Array Of Misfit Dislocations Research Articles

Nonequilibrium phonon transport across nanoscale interfaces

Despite the ubiquity of applications of heat transport across nanoscale interfaces, including integrated circuits, thermoelectrics, and nanotheranostics, an accurate description of phonon transport in these systems remains elusive. Here we present a theoretical and computational framework to describe phonon transport with position, momentum, and scattering event resolution. We apply this framework to a single-material nanoparticle for which this multidimensional resolution offers insight into the physical origin of phonon thermalization and the length-scale dependent anisotropy of driven phonon distributions. We extend the formalism to handle interfaces and investigate the specific case of semicoherent materials interfaces by computing the coupling between phonons and interfacial strain resulting from a periodic array of misfit dislocations. We calculate the thermal interface conductance within the technologically relevant Si-Ge heterostructures and obtain $G=173.2\phantom{\rule{4.pt}{0ex}}\text{MW}\phantom{\rule{0.16em}{0ex}}{\text{m}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\text{K}}^{\ensuremath{-}1}$, in good agreement with previous experimental and theoretical work. Finally we comment on future applications of our framework including coherent and driven phonon effects in nanoscale materials, which are increasingly accessible via ultrafast, terahertz, and near-field spectroscopies.

Structural analysis and resistivity measurements of InAs and GaSb fins on 300 mm Si for vertical (T)FET

We report on the uniform selective area growth of InAs and GaSb by metal-organic vapor phase epitaxy on a patterned shallow trench isolation SiO2/Si 300 mm template. High-quality InAs fins are realized via direct InAs nucleation on Si in the trenches. 60° interfacial misfit dislocation arrays formed along the {111} oriented InAs/Si interfaces accommodate most of the lattice mismatch such that threading dislocation generation from residual strain is minimized. GaSb grown on a thick GaAs buffer (partial filling of the trench) suffers from twin formation. The twin density is found to decrease with increasing growth temperature. To maximize the volume of low-defect density material inside the trench, the GaSb growth is initiated as close as possible to the trench bottom. Therefore, uniform high-quality GaSb fins are grown on a very thin low-temperature GaAs and the newly developed InAs seed in the V-groove. High-resolution x-ray diffraction reciprocal space maps show that the InAs and GaSb fins are nearly completely relaxed. The resistivity of undoped and n-doped InAs and undoped and p-doped GaSb fins is measured on as-grown material by micro-4-point-probe without the need for additional complicated device processing. The values are compared to those required for devices as presented in modeling papers. The result is encouraging for the ultra-large-scale integration of vertical nanowire III-V (tunnel) field-effect transistor on 300 mm Si.

Direct growth of ZnTe on Si(100) and Si(111) substrate by molecular beam epitaxy

ZnTe was directly grown on Si(100) and Si(111) substrate respectively using elemental sources by molecular beam epitaxy. It was found that ZnTe can be grown on both Si(111) and Si(100) substrates in alignment with the orientation of (111). A microscopic growth interface model of diamond crystal structure was proposed to explain this phenomenon. This is a supplement to the existing theory of predicting possible crystalline orientation alignment relationship based on lattice mismatch value in the heteroepitaxial growth on (100) surfaces of zinc blende structure. High resolution transmission electron microscopy (HRTEM) was used to investigate the ZnTe(111)/Si(100) and ZnTe(111)/Si(100) interface. Application of digital image processing involving a filtered inverse fast Fourier transformation revealed an array of misfit dislocations at the ZnTe/Si(111) interface.

Zn segregation in interface between Mg17Al12 precipitate and Mg matrix in Mg–Al–Zn alloys

The interface between continuous Mg17Al12 precipitate and the Mg matrix in Mg–9Al–3Zn alloy has been characterized using aberration-corrected scanning transmission electron microscopy. It is found that Zn segregation occurs in the partially-coherent interface that is parallel to the basal plane of the Mg matrix and contains an array of misfit dislocations. The segregated Zn atoms substitute for the Al atoms within the interface and the segregation is not affected by the presence of the misfit dislocations. First-principles calculations suggest that Zn segregation is energetically favored.

Observation of heterostructure epitaxy of Pt-doped Ni-monosilicide on Si(001)

The objective of this study was to determine detailed microstructure of a Ni1–xPtxSi film formed via a melting/quenching process using high temperature laser annealing on a Si(001) substrate. The orthorhombic Ni1–xPtxSi film was found to be able to epitaxially grow with a crystallographic relationship of Ni1–xPtxSi[010]//Si[110], Ni1–xPtxSi(400)//Si(33¯1), and Ni1–xPtxSi (104)//Si(004). Volume expansion of the Ni1–xPtxSi film due to Pt incorporation was mainly accommodated by an increase in only one direction nearly parallel to the film surface (lattice parameter a). This was explained by the minimum coherent strain at the Ni1–xPtxSi (104)/Si(004) interface with an epitaxial growth tendency. Atomic-scale scanning transmission electron microscopy analyses revealed that the interface of Ni1–xPtxSi/Si had a repetitive atomic-step feature with energetically favorable Ni1–xPtxSi(004) terraces and (400) structural ledges that could increase the coherent area. By generating an array of misfit dislocations with an extra half plane of Ni1–xPtxSi(020), the elastic strain was further relieved.

Perfect Strain Relaxation in Metamorphic Epitaxial Aluminum on Silicon through Primary and Secondary Interface Misfit Dislocation Arrays.

Understanding the atomically precise arrangement of atoms at epitaxial interfaces is important for emerging technologies such as quantum materials that have function and performance dictated by bonds and defects that are energetically active on the micro-electronvolt scale. A combination of atomistic modeling and dislocation theory analysis describes both primary and secondary dislocation networks at the metamorphic Al/Si (111) interface, which is experimentally validated by atomic resolution scanning transmission electron microscopy. The electron microscopy images show primary misfit dislocations for the majority of the strain relief and evidence of a secondary structure allowing for complete relaxation of the Al-Si misfit strain. This study demonstrates the equilibrium interface that represents the lowest energy structure of a highly mismatched and semicoherent single-crystal interface with complete strain relief in an atomically abrupt structure.

In-plane InSb nanowires grown by selective area molecular beam epitaxy on semi-insulating substrate

In-plane InSb nanostructures are grown on a semi-insulating GaAs substrate using an AlGaSb buffer layer covered with a patterned SiO2 mask and selective area molecular beam epitaxy. The shape of these nanostructures is defined by the aperture in the silicon dioxide layer used as a selective mask thanks to the use of an atomic hydrogen flux during the growth. Transmission electron microscopy reveals that the mismatch accommodation between InSb and GaAs is obtained in two steps via the formation of an array of misfit dislocations both at the AlGaSb buffer layer/GaAs and at the InSb nanostructures/AlGaSb interfaces. Several micron long in-plane nanowires (NWs) can be achieved as well as more complex nanostructures such as branched NWs. The electrical properties of the material are investigated by the characterization of an InSb NW MOSFET down to 77 K. The resulting room temperature field effect mobility values are comparable with those reported on back-gated MOSFETs based on InSb NWs obtained by vapor liquid solid growth or electrodeposition. This growth method paves the way to the fabrication of complex InSb-based nanostructures.

GaSb and GaSb/AlSb Superlattice Buffer Layers for High-Quality Photodiodes Grown on Commercial GaAs and Si Substrates

The objective of this work is the integration of InGaAs/GaSb/GaAs heterostructures, with high indium content, on GaAs and Si commercial wafers. The design of an interfacial misfit dislocation array, either on GaAs or Si substrates, allowed growth of strain-free devices. The growth of purposely designed superlattices with their active region free of extended defects on both GaAs and Si substrates is demonstrated. Transmission electron microscopy technique is used for the structural characterization and plastic relaxation study. In the first case, on GaAs substrates, the presence of dopants was demonstrated to reduce several times the threading dislocation density through a strain-hardening mechanism avoiding dislocation interactions, while in the second case, on Si substrates, similar reduction of dislocation interactions is obtained using an AlSb/GaSb superlattice. The latter is shown to redistribute spatially the interfacial misfit dislocation array to reduce dislocation interactions.

Molecular dynamics studies of InGaN growth on nonpolar (112¯0) GaN surfaces

We have performed direct molecular dynamics (MD) simulations of heteroepitaxial vapor deposition of $\mathrm{I}{\mathrm{n}}_{x}\mathrm{G}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{N}$ films on nonpolar $(11\overline{2}0)$ wurtzite-GaN surfaces to investigate strain relaxation by misfit-dislocation formation. The simulated growth is conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN substrate. We apply time-and-position-dependent boundary constraints to affect the appropriate environments for the vapor phase, the near-surface solid phase, and the bulklike regions of the growing layer. The simulations employ a newly optimized Stillinger-Weber In-Ga-N system interatomic potential wherein multiple binary and ternary structures are included in the underlying density-functional theory and experimental training sets to improve the treatment of the In-Ga-N related interactions. To examine the effect of growth conditions, we study a matrix of 63 different MD-growth simulations spanning seven $\mathrm{I}{\mathrm{n}}_{x}\mathrm{G}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{N}$-alloy compositions ranging from $x=0.0$ to $x=0.8$ and nine growth temperatures above half the simulated melt temperature. We found a composition dependent temperature range where all kinetically trapped defects were eliminated, leaving only quasiequilibrium misfit and threading dislocations present in the simulated films. Based on the MD results obtained in this temperature range, we observe the formation of interfacial misfit and threading dislocation arrays with morphologies strikingly close to those seen in experiments. In addition, we compare the MD-observed thickness-dependent onset of misfit-dislocation formation to continuum-elasticity-theory models of the critical thickness and find reasonably good agreement. Finally, we use the three-dimensional atomistic details uniquely available in the MD-growth histories to directly observe the nucleation of dislocations at surface pits in the evolving free surface.

Reduction of threading dislocation density in SiGe epilayer on Si (0 0 1) by lateral growth liquid-phase epitaxy

Si0.973Ge0.027 epilayers were grown on a Si (0 0 1) substrate by a lateral liquid-phase epitaxy (LLPE) technique. The lateral growth mechanism favoured the glide of misfit dislocations and inhibited the nucleation of new dislocations by maintaining the thickness less than the critical thicknesses for dislocation nucleation and greater than the critical thickness for glide. This promoted the formation of an array of long misfit dislocations parallel to the [1 1 0] growth direction and reduced the threading dislocation density to 103 cm−2, two orders of magnitude lower than the seed area with an isotropic misfit dislocation network.

Asymmetric, compressive, SiGe epilayers on Si grown by lateral liquid-phase epitaxy utilizing a distinction between dislocation nucleation and glide critical thicknesses

Uniaxially strained Si1−xGex channels have been proposed as a solution for high mobility channels in next-generation MOSFETS to ensure continued device improvement as the benefits from further miniaturisation are diminishing. Previously proposed techniques to deposit uniaxially strained Si1−xGex epilayers on Si (0 0 1) substrates require multiple deposition steps and only yielded thin strips of uniaxially strained films. A lateral liquid-phase epitaxy (LLPE) technique was developed to deposit a blanket epilayer of asymmetrically strained Si97.4Ge2.6 on Si in a single step, where the epilayer was fully strained in the growth direction and 31% strain-relaxed in the orthogonal direction. The LLPE technique promoted the glide of misfit dislocations, which nucleated in a region with an orthogonal misfit dislocation network, into a region where the dislocation nucleation was inhibited. This created an array of parallel misfit dislocations which were the source of the asymmetric strain. By observing the thicknesses at which the dislocation network transitions from orthogonal to parallel and at which point dislocation glide is exhausted, the separate critical thicknesses for dislocation nucleation and dislocation glide can be determined.

Ordered misfit dislocations in epitaxial Gd doped CeO 2 thin films deposited on (001)YSZ single crystal substrates

Abstract Misfit dislocations are ubiquitous in thin film systems, and their presence can profoundly affect the chemical and physical properties of materials. In the present paper, we investigate the misfit dislocation array present at the interface of a Gd doped CeO 2 thin film epitaxially grown on a (001) yttria stabilized zirconia (YSZ) single crystal substrate. Because of the large misfit strain (-4.9%), the growth takes place by domain-matching epitaxy with the formation of geometrical misfit dislocations. Transmission electron microscopy (TEM) observations, combined with geometrical phase analysis and strain field calculations (in the case of elastic isotropy), reveal that the misfit dislocations are of purely edge type with Burgers vector b = ½[110] and with the dislocations lines parallel to the [1–10] direction. X-ray diffraction, combined with Monte Carlo simulations, allow to quantify the statistical properties of the dislocations ensemble. It is found that the dislocations are distributed according to a Gamma distribution with a mean dislocation spacing of 7.4 nm and with a spacing ranging from 3.5 to 12 nm, in excellent agreement with TEM observations and with the values expected from the relaxation of the misfit strain.

Bulk InAsSb with 0.1 eV bandgap on GaAs

We report on the growth of near-minimum bandgap (0.1 eV) bulk InAs0.54Sb0.46 on GaAs with pronounced photoluminescence. Combining strain-mediating techniques effectively manages the ∼10% lattice mismatch. An interfacial misfit (IMF) dislocation array allows a GaAs substrate and a GaSb buffer layer to act as a direct substitute for a conventional GaSb substrate. We further increase the lattice constant with a linearly graded metamorphic buffer layer of AlGaInSb, upon which we grow an AlInSb virtual substrate with the targeted lattice constant of the active InAsSb region. We observe that the graded buffer not only manages the mismatch between GaSb and InAsSb but also reduces the density of residual threading dislocations from the GaSb/GaAs IMF by a factor of ∼10×. Material characterization demonstrates the viability of using the coupled approach of metamorphic, graded buffers and IMF arrays to manage the large lattice mismatch between the substrate and the mixed group V ternary InAsSb.

Effect of asymmetric strain relaxation on dislocation relaxation processes in heteroepitaxial semiconductors

The effect of asymmetric interfacial strain configurations upon the generation of misfit dislocation arrays in lattice mismatched epitaxy is considered. For example, elastic strain relaxation for Si1−xGex/Si(110) films is uniaxial, assuming glide on {111} planes as expected for the diamond cubic system, which leads to asymmetric strain relief. Here, we extend our previously developed relaxation model for generation of dislocation arrays in SiGe/Si, by accounting for how the different energetics of asymmetrically strained films affect the kinetics of the relaxation process. Similarly, non-polar III-nitride epitaxial films have asymmetric strain from the outset of growth due to the different c/a lattice parameter ratios. In both systems, the asymmetric strain is represented by an additional term in the misfit dislocation applied stress equation. In SiGe/Si(110), a simple elasticity analysis of the strain produced by the uniaxial array of dislocations predicts that the relaxation orthogonal to the dislocation line direction occurs at a faster rate than predicted by purely biaxial strain relief due to the contributions of the strain parallel to the dislocations. This difference is because the strain parallel to the dislocation line directions continues to resolve stress onto the misfit dislocations even as the orthogonal strain is minimized. As a result, the minimum strain energy is predicted to occur for a dislocation spacing, which produces tensile layer strain in the orthogonal direction. Such tensile strain may modify the (opto)electronic properties of a Si, Ge, or GeSi epilayer but is only predicted to occur for advanced stages of relaxation. These asymmetric derivations are applicable to any thin film system where strain is not strictly biaxial.

Relationship between dislocations and misfit strain relaxation in InGaAs/GaAs heterostructures

Large lattice mismatched heterostructures In0.78Ga0.22As/GaAs were grown with a low-temperature (LT) InGaAs buffer. Misfit dislocation arrays were observed at the LT-buffer/GaAs interfaces. Transmission electron microscopy (TEM) was used to investigate the microstructures of the heterointerfaces. The relationship between misfit dislocations and strain relaxation at the interface was analysed. It was found that strain redistribution gives rise to the discrepancy of interfacial structure and misfit strain relaxation for different samples. The experimental results are in favor of the conclusion and confirm the analysis we proposed.

Metamorphic growth of relaxed single crystalline aluminum on silicon (111)

Structural characteristics of aluminum thin films have been grown on the 1 × 1, 7 × 7, and √3 × √3 reconstructed Si (111) surfaces by molecular beam epitaxy demonstrating a connection between the nucleation kinetics and grown-in defects of metamorphic epitaxial thin films. High resolution x-ray diffraction symmetric scans and (111) pole figures show that growth on the 1 × 1 reconstructed Si surface produces polycrystalline Al with (100) and (111) diffraction peaks and a large degree of growth twin as determined by a sixfold symmetric pole figure. Growth on the 7 × 7 reconstructed Si surface results in a twinned crystal exhibiting only Al (111) peaks with a sixfold symmetric pole figure. Growth of Al on the √3 × √3 reconstructed surface realizes nearly twin-free single crystal Al (111) film. Atomic force microscopy demonstrates that the Al film roughness improves with crystal quality. Scanning transmission electron microscopy (STEM) shows the twins originate at the substrate/film interface and extend to the film surface indicating that they are growth defects that form during the first few layers of aluminum growth. In addition, STEM indicates that the misfit strain is relaxed within a few monolayers of the interface through a periodic array of misfit dislocations.

Selective area heteroepitaxy of GaSb on GaAs (001) for in-plane InAs nanowire achievement

The growth of in-plane GaSb nanotemplates on a GaAs (001) substrate is demonstrated combining nanoscale patterning of the substrate and selective area heteroepitaxy. The selective growth of GaSb inside nano-stripe openings in a SiO2 mask layer is achieved at low temperature thanks to the use of an atomic hydrogen flux during the molecular beam epitaxy. These growth conditions promote the spreading of GaSb inside the apertures and lattice mismatch accommodation via the formation of a regular array of misfit dislocations at the interface between GaSb and GaAs. We highlight the impact of the nano-stripe orientation as well as the role of the Sb/Ga flux ratio on the strain relaxation of GaSb along the [110] direction and on the nanowire length along the [1-10] one. Finally we demonstrate how these GaSb nanotemplates can be used as pedestals for subsequent growth of in-plane InAs nanowires.

Unveiling the Semicoherent Interface with Definite Orientation Relationships between Reinforcements and Matrix in Novel Al3BC/Al Composites.

High-strength lightweight Al-based composites are promising materials for a wide range of applications. To provide high performance, a strong bonding interface for effective load transfer from the matrix to the reinforcement is essential. In this work, the novel Al3BC reinforced Al composites have been in situ fabricated through a liquid-solid reaction method and the bonding interface between Al3BC and Al matrix has been unveiled. The HRTEM characterizations on the Al3BC/Al interface verify it to be a semicoherent bonding structure with definite orientation relationships: (0001)Al3BC//(11̅1)Al;[112̅0]Al3BC//[011]Al. Periodic arrays of geometrical misfit dislocations are also observed along the interface at each (0001)Al3BC plane or every five (11̅1)Al planes. This kind of interface between the reinforcement and the matrix is strong enough for effective load transfer, which would lead to the evidently improved strength and stiffness of the introduced new Al3BC/Al composites.

Epitaxial growth of GaSb and InAs fins on 300 mm Si (001) by aspect ratio trapping

We report on the monolithic integration of GaSb and InAs fins on on-axis 300 mm Si (001) by metal-organic chemical vapor deposition. The thickness of the GaAs/Si (001) fins used as a template is optimized to allow the formation of {111} facets and the confinement of defects generated at the GaAs/GaSb and GaAs/InAs interfaces by means of the aspect ratio trapping technique. Anti-phase domains are avoided via a careful design of the GaAs/Si interface. Threading dislocations in GaSb are controlled through the formation of an interfacial misfit dislocation array along the GaSb/GaAs [1¯11] and [11¯1] interfaces. Defects on InAs are controlled through the promotion of a two-dimensional growth, which spontaneously occurs on GaAs {111} planes. The results represent a step forward towards the integration of III–V nano-scale photonic and electronic components on a Si complementary metal-oxide-semiconductor compatible platform using a precisely engineered GaAs on Si template.

Formation of periodic interfacial misfit dislocation array at the InSb/GaAs interface via surface anion exchange

The relationship between growth temperature and the formation of periodic interfacial misfit (IMF) dislocations via the anion exchange process in InSb/GaAs heteroepitaxy was systematically investigated. The microstructural and electrical properties of the epitaxial layer were characterized using atomic force microscope, high-resolution x-ray diffraction, transmission electron microscopy, and Hall resistance measurement. The formation of interfacial misfit (IMF) dislocation arrays depended on growth temperature. A uniformly distributed IMF array was found in a sample grown at 310 °C, which also exhibited the lowest threading dislocation density. The analysis suggested that an incomplete As-for-Sb anion exchange process impeded the formation of IMF on sample grown above 310 °C. At growth temperature below 310 °C, island coalescence led to the formation of 60° dislocations and the disruption of periodic IMF array. All samples showed higher electron mobility at 300 K than at 77 K.