... In semiconductors, inversion symmetry is also broken by the dc electric field DCF in the subsurface space-charge region SCR , which is created by initial band bending and/or external bias application. ... These differences in bias dependences of static and modulated EFISH intensities can be explained by the influence of traps interface states , located at or near the Si- SiO2 interface, with a charge dependent on the interface potential. ... 4 N. Bloembergen and Y. R. Shen, Phys. Rev. 141, 298 1966 ...