Research Of Broadband Terahertz Wave Modulators Based On Graphene

The terahertz portion of the electromagnetic spectrum is experiencing a substantial growth in interest, with new applications in security, medicine and communications, among others, emerging at a rapid pace. However, the research of terahertz device application is relatively scarce, this phenomenon seriously limits the practical application of terahertz technology and rapid development. Because the research on THz spectrum of the available functions of electronic materials and terahertz devices is very meaningful. In recent years, due to its unique band structure and the electrical transport properties graphene has acquired widely attention. At the same time, the graphene in the field of terahertz functional device also show huge potential and application value. Based on above background, this paper introduced the preparation of the THZ wave modulator based on graphene respectively by optical control and electrical control, and researched THz modulation performance under different situations.Firstly, we have a research in the transfer method of large area graphene grown via CVD process. We make the improvement and optimization of the process and the parameters in the graphene transfer method. By the optimization of graphene transfer process, the metal impurity particles and the photoresist residue on the surface of graphene were prevented which was usually happened during the traditional transfer technology.In addition, using the effect of photogenic charge carrier at the interface of the Si substrate and graphene leading to the low transmission of THz wave, we produced the THz modulator controlled by laser based on graphene/Si substrate. However, the electrical properties such as transconductance and mobility of graphene was fallen down by the impurities, adsorption of water vapor and the charged impurity scattering on the surface of graphene. In this paper, the graphene film was modified by spinning coated different thickness of 3-Aminopropyltriethoxysilane(3-AT) and Dimethyl sulfoxide(DMSO). That would improve the transport properties of graphene, and enhance the modulation of terahertz wave.Finally, we prepared the THz wave modulator based on large-area graphene fieldeffect transistor. An ultrathin Al2O3 film(～60 nm) is deposited by an atomic-layerdeposition(ALD) technique as a large-area high-? gate dielectric layer. Al2O3 film has a high dielectric constant compared with Si O2, which could effectively reduce the coulomb scattering and the cavity effect in order to gain a larger transconductance of graphene. That would improve the modulation depth and modulation speed of THz modulator. Our modulator has achieved a modulation depth of 22 % and modulation speed of 170 k Hz in a frequency range from 0.4 to 1.5 THz by adjusting the back gate to control the carrier concentration in graphene. It’s quite significant for the future application of THz technology.