研究目的
Investigating the optimization of porous silicon Bragg reflectors for achieving narrow spectral resonances to enhance refractive index-based sensing accuracy.
研究成果
The study demonstrates that compensating for depth-related etch rate variations enables the fabrication of porous silicon Bragg reflectors with porosity modulations below 1%, achieving absorption-limited spectral widths of 7 nm. These narrowband reflectors offer improved sensing capabilities for monitoring refractive index changes, with potential applications in detecting low analyte concentrations in biological and chemical sensing.
研究不足
The study is limited by the need for precise control over etching conditions to achieve the desired porosity modulation and layer uniformity. The presence of absorption and scattering losses in the porous silicon also limits the maximum reflectivity achievable.
1：Experimental Design and Method Selection:
The study involved the fabrication of porous silicon Bragg reflectors with alternating high and low porosity layers to achieve narrow spectral resonances. The methodology included compensating for depth-related etch rate variations to ensure uniform layer thickness.
2：Sample Selection and Data Sources:
Boron-doped single-side polished silicon wafers were used as substrates. The optical properties of the fabricated films were characterized using spatially resolved spectral reflection measurements.
3：List of Experimental Equipment and Materials:
A custom made electrochemical cell, Keithley 2400 Source Meter for etching, FEI Nova NanoSEM 450 for SEM imaging, and a Nikon LV-100 upright microscope for optical characterization.
4：Experimental Procedures and Operational Workflow:
The silicon wafers were anodized in a solution containing hydrofluoric acid, water, and ethanol. The etching current was alternated to create layers of differing porosity. Optical characterization was performed using a USB spectrometer.
5：Data Analysis Methods:
Reflectance spectra were simulated using the Transfer-Matrix method to assess the thickness and porosity of individual layers. Optical constants were related to porosity using the Bruggeman effective medium model.
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