NONLINEAR-OPTICAL SPECTROSCOPY OF SI-HETEROSTRUCTURE INTERFACES

Strain, dislocations, and electrically active defects at and near the interface of Si/SiO2 and Si/GaP heterostructures are analyzed by optic al second-harmonic spectroscopy. For plasma oxides deposited on Si(001 ) and Si(111), time-dependent second-harmonic experiments reveal that near-interface oxide defects trap charge by the tunneling of photoexci ted electrons from the Si conduction band. The space-charge field-indu ced second-harmonic transients are resonantly enhanced by two-photon E (1) transitions in silicon. In GaP epilayers grown on Si(001) the bulk dipole-allowed electro-optical effect is suppressed by the formation of antiphase domains. In contrast, in Gap films grown on Si(111) and v icinal Si(001) the density of antiphase domains is considerably reduce d yielding an enhancement of the second-order nonlinear optical respon se by two orders of magnitude. (C) 1996 American Vacuum Society.