Structural and optical characteristics of Ge_1−xSnx/Ge superlattices grown on Ge-buffered Si(001) wafers

We report an investigation on low dimensional Ge1−xSnx/Ge heterostructures. A series of strained-layer Ge1−xSnx/Ge superlattices with various Sn contents up to a threshold value that affords a direct bandgap is achieved by the technique of low temperature growth using molecular beam epitaxy. The Sn composition, strain status, and crystallographic are systematically characterized by cross-sectional transmission electron microscope and x-ray diffraction. Optical absorption measurements were carried out at room temperature to determine the bandgap energies of the Ge1−xSnx/Ge superlattices. Analyzing the direct transition energies reveals the room-temperature quantum confinement in the Ge1−xSnx/Ge superlattices. Present investigation demonstrates the growth and the quantum confinement of Ge1−xSnx/Ge superlattices, moving an important step forward toward the development of high-performance photonic devices based on Sn-containing group-IV low-dimensional structures.