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Abstract This study reports a pulsed laser deposition-assisted synthesis of highly metallic titanium nitride (TiN) and a series of semiconducting titanium oxynitride (TiN_xO_y) compounds in thin film form with tunable plasmonic properties by carefully altering the nitrogen (N)-oxygen (O) ratio. The N/O ratio was controlled from 0.3 (highest oxygen doping of TiN) to ~ 1.0 (no oxygen doping of TiN) by growing the TiN films under nitrogen pressures of 50, 35, and 10 mTorr and high vacuum conditions of 2 × 10⁻⁶ Torr with no external gas introduced. The presence of nitrogen in the deposition chamber during the film growth affects the gas phase oxidation of TiN to TiN_xO_yby increasing the mean free path-dependent N and O inter-collisions per second by two to three orders of magnitudes. The evidence of increased oxidation of TiN to TiN_xO_ywith an increase in nitrogen deposition pressure was obtained using X-ray photoelectron spectroscopy analysis. While the TiN samples deposited in high vacuum conditions had the highest reflectance, TiN_xO_ythin films were also found to possess high reflectance at low frequency with a well-defined edge around 20,000 cm⁻¹. Furthermore, the vacuum-deposited TiN samples showed a large negative dielectric constant of -330 and the largest frequency of zero-crossing at 25,000 cm⁻¹; the TiN_xO_ysamples deposited in the presence of nitrogen ambient also showed promising plasmonic applications at the near-mid infrared range. A comparison of the dielectric constant and loss function data of this research with the literature values for noble metals seems to indicate that TiN and TiN_xO_yhave the potential to replace gold and silver in the visible and near-infrared spectral regions. 

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.