Fabrication and characterization of In–Ga–Zn–O/NiO structures

Undoped and Li-doped NiO films have been prepared by radio frequency sputtering and electron-beam evaporation techniques. These sputtered films prepared at a lower pressure of 2.6 × 10− 1 Pa show no diffraction peaks and their surfaces are smooth. These films are p-type semiconductors and their resistivity is dependent on an O2-partial pressure. A minimum resistivity of 0.39 Ω cm is attained for a Li-doped NiO film prepared at RF power of 20 W in 50% O2 atmosphere. In contrast, Li-doped NiO films prepared by electron-beam evaporation exhibit no diffraction peaks, but their surface is not smooth. The fabrication of pn-junction is carried out between NiO films and amorphous n-type transparent oxide films, e.g., In–Zn–O and In–Ga–Zn–O. No rectification characteristic is seen at an interface of In–Zn–O and Li-doped NiO films, while the rectification characteristic is achieved in In–Zn–O/In–Ga–Zn–O/NiO/Au device. The threshold voltage of 2.3 V is estimated from the current vs. voltage characteristic.