Optical second-harmonic generation studies of the structure of porous silicon surfaces

Abstract Characterization of porous silicon (PS) on the atomic scale is difficult and optical techniques offer certain advantages. High vacuum studies of PS by optical second-harmonic generation (SHG) are presented. Excitation wavelengths corresponding to a surface state and a suspected strain resonance from clean Si surfaces are used. Hydrogen-terminated and clean surfaces of Si(100) and PS are compared. The H-terminated surfaces give no signal under the excitation conditions used. On desorbing the hydrogen, a stable SH signal is obtained from the PS which has a polarization behaviour consistent with a significant contribution from surfaces of {111} orientation.