| Abstract
| - Time-resolved second-harmonic generation (SHG) was used to study the hot-carrier dynamics and nonlinearoptical properties of S-terminated and Cl-terminated Ge(111) interfaces on the femtosecond time scale. Thehot-carrier second-order nonlinear optical susceptibilities were determined to be 720 ± 50 times greater thanthe valence-band second-order nonlinear optical susceptibilities for the Ge(111)−S system and 880 ± 100times greater in the Ge(111)−Cl system. Furthermore, the ground- and excited-state second-order nonlinearoptical susceptibilities are suggested to be out of phase for Ge(111)−S and Ge(111)−Cl systems, leading toa pump-induced decrease in the SHG signal as opposed to the increase in the SHG signal observed in theGe(111)−GeO2 system. Although the SHG response reaches a steady state in 415 ± 90 fs in the Ge(111)−GeO2 system, a faster response is observed in the Ge(111)−S system, 220 ± 85 fs, and in the Ge(111)−Clsystem, 172 ± 50 fs. This suggests significantly faster carrier cooling at the Ge(111)−Cl and Ge(111)−Sinterfaces, with significant implications for hot-carrier mediated device degradation, and migration to high-Kdielectrics.
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