High-resolution x-ray diffraction and transmission electron microscopy studies of InGaAs/InP superlattices grown by gas-source molecular beam epitaxy

Abstract

A three-crystal geometry has been used for high-resolution x-ray diffraction (XRD) along with lattice imaging transmission electron microscopy (TEM) to study two high-quality InGaAs/InP multiquantum well structures grown on (100) InP. These superlattices were prepared by gas-source molecular beam epitaxy using a computer controlled system and were found to have excellent optical properties. Cross-section TEM and the presence of sharp satellite reflections in the XRD profiles demonstrate very smooth interfaces with well-defined modulated structures which could be derived from a kinematic XRD step model. For one of these superlattices, excellent agreement between the step model and the measurements is obtained when the model assumes that each period consists only of the well and the barrier with ideally sharp interfaces. For the other superlattice an additional approximately 9-Å-thick layer of approximate composition In0.47Ga0.53As0.985P0.015 had to be assumed on one side of each quantum well. This additional layer is attributed to substitution of ambient P for 1.5 at. % of the As during growth interruption and is easily eliminated. The comparison of these two structures demonstrates the extreme sensitivity of the high-resolution XRD method in conjunction with the step model to study very small modifications in superlattice characteristics.