Dislocations In Gallium Arsenide Research Articles

Finite element modeling of dislocation reduction in GaAs and InP single crystals grown from the VGF process

Dislocations in gallium arsenide (GaAs) and indium phosphide (InP) crystals are generated by thermal stresses induced during their solidification process of crystal growth. High dislocation density in these crystals will reduce the performance and reliability of the GaAs- and InP-based microelectronic and photonic devices/circuits. It has been known that doping impurity atoms into GaAs and InP crystals during their solidification process can significantly reduce dislocation densities generated in these crystals. A viscoplastic constitutive equation that couples a microscopic dislocation density and impurity atoms with a macroscopic plastic deformation is employed in a transient finite element model for predicting the dislocation density generated in the undoped and doped GaAs and InP crystals grown by the vertical gradient freeze (VGF) process. The effects of crystal growth parameters (i.e., imposed temperature gradient, crystal diameter, and crystal growth rate) on dislocation generation are also investigated. The numerical results show that doping impurity can significantly reduce the dislocation density generated in these crystals. It also shows that dislocation density reduces drastically as the crystal diameter and imposed temperature gradient decrease, but the crystal growth rate has almost no effect on dislocation generation in these crystals.

Finite element simulation of dislocation generation in doped and undoped GaAs single crystals grown from the melt

Dislocations in gallium arsenide (GaAs) single crystals are generated by excessive stresses that are induced during the crystal growth process, and the fabrication and packaging of microelectronic devices/circuits. The presence of dislocations has adverse effects on the performance, lifetime and reliability of the GaAs-based devices/circuits. It is well known that dislocation density can be significantly reduced by doping impurity atoms into the GaAs crystal and/or decreasing the thermal stresses in the crystal during its growth process. A transient finite element model is developed to simulate the dislocation generation in GaAs crystals grown from the melt. A viscoplastic constitutive equation that couples a microscopic dislocation density with a macroscopic plastic deformation is employed to formulate this transient finite element model, where the dislocation density is considered as an internal state variable and the doping impurity is represented by a drag-stress in this constitutive model. GaAs single crystals grown by the vertical gradient freeze process are adopted as an example to study the influences of doping impurity on dislocations generated in the grown crystal. The calculated results show that doping impurity can significantly reduce dislocation generation and produces low-dislocation GaAs crystals.

Why are arsenic clusters situated at dislocations in gallium arsenide?

The interaction of arsenic with dislocations in gallium arsenide has been studied. By performing molecular dynamics simulations with a Tersoff-type interaction potential and simulating the microscopic diffusion–drift–aggregation process based on the kick-out mechanism, we obtained that arsenic clusters are preferably situated at dislocations from energetic and kinetic reasons. This formation of arsenic clusters explains why the radius of the cylinder with an increased free electron concentration around dislocations in n-type sulfur-doped gallium arsenide extends up to about 10 μm, as revealed by Raman scattering.

Microscopic structure of the 90° and 30° partial dislocations in galliumarsenide

We performed a theoretical investigation on the atomic structure of {111} glidepartial dislocations in gallium arsenide. The calculations were carried out using abinitio total energy methods, based on the density functional theory and thepseudopotential model. We addressed the microscopic structure of the 90° partialand the 30° partial dislocations. Our results show that the atomic configurations ofthe dislocation cores are similar to those proposed for the same dislocations innon-polar semiconductors. For the 90° partial, the double-period reconstruction isenergetically more favourable than the single-period reconstruction. In addition,we computed the interaction of intrinsic defects with the dislocation cores.

Synchrotron X-ray topography of electronic materials.

Large-area transmission, transmission section, large-area back-reflection, back-reflection section and grazing-incidence topography are the geometries used when recording high-resolution X-ray diffraction images with synchrotron radiation from a bending magnet, a wiggler or an undulator of an electron or a positron storage ring. Defect contrast can be kinematical, dynamical or orientational even in the topographs recorded on the same film at the same time. In this review article limited to static topography experiments, examples of defect studies on electronic materials cover the range from voids and precipitates in almost perfect float-zone and Czochralski silicon, dislocations in gallium arsenide grown by the liquid-encapsulated Czochralski technique, the vapour-pressure controlled Czochralski technique and the vertical-gradient freeze technique, stacking faults and micropipes in silicon carbide to misfit dislocations in epitaxic heterostructures. It is shown how synchrotron X-ray topographs of epitaxic laterally overgrown gallium arsenide layer structures are successfully explained by orientational contrast.

Effects of doping impurity and growth orientation on dislocation generation in GaAs crystals grown from the melt: A qualitative finite-element study

Dislocations in gallium arsenide (GaAs) crystals are generated by excessive thermal stresses induced during the crystal growth process. The presence of dislocations has adverse effects on the performance and reliability of the GaAs-based devices. It is well known that dislocation density can be significantly reduced by doping impurity atoms into a GaAs crystal during its growth process. A viscoplastic constitutive equation that couples the microscopic dislocation density with the macroscopic plastic deformation is employed in a crystallographic finite element model for calculating the dislocation density generated in the GaAs crystal during its growth process. The dislocation density is considered as an internal state variable and the drag stress caused by doping impurity is included in this constitutive equation. A GaAs crystal grown by the vertical Bridgman process is adopted as an example to study the influences of doping impurity and growth orientation on dislocation generation. The calculated results show that doping impurity can significantly reduce the dislocation density generated in the crystal. The level of reduction is also influenced by the growth orientation during the crystal growth process.

Observation of defects in crystal surface layers by grazing-incidence diffraction X-ray topography

Threading dislocations in gallium arsenide and point defects in silicon were observed for the first time by X-ray topography under grazing-incidence diffraction conditions. A new type of contrast on polished surfaces has been resolved for single crystals with defects. The characteristics of grazing-incidence diffraction topography are discussed.

EBIC contrast study of the recombination mechanism at dislocations in GaAs

AbstracL The energy bands associated with dislocations in gallium arsenide create, even in the space charge region (SCR) of a Schottky diode, electric fields which can cancel the Schottky field near the dislocation line. Therefore, minority carriers created in these regions recombine at the dislocation line, giving rise to an EBIC contrast. Solution of Poisson's equation allows us to determine the variation of the dislocation capture radius with depth in the SCR, and to obtain a quantitative estimate of the EBIC contrast. The theoretical results in which saturation effects can be introduced are compared with experimental ones obtained on both a and fl dislocation types. This comparison leads us to conclude that the saturation effect is not efficient in GaAs, and we suggest that it is probably cancelled by a current flowing along the dislocation line.

Experimental evidence for creation of luminescence quenching localized defects by moving dislocations in gallium arsenide

The production of luminescence quenching localized defects by moving dislocations in GaAs plastically deformed at 350 °C has been established by low-temperature (80 K) band-edge cathodoluminescence (CL) and chemical etch-pit studies. Specimens were deformed to two levels, (1) measurable macroscopic plastic deformation, and (2) 20% of the stress applied in (1). It was established by CL and chemical etching that numerous dislocations were generated on the four {111} stressed slip planes of the macroscopically deformed specimen. Uniform bands of reduced CL signal were correlated to bands of enhanced etching in the lightly deformed samples. It was established from the etching and CL images that these bands are not produced by deformation-induced dislocations but must consist of numerous localized luminescence quenching (Refs. 1–3) defects (e.g., point defects and small dislocation loops) created by the passage of dislocations.

Structure and energy level calculations of dislocations in gallium arsenide

Abstract The geometry of dislocations in the sphalerite structure is described and illustrated. Particular attention is given to the dissociated set of dislocations. Calculations of the energy levels of the 30° and 90° glide partials are made using a tight-binding Hamiltonian and a supercell containing a pair of dislocations of opposite sign. Two sets of parameters describing the Hamiltonian are used. Several models of the core structure of each partial are analysed. The results suggest that, at low temperature, core reconstructions occur leading to full bands separated from empty ones. These conclusions are compared with experimental results based on electrical, photo-conductivity, and particularly, velocity measurements on doped plastically deformed gallium arsenide. In general, the agreement between the theoretical results and experiments is satisfactory.

Arsenic precipitation at dislocations in GaAs substrate material

High-resolution diffraction utilizing an analytical electron microscope has been employed to identify small (∼500 Å-diam) precipitates attached to line dislocations in gallium arsenide. The results show that the precipitates consist of crystallites of elemental hexagonal arsenic embedded within the gallium arsenide matrix. Precipitates were observed in a range of semi-insulating, p-type, and n-type material and were not dependent on the presence of specific additional dopants for their occurrence. The way in which the particles may originate is discussed.

Dislocation states in gallium arsenide

Abstract The continued fraction method is used to study the electronic states associated with the 60° dislocations in gallium arsenide. Details of the cation and anion dislocation bands are given and the effects of the net dislocation core charge on the states emphasized.

Electronic States Associated with 60° Dislocations in Gallium Arsenide

Electronic States Associated with 60° Dislocations in Gallium Arsenide

The optimum choice of reflexion to reveal dislocations in gallium arsenide by X-ray reflexion topography

Single-crystal reflexion topographs from various planes in gallium arsenide are presented and the contrast is compared, in some cases, with double-crystal topograph equivalents. Theory is presented to explain the numerous effects observed but principally the lack of contrast when the absorption distance is small. This aspect of reflexion theory is combined with an evaluation of the effective tilt round a dislocation at various depths below the surface. Tables are also presented giving good and bad choices of reflecting planes for single-crystal topography in gallium arsenide.

Développements d'une technique de topographie en réflexion des rayons X

An X-ray reflexion topography camera has been designed to study structural defects near the surface of monocrystalline semiconductors. Large surfaces can be covered by means of successive fixed exposures. A surface of 30 mm x 10 mm for example can be studied in less than ten minutes on nuclear emulsions. The conditions for the observations of dislocations in gallium arsenide have been examined: the choice of reflecting planes is limited by the depth of penetration of X-rays, so that the effective crystal thickness must be of the order of the width of a dislocation image (2-5 microns). Studies to which these observations can be applied are numerous: structural defects induced by diffusion, lattice strains, orientation of dislocations near the surface, structural evolution of silicon during integrated circuits elaboration, structure of cleavage surfaces, lapping and polishing defects, structural defects of epitaxic layers.