A miniaturized terahertz radiation source based on a photocathode vacuum diode array

Abstract

The application provides a miniaturized terahertz radiation source based on a photocathode vacuum diode array, which comprises a photocathode vacuum diode array, a first antenna arm and a second antenna arm, the two antenna arms are symmetrically and oppositely arranged to form a butterfly-shaped antenna, the first antenna arm is connected with a metal anode of the photocathode vacuum diode array, and the second antenna arm is connected with a photocathode of the photocathode vacuum diode array, the photocathode vacuum diode array is sealed on the outside periphery, and the photocathode vacuum diode array is in the shape of a cube or a cylinder. The distance between the cathode and the anode of the structure reaches the order of magnitude of microns and nanometers, a large electric field can be realized under a small voltage, the working requirement of a large voltage of a traditional vacuum electron device is reduced, and the disadvantage of large size is also abandoned. Meanwhile, the array arrangement of the vacuum channel can effectively utilize the space charge repulsion force of adjacent electron beams to realize self-focusing transmission of the electron beams. The increase of the array number can effectively improve the electron beam flow rate, thereby increasing the current reaching the metal anode and improving the radiation power.

Description

[TECHNICAL FIELD]

[0001] The present application relates to the field of semiconductor optoelectronics and the field of terahertz device technology, and specifically designs a miniaturized terahertz radiation source based on a photoelectric cathode vacuum diode array. [BACKGROUND]

[0002] Terahertz waves refer to electromagnetic waves with a frequency of 0.1-10 THz, and their wavelengths are between microwaves and infrared. Terahertz waves have high spectral resources and data transmission capabilities. Terahertz technology is widely used in military defense, space communication, safety detection, and imaging, and provides new possibilities for the development of human society. Terahertz sources are the basis of terahertz technology and the core component of terahertz application systems. The output power level of the terahertz source directly affects the performance indicators of the entire system.

[0003] In recent years, micro-nano scale high-power integrated terahertz sources have been the focus of research. In ("Frequency-tunable continuous terahertz source based on GaAs plasma photomixer", Applied Physics Letters, 2015, Vol. 107, No. 13, pages 131111-1-131111-4, authors: S.H. Yang, M. Jarrah I), the photoconductive antenna studied achieved a continuous wave terahertz radiation power of 17 μW at a frequency of 1 THz. Due to factors such as lattice scattering in semiconductor materials, the energy loss of carriers is large, and the terahertz radiation power is usually limited to the μW level. To solve this problem, Professor Ruan Cunjun's team at Beijing University of Aeronautics and Astronautics proposed a terahertz radiation source based on a photoelectric cathode and a vacuum channel ("Terahertz radiation source and method of manufacturing the same", CN109713553A, 2019, authors: Ruan Cunjun, Dai Jun, Zhang Xingyun). This miniaturized terahertz radiation source is expected to increase the output power to the mW level. However, due to the influence of the space charge effect of electrons, the high flow rate transmission of photoelectrons in a single vacuum channel poses a great challenge, directly limiting the further improvement of the output power of the terahertz source device. [SUMMARY]

[0004] To overcome the shortcomings of the prior art, the present application proposes a miniaturized terahertz radiation source based on a photoelectric cathode vacuum diode array, which can effectively improve the flow rate of the electron beam through the self-focusing effect of the electron beam in adjacent vacuum channels, thereby converting more electron energy into greater power terahertz wave radiation output.

[0005] The miniaturized terahertz radiation source based on a photoelectric cathode vacuum diode array of the present application adopts the following technical solutions:

[0006] A miniaturized terahertz radiation source based on a photocathode vacuum diode array, comprising a photocathode vacuum diode array, a first antenna arm and a second antenna arm, the two antenna arms are symmetrically and oppositely arranged to form a butterfly-shaped antenna, and the first antenna arm is connected with the metal anode of the photocathode vacuum diode array, and the second antenna arm is connected with the photocathode of the photocathode vacuum diode array, the photocathode vacuum diode array is sealed outside the periphery, and the photocathode vacuum diode array is in the shape of a cube or a cylinder.

[0007] Further, when the photocathode vacuum diode array is in the shape of a cube, the first antenna arm and the second antenna arm are in the shape of a trapezoid, and the short parallel edges of the first antenna arm and the second antenna arm are connected with the vacuum transistor array.

[0008] Further, when the photocathode vacuum diode array is in the shape of a cylinder, the first antenna arm and the second antenna arm are in the shape of a trapezoid as a whole, and the connection parts of the antenna arms with the vacuum transistor array are connected with the edges of the cylinder in the shape of a circular arc.

[0009] Further, the photocathode vacuum diode array is composed of n×n photocathode vacuum diodes, and the entire photocathode vacuum diode array is in a vertical structure.

[0010] Further, the photocathode vacuum diode array is sequentially composed of a metal grating array layer, a substrate layer, a photocathode layer, a vacuum channel array layer and a metal anode layer from top to bottom; the light irradiation area of the photocathode is controlled by the metal grating array layer, so that the photocathode layer forms an array emission; and the electron beam transmitted in the vacuum channel array layer can improve the electron flow rate through the self-focusing effect, thereby increasing the current reaching the metal anode layer and improving the terahertz wave radiation power.

[0011] Further, the substrate layer is in the shape of a square or a circular column, and is made of sapphire or diamond with a high thermal conductivity coefficient; the metal grating array layer is evaporated on the upper surface of the substrate layer, and the photocathode layer is grown on the lower surface of the substrate layer.

[0012] Further, the photocathode layer is in the shape of a square or a circular column, and is a multi-alkali photocathode with a three-layer structure from top to bottom, i.e., a Na2KSb layer, a K2CsSb layer and a Sb·Cs layer.

[0013] Further, the photocathode layer is in the shape of a square or a circular column, and is a multi-alkali photocathode with a three-layer structure from top to bottom, i.e., a Na2KSb layer, a K2CsSb layer and a Sb·Cs layer.

[0014] Further, the base shape of the vacuum channel array layer is a cube or a circular column, and the material is silicon dioxide, which is used to insulate the photoelectric cathode layer and the metal anode layer, and support the metal grating array layer, the substrate layer, the multi-alkali photoelectric cathode layer, and is used to isolate adjacent vacuum channels; the vacuum channel array layer comprises n*n circular vacuum channels, and the base of the vacuum channel array layer, together with the photoelectric cathode layer above and the metal anode layer below, forms n*n vacuum closed cavities, and the height of the vacuum channel is in the order of microns or nanometers.

[0015] Further, the metal anode layer has the same shape and size as the photoelectric cathode layer, and the material is Kovar alloy with low thermal expansion coefficient.

[0016] Further, the photoelectric cathode is connected to a negative bias, the metal anode is connected to 0 potential, and the potential difference is 10V-60V.

[0017] The application has the following advantages:

[0018] The distance between the anode and the cathode of the miniaturized photoelectric cathode vacuum diode array reaches the order of microns or nanometers, so that a large electric field can be realized by using a small voltage, and compared with a traditional vacuum electron terahertz source, the terahertz source has the advantages of miniaturization, integrability and low working voltage. At the same time, compared with a single vacuum channel terahertz radiation source, the application can reduce the interception and wall collision of the electron beam, improve the electron flow rate, increase the current reaching the metal anode, and thus improve the terahertz wave radiation power, by using a vacuum channel array and the self-focusing effect of adjacent electron beams. [BRIEF DESCRIPTION OF DRAWINGS]

[0019] Figure 1 is a schematic diagram of a cubic photoelectric cathode vacuum diode array miniaturized terahertz radiation source;

[0020] Among them, 101 represents a first antenna arm; 102 represents a cubic photoelectric cathode vacuum diode array; 103 represents a second antenna arm;

[0021] Figure 2 is a schematic diagram of a cubic micro photoelectric cathode vacuum diode 5*5 array structure;

[0022] Among them, 201 represents a metal grating layer; 202 represents a substrate layer; 203 represents a photoelectric cathode layer; 204 represents a vacuum channel array layer; 205 represents a metal anode layer;

[0023] Figure 3 is a schematic diagram of a cubic photoelectric cathode vacuum diode structure;

[0024] Wherein, 301 represents a metal grating layer; 302 represents a substrate layer; 303 represents a Na2KSb layer; 304 represents a K2CsSb layer; 305 represents a Sb-Cs layer; 306 represents an insulating matrix; 307 represents a vacuum channel; 308 represents a metal anode layer;

[0025] Figure 4 Is a cylindrical photoemissive cathode vacuum diode array miniaturized terahertz radiation source structure schematic diagram.

[0026] Wherein, 401 represents a first antenna arm; 402 represents a cylindrical photoemissive cathode vacuum diode array; 403 represents a second antenna arm.

[0027] Figure 5 Is a plot of anode total current of a vacuum diode array under different channel arrays.

[0028] Figure 6 Is a plot of electron flow rate of a vacuum diode array under different channel arrays.

[0029] Figure 7 Is a plot of radiation power of a micro terahertz source under different channel arrays. [DETAILED DESCRIPTION]

[0030] In order to make the technical means of the present application clear and explicit, the present application will be further described below in conjunction with the drawings, wherein the terms "first", "second" are only used for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. It should be noted that if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, or the orientation or positional relationship of the product when it is usually placed, which is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0031] Example 1

[0032] Figure 1 Is a schematic diagram of a cubic photoemissive cathode vacuum diode array miniaturized terahertz radiation source structure of the present embodiment.

[0033] This embodiment includes a cubic photocathode vacuum diode array 102, a first antenna arm 101, and a second antenna arm 103. The two antenna arms form a butterfly antenna, and the two antenna arms are symmetrically staggered on both sides to form a butterfly antenna. The first antenna arm 101 is connected to the metal anode of the cubic photocathode vacuum diode array 102, and the second antenna arm 103 is connected to the photocathode of the cubic photocathode vacuum diode array 102. The outer periphery of the cubic photocathode vacuum diode array 102 is sealed.

[0034] In this embodiment, the photocathode vacuum diode array is cubic in shape, and the first antenna arm 101 and the second antenna arm 103 are trapezoidal in shape. The short parallel sides of the first antenna arm 101 and the second antenna arm 103 are connected to the photocathode vacuum diode array.

[0035] The miniaturized antenna used in this embodiment is a butterfly antenna. Through optimized design to achieve impedance matching, reflections are reduced, energy conversion efficiency is improved, and more electromagnetic energy is radiated in the form of terahertz waves. Simultaneously, the butterfly antenna has a certain directionality, enabling it to concentrate energy for transmission or reception in a specific direction. The first antenna arm 101 is directly connected to the metal anode, and the second antenna arm 103 is connected to the photocathode. This layout and direct electrical connection effectively reduce energy losses during transmission, facilitating rapid conversion and efficient coupling of electronic energy, thereby achieving efficient terahertz wave radiation. Furthermore, the overall open structure of the butterfly antenna aids in heat dissipation.

[0036] like Figure 2 As shown, the cubic photocathode vacuum diode array consists of 5×5 photocathode vacuum diodes. The entire photocathode vacuum diode array has a vertical structure. From top to bottom, the photocathode vacuum diode array consists of a metal grating layer 201, a substrate layer 202, a photocathode layer 203, a vacuum channel array layer 204, and a metal anode layer 205.

[0037] The metal grating layer 201, serving as a single layer in the entire vertical structure, is made of Cr metal, which has a low coefficient of thermal expansion. The diameter of its transparent circular hollow aperture is equal to the diameter of the vacuum channel in the vacuum channel array layer 204. It is engineered using semiconductor photolithography. The metal grating layer serves two purposes: first, it enables array point emission of the photoelectric emission, increasing electron flux and thus increasing the current reaching the anode; second, it provides heat dissipation for the photocathode.

[0038] like Figure 3The diagram shown is a schematic of a cubic photocathode vacuum diode single-channel structure in this embodiment. The photocathode vacuum diode consists of the following layers from top to bottom: metal grating layer 301, substrate layer 302, Na2KSb layer 303, K2CsSb layer 304, Sb·Cs layer 305, insulating substrate 306, vacuum channel 307, and metal anode layer 308.

[0039] The substrate layer 302 is a sapphire substrate or a diamond substrate. The sapphire / diamond substrate has a single crystal structure. The multi-alkali cathode grown on the single crystal substrate may become a quasi-single crystal structure, which can greatly improve the cathode emission current density.

[0040] The multi-alkali photocathode layer has a three-layer structure, consisting of a Na₂KSb layer 303, a K₂CsSb layer 304, and an Sb·Cs layer 305 from top to bottom. In the three-layer structure of the multi-alkali cathode, the Na₂KSb layer 303 serves as the absorption layer, being heavily antimony-doped p-type Na₂KSb with a thickness of approximately 100 nm. Below the absorption layer, the strongly n-type K₂CsSb layer 304 serves as the surface layer, with a thickness of approximately 1 nm to 3 nm. Below the surface layer is the Sb·Cs layer 305, which serves as the dipole layer, with a thickness of only a few atomic layers.

[0041] The insulating substrate 306 and the vacuum channel 307 are on the same layer, with the same height, reaching the micro-nano scale, and together constitute the vacuum channel array layer 204. The material of the insulating substrate 306 includes, but is not limited to, silicon dioxide. The vacuum channel 307 is a cylindrical structure with a diameter and height approximately equal. In actual fabrication, a vacuum channel mask is designed on the surface of the insulating substrate 306, and the vacuum channel 307 is fabricated using dry etching technology. Because the height of the vacuum channel 307 reaches the micro-nano scale, it allows charge carriers in the current to undergo ballistic transport within the vacuum channel, enabling the device to achieve ultra-wideband operation in the THz band.

[0042] In this embodiment, an indium sealing material (not shown in the figure) is used to electrically connect the metal grating layer 201, the substrate layer 202, and the photocathode layer 203 to each other, which is used to connect the first antenna arm 101.

[0043] The photocathode is connected to a negative bias voltage, and the metal anode is connected to 0 potential, with a potential difference of 10V-60V.

[0044] When the photocathode vacuum diode array terahertz radiation source is operating, the lasers generated by two finely tunable distributed feedback (DFB) lasers are combined and beat-frequency to produce an intensity-amplitude modulated optical signal. The beat frequency is located in the terahertz band, and the combined beams produce superimposed intensity signals that are incident on the photocathode, exciting a high-frequency oscillating current. A high-frequency electron beam is emitted from the photocathode layer and accelerated through the micro-nano-scale vacuum channel array layer under the action of a bias voltage to gain kinetic energy. It is then received by the metal anode layer and finally radiated as a high-power terahertz wave through the terahertz antenna. The high current-density electron emission from the photocathode is the core physical process of this high-power continuous-wave terahertz radiation source.

[0045] Applying a small voltage to the micrometer-scale vacuum channel array layer creates a large electric field, effectively reducing the electron affinity of the cathode. After activation, the photocathode's potential barrier is lowered, enabling zero-barrier electron emission under high field strength, overcoming the low electron emission efficiency problem of traditional vacuum optoelectronic devices. Charge carriers in the current undergo lattice-free scattering within the vacuum channel array layer, achieving ballistic transport and converting high-energy electrons into coherent, high-power terahertz radiation output. Furthermore, the metallic grating layer effectively conducts heat to the cathode, supporting higher laser power density for greater radiation power.

[0046] Example 2

[0047] like Figure 4 The diagram shown is a schematic of a cylindrical photocathode vacuum diode terahertz radiation source, with a structure similar to the cubic photocathode vacuum diode terahertz radiation source in Example 1. Figure 1 Similarly, the overall structure presents a butterfly antenna shape. When the number of vacuum transistor arrays is the same, the side length of the orthographic projection of the cube is equal to the orthographic projection diameter of the cylinder.

[0048] When the photocathode vacuum diode array is cylindrical, the first antenna arm 401 and the second antenna arm 403 are trapezoidal in shape, and the connection part of the antenna arm with the cylindrical vacuum transistor array 402 is arc-shaped along the edge of the cylinder.

[0049] The micro-sized photocathode vacuum diode terahertz radiation source of the above embodiment abandons the traditional photoconductive antenna design of extracting energy and generating radiation by using a terahertz antenna through the movement of carriers with low electron mobility in a semiconductor by laser excitation of a semiconductor photocathode material. Instead, a laser excitation of a multi-alkali photocathode with a large current density is adopted to generate high-frequency current moving in a micro-nano-sized vacuum channel array to obtain a very high carrier density, high electron mobility and high energy conversion efficiency, so that the continuous wave terahertz radiation power can be increased by three orders of magnitude from μW of the traditional photoconductive antenna to about mW. Unlike the traditional vacuum diode, this scheme greatly improves the electron flow rate by using the channel array form to transport electrons.

[0050] Figure 5 and Figure 6 The anode current and flow rate curves with the anode voltage under different vacuum channel arrays are given respectively. As shown in Figure 5 and Figure 6 When the 9×9 vacuum channel array (81 vacuum channels) works at 60V bias, the anode current reaches a maximum value of 0.041A (see Figure 5 ), and the corresponding electron flow rate reaches 99.2% (see Figure 6 ). In a 10×10 vacuum channel array, 100% electron flow rate can be achieved. High electron flow rate means that most of the electrons emitted from the photocathode can successfully pass through the vacuum channel array layer and obtain large kinetic energy to reach the anode, thereby providing a guarantee for high-power terahertz radiation. Figure 7 The radiation power of the micro terahertz source under different vacuum channel arrays is given. As shown in Figure 7 When the 9×9 vacuum channel array works at 60V bias, the radiation power reaches a maximum value of about 75mW. The research results show that by increasing the number of vacuum channels, the electron flow rate and the anode current can be effectively improved, thereby improving the radiation power of the terahertz wave.

[0051] Any technical solution that belongs to the principle of the present application falls within the protection scope of the present application. For those skilled in the art, some improvements made without departing from the principle of the present application should also be considered as falling within the protection scope of the present application.

Claims

1. A miniaturized terahertz radiation source based on a photocathode vacuum diode array, characterized in that, The micro-THz radiation source comprises a photocathode vacuum diode array, a first antenna arm and a second antenna arm, the two antenna arms are symmetrically and oppositely arranged to form a butterfly antenna, the first antenna arm is connected with the metal anode of the photocathode vacuum diode array, and the second antenna arm is connected with the photocathode of the photocathode vacuum diode array, the photocathode vacuum diode array is sealed on the outside periphery, and the photocathode vacuum diode array is in the shape of a cube or a cylinder; the photocathode vacuum diode array is sequentially arranged from top to bottom as a metal grating array layer, a substrate layer, a photocathode layer, a vacuum channel array layer and a metal anode layer; the arrangement structure of the photocathode vacuum diode array controls the light irradiation area of the photocathode through the metal grating array layer, so that the photocathode layer forms an array emission; and then the electron beam transmitted in the vacuum channel array layer can improve the electron flow rate through the self-focusing effect, finally the current reaching the metal anode layer is increased and the THz wave radiation power is improved.

2. The miniaturized terahertz radiation source of claim 1, wherein, When the photocathode vacuum diode array is in the shape of a cube, the first antenna arm and the second antenna arm are in the shape of a trapezoid, and the short parallel edges of the first antenna arm and the second antenna arm are connected with the vacuum transistor array.

3. The micro-THz radiation source according to claim 1, when the photocathode vacuum diode array is in the shape of a cylinder, the first antenna arm and the second antenna arm are in the shape of a trapezoid as a whole, and the connection parts of the antenna arms with the vacuum transistor array are in the shape of a circular arc and are connected with the edges of the cylinder.

4. The micro-THz radiation source according to claim 1, the photocathode vacuum diode array is composed of n´n photocathode vacuum diodes, and the whole photocathode vacuum diode array is in a vertical structure.

5. The micro-THz radiation source according to claim 1, the substrate of the metal grating array layer is a square or cylindrical metal sheet, the material is Cr with a small thermal expansion coefficient, the metal sheet substrate contains n´n hollow cylinders with micron-level light transmission, and the diameter of each hollow cylinder is the same as the diameter of the corresponding vacuum channel below.

6. The micro-THz radiation source according to claim 1, the substrate layer is in the shape of a square or a circular column, the material is sapphire or diamond with a high thermal conductivity, the upper surface of the substrate layer is coated with a metal grating array layer, and the lower surface of the substrate layer is grown with a photocathode layer.

7. The micro-THz radiation source according to claim 1, the photocathode layer is in the shape of a square or a circular column, and is a multi-alkali photocathode with a three-layer structure from top to bottom, i.e., a Na2KSb layer, a K2CsSb layer and a Sb·Cs layer.

8. The micro-THz radiation source according to claim 1, the substrate of the vacuum channel array layer is in the shape of a square or a circular column, and the material is silicon dioxide, which is used for insulating the photocathode layer and the metal anode layer, supporting the metal grating array layer, the substrate layer and the multi-alkali photocathode layer, and isolating adjacent vacuum channels; the vacuum channel array layer contains n´n circular vacuum channels, the substrate of each circular vacuum channel together with the photocathode layer above and the metal anode layer below forms an n´n vacuum closed cavity, and the height of the vacuum channel is in the order of microns or nanometers.

9. The miniaturized terahertz radiation source of claim 1, wherein the metal anode layer has the same shape and size as the photocathode layer, and is made of Kovar alloy having a low thermal expansion coefficient.

10. The miniaturized terahertz radiation source of claim 1, wherein the photocathode is connected to a negative bias voltage, and the metal anode is connected to 0 potential, and the potential difference is 10 V to 60 V.

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