The Depolarization and Angular Spectral Properties of Nano-Roughened Structures on Si Wafer
Date Issued
2009
Date
2009
Author(s)
Meng, Fan-Shuen
Abstract
In this thesis, morphologically controlled Si nano-pillars/nano-rods based sub-wavelength semiconductor anti-reflective structure (SSAS) surface exhibits great anti-reflection (AR) ability are demonstrated. Extremely small reflectance dip of <3% at 400-500 nm for Si nano-pillars is extraordinary when comparing with Si nano-rods, in which the reflectance vs. L/lambda for Si nano-pillars coincides well with the graded-index multilayer based modeling spectrum. On the other hand, Si nano-rods preserve its flattened reflectance spectrum up to 1700 nm, whereas the Si nano-pillar surface reflectance monotonically increases to approach that of bulk Si. Furthermore, the SSAS surface with different geometrical factors are successfully fabricated and investigated. As the increasing the Si nano-pillar height to 240 nm, the Brewster angles phenomenon observed for the TM-mode reflectance completely diminishes due to the decreasing of polarization ratio to 52.9%. Besides, the simulation curves by employing graded refractive index model with infinite layers are in good agreement with the measured reflectance data of 150nm-thick and 210nm-thick SSAS surface. Although SSAS efficiently suppress the reflectance over a wide spectral bandwidth, the SSAS surface based solar cells with SSAS surface fabricated upon semi-manufactured cells directly still exhibit poor I-V characteristics with the improvement of AR ability. Then we fabricate SSAS surface directly upon quartz substrate to analyze the optical reflectance and transmittance. The reason that SSAS surface suppresses surface reflectance from 30% to 5% but the transmittance decreases from 15% to 3% simultaneously results in the energy conversion efficiency is still unimprovement.
Subjects
Nano-rod
Nano-pillar
Morphological Control
Anti-reflection
Depolarization
Graded Refractive Index
Type
thesis
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