Effects of single-crystalline GaN target on GaN thin films in pulsed laser deposition process

The effects of a GaN single-crystal target (SC-GaN) of laser-ablated GaN thin films on sapphire were investigated. GaN thin films were grown on a single-crystalline c-plane sapphire substrate using the SC-GaN. Unlike the usual growth behavior in laser ablation of a sintered ceramics GaN target (CR-GaN), the rocking curves of the obtained GaN films were superimposed patterns composed of sharp and broad components. The interface between the GaN film and sapphire substrate was atomically flat and sharp. To investigate the effects of the target on the plume of a pulsed laser deposition process in detail, the plume was analyzed by Langmuir probe methods and optical emission spectroscopy (OES). The Langmuir probe results showed that the electron temperature for the plume of an SC-GaN was nearly one third of that of a CR-GaN, although the ion density in the plume of the SC-GaN was found to be greater than the ion density in that of the CR-GaN. OES data showed a significant fraction of the oxygen species in the plume of the CR-GaN. These are thought to be the primary cause of damage and/or impurity to growing films in the plume of the CR-GaN.