JP6616160B2 - Photoconductive element and measuring device - Google Patents

Description

  The present invention relates to a technical field of a photoconductive element capable of emitting or detecting an electromagnetic wave such as a terahertz wave and a measuring apparatus including such a photoconductive element.

  A terahertz wave measuring device is known as a measuring device for measuring the characteristics of a sample. The terahertz wave measuring apparatus measures the characteristics of the sample in the following procedure. First, pump light (in other words, excitation light), which is one laser light obtained by branching ultrashort pulse laser light (for example, femtosecond pulse laser light), generates terahertz waves to which a bias voltage is applied. The element is irradiated. As a result, the terahertz wave generating element emits terahertz waves. The terahertz wave emitted from the terahertz wave generating element is irradiated to the sample. The terahertz wave irradiated 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 gives an optical delay (that is, an optical path length difference) to the pump beam. The terahertz wave detecting element irradiated with the probe light (in other words, excitation light) irradiated 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 generating element and a terahertz detecting element, a substrate, a pair of electrode layers formed on the substrate so as to form an antenna separated by a gap, and a photoconductive layer formed in the gap There exists a photoconductive element provided with (for example, refer patent document 1).

JP 2005-26347 A

  In the photoconductive element 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). Has been. Furthermore, the side surface of the photoconductive layer is electrically connected to the side surfaces of the pair of electrode portions.

  Here, in the photoconductive element described in Patent Document 1, the distance between the 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 the photoconductive property. It is always constant regardless of the position along the height direction of the layer (that is, the incident direction or the propagation direction of the excitation light). On the other hand, the beam diameter of the excitation light irradiated on the photoconductive layer (that is, the width of the optical path of the excitation light along the predetermined direction intersecting the incident direction or the propagation direction of the excitation light) is high in the photoconductive layer. It fluctuates according to the position along the vertical direction. For this reason, the shape of the pair of electrode portions is selected in consideration of fluctuations in the beam diameter of the excitation light (for example, the interval between the pair of electrode portions is set to an appropriate interval), thereby improving the performance of the photoconductive element. It is estimated that there is room for improving (for example, improving the S / N ratio).

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

  Examples of problems to be solved by the present invention include the above. It is an object of the present invention to provide a photoconductive element in which a distance between a pair of electrodes sandwiching a photoconductive layer is appropriately set, and a measuring apparatus including such a photoconductive element.

  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 intersecting the incident direction of the excitation light. The distance between the pair of electrodes along the predetermined direction is such that the front surface and the back surface are located in a region between the front surface and the back surface of the photoconductive layer facing the front surface along the incident direction. It is minimized at a predetermined position different from the end position.

  A first example of the measuring apparatus according to the present invention includes: an emission unit that emits an electromagnetic wave to a sample; and a detection unit that detects the electromagnetic wave irradiated to the sample. At least one of the irradiation unit and the detection unit One includes the first example of the photoconductive element of the present invention described above.

FIG. 1 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus according to the present embodiment. 2A is a top view showing the top surface of the terahertz wave generating element of the first embodiment, and FIG. 2B is a cross-sectional view taken along the line II-II ′ of the terahertz wave generating element shown in FIG. It is sectional drawing shown. FIG. 3 is an enlarged cross-sectional view of the cross section near the third electrode portion and the photoconductive layer in the II-II ′ cross section of the terahertz wave generating element shown in FIG. FIG. 4 is a cross-sectional view showing four terahertz wave generating elements of comparative examples together with the terahertz wave generating element of this example. FIG. 5A is a top view showing the top surface of the terahertz wave generating element of the second embodiment, and FIG. 5B is a diagram showing V (1) −V of the terahertz wave generating element shown in FIG. (1) It is sectional drawing which shows a cross section, FIG.5 (c) is sectional drawing which shows the V (2) -V (2) 'cross section of the terahertz wave generation element shown to Fig.5 (a). 6A is a top view showing 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 shown in FIG. It is sectional drawing shown. FIG. 7A is a top view showing 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). VII (1) -VII (1) ′ section) of FIG. 7 (c) is a sectional view of the terahertz wave generating element of the fourth embodiment (VII (2) in FIG. 7 (a)). It is sectional drawing which shows -VII (2) 'cross section).

  Hereinafter, description will be made on embodiments of the photoconductive element and the measurement device.

(First Embodiment of Photoconductive Element)
<1>
The photoconductive element of the present embodiment includes a photoconductive layer on which excitation light is incident on the surface, and a pair of electrodes that sandwich the photoconductive layer along a predetermined direction intersecting the incident direction of the excitation light, the predetermined direction The distance between the pair of electrodes along the surface is an end position where the front surface and the back surface are located in a 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 this embodiment, the distance between the pair of electrodes that sandwich the photoconductive layer is set appropriately. As a result, the performance of the photoconductive element (for example, generation efficiency or detection efficiency of electromagnetic waves such as terahertz waves) is improved.

<2>
In another aspect of the photoconductive element of the present embodiment, the predetermined position is a position where the beam diameter along the predetermined direction of the excitation light transmitted through the photoconductive layer 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 minimum as described above, the change tendency of the distance between the pair of electrodes along the incident direction is the incidence 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 of the present embodiment, each of the pair of electrodes includes a contact surface in contact with the photoconductive layer, and an interval between the pair of electrodes along the predetermined direction is the predetermined direction. The distance between the pair of contact surfaces along.

  According to this aspect, the distance between the pair of contact surfaces corresponding to the distance between the pair of electrodes that sandwich the photoconductive layer is appropriately set.

<5>
As described above, in another aspect of the photoconductive element in which each of the pair of electrodes includes a contact surface, the contact surface has a shape distributed along the outer edge of the optical path of the excitation light that passes through the photoconductive layer. 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 the plane intersecting the incident direction is along the outer edge of the optical path of the excitation light that passes through the photoconductive layer. The arc shape is distributed.

  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 element of the present embodiment, one of the pair of electrodes is at least partially part of the pair so that the distance between the pair of electrodes along the predetermined direction at the predetermined position is minimized. Protrudes toward the other electrode.

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

<8>
In another aspect of the photoconductive element of the present embodiment, a pair of first portions sandwiching 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 along the predetermined direction. The interval along the predetermined direction of the pair of electrodes is greater than the interval along the predetermined direction of the pair of second portions not sandwiching the optical path of the excitation light having the predetermined intensity or more between the pair of electrodes along the predetermined direction. small.

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

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

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

(Embodiment of measuring device)
<10>
The measurement apparatus according to the present embodiment includes an irradiating unit that irradiates a sample with an electromagnetic wave, and a detecting unit that detects the electromagnetic wave irradiated to the sample. At least one of the irradiation and emitting unit and the detecting unit is described above. The photoconductive element of the present embodiment (including various aspects thereof) is included.

  According to the measurement apparatus of the present embodiment, it is possible to suitably enjoy the same effects as those that can be enjoyed by the above-described photoconductive element of the present embodiment.

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

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

  The operation and other gains of the photoconductive element and measurement apparatus of the present embodiment will be described in more detail in the following examples.

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

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

(1) Configuration of Terahertz Wave Measuring Device 100 First, the configuration of the terahertz wave measuring device 100 of the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a 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 sample 10 or reflects the terahertz wave THz reflected by the sample 10 (that is, the terahertz wave irradiated on the sample 10). THz) is detected. 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 (that is, a terahertz region) around 1 terahertz (1 THz = 10 ¹² Hz). The terahertz region is a frequency region that combines light straightness and electromagnetic wave transparency. 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 irradiated on the sample 10.

  Here, since the period of the terahertz wave THz is a period of 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 a pump-probe method based on time delay scanning. Hereinafter, the terahertz wave measuring apparatus 100 that employs such a 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 “irradiation 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 detecting element 130 which is a specific example of “detecting means”, a bias voltage generating unit 141, an IV (current-voltage) converting unit 142, And a control unit 150.

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

  The beam splitter 161 branches the pulsed laser light LB into pump light LB1 and probe light LB2, which are specific examples of “excitation light”. The pump light LB1 is incident on the terahertz wave generating element 110 through a light guide path (not shown). On the other hand, the probe light LB2 enters the optical delay mechanism 120 via a light guide path and a reflecting mirror 162 (not shown). 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 bias voltage generation unit is provided in the gap 115 (see FIG. 2 and the like) included in the terahertz wave generation element 110 via the electrode layers 113 and 114 (see FIG. 2 and the like) included in the terahertz wave generation element 110. The bias voltage generated by 141 is applied. When pump light LB1 is irradiated to gap portion 115 while an effective bias voltage (for example, a bias voltage other than 0V) is applied to gap portion 115, photoconductive layer 112 (see FIG. 2)) is 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-shaped current signal in the order of subpicoseconds or in the order of femtoseconds corresponding to the generated carrier. The generated current signal flows through the electrode layers 113 and 114. As a result, the terahertz wave generating element 110 emits the terahertz wave THz resulting from the pulsed current signal.

  The terahertz wave THz emitted from the terahertz wave generating element 110 is transmitted through the half mirror 164. As a result, the terahertz wave THz transmitted through the half mirror 164 is applied to the sample 10. The terahertz wave THz irradiated on 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 the terahertz wave THz incident on the terahertz wave detection element 130. Specifically, when the probe light LB2 is irradiated to the gap portion 115 (see FIG. 2 and the like) included in the terahertz wave detection element 130, 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 detecting element 130 is irradiated with the terahertz wave detecting element 130 with the probe light LB2 being irradiated on the gap portion 115, the signal intensity of the current signal flowing through the electrode layers 113 and 114 becomes the light intensity of the terahertz wave THz. Will change accordingly. A current signal whose signal intensity varies 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 (that is, the optical path length difference) between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. 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 generation element 110 (or the timing at which the terahertz wave generation element 110 emits the terahertz wave THz) and the probe light LB2 at the terahertz wave detection element 130 The time difference from the timing at which the light enters (or the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz) is adjusted. 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 millimeters (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 1 picosecond. Become. In this case, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is delayed by 1 picosecond. Considering that the terahertz wave THz having the same waveform repeatedly enters the terahertz wave detecting element 130 at intervals of about several tens of MHz, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is gradually shifted. Thus, 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). In order to measure the characteristics of the sample 10, the control unit 150 includes a lock-in detection unit 151 and a signal processing unit 152.

  The lock-in detection unit 151 performs synchronous detection on the voltage signal output from the IV conversion unit 142 using the bias voltage generated by the bias voltage generation unit 141 as a reference signal. As a result, the lock-in detection unit 151 detects a sample value of the terahertz wave THz. Thereafter, the same 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). The waveform (time waveform) of the terahertz wave THz 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 the 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. Note that the configuration of the terahertz wave generating element 110 is the same as that of the terahertz wave detecting element 130. Accordingly, the configuration of the terahertz wave generating element 110 will be described below. However, the following description can be similarly applied to the terahertz wave detection element 130. Furthermore, 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 the terahertz wave generating element 110-1 of the first embodiment First, referring to FIGS. 2A and 2B, the terahertz wave generating element 110 of the first embodiment (hereinafter, For the sake of convenience, the configuration of “terahertz wave generating element 110-1”) will be described. FIG. 2A is a top view showing the top surface of the terahertz wave generating element 110-1 of the first embodiment. FIG. 2B is a cross-sectional view showing a II-II ′ cross section of the terahertz wave generating element 110-1 shown in FIG.

  As shown in FIGS. 2A and 2B, the terahertz wave generating element 110-1 includes the substrate 111 and light formed on one surface (the surface on the + Z-axis direction side) of the substrate 111. 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 are provided. That is, in the terahertz wave generating 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 other shapes.

  The photoconductive layer 112 is a layer that generates carriers (for example, electrons or holes) when irradiated with the above-described pump light LB1. The photoconductive layer 112 includes, 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 the irradiation of the pump light LB1 to the photoconductive layer 112 flow. However, when the electrode layers 113 and 114 constitute the terahertz wave detection element 130, the electrode layers 113 and 114 are current signals corresponding to carriers generated due to the irradiation of the probe light LB2 to the photoconductive layer 112. And a pair of electrode layers through which a current signal according to the light intensity of the terahertz wave THz irradiated to the terahertz wave detecting element 130 flows. At least one of the electrode layers 113 and 114 is made of 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 of at least one).

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

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

  The electrode layer 114 includes a first electrode part 114-1, a second electrode part 114-2, and a third electrode part 114-3 that are physically integrated or electrically connected. The first electrode portion 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, toward 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 in the + Z-axis direction (that is, along the stacking direction) starting from the substrate 111. The shape of the electrode layer 114 (the shape on the XY plane) is the alphabet “T”.

  The second electrode part 114-2 can function as an antenna. For example, the second electrode portion 114-2 can function as a so-called dipole antenna. The first electrode unit 114-1 can function as an antenna and can function as a transmission line through which a current signal flows through 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 excitation of the pump light LB1) from the photoconductive layer 112. However, the 1st electrode part 114-1, the 2nd electrode part 114-2, and the 3rd electrode part 114-3 may function as an antenna of other shapes (for example, what is called a bow tie type antenna).

  A gap 115 in which 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. A photoconductive layer 112 is formed in the gap portion 115. Accordingly, 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 side surface 113-3a on the −X axis side of the third electrode portion 113-3 is in contact with the side surface 112c on the + X axis side of the photoconductive layer 112. The side surface 114-3a on the + X-axis side of the third electrode portion 114-3 is in contact with 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 the Y-axis direction of each of the second electrode portions 113-2 and 114-2 and the third electrode portions 113-3 and 114-3. It is larger than the width along. That is, the photoconductive layer 112 protrudes along the Y-axis direction when viewed from the second electrode portions 113-2 and 114-2 and the third electrode portions 113-3 and 114-3. Even in this case, the portion of the photoconductive layer 112 protruding along the Y-axis direction is separated from the region irradiated with the pump light LB1 indicated by the dotted circle in FIG. For this reason, 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 along the Y-axis direction of the photoconductive layer 112 is the width along the Y-axis direction of each of the second electrode portions 113-2 and 114-2 and the third electrode portions 113-3 and 114-3. It 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 (in the example illustrated in FIG. 2B, toward the −Z axis direction, which is a specific example of “incident direction”). ) 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 so that the beam diameter of the pump light LB1 becomes the smallest (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. Here, “the beam diameter of the pump light LB1” means a diameter of a cross section parallel to the XY plane of the optical path of the pump light LB1.

  In the present embodiment, the electrode layers 113 and 114 have a shape corresponding 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 corresponding to the propagation mode of the pump light LB1 inside the photoconductive layer 112.

  Hereinafter, the shapes 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 vicinity of 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, the interval between the third electrode portion 113-3 and the third electrode portion 114-3 (that is, the interval along the X-axis direction, hereinafter referred to as “electrode interval”) is The minimum value is obtained 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 along the X-axis direction between the side surface 113-3a and the side surface 114-3a. In other words, the position where the electrode interval is the smallest among the positions on the virtual straight line along the Z-axis direction that is the incident direction of the pump light LB1 is the predetermined position. Furthermore, in other words, the distribution mode along the Z-axis direction of the electrode interval (that is, the incident direction of the terahertz wave THz) is a distribution mode in which the electrode interval is minimized at a predetermined position. In other words, 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) is along the Z-axis direction and the electrode layers 113 and 114 are light In the cross section of the terahertz wave generating element 110 along the plane along the X-axis direction that sandwiches the conductive layer, the electrode interval is 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 the predetermined position is smaller than the electrode interval at other positions shifted from the predetermined position in the Z-axis direction.

  The predetermined position where the electrode interval is minimized 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 the positions on a virtual straight line along the Z-axis direction.

  More specifically, the predetermined position coincides with a focal position at which the beam diameter (that is, the diameter in the X-axis direction) of the pump light LB1 transmitted through the photoconductive layer 112 is minimum. However, the “predetermined position matches the focal position” state here can be regarded not only as the predetermined position exactly matches the focal length but also as the predetermined position substantially matches the focal distance. 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 spacing changes along the Z-axis direction as follows. First, in the 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. In other words, 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 in 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 that the electrode interval at a position closer to the focal position becomes smaller. In other words, the electrode interval at a certain position in the region between the back surface 112b and the focal position increases continuously as the certain position moves in the −Z-axis direction. That is, the change tendency of the electrode interval along the Z-axis direction is the same as the change 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 the cross section having the optical path along the XZ plane). It can be said that it has a shape.

  However, the electrode spacing may vary in a manner different from that shown in FIG. That is, the electrode interval may be changed in any way as long as it is the minimum at the predetermined position. For example, the electrode interval at a certain position in the region between the surface 112a and the predetermined position may be decreased step by step as the certain position moves in the −Z axis direction. For example, the electrode interval 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 3rd electrode parts 113-3 and 114-3 is located in the outer side of the optical path of 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. Therefore, the propagation of the pump light LB1 is not inhibited by the third electrode portions 113-3 and 114-3 in the photoconductive layer 112.

  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 made of GaAs is formed, the temperature of the substrate 111 is about 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 buffer layer). , Referred to as “GaAs supply ratio”) is approximately 5 to 30 and the film formation rate of 1 micron per hour may be obtained.

  Thereafter, the photoconductive layer 112 having a thickness of about 1 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 in an environment where the temperature of the substrate 111 is approximately 500 degrees or less and a film formation 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 where the GaAs supply ratio is higher than that and a film formation rate of 1 micron per hour is obtained.

  Thereafter, 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. 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 a lithography technique and an etching technique). The photoconductive layer 112 is patterned. As a result, the photoconductive layer 112 having the shape shown in FIG. However, the photoconductive layer 112 uniformly formed 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 using a known film formation method (for example, sputtering method, vacuum deposition method, metal growth method, spray method, etc.) or a known patterning method. Is done. Thereafter, dicing is performed. As a result, the manufacture of the terahertz wave generating element 110-1 is completed.

  According to the terahertz wave generating element 110-1 having the configuration described above, the electrode interval is not minimized 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 positioned. 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 inventors of the present application simulated the generation efficiency of the terahertz wave THz in the four terahertz wave generating elements of the comparative example shown in FIG. 4 and the terahertz wave generating element 110-1 of the present example by computer computation. The terahertz wave generating element of the first comparative example is a terahertz wave generating element in which the electrode interval 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 electrode interval is constant and the beam diameter of the pump light LB1 is minimum on the surface 112a of the photoconductive layer 112. The terahertz wave generating element of the third comparative example has a terahertz wave generating element in which 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. The terahertz wave generating element of the fourth comparative example generates terahertz waves 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 decreases along the direction from the front surface 112a to the back surface 112b. It is an 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 the present embodiment is higher than the generation efficiency of any of the terahertz wave generation elements of the first to fourth comparison examples. Also obtained good results. Specifically, the inventors of the present application assume that the signal intensity (that is, the current value) of the current signal generated by irradiating the terahertz wave generating element 110-1 of the present embodiment with the pump light LB1 having the intensity is 1. As a result, the signal intensity of the current signal generated by irradiating the terahertz wave generating element of the first comparative example with the pump light LB1 having the same intensity was 0.83. The inventors of the present application obtained a result that the signal intensity of the current signal generated by irradiating the terahertz wave generating element of the second comparative example or the third comparative example with the pump light LB1 having the same intensity becomes 0.94. The inventors of the present application obtained a result that the signal intensity of the current signal generated by irradiating the terahertz wave generating element of the fourth comparative example with the pump light LB1 having the same intensity becomes 0.77. The greater the signal strength of the current signal, the greater the signal strength of the generated terahertz wave THz. Therefore, the result of the simulation shows that the generation efficiency of the terahertz wave THz of the terahertz wave generating element 110-1 of this example is good.

  Here, the signal intensity of the current signal increases as the number of carriers generated by 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 to each part of the photoconductive layer 112 by the pump light LB1 increases. The amount of energy given to each part of the photoconductive layer 112 by the pump light LB1 increases as the intensity of the pump light LB1 increases when reaching each part of the photoconductive layer 112.

  In addition, the signal strength of the current signal increases as the carrier moving speed increases. The carrier moving speed increases as the strength of the electric field applied to the photoconductive layer 112 increases. The strength of the electric field applied to the photoconductive layer 112 increases as the electrode spacing 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 becomes as large as possible when reaching each part of the photoconductive layer 112, and the electrode interval becomes as small as possible. It is sufficient to satisfy the second characteristic. Based on the result of the simulation, it can be said that the terahertz wave generating element 110-1 of this example satisfies the first characteristic and the second characteristic in a balanced manner as compared with the terahertz wave generating element of each comparative example. . Specifically, the first and second characteristics are that the terahertz wave generating element 110-1 has a minimum electrode spacing 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 positioned. It is well-balanced by the characteristics of Further, in the first characteristic and the second characteristic, the change tendency of the electrode interval along the Z-axis direction is the same as the change tendency of the beam diameter along the Z-axis direction (that is, the third electrode portion 113-3). And 114-3 have a shape distributed along the outer edge of the optical path of the pump light LB1), and are also well-balanced.

  Although the terahertz wave detecting element 110 has been described as an example so far, the terahertz wave detecting element 130 also has an electrode interval 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 positioned. The detection efficiency of the terahertz wave THz by the terahertz wave detection element 130 is improved as compared with the terahertz wave detection element that is not minimized. Specifically, the signal intensity of the terahertz wave THz detected by the terahertz wave detection element 130 is larger than that of the terahertz wave detection 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 Generating Element 110-2 of Second Example Next, referring to FIGS. 5A to 5C, the terahertz wave generating element 110 of the second example (hereinafter referred to as “the terahertz wave generating element 110”) is described. For convenience, the configuration of “terahertz wave generation element 110-2”) will be described. FIG. 5A is a top view showing the top surface of the terahertz wave generating element 110-2 of the second embodiment. FIG. 5B is a cross-sectional view showing a V (1) -V (1) ′ cross section of the terahertz wave generating element 110-2 shown in FIG. FIG.5 (c) is sectional drawing which shows the V (2) -V (2) 'cross section of the terahertz wave generation element 110-2 shown to Fig.5 (a).

  As shown in FIG. 5A to FIG. 5C, the terahertz wave generating element 110-2 of the second embodiment has a photoconductive layer as compared with the terahertz wave generating element 110-1 of the first embodiment. 112 and the third electrode portions 113-3 and 114-3 are different in shape. Other configuration requirements of the terahertz wave generation element 110-2 of the second embodiment may be the same as other configuration requirements of the terahertz wave generation element 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 an ellipse (or a circle). The reason why the shape of the photoconductive layer 112 is set to be oval is that the beam shape of the pump light LB1 on the XY plane is circular.

  In accordance with the shape of the photoconductive layer 112 being elliptical, the shape of each of the third electrode layers 113 and 114 on the XY plane is an arc shape that is 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 certain position approaches the predetermined position (focal position) along the Z-axis direction and the certain position increases in the Y-axis direction. Along the distance from the center of the photoconductive layer 112, the distance decreases. For example, as shown in FIGS. 5B and 5C, the electrode interval d2 at a predetermined position in the cross section along the XZ plane relatively far from the center of the photoconductive layer 112 (FIG. 5C). Is smaller than the electrode interval d1 (see FIG. 5B) at a predetermined position in the cross section along the XZ plane relatively close to the center of the photoconductive layer 112.

  As a result, the electrode spacing is smaller than when 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 Generating Element 110-3 of Third Embodiment Next, referring to FIGS. 6A to 6B, the terahertz wave generating element 110 of the third embodiment (hereinafter referred to as “ the terahertz wave generating element 110-3” ). For convenience, the configuration of “terahertz wave generating element 110-3”) will be described. FIG. 6A is a top view showing the top surface of the terahertz wave generating element 110-3 of the third embodiment. FIG. 6B is a cross-sectional view showing a VI-VI ′ cross section of the terahertz wave generating element 110-3 shown in FIG.

  As shown in FIG. 6A to FIG. 6B, the terahertz wave generating element 110-3 of the third embodiment is more photoconductive than the terahertz wave generating element 110-1 of the first embodiment. 112 and the third electrode portions 113-3 and 114-3 are different in shape. Other configuration requirements of the terahertz wave generation element 110-3 of the third embodiment may be the same as other configuration requirements of the terahertz wave generation element 110-1 of the first embodiment.

  Specifically, in the first embodiment described above, the third electrode portion 113-3 has a shape distributed along the outer edge of the optical path of the pump light LB1, and therefore, in 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 projecting toward the third electrode portion 114-3 (for example, projecting in a convex shape, the same applies hereinafter). In a certain cross section along the XZ plane, the second portion 113-32 which is the other 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 that 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 protrude toward the side surface 114-3a.

  Furthermore, in the first embodiment described above, 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 first electrode portion 114-3 has a shape in a certain section along the XZ plane. The three-electrode portion 114-3 as a whole protrudes in a convex shape toward the third electrode portion 113-3 (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 114-31 which is a part of the third electrode portion 114-3 is formed. , Protruding 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 protrude toward the side surface 113-3a.

  As a result, the entire third electrode portion 113-3 protrudes convexly toward the third electrode portion 114-3 and the entire third electrode portion 114-3 extends to the third electrode within a certain cross section along the XZ plane. Compared with the terahertz wave generating element protruding in a convex shape toward the portion 113-3, the electrode interval does not become unnecessarily narrow. Accordingly, the parasitic capacitance between the third electrode portion 113-3 and the third electrode portion 114-3 is relatively reduced.

(2-4) Configuration of the terahertz wave generating element 110-3 of the fourth embodiment Subsequently, referring to FIGS. 7A to 7C, the terahertz wave generating element 110 of the fourth embodiment (hereinafter referred to as “ the terahertz wave generating element 110-3” ). For convenience, the configuration of “terahertz wave generating element 110-4” will be described. FIG. 7A is a cross-sectional view showing a cross section along the XY plane of the terahertz wave generating element 110-4 of the fourth embodiment. FIG. 7B is a cross-sectional view showing a cross section (corresponding to the 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 showing 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 FIG. 7A to FIG. 7C, the terahertz wave generating element 110-4 of the fourth embodiment is more photoconductive than the terahertz wave generating element 110-1 of the first embodiment. 112 and the third electrode portions 113-3 and 114-3 are different in shape. Other structural requirements of the terahertz wave generating element 110-4 of the fourth embodiment may be the same as other structural requirements of the terahertz wave generating element 110-1 of the first embodiment.

  Specifically, in the fourth embodiment, as shown in FIG. 7A, the third electrode portions 113-3 and 114-3 are along the X-axis direction in a certain cross section along the XY plane. The distance between the pair of third portions 113-33 and 114-33 that sandwich the pump light LB1 is a pair of third electrodes 113-3 and 114-3 that does not sandwich the pump light LB1 along the X-axis direction. It becomes smaller than the interval between the fourth portions 113-34 and 114-34. Alternatively, the pair of third portions 113-33 and 114 that sandwich 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 in a certain cross section along the XY plane. -33 is spaced apart between the pair of fourth portions 113-34 and 114-34 that do not sandwich 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. It becomes smaller than the interval between. For example, FIG. 7B shows a pair of third portions 113- that sandwich 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 indicates that the distance at a predetermined position between 33 and 114-33 is d3. For example, FIG. 7B shows a pair of fourth portions 113 that do not sandwich the pump light LB1 along the X-axis direction among the third electrode portions 113-3 and 114-3 in a certain cross section along the XY plane. This indicates that the interval at the predetermined position between −34 and 114-34 is d4 (where d4> d3).

  As a result, the electrode spacing does not become unnecessarily narrow 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). Accordingly, the parasitic capacitance between the third electrode portion 113-3 and the third electrode portion 114-3 is relatively reduced.

  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 generating element that generates (in other words, emits) an arbitrary electromagnetic wave different from the terahertz wave may have the same structure as the above-described terahertz wave generating element 110. An arbitrary electromagnetic wave detection element that detects an arbitrary 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 generating element and the arbitrary electromagnetic wave detecting element preferably enjoys the same effect as the effect that the terahertz wave generating element 110 or the terahertz wave detecting element 130 can enjoy. Can do.

  The present invention is not limited to the above-described embodiments, and can be changed as appropriate without departing from the scope or spirit of the invention that can be read from the claims and the entire specification. In addition, the measuring device is also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 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 part 120 Optical delay mechanism 130 Terahertz wave detecting element 150 Control part 151 Lock-in detection part 152 Signal processing LB1 Pump light LB2 Probe light THz Terahertz wave

Claims (11)

A photoconductive layer on which excitation light is incident on the surface, and a pair of electrodes that sandwich the photoconductive layer along a predetermined direction intersecting the incident direction of the excitation light,
The distance between the pair of electrodes along the predetermined direction is an end where the front surface and the back surface are located in a region between the front surface and the back surface of the photoconductive layer facing the front surface along the incident direction. A photoconductive element characterized by being minimized at a predetermined position different from the part position. 2. The photoconductive element according to claim 1, wherein the predetermined position is a position where a beam diameter along the predetermined direction of the excitation light transmitted through the photoconductive layer is minimized. The photoconductive element according to claim 2, wherein a change tendency of the distance between the pair of electrodes along the incident direction is the same as a change tendency of the beam diameter along the incident direction. Each of the pair of electrodes includes a contact surface in contact with the photoconductive layer,
4. The photoconductive element according to claim 1, wherein an interval between the pair of electrodes along the predetermined direction is an interval between the pair of contact surfaces along the predetermined direction. 5. . The light according to any one of claims 1 to 4, wherein the contact surface has a shape distributed along an outer edge of an optical path of the excitation light that passes through the photoconductive layer. Conductive element. 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 that passes through the photoconductive layer. The photoconductive element according to any one of 1 to 5. One of the pair of electrodes protrudes at least partially toward the other of the pair of electrodes so that a distance between the pair of electrodes along the predetermined direction is minimized at the predetermined position. The photoconductive element according to any one of claims 1 to 6. An interval along the predetermined direction of the pair of first portions sandwiching the optical path of the excitation light having a predetermined intensity or more along the predetermined direction in the plane intersecting the incident direction is the pair of electrodes. The distance between the pair of second portions not sandwiching the optical path of the excitation light having the predetermined intensity or more among the electrodes along the predetermined direction is smaller than the distance along the predetermined direction. The photoconductive element according to claim 1. The photoconductive element according to any one of claims 1 to 8, wherein the pair of electrodes are formed outside an optical path of the excitation light. An irradiation means for irradiating the sample with electromagnetic waves;
Detecting means for detecting the electromagnetic wave irradiated to the sample,
At least one of the said irradiation means and the said detection means contains the photoconductive element as described in any one of Claim 1 to 9. The measuring device characterized by the above-mentioned. The measuring apparatus according to claim 10, wherein the electromagnetic wave includes a terahertz wave.

Images