Polarity of space charge fields in second-harmonic generation spectra of Si(100)/SiO2 interfaces

Optical second-harmonic generation spectra of Si(100)/SiO2 interfaces exhibit characteristic differences for positively or negatively charged space charge regions (SCRs). These differences originate from interference of the second-harmonic light generated in the SCR with that generated by Si atoms in immediate proximity to the oxide and characterize the direction of the electric field of the SCR. The sensitivity of second-harmonic generation to the sign of the space charge is demonstrated for the negative space charge at alkali-metal-modified Si(100)/SiO2 interfaces, and for the positively charged accumulation layer caused by laser-induced surface traps in thin oxides.