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Photocurrent Spectroscopy (photocurrent + spectroscopy)

Distribution by Scientific Domains

Physics and Astronomy	80%

Selected Abstracts

Photocurrent spectroscopy of single InAs/GaAs quantum dots

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2005
G. Fasching
Abstract In this work, we present a carrier escape study from InAs/GaAs self assembled QD's by the use of photocurrent measurements. As a function of the applied field, we detect a shift of the exciton ground state transition due to the quantum-confined Stark shift. ¿From the measured Stark shift S = 4:3 meV we deduce a exciton dipole moment of p = (4.3 ± 0.2) × 10,29 Cm. The tunneling time, which is directly related to the observed photocurrent linewidth due to , , ,/(2,), changes by a factor of five in the photocurrent regime. The measured linewidth dependency on the electric field is modelled by a simple 1D WKB approximation for the tunneling process, which shows that the energetic position of the wetting layer is important for the measured tunneling time out of the dot. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Coherent Properties of Quantum Dot Two-Level Systems

ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2006
Artur Zrenner
In a single self-assembled InGaAs quantum dot, the one-exciton ground-state transition defines a two-level system, which appears as an extremely narrow resonance of only a few ,eV width. The resonant interaction of this two-level system with cw laser fields can be studied in detail by photocurrent spectroscopy, revealing the fine structure of the excitonic ground state as well as the effects of nonlinear absorption and power broadening. For the case of pulsed laser fields and in the absence of decoherence, the two-level system represents a qubit. Excitations with ps laser pulses result in qubit rotations, which appear as Rabi oscillations in photocurrent experiments. Double pulse experiments further allow us to infer the decoherence time and to perform coherent control on a two level system. [source]

Towards optical-quality nanocrystalline diamond with reduced non-diamond content

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2009
Z. Remes
Abstract Our nominally undoped nanocrystalline diamond (NCD) films were deposited on fused silica substrates by the microwave plasma enhanced chemical vapor deposition (MW CVD) at a relatively low temperature below 600,°C. They show high dark resistivity and measurable photosensitivity after surface oxidation. We present the "true" optical absorptance spectra calculated from transmittance T and reflectance R measurements corrected on the surface scattering and compare them with the normalized photocurrent spectra. The optical scattering does not allow to evaluate the small optical absorption in visible and near IR range from the T and R spectra. The photocurrent spectra were measured in the ultraviolet, visible, and near infrared optical range using the dual beam photocurrent spectroscopy (DBP) under constant UV illumination. Previously, NCD films often showed non-diamond content with the photo-ionization threshold at 0.8,eV increasing significantly the optical absorption in near IR and visible region. Here, we show that the non-diamond content can be reduced by several orders of magnitude by depositing NCD on the carefully selected UV-grade fused silica substrates under the optimized growth conditions followed by the post-deposition chemical etching and cleaning. Unlike the NCD layers with high non-diamond content, the NCD layers with reduced non-diamond content are stable up to 450,°C. [source]

Observation of new defect levels in nanodiamond membranes

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2005
R. Kravets
Abstract This paper reports on a new set of defect features in thin membrane nanodiamond. The samples were stud-ied using Fourier transform photocurrent spectroscopy. We have observed four dominant new peaks in nanocrystalline diamond: two sharp peaks at 0.36 and 0.40 eV and broad bands at 0.27 and 0.57 eV. The first of these peaks is suggested to originate from a currently unknown bulk impurity; the other three are surface-related and are especially prone to surface effects such as absorption/desorption over time. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The evolution of the electric field in an optically excited semiconductor superlattice

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2005
Alvydas Lisauskas
Abstract We report on time-resolved photocurrent spectroscopy of an intrinsic GaAs/Al0.3Ga0.7As superlattice subsequent to femtosecond optical excitation. Information on the spatio-temporal evolution of the densities of electrons and holes and on the internal electric field is obtained by tracing Wannier-Stark photocurrent spectra as a function of delay time for various bias fields and pump excitation intensities. The experimental results are supplemented by simulations. We employ the combined information to define the conditions to be met for succesful pump-probe Bloch gain experiments. In particular, we find that field screening sets on upper limit for the carrier density of 1016 cm,3, and that the time window during which gain should be found is defined by the duration of the sweep-out of the optically injected electrons from the superlattice which occurs within about 10 ps after excitation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]