Method for measuring intrinsic carrier mobility of semiconductor material

Abstract

The invention discloses a method for measuring the intrinsic carrier mobility of a semiconductor material, and relates to the technical field of semiconductor material performance measurement. The method comprises the following steps: establishing a measurement system for the intrinsic carrier mobility of the semiconductor material; using an optical delay line to continuously change the relative time delay between the probe light and the pump light, obtaining the light intensity of the probe light under the action of the pump light and without the action of the pump light, testing to obtain a transient reflection dynamic spectrum of the semiconductor material, and extracting to obtain a Brillouin oscillation signal; calculating an electron deformation potential, a hole deformation potential and a semiconductor material elastic modulus based on the Brillouin oscillation signal; and calculating the intrinsic carrier (electron and hole) mobility of the semiconductor material based on the electron deformation potential, the hole deformation potential and the elastic modulus of the semiconductor material. Aiming at the lack of a method for experimentally measuring the intrinsic carrier mobility of a material at present, the measurement method disclosed by the invention fills the blank in the field.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material property measurement, and particularly relates to a method for measuring the intrinsic carrier mobility of semiconductor materials. Background Art

[0002] Carrier mobility is one of the decisive factors for the carrier diffusion length of semiconductor materials and is a key parameter affecting the performance of semiconductor devices. The influencing factors of perovskite carrier mobility can be divided into two categories, namely intrinsic factors and extrinsic factors. The intrinsic factors are mainly the electron-lattice coupling (electron-phonon scattering) of the material, which depends on the inherent properties of the material (such as the material structure) and is inevitable; extrinsic factors, such as electron-defect scattering, carrier-carrier scattering, etc., are closely related to the material preparation process, carrier concentration, etc. The carrier mobility affected only by intrinsic factors is the intrinsic carrier mobility of the material, which is the optimal carrier mobility that the material can achieve under specific working temperature conditions. Quantitatively obtaining the intrinsic carrier mobility of semiconductor materials and giving the limit of the carrier transport performance of the materials can guide the design of semiconductor materials, the preparation of thin films, and the optimization of device structures, which is of great significance for the development of high-performance semiconductor devices.

[0003] The methods for measuring carrier mobility can be divided into two categories. One is the electrical characterization method, such as the Hall effect method, the time-of-flight method, the space charge limited current, etc.; the other is the non-contact characterization method, such as terahertz spectroscopy. Compared with the electrical measurement method, the non-contact measurement method can avoid the interference of the metal-semiconductor contact problem and can better reflect the carrier transport performance of the material. Terahertz spectroscopy has been widely used in the measurement of semiconductor material carrier mobility. This technology can not only extract the carrier mobility through the change of terahertz transmittance, but also obtain the defect state density and the carrier recombination process through the analysis of photoconductivity dynamics. However, due to the inability to exclude the influence of non-intrinsic factors such as defects, the carrier mobility measured by terahertz spectroscopy reflects the actual carrier mobility under the combined action of intrinsic and extrinsic factors, rather than the intrinsic carrier mobility of the material. In short, there is currently a lack of an experimental method for experimentally measuring the intrinsic carrier mobility of materials.

[0004] In view of the technical problems existing in the prior art, the present invention proposes a non-contact method for measuring the elastic modulus of materials based on femtosecond transient spectroscopy. In this technical solution, a femtosecond laser pulse is used to excite the semiconductor material to generate a thermoelastic pressure, and then the thermoelastic pressure is transmitted into the material. By using the probe pulse at different times, the Brillouin oscillation frequency of the material is detected, and then the elastic modulus of the material along the transmission direction is calculated, and further the mobility of the intrinsic carriers (electrons and holes) of the semiconductor material is calculated. Summary of the Invention

[0005] The object of the present invention is to provide a method for measuring the intrinsic carrier mobility of a semiconductor material, so as to solve the problem in the above-mentioned background technology that the existing experimental method for measuring the carrier mobility of a material measures the actual carrier mobility under the combined action of intrinsic and non-intrinsic factors, rather than the intrinsic carrier mobility of the material, and there is currently a lack of an experimental method for experimentally measuring the intrinsic carrier mobility of a material.

[0006] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0007] The present invention proposes a method for measuring the intrinsic carrier mobility of a semiconductor material in the first aspect, including the following steps:

[0008] S1. Select a semiconductor material as a sample, build a measurement system for the intrinsic carrier mobility of the semiconductor material, and use a femtosecond laser pulse to excite the semiconductor material;

[0009] S2. Detect the Brillouin oscillation signal by using the measurement system: continuously change the relative time delay between the probe light and the pump light by using an optical delay line, and obtain the light intensity of the probe light with and without the action of the pump light, and test to obtain the transient reflection dynamics spectrum of the semiconductor material; extract the Brillouin oscillation signal based on the transient reflection dynamics spectrum;

[0010] S3. Based on the Brillouin oscillation signal, obtain the elastic modulus of the semiconductor material and the characterization of the relative defect state density of the semiconductor material, and calculate the electron deformation potential and the hole deformation potential;

[0011] S4. Calculate the intrinsic carrier mobility of the semiconductor material based on the electron deformation potential, the hole deformation potential and the elastic modulus of the semiconductor material.

[0012] Preferably, the S1 is specifically as follows:

[0013] The measurement system includes: a femtosecond laser, a beam splitter, a mirror, a convex lens, a sapphire crystal Sapphire, an OPA system, an optical delay line ODL, and a spectrometer;

[0014] The 800-nm femtosecond pulsed light with a repetition frequency of 1 kHz emitted from the femtosecond laser is split into a probe optical path and a pump optical path by the beam splitter;

[0015] After the pump light enters the OPA system, it is modulated into a high-energy monochromatic pulsed light with a repetition frequency of 500 Hz and a wavelength of 400 nm or any wavelength in the range of 460-700 nm; the modulated pump light is reflected and focused, and then converges on the sample Sample;

[0016] The probe light enters the optical delay line (ODL) to control the time delay between the pump light and the probe light; after the probe light exits the optical delay line (ODL), it is focused onto the sapphire crystal (Sapphire) to generate supercontinuum white light; the supercontinuum white light is split by a beam splitter into a reference optical path and a probe optical path;

[0017] The reference light, after being reflected and focused, finally enters the spectrometer;

[0018] The probe light is focused on the sample (Sample) and spatially overlapped with the pump light; the probe light carrying the sample information reflected from the sample surface, after being reflected and focused, finally enters the spectrometer.

[0019] Preferably, the S2 is specifically as follows:

[0020] The repetition frequency of the pump light is modulated to 500 Hz, and the repetition frequency of the probe light remains at 1 kHz, with a period of 2 ms; within the first 1 ms of a cycle at time 0, due to the time coincidence of the probe light and the pump light, the light intensity of the probe light under the action of the pump light is acquired; within the second 1 ms of the same cycle, the light intensity of the probe light without the action of the pump light is acquired;

[0021] The transient reflectivity change amplitude at time 0 of the semiconductor material surface is calculated as follows:

[0022]

[0023] where is the light intensity of the reflected light at wavelength λ at time t after pump excitation; is the light intensity of the reflected light at wavelength λ without pump;

[0024] Based on the time 0, the optical path of the probe light is extended, and the transient reflectivity change amplitude after the pump light acts for x ps is detected. And so on, by continuously changing the relative time delay between the probe light and the pump light using the optical delay line, the complete transient reflection dynamics spectrum of the semiconductor material is tested;

[0025] The carrier signal background is obtained based on the smoothing function of the adjacent averaging method, and the Brillouin oscillation signal is obtained by subtracting the carrier signal background from the original data of the transient reflection dynamics spectrum.

[0026] Preferably, in S3, the calculation of the electron deformation potential and the hole deformation potential is specifically as follows:

[0027] Excitation lights with excitation photon energies of hv1 and hv2 and the same excitation photon number density N are selected to excite the same sample. At hv - E g >> E g - Et When this is done, the ratio α of the amplitudes of the two Brillouin oscillation signals is measured to obtain the deformation potential stress σ d and the thermoelastic stress σ under two excitation conditions T1 and σ T2 The expressions of are as follows:

[0028]

[0029] Under the same excitation conditions, two single-crystal samples with different defect state densities with excitation defect state densities of n and εn respectively are obtained, and the following relational expressions are obtained:

[0030]

[0031] σ d1 -σ d2 =(1 - ε)nd h

[0032] σ d1 =-Nd e -(N - n)d h

[0033] Among them, σ T1 and σ T2 are the thermoelastic stresses of two semiconductor materials under the same excitation conditions, and σ d1 and σ d2 are the deformation potential stresses of two semiconductor materials; ε is the known relative defect state density coefficient;

[0034] The electron deformation potential d e , the hole deformation potential d h , and the electron defect state density n are obtained in sequence.

[0035] Preferably, the S4 is specifically as follows:

[0036] The calculation of the intrinsic carrier mobility of the semiconductor material is as follows:

[0037]

[0038] Among them, μ is the intrinsic carrier mobility; is the reduced Planck constant, e is the elementary charge, k b is the Boltzmann constant, T is the absolute temperature, and m* is the effective mass of an electron or a hole (which can be obtained by referring to the literature); C is the elastic modulus along the crystal axis direction; d is the deformation potential of an electron or a hole, which is d e when describing the intrinsic electron mobility and d is d h when describing the intrinsic hole mobility. When calculating the intrinsic carrier mobility of an electron or a hole, the effective mass m* and the deformation potential d of the corresponding type of carrier need to be substituted into the above formula respectively.

[0039] Preferably, the elastic pressure of the semiconductor material along the transmission direction is calculated based on the electron deformation potential and the hole deformation potential as follows:

[0040] The elastic pressure generated by photoexciting the semiconductor material is proportional to the initial amplitude of the time-domain Brillouin oscillation signal. The elastic pressure σ includes the thermoelastic pressure σ T and the deformation potential pressure σ d ; that is

[0041]

[0042] σ d = -(N - n)d h - Nd e

[0043]

[0044] where B and β are the known bulk modulus of elasticity and the coefficient of linear expansion respectively, C p is the known material heat capacity; n is the density of electron defect states; hv represents the excitation photon energy, N represents the excitation photon density, and hv and N are experimental parameters; E g - E t represents the energy difference between the defect state and the bottom of the conduction band; d e represents the electron deformation potential, and d h represents the hole deformation potential.

[0045] Preferably, obtaining the elastic modulus of the semiconductor material in S3 is specifically as follows:

[0046] The semiconductor material is measured by the time-domain Brillouin scattering technique to obtain the Brillouin oscillation signals under the incident conditions along different crystal directions, the oscillation frequencies are extracted, and the elastic modulus of the corresponding material is given; the elastic modulus C is expressed as:

[0047] C = f 2 λ 2 ρ / (4n 2 )

[0048] where λ is the experimental detection wavelength, f is the Brillouin oscillation frequency, n is the refractive index of the material at the detection wavelength, and ρ is the material density; by measuring the Brillouin oscillation frequency f at a specific detection wavelength λ, the elastic modulus of the material in this incident direction can be determined.

[0049] Preferably, obtaining the relative defect state density characterization of the semiconductor material in S3 is specifically as follows:

[0050] By using the time-domain Brillouin scattering technique to characterize the Brillouin oscillation signals of samples with different defect state densities, and based on the fact that the Brillouin oscillation relaxation rate is proportional to the defect state density of the material, the ratio of the defect state densities is inferred from the ratio of the Brillouin oscillation relaxation rates of the material.

[0051] Preferably, the energy difference E g -E t between the defect state and the bottom of the conduction band is specifically as follows:

[0052] The transient absorption spectroscopy technique is used to measure the transient absorption spectroscopy signals of each semiconductor single crystal material, determine the bleach peaks corresponding to the defect state energy level and the bottom of the conduction band, and calculate the energy difference between the defect state energy level and the bottom of the conduction band.

[0053] In the second aspect, the present invention proposes a measurement system applied to a method, including: a femtosecond laser, a beam splitter, a mirror, a convex lens, a sapphire crystal Sapphire, an OPA system, an optical delay line ODL, and a spectrometer;

[0054] Two beam splitters are provided, namely a first beam splitter S1 and a second beam splitter S2;

[0055] Seventeen mirrors are provided, namely a first mirror M1 to a seventeenth mirror M17;

[0056] Seven convex lenses are provided, namely a first convex lens L1 to a seventh convex lens L7.

[0057] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0058] (1). The traditional experimental method cannot experimentally measure the intrinsic carrier mobility of the material. The present invention provides a method for experimentally measuring the intrinsic carrier mobility of the material, making it possible to experimentally measure the intrinsic carrier mobility, thereby giving the limit of the carrier transport performance of the material, and further providing guidance for the preparation of semiconductor materials and the optimization of device performance.

[0059] (2). In the present invention, through the extraction and analysis of transient reflection dynamics, the key parameters (material electron deformation potential, hole deformation potential, elastic modulus) required for measuring the intrinsic carrier mobilities of electrons and holes are measured, breaking the limitation of only relying on theoretical calculations to roughly estimate the intrinsic carrier (electron and hole) mobilities, making it possible to experimentally measure the intrinsic carrier (electron and hole) mobilities, filling the gap in the field. Experimentally measuring the intrinsic carrier mobility of the material can quantitatively evaluate the influence of non-intrinsic factors such as defects on the carrier migration characteristics, and provide guidance for material optimization.

[0060] (3) In the present invention, the semiconductor material is measured by a measurement system, and multiple properties of the semiconductor material, such as the intrinsic carrier mobility, elastic pressure, elastic modulus, relative defect state density, etc., can be measured. Description of the Drawings

[0061] Figure 1 It is a schematic structural diagram of the measurement system in the present invention. Detailed Embodiments

[0062] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0063] Embodiment 1:

[0064] A method for measuring the intrinsic carrier mobility of a semiconductor material mainly includes the following steps:

[0065] Step 1, build a measurement system for the intrinsic carrier mobility of the semiconductor material;

[0066] The measurement system includes a femtosecond laser, a beam splitter, a mirror, a convex lens, a sapphire crystal Sapphire, an OPA system, an optical delay line ODL, and a spectrometer; among them, two beam splitters are provided, namely the first beam splitter S1 and the second beam splitter S2; 17 mirrors are provided, namely the first mirror M1 to the seventeenth mirror M17; seven convex lenses are provided, namely the first convex lens L1 to the seventh convex lens L7, as Figure 1 shown.

[0067] The working process of the measurement system is as follows: The 800nm femtosecond pulsed light with a repetition frequency of 1kHz emitted from the femtosecond laser first passes through the first beam splitter S1 and is divided into a probe optical path and a pump optical path. Among them, the pump light enters the OPA system and is modulated into a high-energy monochromatic pulsed light with a repetition frequency of 500Hz and a wavelength of 400nm or any wavelength in the range of 460 - 700nm. The modulated pump light is reflected by the first mirror M1 and the second mirror M2 and focused by the first convex lens L1, and finally converges on the sample Sample;

[0068] The probe light is reflected by the third mirror M3 and the fourth mirror M4 and then enters the optical delay line ODL to control the time delay between the pump light and the probe light. After the probe light exits the optical delay line ODL, it is redirected by the mirror group composed of the fifth mirror M5 and the sixth mirror M6, and finally focused on the sapphire crystal Sapphire by the second convex lens L2 to generate supercontinuum white light. The supercontinuum white light is collimated by the third convex lens L3 and then redirected by the mirror group composed of the seventh mirror M7, the eighth mirror M8, and the ninth mirror M9, and then is split into a reference optical path and a probe optical path by the second beam splitter S2.

[0069] The reference light is redirected by the mirror group composed of the tenth mirror M10 and the eleventh mirror M11 and then focused by the fourth convex lens L4, and finally enters the spectrometer.

[0070] The probe light is focused on the sample Sample by the fifth convex lens L5 and spatially coincides with the pump light; the probe light carrying the sample information reflected from the sample surface is reflected by the mirror group composed of the twelfth mirror M12, the thirteenth mirror M13, the fourteenth mirror M14, the fifteenth mirror M15, the sixteenth mirror M16, and the seventeenth mirror M17, and is collimated by the sixth convex lens L6 and focused by the seventh convex lens L7, and finally enters the spectrometer.

[0071] Step two, use a measurement system to detect the Brillouin oscillation signal;

[0072] 1) Measure the change in the transient reflectivity of the semiconductor material surface;

[0073] For the detection of the Brillouin oscillation signal, since the repetition frequency of the pump light entering the OPA in the present invention is modulated to 500 Hz, and the repetition frequency of the probe light remains at the original 1 kHz, then 2 ms can be regarded as a period. Assume that within the first 1 ms of a period at time 0, since the probe light and the pump light achieve time coincidence, it is equivalent to having the pump light and the probe light acting on the material surface simultaneously. At this time, the spectrometer detects the intensity of the probe light reflected after the pump light modulates the reflectivity of the sample surface; subsequently, within the second 1 ms of the same period, since the repetition frequency of the pump light is only 500 Hz, at this time, only the probe light acts on the material surface and there is no pump light, that is, at this time, the spectrometer detects the intensity of the probe light reflected when the reflectivity of the material surface is not modulated. Thus, the intensities of the probe light with and without the action of the pump light are obtained.

[0074] Substitute the obtained intensity of the probe light into the following formula (1), and the change in the transient reflectivity of the material surface at time 0 can be calculated Amplitude.

[0075]

[0076] Among them, is the intensity of the reflected light at wavelength λ at time t after pump excitation; is the intensity of the reflected light at wavelength λ without pump.

[0077] 2) Measure the complete transient reflection dynamics spectrum of the semiconductor material;

[0078] In order to obtain the complete transient reflection dynamics spectrum, it is necessary to change the time difference between the probe light and the pump light reaching the material surface. For this purpose, the present invention uses an optical delay line ODL in the probe light path to achieve a time delay relative to the pump light by increasing the optical path of the probe light.

[0079] Assume that based on the time of 0, by extending the optical path of the probe light, the probe light pulse reaches the sample surface 1 ps after the pump light pulse arrives at the material surface. At this time, detection is carried out to obtain the amplitude change of the transient reflectivity after the pump light acts for 1 ps. By analogy, by continuously changing the relative time delay between the probe light and the pump light using the optical delay line, the complete transient reflection dynamics spectrum of the semiconductor material can be measured.

[0080] 3) Calculate the Brillouin oscillation signal;

[0081] Since the excitation light energy is higher than the material bandgap, after the pump pulse excites the material surface, deformation potential stress and thermal expansion stress will be generated to promote the generation of coherent acoustic phonons (CAP). And the CAP will modulate the local dielectric constant to form an optical interface that moves from the sample surface into the crystal at the sound velocity v. The movement of this optical interface changes the local refractive index and will reflect the probe light that penetrates into the material. The probe light reflected from the material surface and the probe light reflected from the optical interface will interfere with each other because they meet the interference conditions. At the same time, because this optical interface will propagate into the crystal at a certain sound velocity v, the phase difference between the probe light reflected from the surface and the probe light reflected from the optical interface will change linearly with time. Therefore, the obtained transient reflection dynamics spectrum will be superimposed with a Brillouin oscillation signal induced by CAP that changes sinusoidally.

[0082] In order to extract the CAP signal (oscillation signal) in the TR dynamics, the present invention obtains the carrier signal background by using a smoothing function based on the adjacent averaging method, and obtains a pure Brillouin oscillation signal by subtracting the carrier signal background from the original data.

[0083] Step three: Calculate various parameters such as the electron deformation potential, hole deformation potential, and elastic modulus of the semiconductor material;

[0084] The elastic pressure (σ) generated by photoexciting the semiconductor material is proportional to the initial amplitude of the Brillouin oscillation signal in the time domain, that is

[0085]

[0086] Among them, B and β are the bulk modulus of elasticity and the coefficient of linear expansion (which can be obtained by referring to the literature), and C p is the heat capacity of the material (a parameter that can be obtained by referring to the literature); n is the density of electronic defect states; the thermoelastic pressure σ T is the deformation potential pressure σ d is (-(N - n)d h -Nd e ).

[0087] Given the excitation photon energy (hv, an experimental parameter), the excitation photon density (N, an experimental parameter), the elastic modulus (C), and the energy difference (E g -E t ) between the defect state and the bottom of the conduction band, the deformation potentials d e and d h of electrons and holes can be respectively given by the following steps:

[0088] Select excitation lights with photon energies of hv1 and hν2 and the same excitation photon number density to excite the same sample. When hν - E g >> E g -E t , the ratio α of the amplitudes of the two oscillation signals measured experimentally can give the expressions of the deformation potential pressure σ d and the thermoelastic pressures σ T1 and σ T2 under the two excitation conditions, that is:

[0089]

[0090] Furthermore, under the same excitation conditions, two single-crystal samples with different defect state densities and defect state densities of n and εn (ε is the relative defect state density coefficient and is assumed to be known) are excited to obtain the following relationship:

[0091]

[0092] σ d1 -σ d2 =(1 - ε)nd h (7)

[0093] σ d1 =-Nd e -(N - n)d h (8)

[0094] Among them, σ T-1 and σ T-2The thermoelastic pressure of two materials under the same excitation condition, σ d1 and σ d2 are the deformation potential pressures of the two materials. From formulas (6) to (8), the electron deformation potential d e , the hole deformation potential d h , and the defect state density n can be obtained in sequence.

[0095] In the above analysis, the elastic modulus (C), the energy difference (E g -E t ) between the defect state and the bottom of the conduction band, and the relative defect state density (ε) of the material need to be experimentally measured. This invention will introduce the experimental measurement schemes for these three parameters respectively:

[0096] In this embodiment, extraction of the elastic modulus of semiconductor materials:

[0097] The elastic modulus of the material can be expressed as C = f 2 λ 2 ρ / (4n 2 )(where λ is the experimental detection wavelength, f is the Brillouin oscillation frequency, n is the refractive index of the material at the corresponding detection wavelength, and ρ is the material density, all of which can be obtained from literature). It can be seen that by measuring the Brillouin oscillation frequency f at a specific detection wavelength λ, the elastic modulus of the material in the incident direction can be determined.

[0098] Use the time-domain Brillouin scattering technique to measure semiconductor materials, obtain the Brillouin oscillation signals under the incident conditions along different crystal directions, extract the oscillation frequencies, and give the elastic moduli of each material.

[0099] In this embodiment, characterization of the relative defect state density of semiconductor materials:

[0100] The Brillouin oscillation relaxation rate is proportional to the defect state density of the material. By comparing the Brillouin oscillation relaxation rates of different semiconductor materials, the ratio of their defect state densities can be given. The time-domain Brillouin scattering technique will be used to characterize the Brillouin oscillation signals of samples with different defect state densities, and the ratio of their defect state densities will be inferred from the ratio of the oscillation relaxation rates of the materials.

[0101] In this embodiment, characterization of the energy difference between the bottom of the conduction band and the defect state energy level:

[0102] According to literature reports, the charge filling of the conduction band and the defect state in semiconductor materials will cause ground state bleaching in the transient absorption spectrum signal. The energy difference between the defect state and the bottom of the conduction band can be estimated from the difference in the peak positions of the two bleaching peaks. Use the transient absorption spectrum technique to test the transient absorption spectrum signals of each semiconductor single crystal material, identify the bleaching peaks corresponding to the defect state energy level and the bottom of the conduction band, and estimate the energy difference between the defect state energy level and the bottom of the conduction band.

[0103] In summary, substituting the parameters calculated above into formula (2) enables the calculation of the elastic pressure of the semiconductor material along the transmission direction.

[0104] Step four, calculate the intrinsic carrier mobility of the semiconductor material;

[0105] The intrinsic carrier mobility of the semiconductor material can be experimentally measured by the following method:

[0106] Substituting the electron (hole) deformation potential and the elastic modulus into formula (9) can give the intrinsic carrier mobility of the material.

[0107]

[0108] Among them, is the reduced Planck constant, e is the elementary charge, k b is the Boltzmann constant, T is the absolute temperature, m* is the effective mass of the carrier, and these parameters can be obtained by referring to relevant materials; C is the elastic modulus along the crystal axis direction; d is the deformation potential of electrons or holes, and d is d e when describing the intrinsic electron mobility, and d is d h when describing the intrinsic hole mobility. The electron and hole deformation potentials are measured by the above experiments. When calculating the intrinsic carrier mobility of electrons or holes, the effective mass and deformation potential of the corresponding type of carrier need to be substituted into the above formula respectively.

[0109] The above is only used to help understand the method of the present invention and its core essence, but the protection scope of the present invention is not limited thereto. For those of ordinary skill in the art in the technical field of the present invention, any equivalent substitution or change made within the technical scope disclosed by the present invention according to the technical solution and inventive concept of the present invention should be covered within the protection scope of the present invention. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for measuring the intrinsic carrier mobility of a semiconductor material, characterized in that, It includes the following steps: S1. Select a semiconductor material as a sample, set up a measurement system for the intrinsic carrier mobility of the semiconductor material, and use a femtosecond laser pulse to excite the semiconductor material; S2. Detect the Brillouin oscillation signal using the measurement system: Continuously change the relative time delay between the probe light and the pump light using an optical delay line, and obtain the light intensity of the probe light with and without the action of the pump light, and test to obtain the transient reflection dynamics spectrum of the semiconductor material; Extract the Brillouin oscillation signal based on the transient reflection dynamics spectrum; S3. Based on the Brillouin oscillation signal, obtain the elastic modulus of the semiconductor material and the characterization of the relative defect state density of the semiconductor material, and calculate the electron deformation potential and the hole deformation potential; S4. Based on the electron deformation potential, the hole deformation potential, and the elastic modulus of the semiconductor material, calculate the intrinsic carrier mobility of the semiconductor material.

2. The method according to claim 1, wherein The specific content of S1 is as follows: The 800-nm femtosecond pulsed light with a repetition frequency of 1 kHz emitted from the femtosecond laser is split into a probe light path and a pump light path by a beam splitter; After the pump light enters the OPA system, it is modulated into a high-energy monochromatic pulsed light with a repetition frequency of 500 Hz and a wavelength of 400 nm or any wavelength in the range of 460 - 700 nm; The modulated pump light is reflected and focused, and then converges on the sample Sample; The probe light enters the optical delay line ODL to control the time delay between the pump light and the probe light; After the probe light exits the optical delay line ODL, it is focused on the sapphire crystal Sapphire to generate supercontinuum white light; The supercontinuum white light is split into a reference light path and a probe light path by a beam splitter; The reference light is reflected and focused, and finally enters the spectrometer; The probe light is focused on the sample Sample and spatially coincides with the pump light; The probe light carrying the sample information reflected from the sample surface is reflected and focused, and finally enters the spectrometer.

3. The method according to claim 1, wherein The specific content of S2 is as follows: The repetition frequency of the pump light is modulated to 500 Hz, and the repetition frequency of the probe light remains 1 kHz, with a period of 2 ms; In the first 1 ms of a period at time 0, due to the time coincidence of the probe light and the pump light, the light intensity of the probe light with the action of the pump light is obtained; In the second 1 ms of the same period, the light intensity of the probe light without the action of the pump light is obtained; Calculate the amplitude of the change in the transient reflectivity of the semiconductor material surface at time 0; Based on time 0, extend the optical path of the probe light, and detect the amplitude of the change in the transient reflectivity x ps after the action of the pump light, and so on. By continuously changing the relative time delay between the probe light and the pump light using the optical delay line, test to obtain the complete transient reflection dynamics spectrum of the semiconductor material; Obtain the carrier signal background based on the smoothing function of the adjacent averaging method, and obtain the Brillouin oscillation signal by subtracting the carrier signal background from the original data of the transient reflection dynamics spectrum.

4. The method according to claim 3, wherein In S3, the calculation of the electron deformation potential and the hole deformation potential is specifically as follows: Select excitation lights with excitation photon energies of hν1 and hν2 respectively, which have the same excitation photon number density N, to excite the same sample. In the case of hν - E g >> E g -E t When, measure the ratio α of the amplitudes of the two Brillouin oscillation signals to obtain the deformation potential pressure σ d and the thermoelastic pressures σ T1 and σ T2 under the two excitation conditions, namely: Under the same excitation conditions, two single-crystal samples with different defect state densities of n and εn are excited to obtain the following relationship: σ d1 -σ d2 =(1 - ε)nd h σ d1 = -Nd e -(N - n)d h Among them, σ T1 and σ T2 are the thermoelastic pressures of two semiconductor materials under the same excitation conditions, σ d1 and σ d2 are the deformation potential pressures of two semiconductor materials; ε is the known relative defect state density coefficient; B and β are the known bulk modulus of elasticity and linear expansion coefficient respectively, C p is the known material heat capacity; hv represents the excitation photon energy, N represents the excitation photon density, hν and N are experimental parameters; n is the electron defect state density; E g -E t represents the energy difference between the defect state and the bottom of the conduction band; Successively obtain the electron deformation potential d e and the hole deformation potential d h and the electron defect state density ne.

5. The method according to claim 4, wherein The specific content of S4 is as follows: The calculation of the intrinsic carrier mobility of the semiconductor material is as follows: Among them, μ is the intrinsic carrier mobility; is the reduced Planck constant, e is the elementary charge, k b is the Boltzmann constant, T is the absolute temperature, m* is the effective mass of electrons or holes; C is the elastic modulus along the crystal axis direction; d is the deformation potential of electrons or holes, and d is d when describing the intrinsic electron mobility e and d is d when describing the intrinsic hole mobility h .

6. The method according to claim 4, characterized in that Based on the electron deformation potential and the hole deformation potential, the elastic pressure of the semiconductor material along the transmission direction is calculated as follows: The elastic pressure generated by photoexciting a semiconductor material is proportional to the initial amplitude of the time-domain Brillouin oscillation signal. The elastic pressure σ includes the thermoelastic pressure σ T and the deformation potential pressure σ d ; that is Among them, d e represents the electron deformation potential, and d h represents the hole deformation potential.

7. The method according to claim 5, characterized in that, In step S3, obtaining the elastic modulus of the semiconductor material specifically includes: Measuring the semiconductor material by using the time-domain Brillouin scattering technique to obtain the Brillouin oscillation signals under the incident conditions along different crystal orientations, extracting the oscillation frequencies, and giving the elastic modulus of the corresponding material; the elastic modulus C is expressed as: C = f 2 λ 2 ρ / (4n 2 ) where λ is the experimental detection wavelength, f is the Brillouin oscillation frequency, n is the refractive index of the material at the corresponding detection wavelength, and ρ is the material density.

8. The method according to any one of claims 4-7, characterized in that In step S3, obtaining the characterization of the relative defect state density of the semiconductor material specifically includes: Using the time-domain Brillouin scattering technique to characterize the Brillouin oscillation signals of samples with different defect state densities. Based on the fact that the Brillouin oscillation relaxation rate is proportional to the material defect state density, the ratio of the defect state densities is inferred from the ratio of the Brillouin oscillation relaxation rates of the materials.

9. The method according to any one of claims 4-7, characterized in that, The energy difference E between the defect state and the bottom of the conduction band g -E t , specifically: Using the transient absorption spectroscopy technique to test the transient absorption spectroscopy signals of each semiconductor single crystal material, determining the bleach peaks corresponding to the defect state energy levels and the conduction band bottom, and calculating the energy difference between the defect state energy levels and the conduction band bottom.

10. A measurement system applied to the method according to any one of claims 1-7, characterized in that, Including: Femtosecond laser, beam splitter, mirror, convex lens, sapphire crystal Sapphire, OPA system, optical delay line ODL, spectrometer.

Images