X-RAY DIFFRACTION MEASUREMENT OF SEGREGATION-INDUCED INTERFACE BROADENING IN INXGA1-XAS/GAAS SUPERLATTICES

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 A, each with nominally 10-A-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 A. 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 A 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 A for the InGaAs layers and 2.0–3.0 A for the GaAs layers.