A Model for the Critical Height for Dislocation Annihilation and Recombination in GaN Columns Deposited by Patterned Growth

2004 ◽  
Vol 831 ◽  
Author(s):  
M. E. Twigg ◽  
N. D. Bassim ◽  
C. R. Eddy ◽  
R. L. Henry ◽  
R. T. Holm ◽  
...  
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Column Height ◽  
Critical Height ◽  
Patterned Growth ◽  
Sapphire Substrates ◽  
Density Reduction ◽  
Vertical Leakage ◽  
Dislocation Annihilation ◽  
Gan Film

ABSTRACTIn order to reduce vertical leakage in III-nitride detectors, we have grown a patterned array of hexagonal GaN columns on masked heteroepitaxial GaN template layers using a-plane sapphire substrates. In addition to eliminating cracking, we have found that for GaN columns tens of microns in diameter and several microns high, the dislocation density is also significantly reduced. We have developed a simple closed-form analytical model for predicting the critical column height for the onset of the reduction in the dislocation density. Among the predictions of this model is that the critical column height for the onset of dislocation density reduction is proportional to the product of column width and the grain size of the GaN film.

Heteroepitaxy of III-V Compounds on Si Substrates for Solar Cells and Led

1989 ◽  
Vol 145 ◽  
Author(s):  
Masafumi Yamaguchi ◽  
Susumu Kondo
Keyword(s):  
Solar Cells ◽  
Dislocation Density ◽  
High Efficiency ◽  
Chemical Vapor ◽  
Organic Chemical ◽  
Heteroepitaxial Growth ◽  
Misfit Stress ◽  
Si Substrates ◽  
Density Reduction ◽  
Dislocation Annihilation

AbstractHeteroepitaxial growth of GaAs, InP, GaP and InGaP on Si substrates is studied using MOCVD (Metal-Organic Chemical Vapor Deposition). High qgaliti GaAs films on Si, with a dislocation density of about 106 cm−2, are obtained by combining strained- layer superlattice insertion and thermal cycle annealing. Reduction of dislocation density in the III-V compounds on Si is discussed based on a simple model, where dislocation annihilation is assumed to be caused by dislocation movement under thermal and misfit stress. As a result of dislocation density reduction, high-efficiency GaAs-on-Si solar cells with total-area efficiencies of 18.3% (AMO) and 20% (AM1.5), and red and yellow emissions from InGaP-on-Si light-emitting diodes (LEDs) have been realized.

The Dislocation Structure and Deformation Mechanism of Tib2/Nial Composites

1990 ◽  
Vol 213 ◽  
Author(s):  
L. Wang ◽  
R.J. Arsenault
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Screw Dislocation ◽  
Dislocation Structure ◽  
Deformation Mechanism ◽  
Volume Fraction ◽  
Dislocation Generation ◽  
Screw Dislocations ◽  
Size Refinement ◽  
Dislocation Annihilation

ABSTRACTDislocation structures in 0, 10, and 20 V% TiB2/NiAl composites have been thoroughly investigated with a 1 MeV HVEM after compression testing at 760–1000° C. Samples with 0 and 10 V% TiBl2/NiAl additions have almost identical dislocation structures which can be described as a<100> screw dislocations with extensive jogs and superjoqs. Prismatically punched dislocations were observed in all of the deformed composites and deformed samples of 20 V% TiB2/NiAl had extensive dislocation generation around the particles. Dislocation density, grain size, and the tendency for dislocation reactions or networks forming during deformation decrease as the volume fraction of TiB2 increases. Also, since a predominance of screw dislocation was observed, the rate controlling process is not likely to be dislocation annihilation or climb, but dislocation generation. The grain size refinement could play an important role in the strengthening of the composites.

Dislocation density reduction in heteroepitaxial III-V compound films on Si substrates for optical devices

1991 ◽  
Vol 6 (2) ◽  
pp. 376-384 ◽  
Author(s):  
Masafumi Yamaguchi
Keyword(s):  
Dislocation Density ◽  
High Efficiency ◽  
Chemical Vapor ◽  
Organic Chemical ◽  
Misfit Stress ◽  
Si Substrates ◽  
Density Reduction ◽  
Strained Layer Superlattice ◽  
Dislocation Movement ◽  
Dislocation Annihilation

The reduction of dislocation density in heteroepitaxial III-V compound films on Si substrates has been studied using MOCVD (Metal-Organic Chemical Vapor Deposition). High-quality GaAs films on Si, with a dislocation density of about 106 cm−2, have been obtained by combining strained-layer superlattice insertion and thermal cycle annealing. Reduction of dislocation density in the III-V compounds on Si is discussed based on a simple model, where dislocation annihilation is assumed to be caused by dislocation movement under thermal and misfit stress. As a result of dislocation density reduction, high-efficiency GaAs-on-Si solar cells with total-area efficiencies of 18.3% (AM0) and 20% (AM1.5), and red and yellow emissions from InGaP-on-Si light-emitting diodes have been realized. Moreover, future prospects of heteroepitaxy of III-V compounds on Si are also discussed.

Dislocation Engineering in Multicrystalline Silicon

2009 ◽  
Vol 156-158 ◽  
pp. 11-18 ◽  
Author(s):  
Mariana I. Bertoni ◽  
Clémence Colin ◽  
Tonio Buonassisi
Keyword(s):  
High Temperature ◽  
Dislocation Density ◽  
Temperature Treatment ◽  
Multicrystalline Silicon ◽  
High Temperature Treatment ◽  
Face Centered Cubic ◽  
Ambient Conditions ◽  
Density Reduction ◽  
Dislocation Movement ◽  
Dislocation Annihilation

Dislocations are known to be among the most deleterious performance-limiting defects in multicrystalline silicon (mc-Si) based solar cells. In this work, we propose a method to remove dislocations based on a high temperature treatment. Dislocation density reductions of >95% are achieved in commercial ribbon silicon with a double-sided silicon nitride coating via high temperature annealing under ambient conditions. The dislocation density reduction follows temperature-dependent and time-dependent models developed by Kuhlmann et al. for the annealing of dislocations in face-centered cubic metals. It is believed that higher annealing temperatures (>1170°C) allow dislocation movement unconstrained by crystallographic glide planes, leading to pairwise dislocation annihilation within minutes.

Computation on continuous grain refinement in AA1050 aluminum during repetitive tube expansion and shrinking technique

2015 ◽  
Vol 232 (4) ◽  
pp. 307-318
Author(s):  
H Jafarzadeh ◽  
K Abrinia
Keyword(s):  
Finite Element Method ◽  
Plastic Deformation ◽  
Grain Size ◽  
Finite Element ◽  
Dislocation Density ◽  
Severe Plastic Deformation ◽  
Grain Refinement ◽  
Half Cycle ◽  
Tube Expansion ◽  
Element Method

The microstructure evolution during recently developed severe plastic deformation method named repetitive tube expansion and shrinking of commercially pure AA1050 aluminum tubes has been studied in this paper. The behavior of the material under repetitive tube expansion and shrinking including grain size and dislocation density was simulated using the finite element method. The continuous dynamic recrystallization of AA1050 during severe plastic deformation was considered as the main grain refinement mechanism in micromechanical constitutive model. Also, the flow stress of material in macroscopic scale is related to microstructure quantities. This is in contrast to the previous approaches in finite element method simulations of severe plastic deformation methods where the microstructure parameters such as grain size were not considered at all. The grain size and dislocation density data were obtained during the simulation of the first and second half-cycles of repetitive tube expansion and shrinking, and good agreement with experimental data was observed. The finite element method simulated grain refinement behavior is consistent with the experimentally obtained results, where the rapid decrease of the grain size occurred during the first half-cycle and slowed down from the second half-cycle onwards. Calculations indicated a uniform distribution of grain size and dislocation density along the tube length but a non-uniform distribution along the tube thickness. The distribution characteristics of grain size, dislocation density, hardness, and effective plastic strain were consistent with each other.

Simulation of Grain Growth of Materials Produced by Severe Plastic Deformation

2011 ◽  
Vol 409 ◽  
pp. 597-602
Author(s):  
Yuichi Mizuno ◽  
Kenji Okushiro ◽  
Yoshiyuki Saito
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Dislocation Density ◽  
Severe Plastic Deformation ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Boundary Migration ◽  
Interface Energy ◽  
Diffusion Reaction ◽  
Field Methods

Grain boundary migration in materials under severe plastic deformation was simulated by the phase field methods. The interface energy and dislocation density on growth kinetics were simulated on systems of 2-dimensional lattice. .In inhomogeneous systems grain size distributions in simulated grain structures were binodal distributions. The classification of the solution of differential equations based on the mean-field Hillert model describing temporal evolution of the scaled grain size distribution function was in good agreement with those given by the Computer simulations. Effect of dislocation on thermodynamic stability was taken into consideration. Dislocation density distribution was calculated by a equation based on the diffusion-reaction equation.. Scaled grain size distribution was known to be affected by the dislocation.

Superplastic Behavior of a Cu-Cr-Zr Alloy Subjected to ECAP

2016 ◽  
Vol 838-839 ◽  
pp. 404-409
Author(s):  
Roman Mishnev ◽  
Iaroslava Shakhova ◽  
Andrey Belyakov ◽  
Rustam Kaibyshev
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Strain Rate ◽  
Temperature Interval ◽  
Rate Sensitivity ◽  
Tensile Tests ◽  
Superplastic Behavior ◽  
Average Grain Size ◽  
Gauge Section ◽  
Zr Alloy

A Cu-0.87%Cr-0.06%Zr alloy was subjected to equal channel angular pressing (ECAP) at a temperature of 400 °C up to a total strain of ~ 12. This processing produced ultra-fine grained (UFG) structure with an average grain size of 0.6 μm and an average dislocation density of ~4×1014 m-2. Tensile tests were carried out in the temperature interval 450 – 650 °C at strain rates ranging from 2.8´10-4 to 0.55 s-1. The alloy exhibits superplastic behavior in the temperature interval 550 – 600 °C at strain rate over 5.5´10-3 s-1. The highest elongation-to-failure of ~300% was obtained at a temperature of 575 °C and a strain rate of 2.8´10-3 s-1 with the corresponding strain rate sensitivity of 0.32. It was shown the superplastic flow at the optimum conditions leads to limited grain growth in the gauge section. The grain size increases from 0.6 μm to 0.87 μm after testing, while dislocation density decreases insignificantly to ~1014 m-2.

Epitaxial Lateral Overgrowth of GaN on SiC and Sapphire Substrates

1998 ◽  
Vol 537 ◽  
Author(s):  
Zhonghai Yu ◽  
M.A.L. Johnson ◽  
J.D. Brown ◽  
N.A. El-Masry ◽  
J. F. Muth ◽  
...  
Keyword(s):  
Single Crystal ◽  
Epitaxial Lateral Overgrowth ◽  
Threading Dislocations ◽  
Growth Processes ◽  
Mbe Growth ◽  
Sapphire Substrates ◽  
Lateral Overgrowth ◽  
Movpe Growth ◽  
Gan Film ◽  
Growth Experiments

AbstractThe epitaxial lateral overgrowth (ELO) process for GaN has been studied using SiC and sapphire substrates. Both MBE and MOVPE growth processes were employed in the study. The use of SiO2 versus SiNx insulator stripes was investigated using window/stripe widths ranging from 2 μm/4 μm to 3 μm/15 μm. GaN film depositions were completed at temperatures ranging from 800°C to 1120°C. Characterization experiments included RHEED, TEM, SEM and cathodolumenescence studies. The MBE growth experiments produced polycrystalline GaN over the insulator stripes even at deposition temperatures as high as 990°C. In contrast, MOVPE growth produced single-crystal GaN stripes with no observable threading dislocations.

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