scholarly journals Annihilation Radii for Dislocations Intercepting a Free Surface with Application to Heteroepitaxial Thin Film Growth

1998 ◽  
Vol 535 ◽  
Author(s):  
M. Chang ◽  
S.K. Mathis ◽  
G.E. Beltz ◽  
C.M. Landis
Keyword(s):  
Free Surface ◽  
Film Thickness ◽  
Film Growth ◽  
Interaction Force ◽  
Critical Issue ◽  
Dislocation Motion ◽  
Threading Dislocations ◽  
Fusion Reactions ◽  
Gaas Films ◽  
Preliminary Experimental Data

AbstractOne critical issue in heteroepitaxial, lattice mismatched growth is the inevitable appearance of threading dislocations which reside in the relaxing film and degrade its semiconducting properties. It has been shown in previous work that threading dislocations interact with each other through a series of annihilation and fusion reactions to decrease their density as the film thickness increases and follow a 1/h decay, where h is the film thickness. A characteristic reaction radius is associated with these interactions. In previous simulations, the reaction radius was taken to be a constant value estimated using a simple approximation based on infinite, parallel dislocation lines. Here, a continuum-based elasticity approach is taken to more accurately quantify the reaction radius by comparing the Peach-Koehler force of one dislocation acting on another at a free surface with the lattice resistance to dislocation motion. The presence of the free surface gives rise to a moderate reduction of the interaction force. Results are compared with preliminary experimental data for GaAs films grown on InP.

scholarly journals Threading Dislocations Piercing the Free Surface of an Anisotropic Hexagonal Crystal: Review of Theoretical Approaches

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Salem Neily ◽  
Sami Dhouibi ◽  
Roland Bonnet
Keyword(s):  
Free Surface ◽  
Fourier Series ◽  
Dislocation Core ◽  
Surface Region ◽  
Double Fourier Series ◽  
Threading Dislocations ◽  
Core Size ◽  
Hexagonal Crystal ◽  
Integral Formalism ◽  
Theoretical Approaches

Inclined threading dislocations (TDs) piercing the oriented free surface of a crystal are currently observed after growth of oriented thin films on substrates. Up to date the unique way to treat their anisotropic elastic properties nearby the free surface region is to use the integral formalism, which assumes no dislocation core size and needs numerical double integrations. In a first stage of the work, a new and alternative approach to the integral formalism is developed using double Fourier series and the concept of a finite core size, which is often observed in high-resolution transmission electron microscopy. In a second stage, the integral formalism and the Fourier series approaches are applied to the important case of a TD piercing the basal free surface of a hexagonal crystal. For this particular geometry, easy-to-use expressions are derived and compared to a third approach previously known for a plate-like crystal. Finally, the numerical interest and the convergence of these approaches are tested using the basal free surface of the GaN compound, in particular for TDs with Burgers vectors c and (a + c).

scholarly journals Phase Transition in Iron Thin Films Containing Coherent Twin Boundaries: A Molecular Dynamics Approach

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3631 ◽  
Author(s):  
Binjun Wang ◽  
Yunqiang Jiang ◽  
Chun Xu
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Molecular Dynamics ◽  
Free Surface ◽  
Transition Temperature ◽  
Film Thickness ◽  
Martensitic Phase ◽  
Martensitic Transition ◽  
Twin Boundaries ◽  
Martensitic Phase Transition

Using molecular dynamics (MD) simulation, the austenitic and martensitic phase transitions in pure iron (Fe) thin films containing coherent twin boundaries (TBs) have been studied. Twelve thin films with various crystalline structures, thicknesses and TB fractions were investigated to study the roles of the free surface and TB in the phase transition. In the austenitic phase transition, the new phase nucleates mainly at the (112)bcc TB in the thicker films. The (111¯)bcc free surface only attends to the nucleation, when the film is extremely thin. The austenitic transition temperature shows weak dependence on the film thickness in thicker films, while an obvious transition temperature decrease is found in a thinner film. TB fraction has only slight influence on the austenitic temperature. In the martensitic phase transition, both the (1¯10)fcc free surface and (111)fcc TB attribute to the new body-center-cubic (bcc) phase nucleation. The martensitic transition temperature increases with decreased film thickness and TB fraction does not influent the transition temperature. In addition, the transition pathways were analyzed. The austenitic transition obeys the Burgers pathway while both the Kurdjumov–Sachs (K–S) and Nishiyama–Wassermann (N–W) relationship are observed in the martensitic phase transition. This work may help to understand the mechanism of phase transition in the Fe nanoscaled system containing a pre-existing defect.

scholarly journals Mechanisms of Enhanced Ionic Conduction at Interfaces in Ceramics

1994 ◽  
Vol 357 ◽  
Author(s):  
D. Lubben ◽  
F. A. Modine
Keyword(s):  
Film Thickness ◽  
Ionic Conduction ◽  
Defect Density ◽  
Ionic Conductivities ◽  
Dislocation Motion ◽  
Extended Defects ◽  
Epitaxial Relationship ◽  
Extended Defect ◽  
Charge Layer ◽  
Fine Grained

AbstractA large enhancement in the ionic conductivity of certain compounds occurs when the compound is produced as a composite material containing a finely-dispersed non-conductor such as SiO2 or Al2O3 This effect has been reported on for more than 20 years, and it is well established that the enhancement is associated with the presence of interfaces. The popular explanation has been based on a model which contends that the enhancement is due to a space-charge layer which forms to compensate a net charge layer at an interface. A different model proposes that extended defects such as dislocations and grain boundaries, either resulting from or stabilized by the interface, are responsible for the enhancement. This paper describes recent experiments which strongly support the latter model. The ionic conductivities of LiI and CaF2 thin films grown on sapphire(0001) substrates were monitored in-situ during deposition as a function of film thickness and deposition conditions. LiI films grown at 27°C exhibited a region of enhanced conduction within 100 nm of the substrate and a lesser enhancement as the film thickness was increased further. This conduction enhancement was not stable but annealed out with a characteristic log(time) dependence. The observed annealing behavior was fit with a model based on dislocation motion which implies that the increase in conduction near the interface is due to extended defects generated during the growth process. LiI films grown at higher temperatures (100°C) in order to reduce the grown-in defects showed no interfacial conduction enhancement. X-ray diffraction measurements suggest that these high-temperature LiI films nucleate as faceted epitaxial islands with a stable misfit dislocation density defined by the epitaxial relationship between the substrate and film. CaF2 films grown at 200°C showed a behavior similar to the 27°C LiI films, with a region of thermally unstable enhanced conduction that occurs within 10 nm of the substrate. Amorphous Al2O3 films deposited over the CaF2 layers created no additional enhancement but did increase the stability of the conduction, consistent with an extended defect model. Simultaneous deposition of CaF2 and Al2O3 produced films consisting of very-fine-grained CaF2 and particles of amorphous Al2O23 (5-10 nm grain and particle size) and a high defect density which was stable even well above the growth temperature. Measured conduction in the composite at 200°C was approximately 360 times that of bulk CaF2.

Exciton binding energies in GaAs films on AlxGa1−xAs substrates

2015 ◽  
Vol 29 (30) ◽  
pp. 1550213 ◽  
Author(s):  
Zhenhua Wu ◽  
Lei Chen ◽  
Qiang Tian
Keyword(s):  
Film Thickness ◽  
Significant Influence ◽  
Heavy Hole ◽  
Dimensional Space ◽  
Light Hole ◽  
Binding Energies ◽  
Substrate Thickness ◽  
Dimensional Approach ◽  
Anisotropic System ◽  
Gaas Films

We use the fractional–dimensional approach (FDA) to study exciton binding energies in GaAs films on [Formula: see text] substrates. In this approach, the Schrödinger equation for a given anisotropic system is solved in a noninteger-dimensional space where the interactions are assumed to occur in an isotropic effective environment. The heavy-hole and light-hole exciton binding energies are calculated as functions of the film thickness and substrate thickness. The numerical results show that both the heavy-hole and light-hole exciton binding energies decrease monotonously as the film thickness increases. When the film thickness and the substrate thickness is relatively small, the change of substrate thickness has comparatively remarkable influence on both heavy-hole and light-hole exciton binding energies. As the substrate thickness increases, both the heavy-hole and light-hole exciton binding energies increase gradually. When the film thickness or the substrate thickness is relatively large, the change of substrate thickness has no significant influence on both heavy-hole and light-hole exciton binding energies.

Observation of GaAs/Si Epitaxial Interfaces by Atomic Resolution Electron Microscopy

1986 ◽  
Vol 67 ◽  
Author(s):  
N. Otsuka ◽  
C. Choi ◽  
Y. Nakamura ◽  
S. Nagakura ◽  
R. Fischer ◽  
...  
Keyword(s):  
Substrate Surface ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Si Substrates ◽  
Voltage Electron ◽  
Resolution Electron ◽  
Gaas Films ◽  
Substrate Surfaces

ABSTRACTRecent studies have shown that high quality GaAs films can be grown by MBE on Si substrates whose surfaces are slightly tilted from the (100) plane. In order to investigate the effect of the tilting of substrate surfaces on the formation of threading dislocations, the GaAs/Si epitaxial interfaces have been observed with a 1 MB ultra-high vacuum, high voltage electron microscope. Two types of misfit dislocations, one with Burgers vectors parallel to the interface and the other with Burgers vectors inclined from the interface, were found in these epitaxial interfaces. The observation of crosssectional samples perpendicular to each other has shown that the tilting of the substrate surface directly influences the generation of these two types of misfit dislocations. The mechanism of the reduction of threading dislocations by the tilting of the substrate surface is discussed based on these observations.

scholarly journals Enhanced Ionic Conduction at the Film/Substrate Interface in LiI Thin Films Grown on Sapphire(0001)

1993 ◽  
Vol 318 ◽  
Author(s):  
D. Lubben ◽  
F. A. Modine
Keyword(s):  
Thin Films ◽  
Film Thickness ◽  
Ionic Conduction ◽  
High Vacuum ◽  
Dislocation Motion ◽  
Ultra High Vacuum ◽  
Vacuum System ◽  
Substrate Interface ◽  
Interdigital Electrodes ◽  
Film Substrate

ABSTRACTThe ionic conductivity of LiI thin films grown on sapphire(0001) substrates has been studied in situ during deposition as a function of film thickness and deposition conditions. LiI films were produced at room temperature by sublimation in an ultra-high-vacuum system. The conductivity of the Lil parallel to the film/substrate interface was determined from frequency-dependent impedance measurements as a function of film thickness using Au interdigital electrodes deposited on the sapphire surface. The measurements show a conduction of ∼5 times the bulk value at the interface which gradually decreases as the film thickness is increased beyond 100 nm. This interfacial enhancement is not stable but anneals out with a characteristic log of time dependence. Fully annealed films have an activation energy for conduction (σT) of ∼0.47 ± .03 eV, consistent with bulk measurements. The observed annealing behavior can be fit with a model based on dislocation motion which implies that the increase in conduction near the interface is not due to the formation of a space-charge layer as previously reported but to defects generated during the growth process. This explanation is consistent with the behavior exhibited by CaF2 films grown under similar conditions.

scholarly journals Deposition of Al Thin Film on Steel Substrate: The Role of Thickness on Crystallization and Grain Growth

Metals ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 12 ◽  
Author(s):  
Hayk Khachatryan ◽  
Sung-Nam Lee ◽  
Kyoung-Bo Kim ◽  
Moojin Kim
Keyword(s):  
Thin Film ◽  
Optical Properties ◽  
Film Thickness ◽  
Grain Growth ◽  
Growth Process ◽  
Film Growth ◽  
Specular Reflection ◽  
Steel Substrate ◽  
Al Thin Film

In this study, we deposited aluminum (Al) films of different thicknesses on steel substrate and examined their phase, microstructure, and film growth process. We estimated that films of up to 30 nm thickness were mainly amorphous in nature. When the film thickness exceeded 30 nm, crystallization was observed. The further increase in film thickness triggered grain growth, and the formation of grains up to 40 nm occurred. In such cases, the Al film had a cross-grained structure with well-developed primary grains networks that were filled with small secondary grains. We demonstrated that the microstructure played a key role in optical properties. The films below 30 nm showed higher specular reflection, whereas thicker films showed higher diffuse reflections.

Regulation of film thickness, surface roughness and porosity in thin film growth using deposition rate

2009 ◽  
Vol 64 (17) ◽  
pp. 3903-3913 ◽  
Author(s):  
Gangshi Hu ◽  
Gerassimos Orkoulas ◽  
Panagiotis D. Christofides
Keyword(s):  
Thin Film ◽  
Surface Roughness ◽  
Film Thickness ◽  
Deposition Rate ◽  
Film Growth ◽  
Thin Film Growth

High-resolution transmission electron microscopy (HRTEM) observation of dislocation structures in AlN thin films

2008 ◽  
Vol 23 (8) ◽  
pp. 2188-2194 ◽  
Author(s):  
Yuki Tokumoto ◽  
Naoya Shibata ◽  
Teruyasu Mizoguchi ◽  
Masakazu Sugiyama ◽  
Yukihiro Shimogaki ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Film Growth ◽  
Threading Dislocations ◽  
Organic Vapor ◽  
Transmission Electron ◽  
Hrtem Observation ◽  
Metal Organic ◽  
Edge Dislocations

The structure and configuration of threading dislocations (TDs) in AlN films grown on (0001) sapphire by metal–organic vapor phase epitaxy (MOVPE) were characterized by high-resolution transmission electron microscopy (HRTEM). It was found that the TDs formed in the films were mainly the perfect edge dislocations with the Burgers vector of b = ⅓〈11¯20〉. The majority of the edge TDs were not randomly formed but densely arranged in lines. The arrays of the edge TDs were mainly observed on the {11¯20} and {10¯10} planes. These two planes showed different configurations of TDs. TD arrays on both of these planes constituted low-angle boundaries. We suggest that these TDs are introduced to compensate for slight misorientations between the subgrains during the film growth.

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