It was noted that chemical-vapor-deposited ZnO films generally exhibited n-type conductivity. A compensation doping process was required in order to achieve piezoelectric ZnO, which was needed for surface acoustic wave, bulk acoustic wave, and micro-electromechanical system devices. Here, a gas-phase diffusion process was developed to achieve piezoelectric (11•0) ZnO films. Comparative X-ray diffraction and scanning electron microscopy measurements confirmed that high crystal quality and good surface morphology were preserved after diffusion. Photoluminescence measurements showed a broad band emission with a peak wavelength at ∼580nm, which was associated with Li doping. The surface acoustic wave, including both Rayleigh-wave and Love-wave modes, was achieved along different directions in piezoelectric (11•0) ZnO films grown on an r-plane sapphire substrate.

Li Diffusion in Epitaxial (11¯20)ZnO Thin Films. Wu, P., Zhong, J., Emanetoglu, N.W., Chen, Y., Muthukumar, S., Lu, Y.: Journal of Electronic Materials, 2004, 33[6], 596-9