Determination of the optimal cation composition of ferroelectric (ZnxCd1−x)S thin films for applications to silicon-based nonvolatile memories

Thin films of ferroelectric binary mixed II–VI compounds such as (ZnxCd1−x)S, as well as (ZnyCd1−y)Te and (ZnzCd1−z)Se (0⩽x,y,z⩽1), were examined from the standpoint of the application to Si-based nonvolatile memories. Electronic-band discontinuities at the ferroelectric–Si interface decreased significantly with increase in the atomic number of the constituent chalcogenide atoms, which favored (ZnxCd1−x)S as the most potential gate ferroelectrics among the three compounds. Polarization-field (P–E) characteristics of the (ZnxCd1−x)S films were found to largely depend on the cation composition. No hysteretic behaviors in the P–E curves were observed for high-Zn concentrations above x=0.5, while the P–E curves traced hysteretic loops due to the ferroelectricity for x<0.5. The remnant polarization was greatly dependent on the Zn concentration, and yielded a maximum of 0.03 μC/cm2 for x=0.3. On the other hand, the coercive field was not composition dependent, and was approximately 12 kV/cm.