Investigations Of Electrical And Optical Properties Of Graphene Field Effect Transistor For Terahertz Wave Generation

The terahertz(THz) is broadly applied to submillimeter-wave energy that fills the wavelength range between infrared and microwave/millimeter wave. THz technology has a wide application prospect in imaging, environment monitoring, biomedical, military, etc. In recent years, the symmetric heterostructures of double graphene layers(GLs) with resonant tunnelling(RT) and plasma oscillation have attracted great interests for applications of detection and modulation at THz range. In this paper, the symmetric heterostructures of double graphene field effect transistors(FET) are proposed, which possess high electronic mobility and gated two-dimensional electron/hole(2EDG/2HDG) plasma in its channel, to explore the resonant excitation of plasma oscillations and detect or manipulate electromagnetic waves over the THz frequency band. Besides, the Bardeen transfer Hamiltonian approach and hydrodynamic equations coupled with the Poisson equation in the gradual-channel approximation are under concerned with discussions. The results are list as follows:First, we have derived the relation of quasi-Fermi energies in GLs and gate voltages, utilizing the charge neutrality condition with the geometrical and quantum capacitances, and aligned Dirac points in GLs. We discuss the nonlinearity of the inter-GL current tunnelling versus voltage characteristics, especially in the local value of the inter-GL RT current density distribution; the plasma velocity and the characteristic frequency of resonant plasma wave both in stationary states. Besides, we have achieved the dynamic negative differential conductance in our model with small ac signal-voltage component.Second, we have specified the configuration parameters with barrier thickness of 0.5 nm, high dielectric constant of gate oxide and hexagonal Boron Nitride(hBN) as an inter-layer. We have calculated the nonlinearity of the inter-GL current density, and obtained as higher as 106 of the current on-and-off ratio(Ion/Ioff). Then we focus on dynamic dynamic negative differential conductance(NDC) spectrum with qualified structural parameters. The results have shown that, with the coherence length of graphene unchanged, the NDC lies on lower electron-hole collision frequencies and lower plasma frequencies in THz range that can be tuned by gate voltages. The coherence lengths of graphene that short enough to submicronmeter demonstrate much sharper and clearer NDC as well as higher plasma frequencies. The generation of NDC enables the excitation and enhancement of the plasma oscillations, which can be weaken the landau damping, and the detection and radiation amplification in THz range.Third, we have investigated double GLs FET as a THz detector by incoming electromagnetic radiation received by an antenna. The source/drain electrodes receive the incident frequency connected with outside signal, then the incident frequency excited and resonate with the plasma wave in graphene channels, thus the detection response occur. The results indicate that we can obtain much sharper and higher peak value of volt-watt responsivity as long as the electron-hole collision frequencies lower enough, even higher than the responsivity in stationary states. The highest peak value can reach 107 V/W above. We have also changed the coherence lengths of graphene, and found the response peak decreased inconspicuously while lengthen the graphene channel. But the response peak can increase significantly by applying higher gate voltages. The structure parameter we defined has achieved the response peak value of 105 V/W at least in relatively lower THz range. The symmetric heterostructures of GLs FET are very promising for realizing terahertz detection. Finally, we have discussed the transmittance and absorbance of the structure under the THz electromagnetic radiation, based on plasma in graphene coupling with photon that form of surface plasmons. The simulation results show that the light absorption can be increased properly in lower THz frequency and turn out the potential applications of optical detection and modulation.