Blue Shift in Ultraviolet Absorption Spectra of Oxygen Doped Titanium Nitride Thin Films

The objective of this study is to investigate the effect of film thickness on the bandgap of oxygen (O2)-doped titanium nitride (TiN) thin films. To accomplish this, high-quality two-dimensional O2-doped TiN films have been prepared on single-crystal sapphire substrates using a pulsed laser deposition method. The film thicknesses were varied from 3 to 100 nm by varying the number of laser pulses, while other deposition parameters are kept constant. X-ray diffraction (XRD) patterns have shown that the films grow in (111) orientation on the sapphire substrate. The increase in the intensity of the XRD (111) peak also demonstrates a better orientational alignment of the TiN films with substrate as the film thickness increases. The x-ray rocking curve has been used to measure the full width half maxima (FWHM) for each film. The FWHM values has been found to vary from 0.07 to 0.2° as the film thickness decreases. This is taken to indicate that the grain size decreases with a decrease in film thickness. Ultraviolet visible spectroscopy measurements in the wavelength range (200–800 nm) have been performed as well, which indicates an increase in the bandgap of O2-doped TiN films with a decrease in film thickness. The decrease in the film thickness leads to a blue shift of the peak in the ultraviolet-visible absorption (UV-A) region; this blueshift is accompanied by an increase in the bandgap of O2-doped TiN from 3.2 to 3.8 eV. The change in the bandgap due to a change in film thickness has been explained using the quantum confinement effect.