35 research outputs found
Electron-hole correlation effects in the emission of light from quantum wires
We present a self-consistent treatment of the electron-hole correlations in
optically excited quantum wires within the ladder approximation, and using a
contact potential interaction. The limitations of the ladder approximation to
the excitonic low-density region are largely overcome by the introduction of
higher order correlations through self consistency. We show relevance of these
correlations in the low-temperature emission, even for high density relevant in
lasing, when large gain replaces excitonic absorption.Comment: 4 paes 3 figure
Role of bound pairs in the optical properties of highly excited semiconductors: a self consistent ladder approximation approach
Presence of bound pairs (excitons) in a low-temperature electron-hole plasma
is accounted for by including correlation between fermions at the ladder level.
Using a simplified one-dimensional model with on-site Coulomb interaction, we
calculate the one-particle self-energies, chemical potential, and optical
response. The results are compared to those obtained in the Born approximation,
which does not account for bound pairs. In the self-consistent ladder
approximation the self-energy and spectral function show a characteristic
correlation peak at the exciton energy for low temperature and density. In this
regime the Born approximation overestimates the chemical potential. Provided
the appropriate vertex correction in the interaction with the photon is
included, both ladder and Born approximations reproduce the excitonic and free
pair optical absorption at low density, and the disappearance of the exciton
absorption peak at larger density. However, lineshapes and energy shifts with
density of the absorption and photoluminescence peaks are drastically
different. In particular, the photoluminescence emission peak is much more
stable in the ladder approximation. At low temperature and density a sizeable
optical gain is produced in both approximations just below the excitonic peak,
however this gain shows unphysical features in the Born approximation. We
conclude that at low density and temperature it is fundamental to take into
account the existence of bound pairs in the electron-hole plasma for the
calculation of its optical and thermodynamic properties. Other approximations
that fail to do so are intrinsically unphysical in this regime, and for example
are not suitable to address the problem of excitonic lasing.Comment: 14 pages, 12 figure
Gain in a quantum wire laser of high uniformity
A multi-quantum wire laser operating in the 1-D ground state has been
achieved in a very high uniformity structure that shows free exciton emission
with unprecedented narrow width and low lasing threshold. Under optical pumping
the spontaneous emission evolves from a sharp free exciton peak to a
red-shifted broad band. The lasing photon energy occurs about 5 meV below the
free exciton. The observed shift excludes free excitons in lasing and our
results show that Coulomb interactions in the 1-D electron-hole system shift
the spontaneous emission and play significant roles in laser gain.Comment: 4 pages, 4 figures, prepared by RevTe
Mott transition from a diluted exciton gas to a dense electron-hole plasma in a single V-shaped quantum wire
We report on the study of many-body interactions in a single high quality
V-shaped quantum wire by means of continuous and time-resolved
microphotoluminescence. The transition from a weakly interacting exciton gas
when the carrier density n is less than 10^5 cm^-1 (i.e. n aX < 0.1, with aX
the exciton Bohr radius), to a dense electron-hole plasma (n > 10^6 cm^-1, i.e.
n aX > 1) is systematically followed in the system as the carrier density is
increased. We show that this transition occurs gradually : the free carriers
first coexist with excitons for n aX > 0.1, then the electron-hole plasma
becomes degenerate at n aX = 0.8. We also show that the non-linear effects are
strongly related to the kind of disorder and localization properties in the
structure especially in the low density regime.Comment: 5 figure
Photoluminescence Study of V-Groove Quantum Wires: The Influence of Disorder on the Optical Spectra and the Carrier Thermalization
Photoluminescence study of V-groove quantum wires: The influence of disorder on the optical spectra and the carrier thermalization
We report on time-resolved and steady-state photoluminescence studies of GaAs/AlGaAs V-groove quantum wire structures. Steady-state photoluminescence experiments are performed in the temperature range from 8 to 200 It. We evaluate the relation between photoluminescence excitation and absorption and determine experimentally the optical density in order to analyze the temperature dependence of the photoluminescence spectra. We find that, at a temperature above 60 K, the photoexcited electron-hole pairs reach a thermal equilibrium at the lattice temperature while, at a temperature below about 60 K, they do not reach a quasi-equilibrium in the steady-state. Time-resolved photoluminescence studies performed at a carrier density of about 2 x 10(4) cm(-1) indicate that, at 60 K, a quasi-equilibrium is reached on a time scale of 10 ps. Furthermore, the hot carriers cool in about 100 ps to the lattice temperature. At 8 K, however, evidence of a non-thermal carrier distribution is found at the earliest times, which suggests that carriers in extended states are not in thermal equilibrium with carriers in localized states
Intrasubband and intersubband scattering in semiconductor quantum wires
We have performed low-density (< 10(5) cm(-1)) time-resolved photoluminescence experiments that probe the relaxation of photo-excited carriers in a quantum wire. Our results show that carrier-carrier collisions are dominant at very short times both for intra- and for inter-subband scattering as only expected if non-Markovian effects are taken into account. (C) 1999 Elsevier Science B.V. All rights reserved
Excitonic corrections and band gap renormalization in quantum wires
We present a theoretical analysis of experimental photoluminescence spectra in highly excited semiconductor quantum wires. We show that the inclusion in the theory of electron-hole correlations strongly modifies the shape of emission spectra at any density. We discuss the role of these correlations in the evaluation of the band gap renormalization. The calculated energy- and density-dependence of the broadening agree qualitatively with the experimental results. The broadening is also comparable in magnitude to the band gap renormalization, implying the relevance of a combined self-consistent calculation of the two. (C) 1999 Elsevier Science Ltd. All rights reserved