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61.
On the reverse leakage current of Schottky contacts on free-standing GaN at high reverse biases
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In this work, a dislocation-related tunneling leakage current model is developed to explain the temperature-dependent reverse current–voltage(I–V –T) characteristics of a Schottky barrier diode fabricated on free-standing GaN substrate for reverse-bias voltages up to-150 V. The model suggests that the reverse leakage current is dominated by the direct tunneling of electrons from Schottky contact metal into a continuum of states associated with conductive dislocations in GaN epilayer.A reverse leakage current ideality factor, which originates from the scattering effect at metal/GaN interface, is introduced into the model. Good agreement between the experimental data and the simulated I–V curves is obtained. 相似文献
62.
63.
Plasticity is governed by the evolution of, in general anisotropic, systems of dislocations. We seek to faithfully represent this evolution in terms of density-like variables which average over the discrete dislocation microstructure. Starting from T. Hochrainer's continuum theory of dislocations (CDD) (Hochrainer, 2015), we introduce a methodology based on the ‘Maximum Information Entropy Principle’ (MIEP) for deriving closed-form evolution equations for dislocation density measures of different order. These equations provide an optimum representation of the kinematic properties of systems of curved and connected dislocation lines with the information contained in a given set of density measures. The performance of the derived equations is benchmarked against other models proposed in the literature, using discrete dislocation dynamics simulations as a reference. As a benchmark problem we study dislocations moving in a highly heterogeneous, persistent-slip-band like geometry. We demonstrate that excellent agreement with discrete simulations can be obtained in terms of a very small number of averaged dislocation fields containing information about the edge and screw components of the total and excess (geometrically necessary) dislocation densities. From these the full dislocation orientation distribution which emerges as dislocations move through a channel-wall structure can be faithfully reconstructed. 相似文献
64.
A. N. Danilewsky A. Crll J. Tonn M. Schweizer S. Lauer K. W. Benz T. Tuomi R. Rantamki P. McNally J. Curley 《Crystal Research and Technology》2009,44(10):1109-1114
The behaviour of dislocations in GaSb crystals grown in space both from a stoichiometric melt (floating zone method, FZ) and a Bi solution (floating solution zone, FSZ) respectively, is studied. Predominantly straight 60° dislocations with Burgers vectors of the type b = a/2 <110> in (111) glide planes are identified. In the 20 mm long FZ single crystal the linear growing out of the dislocations is observed which reduces the dislocation density in the centre of the crystal to values below 300 cm–2. The Bi incorporation in the FSZ crystal results in a misfit between seed and grown crystal and in a network of misfit dislocations at the interface. Thermocapillary convection during growth as well as the surface tension may be the reasons for the presence of curved dislocations and the higher dislocation density within a 1 – 2 mm border region at the edges of both of the crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
65.
66.
Discrete dislocations in graphene 总被引:1,自引:0,他引:1
In this work, we present an application of the theory of discrete dislocations of Ariza and Ortiz (2005) to the analysis of dislocations in graphene. Specifically, we discuss the specialization of the theory to graphene and its further specialization to the force-constant model of Aizawa et al. (1990). The ability of the discrete-dislocation theory to predict dislocation core structures and energies is critically assessed for periodic arrangements of dislocation dipoles and quadrupoles. We show that, with the aid of the discrete Fourier transform, those problems are amenable to exact solution within the discrete-dislocation theory, which confers the theory a distinct advantage over conventional atomistic models. The discrete dislocations exhibit 5-7 ring core structures that are consistent with observation and result in dislocation energies that fall within the range of prediction of other models. The asymptotic behavior of dilute distributions of dislocations is characterized analytically in terms of a discrete prelogarithmic energy tensor. Explicit expressions for this discrete prelogarithmic energy tensor are provided up to quadratures. 相似文献
67.
This paper develops a gradient theory of single-crystal plasticity based on a system of microscopic force balances, one balance for each slip system, derived from the principle of virtual power, and a mechanical version of the second law that includes, via the microscopic forces, work performed during plastic flow. When combined with thermodynamically consistent constitutive relations the microscopic force balances become nonlocal flow rules for the individual slip systems in the form of partial differential equations requiring boundary conditions. Central ingredients in the theory are geometrically necessary edge and screw dislocations together with a free energy that accounts for work hardening through a dependence on the accumulation of geometrically necessary dislocations. 相似文献
68.
M. Ricker J. Bachteler H.-R. Trebin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):351-363
In quasicrystals, there are not only conventional, but also phason displacement fields and associated Burgers vectors. We
have calculated approximate solutions for the elastic fields induced by two-, three- and fivefold straight screw- and edge-dislocations
in infinite icosahedral quasicrystals by means of a generalized perturbation method. Starting from the solution for elastic
isotropy in phonon and phason spaces, corrections of higher order reflect the two-, three- and fivefold symmetry of the elastic
fields surrounding screw dislocations. The fields of special edge dislocations display characteristic symmetries also, which
can be seen from the contributions of all orders.
Received 21 February 2001 and Received in final form 27 June 2001 相似文献
69.
Subhash Bhatia Noor Asmawati binti Mohd Zabidi Megat Harun Al Rashid bin Megat Ahmad 《Reaction Kinetics and Catalysis Letters》2001,74(1):87-92
The catalytic activity of Ni/MgO catalysts was studied for the oxidative coupling of methane (OCM). The catalysts were characterized
using transmission electron microscope (TEM) and XRD. The increase in C2+ selectivity of Ni/MgO was attributed to the presence
of bulk dislocations and MgNiO2 phase.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
70.
In nearly all cases when an epitaxial layer of HgCdTe is grown on a CdZnTe substrate, there will be a finite lattice mismatch
due to the lack of precise control over the ZnTe mole fraction. This leads to strains in the layer, which can be manifested
in one or more ways: (1) as misfit dislocations near the interface, (2) as threading dislocations, (3) as surface topographical
textures, and (4) as cross-hatch lines seen by x-ray topography. We have found that much of the strain can be relieved by
growing on a reticulated substrate. Specifically, when the substrate has been etched to form mesas prior to growth of the
layer, the resulting layer on the tops of the mesas shows evidence of significantly reduced strain. CdZnTe substrates oriented
(111)A were prepared with two sets of mesas on 125 μm centers and 60 μm centers, and with other planar areas remaining for
comparison. From a Hg melt, a layer of LWIR HgCdTe was grown about 16 μm thick on each substrate. Nomarski microscopy showed
that the layers on the mesa tops were extremely flat, showing no sign of curvature or surface texture. X-ray topography showed
no cross hatch on the mesa tops, while the usual cross hatch appeared in the planar regions. The LPE layer extended laterally
beyond the edges of the original mesa because of faster growth in non-(111) directions. Samples were cleaved and examined
in cross section. The linear density of etch pits seen in the cross section near the substrate, which represent misfit dislocations,
was three times lower in the layer on the mesas than in the layer in the unpatterned region, although both regions have the
same layer/substrate lattice mismatch. When an epilayer is grown on an unpatterned wafer (the conventional approach), the
growth in any small region is confined laterally by the growing layer in the neighboring regions. However, when growth occurs
on a reticulated surface, the lateral confinement is removed, providing strain relief and fewer defects. 相似文献