The optical properties of porous Si terminated by various hydrophilic organic molecules were investigated to clarify the influence of the molecular length on the optical properties. In the case of porous Si terminated with hydrophilic organic molecules, surface oxidation of porous Si was restrained and the photoluminescence (PL) properties were more stable than those of the as-prepared sample. The PL of porous Si terminated with organic molecules was caused by the quantum size effect, which was confirmed on the basis of measured PL decay curves. The molecular length of the surface-terminated molecules did not affect the PL properties. Therefore, surface termination with hydrophilic organic molecules is an effective method to improve the stability of the optical properties of porous Si.

The effects of the surface termination of a porous Si surface by propionic acid and by undecylenic acid on their hydrophilicity and luminescence stability were studied. In the measurements of the contact angle of water droplets on porous Si films, the hydrophilicity of porous Si is improved by the surface termination each types of organic molecule. The PL intensity of as-prepared porous Si decreased with increasing aging time in ambient air. As PL quenching involves PL blue shift and increasing Si–O bonds density, nonradiative recombination centers are formed in the surface oxide. After the hydrosilylation process of propionic acid and undecylenic acid, PL intensity decreased and became 30% that of as-prepared porous Si film. However, the PL intensity was stable and exceeded that of the as-prepared film after 1000 min of aging in the ambient air. The PL stabilities are contributed to the termination by organic molecules that inhibits surface oxidation.