Terahertz Wave Modulator Based On MIS Capacitor

Terahertz wave is the last electromagnetic frequency band to be adopted by human Earlier,due to the lack of efficient terahertz source and detectors,the application of terahertz wave has not been well developed.At present,a vast range of applications have been envisioned for the terahertz wave,which covers such fields as national defense,health care,telecommunication,environment.As for the research of terahertz devices,terahertz wave modulators are essential for many terahertz technologies.Here we prepared a terahertz wave modulator based on MIS capacitor.The modulation performance was studied when laser and voltage bias were applied as the stimuli Meanwhile,the fabrication process was also optimizedIn this thesis,we first discussed the preparation of graphene/boron nitride/p-silicon MIS capacitor,and the fabrication process was optimized.Comparison study show that graphene/boron nitride heterostructure modified silicon has two time higher modulation depth and faster modulation speed than the graphene modified silicon at laser power of 100 mW.The improvement can be attributed to the thin boron nitride dielectric layer,which can more effectively separate the photogenerated electrons and holes in comparison with graphene modified silicon.After that,MIS capacitor was prepared using boron nitride as dielectric layer and graphene as the conducting layer.Experimental results show that upon laser irradiation the THz modulation is determined by the three states of accumulation,depletion and inversion when the bias voltage is applied to the MIS capacitor.The silicon substrate is connected to the ground.From 0.2 to 1 THz,when negative bias is applied,the modulation depth will increased up to 52%as bias increase.When positive bias is applied,interfacial charge can vary due to the formation of depletion and the inversion layer.The THz transmission would increase at first and then gradually decrease at the threshold voltage.The maximum modulation depth can be up to 65%.Compared with a conventional silicon terahertz wave modulator,it has lower insertion loss,lower working voltage,and can be produced in large scale.It has provided a new route for better terahertz wave modulators.It also provide a new direction of development for flexible terahertz devices.