Evaluation of stacking faults and associated partial dislocations in AlSb/GaAs (001) interface by aberration-corrected high-resolution transmission electron microscopy (original) (raw)
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Strain-relief mechanisms and nature of misfit dislocations in GaAs/Si heterostructures
Materials Science and Engineering: A, 1989
The nucleation and glide of misfit dislocations in the GaAs/Si system is investigated using transmission electron microscopy. GaAs epilayers of different thicknesses were examined by electron microscopy (plan and cross-section) and the elastic strain remaining in the film related to the average spacing of the misfit dislocations at the interface. The GaAs epilayer lO00 d thick contains mostly 60 ° misfit dislocations whose average spacing is larger than the equilibrium dislocation spacing. The 2000.d and thicker GaAs epilayers contain predominantly 90 ° misfit dislocations with an average spacing between the dislocations less than the equilibrium dislocation spacing. The 90 ° dislocations are thought of as being formed by the reaction of 60 ° dislocations. A model is developed based on minimum energy considerations to determine the strain-thickness relationship. Nucleation and glide of a 60 ° half loop in the presence of neighboring half loops is used to calculate the dislocation energy. The mixed 60 ° dislocations are only half as effective as the 90 ° dislocations in relieving the lattice mismatch, but the glissile 60 ° dislocations are easier to form. The formation of sessile 90 ° dislocations at the interface is explained on the basis of dislocation reactions. The theoretical predictions of strain relaxation are compared with experimental observations using high-resolution electron microscopy.
Applied Physics Letters, 2011
The interfacial misfit ͑IMF͒ dislocation array of an epitaxial GaSb film on a Si substrate has been imaged with high-angle annular dark-field scanning transmission electron microscopy ͑HAADF-STEM͒. The mismatch strain accommodation through dislocation formation has been investigated using geometric phase analysis ͑GPA͒ on HAADF-STEM images with atomic resolution to probe the defects' local strain distribution. These measurements indicate that the lattice parameter of the epitaxial film recovers its bulk value within three unit cells from the interface due to the relaxation through IMF dislocations. The atomic number contrast of the HAADF-STEM images and energy dispersive x-ray spectrometry illustrate the formation of islands of AlSb buffer layer along the interface. The role of the AlSb buffer layer in facilitating the GaSb film growth on Si is further elucidated by investigating the strain field of the islands with the GPA.
Crystals
We report on the role of AlSb material in the reduction of threading dislocation density (TDD) in the GaSb/AlSb/GaAs system. The AlSb layers were grown using low-temperature (LT) MBE, exploiting the interfacial misfit (IMF) dislocation array. AlSb layers with four different thicknesses in the range of 1–30 nm were investigated. The results showed the inhibiting role of LT-AlSb layers in the reduction of TDD. Values of TDD as low as 2.2 × 106 and 6.3 × 106 cm−2 for samples with thin and thick AlSb layers were obtained, respectively. The filtering role of AlSb material was proven despite the IMF-AlSb/GaAs interface’s imperfectness caused by the disturbance of a 90° dislocation periodic array by, most likely, 60° dislocations. The dislocation lines confined to the region of AlSb material were visible in HRTEM images. The highest crystal quality and smoother surface of 1.0 μm GaSb material were obtained using 9 nm thick AlSb interlayer. Unexpectedly, the comparative analysis of the resu...
Reorientation of Misfit Dislocations During Annealing in InGaAs/GaAs(001) Interfaces
MRS Proceedings, 1993
ABSTRACTTransmission electron microscopy is applied to investigate the effect of post-annealing on misfit dislocations in an In0.2Ga0.8As/GaAs(001) heterostructure. An orthogonal array of 60º dislocations along [110] and [110] directions was observed in the interfaces of the samples grown by MBE at 520 ºC. When the as-grown samples were annealed at temperatures ranging from 600 to 800 ºC, the 60º dislocations were gradually reoriented by dislocation reactions occurring at the 90º intersections followed by nonconservative motion driven by dislocation line tension and the residual elastic misfit strain. The final result of this process was a dislocation array lying along [100] and [010] directions. The reoriented u=<100> dislocation has a Burgers vector , which is the same as that of 60º dislocation, but the edge component of its Burgers vector in the (001) interfacial plane is larger than that of 60º dislocation by a factor of , resulting in a greater contribution to elastic st...
Etch pit patterns of misfit dislocations in ALGaAs/GaAs heterostructures
Materials Letters, 1988
Misfit dislocations at the A&Gaa ?As/GaAs heterojunction have been revealed by an etching technique on the cleaved interface. On the ( 1 ia) cleaved surfaces, the dislocation etch pits are revealed as upright pyramids, while on the ( 110) surfaces, i.e. parallel to the primary flat, they are reveaied as inverted pyramids.
Dislocations in medium to highly mismatched III–V epitaxial heterostructures
Journal of Crystal Growth, 1993
Strain induced dislocations have been studied in medium mismatched In~Ga 1 _~As/GaAssingle layers (0.57% <f < 1.07%) and superlattice heterostructures (0.43% <f <2.1%) and highly mismatched (f 3.8%) InP/GaAs single layers. The location, propagation and nature of misfit dislocations have been investigated using electron microscopy techniques. The InGaAs/GaAs single layers were grown with different compositions and thicknesses directly onto the GaAs substrate without any GaAs buffer layers. In this case misfit dislocations were found to be confined at the heterointerface or within 150-200 nm of the interface, mostly inside the epilayer. On the contrary, a GaAs buffer layer was grown between the superlattice structures and the substrates. For 0.43% <f < 1.35 misfit dislocations were confined inside the buffer layers or at the buffer-superlattice interface, without threading the superlattice. For higher mismatch values (f= 2.1%), the superlattice presented both interfacial and threading dislocations. Asymmetric dislocation movement induced by the electron beam in a scanning electron microscope on as-grown samples, most likely associated with metastahility of the superlattices, was observed when thickness and composition were such that a low linear dislocation density (< 2x l0~cm') was present. Mainly 60°type misfit dislocations were observed in all the lnGaAs/GaAs structures investigated. The InP/GaAs heterostructures had a higher linear dislocation density (= 106 cm 1) and planar defects were found to thread the epilayers from the heterointerface up to the free surface. The density of these defects was found to decrease as the free surface was approached. Both 60°and 90°type dislocations were found in this system.
Threading Dislocation Density Reduction in GaAs on Si Substrates
Japanese Journal of Applied Physics, 1988
GhtrÃyhvprÃvhpuÃirrrÃBhIÃhqà 6y 2 O 3 (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 30º 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 7x10 9 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 (~2x10 8 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 qvyphvÃhrÃrrÃvÃuvturyvÃprpvhyÃU@HÃvpthuÃsÃBhI 6y 2 O 3 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.
Misfit dislocations in GaAsN/GaAs interface
Journal of Materials Science-Materials in Electronics, 2003
Highly strained GaAsN layers were grown on GaAs by metal-organic vapor phase epitaxy and studied by synchrotron X-ray topography and X-ray diffraction. The critical thickness for mis®t dislocation formation of the GaAs 0.965 N 0.035 epitaxial layer on GaAs was found to be between 50 and 80 nm. In layers thicker than the critical thickness a mis®t dislocation network was observed. The network was found to be isotropic and uniform. The relaxation of the strained epilayer begins through the mis®t-dislocation generation and continues via formation of cracks. The cracks are not distributed as uniformly as mis®t dislocations.
Applied Surface Science, 1998
In-situ X-ray topography (XRT) studies of misfit dislocation generation and movement in epitaxial InGaAs strained-layer structures on (001) GaAs are described. Examination of the changes in dislocation structure during a series of successive post-growth in-vacuo sample anneals has, for the first time, yielded activation energies of 0.7 and 0.8 eV for the formation of a-and /3-misfit dislocations (MDs) by the initial glide of substrate threading dislocations (TDs) in the InGaAs epilayer. The introduction of MDs by this method is supplemented by the presence of an additional MD generation process. The activation energy for this is found to be comparable to that required to initiate the glide of a TD. The XRT studies have also confirmed the existence of MD cross-slip events, where a to /3 cross-slip was lound to have an activation energy of 1.2 eV and to be much more common than the reverse /3-a cross-slip process.