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 Initial Stages of MBE Growth of InSb on GaAs(100) - A High Misfit Heterointerface

1989 ◽  
Vol 159 ◽  
Author(s):  
C.J. Kiely ◽  
A. Rockett ◽  
J-I. Chyi ◽  
H. Morkoc
Keyword(s):  
Three Dimensional ◽  
Misfit Strain ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Island Growth ◽  
Mbe Growth ◽  
Edge Type ◽  
Transmission Electron ◽  
Interfacial Defects ◽  
Square Array

ABSTRACTThe initial stages of heteroepitaxy of InSb on GaAs(100) grown by MBE have been studied by transmission electron microscopy. Three dimensional InSb island growth occurs in which the majority of the 14.6% misfit strain is accommodated by a square array of a/2<011= edge-type misfit dislocations. The implications of each island having a well defined defect array before coalescence into a continuous epilayer are discussed. Some 600-type a/2<101= interfacial defects and associated threading dislocations are also observed in coalesced films and possible reasons for their existence are explained. A strong asymmetrical distribution of planar defects in the InSb islands is observed and the origin of the asymmetry is discussed. Finally some evidence for local intermixing in the vicinity of the interface is presented.

Misfit Strain Relief Beyond the Critical Thickness Using Curvature Measurements and in Situ Characterization of the Magneto-Optic Kerr Effect

1994 ◽  
Vol 356 ◽  
Author(s):  
H. E. Inglefield ◽  
G. Bochi ◽  
C. A. Ballentine ◽  
R. C. O’Handley ◽  
C. V. Thompson
Keyword(s):  
Film Thickness ◽  
Magnetic Anisotropy ◽  
Kerr Effect ◽  
Critical Thickness ◽  
Misfit Strain ◽  
Misfit Dislocations ◽  
Wafer Curvature ◽  
Curvature Measurements ◽  
Magneto Optic

AbstractEpitaxial misfit has been characterized in Ni/Cu/Si (100) as a function of Ni film thickness using wafer curvature measurements. This strain can be related to measurements of magnetic anisotropy made in the deposition system using the magneto-optic Kerr effect. Films were deposited using molecular beam epitaxy (MBE) with varying Ni epilayer thickness between 10 and 1000Å. The change in wafer curvature due to misfit strain was measured using optical interferometry and the strain was calculated using Stoney’s equation. Transmission electron microscopy was used to characterize misfit dislocations at the Ni/Cu interface. It has been determined that misfit strain can have a very strong effect on magnetic anisotropy, particularly in the regime between the critical thickness and complete misfit accommodation, where strain has been found to decrease significantly as a function of film thickness. A critical strain has been determined at which a transition in the direction of magnetization easy axis from perpendicular to the film to in the film plane occurs. This discovery allows the use of Kerr effect measurements to characterize misfit strain in situ.

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.

Si1-xGex Critical Thickness for Surface Wave Generation During UHV-CVD Growth at 525°C

1995 ◽  
Vol 399 ◽  
Author(s):  
H. Lafontaine ◽  
D.C. Houghton ◽  
B. Bahierathan ◽  
D.D. Perovic ◽  
J.-M. Baribeau
Keyword(s):  
Electron Microscopy ◽  
Surface Waves ◽  
Critical Thickness ◽  
Critical Value ◽  
Misfit Dislocations ◽  
Cross Sectional ◽  
Force Microscopy ◽  
Atomic Force ◽  
Transmission Electron ◽  
Cvd Growth

ABSTRACTSeveral Si1-xGex/Si heterostructures were grown at 525°C using a commercially available UHV-CVD reactor. Layers with a germanium fraction ranging from 0.15 to 0.5 were examined by means of cross-sectional transmission electron microscopy and atomic force microscopy. Surface waves were found in layers with a thickness above a critical value which decreases rapidly as the Ge fraction is increased. Both experimental and modeling results show that surface waves are generated before misfit dislocations for Ge fractions above 0.3.

Effects of Asperities in Elastohydrodynamic Lubrication

1980 ◽  
Vol 102 (3) ◽  
pp. 374-378 ◽  
Author(s):  
M. Kaneta ◽  
A. Cameron
Keyword(s):  
Film Thickness ◽  
Glass Plate ◽  
Three Dimensional ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Critical Value ◽  
Optical Interferometry ◽  
Asperity Height ◽  
Height Ratio ◽  
Pure Rolling

Optical interferometry was used to study rough surfaces under lubricated point contact. Three dimensional “asperities” of chromium were sputtered onto a steel ball which was run against a smooth glass plate under both rolling and sliding. The experimental results were compared with the various published theories. The film thicknesses found in sliding are different from those observed in pure rolling, which are nearly equal to the theoretical values. Film thickness collapse occurred when the central film thickness/half asperity height ratio (λ ratio) reached a critical value.

Critical Thickness of Surface Film in Boundary Lubrication

1956 ◽  
Vol 23 (3) ◽  
pp. 458-460
Author(s):  
I-Ming Feng ◽  
C. M. Chang
Keyword(s):  
Film Thickness ◽  
Boundary Lubrication ◽  
Critical Thickness ◽  
Surface Film ◽  
Critical Value ◽  
Rapid Decrease ◽  
Experimental Results ◽  
Equivalent Thickness ◽  
Pure Metals

Abstract When the combined equivalent thickness of the surface film approaches and finally becomes greater than the critical value, the weakening of the interlocking effect of the plastic roughening results in rapid decrease in wear and ultimately reduces wear to practically zero. This is verified by experimental results of wear of pure metals with controlled surface film thickness in the region near the critical thickness.

Critical Thickness for Three-Dimensional Epitaxial Island Growth

1988 ◽  
Vol 130 ◽  
Author(s):  
K. Jagannadham ◽  
J. Narayan
Keyword(s):  
Dislocation Loop ◽  
Misfit Dislocation ◽  
Critical Thickness ◽  
Three Dimensional ◽  
Surface Boundary ◽  
Dislocation Loops ◽  
Island Growth ◽  
Interfacial Dislocation ◽  
Burgers Vector ◽  
Surface Boundary Conditions

AbstractThe generation of misfit dislocation loops in three-dimensional epitaxial islands grown on thick substrates is analyzed. The coherent strain in the island is described by virtual interfacial dislocation loops situated in the interface. The traction free surface boundary conditions are satisfied by the surface dislocation loops situated on the surface of the island. A misfit dislocation loop is formed and the changes in the energy of the configuration used to determine if the total energy is lowered. The numerical analysis is carried out forhemispherical islands of GaAs grown on (100) silicon with a misfit dislocation of Burgers vector 3.84 Å. It has been found energetically favorable to nucleate a misfit dislocation loop at a distance of 3 å from the interface when the radius of the hemispherical island is equal to or greater than 40 å. In addition, a misfit dislocation loop could be nucleated at a larger distance from the interface when the size of the island is larger.

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.

Surface nucleated half-loops in strained epilayers

1990 ◽  
Vol 48 (4) ◽  
pp. 560-561
Author(s):  
Eric P. Kvam
Keyword(s):  
Growth Temperature ◽  
Critical Thickness ◽  
Three Dimensional ◽  
Mechanical Damage ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Dislocation Type ◽  
Dimensional Growth ◽  
Edge Dislocations

Mismatched epilayers, grown beyond some critical thickness, have commonly been observed to have arrays of misfit-relieving dislocations at the heterointerface. In diamond or sphalerite structures, these arrays are orthogonal <110> networks of long 60° type dislocations, which are glissile and have inclined Burgers vectors. Up to the point at which growth becomes three-dimensional (about 2% mismatch in the (In,Ga)As/GaAs system), internal defects act as the sources for the misfit dislocations. Examples of such sources include pre-existing threading dislocations, internal loops, precipitates, and mechanical damage.In higher mismatch two-dimensional growth, such as can be produced in the GeSi/Si(001) system, the density of epithreading dislocations suddenly increases as the length of interfacial misfit dislocations falls. Almost simultaneously, the misfit dislocation type changes from 60° to edge. While in-situ hot stage experiments have shown that 60° type dislocations become mobile at about the growth temperature of the epilayer, and have observable velocities from this temperature on up, our observations of edge dislocations in the same system have shown that velocities for edge dislocations are essentially nil (measurable limit <lnm/s) even at 750°C, some 200°C above the growth temperature.

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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