122 research outputs found
Electron backscattering from stacking faults in SiC by means of \textit{ab initio} quantum transport calculations
We study coherent backscattering phenomena from single and multiple stacking
faults (SFs) in 3C- and 4H-SiC within density functional theory quantum
transport calculations. We show that SFs give rise to highly dispersive bands
within both the valance and conduction bands that can be distinguished for
their enhanced density of states at particular wave number subspaces. The
consequent localized perturbation potential significantly scatters the
propagating electron waves and strongly increases the resistance for -doped
systems. We argue that resonant scattering from SFs should be one of the
principal degrading mechanisms for device operation in silicon carbide.Comment: 5 pages, 4 figure
Structural and electronic characterization of (2,3(3)) bar-shaped stacking fault in 4H-SiC epitaxial layers
Crystallographic, electronic, and energetic analyses of the (2, 3_3) [or (2, 3, 3, 3) in the standard Zhadanov notation] bar-shaped stacking fault, observed in as-grown 4H-SiC epitaxial layers, are presented. The defect has been identified by means of spatially resolved microphotoluminescence (μ-PL) measurements at different emission wavelengths, focusing on the emission peak at 0.3 eV below the conduction band. Low temperature μ-PL measurements have also been performed. The defect has been identified and characterized using high resolution transmission electron microscopy. Experimental results are correlated and validated by the calculations of the Kohn–Sham electronic band structure and the defect formation energy
Phonon Driven Nonlinear Electrical Behavior in Molecular Devices
Electronic transport in a model molecular device coupled to local phonon
modes is theoretically analyzed. The method allows for obtaining an accurate
approximation of the system's quantum state irrespective of the electron and
phonon energy scales. Nonlinear electrical features emerge from the calculated
current-voltage characteristics. The quantum corrections with respect to the
adiabatic limit characterize the transport scenario, and the polaronic
reduction of the effective device-lead coupling plays a fundamental role in the
unusual electrical features.Comment: 14 pages, 4 figure
An Experimental Evaluation of Resistive Defects and Different Testing Solutions in Low-Power Back-Biased SRAM Cells
This paper compares different types of resistive defects that may occur inside low-power SRAM cells, focusing on their impact on device operation. Notwithstanding the continuous evolution of SRAM device integration, manufacturing processes continue to be very sensitive to production faults, giving rise to defects that can be modeled as resistances, especially for devices designed to work in low-power modes. This work analyzes this type of resistive defect that may impair the device functionalities in subtle ways, depending on the defect characteristics and values that may not be directly or easily detectable by traditional test methods. We analyze each defect in terms of the possible effects inside the SRAM cell, its impact on power consumption, and provide guidelines for selecting the best test methods
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Perspectives and advantages of the use of excimer laser annealing for MOS technology
The integration of excimer laser annealing (ELA) into the MOS device technology has been studied and evaluated within the frame of the IST project FLASH (Fundamentals and applications of laser processing for highly innovative MOS technology), funded by the European Commission. The final aim of the project was to demonstrate that ELA can be applied as a reliable, effective and advantageous process in the context of semiconductor device fabrication. Some of the results of this activity are summarised, relative to the experimental characterization and theoretical modelling. The electrical characterization of the transistor fabricated by ELA is also presented, showing a device yield of 90% on wafer
Insulator-metal transition in biased finite polyyne systems
A method for the study of the electronic transport in strongly coupled
electron-phonon systems is formalized and applied to a model of polyyne chains
biased through metallic Au leads. We derive a stationary non equilibrium
polaronic theory in the general framework of a variational formulation. The
numerical procedure we propose can be readily applied if the electron-phonon
interaction in the device hamiltonian can be approximated as an effective
single particle electron hamiltonian. Using this approach, we predict that
finite polyyne chains should manifest an insulator-metal transition driven by
the non-equilibrium charging which inhibits the Peierls instability
characterizing the equilibrium state.Comment: to appear at EPJ
Mass Renormalization in the Su-Schrieffer-Heeger Model
This study of the one dimensional Su-Schrieffer-Heeger model in a weak
coupling perturbative regime points out the effective mass behavior as a
function of the adiabatic parameter , is the
zone boundary phonon energy and is the electron band hopping integral.
Computation of low order diagrams shows that two phonons scattering processes
become appreciable in the intermediate regime in which zone boundary phonons
energetically compete with band electrons. Consistently, in the intermediate
(and also moderately antiadiabatic) range the relevant mass renormalization
signals the onset of a polaronic crossover whereas the electrons are
essentially undressed in the fully adiabatic and antiadiabatic systems. The
effective mass is roughly twice as much the bare band value in the intermediate
regime while an abrupt increase (mainly related to the peculiar 1D dispersion
relations) is obtained at .Comment: To be published in Phys.Rev.B - 3 figure
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