Local Carrier Density Research Articles

Effect of local potential variations in the model of hole superconductivity

In the model of hole superconductivity the strength of the pairing interaction depends on the local carrier density. This gives rise to a dependence of the gap function Δ k on the band energy ϵ k . Fluctuations in the local potential energy will result in different values of Δ k at the Fermi energy and hence in different values of the local energy gap. In particular, the energy gap can be sharply reduced. We study this behavior by numerical solution of the Bogoliubov-de Gennes equations for the model. The behavior is contrasted with what occurs in the attractive Hubbard model, where local potential fluctuations have negligible effect. The physical origin of this behavior and the possible relevance to high- T c oxides is discussed.

Phonon-wind-driven transport of photoexcited carriers in a semiconductor quantum well.

The in-plane transport of photoexcited carriers in ${\mathrm{GaAsAl}}_{0.3}$${\mathrm{Ga}}_{0.7}$As multiple quantum wells is measured optically with 10 ps and 4 \ensuremath{\mu}m resolution. The local carrier density is measured by the bleaching of the excitonic absorption line. The expansion of the photoexcited carriers following a 6-ps pump pulse is found to be a strong function of excitation power and ambient temperature. At low powers, with initial carrier densities ${n}_{0}$\ensuremath{\le}2\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, the spatial distribution is well described by a single expanding Gaussian profile corresponding to an effective diffusion constant ${D}_{\mathrm{eff}}$(${n}_{0}$,T). The power and temperature dependence suggests a phonon-wind driving mechanism. At higher densities (${n}_{0}$>2\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$) a narrow spatial profile appears which we attribute to ``thermal confinement'' of carriers within a phonon hot spot. After some delay, the ``confined''-carrier distribution is observed to undergo a rapid expansion. This unusual effect is attributed to the ``explosion'' of the phonon hot spot, as predicted by Kazakovtsev and Levinson.

Generalized treatment of spatial and temporal column parameters, applicable to gas, liquid and supercritical fluid chromatography : I. Theory

Starting with Darcy's law, rearranged and expressed in terms of the local carrier density at a given temperature, general equations are derived for the spatial and temporal density distribution functions, average densities and column profiles of the mobile-phase fluid, and the observed (column-averaged) capacity factor(s) and column profiles of the solute component(s). These more direct, exact and tractable equations are applied to gas, liquid and supercritical fluid chromatography, and the results are discussed.

Comparison of Auger recombination in GaInAs-AlInAs multiple quantum well structure and in bulk GaInAs

Carrier lifetime has been measured in GaInAs-AlInAs multiple quantum well structures and in thick GaInAs samples for local carrier densities between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 \times 10^{17}</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5 \times 10^{19}</tex> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Carrier lifetime and Auger recombination are found to be very close (±20 percent) in the two structures. The Auger limited T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> values calculated for DH and MQW lasers are found to be, respectively, 93 and 170 K. Optimization of the quantum well laser as a function of the number of wells in the active region is discussed.

Auger recombination in GaInAsAlInAs multiple quantum well structure

Abstract Carrier lifetime has been measured in GaInAsAlInAs Multiple Quantum Well Structures and in thick GaInAs samples for local carrier density between 2×1017 and 5×19cm−3. Carrier lifetime and Auger recombination are found to be very close (± 20 %) in the two structures.

Statistics of Carrier Recombination at Disordered Regions in Semiconductors

In semiconductors, when a region of local disorder is produced (e.g., by neutron irradiation), the defects contained in the region affect the local equilibrium carrier densities and act as effective recombination centers. In this paper, expressions are given for the transient carrier lifetime at low excess carrier densities, and for the steady-state lifetime at low defect concentrations. Results agree well with experimental observations of neutron-irradiated silicon.