Enhanced nonlinear optical susceptibilities in phosphorene nanoribbons: Ab initio study

Abstract

Using density functional theory method, the linear optical absorption spectra and nonlinear optical susceptibilities of hydrogen passivated armchair and zigzag Phosphorous Nanoribbons (aPNR and zPNR) as well as α-phase phosphorous monolayer were calculated. It was observed that the crystallographic direction has a strong effect on the band edge absorption which in turn leads to optical anisotropy as well as a red shift of the absorption spectra by increasing the width. The calculated absorption values are in the order of 105 cm-1 and are very close to the experimentally measured ones. It was also observed that the 2nd order nonlinear optical susceptibility, χ(2), in the nanoribbons is enhanced by two orders of magnitude. This effect is caused by breaking the centro-symmetric structure of monolayer phosphorene as a result of hydrogen surface termination. The calculated 3rd order susceptibilities, χ(3), are in the order of ≈10-13esu (≈10-21 m2/V2) which are in close agreement with experimentally reported values as well as those computed based on the relativistic picture of electron. The closeness of our results to experimental values strongly supports the reliability of our method in calculating the nonlinear optical susceptibilities of phosphorene and other nanostructures in general. The enhanced 2nd order optical nonlinearity in phosphorene promises a better second harmonic and frequency difference (THz) generation.