OPTICAL 2ND-HARMONIC GENERATION STUDIES OF THE STRUCTURE OF POROUS SILICON SURFACES

Characterization of porous silicon (PS) on the atomic scale is difficu lt and optical techniques offer certain advantages. High vacuum studie s of PS by optical second-harmonic generation (SHG) are presented. Exc itation wavelengths corresponding to a surface state and a suspected s train resonance from clean Si surfaces are used. Hydrogen-terminated a nd clean surfaces of Si(100) and PS are compared. The H-terminated sur faces give no signal under the excitation conditions used. On desorbin g the hydrogen, a stable SH signal is obtained from the PS which has a polarization behaviour consistent with a significant contribution fro m surfaces of {111} orientation.