N. H. Karam

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.

Laser selective deposition of GaAs on Si

GaAs films have been selectively deposited on Si substrates by laser induced chemical vapor deposition. An Ar+ laser was used to provide the required local heating on an otherwise relatively cool substrate to deposit GaAs spots and write GaAs lines. The deposition parameters were adjusted to deposit films with diameters in the range 1.5–500 μm and thicknesses in the range of 200 A to several microns. Optical, chemical, and structural properties of the selectively deposited films have been studied. This technique can have potential applications in integrating optical and electronic devices on Si substrates.

Direct writing of GaAs monolayers by laser‐assisted atomic layer epitaxy

Direct writing of GaAs epitaxial monolayers has been achieved by laser‐assisted atomic layer epitaxy (LALE) technique on GaAs substrates. Sequential exposures of the substrate to trimethylgallium (TMG) and arsine (AsH3) were separated by periods of hydrogen purging to prevent mixing. Laser beam scanning of the samples took place either during the flow of TMG or AsH3. The selectively grown films at the one monolayer per cycle condition have a mirrorlike surface and a flat top thickness profile. LALE has been realized at temperatures as low as 300 °C and over a wide range of TMG flux and laser power densities. Photoluminescence results of the deposited films show that their quality are comparable to those achieved by conventional ALE.

Recent progress in atomic layer epitaxy of III–V compounds

Abstract Atomic layer epitaxy (ALE) has been recently established as a new growth technique which allows control of the growth process at the monolayer level through a self-limiting growth mechanism. We report here on recent progress and current problems facing this technology. Side wall growth by ALE has been demonstrated with deposited structures that differ from conventional chemical vapor deposition growth. Also ALE shows promise in the growth of GaAs on nonpolar substrates such as Ge. The problem of background doping in ALE films will be addressed.

Laser direct writing of single‐crystal III‐V compounds on GaAs

Laser selective chemical vapor deposition and direct writing of GaAs and its ternary alloys with P have been achieved on GaAs substrates. An Ar+ laser is used to locally heat areas where selective deposition is desired on a substrate which is uniformly biased to a temperature in the range of 25–500 °C. Epitaxial growth was achieved by carefully controlling the deposition parameters to reach growth rates low enough, typically 20 A/s, for the reaction kinetics of the pyrolitic process to take place. Cross‐sectional transmission electron microscopy and photoluminescence results indicate that the quality of the deposited material is comparable to that grown with the conventional metalorganic chemical vapor deposition technique.

Low‐temperature (250 °C) selective epitaxy of GaAs films and p‐n junction by laser‐assisted metalorganic chemical vapor deposition

Low‐temperature selective epitaxial growth of device quality GaAs has been achieved by laser‐assisted chemical vapor deposition (LCVD). GaAs substrates thermally biased to temperatures in the range 250–500 °C were irradiated by an Ar ion laser to induce localized deposition of GaAs. Carefully selected growth conditions resulted in growth rates as low as a monolayer per second at 250 °C. This is the lowest substrate temperature for epitaxial GaAs with optical and structural quality comparable to those achieved in conventionally metalorganic chemical vapor deposition grown GaAs. Also reported is the first p‐n junction by LCVD technique using zinc as the p‐type dopant. This new low‐temperature selective deposition process can lead to maskless fabrication of multicomponent devices on the same wafer.

Molecular stream epitaxy of ultrathin InGaAs/GaAsP superlattices

Molecular stream epitaxy allows several molecular beam epitaxy (MBE) concepts to take place in a metalorganic chemical vapor deposition reactor. In this technique, the growth of InGaAs/GaAsP superlattices proceeds by rotating the substrate between two gas streams, one containing trimethylgallium (TMG), triethylindium, and AsH3 and the other containing TMG, PH3, and AsH3. This technique eliminates gas flow transients and provides a method to mechanically shear off the gaseous boundary layer between successive exposures. Ultrathin strained‐layer superlattices (SLS’s) with 8‐A‐thick films have been obtained. The optical properties of these SLS’s are comparable to those obtained for equivalent superlattices by gas source MBE.

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.

Laser Enhanced Selective Epitaxy of ιii-V Compounds

Selective epitaxial growth of III-V compounds based on GaAs has been achieved using Ar + ion laser assisted chemical vapor deposition (LCVD) on GaAs substrates. The growth rate, at carefully selected growth conditions, can be controlled to a few A/s at bias temperatures as low as 250°C by conventional LCVD multi-scan technique. Typical Gaussian thickness profiles are achieved by this growth technique. On the other hand, flat top thickness profiles are achieved with direct writing of GaAs mono-layers by laser assisted atomic layer epitaxy (LALE). X-ray topography is demonstrated as a powerful tool for characterizing the grown films and photoluminescence shows that the quality of the grown films are comparable with those grown by conventional MOCVD or ALE.