Annealing Effects of ZnO Seed Layers on Structural and Optical Properties of ZnO Nanorods Grown on R-plane Sapphire Substrates by Hydrothermal Method

ZnO nanorods were hydrothermally grown on R-plane sapphire substrates coated with an as-grown ZnO seed layer and with ZnO seed layers annealed at different temperatures. The effects of the seed-layer annealing temperature on the structural and optical properties of the ZnO nanorods were investigated using scanning electron microscopy, X-ray diffraction, and photoluminescence. ZnO nanorods and nanosheets grew on the as-prepared seed layer. Only ZnO nanorods grew on the ZnO seed layer annealed above 700 degrees C. The structural and optical properties of the ZnO nanorods were significantly enhanced when the seed layers were annealed at 700 degrees C. A cubic equation was used to establish the non-linear exciton radiative lifetime of the free exciton emission peak. Varshni's empirical equation fitting parameters were alpha = 4 x 10(-8) eV/K, beta = 1 x 104 K, and Eg(0) = 3.335 eV; the activation energy was similar to 94.6 meV.