研究目的
Investigating the ultrafast evolution and spectral dynamics of the shift current in ferroelectric semiconductor SbSI, focusing on its origin from the geometric Berry phase and its potential applications in ultrafast sensors and solar cells.
研究成果
The shift current in SbSI exhibits ultrafast dynamics with a net charge flow and subpicosecond relaxation, consistent with first-principles calculations. It dominates photocurrent above the bandgap, showing distinct characteristics from in-gap processes. This understanding advances potential applications in dissipationless ultrafast electronic devices, such as sensors and solar cells, by leveraging the geometric Berry phase effects.
研究不足
The experimental spectra show smeared fine structures above 2.2 eV compared to theory, possibly due to instrumental factors or sample conditions. Scattering effects are not fully incorporated in the shift current formalism, and the ferroelectric polarization may not be fully developed at experimental temperatures. The study is limited to SbSI and may not generalize to other materials without further investigation.
1：Experimental Design and Method Selection:
The study uses terahertz emission spectroscopy to analyze ultrafast charge dynamics in SbSI single crystals. The methodology involves detecting terahertz electromagnetic waves emitted due to photo-induced charge currents, with factor analysis to resolve signals from different origins such as shift current and in-gap optical rectification. First-principles calculations based on density-functional theory are employed to support experimental findings.
2：Sample Selection and Data Sources:
Single crystals of SbSI were grown by physical vapor transport, with typical dimensions of 5 mm × 0.5 mm × 0.4 mm, and the c axis aligned along the longest orientation. Silver electrodes were attached along the c axis for electrical measurements. Data were collected by scanning excitation photon energy from 0.5 to 2.6 eV at 22 points.
3：5 mm × 4 mm, and the c axis aligned along the longest orientation. Silver electrodes were attached along the c axis for electrical measurements. Data were collected by scanning excitation photon energy from 5 to 6 eV at 22 points.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes a variable-wavelength laser (130 fs pulse duration, 1 kHz repetition rate), ZnTe (110) crystal for electrooptic sampling of terahertz waves, Peltier stage for temperature control, transimpedance amplifier for photocurrent measurements, and digitizing oscilloscope. Materials include SbSI single crystals and reference ZnTe crystals.
4：Experimental Procedures and Operational Workflow:
Samples were poled by cooling through the transition temperature under an external electric field. Terahertz waveforms were measured in reflection geometry using the laser for excitation and ZnTe for detection. The terahertz signals were analyzed to extract base waveforms via factor analysis. Photocurrent and polarization dependence were measured with electrodes and polarimetry setups.
5：Data Analysis Methods:
Factor analysis was used to decompose terahertz spectra into components attributed to shift current and in-gap optical rectification. First-principles calculations provided theoretical spectra for comparison. Data fitting involved equations for shift current and carrier dynamics, with statistical analysis of temperature and energy dependencies.
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