Ferroelectricity in Li-Doped ZnO:X Thin Films and their Application in Optical Switching Devices

We have proposed the application of ZnO:X (X=Li,Ni,Al etc.) films in monolithic optical integrated circuits (OICs). [rf1] To realize the optical switching device, dielectric properties of ZnO:Li deposited on SiO2/p-Si were evaluated in detail. From the results of the frequency dependence of the dielectric permittivity and the loss, and the temperature dependence of ac conductivity at various frequencies, the existence of mobile Li ion was confirmed. The pulsed C–V measurements [rf2] revealed that not only the mobile Li ion but also the ferroelectricity of ZnO:Li contributed to the hysteresis in the normal C–V behavior. To determine the processes assumed to occur in the switching device structure, a prototype of the waveguide structure was fabricated. Although the relationship between the refractive indices of the core and clad layers satisfied the required condition for propagation, several processes such as interdiffusion of doped ions, band alignment and/or rearrangement of space charge when applying the bias voltage were also revealed.