研究目的
To establish, as unambiguously as possible, the carrier dynamics and related constants of the moderately mesoporous material, with a stabilised native oxide protective shell.
研究成果
The carrier dynamics in porous silicon with ~50% porosity and native oxide chemistry are governed by the Shockley-Read-Hall recombination process with a characteristic time constant of 375 picoseconds. The contribution of diffusion is insignificant as it is suppressed by the high rate of scattering.
研究不足
The study is limited by the fast recombination in the samples, making it nearly impossible to observe diffusion. The samples investigated had such a fast recombination that the inequality 1/τ ≥ Dα^2_pump must hold to observe diffusion, which was not the case.
1：Experimental Design and Method Selection:
The study used time-resolved femtosecond pump-probe method to simultaneously measure reflectance and transmittance spectra in the temporal range up to 210 ps after the excitation by a femtosecond laser pulse. The method uses the simultaneous recording of the time-resolved reflectance and transmittance interference fringes over the probe beam spectral range of 60 nm interacting with a thin optical p-Si membrane slab.
2：Sample Selection and Data Sources:
Free-standing thin membranes of p-Si were used to avoid problems associated with fabrication of reproducible, low resistivity and stable contacts on a p-Si surface.
3：List of Experimental Equipment and Materials:
A Coherent ultrafast laser system delivering 60-fs pulses at the repetition rate of 1 kHz, spectrometers (Ocean Optics QE65 Pro), and a combination of a half-wave plate and Brewster angle reflection from a glass block for adjusting the pump fluence.
4：Experimental Procedures and Operational Workflow:
The probe and pump beam were focused to spot diameters of ~100 and ~300 μm, respectively. The incident angle of the probe beam was set to 45° and the angle difference between the pump and probe beams was ~20°.
5：0°.
Data Analysis Methods:
5. Data Analysis Methods: The experimental data was analyzed using a method based on the Wentzel-Kramers-Brillouin (WKB) approximation and the Drude model.
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