Radio Frequency Magnetron-Sputtered Germanium Nanoislands

Abstract

Conversion of bulk structures into nanoscale involves the remarkable change in physical properties of materials. It provides the possibility of observing novel behavior such as size-dependent structural and optical properties. Obtaining highly monodisperse semiconductors nanostructure and their characterization for optoelectronic application are the key issues. We use magnetron sputtering method for the fabrication of Ge/Si, [Ge/Si]×2, and Ge/SiO2/Si semiconductor heterostructure because it has a high deposition rate, and is easy, economic, and safety. The estimated sizes of Ge nanoislands are ~8 to ~29 nm. Varieties of growth parameters such as four substrate temperature, four annealing time, two annealing temperature, four deposition time, four rate of Ar flow, and four radio frequency power are used to optimize the surface morphology and optical behavior of Ge nanoislands. For bilayer samples, different spacer thickness from 10 to 40 nm and for multilayer SiO2 thickness of 30–50 nm are used. Structural and elemental analyses are carried out using X-ray diffraction (XRD), energy dispersive X-ray (EDX), field emission scanning electron microscope (FESEM), and scanning electron microscope (SEM). Results for atomic force microscopy (AFM) micrograph, root mean square roughness, number density, shape, and size distribution are presented. We use Scherrer equation to estimate the size and Williamson-Hall plot to estimate the strain effect. The XRD also demonstrates poly-crystalline nature of the nanoislands. The optical properties of samples are investigated by room temperature photoluminescence (PL) and Raman spectroscopy. The existence of strong blue-violet PL and corresponding blue and red shift are attributed to the quantum confinement effect, size distribution, strain, intermixing, and possibility of formation of core–shell-like structure. The shift of Ge-Ge phonons mode is understood in terms of phonon confinement, strain relaxation, and material intermixing.