Carrier Relaxation (carrier + relaxation)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Excitation relaxation in copper selenide nanowires

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2009
Gediminas Ju
Abstract Ultrafast nonequilibrium charge carrier relaxation in highly ordered Cu2,xSe nanowires of 8 nm, 13 nm and 25 nm diameter was investigated by means of femtosecond pump,probe absorption spectroscopy. Transient absorption bleaching was observed in the region of the near infrared absorption band, whereas an induced absorption dominated at higher energies. The transient absorption kinetics is almost independent of the excitation and probe wavelength and shows a biexpoenetial charge carrier recombination with the excitation intensity dependent decay rates. The initial ultrafast relaxation, which gets slower at higher excitation intensities, is followed by the slower decay component emerging at high intensities. These relaxation peculiarities are discussed in terms of recombination enhancement by intragap states, and relaxation kinetics is described by a theoretical model of two concurrent relaxation channels involving deep and shallow impurity levels. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Room temperature intraband Raman emission and ultrafast carrier relaxation in GaN/AlN quantum dots

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
L. Nevou
Abstract We report on the intraband emission at room-temperature from GaN/AlN quantum dots grown by plasma-assisted molecular beam epitaxy as well as on the measurements of GaN quantum dot intraband relaxation using femtosecond spectroscopy. The quantum dots exhibit s-pz intraband absorption peaked at 1.55 ,m. The pz -s intraband luminescence at , = 1.48 ,m is observed under optical excitation at , = 1.34 ,m. The population of the pz state arises from Raman scattering by GaN A1 longitudinal optical phonons. Based on the emission spectral shape, we estimate that the homogeneous linewidth of the s-pz intraband transition is less than 4 meV. The carrier lifetime of the pz state (T1) is measured by femtosecond pump-probe spectroscopy. T1 = 165 fs while the thermalization of electrons in the ground state proceeds in 1.5 ps. The saturation intensity of the s-pz intraband absorption is estimated to be in the 15 to 137 MW/cm2 range taking into account the uncertainty on the pump beam waist. These results demonstrate the promising capabilities of GaN/AlN QDs for application to telecom intraband lasers as well as multi-Tbit/s all-optical switching devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [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]

Trap-sensitive relaxation of hot carriers in ZnO:Cu,Al

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006
I. Konovalov
Abstract Modulated photoconductivity measurements with x-ray excitation were performed on ZnO:Cu,Al thin films. We found a strong variation of the modulated photocurrent with temperature starting from the excitation energy approximately equal the binding energy of Cu 2p3 core electrons and above. Strong temperature sensitivity at ,280 K suggests participation of thermally activated trap states in the process of hot carrier relaxation. The shape of the temperature dependence was satisfactorily fitted by the respective calculation. No comparable deviations of the temperature sensitivity were observed when the Cu 2s electrons were excited. We explain the observations by assumption of fast local transitions from a valley in the conduction band into the trap state according to the symmetry selection rules. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Thermalization and recombination in exponential band tail states

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
M. Niehus
Abstract We present an analytical model that combines the complementary experimental evidence of spatial dispersion (DAP recombination) and energetic dispersion (band tails). The model describes the competition between thermalization and recombination of excess carriers trapped in exponentially distributed (in energy), discrete localized (in space) states. We use the energy dependence of the relaxation rates to derive the energy and time dependence of sub gap photoluminescence. The model predicts that the yellow luminescence band (YLB) and blue luminescence band (BLB) commonly observed in GaN are not separate entities, but reflect the competition of thermalization and recombination. A distinct kink is observed in transient PL in the microsecond range, in the limiting cases of strong tailing and/or low temperatures, indicating the transition from thermalization-limited to (radiative) recombination-limited excess carrier relaxation. Both prediction are in line with experiment, and able to resolve interpretational difficulties. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Output power saturation in InAs/GaAs quantum dot lasers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003
M. Wasiak
Abstract An attempt has been made to understand the lasing properties of self-assembled InAs/GaAs quantum dots and to describe saturation effects in quantum dot level populations. The new, improved rate equation model has been developed. The impact of carrier relaxation and level depopulation inside quantum dots on lasing properties, in particular on gain depressing and output power saturation, is discussed. [source]