Impact of annealing on surface morphology and photoluminescence of self-assembled Ge and Si quantum dots

Controlled growth and characterization of germanium (Ge) and silicon (Si) nanostructure are the key issues for optoelectronic device fabrication. The role of post-annealing on the structural and optical properties of radio frequency (rf) magnetron sputtering grown of Ge and Si quantum dots (QDs) deposited on Si(100) substrate is studied. Atomic force microscopy confirmed the formation of Si and Ge QDs with estimated sizes lower than ~17 nm and ~14 nm respectively. The X-ray diffraction analysis revealed the formation of Si and Ge QDs accompanied by SiO₂ with estimated sizes of ~5 and ~7 nm for post-annealed Si and pre-annealed Ge QDs respectively. The room temperature photoluminescence spectra for Ge and Si demonstrated an emission peak at 3.20 and 2.72 eV respectively, which are attributed to the electron and hole recombination within QDs. A shift in the PL peak is observed through annealing which is ascribable to the changes in size of QDs and quantum confinement effect. The thermal annealing at 600 °C is found to play an important role in controlling the shape, number density, root mean square (rms) roughness and the energy shift of the luminescence band for both Si and Ge QDs. The influence of annealing on growth morphology for Ge QDs is appeared to be stronger than Si.