CRITICAL THICKNESS FOR Nb NANOFILM ON SAPPHIRE SUBSTRATE: AN EXAMPLE TOWARD UNDERSTANDING EVOLUTION OF COHERENT NANOSTRUCTURES

2011 ◽  
Vol 10 (01n02) ◽  
pp. 351-354 ◽  
Author(s):  
ARUN KUMAR ◽  
ANANDH SUBRAMANIAM
Keyword(s):  
Stress State ◽  
Edge Dislocation ◽  
Sapphire Substrate ◽  
Critical Thickness ◽  
Lattice Mismatch ◽  
Energy Criterion ◽  
Misfit Dislocations ◽  
Combined Simulation ◽  
Triangular Network ◽  
Theoretical Analyses

On growth beyond critical thickness, interfacial misfit dislocations partially relax the misfit strains in epitaxially grown nanofilms. In this study the stress state and growth of nanofilms are simulated using Finite Element Method (FEM) by imposing stress-free strains, corresponding to the lattice mismatch between Nb nanofilm and Sapphire substrate. On growth of the Nb nanofilm, a triangular network of edge misfit dislocations nucleates at the (0001) Al 2 O 3∥(111) Nb interface. Using a combined simulation of a coherently strained nanofilm and an edge dislocation, the critical thickness for the nucleation of an edge dislocation is determined using an equilibrium energy criterion. Theoretical analyses in literature use only the component of the Burgers vector parallel to the interface, which is an erroneous description of the stress state and energetics of the system. In this investigation the full interfacial edge dislocation is simulated using standard commercially available software and comparisons are made with results available in literature to bring out the utility of the methodology.

Structural properties of GaAs/InGaAs/GaAs (001) and InGaAs/GaAs (001) heterostructures and correlation with electronic properties

1990 ◽  
Vol 48 (4) ◽  
pp. 602-603
Author(s):  
J.M. Bonar ◽  
R. Hull ◽  
R. Malik ◽  
R. Ryan ◽  
J.F. Walker
Keyword(s):  
Band Gap ◽  
Electronic Properties ◽  
Gaas Substrate ◽  
Critical Thickness ◽  
Lattice Mismatch ◽  
Band Offset ◽  
Misfit Dislocations ◽  
Gaas Substrates ◽  
Gaas Structure ◽  
Low X

In this study we have examined a series of strained heteropeitaxial GaAs/InGaAs/GaAs and InGaAs/GaAs structures, both on (001) GaAs substrates. These heterostructures are potentially very interesting from a device standpoint because of improved band gap properties (InAs has a much smaller band gap than GaAs so there is a large band offset at the InGaAs/GaAs interface), and because of the much higher mobility of InAs. However, there is a 7.2% lattice mismatch between InAs and GaAs, so an InxGa1-xAs layer in a GaAs structure with even relatively low x will have a large amount of strain, and misfit dislocations are expected to form above some critical thickness. We attempt here to correlate the effect of misfit dislocations on the electronic properties of this material.The samples we examined consisted of 200Å InxGa1-xAs layered in a hetero-junction bipolar transistor (HBT) structure (InxGa1-xAs on top of a (001) GaAs buffer, followed by more GaAs, then a layer of AlGaAs and a GaAs cap), and a series consisting of a 200Å layer of InxGa1-xAs on a (001) GaAs substrate.

Equilibrium Analysis of Lattice-Mismatched Nanowire Heterostructures

2002 ◽  
Vol 737 ◽  
Author(s):  
E. Ertekin ◽  
P.A. Greaney ◽  
T. D. Sands ◽  
D. C. Chrzan
Keyword(s):  
Simple Model ◽  
Misfit Dislocation ◽  
Critical Thickness ◽  
Lattice Mismatch ◽  
Equilibrium Analysis ◽  
Misfit Dislocations ◽  
Model Based ◽  
Large Lattice ◽  
Large Lattice Mismatch

ABSTRACTThe quality of lattice-mismatched semiconductor heterojunctions is often limited by the presence of misfit dislocations. Nanowire geometries offer the promise of creating highly mismatched, yet dislocation free heterojunctions. A simple model, based upon the critical thickness model of Matthews and Blakeslee for misfit dislocation formation in planar heterostructures, illustrates that there exists a critical nanowire radius for which a coherent heterostructured nanowire system is unstable with respect to the formation of misfit dislocations. The model indicates that within the nanowire geometry, it should be possible to create perfect heterojunctions with large lattice-mismatch.

Misfit dislocations between boron-doped homoepitaxial films and diamond substrates studied by X-ray diffraction topography

2018 ◽  
Vol 51 (6) ◽  
pp. 1684-1690 ◽  
Author(s):  
Marina González-Mañas ◽  
Beatriz Vallejo
Keyword(s):  
Critical Thickness ◽  
Lattice Mismatch ◽  
Lattice Parameter ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Boron Doped Diamond ◽  
X Ray ◽  
Boron Doped ◽  
Slip Planes ◽  
Half Loop

Boron-doped diamond epilayers grown over diamond substrates have a different lattice parameter from the undoped diamond substrate, which introduces a lattice mismatch between substrates and epilayers. This can generate misfit dislocations at the interface when the epilayer reaches a certain critical thickness. For a boron concentration of about 1 × 1020 atoms cm−3, the calculated lattice mismatch is about 1.3 × 10−4 and the critical thickness is of the order of 0.2 µm. In the epilayers studied, grown over high-pressure high-temperature 1b (001) substrates, the lattice mismatch and the epilayer thickness are 1.3 × 10−4, 30 µm and 6.5 × 10−4, 4 µm. The epitaxial strain has been relaxed by the generation of two orthogonal misfit dislocation systems. These are edge dislocations parallel to the [100] and [010] directions with a Burgers vector making an angle of 45° with the (001) interface. Their lengths are 40–60 µm and their lineal densities 200–240 cm−1. They are heterogeneously nucleated, propagated in the form of half-loops along the slip planes (011) and (101), respectively, and related mainly to 〈111〉 threading dislocations emerging from octahedral growth sectors. Another kind of half-loop originates from the substrate growth sector boundaries. Limited X-ray topography has been demonstrated to be a very useful tool to discriminate between substrate and epilayer defects when their lattice mismatch is not sufficient to separate such defects in conventional Lang topography. X-ray section topography has confirmed the presence of [001] dislocations in the epilayers and the misfit half-loops related to threading dislocations propagating from the interface.

Electron microscopy of GaAs grown on Si- and Ge-based substrates

1991 ◽  
Vol 49 ◽  
pp. 854-855
Author(s):  
D.P. Malta ◽  
J.B. Posthill ◽  
M.L. Timmons ◽  
P.R. Sharps ◽  
R. Venkatasubramanian ◽  
...  
Keyword(s):  
Critical Thickness ◽  
Lattice Mismatch ◽  
Low Cost ◽  
Antiphase Domain ◽  
Threading Dislocation ◽  
Misfit Dislocations ◽  
Thermally Induced ◽  
Induced Stress ◽  
Dislocation Reduction ◽  
Domain Boundaries

A GaAs-on-Si technology is desirable to take advantage of the mobility and direct bandgap of GaAs in combination with the crystalline quality, low cost and established technology of Si. Differences in lattice constant (4.1%), thermal expansion coefficient (a factor of ~ 3), and bonding polarity between the two materials can lead to problems such as: threading dislocation formation, thermally induced stress and delamination, and antiphase domain boundaries (APBs), respectively. The lattice mismatch is responsible for the formation of (necessary) misfit dislocations which can concurrently create threading dislocations with typical densities in the range of 106 - 108cm-2. This density of electrically active defects in a device region is highly undesirable.A proposed scheme for lattice mismatch accommodation and potential threading dislocation reduction has previously been reported in which each layer of a SixGe1-x multilayer structure (MLS) is grown beyond the critical thickness with a progressively higher Ge composition than the previous layer.

The Accommodation of Lattice Mismatch on the (111) Interphase Boundary Plane in FCC Metals

1990 ◽  
Vol 209 ◽  
Author(s):  
P. Gumbsch ◽  
H.F. Fischmeister
Keyword(s):  
Lattice Mismatch ◽  
Boundary Plane ◽  
Embedded Atom Method ◽  
Misfit Dislocations ◽  
Embedded Atom ◽  
Interfacial Energies ◽  
Large Lattice ◽  
Metal Metal ◽  
Large Lattice Mismatch ◽  
Triangular Network

ABSTRACTUsing the embedded atom method we atomistically model the accommodation of the lattice nismatch and study the propertiesof the misfit dislocations in parallel oriented bicrystals. We calculate and analyze in detail the excess interfacial energies on the (100) and (111) boundary planes. The Ag/Ni system is chosen as a model system for metal/metal interfaces with a large lattice mismatch.Among the possible boundary planes in parallel oriented fcc bicrystals, the ones with terminating {111} planes arc energetically most favourable and are most often observed in experiments. This can be explained by a detailed analysis of the elastic strain fields in the interfaces, which correspond to networks of misfit dislocations. While the misfit dislocations on the (100) and (011) planes have a ½[01ī] Burgers vector, those on (111) can dissociate into misfit partials. The elastic strains connected with the misfit partials are, of course, much smaller than those for other types of misfit dislocations. The misfit partials form a triangular network within the boundary plane.

HIGH RESOLUTION ELECTRON MICROSCOPE STUDY OF CdTe-Cd0.6Mn0.4 Te SUPERLATTICES

1985 ◽  
Vol 56 ◽  
Author(s):  
C. CHOI ◽  
N. OTSUKA ◽  
L. A. KOLODZIEJSKI ◽  
R. L. GUNSHOR-a
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Phase Contrast ◽  
Electron Microscope Study ◽  
Lattice Mismatch ◽  
Thick Layer ◽  
High Resolution Electron Microscopy ◽  
Misfit Dislocations ◽  
Resolution Electron ◽  
High Resolution Electron Microscope

AbstractStructures of CdTe-Cd0.6Mn0.4Te superlattices which are caused by the lattice mismatch between suterlattice layers have been studied by high resolution electron microscopy (HREM). In thin-layer superlattices, the crystal lattice in each layeris elastically distorted, resulting in the change of the crystal symmetry from cubic to rhombohedral. The presence of the small rhombohedral distrotion has been confirmed through a phase contrast effect in HREM images. In a thick-layer superlattice, the lattice mismatch is accommodated by dissociated misfit dislocations. Burgers vectors of partial misfit dislocations have been identified from the shift of lattice fringes in HREM images.

scholarly journals Simulation and Analysis of GaN Wafer Bowing on Sapphire Substrate

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Wang Bin ◽  
Qu Yu-xuan ◽  
Hu Shi-gang ◽  
Tang Zhi-jun ◽  
Li Jin ◽  
...  
Keyword(s):  
Sapphire Substrate ◽  
Mass Production ◽  
Large Scale ◽  
Lattice Mismatch ◽  
Wafer Surface ◽  
Heteroepitaxial Growth ◽  
Analysis Software ◽  
Element Analysis ◽  
Modern Mass ◽  
The Mathematical Model

During the process of heteroepitaxial growth, if the lattice constant of the growing film differs from that of the substrate, the wafer surface bows, regardless of whether the lattice mismatch occurs or not. As the growth in large-scale wafers speeds up, bowing effects are becoming more and more important. Wafer bowing has a direct impact on the yield in modern mass-production compound semiconductor industries. By using finite element analysis software, the bowing deformation of the GaN wafer on sapphire substrate can be studied. This paper summarizes the causes of bowing deformation, builds the mathematical model, and deduces the relation equation of the wafer bowing. The results show that epitaxial wafer bowing has a linear relationship with the square of the diameter of the substrate but has little relationship with the thickness of the substrate. Moreover, the relation equation of the wafer bowing is also simplified finally.

Defect Characterization of InAs Films Grown by Two-Step MOCVD on (100) InP Substrates

1992 ◽  
Vol 280 ◽  
Author(s):  
A. K. Ballal ◽  
L. Salamanca-Riba ◽  
D. L. Partin
Keyword(s):  
Electron Microscopy ◽  
Lattice Mismatch ◽  
Misfit Strain ◽  
Organic Chemical ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Epitaxial Relationship ◽  
Cross Sectional ◽  
Plan View ◽  
Inp Substrates

ABSTRACTIn this paper we investigate the defect morphology and misfit strain in InAs films grown on (100) InP substrates using two-step metal organic chemical vapor deposition (MOCVD). High quality InAs films were obtained despite the 3.2% lattice-mismatch between the InAs film and the InP substrate. Cross-sectional and plan-view transmission electron microscopy has been used to characterize the ∼3μm thick InAs films. Almost all the lattice mismatch is accomodated by an orthogonal array of pure edge Lomer dislocations which are favored over the 60° type since they are more efficient in relieving misfit strain. In addition to misfit dislocations, threading dislocations were observed propagating through the film. Most of the threading dislocations were 60° type dislocations along the < 211 > and < 110 > directions on inclined {111} planes. The threading dislocations originate from island coalescence during film growth. High resolution electron microscopy shows the epitaxial relationship between the film and the substrate and reveals an abrupt and sharp interface with periodic dislocation cores.

Strain Relaxation in GaN/AlN Films Grown on Vicinal and On-Axis SiC Substrates

2006 ◽  
Vol 527-529 ◽  
pp. 1513-1516
Author(s):  
J. Bai ◽  
X. Huang ◽  
Balaji Raghothamachar ◽  
Michael Dudley ◽  
B. Wagner ◽  
...  
Keyword(s):  
High Resolution ◽  
Lattice Mismatch ◽  
Strain Relaxation ◽  
Crystalline Quality ◽  
Misfit Dislocations ◽  
Vicinal Surface ◽  
Burgers Vector ◽  
Surface Steps ◽  
Transmission Electron ◽  
Initial Stage

Strain relaxation in the GaN/AlN/6H-SiC epitaxial system grown by vicinal surface epitaxy (VSE) is investigated and compared with that in on-axis epitaxy. High resolution x-ray diffraction (HRXRD) measurements show that GaN films grown by VSE have improved crystalline quality. High resolution transmission electron microscope (HRTEM) studies reveal that there are two types of misfit dislocations (MDs) at AlN/6H-SiC interfaces: 60˚ complete dislocations along <1120 > directions with Burgers vector 1/3<1120 > and 60˚ Shockley partials along <10 10 > directions with Burgers vector 1/3<10 10 >. The latter are usually geometrical partial misfit dislocations (GPMDs) that are dominant in VSE to accommodate the lattice mismatch and stacking sequence mismatch simultaneously. In VSE, it is the high-density GPMDs formed at the vicinal surface steps that facilitate rapid strain relaxation at the initial stage of deposition and hence lead to superior crystalline quality of the subsequently grown GaN films.

Misfit Dislocations at II-VI/GaAs Interfaces

1990 ◽  
Vol 183 ◽  
Author(s):  
A. F. Schwartzman
Keyword(s):  
Lattice Mismatch ◽  
High Resolution Electron Microscopy ◽  
Interfacial Structure ◽  
Misfit Dislocations ◽  
Extended Defects ◽  
Partial Dislocations ◽  
Resolution Electron ◽  
Before And After ◽  
Slip Planes ◽  
Efficient Type

AbstractHigh-resolution electron microscopy -is used to characterize the defect structure of CdTe/GaAs and ZnTe/GaAs heterojunctions before and after annealing. For as-deposited films, a variety of defects exist both in the form of perfect misfit dislocations at the interface and extended defects into the thin film. The extended defects result from dissociation of 60° dislocations and reactions between perfect and partial dislocations lying on intersecting slip planes. The annealed interfaces consist of a periodic array of perfect edge Lomer dislocations, the most efficient type of misfit dislocation for accomodating the lattice mismatch, 14.6 % for CdTe/GaAs and 8 % for ZnTe/GaAs. In both cases, the spacing between dislocations corresponds to the value predicted for completely strain-free thin fims, 31 and 54 Å for CdTe and ZnTe respectively. This paper concentrates on the different dislocation reactions which transform the interfacial structure from the as-deposited case to the annealed case.

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