The Formation and Morphology of Highly Doped N-type Porous Silicon: Effect of Short Etching Time at High Current Density and Evidence of Simultaneous Chemical and Electrochemical Dissolutions

Porous silicon (PS) was successfully prepared from highly doped n-type silicon (Si) substrate. The PS was electrochemically formed within a short etching time ( 5 min) at 300 mA cm^–2 in 1:1 (v/v) hydrofluoric acid (HF) (49%) and ethanol (95%) electrolyte. The PS surface featured both spherical and irregular shaped pores with constant average diameters regardless of etching time. However, the cross-section morphology of the PS was dependent on etching time where the structure changed from vertically arrayed columns with side branching to unbranched and smooth walls with a corresponding increase in porosity from 25 to 70%. The PS showed a trend of increasing surface roughness as the etching time was prolonged up to 180 s. However, for longer etching times, the roughness demonstrated a decrease. The conductivity of the PS was reduced as the porosity increased. These results therefore suggested the occurrence of simultaneous chemical and electrochemical dissolutions.