| Silicon-based semiconductors are the cornerstone of the modern electronics industry,and their heterojunction coupling with emerging two-dimensional(2D)materials can be used in a variety of electronic and photoelectric devices.Among them,graphene/silicon heterojunction,as the most widely studied silicon-2D material composite structure,has been demonstrated to have strong rectification properties and high photoresponse properties.At the same time,due to the high carrier mobility of graphene,this structure is also the best choice for terahertz wave modulators.It can be predicted that based on this structure,different modification of the surface interface of silicon and graphene can realize the optimal design for different photoelectric functions,and finally obtain multi-functional and high-performance photoelectric response devices.The main research contents of this dissertation are as follows:1?According to the absorption test theory in terahertz time domain and frequency domain,the refractive index,extinction coefficient and complex permittivity of graphene/Mn Zn ferrite/Si heterojunction in the terahertz band were tested by Fourier transform.The mechanism of interaction between magnetic moment,spin,conductance and terahertz wave under the action of electric field and external magnetic field is proposed for the first time.2?The preparation method of high-quality Mn Zn ferrite films was studied.The effects of sputtering power,sputtering gas pressure,substrate temperature and annealing on the structure and properties of Mn Zn ferrite films grown by magnetron sputtering were studied by using vibrating sample magnetometer,X-ray diffraction spectrum,atomic force microscope and other material characterization methods.On this basis,graphene/Mn Zn ferrite/p-Si heterojunction devices were constructed,which exhibited obvious photoresponse under short-wave infrared light with a wavelength of 915 nm and a power of 1 W.At the same time,the transmission modulation of terahertz waves can be realized by adjusting the source-gate voltage.When a gate voltage of-25 V and a magnetic field perpendicular to the film surface is applied,the real parts of the complex refractive index and the complex permittivity increase accordingly.Due to the anomalous Zeeman effect and anisotropic magnetoresistance effect of Mn Zn ferrite film,the overall conductivity and refractive index of the film change,which makes the external magnetic field have a phase modulation effect on terahertz waves.And it is proved that the graphene/Mn Zn ferrite/Si heterojunction under the action of magnetic field can be applied as a phase modulator.3?Multifunctional photodetectors and terahertz modulation devices based on graphene/Ti O2/p-Si structure have been prepared.As a photodetector,under-2 V bias,the highest responsivity is 3.6 A/W.The external quantum efficiency is 6001%.The specific detectivity is 4×1013 Jones.The rise time is 69.59?s and the fall time is 162.4?s under the light of 750 nm wavelength.As an electric field excited terahertz modulator,it works in normally-on state(0 V prevents transmission),and the modulation depth is about 23%at-15 V.When used as a photoexcited terahertz modulator,the insertion of Ti O2films enhanced the separation of photoexcited carriers in Si,making the modulation performance of graphene/Ti O2/p-Si significantly higher than that of Si and graphene/Si.Under the 808 nm laser,the modulation depth of graphene/Ti O2/p-Si is as high as 70.3%,and the modulation speed is 5 k Hz.4?The Pt particle composite layer introduced inside the titanium oxide(Ti O2@Pt)will introduce a recombination energy level in the center of the Ti O2 forbidden band,which result the reduction of the recombination barrier and reduce the carrier lifetime of the device.Therefore,the speed of graphene/Ti O2@Pt/Si photodetector and the speed of terahertz modulator get improved.For the entire effective detection light field,the external quantum efficiency is above 70%,and the highest is 87%.Under the 808 nm laser pumping at 3.5 k Hz,the relaxation time of the device is reduced to 40.08?s,while its rise time is 14.75?s.Meanwhile,the THz modulation depth of graphene/Ti O2@Pt/Si device can reach 81%under 808 nm laser pumping.And the modulation speed is increased to 7.8 k Hz.5?A self-feedback all-optical modulation terahertz system is constructed based on a multifunctional photodetector and a terahertz modulator.The optical response signal of the graphene/Ti O2@Pt/p-Si modulator and the modulated laser control signal are coupled through a logic gate circuit to realize real-time feedback during the terahertz dynamic modulation process.When the optical response signal is not synchronized with the modulation signal,an alarm output is given. |
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