Effect of Thermal Annealing and Growth of ZnO: Li Thin Film by Pulesd Laser Deposition

Abstract

ZnO:Li epilayers were synthesized on sapphire substrates by the pulesd laser deposition (PLD) after the surface of the ZnO:Li sintered pellet was irradiated by the ArF (193 nm) excimer laser. The growth temperature was fixed at <TEX>$400^{\circ}C$</TEX>. The crystalline structure of epilayers was investigated by the photoluminescence (PL) and double crystal X-ray diffraction (DCXD). The carrier density and mobility of epilayers measured by van der Pauw-Hall method are <TEX>$2.69\times10cm^{-3}$</TEX> and <TEX>$52.137cm^2/V{\cdot}s$</TEX> at 293 K, respectively. The temperature dependence of the energy band gap of epilayers obtained from the absorption spectra is well described by the Varshni's relation, <TEX>$E_g(T)=3.5128eV{\cdot}(9.51\times10^{-4}eV/K)T^2/(T+280K)$</TEX>. After the as-grown ZnO:Li epilayer was annealed in Zn atmospheres, oxygen and vaccum the origin of point defects of ZnO:Li has been investigated by PL at 10 K. The Peaks of native defects of <TEX>$V_{zn},\;V_o,\;Zn_{int},\;and\;O_{int}$</TEX> showned on PL spectrum are classified as a donors or accepters type. We confirm that <TEX>$ZnO:Li/Al_2O_3$</TEX> in vacuum do not form the native defects because ZnO:Li epilayers in vacuum existe in the form of stable bonds.