Steady-state and transient electron transport within bulk wurtzite zinc oxide

We study the steady-state and transient electron transport that occurs within bulk wurtzite zinc oxide using an ensemble semi-classical three-valley Monte Carlo simulation approach. We find that for electric field strengths in excess of 180 kV/cm, the steady-state electron drift velocity associated with bulk wurtzite zinc oxide exceeds that associated with bulk wurtzite gallium nitride. We also present evidence to suggest that the negative differential mobility exhibited by the velocity-field characteristic associated with bulk wurtzite zinc oxide is not related to transitions to the upper valleys. The transient electron transport that occurs within bulk wurtzite zinc oxide is studied by examining how electrons, initially in thermal equilibrium, respond to the sudden application of a constant electric field. From these transient electron transport results, we conclude that for devices with dimensions smaller than 0.1 μm, gallium nitride based devices will offer the advantage, owing to their superior transient electron transport, while for devices with dimensions greater than 0.1 μm, zinc oxide based devices will offer the advantage, owing to their superior high-field steady-state electron transport.     

Convergence parameter associated with a Markov chain and a family of functions

The proposed definition of convergence parameter R(W) corresponding to a Markov chain X with a measurable state space (E,?) and any nonempty setW of bounded below measurable functions f: E → ? is wider than the well-known definition of convergence parameter R in the sense of Tweedie or Nummelin. Very often, R(W) < ∞, and there exists a set playing the role of the absorbing set inNummelin’s definition ofR. Special attention is paid to the case in whichE is locally compact, X is a Feller chain on E, and W coincides with the family ? ₀ ⁺ of all compactly supported continuous functions f ≥ 0 (f ? 0). In particular, certain conditions for R(? ₀ ⁺ )^?1 to coincide with the norm of an appropriate modification of the chain transition operator are found.     

Motion of a planar domain wall in the ferroelectric-ferroelastic gadolinium molybdate

The lateral motion of a planar domain wall (PDW) in an electric field and the spontaneous rotation of the wall in the initial position after the field is switched off were investigated in the improper ferroelectric-ferroelastic gadolinium molybdate Gd₂(MoO₄)₃, using optical visualization and measurement of the switching currents. The characteristic behavior found for the PDW is attributed to the delay of the volume screening of the depolarizing fields. It is shown that the dependence of the motion of the PDW on the switching duration in an ac field is due to the redistribution of the screening charges. Fiz. Tverd. Tela (St. Petersburg) 41, 126–129 (January 1999)     

Struktur,Eigenschaften und NMR-spektroskopische Charakterisierung von Cp2Zr(Pyridin)(Me3SiCCSiMe3)

Structure, Properties, and NMR Spectroscopical Characterization of Cp₂Zr(pyridine)(Me₃SiC?CSiMe₃) Displacement of the THF ligand in Cp₂Zr(THF)(Me₃SiC?CSiMe₃) ( 1 ) with pyridine yields Cp₂Zr(η¹-NC₅H₅)(Me₃SiC?CSiMe₃) (3). Unlike 1 , the complex 3 is stable in hydrocarbon solvents. According to the temperature dependent ¹H and ¹³C NMR spectra, the structure of complex 3 in solution is dynamic due to a rotation of the alkyne ligand. In addition, when 3 is dissolved in pyridine an easy exchange between coordinated and free molecules of pyridine takes place. In the solid state complex 3 displays a tetrahedral coordination sphere at the zirconium center composed of Cp ligands, alkyne and pyridine as shown by an X-ray structure analysis. The complex 3 reacts readily with water and carbon dioxide giving the same products as in the case of 1 .     

Current collapse and reliability of III‐N heterostructure field effect transistors

Measurements of GaN HFET lifetime as a function of temperature show that different degradation mechanisms are involved at low temperatures (close to room temperature) and high temperatures (above 150 °C). The degradation at low temperatures is linked to the trap generation and can be explained using the current collapse model. At higher tempe‐ ratures, other degradation mechanisms become important or even dominant. The current collapse related degradation can be diminished by using improved device design, which will greatly increase the overall lifetime (up to long lifetimes obtained by extrapolating high temperature data to room temperature). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polarization switching in heterophase nanostructures: PLZT relaxor ceramics

The polarization switching is experimentally investigated in hot-pressed PLZT-x/65/35 ceramics with a lanthanum content from 5 to 12 at. %. The specific features in the temperature dependence of the polarization switching in a heterophase state are interpreted by analyzing the change in the switched charge measured over wide ranges of fields and temperatures. Particular emphasis is placed on the role of depolarization fields induced by interphase boundaries. A model of the evolution of polydomain nanostructures with a change in the temperature and in the response to an external field is considered. It is assumed that the low-temperature dielectric anomaly and the temperature hysteresis are associated with the loss of stability of a large-scale domain structure and its transformation into a nanodomain state.