Origination of the direct-indirect band gap transition in strained wurtzite and zinc-blende GaAs nanowires: A first principles study

Recent work has demonstrated that uni-axial strain applied to wurtzite (WZ) GaAs nanowires leads to an interesting direct-indirect band gap transition. Here, we explored the potential of strain engineering on electronic structures of one-dimensional WZ and zinc-blende (ZB) GaAs nanowires along the (0001) and (111) directions, respectively. The studied strain includes uni-axial strain, radial strain, and strain along zigzag and armchair directions in the cross section of the nanowires and shear strains. It was further found that whether a strain can trigger the direct-indirect band gap transition in the GaAs nanowires depends strongly on the type of applied strain. It requires less strain energy to convert the indirect gap to be direct in both the WZ and the ZB nanowires through applying a radial strain in the cross section, compared with applying a strain in the zigzag direction.