Study On Terahertz Photoconductive Antennas Integrated With Nano-Metamaterials

Terahertz usually refers to electromagnetic waves with a frequency between 0.1-10 THz.Terahertz spectroscopy is a common method for studying the properties of various materials in terahertz band,and it has an irreplaceable role.The core of this technology is terahertz time-domain spectroscopy system.Photoconductive antenna is commonly used as emitter in the terahertz time-domain spectroscopy system,and its working performance determines the actual performance of the system to a certain extent.At present,the performance of the photoconductive antenna still has some shortcomings--the power and efficiency of the generated terahertz wave is still weak and low.Therefore,how to improve the performance of photoconductive antenna is one of the hot researches in the past decade.The rise of metamaterials has provided researchers with new research methods and ideas--using the singular electromagnetic response characteristics of metamaterials,it is expected to improve the performance indicators of photoconductive antennas.The existing experimental research,using metal metamaterials to improve the performance of photoconductive antenna,not only exhibit metallic ohmic loss,but also fail to achieve full-phase modulation,thus,a novel method has been proposed in this paper to address the above issues.The combination of the dielectric metamaterials and photoconductive antenna can achieve high absorption of pump light by the antenna section,so that the excitated electric field of pump light is localized in the interface between the nanostructure and substrate,the ratio of carriers in the surface of semiconductor substrate can be improved,and more carriers are promoted to the antenna electrode smoothly,therefore,the quantum efficiency of the photoconductive transmitting antenna is improved.This design not only enhances terahertz radiation,but also makes full use of the limited area of antenna section.During the research,the electromagnetic field simulation software CST was used to simulate cell structure of the nanopillar array and analyze the electric field,the structure has obvious anti-reflection effect at 800 nm wavelength and the excitation electric field can be localized in substrate surface.The structure is arranged on the antenna section near the anode of photoconductive antenna.After the unit structure is designed,the micro-nanometer processing technology are used to process samples,then the reflectance measurement system is designed and constructed to measure the reflection of samples for 800 nm pump wavelength.The experimental results show that the samples have obvious anti-reflection effect near the 800 nm wavelength,which is consistent with the electromagnetic simulation results.Finally,the terahertz time-domain spectroscopy system is used to measure the amplitude of terahertz radiation,The time domain and frequency domain signals of samples and reference are obtained,the results show that the existence of nanostructures has an effect on the improvement of antenna performance.The maximum electric field amplitude in the terahertz time domain was increased by 1.34 times,the terahertz radiation power is increased by 1.35 times at 0.91 THz,and the spectrum is broadened.The author combines the two research hotspots of dielectric metamaterials and photoconductive antenna to provide new ideas and methods for the development of photoconductive antenna,which is of significance for the development and application of terahertz technology.