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.

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.

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.

Anisotropic Lattice Relaxation and its Mechanism of ZnSe Epilayer Grown on (001) GaAs Substrate by Molecular Beam Epitaxy

1995 ◽  
Vol 399 ◽  
Author(s):  
C.S. Kim ◽  
S.K. Noh ◽  
H.J. Lee ◽  
Y.K. Cho ◽  
Y.I. Kim ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Gaas Substrate ◽  
Molecular Beam ◽  
Rotation Angle ◽  
Lattice Relaxation ◽  
High Dislocation Density ◽  
Sinusoidal Oscillation ◽  
Double Crystal ◽  
X Ray ◽  
Anisotropic Lattice

ABSTRACTWe have investigated anisotropic lattice relaxation and its mechanism of ZnSe epitaxial layer grown on (001) GaAs substrate by MBE. Double-crystal X-ray rocking curves for (004), {115} and {404} reflections were measured as a function of the azimuthal rotation angle of the sample. We observed the sinusoidal oscillation of the FWHM of the epilayer peak for (004) reflections due to the asymmetric dislocation density along two orthogonal <110> directions, and the direction of the maximum FWHM corresponding to high dislocation density is along [110]. In addition, the strain along [110] is smaller than that along [1-10], indicating that the layer suffered anisotropic lattice relaxation. The direction of larger relaxation([l-10]) is not consistent with that of high dislocation density([110]). The results suggest that the asymmetry in dislocation density is not responsible for the anisotropic relaxation of the ZnSe epilayer.

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.

Dislocation Distribution in Graded Composition IngaAs Layers

1993 ◽  
Vol 325 ◽  
Author(s):  
S.I. Molina ◽  
G. Gutiérrez ◽  
A. Sacedón ◽  
E. Calleja ◽  
R. García
Keyword(s):  
Detection Limit ◽  
Dislocation Density ◽  
Layer Thickness ◽  
Gaas Substrate ◽  
Ingaas Layer ◽  
Constant Composition ◽  
Defect Distribution ◽  
Dislocation Distribution

The defect distribution of a graded composition InGaAs layer grown on GaAs by MBE has been characterized by TEM (XTEM, PVTEM, HREM). The observed configuration does not correspond completely with that theoretically predicted. Dislocation misfit segments are in a quantity much bigger than in constant composition layers. Dislocation density is quite uniform up to a certain layer thickness t1. Few dislocations are observed between this t1 thickness and a larger thickness t2. Dislocation density is below the detection limit of XTEM for thicknesses bigger than t2. Some dislocations are observed to penetrate in the GaAs substrate.Several mechanisms (reactions between 600 dislocations, Hagen-Strunk and modified Frank-Read processes) are proposed to explain the interactions of dislocations in the epilayer and their penetration in the substrate.

On the Critical Layer Thickness of Strained-Layer Heteroepitaxial CoSi2 Films on 〈111〉Si

1987 ◽  
Vol 91 ◽  
Author(s):  
David N. Jamieson ◽  
G. Bai ◽  
Y. C. Kao ◽  
C. W. Nieh ◽  
M-A. Nicolet ◽  
...  
Keyword(s):  
Critical Thickness ◽  
Ion Beam ◽  
Thin Layers ◽  
Maximum Magnitude ◽  
Critical Layer Thickness ◽  
Double Crystal ◽  
Strained Layers ◽  
X Ray ◽  
Planar Growth

ABSTRACTThe technique of Double Crystal X-Ray Diffractometry (DXD) and ion beam channeling are applied to investigate, as a function of thickness, the average perpendicular strain and crystal quality of CoSi2 layers grown by MBE on 〈111〉Si. The results show that thin layers (from 20 to 30 nm) are partially relaxed but with a strain greater than that expected for a free CoSi2 lattice. For layers thicker than 30nm the magnitude of the CoSi2 strain incrgases to 1.7%, somewhat less than the maximum magnitude strain expected for coherent growth (2.1%). For layers thicker than 50 nm, the perpendicular strain relaxes very slowly, with the strain at 225 nm only 5% less than that at 50nm. It was concluded that a coherent epitaxial layer does not form initially and the relaxation of the strained layers is not consistent with a planar growth mechanism of the CoSi2 epilayers. Therefore the concept of a critical thickness, below which the epilayers are strained and above which the epilayers are relaxed, cannot be applied to our CoSi2/Si system.

Hrxrd Study of the Strain Properties of MBE-Grown ZnSe and ZnSTe on GaAs

1994 ◽  
Vol 340 ◽  
Author(s):  
I.K. Sou ◽  
S.M. Mou ◽  
Y.W. Chan ◽  
G.C. Xu ◽  
G.K.L. Wong
Keyword(s):  
Layer Thickness ◽  
Gaas Substrate ◽  
Critical Thickness ◽  
Dynamical Theory ◽  
X Ray Diffraction ◽  
Strained Layers ◽  
X Ray ◽  
Znse Layer ◽  
Vegard’S Law ◽  
First Time

ABSTRACTWe have studied the structural properties of MBE-grown ZnSe/GaAs and ZnSTe/GaAs heterostructures using high resolution X-ray diffraction (HRXRD). The transition from pseudomorphic to partially and then fully relaxed strained layers is observed as a function of ZnSe layer thickness. The critical thickness for the on-set of strained relaxation for ZnSe on GaAs(001) is determined to be between 1600 and 1850 Å. Using a simulation program based on the dynamical theory, the poisson's ratio of ZnSe is accurately determined to be v=0.380±0.002. A set of ZnSl-xTex epilayers with 0 ≤ × ≤ 1 was grown on GaAs by MBE for the first time. A linear dependence of the lattice constant upon Te composition is found, which agrees well with the Vegard's Law. The characteristic behaviors of inclination between the layer and substrate planes as a function of layer thickness has been studied on both ZnSe/GaAs and ZnSTe/GaAs systems. The atomic planes of both ZnSe and ZnSTe layers are observed to tilt from those of the GaAs substrate.

Defect morphology in thick relaxed layers of InGaAs on GaAs

1990 ◽  
Vol 48 (4) ◽  
pp. 668-669
Author(s):  
R H Dixon ◽  
P Kidd ◽  
P J Goodhew
Keyword(s):  
Electron Microscopy ◽  
Surface Morphology ◽  
Growth Conditions ◽  
X Ray Diffraction ◽  
Double Crystal ◽  
Strained Layers ◽  
Good Surface ◽  
Transmission Electron ◽  
Device Structures ◽  
Surface Morphologies

Thick relaxed InGaAs layers grown epitaxially on GaAs are potentially useful substrates for growing high indium percentage strained layers. It is important that these relaxed layers are defect free and have a good surface morphology for the subsequent growth of device structures.3μm relaxed layers of InxGa1-xAs were grown on semi - insulating GaAs substrates by Molecular Beam Epitaxy (MBE), where the indium composition ranged from x=0.1 to 1.0. The interface, bulk and surface of the layers have been examined in planar view and cross-section by Transmission Electron Microscopy (TEM). The surface morphologies have been characterised by Scanning Electron Microscopy (SEM), and the bulk lattice perfection of the layers assessed using Double Crystal X-ray Diffraction (DCXRD).The surface morphology has been found to correlate with the growth conditions, with the type of defects grown-in to the layer (e.g. stacking faults, microtwins), and with the nature and density of dislocations in the interface.

Very Thick Coherently Strained GexSi1−x Layers Grown in a Narrow Temperature Window

1991 ◽  
Vol 220 ◽  
Author(s):  
C. H. Chern ◽  
K. L. Wang ◽  
G. Bai ◽  
M. -A. Nicolet
Keyword(s):  
Growth Temperature ◽  
Strain Relaxation ◽  
Gas Pressure ◽  
High Density ◽  
Misfit Dislocations ◽  
High Quality ◽  
Strained Layers ◽  
Temperature Window ◽  
Residual Gas

ABSTRACTStrain relaxation of GexSi1−x layers is studied as a function of growth temperature. Extremely thick coherently strained layers whose thicknesses exceed more than fifty times of the critical thicknesses predicted by Matthews and Blakeslee's model were successfully grown by MBE. There exits a narrow temperature window from 310 °C to 350 °C for growing this kind of high quality thick strained layers. Below this temperature window, the layers are poor in quality as indicated from RHEED patterns. Above this window, the strain of the layers relaxes very fast accompanied with a high density of misfit dislocations as the growth temperature increases. Moreover, for samples grown in this temperature window, the strain relaxation shows a dependence of the residual gas pressure, which has never been reported before.

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