Metal–organic chemical vapor deposition of p-type NiO and NiO/β-Ga2O3 PN diodes

In this work, p-type NiO thin films were grown on (010) β-Ga2O3 substrates via metal–organic chemical vapor deposition (MOCVD). The growth conditions, including Ni(dmamb)2 (Ni precursor) molar flow rate, oxygen flow rate, and growth temperature, were systematically tuned to achieve p-type NiO thin films. With a relatively high O2 flow rate of 10 000 sccm, the grown NiO film exhibited smooth surface morphologies with a root mean square roughness value of 2.39 nm. The measured hole concentration ranged from 1 × 1016 to 4.5 × 1016 cm−3, with room-temperature mobility varying between 3 and 1.7 cm2/V s. Cross-sectional scanning transmission electron microscopy imaging and analysis revealed a NiGa2O4 interfacial layer formed between the p-type NiO thin film and β-Ga2O3 substrate, due to Ni diffusion. Given the challenges of achieving p-type conductivity in β-Ga2O3, NiO has emerged as a potential alternative material. Furthermore, in situ MOCVD grown NiO/β-Ga2O3 heterojunction was used to fabricate PN diodes with two different diameters: 100 and 200 μm. This study represents the first demonstration of all-MOCVD growth of p-NiO/β-Ga2O3 PN diodes on (010) Sn-doped β-Ga2O3 substrates. Compared to radio frequency sputtering and atomic layer deposition of p-NiO, MOCVD allows the continuous growth of p-NiO on top of Ga2O3, which can potentially suppress interface defects and impurity contamination. The breakdown voltages of the MOCVD grown NiO/β-Ga2O3 PN diodes were measured as 348 and 267 V for the 100 and 200 μm diameter devices, respectively. The knee voltages (Vknee) were extracted as 4.7–5.2 V.