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Potential Fluctuations (potential + fluctuation)

Distribution by Scientific Domains

Physics and Astronomy	81%

Selected Abstracts

Micro-analysis of light emission properties of GaN-based laser diodes

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
M. Godlewski
Abstract In-depth and in-plane changes of emission intensity from GaN-based laser diode structures were studied using cathodoluminescence, photoluminescence (PL), micro-PL and a Kelvin probe (potential fluctuations). We show that even at high excitation density potential fluctuations are not screened in active layers of laser diode structures. Potential fluctuations are enhanced in p-type doped layers. We also found that dislocations are formed there, which can penetrate to active region of LD devices. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Potential fluctuations in disordered semiconductors measured by transport and optical methods

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2004
P. Bozsoki
Abstract From the recent analysis of the potential fluctuations in disordered semiconductors on the basis of optical and transport measurements [1] it was concluded that these two different kinds of phenomena evidence extremely different energy scales of the random potential in the same sample. We resolve this puzzle using for the analysis of experimental data the well-known theories of transport and optical absorption in a disordered system with long-range potential fluctuations, caused by charged impurities [2, 3]. The key point in our consideration is the essential difference between the density of states caused by the long-range fluctuations and the shape of the absorption coefficient. The latter is known to depend essentially not only on the fluctuation probability but also on the tunnelling efficiency of the optically excited electrons in the potential relief provided by the fluctuations [2]. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Optical properties of semiconductors with the Coulomb potential fluctuation: case of co-doped ZnSe:(N,Cl)

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004
Igor L. Kuskovsky
Abstract We discuss properties of cw and time-resolved photoluminescence (PL) as well as photoluminescence excitation (PLE) from co-doped ZnSe:Cl,N samples. These samples are characterized by the presence of the potential fluctuations due to charged donors and acceptors. We compare intensity dependent cw PL with the theory and find a good agreement. We also find that the material parameters obtained from cw PL and time-resolved PL agree well. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Characterization of depolarization and repolarization phases of mitochondrial membrane potential fluctuations induced by tetramethylrhodamine methyl ester photoactivation

FEBS JOURNAL, Issue 7 2005
Angela M. Falchi
Depolarization and repolarization phases (D and R phases, respectively) of mitochondrial potential fluctuations induced by photoactivation of the fluorescent probe tetramethylrhodamine methyl ester (TMRM) were analyzed separately and investigated using specific inhibitors and substrates. The frequency of R phases was significantly inhibited by oligomycin and aurovertin (mitochondrial ATP synthase inhibitors), rotenone (mitochondrial complex I inhibitor) and iodoacetic acid (inhibitor of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase). Succinic acid (mitochondrial complex II substrate, given in the permeable form of dimethyl ester) abolished the rotenone-induced inhibition of R phases. Taken together, these findings indicate that the activity of both respiratory chain and ATP synthase were required for the recovery of the mitochondrial potential. The frequency of D phases prevailed over that of R phases in all experimental conditions, resulting in a progressive depolarization of mitochondria accompanied by NAD(P)H oxidation and Ca2+ influx. D phases were not blocked by cyclosporin A (inhibitor of the permeability transition pore) or o -phenyl-EGTA (a Ca2+ chelator), suggesting that the permeability transition pore was not involved in mitochondrial potential fluctuations. [source]

Profiling of light emission of GaN-based laser diodes with cathodoluminescence

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006
M. Godlewski
Abstract Cathodoluminescence is applied for evaluation of in-plane variations of light emission from GaN-based laser diode structures. We demonstrate that potential fluctuations affect significantly emission of laser diodes for e-beam currents above thresholds for a stimulated emission. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Three-dimensional localization of excitons in the InAs/GaAs wetting layer , magnetospectroscopic study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2009
A. Babinski
Abstract Magnetospectroscopic studies of individual excitonic states confined in potential fluctuations in the InAs/GaAs wetting layer (WL) are presented. A neutral exciton and a trion emission have been identified. They split in magnetic field in two components of orthogonal circular polarizations. The respective Zeeman splitting changes linearly with magnetic field up to 10 T. A significant scatter of the effective excitonic g *-factor is observed, reflecting the distribution of sizes and compositions of potential fluctuations in the WL. The distribution affects also diamagnetic shift of the excitonic emission. The observed properties of the excitons are consistent with a picture of shallow quantum dots formed in the WL due to In composition fluctuations. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Micro-analysis of light emission properties of GaN-based laser diodes

Antiferromagnetic phase in doped semiconductors near the insulator,metal phase transition

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2006
A. I. Veinger
Abstract We show for n -type semiconductors, using Ge:As and 4H -SiC:N as examples, that the spin density measured by electron spin resonance (ESR) falls sharply near the insulator,metal (IM) transition. Two reasons might be responsible for this phenomenon: potential fluctuations with concentration of the electrons in local minima or local antiferromagnetic spin pairing ("spin glass") in the insulating state just below the IM transition. In the investigated semiconductors manifestation of the latter is observed as a change from Curie to a Curie,Weiss behaviour with negative constant ,. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Optical properties of semiconductors with the Coulomb potential fluctuation: case of co-doped ZnSe:(N,Cl)

Kinetics of radiative recombination of the "pseudo-donor,pseudo-acceptor" pairs in InGaN/GaN

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2004
A. J. Zakrzewski
Abstract It was shown that the recombination kinetics of electrons and holes localized on potential fluctuations in quantum wells could be calculated exactly in terms of hypergeometric functions. Our algorithms are much easier for coding and much faster and more accurate then previously developed. Moreover, our approach enables real time processing of experimental data. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Potential fluctuations in disordered semiconductors measured by transport and optical methods

Mg in GaN: the structure of the acceptor and the electrical activity

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2003
H. Alves
Abstract We investigated GaN and AlGaN grown by metal organic chemical vapour deposition (MOCVD) and molecular beam epitaxy (MBE) doped with different Mg concentrations by photoluminescence Hall-effect and SIMS measurements. Optically detected magnetic resonance (ODMR) experiments were used to study the structure of the Mg-acceptors. The ODMR experiments reveal that the spin-density of the hole is equally distributed on the four nearst Nitrogen neighbors. Structural variations observed for Mg in MOCVD material are explained in terms of crystalfield variations caused by potential fluctuations due to the presence of compensating donors. Especially for highly doped MOCVD samples saturation of the free hole concentration and a strong 2.9 eV recombination are observed. Considering that compensating donors like nitrogen vacancies hydrogen and complexes of both form during growth we are able to calculate the experimental determined free hole concentrations. In MOCVD samples codoped with Mg and Si a decrease of the acceptor binding energy with increasing donor concentration was observed. The effect is caused by Coulomb interaction between the ionized acceptors and the free holes. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Role of sarcoplasmic reticulum in control of membrane potential and nitrergic response in opossum lower esophageal sphincter

BRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2003
Yong Zhang
We previously demonstrated that a balance of Ca2+ -activated Cl, current (ICl(Ca)) and K+ current activity sets the resting membrane potential of opossum lower esophageal sphincter (LES) circular smooth muscle at ,,41 mV, which leads to continuous spike-like action potentials and the generation of basal tone. Ionic mechanisms underlying this basal ICl(Ca) activity and its nitrergic regulation remain unclear. Recent studies suggest that spontaneous Ca2+ release from sarcoplasmic reticulum (SR) and myosin light chain kinase (MLCK) play important roles. The current study investigated this possibility. Conventional intracellular recordings were performed on circular smooth muscle of opossum LES. Nerve responses were evoked by electrical square wave pulses of 0.5 ms duration at 20 Hz. In the presence of nifedipine (1 ,M), substance P (1 ,M), atropine (3 ,M) and guanethidine (3 ,M), intracellular recordings demonstrated a resting membrane potential (MP) of ,38.1±0.7 mV (n=25) with spontaneous membrane potential fluctuations (MPfs) of 1,3 mV. Four pulses of nerve stimulation induced slow inhibitory junction potentials (sIJPs) with an amplitude of 6.1±0.3 mV and a half-amplitude duration of 1926±147 ms (n=25). 1H -[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a specific guanylyl cyclase inhibitor, abolished sIJPs, but had no effects on MPfs. Caffeine, a ryanodine receptor agonist, hyperpolarized MP and abolished sIJPs and MPfs. Ryanodine (20 ,M) inhibited the sIJP and induced biphasic effects on MP, an initial small hyperpolarization followed by a large depolarization. sIJPs and MPfs were also inhibited by cyclopiazonic acid, an SR Ca2+ ATPase inhibitor. Specific ICl(Ca) and MLCK inhibitors hyperpolarized the MP and inhibited MPfs and sIJPs. These data suggest that (1) spontaneous release of Ca2+ from the SR activates ICl(Ca), which in turn contributes to resting membrane potential; (2) MLCK is involved in activation of ICl(Ca); (3) inhibition of ICl(Ca) is likely to underlie sIJPs induced by nitrergic innervation. British Journal of Pharmacology (2003) 140, 1097,1107. doi:10.1038/sj.bjp.0705537 [source]