Raman scattering and room-temperature visible photoluminescence from Ge nanocrystals embedded in SiO 2 thin films

Abstract

Germanium nanocrystals (nc-Ge) embedded in SiO 2 glassy matrix have been prepared on glass substrates and silicon (100) wafers by an rf cosputtering technique and post-annealing treatment in vacuum atmosphere. Using Raman spectrometry, X-ray diffraction, and UV/VIS/NIR transmittance and reflectance measurements, we have investigated the structures and the optical properties of the Ge-SiO 2 composite films. The results show that Ge nanocrystals could be formed in Ge-SiO 2 composite films by thermal annealing. The growth of nc-Ge is associated with the thermodynamical breakup of GeO bonds and/or evacuation of oxygen atoms. As the size of nc-Ge reaches 4.6 nm, the efficient optical band gap of the Ge-SiO 2 composite film is found to shift to higher energy. Furthermore, broad-band multi-peak photoluminescence (PL) spectra are observed at room temperature. It is found that there exist Ge nanocrystals only in the emitting samples, and the emitting energy is approximately 2.05 eV. The multi-peak PL spectrum is considered to result from the different local environments of Ge nanocrystals in annealed sample.