness, spot size, and photon energy.

[0011] As a preferred technical solution of the present invention: In step S1.1, The non-equilibrium carrier concentration excited in the sample is: (1) where is the laser generation rate, is the laser pulse time, is the loss of the laser passing through the optical system to reach the sample surface, is the laser power, sample reflectivity, absorption coefficient of the sample for this laser, sample thickness, spot size, photon energy.

[0012] As a preferred technical solution of the present invention: In step S1.3, excess carriers are generated by laser excitation. In the case of low injection, the recombination process of excess carriers mainly consists of three parts: SRH recombination , radiative recombination , Auger recombination , carrier lifetime and recombination rate are related as: (2) where is the SRH recombination coefficient, is the radiative recombination coefficient, is the photon recycling factor, a parameter reflecting the process of photons emitted by radiative recombination being repeatedly absorbed, is the Auger recombination coefficient; where the low injection case refers to the case where the electron concentration of the injected excess carriers is less than the equilibrium electron concentration.

[0013] As a preferred technical solution of the present invention: In step S1.3, the excess carrier concentration satisfies the following equation: (3) After pulsed laser excitation in the test, , Equation (3) is rewritten as: (4) Solving Equation (4) can obtain ; In the carrier recombination of the sample, only radiative recombination emits photons to generate fluorescence signals. Therefore, the relationship between the oscilloscope response signal and the carrier concentration inside the sample is calculated as follows: (5) where represents the collection ability of the optical system for fluorescence and the response rate of the detector, represents the carrier fluorescence lifetime, that is, twice the time it takes for the response curve to decay to 1 / e of its maximum value; Actually, the carrier lifetime of the material consists of the bulk lifetime and the surface recombination lifetime in two parts: (7).

[0014] Compared with the prior art, the carrier lifetime test method of variable excitation intensity time-resolved photoluminescence of the present invention has the following beneficial effects: The present invention uses the carrier decay curve measured by time-resolved photoluminescence technology and the corresponding physical model to analyze the carrier lifetime, solves the problem of how to accurately measure each component of the bulk carrier lifetime, clearly calculates the SRH recombination lifetime through the derivation of the relationship formula, and at the same time analyzes and obtains the specific values of the radiative recombination lifetime and the Auger recombination lifetime, determines their contributions to the total lifetime under different conditions, and is used to more accurately measure and analyze the carrier lifetime characteristics of semiconductor materials to achieve a comprehensive evaluation of the material performance. The carrier lifetime test method of variable excitation intensity time-resolved photoluminescence of the present invention, through quadratic fitting, respectively obtains the specific values of the fluorescence lifetime of the chemical reaction on the sample surface and the radiative recombination luminescence lifetime in the body and their proportions in the total fluorescence signal, can more accurately understand the contributions of different luminescence mechanisms in the sample, distinguish the effects of surface defects and bulk recombination centers on the carrier lifetime, and help optimize the performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the schematic diagram of double-exponential fitting in the present invention; Figure 2(a) is image Figure 2(b) is based on fitting the SRH lifetime; Figure 3 is image and the surface recombination lifetime. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

[0017] The carrier lifetime testing method of variable excitation intensity time-resolved photoluminescence according to the present invention provides a carrier lifetime testing method. First, the decay curve of the non-equilibrium carrier concentration of the sample over time is obtained through the pulsed excitation time-resolved photoluminescence response technique; secondly, the carrier lifetime is obtained by fitting the decay curve and analyzed; finally, the carrier lifetime data under different excitation intensities are fitted to obtain the SRH lifetime and surface recombination lifetime of the sample.

[0018] The carrier lifetime testing method of variable excitation intensity time-resolved photoluminescence according to the present invention comprises the following steps: 1. Obtain the decay curve of the non-equilibrium carrier concentration of the sample over time through the pulsed excitation time-resolved photoluminescence response technique.

[0019] Build a test system. Select a pulsed laser with an appropriate wavelength (capable of exciting the sample to have intrinsic absorption). After passing through the optical system, it is irradiated onto the surface of the sample to be tested. The surface of the sample is irradiated by light, and the valence band electrons inside absorb photons with energy greater than Eg at a certain rate and are excited to the conduction band, generating non-equilibrium carriers in the conduction band and valence band respectively; after a short relaxation time, the non-equilibrium carriers diffuse in the conduction band / valence band and simultaneously relax to lower energy states near the bottom of the conduction band / top of the valence band in the form of thermal radiation; finally, the relaxed electrons and holes recombine radiatively by releasing photons, so that the electrons excited to the conduction band return to the valence band again. Use a detector to collect the photons released during the radiative recombination of electrons and holes, that is, the fluorescence signal and display it on an oscilloscope. Among them, an attenuation sheet can be used in the optical system to obtain fluorescence response signals under different excitation intensities; the sample can be placed in a Dewar to test the fluorescence signals at different temperatures according to requirements.

[0020] Non-equilibrium carrier concentration of the excited sample Calculation: (1) Where is the laser generation rate, is the laser pulse time, is the loss of the laser passing through the optical system and reaching the sample surface, is the laser power, is the sample reflectivity, is the absorption coefficient of the sample for this laser, is the sample thickness, is the spot size, is the photon energy.

[0021] Excess carriers are generated by laser excitation. In the case of small injection (for example, the electron concentration of excess carriers injected into the sample InAs is less than the equilibrium electron concentration, ) The recombination process of excess carriers mainly consists of three parts (all using the recombination rate (denoted as), SRH recombination , radiative recombination , Auger recombination Carrier lifetime and recombination rate The relationship can be expressed as: (2) where is the SRH recombination coefficient, is the radiative recombination coefficient, is the photon recycling factor, a parameter reflecting the process of photons emitted by radiative recombination being repeatedly absorbed, is the Auger recombination coefficient.

[0022] Excess carrier concentration satisfies the following equation: (3) After pulsed laser excitation in the test, , Equation (3) is rewritten as: (4) Solving Equation (4) can obtain .

[0023] In the carrier recombination of the sample, only the photons emitted by radiative recombination generate fluorescence signals. Therefore, the relationship between the oscilloscope response signal and the carrier concentration inside the sample is calculated as: (5) where represents the fluorescence collection ability of the optical system and the response rate of the detector, represents the carrier fluorescence lifetime, which is twice the time it takes for the response curve to decay to 1 / e of its maximum value.

[0024] In fact, the carrier lifetime of the bulk material consists of two parts: the bulk lifetime and the surface lifetime : (7) As a group III-V material, InAs has an extremely fast surface recombination velocity. Therefore, for samples directly exposed to air, the surface recombination has a great impact on the carrier lifetime test. Surface recombination occurs in the form of indirect recombination through surface states (or surface energy levels). The energy released during this recombination process may be radiated in the form of photons, or may be converted into heat energy or other forms of energy. The fluorescence emitted in the form of photons has a non-negligible impact on the experimental test.

[0025] To improve the accuracy of obtaining the bulk lifetime from the decay curve, a double-exponential function is used to fit it as Figure 1 shown, and the fitting starts from the maximum value of the response: (8) and are the function fitting coefficients, is the offset compensation of the response curve, and the carrier fluorescence lifetime is obtained as in Equation (5) , then the long carrier lifetime represents the bulk lifetime of the material, and the short carrier lifetime represents the surface recombination lifetime of the material. These two parameters reflect the characteristic time scales of different recombination mechanisms inside the material. By knowing the thickness of the sample to be measured, the surface recombination velocity of the sample can be calculated through Equation (9).

[0026] (9) 2. Analyze and fit the carrier fluorescence lifetime obtained from the response curve.

[0027] According to Equation (2), the relationship between the carrier fluorescence lifetime and the excess carrier concentration can be obtained: (10) Plot the image as shown in Figure 2(a). Under low injection conditions, fit the long carrier lifetime according to Equation (10). As shown in Figure 2(b), take the reciprocal of the intercept obtained from the fitting, which is the SRH lifetime of the sample.

[0028] Plot the image as Figure 3 shown. It is observed that under high injection (the injected excess carrier electron concentration is greater than the equilibrium electron concentration) conditions, the short carrier lifetime remains stable. This is because when the injected excess carrier concentration increases to a certain extent such that all recombination centers are completely occupied by carriers, additional band-edge excitons can no longer recombine effectively through the SRH recombination pathway, and they will instead seek other recombination pathways. An important alternative pathway is through interlayer radiative recombination, i.e., excitons may cross different material layers or interfaces and use surface states as the medium for recombination. In the present invention, the short carrier lifetime at this time is taken as the surface recombination lifetime of the material.

[0029] The technical fields involved in the present invention include semiconductor physics and materials science, time-resolved photoluminescence (TRPL) technology. TRPL is an advanced non-contact measurement technology used to study the carrier recombination process in semiconductor materials. By measuring the change in the light intensity emitted by the sample over time after laser excitation, key information such as carrier lifetime and recombination mechanism can be revealed), carrier lifetime measurement (carrier lifetime is an important parameter in semiconductor physics, which directly affects the performance of semiconductor devices. For semiconductor materials such as InAs, accurate carrier lifetime measurement is crucial for optimizing device design and improving device performance), and the study of SRH recombination and surface recombination mechanisms.

[0030] The above specific embodiments are used to explain the present invention, which are only the preferred embodiments of the present invention and do not limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and scope of the protection of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A method for testing the carrier lifetime of time-resolved photoluminescence with variable excitation intensity, comprising the following steps: S1. Obtaining the decay curve of the non-equilibrium carrier concentration of the sample to be tested with respect to time by pulsed excitation time-resolved photoluminescence response: Fitting the decay curve using a double-exponential function, starting from the maximum value of the response: （8） Among them, and are function fitting coefficients, is the offset compensation of the response curve, is the long carrier lifetime reflecting the bulk lifetime of the material, is the short carrier lifetime; S2. According to the decay curve, fitting the carrier lifetime data at different excitation intensities to obtain the SRH lifetime and surface recombination lifetime of the sample: Among them, the carrier fluorescence lifetime Relationship with the excess carrier concentration: （10） Among them, is the SRH recombination coefficient, is the radiative recombination coefficient, is the photon recycling factor, a parameter reflecting the process of repeated absorption of photons emitted by radiative recombination, is the Auger recombination coefficient, is the excess carrier concentration, is the SRH recombination lifetime, is the radiative recombination lifetime, is the Auger recombination lifetime; Draw an image, and for a long carrier lifetime under low injection fit according to Equation (10), and take the reciprocal of the intercept obtained from the fitting to obtain the SRH lifetime of the sample; Draw an image, at high injection, with a short carrier lifetime maintained stably, and select the short carrier lifetime at this time which is the surface recombination lifetime of the material.

2. The carrier lifetime testing method for variable excitation intensity time-resolved photoluminescence according to claim 1, characterized in that: Step S1 specifically includes the following steps: In the pulsed excitation time-resolved photoluminescence response technique, by building a test system and selecting a pulsed laser with an appropriate wavelength to irradiate the surface of the sample, the decay curve of the non-equilibrium carrier concentration of the sample with respect to time can be measured. The following is a detailed analysis of this process: S1.

1. Exciting and generating non-equilibrium carriers: Using a pulsed laser that can excite the sample to undergo intrinsic absorption, after passing through the optical system, it irradiates the surface of the sample to be tested; after the surface of the sample is irradiated by light, the valence band electrons inside the sample absorb photons with energy greater than Eg at a certain rate and are excited to the conduction band, generating non-equilibrium carriers in the conduction band and valence band respectively; S1.

2. Diffusion and relaxation: After a relaxation time, the non-equilibrium carriers diffuse in the conduction band / valence band and simultaneously relax to lower energy states near the bottom of the conduction band / top of the valence band in the form of thermal radiation; S1.

3. Recombination and release: After relaxation, the electrons and holes recombine radiatively in the form of photon emission, so that the electrons optically excited to the conduction band return to the valence band again; using a detector to collect the photons released during the radiative recombination of electrons and holes, that is, the fluorescence signal, and display it on an oscilloscope; S1.

4. Calculation and analysis: The calculation of the non-equilibrium carrier concentration excited in the sample involves factors such as the laser generation rate, laser pulse time, loss of the laser passing through the optical system to reach the sample surface, laser power, sample reflectivity, sample absorption coefficient for this laser, sample thickness, spot size, and photon energy.

3. The carrier lifetime testing method for variable excitation intensity time-resolved photoluminescence according to claim 2, wherein: In step S1.1, the sample is excited with a non-equilibrium carrier concentration which is （1） Among them is the laser generation rate, is the laser pulse time, is the loss of the laser passing through the optical system to reach the sample surface, is the laser power, is the sample reflectivity, is the absorption coefficient of the sample for this laser, is the sample thickness, is the spot size, is the photon energy.

4. The method for testing the carrier lifetime of variable excitation intensity time-resolved photoluminescence according to claim 2, characterized in that: In step S1.3, Excess carriers are generated by laser excitation. In the case of low injection, the recombination process of excess carriers mainly consists of three parts: SRH recombination , radiative recombination , Auger recombination , carrier lifetime and recombination rate can be expressed as: （2） Among them is the SRH recombination coefficient, is the radiative recombination coefficient, is the photon recycling factor, a parameter reflecting the process of repeated absorption of photons emitted by radiative recombination, is the Auger recombination coefficient; Among them, the small injection case refers to the case where the injected excess carrier electron concentration is less than the equilibrium electron concentration.

5. The method for testing the carrier lifetime of variable excitation intensity time-resolved photoluminescence according to claim 2, characterized in that: In step S1.3, Excess carrier concentration Satisfies the following equation: （3） After pulsed laser excitation during the test, , Equation (3) is rewritten as: （4） Solving Equation (4) gives ; In the carrier recombination of the sample, only radiative recombination emits photons to generate a fluorescence signal, so the relationship between the oscilloscope response signal and the carrier concentration inside the sample is calculated: （5） wherein represents the fluorescence collection ability of the optical system and the response rate of the detector, represents the carrier fluorescence lifetime, that is, twice the time it takes for the response curve to decay to 1 / e of its maximum value; in fact, the carrier lifetime of the bulk material is composed of the bulk lifetime and the surface lifetime in two parts Composition: （7）。

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