666 research outputs found
Carbon-doped high mobility two-dimensional hole gases on (110) faced GaAs
Carbon-doped high mobility two-dimensional hole gases grown on (110) oriented
GaAs substrates have been grown with hole mobilities exceeding 10^6 cm^2/Vs in
single heterojunction GaAs/AlGaAs structures. At these high mobilities, a
pronounced mobility anisotropy has been observed. Rashba induced spin-splitting
in these asymmetric structures has been found to be independent on the
transport direction
A double-dot quantum ratchet driven by an independently biased quantum point contact
We study a double quantum dot (DQD) coupled to a strongly biased quantum
point contact (QPC), each embedded in independent electric circuits. For weak
interdot tunnelling we observe a finite current flowing through the unbiased
Coulomb blockaded DQD in response to a strong bias on the QPC. The direction of
the current through the DQD is determined by the relative detuning of the
energy levels of the two quantum dots. The results are interpreted in terms of
a quantum ratchet phenomenon in a DQD energized by a nearby QPC.Comment: revised versio
Phonon-mediated vs. Coulombic Back-Action in Quantum Dot circuits
Quantum point contacts (QPCs) are commonly employed to capacitively detect
the charge state of coupled quantum dots (QD). An indirect back-action of a
biased QPC onto a double QD laterally defined in a GaAs/AlGaAs heterostructure
is observed. Energy is emitted by non-equilibrium charge carriers in the leads
of the biased QPC. Part of this energy is absorbed by the double QD where it
causes charge fluctuations that can be observed under certain conditions in its
stability diagram. By investigating the spectrum of the absorbed energy, we
identify both acoustic phonons and Coulomb interaction being involved in the
back-action, depending on the geometry and coupling constants
Carbon doped symmetric GaAs/AlGaAs quantum wells with hole mobilities beyond 10^6 cm^2/Vs
Utilizing a novel carbon doping source, we prepared two-dimensional hole
gases in a symmetric quantum well structure in the GaAs/AlGaAs heterosystem.
Low temperature hole mobilities up to 1.2 x 10^6 cm^2/Vs at a density of 2.3 x
10^11 cm^-2 were achieved on GaAs (001) substrates. In contrast to electron
systems, the hole mobility sensitively depends on variations of the quantum
well width and the spacer thickness. In particular an increase of the quantum
well width from an optimal value of 15 nm to 18 nm is accompanied by a 35 %
reduction of the hole mobility. The quality of ultrahigh-mobility electron
systems is not affected by the employed carbon doping source
- …