Comprehensive strain analysis in thin films based on high-resolution x-raydiffraction: Application to implanted LiNbO3 - art. no. 205420

Strain analysis of thin film heterostructures is expanded to noncubic cryst alline symmetries with special attention to the practically important hexag onal and rhombohedral systems. The developed formalism is rather general an d can be used to study systems with highly anisotropic lattice mismatches ( even unknown) and strain degrees. It is applied here to analyze complex str uctural modifications in the near-surface waveguide layers produced by He-i mplantation in Y-cut LiNbO3 wafers, which initially have the rhombohedral B ravais lattice. Experimental results, obtained by x-ray mapping of reciproc al space in the vicinity of symmetric and asymmetric reflections, showed a strong anisotropy of the layer-lattice mismatch in plane perpendicular to t he three-fold axis. This result unequivocally indicates that the initial rh ombohedral symmetry of the unit cell is broken as a result of ion implantat ion. Experimental findings are explained in terms of strain-induced orderin g of point defects, which is a well-known phenomenon in the field of physic al metallurgy, but has never been mentioned in the studies of thin film str uctures for microelectronics and optoelectronics. Since this phenomenon can be important to other layered structures, it is included into a general so lution of the elasticity problem.