Epitaxial growth of metal fluoride thin films by pulsed-laser deposition

We 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.