Sheet resistance of LiNbO3 wafers processed in radio-frequency plasma of hydrogen

Radio-frequency discharge of 13.56MHz in hydrogen was used for processing single domain crystalline LiNbO3 wafers under an electrodeless capacitive coupling. At a pressure of 0.5 torr and RF input power of 250 W a surface layer of approx. 0.5 μm on the LiNbO3 wafers was created in which the niobate structure was strongly injured. The Li concentration dropped almost to zero at the very surface and only niobium oxides remained there. After the surface modification the wafers lost their insulating properties and became electrically conducting. The sheet resistance was measured and revealed a semiconducting character. We discuss possible mechanisms of the charge carriers creation in the material during the plasma processing. The nuclear method NDP (Neutron Depth Profiling) has been used for the lithium depth profiling and the four-point probe technique for the sheet resistanace measurements.