As an n-type semiconductor, the material can be
effectively doped with an appropriate donor. Both stoichiometry
and dopant impurities affect the electrical
and optical characteristics to the point that ZnO can
either be a near-insulator or a semi-metal. A potential
low-cost alternative to tin-doped indium oxide, ZnO
films could be used as less expensive transparent electrode
material for use as a window layer for solar cell
devices and a transparent conducting layer for electroluminescent
devices. For practical applications undoped
ZnO films are inferior to indium- or tin- based oxide
films.