Carrier Dynamics (carrier + dynamics)

Distribution by Scientific Domains
Physics and Astronomy92%

Selected Abstracts

The Effect of Thermal Treatment on the Morphology and Charge Carrier Dynamics in a Polythiophene,Fullerene Bulk Heterojunction,

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2005
J. Savenije
Abstract The influence of various thermal treatment steps on the morphology and the photoconductive properties of a non-contacted, 50,nm thick blend (50:50,wt.-%) of [6,6]-phenyl C61 -butyric acid methyl ester (PCBM) and poly(3-hexyl thiophene) (P3HT) spin-coated from chloroform has been studied using transmission electron microscopy (TEM) and the electrodeless time-resolved microwave conductivity technique. After annealing the film for 5,min at 80,°C, TEM images show the formation of crystalline fibrils of P3HT due to a more ordered packing of the polymer chains. The thermal treatment results in a large increase of the photoconductivity, due to an enhancement of the hole mobility in these crystalline P3HT domains from 0.0056,cm2,V,1,s,,1 for the non-annealed sample to 0.044,cm2,V,1,s,,1 for the sample annealed at 80,°C. In contrast, the temporal shape of the photoconductivity, with typical decay half-times, ,1/2, of 1,,s for the lowest excitation intensities, is unaffected by the temperature treatment. Further annealing of the sample at 130,°C results in the formation of three different substructures within the heterojunction: a PCBM:P3HT blend with PCBM-rich clusters, a region depleted of PCBM, and large PCBM single crystals. Only a minor increase in the amplitude, but a tenfold rise of the decay time of the photoconductivity, is observed. This is explained by the formation of PCBM-rich clusters and large PCBM single crystals, resulting in an increased diffusional escape probability for mobile charge carriers and hence reduced recombination. [source]

Nonlinear optical microscopy of a single self-assembled InGaAs quantum dot

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006
M. Wesseli
Abstract Carrier dynamics in InGaAs/GaAs quantum dots is analyzed with highly sensitive two-color femtosecond transmission spectroscopy. Especially, a single artificial atom is addressed in the optical near-field of a nanometer scale shadow mask. Resonantly exciting the wetting layer beneath the nanoisland, we detect transmission changes of the quantum dot with narrowband femtojoule probe pulses. We find bleaching signals in the order of 10,5 that arise from individual interband transitions. Moreover, the nonlinear optical response reveals a picosecond dynamics associated with carrier relaxation in the quantum dot. As a result, we have demonstrated an ultrafast optical tool for both manipulation and read-out of a single self-assembled quantum dot. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Chemical bath deposition of CdSe and CdS nanocrystalline films: tailoring of morphology, optical properties and carrier dynamics

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2008

Abstract We review the results of our research towards tailoring morphology and optical properties of films consisting of closely-spaced nanocrystals of CdSe and CdS whose optical band-gap can be tuned to cover the whole visible spectral range. On basis of the obtained results, in particular of photoexcited carrier dynamics, we have proposed a microscopic model that describes well the optical properties of the films. We have also showed that the spin relaxation of electrons in these nanocrystalline films is different than that in mutually isolated nanocrystals of the same size. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Analysis of traps in CVD diamond films through thermal depumping of nuclear detectors

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2004
A. Balducci
Abstract Carrier free paths in Chemical Vapour Deposition (CVD) diamond films depend on the presence of traps, which therefore strongly affect the performance of those CVD diamond based devices which rely on the electronic properties of the material, like radiation detectors. For the same reason, these devices can in turn be used as tools to study carrier dynamics. It is well known that some traps may be saturated by pre-irradiation with ionizing radiation (e.g. ,-particles), a process called "pumping" or "priming". Not all traps behave in the same way. Due to the large bandgap of diamond, both shallow (not affected by pumping) and deep traps for electrons and holes may exist. We measured, using 5.5 MeV 241Am ,-particles, the response of high quality CVD diamond based detectors after successive annealing steps performed at selected temperatures. The analisys of the decay of the detector efficency with annealing time at several temperatures allows a quantitative evaluation of the activation energy of these defects. Two main trapping centres connected to the pumping process were found, both related to holes, having activation energies of about 1.6 eV and 1.3 eV respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Low-temperature MBE-grown GaBiAs layers for terahertz optoelectronic applications

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009
Vaidas Pa, ebutas
Abstract Gallium bismide arsenide epitaxial layers were grown by molecular-beam-epitaxy at low substrate temperatures and investigated for their suitability in terahertz optoelectronic applications. Optical pump-terahertz probe measurements on these layers have shown that carrier dynamics can be described using two characteristic times. The faster decay component has characteristic times shorter than 1 ps, whereas the slower component decays in several tens of picoseconds. Fitting the electron lifetimes dependence on optical excitation level the electron trapping cross-section and trap density were determined. The possible mechanism of carrier recombination was discussed. The photoconductive terahertz emitters and detectors made from GaBiAs layers have been manufactured and used in time-domain spectroscopy system with a signal bandwidth larger than 4.5 THz. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Quantum dots to double concentric quantum ring structures transition

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2009
S. Bietti
Abstract Making use of the droplet,epitaxial technique, we realized a series of GaAs/AlGaAs nanostructured samples, starting from the same initial Ga droplet configuration, in which the nanostructure morphologies are progressively changed, via the As partial pressure provided during the growth, from islands, to single rings and, eventually, to concentric ring structures. We report a detailed characterization of the different structure morphologies, electronic structures and carrier dynamics via AFM and photoluminescence measurements as well as through theoretical simulations. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Carrier transport studies of dichromatic InGaN-based LEDs with spacer bandgap dependence

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
Shih-Wei Feng
Abstract Carrier transport of dichromatic InGaN-based LEDs with AlGaN spacer bandgap dependence has been studied. TREL measurements show that carrier dynamics could be well explained by the combined effects of carrier effective mass, carrier mobility, quantum confinement, and device structures. The experimental results provide important information for device designs. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Time-resolved photoluminescence and steady-state optical studies of GaInNAs and GaInAs single quantum wells

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007
Y. Sun
Abstract Time-resolved photoluminescence spectroscopy is used to investigate carrier dynamics of Ga1,xInxNyAs1,y (x , 0.33, y , 0.01) single quantum well (QW) structures. PL spectra measured as a function of temperature together with the PL decay times at wavelengths around and below the PL peak energy are used to determine de-trapping activation energies and time constants. The results are interpreted in terms of simultaneous thermal excitation of deep localized excitons to shallow localized states. According to the model, with increasing temperatures, localized excitons gain enough thermal energy to populate the free exciton states in quantum well with shorter lifetimes due to coherent nature of free excitons. In addition, at temperatures around and above 80 K, more non-radiative channels become available to compete with the radiative processes leading to shorter time constants. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Barrier-to-well carrier dynamics of InGaN/GaN multi-quantum-wells grown by plasma assisted MBE on bulk GaN substrates

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
K. P. Korona
Abstract We present study of carrier dynamics in GaInN/GaN multi quantum wells (MQWs) with screened electric fields. The PL emission showed clearly resolved peaks emitted from the Ga0.9In0.1N QWs (at about 3.1 eV, FWHM 30-50 meV). Two samples with 2.5-nm-QWs and 4-nm-QWs showed decay-times of 1.1 ns and 2.3 ns. The decay-rates in the barriers were thermally activated, activation energies were 21 meV and 46 meV, for the 2.5-nm-QWs and 4-nm-QWs structures, respectively. Analysis of correlation between rising-rates of the MQW PL and the decay-rates of the barriers PL confirmed increase of transport through barrier. The MQW PL energy changed with time. The phenomenon was due to trapping of excitons on donors or localization in potential minima. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Defect density dependence of carrier dynamics in AlGaN multiple quantum wells grown on GaN substrates and templates

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
G. A. Garrett
Abstract Subpicosecond time-resolved photoluminescence (TRPL) has been used to compare the room temperature carrier dynamics in Al0.1Ga0.9N/Al0.3Ga0.7N multiple quantum well (MQW) structures simultaneously deposited on a high quality free standing HVPE GaN substrate (dislocation density ,1 × 107cm,2) and 1 µm MOCVD GaN template on sapphire. The PL lifetime of ,500 ps in the MQW on GaN substrate is about 5 times longer than that for the MQW on GaN template, with a concomitant increase in CW PL intensity. This behavior is attributed primarily to an increase in nonradiative lifetime associated with a 100 times reduction in dislocation density in the GaN substrate. The observation that the PL lifetime in the MQW falls short of the ,900 ps dominant decay time in the GaN substrate may be indicative of generation of additional defects and dislocations due to substrate surface preparation, strain relaxation, and nonoptimal growth temperature associated with the difference in heating of the thin GaN template on sapphire and the thick GaN substrate. An extended PL rise time of greater than 20 ps for the MQW emission when above barrier pumping is employed implies that both wells and barriers are of high quality. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]