FOURIER-TRANSFORM IR MONITORING OF POROUS SILICON PASSIVATION DURING POSTTREATMENTS SUCH AS ANODIC-OXIDATION AND CONTACT WITH ORGANIC-SOLVENTS

The surface passivation of porous silicon is a determining factor in the emission efficiency of the material. The hydrogen surface coverage has been shown to provide very efficient passivation. In this work, we have performed Fourier transform IR (FTIR) measurements to monitor the Si-H surface coverage, which is readily obtained after the layer formation in HF, during different post-treatments (anodic oxidation and contact with organic solvent) and to relate it to the emission efficiency. FTIR studies, performed at different steps of the electrochemical oxidation, indicate that, during the anodic treatment, the hydrogen surface coverage is preserved and that the oxidation takes place on the back bonds of the surface silicon atoms. The importance of the hydrogen coverage is also shown by the analysis of porous layers treated in boiling CCl4 after formation. This treatment provokes the desorption of the hydrogen atoms and results in a drastic decrease in the photoluminescence. When samples are immersed in boiling methanol after formation, FTIR analyses show that there is also a partial loss of the hydrogen coverage! but accompanied with an oxidation of the material, so that no significant changes in the emission efficiency can be observed.