On the zinc nitride properties and the unintentional incorporation of oxygen

Zinc nitride films were prepared by radio-frequency magnetron sputtering in N2/Ar ambient using different substrates (glass and thermally-oxidized-Si) and buffer layers (low-temperature Zn3N2 and ZnO). Resonant Rutherford backscattering (RBS) allowed determining ZnxNy stoichiometry and thickness. Despite the sputtering system was operated in high vacuum conditions, unintentional oxygen incorporation during growth was detected. Calculations of the relative oxygen concentration showed that the oxygen content was very dependent on the growth rate. Ex-situ oxidation was also analyzed by resonant RBS and compared with the results of as-grown layers. Scanning electron microscopy and X-ray diffraction revealed that surface morphology and crystal orientation were strongly dependent on the substrate temperature (Ts). In addition, optical transmission measurements show a reduction of the optical energy band gap from 1.46 to 1.25 eV as Ts increased. The electrical properties were examined as a function of growth rate, total working gas flux and Ts aiming to maximize electron mobility. From those studies, it was found that Hall mobility increased significantly as the growth rate decreased. A maximum mobility of 100 cm2/Vs and a minimum carrier concentration of 3.2 × 1018 cm−3 were achieved at a Ts of 423 K and a growth rate of 4.44 nm/min.