Absorption Enhancement of GaAs Slab with Geometrically Varying Periodic Array of SiO2 Nanostructures

In this work we present a systematic study on absorption enhancement in thin-film GaAs slabs having two-dimensional periodic arrays of SiO
₂
nanostructures. Nanostructures in the form of circle, square and triangles having dimensions ranging from 50 nm to 120 nm are considered to be periodically embedded into GaAs slabs having thicknesses ranging from 100 nm to 500 nm. Finite difference time domain based analysis of these structures, which essentially constitute two-dimensional photonic crystals, show that the peak absorption characteristics of the enhanced absorption profile are in fact intricately related to the curvature of the nanostructure. Increased optical path length with increasing curvature results in the highest absorption in circular arrays, whereas about 20% lower peak absorption is obtained in thin-films having triangular arrays. A quantitative estimate of curvature is presented in this work, which appears to be in direct correlation with the peak absorptions obtained for different nanostructures. Also for small curvatures of the nanostructures, their size variation appears to have less of an effect on the overall absorption profile. Moreover, absorption characteristics of the thin film appear to be less dependent on its thickness if the curvature of the nanostructures is decreased. For all geometrical shapes however, increasing film thickness results in an increase of the bandwidth of the absorption profile. It is envisaged that the results presented here will serve as guidelines for photon-management employing easily realizable photonic structures in high-efficiency thin-film solar cells.