Second-harmonic generation from Si/SiO2/Hf(1-x)SixO2 structures

Optical second-harmonic generation (SHG) is used to characterize thin films of Hf(1-x)SixO2 (x=0, 0.3, 0.45, 0.65, and 1) deposited by atomic layer epitaxy at 375 degrees C on Si substrates with 11 A SiO2 buffer layers. Reflected SHG intensity measured at room temperature increases monotonically with Hf content for as-deposited samples and varies strongly with the temperature (600-1000 degrees C) of postdeposition rapid anneals in NH3. Spectroscopic analysis shows that the variable SHG component peaks at SH photon energy of 3.37 eV-the bulk silicon E-1 critical point energy-a clear signature of electric-field-induced second-harmonic generation in the bulk Si space-charge region. The results suggest that SHG is a sensitive, potentially in situ, probe of internal electric fields attributable to composition- and annealing-dependent fixed charge in the oxide layers.