Fabrication and characterization of NiO/AZO heterojunction thin film diodes by radio frequency magnetron sputtering

This study focuses on the fabrication and investigation of the properties of the heterojunction p-NiO/n-Al-doped ZnO via the radio frequency magnetron sputtering method. We conducted a detailed evaluation of the crystal structure, optical properties, and electrical properties of the NiO and Al-doped ZnO monolayers using advanced techniques such as X-ray diffraction, ultraviolet-visible spectroscopy, and Hall effect measurements. X-ray diffraction results show that the NiO thin film crystallizes in the (111) and (200) peaks with a characteristic NaCl-type cubic structure, while the Al-doped ZnO thin film preferentially develops in the (002) peak, exhibiting a hexagonal wurtzite structure. UV-Vis transmission spectrum analysis indicates that the NiO and Al-doped ZnO thin films exhibit transmittance rates of 52 and 92% in the visible light region, respectively. The optical band gap energy was determined to be 3.45 eV for NiO and 3.36 eV for Al-doped ZnO, respectively. In addition, the carrier concentration in both single layers reached a high level, around 10¹⁹ cm^-3. The J-V characteristics under optimal conditions confirmed the formation of the NiO/AZO heterojunction with a turn-on voltage of 0.67 V, an ideality factor of 4.44, and a barrier potential height of 0.5 eV. Especially, the influence of light with a wavelength of 365 nm, this heterojunction clearly exhibited the characteristics of a photodiode. These results demonstrate the remarkable potential applications of the p-NiO/n-AZO heterojunction in the fields of optoelectronics and light sensors.