JP2019169582A - Electromagnetic wave measuring device - Google Patents

Abstract

To provide an electromagnetic wave measuring device having a large dynamic range and capable of detecting electromagnetic waves with high sensitivity.SOLUTION: An electromagnetic wave measuring device includes an electromagnetic wave generating element 20 including a first substrate 21 and a first photoconductive layer 23 epitaxially grown on the first substrate, and an electromagnetic wave detecting element 30 including a second substrate 31 and a second photoconductive layer 33 epitaxially grown on the second substrate, and the degree of deviation of a lattice constant between the first substrate and the first photoconductive layer in the electromagnetic wave generating element is smaller than the degree of deviation of the lattice constant between the second substrate and the second photoconductive layer in the electromagnetic wave detecting element.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a photoconductive element that generates an electromagnetic wave for measurement and an electromagnetic wave measuring apparatus including the photoconductive element that detects the electromagnetic wave.

  Conventionally, a target object is irradiated with a terahertz wave that is an electromagnetic wave in a frequency band (for example, 0.1 to 10 THz) between radio waves and infrared light, and a reflected wave or a transmitted wave from the target object is subjected to time domain spectroscopy. A technique for measuring (analyzing) by means of is known. Such an analysis system includes a photoconductive element that generates a terahertz wave and a photoconductive element that detects a reflected wave or a transmitted wave from an object of the terahertz wave generated by the generating element. For example, Patent Literature 1 discloses a terahertz wave generation detection system including an optical switch as an emitter that generates a terahertz wave and an optical switch as a detector for detecting the terahertz wave.

JP 2006-86227 JP

  For example, when measuring electromagnetic waves, it is preferable that the photoconductive element as the electromagnetic wave generating element generates high output electromagnetic waves, and the photoconductive element as the detection element detects the electromagnetic waves with high sensitivity and high accuracy. .

  For example, when analyzing an object using terahertz time domain spectroscopy, the generation element generates a high-power terahertz wave, the detection element can detect terahertz waves with high sensitivity, and the terahertz wave generated by the detection element It is preferable that the S / N ratio and the dynamic range indicating the detection results are large.

  The present invention has been made in view of the above points, and it is an object of the present invention to provide an electromagnetic wave measuring apparatus that can generate high-power electromagnetic waves and detect electromagnetic waves with high sensitivity and high dynamic range. I am trying.

  According to a first aspect of the present invention, there is provided an electromagnetic wave generating element including a first substrate and a first photoconductive layer epitaxially grown on the first substrate, and a second substrate epitaxially grown on the second substrate and the second substrate. An electromagnetic wave detecting element including two photoconductive layers, and the degree of deviation of the lattice constant between the first substrate and the first photoconductive layer in the electromagnetic wave generating element is the second substrate in the electromagnetic wave detecting element. It is characterized by being smaller than the degree of deviation of the lattice constant between the first photoconductive layer and the second photoconductive layer.

1 is a perspective view of an electromagnetic wave measurement device according to Embodiment 1. FIG. It is a figure which shows the structure of the electromagnetic wave generation element and electromagnetic wave detection element in the electromagnetic wave measuring device which concerns on Example 1. FIG. 1 is a schematic circuit diagram of an optical measurement system including an electromagnetic wave measurement device according to Example 1. FIG. It is a figure which shows the structural example of the electromagnetic wave generation element of the electromagnetic wave measuring device which concerns on Example 1, and an electromagnetic wave detection element. It is a figure which shows the dynamic range of the electromagnetic waves which generate | occur | produced from the electromagnetic wave generation element of the electromagnetic wave measuring device which concerns on Example 1, and the electromagnetic wave generation element which concerns on a comparative example. It is a figure which shows the dynamic range of the electromagnetic waves detected by the electromagnetic wave detection element of the electromagnetic wave measuring device which concerns on Example 1, and the electromagnetic wave detection element which concerns on a comparative example. It is a figure which shows the preferable range of the shift | offset | difference degree of the lattice constant in the electromagnetic wave generating element of the electromagnetic wave measuring device which concerns on Example 1. FIG. It is a figure which shows the preferable range of the shift | offset | difference degree of the lattice constant in the electromagnetic wave detection element of the electromagnetic wave measuring device which concerns on Example 1. FIG. 6 is a perspective view of an electromagnetic wave generation element and an electromagnetic wave detection element in an electromagnetic wave measurement device according to Modification 1 of Embodiment 1. FIG. 6 is a top view of an electromagnetic wave generation element and an electromagnetic wave detection element in an electromagnetic wave measurement device according to Modification 1 of Embodiment 1. FIG.

  Examples of the present invention will be described in detail below.

  FIG. 1 is a perspective view of an electromagnetic wave measuring apparatus (hereinafter, simply referred to as a measuring apparatus) 10 according to the first embodiment. The measuring device 10 receives the pulsed light P1 and generates the electromagnetic wave W1, and detects the electromagnetic wave W2 upon receiving the pulsed light P2 and the electromagnetic wave generating element 20 (hereinafter sometimes referred to as a generating element) 20. An electromagnetic wave detecting element (second photoconductive element, hereinafter may be referred to as a detecting element) 30.

  In the present embodiment, the detection element 30 detects the electromagnetic wave reflected or transmitted by the sample S as the electromagnetic wave W2 after the sample S is irradiated with the electromagnetic wave W1 generated by the generation element 20. That is, the measuring device 10 is an analyzer that generates a terahertz wave and analyzes the sample S using the terahertz wave.

  First, the generating element 20 includes a substrate 21 made of a semiconductor crystal (hereinafter referred to as a first substrate) 21 and a buffer layer 22 made of a semiconductor crystal epitaxially grown on the first substrate 21 using the first substrate 21 as a growth substrate. And a photoconductive layer (hereinafter referred to as a first photoconductive layer) 23 made of a photoconductive semiconductor crystal epitaxially grown on the buffer layer 22.

  The first substrate 21 is made of, for example, single crystal GaAs, InP, Si, or the like. The buffer layer 22 and the first photoconductive layer 23 are made of, for example, GaAs, AlGaAs, InGaP, AlAs, InP, InAlAs, InGaAs, GaAsSb, InGaAsP, InAs, InSb, or the like. In the present embodiment, the first substrate 21, the buffer layer 22, and the first photoconductive layer 23 have a rectangular upper surface shape.

  The first photoconductive layer 23 has an irradiated region 23G of the pulsed light P1, which is a region irradiated with the pulsed light P1. The generation element 20 includes a pair of drive electrodes 24A and 24B (hereinafter referred to as a first electrode pair 24) that are formed on the first photoconductive layer 23 and are spaced apart from each other on the irradiated region 23G of the pulsed light P1. Have. The first electrode pair 24 is made of, for example, a metal film or a transparent conductive film patterned on the first photoconductive layer 23. The first electrode pair 24 is connected to a power source PS such as a voltage source.

  The irradiated region 23G of the pulsed light P1 in the first photoconductive layer 23 corresponds to the region between the drive electrodes 24A and 24B of the first electrode pair 24 on the upper surface of the first photoconductive layer 23. Hereinafter, the irradiated region 23G of the pulsed light P1 is referred to as an interelectrode region of the first photoconductive layer 23.

  When pulse light (pump light) P1 is irradiated to the interelectrode region 23G of the first photoconductive layer 23 in a state where a voltage is applied by the first electrode pair 24, the first photoconductive layer 23 is photoexcited. Carriers (ie photocurrents) are generated. The first photoconductive layer 23 emits an electromagnetic wave W1 having a wavelength (frequency) corresponding to the pulse width of the pulsed light P1.

  In the present embodiment, the generation element 20 emits a terahertz wave by irradiating the interelectrode region 23G of the first photoconductive layer 23 with laser light having a pulse width of femtoseconds as the pulsed light P1. This is a terahertz wave generating element.

  Next, the detection element 30 includes a substrate (hereinafter referred to as a second substrate) 31 made of a semiconductor crystal and a buffer layer made of a semiconductor crystal epitaxially grown on the second substrate 31 using the second substrate 31 as a growth substrate. 32 and a photoconductive layer (hereinafter referred to as a second photoconductive layer) 33 made of a photoconductive semiconductor crystal epitaxially grown on the buffer layer 32.

  The second substrate 31 is made of, for example, single crystal GaAs, InP, Si, or the like. The buffer layer 32 and the second photoconductive layer 33 are made of, for example, GaAs, AlGaAs, InGaP, AlAs, InP, InAlAs, InGaAs, GaAsSb, InGaAsP, InAs, InSb, or the like. In the present embodiment, the second substrate 31, the buffer layer 32, and the second photoconductive layer 33 have a rectangular top surface shape.

  The second photoconductive layer 33 has an irradiated region 33G of the pulsed light P2, which is a region irradiated with the pulsed light P2. The detection element 30 is formed on the second photoconductive layer 33, and a pair of detection electrodes 34A and 34B (hereinafter referred to as a second electrode pair 34) that are separated from each other on the irradiated region 33G of the pulsed light P2. Have. The second electrode pair 34 is made of, for example, a metal film or a transparent conductive film patterned on the second photoconductive layer 33. The second electrode pair 34 is connected to a measuring instrument ME such as an ammeter.

  The irradiated region 33G of the pulsed light P2 in the second photoconductive layer 33 corresponds to the region between the drive electrodes 34A and 34B of the second electrode pair 34 on the upper surface of the second photoconductive layer 33. Hereinafter, the irradiated region 33G of the pulsed light P2 is referred to as an interelectrode region of the second photoconductive layer 33.

  When the electromagnetic wave W2 enters the second photoconductive layer 33 in a state where the inter-electrode region 33G of the second photoconductive layer 33 is irradiated with the pulsed light (probe light) P2, the second photoconductive layer 33 enters the second photoconductive layer 33. The photoexcited carrier (ie photocurrent) varies. This photoexcited carrier appears as a current (detection signal) in the second electrode pair 34. In other words, the detection element 30 detects the electromagnetic wave W2 by irradiating the inter-electrode region 33G of the second photoconductive layer 33 with the pulsed light P2.

  In the present embodiment, the detection element 30 detects a terahertz wave by irradiating the inter-electrode region 33G of the second photoconductive layer 33 with a laser beam having a femtosecond pulse width as the pulsed light P2. This is a terahertz wave detecting element.

  Thus, in the present embodiment, the generation element 20 receives the laser beam pulsed to have a femtosecond pulse width as the pulsed light P1, and emits a terahertz wave as the electromagnetic wave W1. The detection element 30 receives the same laser beam as the pulsed light P1 as the pulsed light P2, and detects a terahertz wave as the electromagnetic wave W2.

  In the present embodiment, the generation element 20 and the detection element 30 have the light having a light energy larger than the band gap of the first and second photoconductive layers 23 and 33 as the first pulse light P1 and P2. The second photoconductive layers 23 and 33 are irradiated to perform the generation operation of the electromagnetic wave W1 and the detection operation of the electromagnetic wave W2, respectively.

  Specifically, in the first and second photoconductive layers 23 and 33, a photoelectric effect is generated by the light energy of the pulsed light P1 and P2, respectively, and thereby photoexcited carriers for generating and detecting electromagnetic waves W1 and W2 Is generated. In the present embodiment, the generation element 20 and the detection element 30 are configured such that light having a wavelength in the range of 1.45 to 1.65 μm is emitted as the first and second photoconductive layers 23 and 1 as pulsed light P1 and P2. By irradiating 33, the operation of generating the electromagnetic wave W1 and the operation of detecting the electromagnetic wave W2 are performed.

FIG. 2 is a diagram illustrating a configuration relationship between the generation element 20 and the detection element 30. In the present embodiment, the first substrate 21 of the generating element 20 is made of a cubic semiconductor crystal having a lattice constant a ₁ . The first photoconductive layer 23 of the generating element 20 is made of a cubic semiconductor crystal having a lattice constant a ₂ . Note that the buffer layer 22 of the generating element 20 is made of a cubic semiconductor crystal having a lattice constant within a range between the lattice constant a ₁ and the lattice constant a ₂ .

The second substrate 31 of the detection element 30 is made of a cubic semiconductor crystal having a lattice constant a ₃ . The second photoconductive layer 33 of the detection element 30 is made of a cubic semiconductor crystal having a lattice constant a ₄ . The buffer layer 32 of the detection element 30 is made of a cubic semiconductor crystal having a lattice constant within a range between the lattice constant a ₃ and the lattice constant a ₄ .

Here, in the present embodiment, the degree D ₁ of lattice constant deviation between the first substrate 21 and the first photoconductive layer 23 in the generating element 20 is defined by the following formula 1.

また、検出素子３０における第２の基板３１と第２の光伝導層３３との間の格子定数のずれ度合Ｄ₂を、以下の式２で定義する。

Further, the degree D ₂ of lattice constant deviation between the second substrate 31 and the second photoconductive layer 33 in the detection element 30 is defined by the following formula 2.

そして、計測装置１０においては、発生素子２０における上記した格子定数のずれ度合Ｄ₁は、検出素子３０における上記した格子定数のずれ度合Ｄ₂よりも小さくなる（Ｄ₁＜Ｄ₂の関係を満たす）ように構成されている。

In the measuring apparatus 10, the above-described lattice constant deviation degree D ₁ in the generation element 20 is smaller than the above-described lattice constant deviation degree D ₂ in the detection element 30 (the relation of D ₁ <D ₂ is satisfied). ) Is configured as follows.

  In the present embodiment, the degree of deviation of the lattice constant is defined as indicating the magnitude of the difference between the lattice constants when the average value of each lattice constant is used as a reference. In this example, as indicated by the above formula, the degree of deviation of the lattice constant was quantified as a percentage. In the present embodiment, the generation element 20 and the detection element 30 are configured such that the numerical value of the degree of deviation of the lattice constant satisfies the relationship described above.

  FIG. 3 is a circuit diagram schematically showing a configuration of an optical measurement system (hereinafter simply referred to as a measurement system) 60 using the terahertz time domain spectroscopy including the measurement apparatus 10. The measurement system 60 will be described with reference to FIG. Hereinafter, the electromagnetic wave W1 emitted from the generating element 20 will be described as a terahertz wave, and the electromagnetic wave W2 incident on the detection element 30 will be described as a terahertz wave.

  The measurement system 60 places the sample (measurement object) S in the path through which the terahertz wave W1 generated by the generation element 20 propagates, and transmits the sample S (or reflected by the sample S or the like). And the time waveform of the terahertz wave W2 without the sample S are Fourier transformed to obtain information on the amplitude and phase of the terahertz wave W2. The measurement system 60 can measure detailed physical properties such as the complex refractive index and complex dielectric constant of the sample S, for example.

  The measurement system 60 includes a laser irradiation device 61 that generates femtosecond pulsed laser light as the pulsed light P1 and P2, a beam splitter 62 that separates the pulsed light P1 and P2 from the laser irradiation device 61, the generation element 20 and the detection. Including a device 30, a delay circuit 63 that delays the pulsed light P2 incident on the detection device 30, a power source PS that applies a voltage to the generation device 20, a measuring device ME that measures a detection signal from the detection device 30, and the same And a signal processing circuit 68.

  The measurement system 60 has a general configuration as a measurement system using time domain spectroscopy. For example, the measurement system 60 is bonded to the generating element 20 and the first optical system 64 such as a hemispherical lens that efficiently extracts the terahertz wave W1 and the hemispherical lens that is bonded to the detecting element 30 and efficiently captures the terahertz wave W2. The second optical system 65 is included.

  First, laser light including pulsed light P1 and P2 emitted from the laser irradiation device 61 is divided into pump light (pulsed light P1) and probe light (pulsed light P2) by the beam splitter 62.

  The pulsed light P1 is collected by the condensing lens CL1 and enters the interelectrode region 23G of the generating element 20. The generating element 20 generates a terahertz wave W <b> 1 by applying a voltage to the first electrode pair 24. The terahertz wave W <b> 1 passes through the first optical system 64, is collected by the third optical system 66, and is applied to the sample S. The terahertz wave W <b> 2 that has passed through the sample S is collected by the fourth optical system 67 and is incident on the detection element 30 via the second optical system 65.

  On the other hand, the pulsed light P2 is given a time delay by the delay circuit 63 having a plurality of reflecting mirrors M, is condensed by the condenser lens CL2, and is incident on the inter-electrode region 33G of the detection element 30. The signal detected by the detection element 30 is measured by the measuring instrument ME and input to the signal processing circuit 68.

  The signal processing circuit 68 stores the time waveform of the terahertz wave W2 that has passed through the sample S and the time waveform of the terahertz wave W2 in the absence of the sample S as time-series data, respectively, and performs Fourier transform processing on this in the frequency space. Convert. In this way, the measurement system 60 obtains a spectrum of intensity amplitude and phase of the terahertz wave W2 from the sample S.

FIG. 4 is a diagram illustrating a detailed configuration example of the generation element 20 and the detection element 30. In the present embodiment, the first substrate 21 of the generating element 20 has an InP composition. In this case, the lattice constant a ₁ of the first substrate 21 is about 5.8687Å. In addition, the first photoconductive layer 23 of the generating element 20 has a composition of In ₅₃ Ga ₄₇ As. In this case, the lattice constant a ₂ of the first photoconductive layer 23 is about 5.8687Å. Therefore, the deviation degree D ₁ between the lattice constant a ₁ and the lattice constant a ₂ is about 0%. In the present embodiment, the buffer layer 22 of the generating element 20 is made of a semiconductor crystal having the same lattice constant (about 5.8687Å) as the first substrate 21 and the first photoconductive layer 23. Having a composition.

In the present embodiment, the second substrate 31 of the detection element 30 has a GaAs composition. In this case, the lattice constant a ₃ of the second substrate 31 is about 5.65325Å. The second photoconductive layer 33 of the detection element 30 has a composition of In ₅₃ Ga ₄₇ As and contains Be as a dopant. In this case, the lattice constant a ₄ of the second photoconductive layer 33 is about 5.8687Å. Accordingly, the degree of deviation D ₂ between the lattice constant a ₃ and the lattice constant a ₄ is about 3.7%. In the present embodiment, the buffer layer 32 of the detection element 30 is made of a semiconductor crystal having a lattice constant between the second substrate 31 and the second photoconductive layer 33 and has, for example, a composition of InAlAs.

FIG. 5 is a diagram illustrating a dynamic range of the terahertz wave W1 that is the electromagnetic wave W1 generated by the generating element 20, and a dynamic range of the terahertz wave generated by the generating element 110 according to the comparative example. The generation element 110 according to the comparative example includes a buffer layer 22 and a first photoconductive layer 23 epitaxially grown on a GaAs substrate having a GaAs composition instead of the InP substrate as the first substrate 21. In the generation element 110, the lattice constant deviation degree D ₀₁ between the GaAs substrate and the first photoconductive layer 23 is about 3.7% when calculated using Equation 1 similar to that of the generation element 20. .

As shown in FIG. 5, it can be seen that the generation element 20 generates a terahertz wave with a higher dynamic range than the generation element 110 according to the comparative example. This is because, in the generation element 20, the first photoconductive layer 23 having a lattice constant a ₂ having a small deviation D ₁ with respect to the lattice constant a ₁ of the first substrate 21 is grown. This is probably because the first photoconductive layer 23 is formed.

  Specifically, almost no crystal defects (for example, dislocations) are generated in the first photoconductive layer 23 having high crystallinity, and as a result, many carriers with high mobility are generated in the first photoconductive layer 23. It becomes. Therefore, it is considered that a high-power terahertz wave is generated from the generating element 20.

  Next, FIG. 6 is a diagram illustrating a dynamic range indicating the detection result of the electromagnetic wave (terahertz wave) W2 by the detection element 30 and a dynamic range indicating the detection result of the terahertz wave by the detection element 120 according to the comparative example. .

The detection element 120 according to the comparative example includes a buffer layer 32 and a second photoconductive layer 33 that are epitaxially grown on an InP substrate having an InP composition instead of the GaAs substrate as the second substrate 31. In the detection element 120, the lattice constant deviation degree D ₀₂ between the InP substrate and the second photoconductive layer 33 is about 0% when calculated using Expression 2 similar to that of the detection element 30. In order to obtain the result shown in FIG. 6, a measurement system in which the detection element 30 and the detection element 120 were replaced in the measurement system 60 was prepared, and terahertz waves obtained by the measurement system were detected.

As shown in FIG. 6, it can be seen that the detection element 30 has detected the terahertz wave in a higher dynamic range than the detection element 120 according to the comparative example. This is because, in the detection element 30, the second photoconductive layer 33 having a lattice constant a ₄ having a relatively large deviation degree D ₂ with respect to the lattice constant a ₃ of the second substrate 31 is grown. This is probably because the second photoconductive layer 33 having a relatively low crystallinity was formed.

  Specifically, the relatively low crystalline second photoconductive layer 33 has a relatively short carrier lifetime. That is, carriers generated by the incidence of the terahertz wave disappear in a relatively short time. Thus, it is considered that the terahertz wave was detected from the detection element 30 with a high dynamic range.

In this embodiment, the crystallinity of the first photoconductive layer 23 is more than the difference between the simple lattice constants a ₁ and a ₂ between the first substrate 21 and the first photoconductive layer 23. The structure of the generating element 20 is determined by using the lattice constant deviation degree D ₁ as an index directly connected to. Similarly, the configuration of the second substrate 31 and the second photoconductive layer 33 is also determined for the detection element 30 using the lattice constant deviation degree D ₂ . This is because the quantitative value indicating crystallinity strongly depends on the ratio between lattice constants. Therefore, the generating element 20 surely has a preferable configuration for generating the electromagnetic wave W1 at a high output. Moreover, the detection element 30 will certainly have a preferable configuration for detecting the electromagnetic wave W2 with high accuracy and dynamic range.

In the present embodiment, the case where the generating element 20 is constituted by the first substrate 21 and the first photoconductive layer 23 having the deviation degree D ₁ of about 0% has been described. In the present embodiment, the case where the detection element 30 is configured by the second substrate 31 and the second photoconductive layer 33 having a deviation degree D2 of about 3.7% has been described. However, the configuration of the generation element 20 and the detection element 30 is not limited to this.

FIG. 7 is a diagram illustrating a preferable range of the lattice constant deviation degree D ₁ in the generation element 20. FIG. 7 is a diagram illustrating a relationship between the shift degree D ₁ and the amplitude of the detection signal of the generated terahertz wave. As shown in FIG. 7, for example, a pulsed light P1 having a wavelength in the range of 1.45 to 1.65 μm is received to generate a high-output terahertz wave in a wavelength band of 30 to 3000 μm and a detection signal having a high amplitude. In consideration of obtaining it, the deviation degree D ₁ of the lattice constant between the first substrate 21 and the first photoconductive layer 23 in the generating element 20 is preferably 1.3% or less, and more preferably 0 to 0. It can be seen that it is preferably within the range of 9%.

FIG. 8 is a diagram illustrating a preferable range of the lattice constant deviation degree D2 in the detection element 30. FIG. FIG. 8 is a diagram illustrating a relationship between the shift degree D2 and the amplitude of the detection signal of the terahertz wave. As shown in FIG. 8, in consideration of detecting terahertz waves in a wavelength band of 30 to 3000 μm with high detection sensitivity and dynamic range upon receiving pulsed light P2 having a wavelength in the range of 1.45 to 1.65 μm, The deviation D ₂ of the lattice constant between the second substrate 31 and the second photoconductive layer 33 in the detection element 30 is preferably 2.5% or more, and more preferably 2.8 to 4.2%. It can be seen that it is preferable to be within the range.

However, the semiconductor crystal used as the first photoconductive layer 23 of the generating element 20 preferably has a relatively high crystallinity, and the semiconductor crystal used as the second photoconductive layer 33 of the detection element 30 is a crystal lower than this. It is preferable to have the property. Accordingly, as described above, the lattice constant deviation degree D ₁ between the first substrate 21 and the first photoconductive layer 23 in the generating element 20 is the second substrate 31 and the second photoconductive in the detection element 30. What is necessary is just to be smaller than the deviation degree D ₂ of the lattice constant with the layer 33.

  In consideration of the stable growth of the first photoconductive layer 23 and the second photoconductive layer 33 so as to have a crystallinity within a preferable range, the generation element 20 and the detection element 30 include the buffer layer 22. And 32 respectively.

In particular, the detection element 30 preferably has a stable and high detection sensitivity and a high detection dynamic range. Accordingly, the detection element 30 is provided between the second substrate 31 and the second photoconductive layer 33, and the second substrate 31 (lattice constant a ₃ ) and the second photoconductive layer 33 (lattice constant a). It is preferable to have a buffer layer 32 made of a semiconductor crystal having a lattice constant between ₄ ) and ₄ ).

  Similarly, when the buffer layer 22 is provided in the generating element 20, the buffer layer 22 is preferably composed of a semiconductor crystal having a lattice constant between the first substrate 21 and the first photoconductive layer 23. .

  In the present embodiment, the case where the first substrate 21, the buffer layer 22, and the first photoconductive layer 23 of the generating element 20 have the compositions of InP, InGaAs, and InGaAs, respectively, has been described. In the present embodiment, the case where the second substrate 31, the buffer layer 32, and the second photoconductive layer 33 of the detection element 30 have compositions of GaAs, InAlAs, and InGaAs, respectively, has been described.

  However, the generation element 20 and the detection element 30 can be configured using the various semiconductor materials described above as long as the relationship of the lattice constant deviation degree is satisfied. In consideration of forming the generation element 20 and the detection element 30 as elements for generating and detecting terahertz waves and obtaining preferable crystallinity, the first substrate 21 and the first photoconductive layer having the above-described composition are used. 23, the second substrate 31 and the second photoconductive layer 33 are preferably used.

  Further, the configuration of the first electrode pair 24 and the second electrode pair 34 described above is merely an example. For example, in the present embodiment, the first electrode pair 24 and the second electrode pair 34 are configured to form a dipole antenna. However, the first electrode pair 24 and the second electrode pair 34 may be configured and arranged to form an arbitrary antenna such as a bowtie antenna, a stripline antenna, or a spiral antenna.

As described above, in this embodiment, the measuring apparatus 10 is epitaxially grown on the first substrate 21 made of the semiconductor crystal having the lattice constant a _{1 and} the semiconductor substrate having the lattice constant a ₂ . The electromagnetic wave generating element 20 including the first photoconductive layer 23, the second substrate 31 made of a semiconductor crystal having a lattice constant a ₃ , and the semiconductor crystal having a lattice constant a ₄ and epitaxially grown on the second substrate 31. And an electromagnetic wave detection element 30 including the second photoconductive layer 33.

In addition, the degree D ₁ of lattice constant deviation between the first substrate 21 and the first photoconductive layer 23 in the electromagnetic wave generating element 20 is expressed as follows:

の式１で定義し、電磁波検出素子３０における第２の基板３１と第２の光伝導層３３との間の格子定数のずれ度合Ｄ₂を、

The lattice constant deviation degree D ₂ between the second substrate 31 and the second photoconductive layer 33 in the electromagnetic wave detection element 30 is defined as

の式２で定義した場合、当該ずれ度合Ｄ₁は、当該ずれ度合Ｄ₂よりも小さい。従って、高出力の電磁波Ｗ１を発生させ、かつ高感度かつ高ダイナミックレンジで電磁波Ｗ２を検出することが可能な電磁波計測装置１０を提供することができる。

In this case, the deviation degree D ₁ is smaller than the deviation degree D ₂ . Therefore, it is possible to provide the electromagnetic wave measuring apparatus 10 that can generate the high-power electromagnetic wave W1 and detect the electromagnetic wave W2 with high sensitivity and high dynamic range.

  FIG. 9 is a perspective view of the generation element 20 and the detection element 30A in the measurement apparatus 10A according to the modification of the first embodiment. FIG. 10 is a schematic top view of the generation element 20 and the detection element 30A. The measurement apparatus 10A will be described with reference to FIGS.

  The measurement apparatus 10A has the same configuration as the measurement apparatus 10 except for the configuration of the detection element 30A. In this modification, the detection element 30 </ b> A has the same configuration as the detection element 30 except for the configuration of the second photoconductive layer 35. The second photoconductive layer 35 has a smaller upper surface size than the first photoconductive layer 23.

  More specifically, as shown in FIG. 10, the first photoconductive layer 23 has an upper surface 23S having an irradiated region 23G of the pulsed light P1. On the other hand, the second photoconductive layer 35 has an irradiated region 35G of the pulsed light P2 and has an upper surface 35S that is smaller than the upper surface 23S of the first photoconductive layer 23.

  In the present modification, the second substrate 31 of the detection element 30A has the same shape as the first substrate 21 of the generation element 20 and has the same top surface size. In addition, the first photoconductive layer 23 of the generating element 20 is formed on the entire first substrate 21.

  On the other hand, the second photoconductive layer 35 of the detection element 30 </ b> A is formed only in a partial region on the second substrate 31. For example, most of the upper surface 35S of the second photoconductive layer 35 is covered with the second electrode pair 36 (first and second detection electrodes 36A and 36B) except for the irradiated region 35G of the pulsed light P2. ing. In the present modification, the upper surface of the buffer layer 32 is partially exposed.

  Since the second photoconductive layer 35 of the detection element 30A has a smaller upper surface 35S than the first photoconductive layer 23 of the generation element 20, the dynamic range indicating the detection result of the terahertz wave by the detection element 30A is increased.

  Specifically, the second photoconductive layer 35 has a structure in which the irradiated region 35G of the pulsed light P2 that is the detection region of the electromagnetic wave W2 is left and other regions are partially removed. This suppresses the generation of excited carriers in a region other than the irradiated region 35G that is not irradiated with the pulsed light P2. Note that generation of excited carriers in a region other than the irradiated region 35G may lead to generation of noise.

  On the other hand, in the generating element 20, it is preferable that the first photoconductive layer 23 has a large volume in consideration of generating many electromagnetic waves W1. Therefore, by reducing the upper surface 35S of the second photoconductive layer 35 and making its area (volume) smaller than that of the first photoconductive layer 23, generation of noise in the output from the detection element 30A is suppressed, Detection sensitivity and detection accuracy will be improved.

  As shown in FIG. 10, in this modification, the detection element 30A is formed on the second photoconductive layer 35, and on the irradiated region 35G of the pulsed light P2 in the second photoconductive layer 35. It has the 2nd electrode pair 36 which consists of the 1st and 2nd detection electrodes 36A and 36B spaced apart from each other. Further, the second electrode pair 36 is separated by a distance that is smaller than the separation distance of the first electrode pair 24 of the generating element 20.

  More specifically, in the present modification, as shown in FIG. 10, the first and second drive electrodes 24A and 24B in the generating element 20 are first and second opposing portions 24A1 that face each other. And 24B1. The first and second facing portions 24A1 and 24B1 are disposed to face each other with a first distance G1.

  The first drive electrode 24A has a first connection portion 24A2 connected to the first facing portion 24A1. The second drive electrode 24B has a second connection portion 24B2 connected to the second facing portion 24B1.

  In other words, the generating elements 20 are formed on the first photoconductive layer 23 and are separated from each other by a first distance G1 on the irradiated region 23G of the pulsed light P1 in the first photoconductive layer 23. A first electrode pair 24 is provided.

The first and second detection electrodes 36A and 36B in the detection element 30A are respectively
The first and second facing portions 36A1 and 36B1 are opposed to each other at a second distance G2. The first detection electrode 36A has a first connection portion 36A2 connected to the first facing portion 36A1. The second detection electrode 36B has a second connection portion 36B2 connected to the second facing portion 36B1.

  In other words, the detection element 30 </ b> A is formed on the second photoconductive layer 35, and on the second photoconductive layer 35 on the irradiated region 35 </ b> G of the pulsed light P <b> 2, the second smaller than the first distance G <b> 1. A second electrode pair 36 is provided that is separated from each other by a distance G2.

  By making the separation distance of the second electrode pair 36 in the detection element 30A smaller than the separation distance of the first electrode pair 24 in the generation element 20, the generation amount of the electromagnetic wave W1 is improved in the generation element 20, and the detection element 30A. Then, the detection accuracy of the electromagnetic wave W2 is improved.

  Specifically, in the generating element 20, the first electrode pair 23 is relatively separated from each other to increase the carrier generation region, and the output of the electromagnetic wave W1 is improved. Further, in the detection element 30A, generation of unnecessary carriers that may hinder detection accuracy is suppressed by reducing the separation distance of the second electrode pair 36. Therefore, noise generation in detection is suppressed.

  As described above, in this modification, not only the deviation of the lattice constant between the generation element 20 and the detection element 30A, but also the top surface shapes of the first and second photoconductive layers 23 and 35, and the first and second The distance between the second electrode pair 24 and 36 is adjusted. Thus, it is possible to provide an electromagnetic wave measurement device 10A that can generate the high-power electromagnetic wave W1 and can detect the electromagnetic wave W2 with high sensitivity and high dynamic range.

  In this modification, the generation element 20 has the first photoconductive layer 23 formed on the entire surface of the first substrate 21, and the detection element 30A is partially removed from the second photoconductive layer. The case where the layer 35 is provided has been described.

  However, the configuration of the first and second photoconductive layers 23 and 35 is not limited to this. The area of the upper surface 35S of the second photoconductive layer 35 of the detection element 30A only needs to be smaller than the area of the upper surface 23S of the first photoconductive layer 23 of the generating element 20.

10, 10A Electromagnetic wave measuring device 20 Electromagnetic wave generating element 21 First substrate 22 Buffer layer 23 First photoconductive layer 30, 30A Electromagnetic wave detecting element 31 Second substrate 32 Buffer layer 33, 35 Second photoconductive layer

Claims (7)

An electromagnetic wave generating element comprising: a first substrate made of a semiconductor crystal having a lattice constant a ₁ ; and a _first photoconductive layer made of a semiconductor crystal having a lattice constant a ₂ and epitaxially grown on the first substrate;
An electromagnetic wave detecting element including a second substrate made of a semiconductor crystal having a lattice constant a ₃ and a second photoconductive layer made of a semiconductor crystal having a lattice constant a ₄ and epitaxially grown on the second substrate,
The lattice constant deviation degree D ₁ between the first substrate and the first photoconductive layer in the electromagnetic wave generating element is expressed as follows:

The degree of lattice constant deviation D ₂ between the second substrate and the second photoconductive layer in the electromagnetic wave detecting element is defined by:

In the electromagnetic wave measuring apparatus, the deviation degree D ₁ is smaller than the deviation degree D ₂ . The first substrate and the first photoconductive layer are made of a semiconductor crystal having a lattice constant in which the deviation degree D ₁ is 1.3% or less,
2. The electromagnetic wave measuring apparatus according to claim 1, wherein the second substrate and the second photoconductive layer are made of a semiconductor crystal having a lattice constant in which the deviation degree D ₂ is 2.5% or more. The electromagnetic wave detecting element is formed between the second substrate and the second photoconductive layer, and is made of a semiconductor crystal having a lattice constant within a range between the lattice constant a ₃ and the lattice constant a _4. The electromagnetic wave measuring device according to claim 1, further comprising a buffer layer. The first substrate of the electromagnetic wave generating element has a composition of InP;
The first photoconductive layer of the electromagnetic wave generating element has a composition of InGaAs;
The second substrate of the electromagnetic wave detection element has a composition of GaAs;
The electromagnetic wave measuring apparatus according to any one of claims 1 to 3, wherein the second photoconductive layer of the electromagnetic wave detecting element has a composition of InGaAs.   The electromagnetic wave generation element and the electromagnetic wave detection element perform an electromagnetic wave generation operation and a detection operation, respectively, when irradiated with pulsed light having a wavelength in the range of 1.45 to 1.65 μm. The electromagnetic wave measurement apparatus according to any one of 1 to 4. The first photoconductive layer of the electromagnetic wave generating element has an upper surface having an irradiated region of the pulsed light,
6. The second photoconductive layer of the electromagnetic wave detection element has an upper surface smaller than the upper surface of the first photoconductive layer and has an irradiated region of the pulsed light. The electromagnetic wave measuring apparatus of description. The electromagnetic wave generating element has a first electrode pair formed on the first photoconductive layer and spaced apart from each other at a first distance on the irradiated region of the pulsed light,
The electromagnetic wave detection elements are second electrodes formed on the second photoconductive layer and separated from each other at a second distance smaller than the first distance on the irradiated region of the pulsed light. It has a pair, The electromagnetic wave measuring device of Claim 6 characterized by the above-mentioned.

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