Composition inhomogeneities in the buffer layers of In0.52Al0.48As/InxGa1−xAs/InP multiquantum well structures driven by In segregation

Abstract

Transmission electron microscopy was used to study the morphology of InxGa1−xAs/In0.52Al0.48As multiquantum well (MQW) structures epitaxied at 510 °C over a In0.52Al0.48As buffer grown at 550 °C on a (100) InP substrate by molecular beam epitaxy. The plan-view images showed some squared contrast inhomogeneities oriented along the 〈010〉 directions. The projection of such contrast inhomogeneities along the (011) zone axis reveals the presence of contrast fringes along a direction slightly tilted from {111} planes, in particular at ≂35°–45° from (100). These contrast features extend only in the buffer layer, whereas they disappear completely when they reach the MQW structure, i.e., where the growth temperature is reduced. The origin of such a contrast pattern has been related to In composition inhomogeneities alternating on {101} planes, driven by In segregation during the growth of InAlAs at relatively high temperatures.