Optical, electronic, and transport properties of nanocrystalline titanium nitride thin films

Abstract

Spectroscopic ellipsometry (SE) was employed to get insights on the optical, electronic, and transport properties of nanocrystalline titanium nitride (TiNx) films with respect to their microstructure and stoichiometry. The films’ properties can be tailored by varying the energy of bombarding ions during sputter deposition and the substrate temperature (Td). The best metallic behavior of TiNx (resistivity 40 μΩ cm and conduction density 5.5×1022 electrons/cm3) has been observed in films developed with energy above 100 eV and Td⩾400 °C. A redshift of the optical gaps has been observed for overstoichiometric films, suggesting it as a sensitive probe to investigate the TiNx stoichiometry. The energy, strength, and broadening of the interband transitions were studied with respect to the energy of ions and Td and they were explicitly correlated with the TiNx crystal cell size and grain orientation. On the other hand, the study of intraband absorption has provided the conduction electron density with respect to ion energy and Td, which promotes the densification of TiNx films due to different mechanisms. Combined SE and x-ray analysis was used to identify the electron scattering mechanisms, showing that the main electron scattering sites are the grain boundaries and the Ti vacancies for stoichiometric (x=1) and overstoichiometric (x∼1.1) films, respectively.