Design engineering of non-linear graded InAlAs metamorphic buffer layers for efficient reduction of misfit dislocation density

•Non-linear graded InAlAs buffer is proposed for efficient dislocation reduction.•Metamorphic InAlAs/GaAs structures with optimized graded buffer were grown by MBE.•Impact of highly strained 2–10 nm GaAs layer on dislocation density was studied.•No elastic strains relaxation in virtual substrate at inverse step value 0.75) buffer layer (MBL) grown on GaAs with an optimized non-linear graded composition profile along the growth direction is proposed for enhanced reduction of misfit dislocation (MD) density in highly mismatched III-V/GaAs metamorphic heterostructures. The equilibrium distributions of MD density throughout such InxAl1-xAs/GaAs MBLs are calculated. The influence of the initial composition (xmin) of MBL and the elastically strained thin GaAs layer embedded into the InxAl1-xAs MBL on the MD density distribution was studied. An optimum value of the inverse step (Δ), representing the difference between the top In content of the InxAl1-xAs MBL and that of a In0.75Al0.25As virtual substrate (VS) grown atop is determined. It was theoretically shown that Δ above 0.04 results in relaxation of the elastic stresses in VS via formation of the MDs, while the lower Δ values allow growing the VS completely free of MDs. Finally, the metamorphic In0.75Al0.25As/graded-InAlAs/GaAs heterostructures differing from each other by only the composition profile of the graded-InAlAs MBL were grown by MBE on GaAs(001) and studied by atomic force microscopy. The structure with proposed optimized non-linear graded (x = 0.05–0.77) MBL demonstrated the ∼ 1.5 times less MD density as compared to that with the convex-graded (x = 0.05–0.81) MBL, which was estimated to be at the level of ∼ 2·107 cm−2.