Investigation of residual dislocations in VGF-grown Si-doped GaAs (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.
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.
Optimization of VGF-growth of GaAs crystals by the aid of numerical modelling
Journal of Crystal Growth, 2002
The VGF growth of Si-doped GaAs crystals is improved considerably by optimizing the design of the crucible support and the temperature profile during the growth run. Inverse simulation with the software program CrysVUN++ was used for this procedure. The criteria for the optimized conditions are flat phase boundaries and low thermal stress during the whole growth run. The crystals which were grown according to the simulated conditions indeed showed flat phase boundaries and a very low EPD (o100 cm À2 ) within the whole crystal. It is shown that the growth conditions in the seed well and conical part of the crystal have a major influence on the dislocation density in the whole crystal. r (G. M . uller). 0022-0248/02/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 -0 2 4 8 ( 0 1 ) 0 2 3 2 4 -7 G. M . uller, B.
Prediction of dislocation generation during Bridgman growth of GaAs crystals
Journal of Crystal Growth, 1992
Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.
Dislocation multiplication in GaAs : inhibition by doping
Revue de Physique Appliquée, 1989
L'amélioration de la qualité cristalline par dopage électrique ou isoélectronique des cristaux de GaAs obtenus par la méthode L.E.C. est reliée aux modèles thermoélastiques donnant les contraintes en cours de croissance. On en déduit les structures de dislocations dans les cristaux bruts de croissance et recuits, en particulier A la lumière des r6sultats de d6formation plastique. L'addition de diff6rents éléments des colonnes II-III-IV-V-VI dans GaAs est envisagée et son influence sur les mécanismes d'établissement de la sousstructure de dislocations est discutée.
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.
The effect of dislocation core structure on the plastic and fracture behavior of GaAs and InP
Physica Status Solidi (c), 2005
The core of non-screw dislocations in compound semiconductors of, say, the type AB, consists of either all A atoms or all B atoms. These dislocations, known as α and β dislocations, have very different properties including different mobilities, with the difference increasing with decreasing temperature. The different core nature of α and β dislocations affects the mechanical properties of compound semiconductors, including their plastic and fracture behavior. In this paper, we report on an investigation of the mechanical properties of two compound semiconductors, GaAs and InP. The measurements include the brittle-to-ductile transition temperature, determined by 4-point bend tests, as well as indentation plasticity and fracture. The results of subsequent TEM investigation of the configuration and core nature of dislocations in GaAs will also be reported. The observed asymmetries in the plastic and fracture behavior of the two crystals are interpreted and discussed in terms of the different core nature of dislocations. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Journal of Applied Crystallography, 2001
By means of a heat treatment that was part of a molecular beam epitaxy (MBE) growth procedure, dislocation bundles have been induced in two-inch-diameter undoped (001) GaAs substrates. On the basis of contrast variations in synchrotron-based single-crystal X-ray transmission topograms that were recorded under conditions of high anomalous transmission, these dislocation bundles have been classified into three different types. Dislocation bundles of the majority type start at the sample edges in regions around the four 〈100〉 peripheral areas, glide typically up to about 1.5 cm into the bulk of the wafer following perpendicular 〈110〉 line directions, and form a pseudo-symmetric fourfold set. There are dislocations with two different Burgers vectors in each majority-type dislocation bundle and the extended segments of all of these dislocations are of the 60° type. In order to explain complementary experimental results, it is suggested that dislocation pairs are formed in the majority-ty...