Plume expansion of pulsed laser ablated zinc oxide

High Quality Zinc Oxide thin films have been deposited in the past using pulsed laser ablation. It has been shown that a laser energy density of 3-4 J/cm ² produces epitaxial films with reasonably high resistance and good optical properties'. However, the reason the pulsed laser ablation process is optimized at these laser energy densities was not known. Single electric probes and optical emission spectroscopy are used to obtain plasma parameters to better understand the deposition of ZnO films. For laser energy densities less than 4.5 J/cm ², the electron and ion densities are found to increase monotonically with laser energy density. However, above this critical laser energy density, the plasma density decreases, while electron temperatures remaining constant between 2-5 eV, Above the critical laser energy density, material is no longer evaporated and ionized off of the surface of the target but blown off in a phase explosion. This leads to the decrease in measured plasma density since most of the materials ejected from the target surface are particulates rather than vapor and plasma above this laser energy density.