Optical properties of pseudomorphic Ge1−xSnx (x = 0 to 0.11) alloys on Ge(001)

Abstract

The characterization of the optical properties of pseudomorphic Ge1−xSnx/Ge/Si (x = 0 to 0.11) alloys from the IR to UV is presented. The Ge1−xSnx alloys were epitaxially grown on relaxed Ge grown on Si. Rutherford backscattering (RBS) and RBS ion channeling methods were used to confirm the Sn composition and substitutional nature of the Sn into the Ge lattice. The pseudomorphic nature of the Ge1−xSnx on Ge is confirmed using high resolution x-ray diffraction (HRXRD) and transmission electron microscopy. Although HRXRD reciprocal space maps indicated that the Ge1−xSnx was pseudomorphic to Ge, the shape of the Bragg peaks indicated that the sample surface was rough. The rough surface morphology is confirmed using atomic force microscopy. The complex dielectric function is reported in the IR, visible, and UV spectrum in the wavelength range of 0.2–5.06 eV. The E1, E1 + Δ1, E2, and E0 critical points are extracted using second and third derivative line shape fitting and are compared with the elastic theory calculations of strained Ge1−xSnx (x = 0 to 0.11) alloys and fully relaxed Ge1−xSnx (x = 0 to 0.11) alloys. The E0 critical point energies are observed to have slightly larger values than those calculated for completely relaxed Ge1−xSnx alloys due to the presence of compressive strain.