NiO/Si heterostructures formed by UV oxidation of nickel deposited on Si substrates

Nickel oxide (NiO) is one of few metal-oxide semiconductors showing a p-type conductivity and can be combined with an n-type semiconductor to fabricate a pn diode. In this study, isotype and anisotype heterojunction diodes were fabricated by ultraviolet (UV) oxidation at 350 °C of metallic Ni deposited on p- and n-Si substrates. The I-V characteristics of the NiO/p-Si diode do not show rectification, while those of the NiO/n-Si diode show rectification with a difference of two orders of magnitude between the currents at 2 and −2 V. The linear C−2 -V characteristics of the NiO/n-Si and secondary ion mass spectroscopy profile confirm that the UV oxidation temperature is low enough so as not to affect deep inside the Si. The NiO layers formed by the oxidation of Ni under UV illumination are found to be more conductive and more suitable for the diode fabrication than those by the thermal oxidation of Ni without UV illumination at the same temperature. Because the oxidation temperature is relatively low and can be further reduced, the UV oxidation can become an important process technology to form various metal-oxide semiconductors from printed metals for future printed flexible electronics.