Determination of the free exciton energy in ZnO nanorods from photoluminescence excitation spectroscopy

摘要

Temperature-dependent photoluminescence excitation (PLE) spectroscopy is used to study nominally undoped and indium-doped ZnO nanorods grown by thermal evaporation method. Clear differences in PLE features between the two samples are observed. We demonstrate that the first derivative of the PLE spectra can be used to determine the free exciton energy for both samples. The physics behind is understood either in terms of competing absorption and recombination to the green emission band being monitored, or based on the analogy between the first derivative of PLE and photoreflectance spectroscopy. Two residual donor levels located at about 37 and 120 meV below the conduction band minimum are identified from the PLE spectra.