Analysis of thermal-treatment-induced dislocation bundles in GaAs wafers by means of X-ray transmission topography and complementary methods (original) (raw)
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Journal of Crystal Growth, 1999
GaAs single crystals (silicon-doped, 2 inch) with extremely low dislocation densities (etch pit density (EPD) 50-1000 cm\) were grown by the vertical gradient freeze method. In these crystals we characterised different types of dislocations by the aid of white beam X-ray diffraction topography and infrared transmission microscopy. It was found for decreasing dislocation densities (EPD(200 cm\), that dislocations having a line vector l, which is parallel to the [0 0 1] growth direction of the crystals, become more and more dominant. These residual dislocations are induced by the seeding process (so far we were using LEC-grown seed crystals). These residual dislocations cannot be avoided by minimising the thermal stress during the crystal growth process.
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.
Synchrotron X-ray topography study of defects in epitaxial GaAs on high-quality Ge
Nuclear Instruments and Methods in Physics Research, 2006
Crystal defects of GaAs thin films deposited by metalorganic vapour phase epitaxy on high-quality Ge substrates are studied by synchrotron x-ray topography. The GaAs thin films were measured to have ≈ 500 dislocations cm −2 , which is a similar number to what plain Ge substrates show. The dislocation densities measured are also smaller than for instance those of high-quality vapour pressure controlled Czochralski grown GaAs wafers, which typically have dislocation densities of ≈ 1500 cm −2. The GaAs films grown on both sides of two-sided substrates display very good crystal quality throughout the sample.
Comparison of Experiments and Theories for Plastic Deformation in thermally processed GaAs Wafers
Crystal Research and Technology, 2000
Different types of dislocation bundles were identified in thermally processed (001) GaAs wafers. Synchrotron based single crystal X-ray transmission topography, scanning infrared polariscopy, visible light interferometry, standard Nomarski microscopy, and Makyoh topography had been applied for this purpose and allowed for a classification of the dislocation bundles into one distinct majority and a generic minority type. The currently accepted theories are briefly discussed and it is shown that their disagreement with the core of the experimental observations is due to oversimplifications. A new theory is finally presented in a concise manner and its excellent agreement with all of the available experimental evidence is demonstrated.
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.
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.
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.
physica status solidi (a), 2005
Dedicated to Professor Horst P. Strunk on the occasion of his 65th birthday PACS 61.72.Ff, 61.72.Lk, 81.05.Ea, 81.10.Fq Bulk GaAs and InP crystals with diameter of 4″ or more can now be grown with very low dislocation densities (EPD considerably below 1000 cm -2 ) using the Vertical Gradient Freeze (VGF) growth technique and rigorous process optimization by the aid of numerical simulation. It turns out that the usually dominating 60°-dislocations are no longer the dominating type if the dislocation density is in the range of EPD = 100 cm -2 or below. The goal of growing large dislocation-free GaAs and InP crystals like Si can only be reached if the types of these "residual dislocations" are identified and their origin is fully understood. This paper therefore reviews the present knowledge about these residual dislocations in GaAs and InP for various dopants.