Terahertz photoconductive antenna with nano electrode array unit structure

Abstract

According to the terahertz photoconductive antenna with the nano electrode array unit structure, the nano metal array is deposited between the parallel electrodes, so that under the condition of the same light intensity and bias voltage, the generated light current is obviously enhanced, and the light absorptivity is obviously increased. Compared with a traditional PCA device, the photocurrent of the terahertz photoconductive antenna provided by the invention can be increased by more than ten times, and the light absorptivity is increased by more than one time. Furthermore, by introducing a nanoelectrode topological graph design into a fillet, the design can be added between any electrodes to improve the light absorptivity and the light current, the conversion power of light-terahertz waves is enhanced, and the method has excellent universality and sensitivity.

Description

Technical Field

[0001] The invention belongs to the field of terahertz photoconductive antennas, in particular to a terahertz photoconductive antenna with nanoelectrode array units. Background Art

[0002] Terahertz waves generally refer to electromagnetic waves with a frequency between 0.1 and 10 THz (wavelength between 30 and 3000 μm), with a band between infrared and radio frequency, and have the characteristics of high security, high penetration, high spectral resolution, and high bandwidth. These excellent characteristics make it have broad application prospects in the fields of multi-dimensional imaging, high-bandwidth communication, environmental monitoring, military radar, etc.

[0003] Photoconductive antenna (PCA) is one of the commonly used terahertz generating devices. The generation mechanism is called photogenerated terahertz, which has the advantages of high compactness and wide-spectrum radiation. The principle of photogenerated terahertz generating terahertz waves is as follows: femtosecond laser irradiates the photosensitive material, the electrons in the material undergo energy level transitions, and electron-hole pairs (free carriers) are generated. Under the action of external bias, transient current is formed, and electromagnetic waves are radiated outward. Under specific materials and specific electrode sizes, electron waves in the terahertz frequency band can be generated. Since the efficiency of PCA in generating terahertz waves is low, how to improve the efficiency of terahertz generation has become a key issue for PCA to move towards practical application.

[0004] At present, the main technical means to improve the efficiency of PCA in generating terahertz waves include: from the aspect of material selection, substrate materials with high carrier mobility, low carrier lifetime and high breakdown voltage can be selected; from the aspect of substrate structure, methods such as improving electrode topology, introducing nano-sized plasma electrodes, and coating anti-reflection dielectric films can be adopted. Among them, the introduction of nano-sized plasma electrodes has a very significant effect and has been widely studied due to its high degree of integration. The main manufacturers of existing PCA devices include European and American manufacturers such as BATOP, Teravil, and HHI, and there is a lack of reports on related products in China. Therefore, in order to break through the technology and achieve domestic substitution of equal or even better quality products, relevant research is very urgent and of great significance.

[0005] Based on the above background, the present invention proposes a PCA-based nanoplasma electronic solution with high integration, high reliability and high conversion efficiency to improve the conversion efficiency of terahertz PCA, promote its products towards localization, productization and marketization, and fill the gaps in related fields in China. Summary of the invention

[0006] In order to solve the problems of low conversion efficiency and low terahertz radiation power of existing terahertz photoconductive antennas, the present invention proposes a terahertz photoconductive antenna with a nanoelectrode array. The terahertz photoconductive antenna comprises a semiconductor substrate, a metal electrode, a nanoelectrode array unit and a dielectric film; wherein the nanoelectrode array unit is composed of a topological pattern of regular n-gonal nanoelectrodes, wherein n is a positive even number.

[0007] Furthermore, the semiconductor substrate is 100° gallium arsenide or low temperature grown gallium arsenide, and the electron mobility is greater than 5500 cm 2 / (V·s), dark current is less than 5nA@10V, and thickness is 400~625μm.

[0008] Furthermore, the dielectric film is silicon nitride or silicon dioxide, and has a thickness of 200-400 nm.

[0009] Furthermore, the metal electrodes are parallel strip-line structures and are symmetrically distributed, the metal electrodes have a length of 1 mm to 1.5 mm, a width of 10 μm to 25 μm, an electrode spacing of 50 μm to 100 μm, and a thickness of 200 nm to 400 nm.

[0010] Furthermore, the metal electrode material is Au.

[0011] Furthermore, the nanoelectrode array units are arranged between the metal electrodes and are distributed at periodic intervals, and the electrode distribution period p follows Where α is the coefficient, λ is the wavelength of the incident light, and ε d , ε m are the relative dielectric constants of dielectric and metal respectively.

[0012] Furthermore, the periodic interval distribution of the nanoelectrode array units is set to 120 nm, the diameter of the nanoelectrode is 90 nm, and the height of the nanoelectrode is 150 nm.

[0013] Furthermore, the nanoelectrode array units are arranged in a staggered manner or in a neat arrangement.

[0014] Furthermore, the topological figure includes a rounded corner structure, and the curvature radius of the rounded corner structure is one fifth to one tenth of the radius of the topological figure.

[0015] Furthermore, the light source of the terahertz photoconductive antenna is a femtosecond pulse laser with a central wavelength of 780nm, the emission power of the femtosecond pulse laser is 10mW~100mW, the pulse width is 100fs, the repetition period is 50MHz, and the light source is linearly polarized light; the DC bias power supply bias voltage of the terahertz photoconductive antenna is between 10V and 70V.

[0016] Compared with the traditional PCA technology, the present invention has the following advantages: due to the deposition of nanometal arrays between parallel electrodes, the photocurrent generated under the same light intensity and bias voltage conditions is significantly enhanced, and the light absorption rate is significantly increased. After simulation and optimization, the PCA with a nanometal array structure can increase the photocurrent by more than ten times and the light absorption rate by more than double compared with the traditional PCA without this mechanism. In addition, the nanoelectrode topological graphic design of the invention introduces rounded corners, which can be introduced between any electrodes to improve the light absorption rate and photocurrent.

[0017] Under the same light intensity incident conditions, the nanoelectrode array introduced in the present invention causes local light field multiplication, thereby increasing the carrier concentration and photocurrent. The increase in photocurrent increases the radiated terahertz wave power, thereby increasing the light-terahertz conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0019] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which this application can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by this application, should still fall within the scope of the technical contents disclosed in this application.

[0020] Figure 1 It is a three-dimensional stereogram of the present invention.

[0021] Figure 2 This is a plan view of the present invention.

[0022] Figure 3 It is a side view of the present invention.

[0023] Figure 4 This is a light field simulation diagram of the present invention.

[0024] Figure 5 This is a photocurrent simulation diagram of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the embodiments in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0026] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0027] The main structure of the present invention includes: substrate material, metal electrode, nanoelectrode array and a dielectric film. External instruments include: 780nm femtosecond laser, DC bias power supply. The unit topology structure, distribution mode and manufacturing process of the nanoelectrode array are the key technologies of the present invention.

[0028] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: electron beam exposure is used to transfer the nanoelectrode pattern, and after the intermediate steps of development and cleaning, Au is grown in the nanoelectrode area by magnetron sputtering or electron beam evaporation technology, and then the metal electrodes are adhered to the two sides of the nanoelectrode array through similar steps after degumming, cleaning and annealing, and finally a layer of dielectric film is deposited by chemical vapor deposition (PECVD) method to achieve the purpose of anti-reflection and protection.

[0029] Principle of the invention: Based on the traditional PCA technical solution, a nanometal array is deposited between two electrodes, and the metal and dielectric are combined into a plasma material. The light irradiated on the material will generate surface plasmon polaritons (SPP). SPP will reduce the scattering of light on the substrate surface. When light of a specific wavelength is incident on the surface, it resonates with the nanometal electrode, thereby generating a surface magnetic field. The surface magnetic field concentrates the light energy on a sub-wavelength scale, significantly amplifying the local light field, and then under the action of the electric field applied by the bias voltage, the carrier generation rate is increased, the photocurrent is increased, and the radiated THz wave power is enhanced.

[0030] Specifically, in the present invention, a femtosecond pulse laser with a central wavelength of 780 nm is selected as a PCA light source, with an emission power between 10 mW and 100 mW, a pulse width of 100 fs, a repetition period of 50 MHz, and linearly polarized light.

[0031] Use a DC bias power supply with a bias voltage between 10V and 70V.

[0032] The substrate material is 100-degree-crystal GaAs or low-temperature grown GaAs, with an electron mobility greater than 5500cm 2 / (V·s), dark current is less than 5nA@10V, and thickness is 400~625μm.

[0033] The metal electrode material is Au, and the structure is as follows Figure 2 As shown, it is a parallel strip line structure, the electrode length is 1 to 1.5 mm, the width is 10 to 25 μm, the electrode spacing is 50 μm to 100 μm, and the electrode thickness is 200 to 400 nm.

[0034] The nanoelectrode array material is Au or Ag, and the structure is as follows Figure 2 As shown, the electrode array is periodically distributed between parallel electrodes, and the electrode distribution period p follows Where α is the coefficient, λ is the wavelength of the incident light, and ε d , ε m are the relative dielectric constants of dielectric and metal respectively.

[0035] The nanoelectrode topology adopts a regular n-gon structure (n is an even number), the electrode period is set to 120nm, the electrode diameter is 90nm, and the electrode height is 150nm. A staggered arrangement or a regular arrangement is adopted, such as Figure 3 shown.

[0036] Taking into account the feasibility of the process, we introduce a rounded corner structure into the topological figure, and the radius of curvature of the rounded corner is one-fifth to one-tenth of the radius of the topological figure.

[0037] The dielectric film material is silicon nitride (Si3N4). For a central wavelength of 780nm, a 300nm thick silicon nitride film deposited by chemical vapor deposition (PECVD) technology can achieve an anti-reflection effect with a transmittance of more than 99%. In addition, the silicon nitride dielectric film can also achieve passivation and protection of the PCA surface.

[0038] Example 1

[0039] like Figure 1 The three-dimensional structure diagram of a photoconductive antenna with a working wavelength of 780nm, a bias voltage of 50V and a nano-array electrode is shown. From front to back, it is: a silicon nitride film of a certain thickness, the antenna main electrode and the nano-electrode array, and a gallium arsenide substrate.

[0040] Figure 2 , Figure 3The front view and side view of the photoconductive antenna are respectively. According to the direction of light incidence, they are: silicon nitride film, antenna main electrode and nanoelectrode array, gallium arsenide substrate, where a nanoelectrode array is deposited in the gap between the antenna main electrode. Since the photon energy of 780nm wavelength is greater than the bandgap width of gallium arsenide, the electrons in gallium arsenide are excited to the conduction band to generate electron-hole pairs, which generate photocurrent and radiate terahertz waves under the condition of electrode bias. Due to the specific size and periodic arrangement of the nanoelectrode array, plasmon polarization elements are generated on the surface of gallium arsenide, the light intensity is significantly increased locally, the carrier concentration is increased, the photocurrent is increased, and ultimately the power of the radiated terahertz wave is increased.

[0041] The antenna main electrode material is Au, which is distributed in parallel and symmetrical manner, with a length of b=1.5 mm, a width of c=25 μm, a spacing of a=100 μm, and a thickness of h=200 nm.

[0042] The substrate is GaAs or LT-GaAs, with a size of 1.5mm×3mm and a thickness of d=625μm. GaAs has the characteristics of high electron mobility, short carrier lifetime, and strong voltage resistance, which makes it have unique advantages in the context of photogenerated terahertz applications.

[0043] The thickness of the silicon nitride film is selected to be 200-400nm at a working wavelength of 780nm, and the optimal thickness is preferably around 300nm. At this thickness, the silicon nitride film can achieve a transmittance of more than 99%, which is significantly improved compared to the transmittance of less than 70% without the film.

[0044] The topological figure of the nanoelectrode array unit is a regular hexagon, with a circumscribed circle radius r=50nm, a period p=120nm, and a height e=150nm.

[0045] The nanoelectrode array will introduce the SPP effect on the GaAs surface, resulting in an increase in the local light field, an increase in the carrier generation rate, and an increase in the photocurrent. The simulation results are as follows: Figure 4 shown.

[0046] The simulated photocurrent changes with bias voltage as shown in Figure 5 As shown, after the introduction of the nanoelectrode array, the photocurrent density saturation value is 8 times that without this structure.

[0047] The terahertz photoconductive antenna with nanoelectrode array units proposed in the present invention optimizes and improves the structure of traditional PCA devices, can be fully domestically produced and has superior performance, breaking the long-term monopoly of foreign countries, unfavorable situations such as inflated prices, and achieving "bottleneck" technology breakthroughs and commercialization.

[0048] It should be noted that, according to the needs of implementation, each step / component described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention. It should be understood that, for those of ordinary skill in the art, improvements or changes can be made based on the above description, and all such improvements and changes should fall within the scope of protection of the claims attached to the present invention.

[0049] In this article, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that an article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, the elements defined by the statement "comprising a ..." do not exclude the presence of other identical elements in the article or device comprising the above elements.

[0050] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A terahertz photoconductive antenna with a nanoelectrode array unit structure, characterized in that: It comprises a semiconductor substrate, a metal electrode, a nano-electrode array unit and a dielectric film; wherein the nano-electrode array unit is composed of a topological pattern of a plurality of regular n-gon nano-electrodes, wherein n is a positive even number.

2. The terahertz photoconductive antenna according to claim 1, characterized in that: The semiconductor substrate is GaAs with a crystal orientation of 100 or low-temperature grown GaAs, and the electron mobility is greater than 5500 cm 2 / (V·s), dark current is less than 5nA@10V, and thickness is 400~625μm.

3. The terahertz photoconductive antenna according to claim 1, characterized in that: The dielectric film is silicon nitride or silicon dioxide, and has a thickness of 200-400 nm.

4. The terahertz photoconductive antenna according to claim 1, characterized in that: The metal electrodes are parallel strip-line structures and are symmetrically distributed. The metal electrodes have a length of 1 mm to 1.5 mm, a width of 10 μm to 25 μm, an electrode spacing of 50 μm to 100 μm, and a thickness of 200 nm to 400 nm.

5. The terahertz photoconductive antenna according to claim 4, characterized in that: The metal electrode material is Au.

6. The terahertz photoconductive antenna according to claim 5, characterized in that: The nanoelectrode array units are arranged between the metal electrodes and are distributed at periodic intervals. The electrode distribution period p follows Where α is the coefficient, λ is the wavelength of the incident light, and ε d , ε m are the relative dielectric constants of dielectric and metal respectively.

7. The terahertz photoconductive antenna according to claim 6, characterized in that: The periodic interval distribution of the nanoelectrode array units is set to 120 nm, the diameter of the nanoelectrode is 90 nm, and the height of the nanoelectrode is 150 nm.

8. The terahertz photoconductive antenna according to claim 6, characterized in that: The nano-electrode array units are arranged in a staggered manner or in a neat manner.

9. The terahertz photoconductive antenna according to claim 1, characterized in that: The topological figure includes a rounded corner structure, and the curvature radius of the rounded corner structure is one fifth to one tenth of the radius of the topological figure.

10. The terahertz photoconductive antenna according to claim 1, characterized in that: The light source of the terahertz photoconductive antenna is a femtosecond pulse laser with a central wavelength of 780nm. The emission power of the femtosecond pulse laser is 10mW-100mW, the pulse width is 100fs, the repetition period is 50MHz, and the light source is linearly polarized light; the DC bias power supply bias voltage of the terahertz photoconductive antenna is between 10V and 70V.

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