OPTICAL AND ELECTRONIC-PROPERTIES OF COBALT-DOPED ZINC-OXIDE FILMS PREPARED BY THE SPUTTERING METHOD

In-doped ZnO, Co-doped ZnO and Li-doped NiO are successively deposited on quartz by the sputtering method. A current versus voltage curve of the three-layer device, in which the In-doped ZnO and Li-doped NiO are used as electrodes, reveals that the In-doped ZnO is an ohmic electrode and the Li-doped NiO is a blocking electrode with respect to electron injection. In photocurrent spectra of the three-layer device, there are two distinct peaks around 41 0 and 640 nm. The former is ascribed to the photoionization caused by the electric-dipole transition from the ground states, 4A2(F), to the conduction band, and the latter to the thermal emission from electronic excited states of Co2+, 4T1 (P).