Research On Micro-Nano Structure Enhanced Silicon-based Terahertz Functional Devices

Terahertz?THz?wave is located in the cross area of electronics and photonics in the electromagnetic spectrum.It has many excellent properties,such as broadband,low energy and good coherence.It has a broad application prospect in wireless communication,security inspection,nondestructive detection,medical imaging,weapon guidance and many other aspects.Among them,the terahertz imaging technology is a hot spot in the terahertz wave research field at present,and the high-efficiency terahertz wave modulator is one of the key factors to improve the imaging level.Among the existing terahertz modulation devices,silicon-based all-optical terahertz modulators have attracted much attention due to their advantages such as simple structure,easy high-density integration,and their manufacturing technology compatible with existing CMOS processes.The reflectivity of semiconductor silicon to the laser in the wavelength range of 400¹100 nm is as high as 40%⁶0%.Its low laser utilization rate not only reduces the modulation depth of the device,but the reflected laser will also cause interference and noise to the application system.Based on this,this paper mainly focuses on how to improve the modulation depth of silicon-based optical controlled terahertz wave modulator and the utilization ratio of pump laser.The influence of silicon surface micro-nano structure and surface passivation technology on its modulation performance is studied,and the modulation performance of the device is verified by terahertz imaging experiment.The main work includes:Firstly,the effect of the silicon surface microstructure on the performance of the modulator is studied.Black silicon with a micron-scale pyramid structure is prepared on a silicon wafer by chemical etching,and the reflectivity of black silicon to light in the wavelength range of 400¹100 nm is only 25%,which is much lower than that of high-resistance silicon?54%?,which greatly reduces the reflection effect on the laser,improves the laser utilization rate,and further improves the terahertz modulation depth.Under the action of 808 nm laser,the THz wave modulation depth of black silicon can reach 80%at 1.2 W.Secondly,the effect of silicon surface passivation on the performance of the modulator is studied.Using HF solution and Al₂O₃ thin film to passivate the semiconductor silicon,both have a great effect on improving the modulation performance of the terahertz wave.Under the action of 808 nm laser,the THz wave modulation depth of HF passivated silicon modulator can reach 90%at 1.2 W,while the THz wave modulation depth of Al₂O₃ passivated silicon modulator can reach 94%.We found that the terahertz wave modulation performance of HF-passivated silicon modulator is unstable,and its terahertz wave modulation performance is gradually weakening with the passage of time.Finally,a combination of black silicon with a pyramid structure and a silicon surface passivation method is used to passivate the black silicon with an Al₂O₃ thin film to form a micron-sized pyramid structure and a nano-scale thin film passivation layer.To prepare a black silicon surface passivation optically controlled THz wave modulator.Under the action of 808 nm laser,the THz wave modulation depth of the modulator can reach 91.2%at 1.2 W;at low laser power,the THz wave modulation depth of the modulator is greatly improved,and the modulation depth can reach 41.3%at 0.2 W.Using this modulator and digital micromirror spatial light modulator,a terahertz imaging system was built,which successfully realized 10×10 and 15×15 array imaging.