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 t he 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 th e Si-H surface coverage, which is readily obtained after the layer for mation in HF, during different post-treatments (anodic oxidation and c ontact with organic solvent) and to relate it to the emission efficien cy. FTIR studies, performed at different steps of the electrochemical oxidation, indicate that, during the anodic treatment, the hydrogen su rface coverage is preserved and that the oxidation takes place on the back bonds of the surface silicon atoms. The importance of the hydroge n coverage is also shown by the analysis of porous layers treated in b oiling CCl4 after formation. This treatment provokes the desorption of the hydrogen atoms and results in a drastic decrease in the photolumi nescence. When samples are immersed in boiling methanol after formatio n, FTIR analyses show that there is also a partial loss of the hydroge n coverage! but accompanied with an oxidation of the material, so that no significant changes in the emission efficiency can be observed.