Characterization of short-period Si m Ge n superlattices by high-resolution transmission electron microscopy and X-ray diffraction

Abstract

High-resolution and analytical transmission electron microscopy as well as X-ray diffraction were used to characterize the structure of short-period strained-layer (Si m Ge n ) N superlattices ( m monolayers Si, n monolayers Ge, total number of periods N < 200, total thickness < 350 nm). The superlattices were grown by low-temperature molecular beam epitaxy ( T = 300–500 °C) on different SiGe alloy buffer layers on Si(100) substrates. By a combination of these methods, detailed information can be obtained about periodicity, interface roughness on an atomic scale, strain and average composition of the superlattices. Superlattices of good morphology were grown, although defects were still present. Superlattices on thin buffers contained rather high defect-densities in general, whereas the defect-densities were much lower for superlattices grown on thick buffers, especially for those with composition gradients.