Structural, electrical and optical properties of yttrium-doped ZnO thin films prepared by sol-gel method

Yttrium-doped ZnO thin films were deposited on silica glass substrates by the sol-gel method. The structural, electrical and optical properties of yttrium-doped ZnO thin films were investigated systematically and in detail. All the thin films have a preferred ( 0 0 2) orientation. When compared with the electrical resistivity values of films without annealing treatment, the values of films annealed in the reducing atmosphere were decreased by about three orders of magnitude. The lowest electrical resistivity value was 6.75 x 10(-3) Omega cm, which was obtained in the 0.5 at% yttrium-doped ZnO thin film annealed in nitrogen with 5% hydrogen at 500 degrees C. In room-temperature photoluminescence ( PL) spectra, two PL emission peaks are found in the pure ZnO thin film; one is the near-band-edge ( NBE) emission at 3.22 eV and the other is a green emission at about 2.38 eV. Nevertheless, the green emission is not found in the PL of the yttrium-doped ZnO thin films. The low-temperature PL spectrum of the undoped ZnO thin film at 83K is split into well-resolved free and bound excition emission peaks in the ultraviolet region, but the NBE emission of the 5 at% yttrium-doped ZnO thin film at 83K has only one broad emission peak.