Control of photoluminescence energy of Si nanocrystals by Ge doping

Abstract

SiGe alloy nanocrystals (nc-Si 1− x Ge x ) as small as 4–5 nm in diameter were prepared and their photoluminescence (PL) properties were studied as a function of the Ge content. The growth of nc-Si 1− x Ge x in SiO 2 matrices was confirmed by high-resolution transmission electron microscopy, electron diffraction and Raman spectroscopy. The PL spectra of nc-Si 1− x Ge x were found to be sensitive to the Ge content. For the sample without Ge doping, a PL peak was observed at around 1.45 eV; the peak was assigned to the radiative recombination of electron–hole pairs confined in Si nanocrystals. As the Ge content increased, the PL peak shifted to lower energies although the average diameter of nc-Si 1− x Ge x was almost the same for all the samples. This result indicates that the Ge doping is an effective method to control the band gap energy of Si nanocrystals.