Threading Dislocation Density Reduction in GaN/Sapphire Heterostructures.

1999 ◽  
Vol 595 ◽  
Author(s):  
A. Kvit ◽  
A. K. Sharma ◽  
J. Narayan
Keyword(s):  
Basal Plane ◽  
Stacking Faults ◽  
High Density ◽  
Thin Layers ◽  
Interfacial Region ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Plan View ◽  
Partial Dislocations

AbstractLarge lattice mismatch between GaN and α-Al2O3 (15%) leads to the possibility of high threading dislocation densities in the nitride layers grown on sapphire. This investigation focused on defect reduction in GaN epitaxial thin layer was investigated as a function of processing variables. The microstructure changes from threading dislocations normal to the basal plane to stacking faults in the basal plane. The plan-view TEM and the corresponding selected-area diffraction patterns show that the film is single crystal and is aligned with a fixed epitaxial orientation to the substrate. The epitaxial relationship was found to be (0001)GaN∥(0001)Sap and [01-10]GaN∥[-12-10]Sap. This is equivalent to a 30° rotation in the basal (0001) plane. The film is found to contain a high density of stacking faults with average spacing 15 nm terminated by partial dislocations. The density of partial dislocations was estimated from plan-view TEM image to be 7×109 cm−2. The cross-section image of GaN film shows the density of stacking faults is highest in the vicinity of the interface and decreases markedly near the top of the layer. Inverted domain boundaries, which are almost perpendicular to the film surface, are also visible. The concentration of threading dislocation is relatively low (∼;2×108 cm−2), compared to misfit dislocations. The average distance between misfit dislocations was found to be 22 Å. Contrast modulations due to the strain near misfit dislocations are seen in high-resolution cross-sectional TCM micrograph of GaN/α-Al2O3 interface. This interface is sharp and does not contain any transitional layer. The interfacial region has a high density of Shockley and Frank partial dislocations. Mechanism of accommodation of tensile, sequence and tilt disorder through partial dislocation generation is discussed. In order to achieve low concentration of threading dislocations we need to establish favorable conditions for some stacking disorder in thin layers above the film-substrate interface region.

Electron Microscopy Investigation of the Role of Surface Steps in the Generation of Dislocations during MOCVD Growth of GaN on 4H-SiC

2006 ◽  
Vol 527-529 ◽  
pp. 1509-1512 ◽  
Author(s):  
N.D. Bassim ◽  
Mark E. Twigg ◽  
Michael A. Mastro ◽  
Philip G. Neudeck ◽  
Charles R. Eddy ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Substrate Surface ◽  
Atomic Scale ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Nucleation Layer ◽  
Plan View ◽  
Surface Steps

Through the use of specially-prepared on-axis SiC substrates with patterned mesa tops completely free of atomic-scale surface steps, we have previously reported the growth of highquality GaN heteroepitaxial films with greatly reduced threading dislocation densities on the order of 107/cm2. In these films, we reported a defect substructure in which lateral a-type dislocations are present in the nucleation layer but do not bow into threading dislocations during the subsequent GaN growth. This study focuses further on the role of SiC substrate surface steps in the generation of misfit, a-type, and threading dislocations at the heteroepitaxial interface. By using weak-beam imaging (both to eliminate Moiré effects and to observe narrow dislocation images) from plan-view transmission electron microscopy (TEM), we identify dislocations generated on stepped and unstepped mesas and compare their geometries. We observe that misfit dislocations nucleated on an unstepped SiC mesa are confined to one set of a-type Burgers vectors of the form g=1/3 [2110] _ _ , straight and well-ordered so that they are less likely to interact with each other. On the other hand, misfit dislocation structures on a stepped SiC mesa surface are not nearly as well-ordered, having bowed structure with threading dislocations that appear to nucleate at SiC surface steps.

scholarly journals Dissociation Behavior of Dislocations in Ice

Crystals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 386
Author(s):  
Takeo Hondoh
Keyword(s):  
Basal Plane ◽  
Dislocation Line ◽  
Stacking Faults ◽  
Physical Models ◽  
Time Constants ◽  
Burgers Vector ◽  
Partial Dislocations ◽  
Perfect Dislocation ◽  
Low Energies ◽  
Dissociated State

Dislocations in ice behave very differently from those in other materials due to the very low energies of stacking faults in the ice basal plane. As a result, the dislocations dissociate on the basal plane, from a perfect dislocation into two partial dislocations with equilibrium width we ranging from 20 to 500 nm, but what is the timescale to reach this dissociated state? Using physical models, we estimate this timescale by calculating two time-constants: the dissociation-completing time td and the dissociation-beginning time tb. These time constants are calculated for two Burgers vectors as a function of temperature. For perfect dislocations with Burgers vector <c + a>, td is more than one month even at the melting temperature TM, and it exceeds 103 years below −50 ℃, meaning that the dissociation cannot be completed during deformation over laboratory timescales. However, in this case the beginning time tb is less than one second at TM, and it is within several tens of minutes above −50 ℃. These dislocations can glide on non-basal planes until they turn to the dissociated state during deformation, finally resulting in sessile extended dislocations of various widths approaching to the equilibrium value we. In contrast, for perfect dislocations with Burgers vector <a>, td is less than one second above −50 ℃, resulting in glissile extended dislocations with the equilibrium width we on the basal plane. This width is sensitive to the shear stress τ exerted normal to the dislocation line, leading to extension of the intervening stacking fault across the entire crystal grain under commonly accessible stresses. Also, due to the widely dissociated state, dislocations <a> cannot cross-slip to non-basal planes. Such behavior of extended dislocations in ice are notable when compared to those of other materials.

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.

Tem Characterization of ZnO and AIN/ZnO Thin Films Grown on Sapphire

1998 ◽  
Vol 526 ◽  
Author(s):  
K. Dovidenko ◽  
S. Oktyabrsky ◽  
A. K. Sharma ◽  
J. Narayan
Keyword(s):  
Single Crystal ◽  
Pulsed Laser Deposition ◽  
Basal Plane ◽  
Pulsed Laser ◽  
Laser Deposition ◽  
Zno Films ◽  
Threading Dislocation ◽  
Epitaxial Relationship ◽  
Spinel Layer ◽  
Plan View

AbstractThin (~ 250 nm) films of ZnO grown by pulsed laser deposition on basal plane of sapphire were studied by transmission electron microscopy (TEM). Plan-view TEM study proved the films to be single crystal with the following epitaxial relationship with the substrate: (0001)znO || (0001)sap with the 30 30° in-plane rotation - [0110]ZnO || [1210]sap. Dislocations lying mostly in basal plane of ZnO and aligned along both <:1010> and <1120> directions having b=1/3[1120] were found. ZnO films were found to have layered growth morphology contrary to columnar morphology of III-nitrides. Consequently, the threading dislocation density in ZnO films (opposing to the AIN and GaN) drops very fast with the thickness: down to 107cm-2 at ~ 250 nm. The effect of post-annealing (which caused significant improvement in electrical and optical properties) on the microstructure of ZnO films was also studied. Contrary to the atomically sharp and clean interface in the as-deposited films, the post-annealed ZnO/sapphire interface contained reacted layer of 30 - 60 A thickness. The structure of the interlayer was determined to be ZnAl2O4 (spinel). The formation of this single crystal spinel layer did not cause deterioration of the ZnO film structure or properties. We have also explored the possibilities of using ZnO as a buffer for III-nitride growth. The epitaxial AIN films were grown on top of the ZnO layer by pulsed laser deposition. Thin (20 -60 A) interfacial reaction layer (also spinel ZnAm2O4) was observed between AIN and ZnO. Formation of this interlayer is studied in conjunction with the AIN epitaxy and the characteristics of defects and interfaces.

Mechanisms of Stacking Fault Growth in SiC PiN Diodes

2004 ◽  
Vol 815 ◽  
Author(s):  
R. E. Stahlbush ◽  
M. E. Twigg ◽  
J. J. Sumakeris ◽  
K. G. Irvine ◽  
P. A. Losee
Keyword(s):  
Basal Plane ◽  
Stacking Faults ◽  
Stacking Fault ◽  
Drift Region ◽  
Pin Diodes ◽  
Current Time ◽  
Partial Dislocations ◽  
Initial Evolution ◽  
A Chain ◽  
Fault Growth

AbstractThe early development of stacking faults in SiC PiN diodes fabricated on 8° off c-axis 4H wafers has been studied. The 150μm drift region and p-n junction were epitaxially grown. The initial evolution of the stacking faults was examined by low injection electroluminescence using current-time product steps as low as 0.05 coul/cm2. The properties of the dislocations present before electrical stressing were determined based on previously observed differences of Si-core and C-core partial dislocations and the patterns of stacking fault expansion. The initial stacking fault expansion often forms a chain of equilateral triangles and at higher currents and/or longer times these triangles coalesce. All of the faulting examined in this paper originated between 10 and 40 μm below the SiC surface. The expansion rate of the bounding partial dislocations is very sensitive to the partials' line directions, their core types and the density of kinks. From these patterns it is concluded that the stacking faults originate from edge-like basal plane dislocations that have Burgers vectors either parallel or anti-parallel to the off-cut direction. Evidence for dislocation conversions between basal-plane and threading throughout the epitaxial drift region is also presented.

Cross Section and Plan View STEM Analysis on Identical Conversion Point of Basal Plane Dislocation to Threading Edge Dislocation of 4H-SiC

2016 ◽  
Vol 858 ◽  
pp. 397-400
Author(s):  
Takahiro Sato ◽  
Yoshihisa Orai ◽  
Toshiyuki Isshiki ◽  
Munetoshi Fukui ◽  
Kuniyasu Nakamura
Keyword(s):  
Cross Section ◽  
Edge Dislocation ◽  
Basal Plane ◽  
Dislocation Line ◽  
Plan View ◽  
Conversion Point ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Basal Plane Dislocation

Cross section and plan view dislocation analysis at the conversion point of a basal plane dislocation (BPD) into a threading edge dislocation (TED) in a silicon carbide epitaxial wafer was developed using a newly modified multi directional scanning transmission electron microscopy (STEM) technique. Cross section STEM observation in the [-1100] direction, found a conversion point located 5.5 μm from the surface, where two dislocation lines in the basal plane convert into one dislocation line nearly along the hexagonal c axis was observed. Using plan view STEM observation along the [000-1] direction, it is confirmed that the dislocation lines are two partial dislocations of a BPD and one TED by g·b invisibility analysis. This new technique is a powerful tool to evaluate the fundamental dislocation characteristics of power electronics devices.

Overlapping Shockley/Frank Faults in 4H-SiC PiN Diodes

2006 ◽  
Vol 527-529 ◽  
pp. 383-386 ◽  
Author(s):  
Mark E. Twigg ◽  
Robert E. Stahlbush ◽  
Peter A. Losee ◽  
Can Hua Li ◽  
I. Bhat ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Light Emission ◽  
Stacking Faults ◽  
Dark Field ◽  
Pin Diodes ◽  
Plan View ◽  
Planar Defects ◽  
Burgers Vector ◽  
Partial Dislocations ◽  
Transmission Electron

Using light emission imaging (LEI), we have determined that not all planar defects in 4H-SiC PiN diodes expand in response to bias. Accordingly, plan-view transmission electron microscopy (TEM) observations of these diodes indicate that these static planar defects are different in structure from the mobile stacking faults (SFs) that have been previously observed in 4H-SiC PiN diodes. Bright and dark field TEM observations reveal that such planar defects are bounded by partial dislocations, and that the SFs associated with these partials display both Frank and Shockley character. That is, the Burgers vector of such partial dislocations is 1/12<4-403>. For sessile Frank partial dislocations, glide is severely constrained by the need to inject either atoms or vacancies into the expanding faulted layer. Furthermore, these overlapping SFs are seen to be fundamentally different from other planar defects found in 4H-SiC.

scholarly journals The heterogeneous nucleation of threading dislocations on partial dislocations in III-nitride epilayers

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
J. Smalc-Koziorοwska ◽  
J. Moneta ◽  
P. Chatzopoulou ◽  
I. G. Vasileiadis ◽  
C. Bazioti ◽  
...  
Keyword(s):  
Heterogeneous Nucleation ◽  
Physical Mechanism ◽  
Dislocation Nucleation ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Physical Mechanisms ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Device Applications ◽  
Very High

Abstract III-nitride compound semiconductors are breakthrough materials regarding device applications. However, their heterostructures suffer from very high threading dislocation (TD) densities that impair several aspects of their performance. The physical mechanisms leading to TD nucleation in these materials are still not fully elucidated. An overlooked but apparently important mechanism is their heterogeneous nucleation on domains of basal stacking faults (BSFs). Based on experimental observations by transmission electron microscopy, we present a concise model of this phenomenon occurring in III-nitride alloy heterostructures. Such domains comprise overlapping intrinsic I1 BSFs with parallel translation vectors. Overlapping of two BSFs annihilates most of the local elastic strain of their delimiting partial dislocations. What remains combines to yield partial dislocations that are always of screw character. As a result, TD nucleation becomes geometrically necessary, as well as energetically favorable, due to the coexistence of crystallographically equivalent prismatic facets surrounding the BSF domain. The presented model explains all observed BSF domain morphologies, and constitutes a physical mechanism that provides insight regarding dislocation nucleation in wurtzite-structured alloy epilayers.

Nucleation of misfit and threading dislocations in GaSb/GaAs(001) heterostructure

1996 ◽  
Vol 54 ◽  
pp. 946-947
Author(s):  
W. Qian ◽  
M. Skowronski ◽  
R. Kaspi ◽  
M. De Graef
Keyword(s):  
Lattice Mismatch ◽  
Strain Relaxation ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Extended Defects ◽  
Large Lattice ◽  
Threading Dislocation Density ◽  
Small Lattice ◽  
Large Lattice Mismatch

GaSb thin film grown on GaAs is a promising substrate for fabrication of electronic and optical devices such as infrared photodetectors. However, these two materials exhibit a 7.8% lattice constant mismatch which raises concerns about the amount of extended defects introduced during strain relaxation. It was found that, unlike small lattice mismatched systems such as InxGa1-xAs/GaAs or GexSi1-x/Si(100), the GaSb/GaAs interface consists of a quasi-periodic array of 90° misfit dislocations, and the threading dislocation density is low despite its large lattice mismatch. This paper reports on the initial stages of GaSb growth on GaAs(001) substrates by molecular beam epitaxy (MBE). In particular, we discuss the possible formation mechanism of misfit dislocations at the GaSb/GaAs(001) interface and the origin of threading dislocations in the GaSb epilayer.GaSb thin films with nominal thicknesses of 5 to 100 nm were grown on GaAs(001) by MBE at a growth rate of about 0.8 monolayers per second.

A Refined Model For Threading Dislocation Filtering In InxGa1−xAs/GaSAs Epitaxial Layers

1996 ◽  
Vol 442 ◽  
Author(s):  
G. Macpherson ◽  
P. J. Goodhew
Keyword(s):  
Large Scale ◽  
Critical Thickness ◽  
Thin Layers ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Refined Model ◽  
Force Microscopy ◽  
Atomic Force ◽  
Dislocation Densities ◽  
High Level

AbstractA model is presented for the filtering of threading dislocations in InxGa1−xAs/GaAs epitaxial single layers by accurate control of the layer thickness. The model developed differs from previous models since the InxGa1−xAs growth is restricted to less than ten times the Matthews and Blakeslee critical thickness (hc) where the asymmetry in the [110] and [110] dislocation densities is the greatest. Beyond this thickness it is shown that the removal or annihilation of threading dislocations (TDs) in the epilayer is more than offset by the introduction of new TDs from spiral and Frank-Read type sources. Results from strain sensitive etching with CrO3 aqueous solutions show that the TD density can be reduced by up to a factor of ten below that found in the substrate. Atomic force microscopy shows that these thin layers maintain a high level of surface quality with an absence of striations. Evidence is also shown that this type of defect etching is suitable for revealing large scale dislocation blocking in samples that have been grown significantly beyond 10hc.

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