High-resolution x-ray diffraction has been used to characterize Si/GaAs superlattices grown on GaAs substrates by molecular beam epitaxy. A typical superlattice structure consisted of ten periods of thin (<5 Å) layers of pseudomorphic silicon alternating with thick GaAs layers; typical GaAs thicknesses range from approximately 100 to 1850 Å. X-ray rocking curves showed sharp and intense satellite peaks (out to 22 orders in one case), indicating a high level of structural quality. Excellent agreement has been obtained between the observed diffraction patterns and those calculated via dynamical simulation. Structural models in which the silicon exists as 2.7 Å bilayers with interfacial Si/GaAs alloy transition layers of either monolayer or bilayer thickness fully describes the observed diffraction patterns.
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 Å for the GaAs and silicon layers, respectively. Excellent agreement between the experimental and the simulated profiles was observed.
The growth of high quality Si/GaAs superlattices on GaAs substrates using molecular beam epitaxy is described. A typical superlattice structure consisted of ten periods of thin (<5Å) layers of pseudomorphic silicon alternating with thick GaAs layers; typical GaAs thicknesses range from 100Å to 1850Å. In situ reflection high energy electron diffraction analysis of the structures during growth showed the silicon layers developed a (3 ×1) reconstruction, while the GaAs exhibited a (4×2)→(3×2)→(3×1)→(2×4) reconstruction sequence. Both observations agree with prior studies of the growth of embedded silicon in GaAs/Si/GaAs heterostructures. X-ray diffraction using the (004) reflection showed sharp and intense satellite peaks (out to 22 orders in one case), indicating a high level of structural quality. Very good agreement has been obtained between observed diffraction patterns and those calculated via dynamical simulation.
The stability of GaAs/Si superlattices grown on GaAs substrates using molecular beam epitaxy is described. Typical superlattice structures consisted of ten periods of thin (less than 6.5A thick) layers of pseudomorphic silicon alternating with thick GaAs layers. We have examined the As 2 /Ga flux conditions required for the growth of high quality superlattices and have found that the structural perfection is extremely sensitive to the V/III flux ratio. The best superlattices were grown under condition that were just barely enough arsenic to produce a stable (2 x 4) surface reconstruction in the GaAs layers; increases in the arsenic overpressure resulted in a progressive trend towards 3-D growth of the GaAs on the pseudomorphic Si. In addition, we have examined the stability of GaAs/Si superlattices towards post-growth annealing. Double crystal x-ray diffraction scans showed little change in superlattice structure following rapid thermal anneals at 800°C; at 900'C, however, all but the first order satellite reflections disappeared. We attribute this behavior to the relaxation of pseudomorphic strin and the generation of misfit dislocations at the higher anneal temperature.
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