1 research outputs found
Unsaturated Drift Velocity of Monolayer Graphene
We
observe that carriers in graphene can be accelerated to the
Fermi velocity without heating the lattice. At large Fermi energy
|<i>E</i><sub>F</sub>| > 110 meV, electrons excited by
a
high-power terahertz pulse <i>E</i><sub>THz</sub> relax
by emitting optical phonons, resulting in heating of the graphene
lattice and optical-phonon generation. This is owing to enhanced electron–phonon
scattering at large Fermi energy, at which the large phase space is
available for hot electrons. The emitted optical phonons cause carrier
scattering, reducing the drift velocity or carrier mobility. However,
for |<i>E</i><sub>F</sub>| ≤ 110 meV, electron–phonon
scattering rate is suppressed owing to the diminishing density of
states near the Dirac point. Therefore, <i>E</i><sub>THz</sub> continues to accelerate carriers without them losing energy to optical
phonons, allowing the carriers to travel at the Fermi velocity. The
exotic carrier dynamics does not result from the massless nature,
but the electron–optical-phonon scattering rate depends on
Fermi level in the graphene. Our observations provide insight into
the application of graphene for high-speed electronics without degrading
carrier mobility