ZnO adopts the hexagonal close packing wurtzite structure in which oxygen ions are stacked along the [001] direction and Zn2+ cations occupy one-half of the tetrahedral sites. The presence of lattice defects consisting of oxygen vacancies and involving interstitial (Zn2+-2e-) pairs and cation and anion vacancies makes ZnO an intrinsic n-type semiconductor with a band-gap of~ 3.3 eV. The synthetic procedure adopted to obtain ZnO and/or the presence of dopants within the ZnO lattice strongly influence the resistivity. Thin films of ZnO have a ...