Influences of deposition power of GZO thin films on the properties of the heterojunction diode based on a NiO/GZO bi-layer structure

A compound of ZnO with 3 wt% Ga2O3 (ZnO : Ga2O3 = 97 : 3 in wt%, GZO) was sintered at 1400 degrees C as a GZO target. Radio frequency magnetron sputtering was used to deposit nickel oxide thin films (NiO, deposition power of 100 W) and GZO thin films (deposited at 300 degrees C by changing the deposition power from 50 W to 150 W) on glass substrates to form p(NiO)-n(GZO) heterojunction diodes with high transmittance. The structural, optical, and resistivity properties of the GZO and NiO thin films and NiO/GZO heterojunction devices were investigated with scanning electron microscopy (SEM), X-ray diffraction (XRD) patterns, UV-visible spectroscopy, Hall-effect analysis, and current-voltage (I-V) analysis. XRD analysis showed that only the (111) diffraction peak of NiO and the (002) and (004) diffraction peaks of ZnO (GZO) were observable in the NiO/GZO heterojunction devices, and the GZO thin films showed a good c-axis orientation perpendicular to the glass substrates. The variations in the optical band gap (E-g value) of the GZO thin films were evaluated from the plots of (ahv) = c(hv - E-g)(1/2), revealing that the measured Eg value decreased with increasing deposition power. For the deposited GZO thin films, both the carrier concentration and mobility linearly decreased and the resistivity increased approximately with increasing deposition power. When the sputtering deposition power for the GZO thin films was deposited at different power, the I-V characteristics confirmed that a p-n junction characteristic was successfully formed in the NiO/GZO heterojunction devices.