p-type conduction in unintentional carbon-doped ZnO thin films

p-type conduction has been observed in unintentional carbon-doped ZnO thin films grown by metal organic chemical vapor deposition through postgrowth annealing treatment. The existence of carbon, which has been verified by secondary ion mass spectrometry and x-ray photoelectron spectroscopy, was predicted to immobilize the oxygen in the interstitial site in ZnO thin films after annealing. Using first principles calculations, the formation of carbon-oxygen cluster defect in ZnO was found to be favorable and acts as a shallow acceptor. The cryogenic photoluminescence of the p-type carbon-doped ZnO thin films shows an additional peak located at 3.3564 eV, which was attributed to the acceptor (carbon-oxygen cluster defect) bound exciton emission. (C) 2007 American Institute of Physics.