JP2004349582A - Method and device of measuring defect in solid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring method of any defect in a solid being which finds the size of any lattice defect existent in a trace quantity in a solid such as semiconductor crystals and semiconductor nanocrystals, images a lattice defect distribution, and is applicable to the estimation of electric conductance characteristics for defining the optical response performance of a device. <P>SOLUTION: The relaxation times of coherent phonons or optical excitation carriers excited by a pump&probe spectroscopic method using a femtosecond pulsed laser are measured, and the size of the lattice defect is estimated using the formula: τ=1/Ntσv<SB>th</SB>(τ:relaxation time of coherent phonon (optical excitation carrier), N<SB>t</SB>: defect density, σ: scattering cross section, and v<SB>th</SB>: rate of thermal diffusion). Further, use is made of a microscope objective lens as a condenser for focusing pumping light and probe light onto a solid sample. Hereby, a reflectivity change is measured while scanning the solid sample with an X-Y stage two-dimensionally to plot two-dimensionally the oscillation amplitude or signal intensity of a change in the reflectance or the relaxation time of the coherent phonons or the optical excitation carriers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The invention of this application relates to a method and an apparatus for measuring defects in a solid. More specifically, the invention of this application can determine the size of a small amount of lattice defects existing in a solid such as a semiconductor crystal and a semiconductor nanocrystal, can further image the lattice defect distribution, and can improve the optical response of the device. The present invention relates to a method and an apparatus for measuring defects in a solid which can be applied to the evaluation of electric conduction characteristics that determine performance.
[0002]
[Prior art and its problems]
Since the electrical conduction characteristics that determine the optical response performance of a semiconductor device depend on defects in the semiconductor material used for the device, it is extremely important to accurately inspect and detect the state of the defect.
[0003]
Conventionally, non-destructive and non-contact methods have been used for inspection and detection of defects in solids such as semiconductors.For example, methods using light diffraction phenomena, and methods for detecting light including micro Raman spectroscopy have been used. Techniques using the scattering phenomenon, photoacoustic imaging, and the like are known.
[0004]
Above all, micro-Raman spectroscopy, in which Raman scattered light from a solid is acquired at high speed by a CCD camera or the like, has been actively used in the industrial field until now as a technique for imaging a defect distribution on the order of 1 μm.
[0005]
In this microscopic Raman spectroscopy, the excitation laser light normally split by a beam splitter is applied to a measurement point on a sample using an objective lens, and the Raman scattered light generated thereby is again passed through the same objective lens. , Through a spectroscope, using a CCD photodiode array or the like. The Raman spectrum thus obtained is obtained, and the density distribution state of defects can be visualized by plotting Raman spectrum intensity and the like at each measurement point (Patent Documents 1 and 2).
[0006]
The measurement principle of Raman scattering spectroscopy including this microscopic Raman spectroscopy is to detect weak scattered light of a laser due to lattice vibration (phonon) in a solid irradiated with the laser. Lattice vibration is sensitive to crystal distortion and lattice defects, and appears with a decrease in scattered light intensity or a shift in the peak frequency of the phonon spectrum with the presence of defects.
[0007]
However, in Raman scattering spectroscopy, it is difficult to detect a peak having an extremely narrow spectral width due to the limitation of the measurement accuracy of the spectroscope. For example, when a double monochromator is used, a resolution of about 0.5 cm ^-1 (Kaiser) is obtained. Although it can be obtained, it is difficult to accurately measure a peak having a line width smaller than that. On the other hand, in Raman scattering spectroscopy, since a continuous wave (CW) laser is usually used as a laser for irradiating a solid, the obtained defect distribution is obtained by integrating time. For example, lattice defects are generated by ion irradiation. It was not possible to measure time-varying phenomena, such as the appearance of moving.
[0008]
[Patent Document 1]
JP-A-5-223637
[Patent Document 2]
JP 2001-215193 A
[0009]
Therefore, the invention of this application has been made in view of the circumstances described above, and solves the problems of the prior art to reduce the size of lattice defects present in a minute amount in solids such as semiconductor crystals and semiconductor nanocrystals. It is an object of the present invention to provide a defect measuring method and a defect measuring device in a solid which can be used for imaging and lattice defect distribution, and which can be applied to an evaluation of an electric conduction characteristic which determines a light response performance of a semiconductor device. I have.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the invention of this application first uses a femtosecond pulse laser as pump light and probe light, and at least one of the pump light and probe light is time-delayed by an optical delay circuit. Then, the coherent phonon, which is a lattice vibration having a uniform phase in the solid sample, is excited by pump light irradiation by condensing the solid sample with the lens, and the solid sample is irradiated with the probe light by condensing with the lens. By measuring the change in the reflectance of the solid sample, the relaxation time of the excited coherent phonon corresponding to the decay time of the oscillation amplitude in the change in the reflectance is obtained, and τ _p = 1 / N _t σv _th (where τ _p is the coherent The phonon relaxation time, N _t is the defect density, σ is the scattering cross section, and v _th is the thermal diffusion rate) are used to determine the scattering cross section σ. Provided is a method for measuring defects in a solid, which is characterized by obtaining the size of lattice defects.
[0011]
Second, the invention of this application uses a femtosecond pulse laser as pump light and probe light, delays at least one of the pump light and probe light with an optical delay circuit, and collects the solid sample with a lens. The carrier in the solid sample is excited by pump light irradiation with light to be a photoexcited carrier, and the reflectivity of the solid sample is measured by measuring the change in the reflectivity of the solid sample by irradiating probe light by condensing the solid sample with the lens. seek relaxation time of photoexcited carriers corresponding to the decay time of the signal intensity in the _{change, τ c = 1 / N t} σv th (τ c is the relaxation time of the photo-excited carriers, N _t is the defect density, sigma is the scattering cross-sectional area, v _(th is the thermal diffusion rate), and the size of the lattice defect is obtained by obtaining the scattering cross section σ using the equation:
[0012]
Third, a femtosecond pulse laser is used as a pump light and a probe light, and at least one of the pump light and the probe light is time-delayed by an optical delay circuit. Excitation excites coherent phonons, which are lattice vibrations with a uniform phase in the solid sample, and the pump light is used to measure the change in reflectance of the solid sample by irradiating the solid sample with probe light by condensing light with the lens. Using a microscope objective lens as a lens that focuses the probe light on the solid sample, the reflectance change is measured while the solid sample is two-dimensionally scanned on an XY stage, and the relaxation time or reflectance change of the obtained coherent phonon is measured. Is characterized by obtaining a two-dimensional image reflecting the defect density by plotting the vibration amplitude at Providing a defect measuring method in.
[0013]
Fourth, a femtosecond pulse laser is used as a pump light and a probe light, and at least one of the pump light and the probe light is time-delayed by an optical delay circuit. When a change in the reflectance of the solid sample is measured by irradiating the solid sample with the probe light by condensing the solid sample with the above-described lens and exciting the carrier in the solid sample, pump light and probe light are applied to the solid sample. Using a microscope objective lens as a focusing lens, the solid sample is two-dimensionally scanned on an XY stage, and the change in reflectance is measured. The relaxation time of the photoexcited carriers or the signal intensity at the change in reflectance is measured in two dimensions. Provided is a method for measuring defects in a solid, characterized by obtaining a two-dimensional image reflecting the defect density by plotting.
[0014]
Fifth, in the method for measuring defects in a solid according to the fourth aspect of the invention, the optical delay circuit is fixed at a predetermined delay time, and the reflectance change is measured while scanning the solid sample two-dimensionally. The solid-state is characterized in that a two-dimensional plot of the signal intensity in the change in reflectance of the solid is obtained, and the same operation is repeated for a number of predetermined delay times to obtain a time-resolved two-dimensional image of the optical carrier caused by the defect distribution. Provide a method of measuring defects in the inside.
[0015]
Sixth, in the method for measuring defects in a solid according to any one of the second, fourth and fifth inventions, when the solid sample is a semiconductor, the center wavelength is set to an energy not less than the band gap of the semiconductor sample and near the band gap of the semiconductor sample. Provided is a method for measuring defects in a solid, characterized by using a laser as a light source to easily shorten the relaxation time due to defects in the process of relaxing photoexcited carriers.
[0016]
Seventhly, there is provided a defect measuring apparatus in a solid for performing the defect measuring method in a solid according to the first or second invention, wherein at least 1) a laser light source for oscillating a femtosecond pulse laser, and 2) a femtosecond pulse. Light branching means for branching a laser into a pump light and a probe light; 3) a time delay circuit for delaying at least one of the pump light and the probe light for a predetermined time; and 4) focusing the femtosecond pulse laser on a solid sample. 5) a light receiving means for receiving the probe light after irradiating the solid sample; 6) a current amplifying means for receiving and amplifying the signal of the probe light received by the light receiving means; and 7) its amplification. And a recording means for recording a signal obtained by the measurement.
[0017]
Eighthly, there is provided an apparatus for measuring defects in a solid for performing the method for measuring defects in a solid according to any one of the third to fifth aspects, wherein at least 1) a laser light source for oscillating a femtosecond pulse laser; Light branching means for branching a second pulse laser into a pump light and a probe light; 3) a time delay circuit for delaying at least one of the pump light and the probe light for a predetermined time; and 4) applying the femtosecond pulse laser to a solid sample. A microscope objective lens for condensing, 5) an XY stage for moving the solid sample two-dimensionally, 6) light receiving means for receiving probe light after irradiating the solid sample, and 7) light receiving means. Defect measurement in a solid object comprising: a current amplifying means for receiving and amplifying a signal of a received probe light; and 8) a recording means for recording the amplified signal. Also it provides the equipment.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention of this application has the features as described above, and embodiments thereof will be described below.
[0019]
In the invention of this application, as shown in JP-A-2002-214137, for example, a femtosecond (1 fs = 10 ⁻¹⁵ s) pulse laser is used as pump light (excitation light) and probe light, and the pump light and probe light are used. At least one of which is time-delayed by an optical delay circuit, and excites coherent phonons, which are lattice vibrations in phase in the solid sample by irradiating pump light by condensing with a lens onto the solid sample, The change in reflectivity of the solid sample is measured by so-called pump and probe spectroscopy, which measures the change in reflectivity of the solid sample by irradiating the probe light with the light condensed by a lens, and excitation corresponding to the decay time of the vibration amplitude in the change in reflectivity is measured. Calculated relaxation time of the coherent phonon
τ _p = 1 / N _t σv _th
(Τ _p is the coherent phonon relaxation time, N _t is the defect density, σ is the scattering cross section, and v _th is the thermal diffusion rate)
The main feature is that the size of the lattice defect is obtained by obtaining the scattering cross section σ using the following equation.
[0020]
Alternatively, the size of lattice defects in a solid can be determined by measuring the relaxation time of photoexcited carriers instead of coherent phonons, and a femtosecond pulse laser is used as pump light and probe light, and the pump light and probe light At least one of them is time-delayed by an optical delay circuit, and the electrons or holes that are carriers in the solid sample are excited by pumping light by condensing the solid sample with a lens to form a photo-excited carrier. The change in reflectivity of a solid sample is measured by irradiating probe light by focusing light with a lens, so-called pump-and-probe spectroscopy. The change in reflectivity is measured, and light excitation corresponding to the decay time of the signal intensity due to the change in reflectivity is measured. Find the relaxation time of the carrier,
τ _c = 1 / N _t σv _th
(Τ _c is the relaxation time of photoexcited carriers, N _t is the defect density, σ is the scattering cross section, and v _th is the thermal diffusion rate)
It is also possible to obtain the size of the lattice defect by obtaining the scattering cross section σ using the following equation.
[0021]
As described above, the following relational expression called Shockley-Read-Hall (SRH) recombination statistics exists between the defect density and the relaxation time of photoexcited carriers (or the relaxation time of coherent phonons).
τ _c = 1 / N _t σv _th
(Τ _c is the relaxation time of photoexcited carriers (coherent phonons), N _t is the defect density, σ is the scattering cross section, and v _th is the thermal diffusion rate)
The defect density _{N t} the Monte Carlo simulation (J.F.Zegler in this formula, J.P.Biersack, U.Littmark, in The Stopping and Range of Ions in Solids, Vol. 1 (Pergamon Press, New York, 1985 )), A defect depth distribution (usually Gaussian distribution) generated in GaAs by He ions is obtained, and since it corresponds to the defect generation efficiency per He ion, the defect depth distribution is calculated from the entire area of the defect depth distribution. Find the average value of the generation efficiency in the depth direction and the depth of the defect distribution,
N _t = (Ion irradiation surface density) × (Average value of defect generation efficiency) ÷ (Depth of defect distribution)
Required by Further, v _th is a constant peculiar to the substance and is an average speed at which phonons and carriers thermally diffuse.
[0022]
Therefore, using the relaxation time of photoexcited carriers or the relaxation time of coherent phonons and N _t and v _th obtained in the experiment, the scattering cross section σ can be obtained by performing least square fitting. The diameter (2R) of the defect center can be immediately determined using the relationship σ = πR ² .
[0023]
As described above, the size of lattice defects in a solid sample can be accurately determined by using the method for measuring defects in a solid according to the invention of the present application. The present invention can be applied to the evaluation of the crystallinity of crystals, semiconductor nanocrystals, and the like, and the evaluation of the electrical conductivity in a semiconductor device can be performed on the spot.
[0024]
In addition, a femtosecond pulse laser is used as pump light and probe light, and at least one of the pump light and probe light is time-delayed by an optical delay circuit. Excitation of coherent phonons, which are lattice vibrations in phase with each other, and when measuring the change in the reflectance of the solid sample by irradiating the solid sample with the probe light by condensing the light with the lens, the pump light and the probe are applied to the solid sample. Using a microscope objective lens as a lens for condensing light, the change in reflectance is measured while the solid sample is scanned two-dimensionally on an XY stage, and the oscillation time in the relaxation time or the change in reflectance of the obtained coherent phonon is measured. By plotting in two dimensions, a two-dimensional image reflecting the defect density can be obtained.
[0025]
Similarly, when measuring the reflectance change by the pump & probe spectroscopy, a microscope objective lens is used as a lens for condensing the pump light and the probe light on the fixed sample, and the sample is two-dimensionally scanned on an XY stage. A two-dimensional image reflecting the defect density can also be obtained by measuring the reflectance change and plotting the relaxation time of the obtained optical carrier or the signal intensity in the reflectance change in two dimensions. Further, while the optical delay circuit is fixed at a predetermined delay time (for example, 1 ps), the reflectance change is measured while the sample is two-dimensionally scanned on the XY stage, and the signal intensity at the reflectance change at the predetermined delay time is measured. A time-resolved two-dimensional image of the optical carrier caused by the defect distribution can be obtained by plotting in two dimensions and repeating the same operation for a large number of each predetermined delay time.
[0026]
That is, regarding imaging of defect density, when measuring relaxation time of coherent phonons or photoexcited carriers by pump & probe spectroscopy, a measurement sample is placed under an objective lens of a microscope by an XY stage such as an XY axis microstage. For example, the reflectance change is measured at a certain point, and then the XY-axis microstage is moved, for example, by 1 μm, and the reflectance change is measured at that point. . This operation is repeated over a certain region (for example, a 1 cm × 1 cm region) of the measurement sample to map the vibration amplitude or signal intensity in the reflectance change obtained with a resolution of about 1 μm, or to set the coherent phonon or the photoexcitation carrier relaxation time. You can get the mapping.
[0027]
Therefore, in the method for measuring defects in a solid according to the invention of the present application, coherent phonons or photoexcited carriers are excited in a solid sample by pump-and-probe spectroscopy using a femtosecond pulse laser, and the relaxation time of the coherent phonons or the photoexcited carriers is increased. The size of lattice defects can be estimated from the change in the relaxation time of the sample, that is, the change in the reflectivity in the solid sample, and the vibration amplitude and signal intensity at the change in the relaxation time or the change in the reflectivity of the coherent phonon or photoexcited carrier can be measured. Not only can a two-dimensional image of the defect density be accurately obtained, but also a time-resolved two-dimensional image of the optical carrier caused by the defect distribution can be accurately obtained.
[0028]
Further, in the invention of this application, the relaxation time of coherent phonons or photoexcited carriers can be directly measured as the oscillation amplitude of the reflectance change or the decay time of the signal intensity. It has excellent sensitivity to (narrow) coherent phonons or photoexcited carriers, and can be applied to the case where the life of phonons is extended at extremely low temperatures such as liquid helium temperature.
[0029]
Further, since the method for measuring defects in a solid according to the invention of the present application has a time resolution, scattering phenomena due to defects of electrons (phonons) that change with time in a device or the like from both the relaxation time of coherent phonons and the relaxation time of photoexcited carriers. Can be measured on the spot.
[0030]
When the solid sample is a semiconductor, a laser having a band gap (for example, 1.4 eV at room temperature in the case of GaAs at room temperature) of the semiconductor sample and having a center wavelength at an energy near the band cap is used as a light source (in the case of GaAs). A laser light source having a center wavelength around 850 nm), which can easily shorten the relaxation time due to defects in the relaxation process of photoexcited carriers, and dramatically increases the S / N ratio of a two-dimensional image of defect density. It can be improved.
[0031]
Next, an example of an apparatus for measuring defects in a solid for performing the method for measuring defects in a solid according to the invention of this application is shown in FIG.
[0032]
A femtosecond pulse laser light source (1) is used as a light source, and a femtosecond pulse laser oscillated from the light source is reflected by a mirror (2) and probe light (5) and pump light ( (Excitation light) (6). The time delay between the probe light (5) and the pump light (6) is given by the optical delay circuit (7). At this time, the step interval of the stepping motor is preferably about 1 μm to 3 μm, but may be more or less. It can also be implemented. The pump light (6) is modulated by the optical modulator (8) at a frequency of about 2 kHz. (4) is a half-wave plate.
[0033]
Then, in the pre-condenser section of the sample for the time-resolved reflectivity measurement, a beam corresponding to the pump light (6) and the probe light (5) is condensed by one objective lens (9) and irradiated to the solid sample (10). ing.
[0034]
When the size of the defects uniformly distributed is obtained by the method of the invention of this application, it can be carried out even if the objective lens (9) is changed to a normal single lens.
[0035]
The probe light (5) is reflected by the solid sample (10), passes through the objective lens (9) again, is reflected by the beam splitter (3), and is condensed on the lens (11). -Captured by the PIN photodetector (12). The photocurrent signal from the Si-PIN photodetector (12) is input to a current amplifier (current amplifying means) (13), where the signal is amplified to about 10 ⁵ to 10 ⁷ times. As the current amplifier (13), it is preferable to use, for example, SR530 manufactured by Stanford Research Systems, USA. In this case, it is desirable to apply a band-pass filter to the signal to be amplified. For example, by using a band-pass filter of 1 kHz to 3 kHz, low-frequency noise and high-frequency noise can be reduced.
[0036]
The signal output from the current amplifier (13) is input to the lock-in amplifier (14). Here, only the signal frequency-tuned by the trigger signal from the optical modulator (8) is amplified about 10 times and recorded by the computer (recording means) (15).
[0037]
By using such an apparatus, the method for measuring defects in a solid according to the invention of the present application as described above can be implemented.
[0038]
Hereinafter, embodiments will be described with reference to the accompanying drawings, and embodiments of the present invention will be described in more detail. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail.
[0039]
【Example】
<Example 1>
First, according to one embodiment of the method for measuring defects in a solid according to the invention of the present application, semiconductor GaAs subjected to ion irradiation was used as a solid sample, and the defect size of the semiconductor GaAs was determined.
[0040]
FIG. 2 shows an example of a time-resolved reflectance signal obtained in ion-irradiated semiconductor GaAs using the apparatus for measuring defects in a solid in FIG. However, as a lens for condensing the pump light and the probe light before the solid sample, a single lens having a focal length of 10 cm is used instead of the microscope objective lens in order to determine the size of the defect. In addition, ion irradiation was performed in an ultrahigh vacuum chamber at 10 ⁻⁹ Torr using accelerated He ions accelerated at 5 eV, and FIG. 2A is a graph showing a change in reflectance of a solid sample before ion irradiation. (B) to (d) are graphs showing changes in the reflectance of the solid sample after irradiating the solid sample with He ions, and the respective irradiation densities are (b) 9.4 × 10 ¹² He ⁺ / cm ² , (C) 1.9 × 10 ¹³ He ⁺ / cm ² and (d) 3.0 × 10 ¹³ He ⁺ / cm ² . A signal component which rises rapidly with a delay time of zero and attenuates slowly represents the relaxation of photo-excited carriers generated when the semiconductor is excited with light having a band gap or more, and an oscillation component (oscillation) having an intensity of about several% of the carrier signal. (Amplitude) corresponds to coherent phonons which are lattice vibrations having the same phase. The vibration mode corresponds to the longitudinal wave optical (LO) phonon of GaAs, which has a frequency of about 8.8 THz, which translates to a time period of about 114 fs. Although the defect size can be identified from the coherent phonon relaxation time (oscillation amplitude decay time), here the defect size was determined from the carrier relaxation time (signal intensity decay time). The inset of FIG. 2 is a plot of carrier relaxation time versus defect density. Here, the defect density was calculated for the above irradiation conditions using Monte Carlo simulation. This relationship is expressed by the SRH equation,
τ _c = 1 / N _t σv _th
(Τ _c is the relaxation time of photoexcited carriers, N _t is the defect density, σ is the scattering cross section, and v _th is the thermal diffusion rate)
The scattering cross section σ = 6.2 × 10 ⁻¹⁶ cm ² was obtained by performing least-squares fitting using. From this, it was immediately found that the size of the GaAs defect was 2.8%.
<Example 2>
Next, FIG. 3 shows an example in which defect distribution imaging is performed. FIG. 3 shows a solid state obtained by fixing an optical delay circuit at a predetermined delay time (1 ps) near the boundary between the ion irradiation region and the ion non-irradiation region of the GaAs sample as shown in FIG. The reflectance change is measured while scanning the sample in two dimensions, and the signal intensity in the reflectance change with a delay time of 1 ps is plotted in two dimensions, and the same operation is repeated for a large number of each predetermined delay time. 3 also shows a time-resolved two-dimensional image of an optical carrier caused by a defect distribution.
[0041]
The He ion irradiation density on the sample was 1.9 × 10 ¹² He ⁺ / cm ² and the spatial resolution of the sample scanning was 10 μm. In FIG. 3, the signal intensity of the change in reflectance is large in a bright area, and the signal intensity of the change in reflectance is small in a dark area.
[0042]
From FIG. 3, it can be seen that the boundary between the ion irradiation area and the ion non-irradiation area clearly appears. Therefore, it was found that an image of a defect distribution caused by the ion irradiation of the semiconductor GaAs can be obtained by the invention of this application.
[0043]
【The invention's effect】
As described in detail above, according to the invention of this application, it is possible to determine the size of lattice defects present in a minute amount in a solid such as a semiconductor crystal and a semiconductor nanocrystal, and to image the distribution of lattice defects, and to improve the optical response performance of the device. Provide a method for measuring defects in solids that can be applied to the evaluation of electrical conduction characteristics that determine the coherent phonon or carrier relaxation measurement device by combining a microscope with a compact laser and optical system It becomes possible.
[0044]
Conventional micro-Raman spectroscopy has not been able to evaluate the electrical conduction dynamics in semiconductor devices, but the method for measuring defects in solids according to the invention of this application has time resolution, so coherent phonon relaxation and carrier The evaluation of the electrical conductivity and the like in the device can be measured on the spot from both of the relaxation of the stress.
[Brief description of the drawings]
FIG. 1 is a diagram exemplifying an apparatus used for a method for measuring defects in a solid according to the invention of the present application.
FIG. 2 is a graph showing the relationship between the delay time and the time-resolved reflectance when the size of a GaAs defect is obtained by the method for measuring defects in a solid according to the invention of the present application.
FIG. 3 is a two-dimensional image obtained when a defect distribution of GaAs is obtained by the method for measuring defects in a solid according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Femtosecond pulse laser light source 2 Mirror 3 Beam splitter 4 1/2 wavelength plate 5 Probe light 6 Pump light 7 Optical delay circuit 8 Optical modulator 9 Objective lens 10 Solid sample 11 Lens 12 Si-PIN photodetector 13 Current amplifier 14 Lock-in Amplifier 15 Computer

Claims (8)

A femtosecond pulse laser is used as pump light and probe light, and at least one of the pump light and probe light is time-delayed by an optical delay circuit. By exciting the coherent phonon, which is a lattice vibration with uniformity, and measuring the change in the reflectance of the solid sample by irradiating the solid sample with the probe light by condensing with the lens, the attenuation of the vibration amplitude due to the change in the reflectance is measured. Find the relaxation time of the excited coherent phonon corresponding to time,
τ _p = 1 / N _t σv _th
(Τ _p is the coherent phonon relaxation time, N _t is the defect density, σ is the scattering cross section, and v _th is the thermal diffusion rate)
A method for measuring defects in a solid, wherein the size of a lattice defect is obtained by obtaining a scattering cross section σ using the following formula: Using a femtosecond pulse laser as pump light and probe light, at least one of the pump light and probe light is time-delayed by an optical delay circuit, and the carrier in the solid sample is irradiated by the pump light by condensing the solid sample with a lens. Is excited into a photoexcited carrier, and the solid sample is irradiated with a probe light by condensing the light with the lens to measure a change in reflectance of the solid sample. Find the relaxation time of the carrier,
τ _c = 1 / N _t σv _th
(Τ _c is the relaxation time of photoexcited carriers, N _t is the defect density, σ is the scattering cross section, and v _th is the thermal diffusion rate)
A method for measuring defects in a solid, comprising determining a size of a lattice defect by obtaining a scattering cross section σ using the following equation. A femtosecond pulse laser is used as pump light and probe light, and at least one of the pump light and probe light is time-delayed by an optical delay circuit. When the coherent phonon, which is a lattice vibration with uniformity, is excited and the reflectance change of the solid sample is measured by irradiating the solid sample with the probe light by condensing with the lens, the pump light and the probe light are applied to the solid sample. Using a microscope objective lens as a focusing lens, the solid-state sample is two-dimensionally scanned on an XY stage, and the reflectance change is measured. The relaxation time of the obtained coherent phonon or the vibration amplitude in the reflectance change is two-dimensionally measured. A method for measuring defects in a solid, comprising obtaining a two-dimensional image reflecting the defect density by plotting Using a femtosecond pulse laser as pump light and probe light, at least one of the pump light and probe light is time-delayed by an optical delay circuit, and the carrier in the solid sample is irradiated by the pump light by condensing the solid sample with a lens. When the change in the reflectance of the solid sample is measured by irradiating the solid sample with the probe light by condensing the light with the lens, the pump is used as a lens for condensing the pump light and the probe light on the solid sample. Using a microscope objective lens, the solid sample is scanned two-dimensionally on an XY stage, and the change in reflectance is measured. The relaxation time of the photoexcited carriers or the signal intensity at the change in reflectance is plotted in two dimensions. A method for measuring defects in a solid, comprising obtaining a two-dimensional image reflecting density. 5. The method for measuring defects in a solid according to claim 4, wherein the optical delay circuit is fixed at a predetermined delay time, and the reflectance change is measured while scanning the solid sample two-dimensionally. A method for measuring defects in a solid, comprising plotting the signal intensity in two dimensions and repeating the same operation for each of a plurality of predetermined delay times to obtain a time-resolved two-dimensional image of the optical carrier caused by the defect distribution. . 6. The method for measuring defects in a solid according to claim 2, wherein, when the solid sample is a semiconductor, a femtosecond pulse having a center wavelength equal to or more than the band gap of the semiconductor sample and having energy near a band gap of the semiconductor sample. A method for measuring defects in a solid, characterized by using a laser to easily reduce the relaxation time due to defects in the process of relaxing photoexcited carriers. An apparatus for measuring defects in a solid, which performs the method for measuring defects in a solid according to claim 1 or 2, wherein at least:
1) a laser light source that oscillates a femtosecond pulse laser;
2) optical branching means for branching the femtosecond pulse laser into pump light and probe light;
3) a time delay circuit for delaying at least one of the pump light and the probe light for a predetermined time;
4) a lens for focusing the femtosecond pulse laser on a solid sample;
5) light receiving means for receiving the probe light after being irradiated on the solid sample;
6) current amplifying means for receiving and amplifying the signal of the probe light received by the light receiving means;
7) recording means for recording the amplified signal;
An apparatus for measuring defects in a solid, comprising: A defect measuring apparatus in a solid for performing the defect measuring method in a solid according to any one of claims 3 to 5, wherein at least:
1) a laser light source that oscillates a femtosecond pulse laser;
2) optical branching means for branching the femtosecond pulse laser into pump light and probe light;
3) a time delay circuit for delaying at least one of the pump light and the probe light for a predetermined time;
4) a microscope objective lens for focusing the femtosecond pulse laser on a solid sample;
5) an XY stage for moving the solid sample in two dimensions;
6) light receiving means for receiving the probe light after being irradiated on the solid sample;
7) current amplifying means for receiving and amplifying a signal of the probe light received by the light receiving means;
8) recording means for recording the amplified signal;
An apparatus for measuring defects in a solid, comprising:

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