Снижение плотности дислокаций в метаморфных гетероструктурах путем оптимизации конструкции буферного слоя с нелинейным профилем изменением состава

Abstract

Equilibrium distributions of misfit dislocation density along the growth direction of metamorphic buffer layers InxAl1-xAs/GaAs with maximum In content xmax ≥ 0.77 and different non-linear graded composition profiles (x ∝ z1/n) are calculated. The effect of the initial In composition (xmin) of InxAl1-xAs buffer layer with convex-graded (n = 2) composition profile on misfit dislocation density as well as amount of residual stresses at its top part is considered. Using computational approach, it was shown that a dislocation-free region is formed under thin tensile-strained GaAs layer (1–10 nm) inserted into InAlAs metamorphic buffer layer, which agrees with experimental data obtained early by transmission electron microscopy. Novel non-linear graded composition profile of metamorphic buffer layer has been proposed, which results in twice reduction of misfit dislocation density as compared to the convex-graded one. In addition, equilibrium distributions of misfit dislocation density in the HEMT heterostructures with two-dimensional electron channel In0.75Ga0.25As/In0.75Al0.25As, which are based on InxAl1-xAs/GaAs metamorphic buffer layer of various designs, are calculated. The values of inverse steps (∆), representing the difference between the maximum In content of InxAl1-xAs (xmax) and In content of In0.75Al0.25As virtual substrate, at which relaxation of the elastic strains in 2D channel In0.75Ga0.25As/In0.75Al0.25As doesn’t occur, are calculated for metamorphic buffer layers InxAl1-xAs with convex-graded and optimized non-linear graded composition profiles.