Defect mediated optical emission of randomly oriented ZnO nanorods and unusual rectifying behavior of Schottky nanojunctions

We report on the interrelation of optical emission of randomly oriented ZnO nanorod system with the carrier transport properties of Ag/ZnO nanorod-based rectifying junctions. The ZnO nanorods, exhibiting a hexagonal wurtzite phase, were fabricated by a cost-effective rapid thermal annealing process and at different annealing temperatures. The photoluminescence spectra of the as grown samples have revealed various Zn and O related native defects (e.g., vacancies, interstitials etc.) located at similar to 400, 428, 491, and 535 nm. As evident from the I-V characteristic curves, though all the Ag/ZnO nanojunctions show Schottky behavior, the nanorods grown at a temperature of 550 degrees C and 650 degrees C are characterized by very large ideality factors of respective values 35.4 and 33.2, apart from displaying unusually high reverse currents. Whereas, the samples grown at 450 degrees C and 750 degrees C show usual rectifying nature having relatively lower ideality factors (18.4 and 12.2), along with low leakage-current under reverse biasing. The enhancement or suppression of the reverse currents can be attributed to the eventual lowering or raising of the Schottky barrier heights which result from the variation in the native defect states of various ZnO nanorod systems. Correlating optical events and electrical response through native defects would find scope in assessing figure of merit and sensitivity while making rectifying nanojunctions and single electron devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3631792]