Energy relaxation via confined and interface phonons in quantum-wire systems (original) (raw)
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Hot-electron relaxation dynamics in quantum wires
Journal of Applied Physics, 1994
simulations of hot nonequilibrium electron relaxation in rectangular GaAs quantum wires of different cross sections are carried out. The simulations demonstrate that the initial stage of hot-electron cooling dynamics is determined by cascade emission of optical phonons and exhibits strong dependence on the excitation energy. The second (slow) relaxation stage is controlled by strongly inelastic electron interactions with acoustic phonons as well as by nonequilibrium (hot) optical phonons. The relaxation times obtained in our simulations are in good agreement with the results of recent luminescence experiments. At low electron concentrations where hot phonon effects are negligible the cascade emission of optical phonons may lead to the overcooling of the electron system to temperature below the lattice temperature. These electrons then slowly (during tens of picoseconds) relax to equilibrium due to the interaction with acoustic phonons. At certain excitation energies strong intersubband electron scattering by optical phonons leads to electron redistribution among subbands and intersubband population inversions. If the electron concentration exceeds lo5 cm-', hot phonon effects come into play. In contrast to bulk materials and quantum wells, hot phonon effects in quantum wires exhibit strong dependence on the initial broadening of the energy distribution of the electrons. The very initial electron gas relaxation stage in quantum wires is faster in the presence of hot phonons, while for t>OS ps the hot phonon thermalization time defines the characteristic electron cooling time.
Semiconductor Science and Technology, 1994
We present results of Monte Carlo simulations of electron relaxation dynamics in rectangular GaAs quantum wires (awls) embedded in AIAs. Electron interactions with confined LO phonons, interface optical phonons, bulk-like acoustic phonons as well as non-equilibrium (hot) optical phonons have been taken into account. It has been found that hot phonons come into play at electron concentrations exceeding 105cm-'. In awls electrons having appreciably different initial energies generate non-equilibrium phonons at different q-space regions which do not overlap. In turn, these phonons can be reabsorbed only by the electrons that have generated them. Consequently, hot-phonon effects become weaker as the energy distribution of excited electrons broadens. This result is in complete contrast to the case of bulk materials and quantum wells where the injected electron energy distribution virtually does not affect non-equilibrium phonon build-up and the reabsorption rate.
Hot-phonon effects on electron transport in quantum wires
Journal of Applied Physics, 1996
Hot ͑nonequilibrium͒ phonon effects on electron transport in rectangular GaAs/AlAs quantum wires have been investigated by a self-consistent Monte Carlo simulation. Confinement and localization of optical phonons have been taken into account. We have demonstrated that at room temperature hot optical phonons lead to a significant increase in electron drift velocity. This hot-phonon drag effect is due to the strongly asymmetric nonequilibrium phonon distribution. As a result, phonon absorption for forward transitions ͑electron gains momentum along electric field͒ is enhanced, whereas absorption for backward transitions ͑electron gains momentum against electric field͒ is suppressed. At low temperatures diffusive heating of electrons by hot phonons dominates over hot-phonon drag and the electron drift velocity decreases.
Relaxation of Electrons in Weakly-Onedimensional Semiconductor Quantum Wires Mediated by LO-Phonons
Helvetica Physica Acta, 1996
A weakly-onedimensional heterostructure is a quantum wire structure tailored so that the carriers are tightly confined in a direction, weakly confined in another and free to move in the third. The electronic bound states are computed using the envelope function approximation in the frame on the kp theory and the adiabatic approximation. Transition rates of the electrons from ally bound stale to ally other bound state mediated bg the LO-phonons are then evaluated. The lifetimes of excited levels and average energy with respect to time are ...
Influence of Phonon Dimensionality on Electron Energy Relaxation
Physical Review Letters, 2007
We studied experimentally the role of phonon dimensionality on electron-phonon (e-p) interaction in thin copper wires evaporated either on suspended silicon nitride membranes or on bulk substrates, at sub-Kelvin temperatures. The power emitted from electrons to phonons was measured using sensitive normal metal-insulator-superconductor (NIS) tunnel junction thermometers. Membrane thicknesses ranging from 30 nm to 750 nm were used to clearly see the onset of the effects of twodimensional (2D) phonon system. We observed for the first time that a 2D phonon spectrum clearly changes the temperature dependence and strength of the e-p scattering rate, with the interaction becoming stronger at the lowest temperatures below ∼ 0.5 K for the 30 nm membranes.
Mutual Hot-Phonon Effects in Coupled GaAs Quantum Wires
physica status solidi (b), 1998
Hot phonon effects on electron transport in coupled GaAs quantum wires embedded in AlAs have been investigated by a self-consistent Monte Carlo simulation. These results take into account optical phonon confinement within the GaAs region and localization at its boundaries which is caused by the presence of GaAs/AlAs heterointerfaces. Electrical confinement of electrons in several spatially separated quantum wire channels inside the GaAs region with common optical phonons (confined within the whole GaAs bar) is assumed. We have investigated numerically mutual interaction of electrons and phonons over a wide range of electric fields (0`E`1000 V/cm) and lattice temperatures (30 K T 300 K). We demonstrate that in a system of two quantum wires coupled through the common confined optical phonons, electron transport in one wire significantly affects electron transport in the second wire due to the presence of the strong mutual hot-phonon drag between these electron channels. This leads to a sufficient modification of the carrier veloc-ity±field characteristics in the structures investigated.
Electron-confined phonon interaction in a quantum wire with parabolic potential
Physics Letters A, 1992
We have studied the electron-confined phonon interaction within a rectangular quantum wire with an additional parabolic potential. Formulae for the polaron self-energy and the electron effective mass along the wire are derived. Numerical calculations are performed for a typical GaAs quantum wire,
Confined-phonon effects in the band-gap renormalization of semiconductor quantum wires
Physical Review B
We calculate the band-gap renormalization in quasi-one-dimensional semiconductor quantum wires including carrier-carrier and carrier-phonon interactions. We use the quasistatic approximation to obtain the selfenergies at the band edge that define the band-gap renormalization. The random-phase approximation at finite temperature is employed to describe the screening effects. We find that confined LO-phonon modes through their interaction with the electrons and holes modify the band gap significantly and produce a larger value than the static ⑀ 0 approximation. ͓S0163-1829͑98͒01007-8͔
Phonon renormalization effects in photoexcited quantum wires
Physical review. B, Condensed matter, 1995
We study the effects of screening on polaronic corrections to the effective band edge in a quasione-dimensional GaAs quantum wire. We 6nd that the screening effects and finite well width considerably reduce the polaron energy and oppose the polaronic band-gap renormalization. We calculate the polaronic effective mass as a function of the carrier density and temperature. Effects of the vertex corrections to the conductionand valence-band edges are also discussed.
Solid State Communications, 1996
We present a fully dynamical and finite temperature study of the hotelectron momentum relaxation rate and the power loss in a coupled system of electron-hole plasma and bulk LO-phonons in a quantum wire structure. Interactions of the scattered electron with neutral plasma components and phonons are treated on an equal footing within the random-phase approximation. Coupled mode effects substantially change the transport properties of the system at low temperatures. Particularly, the "plasmon-like" and "LO-phonon-like" excitations yield comparable rates which, as a consequence of the singular nature of the 1D density of states, can be large at the threshold. This is in contrast to room temperature results where only the LOphonon mode contributes significantly to the rate. The density and temperature dependence of the power loss reveals that dynamical screening effects are important, and energy-momentum conservation cannot be satisfied above a certain density for a given initial energy.