Terahertz Oscillations of Hot Electrons in Graphene
University of Illinois - Urbana Champaign United States
Pagination or Media Count:
Once a uniform electric field is turned on in graphene, carriers accelerate ballistically until they are scattered by optic phonons and the process repeats itself. In this dissertation, I will show that the oscillatory nature of the motion of the carrier distribution function manifests in damped oscillations of carrier drift velocity and average energy. In appropriate fields, the frequency of such oscillations can be in the terahertz THz range. The randomizing nature of optical phonon scattering on graphenes linear band structure further limits terahertz observation to a range of sample lengths. I will also show that when an ac field is superimposed onto the appropriate dc field, hot carriers in graphene undergo an anomalous parametric resonance. Finally, this dissertation shows that in graphene, the motion of carriers under the influence of temporarily and spatially modulated scattering is characterized by sharp resonances. Such resonances occur when the period of the ac field applied equals the time taken by the quasi-ballistic carriers to travel a spatial distance corresponding to the wavelength of the field. I will also show that such scattering can be realized on graphene sheets on periodically spaced gates energized by an a-c bias. Appropriate fields and gate separation will result in high Q-factor resonances in the THz range. The resonant frequencies are tunable with the gate separation, and higher harmonics with large Q-factors can also be achieved.
- Nuclear Physics and Elementary Particle Physics
- Electricity and Magnetism