Nonquadratic second-harmonic generation from semiconductor-oxide interfaces

Abstract

Second harmonic generation on ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ interfaces shows unusual nonmonotonic, nonquadratic behavior. This behavior depends strongly on laser wavelength and surface termination. It is present for oxide-covered samples at second-harmonic wavelengths of 373 nm (3.32 eV), but not at 415 nm (2.99 eV). It is absent at both wavelengths for H-terminated samples. This behavior is consistent with photomodulation of an interfacial electric-field-induced contribution to the second-harmonic response of the system.