Superior transport and optical properties of titanium oxynitride thin films: Liquid nitrogen assisted condensation of unwanted residual oxygen during film deposition

This work reports our findings on how to mitigate an unwanted oxygenation process during the deposition of titanium oxynitride films (Ti-N-O) by a pulsed laser deposition method. The oxygenation is unavoidably caused by the residual oxygen in the chamber and/or oxygen impurity in the ambient gas used during the film deposition. The unwanted oxygenation process is controlled by means of an in-situ condensation process of residual/impurity oxygen on a metal trap held at liquid nitrogen temperature and placed near the film deposition stage. The oxygenation mitigation process results in achieving desired transport and optical properties in the Ti-N-O thin films. The optical properties of Ti-N-O films were found to be governed by intraband mechanism for N/O ratio (xx) in the film and by free electrons mechanism for N/O ratio (xx). The Ti-N-O films were found to possess both direct and indirect band gaps. The bandgap was found to reduce from 2.64 eV – 1.70 eV for direct and 1.70 eV – 0.36 eV for indirect. The presence of both direct and indirect bandgap is thought to be caused by the presence of strain in the material, which reduce the band gap and stimulated direct-to-indirect band gap transition. According to our x-ray diffraction measurements and analysis, a reduction in intensity and a shift of both (111) and (222) TiNO peaks to higher angles is observed as nitrogen pressure was increased. A counter-relationship of Bragg’s peak breadth was observed with the (111) and (222) peaks; the breadth of the (111) peak reduced while that of (222) increased with increasing nitrogen pressure. We have also observed higher lattice constant, crystallinity, and microstrain in the TiNO thin film samples deposited in the presence of liquid nitrogen trap with respect TiNO films deposited without liquid nitrogen trap.