Control of threading dislocations by Al(Ga)InAs reverse-graded buffers grown on GaAs substrates

High-quality strain-relaxed InP layers with undulating step-graded Al(Ga)InAs buffers were grown on GaAs substrates by metal-organic chemical vapor deposition. Transmission electron microscopy, high-resolution electron microscopy (HREM), atom force microscopy, and photoluminescence were carried out to characterize the metamorphic buffers. V-shaped dislocations in [001] Al(Ga)InAs reverse-graded layers were observed by HREM and the behavior of reverse-graded layers was simulated theoretically using analytical models. Both the experimental and theoretical results indicated that the insertion of reverse-graded layers with appropriately designed thicknesses and In grading coefficients promotes the annihilation and coalescence reactions between threading dislocations and reduces threading dislocations density.