Nitride-stressor and quantum-size engineering in ge quantum-dot photoluminescence wavelength and exciton lifetime

We report local nitride-stressor engineering in combination with quantum-size tunability in Ge quantum dots (QDs) for tailoring photoluminescence (PL) wavelength and exciton lifetime. Spherical-shaped Ge QDs with tunable diameters ranging from 25–90 nm embedded within layers of thermally-grown SiO₂ and chemical-vapor-deposited Si₃N₄ were fabricated by thermal oxidation of lithographically-patterned poly-Si_0.85Ge_0.15 pillars on top of buffer layers of SiO₂ and Si₃N₄, respectively, in a self-organization approach. The effects of local stressors and quantum confinement on the strain and optical properties of Ge QDs were systematically investigated using Raman and PL measurements. We observed that when Ge QD diameter gets smaller than 60 nm, quantum confinement sets in and has a predominant influence on PL wavelength and exciton lifetime. Our self-organized Ge QD/Si₃ N₄ system provides a generic building block for the fabrication of active photonic devices on Si₃N₄ platform.