Search results for " Semiconductor"
showing 10 items of 332 documents
Temperature dependence of spin depolarization of drifting electrons in n-type GaAs bulks
2010
The influence of temperature and transport conditions on the electron spin relaxation in lightly doped n-type GaAs semiconductors is investigated. A Monte Carlo approach is used to simulate electron transport, including the evolution of spin polarization and relaxation, by taking into account intravalley and intervalley scattering phenomena of the hot electrons in the medium. Spin relaxation lengths and times are computed through the D'yakonov-Perel process, which is the more relevant spin relaxation mechanism in the regime of interest (10 < T < 300 K). The decay of the initial spin polarization of the conduction electrons is calculated as a function of the distance in the presence of…
Heusler Compounds—A Material Class With Exceptional Properties
2011
The class of Heusler compounds, including the XYZ and the X2YZ compounds, has not only an endless number of members, but also a vast variety of properties can be found in this class of materials, ranging from semiconductors, half-metallic ferromagnets, superconductors, and topological insulators to shape memory alloys. With this review article, we would like to provide an overview of Heusler compounds, focusing on their structure, properties, and potential applications.
New Heusler Compounds and Their Properties
2013
Spintronics is a multidisciplinary field and a new research area. New materials must be found for satisfying the different types of requirement. The search for stable half-metallic ferromagnets and ferromagnetic semiconductors with Curie temperatures higher than room temperature is still a challenge for solid state scientists. A general understanding of how structures are related to properties is a necessary prerequisite for material design. Computational simulations are an important tool for a rational design of new materials. The new developments in this new field are reported from the point of view of material scientists.
Ab Initio Thermodynamics of Oxygen Vacancies and Zinc Interstitials in ZnO.
2015
ZnO is an important wide band gap semiconductor with potential application in various optoelectronic devices. In the current contribution, we explore the thermodynamics of oxygen vacancies and zinc interstitials in ZnO from first-principles phonon calculations. Formation enthalpies are evaluated using hybrid DFT calculations, and phonons are addressed using the PBE and the PBE+U functionals. The phonon contribution to the entropy is most dominant for oxygen vacancies, and their Gibbs formation energy increases when including phonons. Finally, inclusion of phonons decreases the Gibbs formation energy difference of the two defects and is therefore important when predicting their equilibrium c…
X-ray-absorption fine-structure study of ZnSexTe1−x alloys
2004
X-ray-absorption fine-structure experiments at different temperatures in ZnSexTe1−x (x=0, 0.1, 0.2, 0.55, 0.81, 0.93, 0.99, and 1.0) have been performed in order to obtain information about the structural relaxation and disorder effects occurring in the alloys. First and second neighbor distance distributions have been characterized at the Se and Zn K edges, using multiple-edge and multiple-scattering data analysis. The first neighbor distance distribution was found to be bimodal. The static disorder associated with the Zn–Te distance variance did not depend appreciably on composition. On the other hand, the static disorder associated with the Zn–Se distance increased as the Se content dimi…
Thickness scaling of space-charge-limited currents in organic layers with field- or density-dependent mobility
2006
An exact solution is provided for the current density-voltage (J –V) characteristics of space-charge limited transport of a single carrier in organic layers with field-dependent mobility of the type μ (E) = μ0 exp (γ √E. The general scaling relationship for field-dependent mobility occurs in terms of the variables JL and V /L. For the density-dependence of the mobility found in organic field-effect transistor measurements, the thickness scaling occurs in terms of different variables, J1/βL and V /L. The proposed scaling is a useful test for distinguishing field- and carrier density-dependent mobility in disordered organic semiconductors. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Phonon Scattering through a Local Anisotropic Structural Disorder in the Thermoelectric Solid Solution Cu_2Zn_(1−x)Fe_xGeSe_4
2013
Inspired by the promising thermoelectric properties of chalcopyrite-like quaternary chalcogenides, here we describe the synthesis and characterization of the solid solution Cu(2)Zn(1-x)Fe(x)GeSe(4). Upon substitution of Zn with the isoelectronic Fe, no charge carriers are introduced in these intrinsic semiconductors. However, a change in lattice parameters, expressed in an elongation of the c/a lattice parameter ratio with minimal change in unit cell volume, reveals the existence of a three-stage cation restructuring process of Cu, Zn, and Fe. The resulting local anisotropic structural disorder leads to phonon scattering not normally observed, resulting in an effective approach to reduce th…
Oligothiophenes for Pattern Formation by Stamping
2003
Oligothiophene monomers with a fixed length varying from 3 to 5 thiophene rings were prepared by Stille coupling. They were functionalised with one or two methacrylate groups to allow polymerization and cross-linking. These monomers can be patterned with the help of soft silicon stamps (e.g., with the micro-injection moulding in capillaries process) on substrates like glass or flexible polymer foils. If a photoinitiator has been added, they can then be hardened by exposure to UV-light through the transparent stamp. Afterwards the stamp can be removed. This allows the preparation of several centimeters long oligothiophene lines of a width varying between 50 and 0.5 μm. These lines of semicon…
Chemical and Structural Trends in the Spin-Admixture Parameter of Organic Semiconductor Molecules
2019
Spin mixing in organic semiconductors is related to spin–orbit coupling (SOC). However, a detailed study analyzing the dependence of the spin-admixture parameter (γ) on structural and material para...
Theoretical study of Zn and Cd interstitials and substitutional interstitials in CuInSe2 via hybrid functional calculations
2013
We have investigated the formation of Zn and Cd interstitials in the CuInSe2 solar cell material via density-functional-theory (DFT) calculations by employing the HSE06 hybrid functional. The computed formation energies for Zn interstitials were in the range of 2.09-2.68 e V, and in the range of 2.04-2.25 eV for substitutional interstitials. In constrast, the formation energies of Cd interstitials and substitutional interstitials were between 1.85-2.75 eV and 2.41-2.64 eV, respectively. Thus, these results indicate, that Cd interstitials are more likely to be formed than Zn interstitials, and that in case of Zn inclusion into CuInSe2 Zn atoms will prefer to adopt substitutional interstitial…