Tuning of the Optical Emission Polarization of ZnO Nanorods by an Applied Hydrostatic Pressure

In the present work, we have performed a systematic theoretical study of the electronic and optical properties of ZnO nanorods as a function of an externally applied hydrostatic pressure. Our calculations are based on the empirical pseudopotential method and configuration interaction to consider the excitonic effects. The optical emission polarization is found to exhibit a transition between in-plane and out-of-plane polarization with increasing pressure. The critical value of the hydrostatic pressure at which the crossover takes place appears to depend strongly on the nanorod's radius. In particular, when the nanorod's radius is smaller than the ZnO exciton Bohr radius, the necessary pressure to reach the crossover point is significantly smaller than the pressure required for a nanorod with radius larger than the exciton Bohr radius. For large pressures, the lowest exciton state is a nearly pure state (0,0), where electron and hole have dominant S-orbital character and the hole has a nearly pure parentage from the bulk Bloch C-band.