Effect of Rapid Thermal Annealing Ambient on Photoluminescence of ZnO Films

The effects of rapid thermal annealing (RTA) ambient on photoluminescence (PL) of sputtered ZnO films are investigated. The RTA at 800 degrees C under either oxygen (O-2) or argon (Ar) ambient can remarkably enhance the PL of the ZnO films due to the improved crystallinities of the ZnO films. It is somewhat unexpected that the ZnO film which received the RTA under O-2 ambient exhibits weaker near-band-edge (NBE) PL than that which received the RTA under Ar ambient. It is supposed that a certain amount of negatively charged oxygen species exist on the surface of the ZnO film that received the RTA under O-2 ambient, leading to a build-in electric field. This in turn reduces the recombination probability of photo-generated electrons and holes, resulting in the suppressed NBE PL.