Characterization of charge-carrier dynamics in thin oxide layers on silicon by second harmonic generation

Abstract

First measurements of time-dependent second-harmonic generation (SHG) at a $\mathrm{S}\mathrm{i}/({\mathrm{ZrO}}_{2}{)}_{x}({\mathrm{SiO}}_{2}{)}_{1\ensuremath{-}x}$ interface show a behavior that is drastically different from similar measurements at ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ interfaces. We suggest that in ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ only electron injection is important, while both electrons and holes contribute to the dynamics at the $\mathrm{S}\mathrm{i}/({\mathrm{ZrO}}_{2}{)}_{x}({\mathrm{SiO}}_{2}{)}_{1\ensuremath{-}x}$ interface. Multiphoton excitation occurs in Si for all oxides, and involves direct interband transitions. The marked difference between the two systems is related to the population of multiphoton excited states in Si, the corresponding conduction- and valence-band offsets, and trapping/detrapping processes in the oxides. Our measurements confirm the existence of an initial built-in field at the interface.