FTIR and photoluminescence studies of porous silicon layers oxidized in controlled water vapor conditions

Abstract

A study is presented on the evolution of the FTIR features and the changes in the photoluminescence (PL) spectra of chemically oxidized porous silicon layers (PSLs) successively aged under controlled conditions. The PSLs were prepared by the electrochemical method to guarantee uniformity over extended areas. Just after the silicon porification process, the FTIR spectra of the PSLs show silicon-hydrogen bands related to the hydrogen terminated porous silicon surface. As the PSLs oxidized, various vibrational modes were modified. The new observed vibrational frequencies are related to the defective silicon oxide formed at the porous silicon surface. The room temperature PL spectra of freshly prepared PSLs show a characteristic peak located at $\sim $700 nm. The intensity of the PL signal on chemically oxidized samples increased by an order of magnitude; afterwards, when the samples were aged in saturated water vapor conditions, the PL spectra were strongly modified. These changes indicated that the PSL structure is modified by the oxidization processes applied. Analysis of the FTIR data and the behavior of the PL signal enable us to interrelate the quantum size related effects and the formation of some kind of defect in the silicon oxide film over the PSLs. The characteristics of the PSLs reported in this paper are perfectly reproducible in the conditions used for the sample preparation; therefore, these films can be used in different applications.