Enhancement of near-band-edge photoluminescence from ZnO films by face-to-face annealing

The influence of post-growth annealing on the luminescent properties of ZnO films was investigated. The non-radiative recombination centers in the films can be removed effectively by annealing at high temperature. Annealing in open ambient caused visible luminescence related defect centers to be formed and degraded the emission efficiency of near band edge (NBE) ultraviolet photo luminescence. To overcome this problem, a face-to-face annealing technique is used. It is found that by confining the surface of the films exposed to the ambient during annealing, the luminescent efficiency of NBE ultraviolet emission is enhanced significantly, and the formation of visible luminescence related defect centers is suppressed. This is attributed to the reduction in the rate of formation of vacancies (oxygen and/or zinc) at the surface region, which in turn decreases the bulk defect density in the ZnO films. The sublimation of ZnO is suppressed effectively by face-to-face annealing, and the roughness of the film surface is also improved, as compared to annealing in open air. (C) 2003 Elsevier B.V. All rights reserved.