Effect of annealing temperature on the characteristics of the modified spray deposited Li-doped NiO films and their applications in transparent heterojunction diode

Modified spray method (m-SM) was used to fabricate 8 at%-lithium-doped NiO (NiO:8-Li) films using the nickel nitrate [Ni(NO3)2·6H2O] and lithium nitrate (LiNO3) solutions. The NiO:8-Li solutions were sprayed on glass substrates and annealed at various temperatures. It found that the resistivity was decreased and the optical bandgap value were increased as annealing temperature of the NiO:8-Li films was increased from 400 °C to 600 °C. As the annealing temperature increased, the ratio (fitting area) of Ni3+/Ni2+ in the NiO:8-Li films decreased, which was caused by the increasing in carrier concentration. When the NiO:8-Li films was deposited on ITO glass substrates, the rectifying current-voltage (I-V) properties confirmed that a p-n heterojunction diode characteristic was successfully formed in a NiO:8-Li/ITO structure. The NiO:8-Li/ITO heterojunction parameters such as ideality factor (n), barrier height (φb), and series resistance (Rs) were determined using conventional forward bias I-V characteristics, Cheung׳s and Norde׳s methods. The ideality factor of 3.3, barrier height of ~0.72 eV, and the series resistance of ~0.21 kΩ were estimated using I-V characteristics.