JP2016192458A - Photoconductive element, measurement device and manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoconductive element capable of achieving both efficient generation of carriers due to an irradiation of a laser beam and suppression of loss of a current signal flowing through a pair of electrode layers in accordance with carriers, while avoiding complexity in manufacturing processes.SOLUTION: A photoconductive element (110, 130) is irradiated with a laser beam (LB1, LB2) to emit or detect an electromagnetic wave (THz). The photoconductive element includes a substrate (111), a photoconductive layer (112) and a pair of electrode layers (113a, 113b). Each of the pair of electrode layers includes: (i) a second electrode portion (113a-2, 113b-2) adjacent to a gap portion (114) where is to be irradiated with the laser beam; and (ii) a first electrode portion (113a-1, 113b-1) electrically connected to the second electrode portion. The transmittance of the second electrode portion with respect to the laser beam is larger than the transmittance of the first electrode portion with respect to the laser beam.SELECTED DRAWING: Figure 3

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, a measuring apparatus including such a photoconductive element, and a manufacturing method for manufacturing such a photoconductive element.

  A terahertz wave measuring device is known as a measuring device for measuring the characteristics of a measurement object. The terahertz wave measuring apparatus measures the characteristics of the measurement object according to 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), is emitted from a terahertz wave to which a bias voltage is applied. The element is irradiated. As a result, the terahertz wave emitting element emits a terahertz wave. The terahertz wave emitted from the terahertz wave emitting element is irradiated to the measurement object. The terahertz wave irradiated to the measurement object is reflected by the measurement object or passes through the measurement object. The terahertz wave reflected by the measurement object or transmitted through the measurement object is another laser light obtained by branching the ultrashort pulse laser light and has an optical delay (that is, an optical path length relative to the pump light). The terahertz wave detecting element irradiated with the probe light (in other words, excitation light) to which the difference is applied is irradiated. As a result, the terahertz wave detection element detects a terahertz wave reflected by the measurement object or transmitted through the measurement object. The terahertz wave measuring apparatus measures the characteristics of the measurement object 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 emitting element and a terahertz detecting element, a substrate, a photoconductive layer formed on the substrate, and a pair of electrode layers formed on the substrate and arranged to form an antenna separated by a gap portion, There exists a photoconductive element provided with (for example, refer patent document 1). As another example of the terahertz wave emitting element and the terahertz detecting element, there is a photoconductive element including a substrate, a photoconductive layer formed on the substrate, and a transparent electrode layer sandwiching the photoconductive layer (for example, Patent Documents). 2).

JP 2005-26347 A International Publication No. 2010/006440 Pamphlet

  The photoconductive element generally emits terahertz waves as follows. First, when a bias voltage is applied to the pair of electrode layers, the bias voltage is applied to a gap portion formed by the pair of electrode layers. When laser light is irradiated to the gap part (particularly, the photoconductive layer formed in the gap part) in a state where a bias voltage is applied to the gap part, the laser beam is applied to the photoconductive layer irradiated with the laser light. Carriers are generated by photoexcitation with light. When carriers are generated, a current signal corresponding to the generated carriers is generated in the photoconductive element. The current signal flows through the pair of electrode layers. As a result, the photoconductive element emits terahertz waves from the pair of electrode layers.

  Furthermore, the photoconductive element generally detects a terahertz wave as follows. When laser light is irradiated to the gap portion (particularly, the photoconductive layer formed in the gap portion), carriers are generated in the photoconductive layer irradiated with the laser light by photoexcitation with the laser light. As described above, when carriers are generated, a current signal corresponding to the generated carriers flows through the pair of electrode layers. Here, when the photoconductive element is irradiated with the terahertz wave while the gap is irradiated with the laser beam, the signal intensity of the current signal flowing through the pair of electrode layers changes according to the intensity of the terahertz wave. As a result, the photoconductive element can detect a terahertz wave by detecting a current signal flowing through the pair of electrode layers.

  Thus, in order for the photoconductive element to emit or detect terahertz waves, it is necessary to irradiate the photoconductive layer with laser light. On the other hand, a pair of electrode layers is formed on the photoconductive layer. Here, as described in Patent Document 1, when the pair of electrode layers is a metal electrode, the transmittance of the pair of electrode layers with respect to the laser light is relatively low or substantially zero. For this reason, the pair of electrode layers may hinder the irradiation of the laser light on the photoconductive layer. Therefore, the pair of electrode layers may hinder efficient generation of carriers. As a result, a technical problem that the emission efficiency or detection efficiency of the terahertz wave deteriorates may occur.

  Therefore, in order to solve such a technical problem, as described in Patent Document 2, a countermeasure for forming a transparent electrode layer on the entire surface and back surface of the photoconductive layer can be considered. However, the electrical resistance value of the transparent electrode is higher than the electrical resistance value of the metal electrode. For this reason, the loss of the current signal which flows into an electrode layer according to a carrier will increase. As a result, a technical problem that the emission efficiency or detection efficiency of the terahertz wave deteriorates may occur. In addition, when the transparent electrode layer is formed on the entire front and back surfaces of the photoconductive layer, there arises a technical problem that the manufacturing process of the photoconductive element is complicated.

  Thus, the conventional photoconductive element avoids complication of the manufacturing process, but efficiently generates carriers due to laser light irradiation, and loss of a current signal flowing in the pair of electrode layers according to the carriers. There is a technical problem that it is difficult to achieve both of these.

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

  Examples of problems to be solved by the present invention include the above. The present invention makes it possible to achieve both efficient generation of carriers due to laser light irradiation and suppression of loss of a current signal flowing in a pair of electrode layers according to the carriers, while avoiding complication of the manufacturing process. It is an object of the present invention to provide a possible photoconductive element, a measuring device including such a photoconductive element, and a manufacturing method for manufacturing such a photoconductive element.

  A first example of the photoconductive element of the present invention is a photoconductive element that emits or detects an electromagnetic wave when irradiated with a laser beam, and includes a substrate, a photoconductive layer formed on the substrate, A pair of electrode layers formed on one surface of the photoconductive layer, each of the pair of electrode layers being (i) the pair of electrode layers not formed and being irradiated with the laser light. A second electrode part adjacent to the gap part to be provided; and (ii) a first electrode part electrically connected to the second electrode part, and the transmittance of the second electrode part with respect to the laser light Is larger than the transmittance of the first electrode portion with respect to the laser beam.

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

  A first example of the manufacturing method of the present invention is a manufacturing method for manufacturing the above-described first example of the photoconductive element of the present invention, and the one surface of the photoconductive layer formed on the substrate. A first step of forming an electrode material on the first region where the first electrode portion is to be formed and the second region where the second electrode portion is to be formed; and at least the second region. A second step of masking the electrode material, and a third step of further forming the electrode material on the electrode material formed on the first region and not masked.

FIG. 1 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus according to the present embodiment. FIG. 2A is a top view showing the top surface of the terahertz wave emitting element of this embodiment, and FIG. 2B is a diagram of II (1) -II (II) of the terahertz wave emitting element shown in FIG. 1) is a cross-sectional view showing a 'cross section, and FIG. 2 (c) is a cross-sectional view showing a II (2) -II (2) ′ cross section of the terahertz wave emitting element shown in FIG. 2 (a). FIG. 3 is a perspective view showing the configuration of the terahertz wave emitting element according to the present embodiment. FIG. 4 is a flowchart showing a flow of a manufacturing method of the terahertz wave emitting element. FIG. 5 is a graph showing a spectrum obtained by Fourier transforming the waveform of the terahertz wave emitted from the terahertz wave emitting element. FIG. 6 is a top view showing an upper surface of a terahertz wave emitting element according to a modification.

  Hereinafter, description is advanced about embodiment of a photoconductive element, a measuring device, and a manufacturing method.

(Embodiment of photoconductive element)
<1>
The photoconductive element of the present embodiment is a photoconductive element that emits or detects electromagnetic waves when irradiated with laser light, and includes a substrate, a photoconductive layer formed on the substrate, and the photoconductive layer. A pair of electrode layers formed on one surface, each of the pair of electrode layers being (i) a gap portion where the pair of electrode layers are not formed and to which the laser beam is to be irradiated And (ii) a first electrode part electrically connected to the second electrode part, and the transmittance of the second electrode part with respect to the laser light is determined by the laser. It is larger than the transmittance of the first electrode portion with respect to light.

  The photoconductive element of this embodiment can emit or detect electromagnetic waves such as terahertz waves. Note that the photoconductive element of the present embodiment may emit or detect electromagnetic waves in the operation mode described in the item “Problems to be Solved by the Invention”.

  Particularly in the present embodiment, each of the pair of electrode layers includes a first electrode portion and a second electrode portion that are electrically connected. The second electrode part is adjacent to the gap part. The first electrode portion may not be adjacent to the gap portion. Therefore, the second electrode part is an electrode part formed at a position closer to the gap part than the first electrode part. In other words, the first electrode portion is an electrode portion that is formed at a position farther from the gap portion than the second electrode portion.

  Since the second electrode part is adjacent to the gap part, there is a high possibility that part of the laser light applied to the gap part is also applied to the second electrode part. In the present embodiment, the transmittance of the second electrode portion with respect to the laser light is larger than the transmittance of the first electrode portion with respect to the laser light. That is, the transmittance of the second electrode layer formed around the gap is relatively large. For this reason, the laser light is likely to reach the photoconductive layer formed on the lower side of the second electrode portion because it is relatively easy to pass through the second electrode portion. Therefore, the light amount of the laser light applied to the photoconductive layer is relatively smaller than that of the photoconductive element of the first comparative example in which the first electrode portion having a relatively small transmittance is formed adjacent to the gap portion. Become bigger. For this reason, the efficient production | generation of the carrier resulting from irradiation of the laser beam to a gap part is implement | achieved. As a result, deterioration of the emission efficiency or detection efficiency of electromagnetic waves is suppressed.

  On the other hand, as will be described in detail later, an increase in the transmittance of the second electrode portion for realizing efficient generation of carriers may cause an increase in the electrical resistance value of the second electrode portion. An increase in the electric resistance value of the second electrode portion leads to an increase in loss of a current signal corresponding to the carrier. However, in this embodiment, each of the pair of electrode layers includes not only the second electrode part but also the first electrode part having a relatively low transmittance with respect to the laser beam. The decrease in the transmittance of the first electrode part can lead to a decrease in the electric resistance value of the first electrode part. For this reason, the current signal corresponding to the carrier flows to the first electrode part that is electrically connected to the second electrode part via the second electrode part and has a relatively small electrical resistance value. For this reason, compared with the photoconductive element of the 2nd comparative example provided with only the 2nd electrode part with relatively large transmissivity of each of a pair of electrode layers, the loss of the current signal according to a carrier increases. It is suppressed. As a result, deterioration of the emission efficiency or detection efficiency of electromagnetic waves is suppressed.

  In addition, in the present embodiment, the pair of electrode layers is further formed on one surface of the photoconductive layer. That is, the pair of electrode layers are not formed on one surface and the other surface (that is, the back surface) of the photoconductive layer, respectively. For this reason, since it is not necessary to form an electrode layer on each of the two surfaces of the photoconductive layer, complication of the manufacturing process of the photoconductive element is avoided.

  As described above, the photoconductive element of the present embodiment avoids complication of the manufacturing process, but efficiently generates carriers due to laser light irradiation, and current signals that flow through the pair of electrode layers according to the carriers. It is possible to achieve both suppression of loss.

<2>
In another aspect of the photoconductive element of this embodiment, the electrical resistance value per unit length of the first electrode portion is smaller than the electrical resistance value per unit length of the second electrode portion.

  According to this aspect, the current signal corresponding to the carrier flows through the second electrode portion to the first electrode portion having a relatively small electrical resistance value. For this reason, compared with the photoconductive element of the 2nd comparative example provided only with the 2nd electrode part with which each electric resistance value of a pair of electrode layers is relatively large, the increase in the loss of the current signal according to a carrier Is suppressed.

<3>
In another aspect of the photoconductive element of the present embodiment, the film thickness of the second electrode portion is smaller than the film thickness of the first electrode portion.

  The decrease in the film thickness of the electrode part can lead to an increase in the transmittance of the electrode part and an increase in the electrical resistance value of the electrode part. For this reason, according to this aspect, the state in which the transmittance of the second electrode portion is larger than the transmittance of the first electrode portion can be realized relatively easily by adjusting the film thickness. Furthermore, a state in which the electrical resistance value per unit length of the first electrode part is smaller than the electrical resistance value per unit length of the second electrode part is relatively easily realized by adjusting the film thickness.

<4>
In another aspect of the photoconductive element of the present embodiment, the first electrode portion is made of a metal electrode material or a transparent electrode, and the second electrode portion is made of a transparent electrode material.

  The transmittance of the transparent electrode material is generally larger than the transmittance of the metal electrode material. On the other hand, the electrical resistivity of the transparent electrode material is generally larger than the electrical resistivity of the metal electrode material. For this reason, according to this aspect, the state in which the transmittance of the second electrode portion is greater than the transmittance of the first electrode portion is realized relatively easily by selecting the material of the electrode portion. Furthermore, the state in which the electrical resistance value per unit length of the first electrode part is smaller than the electrical resistance value per unit length of the second electrode part is realized relatively easily by selecting the material of the electrode part.

<5>
In another aspect of the photoconductive element of the present embodiment, the first electrode portion extends along a first direction, and the second electrode portion extends in a second direction that intersects the first direction. Along and toward the gap.

  According to this aspect, a pair of 2nd electrode part with which a pair of electrode layer is provided can function as a dipole antenna, for example.

(Embodiment of measuring device)
<6>
The measurement apparatus according to the present embodiment includes an emission unit that emits an electromagnetic wave to a measurement object, and a detection unit that detects the electromagnetic wave irradiated to the measurement object, and includes at least one of the emission unit and the detection unit. One includes the above-described photoconductive element of the present embodiment (including various aspects thereof).

  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.

<7>
In another aspect of the measurement apparatus 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 measurement object 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.

(Embodiment of manufacturing method)
<8>
The manufacturing method according to the present embodiment is a manufacturing method for manufacturing the photoconductive element according to the present embodiment described above (including various aspects thereof), and the one of the photoconductive layers formed on the substrate. A first step of forming an electrode material on a first region of the surface where the first electrode portion is to be formed and a second region where the second electrode portion is to be formed; and at least in the second region A second step of masking the electrode material formed, and a second step of further forming the electrode material or another electrode material on the electrode material formed on the first region and not masked. 3 steps.

  According to the manufacturing method of the present embodiment, the above-described photoconductive element of the present embodiment is preferably manufactured. For example, the cost or time required to manufacture the photoconductive element is reduced.

  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, the photoconductive element of the present embodiment includes the second electrode portion having a relatively large transmittance with respect to the laser light and the first electrode portion having a relatively small transmittance with respect to the laser light. The measuring device of this embodiment includes the photoconductive element of this embodiment. The manufacturing method of this embodiment forms an electrode material on the first and second regions, masks the electrode material formed on the second region, is formed on the first region, and is masked. An electrode material is further formed on the non-electrode material. Therefore, while avoiding complication of the manufacturing process, it is possible to achieve both efficient generation of carriers due to laser light irradiation and suppression of loss of current signals flowing in the pair of electrode layers according to the carriers.

  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 provided with a terahertz wave emitting element 110 and a terahertz wave detecting element 130 that are specific examples of “photoconductive elements” and that is a specific example of “measuring device” will be described. 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 measurement target object 10 with the terahertz wave THz, and transmits the measurement target object 10 or reflects the terahertz wave THz reflected by the measurement target object 10 (that is, the measurement target object). The terahertz wave THz irradiated on the object 10 is detected. In the example shown in FIG. 1, the terahertz wave measuring apparatus 100 detects the terahertz wave THz reflected by the measurement object 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 measurement target object 10 by analyzing the terahertz wave THz applied to the measurement target object 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 emitting element 110, which is a specific example of “emission 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. The pump light LB1 enters the terahertz wave emitting 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 emitting element 110 emits a terahertz wave THz. Specifically, a bias voltage generation unit is provided in the gap 114 (see FIG. 2 and the like) included in the terahertz wave emitting element 110 via the electrode layers 113a and 113b (see FIG. 2 and the like) included in the terahertz wave emitting element 110. The bias voltage generated by 141 is applied. When pump light LB1 is irradiated to gap portion 114 in a state where an effective bias voltage (for example, a bias voltage other than 0 V) is applied to gap portion 114, a photoconductive layer formed below gap portion 114. 112 (see FIG. 2 and the like) is irradiated with 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 emitting element 110 generates a pulse-shaped current signal in the subpicosecond order or in the femtosecond order according to the generated carrier. The generated current signal flows through the electrode layers 113a and 113b. As a result, the terahertz wave emitting element 110 emits the terahertz wave THz resulting from the pulsed current signal.

  The terahertz wave THz emitted from the terahertz wave emitting 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 measurement object 10. The terahertz wave THz irradiated on the measurement object 10 is reflected by the measurement object 10. The terahertz wave THz reflected by the measurement object 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 beam LB2 is irradiated to the gap 114 (see FIG. 2 and the like) included in the terahertz wave detecting element 130, the photoconductive layer 112 (see FIG. 2 and the like) formed below the gap 114. Reference) is irradiated with the probe light LB2. 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 in the electrode layers 113a and 113b (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 detection element 130 in a state where the probe light LB2 is irradiated on the gap portion 114, the signal intensity of the current signal flowing through the electrode layers 113a and 113b becomes 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 113a and 113b.

  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 emitting element 110 (or the timing at which the terahertz wave emitting element 110 emits the terahertz wave THz), and the probe light LB2 becomes the terahertz wave detecting 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 measurement object 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 measurement object 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 measurement object 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 measurement object 10 based on the frequency spectrum.

(2) Configuration of Terahertz Wave Output Element 110 and Terahertz Wave Detection Element 130 Next, the configuration of the terahertz wave output element 110 and the terahertz wave detection element 130 will be described. Note that the configuration of the terahertz wave emitting element 110 is the same as that of the terahertz wave detecting element 130. Therefore, the configuration of the terahertz wave emitting element 110 will be described below with reference to FIGS. 2A to 2C and FIG. FIG. 2A is a top view showing the top surface of the terahertz wave emitting element 110 of the present embodiment. FIG. 2B is a sectional view showing a II (1) -II (1) ′ section of the terahertz wave emitting element 110 shown in FIG. FIG. 2C is a cross-sectional view showing a II (2) -II (2) ′ cross section of the terahertz wave emitting element 110 shown in FIG. FIG. 3 is a perspective view illustrating a configuration of the terahertz wave emitting element 110 according to the present embodiment. However, the following description can be similarly applied to the terahertz wave detection element 130. Further, in the following description, the terahertz wave emitting 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.

  As shown in FIG. 2A to FIG. 2C and FIG. 3, the terahertz wave emitting element 110 is formed on the substrate 111 and one surface of the substrate 111 (the surface on the + Z-axis direction side). The photoconductive layer 112 and a pair of electrode layers 113 (that is, electrode layers 113a and 113b) formed on one surface (the surface on the + Z-axis direction side) of the photoconductive layer 112 are provided. That is, in the terahertz wave emitting element 110, the substrate 111, the photoconductive layer 112, and the pair of electrode layers 113 are stacked in the Z-axis direction (that is, the direction orthogonal to the XY plane parallel to the surface of the substrate 111). It has a laminated structure laminated along.

  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 in which carriers (for example, electrons or holes) are generated when the pump light LB1 or the probe light LB2 is irradiated. 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 photoconductive layer 112 has a plate shape. However, the shape of the photoconductive layer 112 may be other shapes. The size of the photoconductive layer 112 (particularly along the XY plane) is the same as the size of the substrate 111 (particularly along the XY plane). The size of the photoconductive layer 112 (particularly along the XY plane) may be different from the size of the substrate 111 (particularly along the XY plane).

  The electrode layers 113a and 113b are a pair of electrode layers to which the above-described bias voltage is applied and a current signal corresponding to carriers generated due to the irradiation of the pump light LB1 to the photoconductive layer 112 flows. However, when the electrode layers 113a and 113b constitute the terahertz wave detecting element 130, the electrode layers 113a and 113b are current signals corresponding to carriers generated due to 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.

  The electrode layer 113a includes a first electrode portion 113a-1 and a second electrode portion 113a-2 that are physically integrated or electrically connected. The first electrode portion 113a-1 extends along the Y-axis direction. The second electrode portion 113a-2 extends along the X-axis direction orthogonal to the Y-axis direction. The second electrode portion 113a-2 extends toward the electrode layer 113b starting from a part of the first electrode portion 113a-1. The shape of the electrode layer 113a (the shape on the XY plane) is the letter “T”.

  The electrode layer 113b includes a first electrode portion 113b-1 and a second electrode portion 113b-2 that are physically integrated. The first electrode portion 113b-1 extends along the Y-axis direction. The second electrode portion 113b-2 extends along the X-axis direction orthogonal to the Y-axis direction. The second electrode portion 113b-2 extends toward the electrode layer 113a starting from a part of the first electrode portion 113b-1. The shape of the electrode layer 113b (the shape on the XY plane) is the alphabet “T”.

  Each of the second electrode portions 113a-2 and 113b-2 can function as an antenna. For example, the second electrode portions 113a-2 and 113b-2 can function as so-called dipole antennas. On the other hand, each of the first electrode portions 113a-1 and 113b-1 can function as an antenna, and a transmission line through which a current signal flows via the second electrode portions 113a-2 and 113b-2 that can function as an antenna. Can function as. For example, the first electrode portions 113a-1 and 113b-1 can function as so-called parallel transmission lines.

  A gap 114 where the electrode layers 113a and 113b are not formed is ensured between the second electrode portion 113a-2 and the second electrode portion 113b-2. Accordingly, each of the second electrode portions 113a-2 and 113b-2 is an electrode portion adjacent to the gap portion 114 (in other words, defining or forming the gap portion 114). The pump light LB1 (further, the probe light LB2) is preferably applied to the gap portion 114. That is, the pump light LB1 (and the probe light LB2) is preferably applied to at least the photoconductive layer 112 formed below the gap portion 114.

  In the present embodiment, in particular, the transmittance of each of the second electrode portions 113a-2 and 113b-2 with respect to the pump light LB1 (further, the probe light LB2) is the first with respect to the pump light LB1 (further, the probe light LB2). It is larger than the transmittance of each of the electrode portions 113a-1 and 113b-1. Hereinafter, when there is no special description, “transmittance” means the transmittance with respect to the pump light LB1 (further, the probe light LB2). For example, the transmittances of the second electrode portions 113a-2 and 113b-2 are larger than the first predetermined value, while the transmittances of the first electrode portions 113a-1 and 113b-1 are the first predetermined value. May be smaller. For example, the transmittances of the second electrode portions 113a-2 and 113b-2 may be relatively large, while the transmittances of the first electrode portions 113a-1 and 113b-1 may be relatively small. .

  Furthermore, per unit length along each of the electric resistance values of the first electrode portions 113a-1 and 113b-1 (for example, the direction perpendicular to the Z-axis direction that is the thickness direction (that is, the direction along the XY plane)) Of the second electrode portions 113a-2 and 113b-2 is smaller than the electric resistance values of the second electrode portions 113a-2 and 113b-2. For example, the electrical resistance values of the first electrode portions 113a-1 and 113b-1 are smaller than the second predetermined value, while the electrical resistance values of the second electrode portions 113a-2 and 113b-2 are the second values. It may be larger than a predetermined value. For example, the electrical resistance values of the first electrode portions 113a-1 and 113b-1 are relatively small, while the electrical resistance values of the second electrode portions 113a-2 and 113b-2 are relatively large. Also good.

  In order to satisfy the above-described conditions of transmittance and electric resistance, the materials of the first electrode portions 113a-1 and 113b-1 and the second electrode portions 113a-2 and 113b-2 may be appropriately selected. . Specifically, the transmittance of the transparent electrode material is generally larger than the transmittance of the metal material. Furthermore, the electrical resistivity of the transparent electrode material is generally larger than the electrical resistivity of the metal material. For this reason, while each of 2nd electrode part 113a-2 and 113b-2 is comprised from a transparent electrode material, each of 1st electrode part 113a-1 and 113b-1 may be comprised from the metal material. . The transparent electrode material may be at least one of ITO, IZO, AZO, GZO and IGZO, for example. For example, the metal material may be at least one of Au, AuCr, AuGeNi, and AuSn. Alternatively, each of the second electrode portions 113a-2 and 113b-2 is made of an electrode material having a relatively large transmittance and a relatively large electrical resistance value, while the first electrode portions 113a-1 and 113b-2 Each of 113b-1 may be made of an electrode material having a relatively small transmittance and a relatively small electric resistance value.

  In order to satisfy the above-described conditions of transmittance and electric resistance, the thicknesses of the first electrode portions 113a-1 and 113b-1 and the second electrode portions 113a-2 and 113b-2 (that is, in the Z-axis direction). (Size along) may be adjusted appropriately. Specifically, as the film thickness of an electrode (particularly a transparent electrode) decreases, generally, the electrode transmittance increases while the electrical resistance value of the electrode increases. For this reason, the film thickness of each of the second electrode parts 113a-2 and 113b-2 may be smaller than the film thickness of each of the first electrode parts 113a-1 and 113b-1. 2A to 2C and FIG. 3, the film thicknesses of the first electrode portions 113a-1 and 113b-1 and the second electrode portions 113a-2 and 113b-2 are adjusted. An example of the terahertz wave emitting element 110 is shown.

  The terahertz wave emitting element 110 having the configuration described above is manufactured as follows. Hereinafter, a method of manufacturing the terahertz wave emitting element 110 will be described with reference to FIG. FIG. 4 is a flowchart showing a flow of a manufacturing method of the terahertz wave emitting element 110.

  As shown in FIG. 4, first, a substrate 111 is loaded into an MBE (Molecular Beam Epitaxy) apparatus (step S11). Thereafter, a buffer layer having a thickness of about 0.1 to 0.5 microns is formed on the substrate 111 (step S12). 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 3 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 (step S13). 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 a known film formation method (for example, sputtering method, vacuum deposition method, metal growth method, spray method, etc.) or a known patterning method is used. The electrode layers 113a and 113b are formed on the photoconductive layer 112 by using (for example, a patterning method combining a lithography technique and an etching technique) (step S14 to step S16). Thereafter, dicing is performed (step S17). As a result, the manufacture of the terahertz wave emitting element 110 is completed.

  Hereinafter, when the first electrode portions 113a-1 and 113b-1 having a relatively large thickness and the second electrode portions 113a-2 and 113b-2 having a relatively small thickness are formed on the photoconductive layer 112, The manufacturing method will be described.

  First, of the one surface of the photoconductive layer 112, the first region where the first electrode portions 113a-1 and 113b-1 are to be formed and the second region where the second electrode portions 113a-2 and 113b-2 are to be formed. An electrode material is formed (in other words, film formation or deposition) in the region (step S14). In this case, the electrode material is formed until the film thickness of the electrode material becomes equal to the target value of the film thickness of the second electrode portions 113a-2 and 113b-2 (hereinafter referred to as “second target film thickness”). The As a result, all of the second electrode portions 113a-2 and 113b-2 are formed in the second region. On the other hand, in the first region, an electrode material having a second target film thickness that is smaller than a target value of the film thickness of the first electrode portions 113a-1 and 113b-1 (hereinafter referred to as “first target film thickness”). Is only formed. Therefore, only a part of the first electrode portions 113a-1 and 113b-1 is formed in the first region.

  Thereafter, at least the second electrode portions 113a-2 and 113b-2 formed in step S14 are masked (step S15). For example, a jig, resist, or the like serving as a mask is formed on the second electrode portions 113a-2 and 113b-2 formed in step S14.

  Thereafter, an electrode material is further formed on the electrode material formed in the first region and not masked in step S15 (step S16). In this case, the electrode material is formed until the film thickness of the electrode material becomes the same as the first target film thickness. That is, in step S16, the remaining part of the first electrode parts 113a-1 and 113b-1 is further formed on part of the first electrode parts 113a-1 and 113b-1 formed in step S14. The As a result, the first electrode portions 113a-1 and 113b-1 are formed in the first region.

  The second electrode portions 113a-2 and 113b-2 may be formed after the first electrode portions 113a-1 and 113b-1 are formed. The first electrode portions 113a-1 and 113b-1 may be formed after the second electrode portions 113a-2 and 113b-2 are formed. Further, the first electrode portions 113a-1 and 113b-1 and the second electrode portions 113a-2 and 113b-2, which are appropriately selected from materials, may be formed on the photoconductive layer 112 in the same flow. .

  According to the terahertz wave emitting element 110 having the configuration described above, the following technical effects can be obtained.

  First, in this embodiment, since the second electrode portions 113a-2 and 113b-2 are adjacent to the gap portion 114, a part of the pump light LB1 irradiated to the gap portion 114 is part of the second electrode portion. There is a high possibility of irradiation to 113a-2 and 113b-2. Here, the transmittances of the second electrode layers 113a-2 and 113b-2 formed around the gap 114 are relatively large. For this reason, since the pump light LB1 is relatively easily transmitted through the second electrode portions 113a-2 and 113b-2, the photoconductivity formed below the second electrode portions 113a-2 and 113b-2. It becomes easier to reach the layer 112. Therefore, compared with the terahertz wave emitting element of the first comparative example in which the first electrode portions 113a-1 and 113b-1 having relatively low transmittance are formed adjacent to the gap portion 114, the photoconductive layer 112 has The light quantity of the pump light LB1 irradiated becomes relatively large. For this reason, the efficient production | generation of the carrier resulting from irradiation of the pump light LB1 to the gap part 114 is implement | achieved. As a result, deterioration of the emission efficiency or detection efficiency of the terahertz wave THz is suppressed.

  On the other hand, as will be described in detail later, the increase in transmittance of the second electrode portions 113a-2 and 113b-2 for realizing efficient generation of carriers is caused by the second electrode portions 113a-2 and 113b-2. May lead to an increase in electrical resistance. For example, a decrease in the film thickness of the second electrode portions 113a-2 and 113b-2 leads to an increase in the transmittance of the second electrode portions 113a-2 and 113b-2, while the second electrode portions 113a-2 and 113b. -2 leads to an increase in electrical resistance value. The increase in the electric resistance value of the second electrode portions 113a-2 and 113b-2 is an increase in the loss of the current signal corresponding to the carrier (that is, the loss of the current signal flowing through the second electrode portions 113a-2 and 113b-2). Increase). However, in this embodiment, not only the second electrode portions 113a-2 and 113b-2 but also the first electrode portions 113a-1 and 113b-1 having relatively small electrical resistance values are provided on the photoconductive layer 112. Is formed. For this reason, a current signal corresponding to the carrier flows to the first electrode portions 113a-1 and 113b-1 via the second electrode portions 113a-2 and 113b-2. Therefore, compared with the photoconductive element of the second comparative example in which the electrode layers 113a and 113b are configured only from an electrode material having a relatively large transmittance (for example, a relatively small or transparent electrode material). Thus, an increase in the loss of the current signal corresponding to the carrier is suppressed. As a result, deterioration of the emission efficiency or detection efficiency of electromagnetic waves is suppressed.

  When the deterioration of the electromagnetic wave emission efficiency or the detection efficiency is suppressed, the deterioration of the S / N ratio of the terahertz wave emission element 110 is suitably suppressed. The deterioration of the S / N ratio corresponds to the narrowing of the dynamic range of the terahertz wave emitting element 110. As shown in FIG. 5, the dynamic range includes the signal level of the signal component included in the terahertz wave THz (“signal (S)” in FIG. 5) and the noise component included in the terahertz wave THz (“noise” in FIG. 5). (N) ") corresponding to the difference from the signal level. In this embodiment, narrowing of the dynamic range is suppressed. That is, the dynamic range becomes relatively large.

  In addition, in this embodiment, the electrode layers 113 a and 113 b are further formed on one surface of the photoconductive layer 112. That is, the electrode layers 113a and 113b are not formed on one surface and the other surface (that is, the back surface) of the photoconductive layer 112, respectively. For this reason, since it is not necessary to form the electrode layer 113a or 113b on each of the two surfaces of the photoconductive layer 112, the manufacturing process of the terahertz wave emitting element 110 is not complicated.

  As described above, the terahertz wave emitting element 110 according to the present embodiment avoids complication of the manufacturing process, and the electrode layers 113a and 113b according to the efficient generation of carriers due to the irradiation of the pump light LB1 and the carriers. It is possible to achieve both suppression of loss of the current signal flowing through the. Similarly, the terahertz wave detection element 130 according to the present embodiment avoids complication of the manufacturing process, and the electrode layers 113a and 113b are formed on the electrode layers 113a and 113b according to the efficient generation of carriers due to the irradiation of the probe light LB2 and the carriers. It is possible to simultaneously suppress the loss of the flowing current signal.

  In addition, in this embodiment, as a method for forming the electrode layers 113a and 113b on the photoconductive layer 112, (i) all of the second electrode portions 113a-2 and 113b-2 are formed on the photoconductive layer 112. And a part of the first electrode portions 113a-1 and 113b-1, and then (ii) masking the second electrode portions 113a-2 and 113b-2, and then (iii) already formed A method of further forming the remaining part of the first electrode parts 113a-1 and 113b-1 on a part of the first electrode parts 113a-1 and 113b-1 is employed. For this reason, compared with the manufacturing method of the comparative example which forms the electrode layers 113a and 113b comprised only from a metal material, the cost (for example, expense cost and time cost) which manufactures the electrode layers 113a and 113b reduces. .

  The effect of efficient carrier generation is realized mainly by the second electrode portions 113a-2 and 113b-2 that are formed adjacent to the gap portion 114 and have a relatively high transmittance. On the other hand, the effect of suppressing the loss of the current signal according to the carrier is mainly realized by the first electrode portions 113a-1 and 113b-1 having a relatively small electric resistance value. For this reason, the terahertz wave emitting element 110 has the transmittance of the second electrode portions 113a-2 and 113b-2 larger than the first predetermined value instead of satisfying the above-described transmittance condition, A first predetermined value used to indicate that the transmittance of each of the first electrode portions 113a-1 and 113b-1 is relatively high in the transmittance of the second electrode portions 113a-2 and 113b-2. May satisfy the condition that the third predetermined value is irrelevant. That is, the respective transmittances of the first electrode portions 113a-1 and 113b-1 may be the same as or larger than the respective transmittances of the second electrode portions 113a-2 and 113b-2. It can be small. Similarly, in the terahertz wave emitting element 110, instead of satisfying the above-described condition of the electric resistance value, the electric resistance values of the first electrode portions 113a-1 and 113b-1 are smaller than the second predetermined value. The second electrode parts 113a-2 and 113b-2 are used to indicate that the electric resistance values of the first electrode parts 113a-1 and 113b-1 are relatively small. 2 The condition that the value is an arbitrary fourth predetermined value unrelated to the predetermined value may be satisfied. That is, the electrical resistance values of the second electrode portions 113a-2 and 113b-2 may be the same as or smaller than the electrical resistance values of the first electrode portions 113a-1 and 113b-1. It can be big or big. Even in this case, the terahertz wave emitting element 110 can preferably enjoy the above-described effects. The same can be said for the terahertz wave detecting element 130.

  In the above description, the second electrode portions 113a-2 and 113b-2 are described using an example that can function as a so-called dipole antenna. However, the second electrode portions 113a-2 and 113b-2 may be antennas having other shapes. In this case, the second electrode portions 113a-2 and 113b-2 preferably have a shape that can function as an antenna having another shape. As an example of an antenna having another shape, for example, a so-called bow-tie antenna is exemplified. As an example of an antenna having another shape, for example, as shown in FIG. 6, each of the second electrode portions 113 a-2 and 113 b-2 includes a plurality of electrode portions extending along the X-axis direction, and the second electrode An antenna (so-called comb-shaped antenna) in which a plurality of electrode portions provided in the portion 113a-2 and a plurality of electrode portions provided in the second electrode portion 113b-2 are alternately arranged along the Y-axis direction is exemplified. .

  In the above description, the second electrode portion 113a-2 is directly connected to the first electrode portion 113a-1. Similarly, the second electrode portion 113b-2 is directly connected to the first electrode portion 113b-1. However, another electrode part may be formed between the second electrode part 113a-2 and the first electrode part 113a-1. Similarly, another electrode part may be formed between the second electrode part 113b-2 and the first electrode part 113b-1.

  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. The measuring device and the manufacturing method are also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Measurement object 100 Terahertz wave measuring device 101 Pulse laser apparatus 110 Terahertz wave emitting element 111 Substrate 112 Photoconductive layer 113a, 113b Electrode layer 114 Gap part 120 Optical delay mechanism 130 Terahertz wave detecting element 150 Control part 151 Lock-in detection part 152 Signal processor LB1 Pump light LB2 Probe light THz Terahertz wave

Claims (7)

A photoconductive element that emits or detects electromagnetic waves when irradiated with laser light,
A substrate,
A photoconductive layer formed on the substrate;
A pair of electrode layers formed on one surface of the photoconductive layer,
Each of the pair of electrode layers includes: (i) a second electrode portion where the pair of electrode layers are not formed and adjacent to the gap portion to be irradiated with the laser beam; and (ii) the second electrode. A first electrode part electrically connected to the part,
The photoconductive element, wherein the transmittance of the second electrode portion with respect to the laser light is larger than the transmittance of the first electrode portion with respect to the laser light. 2. The photoconductive element according to claim 1, wherein an electrical resistance value per unit length of the first electrode portion is smaller than an electrical resistance value per unit length of the second electrode portion. The film thickness of the said 2nd electrode part is smaller than the film thickness of the said 1st electrode part. The photoconductive element of Claim 1 or 2 characterized by the above-mentioned. The first electrode part is composed of a metal electrode material or a transparent electrode material,
The said 2nd electrode part is comprised from the transparent electrode material. The photoconductive element as described in any one of Claim 1 to 3 characterized by the above-mentioned. Emitting means for emitting electromagnetic waves to the measurement object;
Detecting means for detecting the electromagnetic wave irradiated to the measurement object,
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 4. The measuring device characterized by the above-mentioned. The measuring apparatus according to claim 5, wherein the electromagnetic wave includes a terahertz wave. A manufacturing method for manufacturing the photoconductive element according to any one of claims 1 to 4,
An electrode material on the first region where the first electrode portion is to be formed and the second region where the second electrode portion is to be formed, of the one surface of the photoconductive layer formed on the substrate. Forming a first step;
A second step of masking at least the electrode material formed in the second region;
And a third step of further forming the electrode material or another electrode material on the electrode material formed on the first region and not subjected to the masking.