Optical and structural investigations of self-assembled Ge/Si bi-layer containing Ge QDs

• Published in: Journal of luminescence 2014-10, Vol.154, p.51-57
• Main Authors: Samavati, Alireza, Othaman, Z., Ghoshal, S.K., Dousti, M.R.
• Format: Article
• Language: English
• Subjects: Chemical interdiffusion; diffusion barriers; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Deposition by sputtering; Diffusion in solids; Exact sciences and technology; Germanium quantum dots; Intermixing; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Nanoscale materials and structures: fabrication and characterization; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Photoluminescence; Physics; Quantum dots; Raman spectroscopy; Transport properties of condensed matter (nonelectronic)
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/j.jlumin.2014.04.003

We report the influence of Si spacer thickness variation (10–40nm) on structural and optical properties of Ge quantum dots (QDs) in Ge/Si(100) bi-layer grown by radio frequency magnetron sputtering. AFM images reveal the spacer dependent width, height, root mean square roughness and number density of QDs vary in the range of ~12–25nm, ~2–6nm, ~1.95–1.05nm and ~0.55×1011–2.1×1011cm−2, respectively. XRD patterns exhibit the presence of poly-oriented structures of Ge with preferred growth along (111) direction accompanied by a reduction in strain from 4.9% to 1.2% (estimated from Williamson–Hall plot) due to bi-layering. The room temperature luminescence displays strong blue–violet peak associated with a blue shift as much as 0.05eV upon increasing the thickness of Si spacer. This shift is attributed to the quantum size effect, the material intermixing and the strain mediation. Raman spectra for both mono and bi-layer samples show intense Ge–Ge optical phonon mode that is shifted towards higher frequency. Furthermore, the first order features of Raman spectra affirm the occurrence of interfacial intermixing and phase formation during deposition. The excellent features of the results suggest that our systematic method may constitute a basis for the tunable growth of Ge QDs suitable in nanophotonics. •High quality bilayered hetero-structure Ge\Si using economic and easy rf magnetron sputtering fabrication method.•The role of phonon-confinement and strain relaxation mechanisms.•Influence of bilayering on evolutionary growth dynamics.•Band gap shift of visible PL upon bilayering.