Research On Semiconductor Spatial Terahertz Modulator Enhanced By Nanoparticles For Imaging Applications

Terahertz(THz)wave refers to electromagnetic wave whose frequency ranges from 0.1 THz to 10 THz.THz wave has many excellent characteristics,such as selective penetration,water sensitivity,fingerprint characteristics and low photon energy,which makes it have great potential in non-contact non-destructive imaging.In the past two decades,with the rapid development of THz sources and detectors,THz imaging technologies have gradually become a research hotspot.Among them,active THz compressive sensing imaging is one of the important technological solutions.The spatial terahertz modulator is the key components for the THz compressive sensing imaging system.Silicon-based optical THz spatial modulators excel in broadband,low insertion loss and fast modulation speed.However,the modulation depth of bare silicon is usually small.Further,due to the diffusion of photo-generated charge carriers,the spatial resolution of existing silicon-based modulators is inferior.In this thesis,a novel semiconductor array spatial terahertz modulator is fabricated by reducing the size of silicon(?3 mm),which is patterned on quartz substrates with double-sided PET glue.It effectively reduces the diffusion of photo-generated carriers in silicon wafers.The optical modulation depth is enhanced by self-assembled plasmonic gold nanoparticles monolayer.The interaction between terahertz wave and gold nanoparticle coated silicon arrays of different sizes as well as their optical modulation performance are studied in details in this thesis.When the size of silicon wafer is 1 mm,2 mm and 3 mm,the modulation depth is 42%,57% and 70% respectively.The reducing modulation depth at small size can be attributed to the defects at the edge that act as the recombination center of the photo-generated carriers.When the size of the silicon wafer is small,the photo-generated carriers are easy to diffuse to the edge for recombination,resulting in lower equilibrium carrier concentration in the silicon and lower optical modulation depth.As the size of silicon increase,the recombination of photo-generated charge carriers at the edge is alleviated,giving higher modulation depth of terahertz wave.By comparing the spatial modulation of nanoparticles enhanced small silicon(3 mm×3 mm)array with that of large silicon wafer(10 mm×10 mm),it is found that the small silicon array has a high spatial resolution.In addition,the array spatial modulator is applied to the compressed sensing imaging,and a clear and higher resolution image is obtained.The semiconductor spatial modulator enhanced by nanoparticles studied in this thesis has the characteristics of moderate modulation speed,high optical modulation depth and high spatial resolution,which provides a new type of spatial modulator for terahertz compressed sensing imaging system.