Molecular beam epitaxy of PbTe/EuTe superlattices and their structural investigation by x-ray diffraction using reciprocal space mapping

Abstract

Molecular beam epitaxial growth of PbTe/EuTe superlattices on (111) BaF2 was studied using reflection high energy electron diffraction (RHEED). The surface reconstructions of EuTe, its nucleation and critical layer thickness on (111) PbTe were investigated by in situ RHEED. From these studies, the optimum conditions for the growth of PbTe/EuTe superlattices were derived. PbTe/EuTe superlattice (SL) samples were investigated by high resolution x-ray diffraction. Triple axis x-ray diffractometry was employed to characterize the structural parameters of a PbTe/EuTe SL sample (87.6 PbTe monolayers/5 monolayers EuTe) deposited on a 4 μm thick PbTe buffer layer. Reciprocal space maps around the (222) and (264) Bragg reflections are used to analyze the strain status of the SL layers with very high precision. Using reciprocal space mapping, the small strain gradient present within the SL along growth direction can be determined quantitatively. The full width at half-maximum (FWHM) values of (222) SL x-ray diffraction peaks along and perpendicular to the [111] growth direction were measured. It was found that along the [111] direction the FWHM’s increase with satellite number, which is most probably caused by either lateral superlattice thickness variations of 0.4% for the x-ray spot size of 1×8 mm2 or a thickness variation in growth direction of 1.5%. The broadening of the main superlattice peak perpendicular to the [111] growth direction indicates the presence of mosaicity in the superlattice layers, which obscures due to its magnitude the measurement of lateral interface roughness.