High resolution x-ray diffraction analysis of Si/GaAs superlattices

Abstract

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.

Stability of GaAs/Si Superlattices During MBE Growth and Post-Growth Annealing

“…In addition, the integrity of the GaAs grown on the pseudomorphic silicon can be questioned, due to the differences in crystal symmetry and surface chemistry. Previous work on GaAs/Si superlattices has also shown a degradation with a decreasing growth rate [4]. In particular, they observed a decrease in structural perfection with decreasing growth rate, presumably due to an increase in the number of (three dimensional) GaAs islands on the CaF 2 surface with increasing Ga flux [7].…”

“…Recently a number of groups have reported the successful molecular beam epitaxy (MBE) growth of superlattices consisting of thin (< 5A) layers of pure silicon alternating with thicker layers of GaAs [3][4][5]. X-ray rocking curves from these superlattices typically exhibit narrow satellite reflections; satellites out to the twenty-second order have been observed, indicating a high level of structural perfection [4].…”

“…X-ray rocking curves from these superlattices typically exhibit narrow satellite reflections; satellites out to the twenty-second order have been observed, indicating a high level of structural perfection [4]. Independent analysis by reflection high energy electron diffraction (RHEED) [3,4] and Raman spectroscopy [5] suggested that the silicon was present as continuous, pseudomorphic layers. Given that the silicon layers are extremely thin, it is natural to speculate on their stability during the epitaxial growth process or during post-growth processes such as rapid thermal annealing.…”

High Resolution X-ray Scattering Methods For ULSI Materials Characterization

“…Figure 8 shows a (004) Si/GaAs superlattice grown on GaAs [12]. Due to the lattice mismatch between the two materials, the silicon layers had to be kept very thin (~3Å) while the GaAs layers could be thicker (336Å in this case).…”

“…Strained layer growth showing an independent substrate and layer (left), a layer/substrate system transitioning from fully strained to fully relaxed (center), and the effect of tilt and shear distortions (right).Rocking angle (arcseconds) Double axis rocking curve from a 10-period Si/GaAs superlattice[12].…”