High-resolution x-ray diffraction studies of InGaAs(P)/InP superlattices grown by gas-source molecular-beam epitaxy

Abstract

High-resolution x-ray diffraction studies have been carried out to determine the structural perfection and periodicity for a number of high-quality InGaAs/InP superlattices and one InGaAsP/InP superlattice grown by gas-source molecular-beam epitaxy. For comparison, high-resolution diffraction both with a three-crystal geometry and with a four-crystal monochromator was used along with conventional double-crystal x-ray diffractometry. The best resolution in the x-ray satellite patterns was obtained with the four-crystal monochromator, providing a resolution of one molecular layer in the periodicity of the superlattice. The presence of sharp satellite reflections in the x-ray diffraction profiles demonstrate smooth interfaces with well-defined modulated structures which could be derived from a kinematical diffraction step model. For some 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 other superlattices a thin strained layer had to be assumed on either one or both sides of each quantum well. The comparison of these structures demonstrates the extreme sensitivity of the high-resolution method in conjunction with the step model, to study very small modifications in superlattice periodicities.