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 (0less than or equal tox,y,zless than or equal to1), 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 muC/cm(2) for x=0.3. On the other hand, the coercive field was not composition dependent, and was approximately 12 kV/cm. (C) 2002 American Institute of Physics.