535 research outputs found
Hydrodynamic model for electron-hole plasma in graphene
We propose a hydrodynamic model describing steady-state and dynamic electron
and hole transport properties of graphene structures which accounts for the
features of the electron and hole spectra. It is intended for electron-hole
plasma in graphene characterized by high rate of intercarrier scattering
compared to external scattering (on phonons and impurities), i.e., for
intrinsic or optically pumped (bipolar plasma), and gated graphene (virtually
monopolar plasma). We demonstrate that the effect of strong interaction of
electrons and holes on their transport can be treated as a viscous friction
between the electron and hole components. We apply the developed model for the
calculations of the graphene dc conductivity, in particular, the effect of
mutual drag of electrons and holes is described. The spectra and damping of
collective excitations in graphene in the bipolar and monopolar limits are
found. It is shown that at high gate voltages and, hence, at high electron and
low hole densities (or vice-versa), the excitations are associated with the
self-consistent electric field and the hydrodynamic pressure (plasma waves). In
intrinsic and optically pumped graphene, the waves constitute quasineutral
perturbations of the electron and hole densities (electron-hole sound waves)
with the velocity being dependent only on the fundamental graphene constants.Comment: 11 pages, 6 figure
Electrically-induced n-i-p junctions in multiple graphene layer structures
The Fermi energies of electrons and holes and their densities in different
graphene layers (GLs) in the n- and p-regions of the electrically induced n-i-p
junctions formed in multiple-GL structures are calculated both numerically and
using a simplified analytical model. The reverse current associated with the
injection of minority carriers through the n- and p-regions in the
electrically-induced n-i-p junctions under the reverse bias is calculated as
well. It is shown that in the electrically-induced n-i-p junctions with
moderate numbers of GLs the reverse current can be substantially suppressed.
Hence, multiple-GL structures with such n-i-p junctions can be used in
different electron and optoelectron devices.Comment: 7 pages, 6 figure
Preliminary experimental results of gas recycling subsystems except carbon dioxide concentration
Oxygen concentration and separation is an essential factor for air recycling in a controlled ecological life support system (CELSS). Furthermore, if the value of the plant assimilatory quotient is not coincident with that of the animal respiratory quotient, the recovery of oxygen from the concentrated CO2 through chemical methods will become necessary to balance the gas contents in a CELSS. Therefore, oxygen concentration and separation equipment using Salcomine and O2 recovery equipment, such as Sabatier and Bosch reactors, were experimentally developed and tested
Plasma mechanisms of resonant terahertz detection in two-dimensional electron channel with split gates
We analyze the operation of a resonant detector of terahertz (THz) radiation
based on a two-dimensional electron gas (2DEG) channel with split gates. The
side gates are used for the excitation of plasma oscillations by incoming THz
radiation and control of the resonant plasma frequencies. The central gate
provides the potential barrier separating the source and drain portions of the
2DEG channel. Two possible mechanisms of the detection are considered: (1)
modulation of the ac potential drop across the barrier and (2) heating of the
2DEG due to the resonant plasma-assisted absorption of THz radiation followed
by an increase in thermionic dc current through the barrier. Using the device
model we calculate the frequency and temperature dependences of the detector
responsivity associated with both dynamic and heating (bolometric) mechanisms.
It is shown that the dynamic mechanisms dominates at elevated temperatures,
whereas the heating mechanism provides larger contribution at low temperatures,
T=35-40 K.Comment: 7 pages, 4 figure
- …