Anisotropic microstructure in Cd 1− xMn xTe/Cd 1− yMn yTe superlattices studied by X-ray diffraction

Abstract

High-resolution X-ray diffraction studies of MOCVD-grown Cd 1− x Mn x Te/Cd 1− y Mn y Te superlattices on a (001) GaAs substrate have been carried out. Topographs and rocking-curve maps were taken from two directions at right angles to each other ([110] and [ 1 10], the latter being the gas flow direction). The structural properties and uniformity of the Cd 1− x Mn x Te/ Cd 1− y Mn y Te superlattice epilayers have been established from analyses of both rocking-curve maps and topographs. An anisotropic mosaic structure, where the mosaic blocks are well ordered along the [ 1 10] direction and disordered along the [110] direction, is proposed in order to explain these observations. It is shown that combinations of rocking-curve maps and topographs give a much more informative characterisation than a single-point measurement. The satellite peaks of the double-crystal rocking curve of Cd 1− x Mn x Te/Cd 1− y Mn y Te superlattices have been observed using an asymmetric 335 Bragg reflection. The angular positions of the observed satellites have been investigated and compared with the predictions of a standard theoretical formula, extended to the case of asymmetric reflections. The rocking curves of Cd 1− x Mn x Te/Cd 1− y Mn y Te superlattices have also been simulated using the Takagi-Taupin equations. The agreement obtained is quite satisfactory.