Apparatus and method for evaluating physical properties

Abstract

To easily identify an electronic state of a sample in a non-contact and non-destructive manner.SOLUTION: A physical property evaluation device includes: a pulse laser light source 1 that emits pulse laser light; a beam splitter 3 that splits the pulse laser light into probe light and pump light; a delay circuit 5 that changes a delay time of the pump light to the probe light; a chopper 9 that modulates intensity of the pump light; a concave surface mirror 15 that guides the probe light and the pump light modulated in intensity to a sample 30; a light detector 16 that detects the probe light reflected by the sample 30; a lock-in detector 18 that detects a signal having a modulation frequency of the chopper 9 of output signals of the light detector 16 as a change in reflectivity of the sample 30; an initial phase calculation unit 20 that calculates an initial phase of a phonon on the basis of the change in reflectivity; and an electronic state identification unit 21 that identifies an electronic state of the sample 30 on the basis of the initial phase of the phonon.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a physical property evaluation apparatus and method for evaluating the physical properties of thin films in a non-contact, non-destructive manner. [Background technology]

[0002] To fabricate high-speed electronic devices, it is necessary that the electrons in the materials used have high velocity (high mobility). Recently, Dirac electrons, which have a different energy-momentum dispersion relation than ordinary electrons, have attracted attention as electrons with high mobility, and research is actively being conducted on them. For example, bismuth, a semimetal, is the system in which Dirac electrons were first discovered in a solid state (Non-Patent Literature 1).

[0003] On the other hand, one of the important conditions for the operation of electronic devices is that their electrical properties are those of a semiconductor with a band gap. In 1967, theoretical studies pointed out that bismuth undergoes a transition from a semimetal to a semiconductor due to quantum size effects when its film thickness reaches about 30 nm (Non-Patent Literature 2).

[0004] Recent advancements in thin-film technology have made it possible to fabricate high-quality bismuth thin films. As a result, the phase transition of bismuth from semimetal to semiconductor has been confirmed through photoelectron spectroscopy (Non-Patent Document 3) and electrical conductivity measurements (Non-Patent Documents 4 and 5).

[0005] The methods disclosed in Non-Patent Documents 3-5 require sample pretreatment before measurement. Photoelectron spectroscopy requires cleaning of the sample surface. Electrical conductivity measurement requires the creation of metal electrodes on the sample. Furthermore, photoelectron spectroscopy requires measurement under vacuum. However, for bismuth to be used as a material for electronic devices, it is necessary to evaluate its physical properties on the device under operating conditions, and there is a need for non-destructive, non-contact evaluation of physical properties under atmospheric conditions.

[0006] Non-contact, non-destructive, and atmospheric measurement methods for evaluating material properties include optical methods such as those described in (I) to (III) below (Non-Patent Literature 6). (I) Reflectance measurement. (II) Transmittance measurement. (III) Ellipsometry (polarization analysis method).

[0007] Figure 11 shows the configuration of a microspectrophotometric device capable of measuring reflectance and transmittance (Non-Patent Literature 6). Reflectance and transmittance can be measured using the device shown in Figure 11, which consists of an epi-refractory microscope with a spectrometer mounted on top. When measuring reflectance, a white light source 100, such as a halogen lamp, is used. White light from the light source 100 passes through a half-mirror 101 and an objective lens 102 and enters the sample 110. The light reflected from the sample 110 passes through the objective lens 102 again, and a portion of it enters the observation optical system 103, allowing the measurement position to be confirmed with the naked eye. The light reflected from the sample 110 also enters a diffraction grating 104. The light spectrally separated by the diffraction grating 104 is reflected by a mirror 105 and each wavelength is detected simultaneously by a multi-channel line sensor 106. The reflectance can be calculated from the amount of reflected light from the sample 110. On the other hand, when measuring transmittance, a white light source 107 is used. White light from the light source 107 enters the sample 110 through the objective lens 108.

[0008] By measuring the absorption rate of a bismuth thin film, absorption coefficients corresponding to film thicknesses of 12 nm, 20 nm, and 50 nm can be obtained, as shown in Figure 12 (Non-Patent Literature 7). However, the measurement of absorptivity was limited to measurements on transparent substrates, making it inapplicable to samples such as electronic devices on opaque substrates. Furthermore, the measurement of reflectivity presented a challenge: interference effects appeared in the spectrum due to multiple reflections at the film interface, making it difficult to evaluate the optical properties.

[0009] The principle of ellipsometry is shown in Fig. 13 (Non-Patent Document 8). When white light 200 is linearly polarized as shown in the state of 201 in Fig. 13 and irradiated obliquely onto the sample 210, the reflected light from the sample 210 changes to elliptically polarized light as shown in the state of 202 in Fig. 13. Thus, ellipsometry irradiates light with a known polarization state onto the sample surface, measures the change in the polarization state during reflection for each wavelength of light, and determines the optical constants of the sample 210. However, in the analysis, a model that can correctly describe the film thickness, optical constants, and the object to be measured for each layer is required, and there is a problem that complex analysis is needed.

[0010] As described above, a method for simply identifying the electronic state of a bismuth thin film under non-contact, non-destructive conditions and at atmospheric pressure, regardless of the type of substrate, has not been known in the past.

Prior Art Documents

Non-Patent Documents

[0011]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

[0012] The present invention was made to solve the above problems and aims to provide a physical property evaluation apparatus and method that can easily identify the electronic state of a thin film sample in a non-contact, non-destructive manner. [Means for solving the problem]

[0013] The present invention provides a physical property evaluation apparatus comprising: a pulsed laser light source configured to emit pulsed laser light; a beam splitter configured to split the pulsed laser light into a first light and a second light; a delay circuit configured to change the delay time of the second light relative to the first light; a chopper configured to intensity modulate the second light; an optical system configured to guide the first light and the intensity-modulated second light to a sample; a first photodetector configured to detect the first light reflected by the sample or the first light transmitted through the sample; a lock-in detector configured to detect the signal of the modulation frequency of the chopper from the output signal of the first photodetector as a change in the reflectance or transmittance of the sample; an initial phase calculation unit configured to calculate the initial phase of phonons based on the change in reflectance or transmittance; and an electronic state identification unit configured to identify the electronic state of the sample based on the initial phase of phonons.

[0014] Furthermore, one example configuration of the physical property evaluation apparatus of the present invention further comprises a second photodetector configured to detect the first light before it is incident on the sample, a difference detector configured to output a difference signal between the output signal of the second photodetector and the output signal of the first photodetector, and a characteristic calculation unit configured to calculate the change in reflectance or the change in transmittance by dividing the intensity of the difference signal shown by the output of the lock-in detector by the intensity of the first light shown by the output of the second photodetector, wherein the lock-in detector detects the signal of the modulation frequency of the chopper from the difference signal obtained by the difference detector instead of the output signal of the first photodetector, and the initial phase calculation unit calculates the initial phase of the phonon based on the change in reflectance or the change in transmittance calculated by the characteristic calculation unit.

[0015] Furthermore, one example of the physical property evaluation apparatus of the present invention comprises a waveplate and polarizer configured such that the first light before it is incident on the sample is linearly polarized at a 45-degree angle to a horizontal plane perpendicular to the surface of the sample, and a polarizing beam splitter configured to separate the first light reflected by the sample or the first light transmitted through the sample into two lights with different polarization states, wherein the first photodetector consists of two photodetectors: one configured to detect one of the lights separated by the polarizing beam splitter, and the other configured to detect the other light separated by the polarizing beam splitter, and the output of the two photodetectors The system further comprises a difference detector configured to output a difference signal, and a characteristic calculation unit configured to calculate the change in reflectance or the change in transmittance by dividing the intensity of the difference signal shown by the output of the lock-in detector by the intensity of the light shown by the output of one of the two photodetectors, wherein the lock-in detector detects the signal of the modulation frequency of the chopper from the difference signal obtained by the difference detector instead of the output signal of the first photodetector, and the initial phase calculation unit calculates the initial phase of the phonon based on the change in reflectance or the change in transmittance calculated by the characteristic calculation unit. Furthermore, in one example configuration of the physical property evaluation apparatus of the present invention, the electronic state identification unit is characterized in that it identifies the electronic state of the sample based on the initial phase of the phonons calculated by the initial phase calculation unit and a known relationship between the initial phase of the phonons and the electronic state of the material constituting the sample.

[0016] Furthermore, the present invention provides a method for evaluating physical properties, comprising: a first step of dividing pulsed laser light into a first light and a second light, changing the delay time of the second light relative to the first light, and irradiating a sample with the first light and the intensity-modulated second light; a second step of detecting the first light reflected by the sample or the first light transmitted through the sample using a first photodetector; a third step of detecting the signal of the intensity-modulated frequency from the output signal of the first photodetector as a change in the reflectance or transmittance of the sample; a fourth step of calculating the initial phase of phonons based on the change in reflectance or transmittance; and a fifth step of identifying the electronic state of the sample based on the initial phase of phonons.

[0017] Furthermore, one example configuration of the physical property evaluation method of the present invention further includes, between the second step and the third step, a sixth step of detecting the first light before it is incident on the sample using a second photodetector, and a seventh step of outputting a difference signal between the output signal of the first photodetector and the output signal of the second photodetector, wherein the third step includes detecting a signal of the intensity modulation frequency from the difference signal instead of the output signal of the first photodetector, wherein between the third step and the fourth step, an eighth step of calculating the change in reflectance or the change in transmittance by dividing the intensity of the difference signal obtained in the third step by the intensity of the first light indicated by the output of the second photodetector, wherein the fourth step includes calculating the initial phase of the phonon based on the change in reflectance or the change in transmittance calculated in the eighth step.

[0018] Furthermore, in one example configuration of the physical property evaluation method of the present invention, the first step includes adjusting the first light before it is incident on the sample so that it is linearly polarized at an angle of 45 degrees with respect to a horizontal plane perpendicular to the surface of the sample; the second step includes separating the first light reflected by the sample or the first light transmitted through the sample into two lights with different polarization states, detecting one of the separated lights with one of the two first photodetectors, and detecting the other separated light with the other of the two first photodetectors; and between the second step and the third step, outputting a difference signal of the outputs of the two first photodetectors. The method further includes a sixth step, the third step of detecting a signal of the difference signal at the intensity modulation frequency instead of the output signal of the first photodetector, and between the third step and the fourth step, an eighth step of calculating the change in reflectance or the change in transmittance by dividing the intensity of the difference signal obtained in the third step by the intensity of the light shown by the output of one of the two first photodetectors, the fourth step of calculating the initial phase of the phonon based on the change in reflectance or the change in transmittance calculated in the eighth step. Furthermore, in one example configuration of the physical property evaluation method of the present invention, the fifth step is characterized in that it includes a step of identifying the electronic state of the sample based on the initial phonon phase calculated in the fourth step and a known relationship between the initial phonon phase and the electronic state of the material constituting the sample. [Effects of the Invention]

[0019] According to the present invention, by providing a pulsed laser light source, a beam splitter, a delay circuit, a chopper, an optical system, a first photodetector, a lock-in detector, an initial phase calculation unit, and an electronic state identification unit, the electronic state of a sample such as a bismuth thin film can be easily identified non-contact and non-destructively. [Brief explanation of the drawing]

[0020] [Figure 1] Figure 1 is a block diagram showing the configuration of a physical property evaluation apparatus according to a first embodiment of the present invention. [Figure 2] Figure 2 is a flowchart illustrating the operation of a physical property evaluation apparatus according to the first embodiment of the present invention. [Figure 3] Figure 3 shows the measurement results of the physical property evaluation apparatus according to the first embodiment of the present invention. [Figure 4] Figure 4 shows the relationship between the phonon generation process and the initial phase of the phonons. [Figure 5] Figure 5 shows the results of measuring the laser intensity dependence of the initial phonon amplitude. [Figure 6] Figure 6 is a flowchart illustrating another operation of the physical property evaluation apparatus according to the first embodiment of the present invention. [Figure 7] Figure 7 is a block diagram showing the configuration of a physical property evaluation apparatus according to a second embodiment of the present invention. [Figure 8] Figure 8 is a flowchart illustrating the operation of a physical property evaluation apparatus according to a second embodiment of the present invention. [Figure 9] Figure 9 is a flowchart illustrating another operation of the physical property evaluation apparatus according to a second embodiment of the present invention. [Figure 10] Figure 10 is a block diagram showing an example of the configuration of a computer that realizes a physical property evaluation apparatus according to the first and second embodiments of the present invention. [Figure 11] Figure 11 is a block diagram showing the configuration of a microspectrophotometer. [Figure 12] Figure 12 shows the film thickness dependence of the absorption coefficient of a bismuth thin film. [Figure 13] Figure 13 is a diagram illustrating the principle of ellipsometry. [Modes for carrying out the invention]

[0021] [Principle of the invention] In this invention, the electronic state (metal / semiconductor) of a bismuth thin film is detected non-contact, non-destructively, and under atmospheric pressure by the following procedure.

[0022] (Procedure 1) Time-resolved reflectance measurement is performed using a pump-probe method with high-intensity ultrashort pulse laser light. In this invention, non-contact and non-destructive detection is possible by using light. Furthermore, by focusing the light and irradiating the sample, detection is possible with spatial resolution of the focal diameter of the light. Moreover, since only the change due to the pump light is detected, the effect of multiple reflections does not contribute to the result.

[0023] (Step 2) From the time-resolved reflectance obtained in Step 1, the parameters related to phonons (initial amplitude, frequency, relaxation rate, initial phase) are determined. The initial phase of a phonon reflects the electronic state involved in the phonon generation process. Therefore, when the electronic state of the bismuth thin film changes with the phase transition, a change in the initial phase of the phonon, reflecting the change in the electronic state, can be observed.

[0024] (Step 3) When detecting the signal, high-sensitivity detection is performed by using differential detection or lock-in detection. -3 ~10 -6 This makes it possible to detect changes in reflectance ΔR / R or transmittance, allowing for the observation of signals originating from phonons and the determination of the initial phase.

[0025] [First Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a block diagram showing the configuration of a physical property evaluation apparatus according to the first embodiment of the present invention. The physical property evaluation apparatus includes a pulsed laser light source 1 that emits high-intensity ultrashort pulse laser light, a mirror 2 that reflects the pulsed laser light emitted from the pulsed laser light source 1, a 5% beam splitter 3 that splits the pulsed laser light into pump light (second light) and probe light (first light), a mirror 4 that reflects the pump light, a delay circuit 5 that changes the delay time of the pump light relative to the probe light, a mirror 6 that reflects the pump light, a wave plate 7, a polarizer 8, a chopper 9 that modulates the intensity of the pump light, a mirror 10 that reflects the probe light, a wave plate 11, a polarizer 12, a beam splitter 13 that splits the probe light into two, and a probe light detection The system includes a photodetector 14, a concave mirror 15 (optical system) that reflects pump light and probe light and guides them to the sample 30 to be measured, a photodetector 16 that detects reflected light from the sample 30, a difference detector 17 that outputs a difference signal between the output signal of the photodetector 14 and the output signal of the photodetector 16, a lock-in detector 18 that detects the signal of the modulation frequency of the chopper 9 from the output signal of the difference detector 17, a characteristic calculation unit 19 that calculates the change in reflectance of the sample 30, an initial phase calculation unit 20 that calculates the initial phase of phonons based on the change in reflectance, and an electronic state identification unit 21 that identifies the electronic state of the sample 30 based on the initial phase of phonons.

[0026] Figure 2 is a flowchart illustrating the operation of the physical property evaluation apparatus in this embodiment. A commercially available pulsed laser light source 1 was used, with a repetition frequency of 3 kHz, an energy of 2 μJ / pulse per pulse, a center wavelength of 780 nm, and a time width of 20 fs. The pulsed laser light emitted from the pulsed laser light source 1 is incident on the 5% beam splitter 3 via the mirror 2, and is split into pump light 40 and probe light 41 by the 5% beam splitter 3.

[0027] The pump light 40 is incident on the chopper 9 via mirror 4, delay circuit 5, mirror 6, waveplate 7, and polarizer 8. The delay circuit 5 is equipped with a retroreflector 50, which reflects the incident pump light 40 in a direction parallel to and opposite to the direction of incidence. The delay circuit 5 can change the optical path length (delay time) of the pump light 40 by moving the retroreflector 50 along the direction of arrow 51. The delay circuit 5 can create a time difference Δt between the pump light 40 and the probe light 41. In addition, the waveplate 7 and polarizer 8 can be used to adjust the polarization and intensity of the pump light 40. The chopper 9 modulates the intensity of the pump light 40 (on / off modulation) at a frequency f0 that is half the repetition frequency of the pulsed laser light source 1, for example.

[0028] Meanwhile, the probe light 41 passes through the mirror 10, the waveplate 11, and the polarizer 12. The waveplate 11 and the polarizer 12 allow for adjustment of the polarization and intensity of the probe light 41. The polarization direction of the probe light 41 is adjusted, for example, to be perpendicular to the polarization direction of the pump light 40. The beam splitter 13 splits the probe light 41 into two.

[0029] The pump light 40, whose intensity is modulated by the chopper 9, and one of the probe beams 41, which is split by the beam splitter 13, are reflected by the concave mirror 15 and incident on the sample 30. In this way, the pump light 40 and the probe beam 41 irradiate the sample 30 (Figure 2, step S100), and the pump light 40 excites the sample 30. The carrier-phonon dynamics excited by the pump light 40 are detected through the optical constant of the probe beam 41.

[0030] The photodetector 14 detects the other probe light 41 that has been split by the beam splitter 13 and converts it into an electrical signal (Figure 2, step S101). The photodetector 16 detects the reflected light from the sample 30 of the probe light 41 and converts it into an electrical signal (Figure 2, step S102).

[0031] The difference detector 17 outputs the difference signal between the output signal of the photodetector 14 and the output signal of the photodetector 16 (Figure 2, step S103). The lock-in detector 18 uses the drive signal of the chopper 9 as a reference signal. The lock-in detector 18 detects the signal at the frequency of the reference signal (the modulation frequency of the chopper 9) from the difference signal obtained by the difference detector 17 (Figure 2, step S104). In this way, by processing the difference signal with the lock-in detector 18 synchronized with the chopper 9, the difference signal can be detected as a function of the time difference Δt. -3 ~10 -6 It is possible to detect transient changes in reflectance (or transient transmittance).

[0032] The characteristic calculation unit 19 calculates the change in reflectance ΔR / R of the sample 30 by dividing the intensity of the difference signal shown by the output of the lock-in detector 18 by the intensity of the probe light shown by the output of the photodetector 14 (Figure 2, step S105).

[0033] The initial phase calculation unit 20 calculates the initial phase of the phonon based on the change in reflectance ΔR / R calculated by the characteristic calculation unit 19 (Figure 2, step S106). The electronic state identification unit 21 identifies the electronic state (metal / semiconductor) of the sample 30 based on the initial phonon phase calculated by the initial phase calculation unit 20 (Figure 2, step S107).

[0034] Figures 3(A) and 3(B) show the measurement results of the physical property evaluation apparatus when a bismuth single crystal thin film was used as sample 30. Here, the change in reflectance ΔR of sample 30, obtained by processing the output signal of the photodetector 16 with a lock-in detector 18 synchronized with the chopper 9, is shown. Figure 3(A) shows the transient reflectance ΔR of a bismuth single crystal thin film with a thickness of 200 nm, and Figure 3(B) shows the transient reflectance ΔR of a bismuth single crystal thin film with a thickness of 20 nm. In both cases, the intensity of the pump light was set to 3.3 μJ / pulse. It has been identified that the bismuth single crystal thin film with a thickness of 200 nm is a semiconductor, and the bismuth single crystal thin film with a thickness of 20 nm is a semimetal (Non-Patent Literature 1).

[0035] The periodic vibration components of the measurement results in FIGS. 3(A) and 3(B) are derived from the A of bismuth 1g optical phonon mode. The transient reflectivity ΔR of the bismuth single crystal thin film can be expressed by Equation (1).

[0036] [Number]

[0037] A in Equation (1) ph is the initial amplitude of the phonon, ω ph is the frequency of the phonon, Γ ph is the relaxation rate of the phonon, φ ph is the initial phase of the phonon, A e is the initial amplitude of the carrier component, Γ e is the relaxation rate of the carrier response. Also, H(t) is a step function that rises stepwise at t = 0.

[0038] By fitting Equation (1) so that it matches the transient reflectivity ΔR of the measurement results, the initial amplitude A ph and frequency ω ph and relaxation rate Γ ph and initial phase φ ph can be obtained. The curve L1 in FIGS. 3(A) and 3(B) shows the result of fitting by Equation (1). The curve L2 corresponds to the first term of Equation (1), and L3 corresponds to the second term of Equation (1). The first term of Equation (1) is a non-vibrating component derived from carrier dynamics (initial amplitude Ae, relaxation rate Γe). The phonon frequency ω ph and relaxation rate Γ ph and initial phase φ ph obtained as a result of the calculation are shown in Table 1.

[0039] [Table 1]

[0040] Note that the initial phase φ phWhen nπ±0.02, it exhibits a cosine-type oscillation (where n is an integer), with an initial phase of φ. ph When the value is (n+1 / 2)π±0.03, it is classified as a sine-type oscillation.

[0041] The initial phase φ of the phonon ph Previous studies have indicated that this depends on the shift in the equilibrium internuclear distance that occurs when transitioning from the ground state to the excited state (References: "R. Merlin, "Generating coherent THz phonons with light pulses", Solid State Communications, Vol.102, pp.207-220, 1997", "Min-Cheol Lee, et al., "Strong spin-phonon coupling unveiled by coherent phonon oscillations in Ca2RuO4", Physical Review B, vol.99, 144306, 2019").

[0042] Figures 4(A) and 4(B) show the relationship between the phonon generation process and the initial phase of the phonon, as disclosed in the references. According to the references, when transitioning from the ground state to the excited state, if there is no displacement (displacement ΔQ) between the excited and ground states, the oscillation becomes sine-type, as shown in Figure 4(A). ph If there is a φ, the vibration becomes cosine as shown in Figure 4(B) when the displacement from sine to cosine reaches its maximum. In other words, the initial phase φ of the phonon ph This is greatly influenced by the electronic state at the time of phonon generation.

[0043] As shown in the curve L3 in Figures 3(A) and 3(B) and in Table 1, the initial phase φ of the coherent phonon of bismuth with a film thickness of 200 nm ph The cosine type is observed, and the initial phase φ of the coherent phonons of bismuth with a film thickness of 20 nm ph It was found that it exhibits a sine type.

[0044] For samples with film thicknesses of 200 nm and 20 nm, the initial phonon amplitude A ph The results of measuring the laser intensity dependence are shown in Figure 5. The vertical axis on the left of Figure 5 represents the initial amplitude A in a bismuth single crystal thin film with a thickness of 200 nm. ph The vertical axis on the right represents the initial amplitude A in a bismuth single crystal thin film with a thickness of 20 nm. ph According to Figure 5, in the case of bismuth with a film thickness of 200 nm, the initial amplitude A ph The initial amplitude A changes linearly with respect to the laser intensity, and in the case of bismuth with a film thickness of 20 nm, ph It was found that the phonon changes quadratically with respect to laser intensity. This result suggests that in the case of bismuth film thickness of 200 nm, phonons are generated through a one-photon process, while in the case of bismuth film thickness of 20 nm, phonons are generated through a two-photon process.

[0045] Based on the above results, the electronic state of the sample changes with the change in film thickness, and phonons are generated through different electronic states in the samples with a film thickness of 20 nm and 200 nm, resulting in an initial phase φ ph I believe we were able to observe that difference. Therefore, perform the following steps (a) and (b) to determine the initial phase φ of the phonon. ph The relationship between this and the electronic state of the bismuth single crystal thin film should be investigated in advance.

[0046] (a) Prepare multiple bismuth single crystal thin films with uniform thickness, measure their electrical conductivity, and identify whether the bismuth single crystal thin film is a semiconductor or a metal based on the measured electrical conductivity. (b) For the bismuth single crystal thin film whose electronic state was identified by procedure (a), the initial phase of the phonons φ was determined using the physical property evaluation apparatus shown in Figure 1. ph Measure it.

[0047] The initial phase φ of the phonon is determined by procedures (a) and (b). ph This allows us to obtain the relationship between this and the electronic state of a bismuth single crystal thin film. The initial phase calculation unit 20 calculates the initial phase φ of the phonon by fitting as described above. ph Calculate (step S106). The electronic state identification unit 21 uses the initial phase φ of the phonons calculated by the initial phase calculation unit 20 for the sample 30 whose electronic state is unknown. ph And the initial phase φ of the phonon ph Based on the known relationship between the electronic state of the bismuth single crystal thin film and the sample, the electronic state of sample 30 is identified (step S107).

[0048] As described above, the initial phase φ of the phonon ph Through observation, the electronic state (semimetallic / semiconductor) of a bismuth thin film sample can be identified. This invention allows for the identification of the initial phase φ of phonons as a result of changes in the electronic state due to other physical quantities, such as temperature, pressure, and impurity concentration. ph It can also be applied to systems where the coefficient of change changes. Furthermore, the present invention has the versatility to measure regardless of the shape of the sample (gas, liquid, solid).

[0049] The initial phase φ of the phonon observed in this invention ph The resolution is the phonon period t ph [sec] and the time width t of the pulsed light used for measurement pulse Determined by [sec], 2πt ph / t pulse It is given in [radians]. That is, 2πt ph / t pulse [radian] or greater initial phase φ ph In any system where a change occurs, it is possible to detect the change in the electronic state using the present invention.

[0050] In the configuration shown in Figure 1, the photodetector 16 detects reflected light from the sample 30, but it may also be configured to detect probe light transmitted through the sample 30. The operation of the physical property evaluation device in this case is shown in Figure 6.

[0051] The photodetector 16 detects the transmitted light of the probe light 41 from the sample 30 and converts it into an electrical signal (Figure 6, step S102a). The characteristic calculation unit 19 calculates the change in transmittance of the sample 30 by dividing the intensity of the difference signal shown by the output of the lock-in detector 18 by the intensity of the probe light shown by the output of the photodetector 14 (Figure 6, step S105a).

[0052] The initial phase calculation unit 20 performs fitting so that the change in transmittance calculated by the characteristic calculation unit 19 matches equation (1), thereby determining the initial phase φ of the phonon. ph The value is calculated (Figure 6, step S106a). The operation of the electronic state identification unit 21 is the same as described above.

[0053] In this embodiment, ΔR / R was calculated as the change in reflectance of sample 30, but ΔR may be calculated instead. In this case, the beam splitter 13, photodetector 14, difference detector 17, and characteristic calculation unit 19 become unnecessary. The lock-in detector 18 only needs to detect the signal at the frequency of the reference signal from the output signal of the photodetector 16. The initial phase calculation unit 20 performs fitting so that the change in reflectance ΔR of sample 30 detected by the lock-in detector 18 matches equation (1), thereby calculating the initial phase φ of the phonon. ph You just need to calculate that.

[0054] Even when the photodetector 16 detects probe light transmitted through the sample 30, the beam splitter 13, photodetector 14, difference detector 17, and characteristic calculation unit 19 may be omitted. The lock-in detector 18 only needs to detect the signal at the frequency of the reference signal from the output signal of the photodetector 16. The initial phase calculation unit 20 calculates the initial phase φ of the phonon by fitting the change in transmittance of the sample 30 detected by the lock-in detector 18 to equation (1) so that it matches. ph You just need to calculate that.

[0055] [Second Example] Next, a second embodiment of the present invention will be described. Figure 7 is a block diagram showing the configuration of a physical property evaluation apparatus according to the second embodiment of the present invention. The physical property evaluation apparatus of this embodiment includes a pulsed laser light source 1, a mirror 2, a 5% beam splitter 3, a mirror 4, a delay circuit 5, a mirror 6, a wave plate 7, a polarizer 8, a chopper 9, a mirror 10, a wave plate 11, a polarizer 12, a concave mirror 15, a difference detector 17, a lock-in detector 18, a characteristic calculation unit 19, an initial phase calculation unit 20, an electronic state identification unit 21, a polarizing beam splitter 22 that separates the probe light reflected by the sample 30 into two lights with different polarization states, a photodetector 23 that detects one of the lights separated by the polarizing beam splitter 22, and a photodetector 24 that detects the other light separated by the polarizing beam splitter 22.

[0056] Figure 8 is a flowchart illustrating the operation of the physical property evaluation apparatus in this embodiment. In this embodiment, the waveplate 11 and polarizer 12 are used to adjust the probe light 41 before it enters the sample 30 so that it is linearly polarized and tilted 45 degrees with respect to the horizontal plane. Here, the horizontal plane refers to a plane perpendicular to both the surface of the sample 30 and the plane of the paper (the plane containing the optical axes of the pump light 40 and the probe light 41).

[0057] The polarizing beam splitter 22 separates the reflected light from the sample 30 of the probe light 41 into longitudinally polarized and transversely polarized light (Figure 8, step S108). The photodetector 23 detects one of the light beams separated by the polarization beam splitter 22 (for example, transversely polarized light) and converts it into an electrical signal (Figure 8, step S109). The photodetector 24 detects the other light (e.g., longitudinally polarized light) separated by the polarizing beam splitter 22 and converts it into an electrical signal (Figure 8, step S110).

[0058] In this embodiment, the difference detector 17 outputs the difference signal between the output signal of the photodetector 23 and the output signal of the photodetector 24 (Figure 8, step S103b). The operation of the lock-in detector 18 is the same as in the first embodiment. In this embodiment, the characteristic calculation unit 19 calculates the change in reflectance ΔR / R of the sample 30 by dividing the intensity of the difference signal shown by the output of the lock-in detector 18 by the intensity of the transverse polarization shown by the output of the photodetector 23 (or the intensity of the longitudinal polarization shown by the output of the photodetector 24) (Figure 8, step S105b).

[0059] The operation of the initial phase calculation unit 20 and the electronic state identification unit 21 is the same as in the first embodiment. In this way, in this embodiment, by detecting spatially anisotropic optical changes caused by photoexcitation in the crystal, it is possible to detect phonons with low symmetry that are difficult or impossible to detect in the first embodiment.

[0060] In the configuration shown in Figure 7, the polarizing beam splitter 22 separates the reflected light from the sample 30 into longitudinally polarized and transversely polarized light. However, it may also be configured to separate the probe light transmitted through the sample 30 into longitudinally polarized and transversely polarized light. The operation of the physical property evaluation apparatus in this case is shown in Figure 9.

[0061] The polarizing beam splitter 22 separates the probe light transmitted through the sample 30 into longitudinally polarized and transversely polarized beams (Figure 9, step S108c). The characteristic calculation unit 19 calculates the change in transmittance of the sample 30 by dividing the intensity of the difference signal shown by the output of the lock-in detector 18 by the intensity of the transverse polarization shown by the output of the photodetector 23 (or the intensity of the longitudinal polarization shown by the output of the photodetector 24) (Figure 9, step S105c).

[0062] The initial phase calculation unit 20 performs fitting so that the change in transmittance calculated by the characteristic calculation unit 19 matches equation (1), thereby determining the initial phase φ of the phonon. ph The value is calculated (Figure 9, step S106c). The operation of the electronic state identification unit 21 is the same as described above.

[0063] The characteristic calculation unit 19, initial phase calculation unit 20, and electronic state identification unit 21 described in the first and second embodiments can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in Figure 10.

[0064] The computer comprises a CPU 300, a storage device 301, and an interface device (I / F) 302. Photodetectors 14, 16, 23, 24 and a lock-in detector 18 are connected to the I / F 302. The program for realizing the physical property evaluation method of the present invention is stored in the storage device 301. The CPU 300 executes the processes described in the first and second embodiments according to the program stored in the storage device 301. [Industrial applicability]

[0065] This invention can be applied to techniques for evaluating the physical properties of thin films. [Explanation of symbols]

[0066] 1...Pulsed laser light source, 2,4,6,10...Mirrors, 3...5% beam splitter, 5...Delay circuit, 7,11...Waveplate, 8,12...Polarizer, 9...Chopper, 13...Beam splitter, 14,16,23,24...Photodetector, 15...Concave mirror, 17...Differential detector, 18...Lock-in detector, 19...Characterization unit, 20...Initial phase calculation unit, 21...Electronic state identification unit, 22...Polarization beam splitter.

Claims

1. A pulsed laser light source configured to emit pulsed laser light, A beam splitter configured to split the pulsed laser light into a first beam and a second beam, A delay circuit configured to change the delay time of the second light relative to the first light, A chopper configured to modulate the intensity of the second light, An optical system configured to guide the first light and the intensity-modulated second light to a sample, A first photodetector configured to detect the first light reflected by the sample or the first light transmitted through the sample, A lock-in detector configured to detect the signal of the modulation frequency of the chopper from the output signal of the first photodetector as a change in the reflectance or transmittance of the sample, An initial phase calculation unit configured to calculate the initial phase of a phonon based on the change in reflectance or the change in transmittance, An electronic state identification unit configured to identify whether the sample is a semiconductor or a semimetal based on the initial phase of the phonons, A physical property evaluation device characterized by comprising the following features.

2. In the physical property evaluation apparatus according to claim 1, A second photodetector configured to detect the first light before it is incident on the sample, A difference detector configured to output a difference signal between the output signal of the second photodetector and the output signal of the first photodetector, The system further comprises a characteristic calculation unit configured to calculate the change in reflectance or the change in transmittance by dividing the intensity of the difference signal shown by the output of the lock-in detector by the intensity of the first light shown by the output of the second photodetector, The lock-in detector detects, instead of the output signal of the first photodetector, the signal of the modulation frequency of the chopper from the difference signal obtained by the difference detector, The initial phase calculation unit calculates the initial phase of the phonon based on the change in reflectance or the change in transmittance calculated by the characteristic calculation unit. A physical property evaluation apparatus characterized by the following features.

3. In the physical property evaluation apparatus according to claim 1, A waveplate and polarizer configured such that the first light incident on the sample is linearly polarized at a 45-degree angle to a horizontal plane perpendicular to the surface of the sample, The system further comprises a polarizing beam splitter configured to separate the first light reflected by the sample or the first light transmitted through the sample into two lights with different polarization states. The first photodetector consists of two photodetectors: one configured to detect one of the light beams separated by the polarizing beam splitter, and the other configured to detect the other light beams separated by the polarizing beam splitter. A difference detector configured to output the difference signal of the outputs of the two photodetectors, A characteristic calculation unit is configured to calculate the change in reflectance or the change in transmittance by dividing the intensity of the difference signal shown by the output of the lock-in detector by the intensity of the light shown by the output of one of the two photodetectors. Furthermore, The lock-in detector detects, instead of the output signal of the first photodetector, the signal of the modulation frequency of the chopper from the difference signal obtained by the difference detector, The initial phase calculation unit calculates the initial phase of the phonon based on the change in reflectance or the change in transmittance calculated by the characteristic calculation unit. A physical property evaluation apparatus characterized by the following features.

4. In the physical property evaluation apparatus according to any one of claims 1 to 3, The physical property evaluation apparatus is characterized in that the electronic state identification unit identifies whether the sample is a semimetal or a semiconductor based on the initial phase of the phonons calculated by the initial phase calculation unit and a known relationship between the initial phase of the phonons and whether the material constituting the sample is a semimetal or a semiconductor.

5. A first step involves splitting a pulsed laser beam into a first beam and a second beam, varying the delay time of the second beam relative to the first beam, and irradiating the sample with the first beam and the intensity-modulated second beam. A second step involves detecting the first light reflected by the sample or the first light transmitted through the sample using a first photodetector. A third step involves detecting the signal of the intensity modulation frequency among the output signals of the first photodetector as a change in the reflectance or transmittance of the sample, A fourth step of calculating the initial phase of a phonon based on the change in reflectance or the change in transmittance, A fifth step of identifying whether the sample is a semiconductor or a semimetal based on the initial phase of the phonons. A method for evaluating physical properties characterized by including [something].

6. In the physical property evaluation method according to claim 5, Between the second step and the third step, a sixth step is taken in which the first light before it is incident on the sample is detected by a second photodetector, The method further includes a seventh step of outputting a difference signal between the output signal of the first photodetector and the output signal of the second photodetector, The third step includes detecting the signal of the intensity modulation frequency from the difference signal instead of the output signal of the first photodetector, Between the third step and the fourth step, an eighth step is further included in which the change in reflectance or the change in transmittance is calculated by dividing the intensity of the difference signal obtained in the third step by the intensity of the first light indicated by the output of the second photodetector. A method for evaluating physical properties, characterized in that the fourth step includes a step of calculating the initial phase of a phonon based on the change in reflectance or the change in transmittance calculated in the eighth step.

7. In the physical property evaluation method according to claim 5, The first step includes adjusting the first light, before it is incident on the sample, so that it is linearly polarized and inclined at 45 degrees with respect to a horizontal plane perpendicular to the surface of the sample. The second step includes separating the first light reflected by the sample or the first light transmitted through the sample into two lights with different polarization states, detecting one of the separated lights with one of the two first photodetectors, and detecting the other separated light with the other of the two first photodetectors. The process further includes a sixth step between the second and third steps of outputting a difference signal of the outputs of the two first photodetectors, The third step includes detecting the signal of the intensity modulation frequency from the difference signal instead of the output signal of the first photodetector, Between the third step and the fourth step, an eighth step is further included in which the change in reflectance or the change in transmittance is calculated by dividing the intensity of the difference signal obtained in the third step by the intensity of the light indicated by the output of one of the two first photodetectors. The fourth step includes calculating the initial phase of a phonon based on the change in reflectance or the change in transmittance calculated in the eighth step. A method for evaluating physical properties characterized by the following features.

8. In the physical property evaluation method according to any one of claims 5 to 7, The fifth step is a method for evaluating physical properties, characterized in that it includes a step of identifying whether the sample is a semimetal or a semiconductor based on the initial phase of the phonons calculated in the fourth step and a known relationship between the initial phase of the phonons and whether the material constituting the sample is a semimetal or a semiconductor.

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