Optical Properties of Li:ZnO Thin Films with [101] Orientation

[101] oriented Li:ZnO thin films were prepared on lime-glass substrates by using a r.f. magnetron sputtering method. The effect of annealing temperature on the optical properties of Li:ZnO thin films was investigated. Comparing with [002] oriented Li:ZnO film, the as-deposited [101] oriented film has wide band gap (Eg), though it red-shifts from 3.37 to 3.29 eV after annealing at 560-580℃, company-ing with the shrinkage of unit cell. When the [101] oriented Li:ZnO film is annealed at high temperature (610℃), its band gap shifts back to 3.35eV. The photoluminescence (PL) studies confirm that there exhibit 399nm, 421nm and 468nm PL peaks for all the films. However, when the films are annealed at 560-580℃, the near-band-edge (NBE) emission peak at 380nm of the samples disappears and the band-to-band UV emission near 360nm slightly shifts to large wavelength due to the decrease of Eg. It is considered that the PL peak of 399nm is induced by Li dopant and the other peaks are arisen from the intrinsic defects in ZnO lattice structure. The effects of Li dopant on the structural and optical characteristics were also discussed.