Plasmon Emission Research Articles

Far-infrared emission spectroscopy of hot two-dimensional plasmons in Al0.3Ga0.7As/GaAs heterojunctions

We have investigated the radiative decay of hot two-dimensional (2D) plasmons in Al0.3Ga0.7As/ GaAs heterostructures by far-infrared emission spectroscopy and determined the spectral line shape of the radiation. Narrowband plasmon emission lines are obtained in the terahertz regime. The experimentally observed energies of plasmon emission are in good agreement with the results of a recently developed full grating theory. The plasmon emission intensity is found to increase with increasing input electrical power to the electron system and follows the Bose–Einstein distribution law characterized by the electron temperature of the hot 2D electron system. This fact indicates that 2D plasmons are thermally excited in the present experimental regime.

Suppression of atomic radiation in a cylindrical nanocavity

An excited atom placed inside a cylindrical nanocavity cannot radiate if the frequency of emission is below the cutoff frequency for electromagnetic wave propagation in the cavity. However, we demonstrate that it can be de-excited through the emission of surface plasmons. The observable effect will be a substantial enhancement in the lifetime of dipole-allowed transitions. The recently discovered carbon nanotubules will be explored as potential nanometer scale cylindrical cavities and the lifetimes of excited states of Helium (2p → 1s) in the earbon nanocavities will be calculated as an example of this nonradiative decay mechanism. The dependence of the transition rate as a function of the radial distance from the tube surface is studied by varying the initial radial quantum number of the center-of-mass wavefunction for an atom confined within the nanotube. The results of the calculation are used to explore the possible application of concentric carbon nanotube structures as TEM waveguides.

Light emission from STM by means of the Cherenkov effect

In the present work we have shown experimentally that the light emission intensity from a STM tunneling junction depends exponentially on the tunneling distance, and we believe that the decay constant is equal to the mean wave vector of the surface plasmons excited by the tunneling electrons. Our estimation of the plasmon phase velocity shows that this is about two times smaller than the Fermi velocity of the electrons inside the metal. Theoretically, we have developed a description of the phenomenon based on resonant Cherenkov interaction between the tunneling electrons and the propagating surface plasmons. Our calculations of the dispersion law of the surface plasmons and the quantum efficiency for plasmon emission by the tunneling electrons are in qualitative agreement with the experimental data.

Cavity quantum electrodynamics in a carbon nanotube

Abstract An excited atom placed inside a metallic carbon nanotube cannot radiate if the frequency of its emission is below the cutoff frequency for electromagnetic wave propagation in the cavity. However, we demonstrate that it can be de-excited through the emission of surface plasmons on the nanotube. The observable effect will be a substantial enhancement in the lifetime of dipole-allowed transitions. The lifetimes of excited states of Helium (2p → 1s) in the carbon nanocavities are calculated for this nonradiative decay mechanism and the radial dependence of the lifetimes discussed.

Many-body exchange-correlation effects in the lowest subband of semiconductor quantum wires.

We consider theoretically the electron-electron-interaction-induced exchange-correlation effects in the lowest subband of quasi-one-dimensional GaAs quantum-wire structures. We calculate, within the leading-order dynamical-screening approximation (i.e., the so-called GW approximation of the electron-gas theory), the electron self-energy, spectral function, momentum distribution function, inelastic-scattering rate, band-gap renormalization, and the many-body renormalization factor at both zero and finite temperatures, and both with and without impurity-scattering effects. We also calculate the effects of finite temperatures and finite impurity scattering on the many-body properties. We propose the possibility of a hot-electron transistor device with a large negative differential resistance which is based on the sudden onset of plasmon emission by energetic ballistic electrons in one dimension. The issue of the existence or nonexistence of the Fermi surface among the interacting one-dimensional quantum-wire electrons is critically discussed based on our numerical results.

Coulomb lifetime and electronic distribution function in a drifting two-dimensional electron gas.

The nonequilibrium distribution function of a two-dimensional electron gas (2DEG) drifting under a high electric field is calculated within the Lei-Ting approach of high-field transport. The separation of the center-of-mass motion from the relative motion of the electrons leads to anisotropic interactions with impurities and phonons that disturb the relative electron gas from a thermodynamic equilibrium state. The correcting amount to the equilibrium momentum distribution function turns out to be the product of the impurity and phonon interactions scattering rate by the particle Coulomb lifetime. This last one is expressed from the full spectral density functions so that its validity extends beyond the quasiparticle theory frame. The importance of a self-consistent calculation is first illustrated by a study of the zero-temperature many-body properties of the Coulomb gas: the plasmaron is shown to be an actual excitation; the threshold for plasmon emission is softened, and undamped Fermi-level particles are found to have a spectral weight nearly equal to unity. Then, within the drifting hot-electron gas, the Doppler shift of the LO-phonon frequencies is shown to enhance the plasmon--LO-phonon coupling. Since the electron--LO-phonon scattering rate is similar to the Coulomb damping rate that characterizes the electron-electron interaction strength, the linear handling of the electron--LO-phonon interaction is questionable for a 2DEG drifting under a high electric field.

Electronic Properties of Quasi-One-Dimensional Semiconductor Nanostructures: Plasmons and Exchange-Correlation Effects in Quantum Wires

We review the many-body exchange-correlation properties of electrons confined to the lowest sub-band of a quantum wire, including effects of impurity scattering. Without impurity scattering, the virtual excitations of arbitrarily low energy one-dimensional plasmons destroy the Fermi surface of the electrons, whereas the presence of impurity scattering damps out the low energy plasmons and restores the Fermi surface. The electron inelastic scattering rate r in the absence of scattering is zero below a critical wavevector kc corresponding to the plasmon emission threshold, above which r diverges as (k - kc )-1/2 for k -t kc. For typical wire widths and electron densities currently available, the calculated bandgap renormalisation is found to be on the order of 10-20 meV. We also calculate the finite-temperature inelastic scattering rates and mean free paths of electrons injected into a quantum wire containing a quasi-one-dimensional electron gas. We show that there is a very sharp increase in the electron scattering rate at the one-dimensional plasmon emission threshold. Based on these results, we suggest the possibility of a one-dimensional hot-electron device which possesses an I - V curve with a sharp onset of a large negative differential resistance. We also present a general method for obtaining expressions for the analytic continuation of finite-temperature self-energies which are suitable for use in numerical computations. In the case of the GW approximation for the self-energy, this method gives the finite-temperature generalisation of the zero-temperature 'line and pole' decomposition. This formalism is used to calculate the finite-temperature self-energy and bandgap renormalisation of electrons in the extreme quantum limit of a quantum wire. A brief review of the experimental and theoretical status of plasmons in quantum wire structures is given.

Large negative differential resistance in a quasi-one-dimensional quantum wire

We calculate finite temperature inelastic scattering rates and mean free paths of electrons injected into a quantum wire containing a quasi-one-dimensional electron gas. We show that there is a very sharp increase in the electron scattering rate at the one-dimensional plasmon emission threshold. Based on these results, we suggest the possibility of a one-dimensional hot-electron device which possesses an I-V curve with a sharp onset of a large negative differential resistance.

Double wavelength selective GaAs/AlGaAs infrared detector device

We demonstrate the first GaAs/AlGaAs multiquantum well infrared detector device with double wavelength selectivity and high wavelength resolution. By applying an efficient light coupling mechanism, which is based upon the excitation and emission of surface plasmons, we have achieved a responsivity R of 2.20 A/W and a detectivity D* of 2.2×1011 cm √Hz/W for λ=7.38 μm at a temperature T=5 K for a 300 K background irradiance and a 90° field of view, which are one of the highest values reported to date.

Many-body properties of a quasi-one-dimensional semiconductor quantum wire.

We study the many-body exchange-correlation properties of electrons confined to the lowest subband of a quantum wire, including effects of impurity scattering. Without impurity scattering, virtual excitations of arbitrarily low-energy plasmons destroy the Fermi surface of the electrons, whereas the presence of impurity scattering damps out these plasmons and restores he Fermi surface. The electron inelastic scattering rate \ensuremath{\Gamma} in the absence of scattering is zero below ${\mathit{k}}_{\mathit{c}}$ corresponding to the plasmon emission threshold, above which \ensuremath{\Gamma} diverges as (k-${\mathit{k}}_{\mathit{c}}$${)}^{\mathrm{\ensuremath{-}}1/2}$ as k\ensuremath{\rightarrow}${\mathit{k}}_{\mathit{c}}$. For typical wire widths and electron densities currently available, the band-gap renormalization is found to be 10--20 meV.

Cooling by plasmon emission of high energy electrons in semiconductors

The authors present a Monte Carlo study of the Coulomb interaction in polar semiconductors involving both single-particle (screened carrier-carrier interaction) and collective excitations (plasmon scattering). Relaxation of high energy carriers, created by laser excitation, occurs through the interaction with the lattice (mainly via optical phonon emission) and with other carriers. The lattice (mainly via optical phonon emission) and with other carriers. The importance of the latter mechanism has been demonstrated recently by time-resolved and CW hot (e, AA) luminescence experiments which allow the authors to distinguish the separate contributions due to phonon and intercarrier scattering. They study the energy exchange mechanisms in a multi-component plasma using an ensemble Monte Carlo simulation where the intercarrier scattering is treated with two different approaches, the first based on a k-space model that allows the separation of short range (single-particle collisions) and long range (plasmon scattering) Coulomb potential, the second adopting a molecular dynamics scheme. The results of the simulation and the comparison between the two models are discussed for both GaAs and InP. A very good agreement with the experimental results is found.

Integrated wavelength-selective GaAs/AlGaAs multi-quantum-well detectors

As a first step to the realization of an integrated solid state infrared spectrometer the authors have fabricated integrated GaAs/AlGaAs infrared detectors with double wavelength selectivity. An efficient coupling mechanism based upon the excitation and emission of surface plasmons has been applied to achieve high responsivity.

Ensemble Monte Carlo study of electron transport in degenerate bulk GaAs

A theoretical investigation is presented of the effect of ionized impurity scattering, electron-electron interaction, and degeneracy, both separately and collectively, on the bulk steady-state transport properties of degenerate GaAs. The calculations are performed using an ensemble Monte Carlo simulation that includes an analytic nonparabolic formulation of the three principal valleys in the conduction band and all of the important phonon scattering mechanisms. It is found that the overall velocity-field characteristic is determined primarily by the action of electron-plasmon scattering at high electric fields (near the intervalley threshold field). At lower fields, below which the electrons are not heated to the threshold energy for plasmon emission, ionized impurity scattering is the most dominant mechanism. In addition the effects of degeneracy are also important throughout. Only the short-range electron-electron interaction has little effect on the velocity-field curve owing to the fact that it does not alter the net momentum or energy of the electron gas in steady-state bulk material.

Light emission of plasmons during ion bombardment of silver surfaces

Photon emission during silver surface bombardment by H +, H 2 +, H 3 +, He +, Ne + and Ar + ions with energies from 7 to 21 keV was investigated. A continuum radiation was found in the spectral region from 200 to 630 nm with the energetic position of the maximum close to the plasmon energy of silver. The influence of the ion mass, energy and observation angle of radiation upon properties of this continuum radiation has been studied. The observed continuum radiation is linearly polarized. It is supposed that the observed continuum radiation is a result of radiative relaxation of silver plasmons.

Acoustic-phonon emission by two-dimensional plasmons

Acoustic-wave emission of two-dimensional plasmons in a semiconductor or superconductor microstructure is investigated using the phenomenological deformation potential within the jellium model. The plasmons are excited by the external electromagnetic (e.m.) field. The power conversion coefficient of e.m. energy into acoustic-wave energy is also estimated. It is shown that the coherent transformation has a sharp resonance at the plasmon frequency of the two-dimensional electron gas (2DEG). The incoherent transformation of the e.m. energy is generated by ohmic dissipation of the 2DEG. The method proposed for coherent-phonon-beam generation can be very effective for a high-mobility 2DEG and for thin superconducting layers if the plasmon frequency \ensuremath{\omega} is smaller than the superconducting gap 2\ensuremath{\Delta}.

Quasihole lifetimes in electron gases and electron-hole plasmas in semiconductor quantum wells.

The lifetime of a final-state quasihole (i.e., an empty state under the Fermi level created, for example, by interband optical transitions) due to inelastic-scattering processes is calculated as a function of the quasihole energy in {ital n}-type and {ital p}-type modulation-doped quantum wells as well as in electron-hole plasmas in undoped quantum wells. Carrier-carrier scattering and carrier--longitudinal-optical-phonon interactions are considered for the energy-relaxation processes. For carrier-carrier scattering, quasiholes are found to decay through single-particle excitations without plasmon emission at zero temperature. The dependences of the scattering lifetimes on the well width, carrier density, in-plane effective carrier mass, and temperature are studied. The effects of static and dynamic dielectric screening are compared. The relevance of these results to recent luminescence data in modulation-doped quantum wells and to recent thermalization data in hot plasmas in undoped quantum wells is discussed.

Plasmons and quasiparticles in quantum well systems

Plasmon modes are calculated for both a single quantum well-multiple subband and a double quantum well-single subband structure within a response formalism which allows the calculation of the non-local screened interaction. The self energy for the electron states is evaluated in both cases so that the quasiparticle properties can be calculated. Effective mass changes and lifetimes for the emission of plasmons are described as a function of the system parameters.

Strongly directional emission from AlGaAs/GaAs light-emitting diodes

We show for the first time that strongly directional emission of defined polarization can be achieved from conventional AlGaAs/GaAs double-heterostructure surface-emitting light-emitting diodes (LEDs) via coupling to surface plasmons. By microstructuring the surface, we have fabricated LEDs with a beam divergence of less than 4° and an increased quantum efficiency. It is demonstrated that the surface plasmon excitation and emission mechanism have the potential to improve the performance of LEDs.

On the beattie-landsberg theory of interband auger recombination in semiconductors

It is shown that the conventional picture of the interband Auger recombination, as presented in the Beattie-Landsberg theory, is inadequate in a fundamental way. In that picture, the recombination arises from direct and pairwise energy and momentum transfer to single-particle excitations occuring through screened matrix elements. The role played by the collective electronic density fluctuations is clarified, and the enhancement of the recombination rate, due to plasmon emission, in heavily doped narrow-gap semiconductors is calculated within the context of the theory we develop in this work.

Many-body effects in layered 2D electron gas systems

Plasmon pole approximations to the screened interaction for electrons in double-layered 2D electron gas and infinite layered electron gas systems are described and are used to calculate the effective mass and correlation energy for quasiparticles in such systems via the self-energy. Both symmetric and asymmetric double-layer systems, with different electron densities in each layer, are considered. The effective mass shows interesting behaviour as a function of layer separation and areal electron density and some qualitative differences between results for the two-layer and infinite layered electron gas systems are pointed out. Quasiparticle lifetimes to plasmon emission are also calculated for these layered structures within the random-phase approximation. Acoustic plasmons are seen to provide a low-energy loss mechanism for small interlayer separations.