Abstract
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.