Effect of the doping level on the radiative life time in ZnO nanowires

The emission properties of ZnO nanowires grown by metal organic vapor phase epitaxy on sapphire and p-type GaN are compared using temperature dependent time resolved photoluminescence. The temperature dependence of the radiative decay time of nanowires grown on sapphire is well understood considering an exciton thermalization in a 3D density of states. In the case of growth on GaN, a great increase of the radiative decay time is observed compared to nanowires grown on sapphire. This increase of the radiative decay time could be due to a band bending effect that separates the electron and the hole. This band bending effect depends on the residual doping level and is not seen in the case of nanowires grown on sapphire probably because of a very high residual doping level that can be estimated from the radiative decay time temperature dependence.