Antiphase Boundaries In GaAs Research Articles

Formation Energies of Antiphase Boundaries in GaAs and GaP: An ab Initio Study

Electronic and structural properties of antiphase boundaries in group III-V semiconductor compounds have been receiving increased attention due to the potential to integration of optically-active III-V heterostructures on silicon or germanium substrates. The formation energies of {110}, {111}, {112}, and {113} antiphase boundaries in GaAs and GaP were studied theoretically using a full-potential linearized augmented plane-wave density-functional approach. Results of the study reveal that the stoichiometric {110} boundaries are the most energetically favorable in both compounds. The specific formation energy γ of the remaining antiphase boundaries increases in the order of γ{113} ≈ γ{112} < γ{111}, which suggests {113} and {112} as possible planes for faceting and annihilation of antiphase boundaries in GaAs and GaP.

A study of the evolution process of antiphase boundaries in GaAs on Si

A study by high resolution electron microscopy and conventional transmission electron microscopy of the process of closure of antiphase boundaries (APB) in atomic layer molecular beam epitaxy (ALMBE) grown GaAs on silicon is reported. A parallelepipedical shape, closed at the top by another boundary with a semispheric shape, is proposed for the during growth suppressed APBs in GaAs epilayers. Antiphase boundaries are mostly located in {100} plans. Sixty degree dislocations are involved in the process of bending of APBs from {110} to {11n} planes; this bending is the initial step which must take place to get a single domain by interaction of two APBs. The proposed shape for closed APBs is in good agreement with the quasi two-dimensional growth observed for GaAs grown on silicon by ALMBE.

Experimental evidence of the structure of annihilation of antiphase boundaries in GaAs on Si

A high-resolution electron microscopy (HREM) study on antiphase boundaries in GaAs grown on Si is presented. HREM images of two close antiphase boundaries appearing mainly on the {110} planes which abruptly disappear suggest some ideas on the mechanisms of annihilation of these defects.

Energetics of antiphase boundaries in GaAs.

Structural energies of antiphase boundaries in GaAs are studied theoretically using a pseudopotential density-functional approach. The formation energy is calculated for several antiphase boundaries having different orientation and stoichiometry. The lowest-energy (110) and (001) boundaries are predicted to be stoichiometric (having no net excess of As or Ga atoms at the interface), while the (111) antiphase boundary is predicted to be nonstoichiometric. The (110) boundary has the lowest formation energy per unit area of those studied. Simple models of the energetics are discussed and compared with the first-principles results. Simple wrong-bond counting is found to be grossly inadequate. An extended model of pair interactions involving a Madelung sum for distant neighbors is formulated and found to give a reasonable description of stoichiometric antiphase boundaries. Nonstoichiometric antiphase boundaries require special treatment, as they generally have a partially filled donor or acceptor band and should be treated as metallic.

A quantitative analysis of strong-beam α fringes from {110} antiphase boundaries in GaAs

Abstract The reliability of a quantitative comparison of contrast between experimental and simulated strong-beam transmission electron microscope images depends on an accurate determination of a number of parameters. It is shown that, by recording simultaneous bright-field and dark-field images, the main sources of uncertainty in such an analysis, namely the crystal potential and the absorption parameter, can be reduced substantially. This technique has been employed in order to determine the rigid-body translation across {110} antiphase boundaries in GaAs, by analysis of strong-beam α fringes.

Rigid-body translation and bonding across {110} antiphase boundaries in GaAs

A transmission-electron-microscope strong-beam technique is used to investigate the rigid-body translation across {110} antiphase boundaries in GaAs. The results show a translation in the 〈001〉 direction parallel to the plane of the boundary. The magnitude of the translation is determined, and the antisite bond lengths are discussed in terms of the tetrahedral radii of Ga and As. Given this knowledge of the rigid-body translation, the absolute polarity of a GaAs grain can be determined immediately from a bright-field image of the {110} antiphase boundary.

The determination of the rigid-body translation across anti-phase boundaries in GaAs

The growth of a polar material on a non-polar substrate leads to the possibility of anti-phase boundary (APB) formation. Across the boundary there will be bonding between like atoms. The stoichiometry of the material may, or may not, be affected, depending on the relative proportion of A-A and B-B bonds in the boundary. This will depend on the crystallographic orientation of the boundary plane. Because of the different nature of the bonding at an APB, it has been assumed that the physical properties, particularly the electrical characteristics, of the polar layer will be adversely affected by the presence of APBs. Much effort has therefore gone into the development of growth conditions which minimize the likelihood of APB formation, particularly in the GaAs on Si system.Little work, however, has been done on the fine-structure of the APB itself. In this paper the results of a quantitative comparison of the α fringes produced in 2-beam images of APBs, with calculated images will be presented. The theoretical images were calculated using the COMIS program, which uses a manybeam formalism based on the Howie-Whelan equation. The samples were prepared from GaAs epilayers deposited on a (100) Ge substrate. The Ge substrate was removed by mechanical polishing prior to ion milling of the epilayer in a liquid nitrogen cooled specimen stage. The epilayer was examined at a number of low index zone axes, using a number of different 2-beam conditions. A representative selection is shown in figure 1. Images A, B, and C, were obtained close to the [001] zone axis, image D was obtained near the [101] zone axis and shows the horizontal APB nearly flat-on, but out of contrast. Near the [101] zone axis this APB appears as a line defect, and therefore must lie on the (101) plane.

Determination of the lattice translation across antiphase boundaries

This paper describes a method for quantitative comparisons of electron microscope bright-field images with computer-simulated images. The applicability of the technique is demonstrated by preliminary investigations of the rigid-body lattice translation across antiphase boundaries in GaAs and β-SiC.

On the use of convergent-beam electron diffraction for identification of antiphase boundaries in GaAs grown on Si

Dynamical coupling effects between the (200) reflection and weak odd-index reflections in the Bragg position in convergent-beam diffraction patterns has been used to detect antiphase boundaries (APBs) in GaAs grown on (001) Si. It was shown that APBs lie in most cases on energetically favorable {110} planes and effectively stop the propagation of dislocations, twins and stacking faults. The formation of APBs is promoted by Si surface contamination and irregularities.

Lattice imaging of antiphase boundaries in GaAs grown on Si

The growth of GaAs on Si has been recognized as a highly desirable technology goal for a number of years. However, the large lattice misfit between GaAs and Si and the problem of growing a polar crystal on a nonpolar substrate can result in a high density of lattice defects, including antiphase disorder. At an antiphase boundary (APB) the Ga-As bonds are replaced by As-As and Ga-Ga bonds. It is expected that APBs can be highly charged, and they might collect charged impurities unless alternating As-As and Ga-Ga bonds are so close that they can neutralize each other. APBs can result from the coalescence of GaAs domains independently nucleated on the Si substrate. This can occur due to a single step or an odd number of (a/4) Si surface steps, or when the coalescing domains have grown so that one domain starts with a Ga layer and the other domain starts with an As layer.

Faceted antiphase boundaries in GaAs grown on Ge

Interest has recently increased in the possibility of growing III-V compounds epitactically on non-polar substrates to produce device quality material. Antiphase boundaries (APBs) may then develop in the GaAs epilayer because it has sphalerite structure (face-centered cubic with a two-atom basis). This planar defect may then influence the electrical behavior of the GaAs epilayer. The orientation of APBs and their propagation into GaAs epilayers have been investigated experimentally using both flat-on and cross-section transmission electron microscope techniques. APBs parallel to (110) plane have been viewed at the atomic resolution and compared to simulated images.Antiphase boundaries were observed in GaAs epilayers grown on (001) Ge substrates. In the image shown in Fig.1, which was obtained from a flat-on sample, the (110) APB planes can be seen end-on; the faceted APB is visible because of the stacking fault-like fringes arising from a lattice translation at this interface.

Antiphase boundaries in GaAs

Antiphase boundaries in GaAs have been produced by growing the GaAs on {001} Ge substrates. The GaAs was grown by the technique of organometallic vapor phase epitaxy to a thickness in excess of 1 μm. The antiphase boundaries are shown to be faceted with facets parallel to the {110} planes being particularly common. The rigid-body translation at the different facet planes is shown to be small for the {110} planes but it can be large for other facet planes.

DEFECTS IN GaAs GROWN ON Ge SUBSTRATES

AbstractThe growth of polar semiconducting materials on non-polar semiconducting substrates is illustrated by experimental observations of GaAs grown on Ge substrates and on Ge epilayers which had been grown on Si substrates. The GaAs epilayers are grown in each case by metal-organic, vapor-phase deposition. The GaAs/Ge heterophase junction, the grain boundaries in GaAs grown on {110} Ge and on {001} Ge/Si composit substrates and the anti-phase boundaries in GaAs grown on {001} Ge substrates are eat.h illustated. The interfaces have been studied by transmission electron microscopy and reveal the pronounced faceting of the anti-phase boundaries in GaAs. Also demonstrated experimentally is the strong interaction between dislocations/grain boundaries and these anti-phase boundaries.