Reduction of Misfit Dislocation Density in Finite Lateral Size Sil-xGex Films Grown by Selective Epitaxy

1993 ◽  
Vol 298 ◽  
Author(s):  
L. Vescan ◽  
T. Stoica ◽  
C. Dieker ◽  
H. LÜth
Keyword(s):  
Dislocation Density ◽  
Misfit Dislocation ◽  
Equilibrium Model ◽  
Size Dependence ◽  
Critical Thickness ◽  
Misfit Dislocations ◽  
Lateral Size ◽  
Relaxation Model ◽  
Main Hypothesis ◽  
Strained Layers

AbstractIn Si0.88Ge0.12/Si strained layers misfit dislocations formed during growth in small pads are generated at a significantly higher critical thickness than on extended areas, while pads of lateral size of 10 μm or smaller show no evidence of misfit dislocations at all. The SiGe layers investigated were selectively grown on patterned substrates with pad sizes from 2 μm to 1 cm. An elastic relaxation model was used to calculate the pad size dependence of the critical thickness. The main hypothesis of the model is that the density of misfit dislocations is solely affected by the elastic relaxation at the edges of small epitaxial areas. This equilibrium model is able to explain the observed absence of misfit dislocations on small pads, however it predicts a critical thickness for finite sizes much lower than the observed one.

Misfit Dislocations at the Critical Thickness for Ingaas/Gaas Strained Layers

1990 ◽  
Vol 202 ◽  
Author(s):  
G. S. Green ◽  
B. K. Tanner ◽  
A. G. Turnbull ◽  
S. J. Barnett ◽  
M. Emeny ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Gaas Substrate ◽  
Critical Thickness ◽  
Thickness Variation ◽  
Misfit Dislocations ◽  
Ingaas Layer ◽  
Double Crystal ◽  
Strained Layers ◽  
Interference Fringes ◽  
Symmetric Reflection

ABSTRACTThe contrast of misfit dislocations in an InGaAs layer, close to the critical thickness and capped with GaAs grown by MBE on a (001) oriented GaAs substrate has been investigated by double axis synchrotron X-radiation topography. The layer thickness variation as a function of position has been measured to a precision of 1A by matching interference fringes observed in the 004 symmetric reflection double crystal rocking curves with simulations. The misfit dislocation density is highly anisotropic, varying from zero to a high value with increasing thickness. The contrast of the dislocations in the 004, 224 and 044 reflections has been examined in detail. All of the long dislocation segments characterized were 60° in character with ½<110> Burgers vectors inclined to the specimen surface. No dislocations were found which did not appear to be of this type. A surprising difference in contrast of the background in the 224 and 224 reflections is discussed.

Strain and misfit dislocation density in finite lateral size Si1−x Gex films grownby selective epitaxy

1997 ◽  
Vol 292 (1-2) ◽  
pp. 213-217 ◽  
Author(s):  
B. Holländer ◽  
L. Vescan ◽  
S. Mesters ◽  
S. Wickenhäuser
Keyword(s):  
Dislocation Density ◽  
Misfit Dislocation ◽  
Lateral Size ◽  
Selective Epitaxy

Rapid Thermal Processing of Buried Sil−xGex Strained Layers; Photoluminescence Decay and Misfit Dislocation Generation.

1990 ◽  
Vol 198 ◽  
Author(s):  
D.C. Houghton ◽  
N.L. Rowell
Keyword(s):  
Quantum Wells ◽  
Misfit Dislocation ◽  
Thermal Processing ◽  
Internal Quantum Efficiency ◽  
Dislocation Nucleation ◽  
Multiple Quantum ◽  
Misfit Dislocations ◽  
Dislocation Generation ◽  
Strained Layers ◽  
Wide Range

ABSTRACTThe thermal constraints for device processing imposed by strain relaxation have been determined for a wide range of Si-Ge strained heterostructures. Misfit dislocation densities and glide velocities in uncapped Sil-xGex alloy layers, Sil-xGex single and multiple quantum wells have been measured using defect etching and TEM for a range of anneal temperatures (450°C-1000°C) and anneal times (5s-2000s). The decay of an intense photoluminescence peak (∼ 10% internal quantum efficiency ) from buried Si1-xGex strained layers has been correlated with the generation of misfit dislocations in adjacent Sil-xGex /Si interfaces. The misfit dislocation nucleation rate and glide velocity for all geometries and alloy compositions (0<x<0.25) were found to be thermally activated processes with activation energies of (2.5±0.2)eV and (2.3-0.65x)eV, respectively. The time-temperature regime available for thermal processing is mapped out as a function of dislocation density using a new kinetic model.

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.

The Critical Thickness of Layers Subject to Anisotropic Misfit.

1991 ◽  
Vol 239 ◽  
Author(s):  
Richard Beanland
Keyword(s):  
Dislocation Density ◽  
Layer Thickness ◽  
Critical Thickness ◽  
Theoretical Calculations ◽  
Critical Layer ◽  
Epitaxial Layers ◽  
Misfit Dislocations ◽  
Critical Layer Thickness ◽  
New Formulation

ABSTRACTIt is well known that it becomes energetically favourable for misfit dislocations to be introduced into strained epitaxial layers above a certain ‘critical’ layer thickness, hc. To date, theoretical calculations of hc have only been made for cases of isotropie misfit - i.e. cases where the misfit is the same for every direction in the interface. Using a new formulation of the Frank-Bilby equation and the concept of coherency dislocations, it is now possible to treat cases of anisotropie misfit, such as silicon on sapphire (SOS). The method used to obtain the critical thickness is described, and values of hc and equilibrium dislocation density are given for various materials systems.

Dislocation Behaviour in GexSi1-x Epilayers on (001)Si

1989 ◽  
Vol 160 ◽  
Author(s):  
Eric P. Kvam ◽  
D.M. Maher ◽  
C.J. Humphreys
Keyword(s):  
Dislocation Density ◽  
Film Thickness ◽  
Critical Thickness ◽  
Three Dimensional ◽  
Critical Value ◽  
Misfit Dislocations ◽  
Island Growth ◽  
Edge Type ◽  
Dislocation Behaviour ◽  
Step Mechanism

AbstractWe have observed that the nature of misfit dislocations introduced near the critical thickness in GexSi1-x alloys on (001)Si changes markedly in the region 0.4 ≤ x ≤ 0.5. At or below the lower end of this compositional range, the observed microstructure is comprised almost entirely of 60° type dislocations, while at the high end, the dislocation structure is almost entirely Lomer edge type. Concurrent with this change, the dislocation density at the top of the epilayer varies by a factor of about 60X. Similarly, several other observables (e.g. dislocation length and spacing) also change appreciably.Part of the reason for the morphological variation seems to be a change in the source for dislocation introduction, in conjunction with a change in glide behaviour of dislocations as a function of film thickness. Evidence will be presented that indicates strain, as well as thickness, has a critical value for some dislocation introduction mechanisms, and that these together determine the resulting microstructure.Furthermore, it appears unlikely that the edge-type Lomer dislocations which appear at about x = 0.5 are either introduced directly, by climb, or grown in, as in the three-dimensional island growth and coalescence which occurs when x approaches unity. Instead, a two-step mechanism involving glissile dislocations is proposed and discussed.

The Roles of Stress, Geometry and Orientation on Misfit Dislocations Kinetics and Energetics in Epitaxial Strained Layers.

1991 ◽  
Vol 239 ◽  
Author(s):  
R. Hull ◽  
J. C. Bean ◽  
F. Ross ◽  
D. Bahnck ◽  
L. J. Pencolas
Keyword(s):  
Misfit Dislocation ◽  
Lattice Mismatch ◽  
Strain Relaxation ◽  
Misfit Dislocations ◽  
Slip Systems ◽  
Strained Layers ◽  
Burgers Vector ◽  
Partial Dislocations ◽  
Strain Stress ◽  
Kinetics Of

ABSTRACTThe geometries, microstructures, energetics and kinetics of misfit dislocations as functions of surface orientation and the magnitude of strain/stress are investigated experimentally and theoretically. Examples are drawn from (100), (110) and (111) surfaces and from the GexSi1–x/Si and InxGa1–x/GaAs systems. It is shown that the misfit dislocation geometries and microstructures at lattice mismatch stresses < - 1GPa may in general be predicted by operation of the minimum magnitude Burgers vector slipping on the widest spaced planes. At stresses of the order several GPa, however, new dislocation systems may become operative with either modified Burgers vectors or slip systems. Dissociation of totál misfit dislocations into partial dislocations is found to play a crucial role in strain relaxation, on surfaces other than (100) under compressive stress.

A Theoretical Calculation of Misfit Dislocation and Strain Relaxation in Step-graded InxGa 1-x N/GaN Layers

2011 ◽  
Vol 403-408 ◽  
pp. 456-460 ◽  
Author(s):  
Md. Arafat Hossain ◽  
Md. Rafiqul Islam
Keyword(s):  
Theoretical Calculation ◽  
Layer Thickness ◽  
Misfit Dislocation ◽  
Residual Strain ◽  
Critical Thickness ◽  
Strain Relaxation ◽  
Misfit Strain ◽  
Misfit Dislocations ◽  
Uniform Layer ◽  
Dislocation Energy

This paper presents a theoretical calculation of misfit dislocation and strain relaxation in compositionally step graded InxGa1-xN grown on GaN using the total dislocation energy at each interface. The results also compared with uniform layer of In0.17Ga0.83N and In0.14Ga0.86N grown differently on GaN. Due to having residual strain and a step increase in indium composition a lower misfit strain in upper layers and hence larger critical thickness at each interface has been reported. These effects significantly reduced the misfit dislocations from 2.6×105cm-1to 9.5×104cm-1in step graded In0.14Ga0.86N(500nm)/In0.09Ga0.91N(100nm)/In0.05Ga0.95N(100nm)/GaN layers instead of a uniform In0.14Ga0.86N(700nm)/GaN. A small residual strain of 0.0007 after 700 nm graded layer thickness has been reported with 87.04% strain relaxation.

Tilts in Thin Strained Layers.

1991 ◽  
Vol 238 ◽  
Author(s):  
Richard Beanland
Keyword(s):  
Band Gap ◽  
Misfit Dislocation ◽  
Side Effect ◽  
Epitaxial Films ◽  
Misfit Dislocations ◽  
Poisson Effect ◽  
Strained Layers ◽  
Band Gap Engineering ◽  
Recent Formulation ◽  
Coherency Strains

ABSTRACTThere is considerable interest at present in the mechanisms of tilting of epitaxial films, such that low index planes in layer and substrate have slightly different orientations. There are two primary causes of this effect: a) coherency strains and b) the action of misfit dislocations. It is important to distinguish between the two effects, particularly in the case of strained layers used for band-gap engineering. Using a recent formulation of the Frank-Bilby equation for the dislocation content of interfaces, it is shown how planes may be rotated in coherent layers due to both the Poisson effect and anisotropic misfit. An advantage of the Frank-Bilby equation is that it allows consideration of semicoherent layers. It is shown that a side effect of misfit dislocation introduction can be to introduce a further rotation of the epitaxial layer. Both these effects have been measured experimentally. The amount and the sense of rotation is compared to theory.

Modified Dislocation Structures in GexSi1-x Double Epilayers on (001)Si

1989 ◽  
Vol 160 ◽  
Author(s):  
Eric P. Kvam
Keyword(s):  
Misfit Dislocation ◽  
Critical Thickness ◽  
Misfit Dislocations ◽  
Strain Relief ◽  
Edge Type

AbstractDouble epilayers of different compositions of GexSi1-x on (001)Si are observed to have dislocation contents which differ markedly from similar single epilayers. An initial epilayer, grown below its critical thickness, underwent substantial misfit dislocation introduction, while a second epilayer, grown at a composition where edge-type misfit dislocations are normally observed to dominate the morphology, contained mostly 60° type dislocations. It is suggested that dislocation entry into the upper, high mismatch epilayer allows many dislocations to enter the buried, low mismatch epilayer, and that this in turn affects the dislocation morphology in the upper layer through strain relief.

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