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Register a new userInjection terahertz laser using the resonant inter-layer radiative transitions in double-graphene-layer structure
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We propose and substantiate the concept of terahertz (THz) laser enabled by the resonant electron radiative transitions between graphene layers (GLs) in double-GL structures. We estimate the THz gain for TM-mode exhibiting very low Drude absorption in GLs and show that the gain can exceed the losses in metal-metal waveguides at the low end of the THz range. The spectrum of the emitted photons can be tuned by the applied voltage. A weak temperature dependence of the THz gain promotes an effective operation at room temperature.
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We study the dynamic effects in the double graphene-layer (GL) structures with the resonant-tunneling (RT) and the negative differential inter-GL conductivity. Using the developed model, which accounts for the excitation of self-consistent oscillations of the electron and hole densities and the ac electric field between GLs (plasma oscillations), we calculate the admittance of the double-GL RT structures as a function of the signal frequency and applied voltages, and the spectrum and increment/decrement of plasma oscillations. Our results show that the electron-hole plasma in the double-GL RT structures with realistic parameters is stable with respect to the self-excitation of plasma oscillations and aperiodic perturbations. The stability of the electron-hole plasma at the bias voltages corresponding to the inter-GL RT and strong nonlinearity of the RT current-voltage characteristics enable using the double-GL RT structures for detection of teraherz (THz) radiation. The excitation of plasma oscillations by the incoming THz radiation can result in a sharp resonant dependence of detector responsivity on radiation frequency and the bias voltage. Due to a strong nonlinearity of the current-voltage characteristics of the double-GL structures at RT and the resonant excitation of plasma oscillations, the maximum responsivity, $R_V^{max}$, can markedly exceed the values $(10^4 - 10^5)$~V/W at room temperature.
It is by now well established that high-quality graphene enables a gate-tunable low-loss plasmonic platform for the efficient confinement, enhancement, and manipulation of optical fields spanning a broad range of frequencies, from the mid infrared to the Terahertz domain. While all-electrical detection of graphene plasmons has been demonstrated, electrical plasmon injection (EPI), which is crucial to operate nanoplasmonic devices without the encumbrance of a far-field optical apparatus, remains elusive. In this work, we present a theory of EPI in double-layer graphene, where a vertical tunnel current excites acoustic and optical plasmon modes. We first calculate the power delivered by the applied inter-layer voltage bias into these collective modes. We then show that this system works also as a spectrally-resolved molecular sensor.
We describe a technique which allows a direct measurement of the relative Fermi energy in an electron system using a double layer structure, where graphene is one of the two layers. We illustrate this method by probing the Fermi energy as a function of density in a graphene monolayer, at zero and in high magnetic fields. This technique allows us to determine the Fermi velocity, Landau level spacing, and Landau level broadening in graphene. We find that the N=0 Landau level broadening is larger by comparison to the broadening of upper and lower Landau levels.
We induce surface carrier densities up to $sim7cdot 10^{14}$cm$^{-2}$ in few-layer graphene devices by electric double layer gating with a polymeric electrolyte. In 3-, 4- and 5-layer graphene below 20-30K we observe a logarithmic upturn of resistance that we attribute to weak localization in the diffusive regime. By studying this effect as a function of carrier density and with ab-initio calculations we derive the dependence of transport, intervalley and phase coherence scattering lifetimes on total carrier density. We find that electron-electron scattering in the Nyquist regime is the main source of dephasing at temperatures lower than 30K in the $sim10^{13}$cm$^{-2}$ to $sim7 cdot 10^{14}$cm$^{-2}$ range of carrier densities. With the increase of gate voltage, transport elastic scattering is dominated by the competing effects due to the increase in both carrier density and charged scattering centers at the surface. We also tune our devices into a crossover regime between weak and strong localization, indicating that simultaneous tunability of both carrier and defect density at the surface of electric double layer gated materials is possible.
We propose the concept of terahertz (THz) photomixing enabled by the interband electron transitions due to the absorption of modulated optical radiation in double-graphene layer (double-GL) structures and the resonant excitation of plasma oscillations. Using the developed double-GL photomixer (DG-PM) model, we describe its operation and calculate the device characteristics. The output power of the THz radiation exhibits sharp resonant peaks at the plasmonic resonant frequencies. The peak powers markedly exceed the output powers at relatively low frequencies. Due to relatively high quantum efficiency of optical absorption in GLs and short inter-GL transit time, the proposed DG-PM operating in the resonant plasma oscillation regime can surpass the photomixers based on the standard heterostructures .
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