393 research outputs found
Electrical and structural degradation of GaN high electron mobility transistors under high-power and high-temperature Direct Current stress
We have stressed AlGaN/GaN HEMTs (High Electron Mobility Transistors) under high-power and high-temperature DC conditions that resulted in various levels of device degradation. Following electrical stress, we conducted a well-established three-step wet etching process to remove passivation, gate and ohmic contacts so that the device surface can be examined by SEM and AFM. We have found prominent pits and trenches that have formed under the gate edge on the drain side of the device. The width and depth of the pits under the gate edge correlate with the degree of drain current degradation. In addition, we also found visible erosion under the full extent of the gate. The depth of the eroded region averaged along the gate width under the gate correlated with channel resistance degradation. Both electrical and structural analysis results indicate that device degradation under high-power DC conditions is of a similar nature as in better understood high-voltage OFF-state conditions. The recognition of a unified degradation mechanism provides impetus to the development of a degradation model with lifetime predictive capabilities for a broad range of operating conditions spanning from OFF-state to ON-state.United States. Office of Naval Research.Design-for-Reliability Initiative for Future Technologies. Multidisciplinary University Research Initiative
Physics of InAIAs/InGaAs Heterostructure Field-Effect Transistors
Contains an introduction, reports on two research projects and a list of publications.Joint Services Electronics Program Contract DAAL03-92-C-0001Joint Services Electronics Program Grant DAAH04-95-1-0038Raytheon Corporation Contract 90-58203Texas Instruments Agreement dated 08/14/9
МУЗЕЇ ДНІПРОПЕТРОВСЬКОЇ ОБЛАСТІ НА СУЧАСНОМУ ЕТАПІ
Розглянуто діяльність музеїв, участь їх у краєзнавчому русі, кількісні та якісні показники розвитку музейної галузі Дніпропетровської області на сучасному етапіAuthors have examined museum activities, their role in the movement of local lore, quantitative and qualitative indices of museum development in the Dniepropetrovsk region at present stage
Probing Spin-Charge Separation in Tunnel-Coupled Parallel Quantum Wires
Interactions in one-dimensional (1D) electron systems are expected to cause a
dynamical separation of electronic spin and charge degrees of freedom. A
promising system for experimental observation of this non-Fermi-liquid effect
consists of two quantum wires coupled via tunneling through an extended uniform
barrier. Here we consider the minimal model of an interacting 1D electron
system exhibiting spin-charge separation and calculate the differential
tunneling conductance as well as the density-density response function. Both
quantities exhibit distinct strong features arising from spin-charge
separation. Our analysis of these features within the minimal model neglects
interactions between electrons of opposite chirality and applies therefore
directly to chiral 1D electron systems realized, e.g., at the edge of integer
quantum-Hall systems. Physical insight gained from our results is useful for
interpreting current experiment in quantum wires as our main conclusions still
apply with nonchiral interactions present. In particular, we discuss the effect
of charging due to applied voltages, and the possibility to observe spin-charge
separation in a time-resolved experiment.Comment: 9 pages, 3 figures, expanded version with many detail
Genetic Predisposition for Immune System, Hormone, and Metabolic Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Pilot Study
Introduction: Myalgic Encephalomyelitis/ Chronic Fatigue Syndrome (ME/CFS) is a multifactorial illness of unknown etiology with considerable social and economic impact. To investigate a putative genetic predisposition to ME/CFS we conducted genome-wide single-nucleotide polymorphism (SNP) analysis to identify possible variants.Methods: 383 ME/CFS participants underwent DNA testing using the commercial company 23andMe. The deidentified genetic data was then filtered to include only non-synonymous and nonsense SNPs from exons and microRNAs, and SNPs close to splice sites. The frequencies of each SNP were calculated within our cohort and compared to frequencies from the Kaviar reference database. Functional annotation of pathway sets containing SNP genes with high frequency in ME/CFS was performed using over-representation analysis via ConsensusPathDB. Furthermore, these SNPs were also scored using the Combined Annotation Dependent Depletion (CADD) algorithm to gauge their deleteriousness.Results: 5693 SNPs were found to have at least 10% frequency in at least one cohort (ME/CFS or reference) and at least two-fold absolute difference for ME/CFS. Functional analysis identified the majority of SNPs as related to immune system, hormone, metabolic, and extracellular matrix organization. CADD scoring identified 517 SNPs in these pathways that are among the 10% most deleteriousness substitutions to the human genome
Conductance oscillations in strongly correlated fractional quantum Hall line junctions
We present a detailed theory of transport through line junctions formed by
counterpropagating single-branch fractional-quantum-Hall edge channels having
different filling factors. Intriguing transport properties are exhibited when
strong Coulomb interactions between electrons from the two edges are present.
Such strongly correlated line junctions can be classified according to the
value of an effective line-junction filling factor n that is the inverse of an
even integer. Interactions turn out to affect transport most importantly for
n=1/2 and n=1/4. A particularly interesting case is n=1/4 corresponding to,
e.g., a junction of edge channels having filling factor 1 and 1/5,
respectively. We predict its differential tunneling conductance to oscillate as
a function of voltage. This behavior directly reflects the existence of novel
Majorana-fermion quasiparticle excitations in this type of line junction.
Experimental accessibility of such systems in current cleaved-edge overgrown
samples enables direct testing of our theoretical predictions.Comment: 2 figures, 10 pages, RevTex4, v2: added second figure for clarit
Testing Bell's inequality using ballistic electrons in semiconductors
We propose an experiment to test Bell's inequality violation in condensed-matter physics. We show how to generate, manipulate, and detect entangled states using ballistic electrons in Coulomb-coupled semiconductor quantum wires. Due to its simplicity (only five gates are required to prepare entangled states and to test Bell's inequality), the proposed semiconductor-based scheme can be implemented with currently available technology. Moreover, its basic ingredients may play a role towards large-scale quantum-information processing in solid-state devices
Mesoscopic effects in tunneling between parallel quantum wires
We consider a phase-coherent system of two parallel quantum wires that are
coupled via a tunneling barrier of finite length. The usual perturbative
treatment of tunneling fails in this case, even in the diffusive limit, once
the length L of the coupling region exceeds a characteristic length scale L_t
set by tunneling. Exact solution of the scattering problem posed by the
extended tunneling barrier allows us to compute tunneling conductances as a
function of applied voltage and magnetic field. We take into account charging
effects in the quantum wires due to applied voltages and find that these are
important for 1D-to-1D tunneling transport.Comment: 8 pages, 7 figures, improved Figs., added Refs. and appendix, to
appear in Phys. Rev.
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