4 research outputs found
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Ultrahigh Hot Carrier Transient Photocurrent in Nanocrystal Arrays by Auger Recombination.
In this report, we show that a new mechanism for carrier transport in solution-processed colloidal semiconductor nanocrystal arrays exists at high excitation intensity on ultrafast time scales and allows for facile intrinsic transport between as-prepared nanocrystals over long distances. By combining a high speed photoconductive switch with an ultrafast laser excitation in a sub-40 ps photoconductor, we observed transient photocurrents with peak densities of 3 × 104 - 106 mA/cm2 in self-assembled PbSe nanocrystals capped with long native oleic acid ligands. The ratio between the transient photocurrent peak and the steady-state dark current is 10 orders of magnitude. The transient mobility at the peak current is estimated to range between 0.5-17.5 cm2/(V s) for the various nanocrystal sizes studied, which is 6 to 9 orders of magnitude higher than the dark current steady-state mobility in PbSe, CdSe, and CdTe nanocrystals capped with native ligands. The results are analyzed using a kinetic model which attributes the ultrahigh transient photocurrent to multiple photogenerated excitons undergoing on-particle Auger recombination, followed by rapid tunneling at high energies. This mechanism is demonstrated for a wide range of PbSe nanocrystals sizes (diameters from 2.7 to 7.1 nm) and experimental parameters. Our observations indicate that native ligand-capped nanocrystal arrays are promising for optoelectronics applications wherein multiple carriers are photoinjected to interband states
Absence of Coulomb Blockade in the Anderson Impurity Model at the Symmetric Point
In this work, we investigate the characteristics of the electric current in
the so-called symmetric Anderson impurity model. We study the nonequilibrium
model using two complementary approximate methods, the perturbative quantum
master equation approach to the reduced density matrix, and a self-consistent
equation of motion approach to the nonequilibrium Green's function. We find
that at a particular symmetry point, an interacting Anderson impurity model
recovers the same steady-state current as an equivalent non-interacting model,
akin a two-band resonant level model. We show this in the Coulomb blockade
regime for both high and low temperatures, where either the approximate master
equation approach and the Green's function method provide accurate results for
the current. We conclude that the steady-state current in the symmetric
Anderson model at this regime does not encode characteristics of a many-body
interacting system