OXIDE-THICKNESS DEPENDENCE OF 2ND-HARMONIC GENERATION THICK THERMAL OXIDES ON SI(111)

We show here that the oxide-thickness dependence of the s-polarized SH G from Si(111) covered with a thick thermal oxide is completely descri bed by multiple reflections in the oxide film. For the p-polarized res ponse, a strong enhancement with thickness is observed, which cannot b e explained in this way. These measurements show that one should be ca utious in analyzing the SHG from a buried interface, and carefully tak e into account the linear optics involved.