Characterization of X-ray radiation damage in Si/SiO2 structures using second-harmonic generation

We report the first application of second-harmonic generation (SHG) measure ments for the characterization of X-ray radiation damage in Si/SiO2 structu res. The main advantage of this experimental technique is that it is noninv asive, contactless, and sensitive to the electric held at the interface. In teraction of intense 800 mn femtosecond laser pulses with Si/SiO2 structure s results in electron-hole pair creation in the Si, multiphoton carrier inj ection and second-harmonic generation. The time-dependent second-harmonic ( doubled frequency) signal is a measure of the dynamic electric field at the interface. This dynamic field is created and altered by unequal electron-h ole injection into the oxide, trapping/detrapping of charges, and carrier r ecombination processes. We find that the SHG response from Si/SiO2 samples before and after X-ray irradiation is significantly different. Thus, SHG is a promising technique for the characterization of radiation damage in Si/S iO2 structures. In particular, SHG is especially useful in characterizing d amage in ultrathin oxide layers, for which conventional electrical measurem ents may not be sufficiently sensitive to the kinds of defects observable v ia optical methods.