Size reduction in crystal grains in LiNb0.5Ta0.5O3 thin films by controlling nucleation density during thermal plasma spray chemical vapor deposition

Two approaches were applied to thermal plasma spray chemical vapor deposition (TPS CVD) in order to reduce crystal grain size or/and surface roughness of LiNb0.5Ta0.5O3 thin films while retaining the advantages of this method, such as high deposition rate. The first method consists of a two-step deposition, where the nucleation density is controlled in the first step and the film with high crystallinity is deposited in the second step. The surface roughness and grain size could be reduced from 1 nm to 7.7 nm, and from 200-350 nm to 120-180 nm, respectively. In the second approach, employing a one-step TPS CVD process, the conventional precursor was substituted by a double-alkoxide precursor and grain size in the deposited films could be reduced to 50-80 nm. Both approaches adopted in this work permitted to reduce the optical propagation loss.