The effect of ultrathin oxides on luminescent silicon nanocrystallites

The effect of ultrathin oxides on nanocrystallites of luminescent porous silicon is studied using infrared, optical, and Auger spectroscopy. Room-temperature oxidation is performed using H₂O₂ immersion and UV ozone interactions, producing oxides of ∼5 and ∼10 Å, respectively. The H₂O₂ oxidized sample is optically active, while the ozone oxidized sample is not active. UV-ozone produces a transverse optical Si-O-Si mode blueshifted by ∼90cm^-1 from bulk oxide, which H₂O₂ does not produce. Auger Si LVV spectra show an oxidelike signal for UV/ozone samples and a Si-like signal for H₂O₂ samples. We discuss this in terms of different oxidation behaviors that either preserve or break Si-Si dimers that may be responsible for the optical behavior.