Piezotronic effects on the optical properties of ZnO nanowires.

We report the piezotronic effects on the photoluminescence (PL) properties of bent ZnO nanowires (NWs). We find that the piezoelectric field largely modifies the spatial distribution of the photoexcited carriers in a bent ZnO NW. This effect, together with strain-induced changes in the energy band structure due to the piezoresistive effects, results in a net redshift of free exciton PL emission from a bent ZnO NW. At the large-size limit, this net redshift depends only on the strain parameter, but it is size-dependent if the diameter of the NW is comparable to that of the depletion layer. The experimental data obtained using the near-field scanning optical microscopy technique at low temperatures support our theoretical model.