STRUCTURAL CHARACTERIZATION OF PROTON EXCHANGED LiNbO3 BY MICRO-RAMAN SPECTROSCOPY AND POLARIZED VISIBLE LIGHT MICROSCOPY

LiNbO3 wafers were proton exchanged (PE), annealed for various times, and the X-faces polished to provide a side view of the PE region. Micro-Raman images of the PE region were obtained by stepping a focused laser beam across the X-face starting below the PE region and moving parallel to the Z-axis towards the wafer surface. Micro-Raman images reveal that chemical bonding in the PE regions differ from that in LiNbO3 and that chemical bonding in the unannealed PE region varies significantly with depth (along the Z-axis). Annealing reduced proton concentration by driving protons deeper into the wafer, thereby expanding the PE region. The duration of anneal does not significantly alter PE depth but does affect the chemical bonding and the PE/LiNbO3 interface. Images of PE/LiNbO3 were also obtained by polarized visible light microscopy. Contrast is observed between the PE region and LiNbO3 when viewing transmitted Z-polarized white light. Exchange depths determined from polarized light microscopy are in good agreement with those obtained from micro-Raman images.