Nonlinear optical characterization of Si/high-k dielectric interfaces
Abstract
Sum frequency generation between a Ti:Sapphire beam and white light
continuum is performed to obtain spectral information from GaAs(001). The experimental
difficulties are analyzed and possible solutions and extensions to the
technique proposed. The phase of second harmonic generation (SHG) is measured
using a frequency domain technique. Phase shifts in GaAs under azimuthal
rotation are observed and explained. The phase of the surface second order susceptibility
tensor elements of Si is measured. For the first time SHG phase from
Si/SiO2 and Si/SiO2/Hf-silicate is measured with a temporal resolution better
than one second. Si/SiO2/Hf(1−x)SixO2 stack structures are studied using rotational
anisotropic, spectroscopic, and time dependent SHG. It is found that the
signal is affected by Si content (x) and by annealing history of the samples. The
results show that SHG is sensitive to the phase separation of the silicates bulk
due to spinodal decomposition. A heuristic model based on Hf-O-Si polarizable
units that explains the observed trends is presented.
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