Determination of crystal polarities of piezoelectric thin film using scanning nonlinear dielectric microscopy

Using scanning nonlinear dielectric microscopy (SNDM), we determined the polarities of ZnO thin films on various substrates including polar materials. In conventional methods based on detecting the piezoelectric and pyroelectric responses, it is very difficult to determine the polarities of thin films, particularly in the case of growing these films on the polar substrates, because the detected signals from thin films are very small and those from the substrates are large. Our SNDM method, however, enables us to determine the polarities of thin films on polar substrates easily. We also determined experimentally that ZnO thin films grew with a sign opposite to the substrate polarity and it was suggested that pyroelectric effects mainly governed the polarity of ZnO films.