Photo absorption enhancement in strained silicon nanowires: An atomistic study

The absorption spectra of silicon nanowires are calculated using semi-empirical sp(3) d(5) s* tight binding and Density Functional Theory methods. The roles of diameter, wave function symmetry, strain, and crystallographic direction in determining the absorption are discussed. We find that compressive strain can change the band edge absorption by more than one order of magnitude due to the change in wave function symmetry. In addition, photon polarization with respect to the nanowire axis significantly alters the band edge absorption. Overall, the band edge absorption of [ 110] and [100] silicon nanowires can differ by as much as three orders of magnitude. We find that compared to bulk Silicon, a strained Silicon nanowire array can absorb infrared photons (1.1 eV) approximately one hundred times better. Finally, we compare a fully numerical and a computationally efficient semi-analytical method, and find that they both yield satisfactory values of the band edge absorption. Published by AIP Publishing.