Hot-phonon generation in GaAs/AlxGa1−

Abstract

Using picosecond Raman scattering, hot-phonon occupation numbers (N) of GaAs and GaAs-like LO phonons have been studied over a wide range of structural parameters in more than 30 GaAs/Al Gal As superlattices. In addition, simultaneous measurements of these LO phonon modes in bulk GaAs and Al Gal "As alloys are made for comparison. N values of both GaAs and GaAs-like modes of the superlattices are comparable to or larger than those of bulk GaAs or Al Gal As alloys for x &0.2. On the other hand, N values of GaAs or GaAs-like LO phonons are much smaller for 0

Percolation of carriers through low potential channels in thickAlxGa1Kim1, Ko2, Kim3 et al. 1996Phys. Rev. BSelf Cite27390View full textAdd to dashboardCite

“…We note that this ''phase diagram'' is very similar to that obtained for the optical-phonon transport studied by time-resolved Raman scattering. [52][53][54] It is possible that both phonon and carrier transport can be facilitated by the existence of intrinsic clustering and inhomogeneities in the barrier. For the regions of xϾ0.35 and the barrier thickness of Ͼ50-100 Å, other mechanisms such as the dipole-dipole interaction, photon reabsorption, and polariton transfer may dominate transport.…”

Going beyond the mean-field approximations of alloys and alloy superlattices: a few puzzles solved?

“…Therefore there is some nontrivial x c such that, when x . x c , all GaAs-like optical phonons are localized, justifying the method of Parayanthal and Pollak 23 to fit the asymmetric line shape of Raman-active phonons. In contrast, when x , x c , a finite fraction of GaAs-like optical phonons is extended, whereas the states near the edges of the branch are localized.…”

“…Figure 7 shows a PLE spectrum at 14 K of a molecular-beam epitaxy-GaAs͞Al x Ga 1-x As͞GaAs (10 nm͞20 nm͞5 nm) ADQW with x 0.28 when the WW continuum is excited (top left-hand curve). Very strong ASL with a normalized efficiency of ϳ10 23 is observed. At the bottom of the figure an anti-Stokes PLE spectrum is shown with the photoluminescence window at the peak of the NW HH and excitation energies scanned across the WW excitons and continuum.…”

“…It is well known now that a nonequilibrium hot-phonon population probed by Raman scattering can be, when properly analyzed, a sensitive probe of the spatial extent of the Raman-active LO phonons. 18,23 This is essentially because the hot-phonon distribution curve generated by the hot-electron relaxation is a strong function of the phonon wave vector and therefore of the spatial extent. Although the details are given elsewhere, 23 once the hotphonon occupation number properly normalized to that of bulk GaAs under the same experimental conditions is known we can deduce the coherence length of the Ramanactive GaAs or GaAs-like LO phonons in GaAs͞Al x Ga 1-x As quantum wells or Al x Ga 1-x As alloy, using the hot-phonon distribution curve.…”

Nonequilibrium optical-phonon population by sequential resonant tunneling in GaAs-AlAs superlattices

“…Previous Raman investigations focused on the nonequilibrium phonon population generated by the relaxation of photoexcited hot carriers. [5][6][7][8][9][10][11][12] For nonresonant Raman studies of a system at thermal equilibrium, the ratio of the anti-Stokes ͓I AS ( i ϭϪ LO , s ϭ)͔ and Stokes ͓I S ( i ϭ, s ϭϪ LO )͔ intensities is approximately equal to the ratio N/(Nϩ1͒,where i and s stand for the excitation and scattering frequency, respectively. N is the Bose-Einstein occupation factor.…”