The epitaxial growth of KTiOPO_4 (KTP) films on different natural faces of KTi_(1-x)Ge_xOPO_4 substrates was studied. The growth on faces (100) and (201) is generally of high quality, irrespective of the growth time or concentration of germanium in the substrates. On the other hand, the epitaxial growth on the face (101) is always of poor quality, and the defects are pyramids, even when the germanium content in the substrate is low and the growth time is short. The films on faces (011) and (110) generally have small hillocks as defects and for high concentrations of Ge in the crystals some cracks begin to appear. The film thickness, depending on the growth time and the face considered was measured by scanning electron microscopy (SEM) using backscattered electrons. The diffusion of germanium from the substrate to the film is very low, as demonstrated by electron probe microanalysis measurements and SEM observations. The difference in the refractive indices n_y and n_z of KTP and KTi_(0.92)Ge_(0.08)OPO_4 are on the order of 0.01, which could be enough to produce wave guides. Finally, it was observed that the second harmonic generation response of KTP substituted with Ge decreases as the Ge content in the crystal increases.
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