High-frequency generation device
By using a low dielectric constant material for the electron traveling layer in UTC-PD high-frequency generators, the capacitance is reduced, allowing for both high-frequency and high-output terahertz wave generation, surpassing conventional output limits.
Patent Information
- Application Number
- JP2023209231
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-12-12
- Publication Date
- 2025-06-24
AI Technical Summary
In typical UTC-PD high-frequency generators, the upper limit frequency of the AC current decreases inversely with capacitance, making it challenging to achieve both high frequency and high output simultaneously due to the limitations imposed by the semiconductor-based electron transport layer.
The high-frequency generator incorporates an electron traveling layer made of a low dielectric constant material, which reduces capacitance without decreasing the element area, allowing for increased current and terahertz wave output.
This configuration enables high-frequency operation while achieving significantly higher terahertz wave output, exceeding conventional limits by increasing the current amount without lowering the response frequency.
Smart Images
Figure 2025093526000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a high-frequency generator.
Background Art
[0002] With the increase in communication traffic, increasing the capacity of wireless as the last access of the network, eliminating the speed difference between wired and wireless, and making the interface high-speed wireless are important issues. As a technology capable of realizing these, terahertz waves (electromagnetic waves with a carrier frequency of about 100 GHz or higher) have attracted attention. In particular, in short-distance high-capacity wireless technology, high-speed wireless of the interface using terahertz waves has become an urgent issue.
[0003] To generate terahertz waves, there is a technique using a uni-traveling carrier photodiode (UTC-PD). In this technique, first, two light waves with different optical frequencies, that is, different wavelengths, are input to the UTC-PD. As a result, an electron current, that is, an alternating current, whose generation amount changes at the same frequency as the optical frequency difference between the two light waves generated in the photoelectric conversion layer (light absorption layer) of the UTC-PD is made to travel in the electron traveling layer. The alternating current traveling in the electron traveling layer is made to reach the anode electrode, and terahertz waves are radiated from an antenna connected to the anode electrode.
[0004] As a high-frequency generator using a UTC-PD, for example, the configuration shown in FIG. 4 can be considered. This high-frequency generator constitutes a UTC-PD with a cathode electrode 201, a photoelectric conversion layer 202 provided on the cathode electrode 201, an electron traveling layer 203, and an anode electrode 204 provided on the electron traveling layer 203. The photoelectric conversion layer 202 is generally composed of a p-type semiconductor, and the electron traveling layer 203 is composed of an undoped semiconductor. Further, an antenna 205 is provided on the anode electrode 204. Note that the antenna 205 is composed of a thin sheet-like metal and is supported by a support structure 206 provided on the cathode electrode 201 serving as a base.
[0005] 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 into the UTC-PD (photoelectric conversion layer 202) of the high frequency generating device described above, a flow of electrons, i.e., an alternating current, whose generation amount changes at a frequency of 0.3 THz, which is the difference frequency between these two frequencies, or 300 GHz, is generated in the photoelectric conversion layer 202. This alternating current is supplied to antenna 205, and electromagnetic waves with a frequency of 300 GHz are radiated from antenna 205 into the air. [Prior art documents] [Non-patent literature]
[0006] [Non-Patent Document 1] T. Ishibashi and H. Ito, "Uni-traveling-carrier photodiodes", Journal of Applied Physics, vol. 127, 031101, 2020. Summary of the Invention [Problem to be solved by the invention]
[0007] In a typical UTC-PD, the flow of electrons, which is an AC current generated in the photoelectric conversion layer (p-type absorber), travels through the electron transit layer [Non-Patent Document 1, Fig. 3(a)]. The capacitance of the region where the electrons travel is the capacitance of the UTC-PD, and the upper limit frequency of the AC current that the UTC-PD can generate decreases in inverse proportion to this capacitance. Specifically, the upper limit frequency f of the UTC-PD is f=1 / 2πCR. In this formula, C is the capacitance of the electron transit layer, and R is the resistance of the antenna. The 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 of the electron transit layer. r , C=ε0ε using the dielectric constant of vacuum ε0 r It is expressed as S / d.
[0008] Since the electron transport layer is a semiconductor, ε ris 10 or more. In order to increase the emitted terahertz wave, it is necessary to increase the intensity of the incident light wave to increase the alternating current generated. However, there is an upper limit to the current density allowed in the semiconductor. If the area of the element (electron traveling layer) in plan view is increased to increase the current amount, the capacitance C increases according to the above formula, and the upper limit frequency decreases. For this reason, there has been an essential problem that high-frequency operation and high output cannot be achieved simultaneously. For example, at a frequency of 300 GHz, the upper limit of the output is 100 μW.
[0009] The present invention has been made to solve the above problems, and an object thereof is to enable both high frequency and high output by reducing the capacitance without reducing the element area.
Means for Solving the Problems
[0010] The high-frequency generator according to the present invention includes a cathode electrode, a photoelectric conversion layer formed on the cathode electrode and composed of a semiconductor to generate electrons by photoelectric conversion, an electron traveling layer disposed on the photoelectric conversion layer and composed of a low dielectric constant material having a lower dielectric constant than the semiconductor to allow the electrons generated in the photoelectric conversion layer to travel, an anode electrode formed in contact with the electron traveling layer, and an antenna that emits terahertz waves based on the electrons generated in the photoelectric conversion layer.
Effects of the Invention
[0011] As described above, according to the present invention, since the electron traveling layer is composed of a low dielectric constant material having a lower dielectric constant than the semiconductor, the capacitance can be reduced without reducing the element area, and both high frequency and high output can be achieved.
Brief Description of the Drawings
[0012]
Figure 1
Figure 2
Figure 3
Figure 4
Embodiments for Carrying Out the Invention
[0013] Hereinafter, a high-frequency generator according to an embodiment of the present invention will be described with reference to FIG. 1. This high-frequency generator includes a cathode electrode 101, a photoelectric conversion layer 102, an electron traveling layer 103, an anode electrode 104, and an antenna 105.
[0014] The cathode electrode 101 can be formed of, for example, a semiconductor having a predetermined conductivity type. Also, the cathode electrode 101 can be formed of a metal. The photoelectric conversion layer 102 is formed of a semiconductor on the cathode electrode 101 and generates electrons by photoelectric conversion. The photoelectric conversion layer 102 is a light absorption layer and can be formed of, for example, a p-type semiconductor.
[0015] The electron traveling layer 103 is disposed on the photoelectric conversion layer 102 and is formed of a low-dielectric constant material having a lower relative permittivity than that of the semiconductor, and causes the electrons generated in the photoelectric conversion layer 102 to travel. The electron traveling layer 103 formed of the above-described low-dielectric constant material becomes such that electrons tunnel and travel by making the thickness as thin as 1 μm or less.
[0016] Also, the electron traveling layer 103 can be formed of a space formed between the photoelectric conversion layer 102 and the anode electrode 104, and a gas can be disposed or it can be made into a vacuum. For example, as shown in FIG. 2, the cathode electrode 101 is configured as a substrate (base), and an electrode support structure 106 made of an insulating material is provided thereon. By supporting and fixing the anode electrode 104 at a predetermined interval on the photoelectric conversion layer 102 by the electrode support structure 106, an electron traveling layer 103 by a space can be provided between the photoelectric conversion layer 102 and the anode electrode 104. Also, the electrode support structure 106 can support the sheet-like antenna 105.
[0017] The anode electrode 104 is formed in contact with the electron transport layer 103. The anode electrode 104 can be composed of, for example, a metal. The antenna 105 radiates terahertz waves based on the electrons generated in the photoelectric conversion layer 102. For example, the antenna 105 receives electrons from the anode electrode 104 and radiates terahertz waves based on the received electrons.
[0018] Note that a diffusion prevention layer for preventing the diffusion of electrons can be provided on the cathode electrode 101 side of the photoelectric conversion layer 102 (not shown). Further, when the cathode electrode 101 is composed of a metal, a contact layer made of a p-type semiconductor can be provided on the photoelectric conversion layer 102 side of the cathode electrode 101 (not shown). Also, a contact layer made of an n-type semiconductor can be provided between the electron transport layer 103 and the anode electrode 104 (not shown).
[0019] In order to generate terahertz waves, when two light waves with different optical frequencies (different wavelengths) are incident on the photoelectric conversion layer 102, an electron flow, that is, an alternating current, whose generation amount changes at the same frequency as the optical frequency difference between these light waves is generated. The generated electrons are emitted from the surface of the photoelectric conversion layer 102 to the electron transport layer 103, pass through the electron transport layer 103, are supplied to the antenna 105, and terahertz waves are radiated from the antenna 105. For example, when a laser beam with an optical frequency of 193.0 THz and a laser beam with an optical frequency of 193.3 THz are simultaneously irradiated on the photoelectric conversion layer 102, an electron flow, that is, an alternating current, with a frequency of 0.3 THz, which is the difference frequency between these, that is, 300 GHz, is generated, and an electromagnetic wave with a frequency of 300 GHz is radiated into the air from the antenna 105.
[0020] Here, if a material with a relative permittivity lower than that of a semiconductor is used for the electron transport layer 103, the area can be increased while maintaining a small capacitance required for 300 GHz response, and the current amount can be increased. Since the terahertz wave output radiated from the antenna 105 is proportional to the square of the current amount, the terahertz wave output can be increased by increasing the current amount.
[0021] For example, since a gas or vacuum at a pressure lower than atmospheric pressure has a relative permittivity of 1 / 10 or less of that of a semiconductor, if the electron traveling layer 103 is formed from these, the area can be increased by a factor of 10 or more without changing the capacitance, and the current amount can be increased by a factor of 10 or more. As a result, the terahertz wave output radiated from the antenna 105 can be 100 times the conventional upper limit of 100 μW, that is, 10 mW.
[0022] Incidentally, in order for electrons to be emitted from the photoelectric conversion layer 102 to the electron traveling layer 103 made of a gas or vacuum, it is necessary to exceed the energy potential wall, that is, the electron affinity, when looking from the inside to the outside of the photoelectric conversion layer 102 which is a semiconductor. In order to lower this energy potential and eliminate the energy potential wall, as shown in FIG. 3, an intermediate layer 107 made of an alkali metal can be provided between (at the interface of) the photoelectric conversion layer 102 and the electron traveling layer 103. The intermediate layer 107 can be composed of, for example, cesium. By providing the intermediate layer 107, the energy potential wall can be eliminated, and almost all of the electrons generated in the photoelectric conversion layer 102 can be guided as an electric current to the electron traveling layer 103.
[0023] As described above, according to the present invention, since the electron traveling layer is made of a low dielectric constant material having a lower relative permittivity than a semiconductor, the capacitance can be reduced without reducing the element area, and both high frequency and high output can be achieved simultaneously. According to the present invention, since the area can be increased without increasing the capacitance, it is possible to increase the current amount without lowering the response frequency of the photodiode. As a result, a high frequency generator that radiates a high output terahertz wave can be realized.
[0024] Note that the present invention is not limited to the embodiments described above, and it is obvious that many modifications and combinations can be implemented by those with ordinary knowledge in the art within the technical idea of the present invention.
Explanation of Reference Numerals
[0025] 101... Cathode electrode, 102... Photoelectric conversion layer, 103... Electron transport layer, 104... Anode electrode, 105... Antenna.
Claims
1. A cathode electrode, A photoelectric conversion layer composed of a semiconductor and formed on the cathode electrode, which generates electrons by photoelectric conversion, An electron transport layer disposed on the photoelectric conversion layer and composed of a low dielectric constant material having a lower relative dielectric constant than the semiconductor, which allows the electrons generated in the photoelectric conversion layer to travel, An anode electrode formed in contact with the electron transport layer, And an antenna that emits terahertz waves based on the electrons generated in the photoelectric conversion layer A high-frequency generator comprising the same.
2. In the high-frequency generator according to Claim 1, The antenna receives electrons from the anode electrode and emits terahertz waves based on the received electrons. A high-frequency generator.
3. In the high-frequency generator according to Claim 1 or 2, The electron transport layer is composed of a space formed between the photoelectric conversion layer and the anode electrode, and a gas is disposed or it is in a vacuum. A high-frequency generator.
4. In the high-frequency generator according to Claim 3, A high-frequency generator further comprising an intermediate layer composed of an alkali metal formed between the photoelectric conversion layer and the electron transport layer.