JP2020036037A - Photoconductive element and measurement device - Google Patents

Abstract

To appropriately set an interval between a pair of electrodes sandwiching a photoconductive layer.SOLUTION: A photoconductive element 110 comprises: a photoconductive layer 112 in which excitation light LB1 is incident on the surface 112a thereof; and a pair of electrodes 113-3, 114-3 sandwiching the photoconductive layer along a predetermined direction X intersecting with an incident direction Z of the excitation light. Shape of each of the pair of electrodes on a plane intersecting the incident direction is an arc shape distributed along the outer edge of an optical path of the excitation light which the photoconductive layer transmits.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a technical field of a photoconductive device capable of emitting or detecting an electromagnetic wave such as a terahertz wave.

  A terahertz wave measuring device is known as a measuring device for measuring characteristics of a sample. The terahertz wave measuring device measures characteristics of a sample in the following procedure. First, pump light (in other words, excitation light), which is one laser light obtained by splitting an ultrashort pulse laser light (for example, a femtosecond pulse laser light), is generated by a terahertz wave to which a bias voltage is applied. Irradiates the element. As a result, the terahertz wave generating element emits a terahertz wave. The terahertz wave emitted from the terahertz wave generating element is irradiated on the sample. The terahertz wave applied to the sample is reflected by the sample or transmitted through the sample. The terahertz wave reflected by the sample or transmitted through the sample is another laser beam obtained by branching the ultrashort pulse laser beam, and has an optical delay (that is, an optical path length difference) with respect to the pump light. The terahertz wave detection element irradiated with the probe light (in other words, the excitation light) is irradiated. As a result, the terahertz wave detecting element detects the terahertz wave reflected by the sample or transmitted through the sample. The terahertz wave measuring apparatus measures the characteristics of the sample by analyzing the detected terahertz wave (that is, a terahertz wave in the time domain and a current signal).

  As an example of a terahertz wave generation element and a terahertz detection element, a substrate, a pair of electrode layers formed on the substrate and arranged to form an antenna separated by a gap, and a photoconductive layer formed in the gap There is a photoconductive element provided with (for example, see Patent Document 1).

JP 2005-26347 A

  In the photoconductive device described in Patent Document 1, the photoconductive layer is formed between a pair of electrode portions extending toward the gap portion of the pair of electrode layers (that is, a gap portion between the pair of electrode portions). Have been. Further, the side surfaces of the photoconductive layer are electrically connected to the side surfaces of the pair of electrode portions.

  Here, in the photoconductive element described in Patent Literature 1, the distance between a pair of electrode portions sandwiching the photoconductive layer (the width along a predetermined direction intersecting the incident direction or the propagation direction of the excitation light) is equal to the photoconductive layer. It is always constant regardless of the position along the height direction of the layer (that is, the incident direction or propagation direction of the excitation light). On the other hand, the beam diameter of the excitation light applied to the photoconductive layer (that is, the width of the spread of the optical path of the excitation light along a predetermined direction intersecting the incident direction or the propagation direction of the excitation light) is higher than the height of the photoconductive layer. It fluctuates according to the position along the vertical direction. Therefore, by selecting the shape of the pair of electrode portions in consideration of the fluctuation of the beam diameter of the excitation light (for example, setting the interval between the pair of electrode portions to an appropriate interval), the performance of the photoconductive element is improved. It is estimated that there is room for improving (for example, improving the S / N ratio).

  Note that the above-described technical problem also occurs in any measuring device that measures characteristics of a sample using an electromagnetic wave different from a terahertz wave as long as the measuring device includes a photoconductive element.

  The problems to be solved by the present invention include those described above as examples. An object of the present invention is to provide a photoconductive element in which a distance between a pair of electrodes sandwiching a photoconductive layer is appropriately set.

  A first example of the photoconductive element of the present invention includes a photoconductive layer on which excitation light is incident on a surface, and a pair of electrodes that sandwich the photoconductive layer along a predetermined direction that intersects the direction of incidence of the excitation light. The shape of each of the pair of electrodes on a plane intersecting the incident direction is an arc shape distributed along the outer edge of the optical path of the excitation light transmitted through the photoconductive layer.

FIG. 1 is a block diagram illustrating a configuration of the terahertz wave measurement device according to the present embodiment. FIG. 2A is a top view illustrating the top surface of the terahertz wave generating device of the first embodiment, and FIG. 2B is a cross-sectional view taken along line II-II ′ of the terahertz wave generating device illustrated in FIG. FIG. FIG. 3 is an enlarged cross-sectional view of a section near the third electrode portion and the photoconductive layer in the II-II ′ cross section of the terahertz wave generating element illustrated in FIG. FIG. 4 is a cross-sectional view showing four terahertz wave generating elements of a comparative example together with the terahertz wave generating element of the present embodiment. FIG. 5A is a top view illustrating the top surface of the terahertz wave generating element of the second embodiment, and FIG. 5B is a diagram illustrating the V (1) -V of the terahertz wave generating element illustrated in FIG. FIG. 5C is a cross-sectional view showing a (1) ′ cross section, and FIG. 5C is a cross-sectional view showing a V (2) -V (2) ′ cross section of the terahertz wave generating element shown in FIG. 5A. FIG. 6A is a top view illustrating the top surface of the terahertz wave generating element of the third embodiment, and FIG. 6B is a cross-sectional view taken along the line VI-VI ′ of the terahertz wave generating element illustrated in FIG. FIG. FIG. 7A is a top view illustrating the top surface of the terahertz wave generating element of the fourth embodiment, and FIG. 7B is a cross-sectional view of the terahertz wave generating element of the fourth embodiment (in FIG. 7A). FIG. 7C is a cross-sectional view showing a VII (1) -VII (1) ′ cross section of FIG. 7A. FIG. 7C is a cross section of the terahertz wave generating element of the fourth embodiment (VII (2) in FIG. FIG. 7B is a cross-sectional view showing (VII (2) ′ cross section).

  Hereinafter, embodiments of the photoconductive element and the measuring device will be described.

(First Embodiment of Photoconductive Element)
<1>
The photoconductive element of the present embodiment includes a photoconductive layer on the surface of which excitation light is incident, and a pair of electrodes that sandwich the photoconductive layer along a predetermined direction that intersects the direction of incidence of the excitation light; The distance between the pair of electrodes along, the end position where the front surface and the back surface are located in the region between the front surface and the back surface of the photoconductive layer facing the front surface along the incident direction. Are minimized at different predetermined positions.

  According to the photoconductive element of the present embodiment, the interval between the pair of electrodes sandwiching the photoconductive layer is appropriately set. As a result, the performance of the photoconductive element (for example, the efficiency of generating or detecting electromagnetic waves such as terahertz waves) is improved.

<2>
In another aspect of the photoconductive device of the present embodiment, the predetermined position is a position where a beam diameter of the excitation light passing through the photoconductive layer in the predetermined direction is minimized.

  According to this aspect, the distance between the pair of electrodes sandwiching the photoconductive layer is appropriately set based on the propagation mode of the excitation light applied to the photoconductive layer.

<3>
In another aspect of the photoconductive element in which the predetermined position is the position where the beam diameter of the excitation light is minimized as described above, the changing tendency of the interval between the pair of electrodes along the incident direction is such that the beam diameter is smaller than the incident diameter of the beam diameter. It is the same as the change tendency along the direction.

  According to this aspect, the distance between the pair of electrodes sandwiching the photoconductive layer is appropriately set based on the propagation mode of the excitation light applied to the photoconductive layer.

<4>
In another aspect of the photoconductive element according to the present embodiment, each of the pair of electrodes includes a contact surface that is in contact with the photoconductive layer, and the interval between the pair of electrodes along the predetermined direction is equal to or smaller than the predetermined direction. Along the distance between the pair of contact surfaces.

  According to this aspect, the interval between the pair of contact surfaces corresponding to the interval between the pair of electrodes sandwiching the photoconductive layer is appropriately set.

<5>
In another aspect of the photoconductive element in which each of the pair of electrodes has a contact surface as described above, the contact surface has a shape distributed along an outer edge of an optical path of the excitation light transmitted through the photoconductive layer. are doing.

  According to this aspect, the shape of the pair of electrodes sandwiching the photoconductive layer is appropriately set based on the propagation mode of the excitation light applied to the photoconductive layer.

<6>
In another aspect of the photoconductive element of the present embodiment, the shape of each of the pair of electrodes on a plane intersecting the incident direction is along an outer edge of an optical path of the excitation light transmitted through the photoconductive layer. It is a distributed arc shape.

  According to this aspect, the shape of the pair of electrodes sandwiching the photoconductive layer is appropriately set based on the propagation mode of the excitation light applied to the photoconductive layer.

<7>
In another aspect of the photoconductive device of the present embodiment, one of the pair of electrodes is at least partially disposed such that an interval between the pair of electrodes along the predetermined direction at the predetermined position is minimized. Projecting toward the other of the electrodes.

  According to this aspect, if formation of a portion of one electrode protruding toward the other electrode is minimized, the parasitic capacitance between the pair of electrodes can be reduced.

<8>
In another aspect of the photoconductive element of the present embodiment, a pair of first portions sandwiching, along the predetermined direction, an optical path of the excitation light having a predetermined intensity or more among the pair of electrodes in a plane intersecting the incident direction. The interval along the predetermined direction is longer than the interval along the predetermined direction between a pair of second portions of the pair of electrodes that do not sandwich the optical path of the excitation light having the predetermined intensity or more along the predetermined direction. small.

  According to this aspect, since the interval between the pair of second portions is not unnecessarily narrowed, compared with the case where the interval between the pair of electrodes is constant in a plane intersecting the incident direction, Parasitic capacitance between the electrodes can be reduced.

<9>
In another aspect of the photoconductive device of the present embodiment, the pair of electrodes is formed outside an optical path of the excitation light.

  According to this aspect, propagation of the excitation light is not hindered by the pair of electrodes.

(Embodiment of measuring device)
<10>
The measurement device of the present embodiment includes an irradiation unit that irradiates the sample with an electromagnetic wave, and a detection unit that detects the electromagnetic wave applied to the sample, and at least one of the irradiation / emission unit and the detection unit is configured as described above. Of the present embodiment (including various aspects thereof).

  According to the measuring device of the present embodiment, the same effects as those that can be enjoyed by the photoconductive element of the present embodiment described above can be suitably enjoyed.

<11>
In another aspect of the measurement device of the present embodiment, the electromagnetic wave includes a terahertz wave.

  According to this aspect, the measurement device can operate as a terahertz wave measurement device that measures the characteristics of the sample using the terahertz wave. The measuring device that operates as such a terahertz wave measuring device can also preferably enjoy the same effects as those that can be enjoyed by the photoconductive element of the present embodiment described above.

  The operation and other gains of the photoconductive device and the measuring device according to the present embodiment will be described in more detail in the following examples.

  As described above, in the photoconductive element of the present embodiment, the distance between the pair of electrodes is minimized at a predetermined position different from the end position where the front and back surfaces of the photoconductive layer are located. The measuring device according to the present embodiment includes the photoconductive device according to the present embodiment. Therefore, a photoconductive element having an appropriate shape according to the beam diameter of the excitation light, and a measuring device including such a photoconductive element are provided.

  Hereinafter, embodiments of the photoconductive device and the measuring device will be described with reference to the drawings. In particular, in the following, a terahertz wave measuring device 100, which includes a terahertz wave generating element 110 and a terahertz wave detecting element 130, each of which is a specific example of a "photoconductive element", and is a specific example of a "measuring device", will be described. Proceed with explanation.

(1) Configuration of Terahertz Wave Measurement Apparatus 100 First, the configuration of the terahertz wave measurement apparatus 100 of the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus 100 according to the present embodiment.

  As shown in FIG. 1, the terahertz wave measuring apparatus 100 irradiates the sample 10 with the terahertz wave THz, and transmits the terahertz wave THz transmitted through the sample 10 or reflected by the sample 10 (that is, the terahertz wave irradiated on the sample 10). THz). In the example shown in FIG. 1, the terahertz wave measuring apparatus 100 detects the terahertz wave THz reflected by the sample 10.

The terahertz wave THz is an electromagnetic wave including an electromagnetic wave component belonging to a frequency region around 1 terahertz (1 THz = 10 ¹² Hz) (that is, a terahertz region). The terahertz region is a frequency region having both light straightness and electromagnetic wave transmittance. The terahertz region is a frequency region in which various substances have unique absorption spectra. Therefore, the terahertz wave measuring apparatus 100 can measure the characteristics of the sample 10 by analyzing the terahertz wave THz applied to the sample 10.

  Here, since the cycle of the terahertz wave THz is on the order of sub-picoseconds, it is technically difficult to directly detect the waveform of the terahertz wave THz. Therefore, the terahertz wave measuring apparatus 100 indirectly detects the waveform of the terahertz wave THz by employing the pump-probe method based on the time delay scanning. Hereinafter, the terahertz wave measuring apparatus 100 employing the pump-probe method will be described more specifically.

  As shown in FIG. 1, the terahertz wave measuring apparatus 100 includes a pulse laser apparatus 101, a terahertz wave generating element 110 which is a specific example of “irradiating means”, a beam splitter 161, a reflecting mirror 162, and a reflecting mirror 163. A half mirror 164, an optical delay mechanism 120, a terahertz wave detection element 130 as a specific example of a “detection unit”, a bias voltage generation unit 141, an IV (current-voltage) conversion unit 142, And a control unit 150.

  The pulse laser device 101 generates a sub-picosecond order or femtosecond order pulsed laser beam LB having a light intensity according to the drive current input to the pulse laser device 101. The pulse laser beam LB generated by the pulse laser device 101 enters the beam splitter 161 via a light guide (not shown) (for example, an optical fiber).

  The beam splitter 161 splits the pulsed laser light LB into a pump light LB1 and a probe light LB2, each of which is a specific example of the “excitation light”. The pump light LB1 enters the terahertz wave generation element 110 via a light guide path (not shown). On the other hand, the probe light LB2 is incident on the optical delay mechanism 120 via a light guide path (not shown) and the reflecting mirror 162. Thereafter, the probe light LB2 emitted from the optical delay mechanism 120 is incident on the terahertz wave detection element 130 via the reflecting mirror 163 and a light guide path (not shown).

  The terahertz wave generating element 110 emits a terahertz wave THz. Specifically, the gap voltage 115 (see FIG. 2 and the like) provided in the terahertz wave generating element 110 is connected to the bias voltage generating section via the electrode layers 113 and 114 (see FIG. 2 and the like) provided in the terahertz wave generating element 110. The bias voltage generated by 141 is applied. When the pump light LB1 is applied to the gap 115 while an effective bias voltage (for example, a bias voltage other than 0 V) is applied to the gap 115, the photoconductive layer 112 formed in the gap 115 (FIG. 2 etc.) are irradiated with the pump light LB1. In this case, carriers are generated in the photoconductive layer 112 irradiated with the pump light LB1 by light excitation by the pump light LB1. As a result, the terahertz wave generating element 110 generates a pulse-like current signal on the order of subpicoseconds or on the order of femtoseconds according to the generated carrier. The generated current signal flows to the electrode layers 113 and 114. As a result, the terahertz wave generating element 110 emits a terahertz wave THz caused by the pulsed current signal.

  The terahertz wave THz emitted from the terahertz wave generating element 110 passes through the half mirror 164. As a result, the terahertz wave THz transmitted through the half mirror 164 is irradiated on the sample 10. The terahertz wave THz applied to the sample 10 is reflected by the sample 10. The terahertz wave THz reflected by the sample 10 is reflected by the half mirror 164. The terahertz wave THz reflected by the half mirror 164 enters the terahertz wave detection element 130.

  The terahertz wave detection element 130 detects a terahertz wave THz incident on the terahertz wave detection element 130. Specifically, when the gap portion 115 (see FIG. 2 and the like) provided in the terahertz wave detection element 130 is irradiated with the probe light LB2, the photoconductive layer 112 (see FIG. 2 and the like) formed in the gap portion 115 is irradiated. The probe light LB2 is irradiated. In this case, carriers are generated in the photoconductive layer 112 irradiated with the probe light LB2 by light excitation by the probe light LB2. As a result, a current signal corresponding to the carrier flows through the electrode layers 113 and 114 (see FIG. 2 and the like) included in the terahertz wave detection element 130. When the terahertz wave detection element 130 is irradiated with the terahertz wave THz while the probe light LB2 is irradiated on the gap portion 115, the signal intensity of the current signal flowing through the electrode layers 113 and 114 becomes equal to the light intensity of the terahertz wave THz. Will change accordingly. A current signal whose signal intensity changes according to the light intensity of the terahertz wave THz is output to the IV conversion unit 142 via the electrode layers 113 and 114.

  The optical delay mechanism 120 adjusts the difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2 (that is, the optical path length difference). Specifically, the optical delay mechanism 120 adjusts the optical path length difference by adjusting the optical path length of the probe light LB2. When the optical path length difference is adjusted, the timing at which the pump light LB1 enters the terahertz wave generating element 110 (or the timing at which the terahertz wave generating element 110 emits the terahertz wave THz) and the time at which the probe light LB2 is detected by the terahertz wave detecting element 130 (Or a timing at which the terahertz wave detection element 130 detects the terahertz wave THz). The terahertz wave measuring apparatus 100 indirectly detects the waveform of the terahertz wave THz by adjusting the time difference. For example, when the optical path of the probe light LB2 is increased by 0.3 mm (however, the optical path length in the air) by the optical delay mechanism 120, the timing at which the probe light LB2 enters the terahertz wave detection element 130 is delayed by one picosecond. Become. In this case, the timing at which the terahertz wave detection element 130 detects the terahertz wave THz is delayed by one picosecond. Considering that the terahertz wave THz having the same waveform repeatedly enters the terahertz wave detection element 130 at intervals of about several tens of MHz, the timing at which the terahertz wave detection element 130 detects the terahertz wave THz is gradually shifted. Thereby, the terahertz wave detection element 130 can indirectly detect the waveform of the terahertz wave THz. That is, the lock-in detection unit 151 described later can detect the waveform of the terahertz wave THz based on the detection result of the terahertz wave detection element 130.

  The current signal output from the terahertz wave detection element 130 is converted into a voltage signal by the IV conversion unit 142.

  The control unit 150 measures the characteristics of the sample 10 based on the detection result of the terahertz wave detection element 130 (that is, the voltage signal output from the IV conversion unit 142). The control unit 150 includes a lock-in detection unit 151 and a signal processing unit 152 for measuring characteristics of the sample 10.

  The lock-in detector 151 performs synchronous detection on the voltage signal output from the IV converter 142 using the bias voltage generated by the bias voltage generator 141 as a reference signal. As a result, the lock-in detection unit 151 detects a sample value of the terahertz wave THz. After that, the similar operation is repeated while appropriately adjusting the difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2 (that is, the optical path length difference), so that the lock-in detection unit 151 performs the terahertz wave operation. The terahertz wave THz waveform (time waveform) detected by the detection element 130 can be detected. The lock-in detection unit 151 outputs a waveform signal indicating the waveform of the terahertz wave THz detected by the terahertz wave detection element 130 to the signal processing unit 152.

  The signal processing unit 152 measures characteristics of the sample 10 based on the waveform signal output from the lock-in detection unit 151. For example, the signal processing unit 152 acquires the frequency spectrum of the terahertz wave THz using terahertz time domain spectroscopy, and measures the characteristics of the sample 10 based on the frequency spectrum.

(2) Configuration of Terahertz Wave Generation Element 110 and Terahertz Wave Detection Element 130 Next, the configuration of the terahertz wave generation element 110 and the terahertz wave detection element 130 will be described. The configuration of the terahertz wave generating element 110 is the same as the configuration of the terahertz wave detecting element 130. Therefore, the configuration of the terahertz wave generating element 110 will be described below. However, the following description is similarly applicable to the terahertz wave detection element 130. Further, in the following description, the terahertz wave generating element 110 will be described using a three-dimensional coordinate space defined by an X axis, a Y axis, and a Z axis that are orthogonal to each other.

(2-1) Configuration of Terahertz Wave Generating Element 110-1 of First Embodiment First, referring to FIGS. 2A and 2B, the terahertz wave generating element 110 of the first embodiment (hereinafter referred to as “Terahertz wave generating element 110-1” ) will be described. The configuration of the “terahertz wave generating element 110-1” for convenience will be described. FIG. 2A is a top view illustrating the top surface of the terahertz wave generating element 110-1 according to the first embodiment. FIG. 2B is a cross-sectional view illustrating a II-II ′ cross section of the terahertz wave generation element 110-1 illustrated in FIG.

  As shown in FIGS. 2A and 2B, the terahertz wave generating element 110-1 includes a substrate 111 and light formed on one surface (the surface on the + Z axis direction side) of the substrate 111. The semiconductor device includes a conductive layer 112 and a pair of electrode layers (that is, electrode layers 113 and 114) formed on one surface of the substrate 111. That is, in the terahertz wave generation element 110-1, the substrate 111, the photoconductive layer 112, and the electrode layers 113 and 114 are stacked in the Z-axis direction (that is, the direction orthogonal to the XY plane parallel to the surface of the substrate 111). ).

  The substrate 111 is a semiconductor substrate. For example, the substrate 111 may be an InP (indium phosphide) substrate, a GaAs (gallium arsenide) substrate, a Si (silicon) substrate, or the like. The shape of the substrate 111 is a plate shape, but may be another shape.

  The photoconductive layer 112 is a layer in which carriers (for example, electrons or holes) are generated by irradiation with the above-described pump light LB1. The photoconductive layer 112 is made of, for example, GaAs, AlGaAs (aluminum gallium arsenide), InGaP (indium gallium phosphide), AlAs (aluminum arsenide), InP, InAlAs (indium aluminum arsenide), InGaAs (indium gallium arsenide), GaAsSb (gallium). It is composed of at least one of antimony arsenide), InGaAsP (indium gallium arsenide phosphide), InAs (indium arsenide), InSb (indium antimonide), and the above-mentioned material grown at a low temperature.

  The electrode layers 113 and 114 are a pair of electrode layers to which the above-described bias voltage is applied. Further, the electrode layers 113 and 114 are a pair of electrode layers through which current signals corresponding to carriers generated due to irradiation of the photoconductive layer 112 with the pump light LB1 flow. However, when the electrode layers 113 and 114 constitute the terahertz wave detecting element 130, the electrode layers 113 and 114 are current signals corresponding to carriers generated due to irradiation of the photoconductive layer 112 with the probe light LB2. And a pair of electrode layers through which current signals corresponding to the light intensity of the terahertz wave THz applied to the terahertz wave detection element 130 flow. At least one of the electrode layers 113 and 114 includes a transparent electrode material (for example, at least one of ITO, IZO, AZO, GZO, and IGZO) and a metal material (for example, Au, AuCr, AuGeNi, and AuSn). At least one).

  The electrode layer 113 includes a first electrode unit 113-1, a second electrode unit 113-2, and a third electrode unit 113-3 which are physically integrated or electrically connected. The first electrode unit 113-1 extends along the Y-axis direction. The second electrode unit 113-2 extends from the part of the first electrode unit 113-1 toward the electrode layer 114 (that is, in the −X-axis direction). The third electrode portion 113-3 is in contact with the −X-axis side surface of the second electrode portion 113-2 and extends from the substrate 111 in the + Z-axis direction (that is, along the stacking direction). The shape (shape on the XY plane) of the electrode layer 113 is the letter "T".

  The second electrode unit 113-2 can function as an antenna. For example, the second electrode unit 113-2 can function as a so-called dipole antenna. The first electrode unit 113-1 can function as an antenna, and can also function as a transmission line into which a current signal flows via the second electrode unit 113-2 that can function as an antenna. For example, the first electrode unit 113-1 can function as a so-called parallel transmission line. The third electrode portion 113-3 can function as an antenna and can function as an electrode for extracting a current signal (that is, a carrier generated by the excitation of the pump light LB1) from the photoconductive layer 112. However, the first electrode portion 113-1, the second electrode portion 113-2, and the third electrode portion 113-3 may function as an antenna of another shape (for example, a so-called bow-tie antenna).

  The electrode layer 114 includes a first electrode unit 114-1, a second electrode unit 114-2, and a third electrode unit 114-3 which are physically integrated or electrically connected. The first electrode unit 114-1 extends along the Y-axis direction. The second electrode portion 114-2 extends from the part of the first electrode portion 114-1 toward the electrode layer 113 (that is, in the + X axis direction). The third electrode portion 114-3 is in contact with the side surface on the + X-axis side of the second electrode portion 114-2 and extends from the substrate 111 toward the + Z-axis direction (that is, along the stacking direction). The shape (shape on the XY plane) of the electrode layer 114 is the letter "T".

  The second electrode unit 114-2 can function as an antenna. For example, the second electrode unit 114-2 can function as a so-called dipole antenna. The first electrode unit 114-1 can function as an antenna and can also function as a transmission line into which a current signal flows via the second electrode unit 114-2 that can function as an antenna. For example, the first electrode unit 114-1 can function as a so-called parallel transmission line. The third electrode portion 114-3 can function as an antenna and can function as an electrode for extracting a current signal (that is, carriers generated by the excitation of the pump light LB1) from the photoconductive layer 112. However, the first electrode portion 114-1, the second electrode portion 114-2, and the third electrode portion 114-3 may function as an antenna of another shape (for example, a so-called bow-tie antenna).

  A gap portion 115 where the electrode layers 113 and 114 are not formed is secured between the third electrode portion 113-3 and the third electrode portion 114-3. The photoconductive layer 112 is formed in the gap 115. Therefore, each of the third electrode portions 113-3 and 114-3 sandwiches the photoconductive layer 112 along the X-axis direction which is a specific example of the "predetermined direction". The −X-axis side surface 113-3a of the third electrode portion 113-3 contacts the + X-axis side surface 112c of the photoconductive layer 112. The side surface 114-3a on the + X axis side of the third electrode portion 114-3 contacts the side surface 112d on the −X axis side of the photoconductive layer 112. Each of the side surface 113-3a and the side surface 114-3a is a specific example of a “contact surface”.

  In the example shown in FIG. 2, the width of the photoconductive layer 112 along the Y-axis direction is equal to the width of the second electrode units 113-2 and 114-2 and the third electrode units 113-3 and 114-3 in the Y-axis direction. Greater than the width along. That is, the photoconductive layer 112 protrudes along the Y-axis direction when viewed from the second electrode units 113-2 and 114-2 and the third electrode units 113-3 and 114-3. Even in this case, the portion of the photoconductive layer 112 protruding along the Y-axis direction is apart from the area irradiated with the pump light LB1 indicated by the dotted circle in FIG. Therefore, the portion of the photoconductive layer 112 protruding along the Y-axis direction does not adversely affect the operation of the terahertz wave generating element 110. However, the width of the photoconductive layer 112 along the Y-axis direction is equal to the width of each of the second electrode units 113-2 and 114-2 and the third electrode units 113-3 and 114-3 along the Y-axis direction. They may be the same.

  The surface 112a on the + Z-axis side of the photoconductive layer 112 is irradiated with pump light LB1. Specifically, the pump light LB1 emitted from the beam splitter 161 is directed toward the surface 112a (toward the −Z-axis direction, which is one specific example of the “incident direction” in the example shown in FIG. 2B). ) Propagate in space. The pump light LB1 that has reached the surface 112a passes through the inside of the photoconductive layer 112 in the −Z-axis direction. The pump light LB1 is applied to the photoconductive layer 112 such that the beam diameter of the pump light LB1 is minimized (that is, condensed) at the focal position inside the photoconductive layer 112. That is, the pump light LB1 propagates while reducing the beam diameter toward the focal position inside the photoconductive layer 112, and propagates while increasing the beam diameter after reaching the focal position. The “beam diameter of the pump light LB1” here means a diameter of a cross section of the optical path of the pump light LB1 parallel to the XY plane.

  In this embodiment, the electrode layers 113 and 114 have a shape according to the propagation mode of the pump light LB1 inside the photoconductive layer 112. Specifically, the third electrode portions 113-3 and 114-3 have a shape according to the propagation mode of the pump light LB1 inside the photoconductive layer 112.

  Hereinafter, the shape of the third electrode portions 113-3 and 114-3 will be further described with reference to FIG. FIG. 3 is an enlarged cross-sectional view of the section near the third electrode portions 113-3 and 114-3 and the photoconductive layer 112 in the II-II ′ cross section of the terahertz wave generating element 110-1 shown in FIG. It is.

  As shown in FIG. 3, an interval between the third electrode unit 113-3 and the third electrode unit 114-3 (that is, an interval along the X-axis direction, hereinafter, referred to as “electrode interval”) is , At a predetermined position determined according to the propagation mode of the pump light LB1 inside the photoconductive layer 112. The electrode interval substantially corresponds to the interval between the side surface 113-3a and the side surface 114-3a along the X-axis direction. In other words, the position on the virtual straight line along the Z-axis direction which is the incident direction of the pump light LB1 has the minimum electrode interval at the predetermined position. In other words, the distribution of the electrode intervals along the Z-axis direction (that is, the direction of incidence of the terahertz wave THz) is such that the electrode interval is minimized at a predetermined position. In other words, it is along the Z-axis direction which is the XZ plane (that is, the incident direction of the pump light LB1 (in other words, the propagation direction of the pump light LB1 in the photoconductive layer 112), and the electrode layers 113 and 114 In a cross section of the terahertz wave generating element 110 along a plane along the X-axis direction that sandwiches the conductive layer), the electrode interval becomes minimum at a predetermined position. For this reason, in the cross section of the terahertz wave generating element 110 along the XZ plane, the electrode interval at a predetermined position is smaller than the electrode interval at another position shifted from the predetermined position in the Z-axis direction.

  The predetermined position where the electrode interval is minimum is a position different from the end position where the front surface 112a and the back surface 112b are located in the region between the front surface 112a and the back surface 112b. In other words, the predetermined position is a position different from the end position among positions on a virtual straight line along the Z-axis direction.

  More specifically, the predetermined position coincides with the focal position where the beam diameter (that is, the diameter in the X-axis direction) of the pump light LB1 transmitted through the photoconductive layer 112 is minimized. However, the state where the "predetermined position coincides with the focal position" here is not only a state where the predetermined position exactly coincides with the focal length, but also a state where the predetermined position substantially coincides with the focal length. This includes a state where there is a deviation between the predetermined position and the focal position as much as possible (that is, there is a deviation along the Z-axis direction).

  In the example shown in FIG. 3, the electrode interval changes as follows along the Z-axis direction. First, in a region between the surface 112a and the focal position (that is, a predetermined position, the same applies hereinafter), the electrode interval changes so that the electrode interval at a position closer to the focal position becomes smaller. That is, the electrode interval at a certain position in the region between the surface 112a and the focal position continuously decreases as the certain position moves toward the −Z-axis direction. On the other hand, in the region between the back surface 112b and the focal position, the electrode interval changes so as to become smaller as the electrode interval at a position closer to the focal position becomes shorter. That is, the electrode spacing at a certain position in the region between the back surface 112b and the focal position continuously increases as the certain position moves toward the −Z-axis direction. That is, the changing tendency of the electrode interval along the Z-axis direction is the same as the changing tendency of the beam diameter along the Z-axis direction. Therefore, each of the third electrode portions 113-3 and 114-3 is substantially distributed along the outer edge of the optical path of the pump light LB1 (particularly, the outer edge of a cross section having an optical path along the XZ plane). It can be said that it has a shape.

  However, the electrode spacing may be changed in a manner different from the manner shown in FIG. That is, the electrode spacing may be changed in any way as long as it becomes minimum at the predetermined position. For example, the electrode spacing at a certain position in the region between the surface 112a and the predetermined position may decrease stepwise as the certain position moves toward the -Z axis direction. For example, the electrode spacing at a certain position in the region between the back surface 112b and the predetermined position may increase stepwise as the certain position moves in the −Z-axis direction.

  Each of the third electrode units 113-3 and 114-3 is located outside the optical path of the pump light LB1. That is, each of the side surfaces 113-3a and 114-3a is not located inside the optical path of the pump light LB1. Accordingly, the propagation of the pump light LB1 in the photoconductive layer 112 is not hindered by the third electrode portions 113-3 and 114-3.

  The terahertz wave generating element 110-1 having the configuration described above is manufactured as follows. First, the substrate 111 is loaded into an MBE (Molecular Beam Epitaxy) apparatus. Thereafter, a buffer layer having a thickness of about 0.1 to 0.8 microns is formed on the substrate 111. For example, when a buffer layer composed of GaAs is formed, the temperature of the substrate 111 of the buffer layer is approximately 500 to 600 degrees, and the ratio of the intensity of the As molecular beam to the intensity of the Ga molecular beam (hereinafter referred to as “the intensity”) , "GaAs supply ratio") is about 5 to about 30 and a film formation rate of 1 micron per hour can be obtained.

  Thereafter, the photoconductive layer 112 having a thickness of about 1 micron to 4 microns is uniformly formed on the substrate 111 on which the buffer layer is formed by using a known film forming method or the like. For example, when the photoconductive layer 112 made of InGaAs is formed, the photoconductive layer 112 is formed in an environment where the temperature of the substrate 111 is approximately 500 ° C. or less and a deposition rate of 1 micron per hour can be obtained. May be formed. For example, when the photoconductive layer 112 made of GaAs is formed, the photoconductive layer 112 is used when the temperature of the substrate 111 is approximately 400 degrees or less and the GaAs supply ratio is formed when the buffer layer is formed. It may be formed in an environment in which the GaAs supply ratio is equal to or higher than that and the film formation rate is 1 micron per hour.

  After that, the photoconductive layer 112 may be subjected to a thermal annealing process. For example, when the photoconductive layer 112 is made of GaAs, the photoconductive layer 112 is subjected to thermal annealing for about 5 to 10 minutes in an environment where the temperature of the substrate 111 is about 600 degrees. Is also good.

  Thereafter, the substrate 111 on which the photoconductive layer 112 is formed is taken out from the MBE apparatus, and is uniformly formed on the substrate 111 by using a known patterning method (for example, a patterning method combining lithography and etching techniques). The photoconductive layer 112 is patterned. As a result, the photoconductive layer 112 having the shape shown in FIG. However, the photoconductive layer 112 formed uniformly on the substrate 111 may be patterned using a machining method instead of the lithography technique and the etching technique.

  Thereafter, the above-described electrode layers 113 and 114 are formed on the substrate by a known film formation method (for example, a sputtering method, a vacuum evaporation method, a metal growth method, a spray method, or the like) or a known patterning method. Is done. Thereafter, dicing is performed. As a result, the manufacture of the terahertz wave generation element 110-1 is completed.

  According to the terahertz wave generating element 110-1 having the above-described configuration, the electrode spacing does not become minimum at a predetermined position different from the end position where the front surface 112a and the back surface 112b of the photoconductive layer 112 are located. Compared with the terahertz wave generating element, the generation efficiency of the terahertz wave THz by the terahertz wave generating element 110-1 is improved. Specifically, the signal level of the signal component of the terahertz wave THz emitted from the terahertz wave generating element 110-1 is higher than that of the terahertz wave generating element of the comparative example. As a result, the S / N ratio of the terahertz wave generating element 110-1 is improved as compared with the terahertz wave generating element of the comparative example. That is, the generation efficiency of the terahertz wave THz is improved.

  Here, the present inventors simulated the generation efficiency of the terahertz wave THz in the terahertz wave generating element of the four comparative examples and the terahertz wave generating element 110-1 of the present example shown in FIG. Note that the terahertz wave generating element of the first comparative example is a terahertz wave generating element in which the electrode spacing is constant and the beam diameter of the pump light LB1 is minimized inside the photoconductive layer 112. The terahertz wave generating element of the second comparative example is a terahertz wave generating element in which the distance between the electrodes is constant and the beam diameter of the pump light LB1 on the surface 112a of the photoconductive layer 112 is minimized. The terahertz wave generating element of the third comparative example is such that the beam diameter of the pump light LB1 is minimized on the front surface 112a of the photoconductive layer 112 and the electrode interval gradually increases along the direction from the front surface 112a to the back surface 112b. It is. In the terahertz wave generating element of the fourth comparative example, the terahertz wave generation in which the beam diameter of the pump light LB1 is minimized on the back surface 112b of the photoconductive layer 112 and the electrode interval gradually narrows in the direction from the front surface 112a to the back surface 112b. Element.

  As a result of the simulation, the inventors of the present application have found that the generation efficiency of the terahertz wave THz of the terahertz wave generation element 110-1 of this embodiment is higher than that of any of the terahertz wave generation elements of the first to fourth comparative examples. Was also good. Specifically, the present inventors assume that the signal intensity (that is, the current value) of the current signal generated by irradiating the pump light LB1 with a certain intensity to the terahertz wave generation element 110-1 of this embodiment is 1. The result was that the signal intensity of the current signal generated by irradiating the pump light LB1 of the same intensity to the terahertz wave generating element of the first comparative example was 0.83. The inventors of the present application obtained the result that the signal intensity of the current signal generated by irradiating the pump light LB1 of the same intensity to the terahertz wave generating element of the second comparative example or the third comparative example was 0.94. The inventors of the present application obtained a result that the signal intensity of a current signal generated by irradiating the pump light LB1 of the same intensity to the terahertz wave generation element of the fourth comparative example was 0.77. As the signal strength of the current signal increases, the signal strength of the generated terahertz wave THz also increases. Therefore, the result of the simulation indicates that the generation efficiency of the terahertz wave THz of the terahertz wave generation element 110-1 of this embodiment is good.

  Here, the signal intensity of the current signal increases as the number of carriers generated by the optical excitation of the pump light LB1 increases. The number of carriers generated by photoexcitation increases as the integrated value of the amount of energy given by the pump light LB1 to each part of the photoconductive layer 112 increases. The amount of energy given by the pump light LB1 to each part of the photoconductive layer 112 increases as the intensity of the pump light LB1 at the time when the light reaches the respective parts of the photoconductive layer 112 increases.

  Further, the signal strength of the current signal increases as the moving speed of the carrier increases. The moving speed of the carrier increases as the intensity of the electric field applied to the photoconductive layer 112 increases. The intensity of the electric field applied to the photoconductive layer 112 increases as the distance between the electrodes decreases.

  Therefore, in order to improve the generation efficiency of the terahertz wave THz, the first characteristic that the intensity of the pump light LB1 at the time of reaching each part of the photoconductive layer 112 becomes as large as possible, and the electrode interval becomes as small as possible. What is necessary is just to satisfy the second characteristic. Based on the results of the simulation, it can be said that the terahertz wave generating element 110-1 of the present embodiment satisfies the first characteristic and the second characteristic in a better balance than the terahertz wave generating elements of each comparative example. . Specifically, the first and second characteristics are such that a terahertz wave generating element 110-1 has a minimum electrode interval at a predetermined position different from an end position where the front surface 112a and the back surface 112b of the photoconductive layer 112 are located. The characteristics are well-balanced. Further, in the first characteristic and the second characteristic, the changing tendency of the electrode interval along the Z-axis direction is the same as the changing tendency of the beam diameter along the Z-axis direction (that is, the third electrode unit 113-3). , And 114-3 have a shape distributed along the outer edge of the optical path of the pump light LB1).

  Although the terahertz wave detecting element 110 has been described above as an example, the terahertz wave detecting element 130 also has an electrode spacing at a predetermined position different from an end position where the front surface 112a and the back surface 112b of the photoconductive layer 112 are located. The detection efficiency of the terahertz wave THz by the terahertz wave detecting element 130 is improved as compared with the terahertz wave detecting element which is not minimized. Specifically, the signal intensity of the terahertz wave THz detected by the terahertz wave detecting element 130 is larger than that of the terahertz wave detecting element of the comparative example. As a result, the S / N ratio of the terahertz wave detection element 130 is improved as compared with the terahertz wave detection element of the comparative example.

(2-2) Configuration of Terahertz Wave Generation Element 110-2 of Second Embodiment Next, referring to FIGS. 5A to 5C, the terahertz wave generation element 110 of the second embodiment (hereinafter referred to as “Terahertz wave generation element 110”) , For convenience, referred to as “Terahertz wave generating element 110-2”). FIG. 5A is a top view illustrating the top surface of the terahertz wave generation element 110-2 according to the second embodiment. FIG. 5B is a cross-sectional view illustrating a V (1) -V (1) ′ cross section of the terahertz wave generating element 110-2 illustrated in FIG. 5A. FIG. 5C is a cross-sectional view illustrating a V (2) -V (2) ′ cross section of the terahertz wave generation element 110-2 illustrated in FIG. 5A.

  As shown in FIGS. 5A to 5C, the terahertz wave generator 110-2 of the second embodiment has a photoconductive layer compared to the terahertz wave generator 110-1 of the first embodiment. The third embodiment is different in that the shapes of the second electrode 112 and the third electrode units 113-3 and 114-3 are different. The other components of the terahertz wave generator 110-2 of the second embodiment may be the same as the other components of the terahertz wave generator 110-1 of the first embodiment.

  Specifically, the shape of the photoconductive layer 112 on the XY plane (that is, the plane intersecting the incident direction of the pump light LB1) is elliptical (or circular). The reason why the shape of the photoconductive layer 112 is set to be elliptical is that the beam shape of the pump light LB1 on the XY plane is circular.

  As the shape of the photoconductive layer 112 becomes elliptical, the shape of each of the third electrode layers 113 and 114 on the XY plane becomes an arc shape concave toward the photoconductive layer 112. Therefore, the electrode interval at a certain position in the region between the front surface 112a and the back surface 112b is such that the closer the certain position is to a predetermined position (focal position) along the Z-axis direction, and the more the certain position is in the Y-axis direction. The distance becomes smaller as the distance from the center of the photoconductive layer 112 increases. For example, as shown in FIGS. 5B and 5C, the electrode spacing d2 at a predetermined position in a cross section along the XZ plane relatively far from the center of the photoconductive layer 112 (FIG. 5C) (See FIG. 5B) is smaller than the electrode spacing d1 at a predetermined position in a cross section along the XZ plane relatively close to the center of the photoconductive layer 112.

  As a result, the distance between the electrodes is smaller than when the shape of the photoconductive layer 112 on the XY plane is rectangular (rectangular or square). Therefore, the generation efficiency of the terahertz wave THz is further improved.

(2-3) Configuration of Terahertz Wave Generator 110-3 of Third Embodiment Next, referring to FIGS. 6A to 6B, the terahertz wave generator 110 of the third embodiment (hereinafter referred to as “Terahertz wave generator 110”) will be described. The configuration of the “Terahertz wave generating element 110-3” will be described. FIG. 6A is a top view illustrating the top surface of the terahertz wave generation element 110-3 according to the third embodiment. FIG. 6B is a cross-sectional view illustrating a VI-VI ′ cross section of the terahertz wave generation element 110-3 illustrated in FIG.

  As shown in FIGS. 6A and 6B, the terahertz wave generating element 110-3 of the third embodiment has a photoconductive layer compared to the terahertz wave generating element 110-1 of the first embodiment. The third embodiment is different in that the shapes of the second electrode 112 and the third electrode units 113-3 and 114-3 are different. The other components of the terahertz wave generator 110-3 of the third embodiment may be the same as the other components of the terahertz wave generator 110-1 of the first embodiment.

  Specifically, in the first embodiment described above, since the third electrode portion 113-3 has a shape distributed along the outer edge of the optical path of the pump light LB1, the third electrode portion 113-3 has a certain cross section along the XZ plane. In FIG. 2, the third electrode portion 113-3 as a whole protrudes in a convex shape toward the third electrode portion 114-3 (see FIG. 2B). On the other hand, in the third embodiment, as shown in FIG. 6B, in a certain cross section along the XZ plane, the first portion 113-31 which is a part of the third electrode portion 113-3 is formed. , And protrudes toward the third electrode portion 114-3 (for example, protrudes in a convex shape, the same applies hereinafter). In a cross section along the XZ plane, the second portion 113-32, which is another part of the third electrode portion 113-3, does not protrude toward the third electrode portion 114-3. In other words, in a cross section along the XZ plane, the first side surface portion 113-31a, which is a part of the side surface 113-3a, protrudes toward the side surface 114-3a. In a cross section along the XZ plane, the second side surface portion 113-32a, which is another part of the side surface 113-3a, does not project toward the side surface 114-3a.

  Further, in the above-described first embodiment, since the third electrode portion 114-3 has a shape distributed along the outer edge of the optical path of the pump light LB1, the third electrode portion 114-3 has a shape in a cross section along the XZ plane. The three electrode portions 114-3 as a whole protrude toward the third electrode portion 113-3 in a convex shape (see FIG. 2B). On the other hand, in the third embodiment, as shown in FIG. 6B, in a certain cross section along the XZ plane, the first portion 114-31 which is a part of the third electrode portion 114-3 is formed. , And protrudes toward the third electrode portion 113-3. In a cross section along the XZ plane, the second portion 114-32, which is another part of the third electrode portion 114-3, does not protrude toward the third electrode portion 113-3. In other words, in a cross section along the XZ plane, the first side surface portion 114-31a, which is a part of the side surface 114-3a, protrudes toward the side surface 113-3a. In a cross section along the XZ plane, the second side surface portion 114-32a, which is another part of the side surface 114-3a, does not project toward the side surface 113-3a.

  As a result, in a certain cross section along the XZ plane, the entirety of the third electrode portion 113-3 protrudes toward the third electrode portion 114-3 and the entirety of the third electrode portion 114-3 becomes the third electrode portion. As compared with the terahertz wave generating element that protrudes toward the portion 113-3, the electrode interval is not reduced more than necessary. Therefore, the parasitic capacitance between the third electrode unit 113-3 and the third electrode unit 114-3 becomes relatively small.

(2-4) Configuration of Terahertz Wave Generator 110-3 of Fourth Embodiment Next, referring to FIGS. 7A to 7C, the terahertz wave generator 110 of the fourth embodiment (hereinafter referred to as “Terahertz wave generator 110”) will be described. , For convenience, referred to as “Terahertz wave generating element 110-4”). FIG. 7A is a cross-sectional view illustrating a cross section along the XY plane of the terahertz wave generation element 110-4 of the fourth embodiment. FIG. 7B is a cross-sectional view illustrating a cross section (corresponding to a VII (1) -VII (1) ′ cross section in FIG. 7A) of the terahertz wave generating element 110-4 of the fourth embodiment. FIG. 7C is a cross-sectional view illustrating a cross section (corresponding to the VII (2) -VII (2) ′ cross section in FIG. 7A) of the terahertz wave generating element 110-4 of the fourth embodiment.

  As shown in FIGS. 7A to 7C, the terahertz wave generating element 110-4 of the fourth embodiment is different from the terahertz wave generating element 110-1 of the first embodiment in the photoconductive layer. The third embodiment is different in that the shapes of the second electrode 112 and the third electrode units 113-3 and 114-3 are different. The other components of the terahertz wave generator 110-4 of the fourth embodiment may be the same as the other components of the terahertz wave generator 110-1 of the first embodiment.

  Specifically, in the fourth embodiment, as shown in FIG. 7A, in a certain cross section along the XY plane, the third electrode portions 113-3 and 114-3 extend along the X-axis direction. The interval between the pair of third portions 113-33 and 114-33 that sandwiches the pump light LB1 is a pair of third electrodes 113-3 and 114-3 that do not sandwich the pump light LB1 along the X-axis direction. It is smaller than the interval between the fourth portions 113-34 and 114-34. Alternatively, in a cross section along the XY plane, a pair of third portions 113-33 and 114 sandwiching the pump light LB1 having a predetermined intensity or more along the X-axis direction among the third electrode portions 113-3 and 114-3. The interval between −33 is the distance between the pair of fourth portions 113-34 and 114-34 of the third electrode portions 113-3 and 114-3 that do not sandwich the pump light LB1 having a predetermined intensity or more along the X-axis direction. Smaller than the spacing between them. For example, FIG. 7B shows a pair of third portions 113-3 sandwiching the pump light LB1 along the X-axis direction among the third electrode portions 113-3 and 114-3 in a cross section along the XY plane. It shows that the interval at a predetermined position between 33 and 114-33 is d3. For example, FIG. 7B illustrates a pair of fourth portions 113 of the third electrode portions 113-3 and 114-3 that do not sandwich the pump light LB1 along the X-axis direction in a cross section along the XY plane. The distance at a predetermined position between −34 and 114-34 is d4 (where d4> d3).

  As a result, in a region where the third electrode portions 113-3 and 114-3 do not sandwich the pump light LB1 (that is, a region where carriers are not generated or hardly generated), the electrode interval is not reduced more than necessary. Therefore, the parasitic capacitance between the third electrode unit 113-3 and the third electrode unit 114-3 becomes relatively small.

  In the above description, the description has been made using the terahertz wave generating element 110 and the terahertz wave detecting element 130. However, any electromagnetic wave generation element that generates (in other words, emits) any electromagnetic wave different from the terahertz wave may have a structure similar to that of the above-described terahertz wave generation element 110. Any electromagnetic wave detection element that detects any electromagnetic wave different from the terahertz wave may have the same structure as the above-described terahertz wave detection element 130. Even in this case, each of the arbitrary electromagnetic wave generation element and the arbitrary electromagnetic wave detection element preferably enjoys the same effect as the above-mentioned effect that the terahertz wave generation element 110 or the terahertz wave detection element 130 can enjoy. Can be.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit or spirit of the invention which can be read from the claims and the entire specification, and a photoconductive element with such a change And a measuring device are also included in the technical scope of the present invention.

REFERENCE SIGNS LIST 10 sample 100 terahertz wave measuring apparatus 101 pulse laser apparatus 110 terahertz wave generating element 111 substrate 112 photoconductive layer 113, 114 electrode layer 115 gap section 120 optical delay mechanism 130 terahertz wave detecting element 150 control section 151 lock-in detecting section 152 signal processing Section LB1 Pump light LB2 Probe light THz Terahertz wave

Claims (1)

A photoconductive layer on which excitation light is incident on the surface, and a pair of electrodes sandwiching the photoconductive layer along a predetermined direction intersecting the incident direction of the excitation light,
The shape of the pair of electrodes on a plane intersecting the incident direction is an arc shape distributed along an outer edge of an optical path of the excitation light transmitted through the photoconductive layer. element.

Images