High frequency generator

Abstract

To provide a high-output high-frequency generator having a simple configuration.SOLUTION: A high frequency generator (10) of the present invention includes a photoelectric conversion layer (11) that generates electrons by photoelectric conversion, an electron transit layer (101) that allows electrons to transit in the photoelectric conversion layer, an anode layer (12) that is disposed in contact with the electron transit layer and is made of a semiconductor, an anode electrode layer (13) that is disposed in contact with the anode layer and is made of a metal, and an antenna (14) that radiates terahertz waves based on an alternating current generated by the transit of electrons.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a high frequency generator comprising a photodiode. [Background technology]

[0002] With the increase in communication traffic, there is a need to increase the capacity of wireless networks as the last access point, eliminate the speed difference between wired and wireless networks, and enable high-speed wireless interfaces. Terahertz waves (electromagnetic waves with a carrier frequency of approximately 100 GHz or higher) are attracting attention as a technology that can achieve these goals. In particular, for short-distance, high-capacity wireless technology, the development of high-speed wireless interfaces using terahertz waves is an urgent issue.

[0003] The following method, for example, is used to generate terahertz waves. When two light waves with different optical frequencies, i.e., different wavelengths, are input to a photodiode, an electron flow is generated in the p-type semiconductor photoelectric conversion layer (cathode electrode layer), which has a small band gap. The amount of this electron flow changes at the same frequency as the optical frequency difference between the two input light waves. This electron flow is made to travel through the electron transit layer and reach the n-type semiconductor collector layer (anode electrode layer), where terahertz waves are emitted from an antenna connected to the p-type semiconductor photoelectric conversion layer (cathode electrode layer) and the n-type semiconductor collector layer (anode electrode layer).

[0004] 3, when laser light with an optical frequency of 193.0 THz and laser light with an optical frequency of 193.3 THz are simultaneously input as optical signal 1, electrons whose generation amount varies at a frequency of 0.3 THz, which is the difference frequency between these, i.e., 300 GHz, are generated in p-type semiconductor photoelectric conversion layer (cathode electrode layer) 21. A voltage is applied by DC power supply 25 so that the potential of n-type semiconductor collector layer (anode electrode layer) 22 is higher than that of p-type semiconductor photoelectric conversion layer (cathode electrode layer) 21.

[0005] Figure 4 shows an energy band diagram of each layer of the photodiode. In the diagram, the lower part has a higher potential than the upper part. A potential difference is generated between the p-type semiconductor photoelectric conversion layer (cathode electrode layer) 21 and the n-type semiconductor collector layer (anode electrode layer) 22 by a DC power supply.

[0006] This potential difference causes electrons to travel (white arrow 2) from p-type semiconductor photoelectric conversion layer 21 to n-type semiconductor collector layer 22 in electron transit layer 201, and current flows from n-type semiconductor collector layer 22 to p-type semiconductor photoelectric conversion layer 21. Of this current, the DC component (indicated by a single black arrow in the figure) flows to DC power supply 25, and the AC component (indicated by a double black arrow in the figure) is supplied to antenna 24, which then radiates electromagnetic waves with a frequency of 300 GHz into the air.

[0007] As a technology for generating terahertz waves, a configuration in which electrons generated in a photoelectric conversion layer flow through an electron transit layer is described (Patent Document 1). In this document, the anode and cathode are defined in the opposite way to the specification of the present application.

[0008] In this technology, electrons generated in the photoelectric conversion layer (p-type absorber) of the photodiode travel within the electron transit layer. The electrical capacitance of the region where the electrons travel is the electrical capacitance of the photodiode, and the upper limit frequency of the AC current that the photodiode can generate decreases in inverse proportion to this electrical capacitance. Specifically, the upper limit frequency f of the photodiode is f=1 / 2πCR. Here, C is the electrical capacitance of the electron transit layer, and R is the impedance of the antenna. The electrical capacitance C of the electron transit layer is determined by the area S of the photoelectric conversion layer, the thickness d, and the relative dielectric constant ε r , using the dielectric constant of vacuum ε0, C=ε0ε r S / d. Since the electron transport layer is a semiconductor, ε ris 10 or more. In order to increase the emitted terahertz waves, it is necessary to increase the intensity of the incident light waves and the amount of AC current generated, but there is an upper limit to the current density that can be tolerated in semiconductors. Therefore, if the area is increased to increase the amount of current, the capacitance C increases according to the above formula, and the upper limit frequency decreases. Thus, there has been a problem in that high-frequency operation and high output cannot be achieved at the same time. For example, at a frequency of 300 GHz, the upper limit of output is 100 μW.

[0009] To solve this problem, a vacuum photodiode has been disclosed that uses a material with a lower dielectric constant than a semiconductor for the electron transport layer (Reference 2). This allows the area of ​​the photoelectric conversion layer to be increased while maintaining the small capacitance required for 300 GHz response, thereby increasing the amount of current. Since the terahertz wave output radiated from the antenna is proportional to the square of the amount of current, increasing the amount of current increases the terahertz wave output.

[0010] FIG. 5 shows an example of the configuration of a high frequency generator 30 that uses a gas or vacuum at a pressure lower than atmospheric pressure as the electron transit layer 301 of a photodiode.

[0011] Figure 6 shows an energy band diagram of each layer of a vacuum photodiode. A potential difference is generated between the p-type semiconductor photoelectric conversion layer (cathode electrode layer) 31 and the n-type semiconductor collector layer (anode electrode layer) 32 by a DC power supply 35. This potential difference causes electrons to travel from the p-type semiconductor photoelectric conversion layer 31 to the n-type semiconductor collector layer 32, and a current flows from the n-type semiconductor collector layer 32 to the p-type semiconductor photoelectric conversion layer 31. Of this current, the DC component (shown by the single black arrow in Figure 5) flows to the DC power supply 35, and the AC component (shown by the double black arrow in Figure 5) is supplied to the antenna 34, which then radiates electromagnetic waves with a frequency of 300 GHz into the air.

[0012] In this photodiode, the area of ​​the photoelectric conversion layer can be increased by 10 times without increasing the electrical capacitance, which allows for a 10-fold increase in the amount of current. As a result, the terahertz wave output radiated from the antenna can be increased to 10mW, 100 times the conventional upper limit of 100μW.

[0013] Cited Document 2 discloses an example in which a cathode is disposed inside a vacuum tube and an anode is disposed on the inner wall of the vacuum tube, with wiring extending from each to the outside of the vacuum tube. [Prior art documents] [Non-patent literature]

[0014] [Non-Patent Document 1] J. Appl. Phys. 127, 031101 (2020); doi: 10.1063 / 1.5128444. [Non-patent document 2] Rev. Sci. Instrum. 68 (2), pp. 1142-1148 (1997). Summary of the Invention [Problem to be solved by the invention]

[0015] In conventional vacuum photodiodes, the entire photodiode is placed inside a vacuum chamber to create a vacuum space, and electrical wiring is run from a DC power source outside the chamber to the chamber to apply voltage between the p-type semiconductor photoelectric conversion layer (cathode electrode layer) and the n-type semiconductor collector layer (anode electrode layer). This necessitates the installation of voltage application terminals and wiring cables inside the vacuum chamber, which makes the high-frequency generator too large for use in communications components, posing a problem. [Means for solving the problem]

[0016] In order to solve the above-mentioned problems, the radio frequency generator according to the present invention includes a photoelectric conversion layer that generates electrons by photoelectric conversion, an electron transit layer that transits the electrons in the photoelectric conversion layer, an anode layer made of a semiconductor and arranged in contact with the electron transit layer, an anode electrode layer made of a metal and arranged in contact with the anode layer, and an antenna that radiates terahertz waves based on an alternating current generated by the transit of the electrons.

[0017] Furthermore, the high-frequency generator according to the present invention includes a photoelectric conversion layer that generates electrons by photoelectric conversion, an electron transit layer that transits the electrons in the photoelectric conversion layer, an anode layer made of a semiconductor and arranged in contact with the electron transit layer, an anode electrode layer made of a p-type semiconductor and arranged in contact with the anode layer, and an antenna that radiates terahertz waves based on an alternating current generated by the transit of the electrons. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a high-power high-frequency generator having a simple configuration. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a high frequency generator according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the operation of the high frequency generating device according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of a conventional high-frequency generator. [Figure 4] FIG. 4 is a diagram for explaining the operation of a conventional high frequency generator. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of a conventional high-frequency generator. [Figure 6] FIG. 6 is a diagram for explaining the operation of a conventional high frequency generator. DETAILED DESCRIPTION OF THE INVENTION

[0020] First Embodiment A high frequency generator according to a first embodiment of the present invention will be described with reference to FIGS.

[0021] <Configuration of high frequency generator> 1, the high frequency generator according to this embodiment includes a vacuum photodiode including a photoelectric conversion layer (cathode layer) 11 made of a p-type semiconductor, an anode layer 12 made of an n-type semiconductor, and an anode electrode layer 13 made of a metal, and an antenna 14. The photoelectric conversion layer (cathode layer) 11 and the anode layer 12 are disposed opposite each other with a space (electron transit layer) 101 in between. In the figure, a single black arrow indicates the path of a direct current, and a double black arrow indicates the path of an alternating current.

[0022] The anode electrode layer 13 is disposed in contact with the anode layer 12 to form a metal-semiconductor junction.

[0023] For example, the material of the photoelectric conversion layer (cathode layer) 11 is InGaAs, which absorbs light with a wavelength of 1550 nm, the material of the anode layer 12 is InP, which does not absorb light with a wavelength of 1550 nm, and the material of the anode electrode layer 13 is Au.

[0024] The photoelectric conversion layer (cathode layer) 11, the anode layer 12, and the anode electrode layer 13 are connected via a short circuit or a resistor to form a DC circuit.

[0025] The photoelectric conversion layer (cathode layer) 11 and the anode layer 12 are connected to an antenna 14 to form an AC circuit.

[0026] The electron transit layer 101 disposed between the photoelectric conversion layer (cathode layer) 11 and the anode layer 12 is filled with a gas such as air or nitrogen. Alternatively, this region may be a vacuum to reduce the probability of collisions between electrons and gas molecules. "Vacuum" refers to a state in which the region is filled with a gas at a pressure lower than atmospheric pressure, and includes an absolute vacuum.

[0027] In order to form a region (electron transit layer) 101 filled with gas in the photoelectric conversion layer (cathode layer) 11 and the anode layer 12, at least the photoelectric conversion layer (cathode layer) 11, the anode layer 12, and the anode electrode layer 13 are sealed in an airtight package.

[0028] Alternatively, one of the photoelectric conversion layer (cathode layer) 11 and the anode layer 12 may have a convex structure on a portion of the surface facing the other layer, with the tip of the convex structure being in contact with the other surface, thereby forming a gas-filled region (electron transit layer) 101 between the region on one surface that does not have a convex structure and the other layer. For example, the photoelectric conversion layer (cathode layer) 11 and the anode layer 12 may be connected by a convex structure on their peripheral portions, with the electron transit layer 101 formed in the region inside the peripheral portion.

[0029] In order to generate terahertz waves, when two light waves with wavelengths shorter than the bandgap wavelength of the photoelectric conversion layer (cathode layer) 11 and different optical frequencies (different wavelengths) are incident on the photoelectric conversion layer (cathode layer) 11 (arrow 1 in the figure), a flow of electrons is generated in the photoelectric conversion layer (cathode layer) 11, the amount of which changes at the same frequency as the optical frequency difference between these light waves. The electrons are emitted from the surface of the photoelectric conversion layer (cathode layer) 11 into the space (electron transit layer) 101 between the photoelectric conversion layer (cathode layer) 11 and the anode layer 12 (arrow 2 in the figure).

[0030] Figure 2 shows the energy band diagram of each layer of a vacuum photodiode. In the diagram, the lower part has a higher potential than the upper part. E C is the energy edge of the valence band, E V indicates the energy edge of the conduction band. The dotted line in the figure indicates the potential for electrons in the electron transit layer 101.

[0031] An internal voltage is generated between the anode layer 12 and the anode electrode layer 13 due to the metal-semiconductor junction, and the potential of the anode layer 12 becomes higher than the potential of the anode electrode layer 13 .

[0032] Because the anode electrode layer 13 is made of metal, it can be considered to have the same potential as the short-circuited (connected) photoelectric conversion layer (cathode layer) 11. As a result, the anode layer 12 has a higher potential than the photoelectric conversion layer (cathode layer) 11, and therefore electrons emitted from the photoelectric conversion layer (cathode layer) 11 in the electron transit layer 101 transit toward the anode layer 12. In other words, electrons can be transited without applying a DC voltage from the outside.

[0033] Of the currents generated by the electrons' movement, DC current circulates in the DC circuit due to DC short-circuiting. AC current is supplied to antenna 14, and terahertz waves are emitted from antenna 14. For example, when laser light with an optical frequency of 193.0 THz and laser light with an optical frequency of 193.3 THz are simultaneously irradiated onto photoelectric conversion layer (cathode layer) 11, an AC current with a frequency of 0.3 THz, which is the frequency difference between these laser lights, or 300 GHz, is supplied to antenna 14. Electromagnetic waves with a frequency of 300 GHz are emitted from antenna 14 into the air.

[0034] The appropriate length of the antenna 14 is approximately half the wavelength of the emitted radio waves. Since the wavelength of 300 GHz is 1 mm, the appropriate length of the antenna 14 is 0.5 mm. The photoelectric conversion layer (cathode layer) 11, anode layer 12, and anode electrode layer 13 that make up the vacuum photodiode are each chips measuring approximately 1 mm square or less. The wiring connecting each layer is formed on the semiconductor chip. Therefore, the overall size of the high-frequency generator (device) including the vacuum photodiode, antenna 14, and wiring is approximately a few mm square (1 mm to 5 mm), so it can be easily enclosed in a small vacuum package.

[0035] In this way, by using a vacuum photodiode with an n-type semiconductor anode layer and an anode electrode layer in contact with each other, a metal-semiconductor junction is formed between the anode layer and the electrode layer, generating an internal voltage. As a result, a potential difference occurs between the surface of the anode layer facing the electron transit layer and the p-type semiconductor photoelectric conversion layer (cathode layer). This potential difference allows electrons to transit without applying an external voltage, enabling the vacuum photodiode to operate.

[0036] Furthermore, by forming a layer made of cesium on the surface of the photoelectric conversion layer (cathode layer) on the electron transit layer side, the efficiency of electron emission from the photoelectric conversion layer (cathode layer) can be improved.

[0037] According to the radio frequency generator of this embodiment, the vacuum photodiode can be operated by applying an internal voltage generated within the vacuum photodiode to cause electrons to travel without applying an external voltage, which eliminates the need for a DC power supply, voltage application terminals, or wiring cables, thereby realizing a radio frequency generator with a simple configuration.

[0038] Furthermore, the high frequency generator according to this embodiment has a small electrical capacity necessary for high frequency, especially terahertz, response, and can increase the area of ​​the photoelectric conversion layer, increase the amount of current, and increase the output of terahertz waves.

[0039] In this embodiment, an example in which the anode electrode layer is made of metal has been described, but the anode electrode layer may also be made of a p-type semiconductor. That is, a vacuum photodiode may have a configuration in which an n-type semiconductor anode layer and a p-type semiconductor anode electrode layer are in contact with each other. With this configuration, a p-n junction is formed between the anode layer and the electrode layer, generating an internal voltage. As a result, a potential difference occurs between the surface of the anode layer facing the electron transit layer and the p-type semiconductor photoelectric conversion layer (cathode layer). This potential difference allows electrons to transit without applying an external voltage, thereby operating the vacuum photodiode.

[0040] In the embodiment of the present invention, an example in which the photoelectric conversion layer is made of a p-type semiconductor has been shown, but the present invention is not limited to this. The photoelectric conversion layer may be made of a p-type semiconductor or an undoped semiconductor.

[0041] In the embodiment of the present invention, an example in which the anode layer is made of an n-type semiconductor has been shown, but this is not limiting. The anode layer may be made of a p-type semiconductor or an undoped semiconductor. When the anode layer is made of a p-type semiconductor, an n-type semiconductor or a metal may be used for the anode electrode layer.

[0042] In the embodiment of the present invention, an example using a vacuum photodiode has been shown, but a photodiode in which the electron transit layer is formed in the atmosphere may also be used, or a photodiode using a semiconductor for the electron transit layer may also be used.

[0043] In the embodiment of the present invention, an example has been shown in which two light waves with different wavelengths are incident on a photodiode to generate terahertz waves, but a configuration in which an optical signal with a single wavelength is received by a photodiode may also be used.

[0044] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration and manufacturing method of the high frequency generator and the high frequency generation method are shown, but the present invention is not limited to these. Anything that can demonstrate the functions and effects of the high frequency generator and the high frequency generation method may be used.

[0045] It should be noted that the present invention is not limited to the above-described embodiments, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0046] A part or all of the above-described embodiment or an example thereof can be described as, but is not limited to, the following supplementary notes.

[0047] (Supplementary Note 1) A radio frequency generator comprising: a photoelectric conversion layer that generates electrons by photoelectric conversion; an electron transit layer that transits the electrons in the photoelectric conversion layer; an anode layer made of a semiconductor and disposed in contact with the electron transit layer; an anode electrode layer made of a metal and disposed in contact with the anode layer; and an antenna that radiates terahertz waves based on an alternating current generated by the transit of the electrons.

[0048] (Supplementary Note 2) A radio frequency generator comprising: a photoelectric conversion layer that generates electrons by photoelectric conversion; an electron transit layer that transits the electrons in the photoelectric conversion layer; an anode layer made of a semiconductor and disposed in contact with the electron transit layer; an anode electrode layer made of a p-type semiconductor and disposed in contact with the anode layer; and an antenna that radiates terahertz waves based on an alternating current generated by the transit of the electrons.

[0049] (Supplementary Note 3) The high frequency generator according to Supplementary Note 1 or Supplementary Note 2, wherein the electron transit layer is made of a gas.

[0050] (Appendix 4) The high frequency generator according to appendix 3, wherein the pressure of the gas is lower than atmospheric pressure.

[0051] (Appendix 5) The high frequency generator according to appendix 1 or 2, wherein the electron transit layer is a vacuum.

[0052] (Appendix 6) The high frequency generator according to any one of appendices 1 to 5, further comprising a layer made of cesium on the surface of the photoelectric conversion layer facing the electron transit layer.

[0053] (Supplementary Note 7) The high frequency generator according to any one of Supplementary Notes 1 to 6, wherein the photoelectric conversion layer is made of a p-type semiconductor.

[0054] (Appendix 8) The high frequency generator according to any one of appendices 1 to 7, wherein the anode layer is made of an n-type semiconductor.

[0055] (Supplementary Note 9) The high frequency generator according to any one of Supplementary Notes 1 to 8, wherein the two input signal lights have different frequencies, and terahertz waves are emitted based on the frequency difference between the two signal lights.

[0056] (Supplementary Note 10) The high frequency generator according to any one of Supplementary Notes 1 to 9, wherein the length of the antenna is about half the wavelength of the terahertz wave.

[0057] (Appendix 11) The high frequency generator according to any one of Appendices 1 to 10, having a size of 1 mm square or more and 5 mm square or less.

[0058] (Appendix 12) A method for generating a high frequency wave using a high frequency wave generator including a photoelectric conversion layer, an electron transit layer, an anode layer, an anode electrode layer, and an antenna, the method comprising the steps of: inputting two signal lights having different frequencies to the photoelectric conversion layer; photoelectrically converting the two signal lights by the photoelectric conversion layer to generate electrons; converting the electrons into an alternating current according to the frequency difference between the two signal lights by an internal voltage generated between the anode layer and the anode electrode layer; and radiating terahertz waves by the antenna based on the alternating current. [Industrial Applicability]

[0059] The present invention relates to an apparatus and method for generating high frequency waves, particularly terahertz waves, and is applicable to communication systems and their interfaces. [Explanation of symbols]

[0060] 10 High frequency generator 11 Photoelectric conversion layer 101 Electron transit layer 12 Anode layer 13 Anode electrode layer 14 Antenna

Claims

1. a photoelectric conversion layer that generates electrons by photoelectric conversion; an electron transit layer that transits the electrons in the photoelectric conversion layer; an anode layer made of a semiconductor and disposed in contact with the electron transit layer; an anode electrode layer made of a metal and arranged in contact with the anode layer; an antenna that emits terahertz waves based on an alternating current generated by the movement of the electrons; Equipped with a high frequency generator.

2. a photoelectric conversion layer that generates electrons by photoelectric conversion; an electron transit layer that transits the electrons in the photoelectric conversion layer; an anode layer made of a semiconductor and disposed in contact with the electron transit layer; an anode electrode layer made of a p-type semiconductor and arranged in contact with the anode layer; an antenna that emits terahertz waves based on an alternating current generated by the movement of the electrons; Equipped with a high frequency generator.

3. 3. The high frequency generator according to claim 1, wherein the electron transit layer is made of a gas.

4. 4. The radio frequency generator of claim 3, wherein the pressure of the gas is lower than atmospheric pressure.

5. 3. The high frequency generator according to claim 1, wherein the electron transit layer is a vacuum.

6. 3. The high frequency generator according to claim 1, further comprising a layer made of cesium on a surface of the photoelectric conversion layer facing the electron transit layer.

7. 3. The high frequency generator according to claim 1, wherein the photoelectric conversion layer is made of a p-type semiconductor.

8. 3. The high frequency generator according to claim 1, wherein the anode layer is made of an n-type semiconductor.

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