Photoluminescence emitted from Si vs. Ge nanocrystals embedded in a SiO ₂ matrix

Luminescences from Si and Ge nanocrystals were experimentally investigated. Si and Ge ions were implanted into 300 nm-thick SiO ₂ films grown on crystalline Si at an energy of 55 keV with doses of 1×10 ¹⁷ cm ^-2 and 3×10 ¹⁶ cm ^-2 for Si implantation and at 100 keV with a dose of 3×10 ¹⁶ cm ^-2 for Ge implantation. Visible photoluminescences around 1.72 eV (720 nm) and 2.14 eV (580 nm) were observed from the samples annealed at 1100 °C after Si and Ge implantation, respectively. The results of the x-ray photoelectron spectroscopy (XPS) measurements and passivation annealing supported the presence of nanocrystals. The theoretical exciton energy values in the Si and the Ge nanocrystals, based on the quantum confinement theory, corresponded well to our experimental results.