Significance of Al on the morphological and optical properties of Ti1−xAlxN thin films

TiN and Ti1−xAlxN thin films with different aluminum concentrations (x = 0.35, 0.40, 0.55, 0.64 and 0.81) were synthesized by reactive magnetron co-sputtering technique. The structure, surface morphology and optical properties were examined using Grazing Incidence X-ray Diffraction (GIXRD), Atomic Force Microscopy (AFM), Raman spectroscopy and spectroscopic ellipsometry, respectively. The structure of the films were found to be of rocksalt type (NaCl) for x = 0.0–0.64 and X-ray amorphous for x = 0.81. AFM topographies show continuous mound like structure for the films of x between 0.0 and 0.64, whereas the film with x = 0.81 showed smooth surface with fine grains. Micro-Raman spectroscopic studies indicate structural phase separation of AlN from TiAlN matrix for x > 0.40. Ti1−xAlxN has the tendency for decomposition with the increase of Al concentration whereas c-TiN and hcp-AlN are stable mostly. The optical studies carried out by spectroscopic ellipsometry measurements showed a change from metallic to insulating behavior with the increase in x. These films are found to be an insulator beyond x = 0.81.

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► AlN separation from Ti1−xAlxN was observed by Micro-Raman spectroscopy for x > 0.40.
► Systematic change from metallic (TiN) to insulating (Ti1−xAlxN (x = 0.81)) behavior has been seen from ellipsometric study.
► Refractive index of Ti1−xAlxN (x = 0.81) on Si substrates is reported for the first time.
► Surface roughness of Ti1−xAlxN (x = 0.81) decreases which is also reported for the first time.