Effective method to extract optical bandgaps in Si nanowire arrays

OPTICS LETTERS 36(14) 2677-2679

https://doi.org/10.1364/OL.36.002677

Jin-Young Jung,Keya Zhou,Han-Don Um,Zhongyi Guo,Sang-Won Jee,Kwang-Tae Park and Jung-Ho Lee

Abstract A simple method to extract the optical bandgap of Si nanowire (SiNW) arrays that utilizes the reflection spectra of freestanding SiNW arrays is presented in this Letter. At a fixed nanowire diameter, three different wire lengths reproducibly formed a cross point in their reflectance curve plots. The cross point wavelength corresponded to the optical bandgap, as verified by the classical Tauc’s model. The optical bandgap of the SiNW arrays (112nm112nm in average diameter) was measured to be ∼1.19eV∼1.19eV, which is larger than the ∼1.08eV∼1.08eV bandgap of bulk Si. Further decreasing the wire diameter to 68nm68nm caused an increase of the bandgap to ∼1.24eV∼1.24eV, which is closer to the optimal bandgap (∼1.40eV∼1.40eV) required to achieve the highest conversion efficiency in single-junction photovoltaic devices. Our method suggests that the multijunction tandem structure can be realized via control of the diameter of SiNW arrays.