X-ray diffraction θ-2θ scans and kinematical simulations were used to study the composition modulation in coherently strained ten period InxGa1-xAs/GaAs superlattices grown by molecular beam epitaxy (MBE). Superlattice periods (Λ) were 34.5, 55.0, and 92.0 Å, each with nominally 10-Å-thick In0.5Ga0.5As layers. Simulations using exponential In composition modulations, as expected due to In segregation during MBE growth, produced the best fits to the experimental data. The measured 1/e segregation lengths ranged from 11 to 16 Å. Since this distance was larger than the InGaAs layer thickness, the maximum In concentration reached in the samples was only x ≈0.20-0.25. For the Λ= 34.5 Å sample, since the GaAs layer was also thin, the composition modulation varied with each period of the superlattice. The simulation also showed layer thickness fluctuations which varied from 1.0 to 2.0 Å for the InGaAs layers and 2.0-3.0 Å for the GaAs layers.
ASJC Scopus subject areas
- Physics and Astronomy(all)