Structural, Optical and Electrical Properties of Transparent Conductive -Doped ZnO Thin Films Grown by Pulsed Laser Deposition

In$_2$O$_3$-doped ZnO thin films (In: 0.1 at.\%) were deposited on sapphire (0001) substrates at various temperatures (100 -- 600 $^{\circ}$C) by using pulsed laser deposition technique. An X-ray diffractometer was used to investigate the structural properties of the thin films. The thin films were found to have a preferred (002) orientation, and the peak intensity of the (002) orientation was found to increase with increasing growth temperature. With increasing growth temperature, the peak position of the ZnO (002) orientation shifted to the larger-angle side. An atomic force microscope was used to investigate the surface morphologies of the thin films. The grain size and the roughness of the thin films increased with increasing growth temperature. The transmittances of the thin films measured with a spectrophotometer were used to derive the band gap energies of the thin films. The band gap energies of In$_2$O$_3$-doped ZnO thin films were found to be larger than the undoped ZnO thin film due to the Burstein-Moss effect, and the band gap energy was found to decrease with increasing growth temperature. A spectrometer was used to investigate the photoluminescent (PL) properties of the thin films. All of the thin films showed near-band-edge emission and no deep-level emissions. This is due to the compensation of the oxygen vacancies in the thin films. Comparing the band-gap energies calculated from the absorption edge and the peak positions of the PL spectra, we calculated the Stokes shifts for the thin films. Hall measurements indicated that all the thin films were n-type semiconductors. The resistivity decreased and the mobility increased with increasing growth temperature.