Ge nanocrystals of diameters ranging from 4 to 10 nm were synthesized by ion implantation of ${\mathrm{Ge}}^{+}$ ions into ${\mathrm{SiO}}_2$ films followed by annealing. Confinement of its optical phonon and of the quasi-two-dimensional $E_1$ exciton have been observed at room temperature by resonant Raman scattering. The observed size-dependent blueshifts of the $E_1$ excitons energy (which can be larger than 0.7 eV) are found to be in good agreement with a theoretical calculation based on the effective mass approximation.

• Received 8 November 1999

DOI:https://doi.org/10.1103/PhysRevB.62.1584