J. C. L. Tarn

Interactions of dislocations in GaAs grown on Si substrates with InGaAs‐GaAsP strained layered superlattices

InGaAs‐GaAsP strained‐layered superlattices have been used as a buffer layer to reduce the dislocation density in GaAs grown on Si substrates. These superlattices have been grown lattice matched to GaAs. Several interactions between the strain field of the strained layered superlattice [GaAs1−yPy‐InxGa1−xAs (y=2x)] and the threading dislocations in GaAs/Si are observed. Mixed dislocations are strongly affected by the strain field of the superlattice, however, the interactions with the edge dislocations are less likely to occur. The stress field associated with the strained layered superlattice has a shear component that forces the 60° mixed dislocations to bend at the strained layered superlattice interfaces. Dislocations annihilation or repulsion are observed at the superlattice interfaces.

Effectiveness of strained‐layer superlattices in reducing defects in GaAs epilayers grown on silicon substrates

In GaAs‐GaAsP strained‐layer superlattices grown lattice matched to GaAs are effective buffer layers in reducing dislocations in epitaxial GaAs films grown on Si substrates. The strained‐layer superlattice structure permits high values of strain to be employed without the strained‐layer superlattice generating dislocations of its own. We find that the strained‐layer superlattice buffer is extremely effective in blocking threading dislocations of low density and is less effective when the dislocation is high. It appears that for a given strained‐layer superlattice there is a finite capacity for blocking dislocations. Transmission electron microscopy has been used to investigate the role of the superlattice buffer layer.

Combined effect of strained‐layer superlattice and annealing in defects reduction in GaAs grown on Si substrates

The high defect density in GaAs grown on Si can be reduced by the combined use of the strained superlattices (InGaAs‐GaAsP) and annealing. The strained‐layer superlattice (SLS) bends the dislocations and acts as a medium for dislocations interactions, and annihilations. Highly strained SLS (∼2%) is required to bend the dislocations and keep them bent at the SLS interfaces. The SLS coupled with annealing permits a remarkable reduction of threading dislocation density. Annealing provides the energy for threading dislocations to interact with the SLSs and improves their efficiency significantly.

Observation of antiphase domain boundaries in GaAs on silicon by transmission electron microscopy

Boundaries between different antiphase domains have been unambiguously identified in heteroepitaxial GaAs on silicon substrates by transmission electron microscopy. A simple and reliable method is described for assessing the presence or absence of these domain boundaries in GaAs. The domain size was found to be as small as ∼0.1 μm in GaAs that had been grown on nominal Si(001) in which a buried, implanted oxide had been previously formed. These boundaries are expected to degrade electrical performance and device reliability modify electronic transport and degrade device performance.

Growth of GaAs on High Temperature Hydrogen Pretreated (100) Si Substrates by Molecular Beam Epitaxy

High-quality GaAs epitaxial layers have been grown by molecular beam epitaxy on nominally (100) oriented silicon substrates that were previously annealed in a hydrogen ambient at 1250°C. The growth procedure involves an in situ thermal annealing step after the initial deposition of a thin GaAs buffer layer. Rutherford backscattering and channeling of 2.1 MeV He+ ions, interference optical microscopy, transmission electron microscopy, and X-ray diffraction techniques have been used to characterize these layers. Comparative studies indicate that the epitaxial layers grown on hydrogen-ambient annealed substrates have a superior surface morphology and a lower interface disorder than those on the chemically cleaned nominal silicon (100) substrates. Furthermore, a significant reduction in the density of microtwins is observed in layers grown on the preannealed substrates. This improvement in crystalline quality may be attributed to a lower degree of disorder at the silicon surface that was achieved by high temperature hydrogen-ambient annealing. However, dislocation densities were comparable and the presence of antiphase domain boundaries were observed in both cases.

Defect Reduction in GaAs Epilayers on Si Substrates Using Strained Layer Superlattices

In x Ga1 1-x As-GaAs l-y P y strained layer superlattice buffer layers have been used to reduce threading dislocations in GaAs grown on Si substrates. However, for an initially high density of dislocations, the strained layer superlattice is not an effective filtering system. Consequently, the emergence of dislocations from the SLS propagate upwards into the GaAs epilayer. However, by employing thermal annealing or rapid thermal annealing, the number of dislocation impinging on the SLS can be significantly reduced. Indeed, this treatment greatly enhances the efficiency and usefulness of the SLS in reducing the number of threading dislocations.

Criterion for blocking threading dislocations by strained buffer layers in GaAs grown on Si substrates

An energy model has been used to calculate the minimum critical thickness in strained‐layer superlattices that is required to block threading dislocations. The model calculates the total change in the system energy that results from the presence of a bent dislocation segment at the strained interface. The calculations show that a threading dislocation has to overcome an energy barrier before gliding along the strained‐layer interface becomes favorable. The model predicts that the process of blocking threading dislocations by strained‐layer structures can be thermally activated.

Molecular‐beam epitaxial growth and microstructural characterization of GaAs on Si with a buried implanted oxide

The direct growth of GaAs by molecular‐beam epitaxy on nominally (100)‐oriented silicon with a buried implanted oxide is demonstrated. Nomarski interference contrast optical microscopy, transmission electron microscopy, and Rutherford backscattering techniques have been employed to characterize these layers. The formation of hillocks and a uniform layer of GaAs in the intervening regions between hillocks have been observed. Microtwins and threading dislocations are the predominant defects in these layers. Furthermore, we report the absence of antiphase domain boundaries within the GaAs hillocks.

Comparative studies of defects in GaAs on silicon substrates using electron‐beam‐induced current and transmission electron microscopy

We report the use of electron‐beam‐induced current imaging and transmission electron microscopy techniques to examine defects in heteroepitaxial films of GaAs on Si. The electron‐beam‐induced current method has been successfully applied to obtain dark spot micrographs revealing the distribution of electrically active defects in the GaAs epilayer. Relatively large areas of dark contrast corresponding to regions of high defect density (enhanced recombination) have been identified. In contrast, within the intervening regions between these electrically active centers, areas associated with uniform electrical quality have been observed. Furthermore, in a comparative study of the microstructural character of defects using transmission electron microscopy, we have also identified corresponding regions of high and low defect density. The role of electrically active defects in determining the minority carrier lifetimes and diffusion lengths in the GaAs epilayer is also discussed. Moreover, it has been demonstrated...