WO2017104697A1 - テラヘルツ検出センサ及びテラヘルツ画像測定装置 - Google Patents
テラヘルツ検出センサ及びテラヘルツ画像測定装置 Download PDFInfo
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- WO2017104697A1 WO2017104697A1 PCT/JP2016/087196 JP2016087196W WO2017104697A1 WO 2017104697 A1 WO2017104697 A1 WO 2017104697A1 JP 2016087196 W JP2016087196 W JP 2016087196W WO 2017104697 A1 WO2017104697 A1 WO 2017104697A1
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- terahertz
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Images
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/02—Details
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
- G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
- G01Q60/18—SNOM [Scanning Near-Field Optical Microscopy] or apparatus therefor, e.g. SNOM probes
- G01Q60/22—Probes, their manufacture, or their related instrumentation, e.g. holders
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/02—Details
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
- H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
- H01L31/0264—Inorganic materials
- H01L31/028—Inorganic materials including, apart from doping material or other impurities, only elements of Group IV of the Periodic Table
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/09—Devices sensitive to infrared, visible or ultraviolet radiation
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2203/00—Function characteristic
- G02F2203/13—Function characteristic involving THZ radiation
Definitions
- the present invention relates to a terahertz detection sensor and a terahertz image measurement apparatus that detect weak terahertz light.
- Terahertz light is expected to be applied in a wide range of fields from basic academic fields such as radio astronomy, material science, and biomolecule spectroscopy to practical fields such as security, information communication, environment, and medicine. For example, when active measurement is performed by irradiating an object with terahertz light and measuring an image of the reflected light or transmitted light, an object that has not been seen until now can be seen.
- Patent Documents 1 to 3 include techniques using active measurement using this type of terahertz light.
- the technique of Patent Document 1 uses a semiconductor chip in which a two-dimensional electron gas (described later) is formed at a fixed position from the surface, and irradiates terahertz light while applying a magnetic field to the semiconductor chip. By measuring the current flowing through the carbon nanotube by this irradiation, the intensity and frequency of weak terahertz light are detected.
- the “two-dimensional electron gas” refers to an electron that moves in a two-dimensional plane along a junction interface between a semiconductor and an insulator or a junction interface between different semiconductors. That is, a state where electrons serving as carriers are distributed in a plane is called a two-dimensional electron gas.
- a heterogeneous semiconductor means a different type of semiconductor or a semiconductor having a different structure using an inversion layer or the like.
- Patent Document 3 irradiates an object with terahertz illumination light (wavelength: 4 ⁇ m to 10 mm), and detects scattered light from an electrode that is an example of the object as a signal with a scattered light detector. It detects foreign matter contained in the surface or electrodes, for example, metallic foreign matter.
- terahertz illumination light wavelength: 4 ⁇ m to 10 mm
- the technique using the active measurement by the terahertz light as shown in Patent Documents 1 to 3 described above is useful for knowing the interaction between the molecules of the sample, for example.
- infrared rays it is limited to specific intermolecular detection, but not limited to terahertz light.
- the wavelength of terahertz light is about three orders of magnitude longer than that of visible light
- an image of molecules using terahertz light is an image that is about three orders of magnitude coarser than visible light.
- the molecule is of nm (nanometer) size
- mm millimeter
- This near-field light is a form of various near-field light, and the near-field light exists without passing through the hole.
- the near-field light is confined in a region narrower than the half wavelength of the terahertz light, when the near-field light strikes with a tungsten needle, the near-field light is scattered by the needle and converted into propagating light. By detecting this propagating light, it is possible to see an image of the molecule.
- the sample is affected by the irradiation of the terahertz light from the outside.
- the image of the molecule is affected by the measurement.
- PHB intracellular energy storage substance
- PHB intracellular energy storage substance
- the resonance frequency near 2.4 THz is an image of hydrogen bonding of the PHB molecule
- the resonance frequency near 2.9 THz is a vibration image of the helical structure of the PHB molecule.
- the wavelength is increased only at each resonance frequency, and an image of each resonance frequency of the PHB molecule can be seen by adjusting the detection operation to each resonance frequency, but this is impossible at this time.
- the present invention has been made in view of such a background.
- a terahertz detection sensor and a terahertz image that can appropriately perform passive measurement using terahertz light and can select an arbitrary terahertz frequency in passive measurement. It is an object to provide a measuring device.
- a terahertz detection sensor is a terahertz detection sensor that detects terahertz light, has a shape smaller than the wavelength of terahertz light, and detects near-field light of the terahertz light. It is characterized by comprising a detection point and a semiconductor substrate on which the detection point is formed.
- the terahertz image measuring apparatus of the present invention detects the near-field light of terahertz light emitted from a sample, and the terahertz detection sensor according to claim 1 is irradiated from the sample to the terahertz detection sensor.
- a coil that is wound around the optical axis of the terahertz light and is disposed around the sample and the terahertz detection sensor, and applies a magnetic field generated by current flowing through the coil to the terahertz detection sensor.
- a measurement control unit that is tuned to a specific frequency of terahertz light.
- a terahertz detection sensor and a terahertz image measurement apparatus that can appropriately perform passive measurement using terahertz light and can select an arbitrary terahertz frequency in passive measurement.
- FIG. 5 is a side view showing a semiconductor substrate in which an AlGaAs layer is stacked on a GaAs substrate in a method for manufacturing a terahertz detection sensor.
- the manufacturing method of a terahertz detection sensor it is a side view which shows the state which shaved the AlGaAs layer by the etching.
- the state which formed each electrode on the GaAs substrate in the manufacturing method of a terahertz detection sensor.
- FIG. 5 is a diagram showing the relationship between the position (0 to 14 ⁇ m) of the above-described conventional terahertz detection element on the horizontal axis and the terahertz detection signal level (arbitrary scales L0 to L4) on the vertical axis.
- It is a block diagram of a magnetic field generation part. It is a formation figure of the Landau level by the magnetic field application for demonstrating the terahertz light detection principle. The figure which shows the waveform of the terahertz light of the specific frequency f in case the terahertz detection signal level of a vertical axis
- shaft becomes sharply high in the predetermined magnetic field value of a horizontal axis, and shows the waveform of the terahertz light of the specific frequency f 0.7 THz.
- shaft becomes sharply high in the predetermined magnetic field value of a horizontal axis, and shows the waveform of the terahertz light of the specific frequency f 2.6 THz. is there.
- FIG. 1 is a diagram illustrating a configuration of a terahertz image measurement apparatus using a terahertz detection sensor according to an embodiment of the present invention.
- a terahertz image measuring apparatus 10 shown in FIG. 1 includes a GaAs (gallium / hidden) vibration unit 11, an AC power source (power source) 12, a terahertz detection sensor 13, and a voltage detection unit 14 fixed to the lower end surface of the piezoelectric substrate 10 a.
- a Z-layer piezo substrate (Z piezo substrate) 15 a Y-layer piezo substrate (Y piezo substrate) 16, an X-layer piezo substrate (X piezo substrate) 17, a magnetic field generation unit 19, a computer, etc.
- a measurement control unit 20 A terahertz image measurement target sample 18 is placed and fixed on a Z-layer piezoelectric substrate 15.
- the GaAs vibration part 11 comprises the vibration part of a claim.
- the vibrating part may be a vibrating member such as a piezoelectric material.
- the terahertz detection sensor (sensor) 13 detects terahertz light that the sample 18 emits naturally.
- the detection principle is as follows: (1) The terahertz electric field is detected by the gate electrode, and the current is modulated at a high speed. (2) The small sensor has a small specific heat and uses the heating effect. (3) Impurities in the material For example, a terahertz response of a carrier trapped in a level is used. (4) In the case of a magnetic field application type sensor, which will be described later, photoconduction associated with electronic excitation of a Landau level is used. However, such a detection principle is the same for the sensor 13A using the graphene 32 shown in FIG. 9 described later.
- the measurement control unit 20 measures an image of the molecule of the sample 18 by detecting the terahertz light.
- the sensor 13 is provided with a terahertz light detection point (detection point) described later.
- the detection point has a planar shape with a size smaller than the wavelength of the terahertz light, and detects near-field light of the terahertz light at a position near the sample 18. That is, in the present embodiment, the sensor 13 may be expressed as detecting terahertz light, but actually includes detecting near-field light of terahertz light.
- the GaAs vibrating portion 11 is formed by integrally forming a rectangular parallelepiped base end portion 11a and a plate-like portion 11b protruding flush with the lower surface of the base end portion 11a by molding a GaAs semiconductor material. .
- a sensor 13 is fixed to the lower surface of the distal end of the plate-like portion 11b.
- a detection point is provided on the surface opposite to the fixed surface of the sensor 13.
- a power source 12 is connected to the base end portion 11a. When a voltage is applied from the power source 12 to the base end portion 11a, the base end portion 11a vibrates at a constant vibration frequency due to the piezo effect, and the plate-like portion 11b accordingly has the same vibration frequency. Vibrates up and down.
- the voltage detection unit 14 is configured by an inverting amplifier or the like, detects a voltage obtained by detecting a current corresponding to the vibration of the GaAs vibration unit 11, and supplies a control voltage V1 corresponding to the detection voltage to the Z piezo substrate 15. Apply to. That is, the voltage detection unit 14 detects a voltage obtained by detecting a current corresponding to the amplitude of the plate-like portion 11b due to the vibration of the base end portion 11a, and the control voltage V1 corresponding to the detected voltage is detected as the Z piezo substrate 15. Apply to.
- the current according to the vibration of the base end portion 11a there are two cases: detecting the current from the frequency in vibration and detecting the current from the amplitude in vibration.
- the Z piezo substrate 15 expands and contracts in the Z direction (up and down direction) according to the magnitude of the control voltage V1, and moves the sample 18 placed and fixed on the Z piezo substrate 15 up and down. Is maintained at a predetermined interval. This is because even when the detection surface of the sample 18 at the sensor 13 is uneven, the terahertz light detection state at the sensor 13 is kept constant so as not to fluctuate.
- the detection voltage V1 of the voltage detector 14 is applied to the piezo substrate 10a, the piezo substrate 10a is expanded and contracted in the vertical direction in the same manner as the Z piezo substrate 15, and the sensor 13 is held at a predetermined interval with respect to the sample 18. Also good. At this time, if the piezo substrate 10a is made small, the response speed by the voltage V1 increases, so that the sensor 13 can be moved up and down with respect to the sample 18 at high speed.
- the Y piezo substrate 16 expands and contracts in the Y direction (left and right direction) in response to voltage application from an AC power supply (not shown), and the X piezo substrate 17 expands and contracts in the X direction (front and rear direction) in response to voltage application. .
- the sample 18 moves in the left-right and front-rear direction, so that the sensor 13 can detect terahertz light at a predetermined position of the sample 18.
- the coarse movement piezo substrate 1 is disposed under the X piezo substrate 17, and an AC (not shown) is connected to the coarse movement piezo substrate 1. It is preferable to align the sample 18 in a large space by applying a voltage from a power source.
- FIG. 2 is a perspective view showing the configuration of the terahertz detection sensor 13.
- the sensor 13 shown in FIG. 2 includes a rectangular parallelepiped GaAs substrate 21, a two-dimensional electron gas part (gas part) 22 as a terahertz light detection point formed at one corner of the upper surface of the substrate 21, and the gas part 22.
- four electrodes 23a, 23b, 23c, and 23d that are electrically connected to each other and extend in an independent manner.
- Each of the electrodes 23a to 23d is formed of a conductive material such as gold, and a connection end to the gas portion 22 is pointed like a needle, extends from the needle-like connection end into an elongated fan shape, and extends to the edge of the substrate 21. Is formed.
- each of the electrodes 23a to 23d has a belt-like shape in which the tip is tapered like a needle, and includes a pair of electrodes joined to the detection point (gas portion 22) at the needle-like tip.
- the electrode has a region in which an electric field whose length is longer than the wavelength of terahertz waves (including half wavelength and quarter wavelength) and less than the wavelength of terahertz waves (including half wavelength and quarter wavelength) is concentrated. It is designed to receive terahertz waves.
- a conductive wire 24 connected to the measurement control unit 20 is connected to each of the electrodes 23a to 23d. Two or more conductive wires 24 may be connected in parallel to one electrode 23a so that even if one wire is disconnected due to disconnection or the like, a signal can be transmitted through the remaining wires.
- the measurement control unit 20 causes electrons in the two-dimensional electron gas in the gas unit 22 to move by passing a current from the conductive wire 24 to the gas unit 22 through two electrodes (for example, 23a and 23d on both sides), and the sample An operation of detecting near-field light of 18 terahertz light is performed. Further, the measurement control unit 20 receives the detection voltage of the terahertz light detected by the gas unit 22 from the conductive wire 24 connected to the other two electrodes 23b and 23c, and measures the terahertz image of the molecule of the sample 18. .
- the first electrode described in the claims is configured by the two electrodes 23a and 23d through which current flows, and the second electrode described in the claims is configured by the other two electrodes 23b and 23c through which the detection voltage of the terahertz light is transmitted. ing.
- the sensor 13 is formed by a HEMT (High Electron Mobility Transistor) or the like in which a two-dimensional electron gas is formed at a certain position (distance) from the surface.
- the HEMT is a transistor using a two-dimensional electron gas, and has a feature that a two-dimensional electron gas is formed by modulation doping and has a high electron mobility. Accordingly, the sensor 13 uses a gate voltage generated by detecting the near-field light of the terahertz light emitted from the sample 18, and uses an electron current flowing from a source (not shown) to a drain on the two-dimensional electron gas using high electron mobility. And can be controlled at high speed.
- the gate voltage is supplied to a gate (not shown), and the gate and the source and drain on the two-dimensional electron gas are the MOSFET (Metal-Oxide-Semiconductor-Field-Effect-Transistor) gate voltage and the source on the two-dimensional electron gas. And corresponding to the drain.
- MOSFET Metal-Oxide-Semiconductor-Field-Effect-Transistor
- the sensor 13 is formed using a semiconductor substrate in which an AlGaAs (aluminum, gallium, elbow) layer 22a is laminated on a GaAs substrate 21.
- a two-dimensional electron gas 22g in which electrons moving in a two-dimensional plane are distributed along the junction interface between the GaAs substrate 21 and the AlGaAs layer 22a.
- Other semiconductor substrates include Si layer and SiGe (silicon germanium) layer, AlGaAs layer and InGaAs (indium gallium nitrogen) layer, GaN (gallium nitrogen) layer and AlGaN (aluminum gallium nitrogen) layer, etc. Combinations may be used.
- the planar rectangular AlGaAs layer 22a is cut by etching and shaped so that one corner of the rectangular shape remains smaller than the wavelength of Mr. terahertz light.
- the two-dimensional electron gas portion 22 is formed by both the remaining AlGaAs layer 22a and the two-dimensional electron gas 22g on the lower surface side.
- a conductive material such as gold is fixed on the GaAs substrate 21 by vapor deposition or the like to form the electrodes 23a to 23d (see FIG. 1), and the sensor 13 is manufactured. Thereafter, each of the electrodes 23a to 23d is connected to the measurement control unit 20 by a conductive wire 24 as shown in FIG.
- the two-dimensional electron gas portion 22 formed by the etching shown in FIG. 3B has a planar shape capable of efficiently detecting the near-field light of the terahertz light emitted from the sample 18, for example, an elliptical shape having a size of 0.8 ⁇ m to 1 ⁇ m. Etc. are formed.
- the planar shape of the gas unit 22 may be various shapes such as a circle, a polygon, and a star as long as near-field light of terahertz light can be detected efficiently.
- the size of the two-dimensional electron gas unit 22 is currently about 0.3 ⁇ m at the minimum in actual size (it is obvious that this size will be further reduced in the future). There are 2 ⁇ m and about 5 ⁇ m.
- the sizes of these gas portions 22 correspond to the aperture size of the terahertz light detection element (conventional sensor) by conventional active measurement.
- about 0.9 ⁇ m, about 2 ⁇ m, and about 5 ⁇ m are hereinafter referred to as 0.9 ⁇ m, 2 ⁇ m, and 5 ⁇ m.
- an aperture through which a part of the terahertz light passes is opened in a metal film provided via a probe on a heterogeneous junction semiconductor having a two-dimensional electron gas.
- the aperture has a diameter smaller than the wavelength of the terahertz light, and when the terahertz light is irradiated from above the metal film toward the aperture, near-field light leaks to the position of the probe on the opposite side of the aperture, This near-field light is detected with a two-dimensional electron gas through a probe.
- the near-field light of the terahertz light emitted from the sample 18 by being close to the sample 18 can be detected without passing through the aperture.
- FIG. 4 the position (0 to 14 ⁇ m) of the above-described conventional terahertz detection element (conventional sensor) is shown on the horizontal axis, and the terahertz detection signal level (in arbitrary scales L0 to L4) by near-field light detection that has passed through the aperture is shown on the vertical axis.
- the relationship to In the position of the terahertz detection element on the horizontal axis, the range indicated by the double arrow of 5 ⁇ m indicates the position of the aperture of the diameter size 5 ⁇ m in the conventional sensor.
- the resolution for detecting the terahertz light in the diameter sizes of 0.9 ⁇ m, 2 ⁇ m, and 5 ⁇ m of each aperture shown in FIG. 4 is compared.
- the diameter of the aperture is 5 ⁇ m
- the amount of near-field light transmitted through the terahertz light is larger than in the case of other apertures (0.9 ⁇ m, 2 ⁇ m), so that the rise of the terahertz detection signal Ts1 detected by the near-field light detection The falling edge is gentler than in the case of other apertures (0.9 ⁇ m, 2 ⁇ m).
- the distance between 90% and 10% of the maximum value 100% of the terahertz detection signal Ts1 (or Ts2 and Ts3 described later) is the resolution.
- This resolution is determined by the size of the aperture (in this case, 5 ⁇ m). Accordingly, when the aperture diameter is 5 ⁇ m, the resolution is lower than in the case of other apertures (0.9 ⁇ m, 2 ⁇ m).
- the aperture diameter is 2 ⁇ m
- the amount of near-field light is smaller than the aperture diameter 5 ⁇ m and larger than 0.9 ⁇ m, so that the falling edge of the terahertz detection signal Ts2 is steeper than in the case of the aperture having a diameter of 5 ⁇ m. Therefore, when the aperture diameter is 2 ⁇ m, the resolution is higher than when the aperture has a diameter of 5 ⁇ m.
- the aperture diameter is 0.9 ⁇ m
- the amount of near-field light is smaller than the aperture diameter of 2 ⁇ m, so that the falling edge of the terahertz detection signal Ts2 is steeper than that of the aperture of 2 ⁇ m diameter. Accordingly, when the aperture diameter is 0.9 ⁇ m, the resolution is higher than that of the aperture having a diameter of 2 ⁇ m.
- the terahertz light equivalent to the case where the aperture diameter size of the conventional sensor is 0.9 ⁇ m, 2 ⁇ m, and 5 ⁇ m is used. Detection resolution can be obtained.
- FIG. 5A shows a configuration diagram of the magnetic field generator 19, and FIG. 5B shows a Landau level formation diagram by applying a magnetic field for explaining the terahertz light detection principle.
- the Landau level is a level of discontinuous (discrete) energy that can be taken when a charged particle undergoes cyclotron motion (circular motion) in a magnetic field.
- the magnetic field generator 19 includes a coil 19a that is wound around the optical axis of the terahertz light generated from the sample 18 and applied to the sensor 13, and a current (coil current) that flows through the coil 19a. ), And a voltmeter 19c that measures the voltage at both ends of the coil 19a.
- the magnetic field generator 19 generates a magnetic field B indicated by a broken-line arrow Y3 by applying a current to the coil 19a and applies it to the sensor 13.
- the magnetic field B can be uniquely determined from the coil current.
- the horizontal axis represents the density of states
- the vertical axis represents the energy of electrons.
- cyclotron absorption of the two-dimensional electron gas unit 22 is used.
- the measurement control unit 20 of the apparatus 10 changes the strength (magnetic field value) of the magnetic field B applied to the sensor 13 while changing the current value flowing through the coil 19 a, and the terahertz detection signal of the sample 18 detected by the sensor 13. Adjust to the magnetic field value where the level rises and rises.
- the frequency of the protruding terahertz detection signal is a characteristic resonance frequency (specific frequency). Therefore, the magnetic field value can be tuned to a specific frequency by matching the position where the detection signal level protrudes. In other words, the terahertz frequency can be selected.
- the measurement control unit 20 reads the value of the current flowing through the coil 19a from the ammeter 19b and reads the level of the terahertz detection signal from the voltmeter 19c.
- the frequency of the protruding terahertz detection signal becomes a characteristic resonance frequency (specific frequency).
- the magnetic field B generated by the magnetic field generator 19 under the control of the measurement controller 20 may be as shown in FIGS. 6A to 6E.
- FIG. 7 shows a terahertz emission intensity distribution diagram when the frequency of the terahertz light is selected by changing the magnetic field value and the distribution of the emission intensity of the selected terahertz light is actually measured by passive measurement.
- this experiment was performed using a vibrating member other than this as the GaAs substrate 21 of the terahertz image measuring apparatus 10.
- the emission intensity of the terahertz light is weak at the left corner portion and the right corner portion as indicated by S1, and S2, S3, S3, S4 is stronger.
- the emission intensity of the terahertz light is weak at the lower portion as indicated by S1, and becomes stronger at S2, S3, and S4 as it goes upward from this position.
- the terahertz image measurement apparatus 10 shows the position of the sensor 13 on the horizontal axis (0 to 3.5 ⁇ m) when the terahertz image measurement apparatus 10 performs an active measurement experiment, and the terahertz by near-field light detection by the sensor 13 on the vertical axis.
- the relationship with the detection signal level (arbitrary scale: 0 to 10) is shown.
- this experiment was performed using a vibrating member other than this as the GaAs substrate 21 of the terahertz image measuring apparatus 10.
- the position of the sensor 13 is between about 2 ⁇ m and 2.3 ⁇ m, and the spatial resolution due to the distance between 90% and 10% of the above-mentioned maximum terahertz detection signal value of 100% is as high as 280 nm.
- near-field light of terahertz light emitted from the sample 18 was detected.
- the falling edge of the terahertz detection signal at the time of detection is steep as shown in the figure.
- a detection point for detecting the near-field light of the terahertz light when the sensor 13 for detecting the terahertz light has a shape having a size smaller than the wavelength of the terahertz light and is irradiated with the terahertz light.
- the detection point since the detection point has a shape having a size smaller than the wavelength of the terahertz light, when the terahertz light naturally emitted from the sample is irradiated to the detection point in a state where an operating current is passed through the detection point, The near-field light of the irradiated terahertz light can be detected. Since the near-field light has a wavelength smaller than the half wavelength of the terahertz light, the size of the detection point corresponding to this wavelength makes it possible to measure the nm-sized molecule image of the sample with high resolution. This measurement is a passive measurement for measuring terahertz light naturally emitted from a sample.
- an operating current can be passed to the detection point via the first electrodes 23a and 23d. Further, when the near-field light of the terahertz light emitted from the sample is detected at the detection point, this detection voltage can be output to the external measurement control unit via the second electrodes 23b and 23c. For this reason, the measurement control unit 20 can measure an image of nm-sized molecules of the sample with high resolution.
- Each of the first electrodes 23a and 23d and the second electrodes 23b and 23c has a belt-like shape in which the tip extends in a needle shape, and the needle-like tip is joined to a detection point. It was set as the structure which comprises.
- the tips of the first electrodes 23a and 23d and the second electrodes 23b and 23c extend in a needle shape, the reception sensitivity of the terahertz wave can be improved by the antenna effect.
- Each of the first electrodes 23a, 23d and the second electrodes 23b, 23c has a pair of electrodes in which the tips have a belt-like shape extending in a needle shape, and the needle-like tips are joined to the detection point.
- the electrode has an electric field whose length is longer than the wavelength of terahertz waves (including half wavelength and quarter wavelength) and less than the wavelength of terahertz waves (including half wavelength and quarter wavelength). Is configured to receive terahertz waves in a region where the waves are concentrated.
- the tips of the first electrodes 23a, 23d and the second electrodes 23b, 23c extend in a needle shape, and the pair of electrodes at the extending tips has a length equal to or longer than the wavelength of the terahertz wave.
- the terahertz wave is received in a region where the electric field less than the wavelength of the terahertz wave is concentrated, the reception sensitivity of the terahertz wave can be further improved by the antenna effect.
- the semiconductor substrate has a high electron mobility transistor structure in which an AlGaAs layer 22a is stacked on a GaAs layer 21, and a two-dimensional electron gas 22g is distributed at the interface between the AlGaAs layer 22a and the GaAs layer 21.
- the detection point has a structure in which the AlGaAs layer 22a is shaped into a size smaller than the wavelength of the terahertz light, and the two-dimensional electron gas 22g is distributed at the interface between the shaped AlGaAs layer 22a and the GaAs layer 21.
- the near-field light of the terahertz light that is naturally emitted from the sample can be detected with the two-dimensional electron gas 22g as a detection point.
- the near-field light can be detected at high speed because the electron mobility is high.
- the terahertz image measuring device 20 was configured as follows. That is, the sensor 13 that detects the near-field light of the terahertz light emitted from the sample 18 and the optical axis of the terahertz light irradiated from the sample 18 to the sensor 13 are wound around the sample 18 and the sensor 13.
- a magnetic field generation unit 19 that has a coil 19a to be arranged and applies a magnetic field generated when a current is passed through the coil 19a to the sensor 13; Further, by supplying a current to the coil 19a and changing the value of the flowing current, the strength of the magnetic field is changed to a magnetic field value at which the detection signal level of the sample terahertz light detected by the sensor 13 protrudes and becomes higher.
- the measurement control unit 20 is tuned to a specific frequency.
- the magnetic field value can be tuned to a specific frequency by matching the position where the terahertz light detection signal level at the sensor 13 protrudes.
- the terahertz frequency can be selected. Therefore, it is possible to display an image of a sample molecule that emits terahertz light of the selected frequency.
- a GaAs vibrating portion 11 that vibrates the sensor 13 fixed to the distal end portion of the plate 11b extending from the base end portion 11a in the direction of the distance from the sample 18 by applying a voltage to the base end portion 11a;
- the sample 18 is placed and fixed with a gap between the sample 18 and the sample 18 in the direction of the gap so that the gap is fixed according to the voltage at which the vibration of the GaAs vibrating portion 11 is detected.
- a Z piezo substrate 15 to be moved.
- the tip of the plate (plate-like part) 11b extending from the base end part 11a is slightly caused by van der Waals force when the distance between the sample 18 and the sensor 13 is on the order of nm.
- the vibration frequency of the GaAs vibrating portion 11 is slightly shifted. Since this deviation is reflected in the voltage at which the vibration of the vibration unit 11 is detected, feedback is applied in the moving direction of the Z piezo substrate 15 so that the deviation is constant, and the surface of the sample on the sensor 13 side is uneven. Even if it exists, the front-end
- FIG. 9 is a perspective view showing a configuration of a terahertz detection sensor 13A of another example.
- a sensor 13A shown in FIG. 9 is used as the sensor 13 of the terahertz image measurement apparatus 10 shown in FIG.
- the sensor 13A shown in FIG. 9 is formed in a rectangular parallelepiped Si (silicon) substrate 31a, a SiO 2 (silicon dioxide) substrate 31b laminated on the Si substrate 31a, and a corner portion on the upper surface of the SiO 2 substrate 31b.
- the graphene 32 serving as the terahertz light detection point and the four electrodes 23a to 23d similar to those described above are provided on the graphene 32.
- a conductive wire 24 connected to the measurement control unit 20A is connected to each of the electrodes 23a to 23d.
- the sensor 13A is also disposed in the coil 19a of the magnetic field generator 19 together with the sample 18 as shown in FIG. 5A.
- the measurement control unit 20A moves the electrons in the graphene 32 by flowing current to two electrodes (for example, 23a and 23d on both sides) via the conductive wire 24, and generates near-field light of terahertz light emitted from the sample 18. Make the action to detect.
- the measurement control unit 20 receives an output voltage corresponding to the near-field light of the terahertz light detected by the graphene 32 from the other two electrodes 23 b and 23 c via the conductive wire 24, and the terahertz of the molecule of the sample 18 Measure the image.
- the graphene 32 has a single-layered hexagonal lattice structure made of carbon atoms and bonds thereof, and has a single wire mesh shape.
- charge carriers interact with the periodic field of the atomic lattice to form quasiparticles.
- the quasiparticles in graphene 32 have characteristics that are different from those of such a three-dimensional material.
- the energy band of a typical three-dimensional semiconductor is represented by a valence band that forms the shape of the lower parabola 41 as shown in FIG. 10B with energy on the vertical axis and momentum on the horizontal axis. It has a conduction band that is located above and forms the shape of a parabola 42 opposite to the parabola 41. There is an open band gap between the valence band and the conduction band.
- the energy band of graphene 32 has the form of two cones 44 and 45 in which the vertices abut, as shown in FIG. 10C.
- the contact point between the two cones 44 and 45 is called a Dirac point.
- This form of energy band is characterized by the energy E of a quasiparticle that behaves like Dirac fermions, which are zero mass electrons, and the momentum k. These quasiparticles move at about several percent of the speed of light. Due to such a special band structure, it is known that the electron mobility in the graphene 32 is very high even at room temperature (10 to 100 times or more that of a normal semiconductor).
- the Fermi energy (chemical potential of a Fermi particle system at absolute zero) in a normal three-dimensional material such as a semiconductor is proportional to the carrier density, but the Fermi energy in the graphene 32 is proportional to the square root of the carrier density. It has been confirmed. Since graphene 32 has a symmetric structure in which the valence band and the conduction band coincide with each other at the Dirac point, by applying a gate voltage (by raising and lowering the Fermi energy), carriers are also transferred to electrons. It can also be (electron and hole symmetry).
- FIG. 11A shows the relationship between the magnetic field B and the electron energy E in a normal semiconductor.
- FIG. 11B shows the same relationship in graphene 32.
- the interval n 0, 1, 2, 3 is constant.
- the sensor 13A was manufactured by paying attention to such characteristics of the graphene 32. A method for manufacturing the sensor 13A will be described. As shown in FIG. 12A, an element in which graphene 32A is laminated on the upper surface of a SiO 2 substrate 31b laminated on a Si substrate 31a is used.
- the rectangular graphene 32A is cut by etching using an oxygen asher or the like, and shaped so that one corner portion of the rectangular shape remains as a graphene 32 having a predetermined size.
- the shape of the graphene 32 has a planar shape having a size smaller than the wavelength of the terahertz light like the shape of the two-dimensional electron gas part 22 described above, and the near-field light of the terahertz light emitted from the sample 18 itself is obtained. The shape can be detected efficiently.
- a conductive material such as gold is fixed on the GaAs substrate 21 by vapor deposition or the like to form the electrodes 23a to 23d (see FIG. 9), and the sensor 13A is manufactured. Thereafter, each of the electrodes 23a to 23d is connected to the measurement control unit 20A (FIG. 9) by the conductive wire 24.
- the magnetic field generation unit 19 is generated from the sample 18 and is wound around the optical axis of the terahertz light applied to the sensor 13, and an ammeter 19b that displays a current (coil current) that flows through the coil 19a. And a voltmeter 19c that measures the voltage at both ends of the coil 19a. Then, a magnetic field B is generated by passing a current through the coil 19a and applied to the sensor 13A including the graphene 32. The magnetic field B can be uniquely determined from the coil current.
- Photoconduction is a phenomenon in which electrical conductivity changes when light is applied to an insulator or semiconductor. In a normal semiconductor, this phenomenon occurs because electrons are excited from a valence band to a conduction band or from an impurity level to a conduction band by light absorption to generate extra conduction electrons or holes.
- the conduction of extra electrons and holes excited in the upper and lower Landau levels across the Fermi level causes a change in electrical conductivity. Since it is in a magnetic field, an increase in electrical conductivity results in an increase in electrical resistivity.
- the photon energy hf of the terahertz light when cyclotron absorption occurs is equal to the energy interval of the Landau level when cyclotron absorption occurs.
- n 1 to 2
- the following expression (7) is established.
- hf (C2 (B
- C2 (that is, h * , e, m * ) other than the magnetic field B is a known constant from this equation (7), the frequency f of the terahertz light can be obtained from the magnetic field B when cyclotron absorption occurs.
- the measurement control unit 20A changes the strength (magnetic field value) of the magnetic field B applied to the sensor 13A while changing the current value flowing through the coil 19a of the magnetic field generation unit 19, and the sensor 13A
- the terahertz detection signal level (signal level) of the sample 18 to be detected is adjusted to a magnetic field value that protrudes and becomes high.
- the frequency of the protruding terahertz detection signal is a characteristic resonance frequency (specific frequency). Therefore, the magnetic field value can be tuned to a specific frequency by matching the position where the signal level protrudes. In other words, the terahertz frequency can be selected.
- the vertical axis indicates the terahertz detection signal level in an arbitrary scale
- the horizontal axis indicates the magnetic field B in Tesla [T].
- the magnetic field B generated by the magnetic field generation unit 19 is set to a specific frequency as a magnetic field value 0.1 [T] where the signal level is abruptly high as shown in FIG. 13A.
- the semiconductor substrate on which the graphene 32 shown in FIG. 9 an example using the Si substrate 31a and the SiO 2 substrate 31b has been given, but hexagonal boron nitride (h-BN), silicon carbide (
- the semiconductor substrate may be formed using SiC) or the like.
- a superconductor having a planar shape smaller than the wavelength of the terahertz light and capable of efficiently detecting near-field light of the terahertz light emitted from the sample 18 itself can be used as a detection point.
- materials such as semiconductor nanowires and carbon nanotubes may be used.
- FIG. 15 is a diagram illustrating a configuration of a terahertz detection point according to another example 1 of the terahertz detection sensor 13 (FIG. 2) of the present embodiment.
- the detection point according to the other example 1 shown in FIG. 15 is formed by combining the probe 51 with the tip pointed like a needle on the two-dimensional electron gas unit 22.
- the probe 51 is obtained by processing a metal such as tungsten or a semiconductor such as silicon into a needle shape (or a line shape). Silicon is formed into a needle shape by anisotropic etching, for example.
- the probe 51 corresponds to a gate on a MOSFET that controls between the source and drain of the two-dimensional electron gas unit 22, and is a gate voltage obtained by detecting near-field light of terahertz light emitted from the sample 18, The electron current flowing from the source to the drain on the two-dimensional electron gas 22g is controlled at high speed using high electron mobility. Since the probe 51 is pointed like a needle, the detection size of the terahertz light in the space is reduced, so that the spatial resolution when detecting near-field light can be increased.
- FIG. 16 is a diagram illustrating a configuration of a terahertz detection point according to another example 2 of the terahertz detection sensor 13 of the present embodiment.
- the detection point according to the other example 2 shown in FIG. 16 is a point 22a1 having a pointed part of the surface of the AlGaAs layer 22a of the two-dimensional electron gas unit 22.
- the electron current flowing in the two-dimensional electron gas 22g by detecting the near-field light of the terahertz light emitted from the sample 18 is converted at high speed using high electron mobility. Can be controlled. Even with the needle shape 22a1, like the probe 51, the spatial resolution at the time of detecting near-field light can be increased.
- FIG. 17 is a diagram illustrating a configuration of a terahertz detection point according to another example 3 of the terahertz detection sensor 13A (FIG. 9) of the present embodiment.
- the detection point according to the other example 3 shown in FIG. 17 is a probe 53 made of needle-like (or linear) carbon nanotubes perpendicular to the surface of the graphene 32 formed at one corner of the upper surface of the SiO 2 substrate 31b on the Si substrate 31a. It is a thing that stands. Even when the carbon nanotube probe 53 is erected in this way, the probe 53 is formed in a needle shape (or a line shape), so that the detection size of the terahertz light in the space is reduced. The spatial resolution of time can be increased.
- FIG. 18 is a diagram illustrating a configuration of a terahertz detection point according to another example 4 of the terahertz detection sensor 13A (FIG. 9) of the present embodiment.
- the detection point according to the other example 4 shown in FIG. 18 is that a part of the top corner portion of the SiO 2 substrate 31b is sharpened to a needle shape 31b1, and the graphene 32B is formed at the corner portion including the needle shape 31b1.
- the surface of the graphene 32B is pointed like a needle like the probe 53 described above, the spatial resolution when detecting near-field light can be increased.
- FIG. 19 is a diagram showing a configuration of an Si vibrating section 62 as another example of the vibrating section (GaAs vibrating section 11 in FIG. 1) in the terahertz image measuring apparatus 10. Similar to the GaAs vibrating portion 11, the Si vibrating portion 62 is integrally formed with a rectangular parallelepiped base end portion 62 a and a plate-like portion 62 b protruding flush along the lower surface of the base end portion 62 a. The sensor 13 is fixed to the lower surface of the distal end portion of the plate-like portion 62b. The base end portion 62 a is fixed to the piezo substrate 10 a via the piezo substrate 61.
- the Si vibrating portion 62 When the power supply voltage V2 is applied to the piezo substrate 61, the Si vibrating portion 62 is vibrated at a constant vibration frequency due to the piezo effect, and accordingly, the plate-like portion 62b is vibrated up and down at the same vibration frequency. It has become. In addition, a voltage corresponding to the vibration of the Si vibration unit 62 is detected by the voltage detection unit 14.
- the sensor 13 detects the terahertz light of the sample 18 in the same manner as the operation of the GaAs vibrating part 11 linked to the Z piezo substrate 15 described above.
- the operation can be kept constant.
- the Si vibrating part 62 constitutes the vibrating part described in the claims.
- the vibrating portion may be a vibrating member such as a piezoelectric material, or a vibrating member such as a tuning fork that vibrates according to the vibration of the piezo substrate 61.
- the terahertz image measuring apparatus described above can be implemented not only by passive measurement but also by active measurement.
- SYMBOLS 10 Terahertz image measuring apparatus 10a Piezo substrate 11 GaAs vibration part 12 AC power supply 13, 13A Terahertz detection sensor 14 Voltage detection part 15 Z layer piezo substrate (Z piezo substrate) 16 Y layer piezo substrate (Y piezo substrate) 17 X layer piezo substrate (X piezo substrate) 18 Sample 19 Magnetic field generator 19a Coil 19b Ammeter 19c Voltmeter 20 Measurement controller 21 GaAs substrate 22 Two-dimensional electron gas part (detection point) 22a AlGaAs layer 22g Two-dimensional electron gas 23a-23d Electrode 31a Si substrate 31b SiO 2 substrate 32 Graphene (detection point) 51 probe 53 probe (carbon nanotube) 61 Piezoelectric substrate 62 Si vibrating part B Magnetic field
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Abstract
Description
特許文献1の技術は、表面から一定位置に2次元電子ガス(後述)が形成された半導体チップを用い、この半導体チップに磁場を印加しながらテラヘルツ光を照射する。この照射によりカーボンナノチューブに流れる電流を計測することで、微弱なテラヘルツ光の強度と周波数を検出するものである。なお「2次元電子ガス」とは、半導体と絶縁体との接合界面、又は異種半導体同士の接合界面に沿った2次元平面を運動する電子をいう。つまり、キャリアとなる電子が平面状に分布する状態を2次元電子ガスという。なお、本明細書において、異種半導体とは、異なる種類の半導体や、反転層等を利用した異なる構造の半導体をいう。
<実施形態の構成>
図1は、本発明の実施形態に係るテラヘルツ検出センサを用いたテラヘルツ画像測定装置の構成を示す図である。
アパーチャの径が5μmの場合、テラヘルツ光が透過した近接場光の量が他のアパーチャ(0.9μm,2μm)の場合よりも多いので、近接場光検出により検出されるテラヘルツ検出信号Ts1の立ち下がりエッジは、他のアパーチャ(0.9μm,2μm)の場合よりも緩やかになる。この場合、テラヘルツ検出信号Ts1(又は、後述のTs2,Ts3)の最大値100%の90%~10%の間の距離が分解能となる。この分解能は、アパーチャの大きさ(この場合、5μm)で決まる。従って、アパーチャの径が5μmの場合は、分解能が他のアパーチャ(0.9μm,2μm)の場合よりも低くなる。
(h/2π)eB/m* …(1)
この現象はサイクロトロン吸収、或いはサイクロトロン共鳴と呼ばれる。
ここで、hはプランク定数、eは電荷素量、Bは磁場、m*は結晶中の電子の有効質量(例えばGaAsであれば、自由電子の質量の約0.0665倍)である。
hf=(h/2π)eB/m* …(2)
この式(2)から磁場B以外のh,e,m*は既知の定数であるので、サイクロトロン吸収が生じる際の磁場Bからテラヘルツ光の周波数fを求めることができる。
以上説明したように、本実施形態のテラヘルツ検出センサ13とテラヘルツ画像測定装置10によれば、次のような効果が得られる。
図9は、他例のテラヘルツ検出センサ13Aの構成を示す斜視図である。図9に示すセンサ13Aは、図1に示すテラヘルツ画像測定装置10のセンサ13として用いられるものである。
このような特殊なバンド構造により、グラフェン32中の電子移動度は、室温であっても非常に高速(通常の半導体の10倍~100倍以上)であることが知られている。
半導体:En=(n+0.5)h*eB/m* …(3)
グラフェン:En=c*(2eh*B|n|)0.5 …(4)
式(3)及び(4)において、c*はディラックフェルミオンの速度、eは電荷素量、h*はプランク定数hの1/(2π)、Bは印加磁場、nはランダウ準位の指数、m*は結晶中の電子の有効質量(例えばGaAsならば、自由電子の質量の0.0665倍)である。
半導体:En=C1(n+0.5)B・・・(5)
グラフェン:En=C2(B|n|)0.5・・・(6)
図12Aに示すように、Si基板31aの上に積層されたSiO2基板31bの上面にグラフェン32Aが積層された素子を用いる。
次に、図12Cに示すように、金等の導電材料をGaAs基板21の上に蒸着等により固着させて各電極23a~23d(図9参照)を形成し、センサ13Aを製作する。この後、各電極23a~23dを導電線24で測定制御部20A(図9)に接続する。
磁場発生部19は、試料18から発生され、センサ13に照射されるテラヘルツ光の光軸を囲んで巻回されるコイル19aと、コイル19aに流される電流(コイル電流)を表示する電流計19bと、コイル19aの両端の電圧を計測する電圧計19cとを備えて構成される。そして、コイル19aに電流を流すことにより磁場Bを発生させて、グラフェン32を備えるセンサ13Aに印加する。磁場Bは、コイル電流から一義的に求めることが可能となっている。
hf=(C2(B|2|)0.5-C2(B|1|)0.5 …(7)
この式(7)から磁場B以外のC2(即ち、h*,e,m*)は既知の定数であるので、サイクロトロン吸収が生じる際の磁場Bからテラヘルツ光の周波数fを求めることができる。
例えば、測定制御部20Aの制御により、磁場発生部19で発生される磁場Bを、図13Aに示すように、信号レベルが6と急峻に高くなる磁場値0.1[T]として、特定周波数f=0.76THzを選択し、この特定周波数f=0.76THzのテラヘルツ光を発する試料18の分子のテラヘルツ画像を表示することができる。
図15は本実施形態のテラヘルツ検出センサ13(図2)の他例1によるテラヘルツ検出ポイントの構成を示す図である。
図15に示す他例1による検出ポイントは、2次元電子ガス部22の上に、先端が針状に尖ったプローブ51を合体させて形成したものである。
このプローブ51は、先端が針状に尖っているので空間上のテラヘルツ光の検出サイズが小さくなり、このため、近接場光の検出時の空間解像度を上げることができる。
図16は本実施形態のテラヘルツ検出センサ13の他例2によるテラヘルツ検出ポイントの構成を示す図である。
図16に示す他例2による検出ポイントは、2次元電子ガス部22のAlGaAs層22aの表面の一部を尖って針状22a1としたものである。この針状22a1においても、上述したプローブ51と同様に、試料18が発するテラヘルツ光の近接場光を検出することにより2次元電子ガス22gに流れる電子電流を、高い電子移動度を利用して高速に制御することができる。この針形状22a1でも、プローブ51と同様に、近接場光の検出時の空間解像度を上げることができる。
図17は本実施形態のテラヘルツ検出センサ13A(図9)の他例3によるテラヘルツ検出ポイントの構成を示す図である。
図17に示す他例3による検出ポイントは、Si基板31a上のSiO2基板31bの上面一隅部分に形成されたグラフェン32の表面に、垂直に針状(又は線状)のカーボンナノチューブによるプローブ53を立てたものである。このようにカーボンナノチューブによるプローブ53を立てた場合でも、プローブ53が針状(又は線状)に形成されているので空間上のテラヘルツ光の検出サイズが小さくなり、このため、近接場光の検出時の空間解像度を上げることができる。
図18は本実施形態のテラヘルツ検出センサ13A(図9)の他例4によるテラヘルツ検出ポイントの構成を示す図である。
図18に示す他例4による検出ポイントは、SiO2基板31bの上面一隅部分の一部を針状31b1に尖らせて、この針状31b1を含む一隅部分にグラフェン32Bを形成したものである。この構成においては、グラフェン32Bの表面が上述したプローブ53と同様に針状に尖っているので、近接場光の検出時の空間解像度を上げることができる。
図19はテラヘルツ画像測定装置10における振動部(図1ではGaAs振動部11)の他例としてのSi振動部62の構成を示す図である。
Si振動部62は、GaAs振動部11と同様に、直方体形状の基端部62aと、この基端部62aの下面に沿って面一に突き出た板状部62bとが一体形成されている。板状部62bの先端部下面にはセンサ13が固定されている。基端部62aは、ピエゾ基板61を介してピエゾ基板10aに固定されている。ピエゾ基板61には電源電圧V2が印加されることによって、ピエゾ効果によりSi振動部62を一定の振動周波数で振動し、これに応じて板状部62bを同じ振動周波数で上下に振動するようになっている。また、Si振動部62の振動に応じた電圧は電圧検出部14で検出されるようになっている。
10a ピエゾ基板
11 GaAs振動部
12 交流電源
13,13A テラヘルツ検出センサ
14 電圧検出部
15 Z層のピエゾ基板(Zピエゾ基板)
16 Y層のピエゾ基板(Yピエゾ基板)
17 X層のピエゾ基板(Xピエゾ基板)
18 試料
19 磁場発生部
19a コイル
19b 電流計
19c 電圧計
20 測定制御部
21 GaAs基板
22 2次元電子ガス部(検出ポイント)
22a AlGaAs層
22g 2次元電子ガス
23a~23d 電極
31a Si基板
31b SiO2基板
32 グラフェン(検出ポイント)
51 プローブ
53 プローブ(カーボンナノチューブ)
61 ピエゾ基板
62 Si振動部
B 磁場
Claims (12)
- テラヘルツ光を検出するテラヘルツ検出センサにおいて、
テラヘルツ光の波長よりも小さいサイズの形状であって、前記テラヘルツ光の近接場光を検出する検出ポイントと、
前記検出ポイントが表面に形成された半導体基板と
を備えることを特徴とするテラヘルツ検出センサ。 - 前記半導体基板の表面に、前記検出ポイントに電流を流すための第1電極と、当該第1電極を介して電流が流された当該検出ポイントに、前記近接場光の照射時に検出される電圧を出力する第2電極とが形成されている
ことを特徴とする請求項1に記載のテラヘルツ検出センサ。 - 前記第1電極及び前記第2電極の各々は、先端が針状に先細って延びる帯状を成し、当該針状の先端が前記検出ポイントに接合された1対の電極を含んで成る
ことを特徴とする請求項1に記載のテラヘルツ検出センサ。 - 前記半導体基板は、上下に積層される半導体の種類や構造が異なる異種半導体同士の界面に2次元電子ガスが分布した高電子移動度トランジスタ構造であり、
前記検出ポイントは、前記積層された最上層の半導体層が前記テラヘルツ光の波長よりも小さいサイズの形状に成形され、当該成形された半導体層と、この下の半導体層との界面に2次元電子ガスが分布した構造である
ことを特徴とする請求項1に記載のテラヘルツ検出センサ。 - 前記半導体基板は、GaAs層上にAlGaAs層が積層され、当該AlGaAs層と当該GaAs層との界面に2次元電子ガスが分布した高電子移動度トランジスタ構造であり、
前記検出ポイントは、前記AlGaAs層が前記テラヘルツ光の波長よりも小さいサイズの形状に成形され、当該成形されたAlGaAs層と前記GaAs層との界面に2次元電子ガスが分布した構造である
ことを特徴とする請求項4に記載のテラヘルツ検出センサ。 - 前記検出ポイントは、当該検出ポイントの上に先端が尖った針状又は線状の金属及び半導体の何れか一方によるプローブが合体して備えられている
ことを特徴とする請求項4に記載のテラヘルツ検出センサ。 - 前記半導体基板は、上下に種類が異なる半導体を積層した構造であり、
前記検出ポイントは、前記積層された最上層の半導体層の上に、前記テラヘルツ光の波長よりも小さいサイズの形状に成されたグラフェンである
ことを特徴とする請求項1に記載のテラヘルツ検出センサ。 - 前記半導体基板は、Si層上にSiO2層を積層した構造であり、
前記検出ポイントは、前記SiO2層の上に、前記テラヘルツ光の波長よりも小さいサイズの形状に成されたグラフェンである
ことを特徴とする請求項7に記載のテラヘルツ検出センサ。 - 前記検出ポイントは、当該検出ポイントの上に先端が尖った針状又は線状のカーボンナノチューブによるプローブが合体して備えられている
ことを特徴とする請求項7に記載のテラヘルツ検出センサ。 - 前記第1電極及び前記第2電極の各々は、先端が針状に先細って延びる帯状を成し、当該針状の先端に前記検出ポイントに接合された1対の電極を含み、当該電極は、長さがテラヘルツ波の波長以上で、且つ、テラヘルツ波の波長未満の電界が集中する領域でテラヘルツ波を受信する
ことを特徴とする請求項1に記載のテラヘルツ検出センサ。 - 試料から発せられるテラヘルツ光の近接場光を検出する請求項1又は2に記載のテラヘルツ検出センサと、
前記試料から前記テラヘルツ検出センサに照射されるテラヘルツ光の光軸を囲んで巻回され、当該試料及び当該テラヘルツ検出センサの周囲に配置されるコイルを有し、当該コイルに電流が流されて発生する磁場を当該テラヘルツ検出センサへ印加する磁場発生部と、
前記コイルに電流を流し、この流れる電流値を変えることにより前記磁場の強さを、当該テラヘルツ検出センサで検出される前記試料のテラヘルツ光の検出信号レベルが突出して高くなる磁場値とし、テラヘルツ光の特定周波数に同調させる測定制御部と
を備えることを特徴とするテラヘルツ画像測定装置。 - 基端部から延びる板状の先端部に固定した前記テラヘルツ検出センサを、当該基端部への電圧印加により前記試料との間隔方向に振動させる振動部と、
前記テラヘルツ検出センサと前記試料との間に間隙を介して当該試料を載置固定し、前記振動部の振動を検出した電圧に応じて、前記載置固定された試料を、前記間隙が一定となるように当該間隙方向に移動させるピエゾ基板と
を備えることを特徴とする請求項11に記載のテラヘルツ画像測定装置。
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