Enhancement of the piezoelectric coefficient in hexagonal Mg_xZn_1-xO films at lower Mg compositions

Wurtzite structure materials such as ZnO exhibits piezoelectric and semiconducting properties with piezoelectric coefficient as a dominant physical characteristic. We investigate the dependence of the piezoelectric coefficient on the Mg content in the Mg_xZn_1-xO thin films deposited on Si (111) substrate by radio frequency magnetron sputtering. The deposition temperature is fixed at 250 °C and all the films have near equal thickness (380 nm). All Mg_xZn_1-xO films show high crystallinity with strong preferential orientation along [0001] growth direction. Moreover, the diffraction peaks shift toward higher angles which confirms the substitution of the smaller ionic radius of magnesium at zinc site. The piezoelectric coefficient of Mg_xZn_1-xO films as measured by piezoelectric force microscopy, exhibits the maximum (54.1 pm/V) at an intermediate Mg concentration (x = 0.28), which is largely improved as compared to ZnO. The Mg_xZn_1-xO films hold great promise to be applied in piezoelectric nanogenerator (NG).