Light Emission From Hydrogenated and Unhydrogenated Si-Nanocrystal/Si Dioxide Composites Based on PECVD-Grown Si-Rich Si Oxide Films

Hydrogenated and unhydrogenated Si-nanocrystal/Si dioxide (Si-nc/SiO₂) composites were obtained from Si_yO _1-y (y=0.36,0.42) thin films deposited by plasma-enhanced chemical vapor deposition. The unhydrogenated composites were fabricated by promoting the Si precipitation through the thermal annealing of the films in the flowing pure Ar at temperatures up to 1100degC. The hydrogenated composites were obtained from identical films by replacing the Ar with (Ar+5% H₂) in the annealing step. The photoluminescence (PL) of the composites was studied as a function of the annealing temperature (T), annealing time, and pump laser power. The PL intensity increases with increasing annealing temperature and time; however, it increases faster and attains several hundreds percent larger values when the annealing is performed under (Ar+5% H₂) as compared to the annealing under pure Ar. Fourier-transform infrared spectra show that H in these hydrogenated samples incorporates mainly as Si-H bonds. The dependence of the PL spectra on y,T, and laser power are consistent with the assumption that light emission in both the hydrogenated and unhydrogenated Si-nc/SiO₂ composites originates from the bandgap transitions involving the electron quantum confinement in the Si-ncs. The PL spectra from the hydrogenated films are skewed to the red as compared to those from the unhydrogenated ones. The bulk of the data indicates that H passivates the nonradiative recombination centers, most probably Si dangling bonds in disordered Si-nc/SiO₂ regions, thus increasing the number of Si-ncs that contribute to the PL and modifying the distribution of the emission wavelengths