Epitaxial Growth of Metal Fluoride Thin Films by Pulsed-Laser Deposition

ABSTRACTWe have investigated the growth of GdLiF4 thin films for optical waveguide applications using pulsed-laser deposition (PLD). Epitaxial, c-axis oriented GdLiF4 films have been grown from undoped GdLiF4 targets in an on-axis PLD geometry on (100) CaF2. These films exhibit a high density of particulates on the surface which are ejected from the target in the ablation process. Growth from Nd-doped polycrystalline GdLiF4 ablation targets results in relatively smooth films with lower particulate densities, as Nd doping significantly increases the optical absorption of GdLiF4 at the ablation laser wavelength of 193 nm and permits efficient pulsed-laser deposition. Optical emission spectra of the ablation pume reveals the presence of atomic fluorine, gadolinium, and lithium, indicating the dissociation of the metal-fluorine bonds in the ablation process. In addition, we find that the residual background oxygen pressure must be sufficiently reduced to avoid the formation of Gd4O3F6 as an impurity oxy-fluoride phase in the films.