Structure Of Stacking Faults Research Articles

Structure of In-Grown Stacking Faults in the 4H-SiC Epitaxial Layers

We investigated the structure of the in-grown stacking faults (SFs) in the 4H-SiC epilayers. The in-grown SFs exhibited the photoluminescence (PL) peaks representing phonon replicas with bandgap of 2.710 eV. The in-grown SFs were confirmed to be triangular-shaped by PL mapping and KOH etch pit observation. High-resolution TEM image showed that the in-grown SFs have an identical stacking sequence that differ from single or double Shockley SF. In addition, the density of the in-grown SF depended on growth conditions.

Structural analysis and reduction of in-grown stacking faults in 4H–SiC epilayers

We investigated the structure of in-grown stacking faults in the 4H–SiC(0001) epilayers. The in-grown stacking faults nucleate near the substrate/epilayer interface and expand the area with increasing epilayer thickness in a triangular shape. From transmission electron microscope observation, the formation of 1c of 8H polytype was confirmed in the in-grown stacking fault area. We also investigated the dependence of in-grown stacking fault density on the epitaxial growth rate, growth temperature, and substrate surface preparation.

Intersecting basal plane and prismatic stacking fault structures and their formation mechanisms in GaN

AbstractComparative TEM studies have been carried out on GaN/AlN epifilms grown on both on-axis and off-cut 6H-SiC substrates to study the defects formed in the GaN/AlN films and the state of strain relaxation at the interface. Prismatic Stacking Faults (PSFs) are observed to form at I1 type substrate steps in both the on-axis and vicinal samples. In the vicinal samples, the PSFs expand into GaN/AlN film forming intersecting stacking fault configurations comprising faults that fold back and forth from the basal plane (I1 Basal-Plane Stacking Faults; BSFs) to the prismatic plane (PSFs). On the other hand, in the on-axis sample the PSFs are observed to mostly annihilate each other to form enclosed domains confined to the near-interface region. In addition, HRTEM studies suggest the existence of Geometric Partial Misfit Dislocations (GPMDs) at the SiC/AlN interface of the vicinal sample, which form at I2 type substrate steps. These GPMDs simultaneously accommodate the lattice mismatch and stacking sequence mismatch present at the SiC/AlN interface. This provides explanation of the improved strain relaxation observed in the vicinal versus the on-axis sample.

Energetics and electronic structure of stacking faults in ZnO

The energetics and electronic structures of basal-plane stacking faults in wurtzite (WZ) ZnO are studied using first-principles density-functional total energy calculations. All the basal-plane stacking faults are found to have very low formations energies. They also introduce a downward shift at the conduction-band minimum (CBM). However, plane-averaged charge densities of the CBM state reveal that the CBM states are not very localized, indicating that these stacking faults should be electronically inert. The high concentration of these stacking faults can result in embedded zinc-blende (ZB) ZnO surrounded by WZ materials. The WZ/ZB interface exhibits a type-II lineup with $\ensuremath{\Delta}{E}_{V}\ensuremath{\approx}0.037\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and $\ensuremath{\Delta}{E}_{C}\ensuremath{\approx}0.147\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$.

Microstructure evolution and fracture behaviour for electron beam welding of Ti-6Al-4V

The effect of microstructural characteristics on fracture behaviour mechanism for electron beam welding of Ti-6Al-4V was investigated. The results indicated that the welded microstructure composed of coarse needle α + β phases presenting disordered and multidirectional short needle morphology to make fracture mechanism complex. The coarse grains in weld seam with microhardness 536 HV were easy to be fractured in the region where welding heat input was ≥ 68.8 kJ/m. There exists flat curves of Ti, Al and V, Fe concentration distribution fluctuation to cause microstructural amplitude-modulated decomposition to increase the joint ductility and cleavage strength. The uneven distribution of the partial micropores located at the interior of the specimen acting as crack initiation sites lead to non-linear branch propagating path. The α + β interlaced structure results in the fracture location near α/β interface. The existence of stacking fault structure caused pile-up of dislocation to produce micropores to be new fracture initiation sites.

Stacking faults in heavily nitrogen doped 4H-SiC

A high density of planar defects is observed by scanning and transmission electron microscopy in wafers cut from 4H-SiC crystals containing nitrogen above about 2 × 10 19 cm -3 and heat treated at 1100 °C. All of the planar defects observed by high-resolution transmission electron microscopy have the same structure comprising six Si-C bilayers in cubic stacking sequence Such a lamella can originate from two stacking faults in neighbouring basal planes and is therefore called double stacking fault. The recently proposed quantum well model of the electronic structure of the double stacking faults is used to explain the characteristic luminescence band at about 500 nm and the strong anisotropy of the electrical resistivity in the heavily doped, heat treated wafers.

Insight into the Degradation Phenomenon in SiC Devices from Ab Initio Calculations of the Electronic Structure of Single and Multiple Stacking Faults

Soon after the discovery of the problem with electrical degradation of bipolar SiC devices, we started to perform ab initio calculations in order to evaluate the hypothesis that the degradation is ...

How to affect stacking fault energy and structure by atom relaxation

By a simulated annealing method with a parameterized tight-binding potential, the properties of structure and energy of a generalized stacking fault are investigated. It is shown that for metal Pd, the second-layer spacing from the stacking fault plane expands initially and then contracts with the variation of the stacking fault variable from 0 to 1. The effect of atom relaxation on stacking fault energy is shown to be small. For another metal Pt, the second-layer spacing contracts and the effect of atom relaxation on the stacking fault energy is found to be obvious. In addition, the calculated stacking fault energy is in agreement with experimental results for the two metals.

Reply to “Comment on ‘Local dimer-adatom stacking fault structures from3×3to13×13alongSi(111)−7×7domain boundaries’ ”

Itoh criticized a recent paper [Phys. Rev. B 58, 13824 (1998)] by us in a Comment. We generally disagree with his criticisms and clarify the issues in this Reply based mainly on two points of argument: A soft lattice matching condition that fulfills the energy minimization criteria is more suitable for analysis of defective structures; and, the atomic structures of the basic domain boundaries (DB) are determined by the cohesive energy while the entropic effect determines the density of the DB's and their distribution on the whole surface.

Energies and structures of stacking faults of Ag from the tight-binding method calculation

The generalized stacking fault (GSF) structure and corresponding energy of Ag are studied by a tight-binding potential combined with a simulated annealing method. The potential is chosen to fit band structures and total energies from a set of first-principle calculations (Mehl M J and Papaconstantopoulos D A 1996 Phys. Rev. B 54 4519). It is found that the relaxed stacking fault energy (SFE) and anti-SFE are equal to 38 mJ m−2 and 126 mJ m−2, respectively, and are in agreement with first-principle calculations and experiment. At the same time our numerical calculations also show that the calculated generalized stacking energy as a function of displacement provides support for previous theoretical studies. In addition, the relaxed structure properties of the GSF of metal Ag are presented.

Modeling generalized stacking faults in Au using the tight-binding potential combined with a simulated annealing method

The tight-binding potential combined with a simulated annealing method is used to study the generalized stacking fault (GSF) structure and corresponding energy of gold. The potential is chosen to fit band structures and total energies from a set of first-principle calculations [Phys. Rev. B 54, 4519 (1996)]. It is found that the relaxed stacking fault energy (SFE) and unstable SFE are equal to 46 and 102 mJ/m2, respectively, and are in good agreement with first principles calculations and experiment. In addition, the structure properties of the relaxed GSF of metal Au are also presented.

On the strengthening effects of interfaces in multilayer fee metallic composites

Abstract The slip behaviour in coherent and semicoherent metallic bilayer composites is examined by atomic simulation in the Cu/Ni and Cu/Ag systems. The coherent interface in Cu/Ni, although energetically unfavourable relative to the semicoherent interface in thick layers, reveals several interesting phenomena. Linear elastic predictions of lattice strains to achieve coherency (removing the 2.7% lattice mismatch) are found not to satisfy equilibrium. The cause is nonlinearity in the elastic response. The application of stresses needed for glide dislocations to cross the interface or to escape from the interface exacerbates the nonlinearities in the elastic response of the system. Koehler forces, arising from elastic mismatch, are in some cases observed to have the wrong sign relative to linear elastic predictions. Core structures of misfit dislocations in semicoherent interfaces are observed to be quite different in the cube-on-cube oriented Cu/Ni and Cu/Ag systems with interfaces parallel to (010). In the former case, the (α/2){110) misfit dislocations have very narrow cores in the plane of the interface but dissociate into Lomer-Cottrell locks out of the interface towards the Cu side. The dissociation is enhanced by the application of tensile stresses and can lead to reactions that form continuous stacking-fault structures. Such structures are shown to be potent barriers to slip. The stability of such structures are analysed and, within the approximations used, we find that such structures may be more stable than the usual two-dimensional flat grid of misfit dislocations. The misfit dislocations at Cu-Ag interfaces, on the other hand, are wide and so fairly mobile in the interface plane. Reactions between misfit dislocations and glide dislocations are discussed.

Structure of recombination-induced stacking faults in high-voltage SiC p–n junctions

The structure of stacking faults formed in forward-biased 4H- and 6H-SiC p–n− diodes was determined using conventional and high-resolution transmission electron microscopy. Typical fault densities were between 103 and 104 cm−1. All observed faults were isolated single-layer Shockley faults bound by partial dislocations with Burgers vector of a/3〈1–100〉-type.

Formation and annihilation of various stacking-fault half units in dimer–adatom–stacking-fault structures on quenched Si(111) surfaces

The formation and annihilation of a stacking-fault (SF) half unit in dimer--adatom--stacking-fault (DAS) structure on the Si(111) surface have been investigated quantitatively by the scanning tunneling microscopy observations of the quenched surface at several temperatures ranging from 380 to $500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ It has been revealed that the formation rate of the SF half unit increases with the number of corner holes shared with the preexisting DAS domain and decreases with the size of the SF half unit. The annihilation of the SF half unit sharing one corner hole becomes more frequent than its formation at higher temperatures. From the Arrhenius plots, the activation energies for the formation and the annihilation have been deduced to be around 1.5--1.7 eV and 2.4 eV, respectively.

Formula omitted] a surface phase with a variable composition

Using scanning tunneling microscopy, the changes in the morphology and atomic structure of the Si(111)5 3 ×5 3 -Sb surface during Sb desorption have been studied. It has been found that the Si(111)5 3 ×5 3 -Sb surface phase does not have a definite composition. In attempting to explain the 5 3 ×5 3 long-range order stability in a wide Si and Sb coverage range it has been suggested that Sb atoms partially substitute for the boundary Si dimers in the basic 5×5 dimer–adatom–stacking-fault structure. A possible model of the Si(111)5 3 ×5 3 -Sb reconstruction satisfying this requirement has been proposed.

Heteroepitaxial strain in alkali halide thin films: KCl on NaCl

We have performed Monte Carlo simulations of the properties of a NaCl (001) surface covered by full or partial layers of KCl, for coverages up to 5 monolayers (ML). A wide variety of structures of the film is found. For integer ML coverages we find the continuous, so-called floating mode rumple structure, as was previously found in the KBr/NaCl system. However, for a coverage of $\ensuremath{\sim}2.1\mathrm{ML},$ we find a discrete structure of periodicity 3:4 of small regularly spaced KCl pyramids. It has the same scattering characteristics as the structure observed by Henzler et al. [Phys. Rev. B 52, 17 060 (1995)], but it is two-dimensional modulated, rather than the rowlike stacking fault structure proposed by Henzler et al. Also, at a coverage of $\ensuremath{\sim}0.8\mathrm{ML}$ there is a stable 3:4 structure. Other structures are found at intermediate coverages, corresponding to regular arrays of dislocation lines with periodicity 9:10. A further growth from such structures would give rise to growth of a $\ensuremath{\sim}5\ifmmode^\circ\else\textdegree\fi{}$ miscut KCl crystal relative to the NaCl lattice. The reciprocal space patterns corresponding to the continuous and the discrete film deformations are also calculated.

Size changes ofn×nstacking-fault half units of dimer–adatom–stacking-fault structures on quenched Si(111) surfaces

Size changes of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>n</mml:mi><mml:mo>×</mml:mo><mml:mi>n</mml:mi></mml:math>stacking-fault half units of dimer–adatom–stacking-fault structures on quenched Si(111) surfaces

Initial surface reconstructions on solid-phase homoepitaxially grown amorphous silicon overlayers on Si(111)-7×7 surface

The initial nucleation stage of surface reconstructions which appear during the crystallization of vacuum-deposited amorphous silicon (a-Si) overlayers on clean Si(111)-7×7 surfaces was investigated by scanning tunneling microscopy. When the initial a-Si coverage of less than ∼4ML (monolayers) was annealed at 300°C, the surface exhibited reordered adatoms. The adatom trimers were confined in half-units of the substrate 7×7 dimer–adatom–stacking fault reconstruction and T4-adatom domains with 2×2 or c(2×4) configuration were stabilized. When more than ∼4ML thick a-Si overlayers were annealed, however, the surface exhibited reconstructed islands at the initial nucleation stage of the surface reconstruction. For both cases, a corner hole structure consisting of a six-adatom ring was noticed at the same time as the 2×2 and c(2×4) formation. The nucleation of these surface reconstructions is discussed in terms of the buried substrate dimer–stacking fault structure.

Rearrangement of dimers in a dimer–adatom–stacking fault structure on an Si(111) surface

During in situ scanning tunneling microscopy (STM) observations of quenched Si(111) surfaces at a temperature around 400–500°C, the structure with the adatom arrangement which is not coincident with the normal dimer–adatom–stacking fault (DAS) structure was often observed. The flipping between this structure and the normal DAS stacking fault (SF) half unit frequently occurred. From the adatom arrangement and the strong preference of the adatoms for the sites adjacent to the dimers, it has been concluded that the dimers in the DAS structures are rearranged frequently during the flipping.

Erratum: Local dimer-adatom stacking fault structures from 3×3 to 13×13 along Si(111)-7×7 domain boundaries [Phys. Rev. B58, 13 824 (1998)

Erratum: Local dimer-adatom stacking fault structures from 3×3 to 13×13 along Si(111)-7×7 domain boundaries [Phys. Rev. B<b>58</b>, 13 824 (1998)