Growth of InGaSb/AlInGaSb quantum cascade laser structures on GaSb substrates by molecular beam epitaxy.

• 3 μm-thick InGaSb/AlInGaSb QCL structures grown on GaSb substrates. • An InGaSb composition graded buffer layer used. • Inverted pyramid-shaped defects caused by oxygen. • Threading dislocation density of 1 × 107 cm−2. An InGaSb/AlInGaSb terahertz quantum cascade laser (THz-QCL) structure was grown by molecular beam epitaxy (MBE) on a GaSb substrate with introducing an InGaSb composition graded buffer layer. It was found that the occurrence of inverted pyramid-shaped defects with a size of several micrometers is related to oxygen. The lattice matching condition between InGaSb and AlInGaSb was investigated. We grew a 3 μm-thick In 0.19 Ga 0.81 Sb/Al 0.19 In 0.16 Ga 0.65 Sb THz-QCL active region with a threading dislocation density of ∼ 1 × 107 cm−2. The threading dislocation density remained nearly unchanged after a several-micrometer-thick QCL region. The density of defects of several micrometers in size was ∼ 6 × 103 cm−2. [ABSTRACT FROM AUTHOR]