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Electron Concentration (electron + concentration)

Distribution by Scientific Domains

Physics and Astronomy	90%
Polymers and Materials Science	9%

Distribution within Physics and Astronomy

Solid State Physics	85%
General & Introductory Physics	14%

Selected Abstracts

Experimental Study and Modelling of Formation and Decay of Active Species in an Oxygen Discharge

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005
A.-M. Diamy
Abstract A microwave (2.45 GHz) oxygen discharge (3 hPa, 150 W, 50 mL.min,1) is studied by optical emission spectroscopy of O(5P) (line 777.4 nm) and of the atmospheric system of O2(head-line 759.4 nm). Calibration of the spectral response of the optical setup is used to determine the concentrations of O(5P) and O2(b). The concentration of the O(5P) atoms is in the range 108,109 cm,3 and the concentration of the O2(b) molecules is in the range 1014 , 2 × 1014 cm,3 along the discharge tube. An attempt is made to simulate the experimental results by using coupling the Boltzmann equation, homogeneous energy transfer V-V and V-T, heterogeneous reactions on the walls (energy transfer and recombination of atoms) and a kinetic scheme (electronic transfer and chemical reactions). The Boltzmann equation includes momentum transfer, inelastic and superelastic processes and e-e collisions. V-V and V-T transfer equations are obtained from the SSH theory and the kinetic scheme includes 65 reactions with 17 species [electrons e, ions O, and O2,, fundamental electronic neutral species O(3P), O2, O2(X,v), O3 and excited neutral species O2(a), O2(b), O2(A), O(1D), O(1S), O(5P), O(4d 5Do), O(5s 5So), O(3d 5Do) and O(4s 5So)]. A fair agreement between experimental results and modelling is obtained with the following set of fitting values: , heterogeneous deactivation coefficient for O2(b) , = 2.6 × 10,2; , rate constant of reaction [O(1D) + O(3P) , 2 O(3P)] k34 = 1.4 × 10,11 cm3.s,1; , electron concentration in the range 1010 , 1011 cm,3. Modelling shows that the recombination coefficient for oxygen atoms on the silica wall (range 1.4 × 10,3 , 0.2 × 10,3) is of the same order as the values obtained in a previous paper and that the ratio ([O] / 2 [O2]initial) is about 33,50%. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electron-Enhanced Hole Injection in Blue Polyfluorene-Based Polymer Light-Emitting Diodes,

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2004
T. van, Woudenbergh
Abstract It has recently been reported that, after electrical conditioning, an ohmic hole contact is formed in poly(9,9-dioctylfluorene) (PFO)-based polymer light-emitting diodes (PLED), despite the large hole-injection barrier obtained with a poly(styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) anode. We demonstrate that the initial current at low voltages in a PEDOT:PSS/PFO-based PLED is electron dominated. The voltage at which the hole injection is enhanced strongly depends on the electron-transport properties of the device, which can be modified by the replacement of reactive end groups by monomers in the synthesis. Our measurements reveal that the switching voltage of the PLED is governed by the electron concentration at the PEDOT:PSS/PFO contact. The switching effect in PFO is only observed for a PEDOT:PSS hole contact and not for other anodes such as indium tin oxide or Ag. [source]

Hall effect anomalies in n-type Pb1,xEux Se layers grown on silicon

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2007
A. Almaggoussi
Abstract Transport measurements (resistivity and Hall density) were made in the temperature range 10,300 K on n-Pb1,xEux Se (0 , x , 8%) epilayers grown by molecular beam epitaxy on silicon substrates. In the vicinity of 77 K anomalies of electron concentration were observed. To explain this anomalous behaviour, a model is proposed based on the existence of three levels: two donors and one acceptor. The origin of these levels is attributed to native defects. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Convertibility of conductivity type in reactively sputtered ZnO thin films

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
S. Tüzemen
Abstract Possible negative- U behavior of the VO donor may explain rather unusual free carrier properties in as-sputtered ZnO thin films grown at extremely Zn-rich conditions. VO can act as a source of free electron concentration at sample temperatures above 210 K. Below this temperature it changes its charge state to an inactive neutral charge state where it cannot act as a donor because of a thermal barrier with a threshold temperature of 170,210 K. The thermal barrier for an electron to go to neutral charge state from positive charge state is approximately 162 meV. Material can be converted to p-type by annealing VO centers. O-rich growth conditions with low [VO] may result in p-type conductivity. [source]

Spin properties of trions in a dense 2DEG

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2010
V. Kochereshko
Abstract Reflectivity and photoluminescence spectra from CdTe/CdMgTe modulation-doped quantum well structures were studied. We have found that in reflectivity spectra the value and the sign of the Zeeman splitting of the trion lines depend on the electron concentration in the quantum well, whereas, the value and sign of the exciton line splitting are constant for all studied electron concentrations. On the other hand, in the photoluminescence spectra the sign and value of the Zeeman splitting are the same for trion and exciton. Such "renormalization" of the trion g -factor is explained in the model of combined exciton,electron processes. [source]

Mg-doped InN and InGaN , Photoluminescence, capacitance,voltage and thermopower measurements

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008
J. W. Ager III
Abstract The bandgap range of InGaN extends from the near-IR (InN, 0.65 eV) to the ultraviolet. To exploit this wide tuning range in light generation and conversion applications, pn junctions are required. The large electron affinity of InN (5.8 eV) leads to preferential formation of native donor defects, resulting in excess electron concentration in the bulk and at surfaces and interfaces. This creates difficulties for p-type doping and/or measuring of the bulk p-type activity. Capacitance,voltage measurements, which deplete the n-type surface inversion layer, have been used to show that Mg is an active acceptor in InN and Inx Ga1,xN for 0.2 < x < 1.0, i.e. over the entire composition range. Mg acceptors can be compensated by irradiation-induced native donors. Thermopower measurements were used to provide definitive evidence that Mg-doped InN has mobile holes between 200 K and 300 K. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The effect of oxygen content on the electrical characteristics of ZnO

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007
E. S. Jung
Abstract This work presents the influence of the variation of oxygen content in the ZnO films on their electrical characteristics. We applied the post-thermal annealing in N2 and air ambient to control the oxygen content of ZnO films, which improved crystallinity and optical properties of ZnO films. The oxygen concentration was measured by Auger electron spectroscopy and the electrical characteristics were obtained by Hall measurement in the van der Pauw configuration and transmission line method. As result, it was shown that the electron concentration varies from 1016 to 1021/cm3, while the resistivity from 10,3 to tens ohm-cm with respect to Zn/O concentration ratio. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The way composition affects martensitic transformation temperatures of Ni,Mn,Ga Heusler alloys

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2007
X. Q. Chen
Abstract A systematic substitution of Ge, Si, C and Co for Ga in the non-stoichiometric Ni,Mn,Ga alloys was performed. The relationship between the compositions of different elements including Ni, Mn, Ga, Ge, Si, C, Co, In and martensitic transformation temperature (Ms) was studied in detail for the present alloys together with data collected from a variety of sources. It is found that Ms is a sensitive parameter to the composition. The size factor and electron concentration are usually thought to be the way the composition influences Ms in the Ni,Mn,Ga alloys. Here, analyzing by linear regression, the electron density maybe a most appropriate parameter to describe the way the composition influences Ms when compared with size factor and electron concentration. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Conduction band filling in In-rich InGaN and InN under hydrostatic pressure

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
G. Franssen
Abstract We demonstrate the effect of conduction band shape evolution of InGaN with increasing In content and applying hydrostatic pressure. The influence of conduction band filling on the hydrostatic pressure dependence of photoluminescence in In0.7Ga0.3N and InN is investigated. It is found that the PL pressure coefficient dEPL/dp of InN changes from ,27 meV/GPa to ,21 meV/GPa when the electron concentration increases from 3.6×1017 cm,3 to 1.1×1019 cm,3. In contrast, no significant change of dEPL/dp with electron concentration was observed for In0.7Ga0.3N. We conclude that the pressure sensitivity of the Fermi level, which is responsible for the lowering of dEPL/dp with respect to dEG/dp in InN, is much less prominent in In0.7Ga0.3N than in InN. We attribute this difference to the larger band gap of In0.7Ga0.3N, which lowers the pressure sensitivity of m*. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Origins of n-type residual carriers in RF-MOMBE grown InN layers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
Kosuke Iwao
Abstract We have investigated quantitatively on the origins of residual electrons in InN layers to make clear some roles of oxygen incorporation for band-gap widening. It has been found out that a linear relation was observed between oxygen and residual electron concentrations for InN layers grown by RF-MOMBE using TMIn source, although the residual electron concentration is super-linearly dependent on oxygen concentration for InN layers grown by RF-MBE using metal In source. The experimental results strongly indicate that oxygen atoms and/or nitrogen vacancies induced by oxygen incorporation are major origins of the residual carrier concentrations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

n-Al0.75Ga0.25N epilayers for 250 nm emission ultraviolet light emitting diodes

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
W. H. Sun
Abstract We have developed a unique approach combining migration-enhanced metalorganic chemical vapor deposition (MEMOCVD) high temperature AlN buffer layers and AlGaN/AlN superlattices (SLs) to yield high quality ( HQ) AlGaN layers for 250 nm LEDs. Symmetric/asymmetric X-ray diffraction (XRD) and room temperature photoluminescence measurements were used to study the high-structural and optical quality. The (002) and (114) rocking curve full width at half,maximum (FWHM) of 1.4 µm n-Al0.75Ga0.25N grown over AlGaN/AlN buffer were 143 and 565 arcsec, respectively. Crack-free Al0.75Ga0.25N layers with electron concentration as high as 1 × 1018 cm,3 and Hall mobility about 50 cm2/V.s were successfully grown and used for sub-milliwatt power (0.12 mW at a pulse pump current of 300 mA) 250 nm deep ultraviolet light emitting diodes (UVLEDs). In addition, for comparison, we prepared n-AlGaN only using high temperature AlN without SLs inserted. The experiments show that the AlGaN/AlN SLs inserted play a crucial role in improving structural and optical quality of high Al-composition AlGaN epilayers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

High-speed and high-frequency electron effects in nitride semiconductors for terahertz applications

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
K. W. Kim
Abstract We discuss the basic properties of the transient hot-electron transport and dynamic mobility in group-III nitrides under dominant electron,polar-optical-phonon scattering determining their capability for applications in THz frequency range. For bulk samples with high electron concentration, we provide the phase-plane analysis of the time-dependent transient transport and classification of different transient regimes depending on the initial conditions. The calculations predict a frequency interval with negative dynamic electron mobility where the amplification and generation of microwaves in THz frequency range is possible. For quantum-well heterostructures with low electron concentration under the streaming regime at moderate fields, we have revealed THz frequency windows of the negative microwave mobility, which enables the development of a tunable THz laser based on nitride quantum heterostructures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Field-effect transistors based on AlGaN/GaN/AlGaN double-heterostructures grown by MBE

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005
S. B. Aleksandrov
Abstract The double heterostructure (DHS) high-electron mobility transistor (HEMTs) grown by ammonia molecular beam epitaxy (MBE) is investigated both experimentally and theoretically. The band diagram and the sheet 2D electron concentration are computed, predicting alternating electron and hole slabs to co-exist in the structure. The DC characteristics of the DHS HEMT with the 1 µm gate are measured to asses the device performance. A breakdown threshold up to ,200 V is demonstrated for the source/drain voltage in DC operation. The parameters of the DHS and conventional AlGaN/GaN single-heterostructure HEMTs are compared. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Properties of n-layers formed by low-energy ion beam milling of chalcogenides epitaxial films

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2003
N. N. Berchenko
Abstract The paper presents the preliminary results of experiments performed to study the influence of low-energy Ar ions on the electrical properties of p- and n-type PbTe epitaxial films under ion beam milling. We demonstrate that this treatment causes p-to-n conversion in p-PbTe and increases the electron concentration in n-PbTe, with the electron mobility decreasing. The character of changes in the electrical properties allows to conclude that ion beam milling creates additional donor centres due to the preferential sputtering of tellurium. [source]

Probe Diagnostics of Expanding Plasmas at Low Gas Pressure

PLASMA PROCESSES AND POLYMERS, Issue 2 2006
Mariya Dimitrova
Abstract Summary: Results from tandem-type probe diagnostics of a plasma source based on an inductive discharge are presented in this study. The driver region is in the classical form of a cylindrically shaped inductive discharge, with a coil positioned over a gas discharge tube, whereas a bigger metal chamber provides volume for plasma expansion. Low pressure argon discharges were studied. The axial profiles of the plasma parameters were measured in the discharge in the metal chamber. The results obtained show that decreasing electron temperature and plasma density with increasing distance from the driver characterizes the behavior of the expanding plasmas. Moreover, two regions with different rates of variation of the plasma parameters complete the plasma expansion volume: a faster drop close to the driver and slow axial changes away from it. The gas pressure and power applied for the discharge maintenance were the external parameters varied. Axial profiles of the electron concentration in the plasma expansion region of an inductive discharge. [source]

Lattice distortion (Peierls Transition) caused by spin interaction in the chaotic impurity system of a semiconductor

ANNALEN DER PHYSIK, Issue 12 2009
A. Zabrodskii
Abstract The effect of an elastic spontaneous distortion of the crystal lattice of a doped semiconductor Ge:As near the insulator,metal (IM) phase transition has been discovered. The effect is manifested in the electron spin resonance (ESR) of neutral As atoms as a splitting of the single resonance absorption line. It observed at electron concentrations in the range 0.8 < n/nC < 1 at low temperatures T < 100 K (nC = 3.7 × 1017 cm -3 is the critical electron concentration for the IM phase transition). The splitting is the strongest along each of the six [110] directions, which indicates that the local lattice distortion occurs just in these directions. As a result, a sample is possibly divided into separate domains differing in the directions of compressive or tensile deformations. A study of concentration, temperature, and angular dependences of the effect has shown that the phenomenon discovered can be understood in terms of the Peierls spin transition model. [source]

Optical properties of InN grown on Si(111) substrate

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010
E. Sakalauskas
Abstract A comprehensive characterization of the optical properties of wurtzite InN films grown by molecular beam epitaxy on Si(111) substrates is presented. Two types of films are investigated in this work: InN on AlN/Si(111) and InN on GaN/AlN/Si(111). Their properties are compared to a layer deposited on GaN/sapphire substrate. The dielectric function (DF) is obtained from spectroscopic ellipsometry (SE). The infrared studies yield the plasma frequency and thus the electron density, while the interband absorption is probed between 0.56 and 9.8,eV. For InN grown on Si(111) substrate, the absorption onset is slightly shifted to higher energies with respect to the InN film grown on GaN/sapphire which can be attributed to higher electron concentrations. Despite this, strongly pronounced optical transitions due to critical points of the band structure are found in the high-energy part of the DF. It emphasizes the already promising quality of the InN films on silicon. Band-gap renormalization (BGR), band filling, and strain are taken into account in order to estimate the intrinsic band gap of wurtzite InN. For the InN layers on silicon, we get a band gap between 0.66 and 0.685,eV. [source]

Recombination processes with and without momentum conservation in degenerate InN

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2006
E. Valcheva
Abstract We report on a theoretical approach in which the two cases of recombination with and without momentum conservation in optically excited high carrier concentration InN are considered. The calculations are used to analyze emission spectra of n-type InN layers of electron concentrations from 7.7 × 1017 to 1.4 × 1019 cm,3 studied in the temperature range between 9 and 100 K. The spectra peak near 0.7 eV and the applicability of the two approaches with increasing carrier concentration is estimated. Different transition mechanisms are considered in order to properly account for the observed features in the spectra. Recombination processes involving acceptor- and donor-like localized states are discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spin properties of trions in a dense 2DEG

Carrier-induced refractive index change in InN

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2008
C. Bulutay
Abstract Rapid development of InN technology demands comprehensive assessment of the electronic and optoelectronic potential of this material. In this theoretical work the effect of free electrons on the optical properties of the wurtzite phase of InN is investigated. The blue shift of the optical absorption edge by the free-carrier band filling is known as the Burstein-Moss effect for which InN offers to be a very suitable candidate as has been recently demonstrated experimentally. Due to well known Kramers-Kronig relations, a change in absorption is accompanied by a change in the index of refraction. Considering n-type InN samples with free electron concentrations ranging from 5×1017 to 5×1020 cm,3, and employing a nonlocal empirical pseudopotential band structure, it is shown that this leads to a few percent change of the index of refraction. These carrier-induced refractive index changes can be utilized in optical switches, futhermore it needs to be taken into account in the design of InN-based optical devices such as lasers and optical modulators. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]