JP2006237313A - Electromagnetic wave generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the plasma wave strength is reduced by the fact that plasma waves are out of phase with each other. <P>SOLUTION: This electromagnetic wave generating device comprises a semiconductor substrate 5, a plurality of nano-wire-shaped semiconductor layers 4, an insulating film 6, a plurality of gate electrodes 1 whose gate length is made equal to 1/4 of the plasma wave period, a plurality of drain electrodes 3 corresponding to the plurality of nano-wires, and a source electrode 2. The plurality of drain electrodes are electromagnetically coupled to each other by injection synchronization to suppress the canceling due to antiphase, so that the strength of the plasma wave is multiplied by the number of nano-wires. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor element that operates in a high frequency region of about 1 THz.

  Conventional semiconductor elements have been improved in operation speed mainly by miniaturizing the element structure. For example, a high electron mobility transistor effectively suppresses impurity scattering by using a two-dimensionally distributed two-dimensional electron gas, but the high-speed operation up to several hundred GHz has been reported. For the formation, an ultrafine processing technique of at least 30 nm or less is required. This is because charge (electron) movement is used for signal transmission, and the movement speed is limited by the saturation speed of the material, so that delay due to channel travel time cannot be avoided.

  As a prior art for this problem, several semiconductor elements that do not directly transfer charges in signal transmission have been proposed. One is an element that utilizes plasma oscillation of a high-concentration electron fluid in an FET channel proposed by M. Shur et al. (See Non-Patent Documents 1 and 2). The electron density wave corresponding to the oscillation frequency of the plasma oscillation is hereinafter referred to as a plasma wave, and an element in which a plasma wave is formed in a channel is defined as a plasma wave element. FIG. 10 shows the structure of the plasma wave element shown in Non-Patent Document 1. It has a structure similar to that of a high electron mobility field effect transistor (FET, HEMT), and a plasma wave is formed in the two-dimensional electron gas 54. In Non-Patent Document 2, it is observed that a plasma wave oscillating at about 1 THz is formed in the two-dimensional electron gas 54 of FIG. 10 and a weak (about several nW) electromagnetic wave is radiated.

  In addition, Ideshita shows an electromagnetic wave amplifying element using the two-fluid instability phenomenon that occurs in a system in which two fluids, that is, a heavy fluid consisting of holes and electrons as shown in FIG. It has been proposed (see Patent Document 1). By using the slow wave circuit 61 having a comb electrode structure, the terahertz wave introduced to the input unit 65 is amplified and extracted from the output unit 66.

  In the present invention, a plurality of periodic gate electrodes 1 are provided as shown in FIG. On the other hand, although it does not have the purpose of generating a plasma wave, a photoconductive element (see Non-Patent Document 3) by XG Peralta et al. Is shown in FIG. FIG. 12B shows a conductance modulation element (see Non-Patent Document 4) by AM Hashim et al.

Further, in the present invention, injection locking is performed inside the element using the antenna element 11 as shown in FIG. Although not a plasma wave element, as an antenna configuration for performing injection locking using an oscillation element such as an FET, FIG. 13 shows an active antenna for transmission (see Patent Document 2) by Fujii et al. FIG. 14 shows a resonator that performs power combining (see Patent Document 3) as a general technical level for performing injection locking.
JP-A-8-139306 Japanese Utility Model Publication No. 6-73909 JP 2000-77946 A Phys. Rev. Lett. V71 (1993) p2465 Appl. Phys. Lett. 84 (2004) 2331 Appl. Phys. Lett. 81 (2002) 1627 Ext. Abst. 2004 Int. Conf. Solid State Dev. And Mat. (2004) 664

  In Non-Patent Documents 1 and 2, although theoretical operation enables high-frequency operation, in practice, electromagnetic waves are extremely weak or the operation range is limited. Further, in Patent Document 1, there is a problem that the structure is extremely complicated, and it is necessary to introduce an electromagnetic wave for amplification from the outside, which is not practical. In particular, the structure according to Non-Patent Document 2 is the first case where generation of electromagnetic waves at a high frequency is observed without irradiating light or the like from the outside. It can be considered as one of the factors that prevent it.

  The structures shown in Non-Patent Documents 3 and 4 have a periodic electrode structure, but these are not intended to generate electromagnetic waves, and in order to receive plasma waves irradiated from the outside, Its purpose is to combine efficiently with waves. Therefore, the width of the electrode corresponding to the gate length of the FET is half of the period of the electrode.

  As a result of examining the refractive index of the plasma wave in the channel of the FET, it has been clarified that the refractive index is as large as about 300. As a result, for example, in Non-Patent Document 3, it is considered that a plasma wave having 1 to 2 wavelengths is excited below one electrode. Further, in Non-Patent Document 4, the wavelength of the plasma wave formed under the electrode is 0.15 wavelength, which is considered not to be coupled with the plasma wave at all. In Non-Patent Document 4, the expected negative conductance is not observed. Thus, even if the gate electrode is formed periodically, if the purpose is not to generate a plasma wave, the period and width of the electrode take specific values so as to match the wavelength of the plasma wave. You can see that it is not.

  Therefore, the number of gate electrodes and the number of nanowires are reduced by arranging the gate electrodes with a period Λ of the wavelength of the plasma wave, setting the length of the gate electrodes (gate length L) to Λ / 4, and arranging a plurality of nanowires. We decided to increase the intensity of electromagnetic waves in proportion to the number.

  However, when a plurality of nanowires are arranged, if the nanowires are not produced with good uniformity, the refractive index changes by changing the velocity of the plasma wave due to variations in the voltage applied to the nanowire channel region. As a result, it was found that the phase of the plasma wave also changed. FIG. 4 shows a conceptual diagram of plasma wave intensity when a plurality of nanowires are arranged. As shown in FIG. 4A, when the drain electrode is shared, if the nanowire has a structural variation and the phase of the plasma wave slightly varies, There was a problem that the output was canceled and the output decreased. In the case of the figure, there are five nanowires, but the output of electromagnetic waves can only be output from one nanowire. When the nanowire width is large, this phase reversal is caused by a partial difference in the thickness of the insulating film between the nanowire and the electrode, which can be improved by controlling the uniformity of the insulating film very precisely. In order to improve the yield, a device structure in which the phase does not change even if the uniformity of the film thickness varies somewhat is required. In addition, when the cross-sectional area of the nanowire is reduced in order to increase the output, there is a problem that the influence of the variation in the cross-sectional area of the nanowire increases and the variation in carrier density increases. When the width of the nanowire is about half the wavelength of the plasma wave, it is difficult to be affected by variations in the cross-sectional area, but when the width is 100 nm or less, the carrier density increases as the width is reduced. Accordingly, the device structure of the present invention that is not easily affected by variations in the width of the nanowire is required particularly when the width of the nanowire is 100 nm or less.

  The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide a semiconductor device based on a novel operation principle with high yield by utilizing stably coupled plasma oscillation.

In order to solve the above-described conventional problems, the electromagnetic wave generator of the present invention includes a plurality of nanowires as shown in FIG. 1, and a drain electrode is individually installed on each nanowire. The gap is capacitively coupled by a capacitive coupling portion 10 made of a thin conductive wire so that only a high-frequency component of a specific wavelength is guided. Alternatively, between the drain electrodes, a high frequency component is cut by a filter structure having an L component so that only a DC component can be applied, and the antenna element 11 is capacitively coupled. Electromagnetic waves generated by plasma waves generated in each nanowire are radiated in the vicinity through the capacitive coupling portion 10 or the antenna 11 formed on the drain electrode. As a result, since the injection locking between the antennas whose phases are matched as shown in FIG. 4 (b) occurs, when the number of antennas matched in phase and n _n1, the peak intensity of the plasma wave spectrum P _P is one of Compared to the case, (n _n1 ) increases ^3/2 times. As shown in FIG. 4C, in the case of (b), since injection locking occurs in each phase, multimode plasma waves are generated in the entire nanowire, and cancellation due to phase inversion occurs. Disappear. As a result, it was found that the integrated intensity of the plasma wave did not decrease (P∝Σn _n1 ).

  Furthermore, as shown in FIG. 8, by using the electromagnetic wave from the antenna element formed on the drain electrode, injection locking is performed between the drain electrode and the gate electrode, thereby improving the phase matching and suppressing the multimode. Made possible.

  In the structure of Patent Document 2 shown in FIG. 13, injection locking is performed between the gate electrodes of the oscillation element 85 using the coupling circuit 82, and injection locking using the antenna 83 is not performed. The present invention is different in that the drain electrodes are electromagnetically coupled to perform injection locking. As a result, in the present invention, the resonator 84 and the coupling circuit 82 are not required, and the size can be reduced.

  Further, in Patent Document 3 shown in FIG. 14, a Gunn diode is installed in the fundamental mode waveguide 94, and the electromagnetic wave reflected by the reflecting plate 93 is coupled to the fundamental mode waveguide 94 again. Power combining is performed by synchronizing, and one Gunn diode is arranged in each fundamental mode waveguide 94. In the present invention, each nanowire is integrated on the same substrate, and power combining is possible by arranging a high impedance lead wire between the drain electrodes without using a waveguide array. Compared with the case where a wave tube is used, the size can be extremely reduced. In addition, unlike the case where electromagnetic waves are coupled to the entire Gunn diode, in the case of the plasma wave device of the present invention, the drain electrode is open, so that the drain ends of all the nanowires have the largest electromagnetic wave amplitude (antinode part). The electromagnetic coupling is realized with very high efficiency.

  As described above, according to the present invention, in the electromagnetic wave generator that forms a plurality of nanowire structures and shares a plurality of gate electrodes, by performing injection locking, there is a variation in the phase of the plasma wave due to a variation in the process. In addition, the plasma wave intensity can be added and the Q value is increased to provide a high-power electromagnetic wave generating element.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) <When nanowire width is 20 nm or more>
FIG. 1 is a schematic diagram of an electromagnetic wave generating element according to Embodiment 1 of the present invention. Also in FIG. 1 and subsequent figures, the same components are denoted by the same reference numerals, and description thereof is omitted.

  1A and 3A, the semiconductor layer 4 is deposited on the substrate 5 with the insulating layer 6 interposed therebetween. Here, since Ge is used for the semiconductor layer, a so-called GOI structure is employed. The semiconductor layer 4 has a nanowire 4 structure having a width of 400 nm or less by etching. This is because the wavelength of the plasma wave formed in the nanowire is 800 nm, and it is necessary to set the wavelength to 400 nm or less, which is a half wavelength, in order to obtain a single transverse mode. As the nanowire is made thinner, the conducting electrons are strongly affected by surface scattering, and scattering other than electron-electron scattering becomes significant. Therefore, the width of the nanowire needs to be 3 nm or more. The periphery of the nanowire 4 is covered with an insulating film 7 made of silicon oxide or the like to protect it from the influence of ambient humidity or the like. A gate electrode 1 is formed on the insulating film 7 in a direction perpendicular to the nanowire 4. In the present embodiment, Ge is used for the semiconductor layer. This is because when Si is used, the effective mass is large, so that the generation of plasma waves becomes unstable and the output is also small. is there. Therefore, the improvement of the characteristics shown in this embodiment is not recognized in Si. It has been found that a plasma wave device using a group IV element not containing arsenic can be realized for the first time by using Ge having an effective mass smaller than that of Si. Injection locking is applied between the drain electrodes by using the capacitive coupling portion 10 or the antenna element 11. As a result, the drain electrodes are electromagnetically coupled (weakly coupled). Particularly in these cases, the drain electrodes are not strongly coupled but are weakly coupled. This means that when the coupling is strong, the drain electrode is AC conductive, and when the coupling is weak, the drain electrode is AC nonconductive and electromagnetically coupled to each other. ing. The point of the present invention is to perform injection locking to each nanowire by making this drain electrode weakly coupled, and obtain a high electromagnetic wave output as shown in FIG.

<Dependence of plasma wave output on the number of nanowires>
A plurality of nanowires 4 may be formed, and the output of electromagnetic waves increases as the number of wires increases. By increasing the number of nanowires to 10 or more, it is confirmed that the Q value is improved by resonance between nanowires. When the width of the nanowire is about 400 nm, 200 nanowires can be arranged even when the nanowire is arranged at a cycle of 500 nm and the total gate width W _total is 100 μm. In this embodiment, the width of the nanowire is 200 nm. In this case, the number of nanowires may be about 10 in order to obtain an output of 25 mW, which is about 10 times that of the conventional one.

<Nanowire width dependence of plasma wave output>
FIGS. 3A to 3C show the distribution of electrons in the nanowire, and FIG. 3D shows the relationship of the electron density at each location of the nanowire structure shown in FIGS. As shown in FIG. 3A, when the width of the nanowire is 20 nm or more (W _L ), the channel 8 is formed on the side wall of the nanowire 4 on the gate electrode 1 side. On the other hand, as shown in FIG. 3B, by setting the width of the nanowire to 20 nm or less (W _S ), the channel leaves the side wall, and the portion where the electron density is maximum becomes the central portion of the nanowire. As a result, the electron density is about 20% larger than that in the case (a). Furthermore, as shown in FIG. 3C, by providing the conductive layer 9 below the nanowire, the electron density is strengthened and the electron density is increased about twice as compared with the case of FIG. I knew it was possible. Thus, by narrowing the width of the nanowire, the electron density can be increased, and the output of the electromagnetic wave can be increased in proportion to the electron density.

  Here, in order to increase the electron density, the width of the nanowire was set to 20 nm. In this case, about 50 nanowires were required to obtain an output of 25 mW. When the gate width W is widened and the number is 10 or less, the output of electromagnetic waves increases, but on the other hand, the Q value decreases due to a decrease in the uniformity of the electron density inside the nanowire. Further, as the number of nanowires is reduced and the number is increased to 200 or more, the phase shift due to the variation in the width of the nanowire becomes more significant. Therefore, about 10 to 200 nanowires were appropriate. Here, the narrower the width of the nanowire is, the more the number of nanowires is necessary, and the necessity of performing injection locking as in the present invention to correct the phase shift becomes extremely high.

  Although the nanowire width is 200 nm in this embodiment, the characteristics of the element in which the nanowire width is 20 nm and the electron density is increased are described in Embodiment 3.

<Dependence of plasma wave output on the number of gate electrodes>
As shown in FIG. 2C, the BB ′ cross section of FIG. 1A is arranged with a plasma wave period Λ of about 800 nm. Within the range of the plasma wave gain, by changing the electrode period Λ, the wavelength of the plasma wave changes to coincide with the period. Therefore, the frequency and intensity of plasmons can be changed by adjusting the period of the electrodes. The width (gate length) L of the gate electrode was 200 nm, which is Λ / 4. As a result, it became clear that an independent plasma wave was formed below each gate electrode, and the intensity of the plasma wave increased in proportion to the number _{ng of the} gate electrode.

  The difference between the present invention and the conventional oscillation element will be described in detail with reference to FIG. In the case of the structure of the oscillation element shown in Non-Patent Document 1 as shown in FIG. 10, there is one gate electrode 1, and a plurality of orders of plasma waves are formed below the gate electrode 1 as shown in FIG. Has been generated. The plasma wave output in this case is as follows.

P = CU ₀ ² Wν ₀ α ² (1)
Here, C is the capacitance under the gate electrode, U ₀ is the DC component of the voltage applied to the channel under the gate electrode, W is the width of the nanowire, ν ₀ is the velocity of electrons, and α is the voltage applied to the gate electrode. Is defined as a modulation degree α = U ₁ / U ₀ (= AC component / DC component) where U = U ₀ + U ₁ exp (−iωt). Patent Document 1 and Non-Patent Documents 2 to 4 disclose devices having a plurality of gate electrodes, but as shown in FIG. A plasma wave less than 3 is formed.

By the way, in the case of Formula (1), it turns out that the output P does not show gate length L dependence. However, in this embodiment, by describing the expression of the output P as a function of the gate length L as follows, it is clarified that the output can be described as having a gate length dependency. I was able to. That is,
P = (CU ₀ ² WL) · (ν ₀ / L) · α ² = E · n _m · α ² (2)
Here, the first term of the product on the right side of the equation (2) is energy E = CU ₀ ² WL stored in the gate electrode, and the second term is the number of round trips of electrons traveling back and forth below the gate electrode is _nm = ν _0. / L. Even if the electrodes are divided, the total length L of the electrodes is constant, so that the energy E stored in the electrodes is constant. On the other hand, by increasing the number n _g of the electrodes, the length of one per electrode L / n _g, and the reciprocal number of the electron becomes _{n 'm = n g · ν} 0 / L. as a result,
P ′ = E · n ′ _m · α ² = n _g · P
Thus, it was found that the output of the electromagnetic wave was _ng times. Here, in order for electrons to reciprocate accurately under each electrode, the source 2 side of the gate electrode 1 needs to be short-circuited and the drain electrode 3 side needs to be open. Therefore, it has been found that the gate electrodes should be arranged at intervals of the plasma wave wavelength Λ and the length of the gate electrode 1 should be Λ / 4. The reason why the period of the gate electrode 1 is not Λ / 2 is that an electric field having the same phase needs to be induced in the gate electrode in order to connect the gate electrodes 1 in parallel. By arranging the gate electrode 1 in this way, electron reciprocation occurs independently at the lower part of each gate electrode, and a plasma wave is generated. Therefore, the intensity P ′ of the plasma wave is equal to the number of electrodes. It can be _ng times.

As a result of evaluating the refractive index of the plasma wave, it has been clarified that the refractive index n _eff is about 300 when the electron concentration n _s in the semiconductor layer is 10 ¹² cm ⁻² . This is an extremely large value of about 100 times because the refractive index of light in the semiconductor is about 3. This knowledge has led to the development of capturing the nanowire structure of the plasma wave device as a waveguide of an optical system, and the basis of the basic idea of the present application has been completed. If you increase the electron concentration _{n s} to 2 × 10 ¹² cm ^-2 is the electron concentration dependence of the refractive index becomes _{Δn eff / Δn s = -6 ×} 10 -12, n eff is to 294 Decrease. Thus, since the relationship between the refractive index and the electron concentration has been clarified, when the frequency of the plasma wave in the semiconductor layer is 1 THz or more, the period Λ of the plasma wave is 0.8 μm, and the gate electrode is Λ / It was found that about 200 nm, which is 4, is sufficient. Even in the case of an InAlAs / InGaAs HEMT or the like that has conventionally achieved the maximum speed, if the gate length is 200 nm, ft and fmax are as low as about 300 GHz. The plasma wave generating element of this embodiment has an advantage that an ultra-high frequency can be generated by a simple process because an electromagnetic wave of 1 THz or more can be generated even when the gate length is 200 nm.

An example of a method for manufacturing an electromagnetic wave generating element is shown in FIG. After the SiGe mixed crystal 4 is grown on the Si substrate 5, O ⁺ ions are implanted into the interface between the SiGe and the Si substrate to perform high-temperature annealing as the oxide film layer 6, and then the surface 12 is oxidized. As a result, Si and oxygen are preferentially bonded, the Ge concentration in the SiGe layer is concentrated, and the Ge thin film 4 (film thickness is 2 to 10 nm) sandwiched between the insulating films 6 and 12 made of SiO ₂ is formed. A GOI substrate is produced (a). Next, the insulating film 12 and the Ge thin film are dry-etched into stripes having a width of 200 nm and an interval of 110 μm so as to form the nanowire structure 4 (b). After the insulating film 7 made of SiO ₂ is deposited on the entire surface of the substrate, a resist is applied and the electrode portion is exposed and removed, and silver is deposited and lift-off is performed to produce the gate electrode 1 having a gate length of 200 nm (c ). The source electrode 2 and the drain electrode 3 are formed by lift-off (d). Finally, as shown in FIG. 1 (a) (not shown in FIG. 5), a capacitive coupling portion is formed by connecting high-impedance gold or copper conductors having a width of about 10 μm between adjacent drain electrodes. Get 10. The length of the capacitive junction 10 is 110 μm, which is the interval between the nanowires. As shown in FIG. 1C, the dielectric constant around the conducting wire is about 4, so the frequency is 1. It has an electromagnetic wave wavelength of 3 THz. On the other hand, if the interval between the nanowires is a half wavelength, the chip area can be reduced to half (when the number of nanowires is ten, the total gate width W _total is about 500 μm). In this case, plasma waves having opposite phases are generated in the nanowires adjacent to each other. However, since the phases are merely inverted, the frequencies are the same, and oscillation in a single mode is possible. In order to further narrow the interval between the nanowires, the conductive wire between the drain electrodes having a high impedance may be folded back in a zigzag manner like the filter 13 in FIG. In the case of turning back, the coupling efficiency can be changed by adjusting the number of turns and the interval between the conductors.

FIG. 6 shows the result of performance comparison between the electromagnetic wave generating element of the present embodiment and the element shown in the non-patent literature. When Ge is used, the effective mass m * is about 20% larger than that of InGaAs used in Non-Patent Document 1. However, since both Non-Patent Documents 1 and 2 use arsenic (As), when using arsenic free, the effective mass is slightly large, but the use of Ge is desired. In the case of Non-Patent Document 2, the effective gate length L _eff is 0.1 μm or less, the band gap is small, and since it is a direct transition, avalanche breakdown occurs and the voltage U ₀ can be applied only about 0.08V. Here, the effective gate length is _defined as L _eff = L + 2δ including the thickness δ of the depletion layer formed around the length L of the gate electrode. For this reason, the output of electromagnetic waves is smaller than that of Non-Patent Document 1, although the effective mass is as extremely small as 0.042.

On the other hand, since Ge is an indirect transition, operation does not become unstable even when a voltage of about 0.5 V is applied. As a result, the non-patent document 1 and the present embodiment have substantially the same maximum value of the electron drift velocity v ₀ . The total gate width W _total is conventionally about 100 μm because it is based on a normal HEMT element, but in the case of the present embodiment, it is nanowired to about 200 nm. FIG. 6 shows the result when W = 200 nm. The degree of modulation α is about 0.5. The sheet carrier density is about 10 ¹² cm ^{-2 for} a nanowire of about 200 nm. The length L _eff of the gate electrode was set to 200 nm in consideration of process easiness. The device length was 500 μm. As a result, the number of gate electrodes is 625 per nanowire. The period of the gate electrode was set to 0.8 μm, which is four times the length of the gate electrode. In addition, the number _n n of the nanowire was ten. As a result, the output P ′ of the non-patent document is 2 mW, whereas in this embodiment (this application 1), the output P ′ is 25 mW, which is 10 times or more. This is because canceling due to a difference in phase is suppressed by performing injection locking using a conducting wire. In addition, the Q value indicating the performance of the resonator is 3 in the case of the present embodiment, which is about twice as large as the conventional 1.2 and 1.8. Thus, it has been found that the Q value is improved by performing injection locking.

<Reason for making nanowire width 400 nm or less>
In the above description, the increase in the carrier concentration due to the semiconductor layer having a nanowire structure has been described. In this case, a great effect was obtained by setting the width of the nanowire to 20 nm or less, but even when the width of the nanowire is 400 nm or less, it has a high advantage over the conventional case where the gate width is 100 μm. . The advantages of using a nanowire structure of 400 nm or less will be described below. In this embodiment, the improvement in output was confirmed by using periodically arranged electrodes, but when this periodic electrode structure is used in Non-Patent Documents 1 and 2 that do not have a nanowire structure, As shown in FIG. 7, the wavefront of the plasma wave is greatly disturbed. The reason will be described below. As shown in FIG. 7A, by short-circuiting the gate electrode 1 and the source 2, the gate voltage U ₀ applied to the semiconductor layer is low on the source side 2 and increases toward the drain electrode 3 side. ing. As a result, the velocity s of the plasma wave is
s = (eU ₀ / m) ^1/2 (3)
In as indicated, showing the same tendency as U _0. The frequency fp (wavelength) of the propagating plasma wave is
fp = s / 4L (4)
Although fp does not change in the nanowire, it is necessary to increase L as s increases. As a result, as shown in FIG. 7B, the wavefront of the plasma wave (indicated by a dotted line) is bent toward the drain electrode 3 as indicated by the arrow in the direction of the wavefront. Since the plasma wave reciprocates in the two-dimensional electron gas 54, plasma waves having a plurality of wave fronts are mixed in the two-dimensional electron gas, and the modes interfere with each other as shown in FIG. There will be many modes. As described above, when a plurality of modes exist at the same time, there is a problem that a resonance phenomenon hardly occurs, the Q value is lowered, and the plasma wave becomes unstable. However, as shown in FIG. 7D, when the nanowire width is reduced to about 400 nm which is a half wavelength to form the nanowire shape 4, only one mode in the lateral direction can exist. Further, as shown in FIG. 7D, since the wavefront cannot be bent, a plurality of modes do not occur although the coupling coefficient of the plasma wave partially decreases when viewed from the whole nanowire. As a result, stable plasma waves can be generated. As described above, in the present embodiment, the nanowire width is shown for two types of 20 nm and 200 nm. By making the nanowire width half or less of the wavelength of the plasma wave, the influence of the nonuniformity of the gate voltage is reduced. The generation of unacceptable plasma waves became possible, and the increase of plasma waves by multiple electrodes became possible.

<Relationship between number of nanowires and Q value>
By the way, when several nanowire is arrange | positioned in parallel, the electromagnetic waves in each nanowire will couple | bond together by a gate electrode and a drain electrode. As a result, plasma waves with the same phase are formed throughout the nanowire, and a significantly high Q value is obtained. That is, an electromagnetic wave having a very narrow line width is generated at a frequency corresponding to the period of the gate electrode. In the case of the electromagnetic wave generating elements shown in Non-Patent Documents 1 and 2, since the semiconductor layer is not divided, the structure is not synchronized with a plurality of resonators. In equation (2), the integrated intensity with respect to the frequency of the electromagnetic wave is shown as the intensity of the electromagnetic wave. When such a high Q value is obtained, the peak intensity P _P of the electromagnetic wave at a specific frequency is the Q value. It becomes extremely large when the value is low. For example, when it is assumed that about n _n nanowires are synchronized, it is considered that the intensity becomes P _P ∝√n _n. Therefore, in the case of 100 nanowires, the peak intensity is one in comparison with the case of one. It was found that 10 times the electromagnetic wave peak intensity was obtained.

In FIG. 6, the Q value is expressed as Q = sτ√n _n / L _eff
In the electromagnetic wave generating element in which the gate electrode having a length of Λ / 4 is periodically arranged as a nanowire as shown in FIG. 8, the output and the Q value are set to 10 by taking injection locking between the drain electrodes. It was found that it can be improved to double and triple. Further, the frequency fp of the plasma wave is 1.3 THz, which is about the same value as that of Non-Patent Document 1, and even if the gate length is 200 nm, an electromagnetic wave of 1 THz or more can be generated. It was found that can be generated.

  Note that in this embodiment mode, a multilayer film containing silver is used for the gate electrode; however, other materials such as gold, titanium, and chromium may be used as long as the material easily generates plasma waves.

(Embodiment 2) <When an antenna element is used>
In the first embodiment, injection locking is performed by installing a high-impedance conductor between the drain electrodes. In this case, the distance between the drain electrodes that can be electromagnetically coupled to each other is about four even when they are farthest apart. It was. However, as shown in FIG. 1 (b), by forming a metal wire of about ¼ wavelength on the drain electrode, it functions as the antenna element 11, so that injection locking is achieved even between at least about 10 antenna elements. I found it possible. In FIG. 1B, the drain electrodes 3 are coupled by a low-pass filter 13 so that a DC drain voltage can be applied. As a result, each nanowire 4 can be operated independently. On the other hand, the drain electrodes 3 are coupled to each other by the antenna element 11. In the case of the first embodiment, the canceling could not be sufficiently suppressed when there is a lump of nanowires having the same phase. However, in the case of the present embodiment, it is possible to electromagnetically couple with a sufficiently separated nanowire. It was found that canceling can be sufficiently suppressed.

  In the case of the first embodiment, it is necessary to keep the distance between the nanowires to about 55 μm even in the case of the half wavelength of the electromagnetic wave. However, in the case of the present embodiment, the antenna element is a dipole antenna. There is an advantage that the nanowires can be arranged more densely for electromagnetic coupling regardless of the interval. In the present embodiment, it has been found that 50 nanowires can be arranged at intervals of 2 μm to make the total gate width 100 μm.

  A method for manufacturing the element of this embodiment is described below. The process up to FIG. 5D for producing the source electrode and the drain electrode is the same as that of the first embodiment. Thereafter, the whole is filled with a resist of about 100 μm, and then a hole having a diameter of about 10 μm is formed in the resist on the drain electrode 3 until it reaches the drain electrode. The resist can be formed by adhering a thick resist on the film, exposed by contact exposure, and developed to form a resist with a high aspect ratio. Finally, gold is deposited in the resist hole by electroplating from the drain electrode to form a gold antenna element 11 having a diameter of about 10 μm and a length of about 80 μm to obtain an electromagnetic wave generating element.

  Further, FIG. 8 shows a configuration of an electromagnetic wave generating element that couples an electromagnetic wave radiated from the drain electrode to the gate electrode. In the case of the structure of FIG. 8A, the gate electrodes are connected by the low pass filter 13. As a result, the gate electrodes are in a state where the phases may be reversed. However, the weak coupling with the antenna element 11 formed on the drain electrode 3 causes the gate electrode to vibrate in the same phase as the drain electrode. As a result, the entire gate electrode operates in the same phase. Furthermore, by using the structure of FIG. 8B, the coupling between the gate electrodes can be increased. In addition, the coupling between the gate electrode and the drain electrode can be increased. As a result, it is possible to more stably couple the electromagnetic wave having the same phase as that of the drain electrode to the gate electrode.

(Embodiment 3) <When nanowire width is 20 nm or less>
In Embodiment 1, the width of the nanowire is set to 20 nm or more. However, when the width W of the nanowire is set to 20 nm or less, the radiation efficiency of electromagnetic waves is further improved. The intensity of electromagnetic waves is shown in this application 2. Hereinafter, the width of the nanowire and the intensity of the plasma wave will be described in detail.

In the first embodiment, the width of the nanowire is 200 nm. However, as the width of the nanowire is reduced, the electron density n _s = CU ₀ / e in the nanowire increases. On the other hand, the intensity of the plasma wave is expressed as a function of electron density as follows.

P = CU ₀ ² Wν ₀ α ² = en _s U ₀ Wν ₀ α ² (5)
From equation (5), in proportion to the electron density n _s It can be seen that the intensity P of the plasma waves is increased. Here, the shape dependence of the electron density will be described again in detail with reference to FIG. The electron distribution when the width of the nanowire 4 is changed (ac) is shown. When the width of the semiconductor layer is set to 20 to 400 nm as shown in the first embodiment, carriers are concentrated on the interface between the nanowire 4 and the insulating film 7 on the electrode side to form a channel 8 (a). On the other hand, by setting the width W of the nanowire 4 to 20 nm or less as in the present embodiment, the carrier has a maximum value near the center of the nanowire 4 (b). As a result, as shown in FIG. 3 (d), the electron density n _s is increased about 20% more of (a) (b) with respect to the first embodiment shown in. Further, when the conductive layer 9 is formed by doping the surface of the substrate 5, a potential wall is also formed on the substrate side, and electron confinement becomes strong. As a result, electrons gather near the center of the nanowire, and the electron density increases about twice that of the first embodiment as shown in (c). Thus, the electron density could be increased by reducing the width of the nanowire 4.

  Here, when the electron distribution is confined inside the channel as in this embodiment, the peak of the electron density is located at the center of the semiconductor layer, so that the plasma wave has a three-dimensional dispersion relationship. Although generally considered, as a result of examining the dispersion of the plasma wave, it became clear that the plasma wave has a one-dimensional dispersion relationship in the case of the nanowire as in the present embodiment. Further, it has been clarified that the one-dimensional dispersion relation is equivalent to the two-dimensional dispersion relation shown in the first embodiment. It was found that even for nanowires of 20 nm or less, the formula (5) can be applied, and the intensity of the plasma wave is proportional to the electron density. As a result, it was clarified that the plasma wave intensity about twice that of the first embodiment can be obtained.

From equation (5), C increases as the electron density increases, and the output P increases. Therefore, by reducing the width W of the nanowire 4, the output of the plasma wave per unit nanowire width can be increased. However, if the number of nanowires is kept constant and only the width W of the nanowires 4 is reduced, the total intensity of the plasma waves decreases as can be seen from the equation (5). Therefore, in order to increase the intensity of the total plasma wave, it is necessary to arrange a plurality of nanowires 4 in parallel by reducing the width of the nanowires 4. When the width W of the nanowire is 20 nm, the carrier density _ns is twice that in the first embodiment (application 1). As a result, the number of nanowires must be increased 10 times as much as the width of the nanowires is reduced to 1/10. However, as shown in this application 2 of FIG. all right. The Q value at this time was 6.7, and the Q value could be increased more than twice compared with the first application.

(Embodiment 4) <When using an external resonance structure>
And narrower electromagnetic waves of the line width of the electromagnetic wave generating element shown in Embodiments 1 to 3, in order to increase the peak intensity P _P, the electromagnetic wave generator reflected and again antenna element externally radiated electromagnetic wave from The Q value can be further increased by combining with. In FIG. 9, the plasma element 22 is installed in the cavity made of the reflecting plate 20. By setting the distance between the reflector and the plasma wave element to λ / 2 (23), which is half of the wavelength of the electromagnetic wave λ, the electromagnetic wave is coupled to the plasma element. Here, since the porous structure 26 is formed in the portion where the electromagnetic wave radiation wave 25 is extracted from the cavity, only an electromagnetic wave having a specific wavelength determined by the porous structure can be extracted from the cavity to the outside. In this porous structure, the spectral line width of the electromagnetic wave can be reduced to about 1/5 by setting the hole diameter to about 1/3 of the wavelength of the electromagnetic wave. Since all electromagnetic waves having wavelengths that cannot pass through the porous structure are reflected by the porous structure, a large amount of energy is accumulated in the cavity. As a result, the intensity of the radiation wave to increase minute line width of the electromagnetic wave is reduced, the peak intensity P _P about 5 times as compared with the case of using the plasma device by itself was found to increase. The structure shown in Embodiment Mode 2 is desirable for the plasma element used in this embodiment mode, which is easily coupled with external electromagnetic waves.

  An electromagnetic wave generating element according to the present invention has a plurality of nanowire semiconductor layers and a periodic gate electrode, and an oscillation element of about 1 THz, which can obtain an electromagnetic wave output independent of nanowire variations by performing injection locking on the drain electrode. Useful as.

Schematic of the electromagnetic wave generating element in Embodiment 1 of the present invention FIG. 3 is a relationship diagram between the plasma wave output of the electromagnetic wave generating element and the length of the gate electrode in the first embodiment of the present invention. Explanatory drawing of the electron density of the electromagnetic wave generating element in Embodiment 1 and 3 of this invention Explanatory drawing of the plasma wave intensity | strength of the electromagnetic wave generator in Embodiment 1 of this invention Explanatory drawing of the manufacturing method of the electromagnetic wave generator in Embodiment 1 of this invention The figure which shows the characteristic table | surface of the electromagnetic wave generating element in Embodiment 1 and 3 of this invention Explanatory drawing of the wave front of the plasma wave of the electromagnetic wave generating element in Embodiment 1 and 3 of this invention Schematic of the electromagnetic wave generating element in Embodiment 2 of the present invention Schematic of the electromagnetic wave generating element in Embodiment 4 of the present invention Schematic diagram of conventional electromagnetic wave generator Schematic diagram of conventional electromagnetic wave generator Schematic diagram of a conventional electromagnetic wave receiving element Schematic diagram of conventional injection locking circuit Schematic diagram of a conventional waveguide for injection locking

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gate electrode 2 Source electrode 3 Drain electrode 4 Nanowire 5 Substrate 6 Insulating film 7 Insulating film 8 Channel 9 Conductive layer 10 Capacitive coupling part 11 Antenna element 12 Insulating film 13 Filter 20 Reflector 21 Radiation hole 22 Plasma element 23 λ / 2
24 reflected wave 25 radiated wave 26 porous structure 51 gate 52 source 53 drain 54 two-dimensional electron gas 55 substrate 56 cladding layer 57 barrier layer 61 slow wave circuit 62 electron layer contact 63 hole layer contact 64 two fluid layer 65 input part 66 output Part 71 Gate 72 Source 73 Drain 74 First quantum well 75 Second quantum well 76 Two-dimensional electron gas 77 Substrate 78 Barrier layer 79 Barrier layer 81 Oscillator
82 Coupling circuit
83 Antenna
84 Resonator
85 Oscillator
86 Feedback capacity
87 Output matching circuit
91 Basic mode waveguide array
92 Overmode waveguide
93 Reflector
94 fundamental mode waveguide
95 First impedance matcher
96 Second impedance matcher

Claims (4)

The semiconductor substrate includes a semiconductor substrate, a semiconductor layer, an insulating film, a plurality of gate electrodes, a drain electrode, and a source electrode, wherein one side of the cross section of the semiconductor layer is less than or equal to half the wavelength of the plasma wave, The gate length of the previous gate electrode is ¼ of the period, a plurality of semiconductor layers are arranged in parallel, and the drain electrode formed in each of the plurality of semiconductor layers An electromagnetic wave generating device, wherein regions exhibiting conductivity are formed, and the regions exhibiting conductivity are coupled to each other by electromagnetic waves. The electromagnetic wave generator according to claim 1, wherein a region showing conductivity is formed in each of the plurality of gate electrodes, and the regions showing conductivity are coupled to each other by electromagnetic waves. 3. The electromagnetic wave generating device according to claim 1, wherein regions having conductivity are formed in the drain electrode and the gate electrode, and the regions having conductivity are coupled to each other by electromagnetic waves. 4. The electromagnetic wave generator according to claim 1, wherein the electromagnetic wave generator is installed in a cavity that reflects the electromagnetic wave, and the electromagnetic wave emitting part of the cavity has a porous structure.

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