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Showing 1 to 20 of 108 for “"Dislocation Density"”.
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Modeling dislocation density evolution in continuum crystal plasticity
Dislocations are the singly most important material defects in crystal plasticity, and although dislocation mechanics has long been understood as the underlying physical basis for continuum crystal plasticity formulations, explicit consideration of crystallo- graphic dislocation mechanics has been …
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Dislocation density reduction in multicrystalline silicon through cyclic annealing
… by material defects, and in particular by dislocations. Reducing dislocation densities in multicrystalline silicon solar cells could greatly increase their efficiency while only marginally increasing their manufacturing cost, making solar energy much more affordable. Previous studies have …
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Low Dislocation Density Gallium Nitride Templates and Their Device Applications
… epitaxy lateral overgrowth (ELO) can reduce dislocation densities down to ∼10-6 cm-2 in the lateral growth area, but requires ex situ photolithography steps. Hence, an in situ method using a SiNx interlayer (nano-scale ELOG) has emerged as a promising technique. The GaN templates prepared by …
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Geometrically-necessary dislocation density in continuum plasticity theory, FEM implementation and applications
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.
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Development and preliminary numerical investigations of a dislocation density-based finite-strain rate-dependent elastoplasticity constitutive model
… and preliminary numerical investigations of a dislocation density-based finite-strain rate-dependent elastoplasticity constitutive model Finite-strain elastoplasticity constitutive models suitable for process-scale simulation are typically developed from empirical observations of phenomena of …
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Molecular beam epitaxy of InAsP graded buffers: From mid-infrared quantum wells to InAs virtual substrates with low threading dislocation density
… GaAs or InP substrates, defects like threading dislocations and misfit dislocations harm the performance of these metamorphic structures. This thesis explores metamorphic growth on InP using InAsP graded buffers grown with molecular beam epitaxy. The first part of this thesis analyzes the …
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Modelling of dislocation-mobility-controlled brittle-to-ductile transition
… by the competition between cleavage fracture and dislocation activity at crack tips. The transition can be determined by one of two successive processes--dislocation nucleation and dislocation motion. In this thesis two models are developed to study the various aspects of a dislocation-mobility …
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High mobility strained Si/SiGe heterostructure MOSFETs : channel engineering and virtual substrate optimization
… onto silicon substrates. In this thesis, dislocation dynamics in compositionally graded SiGe layers are explored and mobility enhancements in strained Si/SiGe metal-oxide-semiconductor field-effect transistors (MOSFETs) are evaluated. These results demonstrate the dramatic increases in …
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Bauschinger effect in Nb and V microalloyed line pipe steels
… and transmission electron microscopy. The dislocation density and (Ti,Nb,V,Cu)-rich particle diameter, volume fraction and number density were measured for as-rolled and annealed (30 min. at 400 \(^0\)C and 550 \(^0\)C) steels. The Bauschinger effect was measured during compression-tension …
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Modeling dynamic impact of layered structures
… material and interface response to strain. Two dislocation-based constitutive models are proposed and implemented into dynamic simulations using finite element analysis. The Gilman model characterizes plastic flow as a function of mobile dislocation density and accounts for dislocation …
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Charakterisierung und Optimierung von (Al, Ga)N-basierten UV-Photodetektoren
In this work, the influence of dislocation density, heterostructure design and detector geometry on the electro-optic properties of AlGaN-based metal-semiconductor-metal photodetectors (MSM PD) was investigated. The focus was on the realization of Schottky-type MSM PD suitable for photodetection …
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Quantification of fatigue damage in AISI 316L stainless steel using X-Ray powder diffraction (XRD)
… in the study involves the calculation of dislocation density in the material. The evolution of dislocation density in steels is an important aspect of the mechanical response. It could potentially be used as a fingerprint to relate the material state to the life-consumption fraction in …
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The influence of microstructure on electrical resistivity in palladium alloys
… in resistivity after annealing. The effect of dislocations and structural order on resistivity has been investigated in order to determine the mechanisms whereby changes in resistivity occur in these alloys. The electrical resistivity of palladium-tungsten and palladium-molybdenum alloys has …
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III-V compositionally graded buffers for heterostructure integration
… or abrupt strain introduction) on threading dislocation density, surface roughness, epi-layer relaxation, and tilt. We find that gradual introduction of strain causes increased dislocation densities (>10⁶ cm-²) and tilt of the epi-layer (> 0.10°). A method of abrupt strain initiation is …
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Design, growth and optimization of 2-μm InGaSb/AlGaSb quantum well based VECSELs on GaAs/AlGaAs DBRs.
… challenge is therefore to reduce the threading dislocation density in the active region without a very thick metamorphic bu\u21b5er and this is achieved by inducing 90! interfacial misfit dislocation arrays between the GaSb and GaAs layers. In this work cross section transmission electron …
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Substrate and channel engineering for improving performance of strained-SiGe MOSFETs
… developed Si platform, a low threading dislocation density SiGe platform is required. A relaxed SilGe. graded buffer creates a larger lattice constant on a Si substrate while providing low threading dislocation densities (TDD) on the order of 105 cm-2. For many III-V devices on Si, such …
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GaAsP/InGaP heterojunction bipolar transistors for III-V on Si microelectronics
… via a SiGe graded buffer with a threading dislocation density of 3.7 x 106 cm-2 measured by PV-TEM and EBIC. This density is appropriate for fabrication of minority-carrier devices such as HBTs. GaAsP/InGaP HBTs were fabricated on both GaAs and Si substrates with a range of defect densities …
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Limited-area growth of Ge and SiGe on Si
… improve the surface morphology and reduce the dislocation density in limited-area heteroepitaxy of Ge and SiGe on Si (100) substrates. Low pressure chemical vapor deposition was investigated for two limiting cases of strain states: thin, strained, high Ge content SiGe films for transistor …
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Preparation and characterization of AlGaN structures for UVA LEDs
… and how effective is it? b) How to achieve a low dislocation density template for UV (310-350 nm) LEDs where no native substrates for homoepitaxy are available for low-mid Al content AlGaN? III-Nitride based LEDs generally use AlGaN as an electron blocking layer (EBL) to prevent surplus electron …
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