Silicon surface functionalization based on cavitation processing

Functionalization of semiconductor substrates, specifically silicon, has focused attention toward such technological applications as photovoltaic and biosensing. Several common chemical approaches have been employed for this purpose. In this paper, we focus on the alternative approach dealing with ultrasound-assisted modification of silicon. The aim was to identify the chemical functional groups and to evaluate the biocompatibility of the ultrasonically processed semiconductor. The properties of the Boron-doped p-type (100) silicon wafers subjected to cavitation impacts have been studied. It was shown that high-intensity (15 W/cm2) and high-frequency (1 ÷ 6 MHz) sonication of silicon wafers in the liquid nitrogen in focused mode of acoustic action induces changes of the optical, chemical, and structural properties of semiconductor surface. The cavitation processing of the Si samples besides a structuring of semiconductor surface and possible phase transformation of bulk material, results in the formation of functional oxide layers consisted of such materials as SiO2, CaSiO3 and Ca2SiO4. The formation of a new phase on the silicon surface is confirmed by the results of X-ray diffraction and μ-Raman spectroscopy investigations. The obtained composite structure has demonstrated photoluminescence in the spectral range of 500-800 nm. Biocompatibility of the ultrasonically processed wafers was confirmed by the hydroxyapatite formation on the Si surface after storage in simulated body fluid solution.