Showing papers by "David Broido published in 1990"

Electromagnetic response of quantum dots.

Abstract: Les interactions a plusieurs corps ne produisent aucun deplacement significatif dans la frequence d'absorption de l'infra-rouge lointain pour un systeme de points quantiques bien separes avec des potentiels de confinement paraboliques. Ceci est contraire au resultat base sur l'approximation de la phase aleatoire, mais en bon accord avec de recents resultats experimentaux

Self-Consistent Far-Infrared Response of Quantum-Dot Structures

Abstract: We develop a first-principles, self-consistent theory of the far-infrared (FIR) electromagnetic response for electrons confined in a quantum dot. We find that for small electron number ${\mathit{n}}_{\mathit{e}}$, the FIR absorption spectrum corresponds to that associated with parabolic confinement, i.e., absorption dominated by a single peak, which occurs at the frqeuency corresponding to the interlevel separation of the parabolic potential, and is roughly independent of ${\mathit{n}}_{\mathit{e}}$. For large electron number, an upward shift in the resonance frequency occurs as the electron density probes the increasingly nonparabolic curvature of the dot potential. Effects of an applied magnetic field are also investigated.

Room-temperature emission of highly excited GaAs/Ga1-xAlxAs quantum wells

Abstract: The emission spectra of GaAs/${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As quantum wells were studied under high optical excitation at room temperature. Mesa structures of 50 \ensuremath{\mu}m in size were used to confine the electron-hole carrier system laterally and thus to produce a uniform high density of carriers. Carrier densities were sufficient to fill the quantum well to the top of the ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As barrier, and electron subbands up to n=3 were filled. Accurate values of the densities and temperatures were obtained by fitting the spectra using calculations of the full coupled valence bands for the hole dispersion relations and for the optical matrix elements. The resulting band-gap renormalizations were found to depend on the subband index. Theoretical results based on an extension of the local-density approach are presented which are consistent with the observed subband dependence of the band-gap renormalization.

Magneto‐optical transitions in GaAs‐AlGaAs coupled double quantum wells

Abstract: Magnetophotoluminescence excitation spectroscopy has been employed to study GaAs‐AlGaAs coupled double quantum wells. The investigations were undertaken at liquid helium temperatures and in magnetic fields up to 15 T applied parallel to the growth direction. In zero magnetic field, under flat‐band conditions, the spectrum is dominated by ground‐state excitonic transitions between electron and hole states with envelope functions of the same symmetry. In a magnetic field, the oscillator strengths of excited excitonic states are enhanced and four series of transitions are observed. The spectral features corresponding to the ground state and the excited states have been analyzed and these results were utilized to determine the exciton binding energies for several excitonic transitions of different subbands in this coupled double quantum‐well structure. A number of additional features are visible at higher magnetic fields; some of these peaks are believed to be associated with 2p exciton transitions between ho...

Mixing of excitons and continuum states in quantum wells.

Abstract: Presentation d'un modele pour le spectre d'absorption excitonique qui inclut la diffusion inter-sous-bande et l'interaction des etats excitoniques lies et de continuum. Ce modele est applique au cas d'un puits quantique soumis a une contrainte uniaxiale

Coupling of plasma modes in a Si accumulation layer

Abstract: We perform a realistic calculation of the plasma-mode spectrum for a Si(100) accumulation layer as a function of electron density, ${n}_{s}$, and [100] stress, P. For this system, the strong coupling of the intrasubband- and first-intersubband plasma modes is revealed through an avoided crossing of the mode dispersions. We provide a more fundamental illustration of this phenomenon by calculating, as well, the reflectivity spectra, and we show that a strong exchange of oscillator strengths between the two modes occurs. We obtain very good quantitative agreement with the experimental results of Oelting, Heitmann, and Kotthaus [Phys. Rev. Lett. 56, 1846 (1986)].

Theory of the Electronic and Optical Properties of Semiconductor Heterostructures

Abstract: : The research performed during the period of funding can be categorized into two areas. First, a theoretical investigation of the optical properties of strained layer quantum wells grown along the 111 crystallographic direction, and second, an examination of the far infrared response of quantum dot systems. (Author)