Photo absorption enhancement in strained silicon nanowires: An atomistic study

TL;DR

This study investigates how strain, diameter, and crystallographic orientation affect the optical absorption of silicon nanowires, revealing significant enhancement under strain and polarization effects, with implications for infrared photodetectors.

Contribution

It provides an atomistic analysis of absorption in strained silicon nanowires, highlighting the impact of strain and orientation, and compares numerical and semi-analytical methods for efficiency.

Findings

Compressive strain can increase band edge absorption by over an order of magnitude.

Photon polarization significantly influences absorption, with differences up to three orders of magnitude.

Strained silicon nanowire arrays absorb infrared photons about 100 times better than bulk silicon.

Abstract

The absorption spectra of silicon nanowires (SiNW) are calculated using semi-empirical $sp^{3}d^{5}s^{*}$ tight binding (TB) and Density Functional Theory (DFT) methods. The role 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 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.