Abstract -Coulomb-driven terahertz-frequency intrinsic current oscillations in a double-barrier tunneling structure

O. Jonasson and I. Knezevic

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.165415

We investigate time-dependent, room-temperature quantum electronic transport in GaAs/AlGaAs double-barrier tunneling structures (DBTSs). The open-boundary Wigner-Boltzmann transport equation is solved by the stochastic ensemble Monte Carlo technique, coupled with Poisson's equation and including electron scattering with phonons and ionized dopants. We observe well-resolved and persistent terahertz-frequency current-density oscillations in uniformly doped, dc-biased DBTSs at room temperature. We show that the origin of these intrinsic current oscillations is not consistent with previously proposed models, which predicted an oscillation frequency given by the average energy difference between the quasibound states localized in the emitter and main quantum wells. Instead, the current oscillations are driven by the long-range Coulomb interactions, with the oscillation frequency determined by the ratio of the charges stored in the emitter and main quantum wells. We discuss the tunability of the frequency by varying the doping density and profile.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.165415

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• Published 14 October 2014
• Received 4 May 2014
• Revised 26 September 2014

©2014 American Physical Society

Abstract-Coulomb-driven terahertz-frequency intrinsic current oscillations in a double-barrier tunneling structure

O. Jonasson and I. Knezevic

https://journals.aps.org/prb/accepted/fa075O46F2c15429d22884402ffae99d512a20258

We investigate time-dependent, room-temperature quantum electronic transport in GaAs/AlGaAs double-barrier tunneling structures (DBTSs). The open-boundary Wigner-Boltzmann transport equation is solved by the stochastic ensemble Monte Carlo technique, coupled with Poisson's equation and including electron scattering with phonons and ionized dopants. We observe well-resolved and persistent THz-frequency current density oscillations in uniformly-doped, dc-biased DBTSs at room temperature. We show that the origin of these intrinsic current oscillations is not consistent with previously proposed models, which predicted an oscillation frequency given by the average energy difference between the quasi-bound states localized in the emitter and main quantum wells. Instead, the current oscillations are driven by the long-range Coulomb interactions, with the oscillation frequency determined by the ratio of the charges stored in the emitter and main quantum wells. We discuss the tunability of the frequency by varying the doping density and profile.

Abstract-Terahertz-frequency electronic transport in graphene

N. Sule, K. J. Willis, S. C. Hagness, and I. Knezevic
https://journals.aps.org/prb/accepted/f1076O3dG0313f2b82308c24eff2c3c243647ae6a


We calculate the room-temperature complex conductivity \sigma(\omega) of suspended and supported graphene at terahertz frequencies (100\,{\mathrm{GHz}}\text{--}10\,{\mathrm{THz}}) by employing a self-consistent coupled simulation of carrier transport and electrodynamics. We consider a wide range of electron (n=1012\text{--}\,1013\,{\mathrm{cm}-2}) and impurity densities ( N\mathrm{i}=8\times 1010\text{--}\, 2\times 1012\,{\mathrm{cm}-2}). For graphene supported on SiO2, there is excellent agreement between the calculation with clustered impurities and the experimentally measured \sigma(\omega). The choice of substrate (SiO2 or h-BN) is important at frequencies below 4 THz. We show that carrier scattering with substrate phonons governs transport in supported graphene for N\mathrm{i}/n0.1, and transport enters the electron-hole puddle regime for N\mathrm{i}/n>0.5. The simple Drude model, with an effective scattering rate \Gamma and Drude weight D as parameters, fits the calculated \sigma (\omega) for supported graphene very well, owing to electron-impurity scattering. \Gamma decreases with increasing n faster than n-1/2 and is insensitive to electron-electron interaction. Both electron-electron and electron-impurity interactions reduce the Drude weight D, and its dependence on n is sublinear.