LAUSR

Abstract Effects of atmosphere, temperatures and duration time on the surface topography and the electrical conductivity of LiNbO3 single crystals deposited with a 300-nm-thick layer of different metal films (Al, Mg and Zn) had been systematically investigated. LiNbO3 samples covered with Al film annealed at 500 °C for 6 h in different atmosphere were firstly studied. There were a lot of small holes generated after the residual film cleaning. In addition, the surface roughness was enhanced with increasing pressure. Compared with areas that without metal Al coated, a sharp step was formed, especially the deep step of about 125 nm in 3%H2+Ar atmosphere. The I V curves reveal that the electrical conductivity of sample surface annealed at normal pressure was better than that in low vacuum. The current value was up to about 20 mA at 10 V in 3%H2+Ar, resulting in the conductivity significantly improved. Subsequently, samples deposited with different metal (Zn, Mg and Al, respectively) films annealed at 400 °C for 6 h in 3%H2+Ar were discussed. After wet etching, interestingly, a large number of nano-sized protrusions were formed on the surface. Both of samples coated with Mg and Zn films presented no obvious step depth, while a clear step about 13 nm was formed for Al-coated samples. The I V curves show that the surface conductivity of Zn-coated samples achieved the maximum of about 2.5 mA at 5 V among the three metals. Furthermore, Zn-coated samples annealed at different temperatures and holding time in 3%H2+Ar were also analyzed. After pickling, also, there were a lot of nanobulges appeared across the surface. With the temperatures keeping growth and the time extending, the nanobulges became much more compact and well-distributed. At the same time, the surface conductivity of samples would be gradually and effectively enhanced. The PL and XPS spectrums have indicated that more oxygen vacancies formed with increasing temperatures and holding time, resulting in the significant improvement in surface conductivity. The conduction mechanisms of sample surface can behave differently owing to the various annealing conditions.