A Study of Transport and Optical Properties of Liquid Nitrogen-Assisted Deposition of Titanium Oxynitride Thin Films

This study presents a method to prevent an undesirable oxygenation process that occurs during the deposition of Ti-N thin films using the pulsed laser deposition technique. Nitrogen gas at various pressures from 0 mTorr to 50 mTorr was utilized during deposition and the oxygenation process occured because of the presence of residual oxygen in the deposition chamber or oxygen impurities in the N₂ gas used during the film deposition. The method involves using a metal trap kept at liquid nitrogen temperature to condense the residual/impurity oxygen, which helps control the oxygenation process and results in desired transport and optical properties of the Ti-N-O thin films. The optical, electrical, and stoichiometric properties of the films depend on their N/O ratio. Direct band gap transition was observed in the material, and we also take note of other important properties like stacking faults, texture coefficient, Urbach energy, dielectric constants, optical conductivity, refractive index, extinction coefficient, and skin depth. The x-ray diffraction measurements show a reduction in the intensity and shift of the (111) and (222) TiNO peaks to higher angles with increasing nitrogen pressure during growth. The study also found that increasing the deposition N₂ pressure of the TiNO thin films resulted in increased metallicity of the films as indicated by the reduction in bandgap from 2.64 eV to 1.70 eV, however, an increase in resistivity from 133 µΩcm to 3177 µΩcm was observed due to increase in surface scattering induced by increase in dislocation density.<br/><br/><br/>This work was supported by the National Science Foundation, NSF-PREM through MRSEC [grant No. DMR-2122067].