Studies of lattice mismatch and threading dislocations in GaAs/Si grown by MBE (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.
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.
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.
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.
Journal of Applied Physics, 1993
Thick (--3 IBM) films of In,Ga,-As grown on GaAs( 100) substrates, across the whole composition range, have been examined by transmission electron microscopy and double-crystal x-ray diffmction. The results were compared with the observed growth mode of the material determined by in situ reflection high-energy electron diffraction in the molecular beam epitaxy growth system. The quality of the material degraded noticeably for compositions up to X-0.5 associated with an increased density of dislocations and stacking faults. In contrast, improvements in quality as x approached 1.0 were correlated with the introduction of an increasingly more regular array of edge dislocations. 1731
Interfacial Stability and Misfit Dislocation Formation in InAs/Gaas(110) Heteroepitaxy
MRS Proceedings, 1997
ABSTRACTA comprehensive atomic-scale study is presented of the mechanical behavior of the InAs epitaxial film, the interfacial stability with respect to misfit dislocation formation, and the film surface morphology in InAs/GaAs(110) heteroepitaxy. If a GaAs buffer layer of ten-monolayer thickness is used in the epitaxial growth, a transition is predicted from a coherent to a semi- coherent interface consisting of a regular array of edge interfacial misfit dislocations at a critical film thickness of six monolayers. A second transition to a semicoherent interface consisting of a completely developed network of perpendicularly intersecting misfit dislocations is predicted at thicknesses greater than 150 monolayers. Our simulation results are in excellent agreement with recent experimental data.
Misfit dislocations and antiphase domain boundaries in GaAs/Si interface
Journal of Applied Physics, 1994
The interaction of the antiphase boundaries that are formed at the early stage of growth with the interfacial misfit dislocations is studied by transmission electron microscopy using contrast criteria. Experimental analysis has shown that the shifting of the misfit dislocation families, by half of their periodicity, is due to their intersection with antiphase boundaries emanating from demisteps on the Si substrate. The observed discontinuity of dislocation lines is attributed to dynamical contrast conditions. The antiphase boundaries do not interrupt the continuity of the network of dislocations. The dichromatic theory of interfacial defects is applied in order to illustrate the geometrical features of the pattern. The disymmetrization mechanism of the pattern obeys the principle of symmetry compensation. A symmetry analysis of the GaAs/Si interface justifies the agreement of the observations with the structural model.
Applied Microscopy, 2014
Dislocation density and distribution in epitaxial GaAs layer on Si are evaluated quantitatively and effectively using image processing of transmission electron microscopy image. In order to evaluate dislocation density and distribution, three methods are introduced based on line-intercept, line-length measurement and our coding with linescanning method. Our coding method based on line-scanning is used to detect the dislocations line-by-line effectively by sweeping a thin line with the width of one pixel. The proposed method has advances in the evaluation of dislocation density and distribution. Dislocations can be detected automatically and continuously by a sweeping line in the code. Variation of dislocation density in epitaxial GaAs films can be precisely analyzed along the growth direction on the film.
Revealing of threading and misfit dislocations in partially relaxed InGaAs/GaAs heterostructures
physica status solidi (c), 2004
Both threading and misfit dislocations in partially relaxed InGaAs/GaAs heterostructures with a small lattice-mismatch have been investigated by means of chemical etching and atomic force microscopy (AFM). An anisotropic etching in HF-H 2 SO 4 -H 2 O 2 based aqueous solution was successfully used to determine the polarity of the crystallographic surfaces and an ultrasonic-vibration aided etching in CrO 3 -HF-H 2 O based solution was employed to reveal threading dislocations on the heterostructure surfaces. AFM measurements of surface morphology of the structures revealed a well-resolved cross-hatch pattern, which reproduced the network of underlying misfit dislocations, and, in addition, the outcrops of threading dislocations on the surface in a form of characteristic craters. Analysis of the results allowed drawing a conclusion on the mechanism of misfit strain relaxation in the investigated heterostructures.