Fabrication of preferential orientation ZnO thin films with exposed holes by high temperature annealing low-temperature-grown ZnO thin films on different substrates

In this work, we report that (001) preferential orientation ZnO thin films with exposed holes grown on Si(100), Si(111) and sapphire(001) substrates by magnetron sputtering are fabricated high temperature annealing. It is found that the ZnO thin films with exposed holes grown on Si (100) and sapphire(001) substrates only represent (001) orientation hexagonal structure ZnO, while the ZnO thin films with exposed holes grown on Si(111) substrates not only show (001) orientation hexagonal structure ZnO but also exhibit cubic sphalerite structure ZnO. It is also found that the density of the exposed holes for the ZnO thin films grown on Si(100) and Si(111) substrates are of appropriately 1.74 x 10(8) cm(-2) and 0.85 x 10(8) cm(-2), respectively, but 0.04 x 10(8) cm(-2) for the ZnO thin films grown on sapphire(001) substrates. Meanwhile, the size (about 300-450 nm) of the exposed holes for the ZnO thin films on Si(111) substrates is bigger than that (similar to 180 nm) on Si(100) and sapphire(001) substrates. Further study reveals that the residual stress is significantly affected by the number of the holes on the ZnO surface, and the formation of the exposed holes is beneficial to reducing the residual stress: as the increase of the number and size of the exposed holes, the residual stress is reduced and changed from compress stress to tensile stress; further increase of those of the exposed holes results in larger tensile stress. Finally, formation model of the exposed holes on the ZnO thin films surface has also been proposed.