Rapid Annealing of Black ZnO Thin Films Prepared by Pulsed Laser Deposition

ZnO thin films were deposited by pulsed laser deposition (fluence 2.2 J/cm²) in vacuum on different substrates kept at room temperature. This temperature allowed for fast film growing, however the as-prepared films had low transparency. To improve this optical property, keeping up at the same time the high electric conductivity of the films, post-annealing procedures in vacuum and in air were carried out. The influence of these procedures on the optical absorption, photoluminescence and electrical properties has been investigated. It is shown that the annealing in air improves only the transparency of such a film, however its conductivity decreases markedly. In turn, vacuum annealing for 3 min. at 600° C results in better transparency of the films, with their electric conductivity kept high.