Second-harmonic intensity and phase spectroscopy as a sensitive method to probe the space-charge field in Si(100) covered with charged dielectrics

A space-charge region (SCR) can develop in silicon due to the presence of built-in charges in dielectric thin films that are used in silicon-based device architectures. To study both the strength and polarity of the electric field in such a SCR, the authors performed second-harmonic (SH) generation spectroscopy in the vicinity of the E-1 critical point (2.7-3.5 eV) of silicon. As multiple contributions add coherently to SH intensity spectra, the electric-field-induced contribution cannot always be distinguished unambiguously from the intensity data in the absence of complementary phase information. Combined SH intensity and phase measurements were therefore performed to resolve this ambiguity. Using a coherent superposition of critical-point-like resonances with excitonic line shapes, the intensity and phase spectra of several SiO2- and Al2O3-based samples were simultaneously modeled. This analysis reveals that not only the polarity of the space-charge field can be determined unambiguously but also that the sensitivity to the electric field strength is significantly enhanced. (C) 2014 American Vacuum Society.