Photoluminescence Study of Deep Level Defects in ZnO Thin Films

In the present work, zinc oxide (ZnO) thin films were prepared by heating, at 500 degrees C, metallic Zn films deposited onto Si (100) substrates by RF magnetron sputtering. According to the x-rays diffraction patterns, the polycrystalline hexagonal ZnO phase (wurtzite) was obtained with a preferential orientation along the (101) planes. The increase of both the crystallites size and the Zn-O bond length, as a function of the heating time, reflect the improvement of the crystalline quality of the investigated films. The investigated films emitted in ultraviolet, visible and infrared regions. The ultraviolet emission was linked to the crystalline quality of the films. All the visible emission related defects were identified. Their concentrations vary differently as a function of the heating time. The infrared emission originated from the oxygen anti-sites (O-Zn). The correlation between the decrease of the electrical resistivity and the increase of both 2+ charged oxygen vacancies (V-O(++)) and hydrogen impurities (H-I) defects suggested that the unintentional n-type conductivity in ZnO came from the collective contribution of V-O(++) and H-I defects.