Deposition of sputtered NiO as a p-type layer for heterojunction diodes with Ga2O3.

The characteristics of sputtered NiO for use in pn heterojunctions with Ga₂O₃ were investigated as a function of sputtering parameters and postdeposition annealing temperature. The oxygen/ nickel and Ni₂O₃/NiO ratios, as well as the bandgap and resistivity, increased as a function of O₂/Ar gas flow ratio. For example, the bandgap increased from 3.7 to 3.9 eV and the resistivity increased from 0.1 to 2.9 Ω cm for the O₂/Ar ratio increasing from 1/30 to 1/3. By sharp contrast, the bandgap and Ni₂O₃/NiO ratio decreased monotonically with postdeposition annealing temperatures up to 600 °C, but the density of films increased due to a higher fraction of NiO being present. Hydrogen is readily incorporated into NiO during exposure to plasmas, as delineated by secondary ion mass spectrometry measurements on deuterated films. The band alignments of NiO films were type II-staggered gaps with both α- and β-Ga₂O₃. The breakdown voltage of NiO/β-Ga₂O₃ heterojunction rectifiers was also a strong function of the O₂/Ar flow ratio during deposition, with values of 1350 V for 1/3 and 830 V for 1/30. [ABSTRACT FROM AUTHOR]