JPH06194312A - Time-resolved fluorecent excitation spectrum measuring equipment - Google Patents

Abstract

PURPOSE:To allow measurement of time-resolved fluorescent excitation spectrum over a wide energy region by measuring the excitation spectrum of crossing correlation light of a fluorescent light emitted from a semiconductor material and an optical gate pulse. CONSTITUTION:Optical pulses from a quite short pulse light source 1 are branched by an optical element 5 into a sample excitation light and a gate pulse light. The sample excitation light is projected onto a point of a nonlinear optical crystal 3 of a sample 16 through an optical system 6. The gate pulse light is projected onto same point of the crystal 3 through an optical system 10. The crystal 3 is then rotated on a rotary stage 4 and a conversion light generated therefrom is introduced to a spectrometer 17 and measured by means of a signal analyzer 14. The sample 16 is then irradiated with the light from a continuous oscillation light source 2 and a conversion light component is extracted by the analyzer 14 thus measuring the fluorescent excitation spectrum at an arbitrary time lag. Measurement is performed while varying the difference of optical path length of an optical delay path 9 and the operation is repeated by a controller 15 thus measuring the time-resolved fluorescent excitation spectrum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time-resolved measuring apparatus for fluorescence excitation spectra emitted from semiconductor materials.

[0002]

2. Description of the Related Art Conventional fluorescence excitation spectrum measurement involves irradiating a sample with light having an energy higher than the band gap of the sample, measuring the intensity at a certain wavelength of the fluorescence spectrum generated at that time, and irradiating the sample. The fluorescence excitation spectrum is measured by continuously scanning the wavelength of the light. However, this conventional example is limited to steady-state measurement, and it is necessary to add a time-resolved measurement function to perform time-resolved fluorescence excitation spectrum measurement.

FIG. 3 is a diagram showing an example of a conventional apparatus for time-resolved measurement of fluorescence intensity emitted from a semiconductor.
In the figure, 17 is an ultrashort optical pulse light source for generating an optical pulse having an energy higher than at least the band gap of the measurement sample, 18 is an optical system for irradiating the sample with the optical pulse, 19 is the measurement sample, and 20 is A spectroscope, 21 is an optical system for collecting and introducing the fluorescence emitted from the measurement sample into the spectroscope, 22 is a photodetector for detecting the dispersed fluorescence,
Reference numeral 23 is a signal analysis device for measuring the output signal of the photodetector.

In the conventional time-resolved fluorescence measurement, the measurement sample 19 is irradiated with the light pulse from the ultrashort pulse light source 17, the fluorescence generated at that time is dispersed by the spectroscope 20, and the dispersed arbitrary wavelength is measured. Change in fluorescence intensity at time is detected by the photodetector 22, and the output signal is detected by the signal analysis device 2
In 3, the time-resolved data is stored and averaged, and the results are output to measure the change in fluorescence intensity over time.

[0005]

As described above, in order to measure a time-resolved fluorescence excitation spectrum using a conventional time-resolved fluorescence measurement apparatus, the wavelength of the light pulse for exciting the sample is continuously changed, as described above. It is necessary to make it variable and to measure the wavelength dependence of the fluorescence intensity at any wavelength of the fluorescence spectrum. At this time, wavelength tuning is performed by adjusting the wavelength selection element provided in the ultrashort optical pulse light source, but since the optical length of the ultrashort optical pulse light source changes as the wavelength changes,
The generation of the light pulse is stopped, and as a result, the wavelength cannot be tuned, and the time-resolved fluorescence excitation spectrum cannot be measured.

The time-resolved fluorescence excitation spectrum measuring apparatus of the present invention has been made in view of these problems.
The purpose is to measure the excitation spectrum of the cross-correlation light between the fluorescence emitted from the semiconductor material and the optical gate pulse, and obtain the time of the fluorescence excitation spectrum from near the band gap of the semiconductor material to the energy region higher than the band gap. It is to provide a decomposition measuring device.

[0007]

In order to achieve the above-mentioned object, the time-resolved fluorescence excitation spectrum measuring apparatus of the present invention has a structure in which fluorescence from a semiconductor material to be measured generated by light pulse irradiation intersects with gate pulse light. A time-resolved fluorescence measurement device that generates correlated light by a nonlinear optical effect in a nonlinear optical crystal and measures the time change of its intensity, a continuous wave light source that can continuously change the wavelength, and the cross-correlated light Of the fluorescence emitted from the semiconductor material by the sample excitation light, and a gate for automatically controlling the cross-correlated light in synchronization with them, The excitation spectrum of the cross-correlation light of the pulsed light is measured by continuous wavelength scanning of the continuous wave light, set at an arbitrary time, and the excitation spectrum of the cross-correlation light is measured again. By repeating the, measuring the time variation of the fluorescence excitation spectra.

[0008]

That is, in the time-resolved fluorescence excitation spectrum measuring apparatus of the present invention, the nonlinear optical crystal is irradiated with fluorescence having energy near the band gap and gate pulse light from the measurement sample, and fluorescence and gate are applied in the nonlinear optical crystal. The excitation spectrum of the correlated light is measured by generating the correlated light of the pulsed light and scanning the light from the continuous wave light source that irradiates the sample with the continuous wavelength. After one wavelength scan, the optical delay path is continuously measured. The time-resolved fluorescence excitation spectrum is measured by repeating the measurement of the excitation spectrum described above by changing the delay time with.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a time-resolved fluorescence excitation spectrum measuring apparatus in one embodiment of the present invention. In FIG. 1, 1 is an ultrashort optical pulse light source, 2 is a continuous oscillation light source, 3 is a non-linear optical crystal, 4 is a rotary stage for rotating the non-linear optical crystal, and 5 is for branching an optical pulse generated from the light source 1. , 6 is an optical system for irradiating a measurement sample (semiconductor material) 16 with a light pulse, 7
Is an optical system for irradiating the measurement sample 16 with continuous wave light generated from the light source 2, 8 is an optical system for condensing fluorescence emitted from the measurement sample 16 and irradiating it onto the nonlinear optical crystal, 9
Is an optical delay path, 10 is an optical system for irradiating the nonlinear optical crystal with gate pulse light, 11 is a spectroscope, 12 is light that is converted by the correlation between fluorescence and gate pulse light in the nonlinear optical crystal. , Optical system for introducing into spectroscope, 13
Is a photodetector for detecting the converted light dispersed by the spectroscope, 14 is a signal analysis device as a time-resolved fluorescence measuring device for measuring the signal from the photodetector, and 15 is the wavelength of the light source 1. This is a controller for continuously varying, causing the analyzer 14 to measure a signal in synchronization with this, and setting the delay time by the optical delay path.

The optical pulse generated from the ultrashort pulse light source 1 is branched into two optical paths by the optical element 5. One is sample excitation light and the other is gate pulse light. The sample excitation light is irradiated onto the measurement sample 16 by the optical system 6, and at this time, the measurement sample 1
The fluorescence emitted from 6 is condensed by the optical system 8 and is applied to one point of the nonlinear optical crystal 3. The gate pulse light passes through the optical delay path 9 and is applied by the optical system 10 to the same point on the nonlinear optical crystal 3 as the point where the fluorescence is applied.

Next, the nonlinear optical crystal 3 is attached to the rotary stage 4
And the rotation angle is set so that the correlated light due to the fluorescence and the gate pulse light in the nonlinear optical crystal 3 is converted most efficiently by the nonlinear optical effect. The generated converted light is condensed by the optical system 12 and introduced into the spectroscope 11. The converted light split by the spectroscope 11 is detected by the photodetector 13, converted into an electric signal, and then measured by the signal analysis device 14.

Then, the continuous oscillation light source 2 generates light having an output at least one digit lower than the output of the sample excitation light generated from the ultrashort pulse light source 1, and the optical system 7 irradiates the measurement sample 16 at this time. The converted light component increased by the generated carriers is extracted and measured by the signal analysis device 14, and its wavelength dependence is measured by continuously changing the wavelength of the continuous wave light source 2 to oscillate the continuous wave light source 2. Fluorescence excitation spectra at any delay time are measured over a range of wavelengths. Further, the optical path difference of the optical delay path 9 is changed, the delay time of the gate pulse light with respect to the fluorescence is newly set, the above-described fluorescence excitation spectrum is measured, and the controller 15 repeats this to repeat the time-resolved fluorescence. The excitation spectrum can be measured.

FIG. 2 is a graph showing time-resolved measurement of the fluorescence excitation spectrum emitted from the sample 16 observed by the above-mentioned measuring method. In the figure, the time at which the delay time is t ₀ corresponds to the time at which the intensity of the autocorrelation waveform due to the scattered light on the sample surface of the light pulse and the gate pulse light becomes maximum, and this time is the origin of the time axis, that is, the measurement sample. The moment when the light pulse is excited.

Then, the optical delay path shifts the delay time of the gate pulse light with respect to the fluorescence from t ₀ by an arbitrary delay time, and the excitation spectrum of the cross-correlated light of the fluorescence and the gate pulse light is measured. Immediately after the light pulse excitation, most of the carriers generated by the light pulse irradiation are still distributed in a high energy state, and the absorption coefficient of the measurement sample reflects this, so the output of the light pulse for sample excitation is at least one digit or less. When the sample is irradiated with continuous wave light having a wavelength of, and the wavelength of the sample is continuously changed, the correlated light intensity changes reflecting the absorption coefficient of the measurement sample immediately after the optical pulse excitation. Therefore, the fluorescence excitation spectrum immediately after the light pulse excitation can be measured from the wavelength dependence of the correlated light intensity. The spectrum at time t ₁ in FIG. 2 corresponds to the fluorescence excitation spectrum immediately after the above-described optical pulse excitation.

Further, since the carriers distributed in a high energy state relax toward the band edge as the time elapses from t _1, the absorption coefficient of the absorption coefficient reflecting the energy distribution of the carriers at the time set in the optical delay path. As a change, the fluorescence excitation spectrum will be measured.

In this embodiment, as described above, the time-resolved fluorescence excitation spectrum is measured by measuring the time dependence of the fluorescence of the measurement sample and the excitation spectrum of the cross-correlation light generated by the nonlinear optical effect of the gate pulse light. Therefore, it is possible to measure not only the time-resolved excitation spectrum in a narrow energy region near the band gap of the measurement sample as in the conventional example but also the time-resolved fluorescence excitation spectrum in a wide wavelength variable region of the continuous wave light source. . Therefore, it is obvious that the continuous wave light source for measuring the excitation spectrum can be arbitrarily selected according to the energy region to be measured, and a plurality of light sources can be used.

Further, since the time resolution in this embodiment is based on the non-linear optical effect, it is not limited by the time resolution based on the electrical signal processing performed in the photodetector or the signal analysis device in the conventional example. Instead, it is determined by the time width of the optical pulse, the size and type of the nonlinear optical crystal, and the optical path difference amount in the optical delay path. Therefore, it is obvious that the time width of the optical pulse, the type and size of the nonlinear optical crystal, and the optical path difference amount in the optical delay path can be arbitrarily set according to the required time resolution and the correlated light intensity.

In this embodiment, an example of measuring the time-resolved fluorescence excitation spectrum of the measurement sample has been described, but the present invention can be applied to the following measuring methods. That is, the wavelength of continuous wave light is arbitrarily set, the sample is irradiated with this, and the time change of the intensity of the converted light component increased by the carriers generated at this time is changed by changing the optical path difference of the optical delay path. It is obvious that it can be applied to the lifetime measurement of fluorescence at an arbitrarily set wavelength. It is also apparent that the controller 15 can be applied to the measurement of the wavelength-resolved fluorescence lifetime by repeating the above operation.

[0019]

As described above, since the time-resolved fluorescence excitation spectrum measuring apparatus of the present invention measures the excitation spectrum of the cross-correlation light of the fluorescence emitted from the semiconductor material and the optical gate pulse, it is not possible to use the conventional method. It is possible to measure the time-resolved fluorescence excitation spectrum over a wide energy range that was possible. Furthermore, since the measurement is based on the nonlinear optical effect, high time resolution measurement can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a time-resolved fluorescence excitation spectrum measuring apparatus according to the present invention.

FIG. 2 is a diagram showing an example of time-resolved measurement of a fluorescence excitation spectrum by the time-resolved fluorescence excitation spectrum measuring apparatus of the present invention.

FIG. 3 is a configuration diagram of an apparatus to which a conventional time-resolved fluorescence spectrum measuring method is applied.

[Explanation of symbols]

1 ... Ultrashort pulse light source, 2 ... Continuous oscillation light source, 3 ... Non-linear optical crystal, 4 ... Rotation stage, 5 ... Optical element, 6, 7,
8, 10, 12 ... Optical system, 9 ... Optical delay path, 11 ... Spectrometer, 13 ... Photodetector, 14 ... Signal analysis device, 15 ... Controller, 16 ... Measurement sample.

Claims (1)

[Claims] 1. A time for measuring cross-correlation light of fluorescence from a semiconductor material to be measured generated by light pulse irradiation and gate pulse light by a non-linear optical effect in a non-linear optical crystal, and measuring a time change of its intensity. Decomposition fluorescence measurement device, continuous wave light source capable of continuously changing wavelength, time change of intensity of the cross-correlated light, wavelength change of continuous wave light source, and automatic cross-correlation light synchronized with them Equipped with a controller to control, the fluorescence emitted from the semiconductor material by the sample excitation light, and the excitation spectrum of the cross-correlation light of the gate pulse light is measured by continuous wavelength scanning of continuous oscillation light, and at any time It is characterized in that the time change of the fluorescence excitation spectrum is measured by repeating the setting and measurement of the excitation spectrum of the cross-correlated light again. Time-resolved fluorescence excitation spectrum analyzer.