R. J. Matyi

Fundamental issues in heteroepitaxy---A Department of Energy, Council on Materials Science Panel Report

During the past decade, nonequilibrium techniques have been developed for the growth of epitaxial semiconductors, insulators, and metals which have led to new classes of artificially structured materials. Structures can now be grown which present the materials scientist with systems that exhibit new properties and demonstrate new physical concepts. For example, quantum-well structures with molecular dimensions give rise to new phenomena resulting from quantum mechanical effects. Layered structures with periodicity of a few atomic layers result in coherent behavior for long-range interactions such as magnetism in metallic systems. Metastable structures can be generated which possess important properties not present in equilibrium systems. Studies of these materials are leading to significant advances in our basic understanding of the physics of materials as well as to important new technologies. Despite the rate of progress and the large number of laboratories throughout the world with active programs in various aspects of epitaxial growth, our current understanding of the processes which control growth at a fundamental, atomic level is remarkably primitive. Much of the work to date has been driven by the motivation to produce high quality materials for high performance electronic devices. As a result, most of the effort in epitaxial materials hasmorexa0» concentrated on semiconductors, particularly GaAs and related compounds.«xa0less

Development of a glass-bonded compliant substrate

Abstract The critical thickness limitation for lattice-mismatched heteroepitaxial growth could potentially be removed by the use of a compliant substrate. This work presents initial results for the development of a compliant substrate consisting of a ∼10xa0nm GaAs layer (template layer) bonded to a GaAs “handle wafer” through a borosilicate-glass. The glass concentration is chosen to have a moderate viscosity at the temperature used during lattice-mismatched growth. Compliant substrates using 30 and 50xa0mol% B 2 O 3 glass as the bonding layer were used in the growth of 2xa0μm of In 0.40 Ga 0.60 As (∼3.1% lattice mismatch to GaAs). X-ray diffraction demonstrated that epitaxy was achieved between the growth and template layer. Optical microscopy, atomic force microscopy, and scanning electron microscopy were also used to characterize both the initial borosilicate-glass-bonded compliant substrate as well as the grown structures.

Vapor Growth and Characterization of Cr-Doped ZnSe Crystals

Abstract Cr-doped ZnSe single crystals were grown by a self-seeded physical vapor transport technique in both vertical (stabilized) and horizontal configurations. The source materials were mixtures of ZnSe and CrSe. Growth temperatures were in the range of 1140–1150°C and the furnace translation rates were 1.9–2.2xa0mm/day. The surface morphology of the as-grown crystals was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different features of the as-grown surface of the vertically and horizontally grown crystals suggest that different growth mechanisms were involved in the two growth configurations. The [Cr] doping levels were determined to be in the range of 1.8–8.3×10 19 xa0cm −3 from optical absorption measurements. The crystalline quality of the grown crystals were examined by high-resolution triple-crystal X-ray diffraction (HRTXD) analysis.

High resolution x‐ray diffraction analysis of annealed low‐temperature gallium arsenide

High resolution x‐ray diffraction methods have been used to characterize GaAs grown at low substrate temperatures by molecular beam epitaxy and to examine the effects of post‐growth annealing on the structure of the layers. Double crystal rocking curves from the as‐deposited epitaxial layer show well‐defined interference fringes, indicating a high level of structural perfection despite the presence of excess arsenic. Annealing at temperatures from 700 to 900u2009°C resulted in a decrease in the perpendicular lattice mismatch between the GaAs grown at low temperature and the substrate from 0.133% to 0.016% and a decrease (but not total elimination) of the visibility of the interference fringes. Triple‐crystal diffraction scans around the 004 point in reciprocal space exhibited an increase in the apparent mosaic spread of the epitaxial layer with increasing anneal temperature. The observations are explained in terms of the growth of arsenic precipitates in the epitaxial layer.

Effect of reactor geometry and growth parameters on the uniformity and material properties of GaNsapphire grown by hydride vapor-phase epitaxy

Abstract The effects of flow rate variation and geometry on the growth rate, growth uniformity and crystal quality were investigated in a horizontal gallium nitride vapor-phase epitaxy reactor. The effects of these parameters, were studied through the comparison of numerical model predictions to experimentally observed values. Gas-phase reactions between Groups III and V sources and deposition of material on the wall are shown to lead to reduced overall growth rates and may be responsible for inferior crystal quality. A low ammonia concentration is correlated with the deposition of polycrystalline films. A low V III ratio and ammonia concentration lead to inferior crystalline quality and increased yellow luminescence. An optimum HVPE growth process requires selection of reactor geometry and operating conditions to minimize gas-phase reactions and wall deposition while providing a uniform reactant distribution across the substrate.

INGAAS HETEROEPITAXY ON GAAS COMPLIANT SUBSTRATES : X-RAY DIFFRACTION EVIDENCE OF ENHANCED RELAXATION AND IMPROVED STRUCTURAL QUALITY

In0.44Ga0.56As (3% mismatch) films 3 μm thick were grown simultaneously on a conventional GaAs substrate, glass-bonded GaAs compliant substrates employing glasses of different viscosity, and a twist-bonded GaAs compliant substrate. High-resolution triple-crystal x-ray diffraction measurements of the breadth of the strain distribution in the films and atomic force microscopy measurements of the film’s surface morphology were performed. The films grown on the glass-bonded compliant substrates exhibited a strain distribution whose breadth was narrowed by almost a factor of 2 and a surface roughness that decreased by a factor of 4 compared to the film simultaneously grown on the conventional substrate. These improvements in the film’s structural quality were observed to be independent of the viscosity of the glass-bonding media over the range of viscosity investigated and were not observed to occur for the film grown on the twist-bonded substrate.

Triple crystal x‐ray diffraction analysis of chemical‐mechanical polished gallium arsenide

High‐resolution triple crystal x‐ray diffraction has been used to monitor the magnitude of diffuse scattering from chemical‐mechanical (CM) polished GaAs. The diffuse scattering, which is attributed to kinematic scattering arising from polish‐induced crystallographic defects, was found to be only slightly affected when each of four CM polish parameters (bromine concentration in Br2/methanol, total polish time, polish pad rotation speed, and force on sample) was varied individually. The combined effect of increases in both the pad rotation speed and the force on the sample increased the magnitude of the diffuse scattering, suggesting the generation of mechanical damage. When all four variables were increased to their maximum values, the diffuse scattering increased dramatically and became anisotropic. We have expressed the magnitude of the diffuse scattering in terms of an ‘‘excess intensity’’ in reciprocal space to provide a semi‐quantitative relation between CM polish parameters and the generation of pol...

Experimental test for elastic compliance during growth on glass-bonded compliant substrates

Highly mismatched films (In0.44Ga0.56As, 3% mismatch) grown well beyond their critical thickness (to 3 μm) on GaAs glass-bonded compliant substrates exhibit surfaces four times smoother and strain distributions twice as narrow as films grown simultaneously on conventional GaAs substrates. The compliant substrates consist of a thin (∼10 nm) GaAs template layer bonded via a borosilicate glass to a mechanical handle wafer. The improvement of highly mismatched films grown well beyond their critical thickness on compliant substrate structures is commonly modeled in terms of an elastic partitioning of strain from the film to the thin (∼10 nm) single-crystal template layer. The present study is a direct test for this mechanism of elastic compliance. A comparison is reported of the strain in 92 nm In0.09Ga0.91As films and 76 nm In0.03Ga0.97As films grown simultaneously on conventional GaAs substrates and the compliant substrates responsible for the improved structural quality of In0.44Ga0.56As films. Elastic part...

Growth of Si/GaAs superlattices by molecular beam epitaxy

The growth and characterization of a ten period silicon/GaAs superlattice by molecular beam epitaxy is described. Reflection high energy electron diffraction of the surface reconstruction during growth of the GaAs layers showed the (4×2)→(3×2) →(3×1)→(2×4) sequence reported previously for GaAs grown on pseudomorphic silicon, although the intermediate stages were much more persistent than previously reported. X‐ray diffraction revealed satellite peaks clearly visible out to the fourth order, indicating a high degree of structural perfection. Comparison of the experimental diffraction profile and that obtained using a dynamical diffraction simulation yielded average layer thicknesses of 440 and 2.7 A for the GaAs and silicon layers, respectively. Excellent agreement between the experimental and the simulated profiles was observed.

Characterizations of ZnSe single crystals grown by physical vapor transport

Abstract ZnSe bulk crystals were grown by self-seeded physical vapor transport technique in horizontal and vertical configurations. The impurities and defects in the grown crystals were studied by glow discharge mass spectroscopy (GDMS) and low-temperature photoluminescence (PL) measurements. The PL results on the starting material and the grown crystals are consistent with the low impurity levels measured by GDMS. The crystalline quality of the grown crystals was examined by synchrotron white beam X-ray topography (SWBXT) and high-resolution triple X-ray diffraction (HRTXD). The SWBXT shows that, aside from twins, the overall crystalline quality of the vapor-grown ZnSe crystals, especially in the contactless grown region, was quite high. The HRTXD results are in line with the SWBXT findings. The comparison between the HRTXD on a chemical-mechanically polished and a cleaved surface seems to indicate that polishing damage can obscure the true microstructure in the as-grown ZnSe crystals.