Investigation On Electroluminescence Of ZnO Nanorods

Zinc oxide(ZnO) with wide band gap is a group two and group six semiconductor.Its band gap is3.37eV and its exction-binding energy is60meV at the roomtemperature, which makes excition recombination luminescence more easily at roomtemperature and high temperature. ZnO is considered as a promising material forvarious photonic and electrical applications with its special physical and chemicalproperties. In this paper, ZnO nanorods were prepared by the chemical bath depositionmethod which can be used in the electroluminescent device as the light-emitting layer.Meanwhile, we constructed ITO/ZnO nanorods/Ag and ITO/ZnO nanorods/Alq3/Agelectroluminescent devices and their electroluminescence mechanisms were also studied.Firstly, ZnO nanorods were grown on ITO conducting glass substratessuccessfully by the chemical bath deposition method. The morphology, structure andphotoluminescence of ZnO nanorods were analyzed. As the growth velocities of ZnOnanorods were different, the morphology produces a taper tip. There wre two peaksaccording to the PL spectrum. One was in the ultraviolet region, the other was inthe visible light range. Otherwise, This method had drawn extensive interests onaccount of the low growth temperature(＜100℃), low cost and good potential forscale-up with general substrates.Secondly, The ZnO light-emitting devices with Alq3insulating layer and withoutinsulating layer were constructed, respectively. Their photoluminescent andelectroluminescent properties were tested and studied. The photoluminescent spectrashowed that the520nm peak of Alq3increases while the380nm peak of ZnOdecreases. This phenomenon was ascribed to the energy transfer from the excitons ofZnO to Alq3molecules. The random lasing action was observed in theelectroluminescent spectra of ZnO nanorods and it was considered that this action wascaused by the light resonance in inner nanorods and the irregular arrays of nanorods.Compared to the ZnO nanorods LED without insulating layer, the LED with Alq3layer exhibited a threshold voltage about1.6V in the I-V curve and the operatingvoltage decreases from30V to18V. Meanwhile the luminous color of the LED withAlq3layer changes from yellow-green to violet.It was indicated that the vertically aligned growth and uniform heights of ZnO nanorods were critical for the electroluminescence of the EL devices without p-njunction based on the ZnO nanorod arrays.The discovery of random lasing made ZnOnanorods have more potential applications in optoelectronic devices.