Surface morphology evolution in highly mismatched Sb-graded buffer layers on GaAs

Ternary GaAs1−ySby and quaternary Al0.5Ga0.5As1−ySby compositionally step-graded buffer structures graded to a 4.6% mismatch on GaAs were evaluated by transmission electron microscopy. Cross-sectional bright field imaging (g=004) revealed the presence of compositional modulations parallel to the (001) interface with a period of 1–2 nm that were used to establish the morphology of the growth surface during buffer layer deposition. Analysis of the Sb-graded ternary structures shows that the growth surface remained planar with a maximum peak-to-valley height of 4.4±0.6 nm located near the topmost layer. A threading dislocation density of 108–109 cm−2 was measured in both types of buffer layers and an improvement in peak-to-valley amplitude (2.3±0.5 nm vs 4.4±0.6 nm) was observed in the Al-containing quaternary alloys.